Showing papers in "Geological Society, London, Special Publications in 2016"

The global Hangenberg Crisis (Devonian–Carboniferous transition): review of a first-order mass extinction

Abstract: Abstract The global Hangenberg Crisis near the Devonian–Carboniferous boundary (DCB) represents a mass extinction that is of the same scale as the so-called ‘Big Five’ first-order Phanerozoic events. It played an important role in the evolution of many faunal groups and destroyed complete ecosystems but affected marine and terrestrial environments at slightly different times within a short time span of c. 100–300 kyr. The lower crisis interval in the uppermost Famennian started as a prelude with a minor eustatic sea-level fall, followed rather abruptly by pantropically widespread black shale deposition (Hangenberg Black Shale and equivalents). This transgressive and hypoxic/anoxic phase coincided with a global carbonate crisis and perturbation of the global carbon cycle as evidenced by a distinctive positive carbon isotope excursion, probably as a consequence of climate/salinity-driven oceanic overturns and outer-shelf eutrophication. It is the main extinction level for marine biota, especially for ammonoids, trilobites, conodonts, stromatoporoids, corals, some sharks, and deeper-water ostracodes, but probably also for placoderms, chitinozoans and early tetrapods. Extinction rates were lower for brachiopods, neritic ostracodes, bryozoans and echinoderms. Extinction patterns were similar in widely separate basins of the western and eastern Prototethys, while a contemporaneous marine macrofauna record from high latitudes is missing altogether. The middle crisis interval is characterized by a gradual but major eustatic sea-level fall, probably in the scale of more than 100 m, that caused the progradation of shallow-water siliciclastics (Hangenberg Sandstone and equivalents) and produced widespread unconformities due to reworking and non-deposition. The glacio-eustatic origin of this global regression is proven by miospore correlation with widespread diamictites of South America and South and North Africa, and by the evidence for significant tropical mountain glaciers in eastern North America. This isolated and short-lived plunge from global greenhouse into icehouse conditions may follow the significant drawdown of atmospheric CO2 levels due to the prior massive burial of organic carbon during the global deposition of black shales. Increased carbon recycling by intensified terrestrial erosion in combination with the arrested burial of carbonates may have led to a gradual rise of CO2 levels, re-warming, and a parallel increase in the influx of land-derived nutrients. The upper crisis interval in the uppermost Famennian is characterized by initial post-glacial transgression and a second global carbon isotope spike, as well as by opportunistic faunal blooms and the early re-radiation of several fossil groups. Minor reworking events and unconformities give evidence for continuing smaller-scale oscillations of sea-level and palaeoclimate. These may explain the terrestrial floral change near the Famennian–Tournaisian boundary and contemporaneous, evolutionarily highly significant extinctions of survivors of the main crisis. Still poorly understood small-scale events wiped out the last clymeniid ammonoids, phacopid trilobites, placoderms and some widespread brachiopod and foraminiferan groups. The post-crisis interval in the lower Tournaisian is marked by continuing eustatic rise (e.g. flooding of the Old Red Continent), and significant radiations in a renewed greenhouse time. But the recovery had not yet reached the pre-crisis level when it was suddenly interrupted by the global, second-order Lower Alum Shale Event at the base of the middle Tournaisian.

Metallogeny and its link to orogenic style during the Nuna supercontinent cycle

Abstract: The link between observed episodicity in ore deposit formation and preservation and the supercontinent cycle is well established, but this general framework has not, however, been able to explain a lack of deposits associated with some accretionary orogens during specific periods of Earth history. Here we show that there are intriguing correlations between styles of orogenesis and specific mineral deposit types, in the context of the Nuna supercontinent cycle. Using animated global reconstructions of Nuna's assembly and initial breakup, and integrating extensive databases of mineral deposits, stratigraphy, geochronology and palaeomagnetism we are able to assess spatial patterns of deposit formation and preservation. We find that lode gold, volcanic-hosted-massive-sulphide and nickel–copper deposits peak during closure of Nuna's interior ocean but decline during subsequent peripheral orogenesis, suggesting that accretionary style is also important. Deposits such as intrusion-related gold, carbonate-hosted lead-zinc and unconformity uranium deposits are associated with the post-assembly, peripheral orogenic phase. These observations imply that the use of plate reconstructions to assess orogenic style, although challenging for the Precambrian, can be a powerful tool for mineral exploration targeting.

Enhanced volcanic hot-spot detection using MODIS IR data: results from the MIROVA system

Abstract: Abstract We describe a new volcanic hotspot detection system, named Middle InfraRed Observation of Volcanic Activity (MIROVA), based on the analysis of infrared data acquired by the Moderate Resolution Imaging Spectroradiometer sensor (MODIS). MIROVA uses the middle infrared radiation (MIR), measured by MODIS, in order to detect and measure the heat radiation deriving from volcanic activity. The algorithm combines spectral and spatial principles, allowing the detection of heat sources from 1 megawatt (MW) to more than 10 gigawatt (GW). This provides a unique opportunity to: (i) recognize small-scale variations in thermal output that may precede the onset of effusive activity; (ii) track the advance of large lava flows; (iii) estimate lava discharge rates; (iv) identify distinct effusive trends; and, lastly, (v) follow the cooling process of voluminous lava bodies for several months. Here we show the results obtained from data sets spanning 14 years recorded at the Stromboli and Mt Etna volcanoes, Italy, and we investigate the above aspects at these two persistently active volcanoes. Finally, we describe how the algorithm has been implemented within an operational near-real-time processing chain that enables the MIROVA system to provide data and infrared maps within 1–4 h of the satellite overpass.

