calculating velocity fields across plate boundaries from observed shear rates summary a general horizontal velocity field can be expressed uniquely in terms of the velocities at points along a line and an integral function of the 2 d shear rate consequently the relative motion across a plate boundary can be calculated from observed shear rates by taking the velocities along a line within one of the plates to be zero

distribution of bedrock and alluvial channels in forested mountain drainage basins mountain river networks often consist of both bedrock and alluvial channels1 5 the spatial distribution of which controls several fundamental geomorphological and ecological processes6 7 the nature of river channels can influence the rates of river incision and landscape evolution1 2 as well as the stream habitat characteristics affecting species abundance and aquatic ecosystem structure8 11 studies of the factors controlling the distribution of bedrock and alluvial channels have hitherto been limited to anthropogenic badlands12 here we investigate the distribution of channel types in forested mountain drainage basins and show that the occurrence of bedrock and alluvial channels can be described by a threshold model relating local sediment transport capacity to sediment supply in addition we find that valley spanning log jams create alluvial channels hospitable to aquatic life in what would otherwise be bedrock reaches the formation of such jams depends critically on the stabilizing presence of logs derived from the largest trees in the riverside forests suggesting that management strategies that allow harvesting of such trees can have a devastating influence on alluvial habitats in mountain drainage basins

the early rhuddanian survival interval in the lower silurian of the oslo region a third pulse of the end ordovician extinction abstract ordovician silurian boundary layers with rhuddanian strata are exposed as a long continuously fossiliferous sequence in the solvik formation in the asker area central oslo region norway brachiopods belonging to benthic assemblage 5 are preserved in the lower parts of the formation this level is investigated for the presence of a survival interval after the last end ordovician extinction event the criteria for a survival interval include taxa that are dwarfed long ranging eurytopic often opportunistic as well as assemblages that show low density and diversity four species isorthis prima leangella scissa dicoelosia osloensis and eoplectodonta duplicata were collected and measured the three former were dwarfed compared to a younger aeronian fauna belonging to the same benthic assemblage detailed investigations showed a statistically significant two step reduction in size for all but d osloensis the first interval immediately above the last end ordovician extinction event displays dwarfed brachiopods but diversity is high and the number of long ranging and eurytopic species is low due to the presence of globally and locally relict ordovician species the second interval the upper parts of lower rhuddanian shows all the characteristics of a survival interval in which the sizes are statistically significantly smaller than both those in the interval below and those in the aeronian interval above no lithological change within lower rhuddanian strata could be linked to the pronounced reduction in size the second step in size reduction may be related to global occurrence of anoxia in the deep oceans with a pulse of anoxic water pushed onto the shelf at that time it is coeval with a short negative 13 c excursion found in some locales signifying a brief period of global warming the results suggest a protracted extinction event through parts of the early rhuddanian and a third and final extinction event followed by a clear survival interval

geomorphic changes in a complex gully system measured from sequential digital elevation models and implications for management high resolution digital elevation models dems were derived from sequential aerial photography of an active uvio mass movement gully complex in new zealand s north island east coast region to measure geomorphic changes over approximately one year the gully showed a complex behaviour combining uvial and mass movement erosion deposition and reworking of materials stored in an active debris fan during the measurement period 5200 1700 m3 of material were eroded from the 8 7 ha gully complex and 670 180 m3 from the 0 8 ha depositional fan giving a total of 5870 1710 m3 for the entire gully complex fan system the results provide a high resolution description of gully behaviour over a short time period and also demonstrate that mass movement slumping and debris ows accounted for almost 90 per cent 4660 200 m3 of the sediment generated this erosional response is described in terms of gully evolution by comparing the gully complex to other systems in the region in various stages of development the effect of gully evolution on geomorphic coupling between the gully complex and channel system is described and coupling is also shown to vary with the magnitude and frequency of rainfall events from a land management perspective the success of strategies such as tree planting to mitigate against gully erosion depends on the stage of gully development particularly on whether or not mass movement erosion has begun in contrast to gully rehabilitation efforts elsewhere basin wide afforestation in the early stages of gully incision is favoured over riparian planting given that mass movement assisted by excessive groundwater pressure is the main process leading to uncontrollable gully expansion to protect land effectively against continuing gully erosion of headwater catchments and resulting downstream aggradation it is necessary for land managers to understand the spatial and temporal variability of gully development fully so that mitigation efforts can be targeted appropriately copyright 2003 john wiley sons ltd

brachiopod faunas after the end ordovician mass extinction from south china testing ecological change through a major taxonomic crisis classification of extinction events and their severity is generally based on taxonomic counts the ecological impacts of such events have been categorized and prioritized but rarely tested with empirical data the ecology of the end ordovician extinction and subsequent biotic recovery is tracked through abundant and diverse brachiopod faunas in south china the spatial and temporal ranges of some 6500 identified specimens from 10 collections derived from six localities were investigated by network and cluster analyses nonmetric multidimensional scaling and a species abundance model depth zonations and structure of brachiopod assemblages along an onshore offshore gradient in the late katian were similar to those in the latest ordovician earliest silurian post extinction fauna within this ecological framework deeper water faunas are partly replaced by new taxa siliciclastic substrates continued to be dominated by the more ordovician orthides and strophomenides shallow water carbonate environments hosted atrypides athyridides and pentamerides with the more typical ordovician brachiopod fauna continuing to dominate until the late rhuddanian the end ordovician extinctions tested the resilience of the brachiopod fauna without damage to its overall ecological structure that commenced later at the end of the rhuddanian

block rotation by strike slip faulting structural and paleomagnetic evidence geometric analysis shows that motion of sets of strike slip faults should cause block rotation otherwise the distorted fault domain would not fit with its surrounding the sense of the block rotation depends on the sense of fault slip and the spacing and orientation of the faults all of which can be obtained from structural data the predictions of the geometric model can then be independently tested by paleomagnetic measurements the model was tested in northern israel structural data reveal several domains of contemporaneous right and left lateral strike slip faults paleomagnetic measurements show that in a domain of nnw trending left lateral faults blocks rotated 23 3 8 2 clockwise and in a domain of right lateral faults blocks rotated 22 4 9 0 anticlockwise these results are in agreement with the prediction of the geometric analysis of the structure the combined results of the heterogenous deformation of the area resembles a pure shear which allows n s extension by about 1 3 in other domains rotations of 34 6 9 1 and 53 1 11 0 were found in their original orientation the left and right lateral faults intersected at angles of 60 70 enclosing the principal axis of shortening in accordance with theories of brittle failure as a result of block rotations this angle is now larger and may reach 110 the results demonstrate large block rotations in different senses in domains of strike slip faults the independent structural and paleomagnetic data can be interpreted within the framework of a simple geometric model northern israel is considered to be a good model for this efficient mechanism of intraplate deformation which is expected to occur in similar tectonic settings elsewhere

channel processes following land use changes in a degrading steep headwater stream in north island new zealand abstract in headwater streams in steep land settings narrow and steep valley floors provide closely coupled relationships between geomorphic components including hillslopes tributary fans and channel reaches these relationships together with small catchment sizes result in episodic changes to the amount of stored sediment in channels major sediment inputs follow high magnitude events subsequent exponential losses via removal of material can be represented by a relaxation curve the influence of hillslope and tributary processes on relaxation curves and that of altered coupling relations between components were investigated along a 1 3 km reach of a degrading channel in the 4 8 km2 weraamaia catchment new zealand extensive deforestation in the late 19th and early 20th centuries followed by invasion of scrubs and reforestation induced changes to major erosion types from gully complexes to shallow landslides changes in the size and pattern of sediment slugs from 1938 to 2002 were analysed from air photographs tied to detailed field measurement the rate and calibre of sediment flux changed progressively following substantive hillslope input in a storm in 1938 subsequently the channel narrowed and incised decoupling tributary fans from the main stem thereby scaling down the size of sediment slugs as a consequence the dominant influence on the behaviour of sediment slugs and associated relaxation processes changed from tributary fans to the type and distribution of bedrock outcrops along the reach

channel bed adjustments following major aggradation in a steep headwater setting findings from oyabu creek kyushu japan abstract a typhoon in 1993 induced major aggradation along oyabu creek a steep gravel bed mountain stream in kyushu japan processes of sediment reworking are inferred from a 7 year monitoring program that measured adjustments to channel cross sections the longitudinal profile and the extent distribution of bedrock outcrops along a 3 km study reach over time the reach adopted a riffle and pool structure with notable increase in the area of exposed bedrock on the bed this adjustment process was characterised by progressive reduction in sediment storage change per unit flow the relaxation pathway following disturbance induced by the typhoon was shaped by the magnitude and frequency of subsequent rainfall events the capacity of these events to transport available sediments and physical linkages between reaches adjacent subreaches demonstrated differing relaxation pathways in response to these influences induced by spatial and temporal variability in threshold conditions along the channel longer term evidence indicates that responses to major disturbance such as the 1993 typhoon occur as cycles of around 20 year duration a relaxation period of 7 years is required to attain a quasi equilibrium bed configuration and rate of sediment flux the timeframe of cycles is considered to reflect changes to hillslope channel bed coupling marking the period required to generate sufficient sediment stores to reactivate phases of aggradation and subsequent degradation

lateral segmentation within the subducting lithosphere three dimensional structure beneath the north island new zealand abstract three dimensional 3 d velocity structure beneath the north island new zealand is determined by the inversion of travel time data from local earthquakes and the result is compared with the 3 d attenuation structure previously obtained in the upper mantle a high velocity and high q zone represents the subducting pacific plate the slab is dipping steeply to the northeast of the island possibly continuing to the tonga kermadec trench in the southwestern part it dips gently and seems to continue to the alpine fault in the south island two discontinuities in the velocity structures are found beneath the north island between these boundaries is a high velocity slab bending both the ends deeper the discontinuous structure along with the attenuation structure and the other seismological evidence indicates the segmentation within the subducting lithosphere the slab is likely to be torn at the segmentation boundary

dynamic variation of middle to late ordovician cephalopod provincialism in the northeastern peri gondwana region and its implications abstract middle to late ordovician cephalopod occurrence data from south china and adjacent terranes in the northeastern peri gondwana region are used to define biogeographic provinces several multivariate methods are adopted for biogeographic analysis including cluster analysis non metric multidimensional scaling and network analysis during the middle ordovician three biogeographic provinces in this region are recognized the australia the north china tibet sibumasu nts and the south china altun sa provinces in the late ordovician three provinces with modified geographic ranges may also be recognized as the cephalopods of the tibetan region and sibumasu terrane changed significantly and accordingly they have been included with south china altun to form a south china tarim tibet sibumasu province stts while the other two late ordovician provinces are the australia and the north china provinces the dynamic variation of cephalopod provincialism in the northeastern peri gondwana region may have been controlled by the changing palaeolatitude and differentiated movement of these plates or terranes from the middle through late ordovician

flow resistance estimation in mountain rivers examination of the flow resistance of high gradient gravel and boulder bed rivers using data collected in british mountain rivers with slopes of 0 4 4 shows that there are differences in resistance variation between mountain and lowland rivers and that between site variations do not necessarily reflect at a site variations comparison of data with the familiar resistance equation relating the dracy weisbach friction factor to the logarithm of relative submergence shows that the equation tends to overestimate the resistance in uniform flow the equation also tends to underestimate the rate of change of resistance at a site as discharge varies with high gradients the influences of nonuniform channel profile sediment size distribution channel slope and sediment transport are reviewed but the data do not allow any quantification of these effects instead an empirical approach based on the available data is presented allowing the friction factor to be calculated from the relative submergence with an error of up to n25 to n35 a summary of the field data is included

