University of Southern California Dissertations and Theses

Petrology and diagenesis of the early Miocene Skooner Gulch and Gallaway Formations, Point Arena, California

(USC Thesis Other)

Petrology and diagenesis of the early Miocene Skooner Gulch and Gallaway Formations, Point Arena, California

PDF

Download

Open document

Flip pages

Download a page range

Download transcript

Copy asset link

Request this asset

Transcript (if available)

Content PETROLOGY AND DIAGENESIS OF THE EARLY MIOCENE
SKOONER GULCH AND GALLAWAY FORMATIONS,
POINT ARENA, CALIFORNIA
by
Joann Evelyn Welton
A Thesis Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillm ent of the
Requirements for the Degree
MASTER OF SCIENCE
(Geological Sciences)
June, 1980
UMI Number: EP58680
All rights reserved
INFORMATION TO ALL USERS
The quality of this reproduction is dependent upon the quality of the copy submitted.
In the unlikely event that the author did not send a complete manuscript
and there are missing pages, these will be noted. Also, if material had to be removed,
a note will indicate the deletion.
UMI’
Dissertation Publishing
UMI EP58680
Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author.
Microform Edition © ProQuest LLC.
All rights reserved. This work is protected against
unauthorized copying under Title 17, United States Code
ProQuest
ProQuest LLC.
789 East Eisenhower Parkway
P.O. Box 1346
Ann Arbor, Ml 48106- 1346
UNIVERSITY OF SOUTHERN CALIFORNIA
THE GRADUATE SCHOOL
UNIVERSITY PARK
LOS ANGELES. CALIFORNIA 90007
This thesis, written by
Joann Evelyn Welton
under the direction of h..er...Thesis Committee,
and approved by all its members, has been pre
sented to and accepted by the Dean of The
Graduate School, in partial fulfillment of the
requirements for the degree of
Master of Science
Dean
THESIS COMMITTEE
ACKNOWLEDGEMENTS
| I would like to express my appreciation to my thesis
’ advisor, Dr. Robert H. Osborne, for his support and val-
i
juable suggestions, and to Drs. J.L. Anderson and D.E. Ham-
| !
imond, for th eir careful review of this manuscript. j
Special thanks to J. Allen, D. Richards, P. Kimbrell, I
M. Bass, D. Morse, J. Castle, R. Jones and T. Bube, for
their help and assistance in various stages of this pro
ject. I am especially grateful to D. Kosiur, for his ad
vise and help in obtaining both the microprobe and NMR
analyses.
I would also lik e to thank Chevron Oil Field Research
Company, La Habra, C alifornia, especially Mr. F.L. Campbell,
for their support and permission to use the equipment and
f a c i l i t i e s at Chevron Oil Field Research Company for this
study. Without their help, this type of study would not
have been possible.
Finally, I would lik e to thank my husband, Bruce, for
his constant encouragement, extreme patience and many
helpful discussions during all phases of this work.
TABLE O F CONTENTS
j ACKNOW LEDGEMENTS.......................................................................
I LIST O F FIGURES.........................................................................
! LIST O F TABLES...........................................................................
| ABSTRACT........................................................................................
| INTRODUCTION...............................................................................
Historical Review........................... ..............................
Regional Geology.............................................................
PROCEDURES....................................................................................
STRATIGRAPHY A N D AGE...............................................................
Skooner Gulch Formation............. , ..............................
Gall away Formation.........................................................
Lower Gall away Formation............................................
Redefinition of the Skooner Gulch and Gall away
Formational boundary............................................
Middle Gall away Formation........................................
Upper Gall away Formation............................................
DEPOSITIONAL HISTORY.............................................................
PETROGRAPHY..................................................................................
Petrography of the Skooner Gulch Formation....
Petrography of the lower Gall away Formation...
Petrography of the middle Gall away Formation..
Petrography of the upper Gall away Formation...
PROVENANCE....................................................................................
Page
DIAGENESIS.............................................................................................. 53
Origin of the matrix in graywackes.................................. 54
Authigenic versus de trital clay........................................ 59
Origin and significance of the interbedded
mudstone and dark laminae............................................ 60
Significance of soft sediment deformation
and bioturbation............................. 65
Bioturbation.................................................... 67
Porosity and permeability..................................................... 71
S tra tific a tio n ........................................................................... 72
DIAGENESIS O F THE SKO O NER G ULCH FORMATION................................ 73
Quartz diagenesis..................................................................... 73
Feldspar diagenesis................................................................. 76
Clay di agenesis......................................................................... 80
Calcite cementation................................................................. 80
Pyrite and iron oxides....................... 82
DIAGENESIS O F THE MASSIVE SANDSTONE O F THE
G ALLAW AY FORMATION......................................... 84
Quartz diagenesis.................... ....................................... 84
Feldspar diagenesis................................................ 86
Authigenic clay diagenesis.................................................. 89
DIAGENESIS O F THE FINELY-LAMINATED SANDSTONE O F
THE G ALLAW AY FORMATION................................................................. 92
Quartz diagenesis................................................ 92
Page !
Feldspar diagenesis................................................................. 95
Clay diagenesis................................................................................... 101 I
Carbonate di agenesis......................................................................... 108
SU M M A R Y AND CONCLUSIONS........................................................ 115
REFERENCES........................................................................................................ 118
V
']
LIST O F FIGURES
Figure Page
I. Geologic map and index map of the study area
showing location of stratigraphic sections
and sample lo calities (modi
and others, 1976)
2. Stratigraphic section and
of the Skooner Gulch (Tsg)
tions, in relation to Mutti
model........................................
fied from Phillips
nferred lateral position
and Gall away (Tg) Forma
's (1977) deep-sea fan
........................................................................ 15
3. SECTION 1 (lower Gall away Formation).............. 17
4. SECTION 2 (middle Gall away Formation)...................................... 21
5. SECTION 3 (middle Gall away Form ation)..,................................... 22
6. SECTION 4 (upper Gall away Formation)........... , ...................... 25
7. QFL diagram of the Skooner Gulch and Gall away
Formation................................................................................................. 28
8. Composition of plagioclase feldspars from the
Skooner Gulch and Gall away Formations in terms of
molecular Albite (Ab), Anorthite (An), and Or-
thoclase (Or) as determined by electron microprobe 37
9. Source rock determination based on plot of quartz
undulosity and polycrystallinity (a fte r methods
of Basu and others, 1975).... ........................ 51
10. Comparison between d e trita l and authigenic clay............... 61
11. SEM micrographs showing the morphology and d is tr i
bution of d e trital clay in two zones in the Gal la-
way Formation........................................................................................ 62
12. SEM micrographs showing the composition of dark
laminae in the upper Gall away Formation.................................. 64
13. SEM micrographs showing composition of lig h t
laminae in the upper Gall away Formation.................................. 66
vi
Figure Page
14. Photograph and thin section photomicrograph of
a burrow in the middle Gall away Formation............................. 69
15. SEM micrographs of quartz overgrowths in a burrow 70
16. SEM micrographs showing grain contact and
rock fragment within the Skooner Gulch Formation............... 74
17. SEM micrographs of quartz overgrowths in the
Skooner Gulch Formation................................................................... 75
18. SE M micrographs of quartz overgrowths and clay
rim in the Skooner Gulch Formation............................................ 77
19. SEM micrographs of microcrystalline quartz in
the Skooner Gulch Formation........................................................... 78
20. SEM micrographs of altered feldspar grains in the
Skooner Gulch Formation................................................................... 79
21. SEM micrographs of K-feldspar overgrowths and clay
rims in the Skooner Gulch Formation.......................................... 81
22. SEM micrographs of clay-rich calcite cement in
the Skooner Gulch Formation........................................................... 83
23. SEM micrographs showing grain contact and deformed
micas in massive sandstone beds in the Gallaway
Formation................................................................................................ 85
24. SEM micrographs showing morphology and distribution
of authigenic quartz in the massive sandstone beds
of the Gallaway Formation........................... .................................... 87
25. SEM micrographs showing the morphology of an altered
plagioclase grain and authigenic K-feldspar overgrowths
in the massive sandstone beds of the Gallaway Formation. 88
26. SEM micrographs showing the morphology and distribution
of authigenic K-feldspar and smectite in the massive
sandstone beds of the Gallaway Formation.................................. 90
27. SE M micrographs showing the morphology of authigenic
illite -s m e c tite in the massive sandstone beds of the
Gallaway Formation.............................................................................. 91
Figure
28. SEM micrographs of pore-bridging illite and ill ite -
smectite clay in the massive sandstone beds of the
Gal 1 away Formati o n , ..........................................................
29. SEM micrographs showing the morphology of authigenic
kaolinite in the massive sandstone beds of the
Gallaway Formation..............................................................................
30. SEM micrographs showing evidence of mild compaction
in the finely-laminated sandstone beds of the
Gallaway Formation..............................................................................
31. SEM micrographs showing distribution of authigenic
quartz in the finely-laminated sandstones of the
Gallaway Formation..............................................................................
32. SEM micrographs showing morphology and distribution
of quartz druse in the sandstone dikes and micro
crystalline quartz-clay cements in the finely-lam in
ated sandstone beds of the Gallaway Formation.....................
33. SEM micrographs of a resorbed plagioclase feldspar
grain from the finely-1aminated sandstone beds of
the Gallaway Formation.....................................................................
34. SEM micrographs showing the morphology of altered
plagioclase feldspar grains in the finely-laminated
sandstone beds of the Gallaway Formation................................
35. SEM micrographs of authigenic K-feldspar overgrowths
on a d e trital plagioclase feldspar in the fin ely-
laminated sandstones of the middle Gallaway Formation...
36. SEM micrographs of K-feldspar overgrowths in the
finely-laminated sandstones and d e trita l feldspar
devoid of authigenic overgrowths from the sand
stone dikes in the Gallaway Formation......................................
37. SEM micrographs of a volcanic rock fragment and
smectite clay coatings in the finely-laminated
sandstones of the Gallaway Form ation,.,.................................
38. SEM micrographs showing the morphology of pore-
lining smectite in the Gallaway Formation..............................
39. SEM micrographs showing morphology of authigenic
chlorite and kaolinite in the finely-laminated
sandstones of the Gallaway Formation........................................
Page
i
I
93 ;
94
96
97
98
99
100
102
103
104
106
107
vi i i
Figure Page
40. SEM micrographs of p o re -fillin g calcite cement
with authigenic clay inclusions in the fin e ly -
laminated sandstones of the Gallaway Formation.......................... 109
41. SEM micrographs showing relationship of auth
igenic illite -s m e c tite to calcite cement in the
finely-laminated sandstones of the Gallaway
Formation..................................................................................................... 110
42. SEM micrographs of p a rtia lly dissolved calcareous
Foraminifera and authigenic dolomite rhomb from
the lower Gallaway Formation.................................................. 112
43. SEM micrographs showing two forms of authigenic
dolomite from the Gallaway Formation..................... 113
LIST O F TABLES
Table
1. Summary of petrologic and sedimentologic differences
between the Skooner Gulch and Gallaway Formations....
2. Modal analysis of Skooner Gulch and Gallaway
Formations based upon thin section point counts
(400 points per section)...........................................................
3. Microprobe analyses of potassium feldspars.....................
4. Microprobe analyses of plagioclase feldspars.................
5. Porosity and permeability (NMR)............................................
6. Summary of the major authigenic minerals recognized
in the Skooner Gulch and Gallaway Formations (by
sample)...............................................................................................
7. Abundance of major authigenic minerals by lithofacies
in the Skooner Gulch and Gallaway Formations.................
Abstract
; Early Miocene deep-sea fan deposits of the Skooner j
i I
j Gulch and Gallaway Formations near Point Arena, C alifo rn ia ,!
I
were examined to determine which factors influence of con
trol diagenesis in fine-grained tu rb id ite deposits. The
sequence represents outer fan depositional lobes, lobe
fringe and basin plain deposits as defined by Mutti (1977).
I
| Four representative stratigraphic sections were sam-
!
| pled and analysed using the scanning electron microscope
(SEM), energy dispersive X-ray (EDX), X-ray d iffra c tio n
j (XRD), nuclear magnetic resonance (NMR), electron micro
probe and thin section analysis. Results indicate that d ia
genesis of a tu rb id ite sequence is complex and does not in
volve uniform changes in d e tr ita l and authigenic minerals.
Factors affecting diagenesis include variations in the
original depositional environment, sediment composition,
texture, s t r a t i f i c a t i o n , frequency of interbedded shale
beds, bioturbation, degree of compaction, and original por
osity and permeability.
Diagenetic changes recognized were: alteratio n and re
sorption of unstable d e t r it a l grains such as feldspar,
rock fragments and d e t r it a l clay; formation of authigenic
x i
quartz, K-feldspar and clay cement causing a reduction in
porosity and permeabi1i t y ; formation of iron oxide coatings
(hematite) and pyrite; and replacement or incorporation of
d e t r it a l and authigenic minerals in late stage carbonate
cements. All of the diagenetic changes observed can occur
at r e la t iv e ly low temperatures and shallow to moderate
burial depths.
INTRODUCTION
Diagenetic studies of fine-grained sandstone are rare ,
!(Galloway, 1 974; Boles and Franks, 1 979 ; Almon and Davies, j
i!979) and diagenetic studies of tu rb id ite deposits are even
rarer (Morris and others, 1979). Previous studies have !
jstressed gross diagenetic changes, ignoring important in-
Itraformational variations. The purpose of this study is to
i
determine whether diagenesis is uniform throughout a tur- j
■ b i d i t e sequence and what factors actually influence or con-
11ro1 diagenesis of a tu rb id ite deposit.
I
Approximately 400 m of alternating finely-laminated :
I |
jturbidite sandstone and mudstone, with occasional massive j
jsandstone beds of the early Miocene (Saucesian) Skooner
! I
I !
jGulch and Gallaway Formation are continuously exposed along
sea c l i f f s and in the existing in te r tid a l zone south of
Point Arena, California (Fig. 1). Well preserved sedimen-
I
itary structures with recognizable Bouma divisions (Bouma,
119 62) record the complex vertical and late ra l variation of |
| i
a deep-sea fan system which p a r t i a l l y i n f i l l e d a postulated
Tertiary Gualala Basin (Nilsen, 1979), This provides an
j
excellent study area to determine what factors affect dia-
igenesis of a tu rb id ite deposit.
The major problems to be discussed include: the effect '
of the original depositional environment on the diagenetic |
Tg
JW -2
POINT ARENA FM.
GALLAWAY FM.
SKOONER GULCH FM.
IVERSEN BASALT
Sample locality
Dip and Strike
Fault
(Bonebed) —
5 0 0
_ _I
METERS
Figure 1 - Geologic map and index map of the study area
showing location of stra ti graphic sections
and sample lo c a litie s (modified from Phillips
and others, 1976). Key: PA = Point Arena;
S C = Santa Cruz Mountains; SAF = San Andreas
Fault.
history; the origin of argillaceous sandstone ( graywackes) ;
d i f f e r e n tia t io n of d e t r it a l and authigenic minerals; s ig n i
ficance and composition of dark laminations within fin e ly -
laminated sandstone beds; significance of interbedded mud
stone and its affec t on sandstone cementation; original
porosity and permeability and its influence on la t e r dia-
genesis; effect of bioturbation and its role in the re-
i i
d is tribu tion of d e tr it a l clay; d istribution and importance
of carbonate cementation; and variations in clay mineral
i
| composition.
Hi stori cal revi ew
j Kleinpell (1937, Table XVI) recorded the f i r s t paleon- !
tologic data from the Point Arena area. His samples were
collected from the base and top of the Gallaway Formation
!
(as recognized herein) and possibly the overlying Point
Arena Formation. Kleinpell (1937) considered the Gallaway
Formation benthic foraminiferal assemblage to represent j
the lower Zemorrian Uvigerina gal 1owayi Zone; but la t e r ,
based upon additional faunal evidence, reinterpreted the
age to be either Zemorrian or Saucesian (Kleinpell and j
Weaver, 1 963).
Weaver (1943, 1944) was the f i r s t geologist to map the
area studied and assigned the names Skooner Gulch and G alla
way Formations to the lower Miocene units which l i e s t r a t i -
graphically below the siliceous shale at Ross Creek. Weaver
* 3
(1943) o r ig in a lly included the basal basalt sequence and
the overlying coarse-to fine-grained sandstone into a
single lith o s tra tig ra p h ic unit, the Skooner Gulch Formation.
Later Weaver (1944) separated i t into two formations; the |
Iverson Basalt and the Skooner Gulch Formation. j
|
Wentworth (1966, 1972) published the f i r s t detailed !
i
regional study of the entire Gualala block, including geo
chemical analysis of the Iverson Basalt. He primarily con
centrated on the Cretaceous and lower T e rtia ry units south
of the study area, but b r ie f ly mentions the Miocene rocks
of this study. Based on fi e l d relationships, he placed the
contact between the Gallaway Formation and the Skooner Gulch
I I
[Formation just above a glauconitic, vertebrate-bearing bone-
i !
[bed. Wentworth recognized that tu rb id ity currents were the
major depositional mechanism for these units.
Addicott (1967) described a sparse molluscan fauna of
Vaqueros age from the base of the Skooner Gulch Formation
and correlated these specimens with identical species in
the Santa Cruz Mountains, 140 miles south of Point Arena
(Fig. 1). A cheektooth of the marine mammal, Desmostylus,
i :
scattered sharks' teeth and bone fragments also were re- j
ported from near the top of the Skooner Gulch Formation
(lower Gallaway Formation of this report).
Boyle (1967) presented a regional description of the
Skooner Gulch and Gallaway Formations. He included some
petrographic and X-ray d i ffr a c t io n analyses, but his work
4
was of a more general nature and did not include detailed
i
! descriptions or analyses of the depositional or diagenetic
history of the deposits.
| Murata and others (1969) determined the isotopic com-
1 position of the authigenic dolomite cement in the lower
Gallaway Formation glauconitic bonebed.
Turner (1970) obtained K-Ar whole rock radiometric
dates of 24.3 + _ 1.3 , 22.6 + 1.2 , 22.8 + 1.1 m.y. for the
Zemorrian-Saucesian Stage boundary, which was postulated
to occur within the overlying Skooner Gulch Formation.
P hillips and others (1976) recollected the entire