Australia and Nuna

Abstract: Abstract The Australian continent records c. 1860–1800 Ma orogenesis associated with rapid accretion of several ribbon micro-continents along the southern and eastern margins of the proto-North Australian Craton during Nuna assembly. The boundaries of these accreted micro-continents are imaged in crustal-scale seismic reflection data, and regional gravity and aeromagnetic datasets. Continental growth (c. 1860–1850 Ma) along the southern margin of the proto-North Australian Craton is recorded by the accretion of a micro-continent that included the Aileron Terrane (northern Arunta Inlier) and the Gawler Craton. Eastward growth of the North Australian Craton occurred during the accretion of the Numil Terrane and the Abingdon Seismic Province, which forms part of a broader zone of collision between the northwestern margins of Laurentia and the proto-North Australian Craton. The Tickalara Arc initially accreted with the Kimberley Craton at c. 1850 Ma and together these collided with the proto-North Australian Craton at c. 1820 Ma. Collision between the West Australian Craton and the proto-North Australian Craton at c. 1790–1760 Ma terminated the rapid growth of the Australian continent.

Review of chrono-, litho- and biostratigraphy across the global Hangenberg Crisis and Devonian–Carboniferous Boundary

Abstract: Abstract Chrono-, litho- and biostratigraphy across the Devonian–Carboniferous transition are reviewed to provide a precise time framework for the global Hangenberg Crisis and for the current search for a revised basal Carboniferous Global Stratotype Section and Point (GSSP). The outer shelf deposits of the Rhenish Massif (Germany) form a lithological standard. Pre- (main Wocklum Limestone), lower (top Wocklum Limestone/Drewer Sandstone to Hangenberg Black Shale), middle (Hangenberg Shale/Sandstone), upper (Stockum Limestone), and post-crisis (Hangenberg Limestone) deposits are defined. Combined with the conodont, ammonoid and miospore zonations and eustatic trends, this succession can be correlated internationally. The contemporaneous successions of the Ardennes serve as a reference for shallow shelf settings. The positive and negative aspects of five options for a redefined Devonian–Carboniferous boundary level are discussed: (1) base of the black shale (main extinction level, base of Bispathodus costatus–Protognathodus kockeli Interregnum and LN Zone), (2) sequence boundary (widespread unconformities) or glacial and regressive peak (base of Hangenberg Sandstone), (3) base of the kockeli Zone and of initial postglacial transgression (base of lower Stockum Limestone), (4) entry of Siphonodella (Eosiphonodella) sulcata (base of upper Stockum Limestone), and (5) base of post-crisis interval (base of Hangenberg Limestone), at approximately the poorly correlated current GSSP level. Due to homonymy, Siphonodella (Siphonodella) hassi Ji, 1985 is renamed as Siphonodella (Siphonodella) jii nom. nov. Consequently, the mid-lower Tournaisian S. (S.) hassi Zone (previous Upper S. (S.) duplicata Zone) becomes the S. (S.) jii Zone.

Four-dimensional context of Earth's supercontinents

Abstract: The supercontinent-cycle hypothesis attributes planetary-scale episodic tectonic events to an intrinsic self-organizing mode of mantle convection, governed by the buoyancy of continental lithosphere that resists subduction during closure of old ocean basins, and consequent reorganization of mantle convection cells leading to opening of new ocean basins. Characteristic timescales of the cycle are typically 500–700 myr. Proposed spatial patterns of cyclicity range from hemispheric (introversion) to antipodal (extroversion), to precisely between those end-members (orthoversion). Advances in our understanding can arise from theoretical or numerical modelling, primary data acquisition relevant to continental reconstructions, and spatiotemporal correlations between plate kinematics, geodynamic events and palaeoenvironmental history. The palaeogeographic record of supercontinental tectonics on Earth is still under development. The contributions in this special publication provide snap-shots in time of these investigations and indicate that Earth’s palaeogeographic record incorporates elements of all three endmember spatial patterns. Introduction: how do we recognize ancient

A geomagnetic polarity timescale for the Permian, calibrated to stage boundaries

Abstract: The reverse polarity Kiaman Superchron has strong evidence for at least three, or prob ably four, normal magnetochrons during the early Permian. Normal magnetochrons are during the early Asselian (base CI1r.1n at 297.94+0.33 Ma), late Artinskian (CI2n at 281.24+2.3 Ma), mid-Kungurian (CI3n at 275.86+2.0 Ma) and Roadian (CI3r.an at 269.54+1.6 Ma). The mixed-polarity Illawarra Superchron begins in the early Wordian at 266.66+0.76 Ma. The Wordian– Capitanian interval is biased to normal polarity, but the basal Wuchiapingian begins the beginning of a significant reverse polarity magnetochron LP0r, with an overlying mixed-polarity interval through the later Lopingian. No significant magnetostratigraphic data gaps exist in the Permian geomagnetic polarity record. The early Cisuralian magnetochrons are calibrated to a succession of fusulinid zones, the later Cisuralian and Guadalupian to a conodont and fusulinid biostratigraphy, and Lopingian magnetochrons to conodont zonations. Age calibration of the magnetochrons is obtained through a Bayesian approach using 35 radiometric dates, and 95% confidence intervals on the ages and chron durations are obtained. The dating control points are most numerous in the Gzhelian–Asselian, Wordian and Changhsingian intervals. This significant advance should provide a framework for better correlation and dating of the marine and non-marine Permian

