sequence stratigraphy of the neoproterozoic infra krol formation and krol group lesser himalaya india a bstract a sequence stratigraphic study of terrigenous and carbonate rocks of the infra krol formation and krol group in the lesser himalaya fold and thrust belt of northern india was undertaken as part of a broader investigation of the significance of carbon isotope data in neoproterozoic successions eight regional stratigraphic discontinuities were traced over a distance of nearly 300 km and interpretations were anchored in a series of local studies involving the mapping of key beds and the measurement of closely spaced sections three of the regional surfaces are interpreted as sequence boundaries on the basis of 1 locally developed incised valleys 60 m deep 2 paleokarstic depressions with 50 m of mappable relief 3 subaerial dissolution and weathering products breccias and calcrete filling vertical fissures dikes cavities and shallow de pressions in underlying carbonate rocks and 4 small scale evidence for sub aerial exposure at an erosion surface the remaining five discontinuities are regional flooding surfaces identified on the basis of either facies changes with an abrupt upward deepening across the surface or transitions in facies stacking patterns typically from forestepping to backstepping a glacio eustatic origin is permitted although not required for the three sequence boundaries but no evidence has been found for marked lowering of sea level at other horizons a mismatch between the stratigraphic location of sequence boundaries and car bon isotope minima suggests that local diagenetic alteration or oceanographic phenomena unrelated to glaciation may be in part responsible for observed isotopic variation and that small ice sheets may have existed during apparently nonglacial times without producing either cap carbonates or negative carbon isotope excursions

reappraising the geomorphology ecology link this thematic virtual special issue highlights a personal selection of 18 recent 2007 2009 contributions to earth surface processes and landforms these papers provide a flavour of recent research that is concerned with furthering our understanding of the many ways in which the biosphere interacts with the physical and chemical processes of sediment transfer transformation much of this research has focused on understanding the mechanics by which the biota can modulate sediment transport and the strength of earth surface materials often with the aim of applying that knowledge to enhance bioremediation methods of erosion control this work continues to be fundamentally important in enhancing our understanding of earth surface processes but often treats the biosphere and physical world as uncoupled entities this selection therefore also provides samples of work that point to an ongoing but significant disciplinary reappraisal in which it is the interactions between ecological and geomorphological realms that are of primary interest

origin and morphology of limestone caves limestone caves form along ground water paths of greatest discharge and solutional aggressiveness flow routes that acquire increasing discharge accelerate in growth while others languish with negligible growth as discharge increases a maximum rate of wall retreat is approached typically about 0 01 0 1 cm yr determined by chemical kinetics but nearly unaffected by further increase in discharge the time required to reach the maximum rate is nearly independent of kinetics and varies directly with flow distance and temperature and inversely with initial fracture width discharge gradient and pco2 most caves require 104 105 yr to reach traversable size their patterns depend on the mode of ground water recharge sinkhole recharge forms branching caves with tributaries that join downstream as higher order passages maze caves form where 1 steep gradients and great undersaturation allow many alternate paths to enlarge at similar rates or 2 discharge or renewal of undersaturation is uniform along many alternate routes flood water can form angular networks in fractured rock anastomotic mazes along low angle partings or sponge work where intergranular pores are dominant diffuse recharge also forms networks and spongework often aided by mixing of chemically different waters ramiform caves with sequential outward branches are formed mainly by rising thermal or h2s rich water dissolution rates in cooling water increase with discharge co2 content temperature and thermal gradient but only at thermal gradients of more than 0 01 c m can normal ground water co2 form caves without the aid of hypogenic acids or mixing artesian flow has no inherent tendency to form maze caves geologic structure and stratigraphy influence cave orientation and extent but alone they do not determine branch work versus maze character

bank accretion and the development of vegetated depositional surfaces along modified alluvial channels this paper describes the recovery of stable bank form and development of vegetated depositional surfaces along the banks of channelized west tennessee streams most perennial streams in west tennessee were straightened and dredged since the turn of the century patterns of fluvial ecological responses to channelization have previously been described by a six stage model dendrogeomorphic tree ring techniques allowed the determination of location timing amount and rate of bank sediment deposition channel cross sections and ecological analyses made at 101 locations along 12 streams encompassing bends and straight reaches show that channel and bank processes initially react vertically to channelization through downcutting a depositional surface forms on banks once bed degradation and heightened bank mass wasting processes have eased or slowed the formation of this depositional surface marks the beginning of bank recovery from channelization dominating lateral processes characteristic of stable or natural channels return during the formation and expansion of the depositional surface suggesting a relation with thalweg deflection point bar development and meanderloop extension characteristic woody riparian vegetation begins to grow as this depositional surface develops and becomes part of the process and form of restabilizing banks the depositional surface initially forms low on the bank and tends to maintain a slope of about 24 mean accretion rates ranges from 5 9 cm yr on inside bends to 0 cm yr on most outside bends straight reaches have a mean accretion rate of 4 2 cm yr the relatively stable convex upward depositional surface expands and ultimately attaches to the flood plain the time required for the recovery process to reach equilibrium averaged about 50 years indicative pioneer speccies of woody riparian vegetation include black willow river birch silver maple and boxelder stem densities generally decrease with time after and initial flush of about 160 stems per 100 m2 together bank accretion and vegetative regrowth appear to be the most important environmental processes involved in channel bank recovery from channelization or rejuvenation

cyclicity and paleoenvironmental dynamics rocknest platform northwest canada the superbly exposed rocknest formation northwest territories canada contains 140 to 160 shallowing upward cycles 1 to 15 m thick that contain distinctive marker beds and can be correlated for 200 km parallel to strike and 120 km perpendicular to strike cycles are grouped according to cycle base lithology which reflects paleogeographic position on the platform shale based cycles of the distal inner shelf pass westward into dolosiltite based cycles then into tufa based cycles of the shoal complex and then into grainstone based cycles of the outer shelf cycles are bounded by erosional surfaces that become less pronounced away from the shoal complex cycles formed in response to small asymmetric rapid rise slow fall eustatic oscillations in sea level 10 m during sea level rise rapid transgression and submergence of tidal flats occurred along the eastern margin of the shoal complex followed by eastward expansion of the shoal complex and slow progradation of tidal flats over lagoonal facies during sea level fall a glacio eustatic model for cyclicity accounts for the data favoring asymmetric eustatic sea level oscillations subaerial exposure and vadose diagenesis of platform during sea level falls arrested progradation and incomplete shoaling of many cycles and cycle periods of 20 000 to 100 000 yr 18 000 to 30 000 yr for rocknest inner shelf slopes ranged from 8 cm km average at high sea level stand to 2 cm km average at low sea level stand tidal flat progradation rates were 7 to 9 km 1 000 yr interaction of inner shelf slope sea level fall rate and sedimentation rate generates complete condensed or expanded cycle profiles one dimensional computer modeling reveals that sedimentation rates of shoal complex facies were 250 cm 1 000 yr that lag times in sedimentation following transgression may have ranged from zero on the shoal complex to 2 000 yr on the distal inner shelf and that subtidal sedimentation rates may have ranged from 80 cm 1 000 yr for the proximal inner shelf to 20 cm 1 000 yr for the distal inner shelf

