A Geotrail in Richmond Park 1 Richmond Park Geotrail In an urban environment it is often difficult to ‘see’ the geology beneath our feet. This is also true within our open spaces. In Richmond Park there is not much in the way of actual rocks to be seen but it is an interesting area geologically as several different rock types occur there. It is for this reason that the southwest corner has been put forward as a Locally Important Geological Site. We will take clues from the landscape to see what lies beneath. Richmond Park affords fine views to both west and east which will throw a wider perspective on the geology of London. Richmond Park is underlain by London Clay, about 51 million years old. This includes the sandier layers at the top, known as the Claygate beds. The high ground near Kingston Gate includes the Claygate beds but faulting along a line linking Pen Ponds to Ham Gate has allowed erosion on the high ground around Pembroke Lodge. Both high points are capped by the much younger Black Park Gravel, which is only about 400,000 years old, the earliest of the Thames series of terraces formed after the great Anglian glaciation. Younger Thames terrace gravels are also to be found in Richmond Park. Useful maps and guide books The Royal Parks have a printable pdf map of Richmond Park on their website: www.royalparks.org.uk/parks/richmond-park/map-of-richmond-park. Richmond Park from Medieval Pasture to Royal Park by Paul Rabbitts, 2014. Amberley Publishing. The Walker’s Guide to Richmond Park by David McDowall, 2006. Published by David McDowell and available through the Friends of Richmond Park. British Geological Survey 1:50,000 sheet 271 South London Section 6 of the Capital Ring: Wimbledon Park to Richmond in The Capital Ring by Colin Saunders, Aurum Press, 2003. Latest version 2016 The route The route described is a circular walk, about 7 km long, beginning and ending at the Kingston Gate car park, open daily during daylight hours (toilets adjacent to the Gate). It conveniently passes Pembroke Lodge, approximately half-way round which makes a good stopping place with refreshments and toilet facilities. Part of the walk (near Pembroke Lodge) is on the Capital Ring and so if coming from the north along the Capital Ring to Pembroke Lodge the early part of the walk can be taken in reverse towards Kingston Gate, then in reverse the last part of the walk to Pen Ponds to re-join the Capital Ring to exit Richmond Park at Robin Hood’s Gate. Start and end at car park next to Kingston Gate TQ 193 706 (shown on the following map) The nearest station is Norbiton, which is a 15-minute walk. The bus stop closest to the Kingston Gate on the main road between Kingston and Putney is called ‘Queens Road, Kingston Hospital’ and is served by buses 57, 85, 213, 371. 2 Map of Richmond Park (south) Geotrail with underlying geology Based upon 1:10,000 TQ17SE and TQ27SW with the permission of the British Geological Survey 3 Age Informal Thickness Description and how they were (not to Member Stage names in area deposited Epoch scale) Period Formation Clay, sand and gravel deposited by 10,000 to Alluvium Alluvium variable existing rivers through (or under) present London Holocene Varies from silt to clay, commonly yellow-brown and massively bedded. 17,000 Langley Silt Brickearth 1-5m Rests on sand & gravel river terrace deposits with sharp base. Devensian Kempton Kempton Sand and gravel, locally with lenses of 100,000 1-9m Maidenhead Park Gravel Park Gravel silt, clay or peat. Taplow Taplow Sand and gravel, locally with lenses of 200,000 1-9m Gravel Gravel silt, clay or peat. Quaternary Lynch Hill Lynch Hill Sand and gravel, locally with lenses of 250,000 1-12m Wolstonian Gravel Gravel silt, clay or peat. Pleistocene Sand and gravel, mostly angular flint, Boyn Hill Boyn Hill 350,000 1-9m some rounded with minor vein Gravel Gravel Hoxnian quartz, quartzite & Greensand chert. Sand and gravel, mostly angular flint, Black Park Black Park 400,000 1-6m some rounded with minor vein quartz Thames Valley Thames Gravel Gravel Anglian and quartzite. ~50 million years where no sediment remains. The area was mostly land during this period. Age Informal Thickness Description and how they were (not to Member names in area deposited Epoch Group scale) Period Formation Variable sands, often iron-rich, 50m Bagshot Up to deposited near shore (current years Sand 35m bedding). There is no evidence that it Bagshot is in Richmond Park Bracklesham Claygate Clay, silt and fine-grained sand, Claygate 15-18m beds deposited in shallow seas Eocene Paleogene 51-54m