Field Trip to Warwickshire.Pdf
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Weekend Field Trip to Warwickshire 17th-19th September 2010 Led by Martyn Bradley (Warwick University) This weekend field trip to Eastern Warwickshire was devised to show us the geology of the vale of the upper Avon around Warwick and Royal Leamington Spa. We would look at the solid geology, Triassic, Jurassic and Quaternary rocks of the region. We would also look at late Quaternary surface features (such as the fabled “Lake Harrison”) and consider the work of local geologist Professor Fred Shotton, whose research led to establishment of the Wolstonian stage of the British Pleistocene. This was an excellent weekend, thoroughly enjoyed by everyone who attended. Pauline Kirtley begins the account.... Saturday 18th The day began sunny and bright, with those staying at the B & B having had a hearty breakfast. A few hiccups early that morning - not helped by Tom’s and my diversion the night before travelling to Warwick - but a fabulous supportive group overcame all. With Guy driving his chariot accompanied by Tim and Julian, they collected Martyn and the hard hats. We met at the first quarry location on the south side of the Avon Valley, Waverley Wood Farm Quarry. Location 1 - Waverley Wood Farm Quarry (436234,271810) Waverley Wood Farm Quarry is a Quaternary sand and gravel extraction site, just south of Bubbenhall village. It lies in the valley of the ancient Bytham River. In early Quaternary times, the Bytham River flowed northeast and east to the Norfolk Coast. Here, Fred Shotton did some extensive work on the glacial drift, leading ultimately to this becoming the type location for the Pleistocene Wolstonian stage. We donned hard hats and jackets, their vividness accentuated by the brilliant sunshine. John Green, Quarry Manager, explained the excavation of the river sand and gravels and how the area would eventually be restored back to its natural level. Gravels that had been taken from Waverley Wood were now in an area that was a land raised site. He suggested that we recycle, put rubbish back as hills, rather than in holes. It was quite exciting standing on Carboniferous quartzite pebbles, which had been brought down by glaciation and worked by the Bytham River. Amongst the pebbles, hand axes had been found. The rounded pebbles were from the Bunter Pebble Beds, Staffordshire. Budleigh Salterton beds came from the south, from Brittany. We were told that on the M6, near Keele, there was an exposure of the Bunter pebble beds. Ice had brought them down and they were then further rounded by rivers. Figure 1 Guy with fossilized wood. Martyn explained that the site exposes (at the base of the excavation) impermeable rocks of the Triassic, Mercia Mudstone Group. These are overlain by 2 m of gravels and sands (Baginton Sands), then a till (Thrussington Till) on top of the gravels. The paleoflow direction (northeast) is readable from sedimentary structures in the sands. John showed us a photograph of an elephant bone – 13 inches across. This is currently in Warwickshire Museum. The quarry has yielded several important finds, including teeth, and the bones of a straight-tusked elephant. These were found in highly fossiliferous channel fills below the Baginton sands/gravels. Palaeolithic finds include several quartzite hand tools. We walked for a while through Bubbenhall Wood, then along tracks to the nearby Ryton Pools Country Park. Mike Moores takes up the story..... Location 2 Ryton Pools Country Park (437226,272515) The group entered the Ryton Pools Country Park from the south access road and immediately came to Pagets Pool (see information board Fig. 2). Martyn explained that the park had the same sequence of Thrussington Till as the previous quarry (Waverley Wood Quarry) and the pool was set on Mercia Sandstone. It was lower than the previous pool but it was not known why. The opposite side of the pool originally had a clean face but regrettably was now overgrowing. This rather hid the original stratigraphy as this was the boundary of the original quarry and hence not showing landfill. The Ryton Pools Country Park had been last excavated in the early 1960s and was then landfilled and areas left to produce the pools and the Country Park in the 1980s. Figure 2 Pagets Pool Information Board Some parts of the site were Woodland Trust, Bird Hides and a Butterfly Park, however we did not have time to visit these as time was tight and coffee beckoned with a loo stop at the Park’s Visitor Centre. We then made our way out of the park towards our cars but used the opportunity to observe the reinstated areas on the way. The area has been excellently reinstated to parkland