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Vertical sequence analysis of late Pliocene pico formation sediments in Adams Canyon, Ventura County, California.

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Vertical sequence analysis of late Pliocene pico formation sediments in Adams Canyon, Ventura County, California.

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Content VERTICAL SEQUENCE ANALYSIS OF
LATE PLIOCENE PICO FORMATION SEDIMENTS
IN ADAMS CANYON, VENTURA COUNTY, CALIFORNIA
by
Thomas Martin Hartnett
A Thesis Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(Geological Sciences)
September 1980
UMI Number: EP58688
All rights reserved
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a note will indicate the deletion.
UMI
Dissertation Publishing
UMI EP58688
Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author.
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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
Thomas Martin Hartnett
under the direction of hX&.-.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
T H p J S I S COMMIT TE E
DEDICATION
Dedicated to the memory of the late Dr. Richard 0.
Stone, former Chairman of the Department of Geological
Sciences, who gave me his advice, support, and friendship.
ACKNOWLEDGMENTS
This thesis has received help from various sources.
Many thanks go to my Mother who has provided understanding
and support throughout my academic career. I would like to
thank Dr. Donn Gorsline for chairing my thesis committee
and for teaching me the principles of marine geology and
sedimentary processes. I would also like to thank the
other members of my committee, Dr. Bernard Pipkin and
Dr. Donald Lamar, for visiting the study area with me,
reviewing earlier drafts of this thesis and offering useful
comments. Talks with Dr. Tor Nilsen and Dr. Marty Link and
turbidite field trips with them were very helpful. Dr.
Link visited my field area and provided me with many sug
gestions. Dr. Robert Bourrouilh helped decide which portion
of Adams Canyon to measure in detail after I had completed
a reconnaissance of Adams Canyon and connecting Saltmarsh
Creek. The Mobil Corporation was important in developing
my interest in ancient deep-sea fan systems by giving me
the opportunity to map and interpret Eocene deep-sea fan
deposits in southwestern Oregon.
Gloria Lee did an excellent job in typing the final
iii
copy of this thesis with promptness above and beyond the
call of duty. Special thanks go to Virginia Wong who has
helped with the field work and virtually did all the
drafting while constantly providing moral support.
IV
TABLE OF CONTENTS
Page
DEDICATION * ii
ACKNOWLEDGMENTS ............. ... .. .. . .. . . iii
LIST OF ILLUSTRATIONS . . . . . . . . . . . . . . . . ix
LIST OF TABLES. ............ xiii
ABSTRACT. .......... ...... xiv
INTRODUCTION. . . . . . . . . . . . . . . . . . . . . 1
General Statement. . . . . . . . . . . . . . . . 1
Structure, Stratigraphy, Paleoecology and
Sediment Types . . . . . . . . . . . . . . . . 2
Previous Work............ 7
Field Work ..................... 7
FAN FACIES ASSOCIATIONS AND THE ORGANIZATION OF THE
MIDFAN SEDIMENTS IN ADAMS CANYON................... 13
SEQUENCE I. ....... 21
Sequence IA: Interchannel ........... 21
Grain size and bed characteristics. .... 40
Structures. . . . . . . . . . . . . . . . . 40
Summary .......... ... 40
Sequence IB: Megasequence .......... 40
Grain size and bed characteristics. .... 43
v
Page
Structures................................ 46
Summary .................................. 46
Sequence IC: Interchannel . .............
•
55
Grain size and bed characteristics. . . .
•
55
Structures................................ 60
Summary..............................
60
SEQUENCE I I ............................. ..
63
Sequence IIA: Megasequence. . . .............
63
Grain size and bed characteristics. . . . 63
Structures................................ •
70
Summary............................... .
•
70
Sequence IIB: Interchannel. . ............. . •
70
Grain size and bed characteristics. . . .
•
70
Structures................................
80
Summary . ............... ........
•
80
Sequence IIC: Interchannel to Near-Channel. . •
81
Grain size and bed characteristics. . . .
•
81
Structures. ..............................
83
Summary......................... .. •
83
SEQUENCE III........................................
89
Sequence IIIA: Megasequence ............... . 89
Grain size and bed characteristics. . . .
•
89
Structures..................... .. 90
Summary............................. .. .
98
Sequence IIIB: Interchannel .......... 98
Page
Grain size and bed characteristics. .... 98
Structures. . . . . . . . . . . . . . . . . 107
Summary . . . . . . . . . . . . . . . . . . 107
Sequence IIIC: Interchannel .......... 107
Grain size, bed characteristics and
structures. . . . . . . . . . . . . . . . 110
Summary ............ 110
Sequence HID: Interchannel .......... 110
Grain size, bed characteristics and
structures. .... ...... 110
Summary ............ 113
SEQUENCE IV . . 118
Sequence IVA: Megasequence............... 118
Grain size and bed characteristics....122
Structures............................. . 122
Summary............................... 130
Sequence IVB : Upper Channel-Fill..................130
Grain size, bed characteristics and
structures................. . 130
Summary...................................138
Sequence IVC: Overbank to Interchannel........... 138
Grain size, bed characteristics and
structures. ........................139
Summary ......................... ..... 144
SEQUENCE V.............. 147
Sequence VA: Megasequence ..................... 14 7
Grain size and bed characteristics. .... 147
vii
Page
i
Structures. . . ......... 157
Summary............ ......................160
Paleocurrents............ . 167
DISCUSSION, ....................... ......... 172
CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . 180
REFERENCES. . . . ................... ........ 182
Figure
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
LIST OF ILLUSTRATIONS
Location and general structural features near
Adams Canyon........ ..
Stratigraphy and paleoecology of Ojai area,
Ventura Basin, California .........
Adams Canyon measured section location and
general geology ............. .......
Diagram showing fan facies associations . . .
Environmental model of a deep-sea fan used in
the present study ............... . .
Continuous sandstone bed thicknesses for Se
quence I, meters 0 to 84............... .
A continuous detailed section of sequence IA
and megasequence IB .. .. ....... .
Sandstone bed percentage for meters 0 - 100
of section and vertical sequence analysis
of sequence IA........................... .
Amalgamation of pebbly sandstone layers at
meter 14.6................. ...............
Wavy bedding in 10 cm thick silt bed at meter
14.6........................................
Shell material oriented concave upward in
medium-thick granule sand layer at meter 32
Flame structures and loadforms of several
centimeters relief at meter 30, Figure 7.
Page
4
8
10
14
19
22
28
41
44
47
49
51
ix
Figure
| 13.
14*
!
15.
16.
17.
18.
I 1 9 *
| 20.
!
! 21.
22 .
23.
24.
25.
26.
27.
28.
Plastic deformation in thick medium-grained
sand bed at meter 35.......................
Vertical sequence analysis of megasequence IB
Detailed section of a portion of IC, inter
channel turbidites.........................
Facies D interchannel turbidites at meter 53.
Amalgamated massive medium- to fine-grained
beds of facies B2 between meters 84 and
94 which are characteristic of megasequence
IIA........................................
Continuous detailed section of megasequence
IIA from meter 84 - 94.......... .
Vertical sequence analysis of megasequence IIA
Sandstone bed thickness data for megasequence
IIA..............................
Continuous sandstone bed thickness for meters
107 - 126, sequence IIB, interchannel
environment....................... ..
Detailed section of interchannel turbidites
of a portion of section IIB from meter
114.5 - 116 ........ ..
Sandstone bed thickness for sequence IIC. . .
Detailed section diagram for a portion of
section IIC, interchannel turbidites from
meter 140 - 142.7 .........................
Twenty cm thick pebbly sandstone bed at meter
142.5 ......................................
Continuous detailed section diagram of meters
158 through 173, megasequence IIIA........
Massive pebbly sandstone layer 70 cm thick
with ripups of siltstone at meter 159 . . .
a) Bottom photo. Dish structures to right of
hammer in thick (12 2 cm) medium- to fine
grained sandstone at meter 168.5 .....
Page
!
53
56
58
61
l
64
1
66
71
1
73
75
78
82
84
86
91
96
99
x
Figure
! 28.
29.
30.
31.
32.
33.
j
j 34.
|
I 35.
35.
37.
38.
39.
40.
41.
42.
b) Top photo. Close up of top of the bed seen
in top portion of photo below showing fluid
escape pipes in convolute bedding ........
Sandstone bed thickness of megasequence IIIA
from meter 158 - 170 showing a thinning
upward trend when compared to overlying bed
thicknesses of section IIIB.......... ..
Vertical sequence analysis of megasequence IIIA
Sandstone bed thickness for meters 190 to 192
of interchannel sequence IIIB............ .
Detailed section diagram for a portion of
sequence IIIB, interchannel turbidites from
meter 190 to 191.9....................... ..
Photo at meter 344 of sequence IIIC, facies D
interchannel turbidites................... .
Interbedded sandstone, siltstone and mudstone
of interchannel sequence HID............ .
Cliff forming exposure of megasequence IVA
abruptly overlying thin-bedded turbidites of
sequence IIID just to left of geology student
Ginny V7ong..................................
Continuous sandstone bed thickness diagram for
meters 37 8 to 493, megasequence IVA........
Continuous detailed section of a portion of
megasequence IVA from meter 37 8 to 38 5.8 . .
Multistoried, amalgamated bodies of megase
quence IVA at meter 39 0. . .................
Sketch of large siltstone and mudstone ripups
at meter 4 90 ..... * ...................
Shallow dish structures at meter 385 of mega
sequence IVA ......................
Continuous vertical sequence analysis of mega
sequence IVA . . . . . . . . . . . . . . . .
Detailed section of a portion of IVC, overbank
deposits from meter 520 to 521.9 ......
Page
99
|
i o i !
i
103
105!
108
111
I
114
116
119
123
126
128
131
133
140
xi
Figure
43. Photo taken at meter 586 near top of section
IVC, facies D, interchannel turbidites . . .
44. Sandstone bed thickness diagram for a portion
of sequence IVC, interchannel turbidites . .
45. Continuous detailed section of a portion of
megasequence VA from meter 588 to 614. . . .
46. Sandstone and conglomerate bed thickness
diagram for a portion of megasequence VA . .
47. Conglomerate bed pinching out beneath head of
the hammer ..... . ......
48. Boulder conglomerate in poorly sorted sandy
mudstone at meter 59 0 of megasequence VA . .
49. Vertical sequence analysis of megasequence VA.
j 50. Clast supported cobble conglomerate close to
j base of megasequence VA near meter 586 . . .
I
i
i 51. Rose diagram for paleocurrent measurements
(Table 3) in the interchannel and channel
sediments....................................
Page
142 '
14 5
|
148 |
I
I
155
158
I
161
163
i
!
165
169
xii
LIST OF TABLES
Table Page
1. FACIES CLASSIFICATION OF SEDIMENT GRAVITY
FLOXtfS (AFTER WALKER AND MUTTI, 1973). .... 3
2. KEY FOR DETAILED SECTION DIAGRAMS............. 27
3. PALEOCURRENT MEASUREMENTS ....................... 16 8
4. COMPARATIVE STUDY OF MIDFAN CHANNEL-FILL
SEQUENCE.........................................174
5. TYPES OF GRAVITY-DRIVEN SEDIMENT FLOWS (AFTER
HAMPTON, 1979, TABLE 1) 177
xiii
ABSTRACT
Late Pliocene deep-water (300 m) turbidites of the
upper Pico Formation form a well-exposed, near-complete
vertical section in Adams Canyon, California. Approxi
mately 700 meters (m) of section were examined in detail,
revealing five sections of channel-fill sediments up to
117 m thick dominated by thick-bedded, coarse- to fine
grained sandstones, pebbly sandstones and conglomerates.
