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Publication Date

2022-05-09

First Advisor

Sara B. Pruss

Document Type

Honors Project

Degree Name

Bachelor of Arts

Department

Geosciences

Keywords

Paleontology, paleoenvironment, paleoecology, petrographic analysis, stratigraphy - Lower Ordovican, Geology - Newfoundland, Canada, Geology - Western Utah, USA, Fossils - Lower Ordovican, GOBE

Abstract

The Great Ordovician Biodiversification Event (GOBE) is known for a significant increase in skeletal abundance of benthic faunas globally, yet the progression of this evolutionary change throughout the Lower Ordovician leading up to this event is unconstrained. We examined Lower Ordovician carbonate deposits from the Catoche Formation, Western Newfoundland, Canada, and Fillmore Formation, western Utah, USA, to quantify skeletal abundance and identify depositional environment(s) which may have influenced temporal changes in abundance. Petrographic studies suggest the Catoche Formation has a low skeletal abundance of 1.7% fossil material in thin section, including unidentified skeletal material, where trilobites make up 37.1% of total fossils; cephalopods make up 22.2% of total fossils, brachiopods make up 9.3%, echinoderms make up 2.1%, and gastropods make up 0.5%. Field observations additionally demonstrate abundant peloidal and micritic sediment and an abundance of flat-pebble conglomerates, demonstrating the common occurrence of storm events at the locality. The Fillmore Formation records different skeletal abundance, where skeletal material makes up 17.0% of total counts of thin sections. Most abundant fossils of the Fillmore Formation are echinoderms (55.1%), brachiopods (19.9%), sponges (16.4%) and trilobites (6.4%). Field observations also suggest a higher-energy shallow marine paleoenvironmental setting more proximal to sponge reefs that did not undergo frequent storm events compared to the Catoche Formation. Differences in skeletal abundance and paleoenvironmental settings leads us to conclude skeletal production may have been higher in shallow marine environments, adjacent to sponge reefs, than lower-energy shallow shelves less proximal to them. My work seeks to understand the varying occurrences of skeletal biomass in the two Lower Ordovician localities and what implications it holds for the initial radiation of the GOBE.

Rights

©2022 Ashley Rivas. 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

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