No abstract

Here we reported the fatty-acids and their δ 13 C values in seep carbonates collected from Green Canyon lease block 185 (GC 185; Sample GC-F) at upper continental slope (water depth: ~540 m), and Alaminos Canyon lease block 645 (GC 645; Sample AC-E) at lower continental slope (water depth: ~2200 m) of the Gulf of Mexico. More than thirty kinds of fatty acids were detected in both samples. These fatty acids are maximized at C 16 . There is a clear even-over-odd carbon number predominance in carbon number range. The fatty acids are mainly composed of n-fatty acids, iso-/anteiso-fatty acids and terminally branched odd-numbered fatty acids (iso/anteiso). The low δ 13 C values (−39.99‰ to −32.36‰) of n-C 12:0 , n-C 13:0 , i-C 14:0 and n-C 14:0 suggest that they may relate to the chemosynthetic communities at seep sites. The unsaturated fatty acids n-C 18:2 and C 18:1 △ 9 have the same δ 13 C values, they may originate from the Beggiatoa/Thioploca. Unlike other fatty acids, the terminally branched fatty acids (iso/anteiso) show lower δ 13 C values (as low as −63.95‰) suggesting a possible relationship to sulfate reducing bacteria, which is common during anaerobic oxidation of methane at seep sites. fatty acids, carbon isotope of individual lipid, sulfate reducing bacteria, anaerobic oxidation of methane, seep carbonate, Gulf of Mexico Citation: Guan H X, Feng D, Wu N Y, et al. Fatty-acids and their δ 13 C characteristics of seep carbonates from the northern continental slope of Gulf of Mexico.

An understanding of the physical properties of hydrate-bearing sediment is necessary for interpretation of geophysical data collected in field settings. We have conducted a laboratory experiment to measure the electrical property of initially water saturated sediment containing natural gas hydrate. When gas hydrate was formed from pore fluid in ocean sediment, bulk sediment resistivity was significantly increased. The resistivity of the sediment was largely changed below 20% hydrate saturation. With the increasing hydrate saturation, the resistivity of sediment was increased and the resistivity of pore fluid was decrease. In the final process of hydrate formation, the resistivity depression was found mainly due to the transition of gas hydrate morphology. The electrical resistivity of hydrate specimens varied from 1.930 Ohm.m to 3.950 Ohm.m for saturation ranging from 0% to 52.68%. Besides, the dependence of the resistivity index versus hydrate saturation is inconsistent with Archies law. The results of our studies have important implications for quantitative laboratory and field calibration of geophysical measurements within gas hydratebearing intervals.