LACUSTRINE DEPOSITIONAL ENVIRONMENTS OF THE PLIO-PLEISTOCENE MANGAS BASIN, SOUTHWESTERN NEW MEXICO

In the shadow of the Mogollon Mountains, to the east, and Burro Mountains, to the west, lies the Pliocene-Early Pleistocene Mangas Basin a north-northwest trending basin in southwestern New Mexico. This basin is a full graben in the northern section and changes to an eastward-tilted half graben in the southern section. During the Pliocene-Early Pleistocene the Mangas Basin contained a southwest flowing axial fluvial system which drained into a closed lake, located near present day Buckhorn, NM. Approximately 200m of fluvial and lacustrine sediment, the Gila conglomerate, filled the basin. Post-Pliocene erosion due to the Gila River and Rio San Francisco has exposed all or part of the Gila conglomerate within the Mangas Basin. The conglomerate consists of fluvial interbedded pebbly sandstones and mudstones in the northern part of the basin and interbedded tuff and lacustrine sandstones, mudstones, limestones, and chert in the southern part of the basin. Research in this area is limited to vertebrate paleontology and diagenesis with reverence to alteration by zeolites and Magadi-type chert.

The focus of this research is on the southern part of the basin containing lacustrine sediment. This study will provide sedimentology and sequence stratigraphy of the lacustrine sediments and determine the geochemistry of the lake.