ABSTRACT: Shore to Basin Stratigraphic Profile of Cenomanian and Turonian (Mid-Cretaceous) Rocks Deposited at the Southwestern Margin of the Western Interior Seaway

Douglas G. Wolfe

The Middle Cretaceous Dakota and Mancos formations exposed in the Zuni basin of New Mexico and the Mogollon Highlands of Arizona contain strata of marine, paralic, and terrestrial origin. Litho- and biostratigraphy indicates these facies are time-equivalent; their geographic distribution through time is determined by both eustacy and tectonics. The Cretaceous section lies on Jurassic rocks northward and progressively older sediments and Precambrian crystalline rocks southwest. Valley fill facies are represented by the Encinal Canyon Member (base), Oak Canyon Member shales, Cliff Dwellers Member sandstones, and the interfingering Clay Mesa Shale. Late middle Cenomanian transgression flooded the paleovalley, formed Seboyeta Bay, and eroded lowstand deposits off paleotopogra hic highs toward the southwest. The Paguate Sandstone overlies the Cliff Dwellers Member or the Clay Mesa Shale. The Whitewater Arroyo Shale overlying the Paguate Sandstone represents an early late Cenomanian eustatic highstand. The overlying Twowells Sandstone marks the top of the eustatic cycle. A transgressive unconformity above the Twowells Sandstone marks the base of the next eustatic cycle and the base of the Rio Salado Shale. Calcareous marlstones mark the base of the middle Rio Salado Shale; noncalcareous mudstones mark the base of the upper Rio Salado Shale. The progradational Atarque Sandstone tops the section and the sequence. Toward the southwest the section becomes increasingly sandy but remains fossiliferous, allowing correlation of redbed conglomerates, thick bentonites, a d dolomitic sandstones in the Mogollon Highlands to the mostly marine Zuni basin strata. Eustacy controlled the timing and extent of deposition in the study area; the position of facies changes coincides with structures active since the Paleozoic.

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