Dworkin, Stephen I.Clark, Stephen M. (Stephen Matthew), 1983-Baylor University. Dept. of Geology.2010-02-022010-02-022009-122010-02-02http://hdl.handle.net/2104/5522One of the basic tenants of organic geochemistry states that significant accumulation of organic matter will not occur in well-oxygenated aqueous environments. Changing abundance of sedimentary organic material, therefore, probably reflects changes in marine and terrestrial conditions on Earth. This study will document the abundance and character of sedimentary organic matter in Cretaceous rocks of Central Texas with the goal of reconstructing the environmental, chemical, and depositional conditions responsible for organic carbon accumulation. Organic carbon content in Central Texas ranges from .2 to over 1.5 weight percent. C/N ratios range from 5 to over 25. The C/N ratios are low in the Grayson and Pearsall formations whereas high C/N ratios are characteristic of the Walnut Clay and Lake Waco formations. Carbon isotope ratios of organic matter range from –28.8 to –22.7‰ (VPDB) with lower values occurring in the middle-Cretaceous. Lastly, most δ¹⁵N values of organic matter hover between 1 to 3‰. Although these data could suggest a terrestrial source, the influence of Cretaceous oceanic anoxic events could be causing a marine signature to appear terrestrial.94029 bytes1810435 bytesapplication/pdfapplication/pdfen-USBaylor University theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. Contact librarywebmaster@baylor.edu for inquiries about permission.Organic matter.Carbon isotopes.Nitrogen isotopes.Geochemistry.Central Texas.ThesisWorldwide access