These "golden spikes" should be related with greatest number ... 1988, KLAPPER 1988, JOHNSON 1989) on the current. Middle/Upper Devonian ... The Middle-Upper Devonian boundary stratotype (KLAPPPER & al. 1987) is in agreement ...
231
Cour. Forsch.-Inst. Senckenberg, 110: 231-236, 2 text-figs.
—
Frankfurt a. M., 12. 6. 1989
Middle-Upper Devonian boundary: ambiguous reality of its stratotype GRZEGORZ RACKI & TOMASZ WRZOLEK*
Abstract The current stratotype of the Middle-Upper Devonian boundary is defined by cryptogenic or biofacies first occurrence of an in dex species of conodont Ancyrodella (of uncertain ancestry) and should be revised or changed; the proposed revision aims at plac ing the stratotype at the Ancyrodella rotundiloba sensu stricto entry level; it is in good accordance with the original definition of the boundary by the Subcommission on Devonian Stratigraphy, i.e. at the base of the Lower asymmetricus Zone. Introduction Stratotype, as defined by the International Stratigraphic Guide (HEDBERG 1976) should be clearly marked and ea sily identifiable. This is especially significant for the global stratotype sections and points ( G S S P ) , that are selected as a basis for world-wide chronostratigraphic interpretations ( C o w i E & al. 1986). These "golden spikes" should be related with greatest number possible of unbroken evolutionary lineages in many groups of fossils, i. e. with fairly non-punctuated record of sedimentation and biological evolution across the boundary under consideration (AGER 1973, JOHNSON 1979).
The present communication presents our methodological reservations, partly also concerns the nomenclatural que stions, supplementing the discussion (SANDBERG & al. 1988, KLAPPER 1988, JOHNSON 1989) on the current Middle/Upper Devonian boundary GSSP (KLAPPER & al. 1987). Some conclusions of our paper are in reference to the recent biostratigraphic research in the Holy Cross Mts., Poland. Discussion The Middle-Upper Devonian boundary stratotype (KLAPPPER & al. 1987) is in agreement with formalities: the de cision has been approved by the International Comission on Stratigraphy to place the marker point at the base of the 4 2 a ' bed at the Col du Puech de la Suque section (CPS-E) of Montagne Noire, France (see Fig. 1). On the other hand, this boundary presents two kinds of weakness, discussed below: a) Questionable correlative value of the defining event The G S S P is at the "cryptogenic or biofacies first occurrence" (in words of SANDBERG & al. 1988) of conodonts, considered by KLAPPER 1987 as Ancyrodella rotundiloba BRYANT, early form and diagnostic for the boundary defi nition. In our opinion this is a really grave argument against the present stratotype. Absence of an ancestral taxon in the Ancyrodella lineage in CPS-E suggests an interruption of some sort in the sec tion : this may be either a physical gap and/or taphonomic event at the base of the 42 a' sampling level (and d e s p i t e the conclusions of KLAPPER & al. 1987 this can be checked by detailed microfacies research), or rather the "sudden" entry of the taxon has a regional aspect and reflects a migration event, i. e. stratal event (JOHNSON 1979, also Fig. 1, herein), with inherent and undetectable imprecision of the boundary correlation (see also an example in AGER 1973: 62 and discussion in BLESS & al. 1987).
*) Silesian University, Chair of Paleontology & Stratigraphy, Mielczarskiego 60, PL 41-200 Sosnowiec, Poland.
232
KLAPPER (1988, see also JOHNSON 1989) suggests a standard value of the current GSSP due to easy correlation with the historical base of the Frasnian in the Belgian succession: the phylogenetically identical advanced early forms of Ancyrodella rotundiloba appear in bed 42 a of CPS-E section, and in bed 41 of Nismes section, where it is preceded by the ancestral species, A. binodosa. This intent correlation still needs additional data as the earliest repre sentatives of the genus in both sections are not illustrated. Despite the use of the same term, the concepts of an early phylogeny of A. rotundiloba of BULTYNCK (1982a, 1983) and KLAPPER (1985) are generally different, which is clearly visible in conclusions of SANDBERG & al. (1988). In BULTYNCK's terms the first occurrences of A. rotundilo ba are recorded in samples 41 (Nismes) and, possibly 46 (CPS-E). Using firmly KLAPPER'S criteria (1985: 26) we can suggest correlation of the GSSP rather with 37 bed of Nismes section, where A. binodosa a morphotype of BUL TYNCK (1982a, 1983), assignable to early A. rotundiloba, is recorded for the first time. Significant for the question of the relationship of A. rotundiloba to A binodosa would be a more detailed analysis of other successions, as e. g. in CHALYMBADSHA & TSHERNYSHEVA (1970) who described transitional species from the Volga-Ural Devonian. It is particularly important for the A. binodosa type level, i. e. the Calumet Member of the Waterways Formation in Western Canada that the true relationships of the morphotypes may be obscured by uncertain range of intraspecific variability resulting from scarce occurrences (2 specimens at the type locality — UYENO 1974: Tab. 4 a , station 181) and dubious distribution patterns of A. binodosa (see UYENO 1974: Tab. 4 b , well SW 16-21, also NORRIS & UYENO 1981). Furthermore, according to BULTYNCK (1983) morpho-phylogenetic analysis leads to conclusion that the Canadian-type (d) morphotype of A. binodosa represents a blind branch of the lineage. Consequently, KLAPPER'S (1985: 23) general assumption that there is a morphological gradation between A. binodosa and A. rotundiloba with in the single phyletic lineage needs at least more detailed evidence. On the other hand, according to BULTYNCK (1983: 167) evolution of the early species of Ancyrodella is connected with major habitat changes: dispersal of the genus towards the deeper-water pelagic facies, connected with both evo lutionary radiation and increase in numerical abundance of the representatives of the genus (Fig. 2). Therefore, the first occurrence of Ancyrodella in a particular section may record various stages of the world-wide transgressive pulse in the Lowermost asymmetricus Chron ( T - R Cycle l i b of JOHNSON & al. 1985); e. g. in the Ardennes the An cyrodella entry coincides with sharp (frequently erosional) contact of the Givet and Frasnes Groups (BULTYNCK 1982a), reflecting the significant facies change (also BULTYNCK & C O E N 1982) caused by deepening. b) Incompatibility with the standard conodont zonation As it was clarified by SANDBERG & al. (1988) the GSSP is placed within the Lowermost asymmetricus Zone: this is in distinct disagreement with the original 1982 decision of the Subcommision on Devonian Stratigraphy to place the series boundary at the base of the Lower asymmetricus Zone. This disparity is a result of differing concepts of Ancyrodella rotundiloba as discussed above. Therefore the strict definition of this species is the most fundamental for the recognition of the base of the Frasnian (see KLAPPER 1988, JOHNSON 1989). Discussion on morphological de tails of the type material was mostly devoted to the shape of the basal pit; the real value of this research is obscured by the fact, that the type horizon of A. rotundiloba (North Evans Limestones of the New York State) is a "composite lag deposit completely mixed during occasional storms" (HUDDLE 1981: B-8, see also B-56 with data on BRYANT'S collecting locality), what may be especially significant for taxonomy of so time-sensitive fossils as Ancyrodella conodonts: the variability range in the type material thus obtained is not a sufficient argument against a narrow defini tion of A. rotundiloba introduced by ZIEGLER (see 1958, also Catalogue of Conodonts, 1973), as proposed by KLAP PER (1985, 1988). In other words, alternatively to KLAPPER'S conceptions it can be claimed that BRYANT'S collection contains two species of phylogenetically and/or biostratigraphically different origins: the "real" A. rotundiloba (sensu lectotype), defining the base of the Lower asymmetricus Zone (in the sense of SANDBERG & al. 1988) and a possi ble ancestral form, represented by a single, (?reworked) specimen. The whole question seems a common problem for revisions of old, not adequately collected material aiming at correct definition of species that are well-established in biostratigraphy. Such a practice is misleading, mostly for the ordinary "grey consuments" of the conodont taxo nomy and stratigraphy (see an example in JOHNSON 1989). c) Middle/Upper Devonian boundary and the Holy Cross conodonts The above mentioned doubts, concerning the applicability of the current Middle-Upper Devonian boundary stratotype came also out during current research of one of us (G. R . ) in the Holy Cross Mts. The two earliest species of Ancyrodella are scarce and are irregularly distributed: they were found in two sections only (Wietrznia and Czarnow, see SZULCZEWSKI 1971 and BULTYNCK 1982b). Acme of the genus (see SZULCZEWSKI 1971) ist evidently re
lated to development of the Early Frasnian onlap during the Lower and Middle asymmetricus Chrones (RACKI in press). The first occurrences of Ancyrodella are accompanied by appearance of the fine-grained, coelenterate-poor
233
lithofacies replacing either shallow-water, coelenterate-rich (partly biostromal) or deeper-water, marly (basinal) se dimentation. The intervals between the entry of the supposedly new species of Ancyrodella and its possible descend ant, A. rotundiloba possibly comprise over 10 m of deposits; the Ancyrodella conodonts are the first wide-platform elements (apart from Polygnathus dengleri BlSCHOFF & ZlEGLER) enriching the shallow-water Icriodus-Polygnathus biofacies. Proposition of change Our methodological reservations concerning the current GSSP of the Middle-Upper Devonian boundary makes the situation comparable to placing the GSSP at the evident gap. In this case this is the absence (?non-recognition) of an immediate ancestor of the index conodont Ancyrodella rotundiloba (early form sensu KLAPPER 1985). Therefore, contrary to the opinion of SANDBERG & al. (1988), we present for consideration an idea of revision, or change of the current GSSP: possibly it can be placed at the base of the 46 bed of the CPS-E section where the early form of Ancy rodella rotundiloba is replaced by A. rotundiloba sensu stricto. Possibly it reflects a phyletic event, with Y-branched speciation pattern (Fig. 2, cf. stratigraphical ranges in BULTYNCK 1982a, KLAPPER 1985: fig. 1), according to JOHNSON (1979) particularly suitable for precise boundary definition. This shift removes all the above mentioned hindrances and corresponds to the original definition of the boundary in terms of standard conodont zonation; it is in agreement with the goniatite record in the section (HOUSE & al. 1985). The re-definition is especially important for reliability of correlation, as the entry of Ancyrodella rotundiloba sensu stricto is an evolutionary event, well established in morpho-phylogenetic aspect (BULTYNCK & JACOBS 1981, BULTYNCK 1982a, 1983, KLAPPER 1985) and is recognizable in many parts of the world (BULTYNCK 1982b), the Holy Cross Mts included. This approach follows thoroughly the interpretation of the Belgian succession by BULTYNCK & C O E N (1982: 42): "the arrival of A. binodosa is in rather rare specimens and is possibly facies-controlled . . . . Thus we favour a boundary at the transition A. binodosa/A. rotundiloba" (translated from Russian). Alternatively, if the taxonomic concept of A. rotundiloba of SANDBERG & al. (1988) and our proposition are re jected, the base of 42 a' bed in the Col du Puech de la Suque section will mark the series boundary only from the purely formal point of view without the appropriate conodont meaning: scarce record and unclear phylogenetic rela tionships within the earliest stages of the Ancyrodella lineage (Fig. 2) will make all the correlative inferrences du bious. Definition of the series (and zonal) boundary based on distribution of rather rare and possibly strongly faciescontrolled species obscures its recognition, as it is exemplified by the base of the Polygnathus asymmetricus Zone (see BULTYNCK 1986 for discussion). To conclude let us make a reference to a remark of KLAPPER (1988: 182), in context of the A. rotundiloba I alata controversy) that " . . . the lower zonal boundary would seem correct (underlin ing ours) in sections lacking the earlier representatives of Ancyrodella evolution". Essentially this is the starting point (!) of our reservations also for the current Middle/Upper Devonian GSSP: we consider the situation a method ological failure and not only an unfortunate case. Acknowledgements It is our pleasant duty to thank Dr. P. BULTYNCK (I. R. S. N. B. in Brussels), Professor A. JACHOWICZ (Silesian University, Sosnowiec), Dr. J. G. JOHNSON (Oregon University, Corvallis) and Dr. W. A. OLIVER, Jr. (U.S. Geological Survey, Washington) for their criticism of an early version of our manuscript, and, to Dr. JOHNSON, for sending us reprints of two papers, relevant for our considerations. With some of the ideas of our reviewers we agree; for the final version of this paper we take the sole responsibility.
References cited AGER, D. V. (1973): The Nature of the Stratigraphical Record. — The MacMillan Press, 1-114, 13 text-figs, 28 pis.; London. BLESS, M. J. M., BOUCKAERT, J. & PAPROTH, E. (1987): Fossil assemblages and depositional environments: limits to stratigra phical correlation. — In: MILLER, J., ADAMS, A. E. & WRIGHT, V. P. (eds): European Dinantian Environments; pp. 61-73, J. Wiley & Sons, Chichester. BULTYNCK, P. (1982 a): Conodont succession and general faunal distribution across the Givetian-Frasnian boundary beds in the type area. — In: Papers on the Frasnian-Givetian Boundary, Geol. Surv. Belgium, 34-59, 8 text-figs., 3 tabs., 3 pis., Brussels. —
(1982 b): The Ancyrodella binodosa - Ancyrodella rotundiloba rotundiloba transition, a datum-level for correlation of the Givetian-Frasnian boundary. — Ibidem, 17-33, 6 text-figs.
234
Fig. 1. Stratotype for the Middle-Upper Devonian boundary at the Col du Puech de la Suque section, Montagne Noir, France, with sequence of diagnostic Ancyrodella lineage species (adopted from KLAPPER 1985, with modifications of SANDBERG & al. 1988); indicated are different aspects of defining events (as defined by JOHNSON 1979) for real (R: accepted) and intent (I: propos ed in this paper) boundary stratotype.
235
— —
(1983): Origin and development of the conodont genus Ancyrodella in the Givetian - early Frasnian. — Fossils and Strata 15: 163-168, 2 text-figs., Oslo. (1986): Accuracy and reliability of conodont zones: the Polygnathus asymmetricus "Zone" and the GivetianFrasnian boundary. — Bull. Inst. roy. Sci. nat. Belg.: Sciences de la Terre 56: 269-280, Bruxelles.
BULTYNCK, P. & COEN, M. (1982): Conodont distribution in the Fromelennes Formation and the lower part of the "Assise de Frasnes" (Middle/Upper Devonian boundary of the Ardennes) [in Russian]. — In: SOKOLOV, B. S. & RZHONSNITSKAYA, M. A. (eds.): Biostratigrafiya Pogranitchnykh Otlozheniy Nizhnego i Srednego Devona, pp. 38-45, Nauka, Leningrad. BULTYNCK, P. & JACOBS, L. (1981): Conodontes et sedimentologie des couches de passage du Givetian au Frasnien dans Nord du Tafilalt et dans le Ma'der (Maroc Presaharien). — Bull. Inst. roy. Sci. Nat. Belgique 53, Science de la Terre 2: 124, 6 text-figs., 10 pis., Brussels. CHALYMBADSHA, V. G. & TSHERNYSHEVA, N. G. (1970): Conodonts of the genus Ancyrodella from the Devonian deposits of Volga-Kamsk area and their stratigraphic significance [in Russian]. — In: Biostratigrafia i Paleontologia Paleozoyskikh Otlozheniy Vostoka Russkoy Platformy i Zapadnogo Priuralia, pp. 81-104, Izdat. Kazanskogo Gos. Univ., Kazan. COWIE, J . W. ZIEGLER, W., BOUCOT, A. J . , BASSET, M. G. & REMANE, J. (1986): Guidelines and Statutes of the Internation (
al Commission on Stratigraphy (ICS). — Cour. Forsch.-Inst. Senckenberg (CFS) 83: 1-14, Frankfurt a. M. HEDBERG, H. D. (1976, ed.): International Stratigraphic Guide. — J. Wiley & Sons, 1-226, 14 text-figs., New York. HOUSE, M. R., KIRCHGASSER, W. T., PRICE, J. D. & WADE, G. (1985): Goniatites from Frasnian (Upper Devonian) and adjacent strata of the Montagne Noire. — Hercynica, 1: 1-21. HUDDLE, J. W. (1981): Conodonts from the Genesee Formation in Western New York. — Geol. Surv. Prof. Pap. 1032-B: 1-66, Washington. JOHNSON, J. G. (1979): Intent and reality in biostratigraphic zonation. — J. Paleontol. 53: 931-942, 8 text-figs., Tulsa. —
(1989): Base of the Upper Devonian in the conodont zonation. — Newsl. Stratigr. 21 (in press), Stuttgart.
JOHNSON, J. G., KLAPPER, G. & SANDBERG, C. A. (1985): Devonian eustatic fluctuations in Euroamerica. — Geol. Soc. Amer. Bull., 96: 567-587, 12 text-figs., Boulder. KLAPPER, G. (1985): Sequence in conodont genus Ancyrodella in Lower asymmetricus Zone (earliest Frasnian, Upper Devonian) in Montagne Noire, France. — Palaeontographica A 188: 19-34, 3 text-figs., 11 pis., Stuttgart. —
(1988): Intent and reality in biostratigraphic zonation: a reply to SANDBERG, ZIEGLER and BULTYNCK (1988). — Newsl. Stratigr. 19 (3): 179-183, Berlin.
KLAPPER, G., GEIST, R. & HOUSE, M. R. (1987): Decision on the Boundary Stratotype for the Middle/Upper Devonian Series Boundary. — Episodes, 10 (2): 97-101, with comment by J. W. COWIE. NORRIS, A. W. & UYENO, T. T. (1981): Stratigraphy and paleontology of the Lowermost Upper Devonian Slave point Formation on Lake Claire and the Lower Upper Devonian on Birch river, northeastern Alberta. — Geol. Surv. Canada Bull. 334: 1-53, Ottawa. RACKI, G. (in press): The Middle-Upper Devonian boundary beds of the Holy Cross Mts, Central Poland: Introduction to ecostratigraphy. — Canad. Soc. Petrol. Geol., Mem. 14, Proc. Ilnd Int. Symp. Dev. Syst., Calgary. SANDBERG, C. A., ZIEGLER, W. & BULTYNCK, P. (1988): Middle-Upper Devonian series boundary as an example of in tent and reality in biostatigraphic zonation. — Newsl. Strat. 18 (2): 117-121, 1 text-fig., Berlin. SZULCZEWSKI, M. (1971): Upper Devonian conodonts, stratigraphy and facial development in the Holy Cross Mts. — Act. Geol. Polonica 21 (1): 1-128, 11 text-figs., 34 pis., 9 tabs., Warszawa.
236
UYENO, T. T. (1974): Conodonts of the Waterways Formation (Upper Devonian) of the northeastern and central Alberta. — Geol. Surv. Can. Bull. 232: 1-93, Ottawa. ZIEGLER, W. (1958): Conodontenfeinstratigraphische Untersuchungen an der Grenze Mitteldevon/Oberdevon und in der AdorfStufe. — Notizbl. Hess. L.-Amt Bodenforsch. 87: 7-77, 7 text-figs., 12 pis., Wiesbaden. —
(1973, ed.): Catalogue of Conodonts. — 1: 1-504, E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart.
Fig. 2. Evolutionary scheme of earliest species of Ancyrodella: progressive distribution pattern based on suggestions of BUL TYNCK (1983) presents a background for approved and proposed revised Middle/Upper Devonian Series boundary GSSP.
