Pleistocene-early holocene climate change: Chronostratigraphy and geoclimate of the Southeast US

Abstract

The purpose of this chapter is to relate the paleo-water table proxy derived from the radiometrically dated stratigraphic units at the Page-Ladson site with late glacial environmental subphases. This study of time, stratigraphy, and paleoclimate includes consideration of: (1) Aspects of the geology and geomorphology of the lower, karst section of the Aucilla River basin, including its tributary, the Wacissa River. (2) Documented evidence of global and regional late Pleistocene climate change through time. (3) Chronostratigraphy and paleoclimate of the Southeast US as determined by the well-dated stratigraphic sequence from the Page-Ladson site. (4) Correlate the global and regional records with those of the paleoclimate data from the Page-Ladson site as a means of developing a geoclimatic record for the Southeastern US. The Page-Ladson site provides a highly stratified sediment column over 6 m deep that spans the period of the late glacial recession. Because many of the sediment levels were originally deposited in a wetland or underwater setting and much of the geologic history of that sediment column remained wet despite two episodes of subaerial exposure, the organic material necessary for obtaining high-quality radiocarbon dates survived and 104 dunbar provided the means to establish chronology. A total of 48 radiocarbon dates have been run on samples collected from seven stratigraphic units. In many, but not all cases, each stratigraphic unit consists of several distinct levels. The levels within a unit are associated by their similar composition (e.g. calcareous silt matrix) compared to the level or levels in the units directly above and below them (silt versus peat versus colluvium). Units are numbered inversely to their age with Unit 1a and 1b being the oldest and Unit 7 the youngest. The upper and lower age range of each stratigraphic unit is noted as are its total number of radiometric dates from each unit. Where appropriate, suites of statically related radiocarbon dates were averaged (see Tables 5.3-5.5). The geologic interpretation of each unit as compiled by Kendrick (Chapter 3) of the Aucilla River Research Project will be reviewed to provide additional information (e.g. where there are conformable and nonconformable contacts and information related to depositional history).