| IODP Proceedings Volume contents Search | ||
|
||
| Expedition reports Research results Supplementary material Drilling maps Expedition bibliography | ||
|
doi:10.2204/iodp.proc.311.207.2009 ResultsElemental compositionTC, TOC, and TN contents show spatial variation across the transect of four sites (Table T1; Figs. F1, F2). Their values gradually decrease from land toward open sea. That is, the highest values are at Site U1329 and the lowest values are at Site U1326. Variation with depth show a similar trend among these elements. TC, TOC, and TN values slightly increase with depth at Sites U1329 and U1327, whereas they decrease with depth at Sites U1325 and U1326 (Fig. F1). In particular, TC values reach 7.34 wt% in the upper part of Site U1328 (Fig. F1), where many massive gas hydrates and authigenic carbonates were found on board (see the "Site U1328" chapter). TOC and TN show a strong positive correlation (R2 > 0.80) (Table T1). Also, moderate or strong positive correlations were observed between TC and TOC and between TC and TN, except for an abnormal value. Organic matter from marine algae typically has an atomic TOC/TN ratio of 4–10; ratios from vascular land plants are ≥20 (Emerson and Hedges, 1988; Meyers, 1994). Most atomic TOC/TN ratios in tested Expedition 311 samples have a range of 4–10 (Table T1; Figs. F1, F2) and are relatively constant with depth. TS content at Site U1328 is higher at the surface and shows a slightly increasing trend with depth. At Site U1326, TS content slightly decreases with depth (Fig. F1). TOC/TS ratios at Sites U1326 and U1328 have a slightly decreasing trend with depth, whereas they are slightly increasing at Sites U1325 and U1329 (Fig. F1). Rock-Eval pyrolysisMost analyzed S2 and S3 values from Expedition 311 samples are <3 mg hydrocarbon [HC]/g rock and 3 mg CO2/g rock (Table T1; Fig. F3). S2 values show vertical and spatial variations through the transect, whereas S3 values do not show any trend (Fig. F3). S2 values are higher at Sites U1329 and U1327, located nearer to land, than at other sites. Additionally, S2 values at Sites U1329 and U1327 slightly increase with depth, whereas S2 values at the other sites are relatively constant irrespective of depth (Fig. F3). Most analyzed HI and OI values are 50–150 mg HC/g TOC and 100–300 mg CO2/g TOC (Table T1; Figs. F3, F4). Plotting modified van Krevelen-type and S2 versus TOC diagrams using analyzed values from Expedition 311, most samples are at Type III evolution. There is a strong positive correlation (R2 > 0.80) between S2 and TOC (Fig. F4). Most analyzed Tmax values were <435°C, which shows that organic matter in the samples is at a thermally immature stage. Tmax did not show vertical variation with depth (Table T1; Fig. F3). However, Tmax has the lowest values (<350°C) in the upper part of lithostratigraphic Unit I (<50 meters below seafloor) at Site U1328 (Fig. F3). This interval contains massive in situ gas hydrates (see the "Site U1328" chapter). Additionally, the Tmax of Unit III at Site U1326 has a lower value and shows variation (Fig. F3). Isotopic compositionMarine organic matter typically has δ13C values from –22‰ to –20‰ (Jasper and Gagosian, 1990; Meyers, 1994). Measured δ13Corg values of Expedition 311 samples generally are from –27.5‰ to –22.5‰. δ13Corg values are higher at Sites U1329 and U1327 compared to the other sites (Table T1; Figs. F1, F2). δ13Corg values slightly increase with depth at Sites U1329, U1327, and U1328, whereas they show a slightly decreasing tend at Site U1325 (Figs. F1, F2). Analyzed δ15Norg values are from –3‰ to 6‰. δ15Norg values are higher at Sites U1329, U1327, and U1328 than at Sites U1325 and U1326. δ15Norg values slightly decrease with depth at Sites U1329, U1327, and U1325, whereas they show a slightly increasing tend at Site U1328 (Table T1; Figs. F1, F2). |
|
