New Mexico Geological Society Annual Spring Meeting — Abstracts

In 1970, Robert Zeller (NM Bureau of Mines Bulletin 96) identified as "unnamed Cretaceous? beds" strata exposed east of Hatchita Peak in the Little Hatchet Mountains, especially in sec. 25, T28S, R16W, Hidalgo County. He claimed these strata have a maximum thickness of 500 m and "could [even] represent a northern remnant of a Mexican marine Jurassic formation." Detailed stratigraphy of these rocks indicates a much thinner section (<150 m) composed of four distinct stratigraphic units. The lowest unit is at least 140 m thick and is mostly olive gray and yellowish brown micritic limestone and dolomite strikingly similar to strata of the Permian Epitaph Dolomite that crop out in the nearby Big Hatchet Mountains. The second unit is about 1 m of yellowish gray metaquartzite that in litholqgy, thickness and stratigraphic position can be correlated to the Permian Scherrer Formation in the Big Hatchet Mountains. The third unit is approximately 80 m thick and consists of dark gray micritic limestone and calcareous sandy shale. The fourth unit is the Lower Cretaceous Hell-to-Finish Formation, with its base chosen at the stratigraphically lowest Paleozoic-limestone-cobble conglomerate. The lower 40 m of the Hell-to-Finish Formation are interbeds of this kind of conglomerate with limestones of unit 3 lithology.

Unit 3 lacks macrofOSSils, and efforts to extract palynomorphs proved unsuccessful. The lack of chert and brachiopod fossils make it highly unlikely that unit 3 is the Permian Concha Limestone, which overlies the Scherrer in theI Big Hatchet Mountains. Furthermore, as Zeller noted, unit 3 is interbedded with the lower part of the Lower Cretaceous Hell-to-Finish Formation. This unit 3 may be of Early Cretaceous age, and we consider it a lower, unnamed member of the Hell-to-Finish Formation. Therefore, most of the rocks near Hatchita Peak that Zeller termed Cretaceous? are Permian, but a relatively thin (80 m or less), apparently Lower Cretaceous marine unit is present at the base of the Hell-to-Finish Formation.