fire ecology of the carboniferous tropical zone abstract fossil charcoal fusain indicating the occurrence of wildfire is common in the carboniferous rocks of north america and europe during the carboniferous these regions lay on the southern margins of the laurasian continent and within the tropical zone this study examines the facies distribution and botanical identity of charcoal in order to investigate the influence of fire on carboniferous tropical ecology new data from charcoal bearing units in eastern canada poland and the british isles are presented and synthesised with previously published data of charcoal occurrence tournaisian visean charcoal bearing strata were deposited in volcanic lacustrine alluvial plain and coastal marine environments in these deposits charred floras are dominated by pro gymnospermous plants whilst uncharred compressed or permineralised floras are dominated by lycopsids uncharred lycopsid remains were probably derived from wetland communities growing close to the depocentres whilst charred gymnospermous remains may have been sourced from well drained extrabasinal settings based on the vertical distribution of charcoal layers in annually laminated lacustrine deposits it is estimated that fires occurred with high frequency approximately every 3 35 years palaeoclimatic analysis indicates that southern laurasia at this time was subject to a seasonal monsoonal tropical climate such environments today are characterised by tropical savannas with high fire frequencies and early carboniferous fire prone gymnospermous plant communities may have represented a comparable vegetation biome namurian stephanian charcoal bearing strata were deposited in alluvial plain coastal plain and coastal marine environments channelised sandstone units interpreted as river channel deposits contain charcoal derived from cordaitaleans and conifers this assemblage records fires in extrabasinal coniferopsid forests mudstone units containing coals are interpreted as the deposits of floodbasins and peat mires hollow uncharred lepidodendrid stumps occur in this facies and contain lepidodendrid charcoal in the stump bases and lepidodendrid pteridosperm coniferopsid and sphenopsid charcoal outside the stumps this assemblage records fires in wetland lepidodendrid dominated forests lepidodendrid trunks comprising of a spongy parenchymatous core surrounded by dense periderm became hollowed out during fire events an estimate of fire frequency based on the vertical spacing of charcoal layers in coals implies that fires occurred every 105 1085 years in the peat mires palaeoclimatic analysis indicates that southern laurasia was subject to a humid tropical climate during the late carboniferous such environments today are characterised by tropical rainforests where fires occur rarely and late carboniferous communities may have represented a comparable biome

la ce and sm nd systematics of siliceous sedimentary rocks a clue to marine environment in their deposition la ce isotopic data together with sm nd isotopic data were determined on siliceous sedimentary rocks cherts in order to elucidate the rare earth element ree character of their sources and the nature of their depositional environments the cherts studied are a late archean chert from the gorge creek group in the pilbara block of western australia triassic cherts from central japan and cretaceous and paleogene deep sea cherts from the central pacific and the caribbean sea the archean chert from the gorge creek group shows chondritic ce and nd isotope ratios at its sedimentation age which indicate that its sources had a time integrated chondritic ree pattern triassic cherts from japan have initial ce and nd isotope ratios that show a direct derivation from their continental source on the other hand for cretaceous and paleogene deep sea cherts having negative ce anomalies in their ree patterns two different sources for ce and nd are revealed from their initial ce and nd isotope data ce from long term light ree depleted oceanic volcanic rocks and nd from light ree enriched continental rocks the reverse nature observed for deep sea cherts is considered to be a reflection of their depositional environment far from a continent these results confirm that the la ce isotopemore system is highly useful in determining the nature and cause of ce anomalies observed in marine sedimentary rocks such as chert less

new constraints on the 138la β decay constant based on a geochronological study of granites from the yilgarn block western australia abstract the decay constant of 138 la has been geochronologically determined using archean granites from the yilgarn block western australia rb sr and sm nd mineral isochron ages were obtained for the two granite samples which are nearly identical with the ion microprobe u pb zircon ages this agreement indicates that the closure date for these samples is the same within analytical error making them suitable for geochronological estimation of the decay constant for 138 la applying a new method of ce isotope analysis with analytical reproducibility of 0 008 la ce isotope data for the studied samples resulted in precise mineral isochrons based on these internal mineral isochrons and ages determined by other geological clocks the decay constant for 138 la was estimated to be 2 33 0 24 10 12 a 1 2

pedogenetic calcretes in early syn rift alluvial systems upper jurassic west cameros basin northern spain exceptional pedogenetic calcretes occur in the earliest syn rift sedimentary record tithonian of the west cameros basin these calcretes show different types of pedogenetic facies nodular massive laminar and brecciated pisolithic and microfabrics brecciated intraclasts carbonate nodules coated clasts and grains etched quartz grains rhizocretions pedotubules and fragmented alveolar septal structures in addition calcrete fragments have been observed in the conglomerate and sandy channelized deposits that form the alluvial systems indicating the reworking of previous calcrete deposits calcrete facies appear organized in several sequences developed over different architectural elements in three different types of alluvial systems the type of calcrete sequence is different depending on the architectural arrangement of each alluvial fan system laminar l mn s and brecciated pisolithic bp l s calcrete sequences are predominant in the alluvial sedimentary record of poorly channelized alluvial systems these calcretes are thick morphologically complex and laterally continuous due to the formation of long term stable subaerial surfaces favored by the intermittent behavior of the alluvial systems massive nodular m n s and laminar l mn s sequences are predominant in highly channelized alluvial systems and develop only locally in interchannel or floodplain areas where sedimentation stops temporally calcrete sequences in the distributive fluvial fan systems can be considered as poorly developed being massive nodular m n s and nodular n s after analyzing the location of these calcrete sequences in the studied record and their genesis and environmental significance their variations can be related to different autocyclic factors such as sedimentation rate channel network organization texture of the host sediment and water table influence also three main allocyclic factors such as climate tectonics and drainage area controlled the carbonate sedimentation and therefore the development of the calcretes

basin evolution and fault reactivation in the western cameros basin northern spain mesozoic cenozoic sedimentation in the cameros basin area strongly reflects tectonic factors the tectonic history is dominated by two principal extensional phases triassic late jurassic early cretaceous and strong pyrenean compression oligocene late variscan nw se and ne sw fault sets were repeatedly reactivated as dip slip and wrench faults respectively throughout extension and compression e w variscan thrust planes showed relatively minor reactivation in this area mesozoic fault control on sedimentation resulted in significant lateral variations in stratigraphic and sedimentological development variation in deformation style and thrust architecture reflects the differing responses of the laterally heterogeneous sequence to oligocene compression

early mississippian sandy siltstones preserve rare vertebrate fossils in seasonal flooding episodes this study is a contribution to the tw eed project tetrapod world early evolution and diversification a major research programme investigating the rebuilding of carboniferous ecosystems following a mass extinction at the end of the devonian smithson et al 2012 this study was funded by nerc consortium grant the mid palaeozoic biotic crisis setting the trajectory of tetrapod evolution led by professor jenny clack university museum of zoology cambridge and involving the universities of cambridge ne j022713 1 leicester ne j020729 1 southampton ne j021091 1 the british geological survey ne j021067 1 and the national museum of scotland

transitional changes in arborescent lignophytes at the devonian carboniferous boundary abstract it is usually considered that after the extinction of the devonian tree archaeopteri s no new arborescent lignophytes were established before the late tournaisian a reassessment of this pattern is presented here based on a three fold approach a re evaluation of the taxic diversity of tournaisian lignophyte trees based on descriptions of new plants from palaeotropical latitudes a study of the patterns of phenotypic changes occurring among early lignophytes using a principal coordinate analysis and a phylogenetic analysis of the affinities of the arborescent taxa the best supported results indicate that a substantial taxonomic and phenotypic diversity of arborescent lignophytes was already established in the first part of the tournaisian including some taxa that persisted until the serpukhovian two genera may have originated in the late devonian and crossed the devonian carboniferous boundary fewer originations and a decrease in phenotypic diversity occurred in the visean the phenotypic distinctiveness of tree stems compared with those of other growth forms in the lignophytes is assessed we propose a scenario in which the presence of lignophyte trees is continuous across the devonian carboniferous boundary with arborescent taxa distinct from archaeopteris already present in the latest devonian possibly in upland floras and diversifying significantly soon after the devonian carboniferous boundary supplementary material a list of taxa characters and matrices used in the principal coordinate analysis and phylogenetic analysis is available at http www geolsoc org uk sup18447

applicability of la ce systematics to planetary samples ce isotopic compositions in several terrestrial and extraterrestrial materials were determined in order to investigate the applicability of using ce as an isotopic tracer to geological processes owing to the low abundances of 138la and 138ce in nature our measurements of 138ce 140ce ratios of natural samples have relatively large 0 02 errors and the variations in ce isotope ratios were barely resolved a tenuous anticorrelation was observed between ece and end for terrestrial basalts and granites indicating that with some improvement in analytical techniques the ce isotopic composition may prove useful as a tracer for geological processes a very low ece predicted from the ce anomaly in the ree pattern of the khohar l3 chondrite nakamura and masuda 1973 was not observed in this study indicating that the ce anomaly may be caused by terrestrial contamination or alteration a low ece estimated for the source of nakhla is consistent with our previous estimate nakamura et al 1982 of a lree depleted source

