The Gela Basin pockmark field in the strait of Sicily (Mediterranean Sea): chemosymbiotic faunal and carbonate signatures of postglacial to modern cold seepage

[摘要] The geo-biological exploration of a pockmark field located at ca. 800 m below sea level inthe Gela basin (Strait of Sicily, Central Mediterranean) provided arelatively diverse chemosymbiotic community and methane-imprintedcarbonates. To date, this is the first occurrence of such a type ofspecialised deep-water cold-seep communities recorded from this key region,before documented in the Mediterranean as rather disjunct findings in itseastern and westernmost basins. The thiotrophic chemosymbiotic organismsrecovered from this area include empty tubes of the vestimentiferanLamellibrachia sp., loose and articulated shells of lucinids (Lucinoma kazani, Myrtea amorpha), vesicomyids (Isorropodon perplexum), andgastropods (Taranis moerchii). A callianassid decapod (Calliax sp.) was consistently found alive inlarge numbers in the pockmark mud. Their post-mortem calcified parts mixed with molluscsand subordinately miliolid foraminifers form a distinct type of skeletalassemblage. Carbonate concretions display δ¹³C values as low as−40‰ PDB suggesting the occurrence of light hydrocarbonsin the seeping fluids. Since none of the truly chemosymbiotic organisms wasfound alive, although their skeletal parts appear at times very fresh, somespecimens have been AMS-¹⁴C dated to shed light on the historicalevolution of this site. Lamellibrachiav and Lucinoma are two of the most significant chemosymbiotictaxa reported from various Mediterranean cold seep sites (Alboran Sea andEastern basin). Specimens from station MEDCOR78 (pockmark #1, Lat.36°46´10.18" N, Long. 14°01´31.59" E, 815 m below sea level) providedages 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-modernage of 484 ± 54 yr cal BP. These ages document that fluid seepage atthis pockmark site has been episodically sustaining thiotrophic macrobenthiccommunities since the end of the Younger Dryas stadial up to sub-recenttimes.

[学科分类] 地球化学与岩石