j Skooner Gulch and Gallaway Formations in an attempt to more
I accurately define the Zemorrian-Saucesion Stage boundary
using benthic Foraminifera. They te n ta tiv e ly assigned the
boundary to within the lower Gallaway Formation.
Regi onal geology
One of the major effects of s t r i k e - s l i p faulting
is the creation of numerous restric ted and r e l a
t iv e ly small p u ll-apart or extensional basins ad
jacent to the major controlling fa u lt system
(Crowell, 1974)
The Gualala basin is one of a series of deep, partly
restricted basins which developed in late Cretaceous time
along the postulated proto-San Andreas Fault System ( N i l -
sen, 1978). From Cretaceous until early Miocene time, up
l i f t and erosion of adjacent plutonic highlands of the
5
Salinian block resulted in periodic basin f i l l i n g by large
arkosic deep-sea fan complexes. The geologic record of these
various fans is recorded in the Gualala Formation (Creta
ceous), German Rancho Formation ( Pal eocene-Eocene) and
Skooner Gulch and Gallaway Formations (Miocene). Since that
time, a portion of the basin termed the Gualala block |
(Weaver, 1944) has been gradually transported northward by
r i g h t - 1a t e r a l , s t r i k e - s l i p motion along the San Andreas
i ;
| Fau11 System.
The complex paleogeographic history of this area has
been discussed by Nilsen and Clark (1975), Clarke and
others (1975), Nilsen (1978), Nilsen and McKee (1979) and j
j
Howell and others (1977). The exact position of the Gualala
basin during Miocene time, re la tiv e to the present day
C alifornia coastline, remains in dispute as a result of
controversy surrounding the amount of la te ra l displacement
■along the San Andreas Fault System (Graham, 1978), Attempts •
I
1 by Nilsen and others (1 974) to document cross fa u lt cor-
j
relations along the San Andreas Fault System apparently
have not been successful (Graham and Berry, 1979). The
exact position of the Gualala basin in early Miocene time
remains in dispute; for example, compare recent reconstruc
tions of Graham and Berry (1979) and Nilsen and Brabb
(1979). Following the work of Graham (1978, 1979), Miocene
sedimen of the Gualala basin are interpreted to have been
deposited in the v i c i n i t y of the present day Santa Cruz
6
Mountai ns ( Fig . 1 ).
PROCEDURES
Ninety-one samples were collected from four major 1
sections and selected outcrops in the Skooner Gulch and
Gallaway Formations (Fig. 1). All beds within each section
jwere measured, sampled and described in d e ta il. Selected
samples were then analysed by thin section, scanning ele c
tron microscope (SEM), energy dispersive X-ray (EDX), nu-
i
clear magnetic resonance (NMR) and microprobe. Analyses
were done on equipment located at Chevron Oil Field Re
search Company, La Habra, C a lifo rn ia , unless otherwise
indicated.
Standard petrographic thin sections, impregnated with
blue epoxy to highlight e ffe c tiv e pore space, were examined |
for all samples. The thin sections were half stained with
sodium c o b a ltin it ra te to aid in d i f f e r e n t ia t in g potassium j
i
i
feldspar from plagioclase feldspar. All sandstone samples
were point counted to determine bulk rock composition (400
points per thin section). Distance between points varied
depending on the apparent diameter of the largest grains.
Both thin section and SEM analyses were used to select
representative samples for X-ray d if f r a c t io n , NMR and
mi croprobe analysis.
A fresh surface was obtained for SEM mounts using a
small rock chopper. The samples were mounted on a copper
[specimen plug using epoxy and dried overnight in a low
'temperature (120° F) drying oven. A thin line of S ilp a in t
was applied to ground the specimen to the plug and then
the sample was coated in a Kinney evaporative coater with
carbon and 6 cm gold wire. SEM analysis was done on an
i
ETEC Autoscan U-l scanning electron microscope (20 KV
accelerating voltage) and an attached KEVEX 5100C energy
jdispersive X-ray system (152 eV resolution).
Id e n tific a tio n of minerals in the SEM was done by
comparing known crystal morphologies, with the elemental
composition determined by EDX analysis. Unknown minerals
jwere isolated in the SEM at 20,000X magnification in a
reduced area mode, so that the actual area on the sample
jscanned was less than 0.5 urn in diameter. All analyses
were run for a fixed total of either 2000 or 4000 counts,
ihorizontal scale of 10 eV and 20% deadtime. All major peaks
above sodium (Z = ll) were displayed on a graph. Since the
ire la tiv e peak heights of each element are roughly propor
tional to the concentration of that element in the sample,
a f a i r l y accurate id e n t ific a tio n of the major elements was
obtained. Results were than compared with thin section and
X-ray d i ffr a c t io n analyses.
Twenty-two samples were selected for X-ray d iffr a c tio n
analysis. XRD was used primarily to determine the major
clay types. The XRD samples were crushed by hand to a fine
powder using a mortar and pestle. The powder was mixed with
d i s t i l l e d water, spread over a vycor slide using a dispos
able pipette and dried overnight. Samples were analysed on i
a General E lec tric automated X-ray diffractometer 5, with
a copper ta rg et, interfaced with a PDP-11 computer.
Porosity and permeability measurements were done using ;
'the pulsed nuclear magnetic resonance (NMR) technique de- ;
veloped by Seevers (1966) and Timur (1969). These measure
ments were done in an attempt to substantiate observations
made during thin section and SEM analysis regarding porosityj
d is tribu tion in finely-lam inated sediment. |
Feldspar composition was determined by electron micro
probe analysis of five carbon coated, polished thin sec
tions. These analyses were done at the University of Cal
ifo rn ia at Los Angeles on an ARL microprobe (15 KV accel
erating voltage) with a computerized Tracor-Northern NS-880
energy dispersive X-ray system. Total count time of each
analysis was 60 seconds (2 0% deadtime). j
1 |
STRATIGRAPHY AND AGE
The stratigrap hic section, from oldest to youngest, is
the Iverson Basalt (+ 275 m), Skooner Gulch Formation (15
to 90 m), Gallaway Formation (.+ _ 400 m) and the Point Arena
Formation (._ + 1200 m). This report deals only with the early
Miocene Skooner Gulch and Gallaway Formations. All beds
9
appear l a t e r a l l y continuous and dip approximately 60° SW.
Individual beds are traceable in sea c l i f f and in te r tid a l
zone exposures, and most are well exposed in a f a i r l y con
tinuous v e rtical sequence along strik e . Four minor faults
were recognized but these are not believed to represent
s ig n ific an t time or stratigraphic breaks. The major pet
rologic and sedimentologic differences between the two
l
formations are summarized in Table 1.
Skooner Gulch Formati on
The Skooner Gulch Formation (early Miocene) consists
of thick beds of lig h t gray, weathering yellow-brown, med
ium to fine-grained arkosic sandstone. The sandstone is
distributed in an elongate wedge, lying with apparent local
unconformity on submarine pillow lavas and breccias of the
Iverson Basalt. The Skooner Gulch Formation forms large r e
sistant c l i f f s parallel to the coast. Exact thickness of
the unit is d i f f i c u l t to determine due to the structural
! configuation of the beds. Two minor faults disrupt the
sequence in the lower part of the section.
These amalgamated sandstone beds appear massive, con
t a i n i n g only occasional mudstone clasts, invertebrate bur
rows and fa in t (?) dish structures. Large groove casts,
several meters long were observed on a bedding surface in
| the lower part of the section. Although i t appears f r ia b le
in some outcrops, c a lc ite cementation is believed to have
Table 1 - Summary of petrologic and sedimentologic differences between the Skooner
Gulch and Gallaway Formations.
Parameter Skooner Gulch Formation
Arkose Rock Type
Mineralogy
Grain size (sandstone)
Bedding type
Bouma sequence
Bedding thickness
Sedimentary structures
Quartz (46-54%)
K-feldspar (26-31%)
Plagioclase (6-10%)
Rock fragments (5-11%)
Cl ay (< 10%)
Pyrite (< 1 %)
K-feldspar>plagioclase
Only authigenic clay
M i c a ( < 1 %)
Medium to fine
Massive, amalgamated
sandstone.
Not applicable
Thick
Dish structures?, mud
stone rip-up clasts.
Gallaway Formation
Lithic arkose
Quartz (20-30%)
K-feldspar (10-12%)
Plagioclase (8-15%)
Rock fragments (5-10%)
Clay (15-20%)
Pyrite (4-5%)
K-feldspar< plaqioclase
Authigenic and detrital clay
Mica (1-4%)
Fine to very fine
Variable, alternating f i n e
ly-laminated sandstone and
mudstone; rare massive
sandstone; abundant convol
ute, rippled and plane beds.
Base cut-out T , T. ,
T and rare T
e a-e
Variable, thick to thin.
Convolute, ripple and plane
beds, dish structures, mud-
Table 1 (Continued)
Parameter
Bioturbati on
Porosity (non-calcite
cemented zones only)
Permeabi1i ty
Hemipelagite beds
Skooner Gulch Formation
Rare; occasional sand-
f i l l e d burrows.
20-24%
'v 80 md
None
Gall away Formation
stone rip-up clasts and
concreti ons.
Common to abundant; bur
rows to mottled beds.
11-39%
0.Q1-1.41 md
Common to abundant
produced a very indurated rock in most of the unit. Numerous
thin, white c a lc ite veins crisscross the bedding surfaces.
Small, white, oval-shaped c a l c i t e - f i 11ed nodules are common
in the lower part of the unit,
A sparse invertebrate fauna was collected and described
by Addicott (1967) from the lower Skooner Gulch Formation.
The specimens are ty p ic a lly small and poorly preserved.
Based upon the occurrence of two molluscan species, T u r r i -
i tel 1 a i n e z a n a forma hof fman i Gabb and Chi amys cf, C _, h e r t -
1 e i n i Loel and Corey (which are re stric ted to the Vaqueros
Stage), Addicott assigned an early Miocene age to the unit.
I t is interesting to note that these specimens were compared!
i
to and considered a geographic range extension of faunas in
ithe Santa Cruz Mountains, the possible original depositional
s ite for the Skooner Gulch Formation.
P h illip s and others (1976) te n ta tiv e ly placed the
jSkooner Gulch Formation in the Zemorrian foraminiferal stage!
and Uvigerina sparsicostata Zone of Kleinpell (1938). Based j
Ion further collecting and a reevaluation of the vertebrate j
fauna of the lower Gallaway Formation, I now consider the
Skooner Gulch and Gallaway Formations to l i e within the
Saucesian Stage of Kleinpell (1938) and are early Miocene
in age.
The la te ra l persistence of these massive sandstone beds
and the lack of crosscutting relationships or conglomeratic
zones indicative of channels suggests that the Skooner Gulch
13
Formation represents a series of large, depositional lobes
sim ilar to those described by Mutti (1977). These beds would
be equivalent to facies B of Mutti and Ricci-Lucchi (1972)
and would presumably occur on the outer fan region of a
deep-sea fan system (Fig, 2).
I
Gal 1 away Formati on
i ‘
The Gallaway Formation consists of a lte rn a tin g , thick
ko thin-bedded l i t h i c arkose, siltsto ne and mudstone depos
ited by tu rb id it y currents. The contact between the Gal la - !
I
way Formation and the underlying Skooner Gulch Formation
appears to be conformable. A d is tin c t color change exists
between the clean, light-colored sandstone of the Skooner
Gulch Formation and the dark, argillaceous sandstone of the |
Gallaway Formation. Contact with the overlying siliceous
mudstone and porcellanite of the Point Arena Formation is
gradational but has been placed at the highest medium-gray j
sandstone bed. Bathyal to abyssal benthic Foraminifera are j
abundant throughout the in t e r t u r b i d it e mudstone and hemi- |
pelagite (P h illip s and others, 197 6). Grain size decreases
upsection, with a corresponding increase in the frequency i
and thickness of pel i tic in tervals. ,
Three major subdivisions of the Gallaway Formation
have been recognized based upon grain size, bed thickness,
sedimentary structures and sand-shale ra tio (J, Welton i_n
P h illip s and others, 1976). Each of these facies w ill be
14
0 1
M <
100*
CHANNELIZED INNER FAN - T pq
LOBE FRINGE OUTER FAN
SANDSTONE LOBE
OUTER FAN SANDSTONE
INTERBEDDED SANDSTONE 8 MUDSTONE
Tsg
DIATOMACEOUS SHALE
Figure 2 - Stratigraphic section and inferred lateral posi
tion of the Skooner Gulch (Tsg) and Gallaway (Tg)
Formations, in relation to Mutti's (1977) deep-
sea fan model. The Skooner Gulch Formation repre
sents outer fan sandstone lobes; the Gallaway
Formation represents lobe fringe and basin plain
deposits. Diatomaceous shale of the Point Arena
Formation (Tpa) overlie the Gallaway Formation.
15
discussed separately in order to more accurately character
ize the deposit.
Lower Gall away Formati on
The lower Gallaway Formation consists predominantly
of alternating beds of medium-gray to greenish-gray, fin e ly
laminated sandstone, siltstone and shaly mudstone. Sand bed
thickness and sand-shale ra tio is highly variable with con
tacts ranging from d is tin c t to gradational. Bouma and
a
Tee ^eds ar-e the most common bedding types. The lowermost
sandstone beds contain localized concentrations of dolomite
glauconite, phosphate and marine vertebrate fo s sils. Sand
stone dikes, 6 to 10 cm wide, dissect the lower beds along
Schooner Gulch Creek. Well preserved, lower bathyal ca lc a r
eous foraminifera occur in the mudstone in tervals.
Several thick beds of medium-grained, lig h t- g r a y ,
weathering yellow-brown sandstone form a resistant headland
at the mouth of Schooner Gulch Creek (Fig. 3), These sand
stone beds average approximate!y 2 m in thickness, with
well-defined bedding contacts. Mudstone rip-up clasts, dish
structures, e l u t r ia t i o n pipes and massive bedding character
ize these sandstone bodies. Well preserved flu t e casts in
dicating a northern transport direction were observed on
one of these beds. Tidal conditions prohibit the detailed
examination of most of these beds.
The lowermost sandstone bed (bonebed) represents a
unique horizon within the Gallaway Formation. The associa-
0
L.
CM 2 0 0
i J
CM
BED THICKNESS
U200
Figure 3 -
m SANDSTONE
0 MUDSTONE
'" O '*
DISH STRUCTURES
R IP -U P CLASTS
J * SANDSTONE DIKE
1 1
ELUTRIATION PIPES
■ SAMPLE POSITION
ion). Stratigraphic
o c u u i u i i u i i u v c i u i v ^ u I o c v j u c i u i i u i j j i j t \ j i p u i u i u i i
of the lower Gallaway Formation. Thickening-upward
cycles are typical of lobe fringe deposits in a
deep-sea fan system (method after Ricci-Lucchi, 1975).
17
tion of arenaceous fo ra m in ife r a , glauconite, phosphate, do l
omite, deep and shallow water sharks and marine mammals
suggests that a period of slow sedimentation occurred in a
reducing environment. This permitted the preservation of
the f r a g ile fossil m aterial. B. Welton i_n P h illip s and
others (1976) described the rich vertebrate fauna from the
top of the horizon and he considered the fauna to be
transported. The glauconite pelloids were either formed i n
situ and la t e r concentrated into pockets and lenses along
;w i t h the phosphate and marine vertebrates by currents, or j
transported from an outer shelf environment with associated
foss i 1 materi a l .
According to the c la s s ific a tio n of Mutti (1977), the
lower Gallaway Formation is believed to represent lobe
fringe deposits (facies D of Mutti and R icci-Lucc hi, 1972),
The c r i t e r i a used to c la ssify such deposits includes: grain
size (fin e to very fin e -g ra in e d ); variable sand-shale r a tio ;
variable sandstone bed thickness; la te ra l persistence of
beds without changes in individual bed thickness; predomi
nantly base-missing Bouma sequences (Tce > ^ c _e ) > abundant
sedimentary structures, ie. mudstone rip-up clasts, dish
structures, e t c .; sharp contacts between sandstone and mud
stone; and occasional hemipelagites. The thick-bedded, med
ium-grained sandstone bodies are believed to represent small
sp illo v e r lobes.
18
Redefi n i t ion of the Skooner Gulch and Gal 1 away formati onal
boundary
The exact location of the formational boundary between
the Skooner Gulch and Gallaway Formation has been poorly
defined. Past workers (Wentworth, 1966; Addicott, 1967;
Boyle, 1967; P h illip s and others, 1976) have described the
contact as gradational somewhere within a 2 m th ick, glau
conitic horizon, rich in marine vertebrates, phosphate and
dolomite (ie . bonebed).
i
My petrographic work c le a rly indicates that the
Skooner Gulch and Gallaway Formations are 1it h o l o g i c a l 1y
separable. The Skooner Gulch Formation sandstone beds are
c la y -f re e , well-sorted arkose; the Gallaway Formation sand
stone beds are argillaceous, l i t h i c arkose. Petrographic
analysis of material from the bonebed indicates i t is an
argillaceous l i t h i c arkose and should be included in the
Gallaway Formation, Thus, based upon both s tra tigrap hic and
petrologic relationships, I have redefined the formational
boundary to include the bonebed horizon in the lower G a l l
away Formation. This provides a more usable formation boun
dary that can be recognized in the f i e l d .
Middle Gal 1 away Formati on
The middle Gallaway Formation consists of a thickening
upward sequence of a lt e rn a tin g , fin ely-lam inated sandstone
and s ilts to n e , with well-preserved sedimentary structures
19
and dark gray to brown mudstone. Two sections were sampled
in detail (Figs. 4 and 5). Unusual round and oval-shaped,
dolomitic concretions occur along some of the bedding sur
faces. These resis tan t concretions contain all of the bed
ding surface features observed elsewhere in the u n it, ex
cept they have been dolomitized. They resemble hamburger
buns and bowling balls and were aptly termed by Boyle (1967)
as the "hamburger beds" and "bowlingball beach". Thin-bed
ded, chocolate-brown hemipelagites occasionally occur
i
throughout the unit.
Bed thickness is highly va riable , ranging from 2 to
44 cm; however, individual beds can be traced l a t e r a l l y
into the existing in t e r tid a l zone with only minor changes
in thickness. The sand-shale ra tio is approximately 1:1,
but also varies. The basal contact of the sandstone with
the overlying mudstone is generally sharp, and frequently
undulatory due to load deformation, The upper contact is
less sharp and occasionally gradational from a sandy mud
stone to a mudstone. This gradation is probably in part due
to extensive reworking by mega-invertebrates.
The sedimentary structures preserved are ty p ic a lly
base-missing, Tcc|e > Tt>-e or Tc-e Bouma sequences. Rare,
massive, fine-grained sandstone beds of Bouma T and com-
a
plete T sequences occur. All of the sandstone units
a — e
contain dark laminae that emphasize the load deformational
structures. Excellent examples of convolute beds, ripple
20
- o
CM
CM
3 0
-J
A j,- VvV:.?/.; /.-.: * .
/vC
*- 100
BED THICKNESS
t il SANDSTONE
H MUDSTONE
V f f c BURROW
FLAME STRUCTURE
DOLOMITIZED
SAMPLE POSITION
Figure 4 - SECTION 2 (middle Gallaway Formation). Stratigraphic
section and vertical sequence analysis for portion
of middle Gallaway Formation at "hamburger beds"
locality. Thickening-upward cycles are typical of
lobe fringe turbidites (method after Ricci-Lucchi,
1975).
21
BOUMA
DIVISIONS
CM
4 0
CM 4 0
-J
BED THICKNESS
m
r'I'V
■
SANDSTONE
MUDSTONE
SANDY MUDSTONE
R IP -U P CLASTS
B IOTURBATION
FLAME STRUCTURES
SAMPLE POSITION
Figure 5 - SECTION 3 (middle Gallaway Formation). Stratigraphic
section and vertical sequence analysis for a complete
Bouma T sequence in the middle Gallaway Formation,
a-e
22
marks, flame structures and mudstone rip-up clasts occur
throughout the deposit. !
i
Abundant traces of horizontal and ve rtical burrows
joccur in both the sandstone and mudstone. In general, j
j i
horizontal branching burrows are more common in the mud
stones and more or less v e r t i c a l , branched and unbranched
burrows, with well defined Sprei te n , occur in the sandstone.
Some of the horizontal forms resemble grazing burrows ty p i-
I
cal of Nere i tes facies of Seilacher (1967). Common ve rtica l
forms include dwelling burrows and possibly "escape"
burrows. In some cases the burrows cut across bedding sur
faces. In rare instances, bioturbation has been so exten
sive that the original laminations have been e n tir e ly
destroyed, together with the sand/mud contact, resulting
in a mottled appearance. These structures closely resemble
burrowing patterns observed in Holocene tu rb idites in
La Jolla fan (Piper and Marshall, 1969).
Bed thickness plots (Fig. 5) following methods of
Ricci-Lucchi (1975) indicate predominantly thickening
upward tu rb id it e cycles which are typical of outer fan
deposits. In addition, the middle Gallaway Formation
contains all of the ch aracteristics used by Mutti (1977)
and previously l is t e d , to define lobe fringe tu rb id ite s .
Postulated position of the sequence in rela tio n to a modern
deep-sea fan system is i l l u s t r a t e d in Figure 2. This unit
i
is assigned to facies D of Ricci-Lucchi (1975).
23
; Upper Gall away Formati on
The upper Gallaway Formation consists predominantly of
a l t e r n a t i n g thick-bedded (40 to 50 cm), dark-gray mudstone
and thin-bedded (3 to 5 cm) chocolate-brown hemipelagite,
occasionally separated by medium-gray, thick to thin-bedded :
j
(5 to 50 cm), f i n e l y - 1 aminated s iltsto ne and sandstone, I n
dividual beds appear l a t e r a l l y continuous into the present
!
in t e r tid a l zone with l i t t l e variation in thickness. The
sand-shale ra tio is low ( approximately 1:4 ). This unit
i
i
eventually grades into the siliceous mudstone and porcel-
