early ordovician reef construction in anhui province south china a geobiological transition from microbial to metazoan dominant reefs the lower ordovician records a transition from microbial to metazoan dominant reefs immediately prior to the great ordovician biodiversification event the hunghuayuan formation late tremadocian early floian of the jianxin section in anhui province south china includes well preserved reefs which consist of a combination of microbial boundstones and microbial lithistid sponge receptaculitid boundstones the microbial boundstones are characteristically made up of nodular or columnar stromatolites produced by an irregular alternation of girvanella rich layers and thick micrite layers in which the filamentous calcimicrobe girvanella and bioclasts occur sporadically microbial biofilms including the filamentous microbes may have trapped and bound lime mud and or precipitated micrite during their growth and metabolic activities these activities contemporaneously contributed to substrate stabilisation encrustation and the construction of microbialite frameworks stromatolites in contrast the microbial lithistid sponge receptaculitid boundstones are characterised by more micritic constituents than skeletal reef building constituents thin and or domal crusts produced by peloid and dense micrite together with various proportions of girvanella occur upon bioclastic sediments and reef building skeletal organisms these micritic crusts with girvanella therefore played roles as binders and stabilisers and as consolidators by encrusting reef building skeletal organisms in the boundstones it is remarkable that the degradation of lithistid sponges due to microbial decay produced micrite in the sponge bodies as a result lithistid sponges played an apparently inconspicuous but potentially significant role as micrite producers as well as automicrite framework constructors these lower ordovician reefs in which microbialites e g stromatolites dominate but coexist with metazoans e g sponges were widespread at the time they provide excellent examples for understanding reefal palaeoecology during the transition from microbe dominant reefs to reefs enriched in metazoans

evidence for a chemical thermal structure at base of mantle from sharp lateral p wave variations beneath central america compressional waves that sample the lowermost mantle west of central america show a rapid change in travel times of up to 4 s over a sampling distance of 300 km and a change in waveforms the differential travel times of the pkp waves which traverse earth s core correlate remarkably well with predictions for s wave tomography our modeling suggests a sharp transition in the lowermost mantle from a broad slow region to a broad fast region with a narrow zone of slowest anomaly next to the boundary beneath the cocos plate and the caribbean plate the structure may be the result of ponding of ancient subducted farallon slabs situated near the edge of a thermal and chemical upwelling

role of inherent geological and climatic characteristics on landscape variability in the tectonically passive western ghat india abstract how does lithological variation affect the landscape and its evolution is a fundamental issue in modern and post orogenic terrains in the absence of active tectonic uplift spatial variation of rock resistance and rainfall distribution are thought to primarily control the fluvial and hillslope processes however these lithologic and climatic controls are difficult to decouple owing to the fact that these post orogenic terrains endure long and complex geomorphic history to examine the relative importance of lithology and rainfall in a post orogenic setting we analyzed west flowing drainage basins in the western ghat wg with a multi proxy analysis we relied on digital topography sediment yield and hydrological data we evaluated topographic relief hypsometry river long profiles and sediment yield to elaborate the importance of spatial variability of rock resistance in the long term evolution of these drainage basins the dominant increase of relief 200 1500 m and decrease of sediment yield 3 32 1 91 ton month km2 from north to south of the escarpment is directly attributed to the rock erodibility and structural characteristics field verification suggests that despite high rainfall condition the channels are mostly detachment limited and therefore lack the abrasive tools we further showed that the harder lithologies sustain higher steepness on the contrary the spatial distribution of satellite derived rainfall showed a negligible effect on the long profile evolution our analysis is also supported by the existing knowledge of chemical denudation rate and implicates that rock hardness and weatheribility defines the topographic characteristics with little or no effect of rainfall in this passive margin setting

early recovery of sponge framework reefs after cambrian archaeocyath extinction zhangxia formation early cambrian series 3 shandong north china abstract reefs dominated by the anthaspidellid sponge rankenella zhangxianensis the calcimicrobe epiphyton and the stem group cnidarian cambroctoconus orientalis together with encrusting microstromatolites occur early in the middle cambrian series 3 late stage 5 of shandong eastern china in the zhangxia formation these in situ components created a tight framework with centimeter scale growth cavities mainly filled by fine grained matrix among them r zhangxianensis and c orientalis mutually attached and locally formed metazoan dominated frameworks these metazoan microbial reefs form thin lenses 505 ma these rankenella reefs indicate recovery of framework building metazoans within 5 million years of the archaeocyath reef decline in structure they resemble archaeocyath reefs as well as early ordovician lithistid sponge microbial reefs having conjoined conical macroskeletons thickly veneered by calcimicrobes and microbial carbonate with largely matrix filled intervening cavities in combination with other sponge microbial reefs reported from australia iran korea and the usa they demonstrate that an anthaspidellid sponge microbial reef consortium was widespread throughout the mid late cambrian

