The stratigraphy of the ‘Corallian’ facies Middle Oxfordian (Upper Jurassic) deposits at Upware, Cambridgeshire, England

The stratigraphy of the 'Corallian' facies Middle Oxfordian (Upper Jurassic) deposits at Upware, Cambridgeshire, England J. K. Wright*, S. R. A. Kellyt and K. N. Paget WRIGHT, J. K., KELLY, S. R. A. & PAGE, K. N. 2000. The stratigraphy of the 'Corallian' facies Middle Oxfordian (Upper Jurassic) deposits at Upware, Cambridgeshire, England. Proceedings of the Geologists' Association, 111, 97-110. At Upware, Cambridgeshire, an inlier of 'Corallian' facies Middle Oxfordian limestone within the more typical mudrock-dominated West Walton Formation sequence of the East Midlands Shelf, forms a topographic feature of low relief for 6 km. Recent deep excavations in the district have revealed the base of these beds, not exposed since the last century. They and the underlying mudrock have yielded prolific bivalve faunas and common ammonite faunas, including both Boreal (Cardioceratidae) and Tethyan (Perisphinctinae) elements. The stratigraphy of these Middle Oxfordian deposits is revised, and the palaeoenvironment of the benthic macroinvertebrate faunas of the succession is discussed. The Boreal bivalve Praebuchia lata (Trautschold), a new record of biostratigraphic significance, is described and figured. *Department of Geology, Royal Holloway, University of London, Egham, Surrey TW20 OEX. tJO, Belvoir Road, Chesterton, Cambridge CB4 iu. §English Nature, The Old Mill House, 37 North Street, Okehampton, Devon EX20 JAR.

1. INTRODUCTION

The Corallian rocks of Upware outcrop in a narrow, lowlying ridge stretching for some 6 Ian along the eastern side of the River Cam, and rising only 5-10 m above the surrounding fens. The rocks are mainly relatively soft and poorly cemented, so that there are no natural exposures. At least four documented quarries or pits have been opened at various times. These four workings are named North Pit [TL 544 728], Dimmock's Cote Quarry (formerly Bridge Pit North [TL 545 724]), Bridge Pit South [TL 542 722] and Commissioners' Pit, otherwise known as Upware South Pit [TL 539 708] (Fig. 1). North Pit and Bridge Pit South no longer show useful exposures, being respectively grassed over or largely infilled. The strata in Commissioners Pit are, at present, well exposed, being actively maintained by the Upware Field Studies Centre, Cambridgeshire County Council. Dimmock's Cote Quarry is being actively worked by the Wicken Lime and Stone Co. Ltd. Both the latter exposures are protected as Sites of Special Scientific Interest under the 1981 Wildlife and Countryside Act. For over 100 years, these Corallian sections have presented problems to stratigraphers. Variations in facies and thickness are extreme, so that each of the occasional temporary sections that has become available (Roberts, 1892; Wedd 1898; Rastall 1909; Arkell 1937) seems to have presented as many new problems as it has solved old ones. Recent reviews of the geology of the area (Worssam & Taylor 1969; Gallois & Cox 1977; Wright 1980; Kelly 1985) have been based largely on the early work and records, combined with studies of poorly located Proceedings of the Geologists' Association, 111,97-110.

ammonites in museum collections. It is not surpnsmg that the conclusions of these authors have conflicted, and that no definitive picture has emerged. The general stratigraphic succession at Upware is shown in Fig.2. In 1993, quarrying began at a deeper level at Dimmock's Cote Quarry, exposing a 0.6 m thick bed of limestone which yielded numerous ammonites (Perisphinctes spp. and Cardioceras spp). Trial holes in the base of the pit revealed several metres of underlying marls never exposed previously at Upware. A fauna of Perisphinctes and Cardioceras, different in important aspects from that found above, was collected from these latter beds. The faunas from Dimmock's Cote Quarry, including the extensive museum collections of ammonites collected over many years from the higher beds, have become of considerable importance in attempts to unravel the complicated history of the Tethyan perisphinctid and Boreal cardioceratid faunas in the British Middle Oxfordian. In 1995, the bivalve Praebuchia lata was collected from Bed 6 at Dimmock's Cote Quarry. This is a very widespread boreal species which has been recorded under a variety of names (see below) in Yorkshire and Scotland, and from Greenland through Siberia to NE Russia, but not previously so far south as the Midlands. In England, its range appears to be restricted to the Cordatum-Glosense zones of the Oxfordian (see Appendix). The bivalve assemblages are otherwise much more typical of Tethyan limestone deposits including such forms as Opis (Coelopis), O. (Trigonopis) and Coelastarte. For full faunal list see pp. 101, 102. 0016--7878/00 $15·00 © 2000 Geologists' Association

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J . K . W R IG H T ET AL.

PERIOD STAGE AGE 112

Aptian 124

0

Barremian

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LITHOSTRATIGRAPHY

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- L2.!'&.Greensand GD

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135-

Valang inian

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141

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SandringhamSandsFm? ,I (clasts In Lower Greensand)

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Volglan 152

Kimme ridgian

Kimmeridge Clay Fm \.

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Callovian

West Walton Fm

Upware Limestone Mbr

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Dimmock's Cote Marl Mbr Lower Elsworth Mbr Oxford Clay Fm

Fig. 2. The lithological succession at Upware showing the stratigraphic relatio nships between the Upware Limestone Member with adjacent strata. Vertical bars represent major nonsequences, although some evidence for the former presence of missing strata lies in the reworked horizons of the Lower Greensand and Gault. Ages in Ma after Harland et al. Armstroy, Cox, Craig, Smith & Smith (1990).

El Gault Clay Fm

_

Ampthill Clay Fm

t:"':"·:':·:"1 Lower

r---l West Walton :.''':.''':.''':.'. Greensand Gp L.----.J Formation

, " Kimmeridge ',' ,',' Clay Fm Fig. 1. Sketch map of the solid geology of the Upware area (after BGS Sheet 188, Cambridge), showing the localities mentioned in the text.

