Isotopic and rock magnetic expression of environmental change at the Pleistocene–Holocene transition in the central Great Plains

Abstract

Abstract In a region too dry for the effective use of the traditional palynological approach, loess deposits of the central Great Plains offer a source of proxy information for the reconstruction of past climates. The Brady soil, a ubiquitous feature developed within the uppermost, late-Pleistocene Peoria loess, recorded the character of vegetation change associated with climate shifts during the Pleistocene–Holocene transition. Stable carbon isotope ratio analysis and two, room-temperature magnetic parameters were used to examine the nature of the change during this period. δ 13 C values derived from soil organic matter indicate that in the late Pleistocene minor populations of drought tolerant (C4) plants were interspersed among the dominant cool-season grasses (C3) in the west, while C3 grasses were accompanied by trees in the east. By the early Holocene, C4 grasses were the dominant vegetation in the west and contributed substantially to the δ 13 C signal in the east. Magnitude of the δ 13 C shift suggests an increase in July mean daily temperature of 8–10°C, according to existing models. Magnetic susceptibility and frequency dependence signal the cessation of loess deposition and development of the Brady soil, and indicate a spatial pattern in the intensity of weathering across the region.