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Pitch Coppice: GSSP for the Gorstian Stage and base of the Ludlow Series

Lithostratigraphic units: Topmost Much Wenlock Limestone Formation and basal Lower Elton Formation. Pitch Coppice is the type section for the base of the Lower Elton Formation.

Pitch Coppice was initially proposed as the standard section for the coincident base of the Ludlow Series and its lower (then Eltonian) stage. This was later endorsed by the Silurian Subcommission (Martinsson et al., 1981).

Locality: Old quarry 35 m south of Wigmore Road (Mortimer Forest stop 3), ~4 km SSW of Ludlow, Shropshire (grid reference SO 472 730). Two further small quarries (Mortimer Forest Stops 1 and 2), within the Much Wenlock Limestone Formation, occur immediately west of Pitch Coppice (grid refs SO 472 730 and SO 471 730).

Lithology and fossil constituents

Pitch Coppice and the two stratigraphically lower quarries (Mortimer Forest Stops 1 and 2) contain the upper 14 m of the Much Wenlock Limestone Formation. Sedimentation here occurred in an extension of the depositional setting represented by the off-reef tract recognised on Wenlock Edge, and the lithology comprises poorly fossiliferous, carbonate mudstones, wackestones and silty mudstones. The lowest beds consist of blue grey carbonate mudstones separated by thin silty mudstone partings (84 cm). Above is a distinctive interval (~4.8 m) of rhythmically bedded carbonate mudstones (beds and nodules) and silty mudstones of equal or greater thickness. Towards the top of the section at Mortimer Forest Stop 1 the silty mudstone content is reduced, resulting in a predominance of carbonate mudstone beds. These give way above (in the quarry Mortimer Forest Stop 2) to nodular limestones with thin silty mudstone partings and a thin bentonite (PC1).

Pitch Coppice quarry (Mortimer Forest Stop 3) exposes the topmost 3.35 m of the Much Wenlock Limestone Formation and 2.8 m of the overlying Lower Elton Formation (Siveter in Aldridge et al. 2000). The GSSP level is at the boundary of these two formations. The Much Wenlock Limestone Fm at Pitch Coppice comprises grey, nodular limestone with thin silty mudstone partings. Additional features include two thin bentonitic bands (PC2 and PC3) and a prominent silty mudstone band (18 cm), 70 cm above the floor of the quarry. The Much Wenlock Limestone Fm yields a sparse but varied macrofauna including bryozoans, Brachiopods (Atrypa, Gypidula, Leptaena, Resserella, Sphaerirhynchia, Strophonella), crinoid ossicles, corals (Favosites, Heliolites, Thecia), gastropods, and rare trilobites (Dalmanites, Proetus).The corals and relatively large brachiopods are characteristic of the unit here.

The basal Lower Elton Fm comprises shaly siltstones with impersistent limestone beds and nodules. Thin (1-2 cm) crinoidal beds indicate episodes of storm sedimentation. A bentonite (PC4) occurs 0.25 m above the base. The fauna of the Lower Elton Formation here is mostly fragmentary, with many species also common to the underlying unit, although small brachiopods are particularly  characteristic (Lawson & White, 1989).


Graptolites recorded from Pitch Coppice are fragments possibly belonging to Saetograptus varians and Neodiversograptus nilssoni from 0.03 m and 0.23 m above the base of the Elton Formation respectively (White, 1981). These suggest the base of the Lower Elton Formation lies at or close to the base of the nilssoni Biozone (Lawson & White, 1989; Ray et al. 2010). No widely correlatable changes in microfaunas occur at the GPTS level (Siveter in Aldridge et al., 2000).

Sequence stratigraphy

Mortimer Forest Stops 1 to 3 contains parasequences PS9 to PS12, as interpreted from Wenlock Edge and the West Midlands (Ray et al., 2010). PS10 is the thickest of the parasequences (~12 m thick) and represents abrupt shallowing near the top of the Much Wenlock Limestone. Above, a prominent silty mudstone band marks the flooding surface of PS11 and the gentle onset of relative sea-level rise. As at the nearby Lea Quarry South and Wren’s Nest Hill near Dudley, the base of the Lower Elton Formation coincides with the base of PS12. This marked deepening is the local reflection of a eustatic change (Highstand 6 of Johnson, 2006). As such the base of PS12 may be a suitable means to correlate the GSSP level at Pitch Coppice more widely across the Midlands Platform.

