Concentrations of volatile hydrocarbon gases were measured from every core using the standard ODP headspace sampling technique and gas chromatographic analysis. Methane only occurred in very minor concentrations (1.8-10 ppmv) (Table T9).
The low gas content at Site 1195 is likely a function of appreciable pore water SO42- concentrations, which limit methanogenesis, and the lack of mature organic matter to provide a thermogenic component to the gas fraction.
A total of 49 pore water samples were recovered from Site 1195 sediments. Samples were taken approximately every 10 m from 9.1 to 517 mbsf. Analyses from Holes 1195A and 1195B are discussed together (Fig. F15; Table T10).
Pore water chloride concentration increases slightly downhole from a value of ~563 mM in the upper few tens of mbsf to ~569 mM at 360 mbsf (Fig. F15A). The data show considerable scatter about this trend. From 360 mbsf to the bottom of the hole at 517 mbsf, the chloride concentration varies between 571 and 564 mM, with no clear trend in the data.
Pore water alkalinity shows little variation in the upper 80-90 mbsf, remaining near 2 mM (Fig. F15B). Over the interval from 80 to 362 mbsf, alkalinity increases steadily to a maximum of 4.62 mM at 362 mbsf. Below that depth, the alkalinity decreases almost linearly to a minimum of 0.65 mM at the bottom of the cored section.
Pore water sulfate concentration shows little change in the upper 100 mbsf, remaining near the seawater value of ~29 mM (Fig. F15C). The concentration decreases by only 1-2 mM to a depth of 175 mbsf, then continues to decrease more rapidly downhole. By the bottom of the cored interval in Hole 1195B, sulfate has decreased to ~13 mM. The change in slope of the sulfate profile at 175 mbsf marks the initiation of sulfate reduction. The first visible evidence of diagenetic iron sulfides are also found at approximately this depth (see "Lithostratigraphy and Sedimentology").
As observed at other sites, ammonium values at Site 1195 show a negative correlation to sulfate values as a response to organic carbon remineralization through sulfate reduction (Fig. F15D). The ammonium concentration remains almost constant, varying between 62 and 77 µM, from 9.1 to 77.5 mbsf. Below 77.5 mbsf, the ammonium concentration rises linearly to just over 800 µM at 350 mbsf. From 350 mbsf to the bottom of the cored interval, the ammonium concentration is fairly constant.
Magnesium and calcium concentrations are also relatively constant in the upper 70-80 mbsf (Fig. F15E, F15F); thereafter, they have opposing downhole trends. Magnesium decreases to 23.5 mM and calcium increases to 36.5 mM near the bottom of Hole 1195B. The two constituents are highly correlated (Fig. F16), with r2 = 0.95. It is not certain whether the linear correspondence between magnesium and calcium results from a 1:1 exchange during low-temperature alteration of basaltic basement rocks that underlie the cored interval or from authigenic dolomite formation. The low alkalinity in Site 1195 pore waters supports the latter mechanism (Fig F15B).
Pore water strontium concentration increases significantly above seawater values in the upper few tens of mbsf, reaching a local maximum of 209 µM at 29.6 mbsf (Fig. F15G). The concentration then decreases to 127 µM at 67.6 mbsf. Thereafter, pore water strontium increases steadily to a concentration of 962 µM at 442.97 mbsf. The value remains near 900 µM to the bottom of the cored interval. The increase suggests fairly constant calcite recrystallization throughout the sedimentary interval.
Potassium concentration is also relatively constant in the upper 80 mbsf, around 11 mM (Fig. F15H). Over the interval from 80 to 360 mbsf, potassium values decrease to ~3.5 mM and remain close to that value to the bottom of the hole.
Perhaps the most interesting feature of Site 1195 pore fluid chemistry is the nearly constant concentration of all constituents in the upper ~80 mbsf. The unchanging concentrations imply either a lack of chemical reaction or a constant renewal of the pore fluids with seawater. The former explanation seems unlikely in light of the fact that there is little difference in lithology between the sediments of the upper 80 m and the underlying units. The latter explanation, however, requires some mechanism by which pore fluid in an 80-m-thick sequence of sediments can be exchanged with overlying seawater. One possibility is that the strong bottom currents that characterize the Marion Plateau might be able to entrain water from within the sediments or cause pressure differences, hydraulic head in effect, from one area to another.
Ninety-three sediment samples were analyzed for carbonate mineralogy from Site 1195 (Fig. F17; Table T11). In the upper 30 mbsf, lithologic Unit I contains ~10% aragonite. Below 30 mbsf, aragonite is absent. Through the base of lithologic Subunit IIIA at 310 mbsf, the sediments are composed almost entirely of calcite, with a few samples at 80-90 and 200-230 mbsf containing 3-5 wt% dolomite. Traces of dolomite were found in many samples, however. In the upper 90 m of lithologic Subunit IIIB, dolomite content increases to ~10%. In the lower 50 m of lithologic Subunit IIIB and in Unit IV, only calcite is present.
