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Early Crioceratites (heteromorphic ammonites) from the lower Hauterivian of south-eastern France: systematics, intraspecific variation and biostratigraphic implications

Abstract : Two acmes of the genus Crioceratites were recorded in the current Crioceratites loryi Zone (lower Hauterivian) in the Lower Cretaceous series of south-eastern France (Vocontian Basin), both in the classic section of the Cheiron ravine (Castellane area) and in the Hauterivian GSSP area at La Charce. The revision of an abundant material allows us to define Crioceratites claveli sp. nov. The first acme and the first part of the second acme correspond to the range of C. claveli sp. nov. and not to C. loryi as previously admitted. The remaining of the second acme is related to this latter species solely. The great abundance of C. claveli sp. nov. in the lower interval Horizon allowed a detailed analysis of its variation around 3 factors: (1) dimorphism; (2) multipolar variation of order two here characterized by an absence of correlation between the ornamental and morphological shell parameters (non-covariant factors); and (3) ontogenic heterochronies, which depend on the robustness of the ornamentation only. On the other hand, the northern edge of the Provençal platform delivered C. jurensis (revised here) from the top part of the Acanthodiscus radiatus Zone, which reduces the gap with the older Crioceratites known in the uppermost Valanginian. Finally, the study of the stratigraphic distribution of C. claveli sp. nov. and C. loryi leads to propose the new C. claveli (Sub)Zone instead of the C. loryi (Sub)Zone. This proposal for the south-eastern France may have extension potential for the Mediterranean Province of the Mediterranean Caucasian Subrealm (Tethyan Realm).
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Submitted on : Wednesday, May 26, 2021 - 11:54:16 AM
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Didier Bert, Stéphane Reboulet, Benjamin Vernet, Stéphane Bersac, Léon Canut. Early Crioceratites (heteromorphic ammonites) from the lower Hauterivian of south-eastern France: systematics, intraspecific variation and biostratigraphic implications. Cretaceous Research, Elsevier, 2021, 126, pp.104903. ⟨10.1016/j.cretres.2021.104903⟩. ⟨insu-03236518⟩

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