block rotation and deformation by strike slip faults 2 the properties of a type of macroscopic discontinuous deformation study of the general features of deformation by systems of subparallel strike slip faults shows that the governing constraints are kinematic the fault blocks must remain in contact with each other and the deformed area must fit with its surroundings as a result fault blocks that move laterally without significant internal deformation also rotate about vertical axes relative to boundaries of the fault domain by an amount that is quantitatively related to fault slip spacing and orientation areas where left and right lateral faults move simultaneously are usually divided into domains that contain faults of one kind only deformation of such multidomain areas is nonhomogeneous but the differences between domains can compensate for each other so that the regional deformation is quite simple strike slip faulting combined with block rotation is an efficient mechanism of deformation because modest offsets and rotations change the linear dimensions of faulted areas by several tens of percents which may often greatly exceed the results of other types of coeval deformation paleomagnetic data can provide an independent measure of block rotations and should be used to supplement structural data block rotation changes the initial angles between right and left lateral faults and also their orientation relative to the stress field the faults probably tend to rotate away from the axis of maximum compression rotated faults continue to move because they are weak surfaces since the deformation depends on geometric factors such as fault orientation and domain geometry it is not simply related to the stress field these properties including rotation of material units characterize discontinuous deformation in general

the dominance of dispersion in the evolution of bed material waves in gravel bed rivers bed material waves are temporary zones of sediment accumulation created by large sediment inputs recent theoretical experimental and field studies examine factors influencing dispersion and translation of bed material waves in quasi uniform gravel bed channels exchanges of sediment between a channel and its floodplain are neglected within these constraints two factors influence relative rates of dispersion and translation 1 interactions between wave topography flow and bed load transport and 2 particle size differences between wave material and original bed material our results indicate that dispersion dominates the evolution of bed material waves in gravel bed channels significant translation requires a low froude number which is uncharacteristic of gravel bed channels and low wave amplitude which for a large wave can be achieved only after substantial dispersion wave material of small particle size can promote translation but it primarily increases bed load transport rate and thereby accelerates wave evolution copyright 2001 john wiley sons ltd

sediment transport storage relations for degrading gravel bed channels 1 in a drainage network sediment is transferred through a series of channel valley segments natural sediment storage reservoirs that are distinguished from their neighbors by their particular capacity to store and transport sediment we propose that the sediment transport capacity of each reservoir is a unique positive function of storage volume which influences sediment mobility and availability through variations in bed surface texture channel gradient and availability of valley floor sediments for erosion examinations of the form of transport storage relations of degrading alluvial reservoirs using published field studies flume experiments and simulations support a conceptual model that includes two phases in phase i filled channels respond to variations in supply primarily by changes in stored sediment volume with little change in transport rate in phase ii channel mobility is responsive to supply through armoring and form roughness although these phases could represent idealized transport limited phase 1 or supply limited phase ii states we propose that every alluvial reservoir responds to changes in sediment inputs by changing both storage and transport rate the propensity for either depending on reservoir characteristics and the sediment exchange processes in the channel transport storage relations for phase ii are approximately linear but examination of numerical simulations and flume experiments indicates that armoring imparts positive curvature simulations of degradation of an alluvial reservoir with channel and valley floor surfaces indicate that interactions between channel lowering and lateral erosion are critical in the manifestation of a transport storage relation better knowledge of transport storage relations could lead to improved sediment routing models for drainage basins wherein component sediment reservoirs dynamically adjust to varying sediment loads

floodplain storage of mine tailings in the belle fourche river system a sediment budget approach arsenic contaminated mine tailings that were discharged into whitewood creek at lead south dakota from 1876 to 1978 were deposited along the floodplains of whitewood creek and the belle fourche river the resulting arsenic contaminated floodplain deposit consists mostly of overbank sediments and filled abandoned meanders along white wood creek and overbank and point bar sediments along the belle fourche river arsenic concentrations of the contaminated sediments indicate the degree of dilution of mine tailings by uncontaminated alluvium about 13 per cent of the 110 106 mg of mine tailings that were discharged at lead were deposited along the whitewood creek floodplain deposition of mine tailings near the mouth of whitewood creek was augmented by an engineered structure about 29 per cent of the mine tailings delivered by whitewood creek were deposited along the belle fourche river floodplain about 60 per cent of that sediment is contained in overbank deposits deposition along a segment of the belle fourche river was augmented by rapid channel migration the proportions of contaminated sediment stored along whitewood creek and the belle fourche river are consistent with sediment storage along the floodplains of perennial streams in other similar sized watersheds

bending within the axial tectonic belt of new zealand in the last 9 myr from paleomagnetic data abstract tongaporutuan stage late miocene 11 6 myr sedimentary rocks at two localities within the axial tectonic belt of new zealand have a direction of magnetisation in which the declination is 020 11 and 030 8 d 95 the directions of magnetisation in rocks of similar age outside the belt have a declination like that of the earth s present axial dipole 360 the clockwise deviation of the declination is inferred to indicate bending of the rocks within the zone of deformation between the pacific and indian plates due to the oblique convergence of these plates

a block model of distributed deformation by faulting it is clear from palaeomagnetic evidence that large and hitherto unexpected rotations about a vertical axis are common in regions of distributed continental deformation we propose a simple two dimensional model to illustrate how fault movement and block rotation within a zone of distributed deformation may be related to the relative motion of the rigid plates that bound the zone one surprizing feature of this model is that the component of strike slip motion on the faults within the deforming zone is in the opposite sense to the strike slip component across the zone as a whole thus slip vectors within the zone are not the same as that between the bounding rigid plates in contrast to deformation at oceanic plate boundaries examples of active fault geometries similar to those of our model can be seen in greece iran and the western usa

high resolution stable isotope stratigraphy of upper ordovician sequences constraints on the timing of bioevents and environmental changes associated with mass extinction and glaciation the two phases of the late ordovician mass extinction are approximately coeval with the periods of rapid climate change associated with the onset and demise of the gondwanan glaciation in this paper we argue that the distinctive late ordovician carbon isotope profile provides a chronostratigraphic ruler against which a sequence of environmental and biotic events may be located the ruler also allows regional and global high resolution correlation of successions representing very different environments cores from the upper ordovician succession of estonia and latvia record a large 1 3 c c a r b o n a t e excursion up to 6 with a similar profile shape the consistent relationship between the chemostratigraphy and biostratigraphy in the baltic region suggests that the isotope profile has a regional chronostratigraphic value the presence of similar profiles in nevada united states suggests that the excursion is a global chronostratigraphic signal this interpretation enables a detailed correlation to be made between upper ordovician shallow marine and basinal sequences that have wholly different faunas successions in the baltic area and in canada that do not display the model profile are interpreted as incomplete reinter pretation of these important successions significantly modifies the global database used to assess the pattern of diversity change during the mass extinction key levels of environmental change have been located against the carbon isotope profile new oxygen isotope data from brachiopod and ostracode calcite set tight limits on the start of the glacial events cooling and sea level fall started at the same stratigraphic level as the start of the carbon isotope excursion the later rise in sea level and fall in oxygen isotope values record the end of the glaciation these restrict the duration of the main glaciation to only 1 5 graptolite zones we propose that models of the carbon cycle should be adapted to be consistent with the temporal relationships between carbon cycling sea level fall and temperature change documented here the chronostratigraphic ruler provided by the carbon isotope profiles is used as a scale to determine the sequence of biotic changes and to allow high resolution correlation of biotic events at different locations this approach identifies regional similarities and differences in the patterns of extinction the main phase of graptolite extinction in the monitor range nevada for example is synchronous with the chitinozoan extinction in the baltic region but chitinozoan taxa survive to higher levels in nevada the benthic faunas in the baltic region demonstrate that the main extinction event corresponded with the beginning of the isotope excursion at the start of the hirnantian the level at which the marine environment started to change rapidly but that there were further extinctions of species within the early hirnantian the cold adapted hirnantia fauna did not appear immediately after the extinction in this area the relationship between the second phase of extinction and the carbon isotope excursion is less clear but the available data suggest that the extinction coincides with a time of rapid environmental change but not at the inception of environmental change as happened in the first phase

reconstructions of the new zealand region for the neogene abstract the major structural elements of the present day plate boundary zone through new zealand are a subduction zone under the northern half of the country linked by a wide transform zone to the southward extension of the plate boundary through fiordland and the macquarie ridge using finite rotations of the pacific australian plate pair a sequence of reconstructions of the relative positions of the plates is presented reconstructions of the plate boundary zone based on paleomagnetic data involve essentially the same structural elements as today but with large clockwise changes in their trend with time

river adjustment to changes in sediment load the effects of tin mining on the ringarooma river tasmania 1875 1984 the mining of alluvial tin in the ringarooma basin began in 1875 reached a peak in 1900 20 and had virtually ceased by 1982 during that time 40 million m3 of mining waste were supplied to the main river quickly replacing the natural bed material and requiring major adjustments to the channel based on estimates of sediment supply from more than 50 widely scattered mines and the frequency of flows capable of transporting the introduced load the river s transport history is reconstructed using a mass conservation model because of the lengthy time period 110 years and river distance 75 km involved the model cannot predict detailed change but it does reproduce the main pattern of sediment movement in which successive phases of aggradation and degradation progress downstream peak storage is predicted in that part of the river where braiding and anastomosis are best developed aggradation was most rapid in the upper reaches close to major supply points becoming slower and later with distance downstream channel width increased by up to 300 per cent where the valley floor was broad and braiding became relatively common bridges had frequently to be replaced while bed levels were still rising in lower reaches degradation began in upper ones notably after 1950 and by 1984 had progressed downriver over 30 km rates of incision reached 0 5 m yr 1 especially in the early 1970s when record high flows occurred as a result of degradation the bed material became gravelly through either reexposure of the original bed or lag concentration of coarser fractions also a narrower unbraided channel has developed the river is beginning to heal itself and upper reaches now have reasonably stable beds but at least another 50 years will be required for the river to cleanse its channel of mining debris

response of a channel with alternate bars to a decrease in supply of mixed size bed load a flume experiment the response of a channel with a topography and modeled bed material size typical of gravel bed rivers to reductions in sediment supply was investigated in a laboratory flume filled and fed with a sand gravel mixture after a series of quasi stationary alternate bars were formed under equilibrium sediment transport feed rate was reduced in two steps to one third and one tenth the initial rate as discharge was held constant the primary response following both reductions was an increase in bed surface particle size as a corridor of intensive bed load transport contracted and local transport rates decreased after the first feed rate reduction the channel incised by twice the mean water depth on average and caused distal bar surfaces to emerge as terracelike features bar roughness decreased and mean boundary shear stress exerted on bed surface particles increased little incision occurred after the second feed rate reduction

