Linguiformis Zone Research Articles

Upper Devonian conodont fauna from Western Hubei, China and its significance

ABSTRACT Pelagic standard conodont biozonation is less applicable to nearshore shallow-water depositional settings close to the peritidal, where it is needed to establish its own conodont zonation. The Upper Devonian Xiejingsi Formation in South China is an important unit for nearshore conodont biostratigraphy investigation as its deposits in the nearshore argillaceous-carbonate mixed facies which yield numerous marine fossils. 25 conodont species belonging to 6 genera of platform elements were described in four sections of this formation in western Hubei, including 9 new species. Based on the conodont distribution in these sections, six nearshore conodont biozones are introduced in ascending order: Polygnathus brevis – Polynodosus changyangensis sp. nov. Assemblage Zone, Icriodus cornutus – Pelekysgnathus arcuatus sp. nov. – Polygnathus brevilaminus Assemblage Zone, Palmatolepis angulata Zone, Palmatolepis angulata – Palmatolepis quadrantinodosalobata Assemblage Zone, Palmatolepis quadrantinodosalobata Zone and Polygnathus planirostratus Zone. The correlation of these biozones with those of pelagic standard ones indicates an age of the Xiejingsi Formation in western Hubei from at least the Frasnian linguiformis Zone to the Famennian Lower rhomboidea Zone. Through constructing nearshore shallow-water conodont biozones based on the establishment of comprehensive conodont succession, this paper provides a case study for high-resolution conodont biostratigraphy investigation in the shallow-water settings.

Mercury isotope evidence for regional volcanism during the Frasnian-Famennian transition

Mercury (Hg) concentrations and isotopes are widely used as proxies for volcanic inputs to paleodepositional systems. Enhanced volcanism during the Late Devonian was previously mainly inferred in the western Paleo-Tethys Ocean region from high Hg enrichments around the Upper Kellwasser horizon (UKW) and Frasnian-Famennian Boundary (FFB). In this study, we generated high-resolution Hg concentration data for four UKW-FFB sections (Walnut Creek and Dupont-GHS in the U.S.A., and Yangdi and Nandong in South China) and Hg isotope data for two of them (Walnut Creek and Nandong) in order to test the geographic distribution and stratigraphic range of volcanic inputs during the Frasnian-Famennian transition. Within the uppermost Frasnian Palmatolepis linguiformis Zone and the lowermost Famennian Lower Pa. triangularis Zone, Nandong (Paleo-Tethys Ocean) exhibits enrichment factors (HgEF > 2) and mass independent fractionations (MIF) of odd isotopes (Δ199Hg ∼0 ‰) that are consistent with significant volcanic inputs. Positive Δ199Hg values and an absence of Hg enrichments in the equivalent stratigraphic intervals at Walnut Creek and Dupont-GHS (peri-Panthalassic region) indicate that Late Devonian volcanism was a regional rather than a global phenomenon, and that it may have been associated with subduction zones and/or a large igneous province (LIP) of limited size in the Paleo-Tethyan region rather than with a major continental LIP of potentially global significance.

BIOSTRATIGRAPHY AND CORRELATION OF DEVONIAN DEPOSITS IN THE SOUTH-WEST SEGMENT OF THE EAST-EUROPEAN PLATFORM BY BRACHIOPODS

