Early Eifelian Research Articles

Relationships between brachiopod fauna (Lochkovian–Frasnian) from northwest Gondwana (Amazonas Basin) and environmental changes during the Devonian

The Devonian marked a significant phase in the evolutionary history of the Brachiopoda. During this period, the Phylum achieved its peak diversity (Emsian) and suffered one of its greatest declines (Frasnian–Famennian), ranking second only to the mass extinction event at the Late Permian period. In Brazil, the Amazonas Basin has a rich record of Devonian brachiopods distributed in four stratigraphic units: i) Manacapuru (Lochkovian), ii) Maecuru (early Eifelian), iii) Ererê (late Eifelian), and iv) Barreirinha (early Frasnian) formations. This article aims to survey the occurrences of brachiopods during the Devonian in the Amazonas Basin and to discuss the possible factors that influenced their diversity. Environmental changes may explain the variation of brachiopod diversity throughout the Devonian in the Amazonas Basin. We noted that the diversity variation of Devonian brachiopods in the Amazonas Basin unfolded in three distinct stages. The peak of brachiopod diversity occurred in the early Eifelian (Maecuru Formation), when the Amazonas Basin was between the subtropical latitudes 30°S and 60°S, under shallow marine and cold conditions, justified by the absence of carbonates, evaporites, and reefs in the region (Stage 1). The first diversity decline is recorded in the Ererê Formation (late Eifelian), attributed to a warmer climate and deeper water than in the Maecuru Formation (Stage 2). During the Frasnian, there was a second diversity decline of brachiopods in the Amazonas Basin (Barreirinha Formation). A major global transgression occurred in the Late Devonian. In this period, the Amazonas basin experienced the deepest marine conditions in its history. The brachiopods of the Barreirinha Formation occur in layers of black shale (offshore), attributed to an anoxic or dysoxic environment of high stress, which explains the low diversity of brachiopods in this unit (Stage 3).

Lithology, Geochemistry of the Middle Devonian Sediments and the Influence of Volcanism on Sedimentation in the Southeast of West Siberia

Abstract —Dataset on the Middle Devonian volcanic-carbonate–terrigenous sediments of Salair and the Kuznetsk trough, submerged northward under the Mesozoic–Cenozoic West Siberian geosyneclise (WSG) cover, have been presented. Mainly deep water sediments composed of thin- and fine-grained clastic material (with predominance of tephroids) and thin-, fine-clastic biodetrital limestones with slope slide breccia, as well as turbidites and peculiar “conglomerate-like” limestones (paleoseismites) were found. Sedimentary and geodynamic environments have been reconstructed for the Middle Devonian strata. Predominantly andesitic composition of pyroclastic ashes with fewer values of felsic and basic volcanic components have been determined. The structures related to the continental margin environments of the Siberian continent, the continental slope and its basement have been found. According to sedimentary and geochemical data, the paleogeodynamic environment within the studied region was relatively stable and generally corresponded to the island arc conditions. The paleoclimate of the source area changed from semi-humid in the late Emsian–early Eifelian (Malaya Salairka age) to aridic in the middle Givetian (Kerlegesh age). Basin sediments formed in the deep water oxic environments with good water aeration, excepting euxinic environments found in the lowermost part of studied succession.

Стратиграфический объем тоупуголъегартской толщи (нижний-средний девон, Полярный Урал)

We refined the age of carbonate and clastic volcanomictic rocks of the Toupugol'egart Formation (D1–2tg) of the Voikar Belt of the Polar Urals, which formed at the final stage of the Polar Ural Island arc development. The analysis of the stratigraphic distribution of fossils of the Toupugol'egart Formation was based on a revision of previously published data and new collections of the authors (algae, tabulatomorphic corals). The stratigraphic range of the Toupugol'egart Formation was extended up to the Karpinsky-Langur regional stages of the Emsian Eifelian of the Devonian. The similarities of the structure, lithological composition and paleontological associations of carbonate sequences of the Toupugol'egart Formation and the upper part of the Malyj Ural Formation (Voikar Belt of the Polar Urals), as well as the Terrigenous-Volcanogenic Formation (eastern slope of the Middle Urals) were noted. The accumulation of these deposits took place in the Late Emsian Early Eifelian, probably during joint sedimentary-volcanogenic cycle within a single extended island-arc system. We assumed a similar evolution of the Polar Ural and Tagil island arcs at the final stage of their formation.

