PALEOCEANOGRAPHY OF THE EAST TEXAS BASIN DURING DEPOSITION OF THE KIMMERIDGIAN HAYNESVILLE FORMATION

The fine-grained, mixed carbonate-siliciclastic Haynesville Formation, and the overlying carbonate-poor, siliciclastic Bossier Formation (Tithonian) preserve an archive of organic-rich sedimentation that records paleoceanographic changes along the northern margin of the Gulf of Mexico during the late Jurassic Period. Mineralogical and geochemical analysis and interpretation of sample suites from thirteen drill cores recovered from six counties (Texas) and five parishes (Louisiana) reveal that the bulk rock characteristics can be largely characterized by their relative shifts in weigh percent (wt.%) aluminum (Al), silicon (Si), and calcium (Ca), which, respectively denote relative mineralogical shifts in the concentration of clay (largely illite), quartz, and calcite. Geochemical identification of authigenic carbonates is also noted, and may ultimately play a role in defining shifts in deposition and/or pore water evolution. Furthermore, by using bulk sulfur, iron, total organic carbon and molybdenum-TOC relationships, it is demonstrated that depositional conditions within the deep portions of the East Texas Basin (ETB) were neither normal marine nor severely restricted during deposition of the Haynesville-Bossier System (HBS).

As a first approximation to understanding HBS deposition in the ETB, stratigraphic changes in %Ca are used to infer changes in the flux of calcite derived from proximal carbonate factories, specifically, the basin-rimming carbonate platform and the Sabine Island Complex. Because carbonate inputs to the deep basin are interpreted to be largely of detrital origin, further refinement of the chemostratigraphic approach is required in order to validate the correlation of the detrital signal across the part of the basin represented by the suite of cores. This is accomplished by using the enrichment factor of molybdenum (EF_Mo), an element that 1) is only enriched in sediments under sulfidic (euxinic) conditions, and, as a consequence, 2) is a direct indicator of the water mass conditions, independent of detrital fluxes. Jointly, the %Ca and EF_Mo demonstrate a pattern of detrital inputs and water mass evolution that can be traced across the sampled portion of the basin and interpreted in terms of their eustatic significance.