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Week-end field meeting: The Upper Eocene—Lower Oligocene beds of the Isle of Wight
Week-end Field Meeting: The Upper Eocene-Lower Oligocene Beds of the Isle of Wight 6-8 October 1972 Report by the Directors: B. DALEY and N. EDWARDS Received 31 May 1973
DALEY, B. & N. EDWARDS, 1974. Week-end Field Meeting: The Upper EoceneLower Oligocene Beds of the Isle of White. Proc. Geol. Ass., 85 (2), 281-292. During the excursion, members studied the lithologies, fossil assemblages and stratigraphy of the Headon, Osborne and Bembridge Beds. On the first field day, the party visited Hatherwood Point and Colwell Bay, to study the Headon Beds brackish and freshwater deposits, and later Hamstead Ledge to examine the Bembridge Marls. On the second day the party first studied the Upper Eocene beds of Whitecliff Bay, including the marine Brockenhurst Bed and later the Bembridge Marls at Gurnard Ledge, where most attention was concentrated on the Insect Limestone. B. Daley, Dept. of Geology, Portsmouth Polytechnic, Portsmouth. N. Edwards, 52 Little Paddocks, Ferring, near Worthing, Sussex.
assembled at the Sentry Mead Hotel, Totland, on the evening of Friday, 6 October. After dinner the Directors briefly described the Upper Eocene-Lower Oligocene beds exposed on the northern coast of the Isle of Wight, and outlined the palaeoenvironmental interpretations proposed in their Ph.D. theses (Edwards, 1967; Daley, 1969). These interpretations were to be discussed during the next two days, by examination of evidence in the field.
TWENTY-TWO MEMBERS
Saturday, 7 October The party first drove to Alum Bay, to examine the Headon Beds (Upper Eocene) exposed at Hatherwood Point (SZ 305860) (see itinerary VIII in Curry, Daley, Edwards, Middlemiss, Stinton & Wright, 1972, 21-3), and descended the steps in Alum Bay Chine to the beach. The bottom of the steps was in Barton Clay (Upper Eocene), the upper beds of which were seen to be truncated by a hitherto unrecorded strike-slip fault hading northwards at about 20°. Walking northwards (down-dip) past exposures in Barton (or Headon Hill) Sands, Messrs A. and C. King found examples of the fossil crustacean 281
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burrow Ophiomorpha nodosa Lundgren, indicative of littoral-marine conditions (Weimer & Hoyt, 1964; Sellwood & Kennedy, 1970). The Directors' discovery of this burrow at Totland Bay (SZ 321866) and on the Hampshire mainland at Barton Cliff (SZ 261923) concurred with other evidence (Curry, 1965), that the sea became very shallow over the whole area before deposition of the Barton Beds ended. Good evidence for subsequent establishment of marsh and swamp conditions was provided by the occurrence of carbonised woody plant roots, exposed by digging, in drab clayey sand (equivalent of Bed L at Barton: Fowler, 1971) overlying the Barton Sands. These had also been seen by the Directors in Bed L at Barton, while equivalent beds in Totland Bay had yielded remains of swamp-growing conifers (Fowler, Edwards & Brett, 1973). At Hatherwood Point the cliff comprises a series of muddy terraces in almost flat-lying Headon and Osborne Beds. The Headon Beds succession was described recently by Stinton (1971) and Cray (1973, 20) and the Osborne Beds by Bosma & Insole (1972). Although slipped mud concealed much of the Lower Headon Beds (27 m.), members could see characteristic lithologies exposed in the lower 7 m. and upper 6 m. Greenish silty and sandy clays and marls were interbedded with pale brown, chalky, micritic limestones 0·25 to 2 m. thick. Some limestones appeared to be transitional to underlying marls, others rested on thin clayey lignite layers. Upper surfaces of limestones were irregular, sometimes strewn with limestone pebbles. The limestones were notable for an abundance of pulmonatesnail shells (Galba and Planorbina spp.), whilst the clays and marls contained Viviparus lentus (Solander), Bithynella sp., Melanoides acuta (1. Sowerby) and, in one bed overlying a limestone, Corbicula pulchra (1. Sowerby) and Dreissena brardii (1. Sowerby). Scutes of pond-turtle (Emys sp.) were picked up from clay surfaces; the remains of Trionyx (soft-shelled turtle), Diplocynodon (alligator), Lepisosteus (gar), Amia (bow-fin) and teeth of Theridomys (rodent) have also been found. The molluscs are characteristic of freshwater lakes, ponds and streams, while the vertebrate assemblage resembles that of these habitats in the southeastern United States. The Directors remarked that the succession appeared to represent the deposits of a river flood-plain lake: the clayey deposits could be analogous to those described by Coleman (1966) from southwestern Louisiana, while the limestones compared well with modern lake 'marls' (lime muds) in the Cambridgeshire fenlands (Skertchley, 1877), small Michigan lakes (Davis, 1900; 1903) and south Florida marshes (Davis, 1943; N. Edwards, personal observations). This interpretation agrees well with palaeobotanical evidence for extensive coastal flood-plain conditions (Fowler, Edwards & Brett, 1973). The 2 m. 'How Ledge Limestone' near the top of the Lower Headon Beds was well exposed, yielding characteristic fossils. The overlying 2 m.
