PROVENANCE OF LATE PALEOZOIC FINE SEDIMENT OF THE ANADARKO BASIN (OK) – EVIDENCES FROM K-AR GEOCHRONOLOGY AND REE SYSTEMATICS OF DETRITAL ILLITE

Sediment chemistry and age determination of detrital phases provide a record of the provenance of sedimentary rocks, which in turn helps to interpret the history of sedimentary basins. This pertains especially to REE which are poorly fractionated during sedimentation thus keeping a memory of the source material.

In this research we separated five aliquots of 2M1 detrital illite from Pennsylvanian shale of the Anadarko basin in order to unveil their K-Ar age and LA-ICP-MS trace-element geochemistry. Fine micaceous illite from the clay fraction was selected as it represents a large portion of rocks’ mineralogy, while the rest is consisted of quartz and authigenic clay minerals.

All samples were found to be of Upper Carboniferous to Lower Permian age (317.8 – 285.1 ± 3 Ma). Their REE geochemistry is typical for mica from intermediate to felsic rocks showing a significant enrichment in LREE concentrations (La/Tb = 60.68-71.53) and relatively low HREE concentrations of ~15-20 relative to chondrite. Negative Eu anomaly (0.17-0.19) and positive anomaly of Gd (0.19-0.21) were also reported, with the latter normally assigned to the presence of organic matter. REE systematics described herein corresponds to REE composition of illite from Pennsylvanian shale of Midland basin, which points to the regional distribution of fine-grained sediment.

Considering the ages and geochemistry of analyzed 2M1 illite we hypothesize that the material was likely derived from a proximal arc region of Carboniferous age that came into being with a subduction of Rheic Ocean beneath the Gondwana margin just prior to the collision with Laurentia.