Abstract
Abstract. The geo-biological exploration of a pockmark field located at ca. 800 m below sea level in the Gela basin (Strait of Sicily, Central Mediterranean) provided a relatively diverse chemosymbiotic community and methane-imprinted carbonates. To date, this is the first occurrence of such a type of specialised deep-water cold-seep communities recorded from this key region, before documented in the Mediterranean as rather disjunct findings in its eastern and westernmost basins. The thiotrophic chemosymbiotic organisms recovered from this area include empty tubes of the vestimentiferan Lamellibrachia sp., loose and articulated shells of lucinids (Lucinoma kazani, Myrtea amorpha), vesicomyids (Isorropodon perplexum), and gastropods (Taranis moerchii). A callianassid decapod (Calliax sp.) was consistently found alive in large numbers in the pockmark mud. Their post-mortem calcified parts mixed with molluscs and subordinately miliolid foraminifers form a distinct type of skeletal assemblage. Carbonate concretions display δ13C values as low as −40‰ PDB suggesting the occurrence of light hydrocarbons in the seeping fluids. Since none of the truly chemosymbiotic organisms was found alive, although their skeletal parts appear at times very fresh, some specimens have been AMS-14C dated to shed light on the historical evolution of this site. Lamellibrachiav and Lucinoma are two of the most significant chemosymbiotic taxa reported from various Mediterranean cold seep sites (Alboran Sea and Eastern basin). Specimens from station MEDCOR78 (pockmark #1, Lat. 36°46´10.18" N, Long. 14°01´31.59" E, 815 m below sea level) provided ages of 11736 ± 636 yr cal BP (Lamellibrachia sp.), and 9609.5 ± 153.5 yr cal BP (L. kazani). One shell of M. amorpha in core MEDCOR81 (pockmark #6, Lat 36°45´38.89" N, Long 14°00´07.58" E, 822 m below sea level) provided a sub-modern age of 484 ± 54 yr cal BP. These ages document that fluid seepage at this pockmark site has been episodically sustaining thiotrophic macrobenthic communities since the end of the Younger Dryas stadial up to sub-recent times.
Highlights
Lamellibrachia and Lucinoma are two of (Hovland and Judd, 1988). They receive much attention the most significant chemosymbiotic taxa reported from var- especially because escaping fluids are often hydrocarbonious Mediterranean cold seep sites (Alboran Sea and Eastern enriched venues in the form of slow seepage, vigorous ventbasin)
In the frame of the EU Hermes and Hermione projects, the Strait of Sicily in the central Mediterranean was targeted as a key area to study sediment instability processes that affect continental margins
We present first data on deep sea pockmarks in the Gela basin resulting in novel information about resident chemosymbiotic communities, biosedimentological processes, authigenic carbonates and seepage temporal variability in this sector of the Mediterranean Sea connecting its western and eastern basins
Summary
A callianassid decapod (Calliax sp.) was consistently Pockmarks are circular to sub-elliptical crater-like depresfound alive in large numbers in the pockmark mud Lamellibrachia and Lucinoma are two of (Hovland and Judd, 1988) They receive much attention the most significant chemosymbiotic taxa reported from var- especially because escaping fluids are often hydrocarbonious Mediterranean cold seep sites (Alboran Sea and Eastern enriched venues in the form of slow seepage, vigorous ventbasin). We present first data on deep sea pockmarks in the Gela basin resulting in novel information about resident chemosymbiotic communities, biosedimentological processes, authigenic carbonates and seepage temporal variability in this sector of the Mediterranean Sea connecting its western and eastern basins
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