Abstract: Paleocurrents of Jackpile Sandstone, Burro Canyon Formation, and Dakota Sandstone of San Juan Basin Region, New Mexico, Colorado, and Utah

Donald E. Owen, Lester J. Walters, Jr., Lynne M. Depetro, John M. Turmelle

Approximately 3,300 cross-bedding orientations from 53 locations were analyzed with computer programs to solve apparent-dip problems, perform tectonic rotations, calculate vector characteristics, and analyze for bimodality. These analyses were undertaken in a basinwide study of sandstone near the Jurassic-Cretaceous boundary in the Four Corners area.

The Jackpile sandstone of the southeastern San Juan basin, was deposited by a largely braided-stream system of moderate dispersion, that transported fine-grained sand eastward from the Mogollon Highlands. The Burro Canyon Formation, in the northern San Juan basin and Chama basin, was deposited by a largely braided-stream system of high dispersion, that transported pebbly sand eastward from the Mogollon highlands.

The lower fluvial sandstone of the Dakota was deposited by an east-flowing meandering-stream system of high dispersion and locally variable direction. Paleoflow means vary from westerly toward the Blanding basin near the Four Corners to northeasterly along the north flank and easterly along the east flank. This fluvial sandstone is absent locally in the southeastern San Juan basin. Along the south and southwest flank, where fluvial sand possibly was reworked by marine currents, cross-bedding indicates southerly paleocurrent directions.

Regressive marine sandstone units, extremely well developed in the southern San Juan basin, were deposited by south-trending longshore-current systems of low dispersion, although northeasterly trends occur in Colorado. These shoreface and shallow-offshore sandstones wedge out seaward into marine Mancos shale and merge shoreward with fluvial Dakota sandstones.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma