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A note on the Weald–Atherfield Clay junction at Brook, Surrey
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A note on the Weald-Atherfield Clay junction at Brook, Surrey A. H. RuffeD RUFFELL, A. H . 1988. A note on the Weald-Atherfield Clay junction at Brook , Surrey. Proc. Geol. Ass., 100(3), 409-11. The junction of the Weald and Atherfield Clays has been recorded throughout the Weald many times in the past 100 years. The only present day exposure of this important horizon, outside the Isle of Wight and Purbeck, is described here in terms of its lithological sequence, palaeontology, and possible corre lation.
Department of Geological Sciences, University of Birmingham, P.O. Box 363. Birmingham . B15 lIT
For seventy years, the overgrown brickpits at Brook, in Surrey (SU9305 3759) exposed a variety of sections in the Weald Clay and Atherfield Clay Formation (Fowler, 1985; Kirkaldy & Wooldridge , 1938; Knowles & Middlemiss, 1958; Thurrell , Worssam & Edmonds , 1968), and provided fossils from the fissicostatus and forbesi zones of the Aptian (Simpson, 1985). During 1986 in an old trial pit across the A286 (SU9293 3765, Fig. 1), excavations were carried out to make room for a horse-training ring , the northern face of which still exposes Weald and Atherfield Clay (Fig. 2). The Weald Clay consists of blocky-weathering blue mudstones, finely laminated grey to black mudstones , and sideritic siltstones and sandstones. Two horizons were found to be fossiliferous , and although preserved only as casts (carbonate material having been leached) , the following fauna was identified rHorizon (a ) (all bivalves), Corbula alata (J. de C. Sowerby) ; ?Filosina gregaria (Casey) ; Myrene spp.; an unidentified Tellinid, possibly Scittila ; and Unio varians. 30 to 40cm above horizon (a) , the ostracods Mantelliana spp.; "Candona" mantelli; and Ampullospira cf. incisa (Blake) occur;. Horizon (b) includes the bivalves:- Unio; Filosina gregaria, F. membranacea (referred to in Ruffell (1988) as " Neomiodon " ); and the angular whorl sections of gastropods similar to Gymnentome and Pseudomelania. The sideritic sandstone at the base of horizon (a) contains current-ripple laminae , whilst a silty ironstone higher in the section has a ripple-marked upper surface. X-ray diffraction shows the Weald Clay to have a ratio of illite 2 to Kaolinite 1, with minor smectite content. The topmost beds of the Weald Clay are obscured by slipped material and vegetation , but the Perna Beds, or Bed 1 (Atherfield Bone-Bed) of Simpson (1985), can be found loose across the top 2 m of the
excavation . The unit is 10 to 30 em thick , sometimes with hollows and pipes at the base, resembling the same unit at Atherfield on the Isle of Wight. A distinct bedding is visible, alternating between coarse, light-brown grit , and medium to coarse , dark brown sand. In thin section , the clasts are seen to be well sorted (within each layer) , well-rounded quartz, limonite , phosphate, siltsto ne and quartzite , the limonite occurs as ooliths which are possibly derived Jurassic material, judging by their poor preservation. These components are seen floating in a micritic matrix along with shelly debris including bivalve and brachiopod fragments, some bryozoan (possibly Syphodictyum) and echinoderm pieces, as well as phosphatic fish scales and teeth, including Hybodus , Lepidotus and ? Lonchidion. The upper sandstone (bed 2 of Simpson , 1985), was not found during the present work ; this is in contrast to other descriptions from the area which record beds with the bivalves Mulletia, Panopea , A etostreon, and the coral Holocystis, but not a basal sandstone or bone-bed , e.g . Salter's (in Bristow, 1862) description of the Haslemere railway cutting, and Butler's (1922) description of the Woodhatch Pit, Redhill. However, at a nearby working at the latter locality Gossling (1929, p. 218) recorded a " red-brown sand, ironshot and pebbly" above the Wealden , which may correspond to the Perna Beds at Brook. The Atherfield Clay at Brook is a mottled grey, brown and pink clay with some disseminated sand and a line of calcareous nodules, 2 to 8 em in size, and yielding A etostreon, Aptolinter aptiensis, and rare fragment s of Panopea , this horizon probably correlates with the larger fossiliferous concretions recorded from the old brickpits 50 m away by Thurrell et al. (1968). Washed and sieved residues yield the foraminif era Hoeglundia chapmani and Arenabulimina spp. This, and the absence of Epistomina or Gavelin ella, denotes the presence of the " (ower" Atherfield Clay of Hart (1973) . X-ray diffraction
409
410
A . H . RUFFELL
ATHER FIEl D CL AY
SANDGATE
BEDS 'PERNA BED S'
-
10lC ALCAREOUS N ODULES
o
"'1
!~ ~
Q
BIVALVES O STRACO DS
~ S ILT
l lRONSTONE
~ SAND)
WE AL D CLAY
A
FIN E lLAM INAT /ON QCOAR SE) k'::lN OT EXP O SED
~ BASE OF EXCA VATION
Fig. 1.
