2.a.1. Lithostratigraphy

The Chapel House Limestone Formation was introduced in the Settle district by Arthurton, Johnson & Mundy (Reference Arthurton, Johnson and Mundy1988) for the succession which underlies the Kilnsey Formation and either unconformably overlies the Tournaisian Stockdale Farm Formation or Lower Palaeozoic rocks. In the type section, the Chapel House Borehole, the formation is 33.6 m thick. The formation is thickest (56 m) in the Stockdale Farm Borehole (SD86SE6; Fig. 1a), adjacent to the Middle Craven Fault. Elsewhere to the north of the North Craven Fault, the formation onlaps, and is locally absent over topographic highs in the Lower Palaeozoic basement and is only 12 m thick in the Silverdale Borehole (Murray, Reference Murray1983).

In the Settle district, the lower part of the formation is dominated by medium to medium-light grey, medium- and coarse-grained grainstone with common Lower Palaeozoic lithoclasts, locally forming conglomerates, and the notable presence of ooids (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988). Other common lithologies are ‘mixed laminites’ comprising interbedded fissile siltstone with sandstone and mudstone laminae, dolomite-mudstone and lime-mudstone with fenestral textures or algal lamination, and argillaceous wackestones are present in the upper part of the formation in the Kilnsey area (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988).

The unconformable base of the Chapel House Limestone Formation in the Silverdale Borehole is overlain by medium grey, fine- to medium-coarse-grained packstone/grainstone with abundant crinoid and brachiopod debris, quartz grains and peloids (Fig. 5). The upper 5.5 m is marked by medium and dark grey lime-mudstone and laminated argillaceous wackestone with fenestral fabrics, abundant quartz grains in laminae and intraclasts with common ostracods and dasycladal green algae. The upper boundary of the formation is marked by a change from lime-mudstone to darker grey coarser grained bioclastic packstones/wackestones of the Kilnsey Formation.

Figure 5. Lithological log for the Silverdale Borehole, showing the position of biostratigraphical samples (EWJ1501−1575) and the range of key foraminifers and algae.

2.a.2. Biostratigraphy

Macrofossils. The Chapel House Limestone Formation is equivalent to the lower part of the Michelinia Zone (C₂) of Garwood & Goodyear (Reference Garwood and Goodyear1924). Michelinia megastoma, found near the top of the formation at Stainforth Beck [38198 46700] and Palaeosmilia murchisoni recovered from the base of the Chapel House Limestone at 191 m depth in the Silverdale Borehole, were considered to indicate an Arundian age (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988).

Microfossils. Foraminifers from the Chapel House and Stockdale Farm boreholes and from Gordale Beck (Fig. 1a) confirm an Arundian age (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988), the diagnostic taxa being Ammarchaediscus (= Viseidiscus) bucullentus, Eoparastaffella simplex (Fig. 3a), Glomodiscus miloni, Latiendothyranopsis menneri solida and Rectodiscus (= Uralodiscus) sp.

In the Silverdale Borehole (Fig. 5; Table 4), the basal sample of the Chapel House Limestone Formation (EWJ1575), located immediately above the basal unconformity upon Lower Palaeozoic basement, contains all of the diagnostic taxa of a late Arundian age, including Glomodiscus rigens (Fig. 3g), Uralodiscus adindanii (Fig. 3h), U. rotundus, U. settlensis (Fig. 3i), Viseidiscus monstratus, Paraarchaediscus at involutus stage, Plectogyranopsis moraviae (Fig. 4g), Eoparastaffella simplex (EWJ1572–75), Latiendothyranopsis menneri solida (EWJ1573–75; Fig. 4c), Eoendothyranopsis, Pseudolituotubella, Nodosarchaediscus and Koninckopora spp. This sample has the richest (35 foraminiferal species) and most diverse assemblage for any sample in the borehole. It also agrees with many of the taxa illustrated by Conil, Longerstaey & Ramsbottom (Reference Conil, Longerstaey and Ramsbottom1980) from the Arundian Michelinia Grandis Beds at Settle and characteristic of their Cf4δ Subzone.

Also in the Silverdale Borehole (Fig. 5), a sample (EWJ1573) located 2 m above the basal sample has less species richness (20) and many Arundian taxa no longer present, but still records the last occurrences of taxa typical of the late Arundian. Some first appearances are still distinctive of the Arundian (e.g. Condrustella, Fig. 3o) and Lituotubella magna (Fig. 4a). The latter taxon was recorded by A. R. E. Strank (unpub. Ph.D. thesis, Univ. Manchester, 1981) from the upper part of the Arundian Dalton Formation close to the contact with the Holkerian Park Limestone Formation in the stratotype Holkerian section at Barker Scar, Cumbria (Ramsbottom, Reference Ramsbottom1981; Waters, Reference Waters, Waters, Somerville, Jones, Cleal, Collinson, Waters, Besly, Dean, Stephenson, Davies, Freshney, Jackson, Mitchell, Powell, Barclay, Browne, Leveridge, Long and McLean2011). The micritic beds with fenestral fabrics in the upper 5.5 m of the Chapel House Limestone are barren of foraminifers.

2.b.1. Lithostratigraphy

The Kilnsey Formation, the type locality of which forms Kilnsey Crag (Figs 1, 6), comprises two distinct units (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988; Table 1). The lower Scaleber Force Limestone Member (also Kilnsey Limestone-with-mudstone) is a dark grey, fine- to coarse-grained, argillaceous, bioclastic and peloidal packstone and subordinate wackestone, with common detrital quartz and beds of mudstone up to 1.8 m thick (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988). The uppermost part of the member at the type locality (Pc4833) is a parallel laminated, argillaceous kamaenid algal packstone dominated by common crinoids, with subordinate brachiopods and bryozoans and minor micritic intraclasts. This member is comparatively more argillaceous than the overlying Scaleber Quarry Limestone Member (also Kilnsey Limestone), which is 29 m thick at Kilnsey Crag and typically comprises medium to dark grey, well-bedded, fine- to coarse-grained bioclastic packstone or grainstone (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988).

