C1 to C7 Hydrocarbons from IPOD Holes 397 and 397A

Abstract

Gases from sediment pockets were monitored onboard ship during continuous coring to a depth of 1453 meters. Gas pockets first appeared at a sediment depth of 80 meters (Hole 397) and continued irregularly to the bottom of Hole 397A. The gas contained small quantities (0.1 to 1.3%) of methane from 30 to 124 meters, with major components of air and C0 2 . The odor of H 2 S was noted in the cores from 9 to 151 meters. Starting at 196 meters, methane became a significant component (43%) and then varied irregularly from 1 to 81 per cent of the gas throughout the rest of the hole. A gas chromatograph installed on board ship at the beginning of Leg 47A allowed monitoring of traces of C 2 to C 5 hydrocarbons in gas pockets. These hydrocarbons, found along with the methane throughout the hole, included 3 to 2000 ppm of C 2 by volume, 1 to 140 ppm of C 3 , 0.1 to 25 ppm of C 4 , and 0.1 to 4 ppm of C 5 . The Cj to C 5 hydrocarbon levels followed lithologic changes to a remarkable degree with proportions of C 2 :C 3 :C 4 :C 5 staying relatively constant in fine-grained sediments and with the (Cj + C 2 )/(C 3 + C 4 + C 5 ) ratio increasing erratically in coarser grained sediments and at most of the unconformities. This indicates hydrocarbons were migrating from fine-grained source beds to coarse-grained reservoir beds and along the more permeable unconformities throughout the hole. Ratios of i-C 5 /n-C 5 and i-C 4 /n-C 4 , appeared to vary with changes in organic source material. Traces of neopentane occurred irregularly and are probably indicative of terpene-derived material. Sediment C± to C 7 , analysis showed that only traces of C 6 and C 7 hydrocarbons were present above 800 meters. Below 800 meters, the C 6 and C 7 hydrocarbons generally increased with sediment depth and age.

Seismic structure of the volcanic apron north of Gran Canaria

“…At Site 953, closest to the uplift structures, the methane concentration is below 34 ppm (Schmincke, Weaver, Firth, et al, 1995), whereas values of up to 54,965 ppm were recorded at Site 955. The same is true for Deep Sea Drilling Project Site 397 (Whelan, 1979). In summary, the methane content can change over short distances, and considerable concentrations can occur locally.…”

Gas Hydrates in Sediments of Holes 497 and 498A, Deep Sea Drilling Project Leg 67

“…Analysis via the Hewlett-Packard is a cold-trap technique in which Ci is not determined. For complete details, consult Whelan (1979). a Measurement made by puncturing liner with needle fitted with gauge.…”

Baja California Passive Margin Transect: Sites 474, 475, and 476

“…The method for rapid gas analyses was evaluated on Leg 47 (von Rad, Ryan, et al, 1977;Whelan, 1979). Samples from core gas pockets were collected through the core liner in "vacutainers" immediately after the cores were brought on deck.…”

“…Sample introduction into the Hewlett-Packard GC was accomplished with a %" × 8" loop packed with 60/80-mesh alumina (Analabs, Activated Alumina F-l) attached to a Carle sampling valve (microvolume valve 2014 or minivolume valve 2818; Whelan, 1979). A stream of dry helium, with the flow rate adjusted to 15 cc/ min.…”