kinematics of cenozoic extension on the south china sea continental margin and its implications for the tectonic evolution of the region abstract in the northern south china sea several large sedimentary basins developed during the cenozoic characterized by episodic rifting clockwise rotation of the rifts an eastward aging breakup unconformity and intensifying crustal extension to the east these features may be summarized by a scissors model the maximum rifting occurred north of the maximum thermal subsidence which was in turn north of the seafloor opening in contrast the nansha microcontinent south of the south china sea basin was dominated by compressional deformation during the cenozoic extension was of subordinate significance and manifested mainly by block faulting and tilting in the late early oligocene maximum tilting occurred in the southern part of the nansha microcontinent at distance from the deep sea basin of the south china sea the asymmetric development of extensional structures around the south china sea basin may be explained by the simple shear model proposed by wernicke 1981 the tectonic development of the south china sea was the consequence of various interactions of three major plates and may be summarized into three stages with dominating influences of respectively the retreat of the west pacific subduction zone in the late cretaceous the hard collision and impinging of india to tibet since the late eocene and the fast northward subduction of the indian ocean australian plate since the late early miocene

nondestructive in situ cellular scale mapping of elemental abundances including organic carbon in permineralized fossils the electron microprobe allows elemental abundances to be mapped at the mm scale but until now high resolution mapping of light elements has been challenging modifications of electron microprobe procedure permit fine scale mapping of carbon when applied to permineralized fossils this technique allows simultaneous mapping of organic material major matrix forming elements and trace elements with mm scale resolution the resulting data make it possible to test taphonomic hypotheses for the formation of anatomically preserved silicified fossils including the role of trace elements in the initiation of silica precipitation and in the prevention of organic degradation the technique allows one to understand the localization of preserved organic matter before undertaking destructive chemical analyses and because it is nondestructive offers a potentially important tool for astrobiological investigations of samples returned from mars or other solar system bodies

reply to discussion on a high precision u pb age constraint on the rhynie chert konservat lagerstatte time scale and other implications journal 168 863 872 we welcome the opportunity to address the points raised by mark et al in their discussion of the chemical abrasion isotope dilution thermal ionization mass spectrometry ca id tims u pb age constraint on the rhynie chert konservat lagerstatte presented by parry et al 2011 and also to make some further observations of our own we begin by briefly providing some context for the benefit of the wider readership two radio isotopic age constraints on the rhynie chert konservat lagerstatte and by corollary its parental hydrothermal hot spring system have recently been published the first of these is a weighted mean 40ar 39ar plateau age of 403 9 2 1 ma 2 derived from the analysis of two samples of vein hosted hydrothermal k feldspar and a single sample of hydrothermally altered andesite mark et al 2011 in order to account for systematic uncertainties associated with the 40ar 39ar geochronometer mark et al 2011 recalculated their individual sample ages with reference to the fish canyon tuff sanidine fcs age of 28 201 ma kuiper et al 2008 thereby producing a u pb comparable mean age of 407 1 2 2 ma 2 an alternative preferred age for the rhynie hot spring activity 407 6 2 2 ma 2 has now been produced from the raw data using the optimization model of renne et al 2010 2011 this discussion the 40ar 39ar system calibrations on which these various ages are based are summarized in table 1 the second radio isotopic age constraint in question is a weighted mean 206pb 238u zircon age of 411 5 1 3 ma 2 including decay constant and tracer calibration related uncertainties mswd 0 12 n 4 yielded by the milton of noth andesite a moderately altered basaltic andesite lava flow cum

