PALEOGEOGRAPHIC INFLUENCES ON SANDSTONE COMPOSITION ALONG AN EVOLVINGPASSIVE MARGIN - AN EXAMPLE FROM THE BASAL CHILHOWEE GROUP (UPPERMOSTPROTEROZOIC TO LOWER CAMBRIAN) OF THE SOUTH-CENTRAL APPALACHIANS

This study demonstrates the utility of combining numerical analysis an d detailed facies analysis to examine the effects of provenance and de positional setting on the composition of ancient sandstone suites from transitional tectonic settings such as those associated with as evolv ing rifted continental margin. By using factor analysis the relative e ffects of provenance and depositional setting on sandstone composition can be examined semiquantitatively. This study examines sandstone com positional variation in the lower Chilhowee Group, which records the r ift-to-drift transition of the Laurentian-Iapetus margin. Cross plots for each data subset were constructed to reflect stratigraphic positio n with respect to the fluvial-marine transition, as independently iden tified from sedimentological criteria, as well as paleogeographic posi tion. The composition of medium-grained sandstones of the basal Chilho wee Group of Tennessee, North Carolina and Virginia mainly reflects th e degree of modification of sediment composition by sedimentary proces ses during transportation. Comparison of petrologic and sedimentologic data from the Tennessee embayment and the Virginia promontory allow i nferences on paleogeography. Low-energy, distal fluvial environments d ominated in the Tennessee embayment, suggesting as area characterized by low relief. Higher-energy, distal, alluvial-fan environments are li mited to the Virginia promontory, indicating that this area was a high er-relief terrain than the Tennessee embayment. Source-rock type was a pparently similar along the entire margin, although the relative abund ance of each lithology was variable. Sandstone composition across the region reflects mainly the effectiveness of fluvial processes in reduc ing the labile fraction. The boundary between the Tennessee embayment and the Virginia promontory records a fundamental tectonic boundary su ch that each segment of the margin experienced a unique stratigraphic evolution.