Paleoenvironmental interpretation and palynoflora of Devonian–Carboniferous subsurface sections from the eastern part of the Moesian Platform (Romania)

Palynomorph assemblages and palynofacies analyses have been performed on several core samples from the Devonian–Carboniferous deposits identified in five wells located within the eastern region of the Moesian Platform. The investigated sections include, in ascending stratigraphic order, the Ţăndărei, Smirna, Călăraşi and Vlaşin formations. Based on the stratigraphic distribution of key taxa identified (miospores, chitinozoans, acritarchs), seven biozone intervals (four for the Devonian and three for the Carboniferous) have been recognized. The oldest samples were dated as being part of the micrornatus–newportense (MN) – lower part of breconensis–zavallatus (BZ) Assemblage Zones (Early Devonian), while the younger ones are assigned to the kosankei–varioreticulatus (KV) – nobilis–junior (NJ) Assemblage Zones (Pennsylvanian). Palynofacies observations suggest a fairly distal depositional environment during the period between the Lochkovian and Pragian times, followed by some proximal/fluvio-deltaic conditions in Emsian–Early Eifelian (top of the Ţăndărei Formation). The upper Tournaisian to Serpukhovian sedimentary rocks of the Călăraşi Formation and lower part of Vlaşin Formation were deposited in inner neritic environments. Mud-dominated dysoxic/anoxic conditions of the Bashkirian, abruptly transitioned to deltaic deposition and oxidizing environments that persisted to the Moscovian.The Early Devonian terrestrial palynoflora is dominated by trilete spores which belong to lowland vegetation (vascular plants), the latter preferring areas with open connections via rivers to marine sedimentary basins. Carboniferous samples yielded only terrestrial miospores of various types of arborescent and herbaceous lycopsids and ferns, suggesting different habitats such as non-flooded wetlands or swamps within coastal plain and continental interiors. These assemblages of Carboniferous miospores are an indication of neutral-humid climatic conditions which existed at the time of deposition.

Crinoids from the Lower (Pragian–Emsian) and Middle (early Eifelian) Devonian of Bolivia (Icla and Belén formations, Malvinokaffric Realm)

AbstractTwo new families and three new genera and species of Crinoidea from the Icla and Belén formations, Bolivian Devonian, are described. The material is identified asMeperocrinus angelinan. gen. n. sp., from the Icla Formation of the Sub-Andina region,Tuberocrinus lapazensisn. gen. n. sp. andAenigmaticumcrinus rochacamposin. gen. n. sp., both from the Belén Formation of the Bolivian Altiplano.Meperocrinus angelinan. gen. n. sp. is an Emperocrinidae, a family described from the Silurian of the United States of America.Tuberocrinus lapazensisn. gen. n. sp. is assigned to a new family of Dimerocrinitacea, the Tuberocrinidae n. fam., which is closely related to Pterinocrinidae that already has representatives in Bolivia (Apurocrinus sucreiMcIntosh), Argentina (Pterinocrinus?australisHaude), and Colombia (Bogotacrinus scheibeiMcIntosh).Aenigmaticumcrinus rochacamposin. gen. n. sp. is also as assigned to a new family of Dimerocrinitacea, the Aenigmaticumcrinidae n. fam.; a family with very distinctive features. These data demonstrate that the Malvinokaffric crinoid fauna in Bolivia has a mixed origin, with forms that arrived in South America from Europe (Old World Realm) and United States of America (Eastern America Realm) during the late Silurian or earliest Devonian, as well as a local stock, which evolved to highly endemic lineages.UUID:http://zoobank.org/f03120c6-264a-4ae9-81e0-46bfe844e65e.

Endocranial morphology of the petalichthyid placodermEllopetalichthys scheiifrom the Middle Devonian of Arctic Canada, with remarks on the inner ear and neck joint morphology of placoderms

Petalichthyid and “acanthothoracid” placoderms have taken pivotal positions in the debate on placoderm — and, by extension, jawed vertebrate — relationships owing to perceived similarities with certain jawless vertebrates. Neurocranial characters are integral to current hypotheses of early gnathostome relationships. Here, we describe the three-dimensionally preserved neurocranial anatomy of the petalichthyid placoderm Ellopetalichthys scheii (Kiær, 1915), from the Middle Devonian (early Eifelian) of Ellesmere Island, Canada. Using X-ray computed microtomography, we generated three-dimensional reconstructions of the endocranial surfaces, orbital walls, and cranial endocavity. These reconstructions verify the absence of a crus commune of the skeletal labyrinth and the complex shape of the petalichthyid endolympathic duct. Details of the craniothoracic joint and occipital musculature fossae help resolve the problematic comparative anatomy of the occipital surface of petalichthyids. These new data highlight similarities with arthrodire placoderms, consistent with older hypotheses of a sister-group relationship between petalichthyids and that clade.

