--> Parasequence variation in the Monterey Formation: Unraveling links between basin evolution and depositional setting

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Parasequence variation in the Monterey Formation: Unraveling links between basin evolution and depositional setting


Sequence stratigraphy has proven to be an invaluable tool for the analysis of coarse-clastic depositional systems and for integrating observations across scales from reflection seismic to SEM. Particularly at the parasequence scale, observations of lithofacies relationships are key for interpretations of depositional environment and understanding depositional systems. Applications to mudstone-dominated depositional sequences have been more limited, despite the fact that mudstones make up more than sixty percent of the sedimentary volume and generally provide the most complete record of sedimentation in a basin. California’s Neogene basins present a unique challenge and opportunity for sequence-stratigraphic analysis. Topographic relief isolated many of the basins and sub-basins from large-scale mainland drainages and their associated clastic-dominated systems. These basins were dominated by hemipelagic sedimentation including a significant biosiliceous component, and thus provide an excellent setting to evaluate the influences of biological productivity and preservation on fine-grained sediment assemblages. The water-depth component of accommodation, which plays a major role in depositional patterns of many clastic-dominated systems, would not be expected to impact slope and basin sedimentation significantly. Thus, consideration of accommodation and base levels are key differences, as are the direct vs. indirect links between nearshore processes and the depositional environments. We use outcrop and subsurface data from the Monterey Formation to characterize parasequences in a variety of margin basin settings (upper and lower slope, axial-basin depocenter) through different periods of basin evolution. Outcrops provide opportunities for direct observation and measurement of strata, but are typically limited in number and represent only part of the stratigraphic column. Subsurface wells are typically more numerous and provide more complete stratigraphic data in the form of continuous well logs. Integrating the data sources at the parasequence scale reveals variations in stratal stacking that characterize different margin-basin environments throughout the depositional sequence, and enhances our understanding of the processes at work. These are important elements in the formation of enhanced depositional models.