stratigraphy sedimentology and isotopic geochemistry of australian neoproterozoic postglacial cap dolostones deglaciation delta 13 c excursions and carbonate precipitation abstract thin d13c excursions in the geologic record they are interpreted to record a brief postglacial anomaly in ocean chemistry in australia the marinoan varanger equivalent 600 ma cap dolostone units exhibit many of the characteristics displayed by such deposits elsewhere around the globe including fine grained dolomitic mineralogy lateral persistenc at basinal scales thin laminae graded beds intervals with abundant marine cements crystal fans and a distinctive negative d13c isotopic signature of up to 5 pdb on the basis of these features the australian examples are interpreted here to be deeper water deposits below storm wave base resulting from an anomalous flux of inorganic carbonate to the sea floor during postglacial transgression detailed isotopic analysis of australian cap dolostones indicates d13c values ranging from 1 to 5 and gen rally becoming more depleted in 13c upsection trace element data indicate some diagenetic stabilization but textural evidence and the presence of similar profiles in different basins argue against a pervasive recrystallization event the range in d13c values between sections as well as more negative 13c values appear to correlate with greater paleobathymetry within basins this implies either 1 only partial preservation of the complete oceanic variation of d13c or 2 precipitation of this peculiar facies owes its genesis to basinal specific oceanographic processes such as proximi y of a given section to a postglacial upwelling zone in the later case d13c values would not represent whole ocean values stratigraphic constraints and paleoenvironmental interpretations suggest that much of this excursion lies within the geologically brief period of postglacial transgression this implies that the cause s of d13c variation likely operated on time scales significantly less than the residence time of carbon in the oceans 105 yr the continent wide and perhaps global nature of cap dolostones indicates that large volumes of carbonate were precipitated during the postglacial transgressive period such large scale carbonate precipitation over the hypothesized short time interval of postglacial transgression must have caused or have been the product of profound changes in the carbon cycle and global climate at tha time similar evidence for transgression and increased carbonate deposition in the holocene are attributed to the changing basin shape and ph of the oceans the coral reef hypothesis of berger 1982 cap dolostones may record a proterozoic equivalent of this process with the substitution of abiotic carbonate precipitation for skeletal precipitation by reef organisms

determining the impact of the holocene highstand at the coastal fluvial interface shoalhaven river south eastern australia with enhanced rates of sea level rise predicted for the next century the upstream extent of sea level influence across coastal plains is a topic of public importance australian coastal rivers provide a testing ground for exploring this issue because the area is tectonically stable was not glaciated and experienced a holocene highstand between 7 4 and 2 ka of up to 1 5 m above australian height datum ahd in the shoalhaven river of new south wales investigation of a confined bedrock reach at wogamia 32 km inland has identified a unit of dark cohesive silt and sand with marine diatoms shell fragments and enhanced pyrite content interpreted as estuarine the unit is up to 13 m thick thickens downstream and is overlain by fluvial channel and floodplain deposits the estuarine unit on laps a remnant pleistocene terrace and extends to approximately 2 2 m ahd optically stimulated luminescence osl and radiocarbon ages suggest that estuarine deposition commenced prior to 7 8 ka cal bp predating the highstand by 500 years and that marine influence in the area continued to 5 3 0 7 ka during this period a delta probably persisted at wogamia where a narrow upstream reach opens out and subsequently advanced to fill the broad shoalhaven coastal embayment although the effect of sea level rise depends on many factors the results suggest that during a highstand at or above present sea level a strong marine influence may extend for tens of kilometres inland and penetrate confined bedrock reaches landward of coastal embayments copyright 2013 john wiley sons ltd

structure and shortening of the kangra and dehra dun reentrants sub himalaya india surface geology oil well seismic reflection and magnetostratigraphic data are integrated to evaluate the structural style and the shortening rate at the himalayan front sub himalaya of northwest india the sub himalaya between the main boundary thrust and the himalayan frontal fault is the primary surface expression of shortening between the himalaya and the indian plate at certain locations the himalayan frontal fault is a blind thrust beneath anticlines of siwalik tertiary molasse parallel to the himalayan orogen the main boundary thrust is sinuous so the width of the sub himalaya ranges from 30 to 80 km where the sub himalaya is narrow nahan salient tertiary rocks are exposed in imbricate thrust sheets where the sub himalaya is broad kangra and dehra dun reentrants alluvium fills wide synclinal valleys duns seismic reflection data reveal that surface anticlines form in association with south vergent thrusts that root in a decollement at the base of the tertiary section reflection profiles and well data also indicate that the basement lithology changes northward from precambrian crystalline rocks beneath the indo gangetic plains to precambrian and cambrian metasedimentary rocks beneath the sub himalaya the sub himalayan decollement dips 2 5 northward beneath the kangra reentrant but it is steeper 6 beneath the dehra dun reentrant the kangra and dehra dun reentrants display fault propagation folds having steep limbs in the north and fault propagation and fault bend folds that have gently north dipping limbs in the south a balanced cross section of the kangra reentrant shows that a minimum of 23 km shortening has occurred since 1 9 1 5 ma yielding a shortening rate of 14 2 mm yr shortening has occurred at a rate of 6 16 mm yr across the dehra dun reentrant these data are similar to other published shortening rates and indicate that approximately 25 of the total india eurasia convergence at this longitude is accommodated within the sub himalaya given continued convergence and the presence of overpressured wells in the kangra reentrant the region is likely at risk from moderate and or great earthquakes in the future

oligocene eustasy from two dimensional sequence stratigraphic backstripping estimates of the magnitudes of changes in third order 0 522 m y eustasy were obtained for oligocene sequences defined by a suite of largely onshore boreholes of the new jersey coastal plain benthic foraminiferal biofacies and multiple age constraints in a sequence stratigraphic framework formed the database for this study the geometry of the margin through time was determined using two dimensional backstripping the depth ranges of benthic foraminiferal biofacies were determined from a combination of standard factor analysis techniques and the backstripped geometries benthic foraminiferal biofacies were then used to determine the depths of the oligocene margin profiles obtained from backstripping the water depths of 16 of these horizons were confirmed by independent benthic biofacies determinations from at least two wells this internal consistency indicates that the data and the twodimensional backstripping approach were robust where benthic biofacies require a vertical shift of the horizons generated by two dimensional backstripping eustatic changes were required and were readily calculated results indicate a major eustatic fall from the end of the eocene to the first record of oligocene deposition subsequent long term shoaling of sea level through the oligocene was 30 m in 10 m y superimposed on this long term trend were higher frequency third order variations in eustasy with amplitudes of 40 m or less

