Cyclic Carbonates and Vail-Sequences on Carbonate Platforms:A Field and Modelling Study

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We will to log in detail, and test for evidence of cyclicity, classic stratigraphic sections in the Late Cambrian and Mississippian of the western U.S. We will examine how the 1 to 10 m cycles may be packaged into larger scale (1 to 10 m.y. duration) Vail-type sequences, utilizing a new application of a technique first used by Fischer (1964), to define short term changes in relative sea level. The technique provides a powerful, objective method of defining eustatic vs. subsidence effects at 1 to 10 m.y. scale, and allows recognition of sequence boundaries in cyclic carbonates. We will run 1-dimensional computer simulations of the stratigraphic sequences logged in the field, and 2-dimensional simulations to generate stratigraphic cross-sections that may be compared with actual cross-sections showing meter scale, vertical as well as lateral changes in rock types. Our models are capable of utilizing complex sea level curves to generate isostatically balanced, simulated stratigraphic sections and cross-sections showing rock changes at the meter-scale, necessary for a study of carbonate cycles. We will perform spectral analysis on deeper water facies in the sequences to determine if there is any record of Milankovitch climatic changes in the deeper water facies. The computer simulations will be constrained with geological data. This approach should provide us with a much firmer understanding of how carbonate cycles are arranged on carbonate platforms, how they are packaged in Vail-sequences, and how the various types of allocyclic and autocyclic mechanisms control their development in the Paleozoic. Research will document the effects of climatic and sea level change on the accumulation of sedimentary rocks.