ABSTRACT

More than 3,000 feet of Pennsylvanian sediments accumulated in the northern New Mexico extension of the Colorado zeugogeosyncline. The thickness north of Pecos is 2,836 feet. Sedimentation was influenced by several major bordering uplands: (1) Uncompahgre-San Luis uplift, (2) Pedernal uplift, (3) Sierra Grande-Las Animas arch, and (4) Front Range. Four facies representing two formations of cyclic deposition are recognized. Each facies corresponds with a distinct member: (1) lower Limestone member of Sandia, consisting of alternating sandstones and limestones, (2) upper Clastic member of Sandia, consisting of sandstones, shales, and coal, (3) lower Gray Limestone member of Madera, consisting of shales and cherty limestones, (4) Arkosic Limestone member of Madera, consisting of arkoses, red and green shales, and thin limestones. Uplift of the borderlands was accelerated in Late Pennsylvanian and Early Permian time. This resulted in sea withdrawal, local flexuring and erosion of Madera sediments, and increased continental sedimentation. The basins and uplifts are shown on a paleotectonic map.

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