geological setting of the early devonian rhynie cherts aberdeenshire scotland an early terrestrial hot spring system abstract the drilling of nine cored boreholes including a deep hole 233 m to a gabbroic basement in the vicinity of the rhynie chert locality has resulted in a major revision of the structure and stratigraphy of the area the main new structural element recognized is a low angle extensional fault system which defines the western edge of a half graben containing the early devonian succession the fault system was the main conduit for the fluids that fed the hot springs and a heat source to the southeast of rhynie is indicated rapid and unexpected lateral and vertical variations in lithology together with new lithological units have been identified the latter include a thick unit of intensely altered lapilli tuffs which are unique to the rhynie basin and to other devonian basins in ne scotland analysis of these lithologies in conjunction with the new structural model allows the succession at rhynie to be correlated with the succession in the rest of the basin and a model of basin evolution and hot spring development to be constructed siliceous sinters were deposited by multiple episodes of hot spring activity and are variably interbedded with shales sandstones and minor tuffs in a unit about 35 m thick sinter deposition was ultimately controlled by repeated subsidence along the basin margin geothermal activity was probably widespread in northern britain in the early devonian but the surface deposits are unlikely to be preserved the rhynie deposit has survived due to a fortuitous combination of circumstances

the cosheston group lower old red sandstone in southwest wales age correlation and palaeobotanical significance upper silurian lower devonian lower old red sandstone facies deposits cropping out in southwest wales are poorly age constrained and difficult to correlate spore assemblages have been recovered from sequences of these deposits belonging to the lower part of the cosheston group the spore assemblages are equated with the breconensis zavallatus and polygonalis emsiensis spore assemblage biozones and indicate an early devonian age late gedinnian late lochkovian siegenian pragian the new biostratigraphical data enable correlation of the lower part of the cosheston group with the senni beds from the main outcrop of the lower devonian in south wales and the welsh borderland in addition the new age data and stratigraphical correlation place important plant megafossil assemblages from the cosheston group and senni beds in a more secure stratigraphical framework thus facilitating comparisons with other lower devonian plant megafossil assemblages and enhancing palaeobotanical understanding evidence from palynofacies analysis supports sedimentological interpretations which suggest that the lower old red sandstone facies deposits belonging to the cosheston group accumulated in a continental fluviatile environment

advanced analytical techniques for studying the morphology and chemistry of proterozoic microfossils this paper outlines the suite of advanced multi scalar techniques currently available in the toolkit of the modern proterozoic palaeobiologist these include non intrusive and non destructive optical laser and x ray techniques plus more destructive ion beam and electron beam methods together these provide morphological mineralogical and biochemical data at flexible spatial scales from that of an individual atom to the largest proterozoic microfossils an overview is given of each technique and a case study from the exceptionally well preserved torridonian biota of nw scotland is presented this microfossil assemblage was first recognized over a century ago but its great diversity and evolutionary importance has only recently come to light due in no small part to the research efforts of martin brasier

arthropod trackways from the early devonian of south wales a functional analysis of producers and their behaviour abundant arthropod trackways assigned to diplichnites gouldi are described from the lower old red sandstone early devonian lochkovian of pant y maes quarry brecon beacons south wales the trackways are preserved on bedding planes of finely laminated planar and rippled siltstones the sedimentology of the succession indicates that these units represent bar top and marginal deposits in a braided fluvial setting two trackway types are recognized type a and b comparisons with contemporaneous myriapodous producers favour kampecarid and eoarthropleurid myriapods respectively functional analysis of the trackways indicates that the producers were not using the most efficient stable walking techniques but instead utilized in phase swimming stroke like gaits together with their occurrence on rippled surfaces and lateral displacement of some trackways attributed to currents this indicates that they were produced sub aqueously

an introduction to the rhynie chert the terrestrialization of life has profoundly affected the biosphere geosphere and atmosphere and the geological magazine has published key works charting the development of our understanding of this process integral to this understanding and featuring in one of the geological magazine publications is the devonian rhynie chert konservat lagerstatte located in aberdeenshire scotland here we provide a review of the work on this important early terrestrial deposit to date we begin by highlighting contributions of note in the geological magazine improving understanding of terrestrialization and palaeozoic terrestrial ecosystems we then introduce the rhynie chert the review highlights its geological setting the caledonian context of the rhynie basin and its nature at the time of deposition of the cherts which host its famous fossils there follows an introduction to the development of the half graben in which the cherts and host sediments were deposited the palaeoenvironment this represented and the taphonomy of the fossils themselves we subsequently provide an overview of the mineralization and geochemistry of the deposit and then the fossils found within the rhynie chert these include six plant genera which continue to provide significant insights into the evolution of life on land a range of different fungi with recent work starting to probe plant fungus interactions lichens amoebae and a range of unicellular eukaryotes and prokaryotes algae and cyanobacteria and finally a range of both aquatic and terrestrial arthropods through continued study coupled with methodological advances rhynie fossils will continue to provide unique insights into early life on land

