Paper No. 10
Presentation Time: 4:20 PM
HIGH-RESOLUTION CORRELATION AND SEDIMENTOLOGY OF CARBONATE-SHALE CYCLES IN THE TYPE CINCINNATIAN (UPPER ORDOVICIAN; KATIAN): IMPLICATIONS FOR A REVIVED "LAYER CAKE STRATIGRAPHY"
BRETT, Carlton E., Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013, DATTILO, Benjamin F., Department of Geosciences, Indiana University Purdue University, Fort Wayne, IN 46805, MCLAUGHLIN, Patrick I., Bedrock Division, Wisconsin Geological and Natural History Survey, 3817 Mineral Point Rd, Madison, WI 53705-5100 and SCHRAMM, Thomas J., Department of Geology and Geophysics, Louisiana State University, E235 Howe-Russell Geoscience Complex, Baton Rouge, LA 70803, brettce@ucmail.uc.edu
Strata of the type Cincinnatian Series form an exemplar of the denigrated notion of “layer cake stratigraphy”; Edward Oscar Ulrich, founder of the “Cincinnati School” of paleontology (ca. 1910s), argued that the stratigraphic record is composed of stacks of continuous, far-traceable layers. This view was fostered by observations of limestone-shale strata, then-exposed on the hillsides and riverbanks of Cincinnati. Subsequently, most geologists rejected this notion and favored a “mosaic” view of strata as local patches, based on studies of modern marine environments. Cincinnati reference sections such as those of Eden and Fairview Parks are now largely overgrown or under concrete. However, new construction has provided sections far more complete than the original outcrops, which demonstrate nearly bed-for-bed matches over the outcrop region and into the subsurface.
Moreover, the typical assumption that shell rich limestones were produced by intervals of local storm winnowing is rejected based on a variety of data: a) limestone bundles splay up-ramp and become highly condensed down-ramp; b) many beds are not winnowed and may contain micritic matrix; c) shell concentrations of background sediments demonstrate that formation of shell beds by winnowing alone would require removal of 10s of meters of mud; d) mudstones also show abundant storm deposition/erosion features; e) shell-rich limestones are associated with concretions and hardgrounds suggesting sediment starvation. A model involving periodic sediment starvation, coupled with storm processing better explains these observations. These findings are of key importance in: a) establishing new, well-documented reference sections for the type Cincinnatian; b) providing a resounding counter to the “mosaic” view and re-establishing a very detailed “layer-cake”; and c) providing data for an evolving view of the stratigraphic record as the response to widespread climatic/sea-level cycles and regional scale catastrophes.
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