2. LITHOSTRATIGRAPHY West Walton Formation Following Gallois & Cox (1977), the beds between the Oxford Clay and the Ampthill Clay in the Upware area are assigned to the West Walton Formation, the base of which is not exposed here at present. Three members are recognized: Lower Elsworth Member Up to 2 m of dark grey clay with ferruginous ooids and thin bands or nodules of argillaceous limestone, also with

ferruginous ooids, were formerly exposed in a well section at Upware, and in a ditch south of Upware (Wedd, 1898). These are assigned to the Lower Elsworth Member of Page (1986). Traces of the unit are still visible at its type locality near Papworth Everard, west of Upware. Dimmock 's Cote Marl Member (new name) More than 4 m of grey, sparsel y fossiliferous marl containing concretions and thin bands of argillaceo us limestone were exposed in temporary sections in sumps A and B (Fig. 3) in the base of Dimmock's Cote Quarry [TL 545 724] in 1993-5. Normally only the top c. I m of the member is currently exposed in the pit. Southwards, the member thins to 1.5 m in a temporary section in the Commissioners Pit (Rastall, 1909), and 0.75 m in a temporary section north of Upware (Wedd, 1898) (see Fig. 6). At both these localities there was the substantial deve lopmen t of coralliferous limeston e lenses with Thecosmilia. Upware Limestone Member This member was first informally termed the 'Upware limestone' by Seeley (186 1) and more formally as the ' Upware Limestone' (Seeley, 1869, p. 2). The name appears to have been little used subsequently until the compilation of the Jurassic correlation table of Wright (1980) and was again used by Kelly (1985). Blake &

99

STRATIGRAPHY O F DEPOSITS AT UPWARE , C AMBRIDGESHIRE

100 m

N

working floor of pit on Crinoid Beds

::::---

r

_

flooded

Wicken ~ Dimmock's Cote

Marl Mbr exposed

0

Upware Limestone Member

Fig. 3. Sketch map of Dimmock's Cote Quarry in May 1997, showing the distribution of the Upware Limestone Membe r and the area where it had been worked out expo sing the underlying Dimmock's Cote Marl Member.

Hudleston (1877) referred to it as 'The Limestone of Upware ' , but generally preferred to refer to it as the 'Coral Rag' , or the 'Corallian ', as have most subsequent workers. The Upware Limestone was formally included as a member, with other silty and calcareous strata including the 'Lower Elsworth Series' , within the West Walton Beds (now Formation) of Gallois & Cox ( 1977). Up to 9 m of the Upware Limestone Member is exposed in Dimmock's Cote Quarry, which may be taken as its type section. A summary of the succession here is given in Fig. 4. The lowest beds consist of relatively hard limestone rich in crinoid debris, named here the Crinoid Bed (0.6 m), with a basal conglomerate (the Sponge Bed) of reworked sponges, bivalves and ammonites. These are succeeded by 7-8 m of very variable, relatively soft oobiomicrites which consist of variably fossiliferous, ooidal and locally argillaceous limestone (4 m), still with crinoid debris. This is succeeded by a 0.6 m bed of slightly harder coral reef-framework limestone , the Coral Bed, which is exposed only on the western side of the pit (Fig. 3). Above, there is a return to relatively soft oobiomicrites. In Commissioners' Pit, the Coral Bed consists of 1 m of reef-framework limestone, and this may be taken as the type locality.

Younger deposits The Ampthill Clay has been seen overlying the Upware Limestone at Bridge Pit South, but no useful exposures exist at present. Historically, Lower Cretaceous Lower Greensand and Gault have been seen lying unconformably upon the member, which appears to have been acting as an area of local topographic relief on the Early Cretaceous sea floor and over which a certain amount of draping of

these younger deposits has occurred . Just south of Commissioners' Pit Gault with the belemnite Neohibolites minimus (Miller) has recently been dredged from the floor of lakes [TL 537 706] at topographic levels below that of the top of the limestone. This draping is shown exaggerated in Fig. 5. Elements of the Sandringham Sands faunas, such as the bivalve Dicranodonta vagans (Keeping), have been found reworked in the base of the Lower Greensand which suggests that the Sandringham Sands could originally have existed as far south as this or that clasts have been current-transported from the margins of the Spilsby Basin in Aptian times (Kelly, 1984, 1985). Immediately north of Commissioners ' Pit, phosphatized fragments of pavlovid-like ammonites are also present in the basal Lower Greensand conglomerate, but it is not clear if these are of true Pavlovia of Late Kimmeridgian sensu anglico (= Bolonian sensu Cope, 1993) age.

3. THE SECTION IN DIMMOCK'S COTE

QUARRY Work at Dimmock's Cote Quarry has proceeded at a considerable rate in recent years. The basal Crinoid Bed of the Upware Limestone is one of the toughest levels and forms the lower working floor of the quarry. As quarrying continues, the Crinoid Bed is being stripped off in an easterly direction. Two sumps have been excavated for draining the site and in April 1995 two of the present authors, SRAK and KNP, arranged to have the one in the northeast of the quarry drained. They were able to log a section 5.25 m into the underlying Dimmock's Cote Marls. Ex situ traces of the latter remain around the sites of the sumps and along the sides of the drainage ditches connecting them (1996).

100

J . K . WRIGHT ET AL.

Lithostratigraphy and zonal biostratigraphy

weathering profile

bed name

bed number

palaeoenvironment

location in pit

weathering zone and topsoil

10

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Fig. 4. Summary of the succession at Dimmock's Cote Quarry based on recent observations.

dredged mudstones from below water level in sumps

..i- Thalassinoides burrows

STRATIGRAPHY OF DEPOSITS AT UPWARE. CAMBRIDGESHIRE

101

E

W

'Isle' of Upware

River Cam

Wicken Sedge Fen

West Walton

Dimmock's Cote Marl Member

Fm

Lower Elsworth Member

not to scale

Fig. 5. Schematic cross-section of the Upware Inlier showing idealized relationships between the lithostratigraphic divisions. Note the unconformities at the bases of the Gault and Lower Greensand units. LGS, Lower Greensand Group.

bernardi (Chavan), Gastrochaenolites (bivalve borings in coral»; gastropods (Bathrotomaria reticulata (J. Sowerby), Trochotoma? tornatillis (Phillips), Buckmania erinus (d'Orbigny), Bourgetia saemanni (Oppel), Pseudomelania headingtonensis (J. Sowerbyj); echinoids (Cidaris' smithii (Wright), Paracidaris florigemma (Phillips»; annelids (Serpula deplexa Phillips, S. sulcata (1. Sowerby), Trypanites (annelid borings in corals»; corals (Fungiastraea arachnoides (Parkinson), lsastraea explanata (Goldfuss); Microsalenia thurmanni Koby, Microsalenia foliosa Roniewicz, Montlivaltia dispar Phillips, Thamnasteria concinna (Goldfussj), sponges (Holcospongia glome rata (Quenstedt), Cliona sp. (sponge borings in corals»; and bryozoa (Terebripora sp. (borings in bivalve shell». 0.6 m

The section exposed in Dimmock's Cote Quarry is as follows: WEATHERING ZONE 10. Brown, pebbly loam and soil, with diffuse contact with limestone below: (note: in places an apparent greater thickness is due to mounding as bunds as part of the quarrying operations).

up to

c. 1.5 m seen

WEST WALTON FORMATION UPWARE LIMESTONE MEMBER 9. Cream-coloured, fossiliferous, soft, pisolitic oobiomicrite, laminated on a 5-10 em scale with regular alternations of micritic and shell-fragment rich bands. Shelly bands in the upper part include reef-phase gastropods and bivalves preserved as moulds of originally aragonitic shells in micritic limestone. Though fossils were not collected from this bed during the course of this survey, Bed 9 has historically yielded the rich faunas of Dimmock's Cote Quarry, and a complete faunal list, based on museum collections, is given below (p. 102). 3-5 m (merges into Bed 7 in E of pit) CORAL BED 8. Coarse, bioclastic, coral-rich limestone (seen only on the west of the pit) and yielding bivalves (Eonavicula quadrisulcata (1. de C. Sowerby), Barbatia (B.) pectinata (Phillips), Grammatodon (G.) aemulum (Phillips), Lithophaga (L.) inclusa (Phillips), Mytilus ungulatus (Young & Bird), lsognomon subplana Etallon, Chlamys (C.) textoria (Schlotheim), Eopecten spondyloides (Roemer), Plicatula (P.) weymouthiana Damon, Plagiostoma rigidum J. Sowerby, Nanogyra nana (J. Sowerby), Lapha gregaria (1. Sowerby), Trigonia (T.) reticulata Agassiz, Neocrassina ovata (W. Smith), ?Praeastarte(?) nummus (Sauvage), Opis (Trigonopis) virdunensis Damon, O. (Coelopis) upwarensis Arkell, Sowerbya triangularis (Phillips), Anisocardia globosa (Roemer), Hiatella (Pseudosaxicava)

7.

