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Field Meeting to the Folkestone Beds (Lower Greensand) of West Surrey
Field Meeting to the Folkestone Beds (Lower Greensand) of West Surrey 1 August 1971
Report by the Director: R. C. PADGHAM Received 14 January 1972
was arranged to demonstrate the sedimentology and lithological variation of the topmost Lower Greensand in the north-west corner of the Weald, where the beds attain their maximum thickness. Thirty-seven members and friends gathered at Guildford Station, and then travelled by coach to a vantage point on the Hog's Back, just above the village of Seale (896482).1 Looking to the south, a narrow vale of Gault Clay separates the Chalk scarp of the Hog's Back from a wide expanse of Folkestone Beds' terrain. The outcrop of the Folkestone Beds, usual1y only about 1 km. in width, is here expanded considerably by a series of east-west flexures superimposed on the north-west closure of the Wealden dome. Two distinct ridges are visible on the outcrop of the Folkestone Beds, here furnished with their typical vegetation cover of birch and conifers. A minor ridge in the middle distance is scarred by a series of working and derelict sand pits, whilst the more prominent feature of Crooksbury Hill forms the skyline. An unusually clear view allowed the distant features of the Hythe Beds slopes and the Chalk Downs to be pointed out by the Director. Mears Pit, Runfold (866474) The coach brought the party to the first exposure of Folkestone Beds at the Runfold Pit of Eb. Mears, close to the A31 road. The sands in this area are 80 m. thick and this pit is located near the top of the succession, like most in the Farnham region. Here the Director outlined the broader aspects of the beds. In their 240 km. of outcrop, the Folkestone Beds can be examined in about 400 artificial exposures, and as these are only located where the deposits are of economic value, it is easy to gain a false impression of their being a 'bottomless pit' of high-grade sand. Mears pit extracts sand dominantly for the building industry. A dip of 5° to the north is shown by the distinctive white, high-silica sands and more argil1aceous sands above. This latter band is referred to erroneously by the pit workers as the 'Gault Seam'. Cross-bedding is the dominant mode of stratification here, and indeed throughout most of THIS FIELD MEETING
1
Locations cited in this report are within the 100 km, grid square SU.
355
356
R. C. PADGHAM
these deposits. Coset thickness varies, the well-defined tabular units being commonly 30-50 em. in height. The foreset laminae may be rich in detrital or secondary iron minerals and they generally meet the base of the units at a shallow angle. The Director has found that the majority of cosets throughout the Weald trend towards the south-east (Padgham, 1971). Redland's Pit, Runfold (875473) This exposure is one of a series of degraded and derelict pits to the east of Runfold. Fine, white sands in the base of the pit are most probably an extension of those seen in the previous exposure. This highly quartzose, brittle sand was formerly worked for foundry use, but the presence of pipeclay bands and lenses, especially in the top 2 m., renders this deposit unsuitable for modern requirements of purity. However, cleaner 'silica sands' of equivalent age are dug and processed at Redhill and Godstone, 40 km. to the east. Within the argillaceous top layers, unlined burrows of Ophiomorpha type were pointed out. Above the white sands a 3 m. cross-bedded unit of glauconitic, loamy sand proved to be of great interest to the party. Members were able to extract large numbers of well-preserved siliceous sponges, notably of Doryderma and Hallirhoa (identified by the British Museum (Natural History». Generally the Folkestone Beds allow only poor fossil collecting, and besides the type-area on the Kent coast, the Farnham district is the most rewarding collecting area. The well-preserved nature of the fossils here suggests that the place of deposition lay close to the source, and that the relative impermeability of the sands due to the layers of clay and carstone has subsequently protected the fossil material from solution.