A thinning of bed thicknesses upward was found in all
five sections along with an associated decrease in grain
sizes. The channel-fill sediments are separated by tens
to hundreds of meters of finer grained plane-parallel
interchannel turbidites. The associations of facies types
along with the cyclic nature of the bed thicknesses
indicates that the entire sequence represents a midfan
environment of deposition. A comparison with equivalent
age midfan channel sediments exposed in Santa Paula Creek
2 km to the east indicates more frequent deposition for
the midfan sediments of Adams Canyon. This is interpreted
as the result of a decrease in the midfan gradient from
east to west causing increased deposition of sediment
gravity flows in the Adams Canyon area. Paleoecological
studies have indicated an infilling sedimentary basin from
early Pliocene to the beginning of the Pleistocene.
Pebbles and other clast composition indicate the
source terrain was Eocene and Miocene sedimentary rocks to
the northeast and crystalline basement towards the east.
A submarine canyon trending west to southwest is indicated
by the paleocurrent data. Flow mechanisms indicated by
structures within the section show that sediment was trans
ported by debris, grain, fluidized and turbulent flows. A
rate of 1 mm/year has been estimated as the overall sedi
mentation rate for the Pliocene sediments in the area.
xv
INTRODUCTION
General Statement
The study of modern turbidites has long been hindered
by their inaccessibility as they accumulated in deep
waters. The recent examinations of deep-sea fans at the
base of the continental slope along with smaller fans in
the southern California borderland have provided a clearer
picture of their morphology and sedimentology during the
last decade. This has tremendously aided in the recog
nition of ancient deep-sea environments in that much of
the extensive turbidite deposits in the geologic record
were formed as prograding deep-sea fans rapidly filled
marine basins. The analysis of these former marine basins
increasingly requires an interpretation of the sedimentary
rocks in terms of their depositional environment. The
study of turbidites has shown these sediments to be much
more than monotonously rhythmic beds. Repetitive sedi
mentary divisions were recognized and termed Bouma divi
sions. These divisions were found to be descriptive of
only some turbidites and are now a subordinate
1
classification to turbidite facies and facies locations
within a turbidite basin (see Table 1). Various subenvi
ronments of deep-sea fans can be recognized in the field
by recently developed criteria for distinguishing facies
and associations of facies.
Structure, Stratigraphy, Paleoecology and Sediment Types
The Plio-Pleistocene section exposed in Adams Canyon
and other canyons along the south flank of Sulphur Moun
tain, is distinctive because it is one of the thickest
known marine sections in the world, varying from 4,545 m
to 5,050 m (Bailey and Jahns, 1954). At its thickest point
near the city of ventura the total Tertiary section is
15,150 m (Yeats, 1976). The Adams Canyon section forms an
east-west striking homocline that dips steeply (70°) to the
south along the south flank of the Sulphur Mountain anti-
clinorium. Uplift of Sulphur Mountain is post-late Plio
cene time accompanied by folding occurred along the east-
west trending Sisar reverse fault (south side up) directly
north (Fig. 1) (Yeats, 1976). The Sulphur Mountain uplift
lies within the larger east-west trending Santa Clara
syncline. The San Cayentano Fault marks the northern
boundary of the syncline and the Oakridge Fault the
southern Boundary (Bailey, 1954). Along the San Cayentano
Fault Eocene age rocks have been thrust over younger,
2
]
Bouma
Sequence
Not
Applicable
TABLE I
^ACIES CLASSIFICATION OF SEDIMENT GRAVITY FLOWS
(AFTER WALKER AND MUTTI, 1973)
Facies A: Coarse-Grained Conglomerate Sandstone
A^ Disorganized Conglomerate
A2 Organized Conglomerate
A3 Disorganized Pebbly Sandstone
A^ Organized Pebbly Sandstone
Facies B: Medium Fine to Coarse Sandstone
Bi Massive Sandstone with Dish Structure
B2 Massive Sandstone without Dish Structure
Bouma
Sequence
Applicable
Facies C: Interbedded Medium to Fine Sandstone and
Mudstone, Proximal Turbidites
Facies D: Interbedded Fine to Very Fine Sandstone,
Siltstone, and Mudstone, Distal Turbidites
Facies E: Interbedded Very Fine to Medium Sandstone,
Overbank Deposits
Bouma
Sequence
Not
Applicable
Facies F: Chaotic Deposits Formed by Downslope
Mass Movement
Facies G: Mudstone, Pelagic and Hemipelagic
Deposits
3
Figure 1. Location and general structural features
near Adams Canyon, striped area shown in
Fig. 3 (adapted from Crowell et a3_.,
1966, Fig. 1).
Santa Ynez Faulk.
SANTA YNEZ MTNS.
OJAT
Thrust
San
FILLMOr
SANTA PAULA
VENTURA
OXNARD
steeply dipping rocks of Miocene and Pliocene age which
are locally overturned near the fault zone (Bailey, 1954).
The measured section in Adams Canyon consists of late
Pliocene (Wheelerian) sediments of the upper Pico Forma
tion. The rocks include interbedded siltstone, sandstone,
mudstone and conglomerate that are poorly to moderately
indurated. The mudstone is usually gray with occasional
thin reddish pelagic mudstone layers while the coarse
grained rocks are light gray or tan. Bedding thicknesses
range from laminated to very thick-bedded (4 80 cm).
Sandstone and conglomerate units generally show coarse-
tail grading or are massive. The sandstones are classified
as arkosic wackes because they contain greater than 10
percent mud matrix. The lenticular nature of the sand
stones and conglomerates can be seen in the few instances
where beds can be traced laterally tens of meters.
Lithified clasts are mainly siltstone and mudstone with
lesser amounts of chert, quartzite, volcanic rock fragments
and igneous rocks. Source areas consisted of Eocene and
Miocene sedimentary rocks to the northeast and crystalline
basement of the San Gabriel Mountains to the east. The
grain sizes in the Pico Formation generally grade laterally
from coarser grained rocks dominant in eastern Ventura
County to finer grained rocks in the west, suggesting an
increase in water depth to the west during deposition
(Weber et al_. , 19 73) .
6
Previous Work
Driver (1928) examined the foraminifera in Adams
Canyon and concluded that it consisted of 4,150 m of
unrepeated Pliocene sediments. Nearby Santa Paula Creek
with equivalent (Plio-Pleistocene) age sediments has been
studied by Natland and Kuenen (1951) in their work on the
sedimentary history of the Ventura Basin. Natland (1957)
studied the stratigraphy in Itfheeler Canyon only 2.4 km to
the west of Adams Canyon. His analysis of paleoecological
data indicated progressive increase in water depths to
greater than 1,200 m until early Pliocene (Repettian) time.
Basin filling and shallowing to 6 00 m continued during
middle Pliocene (Venturian) and depths of 300 m were
present during late Pliocene (Wheelerian) time (Fig. 2).
Crowell et al. (1966) also investigated Santa Paula Creek
and described a variety of turbidite structures.
Field Work
Nearly 700 m of poorly indurated late Pliocene deep-
water sediments were examined during the winter and spring
of 1980 in Adams Canyon. The mouth of this canyon lies
approximately 2 km west of the town of Santa Paula (Fig. 3).
Am abandoned dirt road provides access to the base of the
section. The base of the measured section is approximately
7
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ I
Figure 2 Stratigraphy and paleoecology of Ojai
area, Ventura Basin, California (after
Natland, 1957, Pi.4).
<
DE POSITIONAL ENVIRONMENT
6 0 0 3 0 0 90 0 1200 M
DEPTH
ca
v>
o
c .
e a
c .
Q.
a .
o
a .
CL
o c
D >
5 ®
Figure 3. Adams Canyon measured section location
and general geology. Topographic map
from USGS Santa Paula Peak, California
Quadrangle and the geology is after
Weber et al, (1973). Symbols and ex
planations follow; Tp: Pico Formation,
TQsb: Santa Barbara Formation, ^r"70 :
strike and dip of beds, B: base of
measured section.
/''O il Tanksv -
25 m east of the intersection of Adams Canyon and Saltmarsh
Creek roads (Fig. 3). Stream cutting has been rapid,
leaving excellent exposures of beds dipping steeply south
ward along most of the creek's length. Steep gorges up to
several meters in depth occur in the harder strata that are
eroded at right angles to the strike of the beds.
Field descriptions of the rocks included attitudes of
bedding, primary structures, bedding contacts, textural
variations and the presence or absence of channels. Where
distinct changes occurred in these characteristics, detailed
observations were recorded on data sheets which included
sketches of the section. These figures along with others
necessary for their interpretation are presented in the
descriptions of the measured section. An advantage in
working with these partially lithified sediments is the
easy cleaning and shaping of outcrops to better expose
primary structures and crossbedding in three dimensions
for paleocurrent measurements. Approximately fifty days
were spent in the field.
12
FAN FACIES ASSOCIATIONS AND THE ORGANIZATION
OF THE MIDFAN SEDIMENTS IN ADAMS CANYON
Turbidites and associated resedimented beds are
found in three major depositional environments: slope,
fan, and basin plain of either abyssal continental margin
or deep-sea basin locations (Walker and Mutti, 1973). The
fan system is subdivided using depositional facies and
cycles of sedimentation in differentiating the inner,
middle, and outer fan environments (Fig. 4). Cycles of
thinning and fining upward have been found characteristic
of midfan turbidites while thickening and coarsening
upward cycles indicate prograding outer fan turbidites
(Ricci-Lucchi, 1975). The various depositional facies
(Table 1) of Walker and Mutti (1973) and Ricci-Lucchi
(1975) modified after Howell and Link (1976) are described
as follows: facies A - organized and disorganized conglom
erate and pebbly sandstone, coarse sandstone, thick to mas
sive bedding, lenticular beds with cut-and-fill structures,
nongraded and graded, Bouma A or AE divisions; facies B -
pebbly sandstone and coarse sandstone with or without dish
13
Figure 4 Diagram showing fan facies associations
(after Walker and Mutti, 1973, Fig. 10).
See Table 1 for facies classification.
