Triangularis Zone Research Articles

Middle Ordovician conodont biostratigraphy and paleobiogeography from the Suri formation at the Chaschuil region (Famatina System, NW Argentina)

The fossil record of the Famatina System of NW Argentina has been extensively studied by several authors, but its conodont fauna is poorly known. This contribution analyses a significant conodont association recovered from the Suri Formation cropping out at Chaschuil region (Catamarca province). Conodonts comprise a low diversity association consisting of four genera and five species of significant regional and global biostratigraphic importance: Baltoniodus cooperi Carlorosi, Sarmiento and Heredia, Baltoniodus triangularis (Lindström), Condorodus gracielae Carlorosi, Mestre and Heredia, Erraticodon patu Cooper and Gothodus costulatus Lindström. This association supports a Dapingian age for the bearing strata (Baltoniodus triangularis Zone), and the correlation of strata with some from northern Argentina and those globally referenced sections. Furthermore, the biostratigraphic patterns, distribution and evolution of the recovered species along with the associated fossils allow us to suggest a paleobiogeographic migration pattern that involved the Andean Basin, the Famatina System and the Precordillera during the latest Early Ordovician and the early Middle Ordovician.

Upper Changhsingian to lower Anisian conodont biostratigraphy of the Datuguan section, Nanpanjiang Basin, South China

The Great Bank of Guizhou (GBG) of South China is an important area for the study of Lower Triassic conodont biostratigraphy, but few studies have concerned the clastic facies of this region. The Datuguan section in Luodian County, southern Guizhou Province, is a typical clastic ramp section, preserving a relatively complete conodont succession from the uppermost Permian to lower Middle Triassic. A total of nearly 4000 P1 elements were obtained from this section, and 48 conodont species belonging to 16 genera have been identified, including a new species, Gladigondolella luodianensis sp. nov. 12 conodont biozones have been recognized, namely, the Clarkina yini Zone, the C. meishanensis Zone, the Hindeodus postparvus Zone, the Novispathodus waageni Zone, the Discretella discreta Zone, the Nv. pingdingshanensis Zone, the Icriospathodus collinsoni Zone, the Triassospathodus homeri Zone, the Tr. symmetricus Zone, the Tr. triangularis Zone, the Tr. sosioensis Zone, and the Chiosella timorensis Zone in ascending order. These conodont zones improve the resolution of correlation with other sections in this region, as well as globally. Based on the conodont successions and correlation of lithology, the Permian–Triassic boundary (PTB) and the Griesbachian–Dienerian boundary (GDB) are temporarily placed at the middle of Bed 8, 7 m below the top of the Linghao Formation, and the top of Bed 12, 15 m above the bottom of the Luolou Formation, respectively. The Induan–Olenekian boundary (IOB), the Smithian–Spathian boundary (SSB), and the Olenekian–Anisian boundary (OAB) are drawn at Bed 15–1, Bed 27–1, and Bed 42–2, in terms of the first occurrences (FOs) of Nv. waageni sensu lato, Nv. pingdingshanensis, and Ch. timorensis sensu stricto respectively. The conodonts and ammonoids from the Datuguan section supplement the materials of the Guandao section, which is an important reference section for the definition of OAB. In addition, the distribution of segminiplanate conodonts from the platform margin to the basin center has been determined in the Nanpanjiang Basin, revealing that segminiplanates migrated to equatorial region four times and preferred a narrow mid-depth setting during relatively cooler periods of the Early Triassic, in addition to occupying the more oxygenated deep-water basin at other time.

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.

