PALEOSOLS AND PALEOCLIMATE EVOLUTION, DURHAM 
SUB-BASIN, NORTH CAROLINA

	COFFEY, Brian P., Department of Geological Sciences, 	
		Virginia Polytechnic Institute and State University, 
		Blacksburg, VA  24061-0404
	TEXTORIS, Daniel A., Department of Geology, University of 
		North Carolina, Chapel Hill, NC  27599

Paleosols are increasingly more useful in deriving information about 
paleoclimates.  While ancient soils are commonly used to interpret 
paleoclimatic conditions for a given time, less research has been 
conducted on changes in paleosol horizons in a basin over a time 
interval.  This approach has been taken for the Late Triassic (Carnian) 
Durham sub-basin in central North Carolina.
	Other research within the wet equatorial to dry subtropical 
deposits of the Newark basins of eastern USA indicates a climatic 
transition.  For the Durham sub-basin, this could be a 5 degree shift 
from 10 up to 15 degrees north latitude.  Such changes have been 
attributed to northwest movement of the North American Plate in 
response to the break-up of Pangea.  This tectonism is also the 
accepted cause for the formation of the failed rift basins.
	By comparing paleosol horizons, which formed in mudstones 
of floodplain origin, across the sub-basin from west to east (oldest to 
youngest), changes in paleoclimate are evident.  Features commonly 
found in these predominantly grayish-red to pale red mudstones are 
structures resulting from bioturbation such as mottles and swirls, peds 
due mainly to brecciation caused by shrinkage and swelling of clays, 
and calcite (with less common hematite) nodules due to action 
movement by groundwater and evaporation.  Types of caliche, and 
possibly clay mineralogy, serve as the primary climatic indicators.  
Calcite crusts and nodules become increasingly more common and 
complex to the east (youngest), implying drier conditions.  
Easternmost paleosols are also associated with playa deposits of 
seasonal sands and muds, with periods of limestone and chert 
precipitation.  The most common mature paleosols are calcisols and 
vertisols.  Western paleosols are older stratigraphically and resemble 
argillisols which formed in a more humid paleoclimate.