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of drab marly clay was shown, by digging, to contain irregular borings up to 30 mm. diameter, filled by black shelly sandy clay. These descend from the base of the Middle Headon Beds. The Directors noted that they resemble marine crustacean (Callianassa) borings figured by Schafer (1962, fig. 186), and that they occur in the same stratigraphical position at other localities on the island. The Middle Headon Beds (over 9 m.) were well exposed, comprising greenish and blue sandy clays and sands, drab black and brown below (2 m.), and with a discontinuous freshwater limestone (0'3 m.) at 4 m. from the top. Although at first sight much richer in molluscan species than the Lower Headon Beds, there was an overwhelming numerical dominance of cerithids (Batil/aria and Potamides spp.), oysters (Ostrea velata Wood) and corbiculids (Corbicula obovata (J. Sowerby)). Similar associations occur today in tropical-subtropical estuarine and coastal river-influenced lagoons (Parker, 1964), as in Tabasco, Mexico, where Batil/aria minima Gmelin crawls in myriads on the mud-flats (N. Edwards, personal observation). The Middle Headon development here was interpreted, therefore, as a seaward, marine-influenced aspect of the Lower Headon flood-plain lake environment. Evidence for a period of subaerial exposure and erosion during deposition of the Upper Headon freshwater limestones (9 m.) was the final point examined at this locality. A very irregular topographic surface, with up to 3 m. relief, was easily traced within the limestone series by the occurrence of a lignitic clay bed (1 m.), which thinned-out over 'high' areas. Welllithified limestone nodules and slab-like masses from these high areas occurred also as 'boulders' and cobbles in the lignitic bed, apparently having been undercut by erosion during deposition of the lignite mud. Colour-banded micritic 'crusts', first noted by Jackson (1925), who described this section, were found to be associated with this and other erosion surfaces in the limestones. Similar crusts on limestone surfaces in the Caribbean have been cited by James (1972) as criteria for subaerial exposure. The lignitic bed was found to include bands of crushed planorbid shells, and since it contains remains of aquatic vertebrates like those in the Lower Headon Beds, can be interpreted as a lacustrine deposit. The occurrence of terrestrial mammal remains (Cray, 1973) suggests proximity to land. A limestone bed 1 m. above the lignitic bed yielded good specimens of Theodoxus, Melanopsis and Melanoides, an association found today in shallow-water ponds and canals in North Africa (Gautier, 1928). After lunch, the party drove to Colwell Bay (SZ 327878), to examine the Middle and Upper Headon Beds (see itinerary IX in Curry and others, 1972).Leaving the vehicles in the car-park, the members walked northwards (down-dip) along the shore. The 'How Ledge Limestone', near the top of the Lower Headon Beds, was well exposed behind the beach-huts and PROC. GEOL. ASS., YOLo 85, PART 2,1974
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formed How Ledge on the foreshore. The basal Middle Headon 'Neritina Bed' was covered by down-washed mud, but its characteristic fossils (Theodoxus, Potamides, Corbicu/a) were collected from rain-washed mud surfaces and as sea-washed specimens from the foreshore. Just north ofthe huts a large mass of the 'Oyster Bed' was seen, detached from the cliff. The oyster (0. velata) valves constituted about 90 per cent of the deposit, being packed together in a sandy matrix and clearly not in growth position. Present lack of exposures hinders the study of this interesting deposit, which White (1921) interpreted as a channel-fill in the 'Venus Bed'. The best section in the Middle Headon Beds was seen at Brambles Chine (SZ 330883), as described by Stinton (1971). The blue-grey clayey-sand matrix of the 'Venus Bed' (2 m.) was studded with creamy coloured mollusc shells, notably the paired valves of the typical fossil, Sinodia (' Venus') suborbicularis, of which 60 per cent are in life position (Ager, 1963, 87). Although the overall aspect of the assemblage was marine, the large numbers of oysters, corbiculids and cerithids, coupled with a lack of echinoids and corals, suggested inshore, muddy, river-influenced conditions. The Upper Headon Beds in Colwell Bay (14 m.) lack the thick limestone series seen at Hatherwood Point. Instead, the lowest 4 m. comprises sands, silts and clays, visible along the whole length of the section. These sediments are divisible lithologically into two: a lower, darker more clayey part and an upper, light coloured, more sandy part. The lower part comprises laminated, mainly grey clays, silts and sands, resting on a sharp erosion surface at the top of the Middle Headon Beds. Towards the base are bands of Potamomya sp., a bivalve often referred to the fluvio-estuarine genus Erodona. The upper sandy part was the subject of considerable interest to members. A number of sedimentary structures were pointed out by the Directors, including large- and small-scale cross-stratification, layers of asymmetrical ripples, some showing uniform current orientation, others showing herringbone structure, and less commonly scours with clay pellets, and flat lamination. Flaser bedding of varying types (see Reineck & Wunderlich, 1968) was a feature of the sands. The flasers comprised carbonaceous material in addition to clay, particularly near the upper part of the unit, where laterally continuous carbonaceous laminae also occurred in some places. It was noted that iron staining in the sand often occurred above the flasers or laminae of similar composition, which presumably had led to the formation of small-scale perched water tables. The general absence of bioturbation was, with few exceptions, noteworthy. The top of the sand is marked by an undulose erosion surface, with rusty, sandy concretions or clasts occurring above it. Small vertical roots extended for a distance of
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about 100 em, downwards from this surface. Occasional narrow and sometimes branching cracks extended downwards from this surface. These bore no resemblance to those formed by desiccation and might reflect penecontemporaneous tension cracks formed by the lateral movement of cohesive sediment at the time of deposition. The Directors suggested that the features of the deposit indicated an intertidal environment in perhaps a brackish-water bay. Farther north, at Linstone Chine (SZ 330886), the small, very steep, faulted fold in the Upper Headon Beds was noted. Beyond it, the succession in the upper part of the Upper Headon Beds, described by Tawney & Keeping (1882), was well displayed. The succession of drab silty clays and sands, with only two thin limestone beds, yielded molluscan fossils abundant in numbers but poor in species. Among these were corbiculids, cerithids, Viviparus, Unio and, most notably, Potamomya. The Directors remarked that these Potamomya-Viviparus deposits predominate in the Upper Headon Beds over most of the outcrop area (including the New Forest), and overlie the thick limestone series at Hatherwood Point. They pass up into the equally widespread, mottled green and red clays of the Osborne Beds, badly exposed at the north end of Colwell Bay. The wide extent of these drab Upper Headon deposits, and their mixed assemblage of freshwater and brackish molluscs, suggested analogy with 'estuarine' Lake Pontchartrain, in south-east Louisiana, which suffers marine incursions and large influxes of river flood-water (Darnell, 1961). After tea at Yarmouth, the members were joined by Mr. R. L. E. Ford, a local palaeontologist specialising in the Harostead Beds. The party then continued to Hamstead Ledge (SZ 401920), via the private road which joins the A3054 at SZ 402892. After parking at Harostead, members descended to the shore by the public footpath. Hamstead Ledge is formed of three freshwater limestone beds in the Bembridge Limestone, overlying the Osborne Beds. The uppermost of these limestones, exposed in a low bank, was seen to contain moulds of Galba and Planorbina spp. To the west of Hamstead Ledge the whole of the Bembridge Marls and part of the overlying Harnstead Beds were exposed on the foreshore, since the visit had been planned to coincide with the equinoctial spring tide when these beds become visible at low water. Part of the succession was also visible in the adjacent cliff-section. The Bembridge Marls here comprise approximately 21'5 m. of fresh- and brackish-water sediments, mainly clays and silts, with a profuse but taxonomically restricted molluscan fauna (see Daley, 1972). Considerable interest was shown in the brackish-water sediments immediately overlying the undulose erosion surface at the top of the underlying Bembridge Limestone. This part of the succession is, in descending stratigraphical order, as follows (bed numbers from Daley, 1973):
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HAM X
Green clay with Polymesoda convexa (Brongniart) pre- metres dominant, Melanopsisfusiformis(J. Sowerby), Melanoides acuta (J. Sowerby), Potamaclis turritissima (Forbes) ... 0·61 HAM IX Olive brown mottled clay with ostracod partings and lensoid concentrates, sometimeslithified 0·97 HAM VIII Dark grey mottled clays with ostracods on partings and within polygonal cracks, passing down into clays with partings and bands containing corbiculids, M. acuta, Mytilopsis sp., P. turritissima
HAM VII Light green marl. P. convexa, sometimes in life position, M. acuta, resting on mud-crackedsurface HAM VI Blue-green claywith shellypartingsand bands containing Mytllopsis sp., P. convexa and fewer M . acuta, M. fusiformis, Potamides vagus (Solander) HAM V Greenish-grey clay with bands containing M. acuta, Serpula sp., Viviparus lentus (Solander) ... HAM IV Grey clay with shelly partings and bands containing P. convexa, Corbicula sp, and also M. acuta HAM III Laminated grey clay with complexsystem of cracks HAM II Grey and black clayswith shellypartings and bands with M. acuta, P. convexa, P. vagus and, less commonly, M. fusiformis, Vi lentus
HAM I
0·82
0·06 0·30 0·30 0·46
0·15 0·30
Bleached shell band containing corbiculidsand Ostrea sp. forminga cap on the surfaceof the underlying Bembridge Limestone ... 0·03-0·06
The Directors explained that following the freshwater conditions of Bembridge Limestone times, the sea had transgressed this area from the east and that bed HAM I was the lateral equivalent of the Bembridge Oyster Bed in Whitecliff Bay. There is no clear palaeontological evidence that fully marine salinities were reached at this locality at this time, for the assemblages are restricted to few taxa, and comprise mainly brackish water types. It was pointed out that the assemblages from this part of the succession are comparable with those of brackish water, tropical and subtropical mudflats at the present day (Daley, 1972). Considerable interest was shown in the different types of fossil preservation at this stratigraphical level. In the grey to black, more or less pyritic clays, shells are well preserved, but in the blue-green clays, they are chalky and very friable. The Directors explained that this variation in preservation was apparent in the brackish-water facies at a number of different horizons and localities. It was suggested that the dark colour of the grey clays might have been a primary feature, although it seemed more likely that it had developed in sediments which had passed rapidly through the initial aerobic stage of diagenesis to the anaerobic early burial stage (cf. Fairbridge, 1967) where, under high pH and low Eh, calcium carbonate is stable and FeS (afterwards FeS2) is precipitated. The pyritised surfaces of the shells examined from bed HAM II were thought by the Directors to
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represent the effect of reducing conditions adjacent to decaying shell periostracum (cf. Hudson & Palframan, 1969,404). Freshwater, lacustrine clays higher up the succession were also examined. Beds HAM XXIII-XXV (Daley, 1973) proved to be of most interest since they contain abundant water-plant seeds (Brasenia, Stratiotesy and monocotyledonous leaf fragments, which are mainly concentrated in partings and bands together with freshwater gastropods such as Viviparus and the pulmonate Galba and Planorbina. Their occurrence may reflect the settling out of locally derived life associations eroded during storms. The 'Black Band', which traditionally defines the base of the Hamstead Beds, was examined by some members of the party. It contains freshwater gastropods such as Viviparus and has an autochthonous root system extending downwards from its underside. It should not be confused with another black, lignitic clay (the Nematura Bed) somewhat higher up the Hamstead Beds succession, which has a distinctive brackish-water molluscan fauna. Mr. Ford remarked on the number of mammalian species in the Hamstead Beds which do not occur in older deposits on the island, but which are well known on the Continent from deposits referred to the Lower Oligocene (see also Ford, 1972). Sunday, 8 October The party drove initially to Whitecliff Bay (SZ 642863) to see the Headon, Osborne and Bembridge Beds (see Itinerary I in Curry & others, 1972, 3-5). The Bay was approached via the footpath from Hill Way (Whitecliff Bay Hotel), whilst the vehicles were taken to the next access point, at Howgate Lane (SZ 646871). The party walked northwards (down-dip) from the cliff steps, passing cliffs in the weathered Barton Clay and Barton Sands. The lignitic equivalent of Bed L at Barton was seen to be overlain by only about 8 m, of Lower Headon Beds (A to F of Stinton, 1971), here lacking limestones but otherwise of similar lithology to these beds at Hatherwood Point. The basal Middle Headon 'Brockenhurst Bed' (0'15 m.) (G of Stinton, 1971) was exposed by digging in the cliff. The underlying erosion surface, described by Jackson (1927), and irregular borings in bright green Lower Headon clay (F), were well seen. The borings were full of shelly clayey sand, like that of the 'Brockenhurst Bed'. This latter yielded a number of marine mollusc species, notably Ostrea ventilabrum Goldfuss and Cardita deltoidea (J. Sowerby). The total assemblage of over one hundred species of marine mollusca, several corals, and echinoids, is the largest in the Headon Beds. A similar assemblage in the Upper Oligocene of Hungary has been classified as shallow sublittoral, with salinity> 30 ppm. (Baldi, 1973, 114--15).The microfauna, however, is poor in species by comparison with true open-sea facies (Bhatia, 1957; P. Vella
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and M. Keen, personal communications). The Directors noted that although certain molluscan species in the 'Brockenhurst Bed' have apparent Lower Oligocene affinities, the weight of evidence from Ostracoda (Keen, 1968; 1972), Mammalia (Cray, 1973; Ford, 1972), calcareous nanno-plankton (Martini, 1970) and isopods (Martini, 1972) placed the Eocene-Oligocene boundary higher, probably in the Bembridge MarlsHamstead Beds succession. Ascending the Middle Headon succession, the molluscan assemblage becomes temporarily depleted in a weathered series of clayey fine sands (H to K of Stinton, 1971), comprising only burrowing bivalves (Gari, Sinodia, Cardita). A richer assemblage seen in the overlying beds (L to 8 of Stinton, 1971) included cerithids, corbiculids and O. velata, being more like that of the western localities. The Upper Headon to Bembridge Marls part of the succession was examined in less detail. The Potamomya- Viviparus deposits of the Upper Headon were notable for their thick shell beds, picking out the 60-70° northerly dip of the strata. The Osborne Beds succession beyond, described by Bosma & Insole (1972), were predominantly slipped, green and red clays or marls, with thin creamy coloured chalky limestones, almost devoid of fossils. A grey and brown series (7' 5 m.) near the middle was pointed out as containing Viviparus, Melanopsis, Melanoides and Unio. Traceable in coastal and borehole sections to Hatherwood Point, it has yielded mammals, reptiles, fishes, crustaceans and plants, notably at Wootton Creek (Colenutt, 1888). Resemblance of the Osborne Beds to the Wealden Marls (Lower Cretaceous) and the Keuper Marls, for which the palaeoenvironment is better known, suggested relatively land-locked, shallow-water, lacustrine conditions. An examination of the Bembridge Limestone (8'5 m.) provided good evidence for a lacustrine interpretation. 'Chara' oogonia and moulds of freshwater snails (Galba, Planorbina spp.) were abundant, in lithologies resembling those of the Lower Headon limestones. A clay series in the middle of the Bembridge Limestone included a thin layer of Corbicula, Potamides and Melanoides. The Directors have traced this as far west as Hamstead Ledge. A conglomeratic white limestone at the top of the succession was pointed out as being, by contrast, of very local occurrence. It was perhaps deposited during a period of erosion, following a minor phase of tectonic warping postulated by Daley & Edwards (1971). In Howgate Bay the party examined the overlying Bembridge Marls (Beds WH I-IX, Daley, 1973), visible just above the foreshore. The Directors pointed out that at this locality the 'Bembridge Oyster Bed' (Bed WH II), which in other sections rests directly on the eroded top of the Bembridge Limestone, is here underlain by a blue-green clay (Bed WH I) with brackish-water fossils. The 'Bembridge Oyster Bed' was laid down
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during the last but one of the local Palaeogene transgressions for which evidence still exists, but the fauna is restricted to few taxa, including Ostrea sp. (often bored by the sponge Cliona or encrusted by bryozoa, serpulids and, less commonly, barnacles) and a few other molluscs. An argillaceous limestone, containing small-scale diapiric structures (part of Bed WH III), was briefly examined (see Daley, 1971); this is the equivalent of the 'Insect Limestone' of some north-eastern coastal localities, which the party was to see later in the day. After climbing the tumbled Bembridge Marls cliff the party drove westwards along the central Chalk ridge and lunch was taken at the 'Hare and Hounds', Downend (SZ 533876). The party then proceeded to the southern side of Gurnard Ledge (SZ 464945), via the private road through Whippance Farm. Here, an almost complete succession of Bembridge Marls (21'5 m, thick) succeeds the Bembridge Limestone and is itself overlain by the Hamstead Beds with the 'Black Band' at the base. The lower part of the succession, which is visible on the foreshore and/or in the low cliff above, is as follows (in descending stratigraphical order; bed numbers after Daley, 1973): GURXI
P. convexa, P. vagus bands in a green to grey clay above and forming shelly limestone below GURX Blue-green marls and clays with shell bands. P. convexa (some in life position) and fewer M. acuta, Mytilopsis sp., P. vagus,P.p/ana). Irregular network of calcite-filledveins near top GURIX Shell band with M. acuta, 'Serpula' sp, and fewer V. lentus, P. turritissima GUR VIII Greenish-grey clay with shelly partings and bands with M. acuta and fewer 'Serpula' sp. ... GUR VII Greenish-grey clay with bands of M. acuta and fewer P. convexa ... GUR VI Grey clay, with shelly bands comprising C. obovata, C. pulchra, P. convexa and fewer M. acuta, Serpula. Band of V. lentus near base ... GURV Laterally continuous shell band, often pyritised, comprising corbiculids, P. vagus. Undulose nature of band reflects varying lithification in underlying division GURIV Flat laminated clays, marls and argillaceous limestone, the latter forming a band near the base, referred to as the 'Insect Limestone' and containing fossil insects, plant remains, P. convexa, Galba sp. GUR III Laterally continuous shell band with corbiculids,P. vagus, Ostrea sp, GURII Grey clays with shelly bands and partings comprising corbiculids, M. acuta, M. fusiformis, Mytilopsis sp., Ostrea sp., P. turritissima, P. vagus, V. lentus ... GURI Laterally continuous shell band, varying in thickness above eroded top of underlying Bembridge Limestone and comprising corbiculids, M. acuta and fewer Ostrea sp., P. vagus
metres 0·3()...()·40
0·42 0·09 0'33 0·30 0·52 0·06
0·79 0·06 0'61-0'79
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Members concentrated their attentions on the 'Insect Limestone' and a number of plant and insect fragments were obtained. The latter included wings of fungus flies (Diptera, Mycetophilidae) and oecophyllid ants , and an insect head capsule. In addition the mould of a fossil feather was found by Mr. M. Barker. Whilst bird bones have already been recorded from local Upper Eocene strata, the Directors are not aware of any previous published record of a fossil feather from the local Tertiary. The irregular nature of the junction between the Bembridge Marls and the underlying Bembridge Limestone was also noted, as were branching burrows extending downwards from the junction, resembling those of Callianassa. The erosion surface had formed when the Bembridge Marls sea transgressed the lacustrine sediments of the Bembridge Limestone, the callianassid burrows being characteristic of transgressive beds in the local Palaeogene strata. Before leaving the locality and dispersing, a vote of thanks was made to the Directors and secretary of the Meeting by the Rev. F. M. Hodgess Roper. The Directors thanked the party for their good wishes and interest during the field trip, and also thanked the secretary, Mr . M. Chaplin, for the very efficient way in which he had made arrangements for the Meeting. Thanks are also due to Mr. Paul Whalley of the British Museum (Natural History) for identifying the insect fossils.
REFERENCES AGER, D. V. 1963. Principles 0/ Paleoecology. McGraw-Hili, New York. BALDI, T. 1973. Mollusc Fauna 0/ the Hungarian Upper Oligocene. Akademiei Kiado, Budapest. BHATIA, S. B. 1957. The Paleoecology of the Late Paleogene Sediments of the Isle of Wight, England. Contr, Cushman Lab. foramin. Res., 8, 11-28. BOSMA, A. A. & A. N. INSOLE. 1972. Theridomyinae (Rodentia, Mammal ia) from the Osborne Beds (Late Eocene), Isle of Wight , England. h oc. K. ned. Akad. Wet . B, 75, 133-44. CoLEMAN, J. M. 1966. Ecological Changes in a Massive Freshwater Clay Sequence. Trans. Gulf-Cst, Ass. geol. S ocs., 16, 159-74. COLENUTT, G. W. 1888. On a Portion of the Osborne Beds of th e Isle of Wight. Geol. Mag. (Ser. 2, dec. 3), 5, 358-62. CRAY, P. E. 1973. Marsupalia, Insectivora, Primates, Creodonta and Carnivora from the Headon Beds (Upper Eocene) of Southern England. Bull. Br, Mu s. nat. . Hist. (Geol.), 23, 1-102. CuRRY, D. 1965. The Palaeogene Beds of South-east England. Proc, Geol. Ass., 76, 151-74. - - - , B. DALEY, N. EDWARDS, F . A. MIDDLEMISS, F. C. SUNTON & C. W. WRIGHT. 1972. The Isle 0/ Wight (3rd edition). Geol. Ass. Guide No. 25. DALEY, B. 1969. A Palaeoenvironm ental Study 0/ the Bembridge Marls (Oligocene) 0/ the Isle 0/ Wight, Hampshire. Unpublished Ph.D. thesis, Unive rsity of Reading. - - - & N. EDWARDS. 1971. Palaeogene Warping in the Isle of Wight. Geol. Mag ., 108, 399-405 .
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DALEY, B. & N. EDWARDS. 1971. Diapiric and Other Deformational Structures in an Oligocene Argillaceous Limestone. Sediment. Geol., 6, 29-51. - - - - , . 1972. Macroinvertebrate Assemblages from the Bembridge Marls (Oligocene) of the Isle of Wight, England, and their Environmental Significance. Palaeogeogr, Palaeoclimatol. Palaeoecol., 11, 11-32. - - - . 1973. The Palaeoenvironment of the Bembridge Marls (Oligocene) of the Isle of Wight, Hampshire. Proc. Geol, Ass., 84, 83-93. DARNELL, R. M. 1961. Trophic Spectrum of an Estuarine Community, Based on Studies of Lake Pontchartrain, Louisiana. Ecology, 42, 553-68. DAVIS, C. A. 1900. A Remarkable Marl Lake. J. Geol., 8, 498-503. ----,.1903. A Contribution to the Natural History of Marl, pp. 65-100. In Marl (Bog Lime) and its Application to Industrial Uses. D. J. Hale & C. A. Davies. Geol. Surv, Mich., Lower Peninsula, 8 (3). DAVIS, J. H., Jr. 1943. The Natural Features of Southern Florida, Especially the Vegetation, and the Everglades. Florida geol. Surv, Bull., 25. EDWARDS, N. 1967. Oligocene Studies in the Hampshire Basin. Unpublished Ph.D. thesis, University of Reading. FAIRBRIDGE, R. W. 1967. Phases of Diagenesis and Authigenesis. In G. Larsen & G. V. Chilingar (Eds.), Diagenesis in Sediments. Elsevier, Amsterdam, 19-89. FORD, R. L. E. 1972. A New Fossil Mammal from the Hamstead Beds (Oligocene). Proc. Isle Wight nat. Hist, archaeol. Soc. (1971), 6, 40<>-1. FOWLER, K. 1971. A New Species of Aglaoreidia Erdtman from the Eocene of Southern England. Pollen Spores, 13, 135-47. - - - , N. EDWARDS & D. W. BRETT. 1973. In situ Coniferous (Taxodiaceous) Tree Remains in the Upper Eocene of Southern England. Palaeontology, 16, 205-17. GAUTIER, H. 1928. Recherches sur la Faune des Eaux Continentales de l'Algerie et de la Tunisie. 419 pp. Paris, Thesis. HUDSON, J. D. & D. F. B. PALFRAMAN. 1969. The Ecology and Preservation of the Oxford Clay Fauna at Woodham, Buckinghamshire. Q. 11geol. Soc. Lond., 124, 387-418. JACKSON, J. F. 1925. Notes on the Upper Headon Beds at Headon Hill, Isle of Wight. Proc. Isle Wight nat. ut«. archaeol, Soc. (1924), 1, 275-89. ----.1927. A Note on the Brockenhurst Bed. Proc, Isle Wight nat. Hist, archaeol. Soc. (1926), 1, 465-6. JAMES, N. P. 1972. Holocene and Pleistocene Calcareous Crust (Caliche) Profiles: Criteria for Subaerial Exposure. I. sedim. Petrol., 42,817-36. KEEN, M. C. 1968. Ostracodes de I'Eocene Superieur et l'Oligocene Inferieur dans les Bassins de Paris, du Hampshire, et de la Belgique, et leur Contribution it l'Echelle Stratigraphique. Mem, Bur. Rech, geol. min., 58, 137-45. - - - - . 1972. The Sannoisian and Some Other Upper Palaeogene Ostracoda from North-West Europe. Palaeontology, 15, 267-325. MARTINI, E. 1970. The Upper Eocene Brockenhurst Bed. Geol. Mag., 107, 225-8. - - - - . 1972. Die Gattung Eosphaeroma (Isopoda) in europaischen Alttertiar, Senckenberg. leth., 53, 65-79. PARKER, R. H. 1964. Zoogeography and Ecology of Macro-invertebrates of the Gulf of California and Continental Slope of Western Mexico. In T. H. Van Andel & G. G. Shor (Eds.), Marine Geology ofthe Gulfof California. Am. Assoc. Pet. Geologists, Tulsa, Okla., 331-76. REINECK, H. E. & F. WUNDERLICH. 1968. Classification and Origin of Flaser and Lenticular Bedding. Sedimentology, 11,99-104. SCHAFER, W. 1962. Aktuo-Palaontologie nach Studien in der Nordsee. Waldemar Kramer, Frankfurt-a.-M. SELLWOOD, B. W. & W. J. KENNEDY. 1970. Ophiomorpha nodosa Lundgren, a Marine Indicator from the Sparnacian of South-East England. Proc, Geol. Ass., 81, 99-110. SKERTCHLEY, S. B. J. 1877. The Geology of the Fenland. Mem, geo!. Surv, U.K. STINTON, F. C. 1971. Easter Field Meeting in the Isle of Wight. Proc, Geol, Ass. 82, 403-10.
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E. B. & H. KEEPING. 1882. On the Beds at Headon Hill and Colwell Bay in the Isle of Wight. Q. II geol, Soc. Lond., 37, 85-127. WEIMER, R. J. & J. H. HoYT. 1964. Burrows of Callianassa major Say, Geologic Indicators of Littoral and Shallow Marine Environments. I. Paleont., 38, 761-7. WHITE, H. J. O. 1921. A Short Account of the Geology of the Isle of Wight. Mem.geol. Surv, U.K. (second impression 1968), H.M.S.O.
TAWNEY,
DALEY, B. & N. EDWARDS, 1974. Week-end Field Meeting: The Upper EoceneLower Oligocene Beds of the Isle of White. Proc. Geol. Ass., 85 (2), 281-292. During the excursion, members studied the lithologies, fossil assemblages and stratigraphy of the Headon, Osborne and Bembridge Beds. On the first field day, the party visited Hatherwood Point and Colwell Bay, to study the Headon Beds brackish and freshwater deposits, and later Hamstead Ledge to examine the Bembridge Marls. On the second day the party first studied the Upper Eocene beds of Whitecliff Bay, including the marine Brockenhurst Bed and later the Bembridge Marls at Gurnard Ledge, where most attention was concentrated on the Insect Limestone. B. Daley, Dept. of Geology, Portsmouth Polytechnic, Portsmouth. N. Edwards, 52 Little Paddocks, Ferring, near Worthing, Sussex.
assembled at the Sentry Mead Hotel, Totland, on the evening of Friday, 6 October. After dinner the Directors briefly described the Upper Eocene-Lower Oligocene beds exposed on the northern coast of the Isle of Wight, and outlined the palaeoenvironmental interpretations proposed in their Ph.D. theses (Edwards, 1967; Daley, 1969). These interpretations were to be discussed during the next two days, by examination of evidence in the field.
TWENTY-TWO MEMBERS
Saturday, 7 October The party first drove to Alum Bay, to examine the Headon Beds (Upper Eocene) exposed at Hatherwood Point (SZ 305860) (see itinerary VIII in Curry, Daley, Edwards, Middlemiss, Stinton & Wright, 1972, 21-3), and descended the steps in Alum Bay Chine to the beach. The bottom of the steps was in Barton Clay (Upper Eocene), the upper beds of which were seen to be truncated by a hitherto unrecorded strike-slip fault hading northwards at about 20°. Walking northwards (down-dip) past exposures in Barton (or Headon Hill) Sands, Messrs A. and C. King found examples of the fossil crustacean 281
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burrow Ophiomorpha nodosa Lundgren, indicative of littoral-marine conditions (Weimer & Hoyt, 1964; Sellwood & Kennedy, 1970). The Directors' discovery of this burrow at Totland Bay (SZ 321866) and on the Hampshire mainland at Barton Cliff (SZ 261923) concurred with other evidence (Curry, 1965), that the sea became very shallow over the whole area before deposition of the Barton Beds ended. Good evidence for subsequent establishment of marsh and swamp conditions was provided by the occurrence of carbonised woody plant roots, exposed by digging, in drab clayey sand (equivalent of Bed L at Barton: Fowler, 1971) overlying the Barton Sands. These had also been seen by the Directors in Bed L at Barton, while equivalent beds in Totland Bay had yielded remains of swamp-growing conifers (Fowler, Edwards & Brett, 1973). At Hatherwood Point the cliff comprises a series of muddy terraces in almost flat-lying Headon and Osborne Beds. The Headon Beds succession was described recently by Stinton (1971) and Cray (1973, 20) and the Osborne Beds by Bosma & Insole (1972). Although slipped mud concealed much of the Lower Headon Beds (27 m.), members could see characteristic lithologies exposed in the lower 7 m. and upper 6 m. Greenish silty and sandy clays and marls were interbedded with pale brown, chalky, micritic limestones 0·25 to 2 m. thick. Some limestones appeared to be transitional to underlying marls, others rested on thin clayey lignite layers. Upper surfaces of limestones were irregular, sometimes strewn with limestone pebbles. The limestones were notable for an abundance of pulmonatesnail shells (Galba and Planorbina spp.), whilst the clays and marls contained Viviparus lentus (Solander), Bithynella sp., Melanoides acuta (1. Sowerby) and, in one bed overlying a limestone, Corbicula pulchra (1. Sowerby) and Dreissena brardii (1. Sowerby). Scutes of pond-turtle (Emys sp.) were picked up from clay surfaces; the remains of Trionyx (soft-shelled turtle), Diplocynodon (alligator), Lepisosteus (gar), Amia (bow-fin) and teeth of Theridomys (rodent) have also been found. The molluscs are characteristic of freshwater lakes, ponds and streams, while the vertebrate assemblage resembles that of these habitats in the southeastern United States. The Directors remarked that the succession appeared to represent the deposits of a river flood-plain lake: the clayey deposits could be analogous to those described by Coleman (1966) from southwestern Louisiana, while the limestones compared well with modern lake 'marls' (lime muds) in the Cambridgeshire fenlands (Skertchley, 1877), small Michigan lakes (Davis, 1900; 1903) and south Florida marshes (Davis, 1943; N. Edwards, personal observations). This interpretation agrees well with palaeobotanical evidence for extensive coastal flood-plain conditions (Fowler, Edwards & Brett, 1973). The 2 m. 'How Ledge Limestone' near the top of the Lower Headon Beds was well exposed, yielding characteristic fossils. The overlying 2 m.