14
kL
B A S I C
F A C IE S
C ROU P I N G S
F A C IE S
IN
E A C H
G R O U P
E N V IR O N M E N T
C L A S S IF IC A T IO N
F A C IE S
A S S I G N E D
TO EACH
E N V I R O N M E N T
PROXIMAL-EXOTIC PROXIMAL
F,G A1(A3 A2 ,A4,Bj B2
/ V
1
SLOPE,
CHANNELS
SUBMARINE
inner middle
fan fan
F,G
SOME
Ai ,A3
M IX T U R E
OF
A],A3,G
SOME
C,D
f
B2 'A3'A4
WITH
E
THINNING UP
SEQUENCE
C,E
FANS
oufer
fan
A4, b2,C
t
D,C
THICKENING
UP SEQUENCE
fan
fringe
D
f
THICKENING
UP SEQUENCE
DISTAL
BASIN
PLAIN
t
D,G
structure, beds 50 to 200 cm thick, beds often amalgamated,
broad erosional concave lower surface, sole marks, gener
ally nongraded; facies C - fine- to coarse-grained sand
stone, beds 20 to 150 cm thick, mudstone or siltstone
interbeds, generally even and parallel bedding surfaces,
sole marks, equivalent to Bouma ABCDE to AE divisions,
graded; facies D, Bouma BCDE to CE divisions, beds
laterally persistant and in the past have been referred to
as "distal" turbidites; facies E - very fine- to medium-
grained sandstone, mudstone interbeds, beds 3 to 20 cm
thick, lenticular bedding, parallel bases and wavy tops of
beds, generally nongraded; facies F - chaotic slump
deposits, pebbly mudstone, all retransported deposits;
facies G pelagic mudstone, massive bedding.
The inner fan is one channel characterized by associ
ations of the various facies A and B along with levee
deposits, facies E, enclosed by pelagic muds, facies G.
The high channel walls prevented the overbank flow of
turbidites and resulted in facies G, pelagic muds
dominating the sediments outside the channeled areas
(Normark, 1970). The change in gradient in the midfan
location causes a branching system of small valleys and
channels that are progressively less incised (Nelson
et al., 1970).
Midfan sediments comprise the Adams Canyon measured
section which is nearly 700 m thick. This section
16
is part of the upper Pico Formation and is late Pliocene
in age. It is composed of broadly lenticular massive
sandstones, coarse-grained conglomerate and sandstone of
facies B and A respectively with alternating plane-parallel
strata of medium to fine sandstones, siltstones and mud
stone of facies D, E and C (Table 1) . The organized,
recurrent groups of thicker beds of facies A and B that
form multistoried sand bodies up to 117 m thick
within the section are referred to as megasequences
(Ricci-Lucchi, 1975). By definition megasequences have
sand/shale ratios of greater than one and in this section
the sand/shale ratio often exceeds 50 to 1. The sand /shale
ratios were determined by totalling the thicknesses of the
individual sandstone beds and dividing that number by the
total thickness of the remaining mudstone within each
interval. The average bed thickness of megasequences in
Adams Canyon range from 22 to 88 centimeters. These
megasequences are separated by sequences 47 to 203 m thick
that are defined as having sand/shale ratios less than one.
Sequences are characterized by thinly bedded, plane-
parallel strata that may be found in minor amounts within
the megasequence. A common trend in megasequences is a
thinning of beds, termed a positive cycle, and a decrease
in grain size from the base toward the top (Ricci-Lucchi,
1975). These types of megasequences have been interpreted
as the result of filling of submarine channels (Normark
17
and Piper, 1969). They differ from prograding outer fan
deposits which thicken upward, referred to as a negative
cycles (Ricci-Lucchi, 1975). A midfan environment has
been indicated for the association of facies of the type
described above on the basis of lateral and vertical
stratigraphic relationships and paleocurrent trends by
Walker and Mutti (1973) and Ricci-Lucchi (1975). Five
megasequences are found within the section at Adams Canyon,
all characterized by overall thinning of bed thickness
and decrease in grain sizes upsection. The deep-sea fan
model of Ricci-Lucchi (1978) (Fig. 5) was applied in this
study. These midfan sediments were deposited in waters
between 300 to 600 m deep on the basis of correlations
between the same foraminiferal species found in these
Pliocene sediments and the depth ranges they are found
within present-day offshore waters (Natland, 1957).
18
Figure 5 Environmental model of a deep-sea fan
used in the present study (after Ricci-
Lucchi, 1978, Fig. 14).
19
Aiv
Aiv
Aiv
A - shelf
B i: upper slope
B 2: lower slope
C i : inner fan
Cz’ - middle fan
C3: outer fan
D -' basin plain
C’ . canyon
Vp: principal valleys
Vs: secondary valleys
Cp: peripheral channels
Aiv:intervalley areas
Separation scarps of submarine slides
^ Accum ulations of submarine slides
20
SEQUENCE I
Hundreds of meters of thinly bedded turbidites occur
between the base of the measured section and the junction
of Adams and Saltmarsh Creeks (Fig. 3). Sequence I is 84 m
thick and forms the base of the measured section. It is
divided into three subunits IA, IB and IC. IA consists
of near-channel turbidites and makes up the bottom 5.5 m
of the section. IB is channelized sands consisting of
thin to very thick beds that thin upward and extend upward
to 47 m from the base of the sequence (meter 47). IC is
characterized by thin-bedded interchannel deposits that
continue the thinning upward trend to meter 8 4 at the top
of the section (Fig. 6).
Sequence IA: Interchannel
The beginning of the section is located 25 m east
of the intersection of Adams Canyon and Saltmarsh Creek
roads (Fig. 3). The basal 44 m of the section are
depicted in Figure 7 which includes sequence IA and IB.
See Table 2 for the key to the detailed sections.
Figure 6. Continuous sandstone bed thicknesses for
Sequence I, meters 0 to 84. The graphs
were prepared by measuring the thicknesses
of each sandstone bed in Sequence I.
Breaks in the graph represent covered
intervals.
22
meter
meter
19
IB
10
7
10 100 200
Thickness in cm
meter
31
10 50 100 200
NJ
Thickness in cm
meter
39
IB
36
32
50 10 100 200
Thickness in cm
meter
50
46
IC
44
40
IB
10 50 100 200
to
( j i
Thickness in cm
meter
58
55
IC
51
200 100 10 50
Thickness in cm
meter
NJ
c r >
Thickness in cm
meter
78
IC
74
200 100 50
Thickness in cm
TABLE 2
KEY FOR DETAILED SECTION DIAGRAMS
TEXTURE
A. STRUCTURES
Boulder Load form
cb Cobble
Scour
Pebble
Organic material
(wood, plant, charcoal)
Granule
Shell
Sand ss
Bioturbation structure
Silt
Lenticular, undulose or
wavy bedding
Clay
Flame structure
Convolute lamination
Parallel lamination
Small-scale cross-stratification
DIRECTION CONTACTS
Paleocurrent
270 direction 270
- measured from
cross-bedding
Sharp, flat
Gradational
Undulating
27
Figure 7 A continuous detailed section of sequence
IA and megasequence IB. See Table 2 for
explanation.
28
COLUMN S T R U C T U R E S T E X T U R E S M E TE R
29
COLUMN M E TE R S T R U C T U R E S
30
COLUMN S T R U C T U R E S M E T E R
31
COLUMN S T R U C T U R E S T E X T U R E S M E T E R
r
COLUMN S T R U C T U R E S T E X T U R E S M E TE R
33
S T R U C T U R E S
MilLLilNS
COLUMN M E TE R
34
S T R U C T U R E S T E X T U R E S COLUMN M E T E R
S T R U C T U R E S COLUMN E X T U R E S M E TE R
36
CO LUM N S T R U C T U R E S T E X T U R E S M E TE R
COLUMN M E T E R
COLUMN S T R U C T U R E S
MLiSHiihH
M E TE R T E X T U R E S
Grain size and bed characteristics. Section IA is
composed of very thin- to thin-bedded often lenticular
beds of medium sand and siltstone. The medium sands are
either massive or graded siltstone. Many beds were
observed to lense out within a few meters of the available
outcrop. Laminations, Bouma B, or cross-bedding, Bouma C
divisions are very common.
Structures. The bottoms of the beds are flat to
gently undulating. Scouring was observed to occur at the
bases of approximately a quarter of the beds and maximum
relief is 3 cm but usually 1 to 3 centimeters. The tops
of most beds are wavy due to differential compaction.
Organic material was often observed in parallel and wavy
laminations.
Summary. This sandstone sequence is composed mainly
of Bouma BE and/or CE divisions, facies D and some Bouma
AE and ABCE divisions, facies C (Fig. 8). The beds become
thicker upward near the channel-fill sediments at meter
5.5.
Sequence IB: Megasequence
The first megasequence is 42.5 m thick starting at
meter 5.5 where the sand to shale ratio first exceeds 1
and ends at meter 48 where the ratio becomes less than 1.
The sequence between meters 5.5 and 44 is depicted in
40
Figure 8. Sandstone bed percentage for meters 0 -
100 of section and vertical sequence
analysis of sequence IA. Partial
stratigraphic column shows percentage
of sandstone determined by totaling
the thickness of all sandstone beds in
each interval divided by remaining
thickness of mudstone. Layered columns
show internal organization of section
into sandstone (white) and mudstone
(black). Letters indicate facies inter
pretation, see table 1.
meter
100
sand
100
IIA
IC
50
IB
IA
0
D - C
D
to
Figure 7.
Grain size and bed characteristics. Section IB is
composed of quite variable thickness and sediment types.
Layers of pebbly sandstone to siltstone range from very
thick- (214 cm) to thinly bedded (2 cm) and have flat to
undulating bedding contacts. Organized pebbly sandstones,
facies A^ (Table 1) occur between meters 12 and 27.
Individual beds are characterized by coarse-tail grading
and reverse grading especially near their bases. Amalga
mation between the pebbly sandstones as well as other
granule and coarse sand layers (Fig. 9) is common and the
intervening mudstone layers are completely eroded and
incorporated into the beds as ripups. Ripups of siltstone
and sandstone are also common sometimes up to 1 m in
length. Where amalgamation has not taken place the
mudstone layers are highly deformed and eroded as can be
seen just above and below meter 10 where the mudstone
layers terminate in ripup zones. Sand injection structures
and load pockets were observed at meters 6, 7.2, and 2 2.2
and are indicative of the rapid rate of deposition of
these beds.
Beds of granule to silt size sediment range from thin
(1-2 cm) to thick (116 cm) and the coarser material
usually occurs in the thicker beds. They are found above
and below the pebbly sandstones and are normally graded
or massive with occasional reverse grading. Very thin,
43
Figure 9. Amalgamation of pebbly sandstone layers
at meter 14.6. Top of section is to
the right. Note change in grain sizes
pointed out from granules in lower bed
to small pebbles in upper bed.
44
45
lenticular bedding occurs infrequently in the bottom two-
thirds of the section.
Structures. Scouring is very common at the base of
the coarser grained beds and up to 27 cm deep at the base
of a pebbly sandstone layer. Loadforms were nearly as
common. The thinly bedded sandstone and silt layers (6-
60 cm) are commonly parallel to wavy laminated and/or
cross-bedded as are the tops of a few of the medium-thick
(90-100 cm) layers (Fig. 10). Shell material was observed
in some granule to coarse sand layers from meter 2 3
upward; the shells are often oriented concave upward
(Figure 11).
Some excellent examples of flame structures are found
in this megasequence, especially at meter 30 (Figure 12)
and just above meter 35 where they attain 10 cm of relief.
These structures usually form in the fine sand to silt
upper portion of a bed by loading of the coarse sand to
granule overlying bed. The medium-grained sand bed at
meter 35 (Fig. 13) contains an unusually thick deformed
strata indicating that the layer underwent plastic
deformation during creep flowage downslope.
Summary. The bed thickness diagram (Fig. 6) for
megasequence IB shows a thinning upward trend and a fining
upward of grain sizes also occurs within this section (Fig.
