The application of a Late Burdigalian -Early Langhian Highstand Event in correlating complex Tertiary orogenic carbonate successions within the Central Mediterranean

Résumé En Fr

Large scale eustatic events can be expected to influence marine sedimentation, not only in stable foreland settings but also in tectonically active regions. The signal characterizing each event is unique and can be recognized with confidence in all areas. This hypothesis is tested on successions developed in SE Sicily, and the Tertiary collision zone of N. Sicily and the S. Apennines. The Tertiary ramp carbonates of SE Sicily contain a remarkable hardground development associated with phosphatization in an outer ramp setting. Peripherally to these in situ development the phosphorites occur only as allochthonous clasts associated with a laterally continuous thick package of tabular, cross-stratified and hummocky cross-stratified packstones and grainstones. These are sandwiched between an otherwise tabular bedded, deep water pelagic wackestone sucession. The contained planktonic foraminifera indicate a Late Burdigalian age, below the event but a Latest Burdigalian to Early Langhian age in the overlying strata upramp. The eustatic event is recorded by an onlapping carbonate succession in the E. Hyblea which directly overlies eroded Cretaceous volcanics. Collectively, the studied localities well illustrate the Late Burdigalian global eustatic signal in both deep and shallow platform stable foreland settings, in the central Mediterranean. In contrast, the "Floresta Calcarenites" in the Peloritani Mountains of NE Sicily and a widespread group of isolated bioclastic carbonate outliers extending from Sperlinga through Gangi and westward along the southern Madonie Mountain foothills almost to Polizzi Generosa show the effects of this eustatic event across the Maghrebian thrust belt of N Sicily. These carbonates were generated contemporaneously in shallow water settings sometime in the Late Burdigalian to Early Langhian. Sedimentation style, however, indicates that many of these accumulations subsequently were resedimented down steep slopes from local interbasin highs into localised depocentres. The carbonates overlie a tectonized substratum and are themselves overlain by deep water clays containing Early Langhian planktonic microfauna. The same eustatic event is recognized further afield in the S. Apennines at the Calabro-Lucanian border. Here, lower middle Miocene bioclastic carbonates (Cerchiara Fm.) onlap earlier Tertiary deposits. Similar situations occur in the central-southern Apennines, in the northern Apennines, western Sicily and elsewhere in the Mediterranean. We interpret all these associations as the products of offlap-onlap events apparently contemporaneous with proposed World eustatic event TB 2.3 (HAQ et al, 1987 ; HAQ, 1991). We conclude that the proposed TB 2.3 signal is of sufficient magnitude within the Mediterranean regions to be recogniseable throughout many of the Tertiary orogenic zones. It's value lies in the amplitude and clarity of the signal, at a time of active tectonism and complex fades geometries. The recognition of this onlap-offlap event in further areas will provide a powerful tool not only in lithostratigraphic correlation of complex tectonic regions but also in tectonic event timing and correlations across separate plate margins.

Utilisation d'un Haut-Niveau Marin du Burdigalien supérieur-Langhien inférieur pour correler des successions carbonatées cenozoïques en contexte orogénique, en Méditerranée centrale. Les rampes carbonatées tertiaires du SE de la Sicile contiennent un remarquable niveau durci, phosphaté, dans les rampes externes autour des villes de Donnalucata et Sampieri. Dans les autres secteurs les phosphorites apparaissent seulement en grains allochtones associées latéralement à des packstones et des grainstones à stratifications obliques et structures de tempêtes. Les phosphorites sont contenues dans un ensemble tabulaire de wackestones de milieu pélagique. Le banc situé au dessous est daté du Burdigalien terminal alors que le banc du dessus contient un assemblage de Foraminifères planctoniques du Burdigalien terminal-Langhien inférieur. Cet exemple d'événement eustatique et bien d'autres marqués sur le plateau ibléen par des onlaps illustrent un signal eustatique global tant en mer profonde qu'en domaine littoral de plate-forme stable. A une plus grande échelle, les événements eustatiques, peuvent influencer la sédimentation marine même dans les légions à tectonique active. C'est le cas des calcarénites de Floresta dans les Monts Péloritains au NE de la Sicile. Le même événement eustatique est également reconnu dans le Sud des Apennines sur la bordure calabro-lucanienne et dans le Nord des Apennines. Nous interprétons tous ces événements en terme de offlap-onlap en relation avec l'événement eustatique mondial TE 2.3 (HAQ et al., 1987 ; HAQ 1991) nouvellement reconnu en Méditerranée. La reconnaissance de cet événement offlap-onlap un peu partout en Méditerranée en fait un outil performant non seulement pour la compréhension lithostratigraphique des régions à tectonique complexe mais aussi pour le calibrage des événements tectoniques.