ABSTRACT: Stratigraphy of Upper Cretaceous Rocks in the Zuni Basin, West-Central New Mexico

C. M. Molenaar, W. A. Cobban, D. G. Wolfe

As much as 600 m of Upper Cretaceous rocks is preserved in the Zuni basin, a small Laramide basin south of Gallup, New Mexico. Two references stratigraphic sections were selected for study as part

of the Western Interior Cretaceous Project of the Global Sedimentary Geology Program. In the section at the north end of the basin, these rocks unconformably overlie Jurassic rocks and consist of, in ascending order, 30-40 m of dominantly nonmarine middle to upper? Cenomanian Dakota Sandstone, 200 m of the upper Cenomanian to upper Turonian part of the marine Mancos Shale, 100 m (including tongues of Mancos) of upper Turonian, regressive Gallup Sandstone, and 250 m (top eroded) of upper Turonian to Santonian, nonmarine Crevasse Canyon Formation. In the section at the south end of the basin, Triassic rocks are unconformably overlain by about 30 m of Dakota Sandstone, 120 m of the upper Cenomanian to lower Turonian part of the Mancos Shale, 25 m of middle Turonian regressive Atarque San stone, and 200 m of middle Turonian to Coniacian or Santonian, nonmarine Moreno Hill Formation. The Moreno Hill, which is unconformably overlain by middle Tertiary coarse clastic rocks, is equivalent to much of the marine section at the north end of the Zuni basin.

A cross section between the two reference sections, using intervening measured sections, shows facies changes and intertonguing of marine and nonmarine strata, which record two transgressive-regressive cycles. These cycles include the landward and seaward limits of a complete transgressive-regressive cycle as represented by the 85 m thick, middle to upper Turonian Tres Hermanos Formation and lower part of the overlying 18 m thick upper Turonian Pescado Tongue of the Mancos Shale.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990