Homefield Pit, Runfold (877473) In this adjacent exposure, large tips of carstone left after the sands have been screened provided members with good specimens of encrusting kidney ore (haematite) and fragments of coniferous wood, finely preserved in ochreous limonite. Two prominent bands of carstone can be seen on the north and west faces of this pit and elongated nodules are abundant in the foresets of the cross-bedded sands. On a previous visit the Director was loaned the ferruginous cast ofa large Hypacanthoplites, found by a workman in one of the carstone bands. The Director explained his recent work on the nature of the iron within the beds. Glauconite deposited with the sands has been subjected to the influence of groundwater. Oxidation to limonite has been observed and a further dissolution and redistribution of the iron within the sands is common. Both the widely distributed iron pan and the distinctive coloration of the Folkestone Beds may be derived from this early glauconite source. The irregularly concentric shaped carstone tubes and rucked sheets
FIELD MEETING TO WEST SURREY
357
signify a periodic formation analogous to the Liesegang ring effect observed in colloid chemistry. Sandy Cross Pit (888477) This expanding pit was visited in order to study a unique 8-m. thick cross-bedded unit. This coset-the largest observed anywhere along the outcrop-has been largely quarried away, but remnant faces show remarkably well-defined foresets picked out by the juxtaposition of limonite-rich and limonite-deficient bands. Members were able to examine the 'vermiform burrows', so abundant in this unit. These shallow tubular structures have a concentration of black or brown limonite grains surrounding a completely iron-free core, some 1-3 ern, in diameter. Mr. Gamble noted that these Callianassid-type burrows typically occur in high-density groups and that there is a tendency for a concentration in the limoniterich bands. Each tube has a short entry tunnel and a roughly oval or elongate horizontal passage close to the surface. The incipient development of carstone was also noted in this coset. Over a distance of a few millimetres, there is a progressive increase in the thickness of haematite coating individual quartz grains, to the ultimate filling of all pore space by ferruginous cement. Rejoining the coach, the party travelled to Wrecclesham for lunch. Coxbridge Pit (824458) A short journey brought the party to the famous Coxbridge Pit. Here sands are dug in the uppermost Folkestone Beds, and this pit is almost unique in its reliability as a fossil collecting site, being well documented as such (Shepherd, 1934; Casey, 1961). The passage from the Lower Greensand into the Gault is gradual through 4 m. of transitional deposits. Pale buff, cross-bedded sands pass up into flat-bedded, greyish clayey sands with scattered phosphatic nodules and finally up into basal Gault Clay with abundant nodules. A feature of particular interest was the abundance of ferrugino-phosphatic concretions with clay cores found both in the sand face and (by courtesy of the proprietors) in screen-tips. These tips were diminished rapidly as the party extracted a considerable fauna. Three well-preserved examples of Farnhamia were found, showing borings and encrustations of Serpula on both internal and external shell surfaces. Numerous lamellibranchs and fragments of sponge were also forthcoming and large pieces of silicified wood, some up to 1 kg. in weight, showed evidence of boring by Martesia. The Director indicated the change in conditions of deposition from the clean-washed Folkestone Beds sands through the phosphatic junction loams into the Gault Clay. The variable nature of the junction throughout
358
R. C. PADGHAM
the Weald was described, and the boundary here was contrasted with the 'Sulphur Band' at Folkestone and the 'Iron Grit' in West Sussex. The Devil's Jumps (869396) The party continued by coach past Frensham Pond to the Devil's Jumps, the impressive series of sandy hillocks along the southern edge of the Folkestone Beds outcrop. A clear view to the north showed an 8-km. tract of woods and heathland astride the Ri ver Wey, with Crooksbury Hill and the Hog's Back in the distance. Beyond , the Hale Plateau with its gravel cap was indicated, whilst, to the south, the wooded dip slopes of the subjacent Lower Greensand beds were visible. The Jumps themselves owe their existence to a network of massive cars tone veins binding the otherwise loose sands, resulting in a group of steep-sided, isolated hills. Similar structures underlie the high grounds of Crooksbury, St. Martha's and Kettlesbury Hills to the north. An orientation is evident in the rucked and tubular structures within the carstone; here it is south-west to north-east, and elsewhere an east-to-west orientation may be seen. Although the actual iron content of the carstone may attain 30 per cent , the Director explained that it cannot be used industrially for smelting due to the excessive presence of quartz. Milford Cemetery (913369) On the return journey to Guildford a stop was made at the well-known Puttenham Beds exposure behind Milford Cemetery. The Director noted that these beds, which were formerly named the Loamy Folkestone Beds (Dines & Edmunds, 1929), have since yielded a Sandgate Beds fauna at Headley (Middlemiss, 1961). Unfortunately this exposure is badly overgrown, and some digging into the limonitic loam was necessary to expose the ' Milford Type' burrows described by Middlemiss (1962). In conclusion, the Director summarised the features demonstrated during the Field Meeting. A hastily drawn map was used to demonstrate the palaeogeography of south-east England in Folkestone Beds times, and the significance of the London Platform as an exposed or submerged area of non-deposition was suggested, based on the Director's work both in and beyond the Weald. Detritus from a source to the north or north-west was deposited as Folkestone Beds or their equivalents in a marine shelf environment, covering south-east England and parts of adjacent northern France. Current action, often vigorous, has sorted these highly quartzose sediments, and the locally formed glauconite and organic debris, and produced the cross-bedded units observed. Periods of shallowing and
FIELD MEETING TO WEST SURREY
359
winnowing have given rise to glauconite and phosphate-rich horizons in the sands, particularly at the junction with the Gault. After tea was taken in Godalming, Mr. Gamble, on behalf of the Association, proposed a vote of thanks to the Director and Mrs. Fyffe, the secretary for the meeting. The coach then proceeded to Guildford Station, where the party dispersed. ACKNOWLEDGMENTS The Director would like to thank Mrs. Fyffe for acting as secretary for the meeting, also Mr. H. J. Gamble for identifying the trace-fossils and Professor J. F. Kirkaldy for his comments on this report. Redland Quarries Ltd., Eb. Mears Ltd., Sandy Cross Sand Co., and Mr. J. Bentley kindly allowed the party to visit their pits.
