J.micropalaeontol., 1: 141-147, July 1982

Lincolnshire borehole proves greater extent of the Scarborough Formation (Jurassic : Bajocian)

M.J. BRADSHAW & R.H. BATE Department of Geological Sciences, University of Aston, Birmingham, B4 7ET & Department of Palaeontology, British Museum (Natural History), Cromwell Road, London, SW7 5BD

ABSTRACT-The ostracod fauna of a thin unit of shelly mudstones encountered directly beneath the Great Oolite Group in a recently drilled borehole in north Lincolnshire confirms the presence of the Scarborough Formation, formerly thought of as being confined to the Cleveland Basin. Sandstones and coals separating the Scarborough Formation from typical upper Lincolnshire Limestone calcarenites were probably deposited by delta progradation and are correlated with the regressive Yons Nab Beds and lower Gristhorpe Member of the Cleveland Basin. Discovery of the Gristhorpe Member and the Scarborough Formation beneath the basal Great Oolite unconformity on the East Midlands Shelf suggests that the youngest limestone facies of the Lincolnshire Limestone can be no younger than earliest sauzei Zone, and that the erosional event which preceded deposition of the Great Oolite is of late humphriesianum Zone or younger age. A revised palaeogeography for Scarborough Formation times envisages that following initial westward marine transgression along the axis of the Cleveland Basin, the sea broadened and at its maximum extent covered much of the Market Weighton Block.

INTRODUCTION Between the early Aalenian Dogger Formation and article, Zone or Subzone used without qualification the early Callovian Cornbrash Limestone in the Cleve- refers to ammonite biozones which are regarded as land Basin is a series of thick fluvio-deltaic sandstones tantamount to chronozones; Torrens, 1980). It was and mudstones separated by four thinner, shallow marine therefore with great surprise that a recently drilled bore- deposits, which together compose the Ravenscar Group. hole at Nettleton, north Lincolnshire (Grid Ref. TF Middle Jurassic strata attenuate southward toward the 12459823), some 17 km east of the Bajocian outcrop, East Midlands Shelf and are missing over much of the cored a sandy and argillaceous sequence between typical Market Weighton Block due to both syndepositional upper Lincolnshire Limestone and basal Upper Estuarine i hinning and later erosion, but they reappear on north “Series”, which includes beds whose macrofaunas re- Humberside and thicken southward through Lincoln- semble those of the Scarborough Formation. This paper shire (see Fig. 1 for locations and structural setting). presents a detailed description and interpretation of the The Bajocian of Lincolnshire consists mainly of com- upper Lincolnshire Limestone to basal Upper Estuarine positionally variable but dominantly oolitic limestones, “Series” succession at Nettleton, and important bio- and northward advances of the Lincolnshire Limestone stratigraphic confirmation of age using the ostracod Sea account for the medial two marine units of the fauna. The effect of the Scarborough Formation’s dis- Cleveland succession. At outcrop, however, the topmost covery in Lincolnshire on our understanding of Middle Lincolnshire Limestone (Inferior Oolite Group) is of Jurassic sedimentation patterns is also discussed. (early Bajocian laeviuscufa Subzone or slightly younger *age(Ashton, 1980; Ashton & Parsons, in press), and is SEDIMENTOLOGY AND PALAEONTOLOGY separated by an erosional unconformity from sand- Lincolnshire Limestone stratigraphy has been re- stones and mudstones of the basal Upper Estuarine viewed by Kent (1966) and recently revised by Ashton “Series” (Great Oolite Group), which have not been (1 975,1980). On south Humberside the formation is split biostratigraphically dated but are thought to be of late informally into a lower unit of oolitic and bioclastic, Bajocian or earliest Bathonian age (Bradshaw, 1978). often micritic limestones with varying terrigenous con- No marine representative of the Scarborough Formation, tent (Kirton Beds), and an upper, coarser, often cross- the youngest marine unit within the Ravenscar Group bedded bioclastic oolite (Hibaldstow Beds). The Kirton of North Yorkshire (Fig. 2) and of ?late sauzei to hum- Beds contain a medial argillaceous unit (Raventhorpe phriesianum Zone age (Parsons, 1977) has been recog- Member of Ashton, 1975), which reflects a phase of nised on the East Midlands Shelf (throughout this southward progradation of the Yorkshire Delta. A lower

