Of New Zealand's West Coast
By Thomas Joseph Brown
As any New Zealander will tell you, only the South Island (of the main two) has a “west coast”. It is an area generally isolated by geology (the mountainous spine of that island) and climate (some of the heaviest rainfalls in the world). The “West Coast” district is an area never more than 25 miles wide between mountain and ocean, but it contains a geological wonderland of strange limestone forms, coal measures, and other curious rocks.
The Paparoa Range is a mountainous area, covered in native “bush” (what Americans would call jungle), full of caves and cliffs, with the occasional river disappearing underground. One may even take raft trips through the underground streams-New Zealanders are into thrilling sport. Abundant Tertiary coal measures have fed a continuous mining industry. The Southern Alps to the south and east provide glaciers, gold and greenstone (a nephritic jade).
At Cape Foulwind, near Westport, one can find a curious phenomenon known as the “Fitting Boulders”. These are granitic gneiss (Constant Gneiss) boulders that are independent, but fitting so closely together as to seem as one fractured unit. While listed in geological books as being found about a mile south of Cape Foulwind in coastal cliffs, I found that the boulders right at the Cape also contain this same formative pattern. Figure 1 is a photo of a segment of a cliff at the Cape where this phenomenon takes place. Figure 2 is a drawing of a section of fitting boulders in the cliffs about a mile to the south. It is hypothesized that these boulders are scree from higher cliffs that have fallen to within the spray zone, and that the oceanic location somehow has a major bearing upon this formative curiosity. Similar phenomenon is said to be found along Australia's east coast, across the Tasman Sea.
Figure 1 - Cape Foulwind, New Zealand
Figure 2 - Fitting boulders south of Cape Foulwind, NZ
This “fitting boulder” phenomenon can be found for several dozen miles south of Cape Foulwind. To the south we find Constant Bay, near the town of Charleston. Constant Bay itself is formed from gneiss (hence the name Constant Gneiss) which has the appearance of compressed rocks as shown in Figure 3. Upon close observation it can be seen that these are generally independent rocks compressed by some formative force into the masses we see today. A skeptic will say that these are merely cracked rocks, and in some instances it seems so, as colored seams can be seen through several of the sections. However, close observation will show that these are truly mosaics of independent rocks which have been pressed back together after their original shattering. This appears to be a slightly different phenomenon than the fitting boulders found both north and south of the bay as the entire bay is comprised of this compressed mass, whereas the fitting boulder phenomenon is found in larger rocks along the cliffs.
Figure 3 - Constant Bay, Charleston, New Zealand
While the above mentioned rocks are little known outside of geological curiosity books, the Pancake Rocks at Dolomite Point, Punakaiki are promoted as a tourist attraction, and rightly so. Situated on a beautiful stretch of coastline south of Charleston, Pancake Rocks are a dramatic curiosity as seen in Figure 4. Formed of Potikohua Limestone said to have been deposited during the period approximately 33-22 million years ago, mainly as Oligocene (Tertiary) deposits, but spanning the Oligocene/Miocene boundary. The layering is formed from resistant bands of limestone separated by bands of softer mudstone. The standard textbook explanation is that mechanical weathering has made the limestone layers stand out in relief. Several theories exist as to the nature of these layered deposits. Originally it was thought that the limestone and mudstone were laid down during alternating periods of deposition. Now it is considered that the limestone was subjected to great pressures that caused the mudstone layers to form in a Rube Golderbergish secondary process named stylobedding, whose signature is found occasionally in limestones around the world. Great pressures are evident all along that stretch of coastline.
Figure 4 - Pancake Rocks, Punakaiki, New Zealand
There is a major “unconformity” or “hiatus” in the stratigraphic column at Punakaiki, meaning that there is a large section missing. Unconformities are referred to as “periods of non-deposition and erosion” which in this area stretches from the Paleozoic era, around 400 million years BP to the Eocene coal measures found locally (about 47 Million years BP). This means that the entire Mesozoic Era is missing, consisting of the Triassic, Jurassic and Cretaceous periods, which of course are easily found elsewhere on the island.
