OR/13/006 Geology - Revision history

Ajhil: /* Sequence stratigraphy */

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Sequence stratigraphy

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	Sequence Lmbe-2 comprises the transgressive upper Upnor Formation and the lower leaf of the Reading Formation, the Lower Mottled Clay. The upper Upnor Formation generally consists of non-calcareous, glauconitic, sometimes clayey, SANDS and GRAVELS with a relatively restricted microfauna and palynoflora. The basal beds of the Lambeth Group in the west Hampshire Basin have characteristics of fluvial deposits and contain reworked glauconite derived from material similar to the lower Upnor Formation (Skipper, 1999<ref name="Skipper 1999">SKIPPER, J. 1999. The stratigraphy of the Lambeth Group (Palaeocene) of South East England. Ph. D. Thesis. Imperial College, London, and Natural History Museum.</ref>). In eastern parts of the Greater London area and in parts of Essex and Kent the upper Upnor Formation contains relatively thick accumulations of gravel, deposited from fast flowing marine or estuarine channels. High concentrations of glauconite indicate periods of maximum flood. In Central London and further east, a progressive change from shallow marine to estuarine Upnor Formation deposits becomes shallower and is replaced in some areas by water logged soils and then drier soils of the Reading Formation. Further east in north Kent shallow marine Upnor Formation deposits became emergent and pedogenically altered. The upper part of the sequence tends to be more pedogenically altered than other parts of the Lambeth Group.		Sequence Lmbe-2 comprises the transgressive upper Upnor Formation and the lower leaf of the Reading Formation, the Lower Mottled Clay. The upper Upnor Formation generally consists of non-calcareous, glauconitic, sometimes clayey, SANDS and GRAVELS with a relatively restricted microfauna and palynoflora. The basal beds of the Lambeth Group in the west Hampshire Basin have characteristics of fluvial deposits and contain reworked glauconite derived from material similar to the lower Upnor Formation (Skipper, 1999<ref name="Skipper 1999">SKIPPER, J. 1999. The stratigraphy of the Lambeth Group (Palaeocene) of South East England. Ph. D. Thesis. Imperial College, London, and Natural History Museum.</ref>). In eastern parts of the Greater London area and in parts of Essex and Kent the upper Upnor Formation contains relatively thick accumulations of gravel, deposited from fast flowing marine or estuarine channels. High concentrations of glauconite indicate periods of maximum flood. In Central London and further east, a progressive change from shallow marine to estuarine Upnor Formation deposits becomes shallower and is replaced in some areas by water logged soils and then drier soils of the Reading Formation. Further east in north Kent shallow marine Upnor Formation deposits became emergent and pedogenically altered. The upper part of the sequence tends to be more pedogenically altered than other parts of the Lambeth Group.

	The transgression of the Lower Mottled Clay terrestrial facies eastwards indicates a relative sea level fall due to further uplift in the west. The continuing fall in relative sea level resulted in a period of erosion and weathering that produced a subdued topography and resulted in widespread pedogenesis. Skipper (1999)<ref name="Skipper 1999"></ref> and Page and Skipper (2000)<ref name="Page 2000">PAGE, D, and SKIPPER, J. 2000. Lithological Characteristics of the Lambeth Group. ''Ground Engineering'', ~~'''~~33~~'''~~, 38–43.</ref>, have referred to the sharp boundary marking the end of this sequence as the mid-Lambeth Hiatus, which is now known as the mid-Lambeth Group Hiatus. The top of the deposits are typically pale, often bleached and contain many burrow traces, which may be filled with material from the bed above. These deposits are generally clay overbank deposits with sand filled river channels, but in the east of the London Basin they are mainly sand.		The transgression of the Lower Mottled Clay terrestrial facies eastwards indicates a relative sea level fall due to further uplift in the west. The continuing fall in relative sea level resulted in a period of erosion and weathering that produced a subdued topography and resulted in widespread pedogenesis. Skipper (1999)<ref name="Skipper 1999"></ref> and Page and Skipper (2000)<ref name="Page 2000">PAGE, D, and SKIPPER, J. 2000. Lithological Characteristics of the Lambeth Group. ''Ground Engineering'', 33, 38–43. </ref>, have referred to the sharp boundary marking the end of this sequence as the mid-Lambeth Hiatus, which is now known as the mid-Lambeth Group Hiatus. The top of the deposits are typically pale, often bleached and contain many burrow traces, which may be filled with material from the bed above. These deposits are generally clay overbank deposits with sand filled river channels, but in the east of the London Basin they are mainly sand.

