GEOCHEMICAL CHARACTERISTICS OF WESTERN ROSS SEA (ANTARCTICA) SEDIMENTS

A geochemical study of bottom sediments from 50 stations in various Ross Sea sedimentary environments, ranging from the coastal strip to the external platform, situated off Southern Victoria Land between the David and Mariner glaciers has demonstrated the silicate nature of these sediments and significant variations in the major element concentrations. The presence and concentrations of the trace elements studied (Cr, Ni, Co, V, Cu, Pb, Zn and Cd) differ from one geographic area to another, and within a given basin. A statistical analysis of the geochemical variables using the cluster method shows that Si is independent of the other elements, which group into associations. A multivariate statistical analysis based on geochemical, granulometric and environmental parameters identifies five distinct sediment groups located in different areas of sedimentation and with peculiar geochemical characteristics. Group 1, on the external platform, which comprises very fine sediments, is characterised by the highest contents of Mg, LOI, Cr, Ni and V, and of Cu and Zn. Group 2, from the banks formed by pelitic sands, is distinguished on the basis of lower Cu and Zn and higher Cr and Si. Group 3, on the internal platform consisting of sandy sediments, comprises high values of Na, Al, Ca and Pb and low values of Zn and V. Group 4, in the coarse coastal sands, is enriched in Co and Ca, Na, K and Al. Group 5, formed by materials with different grain-size distribution located south of Coulman Island, is distinguished by a very high content of Zn, Fe, Ti and Na, with Cr, Co, Rb and Si being found at lower levels. The materials are glacial-detrital, are derived from the rocky hinterland formations, and are reworked by transport and deposition processes depending on the energy level of the marine sedimentary environments. Given the scarcity of comparison data from the hinterland rocks it is difficult to establish the parent rocks of these glaciomarine sediments on the basis of geochemical data alone. Only in the case of the sediments south of Coulman Island can one be certain of a contribution from the McMurdo volcanics. For the external platform sediments, the highest contents of Si and L.O.I confirm the input of material from biogenic neoformation.