Fairy Call Beck, North Yorkshire

[SE 712 904]

K.N. Page

Introduction

South-westwards from Fairystones Bridge towards Hutton-le-Hole, near the southern boundary of the North Yorks Moors National Park north of Kirkbymoorside, stream sections in Fairy Call Beck reveal an intermittently exposed but virtually complete Callovian succession including fossiliferous sections in the Cornbrash, Cayton Clay and Osgodby formations. The Redcliff Rock Member of the Osgodby Formation is of particular note here, being distinct from its development in eastern areas of the Cleveland Basin (see Gristhorpe Bay, Yons Nab and Red Cliff-Cunstone Nab GCR site report, this volume).

Description

The sections were described by Wright (1977, 1978) on which the following notes are largely based.

The Cornbrash Formation (c. 0.70 m thick) is well exposed in the stream bed immediately north of Fairystones Bridge (Figure 5.23). Its basal bed is a thin (0.15 m) flaggy and shelly siltstone resting on white clay of the Scalby Formation and passing upwards into silty limestone. Meleagrinella and serpulids are recorded. The overlying 0.55 m of hard limestone with bivalves (including Lopha marshii (J. Sowerby)) forms a ledge in the stream bed. It has recently yielded the brachiopod Microthyridina cf. sublagenalis (Davidson) and the ammonite Macrocephalites cf. terebratus (Phillips) (macro-conch). Immediately above the Cornbrash Formation, traces of grey, silty shale with occasional small, round, calcareous nodules represent the Cayton Clay Formation of which c. 0.4 m is seen.

Intermittent exposures of the overlying Osgodby and Oxford Clay formations are present in the banks of Fairy Call Beck southwestwards from Fairystones Bridge. A composite section is given below. Bed notation for the Redcliff Rock and Langdale members follows Wright (1968, 1978).

Interpretation

The sections in Fairy Call Beck probably represent the most continuously exposed Callovian succession in the western Cleveland Basin and are important reference sections for regional correlation. The succession shows significant differences from that of the eastern Cleveland Basin, and attempts at correlation between the two areas often remain inconclusive.

Wright (1977) considered that the Cornbrash Formation was not easily proved to be either α₁ or  α₃ of the standard subdivisions recognized in the Scarborough district coastal sections (see Gristhorpe Bay, Yons Nab and Red Cliff–Cunstone Nab GCR site report, this volume) but he preferred to classify them as α₃, which he believed overlapped α₁ in this area. The more recent ammonite and brachiopod records reported above indicate the Terebratus Subzone of the Lower Callovian Herveyi Zone.

The exposures of the Redcliff Rock Member were taken by Wright (1978) as a standard for the correlation of subdivisions within β₁ in the western Cleveland Basin (Figure 5.24). The presence of common belemnites in β₂ is unusual for this stratigraphical level in Britain, as are the large guards in β_1b, but these may have been concentrated by sedimentological processes. The record of occasional Kepplerites (Gowericeras) sp. probably indicates the Curtilobus Subzone of the Lower Callovian Koenigi Zone as in the eastern part of the Cleveland Basin; however, this needs confirmation based on a reexamination of the few recovered ammonites. According to Wright (1978), the overall general pattern of sedimentation in the Redcliff Rock Member consists of the establishment of fully marine conditions early on ((β_1b) followed by brackish-water marine conditions (β_1c) and a gradual increase in marine influence through β_1d and β₂.

Fossils are very rare in the Langdale Member and no age-diagnostic form appears to have been recovered. Age assignments are therefore speculative although part, at least, of the member is likely to be of Mid Callovian age. Wright's (1978) record of Quenstedtoceras aff. brasili in the Hackness Rock Member suggests the Lamberti Zone and a Late Callovian age. The latter member is non-ooidal, unlike its more easterly correlatives; this decrease in, or disappearance of, ooids westwards is also seen in ß₂ of the Redcliff Rock Member, and is a consequence of increasing distance from the sources of ooid production (to the north and northeast)

The basal Langdale Member (γ₂) in Fairy Call Beck represents a transgressive phase (γ₁ is absent), and the nature of the sediments is compatible with those fringing a delta, which would possibly have been sited to the northwest of Fairystones Bridge (Wright, 1978). The Hackness Rock Member indicates a period of reduced sedimentation with condensed sequences, prior to rapid subsidence and deposition of the Oxford Clay Formation of presumed Early Oxfordian age.

Conclusions

Fairy Call Beck is a key reference section for the Callovian succession of the western Cleveland Basin showing a complete succession including the Cornbrash, Cayton Clay and Osgodby formations. The exposure of the Redcliff Rock Member here is the most complete and fossiliferous in the area. The fossils that have been recorded aid regional stratigraphical correlation as well as palaeoenvironmental analysis.

References