Devonian Boundary Research Articles

A palynological investigation of the Early-Middle Devonian transition and associated Choteč Event in Northern Spain

In Northern Spain there is a near complete sequence of Devonian rocks that accumulated around a relatively isolated land mass, the Armorican Terrane Assemblage, which was separated from Gondwana to the south and Laurussia to the north. The Lower to Middle Devonian transition records a dramatic facies change from carbonate to siliciclastic sedimentation. The Choteč Event, a global anoxic pulse that occurs just above the Lower-Middle Devonian boundary (392.5–393.1 Ma), has been identified within this transition. These strata are included in the Moniello and Naranco fms in Asturias and the equivalent Santa Lucía and Huergas fms in Leon. They are independently age-contrained based on conodont and invertebrate biotas. For the first time we describe palynomorph assemblages recovered from the Lower to Middle Devonian transition in Northern Spain. The assemblages contain terrestrial (spores) and marine (acritarchs, prasinophycean cysts, chitinozoans) elements, thus recording primary productivity on both the land and in the oceans. The older assemblages belong to the annulatus–sextantii Spore Zone and the younger assemblages the douglastownensis–eurypterota Spore Zone, which is concordant with the independent age constraints. Our analysis of the distribution and diversity of marine and terrestrial palynomorphs supports interpretations of the facies change associated with the Choteč Event as being related to a change to increased rainfall and terrestrial runoff. However, this change is associated with only limited taxon turnover in both land plant spores and marine phytoplankton and chitinozoans.

Genesis of Devonian volcanic-associated Lahn-Dill-type iron ores – part II: trace element fractionation evidences diffuse fluid venting

The iron (Fe)-oxide deposits of the Lahn-Dill-type are composed of haematite-quartz and rare siderite-haematite ores. These ores formed as marine chemical sediments on top of volcaniclastic rocks near the Middle to Late Devonian boundary (∼ 380 Ma). As such, their trace element fractionation patterns provide key information on venting style, ocean chemistry, particle-solution interaction, and depositional environment at the time of ore formation. This study combines WDXRF and ICP-MS/OES whole-rock geochemistry with complementary in-situ LA-ICP-MS analysis, and TEM element mapping of ore samples from the Fortuna Mine (Rhenish Massif, Germany). In-situ measurments were conducted on quartz-haematite, haematite, and siderite-haematite microdomains. Bulk major element contents of the ores indicate (volcani)clastic contamination and post-depositional hydrothermal alteration. Microdomain trace element distributions reveal four different trace element signatures, which are related to: (1) syngenetic apatite formation due to sorption of P and REY from seawater; (2) Fe-(oxyhydr)oxide-specific trace element scavenging and fractionation within the seawater column; (3) diagenetic Fe(III) reduction and trace element mobilisation in pore water; and (4) simultaneous deposition of (volcani)clastic material and Fe-(oxyhydr)oxides. These results show that Lahn-Dill-type iron ore formation resulted from mixing of a low-temperature vent fluid with ambient seawater at high seawater to vent fluid ratios. This likely was related to an environment in which diffuse venting dominated over focused venting, and in which quick Fe-particle precipitation led to formation of haematite-quartz ores. Local diagenetic Fe(III) reduction resulted in post-depositional siderite-haematite ore formation during which trace elements were partially remobilised in pore water.

The Silurian and the Devonian in the Svoge Unit, Western Bulgaria – a brief overview

Five stops, containing Silurian–Devonian strata of the Svoge Unit (Western Bulgaria) are described. At Stop 1 near the village of Tsarichina, Upper Devonian flysch (Katina Formation) can be observed, which ends the Paleozoic marine sedimentation in the area. The other two Devonian formations are observable at stop 2 near the village of Vlado Trichkov. These are the black shales of the Ogradishte Formation and the light shales of the Romcha Formation. At the village of Tseretsel (stop 3), all Silurian units are observed: the bedded cherts (lydites) of the Saltar Formation, the graptolite-bearing black shales of the Mala Reka Formation, and the grey to gray-green laminated shales of the Yabukov Dol Formation. The boundaries of the Silurian System, based on graptolites, were established at the next two stops, respectively at stop 4 the Silurian/ Devonian boundary and at stop 5 the Ordovician/Silurian boundary.

Discovery of the earliest Devonian conodonts from Xinjiang, Northwest China

The base of the Devonian is defined at the first appearance of graptolite Uncinatograptus uniformis uniformis, with the occurrence of trilobite Warburgella rugulosa rugosa and conodont Caudicriodus woschmidti as the auxiliary indicators. Recently some researchers questioned whether Caudicriodus woschmidti can be an indicator, and proposed Caudicriodus hesperius to mark the base of the Devonian in carbonate successions. However, the paleogeographic distribution of this species is mainly in the southern hemisphere or near the equator, and there was no definite record of it in the northern hemisphere during the Early Devonian. Due to lithological restrictions, conodont data of the Silruain–Devonian Boundary (SDB) are relatively rare in China, and Caudicriodus hesperius has not been identified. In this study, specimens of Caudicriodus hesperius were obtained from the base of the Kaokesaiergai Formation in the eastern Junggar, northern Xinjiang, which represents the first record of this taxon in China, suggesting that the age of the formation is Early Devonian, rather than late Silurian as previously believed based on the benthic faunas. The encrinurid trilobites, which commonly occur in the Silurian, were also recorded in the same horizon with C. hesperius, indicating that encrinurids may cross the SDB and range into the earliest Devonian. The discovery of Caudicriodus hesperius in northern Xinjiang significantly expands the paleogeographic range of this index conodont to the Central Asian Orogenic Belt in the northern hemisphere, and suggests that Caudicriodus hesperius may be used as a global index for the base of the Devonian and for possible stratigraphic correlation of the SDB in different paleogeographic and paleotectonic settings.

Genesis of Devonian volcanic-associated Lahn-Dill-type iron ores — part I: iron mobilisation and mineralisation style

Fe-oxide deposits of the Lahn-Dill-type in the eastern Rhenish Massif comprise haematite and quartz with minor siderite, magnetite, and calcite. The deposits are located in the hanging wall of thick volcaniclastic rock sequences and mark the Middle to Late Devonian boundary. Varying ore types with accompanying footwall rocks were sampled from two formerly important ore deposits, the Fortuna mine (Lahn syncline) and the Briloner Eisenberg mine (East Sauerland anticline), in order to elucidate the interplay of processes leading to ore formation. Deposit geology, petrography, and whole-rock geochemistry suggest that the ores formed by iron mobilisation from deeply altered footwall volcaniclastic rocks, subsequent venting of a modified H2O-CO2-Fe-rich and H2S-poor fluid, and precipitation on the seafloor (sedimentary-type), or locally by metasomatic replacement of wall rocks (replacement-type). Petrographic analysis to the sub-micron scale revealed that the sedimentary-type ores most likely formed from a Fe-Si-rich gel and accompanying maturation. Early gel textures include the presence of spherules, aggregates, tubes, and filamentous stalks consisting of nanocrystalline haematite dispersed in a matrix of microcrystalline quartz. Local diagenetic Fe3+ reduction within the gel is indicated by siderite replacement of haematite. Replacement-type ores formed due to a two-step process including coprecipitation of (precursor) haematite and carbonates and subsequent metasomatic replacement by haematite. These ore-forming processes took place during a time when several restricted shallow marine basins in the north-eastern Rheic Ocean were influenced by extensive volcanism and associated hydrothermal fluid flux. Examples of similar volcanic-associated Fe-oxide occurrences of Silurian to Carboniferous age can be categorised as being of Lahn-Dill-type ores as well.