Return to Rodinia? Moderate to high palaeolatitude of the São Francisco/Congo craton at 920 Ma

Abstract: Moderate to high palaeolatitudes recorded in mafic dykes, exposed along the coast of Bahia, Brazil, are partly responsible for some interpretations that the Sao Francisco/Congo craton was separate from the low-latitude Rodinia supercontinent at about 1050 Ma. We report new palaeomagnetic data that replicate the previous results. However, we obtain substantially younger U-Pb baddeleyite ages from five dykes previously thought to be 1.02-1.01 Ga according to the 40Ar/39Ar method. Specifically, the so-called «A-normal» remanence direction from Salvador is dated at 924.2±3.8 Ma, within error of the age for the «C» remanence direction at 921.5±4.3 Ma. An «A-normal» dyke at Ilh»us is dated at 926.1±4.6 Ma, and two «A-normal» dykes at Olivenca have indistinguishable ages with best estimate of emplacement at 918.2±6.7 Ma. We attribute the palaeomagnetic variance of the «A-normal» and «C» directions to lack of averaging of geomagnetic palaeosecular variation in some regions. Our results render previous 40Ar/39Ar ages from the dykes suspect, leaving late Mesoproterozoic palaeolatitudes of the Sao Francisco/Congo craton unconstrained. The combined «A-normal» palaeomagnetic pole from coastal Bahia places the Sao Francisco/Congo craton in moderate to high palaeolatitudes at c. 920 Ma, allowing various possible positions of that block within Rodinia.

Tectonic and magmatic segmentation of the Global Ocean Ridge System: A synthesis of observations

Abstract: Abstract Mid-ocean ridges display tectonic segmentation defined by discontinuities of the axial zone, and geophysical and geochemical observations suggest segmentation of the underlying magmatic plumbing system. Here, observations of tectonic and magmatic segmentation at ridges spreading from fast to ultraslow rates are reviewed in light of influential concepts of ridge segmentation, including the notion of hierarchical segmentation, spreading cells and centralized v. multiple supply of mantle melts. The observations support the concept of quasi-regularly spaced principal magmatic segments, which are 30–50 km long on average at fast- to slow-spreading ridges and fed by melt accumulations in the shallow asthenosphere. Changes in ridge properties approaching or crossing transform faults are often comparable with those observed at smaller offsets, and even very small discontinuities can be major boundaries in ridge properties. Thus, hierarchical segmentation models that suggest large-scale transform fault-bounded segmentation arises from deeper level processes in the asthenosphere than the finer-scale segmentation are not generally supported. The boundaries between some but not all principal magmatic segments defined by ridge axis geophysical properties coincide with geochemical boundaries reflecting changes in source composition or melting processes. Where geochemical boundaries occur, they can coincide with discontinuities of a wide range of scales.

Devonian climate, sea level and evolutionary events: an introduction

Abstract: The face of Planet Earth has changed significantly through geological time. Dynamic processes active today, such as plate tectonics and climate change, have shaped the Earth’s surface and impacted biodiversity patterns from the beginning. Organisms, on the other hand, have the capacity to significantly alter Earth’s hydrological and geochemical cycles, its atmosphere and climate, sediments, and even hard rocks deep down under the surface. Abiotic– biotic interactions characterize Earth’s system history and, together with biotic competition and food webs, were the main trigger of evolutionary change, innovations and biodiversity fluctuations. Within the Palaeozoic, the Devonian was an especially interesting time interval as it was characterized by the ‘mid-Paleozoic predator revolution’ (Signor & Brett 1984; Brett 2003) and the related ‘nekton revolution’ (Klug et al. 2010), characterized by the blooms of free-swimming cephalopods, including the oldest ammonoids, and fish groups (e.g. toothed sharks and giant placoderms), the rise of more advanced vertebrates, including the oldest tetrapods (e.g. Blieck et al. 2007, 2010; Niedzwiedzki et al. 2010), the most extensive reef complexes of the Phanerozoic (e.g. Kiessling 2008), and the ‘greening of land’ by the diversification and spread of land plants, including the oldest forests (e.g. Stein et al. 2012; Giesen & Berry 2013), which resulted in new soil types and changing weathering. These major evolutionary trends did not unfold in a long interval of environmental stability, but in times of numerous and repeated, geologically brief, global events that punctuated prolonged periods, up to several million years in duration, of relative stability, termed ecological-evolutionary subunits (EE subunits: Boucot 1990; Brett & Baird 1995; Brett et al. 2009). The bounding events, even those of lesser intensity, produced major re-structuring in local to global ecosystems and are seen as critical drivers of long-term evolutionary patterns (Brett 2012). These linked abiotic and biotic events and extinctions of different magnitude have been summarized by House (1983, 1985, 2002), Walliser (1984, 1996) and, more recently, by Becker et al. (2012). The Devonian event succession is summarized in Figure 1. Two first-order mass extinctions at the Frasnian–Famennian boundary (Kellwasser Crisis) and at the end of the Devonian (Hangenberg Crisis), characterized by the loss of major fossil groups (classes and orders) and complete ecosystems (e.g. metazoan reefs, early forests), have to be viewed in the context of a complex global event sequence. There are important similarities between discrete pulses/phases of the major biotic crises and individual smaller-scale events. In our understanding, second-order global events are characterized by sudden extinctions in many groups and ecosystems, including the complete disappearance of several widespread and diverse organism groups (orders and families). Examples are the basal Emsian atopus Event, where the planktonic graptolites finally died out, the Taghanic Crisis, Frasnes events and Lower Kellwasser Event. Third-order global events show globally elevated extinction rates, often at lower taxonomic level (genera and species), but within many clades and in several ecosystems. Examples are the Silurian–Devonian boundary Klonk Event, and the Daleje, Chotěc, Kacak, Condroz and Annulata events. Fourth-order global extinctions refer to the sudden disappearance of relatively fewer but widespread groups, which implies a global, not regional, trigger. This category may include the Lochkovian–Pragian boundary

