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  • 2009: PEAT

IODP 320&321: "Pacific Equatorial Age Transect (PEAT)"

Expedition co-chiefs: Heiko Pälike, Hiroshi Nishi, Mitch W. Lyle, Isabella Raffi
Expedition staff scientists: Adam Klaus, Kusali Gamage
IODP Page for Expeditions 320 & 321

Listen to the co-chiefs about the Science Background on YouTube.

A press release about a recent Article in Nature is here. Heather Stoll wrote a nice News and Views piece.

Summary:
Integrated Ocean Drilling Program Expedition 320/321, "Pacific Equatorial Age Transect" (Sites U1331–U1338), was designed to recover a continuous Cenozoic record of the equatorial Pacific by coring above the paleoposition of the Equator at successive crustal ages on the Pacific plate. These sediments record the evolution of the equatorial climate system throughout the Cenozoic. As we gained more information about the past movement of plates and when in Earth's history "critical" climate events took place, it became possible to drill an age transect ("flow-line") along the position of the paleoequator in the Pacific, targeting important time slices where the sedimentary archive allows us to reconstruct past climatic and tectonic conditions. The Pacific Equatorial Age Transect (PEAT) program cored eight sites from the sediment surface to basement, with basalt aged between 53 and 18 Ma, covering the time period following maximum Cenozoic warmth, through initial major glaciations, to today. The PEAT program allows the reconstruction of extreme changes of the calcium carbonate compensation depth (CCD) across major geological boundaries during the last 53 m.y. A very shallow CCD during most of the Paleogene makes it difficult to obtain well-preserved carbonate sediments during these stratigraphic intervals, but Expedition 320 recovered a unique sedimentary biogenic sediment archive for time periods just after the Paleocene/Eocene boundary event, the Eocene cooling, the Eocene–Oligocene transition, the "one cold pole" Oligocene, the Oligocene–Miocene transition, and the middle Miocene cooling. Expedition 321, the second part of the PEAT program, recovered sediments from the time period roughly from 25 Ma forward, including sediments crossing the Oligocene/Miocene boundary and two major Neogene equatorial Pacific sediment sections. Together with older Deep Sea Drilling Project and Ocean Drilling Program drilling in the equatorial Pacific, we can delineate the position of the paleoequator and variations in sediment thickness from ~150°W to 110°W longitude.
Pälike, H., Nishi, H., Lyle, M., Raffi, I., Gamage, K., Klaus, A., and the Expedition 320/321 Scientists, 2010. Expedition 320/321 summary. In Pälike, H., Lyle, M., Nishi, H., Raffi, I., Gamage, K., Klaus, A., and the Expedition 320/321 Scientists, Proc. IODP, 320/321: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.320321.101.2010

Location map of IODP Expeditions 320 & 321 in the equatorial Pacific (between Hawaii and Mexico)

Location of IODP Expedition 320 & 321 drill sites

Plate tectonics and site locations

One of the main principles behind the success of the Expeditions has been the theory of Plate Tectonics. The animation linked on the right shows a reconstruction back in time of where our eight drill sites were: Originating in the equatorial region, and then slowly moving towards the north-west due to the plate motion of the Pacific. At the same time, the basalt underneath the slowly accumulating sediment at each site subsided due to cooling of the originally hot sea-floor by sea water.

PEAT: Scientific drilling targets

The PEAT science program was designed to achieve an age transect along the Pacific paleoequatorial region that spans the early Eocene through middle Miocene periods. Time intervals that were covered by previous ODP legs (particularly ODP 199 and 138) can be integrated with the current transect's results in order to achieve a nearly complete time series. Drill sites target specific time slices of interest (see figure on right) at locations that provide optimum preservation of calcareous sediments. The overall aim is to obtain a continuous well-preserved sediment section that will address the following primary scientific objectives (of equal priority):
  • To document the nature of calcium carbonate dissolution and changes of the CCD over the Cenozoic
  • To determine the evolution of paleoproductivity of the equatorial Pacific during the Cenozoic
  • To validate and extend the astronomical calibration of the geological timescale for the Cenozoic using orbitally forced variations in sediment composition known to occur in the equatorial Pacific
  • To determine temperature (sea surface and benthic), nutrient profiles, and upper water column gradients
  • To improve, date, and intercalibrate bio- and magnetostratigraphic datums at the Equator
  • To improve constraints on the motion of the Pacific plate and the Cenozoic equatorial region, primarily using paleomagnetic methods
  • To make use of the high level of correlation between tropical sediment sections and existing seismic stratigraphy to develop a more complete model of equatorial circulation and sedimentation in the Pacific
additional objectives include also:
  • To provide information about rapid biological evolution and turnover rates during times of climatic stress
  • To improve our knowledge of the reorganization of water masses as a function of depth and time, as our strategy also provides a paleodepth transect
  • To develop a limited north–south transect across the paleoequator, caused by the northward offset of the proposed sites by Pacific plate motion and providing additional information about north–south hydrographic and biogeochemical gradients
  • To obtain a transect of mid-ocean ridge basalt (MORB) samples from a fixed location in the absolute mantle reference frame
  • To use a transect of basalt samples erupted along a flow line in similar environments to study low-temperature alteration processes
IODP Expeditions 320 & 321 relied on a large and excellent team of scientists, technicians, and crew on the Joides Resolution to achieve our aims.