*Volcano Geology Applications to Ancient Volcanism-Influenced Terrains: Paleovolcanism DOI: http://dx.doi.org/10.5772/intechopen.108770*

chemical, biological, and geological aspects that affect sedimentation within a specific area, being possible to distinguish between local environments (e.g., marine and non-marine, fluvial, lacustrine, wind, deep, shallow), defined in geomorphological terms, and tectonic environments with a much broader regional implication [13].

The explosive character of some volcanic activity is widely recognized in subaerial environments, and the distinctive characteristics of the products of this type of volcanic activity are well established. However, in relatively shallow subaquatic environments, explosive volcanic activity with characteristics similar to subaerial ones and with nearly identical products can also occur [64–70]. Likewise, this may be the case for PDC deposits originating in a subaerial environment, but that were ultimately emplaced in a subaqueous environment. In this case, there are no particular characteristics that allow them to be distinguished from purely subaerial or subaquatic deposits of the same type [71–75]. Furthermore, it will be necessary to identify the existing lateral variations within the volcanic deposits and the characteristics of the interbedded epiclastic deposits in order to accurately determine the depositional environment. In deep submarine environments, the hydrostatic pressure of the water column inhibits the vesiculation of magmas (e.g., [76, 77]), such that the volcanic activity will be predominantly effusive, regardless of the type of magma, until the volcanic edifice grows enough for the magma column to reach sufficiently superficial levels where it can experience explosive vesiculation, thus beginning to generate the first pyroclastic products [70, 77].

Depositional environments will also depend strongly on the tectonic setting where they develop, as this will control the geometry of sedimentary basins, rate of subsidence, location of volcanic vents, types of volcanism, local tectonics, and the general sedimentation rate.

Finally, it is worth mentioning that in paleovolcanic terrains in which the mixture of pyroclastic material with sedimentary material (with different proportions of each) is frequent, subsequent transformations experienced by volcanic deposits can cause significant changes with respect to the primary composition and texture of these rocks. However, both the composition and the secondary texture resulting from these transformations can serve to establish groups of deposits based on compositional and textural characteristics that may help their spatial and temporal correlation (**Figure 13**).

#### **Figure 13.**

*Comparison between two microphotographs of crystal-rich, pumice rich ignimbrites from a) Cerro Galan, Argentine (2 ma) and b) Prats d'Aguiló, Catalan Pyrenees, NE Spain (300 ma). Both show a very similar texture, with a similar content of phenocrysts of the same composition (quartz, Q; plagioclase, Pl; biotite, Bi), pumice fragments (P), vitric in the Gerro Galán ignimbrite and devitrified (clay aggregates) in the Prats d'Aguiló ignimbrite, and lithic fragments (L). (credits: Joan Martí).*
