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THE BRISTOL IMPACT LAYER, UNITED KINGDOM

Probable Late Triassic Age

In 1973 glauconite spherules were discovered at Churchwood Quarry, Wickar, Bristol (Grid Reference 713 900) reportedly by Kirkham. This spherulitic deposit has now been totally removed by quarrying operations and the exposure no longer exists. These spherules, which formed a discontinuous layer, were found in the Triassic, Mercia Mudstone (Keuper Marl) which unconformably overlies Lower Carboniferous, Clifton Down Limestone. The spherules are found with shocked quartz and probably represent altered microtektites, which formed by meteorite impact with the Earth. The age of the spherules certainly lies between Late Carboniferous and Late Triassic, with a Late Triassic age more likely. It has been suggested that the age of the spherules is 214 Ma, with the source crater being the 100km diameter Manicouagan Crater in Quebec, Canada. At the time of deposition the Bristol area would have been in the order of 2000km from this crater, as the North Atlantic Ocean had not yet opened up.

It is hoped to add more to this page in the future. In the meantime please enjoy these photos.

 

ABOVE:   A close up of the Bristol Impact Layer. Photo courtesy of Mark Ford (British and Irish Meteorite Society)

 

ABOVE:  The Bristol Impact Layer. Photo courtesy of Mark Ford (British and Irish Meteorite Society)

 

ABOVE:   Another fragment of the Bristol Impact Layer in my collection.

 

References:

Glass, B. P., Koebert, C. and Kirkham, A. 2003. Invited comments on Kirkham's 'Glauconite spherules from the Triassic of the Bristol area, SW England: probable microtektite pseudomorphs'. Proceedinings of the Geologist's Association, 114, 175-179.

Kirkam, A. 2002. Triassic microtektite pseudomorphs of the Bristol area. Geoscientist, 12(7), 17-18.

Kirkham, A. 2003. Glauconite spherules from the Triassic of the Bristol area, SW England: probable microtektite pseudomorphs. Proceedings of the Geologists' Association, 114, 11-21.

Kirkham, A. 2006. Triassic Meteorite Impact? Magazine of the Geologists' Association. 5(4) (December 2006), 21.

Simms, M. J. 2007. Uniquely extensive soft-sediment deformation in the Rhaetian of the UK: Evidence for earthquake or impact? Palaeogeography, Palaeoclimatology, Palaeoecology, 244, 407-423.

Walkden, G., Parker, J. and Kelley, S. 2002. A Late Triassic Impact Ejecta Layer in Southwestern Britain. Sciencexpress, www.scienceexpress.org 14 November 2000, 10-1126, science 1076249; and Science, 298, 2185-2188.

 

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