Geological Society of America

27 Undergraduate and Graduate Geoscience Student Showcase (Posters)

Saturday, 29 March 2025
8:30 AM - 5:30 PM
North Great Hall

MEASURING CARBON ISOTOPIC VARIATIONS AND THEIR RELATIONSHIP TO DOLOMITIZATION IN THE JEFFERSON FORMATION (LATE DEVONIAN)

Paper number: 27-12
Program: Theme Sessions
Time: 8:30 AM – 5:30 PM

Authors

Talon Thompson Presenting Author
State University of New York at Potsdam, Potsdam, NY
Page Quinton
State University of New York at Potsdam, Potsdam, NY
Michael Rygel
State University of New York at Potsdam, Potsdam, NY
Will Eagle
UT Austin, Austin, TX
Mia Keller
Indiana University, Bloomington, IN
Kalen Murphy
Michigan State University, East Lansing, MI
Julia Rudlaff
Michigan State University, East Lansing, MI

Abstract

The Jefferson Formation (Late Devonian) of western Montana is an approximately 170 m thick package of carbonates that represents cyclic deposition along a shallow carbonate platform during the Frasnian (382.7 – 372.2 Ma). Variations and patterns in the extent of dolomitization have long been recognized in the Jefferson Formation but no recent studies have explored the relationship between dolomitization, cyclicity, depositional environment, and recorded stable carbon isotopic values. Here, we test two hypotheses: 1) that dolomitization and carbon isotopic alteration increase to the west in more basinward sections and 2) that dolomitization and carbon isotopic alteration increase toward cycle tops. We test these hypotheses by focusing on four sections in western Montana: Baker Mountain (easternmost), Sacagawea Peak, Cottonwood Canyon Road, and Gibson Reservoir (westernmost). We present 475 new carbon isotopic values paired with detailed sedimentological and petrographic observations. Carbon isotopic values range from -4.44‰ to 3.68‰ with an average of 0.36‰ and fall within the range of normal values for the Late Devonian. We found that carbon isotopic values from the study sections are statistically distinct. These initial results are consistent with hypothesis one, meriting further exploration. The relationship between dolomitization, carbon isotopes, and cyclicity is more complex than that indicated in hypothesis two.

Geological Society of America Abstracts with Programs. Vol. 57, No. 3

doi: 10.1130/abs/2025NE-407530

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