A Summary of Upper Pennsylvanian Regional Substages Defined in NW Spain – the Chrono- Stratigraphic Legacy of Robert H
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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 chrono- stratigraphic 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] © 2021 The Authors DOI: 10.1127/nos/2021/0616 Gebr. Borntraeger Science Publishers, Stuttgart, www.borntraeger-cramer.com 276 J. A. Knight and C. Álvarez-Vázquez 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