The LPTM interval was recovered at Site 999 (Kogi Rise in the Colombian Basin) and Site 1001 (lower Nicaraguan Rise) (Fig. 1A).
The crest of the Kogi Rise at 2800 m water depth lies ~1000 m above the turbidite-laden floor of the Colombian Basin. A complete, almost 1067-m-thick sequence of largely pelagic/hemipelagic sediments from the Maastrichtian to the Pleistocene was recovered at Site 999 (Sigurdsson, Leckie, Acton, et al., 1997). Upper Paleocene and lower to middle Eocene sediments consist of clayey calcareous limestones, clayey calcareous mixed sedimentary rocks with some interbedded ash layers, and nearly pure claystones. The sediments are slightly to moderately bioturbated. Only a few millimeter-thick volcanic ash layers were identified. Sedimentation rate at Site 999 is 32.2 m/m.y. over the interval that includes the LPTM (Sigurdsson, Leckie, Acton, et al., 1997).
Site 1001 is located on the lower Nicaraguan Rise in 3259 m water depth. The Neogene cap is thin, and a continuous Paleocene to Upper Cretaceous sequence was recovered from 165 to 485 mbsf. The upper Paleocene to middle Eocene sediments are primarily composed of calcareous chalk with foraminifers and mixed sedimentary rocks with clay and minor chert and volcanic ash layers. Sedimentation rate for the latest Paleocene and earliest Eocene interval is 37.4 m/m.y. (Sigurdsson, Leckie, Acton, et al., 1997). The upper Paleocene sediments at Site 1001 are characterized by more pronounced pure limestone or claystone end members, whereas at Site 999, the sediments are generally dominated by the mixed clayey calcareous sediment types and pure end members are less represented.
Benthic foraminifer assemblages indicate a lower-bathyal to upper-abyssal (1500-2500 m) late Paleocene water depth for Site 999; and Site 1001 was toward the lower end of this range. Paleomagnetic studies indicate that both sites were closer to the equator in the late Paleocene (~10°N) (Sigurdsson, Leckie, Acton, et al., 1997; Acton et al., Chap. 9, this volume) and Site 999 was more proximal to the Central American Arc (Fig. 1B).
These sites provide a unique data set for examining lithologic variability around the LPTM and the relationship to physical and chemical properties determined by logging. Prior to Legs 165 and 171B the majority of drill sites penetrating upper Paleocene sections either did not obtain any downhole logging data (e.g., Sites 690 and 865) or very limited downhole data in high latitude and shallow marine environments. For example, only natural gamma-ray downhole logs for the Paleocene-Eocene interval were described for a well in the North Sea by Knox (1996) and Neal (1996). In contrast to most other deep-sea sites sampling this interval, sediments and logs obtained from Holes 999B, 1001A, and 1001B provide a complete record of the LPTM, and along with Site 865 in the Western Pacific and Leg 171B sites in the Western Atlantic, also provide relatively rare high-resolution records of low-latitude deep-sea Paleogene stratigraphy (e.g., Bralower et al., 1995; Norris, Kroon, Klaus, et al., 1998).
Because of the relatively wide lithologic range consisting of the end members: nannofossil foraminifer limestones, clays, and volcanic ashes, and in combination with the incomplete recovery, we undertook a high-resolution investigation of physical and chemical properties of both the recovered cores and of the borehole wall using standard and high-resolution downhole logs. The LPTM interval in the cores of Holes 999B, 1001A, and 1001B consists of 0.3-0.97-m-thick clay-rich horizons with significantly lower carbonate contents compared to the surrounding chalks, limestones, and clayey calcareous mixed sediments with some ash layers (Sigurdsson, Leckie, Acton, et al., 1997). Because of the high burial depth (~975 mbsf), the LPTM cores of Hole 999B are relatively lithified (porosity of 22%-27.5%, P-wave velocity of 3.1-3.5 km/s) and contain less water (8.5-11.8 wt% water). The LPTM Cores 165-1001A-27R and 165-1001B-6R, drilled on the Lower Nicaraguan Rise at 235-242 mbsf, contain 25-31 wt% water and still have 50%-61% porosity (Sigurdsson, Leckie, Acton, et al., 1997).