la n ite of the Point Arena Formation. Rare, oval-shaped s i 1 - j
iceous concretions occur along bedding surfaces in the
lower part of the section. One representative section was ;
i !
i j
described in detail from this facies (Fig, 6).
I The mudstone beds appear massive but are frequently
mottled due to intense bioturbation. The mudstone units
are ty p ic a lly coarser than the adjacent hemipelagites, ,
containing more d e t r i t a l s i l t and less well-preserved j
, Foraminifera, Bedding contacts between the mudstone and j
the hemipelagite beds can be d is tin c t but are frequently
gradational. Well-preserved bathyal to abyssal benthic
Foraminifera are concentrated within the hemipelagite,
forming crude laminations. Abundant iron oxide staining
(observed in thin sections of the hemipelagite) appears
to be responsible for the color variation between the two
i
beds .
24
CM 4 0
CM
HOO
BED THICKNESS
SANDSTONE
MUDSTONE
HEMIPELAGITE
FLAME STRUCTURES
BURROW
MOTTLED
SILICEOUS CONCRETION
SAMPLE POSITION
Figure 6 - SECTION 4 (upper Gallaway Formation). Stratigraphic
section and vertical sequence analysis of basin
plain deposit, showing monotonous sequence of
vertically uniform bed thickness, with only oc
casional erratic variations (method after Ricci-
Lucchi, 1975).
25
' The upper Gallaway Formation contains all of the char
a c te r is t ic s typical of basin plain deposits, as defined by
jMutti (1977). Bed thickness plots (Fig, 6) are sim ilar to
. i
those figured by Ricci-Lucchi (1975) for basin plain de
posits, showing monotonous sequences of v e r t i c a l l y uniform
bed thickness with occasional "e rra tic " va ria tio ns. The up- j
per Gallaway Formation is assigned to facies D and G of j
|R ic c i-L u c c h i(1 9 7 5 ). i
i I
|
i
I DEPOSIT IONAL HISTORY
i
i I
In early Miocene time, volcanism (Iverson Basalt)
i
ceased and was followed by a period of erosion and basin
isubsidence, Eventually, arkosic sandstone of the Skooner
| I
iGulch Formation deep-sea fan complex buried the Iverson i
Basalt. Based upon s tra tig ra p h ic relation ship s, sedimentary j
^structures and comparison with modern and ancient deep-sea
kan models (Ricci-Lucchi, 1975; M u tti, 1977), the Skooner
Gulch and Gallaway Formation are believed to represent part
jof a complex series of l a t e r a l l y migrating depositional
lobes located on the outer fan slope (Fig. 2), |
Gradual abandonment or sh iftin g of these depositional !
i s
lobes resulted in the formation of a thickening-upward se
quence of lobe fringe tu rb id ite s (terminology a f te r M u tti,
1977) represented by the lower and middle Gallaway Forma
tion. Wei 1 - preserved benthic Foraminifera occur throughout
26
|the unit in interbedded mudstone and hemipelagite beds, !
1 j
These Foraminifera indicate water depths ranging from bath-
yal to abyssal depths (P h illip s and others, 1976), Density
i
junderflow current mechanisms were also responsible for 1
transportation and concentration of both deep and shallow
water marine vertebrates into the central portion of the
'basin.
Continued basin subsidence, possibly combined with a
reduction in terrigenous sediment supply, resulted in the |
i
end of tu r b id it e deposition during middle Miocene time. This
last phase of tu r b id it e deposition is represented by the !
i
upper Gallaway Formation, with its monotonous sequence of
Jbasin plain mudstone, hemipelagite and occasional thin-bed-
!ded tu rb id it e sandstone beds. Siliceous diatoms, which
! j
f i r s t appear scatter throughout the upper Gallaway Forma- |
i
tio n, increase in abundance upsection, eventually replacing j
the terrigenous Gallaway deposits with siliceous porcellan- j
i
ites and shales termed the Point Arena Formation,
| PETROGRAPHY j
I i
i
Petrography of the Skooner Gulch Formation
; |
The Skooner Gulch Formation consists of medium to
fine-grained (150 to 500 urn), angular to subangular, w e ll- j
sorted arkose (Fig. 7 ) ( cl a s s ific a tio n of McBride, 1 963).
Average composition is 48% quartz, 27% k-feldspar, 8% plag-
27 I
• ► ■
OUARTZITE
• SKOONER GULCH
LOWER GALLAWAY
MIDDLE GALLAWAY SUBLITHARENITE
UPPER GALLAWAY
L IT H IC SUBARKOSE
FELDSPATHIC
ARKOSE
Figure 7 - QFL diagram of the Skooner Gulch and Gallaway Formation.
Results are based on point count analysis of 400 grains
per thin section. The Skooner Gulch Formation consists
of arkoses. The Gallaway Formation consists predominant
ly of lith ic arkoses (classification after McBride,
1962).
28
ioclase feldspar (An-^ _24) * ^ roc^ fragments, and less than
1% clay and mica ( b i o t i t e and muscovite)(Table 2). In divid - !
ual grains are ty p ic a lly touching in a grain-supported fab
ric but show only minor evidence of grain interpenetration
due to compaction. Large c a l c i t e - f i l i e d veins and dusty j
patches of p o r e - f i l l i n g c a lc ite cement occur scattered |
throughout the unit. The exact d is trib u tio n and abundance j
of calcite-cemented sandstone is impossible to evaluate in |
I
the f i e l d but is believed to be extensive.
Approximately 85% of the quartz in the Skooner Gulch
i
jFormation is cle ar, monocrystalline "common" quartz as de-
jfined by Young (1976). Extinction is stra ig ht to s lig h t ly
undulose with some very strained v a rie tie s (c la s s ific a tio n
of Basu and others, 1975). Occasional vacuole strings and j
j i
m icrolites of tourmaline, r u t i l e , hornblende and b i o t it e i
!
[were observed. The p o lyc ry sta llin e quartz (15%) is predom
in a n t ly unstable "new crystal" quartz, with more than three j
| |
jcrystal units, undulose ex tin c tio n , and highly sutured to
I
crenulated boundaries. Well-developed, authigenic quartz
overgrowths are common on many of the d e t r i t a l quartz j
grains and in some cases have completely surrounded the j
J i
d e t r i t a l core. An early clay coating which formed around
the d e t r i t a l grains is v is ib le under the overgrowths,
; One of the major petrologic differences between the
Skooner Gulch and the Gallaway Formations is the composition
and type of feldspar. Orthoclase (untwinned K-feldspar) is
29 !
Table 2 - Modal analysis of Skooner Gulch and Gallaway Formations based upon
thin section point counts (400 points per section).
Skooner
Gul ch
M
I—
C xi
<
ID
O
UJ
■ K
Q UJ
Cxi UJ z i 1 —
< GO Ll J 1 — UJ UJ < UJ
D_ O 1 —
1 — 1 UJ • z _ J 1 — UJ n z 1 —
G O
i —i t — i
SEI 1 — o O * Q Q 1 —1 Z l a . i — i
O z r . > - o o 1 —1
z o C J > < Z l _ J UJ GO 1 —
_ J 1 — < _ J _ J C xi
< C£ O m o m o <
UJ 1 — 1
< o > - _ J i—i i — i
o UJ C l. z ; a .
U_ o o o c _ CD M
5T
J Z M GO a . <
KF PF
(%)
JW-26 15 85 46 26 6 8 1 11 --
1 __ __
1 -- -- - - --
JW-27 14 86 47 31 10 5 3 1 1
1 i __ __ __
JW-49 14 86 51 29 9 7 1
— — 1 __ __
1 -- -- -- -- --
JW-48 17 83 53 28 7 10 1
— — 1 __ __
JW-46 12 88 47 29 9 11 1
— 1 __ __ 1 _ _ i _ _ _ _ _ _
JW-60 12 88 43 20 9 4 1 17 -- 5 -- 1
Lower Gallaway
JW-38 15 85 28 12 15 16 22
JW-23 9 91 14 10
?
2 58
JW-22 40 60 38 9 14 7 11
JW-37A 3 97 14 8 21 11 7
JW-34 1 99 20 13 18 18 26
JW-33 2 98 26 2 23 15 25
J W - 2 9 7 93 19 5 10 4 29
JW-28 18 82 28 10 17 13 24
JW-20 5 95 30 14 21 13 14
JW-63 10 90 24 15 19 10 29
JW-64 5 95 21 12 9 9 4
JW-99 18 82 18 4 16 11 1
JW-61 14 86 20 5 11 5 19
JW-53 14 86 22 7 9 5 21
1 2 1 1 2
1 10 1 3 1 --
13
— 4
1
_ _
2
_ - —
1 -- 1
34 — iL
1
1
— — 2 — 1 -
1 -
1
_ _ _____ _ _
1
3
4 1 1 -- 1
18 1 10 4
2 5 1
2
1
3
3
o
1 1 -- 1
37
_____ _____
1
L.
3
_____ _____
1 --
_____
45 2 1 1 1 --
18 15 4 1 2
21 7 5 1 2
GO
O
Table 2 continued.
Middle
QUARTZ
FELDSPAR
LITHICS
CLAY
CALCITE
DOLOMITE
PYRITE
GLAUC.
ZIRCON
M IC A *
HORNBLENDE
ZEOLITE
SPHENE
PHOSPHATE**
APATITE
Gal 1 away P M T KF PF (X)
JW-78 1 99 19 12 10 19 11 26 1 1
_ _
1
_ _
JW-76 14 86 22 10 14 13 11 18 9 1
---------
1 1
—
JW-68 4 96 17 2 5 2 62 8 1 1 1 1
JW- 67 19 81 21 11 15 13 4
—
30 1
—
1 2 1
—
1
-------- —
JW-66 1 99 4 1 1 92 1 1
dW-80 20 80 30 21 14 10 14 7 2 1 1
JW-81 4 96 23 17 6 2 29 8 8 1 3 1 1 1
JW-82 10 90 23 11 9 8 25 11 4 1 7 1
JW-84 21
Upper Gallaway
79 33 17 14 9 11 12 1 1 1 1
JW-93
—
100 14 15 4 1 11 43
_____
10
_____ _____
2
JW-92 1 99 8 5 5 3 48 17 12 2
JW-90 100 20 9 7 3 34 14 9 4
JW-88 100 12 2 51 15 14 1 4 1 1
JW-87 100 3 1 85 10 1
JW-86 4 96 25 11 15 11 2 28 1 1 1 4 1
Key: P= Polycrystal 1in e ; M= Monocrystalline; T= Total; KF= K-feldspar;
PF= Plagioclase feldspar; GLAUC.= Glauconite;* biotite and muscovite;
** bone fragments and phosphate nodules
[the predominant d e t r it a l K-feldspar, with a minor amount of
microcline ( gridiron-twinned K-feldspar). Microprobe anal
ysis of the d e t r ita l K-feldspars (Table 3) indicates they
tend to be pure va rie tie s with a high percentage of potas
sium. Small, euhedral, authigenic K-feldspar overgrowths are
common on both the d e t r it a l and the plagioclase feldspars.
Minor i l l i t i c clay a lt e r a tio n was observed in both SEM and
thin section on many of the d e t r i t a l grains.
Microprobe analysis of the d e t r i t a l plagioclase fe ld -
l
i
spars indicates predominantly sodic p iagio cla ses: a lb ite
and oligoclase (Table 4). In some cases the plagioclases
show f a in t o s c illa t o r y zoning, typical of hypabyssal and
ivolcanic rocks. A tria n g u la r Or-Ab-An plot (Fig. 8) of the j
microprobed plagioclase grains shows a d e f in ite composition
al break between the majority of Gallaway plagioclase grains
| ;
i i
jand those of the Skooner Gulch, with the l a t t e r generally |
jbeing more a l b i t i c . Minor overlap in the data could r e f l e c t |
i
i
analysis of an authigenic feldspar rather than a d e t r it a l
feldspar, which are very d i f f i c u l t to separate in thin
jsection. Kastner and Siever (1979) indicated that authigenic
feldspars tend to be pure end members of th e ir s e rie s (e ith e r
a lb it e or orthoclase). SEM analysis reveals that most
of the plagioclases show some degree of a lte r a tio n and may
be a l b i t i z e d . In general, this a lte r a tio n is not as complete
as in the Gallaway Formation.
The percentage of l i t h i c fragments in the Skooner
32
Table 3 - Microprobe analyses of potassium feldspars.
Na20
Concentration %
K^0 S i 0 2 CaO ^ 2^3 Fe0
MgO
T i 0 2
Total
% Type Ab
Mole %
An Or
Skooner Gulch Formation - JW-49
0.62
0.36
0.73
15.71 64.98 -------
16.44 64.17 - - - -
16.65 66.66 -------
19.22 -------
19.39 — -
19.43 -------
0.65
0.67
0.91 0.16
101 .18
101.03
103.82
Orthoclase
Orthoclase
Orthoclase
5.68
3.22
6.28
94.32
96.78
93.72
Lower Gallaway Formation - JW-20
2. 50
3.31
13.08 65.09 -------
10.26 65.11 0.73
19.03 0.25
19.40 0.30
-------
0.19 100.13
99.10
Mi croc 1i ne
Mi crocli ne
22.48
31 .60 3.86
77.52
64.54
Lower Gallaway Formation - JW-33
1.15 10.49 67.68 -------
11.18 67.36 - - - -
13.01 68.13 -------
1 1 .29 67.56 0.54
17.43 0.14
18.01 0.21
17.74 -------
18.03 -------
------- -------
96.90
96.76
98.88
99.30
Mi crocli ne
Orthoclase
Orthoclase
Mi crocli ne
14.32 85.68
100.00
100.00
77.42
1 .87
------- -------
19.45 3.13
Middle• Gallaway Formationi - JW-80
0.41
0. 52
16.40 65.95 -------
9.87 50.10 0.22
20.06 0.45
33.68 0.17
0.59
2.36 1 .49
103.86
98.40
Orthoclase
Orthoclase
3.64
7.30 1 .69
96.36
91 .01
Upper Gallaway Formation - JW-86
0.80
0.75
C O
C O
15.33 64.64 -------
16.56 64.67 -------
18.17 0.18
18.17 0.26
------- --------
99.13
100.40
Orthoclase
Orthoclase
7.38
6.43
92.62
93.57
Table 4 - Microprobe analyses of plagioclase feldspars.
Na20 K20
Concentration %
S i 0 2 CaO ^"*2^3 Ti 02
Total
% Type
Mole %
Ab An Or
Skooner Gulch Formation - JW-20
9.39 0.08 67.54 1.12 20.85 0.38
-------
0.22 99.57 Albite 93.36 6.12 0.52
8.63 0.41 62.24 4.98 24.90
------- ------- -------
101 .16 01i goclase 74.08 23.60 2.32
9.67 0.64 69.19 0.21 20.95
------- -------
0.21 100.83 Albite 94.71 1.15 4.14
10.64
-------
67.60 0.60 21 .11 0.15
------- -------
100.09 Albite 97.00 3.00
-------
8.85 0.43 63.26 4.77 24.53 0.44
------- -------
102.28 01 i g o c 1 a s e 75.20 22.38 2.42
9.16 0.47 62.89 4.30 23.80 0.14
------- -------
100.77 01i goclase 77.31 20.06 2.63
10.40 0.18 69.93 0.15 20.82 0.17
------- -------
101.64 Albite 98.12 0.76 1.12
10.04
-------
71 .55 0.15 21 .28
------- -------
0.19 103.21 Albite 99.17 0.83
-------
Lower Gallaway Formation - JW-20
6.80 1 .41 60.08 7.47 26.68 0.29
_ _ _ _ _______ ___
102.72 Andes i ne 57.35 34.85 7.80
5.46 1 .60 58.19 8.90 27.31 0.49
------- -------
101.96 A n d e s i n e 47.77 43.00 9.23
7.66 0.83 62.64 5.07 24.07 0.30
------- -------
100.79 01 i g o c 1 a s e 70.17 24.96 4.87
6.38 1 .08 58.24 8.36 26.84
------- ------- -------
100.90 A n d e s i n e 54.49 39.45 6.06
8.60 1.15 62.91 4.46 23.90
------- ------- -------
101.02 01 i g o c 1 a s e 72.78 20.84 6.38
6.95 1.12 59.10 7.10 25.81 0.43
------- -------
100.50 Andes i ne 59.87 33.81 6.32
6.83 0.99 57. 94 8.15 27.31 0.60
------- -------
101.82 Andes i ne 57.00 37.56 5.44
6.38 1.25 58.27 7.54 26.56
------- -------
0.22 100.22 Andes i ne 56.12 36.65 7.23
Lower Gallaway Formation - JW-33
6.86 1 .22 59.94 7.86 26.43 0.52
____________ ____________
102.84 A n d e s i n e 57.14 36.15 6.71
6.96 1 .27 59.39 7.65 26.16 0.16
------- -------
101.58 Andes i ne 57.91 35.16 6.93
6.52 1 .28 58.50 8.02 26.38 0.37
— — -------
101.69 A n d e s i n e 55.27 37.57 7.16
7.08
f
1 .08 59.75 7.34 25.92 0.20
------- -------
101.38 Andes i ne 59.78 34.23 5.99
Table 4 continued...
Na20 K20
Concentration %
Si02 CaO T i 0 2
Total
% Type
Mol e %
Ab An Or
Lower Gal 1 away Formation - JM-33 continued.. .
6. 78 1.10 59.01 7.36 26.28 0.32
-------------------- --------------------
100.85 Andes i ne 58.59 35.16 6.25
5.89 1 .09 58.29 8.35 26.15 0.19
-------------------- --------------------
99.96 Andes i ne 52.52 41 .10 6.38
6.45 1 .09 59.29 7.31 25.45 0.26
-------------------- --------------------
100.35 Andes i ne 55.91 35.00 9.09
7.46 1 .27 60.68 6.15 24.09 0.33
-------------------- --------------------
99.94 Andes i ne 63.95 29.12 6.93
6.64 1 .56 59.65 7.96 26.14 0.41
--------------------
102.35 Andes i ne 55.03 36.48 8.49
Middle Gallaway Formation - JW-80
7.72 1 .48 61 .17 5.45 24.25 0.42
_ _ _ _
0.31 100.80 01i goclase 65.95 25.71 8.34
8.70 0. 53 62.38 4.82 24.65 0.14
-
--------------------
101.22 01i goclase 74.27 22.76 2.96
11 .09
--------------------
68.26 0.51 20.87 0.21
-------------------- --------------------
100.95 Albite 97.50 2.50
--------------------
6.74 0.88 58.72 8.29 27.81 0.22
-------------------- --------------------
102.67 Andes i ne 56.66 38.48 4.86
6.88 0.80 57.19 8.93 28.20 0.28
-------------------- --------------------
102.29 Andes i ne 55.73 39.99 4.28
11 .26 0.12 68.61 0.82 21 .51
-------------------- -------------------- --------------------
102.32 Albite 95.52 3.84 0.64
9.48 0.21 67.47 0.73 21 .18 0.18
-------------------- --------------------
99.24 Albite 94.63 4.02 1 .35
6.05 0.91 57.40 8.50 27.03 0.37
--------------------
0.16 100.42 Andes i ne 53.33 41 .40 5.27
11 .49 0.35 66.78 1 .24 22.02
-------------------- -------------------- --------------------
101.87 Albite 92.63 5.53 1 .84
10.79 0.13 67.10 1.12 21 .98
-------------------- --------------------
0.14 101.26 Albite 93.90 5.38 0.72
Upper Gallaway Formation - JW- 86
10.15 0.42 64.78 3.89 22.95 0.27
------- --------
102.45 01 i g o c 1 a s e 80.72 17.11 2.17
7.48 0.54 60.76 7.69 26.44
-------------------- -------------------- --------------------
102.91 Andes i ne 61 .91 35.18 2.92
9.59 0.38 63.10 4.18 23.09
-------------------- -------------------- --------------------
100.35 01 i g o c 1 a s e 78.93 19.01 2.06
8.00 0.62 61 .92 6. 53 25.68
-------
102.75 Andes i ne 66.61 30.02 3.37
7.87 0.61 61 .48 6.69 25.59
--------
102.24 Andes i ne 65.75 30.91 3.34
CO
C J 1
Table 4 continued.
Na20
Concentration %
K20 S i 0 2 CaO A1 203 FeO MgO Ti 02
Total
% Type Ab
Mole %
An Or
Upper Gallaway Formation - JW-86 continued...
9.77
8.85
8.35
0.40 68.98 0.36 21.05 0.26 ......................
0.49 63.94 4.43 23.22 - ...................................
0.33 70.1 0 1.45 21.22 ......................
100.82
100.93
101.94
Albite
01igoclase
A1bi te
95.48
76.15
89.18
1 .93
21 .09
8.54
2.59
2.76
2.28
• ► ■
OR
• SKOONER GULCH
LOWER GALLAWAY
MIDDLE GALLAWAY
UPPER GALLAWAY
AB AN
Figure 8 - Composition of plagioclase feldspars from the Skooner
Gulch and Gall away Formations in terms of molecular
Albite (Ab), Anorthite (An), and Orthoclase (Or) as
determined by electron microprobe. Albite is the major
plagioclase in the Skooner Gulch Formation. Intermed
iate plagioclases, Oligocene and Andesine are dominant
in the Gallaway Formation. Exact results are summarized
in Table 4.
37
iGulch Formation is approximately the same as in the over-
i I
I
|lying Gallaway Formation, The most common rock types (in
lorder of abundance) are: volcanic rock fragments, i . e .
jbasalt with wel1-developed, plagioclase laths; f e ls ic
plutonic rocks, i . e . composite quartz and feldspar grains;
sandstone and shale; and rare, metamorphic rock fragments,
i . e , hornblende schist, These rock fragments are noticeably
^better rounded than the other d e t r i t a l grains. This is p a rt
ly due to the lack of overgrowths on the rock fragments,
Large, wel1-developed overgrowths on o r i g i n a l l y subrounded
jdetrital quartz and feldspar grains, has transformed these
!grains into subangular grains. Diagenetic a lte r a tio n of
jrock fragments to clay is common.
i
| Average porosity and permeability (based on NMR mea-
!
surements)( Table 5) is approximately 24% and 80 md perm- !
e a b i l i t y , This figure is obviously only applicable to sand
stone which has not been cemented with c a lc it e , In the
c a lc it e cemented sandstone, c a lc ite completely f i l l s all
Ipore space, eliminating any porosity or permeabi1i t y .
|
Petrography of the 1ower Gal 1 away Formation
j
The lower Gallaway Formation consists of a ltern atin g
i
dark-to lig h t- g r a y , subangular to subrounded, moderately-
; i
;to p o orly-s orted, medium-to fine-grained l i t h i c arkose and
mudstone (Fig. 7)(Table 2). Average composition of the j
sandstone is 23% quartz, 9% K-feldspar, 15% plagioclase,
38 !
Porosity and
Table 5
Permeabi1i ty (NMR)
Formati on Sample No. Grain Size Porosity(%) Permeabi1ity (md)
1. Skooner Gulch JW-48 m.g. 24.0 80.71
2. Lower Gallaway JW-20 m. g. 22.4 0.11
3. Middle Gallaway JVJ-77 v . f . g. 26.7 0.32
4. Middle Gallaway JW-71 v .f.g . 27.1 0.23
5. Middle Gallaway 0 V i - 8 0 m.g. 26.2 1.41
6. Middle Gallaway JW-82 v .f.g . 37.8 0.07
v . f . g. 36.9 0.06
7. Middle Gallaway JVJ-84 f .g. 10.5 0.18
8. Upper Gallaway - light
1 ami nae JW-93 v .f.g . 37.6 0.05
v . f . g. 39.1 0.04
9. Upper Gallaway - dark
laminae JW-93 v .f.g . 23.4 0.01
u>
11% rock fragments, 20% clay (authigenic and d e t r i t a l ) , 4%
pyrite and 3% mica ( b i o t i t e and muscovite). Both grain and
matrix-supported fabrics occur. Localized zones of authi-
jgenic dolomite and p o r e - f i l l i n g c a lc it e cement occur
throughtout the unit. Small euhedral pyrite c ry s ta ls , hem
a t i t e and magnetite are commonly concentrated along bedding
surfaces. Slight compaction is evident by contorted micas.
| Clear monocrystalline ''common" quartz (85 to 99%) with
loccasional vacuaoles and rare to abundant m icrolites of
I
i
jtourmaline and r u t i l e is the most common quartz type. Ex
tin c tio n ranges from s tra ig h t to s li g h t ly undulose, Poly
c r y s t a ll in e grains (1 to 15%) always contain greater than
|
|three crystal units regardless of grain size. Boundaries
!
ivary from sutured to highly crenulated with occasional
's lig h tly stretched v a r ie tie s . They would be c la s s ifie d as
iunstable, "new crystals" or " polygonized" quartz types
j(Young, 1976). Small, rhombohedral quartz overgrowths
(2 urn in diameter) were observed by SEM on most of the
d e t r i t a l quartz grains. These overgrowths t y p ic a lly form
|a uniform grain coating or druse that completely surrounds
i
the d e t r i t a l grain, except where in contact with adjacent
d e t r i t a l grains. The lower Gallaway Formation d i f fe r s from
the Skooner Gulch Formation in that i t contains more plag
ioclase feldspar (16%) than K-feldspar (10%), Microprobe
analysis (Fig. 8) of the plagioclases indicates they are
unstable, intermediate plagioclases: andesine and oligocene
40
(Table 4), Zoned (normal and o s c illa to r y ) and twinned i
i
v a rie tie s are common. A lte ra tio n of these unstable plag- !
ioclases is believed to have been a major source of m a t e r i a l 1
jfor the growth of authigenic minerals, Orthoclase is the
i j
jdominant K-feldspar, with minor amounts of microcline and
i
p e rth ite . Microprobe analysis of some of the K-feldspars
jindicates 1 to 3% Na (Table 3) and trace amounts of Ca,
| i
The K content is generally lower than that of the Skooner i
Gulch K-feldspars. Wel1-developed, euhedral K-feldspar
overgrowths occur on some of the plagioclase grains,
i A wide v a rie ty of rock fragments were id e n t ifie d i n
cluding: sandstone and shale; volcanic rock fragments, i . e .
jbasalt; metamorphic, i . e . hornblende and b i o t i t e schist;
graphic granite; chert; chalcedony; and altered glass shards
complete with flow structure. The rock fragments are t y p i
c a lly unstable and commonly altered.
| Both d e t r i t a l p o r e - f i l l i n g and authigenic clay minerals
i
kere recognized by SEM, These may by c la s s ifie d as eith e r
i
[
jortho-or epimatrix (Dickinson, 1970), XRD indicates a
dramatic increase in i l l i t e , mixed-layer clay and c h lo r ite
with depth of burial throughout the Gallaway Formation.
1 I
Wel1-developed, p o r e - f i l l i n g , authigenic c h lo r ite was ob- j
j i
served in the basal Gallaway Formation and also was detect- j
