Kirtlington Old Cement Works Quarry

[SP 494 199]

Highlights

The Forest Marble Formation (Upper Bathonian) at Kirtlington Old Cement Works in Oxfordshire has yielded a rich and diverse fauna of fishes based on teeth, including a microshark assemblage. This unique freshwater assemblage within an otherwise marine succession also includes an important amphibian component.

Introduction

Kirtlington Old Cement Works Quarry in the village of Kirtlington, Oxfordshire, has produced good faunas of fossil fishes and amphibians from the Forest Marble (Late Bathonian). The quarry was formerly worked for the manufacture of cement, and it closed about 1930 (Figure 12.18). Although exposures were excellent (Odling, 1913; Arkell, 1931), some of the faces became obscured more recently (McKerrow et al., 1969; Palmer, 1973; Freeman, 1979). Fossil fishes, amphibians, reptiles, and mammals have been collected in recent years from the fimbriatus–waltoni Beds and from the Kirtlington Mammal Bed, a microvertebrate locality near the base of the Forest Marble (Freeman, 1976, 1979; Evans, 1989, 1990, 1991, 1992; Evans et al., 1988, 1990; Evans and Milner, 1991, 1994).

Description

The succession in the quarry has been described by Odling (1913, pp. 493–4), Arkell (1931, pp. 570–2), Douglas and Arkell (1932, pp. 123–4), and Richardson (1946, pp. 69–71, 78–9). Additional information has been provided by McKerrow et al. (1969), McKerrow and Kennedy (1973) and Freeman (1979). The following composite section is based on these authors, and Richardson et al. (1946), in particular, with additions from Palmer (1973, 1979) and Torrens (1980, p. 36; numbering of individual beds is from the top down):

This section was recorded by Arkell (1931) in various parts of the quarry, which means that it is not a true log because of the large amount of lateral facies variation. The lower parts (Beds 8–13 in particular) are hard to match with the logs given by McKerrow et al. (1969, p. 58) because certain units, such as the Epithyris Limestone (Bed 11; Bed 1e of McKerrow et al., 1969), are laterally impersistent.

There are problems in correlating the lithostratigraphy of the units in this quarry with those elsewhere in the northern Cotswolds, particularly the boundary between the White Limestone and the Forest Marble (e.g. Odling, 1913; Arkell, 1931, 1947a; Richardson et al., 1946).

McKerrow et al. (1969) attempted a definition based largely on the oysters, and took the base of the Forest Marble to be at the base of the Oyster–Epithyris Marl (Bed 7), as had Arkell (1931) initially. Palmer (1973, p. 61) pointed out that at Kirtlington the Coral–Epithyris Limestone (Bed 5) has a typical White Limestone fauna and lithology, and lowered the Forest Marble-White Limestone boundary to between Beds 4 and 5. Palmer (1979) further argued this point and divided the White Limestone Formation into three members, of which the Ardley Member (Beds 8–13) and the Bladon Member (Beds 5–7) are seen at Kirtlington. Palmer (1979, p. 208, fig. 5) made it clear that his Bladon Member is intended to include both the fimbriatus–waltoni and Upper Epithyris Beds of the Cherwell valley which rest on the A. bladonensis Bed. Torrens (1980, p. 36) recommended that the base of the Forest Marble be taken as 'the base of the clay overlying the Coral-Epithyris bed, or of the bed above at Kirtlington' (i.e. the base of Bed 3 or 4).

Vertebrates occur in the fimbriatus–waltoni Beds (Beds 2o, 3i, 4e, 6f of McKerrow et al., 1969; base of the Bladon Member; Palmer 1979), and the Kirtlington Mammal Bed. The fimbriatus–waltoni Beds are greenish grey or black clay, which is often lignitic toward the base. Phillips (1871) recorded fish remains in association with the large bones of the sauropod dinosaur Cetiosaurus oxoniensis, within lignite resting upon the eroded surface of the underlying limestone. Since then other authors have reported large reptilian bones from the same beds (Richardson et al., 1946; Arkell, 1931) and these are outlined in the GCR volume on fossil reptiles (Benton and Spencer, 1995).

The Kirtlington Mammal Bed (Bed 3p of McKerrow et al. 1969) is an impersistent lens, 21.5 m long and 0.04–0.25 m thick, in the northeastern corner of the quarry ((Figure 12.18); Freeman 1979, p. 136). The fish fauna within this unit occurs as dissociated remains of a variety of bony fishes and sharks. Associated fossils include microscopic freshwater charophytes, indeterminate plant fragments, and ostracods (Evans and Milner, 1994). The tetrapod remains include amphibians, reptiles and mammals (Evans and Milner, 1991, 1994). Most of the vertebrate material occurs as isolated elements, and some specimens show signs of abrasion and transport. However, delicate bones are also preserved in the accumulation. Some remains of marine fish in this horizon are regarded as being derived from the underlying White Limestone, along with marine invertebrates such as corals, brachiopods and echinoderm material (E. Freeman, pers. comm. to Evans and Milner, 1994). By contrast, a few genera (including much of the amphibian material) have most of their skeletal elements preserved, these are possibly those which have been transported least.

