SOURCE-TO-SINK EVOLUTION OF A SUPRADETACHMENT BASIN UNRAVELED BY DETRITAL APATITE FISSION TRACK ANALYSIS: THE GEDIZ GRABEN (MENDERES MASSIF, WESTERN TURKEY)
Résumé
The Tertiary evolution of the Aquitaine basin (northern Pyrenean foreland) is closely linked to
the Pyrenean orogeny and its northern retrowedge. During the Middle Eocene maximum of
Iberia- Eurasia collision (Ypresian- Bartonian) strong denudation of the mountain belt takes
place, partly compensated by the subsidence of the foreland. In the Aquitaine basin this period
is registered by the progressive transition from dominantly marine underfilled sedimentation
to continental overfilled sedimentation. In the proximal part of this system, this overfilling
leads to a massive, kilometer thick, conglomeratic sedimentation while deltaic sedimentation
progressively fills the basin from east to west.
This study focuses on the proximal part of this system in order to characterize (1) the dynamics
of the piedmont sedimentation and its relation to tectonics, climate and denudation of
the orogen, and (2) the transfer of sediments from the piedmont towards more distal areas
, through the definition of types of sedimentary systems and identification of zones of trapping
and bypass . Field study of the syn-orogenic Palassou conglomerates and molasses de
Carcassonne from Mouthoumet massif to Lavelanet has been coupled with interpretation of
subsurface (well logs and seismic profiles) in order to characterize the geometries and contents
of these deposits.
The Ypresien – Late Bartonian system is organized along two main megasequences:
- A continued progradation during Ypresian from deltaic to proximal braided stream
and sheet flood deposits. Clasts are mainly composed of meso-cenozoic cover. This prograding
trend accompanies the onset of thrusting in the foreland. The following retrograding trend
takes place during Lutetian with the sedimentation of lacustrine and floodplain deposits with
intercalated coarse sheet flood deposits.
- The second megasequence displays a major progradation with proximal braided
stream to alluvial fan deposits which traduces uplift and incision of the piedmont. This sequence
register the first input of material derived from the axial zone.
These two sequences display significantly different geometries revealing strong different
controls by tectonics and sediment supply and evolving sediment routing. While the first -underfilled-
sequence is strongly controlled by the deformation of the foreland, the second one is more widespread with limited control of the deformation and progressive sealing of the structures.
Thermochronology as well as refined datations and correlations will complete this early results
and help linking the dynamics of the Pyrenean orogeny and among all the relative influence of
tectonics and climate with the input of sediment and their transfer toward sink areas.
The characterization of the transfer of sediments during the syn-orogenic period will be studied
in the framework of the S2S project (a Total- BRGM collaboration). The current results have
been collected during research programs RGF (BRGM) and Gaia (TIGF/BRGM/AEAG).