Salthill Quarry, Clitheroe: a resource being revitalised

A while ago, SKD published a critique of the poor geoconservation practices on one of England’s most productive Sites of Special Scientific Interest (SSSI) of Mississippian age – the so-called scraped surface at Salthill Quarry, Clitheroe, Lancashire (Grayson, 1981; Bowden et al., 1997; Kabrna, 2011, locality 4) (Fig. 1; and see also Donovan, 2011). The locality is one of the best sites for Mississippian (Lower Carboniferous) echinoderms in northern Europe. It is particularly good for crinoids, but also for rarer blastoids and, if you are willing to process bulk samples, the spines and plates of echinoids (Donovan et al., 2003; Donovan & Lewis, 2011; Donovan, in press). However, when it was visited by SKD in 2010, the geological features were being overgrown by grasses and other plants; that is, the geological SSSI was being transformed, passively, into a botanical nature reserve.

Figure 1
Fig. 1. The crinoid bank (locality 4 of Kabrna, 2011) as it was in 2010, largely obscured by grass (after Donovan, 2011, fig. 1). Collectors (left and middle) approximately define the poor exposure of bedded limestone at that time, which extended a little way past the bush in the centre. The best collecting was along this line and lower, where crinoid debris accumulated as a fossil-enriched gravel. For an earlier view of this slope, see Donovan (2012, fig. 3A, B).

This situation persisted until recently. In April 2014, PK sent the following welcome e-mail to SKD:

“Following a talk on the Carboniferous geology of the Craven Basin two years ago for the Bowland AONB [Area of Natural Beauty] organisation, I levelled a ‘constructive’ criticism of the state of Salthill Quarry’s collecting ground and overgrown localities. I was not aware that in the audience there was a representative of Natural England, and also the Lancashire Wildlife Trust person who manages Salthill. At last things have been addressed this month. Of interest to you will be the turning-over of the slope where the crinoids can be found” (Fig. 2).

Figure 2
Fig. 2. Excavation under way in April 2014. This is approximately the area near the bottom of the slope, marked by the collector on the left in Fig. 1.

The earliest that we could all meet at the site was mid-July 2014 (Fig. 3). That is, for three months, the fresh exposure had been picked over by the local community of enthusiastic amateurs, school groups and so on. Despite arriving late in the day, collecting crinoids was good, certainly better than for many years hitherto. The easiest collecting was from float, which is a gravel rich in crinoid debris, particularly columnals and pluricolumnals, but also with uncommon cups and thecae (Fig. 4).

Figure 3
Fig. 3. Unlike 2010 (Fig. 1), even the sun was shining. The newly re-exposed surface of the crinoid bank, in July 2014, is once again highly productive. The grin on PK’s face suggests he has found something good, while PHD wraps up his latest find in tissue paper. However, this is still far less exposed rock than formerly (compare with Donovan, 2012, fig. 3A, B).

The specimens in Fig. 4 have been chosen to give a taste of some of the variety of material that can be collected (all are at the same magnification). Therefore, some crinoid pluricolumnals are tens of centimetres wide (Fig. 4A), some of the largest known, whereas crinoid cups and theca (Fig. 4D and E) can be dwarfed by them. The most common crinoid theca are those of monobathrid camerates – a group of monocyclic crinoids, which may be golf-ball-like in appearance (Fig. 4C, E and H), the cup being topped by a multi-plated roof called the tegmen. However, pluricolumnals (that is, fragments of crinoid column) and single columnals are far more common than any cup or theca. The pluricolumnal in Fig. 4B has broad radice scars, where the radices (=roots) attached, crossing several columnals and presumably formed part of the attachment structure. Pluricolumnals in Fig. 4F and G are infested by corals. That in Fig. 4F is encrusted by Emmonsia parasitica Phillips, and it was probably an obligate commensal relationship between the coral and the living crinoid (Donovan, in press). Cladochonus sp. (Fig. 4G) has been overgrown by the crinoid as a reaction to overgrowth of the living crinoid (see also Donovan & Lewis, 1999). This has produced a globular pluricolumnal superficially similar to a theca (compare Fig. 4G and H). In short, in a brief visit, the three of use accumulated a collection of crinoid specimens that include a range of sizes, shapes and palaeoecological signatures. All of our specimens are now deposited in the Naturalis Biodiversity Center, Leiden, the Netherlands (prefix RGM).