can the sedimentological and morphological structure of rivers be used to predict characteristics of riparian seed banks abstract seeds are transported by flowing water along with sediment and organic matter and form seed banks within the fluvial landforms or geomorphic units of river systems fluvial processes commonly result in observable gradients in sediment characteristics with elevation above the channel bed this study aims to investigate spatial variability in seed bank characteristics that may be attributed to fluvial processes we compared the extent to which four riparian seed bank characteristics abundance species richness seed mass and seed shape are correlated with 1 fluvially influenced gradients in sediment character percentage of organic matter organic median particle size d50 percentage of fine particles fines and the combined percentage of sand and gravel sand gravel and 2 three geomorphic unit types that form with increasing elevation above the channel bed bars benches and the floodplain seed bank abundance and species richness were weakly yet significantly correlated with sediment gradients significantly increasing with increasing fines and decreasing sand gravel seed bank species richness also significantly increased with increasing organic and decreasing d50 conversely seed abundance was highly variable and relationships between sediment qualities and seed mass and shape were nonexistent we suggest that hydrological factors such as inundation frequency operating most clearly at the geomorphic unit scale ultimately drive spatial variability in riparian seed bank characteristics by 1 directly influencing seed inputs and losses from seed banks via erosion and deposition which is complicated by species specific differences in seed morphology and 2 indirectly influencing seed inputs and losses by mediating seed germination and mortality and the establishment success of plants through impacts on sediment moisture and organic matter content further complexity is added by nonfluvial seed inputs from established vegetation the net result of these influences tends toward decreasing potential for seed losses and increasing potential for seed inputs associated with the reduction in inundation frequency observed from bars to the floodplain for those assessing the potential of the seed bank as a seed source for revegetation sediment sampling for seed bank assays targeted at organic flood debris or fine organic rich sediments such as those typically associated with benches and the floodplain should elicit useful estimations of seed bank composition

evolution of an early proterozoic foreland basin carbonate platform lower pethei group great slave lake north west canada the taltheilei utsingi mclean and blanchet formations form a 175 390 m thick carbonate platform to basin succession in the lower part of the paleoproterozoic pethei group preserved in the eastern arm of great slave lake carbonates accumulated along the south east margin of the slave craton within a foredeep formed during the collision of the slave and churchill cratons the rocks include eight predominantly microbial carbonate facies that comprise five facies associations representing 1 shallow water rimmed shelf 2 shallow water open shelf 3 shallow water ramp 4 upper slope and deep ramp and 5 lower slope and basin plain environments microbialite facies grew by organically mediated precipitation of spar and micritic cement and trapping and binding of lime mud these wholly subtidal facies typically reflect progressive shallowing and changing geometry of the lower pethei sea floor from ramp to open shelf to shallow rimmed shelf with associated slope and basin plain deposition repeated relative sea level changes influenced platform growth this resulted in five shallowing upward packages each separated by an incipient drowning event of varying magnitude antecedent topography and the size of the preceding drowning event strongly influenced the initial growth of each interval this repeated pattern is attributed to interaction between a the inherent tendency of microbial carbonates to aggrade vertically b changing sedimentation rates and c readjustments of relative base level the lower pethei succession is one of few paleoproterozoic examples of carbonate platform growth within a foreland basin it has 1 a low gradient profile 2 extensive slope and basin plain carbonate production and sedimentation 3 no ooids 4 minor terrigenous clastic sediments and 4 a mobile submergent shelf rim lacking substantial carbonate sand shoals

using simulated emergent vegetation to alter stream flow direction within a straight experimental channel river restoration programs often use vegetation to enhance the biological functionality recreational opportunities and aesthetic beauty of degraded stream corridors yet none has used vegetation for the purpose of inducing a straight channel to meander a flume based study was designed to alter the flow pattern within a straight degraded stream corridor by using simulated emergent vegetation of varying density placed at key locations within the channel placement of vegetation zones was determined using an empirical relation for equilibrium meander wavelength based on the imposed flow rate surface flow velocities were quantified using particle image velocimetry the study showed that i flow velocity can be markedly reduced within and near the vegetation zones ii flow can be diverted toward the opposite bank and iii vegetation density controlled the magnitude of these effects

peritidal carbonate platform growth and cyclicity in an early proterozoic foreland basin upper pethei group northwest canada abstract the upper pethei group is a 170 235 m thick largely limestone succession located in the east arm of great slave lake northwest canada strata accumulated in a paleoproterozoic foreland basin during the late stages of marine deposition rocks include nine predominantly stromatolitic facies that are grouped into five facies assemblages 1 marginal peritidal complex 2 back barrier lagoon 3 shelf margin 4 subtidal shelf and 5 slope and basin carbonate sedimentation on the platform involved precipitation of synsedimentary cements within and on stromatolite laminae water column precipitation of carbonate mud and generation and transport of nonskeletal grains stromaclasts ooids oncoids peloids and intraclasts the upper pethei platform is interpreted to have evolved through three basic platform geometries peritidal rimmed shelf subtidal rimmed shelf and subtidal open shelf in response to changes in the rate of creation of accommodation space the peritidal complex and rim behaved in a manner consistent with models of phanerozoic reefal rims and alternatively kept up gave up or caught up to sea level in response to fluctuations in the rate of change of relative sea level and lateral variations in sediment production and accumulation three scales of cycle are recognized 1 overall formation scale upward deepening of the platform 2 laterally traceable decameter scale shallowing upward cycles separated by marine flooding surfaces and 3 laterally discontinuous meter scale shal owing upward peritidal cycles the first two cycle types are interpreted to have been allogenic controlled by changes in eustasy and subsidence rates meter scale cycles are interpreted as mainly autogenic having formed in an aggradational tidal island model the upper petrel platform is similar to other paleoproterozoic foreland basin carbonate platforms important differences however include 1 laterally discontinuous peritidal cycles 2 lack of widespread sand shoals inboard of the shelf rim 3 a thick predominantly carbonate slope and basin succession 4 moderate to low platformal micrite content 5 extensive lagoonal ooid sands and 6 low contents of terrigenous clastics

facies architecture and sequential evolution of an incised valley estuarine fill the cujupe formation upper cretaceous to lower tertiary sao luis basin northern brazil abstract the cujupe formation upper cretaceous lower tertiary represents the uppermost part of the itapecuru group in the eastern margin of the sao luis basin northern brazil this unit consists of deposits formed mainly by tidal processes and is attributed to tidal channel subtidal bay fill tidal shoal sand flat and tidal delta depositional settings five stratigraphic intervals us1 us5 defined by discontinuity surfaces l1 l5 capped by lags were recognized within this unit the cujupe formation represents the estuarine fill of an incised paleovalley the estuarine nature of these deposits is suggested by several indirect lines of evidence including 1 tidally influenced facies associations that change rapidly over short distances 2 dominance of tidal channel deposits and 3 an ichnological assemblage suggestive of highly stressed brackish water conditions the five units and the bounding surfaces of the cujupe formation indicate a complex estuarine setting analysis of facies architecture within the stratigraphic intervals points to deposition in an estuary that changed dramatically from a wave dominated us1 us2 to a tide dominated one us3 such a change in style records amplification of the tidal prism which caused flooding of the estuary as the paleocoast dynamics shifted from wave dominated to tide dominated conditions the flooding process is interpreted to reflect rise in relative sea level during the transgression of the paleovalley the subsequent units us4 and us5 formed in a tide dominated estuarine setting but with increased fluvial influence their origin is attributed to high frequency episodes of progradation that took place during the turnaround from the transgressive to the highstand stage of the estuary evolution

