Middle Givetian Research Articles

A New Addition to the Devonian Elasmobranch Fauna of Michigan, U.S.A.

A tooth of Phoebodus cf. P. sophiae (Chondrichthyes, Elasmobranchii) was recovered from the Middle Devonian, Early Givetian, Rockport Quarry Limestone Formation in Alpena, Michigan. It is the first known record of the taxon in Michigan and the third known locality from North America. It is the oldest known record in North America, and possibly worldwide, and may extend the known temporal range of the genus. Previous known records for P. sophiae have been confined to the middle Givetian Polygnathus varcus conodont zone, and the taxon was thought to be a possible index fossil for the middle Givetian. The present record extends the taxon to the early Givetian P. hemiansatus conodont zone and, thus, complicates the use of P. sophiae as a proxy index fossil for the P. varcus zone.

The Jiwozhai patch reef: A palaeobiodiversity hotspot in middle Givetian (Devonian) of South China

This study is a detailed palaeontological and palaeoecological analysis of a middle Givetian (Middle Devonian) high-diversity patch reef located in a platform interior setting in South China. The location is Jiwozhai, Guizhou Province, in the Dushan Formation. A total of 83 species (including 23 undetermined species) belonging to 44 genera of reef organisms were identified, based on a detailed statistical analysis from 28 quadrats on the vertical section of the patch reef. The main reef builders are laminar and encrusting-behaviour stromatoporoids, laminar tabulate corals, and laminar encrusting chaetetids, forming coverstones to build the reef framework, while abundant massive and branching tabulate corals and solitary rugose corals are also important for the formation of the reef by filling the spaces between the components of the coverstones. Reef dwellers including brachiopods, bryozoans, tubeworms, calcified cyanobacteria and gastropods, are only scarcely distributed in the Jiwozhai patch reef, having little impact on the distribution pattern. Consistent with the densely distributed species at Jiwozhai, complex ecological relationships, including extensive encrustations, spatial competition, and symbiosis have also been found among different organisms. The high biodiversity level of the Jiwozhai patch reef in platform interior emphasizes that understanding of species richness and diversity of functional groups in different habitats is critical for Givetian reef ecosystem reconstruction. Location of the patch reef in a platform interior may be the reason for the high diversity biota. The results from the Jiwozhai patch reef are evidence for a stable reef structure with evenly distributed major reef-frame builders and complex ecological relationships. The high level of species diversity is a common feature in South China, as well localities of many other palaeocontinents during the Givetian Period.

Investigation of some Givetian rugose corals from the Mont d’Haurs Formation in southern Belgium

Cystiphylloides marennense n. sp., C. minimum (Wedekind, 1922), Atelophyllum emsti (Wedekind, 1922), Thamnophyllum godefroidi n. sp., Spinophyllum longiseptatum (Lütte, 1984) and Iowaphyllum sp. have been mainly collected on the south side of the Dinant Synclinorium, close to the boundary between the Lower and the Middle Givetian. Indeed, this material comes mostly from the lower part of the Mont d’Haurs Formation which is characterized by a high biodiversity. The genus Atelophyllum Wedekind, 1925 has been preferred to Mesophyllum Schlüter, 1889 and Lekanophyllum Wedekind, 1924 as the holotype of its type species Atelophyllum emsti has been figured in both transverse and longitudinal sections. A colony of Iowaphyllum is observed for the first time in the Givetian of Belgium. As a whole, the fauna of the Mont d’Haurs Formation is widely distributed in various areas of the Old World Realm (Europe, Asia and Australia). However, it shows strong affinities with the neighbouring countries of Belgium and especially with the Givetian rugose corals of the Eifel Hills, the Bergisches Land and the Sauerland in Germany.

Rare Middle and Upper Devonian dalmanelloid (Orthida) of the Cantabrian Mountains, N Spain

Rare Cantabrian Dalmanellidae (Costisorthis lisae nov. sp.), Dicoelosiidae (Teichertina cf. peregrina, T. cf. ?tzroyensis), and Mystrophoridae (Mystrophora sp., Biernatium sucoi nov. sp., and Biernatium sp. 2) are described and ?gured for the ? rst time in Spain. Most of them are scarce forms that occur only in certain localities. All the species but one came from the lower part of the Portilla (province of León) and Candás (province of Asturias) formations, Faunal Interval 21, Polygnathus rhenanus/P. varcus conodont zone, middle Givetian. The exception is Biernatium sp. 2 that occurs in Asturias in FI 25, Piñeres Fm., Palmatolepis transitans zone, lower Frasnian. Costisorthis ranges from Pragian to Eifelian rocks in central Europe. C. lisae nov. sp., from the Givetian of Asturias di?ers from other Costisorthis species in the weaker development of the distinctive ventral and dorsal plications.

