At Site 1129, in addition to routine monitoring of hydrocarbon and H2S gases for safety, analyses were conducted for inorganic carbon, total carbon, nitrogen, sulfur, and organic matter characterization. The analytical procedures are described in "Organic Geochemistry" in the "Explanatory Notes" chapter.
Concentrations of volatile hydrocarbons and H2S were routinely determined in samples from Holes 1129C and 1129D using standard ODP headspace or vacutainer sampling procedures. The striking results from Site 1129, as at Sites 1127 and 1131, are the high concentrations of methane (C1) and H2S in much of the section (Tables T3, T4). Eight gas pockets occurred in Hole 1129C from 62.3 to 366.3 mbsf, with seven of the eight between 313.9 and 366.3 mbsf. These were sampled directly through the core liner using a gas-tight syringe (vacutainer). Concentrations of C1 in these gas pockets ranged from a low of 313 ppm in the shallow pocket to between 19,344 and 244,598 ppm in the deeper pockets (Table T3). By comparison, gas pockets at Site 1129 were twice as abundant as at Site 1131; however, gas pockets at Site 1127 were much more abundant than at Sites 1129 and 1131. Methane concentrations in the gas pockets at Site 1129 fall between the levels found at Site 1127, which had a high of 585,000 ppm, and Site 1131, which had a high of 81,267 ppm (see "Organic Geochemistry" in the "Site 1127" chapter and "Organic Geochemistry" in the "Site 1131" chapter).
Methane occurs at lower concentrations in the headspace samples from Holes 1129C and 1129D than in vacutainer samples. The lowest values are at the tops and bottoms of the cored interval and reach a maximum at 258.9 mbsf (Table T4; Fig. F13). From 4.5 to 40.3 mbsf, C1 values are <10 ppm. From 49.8 to 258.9 mbsf, C1 increases to 12,043 ppm, the highest value, and then decreases with some scatter to 235 ppm at the bottom of Hole 1129D. The C1 profile at Site 1129 is similar to the profile at Site 1131, except that the maximum in C1 concentration occurs at a deeper level at Site 1129 (see "Organic Geochemistry" in the "Site 1131" chapter).
Ethane (C2) occurs from 49.8 mbsf to the base of Hole 1129D at concentrations as high as 28.9 ppm in headspace samples (Table T4). C1/C2 values in headspace samples from the same depth interval first increase from 40 to 605 and then decrease to a low of 157 at the bottom of Hole 1129D (Table T4; Fig. F13). The same pattern of increasing and decreasing C1/C2 values with depth is present at Site 1131 (see "Organic Geochemistry" in the "Site 1131" chapter). The change in ratio with depth tracks the increase and decrease in C1 concentration, as C2 concentrations do not vary significantly from 135.3 mbsf to the base of Hole 1129C. Heavier hydrocarbon gases (C3+) were detected in a few headspace samples, primarily from 324.3 to 528.6 mbsf in Holes 1129C and 1129D, as well as in the seven deepest gas pockets.
The concentrations of H2S in the eight gas pockets in Hole 1129C range from 313 ppm, in the shallowest pocket, to a high of 136,577 ppm, which is intermediate between values measured from Sites 1127 and 1131 (Table T3). The H2S in headspace samples from Hole 1129C reaches concentrations as high as 40,445 ppm at 324.3 mbsf. The headspace concentrations are lower than those found in gas pockets, although as with the gas pockets, the H2S values are intermediate between those at Sites 1127 and 1131 (Table T4; see "Organic Geochemistry" in the "Site 1127" chapter and "Organic Geochemistry" in the "Site 1131" chapter).
Throughout Hole 1129C, carbonate values are uniform and range primarily from 88 to 94 wt% (Table T5; Fig. F14). Organic carbon (Corg) ranges primarily from 0.3 to 0.7 wt%, with little variation throughout the section, except for one value of 1.46 wt% at 433.0 mbsf (Table T5; Fig. F14).
Nitrogen concentrations are <0.1 wt%, and many samples have no detectable nitrogen. One exception is the sample with highest Corg at 433.0 mbsf, which has a nitrogen content of 0.12 wt%. Sulfur was not detected in any sample (Table T5).
Rock-Eval pyrolysis data for selected samples with higher concentrations of organic carbon from Sites 1127, 1129, 1131, and 1132 indicate that the organic matter is immature type I (Table T6; Fig. F15). Tmax values are generally between 410° and 425°C, and hydrogen indices (HI) range as high as 470. Samples from Site 1127 have higher Tmax and HI values than samples from Sites 1129, 1131, and 1132.