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Late quaternary solution of Chalk at Basingstoke, Hants
Late Quaternary solution of Chalk at Basingstoke, Hants Written discussion of a paper taken as read D. J. WARD and J. COOPER
The Editor.
20 September 1975
Dear Sir. We must compliment Messrs. Chartres & Whalley (1975) on their paper following a competent piece of field and laboratory work. Although the topic of Chalk solution residues has been thoroughly covered by Bonte & Debrabant (1974), we would like to contribute a new element to the current Clay-with-Flints dialogue by citing a few localities where various zones of the Upper Chalk are directly overlain by Tertiary deposits. At these localities, between the Chalk and the overlying Tertiaries, there is usually developed a banded manganiferous clay, the Frindsbury Clay Bed, very similar to the 'manganiferous dark clay', Unit B of Chartres & Whalley (1975). The term 'Frindsbury Clay Bed' is used here as a formal lithostratigraphic unit, stratotype locality Tower Hill, Upper Upnor, Frindsbury, near Rochester, Kent (TQ 7537(0), where the following section is displayed: Unit 4 Thanet Beds (Stourmouth Silts) Unit 3 Thanet Beds (Bullhead Bed); glauconitic sandy clay with rounded and pitted green-coated flints Unit 2 Frindsbury Clay. Alternating orange, white and black banded clay including unweathered flints, silicified fragments of Inoceramus. echinoderm and fish remains and phosphatic microcoprolites Unit I Upper Chalk, Micraster coranguinum Zone (Santonian)
8m+ 15-20 ems
1-8 ems Seen to 3 metres
The fish fauna of Unit 2 was brought to our attention by Mr. P. R. Gurr. From its stratigraphical position the Frindsbury Clay could be thought, not unreasonably, to be Dano-Montian in age, a possible equivalent of the 'fish clay' from Denmark (Christensen, Fregerslev, Simonsen & Theide, 1973). However, its fauna fails to substantiate this and corresponds with that from the chalk below: FAUNAL LIST Echinodermata (determined by Mr A. S. Gale) Aspidaster cf. bu/biferus (Forbes) 'Isocrinus' minutus Valette Bourgueticrinus spp. Metopaster cf. unctatus (Forbes) Cidaris perornata Forbes Phymosoma sp. Cidaris sp. Stereocidaris sceptifera (Mantell) Crateraster quinque/oba (Goldfuss) Pisces Corax' jaekeli (Woodward) Mesiteia greeni (Cappetta) Creto/amna appendicu/ata (Agassiz) ?Mesiteia sp. Enchodus sp. Paratriakis bettrechiensis Herman, in press Heterodontus sp. Paratriakis curvidorsalis (Davis) Hybodus cf. brabanticus (Leriche) 101
102
CORRESPONDENCE
Rhinobatos sp. Scapanorhynchus raphiodon (Agassiz) Scyliorhinus elongatus (Davis) ?Scyliorhinus reussi Herman, in press Scyliorhinus spp.
Squalicorax sp. Squatina sp. Squatirhina cf. kannensis Herman, in press Stephanodus sp.
and many unidentified. teleost teeth and bones. A sample of chalk from Unit I was dissolved in dilute acetic acid and the residue indeed yielded a fauna essentially similar to that of the overlying Frindsbury Clay. At Chestnut Street, Kent (TQ 868637), the Frindsbury Clay development is similar in structure and fauna to that at Tower Hill. At Pegwell Bay, Kent (TR 354643), there is a thinner unit of it, overlying shattered Marsupites Zone Chalk and overlain by a thin tabular band of unweathered flints. At the junction of the near vertical chalk and the sandy Reading Beds at Alum Bay, Isle of Wight, no clay development is seen. The following conclusions concerning chalk residues in general and the Frindsbury Clay in particular can be drawn from these observations:
A. That Frindsbury Clay is a residue derived from the dissolution of the chalk below permeable Tertiary beds. B. That this dissolution could have started in any of the major Tertiary cyclothems where the Chalk surface was above the water table; however, the absence of the Frindsbury Clay from the Alum Bay section would suggest a date later than the Miocene uplift and folding. C. That in their development such residue deposits are self-limiting; that is, the thicker they become the less water permeates through to dissolve the chalk below. D. That paradoxically the lowest division within the bed is the youngest. E. That like other residue deposits they afford an unparalleled opportunity for collecting the concentrated, less soluble, elements of the fauna.
REFERENCES BONTE, A. & P. DEBRABANT. 1974. Etude geochimique de I'argile residuelle de la craie. Annis Soc. geol. N .. 1973,93 (2), 95-115. CHARTRES, C. J. & W. B. WHALLEY, 1975. Evidence for Late Quaternary solution of Chalk at Ba.singstoke, Hampshire. Proc. Geol. Ass. 86(3) 365-72. CHRISTENSEN, L., S. FREGERSLEV, A. SIMONSEN & J. THIEDE. 1973. Sedimentology
D. J. Ward 35 Addington Road West Wickham, Kent
and depositional environment of the Lower Danian fish clay from Stevns Klint, Denmark. Bull. geol. Soc.
Denmark. 22, 193--212. HERMAN, J. (in press). 1976. Les Selaciens des terrains neocretaces et paleocenes de Belgique et des contrees limitrophes. Elements d'une biostratigraphie intercontinentale. Mem. Servir Explic. Cartes geol. min. Belg.. No. 15.
