1. Interpret the vertical structure of the Paleogene oceans and test the Warm Saline Deep Water hypothesis near the proposed source areas, with a related objective to provide critically needed low-latitude sediments for interpreting tropical sea-surface temperature (SST) and climate cyclicity in the Paleogene.
We recovered sediments of Eocene through middle Cretaceous age that form a drape over the Blake Nose. We were able to obtain depth transects of 600- to 700-m water depth in the middle and upper Eocene, and 1200 m in the Danian, the Maastrichtian, and the Cenomanian-late Albian. Sediments of all these ages contain well-preserved calcareous microfossils suitable for geochemical and paleontological study of the vertical structure of the ancient oceans. Furthermore, cyclostratigraphy expressed in color, magnetic susceptibility, and downhole logging data suggest that the duration of magnetozones and biochrons in much of the Paleogene section can be partially tuned to an astronomical time scale. The upper middle Eocene, upper Eocene and the Danian contain particularly well developed cyclic records.
2. Recover complete Paleocene/Eocene and Cretaceous/Paleogene boundaries along a depth transect to describe the events surrounding the boundaries and water depth-related changes in sedimentation of the boundary beds.
We had spectacular success recovering five copies of the K/T boundary at three sites along the Blake Nose transect. Cores at Site 1049 will become classic examples of K/T boundary stratigraphy and micropaleontology, as they contain well-preserved microfossils, an unusually thick ejecta deposit, and a well-preserved record of the repopulation of the world's oceans after one of the largest extinctions to sweep the Earth. We also recovered a complete, or nearly complete record of the upper Paleocene benthic foraminifer extinction. This horizon was complete at only one site, but the sediments retain a record of calcareous microfossils, cyclostratigraphy, and magnetostratigraphy that will greatly advance our knowledge of an event that is represented by unconformities at nearly all sites in the Atlantic Ocean.
3. Interpret the thermocline and intermediate water structure of the low-latitude Cretaceous oceans and refine the biochronology and magnetochronology of this period.
Cores of Maastrichtian chalks and ooze are sufficient for detailed studies of the late Maastrichtian cooling and mid-Maastrichtian extinction event. Likewise, Site 1052 recovered a superb record of lower Cenomanian/upper Albian laminated sediments and well-preserved microfossils that will be used for studies of surface water temperatures during the middle Cretaceous warm period and the paleoceanography of the 'Oceanic Anoxic Events.' Finally, the excellent preservation of both nannofossils and planktonic foraminifers throughout the Aptian, Albian, and Cenomanian will lead to significant improvements in our understanding of the diversity and evolution of these microfossil groups.
4. Study the rate and mode of evolution of marine biota in the Cretaceous and Paleogene oceans.
Leg 171B recovered very well preserved calcareous microfossils, siliceous microfossils, and ammonites suitable for evolutionary and paleoecological study. Fossil material for the middle and late Eocene, Danian, Maastrichtian, and mid Cretaceous (Cenomanian-Aptian) is typically very well preserved. Both radiolarians and calcareous microfossils are abundant and well preserved throughout the middle and upper Eocene and will be used to improve our biochronology as well as in analyses of the evolution of these groups in relation to the upper Eocene meteorite impacts and the long-term Paleogene cooling trend. Foraminifers and diatoms are well preserved in the Danian, and the calcareous fossils all have excellent records across the K/T boundary. The boundary sections we recovered contain much more expanded records of the immediate aftermath of the K/T extinction than have been recovered before by deep-sea drilling. The Maastrichtian section is notable for a striking record of the mid-Maastrichtian extinction, which is marked by an abrupt change in bioturbation intensity and the disappearance of the inoceramid bivalves. The preservation of foraminifer assemblages in the Cenomanian and Albian is amazingly good and will be used in paleoceanographic studies, as well as analyses of paleoecology and depth habitats. Ammonites are frequently preserved in the Albian sequence with the original aragonitic shell and will be used to integrate ammonite and planktonic microfossil biochronologies as well as biogeographic studies.
5. Investigate plate motions using the paleomagnetic signal.
Shipboard data on Cretaceous magnetostratigraphy strongly suggest that the established polar wander path for North America requires fundamental revision. We have increased the number of measurements of middle Cretaceous paleomagnetic poles by a factor of more than 100. Data for the Eocene were not processed shipboard, but we collected oriented cores at all the sites that will be used to greatly improve the polar wander fits for the Eocene.
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