(Table 3) Gas hydrates collected within the Blake Ridge region, DSDP/ODP data

• Main Author: Borowski, Walter S
• Format: Dataset
• Language: English
• Published: PANGAEA 2008
• Subjects: 164-994; 164-994B; 164-996; 164-997; 76-533A; Carbon dioxide; COMPCORE; Composite Core; Deep Sea Drilling Project; DEPTH; sediment/rock; Description; DRILL; Drilling/drill rig; DSDP; DSDP/ODP/IODP sample designation; Ethane; Event label; Glomar Challenger; Joides Resolution; Latitude of event; Leg164; Leg76; Longitude of event; Methane; Nicaraguan Rise; North Atlantic Ocean; North Atlantic/RIDGE; Ocean Drilling Program; ODP; Propane; Sample code/label; δ13C; δ Deuterium; North Atlantic
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.706208; https://doi.org/10.1594/PANGAEA.706208

The Blake Ridge region lies on the passive margin of southeastern North America and contains a large amount of methane gas hydrate. The methane and methane gas hydrate are predominantly biogenic, apparently produced by CO2 reduction. Reflection seismics indicate that bottom-simulating reflectors (BSRs) enclose ~55,000 sq. km, with high-amplitude BSRs covering ~26,000 sq. km. Ocean Drilling Program (ODP) Leg 164 drilled three deep holes on a 10-km-long transect (Sites 994, 995, and 997; water depth 2770-2798 m). Based on sampling and geochemical, thermal, seismic, and borehole geophysical measurements, gas hydrates are most likely present between ~190 and 450 m in sediment column. Gas hydrate is most often disseminated throughout the sediment column, although concentrations occur within specific sedimentary horizons, within supposed fault zones, and at the base of gas hydrate stability (BGHS) where methane recycling produces more pervasive concentrations of gas hydrate. Estimates of gas hydrate inventory are based on a variety of methods including geochemical proxies, vertical seismic profiling, electric logging, and measurements of in situ methane. Over the entire sediment column, at least ~2-4% of pore space volume (1-2% sediment volume) is occupied by methane gas hydrates, but average and maximum estimates are 5.4% and 12%, respectively. Extrapolation of vertical gas hydrate and methane inventory over the area containing high-amplitude BSRs yields estimates of 67-406 Gt (gigatons, 10**15 g) of methane gas hydrate (or 9-52 Gt of methane) and 2.6-27 Gt of methane occurring as gas bubbles below the BGHS. Average values are 185 Gt of gas hydrate and 24 Gt of methane as gas hydrate. Any gas hydrate occurring outside the area underlain by BSRs (as suggested by geochemical evidence) or that associated with low-amplitude BSRs may increase these estimates by an unknown factor. Various data give conflicting pictures of mass transport with Blake Ridge sediments. The data can be reconciled by viewing the upper sedimentary ...