Interaction of Marine and Fluvial Clastic Sedimentation, Central Italy, Tyrrhenian Coast

S. Evangelista, W. E. Full, P. Tortora

An integrated approach was used to study the interaction of fluvial, beach, and marine processes on sedimentation at the west-central coast of Italy along the Tyrrhenian Sea. The study area, 120 km northwest of Rome, is bounded on the north by Mt. Argentario, on the east by Pleistocene volcanics, on the south by the St. Augustine River, and on the west by the 50-m bathymetric isopleth. The primary tools used included field work, textural analysis, high-resolution marine seismic, SEM, and Fourier shape analysis. Field work revealed incised streams, potentially relict beach ridges and lagoons, and relatively steep nearshore marine slopes in the northern portions of the study area.

The result of the shape analysis performed on 56 samples was the definition of four end members. Each end member reflects a sedimentation process. Three end members were directly associated with fluvial sedimentation, and the fourth reflected marine processes. The seismic data along with the SEM analysis strongly supported the interpretation of four processes that dominate the recent sedimentation history.

The sand interpreted to be associated with marine processes was found to represent the smoothest end member. SEM analysis suggests that the smoothing is not due to abrasion but to plastering associated with biologic processes (digestion?) and/or with silica precipitation associated with clay alteration at the freshwater/saltwater interface.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.