Fig. 2.
shows the Atherfield Clay to be less rich in Kaolinite than the Weald Clay, and significantly richer (c. 25%) in smectite . The existence of an exposure showing the Wealden-Lower Greensand transition in the Weald is of importance historically, as it allows comparison with earlier records, as well as being the only Wealden locality to show this section at the present day. The Weald Clay fauna is typical of its position in the sequence (Morter, 1978) as well as that seen on the Isle of Wight (Ruffell, 1988), the presence of the ostracod Mantelliana may denote hypersaline conditions, however the whole fauna suggests marine and
quasi-marine conditions. The Perna beds' lithology shows condensation and probable reworking of Wealden and Upper Jurassic material, the decreased amount of kaolinite in the Atherfield Clay suggests removal of this source during marine transgression.
ACKNOWLEDGMENTS
Thanks are due to Mrs. Susan Ellis of Park Lane, Brook for perm ission to work on her land. This work was carried out under the tenure of a N.E .R .C. studentship.
References BRISTOW, H. W. 1862. Geology of the Isle of Wight. (1st ed .), Mem. geol. Surv. U.K. BUTLER, G. W. 1922. On the Perna Bed and the Weald Clay at Reigate. Proc. Geol. Ass ., 33,313-18. FOWLER, B. 1895. The Hythe Beds of the Lower Greensand in the Liphook and Hindhead district . Proc. Geol. Ass. , 13,361-65 .
GOSSLlNG , F. 1929. The geology of the country around Reigate . Proc. Geol. Ass. , 40, 197-259. HART, M. B. 1973. A correlation of the macrofaunal and microfaunal zonations of the Gault Clay in south-east England. In (Casey, R. & P. F. Rawson; eds.) The Boreal Lower Cretaceous. Geo!. 11. Spec . Iss. 5, Seel House Press, Liverpool. 267-88.
WEALD-ATHERFIELD CLAY JUNCfION
KIRKALDY, 1. F. & S. W. WOOLDRIDGE. 1938. Noles on tbe geology of the country around Haslemere and Midhursl. Proc. Geol. Ass., 49, 135-47. KNOWLES , L. & F. A . MIDDLEMISS. 1958. The Lower Greensand in the Hindhead area of Surrey and Hampshire . Proc. Geol. Ass., 69,205-37. MORTER, A. A. 1978. Weald Clay mollusca . In Worssam, B. c., The stratigraphy of the Weald Clay. Rep. Inst, geol. Sci. 78/11, Appendix 2, 19-23 . RUFFELL, A. H. 1988. Palaeoecology and event stratig-
411
raphy of the Wealden-Lower Greensand transition in the Isle of Wight. Proc. Geol. Ass. 99, 000--000. THURRELL, R. G., B. C. WORSSAM & E. A. EDMONDS. 1968. Geology of the country around Haslemere. Mem . geol. Surv. U.K. SIMPSON, M. I. 1985. The stratigraphy of the Atherfield Clay Formation (Lower Aptian, Lower Cretaceous) at the type and other localities in southern England. Proc. Geol. Ass. , 96,23-45.