Grey clay that weathers brown, sandy Up to years London Clay at top. Five cycles of marine London Clay London 70m Thames Group Thames transgression Stratigraphical column showing details of all the Thames gravels down to the base of the London Clay 4 Leaving the car park by the Exit Only sign, cross the road and head up hill bearing slightly to the right till you reach 66 rudimentary wooden steps which will take you onto the flat plateau at the top. Near the top of the steps an increasing number of the pebbles from the Black Park Gravel can be seen. Stop 1: Black Park Gravel plateau TQ 1947 7075 (at top of steps) The plateau near the King’s Clump is the most extensive on Richmond Park, continuing to the southeast beyond the park for about one kilometre on Coombe Hill. At about 53 metres it is at a similar elevation to the high ground near the Richmond Gate entrance to the Park that encompasses Pembroke Lodge and Sidmouth Wood. It is also the same height as Wimbledon Common to the east, separated by the low ground created by the course of the Steps up to the Plateau of Black Park Gravel Beverley Brook. Both this south end of Richmond Park and the south end of Wimbledon Common are underlain by the full depth of London Clay with the Claygate beds at the top. There is at least a 50 million year time gap between the top of the solid geology (be it Claygate beds or London Clay) and the overlying gravels during which time any later sediments were subsequently eroded. The Black Park Gravel is the earliest of a series of Thames gravels in the London area, deposited only 400,000 years ago. These gravels underlie all of the high plateau areas in this part of London. View of Black Park Gravel plateau from Queen’s Road. Photo: L. Baker 5 Sketch map and section showing geology beneath Richmond Park and Wimbledon Common with Beverley Brook bisecting the plateau (Robinson, 2010). 1 = Isabella Plantation; 2 = King Henry’s Mound; 3 = White Lodge The Black Park Gravel is composed predominantly of flint pebbles originating from the hard grey layers within the softer, white Cretaceous Chalk. The rounded nature of some of them indicates a long period of 6 erosion by flowing water. They may have been recycled through several periods of deposition and erosion. Other pebbles have come from much further away. Triassic ‘Bunter’ pebbles have been found that have been brought from the Midlands by the great Anglian ice sheet that reached as far as Finchley in North London. As the ice melted, about 400,000 years ago the transported pebbles and rock fragments were released into the engorged River Thames and deposited over a wide flood plain. It is likely that the Thames at that time was a braided river with many channels switching course repeatedly, much as can be seen today in places like Iceland where glaciers are retreating. In the Richmond Park area the inclusion of Lower Greensand Chert pebbles implies an element of material from the Weald to the south, probably transported by the Wey/Mole tributary system of the Thames. The Black Park Gravel is also found in East London. In a railway cutting in Hornchurch it overlies the glacial till, left behind by the retreating Anglian ice sheet. This exposure has helped to date the gravel as the earliest of the post-Anglian sequence and the cutting has become a Site of Special Scientific Interest. The same-aged gravel is still quarried at Mark’s Tey, not far from Hornchurch, and recently a boulder of dolerite, an igneous rock that solidified just beneath the surface, was found in the quarry. The nearest solid rock of this nature can be found in the Cleveland Dyke in Yorkshire and the Whin Sill in Northumberland so presumably the boulder was carried nearly all the way to London within the ice sheet before being released into the fast flowing melt water of the Thames. The first gravels after the Anglian glaciations has also revealed human bones at Barnfield Pit, Swanscombe, Kent on the south bank of the Thames. Three separate fragments of human skull were found in the 1930s and 50s. It is thought that they belonged to an early Neanderthal and the bones were those of a female. Perhaps early Neanderthals also roamed the shores of the Thames in Richmond Park as well? To date no artefacts or exotic rock fragments relating to the gravels of this age have been recorded. On the Plateau take the broad path to your left to find the circular enclosure of Scots pines known as King’s Clump [TQ 1951 7089]. It is generally agreed that this is a barrow. It is marked as ‘The King’s Standinge’ on Charles 1’s map of 1637.