Figure 6. At Kilnsey Crag [3974 4681] the upper part of the Scaleber Force Limestone Member is evident beneath a prominent bedding surface near the base of the cliff (arrowed), mainly obscured by the grassy slope. The overlying Scaleber Quarry Limestone Member forms the main face and overhang. The basal part of the Cove Limestone Member (Malham Formation) caps the crag.

East of Kilnsey Crag, the uppermost part of the Scaleber Quarry Limestone Member is exposed at the bottom of Conistone Dib (Fig. 1b). The succession (Pc4820) comprises medium grey, thick-bedded (0.6 m), coarse-grained, densely packed packstone with crinoidal debris, some brachiopod valves and small micritic intraclasts (Fig. 7). Bioclasts and peloids are moderately sorted, with a poorly defined cross-lamination. The bioclasts are dominated by crinoids with minor components of syringoporoids, bryozoans and brachiopods.

Figure 7. Lithological logs for key sections of the Cove Limestone at Conistone Dib and Trollers Gill, showing the position of biostratigraphical samples (Pc4820–32 and DMA320–26) and the range of key foraminifers and alga/algospongia.

In the Greenhow and Skyreholme inliers (Fig. 1b), the absence of a thick interval of ‘dark grey limestone’ was used by Dunham & Wilson (Reference Dunham and Wilson1985) to justify that the equivalent of the Kilnsey Formation was absent at outcrop; our study confirms that interpretation. However, the Scaleber Quarry Limestone Member is considered to be present in the subsurface in Coldstones No. 4 Borehole below 295.2 m (BGS Registration number SE16SW5; Fig. 8). Interpreted as the lower part of the Stump Cross Limestone and Timpony Limestone by Strank (Reference Strank1982 b), this succession is distinctly dominated by medium grey, fine- to medium- or medium-grained limestone, partly dolomitized, with brachiopods, crinoids and coral beds. A thickness for this member of more than 128 m in this borehole is comparable with 135 m recorded in the Cominco S2 Borehole (SD86SW6; Fig. 1a) near Settle (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988).

Figure 8. Lithological logs for key sections in the Greenhow Inlier at Duck Street, Coldstones Quarry and Coldstones No.4 Borehole, showing the position of biostratigraphical samples and the range of key foraminifers.

The Kilnsey Formation in the Silverdale Borehole is 33 m thick (Murray, Reference Murray1983) and is a relatively uniform facies of medium to dark grey, fine- to medium-grained packstones and grainstones with shelly fauna, although some fenestral lime-mudstones are interbedded (Fig. 5). This contrasts with Murray (Reference Murray1983) who described the succession between 146.52 and 171.96 m as grainstone at the base, otherwise wackestone and locally packstone. This is still a moderately shallow-water shelf facies with crinoids, brachiopods, bryozoans, corals, foraminifers and dasyclads and rare ooids. The presence of intraclasts is of some interest, but not distinctive, as they are also present in the overlying Cove Limestone Member. The upper boundary at 146.52 m marks a clear colour change from the mainly dark packstone/wackestone of the Kilnsey Formation to paler coarser grained packstone/wackestone of the overlying Cove Limestone Member. The Kilnsey Formation is thin when compared to Kilnsey Crag. The absence of common argillaceous beds suggests that the Scaleber Force Limestone Member is absent and only the equivalent of the Scaleber Quarry Limestone Member is present in the Silverdale Borehole. The presence of rare ooids within the lower part of the Kilnsey Limestone in this borehole is unusual, but is quite common in the underlying Chapel House Limestone Formation.

2.b.2. Biostratigraphy

Macrofossils. The Scaleber Force Limestone Member is approximately equivalent to the upper part of the Michelinia Zone (C₂) of Garwood & Goodyear (Reference Garwood and Goodyear1924), and the lowest unit (the Gastropod Beds) of their Productus corrugato–hemisphericus Zone (S) (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988). An Arundian age for the Scaleber Force Limestone Member is confirmed by the presence of the brachiopod Delepinea carinata at Mill Scar Lash, River Wharfe [29796 46638], and by the incoming of the corals Siphonodendron martini and Palaeosmilia murchisoni (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988). Brachiopods are dominated by Megachonetes spp. with common Schizophoria resupinata (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988).

The Scaleber Quarry Limestone Member is the equivalent of the Cyrtina carbonaria Subzone (S₂) of Garwood & Goodyear (Reference Garwood and Goodyear1924), together with the lower part of their Nematophyllum minus Subzone (S₂). The presence of the cerioid coral Lithostrotion (Nematophyllum) minus, and the brachiopods Composita ficoidea, rare Davidsonina carbonaria, Linoprotonia ashfellensis and L. corrugatohemispherica, confirm a Holkerian age (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988). The fasciculate coral Siphonodendron scaleberense was also first recorded from Scaleber Quarry (Nudds & Somerville, Reference Nudds and Somerville1987). Dunham & Wilson (Reference Dunham and Wilson1985) noted the presence of the corals Lithostrotion minus and L. (= Siphonodendron) sociale and the brachiopod Linoprotonia ashfellensis in the Coldstones No. 4 Borehole below 306 m (Fig. 8), which they also considered to have a Holkerian aspect.

Microfossils. Foraminifers from the Chapel House, Stockdale Farm and Cominco Sl0 (BGS Registration number SD86SW8) boreholes (Fig. 1a) were used by Strank (in Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988) to confirm an Arundian age (Cf4) for the Scaleber Force Limestone Member. Diagnostic taxa recorded for these boreholes include Ammarchaediscus (= Viseidiscus) bucullentus, Brunsiarchaediscus (= Planoarchaediscus) sp., Glomodiscus miloni, Plectogyranopsis moraviae, Pseudolituotubella hibernica, Rectodiscus (= Uralodiscus) sp. and Tubispirodiscus (= Uralodiscus) settlensis. Conil, Longerstaey & Ramsbottom (Reference Conil, Longerstaey and Ramsbottom1980) also analysed samples from the Scaleber Force Limestone Member at the type locality of Scaleber Force, which they assigned to the Arundian. However, they identified a specimen as cf. Omphalotis minima, whereas the illustrated specimen can be readily assigned to the nominal species. As Conil, Longerstaey & Ramsbottom (Reference Conil, Longerstaey and Ramsbottom1980) recognized, O. minima is one of the guides for the Holkerian (Cf5). The typical assemblage for the Scaleber Force Limestone Member is similar to the basal bed of the Chapel House Limestone in the Silverdale Borehole (see Section 2.a.2 above).