Fauna

It is assumed that older fish specimens labelled 'Kirtlington' in collections came from the fimbriatus–waltoni Beds, where there were extensive excavations for large reptilian remains (e.g. Phillips, 1871), since the microvertebrate remains of the Mammal Bed were not exploited before bulk preparation by Freeman (1976, 1979) and the University College, London, team (Kermack et al., 1987).

(1) fimbriatus–waltoni Beds (data from Phillips, 1871)

Chondrichthyes: Elasmobranchii: Euselachii: Hybodontoidea

Asteracanthus sp.

Hybodus sp.

Osteichthyes: Actinopterygii: Neopterygii: Halecostomi

Pycnodonts indet.

Eomesodon bucklandi Woodward, 1918

Proscinates (Microdon)sp.

Lepidotes sp.

(2) Kirtlington Mammal Bed (data from Freeman, 1979; Evans and Milner, 1991, 1994; Evans et al., 1988, 1990).

Chondrichthyes: Elasmobranchii: Euselachii: Hybodontoidea

Asteracanthus sp.

Hybodus polyprion Agassiz, 1843

Hybodus sp.

Lissodus pattersoni Duffin, 1985

L. wardi Duffin, 1985

Chondrichthyes: Elasmobranchii: Neoselachii:

Batomorphii

Spatbobatis sp.

'batoid'

Osteichthyes: Actinopterygii: Neopterygii: Halecostomi

Eomesodon sp.

Lepidotes sp.

pycnodont indet.

Osteichthyes: Actinopterygii: Neopterygii: Holostei: Halecomorphi

?amioid

TETRAPODA

Amphibia: Lissamphibia: Anura

Eodiscoglossus oxoniensis Evans, Milner and Mussett, 1990

Amphibia: Lissamphibia: Caudata

Marmorerpeton freemani Evans, Milner and Mussett, 1988

M. kermacki Evans, Milner and Mussett, 1988

Salamander A

Salamander B

Amphibia: Lissamphibia: Albanerpetontidae

Celtedens sp.

Interpretation

The biostratigraphy of the Bathonian at Kirtlington is difficult since no ammonites have been found locally, and very few elsewhere in comparable rocks (Torrens, 1969a, 1980). Finds of ammonites in the White Limestone of the Oxford area have permitted correlation of this unit with the subcontractus and morrisi Zones (Mid-Bathonian), and the hodsoni and lower aspidoides Zones (Late Bathonian), while the Forest Marble Formation is largely aspidoides and basal discus Zones (Late Bathonian) on the basis of correlation of beds above and below.

The approximate zonal assignments of the three members of the White Limestone Formation are: Shipton Member, ?subcontractus and morrisi Zones, Ardley Member, ?lower hodsoni Zone, and Bladon Member, ?upper hodsoni–lower aspidoides Zones (Palmer 1979; Torrens, 1980). However, the evidence for zonation of these members is 'not compelling' (Torrens, 1980, p. 37), and ostracod zonation (Bate, 1978) places the White Limestone of the Oxford area in ostracod zones 5–8, the Forest Marble and Cornbrash resolving to the top of zone 8 and above ( = upper discus Zone).

The vertebrate-bearing fimbriatus–waltoni Beds (base of the Bladon Member) are thus dated as upper hodsoni Zone (basal Late Bathonian; Torrens, 1980, p. 36). However, the occurrence of the ostracod Glyptocythere penni in the fimbriatus–waltoni Beds led Bate (1978) to suggest that this unit belongs to the discus Zone. The Kirtlington Mammal Bed falls within the aspidoides or discus Zone (Freeman, 1979, p. 136).

Environmental interpretations have been made on the basis of the sedimentology of the fimbriatus–waltoni Beds. McKerrow et al. (1969, pp. 61–4, 80) interpreted the abundance of lignite and occasional caliche-like nodules as indicating shallow water with occasional subaerial exposure. Palmer (1979, pp. 210–11) noted the complex channelled interdigitations of this unit at Shipton ([SP 47 17]), and suggested that deposition of some of the clays was local and catastrophic, and that the nodules were derived from elsewhere. He also (1979) supposed a quiet-water lagoonal environment subject to periodic current activity and influx of new sediment, perhaps during storms.