The latest encrinurid trilobites from the Lower Devonian of Xinjiang, Northwest China

AbstractEncrinurids are common in Ordovician and Silurian strata but whether they survived into the Early Devonian is still controversial. This paper documents the encrinurid Batocara sp. near the Silurian–Devonian boundary in western Junggar, Xinjiang. The highest horizon of Batocara sp. is located above the first appearance datum of the Devonian conodont Caudicriodus, confirming that encrinurids may cross the Silurian–Devonian boundary. The presence of Caudicriodus angustoides bidentatus, Zieglerodina planilingu and plate-type loboliths of scyphocrinoids above the highest horizon of Batocara sp. indicates that encrinurids here extend only into the lower part of the first conodont zone of the Lochkovian (i.e., Caudicriodus hesperius Biozone). Encrinurids are widely distributed and easily recognized, and unlike graptolites and conodonts are not controlled by lithofacies. Therefore, it might be possible to use the highest horizon of encrinurids as indicator fossils to identify the approximate position of the Silurian–Devonian boundary in areas or sections where graptolites and conodonts are not present, and at least in northwest China.

Late Silurian to earliest Devonian vertebrate biostratigraphy of the Birch Creek II section, Roberts Mountains, Nevada, U.S.A.

Intensive sampling of uppermost Silurian to lowermost Devonian levels of the marine sequence of the Roberts Mountains Formation exposed in the Birch Creek II section, Nevada has yielded assemblages of vertebrate microremains dominated by acanthodian scales. Taxonomic assessment of the vertebrates represented shows a suite and succession of taxa most similar to those recorded from contemporary circum-Arctic assemblages, with scales of the poracanthodid acanthodians Poracanthodes punctatus, P. canadensis, Radioporacanthodes porosus and ischnacanthid Gomphonchus sandelensis most abundant below the Silurian–Devonian (S–D) boundary (as previously determined by conodont and graptolite occurrences), and stem chondrichthyan ‘acanthodians’ Nostovicina laticristata and other Nostovicina spp. (order, family indet.) the most abundant above the boundary. Just one endemic acanthodian taxon, Funicristata nevadaensis nov. gen. nov. sp., was found, in the uppermost Silurian. Agnathan vertebrate remains are rare relative to acanthodian scales, with dermal fragments of heterostracans at fewer than 10 levels and scales of thelodonts from 12 levels scattered throughout the whole section. Thelodonts Apalolepis, Barlowodus spp., ?Boreania, Gonioporus alatus, Lanarkia, Loganellia, Nikolivia, Talivalia, Thelodus, ?Turinia sp. and Trimerolepis spp. are found below the purported S–D boundary. Rare thelodont scales including Boreania sp. cf. minima, N. gutta and a single scale of ?Amaltheolepis sp. are found above the S–D boundary level. The only identifiable gnathostome remains of groups other than acanthodians are from the putative osteichthyan Lophosteus sp. and chondrichthyans Ellesmereia schultzei and Polymerolepis sp., in the uppermost Silurian levels.

Diminutive Epibionts on Crinoid Stems from the Lower/Middle Devonian Boundary in the Barrandian, Czech Republic

Abstract Diminutive crinoid holdfasts and cemented tests of the foraminifers Psammosphaera and Tolypammina were observed on coarse bioclasts in weathered limestones of the Daleje-Třebotov Formation. Specimens were obtained in 1984 by washing so called “white beds” at a temporary locality in Praha- Barrandov. A few millimeter sized bioclasts with epibionts were freed from hard limestone beds of the Třebotov Limestone near the Lower/Middle Devonian boundary by long-term weathering. Many of the crinoid holdfasts attached to pluricolumnals provoked a stereomic response of the host crinoid. Also the growth orientation of the crinoid epibiont is not random and indicates some crinoid-epibiont to crinoidhost interaction. Reaction of host stereome and non-random stem orientation offer direct evidence of epibiont larval settlement and subsequent growth on the stem of a living crinoid host. The extensive growth of the host stereome ended by partial to total engulfing of the epibiont holdfast. This indicates advancing and finally successful defence of the host crinoid against the epibiont. The holdfast gives evidence that the small host crinoids offered a somewhat higher tier for even smaller epibiont crinoids. However, other observed holdfasts indicate fixation of larva and growth over loose bioclasts lying on a sea bed. Location of foraminifer test on bioclasts confims that foraminifers cemented and grew on loose echinodermal and brachiopod remains and preferred crevices and similar protected sites with concave profiles. This is clear evidence that diverse bioclasts (brachiopod shells, pelmatozoan ossicles) provided the hard substrate suitable for epibiont life on a sea bed.

