New insights into the structure of the South Caspian Basin from seismic reflection data, Gorgan Plain, Iran

This research presents an integrated study of 2D seismic reflections and calibrated well data to outline the structural development of the Gorgan Plain on the border of the South Caspian hydrocarbon basin, in the Alborz and Kopeh-dagh ranges of northeast Iran. Eight seismic horizons, including two unconformities, have been identified, ranging in age from Early Jurassic to Quaternary. Analysis and interpretation of geophysical data provide an understanding of the structural geology of the Gorgan Plain, crucial for investigation of structural traps. Seismic interpretation indicates structural features such as deep reverse listric faults (inverted normal faults) for older formations; strike-slip and normal faults in younger sequences; dome and basin interference patterns of folding for all the top formations. Well data demonstrate the occurrence of a disconformity at the base of Upper Cretaceous beds and an angular unconformity at the base of Paleogene. Evidence identified in well and seismic-reflection data proves a complex pattern of tectonic phases since the Early Jurassic. It seems reasonable to suppose that these structural patterns are related to a change in direction of tectonic compression, which in turn has produced structural hydrocarbon traps in crests of domes in the Gorgan area.