This cleaning exercise has done much to re-vitalise what was a tired site (Donovan, 2011), but it must only be regarded a good start. There are other concerns regarding preservation of this site, mainly botanical, but the excavation could be extended laterally (without disturbing any of the rare plants), largely along the strike, behind the photographer of Fig. 3, for perhaps 100m or more. An excavation could also be made to the right of the photographer, up the slope (that is, down section), where it would expose limestone and mudrock beds bearing different crinoid species. Further, it could be extended downslope (left of the photographer) to reveal the overlying cover Leagram Mudstone Member, which has never been particularly well exposed in this part of Salthill Quarry.

Figure 4
Fig. 4. Crinoids from Salthill Quarry, Clitheroe, Lancashire (Kabrna, 2011, locality 4), a selection of what was collected on the morning of 11 July 2014 by the authors (see Fig. 3). Scale bar equals 10mm. (A) RGM [A], Bystrowicrinus (col.) westheadi Donovan, 2013, a giant crinoid pluricolumnal, showing the articular facet.  (B) RGM [B], pluricolumnal with broad radice scar (upper centre) extending across several columnals and formerly part of the attachment structure (‘root’). (C) RGM [C], theca of a platycrinitid monobathrid (=monocyclic) camerate crinoid with basals and high radial plates apparent. Specimen crushed. (D) RGM [D], the conical cup of the small disparid (=monocyclic) crinoid Synbathocrinus sp. Note that none of the thecae or cup illustrated preserves the arms or stem. The endoskeletons of the many crinoids at this site all seem to have started to disarticulate, loosing arms and stems, but did not completely fragment. (E) RGM [E], a small monobathrid camerate theca, probably Amphoracrinus sp. (F) RGM [F], a pluricolumnal encrusted by the coral Emmonsia parasitica Phillips. The crinoid is presumed to have been alive during infestation, as the coral essentially engulfs the pluricolumnal through almost 360⁰, but there is no reaction by the host. (G) RGM [G], a strongly swollen pluricolumnal in which the living crinoid has overgrown the encrusting coral, Cladochonus sp. (compare with Donovan & Lewis, 1999). (H) RGM [H], the monobathrid camerate Amphoracrinus sp.; compare with the somewhat smaller specimen in (E).

In short, thank you. We applaud what has been done by the Lancashire Wildlife Trust to revitalise Salthill Quarry. We hope that this is the beginning of a new era of geological exploration at this site, rather than an end.

References

Bowden, A., Webster, M. & Mitcham, T. 1997. Salthill Quarry geology trail. Geologists’ Association Guides, 58: 30 pp.

Donovan, S.K. 2011. Salthill Quarry, Clitheroe: a resource degraded. Deposits, 25: 46-47.

Donovan, S.K. 2012. Stanley Westhead and the Lower Carboniferous (Mississippian) crinoids of the Clitheroe area, Lancashire. Proceedings of the Yorkshire Geological Society, 59: 15-20.

Donovan, S.K. 2013. Giant crinoid stems from the Lower Carboniferous (Mississippian) of northwest England. Proceedings of the Yorkshire Geological Society, 59: 211-218.

Donovan, S.K. (in press). Palaeoecology and taphonomy of a fossil sea floor, in the Carboniferous Limestone of northern England. Mercian Geologist: 4 pp.

Donovan, S.K. & Lewis, D.N. 1999. An epibiont and the functional morphology of the column of a platycrinitid crinoid. Proceedings of the Yorkshire Geological Society, 53: 321-323.

Donovan, S.K. & Lewis, D.N. 2011. Fossil echinoderms from the Mississippian (Lower Carboniferous) of the Clitheroe district. In Kabrna, P. (ed.), Carboniferous Geology: Bowland Fells to Pendle Hill: 55-96. Craven & Pendle Geological Society, UK.

Donovan, S.K., Lewis, D.N. & Crabb, P. 2003. Lower Carboniferous echinoderms of northwest England. Palaeontological Association Fold-Out Fossils, 1: 12 pp.

Grayson, R. 1981. Salthill Quarry Geology Trail. Nature Conservancy Council, London, 26 pp.abrna, P. 2011. Excursion 5. Pendle Hill and Clitheroe. In Kabrna, P. (ed.), Carboniferous Geology: Bowland Fells to Pendle Hill: 157-165. Craven & Pendle Geological Society, UK.


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