PALEOENVIRONMENTAL AND PALEOCLIMATIC INTERPRETATIONS OF PALEOSPRING DEPOSITS, SOUTHERN KAIBITO PLATEAU, NAVAJO NATION, ARIZONA

Black mats, a generic term referring to dark organic-rich deposits, form in a variety of environments. Previous studies have focused primarily on black mat deposits located in alluvial or lacustrine settings. This study, however, investigates black mats formed within the eolian environment of the Kaibito Plateau. Black mats are relatively common proxy indicators of late Pleistocene mesic conditions across the Southwest. Sedimentologic, micromorphic, and isotopic analyses suggest that these deposits were laid down sometime between about 7,000 and 10,000 years ago during an extended period of increased effective moisture. Confined above a sandstone aquiclude, meteoric water passed through the dune sand as interflow, collected in interdunal depressions, and pooled thus allowing for the deposition of a thick clay bed and dark organic layers. As evaporative processes exceeded precipitation and the water table dropped, a thick dense marl was deposited. Several late Paleo-Indian or early archaic projectile points have been found in association with these black mats. These mesic features represent a dramatically different environment from the windswept arid landscape of the present day Kaibito Plateau.