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 between 18 and 16 Ma. The base of the Monterey does not mark a silica shift in diatom deposition from the North Atlantic to the North Pacific. Rather, a North Atlantic decline of diatoms after ~13 Ma and increasing divergence in nutrient levels between the North Atlantic and North Pacific between ~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 on offshore banks during a period of higher sea level, as inland sections commonly contain thick sequences of diatomaceous sediment. Increasing latitudinal thermal gradients in the latest Miocene, which triggered a biogenic bloom in the equatorial Pacific at 8 Ma, also lead to enhanced diatom deposition in the uppermost Monterey and overlying biosiliceous rocks. Uplift of the California coastal ranges after ~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 at ~4.6 Ma caused a drastic reduction of diatoms in sediments of offshore southern California.
Citation Information
Publication Year | 2022 |
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Title | A refined assessment of the paleoceanographic and tectonic influences on the deposition of the Monterey Formation in California |
DOI | 10.1130/2022.2556(06) |
Authors | John A. Barron |
Publication Type | Book Chapter |
Publication Subtype | Book Chapter |
Series Title | Special Papers of the Geological Society of America |
Index ID | 70232232 |
Record Source | USGS Publications Warehouse |
USGS Organization | Geology, Minerals, Energy, and Geophysics Science Center |