pkp travel times at near antipodal distances implications for inner core anisotropy and lowermost mantle structure abstract previous studies from pkp ab df differential travel times at large distances suggest that the central part of the inner core is very anisotropic these differential times however can be affected greatly by strong heterogeneity in the lowermost mantle here we examine a unique data set of pkp travel times from global digital and analog stations at near antipodal distances where the effects of both inner core anisotropy and mantle heterogeneity are the greatest our results show that the ab df residuals for the polar paths are consistently larger than those of the equatorial paths by over 3 4 standard deviations we also measured df and ab absolute times and found that the df residuals are negatively correlated with the ab df residuals while the ab residuals have a much weaker correlation with the ab df residuals we compare several mantle models with the data our results suggest that the mantle structure can explain part of the residuals of the equatorials paths but cannot explain the polar path anomalies these results strongly suggest that most of the ab df anomalies for the polar paths are likely from the inner core anisotropy and not from mantle heterogeneity assuming a uniform cylindrical anisotropy model the average inner core anisotropy amplitude is about 2 5 on the other hand equatorial paths from events in the west pacific and recorded at south america show a steep azimuthal change in ab df times about 4 s over a 60 azimuthal range the sharp change is well predicted by existing p and s tomographic models the azimuthal change occurs as the ab paths sweep across the great slow anomaly in the central pacific the high correlation between the p and s velocities suggests that the central pacific slow anomaly may be of thermal origin

decline in suspended sediment concentration delivered by the changjiang yangtze river into the east china sea between 1956 and 2013 abstract the temporal evolution of suspended sediment concentration ssc in a river debouching into the ocean provides vital insights into erosion processes in the watershed and dictates the evolution of the inner continental shelf while the delivery of sediment from rivers to the ocean has received special attention in the recent past few studies focused on the variability and dynamics of river ssc especially in the changjiang yangtze river china the longest river in asia here variations in ssc delivered by the changjiang river to the east china sea and possible causes of its variability were detected based on a long term time series of daily ssc and monthly water discharge measured at the datong gauging station the ssc data are further compared to a hydrological analysis of yearly precipitation covering the entire catchment the results indicate the presence of a decline in ssc in the period 1956 2013 which can be divided into three phases i high ssc 0 69 kg m3 in the wet season and low ssc 0 2 kg m3 in the dry season from 1956 to 1970 ii relative high ssc 0 58 kg m3 in the wet season and low ssc 0 15 kg m3 in the dry season from 1971 to 2002 and iii low ssc 0 19 kg m3 in the wet season and very low ssc 0 09 kg m3 in the dry season after 2002 these three periods have a mean yearly ssc values of 0 62 0 42 and 0 18 kg m3 respectively compared with 1956 1970 the slope of the rating curve between ssc and water discharge decreased respectively by 2 and 30 during the period 1971 2002 and 2002 2013 soil erosion dam construction and banks reinforcement along the changjiang river are the main causes of ssc variations fluctuations in water discharge are also controlling the ssc long term variations specifically from 1956 to 1970 the effect of soil erosion overrules that of dam impoundment which is likely responsible for the high ssc during the period 1970 2002 the influence of dam impoundment increases while that of soil erosion decreases which together produce a small reduction in ssc since 2002 the impact of soil erosion further decreases and large scale sediment trapping behind the three gorges dam is responsible for the occurrence of extremely low ssc the results presented herein for the changjiang river can inform a better management strategy of sediment resources and water quality for both the river and the coast our conclusions can be well applied to other rivers discharging in the ocean subject to similar human activities

disorientation of corals in late ordovician lime mudstone a case for ephemeral biodegradable substrate abstract massive coralla representing the tabulate coral agetolites occur on a lime mudstone bed in the upper ordovician xiazhen formation of southeastern china other fossils include solitary rugose corals bryozoans trilobites and mollusks in addition abundant spicules and spicule networks suggest that sponges were widespread the occurrence of intact unabraded fossils in micritic matrix and the absence of high energy sedimentary structures indicate deposition in low energy conditions thin section analysis of disoriented specimens demonstrates that geopetal indicators are consistent with stratigraphic up and differ from the growth axes of the corals implying that geopetal infillings formed after disorientation the growth axes of coralla were not redirected during life suggesting that the corals were either dead at the time of disorientation or died as a result of disorientation an examination of cyclomorphism indicates that the corals died at different times rather than during a single event a close association between sponges and corals is suggested by the presence of spicule networks in calices and intracorallum spaces of agetolites it is hypothesized that disorientation of corals was related to growth on biodegradable substrates we suggest that many coral larvae settled on sponges that formed sponge meadows disorientation of the resulting corals may have occurred when 1 a host sponge could no longer support the weight of a coral and collapsed 2 increasing weight or imbalance of a coral caused it to fall off the sponge or 3 a coral became detached when the sponge died and decomposed if the coral was alive sudden deposition in a disoriented position within muddy sediment resulted in its death disorientation of massive skeletons such as colonial coralla is most commonly attributed to water energy this study suggests that ephemeral substrates may have been involved in some cases

