Lincolnshire Wolds Field Trip 31St August - 2Nd September 2007
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Lincolnshire Wolds Field Trip 31st August - 2nd September 2007 This was a weekend field trip to the Lincolnshire Wolds, with Walton Hall Branch, led by Dr Paul Olver. Report by Patricia Taylor We arrived at the Lincoln Hotel, opposite Lincoln Cathedral, and had a splendid meal. Afterwards, our leader Paul Olver gave us an overview of the geology of the area that we would be looking at. On Saturday, we would travel directly north from Lincoln, along the strike of the Lower Oolite, to look at the the Middle Jurassic exposures in Manton Quarry, then northeast to the chalk scarp at Melton Ross. Saturday afternoon would be spent looking at the red chalk, Cretaceous and Upper Jurassic ironstones and sandstones that underlie the Wolds. On Sunday we would travel south to look again at the Middle Jurassic rocks at Ancaster and Metheringham. Saturday – Location 1, Manton Quarry (ST 942 010) On Saturday morning we set out in convoy to the Manton Quarry, a cement quarry north of Kirton Lindsey. The middle Jurassic strata exposed in the quarry were Kirton cementstones, Kirton shale of the lower Lincolnshire limestone and the Hibaldstow beds of hard limestone, topped by soft but oolitic limestone. These are all shallow water limestones, deposited in the Bajocian stage of the Middle Jurassic. See Figure 1. Figure 1 Bajocian Lincs Limestone at Manton Quarry The floor of the quarry was on the Lower Estuarine Series, which are a thin sequence of sands and clays deposited in low lying, deltaic and coastal flats. The coastal flats were submerged in later Bajocian times, which allowed deposition of the lower Lincolnshire Limestone Series that we could see in the quarry walls. These are occasionally oolitic and contain small bivalves. Saturday – Location 2, Melton Ross Quarry (TA 080 110) Our second location was the Melton Ross Quarry. Here, the white chalk of the Welton Chalk formation contains the ooze floating bivalves Inoceramus labiatus. The white was broken by flint beds. See Figure 1. The black marl bands in the chalk were formed from ash falls from volcanism, somewhere in the North Sea. These marl bands are markers for the lower part of the Welton Chalk Formation. See Figure 2. Above the Welton Chalk were the Burnham Chalk Formation and the Flamborough Chalk Formation containing swimming crinoids with no stems (marsupites). Also within the chalk were tiny black dots of manganese dioxide in the form of pyrolusite. Figure 2 Welton Chalk Formation at Melton Ross Quarry Figure 3 Black Marl Bands, Welton Chalk Formation at Melton Ross Quarry Saturday – Location 3, Nettleton Church (TA 111 002) After lunch at Nettleton, we walked up to the church there. This church is made of the distinctive orange/yellow Claxby Ironstone, which is a coarse oolite that contains many fossil shells including large oyster shells. It is weathering badly. See Figure 4. Figure 4 Claxby Ironstone, Nettleton Church Saturday – Location 4, Red Hill, Donington-on-Bain (TF 249 820) From the main road to the south of Donington-on-Bain, we walked east up Manor Hill road to the top of the hill. From the Manor Hill road, we looked north over Red Hill to the site of the old Claxby Ironstone mine. The Claxby Ironstone had been mined from tunnels in the hillside here, from 1929 to 1968. The land had been greatly disfigured. Since then, the site had been landscaped and was now a pleasant meadow with some “interesting” contours. See Figure 5. Figure 5 Red Hill Ironstone Mine, Now Landscaped Meadow Retracing our steps back down the hill, we left the road to see a small exposure of the Lower Spilsby sandstone that underlies the Claxby Ironstone. This is right at the base of the Lower Cretaceous and straddles the Jurassic/Cretaceous boundary. The Spilsby Sandstone is a coarse glauconitic sandstone that contains fragments of Palaeozoic red jasper, quartz, greenstone and spheroidal rhyolite. The voids in this sandstone were used by Professor Casey to create plaster of Paris moulds that identified the ammonites as the same as those found in the Portland stone on the Jurassic/Cretaceous boundary. See Figure 6. Figure 6 Lower Spilsby Ironstone, Red Hill, Donington-on-Bain The next exposure at Red Hill, Donington-on-Bain, was of Cretaceous white and red chalk overlying carstone (a yellow sandstone). The red chalk is darker at its base becoming paler further up the exposure. The red chalk is thought to have been formed on an uplifted horst structure, where the absence of deep water fauna meant that there was less decay and therefore more oxygen available to oxidise the iron to give the chalk its distinctive red colour. There are few fossils - some brachiopods and very small belemnites. Dark patches of haematite can be found in the red chalk. See Figure 7. Figure 7 Red Chalk, Red Hill, Donington-on-Bain A form of “Hydraulic Chalk” is extracted from the red chalk. This is good for building lime, hardening under water. The final exposure was of the “Roach” iron-rich sandstone. The Fulletby Beds. This was sheltered by a wood, significantly overgrown and difficult to examine in the poor light. This outcrops near Fulletby (TF 305 740). Sunday – Location 1, Copper Hill Quarry (SK 978 426) On Sunday we headed south of Lincoln to the Copper Hill Quarry at Ancaster. Again we were looking at the middle Bajocian. In this magnificent quarry, the top bed was the cross bedded Ancaster Rag sitting on an erosion surface. Beneath this was the Ancaster Freestone - a pale limestone with shell debris, the Wilsford Coral bed and another exposure of the Ancaster Freestone. See Figure 8. Figure 8 Copper Hill Quarry, Ancaster The Ancaster beds were deposited in clear, agitated shallow water. This was readily determined by the presence of abundant ooliths and pisoliths. The floor of the quarry was the Kirton cementstone, seen at our first location on Saturday morning. The quarry exposed a range of shallow water fossils including brachiopods, gastropods and bivalves and a leaf. The Ancaster freestone, a pure oolite with minor shell debris, is an important building stone. It is seen commonly in Stamford and many churches in South Lincolnshire. After lunch in we set off to our last location at Metheringham. We set off for the final location. Sunday – Location 2, The CDS Quarry, Metheringham (TF 054 616) At the CDS Quarry, Metheringham, the top bed was the Kirton cementstone seen previously at the base of the Copper Hill quarry. Below this were rubble, Ancaster freestone in a much thinner layer than the higher beds, and Kirton shale which had been deposited in deep water. See Figure 9. Figure 9 The CDS Quarry, Metheringham These, again, were very shallow water deposits, evidenced by the abundant very large ooliths and pisoliths. Rock from the CDS Quarry is used widely for garden blocks and rockeries, Building Stone and Masonry, keystones and floor tiling. See Figure 10. Figure 10 Pisolite, The CDS Quarry, Metheringham The abundance of fossils in the quarry made us reluctant leave. Our visit to this last quarry brought an end to what had been a fascinating weekend. Thank you Paul for your enduring patience with us. Patricia Taylor .