ed by XRD analysis. Pore-bridging i l l i t e and mixed-layer
clays are the most abundant clay types. This type of clay is
p a rtly responsible for the reduction in permeability between?
between the Skooner Gulch and the Gallaway Formation, Rare
|p o r e - f illin g books of pseudohexagonal k a o lin ite appear to
be a lt e rin g to i l l i t e ,
| Abundant, large (0.5 to 1,0 mm), well-rounded glau-
[conite peloids occur in thin section from the basal bonebed,
i
I
These grains commonly are e ith e r rounded, struetureless
green peloids with occasional fractures and p y rite i n
clusions or elongate peloids, composed of vermicular c h lo r
ite , Composition of the mineral glauconite is known to
Ivary considerably (Thompson and Hower, 1975) but, in gen-
i
era! , i t is a mixture of i l l i t e and smectite.
Porosity and permeability of the clay-cemented sand
stone averages approximately 22,4% porosity and 0.11 md
jpermeabi1ity (Table 5). This dramatic reduction in perm
e a b i l i t y as compared to the Skooner Gulch Formation is i n
terpreted to be the res u lt of the d is tr ib u tio n and morph
ology of the pore-bridging i l l i t e and i l l i t e - s m e c t i t e clays,
i
Recent studies by Neesham (1977) have demonstrated that the
morphology and d is tr ib u tio n of d i f f e r e n t clay minerals has
j
|a s ig n if ic a n t impact on porosity and permeability. Comp
ariso n of SEM and NMR results in this report substantiates
his hypothesis.
Late stage p o r e - f i l l i n g c a lc it e and dolomite cement
have fu rther reduced porosity and permeabi1i t y , No MNR
measurements were taken on these zones. C alcite is the
more common mineral. I t forms dusty, p o r e - f i l l i n g patches
jadjacent to clay rich zones. SEM analysis reveals the pre-
j i
sence of minute clay inclusions within the c a l c i t e , fu rther J
supporting the idea that the c a lc it e has engulfed original I
i
^lay cemented matrix. Occasionally, the ca1c i t e - f i 11ed f r a c
tures, separate and displace portions of the d e t r i t a l
t
I
grains,
j
Small (10 to 20 urn) euhedral dolomite rhombs occur in
selected horizons. They form a major constituent of the
basal bonebed sandstone un it. These dolomite rhombs replace
tnatrix, d e t r i t a l grains and p y rit e , thus are believed to be
i
a la te stage cement. The significance of the dolomite
rhombs w ill be discussed l a t e r ,
^etrograph.y of the middle Gal 1 away Formation
The middle Gallaway Formation consists of l i g h t - t o
dark-gray, fin e - t o very fin e -g ra in e d , angular to subangular,
moderate-to po or!y-sorte d, l i t h i c arkose and mudstone, Av
erage composition of the sandstone is 23% quartz, 13% K-
feldspar, 11% plagioclase, 10% rock fragments, 15% clay,
and 17% c a lc it e (Fig. 7). The sandstone is t y p ic a lly grain-
bupported with grains touching but not in te rp en e tra tin g ,
|The only evidence of compaction is the molding of p lia b le
jnica flakes ( b i o t i t e and muscovite) around the rig id de-
I !
jtrital grains. j
With decreasing grain size, the percentage of recog- |
hizable p o ly c ry s ta llin e quartz decreases. The predominant
! 43 |
quartz type is cle a r, monocrystalline "common" quartz
(Young, 1976) with occasional vacuoles and m ic ro lite s .
jExtinction ranges from s l i g h t l y undulose to nonundulose,
j
(Unstable p o ly c ry s ta llin e grains with more than three cry-
! I
! ;
jstal units, undulose e x tin c tio n , and sutured crystal j
! i
i
[boundaries also occur. This type of quartz would be class- j
i j
jified by Young (1976) as "new cry s ta ls ". Some grains show
(pronounced s tra in . I t appears that with decreasing grain
i
Isize, these unstable p o ly c ry s ta l1ine v a rie tie s are f r a c t -
i !
jured into smaller crystals which then are counted as mono-
jcrystal 1 ine g ra in s , Small (1 to 2 urn in diameter) euhedral ,
quartz overgrowths were observed coating all d e t r i t a l
!
quartz g ra in s . A mixture of m ic ro c ry s ta l1ine (1 to 2 urn
in diameter), hexagonal, prismatic alpha quartz is also
i
common as a po re -lin ing and pore-bridging cement in some 1
i
of the the sandstone, |
|
Nearly equal percentages of K-feldspar and plagioclase j
j
feldspar occur in the middle Gallaway Formation (Table 2).
(Orthoclase is the predominant K-feldspar and occurs in
association with a minor amount of microcline. S light clay
a lt e r a tio n was observed by SEM and probably accounts for
i
ithe small percentage of Mg, Fe and Ti detected by micro
probe analysis (Table 3), Blocky, euhedral K-feldspar over- i
growths occur on both the d e t r i t a l K-feldspars and plagio- |
clases. Is o lated, euhedral K-feldspar grains also occur
scattered throughout the clay matrix. A lte ra tio n of plag-
44
ioclase grains is very common but some unaltered grains were*
iobserved, Oligoclase and andesine (Table 4) are the most
j j
common plagioclase (An23_4^)» with a s ig n if ic a n t amount of
ivery pure a lb it e ( ^ 2- 6^' a"lkite probably represents
authigenic grains. The plagioclase is commonly twinned
jand occasionally zoned.
j A wide v a rie ty of rock fragments occur in the middle |
jGallaway Formation, These include basalt, with euhedral
plagioclase laths , g r a n itic rocks, b i o t i t e schists, shale,
chert, and altered glass fragments. All of the rock frag-
i
1
jments, except chert, show evidence of clay a lt e r a t io n ,
i !
| Variations in grain size and the d is tr ib u tio n and mor-
i
1
phology of clay minerals within the Gallaway Formation play
an important role in the development of porosity and perm- |
iea bility of the samples. Porosity and permeability measure
ments vary from 35.5 to 10.5% and 1.41 to 0.03 md permea
b i l i t y . XRD analysis reveals nearly equal amounts of smect-
!
iite, mixed-layer i 11it e - s m e c t i t e , i l l i t e and k a o lin it e , SEM
janalysis reveals that the d is tr ib u tio n and type of clay is
not uniform throughout the formation. Variation in clay
Imineralogy appears to be e s s e n tia lly an inherited fe a tu re ,
i
|dependent on the original depositional environment. For
example, the lack of porosity in JW-84 is c le a r ly due to the
p o r e - f i l l i n g nature of the orthomatrix. The sample with j
| j
the highest permeability contains the least amount of pore- ,
bridging i l l i t e and numerous large unobstructed pores. In
i ;
45 i
jJW-70, the permeability has been reduced by the growth of
jwide ribbons of i 11ite -s m e c tite which disrupted the pore,
| ,
Icreating tortuous f l u i d flow pathways. Webby, authigenic
jsmectite coatings lin e many of the d e t r i t a l grains. Minor
jpatches of p o r e - f i l l i n g k a o lin ite with s l i g h t l y i l l i t i z e d
I
edges also occurs. A minor amount of the z e o lit e mineral, j
i |
p h i l l i p s i t e , was also observed in both thin section and
during SEM/EDX analysis. P h i l l i p s i t e is a common z e o lite
in marine environments ( I i j i m a , 1978) and appears to have j
jformed by the a lt e r a tio n of volcanic glass.
j Late stage p o r e - f i l l i n g c a lc it e and dolomite cement j
!has engulfed much of the original cl a y - f i l l e d matrix. Cal
c ite is the dominant carbonate p o r e - f i l l i n g with dolomite
being re s tric te d to specific horizons. The c a lc it e is
i !
t y p i c a l l y d i r t y in thin section and SEM analysis indicates
this d irtin es s is due the presence of minute clay pa rticle s j
i i n the c a lc it e . D e t r it a l grains occasionally appear as |
I
I
ghosts within the c a lc it e cement. SEM examination of the
iconcretionary zones indicates almost a ll of the original
i
matrix and d e t r i t a l grains have been replaced by dolomite.
i
jRecrystal1iz e d , wel1 - preserved, fo ram iniferal tests are
|common in the mudstone. The internal chambers of the tests j
! j
are t y p ic a lly f i l l e d with e ith e r c a l c i t e , dolomite or |
p y rite .
46
P etro g ra p h y o f the upper Gal 1 away Formati on
j The upper Gallaway Formation consists predominantly
!
jof very fin e -g ra in e d , angular to subangular, poorly-sorted
j l i t h i c s il t s t o n e , arkose, mudstone, and hem ipelagite. The
|average composition of the sandstone is 19% quartz, 12%
jK-feldspar, 9% plagioclase, 5% rock fragments, 15% clay,
|
28% c a l c i t e , 7% p y rite and 4% mica ( b i o t i t e and muscovite)
(Fig. 7). The compositional variations between this unit
and the remainder of the Gallaway Formation is prim arily
due to variations in grain size rather than variations in
i
source. The alignment and crushed appearance of some of
the foraminifera 1 tests and d e t r i t a l mica indicates compac
tion of the o rig inal sediment. Most of the beds are m atrix-
supported with abundant d e t r i t a l clay.
Nearly a ll of the quartz appears to be c le a r, mono
c r y s t a ll in e "common" quartz (94 to 100%) with rare polycry
s t a l l i n e grains. M ic ro lite s of tourmaline and r u t i l e occur
within the quartz. The predominance of monocrystalline
jquartz is s im ila r to the middle Gallaway Formation and p r i
m arily r e f le c t s va ria tio n in grain size. Individual crystal
i
junits of p o ly c ry s ta l1ine quartz appear as monocrystalline
i
i
jgrains in this size fr a c tio n . Small, authigenic quartz
i
iovergrowths usually surround the d e t r i t a l quartz grains.
iOccasional siliceous concretions replace the dolomitic
i
j
Concretions of the middle Gallaway Formation.
i K-feldspar and plagioclase occur in nearly equal
I 47
amounts in the upper Gallaway Formation (T able 2 ). O rtho-
i
|clase is s t i l l the dominant K-feldspar, with minor amounts
of microcline and p e rth ite . Many of the d e t r i t a l feldspar
igrains are coated with clay, making i t d i f f i c u l t to id e n t
i f y the various minerals in the SEM. Where i d e n t i f i a b l e ,
planar, euhedral K-feldspar overgrowths were observed on
d e t r i t a l K-feldspars and rare cases, a plagioclase feldspar
overgrowth was observed on a d e t r i t a l plagioclase grain.
Authigenic overgorwths were r e s tric te d to sandstone samples
which have some porosity. The plagioclase grains are
predominantly unstable andesine and oligoclase (An-|g_gg)
with rare authigenic a lb it e (Table 4 ) (Fig. 8). The d e t r i
tal plagioclase grains are usually twinned, zoned and high
ly a ltered . A lte ra tio n of the plagioclase tends to be so
complete that only a few slivers of the original d e t r i t a l
grain remains, creating a secondary pore. The t i g h t l y com
pacted surrounding clay and carbonate matrix tends to pre
serve the original grain ou tlin e.
Rock fragments, where i d e n t i f i a b l e , tend to be pre
dominantly volcanics ( b a s a lt ) , plutonics, and a few grains
of sandstone, shale and chert. The decrease in the number
of rock fragments in the upper Gallaway Formation re fle c ts
both a decrease in grain size and diagenesis. Many of
the unstable l i t h i c grains have altered to clay making
i t impossible to separate them from matrix m ate ria l. The
plutonic rock fragments tend to be broken into th e ir in-
48
individual components such as isolated quartz and feldspar i
grains. These grains are then impossible to d i f f e r e n t i a t e j
from d e t r i t a l quartz and feldspar. |
| I
Examination of sandstone, mudstone and hemipelagite ;
beds in the SEM was helpful in separating d e t r i t a l from
authigenic clay. The predominant clay mineral detected by
X-ray d i f f r a c t i o n was smectite, with lesser amounts of
i
j
i l l i t e , k a o lin ite and mixed-layer i l l i t e - s m e c t i t e , Most of
this clay is c le a rly d e t r i t a l , but authigenic smectite and
k a o lin ite occur. The clay matrix may be c la s s ifie d as ortho-
and epimatrix (Dickinson, 1970). The d e t r i t a l clay tends to
be massive and p o r e - f i l l i n g while the authigenic clay forms
grain coatings and bridges. The porosity values of the sand
stone samples varies from 37.6% in the lig h t-c o lo re d zones
to 23.4% in the dark laminae. Permeability only varies from
0.1 to 0.5 md. The significance of this observation w ill be
discussed l a t e r .
Late stage, sparry, p o r e - f i l l i n g c a lc it e cement is the
dominant carbonate mineral. I t can form as much as 41% of
the rock, surrounding both d e t r i t a l grains and matrix. In
addition, small authigenic c a lc it e rhombs, intermixed with
i
i
bl ay occur in the porous sandstone. Inclusions of clay are
I
c le a r ly v is ib le within the c a lc it e p o r e - f i l l i n g . C alcite
: i
cementation does not appear to have been complete since !
i ;
pore space is s t i l l v is ib le and the c a lc it e adjacent to the i
i
i
porous zones is surrounded by wel1-developed, authigenic
cl ay,
Pyrite is very abundant in the mudstone and hemipel-
agite beds. I t occurs as isolated crystals or lenses and
I
!
pockets pa ra lle l to bedding. Wel1-developed framboids and
octahedrons are the most common form. The p y rite is c le a rly
a la te stage mineral, forming in pores and replacing d e t r i
tal grains.
| j
j i
I PROVENANCE
t
i
I I
Determination of the provenance of the Skooner Gulch j
jand Gallaway Formation is d i f f i c u l t due to uncertainties
[regarding the original depositional location. Wentworth
1(1966) suggested the source was a now eroded Salinian I
i i
I I
highland to the west. This is d i f f i c u l t to e ith e r confirm
i i
; I
or disprove. So in this study, heavy mineral, rock frag-
i
ment composition and a plot of quartz undulosity and poly- j
i
!crystall i n i t y ( a f t e r methods of Basu and others, 1975)(Fig. |
9) were made to determine not source area, but only possiblej
source rock types. j
The d e t r i t a l heavy mineral composition of both the
jSkooner Gulch and Gallaway Formation consists prim arily of
a p a t it e , sphene, zircon, magnetite, b i o t i t e and hornblende, ;
These minerals are the dominant heavy minerals that char
ac te rize the granodiorite and quartz d i o r i t e intrusions of
the C a lifo rn ia Coast Ranges (Spotts, 1962; Yancey and Lee,
50
POLYCRYSTALLINE QUARTZ
• SKOONER GULCH
■ LOWER GALLAWAY
▲ MIDDLE GALLAWAY
• UPPER GALLAWAY
j
PLUTONIC
* MIDDLE
/ UPPER RANK
/METAMORPHIC
NON-UNDULATORY
QUARTZ
UNDULATORY
QUARTZ
/ LOW RANK
/ METAMORPHIC
POLYCRYSTALLINE QUARTZ
Figure 9 - Source rock determination based on plot of
quartz undulosity and p o ly c ry s ta llin ity
(a fte r methods of Basu and others, 1975).
Results suggest that the source rocks for
the Skooner Gulch and Gallaway Formations
is low rank metamorphic rocks. 1 (2-3 cry
stal units per g ra in ;—75% of total poly-
c rys tallin e quartz); z ( > 3 crystal units
per grain; >25% of total polycrystalline
q u artz).
51
(1972) and are considered in d ic a tiv e of a Salinian (pluton-
ic) source.
Acid plutonic rock fragments (also in d ic a tiv e of a
Salinian source) are the major rock fragment types in both
| the Skooner Gulch and Gallaway Formation. Basalt, with
! wel1-developed p latio clase laths; hornblende and mica
schists; and a minor amount of ra d io la ria n chert and meta-
sedimentary rocks from the Franciscan Formation also o c c u r . ’
This assemblage of rock fragments suggests that m ultiple
source areas of mixed plutonic, volcanic and metamorphic
rocks fed the Gualala Basin. Both heavy mineral and rock
i
fragment composition indicate that a plutonic source was
domi nan t .
Basu and others (1975) contend that quartz undulosity
and polycrystal 1i n i t y can be used as a source rock in d ic a
tor. A plot of quartz type for the Skooner Gulch and G a ll- j
away Formation (Fig. 9) suggests that the source rocks were
j predominantly low rank metamorphic rocks, rather than plu
tonic. This conclusion is u n lik e ly , due to the lim ite d ex
tent of known low rank metamorphic rocks av aila b le to sup
ply the Gualala Basin and the lack of substantiating e v i
dence from heavy mineral and l i t h i c analyses. One major
problem with the method of Basu and others is that i t d i f
fe re n tia te s plutonic and low rank metamorphic quartz p r i
marily based on undulosity: plutonic quartz is considered
52
nonundulose and low rank metamorphic quartz is undulose, i
This generalization ignores the many cases of undulose plu-
Itonic quartz which occurs in both stable and unstable t e c t - j
i
; i
jonic areas. The Skooner Gulch and Gallaway Formation un- !
jdulose quartz is probably also of plutonic orig in and thus
11he Basu diagram cannot be used to predict possible source
roc ks.
DIAGENESIS
Diagenesis includes " a ll processes, chemical and
physical, which a ffe c t the sediment a f t e r deposition and
i
jup to the lower grade of metamorphism, the greenschist
facies " (P ettijo hn and others, 1972). My work c le a r ly
shows that diagenesis has not been uniform throughout the
Skooner Gulch and Gallaway Formations, The recognized di-
agenetic changes are: a lt e r a tio n and resorption of unstable
d e t r i t a l grains such as feldspar, rock fragments and d e t r i -
I
11a 1 clay; formation of authigenic quartz, K-feldspar and
i
[clay cements; formation of iron oxide coatings (hematite)
j
|and p y rite ; replacement of d e t r i t a l grains and matrix by
[late stage carbonate cements; and reduction in porosity
I i
! I
[and permeability due to the growth of authigenic minerals. i
j !
[In this study I have attempted to describe and define some j
of the factors which have influenced and controlled diagen- j
esis in these formations. A summary compilation of a ll the ;
major authigenic minerals recognized is lis te d in Table 6.
jThe purpose of this table is to allow the reader to rea d ily :
I j
jcompare the coexisting mineral phases recognized. Recon
s t ru c tio n of the diagenetic history has depended prim arily |
Ion the use of the SEM/EDX, in combination with other ana-
|
jly tical tools. The SEM/EDX has been extremely important in
[allowing d i f f e r e n t i a t i o n of d e t r i t a l and authigenic minerals
i
and also for examination of the extremely small (1 to 2 urn |
in diameter or less) diagenetic end products.
Origin of the matrix i n graywac kes
The origin of the matrix in fin e -g ra in e d , argillaceous
sandstone (graywacke) has been in dispute for over two
decades and has been termed the "greywacke problem"
(Cummins, 1962). The d e f in it io n of graywacke accepted in
I
this report follows Cummins ( 1 962:p . 51) where he states
"greywacke is a kind of sandstone in which the sand grains
are set in a fine ’muddy’ matrix. The fine-gra ined matrix
!is at once the essential c h a ra c t e r is tic of greywacke and
I
i
11he essence of the greywacke problem". Although not all
tu rb id ite s are graywackes, the Gallaway Formation with its
; |
!15 to 20% clay m atrix, would be considered a graywacke; the
I
[Skooner Gulch Formation is a pure arkose.
i Cummins (1962) was the f i r s t geologist to challenge
j i
the previously accepted theory that the matrix in gray- !
wackes was of d e t r i t a l o rig in . One of Cummins' major ar- ;
54 l
i ,
Table 6 - Summary of the major a u thige nic minerals recognized in the
Skooner Gulch and Gallaway Formations (by sample).
Sample Number Quartz
K-spar
0/G
PI ag
0/G
Authigenic clay
Pyrite
Calcite
Dolomite
Del
tri tal hosl
Kaol
M-L
Chi
0/G Mxln K
r -T T i
p
k 1
p P L PF P B
S K O O N ER G U LC H
JW-27* (msv) X X X X X X X X
JW-60* 1 1 X X X X X X X
JW-49* " X X X X X
JW-48* " X X X X
JW-46* " X X X X X X X
LO W E R G A LLA W A Y
JW-61* (msv) X X X X X X X X X
JW-53 X X X X
JW-38* (dike) X X X X X X X X
JW-37b X? X X X X X
JW-23 X X X
JW-22* (dike) X X X X X X
JW-33* (msv) X X X X X X
JW-30 X X X? X X X X
JW-29* (concretion) X X X X X X
JW-28* (msv) X X X X X X X
JW-20* (msv) X X X X X X X
JW-99* (concretion) X X X X X
( j i
cn
Table 6 - Summary of major authigenic minerals recognized in the Skooner Gulch and Gallaway Formations
Sample Number Quartz
K-spar
0/G
Plag
0/G Authigenic clay
Pyrite
Calcite
Dolomite
Deitrita ' hos-
t
Kaol
M-L
Chi
0/G Mxln K P K P P L PF P B
MIDDLE G A LLA W A Y
JW-77* ( f 1 ) X X X X X X X X X
JW-76* " X X X X X X X X
JW-73 X X X
JW-71* ( f 1 ) X X X X X X X
JW-70* " X X X X X X X X?
JW-69* " X X X X X
JW-68 X X X
JW-67* ( concretion) X X X X X X X
JW-66 X X X
JW-80* (msv) X X X X X X X X X X
JW-81* " X X X X X X X X X X X
JW-82* ( f l ) X X X X X X X X X X
JW-83 X
JW-84* (msv) X X X X X X X X
UPPER G A LLA W A Y
JW-92 X
JW-93* ( f l - l i g h t 1 am)X
JW-93* (fl-dark lam) X X
JW-91
jW-90*(f 1) X X
JW-89* " X
c n
O '!
Table 6 continued,...
Sample Number
Quartz
K-spar
0/G
Plag
0/G
Authigenic clay
Pyrite
Calcite
Dolomite
Detrital hosi
Kaol
M-L
Chi
0/G Mxln K P K P P L PF P B
UPPER G A LLA W A Y
JW-88 X X X X X X
JW-87 X X X X X X
JW-86* (fl) X X X X X X X X X
Key: 0/6= overgrowth; Mxln= microcrystalline; K = potassium feldspar; P= plagioclase feldspar;
Kaol= kaolinite; M-L= mixed-layer illite-sm ectite; PL= pore-lining; PF= pore-filling;
PB= pore-bridging; Chi = chlorite; lam.= laminae; fl= finely-laminated; msv= massive,
* denotes sandstone
guments against d e t r i t a l matrix was the f a i l u r e of modern
marine geologists to find graywacke-type rocks in P le is to -
jcene and Recent deep-sea t u r b i d i t e cores. He suggested that
|the amount of matrix increased at the expense of sand grains
I by a lt e r a tio n during diagenesis.
Numerous authors have presented evidence to support
Cummins' theory (Kuenen, 1966; Benchley, 1969; Lo vell, 1972;
B uller and McManus, 1973; Galloway, 1974) but most have pre
fe rr e d to q u a lify t h e ir observations by admitting d e t r i t a l
i
