Plio-Quaternary sedimentation on the Wilkes land continental rise: preliminary results

The Wilkes Land continental rise is characterised by mounds and channels with approximately a north–south elongation, perpendicular to the margin. Proximal mound relief is up to 1000 m, decreasing to about 300 m in the central part. During the geophysical and geological survey conducted on in February–March 2000 by the joint Italian and Australian WEGA Project, onboard R/V Tangaroa, 11 piston cores were collected along two transects crossing the channel-mound system. All cores were logged for physical (magnetic susceptibility and density) and acoustic properties (P-wave velocity). Split cores were X-rayed and samples were analysed for clay mineral assemblages, chemical and micropaleontological (diatoms, foraminifera and nannofossils) content. Glacial and interglacial intervals have been recognised in the sediment cores. The interglacial facies consists of massive mud, distinguished by: (a) bioturbated massive mud occasionally with fine-grained ice-rafted debris (IRD), and (b) structureless massive mud with abundant fine to coarse-grained IRD, containing well-preserved open-ocean diatoms. The glacial facies is represented by laminated mud with planar and/or cross laminations, with occasional isolated dropstones, and rare, poorly preserved, sea-ice diatoms. The sharp boundary, characterizing the limit between massive to laminated facies, is interpreted to indicate a fast glacial onset. In contrast, the smooth passage presents from laminated to massive sediments, indicates a gradual glacial waning. Recent down-slope gravity flows have been identified in a turbidite, a normally graded coarse-grained sand, recovered in the thalweg of Jussie Canyon, and probably also in the massive debris facies from the steep side of Mound A. The massive debris is characterised by structureless and unsorted gravel and pebbles within a muddy matrix. Clay mineral assemblages and grain lithologies indicate a hinterland Wilkes Basin and continental shelf provenance for the terrigenous fraction.