Three series of non-isoprenoidal dialkyl glycerol diethers in cold-seep carbonate crests

Three novel series of non-isoprenoidal dialkyl glycerol diethers with an inferred sn-1,2 stereochemistry were tentatively identified in carbonate crusts precipitated from methane-rich bottom-waters and pore-waters associated with Mediterranean mud volcanoes. In the first series of diethers, an 11,12-methylenehexadecyl moiety is ether-bound at the sn-2 position of the glycerol group, and in diethers from the second series, an anteiso pentadecyl group is ether-bound at the sn-2 position. In the third and minor series a pentadecyl moiety is ether-bound at the sn-2 position. In all series, ether-bound C14C17 alkyl units (either n-alkyl, branched alkyl, alkylcyclohexyl or methylenealkyl) occur at the sn-1 position. The two major series are also distinguished by their 13C values, which differ by 1530 at the sites studied. Only the minor series has been previously reported in sediments. Members of the second and third series are similar to diethers containing C16C18 iso, anteiso, and n-alkyl units present in the thermophilic bacteria Thermodesulfobacterium commune, Ammonifex degensii and Aquifex pyrophilus. The first series is unique, in that diethers possessing alkyl chains that contain a cyclopropane ring have never been reported

Methane-related authigenic carbonates of the eastern Mediterranean Sea mud volcanoes and their possible relation to gas hydrate destabilisation

Nautile submersible investigations of mud volcanoes and brine seep areas of the eastern Mediterranean Sea during the MEDINAUT cruise in November 1998 discovered extensive areas of authigenic carbonate crusts associated with methane emissions. Carbonate crusts form pavements, round slabs and circular mounds on the central, most active parts of mud volcanoes and in a fault-related valley where brines have accumulated to form a submarine brine lake. Authigenic carbonate nodules have been recovered from the same areas during the MEDINETH cruise in July 1999. Larg

Clasts from mud volcanoes from the eastern Mediterranean

In the eastern Mediterranean, numerous argilo-kinetic manifestations, commonly named 'mud volcanoes', have been identified and studied in some detail during the last twenty years using several techniques. The Medinaut survey (December 1998) has provided new insights into this phenomenon through twenty deep dives performed with the submersible Nautile within two areas particularly active in terms of mud expulsions: the central Mediterranean ridge south of Crete, and the Anaximander mountains area, south of Turkey. The morphology, petrography, microstructure and biostratigraphy of different clasts sampled in the two areas helped to better understand the mud volcano formation and subsequent evolution. Paleoenvironmental conditions, ranging from deep marine deposition in distal deep-sea-fan environment during the Miocene (Mediterranean ridge) to continental margin conditions (Anaximander mountains), have been evaluated for the composition and age of the various rock types. Macroscopic and microscopic structural observations have revealed a close control of clast shapes by sets of early microfractures (calcite veins, joints) created before the clast expulsion to the seabed surface. Surface features, such as erosion marks, alteration aureoles or calcitic coatings, have also been described on most samples. Finally, erosion traces, alteration aureoles and calcitic coating observed for the first time are interpreted as the result of a complex cold seep context related to mud expulsion and associated fluid venting. © 2001 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS