In contrast to previously drilled sites, sediments from Site 1085 have significantly lower gas concentrations (see "Organic Geochemistry" section, this chapter). As a consequence, the cores show only minor gas expansion cracks, and core disturbance, such as flow-in structures, is rare. Material cored with the extended core barrel below Core 175-1085A-34X at Hole 1085A consists mainly of drilling biscuits ranging in thickness between 2 and 4 cm. Sediments from Site 1085 form two lithostratigraphic units dominated by nannofossil ooze (Fig. 5). Unit I has been subdivided into Subunits IA and IB to reflect the decrease in foraminiferal abundances with depth. Subunit IA extends from Core 175-1085A-1H through 10H at both holes, and Subunit IB is characterized by nannofossil ooze and extends from Cores 175-1085A-11H through 63X. Unit II is a reddish brown, microfaulted and thinly laminated clay-rich nannofossil ooze. Unit II was encountered only in Core 175-1085A-64X.
Subunit IA extends from the top of the hole to Core 10H at Holes 1085A and 1085B and is composed of moderately bioturbated, greenish gray (10Y 7/2, 10Y 6/2), light greenish gray (5Y 7/2), pale olive (5Y 6/3), and dark greenish gray (10Y 5/2) nannofossil-foraminifer ooze. Individual color intervals range in thickness from 80 to 200 cm and grade into one another over 15 to 20 cm. Burrows are present throughout this subunit and vary in diameter between 0.5 and 2 cm. The infill has generally higher abundance of pyrite. Graded, 2- to 17-cm-thick beds rich in foraminifer tests are present within Cores 175-1085A-4H, 6H, and 8H. The thickest beds have sharp, erosive bases. Bivalve shells and a subrounded pebble of pumice are present within the lower 7 cm of a 17-cm-thick bed in interval 175-1085A-4H-2, 10–27 cm. A general characteristic of Subunit IA is the presence of gray mottles 1–3 mm in diameter. These mottles contain abundant finely disseminated pyrite. Subunit IA is characterized by high concentrations of calcium carbonate, which average 69 wt%.
The dominant lithology of Subunit IB is greenish gray (10Y 7/2 and 10Y 6/2), light greenish gray (5Y 7/2), light gray (10Y 7/1), and pale olive (5Y 6/3) nannofossil ooze. Light greenish gray (10Y 6/2) diatom- and foraminifer-rich and dark greenish gray (10Y 5/2) diatom-bearing nannofossil foraminifer ooze are present in intervals between Cores 10H and 12H at Holes 1085A and 1085B. The appearance of diatoms is coincident with a gradual decrease in foraminiferal abundances. Below Core 175-1085A-23H, sediments either contain only trace or rare abundances of foraminifers, except for few short intervals where foraminifers are frequent. All cores have distinct burrows, which vary in diameter between 2 mm and 1 cm (Fig. 6). Zoophycos traces are common in Core 175-1085A-59X (Fig. 7). Gray and light olive-brown mottles, possibly burrows, contain abundant pyrite and are present throughout most of the cores. Below Core 175-1085A-40X, pyrite is in the form of isolated silt- to fine sand-sized grains. Starting with Core 175-1085A-46X, pyrite is present as nodules as much as 1 cm in diameter. A thinly laminated interval of clay-rich nannofossil ooze occurs between Sections 175-1085A-61X-4 and 61X-6. The contact between Subunit IB and Unit II is sharp and occurs in Core 175-1085A-63X. The nannofossil ooze at the base of Subunit IB is angularly discordant with and overlies the thinly laminated sediment of Unit II. Calcium carbonate contents in Subunit IB average 65 wt% and are slightly lower than those of Subunit IA.
The deepest core of Hole 1085A is defined as Unit II, which consists of thinly laminated light gray (5Y 7/1) nannofossil ooze and gray (5Y 5/1) clay-rich nannofossil ooze. The sediments are reddish to olive brown. Laminae have sharp bases, are occasionally graded, and range in thickness from 1 to 5 mm. Packages of laminae within this unit are commonly microfaulted (Fig. 8), convolutely layered, and folded (Fig. 9). This unit is interpreted as a slump block. In Unit II, concentrations of calcium carbonate average 59 wt%, reflecting the slightly more clay-rich nature of these sediments.
The detrital component in sediments from Site 1085 is dominated by clay and trace abundances of silt-sized, subangular mono- and polycrystalline quartz grains. Authigenic minerals are rare or present in trace abundances. Pyrite is present as silt-sized euhedral aggregates or as framboids. The biogenic component in all smear slides consists of abundant to very abundant nannofossils. Foraminifers are abundant in Subunit IA and then decrease gradually from abundant to rare between Cores 175-1085A-11H and 27H. Diatoms are common only in Core 175-1085A-10H and are frequent to rare in Core 175-1085A-11H and 12H. Siliceous spicules are rare between 8.2 and 41 mbsf and between 127 and 142 mbsf at both Holes 1085A and 1085B. Reddish brown, subangular, silt-sized grains with high relief are present in trace amounts in 20-cm-thick intervals in Cores 175-1085A-58X through 64X. These grains may be titanite or rutile. Intervals are spaced 40 to 50 cm apart.
Color reflectance data were measured every 2 cm down to Core 175-1085-8H for Hole 1085A, every 4 cm to the bottom of Hole 1085A, and for the entire Hole 1085B. The total reflectance ranges between 40% and 68% (Fig. 10, Fig. 11). The high calcium carbonate contents at this site (see "Organic Geochemistry" section, this chapter) suggest that the downcore fluctuations in the total reflectance are controlled primarily by the calcium carbonate content of the sediments. The ratio of the red (650 nm) to blue (450 nm) wavelengths varies between 1 and 2 and shows a gradual decrease for the upper 400 mbsf (Fig. 11). Superimposed on this long-term trend, the red/blue ratio values exhibit high-amplitude variations between 0 and 400 mbsf and low-amplitude variations between 400 and 600 mbsf. These low-amplitude variations are inversely correlated to magnetic susceptibility (Fig. 11). The total reflectance displays well-defined and pronounced peaks in the upper 50 mbsf of Holes 1085A and 1085B. High-amplitude variations in total reflectance are observed for the entire drilled sedimentary succession (Fig. 11). Three pronounced events are recognized: high total reflectance values between 100 and 130 mbsf and between 350 and 430 mbsf, corresponding to high calcium carbonate concentrations ~75 and 80 wt% respectively, and low total reflectance values between 430 and 460 mbsf that are 50% lower in carbonate calcium contents than in the overlying sediments. The first event occurs between 2.7 and 3 Ma (see "Biostratigraphy and Sedimentation Rates" section, this chapter) and could be correlated to similar events observed at Sites 1082 and 1084. The second and third events occur between 6.5 and 9.7 Ma (see "Biostratigraphy and Sedimentation Rates" section, this chapter). Dissolution events indicated by higher relative percentages in the planktonic foraminifer fragments have been described in upper Miocene sediments for Site 360 off Cape Agulhas (Melguen, 1978). The minimum in total reflectance values occurs at 9.5 Ma, where carbonate percentages drop to relatively low values.