The Upper Callovian Ammonites Cardioceratidae from Northern Siberia
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Upper Callovian Ammonites Cardioceratidae from Northern Siberia A. S. Alifirova, * and V. G. Knyazevb aTrofimuk
Institute of Petroleum Geology and Geophysics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia b Diamond and Precious Metal Geology Institute, Siberian Branch, Russian Academy of Sciences, Yakutsk, 677891 Russia *e-mail: [email protected] Received April 11, 2019; revised July 16, 2019; accepted November 20, 2019
Abstract—The study of Callovian ammonites Longaeviceras and closely related taxa from the east coast of Anabar Bay (section 109, northern Siberia) is presented. Genera and species previously unknown here, such as Rondiceras milaschevici, Pseudolongaeviceras densicostatum gen. et sp. nov., Platylongoceras holtedahli, and Pseudocadoceras laminatum, are identified. The presence of the Eboraciceras subordinarium Zone in the studied section is not confirmed. The division of genus Longaeviceras into Longoceras and Longaeviceras (including subgenus Soaniceras) is discussed. According to Cardioceras maltonense found in the upper part of the section studied, the age of the Oxfordian beds is defined more accurately. Keywords: northern Siberia, ammonites, Upper Callovian, nomenclature DOI: 10.1134/S0869593820050032
INTRODUCTION Ammonites of the family Cardioceratidae Siemiradzki, 1891, which existed from the Bajocian to Kimmeridgian, are of primary importance for stratigraphy of the Middle–Upper Jurassic deposits of the Panboreal subregion. This article presents new data on the taxonomy of the upper Callovian genus of Cardioceratides Longaeviceras and related taxa and considers previously unknown finds of Callovian and Oxfordian ammonites from the Jurassic section on the east coast of Anabar Bay. The genus Longaeviceras was widespread in the boreal and subboreal areas of the late Callovian. Its representatives, Peltoceras athleta or its boreal counterpart Keyserlingi, are a good indicator of the lower zone of the upper Callovian in Europe. The typical collection of cardioceratids from which this genus was isolated comes from the upper Callovian of England (Buckman, 1918 in Buckman 1909–1930; Callomon and Wright, 1989), while all the topotypes depicted in publications to date were represented by inner whorls of macroconchs. The characteristics of outer whorls, including the body chamber, were given for representatives of this genus collected by Sokolov (1912) from the basin of the Pechora River (Arkell et al., 1957; Meledina, 1977); they were described as other species. Thus, the species composition of the genus Longaeviceras consisted primarily of the species L. longaevum (Leckenby), L. placenta (Leckenby), L. nikitini (Sokolov), and L. keyserlingi (Sokolov). Subsequently, such
species as “L.” staffinense Sykes (lower Oxfordian), “L.” novosemelicum Bodylevsky (upper Callovian), and “L.” polonicum Callomon et Wright were also assigned to this genus. Some experts, however, noted the inconsistency between the morphology of these species and the generic diagnosis of Longaevicera
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