Report on 2011 Geological Mapping project For the Class of 2005 Mapping Fund Castellane Nathan Allen & Emma Woodward Overview of the mapping area Castellane in the southern sub-Alpine chains – approximately 100km NW of Nice in southeast France – is world-renowned for its ammonite fauna (including a stratotype location) and lies in the ‘Réserve Géologique des Alpes de Haute Provence’. The mapping area was centred around the villages of Chasteuil and Taloire at the head of the spectacular Verdon gorge, where the Mesozoic strata record a facies shift from platform to basin (in both time and space); since deformed during the Pyrenean and Alpine orogenies. Project objectives • Identify and define lithological units of the area • Interpret the transition between platform and basin in both time and space; and determine the depositional environments • Investigate structural relationships and attempt to deduce deformation history This work was carried out over July and August 2010 (see below). Total duration of field trip 35 days Duration of fieldwork 28 days Total area mapped 34km2 Transport to and from mapping area On foot Transport around mapping area On foot Hours spent daily in field 06:00 – 16:00 Temperature range 4˚C (early morning) – 38˚C (midday) Accommodation Camping Gorges Verdon (all geology within 3 hours walk) Land use Mixture of natural scrub, private grazing land, and artificial forest. Geological summary The Mesozoic carbonate sequence of Castellane, southeast France, records a transition from basinal (“Dauphinois”) pelagic facies in the north to platform (“Provençal”) neritic facies in the south; although this zone of transition is poorly studied and understood, despite excellent exposure and plentiful fossils. Studying the lithologies and field relationships of the units has allowed detailed reconstruction of the depositional environments, palaeobathymetry, and structural history of the area. The French subalpine basin, a gulf on the NW margin of the young Tethys Ocean, began is development in the Late Triassic. Shallow-water facies dominated the mapping area until a transgression at the End-Tithonian, and a basinal environment persisted throughout the Cretaceous; at the end of which compression from the Pyrenean Orogeny uplifted the region. The Alpine Orogeny compressed the area further, reactivating structures from the Pyrenean compression and original Tethyan rifting, causing the Mesozoic sedimentary cover to slip in a classic example of thin-skinned tectonics, forming the nappes of the present-day 100km Castellane Arc (a Cenozoic fold-and-thrust belt), which forms a bundle of folds whose apex is located in the Castellane area. Mesozoic normal faults determine planes of weakness which have been reactivated in various ways in the Cretaceous and Tertiary tectonic deformations, and this earlier structure is preserved and its inheritance plays a major role in present-day configuration. Looking North, Verdon River View from the North Rim Final Map: .