	Most of the hard beds are from the upper part of this sequence and include silicate cemented beds to the north of London and south of the South Downs, calcium carbonate cemented beds in central and east London and near Arundel in the Hampshire Basin and iron oxide cemented beds in the east, most notably in north Kent.		Most of the hard beds are from the upper part of this sequence and include silicate cemented beds to the north of London and south of the South Downs, calcium carbonate cemented beds in central and east London and near Arundel in the Hampshire Basin and iron oxide cemented beds in the east, most notably in north Kent.

Ajhil: /* Depositional environment and processes */

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Depositional environment and processes

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	===Depositional environment and processes===		===Depositional environment and processes===
	The regional distribution of deposits of the Lambeth Group was recognised as cyclic in nature by Stamp (1921)<ref name="Stamp 1921">STAMP, L D. 1921. On the beds at the base of the Ypresian (London Clay) in the Anglo-Franco-Belgian basin. ''Proceedings of the Geologists’ Association'', '''32''', 57–173.</ref>, an idea developed further by Hester (1965)<ref name="Hester 1965">HESTER, S W. 1965. Stratigraphy and palaeography of the Woolwich and Reading Beds. ''Bulletin of the Geological Survey of Great Britain'', '''23''', 117–137.</ref> and Ellison (1983)<ref name="Ellison 1983">ELLISON, R A. 1983. Facies distribution in the Woolwich and Reading Beds of the London Basin, England. ''Proceedings of the Geological Association'', '''94''', 311–319. </ref>. Four depositional sequences separated by unconformities are now recognised (Knox, 1996a<ref name="Knox 1996a"></ref>; Table 6). The sediments as a whole were laid down in a coastal or possibly estuarine setting (Figure 2.29) in which small fluctuations in sea level led to marked changes in depositional environment.		The regional distribution of deposits of the Lambeth Group was recognised as cyclic in nature by Stamp (1921)<ref name="Stamp 1921">STAMP, L D. 1921. On the beds at the base of the Ypresian (London Clay) in the Anglo-Franco-Belgian basin. ''Proceedings of the Geologists’ Association'', '''32''', 57–173.</ref>, an idea developed further by Hester (1965)<ref name="Hester 1965">HESTER, S W. 1965. Stratigraphy and palaeography of the Woolwich and Reading Beds. ''Bulletin of the Geological Survey of Great Britain'', '''23''', 117–137.</ref> and Ellison (1983)<ref name="Ellison 1983">ELLISON, R A. 1983. Facies distribution in the Woolwich and Reading Beds of the London Basin, England. ''Proceedings of the Geological Association'', '''94''', 311–319.</ref>. Four depositional sequences separated by unconformities are now recognised (Knox, 1996a<ref name="Knox 1996a"></ref>; Table 6). The sediments as a whole were laid down in a coastal or possibly estuarine setting (Figure 2.29) in which small fluctuations in sea level led to marked changes in depositional environment.

	[[Image:OR13006fig2.29.jpg\|thumb\|center\|600px\| '''Figure 2.29'''    Schematic block diagram to illustrate the environment of deposition of the Lambeth Group (Ellison ''et al''., 2004<ref name="Ellison 2004"></ref>). ]]		[[Image:OR13006fig2.29.jpg\|thumb\|center\|600px\| '''Figure 2.29'''    Schematic block diagram to illustrate the environment of deposition of the Lambeth Group (Ellison ''et al''., 2004<ref name="Ellison 2004"></ref>). ]]

