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Chalk Talk

Chalk Talk


Can you imagine a trip to England without a visit to the white cliffs along the south east coast? We couldn’t, so we went. There we stood at the foot of an awe inspiring cliff of sparkling white chalk. Coarse looking, but flat bedding planes divided the towering wall above into endless horizontal layers or strata. It seemed strange however that the shore was covered with hard, rounded pebbles as well as some shiny black fragments with sharp edges rather than white chalk. Closer inspection indicated that the shiny black chunks and the grayish rounded pebbles were of the same material — only the pebbles were rounded and worn by wave action. Now where did these pebbles of hard material come from? When you come to think of it — where did the chalk above come from too?

Most of us are so brainwashed by modern attitudes that we are tempted to label the cliffs as “Old, old, very old!” Before anyone rushes to these conclusions however, there are some strange features of the cliffs of which we should be aware. British geologist Derek Ager, for example, pointed out some problems. In his book The New Catastrophism (1993) he declared that some standard views on these cliffs lead to “ludicrous” or ridiculous conclusions. For example he said, the standard interpretation for such cliffs, which might be 400 m thick, is that the chalk was deposited from a shallow tropical sea over the space of 32 million years. All this seems very fine he pointed out, until one calculates that this works out to about 1 mm of chalk sediment accumulating once every 60,000 or more years. Obviously, he continued “with these kinds of figures one must deduce that these deposits were not continuously deposited, but include enormous gaps with or without contemporaneous erosion.” The flat bedding planes however do not suggest erosion. Indeed, as far as such chalk deposits are concerned, Dr. Ager reflected that he had “no doubt that such ‘unusually long hiatuses’ occur everywhere.” (The New Catastrophism. Cambridge University Press p. 17). Thus all chalk deposits apparently yield strange answers concerning rates of sedimentation. Most of the assumed time interval is represented by gaps between layers rather than the actual sediments.

If the chalk cliffs were deposited faster than the textbooks suggest, one might be permitted to wonder how much faster is a reasonable answer. We soon discover that chalk is a very interesting topic and one that is full of unexpected details. Unusually tiny swimming algal cells which cover their exterior with even tinier plates of calcium carbonate are the source of most of the chalk. Nobody knows why these strange cells develop such a covering. The plates form pretty designs on the algal surface but these might weigh down such tiny organisms. These algae, some of which live today, grow best in tropical seas. Actually little is known about these organisms because larger algae have always been easier to study. We do know however that deep chalk deposits found around the world, are largely composed of the chalky plates from such algal blooms. They might be tiny, but they could nevertheless achieve incredible biomass by means of a fast growth rate. The intriguing thing is that although some of these organisms exist today, we are not accumulating much in the way of chalk deposits at the present time. This rain or dump of algal wall products was massively greater in the past.

Such chalk deposits are widespread across northern Europe. Not only do we find them in south east England and northern France, but also in Belgium, Denmark, the Netherlands and far south into Italy. These deposits are called Cretaceous, based on the Latin word creta meaning chalk. According to the standard secular interpretation, chalk rained down over millions of years from a shallow sea which covered the northern European landmass. Despite their small size, these cells called coccoliths, should have accumulated many times faster than the popular view would suggest. Moreover certain features of the chalk cliffs also seem to indicate a shorter time interval. For a start, the chalk is extremely pure. In the north there is almost no land derived sediment. The English chalk indeed is so pure that it is much softer than commercial blackboard chalk, easy to scrape with a fingernail. When one examines this powder under a light microscope, the coccolith plates are easy to find. Back out in nature one can also find big artifacts. Entombed here and there within the chalk are various familiar marine fossils, particularly sea urchins and ammonites. Sea urchins (related to starfish) like to live on the surface of rocks. They are typically found in shallow seas and along the shore. Ammonites (extinct relatives of octopus) cruised through the open water of these same shallow seas.

