Investigation of Sedimentation and Subsidence Rates in Gorgan Plain Using Basin Modeling

The Gorgan Plain is located in the north of Iran and has mud volcanoes and high-pressure zones. There is limited information on Miocene and older sediments in this area and the available data on the Pliocene and younger sediments do not provide a complete understanding of the geology of these areas. The absence of marker fossils in the sediments has led to ambiguities in age determination and study of layers expansion in the study area. The Cenozoic sediments of Gorgan Plain which include Paleocene-Miocene sediments and Cheleken (Lower Pliocene), Akchagyl (Upper Pliocene), Apsheron (Lower Pleistocene), Baku (Upper Pleistocene) and Neo-Caspian (Holocene) formations, are mainly composed of sandstone and mudstone. This study shows that the thick Pliocene-Present sediments of Gorgan Plain were deposited at high rates, which was simultaneous with the increase in orogenic activity in the region and the gradual separation of the South Caspian Basin from open waters and the change of the sedimentary environment from marine to fluvial-deltaic. Sedimentation rates of Cenozoic deposits increase towards the coastal parts of the Gorgan Plain. The lowest sedimentation rates are in the Paleocene-Eocene deposits, and the highest rates are in the Baku Formation. High sedimentation rate is one of the controlling factors in the formation of mud volcanos and high-pressure zones in the region, and these rates can have a significant impact on the processes and elements of the petroleum system.