Grey, relatively soft, marly pisolite, weathering to pale cream. Recognizable macrofauna is scattered, but a band around 3-4 m above the base yields common echinoids (Collyrites bicordata (Leske), Nucleolites scutatus Lamarck, Holectypus depressus (Leske), etc.). Perisphinctes sp. present (fragmentary macroconch). c. 4 m

CRINOID BED 6b. Coarse biomicrite in two courses, the upper slightly paler and more sparry than the lower. Crinoid debris and pisoids abundant. Recognizable macrofauna scattered through the bed, including common ammonites (Perisphinctes (P.) aff. antecedens Salfeld, Cardioceras (Scoticardioceras) excavatum (J. Sowerby) and C. (Cawtoniceras] cawtonense (Young & Bird»; bivalves (Pholadomya aequalis (1. de C. Sowerby), Pleuromya uniformis (1. Sowerby), Radulopectenfibrosus, (J. Sowerby), Chlamys textoria (Schlotheim) and rare Praebuchia lata); echinoids (Collyrites bicordata, Paracidaris florigemma spines and Nucleolites scutatus); pliosaur jaw fragments and crustacean claw. 0.6 m

102

J . K . WRIGHT ET AI... .

SPONGE BED 6a. Shelly, argillaceous limestone. Fossils often heavily encrusted and the internal spaces filled with micrite. Clasts of the underlying marl common, also clasts of very fine-grained oosparite. The base is sharp but irregular, marked by a horizontal Tlhalassinoides -type burrow system penetrating up to 3 em and infilled with poorly consolidated limestone debris. The prolific fauna includes ammonites (Cardioceras (Cardioceras) cord atifo rme (S. Buckman), C (C) highm oori Arkell, e. (S.) excavatum, C. [Mittcardioceras} sopotense (Ma linowska), e. (Maltoniceras) maltonense (Young & Bird). e. (M.) high worth ense Arkell, e. (Cawtoniceras] cawtonense. e. [Subve rtebriceras) densiplicatum Boden, e. (S.) zenaidae Ilovaisky, Perisphinctes (Perisphinctes) d. antecedens Salfeld [m] and [MI, and P. (?subgenus) sp. A [m])); bivalves (G rypha ea (Bilobissa) dilatata (J. Sowerby), Camptonectes (Borionectes) sp., Radulopecten fi brosus, Lopha gregaria J. Sowerby, Oxytoma expansa, Plagiostoma subrigidum (J. Sowerby) and Eopecten spondyloid es (Roemer)); echinoids (Colyrites bicordata, Nucleolites scutatus, Pseudodiadema hemi spha erica (Agassiz) and Hemicidaris interm edia

(Fleming)); and rare belemnites iPachyte uthis sp.).

0.1-0.15 m

DIMMOCK'S COTE MARL MEMBER 5. Dark grey mudrock with Cardi oceras (M iticardioceras] tenuiserratum (Oppel).

e. (Cawto nice ras) cawtonense, Oxytoma expans a (Phillips), Campto nectes (Camptonectes) auritus (Schlotheim), Phaladomya sp. and Chlamys sp.

0.60 m

4. Grey argillaceous limestone with Thalassinoides and other burrows at the base. 0.1O-D.15 m 3. Dark grey mudrock with scattered Chlamys and Gryphaea in a layer 0.2 m above the base. Scattered small, pale brownish phosphatic patches occur 0.7 m above base, and impersistent argillaceous limestone 1.2 m up. 1.70 m 2. Grey argillaceous,spicular, shelly limestone with ?Pleuromya sp. and (Perisphinctes} sp. ?juv. I.

Dark grey mudrock with scattered Chlamys sp. and lsog nomon subplana Etallon, A concretion with a large Perisphinctes (Arisphinctes} aff. pickeringuis (Young & Bird) [MI was found about the middle, with a band containing Grypha ea just above it Hibolithes sp. was collected 0.1 m higher, with Pleuromya and a small perisphinctid also in the upper part. Impersistent calcareous band near the base.

O.3O-DAO m

seen to 1.50 m

The following were collected from loo se blocks of argillaceous limestone: ammonites (Cardioceras (Mi tic ardioceras) sopotense, C (Subv ertebriceras) zenaidae, Neopriono ceras aff. henrici (d 'Orbigny), Perisphinctes (Arisphinctes] aff. pickeringuis (Young &

Bird) ([m) and [M)) and Perisphinctes (A.) aff. maximu s (Young & Bird ) [M)) , and bivalves, (Camptonec tes lens (1. Sowerby), Chlam ys splendens (Dollfus), Radulopecten fibsosus, Grypha ea (B.) dilatata (1. Sow erby), Oxytoma expansa (Phillips), Pinna lan ceolata (1. Sowerb y), l socyprina cy reniformis (Buvignier) and Phol adom ya aequali s). Th is fauna would be from bed s 2 or 4, although the shallow depth of the drainage ditches at the site may suggest that Bed 4 is the primary source. The following faunal list is of museum specimens from Bed 9. The older name Bridge Pit North is frequently used : ammonites (Perisph inctes (P.) cf. dobrogen sis (Enay ?non Sim ione scu ), Cardioceras (Miticardioceras) tenuiserratum, C. (M altoniceras) malt on ense, C (Subvert ebricera s) densiplicatum, C (S.) zena idae, Neopriono ceras aff. henrici, Euaspidoceras aff. pau cituberculatum (Arkell)); bivalves (A rcomy tilus pectinatus (1. Sowerby), Modiolus (M.) bipartitus J. Sowerby, Mytilus ungulatus, Pteroperna polydon (Buvignier), Gervillella sulcata Etallon, Campt onectes (C) auritu s, Radulopecten fibrosus , R. inaequi costatus (Young & Bird), Spondylopecten (Plesiopecten) subspina (Schlotheim), Gryphaea (B.) dilatata , Trigonia (T.) reticulata Aga ssiz, Myoconcha texta Bu vignier, Opis (Trigonopis) eurvi rostra (W. Smith), Quenstedtia gibbosa Hudleston , Sowerbya triangulari s, Anisocardia globosa, Lithopha ga inelusa (Phillips), Hiatella (Pseudosaxicava) pha seolus (Eudes-Deslongcharnps), Gastroeha ena (G.) moreana (Buvignier), G. (Gastrochaeonopsis) reeondita (Phillips), Pleuromya uniformis, Goni omya litterata (1. Sowerby), Ma ehomya cf. applanata Cossman); ga stropods ( 'Litto rina' muri eata (1. Sowerby), Amberleya meriani (Goldfuss), 'Natica' clytia d'Orbigny, Nerinea cf. Hudleston); rare brachiopods pseudovisursis ( Terebratula' ins ignis var. malton ens is (O ppel)) ; echinoids (Rhabdocidaris sp. , Hemieidaris interm edia, Diplopodia versipora (Woodland), Stomechinus gyratus (Agassiz), Holeetypus depressus, Hyboelypus gibbe rulus Agassiz, Pyguru s pentagonalis (Phillips), Nueleolite s seutatus, Coll yrites bieordata); crinoids (Ap ioe rinus polyploeus (Merian), lsocrinus sp.); annelids (Serpula sulcata); a cru stacean (Glyphaea sp.) ; Rogerella sp. (cirripede borings in Triehites); Thalassinoides sp. (crustacean burrows); algal stromatolites and fossil wood. Addi tion al records probably from Bed 9 in clude Moorellina granulosa Moore (brachiopod), Stromatopora sp . (bryozoa n) , Enaulofungia jlorieeps (Phill ips) and Rhaxella perforata Hinde (spo nge) and Girva nella sp. (alga).

