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

thickness of sets of cross strata and planar strata as a function of formative bed wave geometry and migration and aggradation rate cross strata and planar strata formed by the migration of ripples and dunes or low relief bed waves on upper stage plane beds respectively are the most common internal structures in fluvial sands and sandstones the thickness of cross sets or planar laminae at a given location is controlled by 1 aggradation rate relative to downstream migration rate of bed waves and 2 the succession of bed waves of varying height passing the location a quantitative understanding of this relationship is now appearing based on new theory and experimental studies with ripples dunes and upper stage plane beds in many cases the effects of control 1 can be ignored in such cases only the largest bed waves in a population form cross sets or planar laminae the ratio of mean cross set thickness mean height of formative bed waves is less than 0 4 and the ratio of mean cross set thickness mean height of all bed waves is less than 0 5 a simple quantitative model a modified form of the paola borgman model is presented for predicting the height distributions of bed waves ripples dunes low relief bed waves from the thickness distributions of cross sets or planar laminae if the aggradation rate is appreciable more of the smaller bed waves in a population can form cross sets or planar laminae and the preservation ratios increase to 1 in the case of supercritical climbing ripple cross strata in this case it is necessary to determine the angle of climb and length of the bed waves in order to use the model to predict bed wave height distributions

delta growth and river valleys the influence of climate and sea level changes on the south adriatic shelf mediterranean sea abstract incised valleys across continental margins represent the response of fluvial systems to changes in their equilibrium dynamics mainly driven by base level fall forced by glacial eustatic cycles the manfredonia incised valley formed during the last glacial sea level lowstand when most of the southern adriatic shelf was sub aerially exposed but the outer shelf remained under water the pronounced upstream deepening of the valley is ascribed to river incision of the mis5e highstand coastal prism and related subaqueous clinoform under the influence of mis5 4 sea level fluctuations while the downstream shallowing and narrowing mainly reflects the impact of increased rates of sea level fall at the mis3 2 transition on a flatter mid outer shelf until 15 ka bp the valley fed an asymmetric delta confined to the mid outer shelf testifying that continental and deep marine systems remained disconnected during the lowstand sea level rise reached the inner shelf during the early holocene drowning the valley and leading to the formation of a sheltered embayment confined toward the land at this time part of the incision remained underfilled with a marked bathymetric expression this mini basin was rapidly filled by sandy bayhead deltas prograding from both the northern and southern sides of the valley in this environment protected by marine reworking and where sediment dispersal was less effective the accommodation space was reduced and autogenic processes forced the formation of multiple and coalescing delta lobes bayhead delta progradations occurred in few centuries between 8 and 7 2 ka cal bp confirming the recent hypothesis that in this area the valley was filled during the formation of sapropel s1 this proximal valley fill representing the very shallow water equivalent of the cm thick sapropel layers accumulated offshore in the deeper southern adriatic basin is of key importance in following the signature of the sapropel in a facies tract ideally from the shoreline to the abyss

a thin skinned thrust model for variscan pembrokeshire wales abstract the east and west coasts of pembrokeshire sw wales provide two sections through the variscan fold and thrust belt the evolution of these structures is interpreted in terms of a thin skinned tectonic model balanced cross sections are constructed for the high level imbricate sequences and these allow reasonably accurate estimates of shortening to be made basement control on structures developed in the upper carboniferous cover rocks is minimal though some thrust ramp positions may be determined by the location of earlier normal faults the thrust belt may be divided into two parts according to the depth to the decollement horizon in the north imbricate fans developed from a shallow level detachment shortening is heterogeneous and both thrust periodicity and fold style are partly determined by rheology cumulative tectonic displacement increases to the west across pembrokeshire resulting in a net clockwise rotation of about 40

