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Publication Date

2024-5

First Advisor

Sara B. Pruss

Document Type

Honors Project

Degree Name

Bachelor of Arts

Department

Geosciences

Keywords

Moenkopi Formation, Lower Triassic, carbonates, phosphatization, silicification, end-Permian mass extinction

Abstract

After the end-Permian mass extinction (~251 Ma), global warming and elevated atmospheric carbon dioxide caused increased ocean temperatures, ocean acidification, and ocean anoxia. At least 90% of marine species went extinct during this boundary- and era-defining extinction event. The subsequent Early Triassic interval was characterized by small, opportunistic taxa, abundant microbialites, and delayed ecosystem recovery. Some studies report fossils preserved in unusual ways: replaced by apatite or molded by glauconite and other iron-bearing minerals. This work examines the ophiuroid diversity and taphonomy at three localities of the Virgin Limestone Member of the Moenkopi Formation: Lost Cabin Springs (middle shelf), Blue Diamond (middle-inner shelf), and Muddy Mountains Overton (nearshore, shallow). From each of these localities, we collected ophiuroid lateral arm plates and arm vertebrae belonging to the novel species Ophiosuperstes praeparvus. These specimens were preserved in two main ways: phosphatization and silicification. At Lost Cabin Springs, specimens were primarily phosphatized, at Blue Diamond, most specimens were silicified, and at Muddy Mountains Overton all the specimens were silicified. While the processes of phosphatization and silicification depend heavily on the conditions sustained within microenvironments, this work suggests Muddy Mountains Overton had the largest influx of terrigenous siliciclastic sediments and Lost Cabin Springs had periodic dysoxic/anoxic or sedimentstarved conditions. Blue Diamond likely aligned with the conditions at Muddy Mountains Overton as their preservation styles were similar. Because Ophiosuperstes praeparvus was the only ophiuroid found at these localities, we can likely determine that this species was particularly tolerant of the stressful Early Triassic conditions.

Rights

©2024 Natalie Morgan. Access limited to the Smith College community and other researchers while on campus. Smith College community members also may access from off-campus using a Smith College log-in. Other off-campus researchers may request a copy through Interlibrary Loan for personal use.

Language

English

Comments

iv, 67 pages: color illustrations, charts. Includes bibliographical references (pages 54-67).

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