7). The organized pebbly sandstones are interpreted as
facies and the thinner granule to siltstone beds are
46
Figure 10. Wavy bedding in 10 cm thick silt bed at
meter 27.2. The top of the section is
to the right.
47
48
Figure 11. Shell material oriented concave upward
in medium-thick granule sand layer at
meter 32.
49
50
Figure 12. Flame structures and loadforms of sev
eral centimeters relief at meter 30,
Figure 7. Top of the bed is towards
the top of the photo.
51
5 2
Figure 13. Plastic deformation in thick medium-
grained sand bed at meter 35.

facies 32, C and D turbidites (Fig. 14). These beds are
interpreted as channelized sands to upper channel-fill as
a channel was progressively filled and abandoned.
Sequence IC: Interchannel
This sequence begins above meter 48 where the sand/
shale ratio decreases to less than 1 and continues to
meter 84 (Fig. 8). It is consistent with the trend of
thinning upward sandstones that begins in megasequence 13.
Its relationship to the channelized sands and upper channel-
fill below appears to be interchannel characterized by
thickening upward mudstone layers that become medium-thick
(40 era) to thick (100 cm) at the top of the section.
Above IC the thick sands of megasequence II begin abruptly
at meter 84.
Grain size and bed characteristics. The bed thickness
of individual sand layers as well as grain sizes continues
to decrease between section 13 and IC (Fig. 6). Sandstone
thicknesses average 2 2 cm in IB but decrease upward to
6 cm in IC (Fig. 15). Above meter 80 sandstone all but
disappears and is replaced by thick mudstone layers with
minor thin silt laminations crop out to the top of the
section. Bouma divisions BE, CE and BCE were observed to
occur in 56 percent of the 136 sand layers measured in
this section and while beds with Bouma A divisions at the
55
Figure 14. Vertical sequence analysis of megase
quence IB. Refer to Table 1 and Figure
8 for explanation.
56
meter
? % sand 1 ( ? 0
100
50 -
ui
B2
D
A y
B'
C - D
34
20
A
Figure 15. Detailed section of a portion of IC,
interchannel turbidites. See Table 2
for explanation.
58
M E TE R
base comprise the remainder.
Structures, Contacts were usually flat with few
undulating bottoms from minor scouring (2 cm). Parallel
laminations, wavy bedding and cross-bedding (Fig. 16) are
abundant in this section indicating decreasing and
variable current speeds (Crowell, 1966). Organic material
occurs in the laminated intervals. Amalgamation of sand
layers is rare.
Summary. The thinning upward of sand layers and
associated increase in the thickness of shale layers
throughout this section indicate continued channel retreat
from this area and consequently thinner and thinner inter
channel deposits. Most of the turbidites lack basal Bouma
A divisions and start with either division B or C, facies
D, and are interbedded with some turbidites starting with
Bouma division A, facies C.
60
Figure 16. Facies D interchannel turbidites at
meter 53. Lower bed is parallel lami
nated siltstone, Bouma B, capped by
mudstone, Bouma E division. Upper silt
bed is parallel laminated in its basal
portion and is transitional to slightly
wavy upper portion, Bouma C and is also
capped by mudstone.
61
62
SEQUENCE II
Sequence II consists of three subunits, IIA-C. IIA,
a megasequence begins suddenly above the interchannel
deposits of IC just above meter 84 and crop out to meter
100 where there is 5 m of cover. IIB, interchannel
deposits, start at meter 105 and continue to meter 140.
At that location near-channel deposits characterize the
third subsection, IIC to meter 154.
Sequence IIA: Megasequence
The sand/shale ratio is very high, 7 to 1 compared
to 1 to 4 for the interchannel deposits of sequence IC
below.
Grain size and bed characteristics. This section is
composed of medium- to fine-grained sand in beds for the
main part 40 cm to 154 cm thick (Fig. 17). These sand
stone beds alternate with thin sandstone layers, and very
thin siltstone and silty clay beds that sometimes are
fissile. The sandstone beds are either massive or display
slight normal grading (Fig. 18). Bedding contacts are
Figure 17. Amalgamated massive medium- to fine
grained beds of facies B2 between meters
84 and 94 which are characteristic of
megasequence IIA. The top of the section
is to the left.
6 5
Figure 18. Continuous detailed section of megase-
See quence IIA from meter 84 -
Table 2 for explanation.
66
COLUM N M E T E R
COLUMN S T R U C T U R E S M E T E R
COLUMN M E TE R
j generally flat with minor scouring and occasional load- |
| forms of 1 to 3 cm relief. However, ripups of underlying
| |
[ mudstone and siltstone beds from a few to 75 cm in length i
|
i and 10 cm thick with long-axis imbrication were noted. i
! !
i Amalgamation of sandstone beds is common. i
i i
! j
! Structures. Parallel lamination and cross-bedding j
I |
1 was found in many very thin silt beds and also in the !
: i
silty tops of the normally graded, very thick medium- j
; I
grained sand beds. Organic material is fairly common and I
I sometimes associated with parallel laminations.
Summary. Section IIA represents at least 16 m of j
channel sands of facies B^, massive sandstone without i
dish structures along with some facies C and D turbidites
: i
(Fig. 19). The overall bed thickness data (Fig. 20) indi- !
i [
; cate a thinning upward sequence characteristic of midfan j
channels. j
Sequence IIB: Interchannel
The continuous sequence IIB crop out for 35 m (meter
105-140). The sand/shale ratio declines to 1 to 4 in
this sequence.
Grain size and bed characteristics. Bed thicknesses j
- - - - - - - - - - - - - - - - - - - - - - - - - — -’ - - - - - - - - * - - - - - - - - - j
(Fig. 21) and grain sizes continue to decrease above
i
section IIA. Section IIB (Fig. 22) is composed of thin-
bedded fine sands, siltstones and silty mudstones. |
Figure 19. Vertical sequence analysis of megase
quence IIA. See Figure 8 and Table 1
for explanation.
100
u
c u
- p
sand
100
IIA
IC
50
IB
IA
0
C - D
Bo
B<
b2
C
Bo - C
-j
Figure 20. Sandstone bed thickness data for mega
sequence IIA.
73
93
84
-j
£ > »
meter
Thickness in cm
Figure 21. Continuous sandstone bed thickness for
meters 107 - 126, sequence IIB, inter
channel environment.
75
1
10 50 100 200
Thickness in cm
cn____________________________________
IIB
J _________________________ I____________ I_ _
10 50 100
Thickness in cm
i
200
126
U
CD
-P
CD
6
124
123
-j
-j
IIB
— I ------------1 ________ l_
10 50 100
Thickness in cm
I _
200
Figure 22. Detailed section of interchannel turbi
dites of a portion of section IIB from
meter 114.5 - 116. See Table 2 for
explanation.
ST R U C TU R E S
iN>j,
T E X T U R E S M E TE R S E O . D I R .
X5 CJ C- GO CO CO C .
116
I I B
245
115
I I B
Mudstone layers with thin laminations 1 to 2 mm thick are
usually as thick or thicker than the coarser grained
layers and become thicker toward the top of the section.
Red mudstones from 1 to 3 cm thick commonly are inter
bedded with or top gray mudstone layers. The fine sands
are graded or are massive like the siltstones. Fine sands
and siltstones less than 3 cm thick were noted to lense
out in the lower part of the sequence but most beds have
good lateral continuity. Bedding contacts are flat with
scouring of 4 cm relief uncommon.
Structures. The massive and graded fine sands to
silts consisting of Bouma divisions AE and ABE, facies C
make up 52% of the 120 beds measured in sequence IIB.
Parallel lamination and cross-bedding are also common in
the silty to silty mudstone beds of Bouma BE and BCE
divisions, facies D, in the remainder of the beds.
Summary. Interbedded fine to very fine sandstone,
siltstone and mudstone show a decrease in bed thickness
from thin- to very thin-bedded and the average thickness
is less than 5 cm within this section. Facies C and D
are interbedded in nearly equal amounts upsection. The
thin, fine-grained sand lenses noted in the lower part
of the section may have originated from dilute overbank
deposits filling shallow depressions (Mutti, 1975).
Section IIB is considered representative of interchannel
turbidites deposited increasingly further and further
from a midfan distributary channel.
Sequence IIC: Interchannel to Near-Channel I
j
Sequence IIC is continuous with IIB below and is j
j
located between meters 140 and 154. It differs from the j
|
siltstones and mudstones of the upper part of IIB by the !
introduction of more frequent and thicker sandstone beds
(Fig. 23) as well as pebbly sandstones (Fig. 24). It is
differentiated from the overlying megasequence starting j
at meter 154 by its sand/shale ratio which is just under j
1. j
Grain size and bed characteristics. Section IIC
contains thin (30 cm) to very thin (1 cm) beds of pebbly i
i
sandstone, fine sandstone, siltstone, silty mudstone and j
i
mudstone (Fig. 24). The pebbly sandstones (Fig. 25) make 1
up the thickest layers with the maximum pebble diameters
2 cm and the average size 1 centimeter. The pebbles are j
subrounded and are composed of lithified siltstone. The j
gravel portion was found to vary from being found uniformly
throughout the thinner beds (10-15 cm) to concentrated in
the bottom two-thirds or central portion of thicker beds 1
j
(20-31 cm). Rounded, long-axis imbricated clasts also |
composed of siltstone up to 7 cm in length are found in the'
central portion of some of the thicker beds along with
mudstone ripups. The grain sizes of the matrix material
i
range from medium-grained sand to clay and are poorly j
Figure 23. Sandstone bed thickness for sequence
IIC.
32
142
140
00
( j j
meter
IIC
j_____________i _______ i _
10 50 100
Thickness in cm
i _
200
Figure 24. Detailed section diagram for a portion
of section IIC, interchannel turbidites
from meter 140 - 142.7.
84
COLUMN T R U C T U R E S M E TE R T E X T U R E S
Figure 25. Twenty cm thick pebbly sandstone bed
at meter 142.5. Top of the sequence
is toward the top of the photo. Over-
lying fine-grained sand to silty bed
in basal graded (Bouma A), laminated
siltstone (Bouma B) in central portion
and convolute bedding (Bouma C) in silty
top. Mudstone (Bouma E) caps beds.
36
. >
* ' O. ? 1
&
d f f e J K
g i
sorted. Scouring of 2 to 3 cm relief usually occurred
with the pebbly sandstones and at the base of some of the
fine-grained sands. The fine-grained sands were all less
than 15 cm thick and the siltstones, silty mudstones and
mudstones are less than 8 cm thick. Red pelagic mudstone
often capped gray turbidite mudstone layers. All the
thin beds have flat bases, fairly uniform thicknesses that
can be traced laterally across 15 m of available outcrop.
Structures. Parallel lamination was common in the
tops of beds of all grain sizes especially the fine silts
and silty mudstones. The very thin (3 cm) silt beds were
sometimes cross-bedded as were the thin silty tops of one
pebbly sand layer. Most Bouma divisions consist of AE,
ABE, ABCE couplets of facies C.
Summary. The transition to coarser grain sizes,
thicker beds, ripups of mudstone and cobble size clasts
indicates the presence of a distributary channel. The
Bouma divisions are mainly of facies C (Table 1), proximal
turbidites.
88
SEQUENCE III
Sequence III is divided into four subunits IIIA-D.