Ajhil: /* Lithology */

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Lithology

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	====Lithology====		====Lithology====
	Glauconitic fine-grained sand and gravel beds of rounded black flints are the principal lithologies with, in places, common disarticulated and broken shells of marine to brackish fauna (see Dewey ''et al''., 1924<ref name="Dewey 1924">DEWEY, H, BROMEHEAD, C E N. CHATWIN, C P, and DINES, H G. 1924. The geology of the country around Dartford. ''Memoir of the British Geological Survey (England and Wales)'', Sheet 271. British Geological Survey, Keyworth, Nottingham, UK. </ref>). The proportion of gravels varies considerably. Calcareous, ferruginous and siliceous cements occur locally in beds and masses up to several metres thick (for details see Dewey and Bromehead, 1921<ref name="Dewey 1921"></ref>; Dewey ''et al''., 1924<ref name="Dewey 1924"></ref>), particularly at outcrop in the southeast of the district. Recent excavations for Crossrail and Thames Water projects have found multiple, discontinuous layers of calcite cemented sand and gravel beds in the Blackheath and Oldhaven members up to 750 mm thick in the West Ham and Isle of Dogs areas of east London. Also in these areas, weak calcareous mudstone and strong calcareous siltstone concretions up to 250 mm thick and 450 mm wide occur in the Swanscombe Member.		Glauconitic fine-grained sand and gravel beds of rounded black flints are the principal lithologies with, in places, common disarticulated and broken shells of marine to brackish fauna (see Dewey ''et al''., 1924<ref name="Dewey 1924">DEWEY, H, BROMEHEAD, C E N, CHATWIN, C P, and DINES, H G. 1924. The geology of the country around Dartford. ''Memoir of the British Geological Survey (England and Wales''), Sheet 271. British Geological Survey, Keyworth, Nottingham, UK.</ref>). The proportion of gravels varies considerably. Calcareous, ferruginous and siliceous cements occur locally in beds and masses up to several metres thick (for details see Dewey and Bromehead, 1921<ref name="Dewey 1921"></ref>; Dewey ''et al''., 1924<ref name="Dewey 1924"></ref>), particularly at outcrop in the southeast of the district. Recent excavations for Crossrail and Thames Water projects have found multiple, discontinuous layers of calcite cemented sand and gravel beds in the Blackheath and Oldhaven members up to 750 mm thick in the West Ham and Isle of Dogs areas of east London. Also in these areas, weak calcareous mudstone and strong calcareous siltstone concretions up to 250 mm thick and 450 mm wide occur in the Swanscombe Member.

	In the northeast the Harwich Formation is dominated by relatively fine-grained sand and is generally less pebbly. The succession is known in detail only in Stock Borehole [TQ 7054 0045] where grey-green silty fine-grained sand with scattered broken shell fragments and stringers of black flint gravels are recorded. At outcrop in south Essex, the Harwich Formation consists of green-grey, weathering to pale yellow-brown, highly glauconitic fine to medium-grained sand and gravelly sand. Calcareous mollusc fossils and scattered sharks’ teeth are typical although the shells are decalcified in places.		In the northeast the Harwich Formation is dominated by relatively fine-grained sand and is generally less pebbly. The succession is known in detail only in Stock Borehole [TQ 7054 0045] where grey-green silty fine-grained sand with scattered broken shell fragments and stringers of black flint gravels are recorded. At outcrop in south Essex, the Harwich Formation consists of green-grey, weathering to pale yellow-brown, highly glauconitic fine to medium-grained sand and gravelly sand. Calcareous mollusc fossils and scattered sharks’ teeth are typical although the shells are decalcified in places.

Ajhil: /* Woolwich Formation */

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Woolwich Formation

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	[[Image:OR13006fig2.25.jpg\|thumb\|center\|600px\| '''Figure 2.25'''    Distribution and thickness of the Laminated Beds in London (Ellison ''et al''., 2004<ref name="Ellison 2004"></ref>). ]]		[[Image:OR13006fig2.25.jpg\|thumb\|center\|600px\| '''Figure 2.25'''    Distribution and thickness of the Laminated Beds in London (Ellison ''et al''., 2004<ref name="Ellison 2004"></ref>). ]]
	A second unit of laminated beds occurs higher in the succession and are part of the Upper Shelly Clay around Lewisham where it was formerly known as ‘Striped loams’ (Dewey ''et al''., 1924<ref name="Dewey 1924">DEWEY, H, BROMEHEAD, C E N,CHATWIN, C P, and DINES, H G. 1924. The geology of the country around Dartford. ''Memoir of the British Geological Survey (England and Wales)'', Sheet 271. British Geological Survey, Keyworth, Nottingham, UK.</ref>). The stratigraphical relationships of these laminated beds are uncertain but they probably have an erosive base, cutting down through the Upper Shelly Clay.		A second unit of laminated beds occurs higher in the succession and are part of the Upper Shelly Clay around Lewisham where it was formerly known as ‘Striped loams’ (Dewey ''et al''., 1924<ref name="Dewey 1924">DEWEY, H, BROMEHEAD, C E N, CHATWIN, C P, and DINES, H G. 1924. The geology of the country around Dartford. ''Memoir of the British Geological Survey (England and Wales''), Sheet 271. British Geological Survey, Keyworth, Nottingham, UK.</ref>). The stratigraphical relationships of these laminated beds are uncertain but they probably have an erosive base, cutting down through the Upper Shelly Clay.

	''Basal Boundary''<br>The base of the Laminated Beds is sharply defined with the underlying Lower Shelly Clay (Figure 2.26) or, locally, on the Lower Mottled Clay.		''Basal Boundary''<br>The base of the Laminated Beds is sharply defined with the underlying Lower Shelly Clay (Figure 2.26) or, locally, on the Lower Mottled Clay.

Ajhil: /* Woolwich Formation */

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Woolwich Formation

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	''Distribution''<br>The Lower Shelly Clay occurs principally in east and southeast London (Figure 2.22), north Kent and the eastern edge of the Hampshire Basin. It has been identified recently in boreholes near Wandsworth Bridge [TQ 260 755] but not at Putney Bridge [TQ 242 757] (Jackie Skipper personal communication June 2013). In general, the unit thickens from central London towards the southeast, reaching a maximum of about 6 m.		''Distribution''<br>The Lower Shelly Clay occurs principally in east and southeast London (Figure 2.22), north Kent and the eastern edge of the Hampshire Basin. It has been identified recently in boreholes near Wandsworth Bridge [TQ 260 755] but not at Putney Bridge [TQ 242 757] (Jackie Skipper personal communication June 2013). In general, the unit thickens from central London towards the southeast, reaching a maximum of about 6 m.

	[[Image:OR13006fig2.22.jpg\|thumb\|center\|600px\| '''Figure 2.22'''    Distribution and thickness of the Lower Shelly Clay in London (Ellison ''et al''., 2004<ref name="Ellison 2004">ELLISON, R A, WOODS, M A, ALLEN, D J, FORSTER, A, PHAROAH, T C, and KING, C. 2004. Geology of London. ''Special Memoir for 1:50 000 geological ~~sheets~~ 256 (North London), 257 (Romford), 270 (South London) and 271 (Dartford) (England and Wales)''. British Geological Survey, Keyworth, Nottingham, UK. </ref>). ]]		[[Image:OR13006fig2.22.jpg\|thumb\|center\|600px\| '''Figure 2.22'''    Distribution and thickness of the Lower Shelly Clay in London (Ellison ''et al''., 2004<ref name="Ellison 2004">ELLISON, R A, WOODS, M A, ALLEN, D J, FORSTER, A, PHAROAH, T C, and KING, C. 2004. Geology of London. ''Special Memoir for 1:50 000 geological Sheets 256 (North London), 257 (Romford), 270 (South London) and 271 (Dartford) (England and Wales)''. British Geological Survey, Keyworth, Nottingham, UK.</ref>). ]]

	''Basal Boundary''<br>The basal boundary of the Lower Shelly Clay is sharp, well defined and disconformable on the often pale and bleached, pedogenically altered Lower Mottled Clay. Burrows containing dark clay, lignite or shells may occur in burrows extending up to 1.5 m into the Lower Mottled Clay. In some parts of central London the contrast is between multicoloured clay with calcium carbonate concretions or pale, bleached Lower Mottled Clay and overlying dark grey shelly clay (Figure 2.23).		''Basal Boundary''<br>The basal boundary of the Lower Shelly Clay is sharp, well defined and disconformable on the often pale and bleached, pedogenically altered Lower Mottled Clay. Burrows containing dark clay, lignite or shells may occur in burrows extending up to 1.5 m into the Lower Mottled Clay. In some parts of central London the contrast is between multicoloured clay with calcium carbonate concretions or pale, bleached Lower Mottled Clay and overlying dark grey shelly clay (Figure 2.23).