Subvolcanic gabbro–porphyrite and intrusive diorite, and sulfide mineralization of the Dzhusa volcanogenic massive sulfide deposit (Southern Urals)

Two sequentially formed groups of dikes in the gabbro–porphyrite complex have been distinguished, the ages of which are early Eifelian (early dikes) and early Givetian (late dikes). We have estimated the temperature impact of ore contact metamorphism, which is related to dikes of the Lower Carboniferous Magnitogorsk intrusive complex. A hidden zonality of microimpurities in the ore-forming minerals has been established for the first time by the LA-ICP-MS method. The ore formation age has been determined as early Eifelian–early Givetian.

Devonian trilobites from the Amazonas Basin: systematic diversity, taphonomy, and biogeographic significance

Although the Devonian invertebrate biota of the Amazonas Basin is incompletely known, its unusual mixture of supposedly Malvinokaffric and Appalachian taxa is of considerable biogeographical interest. The history of research on Devonian trilobites from the Amazonas Basin is summarized. These fossils occur in the Maecuru (latest Emsian – early Eifelian) and Ererê (latest Eifelian – early Givetian) formations, representing the families Homalonotidae, Dalmanitidae, and Calmoniidae. Trilobite diversity is higher in the Maecuru (nine named plus six indeterminate taxa) than the Ererê Formation (with only two named taxa), which displays faunal impoverishment generally. None of the Devonian Amazonas Basin trilobite species is known from other Malvinokaffric sites, suggesting very high endemicity within this basin. A taxonomic revision of “Homalonotus” derbyi (Clarke, 1890) is presented and a lectotype is designated. A lectotype and paralectotype are also designated for Eldredgeia paituna (Hartt & Rathbun, 1875). Some taphonomic observations of fossils from the Maecuru Formation are made, and a brief biogeographic synopsis of the Devonian Amazonas biota is also given.

Latest early to early Middle Devonian trilobites from theErbenochileBed, Jbel Issoumour, Southeastern Morocco

A bed on Jbel Issoumour, near Alnif in southeastern Morocco, contains numerous complete trilobites. The bed is located stratigraphically at the base of the El Otfal Formation, immediately above a cliff-forming resistant unit known to local trilobite miners as the ‘grand calcaire’, and is latest Emsian or early Eifelian in age. The fauna exhibits an alpha trilobite diversity of at least eight species, includingErbenochile issoumourensisn. sp.,Acanthopyge (Lobopyge) bassein. sp., andWalliserops lindoein. sp. The absence of lateral palpebral extensions inE. issoumourensisbut their presence in the type species ofErbenochile, E. erbeni, when considered with other differences in the exceptionally large eyes of both species, supports the hypothesis that these palpebral structures functioned as eyeshades inE. erbenibut not inE. issoumourensis. Walliserops lindoeihas a short, stout haft at the base of the trident anterior cephalic projection, which is the most characteristic feature ofWalliserops.This projection inWalliseropsprimarily functioned as a deterrent to predators.

Devonian sea-level change in Bolivia: A high palaeolatitude biostratigraphical calibration of the global sea-level curve

