THE KARST INGREDIENT OF THE NEW PAPAROA NATIONAL PARK
NOTES FROM AN ILLUSTRATED TALK GIVEN IN 'ICE AGE CHAMBER' GLORY HOLE CAVE, YARRANGOBILLY CAVES, KOSCIUSKO NATIONAL PARK
Introduction
The proposed (May 1987) Paparoa National Park is in an area of approximately 30,000ha situated between the coast and the crest of the Paparoa Range in the north west of the South Island of New Zealand. It reaches from the coastline to the crest of the Paparoa Range at Mount Lodge (1,447 metres).
Two major features give character to the area and dominate the theme of the Park. These are the lowland bush and the limestone landscapes. The scenic coastline already plays an important role for recreation and tourism with features like the Pancake Rocks and Truman Track.
Within the boundary of the new Park there is an extensive area (approximately 40%) containing karst features. Until recent years the general public's knowledge of the karst in the area was limited to the karren field at Dolomite Point. Although this area is small it is very accessible and is known internationally as the Pancake Rocks. Cavers were also aware of some cave systems in the Bullock Creek, Fox River, 4 Mile and Ananui Creek areas, however, there still remains much unexplored karst terrain.
The Karst in General
The major geological feature is the limestone syncline running down the western side of the Paparoa Range. On the western side of the syncline the karst plateau rises to 472 metres with an average height of 370 metres. The abrupt edge on this side of the limestone ends with the massive limestone cliffs running 20 kilometres along the coastline. It is these cliffs which give the region its distinctive karst scenery. The karst plateau is dissected by rivers flowing from the Paparoas and there are six major limestone gorges within the new Park. Scenic qualities of these gorges are heightened by steep walls of white limestone contrasting with the rich greens of the bush. The syncline gently dips to the south and the bed of the syncline lies only 40 metres above sea level.
The eastern side of the syncline is not visibly as spectacular as the west though the limestone has been pushed up steeply to 659 metres at Waikori. Along the eastern edge it is also dominated by the foothills of the Paparoas.
There are six distinct beds which make up the tertiary rocks found in the syncline. These are - Mawheranui Group; Brunner Coal Measures found in the north and south and the deepest the Rapahoe Group; the Kaiata Formation, a massive formation of impervious marine mudstone and sandstone which is impervious to water; and the Nile Group of limestone and highly calcareous clastic sediments. This group has two divisions which are the major rock where the karst development has occurred. These are the Tiropahi Limestone and the Potikohua Limestone which are both very rich in calcium. Overlying this is the Blue Bottom group, the Welsh formation and the O'Keefe formation, marine mudstones, and muddy sandstones with minor limestone near the base.
Speleogenesis
Most of the cave systems in the area have been found to the west or in the bed of the syncline. The majority of these caves have developed down in the 5° to 10° dip of the syncline. They usually follow the bedding planes of the Tiropahi or Potikohua Limestones.
Work in the Metro cave by Williams (1970) shows that sea level fluctuations during the Pleistocene had major effects on the cave during its development. No work has been done to relate this to other caves in the area but it is likely that they were affected in the same way. There is growing evidence of the presence of an inland sea behind Punakaiki in recent geological time. Some of the caves are high and dry along cliff faces whilst others are still affected by rainstorms along creek margins i.e. Xanadu in Bullock Creek. There is a range present of caves from those in a state of collapse and decay to others still below the phreatic zone and therefore still developing.
Subfossils and Fossils
There are many rich deposits of subfossils. These are mainly of avian remains but there are reports of reptilian, mammalian and molluscan remains. The extinct moa features in most deposits ranging from the larger species to the small bush moa; their smaller relation the kiwi (one species of kiwi is still present in the region) has also been found. These deposits indicate a rich avifauna was present at some stage in the past.
Fossils found in the caves are from the Tertiary limestones or the Upper Miocene. The fossils so far recorded range from whale bones and part whale skeletons, shark's teeth from many species, fossilised crab claws and several species of sea shells.
Biological Values
The Punakaiki karst is important because it is the only extensive area of lowland karst in New Zealand with its bush cover almost intact. For this reason most of the biological processes which have developed over thousands of years are still in place and operating naturally.
Many of the cave systems in the area receive high food/energy inputs from flooding. Food for glowworms, spiders, carabid beetles etc is carried in by regular flooding. Wetas are also present in most of the caves and recently an unusual wasp which is a parasite on weta eggs has been recorded in the Metro Cave system. In general very little is known about the biology of the Punakaiki karst.
Caves and the public
The Fox River Cave was discovered about 1903 and has been visited by the general public ever since. It was regarded as a tourist cave for many years with a locked gate and caretaker, however, for reasons unknown the gate was removed and not replaced. Recently the cave has received renewed interest with many visitors on a regular basis, no control has lead to a steady deterioration of the speleothems and cave environment. It is still attractive and often the first experience the general public have of a cave in this area.
Unfortunately no accessible and highly decorated cave, which would be ideal for tourist development, has been found. The Metro Cave would be suitable as a show cave with a different type of experience. Its 8km of tubes and passages could provide an adventure type tourist caving experience.
There is a recognised need for the development of a cave in the area which would provide the public with a cave experience. There are several littoral caves along the coast which the public have had access to for many years these are not limestone caves but are in granite, granitic breccia, sandstone and mudstone.
The Future
Karst management in New Zealand is only just being recognised as a very important part of our heritage. The new Department of Conservation now has the responsibility to ensure a national karst resource is managed appropriately. The delicate nature of the karst environment makes this a task without precedent and managers of the Paparoa area must now cater for the needs and judgements of future generations.