The Onano Pyroclastic Formation, closely linked to the genesis and evolution of the Latera Caldera, is one of the largest deposits of the Latera Volcanic Complex (LVC), developed in the western sector of the Vulsini District between 0.3 and 0.1 Ma. The LVC was formed from a central building, originated after the migration of the eruptive activity that had initially characterized the pre-existing Bolsena Volcano. The Onano eruption, dated 0.17 Ma on the basis of geochronological data of the underlying and overlying deposits, is the final step of the most volumetrically important period of volcanic activity during which a series of large pyroclastic flows were emplaced around the caldera. The eruptive dynamics and the depositional mechanisms of the Onano Formation are still subject to different interpretations, because of its stratigraphic and compositional peculiarities. The Onano deposits were field surveyed and sampled in order to: 1) identify the various facies of the deposit, 2) reconstruct the mechanisms of emplacement, 3) hypothesize the eruptive dynamics. Sixteen samples from proximal to distal facies were analyzed for density and porosity, in order to determine the degree of welding of deposit. The considerable variability of density (ranging from 0.64 to 1.83 g/cm 3) and porosity (ranging from 31 to 74 WP%) has allowed to recognize three different facies (F1, F2 and F3). The typical appearance and structure of the deposit, characterized by coarse grain, lack of fine fractions and varying degrees of welding and agglutination, as well the accumulation on high terrain up to 6-7 km far from the center of emission, may suggest the hypothesis of an origin by a lava flow to be reconsidered. We can therefore suggest that the Onano Formation can be regarded as a ballistic origin triggered by intense fissural lava fountaining occurred on the NE edge of Latera Caldera. This mechanism could in some cases have generated a secondary remobilisation of the accumulated pyroclasts (reomorphic process). Further and more detailed field surveys are nevertheless necessary to support this hypothesis.

THE WELDED DEPOSIT OF THE ONANO PYROCLASTIC FORMATION (WESTERN VULSINI, ITALY): DEPOSITIONAL AND STRATIGRAPHIC FEATURES / Jacopo Cabassi; Bruno Capaccioni; Orlando Vaselli; Nadia Pavanelli; Franco Tassi. - STAMPA. - (2010), pp. 1-1. (Intervento presentato al convegno SIMP 2010 tenutosi a Ferrara).

THE WELDED DEPOSIT OF THE ONANO PYROCLASTIC FORMATION (WESTERN VULSINI, ITALY): DEPOSITIONAL AND STRATIGRAPHIC FEATURES

CABASSI, JACOPO;VASELLI, ORLANDO;TASSI, FRANCO
2010

Abstract

The Onano Pyroclastic Formation, closely linked to the genesis and evolution of the Latera Caldera, is one of the largest deposits of the Latera Volcanic Complex (LVC), developed in the western sector of the Vulsini District between 0.3 and 0.1 Ma. The LVC was formed from a central building, originated after the migration of the eruptive activity that had initially characterized the pre-existing Bolsena Volcano. The Onano eruption, dated 0.17 Ma on the basis of geochronological data of the underlying and overlying deposits, is the final step of the most volumetrically important period of volcanic activity during which a series of large pyroclastic flows were emplaced around the caldera. The eruptive dynamics and the depositional mechanisms of the Onano Formation are still subject to different interpretations, because of its stratigraphic and compositional peculiarities. The Onano deposits were field surveyed and sampled in order to: 1) identify the various facies of the deposit, 2) reconstruct the mechanisms of emplacement, 3) hypothesize the eruptive dynamics. Sixteen samples from proximal to distal facies were analyzed for density and porosity, in order to determine the degree of welding of deposit. The considerable variability of density (ranging from 0.64 to 1.83 g/cm 3) and porosity (ranging from 31 to 74 WP%) has allowed to recognize three different facies (F1, F2 and F3). The typical appearance and structure of the deposit, characterized by coarse grain, lack of fine fractions and varying degrees of welding and agglutination, as well the accumulation on high terrain up to 6-7 km far from the center of emission, may suggest the hypothesis of an origin by a lava flow to be reconsidered. We can therefore suggest that the Onano Formation can be regarded as a ballistic origin triggered by intense fissural lava fountaining occurred on the NE edge of Latera Caldera. This mechanism could in some cases have generated a secondary remobilisation of the accumulated pyroclasts (reomorphic process). Further and more detailed field surveys are nevertheless necessary to support this hypothesis.
2010
Abstracts Book SIMP 2010
SIMP 2010
Ferrara
Jacopo Cabassi; Bruno Capaccioni; Orlando Vaselli; Nadia Pavanelli; Franco Tassi
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Utilizza questo identificatore per citare o creare un link a questa risorsa: https://hdl.handle.net/2158/955139
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