For the Scaleber Quarry Limestone Member a foraminiferal assemblage reported by Strank (in Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988) included Archaediscus at angulatus stage (probably transitional forms), A. at concavus stage, Koskinotextularia cribriformis, Nibelia (= Pojarkovella) nibelis and Nodosarchaediscus sp., confirming a Holkerian age (Cf5) for this succession.

Kilnsey Crag shows the transition between the two members of the Kilnsey Formation (Fig. 6). Strank (in Dunham & Wilson, Reference Dunham and Wilson1985) reported that the lowest 7 m of the section, representing the top of the Scaleber Force Limestone, yielded the foraminifers Ammarchaediscus (= Viseidiscus), Glomodiscus and Rectodiscus (= Uralodiscus) but no diagnostic Holkerian genera. Whereas immediately above that level, and approximately coinciding with the base of the Scaleber Quarry Limestone Member, Strank reported the incoming of Koskinotextularia sp. followed higher up by Endothyranopsis crassa (probably E. compressa trans. crassa), Nevillella (= Mstinia) sp., Nibelia (= Pojarkovella) nibelis and nodose archaediscids, and accompanying Brunsia spirillinoides, Eostaffella parastruvei, Glomospiranella dainae and Septabrunsiina sp., which form a characteristic Holkerian foraminiferal assemblage (Table 2).

Resampling of the uppermost part of the Scaleber Force Limestone Member at Kilnsey Crag (Pc4833) records diverse foraminifers (Table 2) of which Archaediscus at concavus stage transitional forms to the angulatus stage, large A. aff. chernoussovensis, Endothyranopsis compressa and Nodosarchaediscus spp. indicate a late Holkerian age (Cf5) (Conil, Longerstaey & Ramsbottom, Reference Conil, Longerstaey and Ramsbottom1980; A. R. E. Strank, unpub. Ph.D. thesis, Univ. Manchester, 1981).

The top of the Scaleber Quarry Limestone Member at Conistone Dib (Pc4820; Fig. 7) records the presence of Archaediscus at angulatus stage, Endothyranopsis compressa trans. crassa, Globoendothyra globulus and Nodosarchaediscus spp., as well as the algospongia Zidella maxima (Table 2). Although the stratigraphic range of the latter is poorly known, it has been associated with the late Viséan upwards (≥ Cf6γ) (Vachard & Cózar, Reference Vachard and Cózar2010). The foraminifers are typically recorded from the early Asbian (Cf6α-β) in Western Europe (Conil, Longerstaey & Ramsbottom, Reference Conil, Longerstaey and Ramsbottom1980).

In the Greenhow Inlier, the lower part of the Coldstones No. 4 Borehole (Fig. 8), below c. 225 m, contains a sparse foraminiferal assemblage including Archaediscus sp., A. stilus, Endothyranopsis crassa (most probably E. compressa trans. crassa), Eostaffella sp., Consobrinella consobrina, Pseudoammodiscus volgensis, Omphalotis cf. minima, Nodosarchaediscus sp., Brunsia sp. and Valvulinella sp. and common alga Koninckopora inflata (Strank, Reference Strank1982 b; Table 3), which Strank attributed as Holkerian. The more fossiliferous part of the borehole from 325.9 m to 295.15 m depth was interpreted as Holkerian to possibly early Asbian in age (Strank, Reference Strank1982 c). The foraminifers from the lower part of the borehole, although sparse and lacking many characteristic taxa, are most probably early Asbian in age (Cf6α-β) as they include some species not known in the Holkerian; the lack of diversity and diagnostic taxa suggests this interval is not late Asbian (Cf6γ) in age.

In the Silverdale Borehole (Fig. 5; Table 4), the incoming of Holkerian taxa coincides with the base of the Kilnsey Formation (EWJ1567), especially with Paraarchaediscus at concavus stage and Omphalotis minima (Fig. 4d), with Pojarkovella sp. (EWJ1566) and Holkeria (EWJ1563; Fig. 3m) appearing in the lower part of the formation. The diagnostic Holkerian taxa appear together in the middle of the Kilnsey Formation (EWJ1562) with the first appearance datum (FAD) of Koskinotextularia sp. (Fig. 3l), Eostaffella parastruvei (Fig. 3p) and Mikhailovella, and with Pojarkovella nibelis (EWJ1561), the latter occurring some 14.5 m above the base of the first Holkerian taxa. The FAD of Endothyranopsis trans. crassa and Paraarchaediscus at angulatus stage in the upper part of the Kilnsey Formation (EWJ1560) is indicative of an early Asbian age, followed near the top of the formation by Nodasperodiscus and Consobrinella consobrina (EWJ1558). The absence of Vissariotaxis from this lower Asbian part of the succession is noteworthy, but is considered a result of the shallow-water facies evident in this borehole. The FAD of Neoarchaediscus aff. incertus, N. stellatus and Koskinobigenerina (EWJ1554; Fig. 3d) from the very topmost bed of the Kilnsey Formation marks the incoming of late Asbian taxa.

In summary, existing published information, mainly based upon coral/brachiopod assemblages, indicates an Arundian age for the Scaleber Force Limestone Member and a Holkerian age for the Scaleber Quarry Limestone Member (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988). This contrasts with our study, in which the foraminiferal/algal assemblages suggest a late Holkerian and early/late Asbian age, respectively, for the upper parts of the two members (Table 2). The Coldstones No. 4 Borehole (Fig. 8), in the Greenhow Inlier, includes a succession lithologically comparable with the Scaleber Quarry Limestone Member and with a similar fauna of probable early Asbian age.

