Abstract
The Burnham Chalk Formation (Upper Cretaceous) in Lincolnshire is particularly well exposed at the large disused quarry at North Ormsby and, in north Lincolnshire, at the Ulceby Vale quarry. Biostratigraphical collecting by the author over a period of more than twenty years, in particular at North Ormsby, has yielded a large and varied fauna from the relatively fossiliferous interval between the Wootton Marls and the Ulceby Marl. This fauna is described herein, and is placed within the context of a reconstructed palaeoenvironmental setting.
Introduction
The Burnham Chalk Formation, the upper part of the flint-bearing Chalk of the Northern Province (Wood & Smith 1978) is exposed at North Ormsby Quarry, Lincolnshire (NGR TF 282 944) (Fig. 1), where the section extends from the base of the formation up to the level of the Vale House Flints Member (Green 2014). At Ulceby Vale Quarry (NGR TA 104 133), the section extends from the level of the North Ormsby Marl up to the Enthorpe Marls (Hildreth 2013). Both sections lie within the Plesiocorys (Sternotaxis) plana biozone (Upper Turonian). Within both quarry sections a prominent flint-rich interval (the Vale House Flints Member) situated between the Wootton Marls and the Ulceby Marl is exposed (Hildreth 2013). The lower part of this member corresponds in age to the Chalk Rock hardground complex of central England and contains faunal elements indicative of that horizon as discussed by previous authors (e.g. Wood 1981, 1992; Hildreth 2013).
Locality map of the Northern Province Chalk (stippled), showing the localities mentioned in the text (*) and major settlements (▪).
The aim of this paper is to build upon the work of previous authors by placing the macrofossils recorded by the author, where possible, within a stratigraphical framework. Attention shall also be drawn to the affinities and differences present at both localities in terms of the macrofaunal record. A palaeoenvironmental reconstruction of the fauna in the Vale House Flints Member is also presented.
Geological description
The Burnham Chalk Formation exhibits a sequence of relatively thickly bedded chalks, interbedded with marlstone bands and flint layers (Figs. 2 and 3). The Vale House Flints Member is 7 m thick at Ulceby Vale Quarry (its type locality) and extends from just above the Wootton Marls up to a level about 1 m below the Ulceby marl (Hildreth 2013). It is more thinly bedding than the rest of the Burnham Formation and contains numerous semi-tabular, carious, flint bands. In addition to exposures present at North Ormsby Quarry, the Vale House Flints Member is also exposed in Lincolnshire at West Ravendale Quarry (NGR TA 227 999) and at the Oaklands pit (NGR TA 207 055), although the exposures are rather inaccessible.
Lithological log of the Vale House Flints Member as exposed at the type locality at Ulceby Vale Quarry, North Lincolnshire (NGR TA 104 133) showing the lithological succession and macrofossil occurrences (after Hildreth 2013, fig. 5; image used with permission of the council of the Yorkshire Geological Society).
Lithological succession of the Vale House Flints Member as exposed at North Ormsby Quarry, Lincolnshire (NGR TF 282 944), showing the lithological succession and macrofossil occurrences. Vertical scale in m.
The change in lithology at the base of the Vale House Flints Member appears to coincide with the appearance of a more-diverse macrofauna (Green 2014). It is noteworthy that the chalk at North Ormsby is relatively soft, unusually so for that in the Chalk of the Northern Province, and also appears to contain a more abundant macrofauna than in successions further north. It is, however, uncertain to what extent this apparent increase in faunal diversity is due to better collecting conditions in these soft chalks, rather than to a more favourable ecological environment (Wood 1992). By contrast, the chalk at Ulceby Vale is significantly harder, which hinders the recovery of macrofossils (Hildreth 2013).
North Ormsby Quarry
The North Ormsby Quarry section (NGR TF 282 944) was previously described by Wood & Smith (1978); however, little information on the macrofauna was published. Hill (1902) was the first geologist to identify the then Holaster (now Plesiocorys) planus zone in the North Ormsby area of Lincolnshire, and his work was followed by that of Rowe (1929), who provided an admirable list of macrofossils. Wood (1992) stated that the Burnham Chalk of the North Ormsby area had a relatively high faunal diversity, but no accompanying data was included. Most recently, the North Ormsby section was described by Green (2014) who provided a skeletal lithological log and an accompanying list of macrofossils.
