The use of UBSU to organize volcanic units successfully helped the lecture of the Quaternary volcanic stratigraphy, helping to reconstruct better the history of a volcano even for its quiescence periods. Nevertheless, the presence of several unconformities of local significance makes difficult their hierarchisation, especially when the stratigraphy of volcanoes is related with the regional geology. We propose to organise the stratigraphy of volcanic rock sequences following the principles of the UBSU, but adopting for them a different nomenclature adopted in classic volcanology. We maintain the terms of Synthem, Supersynthem and Subsynthem only for units at regional scale. This has the advantage to better evidentiate the interplay between the various factors that controll the evolution through time of a volcano and that evaluate the reciprocal influences of volcanism, tectonism and eustatism on sedimentation. This is possible by comparing and by correlating the unconformities developed in different depositional environments. This allows to relate invariantly the organisation of the stratigraphy of a phenomenon like the eruption of volcanoes with the climatic history for Quaternary units and also with the oscillations of the sea level. As in Quaternary stratigraphy, even in volcanic areas it is possible to take into account morphological features related to a geologicl process but it is necessary to consider that flat surfaces in volcanic environment can be also produced directly by volcanic processes: high aspect ratio ignimbrites form flat plateaux; domes emplacing as criptodomes are characterized by flat flankes as for example the dome of Syowa Sinsan in Japan or the Lassen Peak in California. Volcanoes close to the coast develop several terraces that may be related to the same sea level; they are the effect of re-equilibrium processes due to the growth of the volcano or to the huge quantity of sediments deposited by the eruption. These terraces not necessarly correspond to regional sea level oscillations; they may be produced even during low standing of sea level. In these environment we propose to interpret as erosional surfaces due to sea level oscillation of regional significance only those surfaces characterized by the presence of the relative deposits and that are correlable with similar surfaces recognized on other close islands and on the continental coast.
DE RITA, D., Fabbri, M., Sposato, A. (2004). The use of Ubsu in Quaternary volcanic areas: problems and considerations for their solutions..
The use of Ubsu in Quaternary volcanic areas: problems and considerations for their solutions.
DE RITA, Donatella;
2004-01-01
Abstract
The use of UBSU to organize volcanic units successfully helped the lecture of the Quaternary volcanic stratigraphy, helping to reconstruct better the history of a volcano even for its quiescence periods. Nevertheless, the presence of several unconformities of local significance makes difficult their hierarchisation, especially when the stratigraphy of volcanoes is related with the regional geology. We propose to organise the stratigraphy of volcanic rock sequences following the principles of the UBSU, but adopting for them a different nomenclature adopted in classic volcanology. We maintain the terms of Synthem, Supersynthem and Subsynthem only for units at regional scale. This has the advantage to better evidentiate the interplay between the various factors that controll the evolution through time of a volcano and that evaluate the reciprocal influences of volcanism, tectonism and eustatism on sedimentation. This is possible by comparing and by correlating the unconformities developed in different depositional environments. This allows to relate invariantly the organisation of the stratigraphy of a phenomenon like the eruption of volcanoes with the climatic history for Quaternary units and also with the oscillations of the sea level. As in Quaternary stratigraphy, even in volcanic areas it is possible to take into account morphological features related to a geologicl process but it is necessary to consider that flat surfaces in volcanic environment can be also produced directly by volcanic processes: high aspect ratio ignimbrites form flat plateaux; domes emplacing as criptodomes are characterized by flat flankes as for example the dome of Syowa Sinsan in Japan or the Lassen Peak in California. Volcanoes close to the coast develop several terraces that may be related to the same sea level; they are the effect of re-equilibrium processes due to the growth of the volcano or to the huge quantity of sediments deposited by the eruption. These terraces not necessarly correspond to regional sea level oscillations; they may be produced even during low standing of sea level. In these environment we propose to interpret as erosional surfaces due to sea level oscillation of regional significance only those surfaces characterized by the presence of the relative deposits and that are correlable with similar surfaces recognized on other close islands and on the continental coast.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
