Within the past few years there has been an active exploration and development program for petroleum in Triassic sandstones of the northwestern Algerian Sahara. This stratigraphic unit has not been named formally, and no significant fossils have been found in the 150,000-sq km area involved in the program. The present study involves analysis of the sedimentologic characteristics, correlation, and stratigraphic relations. Although there are a few data for such a large area, it has been possible to diagnose local and regional patterns of lithologic variation. These analyses provide a basis for reconstruction of the environmental setting. A major purpose is to provide a preliminary analysis of this important sandstone reservoir to be used in further exploration.

Existing information indicates that Lower Triassic sandstone in the northwest part of the Algerian Sahara was deposited on a post-Hercynian erosion surface in a shallow marine environment. Part of the variability in thickness (50-200 m) is related to irregularities in the Paleozoic erosion surface. There is also an apparent shoreline represented by nondeposition. Sediments are believed to have been derived from local folds, such as the eroded Hassi Messaoud anticline, and from broader uplifts in north-central Algeria.

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