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M26 motorway system and adjacent sections, Surrey and Kent
The Lower Gault of the M251M26 motorway system and adjacent sections, Surrey and Kent H. G. Owen OWEN. H. G. 1996. The Lower Gault of the M25/M26 motorway system and adjacent sections, Surrey and Kent. Proceedings of the Geologists' Association. 107,257-269. New sections in the Lower Gault at Godstone, Oxted- Titsey, Westerham and at Chevening on the M25 motorway and a pit north of Covers Farm, Westerham, are described. These permit the six lithological divisions recognized in the Sevenoaks-Trottiscliffe area of west Kent, to be extended westward to the previously described sections at the Brasted waterworks boring, Kent, and to Buckland , Surrey. Variation in thickness is a marked feature of the Lower Gault in this stretch of the outcrop. Department of Palaeontolo gy, The Natural History Museum, Cromwell Road, London SW7 5BD.
1. INTRODUCTION Prior to the construction of the South London Orbital Motorway M 25fM26 , little was known of the Lower Gault succession at outcrop between Buckland (Surrey ) and Dunton Green (Kent)(Spath. 1923-1943 ; Gossling, 1929; Dine s & Edmunds. 1933; Owen . 1958. 1963; Dines, Buchan , Holmes & Bristow, 1969). The author (Owen, 1971a, 1976) integrated this sparse information with description s of incomplete succession s in the Lower Gault expo sed in pits at Buckland, Tandridge (Surrey), Westerham (Kent) , and a nearly complete borehole succession at Brasted (Kent ). Further east, from Dunton Green to Trotti scliffe, the complete Lower Gault succession is known in some detail (eg. Wright, 1947; Milbourne, 1956, 1962, 1963; Owen, 1971a, 1976). The M25 and M26 motorways between Merstham (Surrey) and Wrotham (Kent), and adjacent road sections, were cut, essent ially, in the outcrop of the Upper Gault and Upper Greensand (Owen, 1996). Much or all of the Lower Gault has been exposed in borings for bridge supports at the M25/A22 Godstone interchange. in surface sections on the track of the M25 between Water Lane (Ox ted) and Titsey Road (Titsey) , in a pit north of Covers Farm, Westerham, situated a little south of the M25 motorway, in borings for bridges at the Croydon and London roads (Westerham) and at the Che vening Interchange of the M25fM26/A21. These sections have provided important new information. A locality map is given in Fig. 1. In the Dunton Green-Trottiscliffe area (Kent), the Lower Gault has been divided into six broad lithological divisions (e.g. Owen , 1971a). Although there is variation in thickness and the distinction between lithological units is not always clear, these broad divisions can now be traced westward from Dunton Green to Buckland. A brief revised classification of the sediments exposed at Buckland initiates the present account. The ammonite zonal and subzonal scheme for the Lower Gault sediments (essentially Middle Albian ) is shown in Table I and the ammonite fauna to be Proceedings of the Geologists ' Association. 107.257-269.
found in them has been listed by the author (Owen. 1971a, pp. 152-5 ). 2. DESCRIPTION OF LOWER GAULT SECTIONS (Figs 2-8) (a) Buckland Sand & Silica Co. sandpit (Fig.S) The Gault-Lower Greensand Junction Beds exposed in this pit [232 512 1] have been described (Owen, 1992, pp. 89 & 91), together with the Lower Gault (Owen, 1958, pp. 149-152; 1971a, pp. 31-33). Until the motorway sections in the Godstone-Limpsfield area became available , it was impossible to correlate accurately the siltier sediments seen at Buckland with the six broad divisions established in west Kent. The correlation is now more readily apparent and is given in Fig . 8. The numbered sequence of beds given previously (e.g. Owen. 1971a, pp. 31-33) is revised herein (Fig. 8). These now coincide with the divisional notation used in northwest Kent: Bed I (Owen, 1971a) renumbered I(i) (probably of Lyelliceras lyelli Subzone age); Beds 2 = I (ii), 3 = I(iii), Bed 4 =division 2 and Bed 5 =3(i) ( Hoplites spathi Subzone); Beds 6-11 = 3(ii) to 3(vii) (Anahoplites intermedius Subzone); Bed 12 = 4(i) (Dimorph oplites niobe Subzone) and Bed 13 = 4(ii) (Mojs isovicsia subdelaruei Subzone), their lithological description and ammonite zonal classification remaining unchanged from the account given by Owen (197Ia). Although divi sion 6, the ' Lautus Zone nodule Bed' , was not detected here in place, large distorted blocks of pale grey clay containing Hysteroceras orbignyi Subzone fossils were present in highly disturbed head deposits overlying the section; pointing to the close proximity of basal Upper Gault at no great distance to the north . Division 6 is present at the Wray Common County Primary School. Reigate [26975092] (noted by Owen, 1971a, p. 53) c. 2 miles (5.0 km ) to the east. The phosphatic pebble ammonites I
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H. G . OWEN
Table 1. Ammo nite zonal and subzo nal scheme for the Midd le Albian Substage in the European (hop litinid) faunal province Subzones
Substage
Zones
UPPER ALBIAN (pars)
Morto niceras inflatum
{ Dipoloceras cristatum
Euhoplites lautus
daviesi { Anahoplites Euhoplites nitidus
MID DLE ALBIAN
Euhoplites meandrinus Mojsisovicsia subdelaruei Dimorphoplites niobe Anahoplites intermedius
I
Euhoplites loricatus
Hoplites dentatus
LOW ER ALBIAN (pars)
Otohoplites auritiformis
collected from this bed at Wray Common inclu de Euhoplites meandrinus Spath and Dimorphop lites niobe Spa th (Euhoplites meandrinus Sub zone co mponen t), Euhoplites nitidus Spath, E. aff. lautus (J. Sowerby), E. opalinus Spa th and Dimorphoplites biplicatus (Mantell) (Euhoplites nitidus Su bzo ne component) and the Dipoloceras cristatum Subzo ne eleme nt consisting of Beudanticeras beudanti (Brongniart), Euhoplites armatus Spath, E. cf. ochetonotus (See ley) and the bivalve Birostrina sulcata (Parkinso n).
(b) Go ds to ne Interchange M25/A22 (Su r rey) (Figs 2 & 8) Surface sections were cut in the lower part of the Upper Gault (Owen, 1996). Kelly-bar auger bori ngs made for the supports of the bridge carrying the M25 over the A22 trunk road [3515 5285], north of Tyler 's Green, Godstone, Surrey, revealed the incomplete Lower Gault sequence given in Fig. 2 and its correlation in Fig. 8; all meas urements being corrected for boring rake and stratal dip. Division 6 was
Li t hol ogy
d iv . 7 6
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THE LOWER GAULT, SURREY AND KENT
struck at a depth of 17.38 m below ground surface and the deepest borings terminated at 23.79 m within the top sediments of division 3. The Gault-Lower Greensand Junction Beds outcrop at the northern side of the sandpit at Tyler's Green [34705218], situated 800 m SSW of the Godstone Interchange. The interchange is situated about 7.5 miles (12 km) eastward of the Buckland Sand & Silica Co. pit. Classification and correlation The basal 0.6 m of the succession yielded only specimens of Birostrina concentrica (Parkinson) but, on lithological grounds, these darkish mid-grey clays can be correlated with the top beds of division 3 in the Oxted-Titsey area described below, situated 3.5 miles (5.6 km) to the ENE of the Godstone borings. The immediately overlying sediments yielded Anahoplites planus (Mantell) and B. concentrica, but no precise subzonal age-diagnostic macrofossils were found. However, these sediments are identical to those at the base of division 4 in the OxtedTitsey section. If this likely classification is correct, the equivalents of divisions 4 and 5 at Godstone are thicker than in the Oxted-Titsey area. The only age-diagnostic ammonites found in the higher sediments of division 4 and basal 5, were specimens of Euhoplites meandrinus Spath at depths of 2.4 m and 3.0 m below division 6 indicating a meandrinus Subzone age for this part of the succession. Division 6 yielded cristatum Subzone fossils only.
