Towards a standard Tithonian to Valanginian calpionellid zonation of the Tethyan Realm

A calpionellid zonal scheme is proposed for the Tithonian through Valanginian pelagic carbonates of the Western Balkan Unit, based on the vertical ranges of 57 chitinoidellid and calpionellid species recognized. This zonal scheme consists of calpionellid zones that are widely accepted in the Mediterranean Realm, such as the zones of Chitinoidella, Praetintinnopsella, Crassicollaria, Calpionella, Calpionellopsis, Calpionellites and Tintinnopsella. Subzonal divisions are comparable to those in the Carpathians. Direct correlations between ammonite and calpionellid ranges suggest that the base of the Upper Tithonian corresponds to the FO of Chitinoidella boneti; that of the Upper Berriasian to the FO of the genus Calpionellopsis; and the base and top of the Lower Valanginian to the FO and LO of the genus Calpionellites respectively. Correlations of the calpionellid zonation in the study area with zonations in other areas are discussed

The Moesian Terrane during the Lochkovian - a new palaeogeographic and phytogeographic hypothesis based on miospore assemblages

The relative position of terranes during the Palaeozoic can be indicated by a combination of palaeomagnetic and floral/faunal evaluation. Palaeomagnetic data are absent from the Moesian Terrane, South-Eastern Europe, and its position is here estimated thanks to palaeophytogeographic considerations based on miospore assemblages. Miospore assemblages have been studied in two boreholes from northern Bulgaria. Preliminary analyses of chitinozoans, acritarchs and phytodebris have already been published. The oldest samples were considered to be of Pridoli age based on chitinozoan data, but here we provide new miospore evidence suggesting a Lochkovian age. This age determination is in accordance with the new interpretations based on previously published acritarch data. It is likely that the previous Pridoli age determination was influenced by Pridoli chitinozoans being reworked into the Lochkovian. The miospores are typical of assemblages only present in a small area of Avalonia and the western part of the Baltica Plate, and belong to the sinuosus-zavallatus (S-Z) Phytogeographic Province, defined here. On the contrary to the miospores, marine palynomorphs have affinity with Gondwanan assemblages. The different palaeogeographic affinities of the different palynomorph groups are not necessarily in contradiction, as it has recently been suggested that the Rheic Ocean did not act, around the Silurian-Devonian boundary, as a hermetic barrier for transoceanic chitinozoan and acritarch exchange. Therefore, the results are tentatively interpreted as indicating that the Moesian Terrane, belonging to the S-Z Province, was close to southern Laurussia during the Lower Devonian. This northern position of the Moesian Terrane during the Lower Devonian conflicts with most current palaeogeographic reconstructions, but partially supports the hypothesis of a migration of this terrane from Gondwana to Laurussia during the Palaeozoic. The possible presence of reworked palynomorphs in the Lochkovian may reflect early tectonic events associated with the close proximity of the Moesian Terrane and the Dobrudgea periphery of Palaeo-Europe. (C) 2004 Elsevier B.V. All rights reserved

Facies transition and biostratigraphic correlation of the Upper Silurian and Lower Devonian in West Bulgaria

Upper Silurian and Lower Devonian shelf deposits in West Bulgaria are exposed in three main Alpine tectonic units: the West Balkan Unit, the Lyubash Monocline and the Morava Unit. The West Balkan and Lyubash units consist of siliciclastic deposits: black graptolitic shales, banded pale shales and black siltstones. The Ludlow, Pridoli, Lochkovian, Pragian and Emsian were recognized on the basis of graptolite and tentaculite faunas. In the Morava Unit, the Ludlow black shales are progressively replaced by clayey limestones and nodular and micritic limestones in the Pridoli and Early Devonian. Newly obtained conodonts show the presence of the siluricus, eosteinhornensis, woschmidti, postwoschmidti, delta-pesavis, sulcatus, dehiscens and gronbergi zones. Petrographic study of the Morava Unit shows an increasing carbonate content and shallowing conditions upwards. The biostratigraphical correlation and facies interpretation reveal the coeval existence of two different depositional environments within the same shelf basin as well as a gradual shift in proximal direction

Berriasian bio- and magnetostratigraphy and magnetic susceptibility of the Barlya section (Western Balkan Unit, Bulgaria) – preliminary results