sedimentary environments of the simla group upper precambrian lesser himalaya and their palaeotectonic significance abstract the simla group of the western lesser himalaya comprises a prograding muddy delta sequence that was built by the collapse of a carbonate shelf during late precambrian time the simla sequence consists of a thick about 1500 m coarsening upwards clastic succession which is divisible into the basantpur chhaosa and sanjauli formations carbonate appears only in the basal formation basantpur formation three subfacies for the basal simla have been discerned a carbonate platform to the northeast basantpur subfacies shallow water with more clastic influence to the south kunihar subfacies and relatively deep water adjacent to a fault scarp to the northwest kashlog subfacies the first signs of deltaic sediments appear in the middle of the basantpur formation and are well developed in the overlying chhaosa formation the overall characteristics of the chhaosa facies are those of a delta front and distributary mouth bar where floods from distributaries and shelf storms lead to very rapid deposition mostly above wave base the uppermost sanjauli formation is relatively thick bedded coarse grained and more frequently cross bedded representing delta platform and distributary channel deposits a significant change in environment of deposition is observed in the overlying beds previously known as the upper sanjauli member and now being separated as the jagas formation the jagas facies suggests major uplifts and a climatic change to semi arid conditions the detritus of the simla delta came from the indian shield situated to the south of the delta most constituents indicate mature sediments with occasional lithoclasts of sedimentary and intraformational characters faulting presumably continued during the deposition of the simla group as is characteristic for rifted continental margins

calcite cementation in the upper floridan aquifer a modern example for confined aquifer cementation models detailed petrographic study of the oligocene suwannee limestone a principal unit of the upper floridan aquifer system indicates that all the calcite cements in the suwannee limestone are precompaction in origin most are clearly associated with either early mineralogical stabilization or oligocene subaerial exposure features none of the cements are in isotopic 18 o and 13 c or trace element fe mn and sr equilibrium with the extant aquifer waters the cements therefore formed prior to the onset of regionally confined freshwater aquifer conditions these rocks have been basically inert with respect to calcite cementation during the past 5 to 10 m y while they have been part of the regional confined aquifer using this modern aquifer as an example it is likely that confined paleoaquifer cementation has been overestimated as an explanation for regional cementation patterns in ancient limestones

a middle proterozoic palaeokarst unconformity and associated sedimentary rocks elu basin northwest canada a major palaeokarst erosion surface is developed within the middle proterozoic elu basin northwestern canada this palaeokarst is named the sub kanuyak unconformity and truncates the parry bay formation a sequence of shallow marine dolostones that were deposited within a north facing carbonate platform under a semi arid climate the sub kanuyak unconformity exhibits up to 90 m of local relief and also formed under semi arid conditions when parry bay dolostones were subaerially exposed during a relative sea level drop of about 180 m caves and various karren developed within the meteoric vadose and phreatic zones their geometry size and orientation were largely controlled by northwest and northeast trending antecedent joints bedding and lithology near surface caves later collapsed forming valleys and intervening towers or walls and plains minor terra rossa formed on top of highs karstification was most pronounced in southern parts of bathurst inlet but decreased northward probably reflecting varying lengths of exposure time along a north dipping slope the kanuyak formation is up to 65 m thick and partially covers the underlying palaeokarst it consists of six lithofacies i breccia formed during collapse of caves as reworked collapse breccia and regolith ii conglomerate representing gravel dominated braided fluvial deposits iii sandstone deposited as braided fluvial and storm dominated lacustrine deposits iv interbedded sandstone siltstone and mudstone of sheet flood origin v dolostones formed from dolocretes and quiet water lacustrine deposits and vi red beds representing intertidal marine mudflat deposits rivers flowed toward the northwest and northeast within karst valleys and caves lakes were also situated within valleys marine mudflat sediments completely cover the palaeokarst to the north a regional correlation of the sub kanuyak unconformity with the intra greenhorn lakes disconformity within the coppermine homocline suggests that similar styles of karstification occurred over an extensive region the elu basin palaeokarst however was developed more landward and was exposed for a longer period of time than the coppermine homocline palaeokarst

a composite reference section for terminal proterozoic strata of southern namibia integrated sequence stratigraphic and chemostratigraphic data yield a framework for correlations of stratigraphic units in the terminal proterozoic to cambrian witvlei and nama groups of namibia coupled with precise u pb zircon age constraints these correlations make it possible to construct a composite reference section for use in calibrating terminal proterozoic chronostratigraphy the namibian reference section starts with two distinct glacial horizons and extends up to within 1 million years of the proterozoic cambrian boundary the two glacial horizons may represent each of two distinct varanger age glaciations better known from the north atlantic region from the higher of the two glacial horizons up the composite stratigraphy preserves one of the thickest and most complete available records of carbon isotope variability in post varanger terminal proterozoic seawater four carbon isotope chemostratigraphic intervals are recognized 1 a postglacial negative 13 c excursion npg interval 2 a rising interval pr interval of increasing positive delta 13 c values 3 a falling interval pf interval characterized by decreasing positive 13 c and culminating in near zero or negative values and 4 an interval of moderately positive relatively invariant 13 c values i interval that extends up to the unconformity that contains the proterozoic cambrian boundary each of these chemostratigraphic intervals can be recognized in widely separated correlative sections around the world by comparing sediment accumulation rate in the radiometrically calibrated namibian stratigraphy with sediment accumulation rates in correlative sections in arctic canada and oman a maximum age of 564 ma is estimated for the end of the younger varanger glaciation 25 m y younger than previous estimates

potential controls of alluvial bench deposition and erosion in southern piedmont streams alabama usa abstract benches are bank attached channel deposits occurring at an elevation between the channel bed and top of banks their occurrence in a variety of geologic and hydrologic settings has led to confusion about the mechanisms driving their formation which in turn contributes to difficulty identifying the active floodplain bankfull stage and the determination of environmental flows in some rivers hydrodynamic modeling software river 2d in combination with sediment particle size analysis and total station topographic surveys was used to simulate flow conditions needed to erode and deposit the d84 d50 and d15 particle sizes of concave and lateral benches in two rivers talladega and hillabee creeks in alabama results suggest that bench erosion requires flows at least 150 larger than benchfull stage at the talladega site while the hillabee site experienced erosion at all discharges meeting and exceeding benchfull flow stage likely owing to its overall smaller sediment particle sizes at both sites the presence of vegetation increased the bench area subjected to deposition but somewhat counterintuitively also helped influence the location of erosion by limiting flow vectors in contrast with previous research findings the occurrence of reverse flow was neither sustained nor widespread at either site these findings provide new insight into alluvial benches suggest that the study benches are relatively stable features under the prevailing hydrologic regime and that in some temperate climate settings such as the southern piedmont localized hydraulic controls on bench formation can be superseded in importance by hydrologic flow regime even in the case of concave benches and where flow regulation is not a factor