The main aim of the paper is to study the detailed distribution of the brachiopod fauna throughout the entire Devonian section from the Silurian-Devonian boundary at the Podilla region to the Devonian-Carboniferous boundary at the SW slope of the Dnipro-Donets Depression (DDD). The Devonian brachiopods (mainly Productids, Spiriferids and Rhynchonellids) of the south-west segment of the East-European Platform (EEP) are reviewed from the DDD, Volhyn-Podilla monocline (VPM) including the L’viv Paleozoic Trough, and Fore-Dobrogea Paleozoic Depression (FDPD). The faunas of these regions are mutually related and compared to the Devonian faunas of the EEP (Russia) and Pripyat’ Depression (Belarus). In recent years several paleontological investigations have broadened and deepened our knowledge of the Devonian biostratigraphy of Ukraine. Based on systematic studies of brachiopods from the SW segment of the EEP we recognize four successive faunas corresponding to four great marine transgressions — Early Devonian (Tiwer Series, the Monograptus uniformis Zone), Middle Devonian (Givetian Stage, the conodont varcus Zone), Late Frasnian (the conodont Upper rhenana — linguiformis Zone), and Early Famennian (the conodont triangularis-crepida Zone). The Early Devonian association includes Howellella angustiplicata, Plectodonta maria, and Daiya navicula and others which are similar to late Silurian brachiopods by their generic features (represented the genus common with the Upper Silurian). The Middle Devonian assemblages contain: Emanuella volhynica, Atrypa (Desquamatia) ventricosa, Chonetes sarcinulata, and Poloniproductus productoides at VPM sections (Givetian Stage, the varcus Zone), as well as Variatrypa sokolovae (Eifelian Stage), but in the DDD sections the impoverished association with Stringocephalus cf. burtini (Eifelian Stage) and Atrypa uralica (Givetian Stage) occur. The Late Frasnian association is represented by dominance of Theodossia tanaica, T. evlanensis, T. livnensis at all regions — VPM, DDD and FDPD (the Upper rhenana — linguiformis zones). The Early Famennian association is represented by ex Cyrtospirifer archiaci = Cyrtospirifer asiaticus and Cyrtospirifer ljachovichensis, Cyrtiopsis sp., Ptychomaletoechia zadonica, Iloerhynchus tichomirovi, Ardiviscus ex gr.herminae, Steinhagella annae etc. at DDD and by the same association plus Dmitria angustirostris at VPM (the triangularis-crepida zones). Brachiopods near the D-C boundary have been recorded so far from the black shales fossiliferous deeper water facies only in DDD: Spinocarinifera nigra, S. fallax, Sphenospira julii, Parallelora sp. (the Siphonodella praesulcata Zone). The result of our systematic study of productids, spiriferids, rhynchonellids, atrypids, and athyrids from Ukrainian sections are in perfect agreement with, and supplement to the previous investigations of Middle and Upper Devonian deposits at VPM and DDD, suggesting their important role for precising boundaries between the Devonian stages and horizons in SW segment of EEP. The essential role of brachiopods for the Devonian biostratigraphy and correlations with the East-European biozonation is confirmed.

Frasnian-Famennian transition in western Thailand: conodonts, biofacies, eustatic changes, extinction

AbstractThe biofacies of the Lower Palmatolepis rhenana Biozone to Palmatolepis triangularis Biozone in the Mae Sariang section, northwestern Thailand, are marked by alternations of Palmatolepis-dominated biofacies and Polygnathus-dominated biofacies related to fluctuations in seawater depth. Fine-grained limestone accumulated through the Lower Palmatolepis rhenana Biozone, Upper Palmatolepis rhenana Biozone, Palmatolepis linguiformis Biozone, Palmatolepis subperlobata Biozone, and Palmatolepis triangularis Biozone. A regression in the Upper rhenana Zone was followed by a recovery transgression that extended up through the linguiformis Zone. Conodont faunas increased until near the end of the linguiformis Zone, but in the overlying subperlobata Zone and triangularis Zone, conodont numbers dropped and most conodont species disappeared. It is possible the event coincides with a glacially forced regression, but there is no evidence of this in the section apart from a positive spike in δ13C. Another possible cause of the global marine extinction event is toxic levels of metals resulting from widespread volcanism. New taxa in this paper are Palmatolepis chaemensis new species, Palmatolepis thamensis new species, and Polygnathus tenellus surinensis new subspecies.UUID: http://zoobank.org/f2b55ba8-fe49-46f6-a2d5-bfd0208f1460

Timing and patterns of the Frasnian–Famennian event: Evidences from high-resolution conodont biostratigraphy and event stratigraphy at the Yangdi section, Guangxi, South China

