Seismic surveys in the Shortanbay area in the south of the North Caspian depression have disclosed several ring structures, which are interpreted as buried craters of possible meteorite impact origin. Many oil and gas fields in the southeast part of Ural-Volga province are associated with ring systems. The South Emba ring structure with diameter of 200 km is recognized in the southeast of the North Caspian depression. Study of satellite images along with geological and geophysical data has disclosed the gigantic Aral ring, which has a diameter on the order of 700 km.
The ring structures of Shortanbay area show up in the pre- Kungurian section of the Lower Permian at depths of 4.0-4.5 km beneath reflector P-1, the first reflector below the Kungurian salt. One of these structures is west of Kotlevskiy-Severnyy salt dome and has a diameter of about 3.5 km. Another such structure is east of this dome; it is not as well expressed. Then to the west of these is yet another possible structure. The morphology of these structures is attributed to meteorite impact.
The structures described here are synchronous, occurring in the Lower Permian section. Continental conditions were maximum in tne Permian for the entire Paleozoic. Platforms almost everywhere became land areas. Salt was deposited in broad internal seas (North Germany and Poland, Near-Urals, North America, North Caspian). The largest catastrophic extinction of life was at the boundary between the Permian and Triassic about 240 million years ago. Only at the end of the Permian did life forms develop that extended into the Mesozoic. The cause of this extreme situation remains unclear.
The traces of cosmic activity on the pre-Kungurian surface suggest that the cause of this profound global change at the end of the Paleozoic may have been intense meteorite bombardment during the first half of the Permian. Geologic and climate changes following this bombardment led to deposition of thick salt beds that covered the impact structures. This created ideal traps for accumulation of hydrocarbons. The volume of the fracture pore space in only one of the structures of Shortanbay area could hold about 250 million tons of oil or 120 billion cubic meters of gas. Similar structures are known in the Williston Basin, where three of the five known buried craters yield commercial oil. It is quite possible that the proposed impact craters of the south of the North Caspian depression are synchronous with those of the Williston Basin.
The possibility for finding zones of impact crushing with good reservoir properties in thde sub-salt section of the North Caspian depression along with a reliable salt seal offers new prospects for this region.
Taken from Zeylik and Zozulin, 1995; digested in Petroleum
Geology, vol. 31, no. 4, 1997, two seismic sections.
Copyright 2002 James Clarke. You are encouraged to print out this
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