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Journal of the Geological Society; 2006; v. 163; issue.4; p. 697-705;
DOI: 10.1144/0016-764920-135
© 2006 Geological Society of London

Original Article

A possible earthquake-triggered mega-boulder slide in a Chilean Mio-Pliocene marine sequence: evidence for rapid uplift and bonebed genesis

S.A. Walsh1 & D.M. Martill2

1 1The Natural History Museum, Department of Palaeontology, Cromwell Road, London SW7 5BD, UK (e-mail: s.walsh@nhm.ac.uk)
2 2University of Portsmouth, School of Earth and Environmental Sciences, Burnaby Road, Portsmouth PO1 3QL, UK

The type area of the Bahía Inglesa Formation (north–central Chile) is structurally complex as a result of active margin subduction at the Peru–Chile Trench. Inliers of subaerially exposed Mesozoic igneous basement are unconformably overlain by a mid-Miocene to late Pliocene marine siliciclastic sequence, which has become known for its abundance of fossil vertebrates found concentrated in a phosphatite on an omission surface. Mega-boulders derived from one of the largest inliers occur exclusively within this bonebed, which appears to have formed after major localized uplift caused removal of a significant thickness of unconsolidated sediment. The mega-boulders were probably dislodged by a high-magnitude earthquake event that accompanied tilting of the sea floor, and their emplacement was an integral part of the processes involved in genesis of the bonebed.