AN INTEGRATED SHELF TO BASIN CHEMO- AND CHRONO-STRATIGRAPHIC CORRELATION OF THE BURNT BLUFF GROUP (BBG) CARBONATES, MICHIGAN BASIN, U.S.A
This study integrates core description, energy dispersive x-ray fluorescence spectroscopy (ED-XRF) elemental data, conodont biostratigraphy, strontium (87Sr/86Sr), and carbon isotopes (δ13C) to investigate sequence stratigraphic relationships in the homogeneous lime mudstones of the Burnt Bluff Group (Llandovery, Silurian), Michigan Basin. Systematic variations in continental proxy elements (Al, Si, K, Ti, Zr), which are interpreted to reflect terrigenous input into the basin, can be correlated between the shelf and basin-center. Positive correlations (R2>0.8) between Al-K, Ti-Zr, Al-Si, and Al-Zr are consistent with a continental origin. The covariance between facies and continental proxy element concentrations is interpreted to reflect changes in shore line trajectory, and are used to identify depositional cycles within the BBG.
Three positive carbon isotope (δ13C) excursions (CIEs) were also identified in two shelf-position wells, and one positive excursion in a basin-center well. The three CIEs on the shelf are interpreted as the global Early Aeronian, Late Aeronian, and Valgu events. The age of the positive CIE in the basin center is unknown. Forthcoming conodont and strontium (87Sr/86Sr) data will be used to refine age of the CIEs and thus the stratigraphy of the BBG. This study suggests that integration of various data types can constrain correlations and more specifically depositional cycles in otherwise homogeneous carbonate rocks.