the end ordovician mass extinction a single pulse event abstract the end ordovician mass extinction eome is widely interpreted as consisting of two pulses associated with the onset and demise of the gondwana glaciation respectively with the second pulse eradicating the distinctive glacially related hirnantian benthic biota hbb a global review of occurrence data of latest ordovician benthic marine organisms reveals that virtually all warm water benthic assemblages previously assigned to the hbb comprise two distinct and clearly postglacial faunas both younger middle and late hirnantian respectively than the cool water hirnantia fauna latest katian to early hirnantian the newly recognised three transitional benthic faunas i e tbfs 1 3 can be closely tied to graptolite conodont and chitinozoan biozonations the hirnantian isotope carbon excursion hice and the glaciation thereby providing an integrated much higher resolution timescale for understanding the tempo and nature of the eome at this finer resolution we postulate a more profound impact of the first pulse of the eome than hitherto envisaged as evidenced by opportunistic expansion of the hirnantia fauna globally and the complete absence of metazoan reefs in its immediate aftermath we also argue based on high quality data from well documented benthic groups in south china i e brachiopods tabulate and rugose corals trilobites and sponges that the magnitude of the second pulse of the eome caused by the deglaciation has been overestimated because the two postglacial faunas i e tbfs 2 3 were part of a subsequent recovery phase of marine ecosystems rather than contributing to biodiversity decline thus it is more plausible to reinterpret the eome as a single pulse rapid event that was followed by a prolonged initial recovery intermittently impeded by climatic shocks through the hirnantian prior to the onset of a progressive reestablishment of marine ecosystems during the early silurian rhuddanian and aeronian associated with an overall amelioration of climatic conditions

extent and bathymetry of north american platform seas in the early silurian the north american craton is 25 covered by lower silurian llandovery rocks based strictly upon the geographic area of surviving marine strata preserved in outcrop and the subsurface this figure does not take into account extensive post silurian tectonics and erosion isolated structural basins in which these strata are found today were not necessarily defined as corresponding topographic basins in the silurian analysis of interbasin structural arches and outliers provides important clues as to the actual extent of early silurian seas information on the age of tectonic origin for 15 prominent arches is reviewed the placement and significance of 11 key outliers is also discussed evidence of this kind indicates early silurian platform seas were among the most extensive of the paleozoic probably more than 65 of the north american craton was then flooded nothing on so vast a scale serves as a recent guide to the past the pliocene holocene bahamian banks do provide however worthy models for the role of bathymetry and water circulation as related to the changeover from laterally monotonous blanket deposits to a more complex mosaic of facies the original bathymetry of early silurian environments may be determined correlated and mapped on the basis of widespread carbonate cycles linked to sea level fluctuations the range of fully integrated facies patterns includes 1 coral stromatoporoid stromatolite paleosol cycles williston basin 2 pentamerid brachiopod coral stromatoporoid stromatolite cycles michigan basin and 3 stricklandiid brachiopod pentamerid brachiopod coral stromatoporoid cycles east iowa basin with shallow bathymetries of 0 30 m the williston class tends to represent mosaic facies while with bathymetries of 0 60 m and 10 90 m the deeper water michigan and iowa classes typically involve blanket deposits bathymetry of other basin deposits generally fits one of these three classes maximum and minimum stands in sea level during late llandovery time are represented by bathymetric maps

the kinematics of the plate boundary zone through new zealand a comparison of short and long term deformations summary surveys of shear strain rates derived from repeated triangulation cover about one quarter of the area of the plate boundary zone through new zealand and are well distributed within it using a method developed by haines relating shear strains to the total strain and velocity fields the dilatational and rotational strain rates and the velocities within the deformed zone are derived the plate boundary zone is shown to be two dimensional for the most part in that gradients of the velocity along the length of the zone are small or zero the shear strain rates are not uniform however they reach a maximum along a central axis and decrease gradually to zero toward the sides nor are the two independent components of strain one involving shortening or extension perpendicular and the other shear parallel to the zone equally developed everywhere there is a clear geographic separation with shortening developed over the subduction thrust and shear developed behind in a zone of wrench faulting time variations in the strain field in part of the region above the subduction interface are related to changes in the degree of coupling across the interface a velocity field is computed the relative velocity of the two plates from this data agree very well with that derived from seafloor spreading data these strain and velocity fields derived from geodetic studies give the short term kinematics of the plate boundary zone the long term kinematics of the zone are estimated from 1 uplift and subsidence data which are related to changes in crustal thickness and hence to dilatational strain and 2 variation in the declination of primary magnetization in rocks of known age related to the rotational strain the rate of rotational strain has increased in time from about 2 to 3 myr 1 10 myr ago to about 9 myr 1 today the increase can be understood as a secondary effect of a developing compressional component increasing the coupling between the plates so that more of the motion parallel to the zone is accommodated by distributed shear and less by aseismic slip the rates of strain averaged over the last 1 myr or so and at a scale length of a few tens of kilometres are closely similar in distribution and magnitude to the strain rates derived from short term kinematics while therefore at scale lengths of a few hundred metres or so faulting is very important and the deformation is discontinuous with unstrained blocks faulted with large but uncertain slip against adjacent blocks the deformation at these longer scale lengths is continuous and regular the two consequences of this study are that 1 strain from geodetic data can be directly related to the average long term deformation and therefore can be an important tool in the study of deformation in regions of current tectonic activity and 2 at scale lengths of a few tens of kilometres the deformation of a region can be described as the deformation of a continuum and we can ignore the effects of faulting

impacts of land use change on patterns of sediment flux in weraamaia catchment new zealand forest clearance between the 1890s and the early 1920s subsequent scrub growth and commencement of an afforestation program in 1979 modified the pattern and rate of sediment delivery to valley floors via shallow landslides and gully complexes in a steep headwater catchment 4 8 km2 in new zealand analysis of the historical record air photograph interpretation and field survey indicates that both erosion types occurred across the catchment in the 1938 storm aggrading channel beds and widening the active channel zone in contrast a 1 in 100 year event in 1988 cyclone bola induced numerous shallow landslides but erosion of gully complexes was largely restricted to subcatchments that retained pasture and the geomorphic impact of this event on channels was small the changing volume and calibre of materials delivered to the valley floor and the distribution of gully complexes altered patterns and rates of channel adjustment after the events and the resulting sediment flux development of gully complexes maintained coupling processes with channels for periods up to 102 years forming wide channels in downstream reaches upstream downstream connectivity along the trunk stream was altered by the formation of a large debris fan at the confluence with a tributary subjected to gully complex erosion in contrast slopes subjected to shallow landslides became decoupled from channels within 10 years accelerating channel degradation and narrowing effective conveyance of a large volume of fine grained materials promoted immediate aggradation of gentle gradient channels downstream as gully complex areas stabilized following an increase in forest and scrub cover channel courses became significant sediment sources although shallow landslide activity will continue to induce intermittent aggradation in the future it is inferred that average sediment yield will continue to diminish to levels approaching those experienced prior to clearcutting and the pattern of sediment flux will recover by 2030

unfolding the wadati benioff zone in the kermadec new zealand region abstract as the deep seismic zones are associated with subducted oceanic crust it is important to establish the extent and continuity of each of these zones using consistent earthquake locations then the former oceanic crust can be restored to the surface of the earth by unfolding the seismic zone about the trench this unfolded crust should be used in plate reconstructions this process has been carried out for the deep seismic zone in the kermadec new zealand region where the deep seismic zone is defined by a careful selection of i s c hypocenters and the former oceanic crust is established by unfolding plate reconstructions using two sets of rotation poles show that the deepest parts of the observed seismic zone along its length were not subducted at the same time further the currently observable zone is not directly associated with earlier volcanism in northwest new zealand between 6 and 20 ma ago

the last 25 ma of rotational deformation in part of the new zealand plate boundary zone abstract the marlborough fault system is a zone of dextral transpression in continental crust and marks the southern end of the hikurangi subduction system between the obliquely convergent australian and pacific plates detailed mapping over an area of 100 km2 has revealed a complex history of deformation during the last 25 ma the development of a thrust belt in the miocene referred to as d1 deformation was synchronous with the deposition of a thick submarine fan complex the beginning of d1 deformation may mark the initiation of the subduction zone in this part of the plate boundary zone subsequently in the plio pleistocene the region formed a zone of dextral shear marked by major strike slip faults and zones of distributed deformation referred to as d2 deformation crustal blocks less than 5 km across may have rotated ca 60 clockwise about vertical axes relative to the pacific plate in the last 4 ma the pattern of deformation during the last 10 ka to 100 years is consistent with the long term d2 deformation and suggests that large crustal blocks resting on the subducted pacific plate have rotated clockwise about vertical axes relative to the pacific plate accommodated by dextral shear further to the sw in the marlborough fault system the overall effect of the deformation has been the rotation of the edge of the southern part of the hikurangi margin from a w to nw trend in the early miocene to a ne trend today

landslide driven erosion and slope channel coupling in steep forested terrain ruahine ranges new zealand 1946 2011 abstract landslides are an important means of conveying sediment from slopes to channels in steepland environments but landsliding is a discontinuous process this means that any single assessment in time of their contribution to the sediment cascade is of limited value to better understand landscape dynamics and the contribution of landslides to slope channel coupling over time this paper quantifies connectivity over a time span of 65 years in small steep headwater catchments in the southern ruahine range new zealand temporal variability in landsliding and slope channel coupling was assessed using six sets of aerial photography flown between 1946 and 2011 from which over 6900 landslides were mapped in arcgis of which up to 78 connected with the stream network estimates of the volume of material delivered by landslide erosion to headwater channels were based on ground survey measurements of selected landslide scars and suggest that between 1946 and 2011 over 5 million m 3 of sediment was delivered from slopes to channels in the 221 km 2 study area forest cover is not sufficient to prevent this erosion these catchment systems are particularly vulnerable to high magnitude storm events which significantly elevate landslide intensity and enhance sediment delivery as occurred in the mid 1970s the legacy of these events remains in these headwater channels with ongoing consequences for stream and hazard management in and adjacent to the ranges

on the causes of mass extinctions the temporal link between large igneous province lip eruptions and at least half of the major extinctions of the phanerozoic implies that large scale volcanism is the main driver of mass extinction here we review almost twenty biotic crises between the early cambrian and end cretaceous and explore potential causal mechanisms most extinctions are associated with global warming and proximal killers such as marine anoxia including the early middle cambrian the late ordovician the intra silurian intra devonian end permian and early jurassic crises many but not all of these are accompanied by large negative carbon isotope excursions supporting a volcanogenic origin most post silurian biocrises affected both terrestrial and marine biospheres suggesting that atmospheric processes were crucial in driving global extinctions volcanogenic atmospheric kill mechanisms include ocean acidification toxic metal poisoning acid rain and ozone damage and consequent increased uv b radiation volcanic darkness cooling and photosynthetic shutdown each of which has been implicated in numerous events intriguingly some of the most voluminous lips such as the oceanic plateaus of the cretaceous were emplaced with minimal faunal losses and so volume of magma is not the only factor governing lip lethality the missing link might be continental configuration because the best examples of the lip extinction relationship occurred during the time of pangaea many of the proximal kill mechanisms in lip extinction scenarios are also potential effects of bolide impact including cooling warming acidification and ozone destruction however the absence of convincing temporal links between impacts and extinctions other than the chicxulub cretaceous example suggests that impacts are not the main driver of extinctions with numerous competing extinction scenarios and the realisation that some of the purported environmental stresses may once again be driving mass extinction we explore how experimental biology might inform our understanding of ancient extinctions as well as future crises