40ar 39ar dating of hydrothermal activity biota and gold mineralization in the rhynie hot spring system aberdeenshire scotland this study presents a new high precision 40ar 39ar age for the devonian hot spring system at rhynie hydrothermal k feldspar sampled from two veins that represent feeder conduits and a hydrothermally altered andesite wall rock date the hydrothermal activity the fossilised biota and syn k feldspar gold mineralization at 403 9 2 1 ma 2 oxygen isotope data for the parent fluid 4 to 2 show that the k feldspar was precipitated from a dominantly meteoric fluid which mixed with magmatic fluids from a degassing magma chamber the 40ar 39ar age 403 9 2 1 ma 2 when recalculated 407 1 2 2 ma 2 with respect to the astronomically tuned age for fish canyon sanidine 28 201 0 023 ma 1 also provides a robust marker for the polygonalis emsiensis spore assemblage biozone within the pragian earliest emsian furthermore the age identifies the devonian pull apart volcano sedimentary basins of the british and irish caledonides and their root zones as specific targets for future gold exploration

soft bodied fossils from the roof shales of the wigan four foot coal seam westhoughton lancashire uk exceptionally preserved fossils are described from the westhoughton opencast coal pit near wigan lancashire uk uppermost westphalian a lower modiolaris chronozone regularis faunal belt the fossils occur within sideritic concretions in a 1 5 metre zone above the wigan four foot coal seam arthropods dominate the fauna and include arachnids arthropleurids crustaceans eurypterids euthycarcinoids millipedes and xiphosurans vertebrates are represented by a single palaeoniscid fish numerous disarticulated scales and coprolites upright sigillaria trees massive bedded units and a general lack of trace fossils in the roof shales of the wigan four foot coal seam suggest that deposition of the beds containing these concretions was relatively rapid discovery of similar faunas at the equivalent stratigraphic level some distance away point to regional rather than localized controls on exceptional preservation

a high precision u pb age constraint on the rhynie chert konservat lagerstatte time scale and other implications abstract an isotope dilution thermal ionization mass spectrometry u pb zircon age of 411 5 1 3 ma obtained from an andesitic lava occurring within the lower devonian rhynie outlier aberdeenshire ne scotland effectively dates the rhynie chert konservat lagerstatte biostratigraphical constraints on the rhynie chert bearing succession indicate that this age lies within the interval early but not earliest pragian earliest emsian accordingly the pragian emsian boundary must post date or closely approximate to 411 5 1 3 ma while the lochkovian pragian boundary must predate 411 5 1 3 ma integration of this new high precision age with an improved temporal framework for late caledonian intrusive activity in ne scotland suggests that the rhynie hot spring system the parental9 hydrothermal system to the rhynie cherts was unrelated to any newer granite9 intrusion rhynie was instead powered by a basaltic andesite magma whose generation and ascent were directly linked to the transcurrent fault movements responsible for the formation of the rhynie basin supplementary material details of analytical techniques id tims u pb geochronology and photomicrographs of zircon and titanite grains recovered from the milton of noth andesite are available at http www geolsoc org uk sup18463

comparative geobarometry of pelitic hornfelses associated with the newer gabbros a preliminary study physical conditions of contact metamorphism have been estimated for pelitic hornfelses collected from the inner aureoles of the morven cabrach knock huntly and belhelvie newer gabbro intrusions using a few well calibrated mineral equilibria inner aureole temperature estimates range from 700 c to 850 c calculated pressures all fall between 4 kbar and 5 kbar implying the existence of between 15 km and 18 5 km of overburden at each locality at the time of intrusion of the newer gabbros the results indicate that the four newer gabbros mentioned above were all emplaced at a similar crustal level and that there has been no net regional tilting of the ne dalradian since then the results are not incompatible with some large scale late stage d 3 gentle folding as implied by the regional isograd pattern

