Date of Award

5-2025

Degree Type

Thesis

Degree Name

Departmental Honors

Department

Geosciences

Abstract

The Drumian Stage of the Cambrian Period is defined by the First Appearance Datum (FAD) of the cosmopolitan trilobite Ptychagnostus atavus in 504.5 Ma strata deposited on the slope and shelf of the Laurentia margin. The Drumian Global Stratotype Section and Point (GSSP), showing the best preserved example of P. atavus compared to global outcrops, is defined in the Drum Mountains of west-central Utah. Due to the inconsistent nature of fossil preservation, researchers have sought secondary proxies to identify Drumian-aged strata in the absence of age-diagnostic fauna. One key proxy is the Drumian Carbon Isotope Excursion (DICE), an ~-2.5‰ carbon isotope excursion oftentimes preserved several meters above the transition between P. atavus and another cosmopolitan trilobite, Ptychagnostus gibbus. However, the DICE shows relatively inconsistent behavior across key Drumian-aged outcrops in the Great Basin. This study takes multiple geochemical datasets across the Stratotype Ridge locality of the Drum Mountains and the Marjum Pass locality of the House Range, two age-equivalent successions of Drumian-aged strata, and highlights the inconsistent behavior of the DICE, questioning whether scientists should use this small-scale excursion to locate Drumian-aged strata in Great Basin outcrops lacking age-diagnostic fauna.

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Faculty Mentor

Carol Dehler

Departmental Honors Advisor

Carol Dehler

Capstone Committee Member

Audrey Warren