Litho-, bio-, and sequence stratigraphy of the Boyle-Portwood Succession (Middle Devonian, Central Kentucky, USA)

The Middle Devonian (Givetian) of central Kentucky is represented by a complex and somewhat enigmatic succession of sandy dolomitic limestones and chert-rich wackestones, silty dolostones, and thin dark shales belonging to the Boyle Formation and Portwood Member of the New Albany Formation. The lower contact of the Boyle Formation is a distinct, regionally angular unconformity on rocks of Late Ordovician to mid-Silurian age. New exposures of Middle Devonian strata in the vicinity of Irvine, Estill County, Kentucky, reveal a series of distinctive depositional sequences, each with a sharply erosive base, overlain by phosphatic grains, fish teeth, and bone-rich quartz sandstone. The lower sequences, forming the Kiddville Member, are siliciclastic-rich, Zoophycos-bioturbated, silty, dolomitic carbonates that contain typical Hamilton brachiopod associations. The Kiddville is missing in some successions apparently owing to erosional overstep by upper Boyle units (Beechwood Member). The upper Boyle, Beechwood Member, is massive and cherty carbonate, which is highly variable in thickness, owing to major erosional truncation/karstification that locally removes the Boyle completely. Conodont studies indicate that much of the upper Boyle is of Po. ansatus Zone and thus middle Givetian in age. It is probably equivalent to the Moscow Formation of New York State. The overlying Portwood Member of the New Albany Shale belongs to the later Po. ansatus and “Oz.” semialternans zones and consists of dark-brownish-grey shales and muddy dolosiltites. In many localities to the west, the basal unit is a lenticular dolomitic breccia, the Duffin Bed, which may represent a lowstand karst breccia that mantles the irregular upper contact of the Boyle Formation at a regional unconformity. A lower dark shale contains rare small brachiopods Emmanuella and Leiorhynchus, suggestive of the lower Tully fauna of the Appalachian Basin; locally, this shale appears to fill paleokarst in the Boyle carbonates. It is overlain by a dolosiltite that has a highly distinctive “megaburrow” trace fossil assemblage on the base and yields rare Tullypothyridina and the conodonts Po. ansatus and “Po.” alveoliposticus, diagnostic of the Lower Tully Limestone in the Appalachian Basin. It is overlain by dark grey to black, typically deformed (seismites) calcareous mudstone of the middle Portwood Member. An upper pale grey, lenticular massive dolomitic bed rests sharply on the middle Portwood in channel-like scours with relief of about 0.5 m and a width of up to tens of meters. This bed yields poorly preserved corals, atrypid brachiopods (Spinatrypa sp.), and phacopid trilobites as is typical of the Upper Tully member. Overlying thinner bedded rhythmically bedded calcareous mudstones and dark shales of the uppermost Portwood yield conodonts of the “Oz.” semialternans Zone; this lithology resembles the Fillmore Glen interval of the Upper Tully Limestone. The sharply overlying black shale of the Trousdale Member yields hermanni Zone elements, indicating correlation with the basal upper Givetian lower Geneseo black shales of the Appalachian Basin. The highly variable thicknesses, complex internal discordances, and abundant seismites of the Portwood and Boyle Formations suggest a dynamic interval with regional far-field tectonics associated with the onset of the third tectophase of the Acadian Orogeny. Despite these tectonic effects, the presence of a consistent internal sequence stratigraphy that correlates with that of the Appalachian Basin and elsewhere reflects strong eustatic effects.

Devonian events: examples from the eastern Palaeotethys (Si Phai section, NE Vietnam)

Recent study of Middle to Upper Devonian deposits in the Dong Van area, northeast Vietnam, has revealed new, more detailed information of both the stratigraphic record of the Si Phai section and global Devonian bioevents. Four possible equivalents of well-known Devonian events of different magnitude were found in Vietnam, an area which is underrepresented in that respect: the (?) Kacak Event, the (?)pumilio Events, the late Middle Givetian Taghanic Event and the Frasnian/Famennian Kellwasser Event. The stratigraphic framework of the Si Phai section allows us to recognise and assess the timing of global Devonian bioevents in Vietnam even though the section is not continuous. An overview of the sedimentological development of the Si Phai section is discussed briefly where carbonates in the section are composed of argillaceous limestones suggesting relatively deep, off-shore conditions. Due to the facies setting, the macrofauna is generally rare and the conodont record is likewise limited in some parts. Nevertheless, it is possible to pinpoint some global event intervals for the first time in Vietnam.

