Sedimentology of the belgian frasnian carbonate platform
This work reflects the integration of different techniques such as field observations, petrography, magnetic susceptibility measurements, isotopic analyses and sequence stratigraphy. The combination of these results allows us to reconstruct the environmental evolution of the shallow water Frasnian carbonate deposits of Belgium. The sedimentological anaylsis provides different facies models, each characterized by its own geographical and stratigraphical position. The lower part of the Frasnian corresponds to a ramp, with shales and crinoidal layers. The middle part of the Frasnian corresponds to a ramp, with shales and crinoidal layers. The middle part of the Frasnian is divided in two platform areas (north and south). The external zone of the platform is dominated by crinoidal deposits, the intermediate part shows biostroms with stromatoporoids and the internal zone presents sub- to supratidal deposits. The Upper part of the Frasnian us a ramp with external deposits made by shales, intermediate belt of rugose corals biostromes abd the shallowest part of the platform is characterized by oncoids and peloids. The major control on facies distribution is the result of sea level varitations, which imply cyclic sedimentation (fourth and third order). Control on lateral variations is related to tectonic movements which imply morphological variations of the platform. We recognized different sequences and each tract of these sequences is characterized by facies, magnetic susceptibility, isotopic and cyclic pattern variations. The sequences defined on the platform are compared to the sequences defined in the basinal area. Finally magnetic susceptibility is used mainly for precise correlations (fourth order). We have showned that magnetic susceptibility signal is directly related to facies, fourth order cycles and third order sequences. The amont of magnetic minerals is probably related to lithogenic inputs.