J. Cooper Department of Palaeontology British Museum (Natural Historv) Cromwell Road, London SW7 5BD
The Editor.
20 September 1975
Dear Sir. We must compliment Messrs. Chartres & Whalley (1975) on their paper following a competent piece of field and laboratory work. Although the topic of Chalk solution residues has been thoroughly covered by Bonte & Debrabant (1974), we would like to contribute a new element to the current Clay-with-Flints dialogue by citing a few localities where various zones of the Upper Chalk are directly overlain by Tertiary deposits. At these localities, between the Chalk and the overlying Tertiaries, there is usually developed a banded manganiferous clay, the Frindsbury Clay Bed, very similar to the 'manganiferous dark clay', Unit B of Chartres & Whalley (1975). The term 'Frindsbury Clay Bed' is used here as a formal lithostratigraphic unit, stratotype locality Tower Hill, Upper Upnor, Frindsbury, near Rochester, Kent (TQ 7537(0), where the following section is displayed: Unit 4 Thanet Beds (Stourmouth Silts) Unit 3 Thanet Beds (Bullhead Bed); glauconitic sandy clay with rounded and pitted green-coated flints Unit 2 Frindsbury Clay. Alternating orange, white and black banded clay including unweathered flints, silicified fragments of Inoceramus. echinoderm and fish remains and phosphatic microcoprolites Unit I Upper Chalk, Micraster coranguinum Zone (Santonian)
8m+ 15-20 ems
1-8 ems Seen to 3 metres
The fish fauna of Unit 2 was brought to our attention by Mr. P. R. Gurr. From its stratigraphical position the Frindsbury Clay could be thought, not unreasonably, to be Dano-Montian in age, a possible equivalent of the 'fish clay' from Denmark (Christensen, Fregerslev, Simonsen & Theide, 1973). However, its fauna fails to substantiate this and corresponds with that from the chalk below: FAUNAL LIST Echinodermata (determined by Mr A. S. Gale) Aspidaster cf. bu/biferus (Forbes) 'Isocrinus' minutus Valette Bourgueticrinus spp. Metopaster cf. unctatus (Forbes) Cidaris perornata Forbes Phymosoma sp. Cidaris sp. Stereocidaris sceptifera (Mantell) Crateraster quinque/oba (Goldfuss) Pisces Corax' jaekeli (Woodward) Mesiteia greeni (Cappetta) Creto/amna appendicu/ata (Agassiz) ?Mesiteia sp. Enchodus sp. Paratriakis bettrechiensis Herman, in press Heterodontus sp. Paratriakis curvidorsalis (Davis) Hybodus cf. brabanticus (Leriche) 101
102
CORRESPONDENCE
Rhinobatos sp. Scapanorhynchus raphiodon (Agassiz) Scyliorhinus elongatus (Davis) ?Scyliorhinus reussi Herman, in press Scyliorhinus spp.
Squalicorax sp. Squatina sp. Squatirhina cf. kannensis Herman, in press Stephanodus sp.
and many unidentified. teleost teeth and bones. A sample of chalk from Unit I was dissolved in dilute acetic acid and the residue indeed yielded a fauna essentially similar to that of the overlying Frindsbury Clay. At Chestnut Street, Kent (TQ 868637), the Frindsbury Clay development is similar in structure and fauna to that at Tower Hill. At Pegwell Bay, Kent (TR 354643), there is a thinner unit of it, overlying shattered Marsupites Zone Chalk and overlain by a thin tabular band of unweathered flints. At the junction of the near vertical chalk and the sandy Reading Beds at Alum Bay, Isle of Wight, no clay development is seen. The following conclusions concerning chalk residues in general and the Frindsbury Clay in particular can be drawn from these observations:
A. That Frindsbury Clay is a residue derived from the dissolution of the chalk below permeable Tertiary beds. B. That this dissolution could have started in any of the major Tertiary cyclothems where the Chalk surface was above the water table; however, the absence of the Frindsbury Clay from the Alum Bay section would suggest a date later than the Miocene uplift and folding. C. That in their development such residue deposits are self-limiting; that is, the thicker they become the less water permeates through to dissolve the chalk below. D. That paradoxically the lowest division within the bed is the youngest. E. That like other residue deposits they afford an unparalleled opportunity for collecting the concentrated, less soluble, elements of the fauna.
REFERENCES BONTE, A. & P. DEBRABANT. 1974. Etude geochimique de I'argile residuelle de la craie. Annis Soc. geol. N .. 1973,93 (2), 95-115. CHARTRES, C. J. & W. B. WHALLEY, 1975. Evidence for Late Quaternary solution of Chalk at Ba.singstoke, Hampshire. Proc. Geol. Ass. 86(3) 365-72. CHRISTENSEN, L., S. FREGERSLEV, A. SIMONSEN & J. THIEDE. 1973. Sedimentology
D. J. Ward 35 Addington Road West Wickham, Kent
and depositional environment of the Lower Danian fish clay from Stevns Klint, Denmark. Bull. geol. Soc.
Denmark. 22, 193--212. HERMAN, J. (in press). 1976. Les Selaciens des terrains neocretaces et paleocenes de Belgique et des contrees limitrophes. Elements d'une biostratigraphie intercontinentale. Mem. Servir Explic. Cartes geol. min. Belg.. No. 15.
J. Cooper Department of Palaeontology British Museum (Natural Historv) Cromwell Road, London SW7 5BD