IIIA is a megasequence which begins at meter 154 and crop
out to meter 173 where there is 4 m of cover. Very thin-
bedded turbidites of facies D and C make up sequence IIIB
which begins at meter 177 and extends upward to approxi
mately meter 300. Sequence IIIC crops out from meter 300
to meter 354 and contains highly laminated silt and silty
mudstone of facies D, distal turbidites. Above, in
sequence HID, facies C, proximal turbidites, are found
to meter 37 6 where megasequence IV begins.
Sequence IIIA: Megasequence
The third megasequence is dominated by pebbly sand
stones and other coarse-grained beds. The sand/shale
ratio becomes very high, 70 to 1.
Grain size and bed characteristics. Megasequence
IIIA consists of thick (80 cm) to very thick (125 cm)
layers of pebbly sandstone which are massive in the bottom
part of the section and are normally graded from basal
89
pebbles to siltstones in the upper layers of the section
(Fig. 26). Maximum pebble diameter is 1.8 cm and the
average size is approximately 0.3 cm. Pebbles are
composed of quartz, red chert, volcanic rock, gneiss and
granodiorite set in a fine- to coarse-grained sand matrix.
Mudstone and siltstone ripups up to 50 cm in length, often
with their long-axis imbricated, occur throughout the
section (Fig. 27). Interbedded with the pebbly sandstones
are granule and coarse- to fine-grained sandstones from 10
to 6 0 cm thick which have slight normal grading and occa
sional strata of granules or pebbles forming thin zones of
reverse grading. Nearly every bed is amalgamated, as a
result mudstone layers are rare and scouring is common; up
to 70 cm of relief occurs at the base of one pebbly bed.
An example of a deformed mudstone layer that was nearly
detached and ripped up occurs just below meter 162 (Fig.
26). Many of the beds prove to be highly lenticular and
thicken laterally as much as half a meter over 15 to 20 m
of exposed outcrop.
Structures. Parallel and wavy lamination, cross
bedding and convolute-bedding were seen in the infrequent
very thinly bedded silt layers and in some of the fine
grained sand to silty tops of the thicker layers. Load-
forms and flame structures of several centimeters relief
as well as small loadpockets were common bedding contact
features throughout megasequence IIIA. Dish structures up
90
Figure 26. Continuous detailed section diagram of
meters 15 8 through 17 3, megasequence
IIIA. See Table 2 for explanation.
91
COLUMN S T R U C T U R E S M E TE R T E X T U R E S
S T R U C T U R E S COLUMN T E X T U R E S M E TE R
93
CO LUMN M E T E R S T R U C T U R E S T E X T U R E S
S T R U C TU R E S T E X T U R E S COLUMN M E T E R
Figure 27. Massive pebbly sandstone layer 70 cm
thick with ripups of siltstone at meter
159. Currents traveled from the left
to the right.
96
VV <:4 V
> < * f \ ,
'• ■ ; ■'-'•'t« 5 K .3 = T .< £)jg
> ' * r \ .
97
to several centimeters in length and 1 cm deep were seen
in several medium- to fine-grained sandstone beds (Fig.
28a). In a very thick (122 cm) sandstone bed dish struc
tures are transitional to fluid escape pipes (Fig. 28b)
indicating that they were formed by a rapid dewatering
process. The minor amount of organic and shell material
observed was associated with parallel laminations and
pebbly sandstone respectively.
Summary. Megasequence IIIA is comprised of cyclically
thinning upward layers (Fig. 29) of organized pebbly sand
stones, facies A4, medium-fine- to coarse-grained sand
stones with dish structure, facies B2, and without dish
structure, facies along with minor amounts of facies
C and D (Fig. 30). This megasequence is interpreted as a
midfan channel that became infilled and abandoned.
Sequence IIIB: Interchannel
This section is mainly very thin-bedded, fine- to
medium-grained sandstones, siltstones, silty mudstones and
mudstones of facies D and C. It has an overall thickness
of 123 m.
Grain size and bed characteristics. Sandstone bed
thickness and average grain sizes are less in IIIB than
IIIA (Fig. 31). The sandstone thicknesses average 33 cm
in IIIA but drop to just under 2 cm in IIIB. Massive
siltstones and silty mudstones less than 4 cm thick
_________ 98
Figure 28. a) Bottom photo. Dish structures to
right of hammer in thick (122 cm)
medium-to fine-grained sandstone at
meter 168.5.
b) Top photo. Close up of top of the
bed seen in top portion of photo below
showing fluid escape pipes in convolute
bedding.
100
Figure 29. Sandstone bed thickness of megasequence
IIIA from meter 15 8 - 170 showing a
thinning upward trend when compared to
overlying bed thicknesses of section
IIIB (Fig. 31).
101
170
u
CD
- M
(D
e
165
158
H
O
to
IIIA
-J ____________________ l___________ I __
10 50 100
Thickness in cm
200
Figure 30. Vertical sequence analysis of megase
quence IIIA. See Table 2 and Figure
for explanation.
104
100
205-
% sand
t i i
IIIB
u
< u
■P
< U
B
173
154
140
IIB
105
Figure 31 Sandstone bed thickness for meters 190
to 19 2 of interchannel sequence IIIB.
105
H
O
a>
meter
191
IIIB
190
10 50
Thickness in cm
predominate within section IIIB and the rare beds of uni
form to graded medium- to fine-grained sandstone are always
less than 7 cm thick (Fig. 32). The beds are separated by
equally thick or thicker layers of gray mudstone sometimes
with paper thin silt laminations. Red, pelagic mudstone
1 to 4 cm thick commonly cap or are interbedded with the
grey mudstone. Bedding contacts are flat with minor
scouring of less than 2 cm relief at the base of the
medium- to fine-grained sandstones. Some of the very thin-
bedded siltstone layers were observed to lense out
laterally over the 2 to 3 m outcrop width. Amalgamation
was rarely observed.
Structures. Siltstones and the silty tops of graded
sandstones are often parallel laminated or cross-bedded.
Sixty percent of the coarse-grained beds start with Bouma
division B or C, facies D and 40 percent begin with Bouma
A division, facies C.
Summary. Section IIIB consists of interbedded very
thin turbidites of facies D and C that become thinner
upwards from IIIA and are interpreted as interchannel
deposits.
Sequence IIIC: Interchannel
Sequence IIIC is continuous with IIIB below and HID
above. It starts just above meter 300 and extends upwards
107
Figure 32. Detailed section diagram for a portion
of sequence IIIB, interchannel turbi
dites from meter 190 to 191.9.
108
S T R U C T U R E S COLUMN M E T E R
to meter 354 differing from the interchannel deposits
above and below it by being composed nearly exclusively
of facies D.
Grain size, bed characteristics and structures. Grain
sizes and bed thicknesses decrease from sequence IIIB to
IIIC. IIIC is mainly grey and red mudstone with some
siltstone and silty mudstone. Bed thicknesses are always
less than 4 cm thick with flat bedding contacts and
i
! good lateral continuity that can be traced over 20 m of
available outcrop. Nearly all beds begin with parallel j
j j
laminations, Bouma B or cross-bedding, Bouma C divisions, j
i
facies D (Fig. 33).
I Summary. Sequence IIIC shows a slight thinning and
[
fining upwards character in relation to IIIB below and j
| consists almost entirely of parallel laminated siltstones j
and silty mudstones of facies D, distal turbidites. It
1 i
! may represent interchannel turbidites deposited by dilute j
turbidity currents further from a distributary channel J
| than sequence IIIB.
' i
!
: i
i Sequence HID: Interchannel j
i I
I I
. j
| Sequence HID continues above IIIC at meter 354 and
i !
|
i crop out to meter 3 77 where megasequence IV abruptly |
t |
begins.
! i
: Grain size, bed characteristics and structures. A |
Figure 33. Photo at meter 344 of sequence IIIC,
facies D interchannel turbidites.
Very thin-bedded (4 cm) siltstone
bed with wavy bedding and faint cross
bedding (Bouma C) interbedded with thick
mudstone layers (Bouma E) comprising
sequence IIIC.
Ill

slight increase in grain size and bed thickness occurs in |
sequence IIID and very coarse- to fine-grained sand and j
siltstone are found in beds up to 15 cm thick. The sand/ [
| j
j shale ratio increases to just under 1 in comparison to j
I 1 to 3 in sequence IIIC. Bedding contacts are flat and |
S |
j minor scouring is present at the bases of some sandstone j
! layers. Beds appear to have uniform thickness over 50 m |
I
j |
I of exposed, though largely inaccessible outcrop due to its
! steepness. Examination of available outcrop revealed that
!
! Bouma divisions ABCE, ABE and ACE of facies C predominate |
| |
| and Bouma divisions BE, facies D occur in minor amounts j
(Fig. 34).
Summary. Sequence IIID is mainly composed of facies
! C, proximal turbidites interbedded with minor amounts of
facies D, distal turbidites that show a slight increase in
both grain size and bed thickness relative to IIIC below.
Though sequence IIID is still representative of inter- |
: channel deposits it seems to indicate a developing channel
|
source that begins abruptly (Fig. 35) with megasequence
IV, the thickest channelized sand body in the section at j
meter 377. j
gure 34. Interbedded sandstone, siltstone and
mudstone of interchannel sequence IIID
The top of the section is to the right

Figure 35. Cliff forming exposure of megasequence
IVA abruptly overlying thin-bedded tur
bidites of sequence h i d just to left of
geology student Ginny Wong. A scoured
contact between massive coarse-grained
amalgamated sandstones is being pointed
out by her. Note the broadly lenticular
nature of these beds as they thicken
from the upper left to the lower right
hand portion of the photo.
116
l t t
SEQUENCE IV
Sequence IV begins abruptly with medium-thick to
1 very thick beds of pebbly, granule and coarse- to fine-
| grained sandstone of megasequence IV. Sequence IV is
| |
| divided into three subunits which demonstrate a thinning
|
j and fining upward sequence indicating a progressive change
|
| from channel deposition, IVA, to upper channel-fill, IVB, !
i j
and overbank and interchannel deposits, IVC. The thick
ness of each unit is approximately 117 m for A, 16 m for B,
I i
| and 77 m for unit C.
j
Sequence IVA: Megasequence
I
j
| Sequence IVA is the thickest megasequence studied
within the section containing the thickest beds (485 cm) !
I !
found within the entire measured section. IVA is made up
| of 117 m of organized pebbly sandstones, facies A^,
massive granule to fine-grained sandstones, facies B^,
| as well as facies C, proximal turbidites. These layers
t
form a thinning (Fig. 36) and fining upwards trends. Load i
deformation and the effects of scouring are the main
structures in these rocks. i np
Figure 36. Continuous sandstone bed thickness
diagram for meters 378 to 493, mega
sequence IVA. Breaks in the graph
represent covered intervals.