REFERENCES CASEY, R. 1961. The Stratigraphical Palaeontology of the Lower Greensand. Palaeontology, 35, 487-621. DINES, H. G. & F. H. EDMUNDS. 1929. The Geology of the Country around Aldershot and Guildford. Mem. geol, Surv. U.K. MIDDLEMISS, F. A. 1961. A Fauna from the Puttenham Beds (Lower Greensand) of Hampshire. Proc. Geol. Ass., 72, 454-459. - - - . 1962. Vermiform Burrows and Rates of Sedimentation in the Lower Greensand. Geol. Mag., 99, 33-40. PADGHAM, R. C. 1971. A Study, Mainly Petrological and Petrochemical, in the Falkestone Beds of the Weald. Unpublished Ph.D. Thesis, University of London. SHEPHERD, W. B. 1934. Some Observations on the Folkestone Beds around Farnham. Proc. Geo!. Ass., 45, 436-444.
Roger C. Padgham Department of Oceanography Liverpool University Liverpool L69 3BX
Report by the Director: R. C. PADGHAM Received 14 January 1972
was arranged to demonstrate the sedimentology and lithological variation of the topmost Lower Greensand in the north-west corner of the Weald, where the beds attain their maximum thickness. Thirty-seven members and friends gathered at Guildford Station, and then travelled by coach to a vantage point on the Hog's Back, just above the village of Seale (896482).1 Looking to the south, a narrow vale of Gault Clay separates the Chalk scarp of the Hog's Back from a wide expanse of Folkestone Beds' terrain. The outcrop of the Folkestone Beds, usual1y only about 1 km. in width, is here expanded considerably by a series of east-west flexures superimposed on the north-west closure of the Wealden dome. Two distinct ridges are visible on the outcrop of the Folkestone Beds, here furnished with their typical vegetation cover of birch and conifers. A minor ridge in the middle distance is scarred by a series of working and derelict sand pits, whilst the more prominent feature of Crooksbury Hill forms the skyline. An unusually clear view allowed the distant features of the Hythe Beds slopes and the Chalk Downs to be pointed out by the Director. Mears Pit, Runfold (866474) The coach brought the party to the first exposure of Folkestone Beds at the Runfold Pit of Eb. Mears, close to the A31 road. The sands in this area are 80 m. thick and this pit is located near the top of the succession, like most in the Farnham region. Here the Director outlined the broader aspects of the beds. In their 240 km. of outcrop, the Folkestone Beds can be examined in about 400 artificial exposures, and as these are only located where the deposits are of economic value, it is easy to gain a false impression of their being a 'bottomless pit' of high-grade sand. Mears pit extracts sand dominantly for the building industry. A dip of 5° to the north is shown by the distinctive white, high-silica sands and more argil1aceous sands above. This latter band is referred to erroneously by the pit workers as the 'Gault Seam'. Cross-bedding is the dominant mode of stratification here, and indeed throughout most of THIS FIELD MEETING
1
Locations cited in this report are within the 100 km, grid square SU.