high resolution sequence stratigraphy of the late namurian in the widmerpool gulf east midlands uk abstract analysis of facies stacking patterns and stratal surfaces within late namurian deltas of the widmerpool gulf has revealed 10 high frequency fourth order depositional sequences sequence correlation is based on the characteristic marine band fauna of their condensed sections in many instances sequence boundaries are difficult to recognize unless there is clearly demonstrable lowstand incision consequently it is often difficult to separate late highstand from falling stage progradation with any degree of confidence sequence thickness variations and the dominance of particular stratal surfaces and systems tracts were controlled by a longer period third order cycle of relative sea level rise and fall during the marsdenian yeadonian major fluvio deltaic sand bodies in the widmerpool gulf were formed by distributary channel progradation e g chatsworth grit during the late highstand and or falling stage systems tracts and by the filling of incised valleys e g ashover grit and rough rock following marked sea level falls channel belt and valley fill orientation was initially influenced by differential compaction but this influence decreased during the late namurian the recognition of incised valley fills within the late namurian has implications for estimating the magnitudes and periodicities of carboniferous relative sea level change

structural controls on palaeozoic basin evolution and inversion in southwest wales the tectonic evolution of sw dyfed is presented in terms of a model of basin evolution and subsequent destruction by reactivation of the basin bounding faults in contractional mode movements along long lived palaeozoic extensional faults were reversed during variscan compression with the pre existing faults accommodating the contraction in addition to the development of a thin skinned thrust and fold system basin analysis of the pre variscan extensional system uses sedimentological and stratigraphical evidence to constrain the timing of movements of the basin bounding faults thus allowing division of the stratigraphy into depositional megasequences related to these extensional movements field examples on all scales illustrate active extension during the palaeozoic structural cross sections through sw dyfed demonstrate the interrelationship of the extensional and contractional deformations with palinspastic restorations of the cross sections illustrating the complexity of the pre variscan template

on the periodicity and magnitude of late carboniferous glacio eustatie sea level changes data from sedimentary cycles in basins from northern england the appalachians and midcontinent us afford an insight into periodicities and controls of late carboniferous glacio eustatic sea level changes lithofacies with identifiable palaeobathymetry are used to assess the magnitude of sea level change in the pennine basin of northern england the method yields a minimum value of 42m walsh power spectral analysis is employed to resolve periodicities of about 120ka within the pennine basin of northern england 212 140 and 93 ka within the midcontinent us succession and 109 84 67 63 ka within the appalachian basin within the pennine basin periodicities and magnitudes are found to be independent of their position within the basin thus any tectonism can be assumed to have had a negligible effect on the transgressions a simplified modelled climatic curve is derived from milankovitch parameters and pleistocene 18 o data this is used in a basin fill model that simulates the thermally subsiding pennine basin the resulting distribution of marine deposits is seen to depend upon both the steady regional subsidence and the magnitude and extent of glacio eustatic transgressions

the relative mobility of natural th pb and po and fallout pu am cs radionuclides in the coastal marine environment results from model ecosystems merl and narragansett bay the relative mobility of nuclides of pb th pu and cs which are widely used as geochemical tracers for sedimentation and bioturbation was investigated in artificial microcosm tanks merl and in narragansett bay their mobility was characterized by their removal rates from the water column their affinity toward particles and their degree of penetration into the surface sediments pb th and pu transport was controlled predominantly by the affinity of these elements to particles and the transport parameters of the particles themselves i e sediment resuspension and mixing rates because of its low distribution coefficient transport of cs was controlled by molecular diffusion through pore water in the winter while in summer cs transport was enhanced due to bioturbation the increase with depth of the cspu ratio in core profiles of merl and narragansett bay sediments is thus caused primarily by the higher mobility of cs

estimating carboniferous sea level fluctuations from gondwanan ice extent the magnitude of carboniferous sea level fluctuations is not well known but the estimates are important for constraining cyclothem models in this paper we apply area volume relations developed for quaternary ice sheets to estimate the glacio eustatic component of sea level fluctuations in the carboniferous utilizing the best estimate of gondwanan ice area at the time of its greatest extent we arrive at a figure of 60 15 m for the isostasy corrected glacio eustatic component this value is nearer the lower limit of sea level estimates for cyclothem fluctuations from other sources

