Avak (crater)

Avak is a rounded formation buried under sedimentary rocks with a diameter of about 8 km and a depth of 1 km ^[2] . The crater’s funnel is bordered by a shaft consisting of metamorphic rocks of the basement thrown upwards and bulk material from emissions from it. In the center there is an uplift with a diameter of about 4 km , where the Lower Cretaceous rocks are elevated to a height of more than 500 m ^[3] . Avak is not expressed in the surface relief ^[4] .

The crater formation time is estimated to be in the range from 95 million to 3 million years ago ^[1] . In it rocks deformed by impact from the Ordovician to Lower Cretaceous age, as well as Pliocene and Pleistocene rocks deposited after the impact were discovered ^[3] . Palynological studies of emissions from the crater (taken at a distance of about 50 km from it) indicate the Middle Turonian - Late Turonian impact time (about 90 million years ago) ^[4] .

Avak provides a "trap" for natural gas in the neighboring South Barrow, East Barrow and Sikulik fields. About 1 billion m³ of gas is concentrated in sandstones of the Jurassic period of these deposits ^[3] .

Avak was discovered using seismic exploration in the study of oil and gas areas of Alaska, conducted by the US Navy from 1943 to 1953. It manifested itself as a rounded structure not reflecting seismic waves, around which radial faults were visible ^[5] .

In order to search for oil and gas, as well as study some rocks, in 1951-1952 (within the framework of the same studies), a well was drilled near the center of Avak, reaching a depth of 1225 m ^[5] . Deformations of rocks in it were found to the very bottom ^[3] . In particular, characteristic signs of shock were found — ^{[3] [4]} . In 1995, researchers from the Geological Survey of Canada and the US Geological Survey discovered in breccia quartz grains obtained from the aforementioned well from a depth of about 700 m, another sign of this effect is ^[3] .