Document Type : Research Paper
Authors
1
Department of Ecology, Institute of science, High technology and environmental science, Graduate University of advanced Technology, Kerman
2
Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, Jiangsu Province, China
Abstract
This study investigates the temporal and spatial distribution of rare microfacies of the Qom Formation and their depositional environments. Detailed examination of 15 stratigraphic sections by the first author, together with a comprehensive review of previous studies, demonstrates that, besides common microfacies, the Qom Formation contains several rare microfacies with limited spatial distributions. These include turbiditic microfacies, breccia, sandy planktonic foraminiferal wackestone, bioturbated bioclastic wackestone, nummulitid packstone, perforate foraminifera–bryozoan–echinid packstone, coral-bearing, intraclast-bearing, Neorotalia-bearing, crinoid grainstone, ooid-bearing, Gastrochaenolites-bearing, peloid-bearing, ostracod-bearing, fenestral mudstone, and stromatolitic bindstone microfacies. Some microfacies, such as ooid-rich, fenestral mudstone, and peloid-rich microfacies, are widespread in the Oligocene–Miocene Asmari Formation but occur only sporadically in the Qom Formation. These rare microfacies represent tidal-flat, lagoonal, shoal/barrier, carbonate-slope, normal-marine, and turbiditic-marine settings. Restricted petrofacies also include mixed carbonate–siliciclastic, gravelly, sandy, conglomeratic, evaporitic, and volcanic-bearing types. Most rare microfacies are Early Miocene in age and occur along the margins of the Central Iranian Desert, particularly the Semnan–Garmsar–Qom region, and in northwestern Iran, especially Mianeh–Bostanabad. Their localized distribution indicates that the Qom Sea was not permanently connected to the open marine realm and that progressive restriction and eventual closure of this connection began during the Early Miocene.
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