At Site 1096, hydrocarbon gases were measured in every core recovered. Inorganic carbon concentration was first measured on approximately one sample per section, with additional sampling later. Elemental analyses were performed on one sample per core. Solvent extraction of organic matter was applied on a subset of five samples. Rock-Eval pyrolysis was performed on five carbonate samples.
For gas monitoring at Site 1096, both headspace and vacutainer sampling were used (Table T22). At Hole 1096A, headspace concentration of methane (C1) exceeded the background level below 50 mbsf and increased downhole (Fig. F27), small amounts of ethane (C2) were present, and propane (C3) occurred below 123 mbsf (Fig. F28). The gas composition remained relatively constant through most of Hole 1096B. Upon recovery of Section 178-1096B-23X-2 (176 mbsf), gas pockets were discovered, and vacutainer sampling was initiated. Vacutainer sampling continued in parallel with headspace sampling during the remainder of Site 1096 operations. Hydrocarbons isobutane (C4) and isopentane (C5) first appeared in Section 178-1096C-11X-3 (293 mbsf) and increased slowly with depth, whereas propane increased more rapidly (Table T22; Fig. F28). The methane:ethane ratio in vacutainer samples decreased downhole but never reached the safety limit of 100.
The increasing amount of C3+ hydrocarbons in Hole 1096C indicates a thermogenic origin of this portion of the gas. This hypothesis is supported by the presence of hydrogen sulfide that forms at temperatures of 130º-140ºC. The shallow depth and estimated temperature of 40º-45ºC (see "Physical Properties") at the bottom of Hole 1096C suggest that the observed heavy hydrocarbons and hydrogen sulfide formed at a greater depth and migrated upward.
Site 1096 is divided into three lithostratigraphic units (see "Lithostratigraphy"). Unit I (0-33 mbsf) consists of diatom-bearing silty clays and contains low concentrations of inorganic and organic carbon, with mean values of 0.12 and 0.13 wt%, respectively. Unit II comprises mainly mud and silt turbidites and thin foraminifer-bearing laminae. Unit II was recovered in Holes 1096A and 1096B, with ~80 m of overlap. Initial routine sampling for carbonate analyses included only one of the foraminifer-bearing laminae in Hole 1096A. Subsequent sampling was targeted directly at eight more of these layers in the upper part of Holes 1096A and 1096B. These thin laminae account for all of the sharp peaks observed in the inorganic carbon data from Site 1096 (Fig. F29). The stratigraphic correlation between Holes 1096A and 1096B is good (see "Composite Depths"), and a correlation between specific inorganic carbon peaks should be possible; however, the widely spaced sampling interval precludes such an effort for now. Total organic carbon concentrations remain low throughout Unit II (Fig. F30), increase sharply at ~180 mbsf at the boundary between Units II and III, and continue to increase downhole, although with large fluctuations. In Unit III, total organic carbon averages 0.36 wt%, but inorganic carbon remains low, 0.10 wt%, except in carbonate-cemented layers that occur in Hole 1096C (Fig. F29; Table T23). The increase of total organic carbon also coincides with the increase of biosiliceous material, which indicates a higher primary productivity by diatoms (see "Biostratigraphy").
Elevated amounts of sulfur occur below 340 mbsf (Table T23) and reflect pyrite occurrences (see "Inorganic Geochemistry") and possibly adsorption of sulfur to organic matter in a reducing environment.
Five samples that contain ~0.5% total organic carbon were selected for organic solvent extraction and gas chromatographic analysis of lipid compounds. Overall, lipid fraction recovery was low, the chromatograms are complex, and the analytical capabilities onboard are limited, which makes interpretation tentative. Nonetheless, all samples show a marine fingerprint, with some differences evident among samples. Samples 178-1096C-16X-4, 64-68 cm; 21X-6, 80-84 cm; and 28X-4, 63-66 cm, show a clear marine algal origin, whereas Samples 178-1096A-2H-1, 100-104 cm, and 178-1096C-35X-4, 59-61 cm, indicate a mixed origin. Samples from Hole 1096C show signs of organic matter maturation and biodegradation by the presence of short carbon chains and increasingly complex and poorly resolved chromatograms.
Rock-Eval pyrolysis was performed on five carbonate samples that contain ~0.5 wt% total organic carbon (Table T24). The values obtained using Rock-Eval compare reasonably well with those calculated from total carbon and inorganic carbon, but the total organic carbon values remain too low (<0.5%) to allow a reliable evaluation of the data.