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

Kowai Formation in the Lake Pukaki area of the Mackenzie Basin, is a tecton ically deformed gravel sequence containing rare, fossiliferous, fine-graine d horizons with pollen assemblages that are unusual in their composition. T he sequence of vegetation types from oldest to youngest is: (1) assemblages with high percentages of Brassospora-type beech and Casuarina: (2) assembl ages with high percentages of araucarian pollen (position uncertain); (3) F uscospora-type beech assemblages; and (4) grassland/scrubland assemblages p receded by a major angular unconformity. The Fuscospora-type beech assembla ges are further divided into sequences where, from oldest to youngest, the paleovegetation is: (a) Fuscospora-type beech with Brassospora-type beech a nd Casuarina; (b) Fuscospora-type beech with Phyllocladus (position uncerta in); (c) Fuscospora-type beech with a variety of pollen types; (d) Fuscospo ra-type beech with podocarps, and (e) Fuscospora-type beech totally dominat es. The age of the beds is Pliocene, as determined by the presence of a num ber 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 P leistocene age. During the early phases of deposition, the climate was warm er and more humid than the present day, as evidenced by the presence of abu ndant araucarian, Nothofagus (Brassospora) beech and Casuarina pollen. Most of the Kowai Formation was deposited at a time when the area was covered i n a Nothofagus (Fuscospora) beech forest, indicative of an interglacial cli mate not dissimilar from that experienced in present-day beech forests. Fro m the top of the sequence. evidence of glacial conditions starts appearing as the forest vegetation disappears to be replaced by grassland/scrubland v egetation.