Paper No. 122-0
KEEFER, David K.1, DEFRANCE, Susan D.2, and MOSELEY, Michael E.2, (1) US Geol Survey, 345 Middlefield Rd, Menlo Park, CA 94025-3561,, (2) Anthropology, Univ of Florida, Gainesville, FL 32611

Alluvial fan sediments exposed at the Late Paleo-Indian site of Quebrada Tacahuay on the far south coast of Peru span the time period from the Late Pleistocene through the mid-Holocene. The alluvial fan containing the site heads in a coastal cordillera that contains no evidence of glaciation. Sediments exposed at the site comprise a typical alluvial fan sequence of incised channel-flow, sheetflood, debris-flow and aeolian deposits, with debris-flow deposits dominating. A Late Paleo-Indian period occupation site is embedded within an aeolian layer and radiocarbon dated to between 12,880 and 11,970 cal. yr B.P. (10,770-10,290 14C yr B.P.), which closely corresponds to the time of the Younger Dryas cold period of the Terminal Pleistocene. Sedimentary sequences above and below this occupation horizon are similar to each other, and with two exceptions, indicate that deposition was taking place as a result of infrequent torrential rainfall in an otherwise arid environment, similar to that of the present day. The two exceptions are thick and coarse incised-channel flood deposits, which probably resulted from repeated floods in broad ancestral main channels of the alluvial fan; one of these deposits immediately underlies the Paleo-Indian occupation horizon and may date to the Allerød/Bølling warm period. The other is immediately below the oldest dated layer at the site, an aeolian sand that is 38,200 years old. Otherwise, both above and below the Paleo-Indian occupation layer, the sedimentary sequence up to a date of ca. 8700 cal. yr B.P. (7,920 14C yr B.P.) is dominated by debris-flow deposits with similar characteristics, indicating that environmental conditions at times of deposition were also similar throughout this time period. These characteristics include: (1) matrices composed of silty to occasionally gravelly sand, (2) reddish colors, (1) the lack of any indications of soil development, except for the local paleosol developed over part of one deposit, (2) the lack of evidence of vegetation, except for single roots in each of two deposits, (3) the absence of fine organic material except for that inferred to be of cultural origin, (4) the common development of large and deep desiccation cracks, and (5) the presence of many bodies of aeolian sand, both as infillings within desiccation cracks and as discrete layers.

GSA Annual Meeting, November 5-8, 2001
General Information for this Meeting
Session No. 122
Archaeological Geology and the Pleistocene-Holocene Transition
Hynes Convention Center: 206
8:00 AM-12:00 PM, Wednesday, November 7, 2001

© Copyright 2001 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.