We identify four major seismostratigraphic units based on reflection packages in the Paleogene sediment column from the central tropical Pacific Ocean by utilizing the site survey for Ocean Drilling Program Leg 199. These units appear to be isochronous and regionally traceable and probably have paleoceanographic significance. We describe and name these seismic horizons and show characteristics that should help identify them. The full Paleogene stratigraphic sequence is almost never present at any given location. In fact, Site 1219 is the only drill site where we have identified all the seismic horizons. The older reflectors disappear to the east because of the younging of basement. To the north, younger seismic horizons cannot be found because of the increasing age of biogenic sediments immediately below the surficial red clay. North of ~15°N, the fossiliferous sediment sequence is early Oligocene or older. We also found it more difficult to identify the reflector sequence from drill sites sited on 56-Ma crust than those on 40-Ma crust because greater offsets along normal faults are present in the region of the older transect. We suspect the major plate reorganization at the time of magnetic reversal C22n (~49-50 Ma) may be responsible in part for the observed faulting at the older sites.
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2Center for Geophysical Investigation of the Shallow Subsurface, Boise State University, Boise ID, 83725, USA. Correspondance author: mlyle@cgiss.boisestate.edu
3Department of Geoscience, University of Michigan, Ann Arbor MI, 48109, USA.
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