PROVENANCE OF SEDIMENTS IN THE WADESBORO TRIASSIC SUB-BASIN: USING MAGNETIC MINERAL SEPARATION TO INVESTIGATE CHANGES IN SEDIMENT PROVENANCE DURING BASIN EVOLUTION

The Wadesboro sub-basin, which together with the Sanford and Durham sub-basins comprise the Deep River Group, is a clastic sedimentary half-graben basin that formed during late Triassic rifting of Pangea. During early stages of basin growth, sediment was likely derived only from the adjacent basin margins and deposited in alluvial fans. As the Wadesboro sub-basin continued to grow both in volume and axial extent it may have linked with the Sanford sub-basin to the northeast (Schlische 1993). This linkage may have caused the Wadesboro sub-basin to transition from a closed to open basin with an axial fluvial system transporting sediments along the length of the combined basins (Gore 1988). The combined sediment load likely was derived from a wider range of source rocks than supplied the alluvial fans during the early stages of filling the Wadesboro sub-basin when it was a closed basin. Magnetic mineral analysis using a Frantz magnetic barrier separator has been used to test the linkage hypothesis. This method classifies mineral assemblages on the basis of their magnetic properties. In this study we examined separates of clastic sediments that range from 125 µm to 250 µm indiameter (Rosenblum 1958). Fine-grained sandstones were sampled from across the basin to provide a representative cross section of the stratigraphy exposed at the surface. Several magnetic mineral assemblage facies were identified and the fluctuations in the abundance of those facies are interpreted as changes in sediment provenance during basin filling, consistent with a transition from closed to open basin conditions as the Wadesboro sub-basin linked with the Sanford sub-basin.