PRELIMINARY GEOCHEMISTRY OF THE BOSSIER-HAYNESVILLE FORMATION FROM EAST TEXAS BASIN, EAST TEXAS AND LOUISIANA

The Jurassic-age mudrocks of the Bossier- Haynesville Formation were deposited in the East Texas Basin of Texas and northwest Louisiana, conformably overlying the Smackover Formation. The goals of the current project are to 1) develop a better understanding of the depositional environment, and 2) utilize chemostratigraphic principles to evaluate depositional and post-depositional signatures across the basin.

Ten cores from eight counties in Texas and two parishes in Louisiana have been studied for their geochemistry. Each core was scanned at a 1-foot interval using a Bruker handheld x-ray fluorescence (XRF) instrument, providing rapid, quantitative analysis of the following elemental concentrations: Mg, Al, S, Si, P, K, Ti, Ca, Mn, Fe, Mo, Cr, Ni, Cu, Zn, Th, Rb, U, Sr, Zr, and V. In addition to metal data, preliminary interpretations for total inorganic carbon (TIC), total organic carbon (TOC), total nitrogen (%N), and bulk rock TOC and N isotopic composition of core samples reveal distinct differences between the Bossier and Haynesville formations. Results from previous geochemical studies suggest that the siliciclastic-dominated Bossier formation has less TOC than the underlying Haynesville formation. Furthermore, the Haynesville is much more carbonate-rich (calcite) than the overlying Bossier. An upwardly increasing trend in Si/Al in some cores suggests increasing detrital quartz influx. A linear relationship between Fe and Al suggest that iron is primarily in clay mineral phases in the Haynesville. Mild enrichments in Mo concentrations and Cr/V ratios reveal periods of anoxic conditions. Peaks of redox-sensitive elements like Mo, Fe and V indicate periodically anoxic conditions during deposition.