Diagenetic mineral development within the Upper Jurassic Haynesville‐Bossier Shale, USA

Abstract Despite recent advances, diagenetic processes in fine‐grained sediments are still relatively poorly understood. Key questions still to be resolved include the types of diagenetic minerals present in mudstones and the extent of element mobility in these low permeability systems. This study utilizes data from the Haynesville‐Bossier Shale, USA , to analyze lithologies, discriminate authigenic phases and identify mobile elements during diagenesis. It has implications for understanding how authigenic minerals develop and the sources of those authigenic minerals in fine‐grained sediments. On the basis of grain‐size and mineralogy five lithologies are designated: (i) silica‐rich argillaceous mudstones; (ii) argillaceous siliceous mudstones; (iii) mixed siliceous mudstones; (iv) mixed mudstones; and (v) authigenically‐dominated mudstones. The diagenetic development of the Haynesville‐Bossier Shale can be divided into early and late diagenesis. Ferroan and non‐ferroan dolomite, framboidal pyrite and bioclast pore‐filling kaolinite and calcite grain replacements and cements all formed during early diagenesis. Late diagenetic mineral phases include illite formed by the illitization of smectite, replacive and displacive chlorite, calcite‐replacive albite, quartz‐replacive calcite and replacive and/or displacive quartz. The presence of extensive late diagenetic mineral precipitates indicates that there was a degree of element mobility on at least the local scale. Aluminium present in albite is most likely to have resulted from the illitization of smectite. Quartz overgrowths probably resulted from illitization and the pressure dissolution at quartz silt grain boundaries. Externally, hydrothermal fluids resulting from regional‐scale igneous activity appear to have played a role in the formation of chlorite and possibly albite. The work indicates that extensive mineral development and element mobility occurred during late diagenesis.