119
meter
410
IVA
391
378
50 10 100 200
460
450
420
Thickness in cm
ro
o
IVA
J_____________________ I____________ i____________ i__
10 50 100 200
Thickness in cm
o
o
in
o
o
cm
o
00
121
i Grain size and bed characteristics. Thick (12-105 cm)
!to very thick (485 cm) beds of pebbly, granule and coarse-
! ’ i
i
!to fine-grained sand abruptly overlie the interchannel j
I 1
I deposits of section IIID (Fig. 35). These beds are usuallyj
! !
normally graded to fine-grained sand to silt tops. Layers j
;of pebbles, granules, and coarse-grained sand commonly
iform reverse grading within beds greater than a meter
jthick. The lenticular nature of these beds over hundreds
j of meters of outcrop is well expressed in a cliff exposure j
i j
i j
:perpendicular to strike (Fig. 35). Bedding contacts are
undulating with scouring (maximum relief of 25 cm) oc
curring at the base of nearly every bed. Intervening j
I i
mudstone layers are rare and highly scoured and deformed j
where they do crop out (see meter 384.3, Fig. 37). Nearly j
every bed is amalgamated and only the changes in grain
sizes reveal the undulating bedding contacts. This results
I
in a 22:1 sand/shale ratio. Mudstone and siltstone clasts j
i i
i
(2-30 cm), often imbricated, are common and occasional j
I
ripups over a meter long occur (Figs. 38 and 39). Igneous I
rock fragments, chert and charcoal fragments are less
|
common and usually less than 3 cm in length.
Structures. Loadforms and flame structures of
;several centimeters relief are very common along basal
contacts and occasionally have 25 cm relief. Load pockets
of coarse-grained sand or granules were also noted. Par- j
allel laminations, wavy bedding and cross-bedding occur j
!
122
Figure 37. Continuous detailed section of a portion
of megasequence IVA from meter 37 8 to
385.8. See Table 2 for explanation.
12 3
C O LUM N S T R U C T U R E S T E X T U R E S M E T E R
124
COLUMN METER SEO.
I V A
D I R . S T R U C T U R E S
WSHV nH
TEXTURES
^oC-cOaisjL
-385
Figure 38. Multistoried, amalgamated bodies of
megasequence IVA at meter 390. Note
hammer beneath meter mark for scale.
The top of the section is to the left.
Large cavity also beneath meter mark
is weathered out mudstone ripup approx
imately 1 m long.
126

Figure 39. Sketch of large siltstone and mudstone
ripups at meter 490.
12
6ZT
1 Meter
in the silty top several centimeters of many normally
!
graded beds. Shell material, usually concave downward was j
!
|often associated with granule portions of beds. Dish j
structures, several centimeters in length and 0.2-0.3 cm j
!deep occur at meter 385 and 451 in the top half of |
! j
'medium- to fine-grained sand (Fig. 40).
Summary. Thick to very thick sandstone beds of
facies B^f massive sand without dish structure, facies B^, !
massive sand with dish structure, with minor amounts of I
I facies A^, organized pebbly sandstone and facies C, i
I proximal turbidites make up megasequence IV (Fig. 41),
S
The first cycle of very thick beds between meter 378 and j
; i
i
I 410 culminates in several beds 2 m thick or greater which j
i
then thin upward to meter 435 where a 3.5 m thick bed !
j
starts the next thinning upward trend. The thinning |
upward trend continues to meter 470 where a 4.85 m thick j
bed is noted (Fig, 36) which begins the last thinning j
upward cycle to the top of IVA.
j
Sequence IVB: Upper Channel-Fill I
Sandstone/shale ratio, bed thickness and grain sizes j
i
i
decrease from IVA through IVB as proximal turbidite facies ;
C sandstones dominate for the next 16 m interval. i
Grain size, bed characteristics and structures. Nor- j
mally graded beds of medium-grained sand to siltstone \
Figure 40. Shallow dish structures at meter 385 of
megasequence IVA.
1311

Figure 41. Continuous vertical sequence analysis
of megasequence IVA. See Table 1 and
Figure 8 for explanation.
133
meter
100
490
378
sand
391
384
IVA
B'
B2
b2
b2
b2
C
c
B2
B-
B2
|A„
u>
4^
398
417
- C
410
393
b2
C
b2
B'
1 m
C
135
428
100
sand
490
422
IVA
420
378
430
428
B-
a4
a4
b2
450
440
3 bi
□ C
4
<
A,
A,
A/
1 m
136
470
A,
B,
B'
488
480
1 m
137
493
0 100
% sand
i i i
u
< 1 )
4J
< D
e
378
1 m
varying from very thin- (5 cm) to thick- (120 cm) bedded,
usually with intervening mudstone layers, indicate a
transition from the channelized sands of IVA to upper
channel-fill deposits of IVB. Bedding contacts are mostly
flat with minor scouring (less than 3 cm relief). Load-
forms are rare within IVB and are only found where sand-
j stone beds are amalgamated. Ripups consisting of mudstone
1 clasts (2 cm) are infrequent and found only within the
I thick-bedded sandstones. The silty and silty mudstone tops
| are often parallel laminated and/or cross-bedded and
I
I
j consist of Bouma divisions ABCE, ABE, ACE and AE, charac-
i teristic of facies C, proximal turbidites. A 2 m
! thick slump structure, facies F, with highly disturbed
I bedding was found at meter 497. It was probably formed
| by local slumping off the edge of the banks of the channel.
Summary. The decrease in bed thickness and grain
| size along with the increased amount of traction structures
| (Bouma B and C divisions) in the tops of the sandstone
| beds characterize IVB. These layers can be clearly
identified as facies C, proximal turbidites. The sediments
are interpreted as upper channel deposits of IVA to over-
I
j bank and interchannel turbidites of IVC.
Sequence IVC: Overbank to Interchannel
Bed thicknesses continue to decrease from sequence IVB
to IVC, and average 2.2 cm thick in IVC, but grain sizes
remain the same in the lower one-third of IVC and gradually
decrease in its upper portion. Facies E, overbank depo
sits are interbedded with increasing amounts of facies
D,interchannel deposits from the bottom to the top of
sequence IVC.
Grain size, bed characteristics and structures.
: Thin- (7 cm) to very thin- (1 cm) bedded medium- to fine- |
grained sandstone, siltstones and silty mudstones are foundj
I
i j
; in section IVC (Fig. 42). These beds are separated by j
equally thick or thicker (33 cm) layers of gray to red j
mudstone, often with very thin (0.1 cm) silty laminations.
Bedding contacts are flat, and infrequent shallow (2 cm) '
scours occur at the base of a few medium- to fine-grained
* sand layers. In the lower third of the section one-half j
of the medium- to fine-grained sandstone and siltstone beds
j i
! were observed to lense out abruptly within the limited j
outcrop. These lenticular beds produce AE Bouma divisions j
i
| which Ricci-Lucchi (1978) described as the overbank
product of large by-passing turbidity currents. The
i !
overbank deposits are interbedded with increasing amounts
j
of parallel laminated, Bouma B division and cross-bedded, 1
Bouma C division siltstones and silty mudstones of facies j
I |
D (Fig. 43). Bouma divisions ABE, facies C, were also
i
I found interbedded in the lower third of the section but j
!
decrease m abundance m the upper portion. Organic ;
: _________________________ 139 j
Figure 42. Detailed section of a portion of IVC
overbank deposits from meter 520 to
521.9. See Table 2 for explanation.
140
S T R U C T U R E S COLUMN T E X T U R E S D I R . M E TE R SEO.
I V C
M
-521
-520
IV C
Figure 43. Photo taken at meter 586 near top of
section IVC, facies D, interchannel
turbidites. Thick mudstone layers
are seen in bottom half of photo over-
lain by wavy and faintly cross-bedded
(Bouma C) fine-grained sandstone and
parallel laminated (Bouma B) top bed
which is directly beneath handle of
the hammer.
142
143
material is common in silty, parallel laminated layers.
Summary, A thinning (Fig. 44] and fining upward
trend continues from IVA through IVB and IVC which is
interpreted as a change in environments from channel, IVA,
to upper channel-fill, IVB, to overbank and interchannel
deposits, IVC.
144
Figure 44. Sandstone bed thickness diagram for a
portion of sequence IVC, interchannel
turbidites.
145
H
C T >
meter
521
IVC
520
10 50
Thickness in cm
SEQUENCE V
Sequence VA: Megasequence
Megasequence VA is the highest, coarsest and most
debris-laden megasequence measured. It is at least 97 m
thick and near the top is covered by alluvium. Above the
covered part of the megasequence near-channel turbidites
of facies C were noted. Conglomerates, pebbly sandy j
mudstones, and massive sandstones dominate this section and
j
conglomerates are concentrated within the bottom 39 meters.
Figure 4 5 describes the basal third of the megasequence. |
Grain size and bed characteristics. The conglomer- |
atic layers are composed of poorly sorted sandstone with
i
greater than 30 percent small pebbles and granules of !
quartz, chert, and igneous rock. Large pebbles (2-6 cm), j
cobbles (6-22 cm), and boulders (22-75 cm) of sandstone, j
mudstone and igneous rocks infrequently compose up to 9 0
!
percent of the basal portion of the megasequence and !
usually constitute less than 5 percent in the remaining !
conglomeratic beds. Beds range from thin (7 cm) to very .
thick (196 cm) (Fig. 46) and are crudely organized, facies!
Figure 45. Continuous detailed section of a por
tion of megasequence VA from meter 58 8
to 614. Diameters of large cobbles and
boulders are indicated in centimeters
within specified clasts. See Table 2
for explanation.
148
COLUMN ST R U C TU R E S T E X T U R E S M E T E R
CO LU M N S T R U C T U R E S T E X T U R E S M E T E R
ST R U C TU R E : T E X T U R E S S E O . D I R . M E T E R
u D. ac w a : u
V A
-602
-601
-600
-599
V A
COLUMN M E TE R
COLUMN S T R U C T U R E S M E TE R SEQ D I R T E X T U R E S
j C - M o i i n ;;
V A
-61
O
-610
O
C>
-609
O
20
-608
V A
M E TE R SEQ S IR U C T U R E S T E X T U R E S COLUMN D I R
U G - M y i c/3
614
V A
-612
V A
154
Figure 46. Sandstone and conglomerate bed thickness
diagram for a portion of megasequence VA.
155
610
S - l
< D
-P
( U
E
VA
600
588
10 100 50 200
Thickness in cm
and A^ have pebbles, cobbles and boulders concentrated
towards the bottom of beds between meters 592 and 614.
Very thick (150 cm) beds of pebbly sandy mudstone, facies
F, are found in the top of the conglomeratic part of section
V to meter 620. Sixty percent of the organized pebbly
sandstones, facies A^, normally grade upwards to thin tops
of laminated siltstone whereas just under 30 percent of the
organized conglomerates, facies A^, do the same. It is
possible to trace laterally a few of these conglomerate
layers and they were found to lense out laterally within
50 m (Fig. 47). The pebbly sandstones and conglomerates
usually form amalgamated layers with undulating bottoms.
I
| These coarser grained beds are interbedded with thin (8 cm)
to thick (95 cm) beds whose grain sizes range from granule
' j
to siltstone of facies , massive sandstone without dish
2
structures, and facies C, proximal turbidites. These
facies constitute the upper 59 m of section. Facies C
turbidites are usually massive or graded from granules or
! coarse-grained sand to siltstone. Many of the facies
have granule or coarse-grained sand bases. Mudstone !
|
I layers, where present, are almost always scoured and |
| I
| highly deformed. j
| Structures. Scouring is found at the base of nearly |
all beds, especially the thicker beds and has a maximum
relief of 15 centimeters. Loadforms are prevalent at the
i bases of the pebbly sandstones usually being 6 cm or less
Figure 47. Conglomerate bed pinching out beneath
head of the hammer. Bed is 30 cm thick
at the right.