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

taphonomy of holocene cryptic biotas from st croix virgin islands information loss and preservational biases surveys of submarine caves and overhanging ledges from st croix virgin islands provide new insights into the preservational processes active therein and into the taphonomy of ancient counterparts comparisons of preservable skeletonized versus nonpreservable unskeletonized components of these modern cryptic communities indicate that there is significant information loss in areals coverage taxonomic richness and diversity of fossilized examples quantitative estimates of such losses have been made in addition skeletal differences between early and late stage successional groups suggest biased representation of the former in the geologic record nonpreservable later colonizers may further erase the record of skeletonized forms through destructive life processes such forms of taphonomic information loss are probable in ancient counterparts and must be considered in accurate reconstruction of cryptic paleocommunities

megablocks of calcified algae in the cow head breccia western newfoundland vestiges of a cambro ordovician platform margin slope and basin deposits in the cow head group of early paleozoic age contain a wide variety of carbonate clasts among the most common largest and most persistent middle middle cambrian to lower middle ordovician are blocks of fine grained white limestone the origin of these clasts is unknown as no limestones of similar lithology have been found in contemporaneous shallow water carbonate deposits anywhere in the northern appalachians petrographic study of these enigmatic limestones reveals that no matter what their age they are of similar composition calcified algae cement and fine grained sediment the predominant algae are epiphyton spp occurring as numerous masses of tiny shrublike and clumplike growths and girvanella spp developed as numerous thin strands and arcuate sheets renalcis spp and stromatolitic algae although locally common are not persistent the algae are surrounded by fibrous calcite cement interpreted to be synsedimentary while the numerous small cavities between algae are partly filled with geopetal marine sediment these blocks are interpreted to be redeposited fragments of reef mounds and buildups which grew along the shallow submerged margin of the north american craton during early paleozoic time these buildups are now probably buried beneath the allochthonous cow head strata the mounds were composed of calcareous algae because there were no large reef building metazoans during this time in geologic history recognition of similar clasts in analogous settings in the quebec and southern appalachians as well as in the cordillera suggests that this facies was both widespread and persistent for more than 70 m y

late ordovician brachiopod communities of southeast china the upper ordovician mid ashgill xiazhen and changwu formations in the zhejiang jiangxi border region of southeastern china contain an abundant and diverse suite of brachiopods a cluster analysis of 59 key samples from 180 collections over 23 000 specimens allowed delineation of eight distinct brachiopod communities herein named the ectenoglossa minor community the eospirifer praecursor community the ovalospira dichotoma community the antizygospira liquanensis sowerbyella sinensis community the kassinella shiyangensis community the altaethyrella zhejiangensis community the tcherskidium jiangshanensis community and the foliomena folium community these communities occur predominantly in limey clayey to silty mudstone facies similar to ziegler s early silurian brachiopod communities in the welsh borderland on the basis of lithological faunal and paleogeographical evidence the eight communities are interpreted to have distributed along an onshore offshore gradient from ba1 to ba6 setting

geomorphic response of the jingjiang reach to the three gorges project operation upstream damming often causes significant downstream geomorphic adjustments remarkable channel changes have occurred in the jingjiang reach of the middle yangtze river since the onset of the three gorges project tgp therefore it is important to investigate the variations in different fluvial variables for better understanding of the channel evolution characteristics as an example of the jingjiang reach recent geomorphic adjustments in the study reach have been investigated quantitatively including variations in sediment rating curve fluvial erosion intensity channel deformation volume and bankfull channel geometry these fluvial variables adjusted in varying degrees in response to the altered flow and sediment regime caused by the tgp operation a focus of this study has been especially paid on the variation in the bankfull channel geometry calculated bankfull dimensions at section and reach scale indicate that i there were significant bank erosion processes in local regions without bank protection engineering with empirical relations being developed to reproduce the variation in bankfull widths at four typical sections ii the variation in the reach scale channel geometry occurred mainly in the component of bankfull depth owing to the construction of large scale bank revetment works with the depth increasing from 13 7 m in 2002 to 15 0 m in 2014 and with an increase in the corresponding bankfull area of about 11 and iii the reach scale bankfull channel dimensions responded to the previous five year average fluvial erosion intensity during flood seasons at zhicheng with higher correlations for the depth and area being obtained when calibrated by the measurements in 2002 2012 furthermore these developed relations for the section and reach scale bankfull channel geometry were also verified by the observed data in 2013 2014 with encouraging results being obtained this article is protected by copyright all rights reserved

