Stratigraphic architecture of deep sea depositional systems in the Southern Tyrrhenian sea: some examples in the Ischia and Stromboli volcanic islands (Southern Italy)

The stratigraphic architecture of deep sea depositional systems has been discussed in detail by Galloway (1998). Some examples in the Ischia offshore are here shown and represented. The submarine slope and base of slope depositional systems represent a major component of marine and lacustrine basin fills, constituting primary targets for hydrocarbon exploration and development. The slope systems are characterized by seven basic facies building blocks, including the turbiditic channel fills, the turbidite lobes, the sheet turbidites, the slide, slump and debris flow sheets, lobes and tongues, the fine-grained turbidite fills and sheets, the contourite drifts and finally, the hemipelagic drapes and fills (Galloway, 1998). The grain size of the supplied sediments is a primary control in the development of the morphology in the channel-lobe systems. The grain size also controls the scale and the importance of slump and debris flow deposits. Siliciclastic slope systems have been divided into two main families. The constructional (allochtonous) systems include the fans, the aprons and the basin floor channels. They have been built from sediments supplied from delta, shore zone, shelf or glacial systems. The facies architecture of the allochtonous systems is mainly determined by the sediment texture and the pattern of supply at the shelf margin. The point sources of supply create the fans. The line sources have created strike-elongated prisms of slope sediments, called the slope aprons. The shelf margin deltas provide a particularly common intermediate source geometry, which forms onlapping delta-fed aprons. Another type is represented by the autochtonous system, including retrogressive aprons, canyon fills and megaslump complexes, recording the slope reworking and sedimentation. The variability in the form and growth of sediment waves on turbidite channel levees has been deeply investigated (Normark et al., 2002). Fine-grained sediment waves have been observed in many modern turbidite systems, generally restricted to the overbank depositional elements. The sediment waves have developed on six submarine fan systems and have been compared by using seismic reflection data coupled with sediment cores. Geological data have documented the upslope migration of the wave forms, with thicker and coarser beds deposited on the up-current flanks of the waves. Some wave fields are orthogonal to channel trend and were initiated by large flows whose direction was controlled by upflow morphology, whereas fields subparallel to the channel levees resulted from local spillover. Other studies have been carried out on the youngest channel-levee systems of the Bengal Fan, resulting from digital sediment echosounder data (Hubscher et al., 1997). Channel levee-systems represent the main architectural elements of submarine fans. Some channel-levee systems of the Ischia continental slope will be shown on seismic profiles. As a result of large input of sediments, the accumulated sediments may be considered as a high resolution record of the climatic history of the earth. The depositional structures reflect all the processes that affect sediment transfer from the hinterland towards the fan, e.g. the sea level and the climatic changes, the mountain uplift and the monsoon activity. The acoustic strata patterns and the downslope development of the channel levee system were examined with the parametric sediment echosounder Parasound. The determination of the age of the sedimentary strata shows turbiditic activity during sea level rise and highstand. The initial formation of the system in the middle fan occurred in the late glacial and outer levee growth stopped with glacial termination. Several vertical, aggradational sediments constitute the inner levees created in