The Permian pyroclastic deposits of the Levín Volcanic Field within the Krkonoše Piedmont Basin were studied in terms of volcanology. Pyroclastic rocks are exposed in two quarries and the study was supported with a 30 m deep borehole K1 penetrating these rocks. The pyroclastic rocks are altered but preserved textures enable reconstruction of eruptive styles. The volcanic sequence exposed in the abandoned Hvězda quarry starts with a phreato-Strombolian pyroclastic rocks rich in basaltic scoria, cuspate glass shards, armoured-and accretionary lapilli overlain with mafic lava. Subsequent activity was phreatomagmatic in style and produced fall-out of accretionary lapilli and accumulation of base surge deposits. Overlying subhorizontally bedded matrix-supported pyroclastic deposits are rich in scoria and contain spindle-shaped bombs. These rocks are interpreted as mafic pyroclastic flow deposits related to Strombolian eruptions. A similar succession capped by scoriaceous fall-out deposit was documented in the K1 borehole. A coherent mafic volcanic rock (lava or sill) terminates the succession exposed in the Hvězda quarry. Agglutinates at the base of the Studenec quarry were produced during Hawaiian eruptions building up a spatter cone. The cone most probably dammed a stream and created an ephemeral lake. Increasing influence of water on eruptive styles is documented in overlying pyroclastic deposits of phreatomagmatic eruptions. Subsequent lava flowed into the lake. Quenching of the lava resulted in formation of pillows enclosed in hyaloclastite breccia. Further up in the exposure, transition of pillow to massive lava has been recognized. Overlaying pyroclastic deposits are matrix-supported and rich in scoria and spindle-shaped bombs. Similarly to the Hvězda quarry, these are interpreted as mafic pyroclastic flow deposits. Volcanic activity in the Levín Volcanic Field was characterized by Hawaiian, Strombolian, phreato-Strombolian and phreatomagmatic eruptions accompanying lava effusions and possibly sills emplacement. The lavas were emitted in both subaerial and subaquatic conditions. The character and distribution of volcaniclastic facies suggests existence of several monogenetic volcanoes.

The Permian pyroclastic deposits on the Principálek Hill SW of Vrchlabí (Czech Republic) were investigated by means of geological mapping and geophysics. The pyroclastic rocks are exposed in several small coherent outcrops, yet many interpretations are based on debris. The preserved textures enable reconstruction of eruptive styles. The volcanism started with phreatomagmatic eruptions documented by the fine-grained tuff with accretionary lapilli at the base. Subsequently, the activity changed to phreato-Strombolian/Surtseyan producing lapilli-tuffs and lapillistones. These events were followed by a Strombolian phase as evidenced by ill-sorted scoriaceous tuff-breccias with volcanic bombs. The uppermost unit consists of welded lava agglutinates and basaltic lavas suggesting a Hawaiian style of eruption. One of the basaltic feeder necks is exposed in a small abandoned quarry. Geophysical surveys were carried out over the extent of pyroclastic deposits. These included gravimetry, magnetometry, and DC resistivity tomography. The magnetic data indicate the occurrence of basaltic dykes in the central part of the pyroclastic deposits. The DC tomography confirms the presence of dykes, enables estimation of the pyroclastic deposits thickness, and provides evidence for the size and position of the maar-diatreme. Gravity data yield an insignificant low associated with the diatreme, which is likely a product of low rock-density contrast between the diatreme and country rocks. We argue that this is due to short time gap between sedimentation and volcanic activity and also related to conjoint burial and diagenetic history of the diatreme and the surrounding country rocks.

Mafic, monogenetic vol ca nism is in creas ingly rec og nized as a com mon man i fes ta tion of post-collisional vol ca nism in late Variscan, Permo-Car bon if er ous intramontane bas ins of Cen tral Eu rope. Al though iden ti fi ca tion of in di vid ual erup tive cen tres is not easy in these an cient suc ces sions, the Perm ian Rožmitál andesites in the Intra-Sudetic Ba sin (NE Bo he mian Mas sif) pro vide an ex cep tion ally de tailed re cord of ex plo sive, ef fu sive and high-level in tru sive ac tiv ity. Based on field study and petrographic and geo chem i cal data on pyroclastic and co her ent rocks, the Rožmitál Suc ces sion is in ter preted as the prox imal part of a tuff ring sev eral hun dred metres in di am e ter. Ini tial ac cu mu la tion of pyroclastic fall and surge de pos its oc curred dur ing phreatomagmatic erup tions, with tran si tions to wards Strombolian erup tions. Gul lies filled with re worked tephra doc ument pe ri ods of ero sion and redeposition. Andesitic blocky lavas capped the volcaniclastic suc ces sion. In va sion of lavas into un con sol i dated sed i ments and em place ment of shal low-level in tru sions in near-vent sec tions re sulted in the for ma tion of jigsaw-and ran domly-tex tured peperites. Most geo chem i cal dif fer ences be tween co her ent andesites and pyroclastic rocks can be linked to in cor po ra tion of quartz-rich sed i ments dur ing the ex plo sive erup tive pro cesses and to later ce men ta tion of the volcaniclastic de pos its by do lo mite. The Rožmitál tuff ring could have been one of sev eral phreatomagmatic cen tres in a monogenetic vol ca nic field lo cated on an al lu vial plain.

facies associations preserve from 22.5 to 20.5 cm SSDS/m, and in palustrine carbonate, 13.5 cm mechanical SSDS/m was found. SSDS in fluvial facies are rare (2.9 cm SSDS/m). The distribution of SSDS in the Sm-1 borehole shows clear relationships to sedimentary facies and processes such as density flows or fluctuation of water level. The relationships of particular structures indicate a relative timing of formation which is as follows: sediment deposition was followed by the formation of mechanical SSDS, then by bioturbation, and finally by deformations due to early diagenetic growth of carbonates and silica. The distribution of SSDS in vertical sections and their direct relationship to sedimentary facies point to endogenic rather than external trigger mechanisms such as seismic activity. The main endogenic trigger mechanisms responsible for the origin of SSDS included a Stephanian semi-humid seasonal climate, basin morphology with relatively steep gradients, and elevated source areas, which created a conducive environment for rapid and repeated deposition of sheetfloods and hyperconcentrated flows and turbidites causing syndepositional loading.

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