(c) Water Lane to Titsey Road M25 (Surrey) (Figs 3 & 8) A nearly complete composite section through the Lower Gault was exposed in the series of cuttings and deep drainage excavations on the motorway track extending from Bovis Bridge 7 [40155398] carrying the M25 over Water Lane, Oxted, to Bridge 10 [4065 5395] carrying the M25 over Titsey Road (B269), Titsey. These include excavations for the large diameter drain on the south side of the motorway between bridges 7 and 8 (which carries the motorway over Pitchfont Lane) and work for the diversion of the River Eden (Bridge 9). The section is shown in Fig. 3 and its correlation in Fig. 8. Late Pleistocene peri-glacial cryoturbation of the near-surface sediments is a feature in this area. Classification and correlation The basal part of the succession was exposed in the culvert excavations for the River Eden (Bridge 9) where the top sediments of the Gault-Lower Greensand Junction Beds were seen (Owen, 1992, p. 94). Division l A of the overlying Lower Gault contains crushed ammonites, essentially species of Hoplites, and Birostrina concentrica, all preserved as pyritic impressions. The sediments are of Lyelliceras lyelli Subzone age in the basal part and can be correlated with the similar sediments of Bed 4 (Owen, 1963, p. 39; 1992, pp. 89-92) at the Coney Hill sandpit, Barrow Green [3775 5250], 2 miles (3.2 km) to the Sw. The top of
261
this succession is probably of spathi Subzone age rather than of lyelli age. Division lB contains Hoplites spp. and Birostrina concentrica preserved with their aragonitic shells and, like division 2 (the 'upper spathi Subzone nodule bed'), is of spathi Subzone age. The clays of division 3 are very fossiliferous and, like similar deposits to the east, the bulk of them are of Anahoplites intermedius Subzone age. However, it was not possible to determine precisely the sediment boundaries between those of the intermedius and Dimorphoplites niobe Subzones. The higher part of the succession is attenuated in comparison with the succession seen at Godstone to the west and the Seven oaks area to the east (Fig. 8) and no precise distinction can be made between divisions 4 and 5 recognizable in the latter area. Bed 4-5 (i) contains scattered large specimens of B. concentrica and ammonites and, like Bed 4-5 (ii) above, could be of either niobe or subdelaruei age. The beds may be correlated by lithology with division 4 and Bed 5(i) in the Sevenoaks area, known to be of niobe Subzone age at the base and of subdelaruei Subzone age above. Bed 4-5 (iii) contains ammonites of Euhoplites meandrinus Subzone age and these occur also in the lower part of Bed 4-5 (iv). However, at 0.33 m above the base of 4-5 (iv), badly preserved Euhoplites spp. of early Euhoplites lautus Zone age are present. Bed 4-5 (v) contains E. lautus (1. Sowerby) and Euhoplites proboscideus (1. Sowerby) indicating a Euhoplites nitidus Subzone age. There is no evidence of any sediments of Anahoplites daviesi Subzone age in Bed 4-5 (vi). Division 6 is the Dipoloceras cristatum Subzone phosphatic pebble bed, similar in fossil content and preservation to that seen at Sevenoaks. Division 6 was seen to strike diagonally northeastwards in a series of north-south orientated drainage trenches, cut in the field north of the motorway track between Pitchfont Lane and the River Eden. Further east on the motorway track, about 320 m east of the Titsey road bridge, excavations for drainage sumps [4105 5410] struck division 6 and penetrated approximately 2 m into the upper sediments of the Lower Gault.
(d) Squerryes Estate pit, Westerham (Kent) (Figs 4 & 8) The Gault-Lower Greensand Junction Beds exposed in this extensive pit worked by The Redland Group pic have been described by the author (Owen, 1992, pp. 91, 93-94). A complete succession through the Lower Gault into the basal beds of the Upper Gault has been exposed since 1980 when the pit was extended northward towards the M25. The section given in Fig. 4 at grid ref. 4330 5430 is situated 650 m SW of the Croydon Road (B2024) bridge site on the M25 described below and 1.75 miles (2.7 km) towards the ENE of the Water Lane-Titsey Road section described previously. The description and Bed notation of the lower part of the Lower Gault given by the author (Owen, 1971a, pp. 28-31) requires some revision, the previous bed numbers being given in parentheses in Fig. 4. The correlation of this section is shown in Fig. 8.
262
H. G. OWEN
div.
Lithology
7
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UPPER GAULT
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&
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bridge). Fawn-grey shelly clay with l errtr cl ea reddish marl.
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marl y I ant I c I as scattered from about the mI dd 1e of the bed downward (absent east of the Titsey Road III
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2 18
Black phosphatic nccur es & fragments of fossils with the shell in a prominent shell seam. Shelly mid-grey clay with a shell Seam containing part-phosphat i sed fossi t s Om02 - Om 03 abova base.
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-GAULT-LOWER GREENSAUO JUNCTION BEDS (Owen 1992)
Fig.3. Lower Gault section on the M25 track between Water Lane bridge [4015 5398J, Oxted and the Titsey Road bridge [40655395], Titsey, Surrey.
Classification and correlation Division lA is of lyelli Subzone age. Divisions IB and 2 (the 'upper spathi nodule bed') are of spathi Subzone age. The basal part of division 3 shows a similar succession to that of all sections seen as far east as Wrotham. The black clays of Bed 3(i) contain Hoplites spp. of late spathi
Subzone age together with large examples of B. concentrica. The glauconitic clay interval Bed 3(ii), like the same bed seen in sections further east, has not yielded agediagnostic fossils but- is probably of earliest intermedius Subzone age. Bed 3 (iii) is also of intermedius Subzone age. Division 3 at Squerryes is substantially reduced in thickness
263
THE LOWER GAULT, SURREY AND KENT
div.
Lithology
7
~ Rather sma [ I brownish-grey phoapha't rc nodules In mldfawni sh-grey she! Iy clay. ( i v ] Mi'd grey, shelly, silty clay. passi ns into: ~ (iii) Fawn-grey s l Ity, shelly cJay passing into:-
6
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Dark. fawnish-grey Sf Ity shelly clay wfth darkcentred, I ight-rinded phosphatic nodules scattered throughout. Passing into: --Ii} Li ghter fawn-grey blocky-bedded shelly clay with buff ochreous part i ngs &: soft radd i sh mar I stone lenticles at the base of the bed. (iii) Clay in patches of I ithology of Beds 4(i,) & 5(,) . (j
fii)
4
metres
Zone
UPPER GAULT
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seam with part-phosphat I sed foss I Is (2 v I i I Battleship grey clay; shelly - part phosphatised. Sparsely shelly battleship grey clay {2 v) Battleship grey clay: shelly-part phosphate/pyritic
(iii) She I I -seam with part-phosphat I sed foss j Is (2 iii) She! Iy batt I ash i p-grey cl ay (2 i i ) . (;) Small phosphat i c nodu l as & part-phosphat I sed foss, I~ (V 1 Darker batt I ash i p-grey pyritic clay with small phosphatic nodules: weathering ferruQ i nous. ( ivI Darkish. battleship-grey clay, pyr,tic. wi t'h pockets of 91 aucon i te '& quartz sand. Scattered part-phoSphatI sed, pyritic fossils. Weather i n9 as Bed lA (i) (iii) Dark, batt I esh i p grey pyritic clay with part -phoeph at i sed P)TltIC ftoas l Is; weather I ns as Bed lA( i)
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Dark, batt leshl p-grey pyritic clay with crushed fossi I S WI th pyr i 're-o-epr aced she I Is. These clays weather to mottlea grey with red ferruginous t errtl c t ea and much selenite.
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GAULT-LOWER GREEtlSAtIO JUNCTI ON BEOS (Owen 1992)
Fig. 4. Lower Gault section at the Squerryes Estate pit [43305430],300 m north of Covers Farm, Westerham, Kent
in comparison with the Water Lane-Titsey Road section and with the Croydon Road Bridge section described next. On the other hand, divisions 4 and 5 are capable of separation at Squerryes and are substantially thicker than at the Water Lane-Titsey Road section, although the overall thickness of the Lower Gault is closely comparable in these two sections. Division 4 contains ammonites normally found in the niobe and subdelaruei Subzones, but in the collecting absence of specimens of Mojsisovicsia, no precise
classification of these sediments can be made. Bed 4 (iii) contains a meandrinus Subzone fauna, as does the basal part of division 5 (Bed 5(i) above. The classification of the remainder of division 5 with the meandrinus Subzone is unsatisfactory. A thin shell seam occurs 0.0\ m below division 6 but has yielded to the author only specimens of the long time-ranging Anahoplites planus (Mantell) and there is no evidence of an early lautus Zone age for these sediments, as in Water Lane-Titsey section.
di v .
t.i tbolocv
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metres
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Shelly mid -grey clay wi t h sca tte red brown pno spha t ,c
( v) ( IV )
nodu le s . She l ly mid- grey c l a y . She I I -seam with brown j sh phosphat i c nodules & Phosphat i sed ammon I to bod y chambers
-...
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3.95
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Gr een i sh - grey f i n e ly g l auco n it i c & S Il t y Cl ay . ( i) Dar k mid -grey shel iy clay . Black pho6phat ic nodu I es &: fragmentary ecs s r Is, wi th the shel l preserved, i n a sha ll sea m. ( i l)
2
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2 . 30
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Part- pho sph a t i sed foss i I s I n da rk - brown phcs pn a t e with sner rs r ep laced by pyrit e .