palaeohydrological characteristics and palaeogeographic reconstructions of incised valley fill systems insights from the namurian successions of the united kingdom and ireland namurian carboniferous eustatic fluctuations drove the incision and backfill of shelf crossing valley systems located in humid subequatorial regions which are now preserved in successions of the united kingdom and ireland the infills of these valleys archive the record of palaeoriver systems whose environmental hydrological and palaeogeographic characteristics remain unclear a synthesis of sedimentological data from fluvial strata of 18 namurian incised valley fills in the united kingdom and ireland is undertaken to elucidate the nature of their formative river systems and to refine regional palaeogeographic reconstructions quantitative analyses are performed of facies proportions of geometries of incised valley fills and related architectural elements and of the thickness of dune scale sets of cross strata reconstruction of the size of the drainage areas that fed these valleys is attempted based on two integrative approaches flow depth estimations from dune scale cross set thickness statistics and scaling relationships of incised valley fill dimensions derived from late quaternary examples the facies organization of these incised valley fills suggests that their formative palaeorivers were perennial and experienced generally low discharge variability consistent with their climatic context however observations of characteristically low variability in cross set thickness might reflect rapid flood recession perhaps in relation to sub catchments experiencing seasonal rainfall variations in facies characteristics including inferences of flow regime and cross set thickness distributions might reflect the control of catchment size on river hydrology the degree to which is considered in light of data from modern rivers palaeohydrological reconstructions indicate that depth estimations from cross set thickness contrast with observations of barform and channel fill thickness and projected thalweg depths exceed the depth of some valley fills limitations in data and interpretations and high bedform preservation are recognized as possible causes with consideration of uncertainties in the inference of catchment size the palaeogeography of the valley systems has been tentatively reconstructed by integrating existing provenance and sedimentological data the approaches illustrated in this work can be replicated to the study of palaeohydrological characteristics and palaeogeographic reconstructions of incised valley fills globally and through geological time

late yeadonian upper sandstone group incised valley supply and depositional systems in the south wales peripheral foreland basin implications for the evolution of the culm basin and for the silesian hydrocarbon plays of onshore and offshore uk abstract the upper sandstone group of south wales has previously been interpreted as a simple nnw sse trending incised valley that was filled during the late yeadonian namurian g1b data presented in this study indicate a far more complex scenario the group is well developed in the pembrokeshire sub basin but it is absent from the main part of the south wales basin located to the east of the penlan axis the principal source area for sediment flux was the forebulge of the basin located to the north in lower palaeozoic foreland strata variscan flexural uplift of this source area and an accompanying rapid high magnitude fall in sea level produced a very high sediment budget thus during the late yeadonian lowstand of sea level massive amounts of sediment were being generated and transported via an incised valley system across the western part of the south wales peripheral foreland basin the location and orientation of the incised supply system and its related interfluves were controlled by intrabasinal synsedimentary variscan structures many of which were reactivated caledonian extensional faults during the succeeding sea level rise the incised valley was filled initially by fluvio deltaic sands and later by estuarine argillaceous sediments the implications of this combined tectonic sedimentological high resolution sequence stratigraphic model for the evolution of the late namurian crackington formation turbidites of the culm basin are discussed examples of silesian incised valley fill sandstone reservoirs developed in the east midlands oilfield and the southern gas basin are briefly summarised and their spatial and temporal distributions are appraised data generated from these case studies are assessed in terms of their use for the modelling of incised valley fill sequences in foreland basins and other tectonic settings

climate of the supercontinent pangea numerous climate models predict that the geography of the supercontinent pangea was conducive to the establishment of a megamonsoonal circulation in general geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the triassic pangea in the late carboniferous had widespread peat formation in what is now central and eastern north america and europe and relatively dry conditions on the colorado plateau the equatorial region of the continent became drier through the end of the carboniferous by the permian the equatorial region of pangea was dry and indicators of aridity and rainfall seasonality became more widespread wind directions from colorado plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time in the triassic climate in the colorado plateau region became relatively wet though still seasonal and the few eolian sandstones indicate a major shift in wind direction at that time in addition sedimentation

