ABSTRACT: Cretaceous Strata of the Black Mesa Area, Northeastern Arizona

K. J. Franczyk, W. P. Elder, J. I. Kirkland, R. M. Leckie

Continental and marine strata of Cenomanian through Santonian age in the Black Mesa area of northeastern Arizona were deposited in the southwestern part of the Western Interior foreland basin away from the tectonically active basin margins. Transgressive and regressive strata, vertical facies changes within both marine and nonmarine units, and unconformities possibly reflect both eustatic changes and tectonism. Erosion has beveled the Cretaceous strata into a wedge that thickens from about 180 m in the southern part of the Black Mesa area to about 570 m in the northwestern part. These strata are being studied as part of the Western Interior Cretaceous Project of the IUGS Global Sedimentary Geology Program in order to ascertain the controls on Cretaceous deposition in the estern United States and to compare these controls with those in other basins of the world.

The Cenomanian nonmarine to marginal-marine Dakota Sandstone, which unconformably overlies Jurassic or older strata, is the basal Cretaceous unit. Disconformably overlying the Dakota is the late Cenomanian through middle Turonian Mancos Shale, which formed in an offshore-marine environment during the first major transgressive-regressive cycle of Cretaceous age in the Black Mesa area. Locally, within the Mancos, possible minor disconformities coincide with faunalzone boundaries. The Mancos grades upward into the marginal-marine and nonmarine Toreva Formation. During the latter part of the Turonian, a eustatic fall and/or regional tectonism produced an unconformity with the Toreva. The Toreva grades into the overlying upper Turonian to Santonian(?) nonmarine, coal-bearing Wepo Formation A transgression into the northernmost part of the area resulted in a disconformity that separates the lower carbonaceous member of the Wepo from the overlying Coniacian Wind Rock Tongue of the Mancos. Subsequent regression formed the Coniacian marginal-marine Rough Rock Sandstone and most of the overlying nonmarine upper carbonaceous member of the Wepo. An ensuing transgression and regression in the northernmost part of the area produced the Santonian marginal-marine Yale Point Sandstone that disconformably overlies the Wepo.

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