different expressions of rifting on the south china sea margins abstract rifting of continental margins is generally diachronous along the zones where continents break due to various factors including the boundary conditions which trigger the extensional forces but also the internal physical boundaries which are inherent to the composition and thus the geological history of the continental margin being opened quite recently in the tertiary in a scissor shape manner the south china sea scs offers an image of the rifting structures which varies along strike the basin margins the scs has a long history of extension which dates back from the late cretaceous and allows us to observe an early stretching on the northern margin onshore and offshore south china with large low angle faults which detach the mesozoic sediments either over triassic to early cretaceous granites or along the short limbs of broad folds affecting palaeozoic to early cretaceous series these early faults create narrow troughs filled with coarse polygenic conglomerate grading upward to coarse sandstone because these low angle faults reactivate older trends they vary in geometry according to the direction of the folds or the granite boundaries a later set of faults characterized by generally e w low and high angle normal faults was dominant during the eocene associated half graben basement deepened as the basins were filling with continental or very shallow marine sediments this subsequent direction is well expressed both in the north and the sw of the south china sea and often reactivated earlier detachments at places the intersection of these two fault sets resulting in extreme stretching with crustal boudinage and mantle exhumation such as in the phu khanh basin east of the vietnam fault a third direction of faults which rarely reactivates the detachments is ne sw and well developed near the oceanic crust in the southern and southwestern part of the basin this direction which intersects the previous ones was active although sea floor spreading was largely developed in the northern part and ended by the late miocene after the onset of the regional mid miocene unconformity known as mmu and dated around 15 5 ma latest miocene is marked by a regional basement drop and localized normal faults on the shelf closer to the coast the se margin of the south china sea does not show the extensional features as well as the northern margin detachments are common in the dangerous grounds and reed bank area and may occasionally lead to mantle exhumation the sedimentary environment on the extended crust remained shallow all along the rifting and a large part of the spreading until the late miocene when it suddenly deepened this period also corresponds to the cessation of the shortening of the nw borneo wedge in palawan sabah and sarawak we correlate the variation of margin structure and composition of the margin mainly the occurrence of granitic batholiths and mesozoic broad folds with the location of the detachments and major normal faults which condition the style of rifting the crustal boudinage and therefore the crustal thickness

palynology of the stonehaven group scotland evidence for a mid silurian age and its geological implications palynomorphs from the stonehaven group indicate a late wenlock to early ludlow age this is older than the currently accepted pridoli age based on fish and arthropods reasons for this discrepancy are discussed a previous correlative of the stonehaven group has been the old red sandstone of kerrera argyll however palynological assemblages from both kerrera and the adjacent succession at oban are in fact younger than that from stonehaven in being of latest silurian to earliest devonian age the palynomorphs from kerra and oban lie beneath the important geochronological tie point of the lorne lavas and suggest that the silurian devonian boundary is older than currently accepted

on the role of isostasy in the evolution of normal fault systems the footwalls of west dipping normal faults that separate the west central colorado plateau from the basin and range province record at least 5 7 km and perhaps as much as 15 20 km of west side up neogene uplift with an axis just 10 20 km west of undeformed plateau strata the uplift is expressed as folding and steep faulting in pre tertiary cratonic and disconformably overlying neogene strata forming a basement cored anticline and coincident topographic high on the western margin of the plateau the authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin profound isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains calling into question several assumptions fundamental to existing models of the evolution of normal fault systems

correlation for the lower palaeozoic the global correlation standards now agreed for the ordovician and silurian systems and partly so for the cambrian system are summarized correlation of the international series and stages with the traditional and revised british series and stages is reviewed as well as with those in north america laurentia