Givetian (Middle Devonian) historical bio- and chronostratigraphical subdivision based on conodonts

The conodont record supports the intended threefold subdivision of the Givetian as envisaged by the International Subcommision on Devonian Stratigraphy into Lower, Middle and Upper Givetian substages. The lower boundary of the Lower Givetian Stage coincides with the lower boundary of the Givetian and it is recognized with the entry of Polygnathus hemiansatus. The lower boundary of the Middle Givetian is identified with the entry of either P. varcus or P. rhenanus. The base of the Upper Givetian is defined with the entry of Schmidtognathus hermanni. The historical review shows the conceptual evolution from a stage with just one and a half zones to one with ten zones that are the basis for the threefold Givetian subdivision. This zonation is mostly based on evolutionarily related conodont genera that are common in pelagic environments. An alternative conodont zonation for shallow-water facies for the Lower and Middle Givetian can also be widely applied. The proposal of subdividing the disparilis Zone into three subzones is not accepted.

Representatives of the family Actinostromatidae (Stromatoporoidea) in the Devonian of southern Poland and their ecological significance

Abstract Stromatoporoids of the family Actinostromatidae are common constituents of Givetian to Frasnian (Devonian) organic buildups. The species-level structure of actinostromatid assemblages from the Devonian of southern Poland is described in the present paper, with special emphasis on ecological factors that influenced species composition of the communities. Nine species of the genera Actinostroma and Bifariostroma are distinguished. Members of the family Actinostromatidae predominated in stromatoporoid assemblages within lower Frasnian carbonate buildup margins. The most diverse actinostromatid faunas were found within the middle Givetian Stringocephalus Bank, in the upper Givetian-lower Frasnian biostromal complex and in the lower Frasnian organic buildups. Species-level biodiversity was lowest within detrital facies which surrounded the Frasnian carbonate buildups. Species of Actinostroma with well-developed colliculi are commonest within the middle Givetian to early Frasnian coral-stromatoporoid biostromal complexes, whereas species with strongly reduced colliculi predominate early-middle Frasnian organic buildups. The skeletal structure of actinostromatids reflects environmental changes, documenting a transition from species with thin, close-set pillars and widely spaced laminae (common in the middle Givetian) to those with long, thick pillars and megapillars (in Bifariostroma), which were predominant during the early and middle Frasnian. The distribution of growth forms among species reveals a significant intraspecific variation. Species of Actinostroma can be either tabular or low domical, depending on the palaeoenvironmental setting. Thus, the present study confirms that stromatoporoid morphology was influenced by environmental conditions.

New information, including anatomy of the secondary xylem, on the genus Brabantophyton (Stenokoleales) from Ronquières (Middle Devonian, Belgium)

Two pyrite permineralized stems and one root are reported from the upper Middle to lowermost Late Devonian (middle Givetian to lowermost Frasnian) locality of Ronquières (Belgium) and identified as Brabantophyton runcariense Momont et al. (Stenokoleales). The stems include a three-ribbed protostele with a central protoxylem strand and other strands disposed along the midplanes of the ribs; each specimen shows secondary xylem. Tracheids of both primary and secondary xylem show circular to elliptical, multiseriate bordered pits. Rays are 1–seriate to 4–seriate; their height is highly variable, ranging from 3 to more than 100 cells. The root includes a four-ribbed protostele. Each rib shows two exarch protoxylem strands. The root also comprises a ring of secondary xylem identical to that of the stems. The characteristics of the secondary vascular anatomy of Brabantophyton appear closer to the seed plants than to any other Devonian plant lineage. However, the presence of a bifacial vascular cambium is not demonstrated, which precludes a definitive assignment of the genus to the lignophytes. A hypothesis about the ontogenetic development of Brabantophyton is proposed on the basis of the different characteristics observed in the different stem specimens of the plant.

Conodont biofacies of the Taghanic transgressive interval (middle Givetian): Polish record and global comparisons

Abstract Conodont biofacies of the Lublin and Łysogóry–Radom basins in SE Poland have been analysed in five cored borehole sections in a narrow interval of the middle Givetian Polygnathus ansatus Zone, corresponding to the global Taghanic transgression. Assemblages exhibiting various proportions of dominant genera, Icriodus (I) and Polygnathus (P), as well as particular P species and a few accessory taxa, reflect both temporal transgression dynamics and lateral facies changes. The latter comprise transition from a brackish lagoon with intermittent open-marine influence, to a carbonate shoal and offshore marly shelf, generally characterized by P–I biofacies, but with a varying proportion of constituent genera and polygnathid species. Comparison of the Polish record with stratigraphically well-constrained, quantitative biofacies evidence worldwide allowed the construction of a 2D nearshore–offshore model for the Euramerican epicontinental faunas connected with Taghanic transgressive facies. The I/P ratio has a diagnostic value for specific sub-environments (very nearshore/shallow-water and drowned platform) but for other settings the Polygnathus ansatus to Polygnathus linguiformis ratio appears more useful. The Moroccan faunas display specific biofacies patterns tentatively explained by different climatic conditions. The conodont biofacies concept has a limited application for palaeogeographically isolated settings, including pelagic-oceanic areas of microcontinents or submarine rises. In other cases (Eastern Australia), palaeobiogeographical bias precludes direct comparisons with the Euramerican model.

An approach to paleoclimatic conditions for Devonian (upper Lochkovian and middle Givetian) ironstone formation, NW Anatolian carbonate platform

Lower-middle Devonian iron-bearing successions were studied along 2 measured stratigraphic sections in the Camdag region of NW Anatolia. Ironstones in the upper part of the Findikli Formation in Kabalakdere are characterized by alternating red and green mudstones and sandstones at the bottom, followed by a series of dolomite, dolomitic limestone with oolitic ironstones, and chamositic mudstones at the top. Conodonts from these carbonates indicate the delta-pesavis zones of the late Lochkovian. The 12- to 45-m-thick Ferizli Formation unconformably overlies the Findikli Formation with a quartz-arenite succession at the bottom. The formation comprises alternating red, iron-rich limestones and dolomitic limestones, where iron-rich bioclastic grainstones are more dominant than iron-rich oolitic grainstones. The dolomitic limestones in this succession mark the ensensis and hemiansatus zones of the middle Givetian age. Mineralogically, the carbonates are dominated by goethitized and chamositized fossil fragments and chamositic oolites. In the oolitic facies, the oolites are made up of iron-bearing carbonates/iron, the bioclast of micritized/ironized brachiopods, and crinoids, whereas the matrix includes goethite, brown iron-silicates, chamosite, sideritic oolites, quartz clasts, and brachiopods. Partial iron precipitation within microborings or precipitation along the spine holes on echinoid grains is observed in the bioclastic grainstone/biosparite facies. Iron peloids are also recognized in the grainstone facies. Iron precipitation could be explained as precipitation of transported and dissolved iron from a terrestrial environment under wet/subtropical climate conditions within oxidizing and increased pH conditions, or as dissolved iron transported by upwelling currents over the shelves and precipitated under an oxidizing environment. The cyclic occurrence of primary iron in a marine carbonate environment and its extensive distribution over large areas indicates that a controlling mechanism for iron-rich carbonates and mudstones could be related to the cooperation of climate, sea level, and oceanographic changes in the middle Givetian. During the late Lochkovian, the same or very similar controlling factors might have operated, where the alternation of red mudstones can be explained by lateral facies changes or changes in terrestrial/nutrient influx.

Warstwy świętomarskie dewonu środkowego Gór Świętokrzyskich i ogniwa żniatyńskiego z SE Lubelszczyzny w świetle wyników badań petrograficznych

PETROGRAPHIC STUDY OF THE MIDDLE DEVONIAN ŚWIĘTOMARZ BEDS OF THE HOLY CROSS MOUNTAINS AND THE ŻNIATYŃ MEMBER FROM THE SE LUBLIN AREA Abstract. In the Holy Cross Mountains, Middle Givetian terrigenous deposits occur only in the Łysogory region. In its eastern part they are found between claystones of the Skaly Beds and biostromal limestones of the Pokrzywianka Beds, whereas in the western part – between claystones of the Skaly Beds and the Nieczulice Beds. These deposits are ascribed to the Świetomarz Beds and consist of mudstones and sandstones reaching about 100 m in thickness. The sandstones are comprised of fi ne-grained quartz arenites, calcareous quartz arenites, rare sublithic arenites, quartz and sublithic wackes, being subordinate to laminated mudstones with plant remnants. The same petrographic characteristics are exhibited by the Żniatyn Member known from the Terebin IG 4 borehole, SE Lublin area. The sources of detrital material for the Świetomarz Beds and the Żniatyn Member were a recycled orogen built of siliciclastic rocks, and a cratonic zone of continental block. The terrigenous material was supplied to the Middle Devonian Łysogory basin from the south-east through a deltaic system. The depositional environment was a proximal and distal area of prodelta that prograded to the west.

