Start |Author Index | View Uploaded Presentations | Meeting Information

2007 GSA Denver Annual Meeting (28–31 October 2007)

Paper No. 5
Presentation Time: 8:00 AM-12:00 PM

FLUVIAL SYSTEMS AND CARBONATE NODULES REVEAL LATE PERMIAN CLIMATE CHANGE AT WAPADSBERG PASS, EASTERN CAPE PROVINCE, SOUTH AFRICA


REID, Samuel B., Department of Geology, Department of Geology, Colby College, 5800 Mayflower Hill, Waterville, ME 04901, GASTALDO, Robert A., Department of Geology, Colby College, 5800 Mayflower Hill Drive, Waterville, ME 04901, NEVELING, Johann, Council for Geosciences, Private Bag x112, Pretoria, 0001, South Africa and TABOR, Neil, Department of Geological Sciences, Southern Methodist University, P.O. Box 750395, Dallas, TX 75275-0395, sbreid@colby.edu

Changes in late Permian climate are crucial to understand the dynamics responsible for the end Paleozoic mass extinction. The Karoo Basin, South Africa, has been the focus for documenting terrestrial ecosystem response because of Permian and Triassic rocks that cross the purported boundary. The present study builds on previously reported stratigraphy at outcrops exposed in Wapadsberg Pass near Graaff Reinet, Eastern Cape province.

The R61 roadcut consists of interfluvial and fluvial deposits of aggradational and degradational landscapes. Floodplain aggradation includes fining-upward sequences of fine sand and silt in m-scale beds. Weakly developed paleosols are identified by vertical to sub-vertical rhizoconcretions and/or horizons of calcite-cemented nodules. Meandering rivers represent initiation of degradational processes and include basal channel deposits of fine-to-medium Qtz-wackes in lenticular geometries. Channels fills consist of either sandstone bar forms and/or siltstone plugs of abandonment. Landscape equilibrium is demonstrated by rooted paleosols and an autochthonous forest litter.

Stable isotope values from carbonate-cemented concretions show a positive δ13C excursion to -5.7 PDB in paleosols ~60 m below the P/T boundary without significant deviation in δ18O SMOW values. Subsequently, δ13C values become more negative upsection reaching -14.9 at the P/T boundary. These trends are interpreted to represent a change from increasingly seasonal to more wetland conditions in the latest Permian. There is no significant change in δ18O SMOW values.

Climate trends based on stable isotope data are augmented by physical stratigraphy. Meandering channel fills are characterized by multiple, stacked paleosols within abandoned channels, indicating the presence of ephemeral conduits and dramatic swings in seasonality. These data may support an overall drying trend in the latest Permian, although wetlands play more of a role in the landscape than previously recognized.

Session No. 28--Booth# 152

T54. Late Paleozoic Glacial-interglacial Climate Changes: Analogs for Present and Future Climate Changes (Posters)
Sunday, 28 October 2007: 8:00 AM-12:00 PM
Geological Society of America Abstracts with Programs. Vol. 39, No. 6, p.85
© Copyright 2007 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.
Back to: T54. Late Paleozoic Glacial-interglacial Climate Changes: Analogs for Present and Future Climate Changes (Posters)
<< Previous Abstract | Next Abstract >>