sediment load change in the yangtze river changjiang a review abstract extensive research into the changing sediment load throughout the yangtze river changjiang basin has been completed over recent years and it provides an ongoing example of how to evaluate the consequences of natural and anthropogenic impacts on sediment processing in a very large fluvial system this paper reviews these recent studies and critically assesses their findings regarding changes in sediment yield load both spatial and temporal variations grain size and rating curves as well as the morphodynamic response of the channel and delta we also discuss the factors driving these changes including climate change soil and water conservation measures dam construction and sand extraction and consider the likely future trends in sediment load based on a consideration of the major outcomes of and discrepancies between recent studies we conclude that sediment supply transport mobilization and deposition in this large river system are complicated by the heterogeneous nature of its morphology and climate as well as the progressive intensification of human activities therefore the identification and interpretation of hydrological and sedimentological changes in the yangtze basin can be difficult and an in depth study of the causal mechanisms of variations in sediment load and the impacts on the yangtze river system is urgently required

an assessment of the suspended sediment rating curve approach for load estimation on the rivers bandon and owenabue ireland abstract this paper presents an assessment of the suspended sediment rating curve approach for load estimation on the rivers bandon and owenabue in ireland the rivers located in the south of ireland are underlain by sandstone limestones and mudstones and the catchments are primarily agricultural a comprehensive database of suspended sediment data is not available for rivers in ireland for such situations it is common to estimate suspended sediment concentrations from the flow rate using the suspended sediment rating curve approach these rating curves are most commonly constructed by applying linear regression to the logarithms of flow and suspended sediment concentration or by applying a power curve to normal data both methods are assessed in this paper for the rivers bandon and owenabue turbidity based suspended sediment loads are presented for each river based on continuous 15 min flow data and the use of turbidity as a surrogate for suspended sediment concentration is investigated a database of paired flow rate and suspended sediment concentration values collected between the years 2004 and 2011 is used to generate rating curves for each river from these suspended sediment load estimates using the rating curve approach are estimated and compared to the turbidity based loads for each river loads are also estimated using stage and seasonally separated rating curves and daily flow data for comparison purposes the most accurate load estimate on the river bandon is found using a stage separated power curve while the most accurate load estimate on the river owenabue is found using a general power curve maximum full monthly errors of 76 to 63 are found on the river bandon with errors of 65 to 359 found on the river owenabue the average monthly error on the river bandon is 12 with an average error of 87 on the river owenabue the use of daily flow data in the load estimation process does not result in a significant loss of accuracy on either river historic load estimates with a 95 confidence interval were hindcast from the flow record and average annual loads of 7253 673 tonnes on the river bandon and 1935 325 tonnes on the river owenabue were estimated to be passing the gauging stations

an upper ordovician sponge bearing micritic limestone and implication for early palaeozoic carbonate successions abstract a potentially new type of non reef sponge bearing micritic limestone is reported from the upper ordovician xiazhen formation of south eastern china the sponges are preserved as incomplete skeletons that consist of curved bifurcated and trifurcated spicules embedded in dark micrite and can only be recognized under a petrographic microscope the characteristics of the spicule networks suggest that the sponges are probably belonging to demosponges however based on the absence of features such as desma zygome a distinct dermal layer and a canal system they are not considered to be lithistids the majority of the sponges are found in a lime mudstone facies together with some micritic portions of wackestone to grainstone facies comprising approximately 13 of the 50 m thick micritic limestone successions it is interpreted that the non lithistid demosponges flourished on soft substrates over shallow marine carbonate platform such sponge bearing carbonates are similar to spiculites and spongolites in terms of being a major constituent of the sedimentary rocks and their potential contribution as sediment producers but affinity and modes of preservation of the xiazhen sponges are significantly different to those of the spiculites and spongolites in light of the present finding it is suggested that non lithistid demosponges may have been more widespread in early palaeozoic non reef carbonates than has previously been recognized thus indicating the critical need for further detailed studies if we are to understand their distributions and sedimentological contributions

