Facies Relationships in Mesa Rica Sandstone (Lower Cretaceous), Tucumcari Basin, East-Central New Mexico: ABSTRACT

Abstract

The Mesa Rica Sandstone, a Lower Cretaceous (Albian) cliff-forming unit in east-central New Mexico, represents a progradational fluvial-dominant deltaic system. On Mesa Rica, south of Conchas Lake, the formation is underlain by the marine (prodelta.) Tucumcari Shale, and is overlain by upper and lower delta-plain deposits of the Pajarito Shale. Clear facies interfingering between the Mesa Rica and Pajarito formations documents a direct genetic link between the two. Whether the Mesa Rica Sandstone lies unconformably on the Tucumcari Shale or is transitional to it is as yet unresolved. Three major sandstone bodies exist within the Mesa Rica formation, each capped by a thin (less than 2-m) mudstone interval. The two basal sandstone bodies record deposition of separate delta lobes; the bottom unit represents progradation toward the south-southeast (215/sup 0/), whereas the upper sandstone exhibits progradation toward the east-southeast (106/sup 0/). For each unit, lobe development was followed by abandonment, often marked by wave reworking. The third major sand body in the Mesa Rica overlies the lower units and records interdistributary deposition. Subenvironments recognized within the marine part of the delta include distal bar, bar front, bar crest, bar back, distributary channel, and beach. Intervening mudstones are similar in lithology tomore » the overlying Pajarito Shale. These units grade southward from nonmarine upper delta plain, containing overbank and levee deposits, to marine-influenced lower delta plain.« less