evolution of high ca high sr c series basalts from grenada lesser antilles the effects of intra crustal contamination basaltic lavas from grenada lesser antilles may be divided into two series on the basis of cao mgo relations the c series roughly corresponds to the ankaramites or high sr series of the earlier literature and may be distinguished from the m series basalts by higher cao at a given mgo and by their strongly augite phyric nature compositional variation within the c series is dominated by fractional crystallization of augite and plagioclase but this was accompanied by assimilation of sedimentary material from the island arc crust the assimilation fractional crystallization process is well illustrated by an increase in 206pb 204pb from 18 6 to 19 4 with fractionation and correlated increases in nd sr zr sm and rb ba the most primitive members of the c series can not be generated from erupted m series near primary basalts but instead show evidence for an origin by olivine fractionation from high mg basalts never seen at the surface these appear to have been derived from a source similar to that of morb but enriched in 87sr and other hydrophile elements by dehydration of subducted lithosphere and in ree and radiogenic pb by a small component of subducted sediment

a new serpukhovian mississippian fossil flora from western argentina paleoclimatic paleobiogeographic and stratigraphic implications an uppermost mississippian serpukhovian fossil flora from western argentina is described for the first time its particular composition includes both warm climate plants typical from the pennsylvanian of gondwana namely pteridosperms sphenophytes as well as arboreous lycopsids and small lycopsids characteristic of cooler climates of pre serpukhovian times a warm temperate climate is inferred for this association which fills a time gap between those pennsylvanian and mississippian classic floras previously known the presence of tomiodendron nothorhacopteris kellaybelenensis and paracalamites allow the recognition of the paraca floral realm in argentina supporting the existence of a nonglacial paleoclimate period developed just before of the bashkirian moscovian gondwanan glaciation and after a latest visean glaciation it likewise would indicate the paleogeographic position of south west gondwana which would have acceded to a warm temperature latitudinal belt during serpukhovian times the recognition of this floral assemblage has relevant biostratigraphic and lithostratigraphic implications for the western margin of gondwana it defines a new zone for western argentina herein named frenguellia eximia nothorhacopteris kellaybelenensis cordaicarpus cesarii fnc zone which is recorded in the oldest known lithostratigraphic unit from the paganzo basin the loma de los piojos formation nom nov

frasnian plants from the dra valley southern anti atlas morocco anatomically preserved plant fragments are reported from devonian marine deposits exposed in the dra valley of southern anti atlas morocco associated conodont and tentaculite faunas indicate that the sediments yielding plants which consist of black shales with intercalated calcareous concretions are early frasnian in age and most probably represent zone 2 of the conodont zonation this is the first record of frasnian plants in north africa the specimens found all correspond to decorticated portions of axes six are referable to callixylon the organ genus corresponding to anatomically preserved axes of the progymnosperm tree archaeopteris based on wood characters especially ray structure they are assigned to the species c henkei formerly described from the famennian of europe one single specimen is compared to xenocladia a cladoxylopsid genus previously known from the middle devonian of europe usa and kazakhstan interestingly archaeopteridales and cladoxylopsida are two groups that dominate the younger plant assemblages of famennian age recently described from the eastern anti atlas callixylon henkei type axes occur both in the frasnian and in the famennian deposits of the anti atlas and they are all devoid of growth rings these results are in accordance with a close position of gondwana and euramerica during late devonian times

late palaeozoic terrestrial habitats and biotas the effect of changing climates abstract the 2009 lyell meeting held at the geological society london reviewed various aspects of the interrelationship between late palaeozoic habitats biotas and climates the following five papers are based on some of the presentations given at the meeting

palaeozoic landscapes shaped by plant evolution fluvial landscapes diversified markedly over the 250 million years between the cambrian and pennsylvanian periods the diversification occurred in tandem with the evolution of vascular plants and expanding vegetation cover in the absence of widespread vegetation landscapes during the cambrian and ordovican periods were dominated by rivers with wide sand beds and aeolian tracts during the late silurian and devonian periods the appearance of vascular plants with root systems was associated with the development of channelled sand bed rivers meandering rivers and muddy floodplains the widespread expansion of trees by the early pennsylvanian marks the appearance of narrow fixed channels some representing anabranching systems and braided rivers with vegetated islands we conclude that the development of roots stabilized the banks of rivers and streams the subsequent appearance of woody debris led to log jams that promoted the rapid formation of new river channels our contention is supported by studies of modern fluvial systems and laboratory experiments in turn fluvial styles influenced plant evolution as new ecological settings developed along the fluvial systems we suggest that terrestrial plant and landscape evolution allowed colonization by an increasingly diverse array of organisms

a classification of rhizogenic root formed calcretes with examples from the upper jurassic lower cretaceous of spain and upper cretaceous of southern france reply abstract studies of fluvial sequences from the upper jurassic and lower cretaceous of the cameros basin spain and the upper cretaceous of the aquitaine basin france have revealed large numbers of calcrete profiles which have formed wholly or largely through the action of plant root calcification those from spain have formed by the calcification of root mats whereas those from france resulted from the accumulation of calcified root cells microcodium these root related rhizogenic calcretes developed in stages allowing developmental time series chronosequences to be identified contrasting with existing models for calcrete profile growth they provide unique examples where vegetation has been the dominant control on profile development and probably indicate specific vegetation types and palaeoecological settings the role of root activity in forming some quaternary calcretes is also discussed

environmental influences on the stable carbon isotopic composition of devonian and early carboniferous land plants abstract systematic analysis of the stable carbon isotopic composition of fossil land plants 13cp has the potential to offer new insights regarding paleoclimate variation and plant environment interactions in early terrestrial ecosystems 13cp was measured for 190 fossil plant specimens belonging to 10 genera of early to late devonian age archaeopteris drepanophycus haskinsia leclercqia pertica psilophyton rhacophyton sawdonia tetraxylopteris and wattieza and 2 genera of early carboniferous age genselia and rhodeopteridium collected from sites located mainly in the appalachian basin 22 30 s paleolatitude for the full carbon isotopic dataset n 309 13cp ranges from 20 3 to 30 5 with a mean of 25 5 similar to values for modern c3 land plants in addition to a secular trend 13cp exhibits both intra and intergeneric variation intrageneric variation is expressed as a small mean 0 45 13c enrichment of leaves and spines relative to stems that may reflect differential compound specific compositions intergeneric variation is expressed as a much larger to 5 spread in the mean 13cp values of coeval plant genera that was probably controlled by taxon specific habitat preferences and local environmental humidity among early devonian taxa sawdonia yielded the most 13c depleted values 27 1 1 7 reflecting lower water use efficiency that was probably related to growth in wetter habitats and leclercqia haskinsia and psilophyton yielded the most 13c enriched values 23 0 1 6 22 3 1 3 and 24 8 1 6 respectively reflecting higher water use efficiency probably related to growth in drier habitats

early syn rift evolution in the west cameros basin upper jurassic nw iberian range spain and pedogenetic calcretes in early syn rift alluvial systems upper jurassic west cameros basin northern spain discussion the brezales formation originally defined as the senora de brezales formation platt 1986 1990 see also martin closas and alonso millan 1998 clemente vidal 2010 comprises a syn rift alluvial fan succession displaying strong lateral and vertical facies changes sacristan horcajada et al 2015 primarily relate these variations to drainage area and basin scale tectonics they suggest that source area lithology can be considered as a constant factor in this regard it is not clear why sacristan horcajada et al fail to discuss the work of platt 1995 which showed how sedimentation and clastic supply was strongly controlled by subcrop geology as well as kilometer and outcrop scale faulting deposition across the area recorded progressive erosion and unroofing of the underlying succession and varying subcrop beneath the complex cimmerian unconformity in the south of the basin a progradational coarsening upwards facies trend noted by sacristan horcajada 2015 reflects local reworking of upper oxfordian sandstones at the unconformity leading to the deposition of red bed sandstones in the basal section of the brezales formation only later did erosion of deeper lying marine jurassic limestones result in the deposition of conglomerates an example occurs at espejon where the brezales formation is not absent as suggested by sacristan horcajada et al 2015 but features a basal

early syn rift evolution in the west cameros basin upper jurassic nw iberian range spain abstract alluvial systems are sensitive sedimentary systems that can preserve useful information about tectonics drainage area lithology and size and climate however research on this subject over the last three decades has made it evident that the interaction of these three factors and their control over the alluvial architecture and facies are complex the stratigraphic and sedimentological analysis of the earliest syn rift sedimentary record tithonian in the west cameros basin has confirmed that sedimentation during the beginning of extension in this area took place in a series of halfgraben basins in which three different types of fan shaped alluvial systems were deposited two relatively large systems specifically a highly channelized alluvial fan system and a distributive fluvial fan system changing downstream to an axial tributary fluvial system were the exception and small poorly channelized alluvial fan systems were the norm a semiarid climate is inferred during this earliest syn rift sedimentary record from the steady and extensive calcrete development this semiarid climate should play an important role both in how coarser sediment discharges to the rift halfgraben basins occurred and in the dominant transverse organization of the alluvial depositional systems however the climate and source area lithology can be considered steady factors so the main factors considered as the cause of these sedimentary and architectural heterogeneities are the tectonics and drainage area sizes and specifically the different behavior of each extensional structure in terms of the rate of tectonic uplift and subsidence this indicates how fault activity and drainage area sizes during the earliest stages of a rift system can generate high degrees of heterogeneity in the architecture of alluvial basins and how this heterogeneity is recorded by the alluvial systems in the form of differences in their facies association and architecture therefore this work concludes that both tectonics and catchment sizes exerted primary control on the sedimentary characteristics of associated alluvial systems in basins generated from this type of extensional setting and care must be taken when making climatic and tectonic interpretations using the sedimentary record of these alluvial systems because many changes that traditionally have been attributed to climate variability can be explained solely by the differential behavior of each extensional structure and or changes in its associated drainage area

evolution of fixed channel alluvial plains in response to carboniferous vegetation the establishment of terrestrial plants during the palaeozoic era was one of the most significant changes to the earth system during the phanerozoic eon the continuing evolution and expansion of land plants irrevocably altered the alluvial landscape the broad unconfined and unconsolidated blankets of coarse sediment found at the start of the cambrian period were replaced by a diverse array of braided and meandering channel styles and stable floodplains by the end of the devonian period here we show that the first appearance of a sedimentary facies suite attributed to low energy organic rich river systems with multiple channels and stable alluvial islands known as anabranching or anastomosing rivers occurred during the carboniferous period our field studies and literature review demonstrate that the appearance of these rivers coincides with the continuing evolution of tree like plants we suggest that increased floodplain stability and new triggers for channel avulsion were provided by the increase in complexity and diversity of root assemblages density of floodplain forests and production of woody debris associated with expansion of arborescence we conclude that the expansion of tree habitats led to the crossing of a threshold in vegetative control of floodplain and river morphology during the carboniferous

lacustrine carbonates and pedogenesis sedimentology and origin of palustrine deposits from the early cretaceous rupelo formation w cameros basin n spain the berriasian rupelo formation of the w cameros basin consists of a 2 200 m thickness of marginal and open lacustrine carbonate and associated deposits open lacustrine facies contain a non marine biota with abundant charophytes both stems and gyrogonites ostracods gastropods and rare vertebrates carbonate production was mainly biogenic the associated marginal lacustrine palustrine facies show strong indications of subaerial exposure and exhibit a wide variety of pedogenic fabrics silicified evaporites found near to the top of the sequence reflect a short hypersaline phase in the lake history the succession was laid down in a low gradient shallow lake complex characterized by wide fluctuations of the shoreline carbon and oxygen stable isotope analyses from the carbonates show non marine values with ranges of 13 from 7 to 11 and 18 from 3 to 7 5 differences in the isotopic composition of open lacustrine carbonates are consistent with sedimentary evidence of variation in organic productivity within the lake analyses from the entire sample suite plot on a linear trend isotopic compositions become lighter with increasing evidence of pedogenic modification this suggests progressive vadose zone diagenesis and influence of meteoric waters rich in soil derived co2 the stable isotope data thus support evidence from petrography and facies relations that palustrine limestones form through pedogenic modification of lake carbonates

fan surface dynamics and biogenic calcrete development interactions during ultimate phases of fan evolution in the semiarid se spain murcia abstract pleistocene alluvial fan surfaces of the campo de cartagena mar menor basin murcia se spain are capped by thick mature calcretes calcrete profiles consist mainly of six different horizons prismatic chalky nodular massive laminar and coated gravels petrographic study of the calcretes has shown the occurrence of features such as alveolar septal structures calcified filaments coated grains spherulites calcified root cells and calcispheres that indicate the biogenic origin of the calcretes mainly induced by plant root related microbial activity the calcretes studied were formed initially in the soil and represented the k horizon development of the calcrete profiles took place in six main stages and was driven by multiple phases of soil formation erosion and reworking the relationships between these processes caused the formation of different calcrete profiles in proximal and distal fan areas in the distal areas which are controlled by limited distal fan aggradation episodic sediment input buried previously developed calcretes and generated new space for calcrete growth by plants growing in the overlying unconsolidated materials this allowed the renewal of calcrete formation and it led to the development of complex composite profiles which are thicker than in proximal areas where surface stabilisation and or dissection enabled calcrete reworking and brecciation these processes of erosion sedimentation reworking and renewed calcrete formation initiated by vegetation were repeated through time they explain the complex macro and microstructures of these calcretes and indicate that calcrete development even reaching mature stages can start before the fan surface is completely abandoned but it requires episodic sedimentation eventually distal fan aggradation and continuous calcrete development throughout the entire fan surface led to the ultimate fan surface induration controlling subsequent landscape evolution so fan surface calcretes cannot be envisaged as simple top surface carbonate accumulations but as complex feedback systems in which pedogenic biogenic and sedimentary processes interact in response to the evolving fan surface dynamics during the terminal phases of fan development in semiarid environments

sources of iron formations in the archean isua and malene supracrustals west greenland evidence from la ce and sm nd isotopic data and ree abundances abstract isotopic ratios of ce and nd and abundances of rare earth elements rees and ba are reported for the iron formations of the archean isua and malene supracrustals west greenland it is suggested that the sm nd system of the isua iron formations was disturbed by metamorphisms at 1680 ma oxide facies iron formation and 2740 ma carbonate facies iron formation however the malene iron formation samples show similar nd isotopic ratios and ree patterns indicating that they suffered little disturbance after deposition at 2800 ma initial ce and nd values estimated at 2800 ma for the malene iron formation are close to chur chondritic uniform reservoir of 3 samples two show negative ce and positive nd and the other gives chondritic ce and negative nd these initial values suggest that the sources for the malene iron formation had a chiefly chondritic or rather mantle like depleted nature without a notable long term negative ce anomaly similar ree features are indicated for the sources of the isua iron formation by the estimated initial ce and nd values at 3760 ma of these samples

the plant fossil record reflects just two great extinction events five great taxonomic extinctions the so called big five mass extinctions are widely recognized in life history at the end of the ordovician frasnian late devonian permian triassic and cretaceous all of them were originally identified in the marine fossil record and have been interpreted as the result of abrupt global environmental changes previous evidence has suggested that terrestrial biota were also subjected to ecological disruption during these events but it is unknown whether they suffered the same level of large scale taxonomic disruption as marine organisms here we show that the plant fossil record in fact only provides evidence of two mass taxonomic extinction events one through the carboniferous permian transition the other during middle late permian times this differs significantly from the mass extinctions recognized in the marine realm and suggests that vascular plants have a special capacity for surviving abrupt environmental changes

considering river structure and stability in the light of evolution feedbacks between riparian vegetation and hydrogeomorphology river ecological functioning can be conceptualized according to a four dimensional framework based on the responses of aquatic and riparian communities to hydrogeomorphic constraints along the longitudinal transverse vertical and temporal dimensions of rivers contemporary riparian vegetation responds to river dynamics at ecological timescales but riparian vegetation in one form or another has existed on earth since at least the middle ordovician c 450 ma and has been a significant controlling factor on river geomorphology since the late silurian c 420 ma on such evolutionary timescales plant adaptations to the fluvial environment and the subsequent effects of these adaptations on fluvial sediment and landform dynamics resulted in the emergence from the silurian to the carboniferous of a variety of contrasted fluvial biogeomorphic types where water flow morphodynamics and vegetation interacted to different degrees here we identify several of these types and describe the consequences for biogeomorphic structure and stability i e resistance and resilience along the four river dimensions of feedbacks between riparian plants and hydrogeomorphic processes on contrasting ecological and evolutionary timescales

ce isotope ratios of n type morb abstract isotope ratios of ce nd and sr and light rare earth elements la ce nd and sm concentrations were measured for sixteen n type morb samples from dsdp sites 420 421 429 597 b and 597 c east pacific rise 504 b costa rica rift and 395 519 a 522 b 562 and 564 mid atlantic ridge all the samples were confirmed as n type morb based on nd and sr isotope ratios and lree patterns the ce isotope ratios ranged from 0 0225616 ce 1 6 to 0 0225633 ce 1 0 averages of ce and nd of n type morb were 1 4 and 9 5 respectively the average of ce is quite different from previous estimates we propose that ce 1 4 should be used as the typical morb ce isotope ratio in future studies

late devonian and early carboniferous alpha diversity ecospace occupation vertebrate assemblages and bio events of southeastern morocco abstract the late devonian was a time of dramatic environmental perturbations affecting marine ecosystems both the kellwasser latest frasnian and the hangenberg crises latest famennian are primarily reported as phases of drastic decreases in marine diversity while the hangenberg crisis is also described as a bottleneck in vertebrate evolution fossil bearing localities with upper devonian strata are of great interest to assess variations in the effects of environmental perturbations on biodiversity for this purpose we examined changes in alpha diversity and ecospace utilization of 21 famennian late devonian and early tournaisian early carboniferous invertebrate associations containing 9828 specimens from madene el mrakib and aguelmous southern maider basin northeastern anti atlas morocco where some layers yield exceptionally preserved gnathostome remains both the invertebrate and vertebrate associations contain predominantly opportunistic and pelagic taxa indicating oxygen depletion near the seafloor in this region nevertheless the ecospace extension was fluctuating and correlated with regional and or global sea level changes and oxygenation of bottom waters in the maider basin the ecospace was depleted after and during several bio events such as the kellwasser and hangenberg crises the annulata event middle famennian as well as during the early tournaisian abiotic as well as biotic changes instability of the invertebrate ecosystem are considered to have influenced famennian vertebrate diversity because they were more or less directly dependent on invertebrates as a food source

chemical composition of hal an isotopically unusual allende inclusion thirty seven major minor and trace elements were determined by inaa and rnaa in samples of hibonite black rim and portions of friable rim from an unusual allende inclusion hal the peculiar isotopic mineralogical and textural properties of hal are accompanied by very unusual trace element abundances the most striking feature of the chemistry is the virtual absence of ce from an inclusion otherwise highly enriched in ree compared to cl chondrites hal is also depleted in sr ba u v ru os and ir relative to other refractory elements of the lithophile elements determined which are normally considered to be refractory in a gas of solar composition sr ba ce u and v are the most volatile in oxidizing gases the distribution of ree between hibonite and rims seems to have been established when hibonite and other refractory minerals were removed at slightly different temperatures from a hot oxidizing gas in which they previously coexisted as separate grains on the basis of hal s chemical and isotopic composition possible locations for the chemical and mass dependent isotopic fractionation are in ejecta from the low temperature helium burning zone of a supernova and in the locally oxidizing environment generated by evaporation of interstellar grains of near chondritic chemical composition

cerium isotope geochemistry of ocean island basalts the source of ocean island basalts is one of geology s major problems and many different models have been proposed one of these involves recycling of continental and oceanic crustal material into the mantle source of ocean island basalt magmas1 2 island arc basalts are an important link in the chain of evidence that supports this model as they display isotope signatures in common with both ocean floor sediment2 4 and ocean island basalts1 5 but hafnium isotope data6 appear either to place severe restrictions on the quantity of sedimentary material recycled into the mantle or to demand very thorough homogenization of this material during the subduction process the lanthanum cerium isotope method7 offers a prospect of applying similar constraints to the recycling of different sediment types into the mantle based on cerium and neodymium isotope systematics here i report cerium isotope ratios for eight ocean island basalts when plotted against published neodymium isotope data these form a mantle array of compositions which indicates coherent behaviour of the two elements during mantle differentiation this precludes the recycling into the deep mantle of ocean floor sediments with a large net cerium anomaly

processes facies and architecture of fluvial distributary system deposits abstract there is evidence from the stratigraphic record of examples of fluvial deposits that were the products of deposition from river systems which had decreasing discharge down flow and transitions from proximal channelised to distal unconfined flow these deposits form fan shaped bodies several tens of kilometres in radius and their stratigraphic architecture is aggradational with no evidence of deep incision driven by base level fall the fluvial systems that generated these deposits formed under conditions for which there is no complete analogue today an endorheic basin with a relatively arid climate adjacent to an uplifted area with higher precipitation a conceptual model for fluvial systems of this type has therefore been built on the basis of outcrop examples and a consideration of the controls on sedimentation proximal areas are characterised by amalgamated coarse pebbly and sandy channel deposits with little preservation of overbank facies channel dimensions are generally smaller in the medial areas but sizes are variable deposits are of braided meandering and simple channels which show varying degrees of lateral migration the channel fills may be mud or sand with overbank flow processes playing an important role in filling channels abandoned on the floodplain after avulsion the proportion of overbank deposits increases distally with sheets of sand deposited as lateral and terminal splays by unconfined flow interconnection of sandstone bodies is poor in the distal areas because channel fill bodies are sparse small and are not deeply incised the radial pattern of the sediment body forms by the repeated avulsion of channels active channels build up lobes on the alluvial plain and rivers switch position to follow courses on lower lying areas the term fluvial distributary system is here used to describe a river system which has a downstream decrease in discharge and has a distal zone which is characterised either by terminal splays on to a dry alluvial plain or a lake delta during periods of lake highstand

origin of negative ce anomalies in barberton sedimentary rocks deduced from la ce and sm nd isotope systematics abstract the origin of sedimentary rocks with negative ce anomalies among several samples derived from the barberton greenstone belt 3250 ma south africa was investigated using la ce and sm nd isotopic systematics together with light rare earth element lree abundances negative ce anomalies were recognized in two sedimentary rocks a banded ferruginous chert and a shale their ce ce values are 0 40 and 0 81 respectively initial ce isotopic ratio calculated for the ferruginous chert 138 ce 142 ce 3250 ma 0 0225059 is far lower than chur value at 3250 ma and even the value at earth formation 138 ce 142 ce chur 4560 ma 0 0225409 the calculated initial ce isotopic ratio for the shale with a ce anomaly is also lower than that of other rocks without ce anomalies these results indicate that the negative ce anomalies were not inherited from an archean redox change but occurred following later episodes of alteration two possible formation models were examined to estimate a plausible occurrence age for the negative ce anomalies one is characterized by ce extraction and the other is by an addition of la nd and sm both models indicate that negative ce anomalies arose before 1100 ma this study suggests that la ce isotopic systematics provides a unique tool to constrain the occurrence age of negative ce anomalies observed in archean sedimentary rocks and gives some hints about the redox condition in the archean ocean and the evolution of the earth

petrology of 1977 to 1998 eruptions of piton de la fournaise la reunion island abstract geochemical and petrological variations in 35 historical eruptions from the april 1977 eruption to the march september 1998 eruption at piton de la fournaise have been analyzed for their major elements abundances mineralogical compositions and oxygen isotopes during these 21 years samplings were repeated several times during eruptions as well as temperature measurements since the end of 1977 to 1998 all erupted lavas except 1998 hudson basalt belong to the group of the steady state basalts however evidences for small degrees of differentiation can be observed during a single eruption the earliest lava emitted contains less phenocrysts and has almost always a lower mgo mgo mgo feot than the lavas emitted later suggesting that it is more differentiated from one eruption to the next between 1977 and 1998 bulk compositions are more and more differentiated towards the first lava of 1998 a process of low pressure fractional crystallisation involving small proportions of olivine clinopyroxene and plagioclase allows to explain this evolution a major result of our study is to show that this evolution does not correspond to a unique fractionation trend over the considered period different types of magmas have been distinguished the first magma type erupted from october 1977 to november 1987 was richer in potassium 0 82 wt in average than the second one and apparently derived from the liquid of the 1977 oceanite the second magma type erupted from february 1988 to september 1998 was poorer in k 2 o 0 69 wt in average in march 1998 a third magma type hudson basalt erupted simultaneously with the second one hudson basalt has undergone a wehrlitic fractionation and is supposed to come from a deeper magma reservoir than other erupted magmas for this period from 1977 to 1998 the 18 o of lavas progressively decreases with time together with the increasing chemical differentiation of the magmas by low pressure fractional crystallisation this variation agrees with the hypothesis of magma contamination at shallow level in the altered volcanic edifice vlastelic i deniel c bosq c telouk p boivin p bachelery p famin v staudacher t 2009 this issue pb isotope geochemistry of piton de la fournaise historical lavas journal of volcanology and geothermal research 184 63 78 this issue overall petrological variations are in good agreement with a model of a shallow reservoir discontinuously supplied between 1977 and 1998 the speed of the variations the coexistence of different liquids the chemical evolution of the lavas during the same eruption lead us to favour a model of chemically stratified reservoir constituted by a complex of dykes sills and laccoliths close to the surface and located above larger magma bodies