crouching shells hidden sponges unusual late ordovician cavities containing sponges abstract marine cavities harbouring cryptic organisms have been ubiquitous throughout the phanerozoic however our knowledge of early cryptic communities is as yet insufficient and how metazoans began to utilize such habitats remains unknown in this study we document demosponge remains within intraskeletal cavities embedded in the micritic succession of a shallow carbonate platform in the upper ordovician katian xiazhen formation of south china molluscs gastropods bivalves and nautiloids and corals the solitary rugosan tryplasma and colonial agetolitids within the succession commonly contain patches of spicular demosponge remains 11 n 45 415 mainly occupying intraskeletal spaces with areas of 1 30 mm2 in thin section sponge occurrence varies according to sedimentary facies within lime mudstone facies sponges commonly occur both inside and outside intraskeletal cavities suggesting that sponges would have inhabited and become preserved within any available space in this environment in contrast when other sessile organisms co occur in wackestone to packstone facies there are fewer sponge occurrences both inside and outside cavities possibly due to competition in open habitats and or their poorer preservation in such environments overall this result suggests that sponges would have exploited cryptic habitats by normal expansion of the open surface biota in addition compared with coeval reef and hardground crypts the xiazhen intraskeletal cryptic biota is monotonous in composition suggesting decoupled occupation of cryptic habitats in different environments

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

ordovician reef systems and settings in south china before the late ordovician mass extinction abstract ordovician reefs of the south china block occur chiefly in three stratigraphic units 1 the middle tremadoc fenhsiang formation and the upper part of the lunshan formation 2 the late tremadoc hunghuayuan formation and 3 the middle ashgill xiazhen sanjushan and daduhe formations the region therefore records part of the early palaeozoic reef expansion episode and permits a broader assessment of change in ordovician reef facies during middle tremadoc time lithistid sponge bryozoan calathium calcimicrobially dominated patch reefs of the fenhsiang formation occur in the high energy belt of the central yangtze platform columnar nonskeletal stromatolites of the lunshan formation coeval with fenhsiang formation occur on the southeastern margin of the platform where low diversity reef attached organisms and the generally fine grained character of the sediment are consistent with a depth below normal wave base calathium and lithistid sponges were the principal reef builders of late tremadoc reefs and were widespread in the areas of yichang hubei province and dongzhi anhui province from the platform centre to its margin settings bryozoan reef builders occur only in the platform centre with a high diversity of reef dwellers such as brachiopods trilobites and nautiloids however during the same time at the platform margins microbes played an important part in reef building together with calathium and lithistid sponges the middle late tremadoc lithistid sponge bryozoan calathium microbial community was replaced by a middle ashgill coral stromatoporoid community and shows that the succession of community replacement during the ordovician took a relatively long time restricted by the black shales of the main part of the yangtze region middle ashgill reef complexes can be found only on the northeast platform of cathaysian land between the yushan jiangxi and changshan zhejiang regions carbonate mudmounds are present on the western margin of the yangtze platform on the northeast platform of cathaysian land patch reefs some higher relief with talus and biostromes of the xiazhen formation consist of high diversity biotas of corals stromatoporoids calcimicrobes brachiopods and gastropods the sanjushan formation is age equivalent to the xiazhen formation and contains carbonate mudmounds that are composed of abundant calcareous algae and calcimicrobia uplift forced a northward extension of cathaysian land and caused a regional relative sea level fall eliminating this reef complex prior to the first extinction event of the late ordovician the daduhe formation carbonate mudmounds occur in the nearshore belt of kangdian land western margin of the yangtze platform and are paraconformably overlain by the hirnantian nancheng formation in total the ordovician reefs of south china show a range of habitats and controls on growth and demise

sediment load responses to climate variation and cascade reservoirs in the yangtze river a case study of the jinsha river abstract climate change and human activities have substantially changed hydrological and geomorphologic processes particularly in upper mountainous catchments the jinsha river basin jrb the uppermost region of the yangtze river and the largest hydropower production region in china was chosen to investigate the sediment load responses to climate variations and human activities the non parametric mann kendall test and double mass curve were used to explore the spatial temporal variations of hydro meteorological variables and quantify the contributions of climate variation and human activities to changes in discharge and sediment load in the jrb from the 1950s to 2015 the results indicate that human activities in particular cascade damming were the governing factor for sediment load changes while climate variations increasing precipitation and snow and glacier melt dominated the discharge changes in the jrb the average annual sediment load at the panzhihua pzh station increased by 42 4 from 1966 1984 to 1985 2010 mainly due to mineral extraction and deforestation followed by a decrease of 75 9 in 2011 2015 because of the operation of the cascade reservoirs in the middle jrb since 2010 the construction of new dams like the xiangjiaba reservoir 2012 and the xiluodu reservoir 2013 in the lower jrb and many other cascade reservoirs since 2010 in the middle jrb further decreased the sediment load by 58 5 bht and 83 8 xjb in the recent five years from 2011 to 2015 although channel erosion downstream of the xjb dam can provide new sediment to the three gorges reservoir tgr the sedimentation rate of the tgr has decreased rapidly and will continue to be reduced due to the construction of more dams in the future

