A THOROUGH GEOCHEMICAL ANALYSIS OF THE AUSTIN CHALK AND UPPER EAGLE FORD SHALE

A single drill core from La Salle, TX was analyzed for its chemical composition and percent concentration of both major and trace elements in order to understand depositional environments and local tectonic activity of the Balcones Fault Zone. The drill core contained the entirety of the Austin Chalk and only a few feet of the Upper Eagle Ford Shale. Samples were taken from 47 boxes at 3 inch intervals which accumulated in a total of 1,680 samples. Calcium values ranged from 5% to 40% with the former values arising from the Upper Eagle Ford Shale and the latter values coming from the Austin Chalk. Sulfur percent composition ranged from 0%-20% and had similar trends as Magnesium which had values from 0.04% to 4.8%. The Austin Chalk contained great values of pyrite, illite, quartz, calcite, and clay. Trace element concentrations suggest that the depositional environment had periods of anoxic or diagenetic events. Copper values that went from 0.9% to nearly zero while Nickel had two high values of 0.15% and low values around 0.001%. Three large trends of sulfur suggests three anoxic events during the deposition of the Austin Chalk. Further analysis of TOC and TIC levels of the Austin Chalk and Upper Eagle Ford Shale will be conducted and interpretations will be followed by presentations and discussions.

Index Terms/Descriptons:

Austin Chalk; Eagle Ford Shale; La Salle County Texas; Cretaceous; cores; sulfur; geochemistry; major elements; trace elements; marine environment; Balcones Fault Zone; paleoenvironment; Texas; United States