4. CORRELATION OF THE DIMMOCK'S COTE SECTION WITH PREVIOUSLY DESCRIBED SECTIONS AT UPWARE Northwards from Dimmock's Cote Quarry, no proper rec ord see ms to ha ve been made of North Pit , but the Crinoid Bed was met with in two well s nearby at High Fen Farm (Wedd, 1898 ). The lithology wa s identical to that seen at Dimmock's Cote Quarry, being very tough, full of

STRATIGRAPHY O F

DEPOSITS AT UPWARE. C A M B R I D G E S H I R E

' Pentacri nus' ossicles, and with numerous perisphinctid ammonites. Southward s from Dimmock 's Cote Quarry, all units thin markedly (Fig. 6). A near-complete sequence through the West Walton Formation can be made out in the records of exposures at the Commissioners' Pit (Wedd, 1898; Rastall, 1909). The Dimmock's Cote Marl Member is 1.5 m thick here, comprising a 'coral rock and marl' (presumably a marl containing lenses of Thecosmilia limestone). No record was kept of the overlying 1.2 m of strata which presumably contain ed the Crinoid Bed, Howeve r, the upper part of the Upware Limestone Member is still exposed to a thickness of 2 m. The lower I m comprises porous, poorly cemented , variably oolitic, bioclastic limestone. The Coral Bed contains tabular or foliaceous colonies of /sastra ea explanata, Thamnasteria concinna and Microsalenia thurmanni set in a fine, pelletal, micritic limestone matrix. Numerous bivalves are present, including Lithophaga inc/usa , Plicatula sp., Opis sp., Barbatia sp., Eonavicula sp. and pectinids, with Para cidaris sp. and Cardioceras (Miticardioceras) tenuiserratum. In Upware village, Wedd (1898) recorded important sections through beds at the junction of the Dimmock's Cote Marl with the Upware Limestone. The Dimmock's Cote Marl was only 0.75 m thick, consisting of soft marls with lenses of Thecosmilia limestone overlain by soft, yellow marl with 'Pentacrinus' , The Crinoid Bed itself consists of a unit 'almost entirely composed of Penta crinu s' ossicles in a yellow, calcareous matrix, 1-2 ft' [0.3 to 0.6 m]. This is overlain by rubbly limestone with Cidaris, 'Pentacrinus' and corals seen to 0.35 m. Almost certainly it was this latter bed, consisting of shelly, micritic limestone with Thamnasteria concinna bored by Lithophaga inc/usa, which was exposed in excavations for house foundations in Upware [TL 53757015] in 1998.

5. CONDITIONS OF DEPOSITION OF THE UPWARE LIMESTONE AND ASSOCIATED FACIES Upware lies on the northwestern margin of the London Platform . The cross-section on BGS Sheet 188 shows Palaeozoic rocks only 140 m below the base of the 'Corallian'. To the southeast (BGS Sheet 206), Early Cretaceous Gault rests directly on the Palaeozoic rocks. To the northwest, the formations of the Ancholme Group thicken markedly. Even within the area of the outlier, there is a noticeable thickening northwards from Upware village to Dimmock's Cote Quarry (Fig. 6 ). Situated thus, the Upware 'Corallian' succession marks the outbuilding into deeper water northwest of the London Platform of a ramp of shallow-water carbonate sediments whose source lay on the London Platform shallows, as already suggested by Gallois & Cox (1977).

Lower Elsworth Member 'Ironshot oolites' are common in beds of this age around the London Platform (Wright, 1980) which appears to

103

have been heavily vegetated, with deep lateritic weathering. The reworking of these latosols is thought to have been the principal source of the large quantities of iron which found their way into the surrounding marine sediments (Burkhalter, 1995). Subsidence everywhere around the platform was thus slow, with the deposition of thin, condensed sequences of sedimentary ironstones.

Dimmock's Cote Marl Member This unit marks the beginning of predominantl y carbonate sedimentation at Upware. Thus, in thin section, the marls are seen to be shelly, with numerous fractured, nonabraded echinoderm and other shell fragments, and scattered quart z grains 100-200 urn in diameter. Calcareous sponge spicules, calcisponges and foraminifera are also seen. Little winnowing can have taken place. The calcareous layers and concretions consist of a variably calcified shelly spiculite. Slightly altered parts of the rock contain the siliceous spicules of Rhaxella perforata Hinde set in a granular, crystalline calcareous matrix. The silica of the spicules is coarsely recrystallized, the original internal structure (Wright, 1983, p. 264) no longer being visible. Zones with siliceous spicules pass into completel y calcified areas with granular calcite replacing the silica of the spicules, and with recrystallized bivalve fragments. The fauna of the Dimmock's Cote Marls is varied, with deep burrowing bivalves (Pholadomya, Goniomya and Pleuromya), occasional shallow burrowing Pinna, and an abundant surface-dwelling faun a of bysally attached forms such as Meleagrinella, Oxytoma, lsognomon and young pectinids, and the reclining Gryphaea. Thecosmilia is present in the south. Belemnite s and ammonites are common . A common microfauna is also present, particularly the foraminifera. Of these, Lenticulina muensteri (Roemer) occurs throughout, Massilina redc/iffen sis Gordon is common in Bed I, with rare Dentalina giimbeli Schwager and Opthalm idium strumosum (GUmbel), and Lenticulina tricarinella (Reuss) and Cytharina serratocostata (GUmbel) occur commonly at the top of the bed, along with holothurian hooks and sclerites, and smooth-shelled ostracods. Bed 3 yields M. redc/iffensis and O. strumosum, and Bed 5 C. serratocostata and well preserved Rhaxella sponge spicules. Conditions thus seem to have been those of an offshore shelf deepening to the north. Solitary corals could grow in the Upware area, but northward s conditions were too deep, though still well oxygenated. Deeper burrowing bivalves did well, and extensive Thalassinoides burrow systems are developed beneath limestone bands, which seem to mark periods of slower sedimentation , characterized by a more prolific bivalve fauna. The sea floor lacked the consistency for many shallow burrowing or epifaunal forms, excepting the reclining Grypha ea. The byssally attached Meleag rinella and Oxytoma may have been anchored to sponges or seaweed. Overall conditions were not especially favourable for life, and the bivalves are often stunted and the foraminifera tiny and immature. In the more argillaceous beds, bivalves tend to occur in

