Is there an Upper Devonian rift zone under the northern front of the Alps separating East and West Armorican crustal segments?
Abstract: Many Cadomian and Early Paleozoic basement units in the Alps are considered to be derived from the East Armorican segment of the Gondwana margin. A common assumption is that this East Armorican crustal segment was shifted into the hinterland of West Armorica via a Variscan dextral shear zone. However, the tectonic separation of West and East Armorica could have started earlier during a Late Devonian rifting event. The respective rift zone is supposed to be hidden under the northern nappes of the Alpine–Carpathian chain. This newly proposed sub-Alpine “Cetic rift” was presumably connected with the Upper Devonian Brevenne rift, which is documented in the northern French Massif Central, the southern Vosges and the southern Black Forest. The combined Brevenne–Cetic rift zone may thus represent a major trans-European structure. It is tentatively interpreted as an ephemeral back-arc rift that opened due to southward subduction activities on the northern side of West Armorica.
Biostratigraphy on ammonoids and foraminifers of Middle Triassic (Pelsonian) Jelovica Limestone Formation (Stara Planina Mts), Eastern Serbia
Abstract: Biostratigraphy and sedimentology of the Pelsonian (Middle Anisian) carbonate Jelovica Fm sequence have been documented in detail in the Spomen Dom section (Jelovica–Visočka Ržana region of the Stara Planina Mts, Eastern Serbia). Abundant ammonoids and foraminifers, together with rare brachiopods, nautiloids, bivalves and crinoids characterize faunal associations of the ammonoid Balatonites balatonicus Zone and the foraminiferal Pilammina densa Zone. This is the first report based on ammonoid and foraminiferal faunas, which allowed initial biostratigraphic subdivision of the Middle Anisian strata from the whole Eastern Serbia region.
Low-grade metamorphic rocks of the Tethys subduction–collision zone in the Medvednica Mt. (NW Croatia)
Abstract: The low-grade metasedimentary rocks of Medvednica Mt. (Northwest Croatia) are associated with ortho-greenschists (metabasalts). The Lower to Upper Triassic age of the protolith of the low-grade metamorphic rocks belonging to the Stari Potok, Adolfovac, Tusti Breg, Bliznec, Mrzljak, and Sljeme lithostratigraphic units is determined on the basis of conodonts and field relationships. The metamorphic age of the Triassic metasedimentary rocks from the Risnjak lithostratigraphic units is assumed to be Jurassic. Petrographic and geochemical analyses of ortho-greenschists point to a tholeiite basic magmatic protolith rock having T-MORB (transitional midocean-ridge basalt) characteristics. The ortho-greenschists of the Sljeme lithostratigraphic unit underwent retrograde metamorphism and show metamorphic zoning from the epidote–amphibolite facies to the lower parts of the greenschist facies. However, the greenschists of the Tusti Breg and Bliznec units are characterized by prograde metamorphism ranging from lower to higher greenschist facies. This metamorphism is associated with Jurassic subduction (165–150 Ma) and closure of the Western Tethys. Retrograde metamorphism took place during the collision of the Adriatic and Eurasian plates in the Lower Cretaceous (125–110 Ma).
Paleoenvironmental and paleoclimatic conditions during the Eocene/Oligocene transition in the southern Hellenic Thrace Basin (Lemnos Island, North Aegean Sea)
Abstract: The late Eocene–early Oligocene paleoenviromental and paleoclimatic conditions in the southern Hellenic Thrace Basin (Lemnos Island, Northeast Aegean Sea) have been determined, based on planktonic and benthic foraminiferal analyses. One hundred thirty-nine mudstone samples were collected from representative outcrops that cover the entire stratigraphic record. The samples correspond to submarine fan (Ifestia, Panagia and Kaspaka sections) and shallow-marine deposits (Kaminia section). The analyses of calcareous nannoplankton and planktonic foraminifera indicate that sedimentation took place during the late Eocene to early Oligocene (Priabonian–Rupelian). The ratio of planktonic to benthic foraminifera, the paleobathymetry and the qualitative analysis of foraminifera support a regional shallowing-upward trend. The presence of Globobulimina suggests that dysoxic conditions prevailed the late Eocene, while the presence of paragloborotaliids, globigerinids and chiloguembelinids in the studied succession could be indicative of a gradual cooling event since the late Eocene. The Eocene/Oligocene boundary is characterized by welloxygenated bottom waters, and the abundance of Catapsydrax unicavus and Paragloborotalia nana suggests a strong cooling event during the early Oligocene (O1 biozone). This decrease in water temperature is most likely linked to the global cold Oi1 event. The early Oligocene is characterized by oxic bottom-water redox conditions that were intermittently interrupted by shorter periods of dysoxic conditions. The occurrence of Bathysiphon indicates the passage of turbidity currents. The recognition of Chiloguembelina cubensis, P. nana and C. unicavus suggests high productivity over the range of the water column, most likely correlated with mixing water during the cold event Oi2. This study decrypted the global paleoenvironmental and paleoclimatic changes that influenced the southern Hellenic Thrace Basin during the Eocene/Oligocene transition.
Deltaic systems of the northern Vienna Basin: The lower-middle Miocene conglomerate bodies
Abstract: The cross-border correlations of the Miocene lithostratigraphic units (Slovakia, Austria) remain poorly constrained, owing to the various sources of clastic material transported into the basin and the low stratigraphic resolution of conglomerates. Therefore, this study is focused on the Lower and Middle Miocene conglomerates in the deltaic systems of the northern Vienna Basin and assesses their implications for cross-border correlations, as well as for the evolution of the Eastern Alpine–Western Carpathians junction area. Revision of lithostratigraphy is based on analyses of the Zohor-1 and Lozorno-1 wells, including the reassessment of published data to account for any refined geochronology and paleogeography. The Lower Miocene Jablonica deltaic system is formed by deposits originating in the alluvial, deltaic, and littoral environments in the basin’s northernmost tip. The conglomerates of exclusively Western Carpathian provenance pass into the deep-water marine mudstones of the Ottnangian Lužice and Karpatian Lakšáry fms. The Karpatian conglomerates at the base of the Zohor-1 well can be correlated both with the conglomerates of the Jablonica deltaic system in the north, as well as with the conglomerates of the Gänserndorf Mb. in the south. The overlying heterolithic flood plain of the deltaic sediments from the Závod Fm. most likely form the facies continuation of the alluvial to flood plain deposits of the Schönkirchen Mb. (upper part of the Aderklaa Fm.). The Middle Miocene deposition starts with terrestrial sediments along the slopes of the Malé Karpaty Mts. dated to 15.2 Ma. Later, along with the Devínska Nová Ves fan-delta, the presence of Orbulina suturalis developed in the marginal parts of the Vienna Basin during the Early Badenian. Despite having the same structural position, it is younger than the Rothneusiedl Formation in the southern part of the Vienna Basin. The provenance of clastics reflects the source in the Central Western Carpathian units and documents the Miocene uplift of the horst structure of the Malé Karpaty Mts.