Ajhil: /* Reading Formation */

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Reading Formation

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	The Reading Formation consists of two leaves, the Lower Mottled Clay and the Upper Mottled Clay. The Lower Mottled Clay was deposited on the Upnor Formation before the mid-Lambeth Group Hiatus, afterwards followed by deposition of the Upper Mottled Clay. The Lower Mottled Clay persists across the entire area of the Reading Formation, but the Upper Mottled Clay is absent from most of the eastern part of the London Basin (Figure 2.16).		The Reading Formation consists of two leaves, the Lower Mottled Clay and the Upper Mottled Clay. The Lower Mottled Clay was deposited on the Upnor Formation before the mid-Lambeth Group Hiatus, afterwards followed by deposition of the Upper Mottled Clay. The Lower Mottled Clay persists across the entire area of the Reading Formation, but the Upper Mottled Clay is absent from most of the eastern part of the London Basin (Figure 2.16).

	[[Image:OR13006fig2.16.jpg\|thumb\|center\|600px\| '''Figure 2.16'''    Reading Formation distribution and main lithologies in London (Ellison ''et al''., 2004<ref name="Ellison 2004"></ref>). ]]		[[Image:OR13006fig2.16.jpg\|thumb\|center\|600px\| '''Figure 2.16'''    Reading Formation distribution and main lithologies in London (Ellison ''et al''., 2004<ref name="Ellison 2004">ELLISON, R A, WOODS, M A, ALLEN, D J, FORSTER, A, PHAROAH, T C, and KING, C. 2004. Geology of London. ''Special Memoir for 1:50 000 geological Sheets 256 (North London), 257 (Romford), 270 (South London) and 271 (Dartford) (England and Wales)''. British Geological Survey, Keyworth, Nottingham, UK.</ref>). ]]
	''Basal Boundary''<br>		''Basal Boundary''<br>
	The boundary of the Lower Mottled Clay with the underlying Upnor Formation is usually diffuse and difficult to place precisely because of pedogenic alteration that may include either migration of clay particles into the Upnor Formation and/or colour mottling. The degree of alteration may be such that it is impossible to identify the boundary accurately. Examples of some of the contact variations identified in rotary borehole cores are in shown in Figure 2.17.		The boundary of the Lower Mottled Clay with the underlying Upnor Formation is usually diffuse and difficult to place precisely because of pedogenic alteration that may include either migration of clay particles into the Upnor Formation and/or colour mottling. The degree of alteration may be such that it is impossible to identify the boundary accurately. Examples of some of the contact variations identified in rotary borehole cores are in shown in Figure 2.17.

Ajhil: /* Upnor Formation */

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Upnor Formation

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	'''2. Laminated silts, clays and fine sand'''<br>The basal transgressive gravel and sand is often succeeded by thinly laminated clay, silt or fine sand. It may contain lignite but in places is extensively bioturbated sometimes destroying the laminations. In the London area, e.g. around Islington, this bed may be up to 7 m thick.		'''2. Laminated silts, clays and fine sand'''<br>The basal transgressive gravel and sand is often succeeded by thinly laminated clay, silt or fine sand. It may contain lignite but in places is extensively bioturbated sometimes destroying the laminations. In the London area, e.g. around Islington, this bed may be up to 7 m thick.

