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Date Permissions Signed

5-18-2018

Date of Award

Fall 1990

Document Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Hansen, Thor A.

Second Advisor

Suczek, Christopher A., 1942-2014

Third Advisor

Schneider, David E., 1937-

Abstract

Danian shelf sediments from the Brazos River region of east-central Texas span approximately the first two million years after the Cretaceous-Tertiary (K-T) extinctions with only minor changes in lithofacies. Study of these virtually continuous stratigraphic sections reveals the nature and timing of the molluscan faunal rebound in the wake of the K- T extinction event. Diverse Late Maastrichtian molluscan faunas were dominated by epifaunal suspension-feeders, primarily oysters. Immediately above the K-T extinction horizon, low-diversity molluscan assemblages were characterized by a bloom in the abundance of the pelagic herbivore family Litiopidae, which were rapidly replaced by a low diversity assemblage dominated by a deposit-feeding bivalve of the family Nuculanidae (Upshaw, 1989; Hansen and Upshaw, 1990). This low diversity assemblage persisted for approximately 300,000 years after the K-T extinctions and may have been caused by the low productivity of the hypothesized "Strangelove" ocean of Hsu (1986).

Diversity rapidly increased to nearly pre-extinction levels within the Globigerina pseudohulloides zone (Plb), roughly 300,000 years after the K-T extinctions. Coinciding with this diversity increase was a change in the composition of the fauna from a roughly even mixture of Cretaceous, Paleocene, and undescribed species to a fauna composed primarily of Paleocene species. The relative proportions of deposit-feeders and suspension-feeders also return to roughly Late Cretaceous levels within this biozone. Above the base of the G. pseudobulloides zone (Plb), the molluscan assemblages were characterized by increased stability. Diversity and trophic proportions of these assemblages persisted at nearly pre-extinction levels for the remainder of the studied interval, a period of at least 1.6 million years. In contrast to the large amount of faunal turnover apparent in the earliest Paleocene, molluscan assemblages within and above the G. pseudobulloides (Plb) biozone are characterized by increased species longevity in the studied sections.

Some faunal constituents were affected more permanently by the K-T extinctions. Epifaunal soft-bottom suspension-feeders such as oysters were a prominent component in local Late Cretaceous faunas, but they never regained their former levels of diversity and abundance in the studied Paleocene stratigraphic sections. Infaunal burrowing carnivorore-scavengers such as Naticidae and various opistobranchs became much more abundant in the Paleocene than they were in the Cretaceous.

Type

Text

Keywords

Danian shelf sediments, Cretaceous-Tertiary extinctions, K-T extinctions

Publisher

Western Washington University

OCLC Number

1079909771

Subject – LCSH

Paleoecology--Texas; Mollusks, Fossil--Texas; Paleontology--Paleocene; Paleontology--Cretaceous; Extinction (Biology)

Geographic Coverage

Texas

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.

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