Greenhouse to icehouse: a biostratigraphic review of latest Devonian-Mississippian glaciations and their global effects

Abstract: The latest Devonian–Mississippian interval records the long-term transition from Devonian greenhouse conditions into the Late Palaeozoic Ice Age (LPIA). This transition was punctuated by three short glaciation events in the latest Famennian, mid-Tournaisian and Visean stages, respectively. Primary evidence for glaciation is based on diamictite deposits and striated pavements in South America, Appalachia and Africa. The aim of this review is to assess the primary biostratigraphic and sedimentological data constraining diamictite deposits through this transition. These data are then compared to the wider record of eustasy, mass extinction and isotope stratigraphy in the lower palaeolatitudes. Precise age determinations are vital to integrate high- and low-palaeolatitude datasets, and to understand the glacial control on wider global changes. Palynological techniques currently provide the best biostratigraphic tool to date these glacial deposits and to correlate the effects of glaciation globally. This review highlights a high degree of uncertainty in the known history of early LPIA glaciation as much of the primary stratigraphic data are limited and/or unpublished. Future high-resolution stratigraphic studies are needed to constrain the history of glaciation both spatially and temporally through the latest Devonian and Mississippian.

Fracture systems of the Northern Volcanic Rift Zone, Iceland: an onshore part of the Mid-Atlantic plate boundary

Abstract: Abstract Few divergent plate boundaries are subaerial. Active rifts in Iceland provide valuable surface information on divergent spreading processes, rifting and faulting. The 200 km long and 50 km wide Northern Volcanic Rift Zone (NVZ) is composed of 7 volcanic systems, each consisting of a central volcano with a transecting fissure swarm. Fractures and postglacial eruptive fissures in the NVZ were analysed using aerial photographs and satellite images to study their characteristics and behaviour. While non-eruptive fractures characterize the distal (c. 40–100 km) parts of the fissure swarms, eruptive fissures are most common at distances less than c. 20–30 km from the central volcano. Fractures within the fissure swarms are generally subparallel, with a N–NNE strike. Irregular orientations are associated with calderas within the central volcanoes Askja and Krafla, and at the junction of the NVZ and the Tjörnes Fracture Zone, where high fracture densities also occur. WNW-orientated fractures at the southern end of the Krafla Fissure Swarm, and the northern end of the Kverkfjöll Fissure Swarm, exhibit surface expressions of a transform zone. The fissure swarms within the rift zone are mostly seismically and geodetically inactive, becoming highly active during rifting events that occur at time intervals of tens to a few hundred years.

Insight into the Eastern Margin of Africa from a new tectonic model of the Indian Ocean

Abstract: Abstract We present a new plate tectonic model for the breakup and dispersal of East and West Gondwana and subsequent formation of the Indian Ocean, focussed on the early evolution of the Eastern Margin of Africa. We start from a tight reconstruction of all the Precambrian pieces. Using primarily ocean-floor fracture zone data, the development of the ocean between India and Antarctica is resolved into four distinct spreading regimes and that between Antarctica and Africa into seven distinct regimes. The movement of Madagascar against Africa is then investigated as part of the plate–circuit closure between Africa and India in the Madagascar–Africa–Antarctica–India–Madagascar system. We conclude that a distinct change in plate tectonic regime off East Africa occurred at about 153 Ma (Kimmeridgian) when transforms were first activated offshore. Before this time, East and West Gondwana were separated by a rift, propagating from NE to SW and starting between 188 and 170 Ma. The model is defined by Euler interval poles, published here for the first time, and a refined global animation that may be inspected and copied from the URL www.reeves.nl/Gondwana. The analysis points to a small number of disruptive events in the otherwise inexorable growth of the oceans.