I
--;
1A (Ill )
Dark-gra y pyriti c cl ay with p yr-r te-r- eot aced shells Deco ml ng drab- gr ey pyr iti c cl ay ca. 1 m 10 be low
t op o f be d
{ I I }
Ii)
Drab . da r k -g rey s i Ity cl ay wi th occas ional mar l y s i t tstono lo n t i c les : pyrit i c & pyri ti c fi lament s 5 11ty da r k- grey er a y wi th patches o f br i ght-green 9 1auconi t i C sand & some ohoschat i c nodu I as GAULT-LOWER GREENSAtlO JUNCT I ON BEDS ( Owe n '9 92 )
1. 00
I = = = = = 1'-0.05 I I -
- --
i
--. = = I
I I
~,
"'"
""" => """
."" .c::>
2.00
0. 50 0 .60
Fig. 5. Lower Gault surface and borehole succession at the M25/Croydon Road (B2024) bridge [5169 5462] and adjacent trenches, Westerham, Kent.
T H E LOWER GAUL T , S U R RE Y
(e) Croydon Road Bridge M251B2024, Westerham (Kent) (Figs 5 & 8) Surface trenches and kelly-bar auger borings (corrected for dip and rake) made for the supports of the bridge carrying the M25 ove r Cro ydon Road (B202 4), Westerham [5169 5462] provided a complete section through the Lower Gault (Fig. 5). The site is situated 650 m NE of the Squerrye s pit and shows a marked increase in the thickness of post-division 2 Lower Gault when compared to that section (Fig. 8). Division 6 outcropped below subsoil in the B 2024 road bed at the north side of the bridge and on the motorw ay track, the rema inder of the Lower Gault successio n being determined from the series of auger borings for the bridge supports. Classification and correlation The lithological succession up to the basal beds of division 3 is essentially the same as that seen in the Squerryes pit, although differing in detail. As with all boreholes in the Lower Gault, it did not prove possible to zone the sediments with precision. However, there is no reason to suppose that the Croydon Road representat ion is significantly different from that of the more pre cisel y zoned sequence at Squerryes. However, division 3 at the Croydon Road sectio n is substantially thicker than at Squerryes and contained an ammonite fauna consisting of Anahoplites intermedius and A. praecox. The shell seam, Bed 3 (iv) and the clays with phosphatic nodules Bed 3 (v), present at Croydon Road and seen in the sections further east as far as Trottiscliffe, were not found in the Squerryes section. Divisions 4 & 5 at Croydon Road are substantially thicker than at Squerryes, although a detailed sequence could not be made out for certain in the weathered clays. Fortunately, this interval was well exposed in the cutting for the M25 at the Lond on Road (A233) bridge site situated 1.2 km to the ENE of the Croydon Road bridge described next.
(I) London Road Bridge M25/A233, Westerham (Kent)
(Figs 6 & 8) At this site, the M25 is in a cutting which exposed below basal Upper Gault (Owen, 1996), a clear section in Lower Gault down to Bed 3 (iv). Below this level the section depend s on the analysis of the auger drill ings made for the bridge supports carrying the London Road (A233) over the motorw ay [5500 4480] . A complet e Lower Gault succession was traversed at this site (Fig. 6) and its correlation with other sections is shown in Fig. 8. Classifica tion and correlation The lithological succession from the top of the GaultLower Greensand Junction Beds to the top of division 3 in the London Road borings and its subzonal classification, is closely comparable to that of the Squerryes and Croydon Road sections. Being deeper than the cutting and much deeper than the Croydon Road borings, more detail could be made out in the unweathered successio n traversed by the
AND K E NT
265
borings. The speed of work precluded, unfortunately. the precise dem arcation between sediments of the niobe, subdelaruei and meandrin us Subzones, but all are present. The boundary between the meandrinu s Subzone sediments and those of the nitidus Subzone was determined precisely at a depth of 0.04 m below division 6. (g) M251M26/A21 Chevening interchange, Chevening (Kent) (Figs 7 & 8) Between the London Road Bridge site and the next easterly section on the motorway at Che vening, the Lower Gault is partly cut-out at outcrop by a WSW-ENE trending strike fault extending from Charmans Farm just south of the M25, Westerham [4543 5510], eastward to a position near Combe Bank Convent, Sundridge [47505560]. North of Brasted , in the Metropolitan Water Board boring [4709 5574] situated just east of Station Road and 230 m south of the M25, 2.4 km east-northeast of the London Road bridge site, a nearly complete Lower Gault section was traversed and was describ ed by' the author (Owen, 1971a, pp. 28- 29). The succession is comparable in thickne ss to that of the London Road section and its correlation is shown in Fig. 8. At the M251M26/A21 Chevening Interchange, Kelly-bar drill ing for the supports of the brid ge carryi ng the Chevening Road over the motorw ay [5685 4948], revealed the incomplete section shown graphically in Fig. 6. Division 6 was struck in the drill ings at about 10 m below ground surface, beneath a basal Upper Gault succession. The correlation of this section with that at Brasted 2.7 km towards the west-southwest and the former Dunton Green Brick, Tile & Pottery Works pit [515 570] situated 2.25 km to the east-northeast (Wright, 1947, pp. 3 15-3 18; Owen, 1971a, pp. 26-28) is shown in Fig. 8. Classification and correlation The correlation diagram (Fig. 8) shows the progressive thinning of the Lower Gault from Brasted to Dunton Green. The Che vening road bridge is situated roughly half-way between these localities. The principal features between the sections are: ( I ) the thickening of division 3 from Brasted to Cheven ing and its thinning between Chevenin g and Dunton Green, although the lithological succession and intermedius Subzone age remains the same; (2) the nearly constant thickne ss of division 4 and the marked attenuation of division 5 from Brasted to Chevening and their coalesce nce and attenuation at Dunton Green . Unfortun ately, it was not possible to zone accurately the clays of division 4 at the Che vening road bridge, other than it is of niobe Subzone age at the base and meandrinus Subzone near the top. Division 5 contains an ammonite fauna of nitidus Subzone age and Division 6 is the cristatum Subzone nodule bed. An incomplete section through the Lower Gault and Gault-Lower Greensand Junction Beds (Owen, 1992, p. 96) was seen in the trench and sumps dug for the Outfall A drain extending from the M26 motorwa y at grid ref. 5045 5745 to the north side of Longford Lake [5055 5680]. The beds were highly weathered and disturbed by late Pleistocene
266
H. G. OWEN
d iv,
Lithology
7 6
I
Brown ph os pha t i c nodu I es In weathered fawn-grey shelly e la~ (vi) Fawn i gh mid-gre y sh elly Clay wi th basal sher I seam. H id-grey she ty c ay weathering f awn l sh . ( IV ) Brown ph o &phat i c nodul es , some farge, in c l ay of ( ii i )
:..-.
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5
r-
./j
( i i I ) Mid -grey shel l y clay wea thering fawnish .
(i i)
~~~~r~~'oured pn o aohat !c nodu les &. part-PhOSPhat lso,d
( , )
Darkish.
fawn-grey.
metres
Zone
UPPER GAULT
shelly clay with lent ieles of
soft e arthy . ferrug i nous marlstone at the base . Top Om 31 i s t i shter I n shade. With pa r r-pyr-r t l s ed f os s i Is .
..
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Dark . Tawn y mi d-gre y s h el ly cl a y .
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O. BO
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I I I
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1992)
Fig. 6. Lower Gault surface and borehole successio n at the M25/London Road (A233) bridge [5500 4480], Westerham, Kent.
267
THE L O W E R GAULT. SURREY AND KENT
d iv .
Lithology
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Zon e
UPPER GAULT
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.....
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Fig. 7. Lower Gau lt succession from auger borings on the M251M26 track for the Chipstead-Chevening road and the A2l overbridges [5685 4948 ], Cheve ning, Kent.
periglacia l cryoturbation, but appeared to be comparab le in thickness and lithology to that of the Dunton Green and St John's brickyard sections to the east (Owen, 1971a, 1976). (h) Otford to Trotti scliffe (Fig. 8) No sections in the Lower Gault were exposed along the M26 motorway track or associated work, eastward of the Outfall A drain until the M26/A20 interchange to the west of the site of the Ford Road clay pit. The old sections in the Lower Gault at Dunton Green, the former Sevenoaks Brick Works at Greatness Lane, Otford [5360 5780] and the former Rugby Portland Cement Co. Ford Road clay pit,
Trottiscliffe [6360 5910] and their correlation with sections further east, have been described in deta il by the author (Owen, 1971a, 1976). They are included in the correlation diagram (Fig. 8) for clarity of the six lithological division s recognized in the Lower Gault in this area. 3. ST RUCTURAL CONT ROLS ON LO WER GAULT SE DIMENTATION The author (Owen, 1971a, pp. 143-1 47; 1976, pp. 495-496) cons idered that sedimentation during the formation of the Lower Gault in northwest Kent and Surrey was controlled by a series of north-northwest to south-southe ast trending
Buckla nd S&S
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~
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A
phosphatic nodules
---~- I --
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.>
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Fig. 8. Correlat ion diagram of the Lower Gault from Buckland, Surrey, eastward to Trottiscliffe, Kent.
