On the preservation of laminated sediments along the western margin of North America

Publication Type  Journal Article
Year of Publication  2003
Authors  van Geen, A.; Zheng, Y.; Bernhard, J. M.; Cannariato, K. G.; Carriquiry, J.; Dean, W. E.; Eakins, B. W.; Ortiz, J. D.; Pike, J.
Journal Title  Paleoceanography
Volume  18
Issue  4
Pages  -
Journal Date  Dec 18
ISBN Number  0883-8305
Accession Number  ISI:000187859900004
Key Words  oxygen-minimum zone; laminations; bioturbation; deglaciation; california margin; santa-barbara basin; oxygen-minimum zone; gulf-of-california; marine-sediments; late pleistocene; varve formation; el-nino; paleoceanographic significance; climate oscillatio
Abstract  

Piston, gravity, and multicores as well as hydrographic data were collected along the Pacific margin of Baja California to reconstruct past variations in the intensity of the oxygen-minimum zone (OMZ). Gravity cores collected from within the OMZ north of 24degreesN did not contain laminated surface sediments even though bottom water oxygen (BWO) concentrations were close to 5 mumol/kg. However, many of the cores collected south of 24degreesN did contain millimeter- to centimeter-scale, brown to black laminations in Holocene and older sediments but not in sediments deposited during the Last Glacial Maximum. In addition to the dark laminations, Holocene sediments in Soledad Basin, silled at 290 m, also contain white coccolith laminae that probably represent individual blooms. Two open margin cores from 430 and 700 m depth that were selected for detailed radiocarbon dating show distinct transitions from bioturbated glacial sediment to laminated Holocene sediment occurring at 12.9 and 11.5 ka, respectively. The transition is delayed and more gradual (11.3-10.0 ka) in another dated core from Soledad Basin. The observations indicate that bottom-water oxygen concentrations dropped below a threshold for the preservation of laminations at different times or that a synchronous hydrographic change left an asynchronous sedimentary imprint due to local factors. With the caveat that laminated sections should therefore not be correlated without independent age control, the pattern of older sequences of laminations along the North American western margin reported by this and previous studies suggests that multiple patterns of regional productivity and ventilation prevailed over the past 60 kyr.

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URL  <Go to ISI>://000187859900004
DOI  Doi 10.1029/2003pa000911