Uranium-series ages of marine terraces, La Paz Peninsula, Baja California Sur, Mexico

Uranium-series dating of coral samples from raised marin terrace deposits between 1.5 and 10 m above sea level in the La Paz Peninsula area, Baja California Sur, yielded ages between 123 ka and 138 ka that are in agreement with previously reported results. The stratigraphy and ages of marine units near the El Coyote Arroyo indicate the presence of two high stands of the sea during the last interglacial or oxygen isotope substage 5e at about 140 ka and 123 ka. Accepting 5 m for the sea level during the last interglacial transgression, we calculate average uplift rates for the marine terraces of about less than or equal to 70 mm/ka and 40 mm/ka. These slow rates of uplift indicate a relative stability of the La Paz peninsula area for the past 140,000 years. In contrast, areas of Baja California affected by major faults experienced higher rates of uplift. Rockwell et al. (1987) reported vertical uplift rates of 180 to 300 mm/ka at Punta Banda within the Aqua Blanca fault zone in northern Baja California.