The rise and fall of a Jurassic bank-basin system : Umbro Marchean Appenines, Italy

Marconi, Manuela (1995) The rise and fall of a Jurassic bank-basin system : Umbro Marchean Appenines, Italy. University of Southampton, Doctoral Thesis.

Abstract

The understanding of the development of carbonate systems has made many progresses in the past twenty years, especially thanks to the careful study of present analogue environments. Because of this greater knowledge, many more studies recently focused on a more detailed research on calciturbidites than in the past. Consequently several examples of carbonate margins studied in the early 1970's, have been recently reviewed and reinterpreted. This thesis studied one example of Jurassic carbonate passive margin from the Umbro-Marchean Apennines (Central Italy), investigated twenty years ago and never updated. The Jurassic sediments in the area represent a case of bank-basin, the development of which was not fully understood. In order to thoroughly explain the evolution of the sedimentation in the case study, a sedimentological and mineralogical approach has been adopted. The study of macro and microfacies and their relationship, and the variation of the mineralogical composition of the sediments helped to picture quite clearly the development of the study system.

The evolution of the bank-basin system was mainly controlled by tectonic: the carbonate platform existing in the area at the end of the Triassic was broken up by a tectonic pulse in the Lotharingian, and banks and basins differentiated. A later mid-Carixian tectonic pulse further fragmented the shallow areas and deepened most blocks to various depths. A substantial environmental change during the Middle Bajocian caused an increase in siliceous productivity and a parallel decrease in carbonate productivity. This change was also responsible for the creation of prolonged hiatuses on the banks and the deposition of cherty facies in the basins. An Early Kimmeridgian environmental variation let to the end of most extensive hiatuses and to a decrease in the amount of siliceous sediments, that ended in the Mid Thitonian. By this time the deposition was uniform everywhere. The development of the whole system was characterised by the creation of banks and basins during the Lias and by the gradual filling of basins during the rest of the Jurassic, coupled with overall subsidence. (DX192696)

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