NEW DATA ON MIDDLE DEVONIAN CONODONTS FROM SW-SARDINIA:THE SU NUARGI II SECTION REVISITED

The conodont collection from the nodular limestone beds of the Su Nuargi II outcrop near Domusnovas in SW-Sardinia (Italy) is restudied for the purpose of reassessing the outcrop and updating the conodont collection to the most recent taxonomy. Su Nuargi II is the most important outcrop in the SW of the island exposing Middle Devonian rocks. Forty-five conodont taxa have been identified in the collection, positioning the outcrop within the interval covering the timorensis to latifossatus zones (Lower to Middle Givetian) slightly widening the interpretation of Olivieri (1985). A new morphotype of Polygnathus linguiformis linguiformis is described. The genera Tortodus and Schmidtognathus are identified for the first time in the Middle Devonian of Sardinia. Additionally, a second Middle Devonian outcrop is discovered in the SW of the Island.

Sedimentary development of a continuous Middle Devonian to Mississippian section from the fore-reef fringe of the Brilon Reef Complex (Rheinisches Schiefergebirge, Germany)

The Brilon-reef complex is one of the biggest Devonian carbonate buildups (*80 km 2 ) of the Rhei- nisches Schiefergebirge. The Burgberg section is located in the southeastern fore-reef area of the Brilon Reef Complex and exposes a succession of strata (117 m thick), which extends from the Middle Givetian (middle varcus conodont Zone) to the Visean (bilineatus cono- dont Zone). Field and microfacies observations led to the definition of nine microfacies that are integrated into a sedimentary model divided into off-reef, intermediate fore-reef, and proximal fore-reef sedimentary domains (SD). The off-reef domain (SD1) is the most distal set- ting observed and is characterized by fine-grained sedi- ments, dominated by pelagic biota and the local occurrence of gravity-flow deposits. The intermediate fore-reef (SD2) is characterized by a mixture of biota and sediments coming from both deeper-water and shallow-water sources and is influenced by storm and gravity-flow currents. In this domain, Renalcis mound- like structures developed locally. Finally, the proximal fore-reef (SD3) corresponds to the most proximal setting that is strongly influenced by gravity-flow currents derived from the Brilon Reef Complex. The temporal evolution of microfacies in the fore-reef setting of the Burgberg section show five main paleoenvironmental trends influenced by the onset, general development, and demise/drowning of the Brilon Reef Complex. Fore-reef to off-reef lithologies and their temporal changes are from the base to the top of the section: (U1)—fine- grained sediments with large reef debris, corresponding to the initial development of the reef building upon submarine volcaniclastic deposits during the Middle Givetian (middle varcus Zone) and first export of reef debris in the fore-reef setting; (U2)—high increase of reef-derived material in the fore-reef area, corresponding to a significant progradation of the reef from the Middle Givetian to the Early Frasnian (maximum extension of the Brilon Reef Complex to the south, disparilis to the falsiovalis conodont biozones); (U3)—progressive decrease of shallow-water derived material and increase of fine-grained sediments and deep-water biota into the fore-reef setting, corresponding to the stepwise with- drawal of the reef influence; from the Middle to the Late Frasnian (jamieae conodont Zone); (U4)—development of a submarine rise characterized by nodular and ceph- alopod-bearing limestones extending from the Late Frasnian to the Late Famennian corresponding to the demise and drowning of the Brilon Reef Complex as a result of the Late Frasnian Kellwasser events (upper rhenana and triangularis conodont biozones); (U5)— significant deepening of the Burgberg area starting in the Late Famennian, directly followed by an aggrading trend marked by pelagic shales overlying the nodular limestone deposits.

Genesis of unusual lithologies associated with the Late Middle Devonian Taghanic biocrisis in the type Taghanic succession of New York State and Pennsylvania

