Paleogeographic and Stratigraphic Constraints on Lower Cretaceous Mesa Rica Delta System, East-Central New Mexico

Robyn Wright, Michael J. Kisucky, Spencer G. Lucas

The Mesa Rica Sandstone of east-central New Mexico undergoes facies transition from nonmarine fluvial distributary channels to fluvial-dominated deltaic strata over an outcrop distance of approximately 40 km. The underlying Tucumcari Shale contains equivalent prodelta deposits, and the overlying Pajarito Shale represents the delta-plain environment. The delta contains two major progradational lobes, each directly traceable into its correlative distributary channel system. Paleoflow within the older distributary system is toward the south-southwest (206°), and progradation of its corresponding delta lobe is also in that direction (215°). Eastward shift in fluvial transport (to 107°) resulted in delta-lobe abandonment and established a younger lobe that progr ded toward the east-southeast (106°). Mesa Rica distributary sandstones correlate westward with alluvial strata of unknown age that have been assigned to the "lower braided interval" of the Dakota Formation or to the Mesa Rica Sandstone. Results of our study clearly link these fluvial deposits to the Mesa Rica delta front, which is of Albian age based on the presence of the index ammonoid Mortoniceras equidistans. We support assignment of these fluvial strata to the Mesa Rica Sandstone and reserve use of the name Dakota Formation for the overlying Cenomanian marine transgressive sandstone.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.