25th International Meeting on Organic Geochemistry IMOG 2011

P-293
Hydrocarbon biomarkers in the bottom sediments of the
hydrothermal fields Ashadze-1 and 2 (MAR, 13°N)
Inna Morgunova, Vera Petrova, Ivan Litvinenko, Georgiy Cherkashev
I.S. Gramberg All-Russia Research Institute for Geology and Mineral Resources of the World Ocean, Saint-
Petersburg, Russian Federation (corresponding author:inik@list.ru)
The rift hydrothermal circulation system is a
complex geostructural formation, which can be used
as a model of natural laboratory for detail geological,
geophysical, geochemical, biological and other
investigations. Enormous amounts of heat released
with the endogenous fluid into near-bottom layers and
their enrichment with a highly mineralized substance
during the fluid discharge stimulates the development
of unique chemosynthetic biocenoses. Specific
patterns of diagenetic transformation of organic
matter (OM) are influenced by a set of physical and
chemical factors.
Samples of sediments (9 stations, 31 sample) were
collected from two active hydrothermal fields
Ashadze-1 and Ashadze-2 (13 ° N, MAR) during the
joint 22 cruise of PMGE and VNIIOkeangeologiya onboard
of the R/V ―Professor Logachev ‖ in 2003. The
significant part of work was conducted during the
French-Russian expedition "Serpentine" on-board
«Pourquoi Pas» in 2007 [1, 2].
The sediments were collected using a box-corer,
TV-grab and drag and kept until the laboratory
investigations in sterile containers at -18 ° C. The
standard analytical procedure included the
determination of elementary (Corg, Norg, Ccarb)
composition of sediments and group and molecular
composition of the soluble part of the dispersed
organic matter (DOM) by methods of preparative
liquid chromatography and GC-MS using Agilent
Technologies GC System 6850/5973.
The comparative study has shown that lowcarbonate
muds and hydrothermal metalliferous
sediments collected directly from the hydrothermal
fields Ashadze-1 and 2 cardinally differ in their
geochemical characteristics from the background
samples: the organic carbon content is sufficiently low
Corg = 0.1 ÷ 0.6%, while hydrocarbons reach 234.4
µg/g of sediment in the surface layer, which is an
order of magnitude greater than the background
values (~ 26 µg/g of sediment). In the group
composition of DOM an increasing content of oil
fraction has been identified and it reaches maximum
values in the sediments of hydrothermal field
Ashadze-1. The presence of isoprenoids, hopenes
and ββ-biohopanes in the composition of DOM gives
the evidence of the fresh biogenic input to the
sediments and the values of maturity indices point to
the intensive OM alteration processes (OEP ~ 1,
sterane C29 20S/(20S +20 R) ≥ 0.5). Three intense
peaks of biphytanes in the high molecular weight
region (C37 ÷ C41) have been detected for both
hydrothermal zones. This similarity allows us to
assume the existence of common processes of DOM
alteration influenced by the hydrothermal
environmental conditions.
A surprisingly high degree of DOM maturity (OEP ~
1) in one of background station surface sediments
agrees with fixed nearby hydrophysical water
anomaly (T °, salinity and turbidity) [3], and indicates
the active thermal catalytic alteration of DOM.
Therefore, the result of two active hydrothermal
fields Ashadze-1 and 2 investigation suggests the
existence of common sources and mechanisms of
DOM generation for them. The similarity may be
connected both with the influence of biological
communities, distributed mainly in sites of
hydrothermal activity, and with specificity of OM
transformation under the whole set of physical and
chemical factors of hydrothermal environment.
References
[1] Beltenev V., Nescheretov A., Shilov V. (2003)
InterRidge News. V. 12. № 1. P. 13-14.
[2] Fouquet Y., G. Cherkashov, J.L. Charlou (2008)
InterRidge News. V. 17. P. 15-19.
[3] Kaminski D.V., Narkevski E.V., Sudarikov S.M.
(2007) Materials from 26 <strong>International</strong> Scientific
conference (school) of marine geology. V. 2. Moscow.
GEOS. 324 p.
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