the palaeogeographical significance of specimens attributed to protolepidodendron scharyanum krejci lycopsida from the middle devonian of north xinjiang china morphology of the leaves of stem compressions originally attributed to protolepidodendron scharyanum from the middle devonian of north xinjiang china is reinvestigated the leaf is three dimensional consisting of one central abaxial segment and four lateral adaxial segments and does not conform to the once bifurcate leaf of protolepidodendron specimens are therefore transferred to leclercqia cf l complexa this is the first unequivocal report of the genus leclercqia in china based on complete leaf morphology the distribution of leclercqia is discussed demonstrating a more or less cosmopolitan genus in the middle devonian the middle devonian flora of north xinjiang shows great similarity to that of venezuela and north america and almost no relationship with that of yunnan south china

sequential faulting explains the asymmetry and extension discrepancy of conjugate margins rifted continental margins are the sites that record the thinning and break up of continents to form new oceans cesar ranero and marta perez gussinye use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this to crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy in which crustal thinning appears to be greater than the extension caused by brittle faulting by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins these authors use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this with crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy where crustal thinning seems to be greater than the extension caused by brittle faulting during early extension cold continental lithosphere thins and subsides creating rift basins if extension continues to final break up the split and greatly thinned plates subside deep below sea level to form a conjugate pair of rifted margins although basins and margins are ubiquitous structures the deformation processes leading from moderately extended basins to highly stretched margins are unclear as studies consistently report that crustal thinning is greater than extension caused by brittle faulting1 2 3 4 this extension discrepancy might arise from differential stretching of brittle and ductile crustal layers2 but that does not readily explain the typical asymmetric structure of conjugate margins5 6 in cross section one margin displays gradual thinning accompanied by large faults and the conjugate margin displays abrupt thinning but smaller scale faulting5 whole crust detachments active from early in the rifting could in theory create both thinning and asymmetry1 but are mechanically problematical furthermore the extension discrepancy occurs at both conjugate margins leading to the apparent contradiction that both seem to be upper plates to a detachment fault7 8 alternative models propose that much brittle extension is undetected because of seismic imaging limitations caused either by subseismic resolution faulting9 invisible deformation along top basement 100 km scale detachments8 or the structural complexity of cross cutting arrays of faults3 here we use depth migrated seismic images to accurately measure fault extension and compare it with crustal thinning the observations are used to create a balanced kinematic model of rifting that resolves the extension discrepancy by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins contrary to current wisdom the observations support the idea that thinning is to a first degree explained by simple andersonian faulting that is unambiguously visible in seismic data

subaqueous silicification of the contents of small ponds in an early devonian hot spring complex rhynie scotland the early devonian rhynie and windyfield cherts of northeast scotland originated as siliceous sinters deposited by hot springs silicification affected both subaerial and subaqueous environments preserving a diverse terrestrial and freshwater biota cherts originally deposited in small shallow pools can be recognised on the basis of both texture and fossil content textures comprise clotted and microcoprolitic textures bacterial coatings on plant axes that can be stromatolitic and a variety of bacterial and fungal meshworks the crustacean lepidocaris the euthycarcinoid heterocrania the charophyte alga palaeonitella and chytrid fungi are typical elements of the aquatic biota observations of modern hot springs in yellowstone national park wyoming u s a demonstrate that shallow ponds and streams on low angle outwash areas and dormant vent orifices provide suitable environmental analogues textures comparable to those described from rhynie are recorded from yellowstone sinters but examples of the