The Middle Devonian (late middle Givetian) Tully Formation in New York State is the type regional expression of the global Taghanic Biocrisis. It is marked by anomalous development of massive to rhythmically bedded, micritic limestone deposits within a vastly thicker Acadian foreland basin clastic succession. Lower-medial Tully carbonates record the incursion of tropical Old World Realm (OWR) taxa (Tully Fauna) and the outage of the long-standing, higher diversity, cooler-water, endemic Eastern Americas Realm (EAR) biota (Hamilton Fauna). Succeeding Tully strata record a return of the Hamilton Fauna followed by its demise due, both to replacement by the lower diversity, cosmopolitan Genesee Fauna and by the overspread of widespread anoxic bottom conditions coupled with the onset of drastically increased sediment input following Tully Group deposition.Massive, micritic limestones, yielding modest diversity Tully Fauna assemblages are particularly characteristic of the lower-medial Tully succession on the western New York Tully platform; these are coeval with nearly barren ribbon limestone and siltstone deposits in the adjacent New Berlin (east-central New York) and central Pennsylvania basins. These depocenters trapped terrigenous sediment and helped to create sediment-starved conditions on the platform. Anomalous Tully carbonate deposition is believed to be coincident with strong super estuarine water mass stratification in offshore Tully shelf and basin settings where a warmer, denser, more saline water mass flowed northward (shoreward) across the study area beneath a counter flow of oxygenated, river-influenced surface water. Dysoxic conditions would have developed below the pycnocline, favoring the Tully Fauna incursion, precipitation of carbonate mud, and possibly promoting the formation of ooidal chamosite.At least five thin (1–30cm-thick) mappable beds of black, ooidal, chamosite, are observed in Taghanic shelf margin, slope, and basin deposits. These beds are typically intensely bioturbated, variably rich in associated siderite, contain corroded low-diversity fossil assemblages, and are regionally associated with condensed lag deposits above unconformities. Work by others suggests that chamosite formation occurs under minimally reducing, post-oxic, interstitial conditions which are followed, in turn, by more strongly reducing conditions which allow for variable siderite and pyrite formation. Terrestrial pedogenic alteration of silicates by evolving land plant communities under warm, humid conditions led to an increased supply of kaolinite as well as Iron oxides and hydroxides that served as precursors to chamosite formation. In the New Berlin Basin, the transgressive, top-Hamilton-base-Taghanic succession is marked by a succession of diastems associated with basin deepening and upward-increasing chamosite occurrence in dysoxic facies. Occurrence of ooidal chamosite in upper medial Tully platform deposits (Smyrna Bed) may reflect water mass stratification and extreme sediment-starvation at the shelf margin. Eastward spectral transformation of sparsely fossiliferous Smyrna ooidal chamosite in the western New Berlin Basin into richly fossiliferous, non-chamositic, equivalent neritic deposits east of that basin, suggests that the counter-flow of oxygen and nutrient-rich, lower salinity water had blocked the denser, restricted water layer from advancing over the eastern Tully clastic shelf closer to shore.

Influence of atrypid morphological shape on Devonian episkeletobiont assemblages from the lower Genshaw formation of the Traverse Group of Michigan: A geometric morphometric approach

Atrypids examined from the lower Genshaw Formation of the Middle Devonian (early middle Givetian) Traverse Group include a large assemblage of Pseudoatrypa bearing a rich fauna of episkeletobionts. We identified two species of Pseudoatrypa – Pseudoatrypa lineata and Pseudoatrypa sp. A based on ornamentation and shell shape. Qualitative examination suggested that the former had fine-medium size ribbing, narrow hinge line, widened anterior, gentle to steep mid-anterior fold, a more domal shaped dorsal valve, and an inflated ventral valve in contrast to the coarse ribbing, widened hinge line, narrow anterior, gentle mid-anterior fold, arched shape dorsal valve, and flat ventral valve of the latter. Geometric morphometric analysis supported two statistically different shapes ( p < 0.01 ) for the two distinct species. This study further examined these atrypids to investigate the influence of morphology on episkeletobiont settlement on the two Pseudoatrypa species. Among the 343 atrypid hosts examined, nearly 50% were encrusted by episkeletobionts. Common encrusters included microconchids, bryozoan sheets, and hederellids. Less common encrusters included auloporid corals, cornulitids, tabulate corals, Ascodictyon, craniid brachiopods, and fenestrate bryozoans. Hederellids, auloporid corals, cornulitids, and tabulate corals encrusted a few living Pseudoatrypa hosts, but determination of pre- or post-mortem encrustation by the majority of episkeletobionts is equivocal. In a very few cases, episkeletobionts crossed the commissure indicating the death of the host. Some episkeletobionts, microconchids and the sheet bryozoans, were more common on Pseudoatrypa lineata, which exhibited more dorsal-ventral convexity than Pseudoatrypa sp. A. Perhaps, P. lineata may have provided a larger surface area for episkeletobiont settlement relative to Pseudoatrypa sp. A. In both the host species, encrustation was heaviest on the convex dorsal valve. This suggests that most of the encrustation occurred in a reclining, dorsal-valve-up life orientation of both species, in which the convex dorsal valve was exposed in the water column and the ventral valve remained in contact with the substrate. However, life orientations of these atrypid species could not be confidently predicted simply from the location preferences of episkeletobionts alone, as the life orientation of the host would also have been a hydrodynamically stable orientation of the articulated shell after death. Most episkeletobionts encrusted the posterior region of both dorsal and ventral valves of the two species, which suggests that the inflated areas of these valves, when exposed, favored the settlement of most episkeletobiont larvae.