Continuous centimeter-scale sampling for conodonts with microfacies and carbon isotope analysis has been carried out across the Frasnian–Famennian (F–F) transition at the Yangdi section, Guangxi, South China. The newly revised conodont biostratigraphy reveals a succession of six zones, ranging from the upper Palmatolepis rhenana zone to lower Palmatolepis crepida zone in ascending order. Based on a detailed analysis of conodont abundance and diversity changes through the section, two intervals involving significant conodont faunal changes were recognized in the uppermost Palmatolepis linguiformis zone at the Yangdi section. The first conodont change occurred at the transition between the lower and upper Pa. linguiformis zone and is marked by the disappearance of Pa. linguiformis, accompanied by the successive disappearances of Pa. eureka, Pa. rhenana, Pa. nasuta, Pa. gigas, Ad. ioides, and Ad. nodosa. The second conodont change appeared in a horizon equivalent to the uppermost Upper Kellwasser Horizon (UKH) and is indicated by the elimination of nearly all Frasnian palmatolepids, ancyrodellids, and polygnathids. Furthermore, the second conodont change is coincident with the decimation of ostracods and tentaculitids and is synchronous with the turnovers of conodont biofacies. In addition, the onset of the δ13Ccarb perturbation is a little earlier than the second conodont change, with the maximum amplitude of excursion right at the start of the Famennian. Therefore, we conclude that the second conodont change represents the F–F mass extinction based on the temporal correlation among δ13Ccarb excursions, pelagic faunal changes, and conodont biofacies turnovers during the F–F boundary interval. According to the high-resolution conodont biostratigraphy together with cyclostratigraphy, the uppermost UKH and whole UKH contain 1 and 12 bundle cycles, respectively. Thus, the time span of the mass extinction and the entire Upper Kellwasser crisis lasted 16–18kyr and ~200kyr, respectively.

First record of Homoctenus (Tentaculitoidea, Homoctenida) from the Late Devonian of northwest Peninsular Malaysia

Meor, H.A.H., Yong, A.M., Zakaria, M.Z.Z. & Ghani, A.A., 2.6.2015. First record of Homoctenus (Tentaculitoidea, Homoctenida) from the Late Devonian of northwest Peninsular Malaysia. Alcheringa 39, 550–558. ISSN 0311-5518.The homoctenid tentaculitoid genus Homoctenus is reported for the first time from Peninsular Malaysia. The fossils derive from the Upper Devonian Sanai Limestone, exposed in the state of Perlis, northwest Peninsular Malaysia. The fossils are closely related to Homoctenus tenuicinctus tenuicinctus and are described as Homoctenus sp. cf. H. tenuicinctus. The homoctenids were recovered from an interval containing a rich conodont assemblage, indicating a Frasnian age (Palmatolepis linguiformis Zone).Meor Hakif Amir Hassan [meorhakif@um.edu.my], Yong Adilah Mustafa [yongadilah@gmail.com], Mohamad Z.Z. Zakaria [zulhafiszariq@siswa.um.edu.my], Azman A. Ghani [azmangeo@um.edu.my], Geology Department, University of Malaya, 50603 Kuala Lumpur, Malaysia. Received 12.4.2015; revised 27.5.2015; accepted 2.6.2015.

Conodont biostratigraphy of late Devonian deposits in the Shirband section (Damghan, NE Iran)

The Upper Devonian deposits are relatively thick and developed in eastern Alborz. These deposits are located in Shirband area which is attributed to Geirud Formation. Shirband Upper Devonian deposits are situated by a discontinuity with the same gradient on Mila Formation and also under Mobarak Formation. The thin limestone, shaly limestone, and shale layers of the Geirud Formation are gradually followed by thin limestone and shale layers of the Mobarak Formation. Study of conodont fossils in this section probably indicates continuity deposits between the Geirud and Mobarak Formations. On the basis of studying conodonts, seven standard biozones were determined with the Famennian age (arranged from oldest to youngest): 1—triangularis to linguiformis zone, 2—crepida zone, 3—rhomboidea zone, 4—trachytera to marginifera zone, 5—postera zone, 6—postera to expansa zone, and 7—praesulcata to sulcata zone.

Discovery of Late Devonian (Frasnian) conodonts from the “Sanai limestone”, Guar Jentik, Perlis, Malaysia

Late Devonian (Frasnian) conodonts (Ancyrodella, Ancyrognathus, Palmatolepis, Polygnathus, Icriodus, Ozarkodina and Belodella) of linguiformis Zone, which includes the Upper Kellwasser Event recorded in Europe, North America, China and elsewhere, are for the first time recorded from Perlis, Malaysia. The conodonts are fairly rich in the uppermost part of the Sanai which was previously reported as of the upper part of Upper Devonian (Famennian) age. Stratigraphically it is located near the top of the Jentik Formation, unconformably overlain by the Lower Carboniferous Kubang Pasu Formation. The limestone is pelagic in nature and consists of planar bedded, grey micritic limestone, with thin shale partings and styliolites. In addition to the conodonts, the limestone contains abundant fossils of tentaculitids, straight-coned nautiloids, trilobites and bivalves. The Sanai has a limited distribution in Malaysia and the assemblage of Malaysian Frasnian conodonts are closely compared with some conodont fauna (linguiformis Zone) of northwestern Thailand.

