Biostratigraphy of Lower Cretaceous from Selected Borehole in central Iraq

Abstract

Sarmord Formation is a significant formation that was deposited in the Lower Cretaceous in North and Central Iraq. It has been studied for biostratigraphic purposes in two subsurface sections of Tikrit oil field wells: T.K.3 and T.K.5 in Tikrit governorate. The formation is known for its importance and studied extensively by researchers. The lithology of Sarmord Formation is limestone and also contains marly limestone and marl. It has a thickness range of 109-286 m. To determine the fauna present in the formation, authors studied 170 thin sections under a microscope. They identified fourteen benthic foraminifera and algae species belonging to sixteen genera, based on the benthic foraminifera. After studying the paleontological data from the investigated area, it was determined that two distinct biozones exist within Sarmord Formation. These biozones were identified as the Choffatella decipiens range zone, which spans the Hauterivian to Early Aptian period, and the Palorbitolina lenticularis range zone, which spans the Late Barremian to Late Aptian period. This information provides insight to the age of Sarmord Formation, which is thought to deposit during the Hauterivian to Aptian period.