Carbon isotope (δ13Ccarb) stratigraphy of the Lower-Upper Ordovician of the Yangtze Platform, South China: Implications for global correlation and the Great Ordovician Biodiversification Event (GOBE)

We present new high-resolution carbonate carbon isotope data (δ13Ccarb) from four sections in the Yangtze Platform, South China, ranging in age from Tremadocian to early Katian. The data have five distinct characteristics: 1) A prominent δ13Ccarb increase from −2.79‰ to 0.13‰ at the base of the Ordovician within the Tremadocian Cordylodus angulatus-Rossodus manitouensis Zone. 2) A positive δ13Ccarb excursion from −2.56‰ to 0.58‰ in the Paltodus deltifer Zone during the late Tremadocian. 3) A gradual increase in δ13Ccarb from −1.16‰ at the top of the Oepikodus communis Zone to a peak of ~0.74‰ in the Baltoniodus triangularis Zone at the Floian-Dapingian boundary. 4) A moderate rise in δ13Ccarb from 0.59‰ to 1.24‰ in the middle Darriwilian Dzikodus tablepointensis Zone. 5) A distinct positive δ13Ccarb excursion from 0.86‰ to 2.32‰ at the base of the Amorphognathus superbus-Hamarodus europaeus Zone during the early Katian. These excursions can be correlated with C-isotopic trends identified in age-equivalent successions in South China, Argentine Precordillera, North America, and Central Sweden, demonstrating their potential for global correlations and providing a composite, high-resolution chemostratigraphic framework for sedimentary records of the Lower-Upper Ordovician in South China. Besides, our data demonstrate a temporal coincidence between the long-term rise in δ13Ccarb and the Great Ordovician Biodiversification Event, suggesting that enhanced organic matter burial and accompanied climatic cooling and oxygenation may have played an important role in promoting the increases in biodiversity during the Ordovician.

Late Devonian (Famennian) to Carboniferous (Mississippian-Pennsylvanian) conodonts from the Anarak section, Central Iran

A relatively complete conodont record from Famennian to the Mississippian/Pennsylvanian boundary was investigated in the Anarak section, Central Iran. The studied interval belongs to the Bahram, Shishtu, Ghaleh and Absheni formations. The Famennian part of the section (Bahram Formation) ranges from the Palmatolepis triangularis Zone into the Bispathodus ultimus Zone. Not all conodont zones could be defined due to the lack of indicative species. Furthermore, it seems likely that a hiatus occurs around the Devonian/Carboniferous (D/C) boundary (most probably from the Siphonodella praesulcata to the ?Siphonodella sulcata–early Siphonodella crenulata conodont zones) based on the lack of stratigraphically important conodonts as well as on sedimentological criteria. The lack of representative siphonodellids and protognathodids at the base of the Mississippian prevents detailed stratigraphic position of the D/C boundary. Lower Carboniferous (Mississippian) rocks are characterized by red nodular limestone which is unique in comparison with other studied sections of the same age in Central Iran. Within the studied section, we could define the Mississippian/Pennsylvanian boundary. The mid-Carboniferous boundary was defined by the occurrence of Declinognathus noduliferus s.l. Conodont biofacies changes (Mississippian genera Gnathodus and Lochriea have been replaced by Pennsylvanian genera Declinognathus and Idiognathodus) are recognized in this section as well.

High-resolution carbon isotope stratigraphy of the Lower and Middle Ordovician succession of the Yangtze Platform, China: implications for global correlation

The Lower and Middle Ordovician of the Yangtze Platform, China, is characterized by a sedimentary succession dominated by carbonate rocks. Three sections spanning the Nantsinkuan/Lunshan, Fenhsiang, Hunghuayuan, and Dawan/Zitai formations, corresponding to the Tremadocian–Dapingian in age, have been sampled for high-resolution δ 13 C chemostratigraphy (542 samples in total). Our new δ 13 C data reveal five tie-points with the potential for global correlation: (1) a positive δ 13 C excursion in the lower Nantsinkuan Formation within the Tremadocian Rossodus manitouensis Zone; (2) an excursion with two peaks roughly within the late Tremadocian Paltodus ‘ deltifer ’ Zone; (3) a positive δ 13 C shift in the lower Hunghuayuan Formation, within the early Floian Serratognathus diversus Zone; (4) a gradual positive δ 13 C shift in the late Floian, ranging from the uppermost S. diversus Zone to the basal Oepikodus evae Zone; (5) a minor negative shift in the lower Dawan/Zitai Formation, within the early Dapingian Baltoniodus triangularis Zone. These excursions are herein used for correlation of the Yangtze Platform strata with successions from South China, North China, the Argentine Precordillera, North America and Baltica. From a palaeogeographical perspective the Gudongkou, Xiangshuidong and Daling sections represent depositional environments along an inner to outer ramp profile. δ 13 C data from these sections show successively heavier (higher) δ 13 C values with increasing depositional depth. This is interpreted as due to remineralization of organic carbon within the carbonate rocks. Supplementary material: Carbon and oxygen isotope data are available at: https://doi.org/10.6084/m9.figshare.c.4767080

