Early Ordovician Greenhouse to Late Ordovician Glacial Transition: Effect on the Cyclic Sedimentary Record, Kentucky-Virginia

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9316057 Read This proposal request funds to study superb outcrops and the extensive core collections of Middle and Late Ordovician rocks in Kentucky so that we can compare them with the Early Ordovician strata, to search for the stratigraphic evidence of possible change from low amplitude eustasy of Early Ordovician greenhouse times to possible higher amplitude eustasy developed during Late Ordovician Gondwana glaciation. We presently have a very large data base on Early Ordovician and Middle Ordovician rocks characteristic of greenhouse conditions, that will serve as a basis for comparison with the younger units. We propose to log bed-by-bed the later Middle and Late Ordovician carbonates and shales which appear to have developed on storm-dominated ramps, documenting any peritidal and shallow to deeper water subtidal cycles, their degree of lateral continuity, their stacking patterns and relation to depositional sequences, and bounding surfaces. We will also examine the cycles for evidence of: 1. long term climate change and 2. evidence of short term emergence (including paleosols, erosion surfaces, negative departures of stable isotope profiles, and meteoric cementation); all these might become more pronounced if glacially driven sea level amplitudes increased into the Late Ordovician. Using detailed regional cross sections of cyclic lithofacies, we will define depositional sequences, and document the relationships and timing of bounding surfaces to the tectonic history of the foreland basin, including peripheral bulge development and prograding clastic rocks along the tectonically active proximal margin. Finally, we will computer model the cycles and the depositional sequences to better constrain the roles of tectonism, low- and high- frequency eustasy, and sediment supply. Defining the stratigraphic signature of greenhouse to global glacial conditions appears to hold the key for a future more detailed global climate subdivision of the Phanerozoic than h as been attempted.