la ce dating of lewisian granulites to constrain the 138la β decay half life the isotope 138la makes up 0 089 of natural lanthanum and exhibits a branched decay by to 138ce and electron capture to 138ba the la ce isotope scheme is a potentially powerful adjunct to the sm nd method for petrogenetic studies but the best determination by counting of the decay half life of la 3 02 x 1011 yr 1 is in conflict with geological half life determinations based on la ce and sm nd mineral isochrons2 4 to test these alternatives i determined a six point la ce isochron on whole rock samples of lewisian granulite facies archaean gneiss from nw scotland here i report based on a half life of 3 02 1011yr a la ce age of 2 990 400 myr 2 which falls very well within the error of a whole rock sm nd date on lewisian granulites of 2 895 100 myr 2 this half life equivalent to a la decay constant of 2 30 10 12 yr 1 is therefore recommended for geological application of the ce isotope method

famennian charcoal of belgium abstract charcoal results from an incomplete combustion of biological material in anoxic conditions and has a high potential for three dimensional cellular preservation most of the belgian upper devonian flora is known through compression fossils mainly from the siliciclastic evieux formation no charcoal bearing layers had been reported to date we have recently identified organic rich beds from three late famennian localities val dieu quarry trooz quarry and arbre quarry the three localities are described from the sedimentological point of view the arbre and trooz quarries contain allochthonous specimens of charcoalified wood they are identified as callixylon in arbre in trooz the specimen belongs either to an undescribed species of callixylon or to another taxon of woody pro gymnosperm the val dieu quarry by contrast yielded a more diverse charcoalified assemblage including leafy remains branches and fertile axes related to ferns sphenopsids and pro gymnosperms this material experienced moderate transportation before burial the val dieu assemblage is exceptional for late devonian deposits as it represents a moderately disturbed litter interpreted as representing a swamp environment and its proximal margins this assemblage is an illustration that the fossil charcoal record can provide a unique opportunity to study in fine detail the evolutionary history and past diversity of life

isotope geochemistry of quaternary deposits from the arid lands in northern china abstract quaternary deposits of various types lacustrine desert sand river loess and loess like deposits from the southwestern tarim basin north tianshan northeast china and the central loess plateau exhibit an nd 0 range from 5 to 12 8 and a 147 sm 144 nd range from 0 110 to 0 140 their nd depleted mantle model ages are between 1 50 and 1 92 ga with a mean value of 1 7 ga th sc ratios vary over a wide range from 0 1 to 2 comparison of these geochemical signatures with those of the old australian shales and modern pacific ocean dust suggests a continuous input of mantle derived material into the crust over geological time the deposits from the north tianshan show clearly different chemical and isotopic features with significantly higher sm nd high 143 nd 144 nd low 87 sr 86 sr and low la lu and th sc ratios relative to those in the deposits from the other areas this indicates a geological control on the local source which has an overall young age and an enrichment of basic components the ce 0 values of two loess samples from the central loess plateau are 1 8 and 3 9 corresponding to depleted mantle model ages of 2 2 and 3 4 ga like the rb sr system the evolution of the la ce isotopic system in the crust may be to some extent decoupled from the sm nd system due to la ce fractionation by sedimentary processes the loess deposits and the desert sand are not distinguishable in isotopic composition but show somewhat different chemical compositions we conclude that the loess can have originated from desert processes since the difference in the chemistry of the desert sand and loess may result from mineral sorting during desert processes and aeolian transportation the loess deposits on the central loess plateau chemically and isotopically resemble the desert loess deposits in the southwestern tarim basin but do not resemble those of the north tianshan accordingly the loess on the plateau may have a source region in the tarim basin but clearly not in the north tianshan

mare glasses from apollo 17 constraints on the moon s bulk composition two previously unreported varieties of mare volcanic glass have been discovered in apollo 17 samples twenty three chemical types of volcanic glass have now been analyzed from the six apollo landing sites these volcanic glasses which may be samples of primary magmas derived from the differentiated lunar mantle define two linear arrays that seem to reflect regional if not global regularities among the source regions of these melts additional systematics among these glasses have been used to estimate the bulk composition of the moon the results suggest that the refractory lithophile elements e g ca al ti ree u are present at abundances of 1 7 chondrites the silicate portion of the moon appears to have a major element composition similar to a volatile si na k depleted earth s upper mantle the theory involving an earth fission origin of the moon can be tested further through trace element analyses e g ni on the volcanic glasses and through determination of the n 36ar ratio and noble gas isotopes from primordial lunar gas trapped within vesicles associated with mare volcanic glass

the geochemistry of lewisian marbles summary to rectify the dearth of published petrographical and analytical data for lewisian marbles 307 samples from nearly all outcrops known have been examined in thin section and 114 samples analysed for 35 elements lewisian marbles can be divided texturally into 1 macrocrystalline generally white pure to silicate rich eg from glenelg 2 microcrystalline often coloured ornamental pure to silicate rich eg from iona 3 microbrecciated grey crushed fine grained silicate opaque rich eg from the loch maree group lmg lewisian marbles are geochemically typical of ancient carbonates tending to have lower contents of trace elements notably sr than younger eg scottish dalradian marbles whereas all analyzed marbles from the south harris and coll foreland outcrops and from the glenelg and kintail inliers are dolostones mgo 15 20 sio 2 5 15 those of the eastern inliers glen strathfarrar shinness are pure limestones mgo 2 eg scardroy inlier microbrecciated lmg marbles flowerdale belt of gairloch furnace belt of loch maree have notably higher chalcophile and siderophile element contents than macrocrystalline marbles in adjacent belts cloiche of gairloch gleann tulacha of loch maree aside from such local differences however limestones and dolostones of the inliers lmg and remaining foreland reveal few non trivial differences in composition moreover lewisian marbles collectively show strong pearson and spearman correlations between elements concentrated in accessory phases eg y la ce k rb al fe co v given established secular variations in the chemistry of global carbonate rocks these relationships between both marble groups and chemical variables are difficult to explain if some lewisian marbles eg s harris represent late scourian and others eg lmg early proterozoic sediments they may provide a tentative hint that most lewisian marbles were deposited contemporaneously

the role of fungal biomineralization in the formation of early carboniferous soil fabrics paleosols in the lower carboniferous limestones of south wales commonly contain needle fibre calcite which is an unusual form of calcite recently shown to form by the calcification of fungal hyphae in present day soils the needle fibre calcite occurs in two associations in the paleosols as coatings on sediment grains and as rhizocretions the former can be compared with the microbial grain coatings of quaternary calcretes the latter represent the sites of fungal coats on roots and are interpreted as probable ectomycorrhizae a symbiotic fungal sheath root association these findings suggest that biomineralization was important in the formation of soil fabrics during the carboniferous as it is in present day soils

combined la ce and sm nd isotope systematics in petrogenetic studies a theoretical model is presented for the coupled evolution of cerium and neodymium isotopes in terrestrial rocks data presented for samples ranging from mid ocean ridge basalts to continental metamorphic rocks show that while mantle derived rocks are dispersed on a ce nd diagram continental crustal rocks form a clearly defined mantle array as analytical techniques improve cerium isotopes will provide valuable constraints in studies of petrogenesis and crustal evolution

cyclic changes in pennsylvanian paleoclimate and effects on floristic dynamics in tropical pangaea abstract wetland floras narrowly define perceptions of pennsylvanian tropical ecosystems the so called coal age such wetlands reflect humid to perhumid climate leading to characterizations of pennsylvanian tropics as everwet swampy these views are biased by the high preservation potential of wetlands sedimentation patterns paleosols and fossil floras indicate the presence of vegetation tolerant of subhumid to dry subhumid perhaps semi arid climate in basins between peat formation times understanding the significance of this seasonally dry vegetation has suffered from conceptual and terminological confusion a clearer view has emerged as models for framing the data have improved basinal floras typical of seasonally dry conditions relatively low soil moisture regimes are well documented but mainly from isolated deposits some of the earliest dominated by primitive pteridosperms flozfern floras occur in clastic rocks between european early pennsylvanian coal beds later early pennsylvanian fern cordaitalean vegetation different from coal floras is preserved in marine goniatite bullions conifers are first suggested by late mississippian potoniesporites pollen about the same time in north america broadleaf foliage lesleya and megalopteris occur in basin margin settings on drought prone limestone substrates the best known xeromorphic floras found between coal beds appear in the middle through late pennsylvanian containing conifers cordaitaleans and pteridosperms the middle pennsylvanian appearances of this flora are mainly allochthonous though parautochthonous occurrences have been reported parautochthonous assemblages are mostly late pennsylvanian the conifer flora became dominant in western and central pangaean equatorial lowlands in earliest permian location of the humid perhumid wetland flora during periods of relative dryness though rarely discussed is as or more perplexing than the spatial location of seasonally dry floras through time wetland plants had few migratory options and possibly survived in small refugia within and outside of basins coupled oscillations in climate sea level and vegetation were driven most likely by glacial interglacial fluctuations perhaps controlled by orbital cyclicity

