In relation to the project for the new cartography at the 1:50.000 scale of Italy, the field research of the northern pontine island in the Borgo Grappa sheet has been realized. Behind the classic lithostratigraphic methodology, the Unconformity Bounded Stratigraphic Units have been used for the organization of the most recent units. Synthems have been instituted only when surfaces related to regional processes, as oscillations of the sea level, have been recognised. Erosive surfaces or terraces which have been recognised only locally and which are not extended all over the three islands have been considered related to local volcanic processes. The volcanic units have been named as eruptive unit, succession and lithosoma. The legend of the sheet is subdivided in parallel columns to evidence temporal and geometrical relationships between synthems, supersinthems, eruptive units and lithosoma. This method has been useful for the resolution of the geological evolution of the islands. The submarine units of the islands have been emplaced after the Upper Pliocene from a dome complex which only in the case of the Ponza island evolved in a subaereous environment. The structural deformations present in the ancient sedimentary units of Zannone are interpreted as due to the thrusts operated by the dome emplacement. The emersion of the island had to occur between 1.6 Ma, (Mt. Tramontana lava at Palmarola) and 1.1 Ma (trachytic Mt. Guardia lava dome at Ponza).The gap in the volcanic activity and the emersion are represented by the development of deep erosion valleys carved in the submarine units. These valleys were filled up by the hydromagmatic and debris flow units erupted by the subaerial Mt. Guardia dome in the southern sector of Ponza. Marine deposits on terraces are present on the three islands at altitudes between 60 m and 120 m above sea level. We correlate this surface and their deposits, to a period after the end of the volcanism, probably during the isotopic stage 22, between 0.9 and 0.8 Ma. The differences in the altitude at which the marine surface is present can be explained by tectonic processes. By field data it is possible to hypothesise a tectonic lineament which would have rise up the northern part of Ponza, Zannone and Palmarola sector respect to the southern part of Ponza. The tectonic lineament could have an almost NE-SW direction and could coincide with the hydrothermally altered area of Cala dell'Acqua in Ponza.
DE RITA, D., Fabbri, M., Cimarelli, C. (2004). Stratigraphy in volcanic areas: The case of the northern Pontine archipelago.
Stratigraphy in volcanic areas: The case of the northern Pontine archipelago
DE RITA, Donatella;CIMARELLI, CORRADO
2004-01-01
Abstract
In relation to the project for the new cartography at the 1:50.000 scale of Italy, the field research of the northern pontine island in the Borgo Grappa sheet has been realized. Behind the classic lithostratigraphic methodology, the Unconformity Bounded Stratigraphic Units have been used for the organization of the most recent units. Synthems have been instituted only when surfaces related to regional processes, as oscillations of the sea level, have been recognised. Erosive surfaces or terraces which have been recognised only locally and which are not extended all over the three islands have been considered related to local volcanic processes. The volcanic units have been named as eruptive unit, succession and lithosoma. The legend of the sheet is subdivided in parallel columns to evidence temporal and geometrical relationships between synthems, supersinthems, eruptive units and lithosoma. This method has been useful for the resolution of the geological evolution of the islands. The submarine units of the islands have been emplaced after the Upper Pliocene from a dome complex which only in the case of the Ponza island evolved in a subaereous environment. The structural deformations present in the ancient sedimentary units of Zannone are interpreted as due to the thrusts operated by the dome emplacement. The emersion of the island had to occur between 1.6 Ma, (Mt. Tramontana lava at Palmarola) and 1.1 Ma (trachytic Mt. Guardia lava dome at Ponza).The gap in the volcanic activity and the emersion are represented by the development of deep erosion valleys carved in the submarine units. These valleys were filled up by the hydromagmatic and debris flow units erupted by the subaerial Mt. Guardia dome in the southern sector of Ponza. Marine deposits on terraces are present on the three islands at altitudes between 60 m and 120 m above sea level. We correlate this surface and their deposits, to a period after the end of the volcanism, probably during the isotopic stage 22, between 0.9 and 0.8 Ma. The differences in the altitude at which the marine surface is present can be explained by tectonic processes. By field data it is possible to hypothesise a tectonic lineament which would have rise up the northern part of Ponza, Zannone and Palmarola sector respect to the southern part of Ponza. The tectonic lineament could have an almost NE-SW direction and could coincide with the hydrothermally altered area of Cala dell'Acqua in Ponza.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