nature and timing of late mississippian to mid pennsylvanian glacio eustatic sea level changes of the pennine basin uk the pennine basin of northern england contains a comparatively complete serpukhovian moscovian succession characterized by high resolution ammonoid zonation and cyclic paralic sedimentation two new isotope dilution thermal ionization mass spectrometry zircon ages from a bentonite deposited during the arnsbergian mid serpukhovian regional substage and tonstein of earliest bolsovian early moscovian regional substage have been determined the weighted mean 206 pb 238 u ages of 328 34 0 55 and 314 37 0 53 ma total uncertainty respectively require modification of the time scale for the western europe regional chronostratigraphy the areal extent of acme ammonoid facies is used as a proxy for the magnitude of 47 discrete flooding events incised valleys major sequence boundaries are used as a proxy for the magnitude of sea level falls the frequency of these events in the light of the new radiometric dating indicates the following 1 there is temporal coincidence between major glaciations in gondwana and phases of increased frequency of sequence boundaries in the pennine basin 2 high amplitude flooding surfaces have an average frequency of c 400 ka 3 average cycle durations during the pendleian early arnsbergian and chokierian bolsovian of c 111 and c 150 ka respectively reflect short duration eccentricities 4 multiple flooding surfaces with the same ammonoid assemblages may equate with sub 100 ka precession or obliquity frequencies supplementary material u pb method description and data procedure for the calculation of the areal extent of marine bands and tables showing a full listing of biostratigraphical data used in the study are available at www geolsoc org uk sup18505

reappraisal of the sequence boundary in time and space case and considerations for an su subaerial unconformity that is not a sediment bypass surface a time barrier or an unconformity abstract the sequence bounding unconformity bears the key defining traits of being a surface separating younger from older strata along which there is evidence of subaerial erosional truncation or subaerial exposure with a significant hiatus indicated van wagoner et al 1988 this subaerial component of sequence boundaries subaerial unconformity su is also broadly considered to form as a topographic surface of sediment bypass carved during relative sea level fall and buried by backfilling during relative sea level rise accordingly the su is commonly presumed to record an approximate time barrier which separates older from younger strata along its full length in this paper we show that regional composite scour rcs surfaces that are traditionally mapped as an integral component of the su were never a single subaerial topographic surface characterized by sediment bypass are not unconformities do not record an effective time barrier and form diachronously at the channel belt scale over the entire fall to rise of a base level cycle these rcs surfaces and by inference the su surfaces they comprise thus do not fully fit key defining characteristics embodied in the conceptual sequence boundary flume observations and field data show that the rcs is buried by fluvial sediment simultaneously as it is scoured accordingly the rcs is perennially covered with stored sediment during formation is only exposed as a subaerial topographic surface at the local place and time where it is undergoing active growth and forms over the duration of local marine drainage during a relative sea level cycle this cut and cover model differs greatly from more established bypass models which assume that the rcs was roughly sediment free and subaerially exposed for long durations of incision during regression and thus preserves a significant depositional hiatus upon later burial instead the rcs may commonly and locally record a hiatus more typical of a facies bounding diastem without a lacuna significantly greater than that of surfaces within the strata it binds fragments of fluvial strata may commonly and sporadically be preserved above the rcs that are older than underlying marine units overrun by this surface consequently the rcs is not an effective time barrier lateral planation by migrating and avulsing channels as the rcs expands laterally after nucleation can place younger fluvial strata over much older units which means that this surface is also composite and highly diachronous laterally at the scale of channel belts the cut and cover model has additional implications not captured by the bypass model first significant sediments may be stored within fluvial strata above the rcs during regression that are not available for contemporary falling stage and lowstand marine shorelines this can result in marine sediment starvation particularly of the sand fraction and in extreme cases can result in sand autodetachment and an absence of regressive marine reservoir sandstones second cutting of the rcs co generates a suprafluvial surface above the covering fluvial strata during regression that may be used as a mappable proxy for the conceptual maximum regressive surface mrs the mrs may be raised above this surface locally by low accommodation aggradation during lowstand normal regression but in either case preserves an approximate time line where not reworked during later transgression third valley development across the rcs does not exclusively form by landward knickpoint growth and may include complexly formed and potentially cross cutting buffer valleys su valley incision can be divided into four modes which include denudation structural buttress and buffer valley components which may work together locally and tend to have variable importance along the shore to hinterland profile although the rcs is not a good rock proxy for the conceptual sequence boundary it remains a very mappable surface which may separate facies of potentially very different origin and reservoir quality the rcs is also inseparable from the su and typically the only terrestrial erosional surface of extent in most short duration sequences its nullification as a sequence boundary would mean abandonment of depositional sequence stratigraphy as a correlation and interpretive tool within these sections an alternative to abandonment of the su as a sequence boundary is to loosen the definition of a sequence boundary to a discrete surface of erosional truncation carved landward of contemporary shorelines that is traceable beyond the scale of a single valley or comparable local system and its correlative surfaces of conformity and or non deposition and continue its use as before

seismogenic structures along continental convergent zones from oblique subduction to mature collision we summarize seismogenic structures in four regions of active convergence each at a different stage of the collision process with particular emphases on unusual deep seated seismogenic zones that were recently discovered along the eastern hellenic arc near crete an additional seismogenic zone seems to occur below the seismogenic portion of the interplate thrust zone a configuration found in several other oblique subduction zones that terminate laterally against collision belts the unusual earthquakes show lateral compression probably reflecting convergence between the subducting lithosphere s flank and the collision zone nearby along oblique zones of recent collision the equivalence between space and time reveals the transition from subduction to full collision in particular intense seismicity beneath western taiwan indicates that along the incipient zone of arc continent collision major earthquakes occur along high angle reverse faults that reach deep into the crust or even the uppermost mantle the seismogenic structures are likely to be reactivated normal faults on the passive continental margin of southeastern china since high angle faults are ineffective in accommodating horizontal motion it is not surprising that in the developed portion of the central taiwan orogen 5 ma seismogenic faulting occurs mainly along moderate dipping 20 30 thrusts this is probably the only well documented case of concurrent earthquake faulting on two major thrust faults with the second seismogenic zone reaching down to depths of 30 km furthermore the dual thrusts are out of sequence being active in the hinterland of the deformation front along the mature himalayan collision zone where collision initiated about 50 ma ago current data are insufficient to distinguish whether most earthquakes occurred along multiple out of sequence thrusts or along a major ramp thrust intriguingly a very active seismic zone including a large mw 6 7 earthquake in 1988 occurs at depths near 50 km beneath the foreland such a configuration may indicate the onset of a crustal nappe involving the entire cratonic crust in all cases of collision discussed here the basal decollement a key feature in the critical taper model of mountain building appears to be aseismic it seems that right at the onset of collision earthquakes reflect reactivation of high angle faults for mature collision belts earthquake faulting on moderate dipping thrust accommodates a significant portion of convergence a process involving the bulk of crust and possibly the uppermost mantle

drainage area and incised valley fills in texas rivers a potential explanation abstract the largest rivers draining to the gulf of mexico in texas are at more advanced stages of valley filling than rivers with smaller drainage areas with corresponding differences in alluvial morphology and architecture and avulsion style this seems to imply that the larger fluvial systems either produce more sediment relative to the accommodation space in the alluvial valleys or that they have undergone longer periods of valley aggradation however it is not clear that either of these is the case this paper presents a theoretical analysis showing that fluvial systems with larger drainage areas can produce more advanced stages of infilling than those with smaller drainage areas but with identical histories and sediment production per unit area due to the nature of the scaling relationships between drainage basin area and incised valley size and between basin area and sediment yield data for rivers in the region shows a strong linear relationship between valley width and drainage area the nonlinear relationship between drainage area and proportion of the incised valley filled is somewhat weaker but still significant and major deviations are readily explained in terms of local inherited morphology or tectonic features results show that major differences in the degree or stage of valley filling could occur due to differences in drainage basin size alone this indicates caution in interpreting incised valley fills of drainage basins of different sizes in terms of sediment supply

