Late Quaternary sedimentation in the Northern Western Basin, Ross Sea, Antarctica: seismostratigraphic features and sedimentary properties of calibrated cores

The northern Western Basin is a sector of the continental shelf of the Western Ross Sea (Fig. 1) that is considered to be the natural northward extension of the Drygalski Basin by many authors. The literature provides a general model of the evolution of the basin and the recent papers of Anderson (1999) and Bart et al. (2000) propose a seismic stratigraphy for the post-Miocene sedimentation. However, the sedimentary processes during the Late Quaternary and, in particular, the Last Glacial Maximum (LGM) are still little understood (Brambati et al. 2001). The preliminary results of the seismic survey (Huntec Deep Tow Boomer, Sub Bottom Profiler 3.5 kHz and 0.2-1kJ Sparker multi-array 150 dip), calibrated with the on-board data of the sediment cores (magnetic susceptibility and physical properties), permitted us to delineate the morphological and seismostratigraphic features of the first few meters of sediment and to divide the basin into four sectors. The longitudinal and cross sections of the southern sector of the basin show a morphological threshold at about 73°10’S characterized by several unconformities (up to four evident), and a wide lateral continuity that tapers toward the axes of the basin where a hummocky morphology prevails. The Central sector has a very articulated morphology with accumulations of non-stratified sediment (diamicton) that rise for 10-20 m and whose widths vary between 100 and 1000 m. The sedimentary series shows at least three planar unconformities and aggrading deposits within a thickness of about 100 ms (twtt), typical of phases of glacial exaration. On the outer shelf, starting from the shelf break, we recognized massive hummocky deposits formed by the reworking of the ice front during successive phases of advance and retreat, while the upper slope is characterized by prograding deposits related to successive advances and retreats of the sheet, which often involved consistent gravitative phenomena (Anderson 1999; Bart et al. 2000; Fanucci et al. 1993; Spezie et al. 1993). The sequences of gravity cores principally show a constant scarcity of open-sea sediments (diatomaceous-mud) that are sometimes found mixed with diamicton deposits. This process could be imputed to winnowing by bottom currents that actually flow into the northern area. There are still arguments over the position of the grounding line of the ice sheet in this sector during the LGM, which various authors have positioned at different latitudes and which could be resolved through consolidation tests and radiometric dating of the sediments sampled. References Anderson J.B., 1999. Cambridge University Press., Cambridge, 289 pp. Bart P.J., Anderson J.B., Trincardi F. & Shipp S.S., 2000. Marine Geology, 166, 31-50. Brambati A., Corradi N., Finocchiaro F. & Giglio F. 2001. In: Gamble J.A., Skinner D.N.B., Henrys S., Lynch R. (Editors), Antarctic Earth Sciences at the Close of a Millennium: Proceedings Volume 8th International Symposium on Antarctic Earth Sciences: Royal Society of New Zealand, Bulletin, 35, 365-372. Fanucci F., Firpo M. & Piccazzo M., 1993. Atti del Convegno "Verso una nuova geografia delle terre polari: sintesi e prospettive". Roma, 21-22 novembre 1991. Mem. Soc. Geol. It., LI, 277-289. Spezie G., Tucci S., Budillon G., Corradi N., Piccazzo M., Fanucci F., Firpo M., Mirabile L. & Ferrari M., 1993. Annali Facoltà Scienze Nautiche, Istituto Universitario Navale, Napoli, LX.