Early Devonian (Lochkovian) eurypterids from the Yunnan province of southwest China

AbstractTwo new eurypterids, a pterygotid Pterygotus wanggaii n. sp. and an adelophthalmoid Parahughmilleria fuea n. sp., are described from the Early Devonian (Lochkovian) Xiaxishancun Formation of Yunnan province, southwest China. This discovery represents the first record of Parahughmilleria from Gondwana and the first Pterygotus from China. Pterygotus wanggaii n. sp. is characterized by the first primary denticles (d1,d1′) being located on the middle part of the cheliceral ramus and third primary denticles (d3,d3′) elongate, even longer than the first primary denticles. Parahughmilleria fuea n. sp. is differentiated by being a large Parahughmilleria with strongly developed lateral epimera from tergites T4 to T12. These discoveries not only extend the geographical extent of the genera Pterygotus and Parahughmilleria from Euramerica to SW China, but also give insight into the similarity of ecosystem structures across the Early Devonian world. In addition, based on previous studies, the new discoveries further support the hypothesis that eurypterids underwent a crisis during the Silurian–Devonian boundary interval.

Drowning, extinction, and subsequent facies development of the Devonian Hönne Valley Reef (northern Rhenish Massif, Germany)

The Hagen-Balve Reef is one of the largest Devonian carbonate complexes in the Rhenish Massif exposed in many former or active, economically significant quarries, especially in the Hönne Valley region at its eastern end. The timing and patterns of reef drowning, final extinction, and the middle Frasnian to middle Famennian post-reefal facies history, including details of the global Kellwasser Crisis, were studied based on two boreholes (HON_1101 and B102) and one outcrop at the Beul near Eisborn. More than 100 conodont samples provided a fine biostratigraphic framework and included new forms left in open nomenclature. The ca. upper 80 m of the new Asbeck Member of the Hagen-Balve Formation consists of relatively monotonous lagoonal successions assigned to four microfacies types. The local diversity of reef builders, mostly stromatoporoids, is low. Fenestral microbialites indicate very shallow and rather hostile back-reef settings. Near the Middle/Upper Devonian boundary, the eustatic pulses of the global Frasnes Events led to a significant backstepping of the reef margin, with reef core/outer slope facies overlying lagoonal facies. This flooding drastically reduced the carbonate accumulation rate and enabled the invasion of drowned back-reef areas by open-water organisms, such as polygnathid conodonts. Within this Eisborn Member, five microfacies types and numerous subtypes are distinguished including low-diversity “coral gardens” and a final, top lower Frasnian parabiostrome dominated by tabulate and colonial rugose corals. There was no cap stage (“Iberg Facies”). Two phases of the Basal Frasnes Event are marked by dark, organic rich limestones with subordinate reef builders. Based on conodont fauna from overlying nodular limestones of the new, (hemi-)pelagic Beul Formation, the final Hönne Valley reef extinction was caused by the eustatic Middlesex Event at the lower/middle Frasnian boundary. Within the Beul Formation, eight subphotic submarine rise microfacies types are distinguished. After a lower middle Frasnian phase of extreme condensation, rich conodont faunas enable the recognition of most upper Frasnian to middle Famennian zones. The global semichatovae Event led to a regionally unique intercalation by four phases of organic-rich, laminated black shales and intervening thin limestones in core HON_1101. The Lower Kellwasser Event is represented in HON_1101 by atypical, moderately Corg-rich, recrystallized, peloidal ostracod-mollusk pack-grainstones. The Upper Kellwasser level begins with an ostracod bloom, followed either by recrystallized mollusk wacke-packstones (HON_1101) or laminated, argillaceous mudstones (B102). The first indicates a rarely documented shallow subphotic, better oxygenated setting than typical Upper Kellwasser facies. As elsewhere, the top-Frasnian conodont extinction was severe. The lower/middle Famennian carbonate microfacies of the Beul Formation is relatively monotonous and typical for an oxic, pelagic submarine rise. The youngest recorded nodular limestones fall in the Palmatolepis marginifera utahensis Zone. Regionally uniform lydites of the Hardt Formation show that the local palaeotopography was levelled before the base of the Viséan. The Hönne Valley case study and comparisons with western parts of the Hagen-Balve Reef and other Rhenish reefs underline the significance of Givetian to middle Frasnian eustatic and anoxic events as causes for reef extinctions.

