A total of 29 headspace samples from Site 1267 (all from Hole 1267A) were analyzed. The concentration of CH4 (C1) in most of the samples was at an atmospheric background level (range = 1.6–2.0 ppmv) and did not exceed 2.3 ppmv in any sample. No hydrocarbon gases higher than C1 were detected.
Interstitial waters from 23 samples were collected at Site 1267 from Hole 1267A (7.5–346.8 mcd). One sample (208-1267A-11H-5, 140–150 cm; 110.6 mcd) consisted of very fine grained clay-rich material, which when squeezed, passed through the filter paper into the syringe. At Site 1262 such sediments were also encountered, but no interstitial waters were recovered. However, by using three sheets of filter paper in the squeezer instead of the usual single sheet, ~3 mL of interstitial water was successfully squeezed from Sample 208-1267A-11H-5, 140–150 cm, before the sediments extruded from the press. This small sample provides insights into the influence of such clay-rich sediments on pore water chemistry. Chemical constituents were determined according to the procedures outlined in "Geochemistry" in the "Explanatory Notes" chapter. Results of the chemical analyses are presented in Table T11.
The pH of pore waters at Site 1267 ranges from 7.28 to 7.47 (average = 7.39 ± 0.05) (Table T11). All values are lower than the average seawater value of 8.1, and no distinct depth trend is recognizable. Salinity typically ranges from 34.0 to 35.5 g/kg (mean value = 34.9 ± 0.3 g/kg).
Alkalinity decreases with depth in Site 1267 pore waters from 3.34 mM at 7.5 mcd to a minimum of 1.17 mM at 334.8 mcd near the base of the section (Fig. F25A). At the transition from APC to XCB coring techniques (between 264.7 and 275.2 mcd), there is a marked increase in alkalinity probably related to increased seawater contamination in the XCB-recovered samples.
The chloride concentrations at Site 1267 are generally constant downhole, with values between 560 and 570 mM (Fig. F25B). Two anomalously low chloride values of 534 and 523 mM occur at depths of 29.2 and 71.2 mcd, respectively. The sodium profile does not exhibit any significant downhole trend, with concentrations varying between 459 and 481 mM (Fig. F25C).
Site 1267 downhole trends in potassium, calcium, and magnesium are consistent with those resulting from exchange with basaltic basement at depth (Gieskes, 1981), with potassium and magnesium decreasing and calcium increasing with depth (Fig. F25D, F25E, F25F). Pore water potassium concentrations decrease with depth from 10.8 mM (7.5 mcd) to 6.9 mM (346.8 mcd) (Fig. F25D).
Interstitial water calcium values increase from 10.1 mM (7.5 mcd) to 26.6 mM (346.8 mcd) (Fig. F25E). The magnitude of the downhole increase in calcium concentrations (16.5 mM) is substantially larger than those observed at Sites 1262–1265 but is only slightly larger than the downhole increase in calcium measured for Site 1266 samples (15.4 mM).
The magnesium pore water profile (Fig. F25F) at Site 1267 is characterized by a general decrease with depth, from 52.4 mM in the shallowest sample (7.5 mcd) to 40.8 mM near the base of the section (334.8 mcd). The deepest sample (346.8 mcd) has an anomalously high magnesium concentration of 53.6 mM, which is close to the value of seawater (54 mM International Association of Physical Sciences of the Ocean certified value), suggesting seawater contamination of this sample. However, a similar seawater influence is not observed for other elements in this sample.
Strontium concentrations increase downhole from 143 µM in the shallowest sample (7.5 mcd) to peak at values between 386 and 412 µM from 49.7 to 110.6 mcd (Fig. F25G). Below 110.6 mcd, strontium concentrations decrease gradually downhole to 255 mM at the base of the section (346.8 mcd). The strontium pore water profile indicates a source of strontium to the interstitial waters between 49.7 and 110.6 mcd and diffusion of this strontium into the pore waters of the sediments above and below. The dissolution and recrystallization of carbonates is considered to be the major source of strontium to pore waters of carbonate-rich sediments (e.g., Baker et al., 1982), suggesting that a zone of carbonate recrystallization exists between 49.7 and 110.6 mcd at Site 1267.
