Foreword
The geopolitical status of Podolia has considerably changed during the past century as it was annexed by Poland, and then restituted to Ukraine as a member of the former USSR, and more recently of the CIS. Hence, many changes have occurred in the spelling of the locality names by the use of different languages and alphabets (Polish, Russian, Ukrainian and English). In the following, we will only use the English transliteration. The different transliterations were compiled thanks to Elga Mark-Kurik (Institute of Geology, Tallinn Technical University, Estonia) and Daniel Drygant (Ukrainian National Academy of Sciences, Lviv), and are given in the appendix.
1 Introduction
Podolia has yielded numerous Late Silurian and Early Devonian vertebrate remains (see exhaustive references in [30]).
The “agnathan” fauna (thelodonts, heterostracans, osteostracans) is by far the most important, considering both the number of available specimens and their stratigraphic distribution. Acanthodians [13,14] and chondrichthyans [13,15] have also been reported. It is noteworthy that placoderms have hitherto never been used as stratigraphic markers. Ninety localities were identified in the Lower Devonian of Podolia, mostly exposed along the Dnister river and around Ternopol, Ivano-Frankivsk and Chernivetky [30]. In this article, we will only retain the localities that yielded placoderm material.
2 Silurian–Devonian stratigraphy in Podolia
In Podolia, the Upper Silurian and Lower Devonian crop out as cuestas along the Dnister river and its northern tributaries. This series is uncomformably overlained by Mesozoic (Jurassic and Cretaceous) and Cenozoic (Neogene) sediments. The whole Palaeozoic sequence is structurally organised as a gently westward dipping monocline [2,18] (Fig. 1).
Simplified geological map of Podolia (Ukraine) and distribution of the studied “actinolepid” species (modified after [2], compiled after [31], pl. I; [16]; [5], fig. 2; [19], figs 1–4; [21], fig. 4) and of the genus Althaspis (within the North–South oriented strip; after the data of [30]).
Fig. 1. Carte géologique simplifiée de la Podolie (Ukraine) et répartition des espèces d’« actinolépides » étudiés (modifié d’après [2], compilation d’après [31], pl. I; [16]; [5], fig. 2; [19], fig. 1–4; [21], Fig. 4) et du genre Althaspis (à l’intérieur de la bande orientée nord–sud ; d’après les données de [30]).
The uppermost Silurian (Pridoli) includes the Malinovetski and Skala groups ([3], fig. 13). The Lower Devonian (Lochkovian and lower Pragian) is composed of the Borshchov, Chortkov and Ivane formations (Tiver “Super-Horizon”), and the Dnister “Series” (Fig. 2). This Dnister “Series” (or Babin Sandstones) is composed of the Old Red “unit” (classically divided into lower, middle and upper parts) and the Plant Group. The placoderm material was recovered from the Dnister “Series”; most specimens were collected on scree deposits. However, it is rather easy to reattribute most specimens to their original layers, based on the facies of their matrix.
Recapitulative table of the major lithic units of the Lower Devonian of Podolia, with main associated facies and faunas (after data from [2] [from [14,21,28]], [1,3,12,15,22,23]).
Fig. 2. Tableau récapitulatif des principales unités lithiques du Dévonien inférieur de Podolie (Ukraine), et principaux faciès et faunes associés (d’après les données de [2] [d’après [14,21,28]], [1,3,12,15,22,23]).
The “actinolepid” arthrodires studied herein come from the Babin Sandstones. Their lithology is typically of Old Red Sandstone facies, with reddish to green sandstones to silty sandstones, and interlayered micaceous and argillaceous beds. The darkest red sandstones occur at the base of the series, and related fossils are lightly coloured. At the top of the series, rocks are lightly coloured, and fossils are darker. Brotzen [6], Narbutas [18], Karatajute-Talimaa ([14], and in [3]) intented to define the boundaries between the three parts of this lithostratigraphic series (Fig. 3). It is noteworthy that some localities are still problematic. These three parts (or “zones” Old Red I, II, III in the older literature) were originally defined on the basis of their different lithofacies [7,14,18]. However, Blieck [2] identified only two different faunas in these red beds, mainly based upon both heterostracans and placoderms.
