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Carbon isotope chemostratigraphy and petrography of the Yucca Formation, West Texas
Biebesheimer, Ellie
Biebesheimer, Ellie
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Abstract
The Yucca Formation is a Lower Cretaceous sedimentary unit found across West Texas. The Cretaceous Period was a time of major global climate change, and the Yucca Formation could record some of those major climatic shifts. However, age constraint must be improved and geochemical climate proxies employed to better understand any possible recorded climatic shifts. By studying the rocks of the Yucca Formation from two localities in Western Texas, this work aimed to 1. Better constrain the age of the Yucca Formation using stable isotope geochemistry, specifically organic carbon stable isotope chemostratigraphy, 2. Correlate the Yucca Formation with strata of the similar age using chemostratigraphy. 3.Determine the usefulness of the Yucca Formation in future paleoclimate work by evaluating the extent of diagenesis, and 4. Make preliminary paleoclimate interpretations using stable isotope proxies.The d13Corg record of the Yucca Formation in Big Bend Ranch State Park provided us with many insights. C-isotope values range from -27.02 to -18.42‰. Carbon isotope excursions that are associated with Aptian-Albian Boundary are identified as well as some associated with Oceanic Anoxic Events (1a and 1b). This allows us to conclude that the Aptian-Albian boundary is recorded within the Yucca Formation strata. Based on this correlation and the currently accepted Geologic Time Scale boundary, a date of 113.2 Ma is assigned to 71 meters above the base of the section exposed in the Lower Shutup of the Solitario in Big Bend Ranch State Park. Evidence of major diagenesis effects on these rocks (seen both in thin section and outcrop) indicates the Yucca Formation at Big Bend Ranch State Park will not be useful in paleoclimate studies. Samples from farther west in the fluvio-lacustrine facies of the Yucca Formation, show little to no diagenetic overprinting has affected those rocks. Preliminary d18Ocarb and d3Ccarb data from these samples shows two distinct trends: a meteoric water trendline and an evaporative trendline.
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Date
2022-08-31
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University of Kansas
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Keywords
Geology, Geochemistry, chemostratigraphy, stable isotope, Yucca Formation