The Sedimentology and Facies Analysis of the Cretaceous Oceanic Red Beds (CORBs) in the Shiranish Formation, Northern of Iraq


Upper Cretaceous Oceanic Red Beds (CORBs) are pelagic sediment deposits that deposited in the Upper Cretaceous basin, with widespread in part of the world as well as in Iraq. This research investigates the deposition of cyclic marl and marly limestone CORBs of six selected sections at the active southern margin of the Tethys during the Late Campanian - Maastrichtian with petrography, microfacies, and depositional environment. As this study was not a consideration in the past, so decided to visit and identify all exposure areas of the Upper Cretaceous period rocks are visited. This study involved two fields touring reconnaissance extended from Darbandikhan city in the east south to Shiranish Village in the west north. Six lithological sections covering the studied area, four sections represent Cretaceous Oceanic Red Beds (CORBs) and two sections without (CORBs) for the purpose of comparison between them. The sections are described in detail and 250 samples were collected from all studied sections. For the petrography and microfacies analysis 149 thin sections were studied. The microfacies analysis showing two major successions with Red Bed and Non-Red Bed marl and marly limestone, occasionally interbedded with thinly beds of shale, sandstone and siltstone. These comprised of five microfacies are Oligostegina Marly Limestone, Globotruncana Marly Limestone, Marlstone with Microfossils, Red Marlstone, and Red to Variegated Calcareous Sandstone with Radiolarian (Debrise Flow) Making 20 thin sections from Gendilly section(GS) (the typical section of this study) for microscopic study of minute fossils (nannofossils) examination, for this study proved that the Cretaceous Oceanic Red Beds (CORBs) dating is Mastrichtian age. The Microfossils and nannofossils tests proved the presence of Danian Age in studied area. This study has proved that the carbonate content in red limestone beds ranged between 53.5-100.0 %, while this percentage ranged in red marly rocks between 20.5-50.0 %, But in the rocks that do not contain red beds, Carbonate content in limestone rocks ranged between 52.0-100.0 %, and in marl rocks this ratio ranged between 27.5-49.5 %.