The Szigliget maar/diatreme, Bakony- Balaton Highland Volcanic Field (Hungary)

A preliminary volcanological mapping has been carried out in the western part of the Bakony- Balaton Highland Volcanic Field (BBHVF) around Szigliget (Hungary) village. Pyroclastic rocks have been found building up the three distinct hillsides in the area. The pyroclastic rock beds in each hillside show similar north-westward dip direction and similar textural and compositional characteristics, suggestive of a complex but closely related volcanic system in the area. The pyroclastic deposits have been grouped into three units according to their textural, compositional and stratigraphic characteristics. Unit 1 which represents the lowermost stratigraphic position crops out in the southern side of the study area. It consists of coarse-grained, matrix-supported massive to weakly bedded, accidental lithic clast-rich, block-bearing lapilli tuffs / tuff breccias, extremely rich in deep-seated accidental lithic and peridotite lherzolite clasts. Unit 2 which represents an intermediate stratigraphic position crops out in the southern and north-east hilltops. It consists of coarse-grained accidental lithic clast-rich, normal graded, bedded, vitric lapilli tuffs / tuff beds. Deep-seated accidental lithic clasts are common, but large peridotite lherzolite fragments are relatively rare. Unit 3 which represents the highest stratigraphic position in the area crops out in the northwestern side. It consists of fine-to-coarse grained, bedded, accidental lithic clast-rich vitric lapilli tuff / tuff beds. Deep-seated lithic clasts as well as peridotite lherzolite fragments are rare. Accidental lithic clasts, derived from shallow prevolcanic strata (Neogene sediments), have a dominant proportion of pyroclastic rocks in this unit. In each unit the volcanic glasses are angular, non- to highly vesiculated tephrite to phono-tephrite shards. The presence of sideromelane glass shards and the large amount of accidental lithic clasts in beds from each units indicate subsurface phreatomagmatic explosive processes during formation of pyroclastic rocks at Szigliget. The pyroclastic rocks are interpreted as part of a former crater rim deposits around maar basin which subsequently subsided inward into a vent. Unit 1 is interpreted to be a lower diatreme deposit and Unit 2 and Unit 3 a series of near-vent pyroclastic density currents and fallout tephra

Inverted volcanic relief: Its importance in illustrating geological change and its geoheritage potential

co-auteur étrangerInternational audienceWe describe volcanic inverted relief sites around the world, making a comparative analysis of thosemost significant sites found fromliterature and our own search on imagery and global topographic maps. Over fifty significant areas of volcanic inverted relief were found. The comparative analysis is based on geoscience values defined by the main geological and landscape elements that define inverted relief. This subjective analysis is open and can be verified and extended if other significant sites emerge, thus forming the basis of a future, exhaustive global comparison of this important geomorphological feature. Invertedreliefoccurswhen valleys transformto ridges due to differential erosion of relatively resistant valley-fill, and weaker slope lithologies. It is found in various geological settings, and it is very common in volcanic terrains, especially monogenetic volcanic fields, where most examples are inverted lava flows. Relief inversion provides a clear indication of slowgeological changes and landscape evolution through erosion and can be thought of in popular terms as a geological clock. Volcanic inverted relief was recognised in the 18th - 19th centuries in the Chaîne des Puys (Auvergne, France), and used as evidence to first support plutonism by Nicolas Desmarest and then support uniformitarianism by George Poulett Scrope. We review the geological and geomorphological features of volcanic inverted relief world-wide, with an emphasis on the classical Auvergne.We explore how volcanic relief inversion chart geological changes, and their value for studying geological systems and landscape evolution. With our comparative analysis we can propose sites with the greatest geoheritage potential for representing inverted relief globally and suggest how this can be valued as geoheritage. As volcanic inverted relief is an important sub-set of all inverted relief, and is generally associated with important surface, volcanic and tectonic processes, and is often ongoing, it can be an important geoheritage component in natural sites.We suggest that it should should be present in the International Union of Geological Sciences (IUGS) Global Geosite list, can be a component of geosites in UNESCO Global Geoparks. It is also a feature for geological criteria (viii) in UNESCO World Heritage sites, where it fulfils all the requirements being both amajor geomorphological feature and a fingerprint of significant geological processes in Earth evolution

A high-resolution Early Holocene-late MIS 3 environmental rock- and palaeomagnetic record from Lake Sf. Ana, Carpathian Mts, Romania

Lacustrine sediments are excellent sources of palaeoenvironmental and palaeoclimatic information because they usually provide continuous and high-resolution records. In centraleastern Europe however lacustrine records that extend beyond the Holocene are rather sparse.Palaeomagnetic records from this region are also insufficiently explored, and usually associated with terrestrial deposits such as loess. In this context, the lacustrine record of Lake Sf. Ana, a volcanic crater lake in the East Carpathians, Romania, provides an important archive for reconstructing past paleomagnetic secular variation in the region from early Holocene to late Marine Isotope Stage (MIS) 3.</p

The Roxolany Tephra' (Ukraine) - new evidence for an origin from Ciomadul volcano, East Carpathians

We present major element glass data and correlations for the Roxolany Tephra' - a so far geochemically unconstrained volcanic ash layer previously described in last glacial (Marine Isotope Stage 2) loess deposits of the Roxolany loess-palaeosol complex in south-west Ukraine. This exceptionally well-preserved, 2-3-cm-thick tephra layer is characterized by a rhyolitic glass composition that is comparable to that of proximal tephra units from Ciomadul volcano in the East Carpathians, central Romania. The chemistry particularly matches that of the final Latest St. Ana Phreatomagmatic Activity pyroclastic fall unit of St. Ana crater that is radiocarbon dated in the proximal Moho coring site (MOH-2) to 29.6 +/- 0.62 cal ka BP. The age of the tephra correlative agrees with the newest radiocarbon and infrared optically stimulated luminescence age constraints from overlying palaeosols and tephra-embedding loess of the Roxolany sequence, respectively, which place the tephra between ca. 33 and 24 cal ka BP, and thus confirm the long-debated chronostratigraphy of this important environmental archive. The occurrence of a distal Ciomadul tephra ca. 350km east of its source indicates great potential for further tephra and cryptotephra findings from this volcanic complex in the south-eastern Mediterranean and Black Sea region