Major sinks of the Changjiang (Yangtze River)-derived sediments in the East China Sea during the late Quaternary

Abstract: The East China Sea (ECS) is a typical marginal sea located between the Eurasian con- tinentandwestPacificOcean.Inthisstudy,wereviewstate-of-the-artresearchprogressonthepos- sible sinks of the Changjiang-derived sediments in the ECS during the late Quaternary. The major sinks of these sediments in the ECS are on the outer shelf and the Okinawa Trough during the last glacial maximum corresponding to a lowstand of sea level. During the deglacial marine transgres- sion, the gently dipping shelf was rapidly inundated and strong tides prevented fine sediment from deposition on the open shelf, resulting in the development of a unique tidal sand ridge sys- tem. With sea level reaching the present situation and the modern marine environment being com- pleted in the early Holocene, the Changjiang sediments mostly accumulated in the river's estuary to build a large delta, with only a fraction reaching the inner shelf and coastal embayments. The late-Quaternary changes in monsoon-climate-induced river flux, sea level and oceanic circulation primarily controlled the source-to-sink transport of the Changjiang sediments in the ECS, and fur- ther determined the stratigraphic framework and sedimentary facies on the shelf.

Timing of the emergence of the Europe–Sicily bridge (40–17 cal ka BP) and its implications for the spread of modern humans

Abstract: Abstract The submerged sill in the Strait of Messina, which is located today at a minimum depth of 81 m below sea level (bsl), represents the only land connection between Sicily and mainland Italy (and thus Europe) during the last lowstand when the sea level locally stood at about 126 m bsl. Today, the sea crossing to Sicily, although it is less than 4 km at the narrowest point, faces hazardous sea conditions, made famous by the myth of Scylla and Charybdis. Through a multidisciplinary research project, we document the timing and mode of emergence of this land connection during the last 40 kyr. The integrated analysis takes into consideration morphobathymetric and lithological data, and relative sea-level change (both isostatic and tectonic), resulting in the hypothesis that a continental land bridge lasted for at least 500 years between 21.5 and 20 cal ka BP. The emergence may have occurred over an even longer time span if one allows for seafloor erosion by marine currents that have lowered the seabed since the Last Glacial Maximum (LGM). Modelling of palaeotidal velocities shows that sea crossings when sea level was lower than present would have faced even stronger and more hazardous sea currents than today, supporting the hypothesis that earliest human entry into Sicily most probably took place on foot during the period when the sill emerged as dry land. This hypothesis is compared with an analysis of Pleistocene vertebrate faunas in Sicily and mainland Italy, including a new radiocarbon date on bone collagen of an Equus hydruntinus specimen from Grotta di San Teodoro (23–21 cal ka BP), the dispersal abilities of the various animal species involved, particularly their swimming abilities, and the Palaeolithic archaeological record, all of which support the hypothesis of a relatively late land-based colonization of Sicily by Homo sapiens.

Influence of regional tectonics and pre-existing structures on the formation of elliptical calderas in the Kenyan Rift

Abstract: Calderas are formed by the collapse of large magma reservoirs and are commonly elliptical in map view. The orientation of elliptical calderas is often used as an indicator of the local stress regime; but, in some rift settings, pre-existing structural trends may also influence the orientation. We investigated whether either of these two mechanisms controls the orientation of calderas in the Kenyan Rift. Satellite-based mapping was used to identify the rift border faults, intra-rift faults and orientation of the calderas to measure the stress orientations and pre-existing structural trends and to determine the extensional regime at each volcano. We found that extension in northern Kenya is orthogonal, whereas that in southern Kenya is oblique. Elliptical calderas in northern Kenya are orientated NW–SE, aligned with pre-existing structures and perpendicular to recent rift faults. In southern Kenya, the calderas are aligned NE–SW and lie oblique to recent rift faults, but are aligned with pre-existing structures. We conclude that, in oblique continental rifts, pre-existing structures control the development of elongated magma reservoirs. Our results highlight the structural control of magmatism at different crustal levels, where pre-existing structures control the storage and orientation of deeper magma reservoirs and the local stress regime controls intra-rift faulting and shallow magmatism. Supplementary material: Details of the Standard Deviation Ellipse function and statistical methods are available at http://www.geolsoc.org.uk/SUP18849.

Pleistocene submerged landscapes and Palaeolithic archaeology in the tectonically active Aegean region

Abstract: Abstract In this paper we review the main, long- and short-term geological and geotectonic processes that have controlled the development of Pleistocene landscapes in the Aegean region above and below the fluctuating sea level. We discuss the potential for further research on reconstruction of submerged landscapes of the continental shelf and beyond with the aim of addressing questions concerning Palaeolithic settlement. The geological, tectonic, morphological and hydrogeological background provides information for the assessment of the natural resources available to hominins. Along with the palaeogeographical evolution of the shallow coastal and shelf areas, they are examined in parallel with the terrestrial archaeological record in order to open windows to future work in a region that has remained marginal to human origins research. On the basis of the multi-variable tectonic evolution and geomorphological configuration of the coastal and shelf areas, we propose to divide the Aegean region into nine geographical units, each with its own geotectonic and morphological history and traits. These units can be further grouped to provide larger neighbouring and culturally meaningful regions, suitable for archaeological analysis, or subdivided to provide smaller target areas in which to work.