THE LOWER GAULT, SURREY AND KENT
ridges and troughs. The effect on sedimentation being tectonically passive and the result of gravity-movement of clay particles down-slope, aided by weak submarine current activity around the topographic features. This concept of passive ridges and troughs needs modification in the light of the depositional and erosional history of the Gault-Lower Greensand Junction Beds (Owen, 1992), together with the new information concerning the Lower Gault. The comparable thickness of the Lower Gault in the Water Lane-Titsey Road and Squerryes sites and the considerable increase in thickness in the 650 m between the latter and the M26 Croydon Road (B2024) bridge site (Fig. 8), is significant. The Gault-Lower Greensand Junction Beds between Westerham and Tandridge show a thick succession of clays and loams which, when coupled to the relatively thin Lower Gault succession above in comparison with that at the Croydon and London Road, Westerham, sections, suggests a slow differential inversion to the south and subsidence to the north. Further north in the Addington, Surrey, borehole (Buchan, Robbie, Holmes, Earp, Bunt & Morris, 1940, pp. 8-9) [3709 6274], division 6 was struck at 268 m depth and the base of the Lower Gault at 274.8 m, giving a thickness of 6.8 m which is even thinner than at Squerryes or at Water Lane-Titsey Road. A deeper sample from 278 m depth (BGS Borings Department Bd 2198) suggests the basal part of the Gault-Lower Greensand Junction Beds with gritty phosphatic nodules. The evidence
269
suggests that during the mammillatum Superzone and the Lower Gault, slight differential movements occurred of individual, tilted, fault-bounded blocks at the northern margin of the Wealden graben, abutting the London Platform. A tectonic cause has been established for the midcristatum Subzone condensation and planing-off of the upper surface of the Lower Gault south of the west-east trending Thames axis from south Essex westward to west London and the absence of the Lower Gault in the region to the north of this axis (Owen, 1971b). Differential movements of fault-bounded blocks flanking the southern margin of the London Platform during the formation of the Upper Gault and Upper Greensand is suggested by the variations in thickness of lithological divisions and the preservation of Callihoplites auritus Subzone sediments by inversion seen in the M23!M25!M26 motorways and adjacent sections (Owen, 1996).
ACKNOWLEDGEMENTS Apart from the County and Department of Transport Engineers together with their staffs and those of the contractors listed previously (Owen, 1996), I am also indebted to the Redland Tiles, Rugby Portland Cement Co. and the former Sevenoaks Brick Works Ltd., for facilities to examine sections on their property.
REFERENCES BUCHAN, S., ROBBIE, J. A., HOLMES, S. C. A., EARP, J. R, BUNT, E. F. & MORRIS, L. S. O. 1940. Water supply of southeast England from underground sources. Part IV. Wartime Pamphlets of the Geological Survey of Great Britain 10, I-59. DINES, H. G., BUCHAN, S., HOLMES, S. C. A. & BRISTOW, C. R. 1969. Geology of the country around Sevenoaks and Tonbridge (Sheet 287 NS). Memoirs of the Geological Survey of Great Britain. - - , & EDMUNDS, F. H. 1933. The geology of the country around Reigate and Dorking (Sheet 286 NS). Memoirs of the Geological Survey of Great Britain. GOSSLING, F. 1929. The geology of the country around Reigate. Proceedings of the Geologists' Association, 40, 197-259. MILBOURNE, R. A. 1956. The Gault at Greatness Lane, Sevenoaks, Kent. Proceedings of the Geologists' Association, 66, 235-242. - - 1962. Notes on the Gault near Sevenoaks, Kent. Proceedings of the Geologists' Association, 72,437-443. - - 1963. The Gault at Ford Place, Wrotham, Kent. Proceedings of the Geologists' Association, 74,55-79. OWEN, H. G. 1958. Lower Gault sections in the northern Weald and the zoning of the Lower Gault. Proceedings of the Geologists' Association, 69, 148-165.
- - 1963. Some sections in the Lower Gault of the Weald. Proceedings of the Geologists' Association, 74,35-53. - - 1971a. Middle Albian stratigraphy in the Anglo-Paris Basin. Bulletin of the British Museum (Natural History) Geology Series, Supplement 8. - - 1971b. The stratigraphy of the Gault in the Thames Estuary and its bearing on the Mesozoic tectonic history of the area. Proceedings of the Geologists' Association, 82, 187-207. - - 1976. The stratigraphy of the Gault and Upper Greensand of the Weald. Proceedings of the Geologists' Association, 86, 475-498. - - 1992. The Gault-Lower Greensand Junction Beds in the northern Weald (England) and Wissant (France), and their depositional environment. Proceedings of the Geologists' Association, 103,83-110. - - 1996. The Upper Gault and Upper Greensand of the M231M251M26 motorway system and adjacent sections, Surrey and Kent. Proceedings of the Geologists' Association, 107, 167-188. SPATH, L. F. 1923-1923. A monograph ofthe Ammonoidea of the Gault. Monographs of the Palaeontographical Society, (2 volumes). WRIGHT, C. W. 1947. The Gault at Dunton Green. In Notes on the geology of the country around Sevenoaks, Kent. Proceedings of the Geologists' Association. 57, 315-318.
Received 19 June 1995; revised typescript accepted 6 February 1996
1. INTRODUCTION Prior to the construction of the South London Orbital Motorway M 25fM26 , little was known of the Lower Gault succession at outcrop between Buckland (Surrey ) and Dunton Green (Kent)(Spath. 1923-1943 ; Gossling, 1929; Dine s & Edmunds. 1933; Owen . 1958. 1963; Dines, Buchan , Holmes & Bristow, 1969). The author (Owen, 1971a, 1976) integrated this sparse information with description s of incomplete succession s in the Lower Gault expo sed in pits at Buckland, Tandridge (Surrey), Westerham (Kent) , and a nearly complete borehole succession at Brasted (Kent ). Further east, from Dunton Green to Trotti scliffe, the complete Lower Gault succession is known in some detail (eg. Wright, 1947; Milbourne, 1956, 1962, 1963; Owen, 1971a, 1976). The M25 and M26 motorways between Merstham (Surrey) and Wrotham (Kent), and adjacent road sections, were cut, essent ially, in the outcrop of the Upper Gault and Upper Greensand (Owen, 1996). Much or all of the Lower Gault has been exposed in borings for bridge supports at the M25/A22 Godstone interchange. in surface sections on the track of the M25 between Water Lane (Ox ted) and Titsey Road (Titsey) , in a pit north of Covers Farm, Westerham, situated a little south of the M25 motorway, in borings for bridges at the Croydon and London roads (Westerham) and at the Che vening Interchange of the M25fM26/A21. These sections have provided important new information. A locality map is given in Fig. 1. In the Dunton Green-Trottiscliffe area (Kent), the Lower Gault has been divided into six broad lithological divisions (e.g. Owen , 1971a). Although there is variation in thickness and the distinction between lithological units is not always clear, these broad divisions can now be traced westward from Dunton Green to Buckland. A brief revised classification of the sediments exposed at Buckland initiates the present account. The ammonite zonal and subzonal scheme for the Lower Gault sediments (essentially Middle Albian ) is shown in Table I and the ammonite fauna to be Proceedings of the Geologists ' Association. 107.257-269.
found in them has been listed by the author (Owen. 1971a, pp. 152-5 ). 2. DESCRIPTION OF LOWER GAULT SECTIONS (Figs 2-8) (a) Buckland Sand & Silica Co. sandpit (Fig.S) The Gault-Lower Greensand Junction Beds exposed in this pit [232 512 1] have been described (Owen, 1992, pp. 89 & 91), together with the Lower Gault (Owen, 1958, pp. 149-152; 1971a, pp. 31-33). Until the motorway sections in the Godstone-Limpsfield area became available , it was impossible to correlate accurately the siltier sediments seen at Buckland with the six broad divisions established in west Kent. The correlation is now more readily apparent and is given in Fig . 8. The numbered sequence of beds given previously (e.g. Owen. 1971a, pp. 31-33) is revised herein (Fig. 8). These now coincide with the divisional notation used in northwest Kent: Bed I (Owen, 1971a) renumbered I(i) (probably of Lyelliceras lyelli Subzone age); Beds 2 = I (ii), 3 = I(iii), Bed 4 =division 2 and Bed 5 =3(i) ( Hoplites spathi Subzone); Beds 6-11 = 3(ii) to 3(vii) (Anahoplites intermedius Subzone); Bed 12 = 4(i) (Dimorph oplites niobe Subzone) and Bed 13 = 4(ii) (Mojs isovicsia subdelaruei Subzone), their lithological description and ammonite zonal classification remaining unchanged from the account given by Owen (197Ia). Although divi sion 6, the ' Lautus Zone nodule Bed' , was not detected here in place, large distorted blocks of pale grey clay containing Hysteroceras orbignyi Subzone fossils were present in highly disturbed head deposits overlying the section; pointing to the close proximity of basal Upper Gault at no great distance to the north . Division 6 is present at the Wray Common County Primary School. Reigate [26975092] (noted by Owen, 1971a, p. 53) c. 2 miles (5.0 km ) to the east. The phosphatic pebble ammonites I
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Table 1. Ammo nite zonal and subzo nal scheme for the Midd le Albian Substage in the European (hop litinid) faunal province Subzones
Substage
Zones
UPPER ALBIAN (pars)
Morto niceras inflatum
{ Dipoloceras cristatum
Euhoplites lautus
daviesi { Anahoplites Euhoplites nitidus
MID DLE ALBIAN
Euhoplites meandrinus Mojsisovicsia subdelaruei Dimorphoplites niobe Anahoplites intermedius
I
Euhoplites loricatus
Hoplites dentatus
LOW ER ALBIAN (pars)
Otohoplites auritiformis
collected from this bed at Wray Common inclu de Euhoplites meandrinus Spath and Dimorphop lites niobe Spa th (Euhoplites meandrinus Sub zone co mponen t), Euhoplites nitidus Spath, E. aff. lautus (J. Sowerby), E. opalinus Spa th and Dimorphoplites biplicatus (Mantell) (Euhoplites nitidus Su bzo ne component) and the Dipoloceras cristatum Subzo ne eleme nt consisting of Beudanticeras beudanti (Brongniart), Euhoplites armatus Spath, E. cf. ochetonotus (See ley) and the bivalve Birostrina sulcata (Parkinso n).
