Abstract
Gelatinous pellicles were observed in three out of ten cores recovered from the Bannock basin (or Bacino Bannock) and in two dredges from its flanks during a cruise of the R.V. Bannock in the E Mediterranean. Similar pellicles have also been detected in two cores recovered from the Tyro basin. The Bannock and Tyro basins are brine-filled depressions which are currently characterized by anoxic sedimentation; in the Bannock basin gypsum precipitation also occurs. The gelatinous pellicles, some mm thick and dark grey to greenish, are always found in very dark sediments of Quaternary age. These pellicles were investigated by optical microscopy, SEM, TEM, flash pyrolysis-GC and flash pyrolysis GC-MS to decipher their nature. Abundant skeletal tests of siliceous and calcareous planktonic organisms (radiolaria, diatoms, silicoflagellates, foraminifera and nannofossils) were observed, together with amorphous organic matter. The pellicles enclosing these remains consist of organic matter; they foliate into submillimetric undulating and anastomosing microlaminae. Cellular structures are never observed, neither in the pellicles nor in the microlaminae. Organic geochemical analyses point to a high contribution of terrestrial material. The organic matter of the pellicles investigated consists of a 'coal-like' material. It is suggested that the pellicles were originally formed at the brine-sea-water interface, but subsequently sank to the bottom due to increasing load of entrapped biogenic and non-biogenic detritus. (Authors' abstract)