15
159
deep but ranging up to 35 cm at the base of a boulder con
glomerate unit (Fig 48). Small flame structures (2 to 3
cm) resulting from loading occur at the silty tops of
some beds. Parallel and wavy lamination frequently are
found in the siltstone tops of the facies C turbidites.
Organic material is fairly common, usually in coarse
grained sand or granule portions of beds.
Summary. Megasequence VA defines a thinning upward ;
!
trend in the top 59 m of the section starting at meter j
625 associated with a decrease in grain size upward. It j
is composed of facies A^r F, and C with the latter i
two facies dominating the top 59 m of megasequence (Fig. !
49). The conglomerates in the lower 39 m of megasequence ;
i
i
show variations in the relationship of clasts to matrix. j
The basal 5 m of the megasequence consists of clast
i
supported boulder layers, 30 cm thick interbedded with
!
massive medium- to fine-grained sands (Fig. 50). The j
central portion contains poorly sorted, matrix supported i
i
cobbles and pebbles which decrease in size upward within
each bed and generally have greater than 50 percent matrix
material (Fig. 45). The third and upper portion consists j
of pebbly sandy mudstones similar to previously described j
!
debris flow deposits (Crowell, 1957). The characteristics i
suggest that the conglomerate units represent sedimentation!
i
of remobilized, unconsolidated sediment. They would fall
into the class of sediment gravity flow deposits
Figure 48. Boulder conglomerate in poorly sorted
sandy mudstone at meter 590 of megase
quence VA. The top of the section is
to the left. Seventy-five cm thick
boulder has compressed underlying sand
bed causing 35 cm of relief along bed
ding contact.
161
162
Figure 49. Vertical sequence analysis of megase
quence VA. See Table 1 and Figure 8
for explanation.
163
164
684
n
Q J
- P
< D
£
586
614
608
601
A-
a4
B2
a2
Ao
a4
a2
C - b2
B2
C
1 m
Figure 50. Clast supported cobble conglomerate
close to base of megasequence VA near
meter 586.
165
166
consisting of debris flows, turbidites, and submarine
landslides (Middleton and Hampton, 1973). The central
crudely graded zone shows the effects of turbulence by its
poor sorting of grain sizes but also resedimentation
because the matrix was unable to support all of the clasts,
at least temporarily. Conglomeratic lithologies of
similar description have been recognized as being upslope
I
j and downslope facies of a single mass movement deposit
i (Cossey and Ehrlich, 1979). The conglomeratic lithologies j
I
seen in megasequence VA were deposited from a number of
seperate mass movements downslope that individually cannot
, be observed to be laterally gradational between conglomer-
i j
; atic types but may represent different facies of debris j
j flows.
I
! Paleocurrents
[ Small scale cross-bedding was examined in the field
j for paleocurrent data which is presented in Table 3 and
i
| Figure 50. In the rose diagram (Fig. 51) paleocurrents
were indicated as being found in either channel or inter- J
i
j channel environments. The cross-bedded units were usually
! less than 1 cm thick and some of the thin and faint units
i
i
were unuseable. The measurements were made by cleaning
| two surfaces at right angles to one another to see the
I cross-bedding in three dimensions. The three dimensional
|
! _ _ 1^1\
TABLE 3
PALEOCURRENT MEASUREMENTS
LOCATION ENVIRONMENT DIRECTION0
1.0 Interchannel 280
4.0 Interchannel 280
5.0 Interchannel 270
5.5 Channel 265
6.7 Channel 280
9.5 Channel 265
10.6 Channel 275
17.3 Channel 270
24.2 Channel 240
29. 8 Channel 280
31.5 Channel 260
38.5 Channel 260
51.1 Interchannel 275
92.0 Channel 275
115.2 Interchannel 245
142.1 Interchannel 255
160. 2 Channel 270
191.0 Interchannel 235
521.1 Interchannel 260
168
Figure 51. Rose diagram for paleocurrent measure
ments (Table 3) in the interchannel and
channel sediments.
169
N
Interchannel
<- h- Channel
Occurrences
W
S
170
orientation of the cross-bedding was found and the sense
of movement perpendicular to the cross-bedding was then
determined. The pre-tilting direction was found by
rotating the plane of cross-bedding around the strike line
into the horizontal.
The direction of current flow overall was west to
southwest for both channel and interchannel deposits.
This agrees with the paleocurrent measurements of Hsu
(1977) and Crowell et a_l. (1966), for early and late
Pliocene age sediments respectively in the area.
According to Barker (1976) the Pliocene sediments' compo
sition indicates an influx of material from the erosion of
uplifted older formations to the northeast. This source
terrain would have been Eocene and Miocene sedimentary
rocks of the ancestral Topatopa Mountains and crystalline
basement from the San Gabriel Mountains further to the
east. The Pliocene submarine canyon was probably oriented
northeast to southwest and transferred sediments from the
basin margin to the east-west trough axis. Hsu's (1977)
studies of the Ventura oil field lower Pliocene turbidites,
which was the first release of information of Shell Oil
Company work in the Ventura Basin in the 1950's emphasize
longitudinal sediment transport in the basin and de-
emphasizes fan deposition. Walker (1978) presents a
modern interpretation of the same data in terms of outer
submarine fan deposits.
171
DISCUSSION
The Adams Canyon measured section is characteristic
of midfan facies associations that form broadly lenticular
bodies of channelized sandstones with lesser amounts of
conglomerate of facies A, B and C. These sediments
alternate with plane-parallel interchannel deposits of
facies D, C and sometimes E. Conformably overlying the
section are intermittently exposed thin sandstone and
mudstone beds also of the upper Pico Formation and the
poorly exposed Plio-Pleistocene marine Santa Barbara
Formation which is comprised of mudstone and some sandstonel
Underlying the section are 200 m of upper Pico thin sand- j
stone and mudstone beds and poorly exposed sandstone, |
mudstone, and conglomerate of the lower Pliocene Repetto
|
Formation. Walker (1978), interpreted the Repetto sedi
ments as depositional lobes in an outer fan environment. j
Natland (1957) established that the Repetto was deep j
water (1,200 m) from paleoecological studies. A deep-sea ’
fan progradational cycle is indicated as the Pliocene |
turbidite basin infilled and shallowed. A trend of fan |
progradation was reported by Johnson (1977) for the middle
to late Pliocene sediments exposed along Santa Paula Creek
which are 2 km along strike to the east,
A comparison of the megasequences measured in Adams
Canyon to those found in midfan channel-fill sequences in
Santa Paula Creek by Johnson (1977) and the northern
Apennines by Ricci-Lucchi (1975) is presented in Table 4.
The thickness of interchannel sediments separating mega
sequences are very similar between Adams Canyon (4 7-203 m)
j and Santa Paula Creek (40-210 m) while the Apennines
i
j megasequences have much less thick interchannel intervals
i (10-80 m)« Most of the interchannel sediments in Adams
! Canyon are 90m or less thick, which correlates well with
j the Appenines, with the exception of the 203 m interval
i
between megasequence III and IV. The thick interchannel
interval probably owes itself to coarse-grained sediments j
t being transported to another area of the midfan during |
that time.
! j
The maximum average layer thickness within individual
megasequences in Adams Canyon (88 cm) is thicker in
J !
! comparison to Santa Paula Creek (56 cm) but both are much
less thick than the Apennines (500 cm). This suggests |
I that there was a higher rate of deposition in the Adams j
Canyon midfan section compared to the Santa Paula midfan j
section and is supported by the greater minimum and maximum
thickness of megasequences in this section (16-117 m) than
| in either of the other two sections. The middle fan
I ____________ 17 3
TABLE 4
COMPARATIVE STUDY OF MIDFAN CHANNEL-FILL SEQUENCE
APENNINES ADAMS CANYON SANTA PAULA
CREEK
SEPARATION OF , « * o _
MEGASEQUENCE 10-80 m 47-203 m 40 210 m
AVERAGE LAYER .. oo oo o c . cc
THICKNESS 40—500 cm 22-88 cm 25-56 cm
THICKNESS OF o c co n ™ o n on+
MEGASEQUENCE 2.5-62.0 m 16 117 m 2.0 70 m
SAND/SHALE 1.5-50 4-50 3.6-50
174
environment in modern fans forms as the result of an
abrupt change of gradient in the submarine topography
(Nelson et al., 1970). It is possible that the Adams
Canyon midfan sediments were deposited in increasing
amounts on a portion of the midfan farther basinward
according to paleocurrent data, with a lower gradient
than the Santa Paula Creek midfan sediments. An expla-
! nation for the thinner average layer thickness in this
; area (88 cm) in comparison to the Apennines (500 cm)
I sediments was suggested by Johnson (1977) by a possible
| narrow shelf margin and/or a direct deltaic feed of sedi
ment to the head of a submarine canyon. It may be
similar to the Pliocene delta reported by Baldwin (1959)
' in the Fillmore area 24 km east of Santa Paula. The
sand/shale ratios are similar within the megasequences
i
between Adams Canyon (4-50) and Santa Paula Creek (3.6-50) |
and both are roughly equivalent to those of the Apennines
(1.5-50). The paleogeographic reconstruction of this late !
, Pliocene basin predicts basin plain sediments were being j
| deposited farther westward during the time of midfan i
deposition in the areas of Santa Paula Creek and Adams
| i
| Canyon. Basin plain pelagic mudstone of late Pliocene age j
1 referred to as the "mudpit shale" is nearly 1,000 m thick !
[
! and is exposed in Hall Canyon near the city of Ventura j
| t
19 km to the west (Bailey and Jahns, 1954).
A number of types of gravity-driven sediment flows j
!_ __ _ __ 175!
were recognized within the measured section and are
summarized in Table 5. The dense,, concentrated turbidity
deposits, facies C, were found in the megasequences and
interbedded with facies D, dilute turbidity current
deposits of the interchannel areas.
The massive sandstones of facies and various facies
A conglomerates cannot be classified under the classic
turbidity current model and are thought to represent grain
j flows, dispersions containing high concentrations of grains
i that flow rapidly on a slope. The dispersions are fre-
I
quently channelized and lose their energy very rapidly at
the base of the slope resulting in deposition of their
entire load, without traction support at the base or
! i
selective sorting of grains (Middleton and Hampton, 1973). j
Grain flows have recently been found for the first time j
on the deep ocean floor off the Bahamas by Mullins and :
!
j Van Buren (1979).
! The dish structures characteristic of facies B.. are j
| l i
| considered indications of fluidized (liquefied) flow j
! !
j where the sediment was supported by pore-fluid expulsion. I
I _ _ |
| Dish structures described in megasequence III (Fig. 26) I
I
were observed to be transitional to fluid escape struc- |
1 i
j i
tures. It has been suggested by Lowe (1975) that these
sediments were deposited initially by normal turbidity j
i currents and that immediately after deposition large |
j
' amounts of water were forced into the sand from underlying J
TABLE 5
TYPES OF GRAVITY-DRIVEN SEDIMENT FLOWS
(AFTER HAMPTON, 1979, TABLE 1)
TYPE OF FLOW SEDIMENT SUPPORT MECHANISM
Turbidity Current Turbulence
Grain Flow Grain Interaction (Dispersive
Pressure)
Liquefied Flow Upward Intergranular Flow
(Pore-Fluid Expulsion)
Debris Flow Matrix Strength
177
beds undergoing loading consolidation which could trigger
renewed flowage. The convolute lamination that overlies
the dish structures at meter 169 (Fig. 28B) are cohesive
upper layers that resisted fluidization and deform hydro-
plastically into convolute lamination (Lowe, 197 5) .
The debris flow deposits in the basal portion of
megasequence VA (Fig. 4 5) were noted to have variations in
clast and mudstone content between individual flows. The
; debris flows may represent lateral or longitudinal vari-
1 ations within a single debris flow or may owe itself to
I different clast sizes available in the source material.
Facies changes within a single debris flow were reported
| by Cossey and Ehrlich (1979). Their upslope facies j
' consisted of boulders in contact representing clasts too
| large for suspension, the intermediate facies was a poorly
: i
i
sorted bouldery pebble mudstone with a downslope facies j
j
of unsorted, pebbly mudstone. These pebbly mudstones were |
i
i j
i traced in outcrop into turbidites and indicate that
turbidites can represent downslope remnants of large mass j
flows that are roughly time equivalent to the boulder \
deposit upslope. Lowe (1972) described similar lithologic j
variations in the Cretaceous of California with boulders
! in contact in the basal portion of the Logan ridge member j
j while its distal two-thirds consists of pebbly mudstones
with few clasts.
The depositional rate for the Pliocene sediments in j
i
! 178
this area has been calculated by Yeats (1976) as 1 mm/yr.
This is equivalent to the rate of accumulation for outer
fan deposits in an Apennine turbidite basin (Mutti et aJL.,
1976) .
The Upper Pliocene turbidite basin shallowed towards
the east and eroding Eocene and Miocene sedimentary rocks
to the northeast and crystalline basement to the east
provided source material to a rapidly infilling basin
(Barker, 19 76). A submarine canyon transported sediments
in a southwestward direction and deposited them in a
channelized midfan portion of a deep-sea fan in the areas
of Adams Canyon and Santa Paula Creek.
179
CONCLUSIONS
A prograding deep-sea fan would be expected to form
a stratigraphic column of midfan sediments overlying outer
! fan sediments. The early Pliocene Repetto Formation in
this area has been interpreted by Walker (1978) as being
i
comprised of outer fan sediments and the late Pliocene
upper Pico Formation in Adams Canyon is here interpreted
as midfan sediments. Continued shallowing of this basin
j
is indicated within the overlying Plio-Pleistocene Santa
Barbara Formation by Natland’s (1957) foraminiferal
correlations. j
j !
| Five megasequences were found in Adams Canyon all of \
i
i which demonstrate thinning and fining upward trends
i
i
I characteristic of infilled and abandoned midfan channels.
I These broadly lenticular, coarse-grained channelized
! i
facies are separated by fine-grained, plane-parallel j
i
i I
layers of interchannel deposits ranging from tens to j
j
' hundreds of meters thick. These sediments originated from j
older exposed formations to the northeast and east and
i
were rapidly transferred into a submarine canyon that j
transported them in a southwestward direction. At the j
mouth of the submarine canyon the sediments formed a deep-
sea fan and in the area of Adams Canyon and Santa Paula
Creek the sediments were deposited in a midfan environment.
Paleocurrent direction measurements indicate that the
Adams Canyon sediments were deposited on a portion of the
midfan farther basinward (westward) than the Santa Paula j
Creek sediments. As the slope of the deep-sea fan
decreased towards the west sediments were deposited in
I
greater amounts and frequency in the Adams Canyon area
i
compared to Santa Paula Creek. This interpretation is
i
; supported by the much thicker megasequences and greater
average layer thickness within the megasequences of Adams
|
Canyon compared to Santa Paula Creek (Table 4). The
midfan sediments of the Adams Canyon and Santa Paula Creek
I
: I
area laterally change facies to basin plain mudstones 1
westward near the city of Ventura. The deep-sea fan model
! can therefore be used as a predictor in the paleogeographicj
j
reconstruction of this late Pliocene basin. |
j
Sediment gravity flow types observed were those of
j turbidity currents, grain flows, fluidized flow, and :
| I
j i
j debris flows. The overall rate of sedimentation for j
I Pliocene sediments in the area is 1 mm/yr. (Yeats, 1976).
181
REFERENCES
Baldwin, E. J., 1959, Pliocene turbidity crrent deposits
in Ventura Basin, California: unpub. M.S. Thesis,
Univ. of Southern Calif., Los Angeles, 64 p.
Bailey, T. L., 1954, Geology of the western Ventura
Basin, Santa Barbara, Ventura, and Los Angeles counties:
Calif. Div. Mines Bull. 170, Map Sheet No. 4.
Bailey, T. L., and Jahns, R. H., 1954, Geology of the
Transverse Range Province, Southern California: Calif.
Div. Mines Bull. 170, Chapt. II, p. 83-106.
Barker, C. T., 1976, Pliocene geology and the Santa Paula
oil field area: Am. Assoc. Petroleum Geologists and
Coast Geol. Soc. Spring Field Trip Guidebook, Pacific
Section, 18 p.
Cossey, S. P., and Ehrlich, R., 1979, A conglomeratic,
carbonate flow deposit, northern Tunisia: a link in
the genesis of pebbly mudstones: Jour. Sed. Petrology,
vol. 49, p. 11-22.
Crowell, J. C., 1957, Origin of pebbly mudstones: Geol.
Soc. America Bull., vol. 68, p. 993-1010.
Crowell, J. C., Hope, R. A., Kahle, J. E., Ovenshine, A. T.,
and Sams, R. H., 1966, Deep-water sedimentary structures,
Pliocene Pico Formation, Santa Paula Creek, Ventura
Basin, California: Calif. Div. Mines Spec. Rept. 89 , 40 p
Driver, H. L., 1928, Foraminiferal section along Adams
Canyon, Ventura County, California: Am. Assoc. Petroleum
Geologists Bull., vol. 12, p. 753-756.
Hampton, M. A., 19 79, Buoyancy in debris flows: Jour. Sed.
Petrology, vol. 49, p. 753-758.
Howell, D. G. and Link, M. H., 1979, Eocene conglomerate
sedimentology and basin analysis, San Diego and southern
California borderland: Jour. Sed. Petrology, vol. 49,
no. 2, p. 517-539.
182
Hsu, K» J., 1977, Studies of Ventura field, California,
1: facies geometry and genesis of lower Pliocene
turbidites: Am. Assoc. Petroleum Geologists Bull.,
vol. 61, p. 137-168.
Johnson, B. A., 1977, Vertical sequence analysis of
Santa Paula Creek, Ventura, California: unpub. M.S.
Thesis, Univ. of Southern Calif., Los Angeles, 204 p.
Lowe, D. R., 1975, Water escape structures in coarse
grained sediments: Sedimentology, vol. 22, p. 157-204.
Lowe, D. R., 1972, Implications of three submarine mass
movement deposits, Cretaceous, Sacramento Valley, Cali
fornia: Jour. Sed. Petrology, v. 42, p. 89-101.
Middleton, G. V. and Hampton, M. A., 1973, Sediment
gravity flows: mechanics of flow and deposition in
Middleton, G. V. and Bouma, A. H., (eds.j Turbidites
and deep-water sedimentation: Soc. Econ. Paleontologists
and Mineralogists Pacific Coast Section, Los Angeles,
p. 1-38.
Mullins, H. T. and Van Buren, H. M., 1979, Modern modified
carbonate grain flow deposit, Jour. Sed. Petrology, v. 49,
p. 747-758.
Mutti, E., 1975, Distinctive thin-bedded turbidite facies
and related depositional environments in the Eocene
Hecho Group (south-central Pyrenees, Spain): Sediment
ology, vol. 24, p. 107-131.
Mutti, E., Nilsen, T. H., and Ricci-Lucchi, F., 1976,
Sedimentology of outer fan depositional lobes of upper
Miocene-Pliocene Laga Formation, east-central Italy,
(Abst.): Am. Assoc. Petroleum Geologists Bull., vol. 60,
p. 701.
Natland, M. L., 1957, Paleoecology of west coast Tertiary
sediments in Ladd, H. S., (ed.), Turbidity Currents and
the Transportation of Coarse Sediment into Deep Water:
Soc. Econ. Paleontologists Mineralogists Pacific Coast
Section, Los Angeles, California, p. 39-78.
Natland, M. L., and Kuenen, Ph. H., 1951, Sedimentary
history of the Ventura Basin, California, and the
action of turbidity currents: Soc. Econ. Paleontologists
Mineralogists Spec. Pub. No. 2, p. 76-107.
183
Nelson, C. H., Carlson, P. R., Byrne, G. V., and Alpha, !
T. R., 19 70, Development of the Astoria Canyon - fan
physiography and comparison with similar systems:
Marine Geology, vol. 8, p. 259-291.
Normark, W. R., 1970, Growth patterns of deep-sea fans:
i Am. Assoc. Petroleum Geologists Bull., vol. 54, p. 2170-
j 2195. |
|
Normark, W. R., and Piper, D. J. W. , 1969, Deep-sea fan- j
valleys, past and present: Geol. Soc. Am. Bull., vol. I
! 80, p. 1859-1866.
Ricci-Lucchi, F., 1978, Turbidites of the northern
Appennines: introduction to facies analysis: Internat.
Geology Rev., vol. 20, no. 2, p. 127-166.
Ricci-Lucchi, F., 1975, Depositional cycles in two turbi-
dite formations of northern Appennines (Italy): Jour.
Sed. Petrology, vol. 45, no. 1, p. 3-43.
I Walker, R. G., 1978, Deep-water sandstone facies and !
! ancient submarine fans: models for exploration for
j stratigraphic traps: Am. Assoc. Petroleum Geologists
j Bull., vol. 62, p. 932-966.
i
Walker, R. G. and Mutti, E., 1973, Turbidite facies and
facies associations in Middleton, G. V. and Bouma, A. H.,
(eds.) Turbidites and deep-water sedimentation: Soc.
Econ. Paleontologists Mineralogists Pacific Section Short
Course, p. 119-159.
Weber, F. H., Jr., Cleveland, G, B., Kahle, J. E.,
: Kiessling, E. F. , Miller, R. V., Mills, M. F., Morton,
D. M., and Cilweck, B. A., 1973, Geology and Mineral
Resources Study of southern Ventura County, California:
Calif. Div. Mines Prelim. Rept. 14, p. 1-39.
Yeats, R. S., 1976, Neogene tectonics of the central
Ventura basin, California in. Fritsche, A. E., Terbest,
Jr., H., and Wornart, W. W. (eds.), The Neogene Sym
posium, selected technical papers on: Paleontology,
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Creator Hartnett, Thomas Martin (author)

Core Title Vertical sequence analysis of late Pliocene pico formation sediments in Adams Canyon, Ventura County, 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-c30-86448

Unique identifier UC11225547

Identifier usctheses-c30-86448 (legacy record id)

Legacy Identifier EP58688.pdf

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