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of drab marly clay was shown, by digging, to contain irregular borings up to 30 mm. diameter, filled by black shelly sandy clay. These descend from the base of the Middle Headon Beds. The Directors noted that they resemble marine crustacean (Callianassa) borings figured by Schafer (1962, fig. 186), and that they occur in the same stratigraphical position at other localities on the island. The Middle Headon Beds (over 9 m.) were well exposed, comprising greenish and blue sandy clays and sands, drab black and brown below (2 m.), and with a discontinuous freshwater limestone (0'3 m.) at 4 m. from the top. Although at first sight much richer in molluscan species than the Lower Headon Beds, there was an overwhelming numerical dominance of cerithids (Batil/aria and Potamides spp.), oysters (Ostrea velata Wood) and corbiculids (Corbicula obovata (J. Sowerby)). Similar associations occur today in tropical-subtropical estuarine and coastal river-influenced lagoons (Parker, 1964), as in Tabasco, Mexico, where Batil/aria minima Gmelin crawls in myriads on the mud-flats (N. Edwards, personal observation). The Middle Headon development here was interpreted, therefore, as a seaward, marine-influenced aspect of the Lower Headon flood-plain lake environment. Evidence for a period of subaerial exposure and erosion during deposition of the Upper Headon freshwater limestones (9 m.) was the final point examined at this locality. A very irregular topographic surface, with up to 3 m. relief, was easily traced within the limestone series by the occurrence of a lignitic clay bed (1 m.), which thinned-out over 'high' areas. Welllithified limestone nodules and slab-like masses from these high areas occurred also as 'boulders' and cobbles in the lignitic bed, apparently having been undercut by erosion during deposition of the lignite mud. Colour-banded micritic 'crusts', first noted by Jackson (1925), who described this section, were found to be associated with this and other erosion surfaces in the limestones. Similar crusts on limestone surfaces in the Caribbean have been cited by James (1972) as criteria for subaerial exposure. The lignitic bed was found to include bands of crushed planorbid shells, and since it contains remains of aquatic vertebrates like those in the Lower Headon Beds, can be interpreted as a lacustrine deposit. The occurrence of terrestrial mammal remains (Cray, 1973) suggests proximity to land. A limestone bed 1 m. above the lignitic bed yielded good specimens of Theodoxus, Melanopsis and Melanoides, an association found today in shallow-water ponds and canals in North Africa (Gautier, 1928). After lunch, the party drove to Colwell Bay (SZ 327878), to examine the Middle and Upper Headon Beds (see itinerary IX in Curry and others, 1972).Leaving the vehicles in the car-park, the members walked northwards (down-dip) along the shore. The 'How Ledge Limestone', near the top of the Lower Headon Beds, was well exposed behind the beach-huts and PROC. GEOL. ASS., YOLo 85, PART 2,1974
19
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formed How Ledge on the foreshore. The basal Middle Headon 'Neritina Bed' was covered by down-washed mud, but its characteristic fossils (Theodoxus, Potamides, Corbicu/a) were collected from rain-washed mud surfaces and as sea-washed specimens from the foreshore. Just north ofthe huts a large mass of the 'Oyster Bed' was seen, detached from the cliff. The oyster (0. velata) valves constituted about 90 per cent of the deposit, being packed together in a sandy matrix and clearly not in growth position. Present lack of exposures hinders the study of this interesting deposit, which White (1921) interpreted as a channel-fill in the 'Venus Bed'. The best section in the Middle Headon Beds was seen at Brambles Chine (SZ 330883), as described by Stinton (1971). The blue-grey clayey-sand matrix of the 'Venus Bed' (2 m.) was studded with creamy coloured mollusc shells, notably the paired valves of the typical fossil, Sinodia (' Venus') suborbicularis, of which 60 per cent are in life position (Ager, 1963, 87). Although the overall aspect of the assemblage was marine, the large numbers of oysters, corbiculids and cerithids, coupled with a lack of echinoids and corals, suggested inshore, muddy, river-influenced conditions. The Upper Headon Beds in Colwell Bay (14 m.) lack the thick limestone series seen at Hatherwood Point. Instead, the lowest 4 m. comprises sands, silts and clays, visible along the whole length of the section. These sediments are divisible lithologically into two: a lower, darker more clayey part and an upper, light coloured, more sandy part. The lower part comprises laminated, mainly grey clays, silts and sands, resting on a sharp erosion surface at the top of the Middle Headon Beds. Towards the base are bands of Potamomya sp., a bivalve often referred to the fluvio-estuarine genus Erodona. The upper sandy part was the subject of considerable interest to members. A number of sedimentary structures were pointed out by the Directors, including large- and small-scale cross-stratification, layers of asymmetrical ripples, some showing uniform current orientation, others showing herringbone structure, and less commonly scours with clay pellets, and flat lamination. Flaser bedding of varying types (see Reineck & Wunderlich, 1968) was a feature of the sands. The flasers comprised carbonaceous material in addition to clay, particularly near the upper part of the unit, where laterally continuous carbonaceous laminae also occurred in some places. It was noted that iron staining in the sand often occurred above the flasers or laminae of similar composition, which presumably had led to the formation of small-scale perched water tables. The general absence of bioturbation was, with few exceptions, noteworthy. The top of the sand is marked by an undulose erosion surface, with rusty, sandy concretions or clasts occurring above it. Small vertical roots extended for a distance of
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about 100 em, downwards from this surface. Occasional narrow and sometimes branching cracks extended downwards from this surface. These bore no resemblance to those formed by desiccation and might reflect penecontemporaneous tension cracks formed by the lateral movement of cohesive sediment at the time of deposition. The Directors suggested that the features of the deposit indicated an intertidal environment in perhaps a brackish-water bay. Farther north, at Linstone Chine (SZ 330886), the small, very steep, faulted fold in the Upper Headon Beds was noted. Beyond it, the succession in the upper part of the Upper Headon Beds, described by Tawney & Keeping (1882), was well displayed. The succession of drab silty clays and sands, with only two thin limestone beds, yielded molluscan fossils abundant in numbers but poor in species. Among these were corbiculids, cerithids, Viviparus, Unio and, most notably, Potamomya. The Directors remarked that these Potamomya-Viviparus deposits predominate in the Upper Headon Beds over most of the outcrop area (including the New Forest), and overlie the thick limestone series at Hatherwood Point. They pass up into the equally widespread, mottled green and red clays of the Osborne Beds, badly exposed at the north end of Colwell Bay. The wide extent of these drab Upper Headon deposits, and their mixed assemblage of freshwater and brackish molluscs, suggested analogy with 'estuarine' Lake Pontchartrain, in south-east Louisiana, which suffers marine incursions and large influxes of river flood-water (Darnell, 1961). After tea at Yarmouth, the members were joined by Mr. R. L. E. Ford, a local palaeontologist specialising in the Harostead Beds. The party then continued to