N HIGH FEN FARM WELLS (Wedd, 1898)

s

UPWARE FIELD SECTION (Wedd, 1898) COMMISSIONERS' PIT UPWARE WELL (Wedd, 1898 and Rastall , 1908) SECTION 'Wedd,1898

DIMMOCK'S COTE QUARRY

NO

§

UPWARE

RECORD

LIMESTONE MEMBER OXFORD CLAY FORMATION

3,....m

~

~

(WEYMOUTH MEMBER)

2

~

Q

~

o

I

SPONGE BED

WEST WALTON FORMATION

DIMMOCK'S COTE MARL MEMBER

I I I I I I I

mudstone

[~:·:3

mudstone with limonite oolilhs

I

~

limestone

I I I I

EI::£i3

limestone with limonite oonths

[-,:1_-1:1

argillaceous limeston e

I

____ .JI I I

* crinoid o t

Fig. 6. Correlation of sections in the Upware inlier.

:to

t'

[------1

I

~

~ coral

_

shell bed

..l-

Thalassinoides burrows

1 km I

STRATIGRAPHY OF DEPOSITS AT UPWARE, CAMBRIDGESHIRE

layers, marking episodes when conditions became more favourable, i.e, an 'Oxytoma Bed' with large, articulated O. expansa forming a local pavement in Bed 5.

Upware Limestone Member Sponge Bed (Bed 6a) The base of this unit is heavily bioturbated into the underlying marls with infilled burrows. It is predominantly bioclastic, the crinoid ossicles and bivalve fragments being markedly abraded, indicating substantial winnowing in the source area. The macrofauna is well preserved, however, and the limestone is markedly argillaceous, indicating little winnowing in the area of deposition. Numerous pale green ooids are present. These are very unusual, apparently being of partly calcified iron silicate, the calcification having taken place shortly after their formation. They are thus spherical to bean-shaped, 0.5-1 mm in diameter, with concentric zones of granular calcite and a greenish clay mineral with the appearance of chamosite or berthierine. No 14 A chamosite peaks are visible on X-ray, but there is a broad, poorly formed peak at 7 A, showing that berthierine is probably present. In his study of Middle Jurassic iron silicate ooids from the Jura, Burkhalter (1995) noted that the sediments in his area of the Jura had been buried to little more than 1 km depth, and he noted that such a depth ought to have been insufficient to convert the original berthierine to chamosite. However, Burkhalter could only find chamosite in the Jura. The presence of berthierine at Upware fits the conventional pattern of iron silicate being present as berthierine in sediments buried to shallow depths. In the Yorkshire Callovian, which has been buried to a depth of at least 3 km (Holliday, 1999), X-ray studies of iron silicate ooids by JKW frequently show a prominent 14A chamosite peak. Clasts of very fine oosparite found in the Sponge Bed indicate penecontemporaneous erosion of a recently lithified source rock at present not known in the area. The fauna of the Sponge Bed appears generally reworked, with bivalves such as Pleuromya, Goniomya and Pholadomya, and some perisphinctid and cardioceratid ammonites, having mudstone infillings. These are probably reworked from the underlying Dimmock's Cote Marl Member. The bivalves, echinoids and belemnite guards are all heavily encrusted with the foraminiferan Nubeculinella, and also some serpulids, bryozoans and small Nanogyra. The ammonites are preferentially encrusted with serpulids. Common irregular but freshly preserved calcareous sponges (not identified) occur up to about 10 em maximum dimension, and are complete with relatively undamaged encrusting serpulid worms, and contain borings (Gastrochaenolites lapidicus Kelly & Bromley) with the bivalve responsible, Lithophaga inclusa, present inside. The fauna thus lacks forms normally associated with deposition of higher energy, bioclastic sands, particularly the thick-shelled Gervillella, and is very much that of the lower energy Dimmock's Cote Marl.

105

Crinoid Bed (Bed 6b) There is then a sudden change to coarse-grained limestone without many large fossils. In thin section, profuse crinoid (probably Isocrinus) ossicles are seen, with many large bivalve fragments, including Trichites. The largest bivalve fragments show infiltration fabrics, with sparry calcite infilling voids beneath the fragments, and with coarse, shelly sand on top. Many smaller shell fragments have a micritic coating, forming pisoids rather than oncoids, as no algal structure or algal tubules are visible in the coating. As in the beds above, common small encrusting foraminifera are caught up in the micrite envelope; also occasional ostracods. The frequent reports of 'sparks' coming from this bed when struck with a pickaxe are explained by the frequent partial replacement of shell fragments by silica, presumably derived from sponge spicules in the marl beneath. One loose specimen of an ammonite body-chamber was largely infilled with chert. The rock thus effectively comprises a chaotic jumble of shell fragments, coral fragments, calcareous sponges, foraminifera, crinoid ossicles and berthierine ooids. It is poorly sorted, varying between a detrital grainstone or a packstone, with some interstitial mud. The fauna contrasts with that of the underlying Sponge Bed in that the whole is fresh and not heavily encrusted, with common echinoids and pectinid bivalves, Perisphinctes, and rare Praebuchia lata. This assemblage represents a fairly robust fauna capable of withstanding moderate currents. The Sponge Bed and Crinoid Bed together bear the hallmarks of a tempestite. Prior to deposition of these beds, there appear to have been lagoons to the southeast with thickets of sponges and of 'Pentacrinus'. Abundant ossicles ascribed to this genus were found in lagoonal lime mud matrix at Upware Village by Wedd (1898). A wide variety of sediments accumulated in this area. In the shallows around the lagoons, micritic envelopes were deposited on shell fragments in large areas of bioclastic shell sand. Echinoids browsed in the muds, and small coral patch reefs grew. Burrowing bivalves colonized slightly deeper areas, where the facies must have been similar to that of the Dimmock's Cote Marl. When this area was swept by a severe storm, a ramp of bioclastic sediment was built out into deeper water to the northwest. Echinoids, ammonites and bivalves were swept along and trapped in the sediment; the bivalves are whole but preserved at all angles, not in life position. Those organisms which survived the storm or recolonized quickly bioturbated the sediment, and burrowed into the underlying marls. Voids are filled with lime mud, and spaces beneath broken shells filled with sparry calcite. Such infiltration fabrics are a classic indicator of a tempestite (Kreisa & Bambach 1982). Bed 7 Initially, there was a return to argillaceous, marly sedimentation. At the east end of Dimmock's Cote Quarry, 4 m of grey, soft, marly, pisoidal limestone rest on the Crinoid Bed. The dark grey colour is believed to be that of the fresh, unweathered rock, rather than a result of being more argillaceous. In thin section, the rock is full of