how important and different are tropical rivers an overview abstract tropical river systems wherein much of the drainage basin experiences tropical climate are strongly influenced by the annual and inter annual variations of the inter tropical convergence zone itcz and its derivative monsoonal winds rivers draining rainforests and those subjected to tropical monsoons typically demonstrate high runoff but with notable exceptions high rainfall intensities from burst weather events are common in the tropics the release of rain forming aerosols also appears to uniquely increase regional rainfall but its geomorphic manifestation is hard to detect compared to other more temperate river systems climate driven tropical rivers do not appear to transport a disproportionate amount of particulate load to the world s oceans and their warmer less viscous waters are less competent tropical biogeochemical environments do appear to influence the sedimentary environment multiple year hydrographs reveal that seasonality is a dominant feature of most tropical rivers but the rivers of papua new guinea are somewhat unique being less seasonally modulated modeled riverine suspended sediment flux through global catchments is used in conjunction with observational data for 35 tropical basins to highlight key basin scaling relationships a 50 year daily model simulation illuminates how precipitation relief lithology and drainage basin area affect sediment load yield and concentration local sediment yield within the amazon is highest near the andes but decreases towards the ocean as the river s discharge is diluted by water influxes from sediment deprived rainforest tributaries bedload is strongly affected by the hydraulic gradient and discharge and the interplay of these two parameters predicts foci of net bedload deposition or erosion rivers of the tropics have comparatively low inter annual variation in sediment yield

how and where do incised valleys form if sea level remains above the shelf edge sequence stratigraphic models predict that during relative sea level fall rivers will cut incised valleys across the exposed continental shelf incision is driven by the exposure of convex up topography and consequent downstream increases in stream power modern shelf profiles from passive margin and foreland basin settings show that profile convexities occur at the shelf edge and at the current highstand coastline the coastal prism in nonglacial times which form much of earth9s history it is unlikely that the shelf edge was subaerially exposed during such periods patterns of incision would have been primarily determined by the shape of the coastal prism on the basis of modern shelf profiles from passive margin and foreland basin settings river incision of as much as 20 to 70 m would be centered upon the preceding highstand coastline and would be restricted to the inner part of the shelf deeper incised valleys would only result from exposure of the shelf edge or from the processes involved in the formation of submarine canyons

interpreting complex fluvial channel and barform architecture carboniferous central pennine province northern england the bashkirian lower brimham grit of north yorkshire england is a fluvio deltaic sandstone succession that crops out as a complex series of pinnacles the three dimensional arrangement of which allows high resolution architectural analysis of genetically related lithofacies assemblages combined analysis of sedimentary graphic log profiles architectural panels and palaeocurrent data have enabled three dimensional geometrical relationships to be established for a suite of architectural elements so as to develop a comprehensive depositional model small scale observations of facies have been related to larger scale architectural elements to facilitate interpretation of the palaeoenvironment of deposition to a level of detail that has rarely been attempted previously thereby allowing interpretation of formative processes detailed architectural panels form the basis of a semi quantitative technique for recording the variety and complexity of the sedimentary lithofacies present their association within recognizable architectural elements and thus the inferred spatio temporal relationship of neighbouring elements fluvial channel fill elements bounded by erosional surfaces are characterized internally by a hierarchy of sets and cosets with subtly varying compositions textures and structures simple cross bedded sets represent in channel migration of isolated mesoforms dunes cosets of both trough and planar tabular cross bedded facies represent lateral accreting and downstream accreting macroforms bars characterized by highly variable yet predictable patterns of palaeocurrent indicators relationships between sandstone dominated strata bounded by third order and fifth order surfaces which represent in channel bar deposits and incised channel bases respectively chronicle the origin of the preserved succession in response to autocyclic barform development and abandonment major episodes of incision probably influenced by episodic tectonic subsidence differential tilting and fluvial incision associated with slip on the nearby north craven fault system overall the succession represents the preserved product of an upper delta plain system that was traversed by a migratory fluvial braid belt system comprising a poorly confined network of fluvial channels developed between major sandy barforms that evolved via combined lateral accretion and downstream accretion