2.c.1 Lithostratigraphy

The Cove Limestone Member, the lower part of the Malham Formation, is named after Malham Cove [3896 4642] (Fig. 1a), where it forms the lower part of the cliff face (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988). This member is typically pale grey, massive to weakly bedded packstone/wackestone lacking prominent palaeokarstic surfaces (Table 1) and typically forms a landscape with grassy slopes. Distinctive lime-mudstone (micrite) beds with fenestral fabrics occur mainly within the upper part of the member (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988). The c. 1.5 m thick ‘Porcellanous Bed’ has been used as a marker (e.g. Garwood & Goodyear, Reference Garwood and Goodyear1924; Ramsbottom, Reference Ramsbottom, Rayner and Hemingway1974) for the top of the Horton Limestone (= top of Cove Limestone Member), but this facies is shown to disappear both northwards towards the Stainmore Basin and southwards where it is not recorded south of the North Craven Fault (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988), or within the current study area.

Above the Kilnsey Formation at Kilnsey Crag (Fig. 6), the Cove Limestone Member comprises coarsely bioclastic packstone/grainstone and is strongly bedded, e.g. at Cool Scar Quarry [39692 46751]. An entire thickness of the member (80 m) is recorded at Conistone Dib (Figs 1b, 9a), comprising very thick beds of pale grey packstone/grainstone with less prominent bedding surfaces and some pale brown dolomitization (Fig. 7). The basal (Pc4821−3) and middle parts of the section (Pc4826 and Pc4828) comprise bioclastic/peloidal grainstone, with common crinoids, foraminifers and intraclasts, with a poorly developed cross-lamination developed in some beds and rare oncoids (Pc4826). The middle of the section (Pc4824 and Pc4825) also includes finer grained bioclastic/peloidal grainstones with more dasycladals and locally (Pc4827) crinoidal/algal packstone with many small intraclasts. The upper part of the member (Pc4830 and Pc4831) comprises bioclastic peloidal grainstones with large brachiopod shells marking a cross-lamination.

Figure 9. Key localities in the Cove Limestone Member. (a) At Conistone Dib [3982 4674], exposed in a meltwater drainage channel. The Gordale Limestone Member forms the distinctive crag at the top of the slope. The locations of some of the sample locations are shown. (b) Massive packstone/grainstone of the Cove Limestone Member at Trollers Gill [40687 46181]. Sample DMA320 is from the base of the right (eastern) wall of the gorge.

In the Skyreholme Inlier (Fig. 1b), Dunham & Wilson (Reference Dunham and Wilson1985) equated the Timpony Limestone with the Cove Limestone Member. However, there is little lithological similarity between the two units (Table 1) and it is assumed that the correlation was based on age. The key section at Trollers Gill (Fig. 9b) was mapped previously as ‘S Beds’ by Anderson (Reference Anderson1928), who recognized an upward succession of ‘white limestone and lime-mudstone, light grey slightly crinoidal limestone, and capped by porcellanous limestone’ with the first appearance of productid brachiopods. The section is lithologically very similar in appearance to the Cove Limestone Member at Conistone Dib, with a monotonous development of at least 25 m of broadly upward-coarsening, massive to very thick-bedded, pale grey packstone/grainstone (Fig. 7). The lower part (DMA320–323) is fine- to medium-grained, skeletal (crinoidal-algal-rich) and peloidal packstone/grainstone, locally with abundant limestone intraclasts. The basal part of this succession (DMA320) includes coated grains and sparse ooids, large cavities containing sparry cements, peloids in geopetal sediment and large limestone intraclasts. The upper part of the succession in the gorge (DMA324–326) is medium- and medium- to coarse-grained, moderately and well-sorted, skeletal (crinoidal-algal-rich) packstone.

The Stump Cross Limestone of Dunham & Stubblefield (Reference Dunham and Stubblefield1945) and Dunham & Wilson (Reference Dunham and Wilson1985) is named after the eponymous showcave located in the Skyreholme Inlier. The base of the unit was taken at the base of the ‘Hemitrypa Bed’, a c. 0.8 m thick ‘pale brown (fawn) bioclastic limestone, overlain by buff dolomitic limestone, in turn passing up to pale grey or white limestone’ (Dunham & Stubblefield, Reference Dunham and Stubblefield1945). This had been described as ‘Porcellanous Limestone’ of Asbian (D₁) age by Hudson (Reference Hudson1938) and may equate with such beds described by Anderson (Reference Anderson1928) in Trollers Gill, although as discussed by Dunham & Stubblefield (Reference Dunham and Stubblefield1945), it is not an accurate description of this succession. There is very limited exposure of this limestone and insufficient lithological distinction to justify recognition of a separate formation, and hence use of the term is discontinued in this study.

In the Greenhow Inlier, there is a marked reduction in grain size in the Coldstones No. 4 Borehole (Fig. 8) above 295.2 m, with a succession of fine-grained limestone, mainly medium grey below 250 m depth and mainly pale grey and thick bedded or massive above, with few macrofossils other than subordinate beds with crinoid ossicles. This succession, previously considered the upper part of the Stump Cross Limestone (Strank, Reference Strank1982 b) is here attributed to the Cove Limestone Member. The uppermost 10 m (224.9–214.9 m depth) are coarse grained and crinoidal, possibly reflecting the coarsening-upward succession recorded in this member at Trollers Gill (Fig. 7).

The Cove Member in the Silverdale Borehole (Fig. 5) is 46 m thick (Murray, Reference Murray1983) and is dominated by pale grey, fairly coarse-grained grainstone and packstone with shelly fauna interbedded with rare fenestral lime-mudstones in the upper 15 m, considered to be the Porcellanous Bed (Murray, Reference Murray1983). Arthurton, Johnson & Mundy (Reference Arthurton, Johnson and Mundy1988) recognized a conspicuous increase in the proportion of grainstones in the Horton in Ribblesdale area, coinciding with a thinning of the member and the presence of the Porcellanous Bed. The upper boundary of the member is repositioned relative to Murray (Reference Murray1983) above the upper lime-mudstone (EWJ1539) at the base of the overlying bed at 95.7 m. The upper 6 m in this member (102−95.7 m) contains palaeokarstic surfaces which are not typical for this member at outcrop in the study area, but in the Settle district are thought to be associated with the Porcellanous Beds (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988).

