Cretaceous Paleogeography: Implications of Endemic Ammonite Faunas

GC7202. Cretaceous Paleogeography: Implications of Endemic Ammonite Faunas, by K. P. Young. 13 p., 4 figs., 3 tables, 1972. ISSN: 2475-3637.


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ABSTRACT
Endemic ammonite faunas evolved from cosmopolitan faunas in a series of successive episodes over about 35 million years of the Cretaceous of the Gulf Coast of the United States. During basin-basin-margin tectonic adjustments the Cretaceous barrier reef was inundated or circumvented so that a cosmopolitan fauna entered the back-reef area. Gradual isolation of the fauna behind the barrier produced endemism. With the next basin adjustment the endemic fauna became extinct, and a new cosmopolitan fauna migrated into the back-reef area, likewise evolving into an endemic fauna in its turn. Six cosmopolitan-endemic cycles have been identified. Geological evidence suggests two or three additional cycles.

Keywords: Cretaceous, ammonites, faunas, Gulf Coast, Texas

CONTENTS
Abstract

Introduction

Paleogeographic setting

Cosmopolitan-endemic cycles of the Comanchean

Trinity faunas

Fredericksburg cycle

Washita endemic faunas

Low generic diversity-a key to endemism

Relation of endemism to depositional cycles

Endemism and correlation

Conclusions

Acknowledgments

References

Figures

1. The Comanchean Shelf behind the barrier reef

2. Block diagram illustrating the back-reef topography for a part of Texas during the Middle Albian

3. Paleogeographic features of Texas during much of the Comanchean

4. Diagrammatic representation of rocks containing endemic and cosmopolitan faunas

Tables

1. Correlation of Comanchean sections for areas from which formations are mentioned in text

2. Alternation of endemic and cosmopolitan zones on the Texas Comanche Shelf

3. Correlation with European zones


Citation
Young, K. P., 1972, Cretaceous Paleogeography: Implications of Endemic Ammonite Faunas: The Universijty of Texas at Austin, Bureau of Economic Geology, Geological Circular 72-2, 13 p.