In previous studies, the distribution of foraminifers and calcareous algae in Mississippian limestones of the Midland Valley of Scotland, Solway Basin and the northern Pennines have been analysed for the interval spanning the Asbian to Arnsbergian regional substages (e.g., Cózar & Somerville Reference Cózar, Somerville and Burgess2004, Reference Cózar, Vachard, Aretz and Somerville2013, Reference Cózar and Somerville2014, Reference Cózar and Somerville2016; Cózar et al. Reference Cózar, Somerville and Burgess2008, Reference Cózar, Somerville and Burgess2010). Within this comprehensive analysis of northern England and Scotland, there are some regions where the foraminiferal and algal assemblages have not been studied yet in detail. Rare conodonts studies were undertaken, although their biostratigraphic results did not contribute significant biostratigraphic advances (e.g., Bowden Reference Bowden2001), and the first occurrence of key conodont taxa is later than in other basins. Traditionally, correlations in these regions were made based mostly on macrofaunal data and lithostratigraphical features (see, e.g., George et al. Reference Forsyth1976; Ramsbottom et al. Reference McLean, Owens, Bodman and McLean1978; Browne et al. Reference Browne, Dean, Hall, McAdam, Monro and Chisholm1999), although these same criteria have been used in more recent publications (cf. Brand Reference Brand2011; Waters et al. Reference Waters, Haslam, Cózar, Somerville, Millward and Woods2014). Unfortunately, the most reliable macrofaunal markers, the ammonoids, are rather scarce north of the Craven Basin (Waters & Condon Reference Stephenson, Williams, Monaghan, Arkley, Smith, Dean, Browne and Leng2012). Owing to the predominance of shales in Scotland, there have also been intense studies on palynomorphs, since the pioneer works of Neves et al. (Reference Kulagina, Gorozhanina, Gorozhanin and Filimonova1973) and Neves & Ioannides (Reference MacGregor1974), and this fossil group is still frequently used in the region (e.g., Francis Reference Farmer and Jones1991; Stephenson et al. Reference Owens, McLean, Simpson, Shell and Robinson2004; Owens et al. Reference MacGregor2005; Ingrams et al. Reference George and Black2020).
The aim of this study is to revise those areas where detailed foraminiferal studies have been previously limited or lacking, such as (i) the upper Viséan limestones of Scotland, in the Fife coast area around St Monans and Kirkcaldy, (ii) East Lothian around the Dunbar coast, (iii) upper Viséan and Namurian limestones in Northumberland coastal sections, south of Berwick-upon-Tweed and (iv) Namurian limestones in inland sections of Northumberland.
1. Biostratigraphic background
Most of the analysed upper Viséan limestones in Scotland are included in the Lower Limestone Formation, with older limestones assigned to the Pathhead Formation in the Fife coast and the Aberlady Formation in East Lothian (Browne et al. Reference Browne, Dean, Hall, McAdam, Monro and Chisholm1999). These latter formations were subsequently simplified under the West Lothian Oil Shale Formation (Fig. 1), originally described from West Lothian (Waters et al. Reference Ramsbottom, Calver, Eagar, Hodson, Holliday, Stubblefield and Wilson2007; Dean et al. Reference Cózar and Somerville2011). Waters et al. (Reference Riley2011b) used the original names of the formations for East Fife and East Lothian (Pathhead and Aberlady formations, respectively). Asbian ammonoids were recorded from the lower part of the Aberlady Formation (Wilson Reference Vachard, Cózar, Aretz and Izart1952), and miospores of the Tripartites vetustus–Rotaspora fracta (VF) zone were reported from the Pathhead Formation (Owens et al. Reference MacGregor2005). This biozone was considered equivalent to the Brigantian substage for the Pathhead Formation and the upper part of the Aberlady Formation (Waters et al. Reference Riley2011b). On the other hand, limestones in the Lower Limestone Formation were previously attributed to the Brigantian (George et al. Reference Forsyth1976; Maddox Reference Kulagina, Pazukhin, Nikolaeva, Kochetova, Zainakaeva, Gibshman, Konovalova, Puchkov, Kulagina, Nikolaeva and Kochetova1988; Karbub Reference Gibshman1993), although, more recently, this formation has been considered to be restricted to the late Brigantian (e.g., MacGregor Reference Holliday, Burgess and Frost1968, Reference Ingrams, McLean, Booth and Bodman1973; Francis Reference Farmer and Jones1991; Browne et al. Reference Browne, Dean, Hall, McAdam, Monro and Chisholm1999) or late Brigantian to basal Pendleian (Waters et al. Reference Ramsbottom, Calver, Eagar, Hodson, Holliday, Stubblefield and Wilson2007, Reference Riley2011b; Cózar et al. Reference Cózar, Somerville and Burgess2008, Reference Cózar, Somerville and Burgess2010; Dean et al. Reference Cózar and Somerville2011).
Figure 1 Lithostratigraphy of the Carboniferous in the Midland Valley (modified from Browne et al. Reference Browne, Dean, Hall, McAdam, Monro and Chisholm1999). Abbreviation: C. Coalfield = Central Coalfield.
In Northumberland, the analysed upper Viséan limestones belong to the upper part of the Tyne Limestone Formation (Asbian) and the Alston Formation (Brigantian) (Waters et al. Reference Ramsbottom, Calver, Eagar, Hodson, Holliday, Stubblefield and Wilson2007, Reference Waters, Millward and Thomas2011a; Dean et al. Reference Cózar and Somerville2011), similar to those for the Pennines in northern England. Recently, Ingrams et al. (Reference George and Black2020) have revised the palynomorphs from the section south of Berwick-upon-Tweed, between Spittal and Scremerston (also studied herein), and they recorded the Asbian Raistrickia nigra–Tripartites marginatus (NM) zone in the Dun Limestone–Woodend Limestone–Spirifer Bed Limestone (Tyne Limestone Formation). The Brigantian VF zone is recorded from the Oxford Limestone upward (Fig. 2).
Figure 2 Lithostratigraphical correlation by Strank (Reference Pattison1981) and Ingrams et al. (Reference George and Black2020) of limestones in the Northumberland Coast.
However, details of limestone-by-limestone correlation have not been published in the recent regional studies, and for this type of information, older publications are necessary. George et al. (Reference Forsyth1976) correlated the Jew Limestone from the Pennines (currently with Member status according to Dean et al. Reference Cózar and Somerville2011) with the Oxford Limestone (also with Member status) in Northumberland, and the Longcraig Limestone in East Lothian (although they did not define precisely which band – lower, middle or upper). Furthermore, they correlated the Lower and Middle Longcraig limestones with the St Monans White Limestone, and the Upper Longcraig Limestone with the St Monans Brecciated Limestone, Hurlet Limestone and Douglas Limestone within the Midland Valley. The base of the Brigantian was located at a level below the Longcraig Limestone, due to the occurrence of the palynological VF zone (Neves et al. Reference Kulagina, Gorozhanina, Gorozhanin and Filimonova1973). This correlation of the Oxford Limestone with the Jew Limestone was based on earlier works (Westoll et al. Reference Strank1955; George & Black Reference Forsyth and Chisholm1971; Holliday et al. Reference George, Johnson, Mitchell, Prentice, Ramsbottom, Sevastopulo and Wilson1975), and it has been widely supported in later studies (Dean et al. Reference Cózar and Somerville2011). A slightly different proposal by Pattison (Reference MacNair1981) correlated the Peghorn Limestone (currently with Member status in Dean et al. Reference Cózar and Somerville2011) in the lower part of the early Brigantian in the Pennines with a limestone below the Oxford Limestone (likely the Watchlaw Limestone). Ingrams et al. (Reference George and Black2020) also located the base of the Brigantian in the Watchlaw Limestone.
A completely different correlation was that proposed by Francis (Reference Farmer and Jones1991), who correlated the Oxford Limestone with the Middle Skateraw Limestone, which occurs stratigraphically some three limestones higher, above the previously correlated middle Longcraig Limestone.
In terms of foraminiferal studies relating to the limestones of the east coast of Scotland and Northumberland, two unpublished PhDs have focused on these regions. The first study, by Strank (Reference Pattison1981), was confined mainly to the Northumberland coastal sections at Beadnell and Spittal (Berwick-upon-Tweed), as well as the inland River North Tyne sections near Barrasford (Fig. 2). In the Beadnell section, she attributed the Budle Limestone and thin limestones above to the early Brigantian, and the Eelwell and Acre limestones (also currently with Member status in Dean et al. Reference Cózar and Somerville2011) to the late Brigantian. She tentatively correlated the Eelwell Limestone with the Cockleshell Limestone or Scar Limestone in the northern Pennines. In the Spittal section, samples from the Dun and Woodend limestones were barren in foraminifers. The Oxford Limestone and Lower Bath-House Wood Limestone were also barren, and the Upper Bath-House Wood Limestone contained lower Brigantian foraminifers, similar to those of the Single Post Limestone in the Pennines, whereas the Shotto Wood Limestone and the Eelwell Limestone were considered by Strank (Reference Pattison1981) to be late Brigantian. In the River North Tyne section, the Lower Bath-House Wood Limestone was attributed to the early Brigantian, and the Upper Bath-House Wood Limestone was correlated with the early/late Brigantian boundary interval, just above the Single Post Limestone. The early/late Brigantian boundary is placed at the base of the upper Posidonia (P2) subzone since the earlier studies by Bisat (Reference Bisat1928), coinciding with the Scar Limestone Member in the northern Pennines (or lateral equivalents). In more recent studies, foraminifers and other fossil groups of this stratigraphic level have been examined (e.g., Conil et al. Reference Carruthers, Burnett and Anderson1980; Strank Reference Pattison1981; Riley Reference Neves and Ioannides1993). In particular, Strank (Reference Pattison1981) studied the Single Post Limestone, Cockleshell Limestone and Scar Limestone in the Askrigg and Alston blocks, and she confirmed that those lower beds might not be present in all the basins in northern Britain, and, also, that the major faunal change, including rugose corals, brachiopods and foraminifers, was recorded in the Cockleshell Limestone. She proposed to reposition the base of the late Brigantian in the Cockleshell Limestone. Owing to those uncertainties, the early/late Brigantian boundary interval is used for these three limestones.
The other foraminiferal study, by Karbub (Reference Gibshman1993), focused on coastal sections in East Fife, at Pittenweem–St Monans and Kirkcaldy, as well as in East Lothian, at Catcraig and Aberlady coastal sections (Fig. 3). However, the results in this PhD thesis are ambiguous, because the attributed ages of some limestones in the text do not correspond to those in the graphic correlations. Thus, at Catcraig and Aberlady, the Middle Longcraig Limestone was assigned to the Asbian (the Carbonifère foraminifères (Cf) Cf6α–Cf6γ subzones of Conil et al. Reference Carruthers, Burnett and Anderson1980), the Upper Longcraig Limestone and Lower Skateraw Limestone to the late Asbian–Brigantian (Cf6γ–Cf6δ subzones) and the Middle–Upper Skateraw limestones and Chapel Point Limestone to the Brigantian (Cf6δ subzone). However, graphically, limestones from the Upper Longcraig, Second Abden and St Monans White limestones were all considered as Brigantian (Fig. 3). Karbub (Reference Gibshman1993) did not record any representative foraminifers in the youngest Barns Ness Limestone. On the other hand, at Kirkcaldy, the First Abden Limestone was assigned to the Asbian (Cf6β–Cf6γ subzones), and the Second Abden Limestone and Seafield Tower Limestone were assigned to the late Asbian to Brigantian (Cf6γ–Cf6δ subzones). At the Pittenweem–St Monans section, the St Monans White Limestone and Charlestown Main Limestone were assigned to the late Asbian–Brigantian (Cf6γ–Cf6δ subzones), and the Mid Kinniny Limestone to the Brigantian (Cf6δ subzone). Other limestone horizons in the section (St Monans Brecciated and St Monans Little limestones) were not sampled by Karbub (Reference Gibshman1993) due to strong dolomitisation. However, in the graphic correlation, the Upper Longcraig Limestone, Second Abden Limestone and St Monans White Limestone were all considered as belonging to the lower part of the Brigantian (Fig. 3), and a plausible early/late Brigantian boundary was not acknowledged.
Figure 3 Lithostratigraphical correlation by Karbub (Reference Gibshman1993) of limestones in the Fife and East Lothian coasts with foraminiferal subzones. Limestones between the St Monans White and Charlestown Main limestones were not sampled by this author due to dolomitisation. Foraminiferal zones based on Conil et al. (Reference Carruthers, Burnett and Anderson1980). Abbreviation: ASB = Asbian.
2. Studied sections
The south coast of the Fife Peninsula has been sampled around St Monans, between Pittenweem and St Monans, and some limestones were sampled farther to the southwest, close to Elie (see MacGregor Reference Holliday, Burgess and Frost1968 and Forsyth & Chisholm Reference Davies, McAdam and Cameron1977 for details of the localities) (Fig. 4; supplementary Appendix 1 available at https://doi.org/10.1017/S1755691020000092). Owing to the poor preservation (dolomitised) and thin nature of the Charlestown Main Limestone, this unit has been also sampled in the abandoned quarry at Charlestown, the type locality on the Firth of Forth (Fig. 4). However, the Charlestown Main Limestone in the quarry has an unusually large thickness due to the development of microbial mounds, and this facies thins out dramatically beyond the quarry, as observed on the coast (Pickard Reference Maddox1992). The lowest limestone beds (Lower and Upper Ardross limestones) and the Mid Kinniny Limestone were not sampled due to strong dolomitisation. Farther to the southwest, the coastal section between Kinghorn and Kirkcaldy was also sampled (MacGregor Reference Holliday, Burgess and Frost1968), except for the Upper Kinniny Limestone, which was also too strongly dolomitised.
Figure 4 Location of the main stratigraphic sections mentioned in the text. Abbreviation: Bh. = borehole.
In East Lothian, the succession from the Lower Longcraig Limestone to the Middle Skateraw Limestone has been analysed by us in the Spilmersford Borehole, which was extensively described by Davies (Reference Cózar and Somerville1974) and Neves & Ioannides (Reference MacGregor1974). The oldest limestones in the borehole are barren in foraminifers. Samples were collected from the Middle Longcraig Limestone to Barns Ness Limestone interval, from coastal outcrops around Cove northwards to Skateraw and to Dunbar (see Davies et al. Reference Cózar and Somerville1986 for details of locations) (Fig. 4; supplementary Appendix 1). The oldest limestones sampled in the region at Cove have been discarded due to poor preservation.
In the Northumberland coast, the upper Viséan limestones of the Alston Formation have been sampled south of Berwick-upon-Tweed, between Spittal and Scremerston (Fowler Reference Dean, Browne, Waters and Powell1926; Ingrams et al. Reference George and Black2020), in the Beadnell coastal section (Carruthers et al. Reference Carruthers, Dinham, Burnett and Maden1927), and in the Boulmer coastal section (Carruthers et al. Reference Carruthers, Dinham, Burnett and Maden1930; Westoll et al. Reference Strank1955), where Namurian limestones of the Stainmore Formation crop out a little farther to the north, in the Howick coast (see Westoll et al. Reference Strank1955 and Farmer & Jones Reference Currie1968 for details of the localities) (Fig. 4; supplementary Appendix 1).
In south Northumberland, some limestones were sampled inland in small quarry sections (Fig. 4; supplementary Appendix 1).
3. Foraminiferal biostratigraphic correlation
In order to establish the biostratigraphic foraminiferal ranges in the studied limestone beds, regional biostratigraphic ranges defined previously for northern England and the Midland Valley region of Scotland (Cózar & Somerville Reference Cózar, Somerville and Burgess2004, Reference Cózar, Vachard, Aretz and Somerville2013, Reference Cózar and Somerville2014, Reference Cózar and Somerville2016; Cózar et al. Reference Cózar, Somerville and Burgess2008, Reference Cózar, Somerville and Burgess2010) are referred to here. Foraminiferal assemblages based on the Cf6δ foraminiferal subzone of Conil et al. (Reference Carruthers, Burnett and Anderson1980) for the entire Brigantian, were subdivided nearly limestone by limestone in Cózar & Somerville (Reference Cózar, Somerville and Burgess2004) and Cózar et al. (Reference Cózar, Somerville and Burgess2010), for the studied interval, ranging between Assemblage 6 for the uppermost early Brigantian, Assemblages 7 to 9 for the late Brigantian and Assemblage 10 for the Great Limestone Member (Fig. 5). However, foraminiferal assemblages from the Pendleian and Arnsbergian have never been defined. Indeed, some foraminifers present in this study show different stratigraphic ranges elsewhere in the Palaeotethys (e.g., Cózar et al. Reference Cózar, Somerville and Burgess2019; Nikolaeva et al. Reference MacGregor2020), but their regional stratigraphic ranges in classical successions from England and Scotland seem to be a more appropriate approach for a detailed bed-by-bed correlation. Due to the different status of the carbonate units in the siliciclastic-dominant upper Viséan and Namurian cyclothemic successions, all the limestone beds formally defined as members within Alston and Stainmore formations (Northumberland) will be considered herein as ‘limestone’, to avoid any potential confusion in lithostratigraphic nomenclature.
Figure 5 Correlation of early Brigantian to basal Pendleian foraminiferal assemblages in western Midland Valley of Scotland (Glasgow and Airdrie), eastern Midland Valley (Kirkcaldy and St Monans–Fife), East Lothian, Northumberland (Berwick-upon-Tweed), Solway Basin (Archerbeck Borehole) and northern England (Rookhope Borehole). Solid lines are correlations discussed in the text. Dashed lines representing correlations from the Midland Valley are based on Browne et al. (Reference Browne, Dean, Hall, McAdam, Monro and Chisholm1999), Cózar et al. (Reference Cózar, Somerville and Burgess2008, Reference Cózar, Somerville and Burgess2010), Solway Basin in Cózar & Somerville (Reference Cózar, Vachard, Aretz and Somerville2013) and Alston Block in Cózar & Somerville (Reference Cózar, Somerville and Burgess2004, Reference Cózar and Somerville2016). Foraminiferal assemblages recorded from the limestones and described in the text are numbered in the far left- and right-hand columns (4–10); the black areas are the intervening siliciclastic rocks that were barren in foraminifers. In addition, the foraminiferal assemblages recognised in each limestone correspond to the number to the left of the columns for each limestone in their respective sections. Note also that unproductive limestones are mostly strongly dolomitised. Abbreviations: e. Brig. = early Brigantian; Pend. = Pendleian; Bh. = borehole; LB-HW = Lower Bath-House Wood Limestone; MB-HW = Middle Bath-House Wood Limestone; UB-HW = Upper Bath-House Wood Limestone.
3.1. Limestones in the St Monans coast
Foraminiferal assemblages in limestones from St Monans are generally poor, compared to limestones in other areas of the Midland Valley of Scotland and the northern Pennines. Moreover, the poverty in foraminifers is a common feature in all the limestones in the Fife coast, as also observed by Maddox (Reference Kulagina, Pazukhin, Nikolaeva, Kochetova, Zainakaeva, Gibshman, Konovalova, Puchkov, Kulagina, Nikolaeva and Kochetova1988) and Karbub (Reference Gibshman1993). This constrains, significantly, the biostratigraphic assessment of the limestone. In many cases, there is insufficient data to distinguish an assemblage from those in the underlying/overlying limestones (supplementary Appendix 2). In this succession (Fig. 5), the oldest sampled carbonate unit, the Upper Ardross Limestone, is completely dolomitised and barren of foraminifers. Moreover, even in limestones with preserved foraminifers, they can be strongly affected by dolomitisation and recrystallisation. The succession at St Monans, in which limestone beds contained foraminifers, include (Fig. 5): St Monans White Limestone (oldest), St Monans Brecciated Limestone, St Monans Little Limestone and Charlestown Main Limestone (sampled from the type locality at Charlestown quarry).
3.1.1. St Monans White Limestone
Foraminiferal assemblages recorded from the St Monans White Limestone show a predominance of long-ranging forms that first occur from the Asbian or older levels, such as Tetrataxis, Endothyra, Pseudoammodiscus and Archaediscus, as well as taxa typically developed during the early Brigantian, such as Neoarchaediscus, Archaediscus ex gr. karreri and Praeostaffellina (supplementary Appendix 2). The occurrence of the large Archaediscus karreri Brady, Archaediscus chernoussovensis Mamet, Neoarchaediscus incertus (Grozdilova & Lebedeva), Neoarchaediscus parvus (Rauser-Chernousova) and Neoarchaediscus akchimensis (Grozdilova & Lebedeva) suggest an early Brigantian age. Furthermore, the occurrence of Asteroarchaediscus bashkiricus (Krestovnikov & Theodorovich) (Fig. 6c) and Asteroarchaediscus pustulus (Grozdilova & Lebedeva) suggest this limestone can be assigned to the uppermost part of the early Brigantian. In northern England (Alston Block), A. bashkiricus was first recorded from the Single Post Limestone (Strank Reference Pattison1981) in the upper part of Assemblage 6 (Fig. 5).
Figure 6 Selected foraminifers from the Fife and East Lothian coastal sections. (a) Neoarchaediscus parvus (Rauser-Chernousova), St Monans White Limestone, sample Pc2977. (b) Tubispirodiscus? sp., St Monans White Limestone, sample Pc2983. (c) Asteroarchaediscus bashkiricus (Krestovnikov & Theodorovich), St Monans White Limestone, sample Pc 2984. (d) Asteroarchaediscus bashkiricus (Krestovnikov & Theodorovich), First Abden Limestone, sample Pc 2998. (e) Biseriella parva (Chernysheva), St Monans Brecciated Limestone, sample Pc2980. (f) Biseriella parva (Chernysheva), Seafield Tower Limestone, sample Pc2996. (g) Howchinia variabilis Cózar, Sanz-López, Blanco-Ferrera, Seafield Tower Limestone, sample Pc2996. (h) Euxinita efremovi (Vdovenko & Rostovtseva), Middle Skateraw Limestone, sample Pc2942. (i) Neoarchaediscus gregorii acutiformis (Grozdilova & Lebedeva), Lower Skateraw Limestone, sample Pc2951. (j) Tubispirodiscus sp., First Abden Limestone, sample Pc2999. (k) Tubispirodiscus sp., First Abden Limestone, sample Pc2999. (l) Tubispirodiscus cf. cornuspiroides (Brazhnikova & Vdovenko), First Abden Limestone, sample Pc2999. (m) Planospirodiscus cf. minimus (Grozdilova & Lebedeva), First Abden Limestone, sample Pc2999. (n) Planospirodiscus sp., First Abden Limestone, sample Pc2999. (o) Planospirodiscus sp., First Abden Limestone, sample Pc2999. (p) Neoarchaediscus parvus (Rauser-Chernousova), Middle Skateraw Limestone, sample Pc2940. (q) Neoarchaediscus shugorensis (Chermnykh), Middle Skateraw Limestone, sample Pc2940. (r) Neoarchaediscus incertus (Grozdilova & Lebedeva), First Abden Limestone, sample Pc2998. (s) Neoarchaediscus postrugosus (Reitlinger), Second Abden Limestone, sample Pc3010. (t) Howchinia gibba (Moeller), Middle Skateraw Limestone, sample Pc2940. (u) Eostaffella mirifica Brazhnikova, Lower Skateraw Limestone, sample Pc2961. (v) Planospirodiscus minimus (Grozdilova & Lebedeva), Middle Skateraw Limestone, sample Pc2945. (w) Neoarchaediscus gregorii (Dain), Middle Skateraw Limestone, sample Pc2940. (x) Cepekia cepeki Vašíček & Růžička, Middle Skateraw Limestone, sample Pc2945. (y) Praeostaffellina sp. nov. cf. Cózar & Somerville, Lower Skateraw Limestone, sample Pc2951. (z) Eolasiodiscus donbassicus Reitlinger, Upper Skateraw Limestone, sample Pc2946. Scale bar = 100 μ.
3.1.2. St Monans Brecciated Limestone
The St Monans Brecciated Limestone contains many of the taxa recorded in the underlying St Monans White Limestone, but it is noteworthy for the first occurrence of Howchinia gibba (Moeller) and Howchinia cummingsi (Hallett) and, most significantly, by the first occurrence of Biseriella parva (Chernysheva) (Fig. 6e). The latter taxon is first recorded from Assemblage 7 of the late Brigantian, possibly equivalent to the Scar Limestone (northern England), the Hurlet Limestone (Glasgow) and Gastropod Limestone (Archerbeck Borehole) in Scotland (Cózar & Somerville Reference Cózar, Somerville and Burgess2004, Reference Cózar, Vachard, Aretz and Somerville2013, Reference Cózar and Somerville2016; Cózar et al. Reference Cózar, Somerville and Burgess2010). This correlation is in agreement with a previous proposal by Forsyth & Chisholm (Reference Davies, McAdam and Cameron1977), who first correlated the St Monans Brecciated Limestone with the Hurlet Limestone.
3.1.3. St Monans Little Limestone
Only one sample from this limestone bed could be analysed due to extensive dolomitisation. However, although it contains a rather poor assemblage, Endothyranopsis sphaerica (Rauser-Chernousova & Reitlinger) is first recorded. This is another typical late Brigantian marker, which is also first recorded from Assemblage 7 in England and Scotland (Cózar & Somerville Reference Cózar, Somerville and Burgess2004, Reference Cózar, Vachard, Aretz and Somerville2013, Reference Cózar and Somerville2016; Cózar et al. Reference Cózar, Somerville and Burgess2010). Thus, the St Monans Little Limestone can be correlated within the Scar Limestone–Five Yard Limestone interval (Fig. 5), but there is no farther faunal evidence to establish a more precise correlation.
3.1.4. Charlestown Main Limestone
In the coast section at St Monans, the Charlestown Main Limestone is completely dolomitised (like the overlying Mid Kinniny Limestone), but in the quarry section at Charlestown, the limestone contains microbial facies with foraminifers, although the latter are not abundant. Generally, microbial facies are not favourable for foraminifers, but, despite this, some of the previously mentioned late Brigantian markers are recorded (e.g., B. parva and E. sphaerica), although no new biostratigraphically important taxa are present, and the available taxa suggest also an Assemblage 7. Browne et al. (Reference Browne, Dean, Hall, McAdam, Monro and Chisholm1999) correlated the Charlestown Main Limestone with the Blackhall Limestone, a fact supported by the presence of the overlying Neilson Shell Bed, which is present in most parts of the Midland Valley, and with ammonoids of the P2c subzone (Currie Reference Cózar and Somerville1954). However, the Neilson Shell Bed does not have the same faunal components across the Midland Valley, and in West Fife, it is much richer than in the Central Coalfield and Glasgow areas, being composed of more abundant organisms adapted to firm substrates instead of muddy substrates (Wilson Reference Waters, Browne, Dean and Powell1966). The correlation of the Blackhall Limestone and Charlestown Main Limestone is plausible, especially if we take into consideration the fact that the underlying St Monans Brecciated and St Monans Little limestones both contain representatives of the foraminiferal Assemblage 7. Nevertheless, this suggested correlation with the Blackhall Limestone is hampered by the fact that the Charlestown Main Limestone does not contain foraminifers typical of the Assemblage 8. This unusual foraminiferal assemblage may be readily explained by the presence of hostile microbial facies that is developed in the quarry. The microbial facies prevents any farther lithological comparison between both limestones, with very distinct lithological features. Furthermore, the Neilson Shell Bed recorded above the Charlestown Main Limestone in the quarry also contains distinct faunal elements of this region. Thus, based on the obtained foraminiferal assemblages (Fig. 5), we could not confirm the previous correlation of the Charlestown Main Limestone with the Blackhall Limestone.
3.2. Limestones in the Kirkcaldy coast
The succession at Kirkcaldy includes the First Abden Limestone (oldest), Second Abden Limestone, Seafield Tower Limestone and Lower, Mid and Upper Kinniny limestones (Fig. 5). According to Karbub (Reference Gibshman1993), the foraminiferal assemblage in the Second Abden Limestone is rich and diverse, whereas other limestones are very poor (supplementary Appendix 2).
3.2.1. First Abden Limestone
This limestone contains assemblages abundant in archaediscids, with a predominance of small Archaediscus and Neoarchaediscus. It is also noteworthy for abundant primitive forms of Tubispirodiscus and Planospirodiscus (Fig. 6j–o), although none of the typical late Brigantian species could be identified. In addition, it is significant for the occurrence of Howchinia hemisphaerica Cózar, Sanz-López & Blanco-Ferrera, a species which is first recorded slightly below the base of the Serpukhovian in northern Spain (Cózar et al. Reference Conil, Longerstaey and Ramsbottom2015) and southern France (Vachard et al. Reference Pickard2016). Furthermore, Karbub (Reference Gibshman1993) recorded Neoarchaediscus gregorii (Dain), a species which usually occurs within the late Brigantian, although it has been rarely documented in the upper part of the early Brigantian (Strank Reference Pattison1981; Somerville & Cózar Reference Somerville and Cózar2005). The occurrences of the above-listed species, as well as Asteroarchaediscus bashkiricus (Fig. 6d), suggest that the First Abden Limestone is, at least, of uppermost early Brigantian age, and it should be correlated with the St Monans White Limestone and the Single Post Limestone in northern England (Fig. 5).
3.2.2. Second Abden Limestone
In contrast to the remarks of Karbub (Reference Gibshman1993), we found a mostly dolomitised outcrop, from which only one productive sample was obtained. Nevertheless, the foraminiferal assemblage recorded contains A. bashkiricus, Asteroarchaediscus rugosus, as well as the occurrence of Neoarchaediscus postrugosus (Reitlinger) (Fig. 6s) and Janischewskina sp. These taxa suggest that the Second Abden Limestone can be correlated with the Scar Limestone in the lower part of Assemblage 7, and with the St Monans Brecciated Limestone (Fig. 5). The First Abden Limestone was considered as the base for the Lower Limestone Formation by some authors (MacNair Reference Kulagina, Pazukhin, Kochetkova, Sinitsyna and Kochetova1917; MacGregor Reference Ingrams, McLean, Booth and Bodman1973). Wilson (Reference Waters, Dean, Jones, Somerville, Waters, Somerville, Jones, Cleal, Collinson, Waters, Besly, Dean, Stephenson, Davies, Freshney, Jackson, Mitchell, Powell, Barclay, Browne, Leveridge, Long and McLean1989) considered the First Abden and Second Abden limestones as a single marine episode, separated by volcanic activity, although he considered the Second Abden Limestone as equivalent to the Hurlet Limestone in Glasgow, and, thus, the base of the Lower Limestone Formation. Previously, Burgess (Reference Burgess1965) interpreted that the abundance of the incertae sedis Algospongia Falsocalcifolium punctatum (Maslov) recorded in the Second Abden Limestone is a typical feature of the Hurlet Limestone and lateral equivalents, and, thus, most authors have now considered the Second Abden Limestone as the base for the Lower Limestone Formation. Certainly, the Hurlet, Broadstone and Main limestones show abundant specimens of this taxon (see supplementary material in Cózar et al. Reference Cózar, Somerville and Burgess2010). However, it is not exclusively confined to this interval, because the acme in northern England is localised from the Assemblage 6 (Cózar & Somerville Reference Cózar, Somerville and Burgess2004). In both the First Abden and Second Abden limestones, F. punctatum is recorded, but it is not particularly abundant, similar to data in Karbub (Reference Gibshman1993), where it is only found in a few levels. In addition, this feature does not seem to be diagnostic, because in the St Monans section, F. punctatum is just as abundant in the St Monans White Limestone as it is in the St Monans Brecciated Limestone. Foraminiferal assemblages of the First Abden Limestone suggest the early–late Brigantian boundary interval, represented as the Single Post Limestone, but clearly late Brigantian markers are not recorded, whereas the Second Abden Limestone contains those late Brigantian markers. Since the base of the Lower Limestone Formation is formally defined in the Hurlet Limestone of Glasgow, at the base of the late Brigantian, this late Brigantian age for the Second Abden Limestone indirectly confirms that it should be considered the equivalent to the base of the Lower Limestone Formation in Fife.
3.2.3. Seafield Tower Limestone
The Seafield Tower Limestone contains a much richer foraminiferal assemblage than the underlying limestones, and significant first occurrences include Biseriella parva (Fig. 6f), Endothyranopsis sphaerica and Climacammina spp., representatives of the Assemblage 7. These taxa are typical late Brigantian markers, which first occur in the Scar Limestone and Five Yard Limestone, an interval with a very similar fauna, and virtually devoid of any foraminiferal markers to distinguish them from one another (Cózar & Somerville Reference Cózar, Somerville and Burgess2004, Reference Cózar and Somerville2016). Using stratigraphic principles, the Seafield Tower Limestone most likely can be correlated with the Charlestown Main Limestone (Fig. 5), as previously inferred by MacGregor (Reference Karbub1930), Forsyth (Reference Davies1970) and Maddox (Reference Kulagina, Pazukhin, Nikolaeva, Kochetova, Zainakaeva, Gibshman, Konovalova, Puchkov, Kulagina, Nikolaeva and Kochetova1988). However, this correlation can be questioned, due to the apparent absence of a typical Neilson Shell Bed above the limestones (Wilson Reference Waters, Browne, Dean and Powell1966), although this was later recognised in the region (e.g., Browne et al. Reference Browne, Dean, Hall, McAdam, Monro and Chisholm1999). Taking into consideration that the underlying Second Abden Limestone is correlated with the Scar Limestone, and that the foraminifers are also representative of the Assemblage 7, it might be reasonable to assume that the Seafield Tower Limestone can be laterally equivalent to the Five Yard Limestone. However, as noted previously, some questions have been posed about the correlation of the Charlestown Main Limestone with the Blackhall Limestone, and the Seafield Tower Limestone could be a similar case as that for the Charlestown Main Limestone, with unrepresentative foraminifers. Moreover, it may be significant to note that the Neilson Shell Bed was not originally recorded above the Seafield Tower Limestone (or any other limestone in the Kirkcaldy section; Wilson Reference Waters, Browne, Dean and Powell1966) (Fig. 5).
3.2.4. Kinniny limestones
In this area, although some foraminifers were recovered from the Lower and Mid Kinniny limestones, they are not sufficiently representative as to infer the presence of younger biozones (supplementary Appendix 2). In contrast, the Upper Kinniny Limestone is completely dolomitised and, hence, barren (see more details of these limestones in Maddox Reference Maddox1988). The correlation of these limestone beds proposed by Browne et al. (Reference Browne, Dean, Hall, McAdam, Monro and Chisholm1999) is adopted here (Fig. 5).
3.3. East Lothian coast
The lower part of the studied succession is extremely poor in foraminifers (Cove Lower to Middle Longcraig limestones), as well as in the upper part (Chapel Point to Barns Ness limestones) (Fig. 5), and, thus, only the intervening limestones contain rich foraminiferal assemblages (supplementary Appendix 2). A similar fact was recorded by Karbub (Reference Gibshman1993) from the Catcraig shore section, with scarce foraminifers from the upper part. On the other hand, the limestones from the Aberlady coastal section contained very poor foraminiferal assemblages, and did not contribute any significant foraminiferal data (Karbub Reference Gibshman1993).
3.3.1. Cove Lower Marine Band to Lower Longcraig limestones
This interval includes samples from the Cove Upper and Spilmersford Beds collected from the Spilmersford Borehole (Fig. 5). These strata are extremely poor in foraminifers, and an imprecise Asbian–early Brigantian age might be inferred. Palynomorphs studied by Neves et al. (Reference Kulagina, Gorozhanina, Gorozhanin and Filimonova1973) and Neves & Ioannides (Reference MacGregor1974) suggested that all these beds might belong to the early Brigantian, because the VF zone was recorded from four levels lower in the Spilmersford Borehole (an unnamed carbonate horizon) below the Upper Longcraig Limestone.
3.3.2. Middle Longcraig Limestone
Although coastal outcrops of Middle Longcraig Limestone are mostly strongly dolomitised, some isolated patches of limestone sampled show a distinct foraminiferal and algal assemblage. It is noteworthy for the occurrence of Neoarchaediscus incertus, as well as Falsocalcifolium, which suggest an age equivalent to the upper part of the early Brigantian in northern England (Assemblages 5–6 in Cózar & Somerville Reference Cózar, Somerville and Burgess2004). In addition, Karbub (Reference Gibshman1993) recorded Loeblichia paraammonoides (Brazhnikova) and Neoarchaediscus parvus, as well as rare Neoarchaediscus gregorii and Asteroarchaediscus. This suite of foraminifers would suggest an uppermost early Brigantian age, mostly due to the occurrence of Asteroarchaediscus, and, hence, typical of Assemblage 6, possibly equivalent to the Single Post Limestone and First Abden Limestone (Fig. 5).
3.3.3. Upper Longcraig Limestone
The Upper Longcraig Limestone is the first limestone in the East Lothian succession with abundant foraminifers, and, as a consequence, it contains numerous markers, such as Biseriella parva, Climacammina and Endothyranopsis sphaerica. These taxa, as well as the relative abundance of Asteroarchaediscus bashkiricus and Asteroarchaediscus rugosus (Rauser-Chernousova), suggest the basal part of the late Brigantian in England and Scotland (Cózar & Somerville Reference Cózar, Somerville and Burgess2004, Reference Cózar, Vachard, Aretz and Somerville2013; Cózar et al. Reference Cózar, Somerville and Burgess2010). In addition, Howchinia acutiformis Cózar, Sanz-López & Blanco-Ferrera is first recorded in this limestone – a taxon recorded from the Serpukhovian in north Spain (Cózar et al. Reference Conil, Longerstaey and Ramsbottom2015, Reference Cózar, Somerville, Mitchell and Medina-Varea2016). All these data suggest that the Upper Longcraig Limestone, with its typical Assemblage 7, can be correlated with the Scar Limestone in northern England, the Hurlet Limestone in the western Midland Valley, and the St Monans Brecciated Limestone and the Second Abden Limestone in Fife (Fig. 5).
3.3.4. Lower Skateraw Limestone
Foraminiferal assemblages in the Lower Skateraw Limestone are rather similar to those in the Upper Longcraig Limestone, but with more abundant Neoarchaediscus, E. sphaerica, Asteroarchaediscus, Praeostaffellina and Parabradyina pararotula Mamet & Pinard. Other new occurrences in this limestone include Howchinia convexa (Brazhnikova), Eostaffella mirifica Brazhnikova (Fig. 6u), Janischewskina typica Mikhailov and ‘Millerella’ tortula Zeller. The first occurrence of J. typica is also located in the Five Yard Limestone of northern England (Cózar & Somerville Reference Cózar, Somerville and Burgess2004). These are typical markers of the late Brigantian Assemblage 7 in Britain (Cózar et al. Reference Cózar, Somerville and Burgess2008; Cózar & Somerville Reference Cózar, Vachard, Aretz and Somerville2013, Reference Cózar and Somerville2016), but also from the Serpukhovian in Western Europe (Cózar et al. Reference Cózar, Somerville and Burgess2019). It is noteworthy for the occurrence of Praeostaffellina sp. nov. (cf. Cózar et al. Reference Cózar, Somerville, Mitchell and Medina-Varea2016) (Fig. 6y), which was previously recorded only from the Five Yard Limestone in the northern Pennines and South Wales (unpublished data).
The first occurrence of the incertae sedis Algospongia Calcifolium okense Shvetsov & Birina is also significant, despite the fact that it is not recorded in any other limestone bed in East Lothian. In northern England, although C. okense first occurs in the Five Yard Limestone, it shows an acme from the Three Yard Limestone to the Great Limestone (Cózar & Somerville Reference Cózar, Somerville and Burgess2004). In contrast, in the western Midland Valley, an acme of C. okense was recorded only in the Dockra Limestone and Blackhall Limestone, at levels correlated with the Three Yard Limestone (Cózar et al. Reference Cózar, Somerville and Burgess2010).
Based on the recorded taxa, the Lower Skateraw Limestone, with its foraminiferal Assemblage 7, is the same as that of the Five Yard Limestone in northern England, and might be correlated with the St Monans Little Limestone based on its stratigraphical position, but it also contains the same foraminiferal assemblages as that recognised in the Charlestown Main Limestone and the Seafield Tower Limestone in Fife (Fig. 5).
3.3.5. Middle Skateraw Limestone
This limestone contains rich foraminiferal assemblages, although has very few new occurrences. Nevertheless, three distinctive features can be highlighted about the Middle Skateraw Limestone: (i) the first occurrence of evolved Planospirodiscus and Tubispirodiscus; (ii) the occurrence of Neoarchaediscus shugorensis (Chermnykh) (Fig. 6q); and (iii) the occurrence of Cepekia cepeki Vašíček & Růžička (Fig. 6x). The discoidal archaediscids, although generally represented by richer assemblages, as well as the first Neoarchaediscus, with whorls and sutures at tenuis stage (cf. Conil et al. Reference Carruthers, Burnett and Anderson1980), together with this species of Cepekia, are recorded in northern England within the interval of the Three Yard to Four Fathom limestones. Unfortunately, the foraminiferal assemblages of both these limestones are rather similar, and the markers of the Four Fathom Limestone, mainly based on eosigmoilinids, are not present in the Middle Skateraw Limestone. However, taking into consideration that the underlying Lower Skateraw Limestone has been considered as laterally equivalent to the Five Yard Limestone, the Middle Skateraw Limestone is correlated with the Three Yard Limestone. It also contains the same foraminiferal assemblage as that of the Blackhall Limestone in Glasgow, and it has been correlated with the Charlestown Main Limestone by Browne et al. (Reference Browne, Dean, Hall, McAdam, Monro and Chisholm1999) (Fig. 5).
3.3.6. Upper Skateraw Limestone to Barns Ness Limestone
This group of limestones contains very few biostratigraphically important new occurrences, and, in general, has rather poor assemblages. However, the occurrence of Eolasiodiscus donbassicus Reitlinger (Fig. 6z) in the Upper Skateraw Limestone is noteworthy. This is because the species is recorded in the lower part of the Serpukhovian in the Urals (e.g., Kulagina et al. Reference Kulagina, Gorozhanina, Gorozhanin and Filimonova2011), and the upper part of the early Serpukhovian in Spain (Cózar et al. Reference Conil, Longerstaey and Ramsbottom2015), but in Britain it was only recorded previously from the late Serpukhovian (Cózar & Somerville Reference Cózar and Somerville2014).
3.4. Northumberland coast
As is the case in most coastal sections in eastern Scotland, the lower limestone beds in the Northumberland coastal sections are also often strongly dolomitised, the foraminiferal assemblages are more impoverished than in the younger strata and some limestones are barren in foraminifers (e.g., Dun Limestone and Barrasford Limestone). However, in general, preservation of the limestones from Berwick-upon-Tweed (Spittal and Beadnell sections) is better than in Scotland.
3.4.1. Woodend Limestone
This limestone was sampled in the Spittal section, and it contains common Archaediscus at angulatus stage (in particular, Archaediscus angulatus Sosnina and Archaediscus chernoussovensis) and Endothyra phrissa (Zeller). The assemblage is possibly representative of the late Asbian (Cózar & Somerville Reference Cózar, Somerville and Burgess2004), although the abundance of Cepekia, A. angulatus and A. chernoussovensis is more typically recorded in the early Brigantian. Nevertheless, those taxa can be rarely recorded from the late Asbian (Waters et al. Reference Riley2017a, Reference Stephenson, Angiolini, Cózar, Jadoul, Leng, Millward and Cheneryb). McLean et al. (Reference Kulagina, Stepanova, Kucheva and Nikolaeva2018) analysed the miospore assemblages in the basal Brigantian stratotype section at Janny Wood, and suggested that the VF zone should be situated at a level below the shales between the Robinson and Birkdale Limestone, or even older, in the latest Asbian. Ingrams et al. (Reference George and Black2020) recorded the NM zone in the Woodend Limestone; however, the occurrence of this biozone in the early Brigantian is not unusual (Cózar et al. Reference Cózar, Sanz-López and Blanco-Ferrera2006). Thus, at present, there is no clear evidence to determine if the Woodend Limestone should be assigned to the late Asbian or early Brigantian, but most probably, it is likely to be of latest Asbian age.
3.4.2. Oxford Limestone
The Oxford Limestone contained productive assemblages in samples from both the Spittal and Beadnell sections. It contains more numerous Neoarchaediscus, Archaediscus at angulatus stage, Howchinia gibba, rare Howchinia longa (Brazhnikova) and common Falsocalcifolium punctatum (supplementary Appendix 2). The only significant new occurrence is the transitional forms between Endothyranopsis crassa (Brady) and E. sphaerica. This foraminiferal suite is typically recorded in the early Brigantian, and the abundance of H. gibba and F. punctatum are located in Assemblage 6 (Cózar & Somerville Reference Cózar, Somerville and Burgess2004). Howchinia longa is recorded from the biozone E in the Montagne Noire, France, from the uppermost part of the early Brigantian (Vachard et al. Reference Pickard2016). In consequence, this limestone might be correlated also with the Linns Limestone in the Archerbeck Borehole and the Tynebottom Limestone in the Rookhope Borehole (Fig. 5).
3.4.3. Budle Limestone to Middle Bath-House Wood Limestone interval
The Budle Limestone is the third limestone above the Oxford Limestone in the Beadnell section, and it occupies a similar stratigraphic position as the Lower Bath-House Wood Limestone in the Spittal section (Fig. 5). These limestones are very thin and also poorly preserved, and, hence, do not contain very rich foraminiferal assemblages. Furthermore, the older Barrasford Limestone, and an unnamed limestone above, were too strongly dolomitised and, hence, not sampled. The Budle Limestone is noteworthy for the occurrence of Asteroarchaediscus pustulus and the Middle Bath-House Wood Limestone for the presence of Asteroarchaediscus bashkiricus. The Middle Bath-House Wood Limestone is also noteworthy for the first occurrence of specimens of Praeostaffellina sp. nov. (cf. Cózar & Somerville Reference Cózar and Somerville2016), which, so far, has only been recorded from a higher stratigraphic level, equivalent to the Five Yard Limestone in the northern Pennines (Cózar & Somerville Reference Cózar and Somerville2016). As described above, A. bashkiricus first occurs from the Single Post Limestone in the Pennines, with which these thin limestones are correlated. In addition, the Lower Bath-House Wood/Budle limestones can also be correlated with the Middle Longcraig Limestone (East Lothian) and St Monans White Limestone/First Abden Limestone (Fife) (Fig. 5).
3.4.4. Upper Bath-House Wood Limestone and Shotto Wood Limestone
These limestones are also poorly preserved and contain limited foraminiferal assemblages. Nevertheless, the Upper Bath-House Wood Limestone records some important taxa, such as common Archaediscus at angulatus transitional to the tenuis stage and ‘Millerella’ tortula (Fig. 7a, c). On the other hand, the Shotto Wood Limestone contains new significant occurrences, such as Janischewskina brigantiensis (Cózar & Somerville) (Fig. 7j), and Eostaffella mirifica. These taxa allow us to assign the interval to the late Brigantian, and it can be correlated with the assemblage 7 of the Scar Limestone (Alston Block), Upper Longcraig Limestone (East Lothian), St Monans Brecciated Limestone and Second Abden Limestone (Fife) (Fig. 5). This biostratigraphy is in agreement with Strank (Reference Pattison1981), who located the early–late Brigantian boundary between the Lower–Upper Bath-House Wood Limestones in the River North Tyne section.
Figure 7 Selected foraminifers from the Northumberland coastal sections. (a) ‘Millerella’ tortula Zeller, Upper Bath-House Wood Limestone, sample Pc3606. (b) ‘Millerella’ tortula Zeller, Eelwell Limestone, sample Pc3572. (c) Archaediscus at angulatus transitional to tenuis stage, Upper Bath-House Wood Limestone, sample Pc3606. (d) Archaediscus at angulatus transitional to tenuis stage, Eelwell Limestone, sample Pc3572. (e) Neoarchaediscus postrugosus (Reitlinger), Acre Limestone, sample Pc3556. (f) Eostaffella mirifica Brazhnikova, Eelwell Limestone, sample Pc3578. (g) Endothyranopsis plana Brazhnikova, Eelwell Limestone, sample Pc3583. (h) Eostaffellina ex gr. paraprotvae Rauser-Chernousova, Acre Limestone, sample Pc3556. (i) Eostaffellina paraprotvae Rauser-Chernousova, Sandbanks Limestone, sample Pc3560. (j) Janischewskina brigantiensis (Cózar & Somerville), Shotto Wood Limestone, sample Pc3607. (k) Eostaffella pseudostruvei (Rauser-Chernousova & Belyaev), Sandbanks Limestone, sample Pc3560. (l) Eostaffellina? sp., Acre Limestone, sample Pc3556. (m) Janischewskina typica Mikhailov, Eelwell Limestone, sample Pc3568. (n) Eostaffellina decurta (Rauser-Chernousova), Sandbanks Limestone, sample Pc3590. (o) Eostaffella ex gr. pseudostruvei (Rauser-Chernousova & Belyaev), Sandbanks Limestone, sample Pc3590. (p) Endothyranopsis sphaerica (Rauser-Chernousova & Reitlinger), Acre Limestone, sample Pc3587. Scale bar = 100 μ (a–i, k, l, n, o); 200 μ (j, m, p).
3.4.5. Eelwell Limestone
The Eelwell Limestone contains rich foraminiferal assemblages with similar abundances in the predominant taxa as those encountered in the underlying limestones. In addition, though, typical late Brigantian markers are commonly recorded, such as Endothyranopsis sphaerica, Climacammina, Janischewskina typica, ‘M.’ tortula, E. mirifica, Praeostaffellina sp. nov., Biseriella parva, Endothyranopsis plana Brazhnikova and Howchinia with umbilical structures (Fig. 7b, f, g, m). Most of these above-mentioned taxa were recorded in levels equivalent to the early Serpukhovian (e.g., Cózar et al. Reference Cózar, Somerville and Burgess2019), and the occurrence of J. typica and Climacammina are more commonly recorded from the Five Yard Limestone, to which the Eelwell Limestone is correlated. This limestone contains the same foraminiferal Assemblage 7 as that of the Lower Skateraw (East Lothian), and St Monans Little/Charlestown Main limestones and Seafield Tower Limestone (East Fife) (Fig. 5). The biostratigraphy recognised herein, using foraminifers, confirms the plausible lateral equivalence proposed by Dean et al. (Reference Cózar and Somerville2011) between the Eelwell, Harelawhill (Archerbeck Borehole) and Five Yard limestones (see Fig. 5).
3.4.6. Acre Limestone
The Acre Limestone has been sampled in three coastal sections (Spittal, Beadnell and Boulmer), but contains less diverse foraminiferal assemblages than the Eelwell Limestone, and the most significant new occurrences are those of Neoarchaediscus postrugosus, Eostaffellina decurta (Rauser-Chernousova), Eostaffellina ex gr. paraprotvae Rauser-Chernousova and Eostaffella ex gr. pseudostruvei (Rauser-Chernousova & Belyaev) (Fig. 7e, h). Eostaffella ex gr. pseudostruvei comprises ancestral forms to the nominal species, which, together with N. postrugosus, were first recorded from Assemblage 8 in the Midland Valley (Cózar et al. Reference Cózar, Somerville and Burgess2010), from the Blackhall Limestone and in the Archerbeck Borehole (Solway Basin) (Cózar & Somerville Reference Cózar and Somerville2013) from the unnamed Limestone X, below the Buccleuch Limestone, which are correlated with the Three Yard Limestone. This level also contains the first Eostaffellina in the northern Pennines (Cózar et al. Reference Cózar, Somerville, Mitchell and Medina-Varea2016). Furthermore, it is also notable for the acme of Calcifolium okense, which extends from the Three Yard Limestone up to the Great Limestone (Cózar & Somerville Reference Cózar, Somerville and Burgess2004). The Acre Limestone can be correlated with the Three Yard Limestone, as well as the Middle Skateraw Limestone (East Lothian) (Fig. 5).
3.4.7. Sandbanks Limestone
This limestone contains many of the previously mentioned taxa, but also the first occurrence of Eostaffellina paraprotvae (Fig. 7i), Eostaffella pseudostruvei (Rauser-Chernousova & Belyaev) (Fig. 7o) and Archaediscus at tenuis stage. All these taxa were recorded in Assemblage 9 from the Four Fathom Limestone in northern England (Cózar & Somerville Reference Cózar and Somerville2016), and Under Limestone of the Archerbeck Borehole (Cózar & Somerville Reference Cózar, Vachard, Aretz and Somerville2013), with which it is correlated (Fig. 5). This assemblage has been also recognised in the Main Hosie/Mid Hosie Limestones of Glasgow (Cózar et al. Reference Cózar, Somerville and Burgess2010).
3.4.8. Cushat to Iron Scar limestones
Most limestones are poorly preserved, and outcrops of the Cushat, Lickar and Iron Scar limestones (Fig. 8) were dolomitised, and barren in foraminifers. Only the Howick Limestone (=Lickar) in the Boulmer section, which is slightly better preserved, contains foraminifers, such as Archaediscus at tenuis stage, Archaediscus angulatus Sosnina and Loeblichia ammonoides (Brady), which are, however, rather unrepresentative for a biostratigraphical assessment, and the correlation adopted here (Fig. 8) is that published by Waters et al. (Reference Waters, Haslam, Cózar, Somerville, Millward and Woods2014).
Figure 8 Correlation of Pendleian–Arnsbergian limestones between Northumberland, Alston Block and Stainmore Trough. Solid lines are correlations discussed in the text. Dashed lines are correlations extracted from Brand (Reference Brand2011) and Cózar & Somerville (Reference Cózar and Somerville2016). Note that unproductive limestones are mostly strongly dolomitised. Abbreviations: CA = Chokierian–Alportian; Kinder. = Kinderscoutian.
3.4.9. Sugar Sands Limestone
The Sugar Sands Limestone is exposed in the Boulmer coast section and generally contains poor foraminiferal assemblages, with most taxa occurring from older levels. However, new important taxa recorded include: Plectostaffella evolutica Rumyantseva, Plectostaffella varvariensis (Brazhnikova & Potievskaya) (Fig. 9m), Calcivertella and Calcitornella. Furthermore, Eostaffella postmosquensis Kireeva first occurs, which is usually associated with the upper part of the late Serpukhovian (e.g., Kulagina et al. Reference Kulagina, Pazukhin, Nikolaeva, Kochetova, Zainakaeva, Gibshman, Konovalova, Puchkov, Kulagina, Nikolaeva and Kochetova2001, Reference Kulagina, Stepanova, Kucheva and Nikolaeva2009), although more primitive forms can occur much earlier (e.g., Cózar et al. Reference Cózar, Somerville and Burgess2010; Kulagina et al. Reference Gibshman, Vevel, Zaytseva and Stepanova2019). This Arnsbergian assemblage suggests a correlation of the Sugar Sands Limestone with the Lower Felltop Limestone in northern England (see Cózar & Somerville Reference Cózar and Somerville2014, Reference Cózar and Somerville2016) (Fig. 8). Similarly, Brand (Reference Brand2011) correlated the Sugar Sands Limestone with the Lower Felltop Limestone based on macrofauna, which is compatible with the foraminiferal data.
Figure 9 Selected foraminifers from Arnsbergian limestones from Northumberland Trough. (a) Eostaffella angusta Kireeva, Corbridge Limestone, sample Pc4037. (b) Eostaffella postmosquensis Kireeva, Lower Foxton Limestone, sample Pc4053. (c) Eostaffella pseudostruvei (Rauser-Chernousova & Belyaev), Sugar Sands Limestone, sample Pc4047. (d) Eostaffella ex gr. pseudostruvei (Rauser-Chernousova & Belyaev), Lower Foxton Limestone, sample Pc4056. (e) Plectostaffella seslavica Rumyantseva, Lower Foxton Limestone, sample Pc4056. (f) Eostaffellina protvae (Rauser-Chernousova), Lower Foxton Limestone, sample Pc4055. (g) Eostaffellina subsphaerica (Ganelina), Lower Foxton Limestone, sample Pc4056. (h) Eosigmoilina robertsoni (Brady), Lower Foxton Limestone, sample Pc4055. (i) Eosigmoilina explicata Ganelina, Lower Foxton Limestone, sample Pc4053. (j) Plectostaffella minima Rumyantseva, Lower Foxton Limestone, sample Pc4053. (k) Loeblichia minima Brazhnikova, Lower Foxton Limestone, sample Pc4054. (l) Eostaffella ex gr. postmosquensis Kireeva, Corbridge Limestone, sample Pc4038. (m) Plectostaffella varvariensis (Brazhnikova & Potievskaya), Sugar Sands Limestone, sample Pc4047. (n) Eostaffellina characteris Reitlinger, Lower Foxton Limestone, sample Pc4054. (o) Plectostaffella bogdanovkensis Reitlinger, Lower Foxton Limestone, sample Pc4056. (p) Eostaffella chomatifera Kireeva, Lower Foxton Limestone, sample Pc4056. (q) Plectostaffella evolutica Rumyantseva, Lower Foxton Limestone, sample Pc4054. (r) Plectostaffella tenuissima Brazhnikova & Vdovenko, Corbridge Limestone, sample Pc4038. (s) Plectostaffella varvariensiformis Brazhnikova & Vdovenko, Lower Foxton Limestone, sample Pc4055. Scale bar = 100 μ.
3.4.10. Lower Foxton Limestone and Upper Foxton Limestone
Both the Lower and Upper Foxton limestones are exposed in the Boulmer coast section, but the Upper Foxton Limestone is dolomitised and barren in foraminifers. The Lower Foxton Limestone, on the other hand, contains abundant foraminifers, including a new suite of first recorded taxa: Eostaffellina (E. protvae Rauser-Chernoussova, E. subsphaerica (Ganelina) and E. characteris Reitlinger), Insolentitheca horrida (Brazhnikova), Eosigmoilina (E. robertsoni (Brady), E. explicata Ganelina and E. elongata Brazhnikova), Brenckleina (B. rugosa (Brazhnikova) and B. aff. rugosa), Plectostaffella (P. tenuissima Brazhnikova & Vdovenko, P. evolutica, P. varvariensiformis Brazhnikova & Vdovenko, P. seslavica Rumyantseva, P. minima Rumyantseva, P. varvariensis and P. bogdanovkensis Reitlinger) and Loeblichia minima Brazhnikova (Fig. 9e–k, n–s). These taxa allow us to correlate this limestone with the Upper Felltop Limestone in northern England (Cózar & Somerville Reference Cózar and Somerville2014, Reference Cózar and Somerville2016) (Fig. 8). The Lower Foxton Limestone is noteworthy for the earliest occurrences of I. horrida and L. minima, which were recorded in the Pennines in slightly younger levels, in the Botany/Grindstone limestones (only one specimen of L. minima was recorded from the Upper Felltop Limestone), a level which is indirectly correlated by its stratigraphic position with the dolomitised Upper Foxton limestone, as Brand (Reference Brand2011) previously proposed.
3.5. South Northumberland
Owing to the poor preservation of the limestones in the Pendleian–Arnsbergian succession in the Northumberland coast at Boulmer, some of the equivalent limestones were sampled from inland quarries in southwest Northumberland. Nevertheless, apart from good exposures of the Great Limestone and Little Limestone, the younger Corbridge Limestone and Thornbrough Limestone are not all that well preserved, occurring in small isolated exposures (Fig. 4).
3.5.1. Great Limestone
The Great Limestone exposed in Brunton Quarry, Chollerford (Fig. 4), contains a typical rich foraminiferal assemblage as that recorded in the Alston Block and Stainmore Trough in the northern Pennines (Cózar & Somerville Reference Cózar, Somerville and Burgess2004). There is a predominance of upper Viséan taxa, such as Archaediscus at angulatus stage, Neoarchaediscus and Endostaffella. Other typical taxa, frequently recorded in the Great Limestone elsewhere, are Calcivertella, Endothyranopsis sphaerica, Archaediscus at angulatus transitional to tenuis stage, Asteroarchaediscus bashkiricus, Biseriella parva and Eostaffella ex gr. pseudostruvei. More significant taxa, that usually occur sparsely, are diversified eosigmoilinids (Brenckleina tenuissima (Brazhnikova), B. rugosa, Eosigmoilina robertsoni and E. explicata) and Eostaffellina decurta, taxa that have been commonly recorded from the Four Fathom Limestone, but are more abundant in the Great Limestone, in the upper part of the early Serpukhovian (Cózar & Somerville Reference Cózar and Somerville2014, Reference Cózar and Somerville2016).
3.5.2. Little Limestone
The foraminiferal assemblages recorded in the Little Limestone from the small quarry at Fallowfield (Fig. 4) are considered to be a continuation of those in the Great Limestone – a fact also observed in the northern Pennines (Cózar & Somerville Reference Cózar, Somerville and Burgess2004, Reference Cózar and Somerville2016). In South Northumberland, new occurrences include Archaediscus at tenuis stage, which likely first occurs from the Four Fathom Limestone or Three Yard Limestone. Also present are Janischewskina delicata (Malakhova) and Janischewskina gibshmanae Cózar, Somerville, Sanz-López & Blanco-Ferrera, which previously had only been recorded in Britain from the Lower Felltop Limestone, much later that in most European basins (e.g., Gibshman Reference Fowler2003; Cózar et al. Reference Cózar, Somerville and Burgess2019; Gibshman et al. Reference Francis and Craig2020; Nikolaeva et al. Reference MacGregor2020).
3.5.3. Corbridge Limestone
The Corbridge Limestone was sampled at Dead Ridge Quarry, Corbridge (Fig. 4), and contains a well-preserved foraminiferal assemblage. New occurrences include: Eostaffellina paraprotvae, Globivalvulina moderata Reitlinger, Insolentitheca horrida, primitive Plectostaffella (P. tenuissima) and Eostaffella ex gr. postmosquensis (Fig. 9l, r). Owing to the presence of the primitive Plectostaffella, the assemblage is similar to that recorded from the Sugar Sands Limestone at Boulmer. The Corbridge Limestone can also be correlated with the Rookhope Shell Band or Lower Felltop Limestone in northern England, but more probably with the latter, as proposed previously by Brand (Reference Brand2011) (Fig. 8).
3.5.4. Thornbrough Limestone
The Thornbrough Limestone was sampled at Thornbrough quarry at Corbridge and in a road section beside the A69 (Fig. 4). The foraminiferal assemblages are rich in Endostaffella, Archaediscus at angulatus stage, Tetrataxis, Eostaffella and Pseudotaxis. Surprisingly, typically evolved taxa (such as eosigmoilinids and Plectostaffella) are not recorded, whereas taxa more commonly recorded from the late Viséan are present, including: Archaediscus at concavus stage, Eostaffella proikensis Rauser-Chernousova, Eostaffella mosquensis Vissarionova, Scalebrina and Cribrostomum. These taxa might suggest a late Asbian age, but because of its stratigraphical position, near the top of the South Northumberland succession, the Thornbrough Limestone is likely equivalent to the Arnsbergian Upper Felltop Limestone (Brand Reference Brand2011) or the younger Grindstone Limestone (Waters et al. Reference Waters, Haslam, Cózar, Somerville, Millward and Woods2014) (Fig. 8). Similarly, incertae sedis Algospongia recorded in the Thornbrough Limestone do not contain typically Brigantian taxa, such as Calcifolium and Falsocalcifolium. Instead Ungdarella uralica Maslov is common, which usually shows its acme in the late Asbian and early Brigantian of Britain and Ireland (Cózar & Somerville Reference Cózar, Sanz-López and Blanco-Ferrera2005a, Reference Cózar, Somerville, Sanz-López and Blanco-Ferrerab). The most advanced foraminiferal species recorded in the Thornbrough Limestone are evolved Asteroarchaediscus, E. paraprotvae, Bradyina sp., Biseriella parva, Calcivertella spp. and Climacammina. However, this assemblage does not suggest anything younger than the Great Limestone–Little Limestone–Crag Limestone interval in northern England (Pendleian), due to the presence of Calcivertella and Eostaffellina, because the other taxa are typically recorded from the late Brigantian.
This apparently older assemblage in the Thornbrough Limestone is not unique, as a similar situation was observed in the Rowlands Gill Borehole, at the northern margin of the Alston Block. There, Riley (Reference Neves, Gueinn, Clayton, Ioannides, Neville and Kruszewska1992) recorded from the Coalcleugh Limestone (a limestone situated between the Lower and Upper Felltop limestones; Fig. 8) the following rich and diverse foraminiferal assemblage, including: Archaediscus (as well as forms named as Paraarchaediscus), Archaediscus karreri, Asteroarchaediscus, Bradyina, Endostaffella, Endothyranopsis crassa, Eostaffella spp. (as Eostaffella and as Millerella), Koskinobigenerina, Mediocris, Neoarchaediscus, Omphalotis, Planoendothya (as Planoendothyra and as Seminovella), Plectogyranopsis, Pseudoammodiscus, Scalebrina (as Calcitornella) and Tetrataxis. Such an assemblage might suggest a likely assignment to the Brigantian, and where the most evolved species are a questionable oblique section of Monotoxinoides cf. subplana and Eosigmoilina? sp. (not illustrated). On the other hand, Riley (Reference Neves, Gueinn, Clayton, Ioannides, Neville and Kruszewska1992) recorded from the overlying Upper Felltop Limestone the same assemblage, but, in addition, Janischewskina sp. (possibly J. gibshmanae), Calcivertella (as Pseudoglomospira) and, from the top sample, Eostaffellina sp. (possibly E. characteris), suggesting a Pendleian–Arnsbergian age.
Subsequently, foraminifers of the Upper Felltop Limestone in the Rowlands Gill Borehole were studied (Stephenson et al. Reference Nikolaeva, Alekseev, Kulagina, Gatovky, Ponemareva and Gibshman2010; Cózar & Somerville Reference Cózar and Somerville2016), using a new set of thin-sections prepared from core samples at different depths in the borehole than those studied by Riley (Reference Neves, Gueinn, Clayton, Ioannides, Neville and Kruszewska1992). Much richer foraminiferal assemblages were recorded, including abundant Eostaffellina, Plectostaffella and eosigmoilinids of Arnsbergian age. In contrast, the assemblages from the Coalcleugh Limestone were composed of Archaediscus at angulatus stage, Archaediscus at concavus stage, Asteroarchaediscus bashkiricus, Bradyina spp. Climacammina spp., Earlandia spp., Endostaffella spp., Endothyra spp., Endothyranopsis sphaerica, Eostaffella mosquensis, Eostaffella parastruvei, Eostaffella proikensis, Neoarchaediscus spp., Palaeotextularia sp., Pseudoammodiscus spp., Tetrataxis spp. and Tubispirodiscus cornuspiroides (Brazhnikova & Vdovenko), as well as common Ungdarella and Nanopora. Thus, it seems that the assemblages recorded by us from the Thornbrough Limestone are closely comparable to those of the Coalcleugh Limestone, but owing to this representing a cyclothem with a thin limestone, possibly similar to the Pike Hill Limestone in the South Northumberland succession, and taking into consideration its stratigraphic position, the Thornbrough Limestone is correlated with the Upper Felltop Limestone (Fig. 8). However, we acknowledge that there is no strong evidence to support this correlation based on the foraminifers and algae. It is recommended that, in the future, sectioning of more core material or sampling from more stratigraphic levels could provide more diagnostic biostratigraphic markers, as was the case for the Upper Felltop Limestone in the Rowlands Gill Borehole. It is difficult to explain the presence of these unusual assemblages. Clearly, they are not reworked, because individual specimens do not show evidence of abrasion and reworking, and the taxa extend their stratigraphical record up to the Arnsbergian, or even to younger stratigraphic levels. The absence of typical Arnsbergian markers can be only attributed to the small quantity of sectioned material, as well as the low abundance of those Arnsbergian markers for any palaeoecological constraint.
4. Conclusions
Sampling of limestones from within the siliciclastic-dominant upper Viséan and Namurian successions of eastern Scotland and Northumberland has been undertaken. A detailed biostratigraphy has been achieved, based principally on foraminifers, which has enabled correlations to be made between these two regions, as well as other parts of the Midland Valley of Scotland and northern England, using previously published data.
The oldest foraminiferal assemblages recorded from St Monans White Limestone/First Abden Limestone (Fife) and Middle Longcraig Limestone (East Lothian) can be correlated with the Single Post Limestone in the northern Pennines (Alston Block), all of which are of early Brigantian age. Older Brigantian foraminiferal assemblages are recorded from the Northumberland coast in the Oxford and Lower-Middle Bath-House Wood Limestones, which can be correlated with the Tynebottom and Single Post Limestones, respectively. There is no foraminiferal evidence in Scotland to help identify basal Brigantian strata and the position of the Asbian/Brigantian boundary.
The base of the late Brigantian in Fife is represented by the St Monans Brecciated Limestone and Second Abden Limestone, and in East Lothian by the Upper Longcraig Limestone. In Northumberland, the base of the late Brigantian is located between the Middle and Upper Bath-House Wood Limestones.
Pendleian and Arnsbergian foraminiferal assemblages are recorded from limestones in the Northumberland Trough, including the Great Limestone, Little Limestone, Sugar Sands Limestone, Lower Foxton Limestone and Corbridge Limestone, which can be correlated with equivalent limestones in the Alston Block. The youngest sampled limestone from Northumberland, the Thornbrough Limestone, is unusual, since it contains foraminifers and algae, which are more typical of older limestones, although this phenomenon has been also observed in the Coalcleugh Limestone and Upper Felltop Limestone from the Alston Block.
5. Supplementary material
Supplementary material is available online at https://doi.org/10.1017/S1755691020000092.
6. Acknowledgements
We would like to thank Mike Browne, Daniel Vachard and an anonymous reviewer for their constructive comments. The authors wish to thank Mark Dean (retired) of the British Geological Survey, Palaeontological Unit (Edinburgh), who facilitated the examination of the Spilmersford Borehole. Fieldwork was funded by the Spanish Ministry of Ciencia, Investigación y Universidades (project CGL2016-78738BTE).
