CROSS SECTION OF UPPER CRETACEOUS ROCKS (DAKOTA SANDSTONE-POINT LOOKOUT SANDSTONE) FROM GALLUP TO LAMY, NORTHERN NEW MEXICO

Rocks along this west-east cross section include the intertongued Dakota Sandstone and Mancos Shale of middle and late Cenomanian age, the Bridge Creek Limestone Member (late Cenomanian and early Turonian), the main body of the Mancos containing the Fairport, Blue Hill, and Semilla Members (all middle Turonian), the Juana Lopez Member (middle and late Turonian) and in the western one half, the intertongued Gallup Sandstone and Crevasse Canyon Formation (late Turonian-late Santonian) that are represented farther east by the Montezuma Valley (late Turonian), El Vado (Coniacian), and Satan (Santonian) tongues of the Mancos. The youngest marine unit is the Point Lookout Sandstone (early Campanian) that is overlain by nonmarine Menefee Formation (early Campanian). Approximate positions of age-diagnostic molluscan fossils are indicated in the cross section. The western one half of the cross section is well documented by Molenaar and Baird (1992) and Molenaar et. al. (1996), but the eastern one half needs considerable additional study. Most of the fossils in the cross section can be related to a sequence of Western Interior ammonite and inoceramid zones (Landman and Cobban, in press) shown separately in the chart.