Accordingly, five sites were drilled down the spine of the Blake Nose, a salient on the margin of the Blake Plateau where Paleogene and Cretaceous sediments have never been deeply buried by younger deposits. The Blake Nose is a gentle ramp extending from ~1000 to ~2700 m water depth, and is covered by a drape of Paleogene and Cretaceous strata that are largely protected from erosion by a thin veneer of manganiferous sand and nodules. We recovered a record of the Eocene period that is nearly complete except for a few short hiatuses in the middle Eocene. The continuous expanded records show Milankovitch-related cyclicity that provides the opportunity for astronomical calibration of at least parts of the Eocene time scale, particularly when combined with the excellent magnetostratigraphic record and the presence of both calcareous and siliceous microfossils. The chemistry of the well-preserved calcareous microfossils will be used to document climate variability when the Earth's climate switched from a greenhouse to an icehouse state.
Leg 171B successfully recovered a suite of critical events in Earth's history that includes the late Eocene radiolarian extinction, late Paleocene benthic extinction, the K/T boundary, the mid Maastrichtian event, and several episodes of organic-rich sediments in the Albian warm period. The upper Paleocene benthic foraminifer extinction occurs within an expanded interval of calcareous sediments unlike most regions of the Atlantic Ocean where calcareous fossils have been severely dissolved just above the extinction horizon. The K/T boundary was recovered at three sites, each with a biostratigraphically and magnetostratigraphically complete sequence that includes the earliest part of the aftermath of the Late Cretaceous extinctions. We managed to recover three copies of the boundary interval at one site in a section that includes a 10- to 17-cm-thick spherule bed, a rusty brown limonitic layer, a dark gray clay bed (planktonic foraminifer Zone P0), and white ooze that represents planktonic foraminifer Zone Pa.
To 171B Introduction
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