355
356
R. C. PADGHAM
these deposits. Coset thickness varies, the well-defined tabular units being commonly 30-50 em. in height. The foreset laminae may be rich in detrital or secondary iron minerals and they generally meet the base of the units at a shallow angle. The Director has found that the majority of cosets throughout the Weald trend towards the south-east (Padgham, 1971). Redland's Pit, Runfold (875473) This exposure is one of a series of degraded and derelict pits to the east of Runfold. Fine, white sands in the base of the pit are most probably an extension of those seen in the previous exposure. This highly quartzose, brittle sand was formerly worked for foundry use, but the presence of pipeclay bands and lenses, especially in the top 2 m., renders this deposit unsuitable for modern requirements of purity. However, cleaner 'silica sands' of equivalent age are dug and processed at Redhill and Godstone, 40 km. to the east. Within the argillaceous top layers, unlined burrows of Ophiomorpha type were pointed out. Above the white sands a 3 m. cross-bedded unit of glauconitic, loamy sand proved to be of great interest to the party. Members were able to extract large numbers of well-preserved siliceous sponges, notably of Doryderma and Hallirhoa (identified by the British Museum (Natural History». Generally the Folkestone Beds allow only poor fossil collecting, and besides the type-area on the Kent coast, the Farnham district is the most rewarding collecting area. The well-preserved nature of the fossils here suggests that the place of deposition lay close to the source, and that the relative impermeability of the sands due to the layers of clay and carstone has subsequently protected the fossil material from solution.
Homefield Pit, Runfold (877473) In this adjacent exposure, large tips of carstone left after the sands have been screened provided members with good specimens of encrusting kidney ore (haematite) and fragments of coniferous wood, finely preserved in ochreous limonite. Two prominent bands of carstone can be seen on the north and west faces of this pit and elongated nodules are abundant in the foresets of the cross-bedded sands. On a previous visit the Director was loaned the ferruginous cast ofa large Hypacanthoplites, found by a workman in one of the carstone bands. The Director explained his recent work on the nature of the iron within the beds. Glauconite deposited with the sands has been subjected to the influence of groundwater. Oxidation to limonite has been observed and a further dissolution and redistribution of the iron within the sands is common. Both the widely distributed iron pan and the distinctive coloration of the Folkestone Beds may be derived from this early glauconite source. The irregularly concentric shaped carstone tubes and rucked sheets
FIELD MEETING TO WEST SURREY
357
signify a periodic formation analogous to the Liesegang ring effect observed in colloid chemistry. Sandy Cross Pit (888477) This expanding pit was visited in order to study a unique 8-m. thick cross-bedded unit. This coset-the largest observed anywhere along the outcrop-has been largely quarried away, but remnant faces show remarkably well-defined foresets picked out by the juxtaposition of limonite-rich and limonite-deficient bands. Members were able to examine the 'vermiform burrows', so abundant in this unit. These shallow tubular structures have a concentration of black or brown limonite grains surrounding a completely iron-free core, some 1-3 ern, in diameter. Mr. Gamble noted that these Callianassid-type burrows typically occur in high-density groups and that there is a tendency for a concentration in the limoniterich bands. Each tube has a short entry tunnel and a roughly oval or elongate horizontal passage close to the surface. The incipient development of carstone was also noted in this coset. Over a distance of a few millimetres, there is a progressive increase in the thickness of haematite coating individual quartz grains, to the ultimate filling of all pore space by ferruginous cement. Rejoining the coach, the party travelled to Wrecclesham for lunch. Coxbridge Pit (824458) A short journey brought the party to the famous Coxbridge Pit. Here sands are dug in the uppermost Folkestone Beds, and this pit is almost unique in its reliability as a fossil collecting site, being well documented as such (Shepherd, 1934; Casey, 1961). The passage from the Lower Greensand into the Gault is gradual through 4 m. of transitional deposits. Pale buff, cross-bedded sands pass up into flat-bedded, greyish clayey sands with scattered phosphatic nodules and finally up into basal Gault Clay with abundant nodules. A feature of particular interest was the abundance of ferrugino-phosphatic concretions with clay cores found both in the sand face and (by courtesy of the proprietors) in screen-tips. These tips were diminished rapidly as the party extracted a considerable fauna. Three well-preserved examples of Farnhamia were found, showing borings and encrustations of Serpula on both internal and external shell surfaces. Numerous lamellibranchs and fragments of sponge were also forthcoming and large pieces of silicified wood, some up to 1 kg. in weight, showed evidence of boring by Martesia. The Director indicated the change in conditions of deposition from the clean-washed Folkestone Beds sands through the phosphatic junction loams into the Gault Clay. The variable nature of the junction throughout
