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:
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