Bergam Quarry

[SO 3564 9974]

Introduction

This disused quarry (locality '8' in (Figure 10.1)) affords the best section in the 'Tankerville Flags' of Lapworth (1916) and has yielded a fauna of late Arenig age, including trilobite species common to the overlying Hope Shales. Apart from those in the 'Shelve Church Beds', this is the only locality in the Shelve area to have yielded a late Arenig fauna.

The 'Tankerville Flags' have been distinguished as the youngest Arenig division in the Shelve area (e.g. Whittard, 1931, p. 326) and are considered to correlate with the hirundo Zone. Whittard (1955–1967) used the term in his trilobite monograph, although in the penultimate part (1966, p. 303) he suggested that, despite its distinctive lithology and fauna, especially of trilobites, it could be applied only to a restricted part of the outcrop of the Mytton Flags. Later, Whittard (1979, p. 8) no longer regarded the 'Tankerville Flags' as a separately mappable unit and included them within the Mytton Formation. Although Whittard (1960, p. 260) gave the type area for the 'Tankerville Flags' lithology, rather imprecisely, as 'Tankerville Mine', Bergam Quarry is effectively the type locality

Description

Bergam Quarry is adjacent to a sharp bend on a minor road, 305 m NNE of Tankerville Mine and 900 m south-west of the Stiperstones Inn. Bluish-grey micaceous flaggy shales and siltstones dip at 84° to the NNW and are cut by a dolerite intrusion 4.3 m wide, to the north of which the shales are pale-grey and altered through a thickness of 3.4 m; shales on the south side are not visibly altered. The base of the Hope Shale Formation is mapped a short distance to the north-west (Whittard, 1979, fig. 7, p. 13), although the junction is not exposed there, nor elsewhere in the Shelve area.

Strachan (1986) recognized the graptolites Expansograptus cf. nitidus (Hall), E. cf. praenuntius (Tornquist), E. cf. suecicus (Tullberg) and stipes of E. cf. hirundo (Salter). No biserial graptolites have been reported. Bergam Quarry is the type locality for the dendroid graptolites Callograptus extensus Bulman and C. tenuis Bulman. The trilobites, described by Whittard (1955–1967) and revised by Fortey and Owens (1987), include Placoparia cambriensis Hicks and Pricyclopyge binodosa (Salter), in common with the Hope Formation, and also Segmentagnostus scoltonensis (Whittard), which is reported from the Pontyfenni Formation (Fennian) and the Llanvirn part of the Llanfallteg Formation in South Wales. Asaphellus whittardi (Bates) occurs both at Bergam and in the early Fennian Cwmfelin Boeth Formation in South Wales, whereas the trinucleid Bergamia rhodesi Whittard, for which Bergam is the type locality, has not been found elsewhere. Other fauna includes hyolithids and orthoconic nautiloids.

Interpretation

Collectively, the trilobite and graptolite faunas place the 'Tankerville Flags' high in the Arenig, and a level within the hirundo graptolite zone has been suggested. However, the extensiform graptolites are not positively identified with species known elsewhere and indicate only a Fennian age, and even if the presence of E. hirundo were confirmed it would not prove the presence of the uppermost Arenig, for that species is long-ranging (Fortey et al., 1990).

The trilobite fauna, too, has long-ranging species that are found in both the late Arenig and the early Llanvirn, with elements from the earlier late Arenig (early Fennian); combined with the lack of biserial graptolites, this suggests that Bergam Quarry lies in the earlier rather than the later Fennian (Figure 10.2) and that the fauna is older than that at Shelve Church (see site report).

The presence of cylcopygid trilobites, graptolites and altheloptic trilobites suggests that the 'Tankerville Flags' were deposited in fairly deep, offshore waters.

Conclusions

Bergam Quarry exemplifies the 'Tankerville Flags' facies of the Mytton Flags Formation and yields a trilobite fauna of Fennian age, including species known from localities in South Wales, that is quite distinct from the fauna of the bulk of the Mytton Flags.

References