The lost paleosols: Masked evidence for emergence and soil formation on the Kimmeridgian Jura platform (NW Switzerland)

Abstract

Lagoonal carbonates of Kimmeridgian age in NW Switzerland formed in a tropical epeiric sea and exhibit indicators of subaerial emergence such as tidal biolaminites, desiccation cracks, flat pebble conglomerates, and fenestral structures. Additionally, 30 dinosaur tracksites from at least six stratigraphic intervals indicate repeated formation of land bridges between the platform and adjacent massifs. Populations of herbivorous and carnivorous dinosaurs necessitate substantial vegetation and consequently a soil cover, but no striking evidence of paleosols have been found within the track bearing sequences. However, two stratigraphic levels exposed in nine outcrops exhibit distinctive hardgrounds that experienced early meteoric diagenesis during times of emergence. Initial induration began with the precipitation of thin micritic meniscus cements. Contemporaneously meteoric waters completely dissolved all aragonite leaving large voids. Iron-hydroxides were precipitated in the uppermost 7-10 cm where they impregnated the porous micrite and constituted a separate cement generation, which caused a penetrative dark red staining. These aspects are suggestive of the formation of Mediterranean-type red soils on the emerged platform. During transgression, the soil was eroded and wavecut hardgrounds were superimposed on the hardgrounds formed during regression. Erosion is evidenced by micro-karst, truncated Gastrochaenolites isp. borings and the physical removal of steinkerns. The eroded material including floral remains provided surplus nutrients leading to eutrophication. This food-rich environment supported the mass-occurrence of gastropods in the nerineoid limestones and oysters (Nanogyra sp.) in the Virgula Marls.

The tracks of giant theropods (Jurabrontes curtedulensisichnogen. & ichnosp. nov.) from the Late Jurassic of NW Switzerland: palaeoecological & palaeogeographical implications

“…The widespread dinosaur track record of the Jura Mountains and the herein reported presence of giant theropods indicate that large parts of the Jura carbonate platform were emergent during several and prolonged time periods allowing the development of a soil (Waite et al 2013) and vegetation cover confirmed by an almost complete juvenile megalosaurid theropod specimen that was described by Rauhut et al (2012) from the Solnhofen Plattenkalke of Painten, SE Germany. This specimen is, as Jurabrontes, Late Kimmeridgian in age.…”

A new chondrichthyan fauna from the Late Jurassic of the Swiss Jura (Kimmeridgian) dominated by hybodonts, chimaeroids and guitarfishes

“…Marty ; Waite et al . ). A food source for the herbivorous dinosaurs was presumably present, and thus firm ground and freshwater must have been present in the vicinity.…”

Trace fossils from the Lower Muschelkalk of Raciborowice Górne (North Sudetic Synclinorium, SW Poland) and their palaeoenvironmental interpretation

“…In siliciclastic deposits, Thalassinoides is indicative of lower shoreface-offshore settings (Pemberton et al 2001;Uchman and Krenmayr 2004;Buatois and Mángano 2011;Chrząstek 2013;La Croix et al 2013). It is also reported from the inner-middle carbonate ramp (Knaust 1998;, and mostly from shallow carbonate deposits (Monaco and Giannetti 2002;Jach 2005;Waite et al 2008Waite et al , 2013Vlahovic et al 2011;Wiedl et al 2012Wiedl et al , 2013. Thalassinoides was described from the upper part of the shallowing upward cycle (Knaust 1998;Pérez-Valera and Pérez-López 2008;Pérez-López and Pérez-Valera 2012).…”