Dolomite chimneys as possible evidence of coastal fluid expulsion, uppermost Otago continental slope, southern New Zealand

Iron oxyhydroxide and sulphide mineralization in hydrocarbon seep-related carbonate submarine chimneys, Gulf of Cadiz (SW Iberian Peninsula)

“…Marine cold seeps and methane vents are common features of continental margins and other geodynamic settings worldwide (see Paull and Neumann, 1987;Brooks et aL, 1991;Ivanov et al, 1991;Whiticar and Werner, 1991;j0rgensen, 1992;Laier et aL, 1992;De Angelis et al, 1993;Dando et al, 1994;Paull et al, 1995;Boehme et aL, 1996;Cable et aL, 1997;Orpin, 1997;Stakes et aL, 1999;DeLong, 2000;Paull et al, 2005, among others) with no elevated temperatures, where methane-rich fluids flow through the conti nental crust and are colonized by large communities of microbial and chemosynthetic organisms. Methane is generated from various sources: thermogenic and biogenic methane and decomposing methane hydrates, and is seeping to the hydrosphere and poten tially to the atmosphere.…”

“…Cold seeps are associated with authigenic carbonates building chemoherms (e.g. Bohrmann et al, 1998Bohrmann et al, , 2002Suess et aL, 1998;Naehr et al, 2000;Pierre et aL, 2000;Peckmann et aL, 2001;Thiel et aL, 2001;Aloisi et aL, 2002;Hlibscher and Kukowski, 2003;Han et al, 2004;Teichert et aL, 2005, among others) that resemble reefs and/or chimneys (Shnukov et aL, 1995;Orpin, 1997;Stakes et al, 1999;Michaelis et aL, 2002;Gulin et aL, 2003).…”

Quaternary shelf structures SE of the South Island, imaged by high-resolution seismic profiling

“…Fishermen dredging for scallops on this bench discovered a collection of chimneys and irregularly-shaped carbonate concretions (Orpin 1992(Orpin , 1997 that have been linked to distinctive vent phenomena observed elsewhere around New Zealand (Lewis & Marshall 1996). Radiocarbon dating has determined that the chimneys are relict features with a maximum age of 33 0009550 years and a stable oxygen and carbon isotope composition consistent with a predominantly marine origin for the fluid that would have flowed through shallow organic-rich sediments at a time when sea level was considerably lower than present (Orpin 1997).…”

“…1) image up to 150 m of sedimentary section within the lowered bench feature on which the chimneys are found (Orpin 1992(Orpin , 1997. Line 1 (Fig.…”

“…1) has been undertaken on the shallow shelf and upper slope (B250 m water depth) off the coasts of Otago and South Canterbury to address a range of structural, sedimentological, stratigraphic and hydrogeological aims (Allan 1990;Johnstone 1990;Orpin 1992;Gray 1993;Orpin 1997;Wilson 1998;Osterberg 2001Osterberg , 2006. These surveys underpin a substantial body of mostly unpublished research conducted as part of a series of postgraduate theses.…”