New Mexico Geological Society Annual Spring Meeting — Abstracts

The Dry Cimarron Valley is located in far northeastern New Mexico and trends eastward from Folsom, New Mexico into Oklahoma. The valley walls expose strata of the Upper Triassic Chinle Formation, Middle Jurassic Exeter Sandstone, Middle to Upper Jurassic Morrison Formation, Cretaceous Glencairn Formation and Dakota Group. The northern rim of the valley is capped by young basalt flows from the Raton-Capulin volcanic field. Scattered throughout the Dry Cimarron Valley are numerous clastic injectites that occur as both plugs (cylindrical features) and dikes (planar features) that protrude upwards from the floor of the valley. The clastic injectites occur stratigraphically below the Exeter Sandstone and are within the Chinle Formation. Observations by previous researchers suggest that the majority of material entrained in the injectites originates from the Chinle Formation, particularly the Sheep Pen Sandstone, Sloan Canyon, Travesser, and Baldy Hill Members. However, no detailed studies have previously been conducted to determine the means of emplacement. In this study a series of oriented samples were collected from an exceptionally well exposed plug and associated dikes located along State Highway 325. Due to the high level of sensitivity and precision achievable, anisotropy of magnetic susceptibility (AMS) has long been used as a tool to investigate the flow and deformation dynamics of igneous and sedimentary rock structures. In this study, AMS sampling targeted the undisturbed Chinle strata on either side of the feature, as well as the margins and center of the injectite. The margins of the injectite are continuous well cemented sandstone, whereas the center contains a chaotic mixture of angular clasts of red siltstone and fine grained well cemented sandstone that is surrounded by a poorly indurated mudstone matrix. Capping this injectite is a thin yellow quartz arenite (the Exeter Sandstone?), which uncomfortably overlies the plug. Preliminary AMS data from the Dry Cimarron injectite reveal a geometrical relationship between the bounding walls of the injectite and the measured magnetic anisotropy; we interpret this to reflect viscous flow during the emplacement process. Detailed petrography conducted on five injectite lithofacies and the host rock reveals a complex paragenesis, including precipitation of quartz overgrowths, kaolinite, calcite, and Fe-oxides, as well as grain and cement dissolution. The injectite facies locally display textures indicative of fluidized emplacement, such as subvertical orientations of the long axes of sand grains. Together our AMS and petrographic data show these conduits exhibit an overall subvertical uniaxial extension fabric with an indicated upward flow direction. We interpret this to reflect vertical transport of viscous medium during the emplacement process. These data demonstrate the benefits of combined rock magnetic and petrographic studies when evaluating flow dynamics within clastic injectites.