A Summary of Upper Pennsylvanian Regional Substages Defined in NW Spain – the Chrono- Stratigraphic Legacy of Robert H

Newsletters on Stratigraphy, Vol. 54/3 (2021), 275–300 Open Access Article Published online January 15, 2021; published in print June 2021

A summary of upper Pennsylvanian regional substages defined in NW Spain – the chronostratigraphic legacy of Robert H. Wagner

John A. Knight1* and Carmen Álvarez-Vázquez1

With 8 figures and 1 table

Abstract. The West European Regional Chronostratigraphic Framework for the later Pennsylvanian reflects the initiatives of the late Robert Wagner (1927–2018) in the Cantabrian Region of N Spain. Complementary to the recognition of substages has been the biostratigraphical application of megafloral zones. These were used to establish a framework of correlation between the classic concepts of Stephanian chronostratigraphy defined in the intramontane successions of the Massif Central, France and new substages in the Cantabrian Region. Through the later Pennsylvanian the Cantabrian Region hosted essentially continuous sedimentation in mixed terrigenous and marine facies, offering correlation between entirely continental successions and the coeval, predominantly marine sucessions of the Russian Platform. The status of the substages defined in the Cantabrian region is summarised: 1) Asturian: proposed to replace Westphalian D; a boundary stratotype has been proposed in the Riosa-Olloniego sector of the Central Asturian Coalfield but has not yet been ratified by the SCCS. The proposed stratotype in the Riosa Valley is now overgrown and incompletely recorded; review of this, or other alternatives in the region, is overdue and required before formal ratification. 2) Cantabrian: the originally proposed stratotype at Tejerina was amended on the basis of subsequent regional mapping supported by fusulinid studies. A revised boundary stratotype was proposed at the base of the Villanueva Marine Formation in the Guardo-Cervera Coalfield, Palencia; this was formally ratified by SCCS in 1989. 3) Barruelian: the boundary stratotype has been established at the base of the Carboneros Member in the Barruelo Coalfield. As proposed and ratified by the SCCS in 1989, this substage was defined to embrace the traditional concept of Stephanian A; this interval corresponds to the Lobatopteris lamuriana zone. The top of this substage is defined by the succeeding proposed Saberian substage, defined in the Sabero Coalfield, León. 4) Saberian: an informal proposal with description of the boundary stratotype has not yet been ratified; conceived to correspond to the lower part of the Stephanian B of the Massif Central and considered essentially coincident with the Alethopteris zeilleri zone. Work currently continues on the characterisation of the proposed Saberian, particularly in the Villablino Coalfield where the lowermost beds are attributed to the A. zeilleri zone and transition to well characterised floras of the Sphenophyllum angustifolium zone. Integration of the biostratigraphic record and currently available radiometric dates indicates: a) the Cantabrian (~ 3.0 Ma) falls across the interface Moscovian-Kasimovian, the base of the Kasimovian coinciding approximately with the middle of the Cantabrian; b) the Barruelian (~ 3.2 Ma) extends from mid-Kasimovian to an age above the base of the Gzhelian; c) the Saberian (minimum 1.5 Ma) falls entirely within the Ghzelian of the global framework; the interval between the approximate top of the Saberian and the base of the Permian, is indicated as reduced to some 1.5 Ma only.

Key words. Stratotypes, Asturian, Cantabrian, Barruelian, Saberian

Authors’ addresses: 1 Centro Paleobotánico, Real Jardín Botánico de Córdoba, Avenida de Linneo, s/n, 14004 Córdoba, Spain * Corresponding author: [email protected]

1. Introduction the efforts and initiatives of the late Robert H. Wagner (1927–2018) (Fig. 1). Robert Wagner served as Secre The historical development of the currently accepted tary to the Subcommission on Carboniferous Strati global scheme of Pennsylvanian chronostratigraphic graphy (SCCS) for some 17 years (1963–1980) and as units (Heckel and Clayton 2006) has been documented Vice-Chairman (1981–1982; 1987–1989) and Chair in detail by Wagner and Winkler Prins (2016). Wagner man (1982–1986); a biography has been published by (2017) subsequently presented a critique of the ‘glo Cleal et al. (2019). In the context of his stratigraphic bal’ chronostratigraphic scheme for the Pennsylvanian work, it is also necessary to recognise the close with particular reference to palaeogeographic areas collaboration of his co-worker, friend and colleague, and highlighting some significant problems of correla Cor Winkler Prins (1939–2019) (Fig. 1), who also tion between regional areas with different tectono- contributed many years to support the work of the stratigraphic history and significantly differing faunal SCCS, as Assistant Secretary (1973–1976), Secretary and floral assemblages. In summary, a strongly argued (1976–1982) and also Chairman of the SCCS Working case was made that for any global scheme the funda Groups on Westphalian A–C and the Upper Carboni mental concepts of chronostratigraphy and biostrati ferous Subdivision (1984–1989). graphy should be respected and the assumption that the one and the other are the same must be rejected (biostratigraphic criteria are not the same as those for establishing chronostratigraphic units); reliance on 2. Historical context a single fossil group should be avoided and stratotypes of series and stages should be based on continuous As documented in Wagner and Winkler Prins (2016), stratigraphic successions with a variety of fossil groups decisions arising from the 8th International Congress which can be used for correlation. The analysis by on Carboniferous Stratigraphy and Geology, held in Wagner and Winkler Prins (2016) and Wagner (2017) Moscow in 1975, defined the aim of the Subcommis underlines the importance of establishing and refining sion to arrive at a worldwide classification of the robust and well-documented regional stratigraphic Carboniferous; preliminary proposals for a truly inter frameworks against which the interpretation of global national chronostratigraphic scheme were published in correlation and chronostratigraphy can be tested. Bouroz et al. (1978). Implicit in these deliberations The objective of the present review is to document was the understanding that the West European strati the status of both ratified and proposed stratotypes of graphic framework, which hitherto had been a major substages for the late Pennsylvanian in the West focus of chronostratigraphic interpretation, would be European region. Inevitably this reflects in large part relegated to a regional framework.

Fig. 1. Robert Wagner with Cor Winkler Prins in 1997 (in Ruesga, Palencia). Photograph from the archive of the Centro Paleobotánico, Real Jardín Botánico de Córdoba. The chronostratigraphic legacy of Robert H. Wagner 277

Against a background of great progress in establishing the Pennsylvanian chronostratigraphic units of the a widely accepted global chronostratigraphic frame Western European framework was to a large extent work for the Pennsylvanian, it has been apparent that driven by the recognition of successive floral assem efforts to attain an internally consistent framework are blages (Bertrand 1937). Thus Westphalian A, B and C heavily dependent on reliable and well-documented (now the Langsettian, Duckmantian and Bolsovian regional successions. The limitations of a global substages) were originally conceived as reflecting chronostratigraphic scheme for the Pennsylvanian the composition of macrofloras. The process adopted based on conodont stratigraphy (Davydov et al. by the SCCS to define the base of the Westphalian D 2004, Ogg et al. 2008) have been commented by a relied almost exclusively on macrofloral evidence number of authors (e. g. Waters and Condon 2012, supported by palynological data (Laveine 1977). His Wagner and Winkler Prins 2016). Reliance primarily torically, the recognition of the divisions of the upper on a single palaeontological group makes chronostra most Westphalian and Stephanian (originally as stages, tigraphic concepts dependent upon interpretation of now substages) has been with reference to successions the systematics, interpretation of evolving lineages and in the central part of Western Europe, i. e. in the Sarre- palaeogeographical constraints of this single group. Lorraine Basin and in the Loire coalfield area of the Nevertheless, the concept of GSSPs (Global Standard Massif Central of France. However, successive reports Stratotype-section and Points) for the definition of prepared under the auspices of the SCCS (Bouroz et al. global chronostratigraphic stages is now accepted to be 1970, Bouroz et al. 1972) have recognised the diffi most reliably based on identifying a “primary” marker culty of establishing stratotypes in intramontane basins within a well-documented gradual transition through a with entirely terrigenous sedimentation, complicated single phylogenetic lineage (Remane 2003), in the case by difficulties of inter-basin correlation, discontinuous of the Pennsylvanian provided by conodont biostrati sections and limited accessibility to reference sections graphy. However, for a number of important regional originally defined in underground workings. areas (e. g. the palaeoequatorial paralic basins of The only area with a thick succession of upper Western Europe or the near palaeo-polar area of Westphalian succeeded by Stephanian strata is in the Australia) direct reference to a succession defined Sarre-Lorraine Basin (Bouroz et al. 1972), where a by conodont biostratigraphy is inapplicable unless disconformity at the horizon of the Holz Conglomerate supported by the integration of several different bios has been proven to represent a major stratigraphic gap tratigraphical schemes and associated radiometric ca between the two successions (Burger et al. 1997, Cleal libration; this reflects the necessary use of “secondary” 2008). Sections of Stephanian strata in the basins of the criteria to support approximate correlation to the Massif Central, including the reference section for the global stage boundaries (Remane 2003). This has Stephanian A (originally of stage status defined in the been the driver for continuing research to refine the Assise de Rive-de-Gier, Loire Basin), corresponded in West European chronostratigraphic framework and to part to this gap but no continuous succession covered define relevant and accessible stratotypes for substages the passage from Westphalian to Stephanian (Bouroz et through to the recognised base of the Permian System. al. 1970). The chronostratigraphy of the earlier Pennsylvanian Fundamental to the approach adopted to re-define of the West European succession has been well defined the later Pennsylvanian chronostratigraphic units of in the British Isles, primarily in the Pennine Basin the West European framework, specifically in the (Owens et al. 1985). This was a relatively tectonically Cantabrian Mountains of NW Spain, was the concept stable palaeogeographic region with a more or less that they should correspond as closely as possible to continuous sedimentary history. It is characterised by the long-standing and widely recognised divisions of mainly terrigenous sedimentation with periodic marine the upper Westphalian and the Stephanian (George and incursions; these were controlled by eustatic sea level Wagner 1972). The definition of chronostratigraphic fluctuations with rapid turnover of diagnostic ammo units covering the uppermost Westphalian and Ste noids and have permitted robust correlation over wide phanian in NW Spain required that they should reflect areas of Western Europe (Waters and Condon 2012). respectively the Westphalian D as recognised in the While the marine transgressions have proved such a Sarre-Lorraine Basin and the Stephanian A, B and C valuable tool on basin scale for definition of intervals divisions recognised in the Massif Central of France. upon which chronostratigraphic divisions have been The rationale for re-definition of these units has been based, it is relevant to note that the original concept of widely discussed, particularly in the context of the 278 J. A. Knight and C. Álvarez-Vázquez

Mar Cantábrico N

Punta (Bay of Biscay) Rubias Amao Gijn Picos de Europa Unit - marine Aviles succcession U. Moscovian - Gzhelian (Merino - Tomé et al. 2006) Ribadesella Ferroñes Llanes

Oviedo Arenas de Cabrales proposed Asturian Ventaniella go Fontecha ie boundary stratotype n Gamonedo Tineo o (Riosa Valley) ll Aller- -O a Fault Lebeña os Nalón Sebarga Ri Mieres area Ponga Sotres area Cangas Fault Puente Beleño Potes Pumar Central Picos Carballo Asturian Coalfield Valden Pisuerga Puerto Pico Rengos -Carrión Ventana Province Cordel La Pernía Redondo Canseco Rucayo Lores Peña Viego Riaño Cildá Tormaleo Castillería Barruelo Villablino Tejerina Carrasconte Ciñera Matallana Transition A. zeilleri megafloral zone to Valderruela Cervera de Pisuerga S. angustifolium zone Sabero La Magdalena Barruelian boundary La Robla Guardo stratotype El Bierzo proposed Saberian boundary Cantabrian boundary stratotype stratotype (Velilla de la Peña section) Post-orogenic cover León Faults Post-Asturian deposits Post-Leonian deposits 0 1020304050km Direction of thrusting Paleozoic undifferentiated (incl. Precambrian)

Fig. 2. Map of Stephanian Coalfields of the Cantabrian Mountains and location of late Pennsylvanian stratotypes (modified from Wagner and Castro 2011 and Knight and Wagner 2014). The Leonian deformation is of mid- to late Asturian age; the Asturian deformation is of mid- to late Barruelian age.

SCCS (e. g. Bouroz et al. 1972), with common recog flora to allow biostratigraphic correlation with the nition and agreement that the correlation between the purely terrigenous successions in the intramontane classic intramontane successions and newly proposed basins of the Massif Central of France (Bouroz et reference successions in mixed facies would be ne al. 1972, Wagner and Winkler Prins 1985a, b). cessarily based on the biostratigraphy of fossil floras. Recognition of floral assemblages was a primary Wagner (1966a, b, c) introduced the concept of a reference for interpreting the interrelationships of Cantabrian Stage as the lowermost unit of the Stepha stratigraphic successions and their general correlation nian Series on the basis of investigations in northern with the successions in Northern Europe and the Spain, where upper Westphalian D strata were found in Massif Central of France (e. g. Wagner 1965). How continuity with a full succession of the lower Stepha ever, the lithostratigraphic and chronostratigraphic nian. This is the only area of Western Europe where framework of the Pennsylvanian sedimentary succes several thousand metres of lower Stephanian strata sions across the Cantabrian Mountains has been un (currently attributed to Cantabrian and Barruelian ravelled through numerous workers over some dec substages) follow in essential continuity upon West ades, taking reference from a number of fossil groups phalian D (the currently proposed Asturian Substage); (fossil plants, fusulinids, coral-brachiopod assem the general outline of the distribution of Stephanian blages). A comprehensive summary of historical con successions and relevant successions of the underlying tributions to establishing the stratigraphic succession Westphalian in northern Spain is illustrated in Fig. 2. in the eastern part of the Cantabrian region is covered The greater part of the lower Stephanian in northern in Martínez-García et al. (1983). Spain is developed in marine facies, with carbonate The varied fossil content has permitted correlation and clastic successions, but also there are sufficient of these sequences across the palaeo-equatorial belt, coal-bearing and other terrigenous intervals with fossil including the foreland basin successions of Northern The chronostratigraphic legacy of Robert H. Wagner 279

Europe, the intramontane continental successions of mainly marked by the lowest (“first”) occurrences of the Sarre-Lorraine and Massif Central coalfields and specified species (and in some cases also the highest or with the predominantly marine successions of the “last” occurrences of some species) and also in some global reference sections of the Russian Platform. cases on the limits of the range of marked abundance of The floral assemblages of the stratigraphic units of a species (epibole in the sense of Laveine 1977). the Massif Central corresponded to individual mega The zonal name proposed by Wagner (1984) for floral zones. In conjunction with these, the strati each megafloral zone reflected a characteristic species graphic framework of the Pennsylvanian successions and follows the guidelines of the International Strati of the Cantabrian Mountains, once established, pro graphic Guide (Salvador 1994) for the naming of vided a basic reference for the species ranges which interval zones, in that the taxon used to name the supported the definition of megafloral zones proposed zone need not necessarily be confined to it. However, by Wagner (1984) as applicable across the palaeo- some complication has arisen from the taxonomic equatorial belt of Euramerica. revision of some of the species used to designate each zone. The principal issue revolves around the systematic revision of the concept of the formgenus Lobatopteris Wagner (Wagner 1958, 1959) and also 3. The relationship of megafloral material identified and illustrated (Wagner 1983) as zones and chronostratigraphic Lobatopteris vestita or as Lobatopteris vestita sensu substages Wagner (in Wagner and Álvarez-Vázquez 2010). Sys tematic revision by Wittry et al. (2015) subsumed A correlative framework for the Carboniferous succes Lobatopteris vestita auctorum within a new construct, sions of northern Spain was progressively developed Crenulopteris acadica. The present authors recognise by Wagner (1962, 1964, 1965), largely based on fossil the need to redefine all this material at specific level, as floras. To a large extent drawing on this work and was recognised by Wagner and Álvarez-Vázquez primarily on records from West and Central Europe, (2010), but a detailed commentary on the systematics Wagner (1984) proposed megafloral zones for the of this material is beyond the scope of the present work. interval ranging from Visean through to lower Per We therefore provisionally maintain Wagner’s mega mian. These have been based on the concurrent ranges floral zonal names (see Fig. 3). of an extensive range of morphospecies, from a In the process of proposing the definition of chron number of taxonomic groupings and floral associa ostratigraphic units based on stratotypes in the Can tions. They have proved of wide application across the tabrian successions, Wagner and colleagues (Wagner palaeoequatorial belt of Pennsylvanian time and have and Winkler Prins 1985a, b, Wagner and Álvarez- been discussed in detail by Cleal (1991), who intro Vázquez 2010, Knight and Wagner 2014) adopted the duced a number of sub-biozones. The most extensive practice of placing the boundaries of chronostrati lists for the megafloral biozones of the Iberian Penin graphic substages of the later Pennsylvanian to coin sula have been presented by Wagner and Álvarez- cide with those of successive megafloral zones, with Vázquez (2010); it may be noted from the taxonomic the intent that these corresponded to the floral char comments of these authors that a substantial number of acter of the classic chronostratigraphic units of the the specific identifications on which the ranges are Massif Central of France. This was convenient for established are subject to revision. The relationship characterising the biostratigraphical features which between megafloral zones and regional chronostrati supported the definition of the chronostratigraphic graphic units recognised in northern Spain is illustrated units. However, it must be stressed that this coinci on Fig. 3. dence of biostratigraphic and chronostratigraphic units The close coincidence of some megafloral biozone would be strictly applicable only in the specific boundaries with chronostratigraphic boundaries was succession in which the substage was defined; the discussed by Wagner (1984) and later Cleal (1991). It limits of biozones may be interpreted at different levels was recognised that “changes in fossil plant assem but a chronostratigraphic boundary must be considered blages are gradational and the choice of biozone immutable. boundaries is therefore somewhat arbitrary” (Cleal It is to be expected that the definition of successive 1991). These are assemblage zones in the normally megafloral zones, based on the concurrent ranges of accepted sense and are interval zones (Salvador 1994) numerous species in an evolving biota, does not 280 Megafloral Time Scale SOTRES zones Ma. 295

JUNCAL et al. 2016 J. C. Álvarez-Vázquez and A. Knight ASSELIAN Autunia conferta

AUTUNIAN BASE PERMIAN ? 298.9 298.9 VILLABLINO PUERTO

phyllum PEÑA CILDÁ Spheno- 300 VENTANA

angustifolium CIÑERA - 11 MATALLANA * SABERO PICOS DE

zeilleri Cascajo EUROPA

Alethopteris 9 SABERIAN 10 Pastora * Quemadas 302.3 * GZHELIAN 8 * Raposa Cavandi WAGNER & ARTIEDA Alejico 303.4 1970 KNIGHT, BURGER & BIEG 2000 Puentellés DOROGOMILOVIAN BARRUELO lamuriana Lobatopteris BARRUELIAN 305 Calero GUARDO- Carboneros KHAMOVNIKIAN 305.5 CERVERA LA PERNÍA/ TEJERINA 7 * Peñacorba Demués COALFIELD CASTILLERÍA Protriticites

STEPHANIAN Brañosera

Taranilla Protriticites KASIMOVIAN KREVYAKINIAN Prado San Salvador Gamonedo 307.0 Barranquito Otero Verdeña * 307.26 CENTRAL ASTURIAN cantabrica COALFIELD Odontopteris CANTABRIAN Choriza MERINO-TOMÉ et al. 2009 MYACHKOVIAN 308.4 Villanueva Urbaneja Areños Lores VAN GINKEL 1971 pteris Sensu vestite Wagner Lobato- RIOSA Casavegas 310 6* Entrerregueras PODOLSKIAN 5* Sotón ASTURIAN Mieres cambriense fauna 310.55 obliqua *

Linopteris Caleras LA PERNÍA/ 311.0 Canales CASAVEGAS SYNCLINE Picos de Europa LA JUSTA - ARAMIL WAGNER & WINKLER PRINS 1985 ARAMO - HUERNA Formation KASHIRIAN FERNÁNDEZ et al. 1988 MOSCOVIAN * 313.16

BOLSOVIAN Aegiranum

Paripteris linguaefolia 3 VEREIAN M.B. * 314.1 Caliza de Peña Redonda 2 * SANTO FIRME LUQUE et al. 1985 * 314.40 4 LEYVA et al. 1985 315 * Reguerón 315.2 Profusulinella

Vanderbeckei VILLA & MERINO-TOMÉ 2016 Lonchopteris rugosa DUCKMANTIAN Alethopteris urophylla M.B. ?316.8 1 * LEGEND WESTPHALIAN Sandstone dominated succession Coarse clastics Terrigenous succession with coals/palaeosols Marine dominated succession BASHKIRIAN LANGSETTIAN 320 Lyginopteris hoeninghausii Lyginopteris Neuralethopteris schlehanii Limestone dominated succession MERINO-TOMÉ, VILLA, BAHAMONDE Unconformable contact & COLMENERO 2006 Marine fauna RUSSIAN PLATFORM Fusulinid samples (Global stages, boundary dates 1 * Tonstein with potential for radiometric dating and tonstein dates after Davydov (for number refer to Table 1) et al. 2012 - GTS2012)

Fig. 3. Framework for age relationships of stratotypes and reference sections in NW Spain for the late Pennsylvanian. Key tonstein horizons, with reference numbers, are listed in Table 1 with corresponding availability of radiometric dates. The chronostratigraphic legacy of Robert H. Wagner 281 support the definition of sharply defined zonal bound have summarised the Carboniferous foreland basin- aries. Additionally, climatic and local edaphic factors fill succession on the basis of a number of unconfor may influence the consolidation of a characteristic mity-bound sequences. Through the Pennsylvanian, zonal assemblage, and thus megafloral zones may be the eastern, foreland-facing margin of the hinterland diachronous at regional scale. It is instructive to note area was bounded by an outward-directed active thrust the results of detailed analysis by Cleal (2007) to system against which a more rapidly subsiding fore compare the chronostratigraphic position of megaflor deep developed, characterised by predominantly ter al subzones in Langsettian-Bolsovian successions of rigenous successions. In contrast, more distally to the South Wales and the Central Pennine Basin of the east, more uniform subsidence was marked by plat Great Britain; discrepancies occur against a time scale form successions of generally thick carbonates in a calibrated by the occurrence of marine bands and the variety of relatively shallow marine environments. The zonal scheme based on non-marine bivalves. picture in detail is, however, considerably more com Furthermore it has been commonly recorded that plex, reflecting that episodes of significant deforma some species, regarded as characteristic of a specific tion occurred at a number of discrete intervals through megafloral zone, may appear at significantly earlier the period, with the generation of nappes, significant time in other depositional areas; a range of factors, thrust displacement, uplift and subsequent tensional including altitude, climate and drainage, have been faulting which controlled local depositional areas. interpreted as influencing the first appearance and The succession of deformational episodes affecting distribution of these species. Opluštil et al. (2016) Pennsylvanian strata in north-west Spain has been document the diachronous appearance of Sphenophyl summarised by Wagner and Martínez-García (1974). lum thonii, an important guide for the angustifolium Illustrated on Fig. 2 is the extent of sediments over Zone, between Bohemia and the Donets Basin and lying the unconformity generated by the Leonian conclude that the stratigraphical ranges of some key deformational episode dated to mid- to late Asturian taxa may differ by as much as 1 Ma between “standard” (ex Westphalian D) age (post-Leonian deposits) and ranges as defined by Wagner (1984) and refined by also sediments overlying the unconformity generated Wagner and Álvarez-Vázquez (2010). Cleal and Cas by the Asturian deformational episode of mid- to late cales-Miñana (2019), document their interpretation Barruelian age (post-Asturian deposits). The youngest that the morphospecies Alethopteris grandinii, embra Variscan deformational phases affecting the Cantab cing the range of a number of synonyms, appeared at a rian Zone occurred during the Permian, which in this much earlier stratigraphic age (Bolsovian) in the up area is represented by a complex pattern of limited land wetland environment of the intramontane basin of outcrops with sedimentary successions including coal- Sarre-Lorraine in contrast to its much later appearance bearing units (see Sotres succession on Fig. 3), lime in the lowland wetlands of paralic basins. stones, volcanics and red beds. Active tectonism, and above all major faulting, was associated with these sediments in the last episode of the Variscan deforma tion (Wagner and Martínez-García 1974). Throughout 4. Outline of Pennsylvanian basin the Cantabrian Zone a clear unconformity delimits a development in the Cantabrian post-orogenic succession comprising a thick develop Mountains ment of Mesozoic and Tertiary strata; Fig. 2 illustrates the unconformable contact of post-orogenic sediments The Cantabrian Zone presents a complex structure (Mesozoic and Cenozoic) overlying Palaeozoic and reflecting the later stages of the Variscan Orogeny Precambrian formations. (Fig. 2). The broad picture is of the south-west branch Nothwithstanding the succession of Variscan defor of the Variscan orogenic belt developing through the mational episodes, overall sedimentation in the Can late Palaeozoic period, with its internal zone (Central tabrian Zone was virtually continuous through the Iberian Zone and West-Asturian-Leonese Zone of Pennsylvanian and occurred in a range of diverse Lotze 1945) forming an emergent hinterland during sedimentary environments, such that for any defined the Carboniferous period. This zone formed the wes time interval, coeval sediments may include entirely tern and south-western limit to an extensive foreland terrigenous or mixed paralic and marine successions, area, the Cantabrian Zone, now preserved as the platform carbonates and turbidite or olistolithic for Cantabrian Mountains. Colmenero et al. (2002) mations. 282 J. A. Knight and C. Álvarez-Vázquez

The proposed and ratified stratotypes for the later Where the unconformity is evidenced by overlying Pennsylvanian in the Cantabrian Zone fall within three later sediments this is always with strongly angular successive depositional units: unconformity. Stephanian sediments (earliest as late- – The Central Asturian Coalfield: from the end of the Barruelian) resting on this unconformity occur as a Duckmantian, siliciclastic sediments developed across number of tectonically isolated coalfield areas, of the whole Cantabrian Zone with the exception of the which the largest is the El Bierzo Coalfield of western carbonate platform in the eastern part of the area in the León. Earliest sedimentation recorded above the As Picos de Europa (Colmenero et al. 2002). In this turian Unconformity is at the eastern end of the Sabero succession terrigenous sediments predominate and Coalfield, from which point progressive westwards are frequently coal-bearing, including the main pro onlap up the basin margin can be demonstrated in a ductive coal seams of the coalfield; limestones are single basin extending across to the Ciñera-Matallana subordinate. This sedimentary sequence was termi Coalfield. Marine proximity and influence can be nated by the Leonian deformational episode (Wagner demonstrated in this basin; the relationship with the 1959, Wagner and Martínez-García 1974) during mid- coalfield areas to the west of the Ciñera-Matallana to late Asturian (ex Westphalian D) time, giving rise to Coalfield can be interpreted as reflecting continued folding and thrusting in the Central Asturian Coalfield, westwards expansion of the one basin although some although further to the east in the Pisuerga-Carrión tectonically controlled basin segmentation cannot be province (see Fig. 2) this episode is represented only excluded. The lowermost part of the succession in the by a widespread disconformity reflecting short-lived Sabero Coalfield hosts upper Barruelian strata and the uplift and erosion. The proposed stratotype of the stratotype of the proposed Saberian Substage. Asturian Substage lies near the western margin of The relative position of these three depositional the Central Asturian Coalfield. basins and the location of the proposed and ratified – The post-Leonian Basin in north-east León and stratotypes is illustrated on Fig. 2. Palencia as described by Wagner and Fernández García (1983); this corresponds to the Pisuerga-Carrión pro vince (Colmenero et al. 2002) and comprises the 5. Synthesis of the chronostrati- Valderrueda Coalfield, its continuation as the Guar do-Cervera Coalfield and the coal-bearing terrigenous graphic substages of the later successions in the Castillería, La Pernía and Redondo Pennsylvanian in the Cantabrian synclines in northern Palencia (see Fig. 2). These strata Zone rest upon the Leonian disconformity; the basin margins are clear to the west and north-west, involving pro The duration and temporal relationship of reference gressive onlap up a fault-stepped basin slope. To the sections for the proposed and ratified substages of the east the basin margin was initially controlled by major Pennsylvanian in the Cantabrian Mountains is illu normal fault lines which were ultimately overstepped, strated on Fig. 3. The columns in this illustration although any further extent is obscured by Mesozoic represent continuity of sedimentation and do not and Tertiary cover. The succession is of mixed marine directly reflect the thickness of sediments. The general and paralic sediments with locally developed lime character of the sedimentary environment is illustrated stones in the eastern part of the basin. This sedimentary on the basis of five categories only: limestone-domi sequence was terminated by the Asturian deforma nated successions, marine clastic successions, terrige tional phase during mid- to late Barruelian time. The nous successions with coals and palaeosols, sandstone- stratotype of the Cantabrian Substage is located on the dominated successions and successions of coarse southern margin of the Guardo-Cervera Coalfield; the clastics and conglomerates. stratotype of the Barruelian Substage is located in the The age relationships have been established where Barruelo Coalfield in the eastern area of the deposi possible on absolute dates obtained from tonsteins tional basin. (pyroclastic ash-falls) by U-Pb CA-ID-TIMS radio – The post-Asturian Basin: The post-Leonian Basin metric dating. It is stressed that this is work in progress, sediments were strongly folded by the Asturian folding in conjunction with researchers at the University of phase with large asymmetrical folds verging south and Oviedo, and some horizons are still under analysis for south-westwards; the extent of this folding phase age determination; some anomalous age relationships across the rest of the Cantabrian Zone is not clear. have been detected and further refinement will require The chronostratigraphic legacy of Robert H. Wagner 283

Table 1. Summary of radiometric dates and tonstein horizons contributing to the age relationship framework for the late Pennsylvanian in NW Spain.

Reference Published source Published sample number and location U-Pb age determina Analytical on Fig. 3 tion by CA-ID-TIMS parameters

1 Pointon et al. 2012 Tonstein T75: Zwartberg Mine, Campine Basin, 317.63 ± 0.39 n=5; Belgium, between Wasserfall and Quaregnon MSWD 0.70 marine bands 2 Pointon et al. 2012 Tonstein Z1: Fürst Leopold Mine, Dorsten, Ruhr 313.78 ± 0.38 n=6; Coalfield, Germany. 10–12 m below Aegiranum MSWD 2.20 Marine Band 3 Waters and Condon Sample EH28155: Sub-High Main Tonstein, 314.37 ± 0.53 n=4; 2012 Holme Pierrepoint Borehole, Nottinghamshire MSWD 1.07 UK. 14 m above Aegiranum Marine Band 4 Merino-Tomé et al. TC-1; Minona Mine, Posada de Llanera, Currently under 2017 Asturias, Spain. 4th Aguila Coal, Santo Firme investigation Coalfield (dated by LA-ICP-MS as 314.4 ±1.3 Ma) 5 Merino-Tomé et al. TC-3 and TC-4; TC3: Pozo María Luisa, Currently under 2017 Langreo, Asturias, Spain; Agapita Coal. TC-4: investigation Pozo Sotón, El Entrego, Asturias, Spain; Loza nita Coal (dating by LA-ICP-MS: TC-3 307.7 ± 1.3, TC-4 307.07 ± 0.9 Ma) 6 Merino-Tomé et al. TC-5; Pozo Sotón, El Entrego, Asturias, Spain; Currently under 2017 2nd Refugio Coal (dated by LA-ICP-MS as investigation 307.12 ± 0.94 Ma) 7 Location reported Tip of Peñacorba Colliery, Barruelo Coalfield, Currently under in Wagner and Palencia, Spain investigation Varker 1971 8 Location reported P22A: pyroclastic tonstein in cross-cut 4E-5S of 302.48 ± 0.48 n=5; in Knight et al. Pozo Sotillos, Sabero, León, Spain; within coal MSWD 1.26 2000; analytical seam 110 m below top of Raposa Formation results this paper (upper Barruelian) 9 Knight and Wagner P93: pyroclastic tonstein from surface exposure P93 – 302.13 ± 0.23 n=4; 2014 in floor of Seam 4N, west of Olleros in Sabero MSWD 0.62 Coalfield; P118: pyroclastic tonstein in cross-cut 7W-5S of P118 – 302.25 ± 0.28 n=2; Pozo Sotillos, Sabero, from roof strata of seam MSWD 0.01 X. Both localities in Herrera Beds (lower Saberian) 10 Bieg and Burger 6 tonsteins reported from Pastora Formation; P162: complex zircon 1992 Present authors – P162 collected from old systematics workings in Santa Lucía open-pit, Matallana Syncline 11 Location reported TC6 of Merino-Tomé et al. 2017: Dated by Currently under in Merino-Tomé et LA-ICP-MS as 304.2 Ma. Present authors – investigation al. 2017 P168 tip of Bienvenida Mine 284 J. A. Knight and C. Álvarez-Vázquez cross-checking of material between laboratories. The cognition of the base of this unit in its conceptual type key age references are highlighted and numbered and area of the Lorraine Coalfield (Laveine 1977) and summary details of the source and status of the dating developed a number of palaeobotanical and palyno procedures are presented in Table 1. logical criteria which together could be expected to In addition the age relationship framework for the define the base of this chronostratigraphic unit in chronostratigraphic substages also draws on zonal comparable successions of Western Europe. These correlation established by fusulinid foraminifera, al included the top of the range of Paripteris spp., the lowing close comparison with the platform carbonates base of the range of Linopteris obliqua var. bunburii and predominantly marine succession of the Picos de and the base of the epibole of the complex around Europa province (Merino-Tomé et al. 2006, 2009) and Neuropteris ovata. through this, with the marine succession of the Russian With reference to these criteria, Cleal (1978, 1984) Platform and the corresponding global stages. identified the base of the Westphalian D succession The conclusion is drawn from Fig. 3, that the respectively in South Wales, in the upper part of the proposed and ratified substages established in the Rhondda Beds of the Lower Pennant Measures, and in Cantabrian Mountains – viz. Asturian, Cantabrian, the Sarre Coalfield in the upper part of the Luisenthal Barruelian and Saberian, can be confidently assigned Formation. In both successions the biostratigraphic absolute time intervals, which are of comparable analyses were performed largely on extensive collec duration to those of the Westphalian substages estab tions of earlier workers, and potential sections for a lished in the paralic area of Western Europe. The stratotype in surface exposure have not been identified. detailed analysis of the fossil floral content and mega The Laveine report (1977) had however suggested that floral zones reported by Wagner and Álvarez-Vázquez the Central Asturian Coalfield was potentially the most (2010) will also be able to be calibrated against this favourable location for selection of a Westphalian D time scale once finalised. stratotype in Western Europe. Reporting preliminary collaborative conclusions with workers on this coal field, the report suggested that the Caleras Beds 6. Background and current status (otherwise referred to as “paquete Caleras”, an infor mal unit based on mining practice) were well char of the proposed and ratified acterised as the lower part of Westphalian D and the Regional Chronostratigraphic contact Westphalian C-D would lie in the underlying Substages of the Pennsylvanian Tendeyón Beds. in Northern Spain Extensive description of the mining lithostrati graphic units (paquetes) which embrace the larger part of the productive coal-bearing succession of the 6.1. Asturian Substage (proposed) Central Asturian Coalfield was provided in the pub This substage has achieved a wide level of acceptance lications of the 10th Carboniferous Congress held in and is commonly referenced by workers on the Penn Madrid in 1983 (Luque et al. 1985, Saénz de Santa sylvanian of Western Europe, in the context that it María et al. 1985, Leyva et al. 1985). These descrip replaces the previous usage of Westphalian D; it is tions were based on a number of long surface sections, identified in the list of regional substages for Western commencing with the Tendeyón Beds and continuing Europe published by the SCCS (Heckel and Clayton upwards through a succession of some 2,400 m of 2006). However, the Asturian has only been outlined in stratigraphic thickness, through to the Sorriego Beds a preliminary proposal (Wagner et al. 2002) and this (Luque et al. 1985). Collections of fossil flora and has not yet been progressed to definition of a boundary palynological samples together confirm this succes stratotype, which would be necessary before submis sion as of Westphalian D age throughout. Although the sion of a formal proposal for ratification to the SCCS. presence of some taxa of foraminifera and also bra Historically, the recognition of the base of the chiopods was recorded, these were considered poorly Westphalian D presented particular challenges due representative and were not reported in detail. How to the absence, at least in the coalfields of northern ever, it was concluded that in this measured section (La Europe, of marine incursions as correlatable horizons. Inverniza-El Cabo section) the lowest strata, the Ten An SCCS working group to address the Westphalian C- deyón Beds, should be considered as already attribu D boundary reviewed the criteria which guided re table to lower Westphalian D and therefore this section The chronostratigraphic legacy of Robert H. Wagner 285 did not provide a suitable boundary stratotype to define although Pecopteris unita Brongniart, considered by the base of Westphalian D. Laveine (1977) to appear at the same level as Neu Wagner and Álvarez-Vázquez (1991) undertook a ropteris ovata, makes its appearance at the top of the wide-ranging review of the floral characterisation of Canales Formation. With respect to the criteria pro the Westphalian D Stage in NW Spain. The three floral posed by Laveine (1977), the upper part of the Canales biozones recognised by Cleal (1984) for the Westpha Formation corresponds to the transition from West lian D of the Sarre and South Wales were equally phalian C to Westphalian D and can potentially host the recognised in NW Spain, the two lower zones (obliqua boundary stratotype for a newly defined Asturian and micromiltoni zones respectively) being identified Substage. in the Central Asturian Coalfield. The uppermost A preliminary proposal for recognition of an Astur biozone, (in the usage of Wagner and Álvarez-Váz ian Stage as the formal name to replace Westphalian D, quez, Lobatopteris vestita zone) was only interpreted with boundary stratotype in the Asturias region, was with considerable doubt in the ESE part of the Central presented by Wagner et al. (2002). The proposed Asturian Coalfield, in contrast to its well-established boundary stratotype is located in the Riosa Valley presence in the coal-bearing successions of northern within a succession recognised as extending across Palencia. The basal part of Westphalian D proved the Canales Formation and the contact with the suc difficult to distinguish on floral evidence although ceeding Mieres Conglomerate Formation (Pello and these authors suggest the base of this unit was probably Corrales 1971). The sedimentology of this succession close to the base of the Caleras Beds, effectively close has been studied by Fernández (1990), from which to the top of the immediately underlying Tendeyón work Wagner et al. (2002) presented a summarised Beds. column for the proposed boundary stratotype. How The fossil flora was a key element in the biostrati ever, reflecting that this was a preliminary proposal, graphical correlation between two important structural there was no definition of a specific location and line of elements of the coalfield, the Riosa-Olloniego subarea section for the stratotype, other than to identify two to the west and the Aller-Nalón subarea covering the possible old railway routes on either side of the Riosa main productive part of the coalfield (García-Loygorri Valley, both of which would require cleaning and 1974). These two subareas are separated by the La detailed measurement. Furthermore, it is clear that Justa–Aramil thrust belt representing considerable further investigation is required to establish if a satis shortening. Drawing also on the evidence of fusulinid factory stratigraphic boundary can be defined either at and brachiopod faunas, this correlation demonstrated the upper contact of the Canales Formation or at a point that the succession of the Riosa-Olloniego subarea within this formation, which is attributed a stratigraphic covered the Westphalian C-D boundary, which was thickness ranging 700–1000 m (Fernández 1990). likely to be situated within the Canales Formation as Fauna reported for correlative horizons in the Aller- defined by Pello and Corrales (1971). Nalón subarea include goniatites (Anthracoceras cam The floral record for the Riosa-Olloniego sector is briense Bisat) in the Generalas Beds and a locally rich essentially limited to the lists published by Jongmans fauna of corals and brachiopods (Feys et al. 1974). To and Wagner (1957); some modification of the identi these considerations can be added that the succession fications and inclusion of some other records (Wagner in the Aller-Nalón subarea hosts a number of pyro 1971) are incorporated in the lists of Wagner and clastic horizons (Feys et al. 1974, Merino-Tomé et al. Álvarez-Vázquez (1991, 2010). The recorded fossil 2017) which are currently awaiting formal reporting of flora had been collected across a section covering the U-Pb CA-ID-TIMS dating (reference horizons 5 and 6 productive coal seams in a succession extending, from on Fig. 3 above). No records of the micropalaeonto the stratigraphically highest Esperanza Formation, logical flora and fauna specifically of the Riosa- through the Mieres Conglomerate Formation, the Olloniego subarea have been published, but it can underlying Canales Formation down to the Caliza be noted that palynological studies have been under Beds. The flora of the Esperanza Formation is recorded taken in numerous sections of the Central Asturian primarily from surface localities and included Neu Coalfield (Chateauneuf 1973, Luque et al. 1985), ropteris ovata Hoffmann and Linopteris obliqua Bun providing a record closely comparable to those of bury throughout. In contrast, the flora of the Canales corresponding successions in Northern Europe. Formation was collected exclusively from under Although a strong case can be made to propose the ground sections; Neuropteris ovata was notably absent formal definition of the base of the Asturian Substage 286 J. A. Knight and C. Álvarez-Vázquez

Fig. 4. Sketch map and image of the proposed Asturian stratotype; see Fig. 2 for regional setting. The Mieres Conglomerate is indicated at the northern end of the section marking the top contact of the Canales Formation; way-up of the section towards the north. for the West European chronostratigraphic framework Asturias, located along old mine rail track (UTM in the Riosa-Olloniego sector of the Central Asturian coordinates: top 30T ETRS89 267578E.4791566N; Coalfield, further work is required to define adequately base 30T 267446E.4791257N). a boundary stratotype. A particular concern is to ensure – Detailed description of stratotype succession in that the selected section presents a sufficiently varied Fernández (1990): upper part only of Canales Forma fossil content to support a decision on the position of tion exposed on section. Top contact defined by sharp the boundary, and that this can be justified with respect contact with Mieres Conglomerate Formation. Mea to the traditional concept of the Westphalian D which sured section comprises a stack of deltaic sequences; the Asturian Substage seeks to replace. The guidance alluvial intervals with relatively thin but worked coals, in the International Stratigraphic Guide (Salvador and also wave-dominated shore-line intervals. Fossil 1994) is explicit that a boundary stratotype should content: fossil plants, marine faunas comprise brachio preferably be well-studied and collected, the results of pods, ostracods, bivalves. the investigation published and the fossils collected from the section be securely stored and easily acces sible for study; this requirement remains to be met. The 6.2. Cantabrian Substage suggested location has the potential to meet require The recognition of a major gap in the stratigraphic ments that it should be well-exposed, after cleaning continuity between the classic sections of the West and preparation, and of easy access. phalian D and the base of Stephanian A as recognised Summary data for the proposed boundary stratotype in the Sarre-Lorraine Coalfield, and the evidence that a (Fig. 4): significant succession of strata in Northern Spain – Proposed boundary stratotype section in upper part of represented this hiatus (Wagner 1966a, b), led to the Canales Formation in the Riosa Valley, province of proposal by Wagner (1965, 1969) to establish the The chronostratigraphic legacy of Robert H. Wagner 287

Cantabrian Stage. This stage (now of substage status) where the Cantabrian strata were interpreted as ex was formally accepted by the SCCS as the basal stage tending up to the base of Stephanian A. These authors of the Stephanian Series (now of stage status) in the 7th therefore made the suggestion that it would be more International Congress on Carboniferous Stratigraphy practical to define the base and the top contact of the and Geology held in Krefeld in 1971 (George and proposed Cantabrian Stage in the one depositional Wagner 1972). The terms of ratification specified that basin. A long stratigraphic section across the Casave the base of the stage should be taken at the base of the gas Syncline (La Pernía Coalfield area) showed the Lores Limestone in the La Ojosa section, near the same floral assemblages demonstrating the passage village of Lores, as described by Wagner and Varker from Westphalian D into Cantabrian, but also a much (1971); this section is located near the northern ex more extensive presence of marine strata, with fusu tremity of the Casavegas Syncline in the La Pernía linid foraminifera and brachiopods which allowed Coalfield area of northern Palencia (see Fig. 2). Mod correlation to the fauna in the United States and in ification of the designated stratotype was subsequently Russia. It was therefore proposed formally in the report proposed by Wagner (1983) and Wagner and Winkler of the SCCS Stephanian Working Group (Bouroz et al. Prins (1985a), to be recognised at a somewhat lower 1972) that the base of the Cantabrian Stage should be stratigraphic level in the Velilla de Tarilonte Section in defined in the La Ojosa Section of the Casavegas the Guardo Coalfield (Palencia, N. Spain). This mod Syncline at the base of the Lores Limestone; there was ification was ratified by SCCS ballot (Engel 1989). presumed equivalence of this limestone with the Although the conceptual process which has led to Barranquito Marine Formation. The Lores Limestone modification of the boundary stratotype of the Can yielded an important fauna of fusulinid foraminifera to tabrian has been touched upon in numerous publica van Ginkel (1965) who assigned this to his Fusulinella tions (e. g. Wagner and Winkler Prins 1994), it is Zone (subzone B; subdivision B3), correlated with the appropriate to summarise the steps leading to what Myachkovsky Horizon of the upper Moscovian Stage. should now be considered a robustly defined substage. Investigation of the post-Leonian Basin in northern The formal proposal for recognition of the Cantabrian Palencia continued through the 1970s, most notably Stage (Wagner 1969) was accompanied by a report on with a coal exploration project for the Guardo Coal the proposed boundary stratotype (Wagner et al. 1969) field under the auspices of the Instituto Geológico y near the village of Tejerina (León). An extensive flora Minero de España, reported in Wagner and Fernández demonstrated an assemblage at the base of the section García (1983). This coalfield constitutes the western which corresponded to the upper part of Westphalian part of the post-Leonian basin, extending from late D, while at several hundreds of metres stratigraphically Asturian age (ex Westphalian D) through to mid- above, the flora incorporated elements of a much more Cantabrian age. Within this interval 21 formations Stephanian character (e. g. Odontopteris cantabrica, of alternating marine and terrigenous facies were Alethopteris bohemica, Pseudomariopteris cordato- recognised; a very extensive fossil flora was collected ovata). The reference section then traverses a relatively in the terrigenous sections. Correlation across the thin (45 m) marine intercalation of coastal (neritic) coalfield has been largely based on mapping and aspect, the Barranquito Marine Formation. This was identification of the marine intervals and comparison then succeeded by a subsequent coal-bearing succes with the sequence of marine intervals recognised in the sion with a characteristic flora of Stephanian aspect eastern, La Pernía, part of the basin, including the (Wagner et al. 1969). At the time the Tejerina section Casavegas Syncline. In summary, it was found that the was proposed as the Cantabrian stratotype, the map Barranquito Marine Formation of Tejerina in northern ping of the Valderrueda Coalfield, of which the Tejer León correlated with the Otero Formation of the ina Syncline is a marginal part, had not been under Guardo Coalfield and the Verdeña Limestone of the taken. It was however assumed that the Barranquito La Pernía area in the eastern part of the basin, while the Marine Formation would be an easily mappable and Lores Limestone of this latter area correlated with the recognisable horizon. much lower Villafría Formation of the Guardo Coal The on-going mapping by Wagner and colleagues in field. the area to the east in NE Palencia is reported in Wagner (1983) developed the argument that the Wagner and Varker (1971), who noted that it may be original intent in selection of the base of the Lores difficult to correlate accurately the Tejerina Section Limestone as the Cantabrian boundary stratotype was with the more continuous section in NE Palencia, that it should be a marine interval equivalent in 288 J. A. Knight and C. Álvarez-Vázquez

Fig. 5. Sketch map and image of the Cantabrian stratotype, looking northwards to where the base of the Cantabrian Substage is marked at the top of a rib of fluviatile sandstones (Acebal Formation) and the contact with the overlying Villanueva Formation; see Fig. 2 for regional setting. The strata are steeply over-turned; way-up of the section is to the south. The Cantabrian succession at this point comprises the marine Villanueva Formation and the coal-bearing Choriza Formation; the person in the photograph is standing close to the line of the major southern boundary fault of the Cantabrian Zone, which juxtaposes the Choriza Formation with Cretaceous strata. position to the Westphalian D-Cantabrian interface and formal acceptance, by ballot, was confirmed in recognised at Tejerina, and that with new information, 1989 (Engel 1989). the boundary stratotype should be changed. Floral The structural and sedimentological development of evidence suggested that the terrigenous Choriza For the post-Leonian Basin in Palencia has been described mation in the Guardo Coalfield represented a signifi in Wagner and Winkler Prins (1985b). This provides an cant floral change reflecting the passage into Cantab overview of the sedimentological and palaeontological rian strata, and a formal proposal was developed characterisation of the Cantabrian Stage (now sub (Wagner and Winkler Prins 1985a) that the boundary stage), including the ranges of flora, algae, foramini stratotype should be taken in the Guardo Coalfield at fera, brachiopods, molluscs, ostracodes, corals and the base of the marine Villanueva Formation imme sponges. An important correlative horizon is the diately underlying the Choriza Formation. The best Brañosera Formation (indicated on the Barruelo col exposed succession suitable for a stratotype was umn of Fig. 3), reflecting a major marine transgression proposed as the road section and natural exposure across the extent of the basin and providing unequi immediately north of the village of Velilla de Tarilonte vocal correlation from the Guardo Coalfield (Taranilla (Palencia) (now renamed Velilla de la Peña; Fig. 5). Marine Formation) eastwards to the La Pernía area and The Villanueva Formation is also correlated to the the Rubagón Valley area of the Barruelo Coalfield (see Urbaneja Formation in the La Pernía section. The Fig. 6). The base of the Brañosera Formation has been proposal to modify the Cantabrian boundary stratotype taken as the limit between the informal division of a was tabled in the 1983 Madrid meeting of the SCCS lower Cantabrian unit and an upper Cantabrian unit The chronostratigraphic legacy of Robert H. Wagner 289

(Wagner and Winkler Prins 1985b), with the inter tion 30T ETRS89 364326E.4743601N; base 30T pretation that this corresponds to the contact between 363833E.4744618N). the uppermost Myachkovsky Horizon (highest Mos – Detailed description of stratotype succession in covian) and the subsequent Krevyakinsky Horizon Wagner and Winkler Prins (1985b): section extends (basal Kasimovian). The Brañosera Formation, in its over some 200 m length from the marine Las Heras type section in the Rubagón Valley, extends over a Formation, with a thin limestone, coarsening upwards stratigraphic thickness of over 1,200 m up to the into cross-bedded sandstones with some thin coals of Peñacorba coal-bearing unit, marking the base of the Acebal Formation; the top of the sandstone unit is a the Barruelo Formation. The upper contact of the clear contact to marine mudstones with some thin Cantabrian Stage, as defined by Wagner and Winkler limestones at the base of the Villanueva Formation. Prins (1985a), would be marked at the boundary The section traverses some 80 m of the Villanueva stratotype for the base of the succeeding Barruelian Formation, with coarsening upwards sequences cul Stage (Fig. 6). In the Rubagón Valley section this was minating in sandstones, followed by the establishment taken as the base of the coal-bearing Carboneros of palaeosols and thin coals of the Choriza Formation. Member, at some 300 m stratigraphically above the Peñacorba Member, at a horizon chosen on the basis of the contained floral assemblage, which corresponded 6.3. Barruelian Substage very closely with that of the classic reference section The Barruelian was proposed as a replacement for the for the Stephanian A at Rive-de-Gier, St. Étienne Stephanian A and correspondingly the definition of region of the Massif Central, France. this unit has endeavoured to reflect the characteristic The upper part of the Cantabrian Substage, in the fossil flora of the classic section in the Faisceau de la reference sections of the post-Leonian basin in Pa Peronnière in the Assise de Rive-de-Gier in the St. lencia, includes a number of horizons which provide Étienne coalfield area of the Massif Central of France potential reference to the global scale through the (Jongmans and Pruvost 1950). The concept of the presence of fusulinid fauna and also pyroclastic Stephanian A was somewhat extended by the correla tonstein bands (ash-fall tuff bands). Van Ginkel tion of this latter section with the succession in the (1971, 1972) reported the occurrence of a fusulinid Cévennes Coalfield also in the region of the Massif fauna in the Rubagón River section, in a thin lime Central (Bouroz and Doubinger 1978). Conceptually stone at some 100 m stratigraphically below the the Stephanian A extended in time up to the base of Peñacorba Member, which, with some reservation, Stephanian B. However, the base of Stephanian B in was attributable to his Protriticites Zone and therefore the coalfields of the French Massif Central proved attributable to a lower Kasimovian age. A pyroclastic enigmatic, due to a stratigraphic hiatus between the tonstein was collected from the tip of the Peñacorba succession of the Assise de Rive-de-Gier, on which Colliery at Barruelo de Santullán, which worked the definition of Stephanian A is based, and the Faisceau Peñacorba coal seams (Wagner and Varker 1971). A de Grüner of the Assise de St, Étienne, on which the hand specimen (reference horizon No. 7 on Fig. 3) has Stephanian B is based (“l’assise intermédiaire de been made available to the present authors and has Saint-Étienne” of Jongmans and Pruvost 1950). The been submitted for radiometric dating (U-Pb CA- hiatus was considered to be covered by successions in TIMS) to the Pacific Centre for Isotopic and Geo the Carmaux and Cévennes coalfields and the contact chemical Research of the University of British Co Stephanian A-B was established as the top of the Zone lumbia, Vancouver, Canada; results are still awaited. de Lentin in the Carmaux Coalfield, coinciding with A second horizon is reported by Wagner and Varker the level at which Lobatopteris lamuriana (Heer) (1971) from the Redondo Coals, at a probably equiva Wagner became extinct in both the Carmaux and lent level to the Peñacorba Member, but this material Cévennes successions (Bouroz and Doubinger 1978). has not since been located. The flora of the succession in the Barruelo Coalfield Summary data on the Stratotype of the Cantabrian has been summarised by Wagner and Winkler Prins Substage (Fig. 5): (1970, 1985b). These authors concluded that the flora – Boundary stratotype at base of Villanueva Forma of the Peñacorba Member appeared marginally older tion, in stream valley and track-side north of village of than that of the Assise de Rive-de-Gier. It is succeeded Velilla de Tarilonte (now renamed Velilla de la Peña), by the marine Loma Member of some 400 m thickness province of Palencia (UTM coordinates: top of sec before the next highest coal-bearing unit, the Carbo 290 J. A. Knight and C. Álvarez-Vázquez

Fig. 6. Sketch map and image of the Barruelian stratotype; see Fig. 2 for regional setting. The basal contact of the Barruelian Substage with the underlying Cantabrian is marked. The strata are overturned and the way-up is to the west. The persons in the image are inspecting the thin seams of the Carboneros Member (Barruelo Formation), the base of which marks the base of the Barruelian, and overlies the sandstones of the Loma Member (Barruelo Formation) seen over the left hand half of the image. neros Member. The flora of the Carboneros Member latter, identifications have been reported in Wagner et was considered to correspond more closely to the Rive- al. (1977); these, including Fusulina and Pseudotriti de-Gier flora. On this basis, the lower boundary of the cites species, were considered insufficient for exact Barruelian was defined at the base of the Carboneros age dating but suggestive that this would be no higher Member in the Barruelo Coalfield. The boundary than Kasimovian. stratotype is exposed in the cutting of a disused mining The top of the Calero Member represents the young railway line near the hamlet of Helechar west of est strata recorded in the depositional history of the Barruelo de Santullán (Fig. 6) and a detailed strati post-Leonian Basin; sedimentation is interpreted to graphic section across the boundary is provided in have ceased with the initiation of uplift and locally Wagner and Winkler Prins (1985b). intense deformation representing the Asturian Folding In the Barruelo Coalfield the Carboneros Member is Phase, which was relatively short-lived within the succeeded by a total of some 800 m of strata (Wagner Barruelian Substage interval. However, the oldest and Winkler Prins op. cit.). This next succeeding unit, sediments deposited after the Asturian Folding Phase, the Polvorín Member, is marine with some brachiopod, in the lower part of the Sabero Coalfield, some 65 km bivalve and gastropod fauna, and thereafter, the suc to the west, were reported by Knight (1971) to have a cession comprises the Calero Member which hosts the flora clearly identifiable as Stephanian A. This flora main productive sequence of coal seams of the coal was recognised as closely similar and effectively field. However, still within the Calero Member there contemporaneous with the flora of the Calero Beds are thin marine bands, including a Lingula band and a and indicative that sedimentation in the post-Asturian calcareous lens between Seams III and IV, reportedly basin had commenced already in Stephanian A, such with brachiopods and fusulinid foraminifera. For the that the Cantabrian region conserved a record of The chronostratigraphic legacy of Robert H. Wagner 291 virtually continuous sedimentation through the Ste be considered marginally younger than that of the phanian A (Bouroz et al. 1972). This conclusion was Calero Beds, but that it can be compared closely to the sustained in the proposal for a new Barruelian Stage flora of the Zone de Lentin, in the Carmaux Coalfield. (Wagner and Winkler Prins 1985a), in which it was The conclusion was drawn that the top of the Stepha proposed that the boundary stratotype would be de nian A should be recognised at the top of the Sucesiva fined in the Barruelo Coalfield and that the lower part Formation and the base of the overlying Quemadas of the stage would be characterised by the succession Formation; this coincides with the base of one of the through to the Calero Beds, but that the upper part of widespread inundation events. With reference to bios the stage would be characterised by the succession in tratigraphic and chronostratigraphic units (Wagner the lower part of the Sabero Coalfield. It was assumed 1984, Wagner and Winkler Prins 1985a, b), this contact that the upper contact of the stage would be defined in must be placed at the top of the lamuriana megafloral the Sabero succession. zone and the upper boundary of the Barruelian Stage. The Sabero succession and its contained flora has The recognition of the lower part of the Sabero been described in some detail by Knight (1983a, b, succession as representative of the upper part of the 1985). The lower part of the Sabero succession shows Barruelian Substage incorporates several characteris the commencement of sedimentation constrained and tic features which can serve to define wider correlation deformed within fault-bounded limits (Alejico Beds). and the duration of the Barruelian. The presence of a Thereafter the Sabero succession is characterised by a number of pyroclastic tonstein (ash-fall tuff) horizons number of major inundation events, with consequent in the Sabero succession has been described by Knight widening of the basin margins with progressive onlap et al. (2000), of which three bands have been located in westwards up the basin margin. The first such event, the upper part of the Raposa Formation and two within near the base of the Raposa Formation, is marked by a the Sucesiva Formation. Investigation of the Sabero marginal marine interval which thickens eastwards to tonsteins for possible radiometric dating (U-Pb CA- fully marine sediments (Iwaniw 1984). Thereafter, ID-TIMS) has been carried out through the Pacific each inundation event initiates a coarsening upwards Centre for Isotopic and Geochemical Research of the cycle (Knight et al. 2000), marked by characteristically University of British Columbia, Vancouver, Canada. fine lacustrine shale units with Leaia bands at their However, not all the bands are available or present base and culminating with alluvial sediments and coal suitable composition of zircons for radiometric dating. formation; these cycles have allowed robust correla Some of the horizons were collected from underground tion with the Ciñera-Matallana Coalfield further west mine workings which are now no longer accessible and (Wagner and Castro 2011, Knight and Wagner 2014). available material is insufficient for dating and in other The overall pattern is of basin-fill with sediment on- cases the zircon systematics are complex and do not lapping up a basin margin to the west. Bivalve faunas support a reliable age determination. Nevertheless, one from horizons throughout the lower part of the Sabero horizon from the upper part of the Raposa Formation and Ciñera-Matallana coalfields and the upper part of (reference horizon No. 8 on Fig. 3; level 11 in Knight et the La Magdalena coalfield, have been studied by al. 2000), has given an apparently reliable age deter Eagar (Eagar and Weir 1971, Eagar 1985), with the mination of 302.48 ± 0.48 Ma with good concordance conclusion that in many cases they present evidence of (n=5); see Fig. 7. This band lies at a stratigraphic near-marine and brackish environments. The post- thickness of 110 m below the top of the Raposa Asturian sedimentation in the Sabero and Ciñera- Formation and correspondingly at the equivalent of Matallana coalfields demonstrates a near-coastal, para some 300–340 m below the Sucesiva-Quemadas con lic, sedimentary environment closely analogous to that tact, taken as the Barruelian top boundary. Full report of the succession of lower Barruelian age in the ing of this age determination and others from the Barruelo Coalfield and overall the composition of Sabero Coalfield is still pending. flora in terms of the representation of the principal Additionally, in the Sabero succession, a long sur taxonomic groups is closely similar. face section, which provides the type section for the Interpretation of the floral composition from the Raposa, Gonzalo, and Sucesiva formations and the four lowest stratigraphic units of the Sabero succes base of the Quemadas Formation, and which also sion, the Alejico Beds, Raposa Formation, Gonzalo provides the boundary stratotype for the Saberian Formation and Sucesiva Formation, has concluded Substage and therefore the top of the Barruelian, (Knight 1974, 1983a) that overall this flora should has been the subject of detailed palynological sampling 292 J. A. Knight and C. Álvarez-Vázquez

Fig. 7. Concordia dia gram for U-Pb radiometric dating of Sabero tonstein Sample P22 (upper Bar ruelian: cross-cut 4E-5S, Raposa Formation, Pozo Sotillos). CA-ID-TIMS dating by Pacific Centre for Isotopic and Geoche mical Research of the Uni versity of British Colum bia, Vancouver, Canada.

by research personnel of the University of Vigo. number of persistent thin coals marks the base of the Formal reporting of these results is currently awaited. Carboneros Member, which has yielded abundant However, it is important to note that this adds a further flora. The succession above the first thin coal, now dimension to the definition of the upper Barruelian, in very overgrown along the old rail track, has previously contrast to the almost total lack of palynological been cleared and measured in detail; renewed cleaning information from the successions of the post-Leonian of the overlying succession is possible. Basin, including the Cantabrian and Barruelian bound – A representative section of the upper part of the ary stratotypes. This lack of palynological information Barruelian and the contact in its boundary stratotype to has been attributed (Wagner pers. comm.) to higher the overlying (proposed) Saberian is located in the coalification rank in the Pisuerga-Carrión province, Sabero Coalfield in a measured section along the although samples collected by the present authors and valley of the Arroyo de la Mina, now with limited submitted to MB Stratigraphy Ltd of UK, have yielded exposure but with the possibility of cleaning the identifiable palynomorphs from the lower Barruelian section along the track to Valdoré; strata identified type section, offering the prospect that further inves as marine on the basis of a bivalve fauna occur at the tigation is justifiable. base of this succession, thereafter the section extends Summary data on the Stratotype of the Barruelian across the stratotypes of the Raposa, Gonzalo and Substage (Fig. 6): Sucesiva formations (Knight 1983a), all upper Bar – Boundary stratotype located on old mine rail track ruelian, up to the contact with the Saberian (base UTM near Helechar, west of Barruelo de Santullán, province 30T ETRS89 322811E.4745935N through to UTM Palencia; short section conserved as a site of geological 30T 322879E.4744961N). importance (LIG): UTM coordinates: 30T ETRS89 394423E.4751795N. – Detailed description of boundary stratotype in 6.4. Saberian Substage (proposed) Wagner and Winkler Prins (1970): the base of the The concept that the top of the then proposed Barrue Carboneros Member marks the base of the Barruelian lian Stage would be defined in the Sabero succession Substage and overlies the Loma Member of the was expressed explicitly by Wagner and Winkler Prins Barruelo Formation, a sandstone-shale succession (1985a); also in the formal proposal for recognition of considered marine with prominent channelling sand the Barruelian (Wagner and Winkler Prins 1985b). stones at its top contact. The appearance of the first of a Implicit was the recognition that the top of the Bar The chronostratigraphic legacy of Robert H. Wagner 293 ruelian would need to be defined by the boundary (2014). The contact is taken at the base of the Que stratotype of a new succeeding chronostratigraphic madas Formation, commencing with a thick lacustrine unit, still to be defined. Wagner and Álvarez-Vázquez shale succession marking a widespread inundation (2010) introduced the term “Saberian” and informally event. This has been correlated to a corresponding proposed that this should be recognised as the chrono abrupt change in lithology marking inundation at the stratigraphic unit in succession to the Barruelian and level of the Tabliza Horizon at the base of the Pastora should coincide with the zeilleri megafloral zone. A Formation in the Ciñera-Matallana Coalfield (see formal proposal for the recognition of the Saberian relevant column on Fig. 3), some 20 km to the west Substage in the West European chronostratigraphic (Knight and Wagner 2014). Correlation of later in scheme (Knight and Wagner 2014) was presented in undation events and coarsening upwards cycles sup the field meeting on Carboniferous and Permian Non- ports the close correlation between these two coalfields marine-Marine Correlation (CPC-2014, Freiberg, Ger as part of a single sedimentary basin. Westwards onlap many) but has not yet been submitted for ratification of this basin is clearly demonstrated in both areas. By through the SCCS. extension, the La Magdalena Coalfield, at some 15 km As conceived by Wagner and Álvarez-Vázquez to the south-west of the Ciñera-Matallana Coalfield, (2010), and further discussed by Wagner and Castro corresponds to the same westwards expanding basin (2011), this substage would correspond with the flora (Wagner and Castro 2011), and a rich flora (Castro of the Zone de Tronquié of the Carmaux Coalfield 2005a, b) is entirely congruent with the floral character (Doubinger and Vetter 1969), which was taken to in the Sabero and Ciñera-Matallana successions. The represent only the lower part of Stephanian B. This floristic character of the Saberian Substage is repre reflects conclusions first expressed by Wagner (in sented by the fossil floras of the succession above the Wagner and Martínez-García 1998) that the Stepha base of the Quemadas Formation in the Sabero Coal nian B, as then recognised in the Massif Central field, the flora above the base of the Pastora Formation (Bouroz and Doubinger 1978), should be re-inter in the Ciñera-Matallana Coalfield and the flora re preted in the light of the detailed record of the flora corded throughout the La Magdalena Coalfield. These of the St-Étienne Coalfield published by Doubinger et floras are listed comprehensively in Wagner and al. (1995). Wagner suggested that a Stephanian B sensu Álvarez-Vázquez 2010 (it can be noted that the flora Carmaux can be distinguished as representing the for Ciñera-Matallana includes the lowest formation, lower Stephanian B in contrast to the later Stephanian the San Francisco Formation, in this coalfield, which B sensu stricto. The Stephanian B sensu Carmaux was according to the correlation in Knight and Wagner interpreted to correspond to the zeilleri megafloral 2014 should be considered uppermost Barruelian). zone, and the Stephanian B sensu stricto to correspond The characteristic features of the Saberian succes to the angustifolium megafloral zone (see Fig. 3). This sion in its type area in the Stephanian coalfields of the concept effectively defined the chronostratigraphic southern margin of the Cantabrian Mountains, have extent of the Saberian and the basis on which the been described in some detail in Knight and Wagner top boundary of the substage would be defined. (2014). In the Sabero Coalfield the total succession of Wagner and Álvarez-Vázquez (2010) identify the Saberian strata comprises some 1,350 m, while in the succession and corresponding flora from the Villablino Ciñera-Matallana coalfield the corresponding thick Coalfield (see Fig. 2), in the western part of the ness is some 1,100 m. In both coalfields there is province of León, as representing the angustifolium abundant evidence that the sedimentary environment, zone. This coalfield area was identified as forming part although dominated by lacustrine and alluvial plain of the same sedimentary basin as Sabero and the sediments, was in a near-coastal environment with intervening tectonically isolated coalfields, with the marine influence evident from bivalve assemblages implication that the boundary at the top of the Saberian (Eagar and Weir 1971, Eagar 1985). In addition, in the would be found near the base of the Villablino-Ca Ciñera-Matallana Coalfield a trilobite pygidium has rrasconte succession. This was suggested explicitly by been found in the base of one of the widespread Knight and Wagner (2014). inundation events (Wagner and Castro 2011), indicat The proposed boundary stratotype (Fig. 8) is located ing the connection to fully marine conditions and on a long naturally well-exposed section in the Sabero suggesting that the inundation events may have Coalfield, which has been described in detail by Knight been driven by glacio-eustatic sea-level change. Pre (1971, 1983a) and summarised in Knight and Wagner liminary results from the palynological investigation in 294 J. A. Knight and C. Álvarez-Vázquez the Sabero Coalfield report the presence of acritarchs also been located in the Puerto Ventana Coalfield in the thick shale succession immediately above the (reference horizon No. 11 on Fig. 3; sample TC 6) boundary stratotype. It is apparent that the flora of and reported by Merino-Tomé et al. (2017) who these coalfields can be considered to reflect a coastal obtained a radiometric date using LA-ICP-MS of alluvial plain and in consequence reflecting a cosmo 304.2 ±1.1 Ma. This is substantially older than would politan flora of the circum-Paleotethys region. be expected from the stratigraphic relationship with While the characteristics of the Saberian succession other successions of the zeilleri megafloral zone, but as are well-defined in the Sabero and Ciñera-Matallana concluded by Merino-Tomé et al. (op. cit.), allowing coalfields (Wagner and Artieda 1970, Knight 1983a, for the margin of error this nevertheless corresponds to Knight et al. 2000), the relationships with other the conclusion that this horizon falls within the Gzhe tectonically isolated areas of terrigenous coal-bearing lian stage of the global time scale (Davydov et al. successions (Fig. 2: La Magdalena, El Bierzo, Carras 2012). Further work is ongoing to verify radiometric conte, Puerto Ventana, Canseco-Rucayo, Viego-Sala age determinations of all the referenced tonstein món) along the southern edge of the Cantabrian horizons using the considerably more precise CA- Mountains is less clear. All these areas include succes ID-TIMS method, with cross-reference between la sions which have yielded floras which can be identified boratories. Initial results, subject to formal reporting in with confidence with the zeilleri megafloral zone. the near future suggest that the Puerto Ventana material However in these, the thick lacustrine intervals are in fact represents an age much closer to 300.5 Ma. absent and in many cases the successions are domi Although subject to further refinement and verifica nated by coarse clastics and often with locally derived tion, the radiometric ages strongly suggest that the conglomerates which can be interpreted as proximal proposed Saberian Substage falls entirely within the alluvial fan deposits (Santos et al. 1990). To a degree Gzhelian Stage of the global timescale (Davydov et al. these depositional environments may reflect the effect 2012) and extends into the upper half of this latter unit. of the basin-fill onlapping against a deeply dissected Current detailed investigation in the Villablino and steep basin margin with palaeovalleys to the west. Coalfield, which complements the very extensive Nevertheless, it cannot be ruled out that there was some collection of fossil flora in the Centro Paleobotánico, basin segmentation, with isolation of local areas, due to Jardín Botánico de Córdoba, supports a preliminary continuing tectonism. However, throughout the area of conclusion of the continuing presence of a flora Saberian deposition in the Cantabrian Mountains it is identifiable as Saberian (zeilleri megafloral zone) in clear that marine influence was never distant. the lower part of this succession (compare Fig. 3) in the A characteristic feature of the lower Saberian inter Carrasconte area. However, it is clear that in the upper val is the presence of a number of pyroclastic tonsteins, part of the Villablino succession, which hosted the reported respectively from the Ciñera-Matallana (Bieg most recent intense coal-mining, the flora is distinctive and Burger 1992) and Sabero (Knight et al. 2000) and closely comparable to the flora of the classic coalfields. Of these, two horizons from Sabero (re Stephanian succession of the St. Étienne Basin, corre ference horizon No. 9 on Fig. 3; levels 31 and 32 in sponding to the angustifolium megafloral zone. Char Knight et al. 2000) have been submitted for radio acteristic floral elements that make their appearance in metric dating and generated absolute ages with a this succession include Alethopteris pennsylvanica, degree of confidence, as reported in Knight and and Sphenophyllum angustifolium. An objective of Wagner (2014). These horizons at thicknesses of this work is to test the concept expressed by Wagner 400 m and 560 m respectively above the base of the and Álvarez-Vázquez (2010) and Knight and Wagner Saberian in its stratotype, indicated ages of 302.13 (2014) that the passage between the zeilleri and ±0.23 Ma and 302.25 ±0.28 Ma. Taken in the context of angustifolium megafloral zones can be clearly defined the dated tonstein horizon from the upper Barruelian of in the Carrasconte-Villablino succession and to eval Sabero, reported above, the base of the proposed uate if a succeeding chronostratigraphic unit should be Saberian Substage can with some confidence be placed proposed based on a boundary stratotype in the Villa at around 302.3 Ma. Of the tonsteins in the Ciñera- blino Coalfield. Matallana Coalfield only one (reference horizon No. Summary data on the Stratotype of the proposed 10 on Fig. 3) has been collected in any quantity from an Saberian Substage (Fig. 8): accessible open-pit working but has thus far proved – Boundary stratotype of the base of the Saberian unsuitable for reliable dating. A tonstein horizon has corresponds to the contact between the Sucesiva For The chronostratigraphic legacy of Robert H. Wagner 295

Fig. 8. Sketch map and image of the proposed Saberian stratotype; see Fig. 2 for regional setting. The basal contact of the proposed Saberian Substage with the underlying Barruelian is marked, indicating the contact between the Sucesiva Formation to the north and the overlying Quemadas Formation (right hand side of image), the base of which defines the basal contact of the proposed Saberian. mation and Quemadas Formation, stratotypes of which been formally ratified. This review necessarily has are defined on the cart track running north of the considered the relationship of the substages (proposed village of Saelices to the village of Valdoré in the Esla and ratified) with megafloral zones, reflecting that Valley (contact coordinates: UTM 30T ETRS89 traditionally the chronostratigraphic units of the later 322828E.4745089N). Pennsylvanian of Western Europe have been primarily – The contact between these formations is well ex defined by fossil flora assemblages. Additionally, the posed, marked by a sudden change to a dark shale presence of a number of pyroclastic tonstein bands succession representing a widespread inundation through these successions provides the basis for an event. Detailed description of the stratotype in Knight ongoing programme of radiometric dating, in progress 1983a. with colleagues from the University of Oviedo. From this, some provisional ages have been incorporated in the present analysis of duration and temporal relation 7. Conclusions ships of the regional substages. The status of the four substages is summarised: The present work reports elements of an ongoing 1. Asturian: still at proposal stage to replace the former programme to continue the resolution of stratigraphic Westphalian D. The proposed stratotype in the Riosa relationships in Pennsylvanian strata in the Cantabrian region of Asturias requires approval and implementa region of N. Spain. This has provided the opportunity tion of a clean-up and thereafter detailed logging to to review the background and status of four regional support the interpretation of the appropriate horizon chronostratigraphic units, some of which are still at the for a boundary stratotype and to confirm correlation to status of proposals, in contrast to others which have the main area of the Central Asturian Coalfield and 296 J. A. Knight and C. Álvarez-Vázquez further east to the area of northern Palencia. These Barruelian Substage extends from mid-Kasimovian latter areas permit characterisation of the proposed to an age certainly above the base of the Gzhelian. Asturian Substage not only by means of fossil flora, but This consequently means that the Saberian falls en also with reference to tonsteins which are the subject of tirely within the Ghzelian of the global framework. radiometric dating, and also to marine faunas including The Saberian, characterised by the zeilleri mega fusulinid foraminifera which can be correlated to the floral zone, clearly occupies a substantial interval of global framework. time within the Gzhelian period. This highlights a 2. Cantabrian: this substage has been ratified by the problem for identification of the succeeding angusti SCCS and its boundary stratotype approved in the folium zone, for which the interval between the ap proximity of Velilla de la Peña in the Guardo-Cervera proximate top of the Saberian and the base of the Coalfield, Palencia. The boundary stratotype is well Permian, with a reference date of 298.9 Ma (Davydov exposed over a relatively short section; the Cantabrian et al. 2012), becomes very reduced to some 1.5 Ma substage has been well-characterised in respect of only. This also places in question the assumptions on numerous published sections in the post-Leonian Ba the time significance of the conferta zone, as ex sin. Corresponds to the cantabrica megafloral zone. pounded by Wagner and Álvarez-Vázquez (2010). 3. Barruelian: this substage has been ratified by the The problem for accommodating the succession of SCCS and its boundary approved in the proximity of floral zones attributed to the uppermost Stephanian is the hamlet of Helechar in the Barruelo Coalfield apparent and forms a focus for current research being (Palencia). The boundary stratotype is located on a undertaken in the Villablino Coalfield, and other disused mine railway section which has statutory successions in the Cantabrian Region which may cover protected status. When approved, the concept of the the interface between the uppermost Stephanian and characterisation and duration of the substage was the Permian. explicitly proposed to be represented also in the lower The conclusion of the present overview is that the part of the succession of the Sabero Coalfield (León). It substages recognised in the Cantabrian region provide was conceived as corresponding to Stephanian A as a robust framework for the late Westphalian-Stepha previously defined in Saint-Étienne Basin of France nian interval in Western Europe, providing a practical and also to the lamuriana megafloral zone. basis on which work in this area continues to progress. 4. Saberian: still at proposal stage. The proposed boundary stratotype is located in a well-exposed natural section north of the village of Saelices in the Sabero Coalfield. The concept for this stage is that it corresponds to the zeilleri megafloral zone and also to lower part of Stephanian B as defined by the The present work has developed flora of the Assise de Tronquié of the Carmaux Acknowledgements. from the many years in which both authors worked closely Coalfield, Massif Central of France. The top of the with the late Robert Wagner. However, in order to bring ideas substage was conceived as being marked by a transi developed over a long period into perspective with current tion to flora of the angustifolium zone, expected to be knowledge, wide-ranging discussions have been necessary; located in the future in the basal part of the succession particular thanks are due to Dr Oscar Merino-Tomé of the of the Villablino Coalfield. Department of Geology of the University of Oviedo and Radiometric dates, still awaiting verification and numerous colleagues, related to provisional results of an ongoing programme of radiometric dating of tonsteins and formal publication, indicate that the duration of suc also orientation on fusulinid biostratigraphy. Special thanks cessive substages can be expressed: Asturian ~ 2.5 Ma, are due to Juan I. Peláez for the preparation of a number of Cantabrian ~ 3.0 Ma, Barruelian ~ 3.2 Ma, Saberian the figures and for his constant assistance in on-going minimum 1.5 Ma. Correlation based on the fusulinid fieldwork. Luis Sardina is also thanked for assisting field foraminifera in conjunction with the provisional radio work. Dr Manuel Juncal is thanked for providing a pre metric dates indicate that the proposed Asturian liminary overview of palynological investigation of the substage falls entirely within the upper part of the Saberian stratotype undertaken at the University of Vigo. The authors acknowledge with thanks the constructive Moscovian of the global framework. The Cantabrian suggestions provided by two unnamed reviewers. This Substage falls across the interface Moscovian-Kasi research was supported by Projects CGL2015-66835-P movian, and the base of the Kasimovian approximately and MCIU-19-PGC2018-099698-B-I00 of the Spanish Gov coincides with the middle of the Cantabrian. The ernment. The chronostratigraphic legacy of Robert H. Wagner 297

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western border of the Central Asturian Coalfield (Cor Wagner, R. H., 1966c. Notes on the Geology of the Palaeo dillera Cantábrica). Trabajos de Geología 4, 365–372. zoic Rocks in the northeastern part of the Province of Pointon, M., Chew, D., Ovtcharova, M., Sevastopulo, G., Palencia, NW Spain. Notas y Comunicaciones Instituto Crowley, Q., 2012. New high precision U-Pb dates from Geológico y Minero de España 86, 31–40. western European Carboniferous tuffs; implications for Wagner, R. H., 1969. Proposal for the recognition of a new time scale calibration, the periodicity of late Carbonifer “Cantabrian” Stage at the base of the Stephanian Series. ous cycles and stratigraphic correlation. Geological So Compte Rendu 6e Congrès Carbonifère, Sheffield 1967 1, ciety of London 169, 713–721. 139–150. Remane, J., 2003. Chronostratigraphic correlations: their Wagner, R. H., 1971. The Westphalian D floras of the importance for the definition of geochronologic units. Olloniego and Esperanza formations in the Central As Palaeogeography, Palaeoclimatology, Palaeoecology 196, turian Coalfield. In: The Carboniferous of Northwest 7–18. Spain. Trabajos de Geología 4, 461–505. Sáenz de Santa María, J. A., Luque, C., Gervilla, M., Wagner, R. H., 1983. Late Westphalian D and early Can Laveine, J. P., Loboziak, S., Brousmiche, C., Coquel, tabrian floras of the Guardo Coalfield. In: Wagner, R. H., R., Martínez-Díaz, C., 1985. Aportación al conocimiento Fernández-García, L. G., Eagar, R. M. C. (Eds.), Geology estratigráfico y sedimentológico del Carbonífero produc and Palaeontology of the Guardo Coalfield (NE León – tivo de la Cuenca Central Asturiana. Compte Rendu 10e NW Palencia), Cantabrian Mts. Serie Informes Instituto Congrès Carbonifère, Madrid 1983 1, 303–326. Geológico y Minero de España, 57–91. Salvador, A., 1994. International Stratigraphic Guide. A guide Wagner, R. H., 1984. Megafloral Zones of the Carbonifer to stratigraphic classification, terminology, and procedure. ous. Compte Rendu 9e Congrès Carbonifère, Washington- Second Edition. International Subcommission on Strati Urbana 1979 2, 109–134. graphic Classification of IUGS International Commission Wagner, R. H., 2017. The ‘global’ scheme of Pennsylvanian on Stratigraphy. Geological Society of America, 214 p. chronostratigraphic units contrasted with the West Euro Santos, J. A., Navarro, D., Horvath, V., 1990. La cuenca pean and North American regional classifications: dis Estefaniense de Canseco-Salamón (Norte de León, Cor cussion of palaeogeographic zones/regions and problems dillera Cantábrica). Un ejemplo de abanicos aluviales of correlation. Stratigraphy 14 (1–4), 405–423. ligados a una zona de fractura. Boletín Geológico y Wagner, R. H., Álvarez-Vázquez, C., 1991. Floral charac Minero 101 (4), 3–21. terisation and biozones of the Westphalian D Stage in NW Villa, E., Merino-Tomé, O., 2016. Fusulines from the Spain. Neues Jahrbuch für Geologie und Paläontologie, Bashkirian/Moscovian transition in the Carboniferous Abhandlungen 183 (1–3), 171–202. of the Cantabrian Zone (NW Spain). Journal of Forami Wagner, R. H., Álvarez-Vázquez, C., 2010. The Carbonifer niferal Research 46 (3), 237–270. ous floras of the Iberian Peninsula: A synthesis with Wagner, R. H., 1958. Lobatopteris alloiopteroides, una geological connotations. Review of Palaeobotany and nueva especie de Pecopteridea del Estefaniense A espa Palynology 162 (3), 238–324. ñol. Estudios Geológicos 14, 38, 81–106. Wagner, R. H., Artieda, J. I., 1970. La cuenca minera Ciñera- Wagner, R. H., 1959. Flora fósil y estratigrafía del Carbo Matallana. S. A. Hullera Vasco-Leonesa, 289 p. nífero de España NW y Portugal N. Estudios Geológicos Wagner, R. H., Castro, M.-P., 2011. Compositional changes 15 (volumen homenaje a M. San Miguel de la Cámara), in mid-Stephanian (Kasimovian) flora in relation to 393–420. alluvial plain deposits derived from westward-receding Wagner, R. H., 1962. A brief review of the stratigraphy and mountains and bordered by the Paleotethys: La Mag floral succession of the Carboniferous in NW Spain. dalena Coalfield, Northwestern Spain. Palaios 26, Compte Rendu 4e Congrès Carbonifère, Heerlen 1958 33–54. 3, 753–762. Wagner, R. H., Fernández-García, L. G., 1983. Upper West Wagner, R. H., 1964. Stephanian floras in NW Spain, with phalian D and Cantabrian strata in the Guardo Coalfield: special reference to the Westphalian D – Stephanian A Tectonics, Sedimentation, Stratigraphy. In: Wagner, boundary. Compte Rendu 5e Congrès Carbonifère, Paris R. H., Fernández-García, L. G., Eagar, R. M. C. (Eds.), 1963 2, 835–851. Geology and Palaeontology of the Guardo Coalfield (NE Wagner, R. H., 1965. Palaeobotanical Dating of Upper León – NW Palencia), Cantabrian Mts. Serie Informes Carboniferous Folding Phases in NW Spain. Memorias Instituto Geológico y Minero de España, 1155. Instituto Geológico y Minero de España 66, 1–169. Wagner, R. H., Martínez-García, E., 1974. The relation Wagner, R. H., 1966a. Sur l'existence, dans la Cordillère between geosynclinal folding phases and foreland move Cantabrique, de séries de passage entre Westphalien et ments in Northwest Spain. Stvdia Geologica, Salamanca Stéphanien: la limite inférieure de ces formations “can 7, 131–158. tabriennes”. Comptes rendus Académie des Sciences, Wagner, R. H., Martínez-García, E., 1998. Floral remains Paris, (D) 262, 1337–1340. from the highest Valdeón Formation, a marine Stephanian Wagner, R. H., 1966b. La succession des séries cantab unit south of the Picos de Europa, and comparisons with riennes et leur limite supérieure. Comptes rendus Aca eastern Asturias. Revista Española de Paleontología 13 démie des Sciences, Paris, (D) 262, 1419–1422. (1), 93–106. 300 J. A. Knight and C. 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Wagner, R. H., Park, R. K., Winkler Prins, C. F., Lys, M., Compte Rendu 10e Congrès Carbonifère, Madrid 1983 4, 1977. The Post-Leonian Basin in Palencia: A Report on 473–483. the Stratotype of the Cantabrian Stage. In: Holub, V. M., Wagner, R. H., Winkler Prins, C. F., 1985b. The Cantabrian Wagner, R. H. (Eds.), Symposium on Carboniferous and Barruelian stratotypes: a summary of basin develop Stratigraphy. IUGS Subcommission on Carboniferous ment and biostratigraphic information. In: Lemos de Stratigraphy (SCCS) Field and General Meeting, Cze Sousa, M. J., Wagner, R. H. (Eds.), Papers on the Carbo choslovakia, 1973. Publications Geological Survey, Pra niferous of the Iberian Peninsula. Anais Faculdade de gue, 89–146. Ciências, Universidade do Porto, Supplement to volume Wagner, R. H., Sánchez de Posada, L. C., Martínez Chacón, 64 (1983), 359–410. M. L., Fernández, L. P., Villa, E., Winkler Prins, C. F., Wagner, R. H., Winkler Prins, C. F., 1994. General overview 2002. The Asturian Stage: a preliminary proposal for the of Carboniferous Stratigraphy. Annales Société géologi definition of a substitute for Westphalian D. In: Hills, que de Belgique 116 (1), 163–174. L. V., Henderson, C. M., Bamber, E. W. (Eds.), Carboni Wagner, R. H., Winkler Prins, C. F., 2016. History and ferous and Permian of the World. Canadian Society of current status of the Pennsylvanian chronostratigraphic Petroleum Geologists, Memoir 19, 832–850. units: problems of definition and interregional correla Wagner, R. H., Varker, W. J., 1971. The distribution and tion. Newsletters on Stratigraphy 49 (2), 281–320. development of post-Leonian strata (upper Westphalian Waters, C. N., Condon, D. J., 2012. Nature and timing of D, Cantabrian, Stephanian A) in northern Palencia, Spain. Late Mississippian to Mid-Pennsylvanian glacio-eustatic Trabajos de Geología 4, 533–601. sea-level changes of the Pennine Basin. U.K. Journal of Wagner, R. H., Villegas, F. J., Fonollá, F., 1969. Description the Geological Society, London 169, 37–51. of the Lower Cantabrian stratotype near Tejerina (León, Wittry, J., Glasspool, I. J., Béthoux, O., Koll, R., Cleal, C. J., NW Spain). Compte Rendu 6e Congrès Carbonifère, 2015. A revision of the Pennsylvanian marattialean fern Sheffield 1967 1, 115–138. Lobatopteris vestita auct. and related species. Journal of Wagner, R. H., Winkler Prins, C. F., 1970. The stratigraphic Systematic Palaeontology 13 (8), 615–643. succession, flora and fauna of Cantabrian and Stephanian A rocks at Barruelo (prov. Palencia), NW. Spain. In: Streel, M., Wagner, R. H. (Eds.), Colloque sur la strati graphie du Carbonifère, Congrès et Colloques, Université Manuscript received: April 24, 2020 de Liège 55, 487–551. Revisions required: September 16, 2020 Wagner, R. H., Winkler Prins, C. F., 1985a. Stratotypes of the Revised version received: September 16, 2020 two lower Stephanian stages, Cantabrian and Barruelian. Manuscript accepted: September 19, 2020