A note on the Weald-Atherfield Clay junction at Brook, Surrey A. H. RuffeD RUFFELL, A. H . 1988. A note on the Weald-Atherfield Clay junction at Brook , Surrey. Proc. Geol. Ass., 100(3), 409-11. The junction of the Weald and Atherfield Clays has been recorded throughout the Weald many times in the past 100 years. The only present day exposure of this important horizon, outside the Isle of Wight and Purbeck, is described here in terms of its lithological sequence, palaeontology, and possible corre lation.
Department of Geological Sciences, University of Birmingham, P.O. Box 363. Birmingham . B15 lIT
For seventy years, the overgrown brickpits at Brook, in Surrey (SU9305 3759) exposed a variety of sections in the Weald Clay and Atherfield Clay Formation (Fowler, 1985; Kirkaldy & Wooldridge , 1938; Knowles & Middlemiss, 1958; Thurrell , Worssam & Edmonds , 1968), and provided fossils from the fissicostatus and forbesi zones of the Aptian (Simpson, 1985). During 1986 in an old trial pit across the A286 (SU9293 3765, Fig. 1), excavations were carried out to make room for a horse-training ring , the northern face of which still exposes Weald and Atherfield Clay (Fig. 2). The Weald Clay consists of blocky-weathering blue mudstones, finely laminated grey to black mudstones , and sideritic siltstones and sandstones. Two horizons were found to be fossiliferous , and although preserved only as casts (carbonate material having been leached) , the following fauna was identified rHorizon (a ) (all bivalves), Corbula alata (J. de C. Sowerby) ; ?Filosina gregaria (Casey) ; Myrene spp.; an unidentified Tellinid, possibly Scittila ; and Unio varians. 30 to 40cm above horizon (a) , the ostracods Mantelliana spp.; "Candona" mantelli; and Ampullospira cf. incisa (Blake) occur;. Horizon (b) includes the bivalves:- Unio; Filosina gregaria, F. membranacea (referred to in Ruffell (1988) as " Neomiodon " ); and the angular whorl sections of gastropods similar to Gymnentome and Pseudomelania. The sideritic sandstone at the base of horizon (a) contains current-ripple laminae , whilst a silty ironstone higher in the section has a ripple-marked upper surface. X-ray diffraction shows the Weald Clay to have a ratio of illite 2 to Kaolinite 1, with minor smectite content. The topmost beds of the Weald Clay are obscured by slipped material and vegetation , but the Perna Beds, or Bed 1 (Atherfield Bone-Bed) of Simpson (1985), can be found loose across the top 2 m of the
excavation . The unit is 10 to 30 em thick , sometimes with hollows and pipes at the base, resembling the same unit at Atherfield on the Isle of Wight. A distinct bedding is visible, alternating between coarse, light-brown grit , and medium to coarse , dark brown sand. In thin section , the clasts are seen to be well sorted (within each layer) , well-rounded quartz, limonite , phosphate, siltsto ne and quartzite , the limonite occurs as ooliths which are possibly derived Jurassic material, judging by their poor preservation. These components are seen floating in a micritic matrix along with shelly debris including bivalve and brachiopod fragments, some bryozoan (possibly Syphodictyum) and echinoderm pieces, as well as phosphatic fish scales and teeth, including Hybodus , Lepidotus and ? Lonchidion. The upper sandstone (bed 2 of Simpson , 1985), was not found during the present work ; this is in contrast to other descriptions from the area which record beds with the bivalves Mulletia, Panopea , A etostreon, and the coral Holocystis, but not a basal sandstone or bone-bed , e.g . Salter's (in Bristow, 1862) description of the Haslemere railway cutting, and Butler's (1922) description of the Woodhatch Pit, Redhill. However, at a nearby working at the latter locality Gossling (1929, p. 218) recorded a " red-brown sand, ironshot and pebbly" above the Wealden , which may correspond to the Perna Beds at Brook. The Atherfield Clay at Brook is a mottled grey, brown and pink clay with some disseminated sand and a line of calcareous nodules, 2 to 8 em in size, and yielding A etostreon, Aptolinter aptiensis, and rare fragment s of Panopea , this horizon probably correlates with the larger fossiliferous concretions recorded from the old brickpits 50 m away by Thurrell et al. (1968). Washed and sieved residues yield the foraminif era Hoeglundia chapmani and Arenabulimina spp. This, and the absence of Epistomina or Gavelin ella, denotes the presence of the " (ower" Atherfield Clay of Hart (1973) . X-ray diffraction
409
410
A . H . RUFFELL
ATHER FIEl D CL AY
SANDGATE
BEDS 'PERNA BED S'
-
10lC ALCAREOUS N ODULES
o
"'1
!~ ~
Q
BIVALVES O STRACO DS
~ S ILT
l lRONSTONE
~ SAND)
WE AL D CLAY
A
FIN E lLAM INAT /ON QCOAR SE) k'::lN OT EXP O SED
~ BASE OF EXCA VATION
Fig. 1.