Diversity and richness of the Devonian terrestrial plants in the Southeastern Mountainous Altay (Southern Siberia): Regional versus global patterns

Devonian deposits of the Southeastern Mountainous Altay, a large region in Southern Siberia, contain abundant remains of terrestrial plants. A semi-quantitative analysis of this regional palaeobotanical record reveals how both the diversity (number of taxa) and richness (number of taxa with an account of their abundances) of floristic assemblages changed during the Emsian–early Famennian time interval. A total of 60 species, representing 42 genera, are known from 8 regional assemblages. Changes in diversity of species and genera occurred simultaneously. The number of taxa was high in the early Emsian, declined in the late Emsian, rose again in the Eifelian–middle Givetian, dropped in the late Givetian, reached the highest values in the early Frasnian, and experienced the greatest decline taking place in the late Frasnian–early Famennian. The standing diversity (number of taxa crossing the time boundaries) was maximal in the Middle Devonian. The dynamics of terrestrial plant richness was similar to that of diversity with an exception of middle Givetian decline in richness despite growth of diversity. The floras were dominated by pteridophytes. Propteridophytes were less abundant, and pinophytes were very rare. Propteridophyte extinctions were high in the middle Givetian, concurrent with a brief decline in pteridophytes. Some regional and global patterns of floral dynamics were similar. However, propteridophyte decline was not abrupt globally. The main abiotic driving factor influencing species richness and diversity appears to have been regional shoreline shifts. It does not appear that climate changes was important for regional changes in phytodiversity, although both regional and global phytodiversity was at its high during the Middle Devonian cooling phase. A comparison of palaeobotanical data from the Southeastern Mountainous Altay and Kazakhstan suggests palaeogeographic proximity and proves an idea of Altay-Mongolian terrane wandered between Gondwana, Kazakhstan, and Siberia. The early Emsian and the early Frasnian, when floras of the study region were diverse and rich, are characterized by the very high degree of similarity. Thus, interregional floral exchanges would facilitate plant radiations.

The global Taghanic Biocrisis (Givetian) in the eastern Anti-Atlas, Morocco

In the Tafilalt of the eastern Anti-Atlas, Morocco, the impact of the polyphase global Taghanic Crisis (upper part of Middle Givetian) on facies and faunas was studied in more than twenty successions of a strongly condensed hemipelagic platform (northern and central Tafilalt), of a more neritic to biostromal area with interspersed shale basins (southern Tafilalt, Amessoui Syncline), and in a predominantly hypoxic basin (southeastern Tafilalt). In the pre-crisis interval, a deepening (Depophase If-Win) and increased nutrient supply allowed faunal blooms of macrofauna, especially of goniatites ( Maenioceras), resulting in the deposition of the fossiliferous Maenioceras Marls (middle part of ansatus Zone) on the platform and of correlative dark goniatite shales in the SE. In the Amessoui Syncline, shales alternate with small-sized but widespread coral-stromatoporoid biostromes. In the western Tafilalt thin styliolinites indicate eutrophic peaks at the top. A significant pre-Taghanic regressive trend (top of Depophase If) is recorded by disconformity-bound, shallowing upwards cycles at the base, within, and at the top of the Upper Sellagoniatites Bed (higher part of ansatus Zone with Polygnathus ovatinodosus) and by corresponding biostromes and calcareous sandstones in the S and SE. The regressive episode allowed the local re-appearance of shallow-water conodonts (youngest known Bipennatus), culminated in an iron-encrusted hardground or intraclastic reworked unit, and caused local extinctions of ammonoids and of reefal fauna. The initial Taghanic Onlap (base of Depophase IIa-Tagh; upper part of ansatus Zone with rare “Po.” alveoliposticus) led to the return of marls and styliolinid-rich nodular limestones or of hypoxic shales in the S and SE. Equivalents of the Lower and Middle Tully Limestones of the North American Taghanic type area can be recognized, may display subcycles, and are separated by a minor regressive phase. A disconformity or distinctive sea-level fall, associated with the final extinction of Sobolewiidae and other goniatites, separates equivalents of the Upper Tully Limestone. The subsequent aff. amplexum Bed (base of Depophase IIa-UT) is characterized by an initial radiation of Pharciceratidae and of some conodonts ( Oz. semialternans Zone), by blooms in branching tabulate corals (youngest known Bainbridgia) and phacopid trilobites, and by a positive carbon isotope excursion. The final extinction of Maenioceratidae and Agoniatitina ( Sellagoniatites) coincided with a minor regression at the top of the Taghanic Crisis interval. Uniquely in the eastern Tafilalt, with the most complete sedimentary record, a thin bioclastic conodont lag is preserved at the base of the Upper Givetian and below the deepening of Depophase IIa-Gen. The post-Taghanic radiation of ammonoids and especially of conodonts falls in the nodular Mzerrebites erraticus Beds ( hermanni Zone) of the platform and in correlative hypoxic goniatite shales and marls of the S and SE. Radiation continued in the subsequent, haematite-rich Lunupharciceras nodules of the platform and in the widespread Lower Marker Bed (both cristatus ectypus Zone) that are separated by disconformities. The Tafilalt record confirms that the Taghanic Crisis was a second order global overturn of pelagic and reefal biota that progressed in at least three distinctive steps over several hundred thousand years. The detailed event stratigraphy allows global correlations and comparisons with other regions (New York type area, Dra Valley, France, Germany) that have been investigated in similar detail. It is assumed that the Taghanic Crisis was primarily driven by repeated and fast eustatic fluctuations and climate change (greenhouse overheating pulses), which were probably linked. Hypoxia/anoxia played only a local role in extinctions. The crisis can be recognized globally but it had very different effects regionally leading variably to faunal migrations, blooms, and extinctions.

Middle Givetian echinoderms from the Schlade Valley (Rhenish Massif, Germany): habitats, taxonomy and ecostratigraphy

Crinoids and ophiocistioids from classical fossil localities of the National Geosite “Schlade Valley”, NE of Bergisch Gladbach (Germany) are reported for the first time. The fossils were derived from the reefal Buchel Formation (lowermost Middle Givetian, Middle Devonian) at the northern flank of the Bergisch Gladbach-Paffrath Syncline (eastern Rhenish Massif). From the abandoned quarry “Im Grubenfeld”, skeletal elements of holothuroids, ophiocistioids and crinoids are documented from a bituminous marly shale horizon in the middle Buchel Formation. The finely bedded shales suffocated an already stressed, muddy “reefal” fauna, which followed on top of a massive Actinostroma stromatoporoid biostrome. The shales characterise an apparently regionally occurring event, herein denominated as “Schlade Event”. It is considered to represent the climax of the transgressive Lower pumilio Event. The autochthonous and vagile epibenthic echinoderm fauna on top of the “Schlade Event Layer” is low diverse. It is regarded, herein, as post disaster fauna, recolonising the dysaerobic softground/soupground together with the well-adapted trilobite Goldius. The cupressocrinitids Halocrinites and Procupressocrinus were recognised from a younger stratum of the upper Buchel Formation within the abandoned “Zimmermann Quarry” near-by. The crinoids settled in high-energy environments of a reef flat in association with characteristic brachiopods (Uncites, Stringocephalus) and bivalves (Eomegalodon) and were swept by storms into reef flat pools. In those exceptional fossil lagerstatten, which are marl-filled obrution deposits, they were parautochthonously preserved together with an autochthonous fauna composed mostly of gastropods and extremely rare allochthonous biota from the open marine realm. Published biozonations of the Buchel Formation, especially on ammonoids, are evaluated, partly corrected and supplemented by ecostratigraphic associations of rugose corals and crinoids. Schlade Event below and Taghanic Event above are major factors controlling biozonation. Taxonomic notes concern revision of the holothuroids from the Schlade Valley and discussion of taxonomic attribution of ophiocistoids and crinoids. All species formerly included in “Abbreviatocrinites” are transferred to genus Halocrinites, which has priority.

The Middle Devonian (Givetian) ammonoid Pharciceras from the New Albany Shale, Kentucky

Pharciceras Hyatt, 1884 is the diagnostic ammonoid of the late middle Givetian Stage of the Middle Devonian Series. It occurs in the Rhenish Massif in Germany, the Montagne Noire in southern France, and in equivalent strata in the Anti-Atlas in southern Morocco. Verified North American occurrences of Pharciceras are confined to the New York succession, where the appearance of the ancestral species P. amplexum (Hall, 1886) in the Upper Tully Limestone represents an important and well-established biostratigraphic datum within the Taghanic onlap interval (see Aboussalam and Becker, 2001 for discussion). In this note we describe a second, distinctly younger, North American species, Pharciceras barnetti n. sp., from the New Albany Shale in eastcentral Kentucky that provides new evidence on the Taghanic onlap interval (Upper Tully/Geneseo Sequence of Baird and Brett, 2003) in the central Appalachian Basin. This occurrence is particularly significant because of its association with conodonts that provide a basis for refined correlations between the central Appalachian Basin and the Taghanic onlap succession in New York.