141 Bradshaw & Bate

0- km 30 DURHAM Inferred limit of marine basin during Scarborough Fmn timas

limit of beds older than the Crinoid Grit

NORTH

YORKSHIRE

Fig. 1

limestone tongue continues into the Cleveland Basin as An account of the lower and middle Lincolnshire the marine Blowgill Beds (Bate, 1967; Hemingway, Limestone at Nettleton is contained in Bradshaw & 1974) whilst an upper limestone tongue, the Cave Oolite, Penney (1982). The Raventhorpe Member and associated lateral equivalent of the Hibaldstow Beds and also the beds are more terrigenous than in their type section at upper Kirton Beds, persists as the Cayton Bay Formation Kirton-in-I,indsey (see Ashton, 1975), suggesting a (of Parsons, 1980; Lebberston Member of Hemingway stronger deltaic influence. The Hibaldstow Beds are and Knox, 1973). themselves unexceptional, but instead of being directly

142 Scarborough Formation in Lincolnshire

143 Bradshaw & Bate and unconformably overlain by the Upper Estuarine Trigonia, Nicaniella (Pressastarte), ? Homomya, Lingula “Series”, they grade up into the sandy and argillaceous and serpulids. A low diversity ostracod fauna (sampled sequence illustrated by Fig. 2. Moderately sorted cal- between 341.47 and 341.49 m, and contained on faunal carenites containing ooids and subordinate bioclasts slide number MPA 17235 in the Institute of Geological become finer grained, very poorly sorted and strongly Sciences Collections, Leeds, consists of Malzia uni- bioturbated, and contain a high proportion of coarse silt carinata Bate, M. bicarinata Bate, Praeschuleridea to very fine sand grade peloidal material, much of which subtrigona intermedia Bate, Fuhrbergiella (Fuhrber- is probably of faecal origin. This transition is ac- giella) horrida horrida Brand & Malz and Glyptocythere companied by the appearance of large numbers of medium scitula Bate. The mudstones are strongly bioturbated and to coarse sand-sized peloids and structureless crypto- contain a relatively high proportion of articulated bi- crystalline intraclasts, reflecting an increase in ooid and valves. Bioturbation is less intense in the claystones skeletal micritization. Intraclasts of quartz-silty wacke- where shell plasters frequently display large numbers of stone also occur and skeletal debris is mainly of mollus- similarly orientated Gervillella valves and Procerithium. can origin ; gastropods (including micromorphic forms) 15 cm of thinly interlayered siltstone and carbonaceous and pectinids are especially abundant, but ostracods and claystone, lacking a calcareous macrofauna, caps this benthic foraminifera are also very common. Grainstones thin (1.17 m) marine sequence beneath a second sharp give way upward to darker argillaceous packstones and contact at 340.52 m. The beds above the contact are then variably calcareous and carbonaceous dark grey mud- easily recognisable as the basal Upper Estuarine stones; thin layers of coarser oolitic material are common. “Series”. This upward increase in mud content is accompanied by a Typically in the East Midlands, the Upper Estuarine higher proportion of whole shells; bivalves dominate, “Series” is divisible into two, a lower rootletted fining- mostly pteriaceans (Gervillella, Isognomon) and pectinids upward sequence of white, yellowish grey and olive grey (both thin-shelled Propeumussium (Parvamussium) and sandstones and siltstones and brown, black and green