geochemistry of ce and nd isotopes and ree abundances in the amitsoq gneisses west greenland abstract ce and nd isotope ratios and rare earth element ree abundances were determined on the archean amitsoq gneisses west greenland samples used were four grey gneisses two white gneisses and one banded gneiss from the isukasia area and one banded grey gneiss from the godthaab area all of the amitsoq gneisses studied here have negative e nd and positive e ce values for the present nd and ce isotopic compositions calculated initial values of e nd and e ce give the following evolution histories of the ree patterns the grey gneiss in the godthaab area is considered to have been derived from a chondritic source with la ce n and nd sm n ratios of 1 1 0 4 and 0 99 0 02 in the chondrite normalized values on the other hand it is concluded that the grey gneisses and the banded gneiss in the isukasia area were formed from a light ree depleted source with la ce n 0 6 0 1 and nd sm n 0 97 0 03 furthermore it is suggested that the white gneisses in the isukasia area may have been produced from a source with a convex ree pattern our study on ce and nd isotopes and ree abundances provides further evidence that fractionated ree patterns were established already in the very early stages of the archean

biogenic laminar calcretes evidence of calcified root mat horizons in paleosols laminar calcretes are described from the lower carboniferous of south wales the upper jurassic of southern england and the upper jurassic lower cretaceous of northern spain they are interpreted as calcified root mats horizontal root systems and are compared with other examples in the geological record and with possible modern analogues all three occurrences consist of virtually identical centimetre to decimetre thick locally organic carbon rich laminar micrites containing up to 50 by volume of millimetre sized typically calcite filled tubular fenestrae set in an irregular but very finely laminated matrix it is suggested that root mat calcretes are probably very common in the geological record in peritidal lacustrine margin and floodplain deposits but owing to their crudely biogenic microstructure they more closely resemble cryptalgal laminites than do other laminar calcretes the recognition of such root mat calcretes in sedimentary sequences not only provides evidence of subaerial exposure and vegetation cover but can also indicate positions of palaeo water tables in certain circumstances

formation and dynamics of vegetated fluvial landforms follow the biogeomorphological succession model in a channelized river feedback between hydrogeomorphological processes and riparian plants drives landscape dynamics and vegetation succession in river corridors we describe the consequences of biogeomorphological feedback on the formation and dynamics of vegetated fluvial landforms based on observations from the channelized isere river in france the channel was laterally confined with embankments and mostly straightened from the beginning of the 1970s to the end of the 1990s alternate bars were progressively but heavily colonized by vegetation this context presented an exceptional opportunity to analyse temporal adjustments between fluvial landforms and vegetation succession from bare gravel bars to mature upland forest as the consequence of biogeomorphological interactions based on a gis analysis of aerial photographs between 1948 and 1996 we show that the spatiotemporal organization of vegetated bars within the river channel observed in 1996 resulted from a bioconstruction and biostabilization effect of vegetation and interactions between bars of varying age size and mobility field measurements in 1996 reflected how a strong positive feedback between sedimentary dynamics and riparian vegetation succession resulted in the construction of the vegetated bars a highly significant statistical association of geomorphological and vegetation variables rv of co inertia analysis 0 41 p 0 001 explained 95 of the variability in just one axis supporting the existence of very strong feedback between geomorphological changes i e the transformation of small bare alternate bars to fluvial landforms covered by mature upland forest and vegetation succession such dynamics reflect the fluvial biogeomorphological successions model as described by the authors earlier 2020 john wiley sons ltd

the terrestrial landscapes of tetrapod evolution in earliest carboniferous seasonal wetlands of se scotland abstract the lower mississippian tournaisian ballagan formation in se scotland yields tetrapod fossils that provide fresh insights into the critical period when these animals first moved onto land the key to understanding the palaeoenvironments where they lived is a detailed analysis of the sedimentary architecture of this formation one of the thickest and most completely documented examples of a coastal floodplain and marginal marine succession from this important transitional time anywhere in the world palaeosols are abundant providing a unique insight into the early carboniferous habitats and climate more than 200 separate palaeosols are described from three sections through the formation the palaeosols range in thickness from 0 02 to 1 85 m and are diverse most are entisols and inceptisols 63 indicating relatively brief periods of soil development gleyed inseptisols and vertisols are less common 37 vertisols are the thickest palaeosols up to 185 cm in the ballagan formation and have common vertic cracks roots are abundant through all the palaeosols from shallow mats and thin hair like traces to sporadic thicker root traces typical of arborescent lycopods geochemical isotope and clay mineralogical analyses of the palaeosols indicate a range in soil alkalinity and amount of water logging estimates of mean annual rainfall from palaeosol compositions are 1000 1500 mm per year the high mean annual rainfall and variable soil alkalinities contrast markedly with dry periods that developed deep penetrating cracks and evaporite deposits it is concluded that during the early carboniferous this region experienced a sharply contrasting seasonal climate and that the floodplain hosted a mosaic of closely juxtaposed but distinct habitats in which the tetrapods lived the diversification of coastal floodplain environments identified here may link to the evolution and movement of tetrapods into the terrestrial realm

physical and climatic parameters which influence the air content in polar ice abstract under present day climatic conditions the air content of polar ice v generally shows a high sensitivity to the atmospheric pressure and hence to the surface elevation of the ice sheet wherethe ice is formed the results presented here are from sixteen different sites fourteen in antartica one in greenland and one in the yukon territories canada and they allow a better understanding of the parameters which influence the air content in ice it is demonstrated the v can be expressed very simply as a function of the atmospheric pressure p i the temperature t i and the porous volume of ice v i at which the air in the firn becomes isolated in terms of pressure from the atmosphere during the process of pore close off our results confirm a v i increase with temperature and show no clear v i dependence on snow accumulation rate the possible non linearity of the v i t i relation we obtain could be due to a wind influence on v i and or to a second order effect of the accumulation rate our v i results are compared to measurements of the volume of closed pores versus depth in the firn to close we discuss the parameterization that we can obtain to interpret the air content variations observed in deep ice cores over periods covering glacial interglacial transitions in terms of paleoclimatic conditions prevailing at the surface of the ice sheet

isotopic compositions of ce nd and sr in ferromanganese nodules from the pacific and atlantic oceans the baltic and barents seas and the gulf of bothnia abstract ferromanganese nodules from the pacific and atlantic oceans the barents and baltic seas and the gulf of bothnia were analyzed for the isotopic compositions of ce nd and sr and the abundances of ree ba and sr ree patterns of barents baltic and bothnian samples show no ce anomaly or even a negative one in contrast to the positive anomaly observed for the pacific and atlantic samples moreover the baltic and bothnian samples have distinctly low end values average end values of the four regions are as follows pacific 5 barents 10 atlantic 11 and baltic inclusive of gulf of bothnia 19 the characteristic low end values of the baltic samples are indicative of the influence of precambrian rocks from the baltic shield of particular interest is the feature of the ce isotopic composition that ece values of the samples from the pacific are negative and those from the other three regions positive this novel finding might suggest a difference in sources of ce between the pacific and other regions these results demonstrate that ce isotopic ratios can be a useful tracer in marine geochemistry in combination with isotopic compositions of nd and sr

upland ecology of some late carboniferous cordaitalean trees from nova scotia and england abstract permineralised logs and charcoal fragments composed of dadoxylon type wood and derived from cordaitalean trees are described from the upper carboniferous westphalian of nova scotia and england they exclusively occur in sandstone bodies interpreted as the deposits of braided meandering and anastomosing river channels the architecture and ecology of this type of cordaitalean has not yet been satisfactorily described estimates of tree height using an allometric approach suggest that the largest trees attained an approximate height of ca 45 m the absence of true growth rings in the logs indicate that they grew under non seasonal humid tropical conditions however the presence of charred wood fragments implies that droughts of sufficient intensity to permit wildfire did occasionally occur the charcoal fragments are usually associated with incised poorly sorted chaotically bedded channel facies interpreted as flood deposits dramatic increases in runoff and sediment discharge are known to follow the destruction of vegetation in modern wildfire events and the high energy charcoal bearing channel facies described may represent a similar geomorphic response to cordaitalean vegetation fires geomorphic sensitivity to fire is greatest for steeply sloping terrains and it is therefore probable that the cordaitaleans described in this paper occupied upland settings this palaeoecological interpretation is supported by occurrence of the cordaitalean remains in river channel deposits immediately downstream of regions of palaeo upland and by the palynological record the presence of upland forests in late carboniferous times has important implications for numerical modelling of global geochemical cycles

