CIROS-1, the most recent scientific drill hole in Victoria Land Basin, Antarctica, cored to 702 m below sea floor (mbsf) near the basin's western margin. The cored sequence is largely marine sandy mudstone and diamictite, with lesser sandstone and conglomerate, and shows a glacial influence throughout. The strata range in age from early Miocene near the sea floor to the Eocene/Oligocene boundary at 702 mbsf, some 800 m above acoustic basement.

The strata cored by CIROS-1 have a uniformly low organic carbon content (average total organic carbon 0.34%), little hydrocarbon generating potential (maximum 0.34 mg hydrocarbons per gram of rock), and a low level of thermal alteration (vitrinite reflectance of 0.36% at 670 m). Kerogen is mainly highly oxidized terrestrial organic matter reworked from older strata.

Residual asphaltic oil was found in minute quantities in sandstone at 632 mbsf. Geochemical studies indicate that it formed at greater depth, probably in nearshore clastic sediments with both marine and terrestrially derived organic matter. Similar coarse- to fine-grained feldspathic sandstones are common in the mudstone that forms the lower half of the core, and offer reservoir potential. Calcite and zeolite cements are common but in-situ porosities range up to 22%, with good dissolution porosity in some intervals.

In balance, the possible prospects of Oligocene strata on the margin of the Victoria Land Basin must be considered low. Source characteristics are unfavorable and only minute amounts of hydrocarbons have been encountered. In addition, the up-dip location of CIROS-1 with respect to the basin center suggests that the possible prospects of the western Victoria Land Basin should also be regarded as low.

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