During the Devonian Period the cool water Malvinokaffric Realm was located at high palaeolatitudes in the southern hemisphere. The Realm is defined by its highly endemic marine benthic fauna, which makes extra-Malvinokaffric correlations problematic. Investigation of the Devonian palynomorphs from an extensive regional sub-surface dataset (24 wells) in the Chaco Basin, Bolivia, reveals the presence of a number of stratigraphically restricted and regionally correlative epiboles (peak abundances) of the distinctive palynomorphs Bimerga bensonii, Crucidia camirense, Evittia sommeri, Petrovina connata and Ramochitina magnifica. These palynomorph epiboles were then located at outcrop by a high-resolution palynological investigation (225 samples) of two Bolivian outcrop localities in the Chaco Basin: Bermejo, Santa Cruz Department and Campo Redondo, Chiquisaca Department. The important Evittia sommeri epibole in the basal Los Monos Formation is related to a marine transgression that is present in both these outcrop sections. Additional chronostratigraphic control on this marine transgression comes from the occurrence of rare goniatites in the base of the Huamampampa Formation at Campo Redondo, which are at least early Eifelian in age (post Chotĕc Event). Based on the goniatite together with spore data, the marine transgression with Evittia sommeri in the basal Los Monos Formation can be tentatively assigned to the Mid Devonian (mid-late Eifelian) Kačák Event. The presence of a datable Malvinokaffric goniatite has shown that key spore taxa which are used zonally in both Laurussia and Gondwana do not all have coincident first occurrences in both areas. Furthermore, despite the appearance of some cosmopolitan elements in the microflora, Mid and Late Devonian spore assemblages in Bolivia are distinct from other regions in being relatively impoverished in both progymnosperm and lycopod spores. This floral difference is attributable to the Malvinokaffric Realm continuing to retain a distinctive cool climatic signature throughout this interval. However, the sporadic occurrences of extra-Malvinokaffric macrofauna in restricted stratigraphic intervals of the Middle Devonian in South America and South Africa are significant. The oldest known occurrence of the extra-Malvinokaffric brachiopod Tropidoleptus in Bolivia is coincident with the late Eifelian basal Los Monos Formation transgression. Hence there was a relationship between influxes of this fauna and marine transgressions, i.e. temporary periods of reduced climatic gradient. The migration of Devonian spores, and particularly heterosporous spores, between Gondwana and Laurussia clearly occurs during the Mid and Late Devonian. This is at variance with models claiming a wide Rheic Ocean during much of the Devonian.

Middle Devonian microfloras from the Chigua Formation, Precordillera region, northwestern Argentina

Abstract Rich palynological assemblages have been obtained from the Middle Devonian Chigua Formation (Chinguillos Group, San Juan Province), western Precordillera, Argentina, at two new localities (Del Chaco and Don Agustín creeks). From the palyniferous levels at Del Chaco Creek, there are two assemblages: one is very rich in microplankton (assemblage 1) whereas the other is dominated by spores (assemblage 2). The level obtained from Don Agustín Creek, poorest in overall taxa, is also rich in microplankton (assemblage 3). Compared with coeval microfloras elsewhere, a late Emsian–early Eifelian, and an early Givetian age are proposed for the first and the second assemblages respectively. A third assemblage (assemblage 3) tentatively represents a timespan around the Givetian–Frasnian boundary. The proposed age based on the palynomorphs reinforces previous palaeontological records. Variation in the microplankton diversity, fluctuations in the microplankton/spore ratio and differences in acritarch morphology are used here to interpret changing proximity to palaeoshoreline and so to recognize fluctuations in relative sea level that occurred during the deposition of the Chigua Formation.

The ontogeny and systematics of the otarionine trilobiteOtarionellafrom the Devonian of the Montagne Noire, France and the Maider, Morocco

AbstractA new otarionine trilobiteOtarionella rastrumsp. nov., from the late Emsian Mont Peyroux Formation (Montagne Noire, France), is described. Silicified remains, recovered from the underlying Bissounel Formation (early to late Emsian), are also attributed to this new species. These isolated silicified sclerites represent metaprotaspid to young holaspid growth stages, which enables the almost complete ontogeny of an otarionine trilobite with a spinose adult morphology to be described for the first time. Comparison with associated larval and juvenile growth stages ofCyphaspisreveal that the pattern of juvenile cranidial spine distribution inOtarionella rastrumsp. nov. differs from all patterns described so far in the Otarioninae, in particular that characterizing the tribe Otarionini. A second species,Otarionella lkomaliisp. nov., known only from a complete articulated specimen discovered in the early Eifelian of southern Morocco, is also described. Like the middle EifelianOtarionella chamaeleo(Basse, 1997), this new species has only ten thoracic segments, with the fourth and the sixth segments each bearing a long axial spine. In the light of the new elements provided by the ontogenetic sequence ofO. rastrumsp. nov. and the adult specimens of this species andO. lkomaliisp. nov., the putative synonymy ofOtarionellaandOtarionis rejected and a restricted concept of the genusOtarionellais defined.

