Very High-resolution seismics as a tool for sequence stratigraphy applied to outcrop scale.- Examples from eastern Tyrrhenian margin Holocene/Pleistocene deposits

Three Eastern Tyrrhenian continental margin areas with very different depositional and tectonic settings were analyzed using single-channel very high-resolution reflection seismics coupled with sea-floor sampling. Fourth- and fifth-order depositional sequences derived from Quaternary glacio-eustatic processes are now buried at shallow depths within the continental shelf. The sequences have been reconstructed in detail with great lateral continuity. The tectonic setting did not influence the development of high-order sequences, which are probably synchronous at a global scale. Within these sequences, it has been possible to recognize all the systems tracts hypothesized by sequence stratigraphy models, confirming that this method does not depend upon time or scale. The geometry of depositional sequences is strongly dependent on sedimentation rate, i.e., on the distance from sources. Local factors such as transport pattern variations caused by sea level changes, paleotopography of the transgressed surface, characteristics of feeding hydrographic nets, and interactions with bioconstructions must be considered because they play an important role in the geometrical development of depositional sequences. In high-order depositional sequences, low-stand systems tracts are volumetrically predominant. High-stand and transgressive systems tracts seem to be linked to point sources because they have a three-dimensional (3-D) geometry. On the contrary, low-stand systems tracts are related to linear sources parallel to the shelf break; they cause the progradation of the whole margin so that they form the margin structure almost entirely.