and paths and an example of this was the path between hedgerows which, although less than 20 years old, looked hundreds (see Fig. 3). We stopped at a viewpoint and looked North/North East towards Coventry and the valley we would be visiting in the afternoon. The area immediately in front of us had been regrassed and was being grazed as if it had been there for centuries. Figure 3 Path and Hedge in Ryton Pools Country Park As we left, we managed to mingle with a group of about 20 ramblers who were heading in the same direction. A good bit of chatting and comments were made especially as we were all carrying our hard hats and reflective jackets. Location 3 Lunch in Wolston village (441245,275530) After a few abortive attempts to go to pubs in the village green most of settled on the benches on the green and had a sandwich lunch from the local Deli or Co-op. There was an interesting picture board showing the importance of Wolston and its association with the internationally recognised sequence of Wolstonian deposits established by local geologist Professor Fred Shotton of Birmingham University. Figure 4 The group Studying the Wolston Information Board During lunch we watched a man walking back and forth along the bank of the village stream, trailing a long stick in the water. Guy suggested he might be punting, but this was later dismissed when he stopped but did not drift away. He was removing litter from the stream. After lunch, Tom Miller continues the account.... Location 4 Wolstonian Sequence Excavation Site SSSI (440998,273115) A short distance to the south of Wolston (about 1 km), towards Stretton-on-Dunsmore, lies Knightlow Hill. On the northern slope of Knightlow Hill there are the remains of an excavation that attempted to expose the important Wolston Sand/Clay and Baginton Sand beds sequence, beneath the Dunsmore gravel. This was an attempt to show and conserve the sequence as a SSSI. A later re-excavation by the Quaternary Research Association (QRA) took place in 1989 and managed (with difficulty) to reexpose the upper 6 m of the section, just revealing the Wolston Sand Beds. Since then, conservation has proved too difficult and dangerous to achieve and the site remains as a grassy hollow. Martyn took us there after lunch and we examined the hollow while Martyn described the heroic attempts by the mechanical digger to achieve the desired result. Figure 5 The Failed Wolstonian Sequence Excavation Site What a shame that this important stratigraphic sequence is no longer there to see. Julian Chard then carries on... Location 5 Fenny Compton Canal (443133,253267) Martyn led us to the Wharf Inn on the A423 and down onto the tow path by the Oxford Canal. Following the canal to the left we came across an open field. Here a bench feature of the field on the far side became apparent. This sparked conversation about the presumed Lake Harrison and the evidence collected that it once existed, ‘Does Lake Harrison hold water?’ A bench is a feature that is a wave-cut platform that marks the upper limit of a previous shoreline. On the hillside in front of us, there was a clear downward slope that took the shape of a beach. We then walked back along the canal towards the pub. Every few meters we would pause long enough to peer across to the other side of the canal and study the bench feature to see if it was still present and if so were there any differences to where we began. We walked all the way till we were standing on a bridge over the entrance to a marina. Here Martyn Bradley collated the evidence and our thoughts on what we had seen and showed us the two sides to the argument. One was that the lake did exist but because of the height variance in the benches along the canal’s far side, it may have occurred in different stages of glacial melting. However the lack of depositional evidence suggests that these benches could have been formed by glacial erosion rather than the shoreline of a lake. This lack of evidence in turn could be misleading as during the time in between present and time of the glacier, the shoreline deposition may have been weathered away. After a well deserved cup of tea at the pub it was decided that there was just not enough evidence to support the theory that a lake existed at this point. Figure 6 Is this Fred Shotton’s Wave-cut Platform? After this pleasurable interlude, we set off for our final location of the day, the Burton Dassett Hills. Pam Konieczny takes up the story...... Location 6 Burton Dassett Hills (443133,253267) After we arrived at Burton Dassett, Martyn took us to Windmill Hill, one of several marlstone capped hills that stand above a flat plain of Lower Lias clays; part of the Charmouth Mudstone formation.