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Ancient Tsunami

10 August 2016

At http://phys.org/print390032709.html …. work on the M4/M5 junction just outside Bristol (south Gloucestershire) has revealed a couple of bone beds going back 200 million years ago. A Kentucky undergraduate at the University of Worcester analysed samples taken 25 years ago (when the motorway junction was built or upgraded) and she has discovered they were not caused by a single flooding event, as previously deduced, but by more than one transgression event. In geochronology large parts of Germany, France and Britain were flooded by the sea 205 million years ago – the so called Rhaetian Transgression event. Tectonic movements are suspected to be at the root of the flooding so this was not a simple tsunami we are told. There are other reasons why land regions would be submerged but these are not discussed. What is known is that the transgression brought to an end a phase of desert like conditions in Europe.

Tiffany Slater analysed tiny fossils of bony fish and shark taken from 9 bore holes surrounding the motorway intersection at Almondsbury. The bore holes were designed to study the underlying geology prior to construction. That is a common geological process. In this case it came up trumps as some 2000 fossils of teeth, scales and bone fragments were used in the study. The conclusion was that the two bone beds originated as a result of separate highly energetic shoreward storms 'during' the transgression period. This was demonstrated by a dramatic difference in bio diversity and fossil sizes between the two bone beds.

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