CaCO3 content at Site 1195 ranges from ~18 to 95 wt% and generally covaries inversely with total organic carbon (TOC) content, which ranges from 0.01 to 0.51 wt%. Note that TOC values from Rock-Eval pyrolysis and CNS analyses provide somewhat similar downsection profiles although values differ greatly (Fig. F18; Tables T11, T12). The peak in CNS-determined TOC content at ~145 mbsf is anomalous, and the reason has not yet been determined.
Hydrogen index (HI) values at Site 1195 range from 60 to 500 mg HC/g TOC (Fig. F18; Table T13), but the low TOC values of some intervals limit the reliability of these results. We performed duplicate and triplicate analyses on these samples, and the results were within 10% of the mean value. Oxygen index (OI) values vary from 0 to 52,980 mg CO2/g TOC (Table T13). In general, high OI values are attributed to the thermal degradation of carbonate minerals during pyrolysis and are not considered in this interpretation. Tmax values range from 302° to 450°C (Table T13), although the most reliable values cluster between 400° and 420°C.
Total S content in Site 1195 sediments ranges from 0 to ~2.22 wt% (Fig. F18; Table T12) and its distribution is similar to that of TOC. C/N and C/S ratios (Fig. F18; Table T11) reflect deposition in a marine environment.
Variations in the generally high CaCO3 content (average = ~82 wt%) of sediments at Site 1195 mostly reflect fluctuations in the ratio of biogenic carbonate and its dilution by terrigenous sedimentation through time. CaCO3 content exhibits an overall decrease from 88 wt% at 0.6 mbsf to 79 wt% at 15 mbsf, an interval containing relatively elevated TOC content and corresponding to the upper half of lithologic Unit I (see "Lithostratigraphy and Sedimentology"). Little to no organic carbon exists in the lower half of Unit I, whereas up to 91 wt% CaCO3 was measured. The base of lithologic Unit I was placed at a phosphatized scour surface (see "Lithostratigraphy and Sedimentology"), which appears to roughly coincide with a slight increase in TOC content to ~>0.1 wt%.
Average CaCO3 contents of 87 wt% and TOC contents of 0.1 wt% were measured in sediment samples from ~40 to 270 mbsf, an interval that corresponds to lithologic Unit II. Much of the CaCO3 content in this interval is attributed to the dominance of planktonic foraminifers in the sediment (see "Biostratigraphy and Paleoenvironments"). In this unit, a relative increase to >0.2 wt% TOC at ~95 mbsf roughly marks the base of lithologic Subunit IIA (see "Lithostratigraphy and Sedimentology"). Lithologic Subunit IIB does not appear to be geochemically distinguishable from Subunit IIC, although C/S ratios in Subunit IIB and the top of Subunit IIC are possibly indicative of the presence of brackish conditions during or shortly after deposition. The base of lithologic Unit II is marked by a relative decrease in CaCO3 content and an increase in TOC content at ~270 mbsf, a horizon that corresponds to scour surfaces and glauconite in the sediment (see "Lithostratigraphy and Sedimentology").
Lithologic Unit III (~256-467 mbsf) is notable for a broad range in inversely covarying CaCO3 and TOC values (Fig. F18) and repeated intervals of thin glauconitic and grainstone layers alternating with meter-thick bioturbated packstone (see "Lithostratigraphy and Sedimentology"). Portions of this geochemical record are similar to conspicuously low CaCO3 and high TOC content horizons observed at Sites 1193 and 1194. At those sites, the horizons also contained elevated total S content. Subunit IIIB also contains high total S contents, relatively elevated TOC, elevated HI, and elevated C/N ratios (~19) that approach the terrestrial C/N field (~25-35) in the upper half (from ~320 to 380 mbsf) and consistently low HI values with relatively elevated TOC values in the lower half (from ~373 to 453 mbsf). These parameters may be indicative of a downsection shift to more oxic conditions in Subunit III. Toward the base of Subunit IIIB at ~450 mbsf, an increase in TOC and total S content is observed immediately overlying a >20% increase in CaCO3 content between ~450 and 460 mbsf. Through all of lithologic Unit III, these geochemical data, collectively considered with observations of higher mud and clay content in this unit (see "Lithostratigraphy and Sedimentology"), are interpreted to reflect more neritic and terrigenous input to the distal periplatform setting of Site 1195.
A decrease to the lowest CaCO3 content (~18%; ~468 mbsf) measured at Site 1195 coincides with a firmground and marks the top of lithologic Unit IV (see "Lithostratigraphy and Sedimentology"). Lithologic Unit IV also displays an overall relative drop in TOC content. The low CaCO3 horizon corresponds to a glauconitic sandstone (see "Lithostratigraphy and Sedimentology") and overlies a unit with relatively elevated CaCO3 (~72% at ~507 mbsf) and lower TOC content.