Hamstead Ledge (SZ 401920), via the private road which joins the A3054 at SZ 402892. After parking at Harostead, members descended to the shore by the public footpath. Hamstead Ledge is formed of three freshwater limestone beds in the Bembridge Limestone, overlying the Osborne Beds. The uppermost of these limestones, exposed in a low bank, was seen to contain moulds of Galba and Planorbina spp. To the west of Hamstead Ledge the whole of the Bembridge Marls and part of the overlying Harnstead Beds were exposed on the foreshore, since the visit had been planned to coincide with the equinoctial spring tide when these beds become visible at low water. Part of the succession was also visible in the adjacent cliff-section. The Bembridge Marls here comprise approximately 21'5 m. of fresh- and brackish-water sediments, mainly clays and silts, with a profuse but taxonomically restricted molluscan fauna (see Daley, 1972). Considerable interest was shown in the brackish-water sediments immediately overlying the undulose erosion surface at the top of the underlying Bembridge Limestone. This part of the succession is, in descending stratigraphical order, as follows (bed numbers from Daley, 1973):
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HAM X
Green clay with Polymesoda convexa (Brongniart) pre- metres dominant, Melanopsisfusiformis(J. Sowerby), Melanoides acuta (J. Sowerby), Potamaclis turritissima (Forbes) ... 0·61 HAM IX Olive brown mottled clay with ostracod partings and lensoid concentrates, sometimeslithified 0·97 HAM VIII Dark grey mottled clays with ostracods on partings and within polygonal cracks, passing down into clays with partings and bands containing corbiculids, M. acuta, Mytilopsis sp., P. turritissima
HAM VII Light green marl. P. convexa, sometimes in life position, M. acuta, resting on mud-crackedsurface HAM VI Blue-green claywith shellypartingsand bands containing Mytllopsis sp., P. convexa and fewer M . acuta, M. fusiformis, Potamides vagus (Solander) HAM V Greenish-grey clay with bands containing M. acuta, Serpula sp., Viviparus lentus (Solander) ... HAM IV Grey clay with shelly partings and bands containing P. convexa, Corbicula sp, and also M. acuta HAM III Laminated grey clay with complexsystem of cracks HAM II Grey and black clayswith shellypartings and bands with M. acuta, P. convexa, P. vagus and, less commonly, M. fusiformis, Vi lentus
HAM I
0·82
0·06 0·30 0·30 0·46
0·15 0·30
Bleached shell band containing corbiculidsand Ostrea sp. forminga cap on the surfaceof the underlying Bembridge Limestone ... 0·03-0·06
The Directors explained that following the freshwater conditions of Bembridge Limestone times, the sea had transgressed this area from the east and that bed HAM I was the lateral equivalent of the Bembridge Oyster Bed in Whitecliff Bay. There is no clear palaeontological evidence that fully marine salinities were reached at this locality at this time, for the assemblages are restricted to few taxa, and comprise mainly brackish water types. It was pointed out that the assemblages from this part of the succession are comparable with those of brackish water, tropical and subtropical mudflats at the present day (Daley, 1972). Considerable interest was shown in the different types of fossil preservation at this stratigraphical level. In the grey to black, more or less pyritic clays, shells are well preserved, but in the blue-green clays, they are chalky and very friable. The Directors explained that this variation in preservation was apparent in the brackish-water facies at a number of different horizons and localities. It was suggested that the dark colour of the grey clays might have been a primary feature, although it seemed more likely that it had developed in sediments which had passed rapidly through the initial aerobic stage of diagenesis to the anaerobic early burial stage (cf. Fairbridge, 1967) where, under high pH and low Eh, calcium carbonate is stable and FeS (afterwards FeS2) is precipitated. The pyritised surfaces of the shells examined from bed HAM II were thought by the Directors to
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represent the effect of reducing conditions adjacent to decaying shell periostracum (cf. Hudson & Palframan, 1969,404). Freshwater, lacustrine clays higher up the succession were also examined. Beds HAM XXIII-XXV (Daley, 1973) proved to be of most interest since they contain abundant water-plant seeds (Brasenia, Stratiotesy and monocotyledonous leaf fragments, which are mainly concentrated in partings and bands together with freshwater gastropods such as Viviparus and the pulmonate Galba and Planorbina. Their occurrence may reflect the settling out of locally derived life associations eroded during storms. The 'Black Band', which traditionally defines the base of the Hamstead Beds, was examined by some members of the party. It contains freshwater gastropods such as Viviparus and has an autochthonous root system extending downwards from its underside. It should not be confused with another black, lignitic clay (the Nematura Bed) somewhat higher up the Hamstead Beds succession, which has a distinctive brackish-water molluscan fauna. Mr. Ford remarked on the number of mammalian species in the Hamstead Beds which do not occur in older deposits on the island, but which are well known on the Continent from deposits referred to the Lower Oligocene (see also Ford, 1972). Sunday, 8 October The party drove initially to Whitecliff Bay (SZ 642863) to see the Headon, Osborne and Bembridge Beds (see Itinerary I in Curry & others, 1972, 3-5). The Bay was approached via the footpath from Hill Way (Whitecliff Bay Hotel), whilst the vehicles were taken to the next access point, at Howgate Lane (SZ 646871). The party walked northwards (down-dip) from the cliff steps, passing cliffs in the weathered Barton Clay and Barton Sands. The lignitic equivalent of Bed L at Barton was seen to be overlain by only about 8 m, of Lower Headon Beds (A to F of Stinton, 1971), here lacking limestones but otherwise of similar lithology to these beds at Hatherwood Point. The basal Middle Headon 'Brockenhurst Bed' (0'15 m.) (G of Stinton, 1971) was exposed by digging in the cliff. The underlying erosion surface, described by Jackson (1927), and irregular borings in bright green Lower Headon clay (F), were well seen. The borings were full of shelly clayey sand, like that of the 'Brockenhurst Bed'. This latter yielded a number of marine mollusc species, notably Ostrea ventilabrum Goldfuss and Cardita deltoidea (J. Sowerby). The total assemblage of over one hundred species of marine mollusca, several corals, and echinoids, is the largest in the Headon Beds. A similar assemblage in the Upper Oligocene of Hungary has been classified as shallow sublittoral, with salinity> 30 ppm. (Baldi, 1973, 114--15).The microfauna, however, is poor in species by comparison with true open-sea facies (Bhatia, 1957; P. Vella
