Deposional environment of the Cable Canyon Sandstone: A mid-Ordovician sandwave complex from southern New Mexico
Lawrence Bruno and Henry S. Chafetz
The Cable Canyon Sandstone was deposited as a sandwave complex that began during the initial stages of a marine transgression. The sandstone forms a roughly symmetrical "teardrop" or lobe that is eight to 13 m thick along its northwest-southeast-trending axis which extends for nearly 150 km; away from this axis, the sandstone gradually thins to less than one meter over a distance of about 120 km. The unit has a conspicuous marine fauna and consists primarily of medium-grained quartz sandstone with a carbonate (mostly dolomite) matrix. In general, the Cable Canyon is coarsest where thickest, and in most cases grain size increases from the base to the middle of the unit, and then decreases from the middle to the top. These coarse siliciclastics must have been deposited by traction transport processes; however, pervasive bioturbation has destroyed most primary sedimentary structures. Where these primary sedimentary structures have been preserved, they display, from bottom to top: ( I) a burrowed zone, 0.6 to 1.0 m thick, with beds and lenses of quartzarenite intercalated with dolomicrite, (2) 0.5 m of medium-scale, trough cross-stratified, coarse-grained sandstone, (3) large-scale, 1.0 to 1.8 m high, lenticular foresets that have small-scale, tabular foresets (which dip in the opposite direction) near their base and (4) 0.5 m of poorly preserved, thin, planar(?), horizontal bedding. This sequence of sedimentary structures indicates that the sandstone was deposited by strong, persistent, highly asymmetrical currents, in waters at least five to 15 m deep. The currents formed subaqueous dunes of quartz sand, analogous to modern sandwave complexes.
- Bruno, Lawrence; Chafetz, Henry S., 1988, Deposional environment of the Cable Canyon Sandstone: A mid-Ordovician sandwave complex from southern New Mexico, in: Cretaceous and Laramide tectonic evolution of southwestern New Mexico, Mack, G. H.; Lawton, T. F.; Lucas, S. G., New Mexico Geological Society, Guidebook, 39th Field Conference, pp. 127-134.