high resolution imaging of lowermost mantle structure under the cocos plate 1 broadband seismic shear waves are analyzed to investigate the fine velocity structure in the lowermost mantle beneath the cocos plate a region where previous studies have indicated the presence of a shear velocity increase about 200 300 km above the core mantle boundary data from 14 south american earthquakes recorded at california broadband networks provide dense ray path sampling of the lowermost mantle in an approximately 700 km long north south corridor roughly 150 km wide application of a simplified seismic migration method that uses a homogeneous background velocity model suggests topography of the previously imaged positive impedance jump varying in depth from north to south by as much as 150 km with a weakly reflecting transition zone in between the migration approach enables examination of small scale spatial variations and out of plane scattering effects topography of the discontinuity may account for observed variations in the amplitude of reflected arrivals or there may be lateral variations in the velocity contrast across the boundary lateral variations of the shear velocity structure within the d layer may produce some apparent topography in the discontinuity image but any such volumetric structure is not yet well enough determined to incorporate in the migration a localized negative impedance contrast reflector or scatterer is imaged at depths about 100 km below the positive reflector in the northern portion of the study area several scenarios can explain these results including 1 a slab that reaches the lowermost mantle 2 the birth of an upwelling beneath a recumbent slab or 3 chemical layering in this region

yangtze river of china historical analysis of discharge variability and sediment flux hydrological records covering a 100 year period from the upper middle and lower yangtze river were collected to examine the temporal and spatial distribution of discharge and sediment load in the drainage basin the yangtze discharge as expected increases from the upper drainage basin downstream only an estimated 50 of the discharge is derived from the upper yangtze with the rest being derived from the numerous tributaries of the middle and lower course however the distribution of sediment load along the yangtze is the reverse of that observed for discharge with most of the sediment being derived from the upper basin a dramatic reduction in sediment load by 0 8 108 tons year occurs in the middle yangtze because of a marked decrease in slope and the change to a meandering pattern from the upper yangtze rock sections considerable siltation also occurs in the middle yangtze drainage basin as the river cuts through a large interior dongting lake system sediment load in the lower yangtze while significantly less than that of the upper river is somewhat higher than the middle yangtze because of additional load contributed by adjacent tributaries a strong correlation exists between the discharge and sediment load along the yangtze drainage basin during the dry season as lower flows carry lower sediment concentration during the wet season a strong correlation is also present in the upper yangtze owing to the high flow velocity that suspends sand on the bed however a negative to poor correlation occurs in the middle and lower yangtze because the flow velocity in these reaches is unable to keep sand in suspension transporting only fine grained particles downstream hydrological data are treated for 30 years 1950 1980 when numerous dams were constructed in the upper yangtze drainage basin at yichang and hankou hydrological stations records revealed a decreasing trend in annual sediment load along with slightly reduced annual discharge at the same stations this can be interpreted as the result of water diversion primarily for agriculture sediment load at datong further downstream is quite stable and not influenced by slightly reduced discharge furthermore sediment concentration at the three hydrological stations increased which can be attributed to sediment loss in association with intensifying human activity especially in the upper drainage basin such as deforestation and construction of numerous dams mean monthly sediment load of these 30 years pulses about 2 months behind discharge implying dam released sediment transport along the entire river basin during the high water stage