(b) Go ds to ne Interchange M25/A22 (Su r rey) (Figs 2 & 8) Surface sections were cut in the lower part of the Upper Gault (Owen, 1996). Kelly-bar auger bori ngs made for the supports of the bridge carrying the M25 over the A22 trunk road [3515 5285], north of Tyler 's Green, Godstone, Surrey, revealed the incomplete Lower Gault sequence given in Fig. 2 and its correlation in Fig. 8; all meas urements being corrected for boring rake and stratal dip. Division 6 was
Li t hol ogy
d iv . 7 6
spathi { Hoplites Lyelliceras lyelli udoson ne ratia { Pse(lsohoplites) steinmanni
metres
Zone
UPPER GAULT
()
Da rk br own phosphat ic nodules & f OBSi 19 in mid- grey she l l y
c lay .
~
.::J'"
................
. 0 . 025 -0 . 50
~.
r;a
5
Mid grey shell y c lay.
2 . 59
::J
~
5'
EiI
(J)
§. ~
(iii) Fawnish mid- grey she ll y clay .
1. 75
iii'
2
4 (i i)
Bro wn ish pho;,p ha t ic nodul e s in a shel l
(i)
f awn lsh mid - gr e y ahally cl ay.
I g:
SGI1Jll .
··= · =·· ·c
0 .02 5
1 . 14
-t-
3 IPllrt)
Da r k i sh mi d gre y 'she l l y clay.
Sun t o:
'"5'...
0 . 61
s ~
Fig.2. Lower Gault sectio n from auger borings made for the supports of the bridge carryi ng the M25 over the A22 , Godstone Interchange, Godsto ne, Surrey [35 15 5285].
THE LOWER GAULT, SURREY AND KENT
struck at a depth of 17.38 m below ground surface and the deepest borings terminated at 23.79 m within the top sediments of division 3. The Gault-Lower Greensand Junction Beds outcrop at the northern side of the sandpit at Tyler's Green [34705218], situated 800 m SSW of the Godstone Interchange. The interchange is situated about 7.5 miles (12 km) eastward of the Buckland Sand & Silica Co. pit. Classification and correlation The basal 0.6 m of the succession yielded only specimens of Birostrina concentrica (Parkinson) but, on lithological grounds, these darkish mid-grey clays can be correlated with the top beds of division 3 in the Oxted-Titsey area described below, situated 3.5 miles (5.6 km) to the ENE of the Godstone borings. The immediately overlying sediments yielded Anahoplites planus (Mantell) and B. concentrica, but no precise subzonal age-diagnostic macrofossils were found. However, these sediments are identical to those at the base of division 4 in the OxtedTitsey section. If this likely classification is correct, the equivalents of divisions 4 and 5 at Godstone are thicker than in the Oxted-Titsey area. The only age-diagnostic ammonites found in the higher sediments of division 4 and basal 5, were specimens of Euhoplites meandrinus Spath at depths of 2.4 m and 3.0 m below division 6 indicating a meandrinus Subzone age for this part of the succession. Division 6 yielded cristatum Subzone fossils only.
(c) Water Lane to Titsey Road M25 (Surrey) (Figs 3 & 8) A nearly complete composite section through the Lower Gault was exposed in the series of cuttings and deep drainage excavations on the motorway track extending from Bovis Bridge 7 [40155398] carrying the M25 over Water Lane, Oxted, to Bridge 10 [4065 5395] carrying the M25 over Titsey Road (B269), Titsey. These include excavations for the large diameter drain on the south side of the motorway between bridges 7 and 8 (which carries the motorway over Pitchfont Lane) and work for the diversion of the River Eden (Bridge 9). The section is shown in Fig. 3 and its correlation in Fig. 8. Late Pleistocene peri-glacial cryoturbation of the near-surface sediments is a feature in this area. Classification and correlation The basal part of the succession was exposed in the culvert excavations for the River Eden (Bridge 9) where the top sediments of the Gault-Lower Greensand Junction Beds were seen (Owen, 1992, p. 94). Division l A of the overlying Lower Gault contains crushed ammonites, essentially species of Hoplites, and Birostrina concentrica, all preserved as pyritic impressions. The sediments are of Lyelliceras lyelli Subzone age in the basal part and can be correlated with the similar sediments of Bed 4 (Owen, 1963, p. 39; 1992, pp. 89-92) at the Coney Hill sandpit, Barrow Green [3775 5250], 2 miles (3.2 km) to the Sw. The top of
261
this succession is probably of spathi Subzone age rather than of lyelli age. Division lB contains Hoplites spp. and Birostrina concentrica preserved with their aragonitic shells and, like division 2 (the 'upper spathi Subzone nodule bed'), is of spathi Subzone age. The clays of division 3 are very fossiliferous and, like similar deposits to the east, the bulk of them are of Anahoplites intermedius Subzone age. However, it was not possible to determine precisely the sediment boundaries between those of the intermedius and Dimorphoplites niobe Subzones. The higher part of the succession is attenuated in comparison with the succession seen at Godstone to the west and the Seven oaks area to the east (Fig. 8) and no precise distinction can be made between divisions 4 and 5 recognizable in the latter area. Bed 4-5 (i) contains scattered large specimens of B. concentrica and ammonites and, like Bed 4-5 (ii) above, could be of either niobe or subdelaruei age. The beds may be correlated by lithology with division 4 and Bed 5(i) in the Sevenoaks area, known to be of niobe Subzone age at the base and of subdelaruei Subzone age above. Bed 4-5 (iii) contains ammonites of Euhoplites meandrinus Subzone age and these occur also in the lower part of Bed 4-5 (iv). However, at 0.33 m above the base of 4-5 (iv), badly preserved Euhoplites spp. of early Euhoplites lautus Zone age are present. Bed 4-5 (v) contains E. lautus (1. Sowerby) and Euhoplites proboscideus (1. Sowerby) indicating a Euhoplites nitidus Subzone age. There is no evidence of any sediments of Anahoplites daviesi Subzone age in Bed 4-5 (vi). Division 6 is the Dipoloceras cristatum Subzone phosphatic pebble bed, similar in fossil content and preservation to that seen at Sevenoaks. Division 6 was seen to strike diagonally northeastwards in a series of north-south orientated drainage trenches, cut in the field north of the motorway track between Pitchfont Lane and the River Eden. Further east on the motorway track, about 320 m east of the Titsey road bridge, excavations for drainage sumps [4105 5410] struck division 6 and penetrated approximately 2 m into the upper sediments of the Lower Gault.
(d) Squerryes Estate pit, Westerham (Kent) (Figs 4 & 8) The Gault-Lower Greensand Junction Beds exposed in this extensive pit worked by The Redland Group pic have been described by the author (Owen, 1992, pp. 91, 93-94). A complete succession through the Lower Gault into the basal beds of the Upper Gault has been exposed since 1980 when the pit was extended northward towards the M25. The section given in Fig. 4 at grid ref. 4330 5430 is situated 650 m SW of the Croydon Road (B2024) bridge site on the M25 described below and 1.75 miles (2.7 km) towards the ENE of the Water Lane-Titsey Road section described previously. The description and Bed notation of the lower part of the Lower Gault given by the author (Owen, 1971a, pp. 28-31) requires some revision, the previous bed numbers being given in parentheses in Fig. 4. The correlation of this section is shown in Fig. 8.
262
H. G. OWEN
div.
