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UNRAVELING MASS EXTINCTIONS: PERMIAN TO EARLY JURASSIC
ONSHORE-OFFSHORE TRENDS OF MARINE STENOLAEMATE
BRYOZOANS
by
Catherine Marie Powers
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(GEOLOGICAL SCIENCES)
December 2009
Copyright 2009 Catherine Marie Powers
Object Description
| Title | Unraveling mass extinctions: Permian to Early Jurassic onshore-offshore trends of marine stenolaemate bryozoans |
| Author | Powers, Catherine Marie |
| Author email | jamet@usc.edu; lespowers@mac.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Geological Sciences |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2009-07-07 |
| Date submitted | 2009 |
| Restricted until | Unrestricted. |
| Date published | 2009-09-30 |
| Advisor (committee chair) | Bottjer, David J. |
| Advisor (committee member) |
Corsetti, Frank Edmands, Suzanne |
| Abstract | Changes in the diversity and environmental distribution of marine stenolaemate bryozoans through the Permian to Early Jurassic interval are used to constrain the timing of environmental stress, determine the degree to which it differentially affected marine settings, evaluate its long-term impact on bryozoan evolution, and review current extinction scenarios for the end-Permian and end-Triassic crises. Results indicate that the end-Permian and end-Triassic mass extinctions were characterized by protracted intervals of environmental stress that initiated during the end-Guadalupian event several million years prior to the end-Permian, and again during the Norian stage prior to the end-Triassic. Environmental degradation lasted into the Early Triassic and Early Jurassic, hampering the recovery of marine communities. Prior to both extinctions offshore settings were affected first, suggesting environmental stress resulted from the gradual encroachment of a deep-water phenomenon onto the shelves, thus precluding catastrophic events as kill mechanisms and supporting long-term oceanographic processes such as widespread euxinia resulting from massive volcanism and global warming. The end-Permian event was the most influential for bryozoans, triggering a permanent change in their paleoenvironmental preferences from onshore to mid-shelf settings and a taxonomic switch between stenolaemate and gymnolaemate bryozoans. The taxonomic switch itself initiated a gradual shift in the overall morphological composition of bryozoan assemblages between erect-dominated Paleozoic communities and encruster-dominated Mesozoic communities. Major changes in the paleoenvironmental preferences of bryozoans were also coupled with fluctuations in their diversity.; Elevated bryozoan extinction rates were concurrent with their disappearance from offshore settings in the Late Permian and Late Triassic. Re-colonization of vacated habitats took place as diversity slowly rebounded in the wake of the extinctions, indicating a return to normal marine conditions. A comparison of survival patterns of stenolaemate bryozoans with other lophophorates during the end-Permian extinction revealed that bryozoans were the most susceptible, experiencing the highest rates of extinction and becoming geographically restricted during the Early Triassic. The most successful lophophorate group, the lingulid brachiopods, possessed a unique physiological adaptation that allowed them to survive in environmentally stressed Early Triassic settings. |
| Keyword | Permian-Triassic; Triassic-Jurassic; mass extinctions; Bryozoa; Brachiopoda; diversity; paleoecology; morphology; paleoenvironments |
| Coverage era | Permian; Early Jurassic; Late Triassic |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m2629 |
| Rights | Powers, Catherine Marie |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | http://www.usc.edu/isd/libraries/services/ask_a_librarian/email/ |
| Filename | etd-Powers-3188 |
| Archival file | uscthesesreloadpub_Volume56/etd-Powers-3188.pdf |
Description
| Title | Page 1 |
| Full text | UNRAVELING MASS EXTINCTIONS: PERMIAN TO EARLY JURASSIC ONSHORE-OFFSHORE TRENDS OF MARINE STENOLAEMATE BRYOZOANS by Catherine Marie Powers A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (GEOLOGICAL SCIENCES) December 2009 Copyright 2009 Catherine Marie Powers |
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