A New Approach for Evaluating Controls on Depositional Sequence Architecture

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Franseen 9527004 For the past decade, concepts of sequence stratigraphy have been applied to studies of carbonate facies. However, in large part, our understanding of the variable that control the location and geometry carbonate depositional sequences are inadequate because of the few studies that are able to isolate these variables. The objectives of this study are to evaluate the effect of variables such as eustatic sea level fluctuation, regional sea level fluctuation, tectonism, substrate paleoslope, leeward versus windward location, siliciclastic input and autogenic controls, by using a unique combination of quantified relative sea level histories, high resolution chronostratigraphic correlations, and selection of localities which allow isolation of different variables. We have selected the Upper Miocene because of exceptional exposures of Upper Miocene carbonate sequences from Mediterranean region. The comparison of shapes and magnitudes of relative sea level fluctuations shown on quantitative relative sea level curves from different areas, combined with field data and high resolution age control from radiometric dating, biostratigraphy and magnetostratigraphy, can provide the detailed data necessary to determine the effects of local, regional and global controls on depositional sequence development. To arrive at the overall goal the proposed project is divided into four phases. Phase I is complete. It was designed to develop a quantitative record of the relative sea level history, chronostratigraphy, and to develop a detailed understanding of the sequence stratigraphy for one locality. It has developed a new method for quantification of relative sea level history (pinning points) based on identification of facies deposited at or just below sea level and on tracing evidence of subaerial exposure on marine rocks down paleoslope. It has also produced a high resolution chronostratigraphy calibrated with radiometric dates. The successful completion of Phase I of this project h as already illustrated significant deviations from commonly accepted sequence stratigraphic models by showing the importance of substrate paleoslope and illustrating that the architecture predicted by the systems tract approach is not applicable. Funding is requested for Phase II and Phase III in this proposal. Phase II will develop the same information as in Phase I in separate localities on the same tectonic block. This information includes geologic mapping, petrography, construction of pinning point curve, magnetostratigraphy, biostratigraphy, and radiometric dating. Time correlation of depositional sequences between the areas will allow the analysis of local variables such as substrate paleoslope, leeward versus windward location, siliciclastic input and autogenic controls while the variable of relative sea level should be held relatively constant because of the location on the same tectonic block. Phase III involves working with other researchers who are studying areas on separate tectonic blocks of the Mediterranean to develop similar quantitative relative sea level histories, chronostratigraphy and sequence stratigraphy in those locations. This comparison will allow analyses of the tectonic effects on relative sea level history and sequence stratigraphy in unites that have experienced the same overall Mediterranean sea level history. Phase IV is the final phase of the study. It will develop similar quantitative relative sea level histories, chronostatigraphy and sequence stratigraphy for sites outside of the Mediterranean to separate local Mediterranean sea level effects from eustatic effects. The purpose of this research is to develop an understanding of the variables that control the location and architecture of carbonate depositional sequences. Thus, the product will be a quantitative understanding of how depositional sequence geometry, location, and facies distribution is controlled by: (1) local variables of paleoslope, autogenic controls, siliciclastic input, and seaw ard versus windward location; (2) regional variables of tectonic controls on accommodation space and Mediterranean sea level, and (3) global sea level. Once the sedimentologic effect of these variables are understood , a better general understanding of the geologic record may be gained, and predictive models may be refined to the point of aiding oil and gas production.