Lithology
7
Zone
UPPER GAULT
metres
* (")
6
Br~wni~h
~
5
phosphatic nodules in shelly mid-qrev clav. (VI) Mid-grey shelly c t ay with scattered dark-brown small septarian phosphatic nodules ca. Om02 below top "A (v) Shell seam with part-phosphatised fossils. IV) Drab, fawn-grey shelly clay. ( iii) Brown-buff phosphat i c nodu I es in drab, fawn-grey she] ly clay.
&
(i I) Dark. fawnish mid-grey shelly clay with limonitic
4
3
r-
l<;:"~';;l":'.f··'7'~~tO.08 l::3
0.28 C)
c::>
c:=o
,0::::;;,
=3
,?02 :-..,0.43
,0.04
ro
~
I '
E} 1.81
&i I
::: ~
bridge). Fawn-grey shelly clay with l errtr cl ea reddish marl.
~
::)
marl y I ant I c I as scattered from about the mI dd 1e of the bed downward (absent east of the Titsey Road III
::J
seams of
0
F:§§~~:;;~O' 74
g- ~
I ...3'
Eawm ah light-grey shet I)' clay with alternatIng lighter and darker bands
to-
0.81
5.36
1Il
~
~
~'
obscured Interval
2 18
Black phosphatic nccur es & fragments of fossils with the shell in a prominent shell seam. Shelly mid-grey clay with a shell Seam containing part-phosphat i sed fossi t s Om02 - Om 03 abova base.
)
- -1- - -
..,.. ~···t:=J···=.·· ...O.03
~...
0.92
:::l"t=rC::>==J:::lI
I I 1f=-~~9 I lA
Drab. dark-grey ena t ev clay, pyritic when freSh. but
wj th
numerous ferrug i nous seams When weathered.
I=~
~
5.00
1Il
-1=====
~.
-GAULT-LOWER GREENSAUO JUNCTION BEDS (Owen 1992)
Fig.3. Lower Gault section on the M25 track between Water Lane bridge [4015 5398J, Oxted and the Titsey Road bridge [40655395], Titsey, Surrey.
Classification and correlation Division lA is of lyelli Subzone age. Divisions IB and 2 (the 'upper spathi nodule bed') are of spathi Subzone age. The basal part of division 3 shows a similar succession to that of all sections seen as far east as Wrotham. The black clays of Bed 3(i) contain Hoplites spp. of late spathi
Subzone age together with large examples of B. concentrica. The glauconitic clay interval Bed 3(ii), like the same bed seen in sections further east, has not yielded agediagnostic fossils but- is probably of earliest intermedius Subzone age. Bed 3 (iii) is also of intermedius Subzone age. Division 3 at Squerryes is substantially reduced in thickness
263
THE LOWER GAULT, SURREY AND KENT
div.
Lithology
7
~ Rather sma [ I brownish-grey phoapha't rc nodules In mldfawni sh-grey she! Iy clay. ( i v ] Mi'd grey, shelly, silty clay. passi ns into: ~ (iii) Fawn-grey s l Ity, shelly cJay passing into:-
6
-5
---
--
i )
---
- - ---- --- --
--
Dark. fawnish-grey Sf Ity shelly clay wfth darkcentred, I ight-rinded phosphatic nodules scattered throughout. Passing into: --Ii} Li ghter fawn-grey blocky-bedded shelly clay with buff ochreous part i ngs &: soft radd i sh mar I stone lenticles at the base of the bed. (iii) Clay in patches of I ithology of Beds 4(i,) & 5(,) . (j
fii)
4
metres
Zone
UPPER GAULT
.,--Ir
()
' ".; .
~
,
...
::f I
0.82
;0 C1l
-- ----0.25 - -- -
n,
~
~
:;
----
0.95
5;
-- J 's" - - ~
==->-0
.-I
1.07
t
curec
0.14
0'
Tough. fawn. shelly clay wIth reddish t errt r cu t arferrug I nous mar I stone a i st,..
0.30 0.23
~
Very dark fawn s i I ty shelly clay with occas r ona t scattered par-f-jmcepnat I sed fossi Is.
~
til
0.00-0.1
o-
as shown.
0.69 .14 0.10
C1l
+
T
3
I
(iiii Very dark-grey to blackish shelly clay ra"ft I ng r n the top Om 10 Into fawn-grey clay
:; !b
(ji)
C1l Q.
(i)
2
she II (Vi) t_) ( iv)
18
(2)
1A
\
ar-eenr en dark-grey clay. Blackish shelly clay.
\\
a tec« phosphatic nodUles & foss; Is with the she! I In a
2.67
~
~
seam with part-phosphat I sed foss I Is (2 v I i I Battleship grey clay; shelly - part phosphatised. Sparsely shelly battleship grey clay {2 v) Battleship grey clay: shelly-part phosphate/pyritic
(iii) She I I -seam with part-phosphat I sed foss j Is (2 iii) She! Iy batt I ash i p-grey cl ay (2 i i ) . (;) Small phosphat i c nodu l as & part-phosphat I sed foss, I~ (V 1 Darker batt I ash i p-grey pyritic clay with small phosphatic nodules: weathering ferruQ i nous. ( ivI Darkish. battleship-grey clay, pyr,tic. wi t'h pockets of 91 aucon i te '& quartz sand. Scattered part-phoSphatI sed, pyritic fossils. Weather i n9 as Bed lA (i) (iii) Dark, batt I esh i p grey pyritic clay with part -phoeph at i sed P)TltIC ftoas l Is; weather I ns as Bed lA( i)
(ii)
c'
t i
tt)~
• • • • • • • c::)~.
=
{g,
=
~
;:,.
~
=
=
........
= =<= = = ""= .,. "'"= = "'= -= = "'" ""= == = = = = = ~
Ciil
~
16
i}
51 ightly lighter band with phosphat I c "fragments of fossi Is ana some part-phosphatised pyritic fossi Is
Dark, batt leshl p-grey pyritic clay with crushed fossi I S WI th pyr i 're-o-epr aced she I Is. These clays weather to mottlea grey with red ferruginous t errtl c t ea and much selenite.
#
i --
.
=
.
0.10 - 0.05 O.10 0.48 O. 18 0.51 0.05 - 0.05 0. 0 0.30
1. 25
0.53
0.53
2.14
GAULT-LOWER GREEtlSAtIO JUNCTI ON BEOS (Owen 1992)
Fig. 4. Lower Gault section at the Squerryes Estate pit [43305430],300 m north of Covers Farm, Westerham, Kent
in comparison with the Water Lane-Titsey Road section and with the Croydon Road Bridge section described next. On the other hand, divisions 4 and 5 are capable of separation at Squerryes and are substantially thicker than at the Water Lane-Titsey Road section, although the overall thickness of the Lower Gault is closely comparable in these two sections. Division 4 contains ammonites normally found in the niobe and subdelaruei Subzones, but in the collecting absence of specimens of Mojsisovicsia, no precise
classification of these sediments can be made. Bed 4 (iii) contains a meandrinus Subzone fauna, as does the basal part of division 5 (Bed 5(i) above. The classification of the remainder of division 5 with the meandrinus Subzone is unsatisfactory. A thin shell seam occurs 0.0\ m below division 6 but has yielded to the author only specimens of the long time-ranging Anahoplites planus (Mantell) and there is no evidence of an early lautus Zone age for these sediments, as in Water Lane-Titsey section.
di v .
t.i tbolocv
6
Bro wn i sh groy phOs pha t i c nodu l e s i n we a t hered f awn-g re y .he l l y cl ay .
metres
Zone
UPPER GAULT
~
/
. ", ' ',"
'" -, ...
..
~
'.: .-' • ,...0 . 05 -0 .,5
~
g: (J>
I
5
i3 Weath e re d b l Y l sh -faw!'l -g I"'6Y ma tt le d she l l y c lay . da rk eni ng I n colour at th e base.
Cll
3 . 71
~
~
s
c(J> I II>
g.
~
iii' ... c
-.
Ql
4
Fawni sh-grey • shol ly , Hoathered c l a y . becom ing a mfa-grey c l ay i n t he basal 0", 50 .
3. 3B
I
::l
Ci'
0' Ql
(v i )
Shelly mid -grey clay wi t h sca tte red brown pno spha t ,c
( v) ( IV )
nodu le s . She l ly mid- grey c l a y . She I I -seam with brown j sh phosphat i c nodules & Phosphat i sed ammon I to bod y chambers
-...
--.
3
1
I
0 .61
-
-
-
1::I' • • t:::l .'t::::I • •
1:I,
0 . 30 0.04
::;.
.....
Cll
~ lb
( til)
Q.
Mid-gre y she I I Y c l a y with broad band s of mor e f awnish mid-grey s he l l y clay .
