Paleogeographic Influences on Sandstone Composition Along an Evolving Passive Margin: An Example from the Basal Chilhowee Group (Uppermost Proterozoic to Lower Cambrian) of the South-Central Appalachians

Abstract

ABSTRACT This study demonstrates the utility of combining numerical analysis and detailed facies analysis to examine the effects of provenance and depositional setting on the composition of ancient sandstone suites from transitional tectonic settings such as those associated with an evolving rifted continental margin. By using factor analysis the relative effects of provenace and depositional setting on sandstone composition can be examined semiquantitatively. This study examines sandstone compositional variation in the lower Chilhowee Group, which records the rift-to-drift transition of the Laurentian-Iapetus margin. Cross plots for each data subset were constructed to reflect stratigraphic position with respect to the fluvial-marine transition, as independently identified from sedimentological criteria, as well as paleogeographic position. The composition of medium-grained sandstones of the basal Chilhowee Group of Tennessee, North Carolina and Virginia mainly reflects the degree of modification of sediment composition by sedimentary processes during transportation. Comparison of petrologic and sedimentologic data from the Tennessee embayment and the Virginia promontory allow inferences on paleogeography. Low-energy, distal fluvial environments dominated in the Tennessee embayment, suggesting an area characterized by low relief. Higher-energy, distal, alluvial-fan environments are limited to the irginia promontory, indicating that this area was a higher-relief terrain than the Tennessee embayment. Source-rock type was apparently similar along the entire margin, although the relative abundance of each lithology was variable. Sandstone composition across the region reflects mainly the effectiveness of fluvial processes in reducing the labile fraction. The boundary between the Tennessee embayment and the Virginia promontory records a fundamental tectonic boundary such that each segment of the margin experienced a unique stratigraphic evolution.