Benchmarking lava-flow models

Abstract: Prediction of the emplacement of volcanic mass flows (lava flows, pyroclastic density currents, debris avalanches and debris flows) is required for hazard and risk assessment, and for the planning of risk-mitigation measures. Numerical computer-based models now exist that are capable of approximating the motion of a given volume of volcanic material from its source to the deposition area. With these advances in technology, it is useful to compare the various codes in order to evaluate their respective suitability for real-time forecasting, risk preparedness and post-eruptive response. A ‘benchmark’ compares codes or methods, all aimed at simulating the same physical process using common initial and boundary conditions and outputs, but using different physical formulations, mathematical approaches and numerical techniques. We set up the basis for a future general benchmarking exercise on volcanic mass-flow models and, more specifically, establish a benchmark series for computational lava-flow modelling. We describe a set of benchmarks in this paper, and present a few sample results to demonstrate output analysis and code evaluation methodologies. The associated web-based communal facility for sharing test scenarios and results is also described.

Permian conodont biostratigraphy

Abstract: Abstract Forty Permian conodont biozones are summarized and 35 additional regional zones are correlated. The Lower Permian is largely zoned on the basis of partial range lineage interval zones of species of Streptognathodus, Sweetognathus, Neostreptognathodus and Mesogondolella. The Middle and Upper Permian are zoned, respectively, on the basis of partial range lineage interval zones of species of Jinogondolella and Clarkina. The ranges of all key taxa to develop this zonation are depicted in relation to the geochronological ages of Permian stages. The lowest Permian succession has been astronomically tuned with 400 kyr cyclothems linked to interpolated ages in the Uralian succession.

MODVOLC: 14 years of autonomous observations of effusive volcanism from space

Abstract: Abstract During the period 28 February 2000–31 December 2013, the MODVOLC system (http://modis.higp.hawaii.edu) autonomously analysed almost 9 trillion (i.e. 9×1012) pixels contained within almost 3 million MODIS images, searching for evidence of high-temperature thermal signatures associated with volcanic eruptions. Thermal unrest, mainly associated with active lava, be it in the form of flows, domes, lakes or confined to vents, was detected at 93 volcanoes during this period of time. The first part of this paper describes the physical basis and operational implementation of the MODVOLC algorithm. The second part presents data to detail the nature of the thermal emission from these 93 volcanoes over the past 14 years.

The late rifting phase and continental break-up of the southern South Atlantic: the mode and timing of volcanic rifting and formation of earliest oceanic crust

Abstract: Abstract Multichannel seismic and potential field data shed light on the final rifting stage in the southern South Atlantic. This was associated with major episodes of magmatism during the Early Cretaceous continental break-up. An asymmetrical simple shear-dominated variable strain rifting model is proposed with the margin asymmetry visible in shelf width, amplitude of magnetic anomalies, orientation of break-up-related sedimentary basins and basement slope angle. Along-margin rotation in spreading- and later rifting-direction from north–south to west–east are of great importance for the asymmetries. Such rotational opening may also explain why the southernmost segments of the South Atlantic are magma starved, with a sharp transition to a volcanic-rifted margin type northwards. Interpretation of pre-M5 (c. 130 Ma) magnetic seafloor spreading lineations constrains the timing of excess break-up-related volcanism and transition to ‘normal’ seafloor spreading. Termination of magnetic anomalies within seaward-dipping reflector sequences points towards a deposition of the volcanics from south to north prior to and during the early rift and opening stages. Identification of previously unknown pre-M5 magnetic lineations offshore Argentina completes the lineation pattern in the southern South Atlantic. The oldest magnetic anomaly related to oceanic spreading is M9 (c. 135 Ma). Older anomalies, previously identified as M11 (c. 137 Ma) offshore Cape Town, are related to structural or magnetization variations within seaward-dipping reflector sequences.

Holocene sedimentary systems on a broad continental shelf with abundant river input: process–product relationships

Abstract: Abstract The region consisting of the Bohai, Yellow and East China seas represents a typical wide continental shelf environment with abundant terrestrial sediment supply. Here, a variety of sedimentary systems have been formed during the Holocene period. These systems have unique characteristics in terms of spatial distribution, material composition, deposition rate, and the timing and duration for their formation, which are related to active sediment-transport processes induced by tides and waves, shelf circulations, and sediment gravity flows. The sedimentary records contained within the deposits have a high temporal resolution, but each with a limited temporal coverage. However, if these records are connected, then they may form a complete archive for environmental change studies. In the field of process–product relationship studies, the mid-Holocene coastal deposits on the Jiangsu coast, the early–middle Holocene sequences of the Hangzhou Bay, the Holocene mud deposits off the Zhejiang–Fujian coasts and the other mud areas over the region are of importance. These systems may be understood by identifying the material supply (from both seabed reworking during the sea-level rise events and river discharges), transport-accumulation processes, the formation of sediment sequences and the future evolution of the sediment systems, for which numerical modelling becomes increasingly important.

The English Chalk and London Clay: two remarkable British bony fish Lagerstätten

Abstract: Abstract The Late Cretaceous (Cenomanian–Maastrichtian) Chalk Group and Eocene (Ypresian) London Clay Formation are two British marine deposits that yield globally significant assemblages of fossil actinopterygian (ray-finned) fishes. Materials from these units, especially the Chalk, featured prominently in the work of Arthur Smith Woodward. Here we summarize the history of study of actinopterygian fossils from the Chalk and London Clay, review their geological and palaeoenvironmental context and provide updated faunal lists. The Chalk and London Clay are remarkable for preserving fossil fishes in three dimensions rather than as the flattened individuals familiar from many other famous Lagerstätten, as well as capturing detailed ‘snapshots’ of marine fish faunas that bracket the major taxonomic shift that took place near the Cretaceous–Palaeogene boundary.

Transform margins: development, controls and petroleum systems – an introduction

Abstract: This paper provides an overview of the existing knowledge of transform margins including their dynamic development, kinematic development, structural architecture and thermal regime, together with the factors controlling these. This systematic knowledge is used for describing predictive models of various petroleum system concept elements such as source rock, seal rock and reservoir rock distribution, expulsion timing, trapping style and timing, and migration patterns. The paper then introduces individual contributions to this volume and their focus. Supplementary material: Location table and map of specific transform examples, structural elements of the Romanche transform margin and glossary of terms used in this article is available at https://doi.org/10.6084/m9.figshare.c.3276407 Gold Open Access: This article is published under the terms of the CC-BY 3.0 license. This volume shows dynamic linkage between new transform margin research and increasing transform margin exploration. It offers a critical set of predictive tools via an understanding of the mechanisms involved in the development of play concept elements at transform margins and their controlling factors. Our introduction to this volume reviews the current knowledge of the transform margins, focusing on their dynamic development, kinematic development, structural architecture, thermal regimes and petroleum systems. The last part of this paper introduces the contributions to this volume.

Enhanced porosity preservation by pore fluid overpressure and chlorite grain coatings in the Triassic Skagerrak, Central Graben, North Sea, UK

Abstract: Current understanding of porosity preservation in deeply buried sandstone reservoirs tends to be focused on how diagenetic grain coatings of clay minerals and microquartz can inhibit macroquartz cementation. However, the importance of overpressure developed during initial (shallow) burial in maintaining high primary porosity during subsequent burial has generally not been appreciated. Where pore fluid pressures are high, and the vertical effective stress is low, the shallow arrest of compaction can allow preservation of high porosity and permeability at depths normally considered uneconomic. The deeply buried fluvial sandstone reservoirs of the Triassic Skagerrak Formation in the Central Graben, North Sea, show anomalously high porosities at depths greater than 3500 metres below sea floor (mbsf). Pore pressures can exceed 80 MPa in the upper part of the Skagerrak Formation at depths of 4000–5000 mbsf, where temperatures are above 140°C. The Skagerrak reservoirs commonly have high primary porosities of up to 35%, little macroquartz cement and variable amounts of diagenetic chlorite grain coats. This research sheds light on the complex controls on reservoir quality in the fluvial sandstones of the Skagerrak Formation by identifying the role of shallow overpressure in arresting mechanical compaction and the importance of chlorite detrital grain coatings in inhibiting macroquartz cement overgrowth as temperature increases during progressive burial.

Transform margins of the Arctic: a synthesis and re-evaluation

Abstract: Abstract Transform-margin development around the Arctic Ocean is a predictable geometric outcome of multi-stage spreading of a small, confined ocean under radically changing plate vectors. Recognition of several transform-margin stages in the development of the Arctic Ocean enables predictions to be made regarding tectonic styles and petroleum systems. The De Geer margin, connecting the Eurasia Basin (the younger Arctic Ocean) and the NE Atlantic during the Cenozoic, is the best known example. It is dextral, multi-component, features transtension and transpression, is implicated in microcontinent release, and thus bears close comparison with the Equatorial Shear Zone. In the older Arctic Ocean, the Amerasia Basin, Early Cretaceous counterclockwise rotation around a pole in the Canadian Mackenzie Delta was accommodated by a terminal transform. We argue on geometric grounds that this dislocation may have occurred at the Canada Basin margin rather than along the more distal Lomonosov Ridge, and review evidence that elements of the old transform margin were detached by the Makarov–Podvodnikov opening and accommodated within the Alpha–Mendeleev Ridge. More controversial is the proposal of transform along the Laptev–East Siberian margin. We regard an element of transform motion as the best solution to accommodating Eurasia and Makarov–Podvodnikov Basin opening, and have incorporated it into a three-stage plate kinematic model for Cretaceous–Cenozoic Arctic Ocean opening, involving the Canada Basin rotational opening at 125–80 Ma, the Makarov–Povodnikov Basin opening at 80–60 Ma normal to the previous motion and a Eurasia Basin stage from 55 Ma to present. We suggest that all three opening phases were accompanied by transform motion, with the right-lateral sense being dominant. The limited data along the Laptev–East Siberian margin are consistent with transform-margin geometry and kinematic indicators, and these ideas will be tested as more data become available over less explored parts of the Arctic, such as the Laptev–East Siberia–Chukchi margin.