First Devonian dipnoans (Vertebrata, Sarcopterygii) from Spitsbergen

For the first time, dipnoan remains are described from the Devonian of Spitsbergen. According to the stratigraphy and the associated vertebrate fauna, they are considered as Late Emsian–Early Eifelian in age. Unfortunately remains are too sketchy and non-diagnostic to be referred or compared to a known Devonian dipnoan. This new material, determined as Dipnoi gen. et sp. indet., is nevertheless important in biostratigraphical and palaeobiogeographical points of view, since it is amongst the earliest dipnoan occurrences, and the first one in the Devonian of Spitsbergen. To citer this article: G. Clément et al., C. R. Palevol 5 (2006) .

Age revision of some Palaeozoic strata of Mongolia based on conodonts

Ages of some Palaeozoic stratigraphic units in Southern Mongolia are revised by means of conodonts. The Arynshand Formation is dated as Early Carboniferous. The upper part of the Gavuu Member of the Mandalovoo Formation near the Bayan–Khoshuu Ruins section in the Mushgai area is definitely the earliest Devonian; a new stratigraphic unit, the Olonovoot Formation, is named for this part. The upper part of the Tsagaanbulag Formation at the Tsakhir Section and the Ulaan-Shand Section should be assigned to the Lochkovian rather than Silurian. The Chuluun Formation is actually late Emsian, and the Tsagaankhaalga Formation is early Eifelian. The Indert Formation is Early Carboniferous.

Integrated Middle Devonian chitinozoan and miospore zonation of the Amazonas Basin, northern Brazil

Middle Devonian chitinozoans were studied from 13 deep wells in the central part of the Amazonas Basin, northern Brazil, and compared with a newly established regional miospore zonation. Of the 23 chitinozoan species encountered, four are newly described: Ancyrochitina multibrachiata, Lagenochitina praeavelinoi, Ramochitina autasmirimense , and Ramochitina herculesi and seven species are retained in open nomenclature because of an insufficient number of well-preserved specimens. The stratigraphic intervals investigated herein correspond to three miospore interval range zones previously defined for the Amazonas Basin, namely, the Grandispora/Samarisporites spp. (GS); late Emsian–early Eifelian, Grandispora permulta (Per); late early Eifelian through the Eifelian–Givetian transition, and Geminospora lemurata-Chelinospora ex. gr. ligurata (LLi); early Givetian. A regional Middle Devonian chitinozoan biozonation, also consisting of three zones, is proposed for the investigated interval. These zones are the interval zone of Angochitina n. sp. A (early Eifelian), the interval zone of Alpenachitina eisenacki (late early to late Eifelian), and the total range zone of Ramochitina stiphrospinata (early Givetian). Des chitinozoaires du Dévonien Moyen ont été étudiés dans 13 forages profonds de la partie centrale du Bassin de l'Amazone (N du Brésil). Leur répartition est comparée à la zonation régionale des miospores proposée récemment. Parmi les 23 espèces de chitinozoaires recensées, quatre sont nouvelles : Ancyrochitina multibrachiata, Lagenochitina praeavelinoi, Ramochitina autasmirimense et Ramochitina herculesi . Sept autres espèces sont laissées en nomenclature ouverte en raison d'un matériel insuffisant. L'intervalle stratigraphique étudié ici correspond à trois zones d'intervalle de miospores, définies précédemment pour le Bassin de l'Amazone. Il s'agit des biozones à Grandispora/Samarisporites spp. (GS) de l'Emsien supérieur–Eifélien inférieur, la zone à Grandispora permulta (Per) de l'Eifélien inférieur tardif à la transition Eifélien–Givétien et la zone à Geminospora lemurata–Chelinospora ex. gr. ligurata (LLi) du Givétien inférieur. Une biozonation régionale des chitinozoaires du Dévonien Moyen, comprenant également trois zones, est proposée. Il s'agit de la zone d'intervalle de Angochitina n. sp. A (Eifélien inférieur), de la zone d'intervalle de Alpenachitina eisenacki (Eifélien inférieur tardif à Eifélien supérieur) et de la zone d'extension totale de Ramochitina stiphrospinata (Givétien inférieur).

K-bentonites, volcanic ash preservation, and implications for Early to Middle Devonian volcanism in the Acadian orogen, eastern North America

Lower to Middle Devonian marine strata in the Appalachian foreland basin feature up to 80 or more thin K-bentonites that represent ancient volcanic ashes. The time vs. space distribution of K-bentonites through the Lochkovian to Eifelian Stages (representing ∼30 m.y.) shows a distinct pattern of clustered multiple beds, several scattered beds, and thick intervals with no K-bentonites. Four clusters of 7 to 15 individual, closely spaced layers occur in the middle Lochkovian (Bald Hill K-bentonites, Kalkberg–New Scotland Formations), late Pragian or early Emsian (Sprout Brook K-bentonites, Esopus Formation) and early Eifelian (two clusters, the Tioga middle coarse zone and Tioga A–G K-bentonites, Onondaga Formation). Detailed examination of these Devonian K-bentonites shows that in many cases they do not represent a single eruption. Multilayered beds, fossil layers within beds, authigenic minerals (e.g., glauconite and phosphate nodules), subjacent hardgrounds, and an irregular distribution of beds through space and time raise questions about the depositional history and preservation potential of volcanic ash in marine environments and the degree to which the beds represent a primary record of volcanism. These and other lines of evidence indicate that postdepositional physical, biological, and geochemical processes (e.g., sedimentation rate, event, and background physical processes, burrowing) have modified the primary record of these water-laid ash-fall events. These factors may lead to preservation of primary ash deposits or to their resedimentation and/or partial to complete mixing with background sediments. The preservation potential, and resulting distribution, of the Devonian K-bentonites can be analyzed across a spectrum of preservational magnafacies. In this paper I present a model of ash preservation; the model incorporates environmentally related physical, biological, and chemical processes active in epicontinental seas and marine foreland basins. Conclusions based on the model indicate that the middle Lochkovian, early Emsian, and early Eifelian were times of peak volcanic activity in eastern North America, related to times of increased tectonism in the Acadian orogen.

Radiometric evidence for Middle Devonian inversion of the Hill End Trough, northeast Lachlan Fold Belt

The publication of a new geological time‐scale by the Australian Geological Survey Organisation and radiometric dates from the Hill End goldfield have prompted the re‐examination of the timing of deformation of the Hill End Trough to determine whether it occurred in Middle Devonian or Early Carboniferous time. Palaeontological evidence from the western trough margin and the Capertee High dates the end of deposition in the trough as late Emsian or early Eifelian (385–382 Ma). After a mid‐Devonian hiatus of at least 15 million years, paralic sedimentation commenced on the Molong and Capertee Highs in late Frasnian or early Famennian time (367–363 Ma). No Upper Devonian sedimentary formations occur in the Hill End Trough. Structural relationships indicate that the oldest mineral veins at Hill End preceded cleavage formation in the deformed trough sedimentary rocks. Early vein muscovites have Middle Devonian 40Ar/39Ar dates of 380–370 Ma. Regional metamorphic biotites from Hill End have well constrained 40Ar/39Ar closing ages of 360–358 Ma (mid‐Famennian). The metamorphic (thermal) maximum which outlasted penetrative deformation, is estimated here by modelling to have been about 370 Ma (latest Givetian). This clearly places the earlier main deformation in the Middle Devonian. Deformation probably began by terminating trough deposition in latest Emsian to early Eifelian time and ended in early Givetian time at about 375 Ma ago. Published pressure and temperature data from the Hill End goldfield suggest that deformation thickened the 6 km sediment column to around 11 km. The thermal model suggests there was post‐deformation erosion of about 4 km and little if any further erosion occurred during Late Devonian to Early Carboniferous time. The shortening accompanying the inversion of the northern Hill End Trough may have been taken up in the region to the south, both east and west of the Copperhannia Thrust, and east of the southern termination of the Capertee High. The general conclusions are not affected by a new Devonian time‐scale discussed in Appendix 2.

