Devonian Carboniferous Transition Research Articles

The global Hangenberg Crisis (Devonian–Carboniferous transition): review of a first-order mass extinction

Abstract The global Hangenberg Crisis near the Devonian–Carboniferous boundary (DCB) represents a mass extinction that is of the same scale as the so-called ‘Big Five’ first-order Phanerozoic events. It played an important role in the evolution of many faunal groups and destroyed complete ecosystems but affected marine and terrestrial environments at slightly different times within a short time span of c. 100–300 kyr. The lower crisis interval in the uppermost Famennian started as a prelude with a minor eustatic sea-level fall, followed rather abruptly by pantropically widespread black shale deposition (Hangenberg Black Shale and equivalents). This transgressive and hypoxic/anoxic phase coincided with a global carbonate crisis and perturbation of the global carbon cycle as evidenced by a distinctive positive carbon isotope excursion, probably as a consequence of climate/salinity-driven oceanic overturns and outer-shelf eutrophication. It is the main extinction level for marine biota, especially for ammonoids, trilobites, conodonts, stromatoporoids, corals, some sharks, and deeper-water ostracodes, but probably also for placoderms, chitinozoans and early tetrapods. Extinction rates were lower for brachiopods, neritic ostracodes, bryozoans and echinoderms. Extinction patterns were similar in widely separate basins of the western and eastern Prototethys, while a contemporaneous marine macrofauna record from high latitudes is missing altogether. The middle crisis interval is characterized by a gradual but major eustatic sea-level fall, probably in the scale of more than 100 m, that caused the progradation of shallow-water siliciclastics (Hangenberg Sandstone and equivalents) and produced widespread unconformities due to reworking and non-deposition. The glacio-eustatic origin of this global regression is proven by miospore correlation with widespread diamictites of South America and South and North Africa, and by the evidence for significant tropical mountain glaciers in eastern North America. This isolated and short-lived plunge from global greenhouse into icehouse conditions may follow the significant drawdown of atmospheric CO 2 levels due to the prior massive burial of organic carbon during the global deposition of black shales. Increased carbon recycling by intensified terrestrial erosion in combination with the arrested burial of carbonates may have led to a gradual rise of CO 2 levels, re-warming, and a parallel increase in the influx of land-derived nutrients. The upper crisis interval in the uppermost Famennian is characterized by initial post-glacial transgression and a second global carbon isotope spike, as well as by opportunistic faunal blooms and the early re-radiation of several fossil groups. Minor reworking events and unconformities give evidence for continuing smaller-scale oscillations of sea-level and palaeoclimate. These may explain the terrestrial floral change near the Famennian–Tournaisian boundary and contemporaneous, evolutionarily highly significant extinctions of survivors of the main crisis. Still poorly understood small-scale events wiped out the last clymeniid ammonoids, phacopid trilobites, placoderms and some widespread brachiopod and foraminiferan groups. The post-crisis interval in the lower Tournaisian is marked by continuing eustatic rise (e.g. flooding of the Old Red Continent), and significant radiations in a renewed greenhouse time. But the recovery had not yet reached the pre-crisis level when it was suddenly interrupted by the global, second-order Lower Alum Shale Event at the base of the middle Tournaisian.

Late Devonian radiolarian-bearing siliceous rocks from the Karamay ophiolitic mélange in western Junggar: Implications for the evolution of the Paleo-Asian Ocean

