Non-structural traps are being sought on the continental shelf of the South Caspian depression. The section there consists of thick Mesozoic-Cenozoic sediments, including Pliocene pays. Regional pinchouts along the borders of the depression and on the flanks of structures along with breaks in deposition due to tectonic uplift have created conditions favorable for stratigraphic and lithologic traps.
Non-structural traps are particularly widespread in the lower part of the middle Pliocene, deposition of which was in a continually expanding basin. Each successive unit lapped over the older, creating zones of pinchout. This is of particular interest for the Productive Unit offshore in the area of the Apsheron Shallows, where hydrocarbon traps are present.
Five large seismo-stratigraphic complexes are recognized in the section of the South Capian depression: Mesozoic, Paleocene-Miocene, middle Pliocene (Productive Unit), upper Pliocene, and Pleistocene.
The Productive Unit (middle Pliocene) differs from the other seismo-stratigraphic complexes by a persistence of horizons and by repetition of the geologic conditions of deposition due to periodic tectonic oscillations and changes in sea level.
The Productive Unit consists of alternating clay-sand and sand-clay rhythms; these show up clearly on the seismic time sections. An angular discordance at the base of the Productive Unit is also traced on the seismic record. Toward the northwest this discordance truncates successively older sediments down to the Cretaceous. In this same direction units in the lower part of the Productive Unit drop out of the section. Thus this surface is not synchronous.
The Productive Unit begins with the sand-clay Kalin Formation (first rhythm), but then to the west of its line of pinchout it begins with the sandy Podkirmakin Formation.(lower second rhythm). Yet farther to the west it begins with the clay-sand Kirmakin Formation (upper second rhythm). The Kalin and Podkirmakin were deposited in water depths of 3-10 m, whereas the more clayey Kirmakin was deposited in depths of 30-50 m.
In some areas the growth of anticlines is recorded in the lower part of the Productive Unit. All these folds are the result of diapirism of thick Paleogene and Miocene clays.
Anticlines, noses, and benches are present on the surface at the base of the Productive Unit. All of these are buried. Zones of pinchout on this surface are of great practical interest for oil and gas.
Taken from Mamedov and Ragimkhanov, 1985, two seismic
sections and one structure map; digested in Petroleum Geology,
Vol. 23, No. 3/4. Copyright 2003 James Clarke. You are encouraged
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