Isotope stratigraphy

δ13Ccarb values from the Much Wenlock Limestone Formation range from 0.44‰ to 1.25‰ and are generally higher than those of the Lower Elton Formation (-1.82‰ to 0.99‰). This more negative upwards change across the Wenlock-Ludlow boundary has also been reported from Pitch Coppice and other locations across the Midland Platform (Marshall et al,. 2012; Blaine et al., 2016) and Welsh Basin (Corfield et al., 1992). These changes correlate with the declining limb of the younger positive peak of the Homerian (Mulde event) positive carbon isotope excursion. Correlation of the many isotope datasets now from the Midland platform suggest some diachroneity of the parasequence boundaries between distal and proximal settings (Blaine et al., 2016).

Other stratigraphy

A magnetostratigraphy has been obtained by Hounslow and others from sections in the mid Sheinwoodian to early Gorstian strata in the Wenlock edge area, the results of which will be presented later. Five bentonitic horizons in the three quarries (Mortimer Forest Stops 1 to 3), are seen as blue-grey or rusty orange bands, slightly more clay rich than the surrounding strata. The thickest of the bentonites (PC4) occurs 0.25 m above the base of the Lower Elton Formation and has been sampled for zircons, but was of insufficient quality and number for radiometric dating (Thomas & Ray, 2011). However, zircons from a bentonite layer in the mid parts of parasequence PS12 at Wrens Nest have yielded a radiometric date of 427.9±0.32 Ma (Cramer et al., 2012).

Source: Mostly derived directly from Thomas & Ray (2011) with additional diagrams from Melchin et al. (2012)



Aldridge, R.J., Siveter, David, J., Siveter Derek J., Lane, P.D., Palmer, D. and Woodcock, N.H. 2000. British Silurian stratigraphy. Geological Conservation Review Series, Joint Nature Conservation Committee, Peterborough. 542 pp.

Blain, J. A., Ray, D. C., & Wheeley, J. R. 2016. Carbon isotope (δ13Ccarb) and facies variability at the Wenlock–Ludlow boundary (Silurian) of the Midland Platform, UK. Canadian Journal of Earth Sciences, 53, 1-6.

Corfield, R.M., Siveter, Derek J., Cartlidge, J.E. and McKerrow, W.S. 1992. Carbon isotope excursions near the Wenlock–Ludlow (Silurian) boundary in the Anglo-Welsh area. Geology 20, 371-374.

Cramer, B. D., Condon, D. J., Söderlund, U. et al. 2012. U-Pb (zircon) age constraints on the timing and duration of Wenlock (Silurian) paleocommunity collapse and recovery during the “Big Crisis”. Geological Society of America Bulletin, 124, 1841-1857.

Johnson, M.E. 2006. Relationship of Silurian sea-level fluctuations to oceanic episodes and events. Geologiska Föreningen I Stockholms Förhandlingar, 128, 123-129.

Lawson, J.D. and White, D.E. 1989. The Ludlow Series in the Ludlow area. In: A global standard for the Silurian System (eds Holland, C.H. and Bassett, M.G.). National Museum of Wales, Geological Series,Cardiff, No. 9, 73-90.

Marshall, C., Thomas, A. T., Boomer, I. & Ray, D. C. 2012. High resolution δ13C stratigraphy of the Homerian (Wenlock) of the English Midlands and Wenlock Edge. Bulletin of Geosciences, 87, 669-679.

Martinsson, A., Bassett, M.G. and Holland, C.H. 1981. Ratification of standard chronostratigraphical divisions and stratotypes for the Silurian System. Lethaia 14, 168.

Melchin, M. J., Sadler, P. M.  Cramer, B. D.  et al. 2012. The Silurian Period, In: The Geologic Time Scale 2012. Gradstein F. et al. (eds), 525-558.

Ray, D. C., Brett, C. E., Thomas, A. T. & Collings, A. V. 2010. Late Wenlock sequence stratigraphy in central England. Geological Magazine, 147, 123-144.

Thomas A.T. & Ray, D.C. 2011. Pitch Coppice: GSSP for the base of the Ludlow Series and Gorstian Stage In: Siluria Revisited: A Field Guide. International Subcommission on Silurian Stratigraphy, Field Meeting 2011 (ed. D.C. Ray), 81 – 85.

White, D.E. 1981. The base of the Ludlow Series in the graptolitic facies. Geological Magazine 118, 566.