GEOARCHAEOLOGICAL EVALUATIONS OF GEOMORPHIC SURFACES LORETO, BAJA CALIFORNIA SUR, MEXICO

Preliminary results suggest there are at least three geomprohic surfaces in the Loreto area. Remnants of these surfaces are recognized in Arroyo las Parras near its head in the Sierra la Gigantia eastward through Loreto to the Mar de Cortez. The most recognizable (extent, elevation, soil development) is tentatively termed the del Barracho surface. Del Barracho, at higher elevations is defined by a stripped Stage III+ carbonate paleosol. Although not traceable to the sea in Loreto, its elevation above the arroyo floor suggests del Barracho is the terrestrial counterpart of the extensive, 10-12 meter elevation, 125,000 to 145,000 years old Mulege marine terrace. Much less extensive and lower in elevation (~5m above the arroyo floor) is the Aeropuerto surface. Its soil development is weak and exposures are rare. The third surface is the modern Arroyo las Parras alluvium. Tentative hypotheses correlate del Barracho with a late Pinedale interstadial, Aeropuerto with mid-Holocene sea level, and Arroyo las Parras with the late Holocene. The presence of a fourth surface, possibly the Latest Pleistocene glacial sea level, is suggested by an off-shore bench.