Lagun downwarp is located in the southeast part of Anadyr basin. It has an isometric form and an area of about 6,000 sq km. There has been no deep drilling, and consequently age and composition of the Cenozoic sediments and prediction of local structures are based on analysis of the wave picture of the seismic records and correlation with the seismic-geologic section of the south border and central zones of Anadyr basin - the Maynits and Central downwarps. About 7,000 km of seismic profiles have been run in the continental part of Lugan downwarp in an area of more than 2,000 sq km.
The following seismic complexes are recognized in the section of Lagun downwarp: I-II, III-IV, V, VI, and VII. These correspond respectively with the Pliocene-upper-middle Miocene, middle-lower Miocene, Oligocene-Eocene, Eocene-Paleocene, and Cretaceous. It seems quite likely that these seismic complexes are composed of clastic sediments and beds of tuff and lavas, the main volume of the units consisting of alternating beds of sandstone, siltstone, and coaly argillite.
The geological and geophysical data show that the Lagun downwarp is a complex asymmetrical block structure that has experienced at least two basic re-ordering of structure during its evolution. The first of these was during the time of formation of the downwarp under conditions of extension and rifting, probably in the final Laramide phase of folding.
The second re-ordering of structural plan took place took place apparently in post-Miocene time - between the Miocene and Pliocene, when conditions of regional extension and sedimentation were interrupted by a strong phase of orogenesis changing into compression. The present structural plan was largely achieved at this time. Several large faults were re-activated, and new faults developed. Horizontal movements played a leading role, leading to extensive overthrusting and wrench faulting along with formation of olistostrom bodies. The overthrust structures are almost everywhere cut by modern faults, largely upthrusts, resulting in a mosaic character.
The following large structural features are recognized in Lagun downwarp: Chimchiney monocline (northwest block), Central Lagun graben (central block), and Pakarvaamo-Lakhtak para-auchthon (southwest block). The Paleocene-Eocene sedimentary complex is host to a group of local anticlinal and domal structures, which are of interest for oil and gas.
Total hydrocarbon resources of Lagun downwarp are assessed at 36.6 million tons (256 million bbls) oil equivalent. Oil dominates at 33.8 million tons (228 million bbls). The question of favorability can be resolved in considerable degree by drilling several deep wells.
Taken from Burlin and Agapitov, 2001; digested in Petroleum
Geology, vol 36, no. 4, in preparation, two maps, one cross section.
Copyright 2002 James Clarke. You are encouraged to print out
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