106

J . K . WRIGHT E T AL.

irregularly shaped pisoid s consisting of shell fragments coated with micritic envelopes. The pisoids have formed around a variety of bioclastic fragments, including biv alve s, calcisponges , serpulids, coral fragments (?Thecosmilia , Thamna steria, ?Rhabdophyllia) and crinoid ossicles. These cla sts are pisoids rather than oncoids, as no algal structure or algal tubule s are visible within them. Numerou s small encru sting foraminifera are incorporated into the pisoid s. Such a fabric is also common in some of the limestones of the Yorkshire Coralli an Group (J. K. W. colin ). The matrix is very fine and micritic, and in the Dunham classification the rock is a wackestone. Bedding is poorly developed, probably having been destroyed by bioturbation. Apart from frequent echinoids, macrofo ssils are generally scarce . The bed thus marks the return to less well circulated conditions, probably in an area marginal to the coral reef. The sea bed was colonized by detritu s-feeding echinoids, but there was not the input of plankton to attract filter-feeding bivalves. The Coral Bed (Bed 8) At Dimmock's Cote Quarry, Bed 8, occuring half way up the west face of the quarry wall , is the only representative of coral-rich facies expo sed in the quarry at present, and is believed to have formed at or near the reef at the western limit of limestone depo sition. The best exposure of this bed is at Commi ssioners ' Pit. The rock here is a biomicrite. Layers and lense s of Microsalenia, Thamnasteria and lsastraea form a reef fram ework, with fine, micritic mud in the interstices and in Gastrochaenolites borings . Layers of this coral rock altern ate with layers of shelly, partly decalcified biomicrite, the fine, micritic matrix of which is full of fragments of Thecosmilia, Thamnasteria, Microsalenia, Nanogyra and Trichites. Most of the larger bivalves are dissolved out and present at mould s. The bivalve fauna of the Coral Bed is characterized by surface and near-surface dwelling form s. Shallow burrowers such as Trigonia, Neocrassina and Sowerbya are accompanied by nestlers such as Barbatia and Opis which occupied spaces in between corals. Byssate forms such as Mytilus, lsognomon and Plagiostoma are common , and there was plenty of scope for colonization of the reef by cemented forms (Plicatula, Nanogyra and Lopha ) and borers (Lithophaga, Gastrochaena). The Coral Bed clearly formed a reef framework, but conditions must have been far from typical of reefs, with little wave action to wash away or destroy delicate bi val ves. The colonial cora ls form thin platey or foliaceous colonies, and not the rounded , dome-shaped masses normall y associated with Corallian reefs. Insalaco ( 1996), in his study of coral morphol ogy at Upware, noted that the interlocking framework of platey corals found here is typical of deep water biostromes. The Upware reef thus seems to have accumulated in a moderately deep area below fairweather wave base in a region of minimal sediment input. Bed 9 At the eastern end of Dimm ock 's Cote Quarry, the highest

3 m of the Upware Limestone consist of tougher, creamcoloured, foss iliferous limeston e. Thi s rock has an abundance of ooids in thin section, set with pisoids, similar to those occ urring below, in a fine, micritic matrix. The ooids are poorly sorted, irregular in shape, and grade into pisoids. In Dunham's terminol ogy the rock is a packstone. The rock is poorly lithified , and sometimes has a 'cream-cheese' texture . The fauna is largely a death assembla ge with decalcified moulds, generally of thinshelled sm all bival ves, and with occasional finely branched corals. The fauna shows an excellent variety, with deep burrowers (Pleuromya, Goniomya) and shallow burrowers (Modiolus, Gervillella, Trigonia, Sowerbya). Epifaunal forms (Gryphaea, Opis) and byssate forms (Mytilus, Pteroperna, young pectens) co lonized the surface, along with a prolific gastropod and echinoid fauna on and ju st beneath the surface. This repre sents a well oxygenated, protected, shelf environment, possibly back-ree f. On the western side of the pit, this tougher bed is seen to 5 m. It is distinctly laminated on a 5-10 em scale, with regular alternations of micritic and shellfragment rich band s. The clasts are packed togeth er in these shelly bands, with much pressure solution. Beds at a comparable level formerly exposed in the centre of the present pit contained Microsalenia in a more micritic matrix . Thi s coral was frequently bored by worms, indicated by the trace fossil Trypanites, and by the boring bivalves Lith ophaga, Ga strocha ena and Gastrochaenop sis. Their borin gs also co ntained occasional exampl es of the squattin g bivalve Hiatella pha seolus , often with two specimens in the same boring. Pisera (1987) described this taxon from the Oxford ian of Poland and it is similar to the species described by Kelly (1980), who identified this squatting mode of life from the Spilsby Sandstone of Lincoln shire. The Microsalenia was frequentl y seen to be encru sted with Plicatula.

6. NOTES ON THE AMMONITE FAUNAS A detailed account of the ammonite faunas of the whole Upware inlier is at present in preparation. We take the opportunity here to figure typical specimens from the Dimmock's Cote Marl and from the Crinoid Bed of the Upware Limestone Member. Specimens whose numbers are prefixed SK are in the S. R. A. Kelly collection. Specimen s whose numbers are prefixed UW or UC are in the J. K. Wright collection. It is our intention once the work is complete to donate all figured specimens to the Sedgewick Museum , Cambridge. Ammoni tes from the Dimmock's Cote Marl and the Crinoid Bed have not been figured previously. In both intervals, perisphinctids and cardioce ratids are about equal in number. Of the cardioceratid s, long-range forms are the most common, but the presence of such forms as Cawtoniceras (Fig. 7D) in the Dimmock 's Cote Marl and Maltoniceras (Figs 8A. B) in the Crinoid Bed establishes that both units prob ably belong to the upper Maltonense Sub zone of the Densiplicatum Zone (Fig. 4). However, the presence of two species of Miticardioceras in Bed 5 of the Dimm ock's Cote Marl, includ ing rare C. (M.) tenuiserratum , suggests

F

Fig. 7. Fossils from the Dimmocks Cote Marl and Upware Limestone (Crinoid Bed), of Dimmock's Cote Quarry. (A, B) Perisphinctes (Arisphinctes) aff. pickeringius (Young & Bird). (A) SK453, [m]. Probably from Bed 4. Largely complete specimen lacking the last quarter of a whorl of body-chamber. x 0.56. (B) UW21, [M]. Bed I. Specimen largely complete, though lacking the last quarter of a whorl of body chamber. x 0.27. (C) Cardioceras (Subvertebriceras) zenaidae Ilovaisky. SK451, [m]. Probably from Bed 4. Largely complete specimen - the ribbing is visible up to the aperture on the reverse of the specimen at the point arrowed. x I. (D) Cardioceras (Cawtoniceras) cawtonense (Blake & Hudleston). UW3, [?m]. Probably from Bed 5. Septate inner whorls, natural size. (E, F, G) Praebuchia lata (Trautschold). SK454, x I. (E) left valve; (F) anterior aspect; (G) right valve. The end of the phragmacone of the ammonites, where visible, is marked by an X.