Late Early Devonian ostracodes from the Torkoz area (SW Morocco) and the Emsian/Eifelian boundary

A new rich and diversified ostracode fauna from the Torkoz area (section Hassi Mouf South, Moroccan Anti-Atlas) is described and the ostracode distribution near the Early/Middle Devonian boundary is discussed. This ostracode fauna of a single limestone bed yields 32 taxa and is compared with the less-diversified ostracode fauna from an adjacent parallel section Hassi Mouf South as well as with a published conodont-bearing sample from section Torkoz. All three ostracode faunas are closely related, and therefore, the same latest Emsian age is postulated. Palynomorphs (acritarchs and prasinophytes) from section Torkoz support this late Early Devonian age and the scarce brachiopod fauna of the equivalent level from section Hassi Mouf South suggests a stratigraphical position very close to the Emsian/Eifelian boundary, probably latest Emsian. Zygobeyrichiasubcylindrica from a thin marly bed embedded in shales, slightly below the ostracode-rich sample from section Hassi Mouf South, and the conodonts of the patulus Zone from section Torkoz, favours the position of the Early/Middle Devonian boundary within the Yeraifia Formation and not in or on top of the Rich 4 Sandstone in the SW Dra Valley area as hitherto published. The latest Early Devonian ostracode faunas from the Torkoz area belong to the shallow-water Eifelian Ecotype of G. Becker. The new genus Karlingrella for Euglyphella? granulosa Blumenstengel, 1962 and the new species Quasillites (Beckjennites) gebeckeri are erected.

Morphologically distinct P1 elements of Zieglerodina (Conodonta) at the Silurian- Devonian boundary: review and correlation

Morphologically distinct P1 elements of Zieglerodina (Conodonta) at the Silurian- Devonian boundary: review and correlation

Endemic earliest Lochkovian species ofCaudicriodus(conodont) from southern Laurentia and the Silurian–Devonian boundary

AbstractTwoCaudicriodusspecies from lowermost Devonian strata in southern Laurentia (Texas–Oklahoma–Western Tennessee),C. anitaesp. nov. andC. murphyisp. nov., are endemic forms that appeared during the positive δ13C excursion associated with the Klonk Event. The otherCaudicriodusspecies that occur during the Klonk Event and that are often used to recognize the base of the Devonian,C. hesperiusandC. woschmidti, differ in that the I elements of the southern Laurentia species possess a middle row of nodes on the transverse ridges of the spindle. The apparatus ofC. murphyisp. nov. possesses three groups of elements in addition to the I element: F elements (short wide coniforms); D elements (denticles on the posterior margin) and C elements (slender coniforms with basally flaring costae). Strong provinciality in slightly younger LochkovianCaudicriodusspecies was demonstrated earlier, and we propose thatCaudicriodusspecies radiated independently into endemic species in different geographic regions just before or during the Klonk Event. A form originally described asC. woschmidti hesperiusby Simpson (1998) is reinterpreted as a late Ludlow–Pridoli species ofPraeicriodus, P. simpsonisp. nov., with an I element and apparatus structure probably ancestral toCaudicriodus.