thicker shelled Camptonectes), but shallow burrowing clay tones, lacking a calcareous macrofauna, succeeded genera (astartids and articids) form a significant minor by a stack of vertically repetitive sequences or rhythms, element and gastropods and serpulids are common. With- each with an erosive bivalve-rich base and a rootletted top in the overlying greenish grey to light olive grey siltstones (Bradshaw, 1978). At Nettleton, only the lower member and sandstones an abundant macrofauna of pectinids appears to be present. Sandstones fine upward into (again mostly P. (Parvamussium) ) and “Astute ” minima mudstones and claystones of varying shades of green and (Phillips), accompanied by Gervillella, Meleagrinella cf. brown ; black, intensely carbonaceous layers also occur lycetti (Rollier), ? Trigonia and high spired gastropods and the sequence is rootletted throughout. Only the base is lost upward whilst macroscopic plant debris remains of the Upper Estuarine “Series” is illustrated in Fig. 2, abundant. Though intensely bioturbated in places, the and the reader is referred to Bradshaw & Penney (1982) sandstones display even lamination with rare low angle for the rest of the Great Oolite succession. erosion surfaces, and contain carbonaceous and micaceous siltstone interlaminae. Thin coal layers occur STRATI GRA PHY toward the top of the sandstones, which are followed The Hibaldstow Beds of north Lincolnshire and south by thinly interlayered very fine sandstone, dark car- Humberside pass north of the Humber into the Cave bonaceous mudstone and minor coal, with rootlets pene- Oolite, a limestone tongue laterally equivalent to the trating down from a capping pyritic coal seam. The latter marine Cayton Bay Formation of the Cleveland Basin is 27 cm thick and becomcs muddy upward, grading into (Bate, 1967; Parsons, 1980). Hence the section en- 3 cm of thinly interlayered carbonaceous mudstone and countered above the Hibaldstow Beds and below the light olive grey siltstone before an important erosion Upper Estuarine “Series” at Nettleton, with its root- surface at 341.69 m. Very light grey unfossiliferous letted sandstones and coal followed by a thin marine unit, sand-filled burrows extend up to 12 cm below but are invites a lithostratigraphic correlation with strata follow- truncated by this surface ; they indicate that sandstone ing the Cayton Bay Formation in Yorkshire, namely the originally followed the interlayered lithology. deltaic Gristhorpe Member (of the Cloughton For- The greenish grey calcitic siltstone above the erosion mation) and the overlying marine Scarborough surface contains thick-shelled bivalve debris, including Formation. oysters, and fines upward into medium grey and olive The abundance of Gervillella acuta, ‘Astarte’ minima grey mudstones and claystones. These beds contain a very and Cucullaea cuncelluta within the marine unit at well preserved macrofauna with extraordinary numbers Nettleton is reminiscent of the Scarborough Formation, of ‘Astarte’ minima and Gervillella acuta (J. de C. in particular the Hundale Shale Member (of Parsons, Sowerby), common Cuccullea cancellata Phillips 1977) on the Yorkshire coast, but the ostracod fauna, (probably a Crammatodon) and Procerithium, also whilst confirming a Scarborough Formation age, suggests Modiolus, Camptonectes, oysters (cf. Praeexogyra), a time correlation with beds at the top of or slightly