jclay probably existed too. All of the above data was gather-j
i
ed from thin section analysis (not SEM/EDX), where i t is
j
ge n e ra lly impossible to id e n t if y the clay species much less
jdet ermine whether or not the clay is d e t r i t a l or authigenic.
I
I i
jWhetten and Hawkins (1970, 1972) added experimental evidence
I |
by subjecting c la y -f re e volcanoclastic sediment to tempera-
! i
i !
tures and pressures equivalent to 3000 to 5000 m of burial j
j
land forming authigenic clay. Current workers s t i l l tend to
acknowledge that both d e t r i t a l and authigenic clay probably
exist in graywackes, but no one has attempted to determine
i
]
jthe exact d i s t r ib u tio n or re latio n sh ip of these two clay
jtypes and what a f f e c t this has had on diagenesis.
; i
I f the sole source of clay matrix in the Gallaway For- |
: I
mation graywackes is the product of the diagenetic a l t e r a - |
tion of unstable grains, then the Skooner Gulch Formation,
which is compositionally sim ila r in its oercentage of un
stable d e t r i t a l grains (excluding clay content), should also
58 ;
contain abundant clay in the matrix. Since the Skooner
Gulch Formation is not a graywacke, other factors must play
a major role in the formation of clay matrix in a graywacke.!
jAuthigenic versus d e t r i t a l cl ay
I Before determining the diagenetic history of a forma
tion i t is imperative that one is able to d i f f e r e n t i a t e the
'd etrita l from the authigenic grains. In the case of the
major framework grains, this is generally not a problem,
but for the fin e-g rained clay matrix this has been a major
iproblem and is c r i t i c a l to defining diagenetic change. I-
Identification of authigenic clays can now be f a i r l y accur
a te ly done using the SEM/EDX. Wilson and Pittman (1977) were
among the f i r s t to characterize and id e n t if y authigenic
! !
clay cements using the SEM. They provided excellent SEM !
' !
Iphotomicrographs and numerous c r ite r a for distinguishing |
jdifferent authigenic clays based upon composition, morpho
logy, stru ctu re, texture and d is t r ib u t io n . The authigenic
iclay are ty p i c a l l y well-formed, with diagnostic crystal
|
habits and chemical compositions.
Very l i t t l e work has been done on d e t r i t a l or allogenic
i
j
jclay i d e n t i f i c a t i o n . Wilson and Pittman (1977) b r i e f l y men-
!
tion the problem and l i s t a few differences between a u t h i
genic and d e t r i t a l clay, but t h e ir examples are not well j
documented. Walker and others (1978) discuss i n f i l t e r e d
d e t r i t a l clay in an arid environment, a specialized occur
rence not applicable to this environment.
!
In order to resolve this problem, I examined several
iof the interbedded mudstone units adjacent to sandstone
jbodies in the Gallaway Formation. A mudstone is by d e f i n i
t i o n composed of d e t r i t a l clay. My work c le a r ly reveals
d i s tin c t differences between d e t r i t a l and authigenic clay.
The d e t r i t a l clay is t y p i c a l l y anhedral , poorly-formed, and
composed of ragged-edged clay p la te le ts which appear matted I
!(F i g . 10a), flo c u la te d , or compacted around d e t r i t a l grains,!
i
‘completely f i l l i n g the pore space. Clay observed in sand- j
!
istone beds with this morphology were termed d e t r i t a l clay j
and were noted to occur sporadically in many of the sand- j
stone beds. This is in marked contrast to the authigenic
clay (Fig. 10b) which occurs as well-formed, p o re -lin in g ,
i
p o r e - f i l l i n g and p o re -b r id g in g c la y s . !
I
i
Origin and significance of the interbedded mudstone
and dark 1 ami nae
A fte r separation of the clay types, one returns to the
j
jauestion of d is t r ib u t io n of the d e t r i t a l clay within the
i
Gallaway Formation and how that relates to diagenesis. De-
i
I t r i t a l clay within the Gallaway Formation appears to be con-j
!
centrated in two d i s t i n c t zones: within the interbedded mud-;
j
i
stone (Fig. 11a) and in th in , dark laminae that characterize;
the fine-graine d sandstone (Fig. l i b ) . j
I t is the presence of these p e l i t i c in terv a ls which I
60 !
Figure 10 - Comparison between detrital and authigenic clay, (a) P ore-filling, raaged-edqed
detrital clay platelets compacted between detrital grains. 3000X. (b) Well-form
ed, webby pore-lining and ribbon-like pore-bridging (arrows) authigenic i l l i t e -
smectite clay. 700X.
F gure 11 - S E M micrographs showing the morphology and distribution of detr tal clay in two
zones of the Gall away Formation, (a) Compacted, anhedra.1 detrital clay from a
mudstone unit between tu rb:d>te sandstones. 2000X- (b) Detrital clay-coated sur
face intermixed with pyrite framboids (arrows) within a dark laminae in the fine
ly-laminated turbidite sandstone beds, 600X.
CD
r o
used to separate the Skooner Gulch Formation from the G all-
away Formation in the f i e l d and which appear to be a major
fa c to r in explaining differences in the diagenesis between !
i j
|the two formations. Although chemical analyses of bulk
|
is hale samples (Boles and Franks, 1979) indicate l i t t l e
change in weight percent of Fe, Mg or Si with depth of
iburial, s ig n if ic a n t amounts of these elements can be tra n s
ferred from the shale to the sandstone during diagenesis.
Thus, growth of authigenic clay has been much greater in
the Gallaway Formation due to a larger supply of dissolved
i
I
ions from the d e t r i t a l clay zones.
The occurrence of dark laminae in the Gallaway Forma
tion represents a major change in the orig in al depositional
jenvironment, from a unit formed by f lu id iz e d grain flow to
!a t u r b i d i t e deposit. Although the exact origin of dark lam
inae is not known (P ettijo hn and others, 1972), they are
believed to represent flu c tu ations in the competance of the
depositing density cu rrent, i . e . a lte rn a tin g coarse to fine
i
deposition.
SEN examination of separated dark and l i g h t laminae i n
d ic a te that the dark laminae are minera1ogica11y d i s t in c t
|
|from the l i g h t laminae. The dark laminae do not contain
iconcentrat i ons of heavy minerals as is generally advocated
Ifor the orig in of dark laminae, but instead contain a con- [
]
centration of d e t r i t a l clay (Fig. l i b ) , mica ( b i o t i t e )
(Fig. 12a) and p y rite (Fig. 12b). The l i g h t laminae are the j
Figure 12 - S E M micrographs showing the composition of dark laminae in the upper Gallaway
Formation, (a) Isolated dark laminae (JW-93) containing detrital clay, biotite
(B)(smooth dark areas) and authigenic pyrite framboids (round balls). 200X.
(b) Enlargement of area outline by black square in (a) showing the morphology
of the euhedral pyrite framboids and pyrite octahedra (arrows). 3000X.
c r >
- p *
'sandstone (Fig. 13a), containing a ll of the typical d e t r i t a l
jframework grains l i s t e d in Table 2. The clay matrix in the
li g h t laminae consists p rim a rily of well-formed, authigenic 1
clay (Fig. 13b), not d e t r i t a l clay, except where b iotu rb a
tion has introduced d e t r i t a l clay into the sandstone from
adjacent mudstone or fin e ly -la m in a te d (dark) zones. !
; j
Measurements indicate that porosity is g re a tly reduced
!in zones containing predominantly dark laminae (24%) but
i * i
I . j
|is higher in the l i g h t laminae (37%). Permeability is very !
| j
|1 ow in both cases (0.01 to 0.05 md) but is lowest in the
dark laminae. The dark laminae are believed to play an im
portant role in disrupting the perm eability of the unit by
j
jcr eating perm eability b a rrie rs . Thus, diagenesis in massive
sandstone, devoid of laminae, is markedly d i f f e r e n t from
diagenesis of fin e ly -la m in a te d sandstone. I
i
|
i
jSignificance of soft sediment deformati on and bioturbation
Two important factors in the r e d is t r ib u tio n of d e t r i t a l
iclay are the post-depositional m odification of the orig inal
i
f a b r ic and texture by soft-sediment deformation (convolute
beds) and bioturbation. Both of these processes occur soon
|after deposition but prior to compaction and l i t h i f i c a t i o n , |
• !
The res u lt is the additional admixture of d e t r i t a l clay intoj
ipreviously w ell-so rted and c la y -f r e e sand. This mixing in j
; !
i t s e l f does not create an argillaceous sandstone, but i t
does provide additional unstable or reactive minerals to the
j 65 i
! I
Figure 13 - S E M micrographs showing composition of light laminae in the upper Gallaway
Formation, (a) Isolated light laminae (JW-93) containing detrital quartz and
K-feldspar grains rimmed with webby, pore-lining authigenic i'llite-sm ectite
clay. 700X. (b) Enlargement of detrital K-feldspar surface showing euhedral,
authigenic K feldspar overgrowths (o') and webby9 authigenic i l l ite-smectite
clay rim (arrow). 3000X.
system, which, during diagenesis can be converted to auth
igenic clay. The eventual r e s u lt is the formation of an a r
gillaceous sandstone or graywacke.
|
| Soft-sediment deformation is caused by the deposition
of unconsolidated sand (containing c la y -r ic h laminae) upon j
s o ft, u n l i t h i f i e d mud. Original bedding of the sand was
j
probably e it h e r planar or cross-laminated. However, dewater-j
! ;
j i n g of the mudstone during compaction resulted in deforma-
I
|tion of the orig in al s t r a t i f i c a t i o n forming perm eability
jbarriers between the disrupted laminae. This allows complex,
j !
time-dependent, microgeochemical environments to develop, j
iin which diagenetic reactions vary. I
i
l
jBioturbation
i
! The Gallaway Formation depositional environment, with
j
its long periods of mud accumulation between turbid flows,
must have been an ideal habitat for burrowing organisms. j
iWel1 - preserved burrows and mottled zones are common through
out the u n it. Although fo s s ils were not found in or assoc
ia t e d with the burrows, recent studies of modern deep-sea
jfan analogues (Piper and Marshall, 1968) suggest that the
Itrace fo s s ils were probably formed by marine invertebrates ,
such as polychaete worms, shrimp and other crustaceans, j
These organisms are known to be extremely e f f e c tiv e in r e
d i s t r ib u t in g and mixing d e t r i t a l mud into sand layers; at
times, completely homogenizing a formerly wel1-o rd e re d ,
67 I
laminated bedding sequence, !
Comparison of a heavily burrowed, fin e ly -la m in a te d !
i
i
sandstone with a non-burrowed, fin e ly -la m in a te d sandstone,
indicates that both units contain abundant authigenic' clay, j
Ibut only the burrowed sandstones contain d e t r i t a l clay in -
i
jtermixed with the authigenic clay. Since a ll of the sand
stones are 1it h o lo g ic a 11y s im ila r (except for the presence
or absence of d e t r i t a l c la y ), a c o rre la tio n between burrow
ed zones and the presence of d e t r i t a l clay appears to be
more than co inciden tal. Bioturbation is believed to be one
i
jof the key factors in introducing d e t r i t a l clay into se
lected sandstone units.
Figure 14a shows an example of an elongate in vertebrate
burrow within a mudstone in te rva l in the middle Gallaway
Formation. The burrow is t y p i c a l , in that i t contains
Icoarser sand-sized d e tr itu s then its surrounding host rock
!
i
(Fig. 14b). Authigenic minerals, such as quartz overgrowths,
clay and p y rite (Fig. 15a) were able to develop in the
large pores of the burrow, but not in the fin e-g ra ine d mud
stone. The p y rite formed due to decomposition of organic
m atter, presumeably by sulphate-reducing bacte ria. Decomp-
iosition of organic matter is probably also responsible for j
! i
lo ca lize d Eh/pH va ria tio n s within the burrow which caused j
jthe p a rt ia l dissolution of authigenic quartz overgrowths j
j
(Fig. 15b). This dissolution of quartz overgrowths is r e
s t r i c t e d to the burrows.
68 !
Figure 14 - Photograph and thin section photomicrograph of a burrow in the middle Gallaway
Formation, (a) Photograph of an elongate burrow in a mudstone unit within the
middle Gallaway Formation (arrow indicates location of the burrow), (b) Thin
section photomicrograph (plane light) through the sam e burrow showing the sharp
contact and grain size variation between the mudstone (M) and the sand-filled
burrow (B). Bar scale equals 68 urn .
Figure 15 - S E M micrographs of quartz overgrowths in a burrow, (a) Detrital quartz grain (Q)
surrounded by a matrix of detrital and authgenic clay and pyrite (arrows) from
inside the burrow illustrated in Figure 14. 2000X. (b) Close-up view of the
detrital quartz grain surface showing slightly dissolved authigenic quartz over
growths (arrow) and iron oxide crystals (H). 10,000X,
' ' ■ j
o
IPoros i ty and permeahi 1 i t.y |
The importance of porosity and permeability on dia- !
genesis of a sandstone has been b r i e f l y alluded to through
out this section. Only a few additional comments are re-
I i
jquired to c l a r i f y the a f fe c t that has had on diagenesis.
i
| Porosity varies according to grain shape and sorting,
but not grain size (McBride, 1977). Fine-to very f i n e
grained sandstone t y p i c a l l y has much higher porosities than
associated coarser-grained layers. This re la tio n s h ip is
a t trib u t e d to grain shape, with angular grains being more
jresistant to compaction than rounded grains (FUchtbauer,
l
|1 9 6 7 ) . The f i ner-gra i ned Gallaway Formation is no exception,
jwith porosity values averaging 22 to 39%, whereas porosity
of the coarser-grained Skooner Gulch Formation is approxi-
i
mately 20 to 24%. Although overall porosity is high in the
Gallaway Formation, individual pores are small, This is a
major fa c to r in c o n tro llin g sandstone diagenesis. The size
and d i s t r ib u t io n of authigenic minerals is lim ited by the
size of the pores. Thus, the authigenic minerals which form-
|ed in the Skooner Gulch Formation, with its larger pores,
i
j
are b e tte r developed than those of the Gallaway Formation.
i
j Permeability measures the a b i l i t y of a sandstone to
i
transmit flu id s and is a function of grain size , s o rtin g , \
\
o rie n ta t io n and packing. According to the Kozeny-Carmen ]
equation (McBride, 1977), perm eability is roughly propor-
! i
tio n a l to porosity and inversely proportional to the square j
!of the spec ific surface. Thus, for two sandstone bodies of !
|equal porosity but d i f f e r e n t grain s ize , the fin e r-g ra in e d
jsandstone w ill have a greater sp e c ific surface to retard
|flow and thus w ill have lower perm eability (McBride, 1977).
I
i
'Permeability of the fin e -g ra in e d Gallaway Formation would
i
!have o r i g i n a l l y been low, but the growth of authigenic min-
! i
i ‘
e r a ls , p rim a rily clays, and the formation of perm eability |
jbarriers , such as the dark laminae, convolute bedding and
I
jmudstone interbeds has fu rt h e r reduced the perm eability to
Hess than 1 m illid a r c y . The coarser-grained Skooner Gulch
i
■Formation has much greater perm eability (80 md) but this !
]
!is la r g e ly due to its larg er grain size (pores) and lack
i
jof authigenic clay cements.
|
i
[S t r a t i f i cati on
F i n a l l y , the la s t major fa cto r on diagenesis is s t r a t - j
i
i f i c a t i o n type; e.g. massive versus fin e ly -la m in a te d sand
stone. The Skooner Gulch Formation contains only massive
jsandstone, so diagenesis has been r e l a t i v e l y homogenous. j
iHowever, in the Gallaway Formation, both bedding types occurj
jand diagenesis has been d i f f e r e n t in each type. Composition-
j j
ia lly , the sandstone beds are a ll s im ila r , containing 15 to j
i !
!20% clay m atrix. D ia g e n e tic a lly , the fin e ly -la m in a te d sand- j
!stone contains both d e t r i t a l and authigenic clay whereas
the massive sandstone contains only authigenic clay. Major
i
^differences in the diagenetic history of each bedding type
72
w ill be described separately below.
I DIAGENSIS OF THE SKOONER GULCH FORMATION
I
i
I
Diagenesis began with minor compaction and pressure
solution at points of grain contact (Fig. 16a). Pressure
| solution has not been extensive but possibly did supply
some of the s i l i c a for the formation of authigenic quartz
overgrowths. A lte ra tio n of d e t r i t a l rock fragments (Fig.
16b), i l l i t i z a t i o n of K-feldspar and a l b i t i z a t i o n or r e
sorption of plagioclase feldspars were probably the major
contributors of dissolved ions for l a t e r diagenetic reac
tions. The major changes which have occurred are: a l t e r a
tion of unstable d e t r i t a l grains; formation of authigenic
quartz and K-feldspar overgrowths; growth of authigenic
clay; p a rt ia l i n f i l l i n g of pore space by c a l c i t e cement;
and formation of authigenic p y r it e , magnetite and iron
oxides.
I
Quartz diagenesis
Three stages of quartz cementation were recognized
in the SEM. The f i r s t stage consists of an early growth
of m ic r o c r y s ta l1ine quartz druse. The druse forms a u n i
form rim of rhombic quartz around the d e t r i t a l quartz
grains (Fig. 17a). An authigenic clay coat l a t e r p a r t i a l l y
covered the druse, in h ib i t in g the continued development
73
b
Figure 16 - S E M micrographs showing grair contact and rock fragment within the Skooner
Gulch Formation, (a) Former point of grain contact (outlined by dashed lines)
appears as a smooth, slightly depressed area formed by mild compaction and
pressure solution. 600X. (b) Well-rounded rock fragment (outlined by dashed
lines) between subangular detrital quartz grains. 300X.
-p *
Figure 17 - S E M micrographs of quartz overgrowths in the Skooner Gulch Formation.
(a) Detrital quartz grain rimmed with large, authigenic quartz overgrowths.
200X. (b) Enlargement of area outlined by black square in (a) showing two
forms of authigenic quartz growth: (1) early, thin rim of small quartz druse
(D) coated with webby authigenic clay (arrows); and (2) large, planar over
growths (o). 1000X.
c n
! of the a u th ig e n ic quartz overgrow ths, by cove rin g p o t e n t i a l
I
quartz nucleation sites .
The second stage of quartz diagenesis is character-
| ized by the growth of some large, planar quartz overgrowthsj
! (Fig. 17b). These overgrowths can completely surround the j
d e t r i t a l core, creating subangular grains (Fig. 18a). |
; i
i Growth occurred where there were gaps in the clay coatings, j
As the s i l i c a supply continued, larger overgrowths develop
ed and grew over the clay-coated surfaces (Fig. 18b). These
overgrowths are not continuously attached to the d e t r i t a l
| grains, but are linked and supported by small bridges of j
i
quartz less than 1 urn thick.
Formation of small ( 5 to 10 urn), is o la te d , euhedral
m ic r o c r y s ta l1ine quartz crystals (Fig. 19) co ns titu te the
j
! th ird phase of quartz diagenesis. The growth of this form
of quartz has been a t t r i b u t e d to high concentrations of
a lk a lie s in the pore f l u i d s , i n t e r f e r i n g with normal quartz
growth ( M i l l o t and others, 1970).
i
!
j
Feldspar di agenesi s
Feldspar diagenesis has included both the dissolutio n
and r e p r e c ip it a t io n of authigenic feldspar in the form of
K-feldspar overgrowths. I l l i t i z a t i o n of d e t r i t a l K-feldspar
(Fig. 20a) and a l b i t i z a t i o n and resorption of plagioclase
feldspar (Fig. 20b) has been a major supplier of dissolved
ions. K-feldspar overgrowths are the major type of feldspar
76
a b
Figure 18 - S E M micrographs of quartz overqrowths and clay rim in the Skooner Gulch Forma
tion. (a) Detrital quartz grain, almost completely surrounded by smooth,
euhedral authigenic quartz overgrowths (o). 300X. (b) Enlargement of the d e tri
tal grain surface (not covered with overgrowths) showing a thin, authigenic
clay rim (arrow) which covered the detrital grain surface prior to formation of
the authigenic quartz cvergrowths. 1000X.
Figure 19 - S E M micrographs of microcrystalline quartz in the Skooner Gulch Formation.
(a) Small (5 to 10 urn), microcrystalline quartz crystals on a detrital
quartz grain. This morphology of quartz is the rarest form observed in the
Skooner Gulch sandstone beds. 200X. (b) Enlargement of area outlined by black
square in (a) showing the morphology of the microcrystalline quartz (Q) and
associated authigenic clay (arrow). 800X.
Figure 20 - S E M micrographs of altered feldspar grains in the Skooner Gulch Formation.
(a) Authigenic clay platelets (arrows) are observable within a partially
resorbed (illitiz e d ) K-feldspar. 1000X. (b) Partially resorbed plagioclase
feldspar. Plagioclase feldspars are typically more altered than K-feldspars.
Alignment of the remaining fragments in (b) suggests resorption is crystal-
1ographically controlled. 50CX.
■ " j
< J D
i n W i i ? i a ? i i s
overgrowth to develop, forming on both d e t r i t a l K-feldspar
'
jand plagioclase hosts. These overgrowths began as small j
j
individual rhombs, scattered across the d e t r i t a l feldspar
jsurface. With continued growth, some of the individual
icrystals merged to form large blocky overgrowths (Fig, 21a),
s im ila r to those described by Waugh (1978). The ir r e g u l a r
I ' !
; |
d i s t r ib u t io n of these overgrowths was probably influenced
i
i
I by the simultaneous development of authigenic clay coats I
(Fig. 21b). The presence of K-feldspar overgrowths on de
t r i t a l plagioclase feldspar grains, suggests that the K/Na
jratio of the pore flu id s must have been high.
| j
Cl ay diagenesis
