SSP3.3

Plinian eruptions are powerful explosive volcanic events that impact large areas with cubic kilometers of magma emplaced as pyroclastic material accumulated in thick blankets around the volcanic vents. The violence of the emplacement mechanism (i.e., fallout or pyroclastic density currents, PDC) and the sudden burial of the landscape, make these types of eruptions extremely dangerous. Aiming to fully understand these phenomena, an accurate reconstruction of the physical behaviour and the historical record of a volcano is critical as starting point for the assessment of volcanic hazard. In this scenario an excellent case is the worldwide-known Plinian AD 79 Vesuvius eruption, which destroyed Roman towns with large effects preserved in different sites around the volcano. This study reports the results of a collaboration between the Archaeological Park of Pompeii and the University of Napoli Federico II to document the stratigraphic sequence and the type and extent of damage and victims buried under meters of pyroclastic material within the Pompeii and Stabiae archaeological sites. A systematic survey of well exposed outcrops along the recent excavations front allowed us to study in detail the facies variations of the different PDC stratigraphic units and how their distribution is affected even by urban structures. At Pompeii, the stratified ash PDC succession ranges in thickness from few tens of centimetres to two metres and shows considerable vertical and lateral variations in its sedimentological features. The layer associated with the most destructive impact on the Roman buildings shows down-current variation in thickness (0 to 330 cm) and texture. Where it is less than 30 cm thick, the deposit is fine-grained and thinly stratified, with few rounded pumice clasts scattered inside the matrix. Where it thickens, the lower part is rich in coarse pumice lapilli and locally shows well-developed stratifications, while the upper part shows an internal arrangement of alternating layers of fine and coarse ash, forming progressive bedforms. Upwards, the sequence is made up of a succession of plane-parallel ash layers with rare pumice lapilli clasts and diffuse accretionary lapilli. This ash sequence is interstratified with four well-sorted, thin lithic-rich layers that exhibit mantling structures of fall deposits. All PDC layers, except the lowermost, are dispersed across the entire Pompeii area, although some are locally missing as a result of the erosive action of the following PDC. At Stabiae, the ash PDC sequence is 83 cm thick. In few rooms of the Roman villa the ash deposits thicken up to 150 cm. Most of the ash layers identified at Pompeii are recognized also at Stabiae. In the upper part of the sequence a new PDC layer, never reported at Pompeii, is here documented for the first time. Damages are documented inside the more destructive ash layer and even in the upper ash layers, providing new insights about the risk assessment in distal areas.

How to cite: Santangelo, I., Scarpati, C., Perrotta, A., Sparice, D., Fedele, L., Chiominto, G., Amoretti, V., Muscolino, F., Rescigno, C., Silani, M., and Osanna, M.: The AD 79 Vesuvius eruption: stratigraphy, lithofacies variations and impact of the pyroclastic current deposits within the archaeological sites of Pompeii and Stabiae (southern Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9665, https://doi.org/10.5194/egusphere-egu21-9665, 2021.