composite transform convergent plate boundaries description and discussion abstract the leading edge of the overriding plate at an obliquely convergent boundary is commonly sliced by a system of strike slip faults this fault system is often structurally complex and may show correspondingly uneven strain effects with great vertical and translational shifts of the component blocks of the fault system the stress pattern and strain effects vary along the length of the system and change through time these margins are considered to be composite transform convergent ctc plate boundaries examples are given of structures formed along three ctc boundaries the aleutian ridge the solomon islands and the philippines the dynamism of the fault system along a ctc boundary can enhance vertical tectonism and basin formation this concept provides a framework for the evaluation of petroleum resources related to basin formation and mineral exploration related to igneous activity associated with transtensional processes

geodetically determined strain across the southern end of the tonga kermadec hikurangi subduction zone summary a method of simultaneous reduction is presented for determining strain rates from multiple triangulation surveys where common triangulation stations have been used but the angles of the old survey have not necessarily been reobserved this method is applied to triangulation in the northern south island at the southern end of the tonga kermadec hikurangi subduction zone from a profile of shear strain across the indian pacific plate boundary the displacement of the indian plate relative to the pacific is calculated to be 54 9 mm yr at an azimuth of 84 f lo in remarkable agreement with the motion predicted by global plate tectonic models most of this motion occurs within a 15okm wide zone bounded on the east by the hikurangi trough within this zone the motion is partitioned near the hikurangi trough no slip is occurring at the upper surface of the subducting pacific plate the subduction thrust and motion is predominantly thrusting normal to the trough axis to the west is a region of predominantly dextral strike slip faulting this pattern is consistent with fitch s model of oblique subduction to the south of the profile a change is observed in the azimuth of the faulting along a line which marks the southern extent of the subduction slab indicating the end of the partitioned motion

morphological controls on the downstream passage of a sediment wave in a gravel bed stream sediment waves in river systems have been widely reported although few studies have examined the interaction between these waves and the morphology of the reaches through which they pass this interaction determines how waves are modified as they propagate downstream this study documents the origin and downstream passage of an avulsion generated sediment wave through a 374 m study reach of the allt dubhaig scotland a nested survey framework was adopted with volumes calculated from cross sections spaced between 10 and 40 m apart documenting the origin and downstream passage of the wave the wave moved through an intensively c 1 m cross section spacing monitored 120 m stretch reach a within the study reach allowing assessment of sediment exchanges between the incoming wave and the local morphology successive surveys show the movement of the wave through and out of the reach and also that areas where wave sediment was deposited did not always correspond with areas of subsequent erosion reach a was divided into three morphologically distinct sub reaches 1a 2a and 3a within which sediment fluxes and the three dimensional distribution of erosion deposition were estimated sediment wave input into 1a and 2a relatively stable sub reaches caused forced bar aggradation and erosion of sediment from elsewhere within the reach which then became part of the wave the downstream transfer of this sediment into unstable 3a caused aggradation and in response widespread erosion which increased the magnitude of the sediment wave as it exited reach a sediment exchange between the recipient reach and the wave depends upon local morphological stability and is a crucial process affecting wave magnitude and attenuation the macroscale sediment wave interacted with rather than overwhelmed the recipient morphology 1998 john wiley sons ltd

patterns of sediment slug translation and dispersion following typhoon induced disturbance oyabu creek kyushu japan a six year monitoring programme characterized the migration dispersion patterns of sediment slugs generated following typhoon induced disturbances in 1993 and 1997 along a single thread gravel bed stream oyabu creek on kyushu island japan this laterally con ned creek comprises rif e pool sequences with intervening bedrock outcrops the passage of sediment pulses associated with sediment slug processes re ected and was controlled by the rif e pool structures which provided channel bed roughness the volume of sediment stored along valley oors and the distribution of bedrock outcrops changes to bed material size following major sediment inputs during the disturbance events also exerted an in uence on subsequent sediment slug processes the sequence of rainfall events together with changes to channel bed structure induced different phases in the sediment slug processes the capacity of a reach to store or trap sediment as recorded by the longitudinal structure of the channel varied during these differing phases copyright 2004 john wiley sons ltd

sediment deposition and transport patterns following a reservoir sediment release a reservoir sediment release on the north fork poudre river supplied 7000 m3 of silt to pebble sized sediment to an originally boulder bed channel deposition along the 12 km of channel downstream from the reservoir occurred primarily in pools during the subsequent snowmelt hydrograph sediment was progressively scoured from the upstream and then the downstream pools initial sediment reworking in the pools created a deep narrow thalweg scoured to the original pool bed with additional sediment deposition in lateral eddies continued reworking reduced but did not completely remove these eddy deposits the channel became supply limited with respect to finer grain sized fractions clay to medium sand first at upstream and then at downstream sites and eventually became supply limited with respect to coarser grain sized fractions coarse sand to pebbles bedload transport rates at a site were strongly linked to the depletion of sediment stored in upstream pools magnitude duration and sequence of flows were all important controls on bedload transport and return of the channel to its prerelease state

focal mechanisms of large earthquakes in the south island of new zealand implications for the accommodation of pacific australia plate motion b the plate motion model nuvel 1 predicts oblique convergence between the pacific and australian plates in the south island of new zealand we used p and sh body waveform analysis to constrain the focal mechanisms of the 15 largest earthquakes ms 5 8 that have occurred in this region since 1964 in order to see how the plate motion is accommodated at the southern end of the alpine fault convergence is achieved by oblique slip movement along a concentrated zone of deformation in the southern offshore region one event may be related to thrusting of the australian plate beneath the pacific plate and another strike slip event probably demonstrates movement on an active strike slip fault system parallel to but offset from the southern limit of the alpine fault this geometry provides a possible mechanism for the rapid uplift of the fiordland region deformation in the northern south island is more distributed in the south west marlborough region partitioning occurs between strike slip faulting in the se and reverse faulting farther nw in the buller region we suggest that the partitioning developed as a consequence of an increasing component of shortening that was accommodated by slip on reactivated pre existing normal faults in the buller region shortening in the buller region may have deflected the ne end of the alpine fault towards the nw forming the prominent bend the marlborough fault system with its youngest and most active faults to the se probably developed in an attempt to maintain a through going strike slip structure as each of the strike slip faults was transported towards the north west partitioning of the opposite polarity with reverse faulting se of the strike slip faulting occurs in north east marlborough the boundary between the two different styles of partitioning in ne and sw marlborough appears to coincide with a change in the nature of the downgoing slab and a change in strike of faults of the marlborough fault system a normal faulting earthquake on the northern edge of the chatham rise probably results from a complex interaction of the buoyant continental crust in that region with the subduction zone and the overlying marlborough fault system

large tectonic rotation of part of new zealand in the last 5 ma abstract detailed paleomagnetic data from the wairoa syncline a middle miocene to the present forearc basin on the east coast of the north island new zealand show that the rate of clockwise rotation for the last 5 ma has been 7 8 ma of which less than 1 5 ma can be explained by apparent polar wander due to motion of the australian or pacific plates this rotation is similar to a present day rate of 7 ma determined from geodetic data between 5 and 20 ma ago the rate of tectonic rotation is poorly determined and may be between 0 and 2 ma the change in the rate of rotation of the wairoa syncline around 5 ma is probably related to a markedly different tectonic style in the new zealand region within the last 5 ma associated with a change in position of the euler poles of rotation for the pacific australian plates

development of channel organization and roughness following sediment pulses in single thread gravel bed rivers large episodic inputs of coarse sediment sediment pulses in forested mountain streams may result in changes in the size and arrangement of bed forms and in channel roughness a conceptual model of channel organization delineates trajectories of response to sediment pulses for many types of gravel bed channels channels exhibited self organizing behavior to various degrees based on channel gradient presence of large in channel wood or other forcing elements the size of the sediment pulse and the number of bed mobilizing flows since disturbance typical channel changes following a sediment pulse were initial decreases in water depth in variability of bed elevations and in the regularity of bed form spacing trajectories of change subsequently showed increased average water depth more variable and complex bed topography and increased uniformity of bed form spacing bed form spacing in streams with abundant forcing elements developed at a shorter spatial scale two to five channel widths than in streams without such forcing mechanisms five to 10 channel widths channel roughness increased as bed forms developed

seismicity structure and tectonics of the wellington region new zealand summary the wellington region lies on the border between the pacific and australian plates the former being subducted the plate interface lies at shallow depth under the region 10 60 km so that detailed and long term monitoring of the seismicity of the zone where large thrust earthquakes are expected to occur is possible hypocentres for events recorded by a 12 station seismic network for the period 1978 1982 7231 events have been refined by the use of a threedimensional velocity model derived from a simultaneous inversion of arrival time data from 129 local events for both hypocentres and velocity the hypocentres show that the subducting pacific plate is defined by a nw dipping zone of relatively intense activity the plate interface as given by the upper envelope of this activity is offset vertically by 7 km on average along a nw se line through cook strait parallel to the direction of absolute motion of the pacific plate rather than to the direction of convergence the strike of the interface at deeper levels also changes across this line this distortion may partly reflect effects of the transition to continent continent type convergence further south within the subducting pacific plate the seismic activity defines two parallel zones separated by about 20 km the lower zone being much less active and perhaps merging with the upper zone at a depth of 80 90 km composite focal mechanisms of events in the upper zone imply predominantly down dip tension with a compression axis perpendicular to the plate interface the mechanism in the lower zone also implies down dip tension but the compression axis has rotated to be horizontal and along strike indicating a component of lateral shearing within the plate these two types of mechanism correlate well with those found previously for events at depths of 150 km or more thus it seems that the large negative buoyancy of the subducted lithosphere dominates the internal stress field throughout the length of the seismically active region the lithosphere acting as a stress guide there is no evidence for a significant number of events with mechanisms indicating thrusting along the plate interface the seismic velocity in the region corresponding to the upper seismic band is close to that typical for oceanic crust which here is probably considerably thicker than normal there is no evidence for a substantial increase in velocity down

sediment erosion dynamics of a gullied debris slide a medium term record medium term post event sediment flux investigations are rare for headwater catchments and particularly sparse for gullied hillslope failures repeat field observation ground photography and cross section measurements of a debris slide scar at the wet swine gill headwater catchment 0 65 km2 in the english lake district uk provide evidence of erosion and deposition dynamics over the medium term 2002 2014 these data are compared to site topographic and meteorological conditions to evaluate potential process response linkages rill and gully erosion networks establish soon after the slide failure 1 february 2002 thereafter gully enlargement proceeds rapidly first by vertical downcutting prior to lateral expansion and gully wall angle decline changes in cross sectional width depth and area 2002 2013 are characterised by statistically significant p 0 05 negative exponential growth models r2 width 0 88 0 97 depth 0 71 0 86 area 0 87 0 93 gully walls were dominated by erosion but the gully bed was characterised by episodic sediment production storage and transfer often leading to temporary deposition specific erosion rates on the gully wall exceeded those on the adjacent slide scar by up to 764 maximum values wall 0 0084 scar 0 0011 m2 m 1 d 1 upslope contributing runoff area and slope gradient are generally important for erosion although linear regression analysis demonstrates weak or insignificant relationships between meteorological conditions and gully scar sediment flux a general conceptual model of slide scar evolution integrating gully growth and capture summarises activity at this site however transferability to locations with terrain characteristics land management practices and climate conditions different to those existing in the uk uplands remains to be tested this investigation adds to growing appreciation of the complexities of sediment dynamics in headwater catchments and provides clear evidence for the potential of early management intervention to counter detrimental post failure sediment erosion which at this site would have been most effective up to 3 4 years following gully initiation

