Three holes were drilled at Site 1088 to a total depth of 233.7 mbsf, recovering Holocene to middle Miocene calcareous ooze. The dominant lithologies are nannofossil ooze, foraminifer-bearing nannofossil ooze, foraminifer nannofossil ooze, and nannofossil foraminifer ooze. Carbonate contents vary from 85 to 95 wt%. The relative abundance of foraminifers decreases progressively downhole (Fig. F5). Siliceous microfossils are intermittent, mainly as a trace component, although some diatom-bearing nannofossil ooze is present. The sediment color is mainly very pale gray with minor, slightly darker (pale gray) interbedded horizons in the upper 25 m. Faint dark laminations and some pyriized burrows are locally present. Volcanic ash was observed in Sections 177-1088B-7H-CC through 9H-CC.
The lithostratigraphic characteristics of the sediments are defined on the basis of primarily visual core descriptions and sediment smear-slide analyses (Fig. F6; "Site 1088 Smear Slides"). Additional information was obtained from spectral reflectance measurements, X-ray diffraction (XRD) for quartz, feldspar, clay, and opal abundances (on a carbonate-free basis), and calcium carbonate contents (Fig. F6; Table T1, also in ASCII format in the TABLES directory). One lithostratigraphic unit was identified at this site.
Intervals: 177-1088A-1H (0-9 mbsf); 177-1088B-1H through 14H (0-129 mbsf); 177-1088C-1H through 13X (0-233.7 mbsf)
Age: Pleistocene to middle Miocene
The upper 20 m of sediment in Hole 1088B consists of very pale gray nannofossil foraminifer ooze with a carbonate content ranging from 85 to 91 wt%. Subordinate, decimeter-scale interbeds of darker, more foraminifer-rich sediment (up to 80% foraminifers) commonly incorporate ice-rafted debris (IRD), rare dropstones, and may also contain diatoms. Analysis of multisensor track (MST) susceptibility and color reflectance data reveals that the darker beds have relatively high susceptibility values that reflect an increased terrigenous sediment content, whereas the pale, pure carbonate intervals have relatively low susceptibility values (Fig. F7). This interval has a lower carbonate content (85-91 wt%). Diatoms were particularly abundant in the darker bed in interval 177-1088B-3H-2, 51-69 cm, where the flora was dominated by Thalassiothrix (see "Chronostratigraphy"). Some of these darker beds appear to have erosional contacts (modified by bioturbation) with the underlying pale nannofossil ooze (Fig. F8).
Below 20 mbsf, the proportion of foraminifers in the dominant lithology decreases to about 30% and the darker beds become less distinct. Between 30 and 120 mbsf, the proportion of foraminifers decreases progressively. In the nannofossil ooze between 120 mbsf and the base of Hole 1088C, foraminifers generally comprise less than 10% of the sediment. Carbonate content is relatively high (generally 90-95 wt%) and increases to the base of the hole, with the exception of a lower carbonate interval between 80 and 130 mbsf. The blue reflectance values show close similarity with the carbonate values (Fig. F9; "Geochemistry"). Below 130 mbsf, smear-slide composition data, carbonate values, and XRD mineralogy (see below) show little change to the base of the hole. Opal in the pre-Quaternary sediments reaches values between 10 and 23 wt%, showing two distinct maxima (~85 and ~156 mbsf) and minima (~98 and 190 mbsf).
Faint, dark blue-gray laminations are present in the nannofossil ooze and similarly colored rings are present around some burrows. Bioturbation is moderate throughout, where visible, but is difficult to discern in the very pale gray nannofossil ooze, which has little internal color contrast. Pyritized burrows are common and locally form firm concretions. A distinctive chert-replaced burrow is present in interval 177-1088C-10X-3, 91-100 cm. Abundant Zoophycos burrows are present in Core 177-1088B-9H.
XRD measurements were performed on the noncarbonate fraction from selected samples (Fig. F6). The uppermost three samples from Hole 1088B were taken from sediments thought to represent glacial and interglacial intervals of the late Quaternary as inferred from lithology and color changes. The samples probably comprise marine isotope Stages (MISs) 5 (1.43 mbsf), 10 (3.46 mbsf), and 11 (4.00 mbsf). Opal contents of the noncarbonate fractions are 9% for MIS 5, 10% for MIS 10, and 15% for MIS 11. Variations of quartz/feldspar values are in accordance with glacial-interglacial changes, with high values (4.4-5.0) in interglacials and lower values (3.5) in glacial MIS 10. The latter may indicate a higher supply of mineralogically immature terrigenous debris from sources with prevailing mechanical weathering, probably through ice-rafting from Antarctica. An additional possibility is that eolian input changes impact the quartz/feldspar values on glacial-interglacial time scales. The clay mineral/(quartz+feldspar) value shows no distinct variations in the late Quaternary samples.
Below the Pleistocene/Pliocene boundary (~20 mbsf), the clay mineral/(quartz+feldspar) value increases downhole, reaching values of 0.25 to 0.32 toward the base of the hole, and mirrors the quartz/feldspar value, which decreases to its lowest values (<2.0) toward the base of the hole. These compositional changes basically reflect changes in grain-size distributions of terrigenous particles, with decreasing coarse silt abun-dances downhole, as seen in smear slides of the noncarbonate samples. This suggests that hemipelagic settling of fine-grained material rather than ice-rafting or eolian input of coarse particles probably dominated during the Miocene.