Smokejacks Brickworks, Surrey

[TQ 112 374]

Introduction

Smokejacks Brickworks, near Ockley, Surrey (Figure 4.2) is part of a network of early Cretaceous (Wealden) GCR sites in southern England (see also GCR site reports for Clockhouse and Auclaye brickworks). The Early Cretaceous strata here are slightly younger (Barremian Stage, c. 128 Ma) than those at Clockhouse Brickworks.

The Smokejacks Brickworks pit is particularly renowned as the site of the 1983 discovery of a new genus of theropod dinosaur Baryonyx walkeri and the enigmatic plant Bevhalstia pebja. Previously, crocodilian and iguanodont remains were found in the 1950s and more recently in 2001 (Nye et al., 2008). The site is not as productive for fossil insects as the nearby Clockhouse Brickworks, but nevertheless fossil insects belonging to ten different orders have been found here and are well preserved in sideritic concretions. Within the quarry there are sections through the Upper Weald Clay, which has been worked as a raw material for brick making for some time. In addition to the fossil arthropod importance of this site, the area is also selected for the GCR for the Jurassic–Cretaecous Reptilia and Wealden selection categories.

Description

The Weald Clay is exposed in Smokejacks Brickworks as a succession of clays with subordinate sandstone of Early Cretaceous (Barremian age), lying well above the Hastings Beds.

This actively worked pit exposes 23 m of Upper Weald Clay beneath BGS bed number 5c (Alfold Sand Member) of early Barremian age, changing from dark blue-grey below to greenish-grey and reddish-brown above, associated with shoaling (Jarzembowski, 1991). A section is given by Batten (1998, (Figure 4.73)).

Fauna

This early Barremian site is famous for having yielded the theropod dinosaur Baryonyx walkeri ('Claws') as well as herbivorous dinosaurs, crocodile and pterosaur bones. Insect remains commonly occur in silty ironstone (sideritic) concretions. Also found in the ironstone are burrows, plant stem/rootlet casts, clay clasts, fish fragments and egg cases, isopods, conchostracans, bivalve fragments and gastropod operculae, ostracods, plant remains including the fusainized fern Weichselia, conifers, and the early aquatic angiosperm Bevhalstia pebja (Hill & Jarzembowski, 1996). The insect remains are often concentrated in partings or thin layers and include ten orders:

Blattaria/Blattodea (cockroaches and cockroachoids)

Coleoptera (beetles)

Diptera (true flies)

Hemiptera (bugs)

Hymenoptera (wasps)

Isoptera (termites)

Mecoptera (scorpionflies)

Neuroptera (lacewings)

Odonata (dragonflies)

Orthoptera (crickets and 'grasshoppers')

Aquatic insects include adult Odonata comprising true dragonflies like the aeschnidiid Lleidoaeschnidium maculatum Fleck & Nel, 2003 and petaluridan Pseudocymatophlebia bennigi Nel et al., 1998 (in its own subfamily Pseudocymatophlebiinae, known only from this pit); darters are represented by the widespread Cretaneophya strevensi Jarzembowski & Nel, 1996a,b and damselflies by the equally widespread Cretarchistigma greenwoodi Jarzembowski et al., 1998.

Blattodea are discussed by Ross (2001) and Orthoptera by Jarzembowski (1999, (Figure 4.74)). A true cricket, bush cricket and grasshopper are formally described and named by Gorochov et al. (2006). Mecoptera include undescribed 'Protomecoptera' and Hemiptera, and an unusual plant hopper (Jarzembowski, 1987). Neuroptera include a psychopsid resembling the typically Purbeck genus Pterinoblattina (Ross and Cook, 1995; Austen et al., 2003). Hymenoptera include the parasitoid Manlaya ockleyensis Rasnitsyn & Jarzembowski known only from here, and the widespread digger wasp Archisphex boothi Jarzembowski (Rasnitsyn, Jarzembowski and Ross, 1998) (Figure 4.78). Coleoptera include basal Archostemata (Zygadenia [Notocupes]: Austen, 2005) and higher beetles (Jarzembowski and Ross, 1993, (Figure 4.75)). Diptera are uncommon, but notables include two species of biting snipe flies: Athericites kensmithi and A. gordoni Mostovski, Jarzembowski & Coram, 2003 (Figure 4.77) and (Figure 4.78) possibly associated with the vertebrates.

Interpretation

The sedimentary environment in which the insect remains are preserved has been interpreted as representing to overbank deposits developed during a flood (Benton and Spencer, 1995, p. 234). The overall environment of deposition of the Weald Clay has been reconstructed by Allen (1976, p. 414) as an alluvial floodplain with lagoons and short-lived sand-filled channels (Figure 4.79). With links to the East Anglian Sea to the north-west, salinities varied from nearly marine to freshwater. All sediments were liable to exposure, as reflected by the presence of large dinosaur footprints in the sands, suncracks and mudflake conglomerates, soil beds and horsetail stems in life position.

The fossil biota combines both terrestrial forms (such as the dinosaurs and trees) and aquatic (freshwater-brackish) ones such as crocodilians, fish and molluscs. The insects and other arthropods also include both terrestrial forms (such as the cockroaches and wasps) and freshwater aquatic ones (such as the ostracods and conchostracans).

The insects are typically preserved in sideritic (iron carbonate) concretions showing more details than the siltstones at Clockhouse Brickworks (see GCR site report). Such ironstone preservation is usually associated with the Carboniferous Coal Measures or even the Lower Tertiary deposits in the UK (Chapter 5). Some insect species from Smokejacks Brickworks are widespread, for example, the orthopteran Panorpidium bimaculatum Gorochov et al., 2006, whereas others belong to genera only know from this pit, e.g. the cricket Speculogryllus Gorochov et al., 2006, and a problematic 'grasshopper' (Baldock, 1999). Mesochlorogomphus crabbi Fleck et al., 2008, is a dragonfly from here uniquely in its own family, Mesochlorogomphidae. Also found is the only Weald Clay representative of the extinct neuropteran (lacewing) family Kalligrammatidae, typically know from the Solnhofen Plattenkalke Lagerstaette. Wealden Neuroptera are dominated by Psychopsidae (silky lacewings) unlike the myrmeleontoid (e.g. antlion)-dominated fauna from the arid Brazilian Lower Cretaceous (Jepson pers.comm.). A relatively humid Weald Clay climate is supported by the much more common cockroach (Blattodea) remains.

Conclusion

Part of a network of sites (see also GCR site reports for Clockhouse and Auclaye brickworks) in the Weald Clay, this early Cretaceous site has younger (Barremian, c. 128 Ma) strata than Clockhouse Brickworks. Although insects are less common here than at Clockhouse Brickworks, nevertheless, fossil representatives of some ten orders of insects have been found in more detailed preservation. The preservational facies — in sideritic ironstones — is more commonly associated with the British Carboniferous and complements the other Wealden insect GCR sites dominated by slltstone or phosphatic concretions. The Smokejacks fossil insects include taxa unique to this pit as well as representations of widespread Lower Cretaceous species. The site is also famous for its reptile remains and was selected separately within the GCR for its fossil reptiles. The extensive excavation offers considerable potential for future finds.

References