A multi-basin redox reconstruction for the Miocene Monterey Formation, California, USA

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doi: 10.1016/j.palaeo.2019.01.031
Author(s): Hancock, Leanne G.; Hardisty, Dalton S.; Behl, Richard J.; Lyons, Timothy W.
Author Affiliation(s): Primary:
University of California at Riverside, Department of Earth Sciences, Riverside, CA, United States
Michigan State University, United States
California State University at Long Beach, United States
Volume Title: Palaeogeography, Palaeoclimatology, Palaeoecology
Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Vol.520, p.114-127. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0031-0182 CODEN: PPPYAB
Note: In English. 110 refs.; illus., incl. geol. sketch map
Summary: Deposition of the Miocene Monterey Formation into numerous basins provides an ideal opportunity to study how preservation of geochemical signatures varies within and among basins as a function of local and global climatic and oceanic conditions. This study presents commonly employed redox indicators, including iron (Fe) speciation and redox-sensitive trace metal concentrations (Mo, U, V), to constrain paleoredox conditions from three Monterey locations: the Santa Barbara Basin, the Santa Maria Basin, and the San Joaquin Basin. The Fe speciation geochemistry of the Santa Barbara and Santa Maria Basin sediments are consistent with a wide range of redox conditions from suboxic to euxinic. These results, in combination with associated phosphorites and trace metal enrichment patterns, indicate oscillatory redox conditions, perhaps with a chemocline that fluctuated above the sediment-water interface on seasonal or multi-year timescales. Overall, these sections were deposited in environments similar to modern phosphorite-forming and upwelling-dominated oxygen minimum zone settings like the Peru Margin. Geochemical evidence indicates that the San Joaquin Basin was generally more restricted and more stably anoxic compared to the other two basins, perhaps more analogous to the modern Cariaco Basin, at least for the studied interval. Iron speciation in the San Joaquin Basin reveals anoxia and euxinia over the entirety of the studied interval, although trace metal concentrations are generally at the low end of those typical of anoxic/euxinic conditions-consistent with a restricted connection with the open ocean. The one exception is an interval c. ∼11.6 million years ago (Ma) with elevated concentrations of redox-sensitive elements that may represent a decrease in basin restriction or an increase in water column sulfide concentrations. The present-day California Margin does not achieve euxinic conditions in similar basinal settings comparable with these Monterey sections, suggesting fundamental differences for the Miocene California margin that may carry implications for global-scale oxygen deficiency in Miocene oxygen minimum zones.
Year of Publication: 2019
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Actinides; Aluminum; Basins; C-13/C-12; California; Carbon; Cenozoic; Cores; Depositional environment; East Pacific; Eh; Expedition 321; Expeditions 320/321; IODP Site U1338; Integrated Ocean Drilling Program; Iron; Isotope ratios; Isotopes; Langhian; Leg 184; Metals; Middle Miocene; Miocene; Molybdenum; Monterey Formation; Naples Beach; Neogene; North Pacific; Northeast Pacific; Northwest Pacific; ODP Site 1146; Ocean Drilling Program; Pacific Equatorial Age Transect; Pacific Ocean; San Joaquin Basin; Santa Barbara Basin; Santa Maria Basin; Sedimentary basins; Serravallian; South China Sea; Stable isotopes; Tertiary; Thorndyke core; Tortonian; Trace metals; Union Leroy core; United States; Upper Miocene; Uranium; Valency; Vanadium; West Pacific
Coordinates: N192724 N192724 E1161622 E1161622
N023028 N023028 W1175811 W1175811
N363000 N365500 W1193500 W1200000
N344000 N354000 W1194500 W1210000
Record ID: 2019046632
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands