Late Devonian Time Research Articles

Biostratigraphic and structural research in the Guedelhinha–Lançadoiras–Algaré sector in the context of the geology of the Neves–Corvo mine region, Iberian Pyrite Belt

Based on drill hole sampling and sedimentary rock dating by palynology, the present research focuses on the palynostratigraphic events established in the key geological section of Guedelhinha–Lançadoiras–Algaré located in the Portuguese Neves–Corvo mine region, Iberian Pyrite Belt. The age data allow detailing the lithostratigraphic sequence and further understanding the complex structural setting, representing an important contribution to the geological knowledge of this sector located to the immediate WNW of the Neves–Corvo VMS deposit. The combination of the studied events allows the reconstruction of the Devonian-Carboniferous sedimentation and paleoenvironments along the Iberian Pyrite Belt. Several stratigraphic hiatuses identified in the Neves–Corvo region by the palynological record are confirmed, mainly occurring from the mid Frasnian to mid Famennian, from the early and mid Strunian, and from the early to late Tournaisian, which were mainly coincident with the worldwide extinction events, in particular during Frasnian–Famennian and Late Devonian times. Extensional tectonics and related gravitational faults, local uplift mechanisms and intense volcanic activity could also explain the lack of palynological data and sedimentary hiatus. In this research, the importance of the late Strunian times in the Iberian Pyrite Belt (Miospore Biozone LN of the Neves Formation) is highlighted, confirming the contemporaneity of felsic volcanism, hydrothermalism, sulphide mineralization precipitation and black shale anoxic sedimentation.

The nature of magnetic anomalies in the southern part of the Barents Sea shelf according to the results of an integrated analysis

Research subject. The anomalous magnetic field of the southern part of the Barents Sea Shelf.Materials and methods. The research was based on a digital matrix (grid) of the anomalous magnetic field (AMP) compiled from the materials of magnetic surveys performed in 2002–2007 by a number of research organizations and research and production companies. A model describing the structure and formation of the magneto-active layer of the southern part of the Barentsevomorsk region was developed. An analysis of the radially averaged field spectrum made it possible to establish the confinement of the upper edges of the field sources to several structural horizons. Band filtering in the frequency domain in accordance with the allocated depth ranges allowed anomalies to be distinguished from other sources. To determine the nature of sources of magnetic anomalies at different levels of the earth’s crust, an integrated analysis of gravimagnetic fields, seismic profiling data and ground studies was conducted.Results. At least two levels of magnetic anomaly sources were found: the distribution of effective magnetization for the low-frequency component of AMP, reflecting the depth structure of the region, and the high-frequency component of AMP, reflecting the distribution of local intrusions in the upper part of the foundation and in the sedimentary cover. The lower level is represented by massive blocks of deep laying and corresponds to the SDR (Seaward Dipping Reflectors) complex, which is an alternation of tectonic plates of continental material with ultrabasite basites that were introduced into the crust at the post-rift stage of the continent’s split. The zone of positive linear anomalies of the magnetic field reflects the divergent boundary of the ancient continental plate of the Baltic, which arose during the fragmentation of the supercontinent of Colombia (Paleopangea) in the middle reef and the formation of the Rifean oceanic basin, which was then veiled by subsequent tectonic processes. The upper structural level indicates the introduction of the main composition into the upper layers of the earth’s crust in the zones of rift-forming faults of magma in late Devonian times during the process of continental rifting on the Svalbard Plate. This is confirmed by the presence of manifestations of the main magmatism within the propagation zone of the South Barents riftogenic depression into the body of the Baltic Shield.Conclusions. The conducted integrated analysis of the anomalous magnetic field and other geological and geophysical data allowed the authors to establish the nature of the sources of magnetic anomalies located at different structural levels of the earth’s crust in the southwestern part of the Barents Sea shelf. The magnetoactive layer of this region is characterized by a complex structure, the section of which includes at least two structural levels, each reflecting certain evolutionary stages of the earth’s crust.

Новые 40Ar/39Ar-данные долеритов Канино-Тиманской провинции внутриплитного магматизма (п-ов Канин)

The Kanin-Timan region is located in the north-east of the European part of Russia and represents the western edge of the Timan-Pechora Plate. In the Devonian time, the Kanin-Timan region experienced rifting processes caused by the influence of a mantle plume. As a result of these processes, the Kanin-Timan dolerite complex was formed, which includes dolerite dikes and basalt sheets. The rocks of the complex have been studied throughout the study region. In the Middle Timan, the basalt plagioclase of the Upper Vorykva cover was dated by the 40Ar/39Ar method, the dating result indicates an age of 389 ± 6 Ma. Dolerites of the Kanin-Timan complex were also dated by the K-Ar method in the last century. As a result of dating, conflicting data on the absolute age from 378 to 288 Ma were obtained. To clarify the age of dolerites, 40Ar/39Ar dating was carried out. According to the isotope age data, the dolerites of the Kanin Peninsula are 419 ± 8 Ma, the age of the basalts of the Upper Vorykva cover is 389 ± 6 Ma. Thus, the magmatic activity that led to the formation of the Kanin-Timan complex in the Kanin-Timan region began earlier on the Kanin Peninsula, and then on the Timan. According to the research results, we believe that the Kanin-Timan complex began its formation in the Early Devonian with the peak during the Middle and Late Devonian time.

Petrogenesis and tectonic setting of Late Devonian high-Mg andesites in the Beishan orogen, NW China

AbstractHigh-Mg andesites (HMAs) are crucial for the reconstruction of plate tectonics, continental margin formation and lithospheric evolution. In this study, we present new fossil age, whole-rock geochemical and Sr–Nd isotope data on the newly discovered Dundunshan Group HMAs in the Dundunshan area of the Beishan orogen (central-southern Central Asian Orogenic Belt). The Dundunshan HMA samples are characterized by high MgO (6.47–7.02 wt%) contents and high Mg# values (67.27–68.77), with SiO2 (58.57–62.13 wt%), Al2O3 (14.49–16.07 wt%) and CaO (5.05–6.24 wt%) resembling typical HMAs. The Dundunshan HMA samples are calc-alkaline and strongly enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs), with slightly negative Eu anomaly and high-field-strength element (HFSE) depletions. Their (87Sr/86Sr)i ratios (0.7041–0.7057) and ϵNd(t) (3.73–5.59) indicate that the Dundunshan HMAs were mainly formed by the interactions between subducted oceanic sediment-derived melts and mantle peridotites. Fossil evidence and published radiometric age data constrain the formation of the Dundunshan HMAs to early Late Devonian time. Sedimentological features of the Middle Devonian Sangejing Formation and regional tectonic correlation suggest that the Hongliuhe–Niujuanzi–Xichangjing Ocean in the Dundunshan area was likely closed during late Middle Devonian time, and that the Dundunshan HMAs were formed in a post-collision extensional setting.

High-Resolution Late Devonian Magnetostratigraphy From the Canning Basin, Western Australia: A Re-Evaluation

Late Devonian time was a period of rapid upheaval in the Earth system, including climate change, sea level changes, widespread ocean anoxia, and the Frasnian-Famennian mass extinction; the cause(s) of these changes remain(s) uncertain. The Lennard Shelf of the Canning Basin in Western Australia contains carbonate reef sections spanning much of the Late Devonian Epoch and has been sampled for paleomagnetic analysis with studies by Hansma and colleagues in 2015 and Playton and colleagues in 2016. However, previous paleomagnetic directions were scattered and their use for magnetostratigraphy has been questioned. Here, rock magnetic data and magnetostratigraphy for a late Devonian drill-core from the Lennard Shelf were analyzed. Three magnetostratigraphic interpretations were made using different paleopoles that showed good correlation with each other and the earlier interpretations by Playton and colleagues in 2016. Additionally, the rock magnetic data revealed the samples contain various mixtures of detrital and diagenetic minerals, the former of which should be viable recorders of primary magnetic signatures. Even in samples with these detrital phases, paleomagnetic data were often noisy and produced ambiguous polarity assignments, likely due to the anomalously weak Devonian field. Because of this ambiguity and the absence of a robust paleopole, broader correlations for this critical time-period will be difficult without additional paleomagnetic data from the late Devonian Period. Expanded data for this interval could eventually shed light on the timing, causes, and rates of the Frasnian-Famennian mass extinction and other environmental shifts in the late Devonian Epoch.

Tracking the Late Devonian high-P metamorphic belt in the Variscan Orogen: New constraints on the PT evolution of eclogites from the Cubito-Moura Unit (SW Iberian Massif)

The Cubito-Moura Unit is a high-P metamorphic succession that occurs in the southern part of the Ossa-Morena Complex (SW Iberian Massif). It includes a series of metasedimentary, metafelsic and metamafic rocks affected by a high-P, low to intermediate-T metamorphic event during Late Devonian times. Geochemistry of the metabasic rocks reveals that the generation of the protoliths occurred in a supra-subduction zone setting during Late Ediacaran to Early Ordovician times, either in a back-arc or fore-arc context. The eclogites contain atoll-like garnets, omphacite, amphibole, phengite (up to Si = 3.38 apfu), paragonite, rutile and quartz. Thermodynamic modelling in the MnNCKFMASTH system indicates a high-P metamorphic event at ~24 kbar and ~ 585 °C followed by a thermal peak at ~19 kbar and ~ 630 °C, and a subsequent exhumation to ~15 kbar. This P-T path indicates deep subduction at c. 370 Ma of this arc-related section. The lithostratigraphy and tectonothermal evolution of the Cubito-Moura Unit are equivalent to that of a number of units along the Iberian, Armorican and Bohemian massifs that can be correlated as a part of the same Basal Allochthonous Terrane. These units define a single Late Devonian high-P, low- to intermediate-T metamorphic belt developed during the first stages of the Variscan Orogeny.

Palynological indications for Silurian – earliest Devonian age strata in the Netherlands

Abstract Knowledge of the stratigraphic development of pre-Carboniferous strata in the subsurface of the Netherlands is very limited, leaving the lithostratigraphic nomenclature for this time interval informal. In two wells from the southwestern Netherlands, Silurian strata have repeatedly been reported, suggesting that these are the oldest ever recovered in the Netherlands. The hypothesised presence of Silurian-aged strata has not been tested by biostratigraphic analysis. A similar lack of biostratigraphic control applies to the overlying Devonian succession. We present the results of a palynological study of core material from wells KTG-01 and S05-01. Relatively low-diversity and poorly preserved miospore associations were recorded. These, nonetheless, provide new insights into the regional stratigraphic development of the pre-Carboniferous of the SW Netherlands. The lower two cores from well KTG-01 are of a late Silurian (Ludlow–Pridoli Epoch) to earliest Devonian (Lochkovian) age, confirming that these are the oldest sedimentary strata ever recovered in the Netherlands. The results from the upper cored section from the pre-Carboniferous succession in well KTG-01 and the cored sections from the pre-Carboniferous succession in well S05-01 are more ambiguous. This inferred Devonian succession is, in the current informal lithostratigraphy of the Netherlands, assigned to the Banjaard group and its subordinate Bollen Claystone formation, of presumed Frasnian (i.e. early Late Devonian) age. Age-indicative Middle to Late Devonian palynomorphs were, however, not recorded, and the overall character of the poorly preserved palynological associations in wells KTG-01 and S05-01 may also suggest an Early Devonian age. In terms of lithofacies, however, the cores in well S05-01 can be correlated to the upper Frasnian – lower Famennian Falisolle Formation in the Campine Basin in Belgium. Hence, it remains plausible that an unconformity separates Silurian to Lower Devonian strata from Upper Devonian (Frasnian–Famennian) strata in the SW Netherlands. In general, the abundance of miospore associations points to the presence of a vegetated hinterland and a relatively proximal yet relatively deep marine setting during late Silurian and Early Devonian times. This differs markedly from the open marine depositional settings reported from the Brabant Massif area to the south in present-day Belgium, suggesting a sediment source to the north. The episodic presence of reworked (marine) acritarchs of Ordovician age suggests the influx of sedimentary material from uplifted elements on the present-day Brabant Massif to the south, possibly in relation to the activation of a Brabant Arch system.

Interplay of southern, western, and northern sources during deposition of North Wales Carboniferous sandstones, determined from heavy minerals, mineral chemistry, and detrital zircon ages

A study of heavy mineral assemblages, rutile compositions, and detrital zircon age populations in Namurian to Westphalian sandstones in North Wales, deposited in the southwestern part of the Pennine Basin of the United Kingdom, has revealed considerable complexity in their provenance history. The Pendleian to Marsdenian Cefn‐y‐fedw Sandstone Formation, which is known to have been derived from the Wales–Brabant Massif (WBM) to the south on the basis of palaeocurrent and petrographic information, has a heavy mineral assemblage characteristic of this southerly provenance, and includes Late Neoproterozoic zircons apparently of local WBM origin. However, the formation is dominated by zircons that were most probably recycled from sandstones of northern origin from the Caledonian Belt that had been previously deposited over the massif during Late Devonian times, and, as such, has a comparable history to the sedimentologically‐equivalent Morridge Formation of the English Midlands. Heavy mineral analysis shows that sandstones in the Brigantian Minera Formation and Yeadonian part of the Bowland Shale Formation are of similar southern provenance. The Yeadonian Gwespyr Sandstone, previously interpreted as having a northern origin, similar to the time‐equivalent Rough Rock, has variations in heavy mineral analysis and zircon spectrum that suggest a complex provenance history and includes sand bodies with northern, western, and southern origins.

VERTEBRATE TAPHONOMY, PALEONTOLOGY, SEDIMENTOLOGY, AND PALYNOLOGY OF A FOSSILIFEROUS LATE DEVONIAN FLUVIAL SUCCESSION, CATSKILL FORMATION, NORTH-CENTRAL PENNSYLVANIA, USA

ABSTRACT The fluvial facies of the Catskill Formation record important ecological events that occurred during Late Devonian time. A well-exposed section between the towns of Blossburg and Covington, in north-central Pennsylvania, contains abundant macrofossils and sedimentary features, making it well-suited for linking Upper Devonian fossil occurrences with depositional environments and sedimentary processes. Strata consist of two distinct fluvial facies: floodplain lithofacies consist of mudrocks, with evidence of pedogenic overprinting and sharp-based sandstones interpreted as crevasse splays; channel-bar lithofacies consist of single- and multi-storied cross-stratified lenticular sandstone bodies interpreted as fluvial channel-bar complexes. Macrofossils occur in 22 discrete horizons spanning > 240 m of stratigraphic succession that include Archanodon bivalve shell impressions, two genera of “placoderms” (Bothriolepis, Phyllolepis), an unidentified acanthodian, and several taxa of sarcopterygian fishes, including lungfish (Dipnoi indet.), Holoptychius, Langlieria, and Sauripterus. Most vertebrate macrofossils are preserved as disarticulated, abraded plates, scales, and bone fragments in sandstone channel-bar deposits. Articulated, unabraded remains are preserved in proximal floodplain deposits. Miospores recovered from Catskill Formation fossil sites in the Blossburg-Covington section belong to the COR subzone of the VCo (Diducites versabilis-Grandispora cornuta) palynological zone, indicating deposition ca. 362 to 361.8 Ma during the late Famennian stage of the Late Devonian. Catskill Formation fluvial strata exposed tens of kilometers to the south and west yield latest Famennian palynomorphs. These broadly contemporaneous continental depositional environments supported Late Devonian vertebrate evolution, including the fin-to-limb transition in tetrapodomorphs, and the possible euryhalinity of vertebrates occupying marine-to-nonmarine transitional habitats.

Paleozoic-Mesozoic tectono-sedimentary evolution and magmatism of the Egersund Basin area, Norwegian central North Sea

This study focuses on the tectonic evolution of the greater Egersund Basin in the Norwegian central North Sea, with special emphasis on Late Paleozoic extensional tectonics following Caledonian collapse and the Variscan Orogeny, and the impact of the basement structural grain on this evolution. The Caledonian collapse likely resulted in development/rejuvenation of the deepest E-W trending structures/depocenters by Late Devonian time. Thus, a late Devonian-?early Carboniferous age can be assigned to the initial extension, which was associated with the development of an E-W striking basin system, to be overprinted by N–S extensional structures of similar age. A phase of regional magmatism at the Carboniferous-Permian transition (≈300 Ma) may be associated with a large igneous province centred on the Skagerrak area. Faulting during late Carboniferous-early Permian was minor within the study area as reflected by uniform sedimentary thicknesses of the uppermost Carboniferous and lower Permian sequences. Major normal faults, mainly trending N–S, were active during a late Permian-Early Triassic rift phase affecting large parts of the central and northern North Sea area. A later phase of extension was initiated in late Middle Jurassic time and the Egersund Basin proper formed during the Late Jurassic-Early Cretaceous. The depocenters that developed during this phase was influenced by the deep Late Paleozoic (sub-salt) structural grain, including strike-slip movements along the Sorgenfrei-Tornquist Zone. Later events include mild inversion along the northern flank of the Egersund Basin, possibly as a Late Cretaceous response to far-field Alpine compression, and Cenozoic regional tilting.

Late Devonian paleogeography in the framework of global plate tectonics

This paper presents Late Devonian (Frasnian–Famennian) global and regional paleogeographic maps displaying present day coastlines, tectonic elements' boundaries, subductions, rifts, spreading centers, transform faults, paleogeographic configuration and volcanism 370 million years ago. The regional maps illustrate the paleoenvironment and paleolithofacies distribution. The Late Devonian was a time of the onset and development of a major collisional event, the Variscan orogeny. The trench-pulling (or slab-pull) effect of the north dipping subduction, which developed along the Laurussia margin, caused the creation of the back-arc Rheno-Hercynian basin, as well as the transfer of tectonic elements. These tectonic elements included Saxothuringian, Southern Proto-Carpathian and Balkan terranes. The Antler and Ellesmerian orogenies constituted major collisional events in North America. The spreading of the Paleotethys Ocean constituted the main extensional event. This spreading is associated with the movement of tectonic elements towards Laurussia, Siberia and Northern Kazakhstan. In addition, a branch of the Paleotethys Ocean was opened between South China and Gondwana, during the Late Devonian times. The spreading was displayed along the proto-Andean margin of western Gondwana and is thought to have opened the newly proposed Chilean Ocean. The development of major rift systems took place throughout Laurussia and Siberia. Late Devonian rifting was associated with volcanic activity, especially prominent in the Viluy rift in Siberia. The deposition, during the Late Devonian time, is characterized by the existence of large carbonate platforms with reefs on large continents and synorogenic flysch in collisional areas. The sea-level dropped towards the Devonian- Carboniferous boundary. The climate was undergoing change from greenhouse to icehouse. The following plate tectonic events could have influenced the extinction of biotas at the Frasnian-Famennian boundary: 1) The very extensive basaltic volcanism in Laurussia and Siberian and along the arcs. 2) The closure of the Rheic Ocean and the development of the Variscan orogeny. 3) Intensive spreading in the Paleotethys and the development of numerous subductions and volcanic arcs. These events resembled a transition from a rift to a drift phase, during the Permian–Mesozoic break-up of Pangaea. This break-up was associated with other biota extinctions. • The paper presents 10 paleogeographic Late Devonian maps. • Late Devonian was a time of the onset of Variscan orogeny. Spreading of the Paleotethys Ocean was the main extensional event. • Late Devonian rifting was associated with volcanic activity, especially prominent in the Viluy rift in Siberia. • The plate tectonic events could have influenced the extinction of biotas.

The structure and evolution of the east Greenland continental margin before spreading started on the Kolbeinsey ridge

An analysis of the deep structure of the East Greenland margin (Blosseville Kyst to Liverpool Land) and of the Jan Mayen microcontinent resulted in the development of a crustal model that was valid for both before their disruption. A joint model clearly demonstrates the net result of rifting phases during Paleozoic, Mesozoic, and Cenozoic time. Starting from the Devonian, a graben-shaped depression about 180 km wide existed between Liverpool Land and the Jan Mayen Ridge; the depression was formed by subsiding of the crystalline basement that was not compensated by sedimentation. The marine basin was approximately 2 km deep during late Devonian time. The west-east joint deep crustal section clearly defines three depths in the upper mantle that fit dome-like surfaces superposed on each other. We interpret these surfaces as temperature fronts of mantle plumes that differ by their time of origin: Paleozoic, Mesozoic to Cenozoic, and late Cenozoic. The rim of the present-day Blosseville Kyst and Liverpool Land shelf is found to be underlain by a basement high that is associated with the axis of a positive free-air gravity anomaly. East of the high along the anomaly axis, we identified a continent-ocean boundary. The present-day phase in the geological evolution of the Greenland-Norwegian region north of Iceland is characterized by an increased thermal state of the lithosphere and manifestations of intraplate tectonics.

U–Pb geochronology, Nd–Sm geochemistry, structural setting, and tectonic significance of Late Devonian and Paleogene intrusions in northern Yukon and northeastern Alaska

A suite of six Devonian granites and one syenite were emplaced into the upper crust of northern Yukon between 364.8 ± 2.7 and 371.2 ± 1.4 Ma. The Bear Mountain syenite and related rhyolite porphyry in adjacent Alaska intruded at 52.3 ± 0.4 and 53.5 ± 0.2 Ma, respectively. A felsic volcaniclastic unit and quartz-phyric sill are newly documented adjacent to the Mount Sedgwick granite. The volcaniclastic unit may indicate the presence of a related volcanic edifice. The presence of xenocrystic zircon grains in most of the intrusions suggests initial emplacement of magmas began 10–20 Myr before final emplacement into the upper crust. A Famennian final intrusion age coincides with Late Devonian encroachment of Ellesmerian deformation into the region. Attendant crustal flexure, or evolving foreland structures, may have facilitated upward migration of the magmas. Geochemistry of the intrusions indicates that the Devonian magmatism was largely derived from partial melting of lower and middle crust, implying widespread mafic magmatic underplating in Middle to Late Devonian time. Only Dave Lord syenite retains evidence of an original mantle geochemical signature. Mantle underplating may have played a role in localizing extension, volcanism, and rifting that led to the Late Devonian opening of the Angayucham ocean basin. The Eocene Bear Mountain pluton is inferred to be a northerly example of widespread Cenozoic within-plate magmatism in Alaska.

Depositional setting, taphonomy and geochronology of new fossil sites in the Catskill Formation (Upper Devonian) of north-central Pennsylvania, USA, including a new early tetrapod fossil

Late Devonian terrestrial floodplain environments were important sites of plant and animal diversification and evolution. Recently discovered fossil sites in the Catskill Formation in north-central Pennsylvania yield important insights into Late Devonian terrestrial environments and ecologies. The fossil sites yield the progymnosperm plant Archaeopteris ssp., Archanodon bivalves, as well as abundant placoderms, acanthodians, and sarcopterygians including a new specimen of an early tetrapod. Most vertebrate fossils occur as abraded and disarticulated teeth, scales, and dermal bone fragments within basal lags of fluvial channel-bar complexes and articulated skull material, well-preserved scales, bones, and teeth in shallow temporary channels that meandered across vegetated floodplains. Fossil sites in these nearly flat-lying fluvial strata occur in multiple stratigraphic horizons spanning hundreds of meters of stratigraphy that represent the Sherman Creek Member and overlying Duncannon Member. The strata coarsen upsection and record progressively larger channel-bar complexes and better-developed paleosols. Applied detrital muscovite 40Ar/39Ar geochronology supplies the first quantitative age data from the sampled strata and provides information on erosion rate parameters and channel network morphology. Detrital ages indicate rapid uplift, erosion, and deposition of sediments in the Catskill fluvial system during Late Devonian time. Detrital ages also indicate temporal variation and lack of depositional linkages among Late Devonian fossil sites. Variations in the fossil assemblages between sites reflect paleoecological variations among paleo-subenvironments (channel-bars vs. floodplains) and/or taphonomic processes. Vertebrate assemblages and fluvial lithofacies documented at the recently discovered sites are broadly comparable with those in slightly younger strata at Red Hill, a well-studied site ~50 km to the west that yields a diverse vertebrate assemblage, including several taxa of early tetrapods. These heterogeneous, shallow, non-marine aquatic habitats were a crucible for experimentation in limb mobility and other specializations among sarcopterygians during Late Devonian time. Integration of paleontological, sedimentological, and geochronological data offers new insights into Late Devonian fluvial ecosystem evolution.

A new species ofHyattechinus(Echinoidea) from the type Devonian of the United Kingdom and implications for the distribution of Devonian proterocidarid echinoids

AbstractMany of the most diverse clades of Late Palaeozoic echinoids (sea urchins) originated in the Devonian period. Our understanding of diversity dynamics of these Late Palaeozoic clades are thus informed by new systematic descriptions of some of their earliest members. The Proterocidaridae are a diverse and morphologically distinct clade of stem group echinoids with flattened tests and enlarged adoral pore pairs, which are first known from the Upper Devonian. We herein report on a new species ofHyattechinus,Hyattechinus anglicusn. sp., from the Upper Devonian of the North Devon Basin, Devon, UK. This is the first DevonianHyattechinusknown from outside of the Appalachian Basin, USA, and provides novel information regarding the palaeogeographic and stratigraphic distribution of proterocidarids in Late Devonian times. We additionally update the stratigraphic distribution of DevonianHyattechinusfrom the Appalachian Basin, following recent biostratigraphic resolution of their occurrences.Hyattechinusappears to have been present in the Rheic echinoderm fauna during Late Devonian times, and comparison of the palaeoenvironmental setting ofHyattechinus anglicuswith that of otherHyattechinusfrom the Famennian of the Appalachian Basin suggests that the genus may have preferred siliciclastic settings. Furthermore, this new taxon increases the diversity of echinoids from the Upper Devonian of Devon to three species.

The Steepbank Formation: a paleokarst diamictite deposit in the Athabasca Oil Sands region of northeastern Alberta, Canada

Abstract The name “Steepbank Formation” is proposed for a paleokarst diamictite deposit that is present along the margins of the Middle Devonian Prairie Evaporite Formation in the Western Canada and Williston sedimentary basins, including the eastern portion of the Athabasca Oil Sands region. This poorly lithified diamictite forms a mappable unit that is distinct in both age and lithology from all contiguous formations. The Steepbank consists of clasts of dolostone, limestone, and siltstone up to the size of boulders with a matrix of silty to sandy calcareous mudstone. The material shows little or no evidence of bedding or sorting. Most clasts are angular and their orientation is commonly random. The diamictite formed in response to the dissolution of thick (up to 300 m) sequences of halite, anhydrite, and gypsum in the Prairie Evaporite Formation and the subsequent failure and collapse of interbedded and overlying insoluble strata. The top contact occurs where the intact strata of an overlying formation can be identified and is commonly gradational. The basal contact with the underlying Keg River Formation is sharp. Both contacts are unconformable. Evaporite dissolution and diamicton deposition likely began in late Middle Devonian time, moving down dip toward the west, and are continuing today near the Athabasca River.

Palaeozoic stromatoporoid futures: A discussion of their taxonomy, mineralogy and applications in palaeoecology and palaeoenvironmental analysis

Palaeozoic stromatoporoids are calcified sponges common between Middle Ordovician and Late Devonian times in reefs and related facies. Taxonomic work is well known, but controversial because of conflict between classification schemes based on the calcareous skeleton versus spicules (which are almost completely lacking in Palaeozoic stromatoporoids); however, lower-level taxonomy (at genus-level) of the calcareous skeleton is considered reliable to be applied in palaeobiological study. Knowledge of stromatoporoid ecology is poorly developed, such that comprehensive information is available for only a few case studies, in some Silurian and Devonian examples. Thus an overall understanding of stromatoporoid responses to environmental conditions has not yet been achieved, although stromatoporoids were likely able to deal with fine-grained sediment where they mostly occur. Many stromatoporoid genera have only certain growth forms, so future focus on the use of low-level taxonomy in ecological studies, by comprehensive sampling in high-resolution studies, may establish the relationships between stromatoporoids and their environments. Intergrown organisms and growth banding in stromatoporoids are aspects that have great potential in such work. Mineralogy of stromatoporoids remains poorly understood. Regardless of their apparent state of preservation (ranging from apparently well-preserved to complete loss of calcareous skeleton features) all stromatoporoids are in fact substantially recrystallized. They underwent a peculiar diagenesis, whereby the calcareous skeleton and gallery cements of all stromatoporoids are overprinted by irregular elongated calcite crystals arranged normal to the growth laminations, most clearly visible in cross-polarized light. Stromatoporoids co-occur with mollusc shells that are always either fully recrystallized or dissolved (present as internal and external moulds); this difference means that while molluscs are likely under-represented in the fossil record, stromatoproids are not, providing confidence for palaeoecological work on their assemblages. Stromatoporoids lack characters which would readily classify them as being originally aragonite or low-Mg calcite; they may have been high-Mg calcite but the evidence is circumstantial. Their peculiar diagenetic fabric also has implications for the debate about the relationship between stromatoporoids and the concept of aragonite/calcite seas, which requires more work.

Provenance and paleogeography of the Neruokpuk Formation, northwest Laurentia: An integrated synthesis

The Neruokpuk Formation is a Neoproterozoic and Cambrian turbiditic succession in northwesternmost Yukon (Canada) and northeastern Alaska (USA), part of a latest Proterozoic to Early Devonian slope and basin succession that is correlated in detail with strata in Selwyn Basin of the northern Canadian Cordillera. It includes quartz-lithic sandstone, locally containing altered detrital feldspar and muscovite indicating that a metamorphic source contributed detritus to the unit. The muscovite yields disturbed Ar-Ar spectra suggesting ages of 1800–1900 Ma. Detrital zircon distributions are dominated by 1800–2000 Ma grains with subsidiary populations of 1000–1600 Ma, 2300–2500 Ma and 2600–2800 Ma grains, consistent with a hybrid provenance dominated by a Laurentian cratonic source. Additional populations are derived from recycled Mackenzie Mountains and possibly Wernecke Supergroups. Integrating the geochronology with the regional stratigraphic setting, structural history, and geochemistry leads to the conclusion that the Neruokpuk Formation was deposited near its present location as part of the autochthonous northwest Laurentian continental margin. Therefore, the eastern part of Arctic Alaska, underlain by the Neruokpuk Formation, has a history that is distinct from the allochthonous western part(s) of the Arctic Alaska terrane. However, the rest of Arctic Alaska is structurally and stratigraphically linked to the eastern part by Late Devonian time.

Significance of detrital zircons in Siluro-Devonian rocks from Iberia

Seven samples of Siluro-Devonian sedimentary rocks from the Cantabrian and Central Iberian zones of the Iberian Variscan belt have been investigated for provenance and contain four main age populations in variable relative proportion: Ediacaran–Cryogenian ( c . 0.55–0.8 Ga), Tonian–Stenian (0.85–1.2 Ga), Palaeoproterozoic ( c . 1.8–2.2 Ga) and Archaean ( c . 2.5–3.3 Ga). Five samples contain very minor Palaeozoic (Cambrian) zircons and six samples contain minor but significant zircons of Middle and Early Mesoproterozoic (Ectasian–Calymmian, 1.6–1.8) age. These data highlight the transition from an arc environment to a stable platform following the opening of the Rheic Ocean. Variations in detrital zircon populations in Middle–Late Devonian times reflect the onset of Variscan convergence between Laurussia and Gondwana. The presence of a high proportion of zircons of Tonian–Stenian age in Devonian sedimentary rocks may be interpreted as (1) the existence of a large Tonian–Stenian arc terrane exposed in the NE African realm (in or around the Arabian–Nubian Shield), (2) the participation, from the Ordovician time, of a more easterly alongshore provenance of Tonian–Stenian zircons, and (3) an increase in the relative proportion of Tonian–Stenian zircons with respect to the Ediacaran–Cryogenian population owing to the drift of the Avalonian–Cadomian ribbon continent, or the progressive burial of Ediacaran–Cryogenian rocks coeval with the denudation of older source rocks from the craton interior. Supplementary material: Tables with the analytical data and the geochronological results are available at http://www.geolsoc.org.uk/SUP18812 .

Geochronology and provenance of detrital zircons from late Palaeozoic strata of central Jilin Province, Northeast China: implications for the tectonic evolution of the eastern Central Asian Orogenic Belt

Here we present new U–Pb and Hf isotopic data for detrital zircons obtained from six samples of late Palaeozoic units from central Jilin Province, Northeast China, and use these data and sedimentary formations to constrain the late Palaeozoic tectonic evolution of the eastern segment of the southern margin of the Central Asian Orogenic Belt. The majority of the detrital zircons from the six samples are euhedral–subhedral and exhibit oscillatory zoning, indicating a magmatic origin. Zircons from sandstones in the Devonian Wangjiajie and Xiaosuihe formations yield seven main age populations (399, 440, 921, 1648, 1864, 1911, and 2066 Ma) and two minor age populations (384 and 432 Ma), respectively. Zircons from a quartz sandstone in the Carboniferous Luquantun Formation yield four age populations (~332, 363, 402, and 428 Ma), and zircons from quartz sandstones of the Permian Shoushangou, Fanjiatun, and Yangjiagou formations yield age populations of 265, 369, 463, 503, and 963 Ma; 264, 310, 337, 486, and 529 Ma; and 262, 282, 312, 338, 380, 465, and 492 Ma, respectively. These data, together with the ages of magmatic zircons from interbedded volcanics and biostratigraphic evidence, as well as analysis of formations, give rise to the following conclusions. (1) The Wangjiajie and Xiaosuihe formations were deposited in an extensional environment during Middle and Middle–Late Devonian time, respectively. The former was sourced mainly from ancient continental material of the North China Craton with minor contributions from newly accreted crust, while the latter was sourced mainly from newly accreted crust. (2) The Luquantun Formation formed in an extensional environment during early–late Carboniferous time from material sourced mainly from newly accreted crust. (3) The Shoushangou, Fanjiatun, and Yangjiagou formations formed during a period of rapid uplift in the late Permian, from material sourced mainly from newly accreted crust.