In the Carnic Alps there are four sections exposing rocks across the Devonian–Carboniferous boundary: the Grüne Schneid and the Kronhofgraben sections in Austria, the Plan di Zermula A and the ...Sentiero per Cresta Verde sections in Italy. All of them are mainly composed of limestone and span from the late Famennian through the Tournaisian. In the Kronhofgraben and Plan di Zermula A sections, the limestone sedimentation is interrupted by black shales interpreted as equivalent of the Hangenberg Black Shales. The Grüne Schneid and the Sentiero per Cresta Verde sections are two of the few sections worldwide, where the calcareous sedimentation is continuous. The main extinction event registered at the end of the Devonian is testified not only in the sections where the calcareous sedimentation was replaced by black shales sedimentation but also in the Grüne Schneid and in the Sentiero per Cresta Verde sections. Data on conodont biostratigraphy and biofacies, the content in ammonoids, and trilobites and geochemistry patterns from all sections are here summarised and reviewed. These data-set allow to conclude that the four Carnic Alps sections positively test the suitability of the timeline proposed by the DCB working group for the definition of the revised Devonian–Carboniferous boundary.
Thylacocephala Pinna, Arduini, Pesarini & Teruzzi 1982 are among the most enigmatic arthropods. Their fossil record is very patchy both geographically and stratigraphically. In this paper we describe ...the first thylacocephalan known from the Carboniferous (Mississippian) of Europe, Concavicaris viktoryni sp. nov. Until now Carboniferous representatives of Thylacocephala were know exclusively from the U.S.A. We discuss the stratigraphic and geological context of occurrence of this new species as well as form and function of the unique carapace micro- and macro-ornamentation. A shape and assumed function of the characteristic lirae on the C. viktoryni sp. nov. carapace present an important supporting argument for the supposed free-swimming or pelagic mode of life in thylacocephalans. Palaeobiogeographical and evolutionary aspects of surprisingly rich but local occurrence of thylacocephalans in the Lower Carboniferous of the Moravian karst are discussed. Possible sympatric evolution from its predecessor Concavicaris incola is also pointed out.
Les Thylacocephala Pinna, Arduini, Pesarini & Teruzzi 1982 sont parmi les arthropodes les plus énigmatiques. Leur présence en tant que fossiles est très fragmentaire à la fois géographiquement et stratigraphiquement. Dans cette étude, nous décrivons le premier Thylacocephala connu du Carbonifère (Mississippien) d’Europe, Concavicaris viktoryni sp. nov. Jusqu’à présent, les représentants de Thylacocephala du Carbonifère étaient exclusivement connus des U.S.A. Nous discutons le contexte stratigraphique et géologique de la présence de cette nouvelle espèce ainsi que la forme et la fonction de la micro- et de la macro-ornementation uniques de la carapace. Une forme et une fonction supposée des lirae caractéristiques sur la carapace C. viktoryni sp. nov. constituent un argument important en faveur du mode de vie supposé libre ou pélagique chez les Thylacocephala. Les aspects paléobiogéographiques et évolutionnaires de la présence étonnamment riche bien que locale des Thylacocephala dans le Carbonifère inférieur du karst de Moravie sont discutés. Une évolution sympatrique possible à partir de son prédécesseur Concavicaris incola est aussi soulignée.
We investigated high-resolution stratigraphic distribution of selected major and trace elements and gamma-ray spectra of fourteen Devonian/Carboniferous (D/C) boundary sections of Europe located in ...the late Palaeozoic Laurussia and Gondwana. The aim was to trace the geochemical signature of a marked forced and normal regressive interval which was associated with rapid progradation of siliciclastics into the marine carbonate systems (Rhenish Massif) and a prominent hiatus in shallow-water ramp settings (Namur–Dinant Basin). This interval represents the late Devonian Hangenberg event (HBE) sensu lato (middle praesulcata conodont zone) as defined by previous authors. This regressive interval (FSST to LST) correlates with thin shale layers (HBE shale) sandwiched between monotonous nodular calcilutite/calcisiltite successions at five pelagic sections of Moravia, Carnic Alps, Montagne Noire, and Pyrenees. In all sections with continuous D/C sedimentation (i.e., except those of the Namur–Dinant Basin), the HBE s.l. interval is accompanied by elevated percentages of detrital proxies (Al, K, Rb, Zr) and changes in their ratios (Zr/Rb, K/Al, Rb/K) which are normally interpreted as indicators of increased siliciclastic input, provenance, and grain size. Zr/Rb and other proxies are traceable even without apparent lithological evidence and can, therefore, facilitate stratigraphic correlation. Paleoredox and productivity proxies (U/Th and Ni/Rb enrichment factors) only rarely show elevated values in the Hangenberg black shale interval, indicating that the associated water dysoxia/anoxia was a local rather than global phenomenon. Global correlations based on the HBE black shales should therefore be dropped in favor of the HBE s.l. interval. Moreover, analysis of sedimentation rates in the upper expansa to kockeli zone interval using the published radiometric ages suggests that the HBE s.l. was a time of significant increase in the rate of siliciclastic supply into the ocean, even in the most distal pelagic sections. Consequently, the previous interpretation of the HBE black shale as a condensed succession deposited during rapid sea-level rise seems unlikely. We interpret the HBE s.l. (i.e., including the HBE black shale) as a marine record of glacioeustatic sea-level drop and increased aeolian transport in connection with late Devonian climatic cooling and glaciation. The set of geochemical markers related to the late Devonian sea-level fluctuation can be used for super-regional to global correlations from platform to basin settings. Moreover, they can facilitate current efforts to determine a new D/C boundary definition.
•Hangenberg events sensu lato recorded rapid detrital influx into marine realms.•Element proxies are perfect tools for neritic to pelagic correlation near D/C boundary.•Hangenberg black shales do not record basin starvation during peak sea level rise.
Mercury (Hg) chemostratigraphy is an efficient tool for tracing distal volcanism, as suggested in many recent studies. In our research, we focused on Hg and other trace element contents in two ...Devonian-Carboniferous boundary sections from two different and spatially distant areas. The Lesní lom section (Czech Republic) was located in the south-eastern part of the Laurussia plate and the Duli (Guangxi, China) section in the South China Plate. In both studied sections, the highest Hg, Hg/Fexs or Hg/Al values occurred at the Devonian-Carboniferous boundary. In Lesní lom, organic matter remineralization was connected with origin of pyrite which sequestered a part of the Hg content. The decoupling of Hg and TOC within the Duli section strata and the significant correlation with Al and Fe may suggest that Hg is hosted primarily by clay particles, derived from the landmass into the marine realm. Mercury was also incorporated into pyrites but the poor correlation between Hg and TS (total sulfur) indicates a possible loss of S during oxygenation events. In the Lesní lom section, and partly in the Duli section, Fe and Mn redox cycling may have played an important role in sediment Hg content. Both sections were influenced by widespread hydrothermal and volcanic activity, indicated by positive Eu anomalies, MSI, Fe/Ti, Zr/Al2O3 and Ti/Al2O3 values. It remains to be clarified whether, besides the interplay of local magmatic activity and redox oscillations, there may have been some additional influence of the multi-phase Viluy Large Igneous Province, although its younger phase (364.4 ± 1.7 Ma) slightly precedes the Hg anomalies obtained.
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•Distribution of Hg and other trace elements from Devonian-Carboniferous boundary•The highest Hg, Hg/TOC, Hg/Al, and Hg/Fe values bellow and in the Hangenberg Events•Anomalous Hg was not simply derived from the increased deposition of organic carbon.•Both sections were influenced by widespread hydrothermal and volcanic activity.•Hg enrichment caused by local hydrothermal and volcanic activity and redox variations
The paper focuses on high-resolution multidisciplinary research on three Devonian–Carboniferous boundary sections in shallow-water carbonate rocks in the Namur–Dinant Basin (Belgium, France). The aim ...of the study is to provide palaeo-environmental reconstructions and correlations supported by several independent quantitative proxies. We describe several correlative horizons and provide their sequence-stratigraphic interpretation based on facies analysis, spectral gamma-ray data, element concentrations (XRF) and δ13Ccarb, with foraminifer-biostratigraphy age control. The most prominent surface is a basal surface of forced regression, which is indicated by a sharp basinwards facies shift and a drop in clay-gamma-ray values and Al concentrations at the base of the Hastière and Avesnelles formations in more distal settings. In proximal settings, this surface merges with a hiatus at the Devonian–Carboniferous boundary inferred from foraminifer biostratigraphy. This hiatus can be correlated with the global Hangenberg sandstone event, which indicates a glacioeustatic sea-level fall. Increasing values of Zr/Al, K/Al, Sr/Al and Mn/Al coincide with the proximal facies of the falling stage system tract and lowstand system tract in the Hastière and Avesnelles formations as a consequence of the enhanced input of siliciclastics and nutrients during low sea levels. The top of the middle Hastière member is interpreted as the maximum regression surface, which is overlain by transgressive system tract of the upper Hastière member. The patterns of gamma-ray, δ13Ccarb, Th/K, Al and Zr/Al curves are well correlated between the studied sections. The δ13Ccarb excursions are correlated with the unnamed excursion in the Upper expansa conodont zone (Carnic Alps) and with the global Hangenberg event s.l. excursion in the kockeli conodont zone. This sequence-stratigraphic framework is used for correlations with deltaic successions from the Tafilalt Basin, Morocco.
The basal surface of the forced regression equivalent to the Hangenberg sandstone event, which is typical for deeper-water settings, is easily recognisable and correlatable with gaps in more-shallow water settings. We suggest that it should be taken into account as a possible candidate for the “natural solution” of the Devonian–Carboniferous boundary in discussions concerning its redefinition.
A multidisciplinary correlation of the Devonian-Carboniferous (D-C) boundary sections from the Moravian Karst (Czech Republic) and the Carnic Alps (Austria), based on conodont and foraminifer ...biostratigraphy, microfacies analysis, field gamma-ray spectroscopy (GRS), carbon isotopes and element geochemistry, is presented in this paper. The study is focused on the interval from the Middle Palmatolepis gracilis expansa Zone (Late Famennian) to the Siphonodella sandbergi Zone (Early Tournaisian). In Lesni lom (Moravian Karst), a positive δ13C excursion in the Bisphatodus costatus - Protognathodus kockeli Interregnum from a distinct laminated carbonate horizon is correlated with a carbon isotope excursion from the Grune Schneid section of the Carnic Alps and is interpreted as the equivalent of the Hangenberg black shales and a local expression of the global Hangenberg Event sensu stricto. Higher up at both sections, a significant increase in the terrigenous input, which is inferred from the GRS signal and elevated concentrations of terrigenous elements (Si, Ti, Zr, Rb, Al, etc.), provides another correlation tieline and is interpreted as the equivalent of the Hangenberg sandstone. Both horizons are discussed in terms of relative sea-level fluctuations and palaeoceanographic changes. Recent studies show that conodont biostratigraphy is facing serious problems associated with the taxonomy of the first siphonodellids, their dependence on facies and discontinuous occurrences of protognathodids at the D-C boundary. Therefore, the correlative potential of geochemical and petrophysical signatures is high and offers an alternative for the refining of the problematic biostratigraphic division of the D-C boundary.
The Devonian–Carboniferous boundary was coeval with the Hangenberg Crisis, which is regarded as a first-order mass extinction event related with large sea-level changes and widespread anoxia. This ...study aims to trace the geochemical paleoproductivity and paleoredox proxies across the Devonian–Carboniferous carbonate-dominated successions of the Namur-Dinant Basin (Belgium, northern France) and the Moravo-Silesian Basin (Czech Republic), located in the Variscan Rhenohercynian Zone. The research was focused on the distribution of oxides (SiO2, Al2O3, Fe2O3, CaO, Na2O, K2O, TiO2, MnO) and trace elements (Th, U, V, Zr, Mo, Zn, Pb, Ni, Cu) measured by ICP-OES and ICP-MS, respectively. The enrichment factors of Mo and U and their ratios were used as the main paleoredox proxies, whereas the enrichment factors of Zn, Cu, Pb, and Ni were employed to trace the paleoproductivity changes. High values of Zr/Al2O3 (>0.001), TiO2/Al2O3 (>0.06), and Fe/Ti (>20) and low values of Al/(Al + Fe + Mn) (<0.35) coinciding with an increase of paleoredox proxies suggest a possible volcanic and hydrothermal source of nutrients, related to Late Devonian and Early Carboniferous extensional magmatism in the Rhenohercynian domain, although a relationship between higher paleoproductivity and enhanced continental runoff of volcanic material cannot be excluded. The studied Devonian–Carboniferous boundary sections from the Namur-Dinant Basin (Gendron-Celles, Ardennes quarry) reveal three levels with similar vectors of Mo and U enrichments. The pre-crisis Famennian pattern is typical for weakly restricted basins with Fe-Mn redox cycling accompanying vertical fluctuations of the oxic/anoxic chemocline close to the sediment/water interface with the influence of particulate shuttle. The MoEF and UEF patterns corresponding to the unrestricted or weakly restricted basin with alternating suboxic to anoxic conditions are considered to represent the transgressive Hangenberg Black Shale Event. The lower Tournaisian MoEF and UEF patterns fall along a vector in the direction of the strongly restricted marine conditions with prevailing suboxic conditions. In the Moravo-Silesian Basin (Lesní lom section), the pre-crisis Famennian MoEF and UEF vector indicates an unrestricted marine trend which converges with that of restricted systems. Redox conditions range from suboxic to euxinic. In the Tournaisian, MoEF and UEF oscillate between oxic and anoxic conditions and fall along a vector of strongly restricted marine conditions. Increased isolation of both studied basins in the Early Tournaisian is regarded as a reflection of a significant eustatic fall during the Hangenberg Crisis, linked to a severe episode of the Gondwana glaciation. These paleohydrographic patterns have correlative potential that should be considered for a revised Devonian-Carboniferous Boundary definition.
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•MoEF and UEF revealed changes in redox and paleohydrographic conditions.•Both basins were moderately restricted in the latest Famennian.•High restriction in the Early Tournaisian resulted from Hangenberg sea-level fall.•Increased hydrothermal input proxies co-occur or precede high productivity and anoxia.•Fluctuations of redox conditions range from oxic to euxinic.
Red colouring in marine red beds (MRB) is commonly attributed to deposition and early diagenesis under specific redox conditions. Therefore, the MRB can be considered time-specific facies. However, ...since red colouring is a subjective criterion, it is difficult to establish a colour limit for the MRB in the scale from grey to yellow, orange, pink to red. Using spectral reflectance, carbonate petrology, bulk-rock and in-situ geochemistry data from three sections of Ordovician orthoceratite carbonates of South China, we addressed the question whether the incipient reddening in the pink carbonates was associated with similar redox changes and palaeoceanographic conditions like in the MRB. The yellowish grey to greyish orange pink (Munsell Rock Colour Chart) carbonates with low concentrations of hematite (< 0.01 %) are transitional from goethite-bearing grey to hematite-enriched true MRB. The red-coloured skeletal interiors, microstromatolites, nodules and filamentous microborings suggest an extensive microbial activity which was accompanied by precipitation of authigenic aluminosilicates (clays). We hypothesize that the microbial clay precipitation is an important intermediate step in Fe transformation from its primary sources to hematite in the MRB. The carbonate deposition was followed by early diagenetic, shallow-subsurface REE fractionation, and FeMn (+Mo, U and V) redox cycling along microbially controlled redox microgradients. The geochemical redox signature of the pink carbonates is very similar to the MRBs of Devonian and Ordovician age. They were deposited under similar palaeoenvironmental conditions on a deeper shelf inhabited by skeletal heterotrophs, with reduced rates of organic matter burial and slow sedimentation rates. The sedimentation of the pink carbonates and MRBs seem to randomly coincide with the coeval global sea-level changes and δ13Ccarb fluctuations suggesting that the local controls of sediment colour override the global ones.
•Siphonodella duplicata sensu Hass (=S. hassi) was revised as S. wilberti.•S. cooperi hassi is synonym of S. obsoleta and S. jii is synonym of S. quadruplicata.•S. wilberti and S. quadruplicata have ...similar morphology of early ontogenetic stages.•Advanced ontogenetic stages with two rostral ridges belong to S. wilberti only.•Maintenance of the wilberti Zone (=hassi/S. (S.) jii zones) is suggested.
Traditionally, biostratigraphy of the terminal Famennian (Upper Devonian) and lower part of the Tournaisian (Mississippian) is based on phylogeny of the conodont genus Siphonodella Branson and Mehl. This study is focused on a Siphonodella species with a long taxonomical history. For the last three decades it was known as S. hassi Ji, 1985 and was used as a zonal index for the eponymic hassi Zone, used worldwide. However, this species faces several taxonomical problems. The main issue is the homonymy of S. hassi and S. cooperi hassi Thompson and Fellows, 1970. However, S. cooperi hassi is a subjective junior synonym of S. obsoleta Hass, 1959. The oldest junior synonym of S. hassi is S. wilberti Bardasheva, Bardashev, Weddige and Ziegler, 2004, and, according to a statement by the International Commission on Zoological Nomenclature, the latter represents the only available name for this species. An additional problem is the similar morphology of early ontogenetic stages of S. wilberti and S. quadruplicata Branson and Mehl, 1944, the youngest stratigraphically important siphonodellid species. In advanced ontogenetic stages, P1 elements that possess two rostral ridges belong to S. wilberti only. The smaller P1 elements having two or less rostral ridges comprise the S. wilberti- S. quadruplicata plexus. Maintenance of the wilberti Zone in the Tournaisian global zonation is suggested.
The continuous and well-accessible Devonian-Carboniferous boundary successions of the Czech Republic are part of the Brunovistulian Unit, which belongs to the Variscan Rhenohercynian Zone of the ...Bohemian Massif. The well-studied sections, with almost continuous carbonate sedimentation, crop out in the Moravian Karst area and are characterised by carbonate turbidites (Lesní lom) and hemipelagic successions (Křtiny). In the Lesní lom quarry, a complete succession of conodont zones of the Devonian-Carboniferous boundary interval (Upper
expansa
,
praesulcata
,
costatus-kockeli
,
kockeli
,
sulcata/kuehni
,
bransoni
,
duplicata
zones) was documented in calciturbidites and can be correlated with coeval foraminiferal zones (
Quasiendothyra kobeitusana
,
Quasiendothyra konensis
and
Tournayellina pseudobeata
zones). The Hangenberg Crisis and its three phases can be well recognised both with lithological, biostratigraphical and geochemical approaches in the Lesní lom section. At Křtiny, the nodular limestones yielded conodonts of the Devonian-Carboniferous boundary interval, but missing protognathodid fauna hampered identification of the
kockeli
Zone. A stratigraphic gap covering the basal part of the
sulcata/kuehni
Zone or strong condensation can be inferred from the occurrence of the transitional morphotype
Si. sulcata-bransoni
at the base of this zone. The tested “Montpellier criterion” for the Devonian-Carboniferous boundary redefinition can be used only in the Lesní lom section, where the first
Protognathodus kockeli
occurs above the regressive Hangenberg Sandstone Event deposits.