The marl sediment of the Kirtlington Mammal Bed contains subangular pebbles of oolitic limestones, comminuted shell debris, individual ooliths and rare silica sand grains, all of which suggest a temporary freshwater pool that received periodic influxes of poorly sorted sediment derived from local erosion of earlier Mid-Jurassic limestones (Freeman, 1979, p. 139). The ostracods, charophytes and fishes lived in the pool, and the plants and tetrapods presumably lived nearby.

As outlined by Evans (1990, p. 234), in Bathonian times Kirtlington lay on or near the south-west shore of a small island barrier some 30 km from the coast of the Anglo-Belgian landmass at a subtropical latitude of about 30°N (Palmer, 1979). Lignite, charophytes and freshwater ostracods and gastropods in the marly sediments suggests a coastal environment, which had low relief, with creeks, lagoons and freshwater lakes, rather like the Florida Everglades (Palmer, 1979). The vertebrate fauna of the Kirtlington Mammal Bed, with its fishes, amphibians and aquatic reptiles (choristoderes, crocodilians and turtles), agrees well with such a palaeoenvironmental scenario. Terrestrial elements, including the albanerpetonid amphibian, lizards, archosaurs and mammals, are much rarer (Evans and Milner, 1994); they may have been transported into the lagoon from inland.

The faunas of the two vertebrate-bearing beds at Kirtlington are rather different, which probably relates to preservational and environmental conditions rather than to the slight age difference. They will be discussed separately.

The only early reference to the fish fauna of Kirtlington is a brief mention of 'teeth of Hybodus, Pycnodus and Strophodus, and scales of Lepidotus'(Phillips, 1871, p. 244). Hybodus is a ubiqitous element in the classic Great Oolite sequences and the presence of this genus in the fimbriatus–waltoni Beds is not remarkable.

The reference to both pycnodont teeth and semionotid scales (Phillips, 1871) is also consistent with a shallow-marine fauna similar composition to other Great Oolite fish-bearing localities (cf. Rayner, 1958). The tetrapod fauna is dominated by long-snouted piscivorous crocodilians.

The fish, amphibians, reptiles and mammals from the Kirtlington Mammal Bed have been summarized by Freeman (1979), Duffin (1985) and Evans and Milner (1991, 1994). Details of the collecting and preparation techniques are given in Freeman (1976, 1979), Kermack et al. (1987) and Evans (1989). The reptiles have been described in the GCR fossil reptile sites volume (Benton and Spencer, 1995) and the mammals will be detailed in the GCR fossil mammal sites volume.

The fish fauna from the Mammal Bed is unremarkable; it contains the typical hybodont shark and halecostome bony fish components found in most Great Oolite Group assemblages. The microvertebrate fauna includes neoselachian teeth (Evans and Milner, 1994), and several may be attributable to the primitive ray Spathobatis, a genus present throughout the British marine Bathonian (D. Ward, pers. comm., 1993; S. Metcalf and C. Underwood, pers. comm.).

The bony fish component consists of disassociated teeth, and scales of various holosteans are the most abundant fossils within both meso- and microfossil fractions. The commonest is the pycnodont Eomesodon bucklandi, although Proscinates (Microdon)and at least one semi-onotid are also present. Microvertebrate samples contain gular plate and mandible fragments of far smaller fish; some of these, with closely spaced crushing teeth, may be a pycnodont. The vast majority of material is generically indeterminate. In many old collections it has been assigned to 'bucket genera' (e.g. Phillips, 1871; Woodward, 1890, 1892, Savage, 1963), especially Eomesodon, Lepidotes (ornamented bones and heavy scales) and Pholidophorus (light bones). Evans and Milner (1994) also record the presence of possible amioid teeth and jaws in the acid residues, which Freeman (1976) referred to Caturus. As with other Bathonian fish assemblages, there is some indication of durophagy (e.g. the hybodonts Asteracanthus and Lissodus, the 'batoid' neoselachian and the semionotid and pycnodont osteichthyans).

The amphibians include the dissociated and fragmentary remains of a frog referrable to the family Discoglossidae (Eodiscoglossus oxoniensis), four species of salamander (Marmorerpeton kermacki, M. freemani and two unnamed forms) and the small salamander-like Celtedens (Figure 12.19). Eodiscoglossus oxoniensis is the earliest identifiable discoglossid frog known, and one of the oldest frogs of modern aspect (Evans et al., 1990). The specimens of E. oxoniensis from Kirtlington are comparable with E. santonjae from the Early Cretaceous of Montsech, Lerida Province, Spain, but they may be clearly distinguished by characters of the ilium and premaxilla. The only older frogs are the primitive Triadobatrachus from the Early Triassic of Madagascar, Vieraella from the Early Jurassic of Argentina and Prosalirus bitis from the Kayenta Formation (Pliensbachian, Early Jurassic) of Arizona (Shubin and Jenkins, 1995).

