A First Report of the Ichnogenus curvolithus From the Mojado Formation, Cerro De Cristo Rey, Sunland Park, New Mexico.

Abstract

As part of a continuing investigation of trace fossils from the lower-most, Albian Sarten Member of the Mojado Formation, we report the first description of Curvolithus simplex at Cerro de Cristo Rey, Sunland Park, New Mexico. C.simplex is a horizontal, three-lobed trace interpreted as a repichnia. Other traces in this ichnoassemblage that are commonly associated with the Cruziana ichnofacies include Thalassinoides, Arthrophycus, Planolities, scratch marks (and others not yet reported). Our Curvolithus specimensare preserved exclusively in convex epirelief on iron-stained, massive sandstones, interbedded with thin grey shales. At this location the lower contact of the Sarten Member is easily distinguishable from the Mesilla Valley Formation below. Although the base of the Mojado Formation was originally defined arbitrarily by the thickness of sandstone interbeds, or a change in sandstone lithology, we see a distinct change in ichnoassemblages between these two Formations, which may be used to define the contact in the future.