The Moma-Zyryanka depression is located in the north of Siberia to the east of the East Siberian craton. It extends in a northwest direction from longitude 144 to 156 degrees east and latitude 64 to 68 degrees north. This basin was the subject of News Letter No. 98. The information presented here duplicates to some extent that of the earlier News Letter; however, there is enough different to warrent re-visiting this subject.
The Moma-Zyryanka depression appears to be a continuation of the Mid-Atlantic spreading center and is on line with a belt of seismic activity to its northwest. See Zonenshain, Kuzmin, and Natapov, American Geophysical Union, Geodynamic Series vol. 21, p. 206.
The region between the Indigarka and Kolym Rivers was above sea level during Early and Middle Jurassic time. Then during the Callovian intensive downwarping accompanied by volcanism marked the beginning of a new and independent tectonic feature, the Moma-Zyryanka basin. During the course of the Oxfordian and Kimmeridgian sediments of the Ilin'tas Formation (2800 m) were deposited in the basin, and intensive volcanism was continuous. Basalt, andesite, various tuffs, shale, and siltstone were deposited in a shallow-water, warm marine basin of normal salinity.
Volcanism weakened at the beginning of the Volgian Stage, but downwarping continued with deposition of clays of the Lamutkin Formation (2000-3000 m). Sandy facies collected in some areas. Next followed clayey and sandy-clayey sediments of the Ust'-Agandzhin Formation (1500 m), where graded bedding is present. In the second half of the Volgian Stage sandy-silty sediments of the Neysat Formation (2000 m) collected along with growth of internal highs within the basin.
Direct communication with the open sea was broken at the end of the Volgian Stage, and the Moma and Zyryanka (Indigirka-Zyryanka) downwarps were essentially separated by the Omulav ridge. Silty-clayey units of the Argatas Formation (2000 m) were deposited in both downwarps.
These Upper Jurassic formations constitute the Bastakh Series, where deposition was exceptionally rapid at 0.9-1.7 mm per year.
Neocomian time saw deposition of 2000 m of sandy-silty sediments of the Ozhogin Formation. The main structural features of the Zyryanka downwarp began to form at this time. During the Aptian the Silyap Formation (2000 m) was deposited. It consists of sandstone, siltstone, coal beds, and lenses of pelitic limestone. Deposition was in shallow, fresh-water basins. Siltstone, shale, sandstone, and coal collected in the Albian to form the Buorkemyus Formation (3000 m).
The Cretaceous formations constitute the Zyryanka Series, where deposition was 0.21-0.23 mm per year.
The Zyryanka downwarp is favorable for oil and gas. The Lower Cretaceous is the main play, and structures are present. This region is probably gas-prone. Surface shows of methane have been recorded at many places.
Taken from Kim (1980); digested in Petroleum Geology, vol 24, no. 3/4.
Copyright 2001 James Clarke. You are encouraged to print out this
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