3.95
c' (J>
Gr een i sh - grey f i n e ly g l auco n it i c & S Il t y Cl ay . ( i) Dar k mid -grey shel iy clay . Black pho6phat ic nodu I es &: fragmentary ecs s r Is, wi th the shel l preserved, i n a sha ll sea m. ( i l)
2
-1 l' ~
0 . 20 0 . 30
•• •<=3I" . C=' . ' o:::=a
0.05
(J>
"tl
n>
Dar f,, -g rey J she I 1'1 c la y
18
Hi
s-.
t h sca t tered pa r t- pho sph at I sed
~
~
~
==
I
foss ilS at abo ut 1m 0 0 below t he top of t he be d .
2 . 30
I I "-> (v I
(IV
I
Da r k -gr e y pyr i t i c cl ay With pyrit i c she l l s o r she , Is pa rtly replaced by p yr i te. J
Part- pho sph a t i sed foss i I s I n da rk - brown phcs pn a t e with sner rs r ep laced by pyrit e .
I
--;
1A (Ill )
Dark-gra y pyriti c cl ay with p yr-r te-r- eot aced shells Deco ml ng drab- gr ey pyr iti c cl ay ca. 1 m 10 be low
t op o f be d
{ I I }
Ii)
Drab . da r k -g rey s i Ity cl ay wi th occas ional mar l y s i t tstono lo n t i c les : pyrit i c & pyri ti c fi lament s 5 11ty da r k- grey er a y wi th patches o f br i ght-green 9 1auconi t i C sand & some ohoschat i c nodu I as GAULT-LOWER GREENSAtlO JUNCT I ON BEDS ( Owe n '9 92 )
1. 00
I = = = = = 1'-0.05 I I -
- --
i
--. = = I
I I
~,
"'"
""" => """
."" .c::>
2.00
0. 50 0 .60
Fig. 5. Lower Gault surface and borehole succession at the M25/Croydon Road (B2024) bridge [5169 5462] and adjacent trenches, Westerham, Kent.
T H E LOWER GAUL T , S U R RE Y
(e) Croydon Road Bridge M251B2024, Westerham (Kent) (Figs 5 & 8) Surface trenches and kelly-bar auger borings (corrected for dip and rake) made for the supports of the bridge carrying the M25 ove r Cro ydon Road (B202 4), Westerham [5169 5462] provided a complete section through the Lower Gault (Fig. 5). The site is situated 650 m NE of the Squerrye s pit and shows a marked increase in the thickness of post-division 2 Lower Gault when compared to that section (Fig. 8). Division 6 outcropped below subsoil in the B 2024 road bed at the north side of the bridge and on the motorw ay track, the rema inder of the Lower Gault successio n being determined from the series of auger borings for the bridge supports. Classification and correlation The lithological succession up to the basal beds of division 3 is essentially the same as that seen in the Squerryes pit, although differing in detail. As with all boreholes in the Lower Gault, it did not prove possible to zone the sediments with precision. However, there is no reason to suppose that the Croydon Road representat ion is significantly different from that of the more pre cisel y zoned sequence at Squerryes. However, division 3 at the Croydon Road sectio n is substantially thicker than at Squerryes and contained an ammonite fauna consisting of Anahoplites intermedius and A. praecox. The shell seam, Bed 3 (iv) and the clays with phosphatic nodules Bed 3 (v), present at Croydon Road and seen in the sections further east as far as Trottiscliffe, were not found in the Squerryes section. Divisions 4 & 5 at Croydon Road are substantially thicker than at Squerryes, although a detailed sequence could not be made out for certain in the weathered clays. Fortunately, this interval was well exposed in the cutting for the M25 at the Lond on Road (A233) bridge site situated 1.2 km to the ENE of the Croydon Road bridge described next.
(I) London Road Bridge M25/A233, Westerham (Kent)
(Figs 6 & 8) At this site, the M25 is in a cutting which exposed below basal Upper Gault (Owen, 1996), a clear section in Lower Gault down to Bed 3 (iv). Below this level the section depend s on the analysis of the auger drill ings made for the bridge supports carrying the London Road (A233) over the motorw ay [5500 4480] . A complet e Lower Gault succession was traversed at this site (Fig. 6) and its correlation with other sections is shown in Fig. 8. Classifica tion and correlation The lithological succession from the top of the GaultLower Greensand Junction Beds to the top of division 3 in the London Road borings and its subzonal classification, is closely comparable to that of the Squerryes and Croydon Road sections. Being deeper than the cutting and much deeper than the Croydon Road borings, more detail could be made out in the unweathered successio n traversed by the
AND K E NT
265
borings. The speed of work precluded, unfortunately. the precise dem arcation between sediments of the niobe, subdelaruei and meandrin us Subzones, but all are present. The boundary between the meandrinu s Subzone sediments and those of the nitidus Subzone was determined precisely at a depth of 0.04 m below division 6. (g) M251M26/A21 Chevening interchange, Chevening (Kent) (Figs 7 & 8) Between the London Road Bridge site and the next easterly section on the motorway at Che vening, the Lower Gault is partly cut-out at outcrop by a WSW-ENE trending strike fault extending from Charmans Farm just south of the M25, Westerham [4543 5510], eastward to a position near Combe Bank Convent, Sundridge [47505560]. North of Brasted , in the Metropolitan Water Board boring [4709 5574] situated just east of Station Road and 230 m south of the M25, 2.4 km east-northeast of the London Road bridge site, a nearly complete Lower Gault section was traversed and was describ ed by' the author (Owen, 1971a, pp. 28- 29). The succession is comparable in thickne ss to that of the London Road section and its correlation is shown in Fig. 8. At the M251M26/A21 Chevening Interchange, Kelly-bar drill ing for the supports of the brid ge carryi ng the Chevening Road over the motorw ay [5685 4948], revealed the incomplete section shown graphically in Fig. 6. Division 6 was struck in the drill ings at about 10 m below ground surface, beneath a basal Upper Gault succession. The correlation of this section with that at Brasted 2.7 km towards the west-southwest and the former Dunton Green Brick, Tile & Pottery Works pit [515 570] situated 2.25 km to the east-northeast (Wright, 1947, pp. 3 15-3 18; Owen, 1971a, pp. 26-28) is shown in Fig. 8. Classification and correlation The correlation diagram (Fig. 8) shows the progressive thinning of the Lower Gault from Brasted to Dunton Green. The Che vening road bridge is situated roughly half-way between these localities. The principal features between the sections are: ( I ) the thickening of division 3 from Brasted to Cheven ing and its thinning between Chevenin g and Dunton Green, although the lithological succession and intermedius Subzone age remains the same; (2) the nearly constant thickne ss of division 4 and the marked attenuation of division 5 from Brasted to Chevening and their coalesce nce and attenuation at Dunton Green . Unfortun ately, it was not possible to zone accurately the clays of division 4 at the Che vening road bridge, other than it is of niobe Subzone age at the base and meandrinus Subzone near the top. Division 5 contains an ammonite fauna of nitidus Subzone age and Division 6 is the cristatum Subzone nodule bed. An incomplete section through the Lower Gault and Gault-Lower Greensand Junction Beds (Owen, 1992, p. 96) was seen in the trench and sumps dug for the Outfall A drain extending from the M26 motorwa y at grid ref. 5045 5745 to the north side of Longford Lake [5055 5680]. The beds were highly weathered and disturbed by late Pleistocene
266
H. G. OWEN
d iv,
Lithology
7 6
I
Brown ph os pha t i c nodu I es In weathered fawn-grey shelly e la~ (vi) Fawn i gh mid-gre y sh elly Clay wi th basal sher I seam. H id-grey she ty c ay weathering f awn l sh . ( IV ) Brown ph o &phat i c nodul es , some farge, in c l ay of ( ii i )
:..-.
(v)
5
r-
./j
( i i I ) Mid -grey shel l y clay wea thering fawnish .
(i i)
~~~~r~~'oured pn o aohat !c nodu les &. part-PhOSPhat lso,d
( , )
Darkish.
fawn-grey.
metres
Zone
UPPER GAULT
shelly clay with lent ieles of
soft e arthy . ferrug i nous marlstone at the base . Top Om 31 i s t i shter I n shade. With pa r r-pyr-r t l s ed f os s i Is .
..
()
-.... . . ... .'. c:II
(f)
c::I
_
Dark . Tawn y mi d-gre y s h el ly cl a y .
lD ~
,..
( , )
Dark-Ish fawnlah ml (j-grey sha lly clay With cccas-eee t t h i n ferruginous l:1arly s t r ea k s . WeI I -deve loped I ant i c I as o f so ft earthy fer rug i no u s mar- I stone occur . n t he l o wer 1m 20 of the bad I part i cular ly at Om 91
'j I. 51
Sl
g; 0 .62
s g I
::l
above base .
~
=
Shell seam with " so l i d " phoaphat I sed ammon i to bOdy chambe r s & sm.. 1 1 ph osphat ic n od u les . ( BasQ of cut t i n g ]
O. BO
.~ "I::Ol "
/
-
2 . 75
~
1
Oari-.-g r ey shel l )' cl ay wI t h sc at t ered dark- bro wn Chosphat j c nccu I es .
