Abstract

Stratigraphic studies of Lower Cretaceous units in the southeastern part of the San Juan basin indicate that the Tres Hermanos Sandstone should be considered as the upper member of the Dakota Sandstone. In the southwestern part of the basin the Twowells Sandstone should be considered as the upper member of the Dakota Sandstone. A persistent tongue of marine shale, separating the Twowells Sandstone Member from the rest of the Dakota Sandstone, is here named the Whitewater Arroyo Shale Member of the Dakota Sandstone.

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