SILICIFICATION OF PLANT REMAINS IN MESSINIAN MARINE-SEDIMENTS IN THE VERA BASIN (AIMERIA, SPAIN)

Silicified fragments of herbaceous plants and trees are common in the ''Coscojar Section'' in the Vera Basin, Almeria (eastern sector of the Betic Cordilleras). These remains are incorporated in Messinian marry sediments deposited in a shallow, proximal marine environment. The pl ant fragments, which are terrestrial in origin, underwent early silici fication with little or no burial. Petrification occurred in pore wate rs enriched in dissolved silica by the dissolution of amorphous silica skeletal debris and involved the impregnation and partial filling of the pores and voids in the plant structures with opal-CT. Subsequently , chalcedony spherulites and quartz grew in the cavities, without opal -CT as precursor mineral. Framboidal pyrite formed simultaneously in s ome cell lumina and other cavities. Finally, the opal-CT-quartz transf ormation took place selectively in some plant remains, probably in con nection with hydrothermal fluids, which caused a later precipitation o f iron oxides, metallic sulphides and/or gypsum in some plant remains. The plant remains of the ''Coscojar Section'' represent a good exampl e of unusual silicification of plants in marine conditions and a rapid , atypical opal-CT-quartz transformation.