Reconstruction of Depositional Environment of Sarchahan Formation (Silurian) in the Persian Gulf

Sarchahan Formation (Silurian) consists of shale and sandstone interbeds in the studied well in the Persian Gulf. Based on petrographic and wire line logs studies, five petrofacies and three facies associations were identified in the Sarchahan Formation. It is composed of fine-grained shale with a high amount of TOC and very thin interbeds of sandstone representing both marine and terrestrial deposits. This facies association comprises the lower parts of the Sarchahan Formation and was deposited in a prodelta sub-environment. Facies association 2 is composed of alternation of sandstone and shaley sandstone with dominance of shaley sandstone. It is deposited in a less deeper and nearer to beach environment compared to facies association 1 with fining upward sequences and represents delta front sub-environment. Facies association 3 is composed of sandstone and shaley sandstone with sandstone dominance and some red mudstone interlayers and anhydrite grains. It is mostly representing coarsening upward sequences which is assigned to delta plain sub-environment. Variations in facies association in combination with palynological studies represent that deposition of the Sarchahan Formation took place in different sub-environments of a delta environment from prodelta to delta plain. The lower part of the formation is represented by a high amount of black shale and higher total organic carbon values which are the result of deposition in the deeper parts of the basin. Meanwhile, the upper part is composed of sandstone and red mudstone which are the result of deposition in the shallower part of delta environment. Cementation, compaction, and dissolution are the main diagenetic features that affected the Sarchahan Formation. Silica and sericite cements are the most abundant cement types in quartzarenite and subarkose petrofacies the development of which resulted in porosity reduction. The comparison with the Arabian plate, the deposition took place in a southward deepening basin into which sediments were introduced from the northern parts.