Clay mineral diagenesis in alternating mudstone‐sandstone beds from Late Palaeozoic strata of the Anadarko Basin, United States

Abstract

Closely interbedded mudstone and sandstone are rarely the focus of clay mineral diagenetic studies; as such, it is not understood if these various rock types follow the same or different diagenetic pathway(s) during burial. Over a depth span of ~2,300 to 4,200 m, 95 core samples of alternating Pennsylvanian mudstone/sandstone from the hydrocarbon‐rich Anadarko Basin in Oklahoma have been characterized petrographically, mineralogically, and chemically. The investigated fine‐grained sediment is argillaceous to siliceous mudstone, dominated by Illite/mica and mixed‐layer illite–smectite. The sandstone is variably classified as quartz and mudclast‐rich litharenite to sub‐litharenite, which is commonly carbonate‐cemented. This contribution provides evidence for a very similar diagenetic evolution of the clay mineral assemblages across all rock types despite the discrepancies in porosity and permeability of the host rock. We posit that the incorporation of micrometre‐scale mudclasts through bioturbation of the sandstone may explain the relatively uniform compositional characteristics of illite–smectite, chlorite, and kaolinite. Inferences are drawn from a detailed clay mineral quantification of these interbedded lithologies aid to our understanding of the clay mineral distribution and speciation in Pennsylvanian strata of the Anadarko Basin, which further helps to constrain the reservoirs' physical, chemical, and structural properties.