Mid- to Late-Wisconsin Pollen Record of San Felipe Basin, Baja California

Abstract

A lacustrine sequence from Laguna Seca San Felipe, Baja California, in the southwestern Sonoran Desert, provides the first record of mid- to late-Wisconsin vegetation in one of the driest regions of North America. Pollen analysis was performed in the intermediate part of the sequence from ca. 44,000 to ca. 13,000 14C yr B.P. according to six 14C radiocarbon dates. Sedimentation of eolian sands prior to 44,000 14C yr B.P. indicates dry conditions. High pollen concentration of montane and chaparral species in the pollen assemblages contrast with the modern desert vegetation. Sixty-four pollen types were identified. The source of mid- to late-Wisconsin sedimentation must have been the plant communities in the surrounding highlands of the basin. Mid-Wisconsin pollen assemblages dominated by pines, junipers, and Artemisia reflect humid conditions in the area. By late Wisconsin time, a significant increment in junipers indicates a lowering in the altitudinal ranges of woodlands/chaparral. Pollen from wind-pollinated species is abundant while desert plants, specifically animal or insect pollinated species, are poorly represented. The San Felipe record does not identify the Last Glacial Maximum as the time of greatest effective moisture, as suggested by pluvial lake levels and other paleoclimatic evidence in the soutwestern United States.