A Comparative mineralogical and geochemical studies of Eocene and Maikop oil shales in Eastern Azerbaijan: Stratigraphic controls on formation of oil and gas hydrocarbons in the South Caspian basin

The South Caspian Basin, subject to intense sedimentation due to its location in the Arabian-Eurasian collision zone, is known worldwide for its rich oil and gas deposits. It is also the region with the densest concentration of mud volcanoes in the world. On the western flank of the basin (East Azerbaijan), numerous surface oil-bearing occurrences and more than 100 oil shale outcrops are recorded. The results of studies carried out to date indicate the role of predominantly Upper Maikop (Lower Miocene) sediments in the formation of rich oil fields. However, the extraction of industrially important oil from Eocene deposits in the western part of the country makes one think positively about their prospects in East Azerbaijan. For the first time, we study the mineralogical and geochemical characteristics of oil shale rocks in the rock-ejecta of mud volcanoes as well as surface outcrops of Eastern Azerbaijan and compare the formation characteristics, and oil and gas potential of the Eocene and Upper Maikop sediments at the Paleogene-Miocene units. The results of our research revealed for the first time the high oil-generation potential of the Middle Eocene oil shale sedimentary complex containing type II kerogen, characterized by a thickness of 200-300 m. We believe that a major contribution to the formation of gas fields in the South Caspian basin is made by the Upper Maikop oil shales, which are formed under conditions of more intense input of terrigenous materials and preserve kerogens of types II-III and III. Compared to the Maikop oil shales, the richness of organic matter in the Eocene oil shales is due to the closer connection of the paleobasin with the sea, and the influence of volcanic ash and higher primary paleobioproductivity on sedimentation.