GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 3.2 527 Geologic evolution of the Apulian platform - Southern Adriatic basin system, based on seismic and well data G. Aiello CNR-IAMC, Sede di Napoli, Naples, Italy Introduction. The tectono-sedimentary evolution of the Apulian Platform – Southern Adriatic Basin system in the time interval ranging between the Mesozoic and the Tertiary is herein described. In particular, seismic and well data here examined have given a higher detail for the time interval ranging between the Aptian-Albian and the Late Miocene. A simplified model of the geologic evolution of the platform-basin system, related to the time interval of the Turonian, Late Senonian, Eocene and Oligocene has been constructed (Fig. 1) and is herein discussed. Jurassic/Middle-Late Cretaceous. During the Late Triassic and up to the Lias the palaeogeography of the whole periadriatic region was characterized by a wide domain of shallow water including areas with a prevalent evaporitic deposition and intra-platform basins (D’Argenio, 1974). An evaluation of the average rate of sedimentation in the Upper Trias – Lias interval has been performed based on the stratigraphy of some deep lithostratigraphic wells drilled in the Apulian region, giving values of about 100-120 m/My. It is well known that the periadriatic carbonate platforms and the adjacent basins formed along the southern margin of the Mesozoic Tethys after the Lias, as a consequence of an extensional tectonic phase allowing for the downthrowing of the original evaporitic domain (D’Argenio et al. , 1973). The Apulian platform and the Southern Adriatic Basin formed starting from the Lias. From the Middle-Late Jurassic up to the Early Cretaceous the platform-basin system was “purely carbonate”, i.e. characterized by the lacking of a significant siliciclastic supply in the basin (Dolan, 1989). In this time interval the production of sediments on the shelf decreased up to 30-40 m/My (Stratigraphic unit 1), whereas in the basin the average rate of sedimentation was less than 10 m/My (lower part of the stratigraphic unit 2). A general landward shift of the carbonate facies during this time interval is suggested by the distribution of marginal and slope carbonate facies drilled by exploration wells. Sedimentologic and sequence stratigraphic studies carried out on marginal and slope facies cropping out in the Gargano Promontory (Graziano, 1992, 1993; Aiello and Graziano, 1993) show the occurrence of a 2 nd Type sequence boundary at the passage from the Albian to the Cenomanian. In any case, the platform equivalent of this margin/slope stratigraphic interval does not crop out onshore and the chaotic seismic response of the platform sequence did not allow for the offshore identification of this sequence boundary (Aiello and Graziano, 1993). It is not possible to precisely know if and with what extension the Albian-Cenomanian event was related with a phase of subaerial exposure of the Apulian platform. In the Southern Adriatic Basin this event correlates with a main variation of sediment dispersal of pelagic sediments: the “Marne a Fucoidi” stratigraphic marker is overlain by the Cenomanian-Turonian “Scaglia calcarea” Formation. Turonian. The next event recorded by the Apulian platform was a long lasting subaerial exposure related with the A bauxitic unconformity. The Turonian unconformity A, marked by the occurrence of bauxites and palaeokarst, testifies an emersion of the Apulian platform lasting for 1-5 My, which well correlates with other unconformities marked by bauxites, documented in other Mediterranean regions (D’Argenio and Mindszenty, 1987). In fact, the age of many bauxitic unconformities documented in the periadriatic region is put in correspondence to the phase of eustatic high of the Cenomanian-Turonian. It represents a peak in the frame of the Fanerozoic on the 2n order eustatic curve of Haq et al. (1987) and then shows a scarce correlation with a lowstand phase of the sea level. This evidence has induced some authors to explain the emersion of the periadriatic carbonate platforms during the Late Cretaceous (D’Argenio and