Plinian eruptions are highly energetic events that release cubic kilometres of magma in the form of pyroclastic material (pumice, lithic clasts and ash). These products tend to accumulate near the vent with considerable thickness. The rapid burial of the territory around the eruptive centre makes these eruptions extremely dangerous. For this purpose, the renowned 79 AD Vesuvius eruption, which destroyed the ancient cities of Pompeii and Stabiae (where Pliny the Elder founds his death) located respectively 10 and 15 km from the vent, was studied in detailed. The recent excavations carried out in collaboration with the Archaeological Park of Pompeii, both in Pompeii and in the Stabian villas, have shown the complete sequence of products of the 79 AD eruption that destroyed and covered these Roman cities. The discovery of thick sequences of reworked material accumulated during previous excavations, testifies for the presence of underground tunnels dug for the Royal House of Bourbon. Fall products of the 79 AD eruptive sequence, accumulated during the main Plinian phase and the successive sustained column phases, were studied in detail to investigate their sedimentological characteristics and how these were influenced by anthropic structures. Results from field investigation show that in both archaeological sites, fall deposits consist of white and grey pumice lapilli in the lower part of the eruptive sequence (units A and B), and of thin, lithic-rich layers interstratified to ash products emplaced by pyroclastic currents, in the highest part of the pyroclastic deposit (units D, G1, G3, I). A new thin lithic-rich layer (X2) has been observed near the top of the sequence at Stabiae. The internal structure of the Plinian pumice lapilli deposit appears weakly stratified in open areas, while it is strongly stratified near steep roofs (e.g., impluvium areas), where the deposit thickens. The observed stratification is confirmed by a significant variation of sedimentological parameters with the stratigraphic height (e.g., median ranging from -3.5 to -0.1), possibly related to fluctuations in the eruptive parameters. Locally, rolling of pyroclastic clasts on sloped roofs produced a well-stratified deposit with laterally discontinuous layers and rounded clasts. Several roofing-tiles, either intact or in fragments, were recovered at various stratigraphic heights in the pumice lapilli deposit both at Pompeii and Stabiae.  These tiles testify for the progressive collapse of the roofs under the increasing load of the falling lapilli clasts.

How to cite: Chiominto, G., Scarpati, C., Perrotta, A., Sparice, D., Fedele, L., Santangelo, I., Amoretti, V., Muscolino, F., Rescigno, C., Silani, M., and Osanna, M.: Plinian eruptions and their impact on human settlements: stratigraphy of the 79 AD Vesuvius fall deposits and detailed study of their downwind and substrate-induced variations inside the archaeological excavations of Pompeii and Stabiae (southern Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11035, https://doi.org/10.5194/egusphere-egu21-11035, 2021.

A volcanic-rich horizon crops along the Northern Apennines chain for about 200 km, in the post-evaporitic sedimentary sequence with an age of 5.5 Ma. Its thickness ranges between 30-200 cm and has been interpreted either as a primary fallout or a giant gravity flow in seawater (Aldinucci et al., 2005; Trua et al., 2010; Cosentino et al., 2013). Here, we focus on the two southernmost occurrences in the Abruzzo region (Central Italy): Castiglione a’ Casauria (CAC 42°14'10'' 13°53'29') and San Vittorino (SVT 42°12'10'' 13°53'29'') villages.

The SVT and CAC deposits are lithified with thickness of 80 and 220 cm, respectively, mildly fractured and greyish to light brown in colour. Four (SVT) and fifteen (CAC) oriented samples coaxial to the field, were cut and polished to expose about 470 and 700 cm², respectively, of their vertical mesoscopic surfaces. The oriented thin sections and powders were prepared according to these mesoscopic attributes.

The XRPD (X-ray powder diffraction) spectra show the presence of a peculiar prominent large shoulder reflecting significative silicate non-crystalline phase, i.e. volcanic glass, plus faint Bragg reflections indicative of minor amounts of quartz, two feldspars (anorthite and sanidine), clinopyroxene, biotite and montmorillonite. The latter mineral results from post-emplacement and secondary crystallization. In addition, calcite and dolomite XRPD peaks occur with intensity inversely proportional to that of the silicate glass, reflecting the abundance or paucity of sedimentary versus volcanic fractions in sub-layers.

The microscopic 2D textures plus compositional features were investigated by SEM and EPMA. Both volcanic layers are very rich in fine-grained (averaging on 200 mm) and highly sorted glassy ashy clasts, while minerals are very poor (< 5 area%) in agreement with XRPD outcomes. Lithified ashes are mainly blocky in shape and un-broken. The ashes plot in the rhyolitic TAS field and overlap those already reported from other Northern Apennine sites. The amount of volatiles (H₂O + CO₂) estimated from EPMA average on about 6 wt.%, in agreement with the quantities of LOI determined on both bulk samples.