Abundant Late Devonian radiolarians occur in the siliceous rocks of the Karamay ophiolitic mélange in western Junggar. The siliceous rocks are interpreted as deposit in a remnant oceanic basin in view of their petrological and geochemical characteristics. New data suggest that the age of the Karamay ophiolitic mélange can be extended from the Ordovician to Late Devonian, thus representing the youngest known oceanic crust in western Junggar, which indicates that the closure of the Paleo-Asian Ocean was at least after the Late Devonian in southern western Junggar. The Carboniferous formation capping the siliceous rocks units comprises, in ascending order, a broad regressive sequence from the abyssal–bathyal turbidites, littoral-neritic carbonates, and calcareous clastic rocks to molasse, indicating that the ocean–continent transformation probably occurred in the Devonian–Carboniferous transition or the early Early Carboniferous. The oceanic basin was filled with volcaniclastic turbidites in the Visean–Serpukhovian, and evolved into a residual sea basin in the Late Carboniferous. The final closure of the Paleo-Asian Ocean in western Junggar was marked by the emergence of molasse in the late Late Carboniferous.

Devonian–Carboniferous transition containing a Hangenberg Black Shale equivalent in the Pho Han Formation on Cat Ba Island, northeastern Vietnam

On Cat Ba Island in northeastern Vietnam, the Devonian to Carboniferous (D–C) transition consists mainly of ramp carbonates intercalated with black shale beds (Beds 1 to 176) in the Pho Han Formation and is one of the few records of the D–C transition of the eastern Paleotethys. The three main facies of the sequence are Facies 1 (alternations of whitish gray to gray limestone and marl), Facies 2 (calcirudite, Bed 115b), and Facies 3 (alternations of dark gray limestone and organic-carbon-rich black shale, Beds 115c–120 and 126–129). The latest Famennian (Siphonodella praesulcata Subzone) conodont assemblage of S. praesulcata, Palmatolepis gracilis, Palmatolepis sigmoidalis, and Rhodalepis polylophodontiformis was recognized in Beds 113–115c. Beds 105–112 commonly contain Palmatolepis expansa, P. gracilis, and P. sigmoidalis. Bed 119 yielded a basal Carboniferous index conodont Siphonodella sulcata. In Beds 116–118, solenoporids such as Pseudochaetetes elliotti and Parachaetetes sp. were characteristic species in organic-carbon-rich dark gray limestone.Facies 1 is characterized by bioclastic, peloidal, and intraclastic grainstone and packstone containing massive normal grading and cross-laminations, and is interpreted to represent deep ramp carbonates above storm wave base. Facies 2 is represented by typical lag deposits overlying a transgressive surface. Facies 3 comprises organic-carbon-rich black shale and minor scour-filling bioclastic, peloidal, and intraclastic packstone, and may represent a marginal basin plain environment surrounding a carbonate ramp. The alternations of organic-carbon-rich black shale and dark gray packstone (Facies 3) show no evidence of bioturbation and have high TOC contents (0.18–5.73wt.%). A minor succession within the transgressive lag deposits (from Bed 115b of Facies 2 to Beds 115c–120 in the lower part of Facies 3) is equivalent to the Hangenberg Black Shale (s. l.) in the middle part of the Siphonodella praesulcata to Siphonodella sulcata zones, because Beds 115b–120 characterized by no evidence of bioturbation and high TOC contents are interpreted to be accumulated in anoxic to dysoxic conditions.

Devonian–Carboniferous transition in the Pho Han Formation on Cat Ba Island, northeastern Vietnam

Devonian–Carboniferous transition in the Pho Han Formation on Cat Ba Island, northeastern Vietnam

Bryozoan diversity in Southern Siberia at the Devonian–Carboniferous transition: New data confirm a resistivity to two mass extinctions