Fig. 2.
shows the Atherfield Clay to be less rich in Kaolinite than the Weald Clay, and significantly richer (c. 25%) in smectite . The existence of an exposure showing the Wealden-Lower Greensand transition in the Weald is of importance historically, as it allows comparison with earlier records, as well as being the only Wealden locality to show this section at the present day. The Weald Clay fauna is typical of its position in the sequence (Morter, 1978) as well as that seen on the Isle of Wight (Ruffell, 1988), the presence of the ostracod Mantelliana may denote hypersaline conditions, however the whole fauna suggests marine and
quasi-marine conditions. The Perna beds' lithology shows condensation and probable reworking of Wealden and Upper Jurassic material, the decreased amount of kaolinite in the Atherfield Clay suggests removal of this source during marine transgression.
ACKNOWLEDGMENTS
Thanks are due to Mrs. Susan Ellis of Park Lane, Brook for perm ission to work on her land. This work was carried out under the tenure of a N.E .R .C. studentship.
References BRISTOW, H. W. 1862. Geology of the Isle of Wight. (1st ed .), Mem. geol. Surv. U.K. BUTLER, G. W. 1922. On the Perna Bed and the Weald Clay at Reigate. Proc. Geol. Ass ., 33,313-18. FOWLER, B. 1895. The Hythe Beds of the Lower Greensand in the Liphook and Hindhead district . Proc. Geol. Ass. , 13,361-65 .
GOSSLlNG , F. 1929. The geology of the country around Reigate . Proc. Geol. Ass. , 40, 197-259. HART, M. B. 1973. A correlation of the macrofaunal and microfaunal zonations of the Gault Clay in south-east England. In (Casey, R. & P. F. Rawson; eds.) The Boreal Lower Cretaceous. Geo!. 11. Spec . Iss. 5, Seel House Press, Liverpool. 267-88.
WEALD-ATHERFIELD CLAY JUNCfION
KIRKALDY, 1. F. & S. W. WOOLDRIDGE. 1938. Noles on tbe geology of the country around Haslemere and Midhursl. Proc. Geol. Ass., 49, 135-47. KNOWLES , L. & F. A . MIDDLEMISS. 1958. The Lower Greensand in the Hindhead area of Surrey and Hampshire . Proc. Geol. Ass., 69,205-37. MORTER, A. A. 1978. Weald Clay mollusca . In Worssam, B. c., The stratigraphy of the Weald Clay. Rep. Inst, geol. Sci. 78/11, Appendix 2, 19-23 . RUFFELL, A. H. 1988. Palaeoecology and event stratig-
411
raphy of the Wealden-Lower Greensand transition in the Isle of Wight. Proc. Geol. Ass. 99, 000--000. THURRELL, R. G., B. C. WORSSAM & E. A. EDMONDS. 1968. Geology of the country around Haslemere. Mem . geol. Surv. U.K. SIMPSON, M. I. 1985. The stratigraphy of the Atherfield Clay Formation (Lower Aptian, Lower Cretaceous) at the type and other localities in southern England. Proc. Geol. Ass. , 96,23-45.