New Mexico Geological Society Annual Spring Meeting — Abstracts

Upper Permian beds in east-central and central New Mexico are characteristically fine-grained clastics, evaporites and carbonates, attesting to little tectonic activity in the region during their deposition. Accumulation of lowermost Triassic units generally occurred on a very low-relief Permian surface that had not been previously deformed during the hiatus represented by the Permian/Triassic unconformity. These conclusions are evidenced by a general lack of coarse-grained facies within the lowest Triassic (including Moenkopi strata southeast of Socorro), shallow or no Triassic scouring below this horizon and upper Permian sandstone and stromatolite marker beds that can be traced laterally for several kilometers. Exceptions exist in the vicinity of Santa Rosa where angular unconformities occur at the bottom of the Triassic as well as basal syntectonic conglomerates present in this area and west of Yeso.

Post-Triassic deformation appears to have followed pre-existing structural trends. A notable example is a belt of northeast-trending and southeast-trending thrusts paralleling the Sierra Grande Arch. Lineaments interpreted from remote sensing imagery reflect well the regional structural grain, which also strongly influenced the distribution of karst features. Sinks typically are areally controlled by intersecting northeast and northwest-oriented lineaments.

A preliminary study of geographically wide-scattered thermal maturation data indicates, because of elevated values, that upper Permian and lower Triassic rocks were once covered by thick deposits. Presumably, these were mostly Cretaceous geosynclinal strata.