7 E

Fig. 8. Ammonites from the Upware Limestone (Crinoid Bed) of Dimmock's Cote Quarry. (A, B) Cardioceras (Maltoniceras) maltonense. SK 438, em]. finely ribbed form. x 1. (C, D, E) Perisphinctes (Perisphinctes] aff. antecedens Salfeld. (C) SK440, em], body chamber including modified ribbing close to the aperture. x 0.73. (D, E) UC39, [M], partially preserved adult specimen with modified ribbing close to the aperture. (E) shows on the left-hand side the reduction in whorl thickness in the last quarter of a whorl up to the aperture. x 0.27. The end of the phragmacone, where visible, is marked by an X.

STRATIGRAPHY OF DEPOSITS AT UPWARE, CAMBRIDGESHIRE

the possibility that this part of the sequence represents the very lowest Tenuiserratum Zone, as Sykes & Callomon (1979) define the base of that zone by the first appearance of this species. The perisphinctid species are represented by both microconch and macroconch forms of the same species. A large, almost complete macroconch and a microconch of Perisphinctes (Arisphinctes) aff. pickeringius from the Dimmock's Cote Marl is shown in Figs 7A,B. This species is replaced in the Crinoid Bed by microconch and macroconch Perisphinctes (P.) aff. antecedens (Figs 8C,D,E). This changeover from faunas dominated by Arisphinctes to faunas dominated by Persisphinctes s.s. is of major importance in the perisphinctid zonation of the Middle Oxfordian of N.W. Europe (Gfowniak, 1997).

ACKNOWLEDGEMENTS Thanks are due to the helpful staff at Wicken Lime and Stone Co. for access to the quarry, and for assistance in collecting data and specimens, including pumping out deep sumps. We are grateful to Professor J. H. Callomon who carefully scrutinized a preliminary manuscript and made many helpful suggestions. As referee, Dr B. M. Cox made many critical suggestions and improved the manuscript substantially. Mr K. D'Souza photographed the ammonites and Miss N. Wilson drew the figures.

APPENDIX A new bivalve record for the Corallian of southern England by S. R. A. Kelly Family BUCHIIDAE Cox, 1953

1933

v. 1981

1986

v. 1990

109

figs 1-5 [altemans Zone, Late Oxfordian, Khanski, Russian Platform]. Pseudomonotonis laevis (Blake & Hudleston); Arkell, p. 200, pI. 24, figs 11-12 [Malton Oolite, Malton; BMNH L20142, Hambleton Oolite, Kepwick, Yorkshire, England]. Praebuchia kirghisensis (Sokolov); Zakharov, p. 60, pI. I, figs 5-7; pI. 2, figs 8-9; text- figs 8a-b [Late Oxfordian-?Kimmeridgian, Siberia]. Praebuchia lata (Trautschold); Sey, p. 130, pI. 17, figs 4-13 [Late Oxfordian ?Early Kimmeridgian, western Priokhot'ya, Far East Russia]. Praebuchia lata (Trautschold); Kelly, p. 136, pI. 3, figs 1,2 [Spaunton Sandstone, Glosense Zone, Late Oxfordian; Hambleton Oolite, ?Cordatum Zone, Early Oxfordian].

Types. Lectotype, designated Sey, 1986, p. 130, TsNIGR No. 11/10941, original of Trautschold, 1860, pI. 7, fig. 8a, Late Oxfordian, Gal'yevo, Moscow. Material. SK 454, a single specimen with valves almost in occlusion, Upware Limestone Member, Dimmock's Cote Quarry, Bed 6. Diagnosis. Shell thin, weakly inflated, subovate, slightly extended in postero-ventral direction; left valve with slightly projecting umbo; right valve only slightly smaller and less inflated than left valve, lacking projecting umbo, hingeline short; peg-like prominent byssal ear at low angle to plane of commissure, and with deep byssal notch; left valve umbo projecting slightly above that of left valve; left and right valve weakly curvoid to obliquoid; exterior smooth, with very fine commarginal growth lines, but extremely fine radial ornament is also present. Dimensions

SK454

Length 38.8 mm

Height 37.5 mm

Breadth (both valves) 14.2 mm

Genus PRAEBUCHIA Zakharov, 1981 Type species. By original designation: Praebuchia orientalis Zakharov, 1981, Upper Callovian-Lower Oxfordian, north Central Siberia, Russia. Praebuchia lata (Trautschold, 1860) (Figs 7E,F,G.) 1860 Aucella lata Trautschold, p. 344, p1.7, figs 8,9. 1877 Avicula laevis sp. nov. Blake & Hudleston, p. 399, pI. 16, fig. 2 [Syntypes: BMNH 20142, Hambleton Oolite, Kepwick, Yorkshire, and BGS Y1795, Lower Calcareous Grit, Oxfordshire, England]. v. 1877 Avicula ovalis Phillips var. obliqua nov. Blake & Hudleston, p. 399, pI. 14, fig. 13 [Holotype by monotypy?, BGS 46266, Upper Calcareous Grit, Late Oxfordian, Pickering, Yorkshire; non B. obliqua (Tullberg 1881)]. ? 1902 Aucella kirghisensis sp. nov. Sokolov, p. 374, pI. 14,

Remarks. This buchiid differs from P. impressae (Quenstedt) which is a smaller species with a much more elongate shape. Both these species have a byssal ear at a low angle to the plane of the commissure. P. lata contrasts with most species of Buchia and other Praebuchia by the smoothness of the shell, relatively low inflation, and almost equal size of the valves. Distribution. P. lata is common in the Spaunton Sandstone of Newbridge Quarry, Yorkshire (Kelly, 1990) and in the Fiodigarry Shale of Staffin Bay, Skye, where it was recorded as Buchia concentrica by Sykes (1975). It occurs more rarely in the Lower Calcareous Grit of Yorkshire and Oxfordshire, and the Hambleton Oolite of Yorkshire. It has also been described as P. kirghisensis from the Late Oxfordian, East Greenland by Suriyk & Zakharov (1982), Late Oxfordian of south Tibet by Li Xiaochi & GrantMackie (1988), Oxfordian of NE Russia by Paraketsov & Paraketsova (1989). The species ranges from the Cordatum to the Glosense Zones in England, but may range up into the Early Kimmeridgian of the Russian Far East.

REFERENCES ARKELL, W. J. 1929-37. A monograph of British Corallian Lamellibranchiata. Palaeontographical Society Monograph. Part 5, 1933,85 (386), 181-228, pis 21-28. - - 1937. The zonal position of the Elsworth Rock, and its alleged equivalent at Upware, Cambridgeshire. Geological Magazine, 74, 445-458.

