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The T/J extinction event

23 December 2011

The boundary between the Triassic and the Jurassic coincided with a major extinction of species – but what caused this to happen? Scientists are now looking at the possibility of an impact from space – see www.physorg.com/print243248317.html. No obvious crater has been found but distortion of the geological layering has been found, a signature of a violent event of some kind. The rocks of Britain are especially rich in Jurassic remains – even within inland counties. However, the boundary event can be seen quite clearly below cliffs in Antrim, and in Somerset and South Wales. There are great sheets of rock attributable to the Triassic and in the cliff faces above layers of limestone and shale rock that contain simply zillions of marine fossils (mainly broken shells). Geology is a somewhat piecemeal business and in this case the researchers from the US have homed in on a visible rock face – carved out by the waters of the River Severn, on the one hand, and the channel between Northern Ireland and Scotland, on the other. Geologists require rock faces where the strata can be clearly plotted in a clear manner. We may note it is there, all the time, under the surface – but it can't be seen unless there are appropriate holes in the ground such as quarries. The basic stratigraphical sequence is as clear as day – much like the stratigraphy at an archaeological site such as a tell or mud brick ruin heap. The sequence is indisputable but the timescale is conjectural.

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