Ammonite assemblages in the Lower to Upper Kimmeridgian boundary interval (Cymodoce to Mutabilis zones) of Tatarstan (central European Russia) and their correlation importance

Abstract

For the first time upper part of the Cymodoce Zone sensu lato (mostly Askepta Subzone) of the Lower Kimmeridgian and the Mutabilis Zone of the Upper Kimmeridgian are described in detail from the Russian Platform. The most fully developed ammonite succession, which includes Boreal, Subboreal and Submediterranean faunal elements, is recognized in southern Tatarstan (Tarkhanovskaya Pristan and Memei sections). The lowermost assemblage, consisting of late representatives of Rasenia and Zonovia was found in the Memei section only (cf. Hantzpergue et al. 1998). Well above, numerous Submediterranean Crussoliceras occurrences were discovered in the upper part of the Cymodoce Zone of the whole area, whereas younger assemblages yielded Boreal Amoebites and/ or Subboreal Rasenioides followed by Aulacostephanoides with some addition of Aspidoceras and Orthaspidoceras above. The aulacostephanid genus Zenostephanus is recorded in the studied region for the first time. Significant lateral variability of the deposits of the Cymodoce and Mutabilis zones in thickness and completeness through a small distance in South Tatarstan along with other evidence suggests the strong influence of synsedimentary tectonics on sedimentation at the Early to Late Kimmeridgian transition of this region. Mass immigration of the Submediterranean ammonites Crussoliceras into the Subboreal Russian Sea resulted in their short-time dominance over a wide area. The Crussoliceras ammonites are recognized also in the condensed sections of the Moscow and Kaluga areas in the north, and their re-deposited records are known (along with uncommon Zenostephanus, Aulacostephanoides and Amoebites) from the basal phosphorite band of the Middle Volgian of the Unzha river (Kostroma area). This "Crussoliceras event", which is well-recognized in Submediterranean areas, as well as the subsequent expansion of Zenostephanus, both correspond to a sea-level high-stand, which resulted in faunal mixing of ammonites indicative of different bioprovinces. They provide key correlative levels which can be recognized around the Lower/Upper Kimmeridgian boundary, especially in the ecotone area of the Russian Sea. These levels include also occurrences of Crussoliceras, Rasenoiodes and rare Amoebites of the kitchini group in the Askepta Subzone, of Aulacostephanoides spp. along with Amoebites peregrinator and Zenostephanus sachsi in the lower part of the Mutabilis Subzone as well as of Aspidoceratidae and Aulacostephanoides in higher parts of this subzone, followed by Orthaspidoceras. At least six successive ammonite assemblages can be recognized through the studied part of the Kimmeridgian, providing interregional correlation with Submediterranean and Boreal sections.

The first record of Late Jurassic megateuthidid belemnites - Chuvashiteuthis aenigmatica gen. et sp. nov. from the upper Kimmeridgian of Central Russia

“…Lowermost level A, belonging to the bayi horizon of the lower Kimmeridgian, is known from the Kostroma region only (Głowniak et al 2010). Level B, characterized by both aspidoceratid ammonites and laevaptychi expands over the upper Kimmeridgian mutabilis Zone, with exception of its presence in lowermost part (Rogov et al 2017). Most well-recognizable level C is also characterized by numerous occurrences of Aspidoceras spp., and is spanning across the upper part of the eudoxus Zone.…”

The ammonite faunas of the upper Hypselocyclum to Divisum zones (Lower Kimmeridgian, Upper Jurassic) at Małogoszcz, Holy Cross Mts., central Poland: their stratigraphical interpretation and evolutionary development

“…The changes in distribution of ammonites were accompanied by important development in their evolution. Such a drastic example of overlapping of ranges of distribution of the ammonite faunas belonging to different lineages and representing the various stages of their evolutionary development has been reported in the successions of central and southern parts of the Russian Platform, especially Tatarstan, central European Russia (see Rogov et al, 2017). The recognized there a narrow stratigraphical horizon with Submediterranean Crussoliceras atavum (Schneid) -C. lacertosum (Fonatnnes), possibly corresponds only to some upper parts of the Divisum Zone, and it is underlain by beds with Subboreal Rasenia and Zonovia, and overlain by beds with Rasenioides, all of them belonging to the upper part of the Cymodoce Zone -the Askepta Subzone.…”

“…The genus evolved probably from the Subboreal Rasenia evoluta, as evidenced by occurrence of the intermediate forms already at the end of the Cymodoce Chron in southern England (Birkelund et al, 1983). These migrated successively into the Arctic areas of the Boreal Province at the boundary between the Early and Late Kimmeridgian as a consequence of a large transgression giving then the onset to the new lineage (e.g., Wierzbowski & Smelror, 2020), but appeared soon thereafter as representatives of the fully developed genus Zenostephanus in north-eastern Europe in areas of the Russian Sea (Rogov et al, 2017). The genus can be considered as a possible forerunner of a group of the Late Kimmeridgian Aulacostephanus, widely distributed in NW, central, and NE European areas, as already suggested by Birkelund & Callomon (1985), which assumption has a large consequences for interpretation of the phylogenetical pattern of development of Aulacostephanidae.…”

New data about Upper Jurassic formations of the Ulyanovsk-Saratov through and the northern part of the Peri-Сaspian Syneclise

“…геля. Здесь свита с размывом залегает на разных горизонтах средней юры, в ее основании часто присутствует прослой окатанных фосфоритовых конкреций[21]. В нижней части свиты присутствует прослой горючих сланцев.История изучения свиты.…”