Middle and Late Devonian brachiopod assemblages, sea level change and paleogeography of Hunan, China

Givetian through middle Famennian brachiopods of Hunan are used to define five biozones, comprising, in ascending order, the Stringocephalus Abundance Zone, the Ambocoeliid-Leiorhynchid Assemblage Zone, the Cyrtospiriferid Assemblage Zone, the Yunnanellina-Sinospirifer Assemblage Zone, and the Yunnanella-Hunanospirifer Assemblage Zone. They correspond approximately to the Po. hemiansatus Zone to Po. varcus Zone, S. hermanni Zone to Pa. punctata Zone, Pa. hassi Zone to Pa. linguiformis Zone, Pa. triangularis Zone to Upper Pa. crepida Zone, and Uppermost Pa. crepida Zone to Pa. marginifera Zone, respectively. Intensified rifting activity in South China during the Devonian began in the middle of the Lower Po. varcus Zone (a level marked by the first appearance of Po. rhenanus), which is consistent with the Lower-Middle Givetian substage boundary suggested by the International Subcommission on Devonian Stratigraphy (SDS). This assumed that rifting activity in the Lower Po. varcus Zone was signified by the deposition of the Baqi Formation in Guangxi and was marked largely by the extensive deposition of the Qiziqiao Formation in central Hunan, which probably led to an opposite pattern of relative sea level change-rising in deeper water trough areas and lowering in carbonate platform areas. The previously recognized S. hermanni Zone sea level rise in platform margin areas of Guangxi can be identified not only in the trough areas but also in platform areas, which probably indicates an overall marine transgression at this time, rather than tectonically induced sea level change. Similarly, this level coincides with the Middle-Upper Givetian substage boundary suggested by the SDS. Although the sea level rise may have occurred in the deeper water trough areas of South China towards the end of the Givetian, platformal areas experienced uplifting at various degrees, especially in the central and northern regions of Hunan where Early Frasnian deposits were apparently absent in many places. Similarly, the end-Frasnian regression led to exposure of many places and absence of early Famennian deposits, which probably accounts for the restricted distribution of the Yunnanellina brachiopod fauna.

δ34SCAS and δ18OCAS records during the Frasnian–Famennian (Late Devonian) transition and their bearing on mass extinction models

Many proposed extinction mechanisms for the Late Devonian (Frasnian–Famennian boundary — FFB) mass extinction event include the spread of anoxia in bottom waters during the two Kellwasser anoxic events, which have in turn been linked to changes in continental weathering, volcanic/hydrothermal fluxes, sea-level and climate change. Although there is strong evidence for bottom water anoxia in epicontinental seas at tropical/equatorial palaeolatitudes, the global extent of these changes is poorly understood, largely due to the lack of an oceanic and high-latitude record. In this study, marine δ34Ssulphate and δ18Osulphate records, derived from the analysis of carbonate-associated sulphate (CAS), were constructed from FFB sections in Belgium and Poland in order to examine the effect of the postulated changes in ocean redox conditions on the global sulphur cycle. The results reveal no overall changes in seawater δ34Ssulphate and δ18Osulphate over the FFB interval suggesting that any changes in sulphur cycling, namely relating to rates of pyrite burial and weathering, were not significant on a global scale. This supports the idea that the Kellwasser events were not oceanic phenomena and that they were restricted to epicontinental seas at low latitudes. The exception to the stability of the FFB δ34Ssulphate record is a brief negative excursion during the mass extinction interval in the linguiformis Zone, albeit based on one datapoint at this level in two different sections. This may be attributable to short, sharp marine regression and an increased flux of light sulphur from weathered pyrite.

