ISSN 00310301, Paleontological Journal, 2011, Vol. 45, No. 4, pp. 379–389. © Pleiades Publishing, Ltd., 2011. Original Russian Text © V.V. Mitta, Jingeng Sha, 2011, published in Paleontologicheskii Zhurnal, 2011, No. 4, pp. 26–34. Ammonite Distribution Across the Jurassic–Cretaceous Boundary in Central Russia V. V. Mittaa and Jingeng Shab aBorissiak Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya ul. 123, Moscow, 117997 Russia email: [email protected] bLPS, Nanjing Institute of Geology and Paleontology, Chinese Academy of Science, No. 39 East Beijing Road, Nanjing, 210008 China email: [email protected] Received November 9, 2010 Abstract—The distribution of ammonites across the Jurassic–Cretaceous boundary of the central part of the Russian Platform is discussed. The nomenclature of Craspedites nodiger (Eichwald, 1962) and Hectoroceras tolijense (Nikitin, 1881) is updated. A new species, Craspedites ultimus sp. nov., is described from the basal horizons of the rjasanensis Zone (Ryazanian Stage). The Hectoroceras tolijense and Hectoroceras kochi faunal horizons lying between the nodiger and rjasanensis zones are united in the kochi Zone of the basal Ryazanian. Previous opinions suggesting a hiatus between the Volgian and Ryazanian stages are reviewed and rejected. Keywords: ammonites, Craspedites, Hectoroceras, Ryazanian Stage, Volgian Stage, Russian platform. DOI: 10.1134/S0031030111040083 INTRODUCTION of different authors on the correlation of the Boreal scales with the presumably uninterrupted Tithonian– The Boreal–Tethyan correlation has been a major Berriasian zonation. However the continuous succes problem for MidMesozoic biostratigraphy. The sepa sion in the interval is not confirmed, as the upper ration of marine basins at the end of the Jurassic led to Tithonian zone (Durangites) is insufficiently studied in the formation of strongly differentiated faunas of dif the stratotype region and still has no index species. ferent origins, Boreal and Tethyan (Submediterra The taxonomic composition and distribution of nean). This presents considerable difficulties for cor ammonites in the jacobi Zone, which is presently con relation of the terminal Jurassic and basal Cretaceous. sidered to be the basal Berriasian zone, are also insuf Consequently, two parallel stages are recognized in the 1 topmost Jurassic (Tithonian in the submediterranean ficiently studied. paleogeographic regions and Volgian in the Boreal Realm); and in the lowermost Cretaceous (Berriasian Mesezhnikov and his colleagues from Leningrad in Submediterranean Province and Ryazanian in the (now St. Petersburg) and Novosibirsk came to a differ Boreal Realm). To reliably establish correlation mark ent conclusion in the 1970s after paleontological and ers, the primary task is to examine the systematic com stratigraphic study of the Jurassic–Cretaceous beds in position and stratigraphic distribution of the guide fos the Ryazan Region. In several outcrops near the vil 2 sils (primarily ammonites, the most important orthos lage of Kuzminskoe in the basin of the Oka River, his tratigraphic group) in regions with the highest group found Late Volgian Garniericeras subclypeiforme potential for Boreal–Tethyan correlation. (Milaschevitsch) in association with the Ryazanian Most authors studying the biostratigraphy of the Riasanites rjasanensis (Nikitin), and R. cf. swistow Jurassic–Cretaceous boundary beds suggest a hiatus between the Volgian and Ryazanian stages (Casey, 1 This Zone in its modern understanding unites the jacobi Zone 1973; Sasonova, 1977; etc.). This hypothesis is based (previously considered to be terminal for the Tithonian) and the grandis Zone (basal Berriasian Zone) of the standard scale. Tak on sharp differences in the composition of the ammo ing priority into account, the zone in its new definition should nite faunas in the Upper Volgian (the fauna repre have been assigned to the Tithonian, and the Berriasian begun sented solely by craspeditids of Boreal origin, i.e., from the occitanica Zone Craspedites and Garniericeras) and at the beginning of 2 These outcrops have been known in the geological literature for the Ryazanian (where ammonites of Tethyan origin a long time. However Pavlow (1894) and Bogoslowsky (1896) indicated the presence of “Oxynoticeras” subclypeiforme and are found in association with younger craspeditids). Craspedites spp. below beds with Riasanites. For a more detailed The duration of this interval in the Russian Platform is historical review and a scheme showing the locations see Mitta estimated differently, depending on the interpretation (2007). 379 380 MITTA, JINGENG SHA (a) (b) М Bed Stage Surites 1.5 spasskensis 6 Riasanites Valanginian rjasanensis 5 5 Riasanites Rjasanensis 4 swistowianus 4 3 Ryazanian Hectoroceras Ryazanian 3 kochi 2c 2 Kochi Hectoroceras 2b 0.5 tolijense 2a 1 Craspedites milkovensis 1 Volgian Craspedites Volgian Nodiger nodiger Fig. 1. Diagrams showing (a) section of the Jurassic and Cretaceous boundary beds near the village of Kuzminskoe, Ryazan Region and (b) ammonoidbased biostratigraphic scale of the upper part of the Volgian–lower part of the Ryazanian. Explana tion: (1) quartz sand, (2) glauconitic sand, (3) clayey sand, (4) sandstone, and (5) phosphorites. ianus (Nikitin) in a thin (up to 0.3 m) sandstone bed RESULTS AND DISCUSSION (Casey et al., 1977; Mesezhnikov et al., 1979). Sum marizing these results, it was suggested that the lower Lithological Description of the Section zone of the Ryazanian Stage (Riasanites rjasanensis) Several exposures dug 5–6 m apart approximately should be interpreted as a “hyperzone” with three 200 m upstream of a dam, near the village of Kuzmin included zones: (1) rjasanensis/subclypeiforme Zone, skoe on the right bank of the Oka River open the fol with Riasanites spp., Euthymiceras spp., Garniericeras lowing beds (from bottom to top, Fig. 1a): subclypeiforme (Milaschevitsch), Craspedites ex gr. (1) Greenishdarkgray glauconitic sand. Visible kaschpuricus (Trautschold); (2) rjasanensis/kochi thickness 0.35 m. Zone, with Hectoroceras kochi Spath, Schulginites sp., Craspedites ex gr. kaschpuricus (Trautschold), Riasan (2) Indistinctly bedded reddishbrown sandstone, ites spp., Euthymiceras spp.; (3) rjasanensis/spassken ochreous on the weathered surface and black or dark sis Zone, with Surites (Surites) spasskensis (Nikitin), gray on the freshly broken surface. Thickness 0.3 m. S. (Caseyiceras) spp., Externiceras solovaticum (Bog The bed consists of three smaller beds, each 0.1 m thick. oslowsky), Borealites suprasubditus (Bogoslowsky), The lower bed (2a), is strongly ferruginous and almost Riasanites spp., Euthymiceras spp. (Mesezhnikov, completely covered by a continuous iron oxide film on 1984). Taking into account the association of late Vol the freshly broken surface. The bed contains infrequent gian and Ryazanian ammonites, Mesezhnikov con Craspedites ex gr. nodiger (Eichwald)/kaschpuricus cluded that there was no gap between these two stages. (Trautschold) (Pl. 3, figs. 1, 2), and Garniericeras sub However his research, primarily on the taxonomy of clypeiforme (Milaschewitch) (Pl. 3, fig. 3). The middle these ammonites and their description, was not con bed (2b) did not contain fossils. The upper (2c) bed tinued, and in the later papers (Abbink et al., 2001; contained numerous poorly preserved R. swistowianus Wimbledon, 2008) a gap between the Volgian and Rya (Nikitin) (Pl. 3, figs. 5, 6), a few R. cf. rjasanensis zanian stages was still assumed. (Nikitin) and Chetaites sibiricus Schulgina (Pl. 3, fig. 7), and a fragment of Craspedites cf. ultimus sp. nov. In 2006, Russian and Chinese workers undertook joint field work studying the Ryazanian Stage and (3) Brownishgray and brown clayey sand in places underlying beds in the Moscow and Ryazan regions. becoming sandy clay. Thickness 0.0–0.15 m. Repeated collection in the outcrops near the village of (4) Phosphoritic, stained brown and gray sand Kuzminskoe supported the conclusion of Mitta (2006) stoneconglomerate. The fossils are usually poorly about the immediate contact of beds with the Late Vol preserved and are represented by fragments. A few rel gian and Ryazanian ammonites. In this paper we will atively complete specimens of Riasanites rjasanensis discuss these and other recent data. (Pl. 3, fig. 4) were also found. Thickness 0.1–0.35 m. PALEONTOLOGICAL JOURNAL Vol. 45 No. 4 2011 AMMONITE DISTRIBUTION ACROSS THE JURASSIC–CRETACEOUS BOUNDARY 381 (5) Brownishyellow loosely cemented quartz zanian Stage of the Moscow Basin. The morphology sandstone. Thickness 0.15–0.2 m. of the new species suggests such a close relationship (6) Lightcolored and yellow, quartz sand. The vis with the Jurassic C. nodiger, that it removes any doubt ible thickness under the layer of soil is 0.45 m. that there was not a significant gap between the nodiger In bed 1, previous workers (Pavlow, 1894; Bog and rjasanensis zones. oslowsky, 1894, 1896; Mesezhnikov et al., 1979) found The Volgian Craspedites, as noted previously by Kachpurites, Garniericeras catenulatum (Fischer) and Mitta (2010), requires revision. Note that the repre other Late Volgian craspeditids, which indicated the sentatives of this genus in the Upper Substage of the Upper Volgian fulgens Zone (and, possibly, the subditus Volgian Stage of the Russian Platform in fact belong to Zone). the same phylogenetic lineage. The macroconchs of Bed 2a also contains the Upper Volgian fauna Craspedites [C. okensis (auct.) C. subditus (Traut (upper part of the nodiger