Stratigraphic relationships at the Jurassic-Cretaceous boundary in east-central New Mexico
John M. Holbrook, Robyn Wright, and Kenneth K. Kietzke
This paper addresses stratigraphic relationships at the Jurassic-Cretaceous boundary in the Tucumcari basin of east-central New Mexico. Where the Albian Tucumcari Shale (marine) overlies nonmarine units of the Jurassic Morrison Formation, the Jurassic-Cretaceous boundary is easily located. However, this contact becomes confused as Tucumcari shales lap out against the unconformity surface toward the north (paleo-landward), and are replaced by marginal marine and fluvial rocks of the Albian Mesa Rica Sandstone. We suggest that uppermost fluvial Morrison sandstones (Jackpile equivalents?) have erroneously been included within the Cretaceous Mesa Rica section. The Jurassic sandstones may be properly distinguished from the Mesa Rica by differences in lateral continuity, stratigraphic position, sandstone texture and mineralogy.
In addition to previously described stratigraphic units in the area, we recognize and informally name the Campana sandstone bed of the Tucumcari Shale. The Campana sandstone bed occupies a stratigraphic position between the Morrison unconformity surface and the overlying Albian marine transgressive surface, and occurs in discontinuous local exposures. This bed represents fluvial aggradation and estuarine inundation associated with base-level rise of the Tucumcari sea. Preservation of the Campana sandstone bed appears to be restricted to paleotopographic lows on the post-Jurassic depositional surface, where as much as two m of relief have thus far been documented. The most likely stratigraphic equivalent to the Campana sandstone bed is the basal sandstone of the Glencaim Formation in northeastern New Mexico.
- Holbrook, John M.; Wright, Robyn ; Kietzke, Kenneth K., 1987, Stratigraphic relationships at the Jurassic-Cretaceous boundary in east-central New Mexico, in: Northeastern New Mexico, Lucas, S. G.; Hunt, A. P., New Mexico Geological Society, Guidebook, 38th Field Conference, pp. 161-165.