. 0 2 ° ·0 4
5
4
{ I V}
0 .07
~ :~~-o.09
~
(iil
( v)
II:lL
..................... ._..·ca.··C!I···c:s···
~ "I::lJ '
0 .02
- - -= ..,.5' - -- ([) (ill )
Broad banded mid-grey shellY clay and l ighter mId " gre y shelly c l ay I
3
~Q) ~.
I (ii ) ( ;)
2 l iB
Dark-grey shel ly c lay .
tv)
1 '"
-..
Dark -gr ey py,. itic c l a y with patches of cver-ea sand .
-.S
0 .92
II = =
= =
""'" ==
I -=I
0.30 0 .30 0 .05
1.30
~
Da.rk -grey p y r i t i c clay with a thin seam of pa rtphoS Dha t i sed ammon i t e s at the base .
4 .BB
=0-
1
Greenish da rk-grey si It y c lay . Oark-gr ey shelly cl ay .
81ack Phosphatic fragment ary f09 B; I & nodules in shell "sDamJ
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=:;'
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.
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Ver y sandy dark-grey c l ay . GAUL T-LOWER GREENSANO J UNCT I ON BEOS (Owen
I I I
0 .63
0 .6 5
1992)
Fig. 6. Lower Gault surface and borehole successio n at the M25/London Road (A233) bridge [5500 4480], Westerham, Kent.
267
THE L O W E R GAULT. SURREY AND KENT
d iv .
Lithology
7
6 5
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UPPER GAULT
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Br own phosphat i e nodu I e e in sh e l ly mid - grey clay .
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B l ack Phosp ha t i c nodu I esana fragmentary f oss i I s w ith t he shel l, in shel l y dark -grey cl a y .
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= =
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Fig. 7. Lower Gau lt succession from auger borings on the M251M26 track for the Chipstead-Chevening road and the A2l overbridges [5685 4948 ], Cheve ning, Kent.
periglacia l cryoturbation, but appeared to be comparab le in thickness and lithology to that of the Dunton Green and St John's brickyard sections to the east (Owen, 1971a, 1976). (h) Otford to Trotti scliffe (Fig. 8) No sections in the Lower Gault were exposed along the M26 motorway track or associated work, eastward of the Outfall A drain until the M26/A20 interchange to the west of the site of the Ford Road clay pit. The old sections in the Lower Gault at Dunton Green, the former Sevenoaks Brick Works at Greatness Lane, Otford [5360 5780] and the former Rugby Portland Cement Co. Ford Road clay pit,
Trottiscliffe [6360 5910] and their correlation with sections further east, have been described in deta il by the author (Owen, 1971a, 1976). They are included in the correlation diagram (Fig. 8) for clarity of the six lithological division s recognized in the Lower Gault in this area. 3. ST RUCTURAL CONT ROLS ON LO WER GAULT SE DIMENTATION The author (Owen, 1971a, pp. 143-1 47; 1976, pp. 495-496) cons idered that sedimentation during the formation of the Lower Gault in northwest Kent and Surrey was controlled by a series of north-northwest to south-southe ast trending
Buckla nd S&S
m
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o
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,4
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.
----- . _... 15
1
LEGEND
20
~
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B B B
" solid " shells
~
ferru ginous streaks
A
phosphatic nodules
---~- I --
marlstone lenticles
~ s andy/ g lauconitic patch es
.>
- - - - - - - - - - - - - sub zonal boundaries div ision al boundaries
Fig. 8. Correlat ion diagram of the Lower Gault from Buckland, Surrey, eastward to Trottiscliffe, Kent.
THE LOWER GAULT, SURREY AND KENT
ridges and troughs. The effect on sedimentation being tectonically passive and the result of gravity-movement of clay particles down-slope, aided by weak submarine current activity around the topographic features. This concept of passive ridges and troughs needs modification in the light of the depositional and erosional history of the Gault-Lower Greensand Junction Beds (Owen, 1992), together with the new information concerning the Lower Gault. The comparable thickness of the Lower Gault in the Water Lane-Titsey Road and Squerryes sites and the considerable increase in thickness in the 650 m between the latter and the M26 Croydon Road (B2024) bridge site (Fig. 8), is significant. The Gault-Lower Greensand Junction Beds between Westerham and Tandridge show a thick succession of clays and loams which, when coupled to the relatively thin Lower Gault succession above in comparison with that at the Croydon and London Road, Westerham, sections, suggests a slow differential inversion to the south and subsidence to the north. Further north in the Addington, Surrey, borehole (Buchan, Robbie, Holmes, Earp, Bunt & Morris, 1940, pp. 8-9) [3709 6274], division 6 was struck at 268 m depth and the base of the Lower Gault at 274.8 m, giving a thickness of 6.8 m which is even thinner than at Squerryes or at Water Lane-Titsey Road. A deeper sample from 278 m depth (BGS Borings Department Bd 2198) suggests the basal part of the Gault-Lower Greensand Junction Beds with gritty phosphatic nodules. The evidence
269
suggests that during the mammillatum Superzone and the Lower Gault, slight differential movements occurred of individual, tilted, fault-bounded blocks at the northern margin of the Wealden graben, abutting the London Platform. A tectonic cause has been established for the midcristatum Subzone condensation and planing-off of the upper surface of the Lower Gault south of the west-east trending Thames axis from south Essex westward to west London and the absence of the Lower Gault in the region to the north of this axis (Owen, 1971b). Differential movements of fault-bounded blocks flanking the southern margin of the London Platform during the formation of the Upper Gault and Upper Greensand is suggested by the variations in thickness of lithological divisions and the preservation of Callihoplites auritus Subzone sediments by inversion seen in the M23!M25!M26 motorways and adjacent sections (Owen, 1996).
ACKNOWLEDGEMENTS Apart from the County and Department of Transport Engineers together with their staffs and those of the contractors listed previously (Owen, 1996), I am also indebted to the Redland Tiles, Rugby Portland Cement Co. and the former Sevenoaks Brick Works Ltd., for facilities to examine sections on their property.
REFERENCES BUCHAN, S., ROBBIE, J. A., HOLMES, S. C. A., EARP, J. R, BUNT, E. F. & MORRIS, L. S. O. 1940. Water supply of southeast England from underground sources. Part IV. Wartime Pamphlets of the Geological Survey of Great Britain 10, I-59. DINES, H. G., BUCHAN, S., HOLMES, S. C. A. & BRISTOW, C. R. 1969. Geology of the country around Sevenoaks and Tonbridge (Sheet 287 NS). Memoirs of the Geological Survey of Great Britain. - - , & EDMUNDS, F. H. 1933. The geology of the country around Reigate and Dorking (Sheet 286 NS). Memoirs of the Geological Survey of Great Britain. GOSSLING, F. 1929. The geology of the country around Reigate. Proceedings of the Geologists' Association, 40, 197-259. MILBOURNE, R. A. 1956. The Gault at Greatness Lane, Sevenoaks, Kent. Proceedings of the Geologists' Association, 66, 235-242. - - 1962. Notes on the Gault near Sevenoaks, Kent. Proceedings of the Geologists' Association, 72,437-443. - - 1963. The Gault at Ford Place, Wrotham, Kent. Proceedings of the Geologists' Association, 74,55-79. OWEN, H. G. 1958. Lower Gault sections in the northern Weald and the zoning of the Lower Gault. Proceedings of the Geologists' Association, 69, 148-165.
- - 1963. Some sections in the Lower Gault of the Weald. Proceedings of the Geologists' Association, 74,35-53. - - 1971a. Middle Albian stratigraphy in the Anglo-Paris Basin. Bulletin of the British Museum (Natural History) Geology Series, Supplement 8. - - 1971b. The stratigraphy of the Gault in the Thames Estuary and its bearing on the Mesozoic tectonic history of the area. Proceedings of the Geologists' Association, 82, 187-207. - - 1976. The stratigraphy of the Gault and Upper Greensand of the Weald. Proceedings of the Geologists' Association, 86, 475-498. - - 1992. The Gault-Lower Greensand Junction Beds in the northern Weald (England) and Wissant (France), and their depositional environment. Proceedings of the Geologists' Association, 103,83-110. - - 1996. The Upper Gault and Upper Greensand of the M231M251M26 motorway system and adjacent sections, Surrey and Kent. Proceedings of the Geologists' Association, 107, 167-188. SPATH, L. F. 1923-1923. A monograph ofthe Ammonoidea of the Gault. Monographs of the Palaeontographical Society, (2 volumes). WRIGHT, C. W. 1947. The Gault at Dunton Green. In Notes on the geology of the country around Sevenoaks, Kent. Proceedings of the Geologists' Association. 57, 315-318.
Received 19 June 1995; revised typescript accepted 6 February 1996