suspended sediment transport rates at the 1 5 year recurrence interval for ecoregions of the united states transport conditions at the bankfull and effective discharge historical flow and suspended sediment transport data from more than 2900 sites across the united states have been analyzed in the context of estimating flow and suspended sediment transport conditions at the 1 5 year recurrence interval flow q1 5 this is particularly relevant with the renewed focus on stream restoration activities and the urgency in developing water quality criteria for sediment data were sorted into the 84 level iii ecoregions to identify spatial trends in suspended sediment concentrations and yields to meaningfully describe suspended sediment transport rates across the united states arguments are developed that in lieu of form based estimates of say the bankfull level a flow of a given recurrence interval q1 5 is more appropriate to integrate suspended sediment transport ratings for the purpose of defining long term transport conditions at a site the effective discharge the use of the q1 5 as a measure of the effective discharge for suspended sediment transport is justified on the basis of literature reports and analytic results from hundreds of sites in 17 ecoregions that span a diverse range of hydrologic and topographic conditions i e coast range arizona new mexico plateau mississippi valley loess plains middle atlantic coastal plain there is sufficient data to also develop regional curves for the q1 5 in all but eight of the ecoregions at the q1 5 the highest median suspended sediment concentrations occur in semiarid environments southwest tablelands arizona new mexico plateau and the mojave basin and range the highest yields occur in humid regions with erodible soils and steep slopes or channel gradients mississippi valley loess plains mvlp and the coast range suspended sediment yields for stable streams are used to determine background or reference sediment transport conditions in eight ecoregions where there is sufficient field data the median value for stable sites within a given ecoregion are generally an order of magnitude lower than for nonstable sites

lower cambrian cavity dwelling endolithic boring sponges in the lower cambrian forteau formation middle bonnia olenellus zone of southern labrador cavities in archaeocyath patch reefs contain preserved coelobiontic endolithic sponges scallops and carbonate chips produced by sponge boring spicules and preserved endolithic sponge body fossils all point to the presence of endolithic sponges in lower cambrian reef cavities the oldest previously described endolithic sponges are early ordovician in age and the oldest previously known reef interior bioerosion is middle ordovician in age the presence of endolithic sponges in reef cavities of the forteau formation therefore extends both the record of endolithic sponges and of reef interior bioerosion from the ordovician to the upper lower cambrian

temporal and spatial variations of sediment rating curves in the changjiang yangtze river basin and their implications the natural hydrologic regime of the changjiang yangtze river in china has been disturbed considerably by intensified human activities over the past five decades in this study sediment rating curves were analyzed based on monthly data of water discharge and suspended sediment concentration at stations in the upper yichang station middle hankou station and lower datong station reaches of the changjiang in different periods from 1955 to 2007 temporal and spatial variations of the sediment rating curves were analyzed with respect to the impact of human activities and watershed characteristics results indicate that human disturbances have had a substantial impact on sediment rating parameters with the magnitude of the impact related to the scale of the river sections as indicated by the sediment rating parameters the sediment transport regimes between the upper and the mid lower reaches differ significantly in particular the impoundment of the three gorges dam in 2003 changed the sediment transport regimes in the upper and mid lower reaches of changjiang into similar regimes characterized by a decrease in the sediment transport capacity of high water discharge furthermore the sediment rating curve at the datong station in 1955 1968 was applied to estimate the potential sediment load 1969 2007 in the absence of human influences the mean annual sediment deficit caused by human activities has increased from 80 mt yr 1969 1985 to 250 mt yr 2003 2007 this indicates that intensified human activities in the changjiang basin especially the construction of the three gorges dam have altered the natural sediment transport process and have thus become a dominant force in changjiang sediment delivery to the sea

questioning the microbial origin of automicrite in ordovician calathid demosponge carbonate mounds calathid demosponge carbonate mounds are a feature of early to middle ordovician shallow marine carbonate depositional environments of tropical to subtropical palaeolatitudes these mounds contain an important amount of autochthonous non skeletal microcrystalline calcium carbonate automicrite conventionally considered microbial in origin here the automicrite of calathid demosponge carbonate mounds tarim basin north west china is broken down into five distinct fabrics an in situ peloidal spiculiferous fabric am 1 an in situ peloidal fabric am 2 an aphanitic microtubular fabric am 3 a minipeloidal fabric am 4 and a laminoid cerebroid fabric am 5 type am 1 occurs with am 2 being succeeded by an assemblage of am 3 and am 4 types am 4 and am 5 are separated by an erosional disconformity a good correlation of fluorescence and cathodoluminescence of automicrites indicates that induced and supported organomineralization produced automicrite probably via the permineralization of non living organic substrates adsorbing dissolved metal humate complexes using a spreadsheet with six parameters and 17 characters am 1 to am 4 turn out to be non microbial in origin instead these automicrites represent relics of calcified metazoan tissues such as siliceous sponges non spiculate sponges or the basal attachment structures of stalked invertebrates fabric am 5 is a microbial carbonate but is post mound in origin forming a drape within a reefal framework established by am 4 the five automicritic fabrics individually or as an assemblage are a common element of ordovician calathid demosponge carbonate mounds in general the reassessment of the origins of these automicritic fabrics holds consequences for understanding of the great ordovician biodiversification event in terms of community structure reef ecology and reef evolution episodically these fabrics are also present in other carbonate build ups stretching from the neoproterozoic over the entire phanerozoic eon the massive calcification of metazoan soft tissue am 1 to am 4 characterizes episodes and conditions of enhanced marine calcification and might be of value to refine secular trends of pco2 ca concentration and mg ca ratio at the scale of individual sedimentary basins

