MESOZOIC

PALAEOGEOGRAPHY

Paleogeography

During the Late Jurassic, the domain of today’s northwestern Swiss Jura Mountains was located at the northern margin of the oceanic Ligurian Tethys and it was the central part of the large, structurally complex, subtropical North-Tethys carbonate platform (Ziegler, 1988; Dercourt et al, 1985, 2000; Smith et al., 1994). It was located at the threshold between boreal depositional areas to the northwest (Paris Basin) and the Tethys sea to the south, and thus subjected to influences from both the tethyan and boreal realm. The climate was subtropical (Bertling & Insalcao, 1998). The palaeolatitude of the Jura platform was approximately 26⁰ to 35⁰ N (Frakes et al., 1992; Smith et al., 1994; Thierry, 2000a, b), which corresponds to the subtropical zone (Fig.1).

Fig. 1: Palaeogeographical map for the Late Kimmeridgian. Modified from Thierry et al., 2000.

The western Tethys was already subject to sinistral translative movements between Africa and Laurasia induced by northward propagation of the Atlantic spreading axis (Ziegler, 1988). As a consequence of these movements, compressional stresses developed in the eastern parts of the Tethys, whereas in the western parts sea-floor spreading diminished. This and accelerated rifting in the North Atlantic led to a general thermal doming and tectono-eustatic sea-level fall, which caused widespread emergence of the Hercynian Armorican, London-Brabant, Central, and Rhenish, and Bohemian Massifs during Late Jurassic times (Late Kimmeridgian unconformity) (Ziegler, 1988), whereas especially the Rhenish massif was a major emergent area during the Oxfordian (Meyer & Schmidt-Kaler, 1989). The emergent massifs were the source for temporarily important terrigenous siliciclastic input into the Paris basin and onto the northern Tethyan shelf (Gygi & Persoz, 1986; Ziegler, 1988; Dercourt et al., 1985, 2000).

Paleoenvironment

On the platform a patchwork of large islands and/or smaller landmasses, which have been surrounded by large tidal flats with sub-, inter- and supratidal depositional environments and open to closed lagoons with variable degree of restriction, can be postulated (Marty et al., 2003).

Small-scale sea-level drops created vast emergent areas in a carbonate lagoon and tidal flat environment, as proved by the numerous track-bearing horizons (Billon-Bruyat & Marty, 2004; Billon-Bruyat et al., 2004). Terrestrial saurischian dinosaurs accessed the platform from the coastal zone of the “Süddeutsche Schwelle” in the northeast (Marty et al., 2003), which was located at the southeastern border of the London-Brabant Massif (Meyer & Schmidt-Kaler, 1989), or from the coastal zone of the Massif Central (Meyer & Lockley, 1996). During the Late Kimmeridgian, dinosaur could habitually enter in this coastal marine environment, as tracks occur on at least 14 levels at three stratigraphic different positions. Further, large saurischian dinosaur populations also suggest the presence of large vegetated areas as a food supply (Meyer & Lockley, 1996).