Sedimentology, palynofacies and hydrocarbon generation potential of the Cretaceous Balambo Formation from Zagros Fold-Thrust Belt, Kurdistan, NE Iraq

Abstract

The Cretaceous Balambo Formation of the Western Zagros Fold-Thrust Belt, in the Iraqi Kurdistan region, was studied in three sections (the Baraw and Sazan outcrop sections and the Baranan-1.G1 well), using three different techniques for determining hydrocarbon generation potential. Optical techniques included studying thin sections and palynological slides, and a geochemical technique was also employed, by applying Rock-Eval pyrolysis to the samples. Lithologically, limestone and shale comprise the largest proportion of the formation. Five microfacies were identified: planktonic foraminiferal wackestone, radiolarian wackestone, fossiliferous wackestone-packstone, fossiliferous wackestone and fossiliferous mudstone-wackestone. The depositional environment of the Balambo Formation was determined to have been an outer shelf–deep water bathyal environment, and the age of the formation extends from Valanginian to Early Turonian in the Baraw section, and from Valanginian to Cenomanian in the Sazan section. The palynological study revealed that amorphous organic matter is the dominant component of the sedimentary organic materials, and phytoclasts and palynomorphs are rare. The paleo-depositional environment of the type-1 palynofacies was a distal suboxic–anoxic basin and that of the type-2 palynofacies was a distal dysoxic–oxic shelf. Both kerogens are of type II, demonstrating that they are oil-prone. The studied organic matter is indigenous, and is mature to post-mature in the Baraw section, immature to mature in the Bn-1 section and mature in the Sazan section. Samples from the Baraw section are of type II/III and III, with a Hydrogen Index (HI) in the range 57–101 mg HC/g TOC. The Bn-1 and Sazan sections were of mixed type II and III kerogen, with an HI in the range 70–458 mg HC/g TOC for the Bn-1 section, and a single value of 135 mg HC/g TOC was obtained for the Sazan section. The results of this study indicate that the samples are capable of generating hydrocarbons (oil and gas).