Understanding the Monterey Formation and Similar Biosiliceous Units across Space and Time
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The Monterey Formation is a Miocene marine unit that occurs extensively in the Coast Ranges and in the continental margins of California, and analogous biosiliceous deposits are found around the Pacific Rim and elsewhere in the world. Classic studies on the diatomaceous deposits that characterize the hemipelagic/pelagic facies of the Monterey Formation have been key to understanding the oceanographic and tectonic conditions that lead to the preservation of large volumes of organic-rich hemipelagic biosiliceous sediments, and the properties of these sedimentary deposits once they convert into rocks. This volume presents a collection of recent studies on the Monterey and other similar biosiliceous deposits that offer modern and updated interpretations of this classic unit and its analogues. The volume is dedicated to the memory of Professor Bob Garrison.
An observational approach to mudstone sequence stratigraphy: The Monterey Formation of California
Published:September 26, 2022
Jon R. Schwalbach, Kevin M. Bohacs, 2022. "An observational approach to mudstone sequence stratigraphy: The Monterey Formation of California", Understanding the Monterey Formation and Similar Biosiliceous Units across Space and Time, Ivano W. Aiello, John A. Barron, A. Christina Ravelo
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Sequence stratigraphy has proven to be an invaluable tool for the analysis of coarse-clastic depositional systems and the integration of observations across scales from reflection seismic to scanning electron microscope. Applications to mudstone-dominated depositional sequences have been more limited, despite the fact that mudstones make up more than 60% of the global sedimentary volume and generally provide the most complete record of sedimentation in a basin.
During the late 1970s and through the 1980s, Bob Garrison and his students at the University of California–Santa Cruz conducted numerous studies that revealed the basic sedimentary and stratigraphic framework of the Monterey Formation in California, advancing our understanding of the sedimentary processes at work in these deep-margin basins. We expanded on that framework using direct observations from outcrops and cores that have been integrated with other subsurface data, as well as a wide variety of information derived from paleontologic, chronostratigraphic, geochemical, and compositional analyses to illustrate a sequence-stratigraphic approach to interpreting fine-grained rocks and their associated depositional systems in these settings. These were some of the earliest investigations of mudstone sequence stratigraphy focused on slope and basinal environments.
In this study, observations from outcrops in the Pismo Basin, California, provided the basis for developing a detailed sequence-stratigraphic framework for the Monterey Formation, expanding on the broad-scale characterization of Garrison and his colleagues. These outcrops represent deposition during different phases of basin evolution and in different borderland-type basin settings (slope and basin depocenters). Comparison of coeval strata from different depositional settings and locations documented variation at both the sequence and parasequence scale. Variation of parasequence character, in particular, provided a valuable tool for enhanced understanding of deposition and diagenesis in these margin basins. Extrapolation to the subsurface using gamma-ray logs greatly enhanced basinwide application compared to limited, partial-stratigraphic-section outcrops, and it facilitated the lateral characterization of mudstone depositional sequences. These elements served as the building blocks for improved models of deposition in margin-basin settings.
- clastic rocks
- depositional environment
- Monterey Formation
- Pismo Basin
- San Luis Obispo County California
- sedimentary rocks
- sequence stratigraphy
- stratigraphic units
- United States
- well logs
- Shell Beach California
- Point Buchon California