2009-2010 Russo-franco-latvian expeditions in the Main Devonian Field (North-western Russia)

In the frame of an international project between the Paleontological Institute of Moscow and the Museum of Paris, a Russo-Franco-Latvian team has been set up to prospect the Main Devonian Field in North-Western Russia (Novgorod and Leningrad Regions). This joined project started in 2009 (one month of field trip), continued in 2010 (one month also) and will end in 2011. The two first years were mainly devoted to the prospecting of historical localities, some discovered and/or exploited by Dmitry Obruchev himself. Such a method is effective but quite time-consuming; i.e. to rediscover the accurate location of the localities by discussing with denizens, to fathom the archives out and to access to non-weathered layers by removing the altered surface. Novgorod and Leningrad Regions are topographically excessively flat. Devonian fields have not been disrupted by tectonic movements and the layers are thus horizontal. Rocks are most often quite unconsolidated (consisting of loose sands or clays) and excavations are thus relatively easy. The lack of relief and the vegetal cover unfortunately lead to few outcrops in the landscape. They are all located along rivers (Lovat’, Syas' and Oredesh rivers for instance) or are represented by outliers. Although most of the localities were easily accessible by cars, others required several kilometers by feet and/or by boat. Roughly 30 localities have been prospected. About one third of them are very interesting such as Borshovo and Goryn' (Luga District) which provided numerous and exquisite fossils of placoderms, agnathans and sarcopterygians. The original locality of the Frasnian tetrapod Obruchevichthys in Russia, Sondala (Leningrad Region), has been rediscovered with near certainty.Origin, ecology and environments of the earliest tetrapods from the Upper Devonian (Frasnian) and paleogeography in the Eastern "Old Red Sandstone Continent"