Fission-track ages and correlation of middle and lower pleistocene sequences from Nebraska and New Zealand

Abstract

Fission-track dates of glass shards from volcanic ash in two rhyolitic pumice beds that are separated by 975 m of Castlecliffian (middle Pleistocene) marine sediments from south-western North Island, New Zealand, indicate that the Castlecliffian Stage began about 1•19 ± 0•14 m.y. ago and ended slightly less than 0•39 ± 0•01 m.y. ago. Correlation of the New Zealand marine sequence with the glacial sequence of eastern Nebraska by fission-track dates indicates that the Nukumaruan/Castlecliffian boundary (early middle Pleistocene) is equivalent to the Nebraskan Aftonian/Kansan boundary at about 1•2 m.y. The Castlecliffian Stage appears to have a time span equivalent to the entire Kansan and Yarmouthian Stages and probably part of the Illinoian Stage of eastern Nebraska. The beginning of the New Zealand Nukumaruan Stage may coincide with the beginning of the Nebraskan Stage, dated at about 2•0 m.y., and these two stages may be of similar duration. The two New Zealand dates show that 975 m of Castlecliffian marine sediment was deposited at a rate of 122 cm per thousand years. Basal Castlecliffian beds have been uplifted at an estimated rate of 453 cm per thousand years.