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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

GOBE, biodiversity, animal abundance, skeletal abundance, depositional environment, point-counts, Nuia, early Paleolithic

Abstract

The Great Ordovician Biodiversification Event (GOBE) is considered the longest prolonged increase in biodiversity in the Earth’s history, though the timing and magnitude of this event varies locally. The physical drivers of the GOBE have been well-researched; however, the interaction of biotic factors like animal abundance, ecology, and diversity with abiotic parameters like depositional environment remain understudied. This research investigates the relationship between animal abundance, biodiversity, and depositional environment in Early and Middle Ordovician sections in the Arrow Canyon Range, southeastern Nevada. In the Arrow Canyon Range, the Pogonip Group preserves the transition from the Cambrian to the Middle Ordovician. The Pogonip Group was deposited in a shallow, subtidal carbonate shelf environment. Environments change throughout this stratigraphic interval and vary from shallow subtidal to shoal environments. Ninety-five samples from the Pogonip Group were point-counted for skeletal abundance and diversity. Synthesis and analysis of field and petrographic observations reveal environmental and biological changes recorded in the Arrow Canyon Range. The average fossil abundance of each unit ranges from 8-14% and does not increase temporally. Biodiversity increases throughout the Pogonip Group with the onset of the GOBE. Nuia, echinoderms, trilobites, and sponges are present in the lowermost unit Opb, compared to Nuia, echinoderms, trilobites, ostracods, sponges, brachiopods, gastropods, unidentified mollusks, and bryozoans in uppermost unit Opf. In the Arrow Canyon Range, the GOBE begins with the start of the Darriwilian. Biodiversity increases throughout the Pogonip Group and the variability of fossil abundance by unit in the context of changing environments suggests that environments play an influential role in animal abundance in the Arrow Canyon Range.

Rights

©2024 Lucy Helms. 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.

Comments

v, 86 pages: color illustrations, charts. Includes bibliographical references (pages 64-80).

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