ecological ranking of phanerozoic biodiversity crises the serpukhovian early carboniferous crisis had a greater ecological impact than the end ordovician we propose a new ecological ranking of the major phanerozoic biodiversity crises in which the serpukhovian biodiversity crisis is ranked fifth in ecological impact lesser than the late devonian but greater than the end ordovician and the end ordovician mass extinction is ranked sixth it is interesting that both the end ordovician mass extinction and the serpukhovian biodiversity crisis were triggered by glaciations other than that common trigger the two events were very different glaciation in the ordovician triggered an enormous jump in the extinction rate of marine organisms and was taxonomically very severe yet the ecological impact of those extinctions was minimal glaciation in the serpukhovian triggered a precipitous drop in the speciation rate but only moderate diversity losses yet the ecological impact of those diversity losses and ecosystem restructuring was an ecological level of magnitude larger than that seen in the end ordovician mass extinction

channel response to sediment wave propagation and movement redwood creek california usa redwood creek north coastal californa usa has experienced dramatic changes in channel confguation since the 1950s a series of large floods in 1955 1964 1972 and 1975 combined with the advent of widespread commercial timber harvest and road building resulted in extensive erosion in the basin and contributed high sediment loads to redwood creek since 1975 no peak flows have exceeded a 5 year recurrence interval twenty years of cross sectional survey data document the downstream movement of a sediment wave in the lower 26 km of this gravel bedded river at a rate of 800 to 1600 m a i durng this period of moderately low flows higher transit rates are associated with reaches of higher unit stream power the wave was initially deposited at a site with an abrupt decrease in channel gradient and increase in channel width the amplitude of the wave has attenuated more than i m as it moved downstream and the duration of the wave increased from eight years upstream to more than 20 years downstream channel aggradation and subsequent degradation have been accommodated across the entire channel bed channel width has not decreased significantly after initial channel widening from large 25 year recurrence interval floods three sets of longitudinal surveys of the streambed showed the highest increase in pool depths and frequency in a degrading reach but even the aggrading reach exhbited some pool development through time the aggraded channel bed switched from functioning as a sediment sink to a significant sediment source as the channel adjusted to high sediment loads from 1980 to 1990 sediment eroded from temporary channel storage represented about 25 per cent ofthe total sediment load and 95 per cent of the bedload exported from the basin

using network analysis to trace the evolution of biogeography through geologic time a case study the biogeographic distribution of organisms has continuously changed through earth9s history as plate tectonics changed the configurations of land masses ocean basins and climate zones yet methods to investigate this dynamic through geologic time are limited here network analysis is used to explore and to visualize the biogeographic history of brachiopods through the entire triassic period many previously recognized biogeographic provinces are found and in addition the stratigraphic ranges of these provinces were identified provinces in the tethys ocean show the lowest degree of connectedness which can be linked to higher evolutionary rates in this tropical ocean basin and possibly also to higher habitat heterogeneity stratigraphically the tethyan provinces are separated largely along the boundaries of the early middle and late triassic this suggests that the events resulting in faunal changes among the index fossils used to define these sub periods also affected the brachiopods however through the 50 m y of the triassic period geographic proximity played a greater role in producing faunal similarity than proximity in geologic age thus network analysis is a viable tool to better understand the dynamic evolution of biogeography through geologic time

environmental control on temporal and spatial differentiation of early silurian pentameride brachiopod communities anticosti island eastern canada the early silurian carbonate succession of anticosti island eastern canada contains a rich and diverse pentam eride brachiopod fauna multivariate analyses of 91 samples total 17 230 specimens confirm a high degree of temporal segregation but only moderate spatial differentiation of the virgiana pentamerus stricklandia ehlersella microcardina lia and clorinda communities most pentameride communities show a wider range of water depth than previously be lieved the v barrandei community occupied a substrate setting from lower ba2 to upper ba3 whereas the v mayvillensis community lived mainly in ba4 the p oblongus community preferred a ba3 setting comparable to the classic pentamerus community but the p palaformis community was predominantly ba4 the stricklandiid communities have a high b diversity dominated by various species of stricklandia ehlersella microcardinalia and kulumbella and occurred most commonly in ba4 but could extend to ba3 environments the clorinda community of anticosti island preferred deep and quiet water settings comparable to its widely accepted ba5 assignment elsewhere at the generic level the virgiana pentamerus and the stricklandiid communities have a largely overlapping ba range but a clear strati graphical separation thus their temporal alternations were not likely controlled by water depth water turbulence or sub

magnetic anomalies and tectonic fabric of marginal basins north of new zealand detailed airborne magnetic studies conducted over the region of the s w pacific marginal basins extending from the solomon islands to new zealand suggest that three major phases of basin formation and island arc development have occurred in this region development of the tasman sea took place during the late cretaceous paleocene development of the basins to the east of the tasman sea occurred predominantly during the oligocene as well as during the upper miocene to recent the south fiji basin consisting of the kupe and minerva abyssal plains is marked by the presence of possibly two rrr triple junction spreading centers that were active between the times of anomalies 13 to 7 36 25 5 m y the kupe abyssal plain shows the presence of residual magnetic anomalies 7 to 13 of the eastern limb of the proposed spreading center the western limb appears to have been subducted beneath the present site of the three kings rise this seafloor spreading phase calculated half spreading rate of 35 mm yr was coincident with the overthrusting phase of the new caledonia ultramafic rocks during that period active volcanism along the then continuous solomons new hebrides fiji lau island arc was taking place magnetic anomalies from 1 to 4 0 8 m y b p are seen to extend along a clearly defined lineation pattern over the north fiji basin analysis of the magnetic anomalies suggests that during the upper miocene at about the time of magnetic anomaly 4 8 m y the solomons lau island arc commenced breaking up through the development of an active spreading center calculated half spreading rate of 35 mm yr located between the new hebrides and fiji portions of the island arc portions of the northeastern sector of the minerva abyssal plain were subducted beneath the north fiji basin during this period between 0 8 m y b p at the time of about anomaly 3 to 2 4 5 3 5 m y the development of the north fiji basin extended into the lau basin and havre trough thus separating the tonga and lau ridges as a result a distinct series of active spreading centers developed southward along the axis of the havre trough lau basin the havre trough is marked by present seismic and submarine volcanic activity residual magnetic anomalies 1 2 0 1 8 m y b p form a symmetrical pattern around the axis of the trough extending south from the lau basin to the active taupo white island volcanic zone of new zealand phases of development of the marginal basins described in this paper may be correlated with phases of changes in the direction and rate of pacific plate motion

post extinction recovery and diversification of reef dwelling brachiopod communities examples from the lower silurian of hudson bay basin canada abstract ziegler s 1965 early silurian brachiopod community zones and boucot s 1975 benthic assemblages have been instrumental in determining the community structures of early middle paleozoic level bottom communities but are difficult to apply to reef ecosystems due to the mixing of level bottom community assemblages in these systems in this study shannon and simpson diversity levels were calculated for reef dwelling brachiopod faunas from several north american and one european localities reef dwelling brachiopod diversity collapsed at the end of the ordovician and did not recover until the mid aeronian when modest diversity reef faunas appeared in the higher tropics reef dwelling brachiopods did not achieve high diversity levels until the telychian when reefs invaded the paleoequatorially located hudson bay and moose river basins the attawapiskat formation telychian contains the earliest known coral stromatoporoid reef complex with associated high diversity brachiopod faunas these faunas were separated into nine community associations through clustering and principal component analyses these associations can be further grouped into a level bottom type and a cryptic type based on dominant brachiopod taxa diversity levels average shell size and substrate type surprisingly the large species pentameroides septentrionalis was able to thrive in the relatively flat and open spaces of inter reef areas and among frame building corals and stromatoporoids within reef cores the absence of stricklandia within the attawapiskat formation is due to the high water temperature of the equatorial seas which were too warm to be invaded by this cool water dependent genus in addition the presence of deep water clorinda and gypidula in the shallow water attawapiskat reefs is explained by the lack of hurricane grade storms in the equatorial region which would be comparable to the quiet water conditions below storm wave base in higher latitudes

sediment pulses in mountain rivers 1 experiments 1 sediment often enters rivers in discrete pulses associated with landslides and debris flows this is particularly so in the case of mountain streams the topographic disturbance created on the bed of a stream by a single pulse must be gradually eliminated if the river is to maintain its morphological integrity two mechanisms for elimination have been identified translation and dispersion according to the first of these the topographic high translates downstream according to the second of these it gradually diffuses away in any given river both mechanisms may operate this paper is devoted to a description of three controlled experiments on sediment pulses designed to model conditions in mountain streams each of the experiments began from the same mobile bed equilibrium with a set rate and grain size distribution of sediment feed in one experiment the median size of the pulse material was nearly identical to that of the feed sediment in the other two the pulse material differed in grain size distribution from the feed sediment being coarser in one case and finer in the other case in all cases the mode of pulse deformation was found to be predominantly dispersive a result that constitutes the main conclusion of this paper the pulses resulted in a notable but transient elevation of sediment transport rate immediately downstream when the pulse was coarser than the ambient sediment the bed downstream remained armored and a migrating delta formed in the backwater upstream when the pulse was finer than the ambient sediment translation was observed in addition to dispersion the presence of the finer material notably elevated the transport of ambient coarse material on the bed downstream in part 2 cui et al 2003 the experimental results are used to test a numerical model

recovery brachiopod associations from the lower silurian of south china and their paleoecological implications a recovery brachiopod fauna occurs in the lower niuchang formation upper rhuddanian lower aeronian llandovery of the xinglongchang section meitan county northern guizhou province south china nine collections were made at the section all of which are dominated by brachiopods and three associations are recognized here and their paleoecology is discussed paleoenvironmental analysis shows a shallowing upward trend for the lower niuchang formation although a global transgression was happening at that time the balance between the global transgression and the regional qianzhong uplift guaranteed a stable environment for the formation of the niuchang formation and the recovery of brachiopods in south china after the end ordovician mass extinction in addition to the traditional methods of principal component analysis and cluster analysis a relatively new technique to paleontology network analysis is applied successfully in this study it is suggested that network analysis could be used as one o

global palaeobiogeographical patterns in brachiopods from survival to recovery after the end ordovician mass extinction abstract extinction events usually disrupt palaeobiogeographical patterns but there have been few detailed studies of the early silurian survival recovery period after the late ordovician mass extinction this paper summarizes and revises published information on the recovery of early and late rhuddanian brachiopod faunas the global dataset consists of 137 occurrences 72 genera and 13 localities of early rhuddanian survival interval and 271 occurrences 91 genera and 26 localities of the late rhuddanian early recovery interval the data are analyzed using cluster analysis nonmetric multidimensional scaling and minimum spanning tree using yule s y coefficient and the raup crick coefficient probabilistic index of similarity the results display palaeolatitudinal distribution patterns for brachiopods during their survival and recovery frequency analysis of the data indicates that cosmopolitan taxa before the mass extinction decreased in their post extinction distribution the survivors were mostly confined to one palaeoplate or even one locality in the survival interval but expanded progressively in the subsequent recovery period

