Modelling the deposition of the phosphorite layers in Malta and reconstruction of the fauna

There are several phosphorite layers within the sedimentary succession of the Maltese Islands. These are related to climatic and ocean circulation pattern changes in the Mediterranean through the late Cenozoic. To decipher the depositional environment and processes related to the emplacement of these layers, several samples were collected from Il-Blata tal-Melh, southern Malta. With the help of CT-scans of these samples, the organisms and clasts within the phosphorites could be reconstructed by segmentation. This enabled the identification of the coral Flabellum spp. and several other organisms such as bivalves, gastropods, serpulids, sponges, foraminifers and fish teeth. The faunal composition, especially the coral Flabellum spp. that were reconstructed from the scans indicates that the phosphorites originated from a deep-water environment with slow currents. The absence of algae in the samples indicates an environment below the photic zone and the formation of micrite between the components also shows that the deposition must have taken place below the wave base, which also fits to the deep-water environment. The corals of the genus Flabellum spp. prefer a fine-grained substrate and with the occurrence of the serpulids it may concern that the substrate was also a hard substrate. The samples contain multiple dark clasts, which were analysed with the aid of thin sections. These showed that they have different micritisation levels than the rest of the matrix and implied that they were derived from a different environment, located in a shallower area below the wave base and have been rounded by transport. The clasts were transported and then embedded into the deep-water environment. Subsequently, the organisms and the clasts were phosphatized together.