Pluridisciplinary palaeo-environmental study in the deposits located in the hanging wall of the active Aigion Fault (Corinth Gulf, Greece).

Lemeille F., Bourdillon C., Guernet C., Sorel D., Manakou M., Berge-Thierry C. and the MICROHOLOCOR Team European Geophysical Society XXVII General Assembly - Nice, 21-26 avril 2002.

Three cored boreholes (205, 60 and 33 m), dedicated to the fitting of deep accelerometers and to geomechanical experiments and geophysical measurements, have been carried out in the framework of thé CORSEIS European Program on a site located nearby the active Aigion Fault. The boreholes crossed the sédiments layers in the hanging wall of the fault close to the prescrit shoreline. The nature and the geometry of the deposits in the site depend on different parameters: eustacy, fault activity, local paleogeography, displacement of the shoreline, variability of the main nearby river and related deltaic deposits, ... 14C dating in the main borehole G1 point out several noteworthy markers and allow to calculate sedimentation rates. This lead to extrapolate the age of the markers in the whole borehole. The bottom of the borehole could be dated around 78 ka BP. A comparison between inferred dating in the borehole and paleotemperature curves and paleo-sealevel charts leads to the calculation of subsidence rates. Some of the anomalies in the sedimentation rates and in the susbsidence rates could be related with fault activity. The paleoenvironement of the deposits has been reconstructed in the whole borehole based on paleoenvironmental criteria (salinity, temperature, energy, oxygenation, water thickness, location vs. shoreline, trophism, freshwater irruptions, lithologic and sedimentological facies, d'80, ... ). All the main sea level transgressions (high stand sea level) recorded in the charts are present in the borehole since marine isotopic stage 5a to present. Preliminary results show that the influence of the nearby fault activity is less important than the eustacy variations. Complementary studies are presently carried out on an outcrop located in the footwall of the fault in order to estimate the régional offset caused by the fault. These results will be compared to data obtained from other methods (palaeoseismological trenches, U/Th cernent fault datings, synsedimentary deformations, tsunami facies, ...) which also provide fault activity periods and deformation rates.