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The Surani anticline has two formations exposed with sands containing a residue of oil--Meotic of the Pliocene and Kliwa of the Oligocene. These represent oil reservoirs which have been depleted by erosion. The oil sands of the upper reservoir bear a normal relation with the anticline but those of the lower do not.
The sand series in which the lower reservoir occurs is oil-free along the crest of the anticline at its highest point and down the north flank, but in going down the south flank and down the plunge to the northeast these sands suddenly are found to carry the oil residue. The break from white "barren" sand to oil sand is along a sharply defined plane. This plane, where it can be seen clearly in a bed dipping 15° south, is inclined 45° to the bedding plane and 60° to the horizontal, with the oil sand being on top and on the downdip side. The plane is thought to represent a former oil-water contact.
These conditions are interpreted to mean that the oil was originally collected in some trap to the south of the Surani anticline and furthermore that this reservoir was formed and depleted before the Surani anticline came into existence. This latter event took place in pre-middle Miocene time. The oil sands one sees today were
at the north limit of the reservoir and at the time of depletion were dipping 45° north.
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