Abstract

The style of activity of a volcano is controlled by the evolution of its magma chamber, as well as external factors and processes, such as the structural framework, the stress field and possibly also the climatic changes. In order to understand the interplay between the various factors controlling the evolution through time of a volcano, the stratigraphy of the volcanic rocks must show both the syn-eruptive and the inter-eruptive products, the latter usually representing much longer period of the volcano life than the former, and how they relate to tectono-sedimentary events at regional scale. Both the Unconformity Bounded Stratigraphic Units (UBSU) and the Allostratigraphy offer tools to organise the stratigraphy based on the hierarchy of the unconformities that bound different rock bodies, i.e. recognising different orders of processes controlling the emplacement of volcanic rocks. This paper proposes to organise the stratigraphy of volcanic rock sequences following the principles of the UBSU and/or the Allostratigraphy. We propose to introduce the Eruptive Unit as the basic lithostratigraphic unit, which comprises the primary products of a single eruption and the deposits of their syn-eruptive reworking. Rock units at a higher or lower hierarchical order will then be associations of eruptive units or part of them respectively. This allows to tie invariantly the organisation of the stratigraphy to a phenomenon (the eruption) that is intrinsically related to the volcano activity, which would make comparable the stratigraphies of different volcanoes, both modern and ancient and at any scale of representation. The legend for volcanic rocks should be compared with the legend for sedimentary rocks of the surrounding plains in order, to evaluate the reciprocal influence of volcanism, tectonism and eustatism on sedimentation, by correlating the unconformities developed in different depositional environments.

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