The Skooner Gulch Formation contains very l i t t l e clay
i(less than 1%). The clay appears to be authigenic and occurs!
as both thin clay rims on d e t r i t a l grains (Fig. 21b) and
jas small clusters of clay (Fig. 19b) within the pores. X-ray
d i f f r a c t i o n and SEFl/EDX analyses indicate that the clay is
Iprim arily i l l i t e and mixed-layer i l l i t e - s m e c t i t e . These
jclay coatings controlled and p a r t i a l l y in h ib ite d the dev-
i j
jelopment of authigenic quartz and feldspar overgrowths, j
I I
jthus helping preserve some of the o rig in a l high porosity j
|and permeab i 1i t y . j
i I
| |
I :
1Ca 1ci te cementati on
Sparry, p o r e - f i l l i n g c a l c i t e cement occurs sporadic-
!______ _ _ _ _ ^ 80 I
&
m
0 0
Figure 21 - S E M micrographs of K-feldspar overgrowths and clay rims in the Skooner Gulch
Formation, (a) Large, euhedral, authigenic K-feldspar overgrowths (o) on a
detrital K-feldspar grain. 500X. (b) Enlargement of detrital surface (arrows)
showing early authigenic clay coating which partially covered the surface.
These clay coatings influenced the distribution of authigenic overgrowths on
the detrital grain surface. "“ IF.. 19
a l l y throughout the formation (Fig. 22a). The c a lc it e ap- '
pears to have been a la te stage event since a ll of the I
authigenic minerals previously described e x ist in both the |
c a l c i t e cemented and uncemented zones. Where present, c a l- |
c it e completely f i l l s a ll pore space and contains abundant j
inclusions of authigenic clay (Fig. 22b). P r e c ip ita t io n of j
c a l c i t e halted fu rt h e r diagenesis. j
| D is t rib u tio n of the c a l c i t e is d i f f i c u l t to determine |
in outcrop. Porosity and perm eability values l i s t e d for the
Skooner Gulch Formation are obviously only applicable to the
j
juncalcite cemented zones, being zero in the c a lc it e cement-
jed zones. Origin of the c a l c i t e is problematic, but could
lhave been the re s u lt of e it h e r in situ dissolution of ca l-
!
jcareous f o s s i l s , oxidation of organic m atter, and/or in-
|
( f i l t r a t i o n from outside sources, such as the Gallaway Forma-
i
|t i on .
!
I
i
! !
jPyri te and iron oxides
A minor amount of authigenic, euhedral p y rite and mag-
inetite (less than 1%) was observed in thin section. These
!
crystals appear to be growing within the pores, but were not
observed in the SEM. Iron oxide coatings (hematite?) were
observed in thin section and minor amounts of iron were de
tected in a ll of the clay analyses by EDX. j
82
M iff u H
i i - i / h i i i i m &
Figure 22 - S E M micrographs of clay-rich calcite cement in the Skooner Gulch Formation.
(a) Late stage pore-filling poikilotopic calcite cement p artially cements
the Skooner Gulch Formation. Dashed lines separate the calcite cemented zones
(C) from the porous, uncemented zones. 20X. (b) Authigenic clay inclusions
(arrows) incorporated within the calcite pore-filling cement. 5000X.
CO
00
DIAGENESIS OF THE MASSIVE SANDSTONE OF THE
GALLAWAY FORMATION !
Several massive, thick-bedded sandstone beds occur j
throughout the lower and middle Gallaway Formation. D ia
genesis appears to be s im ila r in all of these beds, regard
less of t h e i r position within the s t r a t i graphic section.
Extensive bioturbation has not occurred in these units,
p rim a rily due to the coarser grain size and thickness of
the beds. When deposited, these massive sandstone units
contained no fin e-g ra in e d s i l t or clay, only sand-sized de
t r i t u s and th erefore were not su itab le habitats for burrow
ing organisms.
A fte r deposition of the d e t r i t a l grains, compaction and
dewatering resulted in the elim inatio n of excess pore
f l u i d s . Compaction continued un til a minor amount of pres
sure solution occurred at points of grain contact (Fig,
|23a). In general, porosity remained high. S lig h t contortion
Jof d e t r i t a l micas also occurred (Fig. 23b). With additional
I
i
b u r i a l , a lt e r a t io n of unstable rock fragments and feldspar
Igrains began, eventually re su ltin g in the p r e c ip it a tio n of
authigenic minerals.
I
jQuartz diagenesis I
Three stages of quartz formation were recognized in j
the massive sandstone of the Gallaway Formation. The major
I 84 j
00
cn
a b
Figure 23 - S E M micrographs showing grain contact and deformed micas in massive sandstone
beds in the Gallaway Formation, (a) Small, rhombic K-feldspar overgrowths (arrows),
a c o m m o n form of authigenic K-feldspar, surround a point of former grain contact
(outlined by dashed lines. The smooth depression is the result of minor compaction
at this point of former grain contact. 1000X. (b) Compaction of a detrital biotite
grain (M) around a detrital quartz grain (Q). 500X,
differences between this authigenic quartz and that of the
Skooner Gulch Formation is the predominance of the micro
c r y s t a l l i n e form over the la r g e r , euhedral overgrowths, In-
I ~
j i t i a l l y , a thin rim of euhedral quartz overgrowths, or
! I
jquartz druse, covered the d e t r i t a l quartz grain surfaces j
! !
(Fig, 24a). Continued growth resulted in the formation of
large, planar overgrowths (Fig. 24b). For some unknown
reason, possibly due to a change in pore f l u i d chemistry,
development of large r overgrowths was not extensive, In - j
stead, thick coatings of m ic r o c r y s ta llin e quartz and clay
formed and coated a ll d e t r i t a l grains (Fig. 25b), regard-
i i
less of composition. This coating appeared to preserve i
jporosity by i n h ib i t in g both the resorption of d e t r i t a l
Iplagioclases and the growth of additional authigenic miner-
al s . !
i
!
; i
I j
Fe1dspar diagenesis j
Resorption of plagioclase (Fig. 25a) was the most com
mon d estruc tive phase of diagenesis of the feldspars. Well-
! j
jdeveloped, small rhombic K-feldspar overgrowths were the j
| i
f i r s t stage of authigenic feldspar growth (Fig. 23a). These
overgrowths completely surrounded the d e t r i t a l K-feldspar
i
and plagioclase grains. P rim a rily K-feldspar overgrowths j
jhave formed on both d e t r i t a l K-feldspar and plagioclase j
j
hosts. Development of these K-feldspar overgrowths was i n
hibited by the formation of webby, authigenic i l l i t e - s m e c t - i
a b
Figure 24 - S E M micrographs showing morphology and distribution of authigenic quartz in
the massive sandstone beds of the Gall away Formation, (a) Authigenic quartz
druse (D) surrounding a detrital quartz grain. 400X. (b) Enlargement of detrital
quartz surface showing the morphology of the quartz druse (D) and the pre
sence of a few, large, euhedral quartz overgrowths (arrow). 1000X.
00
"-.I
mil iB u i — i
w- i /mu
Figure 25 - S E M micrographs showing the morphology of an altered plagioclase grain and
authigenic K-felds par overgrowths in the massive sandstone beds of the Galla-
way Formation, (a) Partially resorbed, detrital intermediate plagioclase feld
spar grain. Only traces of the original cleavage planes are observable (arrow).
400X. (b) Large, euhedral, authigenic K-feldspar overgrowths (o) on a micro
crystalline quartz coated (arrows) detrital grain. 400X.
CO
0 0
i t e clay coats (Fig, 26a) and m ic ro c r y s ta llin e qu artz-c lay
cements. Occasional la rg e , blocky overgrowths were able to
|
[develop (Fig. 26b), but the to ta l percentage of authigenic '
jfeldspar overgrowths is minor. The existance of K-feldspar
!
[overgrowths on d e t r i t a l plagioclase grains and the develop
ment of m ic r o c r y s ta llin e quartz cement a ll suggests that the
ipore flu id s must have contained a high concentration of K
(McBride, 1977).
I ;
I |
i I
I
I |
jAuthi gen i c cl ay diagenesis
| Authigenic p o re -lin in g and pore-bridging clays are the
wost common clay types. The major clays i d e n t i f i e d were
[ i l l i t e , mixed-layer i l l i t e - s m e c t i t e (Fig. 26b) and occas-
jsional p o r e - f i l l i n g k a o l i n i t e . Several d i f f e r e n t clay mor-
iphologies were observed in the SEM. The e a r l i e s t form was j
jthe webby smectite or i l l i t e - s m e c t i t e (Fig. 26a) p o re -lin in g
i
i
iclay which formed over the quartz and feldspar druses. ;
I i
|These coatings are s im ila r to those described by Galloway \
i
j(197 4) and are c le a r ly separable from l a t e r pore-bridging j
| ( F i g . 27a) and p o r e - f i l l i n g stages of clay cementation. At
[least two d i f f e r e n t types of m ixed-layer clay rims occur.
iOne contains p rim a rily smectite and thus appears smooth and
iwebby (Fig. 26a); the other is more i l l i t i c and appears
f l a k e - l i k e , with elongate i l l i t i c projections (Fig. 27b).
V ariations in clay morphology appear to indicate local v a r
iations in pore f l u i d composition. :
: 89 |
a b
Figure 26 - S E M micrographs showing the morphology and distribution of authigenic K-feldspar
and smectite in the massive sandstone beds of the Gallaway Formation, (a) Large,
blocky, authigenic K-feldspar overgrowths (o) surrounded by webby, pore-lining
and pore-bridging authigenic smectite (arrows). 1500X. (b) Euhedral, authigenic
K-feldspar overgrowths (o) on a detrital grain coated with microcrystalline
quartz and clay. 400X.
b
Figure 27 - S E M micrographs showing the morphology of authigenic illite-sm ectite in the
massive sandstone beds of the Gallaway Formation, (a) Authigenic, mixed-layer
illite-sm ectite is observed coating detrital grains and bridging pores (arrow).
1000X, (b) Enlargement of the detrital grain surface (area outlined by black
square in (a)) showing the ribbon-1ixe projections on the edges of this webby,
illite-sm ectite clay coating. A n earlier formed authigenic quartz druse (D)
is observed under the pore-lining clay, 4000X,
Permeability has been reduced by the formation of pore-
ibridgi ng clays. Two d i f f e r e n t types of pore-bridging clay
were observed: wide ribbons of mixed-layer i l l i t e - s m e c t i t e !
i
j i
i ( F i g . 28a) and thin ribbons of i l l i t e (Fig. 28b). Occasional
1 I
|
patches of p o r e - f i l l i n g k a o lin it e a/re also present (Fig. i
2 9 a ) . The k a o lin it e occurs as small books of i r r e g u l a r l y -
ishaped k a o lin it e p l a t e l e t s . The edges of the individual :
1 j
crystals appear to be a lt e r in g to i l l i t e (Fig. 29b), Rare
i
jtransformation of b i o t i t e to neoformed c h l o r i t e was also
observed.
i i
! !
DIAGENESIS OF THE FINELY-LAMINATED SANDSTONE
l
OF THE GALLAWAY FORMATION
Diagenesis of the fin e ly -la m in a te d sandstone in the
jGallaway Formation has been quite d i f f e r e n t from the massivej
sandstone. Major growth of authigenic minerals has been as
lauthigenic clay rather than quartz or feldspar overgrowths.
The size and d i s t r ib u t io n of authigenic minerals appears to
be d i r e c t l y rela ted to the o rig inal percentage of d e t r i t a l
clay and the size of the pores. Since grain size is t y p i c a l
l y f i n e r , the pore size is smaller. !
! j
In thin section and in the SEM, i t is s t i l l very d i f
f i c u l t to determine i f the sandstone beds were o r i g i n a l l y
g ra in -o r matrix-supported. A high percentage of clay coated
grains makes them appear matrix-supported; however, the
92 j
ih /n il m m i f f lu
Figure 28 - S E M micrographs of pore-bridging illite and illite-sm ectite clay in the massive
sandstone beds of the Gallaway Formation, (a) Wice ribbons of mixed-layer i l
lite-smectite clay bridging a pore between detrital K-feldspar grains. 2000X.
(b) Thin filamentous ribbons of pore-bridging authigenic illite..The pore-bridging
habit of this clay severely reduces permeability forming permeability barriers
to fluid flow. 2000X.
■ i - x y
ir -r &
Q 13 iU 1 1 1 — I
B U N ill M W IS I
Figure 29 - S E M micrographs showing the morphology of authigenic kaolinite in the massive
sandstone beds of the Gallaway Formation, (a) Discrete books of ragged-edged,
authigenic kaolinite are observed fillin g a pore (pore outlined by dashed lines).
500X. (b) Enlargement of kaolinite books showing the morphology of the individual
stacks and the presence of thin illitic clay projections (arrows) on the edges
of the kaolinite books. 1500X.
|amount of remaining porosity, size of the authigenic min
erals that have formed and location of some grain contacts,
suggests that the sandstone beds were grain-supported prio r
!to diagenesis. The subsequent growth of extensive clay-
!
jcoated grains and the f i l l i n g of pores has made this r e
latio n sh ip unclear. Rare, former areas of grain contact
were observed (Fig. 30a) which resemble grain contacts
i
'elsewhere in the formation. The contorted b i o t i t e grains
(Fig. 30b) wedged between d e t r i t a l grains are also e v id
ence of compaction due to b u r i a l.
j
|Quartz diagenesis
P r e c ip ita t io n of authigenic quartz druse occurs on
imost of the d e t r i t a l quartz grains as the f i r s t form of
authigenic s i l i c a (Fig. 31). The only exceptions are the
!
|sandstone dikes in the lower Gallaway Formation which have j
i
only a minor amount of druse (Fig. 32a). In samples lacking
d e t r i t a l clay, m ic ro c r y s ta llin e quartz and authigenic clay
;form a pore-bridaing and p o re -lin in g cement (Fig. 32b).
i
j j
I Fe1dspar diagenesis j
I A lte ra tio n of d e t r i t a l feldspar has been extensive in
the fin e ly -la m in a te d sandstone. In many cases, only s liv e rs 1
of the o rig in a l d e t r i t a l g r a i n remain, but the grain bound
aries are preserved by p o r e - f i l l i n g clay (Figs. 33 and 34).
!
iSome a l b i t i z a t i o n of d e t r i t a l plagioclase was also observed.
b
Figure 30 - S E M micrographs showing evidence of mild compaction in the finely-laminated
sandstone beds of the Gallaway Formation, (a) Smooth, slightly depressed points
of former grain contact (outlined by dashed lines) indicate only mild compaction
has occurred. These contact areas are surrounded by webby, authigenic smectite
clay coatings. 800X. (b) Contorted biotite grain (arrow) wedged between detrital
quartz and feldspar grains. 600X.
a b
Figure 31 - S E M micrographs showing distribution of authigenic quartz in the finely-laminated
sandstones of the Gallaway Formation, (a) Authigenic quartz druse (D) coating the
surface of a detrital quartz grain surrounded by authigenic kaolinite (K) and i l
lite-smectite clay. 500X. (b) Enlargement of area outlined by black square in (a)
showing the morphcogy of the small, euhedral quartz crystals which make up the
drusy coating (D), the larger, quartz overgrowths (o) and webb.y authigenic illite-
smectite clay (arrows). 10,0G0X.
Figure 32 - S E M micrographs showing morphology and distribution of quartz druse in the sand
stone dikes and microcrystal'ine quartz-clay cements in the finely-laminated sand
stone beds of the Gallaway Formation, (a) Detrital quartz grain from the sandstone
dikes showing the irregular, non-uniform distribution of authigenic quartz druse
and webby, smectite clay coatings. 800X. (b) Microcrystal!ine quartz-clay mat
(arrow) bridging pores between detrital grains. 700X.
CO
b
Figure 33 - S E M micrographs of a resorbed plagioclase feldspar grain from the finely-laminated
sandstone beds of the Callaway Formation, (a) The original grain outline of this
resorbed, intermediate plagioclase grain (dashed lines) s preserved by the sur
rounding po re-filling, d e trita l- authigenic clay matrix. 1500X. (b) ED X analysis
of the few remaining fragments of the original detrital grain (arrow) identifies
the original grain as a plagioclase feldspar, 5000X.
■vO
v O
Figure 34 - SE M micrographs showing the morphology of altered plagioclase feldspar grains
in the finely-laminated sandstone beds of the Gall away Formation, (a) Partially
resorbed detrital plagioclase feldspar grain surrounded by detrital-authigenic
clay matrix (dashed lines outline the former grain boundary). 800X. (b) Partially
resorbed detrital plagioclase grain in which the more anorthite-rich portion has
been selectively dissolved firs t. 2500X.
o
.. . . . . . . . . .. . _ ....
The formation of authigenic K-feldspar overgrowths is not
uniform throughout the sequence. Large, blocky K-feldspar
overgrowths were observed on a few samples (Fig, 35), but
are not common. This is because the authigenic and d e t r i t a l
j
clay appears to have grown at the expense of K-feldspar
overgrowths (Fig, 36a). K-feldspar overgrowths have not
formed in the sandstone dikes (Fig, 36b).
Cl ay diagenesis
Both d e t r i t a l and authigenic clay occurs in most of
the sandstones examined. The d e t r i t a l clay comes from re-
i
i
Idistribution of clay from the mudstone interbeds by bur
rowing organisms, This ea rly introduction of d e t r i t a l clay
into some o f th e pore space in h ib ite d diagenesis, by f i l l i n g
i
in the pores and creating impermeable barriers to f l u i d
migrati on,
I l l i t i z a t i o n of rock fragments (Fig. 37a) and d e t r i t a l
|
jplagioclase was a major source of ions for the growth of
jauthigenic clay. Two d i f f e r e n t stages of clay diagenesis
jwere recognized: (1) the formation of authigenic clay rims;
!
jand (2 ) th e formation of p o r e - f i l l i n g and and pore-bridging
!
jauthigenic clay.
Authigenic clay rims are c le a r ly v i s i b l e on some o f
; i
jthe d e t r i t a l grains (Fig. 37b) but are often obscured by |
the growth of additional p o r e - f i l l i n g clay. Only in the more
jporous sandstone can these clay rims be observed, These clayj
0 0 1 iO u I — I
05 -0 00>0 '0 BOS SIS
a b
Figure 35 - S E M micrographs of authigenic K-feldspar overgrowths on a detrital plagioclase
feldspar in the finely-laminated sandstones of the middle Gallaway Formation.
(a) Blocky, euhedral, authigenic K-feldspar overgrowths (o) growing on an unusu
ally clean, detrital plagioclase (P) surface. 1000X. (b) Enlargement of detrital
grain surface showing the morhology of the authigenic K-feldspar overgrowths (o)
(arrow in (a) indicates location of (bj). 5000X.
Figure 36 - S E M micrographs of K-feldspar overgrowths in the finely-laminated sandstones
and detrital feldspar devoid of authigenic overgrowths from the sandstone
dikes in the Gallaway Formation, (a) Authigenic K-feldspar overgrowths (arrow)
on a detrital K-feldspar grain surrounded by authigenic microcrystalline quartz
and clay. 800X. (b) Detrital K-feldspar grain devoid of authigenic overgrowths
from one of the sandstone dikes. 100X.
104
Figure 37 - S E M micrographs of a volcanic rock fragment and smectite clay coatings in the
finely-laminated sandstones of the Gallaway Formation, (a) Altered volcanic
rock fragment containing p artially resorbed plagioclase laths (arrows). 500X.
(b) Webby, authigenic smectite clay coating (arrow) on a detrital quartz grain.
Smooth, bald area (outlined by dashed lines) is an area of former grain contact.
1000X.
rims are analogous to Galloway's (1974) stage I of diagen-
jesis. Since Galloway did not use an SEM, he would not have
Jbeen able to distinguish the minute overgrowths which ty p i-
i
i
jcally coat the d e t r i t a l grain surfaces p rio r to develop-
i
[ment o f th e clay rims. The clay rims are composed of webby,
smectite (Fig. 38) or mixed-layer i l l i t e - s m e c t i t e .
| The second stage of authigenic clay development was the
formation of p o r e - f i l l i n g and pore-bridging clays of varied
composition. S t r a t i g r a p h ic a lly , the clay composition changes
from predominantly smectite in the upper Gallaway Formation
to more i l l i t i c in the lower Gallaway Formation. The bone-
jbed a t th e base of the Gallaway Formation contains the only
example of authigenic c h lo r it e recognized (Fig, 39a). The
d i s t r ib u t io n of clay minerals in the Gallaway Formation
generally agrees with work by Boles and Franks (1979),
which demonstrate that there is a progressive decrease in
smectite and increase in i l l i t e and c h lo r it e with depth of
I
Iburial. This conversion of smectite to i l l i t e can occur at
|
temperatures as low as 60° C and is another source of Si
for the formation of quartz overgrowths and Ca for c a lc it e
cementation. This would correspond to Galloway's (1974)
stage 3 of diagenesis, which occurs at intermediate depths
of burial (900 to 3000 m).
i A minor amount of p o r e - f i l l i n g k a o lin it e occurs
j
jthroughout the sequence (Fig. 39b). The k a o lin it e appears
ionly s l i g h t l y altered to i l l i t e . Rare, isolated books of |
a
Figure 33 - SEM micrographs showing the morphology of pore-~;ining smectite in the Gallaway
Formation, (a) Subangular, detrital quartz grain lined with authigenic quartz
druse (D) and webby, smectite clay (arrow). 500X. (b) Close-up view of the webby,
smectite clay coating. The collapsed appearance of smectite in the S E M is believed
due to dehydration (Wilson and Pittman, 1977), ’ 0,000X.
o
c n
Figure 39 - S E M micrographs showing morphology of authigenic chlorite and kaolinite in the
finely-laminated sandstones of the Gallaway Formation, (a) Euhedral, ragged-
edged platelets of authigenic chlorite (arrow) adjacent to an authigenic quartz
overgrowth (Q). 5000X. (b) Elongate stacks of authigenic kaolinite books (arrows)
partially fillin g a pore in the Gallaway Formation. 1000X.
k a o lin ite were also observed in the c a v itie s of a lt e r in g
d e t r i t a l grains. The amount of k a o lin ite remains r e l a t i v e l y
jconstant throughout the e n tire Gallaway Formation.
i
jCarbonate di agenesis
Late stage authigenic dolomite and c a lc it e occurs spor-|
i