Field observations coupled with analysis on mesoscopic polished rock slices and thin sections do not shown any significant vertical size gradation and sorting, while fossils are almost absent. By contrast, both volcanic-rich deposits show: sedimentary- and volcanic-rich sub-layers, cm-sized volcanic clasts dispersed prevalently on the uppermost sedimentary sub-layers, cm-sized convolute laminations and slumped pseudo-beds. All these features demonstrate mass transport, soft-sediment deformation and fluid escape in seawater. Nonetheless, the absence of rounded ashy clasts, lithic sedimentary rock and classic Bouma sequence features (typical in coeval and adjacent deposits) mirror for local remobilization of poorly consolidated to loose carbonate and tephra deposits. In parallel, the high sorting of fine ashy clasts suggest a primary deposition from a distal fall-out eruptions. The location and features of both SVT and CAC volcanic-rich layers extend the previously inferred distribution of this ancient volcanic eruption.

References

Aldinucci et al., 2005. GeoActa, 4, 2005, pp. 67-82

Cosentino et al., 2013. Geology, 41, pp. 323-326

Trua et al., 2010. Italian Journal of Geosciences, 129, pp. 269-279

How to cite: Potere, D., Iezzi, G., Scisciani, V., Tangari, A. C., and Nazzari, M.: The southernmost occurrence of the volcanic-rich layer of 5.5 Main the Northern Apennines: clues on its deposition, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14794, https://doi.org/10.5194/egusphere-egu21-14794, 2021.

The Neogene volcanism in the western part of Romania is confined to the Apuseni Mountains and surrounding areas. The largest volcanic area is mostly developed in the WNW-ESE oriented, ca. 120 km in length Zărand-Brad-Zlatna Basin.

The Bontău Volcano (Seghedi et al., 2010) is located inside the western part of the Zărand-Brad-Zlatna Basin and it is strongly affected by erosional processes, being crossed in its northern part, from east to west, by the Crișul Alb River.

The Bontău Volcano is known to be active roughly between 14-10 Ma (according to the available K/Ar data) and it has been characterized as a composite or stratovolcano volcano associated with dome complexes, built by calc-alkaline andesitic lavas and pyroclastic deposits (andesite to basaltic andesite). The long-lasting volcanism developed in the Bontău area has a complex build up stages that we recently have found were interrupted by a series of destructive failure events. Several important volcanic collapses of the volcanic edifice took place producing large volcanic debris avalanches followed by numerous debris flows which produced various secondary volcaniclastic deposits that can be observed in different places all around the Bontău volcano. The debris avalanches deposits have not yet been known up to this study. The distribution of the debris avalanche deposits and associated volcaniclastic deposits is the main target of this study. In order to reconstruct Bontău Volcano activity and reconstruct its original morphology we done field observations and sampled the main lithologies to perform petrographic observations and geochemical and isotopic analyses (for the main lithologies).

During our field observations we tried to identify the relationships between debris avalanche deposits and older volcanic bodies (lavas, domes, volcaniclastic). One main important remark is related with the presence of several small basins at the margin of the volcano consisting of a succession of thin planar and cross-bedded sandstone in an alternation of coarse and fine layers associated with discontinuous lapilli trains (including pumices); The deposits are poorly to moderately sorted; with low angle cross lamination in lenses or pockets. Such deposits, as closely associate with debris avalanche deposits have been interpreted as small intra-hummocky basins formed after debris avalanche generation; they are mostly situated at the margins of the volcano.

The presence of multiple debris avalanche deposits can be connected with volcano growing in an extensional environment. We may assume that the long-lived Miocene rift graben system of the Zărand-Brad-Zlatna Basin experienced numerous changes in the fracture propagation and vertical movements that promoted repeated dyke intrusion and facilitated generation of numerous debris avalanches.