paleomagnetic evidence for the age and extent of middle tertiary counterclockwise rotation dixie valley region west central nevada paleomagnetic data obtained from oligocene to lower miocene igneous rocks and middle miocene basaltic rocks at fifteen localities from a region surrounding dixie valley in west central nevada indicate that parts of the area experienced counterclockwise vertical axis rotation and these data provide constraints on the extent and timing of rotation counterclockwise vertical axis rotation probably exceeding 30 is indicated for oligocene to lower miocene rocks in the central part of the study area calculated rotations increase with increasing age of the oligocene to lower miocene rocks indicating that vertical axis rotation was concurrent with ash flow deposition about 23 33 ma paleomagnetic data indicate that middle miocene basaltic rocks about 10 17 ma postdate significant counterclockwise vertical axis rotation although this interpretation is complicated because the rocks were erupted episodically in pulses that apparently were short lived with respect to geomagnetic secular variation counterclockwise rotation was related to a deformation event that predated development of the present basin and range physiography of the area the total amount of crustal rotation in tertiary time in the area is poorly known rotation estimates calculated from time averaged mean directions that incorporate data from a broad range of the oligocene to lower miocene units probably underestimate total tertiary rotation because the mean directions include data from units that postdate much of the rotation for example a rotation estimate for a composite sequence from the central part of the study area is 23 15 whereas estimates from older and younger halves of the sequence are 37 21 and 11 16 respectively paleomagnetic data indicate that oligocene to lower miocene rocks at some localities in the northern and southern parts of the study area e g the golconda canyon locality probably did not experience significant tertiary counterclockwise rotation although the paleomagnetic data alone are insufficient to fully define the geographic area subjected to tertiary counterclockwise rotation the data suggest that a discrete subregion was affected rather than the entire basin and range province

uncertainties in the relative positions of the australia antarctica lord howe and pacific plates since the late cretaceous we determined parameters that describe finite rotations and their uncertainty regions for relative plate motion at the spreading centers between the pacific and antarctica plates between australia and antarctica and between the lord howe rise and australia we combined these to yield a range of possible finite rotations describing the relative positions of the pacific australia antarctica and lord howe plates since the late cretaceous if the pacific australia plate boundary has had its present trend since anomaly 18 time reconstructions show 330 110 km of motion of the pacific plate relative to the lord howe rise since anomaly 5 time 9 8 m y 420 110 km since anomaly 6 time 19 5 m y 770 330 km since anomaly 13 time 35 6 m y and 820 260 km since anomaly 18 time 43 0 m y we examined two cases for times prior to anomaly 18 assuming a late cretaceous age of australia antarctica separation if a plate boundary existed between the lord howe rise and pacific plates since the late cretaceous with no plate boundary in antarctica reconstructions with the lord howe rise fixed predict 610 200 km of westward motion of the pacific plate between the times of anomalies 31 and 22 followed by 260 100 km of northward motion between the times of anomalies 22 and 18 if the lord howe rise was fixed to the pacific plate until the eocene but a plate boundary existed between east and west antarctica reconstructions show very little motion across this boundary between the times of anomalies 31 and 22 followed by convergence between the times of anomalies 22 and 18 this second case also brings 70 80 m y paleomagnetic poles from the pacific and east antarctica plates into better agreement than the first case but large uncertainties in the reconstructions do not allow the first case to be conclusively eliminated

effects of hydraulic roughness on surface textures of gravel bed rivers field studies of forest gravel bed rivers in northwestern washington and southeastern alaska demonstrate that bed surface grain size is responsive to hydraulic roughness caused by bank irregularities bars and wood debris we evaluate textural response by comparing reach average median grain size d50 to that predicted from the total bank full boundary shear stress t0 bf representing a hypothetical reference condition of low hydraulic roughness for a given t0 bf channels with progressively greater hydraulic roughness have systematically finer bed surfaces presumably due to reduced bed shear stress resulting in lower channel competence and diminished bed load transport capacity both of which promote textural fining in channels with significant hydraulic roughness observed values of d50 can be up to 90 smaller than those predicted from t 0 bf we find that wood debris plays an important role at our study sites not only providing hydraulic roughness but also influencing pool spacing frequency of textural patches and the amplitude and wavelength of bank and bar topography and their consequent roughness our observations also have biological implications we find that textural fining due to hydraulic roughness can create usable salmonid spawning gravels in channels that otherwise would be too coarse

tectonic rotations about vertical axes during the last 4 ma in part of the new zealand plate boundary zone the declinations of the primary magnetization of sedimentary rocks in the northern part of the new zealand plate boundary zone after thermal or alternating field cleaning have been used to determine tectonic rotations about vertical axes of rigid crustal blocks the pattern of rotations during the last 4 ma combined with structural style and continuity defines seven structural domains each ca 100 100 200 km across which contain crustal blocks up to 100 km across and 20 km thick large crustal blocks tens of km across in two of these domains have rotated clockwise more than 20 relative to one of the margins of the plate boundary zone in the last 4 ma their behaviour appears to be controlled by the nature of the plate boundaries such as the presence of an underlying subducted slab and the strength of the crust at the back of the overlying crustal wedge small crustal blocks 10 km across may have rotated clockwise through angles greater than 20 during the last 4 ma floating on an underlying zone of more distributed deformation the tectonic rotations of the large crustal blocks and the nature of the deformation at their boundaries combined with an interpolation of the relative plate positions can be used to reconstruct the plate boundary zone at ca 4 ma

influence of storm related sediment storage on the sediment delivery from tributary catchments in the upper waipaoa river new zealand although much is known about overall sediment delivery ratios for catchments as components of sediment production and sediment yield little is known about the component of temporary sediment storage sediment delivery ratios focused on the influence of storm related sediment storage are measured at matakonekone and oil springs tributaries of the waipaoa river basin east coast of new zealand the terrace deposits of both tributaries show abundant evidence of storm related sedimentation especially sediment delivered from cyclone bola a 50 year return rainfall event which occurred in 1988 the sediment delivery ratio is calculated by dividing the volume of sediment transported from a tributary to the main stream by the volume of sediment generated at erosion sites in the tributary catchment because the sediment delivery volume is unknown it can be calculated as the difference between sediment generation volume and sediment storage volume in the channel reach of the tributary the volume of sediment generated from erosion sites in each tributary catchment was calculated from measurements made on aerial photographs dating from 1960 1 44 000 and 1988 1 27 000 the volume of sediment stored in the tributary can be calculated from measurements of cross sections located along the tributary channel which are accompanied by terrace deposits dated by counting annual growth rings of trees on terrace surfaces sediment delivery ratios are 0 93 for both matakonekone catchment and oil springs catchment results indicate that oil springs catchment has contributed more than twice the volume of sediment to the waipaoa river than the matakonekone catchment 2 75 106 m3 vs 1 22 106 m3 although large volumes of sediment are initially deposited during floods subsequent smaller flows scour away much of these deposits the sediment scouring rate from storage is 1 25 104 m3 a 1 for matakonekone stream and 0 83 104 m3 a 1 for oil springs stream matakonekone and oil springs channels respond to extreme storms by instantaneously aggrading then gradually excavating the temporarily stored sediment results from matakonekone and oil springs streams suggest a mechanism by which event recurrence interval can strongly influence the magnitude of a geomorphic change matakonekone stream with its higher stream power is expected to excavate sediment deposits more rapidly and allow more rapid re establishment of storage capacity copyright 1999 john wiley sons ltd

magnitude and frequency of landsliding in a large new zealand catchment knowledge of long term average rates of erosion is necessary if factors affecting sediment yields from catchments are to be understood without such information it is not possible to assess the potential influence of extreme storms and therefore to evaluate the relative importance of various components of a sediment budget a study of the sediment budget for the waipaoa catchment north island new zealand included evaluation of long term rates of landsliding for six landslide prone land systems in the catchment the number of landslides per unit area generated by each of several storms was counted on sequential aerial photographs and correlated with the magnitude of the corresponding storm the resulting relationships were combined with magnitude frequency relationships derived for storms from 70 to 100 year rainfall records in the area to estimate a long term magnitude frequency relationship for landsliding for each land system the long term average values of the areal landslide frequency number of slides per unit area per unit time were then calculated from these relationships the volumes of a sample of landslide scars were measured in the field and the proportion of slides that deliver sediment to channels was determined from aerial photographs these measurements then allowed calculation of the long term average rate of sediment production to streams from landslides for different land systems and types of vegetation results suggest that shallow landslides currently contribute about 15 5 of the suspended sediment load in the waipaoa river above the kanakanaia gauging station and that 75 of the sediment production from the landslides occurs during storms with recurrence intervals of less than 27 years reforestation of 6 3 93 km2 of the slide prone lands in the catchment between 1990 and 1995 resulted in a calculated decrease in slide derived sediment of 10 calculations suggest that reforestation of an additional 3 66 km2 of the catchment in areas with the most sensitive combinations of land system and storm regime could decrease the total sediment inputs from landsliding by about 20

a model for tectonic rotations about a vertical axis abstract the rotation of a rigid ellipsoidal inclusion within a highly viscous fluid orientated so that two of the principal axes remain horizontal is used as a model for the rotation of crustal inclusions in wide zones of continental deformation this model is also applicable to other geological problems involving the rotation of inclusions in a matrix the pattern of behaviour in such a model is shown to be complex in general the rotation rate of the inclusion is a function of all components of the velocity field of the deforming medium and the horizontal aspect ratio of the inclusion however for a given velocity field this aspect ratio must exceed a critical value before the inclusion can rotate continuously inclusions with lower aspect ratios will rotate for a certain range of orientations in an opposite direction to the sense of shear in the deforming zone the possibility of the inclusion changing shape during rotation adds to the complexity of behaviour

post extinction diversification patterns of brachiopods in the early middle llandovery silurian abstract network and frequency distribution analyses of global brachiopod occurrences in the earliest silurian rhuddanian aeronian revealed that brachiopod recovery from the end ordovician mass extinction during the early late rhuddanian was represented mainly by the reestablishment of late ordovician cosmopolitan holdover taxa brachiopods nearly doubled their generic diversity from rhuddanian to aeronian owing to the radiation of both endemic and cosmopolitan taxa associated with an overall post glacial amelioration of global environment and increased habitat heterogeneity as a result of marine transgressions and expansion of epeiric seas a drastic turnover from the ordovician type to silurian type brachiopod faunas took place in the aeronian several million years after the terminal ordovician mass extinction compared with the orders of orthides and strophomenides that radiated and predominated in the ordovician the atrypides and pentamerides displayed pulses of drastic diversification from the rhuddanian to aeronian mainly in tropically located paleoplates to become the most abundant and diverse brachiopod orders in the silurian atrypides recovered in the early rhuddanian whereas diversification of pentamerides was delayed until the aeronian and becoming widespread in south china kazakhstan terranes baltica avalonia and laurentia

arc deformation and marginal basin opening japan sea as a case study we discuss the opening mechanism of the japan sea in miocene time using 1 tectonic and published paleomagnetic data along the eastern margin from the north of hokkaido island to sado island 2 a mechanical model which is tested by small scale physical modeling and 3 crustal structure and bathymetric features in the japan sea which constrain our kinematic model and preopening reconstructions our main conclusions are the following the eastern margin of the japan sea was as a whole a dextral shear zone about 100 km wide this conclusion is supported by the existence of a ductile dextral shear zone in central hokkaido hidaka mountains and associated brittle deformation in western hokkaido and northeastern honshu the stress field during the opening which ended about 12 ma ago at the end of the middle miocene changes from right lateral transpression in the north to right lateral transtension in the south the western margin along the korean peninsula during the same period also was an active dextral shear zone paleomagnetic results indicate that clockwise rotations occurred in the south during the opening and counterclockwise rotations in the north we propose a model of right lateral pull apart deformation with clockwise rotations of rigid blocks in the southern transtensional domain and counterclockwise rotations in the transpressional one small scale physical models show that the clockwise rotation in transtension is possible provided that the eastern boundary pacific side is free of stress the opening stopped and compression subsequently began about 12 ma ago finally we show that the dextral shear which is distributed over the whole japan sea area is accommodated by n s trending right lateral faults and rotation of blocks located between these right lateral faults

