On the preservation of laminated sediments along the western margin of North America
Paleoceanography
By: A. VanGeen, Yen Zheng, J.M. Bernhard, K.G. Cannariato, J. Carriquiry, W.E. Dean, B.W. Eakins, J.D. Ortiz, and J. Pike
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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 24??N did not contain laminated surface sediments even though bottom water oxygen (BWO) concentrations were close to 5 ??mol/kg. However, many of the cores collected south of 24??N 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. Copyright 2003 by the American Geophysical Union.
Suggested Citation
VanGeen, A., Zheng, Y., Bernhard, J., Cannariato, K., Carriquiry, J., Dean, W., Eakins, B., Ortiz, J., Pike, J., 2003, On the preservation of laminated sediments along the western margin of North America: Paleoceanography, v. 18, no. 4, p. 22-1.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | On the preservation of laminated sediments along the western margin of North America |
| Series title | Paleoceanography |
| Volume | 18 |
| Issue | 4 |
| Year Published | 2003 |
| Language | English |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | Paleoceanography |
| First page | 22 |
| Last page | 1 |