Outline of a Permian tetrapod footprint ichnostratigraphy

Abstract: Abstract Tetrapod footprints are among the most common fossil remains in continental Permian strata and thus are of biostratigraphic interest. Based on the vertical distribution of the 13 best-known Permian tetrapod ichnotaxa, three footprint biochrons are suggested for the period: (1) Dromopus – latest Carboniferous (approximately Gzhelian) to late Early Permian (approximately Artinskian), representing ichnoassemblages dominated by tracks of temnospondyls, reptiliomorphs, pelycosaurs and early diapsids; (2) Erpetopus – late Early Permian (approximately Kungurian) to late Middle Permian (approximately Capitanian), representing ichnoassemblages dominated by tracks of non-diapsid eureptiles; and (3) Paradoxichnium – Late Permian (Wuchiapingian and Changhsingian), representing ichnoassemblages dominated by tracks of medium- and large-sized parareptiles, non-diapsid eureptiles and early saurians. This is the most conservative ichnostratigraphic concept, and it may be possible to refine it to almost stage-level resolution by future comprehensive analysis, especially of Permian captorhinomorph and therapsid footprints. Other major tasks to improve Permian tetrapod footprint ichnostratigraphy include enhanced knowledge of Middle Permian tetrapod footprints, and clarification of the palaeoenvironmental factors that may control the distribution of tetrapod footprints in space and time.

MAGFLOW: a physics-based model for the dynamics of lava-flow emplacement

Abstract: Abstract The MAGFLOW model for lava-flow simulations is based on the cellular automaton (CA) approach, and uses a physical model for the thermal and rheological evolution of the flowing lava. We discuss the potential of MAGFLOW to improve our understanding of the dynamics of lava-flow emplacement and our ability to assess lava-flow hazards. Sensitivity analysis of the input parameters controlling the evolution function of the automaton demonstrates that water content and solidus temperatures are the parameters to which MAGFLOW is most sensitive. Additional tests also indicate that temporal changes in effusion rate strongly influence the accuracy of the predictive modelling of lava-flow paths. The parallel implementation of MAGFLOW on graphic processing units (GPUs) can achieve speed-ups of two orders of magnitude relative to the corresponding serial implementation, providing a lava-flow simulation spanning several days of eruption in just a few minutes. We describe and demonstrate the operation of MAGFLOW using two case studies from Mt Etna: one is a reconstruction of the detailed chronology of the lava-flow emplacement during the 2006 flank eruption; and the other is the production of the lava-flow hazard map of the persistent eruptive activity at the summit craters.

Late Pennsylvanian–Early Triassic conchostracan biostratigraphy: a preliminary approach

Abstract: Abstract Conchostracans are one of the most common fossil animal groups of continental deposits from late Palaeozoic to modern times. Their habitats have ranged from perennial lakes of the Carboniferous and Early Permian to seasonal playa lakes and temporary ponds from the late Early Permian into the Triassic, where they could form mass occurrences. This, together with relatively high speciation rates, makes them ideal guide fossils, especially in otherwise fossil-poor wet and dry red beds. Based on material and data collected since the 1980s from both surface outcrops and well cores in central Europe, a preliminary conchostracan zonation is proposed. We used a conservative approach, erecting assemblage zones comprising two or three species instead of species-range zones with only one or, sometimes, two forms. Assemblage zones are more robust and provide more reliability for each delineated time interval. Isotopically dated occurrences of conchostracan zone species, or co-occurrences of conchostracans, insect zone species and marine index fossils such as conodonts and fusulinids, allow us to correlate our assemblage zones with the marine Standard Global Chronostratigraphic Scale.

HOTVOLC: a web-based monitoring system for volcanic hot spots

Abstract: Abstract Infrared (IR) satellite-based sensors allow the detection and quantification of volcanic hot spots. Sensors flown on geostationary satellites are particularly helpful in the early warning and continuous tracking of effusive activity. Development of operational monitoring and dissemination systems is essential to achieve the real-time ingestion and processing of IR data for a timely response during volcanic crises. HOTVOLC is a web-based satellite-data-driven monitoring system developed at the Observatoire de Physique du Globe de Clermont-Ferrand (Clermont-Ferrand), designed to achieve near-real-time monitoring of volcanic activity using on-site ingestion of geostationary satellite data (e.g. MSG-SEVIRI, MTSAT, GOES-Imager). Here we present the characteristics of the HOTVOLC system for the monitoring of effusive activity. The system comprises two acquisition stations and secure databases (i.e. mirrored archives). The detection of volcanic hot spots uses a contextual algorithm that is based on a modified form of the Normalized Thermal Index (NTI*) and VAST. Raster images and numerical data are available to open-access on a Web-GIS interface. Tests are carried out and presented here, particularly for the 12–13 January 2011 eruption of Mount Etna, to show the capability of the system to provide quantitative information such as lava volume and time-averaged discharge rate. Examples of operational application reveal the ability of the HOTVOLC system to provide timely thermal information about volcanic hot spot activity.