developing channel and floodplain dimensions with limited data a case study in the amazon basin this research builds on the concept of hydraulic geometry and presents a methodology for estimating bankfull discharge and the hydraulic geometry coefficients and exponents for a station using limited data only stage discharge and landsat imagery the approach is implemented using 82 streamflow gauging locations in the amazon basin using the estimated values for the hydraulic geometry relations bankfull discharge discharge data above bankfull and upstream drainage area at each site relationships for estimating channel and floodplain characteristics as a function of drainage area are developed specifically this research provides relationships for estimating bankfull discharge bankfull depth bankfull width and floodplain width as a function of upstream drainage area in the amazon basin intended for providing reasonable cross section estimates for large scale hydraulic routing models the derived relationships are also combined with a high resolution drainage network to develop relationships for estimating cumulative upstream channel lengths and surface areas as a function of the specified minimum channel width ranging from 2 m to 1 km i e threshold drainage areas ranging from 1 to 431 000 km2 at the finest resolution i e all channels greater than 2 m or a threshold area of 1 km2 the amazon basin contains approximately 4 4 million kilometers of channels with a combined surface area of 59 700 km2 the intended use of these relationships is for partitioning total floodable area channels versus lakes and floodplain lakes obtained from remote sensing for biogeochemical applications e g quantifying co2 evasion in the amazon basin copyright 2011 john wiley sons ltd

do fossil plants give a climatic signal the agreement in the pattern of major biomes with that of climatic zonation of the earth gives a strong indication that climate is the overriding influence controlling the distribution of plant communities three aspects of plants which may be preserved in the fossil state give a signal of the climatic conditions under which they grew 1 the present climatic association of their 9nearest living relative9 2 leaf physiognomy of arborescent plants 3 the character of their secondary xylem 9wood9 of ordinary usage reflecting by the presence or absence of growth rings the seasonality or lack of it in their environment and the potential for tree growth that it offered the significance and limitations of these 9palaeoclimatic signals9 as they may be read from the fossil plant record are reviewed and evaluated the recent demonstration that stomatal frequency of leaves is responsive to changes in ambient carbon dioxide partial pressure offers promise for direct palaeobotanical evidence for past changes in the level of this climatically significant atmospheric constituent

facies model for fluvial systems in the seasonal tropics and subtropics facies models that summarize the deposits of fluvial systems are well established for humid climate settings and for desert environments but the deposits of rivers in the sub humid and semiarid seasonal tropics have been largely ignored our observations and data from modern streams and recent deposits in northeastern australia show how such rivers with extremely variable discharge have distinctive deposit characteristics that are substantially different from conventional fluvial facies models these properties include 1 erosionally based channel fill lithosomes that exhibit complex lateral facies changes with 2 abundant pedogenically modified mud partings 3 complex internal architecture that may lack the macroform elements typical of other fluvial sediment bodies 4 an abundance of sedimentary structures formed under high flow stage and 5 an abundance of in situ trees that colonize channel floors and are adapted to inundation by fast flowing water we illustrate examples of this fluvial style from the rock record and set out a new facies model the recognition of such a distinctive fluvial character and of changes in character through vertical successions will aid paleoclimate and reservoir analysis

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

upper carboniferous fine grained turbiditic sandstones from southwest england a model for growth in an ancient delta fed subsea fan abstract the upper carboniferous crackington and bude formations of southwest england comprise laminated black mudstones gray siltstones thin medium and thick bedded sandstones and contorted silty sandstones the thick bedded sandstones only occur in the bude formation which overlies the crackington the sandstones were deposited predominantly by turbidity currents in a relatively shallow basin they are unusual for two reasons 1 sediment coarser than fine sand is entirely absent 2 unlike many previously described ancient subsea fan deposits organized bundles of sandstones displaying asymmetric upward thickening or upward thinning sequences are no more common than symmetric sequences and both types of organized bundles are much less common than disorganized nonsequential bundle particularly in the bude formation sediment was supplied directly from a delta to the north by resedimentation of delta front sands and slumping of upper pro delta muds and silts to form a lower pro delta turbidite fan fan growth is not readily explained by current models for single sourced tripartite subsea fans displaying radial growth it developed instead a bipartite growth pattern which was strongly influenced in its upper part by external variables including grain size distributary channel switching and other deltaic processes active tectonism within the basin and possibly sea level fluctuations the fan grew by down slope construction of independent levee channel complexes each of which headed in the upper pro delta and even possibly the delta front slumping and mobilization of argillaceous facies resulted in the random occurrence of contorted beds in all parts of the fan regionally extensive mudstones known as key shales within the fan deposits probably reflect large scal upslope delta lobe abandonment the crati and ebro fans of the mediterranean sea would appear to be good modern analogs for the crackington bude fan system