Middle - Late Devonian boundary conodonts from Anarak and Sar-Ashk sections, Central Iran

Middle - Late Devonian boundary conodonts from Anarak and Sar-Ashk sections, Central Iran

Discovery of scyphocrinoid loboliths in western Junggar, Xinjiang, NW China: Implications for scyphocrinoid paleobiogeography and identification of the Silurian–Devonian boundary

The loboliths, which previously have been called “plurilocular cystoids” in China, are actually the bulbous roots of scyphocrinoids, which occur only, and are widely distributed, in the uppermost Silurian through the lowermost Devonian. Two quite different types of loboliths can be distinguished, the plate- and cirrus-types loboliths, both of which are significant fossils for the correlation of the strata at the Silurian–Devonian boundary. Two lobolith-bearing layers were found in pyroclastic turbidites at the Silurian–Devonian transition in western Junggar, Xinjiang, NW China; all identified loboliths are of the plate type. This discovery provides not only important information for determination of the Silurian–Devonian boundary in western Junggar, but also for the stratigraphic correlation outside of peri-Gongwana and Laurussia. Moreover, the finds are expanding the knowledge of the paleogeographic distribution of scyphocrinoids across facies boundaries between the paleocontinents.

Brachiopods of the Order Spiriferida at the Devonian–Carboniferous Boundary of Transcaucasia

A distinct change in the taxonomic and ecological structure of assemblages of brachiopods of the order Spiriferida is observed at the Devonian and Carboniferous boundary of Transcaucasia. Representatives of the superfamily Cyrtospiriferoidea dominated in the assemblages in the Late Devonian, and became extinct by the end of the Devonian, while the Early Carboniferous is dominated by the superfamily Spiriferoidea. Cyrtospiriferoids represented a complicated subtype of the anchored ecological type ethologically associated with hard substrates, while the spiriferoids represented the main subtype of the anchor ecological type and the weighted subtype of the free-lying ecological type, replacing each other in ontogeny of brachiopods inhabiting mostly soft substrates. Although the Devonian-Carboniferous boundary in Transcaucasia lies within a continuous succession of lithologically uniform carbonate and carbonate-terrigenous rocks, a change in the diversity and ecological type of spiriferids indicates a change in the density of the substrate. This corresponds to a general global shift from the Devonian calcite sea to an aragonite Carboniferous sea, which affected the density of marine substrates. Thus, the stratigraphic procedure in this case can include the diversity analysis of both the taxonomic and ecological compositions of brachiopods.

The Lac au Renard Tephra Cluster: a record of Lochkovian (Lower Devonian) volcanism in the Indian Point Formation, Gaspe Peninsula, Quebec, Canada

Approximately twenty tephra beds, comprising the Lac au Renard Tephra Cluster (new), occur in the Rosebush Cove and Petit Portage members of the Indian Point Formation (Chaleurs Group) on the Gaspe Peninsula of Quebec, Canada. The tephra beds range in thickness from <1.0 cm to 82 cm and occur in a mudrock-dominated sequence with coarser tempestite interbeds. Mineralogically and texturally graded accumulations of phenocrysts mark the bases of the thickest tephra beds. Early diagenetic concretions in one composite tephra preserve pre-compaction fabrics and original hypocrystalline textures with microphenocrysts and devitrified glass shards. The presence of plagioclase, quartz, K-feldspar, biotite, apatite, and zircon suggest a rhyolitic source. The coarseness of the microphenocrysts in the basal accumulations, along with the abundance and thickness of the tephras, suggest that deposition in the Gaspe area was in a proximal position relative to the volcanic source. The zonal graptolites Monograptus praehercynicus and Monograptus aequabilis ssp. from the Petit Portage Member indicate a middle Lochkovian age for the Lac au Renard Tephra Cluster of the Indian Point Formation. Correlation with the tephra cluster that includes the Judds Falls Bentonite in the New Scotland Formation and other possible tephras in the Kalkberg Formation (Helderberg Group) of New York and the Corriganville and Mandata formations of Pennsylvania is likely. The graptolite fauna of the Indian Point and probable correlations to New York may provide additional biostratigraphic constraints on a U–Pb zircon radiometric age determination of 417.6 Ma from New York that has been used to estimate the age of the Silurian–Devonian boundary.

