Palaeogene volcanism

1 November 2014

Cave Hill dominates a portion of the landscape in the northern part of Belfast – see Down to Earth magazine issue 89, 2014 (ISSN 0969-3408) which is just four issues for a pound (great value). Cave Hill is a chalk and flint hill but it is capped by a layer of basalt. This is an igneous rock, formed when hot lava cools. It is dated to around 60 million years ago, a time of intense volcanic activity in many parts of the world. It is known as the early Palaeogene – but comes right after the end of Cretaceous K/T boundary event. Geologically, as far as uniformitarian numbers are concerned, it occurs several million years after the asteroid strike that killed off the dinosaurs – but is this justified?

In the Palaeogene the American plate was 'pulled away' from the European plate (Ireland was at the edge of things) leaving the Atlantic between them. The pulling away caused the Earth's crust to stretch and fracture and fissure opened up where molten magma ascended to spill out on to the surface.

The Co Antrim chalk is exposed in various places and the Cave Hill deposit of chalk is dated to around 80 million years ago (the reasoning here is not elaborated on) so the suggestion is that it was not formed at the end of the Cretaceous but at some point within the Cretaceous (and going by the date that would tend to suggest an Upper Chalk date). Antrim chalk is much harder than the chalk of southern England which may be due to the fact it is covered by impervious basalt and the chalk beneath is not subject to rain percolating through it. The chalk exists in the NE of Ireland, mainly in the Belfast area, with just small outcrops elsewhere – such as in the Killarney area. It is thought erosion has eliminated most of it, a situation that is the geological view concerning chalk above the present escarpment in the Chilterns. How it eroded is assumed to be gradualist in nature.

Chalk was laid down in a shallow sea, is the mainstream view. This means it must have covered large areas of what is now land – in Europe and the Americas. What if the land was already there – as suggested in the interpretation of the Palaeogene? How did the chalk get on the land?

Did the Atlantic exist in the Cretaceous – was it the shallow sea that promulgated all those coccoliths that make up chalk. Catastrophism is a feature that is ignored in geological interpretation but it could explain the complex situation – as major catastrophes occured at the end of Triassic as well as at the end of Cretaceous and end of Jurassic. In lowland England the Jurassic is marked by thick layers of clay. Now, the niggle that intrigues me with this piece on the Palaeogene is that geochronology may have warped our perception of what actually happened. Catastrophism may be obscured by the stretching out in time of an event – various sedimentary layers (and geomorphological intrusions) may have been laid out on the chronology as widely spaced events when in fact some of them may have been contemporary. One only has to consider the recent Mount St Helens eruption. It laid down wide and thick sedimentary layers, How would geologists have interpreted such an event if it had happened millions of years ago. Easy, They would have spaced the different layers out over a very long period of time. Hence, are we sure the Palaeogene volcanism was that widely spaced from the K/T boundary – and that is without considering the chalk formations itself. 

At … there is a study in the journal Science (Oct 31st, 2014) that claims ocean water came early to Earth. Basically, it is saying water came to Earth during the accretion of the planet itself – and there is no reason not to doubt that. However, how does this affect the Palaeogene expansion of the Atlantic – or the expanding earth hypothesis?

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