Lithium concentrations generally increase downhole from 24.6 µM in the shallowest sample (7.5 mcd) to 40.4 µM at the base of the section (346.8 mcd) (Fig. F25H). Similar downhole increases in pore water lithium concentrations have been observed at all other sites with the exception of Site 1264, where the increase with depth starts below ~150 mcd as opposed to the top of the section. At all sites, there is a deep source of lithium from the sediments to the pore waters. However, the source of the pore water lithium remains elusive and could be present at depths greater than the recovered sections.
Pore water boron concentrations are relatively constant at values between 460 and 480 µM from 7.5 to 88.9 mcd, after which boron concentrations increase to values >500 µM to a depth of 164.2 mcd (Fig. F25I). Below 164.2 mcd, boron values drop to between 442 and 471 µM before increasing to values of ~500 µM at 334.8 and 346.8 mcd. At 110.6 mcd, there is a large spike (711 µM) in pore water boron concentrations occurring in the clay-rich sediments of lithostratigraphic Subunit IIA (see "Subunit IIA" in "Unit II" in "Description of Lithostratigraphic Units" in "Lithostratigraphy"). A study of Leg 186 interstitial water samples (Deyhle and Kopf, 2002) concluded that the removal of boron from clays and volcanic ash was responsible for boron enrichment in the pore waters. Therefore, the pore water boron peak at 110.6 mcd suggests that boron is being leached from the clay-rich sediments of lithostratigraphic Subunit IIA.
Pore water barium values are consistently low and fluctuate downhole between 0.21 and 0.51 µM, with the only exception being a concentration of 2.83 µM that occurs at 240.7 mcd (Fig. F25J).
The sulfate pore water profile at Site 1267 displays a downhole decrease from 25.0 mM in the shallowest sample (7.5 mcd) to 21.6 mM at the base of the section (346.8 mcd) (Fig. F25K). The high sulfate concentrations at Site 1267 (average = 23.0 ± 1.4 mM) preclude significant sulfate reduction associated with the microbial decomposition of organic matter (e.g., Gieskes, 1981).
The Site 1267 manganese pore water profile (Fig. F25L) increases sharply from 0.21 µM at the top of the section (7.5 mcd) to 5.59 µM at 16.0 mcd before decreasing to values of ~0.50 µM at 49.7 and 58.7 mcd. Below this, manganese pore water concentrations rise to a second downhole peak of 3.81 µM at 101.6 mcd before dropping to values below 1 µM in the section spanning from 127.9 to 275.2 mcd. From 284.0 mcd, pore water manganese values increase sharply downhole to peak at 9.62 µM at the base of the section (346.8 mcd), which is the highest manganese value measured in all the pore water samples from Leg 208.
Pore water concentrations of dissolved iron are typically low and often below detection limits throughout the section (Table T12; Fig. F25M), but distinct peaks with iron concentrations of 1.40 and 2.15 µM are present at 71.2 and 110.6 mcd, respectively. The peak in dissolved iron at 71.2 mcd occurs in sediments containing iron oxide bands, which can be observed by a drop in chromaticity a* (see Fig. F12; "Lithostratigraphy"); the iron oxide bands provide a likely source for the dissolved iron in this interval. The pore water iron peak at 110.6 mcd occurs in the clay-rich sediments of lithostratigraphic Subunit IIA (see "Subunit IIA" in "Unit II" in "Description of Lithostratigraphic Units" in "Lithostratigraphy") and is coincident with a large peak in pore water boron concentrations. This could indicate that, like with boron, these clays are a source of dissolved iron to the pore waters.
