Abstract

Marine limestones within the upper member of the Late Pennsylvanian Hermosa Formation were sites of evaporite growth that took place during episodes of subaerial exposure. Evidence of former evaporites includes presence of length slow chalcedony and inclusions of evaporite crystals as well as the mimicking of the morphology of the nodule and crystal form of evaporites. Botryoidal, chert-lined vugs represent silicified anhydrite nodules. Pseudomorphs of evaporite crystals are present within nodular chert and are abundant within some burrows systems. The distribution and form of chert suggests that evaporites also precipitated within preexisting desiccation fissures and formed fibrous veins by displacive crystal growth. The most convincing evidence that evaporite growth was responsible for these features is the presence of gypsum in several chert-lined vugs and in several fissures. In all cases, the site of former evaporite growth is within several meters of overlying eolian deposits which give independent evidence of subaerial exposure.