144 Scarborough Formation in Lincolnshire above the Hundale Shale. The abundance of Malzia Member in the Cleveland Basin, and original physical unicarinata in association with M. bicarinata and Glyp- continuity can be reasonably inferred. The upper part of tocythere scitula indicates the topmost part of the the Cayton Bay Formation on the Yorkshire coast con- Glyptocythere polita ostracod Biozone (of Bate, 1965, sists of the Yons Nab Beds, a highly variable but mostly 1978). The boundary between the G. polita and succeed- sandy and poorly calcareous unit which is differentiated ing G.scitula ostracod Biozones, as established by Bate from the overlying Gristhorpe Member sandstones and (1965), is recognised by the last occurrence of species mudstones by the presence of a marine bivalve and characteristic of the G. polita Biozone rather than the echinoderm macrofauna (Bate, 1959, 1967; Livera & first appearance of G.scitula. In the celebrated coastal Leeder, 1981). Using this criterion, the base of the section at Hundale Point near Scarborough (TA 026948), Gristhorpe Member at Nettleton should be drawn with- one of us (Bate, 1965) placed the base of the G. scitula in sandstone at a depth of 345.15 m (Fig. 2). The Biozone below a thick fossiliferous sandstone known as Gristhorpe Member hence becomes the uppermost unit the Crinoid Grit (bed 14 of Bate, 1965; = bed 12, the of the Lincolnshire Limestone Formation, and in its upper part of the Crinoid Grit Member of Parsons, sandy and argillaceous nature is comparable to the 1977). However, as no ostracods were actually obtained stratigraphically lower Raventhorpe Member. The from this unit, the zonal boundary could, with equal justi- 2.56 m of muddy limestones, mudstones and siltstones fication, have been placed above the Crinoid Grit within between the Gristhorpe Member and typical upper the shales of the Spindle Thorn Limestone Member (of Lincolnshire Limestone are provisionally included in Parsons, 1977). The ostracod biostratigraphies of the the Hibaldstow Beds, though a much-needed thorough sections at Ravenscar (NZ 988012) and other investi- investigation of the upper Lincolnshire Limestone north gated localities where the Crinoid Grit is present (Bate, of Lincoln may result in their separation as a formal 1965) are similarly equivocal, and we conclude that this member. distinctive unit is approximately age equivalent to the Nettleton beds. Ammonite evidence indicates that all FAC I ES INT ERPRETATI 0N three Subzones (romani, humphriesianum and blagdeni) The commonly cross-bedded skeletal and oolitic cal- of the Lower Bajocian humphriesianum Zone are repre- carenites and calcirudites (grainstones) of the upper sented in the upper half of the Scarborough Formation Lincolnshire Limestone are moderate to high energy of the Yorkshire coast, above the Crinoid Grit (Parsons, deposits which probably formed in a complex of mobile 1977). The lower part of the formation, including the sand shoals in water depths of up to 10 m (Standard Crinoid Grit, is therefore either of romani Subzone age FaciesBelt 6of Wilson, 1975). At Nettleton, the gradual or may belong to the upper sauzei Zone. Bate's (1965) upward passage from these limestones through mud- concept of the regional palaeogeography in Scarborough stones to siltstones and sandstones capped by coal clearly Formation times, that of a shallow marine embayment indicates coastal progradation (Fig. 2). Within the lime centred along the axis of the Cleveland Basin and opening grainstones at the base of the sequence, the upward in- to the east, was supported by Parsons (1977). However, crease in skeletal and ooid micritization is taken to the evidence for closure to the south with a peripheral indicate slowing rates of carbonate production, probably zone of sandstone deposition was based only on one in response to increasing water turbidity caused by incomplete exposure (Stonecliff Wood, SE 743676; Bate, suspended terrigenous mud. Bioturbation increases 1965) and the Fordon No. 1 Borehole (SE 05857575; upward and sorting worsens due to the admixture of faecal Falcon & Kent, 1960), which was not cored. A recent pellets. The occurrence of plant rootlets near the top of borehole, sited within the Howardian-Flamborough the grainstones suggests very shallow or emergent con- Fault Belt on the margin of the Cleveland Basin (at ditions, possibly near the crest of an offshore bar. The Brown Moor, SE 81266203; Gaunt et al., 1980), en- succeeding argillaceous packstones and claystones countered 2.8 m of fossiliferous Scarborough Formation accumulated on the landward side of the bar and con- in a mainly mudstone facies, and requires that the con- tain thin washover layers of sand-grade peloidal and figuration of the proposed embayment be modified (see micritized oolitic material. The low diversity bivalve- below). We believe that the faunal content and sedi- dominated macrofauna suggests a fairly high stress mentological setting of the thin Scarborough Formation environment, and the lack of stenohaline taxa such as equivalent at Nettleton indicates original physical con- corals and brachiopods, also the paucity of echinoderm tinutity with the Scarborough Formation of Yorkshire, remains, points to fluctuating and probably reduced and hence justifies the use of this lithostratigraphic name salinities. Abundant suspension-feeders, including for the highest beds of the Inferior Oolite Group in shallow burrowing forms, indicate a stable substrate and Lincolnshire. sufficient water turbulence- to carry suspended organic The rootletted sandstones and coal beneath the matter. Shoreface progradation is represented by a Scarborough Formation at Nettleton must signify the coarsening-upward from muddy lithologies to bio- same regression as that represented by the Gristhorpe turbated sandstones. The overlying interlayered sand-