a devonian auriferous hot spring system rhynie scotland the early devonian rhynie hot spring system is the oldest known and is of the low sulphidation type it extends for at least 1 5 km along a major fault zone defining the western margin of an outlier of fluvial and lacustrine sediments plant bearing sinters and andesitic lavas the age of sedimentation and hydrothermal activity has been determined by palynological pragian and radio metric 396 12 ma techniques the outlier is a half graben with a complex stepped western margin the devonian rocks show intense hydrothermal alteration along the fault zone the main alteration minerals are quartz k feldspar calcite hematite and illitic and chloritic clays multiple chert veining and brecciation are widely developed and geyserite and vent material are also present pyrite occurs in veins and all alteration facies sinters and altered rocks contain high concentrations of au as sb hg w and mo gold occurs in arsenian pyrite and as sub micron particles in oxidized rocks the fluid s responsible for most hydrothermal alteration were near neutral with low sulphur and oxygen activities and dominated by meteoric water however incursions of high temperature 300 440 c magmatic fluids occurred with d 65 and 18 o around 8 5 34 s pyrite and initial 87 sr 86 sr ratios vein calcite lie mainly within the ranges 3 4 to 8 5 and 0 71138 to 0 71402 respectively these data indicate that late proterozoic dalradian metasediments are a likely source for s and sr but other sources are possible 13 c values for caliche and vein calcite imply derivation of carbon from non organic sources the rhynie cherts were deposited from a low salinity fluid of probable meteoric origin 18 o chert 13 1 to 16 5 which had interacted with the basement rocks and sediments high xe ar br cl and i cl ratios plant bearing chert yielded an 40 ar 39 ar ratio 292 1 0 6 significantly less than that of modem air and may be the first valid determination of a sample of ancient atmosphere

middle devonian lycopsids from high southern palaeolatitudes of gondwana argentina fossil plants are described from the upper part of the devonian lolen formation sierra de la ventana buenos aires province argentina in the area of estancia las acacias the sequence is composed mainly of dark grey shales and fossils were found in a single horizon where thin inter layered beds of fine reddish brown micaceous sandstones appear where the environment of marine deposition became more shallow the age of the lolen formation is presently established on the basis of brachiopods these being characteristic elements of the malvinokaffric realm from the gondwana lower devonian emsian the fossil plants are remarkably preserved given that they are in rocks that have undergone intense deformation the plants are identified as haplostigma sp and haskinsia cf h colophylla and suggest a middle devonian age givetian for the fossil bearing levels haskinsia identified on the basis of leaf morphology is the first well delimited middle devonian lycopsid genus described from argentina and the record from the most southerly palaeolatitude during the middle devonian haskinsia was distributed in tropical warm temperate and high southern latitude cool temperate zones

soil h2 and co2 surveys at several active faults in japan soil h2 and co2 surveys were carried out along seven active faults and around the aftershock region of the 2000 tottori ken seibu earthquake in japan diffuse co2 effluxes were also measured along one fault and around the 2000 aftershock region the results show highly variable h2 concentration in space and time and it seems that the maximum h2 concentration at each active fault correlates with fault activity as exemplified by the time of the latest big earthquakes even though observed h2 concentrations in four faults were markedly lower than those collected previously in the latter half of the 1970s it is evident that the higher h2 concentrations in this study are due to the addition of the fault gases comparing the chemical composition of trapped gases h2 5 20 and co2 h2 0 5 12 in fractured rocks of drill cores bored at the nojima fault a soil gas sample with the highest h2 concentration showed large amounts of the trapped fault gas diluted with atmospheric component the profile experiment across a fracture zone at the yamasaki fault showed higher h2 concentrations and lower co2 h2 ratios as was observed in soil gas from the fracture zone a few days after the 2000 tottori kei seibu earthquake no co2 effluxes related to the occurrence of earthquakes were observed at the aftershock region however only above the epicenter zone relatively high h2 concentrations in soil gases were observed

the age of the earliest club mosses the silurian baragwanathia flora in victoria australia it is argued that there is overwhelming evidence from a good graptolite record that the earliest club mosses on earth were of gorstian ludlow silurian age and that baragwanathia longifolia lang cookson and its associated flora persisted through the p idoli and into the early devonian showing some changes during this time

3d analogue modeling of the south china sea a discussion on breakup pattern the opening of the south china sea is one of the most important cenozoic events in se asia in order to investigate its tectonic evolution three analogue modeling experiments were compared the modeling results suggest that rifting pattern and orientation change of the rift zone were related to initial theological stratification affected by the ductile flow of silicone lower crust and honey asthenosphere the faults became flattened especially close to the breakup area we conjecture that the slope area may bear relatively hotter and thinner lithosphere than the shelf area from the beginning of rifting due to stretching and mantle upwelling associated with this regional extension which in turn lead to the change in initial rheological stratification and therefore the rifting pattern from shelf to slope in the experiments breakup developed first at isolated points which grew and coalesced to become a single spreading area the conjugate boundaries were either all concave or all convex where a rigid massif was located at the divergent boundary stretching history was different in this case the northern and southern areas thinned rapidly and developed into two deep troughs which may finally evolve into spreading centers the shape of the massif controls the orientation and boundary shape of the spreading area it is interpreted that crustal breakup was more viscous in style and the nw sub sea basin developed along the northern trough of the zhongsha xisha massif macclesfield bank c 2008 elsevier ltd all rights reserved