358
R. C. PADGHAM
the Weald was described, and the boundary here was contrasted with the 'Sulphur Band' at Folkestone and the 'Iron Grit' in West Sussex. The Devil's Jumps (869396) The party continued by coach past Frensham Pond to the Devil's Jumps, the impressive series of sandy hillocks along the southern edge of the Folkestone Beds outcrop. A clear view to the north showed an 8-km. tract of woods and heathland astride the Ri ver Wey, with Crooksbury Hill and the Hog's Back in the distance. Beyond , the Hale Plateau with its gravel cap was indicated, whilst, to the south, the wooded dip slopes of the subjacent Lower Greensand beds were visible. The Jumps themselves owe their existence to a network of massive cars tone veins binding the otherwise loose sands, resulting in a group of steep-sided, isolated hills. Similar structures underlie the high grounds of Crooksbury, St. Martha's and Kettlesbury Hills to the north. An orientation is evident in the rucked and tubular structures within the carstone; here it is south-west to north-east, and elsewhere an east-to-west orientation may be seen. Although the actual iron content of the carstone may attain 30 per cent , the Director explained that it cannot be used industrially for smelting due to the excessive presence of quartz. Milford Cemetery (913369) On the return journey to Guildford a stop was made at the well-known Puttenham Beds exposure behind Milford Cemetery. The Director noted that these beds, which were formerly named the Loamy Folkestone Beds (Dines & Edmunds, 1929), have since yielded a Sandgate Beds fauna at Headley (Middlemiss, 1961). Unfortunately this exposure is badly overgrown, and some digging into the limonitic loam was necessary to expose the ' Milford Type' burrows described by Middlemiss (1962). In conclusion, the Director summarised the features demonstrated during the Field Meeting. A hastily drawn map was used to demonstrate the palaeogeography of south-east England in Folkestone Beds times, and the significance of the London Platform as an exposed or submerged area of non-deposition was suggested, based on the Director's work both in and beyond the Weald. Detritus from a source to the north or north-west was deposited as Folkestone Beds or their equivalents in a marine shelf environment, covering south-east England and parts of adjacent northern France. Current action, often vigorous, has sorted these highly quartzose sediments, and the locally formed glauconite and organic debris, and produced the cross-bedded units observed. Periods of shallowing and
FIELD MEETING TO WEST SURREY
359
winnowing have given rise to glauconite and phosphate-rich horizons in the sands, particularly at the junction with the Gault. After tea was taken in Godalming, Mr. Gamble, on behalf of the Association, proposed a vote of thanks to the Director and Mrs. Fyffe, the secretary for the meeting. The coach then proceeded to Guildford Station, where the party dispersed. ACKNOWLEDGMENTS The Director would like to thank Mrs. Fyffe for acting as secretary for the meeting, also Mr. H. J. Gamble for identifying the trace-fossils and Professor J. F. Kirkaldy for his comments on this report. Redland Quarries Ltd., Eb. Mears Ltd., Sandy Cross Sand Co., and Mr. J. Bentley kindly allowed the party to visit their pits.
REFERENCES CASEY, R. 1961. The Stratigraphical Palaeontology of the Lower Greensand. Palaeontology, 35, 487-621. DINES, H. G. & F. H. EDMUNDS. 1929. The Geology of the Country around Aldershot and Guildford. Mem. geol, Surv. U.K. MIDDLEMISS, F. A. 1961. A Fauna from the Puttenham Beds (Lower Greensand) of Hampshire. Proc. Geol. Ass., 72, 454-459. - - - . 1962. Vermiform Burrows and Rates of Sedimentation in the Lower Greensand. Geol. Mag., 99, 33-40. PADGHAM, R. C. 1971. A Study, Mainly Petrological and Petrochemical, in the Falkestone Beds of the Weald. Unpublished Ph.D. Thesis, University of London. SHEPHERD, W. B. 1934. Some Observations on the Folkestone Beds around Farnham. Proc. Geo!. Ass., 45, 436-444.
Roger C. Padgham Department of Oceanography Liverpool University Liverpool L69 3BX