A new Frasnian placoderm assemblage from the eastern Anti-Atlas, Morocco, and its palaeobiogeographical implications

A preliminary description of a new placoderm assemblage from the upper Frasnian of Morocco shows close similarity to the Bad Wildungen locality in Germany, with the arthrodire taxa Enseosteus, Rhinosteus, Walterosteus, Brachydeirus, Oxyosteus, Brachyosteus, Erromenosteus and Aspidichthys in common. Both horizons are from the late Frasnian, conodont Zone 13 ( bogartensis). The North African assemblage is probably slightly younger, in between the lower and upper part of this Zone, the Upper rhenana to linguiformis Zone. Southern Morocco was located on the northern shelf of Gondwana and Bad Wildungen on the southern shelf of Laurussia during the Upper Devonian. The analysis of five late Frasnian localities is in conflict with the palaeogeographical model from the palaeomagnetic data, indicating a large ocean separating both continents. No palaeobiogeographical barrier to the placoderms was present between these continents, supporting an alternative hypothesis, primarily based on palaeontological data with a small ocean separating Gondwana and Laurussia and a connection in the Late Devonian.

The role of sea-level change and marine anoxia in the Frasnian–Famennian (Late Devonian) mass extinction

Johnson et al. (Johnson, J.G., Klapper, G., Sandberg, C.A., 1985. Devonian eustatic fluctuations in Euramerica. Geological Society of America Bulletin 96, 567–587) proposed one of the first explicit links between marine anoxia, transgression and mass extinction for the Frasnian–Famennian (F–F, Late Devonian) mass extinction. This cause-and-effect nexus has been accepted by many but others prefer sea-level fall and cooling as an extinction mechanism. New facies analysis of sections in the USA and Europe (France, Germany, Poland), and comparison with sections known from the literature in Canada, Australia and China reveal several high-frequency relative sea-level changes in the late Frasnian to earliest Famennian extinction interval. A clear signal of major transgression is seen within the Early rhenana Zone (e.g. drowning of the carbonate platform in the western United States). This is the base of transgressive–regressive Cycle IId of the Johnson et al. (Johnson, J.G., Klapper, G., Sandberg, C.A., 1985. Devonian eustatic fluctuations in Euramerica. Geological Society of America Bulletin 96, 567–587) eustatic curve. This was curtailed by regression and sequence boundary generation within the early linguiformis Zone, recorded by hardground and karstification surfaces in sections from Canada to Australia. This major eustatic fall probably terminated platform carbonate deposition over wide areas, especially in western North America. The subsequent transgression in the later linguiformis Zone, recorded by the widespread development of organic-rich shale facies, is also significant because it is associated with the expansion of anoxic deposition, known as the Upper Kellwasser Event. Johnson et al.'s (Johnson, J.G., Klapper, G., Sandberg, C.A., 1985. Devonian eustatic fluctuations in Euramerica. Geological Society of America Bulletin 96, 567–587) original transgression-anoxia–extinction link is thus supported, although some extinction losses of platform carbonate biota during the preceeding regression cannot be ruled out. Conodont faunas suffered major losses during the Upper Kellwasser Event, with deep-water taxa notably affected. This renders unreliable any eustatic analyses utilising changes in conodont biofacies. Claims for a latest Frasnian regression are not supported, and probably reflect poor biostratigraphic dating of the early linguiformis Zone sequence boundary.

Late Middle to Late Frasnian Atrypida, Pentamerida, and Terebratulida (Brachiopoda) from the Namur–Dinant Basin (Belgium)

In the Namur–Dinant Basin (Belgium), the last Atrypida and Pentamerida originate from the top of the Upper Palmatolepis rhenana Zone (Late Frasnian). Within this biozone, their representatives belong to the genera Costatrypa, Desquamatia (Desquamatia), Radiatrypa, Spinatrypa (Spinatrypa), Spinatrypina (Spinatrypina?), Spinatrypina (Exatrypa), Waiotrypa, Iowatrypa and Metabolipa. No representative of these orders occurs within the Palmatolepis linguiformis Zone. The disappearance of the last pentamerids, mostly confined to reefal ecosystems, is clearly related to the end of the edification of the carbonate mounds; it precedes shortly the atrypid one. This event, resulting from a transgressive episode, which induces a progressive and dramatic deterioration of the oxygenation conditions, takes place firstly in the most distal zones of the Namur–Dinant Basin (southern border of the Dinant Synclinorium; Lower P. rhenana Zone). It is only recorded within the Upper P. rhenana Zone in the Philippeville Anticlinorium, the Vesdre area, and the northern flank of the Dinant Synclinorium. It would seem that the terebratulids were absent during the Famennian in this basin, probably due to inappropriate facies. Among the 13 species described or briefly discussed ( Palmatolepis hassi to Upper P. rhenana zones), Pseudoatrypa godefroidi nov. sp. and Spinatrypina (Exatrypa) marmoris nov. sp. are proposed as new.

