Stratigraphy and depositional environment of the Kyeburn Formation (Cretaceous), a wedge of coarse terrestrial sediments in Central Otago

Abstract

The Cretaceous Kyeburn Formation is a 4000-m thick terrestrial sequence dominated by coarse detritus, which was deposited in a fault-angle depression. The distribution of lithofacies, direction of fining and of increasing pebble roundness, nature of clasts, imbrication, and orientation of channels, indicate derivation of the sediment from the southwest and southeast, where the sequence is today bounded by the Dansey Pass and Waihemo Faults. Breccias close to the boundary faults represent talus deposits; alluvial fan, flolodplain, and lacustrine deposits occur in successively more distal (northward) parts of the basin. The more distal part of the sequence has scattered carbonaceous material and is dominantly grey in colour; the more proximal part is largely red because of a hematite stain, possibly formed by post-depositional oxidation of mafic minerals.