Stratigraphical Interpretation of Chalk Group Macrofossils from the Hog's Back Structure, Surrey
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Stratigraphical interpretation of Chalk Group macrofossils from the Hog's Back structure, Surrey Geology and Regional Geophysics Programme Open Report OR/15/004 BRITISH GEOLOGICAL SURVEY WHATEVER PROGRAMME OPEN REPORT OR/15/004 Stratigraphical interpretation of Chalk Group macrofossils from the Hog's Back structure, Surrey The National Grid and other M A Woods Ordnance Survey data © Crown Copyright and database rights 2012. Ordnance Survey Licence No. 100021290 EUL. Keywords Chalk Group, Macrofossils, Lithostratigraphy, Biostratigraphy, Chronostratigraphy. Map Sheet 285, 1:50 000 scale, Aldershot Bibliographical reference WOODS, M A. 2015. Stratigraphical interpretation of Chalk Group macrofossils from the Hog's Back structure, Surrey. British Geological Survey Internal Report, OR/15/004. pp. Copyright in materials derived from the British Geological Survey’s work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. You may not copy or adapt this publication without first obtaining permission. Contact the BGS Intellectual Property Rights Section, British Geological Survey, Keyworth, e-mail [email protected]. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract. Maps and diagrams in this book use topography based on Ordnance Survey mapping. © NERC 2015. 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This work is in connection with current BGS work to build a physical property model of the Chalk, and will assist in providing surface control for modelled formational boundaries in the subsurface. Contents Foreword ......................................................................................................................................... i Contents ........................................................................................................................................... i Summary ........................................................................................................................................ ii 1 Introduction ............................................................................................................................ 1 2 Locality description and interpretation ............................................................................... 1 Appendix 1 – Author citations for fossil species ................................................................. 19 References .................................................................................................................................... 20 TABLES Table 1. The stratigraphy of the Chalk Group referred to in this report.(not to scale) i OR/15/004; Draft 0.1 Last modified: 2015/01/28 10:27 Summary This work summarises Chalk Group macrofossils, and their stratigraphical interpretation, for 69 localities across the monoclinal fold known as the ‘Hog’s Back’, between Farnham and Guildford, Surrey. This work is in connection with a related project that is developing a Chalk physical property model for southern England. Work across the Hog’s Back infills critical gaps in our knowledge about Chalk stratigraphy and structure in this area. ii OR/15/004; Draft 0.1 Last modified: 2015/01/28 10:27 1 Introduction This report describes the stratigraphical interpretation of Chalk macrofossils from 69 localities collected by M A Woods (MAW), A R Farrant (ARF) and R K Westhead (RKW) across the Hog’s Back structure between Farnham and Guildford, Surrey, in September 2014. The field area is entirely within 1:50 000 geological Sheet 285 (Aldershot). The stratigraphy referred to in this report is given in Table 1, and author citations for fossil species are listed in Appendix 1. This work is in connection with current BGS work to build a physical property model of the Chalk, and will assist in providing surface control for modelled formational boundaries in the subsurface. 2 Locality description and interpretation Detailed below are the localities from which Chalk macrofossils were collected in the course of this work, together with their stratigraphical interpretation. (1) Chalk Pit on north flank of Hog's Back, 150 m SW of Inwood Manor, just N of A31, near Guildford, Surrey. 1:10 000 SU94NW NGR: SU 91116 48423 Specimen nos: WMD 16837 – 16851 The fauna includes: Bivalvia: Cladoceramus undulatoplicatus (fragments) ?Neithea sexcostata (fragment) oyster (?Acutostea incurva) Platyceramus (shell fragments, including thick – i.e. c. 5mm) Echinoidea: cidarid (test fragment) Conclusion: White Chalk Subgroup, Seaford Chalk Formation; basal Santonian, mid M. coranguinum Zone. (2) North-west corner of Greyfriars chalk pit, 275 m NW of Greyfriars Farm, east of Puttenham, Surrey. 1:10 000 SU94NW NGR: SU 94314 48321 Specimen nos: WMD 16852 – 16868 The fauna, collected from a flint-rich interval of nodular chalk, includes the following: Brachiopoda: terebratulid Bivalvia: Inoceramus cuvieri? (fragmentary and crushed- several specimens) Merklinia cf. variabilis Echinoidea: Plesiocorys (Sternotaxis) plana (several specimens) ?P. (S.) plana (crushed) Conclusion: White Chalk Subgroup, lower Lewes Nodular Chalk (? ‘Basal Complex’; Mortimore et al., 2001, p. 279); Turonian, uppermost T. lata Zone or basal P. (S.) plana Zone. (3) Westernmost of two old chalk pits, east of West Farm, c. 520 m east of West Farm, near Runfold, Farnham, Surrey. 1:10 000 SU84NE NGR: SU 87844 48136 1 OR/15/004; Draft 0.1 Last modified: 2015/01/28 10:27 Specimen nos: WMD 16869-16884 The sparse fauna includes the following: Brachiopoda: ?Hyotissa semiplana Kingena lima K. lima? (several) Orbirhynchia sp. Terebratulina striatula Asteroidea: skeletal plates Crinoidea: Bourgueticrinus sp. (columnal) Echinoidea: Micraster sp. (test fragment) The fauna is dominated by small fossils in smooth, hard – firm, rather low density chalk. Platyceramus is notably absent. Conclusion: White Chalk Subgroup, ?lower Newhaven Chalk; ?Santonian (4) Easternmost of two chalk pits, east of West Farm, 750 m ENE of West Farm, near Runfold, Farnham, Surrey. 1:10 000 SU84NE NGR: SU 88069 48212 Specimen nos: WMD 16885 – 16905 The fauna includes the following: Porifera: sponge remains Bryozoa: bryozoans Brachiopoda: Terebratulina? Bivalvia: Acutostrea incurva Mimachlamys cretosa (fragment) oyster ?Platyceramus ?Pseudoperna boucheroni Asteroidea: skeletal plates Echinoidea: Echinocorys (test fragment) The fauna occurs in low density, smooth-textured chalk, locally iron-stained and sponge-rich. No definitive Platyceramus. Conclusion: White Chalk Subgroup, ?lower Newhaven Chalk; ?Santonian. (5) Field brash in field c. 15 m N of old chalk pit, c. 250 m NNW of Conduit Farm, south of Onslow Village, Guildford, Surrey. 1:10 000 SU94NE NGR: SU 97098 48378 Specimen nos: WMD 16906 – 16910 The fauna is dominated by Mytiloides shell fragments in hard chalk, including Mytiloides mytiloides. Conclusion: White Chalk Subgroup, Holywell Nodular Chalk Formation; Turonian, Mytiloides spp. Zone. (6) Chalk pit c. 800 m N of Shoelands Farm, near Puttenham, Surrey. 1:10 000 SU94NW NGR: SU 91274 48152 Specimen nos: WMD 16911 – 16942 2 OR/15/004; Draft 0.1 Last modified: 2015/01/28 10:27 The fauna includes the following: Bivalvia: Inoceramus atlanticus (common) Inoceramus aff. pictus oysters Spondylus? Ammonoidea: