Early & Late Diagenetic Mineral Development within the Upper Jurassic Haynesville-Bossier Shale, USA

Abstract

Summary Despite recent advances, diagenetic processes in fine-grained sediments remain relatively poorly understood. Key questions still to be resolved include how mineral cements develop in low porosity and permeability systems and the extent of element mobility during the diagenesis of fine-grained sediments. This study uses petrographic, mineralogical and geochemical data from the Haynesville-Bossier Shale identify early and late diagenetic mineral development. On the basis of grainsize and mineralogy five facies are designated: (i) silica-rich argillaceous mudstones, (ii) argillaceous siliceous mudstones, (iii) mixed siliceous mudstones, (iv) mixed mudstones and (v) cemented mudstones. The diagenetic development of the Haynesville-Bossier Shale can be divided in to early and late diagenesis. Ferroan and non-ferroan dolomite, framboidal pyrite, and microfossil pore-filling kaolinite cements all formed during early diagenesis. Late diagenetic cements include microcrystalline calcite, euhedral pyrite, replacive and displacive chlorite, calcite-replacive albite, and replacive and/or displacive quartz. Late diagenetic cements would have required a wide range of geochemically mobile elements, (bed scale); illitisation of smectite during late diagenesis is a potential source for these elements. The work impacts porosity and permeability evolution and fracture susceptibility in unconventional shales.