| Previously considered a product of continuous deposition, the New Albany Shale has been found to contain multiple erosional surfaces representative of periods of sediment reworking and non-deposition. Correlations of these laterally extensive erosional surfaces were made within the Late Devonian New Albany Shale. Three types of features indicate erosion surfaces: abrupt lithology change, lag deposits, and visible erosional truncation.; Eight cores of New Albany Shale, located in southeastern Indiana along the Cincinnati Arch, were described in great lithologic detail. Correlations were made using stratigraphic columns, gamma ray log motifs, and the distribution of resistant organic macerals (Tasmanites cysts). In this study I examine the depositional environment of the New Albany black shales. The prevailing theory is that a stratified anoxic water column was present during the time of deposition in the Illinois basin. This view is contradicted by observations such as abundant bioturbation in the black shale layers, lag deposits, and erosional surfaces. Cumulatively, these observations point to a depositional environment with a mixed water column that only intermittently may have been anoxic. |