The Vale House Flints Member exposed at North Ormsby is around 8 m thick (Green 2014). The absence of the Ulceby Marl here indicates that the full succession is not exposed and, thus, its complete thickness is unknown, although measurement indicates a more expanded section than that present at the type locality of Ulceby Vale. Wood (1992) has stated that the Burnham Chalk of this area is relatively thicker than in successions nearer the Humber. Hildreth (2013) stated that there were lateral differences in flint distribution between North Ormsby Quarry in comparison with Ulceby Vale Quarry.
The lowest beds of the Vale House Flints Member at North Ormsby are represented by particularly well-weathered sections, best developed and accessible in the NE face of the quarry, which, upon examination, have yielded a rich fauna (Figs. 4 and 5). Green (2014) observed crinoid and bryozoan debris, small sponges (Porosphaera sp.), and a partially articulated asteroid, assigned to Metopaster ?parkinsoni (Forbes). Orbirhynchia sp., small Terebratulina striatula (Mantell) and asteroid ossicles have also been observed by the author at this level.
A palaeoenvironmental reconstruction of the animal community from the Vale House Flints Member (Upper Turonian stage, Plesiocorys (Sternotaxis) plana biozone) of Lincolnshire. This reconstruction is based upon macrofossils recorded mainly from the localities of the North Ormsby and Ulceby Vale quarries, where the best and most accessible sections of these beds are present. The softer chalk at the former locality afforded easier and more varied collecting. The faunas are indicative of a depositional environment of ‘normal’ conditions prevalent within the White Chalk Group, in contrast to the Chalk Rock hardgrounds present in the south of England. Sponges are represented by such forms as Ventriculites chonoides (Mantell) (1) (Fig. 5B), a form also prominent within the Chalk Rock of southern England. Small brachiopods such as Orbirhynchia sp. (2) are common, as well as the solitary coral Parasmilia sp. (3). Shape variants of the echinoid Echinocorys sp. (4) (Fig. 5C–E), exhibiting a swollen test at mid-height and a pointed apex, are present, albeit rare. Asteroids are represented by Metopaster hunteri (Forbes) (5). Roweaster corbovis (Forbes) (6) is present and is represented by well-preserved specimens at North Ormsby. Plesiocorys (Sternotaxis) plana Mantell (7) is also abundant. Other species recorded include Tylocidaris sp, (8), Inoceramus sp. (9), and rare ammonites such as Lewesiceras mantelli (Wright & Wright) (10) and Hyphantoceras reussianum (d'Orbigny) (11). The former species is depicted within the illustration inside the body chamber of a large ammonite, as was found in the field at Ulceby Vale. Fish are represented by rare isolated teeth such as the squatiniform shark, Scapanorhynchus raphiodon (Agassiz) (12).
Some common macrofossils of the Vale House Flints Member of North Ormsby Quarry. (A) Three-dimensional sponge sp. indet., NOLMS P3692, exhibiting very similar mineralogical preservation to the Flamborough Sponge Bed specimens from East Yorkshire. 105 mm in length and 30 mm across at the widest point. (B) The sponge Ventriculites chonoides (Mantell), NOLMS P3693, in three dimensional preservation. 85 mm long, 60 mm across at the widest point. (C-E) Three views of a shape variant of the holasteroid echinoid Echinocorys sp., NOLMS P3694, exhibiting a retracted base, swollen test and pointed apex. The specimen is 48 mm high, 52 mm across in mid height, and the base 45 mm across.
Several well-preserved, three-dimensional sponges have been recovered by the author from a prominent scree slope and originate from the Vale House Flints Member. These include Ventriculites chonoides (Mantell), ?Doryderma sp. and an unidentified form. These are preserved in a similar manner to sponges in the Flamborough Sponge Beds (Lower Campanian) of Flamborough Head (Reid 1968), this mode of preservation being rare within the lower part of the Burnham Chalk Formation. The presence of V. chonoides in the Vale House Flints Member allows comparison with the Chalk Rock fauna of the central England where large numbers of well-preserved specimens of this species are present (Mortimore et al. 2001; Hildreth 2013).
