Paleoecology and Depositional Environment of the Govanda Formation in the Kurdistan region, northeast of Iraq

Abstract

The Govanda Formation was deposited during the Early-Middle Miocene Epoch in the intermountain areas between Zagros Suture and Imbricate zones. The Paleoecology and depositional environment of the Govanda Formation has been studied in detail in Mergasor and Penjwen districts for the first time. The formation in these two sections from bottom to top is comprised of thick bedded, oyster and chert bearing conglomerate, pebbly sandstone, red-brown shale and siltstone, fossiliferous limestone and detrital limestone. The formation in Mergasor, Beshkariya Village is 85 m thick and in Penjwen, Gole Village is 60 m thick. The study is based on the detailed microscopic analysis on the benthic and planktonic foraminifera with miscellaneous fossils that exists in the carbonate rocks of the Govanda Formation. Larger and smaller benthic foraminifera include the following genera: Operculina sp., Borelis melo sp., Austrotrilina sp., Peneroplis sp., Meanderopsina sp., Miogypsinoids and Miogypsina sp., Archaias sp., Amphistegina sp., Textularia sp., Lepidocyclina sp., Miliolids, Quenquiloculina sp., Pyrgo sp., Spiroloculina sp., Triloculina sp., Ammonia sp., Elphidium sp., Dendritina sp. and Rotalia venoti dominated the limestones of the Govanda Formation. Planktonic foraminifers are mostly includes the following genera: Globigerinoids sp., Globigerina sp., Globorotalia sp. and Orbulina sp. Moreover, miscellaneous fossils include corals, coralline red algae, echinoderms, bivalves, ostracods, bryozoans, brachiopods and serpulid worms (Ditrupa sp.). The paleoecological condition of the formation was interpreted as follow; the temperature of the Govanda basin ranges between 15-30 °C, nutrient level is between eutrophic to mesotrophic, salinity ranged between normal saline to hypersaline water, light intensity ranging from euphotic to mesophotic and less oligophotic zones, the water depths ranged between 0-120 m, the clastic influx was high in the basin, differences in size and shape within foraminifers of the Govanda Formation indicate various depositional environments and ecological conditions, the water energy was moderate. The environment of deposition is interpreted as being ramp environment. Depending on the different microfauna that exist in the formation, four main zones are distinguished in the ramp model of the Govanda Formation as follows; proximal inner ramp setting which includes open lagoon, distal inner ramp setting which includes back-reef environment, proximal middle ramp setting which includes reef and fore-reef environments, distal middle ramp/ proximal outer ramp setting, which includes open marine environment.