Pollen analysis of Pliocene-Pleistocene Kowai Formation (Kurow Group), Mackenzie Basin, South Canterbury, New Zealand

Abstract

Kowai Formation in the Lake Pukaki area of the Mackenzie Basin, is a tectonically deformed gravel sequence containing rare, fossiliferous, fine-grained horizons with pollen assemblages that are unusual in their composition. The sequence of vegetation types from oldest to youngest is: (1) assemblages with high percentages of Brassospora-type beech and Casuarina; (2) assemblages with high percentages of araucarian pollen (position uncertain); (3) Fuscospora-type beech assemblages; and (4) grassland/ scrubland assemblages preceded by a major angular unconformity. The Fuscospora-type beech assemblages are further divided into sequences where, from oldest to youngest, the paleovegetation is: (a) Fuscospora-type beech with Brassospora-type beech and Casuarina; (b) Fuscospora-type beech with Phyllocladus (position uncertain); (c) Fuscospora-type beech with a variety of pollen types; (d) Fuscospora-type beech with podocarps; and (e) Fuscospora-type beech totally dominates. The age of the beds is Pliocene, as determined by the presence of a number of pollen species that last appeared in the Pliocene, along with a few taxa that first appear at the same time. The youngest grassland/ scrubland assemblages, lacking extinct taxa, may be from fluvioglacial sediments of Pleistocene age. During the early phases of deposition, the climate was warmer and more humid than the present day, as evidenced by the presence of abundant araucarian, Nothofagus (Brassospora) beech and Casuarina pollen. Most of the Kowai Formation was deposited at a time when the area was covered in a Nothofagus (Fuscospora) beech forest, indicative of an interglacial climate not dissimilar from that experienced in present-day beech forests. From the top of the sequence, evidence of glacial conditions starts appearing as the forest vegetation disappears to be replaced by grassland/scrubland vegetation. © 2001 Taylor & Francis Group, LLC.