discussion on a high precision u pb age constraint on the rhynie chert konservat lagerstatte time scale and other implications journal vol 168 863 872 we welcome the contribution of parry et al 2011 concerning the age of the globally important rhynie hot spring system aberdeenshire scotland however although we accept that they have provided a valuable and robust u pb age constraint for the milton of noth andesite and the rhynie outlier stratigraphic succession we do not accept that they have constrained the timing of hot spring activity as suggested the geophysical trace of the unexposed milton of noth andesite indicates that it lies immediately adjacent to the rhynie fault zone and runs parallel to it for some 2 km it may even lie within the rhynie fault zone see discussion by rice ashcroft 2004 its stratigraphic position is therefore uncertain parry et al 2011 stated that the exact stratigraphic position is not important because their preferred stratigraphic locations lie within the tillybrachty sandstone and dryden flags formations both of which have consistently yielded spores belonging to the polygonalis emsiensis spore assemblage biozone this assertion is not valid the polygonalis emsiensis spore assemblage biozone may have lasted several million years and thus potentially there could be a significant hiatus between eruption of the andesite and the onset of hot spring activity they further assume that the andesite was linked to an andesitic magma chamber at depth which powered the hydrothermal system this remains speculation accepting the uncertainty in the stratigraphic position and by asserting a maximum thickness of sediment between the andesite and the rhynie cherts and a conservative deposition rate parry et al 2011 attempted to temporally link the andesite to the cherts by calculating the time interval represented by the intervening sediment the estimation of time depends on the absence of unconformities disconformities and faulting with such assumptions and uncertainties casting doubt on the thickness of the intervening sediments

devonian plants from colombia with discussion of their geological and palaeogeographical context plant fossils are described from the cuche formation eastern cordillera colombia in the area of floresta those identified as colpodexylon cf deatsii banks and cf archaeopteris sp suggest an earliest late devonian frasnian age for the formation these or similar taxa are also found in contemporaneous deposits in western venezuela and other elements of the venezuelan flora are found in a geographically intermediate locality all three devonian plant localities in the northwest of south america are within the colombian eastern cordillera and its northern extension the venezuelan perija range an area that has been integrated as a part of the so called eastern andean terrane or central andean province supposedly accreted to the autochthonous block of the guyana shield during the early jurassic or before although both invertebrates and plants from this terrane have strong affinities to north american and european assemblages and might be interpreted as implying a laurussian origin for the eastern andean terrane the evidence is not yet unequivocal with some authors postulating an in situ development of this province

organic chemical differentiation within fossil plant cell walls detected with x ray spectromicroscopy organic matter preserved in cell walls of permineralized plant fossils was analyzed by using scanning transmission x ray microscopy and spectroscopy at energies near the 1s absorption edge of carbon microchemical analyses were performed directly on cellulose acetate peels of the fossils preserving information on the anatomical distribution of organic materials individual tracheid walls in both eocene and early devonian fossils exhibit spatially distinct chemical zoning inherited from original wall biopolymers and cell wall microstructure molecular analysis of submicrometer domains using carbon x ray absorption near edge spectroscopy documents the differential distribution of hydroxylated aromatic and alcohol and or ether carbon in the inner and outer regions of tracheid walls this zonation reflects the deposition of lignin and structural polysaccharides in devonian plants indicating biochemical and developmental pathways similar to those of living tracheophytes