Integrated bio- and magnetostratigraphic data from the Lower to Upper Berriasian of the pelagic succession at Barlya (Western Balkan, Bulgaria) are presented. The investigated interval, 24 m thick, covers the top of the Calpionella elliptica, Calpionellopsis simplex and Calpionellopsis oblonga subzones. Magnetozones from the upper part of M17r up to M16n were identified. The boundary between the Elliptica and Simplex subzones correlates with the lower part of M16r, while the boundary between the Simplex and Oblonga subzones is situated in the lower part of M16n. The magnetic susceptibility reveals an increasing trend from the middle part of M16r which accounts for the increasing supply of fine clastic sediments to the basin

New biostratigraphical data from the Ordovician of Bulgaria

7 páginas, 2 figuras.-- Edited by: G. L. Albanesi / M. S. Beresi / S. H. Peralta.-- Proceedings of the International Symposium on the Ordovician System. San Juan - Argentina 2003.Peer reviewe

Novi nahodki na trilobiti i graptoliti v ordovika na Bulgaria

8 páginas, 2 figuras, 1 lámina.Darriwilian trilobites and graptolites from the Grohoten Formation (Svoge anticliorium, Sofia Stara Planina Mountain) are reviewed in the light of the new records and by direct examination of the original material reported by previous authors between 1934 and 1958 years. Middle Ordovician fossils are distributed in three stratigraphically successive assemblages. The oldest one derives from Lower Oretanian shales with nodules and consists of pendent and extensiform didymograptids (Didymograptus cf. artus, D. cf. spinulosus, D. s.l. ferrugineus), some biserials (Haddingograptus ?), a single benthic atheloptic trilobite (Placoparia balcanica n. sp.), and probably also of rare pelagic form Cyclopyge cf. kossleri. The middle assemblage which is dominated by pelagic trilobites such as Pricyclopyge binodosa binodosa, R binodosa prisca and Microparia sp., and sparse benthic elements (Ectillaenus sp.), is recorded from siltstones and silty shales that directly overlie a variously developed middle, quartzitic member. The presence both of the graptolite Didymograptus murchisoni and the rare biserial forms confirm an Upper Oretanian age for the association. Finally, the third and youngest Middle Ordovician palaeontological horizon is characterized by the occurence of the Dobrotivian cyclopygid trilobite Pricyclopyge binodosa longicephala, which derives from the settled shales and is located well below the latest assemblage of trilobites and brachiopods already of Berounian (Upper Ordovician) age. Closest comparisons of the Bulgarian trilobites are with the cyclopygid biofacies from the deep outer shelf settings of the peri-Gondwanan platform, shown by the record of some typical Bohemian taxa as P. binodosa prisca and P. binodosa longicephala.Proyectos: Nº 2001BG0005, 2001-2002. 602/1996 y 410 de PIGS (IUGS-UNESCO).Peer reviewe

Climate signals in Palaeozoic land plants

The Palaeozoic is regarded as a period in which it is difficult to recognize climate signals in land plants because they have few or no close extant relatives. In addition early, predominantly axial, representatives lack the features, e.g. leaf laminae, secondary growth, used later as qualitative and quantitive measures of past climates. Exceptions are stomata, and the preliminary results of a case study of a single taxon present throughout the Devonian, and analysis of stomatal complex anatomy attempt to disentangle evolutionary, taxonomic, habitat and atmospheric effects on stomatal frequencies. Ordovician-Silurian vegetation is represented mainly by spores whose widespread global distribution on palaeocontinental reconstructions with inferred climates suggest that the producers were independent of major climate variables, probably employing the physiology and behavioural strategies of extant bryophytes, further characterized by small size. Growth-ring studies, first possible on Mid-Devonian plants, have proved most informative in elucidating the climate at high palaeolatitudes in Late Permian Gondwana. Changes in the composition of Carboniferous-Permian low-latitude wetland vegetation are discussed in relation to tectonic activity and glaciation, with most confidence placed on the conclusion that major extinctions at the Westphalian-Stephanian boundary in Euramerica resulted from increased seasonality created by changes in circulation patterns at low latitudes imposed by the decrease of glaciations in most parts of Gondwana