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| Differential weathering of marl and undercutting at Hooton Cliff |
Continuing south along Hooton Cliff, I encountered further examples of well bedded massive limestone and small bryozoan reefs but, with vegetated mounds of quarry waste and thick undergrowth making access a bit difficult, I didn’t investigate them further.
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| The Cadeby Formation at Hooton Cliff |
As always, when undertaking my days out that have a geological element to them, I keep an eye on the possibility of including sites in a field trip for the Sheffield U3A Geology Group and, with the group getting older and becoming less confident in their physical abilities – one consequence of the COVID-19 Pandemic - this is becoming increasingly important.
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| A small bryozoan reef overlain by well bedded limestone |
The exposures at the southernmost end of the escarpment provide the most accessible exposures of the Cadeby Formation, with the reefs and various other lithologies easy to examine closely but, after taking a sample with my Estwing hammer, I didn’t stay here very long.
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| A sample of crystalline limestone from Hooton Cliff |
The specimen that I obtained from this locality is quite different to the one that I collected further to the north, which is uniformly very fine grained and granular when viewed with a hand lens. The surface is very irregular and appears quite crystalline in places, with black specks of a manganese oxide mineral being common.
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| A rift in the limestone at Hooton Cliff |
Wide joints and the development of rifting is also quite common here, with these being infilled with sandy Quaternary sediments of a type that have yielded mammalian fossils at other sites in Doncaster, including the Don Gorge and Denaby Crags; however, ever since being involved in Geoconservation in South Yorkshire back in 1996, I have not known of any initiatives to systematically investigate these sites.
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| A differentially weathered band of marl at the base of Hooton Cliff |
One particularly interesting feature here is thick band of marl, which is both grey/green and red in colour and represents a period when the depositional environment has been dominated by coastal lakes and lagoons – providing evidence of a period of marine regression.
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| A detail of differentially weathered marl and undercutting |
The marl is very soft compared to the limestone and its position is easily determined by the pronounced differential weathering, which has left a large section of the quarry face undercut and the weathered marl forming a distinct slope beneath it.
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| A detail of red marl |
During my surveys of the Cadeby Formation in Rotherham, although I had encountered reddened beds of dolomitic limestone in a quarry at Wood Mill Quarry at the end of Lindrick Dale and in the historic buildings of Letwell, the only other place that I recall seeing marl was in the exposure of the Edlington Formation at Brancliffe Grange.
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| Sites in the Cadeby Formation surveyed in Rotherham |
Although it is probably unlikely that I will use Hooton Cliff as a field trip location for the Sheffield U3A Geology Group, due to it isolation from other sites, it added further to my own knowledge of the Magnesian Limestone outcrop between Mansfield and Knaresborough.
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| The Cadeby Formation at Hooton Cliff |
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