Biogenic Sedimentation in the eastern equatorial Pacific, 0-18 Ma: XRF scanning on Site U1338, IODP Expedition 320/321
Abstract
The equatorial Pacific is a pelagic region with high primary productivity (~200 gC/m2/yr), the bulk of whose sediments are the remains of plankton. The equatorial Pacific is thus an important region to study how productivity and the carbon cycle evolved through the Cenozoic. We have XRF-scanned the 0-18 Ma sediment sequence from Site U1338, Pacific Equatorial Age Transect (PEAT, IODP exp 320/321). Site U1338 is now located at 2°30’N, 117° 58’W. Ocean crust beneath Site U1338 was formed at the East Pacific Rise at a latitude of about 1°S and has been carried to the northwest by Pacific plate movements. Site U1338 crossed the equator at about 12.5 Ma and left the equatorial zone (within 2° of the equator) at about 3 Ma. It thus records sedimentation within the equatorial zone between 18 Ma and 3 Ma. We were able to core and reassemble an essentially complete sedimentary section for the 0-18 Ma time interval, with an average sedimentation rate of 22.5 m/m.y., ranging between 11 and 37 m/m.y. The XRF-scan chemical information (Al, Si, K, Ca, Ti, Fe, Mn, Ba) defines two major dissolution intervals between 3-4.5 Ma and 9.5-11 Ma, marked by multiple events with low CaCO3 and high clay-associated elements. These carbonate dissolution events have been traced throughout much of the eastern equatorial Pacific in other drillsites with a Miocene carbonate section. Poorer preservation of both CaCO3 and bio-SiO2 can also be found in the top of the U1338 sedimentary section, <4 Ma, as Site U1338 left the equatorial zone of high sediment flux and as the sea floor under Site U1338 deepened. The < 4 Ma interval also has significantly slower sedimentation rates, ~12 cm/kyr vs ~27 cm/kyr immediately below. Moderate increases in biogenic mass accumulation rates are associated with the equator crossing between 13 and 12 Ma. High mass accumulation rates of biogenic sediments, presumably high productivity events, are found in a late Miocene interval between 8 and 6 Ma, and another in a diatom-rich interval between 10 and 11 Ma. Both of these events have been found throughout the eastern equatorial Pacific in drillsites separated by > 3000 km, and thus exhibit both the coherent response and huge length scales of the equatorial Pacific productivity zone.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMPP22B..05L
- Keywords:
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- 3099 MARINE GEOLOGY AND GEOPHYSICS / General or miscellaneous;
- 4912 PALEOCEANOGRAPHY / Biogeochemical cycles;
- processes;
- and modeling;
- 4999 PALEOCEANOGRAPHY / General or miscellaneous