ABSTRACT

The Longobucco Sequence is a 1200-m-thick dominantly carbonate miogeoclinal wedge which accumulated in the Mediterranean area during Jurassic time. Sedimentary facies pass upward from continental (3% of the stratigraphic column) at the base, through shelf (6%), slope (14%), to deep-sea turbidites (77%) at the top. Sand framework grains had five sources, four are noncarbonate extrabasinal and one, the most abundant, is carbonate intrabasinal as follows:

1. reworked arenites (quartzarenites, petrofacies A);
2. low-rank metamorphic rocks (litharenites, petrofacies B);
3. eolian or beach arenites (feldspathic-quartzarenites, petrofacies C);
4. granitic and high-grade metamorphic rocks (arkoses, petrofacies D);
5. intrabasinal shelf sediments (peloids, intraclasts, fossils and oolites).

Quartzarenites, which form fluvial and shallow-marine deposits, gradually pass upward through shelf, siliciclast-rich limestone to marly slope deposits with minor interbedded litharenites. Deep-sea fan deposits are chiefly carbonate turbidites, but feldspathic quartzarenites are present in the lower part. Arkoses abruptly replace the feldspathic quartzarenites in the upper part of the section. The litharenitic source is represented throughout the stratigraphic column. Therefore, different terrigenous source areas simultaneously supplied detritus to the sedimentary basin.

The evolution of detrital modes and depositional systems suggests two major tectonic events: latest Early Jurassic and probably Late Jurassic, superimposed on a progressive sinking of the basins. Both the change in depositional systems and sand composition can be related to a complex interplay of microcontinents and oceans which determined local compressive or extensional regimes during Alpine rifting in the Tethys region.