Fossils or frauds?

Press, 11 September 1986, Page 21

Fossils or frauds?

On the coast just north ofWard Beach, in Marlborough, there is an intriguing geological site at a place called Chancet Rocks. Beds of Amuri limestone, often pinkish in colour, outcrop on the shore. Tney have been weathered into interesting shapes, and the beds themselves have been folded and bent, and finally tilted on end, so that they stand upright like sliced bread instead of lying flat like a bed should. But it is not all this distortion that makes the geology so unusual. The beds of limestone contain, along with flint nodules, manv largish, fossil-like shapes. These can best be described as globose, or barrel-shaped cylinders of highly silicons limestone, many with a pronounced central rod, and often joined together in great masses. They originally stood upright but, having been tilted over with the limestone in which they are embedded, they are now lying on their sides. The surrounding limestone, somewhat softer, jfcnds eventuallyxto weather Sway, leaving these objects exposed. I describe them as fossil-like

because there is some argument about their origin and exactly what they are. Until recently they were considered to be fossil sponges about 50 million years old; certainly many of them closely resemble some sponge species.

One of the problems in proving this theory is the difficulty in obtaining the necessary evidence. Living sponges have a framework of small, sharppointed objects called spicules. When sponges are fossilised these can often be extracted from rock rtoterial and identified. Unfortunately, the Amuri limestone does not easily yield up this sort of information.

Another problem which has puzzled palaeontologists is the presence of the marked central rod in many of the specimens. This is a feature not found in any known sponge species. The presence of this rod has led to a proposal that these objects are not sponges at all — in fact, not even fossils.

The suggestion is that they are silica concretions, formed by chemical action around the central rod, and that this rod was originally a vertical burrow made by some marine creature when the iimestSae was still a soft, sea-floor sfediment. The technical name is paramoudra. The occurrence of these "fos-

sils,” whatever they actually are, was of sufficient geological interest to warrant the locality at Chancet Rocks being made into a scientific reserve to protect them from indiscriminate collecting. This was necessary because, as one geologist pointed out, collectors knew the locality far 1 better

than scientists. There were local reports of busloads of collectors arriving to gather specimens; and, as garden ornaments, they threatened the popularity of gnomes. y It is well worth a walk along

the beach at Ward to visit this site; if this is not possible, a medium-sized specimen is on display at Canterbury Museum. You might be able to make up your own mind as to the possible origin of these curiosities.

By

BEVERLEY McCULLOCH