Implications of the metacraton to tectonic-sedimentary-hydrocarbon accumulation processes in the basin:Case study of the Afghanistan-Tajik Basin
Afghanistan-Tadzhikistan Basin,located in the northern margin of the North Tethyan tectonic collision orogeny,west of the Pamir salient.The basin is well known by salt tectonics,characterizing with detachment faults and folds which developed along unique internal geological structures,and there,hydrocarbon reservoirs have been found.In this study,with the utilization of seismic,geological data,and hydrocarbon industrial data in the Afghanistan-Tadzhikistan Basin,we reinterpreted the seismic cross-sections,combined the surface as well as the underground structural-sedimentary features.Because of the salt structures and interlayer detachment,two or three structural bodies were produced,and a variety of complex structural styles were formed such as salt-related anticline,syncline folds and reverse faults.The tectonic evolution of the basin was analyzed,and further hydrocarbon geology was discussed,which were intended for the future exploration and at the same time providing a theory basis.This research shows that the sedimentary cover above the"Hercynian"(Upper Paleozoic)basement is comprised of three major super-sequences:1)the"transitional complex"in the backarc extension environment;2)the stable deposits of the"platform complex";3)the"molasse deposition"during the Alpine compressional phase caused by the India-Eurasia collision.Hydrocarbon in the basin was produced from the prolific pre-salt Lower-Middle Jurassic shales,Eocene/Aptian-Albian shales and argillaceous carbonates hydrocarbon,stored within Cretaceous clastic rocks,Paleogene carbonates,and sealed by Cretaceous regional salt rock and Eocene shale.As a result,they are attributable to two petroleum systems:"the pre-salt system"and"the post-salt system",forming fault related anticline traps,lithology reef traps and others,with a great potential for oil and gas exploration.