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.