NORFOLK ISLAND's BIOTA
AS A RELICT OF GONDWANA C
But Norfolk Island is only 3.2 million years old maximum! How can this be?
Norfolk Island rests on what is known as the Norfolk Ridge which is recognized as a fragment of Gondwana but the Island is much younger. The Norfolk Ridge is one of a series of arcs of land that broke away from the original landmass called Gondwana. These arcs were added to and modified by volcanic activity and sedimentation at various times.There were uplifts and slumping and there were massive rises and falls in the level of the ocean.
There is a percentage of the biota on Norfolk that had to get there by some continuous land connection. Knowledge of the changing sea levels and the geology is important so that we may begin to understand the stages when the various species could have ended up on the flooded volcanic mountain that is called Norfolk Island.
The Island rests on a much larger former 'island', part of the Norfolk Ridge, which once had several volcanic mountains (now submerged) and that the fluctuations of sea level would have allowed animals to spread to newly formed volcanic peaks during periods of low sea level and become stranded during times of high sea levels. Norfolk Island is now the only representative of life on the south end of the Norfolk Ridge, New Caladonia is at the other end of the same Ridge.
GEOLOGICAL OUTLINE AND SEA LEVELS
280 to 190 million years ago (Permian and Triassic) the Araucarian and Podocarp conifers arise in the landscape of Gondwana, then part of the great landmass called Pangaea.
240-140 million years ago; Triassic and Jurassic periods: the Norfolk Ridge, the Lord Howe Rise and New Zealand (collectively Tasmantis) were still part of Australia-Antarctic. By the Mid Jurassic (about 160 million years ago) the continents were in formation. According to the expanding earth theory, the earth was only 80% of its present size.
By the close of the Jurassic (136 million years ago) New Zealand is thought to have been part of a landmass stretching from the Campbell Plateau to New Caledonia and having a width between the Chatham Islands and the Lord Howe Rise. This landmass was to break up. *Cooling began around 136 million years ago (beginning of the Cretaceous) but some time after warming began, the sea reached maximum height by 120 and 110 million years ago, flooding many areas on the globe and then receeded fairly rapidly as the earth cooled again.
80 million years; Late Cretaceous: Tasmantis broke away from Australia-Antartic. This very likely also included the New Guinea-Louisiade Arc. *At this time the seas were so low that most or all of the Norfolk Ridge was above water.
65 million years ago (iridium layer); beginning of the Tertiary period (Paleocene): the arc breaks up into smaller arcs, including the Norfolk Ridge (which includes New Caladonia) and New Guinea-Louisiade arc. At this time an outer arc developed involving the Vanuatu (New Hebrides), Fiji, Lau, Tonga Ridge. Between 80 and 67-65 million years ago the Lord Howe Rise had begun sinking. After 60 million years ago the distance between New Zealand and Australia reached the present day limits. * By about 65 million years the sea levels had become low but levels rose and fell by 54 million years ago (Paleocene).
53-38 million years ago: the Three Kings Rise shifted away from the Norfolk Ridge, forming the Norfolk Basin. It seems that the Norfolk Ridge broke away from the Lord Howe Rise during this time also. Australia and Antarctica broke links about 50 million years ago, Australia became an island continent.*Another period of low sea levels between 54 and 23 million years ago, permitting archipelagic contact, at least, between Norfolk and New Caledonia and perhaps New Zealand. I would argue that the contact with New Caladonia was probably direct at times but not so with New Zealand: this is based on plant and snail species that can not cross oceans, for example, the Podocarpaceae /Nothofagus on the NewZealand side; the Araucariaceae on the Norfolk/New Caladonian side -- species requiring continuous land to disperse).
23 million years ago, at the beginning of the Miocene, the earliest island may have emerged along the Lord Howe Rise (the Island as we know it is the result of volcanic activity 6.9 million years ago during the late Miocene). Not enough is known and it might be the case that more was once above sea level than there is evidence for at present. *Between 23 and 4 million years ago the sea reached record heights, the mid point being 14 million years when sea reached a great low. After the melting of the ice caps, another high was reached about 4 million years ago. The sea rose and fell at least eight times from this period on.
15 million years ago the present ice cap at Antarctica began to form, though forests survived until about 5 million years ago. Between 7 and 6 million years ago there was a great cooling called the 'Terminal Miocene Event', resulting in a dramatic drop in sea levels, then a warming phase from 5 to 3 million years ago, then a cooling (forming the north polar ice cap).
3 million years ago (Pliocene): Volcanic activity which resulted in the formation of Norfolk Island on part of the old platform of the Norfolk Island Ridge. Philip Island was formed during another volcanic phase beginning about 2.79 million years ago. Another volcanic period lasted from 2.8 and 2.32 million years ago, after 2.2 million years ago the forces of erosion shaped the appearance of the Island. * During this time the sea was within 10 metres of the present level.The sea level had dropped considerably by about 2 million years ago and fluctuated, rising during the next million year at one stage to 20 metres above the present level. The sea reached a low at the end of the Pleistocene during the glacial maximim.
*120,000 years ago the glacial maximum had been reached and the sea level fell as much as 200 metres, exposing continental shelves and probably the whole of the Norfolk Ridge, allowing plants and animals to migrate again.
21,650 (+ - 700) years ago, huge amounts of shell-based sands blew up from former lower level beaches as the sea rose. These sands formed the calcarenite rock seen at Kingston and Nepean Island (which rest on basalt rock). There seem to have been three mega barrier dunes: Nepean Island is very likely the remnant of the largest barrier now mostly eroded away, the saprophytic layer found at Cemetery Bay and Slaughter Bay are probably silent testament to this former barrier dune; the next extended from Cemetery Beach, Point Hunter to the remnants along Emily Bay and Slaughter Bay (heavily quarried); the third was partially linked to the second (north-west end of the Emily Bay area) and arcs from present Government House to the rise above the Pier area. The more dense 'massive' calcarenite was formed much later as it overlies the saprophytic layers. *16,000 - 14,000 years ago was the time of the last glacial peak and a time of low seas. A warming by 11,000 years ago led to a sudden cooling by 10,500 lasting till about 9800 years ago. By 9000 years ago there was a similar climate as now, until about 5,000 years ago when a minor ice age began.
By 7000-6000 years ago large swamps were formed at Kingston during lower sea levels as a result of the outer barrier dunes, creating the saprophytic deposits at Cemetery Bay and Slaughter Bay. Dates obtained on surface logs of this deposit are as recent as about 4000 years ago. There is evidence to suggest that sea levels rose for a while around 4000 years ago and beach sands and rounded basaltic boulders covered the saprophytic deposits.
Norfolk Island. 2000-1000 years ago a dense variety of calcarenite "massive calcarenite" was formed over the saprophytic deposit when sea levels rose a bit. Polynesian tools and stone chips have been found in the more recent of these layers, known as "Slaughter Bay Calcarenite". There was another mini-ice age from about 1650 to 1850
By 900-800 years ago a dense dune was built up along Cemetery Beach during a period when the sea level fell slightly. This deposit is very rich in bird, rat (Rattus exulans) and lizard bones, also countless thousands of land snail shells (indicating dense forest). The deposit also contains charcoal and the occasional Polynesian tool. The plant community was destroyed but it is not clear when. At least 800mm to a metre of comparatively loose sand had built up over the area by the time the mid-1830s convict stone road was built.
200 years ago with the arrival of European settlers, clearing, quarrying, levelling, filling, changing the face of the Kingston area.
ORIGIN OF NORFOLK ISLAND SPECIES
There are several possible origins for Norfolk Island species:
(1) By Direct Legacy of Gondwana.
Flora and Fauna (biota) that flourished, diversified and spread during times of low sea levels along the southern half of the Norfolk Ridge. The biota was then marginalized during times of rising seas along the high points of the ridge, the biota possibly changing during the periods of isolation to suit the environment until the seas dropped again. The isolated pockets could spread out again as the land became available. This process being repeated many times. Further marginalization occurred during times of vulcanism or times of extreme cold (though New Zealand would have been colder). A huge number of extinctions must have occurred during these processes. The virtual absence of freshwater molluscs, compared to Lord Howe Island, is testimony to extreme marginalization in the past.
The absence of Nothofagus (Beech) on Norfolk is interesting because it does occur in New Zealand, Australia and New Caledonia.
(2) By Indirect Legacy of Gondwana.
In this scenario the origininal biota cargo was marginalized out of existance but the land was colonized by plants and animals from the northern half of the Norfolk Ridge, that is New Caledonia, during the several periods of extremely low sea levels. The direct Gondwana legacy of New Caledonia is undisputed. The colonizing biota is subjected to marginalization as for (1).
It is possible that New Zealand may have been a source at an early stage but the absence of Podocarps (Huon Pine and Rimu) on Norfolk and the absence of Araucaria in New Zealand seem to make this unlikely. Though 'Araucaria' pollen has been identified for the Late Cretaceous (say 80 - 65 million years ago) in New Zealand, though not thereafter, probably due to cooling and plant competition.
(3) Origin by Migrating Birds
Several species common to Pacific Islands and Australia seem to have found their way to the Island by this means.
(4) Wind and Water
It seems that many species found their way to the Island by these means over time. Some so long ago that they have developed into distinct species. My point is that there are also species that could not possibly have come to the Island in this way, for example, the Norfolk Pine and many of the invertibrates.
(5) Polynesian Settlement
It is known that banana trees and perhaps some tubular plants and weeds were introduced by them. They also introduced the Polynesian rat (Rattus exulans). I suspect that some of the snail species confined to Kingston but not in the earlier fossiliferous deposits were introduced by Polynesians. The introduction of the Polynesian rat had a terrible consequence on several species, such as the lizard on the main Island (they did not reach Philip or Nepean Islands) and on the terrestrial mollusca. The earliest date proposed for the Polynesians is about 1200 years ago.
(6) European Settlement
The impact of European settlement and the introduction of exotic species is well recorded and understood!!!
CONCLUSIONS
There is no dispute regarding origins in the case of points 3 to 6 for possibly the greater percentage of known plant and animal species on the Island, unlike points 1 and 2.
My position is that the remaining percentage owes its origins to either point 1 or 2 or in combination.
For example, the Norfolk Island Pine (Araucaria heterophylla). This is one plant that needs a continuous landmass to spread, the seeds do not survive travel by sea and are not able to disperse by wind. Branches or leaves do not readily take by cuttings. I think the same thing can be said of any of the Araucariaceae; for example, none of the Norfolk or New Caledonia groups have ever naturally found their way to Australia, Lord Howe or New Zealand.
The closest relative is to be found in New Caledonia (which is on the north end of the Norfolk Ridge), particularly Araucaria columnaris.
I am not on a strong position to comment on the other land invertibrates on Norfolk Island but in coming additions to this draft I will argue that most of the indigenous snail species of the Island are descended from species that colonized the Island via a landbridge or as cargo from the break up of Gondwana.
Dr Robert V J P Varman
August 7, 1997
A Process of Elimination
If we eliminate those species which can travel, whether by water, wind or migrating birds, the resemblances begin to diminish. For example, most of the the regularly breeding indigenous land birds have close New Zealand affinities. There are several plants with very close and probably recent affinities to New Zealand and Australia such as the native palm, flax,