Ninth international conference on - Marum

38
Abstracts of oral presentations
The authigenic chimney formation in the Gibraltar diapiric Ridge
(NE Atlantic)
E. Logvina 1 2 , A. Krylov 1 , T. Matveeva 1 , A. Stadnitskaia 3 , T.C.E. van Weering 3,4 , M. Ivanov 5 and V. Blinova 2
1 All-Russia Research Institute for Geology and Mineral Resources of the Ocean (VNIIOkeangeologia), 190121,
1, Angliyskiy ave., St.Petersburg, Russia
(e-mail: Liza_Logvina@mail.ru)
2 St.Petersburg State University (SPbSU), Universitetskaya nab. 7/9, St.Petersburg, Russia
3 Royal NIOZ, Landsdiep 4, 1797 SZ, ’t Horntje, Texel, the Netherlands
4 Department of Peloclimatology and Geomorphology, Free University of Amsterdam, de Bolelaan 1085, 1081
HV Amsterdam, the Netherlands
5 Moscow State University (MSU), 119899, Vorobjevy gory 1, Moscow, Russia
Dredging on the Gibraltar diapiric Ridge during TTR14 cruise onboard R/V “Professor Logachev” yielded a
large amount of carbonate chimneys. Two of them conventionally named as “Big” and “Small” were studied
during this work. The area, where the studied chimneys were sampled, situated on the modern boundary of gas
hydrate stability zone, thus their formation during the Early Pleistocene (Ivanov et al., 2004) might be related to
formation of gas hydrates.
Subsamples for isotopic δ 13 CVPDB, δ 18 OVPDB and XRD analysis were picked out from the chimneys using the
scheme presented on figure 1. The main goal of the study was to reveal possible sources of carbon and oxygen
incorporated into the bulk carbonate material. More than 70 subsamples were measured for δ 13 CVPDB and
δ 18 OVPDB isotopic compositions at the Stable Isotope Laboratory in the Free University of Amsterdam.
Mineralogical composition of carbonates was studied by powder X-ray diffraction (XRD) analyses on apparatus
Rigaku Rint 1200.
Fig. 1 Sketch representing subsamples (1-24) position on the (A) “Big” and (B) “Small” chimneys. The dotted
curves represent inner canals of the chimneys; numbers I-V indicate cross sections position.
XRD shows that both studied chimneys as whole consist of dolomite, calcite, quartz and some amount of
goethite. “Small” chimney characterizes by predominance of dolomite. The highest concentrations of dolomite
observed in the top of the “Small” chimney (section I-II). Calcite concentration is increased to the canal of the
chimney (subsample No1). The “Big” chimney consists predominantly of calcite with some admixture of
dolomite around the canal (subsamples No11&20). The quartz content in the “Small” chimney is higher as
compared to “Big” one. Goethite was identified in different parts of both studied chimneys. Highest content of
goethite in the “Big” chimney observed in the periphery part (subsample No15) and in bottom of the “Small’
chimney (section IV-V, subsamples No6,1).
The obtained δ 13 CVPDB values vary from -2.37 to -27.9‰. There is no significant difference in carbon isotopic
compositions between two studied chimneys. At the same time, negative trend in δ 13 CVPDB distributions from
canal to periphery of the chimneys is remarkable. The variations in measured carbon isotopic values may be
explained by different sources of carbon inherited by carbonate: (a) carbon depleted in 13 C deriving after AOM,
(b) CO2 enriched in 13 C released during methane generation, (c) carbon of ambient sea-water (δ 13 CVPDB ~0‰),
(d) carbon of the autochthonous organic matter (δ 13 CVPDB ~-27‰).
The measured values of δ 18 OVPDB vary from +1.63 to +4.8‰ (+3‰ on average). Most of the measured values are
typical for MDAC (+3…+6‰). The δ 18 OVPDB of the studied chimneys is controlled by combination of the
following factors: (a) the temperature of formation, (b) the carbonate mineralogy, and (c) δ 18 OVPDB composition