|adically throughout the fin e ly -la m in a te d sandstone. The |
exact d i s t r ib u t io n of these cements is d i f f i c u l t to deter- '
I
mine but is believed to be extensive. Both the c a lc it e and j
the dolomite are c le a r ly the las t stage of cementation since
[they contain abundant authigenic clay inclusions and appear
to replace both d e t r i t a l and authigenic grains.
I
| C alc ite is the most common carbonate cement. I t occurs
jin patches, as a sparry, dusty p o r e - f i l l i n g (Fig. 40a) in
!
nearly every thin section; however, none of the sandstone
1 i
was ever completely cemented with c a l c i t e . The c a lc it e does |
not appear to be replacing d e t r i t a l grains and matrix but j
i
only to i n f i l l any ava ila b le pore. Ghosts of d e t r i t a l grains
Iwithin the c a l c i t e are believed to represent previously
I
I
jresorbed d e t r i t a l feldspar grains. A fter p a rtia l resorption
of the d e t r i t a l grain, creating a secondary pore, the ca l-
i
icite simply f i l l e d any existing void. Authigenic clay mat
rix was also incorporated into the c a lc it e cement (Figs. !
I i
40b and 41a). In the pores not f i l l e d with c a lc it e cement,
growth of authigenic clay continued and in places even
fringed the c a l c i t e cement (Fig. 41b). Scattered rhombs of
108
Figure 40 - SE M micrographs of pore-filling calcite cement with authigenic clay inclusions
in the finely-laminated sandstones of the Gallaway Formation, (a) Patch of pore-
fillin g calcite spar (C) partially cementing detrital grains. A large, euhedral
authigenic K-feldspar overgrowth (arrow) is visible. The overgrowth formed prior
to calcite cementation indicating the calcite is a late-stage cement. 300X. (b)
^ Close-up view of calcite cement showing authigenic clay (arrow) incorporated in
the calcite spar (C)t 2000X.
110
S I! Ill gl 1
IBS 10 iH
a b
Figure 41 - S E M micrographs showing relationship of authigenic illite-sm ectite to calcite
cement in the finely-laminated sandstones of the Gallaway Formation, (a) W ei 1 -
formed, authigenic illite-sm ectite (arrow) incorporated into pore-filling cal
cite cement (C), 10,000X. (b) Calcite cement rimmed with authigenic i l l i t e -
smectite partially fillin g a pore. 2500X.
c a lc it e were observed in the porous zones and these rhombs
!may represent precursors to more complete c a l c i t e cementa
tion.
| Three possible sources of Ca for the c a lc it e cement
|are: the dissolution of calcareous Foraminifera (Fig. 42a) i
(a common constituent of the mudstone and hemipelagite);
i
resorption of d e t r i t a l plagioclase grains and rock frag- !
i
I ;
jments; and the conversion of smectite to i l l i t e (which r e -
i i
i
leases Ca). Carbonate ions could be released due to organic j
i
reactions in the mudstone. j
Dolomite cementation occurs in two forms: (1) euhedral i
rhombs scattered throughout the bonebed matrix (Fig. 42b);
i
and (2) dolomitized concretions, located in w ell-de fine d
|horizons in the middle Gallaway Formation. j
I i
The dolomite rhombs are small (10 to 20 urn), clay-
! i
i f i l l e d crystals which were only observed in the bonebed at !
i
the base of the Gallaway Formation. The rhombs appear to
p a r t i a l l y replace all components: d e t r i t a l grains, glaucon
i t e , matrix and p y rite . Murata and others (1969) analysed,
iusing oxygen isotopes, many of the diagenetic carbonates in
the marine Miocene shale of C a lif o r n ia and Oregon, including
I
the dolomite in the Gallaway Formation ( t h e i r Skooner Gulch ;
Formation). Based on t h e i r re s u lts , they hypothesized that
jthe dolomite originated from the dissolution of calcareous
jForaminifera or other fo s s ils and the r e p r e c ip it a tio n of
'carbonate, f i r s t as authigenic c a l c i t e . This would explain
112
Figure 42 - S E M micrographs of partially dissolved calcareous Foraminifera and authigenic
dolomite rhomb from the lower Gallaway Formation, (a) Partially dissolved cal
careous Foraminifera surrounded by authigenic-detrital clay matrix. Dissolved
Foraminifera were important sources of Ca for the formation of carbonate cements.
2000X. (b) Euhedral, authigenic dolomite rhomb, with small clay inclusions (arrows)
from the lower Gallaway Formation bonebed. 4000X.
Figure 43 - S E M micrographs showing two forms of authigenic dolomite from the Gallaway
Formation, (a) Small, euhedral dolomite rhombs (D) scattered throughout a
clay-rich matrix in the lower Gallaway Formation bonebed. 1000X. (b) Example
of a dolomite concretion showing the ghosts of the original detrital grains
(arrows) and matrix in a sandstone which in now totally replaced by dolomite.
500X.
the lack of calcareous Foraminifera in this horizon; only
arenaceous species were found. This authigenic c a lc it e was
l a t e r dolomitized by formational brines. The heavy oxygen
isotope vaulues they determined are typical values for
j " I O r t
jmarine carbonates ( £ 0 = +29.3 /oo, SMOW); the l i g h t
i
jcarbon isotope values (S C ^ = -9 .5 °/oo , PDB) are within
the range of marine concretions. These values suggest re-
|
■latively shallow diagenesis, not deep b u ria l. The oxygen
was probably in equilibrium with marine i n t e r s t i t i a l
waters (personal communication J. A lla n ).
The dolomite concretions are r e s t ric te d in d i s t r ib u -
j
Ition to w ell-de fine d bedding surfaces. Sedimentary s t r u c t - '
i
[ures observed elsewhere in the section are f a i n t l y recog-
!
jnizable within the dolomitized concretions. In these hor
izons, most of the d e t r i t a l grains and matrix have been
j i
jto ta lly replaced by ferroan dolomite or ankerite (Fig. 43b),
I that is c le a r ly post-depositional in o rig in . |
j i
' Dolomitic concretions have not been studied in detail
ibut are possibly the r e s u lt of special permeability zones
I
;which form along bedding surfaces or lo calized concentra
tions of p a r t ic u la r pore flu id s in the environment ( Petti -
john and others, 1972). Boles and Franks (1979) indicate |
; i
that Fe and Mg, released by i l l i t i z a t i o n reactions in shale!
can be transferred to sandstone and react with k a o lin ite
to produce aluminum-rich c h lo r it e and/or c a lc it e to pro
duce ankerite. K ao lin ite is also present in the dolomitic
114|
iconcreti ons.
i
i
SUMMARY AND CONCLUSIONS
| 1. The lith o lo g y and sedimentary structures of the
Skooner Gulch and Gallaway Formations are comparible to
sim ilar depositional sequences representing the outer fan
depositional lobes, lobe fringe and basin plain tu rb id ite s
of Mutti (1977). These two formations are part of an early
Miocene deep-sea fan complex.
2. Contact between the Skooner Gulch Formation and the
Gallaway Formation has been redefined based upon petrograph-
ic analysis and f i e l d rela tion ship s . The base of the glau-
i
c o n it ic , vertebrate-bearing bonebed is now considered the
s
i
base of the Gallaway Formation.
i
j 3. The diagenetic history of the Skooner Gulch Forma
t i o n and the Gallaway Formation have not been uniform due
jto variations in the orig in al depositional environment,
composition, texture, s t r a t i f i c a t i o n , frequency of i n t e r -
i
|bedded shale beds, biotu rb atio n , degree of compaction, and
j
joriginal porosity and perm eability.
I
| 4. Diagenetic changes recognized in both formations
|
i
|include: a lt e r a t io n and resorption of unstable d e t r i t a l
i i
igrains such as fe ldsp ar, rock fragments and d e t r i t a l clay; i
I i
i t
I format ion of authigenic quartz, K-feldspar and clay cements;;
formation of iron oxide coatings and p y rit e ; replacement of i
! 115 |
d e t r i t a l grains and matrix by late stage carbonate cement;
and reduction in porosity and permeability due to the
growth of authigenic minerals. Table 7 summarizes the r e l a
tiv e abundance of the major authigenic minerals observed by
! 1it h o f a c i e s . All of these diagenetic changes can occur at
i r e l a t i v e l y low temperatures and moderate burial depths.
!
| 5. The graywacke examined contains both d e t r i t a l and
authigenic clay matrix. The d e t r i t a l clay was o r i g i n a l l y
deposited as interbedded mudstone and dark laminae within
c la y -fre e sandstone. Soft sediment deformation and biotu r-
bation is prim arily responsible for the sporadic introduc
tion of d e t r i t a l clay into the sandstone. Growth of a u th i
genic clay cement was enhanced by the addition of dissolved
ions from clay mineral transformations within the mudstone
interbeds.
6. Dark- and lig h t-c o lo re d laminae of the f i n e l y - l a m
inated sandstone are p e t r o lo g ic a l1y d i s t i n c t . The dark lam
inae contain d e t r i t a l clay, b i o t i t e and p y rite ; whereas
the l ig h t laminae contain the typical framework grains such
as quartz, feldspar, rock fragments and authigenic clay.
7. Late stage c a lc it e and dolomite cements have par
t i a l l y to completely replaced the orig inal authigenic and
d e t r i t a l matrix and d e t r i t a l framework grains. The c a lc it e
occurs as patchy p o r e - f i 11in g , whereas the dolomite is r e
s t ric te d to specific horizons, producing concretionary beds
116
Table 7 -
Authigenic
Mineral
Quartz
Feldspar
Clay
Carbonate
Abundance o f'm a jo r a u th ig e n ic m inerals by l i t h o f a c i e s in the Skooner Gulch
and Gallaway Formations.
Skooner Gulch Formation
Massive sandstone
(A) early druse
(A) large overgrowths
(R) patchy mxln quartz
(A) large, blocky K-spar
overgrowths
(0-R) plag. overgrowths
(R) authigenic clay
N o detrital clay
(0-A) patchy, sparry calcite
Gallaway I
Massive sandstone
(A) early druse
(C) small overgrowths
(A) mxln quartz coatings
(0-C) small, K-spar
overgrowths
(R) plag. overgrowths
(A) authigenic clay
No detrital clay
(0) patchy, sparry calcite
ion
Finely-laminated sandstone ;
(A) early druse j
(0) small overgrowths i
(0-R) mxln quartz coatings j
i
(0-C) small, K-spar j
overgrowths !
(R) plag. overgrowths
(A) Mixed authigenic-detrital
Authigenic > detrital i
(0-R) patchy, sparry calcite
(R) dolomite rhombs
(R) dolomitized concretions
Key: Mxln = microcrystalline; K-spar = potassium feldspar; Plag. = plagioclase feldspar
(A) = abundant; (C) = com mon; (0) = occasional; (R) = rare
REFERENCES
Addicott, W.O., 1967, Age of the Skooner Gulch Formation,
Mendocino county, C a lifo rn ia : U.S. Geol . Survey Bull.
1254-C, p. C l - C l l .
Almon, W.R. and Davies, D.K., 1 9 7 9 ? Regional diagenetic
trends in the lower Cretaceous Muddy Sandstone, Pow
der River Basin jjn Scholle, P,A. and Schluger, P.R.,
eds., Aspects of diagenesis: Soc. Econ. Paleontolo
gists Mineralologists Spec. Paper No. 26, p. 379-400.
Basu, A., Young, S,W., Suttner, L . J . , James, W.C., and
Mack, G.H., 1975, Re-evaluation of the use of undu-
la to ry extinction and polycrystal 1i n i t y in d e t r i t a l
quartz for provenance in te r p r e ta tio n : Jour. Sed.
Petrology, v. 45, p. 873-882.
Boles, J.R. and Franks, S.G., 1979, Clay diagenesis in
Wilcox sandstones of southwest Texas: implications
of smectite diagenesis on sandstone cementation:
Jour, Sed. Petrology, v. 49, p. 55-70
Bouma, A . H . , 1962, Sedimentology of some flysch deposits:
Amsterdam, E lse v ie r, 168p.
Boyle, M.W., 1967, The stra tig rap h y, sedimentation and
structure of an area near Point Arena, C a lifo rn ia
funpubl. M.S.] : Univ. C a lif o r n ia , Berkeley, 71p .
Brenchley, P ,T ., 1969, Origin of matrix in Ordovician
greywackes, Berwyn H i l l s , North Wales: Jour. Sed.
Petrology, v. 39, p. 1297-1301.
B u ller, A .T ., and McManus, J . , 1973, Modes of t u r b id it e
deposition deduced from g ra in -s iz e analysis: Geol.
Mag., v. 109, p. 491-500.
Clarke, S .H . J r . , Howell, D.G., and Nilsen, T .H ., 1975,
Paleogene geography of C a lifo rn ia i_n Weaver, D.W.,
Hornaday, G.R., and Tipton, A., eds., Paleogene
symposium and selected technical papers: Pacific
Sect. Soc. Econ. Paleontologists Mineralogists
Annual Meeting, p. 121-154.
118
Crowell, J .C ., 1974, Sedimentation along the San Andreas !
Fault, C a lifo rn ia i_n Dott, R .H .J r ., and Shaver, R.H., j
eds., Modern and ancient geosynclinal sedimentation:
Soc. Econ. Paleontologists Mineralogists Spec. Paper
No. 19, p. 292-303.
Cummins, W.A., 1962, The greywacke problem: Liverpool
Manchester Geol. Jour., v. 3, p. 51-72.
Dickinson, W.R., 1970, In te rp re tin g d e t r i t a l modes of gray-
| wacke and arkose: Jour. Sed. Petrology, v. 40, p.
692-707.
I
Fdchtbauer, H . , 1967, Influence of d i f f e r e n t types of dia- j
genesis on sandstone porosity: Proceedings 7th World i
Petroleum Congress, p. 354-369.
Galloway, W.E., 1974, Deposition and diagenetic a lt e r a tio n
of sandstone in northeast Pacific a rc -re la te d basins:
Geol. Soc. America B u l l , , v. 85, p. 379-390.
Graham, S.A., 1 978, Role of Salinian block in evolution of
| San Andreas f a u l t system, C a lifo r n ia : Amer. Assoc.
I Petroleum Geologists B u l l . , v. 62, p. 2214-2231.
I
i
_______________ , 1979, T e r t ia r y paleotectonics and paleogeo-
graphy of the Salinian block jjn Armentrout, J.M.,
Cole, M.R,, and Terbest, H . J r . , eds., Cenozoic
pa 1eogeography of the western United States: Pacific
Sect. Soc. Econ. Paleontologists Mineralogists Paleo-
geography Symposium No. 3, p. 45-51.
_______________ , and Berry, K.D., 1 979 , Early Eocene paleo-
geography of the central San Joaquin Valley: origin
of the Cantua sandstone i_n Armentrout, J.M ., Cole,
M.R., and Terbest, H . J r . , eds., Cenozoic paleogeo-
graphy of the western United States: P ac ific Sect.
Soc. Econ. Paleontologists Mineralogists Paleo-
geography Symposium No. 3, p. 119-127.
;Howell, D.G., Vedder, J.G ., McLean, H., Joyce, J.M.,
Clarke, S . H . J r . , and Smith, G., 1977, Review of
| Cretaceous geology, Salinian and Nacimiento blocks,
| Coast Ranges of C a lifo rn ia i_n Howell, D.G., Vedder,
J .G ., and McDougall, K.A., eds., Cretaceous geology
i of the C a lifo rn ia Coast Ranges west of the San
i Andreas f a u l t : P acific Sect. Soc. Econ. Paleontologist!
j Mineralogists Paleogeography Field Trip Guide No. 2,
I pp. 1-46. !
| I i j i m a , A., 1978, Geologic occurrences of z e o lite in mar-
| ine environments j_n Sand, L.B ., and Mumpton, F.A.,
! eds., Natural z e o lite s ; occurrence, properties and
use: Oxford, Pergamon Press, p. 175-198.
Kastner, M., and Siever, R., 1979, Low temperature f e l d
spars in sedimentary rocks: Amer. Jour. Science,
v. 279, p. 435-479.
K le in p e ll, R.M., 1938, Miocene stratigraphy of C a lifo rn ia :
Tulsa, Amer. Assoc. Petroleum Geologists, 450p.
K le in p e ll, R.M., and Weaver, D.M., 1963, Oligocene b io
stratigraphy of the Santa Barbara embayment, C a l i f
ornia: Univ. C a lifo rn ia Pub!. Geol. Science, v. 43,
250p.
Kuenen, Ph.H., 1966, Matrix of tu r b i d i t e s , experimental
approach: Sedimentology, v. 7, p. 267-297.
Lovell, J .P .B ., 1972, Diagenetic origin of graywacke mat
rix minerals: a discussion: Sedimentology, v. 99,
j p. 141-143.
!
| McBride, E .F ., 1963, A c l a s s i f i c a t i o n of common sandstones:
Jour. Sed. Petrology, v. 33, p. 664-669.
________________ , 1 977 , Sandstones Jji Jonas, E.C. and McBride,
E .F ., Diagenesis of sandstone and shale: application
to exploration for hydrocarbons: Austin, Texas, Univ.
Texas Continuing Education Publ. No. 1, p. 1-120.
M i l l o t , G., 1970, Geology of clays: New York, Springer-
Verlag , 429p.
Morris, R.C., Proctor, K.E., and Koch, M.R., 1979, Petro
logy and diagenesis of deep-water sandstones, Ouchita
Mountains, Arkansas and Oklahoma j_n Scholle, P.A.,
and Schluger, P.R., eds., Aspects of diagenesis: Soc.
Econ. Paleontologists Mineralogists Spec. Paper No.
I 26, p. 263-280.
I
I Murata, K .J ., Friedman, I . , and Madsen, B.M., 1969, Iso-
| topic composition of diagenetic carbonates in marine
Miocene formations of C a lifo rn ia and Oregon: U.S.
j Geological Survey Prof. Paper 614-B, p. B1-B24.
i
i
| M u t t i , E., 1977, D is t in c t iv e thin-bedded t u r b id it e facies
and related depositional environments in the Eocene
Hecho Group (southcentral Pyrenees, Spain): Sedimen-
tology, v. 24, p. 107-131.
120
I M u 11 i , E. and Ricci-Lucchi, F. , 1972, Le t o r b i d i t i d e l l '
; Appennino se tte n trio n a le : introduzione a l l 1a n alisi
j di facies: Mem. Soc. Geol. I t a l i a , v. 11, p. 161-199.
i
Neesham, J.W., 1977, The morphology of dispersed clay in
sandstone reservoirs and its e f fe c t on sandstone
shaliness, pore space and flu id flow properties:
SPE 6858, 8p. |
Nilsen, T .H ., 1978, Late Cretaceous geology of C a lifo rn ia
and the problem of the proto-San Andreas f a u l t j_n
Howell, D.G. and McDougall, K.A., eds., Mesozoic
! paleogeography of the western United States: Pacific i
| Sect. Soc. Econ. Paleontologists Mineralogists Pal-
| eogeography Symposium No. 2, p. 559-573. !
________________, and Brabb, E .E., 1 979 , Geology of the Santa
Cruz Mountains, C a lifo rn ia : Field t r i p guidebook
Geol. Soc. America Cordilleran Sect. Meeting, 37p.
I _______________ , and Clarke, S . H . J r . , 1975, Sedimentation and
! tectonics in the early T e rtia r y continental borderland!
I of central C a lif o r n ia : U.S. Geol. Survey Prof. Paper
! 925, -64p.
(
| ____________, Dibblee, T . W . J r . , and Simoni, T .R ., 1974,
| Stratigraphy and sedimentology of the Cantua member
I of the Lodo Formation, V alle c ito s area, C a lifo rn ia i_n
! Payne, M., ed., The Paleogene of the Panoche Creek-
| Cantua Creek area, central C a lif o r n ia : P acific Sect. |
Soc. Econ. Paleontologists Mineralogists Geologic |
G u i d e b o o k , p . 38-68. |
! i
I _______________ , and McKee, E.H., 1 979, Paleogene paleogeo- ]
graphy of the western United States iji Armentrout,
J.M ., Cole, M.R., and Terbest, H . J r . , eds., Cenozoic
Paleogeography of the western United States: Pacific
Sect. Soc, Econ. Paleontologists Mineralogists P a 1 -
| eogeography Symposium No. 3, p. 257-276.
i
I
: P e ttijo h n , F . J . , P otter, P .E ., and Si ever, R., 1972, Sand
and sandstone: New York, S prin g e r-V e rla g , 618p.
P h i l l i p s , F . J . , Welton, B .J ., and Welton, J . E . , 1976, Pal- j
eontologic studies of the middle T e r t ia r y Skooner |
Gulch and Gallaway Formations at Point Arena, C a l i f - j
ornia Fritsche, A.E., Terbest, H . J r . , and Wornardt,j
W.W., eds., The Neogene symposium: Proceedings Paci- i
f i c Sect. Soc. Econ. Paleontologists Mineralogists
Annual Meeting, p. 137-154.
121
j Piper, D.J.W. and Marshall, N .F., 1969, Bioturbation of
i Holocene sediments on La Jolla deep-sea fan: Jour.
| Sed. Petrology, v. 39, p. 601-606.
i Ricci-Lucchi, F., 1975, Depositional cycles in two t u r b i-
dite formations of northern Appennines ( I t a l y ) : Jour.
; Sed. Petrology, v. 45, p. 3-43.
!
Seevers, D.O., 1 966 , A nuclear magnetic method for deter- j
mining the permeability of sandstones: Trans. SPWLA
138, 682, p. 1-14.
i
i
Seilacher, A., 1967, Bathymetry of trace fo s s ils : Marine
| Geology, v, 5, p. 413-428.
j \
i Spotts, J .H ., 1962, Zircon and other accessory minerals,
| Coast Range b a th o lith , C a lif o r n ia : Geol. Soc. America
| B u l l . , v. 73, p. 1221-1240. j
Thompson, G.R., and Hower, J . , 1975, The mineralogy of j
glauconite: Clays and clay minerals, v. 23, p. 289-3OO.j
Timur, A., 1969, Pulsed nuclear magnetic resonance studies j
of porosity, movable f l u i d s , and permeability of sand-
! stones: Trans. SPWLA 246,775, p. 1-21. i
: j
| Turner, D .L., 1970, Potassium-argon dating of Pacific j
Coast Miocene foram inifera 1 stages: Geol. Soc. Amer- j
ica Spec. Paper 124, p. 91-129. I
| Walker, T .R ., Waugh,B., and Grone, A .J ., 1978, Diagenesis I
in f i r s t - c y c l e desert alluvium of Cenozoic age, south
western United States and northwestern Mexico: Geol. i
' Soc. America B u l l . , v. 89, p. 19-32. j
!
Waugh, B., 1978, Authigenic K-feldspar in B ritis h Permo- |
Tria s s ic sandstones: Jour. Geological Soc. London, I
v. 135, p. 51-56. j
! Weaver, C.E., 1943, Point Arena-Fort Ross region: C a lif o r - !
nia Dept. Resources, Div. Mines Bull. No. 118, p . 6 2 8 -
635. |
| i
J , 1944, Geology of the Cretaceous (Gualala j
j Group) and T e r t ia r y formations along the Pacific
I coast between Point Arena and Fort Ross, C a lifo rn ia :
i Univ. Washington Publ. Geology, v. 6, n. 1, p. 1-29.
Wentworth, C.M., 1966, The upper Cretaceous and lower T e r t
iary rocks of the Gualala area, northern Coast Ranges,
C a lifo rn ia [unpub. PhD.) : Stanford U niv., 197p.
122
Wentworth, C.M., 1968, Upper Cretaceous and lower T e rt ia r y
stra ta near Gualala, C a lifo rn ia and in ferred large
rig h t la t e r a l - s lip on the San Andreas Fault iji Dick
inson, W.R. and Grantz, A., eds., Proceedings on con
ference on geologic problems of San Andreas f a u l t sy
stem: Stanford, C a l i f o r n i a , Stanford Univ. Press, p.
130-143.
Whetten, J.T. and Hawkins, J .W .J r., 1970, Diagenetic o r i
gin of graywacke matrix minerals: Sedimentology, v.
15, p. 347-361.
Wilson, M.D. and Pittman, E.D., 1977, Authigenic clays in
sandstones: recognition and influence on reservoir
properties and paleoenvironmental analysis: Jour.
Sed. Petrology, v. 47, p. 3-31.
Yancey, T.E. and Lee, J.W., 1972, Major heavy mineral
assemblages and heavy mineral provinces of the
central C a lifo rn ia Coast Region: Geol. Soc. America
Bull . , v. 83, p. 2099-21 04.
Young, S.W., 1976, Petrographic textures of d e t r i t a l poly
c r y s t a l l i n e quartz as an aid to in te rp re tin g c r y s t a l
lin e source rocks: Jour. Sed. Petrology, v. 46, p.
595-603.
123