bathymetric and isotopic evidence for a short lived late ordovician glaciation in a greenhouse period the end ordovician glaciation is distinct among phanerozoic glaciations in that co 2 levels were generally high yet major continental ice sheets accumulated on the gondwana supercontinent new oxygen isotopic data indicate substantial changes in sea water temperatures and ice volume coinciding with glacio eustatic changes in sea level reflecting the growth and decay of the gondwana ice cap major glaciation was apparently confined to the hirnantian and was 0 5 1 m y long rather than the 35 m y of earlier estimates carbon isotope values indicate significant changes in carbon cycling as the oceans changed from a state with warm saline bottom waters to a state with cold deep water circulation and then back again we believe that the changes in the carbon cycle effected a reduction in p co 2 levels in the oceans and atmosphere and thus promoted glaciation but were unable to sustain icehouse conditions in a greenhouse world

the late ordovician mass extinction abstract near the end of the late ordovician in the first of five mass extinctions in the phanerozoic about 85 of marine species died the cause was a brief glacial interval that produced two pulses of extinction the first pulse was at the beginning of the glaciation when sea level decline drained epicontinental seaways produced a harsh climate in low and mid latitudes and initiated active deep oceanic currents that aerated the deep oceans and brought nutrients and possibly toxic material up from oceanic depths following that initial pulse of extinction surviving faunas adapted to the new ecologic setting the glaciation ended suddenly and as sea level rose the climate moderated and oceanic circulation stagnated another pulse of extinction occurred the second extinction marked the end of a long interval of ecologic stasis an ecologic evolutionary unit recovery from the event took several million years but the resulting fauna had ecologic patterns similar to the fauna that had become e

morphological evolution of the north fork toutle river following the eruption of mount st helens washington abstract the north fork toutle river nftr has undergone extensive morphological changes following the catastrophic eruption of mount st helens washington in 1980 especially the upper reaches affected by a 2 5 km3 debris avalanche deposit caused by the eruption this paper reports analysis and interpretation of vertical adjustments to the thalweg long profile at some 33 km river reaches redeveloped on the debris avalanche deposit during the 30 year period since the eruption the results confirm that adjustments in the upper part of the study reaches have generally been led by degradation while that in the lower reaches have been led by aggradation with the middle reaches acting as a hinge zone trends of change in the thalweg long profile and bedslope reveal that channel gradients have decreased nonlinearly through time and with distance downstream from the volcano values of stream power have decreased with time commensurately owing to reductions in slope and channel widening while the bed has coarsened so that rates of erosion of the debris avalanche deposit in the upper nftr have slowed to the point that the long profile now perched and slightly steeper is relaxing toward a new equilibrium or graded condition thirty year relaxation paths for thalweg elevation were simulated at seven key cross sections using newly developed comprehensive rate law models based on nonlinear decay in rates of morphological response to perturbation the results indicate that both single and multistep rate law models can simulate the observed records consequently the rate law approach provides an effective method for studying and simulating morphological response of the fluvial system to a major instantaneous disturbance such as a volcanic eruption

evolution of a sediment wave in an experimental channel the routing of bed material through channels is poorly understood we approach the problem by observing and modeling the fate of a low amplitude sediment wave of poorly sorted sand that we introduced into an experimental channel transporting sediment identical to that of the introduced wave the wave essentially dispersed upstream and downstream without translation although there was inconclusive evidence of translation late in the experiment when the wave was only 10 20 grain diameters high alternate bars migrated through zones of differing bed load transport rate without varying systematically in volume celerity or transport rate sediment that overpassed migrating bars was apparently responsible for dispersion of the wave the evolution of the wave was well predicted by a one dimensional model that contains no adjusted empirical constants numerical experiments demonstrate however that the theory does not predict sediment waves that migrate long distances downstream such waves can only be explained by the following processes not represented by the theory selective bed load transport spatial variations in bar and other form roughness the mechanics of mobile armor and perhaps other mechanisms

channel morphology gradient profiles and bed stresses during flood in a step pool channel abstract the stability of a step pool channel is investigated on the basis of measurements during a median annual flood the study reaches range in gradient from 5 to 10 and the flow was 3 m3 s 1 in an 8 m wide channel the estimated shear stress based on the channel gradient was 102 pa which implies that the channel ought to move half meter class boulders calculations of the shear stress using flow resistance equations yield values of about 30 pa these figures imply that the largest boulders in the channel could be moved in fact the channel is stable the effective stress remains well below the threshold to move the large structure forming boulders the steps are stable structures that result from interlocking of the larger stones they are semi randomly located depending on the location of keystones that are deposited in the channel by debris flows or fall out of the banks the high variation in step pool wavelength step height residual pool depth and pool length is indicative of the random nature of step location and structure along a reach there is no convincing evidence that special conditions govern their formation

limits of sediment transfer in an alpine debris flow catchment illgraben switzerland abstract the 9 5 km 2 illgraben catchment located in the rhone valley in the central alps of switzerland is one of the most active debris flow torrents in the alps in this paper we present sediment yield data collected in 2006 for segments where hillslopes and channels form a fully connected network and contrast these with sediment yields measured for disconnected hillslopes the data reveal that sediment yields are 1 2 orders of magnitude larger in segments where hillslopes are connected with the channel network than on disconnected hillslopes support for this conclusion is provided by observations made on 1959 1999 and 2004 aerial photographs that the vegetation cover in the disconnected segments is still intact whereas denudation rates of several centimeters per year in the connected segments have inhibited the establishment of a stable vegetation cover furthermore sediment supplied from hillslopes during the past 40 years has temporarily accumulated along the illgraben channel indicating that the channel aggraded over this period and has not yet recovered an implication of this observation is that initiation of debris flows in the illgraben catchment is limited more by the availability of intense rainfall than sediment in contrast on disconnected hillslopes sediment flux does not appear to be driven by precipitation the petrographic composition of the illgraben fan deposits indicates two distinct sediment sources one related to rockfall and the other to landslides and debris flows the presence of clasts from both sources implies multiple processes of erosion deposition mixing and re entrainment in the catchment before the material is exported to the illgraben fan and to the rhone river in addition delivery of large amounts of coarse grained sediment to the rhone causes a modification of the flow pattern from meandering or anastomosing upstream to braided downstream hence the direct connectivity between hillslope and channelized processes in the illgraben catchment causes not only rapid topographic modifications in the catchment but also morphologic adjustment in the rhone valley downstream

coupling between hillslopes and channels in upland fluvial systems implications for landscape sensitivity illustrated from the howgill fells northwest england abstract the sensitivity of upland fluvial systems depends on the magnitude and frequency of sediment and flood producing events modified by the internal coupling characteristics of the system this paper assesses the role of hillslope channel coupling for the sensitivity of upland geomorphic systems using evidence from a 30 year monitoring programme of geomorphic change in the carlingill valley howgill fells northwest england in the hillslope zone there is little sediment supply to the stream system locally slope failures occur in response to extreme events six such events in 30 years within the ca 6 km 2 carlingill valley in the footslope coupling zone basally induced gullies are major sediment sources to the stream sediment production events occur ca 30 times per year feeding sediment to basal debris cones stream floods which can entrain these sediments occur once every ca 2 5 years stream channel morphology is adjusted to this regime downstream of gullies channels are wide and braided elsewhere they are narrow and single thread as the gullies develop however this coupling weakens and the eroding slopes eventually stabilise by revegetation over the 30 year monitoring period there has been a progressive trend towards gully stabilisation and an associated reduction in channel instability massive destabilisation may occur in response to rare extreme flood events such an event return period 100 years occurred in neighbouring langdale and bowderdale valleys in june 1982 that event destabilised the system causing slope failures fan deposition and in some places a switch in channel style to wide braided channels since 1982 there has been a progressive recovery by slope stabilisation and single thread sinuous channels have become reestablished a different style of extreme event occurred in carlingill in october 1998 in response to the wettest week in the 30 year period a slope failure fed debris flows 400 m downslope almost coupling with the channel system future climatic change could render the system prone to destabilisation through either extreme flood events or through major slope failures

the last million years of deformation in part of the new zealand plate boundary zone abstract tectonic deformation of pleistocene sediments is occurring within the plate boundary zone in the north island of new zealand folds associated with an active fault are forming mainly by flexural slip and contain comformable and unconformable relations which show that the folding started ca 1 0 ma simple geometric models of fold growth indicate that the fold structure has shortened at an average rate of 0 76 0 1 mm a 1 across 4 5 km though with an increase in the last 100 ka of about 1 8 times the average rate which is entirely compatible with the rate of shortening observed in the last 50 years from retriangulation studies areas for 15 km to the southeast of the fold structures show significantly lower horizontal shortening rates the strain rates across the plate boundary zone vary both with position and time with a negative correlation between the uplift pattern and the inferred geological shortening rates this can be explained by the presence of large semi rigid blocks within the plate boundary zone which are back tilting and overriding weaker more rapidly deforming areas the available evidence suggests that a large proportion of the deformation is occurring seismically

modelling sediment transport as a moving wave the transfer and deposition of mining waste abstract the movement of slugs of bedload from a discrete input point down a river has proved difficult to model using conventional finite difference formulations of equations of motion a model is proposed which makes explicit allowance for the mean sediment velocity and through a dispersion coefficient the distribution of sediment velocity about the mean a second comparative model uses the normal mass conservation or sediment transport continuity approach the models have been tested over a 43 month period using data from seven monitored cross sections of the kawerong river on bougainville island papua new guinea a system which receives waste from a large copper mine the dispersion model performs considerably better than the mass conservation model

channel reach morphology controls of headwater streams based in flysch geologic structures an example from the outer western carpathians czech republic a detailed measurement of 93 channel reaches that were classified with an adjusted montgomery buffington 1997 reach scale system provided comprehensive information of approximately 9 at a reach parameters the channel gradient the bankfull width the bankfull depth d90 the percentage of resistant rocks in the bed sediment the number of pieces of large woody debris valley confinement direct sediment inputs and the presence of fluvial accumulations in the stream channel in addition the quantified intensity of sediment transport i e ratio between sediment supply and transport capacity in longitudinal stream profiles during flood events has been estimated by the one dimensional bedload transport model tomsed which was validated in two local streams the principal component analysis of the at a reach parameters did not reveal significant groups of channel reach morphologies thus the selected parameters that exclude sediment transport dynamics within stream longitudinal profile cannot reliably distinguish or predict individual channel reach morphologies nevertheless the channel gradient represented the most significant single explanatory variable for stepped bed morphologies the addition of bedload transport parameters demonstrated that limited sediment supply streams and streams with limited transport capacities featured different successions of the channel reach morphologies in terms of the channel gradient and subsequently the fluvial continuity the bedrock cascades and step pools were significant for the first case whereas cascade and step rapid morphology often occurred in higher sediment supply conditions

