Abstract
The Hauterivian–Barremian series of the Jura Mountains were measured over more than 60 sections along a 200 km long transect between Aix-les-Bains (Savoie Department, France) and Bienne (Bern Canton, Switzerland), which prompted the need for a revision and improvement of the current lithostratigraphic scheme for this stratigraphic interval. A new formation, the Rocher des Hirondelles Formation, is proposed in replacement of the unsuitable Vallorbe Formation, while the Gorges de l'Orbe Formation is formally described. The Gorges de l'Orbe Formation, equivalent to the well-known “Urgonien jaune” facies, consists of two members, namely Montcherand Member and Bôle Member. The Rocher des Hirondelles Formation, equivalent to the “Urgonien blanc” facies, consists of three members, i.e. Fort de l'Écluse Member, Rivière Member and Vallorbe Member. The marly Rivière and Bôle members appear to present time-equivalent lithostratigraphic units, recording a major sedimentological event affecting contemporarily both formations. This study proposes a new sedimentary model opening a new point of view on the long-living controversies about the age of the Urgonian series from the Jura Mountains. The data point to strong diachronic ages of lithostratigraphic units with a late Hauterivian to early Barremian occurrence of the “Urgonian blanc” facies in the Meridional Jura area versus a latest Barremian age in the Central Jura area, reflecting a general progradation of the Urgonian shallow-water carbonate platform from the present-day Meridional Jura area toward external deeper-water shelf environments of the present-day Central Jura area and Molasse basin.
Highlights
The study of the Hauterivian and Barremian shallow-marine Urgonian series from the Jura Mountains has been very controversial from its inception, about 180 years ago, due to its highly complicated nature and 18 Page 2 of 47 A
1 Introduction The study of the Hauterivian and Barremian shallow-marine Urgonian series from the Jura Mountains has been very controversial from its inception, about 180 years ago, due to its highly complicated nature and Editorial handling: Wilfried Winkler. *Correspondence: antoine.pictet@unil.ch Musée Cantonal de Géologie, 1015 Lausanne, Switzerland the lack of benchmarks
Strasser et al (2016), who worked on the Lower Cretaceous series of the Jura Mountains, proposed the Gorges de l’Orbe Formation to replace facies terms such as ‘‘Urgonien jaune’’, “Urgonien inférieur” (Desor & Gressly, 1859) or “Russillien” (Jaccard, 1893), and the Vallorbe Formation to replace terms such as ‘‘Urgonien supérieur’’ or ‘‘Urgonien blanc’’ (Custer, 1928; Desor & Gressly, 1859)
Summary
The study of the Hauterivian and Barremian shallow-marine Urgonian series from the Jura Mountains has been very controversial from its inception, about 180 years ago, due to its highly complicated nature and 18 Page 2 of 47 A. In the course of the project, the lithostratigraphic nomenclature was updated and homogenised for a target scale of 1:25,000 under the direction of the Swiss Committee of Stratigraphy (Strasky et al, 2016) At this occasion, Strasser et al (2016), who worked on the Lower Cretaceous series of the Jura Mountains, proposed the Gorges de l’Orbe Formation to replace facies terms such as ‘‘Urgonien jaune’’ (sensu Remane, 1989), “Urgonien inférieur” (Desor & Gressly, 1859) or “Russillien” (Jaccard, 1893), and the Vallorbe Formation to replace terms such as ‘‘Urgonien supérieur’’ or ‘‘Urgonien blanc’’ (Custer, 1928; Desor & Gressly, 1859). As all previous works, this proposition was based on two largely accepted historical axioms: (i) carbonate platform progradation follows a NE-SW axis based on the strong reduction and disappearance of lithological units in direction of the NE due to an hypothetic proximity of emerged lands (Adatte, 1988; Favre, 1843, 1867; de Loriol & Gilliéron 1869; Steinhauser, 1969; Steinhauser & Charollais, 1971); (ii) main lithostratigraphic units uniformly and contemporaneously deposited through the Jura realm (e.g. Strasser et al, 2016, p. 12)
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