PRELIMINARY ANALYSIS OF TOTAL GAMMA RADIATION, CONODONT ELEMENT ABUNDANCE, AND FINER THAN SAND FRACTION RELATIONSHIPS IN THE LOWER BARNETT SHALE, SAN SABA, TEXAS, UNITED STATES

A preliminary study of an outcropping of the lower Barnett Shale (San Saba, TX) evaluated the relationship between total gamma radiation and the unit’s lithological and faunal characteristics. Three sub-units of the lower Barnett Shale were identified. Sub-unit A is 1.12 meters of shale between the base of the Barnett Shale and the base of a doublet of thin limestone beds. Sub-unit B is 0.66 meters of shale from the base of the limestone doublet to the base of a medium-bedded limestone. Sub-unit C is 1.83 meters of shale from the top of the medium-bedded limestone to the base of a thin limestone bed below a rubbly limestone. Total gamma radiation was measured using a Gamma-Scout handheld Geiger counter. Three-minute collections were run in triplicate at three different levels within each sub-unit. Shale samples were processed to determine the combined mass percentage of silt and clay (finer than sand fraction) and the number of conodont elements in each sample. Total gamma radiation, conodont element abundance, and finer than sand fractions were plotted on a simple graph and compared for each of the three Barnett Shale subunits. Total gamma radiation and conodont element abundance correlated in sub-unit C but not in sub-units A and B. Total gamma radiation and finer than sand fractions correlated in sub-unit C but not in sub-units A and B. Conodont element abundance and finer than sand fractions correlated in all three sub-units. The lower Barnett showed no correlation between gamma radiation and conodont element abundance or between gamma radiation and the finer than sand fraction except in sub-unit C. Throughout the lower Barnett correlation between conodont abundance and the finer than sand fraction was evident. Potential alternate methods of evaluating organic accumulation in the unit include comparing total gamma radiation to total conodont element mass and comparing total gamma radiation to total organic carbon.