Devonian trilobites — Evolution and events

Environmental changes emphasized in event-stratigraphic turnouts are thought to have clearly affected the development of Devonian trilobites. After the latest Silurian/Prídolian/ and earliest Devonian/Lochkovian diversity fall, the Lochkovian-Pragian Boundary Event triggerred the increased diversity period which lasted with some changes until the early Eifelian. The general decline in trilobites, marked by stepwise diversity falls, was strongly accelerated by the Middle Devonian Kacák and Taghanic, and the late Frasnian Kellwasser Events. The progressive Famennian innovations were interrupted by the Hangenberg Event at the Devonian-Carboniferous boundary. The retreat of Devonian trilobites was stepwise, event-stratigraphic turning points were lethal mostly for families showing a decline already prior to the events. Stratigraphic levels of changes in trilobite faunas roughly correspond to those recognizable in some other fossil groups (e.g. ammonoids, dacryoconarids, conodonts etc.), although the effects could have been different. The general retreat of trilobites is believed to have been not caused but only accelerated by event-turnovers.

Biostratigraphy and biogeography of Frasnian, Upper Devonian conodonts

Analysis of Frasnian conodont sequences in the Montagne Noire, southern France, results in the recognition of a conventional zonation consisting of thirteen zones. Graphic correlation of eight Montagne Noire sections with a total of 11 sections in the Alberta Rockies, the Hay River-Trout River areas of the southern Northwest Territories, Canada, the Midcontinent and New York sequences in the United States, and the Canning Basin, Western Australia divides the Frasnian into 34 composite standard units. Most of these sections are dominated by conodonts of the outer-shelf to basinal Palmatolepis biofacies, but those of Hay River-Trout River are occupied by the quite contrasting inner-shelf Polygnathus biofacies. Correlation of the latter with the Montagne Noire zonation is effected only through graphic correlation. The taxonomy of many of the critical species involved in the correlations is based on shape analysis and multielement taxonomy of Palmatolepis.Prevailing opinion is that the Frasnian was a time of cosmopolitanism as exemplified both by benthic organisms, especially corals and brachiopods, as well as conodonts. This contrasts with the Early and Middle Devonian which was a time of significant endemism in benthic fossils and in conodonts. The high point in conodont endemism according to the zone-by-zone analysis of the Early and Middle Devonian (Klapper and Johnson, 1980) was the early Eifelian when there were about 70% endemic species. Although endemism did not reach this high in the Frasnian, analysis of a limited number of intensively collected and studied sections in the Montagne Noire, U.S. and Canada, Western Australia, and the Russian Platform demonstrates levels of endemism ranging from about 30 to 45% in three composites of two zones each. Endemic species occur in both the Palmatolepis and Polygnathus biofacies. Using the Probabilistic Index of Similarity of Raup and Crick (1979), the null hypothesis of randomness is rejected for some paired comparisons between localities representing different biofacies, as would be expected, but it is also rejected between some localities representing the same biofacies on different continents. Although the explanation of significantly dissimilar faunas can be accepted at 95% confidence levels in only a limited number of instances, there are dissimilarities of somewhat lesser magnitude among various paired comparisons. This seems to indicate that the Frasnian was not a time of conodont cosmopolitanism even within the Palmatolepis biofacies.

Lower and middle devonian miospore-based stratigraphy in Libya and its relation to the megafloras and faunas

A review of miospores, faunas and megafloras of the Lower and Middle Devonian in Libya allows new conclusions to be drawn. The application of the Ardenne-Rhenish Devonian miospore zonation in Libya gives the following results. In the North Hammadah Basin, the base of the Tadrart Formation might well be strongly diachronous depsite the lithostratigraphical correlations shown on the base of “Gamma-Ray/Neutron” logs. At least the lower part of the Tadrart Formation in borehole MG-1 is within the lowermost part of the Lochkovian not at its base. In the southern margin of the Hammadah Basin, the Tadrart and Ouan-Kasa formations are probably not older than late Emsian, maybe early Eifelian. The Ouenine Formation I is often absent there or strongly reduced. The isochroneity of the (discordant) lower limit of the Tadrart Formation across the Hammadah Basin is far to be demonstrated. The Caledonian age of the discordance on the southern margin of the Hammadah Basin can obviously be challenged. In the eastern Murzuk area, the plant-bearing Tadrart-Emi Magri formations have a Middle Devonian age according to the plant fossils themselves. The discordance which separates these formations from the Acacus Sandstone at Dor el Goussa has to be late Early Devonian or Middle Devonian because the Acacus Sandstone “Psilophytes” cannot be older than Pragian and can even be younger (Emsian). There is obviously no available argument which could counteract the fossil floral data and prove that the discordance in the eastern Murzuk has the same age as the Silurian/Devonian transitional beds in the northern Hammadah Basin.