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.
Gamma-ray attenuation bulk density as an indicator of diatom valve abundance and fragmentation in Pleistocene biosiliceous sediments of the Bering Sea
*E-mails: mkdrake@ucsc.edu; iaiello@mlml.calstate.edu
*E-mails: mkdrake@ucsc.edu; iaiello@mlml.calstate.edu
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Published:September 26, 2022
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CiteCitation
Michelle K. Drake*, Ivano W. Aiello*, A. Christina Ravelo, 2022. "Gamma-ray attenuation bulk density as an indicator of diatom valve abundance and fragmentation in Pleistocene biosiliceous sediments of the Bering Sea", 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
Multisensor track measurements are a nondestructive method to produce continuously measured high-resolution physical property data sets that are a great asset to a wide range of research, including geotechnical studies and paleoceanography. Interpretation of these physical property data can be challenging because they are typically influenced by multiple variables. This paper specifically focuses on the interpretation of gamma-ray attenuation (GRA) data (a proxy for sediment bulk density) in biosiliceous sediments. The Bering Sea is a basin dominated by biosiliceous sediment, and the late Pleistocene to present core record of Sites U1340 and U1339, drilled during Integrated Ocean Drilling Program (IODP) Expedition 323, has subtle meter-scale changes in the concentration of fine-grained siliciclastic sediment that produce lithologic alternations between diatom ooze and diatom mud. We produced a detailed sedimentologic data set that combined smear slide petrography, scanning electron microscopy, and grain-size analysis for both Sites U1340 and U1339 and correlated it to shipboard GRA bulk density measurements. Results show that bulk density is negatively correlated with diatom abundance and positively correlated with the fragmentation of diatom valves. This study argues that diatom abundance and fragmentation influence sediment packing and drive down-core variability in GRA bulk density. Therefore, denser diatom mud is a result of tightly packed, highly fragmented diatom valves, and diatom ooze is a less dense sediment dominated by whole and less fragmented diatom valves. We suggest that GRA data can be used as a proxy for diatom abundance and an indicator of diatom fragmentation. We include a discussion of how these results may impact the interpretation of ancient bedded siliceous rocks.
- algae
- attenuation
- Bering Sea
- biogenic processes
- Bowers Ridge
- bulk density
- Cenozoic
- clastic sediments
- cores
- diatoms
- electron microscopy data
- Expedition 323
- gamma rays
- grain size
- Integrated Ocean Drilling Program
- IODP Site U1339
- IODP Site U1340
- microfossils
- North Pacific
- Northwest Pacific
- ooze
- Pacific Ocean
- paleo-oceanography
- particles
- physical properties
- Pleistocene
- Quaternary
- sedimentary rocks
- sediments
- SEM data
- siliceous composition
- textures
- upper Pleistocene
- West Pacific
- non-destructive methods