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For most people, the discovery of fossilised wood in a quarry would not be newsworthy.
However, some pieces recently found embedded in limestone alongside some well-known ‘index’ fossils (see aside below) for the ‘Jurassic period’ (supposedly 142–205.7 million years ago) have proved highly significant.
It is not generally realised that index fossils are still crucial to the millions-of-years geological dating, in spite of the advent of radioactive ‘dating’ techniques.
Not all locations have rocks suitable for radioactive ‘dating’, but in any case, if a radioactive ‘date’ disagrees with a fossil ‘date’ then it is the latter which usually has precedence.
Evolutionary geologists consider that the top three metres (10 feet) of the Marlstone Rock Bed represent the whole of the Tenuicostatum Zone, the basal zone of the Toarcian Stage, Amongst the remaining quarries still ‘working’ the top of the Marlstone Rock Bed are the Hornton Quarries at Edge Hill near the village of Ratley, on the north-western edge of the Edge Hill plateau, some 10½ km (6½ miles) north-west of the town of Banbury (Figures 2 and 3).
Building stone, known as ‘Hornton Stone’, has been quarried there since medieval times.
During two visits to the Hornton Quarries, it was established that fossil wood occurs alongside ammonite and belemnite index fossils (see aside below) in the ‘Hornton Stone’, the oxidized silty top of the Marlstone Rock Bed.
Finding this fossil wood in Jurassic limestone suggested the possibility of testing for the presence of radiocarbon (C should be detectable after about 50,000 years, let alone millions of years, even with the most sensitive equipment.
So this fossilised wood from the Marlstone Rock Bed of Jurassic ‘age’ had potential for testing the validity of the fossil dating technique underpinning modern geology.
being oxidized to limonite (hydrous iron oxides), and also in a few areas the sand content is higher.
In the past, the outcrop has been quarried frequently for iron ore or building stone.