Abstract

The Kerrouchen basin, on the southern end of the Middle Atlas Mountains of central Morocco, is an elongated asymmetric basin underlain by metamorphosed Paleozoic basement. With the onset of rifting of Africa from North America in Triassic time, the basin was downfaulted in the southeast against Hercynian granites, which shed 180 meters of alluvial fan conglomerates and sandstones into the basin. Forty kilometers across the basin to the northeast, a Paleozoic meta-sedimentary source terrain contributed sediments to a smaller and separate fluvial sequence, filling in that gently downwarped limb of the basin. Between these two coarser sequences, a mudflat existed which increased in size as tectonic activity diminished. The mudflat deposits eventually transgressed over the coarse sediments and the granites, covering them with red mudstones and localized evaporites. Thickest observable Triassic deposits, in the center of the basin, total approximately 600 meters of section; 275 meters of mudstone covered by 225 meters of basalt, and underlain by 80 meters of fluvial sandstone resting on basement. The basalts, averaging 100 meters thick, are intercalated with the uppermost mudstones. They covered the entire area as a series of flows of varying thickness, samples of which have been radiometrically dated as Triassic. The sequence is conformably covered by Jurassic carbonates consisting of limestones and dolomites deposited with the transgression of Jurassic seas.

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