	'''3. Upper gravelly sands'''<br>To the east of London the upper part of the Upnor Formation comprises up to 5 m of well rounded fine to coarse flint gravel in a clayey sand matrix. This is known as the ‘pebble bed’ (Ellison ''et al''., 1994<ref name="Ellison 1994"></ref> and 2004<ref name="Ellison 2004"></ref>) and is distinct from the basal gravels. Pedogenesis and calcrete formation have altered the matrix removing any sedimentary structure. These deposits are best seen at Orsett Cock Quarry, [TQ 657 811] in Essex (P211781) where gravel beds, up to 50 cm thick, are interbedded and interdigitated with glauconitic fine to medium sand with clay laminations.		'''3. Upper gravelly sands'''<br>To the east of London the upper part of the Upnor Formation comprises up to 5 m of well rounded fine to coarse flint gravel in a clayey sand matrix. This is known as the ‘pebble bed’ (Ellison ''et al''., 1994<ref name="Ellison 1994"></ref> and 2004<ref name="Ellison 2004">ELLISON, R A, WOODS, M A, ALLEN, D J, FORSTER, A, PHAROAH, T C, and KING, C. 2004. Geology of London. ''Special Memoir for 1:50 000 geological Sheets 256 (North London), 257 (Romford), 270 (South London) and 271 (Dartford) (England and Wales)''. British Geological Survey, Keyworth, Nottingham, UK.</ref>) and is distinct from the basal gravels. Pedogenesis and calcrete formation have altered the matrix removing any sedimentary structure. These deposits are best seen at Orsett Cock Quarry, [TQ 657 811] in Essex (P211781) where gravel beds, up to 50 cm thick, are interbedded and interdigitated with glauconitic fine to medium sand with clay laminations.

	[[Image:OR13006_P211781.jpg\|thumb\|center\|500px\| '''P211781'''    View looking east showing the Upnor Formation at Orsett Cock Quarry [TQ 657 811] with inclined sets of well rounded flint gravel ‘pebble’ beds. (BGS photograph P211781). ]]		[[Image:OR13006_P211781.jpg\|thumb\|center\|500px\| '''P211781'''    View looking east showing the Upnor Formation at Orsett Cock Quarry [TQ 657 811] with inclined sets of well rounded flint gravel ‘pebble’ beds. (BGS photograph P211781). ]]

Ajhil: /* Description of the Lambeth Group Formations */

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Description of the Lambeth Group Formations

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	The sands may be completely bioturbated with no primary bedding, and with vertical and subhorizontal burrows filled with sand of contrasting colour to the bioturbated matrix. Rare fragments of carbonaceous material also occur. A few impersistent seams of grey clay and angular clasts derived from such seams have been recorded within dominantly bioturbated beds. Other parts of the succession are well bedded and with horizontal planar lamination, ripple lamination, hummocky and planar cross bedding, and clay drapes. Stringers of well-rounded flint gravels occur on a few bedding surfaces and there are beds of gravelly sand, mostly less than 0.3 m thick. Thin seams of grey clay, angular clay clasts and rounded balls of clay are also present. Ophiomorpha and Macaronichnus burrows are typical in these beds (P211784) and can be seen in the quarries at Upnor and Orsett. Clay-dominated units, up to 0.3 m thick, contain relatively small amounts of sand, arranged in flaser lamination and with lenticular cross-lamination. These strata are well exposed at Lower Upnor Pit, north of Chatham, north Kent [TQ 759 711], Orsett Cock Pit, [TQ 656 811], and Orsett Tarmac Pit near Walton’s Hall Orsett, Essex [TQ 673 803].		The sands may be completely bioturbated with no primary bedding, and with vertical and subhorizontal burrows filled with sand of contrasting colour to the bioturbated matrix. Rare fragments of carbonaceous material also occur. A few impersistent seams of grey clay and angular clasts derived from such seams have been recorded within dominantly bioturbated beds. Other parts of the succession are well bedded and with horizontal planar lamination, ripple lamination, hummocky and planar cross bedding, and clay drapes. Stringers of well-rounded flint gravels occur on a few bedding surfaces and there are beds of gravelly sand, mostly less than 0.3 m thick. Thin seams of grey clay, angular clay clasts and rounded balls of clay are also present. Ophiomorpha and Macaronichnus burrows are typical in these beds (P211784) and can be seen in the quarries at Upnor and Orsett. Clay-dominated units, up to 0.3 m thick, contain relatively small amounts of sand, arranged in flaser lamination and with lenticular cross-lamination. These strata are well exposed at Lower Upnor Pit, north of Chatham, north Kent [TQ 759 711], Orsett Cock Pit, [TQ 656 811], and Orsett Tarmac Pit near Walton’s Hall Orsett, Essex [TQ 673 803].

