GEOCHEMICAL SIGNATURES OF PALEOZOIC SHALES FROM THE MIDLAND BASIN USING MAJOR AND TRACE ELEMENTS: INSIGHTS TO PROVENANCE AND POTENTIAL CRYSTALLINE SOURCE AREAS

Various trace element geochemical studies within the Permian Basin have been conducted on shales for reservoir characterization and paleoredox conditions, with little interests on sediment origins and provenance. Furthermore, studies of provenance have largely been limited to coarse grained lithologies using detrital mineral age dating. Therefore, an opportunity exists to study trace and rare earth elements due to their immobility and affinity toward clay minerals who essentially control their budget shale systems.

Thirty samples from three distinct shales ranging in age from Mississippian to Permian were collected from cores within the northern Midland Basin for trace elements analysis via laser ablation ICP-MS. REE concentrations were normalized to chondrite and show elevated LREE (La/Tb = 46.84 – 62.81), negative Eu anomaly (Eu/Eu* = 0.17 – 0.24), and relatively low HREE (Tb/Lu 1.12 – 1.94). LILE, HFSE, and REE trace elements were also normalized to primitive mantle and show crustal contamination of the magmatic system in its juvenile phase. Based on these normalization plots, the original source rocks for all samples can be characterized as having a primarily felsic composition and formed within a supra subduction zone. Moreover, differentiation of trace element concentrations over time suggests different source areas or source area evolution between Mississippian and Permian time. Additionally, samples plotted with major trace elements fall within the field of felsic igneous provenance, which supports indicated provenance by trace elements.

The creation of a distinct geochemical signature from clay minerals derived from crystalline sources can provide better constrains on potential sediment sources for the Midland Basin. These data in conjunction with detrital mineral age dating will provide a more robust and improved understanding of Midland Basin provenance and sediment dispersal pathways.