The record of the albanerpetontid is one of the oldest of this enigmatic tetrapod family, the oldest being from the Bajocian of Aveyron, France (Evans and Milner 1994). The ?amphibious albanerpetontids are also known from a range of localities including those in the Jurassic of Portugal, the Cretaceous of North America and Spain and the Miocene of France (McGowan, 1994; McGowan and Evans, 1995). Albanerpetonids were slender little animals, superficially not unlike newts.

Marmorerpeton kermacki and M. freemani are the earliest known salamanders (i.e. true Caudata; Evans et al., 1988), more primitive than any other known forms, as shown by the absence of intravertebral spinal nerve foramina in the atlantal centrum. In other features these taxa resemble members of the family Scapherpetonidae, which comprises neotenous forms otherwise known only from the Late Cretaceous and Palaeocene. At present Marmorerpeton is under revision and its tentative attribution to the Scapherpetonidae, is unlikely to stand (S. Evans, pers. comms., 1994). Salamanders A and B are yet to be described.

Comparison with other localities

The fish and amphibian remains from Kirtlington Cement Works compare best with Mid- and Late Bathonian faunas nearby. The fimbriatus–waltoni Bed at Shipton-on-Cherwell quarry [SP 477 175] has yielded abundant fish remains (Evans and Milner, 1994) and a diverse fauna with Lissodus has been recovered from the 'Monster Bed' (Palmer, 1979) at Woodeaton Quarry, Oxfordshire ([SP 534 122]; Freeman, 1979, F. Mussett, pers. comm. to Evans and Milner, 1994). The Forest Marble at Tarlton Clay Pit, near Cirencester [SO 970 001], has yielded a similar but fragmentary fauna to that from the Mammal Bed at Kirtlington, including albanerpetontids and the enigmatic caudates Marmorerpeton, and Kirtlington salamanders A and B (Evans and Milner, 1994). The palaeoenvironment of the Tarlton site is similar to that of the Mammal Bed (Ware and Windle, 1980; Ware and Whatley, 1983). Sections of Forest Marble at both Swyre [SY 525 868] and Watton Cliff, Dorset (q.v.), yield a similar microvertebrate assemblage (Freeman, 1976; Evans and Milner,1994). Marine elements, such as selachian teeth, are much better preserved there, whilst the tetrapod material is generally abraded and water-worn, indicating transport (Evans and Milner, 1994) into a more high-energy offshore environment (Holloway, 1983). Finally, the small section of offshore Forest Marble at the Leigh Delamere service station, Wiltshire [ST 890 790], has also produced fragmentary and rolled microvertebrates including marine selachians and Salamander A (Evans and Milner, 1994; pers. obs., 1993).

Some older localities in the British Bathonian have yielded rich freshwater faunas; for example, Hornsleasow Quarry ([SP 132 323]; earliest Bathonian) has yielded a similar, but less diverse, fish fauna and comparable amphibian remains (Metcalf et al., 1992). At Stonesfield (q.v.; early Mid-Bathonian), and Huntsmans Quarry ([SP 125 254]; early Mid-Bathonian) elements of the Kirtlington fauna, (although no amphibian material) have been recovered. Marmorerpeton also occurs in the Kilmalaug Formation on Skye (Waldman and Evans, 1994).

The Kirtlington Mammal Bed fauna resembles later rather than earlier Mesozoic freshwater assemblages (Evans et al., 1988; Evans and Milner, 1994; pers. comm., 1993). Elements of the tetrapods are found in later assemblages, such as those at Guimarota (Oxfordian) and Solnhofen (Portlandian), the Late Jurassic-Early Cretaceous Purbeck in Dorset (q.v.), the Early Cretaceous at Utia and Las Hoyas, Spain, and the Late Cretaceous of the Lance Formation of North America.

Conclusion

Kirtlington Quarry represents the best late Bathonian site for a variety of amphibian groups, and it is the source of numerous new forms. Marine fishes from the fimbriatus–waltoni Beds are comparable with those from the same unit at several other sites in Oxfordshire, but the variety of material is greater than elsewhere, and the site is still readily accessible for further excavation. The Mammal Bed fauna includes a unique freshwater assemblage of small fishes and amphibians, several of which are the earliest known occurrences of their respective groups (the first discoglossid frog and salamanders). Altogether the diversity of these faunas from different depositional environments gives the site its conservation value.

References