Provenance, shallow to deep diagenesis, and chemical mass balance in supermature arenites and pelites, Ordovician Simpson Group, Oklahoma and Kansas, U.S.A.

Abstract

Abstract This study, considering original detrital compositions and diagenetic alterations, relates sandstone and shale mineral and chemical composition to provenance and mass balance between the sedimentary assemblage and its provenance. Mature quartz-rich sandstones and siltstones with clay-rich shales in cores at depths of 60\u202fm–5.2\u202fkm and burial temperatures of 150\u202f°C from over 50 wells were utilized in this work. These provide the material for analysis of compositions and alterations in coastal and shallow marine clastic sedimentary rocks of the Middle Ordovician Simpson Group in Oklahoma and Kansas, U.S.A. Mineral and geochemical data were obtained by optical petrography, X-ray diffraction, scanning electron microscopy, electron microprobe, and whole rock X-ray fluorescence and ICP/MS analyses. Results of the study show significant progressive diagenetic changes with increased burial depth and temperature. Mineralogically and chemically, less altered rocks are comparable to modern quartz-rich sands and kaolinitic muds in siliciclastic sediments developed during humid tropical weathering in crystalline basement shield provenance in Africa and South America. By analogy to modern tropical cases, muds composed of major kaolinite with minor smectite and illite at deposition, were diagenetically transformed to illite-rich rocks by possible microbial action, at surface to shallow ( 20%) in sandstone buried >3\u202fkm. During deep burial, high temperature (>110\u202f°C) calcite cement from deep basin sources was precipitated in sandstones. Geochemical mass balance estimates, physical, and chemical evidence suggest quartz cement was sourced from within clastic rocks of the Simpson Group with minor external contribution of SiO2. Na is in low abundance due to loss in solution during weathering in the provenance. Rare earth elements (REE) have typical abundances and distributions in shales with enrichment in light REE; littoral environment siltstones and matrix-rich sandstones display enrichment of heavy REE in phosphatic brachiopod shell fragments.