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

The Wilkes Landcontinental rise is characterisedby mounds andchannels with approximately a north–south elongation, perpendicular to the margin. Proximal mound relief is up to 1000 m, decreasing to about 300m in the central part. During the geophysical andgeological survey conductedon in February–March 2000 by the joint Italian andAustralian WEGA Project, onboardR/V Tangaroa, 11 piston cores were collectedalong two transects crossing the channel-moundsystem. All cores were loggedfor physical (magnetic susceptibility andd ensity) and acoustic properties (P-wave velocity). Split cores were X-rayedandsamples were analysedfor clay mineral assemblages, chemical and micropaleontological (diatoms, foraminifera and nannofossils) content. Glacial andinterglacial 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 mudwith abundant fine to coarse-grainedIRD, containing well-preservedopen-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 laminatedfacies, is interpretedto 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, recoveredin the thalweg of Jussie Canyon, andprobably also in the massive debris facies from the steep side of Mound A. The massive debris is characterisedby structureless andunsortedgravel andpebbles within a muddy matrix. Clay mineral assemblages andgrain lithologies indicate a hinterlandWilkes Basin and continental shelf provenance for the terrigenous fraction.