Conodonts and radiolarians from pelagic cherts of the Frasnian–Famennian boundary interval at Bancheng, Guangxi, China: Global recognition of the upper Kellwasser event

The recognition of five standard conodont biozones and five radiolarian zones in the same set of samples from cherts within the Frasnian–Famennian (F–F) boundary interval at Bancheng, southeastern Guangxi, China allowed precise placement of the F–F boundary, and demonstrated the multi-episodic pattern of the F–F mass extinction. Frasnian pelagic radiolarian and conodont faunas had an acme in the lower Palmatolepis linguiformis Zone. In the upper Pa. linguiformis Zone, until the level of the upper Kellwasser extinction (Kw.), members of the radiolarian family Ceratoikiscidae and of the conodont Frasnian populations disappeared. Above the Kw, in the lower Palmatolepis triangularis Zone, new populations of the conodont Pa. triangularis gradually appeared and the survivor radiolarian genus Trilonche gradually re-appeared, both blooming in the lower part of the middle Pa. triangularis Zone. The Nehden extinction (Nd) in the uppermost middle Pa. triangularis Zone interrupted the recovery of the conodont and radiolarian faunas, but above this level the conodont species became more numerous, and the post-extinction radiolarian faunas (including Entactiniidae) recovered gradually.

Progressive drowning of carbonate platform in the Moravo-Silesian Basin (Czech Republic) before the Frasnian/Famennian event: facies, compositional variations and gamma-ray spectrometry

The Moravo-Silesian Basin (MSB; eastern Czech Republic and southern Poland) hosted an extensive shallow-water carbonate platform in the Middle Devonian to Frasnian interval. The platform drowned in a stepwise fashion from the Palmatolepis hassi to the Pa. linguiformis zone. Three types of drowning successions were revealed from conodont biostratigraphy, facies, microfacies and gamma-ray spectrometry data: (A) drowning to periplatform turbidite setting; (B) drowning to (hemi)pelagic seamount setting and (C) drowning associated with the stratigraphical gap. In the lower Pa. hassi zone, rapid subsidence caused the platform to drown locally along the N–S to NW–SE trending faults (type A drowning). In the upper Pa. rhenana to the Pa. linguiformis zone, the drowning accelerated in the western part of the MSB due to locally higher subsidence rates combined with the Late Frasnian biotic crisis (type B). In the southern part of the basin, the platform emerged shortly before the Frasnian/Famennian (F/F) boundary and drowned in the Early to Late Famennian (type C). The primary cause of drowning was differential subsidence at the Laurussian passive margin. Eustatic sea-level fluctuations, if any, contributed only to a minor extent to the Late Frasnian drowning, but were effective in type C drowning during the Famennian. The drowning boundaries are associated with increased contents of K and Th, reflecting the deceleration of carbonate production. Uranium contents display isolated peaks that roughly correlate with the drowning boundaries or the stratigraphic gaps associated with the F/F boundary. The uranium contents are considered to reflect local depositional conditions and are not suitable for stratigraphic correlation. On the other hand, from the K and Th contents, we can infer Late Frasnian sea-level fluctuations with duration on the order of 1 Myr. These cyclic variations in K and Th contents proved to be useful in platform-to-basin stratigraphic correlation.

