HR: 1340h
AN: PP23B-1415    [Abstracts]
TI: Patchy deposits of Cenozoic pelagic sediments in the central Pacific
AU: Lyle, M
EM: mlyle@cgiss.boisestate.edu
AF: Boise State University, Center for Geophysical Investigation of the Shallow Subsurface 1910 University Drive, Boise, MS 1536
AU: * Mitchell, N C
EM: neil@ocean.cf.ac.uk
AF: Cardiff University, School of Earth, Ocean and Planetary Sciences, Main Building, Park Place, Cardiff, CF10 3YE United Kingdom
AB: Export of pelagic carbonate tests from surface waters and their deposition at the sea floor plays a significant role in the CO2 cycle and ability of the oceans to absorb atmospheric CO2. Of importance to these, recent sediment 230Th and 3He measurements have been interpreted as evidence that significant lateral advection of pelagic material occurs in the water column, leading to marked spatial variations in deposition rates and in particular to significant focusing of deposits on the Pacific equator. We report spatially continuous stratigraphy from two 1000 km seismic lines which do show evidence of depositional anomalies near the equator. They show accumulation rates locally enhanced by a factor of two, similar to the proposed modern sediment focusing factors, but the anomalies are surprisingly patchy over the 20 Ma period analyzed - they are not confined to an equatorial region and they are not necessarily found on adjacent seismic profiles. These intermediate-scale anomalies are greater than 100 km across and represent areas of seafloor that received more deposits for one period, then less in following periods, and vice versa. Variogram analysis was used to determine how the spatial scales of deposition changed over the Neogene. The period when the spatial scale of depositional variability was largest correlates with hiatuses in drill cores, a correlation that we interpret as caused by enhanced and spatially heterogeneous carbonate dissolution at that time. The study suggests that seismic stratigraphy has the potential to reveal spatial patterns related to unsteady bottom water flow and chemistry.
DE: 4231 Equatorial oceanography
DE: 4267 Paleoceanography
DE: 4558 Sediment transport
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting