Origin of the Stephanian Red Beds in the Ocejo Basin (Prov. of Leon, Spain)

In the valley of Ocejo (prov. León) a series of alternating conglomerates, sandstones, siltstones, and shales with a red colour are found. This series is 180 m thick, of Stephanian B + C age, and at present dips ± 30°W. Sedimentological analysis gives the following data: (1) quartz is the dominant detrital mineral, hematite and clay form the cement; (2) the components of the conglomerates are chiefly limestones of cobble size, the fine-grained sediments and matrices being chiefly siltstones with varying admixtures of clay size material; (3) the limestone pebbles have low roundness- and flatness-index values. The sediment was deposited by torrents at the foot of a rising mountain area. The source region had a thick cover of red soil on top of limestones. Rapid erosion in these elements caused the deposition of limestone conglomerates in a red matrix during a period in which the climate was warm and humid.