The Upper Devonian orbital cyclostratigraphy and numerical dating conodont zones from Guangxi, South China

The hierarchically organized laminae, bundles, bundlesets and superbundlesets which correspond to a sub-Milankovitch, obliquity or precession, eccentricity and long eccentricity cyclothems, respectively, have been distinguished from the Upper Devonian Frasnian-Famennian (F-F) transitional carbonate successions deposited in the carbonate-basin and slope facies of Guangxi, South China. The durations of cyclothems are 8000-10000a, 16667a or 33333a, 100000a and 400000a, respectively. The ratio of eccentricity to precession, eccentricity to obliquity, and long eccentricity to eccentricity is 1: 6, 1: 3 and 1: 4 in the Devonian, respectively. Orbital cyclostratigraphical studies show that the durations of the conodont falsiovalis Zone, transitans Zone, punctata Zone, Lower hassi Zone, Upper hassi Zone, jamieae Zone, Lower rhenana Zone, Upper rhenana Zone, linguiformis Zone, Lower triangularis Zone, Middle triangularis Zone and Upper triangularis Zone are 0.4, 0.4, 0.4, 0.3, 0.4, 0.2, 0.8, 0.6, 0.8, 0.3, 0.3 and 0.3 Ma from bottom to top, respectively, and the duration of the Frasnian is 4.3 Ma. The conodont is the normal marine organism of the latest mass extinction (the latest linguiformis Zone) and the first recovery (including the whole Lower triangularis and Middle triangularis Zone) in the F-F transition. The conodont mass extinction and recovery lasted 200000-1 00000a and 0.6 Ma, respectively. We consider that average durations of the fossil zones calculated by reported numerical ages divided by fossil zone numbers within a stage or series or system cannot discovery complications and non-uniformity of evolutionary organisms and environments.

Reply to comment on “Orbital cyclostratigraphy of the Devonian Frasnian–Famennian transition in South China”

Although we cannot entirely exclude possible subjective factors under the condition of less-then-ideal outcrop exposure in the course of grouping laminae or beds, classification of hierarchical boundaries is objectively based mainly on the lateral clarity, continuity and stability of boundaries and cyclothems. A highly ranked sedimentary boundary is usually the surface above and below which apparent variations of the stratigraphical architecture pattern take place. The thickness and lithology of grouped beds/laminae are also important criteria in the classification of hierarchical cyclothems and boundaries in similar sedimentary facies and environments. We suggest that hierarchical changes of cyclothems, boundaries and lithology in stratigraphical sequences are common indicators of episodic sedimentation, which correspond ultimately to cyclic or periodic climate and sea level fluctuations related, in some degree, to Milankovitch cycles in tectonically relatively stable regions and periods. Therefore, hierarchical cyclothems, boundaries and lithology can reasonably be selected as proxies of tracing Milankovitch cycles. In contrast to proxies of chemical elements and isotopes recorded in strata, hierarchical cyclothems, boundaries and lithology are not easily influenced by diagenesis and epidiagenesis, even lower-graded metamorphism, which is especially truthful for the pre-Cenozoic sedimentary records. It is difficult to conclusively reply whether a possible bolide impact could have modified orbital parameters and climatic oscillation periods. But, if our deduction that the bundle, bundleset and superbundleset cycles must have been controlled by orbital forcing is considered to be supported by data, the assumption that impact event(s) could have altered long eccentricity periodicity of the early Famennian may be a more suitable, useful and inspirational working hypothesis than the synsedimentary tectonism. Our recent works indicate that of the 15 Frasnian superbundlesets studied in the Du'an and Yangdi sections, 14 show a 1:4 ratio with bundlesets, that is, the ratio of the Frasnian (from the conodont falsiovalis Zone to linguiformis Zone) and early Famennian (from the conodont Lower triangularis Zone to Upper triangularis Zone) long eccentricity to eccentricity is 1:4 and 1:3, respectively.

Extent and duration of marine anoxia during the Frasnian–Famennian (Late Devonian) mass extinction in Poland, Germany, Austria and France

The intensity and extent of anoxia during the two Kellwasser anoxic events has been investigated in a range of European localities using a multidisciplinary approach (pyrite framboid assay, gamma-ray spectrometry and sediment fabric analysis). The results reveal that the development of the Lower Kellwasser Horizon in the early Late rhenana Zone (Frasnian Stage) in German type sections does not always coincide with anoxic events elsewhere in Europe and, in some locations, seafloor oxygenation improves during this interval. Thus, this anoxic event is not universally developed. In contrast, the Upper Kellwasser Horizon, developed in the Late linguiformis Zone (Frasnian Stage) in Germany correlates with a European-wide anoxic event that is manifest as an intensification of anoxia in basinal locations to the point that stable euxinic conditions were developed (for example, in the basins of the Holy Cross Mountains, Poland). The interval also saw the spread of dysoxic waters into very shallow water (for instance, reefal) locations, and it seems reasonable to link the contemporaneous demise of many marine taxa to this phase of intense and widespread anoxia. In basinal locations, euxinic conditions persisted into the earliest Famennian with little change of depositional conditions. Only in the continental margin location of Austria was anoxia not developed at any time in the Late Devonian. Consequently it appears that the Upper Kellwasser anoxic event was an epicontinental seaway phenomenon, caused by the upward expansion of anoxia from deep basinal locales rather than an ‘oceanic’ anoxic event that has spilled laterally into epicontinental settings.