2.c.2. Biostratigraphy

Macrofossils. Little work has been done to establish the age of the Cove Limestone Member in Upper Wharfedale. Macrofauna are sparse, but concentrations of single species of corals and brachiopods including Axophyllum vaughani, Lithostrotion (= Siphonodendron) sociale, Syringopora sp., Linoprotonia ashfellensis and Megachonetes papilionaceous group were reported by Arthurton, Johnson & Mundy (Reference Arthurton, Johnson and Mundy1988) from the Settle district. In the Skyreholme Inlier, Dunham & Stubblefield (Reference Dunham and Stubblefield1945) recorded from the ‘Hemitrypa Bed’ the bryozoan Hemitrypa hibernica and alga Koninckopora inflata in association with Siphonodendron junceum, the last named fossil possibly indicating a late Asbian (D₁) age (see Poty, Reference Poty1984; Mitchell, Reference Mitchell1989). However, according to Nudds (Reference Nudds1980) and Aretz & Nudds (Reference Aretz and Nudds2005), S. junceum first appears in the early Asbian at Little Asby Scar further north in the Stainmore Basin.

Microfossils. A restricted assemblage of foraminifers from the Gordale Scar section [3913 4640], consisting essentially of Archaediscus sp. (non ‘angulatus’ stage) and Koskinotextularia cribriformis, were interpreted as a deeper water Holkerian fauna by Arthurton, Johnson & Mundy (Reference Arthurton, Johnson and Mundy1988). A typical Holkerian (shallow-water) assemblage was considered by Arthurton, Johnson & Mundy (Reference Arthurton, Johnson and Mundy1988) to be present in the Silverdale Borehole, where diagnostic taxa included Archaediscus stilus, Holkeria daggeri, Nibelia (= Pojarkovella) nibelis, Palaeospiroplectammina paprothae and Septabrunsiina tynanti. However, in a reinvestigation of the borehole (Fig. 5; Table 4), the FAD of Endothyranopsis crassa (Fig. 4f), Pseudoendothyra sublimis (EWJ1553) and Archaediscus karreri (EWJ1552), as well as common Neoarchaediscus (including N. stellatus), Koskinobigenerina sp. (Fig. 4j), bilaminar Palaeotextularia and Omphalotis omphalota indicate late Asbian taxa in the lower part of the member, with the FAD of Bibradya inflata indicating a higher horizon of late Asbian age for the top of the member (EWJ1539).

At Conistone Dib, the lowermost beds (Pc4821) comprise the key foraminifers Archaediscus at angulatus stage (Fig. 3c), large A. ex gr. karreri, Koskinobigenerina sp., Neoarchaediscus stellatus and Pseudoendothyra sublimis (Fig. 7; Table 2), which suggest a late Asbian age (Cf6γ) (A. R. E. Strank, unpub. Ph.D. thesis, Univ. Manchester, 1981; Laloux, Reference Laloux1987; Cózar & Somerville, Reference Cózar and Somerville2004; Somerville & Cózar, Reference Somerville and Cózar2005). An additional late Asbian foraminiferal marker is Neoarchaediscus sp. (also from the lower beds, at Pc4822; Fig. 3e) and Endothyranopsis crassa from the upper part of the succession (Pc4830). The Neoarchaediscus Zone is regarded as largely equivalent to the Asbian and Brigantian substages (Conil, Longerstaey & Ramsbottom, Reference Conil, Longerstaey and Ramsbottom1980; Conil et al. Reference Conil, Groessens, Laloux, Poty and Tourneur1991; Riley, Reference Riley1993; Jones & Somerville, Reference Jones, Somerville, Strogen, Somerville and Jones1996), although true occluded forms, particularly N. stellatus, have never been illustrated in England below the upper Asbian (e.g. Conil, Longerstaey & Ramsbottom, Reference Conil, Longerstaey and Ramsbottom1980; A. R. E. Strank, unpub. Ph.D. thesis, Univ. Manchester, 1981; Cózar & Somerville, Reference Cózar and Somerville2004), and previously documented specimens of Neoarchaediscus could be assigned to the problematic genera and subgenera Nodosarchaediscus, Asperodiscus or Nodasperodiscus.

In the Skyreholme Inlier, the basal sample (DMA320) at Trollers Gill (Figs 7, 9b) contains a limited foraminiferal assemblage, which only suggest an Asbian age (Table 3). However, 2 m higher in the succession (DMA321), an assemblage with the first occurrences of Cribrospira aff. panderi, Bibradya grandis, Neoarchaediscus stellatus, Palaeotextularia sp., Pseudoendothyra sublimis (Fig. 3q) and the algospongia Ungdarella uralica is assigned to the late Asbian (Cf6γ) (A. R. E. Strank, unpub. Ph.D. thesis, Univ. Manchester, 1981; Jones & Somerville, Reference Jones, Somerville, Strogen, Somerville and Jones1996; Cózar & Somerville, Reference Cózar and Somerville2004, Reference Cózar and Somerville2005, Reference Cózar and Somerville2013). The assemblages do not change significantly through the section, except for the youngest sample (DMA326), which contains the foraminifers Archaediscus ex gr. karreri and Cribrostomum lecomptei, also markers for the late Asbian (Conil, Longerstaey & Ramsbottom, Reference Conil, Longerstaey and Ramsbottom1980; Cózar & Somerville, Reference Cózar and Somerville2004).

In Coldstones No. 4 Borehole (Fig. 8), Strank (Reference Strank1982 b) recorded between 250 and 205 m a low-diversity foraminiferal assemblage of Archaediscus sp. and A. stilus and abundant alga Koninckopora inflata (Table 3) from the lower part of their Greenhow Limestone. Strank (Reference Strank1982 b) noted the lack of diagnostic taxa, but considered the low diversity suggestive of a Holkerian age, although evidence for early Asbian taxa at greater depths in this borehole (see Section 2.b.2 above) discounts this.

In summary, across the study area, strata mapped as the Cove Limestone Member are most probably late Asbian in age. This contrasts with the Holkerian age previously considered for the member, partly proposed from foraminiferal assemblages in the Silverdale Borehole (Fig. 5), east of Horton in Ribblesdale (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988). Reinvestigation of this borehole suggests there is no evidence of a marked diachroneity within the member across the southern part of the Askrigg Block.

