Greinert, Jens , Bohrmann, Gerhard and Suess, Erwin (2001) Gas Hydrate-Associated Carbonates and Methane-Venting at Hydrate Ridge: Classification, Distribution, and Origin of Authigenic Lithologies. In: Natural Gas Hydrates: Occurrence, Distribution, and Detection. , ed. by Paull, C. K. and Dillon, W. P.. Geophysical Monograph Series, 124 . AGU (American Geophysical Union), Washington, DC, pp. 99-113. ISBN 0-87590-982-5 DOI 10.1029/GM124p0099.

Text Greinert.pdf - Reprinted Version Restricted to Registered users only Download (4MB)

Abstract

Hydrate Ridge is part of the accretionary complex at the Cascadia margin and
is an area of widespread carbonate precipitation induced by the expulsion of
methane-rich fluids. All carbonates on Hydrate Ridge are related to the methanecarbon
pool either through anaerobic methanotrophy or through methanogenesis.
Several petrographically distinct lithologies occur in boulder fields or in massive
autochtonous chemoherm complexes which include methane-associated
diagenetic mudstones and venting-induced breccias. The mudstones result from
methane diagenesis in different sediment horizons and geochemical environments
related to very slow methane venting. Cemented bioturbation casts occur
as fragments, complex framework or as clasts together with bivalve shells as part
of intraformational breccias, which are restricted to chemoherm complexes.
Here, fluids ascend from the sub-seafloor and support aragonite-dominated carbonate
precipitation near or at the sediment surface. Voids within mudclast breccias
are either aragonite-rich indicating a formation near the surface at vent sites
or are cemented by dolomite, which indicates formation in deeper parts of the
sediment column. Brecciation is caused by tectonic or slump processes. In addition,
we recognized a direct relationship between gas hydrates and sediment fracturing
as well as the oxygen isotope composition of carbonate lithologies. Such
gas hydrate-associated carbonates either show layered megapores and veins as
relics of the original gas hydrate fabric or consist of aragonite-cemented intraclast
breccias formed by growing and decomposing gas hydrate near the sediment
surface. Both rock fabrics and the enrichment of 180 in high Mg-calcite
demonstrate carbonate-forming mechanisms of gas hydrate.

Actions (login required)

View Item