Microfacies analysis, depositional setting, and microfossil assemblages of Qamchuqa Formation (Early Cretaceous) in Piramagroon mountains, Sulaymaniyah Governorate, northeastern Iraq

Abstract

The Lower Cretaceous limestone of the Qamchuqa Formation (QF) in the studied area is located in the northeastern limb of Piramagroon Anticline, Sulaymaniyah Governorate, northeastern Iraq. A section is sampled and 103 samples are collected. From these samples, 106 thin sections are prepared for petrographic analysis under binocular and polarizer microscopes. Qamchuqa Formation is usually mostly dolomitized and microfossils are totally or partially destroyed, but fortunately, the studied section is affected by dolomitization only in the upper part, the lower and middle parts are not dolomitized and are rich in well-preserved microfossils of benthic foraminifera with some algae and corals. The purpose of this study is to determine the microfacies, depositional settings, microfossil assemblages, and age. Based on the petrographic studies of the thin sections, seven main types of microfacies are identified, which are represented by grainstone, packstone, wackestone, bindstone, boundstone, rudstone, and mudstone with other six subtypes. Analysis of these microfacies indicates that the Qamchuqa Formation is deposited in shallow water to open marine environments including intertidal, subtidal, lagoon, shoal, and middle ramp. Very rich benthic foraminiferal assemblages are studied and analyzed in thin sections. Twenty-four species of benthic foraminifers belonging to eighteen genera and one species of algae are recognized, of which sixteen species of benthic foraminifera are discovered for the first time. These fauna assemblages indicate the age of Early Hauterivian to Late Cenomanian.