Lamine gelatinose ritrovate in un bacino anossico del Mediterraneo Orientale

Erba, Elisabetta ; Parisi, Elisabetta

Atti della Accademia nazionale dei Lincei. Rendiconti della Classe di scienze fisiche, matematiche e naturali, Série 8, Tome 80 (1986) no. 5, pp. 299-305.

Résumé

Gelatinous laminae were observed in three out of ten cores recovered in Bacino Bannock and in both dredges carried out on its flanks during cruise BAN 84 by R/V Bannock in the Eastern Mediterranean. Bacino Bannock is a depression 3.520 m deep, characterized by present partially anoxic sedimentation and gypsum precipitation. The millimetric laminae, dark grey and greenish in color, are always included in very dark sediments that are Quaternary in age. These gelatinous laminae have been investigated by optical, scanning and transmission electron microscope in order to decipher their nature. We observed abundant skeletal remains of siliceous and calcareous planktonic organisms (Radiolarians, Diatoms, Silicoflagellates, Foraminifers and calcareous Nannofossils) entrapped within amorphous organic matter. Gelatinous laminae including these vegetal and animal remains do not show any cellular structure; they do not react with HCl and are completely destroyed by $H_{2} 0_{2}$. Flash pyrolysis-gas chromatography and flash pyrolysis-gas chromatography-mass spectrometry were carried out to determine the organic matter laminae compounds. We suggest that gelatinous laminae are bacterial in origin and grew at the brine/sea water interface located at — 3.200 m in Bacino Bannock. The floating laminae entrapped biogenic and non biogenic particles and sank to the basin floor after load increasing.

Bibliographie

Blechschmidt G., Cita M.B., Mazzei R. e Salvatorini G. (1982) - Stratigraphy of western Mediterranean and southern Calabrian Ridges, eastern Mediterranean. «Mar. Micropal.», 7, 102-134.

Camerlenghi A. e Cita M.B. (1986) - Setting and tectonic evolution of the Eastern Mediterranean deep-sea basin. «Mar. Geol.», in stampa.

Cita M.B., Aghib F., Cambi A., Camerlenghi A., Corselli C., Erba E., Giambastiani M., Herbert T., Kastens K.A., Leoni C., {author_10}, {author_11}, {author_12}, {author_13} e {author_14} (1985) - Precipitazione attuale di gesso in un bacino anossico profondo: prime osservazioni geologiche, idrologiche, paleontologiche sul Bacino Bannock (Mediterraneo orientale). «Giorn. Geol.», 47 (1-2), 143-163.

Cita M.B. e Corselli C. (1986) - Precipitazione di gesso da brine saline al fondo del Mediterraneo. «Rend. Cl. Sci. Fis. Mat. e Nat., Accad. Naz. Lincei» (in stampa).

Corselli C. e Aghib F. (1986) - Brine formation and gypsum precipitation in Bacino Bannock. «Mar. Geol.», in stampa.

Erba E., Rodondi G., Parisi E., Ten Haven H.L., Nip M. e De Leew J.W. (1986) - Gelatinous laminae in deep anoxic hyper saline basins from the Eastern Mediterranean.«Mar. Geol.» in stampa.

Gartner S. (1977) - Calcareous nannofossils biostratigraphy and revised zonation of the Pleistocene. «Mar. Micropal.», 2, 1-6.

Jongsma D., Fortuin A.R., Huson W., Troelstra S.R., Klaver G.T., Peters J.M., Van Harten D., De Lange e Tenhaven H.L. (1983) - Discovery of an anoxic basin within the Strabo Trench, Eastern Mediterranean. «Nature», 305, 795-797.

[5] Parisi E., Erba E. e Cita M.B. (1986) - Stratigraphy and sedimentation in the anoxic Bannock Basin. «Mar. Geol.», in stampa.

[6] Ryan W.B.F., Thorndike E.M., Ewing M. e Ross D.A. (1969) - Suspended matter in the Red Sea brines and its detection by light scattering. In: Hot brines and recent heavy metal deposits in the Red Sea (Eds. E.T. Degens and D.A. Ross), Springer Verlag, Berlin pp. 153-157

[7] Sheu D.D. e Presley B.J. (1986) - Formation of hematite in the euxinic Orca Basin, Northern Gulf of Mexico. «Mar. Geol.», 69, 309-321.

[8] Scientific Staff Of Cruise Bannock 1984-12 (1985) - Gypsum precipitation from cold brines in an anoxic basin in the Eastern Mediterranean. «Nature», 314 (6007), 152-154.