Sea urchins and some other marine fossils are relatively easy to find in debris at the base of the cliffs. As they are so common, it appears that the sea from which they came was not very deep. It seems reasonable to ask then whether these shallow waters could have existed for millions of years without contamination from sediment laden run-off from the land. This seems most unlikely. Alternatively, this shallow sea might have been so extensive that there was no nearby shore, but this too, would be a highly unusual situation. In any case, the shorter the time interval during which the algae rained down to the sea bottom, the easier it would be for the chalk to overwhelm any incidental sand or clay particles. A heavy rain of algal cells might have come from an extremely thick bloom of the algae in a sea made warm and nutritious from volcanic eruptions. Perhaps swirling currents concentrated the algae into dense patches. A sudden change in temperature or salt content could have killed the algae, causing them to sink suddenly out of the water column. Of course it is no small issue to accumulate hundreds of metres of pure chalk in a very short time. Obviously an amazingly concentrated culture of organisms from vast patches of sea would have been involved. Before the reader dismisses such ideas as too fantastic, however, we should proceed to the next enigma of the chalk cliffs, the source of the hard pebbles lying at the base.

The pebbles actually come from inside the chalk. Shiny dark brown or black rock typically lies along many bedding planes in the upper layers of chalk. This material is actually similar to glass or to quartz in that it consists of silicate crystals. It is so different from the chalk, yet so consistently found in the chalk, that its presence requires special explanation. The standard interpretation is that organisms with glass or silicate walls were initially present in the same deposits as the coccoliths, but that the glass dissolved away. Eventually, so the theory holds, the silicate accumulated in crevices and formed the black hard rock we call chert (or flint). This idea does not work however for the numerous sea urchin fossils and ammonites which still retain their naturally rounded contours, entirely unflattened or compressed. Their formerly hollow interiors are filled with the flint. This had to happen at the same time or quickly after burial, otherwise the organisms would have been flattened by the weight of the sediments above. It may be that rising plumes of hot volcanic silica rich water served to carry these creatures upward through the water so that they were not entombed on the bottom, but at much higher levels. These animals did not necessarily even grow where they were entombed, but may first have been swept in from some relatively remote habitat. In his book Catastrophes in Earth History (1984 Institute for Creation Research), geologist Steven Austin cites one paper which suggests that chert can develop from hot volcanic solutions of silicate which turned to gel as they rose in the water in the water column. This gel in turn rained down on the sea bottom where the material diffused through and crystallized onto the surface of sediments below. Similarly Dr. Austin cites another paper which concludes that common natural cherts must have formed rapidly by crystallization from gel-like precursors at elevated temperatures and pressure. The elevated temperatures associated with these volcanic currents would certainly be enough to kill algae, thereby initiating heavy dumps onto the sea floor.

These issues are strange enough, yet Derek Ager points out another enigma concerning the chalk cliffs. The eroding of these cliffs, he declares, must have been sudden and recent. Thus he states: “I never cease to be astonished at the widespread occurrence of pebble beaches in north-west Europe, almost wholly composed of flint pebbles from the Upper Cretaceous Chalk. The mind boggles at the amount of chalk that must have been eroded to produce them. I know nothing comparable in the geological record, apart from a very recent deposit in the Boulonnais of northern France.” (pp. 170-171). Dr. Ager makes an interesting point. The chalk deposits of England and Europe appear to have been laid down as a continuous sheet. Later on, a break developed which served to isolate England from the continent. At the present time, this erosion is fast. The sea eats at the base of the cliff and the resulting overhangs crash into the sea. Apparently in some places the cliff has been cut back as much as 10-25 m during a single stormy night. The view from the top of the cliff may be great, but it is still high risk real estate! All that is left behind once the sea has done its work, are rounded cherty pebbles on the shore. A quick calculation reveals that three or four thousand years would be ample to produce the modern English Channel.

At any rate, for some tourists to Sussex during the summer of 2002, appreciation of nature and of history, converged to produce not only delightful memories but also interesting reflections and speculations about the past. To be specific, there is too little depth of chalk for long ages to be reasonable. Also the purity of the chalk suggests a fast rate of sinking out of the water column, a rate so extreme that any influx of sediments exerted a negligible impact on the overall product. Moreover the large amount of flint is only awkwardly explained by theories of dissolving silicate walls of certain algae (diatoms) and sponge remains with later recrystallizing of the material. Besides that, silicate obviously entered many fossils before they had time to be compressed by overlying sediments. The secular theory can’t explain this. Alternatively, the flint remains are best explained by hot plumes of dissolved silicate which cooled as it rose in the water column. The hot material would bring down the algae and solidify as rock all in one dramatic crisis. Finally, the fast rate of erosion of the cliffs and huge amount of flint left behind, show us that the English Channel opened up quickly and recently. It all sounds like a relatively recent, terrible flood, to me.

Margaret Helder
December 2002

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