Abstract: Paleocurrent Analysis of Dakota and Subjacent Sandstones, San Juan Basin, New Mexico

Donald E. Owen, Lester J. Walters, Jr., John R. Kostura, Keith Grant

Approximately 1,500 cross-bedding orientations were analyzed in detail with the aid of computer programs to solve apparent-dip problems, correct for tectonic rotations, calculate vector resultants and vector magnitudes, and analyze bimodality. Cross-bedding is very abundant in the fluvial part of the Dakota Sandstone and the subjacent sandstones overlying the Brushy Basin Member of the Morrison Formation but is scarce, although locally present, in the marine sandstone parts of the Dakota.

Fluvial cross-bedding indicates a northeasterly to easterly paleoflow with fairly low dispersion in the Jackpile sandstone and overlying, locally present, fluvial part of the Dakota in the southeastern San Juan basin. In the Chama basin, and adjacent northeastern flank of the San Juan basin, cross-bedding directions are dispersed widely in the fluvial part of the Dakota and the subjacent sandstone referred to as the Burro Canyon Formation; however, an easterly average paleoflow is indicated. In the Dakota of the northwestern San Juan basin, fluvial cross-bedding is oriented northeastward with low dispersion, except near the Four Corners in Utah and Colorado where a paleodivide separated a paleoflow northwestward into the Blanding basin area. Inadequate cross-bedding data along the nor h flank of the San Juan basin in Colorado east of this paleodivide indicate a northerly paleoflow.

Marine sandstones of the Dakota are developed best in the southeastern San Juan basin, but are present in the Chama basin and adjacent areas. These sandstones contain cross-bedding of low dispersion, indicating a southerly to southeasterly paleoflow. Thus, as low-energy marine conditions succeeded fluvial, paleocurrent flow shifted clockwise from northeasterly to southerly.

AAPG Search and Discovery Article #90971©1976 AAPG-SEPM Rocky Mountain Sections 25th Annual Meeting, Billings, Montana