Unconformities may seem to make sense as a simple write-off of the problems they present, but when one maps them out they present immense difficulties in accepting the generally accepted formative process of the geological column. In the American Southwest unconformities abound, but the periods they cover vary from locale to locale, often only miles apart, but allegedly spanning tens of millions of years of “non-deposition and erosion”. In the Grand Canyon there is a 200 million year unconformity with a further anomaly-the two layers are intertoungued, with the same micaceous shale found in both members. In a global sense unconformities are quite an anomaly considering their randomness. They seem to indicate catastrophic action on a global scale. Catastrophism is a concept becoming more accepted in geology these days, with the cometary dinosaur extinction theories having gained popular acceptance after the global mapping of the iridium layer at the Cretaceous/Tertiary (KT) boundary. But there are many anomalies associated with the KT boundary that bring the comet theory into question, and which will be explored in future columns.
To add to the mystery of unconformities, there are also “extra” layers that do not fit the general dating scheme. Deep under the American Midwest there is a member of ancient stratified rock, potentially Precambrian, but certainly not easily fit into the general formative scheme. What is most curious about this deposit is that it is up to three miles thick in places - one giant anomaly - a bit too big to sweep under the rug, because it is the rug!
Another curiosity of limestones in general are the consistencies of the deposits over large areas and over millions and millions of years. Personally I question the “yearly deposition” theory, based largely on this obvious consistency (though also heavily based on “crossbedded” sandstones-a theory to be discussed in future columns). At Punakaiki the limestone deposits are formed from various marine organisms, some of them tiny, such as the Bryozoa, but well ground sea urchin and shellfish fragments are thoroughly blended throughout the entire member. In fact the entire limestone member is a rather consistent cement, broken only by the thin mudstone layers. This amazing consistency, we are supposed to believe, was upheld for about 10 million years in one localized area, even though 200 million years of previous geological records are completely absent. The dating of these rocks is based on a global consideration of the general sequence of life forms found within them. Thus a fossil layer found in New Zealand is given the same “age” as a similar fossil layer found either in Asia, America, Australia or Africa.
What is apparent at Pancake Rocks is the pronounced effect of the compressed formative force that can be seen along the West Coast both to the north and the south. That this formative force pervades igneous, metamorphic and sedimentary rocks shows it to be peculiar to this west coast area. Compressed stratigraphic lines also provide a dramatic entrance when driving into the town of Greymouth from the north. Further to the south are the fjords, which may provide further clues when investigated. One curiosity which may provide a clue is the “Bird's Eye” coal found in the Paparoa coal measures (Figure 5) around Greymouth. While many curiosities are found in coal measures worldwide, and will be brought up in future Columns, this Bird's Eye pattern appears to be unique to the West Coast. It is hypothesized that this pattern is caused by intense tectonic stresses, another signature of the compressive formative force evident up and down the coast.
Figure 5 - Bird's Eye Coal
Paparoa Coal Measures
Greymouth, New Zealand
While many other geological curiosities abound in the Land of the Long White Cloud, from loess deposits and a rhythmic pattern of raised marine terraces to out-of-place strata, they will be explored in future writings, along with any other weird rocks found on this planet-or its nearby neighbors! Readers are welcome to submit pictures of strange and curious rocks in their localities, or found on their travels, and of course musings on their origins or occurrences are most welcome.
References
1. Thornton, Jocelyn, Field Guide to New Zealand Geology, Reed Books, Auckland, 1985
2. Corliss, William R., Science Frontiers: Some Anomalies and Curiosities of Nature, Sourcebook Project, Glen Arm, Maryland, 1994
3. Corliss, William R., Unknown Earth: A Handbook of Geological Enigmas, Sourcebook Project, Glen Arm, Maryland, 1980
4. Corliss, William R., Neglected Geological Anomalies, Sourcebook Project, Glen Arm, Maryland, 1990
5. Corliss, William R., Anomalies in Geology: Physical, Chemical, Biological, Sourcebook Project, Glen Arm, Maryland, 1989
© 1994-2001 Thomas J Brown
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