Marine Aragonite Sea-Floor Growths and Cements in Permian Phylloid Algal Mounds, Sacramento Mountains, New Mexico

Abstract

ABSTRACT A heretofore undocumented example of aragonite botryoid formation on the sea floor is described from shallow-water Wolfcampian (Permian) phylloid algal mounds in the Sacramento Mountains of New Mexico. The cores of these mounds consisted of botryoidal aragonite masses that stood in low relief on the sea floor. The upward growth and coalescence of these masses created a solid, anastomosing framework of inter-botyroid and internal cavities that were simultaneously filled with marine sediment and aragonite fan cements. The resulting inorganic boundstone became the substrate for later phylloid algal mound development. Subsequent algal colonization and contemporaneous aragonite precipitation also resulted in the development of a mixed inorganic-organic facies wherein algal blades are encas d in marine aragonite. Former aragonite constitutes from 50-85% of the total mound rock. The core facies of these inorganic reefs are texturally and, most probably, genetically similar to the many Paleozoic mudmounds throughout the world known variously as Waulsortian mounds. Stromatactis reefs, and zebra limestones. The former marine aragonite is represented by divergent-radial mosaics of coarsely crystalline calcite pseudospar that commonly are replaced by ferroan baroque dolomite. This pseudospar occurs as ray-crystals and composite crystals with included relicts of the precursor fibrous aragonite. This species of calcite is distinct from the radiaxial-fibrous mosaics that commonly replace acicular carbonate fabrics. Mineralogic stabilization of the aragonite to calcite via paramorphic inversion is believed to have occurred in the subaerial environment, with recrystallization to pseudospar occurring in the subsurface. Unresolved problems include the mechanics of fabric-retentive stabilization diagenesis of this aragonite, and the apparent anomaly of aragonite abundance in contrast to Holocene reefs, in which Mg-calcite is the dominant cement mineralogy.