46 research outputs found
Low-diversity conodont and cephalopod assemblages from the Silurian of the Tinduf Basin, Western Sahara
No full textA peculiar cephalopod slab collected in Western Sahara hosts almost monospecific cephalopod
and conodont associations, preliminarily attributed to the Ludfordian based on the occurrence of Wurmiella sp. A Corriga et al., 2021. Arionoceras submoniliforme (Meneghini, 1857) dominates the nautiloid fauna that reveals a clear bimodal orientation. The microfacies analysis documents a cephalopod packstone associated with abundant skeletal elements coated by micrite. The origin and significance of this association are discussed and possibly interpreted as a post-Lau Event fauna, still deeply affected by the extinction event
Ontogeny of Ancyrodelloides carlsi (Boersma) and comments on its generic attribution (Conodonta, Lower Devonian)
No full textThe ontogeny of the Lochkovian conodont species Ancyrodelloides carlsi (Boersma) is demonstrated thanks to a rich population from Morocco. The studied sample includes elements at various growth stages from juvenile to gerontic. The data are confirmed by several elements in collections from several localities in the Carnic Alps (Italy and Austria). The absence of terraces at every stage of growth and the presence of a strong denticulated lateral process confirms the generic attribution of the species to genus Ancyrodelloides. Comments on the apparatus are provided. The geographical distribution of the species, limited to Europe and the Mediterranean region, challenges its stratigraphic value for long distance correlations
A Pridoli-Lochkovian conodont zonation in Sardinia and the Carnic Alps: implications for a global zonation scheme
No full textThe main conodont zonation schemes for the Pridoli and the Lochkovian presents some problems that make difficult their use in several geographical areas. Data from several sections in Sardinia and the Carnic Alps not only allow to built a regional zonation scheme for these areas, but also suggest possible solutions of global validity. In the Carnic Alps and Sardinia, the Přídolí is subdivided into three zones: Eosteinhornensis s.l., Lower and Upper detortus. The latter results after the subdivision of the former detortus Zone on the basis of the Last Appearance Datum of some coniform species (Dapsilodus obliquicostatus, Coryssognathus dubius and Panderodus recurvatus) that became extinct almost simulta-neously in the latest Přídolí. Daps. obliquicostatus is chosen as the marker, being the most common and easily identifi-able species. In the Lochkovian six zones are discriminated: Hesperius, carlsi, transitans, eleanorae, trigonicus and pan-dora β. The hesperius Zone, which includes the postwoschmidti subzone in its upper part, is expanded to include most of the eurekaensis zone of the "global" scheme, because the marker Oz. eurekaensis is not present. The carlsi Zone corre-sponds to the upper part of the eurekaensis Zone and to the lower part of the former mid-Lochkovian delta Zone (= omoalpha Zone). The rest of the Middle Lochkovian is subdivided into the three zones (transitans, eleanorae and trigonicus) already proposed in Nevada and Spain, followed by the pandora β Zone. All the zones are discussed and checked for their applicability in other palaeogeographical regions
GEOLOGY OF MOUNT ZERMULA MASSIF (CARNIC ALPS, NE ITALY)
No full textIn Mt Zermula area rocks of Ordovician to Carboniferous age belonging to the Pre-Variscan sequence of the Carnic Alps crop out. The whole area was overturned during the Variscan orogeny and the higher parts of Mt Zermula represent Devonian shallow water rocks thrusted on top of an Upper Ordovician to Lower Carboniferous succession showing mostly basin to slope depositional environments. This distal sequence is well exposed in the southern flank of Mt Zermula and in the eastern and western sides of the study area. The lithostratigraphic units and their relationships are described. A geological map of the southern part of Mt Zermula is provided, as well as a stratigraphic scheme
The first documented co-occurrence of conodonts and graptolites in Silurian (Telychian) black shales of the Prague Synform, Czech Republic, and its stratigraphical and palaeoecological significance
No full textThe Želkovice locality, located in the south-western part of the Prague Synform, is well-known for its exceptionally well-preserved graptolites in black shales. Despite being studied repeatedly by several authors for over 170 years, no record of conodonts has been found until now. Both conodonts and graptolites are significant biostratigraphic groups of Paleozoic fossils. However, papers about their co-occurrence are rare. Their occurrence is tied to distinct lithofacies, which makes direct biozonal correlation difficult. Their partial overlap sheds new light on ecological niches, resilience, and the palaeoecological conditions of the environment. Determined conodonts belong to cosmopolitan taxa with a long range, inhabiting the deeper, distal parts of the shelf or continental slope. A total of 10 conodont species were identified at the same locality, spanning the entire linnaei Biozone. The occurrence of the index species Distomodus staurognathoides, whose stratigraphic range overlaps with the locally used graptolite linnaei Biozone and the internationally used guerichii Biozone, is documented. This study also documents rare specimens
of pelagic fauna for the first time and discusses hypothetical parasitism and predation in conodonts and graptolites. This is the first study to describe the co-occurrence of both groups within the same lithology (black shale) and stratigraphic level, not only at the Želkovice site, but also elsewhere in the Silurian of the Prague Synform
Upper Silurian and Lower Devonian conodonts from Tafilalt, southeastern Morocco.
