Sedimentation Environments of the Lower Cretaceous Deposits of the North Caspian

Abstract

The article describes the sedimentation environments of Lower Cretaceous (Aptian–Albian) terrigenous deposits in the North Caspian. These rocks are oil and gas reservoirs and are characterized by an uneven distribution of the pelitic and silty fractions, which leads to a high content of residual water, low permeability, and poor consistency of the filtration-capacity properties with each other. A detailed lithological and facies analysis of the rocks was carried out for correct interpretation of geophysical data. The following marine environments predominated in the studied area in the Early Cretaceous: coastal, shallow marine, relatively shallow shelf with active hydrodynamics; relatively deep-water shelf with low hydrodynamics. The sections show a change from shallow to deeper facies and vice versa, which allows us to conclude periodic fluctuations in sea level. The results of lithological analysis clearly indicate the predominance of shallow marine and coastal sediments in the Aptian and deeper, shelf sediments in the Albian. Thus, we can suggest a sea transgression at the end of the Early Cretaceous and detect signs of it in the sections of Aptian–Albian deposits in the North Caspian.