BLAKE, J. F. & HUDLESTON, W. H. 1877. The Corallian rocks of England. Quarterly Journal of the Geological Society of London, 33, (2), 260-402, pis 12-16. BURKHALTER, R. M. 1995. Ooidal ironstones and ferruginous microbialites - origin and relation to sequence

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stratigraphy (Aalenian and Bajocian, Swiss Jura Mountains). Sedimentology, 42, 57-74. COPE, J. C. W. 1993. The Bolonian Stage: an old answer to an old problem. Newsletters on Stratigraphy, 28, 151-156. GALLOIS, R. W. & COX, B. M. 1977. The stratigraphy of the Middle and Upper Oxfordian sediments of Fenland. Proceedings of the Geologists' Association, 88, 207-228. GLOWNIAK, E. 1997. Middle Oxfordian ammonites. In (Glowniak, E., Matyja, B. A., Poulsen, N. E. & Wierzbowski, A.; eds) Oxfordian (Jurassic) meeting in Poland, 26-28 May 1997. International Subcommission on Jurassic Stratigraphy Newsletter, 25, 44-46. HARLAND, W. B., ARMSTRONG, R. L., COX, A. v.. CRAIG, L. E., SMITH, A. G. & SMITH, D. G. 1990. A geologic time scale 1989. Cambridge University Press. HOLLIDAY, D. W. 1999. Palaeotemperatures, thermal modelling and depth of burial studies in northern and eastern England. Proceedings of the Yorkshire Geological Society, 52, 337- 352. INSALACO, E. 1996. The use of Late Jurassic coral growth bands as palaeoenvironmental indicators. Palaeontology, 39, 413-431. KELLY, S. R. A. 1980. Hiatella - a Jurassic bivalve squatter? Palaeontology, 23769-782, pI. 96. - - 1984. Bivalvia of the Spilsby Sandstone and Sandringham Sands (Late Jurassic - Early Cretaceous) of eastern England. Palaeontographical Society Monograph. - - 1985 Jurassic and Cretaceous deposits of Upware, Cambridgeshire (a review and excursion report). Bulletin ofthe Geological Society of Norfolk, 35,3-38. - - 1990. Biostratigrafiya verkhneyurskikh i nizhnemelovikh otlozheniy evropy po bukhiyam [Biostratigraphy of the Upper Jurassic and Lower Cretaceous of Europe by buchias]. In (Menner, V. V: ed.) Granitsa yury i mela [The JurassicCretaceous boundary] Trudy Instituta Geologii i Geofiziki, Sibirshoye Otdeleniye. Nauka, Moscow, 129-151, 2 pis (In Russian with English Abstract; Cyrillic author reads Kelli, S. R.).

KREISA, R. D. & BAMBACH, R. K. 1982. The role of storm processes in generating shell beds in Palaeozoic shelf sequences. In (Einsele, G. & Seilacher, A.; eds) Cyclic and event stratification. Springer-Verlag, Berlin, 200-207. LI XIAOCHI & GRANT-MACKIE, J. A. 1988. Upper Jurassic and Lower Cretaceous Buchia (Bivalvia) from southern Tibet, and some wider considerations. Alcheringa, 12, 249-268. PAGE, K. N. 1986. A new section in the Elsworth Rock (Jurassic, Oxfordian) at Papworth Everard, near Cambridge, England. Proceedings of the Geologists' Association, 97, 229-235. PARAKETSOV, K. V. & PARAKETSOVA, G. I. 1989. Stratigrafiya i fauna verkhneyurskikh i ntzknemelovykb otlozheniy severo-vostoka SSSR [Stratigraphy and fauna ofthe Upper Jurassic and Lawer Cretaceous deposits of northeast USSR]. Nedra, Moscow (In Russian.) PISERA, A. 1987. Boring and nestling organisms from Upper

Jurassic coral colonies from northern Poland. Acta Palaeontologica Polonica. 32,83-104. RASTALL, R. H. 1909. The Geology of Cambridgeshire, Bedfordshire and west Norfolk. In (Moncton, H. W. & Herries, R. S.; eds) Geology in the Field, 124--178. Geologists' Association, London. ROBERTS, T. 1892. The Jurassic rocks of the neighbourhood of Cambridge. Sedgwick Prize Essay for 1886. Cambridge. SEELEY, H. G. 1861. On the Fen Clay Formation. The Geologist, 4,552-553. - - 1869. Index to the fossil remains ofAves, Ornithosauria and Reptilia from the Secondary System of strata arranged in the Woodwardian Museum of the Universty of Cambridge. University of Cambridge, Cambridge. SEY, 1. 1. 1986. Oxfordskiye i kimeridzhskiye bukhiidy zapadnogo priokhot'ya (dal'niy vostok) [Oxfordian and Kimmeridgian buchiids from West Priokhot'ya (Far East)]. In (Yanshin, A. L. & Dagis, A. S.; eds) Trudy Instituta Geologii i Geofiziki, 648, 127-133, pis 17, 18 (In Russian.) SOKOLOV, D. N. 1902. Ueber einige Aucellen aus OstRussland. Bulletin de la Societe Imperiale des Naturalistes de Moscou, New Series, 3, 371-379. SURLYK, F. & ZAKHAROV, V. A. 1982. Buchiid bivalves from the Upper Jurassic and Lower Cretaceous of East Greenland. Palaeontology, 25,727-753, pis 72-77. SYKES, R. M. 1975. 'Facies and faunal analysis ofthe Callovian and Oxfordian stages (Middle-Upper Jurassic) in northern Scotland and East Greenland.' DPhil thesis, University of Oxford. - - & CALLOMON, J. H. 1979. The Amoeboceras zonation of the Boreal Upper Oxfordian. Palaeontology, 22, 839-903, pis 112-121. TRAUTSCHOLD, H. 1860. Recherches geologiques aux environs de Moscou. Couche jurassique de Galiowa. Bulletin de la Societe Imperiale des Naturalistes de Moscou, 33, 338-361, pis. 6-8. WEDD, C. B. 1898. On the Corallian rocks of Upware (Cambridgeshire). Quarterly Journal ofthe Geological Society of Landon, 57, 73-85. WORSSAM, B. C. & TAYLOR, J. H. 1969. Geology of the country around Cambridge. Memoir of the Geological Survey of Great Britain. WRIGHT, J. K. 1980. The Oxfordian Stage. In (Cope, J. C. w.; ed.) A correlation ofJurassic rocks in the British Isles, Part 2, Middle and Upper Jurassic. Geological Society, London, Special Report, 15, 61-76. - - 1983. The Lower Oxfordian of North Yorkshire. Proceedings of the Yorkshire Geological Society, 44, 249-281, pls 18-22. ZAKHAROV, V. A. 1981. Buchiidy i biostratigraphiya boreal'noy verkney yuri i neocoma [Buchiids and biostratigraphy of the boreal Upper Jurassic and Neocomian]. Trudy Instituta Geologii i Geofiziki, 458, 1-271, 60 pis (in Russian).

Manuscript received 10 December 1998; revised typescript accepted 1 December 1999