No full textThe conodont association from three Silurian-Lower Devonian sections (Bou Tchrafine N2, Atrous 3 and Atrous 7) in the Tafilalt (southeast Morocco) are presented. The sections are constituted by cephalopod rich limestones ("Orthoceras limestones") and by crinoidal limestones ("Scyphocrinites limestones") cropping out within thick shaley sequences. The association includes 29 taxa belonging to 13 genera (Ancyrodelloides, Belodella, Dvorakia, Icriodus, Kockelella, Lanea, Oulodus, Ozarkodina, Pelekysgnathus, Polygnathoides, Pseudooneotodus, Wurmiella, Zieglerodina). The conodont fauna allows the recognition of seven conodont zones: ploeckensis and siluricus in the Ludlow, eosteinhornensis s.l., Lower detortus and Upper detortus in the Pridoli, and hesperius and transitans in the Lochkovian. The age of the "Orthoceras limestones" is confirmed as middle Ludfordian (ploeckensis-siluricus zones), whereas it is stated that the "Scyphocrinites limestones" spans the Silurian/Devonian boundary. Some elements of the apparatus of Zieglerodina planilingua and the P2 element of Lanea omus are described. The phylogenetic relationships between genera Lanea and Ancyrodelloides are discussed
Litho-, Chrono- and conodont bio-stratigraphy of the Rauchkofel Boden Section (Upper Ordovician-Lower Devonian), Carnic Alps, Austria.
No full textAn updated stratigraphy of the Rauchkofel Boden Section, a classical reference section for the Carnic Alps that exposes rocks from the Katian (Upper Ordovician) to the Pragian (Lower Devonian) is here presented, following latest developments in conodont taxonomy and biostratigraphy, as well as in chronostratigraphy, and the recent introduction of a new lithostratigraphic outline of the Carnic Alps. The original conodont collection of the ’70s and ʼ80s was restudied and complemented by a detailed resampling in order to achieve a more precise conodont biostratigraphic assignment. Twenty-five conodont Zones are now documented. The lithostratigraphy is precisely fixed to the new lithostratigraphic scheme of the Pre-Variscan sequence by definition of seven distinct formations. Finally, the position of chronostratigraphic boundaries is discussed
Stratigraphic Sections in the La Valute-Chiarsò area (Mt Zermula, Carnic Alps, NE Italy)
No full textNineteen stratigraphic sections which age spans from the Late Ordovician to the early Carboniferous were measured by various scientists in the La Valute Chiarsò area, mainly for litho- and bio-stratigraphic purposes. These data, some still unpublished, are here summarized and updated to the more recent zonation schemes, together with those from spot samples collected in the area
Carboniferous-Permian sequence of Nassfeld area (Carnic Alps, Austria-Italy)
No full textIn the Nassfeld area the post-Variscan sequences of the Carnic Alps is well preserved and consists of Late Palaeozoic to Early Mesozoic units which were deposited in equatorial realms. Of them the lithological and stratigraphical characteristics of the
Carboniferous to Permian sediments are briefly described