Conodont biostratigraphy and astronomical tuning of the Lower–Middle Ordovician Liangjiashan (North China) and Huanghuachang (South China) marine sections

In this study, systematic conodont biostratigraphy and cyclostratigraphy are carried out on Ordovician sections from the North China and South China blocks. The Liangjiashan section, situated on the North China Block margin, accumulated shallow marine carbonate during the Early Ordovician. The Huanghuachang section (GSSP for the Dapingian Stage), situated on the South China Block margin, accumulated thinly bedded carbonates and minor clastics in a deep shelf environment. Conodont biostratigraphy and 405-kyr long-eccentricity cycles interpreted from the Liangjiashan and Huanghuachang sections are used to establish an Astronomical Time Scale (ATS) for the Early–Middle Ordovician period. The ATS indicates that the duration of the Floian Stage is 7.08 ± 0.405 Myr. The temporal ranges of Lower–Middle Ordovician conodont biozones are also estimated: the durations of the Serratognathus bilobatus, Serratognathus extensus, Oepikodus communis, Oepikodus evae, and Baltoniodus triangularis zones are 1.0 Myr, 5.1 Myr, 0.2 Myr, 0.8 Myr, and 0.2 Myr, respectively. The evolution of the ratio of obliquity to total power and short-eccentricity power to total power depicts periodicities of 1 Myr for the s4–s3 term, and 1.9 Myr shifting to 1 Myr for the g4–g3 term. The shift in the g4–g3 term may indicate a chaotic transition in the Mars and Earth orbital motions from a (s4–s3)–2(g4–g3) to (s4–s3)–(g4–g3) resonance state during the Early Ordovician.

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

The Kellwasser events in the Upper Devonian Frasnian to Famennian transition in the Toc Tat Formation, northern Vietnam

AbstractUpper Devonian carbonates of the Toc Tat Formation in the Si Phai Pass area of Dong Van District, northern Vietnam were deposited in carbonate platform, slope, and basin environments. These carbonates yield abundant conodonts indicative of the Palmatolepis nasuta, Pa. linguiformis and Pa. triangularis zones, the Frasnian–Famennian stage boundary being identified by the first occurrence of Pa. triangularis. Two positive carbon isotope excursions are recognized, the lower excursion peaking in the interval of the lower to middle Pa. nasuta Zone, whilst the upper excursion peaks just above the local Frasnian–Famennian boundary. Based on the biostratigraphy, these excursions equate to the Lower and Upper Kellwasser events. Locally, tentaculitoid taxa (Nowakia, Styliolina, Homoctenus, and Metastyliolina?) are abundant in the interval of the Pa. nasuta Zone, but show a drastic decline in abundance before the Lower Kellwasser Event, and only two taxa survived into the Famennian.

Global seawater redox trends during the Late Devonian mass extinction detected using U isotopes of marine limestones