dolomitized middle proterozoic calcretes bathurst inlet northwest territories canada abstract dolostones within the terrigenous clastic middle proterozoic kanuyak formation are interpreted to be dolomitized calcretes dolocretes which formed on a landscape largely devoid of macroscopic organic life the dolocretes up to 5 m thick form beds or masses which either parallel or cross cut host sedimentary rocks and are composed of five elements 1 curvilinear and rectilinear networks of cracks which are filled with detrital terrigenous clastic and carbonate sediments ooids pisoids and cements sediments and cements are laminated and bedded generally parallel to the margins of cracks 2 micritic fibrous columnar and plumose dolomitic cements that were precipitated as calcareous speleothems ooids and pisoids and masses 3 ooids and pisoids that are concentrically laminat d homogenous or coated grains occurring in reversely graded beds and as isolated particles throughout dolocretes it appears that accretionary particles formed in situ based upon polygonal fitting vadose and grapestone fabrics and gradational contacts between ooids pisoids and host sediments 4 deformation structures that include folded and brecciated detrital sediments within cracks brecciated pisoids and minor teepees and 5 surface karren that locally truncate the dolocretes while missing the features commonly associated with higher plants in post silurian calcretes rhizoconcretions root mouldic porosity etc the presence of an array of other common calcrete fabrics e g cracks cements accretionary grains and deformation structures suggests that physical and chemical processes were probably largely responsible for the carbonate precipitates within kanuyak profiles microbiota most likely also contributed to calcretization however if not significantly altered by dolomitization stable carbon and oxygen isotope values do not indicate any significant influence by organic matter

paleosol in galesburg formation kansas city group upper pennsylvanian northern midcontinent u s a evidence for climate change and mechanisms of marine transgression abstract a widespread paleosol in the galesburg formation kansas city group missourian in the northern midcontinent upper pennsylvanian cyclothem mupc outcrop belt exhibits prominent features including repeating sets of synformal slickensides and mukkara or chimney structures which characterize it as a paleo vertisol the galesburg paleosol has pervasive low chroma grayish to greenish coloration an organic matter profile and geochemical characteristics with regard to s fe2o3 mno sio2 and al2o3 that indicate wetter soil conditions than those indicated by equally widespread high chroma paleosols higher in the local stratigraphic succession particularly a high chroma paleo vertisol in the upper lawrence formation the predominance of low chroma i e wetter paleosols throughout the kansas city group in the northern forest city basin southeastern nebraska and southwestern iowa as exemplified by the galesburg paleosol compared to the greater frequency of high chroma i e drier paleosols in overlying pennsylvanian especially virgilian strata implicates decreasing rainfall in the interior of north america during the late missourian the variability in rainfall through this missourian virgilian shift need not have exceeded the range of rainfall 400 1400 mm a associated with modern soil analogs in subtropical to warm temperate north america thus there is an indication of climate change on a longer term time scale 105 106 a than the intra or inter eustatic cycle climate change proposed by other authors for late paleozoic cyclothems in the north american interior regional differences in the nature of transgressive marine strata directly above the galesburg further suggest 1 that important information relevant to reconstruction of the sea level curve is probably missing from the interval between regressive paleosols and subsequent regressive limestones in mupcs and 2 that there were probably appreciable differences in the overall mechanism of deposition of mupc transgressive shales and black core shales within any particular interval of mupc transgressive deposition

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

early carboniferous mississippian paleosols from southwest britain influence of climatic change on soil development abstract the clifton down mudstone a mixed peritidal fluvial sequence of arundian late osagean early meramecian age from southwest britain contains a suite of varied cumulative paleosols temporal changes in soil type within this paleosol suite provide evidence for a shift in the climatic regime during arundian times calcic vertisols in the lower part of the sequence developed on floodplains and are equated to a seasonally semi arid climate in which wetter periods induced vertisol development and promoted leaching in contrast a ferric podzol and thionic gleysols characterize the upper part of the succession and are associated with a thick fluvial sandstone interval the ferric podzol probably developed either in a humid tropical or temperate climate and indicates that there was a shift to a more humid climatic regime during late arundian times thionic gleysols with dolocrete horizons represent brackish hydromorphic marsh soils associated with marine incursions and overprint earlier paleosols

the recognition and interpretation of paleokarsts two examples from the lower carboniferous of south wales abstract criteria for the identification and interpretation of paleokarstic surfaces in ancient carbonate sequences are discussed and two examples of such surfaces are described from the lower carboniferous of south wales one type is compared to kavornossen karren a type of tropical karst well developed today on puerto rico the second example a mammillated paleokarstic surface of a type common in the lower carboniferous is interpreted as a deckenkarren formed beneath a vegetation cover and similar to the makondo karsts of south africa paleokarsts can provide information on the paleoclimates paleohydrology and vegetation cover existing at the time of their formation

latest proterozoic stratigraphy and earth history the end of the proterozoic eon was a time of pronounced biological biogeochemical climatic and tectonic change new bio and chemostratigraphic data provide an improved framework for stratigraphic correlation making possible a deeper understanding of latest proterozoic earth history and providing tools for a chronostratigraphic division of late proterozoic time

chemostratigraphic and sequence stratigraphic constraints on vendian cambrian basin dynamics northeast siberian craton delta 13 chemostratigraphic and sequence stratigraphic data from terminal vendian and earliest cambrian strata of northeast siberia are used to constrain the history of regional basin development these boundary strata consist of 300 to 500 m of latest vendian age carbonate ramp deposits and 100 m of nemakit daldyn age siliciclastic shelf deposits the two successions are separated by a regional paleokarst unconformity six delta 13 c chemostratigraphic profiles of the carbonates exhibit patterns of secular variation similar to those in coeval strata with allowances for local diagenetic and tectonic effects isotopic profiles are used to recognize time lines chemo chrons within individual depositional sequences and to illustrate the geometry of stratigraphie units and variation in subsidence and stratigraphie completeness across the basin the vendian khorbosuonka group and correlative deposits are divided into 3 depositional sequences that record sedimentation from ca 555 to 543 ma in a ge