magnetic polarity stratigraphy of a plio pleistocene marine sequence of north island new zealand abstract thick sequences of relatively undisturbed plio pleistocene sediments in the wanganui basin north island new zealand consist of well exposed silts clayey silts sandstones rare limestones and several tephras oriented specimens were collected from a section more than 2500 m thick and palaeomagnetic measurements were made using a c demagnetisations in fields up to 35 mt with the aid of tephrochronology the age of the upper sequence is now well established and falls within the matuyama epoch the lower two thirds of the section except for the basal 500 m is predominantly normally magnetised and is interpreted as a very extended sequence of the gauss epoch the lowest 500 m then represents the gilbert epoch the plio pleistocene boundary as defined at vrica italy falls within the upper part of the section studied in the upper nukumaruan stage for the first time a reliable correlation is made with the international boundary using as intermediaries the palaeomagnetic and tephrostratigraphy of deep sea cores from the southwest pacific as a result of the high deposition rate of the order of 1 2 m ky and the apparent lack of unconformities the temporal resolution is high short lived magnetic events are detected especially in the lower matuyama and upper gauss epochs these generally correlate well with events reported from other extended sections

sediment pulses in mountain rivers 2 comparison between experiments and numerical predictions 1 mountain rivers in particular are prone to sediment input in the form of pulses rather than a more continuous supply these pulses often enter in the form of landslides from adjacent hillslopes or debris flows from steeper tributaries the activities of humans such as timber harvesting road building and urban development can increase the frequency of sediment pulses the question as to how mountain rivers accommodate pulses of sediment thus becomes of practical as well as academic significance in part 1 cui et al 2003 the results of three laboratory experiments on sediment pulses are reported it was found there that the pulses were eliminated from the flume predominantly by dispersion of the topographic high significant translation was observed only when the pulse material was substantially finer than the ambient load in the river here the laboratory data are used to test a numerical model originally devised for predicting the evolution of sediment pulses in field scale gravel bed streams the model successfully reproduces the predominantly dispersive deformation of the experimental pulses rates of dispersion are generally underestimated largely because bed load transport rates are underestimated by the transport equation used in the model the model reproduces the experimental data best when the pulse is significantly coarser than the ambient sediment in this case the model successfully predicts the formation and downstream progradation of a delta that formed in the backwater zone of the pulse in run 3 the performance of the model is less successful when the pulse is composed primarily of sand this is likely because the bed load equation used in the study is specifically designed for gravel when the model is adapted to conditions characteristic of large sand bed rivers with low froude numbers it predicts substantial translation of pulses as well as dispersion

three dimensional velocity structure of the northern hikurangi margin raukumara new zealand implications for the growth of continental crust by subduction erosion and tectonic underplating traveltimes between shots from nine marine seismic reflection lines and nine onshore recorders were used to construct a 3 d p wave velocity model of the northern hikurangi subduction margin new zealand from north to south between raukumara basin and raukumara peninsula the moho of the overriding plate increases in depth from 17 to similar to 35 km low seismic p wave velocities of 3 5 5 0 km s are localized within a similar to 10 km thick prism in the lower crust of the overriding plate immediately updip of the intersection between the subduction thrust and moho and beneath the topographic crest of east cape ridge and the raukumara range southward this region of low seismic velocities and surface uplift increases in distance from the trench as the thickness of the crust in the overriding plate increases we interpret this low velocity volume to be underplated sedimentary rocks and crustal materials that were tectonically eroded by subduction beneath the trench slope the buoyancy and low strength of these subducted materials are proposed to assist the escape from a subduction channel near the base of the crust and drive local rock uplift in the middle crust our observations of very low velocity suggest high fluid filled porosities of 12 18 and the implied buoyancy anomaly may enhance underplating at greater depths the process is driven by the contrast between upper crustal quartz feldspar mineralogy and the denser diabase or olivine rich lithologies of the lower crust and mantle we estimate a rate of lower crustal underplating at the northern hikurangi margin of 20 7 km 3 ma 1 km 1 since 22 ma we suggest that underplating provides an efficient means of accreting subducted sediment and tectonically eroded material to the lower crust and that the flux of forearc crustal rocks into the mantle at subduction zones may be systematically overestimated

tectonic rotation about the termination of a major strike slip fault marlborough fault system new zealand the marlborough fault system comprises a series of major right lateral strike slip faults that link the alpine fault to the hikurangi subduction zone in the pacific australia plate boundary zone in new zealand all of the major active faults of the marlborough fault system have continuous traces except for the clarence fault which terminates abruptly near the ward syncline paleomagnetic data from upper miocene and lower pliocene sedimentary rocks between the marlborough faults indicate a consistent post early pliocene regional clockwise rotation of about 20 an additional rotation of about 10 is evident at many localities near the termination of the clarence fault it is proposed that the additional rotation relative to the rest of the region is caused by a velocity gradient that likely exists between the active awatere fault and the termination of the clarence fault the existence of such a velocity gradient is consistent with inferences from geodetic strain data which suggest that one third of the displacement in the marlborough fault system occurs between the awatere and clarence faults the kinematics of rotation can be modelled by treating the area as a rigid block that pivots about the termination of the clarence fault the block rotation model satisfies field constraints on the styles of deformation observed at the boundaries of the block and is consistent with available paleomagnetic and geodetic data

a new ecological severity ranking of major phanerozoic biodiversity crises a new ecological severity ranking of the major phanerozoic biodiversity crises is proposed in which the capitanian crisis is ranked lesser than the frasnian late devonian but greater than the serpukhovian end mississippian and the famennian end devonian crisis is ranked as equal in ecological impact to the hirnantian end ordovician two new decouplings between taxonomic severity and ecological severity are revealed in these analyses the capitanian and famennian crises in which the ecological impact of the biodiversity loss was markedly different from the magnitude of the biodiversity loss these analyses also reveal that the great devonian interchange gdi invasive species event in the givetian biodiversity crisis may provide an important palaeoecological analog for the study of present day extinction and homogenization in ecosystems produced by modern invasive species

sediment transfer and transformation of an alluvial valley floor the river south tyne northumbria u k the amounts of alluvial storage and the mechanisms responsible for the dispersal of sediment associated with historic metal mining are examined for a 115 year timespan on a 22 km reach of the river south tyne northern england analysis of lateral and vertical channel change over this period the extent of actively reworked gravels and identification of metals in alluvial units show five sedimentation zones separated by more stable reaches aggradation in the late nineteenth century was followed by a period of storage and local reworking and then incision some reaches show short term storage of sediment injected from tributaries which may be dispersed by floods there is some evidence of transfer of sediment bodies downvalley within sedimentation zones and of a sediment wave movement between zones in lower parts of the south tyne investigated present day incision the variation in the area of actively reworked gravel spreads and the widespread dispersal of fine grained toxic metal mining wastes all have practical implications the intricate response of the channel system to historic changes in sediment supply is not readily described by either a complex response model or a simple translatory wave

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

which tributaries disrupt downstream fining along gravel bed rivers tributaries and other lateral sediment sources can have a significant impact on river bed sediment texture and in turn on channel form sufficiently voluminous or distinct sediment inputs redefine the mainstem grain size distribution punctuating downstream maturation and isolating a sequence of discrete sedimentary links within these links fining processes usually dominate such that models of sorting and abrasion when applied to individual links provide reasonable predictions of grain size change links represent the fundamental natural unit within which fining models can be tested developed and applied identification of significant lateral sources is therefore important yet beyond vague references to relative tributary size sediment load and sediment calibre no criteria exist for the a priori discrimination of such sources in this paper a procedure for identifying significant lateral tributary sources without the benefit of grain size information is outlined a high resolution characterisation of bed material texture along two canadian gravel bed rivers facilitated classification of all their perennial tributaries as either significant or insignificant three absolute tributary basin parameters and their relative counterparts chosen to reflect the likely controls on tributary significance are then used to develop a discriminant function which isolates a large proportion of significant tributaries while minimising incorrect classifications examination of consistently misclassified anomalous tributaries reveals the importance of lateral source spacing and of inconsistencies in the geomorphic history of the contributing basins in turn a general tributary categorisation procedure is suggested which includes a logistic regression model for attaching probability statements to individual classifications the generality of the discriminant and logistic functions cannot be assessed because of the lack of other suitable data sets

effective timescales of coupling within fluvial systems this paper presents a review of the coupling concept in fluvial geomorphology based mainly on previously published work coupling mechanisms link the components of the fluvial system controlling sediment transport down the system and the propagation of the effects of base level change up the system they can be viewed at several scales at the local scale involving within hillslope coupling hillslope to channel coupling and within channels tributary junction and reach to reach coupling at larger scales coupling can be considered as zonal coupling between major zones of the system or as regional coupling relating to complete drainage basins these trends are illustrated particularly by the examples of hillslope to channel coupling in the howgill fells northwest england badland systems in southeast spain alluvial fans in spain usa and uae and base level induced dissection of neogene sedimentary basins in southeast spain as the spatial scales increase so do the timescales involved effective temporal scales relate to magnitude and frequency characteristics recovery time and propagation time the relative importance changing with the spatial scale for downsystem coupling at the local scale the first two are important with propagation time increasing in importance in larger systems especially in those involving upsystem coupling related to base level change the effective timescales range from the individual event with a return period of decades through decadal to century timescales for downsystem coupling to tens to hundreds of thousands of years for the basinwide response to base level change the effective timescales influence the relative importance of factors controlling landform development

multi scalar controls on channel geometry of headwater streams in new zealand hill country abstract catchment reach and local scale controls upon channel geometry are examined for small headwater streams in adjacent sub catchments with variable land use histories in a typical hill country area of the north island of new zealand although systematic downstream increase in channel cross sectional area is evident in one sub catchment a result of catchment scale controls on geometry including discharge and slope marked local variability in channel geometry in the two other sub catchments reflects non systematic patterns of reach scale controls including the distribution of floodplain pockets and associated bank materials and local scale controls such as bedrock outcrops and wood land use change exerts a primary control upon these relationships for a given catchment area streams in native forest are wider and shallower than streams that flow within pasture or pinus plantations increased hillslope erosion following land clearance has instigated the accumulation of post settlement alluvium psa which has altered the boundary conditions and bank materials within which streams flow significant psa accumulation following native forest clearance in one of the sub catchments has allowed the stream to flow entirely within its own alluvial deposits in this instance catchment scale controls on channel geometry are dominant in contrast local scale controls on channel geometry are more important in the other sub catchments where lesser accumulation of psa reflects differences in land clearance these findings indicate that place based understandings which consider the spatial and historical contexts of landscape settings are required to interpret patterns of channel geometry and to inform river rehabilitation initiatives

end ordovician extinctions a coincidence of causes the end ordovician hirnantian extinction was the first of the five big phanerozoic extinction events and the first that involved metazoan based communities it comprised two discrete pulses both linked in different ways to an intense but short lived glaciation at the south pole the first occurring at or just below the normalograptus extraordinarius graptolite biozone mainly affected nektonic and planktonic species together with those living on the shallow shelf and in deeper water whereas the second within the n persculptus graptolite biozone was less focused eradicating faunas across a range of water depths in all about 85 of marine species were removed proposed kill mechanisms for the first phase have included glacially induced cooling falling sea level and chemical recycling in the oceans but a general consensus is lacking the second phase is more clearly linked to near global anoxia associated with a marked transgression during the late hirnantian most recently however new drivers for the extinctions have been proposed including widespread euxinia together with habitat destruction caused by plate tectonic movements suggesting that the end ordovician mass extinctions were a product of the coincidence of a number of contributing factors moreover when the deteriorating climate intensified causing widespread glaciation a tipping point was reached resulting in catastrophe