The Effect of Relative Sea Level Change on the Development of Phylloid Algal Bioherms, Laborcita Formation (Lower Permian), Sacramento Mountains, New Mexico
Ian T. Gordon
The Lower Permian Laborcita Formation, northern Sacramento Mountains, New Mexico, contains spectacular exposures of phylloid algal bioherms interbedded with siliciclastics. My objective is to determine the stratigraphic context of these buildups with respect to relative sea level change. Previous studies of similar buildups indicate that they formed during sea level highstands.
Sections were measured from a thick conglomeratic red bed through the bioherm exposures to the base of Abo Formation red beds. The basal unit is a conglomeratic red bed interpreted as a fluvial system. This basal conglomerate is succeeded by shelf siltstones interbedded with three discrete biolithite layers, which in turn are covered by prodelta siltstones coarsening upwards into delta front sandstones. The subsequent layer is a prominent, continuous, white micrite. This is superseded by heterogeneous, laterally discontinuous, interbedded carbonates and siliciclastics, which form the base of the phylloid algal bioherms. The bioherms are covered by another prodelta siltstone coarsening upwards into a delta front sandstone. This delta is succeeded by red beds interbedded with two discre e wackestone layers. The wackestones contain black carbonate lithoclasts, which are interpreted as shallow-water carbonates.
The phylloid algal bioherms formed during a period of relative sea level highstand. Highstand units are bounded by subaerial exposure surfaces and red beds. Given the extensive updip presence of fan deltas in the Laborcita, the dominant mechanism controlling facies succession is interpreted as autocyclic lobe shifting.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California