As part of the shipboard safety and pollution-prevention monitoring program, hydrocarbon gases were analyzed in each core of Holes 1120B and 1120D by the headspace technique. Methane and higher hydrocarbons could only be recognized in trace concentrations (<100 ppm). These low methane concentrations indicate only small bacterial postdepositional activity because of the lack of organic matter in the sediment. This result is corroborated by almost constant sulfate concentrations in the pore water throughout the hole (see "Inorganic Geochemistry").
The abundance of total, inorganic, and organic carbon and of calcium carbonate in sediments from Holes 1120B and 1120D is summarized in Table T14 (also in ASCII format). Random sampling of all lithologies was performed for carbonate analysis. Organic-carbon measurements were conducted on only five samples because of the obviously low organic-carbon contents indicated by the light sediment color.
Carbonate contents are high throughout the section and range from 84.5 to 98.7 wt% (Fig. F15). These values strongly indicate carbonate-dominated sedimentation with a low supply of terrigenous clastic material. The lowest carbonate values were measured in the three uppermost samples (181-1120B-1H-1, 28-29 cm, 1H-1, 54-55 cm, and 1H-2, 84-85 cm).
Organic-carbon contents in the five samples analyzed are low (<0.41%), suggesting the respiration of most of the organic matter occurred during settling through the water column and during early diagenesis caused by an oxic water column and low sedimentation rates.