Linked assets

University of Southern California Dissertations and Theses

Conceptually similar

PDF

Sedimentary character of the Lower Capistrano Formation, Upper Miocene age: Dana Point Harbor to San Clemente, California

PDF

Stratigraphy and sedimentation patterns Upper Miocene Puente formation (Mohnian-Delmontian) northwestern Puente Hills, Los Angeles County, California

PDF

Depositional systems of the mid-Tertiary Gene Canyon and Copper Basin Formations, eastern Whipple Mountains, California

PDF

Stratigraphy and sedimentary petrology of the Moss Back Member of the Late Triassic Chinle Formation, north Temple Wash - San Rafael Desert area, Emery County, Utah

PDF

Fourier grain-shape analysis of quartz sand from the eastern and central Santa Barbara littoral cell, Southern California

PDF

Pliocene lacustrine stromatolites of the Furnace Creek formation, Death Valley, California

PDF

Oligocene - Miocene Sedimentology of the Tecolote Tunnel section of Southern California

PDF

Stratigraphy and paleomagnetism of upper Vaqueros-lower Topanga Formations (early to middle Miocene), at Point Mugu and La Jolla Canyon, Western Santa Monica Mountains, Ventura County, California

PDF

Paleoenvironmental analysis of the Upper Cretaceous (Santonian/Campanian) Forbes Formation, Sacramento Valley, California

PDF

Physicochemical characterization of sediment facies and paleoclimatic inferences, California Continental Borderland

PDF

Paleoenvironmental analysis of Upper Cretaceous Pleasants Sandstone Member (Williams Formation), Santa Ana Mountains, Southern California

PDF

Solar cyclicity in the lacustrine Green River Formation (Eocene, Wyoming)

PDF

Sedimentation in Sebastian Viscaino Bay and vicinity, Baja California, Mexico

PDF

Sedimentary structures in vibra-cores from the Oxnard Shelf, California

PDF

Utilization of paired cores in sedimentological studies of the Mozambique Channel in the southwest Indian Ocean.

PDF

The Drummond Mine Limestone: Mississippian basin plain carbonate turbidites and hemipelagites in the Pioneer Mountains, Blaine County, south-central Idaho.

PDF

Mineralogic profiles for sand transport within southern California littoral cells: Cliffs, rivers and beaches

PDF

Sedimentology of the Beck Spring Dolomite, eastern Mojave Desert, California

PDF

Petrology and economic value of beach sand from southern Monterey Bay, California

PDF

Depositional environments of the Neogene Hungry Valley Formation: Sedimentary response to the initiation of the San Andreas Fault, Ridge Basin, Southern California

Asset Metadata

Creator Welton, Joann Evelyn (author)

Core Title Petrology and diagenesis of the early Miocene Skooner Gulch and Gallaway Formations, Point Arena, California

Degree Master of Science

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag OAI-PMH Harvest,Sedimentary Geology

Language English

Contributor Digitized by ProQuest (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c30-85806

Unique identifier UC11225520

Identifier usctheses-c30-85806 (legacy record id)

Legacy Identifier EP58680.pdf

Dmrecord 85806

Document Type Thesis

Rights Welton, Joann Evelyn

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA