The Frasnian–Famennian Boundary in Vietnam and Evolutionary Meaning of Fads and Lads
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Newsletters on Stratigraphy, Vol. 51/3 (2018), 327–342 Article Published online December 2017; published in print June 2018 The Frasnian–Famennian boundary in Vietnam and evolutionary meaning of FADs and LADs Jerzy Dzik1,2*, Przemysław Świś2, and Nguyen Duc Phong3 With 10 figures and 1 table Abstract. The latest Frasnian and earliest Famennian conodont assemblages at the Si Phai section in north- ernmost Vietnam are similar to those from coeval strata in Europe, but their taxonomic diversity is signifi- cantly lower and the order of species appearances is different. Unlike most other localities, where ʻPalma- tolepisʼ linguiformis is a very late Frasnian species preceding Klapperilepis ultima, it emerges much earlier at Si Phai, already co-occurring with Ancyrodella lobata. Its contribution to the assemblage is there many times higher than elsewhere. This allows tentative apparatus reconstruction proving its congenerity with Man- ticolepis rhenana, which at Si Phai occurs only in the lowermost portion of the M. linguiformis range. Another peculiar aspect of this Vietnamese section is the abundance of Avignathus in its lower part. In a subsequent sudden change of apparently ecological nature, a diverse set of polygnathids Ctenopolygnathus and Poly - gnathus species followed by Klapperilepis ultima enriched the assemblage. The second dramatic faunal ex- change event resulted in the disappearance of all the palmatolepidids except for K. ultima. The Si Phai con- odont species succession does not differ from those of other regions of the world in that both the first and last occurrences were caused by ecological changes that, apart of this terminal Frasnian event, are not necessarily of global extend. The widely held assumption that most changes in distribution of conodonts were synchro- nous may not be true. A truly reliable age correlation should not be based on ecologically controlled appear- ances and disappearances but on well-documented evolutionary transitions. Unfortunately, evolutionary ori- gin of no one of the palmatolepidid species occurring in Si Phai (with possible exception of Manticolepis winchelli) has been determined elsewhere. This makes the probably phyletic succession of Ancyrodella chronospecies a more reliable tool for age correlation. Key words. Biostratigraphy, Devonian, Kellwasser Event, evolution, phylogeny, conodonts 1. Introduction 1995, 2005, 2008, Dzik & Phong 2016), the function of a geological time marker is performed by biological Whatever approach to the biostratigraphic practice is entities: living organisms. Their characteristics include chosen, would it be relying on environmental control population and ontogenetic variability, the main as- of species distribution (e. g., Klapper 2007b), hypo- pects that change in their phyletic evolution. There are thetical phylogeny of guide fossils (e. g., Ziegler and more than enough data showing that so understood Sandberg 1990) or their phyletic evolution (e. g., Dzik evolution is a continuous process (reviewed in e. g., Authors’ addresses: 1 Institute of Paleobiology, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland. 2 Faculty of Biology, University of Warsaw, Aleja Żwirki i Wigury 101, Warszawa 02-096, Poland. [email protected] 3 Vietnamese Institute of Geosciences and Mineral Resources, 67 Chien Thang, Van Quan, Ha Dong, Hanoi, Vietnam. [email protected] * Corresponding author: [email protected] © 2017 Gebrüder Borntraeger, Stuttgart, Germany www.borntraeger-cramer.de DOI: 10.1127/nos/2017/0418 0078-0421/2017/0418 $ 4.00 eschweizerbart_xxx 328 Jerzy Dzik et al. Dzik 2005, 2008). If it proceeds in isolated popula- China (Qiang 1989, fig. 1). This means that in the Late tions, this results in an increase of morphological dif- Devonian the region was located near Equator proba- ferences and eventually in genetic isolation, that is in bly not far from Australia (Domeier and Torsvik 2014). a speciation. To assume that speciation is a punctua- The lower part of the Toc Tat Formation exposed at the tional process is intellectually and methodologically Si Phai Pass near Dong Van in northernmost Vietnam counterproductive, as there is no way to distinguish the (105° 22Ј 33.05Љ 23° 16Ј 54.77Љ) in sedimentological real beginning of a species from a taphonomic hiatus terms represent the Griotte facies (Kö nigshof et al. or migrational event (Dzik 1999). In this paper we will 2017). They are mainly composed of pelagic limestone show that such exactly is the nature of first appear- (polymict stylobreccia), consisting of tightly packed ances and disappearances of conodont species near the clasts of pelagic bioclastic wackestone (Königshof et celebrated Frasnian–Famennian boundary (Klapper et al. 2017). Conodonts from the section were studied by al. 1993). We present results of study on a Vietnamese Ta Hoa (2007) who located the Famennian-Frasnian locality, remote in respect to the well-known Euro- boundary between samples S 12-8 and S 12-9 (Fig. 1) pean, Australian and North American sections of com- based on occurrence of Palmatolepis triangularis (ap- parable age. The new data show that although evolu- parently misidentified Klapperilepis ultima, as shown tionary successions were probably recorded over vast on Fig. 8K-S) in bed S 12-9. The thin-bedded part of Late Devonian oceanic realms, species successions the section composed of microbial automicrites and may differ dramatically in each of them. brownish shale layers immediately below sample S 12-8 was erroneously proposed to correspond to the Upper Kellwasser Event (Königshof et al. 2017, fig. 6). 2. Geological setting Among samples of other sections in the area studied by ourselves only the strongly tectonically deformed The Late Devonian carbonate rocks cropping out in the Ma Pi Leng Pass (105° 24Ј 37.43Љ 23° 14Ј 26.18Љ) has region at the northernmost tip of Vietnam are in conti- yielded conodonts of comparable age. The conodont nuity with those in the southern Yunnan Province of elements from there are strongly deformed (Fig. 2). 10 cm FAMENNIAN S12-12 K. triangularis Klapperilepis S12-11 Polygnathus A. curvata S12-9a Ctenopolygnathus Icriodus S12-9b Zone M.. linguiformis S12-8c S12-8a S12-8b Avignathus S12-7a A. lobata S12-7b Manticolepis winchelli S12-6 S12-5 S12-4 S12-3 FRASNIAN S12-2 Zone M. nasuta A B S12-1 C D A. nodosa Fig. 1. Si Phai section of the Frasnian–Famennian transition. (A) Exposure with beds’ numbers painted by Ta Hoa (2007). (B) Schematic presentation of the rock column with location of samples taken for this study. (C) Log of percent contribution of specimens of conodont species to samples. (D) Proposed Ancyrodella-based zonation for the section. eschweizerbart_xxx The Frasnian–Famennian boundary in Vietnam 329 A H B C D E F G I1 I 2 J1 J2 K1 K2 Fig. 2. Tectonically deformed elements from a sample taken from the Ma Pi Leng section. (A–E) Manticolepis jamieae (Ziegler and Sandberg, 1990), (A–B) P1 elements ZPAL 25/102, 103, (C) crushed but only slightly deformed P1 element ZPAL 25/101, (D) P2 element ZPAL 25/112, (E) M element ZPAL 25/113. (F–H) Kielcelepis cf. hassi (Müller and Müller, 1957), (F, G) probably undeformed juvenile and strongly deformed mature P1 elements ZPAL 25/100 and 122, (H) com- pressed P2 element ZPAL 25/111. (I) Ancyrodella nodosa Ulrich and Bassler, 1926, P1 element ZPAL 25/104. (J) Parapoly - gnathus brevis (Miller and Youngquist, 1947), P1 element ZPAL 25/105. (K, L) Polygnathus sp. nov. Dzik, 2002, P1 elements ZPAL 25/108 and 107. 3. Material and Methods eralogical electromagnetic separator. Conodont ele- ments were then picked with a wet hair mounted on a Sampling for this study followed the beds’ numbering preparatory needle handle. Selected specimens were (Fig. 1A) of Ta Hoa (2007). Samples of about 2 kg glued to SEM microscope stub with UHU stick glue weight were dissolved in 10–15% formic acid. The and coated with carbon and platinum. The elements residue was enriched for conodonts in the Franz min- show color alteration index (CAI) between CAI 4 and eschweizerbart_xxx 330 Jerzy Dzik et al. 5 (dark brown to black) as already reported by Königs - element of Ancyrodella (Fig. 2I) that fits in the onto - hof et al. (2017). Their preservation is generally poor genetic series of A. nodosa (Fig. 3E-J). This species but varies from sample to sample. Generally, thin beds has been already reported from the lower part of the near the base of the section yielded better preserved Si Phai section by Ta Hoa (2007). Parapolygnathus material than the thick beds above. (ʻPoly gnathusʼ) brevis and a probable member of the Specimens are housed at the Institute of Paleobiol- Avigna thus lineage (perhaps at the stage of evolution ogy, Polish Academy of Sciences, in Warsaw (abbre- prior to development of additional lateral processes, viated ZPAL). thus conspecific with Polygnathus sp. nov. Dzik, 2002) support the age determination as A. nodosa Zone. The samples taken by us from the lowermost part of 4. Identification of conodont the Si Phai Pass exposure were barren. Presumably the apparatus species layers S 12-1 to S 12-3 (the latter bed with flat pebbles) represent too shallow-water environment as for an Königshof et al. (2017) sampled the whole Si Phai sec- abundant occurrence of conodonts. The lowermost tion for conodonts. Our research is concentrated on the productive sample is S 12-4. No palmatolepidid S0 Frasnian–Famennian boundary strata. Beds of similar element has been found there and this precludes any age are widely distributed in the Dong Van Karst Pla- reliable species identification of the generalized pal - teau as shown by a sample from Ma Pi Leng Pass matolepidid, which is represented in the sample by P (Fig. 2). It has yielded numerous conodont elements elements and some S elements tentatively attributed to but they are strongly tectonically deformed. Resulting it.