	[[Image:OR13006fig2.13.jpg\|thumb\|center\|600px\| '''Figure 2.13'''    Distribution of the Upnor Formation in London (Ellison ''et al''., 2004<ref name="Ellison 2004"></ref>). ]]		[[Image:OR13006fig2.13.jpg\|thumb\|center\|600px\| '''Figure 2.13'''    Distribution of the Upnor Formation in London (Ellison ''et al''., 2004<ref name="Ellison 2004">ELLISON, R A, WOODS, M A, ALLEN, D J, FORSTER, A, PHAROAH, T C, and KING, C. 2004. Geology of London. ''Special Memoir for 1:50 000 geological Sheets 256 (North London), 257 (Romford), 270 (South London) and 271 (Dartford) (England and Wales)''. British Geological Survey, Keyworth, Nottingham, UK.</ref>). ]]
	[[Image:OR13006_P211784.jpg\|thumb\|center\|500px\| '''P211784'''    Detail of Upnor Formation. Cross-stratified fine-grained sand overlain by finely-interbedded fine and medium-grained sand and clay. Burrows and clay laminae are seen to stand out on the weathered face. Orsett Depot Quarry, West Pit. Looking south, [TQ 656 810], (BGS photograph P211784). ]]		[[Image:OR13006_P211784.jpg\|thumb\|center\|500px\| '''P211784'''    Detail of Upnor Formation. Cross-stratified fine-grained sand overlain by finely-interbedded fine and medium-grained sand and clay. Burrows and clay laminae are seen to stand out on the weathered face. Orsett Depot Quarry, West Pit. Looking south, [TQ 656 810], (BGS photograph P211784). ]]

Ajhil: /* Lambeth Group */

2021-08-16T11:43:02Z

Lambeth Group

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	The thickness of the Lambeth Group in the London Basin ranges from less than 10 m in the southeast where much of it is eroded away beneath the Harwich Formation (Oldhaven and Blackheath Beds) to about 30 m in the central part of the basin, around Chertsey. In the Hampshire Basin it is generally around 25 m thick; on the Isle of Wight the sequence is up to 50 m thick, and it is thinnest in the far west. Figure 2.10 shows the thickness below London.		The thickness of the Lambeth Group in the London Basin ranges from less than 10 m in the southeast where much of it is eroded away beneath the Harwich Formation (Oldhaven and Blackheath Beds) to about 30 m in the central part of the basin, around Chertsey. In the Hampshire Basin it is generally around 25 m thick; on the Isle of Wight the sequence is up to 50 m thick, and it is thinnest in the far west. Figure 2.10 shows the thickness below London.

	[[Image:OR13006fig2.10.jpg\|thumb\|center\|600px\| '''Figure 2.10'''    Distribution and thickness of the Lambeth Group in London (from Ellison, 2004<ref name="Ellison 2004"></ref>). ]]		[[Image:OR13006fig2.10.jpg\|thumb\|center\|600px\| '''Figure 2.10'''    Distribution and thickness of the Lambeth Group in London (from Ellison, 2004<ref name="Ellison 2004">ELLISON, R A, WOODS, M A, ALLEN, D J, FORSTER, A, PHAROAH, T C, and KING, C. 2004. Geology of London. ''Special Memoir for 1:50 000 geological Sheets 256 (North London), 257 (Romford), 270 (South London) and 271 (Dartford) (England and Wales)''. British Geological Survey, Keyworth, Nottingham, UK.</ref>). ]]

	The Lambeth Group is overlain by sands and gravel beds of the Harwich Formation (Ellison, 1994<ref name="Ellison 1994"></ref>), which in turn is overlain by the London Clay Formation.		The Lambeth Group is overlain by sands and gravel beds of the Harwich Formation (Ellison, 1994<ref name="Ellison 1994"></ref>), which in turn is overlain by the London Clay Formation.