SEDIMENTOLOGY AND CARBON ISOTOPE (δ13C) STRATIGRAPHY OF SILURIAN–DEVONIAN BOUNDARY INTERVAL STRATA, APPALACHIAN BASIN (PENNSYLVANIA, USA)

ABSTRACTSilurian–Devonian boundary interval strata deposited during the expansion of land plants record a major perturbation of the carbon cycle, the global Klonk Event, one of the largest carbon isotope excursions during the Phanerozoic. In the Appalachian Basin, these marine strata record the regional buildup to the Acadian Orogeny. This study reports new sedimentologic, paleontologic, ichnologic, and carbon isotope data from an exceptional quarry exposure in central Pennsylvania, USA, a historically understudied area between better-documented outcrops >500 km away to the southwest (West Virginia, Virginia, Maryland) and northeast (New York). Facies spanning the continuous 113-m thick outcrop are dominantly carbonate and fine-grained siliciclastic strata interpreted as being deposited in supratidal through subtidal environments, including oxygen-limited environments below storm wave base. They record parts of three transgressive-regressive cycles, in the (1) upper Silurian Tonoloway Formation, (2) upper Silurian–Lower Devonian Keyser Formation through lower Mandata Member of the Old Port Formation, and (3) Lower Devonian Mandata through Ridgeley Members of the Old Port Formation. Micrite matrix δ13Ccarb analyses exhibit a large, positive δ13Ccarb excursion (>5‰ amplitude). Outcrops of this interval in the Appalachian Basin occur in two belts, between which correlation has been historically challenging. The regional correlation presented herein is based on carbon-isotope trends and is more consistent with published conodont biostratigraphy and volcanic ash ages, an improvement over published correlations based on lithostratigraphy. Transgressive-regressive trends at the central Pennsylvania study site are not consistent with regional trends, indicating that local controls (tectonics, sediment supply) rather than global (eustasy) dominated depositional patterns in the Silurian–Devonian boundary interval in the Appalachian Basin.

The Old Red Group (Devonian) – Rotliegend Group (Permian) Unconformity in the Inner Moray Firth

Abstract A major stratigraphical problem in the offshore Paleozoic of the Inner Moray Firth is the identification of the top of the Devonian Old Red Sandstone Group beneath the lithologically similar Permian Rotliegend Group. Wireline log criteria for a revised Old Red Group to Permian boundary are given for the Inner Moray Firth. Section lines drawn using these criteria and flattened on the overlying Triassic Smith Bank or Permian Kupferschiefer formations show a relatively thin development of Rotliegend with two depocentres. The underlying Devonian when flattened on the Eday Marl shows a systematic subcrop pattern. There is currently no exposed onshore Old Red to Rotliegend boundary, but the possibility remains that a Permian section is present in the ‘Upper Old Red Sandstone’ of Tarbat in Easter Ross. An exposed Permian–Devonian boundary is present in East Greenland and provides an analogue for the Inner Moray Firth.

Microvertebrates from the Silurian–Devonian boundary beds of the Eastport Formation, Maine, eastern USA

Agnathan and gnathostome remains, associated with lingulid brachiopod fragments and distinctive ostracods, have been extracted from a small calcareous mudstone sample collected from the type section of the Eastport Formation on the northern shore of Moose Island, Maine. The vertebrate assemblage includes osteostracan, anaspid, and thelodont scales, and acanthodian scales, spines and teeth, which support a late Pridoli, or possibly earliest Lochkovian, age for the stratum. The thelodont Paralogania denisoni n. sp. is described, associated with a single thelodont scale referred tentatively to Talivalia? sp. indet., and acanthodians Nostolepis striata, Gomphonchus sandelensis, andPoracanthodes punctatus in a fauna that shows similarities to late Pridoli assemblages in Britain, parts of Europe, Russia, Greenland, and arctic Canada.