The analysis of the basin-fill architectural stratigraphy provides quantitative constraints on the sediment supply to the basins which is in turn is controlled by the interaction of climate and tectonics. When marine sediments are reworked and conglomeratic layers are discontinuous the clast lithological analysis becomes an invaluable tool to deterrnine stratigraphic correlations between outcrops. The clast count in conglomerates deposits, often combined with other types of analysis (e.g. facies analysis, paleocurrent analysis), is a very powerful tool for correlating the conglomeratic layers. Two statistica! analyses of grave] clasts from the Lower Pleistocene deposits in the Lower Cecina Valley (Tuscany, ltaly) have been combined to unravel changes in the palaeo-drainage system. Data from sixteen outcrops were collected and 6400 clasts described. Facies analysis, micro and macro-palaeontology and petrographic characteristics of the grave! deposits have highlighted the presence of three allostratigraphic units. Clast lithology has resulted to be the main discriminator among the different units. Cluster and principal component analyses of the 6400 clasts h ave permitted to improve the stratigraphy of the Lower Pleistocene deposits and to constrain the re-routing of the lower palaeo-Cecina River from a supposedly SE-NW to the presentE-W direction. Short rivers feeding small fan deltas represented by the oldest allostratigraphic unit were abandoned in the Lower Pleistocene, when the re-routing of the Cecina River caused the captures of these streams. This evolution suggests a change in the tectonic regime of the area. The fan deltas developed on the hanging wall of norma! faults sub-parallel to the coast; a change to a transtensile tectonic regime caused the deviation of the main river channel toward the present coast and the formation of a pull-apart basin, which is now exploited by the Cecina River. This case study illustrates the usefulness of statistica! analyses on grave! deposits to infer the tectonic evolution of an area.
Paleogeographic reconstruction in extensional basins using statistical analysis of gravels deposits
Ciampalini A.;SARTI, GIOVANNI;
2009-01-01
Abstract
The analysis of the basin-fill architectural stratigraphy provides quantitative constraints on the sediment supply to the basins which is in turn is controlled by the interaction of climate and tectonics. When marine sediments are reworked and conglomeratic layers are discontinuous the clast lithological analysis becomes an invaluable tool to deterrnine stratigraphic correlations between outcrops. The clast count in conglomerates deposits, often combined with other types of analysis (e.g. facies analysis, paleocurrent analysis), is a very powerful tool for correlating the conglomeratic layers. Two statistica! analyses of grave] clasts from the Lower Pleistocene deposits in the Lower Cecina Valley (Tuscany, ltaly) have been combined to unravel changes in the palaeo-drainage system. Data from sixteen outcrops were collected and 6400 clasts described. Facies analysis, micro and macro-palaeontology and petrographic characteristics of the grave! deposits have highlighted the presence of three allostratigraphic units. Clast lithology has resulted to be the main discriminator among the different units. Cluster and principal component analyses of the 6400 clasts h ave permitted to improve the stratigraphy of the Lower Pleistocene deposits and to constrain the re-routing of the lower palaeo-Cecina River from a supposedly SE-NW to the presentE-W direction. Short rivers feeding small fan deltas represented by the oldest allostratigraphic unit were abandoned in the Lower Pleistocene, when the re-routing of the Cecina River caused the captures of these streams. This evolution suggests a change in the tectonic regime of the area. The fan deltas developed on the hanging wall of norma! faults sub-parallel to the coast; a change to a transtensile tectonic regime caused the deviation of the main river channel toward the present coast and the formation of a pull-apart basin, which is now exploited by the Cecina River. This case study illustrates the usefulness of statistica! analyses on grave! deposits to infer the tectonic evolution of an area.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