Zonation of theBabin SandstonesorOld Red Sandstones (ORS) considered by (A) [6,7], (B, C) [18], (D) Karatajute-Talimaa ([14] and unpublished data), and (E) D. Goujet's (pers. com. after unpublished data taken from the collection of V. Karatajute-Talimaa, Institute of Geology and Geography, Lithuania). Problematic localities in grey. Compiled by E. Mark-Kurik.
Fig. 3. Zonation des Grès de Babin ou Old Red Sandstones (ORS) considérés par (A) [6,7], (B, C) [18], (D) Karatajute-Talimaa ([14] et données non publiées), et (E) D. Goujet (com. pers., d’après des notes inédites prises dans les collections de V. Karatajute-Talimaa, Institut de géologie et de géographie de Lituanie). Les localités problématiques sont indiquées en grisé. Compilé par E. Mark-Kurik.
Contrary to the latter study, three zones can be distinguished, based upon a taxonomic revision of the actinolepids [9]:
- • a lower zone characterized by the occurrence of Kujdanowiaspis podolica (Brotzen, 1934) ([6]; Fig. 4A and B) and Erikaspis zychi (Stensiö, 1945; Fig. 4D and E) (Stensiö [29] described what he considered to be a new species of Kujdanowiaspis; however, an extensive study reveals that this taxon has to be considered as a new genus [11]);
- • a middle zone containing K. podolica, K. buczacziensis (Brotzen, 1934) ([6]; Fig. 4C) and E. zychi;
- • an upper zone characterized by the presence of K. buczacziensis only (Fig. 4F).
The three species of arthrodire placoderms involved in the Lochkovian–Pragian boundary in Podolia. A–B.Kujdanowiaspis podolica (Brotzen, 1934). C. Kujdanowiaspis buczacziensis (Brotzen, 1934). D–E. Erikaspis zychi (Stensiö, 1945). F. Stratigraphic distribution. A and D in left lateral view. B, C, E are subcomplete to incomplete dermal bony skull roofs in dorsal view. K. podolica and K. buczacziensis only differ in size and in the density and size of the tuberculated ornamentation. The dermal plate pattern of E. zychi differs from that of the genus Kujdanowiaspis. Midplanes of symmetry indicated on B, C, E in dashed lines. A modified from [10]: fig. 5; B modified from [9]: pl. 13A, specimen NHM P 18228; C modified after [9]: pl. 27A, specimen Pi 1204; D modified from [11]: fig. 3B; E modified after [11]: fig. 6C, specimen NHRM P 28559. The illustrated specimens are curated in: NHM, Natural History Museum, London, United Kingdom; NHRM, Naturhistoriska Riskmuseet, Stockholm, Sweden; Pi, Paleontological Institute, Tallinn, Estonia. All scale bars equal 1 cm.
Fig. 4. Les trois espèces de placoderme arthrodire évoquées dans le problème de la limite Lochkovien–Praguien en Podolie. A–B. Kujdanowiaspis podolica (Brotzen, 1934). C. Kujdanowiaspis buczacziensis (Brotzen, 1934). D–E. Erikaspis zychi (Stensiö, 1945). F. Répartition stratigraphique. A et D en vue latérale gauche. B, C, E : toits crâniens dermiques et osseux en vue dorsale, subcomplets à incomplets. K. podolica et K. buczacziensis ne diffèrent que par leur taille et par la densité et la taille des tubercules composant l’ornementation dermique. Erikaspis zychi se distingue notamment du genre Kujdanowiaspis par un patron du toit crânien différent et une tuberculation plus grossière. Les plans de symétrie bilatérale sont indiqués en pointillés sur B, C, E. A modifié d’après [10] : fig. 5 ; B modifié d’après [9] : pl. 13A, spécimen NHM P 18228 ; C modifié d’après [9] : pl. 27A, spécimen Pi 1204 ; D modifié d’après [11] : fig. 3B ; E modifié d’après [11] : fig. 6C, spécimen NHRM P 28559. Les spécimens illustrés sont conservés au : NHM, Natural History Museum, Londres, Royaume-Uni ; NHRM, Naturhistoriska Riskmuseet, Stockholm, Suède ; Pi, Paleontological Institute, Tallinn, Estonie. Toutes les barres d’échelles égale 1 cm.
3 The Silurian–Devonian (Pridoli–Lochkovian) boundary
Many geologists have been interested in the Silurian–Devonian succession of Podolia, because the marine sedimentation is continuous through the Pridoli–Lochkovian [20,24]. The base of the Devonian in Podolia coincides with the first occurrence of:
Therefore, the base of the Lochkovian would be situated just above the top of the Borshchov Formation.
It is noteworthy that the stratigraphic series through the Silurian–Devonian boundary near the villages of Volkovsky and Khudkovsty, on the northern edge of the Dnister river [21], differs from the GSSP of Klonk in the Barrandian basin (Czech Republic). According to Nikiforova [21], only the appearance of the trilobite Acastella heberti and the disappearance of the brachiopod Dayia bohemica coincide with the appearance of the graptolite M. uniformis angustidens at the base of the Tajna Formation and at the Silurian–Devonian boundary. Because of the biodiversification observed above this boundary, Nikiforova does not consider the appearance of M. uniformis uniformis as an index of the Lochkovian. Nevertheless, she recognizes that the Tajna Formation contains exclusively Pridolian fossils as compared to the Barrandian of Bohemia.
4 The Lochkovian–Pragian boundary
This boundary is more difficult to establish than the former one. According to the ICS, the Pragian starts with the appearance of the conodont Eognathus sulcatus sulcatus ([25], in [4], Tab. 2, p. 8). However, the Old Red Sandstone facies of the Babin Sandstones does not allow the preservation of such a biostratigraphic marker.
In Podolia, the Lochkovian–Pragian boundary was roughly correlated with the boundary between the Old Red I and II “zones” [2], according to the occurrence of the pteraspidid Althaspis elongata [31]. The genus Althaspis itself is present across the Lochkovian–Pragian boundary in western Europe (Fig. 1; [2], figs. 67, 71–73; [3], p. 246). In Podolia, A. elongata is collected in several localities which correspond to a roughly north–south orientated outcropping strip, from Beremyany in the east to Koropets in the west (Fig. 1). This strip displays in the field the Lochkovian–Pragian transition.
Considering the actinolepid placoderms, it is remarkable that Kujdanowiaspis podolica and Erikaspis zychi are situated in the eastern part of this strip and eastward from it, and that K. buczacziensis is found in its middle and western parts (Fig. 1). These taxa have thus a biostratigraphic value as well. When Brotzen [6] erected several new species of “acanthaspids”, he also provided their preliminary stratigraphic distribution. Denison [8] used all the arthrodire species too: K. podolica, K. buczacziensis, but also K. rectiformis, Phlyctaenaspis extensa, Acanthaspis prominens, A. vomeriformis and A. angusta (those latter being considered as junior synonym of K. podolica and K. buczacziensis by Dupret [9]).
5 Conclusion
It is proposed here to characterize the beginning of the Pragian with the appearance of K. buczcacziensis (Brotzen, 1934) (Fig. 4F). However, most of the specimens come from the base of the series, and only few specimens can be assigned with certainty to K. buczacziensis. As a conclusion, we consider that K. podolica and E. zychi are almost certainly Late Lochkovian and probably Early Pragian in age, and that K. buczacziensis is almost certainly Early Pragian in age.
Acknowledgments
The present article is an excerpt from V. Dupret's PhD thesis which was supervised by Pr. D. Goujet (MNHN, Paris). V.D. obtained financial support from the UMR 5143, département Histoire de la Terre (CNRS, MNHN) for a field expedition to Podolia. V. Voichyshyn and D. Drygant (Ukrainian Academy of Sciences in Lviv) provided much help during this field trip. Transliteration of the localities was essentially initiated by E. Mark-Kurik (University of Technology, Tallinn, Estonia), D. Drygant, and V. Karatajute-Talimaa (Lithuanian Institute of Geography and Geology, Vilnius, Lithuania). Translation of Russian literature was performed by B. Battail (MNHN).
Appendix English transliteration (from Ukrainian) for locality names
| English transliteration | Ukrainian | Russian | Polish | explanation |
| Barysh | Бариш | Барыш | Baryszka | river, Dnister Basin |
| Beremyany | Беремяни | Беремьяньі | Beremiany | locality, Strypa Basin |
| Bila | Била | Белая | Biała | river, Seret Basin |
| Bily Potik | Білий Потік | Белый Поток | Biale Potok = Potok Biały | locality, Seret Basin |
| Buchach | Бучач | Бучач | Buczacz | locality, Strypa b. |
| Buryakivka | Буряківка | Бураковка | Burakówka | locality, Juryn b. |
| Chervonograd | Червоноград | Червоноград | Chervonogród | locality Juryn b. |
| Chortkiv | Чортків | Чортков | Czortków | town |
| Dniester | Дністер | Днестер | Dnister | river |
| Dzvenygorod | Дзвенигород | Дзвенигород | Dźwinogród | locality, Strypa b. |
| Gorodnytsya | Городниця | Городницa | Horodnica | locality, Dnister b. |
| Ivanye | Iване | Иване = Иване-Золóтое | Iwanie | locality, Dnister b. |
| Juryn | Джурин | Джурин | Dżuryn | river, Dnister b. |
| Jurynka | Джуринка | Джуринка | Dżurynka | ruisseau, Juryn b. |
| Khmeleva | Хмелева | Хмелевая | Chmielowa | locality, Dnister b. |
| Kopachinski | Копачинці | Копачинци | --- | locality, Dnister b. |
| Khomyakivka | Хом’яківка | Хом’якoвка | Chomiakówka | locality, Seret b. |
| Koropets | Коропець | Коропец | Koropiec | locality, Koropets b. |
| Kydaniv | Киданів | Киданoв | Kujdanów | locality, Strypa b. |
| Mogylnytsya | Могильниця | Могильницa = Трудовое | Mogielnica | locality, Seret b. |
| Nagiryani | Нaгіряні | Нaгиряни | --- | locality, Juryn b. |
| Nezvyska | Незвиска | Незвиска | Niezwiska | locality, Dnister b. |
| Ostrivchyk | Острівчик | Островчик | Ostrowczyk | locality, Seret b. |
| Perevoloka | Переволока | Переволока | Przewłoka | locality, Strypa b. |
| Pidgaychyky | Підгайчики | Пoдгайчики | Podhajczyki | locality, Seret b. |
| Potochyshche | Поточище | Поточище | Potoczyska | locality, Dnister b. |
| Probabin | Пробабин | Пробабин | Probabin | locality, Dnister b. |
| Rabrovech | --- | Рабровеч | Rabriowiecz | locality, Dnister b. |
| Repintsy | Репінці | Репинцы | Rzepińce | locality, Strypa b. |
| Rizdvyany | Різдвяни | Рездвяны | Ruzdwiany | locality |
| Rublin | Рублін | Рублин | --- | locality |
| Rukomysh | Рyломиш | Рукомыш | Rukomysz | locality, Strypa b. |
| Sapova | Сапова | Сапова | Sapowa | locality, Strypa b. |
| Seret | Серет | Серет | Seret | river |
| Smerkliv | Смерклів | Смерков | Smerkłów | river, Dnister b. |
| Soroky | Сороки | Сороки | Soroki | locality, Strypa b. |
| Stinka | Стінка | Стинка | --- | locality, Dnister b. |
| Strypa | Стрипа | Стрыпа | Strypa | river |
| Terebovlya | Теребовля | Теребовля | Trembowla | town, Seret b. |
| Ternopil | Тернопіль | Тернополь | Tarnopol | town |
| Torske | Toрське | Торское | Torskie | locality, Dnister b. |
| Unizh | Уніж | Униж | Uniz | locality, Dnister b. |
| Ustechko | Устечко | Устечко | Uścieczko = Wojskie | locality, Dnister b. |
| Vilkhovets | Вільховець | Ольовец | Olchowiec | river, Strypa b. |
| Vistrya | Вістря | Вистря | Ostra | locality, Dnister b. |
| Zalishchyki | Заліщики | Залещики | Zaleszczyki | locality Dnister b. |
| Zalissya | Залісся | Залесье | Zalėsie | locality, Koropets b. |
| Zhyznomyr | Жизномір | Жизномер | Żyźnomierz | locality, Strypa b. |
| Zolota Lypa | Золота Липа | Золотая Липа | Złota Lipa | river |