A facies analysis of the Villafranchian continental deposits outcropping in the Castelnuovo Garfagnana and Barga basins allow the reconstruction of their paleoenvironmental evolution that differs significantly from the traditional fluvio- lacustrine interpretation. We identify, at different stratigraphic positions, two main river systems and some tributaries which flowed longitudinally and laterally to the axis of the two basins respectively, the latter fed both by the Apuan and Apennine margins. The mapped deposits were subdivided in five lithostratigraphic units (U1-5). Lying in disconformity on the substratum U1 corresponds to a cohesive sediment anabranching river (sub-type organo-clastic) developed longitudinally to the axis of the two basins in a humid subtropical climate phase. It is characterized by abundant fine organic-rich deposits and lignite accumulation (overbank elements) and by conglomeratic facies (channel-belt elements). An abrupt facies change characterizes the contact between U1 and overlying U2 that is constituted by prevalent conglomeratic deposits (channel-belt elements) and interpreted as a gravel bed-load braided river. U3, U4 and U5 correspond to coalescent fan systems developing transversally to the axis of the two basins. U3 and U4 were interpreted as debris flow dominated fans exclusively, (U3), or prevalently, (U4), constituted by «Macigno» clasts while U5 corresponds to a braided fluvial fan mainly characterized by a high variety of metamorphic clasts. Their influence, as transversal tributaries of the main longitudinal river systems, results both from compositional statistical analyses of conglomeratic deposits and from survey evidences. This paleoenvironmental reconstruction implies that Monte Perpoli high («Soglia di Monte Perpoli » Auctt.) acted as a sedimentary by-pass since the opening of the Castelnuovo Garfagnana and Barga basins.
The Villafranchian deposits of the Castelnuovo Garfagnana and Barga Basins (Lucca, Tuscany, Italy): facies analysis and paleoenviromental reconstruction
SARTI, GIOVANNI;
2002-01-01
Abstract
A facies analysis of the Villafranchian continental deposits outcropping in the Castelnuovo Garfagnana and Barga basins allow the reconstruction of their paleoenvironmental evolution that differs significantly from the traditional fluvio- lacustrine interpretation. We identify, at different stratigraphic positions, two main river systems and some tributaries which flowed longitudinally and laterally to the axis of the two basins respectively, the latter fed both by the Apuan and Apennine margins. The mapped deposits were subdivided in five lithostratigraphic units (U1-5). Lying in disconformity on the substratum U1 corresponds to a cohesive sediment anabranching river (sub-type organo-clastic) developed longitudinally to the axis of the two basins in a humid subtropical climate phase. It is characterized by abundant fine organic-rich deposits and lignite accumulation (overbank elements) and by conglomeratic facies (channel-belt elements). An abrupt facies change characterizes the contact between U1 and overlying U2 that is constituted by prevalent conglomeratic deposits (channel-belt elements) and interpreted as a gravel bed-load braided river. U3, U4 and U5 correspond to coalescent fan systems developing transversally to the axis of the two basins. U3 and U4 were interpreted as debris flow dominated fans exclusively, (U3), or prevalently, (U4), constituted by «Macigno» clasts while U5 corresponds to a braided fluvial fan mainly characterized by a high variety of metamorphic clasts. Their influence, as transversal tributaries of the main longitudinal river systems, results both from compositional statistical analyses of conglomeratic deposits and from survey evidences. This paleoenvironmental reconstruction implies that Monte Perpoli high («Soglia di Monte Perpoli » Auctt.) acted as a sedimentary by-pass since the opening of the Castelnuovo Garfagnana and Barga basins.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
