Paleozoic stratigraphy and palaeogeography of the malaguide complex (betic cordillera) and other western mediterranean related domains (calabria-peloritani terrane)

Résumé

This thesis studies the Paleozoic stratigraphy, palaeogeography and geo-historical evolution of the intra-Alpine terrains outcropping in the Betic Cordillera (Malaguide Complex) and in the equivalent Alpine domains of the Calabria-Peloritani Terrane (Stilo and Longi-Taormina units). Field, stratigraphic and biostratigraphic studies have allowed the division of the Malaguide Complex outcropping in all the three studied areas in three Alpine tectonic units, which are, from bottom to top, Epimetamorphic Malaguide Unit, Lower Malaguide Unit and Upper Malaguide Unit. The succession recorded in the lower units contains turbiditic deposits as those of the Morales and Santi Petri formations, with a probably pre-Devonian and Devonian ages, respectively. On the contrary, the succession recorded mainly in the Upper Malaguide Unit (that crops out to the N of the other units in present-day coordinates) includes Silurian-Devonian limestones, nodular in some places, with several types of fossil remains. Facies included in the lower Alpine Malaguide units correspond to siliciclastic-carbonatic distal (slope and basin) environments, typical of a divergent (passive) continental margin. On the contrary, pre-Carboniferous facies of the Upper Malaguide Unit point to less deep and less distal environments in the pelagic areas of the same margin during Silurian and Devonian times. Therefore, this margin opened to the SE, according to present coordinates, towards regions related to the Paleotethys ocean. The Paleozoic sequence of the Stilo Unit includes pre-Devonian pelites with intercalated metabasites, black shales and limestone beds, and Devonian pelites with limestone intercalations, which show significant lateral and vertical changes of facies. This fact allows to characterize the pelagic areas of a continental margin with similar features to those of the more proximal environments of the palaeomargin recorded in the Malaguide Complex. Lower Devonian deposits studied in the Aspromonte Massif include thicker pelitic intercalations and carbonate facies typical of deeper enviroments. This indicates that the deposition of the southern succession of the Stilo Unit in progresivelly more distal regions of the margin. The rest of the Paleozoic sequence is characterized by Carboniferous lydites and synorogenic siliciclastic (Culm type) deposits, as in the Malaguide Complex, and points to a equivalent tectono-stratigraphic evolution. The abundance of pre-Devonian basic volcanics and volcano-sedimentary formations and the nature of the Silurian-Devonian facies recognized within the Longi-Taormina Unit point to a palaeogeographic location of this unit in more distal realms in a continental margin than that of beds of equivalent age of the Stilo Unit. This location was closer to the intraoceanic rift axis that probably corresponded to the western sector of the Paleotethys. However, the intracontinental features of the mafic vulcanism of the Longi-Taormina Unit exclude the existence of real oceanic crust in the Paleozoic terrains here studied. This indicates that the Paleotethys was closed gradually towards its western sector. The lateral evolution of facies in the Silurian-Devonian successions of the Malaguide Complex and of the Calabria-Peloritani Terrane reveals a proximal-distal equivalent zonation, from NW to SE and N to S (respectively and in present coordinates). Both sections constitute two transects in the same continental margin located to the N and to the NW of the Paleotethys. To sum up, Paleozoic intra-Alpine terrains studied in the Malaguide Complex and in the Stilo and Longi-Taormina units of the Calabria-Peloritani Terrane make part of the northern margin of a narrow and elongated continental crust plate (ribbon continent) incompletely detached from Gondwana in its western end, during the Silurian-Devonian opening of the Paleotethys. This evolution fits well with that known for other nord-Gondwanic intra-Alpine regions during the opening of the Paleotethys. This caused the separation of this ribbon continent from Northern Gondwana, from which most of the Paleozoic terrains further involved in the Alpine belt are derived.