SYNOPSIS OF LEG 199 DRILLING

Eight sites were drilled during Leg 199 to study the Eocene (Table T1; Figs. F2, F3; see Lyle, Wilson, Janecek, et al., 2002, for more detail). Seven of these (Sites 1215, 1216, 1217, 1219, 1220, 1221, and 1222) were located on crust thought to be of late Paleocene age, to target the P/E boundary, also known as the PETM. Of these, Site 1216 was abandoned before reaching basement because of an extensive chert section encountered in the sediment section, and the age of basement was ambiguous at Site 1222. Sites 1217 and 1219 were situated on crust that was slightly too young to contain the P/E boundary section, but the P/E boundary interval was recovered at Sites 1215, 1220, and 1221. All of these sites contain important sediment columns dating from the early Eocene through the Oligocene. An additional site, Site 1218, was drilled on 42-Ma crust to study the late Eocene and the Eocene–Oligocene transition in more detail.

The sediments drilled across the Paleogene equatorial transect fall into the following five broad lithochronostratigraphic units (Fig. F2):

  1. A surficial clay unit, sometimes containing a basal radiolarian ooze, with a basal age ranging from middle Miocene in the south of the transect (Site 1218) to early–middle Eocene in the north (e.g., Sites 1215 and 1216);
  2. A nannofossil ooze/chalk unit whose base is at the E/O boundary and whose top is of early Miocene age in the south (Sites 1218 and 1219) and Oligocene age in the central part of the transect (Sites 1217, 1220, 1221, and 1222); Oligocene–Miocene carbonates are nonexistent in the north (Sites 1215 and 1216);
  3. A middle–upper Eocene radiolarian ooze and radiolarian clay that is present at all sites except those in the north (Site 1215 and 1216);
  4. A lower middle–lower Eocene unit composed of cherts, clays, and radiolarian ooze that is present in varying thicknesses at all Leg 199 sites along the 56-Ma transect except Site 1215 in the extreme north; and
  5. A lower Eocene–upper Paleocene nannofossil ooze or chalk resting upon basalt basement that is recovered at all sites (except Site 1222, where cherts overlie basement, and Site 1216, where the relevant stratigraphic interval was not drilled).

Because of plate tectonics, each site drifted northwestward from the equatorial zone of high productivity as the crust aged. Sites 1215, 1216, and 1217 were always sited north of the equator, with Site 1215 found at ~12N at the Paleocene/Eocene boundary, Site 1216 at 9N, and Site 1217 at 5N (see supplementary table of site positions in Lyle et al., this volume). The remainder of the sites passed through the equatorial zone, 2 of the equator. The position of the sites with respect to the paleo-equator is fundamental to their lithologic history, and their northward passage out of the high-productivity zone is an important factor marking the top of the Oligocene–Miocene carbonates. The top of the carbonates occurs in the upper Miocene at the southern sites and in the Oligocene in the north. Periods when carbonates were deposited are also defined by global changes in the carbonate compensation depth (CCD) (Rea and Lyle, 2005; Shipboard Scientific Party, 2002), to be discussed in more detail later.

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