Reconstruction of the depositional sedimentary environment of Oligocene deposits (Qom Formation) in the Qom Basin (northern Tethyan seaway), Iran

Abstract

During the Rupelian–Chattian, the Qom Basin (northern seaway basin) was located between the Paratethys in the north and the southern Tethyan seaway in the south. The Oligocene deposits (Qom Formation) in the Qom Basin have been interpreted for a reconstruction of environmental conditions during deposition, as well as of the influence of local fault activities and global sea level changes expressed within the basin. We have also investigated connections between the Qom Basin and adjacent basins. Seven microfacies types have been distinguished in the former. These microfacies formed within three major depositional environments, i.e., restricted lagoon, open lagoon and open marine. Strata of the Qom Formation are suggested to have been formed in an open-shelf system. In addition, the deepening and shallowing patterns noted within the microfacies suggest the presence of three third-order sequences in the Bijegan area and two third-order depositional sequences and an incomplete depositional sequence in the Naragh area. Our analysis suggests that, during the Rupelian and Chattian stages, the depositional sequences of the Qom Basin were influenced primarily by local tectonics, while global sea level changes had a greater impact on the southern Tethyan seaway and Paratethys basins. The depositional basins of the Tethyan seaway (southern Tethyan seaway, Paratethys Basin and Qom Basin) were probably related during the Burdigalian to Langhian and early Serravallian.

Depositional Setting of Khurmala Formation (Paleocene-Early Eocene) in Nerwa section, Berat Anticline, Kurdistan Region, Northern Iraq

“…Dolomitized lime mudstone is common in the restricted platform (Wilson, 1975;Flügel, 2010). Miliolids dominate in shallow restricted low turbulence water (Safari et al, 2020), whereas, the occurrence of miliolids within peloids-bioclastic grainstone, which are mainly debris of molluscs that are characterized by semirounded shapes in sparry calcite groundmass suggest a relatively high energy water in back reef/ lagoonal environment (restricted platform) (Al-Dabbas et al, 2014;Tamar-Agha et al, 2015). Rare bryozoan, echinoderms, brachiopods and planktonic foraminifers within benthonic foraminiferal wackestone microfacies can be found in shallow lagoon with open circulation (Flügel, 2010).…”

Geological Features for Geotourism in the Zanjan and Hamadan Area, Northern Iran

“…Every 24 h, the electrical conductivity (EC) and pH of the samples were measured by a WTW Multi 340i instrument and a WTW MultiCal pH-540 m on their arrival in the laboratory. Based on the variations in EC, some typical samples were chosen for chemical analysis by ion chromatography (Methrom 761 Compact IC) which included: K + , Na + , Ca 2+ , Mg 2+ , SO 4 2− , Cl − and NO 3 − ions. Samples selected for chemical analyses of major ions were refrigerated at 5 • C and analyzed within 48 h after collection.…”

“…It overlies the Lower Red For mation and Eocene volcanic rocks. The Qom Formation is overlain by the Upper Re Formation consisted of non-marine siltstones and evaporite-dominated beds [4,[30][31][32].…”

“…Arid climate was not a favorable condition for formation of mature karst and large well-developed cave systems. Rare multilevel caves have developed in some areas due to rapid tectonic uplift, folding and faulting of the terrain [4]. There are more than 850 known caves in Iran with a total length not exceeding 1000 km; many of them not being properly explored.…”