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 abstract 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

strontium isotopic evidence against magma addition in the upper zone of the bushveld complex abstract sr isotopic data from the main and upper zones of the bushveld complex show that the evolution of the upper zone started with a large influx of magma close to the level of the pyroxenite marker a distinctive orthopyroxenite layer in otherwise relatively uniform gabbronorites whole rock samples which span the complete stratigraphic succession ca 2100 m above this layer fall on a single rb sr isochron 2066 58ma and hence have a common initial ratio of 0 7073 1 this ratio is significantly lower than those of the main zone ca 0 7085 below the level of the pyroxenite marker the entire upper zone crystallized from a mixed magma which was thoroughly blended before crystallization this magma had an isotopic ratio intermediate between that of the main zone and the added magma which had an initial ratio of ca 0 7067 further significant magma additions during crystallization are precluded unless they were of the same isotopic composition as the blended magma which is considered improbable hence the layering and mineralogical diversity of the upper zone was produced by internal processes and not produced by magma influxes during crystallization the lithological compositional and isotopic changes at the pyroxenite marker and the petrological coherence of all rocks above this horizon support the placing of the upper zone boundary at this point in the stratigraphy

a chronostratigraphic framework for the north central kaapvaal craton the bushveld complex and the vredefort structure abstract sufficient geochronological data are available pertaining to the north central part of the kaapvaal craton to construct a chronostratigraphic framework for the rock units involved in the vredefort event from the basement rocks at 3170 ma to the waterberg soutpansberg groups deposited between 2025 and 1425 ma the resulting framework forms a convenient chronological guide to the geological evolution of this area and the timing of events such as that at vredefort the basement on which the supracrustal rocks were deposited stabilised from 3170 to 3060 ma but metamorphism and metasomatism of these rocks occurred up to 2800 m y ago in different parts of the craton the first unit of the wits triad the volcaniclastic dominion group was deposited at 3060 ma on the stabilising basement this was followed by the dominantly clastic witwatersrand supergroup and the overlying ventersdorp supergroup the dominantly volcanic ventersdorp rocks are 2700 m y old and form the last unit of the wits triad a considerable time gap of 200 300 ma separates the triad from the lowermost units of the overlying transvaal sequence the age of these volcanic and clastic protobasinal rocks is poorly constrained between 2500 and 2300 ma they may in fact represent eroded remnants of a more extensive depositional cycle the mainly clastic sedimentary part of the transvaal sequence pretoria group has been dated at 2224 ma the upper part of the transvaal sequence rooiberg group is only constrained by the age of the intrusive bushveld complex the bushveld basic layered rocks are well dated at 2060 ma as are the subsequent granites at 2050 ma the vredefort event which post dates the bushveld complex is reasonably well constrained by the age of the bronzite granophyre at 2000 ma deposition of the waterberg and soutpansberg groups which post date the bushveld complex is poorly constrained between the age of the bushveld granites and younger alkaline intrusives at 1425 ma but these sediments and volcanics were probably formed between 2025 and 1752 ma the waterberg group may therefore contain debris from the vredefort structure

arborescent lignophytes in the tournaisian vegetation of queensland australia palaeoecological and palaeogeographical significance abstract a middle tournaisian flora comprising several taxa of arborescent lignophytes is documented for the first time in australia it challenges earlier hypotheses considering that the early mississippian vegetation of australia was impoverished and dominated by small to medium sized arborescent lycopsids until the serpukhovian when climatic conditions became favorable to the thriving of the famous lignophyte dominated rhacopteris flora recorded in australia but also south america the present account is based on anatomically preserved fragments of trunks and branches from two localities of queensland in the broken river province and the burdekin basin three taxa are recognized dameria hueberi gen et sp nov the putative progymnosperm species protopitys buchiana goeppert 1850 and a taxon of uncertain affinities characterized by a pitus type of wood but which differs from the latter genus by anatomical traits relative to its primary body the possible occurrence of subtle growth rings in some of the woods from the burdekin basin and the conifer like traits of the dameria wood are interpreted as ecological clues suggesting that these trees may have inhabited drier settings than the wetland habitats generally inferred for the lycopsids this difference in habitats is suggested to explain the rarity of arborescent lignophytes compared to lycopsids in the australian record of plants of early mississippian age the three taxa reported in this paper represent the earliest record of arborescent lignophytes in australia after the global events that affected the vegetation at the devonian carboniferous boundary and the extinction of archaeopteris they show that the successional pattern of arborescent lignophytes around the devonian carboniferous boundary is comparable to that observed in western europe with the evidence of a diversification occurring as early as the middle tournaisian the palaeogeographic and stratigraphic distribution of protopitys and dameria indicates the occurrence of extensive floral exchanges between southern laurussia and north eastern gondwana in the late devonian to mississippian

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

rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments abstract analyses have been made of ree contents of a well characterized suite of deep sea 4000 m principally todorokite bearing ferromanganese nodules and associated sediments from the pacific ocean ree in nodules and their sediments are closely related nodules with the largest positive ce anomalies are found on sediments with the smallest negative ce anomalies in contrast nodules with the highest contents of other rare earths 3 ree are found on sediments with the lowest 3 ree contents and vice versa 143 nd 144 nd ratios in the nodules 0 51244 point to an original seawater source but an identical ratio for sediments in combination with the ree patterns suggests that diagenetic reactions may transfer elements into the nodules analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to ree contents of nodules and sediments is negligible inter element relationships and leaching tests suggest that ree contents are controlled by a p rich phase with a ree pattern similar to that for biogenous apatite and an fe rich phase with a pattern the mirror image of that for sea water it is proposed that 3 ree concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate processes which favour the enrichment of transition metals in equatorial pacific nodules favour the depletion of 3 ree in nodules and enrichment of 3 ree in associated sediments in contrast ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions

early seed plants from western gondwana paleobiogeographical and ecological implications based on tournaisian lower carboniferous records from argentina the oldest seed occurrences in western gondwana have been recognized in a new stratigraphic section located in western argentina precordillera basin palynological evidence indicates an early mississippian probably tournaisian age for this new succession the two identified early seeds generas pseudosporogonites cf hallei and warsteinia sancheziae n sp were up to now considered as restricted to the devonian of laurussia this finding suggests a dispersal of earliest spermatophytes between laurussia and gondwana during devonian tournaisian times thus accounting for the rheic ocean as a surmountable biogeographic barrier for continental biotas alternatively contrasting biogeographic hypotheses dealing with early spermatophytes rising in paleotropics and then displacing herbaceous communities of non spermatophytes typical from cool high latitudinal regions are explored for explaining the recognized paleobiogeographical pattern the new information supports a weak impact of the devonian carboniferous biotic crisis on earliest seed plant diversity based on preliminary evidences of niches differentiation and ecological dynamics probably affected by wildfires tournaisian gondwanan plant communities from high latitudes are interpreted as being more complex than previously thought and more similar to those reported from laurussia in addition their discovery in a sedimentary environment associated to glacigenic deposits show that this new record might be linked to the coeval glacial age widely recorded elsewhere in gondwana

the sedimentary record of carboniferous rivers continuing influence of land plant evolution on alluvial processes and palaeozoic ecosystems abstract evidence from modern rivers and the deep time geological record attests to the fundamental importance of plant life for the construction of physical habitats within fluvial environments data from an extensive literature review and original fieldwork demonstrates that many landforms and geomorphic features of modern river systems appear in the palaeozoic stratigraphic record once terrestrial vegetation had adopted certain evolutionary advances for example stable point bars are associated with the onset of rooted plants in the siluro devonian and avulsive and anabranching fluvial systems become common at the same time as extensive arborescent vegetation in the carboniferous in this paper we demonstrate a correlation between the diversification of physical fluvial environments and the expansion of terrestrial fauna and flora with an emphasis on the culmination of these trends within carboniferous alluvial systems many extrinsic factors have been considered as possible controls on the evolutionary timelines of terrestrialization for organisms however a fundamental prerequisite for achieving terrestrial biodiversity was the variety of physical habitats especially riparian systems available for newly evolved organisms in association with abundant lowland meandering systems the widespread appearance across carboniferous alluvial plains of fixed channel and anabranching reaches created further physical landforms for colonization and would have promoted increasingly complex hyporheic flow regimes furthermore the associated increase in arborescent vegetation and supply of large woody debris to inland and coastal rivers would have created a wealth of microhabitats for continental organisms we argue that the expanding extent and diversity of physical alluvial niches during the palaeozoic is an underappreciated driver of the terrestrialization of early continental life the study of the deep time fossil and stratigraphic record also illustrates that vegetation is a fundamental prerequisite for the creation of biogeomorphic alluvial landforms and physical habitats and microhabitats