a channel evolution model for subtropical macrochannel systems a channel evolution model cem represents stages of channel development in response to specific types of disturbance in recent years classic incised disturbed cems have provided process based understanding of channel adjustment and formed the cornerstone for river restoration and rehabilitation while broadly applicable to alluvial systems in temperate and semi arid regions these models cannot be assumed to be universally applicable lockyer creek in south east queensland australia has notable macrochannel morphology and is subject to high hydrological variability typical of many subtropical climates the aim of this paper is to present a case study of channel adjustment and evolution in lower lockyer creek to determine if existing cems adequately describe processes of channel adjustment and the associated trajectories of change typical of river systems in subtropical settings lockyer creek has recently been subjected to a spate of flooding resulting in significant channel erosion this offers an ideal opportunity to investigate the nature and rate of channel adjustment processes and place them in context of longer term geomorphic adjustments in these systems specifically we address two questions firstly do the classic incised disturbed cems adequately represent the observed macrochannel adjustment secondly if current cems are inadequate what is the channel evolution model for these systems of which lower lockyer creek is an example results show that these are non incising systems where wet flow bank mass failures wbmfs are the dominant process of channel adjustment they occur within the channel bank top boundary resulting in no change to overall bank top width furthermore subsequent floods deposit sediment in the failure scars and failure headwalls generally do not retreat beyond channel bank top channel adjustment has not followed the evolutionary stages for incised disturbed channels and a new four stage macrochannel cem is outlined for these subtropical systems the proposed cem illustrates a cyclical pattern of erosion by channel bank wbmf followed by re aggradation through deposition and oblique processes contributing to bank rebuilding this cem provides sufficient information to determine the stage of macrochannel adjustment enabling decisions to be made over whether intervention is required or will be successful

facies relations depositional environments and diagenesis in a major early proterozoic stromatolitic carbonate platform to basinal sequence campbellrand subgroup transvaal supergroup southern africa the campbellrand subgroup and its correlative the malmani subgroup of the transvaal supergroup represent a major 2300 2600 ma old carbonate buildup it is on average between 1500 and 1700 m thick and covers an area of approximately 190 000 km2 on the kaapvaal craton the original depository probably extended across the entire 600 000 km2 surface area of the craton and beyond the buildup consists essentially of two major lithofacies assemblages namely a basinal non stromatolitic laminated carbonate and shale sequence with minor chert iron formation and mafic tuff interbeds off the craton to the west and a shallow water stromatolitic carbonate sequence on the craton proper growth faults along the edge of the craton controlled the platform margin defined by columnar stromatolite oolite and carbonate arenite shoal deposits these are flanked basinward by reef like giant subtidal stromatolitic mounds elongated perpendicular to the platform margin and grading into slope deposits consisting of laminated carbonates with interbeds of chaotic dolomite breccia and conophyton stromatolites platform lagoonal deposits consist of dark grey laminoid fenestrate stratified stromatolites interfingering to the interior of the craton with intertidal to supratidal light grey cherty dolomite units with a variety of structures such as domal and stratified stromatolites laminoid fenestrae tepee structures and flat pebble conglomerates the buildup consisted primarily of limestone which was replaced by early diagenetic dolomite the chemical composition of the dolomite is related to depofacies platform margin and lagoonal dolomites are manganese rich basinal dolomites are iron rich and intertidal to supratidal deposits are virtually free of iron and manganeses indications are that the carbonate buildup developed from an early carbonate ramp stage into a mature rimmed carbonate shelf eventually the carbonate shelf was drowned by a major transgression followed by the deposition of the kuruman iron formation

the himalayan passive margin from precambrian to cretaceous times abstract the himalaya passive margin should be separated into the indian himalaya and the pakistan himalaya divided by the nanga parbat haramosh basement uplift in the northwestern syntaxes the indian passive margin shows a complex history involving splitting of microcontinents off the northern gondwana margin from early paleozoic times until the jurassic in contrast the pakistan himalaya formed part of the stable indian shelf until separation from africa started in the jurassic each margin has a distinct stratigraphic history until the mid mesozoic after which they show similar histories until the tertiary the himalaya mountains in india consist of three distinct tectonic units juxtaposed during the neogene by southward thrusting of the northern indian precambrian to mesozoic passive margin the lesser himalaya on the south forms a late precambrian passive margin usually directly overlain by late cretaceous to tertiary clastics its stratigraphy is closest to that of the indian shield in contrast the high himalaya has a thin ordovician to carboniferous shelf sequence deposited after early ordovician deformation and granite intrusion above this thick permian and mesozoic shelf sequences mark the separation of continental blocks off the northern indian margin and the opening of the neotethys ocean the north himalaya formed the slope and basin of this ocean and consists of reactivated paleozoic gneiss domes overlain by thick mesozoic sediments which pass in the northeastern himalaya into an enormously thick sedimentary sequence resting on oceanic crust paleomagnetic and structural evidence indicates at least 500 km of southward thrusting along the main central thrust between the lesser and high himalaya this thrusting together with a further 250 km of erosion at the front of the nappes has removed the entire inner shelf of the himalaya passive margin and can explain the startling contrast between the high and lesser himalaya stratigraphic sequences but there are still discrepancies particularly in the eastern himalaya where precambrian basement is juxtaposed with the north himalaya mesozoic slope these discrepancies can be partly resolved by strike slip movements roughly parallel to the himalaya which have removed parts of the northern indian passive margin such faults of the requisite orientation displacement and age occur in southeast asia where their cumulative displacements can add up to several thousand kilometres similar faults of undoubted pre tertiary age occur in the pakistan himalaya here the passive margin shows a much simpler history of jurassic to miocene subsidence

riparian vegetation and island formation along the gravel bed fiume tagliamento italy after more than 300 years of river management scientific knowledge of european river systems has evolved with limited empirical knowledge of truly natural systems in particular little is known of the mechanisms supporting the evolution and maintenance of islands and secondary channels the dynamic gravel bed fiume tagliamento italy provides an opportunity to acquire baseline data from a river where the level of direct engineering intervention along the main stem is remarkably small against a background of a strong alpine to mediterranean climatic and hydrological gradient this paper explores relationships between topography sediment and vegetation at eight sites along the active zone of the tagliamento a conceptual model of island development is proposed which integrates the interactions between large woody debris and vegetation geomorphic features sediment calibre and hydrological regime islands may develop on bare gravel sites or be dissected from the floodplain by channel avulsion depositional and erosional processes result in different island types and developmental stages differences in the apparent trajectories of island development are identified for each of the eight study sites along the river the management implications of the model and associated observations of the role of riparian vegetation in island development are considered in particular the potential impacts of woody debris removal riparian tree management regulation of river flow and sediment regimes and changes in riparian tree species distribution are discussed

role of a rheophyte in bench development on a sand bed river in southeast australia casuarina cunninghamiana miq is an important rheophytic tree in new south wales australia because it is fast growing and can tolerate flood disturbance widden brook is an active sand bed stream that has widened substantially since initial european settlement in the early 1800s and is characterized by high flood variability and multi decadal periods of alternating high and low flood frequency called flood and drought dominated regimes channel contraction by bench formation is currently occurring conversion of coarse grained point bars to benches is an important process of channel contraction when point bars grow to a height where suspended sediment is first deposited to thicknesses of at least 50 mm by sub bankfull floods rapid establishment of c cunninghamiana occurs as the trees grow they partially block bankside flows thereby locally reducing flow velocity and inducing further deposition on the benches such synergistic relationships between bar height and inundation fine grained sediment deposition tree establishment and the development of a bankside low current velocity zone are fundamental for bench development size class frequency data demonstrate that c cunninghamiana on the benches consists of pure even aged stands with most trees clustering near the average diameter two benches have similar size class frequency distributions but a third has significantly smaller trees recruitment on benches is episodic may occur in areas open to grazing and is dependent on favourable conditions that allow tree survival these favourable conditions include high seed availability low levels of competition deposition of fine sediments and adequate moisture for tree growth although c cunninghamiana germinates on bars seedlings are eliminated by prolonged inundation or flood scour and do not reach maturity recurring catastrophic floods or a sequence of large floods in rapid succession episodically destroy benches by substantial channel widening and initiate a new phase of bar and bench development a conceptual model of the conversion of point bars to benches by thick mud deposition and c cunninghamiana recruitment has been developed for sand bed streams draining similar sandstone catchments copyright 2009 john wiley sons ltd

