Summary of Results from CRP-1, Cape Roberts Project, Antarctica

Poorly consolidated diamicton, silt, sand, gravel, and a mixed skeletal carbonate-terrigenous facies was cored from 16 m down to 43.55 mbsf and dated as 1.25 to 1.80 Ma (early Quaternary) from diatom biostratigraphy. Depositional environments range among 1) possible terrestrial exposure, 2) glacimarine sedimentation from nearby glacier ice, 3) deposition under sea-ice like today and 4) shallow-marine sea-ice free carbonate sedimentation, representing much warmer temperatures than today. At least two cycles of rise and fall in sea level are recognised. The pre-Quaternary section comprises mainly diamictite, sandstone and siltstone, organised in a cyclic fashion considered to reflect 6-8 variations in relative sea level and/or glacial advance-retreat. Depositional environments were largely shallow-water glacimarine with sedimentation associated with temperate-glacier termini. Diatom biostratigraphy and magnetostratigraphy indicate the strata range from 22.4 to 17.5 Ma in age (average sediment accumulation rate of 21 m/my). These strata record the first extensive Neogene volcanism in the region around 18 my ago, and contain the first post-Eocene marine-dinoflagellate assemblage (at least 15 new species). Another first report is of the calcareous dinoflagellate (Thoracosphaera), found in both Miocene and Quaternary sediment at CRP-1. The pre-Quaternary section of CRP-1 reaches down almost to the base of seismic Unit V3, previously interpreted as representing mid-Oligocene shallowing and glacial advance in the Victoria Land Basin. Results from CRP-1 suggests that the base of V3 could be as much as 8 my younger. This should be resolved by future drilling planned off Cape Roberts.