tectono stratigraphic terranes and detachment faulting of the south china sea and sulu sea abstract geoscientific data acquired from the south china sea and sulu sea areas by bgr since 1977 are compiled and interpreted as comprehensive data sets together with available information of commercial wells and drillsites of the ocean drilling program odp generalized stratigraphy and lithology are discussed and correlated with the interpreted seismic profiles on the basis of the stratigraphic and structural analysis 5 main tectono stratigraphic terranes are defined for the south china sea and 4 main terranes for the sulu sea respectively the dangerous grounds reed bank palawan nw borneo trough and palawan island represent terranes of continental origin which developed on the proto china margin by uniform sense low angle simple shearing within the crust in late cretaceous to early paleocene this rift was abandoned and a new westward propagating rift system developed north of the dangerous grounds reed bank area from the middle eocene to the oligocene early miocene together with seafloor spreading in the south china sea basin the leading edge of the southward drifting continental terranes collided with the late cretaceous to early eocene subduction complex of the northernmost terrane of the proto sulu sea continuous convergence of these terranes back arc spreading creating the se sulu sea terrane and the assumed anti clockwise rotation of borneo are responsible for the complex collision compression structures of the sulu sea terranes including the formation of splinters of oceanic crust major right lateral wrench systems are nnw sse running up to 500 km long and cut across most of the identified terranes wrenching presumably ceased 12 to 16 myr ago

non marine arthropod traces from the subaerial ordovician borrowdale volcanic group english lake district arthropod trace fossils are described from the borrowdale volcanic group a sequence otherwise devoid of faunal evidence two forms both made by the same probably myriapod like organism are assigned to the ichnogenera diplichnites and diplopodichnus the lithologies preserving the trace fossils are non marine and may have been deposited in a freshwater lacustrine environment some of the traces were probably made in temporarily emergent conditions the change from one form of trace to the other reflects drying out of the substrate the trace fossils probably record some of the earliest freshwater arthropods before the widespread colonization of land by the group

palaeoecology and plant succession in a borehole through the rhynie cherts lower old red sandstone scotland a cored borehole through the early devonian rhynie cherts at rhynie aberdeenshire ne scotland has revealed 53 chert beds in 35 41 m of core the cherts originated as sinters deposited by hot spring activity chert comprises 4 20 m of the cored succession with the thickest bed representing a single silicification event being 0 31 m thick and the thickest composite chert comprising six beds 0 76 m thick average chert bed thickness is 80 mm forty five plant bearing chert beds are interbedded with sandstones mudstones and shales the sediments were deposited on an alluvial plain with local lakes the area being periodically affected by hot spring activity plants initially colonized both subaerial sand and sinter surfaces rhynia gwynne vaughanii and horneophyton lignieri commonly form the basal parts of the profiles with subsequent colonization by other genera rhynia is commonly found in life position above originally sandy substrates and horneophyton above sinter surfaces the composition of the rhynie vegetation is compared with coeval assemblages and on the basis of current knowledge it is concluded that there is no unequivocal evidence that the plants were adapted to life in the stressed environments in the immediate vicinity of hot springs

continentward dipping detachment fault system and asymmetric rift structure of the baiyun sag northern south china sea abstract the rift architecture and deep crustal structure of the distal margin at the mid northern margin of the south china sea have been previously investigated by using deep seismic reflection profiles however one fundamental recurring problem in the debate is the extensional fault system and rift structure of the hyperextended rift basins baiyun sag and liwan sag within the distal margin because of the limited amount of seismic data based on new 3d seismic survey data and 2d seismic reflection profiles we observe an array of fault blocks in the baiyun sag which were tilted towards the ocean by extensional faulting the extensional faults consistently dip towards the continent beneath the tilted fault blocks and extensional faults a low angle high amplitude and continuous reflection has been interpreted as the master detachment surface that controls the extension process during rifting the continentward dipping normal faults evolved in a sequence from south to north generating the asymmetric rift structure of the baiyun sag the baiyun sag is separated from the oceanic domain by a series of structural highs that were uplifted by magmatic activity in response to the continental breakup at 33 ma and a ridge jump to the south at 26 24 ma therefore we propose that magmatism played a significant role in the continental extension and final breakup in the south china sea