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and M. Keen, personal communications). The Directors noted that although certain molluscan species in the 'Brockenhurst Bed' have apparent Lower Oligocene affinities, the weight of evidence from Ostracoda (Keen, 1968; 1972), Mammalia (Cray, 1973; Ford, 1972), calcareous nanno-plankton (Martini, 1970) and isopods (Martini, 1972) placed the Eocene-Oligocene boundary higher, probably in the Bembridge MarlsHamstead Beds succession. Ascending the Middle Headon succession, the molluscan assemblage becomes temporarily depleted in a weathered series of clayey fine sands (H to K of Stinton, 1971), comprising only burrowing bivalves (Gari, Sinodia, Cardita). A richer assemblage seen in the overlying beds (L to 8 of Stinton, 1971) included cerithids, corbiculids and O. velata, being more like that of the western localities. The Upper Headon to Bembridge Marls part of the succession was examined in less detail. The Potamomya- Viviparus deposits of the Upper Headon were notable for their thick shell beds, picking out the 60-70° northerly dip of the strata. The Osborne Beds succession beyond, described by Bosma & Insole (1972), were predominantly slipped, green and red clays or marls, with thin creamy coloured chalky limestones, almost devoid of fossils. A grey and brown series (7' 5 m.) near the middle was pointed out as containing Viviparus, Melanopsis, Melanoides and Unio. Traceable in coastal and borehole sections to Hatherwood Point, it has yielded mammals, reptiles, fishes, crustaceans and plants, notably at Wootton Creek (Colenutt, 1888). Resemblance of the Osborne Beds to the Wealden Marls (Lower Cretaceous) and the Keuper Marls, for which the palaeoenvironment is better known, suggested relatively land-locked, shallow-water, lacustrine conditions. An examination of the Bembridge Limestone (8'5 m.) provided good evidence for a lacustrine interpretation. 'Chara' oogonia and moulds of freshwater snails (Galba, Planorbina spp.) were abundant, in lithologies resembling those of the Lower Headon limestones. A clay series in the middle of the Bembridge Limestone included a thin layer of Corbicula, Potamides and Melanoides. The Directors have traced this as far west as Hamstead Ledge. A conglomeratic white limestone at the top of the succession was pointed out as being, by contrast, of very local occurrence. It was perhaps deposited during a period of erosion, following a minor phase of tectonic warping postulated by Daley & Edwards (1971). In Howgate Bay the party examined the overlying Bembridge Marls (Beds WH I-IX, Daley, 1973), visible just above the foreshore. The Directors pointed out that at this locality the 'Bembridge Oyster Bed' (Bed WH II), which in other sections rests directly on the eroded top of the Bembridge Limestone, is here underlain by a blue-green clay (Bed WH I) with brackish-water fossils. The 'Bembridge Oyster Bed' was laid down
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during the last but one of the local Palaeogene transgressions for which evidence still exists, but the fauna is restricted to few taxa, including Ostrea sp. (often bored by the sponge Cliona or encrusted by bryozoa, serpulids and, less commonly, barnacles) and a few other molluscs. An argillaceous limestone, containing small-scale diapiric structures (part of Bed WH III), was briefly examined (see Daley, 1971); this is the equivalent of the 'Insect Limestone' of some north-eastern coastal localities, which the party was to see later in the day. After climbing the tumbled Bembridge Marls cliff the party drove westwards along the central Chalk ridge and lunch was taken at the 'Hare and Hounds', Downend (SZ 533876). The party then proceeded to the southern side of Gurnard Ledge (SZ 464945), via the private road through Whippance Farm. Here, an almost complete succession of Bembridge Marls (21'5 m, thick) succeeds the Bembridge Limestone and is itself overlain by the Hamstead Beds with the 'Black Band' at the base. The lower part of the succession, which is visible on the foreshore and/or in the low cliff above, is as follows (in descending stratigraphical order; bed numbers after Daley, 1973): GURXI
P. convexa, P. vagus bands in a green to grey clay above and forming shelly limestone below GURX Blue-green marls and clays with shell bands. P. convexa (some in life position) and fewer M. acuta, Mytilopsis sp., P. vagus,P.p/ana). Irregular network of calcite-filledveins near top GURIX Shell band with M. acuta, 'Serpula' sp, and fewer V. lentus, P. turritissima GUR VIII Greenish-grey clay with shelly partings and bands with M. acuta and fewer 'Serpula' sp. ... GUR VII Greenish-grey clay with bands of M. acuta and fewer P. convexa ... GUR VI Grey clay, with shelly bands comprising C. obovata, C. pulchra, P. convexa and fewer M. acuta, Serpula. Band of V. lentus near base ... GURV Laterally continuous shell band, often pyritised, comprising corbiculids, P. vagus. Undulose nature of band reflects varying lithification in underlying division GURIV Flat laminated clays, marls and argillaceous limestone, the latter forming a band near the base, referred to as the 'Insect Limestone' and containing fossil insects, plant remains, P. convexa, Galba sp. GUR III Laterally continuous shell band with corbiculids,P. vagus, Ostrea sp, GURII Grey clays with shelly bands and partings comprising corbiculids, M. acuta, M. fusiformis, Mytilopsis sp., Ostrea sp., P. turritissima, P. vagus, V. lentus ... GURI Laterally continuous shell band, varying in thickness above eroded top of underlying Bembridge Limestone and comprising corbiculids, M. acuta and fewer Ostrea sp., P. vagus
metres 0·3()...()·40
0·42 0·09 0'33 0·30 0·52 0·06
0·79 0·06 0'61-0'79
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Members concentrated their attentions on the 'Insect Limestone' and a number of plant and insect fragments were obtained. The latter included wings of fungus flies (Diptera, Mycetophilidae) and oecophyllid ants , and an insect head capsule. In addition the mould of a fossil feather was found by Mr. M. Barker. Whilst bird bones have already been recorded from local Upper Eocene strata, the Directors are not aware of any previous published record of a fossil feather from the local Tertiary. The irregular nature of the junction between the Bembridge Marls and the underlying Bembridge Limestone was also noted, as were branching burrows extending downwards from the junction, resembling those of Callianassa. The erosion surface had formed when the Bembridge Marls sea transgressed the lacustrine sediments of the Bembridge Limestone, the callianassid burrows being characteristic of transgressive beds in the local Palaeogene strata. Before leaving the locality and dispersing, a vote of thanks was made to the Directors and secretary of the Meeting by the Rev. F. M. Hodgess Roper. The Directors thanked the party for their good wishes and interest during the field trip, and also thanked the secretary, Mr . M. Chaplin, for the very efficient way in which he had made arrangements for the Meeting. Thanks are also due to Mr. Paul Whalley of the British Museum (Natural History) for identifying the insect fossils.
REFERENCES AGER, D. V. 1963. Principles 0/ Paleoecology. McGraw-Hili, New York. BALDI, T. 1973. Mollusc Fauna 0/ the Hungarian Upper Oligocene. Akademiei Kiado, Budapest. BHATIA, S. B. 1957. The Paleoecology of the Late Paleogene Sediments of the Isle of Wight, England. Contr, Cushman Lab. foramin. Res., 8, 11-28. BOSMA, A. A. & A. N. INSOLE. 1972. Theridomyinae (Rodentia, Mammal ia) from the Osborne Beds (Late Eocene), Isle of Wight , England. h oc. K. ned. Akad. Wet . B, 75, 133-44. CoLEMAN, J. M. 1966. Ecological Changes in a Massive Freshwater Clay Sequence. Trans. Gulf-Cst, Ass. geol. S ocs., 16, 159-74. COLENUTT, G. W. 1888. On a Portion of the Osborne Beds of th e Isle of Wight. Geol. Mag. (Ser. 2, dec. 3), 5, 358-62. CRAY, P. E. 1973. Marsupalia, Insectivora, Primates, Creodonta and Carnivora from the Headon Beds (Upper Eocene) of Southern England. Bull. Br, Mu s. nat. . Hist. (Geol.), 23, 1-102. CuRRY, D. 1965. The Palaeogene Beds of South-east England. Proc, Geol. Ass., 76, 151-74. - - - , B. DALEY, N. EDWARDS, F . A. MIDDLEMISS, F. C. SUNTON & C. W. WRIGHT. 1972. The Isle 0/ Wight (3rd edition). Geol. Ass. Guide No. 25. DALEY, B. 1969. A Palaeoenvironm ental Study 0/ the Bembridge Marls (Oligocene) 0/ the Isle 0/ Wight, Hampshire. Unpublished Ph.D. thesis, Unive rsity of Reading. - - - & N. EDWARDS. 1971. Palaeogene Warping in the Isle of Wight. Geol. Mag ., 108, 399-405 .
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