Two spectacular mass extinctions, namely the Kellwasser and the Hangenberg events, affected the Earth's biota during the Late Devonian–Early Carboniferous. Diverse assemblages of bryozoans are known from the Fasnian–Tournaisian deposits of Southern Siberia, which includes such regions as the Kuznetsk Basin, the Kolyvan'–Tom' Zone, the Rudny Altay, and the Gorny Altay. Our new data establish the stratigraphic ranges of 154 species, which belong to 56 genera and 21 families. These data have been analyzed quantitatively to measure the patterns of diversity dynamics and the changes in the taxonomic diversity structure. The species diversity increased at the Frasnian–Famennian transition. After a short-term, but dramatic decrease in the middle Famennian, the total number of species accelerated in the late Famennian and the Tournaisian. A similar pattern occurred for both genera and families, although the radiation at the Frasnian–Famennian transition was not as large, and total family diversity decreased slightly in the Tournaisian. Changes in total species diversity differed between orders of bryozoans. Changes in taxonomic diversity structure were moderately rapid. The Tournaisian species diversity was governed by the other genera comparing to the early time intervals. Thus, our regional data suggest that bryozoans generally survived both the Frasnian/Famennian and the Devonian/Carboniferous mass extinctions, confirming similar conclusions made earlier with global data. However, a mid-Famennian regional crisis (diversity drop) in the evolution of bryozoans is documented within Southern Siberia. Bryozoan radiations coincided with pulses of basin deepening that occurred during both mass extinction intervals, perhaps explaining why bryozoans were resistant to extinction. The mid-Famennian crisis might have been caused by a rapid regression coupled with basin shallowing.

Etude palynologique et évaluation de l'indice d altération thermique du Paléozoique du forage DOT 1 (bassin des Doukkala centre-ouest marocain)

The palynological study of the Paleozoic section penetrated by well DOT 1 has permitted the establishment of a precise subdivision in this area by recognizing (1) the Permo-Carboniferous, (2) the Devonian-Carboniferous transition, (3) the Lower, Middle and Upper Devonian, (4) the Silurian and the Ordovician. This subdivision was possible by using the rich association of spores, acritarchs and chitinozoans yielded from the studied samples. Formerly, the stratigraphy was established especially by microfauna and facies correlation, whereas only little palynological work had been done. The latest well (DOT 1), however, drilled in this basin in 1987 discovered a complete Paleozoic section in this area. The palynostratigraphy established for this well allowed good correlation with the other ten wells drilled in this basin since 1960 and permits the reevaluation of the Doukkala area. Using the palynofacies and the spore coloration, this study allowed also the evaluation of the type of organic matter and the Thermal Alteration Index (TAI).

Sequence stratigraphy from “spot” outcrops—example from a carbonate-dominated setting: Devonian-Carboniferous transition, Dinant synclinorium (Belgium)

The application of sequence stratigraphy appears to be perfectly valid in isolated “spot” outcrops, which usually are badly exposed and located in areas of strong tectonic overprint. The case study presented here is in a carbonate-dominated setting at the northern edge of the Cornwall-Rhenish basin, during latest Devonian and earliest Carboniferous times. The approach taken involved the analysis of facies and vertical facies evolutions, in combination with detailed biostratigraphy. The subsequent deduction of deepening and shallowing events, and the understanding of the sedimentary response to these events in different palaeogeographical positions, are the basis for lateral correlation of facies sequences. A similar trend in the changes of deepenings and shallowings throughout the area, regardless of lateral facies differentiation, indicates a relationship between bathymetric changes and relative sea-level changes, that is independent of local differences in the sedimentation or subsidence rates. The studied stratigraphic interval, with its apparently “abrupt” changes in facies or lithology, is the sedimentary response to six, gradually changing trends in the rate of relative sea-level fall and rise. End-Devonian, offshore highstand deposits (1) are capped by an unconformity surface or by a surface of submarine erosion and nondeposition, representing a sequence boundary (2). The overlying lowstand unit consists of a basal (3) and an upper (4) part. The basal part contains an oolitic and crinoidal sand shoals, associated with a transgressive lag deposit in offshore position; the upper, main part is a prograding wedge of shallow-marine crinoidal sands, intercalated with increasingly deeper-water shaly facies (higher-order fluctuation). This lowstand unit was deposited during the initial, slow phase of relative sea-level rise. It levelled the topographic relief before the final drowning during the subsequent rapid (near the rise inflection point) relative sea-level rise (5). The associated offshore shales are the deepest facies recorded. They are capped by a prograding unit deposited during a relative highstand (6). The reconstruction of a relative sea-level curve and the subsequent determination of the bounding surfaces, is not only the key to understanding the Devonian-Carboniferous stratigraphy but also a tool for lateral correlation of “spot” outcrops.