2.d.1 Lithostratigraphy

The Gordale Limestone Member (upper part of the Malham Formation) is named after the type locality of Gordale Scar [3913 4640] (Fig. 1a), where the member is 94 m thick (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988). This member also caps Malham Cove, where it forms a limestone pavement, a common feature of this member. It is typically medium-pale to very pale grey packstone/grainstone, well bedded, varying from thick to very thick bedded, and its individual beds tend to form major scar features in the southern part of the district (Table 1).

The member is well represented at the head of Conistone Dib [39922 46821] with a 6 m-thick section of pale grey, very thick-bedded grainstone, with crinoid ossicles, micrite-coated intraclasts, brachiopod valves and rare Siphonodendron corals. The base of the member comprises a bioturbated intraclastic/crinoidal/packstone/grainstone with intraclasts (>1 mm diameter), crinoids and peloids (Pc4832; Fig. 7). In the upper part of Conistone Dib [398771 467735], the basal bed of the Gordale Limestone rests with a small angular discordance on the underlying weakly bedded Cove Limestone.

At Threshfield Quarry, near Grassington (Fig. 1b), the succession comprises very thickly bedded, light grey fine- to medium-grained, moderately sorted, intraclastic-skeletal-peloidal packstone. Bioclasts are dominated by crinoids with minor components of brachiopods. This quarry includes at least four prominent palaeokarstic surfaces (Fig. 10a) and had previously been assigned, erroneously, to the Cove Limestone Member (British Geological Survey, 1989).

Figure 10. Key localities in the Gordale Limestone Member. (a) Threshfield Quarry [3975 4646] includes four prominent palaeokarstic surfaces (arrowed) with associated clay horizons. Quarry face approximately 40 m high. (b) Coldstones Quarry [4125 4641], showing dark grey limestone and mudstone of the Alston Formation of Brigantian age (equivalent to the Hawes, Gayle and Hardrow Scar limestones), underlain by well-bedded ‘Hargate End Limestone’ and more weakly bedded ‘Greenhow Limestone’ of the Gordale Limestone Member. Photograph taken by Paul Witney. (c) Prominent palaeokarstic surface in Coldstones Quarry [41250 46396], overlain by orange clay up to 0.5 m thick which infills hollows present where fractures intersect the karstic surface. The packstone/grainstone is light grey and massive above the clay and light and medium grey bedded below, but with a darker grey laminar calcrete horizon present immediately beneath the palaeokarstic surface. This is the lower of two such surfaces ~7 m apart. British Geological Survey No. P875352.

Above Linton Falls, Bow Bridge (RBH59; Fig. 1b) and 193 m east of Lythe House (RBH51), there is pale grey, well-bedded medium-grained and poorly sorted skeletal-intraclastic-peloidal packstone. Bioclasts present at both localities include micritized crinoids and punctate brachiopods, with trilobites and coral fragments, including Syringopora (RBH59). Nearby, in the River Wharfe (RBH50) is a fine- to medium-grained peloidal-skeletal grainstone/floatstone (boundstone) with spar-filled cavities.

In the Skyreholme Inlier, above the gorge at Trollers Gill, the member comprises c. 50 m of thick and very thick tabular beds of wackestone, locally grainstone, extensively recrystallized to sparry calcite. No clear palaeokarstic surfaces are seen, but the top of the succession is marked by an unconformity, seen at Dibbles Bridge Quarry [405173 462958], where at least 1.3 m of cross-bedded grainstone composed of crinoids and brachiopod debris, along with small ooids, are truncated by the overlying Brigantian Hawes Limestone (Alston Formation; Fig. 7).

At Dry Gill, located immediately north of the North Craven Fault (Fig. 1b), there is a development of dark grey and cherty, fossiliferous, poorly sorted, medium- to coarse-grained grainstone/packstone (DMA327–8). Although previously designated the type locality of the Timpony Limestone (Dunham & Stubblefield, Reference Dunham and Stubblefield1945; Dunham & Wilson, Reference Dunham and Wilson1985, fig. 36), the coarse grain size is more typical of the Hargate End Limestone (Table 1), and is here attributed to be from the upper part of the Gordale Limestone Member.

In the Greenhow Inlier, the member is considered to equate with the upper part of the Greenhow Limestone and overlying Hargate End Limestone of Dunham & Stubblefield (Reference Dunham and Stubblefield1945). At Coldstones Quarry (Figs 1b, 10b), the basal beds comprise pale grey, medium-grained, crinoidal-algal wackestone/packstone (WQ217) and fine- to medium-grained, crinoidal-algal-foraminiferal packstone/grainstone (WQ203). These are overlain by medium-grained, moderately sorted, skeletal, crinoidal, algal and foraminifer-rich, packstone/grainstone, locally with wackestone intraclasts, medium grey (WQ204–5) to pale grey (WQ206–7). The middle part of the face is a dominantly pale grey, intraclastic skeletal (crinoidal-algal-foraminiferal), medium-grained packstone (WQ218). Palaeokarstic surfaces, overlain by thin orange clays, are recognized throughout this succession (Fig. 8). There is evidence of deformation of the packstone/grainstone below, but not above, one such palaeokarstic surface (Fig. 10c). In the upper part of the quarry, the equivalent of the Hargate End Limestone is at least 20 m thick (Figs 8, 10b). The lower part comprises medium and pale grey, thickly but distinctively bedded, mottled, coarse-grained, poorly to moderately sorted intraclastic skeletal (crinoidal-algal) grainstone (WQ216). The uppermost c. 6 m comprise medium grey, medium- to thick-bedded, medium-grained, moderately sorted, skeletal packstone/grainstone/rudstone (WQ215). The top of the formation occurs 4.5 m below the Girvanella Band; 3.5 m were recorded in Coldstones East Quarry (Dunham & Stubblefield, Reference Dunham and Stubblefield1945).

In Coldstones No. 4 Borehole (Fig. 8) the succession between depths of 214.9 and 77.71 m comprises pale grey to grey, very fine- and fine-grained, locally medium-grained, partially dolomitized limestone, with six grey-brown and yellow clay or mudstone beds. An incomplete succession from 77.71 m to 49.94 m, equivalent to the Hargate End Limestone, comprises pale grey and medium grey, fine- and medium-grained limestone, locally crinoidal, and is only distinguished from the underlying ‘Greenhow Limestone’ by the absence of clay interbeds.

At nearby Duck Street Quarry (Figs 1b, 8), the southern quarry comprises mainly pale grey, typically fine-grained and massive packstone in the upper and basal parts of the section, and medium-grained, moderately sorted intraclastic-skeletal-peloidal packstone/grainstone (Fig. 11a) with peloid wackestone intraclasts in the lower part and an isolated bed towards the top (WQ199). Three palaeokarstic surfaces are seen in the southern quarry (Figs 8, 11a). In the northern quarry a palaeokarstic surface with marked relief is underlain by a pale grey, upward-coarsening, well-sorted, trough and tabular cross-bedded, coarse- to very coarse-grained skeletal (crinoidal-algal) packstone/grainstone/rudstone (WQ200), 1.5 m thick, underlain by fine-grained bioclastic packstone/grainstone with wave-ripple cross-lamination (Fig. 11b).

Figure 11. Gordale Limestone Member localities at Duck Street Quarries, Greenhow. (a) Palaeokarstic surface in south quarry [41126 46384], with some ochreous clay infill, overlain by pale grey, fine-grained, bedded grainstone with peloids, foraminifers, crinoid ossicles. The surface is underlain by a pale grey, medium-grained, peloidal grainstone strongly laminated with crinoidal clasts, brachiopod valves and solitary corals in upper 0.6 m, mainly massive or weakly laminated with inverted brachiopod valves, stylolitic surface with cross-lamination 3 m below top. British Geological Survey No. P875355. (b) Section in north quarry [41131 46393] showing coarse- to very coarse-grained, upward-coarsening, trough and tabular cross-bedded, crinoidal packstone/grainstone/rudstone, underlain by fine-grained bioclastic packstone/grainstone with wave-ripple cross-lamination in upper 0.2 m. British Geological Survey No. P875359.

The Gordale Limestone Member in the Silverdale Borehole is 72 m thick (Murray, Reference Murray1983) and shows many similarities to the underlying Cove Limestone Member, being dominated by pale grey limestone with local fenestral lime-mudstone (Fig. 5). The Gordale Limestone is here more typically fine- to medium-grained wackestone to grainstones, on average finer than the Cove Limestone, and the presence of thin green clays (palaeosoils), pedotubules and Davidsonina septosa brachiopod biostromes (Fig. 5), however, are diagnostic of this member. Arthurton, Johnson & Mundy (Reference Arthurton, Johnson and Mundy1988, fig. 13) recognized shale/mudstone horizons at eight levels in the Silverdale Borehole.

2.d.2 Biostratigraphy

Macrofossils. The Davidsonina (Cyrtina) septosa bands, marked by discrete concentrations of drifted brachiopods and corals, commonly with oncolitic coatings (Arthurton, Johnson & Mundy, Reference Arthurton, Johnson and Mundy1988), occur predominantly within the Gordale Limestone Member in the southeast of the Askrigg Block. One such band was collected from Duck Street Quarry by Garwood & Goodyear (Reference Garwood and Goodyear1924) and was used to mark the base of the Hargate End Limestone by Dunham & Stubblefield (Reference Dunham and Stubblefield1945). A further such band was recorded ~25 m below the top of the Gordale Limestone Member in the Silverdale Borehole (Fig. 5).

At Threshfield Quarry (Figs 1b, 10a) (WMD16466–16482) the section includes the corals Dibunophyllum bipartitum and Palaeosmilia murchisoni and the brachiopod Delepinea sp. The co-occurrence of Palaeosmilia murchisoni with Dibunophyllum bipartitum suggests an Asbian to basal Brigantian age. This locality is mentioned by Garwood & Goodyear (Reference Garwood and Goodyear1924) in the context of their Cyathophyllum murchisoni (D₁) Subzone. They state that the Cyrtina septosa band (c. 25–30 m below the top of D₁) is seen here, suggesting a late Asbian age.

At Coldstones Quarry (Fig. 8), macrofauna (WMD16563–16579) include the brachiopods Linoproductus/Linoprotonia sp., ?Linoprotonia hemisphaerica, Linoprotonia ashfellensis, ?Linoprotonia concinniformis and ?Delepinea, and the coral Syringopora sp. Dunham & Wilson (Reference Dunham and Wilson1985) record common Linoprotonia spp. and L. hemisphaerica in early and late Asbian successions. Range plotting of faunal data provided in Garwood & Goodyear (Reference Garwood and Goodyear1924) shows that ‘Productus’ hemisphericus occurs at and above D₁, which, given its record below the Girvanella Band at Coldstones, indicates an Asbian age. ?Linoprotonia concinniformis is mainly of Brigantian age.

Hudson (Reference Hudson1938, p. 311) considered the Dry Gill section as Holkerian (S2) strata. However, the diagnostic post-Holkerian coral Lithostrotion (= Siphonodendron) pauciradiale (Dunham & Stubblefield, Reference Dunham and Stubblefield1945) and Lithostrotion arachnoideum (Hudson, Reference Hudson1938) are recorded at the locality. J. R. Nudds (unpub. Ph.D. thesis, Univ. Durham, 1975) recorded the corals Lithostrotion vorticale and L. (= Siphonodendron) irregulare from this locality, of Holkerian–Asbian and Asbian–early Brigantian age, respectively (Nudds, Reference Nudds1980). The brachiopods Antiquatonia?, Echinoconchus elegans, E. subelegans and Linoproductus? were found during this study (WMD16321–16358). Based on the known ranges of E. elegans and Antiquatonia? and the ranges of the corals identified by J. R. Nudds (unpub. Ph.D. thesis, Univ. Durham, 1975), an Asbian age seems most likely.