The Late Devonian extinction ranks as one of the ‘big five’ Phanerozoic extinctions affecting up to 80% of marine species and is characterized by two major extinction events that are separated by <3 My. The leading hypotheses explaining both extinction events are global cooling and/or widespread marine anoxia. We test the marine anoxia hypothesis by analyzing uranium isotopes (δ238U) across a ∼7 My interval of well-dated Upper Devonian marine limestones from the Devil's Gate Formation in Nevada, USA. The measured δ238U curve shows no co-variation with local sediment-derived redox trends, water-depth dependent facies changes, redox-sensitive metals, TOC, or diagnostic elemental ratios. From these relationships, we infer that the δ238U curve represents global seawater redox conditions. Two negative δ238U excursions (indicating more reducing seawater) are observed with durations of ∼3.8 My (late Frasnian) and ∼1.1 My (early Famennian), respectively. Steady-state modeling of the observed −0.2 to −0.3‰ shifts in δ238U points to a ∼5–15% increase in the total area of anoxic seafloor during these excursions. The late Frasnian negative excursion is broadly coincident with the first extinction event (late rhenana Zone or lower Kellwasser event), whereas the early Famennian negative excursion (lower-middle triangularis zones) occurs after the most intense Frasnian–Famennian boundary (F–F) extinction event (upper Kellwasser event). Compilations of local sediment redox conditions from Upper Devonian marine deposits with conodont zone-level age control indicates that the extinction events were coincident with widespread anoxic deposits accumulating in subtropical epeiric sea and some open ocean settings, supporting previous interpretations that widespread marine anoxia had an important influence on the Late Devonian extinctions. The temporal relationships between global-ocean redox trends represented by the δ238U curve and the newly compiled subtropical marine redox sediment trends indicates that local epeiric seawaters carried a similar U-isotopic composition as the open ocean for the majority of the studied interval except for a brief interval (<500 ky) spanning the F–F boundary.

High resolution bio- and chemostratigraphic framework at the Frasnian-Famennian boundary: Implications for regional stratigraphic correlation between different sedimentary facies in South China

As one of the “Big Five” mass extinctions in Phanerozoic, the Frasnian-Famennian (F-F) boundary event records the extinction of 40 % of marine invertebrate genera. The F-F boundary is defined by the first appearance of conodont Palmatolepis subperlobata as well as the abundant occurrences of Pa. ultima at the base of the Lower Pa. triangularis Zone. The F-F boundary is also broadly coincident with a positive excursion in carbon isotopes, suggesting the possible linkage between the perturbation of marine carbon cycle and the biotic crisis. However, the correlation between conodont biostratigraphy and carbon isotope chemostratigraphy has not been established yet, preventing the high-resolution regional stratigraphic correlation among different sedimentary facies. In this study, we studied the conodont biostratigraphy and analyzed carbonate carbon (δ13Ccarb) and organic carbon (δ13Corg) isotopes of the Baisha section in the Guangxi Province, South China. The first appearance of index conodont fossil Pa. subperlobata for the Lower Pa. triangularis Zone, i.e. the F-F boundary, is coincident with the onset of a 3‰ positive excursion in δ13Ccarb, while Pa. triangularis and Pa. subperlobata occur nearly simultaneously, but predate the disappearances of Pa. linguiformis and other typical Frasnian elements. In addition, a positive excursion in δ13Corg is associated with the decline of δ13Ccarb near the base of the Middle Pa. triangularis Zone, which is marked by the first appearance of Pa. delicatula. Another important Famenian element Pa. minuta, the index fossil for the Upper Pa. triangularis Zone, first appears when δ13Corg starts to decline. The offset between δ13Corg and δ13Ccarb excursions could be attributed to the oceanic anoxia (the Kellwasser Event) near the F-F boundary, followed by the mixing of surface and deep water in earliest Famenian. The high resolution bio- and chemostratigraphic framework can be used as the standard for regional stratigraphic correlation and identification of the F-F boundary in different depositional environments in South China. We propose that the F-F boundary can be identified from a conodont-poor carbonate section by the onset of the positive excursion in δ13Ccarb, whereas the F-F boundary in a non-fossiliferous siliciclastic section might be placed slightly below the positive excursion in δ13Corg.

Age and distribution of the Late Devonian brachiopod genus Dzieduszyckia Siemiradzki, 1909 in southern China