145 Bradshaw & Bate

stones and carbonaceous mudstones contain thin drifted have been removed prior to or during the Scarborough coals and are remarkably poorly bioturbated; they Formation transgression. are penetrated by the well-developed root foundation In addition to revealing the wide spread of the of a capping coal seam and were probably deposited in a Gristhorpe Member regression, the Nettleton Borehole very shallow brackish lagoon. has disclosed a much greater extent of the Scarborough The Scarborough Formation at Nettleton has a sharp Formation than formerly thought. The marine trans- erosive base, and has removed an unknown thickness of gression at Nettleton appears to have coincided with Gristhorpe Member sediments. The macrofauna of the deposition of the Crinoid Grit in Yorkshire. This mudstones and claystones is dominated by non-siphonate latter unit overlaps older Scarborough Formation beds epifaunal and shallow infaunal suspension-feeding away from the axis of the Cleveland Basin (Bate, 1965; bivalves, and is comparable to the upper Hibaldstow Livera & Leeder, 1981). The speculative reconstruction Beds fauna in its rather low diversity and lack of in Fig. 1 of the limits of the marine basin during stenohaline taxa. Dinoflagellate cysts are rare and the Scarborough Formation times takes into account bio- microplankton consists largely of acanthomorph and stratigraphical and sedimentological evidence for initial sphaeromorph acritarchs, indicating a marginal marine westward transgression along the axis of the Cleveland setting; common Botryococcus reveals some input Basin from the Sole Pit Trough (Bate, 1965; Parsons, from freshwater/?brackish environments (Fenton, in 1977). The ammonite fauna supports a stronger marine Bradshaw & Penney, 1982), Shell plasters of aligned connection to northern Germany than to southern Gervillella valves and Procerithium reflect episodes of England (Parsons, op. cit.), and therefore any seaway increased wave or current activity, perhaps associated across central England between the London Platform with storms. and the Pennine Massif must have been shallow and Age-equivalents of the upper Scarborough Formation restricted. The Nettleton discovery suggests that, of Yorkshire are absent at Nettleton, and if deposited contrary to the views of Hemingway (1974) and Gaunt were probably removed by pre-Upper Estuarine et al. (1980), the Market Weighton area could have been “Series” erosion. Regional analysis of the lower part at least partially submerged on its eastern flank during of the Upper Estuarine “Series” suggests initially the maximum extent of the Scarborough Formation sea, isolated lakes which coalesced with rise in lake level and though the abundance of plant debris in the Brown Moor were then infilled, with the development of a broad marsh section (Gaunt et al., 1980) indicates the proximity of drained by small mixed load channels (Bradshaw, 1978). land, perhaps connected westward to an emergent Pcnnine Massif. CONCLUSIONS Finally, the Scarborough Formation’s preservation at The discovery of the Gristhorpe Member and the Nettleton indicates that the erosional event which Scarborough Formation beneath the Chalk Wolds of preceded deposition of the overlying Upper Estuarine north Lincolnshire has implications for the age of the “Series” on the East Midlands Shelf is of late Lincolnshire Limestone Formation at outcrop. The humphriesianum Zone or younger age. The resultant known ammonite faunas of the Lincolnshire Limestone unconformity is believed to be continuous with the well span the discites and laeviuscula Zones of the Lower known unconformity at the base of the Upper Inferior Bajocian (Ashton & Parsons, in press; Ashton, 1980; Oolite over southern England (Bradshaw, 1978). Parsons, 1980), but the highest member at outcrop, the calcarenitic Clipsham Member (of Ashton, 1980), has ACKNOWLEDGEMENTS not yet yielded ammonites. However, as the Scarborough The Nettleton Borehole was drilled as part of the Formation at Nettleton is either of earliest hum- Oxford University Heat Flow project, and M.J.B. phriesianum Zone age or belongs to the upper sauzei thanks Prof. E.R. Oxburgh and Drs. S.R. Penney and Zone, and is preceded by a regressive sequence with sands S. Richardson for allowing access to the core, which and coals, then the youngest limestone facies of the is now housed at the I.G.S., Leeds. Lincolnshire Limestone can be no younger than earliest sauzei Zone. Bearing in mind the interpretation of correlative strata in the Cleveland Basin (Hemingway, 1974; Livera & Leeder, 198l), the upper Hibaldstow Beds and Gristhorpe Member at Nettleton were probably deposited in a deltaic milieu by delta front progradation followed by the establishment of a lower deltaic plain. Fluvial- dominated upper deltaic plain sediments, which form the bulk of the Gristhorpe Member in Yorkshire (Livera & Leeder, op. cit.), are absent at Nettleton, but may

146 Scarborough Formation in Lincolnshire

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