--> Abstract: Magnetostratigraphic studies of late Paleogene-Neogene basins in the central Andes, by Peter Turner, Stephanie Kape, Geoff May, Adrian Hartley, Guillermo Chong, Hans Wilke, and Fin Stuart; #90039 (2005)

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Magnetostratigraphic studies of late Paleogene-Neogene basins in the central Andes

Peter Turner1, Stephanie Kape2, Geoff May3, Adrian Hartley4, Guillermo Chong5, Hans Wilke5, and Fin Stuart6
1 University of Birmingham, Birmingham, United Kingdom
2 CNR International, Aberdeen, United Kingdom
3 Marathon Oil Co, Houston, TX
4 University of Aberdeen, Aberdeen, United Kingdom
5 Universidad Catlolica del Norte, Antofagasta, Chile
6 Scottish Universities Environmental Research and Reactor Centre, East Kilbride, United Kingdom

The Calama and San Pedro Basins in the Central Andes of northern Chile contain thick sequences of continental clastics with associated lacustrine carbonates, diatomites, salt deposits and intercalated volcanic ashes and ignimbrites. Magnetostratigraphy, constrained using 40Ar-39Ar ages of biotite in inter-bedded ashes and comparison with the GPTS has been used to correlate and compare the filling history of the two basins. The advantage of magnetostratigraphy is that genuine time-correlations can be achieved and comparison with the GPTS enables quantification of sedimentation rates and other stratigraphic processes. The San Pedro sequences (Paciencia Gp) were deposited between 30-20Ma during Chrons 6-12 (Rupelian-Aquitanian) and show sedimentation rates ranging from 0.06m/ka in distal settings to 0.20m/ka in proximal fanglomerates. In the Calama basin there are three distinct unconformity-bounded phases of sedimentation and the middle of these (El Loa Gp) is partly time equivalent, but somewhat younger (22-10Ma) than the San Pedro sections. Magnetostratigraphies of surface outcrops and core sections in the Calama basin correspond to Chron 5 of the GPTS (Burdigalian-Serravalian) and sedimentation rates vary little between 0.06 and 0.08m/ka. The relatively slower sedimentation rates are considered to be due to differences in accommodation space and local tectonics that are reflected in the more complex lateral facies variations in the Calama basin. The beauty of magnetostratigraphy is that it produces robust correlations constrained by time-dependent rather than lithology-dependent processes. It also enables a basis for orbital tuning of continental stratigraphy in evaporitic basins which is the future goal of this work.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005