Redefinition of the New Albany Shale of the Illinois basin: An integrated, stratigraphic, sedimentologic, and geochemical study

The results presented in this dissertation directly contradict previous views of the stratigraphy and formation of the Late Devonian New Albany Shale of the Illinois Basin. In the past, the New Albany Shale was thought of as the result of essentially continuous deposition of carbonaceous mud into a largely stratified, anoxic basin over a time span of approximately 20 m.y. Integration of sedimentologic, paleontologic, geophysical, and geochemical observations from one outcrop, three drill cores, and 219 gamma-ray profiles permits a redefinition of New Albany Shale stratigraphy and the establishment of a unified, genetically-based stratigraphic framework. Within this framework, four depositional sequences can be defined, each bounded by laterally extensive erosion surfaces that record considerable truncation and winnowing of underlying strata. Each sequence consists of one to three distinct shale units that have specific lithologic, geophysical and geochemical signatures. Accommodation, the space available for sediment deposition, was influenced by differences in paleotopography, fluctuations in sea level, changes in sediment supply and subsidence, and in turn controlled the formation of each shale unit. Erosional features are common and range from the millimeter to the meter-scale. Together with the depositional sequences they exemplify the discontinuous nature of New Albany Shale deposition.; Integration of observations of sedimentary features in core, outcrop and thin sections, with multiple geochemical and petrographic proxies shows that paleo-redox conditions, rates of primary production, and clastic input varied considerably over time. All of these variables contributed to different degrees at different times to the formation of the New Albany Shale, resulting in multiple black shale types. Optimum organic matter accumulation occurred at intermediate rates of organic production, relatively low to moderate clastic dilution, and strongly oxygen depleted bottom waters.; Following a similar approach, a coherent and genetically-based stratigraphic framework can also be established for correlative black shale successions elsewhere in the eastern U.S. Tight stratigraphic linkage between the various Late Devonian black shale basins, such as the Appalachian, Illinois, and Michigan basins, would help us to better understand the interplay of factors that governed the formation of black shales in each basin.