Chemostratigraphy and Thin Section Petrography of the Smithwick Formation, Fort Worth Basin, San Saba County, TX

E. Niki Hughes
University of Texas at Arlington, Earth and Environmental Sciences Arlington, Texas
[email protected]

Given the diverse interest in organic-rich mudrocks and their prominence within the rock record, it is important to study their occurrence. The purpose of the study is to better understand the depositional environment of the Early Pennsylvanian Smithwick Formation in the Fort Worth Basin of north-central Texas using a chemostratigraphic and petrograhpic analysis. The Smithwick Formation is largely composed of organic-rich mudrocks representing restricted deposition within a foreland basin setting during the early stages of the Ouachita Orogeny.

Primarily using a 1000 foot (350 meter) core from San Saba County, Texas, geochemical analysis of major and minor elements will be determined along with concentrations of total organic carbon (TOC), total nitrogen (%N), total sulfur (%S), and total inorganic carbonate (TIC). The various elemental assemblages determined downcore, coupled with thin section analysis, will be used in a multi-proxy approach to provide insight into the amount of time represented by Smithwick deposition, the degree of restriction of the Fort Worth Basin at the time of Smithwick deposition, redox conditions and various sub-environments preserved in the strata, and the origin of the organic-rich material.

The study will provide a stratigraphic evaluation of the sedimentological and compositional changes that can be used to compare the Smithwick with other organic-rich mudrocks, both ancient and modern, in order to better assess their mechanisms of deposition. Furthermore, the expanded section of Smithwick mudrocks may provide an important Early Pennsylvanian record of sea-level and tectonic change.

AAPG Search and Discovery Article #90094 © 2009 AAPG Foundation Grants in Aid