ODP925: Marine record ODP925

In mcrucifix/pleistocene: Datasets of glacial cycles (ice and ocean)

Description

Benthic forams in Marine record ODP925 from Leg 154, Ceara Rise, Hole C

Usage

data(ODP925)

Format

	A data frame on the following variables.
Site	Site Number (here 925)
Hole	Hole Number (here C)
Core	Core Number (here 1)
Type
Sect
Top
mcd	mean sample core depth
d18O	d18O (per mil)
d13C	d13C (per mil)
species	benthic species only
Age	Age model according to Bickert et al., (see ref. below)

Details

Core recovery ( Oldest sediment cored: Depth (mbsf): 54.50 Nature: clayey nannofossil ooze with foraminifers Age: late Pliocene Measured velocity (km/s): 1.6 Principal results: Site 925 is the shallowest of the depth transect of sites on the Ceara Rise. The site is located beneath warm surface waters that have a mean temperature around 27 deg C. The seafloor at a depth of 3040 m is bathed by North Atlantic Deep Water (NADW) well above the carbonate lysocline. The site was chosen to provide material for investigating the geological history of surface- and deep-water properties in the region. Five holes were drilled at Site 925. Hole 925 A was cored with the RCB from 303.7 to 930.4 mbsf, with spot cores between 101.8 and 110.0 mbsf and between 197.9 and 207.5 mbsf. The hole was logged from 300 to 907 mbsf. Hole 925B was cored with the APC from the mud line to 318.0 mbsf. Hole 925C was cored with the APC from the mud line to 321.5 mbsf and then with the XCB to 360.1 mbsf. Hole 925D was cored with the APC from 2.5 to 354.0 mbsf to ensure complete recovery of the section and to provide sufficient core material for high-resolution, shore-based investigations. Hole 925E was cored with the APC from the mud line to 54.5 mbsf, primarily to provide material for high-resolution interstitial-water sam- pling. Detailed comparisons between the magnetic susceptibility records generated on the MST track, and high-resolution color reflectance gener- ated using a hand-held Minolta color analyzer, demonstrated that the sedimentary sequence to 370 mbsf had been completely recovered. In the composite section that was generated for the site, the deepest part (about 320-360 mbsf) was based on parallel cores recovered using three different drilling methods: APC, XCB, and RCB. The segments recovered by the RCB are so good that they make up a unique yardstick against which the distortions generated by APC and XCB coring may be evaluated. In Site 925 was the shallowest of a transect of sites drilled on the Ceara Rise (see fig. 2, "Introduction" chapter, this volume). The site is in an area of uniform relief; hydrosweep bathymetry coverage shows a range of only 20 m for several kilometers in all directions around the site (Fig. 1). The seismic section (Fig. 2) includes an upper layered sequence down to about 0.3 s (200 m); a middle more seismically incoherent unit between about 0.3 and 0.9 s (300-800 m); a unit with some parallel reflectors between 0.9 and 1.3 s (800-1300 m); and a fairly prominent reflector at around 1.3 s (1300 m) that appears to represent the base of the pelagic section. The deepest objective of drilling, time permitting, was to sample this reflector at 1300 m in the hope that it would provide constraints on the depth history of the rise. Drilling to this depth would also provide information on the nature of the rise soon after it was formed (e.g., whether it was subaerially exposed or covered by reefs). Above that reflector our aim was to recover the entire stratigraphic sequence so that we could obtain mate- rial useful for investigating the history of surface paleoceanography of the region as well as data from the shallowest member of a depth transect designed to record the detailed history of changes in deep- water physical and chemical properties in the western North Atlantic Ocean. We were particularly concerned about obtaining a truly com- plete section, with abundant material available for high-resolution sampling, of the uppermost part of the sediment column. We aimed to sample this upper section in triplicate with the APC to provide the means for high resolution investigation of the whole of the late Neo- gene. Oceanographic conditions in this region have probably been directly affected by the closure of the Panama Isthmus and uplift of the Andes during this time, in addition to having been affected by the globally pervasive effect of increased glaciation. The sediments were also expected to preserve a detailed history of the transport of ter- rigenous matter to the Atlantic Ocean by the Amazon River.

Note

See also the paper : Ramp functions regression: a tool for quantifying climate transitions

Source

Courtesy of F. Bassinot.

References

Shipboard Scientific Party, 1995. Site 925. In Curry, W.B., Shackleton, N.J., Richter, C., et al., Proc. ODP, Init. Repts., 154: College Station, TX (Ocean Drilling Program), 55-152. doi:10.2973/odp.proc.ir.154.104.1995. See http://www-odp.tamu.edu/publications/citations/cite154.html for complete list of scientific-result citations and references, and for notification of use of the present data.

Time scale: T. Bickert, W.B. Curry, and G. Wefer , 16. Late Pliocene to Holocene (2.6-0 ma) western equatorial atlantic deep-water circulation: inferences from benthic stable isotopes, in Shackleton, N.J., Curry, W.B., Richter, C., and Bralower, T.J. (Eds.), 1997 Proceedings of the Ocean Drilling Program, Scientific Results , Vol. 154 , pp. 239–253, http://www-odp.tamu.edu/publications/154_SR/16_CHAP.PDF

Examples

data(ODP925)
with(ODP925,plot(Age,d18O))

mcrucifix/pleistocene documentation built on May 22, 2019, 3:20 p.m.