Dissolved silicon in pore waters from Site 1267 decreases slightly from 369 µM at a depth of 7.5 mcd to 179 µM at 29.2 mcd (Fig. F25N). Below this, the silicon concentrations generally increase downhole to peak at values between 651 and 704 µM from 240.7 to 275.2 mcd before decreasing to 338 µM at the base of the section (346.8 mcd). Although this maximum dissolved silicon concentration of 704 µM at Site 1267 is greater than those observed at Sites 1262 (412 µM) and 1264 (340 µM), it is less than half the amount of dissolved silicon (>1400 µM) measured in the deepest samples from Sites 1263, 1265, and 1266 where cherts were recovered. Dispersed volcanic ash was observed below 148.1 mcd at Site 1267, and the weathering of this silicate material is a likely source of the dissolved silicon in the pore waters.
Although the calcium, potassium, and magnesium interstitial water profiles at Site 1267 suggest that a simple diffusion profile between seawater and basement basalt is responsible for the chemistry of the pore waters, other elements including strontium, lithium, manganese, iron, and silicon indicate that diagenetic processes occurring in the sediments also have a strong impact on the interstitial water chemistry. The pore water profile of strontium from Site 1267 is very similar to that of Site 1262, with both indicating a relatively shallow zone of maximum carbonate recrystallization in the sediments.
Carbonate determinations by coulometry were made for a total of 157 samples from Site 1267 (Table T12; Fig. F26). The carbonate values in Unit I average 92.6 wt%. In clay-rich Subunit IIA, carbonate content drops dramatically (average = 48.0 wt%) before increasing again in Subunit IIB, where the average carbonate value is 83.5 wt%. In Subunit IIC, the average carbonate content is 54.6 wt%. Excluding the high-resolution P/E boundary samples, the average carbonate content in Subunit IIIA is 90.5 wt%, and in Subunit IIIB, carbonate content decreases downhole, giving an average value of 80.3 wt%.
Closely spaced (every 2 to 10 cm) samples were analyzed for carbonate content across the P/E boundary section from Holes 1267A and 1267B (Fig. F26B). Although a small offset in the occurrence of the carbonate minimum interval exists between the Hole 1267A and 1267B records, there are remarkable similarities in the fine structure (e.g., the small dip in carbonate content between 231.6 and 231.7 mcd and the slowing in the rate of recovery of carbonate preservation after the P/E minimum at ~231.3 mcd). At the P/E boundary above 231.6 mcd, carbonate drops from ~80 to <1 wt% within <10 cm of sediment. The carbonate minimum spans over 10 cm, and above 231.5 mcd, the carbonate values increase uphole to ~90 wt% over ~30 cm.
Extraction of organic matter (24-hr duration) was performed on four samples (Samples 208-1267A-1H-5, 140–150 cm, at 7.5 mcd; 16H-4, 140–150 cm, at 164.2 mcd, and 32X-4, 140–150 cm, at 334.8 mcd after squeezing interstitial water, and Sample 15H-7, 23–29 cm, at 155.3 mcd).
Mass chromatograms (m/z 85) of all samples analyzed showed n-C14 through n-C18 alkanes (Fig. F27). Branched isoprenoids were minor components except for pristane and phytane in the aliphatic hydrocarbon fraction of each sample. This feature is generally observed in the sediments of Oligocene age and also in younger sediments from the other Leg 208 sites. The results from Sections 208-1267A-15H-7, 16H-4, and 32X-4 (Fig. F27) indicate that this character of aliphatic hydrocarbons occurs down to the upper Maastrichtian. On the other hand, Paleocene and Eocene samples from Sites 1262 and 1263 showed a predominance of anteiso-alkanes or 3-methyl-hosted branched isoprenoids, some of which are also found as minor components in the samples analyzed.
Pristane and phytane were also abundant in the aliphatic hydrocarbon fraction of all samples, exhibiting clear peaks in the mass chromatograms (Fig. F27).