provenance of late carboniferous sandstones in the pennine basin uk from combined heavy mineral garnet geochemistry and palaeocurrent studies abstract analyses of heavy mineral assemblages garnet geochemistry and palaeocurrent directions may each independently provide useful information on the provenance of sandstones but when such datasets are combined the number of options on the location of possible source areas can be greatly reduced also variations in heavy mineral signatures through a stratigraphical section can be explained in terms of switching between source areas rather than due to unroofing events in a single source area if palaeocurrent directions change at the appropriate levels likewise seemingly random changes in transport direction indicated by palaeocurrent variations through a short stratigraphical section can be shown by the heavy mineral data to be systematic and related to shifts between source areas illustrations of the mutual constraints provided by such combined datasets are drawn from late carboniferous successions of the pennine basin northern england where the contributions of detritus from several distinct source terrains and sediment pathways are well documented hallsworth c r morton a c claoue long j fanning c m 2000 carboniferous sand provenance in the pennine basin uk constraints from heavy mineral and detrital zircon age data sedimentary geology 137 147 185 chisholm j i hallsworth c r 2005 provenance of upper carboniferous sandstones in east derbyshire role of the wales brabant high proceedings of the yorkshire geological society 55 209 233 examples are given of how mineralogically distinct and geographically separated provenances can be identified how variations in heavy mineral suites can be used to identify whether variations in palaeoflow represent variations in provenance and how localised mixing recycling in incised channels can be inferred the final example defines the regional extent of the widespread northerly derived fluvial yeadonian sandstones and provides evidence for the mixing of more local sediment supplies at the basin margins

frozen dynamics of migrating bedforms here we show how a continuum granular flow model can replicate realistic self organizing subaqueous bedforms and we explore how a record of this dynamic topography is transferred into the substrate where it can be fossilized modeled bedform behavior is quantitatively compared to laboratory and field data sediment scouring and deposition by migrating bedforms produce sets of partially preserved bedforms recording nonlinear behavior at the sediment fluid interface model results show the importance of spatial and temporal variations in bedform size and migration rate to the generation of sets addition of net bed aggradation to modeled bedforms allows us to explore the preservation of topography under a wide range of depositional conditions we present new relationships among aggradation rate bedform migration rate and set thickness variability of set thickness is shown to be a product of the competition between bed aggradation and bedform migration rates these results show how using the entire distribution of set thickness for ancient strata can refine estimates of the formative paleoenvironmental conditions

climatic change during the lower carboniferous in euramerica based on multivariate statistical analysis of palynological data abstract lower carboniferous palynological assemblages show marked differences between north and south euramerica in order to assess these regional differences multivariate statistical analysis has been applied to percentage frequency data from palynological assemblages from twenty different localities of euramerica the principal components resulting have been related to climate sensitive rocks such as coal and evaporites this relationship has been interpreted in terms of humidity curves and climatic zones four climatic zones have been recognized a dry a moderately humid and a humid zone the latter zone may be subdivided into a humid and a very humid zone during the lower carboniferous the humid climatic zone and the related palaeoclimatic equator shifts southwards however the very humid conditions present in the uppermost tournaisian to middle visean of spitsbergen have not yet been reached in the lower namurian of western europe and the u s a the southward shift of the palaeoclimatic equator has been interpreted in terms of a northward drift of the euramerican continent the palaeomagnetic evidence available for this northward drift is briefly discussed