THE PLIOCENE DETRITIC DEPOSITS OF THE CON TACT AREAS ARMORICAN MASSIFPARISIAN BASIN, BETWEEN LAVAL AND ANGERS - (FRANCE)

The Pliocene detritic deposits of the contact areas Armorican Massif-P arisian Basin, between Laval and Angers (France). In these contact are as, the Pliocene detritic deposits are not very well-known in spite of numerous geological and geographical studies. Grain size distribution and Mossbauer spectrometry together with Xray analysis of clay sample s make possible to distinguish the surincombant deposits from older Eo cene sand deposits and quaternary alluvial deposits ; it is also possi ble to identify two different internal formations. Thus the marine red sands which were left in place during the Pretiglian sea regression o n uneven terrain, always appear more weathered than the upper insorted gravels, corresponding to a continental layer of more recent apport. During the Quaternary and Pliocene eras, iron hydroxides are all the m ore abundant as the material is old and long weathered.