Microfossils. The key taxa are unequally distributed in the four studied outcrops in the west of the area (Table 2). At Threshfield Quarry (RBH4), assemblages include Protoinsolentitheca fundamenta, Eostaffella parastruvei and Pseudoendothyra sublimis, representative of the late Asbian (Cf6γ) (Cózar & Somerville, Reference Cózar and Somerville2004; Somerville & Cózar, Reference Somerville and Cózar2005). The River Wharfe section (RBH50) contains primitive Neoarchaediscus, and 193 m east of Lythe House (RBH51) Bibradya is recorded; these genera are also markers of the late Asbian (A. R. E. Strank, unpub. Ph.D. thesis, Univ. Manchester, 1981; Jones & Somerville, Reference Jones, Somerville, Strogen, Somerville and Jones1996; Cózar & Somerville, Reference Cózar and Somerville2004). Above Linton Falls (RBH59) there is notable occurrence of Bradyina rotula, used as a marker of the latest Asbian (upper Cf6γ) (Jones & Somerville, Reference Jones, Somerville, Strogen, Somerville and Jones1996; Gallagher & Somerville, Reference Gallagher and Somerville1997; Cózar & Somerville, Reference Cózar and Somerville2004). A similar transition from typical late to latest Asbian foraminiferal assemblages was recorded in the Gordale Limestone Member in the Feizor Borehole (BGS Registration number SD76NE9, southwestern Askrigg Block, Fig. 1a) by Cózar & Somerville (Reference Cózar and Somerville2004).

At Coldstones Quarry (Fig. 8; Table 3), the basal sample (WQ217) includes the foraminifers Archaediscus at angulatus stage, Lituotubella magna, Omphalotis minima, Palaeotextularia sp. and algospongia Fasciella kizilia and Zidella maxima. From the overlying beds (WQ203) can be highlighted the occurrence of Neoarchaediscus stellatus, Neoarchaediscus sp., Omphalotis omphalota, Protoinsolentitheca fundamenta and Pseudoendothyra sublimis, all of them representative of the late Asbian (Cf6γ) (Cózar & Somerville, Reference Cózar and Somerville2004; Somerville & Cózar, Reference Somerville and Cózar2005). In addition, Bibradya grandis (WQ205, Fig. 3s), Cribrostomum lecomptei (WQ206) and Endothyranopsis crassa (WQ207) also suggest a late Asbian age. Rich and diverse foraminiferal assemblages are recorded from near the top of the member (WQ215), highlighted by the occurrence of Archaediscus chernoussovensis, A. ex gr. karreri, A. k. karreri, Bradyina rotula, Cribrospira panderi (Fig. 3r), Endostaffella delicata, E. fucoides, Endothyranopsis crassa, Eostaffella mosquensis, Neoarchaediscus spp., Protoinsolentitheca fundamenta and Pseudoendothyra sublimis. This assemblage can be assigned to the latest Asbian (upper Cf6γ) (Cózar & Somerville, Reference Cózar and Somerville2004).

Above a depth of 204 m in Coldstones No. 4 Borehole (Fig. 8), Strank (Reference Strank1982 b) recorded a much richer and diverse foraminiferal assemblage including Archaediscus enormis, A. karreri, A. grandiculus, Cribrostomum longiseptata (= C. lecomptei), Cribrostomum spp., Palaeotextularia longiseptata, Pseudoendothyra sublimis, Vissariotaxis cf. compressa and Endothyranopsis crassa (Table 3). Strank (Reference Strank1982 b) assigned an Asbian age for these taxa, but they are also representative of the late Asbian (Conil, Longerstaey & Ramsbottom, Reference Conil, Longerstaey and Ramsbottom1980; Cózar & Somerville, Reference Cózar and Somerville2004; Somerville & Cózar, Reference Somerville and Cózar2005). At Duck Street South Quarry (WQ199) and North Quarry (WQ200) (Fig. 8; Table 3) the more significant foraminifers include Cribrostomum spp., C. lecomptei, Endothyranopsis aff. crassa, Eostaffella ex gr. parastruvei, Neoarchaediscus stellatus, Protoinsolentitheca fundamenta and algospongia Ungdarella uralica, allowing an assignment to the late Asbian (Cf6γ).

Important foraminifers from Dry Gill, recorded by Strank (Reference Strank1982 a) include Archaediscus at angulatus stage, A. krestovnikovi, Endothyranopsis crassa, Nodosarchaediscus sp. and Omphalotis minima. Strank (Reference Strank1982 a) considered this assemblage to represent a Holkerian or possibly early Asbian age, although it is more typically represented in the late Asbian (Conil, Longerstaey & Ramsbottom, Reference Conil, Longerstaey and Ramsbottom1980; Jones & Somerville, Reference Jones, Somerville, Strogen, Somerville and Jones1996). Samples collected for this study (DMA327–8) contain Archaediscus at angulatus stage, A. ex gr. karreri, A. karreri grandis, Loeblichiidae, Neoarchaediscus stellatus, Protoinsolentitheca fundamenta, Palaeotextularia spp. and the algospongia Stacheoides tenuis, Ungdarella uralica and Zidella maxima (Table 3), which is consistent with a late Asbian age (Cf6γ) (Cózar & Somerville, Reference Cózar and Somerville2004). Such an age, along with the distinct lithology, is more consistent with the upper part of the Gordale Limestone Member.

In the Silverdale Borehole (Fig. 5; Table 4), the FADs of taxa characteristic of the late Asbian, e.g. Cribrostomum lecomptei (EWJ1534, illustrated at a higher level in Fig. 4b), Palaeotextularia longiseptata (EWJ1529) and Cribrospira panderi (EWJ1521) appear in higher beds in the Gordale Limestone Member. The FADs of important algae include Ungdarella uralica (EWJ1526) and Koninckopora sp. B (EWJ1531). The FAD of Bradyina rotula (EWJ1514, illustrated at a higher level in Fig. 4l) and Parajanischewskina brigantiensis (EWJ1515, Fig. 4i) in the uppermost 7 m of the member suggests proximity to the latest Asbian/Brigantian boundary.

In summary, foraminiferal assemblages suggest a late Asbian age for the Gordale Limestone Member. This is in agreement with observed brachiopod/coral assemblages and is consistent with previous interpretations for this member (Table 1). The base of the member starts close to the lower part of the upper Asbian. A latest Asbian age is recognized locally, especially in the Greenhow Inlier within the former Hargate End Limestone and in the Silverdale Borehole.