lowstand rivers need not incise the shelf an example from the great barrier reef australia with implications for sequence stratigraphic models a key tenet of many sequence stratigraphic models is that sea level lowering causes widespread fluvial incision of the subaerially exposed continental shelf and that river borne terrigenoclastic sediments bypass the lowstand shoreline via canyons to the continental slope and basin floor consequently the occurrence of incised channels is considered a fundamental criterion for the recognition of sequence boundaries in ancient shelf successions contrary to this we argue that rivers may not necessarily incise during glacio eustatic lowstands if they flow out onto a coastal plain flanked by a broad low angle shelf on the great barrier reef shelf fluvial incision did not occur during the last glacial maximum lgm but instead subaerial accommodation was created and infilled as contemporary rivers graded to the lgm bayline incision was restricted to the lowstand shelf break where canyons of limited extent formed by nickpoint retreat

fluvial process and the establishment of bottomland trees the effects of river regulation on bottomland tree communities in western north america have generated substantial concern because of the important habitat and aesthetic values of these communities consideration of such effects in water management decisions has been hampered by the apparent variability of responses of bottomland tree communities to flow alteration when the relation between streamflow and tree establishment is placed in a geomorphic context however much of that variability is explained and prediction of changes in the tree community is improved the relation between streamflow and establishment of bottomland trees is conditioned by the dominant fluvial process or processes acting along a stream for successful establishment cottonwoods poplars and willows require bare moist surfaces protected from disturbance channel narrowing channel meandering and flood deposition promote different spatial and temporal patterns of establishment during channel narrowing the site requirements are met on portions of the bed abandoned by the stream and establishment is associated with a period of low flow lasting one to several years during channel meandering the requirements are met on point bars following moderate or higher peak flows following flood deposition the requirements are met on flood deposits high above the channel bed flood deposition can occur along most streams but where a channel is constrained by a narrow valley this process may be the only mechanism that can produce a bare moist surface high enough to be safe from future disturbance because of differences in local bedrock tributary influence or geologic history two nearby reaches of the same stream may be dominated by different fluvial processes and have different spatial and temporal patterns of trees we illustrate this phenomenon with examples from forests of plains cottonwood populus deltoides ssp monilifera along meandering and constrained reaches of the missouri river in montana

sequence stratigraphy and the interpretation of neoproterozoic earth history abstract the application of sequence stratigraphy to neoproterozoic successions is important for improving the resolution of time correlation within individual sedimentary basins and potentially at a global scale the methodology is illustrated in this paper by reference to two contrasting examples from the flinders ranges adelaide geosyncline of south australia where the younger part of the neoproterozoic to earliest cambrian succession 770 ma to 540 ma has been divided into thirteen unconformity bounded depositional sequences one of the most prominent sequence boundaries at or near the base of the wonoka formation is characterized by a series of buried canyons as much as 1 km deep high resolution sequence stratigraphic studies at umberatana syncline continue to support the view that the canyons were cut subaerially and filled by fluvial and shallow water sediments in contrast to the wonoka canyons sequence boundaries interpreted at the base of the nuccaleena formation seacliff sandstone and near the top of the abc range quartzite are relatively subtle with only limited evidence for erosion and valley incision four sequence boundaries at the level of the sturtian and marinoan varanger glacial deposits and in the vicinity of the precambrian cambrian boundary are thought to correlate with surfaces in the amadeus basin of central australia other prominent sequence boundaries including the wonoka canyons and surfaces within the upper part of the wonoka formation and at the base of the ediacara member of the rawnsley quartzite correspond with a relatively condensed section in the amadeus basin and their lateral persistence beyond the adelaide geosyncline is therefore difficult to evaluate given the lack of precision in biostratigraphy and isotope geochemistry in neoproterozoic rocks and in a marked departure from phanerozoic practice we recommend placement of a terminal proterozoic gssp at a sequence boundary a prime candidate in australia is the sequence boundary at the base of the nuccaleena formation seacliff sandstone immediately above the marinoan glacial rocks in the adelaide geosyncline and its likely correlative at or near the base of the gaylad sandstone in the amadeus basin

paleosols in shallow marine carbonate sequences abstract shallow water carbonate sequences in the geological record commonly exhibit numerous exposure surfaces reflecting emersion of sediment due to progradation processes and sealevel oscillations some ancient platform sequences contain hundreds of such surfaces associated with paleosols fossil soils typically calcretes a wide range of macro and microstructures are associated with these calcretes which are reviewed profile types and stages in profile development can be defined the nature of the exposure surface and associated paleosols can be used to identify the nature of the prevailing climate although hydromorphic effects related to marine flooding of the platforms can modify the paleosols a potentially important use of paleosols is to define the nature of sequence boundaries several studies have identified sets of paleosols with varying maturities reflecting changes in rates of accommodation space creation during sealevel rises and falls

sedimentary evidence of a cambro ordovician orogenic event in the northwestern himalaya abstract the late proterozoic early paleozoic sequence of the tethys himalaya provides evidence of an orogenic episode close to the cambrian ordovician boundary late pan african event pre middle cambrian sediments were deposited on a terrigenous tidal flat gradually passing upward to a peritidal carbonate platform the succession shows an overall transgressive trend which is reproduced at smaller scale by second and third order coarsening upward cycles terminated by the landward shift of carbonate facies during highstands of sea level sandstone petrography suggests a passive continental margin setting for this part of the sequence in middle cambrian times the carbonate platform underwent gradual drowning and outer shelf slope shales with intercalated tuffaceous material erupted from a nearby immature volcanic arc were deposited the shales are overlain by basinal turbidites attesting to the growth of a sandstone lobe enclosed in lobe fringe siltstones in the middle ordovician unconformable alluvial fan conglomerates and braid plain sandstones derived from uplifted sedimentary sequences indicate erosion of a newly formed orogenic belt comparison with early paleozoic and recent counterparts allows to interpret the cambro ordovician sedimentary evolution in terms of foreland basin development the thermal subsidence of a passive margin temporarily reduced by the passage of a peripheral bulge was enhanced strongly by flexural downwarping towards a subduction zone collision of a buoyant continental margin at the trench hampered subduction rapid uplift ensued with formation of a foreland fold thrust belt shedding sedimentary detritus into the adjacent molasse basins

