| The fine-grained, dark, organic, calcareous Haynesville shale (Kimmeridgian) and the overlying carbonate-poor Bossier shale (Tithonian) were deposited during the warmer Jurassic period in the tectonically formed East Texas Basin. Thirteen drill cores recovered from six counties (Texas) and four parishes (Louisiana) have been studied for their geochemistry. Each core was analyzed at a 1-foot interval using a handheld x-ray fluorescence 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, XRD analyses (10 samples from T.W. George), TIC, TOC, %N, and C and N isotopes were generated and integrated in the study. Mineralogical and major elemental geochemistry (e.g. Si/Al) suggests a carbonate-rich Haynesville mudrock coarsening up into siliciclastic dominated Bossier formation. Trace elements (enrichment of Mo (ppm) and Cr/V, Mo-TOC and Fe-S-TOC relationships indicate anoxic-euxinic bottom water conditions turned dysoxic-oxic during the course of Haynesville-Bossier deposition and a deep-water renewal time ∼100 years. The provenance of organic matter was determined to be of lacustrine-marine algae for the Bossier, and of terrestrial plants for the Haynesville shale, based on the C/N ratios. Furthermore, an attempt was made to associate the geochemical transgressive-regressive cycles observed in the Bossier-Haynesville to the global 2nd order sequence, and the more local 3 rd order sequence stratigraphic surfaces observed in the GOM. |
