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.
Refined assessment of the paleoceanographic and tectonic influences on the deposition of the Monterey Formation in California
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Published:September 26, 2022
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CiteCitation
John A. Barron, 2022. "Refined assessment of the paleoceanographic and tectonic influences on the deposition of the Monterey Formation in 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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ABSTRACT
Application of updated diatom biochronology to the Monterey Formation and related biosiliceous rocks reveals the imprint of both global paleoclimatic/paleoceanographic and regional tectonic events. A rise in global sea level combined with regional tectonic deepening associated with the development of the transform California margin resulted in the abrupt onset of deposition of fine-grained Monterey sediments that were relatively free from clastic debris between 18 and 16 Ma. The base of the Monterey Formation does not mark a silica shift in diatom deposition from the North Atlantic to the North Pacific Ocean. Rather, a North Atlantic Ocean decline of diatoms after ca. 13 Ma and increasing divergence in nutrient levels between the North Atlantic and North Pacific Oceans between ca. 13 and 11 Ma coincided with a major enhancement of diatom deposition in the Monterey Formation. A stratigraphically condensed interval of phosphate-rich sediments between 13 and 10 Ma in coastal southern California appears to have resulted from sediment starvation in offshore basins during a period of higher sea level, as inland sections such as those in the San Joaquin Valley commonly contain thick sequences of diatomaceous sediment. Increasing latitudinal thermal gradients in the latest Miocene, which triggered a biogenic bloom in the equatorial Pacific Ocean at 8 Ma, also led to enhanced diatom deposition in the uppermost Monterey Formation and overlying biosiliceous rocks. Uplift of the California coastal ranges after ca. 5.2 Ma resulted in an increasing detrital contribution that obscured the presence of diatoms in onshore sediments. Major reduction in coastal upwelling in the early Pliocene ca. 4.6 Ma then caused a drastic reduction of diatoms in sediments offshore southern California.
- algae
- Atlantic Ocean
- biogenic processes
- California
- carbon dioxide
- Cenozoic
- climate change
- Coast Ranges
- diatoms
- lower Pliocene
- microfossils
- Miocene
- Monterey Formation
- Neogene
- North Atlantic
- North Pacific
- Pacific Ocean
- paleo-oceanography
- paleoclimatology
- paleoenvironment
- Pliocene
- San Joaquin Valley
- sea-level changes
- silica
- siliceous composition
- stratigraphic units
- tectonics
- Tertiary
- United States
- uplifts
- upper Miocene
- upwelling