a conifer dominated palynological assemblage from pennsylvanian late moscovian alluvial drylands in atlantic canada implications for the vegetation of tropical lowlands during glacial phases abstract new research suggests that pennsylvanian coal forests were commonly replaced by conifer dominated vegetation during seasonally dry glacial phases here we describe palynological assemblages from stacked sequences of the middle pennsylvanian late moscovian sydney mines formation of nova scotia canada which lends some support to this hypothesis one critical sample from a widespread redbed succession below the harbour coal is dominated by conifer pollen 55 together with abundant representatives of cordaitaleans other coniferopsids and rare pteridosperms ferns and lepidodendrids it differs markedly from 13 other samples obtained from coals their roof shale limestone and associated channel bodies which are dominated by lepidodendrids marattialean tree ferns cordaitaleans and or calamiteans the latter beds represent coastal wetlands and are attributed to late transgressive and highstand systems tracts whereas the conifer bearing sample represents a dryland alluvial plain and may be attributed to lowstand or earliest transgressive systems tracts three additional samples from grey shale below a sequence boundary late highstand and between a redbed succession and major coal seam early to mid transgressive deposits contain transitional palynofloras with a high proportion of herbaceous gleicheniaceous and sphenopteroid ferns herbaceous lycopsids and sphenophylls interspersed with cordaitaleans and or lepidodendrids the dominance of conifer pollen within the dryland components of well defined sequences which have been linked to relative sea level change promoted by gondwanan glaciation supports the view that pennsylvanian tropical biomes responded to the beat of glacial interglacial cycles

early syn rift evolution in the west cameros basin upper jurassic nw iberian range spain and pedogenetic calcretes in early syn rift alluvial systems upper jurassic west cameros basin northern spain reply first we would like to highlight our appreciation of dr platt s and dr wright s comments and the opportunity they give us to discuss some aspects of our papers sacristan horcajada et al 2015 2016 improving the final state of our work knowledge about sedimentology of alluvial systems has had an important development in recent years with new proposals for models in rift basins where tectonics play a predominant role nichols and fisher 2007 hartley et al 2010 weismann et al 2010 fielding et al 2012 the differential behavior of the extensional structures during the earliest syn rift stage tithonian in the west cameros basin played a key role in the architecture of the various alluvial systems sacristan horcajada et al 2015 as well as the distribution of various calcrete sequences sacristan hocajada et al 2016 we discuss the points raised drs platt and wright in the same order they established with respect to this section of the discussion we consider it important to emphasize several points 1 the types of early syn rift alluvial systems studied from our point of view in the case of the nuestra senora de brezales formation it would be an oversimplification to refer only to alluvial fans the brezales fm abbreviation of nuestra senora de brezales fm see below has been interpreted as the result of clastic sedimentation in alluvial systems alluvial and fluvial fans developed in generally small halfgrabens specifically in our recent studies detailed facies analysis stratigraphic framework and paleogeographic reconstructions have proved that the arrangement of the depositional system was complex and heterogeneous due to the differential behavior of the extensional structures that controlled each halfgraben sacristan horcajada et al 2012b sacristan horcajada et al 2013 sacristan horcajada et al 2015 this different tectonic activity produced that each halfgraben basin displayed different sedimentary architectures and alluvial records although they were developed under similar climatic conditions

sandstone petrography of continental depositional sequences of an intraplate rift basin western cameros basin north spain the cameros basin in central spain is an intraplate rift basin that developed from late jurassic to middle albian time along nw se trending troughs the sedimentary basin fill was deposited predominantly in continental environments and comprises several depositional sequences these sequences consist of fluvial sandstones that commonly pass upward into lacustrine deposits at the top producing considerable repetition of facies this study focused on the western sector of the basin where a total of seven depositional sequences ds 1 to ds 7 have been identified the composition of sandstones permits the characterization of each sequence in terms of both clastic constituents and provenance in addition four main petrofacies are identified petrofacies a is quartzosedimentolithic mean of qm85f2lt13 and records erosion of marine jurassic pre rift cover during deposition of fluvial deposits of ds 1 brezales formation petrofacies b is quartzofeldspathic mean of qm81f14lt5 with p f 1 at the base this petrofacies was derived from the erosion of low to medium grade metamorphic terranes of the west asturian leonese zone of the hesperian massif during deposition of ds 2 jaramillo formation and ds 3 salcedal formation quartzose sandstones characterize the top of ds 3 mean of qm92f4lt4 petrofacies c is quartzarenitic mean of qm95f3lt2 with p f 1 and was produced by recycling of sedimentary cover triassic arkoses and carbonate rocks in the sw part of the basin ds 4 pen acoba formation finally depositional sequences 5 6 and 7 pinilla de los moros hortiguela pantano and abejar castrillo de la reina formations respectively contain petrofacies d this petrofacies is quartzofeldspathic with p f near zero and a very low concentration of metamorphic rock fragments from qm85f11lt4 in pantano formation to qm73f26lt1 in castrillo de la reina formation petrofacies d was generated by erosion of coarse crystalline plutonics located in the central iberian zone of the hesperian massif in addition to sandstone petrography these provenance interpretations are supported by clay mineralogy of interbedded shales thus shales related to petrofacies a and c have a variegated composition illite kaolinite and randomly interlayered illite smectite mixed layer clays the presence of chlorite characterizes interbedded shales from petrofacies b and illite and kaolinite are the dominant clays associated with petrofacies d these petrofacies are consistent with the depositional sequences and their hierarchy an early megacycle consisting of petrofacies a and b ds 1 to ds 3 was deposited during the initial stage of rifting when troughs developed in the west asturian leonese zone a second stage of rifting resulted in propagation of trough bounding faults to the sw involving the central iberian zone as a source terrane and producing a second megacycle consisting of petrofacies c and d ds 4 ds 5 ds 6 and ds 7 sandstone composition has proven to be a powerful tool in basin analysis and related tectonic inferences on intraplate rift basins because of the close correlation that exists between depositional sequences and petrofacies

paleozoic vegetation and the siluro devonian rise of fluvial lateral accretion sets a long standing hypothesis links the increased prominence of meandering rivers in the middle paleozoic to the colonization of terrestrial environments by vegetation this hypothesis is tested using a data set of cambrian to devonian fluvial literature and field examination of key stratigraphic units according to some researchers cambrian to mid silurian river systems were braided in planform with a sharp increase in the abundance of meandering rivers during the silurian devonian although meandering systems were largely identified on the basis of thick mudstones and organized channel deposits the data set record of lateral accretion sets appears to be a robust proxy for the abundance of meandering river point bars lateral accretion is first recorded from pridolian lochkovian strata but is noted in nearly 40 of fluvial case studies by the famennian this trend matches the known record of rooted vegetation suggesting that vegetation progressively stabilized river banks and promoted single thread channels however the presence of precambrian and extraterrestrial meandering systems indicates that vegetation is not essential for meandering and the lack of evidence for cambrian to silurian ludlow point bars is surprising if originally present they may largely have been destroyed by extreme floods chute cut offs in coarse grained meandering systems and eolian activity

a ce nd isotope study of crustal contamination processes affecting palaeocene magmas in skye northwest scotland twelve138ce 136ce isotope determinations 31 nd isotope analyses and 31 ree profiles are presented for tertiary basic to intermediate igneous rocks from the isle of skye nw scotland the aim of this work is to precisely identify the contamination mechanisms of basic magmas emplaced through old crust and to test the effectiveness of ce isotope analysis as a petrogenetic tool

the la ce geochronometer a new dating method the isotope 138la 0 089 of natural lanthanum decays by and electron capture to 138ce and 138ba with a long half life we present here the first age determination using la ce dating an internal la ce isochron of a gabbro from the upper zone of the bushveld south africa yields an age of 2 390 480 2 myr based on the partial decay constant 2 58 10 12 yr 1 this age agrees with the sm nd isochron age 2 050 90 2 myr which was obtained from an aliquot of the same sample solution within the uncertainties of 138la half life and isotopic measurement

a felsic end to bushveld differentiation the similarities in age c 2 06 ga and isotopic composition of the bushveld igneous complex and the overlying rooiberg group felsic volcanic rocks suggest the possibility that the two are cogenetic to investigate this possibility we derive a robust new estimate of the major and trace element bulk composition of the bushveld upper zone and upper main zone uumz using melts thermodynamic modeling we show that this composition fails to reproduce fundamental features of the cumulate sequence such as the presence of primary orthopyroxene at the base of the magma column we investigate the possibility that some amount of evolved magma escaped from the magma chamber and derive a new estimate of the uumz parent magma composition that reproduces generally the observed cumulate sequence our results constrain the amount and composition of the escaped magma and provide evidence of a genetic link between the uumz of the bushveld layered series and the felsic volcanic rocks immediately overlying it we conclude that between 15 and 25 of the original magma volume was expelled and is manifest either as part of the upper rooiberg group lava sequence or the rashoop granophyre distinction is hindered by their almost identical major and trace element compositions a parent magma in which 15 25 rooiberg or rashoop material is added back to the extant cumulate sequence is initially saturated in orthopyroxene and is in major and trace element equilibrium with the phases at the base of the uumz