Conodont biostratigraphical work was done at four sections recently found with occurrence of the rhynchonellide brachiopod genus, Dzieduszyckia Siemiradzki, in southern Guangxi and in the border area between Dushan County of Guizhou and Nandan County of Guangxi, South China. These sections represent two different types of facies, i.e., carbonate platform and intraplatform basin. The conodont analysis reveals that this genus occurs in the Upper triangularis Zone and the Middle crepida Zone at the Dazhai Section, through the Lower to Upper crepida zones at Dalong, and is restricted within the Upper rhomboidea Zone at the two intraplatform basin sections (Changtang and Duli). This result demonstrates that the occurrence of these peculiar rhynchonellide brachiopods in South China, regardless of the depositional environments, is within the Lower Famennian instead of the previously suggested Upper Famennian. Furthermore, this brachiopod genus in South China began to inhabit on the carbonate platform almost since the beginning of the Famennian and did not extend to the intraplatform basin facies until the late Early Famennian.Available biostratigraphic data indicate that during the Early and Middle Famennian, Dzieduszyckia is widely distributed not only in South China, but also throughout the world, such as Morocco and southern Ural.Observation on the new collections from the four studied sections reveals that the peculiar rhynchonellide brachiopods have a great morphological variation within each section. Significant differences existed among the collections from different sedimentary settings and localities, probably reflecting the environmental and geographic constraint on the morphology of Dzieduszyckia. Samples from different layers in the same section have nearly identical morphological variation, suggesting the temporal inheritance in morphology of the rhynchonellide brachiopod.

Review of some Frasnian ahermatypic coral localities from Germany and description of a new genus Spinaxon (Anthozoa, Rugosa, Upper Devonian)

1. IntroductionThe Palaeozoic superorder Rugosa passed through several crises before the final extinction at the Permian–Triassic boundary. The most important one, the global Upper Kellwasser Event at the Frasnian–Famennian boundary, led to the disappearance of all coral reefs; they reappeared during top-Famennian times (Strunian). For a long period, the coral world of the Famennian (both photic and aphotic zones) was a terra incognita – but this changed surprisingly after the monograph of Polish ahermatypic Famennian Rugosa (Rozkowska, 1969), and with the discovery of similar faunas mainly in Germany and Morocco, and also in northern China (Liao & Cai, 1987; Cai, 1988; Wu & Liao, 1988; Guo 1990). Knowledge about Famennian shallow water Rugosa increased more slowly: especially through Sorauf (1992: unique first upper Famennian, though pre-Strunian Rugosa fauna from North America) and Berkowski (2002: first upper Famennian, also pre-Strunian survivors of Frasnian Phillipsastreidae in Poland). Unfortunately, up to now there still are no certain Rugosa occurrences from the basal Famennian (Lower, Middle, and Upper Palmatolepis triangularis Zones, perhaps also Lower Palmatolepis crepida Zone). The only one Rugosa, which I could collect from the Middle Palmatolepis triangularis Zone, together with Nephranops incisus (Roemer, 1866), was an undeterminable ampleximorph taxon from Rubeland in the German Harz Mts.At present, the Upper Givetian and the Frasnian ahermatypic Rugosa are th

The Late Devonian Frasnian–Famennian Event in South China — Patterns and causes of extinctions, sea level changes, and isotope variations

The Frasnian–Famennian (F–F) event may be recognized in various facies areas in South China. In the pelagic cherty basin facies, both Lower and Upper Kellwasser events can seemingly be recognized. In the deeper water carbonate facies, the F–F event level is well controlled in light of conodont biostratigraphy. In the shallow water carbonate and mixed carbonate-shale facies, the F–F boundary may be defined by clear taxonomic distinction in benthic fossils (articulate brachiopods and corals) as well as evidence from minor pelagic fossils. Post-extinction recovery rate of benthic organisms differs in different facies settings and different taxonomic groups. In open shallow water platform to inter-platform depression areas, brachiopods seem to recover quickly, probably in the Middle Pa. triangularis Zone; benthic ostracodes seem to recover at a later stage; recovery of rugose corals did not happen until the uppermost Famennian. Three steps of the F–F mass extinction are postulated: 1) extinction of diverse brachiopods (including most atrypids); 2) extinction of pelagic conodonts; 3) extinction of both benthic faunas (very abundant and diverse rugose corals and ostracodes) and pelagic conodonts. Evidence of an end-Frasnian regression in South China is clear, particularly in shallow water settings. However, in deeper water settings, the picture is complicated, with evidence of both sea level rise and fall in the latest Frasnian. It may be assumed from overall data so far known that crustal evolution itself and associated multiple volcanic/hydrothermal activities may have mainly caused frequent and rapid climatically warming-cooling alterations and sea level changes as well as marine ecologic collapse (eutrophication, microbial blooming, seawater acidification, and anoxia), which may explain the F–F extinction pattern in South China.

Early Triassic conodonts of Jiarong, Nanpanjiang Basin, southern Guizhou Province, South China

Jiarong (Huishui County, Guizhou Province, South China) is a key locality for the study of the Early Triassic recovery after the end-Permian mass extinction. The size reduction of conodonts at the Smithian/Spathian transition was first documented in Jiarong, and it is also a locality that contributes to the documentation of the Early Triassic paleo-seawater temperatures. In the Jiarong sections, thirteen conodont zones were identified for the Early Triassic; in ascending order, they are Hindeodus parvus Zone, Hindeodus sosioensis Zone, Clarkina krystyni Zone, Neoclarkina discreta Zone, Neospathodus cristagalli–Eurygnathodus costatus assemblage zone, Novispathodus waageni eowaageni Zone, Novispathodus waageni waageni Zone, Discretella discreta Zone, Pachycladina–Parachirognathus assemblage zone, Novispathodus pingdingshanensis Zone, Icriospathodus collinsoni Zone, Triassospathodus homeri Zone, Triassospathodus triangularis Zone. These conodont zones in the Jiarong sections improve the global correlation of Early Triassic sections and also provide better regional age constraints in an area that is important for studies of recovery from the extinction. Based on the first appearance of Nv. waageni eowaageni, the Induan/Olenekian boundary is recognized at 3.6m above the base of the Jiarong III Section. The dominance of blade-shaped (segminate) conodonts was replaced by gondola-shaped (segminiplanate) conodonts twice; the first time was in the late Griesbachian, and the second time was in the early Spathian. The dominance of segminiplanate conodonts probably indicates that the deeper seawater environment became more oxygenated during the late Griesbachian and early Spathian for short time intervals, as it is believed that the Griesbachian segminiplanate conodonts favored deeper oxygenated water habitats. A new genus, Spathogondolella gen. nov., and a new species, Spathogondolella jiarongensis sp. nov., have been recognized.

Late Devonian conodonts and event stratigraphy in northwestern Algerian Sahara

Conodonts recovered from the Late Devonian South Marhouma section comprise 5 genera with 31 species (3 undetermined). The fauna establishes the presence of MN Zones 5, undifferentiated 6/7, 8/10 for the Middle Frasnian, the MN Zones 11, 12, 13 for the Upper Frasnian as well as the Early through Late triangularis Zones in the basal Famennian. The outcropping lithological succession is one of mostly nodular calcilutites alternating with numerous marly and shaly deposits, which, in the lower and upper part, comprise several dysoxic dark shale intervals. Among these the Upper Kellwasser horizon can be precisely dated and as such the presence of the terminal Frasnian Kellwasser Event is recognized for the first time in Algeria. Both the Middlesex and Rhinestreet Events cannot yet be precisely located, but supposedly occur among the dark shale horizons in the lower part of the section. However, their assignment to a precise level has so far not been established. Though poor in conodont abundance the South Marhouma section provides first evidence of the presence of several Montagne Noire conodont zones within the so far widely unstudied Frasnian of the Ougarta Chain. As such it is considered representative for the northwestern Algerian Saoura region.

Conodont Biostratigraphy and Age Determination of the Lower‐Middle Triassic Boundary in South Guizhou Province, China

Abstract:The demarcation of the Lower–Middle Triassic boundary is a disputed problem in global stratigraphic research. Lower–Middle Triassic strata of different types, from platform to basin facies, are well developed in Southwest China. This is favorable for the study of the Olenekian–Anisian boundary and establishing a stratotype for the Qingyan Stage. Based on research at the Ganheqiao section in Wangmo county and the Qingyan section in Guiyang city, Guizhou province, six conodont zones have been recognized, which can be correlated with those in other regions, in ascending order as follows: 1, Neospathodus cristagalli Interval‐Zone; 2, Neospathodus pakistanensis Interval‐Zone; 3, Neospathodus waageni Interval‐Zone; 4, Neospathodus homeri‐N. triangularis Assemblage‐Zone; 5, Chiosella timorensis Interval‐Zone; and 6, Neogongdolella regalis Range‐Zone. An evolutionary series of the Early–Middle Triassic conodont genera Neospathodus‐Chiosella‐Neogongdolella discovered in the Ganheqiao and Qingyan sections has an intermediate type named Neospathodus qingyanensis that appears between Neospathodus homeri and Chiosella timorensis in the upper part of the Neospathodus homeri‐N. triangularis Zone, showing an excellent evolutionary relationship of conodonts near the Lower–Middle Triassic boundary. The Lower–Middle Triassic boundary is located at 1.5 m below the top of the Ziyun Formation, where Chiosella timorensis Zone first appears in the Qingyan section, whereas this boundary is located 0.5 m below the top of the Ziyun Formation, where Chiosella timorensis Zone first appears in the Ganheqiao section. There exists one nearly 6‐m thick vitric tuff bed at the bottom of the Xinyuan Formation in the Ganheqiao section, which is usually regarded as a lithologic symbol of the Lower–Middle Triassic boundary in South China. Based on the analysis of high‐precision and high‐sensitivity Secondary Ion Mass Spectrum data, the zircon age of this tuff has a weighted mean 206Pb/238U age of 239.0 ± 2.9 Ma (2σ), which is a directly measured zircon U‐Pb age of the Lower–Middle Triassic boundary. The Ganheqiao section in Wangmo county can therefore provide an excellent section through the Lower–Middle Triassic because it is continuous, the evolution of the conodonts is distinctive and the regionally stable distributed vitric tuff near the Lower–Middle Triassic boundary can be regarded as a regional key isochronal layer. This section can be regarded not only as a standard section for the establishment of the Qingyan Stage in China, but also as a reference section for the GSSP of the Lower–Middle Triassic boundary.

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.

Late Changhsingian radiolarian biostratigraphy from Guangxi, South China and its correlation to conodonts

A well-preserved, abundant radiolarian fauna was obtained from three sections: the Dongpan, Liuqiao, and Paibi sections, in southern Guangxi, South China. Sixteen species belonging to Albaillella and Neoalbaillella, including seven undetermined species, are recognized. On the basis of stratigraphic distribution of these species, two radiolarian zones, the Albaillella triangularis Zone and the Albaillella yaoi Zone, are established. The correlation between radiolarian zones and conodont zones is suggested based on the discovery of coexisting conodonts. Albaillella triangularis and Albaillella yaoi zones correspond to Neogondolella postwangi and Neogondolella yini zones respectively.

Devonian Frasnian-Famennian transitional event deposits of Guangxi, South China and their possible tsunami origin

A suite of event deposits, isochronous and interrelated in origin, occurs widely near the Frasnian-Famennian boundary in Guangxi, South China. It is mainly distributed in the facies areas of the platform-margin slope and inter-platform rift-trough. The rudstone or calcirudite occur in the Liujing section of Hengxian and Luoxiu and Baqi sections of Xiangzhou in the facies area of platform-margin slope. The turbidites are observed in the sections of Yangdi and Baisha of Guilin, Du’an of Debao, Nandong and Sanli of Wuxuan, Xiangtian, Ma’anshan of Xiangzhou, Nayi of Chongzuo, Yunpan of Shanglin in the facies area of inter-platform rift-trough. The massive homogenites occur in sections of Mangchang, Luofu and Road from Nandan to Tian’e and Ma’anshan etc in the facies area of inter-platform rift-trough. Herein event deposits can be correlated in stratohorizon to the turbidite in the bottom of the Lower triangularis Zone in Hony railroad cut of Belgium, Devils Gate of Nevada, USA, Atrous of Morocco, South Urals and Fore-Kolyma of northeastern Siberia of Russia, and erosional discontinuities and brecciation in the Frasnian-Famennian boundary in South Polish-Moravian shelf. The event deposits could be caused by a violent tsunami related to bolide impacts into ocean.