T159 Volcanism, Impacts, Mass Extinctions, and Global Environmental Change III

Tuesday, 20 October 2009
8:00 AM - 12:00 PM
Portland Ballroom 253

AGE DATING MAPCIS (MASSIVE AUSTRALIAN PRECAMBRIAN/CAMBRIAN IMPACT STRUCTURE) A MULTI-MODAL INDIRECT APPROACH

Paper number: T159-3
Program: Technical Sessions
Time: 8:35 AM – 8:50 AM

Authors

Abstract

Background the affected area of MAPCIS is greater than 3 million km2, centered in northern Australia (25°32'S, 131°23'E). This size necessitates an indirect approach of literature review and geology map stratigraphy to collect sufficient data to ascertain the probable age of ~ 545mya. This is based on the knowledge that hundreds of geologists over many decades have collected the samples and the direct data. Methods A review of all known and suspected impacts and ejecta layers within the affected area to find age constraints. Review local orogenies such as the Petermann and Alice Springs, plutonic activity and their possible relationship to the impact. A search through literature and the 1: 250,000 geology maps of central Australia to find the stratigraphic correlation. A search for both proximal and distal ejecta at the PC boundary. I reviewed the Ediacaran extinction event. A review of dating of zircons found on the innermost ridges and of the massive 150km long arcuate deposits of pseudotachylite that surround the impact center.

Results The Acraman and Gosse Bluff impacts constrain the event between ~590mya and 145mya. The Petermann and Alice Springs orogenies constrain it further to 550mya to 450mya. Several smaller impacts dated to the PC boundary are within 150km of the suspected 1800 km trajectory of the MAPCIS bolide. Neoproterozoic layers starting at the PC boundary are found to be cut through and are missing from the impact center. Proximal and distal ejecta match in both type and age, Arkosic sandstones and early Cambrian age. Dating of zircons in the 1 bya Musgrave ranges are reset to dates closer to ~545mya in proximity to the impact center and to the pseudotachylite deposits. Conclusions The age dating of MAPCIS is consistent with the Precambrian/ Cambrian boundary and justifies further direct sampling of targeted sites.