reciprocal interactions and adjustments between fluvial landforms and vegetation dynamics in river corridors a review of complementary approaches abstract until recently one way relationships between flow dynamics geomorphology and plant ecology were considered dominantly when studying the functioning of river systems whereby fluvial landforms and hydrogeomorphic processes drive the evolution of riparian plant communities however biological communities may significantly control geomorphic processes and have strong impacts on landform dynamics in order to fully identify the processes linked to river dynamics changes in time and space of fluvial landforms and associated plant communities conceptual multidisciplinary progress is clearly needed to understand the mutual interactions and feedbacks between fluvial landforms and vegetation community dynamics this paper presents a detailed literature review of fluvial geomorphology riparian plant ecology and hydraulic engineering knowledge the historical and recent development of ecological plant succession theory toward the integration of hydrogeomorphic disturbances is discussed as well as the integration of vegetation within geomorphology as a significant landform control factor incorporating both hydrogeomorphic controls on riparian vegetation dynamics and mechanical impacts of vegetation structures on flow properties and sediment dynamics recent progress in ecology hydraulic engineering and fluvial geomorphology emphasises interdependence between biological and physical forms and processes based on this literature review a fluvial biogeomorphic succession concept is proposed to link fluvial landform and riparian vegetation community evolution within a bi directional model the succession of fluvial landforms and associated vegetation communities is composed of four main critical phases that represent a shift in the relative dominance of hydrogeomorphic and ecological processes as a response to biostabilisation and passive bioconstruction processes the positive feedbacks associated with this shift lead to the development of characteristic biogeomorphic structures such as vegetated banks islands or floodplains which are moderated by the biogeomorphic functional roles of ecosystem engineers that induce or reinforce the positive feedbacks this fluvial biogeomorphic succession concept relates the natural darwinian selection and ecological succession theories to fluvial geomorphology

spinifex basalts with komatiite tholeiite trend from the nansen gakkel ridge arctic ocean abstract during cruise ark iv 3 with rv polarstern 1987 volcanic rocks were recovered from the nansen gakkel ridge ngr a slow spreading half rate approximately 0 5 cm ridge with an axial depth of more than 5000 m the ngr is one of the slowest and deepest mid ocean ridges so far known and calculations based on the distance of sampling location from the axial valley yielded ages of approximately 600 ka for the rocks investigated here according to petrographic and geochemical results i e spinifex textures mg 70 and mgo 9 wt the volcanics are termed komatiitic basalts dark spherical droplets of basanitic composition within the komatiitic basalts are believed to be relicts of an incomplete magma mixing whose basanitic end member could well account for the enriched character of the ngr basalts in terms of rare earth elements ti and incompatible trace elements based on nd isotope as well as high sm nd ratios mantle metasomatism i e veined mantle model could be responsible for the enrichment of incompatible trace elements in the source region of komatiitic basalts of the ngr

age distribution and significance within a sediment budget of in channel depositional surfaces in the normanby river queensland australia we present the results of investigations into alluvial deposition in the catchment of the normanby river which flows into princess charlotte bay pcb in the northern part of the great barrier reef lagoon our focus is on the fine fraction 63 m of alluvial deposits that sit above the sand and gravel bars of the channel floor but below the expansive flat surface generally referred to as the floodplain variously described as benches bank attached bars or inset or inner floodplains these more or less flat lying surfaces within the macro channel have hitherto received little attention in sediment budgeting models we use high resolution lidar based mapping combined with optical dating of exposures cut into these in channel deposits to compare their aggradation rates with those found in other depositional zones in the catchment namely the floodplain and coastal plain in total 59 single grain osl dates were produced across 21 stratigraphic profiles at 14 sites distributed though the 24 226 km2 catchment in channel storage in these inset features is a significant component of the contemporary fine sediment budget i e recent decades last century annually equivalent to more than 50 of the volume entering the channel network from hillslopes and subsoil sources therefore at the very least in channel storage of fine material needs to be incorporated into sediment budgeting exercises furthermore deposition within the channel has occurred in multiple locations coincident in time with accelerated sediment production following european settlement generally this has occurred on a subset of the features we have examined here namely linear bench features low in the channel this suggests that accelerated aggradation on in channel depositional surfaces has been in part a response to accelerated erosion within the catchment the entire contribution of 370 kilotonnes per annum of fine sediment estimated to have been produced by alluvial gully erosion over the last 100 years can be accounted for by that stored as in channel alluvium these features therefore can play an important role in mitigating the impact on the receiving water of accelerated erosion

organic walled microfossils from the chert phosphorite member tal formation precambrian cambrian boundary india the chert member also designated chert phosphorite member of the tal formation in the lesser himalaya contains well preserved organic walled microfossil assemblage the assemblage includes small 25 m acanthomorphic acritarchs sphaeromorphic acritarchs cyanobacterial filaments sponge spicules and thallophytic remains identified as micrhystridium lanceolatum m dissimilare m tornatum m lanatum cf lophosphaeridium sp paracymatiosphaera irregularis cymatiosphaera sp estiastra minima leiosphaeridia sp siphonophycus robustum thalloidal fragments and hexactinellid sponge spicules the present assemblage rich in small acanthomorphs appears to be best developed in upper nemakit daldynian beds based on acritarch biostratigraphy the present work suggests a nemakit daldynian to early tommotian age for the chert member which is in agreement with the formerly proposed age based mainly on small shelly fossils the assemblage is correlatable to the precambrian cambrian boundary microbiotic assemblage from china central asia and east european platform the assemblage shows low diversity of species the characteristic of inshore biota

skeletal microfauna of meishucunian and qiongzhusian precambrian cambrian boundary age from the ganga valley lesser himalaya india the earliest skeletal microfauna of precambrian cambrian age recovered from the lower tal sequence chert phosphorite to calcareous members of the tal formation exposed in the ganga valley lesser himalaya uttar pradesh india has been grouped into three assemblages in ascending order these are assemblage i containing anabarites trisulcatus missarzhevsky tiksitheca korobovi miss circotheca sp turcutheca sp spirellus columnorus jiang and olivooides alveus qian assemblage ii yielding allonia erromenosa jiang a sp cf a erromenosa jiang dimidia simpleca jiang d sp cf d simpleca jiang and hyolithellus sp and assemblage iii comprising pelagiella lorenzi kobayashi auriculatespira madianensis zhou xiao and a andunca he pei the assemblages i and ii are correlatable to the meishucunian zone i and zone iii respectively and the assemblage iii to the qiongzhusian stage of china thus the lower tal sequence is assigned to precambrian cambrian age

geochemical changes across the proterozoic cambrian transition in the durmala phosphorite mine section mussoorie hills garhwal himalaya india abstract the transition from the neoproterozoic nemakit daldynian 1 krol e dolomite to the tommotian lower tal phosphorite chert black shale sequence denotes a period of drastic change in the depositional environment and the chemical milieu of the sedimentation basin these changes are reflected by a marked negative excursion of carbon isotopes phosphorus enrichment trace metal content high organic carbon burial and notably the first appearance of prolific small shelly fauna and burrowing organisms recent studies have documented these changes along several stratigraphic profiles in the mussoorie hills of the garhwal himalaya for which a single profile from the durmala phosphorite mine provides a key section discussed here