Silurian acanthodian biostratigraphy of Lithuania Juozas VALIUKEVIČ IUS Institute of Geology and Geography, T. Š evč enkos 13, 03223 Vilnius (Lithuania) valiukevicius@geo.lt Valiukevič ius J. 2005. — Silurian acanthodian biostratigraphy of Lithuania. Geodiversitas 27 (3) : 349-380. ABSTRACT Silurian acanthodian associations from western Lithuanian deep shelf grapto- lite facies and eastern Lithuanian shallow shelf and lagoonal carbonate facies are described and biozonation (Interval range zones) based on stratigraphic ranges of 45 taxa deduced. The Wenlock Series is characterized by the species-poor Arenaceacanthus arcuatacanalis-Gomphonchus? minutus Acanthodian Zone in east Lithuania, whereas in west Lithuania both of these zonal species occur later, in the Ludfordian (Ludlow). The Nostolepis gracilis and Rohonilepis breviornatus acanthodian zones occur at the end of the Ludlow in these two areas. The Fecundosquama basiglobosa Acanthodian Zone is distinguished in the formations of the Upper Minija Regional Stage (Pridoli) and has a wider regional distribution (discovered also in Latvia, KEY WORDS Estonia and former East Prussia). The latest Pridolian J ū ra Formation is sub- Silurian, divided into four acanthodian zones (from lowest to highest), the Nostolepis Wenlock, Ludlow, alta, Cheiracanthoides planus, Vesperalia perplexa and Endemolepis inconstans Pridoli, zones, and its eastern correlative the Lapė s Formation into three, the Mono- acanthodian microremains, spina erecta, Cheiracanthoides planus and Endemolepis inconstans zones. The faunal associations, biostratigraphic zones, acanthodian associations are the most abundant microvertebrates and are Lithuania. distinguished by the dominance of Nostolepis-derived taxa. RÉSUMÉ Biostratigraphie des acanthodiens du Silurien de Lituanie. Les associations d’acanthodiens du Silurien dans des faciès à graptolites de plateau continental profond en provenance de l’ouest de la Lituanie sont décrites ainsi que celles trouvées dans des faciès carbonatés lagunaires et de plateau continental peu profond de l’est de la Lituanie. La biozonation fondée sur les extensions stratigraphiques de 45 taxa est établie. Les séries du Wenlock sont caractérisées par la zone à acanthodiens pauvre en espèces à Arenaceacanthus arcuatacanalis-Gomphonchus ? minutus dans l’est de la GEODIVERSITAS • 2005 • 27 (3) © Publications Scientifiques du Muséum national d’Histoire naturelle, Paris. www.geodiversitas.com 349 Valiukevič ius J. Lituanie, alors que dans l’ouest de la Lituanie, ces deux espèces de zones appa- raissent plus tard, dans le Ludfordien (Ludlow). Les zones à acanthodiens à Nostolepis gracilis et Rohonilepis breviornatus sont connues à la fin du Ludlow dans ces deux régions. La zone à acanthodiens à Fecundosquama basiglobosa est retouvée dans les formations de l’étage régional de la partie supérieure de Minija (Pridoli) ; elle a une distribution régionale plus vaste (découverte aussi en Lettonie, Estonie et dans l’est de l’ancienne Prusse). La Formation J ū ra MOTS CLÉS datée du Pridoli terminal est subdivisée en quatre zones à acanthodiens (de la Silurien, plus ancienne à la plus récente) : les zones à Nostolepis alta,à Cheiracanthoides Wenlock, Ludlow, planus,à Vesperalia perplexa et à Endemolepis inconstans.Son équivalent orien- Pridoli, tal, la Formation Lapė s, est, quant à elle, partagée en trois zones : à Monospina microrestes d’acanthodiens, erecta,àCheiracanthoides planus et à Endemolepis inconstans. Les associations associations fauniques, zones biostratigraphiques, d’acanthodiens constituent les microvertébrés les plus abondants et elles se Lituanie. remarquent par la prédominance des taxa dérivés de Nostolepis. INTRODUCTION The black, graptolitic sediments are considered to have formed on an open deep shelf in the Silurian rocks of Lithuania are a classic example Ludlow. Borehole cores from the eastern part of of multifacial sediments with marine deep shelf this area are only characterized by graptolites in (western part) and marine shallow shelf and the lower Ludlow. Upwards, carbonate clays and lagoonal (eastern and easternmost part) facies. clayey limestones prevail. This part of the basin Alongside these, is an intermediate strip contain- was a deep shelf in the early Ludlow, then a shal- ing interfingering of beds from both principal low shelf in the late Ludlow and Pridoli. facies fields. This strip occupies a submeridional The shallow shelf and lagoonal sediments (carbo- area incorporating localities (from south north- nate clays, dolomitic marls, nodular limestones, wards) Vilkaviš kis-128, Sutkai-87, G ė luva-99, dolomites) dominant in eastern Lithuania lack Kunkojai-12 boreholes (Fig. 1B) and continues graptolites, but yield diverse shelly benthic and farther north to the Latvian border. A clearcut nektonic faunas. Lagoons existed here during the subdivision of the territory into facies areas is entire Ludlow with short-time exceptions. For complicated because of the water depth and type example, the Sudervė limestones of the Neris of deposition changing over time. The distri- Formation accumulated on the shallow shelf. bution shown in Figure 1B follows published Later, in the Pridoli, shallow shelf sedimentation opinions of Silurian researchers who have inter- prevailed, with formation of nodular-detrital car- preted lithology and facies according to the bonate facies, as exemplified by the red-colored structural-tectonical development of different dolomitic marls and dolomites of the upper part parts of the sedimentary basin (Paš kevič ius 1973, of the Lapė s Formation. Numerous sedimentary 1979, 1994; Paš kevič ius et al.1986; Paš kevič ius gaps distinguish the easternmost stratigraphical & Brazauskas 1987; Lapinskas 2000). It is princi- sections comprising the lagoonal dolomites and pally based on the Late Silurian deposits which dolomitic marls of the Pabradė Formation. yielded most of the acanthodian assemblages The biostratigraphical zonations of different fos- summarized in this study. The western Lithua- sil groups are the basis for the dating geological nian area is dominated by the maximally thick formations and their assignment to the Inter- series of black argillaceous and carbonate clays, national stratigraphical scheme. In Lithuania, this plus marls, and contains rare limestone interbeds. is most completely achieved by graptolites 350 GEODIVERSITAS • 2005 • 27 (3) Silurian acanthodian biostratigraphy of Lithuania 1200 k m A B a r ents S ea N o r w e g ian S ea Atlantic Ocean S w e d en F i nland N o r t h N o r w a y S ea I r eland E s ton i a R u ssi a D enm a r k B altic L a t v i a U n ite d Kin g d om S ea L ith u ani a N e t h e r land s B elar u s B elgiu m G e r m any P o land L u x e m b u r g B a yof C z e c h B i s cay F r anc e R e p u b l i c U k r a i ne S l o v a k i a S w itz e r land A u s t r i a H u n g a r y M o l d o v a S l o v eni a P o r t u g al I t aly R omani a C r o a tia Spa i n B i H S e r b i a - M o n t . B lack s ea B u l g a r i a F Y R O M A l b ani a M e d iterranean S ea G r eec e AFRI CA B L A T V I A 1 3 7 2 4 1 8 ea S 1 6 2 2 5 2 3 2 3 altic 7 B 6 1 44 12 L I T H U A N I A 1 1 7 9 11 99 2 99 87 V i lni u s R U SSI A 128 B E L ARU S P O L A N D 5 0 k m 1 7 2 3 F IG. 1. — Map of Europe showing position of Lithuania ( A ) and a sketch with location of Lithuanian boreholes yielding the majority of the material studied ( B ). Borehole and its original number; 1 , Stoniš kiai; 7 , Krekenava; 8 , Stač i ū nai; 11, Š e š uvis; 12, Kunkojai; 44, Nida; 61, Viduklė ; 87, Sutkai; 99, G ė luva; 128, Vilkaviš kis; 137, Liepkalnis; 162, Kurtuvė nai; 179, Ledai; 241, Butkū nai; 252, Svė dasai; 299, Joč ionys; 323, Graž utė . Legend: 1 , outcrop-boundary of Silurian rocks; 2 , borehole and its original number; 3 , boundary between the west and east Lithuanian facies of Silurian rocks. GEODIVERSITAS • 2005 • 27 (3) 351 Valiukevič ius J. (Paš kevič ius 1965, 1973, 1979, 1994), cono- Beds of the Neris Formation, which corresponds donts (Brazauskas 1987, 1989, 1993), ostracodes to its entry point into the sequence in the upper (Sidaravič ienė 1986, 1997; Sidaravič ienė in part of the Ventspils Formation in the L ūžni-4 Paš kevič ius et al.1994; Paš kevič ius 1994), bra- borehole core in west Latvia (Valiukevič ius chiopods (Paš kevič ius 1958, 1963, 1965; 2003b, 2004b). Thus, the regional lower boun- Musteikis & Puura 1983; Musteikis 1985, 2002; dary of the N . gracilis VZ should be lowered in Musteikis & Paš kevič ius 1999) and vertebrates the Baltic to the late Ludfordian. In Lithuania, (Karatajū t ė -Talimaa 1962, 1968, 1970, 1978; Poracanthodes punctatus Brotzen, 1934 occurs Karatajū t ė -Talimaa et al.1987; Karatajū t ė - through all of the Pridoli, and a correction of its Talimaa & Brazauskas 1994; Talimaa 2000). position as a regional and standard Silurian zonal However, trilobites, bivalves, gastropods and fossil is also needed. Nostolepis alta Märss, 1986 cephalopods are also known, but are less useful occurs through the entire J ū ra Formation in west for detailed zonations. Lithuania, where the lower Girdž iai Beds correla- Previously, Lithuanian acanthodians have not te with the uppermost Kaugatuma Stage in been used for stratigraphical purposes.
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