Inoceramid bivalves include large, fragmented forms, commonly observed in cross section at various levels, which are probably referable to Inoceramus lamarcki stuemckei (Heinz). Small, thin-shelled, finely-ribbed forms, probably Mytiloides sp., also occur. Of particular note is a relatively large inoceramid, found in debris from the Vale House Flints Member, lacking the prominent, rugged, terrace-like rugae of I. lamarcki stuemckei and exhibiting a thin, poorly-inflated shell with finely developed growth lines. At a horizon recorded some 4 m above the Wootton Marls, a large specimen of the ammonite Lewesiceras mantelli (Wright & Wright) some 300 mm in diameter has also been found, in addition to well preserved Plesiocorys plana and the solitary coral, Parasmilia sp. It is noteworthy that the echinoid Roweaster corbovis (Forbes) has not been found in situ at North Ormsby, but it occurs abundantly, and in excellent preservation, in scree material. There is an undoubted horizon of these echinoids present at North Ormsby, but difficulties of access currently preclude identifying the origin of these forms. A shape variant of Echinocorys sp. has also been recovered from scree originating from the Vale House Flints Member, displaying a test with a retracted base, swollen at mid-height and a pointed apex.
Other species have also been recorded from debris from a prominent scree slope, deriving from the Vale House Flints Member, suggestive of the presence of an as yet unlocated, relatively fossiliferous horizon. Recorded species include a partial test of the regular echinoid Tylocidaris? sp. and fragments of large pachydiscid ammonites (Lewesiceras sp.). A tooth of the squatiniform shark Scapanorhynchus raphiodon (Agassiz) has also been recorded, along with a fragment of a possible nautiloid. A poorly preserved heteromorph ammonite may represent the innermost whorls of Hyphantoceras reussianum (d'Orbigny). This species has also been recorded in situ, just beneath the North Ormsby Marl at the present locality. The occurrence of this ammonite at this level is of particular interest, in that it lies stratigraphically below occurrences previously recorded in the Northern Province Chalk (Wood 1981, 1992; Whitham 1991).
Ulceby Vale Quarry
Ulceby Vale Quarry (NGR TA 104 133) has been described by Wood (1992) and Hildreth (2013, 2014). The Vale House Flints Member exposed at the type locality exhibits a thinner section than that present at North Ormsby, measuring 7 m in total; in contrast to the latter locality, the exposed section is complete.
In terms of previous faunal records, Rowe (1929) gave a comprehensive faunal list from the Holaster (now Plesiocorys) planus zone of the Ulceby area. Hildreth (2013) noted the occurrence, in the lowest beds of the Vale House Flints Member, of poorly preserved specimens of the sponge Ventriculites chonoides. The present author also noted the poor preservation of many macrofossils within the Vale House Flints Member at Ulceby Vale, as well as the difficulties arising from the hardness of the matrix that subsequently hindered the recovery of specimens (Hildreth 2013).
The following records of macrofossils that have been recorded are detailed here. Large specimens of the inoceramid bivalve I. lamarcki stuemckei are commonly observed in cross section at Ulceby Vale, as well as small brachiopods and irregular echinoids (Hildreth 2013). The echinoid R. corbovis also occurs within the Vale House Flints Member in a prominent band 3 m below the Ulceby Marl (Green 2014). It is of interest to note that the specimens recorded from Ulceby Vale are often of somewhat poorer preservation than specimens from North Ormsby. Whitham (1991) recorded a prominent band of echinoids (including R. corbovis) from 1 m below the Ulceby Marl at the Kilnwick Percy Quarry, east Yorkshire (NGR SE 843504). Hildreth (2013) recorded a poorly preserved Plesiocorys plana at a prominent stylolitic horizon, 1 m below the Ulceby Marl at Ulceby Vale Quarry, which he tentatively correlated with Whitham's echinoid horizon. It is unclear at present whether the horizon of R. corbovis recorded by the present author at Ulceby Vale is better correlated with Whitham's echinoid band at Kilnwick Percy or whether two echinoid bands may be present. This requires further research.
