Petrography and diagenetic history of the Shurijeh Formation (Late Kimmeridgian–Hautrivian) at Estarkhi section, Kopet-Dagh Basin, NE Iran

The Shurijeh Formation is a Late Jurassic–Early Cretaceous (Late Kimmeridgian–Hauterivian) siliciclastic rock unit of the Kopet-Dagh Basin, up to 392 m thick. In the Estarkhi section, it rests disconformably on the Mozduran Formation (Oxfordian), and is disconformably overlain by carbonate rocks of the Tirgan Formation (Barremian–Aptian). The sandstones are predominantly subarkose, sublitharenite, feldspathic litharenite, and litharenite with minor quartzarenite, rich in quartz and feldspars, sedimentary and igneous rock fragments (plutonic), and rarely metamorphic fragments. Based on petrological and geochemical studies, minor diagenetic events in the early diagenetic stage include cementation by calcite and iron oxide. Deep burial diagenetic events were dominated by compaction, cementation (silica, dolomite, chlorite), fracturing, dissolution, pressure solution, and albitization. Minor late diagenetic events include dissolution and cementation (calcite, iron oxide). Based on diagenetic events, a temperature of >80°C during burial diagenesis is suggested for Shurijeh Formation. The existing porosity is secondary, resulting largely from the dissolution of feldspar and carbonate cement, with some fracture porosity. The porosity and permeability of 11 core plugs average 7.78% and 4.84 md, and the point count of 38 thin sections shows an average porosity of 10.05%. The good porosity and permeability of the middle part of the section predict an acceptable reservoir potential for this formation in the study area.