| |
Introduction
One of the major foci of current climate research involves the Paleocene-Eocene Thermal Maximum and the longer-lasting peak of warmth within the Early Eocene. At these times thermophilic plant lineages extended far poleward of their current extent, and rainforest of a broadly tropical nature reached its maximum extent (Morley 2000). Most of the research on plant macrofossils for these time periods has been on Northern Hemisphere localities while data from the more ocean-dominated Southern Hemisphere are scarce. Two areas where organically preserved plant remains, including leaf cuticle, are located are southeastern Australia and New Zealand. This paper examines the plant fossil record from one region in southern New Zealand.
The New Zealand region rifted away from the Gondwana margin from the Late Cretaceous until the mid Paleocene (Laird 1994;
Laird and Bradshaw 2004). Then, for a time in the Paleocene, no plate boundary existed through New Zealand, and it settled into a tectonically quiescent period. With crustal cooling and an absence of major tectonism, the land surface sank, and there was a regional transgression (with higher frequency sea-level changes superimposed). The east coast of the South Island contains a stratigraphic record of transgression across the paleo-east coast from the Late Cretaceous until perhaps as late as the earliest Miocene. The coastal plain which developed (the Taratu Formation, sensu
Carter 1988) includes frequent coal and an often abundant plant macrofossil record. The changing vegetation of this landscape is slowly being pieced together. In one of the earliest works on New Zealand plant fossils,
von Ettingshausen (1887,
1891) documented leaves from the Late Cretaceous of Shag Point. From the same locality,
Bose (1975) described the first fossil cuticle from New Zealand. Further Late Cretaceous plant remains were described by
Pole (1992,
1995) and
Pole and Douglas (1999) from Shag Point and the more southerly locality of Kaitangata. Macrofossils and cuticle from a new Cretaceous-Cenozoic boundary section at Cave Stream have recently been descried by
Pole and Vajda (2009). A Paleocene macrofossil assemblage from Mount Somers was described by
Pole (1998a), and in the Eocene
Rozefelds et al. (1992) described Lygodium fossils from the Kakahu area. More material from Kakahu was described by
Pole (1997). A further Eocene assemblage from Livingstone was described by
Pole (1994). The palynology of samples from the Taratu Formation been documented in several publications, including
Couper (1953,
1960),
McIntyre (1965,
1968), and
Raine and Wilson (1988).
Pocknall (1990) included discussion of the Taratu Formation in a synthesis of New Zealand's Eocene.
 Kakahu lies to the west of Geraldine, a small town in southern Canterbury (Figure 1). It is a mixture of farmland and bush, in which sedimentary outcrop is poor, with the exception of limestone bluffs. The local Palaeozoic-Mesozoic basement includes a tectonic melange including a block of Carboniferous marble – the first record of the Carboniferous in New Zealand (Jenkins and Jenkins 1971). The basement is directly overlain by Paleogene coal measures, which were mined at several localities in the 19th century. Associated 'pipeclay' deposits are still exploited. The coal measures are overlain by marine sediments, including Oligocene limestone, which forms the steep scarps of the surrounding ridges.
The regional geology was documented by
Wellman (1953), who considered that about 120 m of 'coal measures' were present. Along Bush Creek, the strata dip to the east at 45-65° and along Rapuwai Road the strata dip to the south at 12-20°. The lowest marine strata, a band of corals in the bed of Bush Creek, are Bortonian (Middle Eocene) in age.
Raine (1988) briefly described the palynology of a sample of the Kakahu coal measures. Based on key taxa and the scarcity of Haloragacidites harrisii (Couper) a Teurian (Paleocene) age was assigned, "for at least part of the sequence." Two leaf fossil assemblages were described by
Pole (1997) with 15 taxa in one and 13 in the other. With the exception of some conifers, a Proteaceae (Lomatia novae-zelandiae) and some scraps of Lauraceae, these fossils were impressions without cuticle.
At the invitation of one of the local landowners, Ian Morrison, research has continued in the area. The aim of subsequent visits has been to search for new fossil localities, particularly those which may preserve cuticle, and document the fossils ecologically and stratigraphically.
|