Echinocorys sp. is relatively rare in the Vale House Flints sequence at Ulceby Vale (Wood 1992). A large, thick tested specimen, collected loose from scree originating from above the horizon of the Wootton Marls, exhibited a test with very similar morphological characteristics to a test recorded from the scree slope at North Ormsby Quarry, suggestive of the occurrence within the Vale House Flints Member of a shape variant of this echinoid, from an as of yet undetermined horizon. The use of Echinocorys as a biostratigraphical indicator in the Northern Province Chalk has yet to be fully realised, as noted by Whitham (1991).
The ammonite L. mantelli has also been recorded at Ulceby Vale, both as a fragmentary specimen within the Vale House Flints Member and as fragments upon scree slopes. This is a common element of the Chalk Rock fauna in central England (Wright 1979; Wright & Kennedy 1987). A large steinkern (body chamber) of Lewesiceras from the Vale House Flints Member at Ulceby Vale was broken open and contained a well-preserved, apparently juvenile Lewesiceras, preserved in green glauconite, this being a rare mineral within the Burnham Chalk Formation (Wood 1992). Fish debris has also been observed in another large ammonite steinkern at Ulceby Vale by the author, this possibly demonstrating the preservation potential of the larger ammonite shell against dispersal and dissolution of these faunal elements on the original sea floor. The shielding function of large ammonite shells on the chalk sea floor has been remarked upon by previous authors, the most notable example being the fauna described from the lower Micraster cortestudinarium zone at the Kiplingcotes quarry (Wright 1935, 1979), although at the time the author mistakenly placed this occurrence within the Holaster planus zone (Wood 1981).
Two fragmentary specimens of the heteromorph ammonite H. reussianum have also been obtained from loose scree material from above the Wootton Marls at Ulceby Vale Quarry. The occurrence of this species at Ulceby Vale has not been previously noted, but has been documented on the former site of the adjacent Vale House Quarry at Ulceby (NGR TA 1070 1340) by Mortimore & Wood (1986).
Reconstruction of the palaeoenvironment
The macrofauna as discussed above is depicted in Figure 4 in the context of a life reconstruction, based on the prevailing paleoenvironment present in the Vale House Flints Member of the Burnham Chalk Formation. The specimens were studied from the original macrofossils from the localities under discussion, and placed within their respective life and death positions in the context of the original sea floor. In terms of abundance and diversity, the illustration represents a composite image that brings together the fauna in their most likely respective modes of life and death, but it would not necessarily be the case that such diversity would be present at any one time on the chalk sea floor, given the relatively sparse nature of the macrofossils present in the host sedimentary rock.
Discussion
The exposures of the Vale House Flints Member in the lower part of the Burnham Chalk Formation at North Ormsby and Ulceby Vale quarries represent key sections that are of critical importance for lithostratigraphy and biostratigraphy, these being the best and most accessible sections currently present in Lincolnshire. This member represents a relatively fossiliferous and lithologically distinct unit within the Burnham Chalk Formation which, in its lower part, corresponds to the Chalk Rock of central England. Within this context, both sections are worthy of conservation and future study. The softer chalk at North Ormsby appears to yield a relatively more abundant fauna than that at Ulceby Vale, and in many cases the fossils are often better preserved and also easier to extract. Echinoids are particularly well preserved and common at North Ormsby, and well-preserved, three-dimensional sponges also occur. The present paper strengthens the case for faunal differences as well as affinities in terms of occurrences and preservation factors between the two localities.
Acknowledgements
I thank Mr Richard Treadgold for permitting access to the North Ormsby Quarry for both collection and research purposes, and to the Clugston group of Scunthorpe, North Lincolnshire, for permitting access to Ulceby Vale Quarry. Professor Rory Mortimore is also thanked for his advice and encouragement during preparation of this paper, as well as Professor Steve Donovan and Mr Morgan Vickers for their assistance with figures. Mr Dean Lomax is warmly acknowledged for his helpful comments and informal discussion. I also thank Professor Simon Mitchell and Mr Paul Hildreth for their helpful reviews, and suggestions in order to improve this manuscript.
Funding
This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.
Scientific editing by Stephen K. Donovan
- © 2018 The Author(s). Published by The Geological Society of London for the Yorkshire Geological Society. All rights reserved
References
The macrofauna of the Vale House Flints Member (Burnham Chalk Formation, Upper Turonian, Late Cretaceous) of Lincolnshire and a palaeoenvironmental reconstruction
