Chemical and isotopic signature of bulk organic matter and hydrocarbon biomarkers within mid-slope accretionary sediments of the northern Cascadia Margin gas hydrate system

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doi: 10.1016/j.margeo.2010.05.010
Author(s): Kaneko, Masanori; Shingai, Hiroshi; Pohlman, John W.; Naraoka, Hiroshi
Author Affiliation(s): Primary:
Kyushu University, Department of Earth and Planetary Sciences, Fukuoka, Japan
U. S. Geological Survey, United States
Volume Title: Marine Geology
Source: Marine Geology, 275(1-4), p.166-177. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0025-3227 CODEN: MAGEA6
Note: In English. 61 refs.; illus., incl. 4 tables, sketch map
Summary: The chemical and isotopic compositions of sedimentary organic matter (SOM) from two mid-slope sites of the northern Cascadia margin were investigated during Integrated Ocean Drilling Program (IODP) Expedition 311 to elucidate the organic matter origins and identify potential microbial contributions to SOM. Gas hydrate is present at both locations (IODP Sites U1327 and U1328), with distinct patterns of near-seafloor structural accumulations at the cold seep Site U1328 and deeper stratigraphic accumulations at the slope-basin Site U1327. Source characterization and evidence that some components of the organic matter have been diagenetically altered are determined from the concentrations and isotopic compositions of hydrocarbon biomarkers, total organic carbon (TOC), total nitrogen (TN) and total sulfur (TS). The carbon isotopic compositions of TOC (δ13CTOC=-26 to -22 ppm) and long-chain n-alkanes (C27, C29 and C31, δ13C=-34 to -29 ppm) suggest the organic matter at both sites is a mixture of 1) terrestrial plants that employ the C3 photosynthetic pathway and 2) marine algae. In contrast, the δ15NTN values of the bulk sediment (+4 to +8 ppm) are consistent with a predominantly marine source, but these values most likely have been modified during microbial organic matter degradation. The δ3C values of archaeal biomarker pentamethylicosane (PMI) (-46.4 ppm) and bacterial-sourced hopenes, diploptene and hop-21-ene (-40.9 to -34.7 ppm) indicate a partial contribution from methane carbon or a chemoautotrophic pathway. Our multi-isotope and biomarker-based conclusions are consistent with previous studies, based only on the elemental composition of bulk sediments, that suggested a mixed marine-terrestrial organic matter origin for these mid-slope sites of the northern Cascadia margin. Abstract Copyright (2010) Elsevier, B.V.
Year of Publication: 2010
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 02 Geochemistry; 07 Marine Geology and Oceanography; Accretionary wedges; Biomarkers; British Columbia; C-13/C-12; Canada; Carbon; Cascadia subduction zone; Continental margin sedimentation; Diagenesis; East Pacific; Expedition 311; Gas hydrates; Geochemical indicators; Geochemistry; Hydrocarbons; IODP Site U1327; IODP Site U1328; Integrated Ocean Drilling Program; Isotope ratios; Isotopes; Marine environment; Marine sediments; N-15/N-14; Nitrogen; North Pacific; Northeast Pacific; Organic compounds; Pacific Ocean; Provenance; Sedimentation; Sediments; Slope environment; Stable isotopes; Sulfur; Total organic carbon; Vancouver Island; Western Canada
Coordinates: N484200 N484200 W1265200 W1265200
N484000 N484000 W1265100 W1265100
Record ID: 2010087171
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands