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The depositional environment and provenance of the Santa Clara Formation of the Upper Triassic Barranca Group in eastern Sonora were studied based on a detailed description of 875 m of section and study of 123 thin sections from both outcrops and cores.

The Santa Clara Formation is a cyclic unit with typical fluvial cycles of 4 to 16 m. Highly altered, quartz-rich sandstone is interbedded with black and gray shale and minor beds of graphite and anthracite, which were formerly mined. Detrital chert and remobilized chert cement are significant features of the sandstones of the Barranca. Diagenesis is extensive, of high rank, and commonly blurs the distinction between primary detrital matrix and chemical cement to produce a predominance of quartz-rich wacke.

A quiescent basin with tropical climate, subdued marginal relief, and no active volcanism is inferred for the Santa Clara, and limited crossbedding measurements indicate a source to the north. Basin type and its relation to other Upper Triassic deposits remain major problems.

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