Late Quaternary Environmental Change in the Bonneville Basin, Western USA
Palaeogeography, Palaeoclimatology, Palaeoecology 167 (2001) 243±271 www.elsevier.nl/locate/palaeo Late Quaternary environmental change in the Bonneville basin, western USA D.B. Madsena,*, D. Rhodeb, D.K. Graysonc, J.M. Broughtond, S.D. Livingstonb, J. Hunta, J. Quadee, D.N. Schmitta, M.W. Shaver IIIa aUtah Geological Survey, Salt Lake City, UT 84116, USA bDesert Research Institute, Reno, NV 89512, USA cUniversity of Washington, Seattle, WA 98195, USA dUniversity of Utah, Salt Lake City, UT 84102, USA eUniversity of Arizona, Tucson, AZ 85721, USA Received 9 December 1999; received in revised form 24 July 2000; accepted for publication 7 September 2000 Abstract Excavation and analyses of small animal remains from strati®ed raptor deposits spanning the last 11.5 ka, together with collection and analysis of over 60 dated fossil woodrat midden samples spanning the last 50 ka, provide a detailed record of changing climate in the eastern Great Basin during the late Pleistocene and Holocene. Sagebrush steppe dominated the northern Bonneville basin during the Full Glacial, suggesting that conditions were cold and relatively dry, in contrast to the southern basin, which was also cold but moister. Limber pine woodlands dominated ,13±11.5 ka, indicating increased dryness and summer temperatures ,6±78C cooler than present. This drying trend accelerated after ,11.5 ka causing Lake Bonneville to drop rapidly, eliminating 11 species of ®sh from the lake. From ,11.5±8.2 ka xerophytic sagebrush and shadscale scrub replaced more mesophilic shrubs in a step-wise fashion. A variety of small mammals and plants indicate the early Holocene was ,38C cooler and moister than at present, not warmer as suggested by a number of climatic models.
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