The Devonian–Carboniferous transition and its structural setting at Chillaton, West Devon, England

SummaryBoreholes penetrating the inverted limb of a major fold in an allochthonous thrust sheet at Chillaton, West Devon, revealed highly fossiliferous strata spanning the Devonian–Carboniferous boundary in continuous succession. Details of the fauna, which includes conodonts, trilobites and ostracods, are given. Abundant siphonodellid conodonts allow the boundary to be determined according to the recommendations of the working group on the Devonian–Carboniferous boundary of the IUGS Commission on Stratigraphy. The nature of the imbricate zone beneath the Main Thrust, in which the succession is situated, is described. In addition, the fabrics associated with thrusts which cut the olistostromic succession lower in the tectonic unit are discussed.

Sedimentary environment of Devonian pelagic limestones in the Southern Alps

Primary sedimentary structures combined with the geometry of Devonian and Lower Palaeozoic lithosomes in the Southern Alps (Austria and Italy) suggest many doubts about the published environmental and bathymetric interpretation of some Lower to Middle Devonian pelagic nodular limestones as ‘deep-water’ abyssal deposits. Every graded bed is not necessarily aturbidite; a single or some turbiditic beds are not necessarily deep-water or abyssal deposits; carbonate dissolution does not necessarily take place only below the carbonate compensation depth (CCD). Data show that graded allodapic beds, like those of the Lower to Middle Devonian of the Alps, may have been deposited as storm layers at a depth not exceeding some hundreds of metres. Accordingly the margins between Lower Devonian shallow-water platform and basins were characterized by low gradient and transitional sedimentary conditions. They became very steep only at the Devonian–Carboniferous transition because of synsedimentary block faulting.

Aspects of late devonian and early carboniferous palynology of southern Ireland. III. Palynology of devonian—carboniferous transition sequences with special reference to the bantry bay area, co. cork

The present paper provides: (1) an analysis of the qualitative and quantitative compositional development of Late Devonian-Early Carboniferous palynological assemblages from the Bantry Bay and other sections of southern Ireland; (2) a scheme of successive phases, (inter) regionally recognizable in the gradual compositional development of Late Devonian-Early Carboniferous palynological assemblages; (3) a palynological zonation based on three successive assemblages zones ( Retispora lepidophyta Assemblage Zone, Verrucosisporites nitidus Assemblage Zone, Spelaeotriletes pretiosus Assemblage Zone); and (4) two palaeogeographically related local phases, within the scheme of regional phases. It is concluded that: (1) the scheme of regional phases, in combination with the assemblage zones recognized, provides a more realistic tool for long-range palynostratigraphical correlation than the earlier proposed schemes of concurrent range zones; (2) the assemblage zones may be used for chronostratigraphical purposes, the boundary between the Retispora lepidophyta Assemblage Zone and the Verrucosisporites nitidus Assemblage Zone approximates the conventional Devonian-Carboniferous boundary; (3) the palaeogeographically related local phases may be considered to reflect floras of the coastal and alluvial plain, and the coastal-deltaic area, respectively; (4) within southern Ireland, the palynologically determined Devonian-Carboniferous boundary lithostratigraphically correlates with a thin mudstone unit (Claystone Member, Castle Slate Member). The taxonomical part includes: (1) an emended diagonosis of Lophozonotriletes; (2) formal proposals of new combinations of Ceratosporites delicatus, Asperispora acuta, Asperispora perlota and Diaphanospora scolecophora; and (3) the establishment of the Verrucosisporites nitidus morphon and the Dictyotriletes submarginatus morphon.