Depositional history of Lower Cretaceous strata in northeastern New Mexico: Implications for regional tectonics and depositional sequences
Lower Cretaceous strata in northeastern New Mexico reflect deposition during marine transgression and regression associated with the Kiowa-Skull Creek cycle. Development of regionally significant unconformities can be directly related to shoreline shifts during this cycle. Topography related to Early Cretaceous tectonic activity on crystalline basement structures, including the Dalhart Basin, Tucumcari Basin, and the intervening Bravo Dome, also had a direct effect on Early Cretaceous deposition and is reflected by thickness trends in marine strata. The Kiowa-Skull Creek transgression was preceded by infilling of paleovalleys represented by the Long Canyon and Campana sandstone beds of the Glencairn Formation and Tucumcari Shale, respectively. The Long Canyon and Campana sandstone beds are equivalent to the Plainview Formation of central Colorado, and together they represent an extensive drainage network, developed over a correlative unconformity, that is preserved throughout most of the southern Western Interior. Glencairn and Tucumcari marine shales represent clastic deposition during Kiowa-Skull Creek transgression and early regression. Base-level drop associated with Kiowa-Skull Creek regression resulted in dramatic shoreline regression and deposition of fluvial channel sandstone in the Dalhart Basin, which maintained a low offshore gradient. This produced an erosional unconformity at the base of Mesa Rica channel sandstone that correlates with the well-documented erosional surface at the base of the Muddy Sandstone in central Colorado. The Tucumcari Basin, which maintained a steeper offshore gradient, accumulated marine-deltaic Mesa Rica Sandstone at this time. Marine strata in both the Tucumcari and Dalhart Basins thin toward the Bravo Dome. Mesa Rica and upper Tucumcari strata represent the only extensive marginal-marine lowstand deposits found on the High Plains to date, associated with the southern arm of the Kiowa-Skull Creek sea. Major Mesa Rica deposition was followed by transgression that infilled only those Mesa Rica fluvial channels that were active at that time and, also, that deposited marine-influenced strata of the basal Pajarito Formation. This event most likely represents onset of the Greenhorn cycle in northeastern New Mexico. Other crystalline basement structures in the northern part of the United States Western Interior Basin were active during Early Cretaceous time. Tectonism in these areas may be related to structures in northeastern New Mexico and thus may be expressions of broad-scale crustal strain in the Early Cretaceous Western Interior that is undocumented by present tectonic models.