Community succession in small bioherms of algae and sponges in the Lower Permian of New Mexico

Abstract

Small organic mounds outcrop in the Lower Permian Laborcita Formation of the northern Sacramento Mountains of southcentral New Mexico. These small organic structures, up to I'm in height and 3 m in diameter, are unique because they show a well developed vertical biolic zonation. This zonation consists of an initial pioneer community composed of small digitate or plumose colonies of algae and foraminifers (Stage 1). This is followed by a climax community that is first dominated by laminar colonies of the red alga Archaeolithophyllum (Stage 2). and followed by a terminal community composed of minor Archaeolithophyllum, erect heliosponges and brachiopods, dominated by the form Composita (Stage 3). Evidence suggests that the mounds initially developed in shallow water within an open lagoon but. with continued transgression and rapid deepening of the depositional environment. the biota responded to the changes. The organic buildups were killed off by sudden influx of clastics from a tectonically active nearby landmass.