Insights into the Sequence Stratigraphy of the Dakota Interval (Cretaceous) in the San Juan Basin, Northwestern New Mexico and Southwestern Colorado

Owen, Donald E. ¹, Charles F. Head² (1) Dept. Earth & Space Sciences, Lamar University, Beaumont, TX (2) Burlington Resources, Inc, Farmington,

The Dakota producing interval comprises the Burro Canyon Formation (Lower Cretaceous), Dakota Sandstone with intertongued lower Mancos Shale (Cenomanian), and the Graneros Shale Member of the Mancos (Cenomanian-Turonian). Data from 85 measured sections, 32 cores, and 7,000 wells were integrated to construct a regional stratigraphic framework that correlates outcrops that surround the San Juan Basin with the subsurface of the entire San Juan Basin. All of these strata were deposited on the west flank of the Western Interior seaway in coastal plain, shoreface, and offshore marine environments. The Burro Canyon forms a complete sequence of braided-stream pebbly sandstones bounded by the K1 and K2 unconformities. The second sequence consists of the Encinal Canyon and Oak Canyon Members of the Dakota, a transgressive sequence tract bounded by the K2 and K3 unconformities. The third sequence begins with the White Rock Mesa Member of the Dakota, a meanderingstream, coastal-plain clastic wedge from the west superjacent to the K3 unconformity. East of this wedge and seaward of the shoreface, the K3 unconformity grades into a correlative conformity at the base of the Cubero Sandstone Member of the Dakota. A pair of transgressive Mancos Shale tongues (Clay Mesa and Whitewater Arroyo Members) superjacent to marine-flooding surfaces grade upward into regressive shoreface Dakota tongues (Paguate and Twowells Members); these complete the third sequence with a possible sequence boundary in the Twowells. The A, X, and D bentonites in the upper two sequences provide prominent age-marker beds recognizable in both outcrops and subsurface.

AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana