The mineralogy and sedimentation environment of the Neogene marly limestones Aitoloakarnania (Greece)

pp. 75-84
Department of Geology, University of Patras, 261 10 Patras, Greece

The 70 m thick Pliocene lacustrine marly limestone at Agios Ilias has been sampled in detail and analysed for grain size, clay mineralogy, CaCO3 and Corg. Two types of terrigenous fraction are seen: one with a substantial amount of coarse silt, the other with little sediment coarser than 6 φ. Sometimes there is an inverse relationship between abundance and grain size ofterrigineous fraction. The higher silt and sand content of the less terrigenous marly limestones indicate wind-blow transport of sediment; the clay rich, more terrigenous marly limestones may reflect stream input of suspended material. The illite, montmorillonite and kaolinite comprising the clay fraction are probably of detrital origin. The marty·limestones consist of > 80% CaC03. Calcium carbonate precipitates inorganically resulting from photosynthetic increase of the pH. The very low organic carbon and general lack of stratification show a well oxygenated bioturbated lake floor. Variation in Corg ret1ect proximity to the lake margin. There is no evidence of evaboritic playa conditions. The marly limestooes are contrasted with other Neogene lacustrine marly limestopes in the Peloponesse in terms of source area, clay mineralogy and fossil content.