The Frasnian-Famennian (mid-Late Devonian) boundary in the type section of the Long Rapids Formation, James Bay Lowlands, northern Ontario, Canada

Utilizing a combination of conodont-based biostratigraphy and geochemistry, the Frasnian–Famennian (F/F, mid-Late Devonian) boundary was located in the Long Rapids Formation, northern Ontario. It is present in a black shale sequence, 21.46 m above the base of the Long Rapids Formation, just above a carbonate bed that has similarities to the Upper Kellwasser Limestone, recognized as a lithological marker for the F/F boundary in Germany, Belgium, and France. There is no evidence of an impact event, and sedimentation across the boundary is continuous, although there is a discontinuity layer just below the boundary and the early part of the linguiformis Zone (of the standard Late Devonian conodont zonation) is missing. Strong positive δ 13C (organic and carbonate) values were identified and are interpreted as evidence of mass mortality in anoxic waters at the F/F extinction; positive δ18O values suggest the extinction was also accompanied by a temperature drop. Negative δ34S values also indicate anoxia, and negative δ15N values provide evidence of reduced surface-water productivity. No iridium anomaly was found at the boundary, although higher than usual values were found about 85 cm below the F/F boundary. Sedimentological and biological evidence in the Long Rapids Formation indicates that the F/F extinction was coincident with major sea-level fluctuations in the late Frasnian, including a transgression beginning at the end of the linguiformis Zone and continuing through the Early triangularis Zone and beyond. Marine oscillations were accompanied by anoxia, which appears to be the killing mechanism for the conodont and other end Frasnian extinctions.

The Frasnian/Famennian boundary interval in the South Polish–Moravian shelf basins: integrated event-stratigraphical approach

The Late Devonian mass extinction event near the Frasnian/Famennian (F/F) boundary has been analysed using conodont biostratigraphy and biofacies, sedimentology, magnetic susceptibility and geochemistry in reference sections of the South Polish–Moravian shelf (Holy Cross Mountains, Cracow and Brno areas). High-resolution biostratigraphic study revealed difficulties in the precise recognition of this ‘natural’ stage boundary, but confirmed the occurrence of a major (third-order) sequence boundary in the F/F transition in an active synsedimentary tectonic setting, marked by erosional discontinuities, hardgrounds and brecciation or omission surfaces. Conclusive evidence of an extraterrestrial impact has not been found. Among Earth-bound factors, the main devastating role in the shelf habitats is ascribed to fluctuating anoxia and/or nutrient dynamics in a disturbed greenhouse climatic setting. The long-term facies changes were determined by a conspicuous break in carbonate production, accompanied by replacement of mature stromatoporoid–coral reefs by pioneer shelly-crinoid banks, microbial mounds and localised oolitic bars. The key F/F passage interval was marked by intermittent but generally accelerated periplatform ooze/debris input and severe storm events, as well as by probably highly fluctuating oxygenation and biological overproduction, best manifested in radiolarian–silicisponge and cephalopod acmes. Eutrophication phenomena, at least partly stimulated by various hydrothermal and volcanic processes, were one of the major biogeochemical processes during this climax of the Late Devonian biotic crisis. However, significant oceanographic perturbations were also linked with the onset of the transgressive–hypoxic Upper Kellwasser Event, still within the latest Frasnian linguiformis Zone, i.e., well before the F/F conodont collapse. Implied variations in the redox state of seawater through the Kellwasser timespan, probably in regionally highly variable temporal scales, are in agreement with recent palaeoecological and biogeochemical inferences, in particular suggesting recovering oxygenation just prior to the F/F boundary in the other Laurussian intrashelf basins. All the data support a long-time, multicausal Earth-bound crisis instead a worldwide cosmic catastrophe.