Author's name : Yves SUDREAU

 Title : The restoration of nappe-thrust parautochtonous units. The use of balanced cross-sections concept. The study of several cases around Marseilles.
 

The purpose of this work concerns applications of restoration methods upon overthrusted parautochtonous units beneath Etoile nappe-thrust in the neighbourhood of Marseilles (Provence, France).
The restoration of carried imbrications below nappe-thrust is made from the analysis of thrust surfaces geometry and use of balanced cross-section techniques.
The studied example is the restoration of parautochtonous structures from the northern front of Etoile, Allauch hills and Sainte-Baume massif.
Known data and conceptions peculiar to regional model are compared with new methods of analysis of thrust surfaces geometry and the concept of balanced cross-sections.
Although these new methods are more general, they are applied to many thrusted structures and are also more accurate since they imply several direct and simple rules.
Thus we restore with these rules. According to the available information types, various methods are applied :
        - Cartographical restoration with cutt-off lines.
        - Cross-section balance with graphical software.
        - Cross-section area.
Without data to evaluate the slip from geometrical arguments, restoration will be made from stratigraphic discriminations between autochtonous, parautochtonous and allochtonous units. The use of these methods may define autochtonous structures before the emplacement of nappe thrust by paleostructures inherited from albocenomanian and maastrichtian stages. These previous structures explain some anomalies and involve some more general results which go beyond the regional framework. Thus several structural rules are adjusted with these previous structures.
 

e-mail : ysudreau@free.fr