Miocene bioherms and associated structures in the Upper Coralline limestone of the Maltese Islands: their lithification and palaeoenvironment

An extensive sequence of small patch-reefs occurs within the middle member of the Upper Coralline Limestone Formation (Upper Miocene) in western Malta. In the lower horizons of the Tal Pitkal Member these structures are lensoidal in cross section and are surrounded by coarse flanking biosparites. Towards the top of the member they become more irregular in form. Extensive biostrome developments occur in association with the later structures but unlike the patch-reefs they were killed off periodically by episodes of exposure. The resistance of these structures to wave action is verified by the presence of extensive mollusc borings both in patch-reefs and biostromes. The initial binders within both structures are considered to be stromatolitic algae. Early diagenetic rims were also precipitated around allochems and added further strength to the frame work. Within this framework pelleted micrites accumulated which contrast strongly with the sparite cements of the flanking sediments. The organic framebuilders were finally killed off by a particularly strong episode of submarine erosion, with the subsequent establishment of an oolite shoal over the entire region.