Acknowledgements: This work was supported by a grant of the of Ministry of Research and Innovation, CNCS – UEFISCDI, project number PN-III-P4-ID-PCCF-2016-4-0014, within PNCDI III.

How to cite: Stefan, G. C., Mirea, V., and Seghedi, I.: The Bontău Volcano, Apuseni Mts. (Romania), source for numerous debris avalanche deposits, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10855, https://doi.org/10.5194/egusphere-egu21-10855, 2021.

Maden Complex is a volcano-sedimantary unit, mainly composed of shallow and deep marine sedimentary rocks and associated volcanics. Deep marine units of Maden Complex, exposed between Çatak (Van) and Kozluk (Batman) regions have been studied with a combined sedimentological and paleontological approaches. The following species are recorded within the Melefan formation: Morozovella aragonensis, Acarinina collactea, Acarinina cf. esnehensis, Acarinina soldadoensis, Acarinina boudreauxi, Acarinina bullbrooki, Acarinina mckanni, Acarinina pentacamerata, Acarinina cf. pseudosubsphaerica, Acarinina topilensis, Acarinina esnehensis, Chiloguembelina sp., Globanomalina planoconica, Globanomalina australiformis, Globigerinatheka sp., Parasubbotina hagni, Pearsonites broedermanni, Pseudoglobigerinella bolivariana,   Planoglobanomalina pseudoalgeriana, Pseudohastigerina wilcoxensis,  Subbotina roesnaensis, Subbotina yeguaensis. Based on the defined planktonic foraminiferal species, the unit corresponds to the E7 zone and the depositional age of the formation is proposed as Early Eocene (Ypresian) to Middle Eocene (Lutetian). The deep marine sedimentary sequence mainly consists of pinkish to red colored micritic limestones including shale intercalations. The formation is represented by the pelloidal wackestone-packstone facies and comprises abundant planktonic foraminiferal assemblages.

How to cite: Atakul-Özdemir, A., Özkan-Altıner, S., Tancan, S., Özdemir, Y., Mercan, Ç., Oyan, V., and Güleç, N.: Biostratigraphy and microfacies of the sedimentary sequences within volcano-sedimentary Maden Complex in Southeastern Turkey, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14829, https://doi.org/10.5194/egusphere-egu21-14829, 2021.

Maden Complex exposed in Eastern Turkey, is a succession of volcano-sedimentary rocks and tectonically overlain by Bitlis Metamorphics and Cretaceous ophiolitic rocks. The succession includes shallow-water deposits and deep marine pelagic sediments intercalated with pillow lavas ranging from a few centimeters to ten meters in diameter. The planktonic foraminiferal assemblages from micritic limestones and zircon U-Pb ages from selected sedimentary rocks indicate the age of Late Ypresian - Early Lutetian. Plagioclase and  clinopyroxenes are the main mineral phases, olivine rarely found as altered phenocrysts. Clinopyroxenes are augite and diopside, and their compositions are ranging between Wo_44-51, En_27-43, Fe_10-21. The anorthite contents of plagioclases are between 32- 67 % in unaltered grains. The crystallization temperatures and pressures obtained from clinopyroxene chemistry are ranging from 1126 to 1250^oC and 3 to 8 Kbar, respectively. The majority of the volcanic/subvolcanic rocks are subalkaline-tholeiitic basalts however; a few andesitic and rhyolitic derivatives are also present. The whole – rock and  Sr-Nd-Pb isotope compositions reveal that the  basaltic rocks are originated from E-MORB like asthenospheric mantle source without a subduction component.

How to cite: Özdemir, Y., Mercan, Ç., Oyan, V., Atakul-Özdemir, A., Güleç, N., and Özkan-Altıner, S.: Petrolgy of the volcanic/subvolcanic members of the volcano-sedimentary Maden Complex in Eastern Turkey, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15060, https://doi.org/10.5194/egusphere-egu21-15060, 2021.