Ajhil: /* Lambeth Group */

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Lambeth Group

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	[[Image:OR13006fig2.9.jpg\|thumb\|center\|600px\| '''Figure 2.9'''    Schematic diagram showing the relationship of the informal lithological units in the Lambeth Group in central London (after Ellison, 2004<ref name="Ellison 2004">ELLISON, R A, WOODS, M A, ALLEN, D J, FORSTER, A, PHAROAH, T C, and KING, C. 2004. Geology of London. ''Special Memoir for 1:50 000 geological Sheets 256 (North London), 257 (Romford), 270 (South London) and 271 (Dartford) (England and Wales)''. British Geological Survey, Keyworth, Nottingham, UK.</ref>). ]]		[[Image:OR13006fig2.9.jpg\|thumb\|center\|600px\| '''Figure 2.9'''    Schematic diagram showing the relationship of the informal lithological units in the Lambeth Group in central London (after Ellison, 2004<ref name="Ellison 2004">ELLISON, R A, WOODS, M A, ALLEN, D J, FORSTER, A, PHAROAH, T C, and KING, C. 2004. Geology of London. ''Special Memoir for 1:50 000 geological Sheets 256 (North London), 257 (Romford), 270 (South London) and 271 (Dartford) (England and Wales)''. British Geological Survey, Keyworth, Nottingham, UK.</ref>). ]]
	The Reading Formation comprises the Upper and Lower Mottled Clay (Ellison ''et al''., 1994<ref name="Ellison 1994">ELLISON, R A, KNOX, R W O'B, JOLLEY, D W, and KING, C. 1994. A revision of the lithostratigraphical classification of the early Palaeogene strata of the London Basin and East Anglia. ''Proceedings of the Geological Association'', '''105''', 187–197.</ref>; Ellison ''et al''., 2004<ref name="Ellison 2004"></ref>). Industry practice in the London area is based on the work by Skipper (Page and Skipper, 2000<ref name="Page 2000">PAGE, D, and SKIPPER, J. 2000. Lithological Characteristics of the Lambeth Group. ''Ground Engineering'', 33, 38–43. </ref>), and uses a slightly different classification. Pedogenically altered deposits are included within the Reading Formation either as the Lower or Upper Mottled Beds. The Lower Mottled Beds, therefore, includes the pedogenically altered, Upnor Formation as defined by Ellison ''et al''. (1994)<ref name="Ellison 1994"></ref> and Aldiss (2012)<ref name="Aldiss 2012"></ref> and may be called mottled Upnor Formation.		The Reading Formation comprises the Upper and Lower Mottled Clay (Ellison ''et al''., 1994<ref name="Ellison 1994">ELLISON, R A, KNOX, R W O'B, JOLLEY, D W, and KING, C. 1994. A revision of the lithostratigraphical classification of the early Palaeogene strata of the London Basin and East Anglia. ''Proceedings of the Geological Association'', '''105''', 187–197.</ref>; Ellison ''et al''., 2004<ref name="Ellison 2004">ELLISON, R A, WOODS, M A, ALLEN, D J, FORSTER, A, PHAROAH, T C, and KING, C. 2004. Geology of London. ''Special Memoir for 1:50 000 geological Sheets 256 (North London), 257 (Romford), 270 (South London) and 271 (Dartford) (England and Wales)''. British Geological Survey, Keyworth, Nottingham, UK.</ref>). Industry practice in the London area is based on the work by Skipper (Page and Skipper, 2000<ref name="Page 2000">PAGE, D, and SKIPPER, J. 2000. Lithological Characteristics of the Lambeth Group. ''Ground Engineering'', 33, 38–43. </ref>), and uses a slightly different classification. Pedogenically altered deposits are included within the Reading Formation either as the Lower or Upper Mottled Beds. The Lower Mottled Beds, therefore, includes the pedogenically altered, Upnor Formation as defined by Ellison ''et al''. (1994)<ref name="Ellison 1994"></ref> and Aldiss (2012)<ref name="Aldiss 2012"></ref> and may be called mottled Upnor Formation.

	The thickness of the Lambeth Group in the London Basin ranges from less than 10 m in the southeast where much of it is eroded away beneath the Harwich Formation (Oldhaven and Blackheath Beds) to about 30 m in the central part of the basin, around Chertsey. In the Hampshire Basin it is generally around 25 m thick; on the Isle of Wight the sequence is up to 50 m thick, and it is thinnest in the far west. Figure 2.10 shows the thickness below London.		The thickness of the Lambeth Group in the London Basin ranges from less than 10 m in the southeast where much of it is eroded away beneath the Harwich Formation (Oldhaven and Blackheath Beds) to about 30 m in the central part of the basin, around Chertsey. In the Hampshire Basin it is generally around 25 m thick; on the Isle of Wight the sequence is up to 50 m thick, and it is thinnest in the far west. Figure 2.10 shows the thickness below London.