Cambrian, Ordovician and Silurian pedostratigraphy and global events in Australia

Abstract

Paleosols are used for stratigraphic correlation of Quaternary sediments because they reflect chronologically synchronous changes of glacial and interglacial paleoclimates. One obvious paleoclimatic indicator is depth to carbonate nodules as a proxy for mean annual precipitation. Paleosol sequences of the Flinders Ranges (Cambrian, South Australia), Kalbarri (Ordovician, Western Australia) and Grampians (Silurian, Victoria) show variation in depth to carbonate through time, but occasional transient excursions to very deep (>50 cm) carbonate. These pedostratigraphic spikes correspond to times of unusually high precipitation and temperature, but also to internationally recognised negative carbon isotope anomalies and mass extinctions, including the Late Ordovician extinctions. These deep-calcic excursions can be correlated across Australia. Like magnetostratigraphy and chemostratigraphy, pedostratigraphic spikes provide calibration points for sequences less-precisely dated by paleontology or radiometry. Also like magnetostratigraphy and chemostratigraphy, pedostratigraphic correlations are best with numerous excursions spaced at irregular intervals and assuming constant local rate of sedimentation. Pedostratigraphy refines geological dating of Paleozoic and Precambrian redbeds and early terrestrial fossils.

Key Words:

• Australia
• Cambrian
• Ordovician
• paleoclimate
• paleosol
• pedostratigraphy
• Silurian

Acknowledgements

Barbara and Warren Fargher graciously allowed access to Wirrealpa Station. Permission for research in Flinders Ranges National Park was approved by Kate Wood, Ken Anderson, Darren Crawford, Arthur Coulthard, and Pauline Coulthard. Permission for research in Kalbarri National Park was approved by Kieran McNamara, Mike Paxman and Russell Asplin. Examination of cores was aided by Brian Logan and Michael Willison at the Primary Industries and Resources South Australia Core Library in Glenside, Avi Olchina and Ken Sherring at the Geoscience Victoria Core Library in Werribee, and Chris Brooks at the Geological Survey of Western Australia Core Library in Carlisle. Ian Johnson, Diane Retallack and Christine Metzger helped with fieldwork. Arthur Mory and Ken McNamara provided helpful and detailed reviews. Funded by American Chemical Society PRF grant 45257-AC8.