Scientific drilling of sediments at Darwin Crater, Tasmania

Abstract

A 70 m long continental sediment record was recovered at Darwin Crater in western Tasmania, Australia. The sediment succession includes a pre-lake silty sand deposit overlain by lacustrine silts that have accumulated in the ∼816 ka meteorite impact crater. A total of 160 m of overlapping sediment cores were drilled from three closely spaced holes. Here we report on the drilling operations at Darwin Crater and present the first results from petrophysical whole core logging, lithological core description, and multi-proxy pilot analysis of core end samples. The multi-proxy dataset includes spectrophotometry, grain size, natural gamma rays, paleo- and rock magnetism, loss on ignition, and pollen analyses. The results provide clear signatures of alternating, distinctly different lithologies likely representing glacial and interglacial sediment facies. Initial paleomagnetic analysis indicate normal magnetic polarity in the deepest core at Hole B. If acquired at the time of deposition, this result indicates that the sediment 1 m below commencement of lacustrine deposition post-date the Matuyama–Brunhes geomagnetic reversal ∼773 ka.