acoustic doppler current profiler surveys along the yangtze river an acoustic doppler current profiler is used to characterize the river velocity against the morphology of the yangtze river from chonqing to the sea high flow velocities occur in the three gorges section and lower velocities in the middle and lower reaches of the river this is largely due to the change in river pattern from a high gradient deeply cut valley to a flat fluvial plain flow velocities fluctuate in the middle yangtze due to the presence of meander bends of different length there are numerous smaller velocity fluctuations in the lower yangtze channel that reflect multichannel pattern with numerous sand bars and a river morphology affected by bedrock outcrops water depths of 40 100 m occur in the three gorges valley but decrease to 15 40 m in the middle and lower yangtze at the gezhou reservoir 30 km downstream of the three gorges damsite velocity drops to low 1 0 m s 1 20 km reach a second low velocity 0 5 m s 1 zone about 20 km in length is located in the lower yangtze near the coast probably due to the tidal influence the results from this research will serve as a datum for evaluating changes to the river once the three gorges dam is completed in 2009

middle cambrian siliceous sponge calcimicrobe buildups daegi formation korea metazoan buildup constituents in the aftermath of the early cambrian extinction event abstract numerous decimetre to metre scale carbonate buildups dominated by siliceous sponges and the calcimicrobe epiphyton are reported from the middle cambrian series 3 daegi formation of korea these siliceous sponge epiphyton buildups consist predominantly of grey micritic boundstones with dark clots and or white clumps the boundstones contain sponge spicule networks interpreted as the calcified remains of siliceous sponges the white clumps and dark clots in the boundstones represent variously preserved epiphyton siliceous sponges form constructional pore space and are commonly encrusted by epiphyton the sponges were probably the primary frame builders providing substrates for the attachment and subsequent growth of epiphyton epiphyton is considered to be a binder when covering the surface of siliceous sponges and a subordinate frame builder when filling depositional voids created by siliceous sponges or growing on top of other epiphyton growth bundles the siliceous sponge epiphyton buildups of the daegi formation show similarities to previously described late cambrian furongian anthaspidellid calcimicrobe buildups from iran and the usa together with recently reported examples from the zhangxia formation of eastern china the sponge epiphyton buildups from korea represent some of the oldest metazoan calcimicrobe buildups after the extinction of most archaeocyaths at the end of the early cambrian series 2 this implies that the incorporation of metazoans in middle cambrian series 3 carbonate buildups occurred much earlier than previously known the buildup forming siliceous sponges described in this study demonstrate that their role in early phanerozoic carbonate buildups has been grossly underestimated

sediment transporting flows in headwater streams the equilibrium alluvial stream channel has a geometry that allows it to pass the water and sediment supplied from the watershed at the same time the equilibrium alluvial channel is built and maintained by the flows and sediment delivered to it a prerequisite for understanding the creation of the equilibrium channel is an understanding of the sediment conveyance and competence of the flows the channel receives this study describes the bed load transport regime as it is linked to hydrology and geomorphology in 23 headwater gravel bed streams in snowmelt dominated parts of central and northern idaho at sites drainage areas range from 1 29 to 381 km 2 stream gradients range from 0 0042 to 0 0747 and median bed surface particle sizes range from 4 to 207 mm stream architecture includes riffle pool planar and step pool beds the bed load is much finer than the surface and subsurface material suggesting selective transport of the finer sizes nonetheless the majority of the load is sand at all flow discharges progressively coarser sediment was collected as flow discharge increased and painted rock experiments documented the transport of coarser particles at higher discharges the supply of sediment to the streams appears limited as indicated by observed clockwise hysteresis in bed load transport rates during each spring snowmelt and by the coarse surface armor observed at sites flows above bankfull discharge move 37 of the bed load whereas flows between mean annual discharge and bankfull move 57 of the bed load the bed load effective discharge has a recurrence interval that averages 1 4 yr and the magnitude of effective discharge averages 80 of bankfull discharge the recurrence interval of bankfull discharge averages 2 0 yr the ratio of effective discharge to bankfull discharge is independent of basin size grain size and gradient although the ratio increases with the relative magnitude of large infrequent events

a new middle ordovician bivalve siliceous sponge microbe reef building consortium from north china abstract a new reef building consortium from a middle ordovician succession of the western north china platform is described consisting mainly of bivalves siliceous sponges and microbial carbonates epiphyton like renalcis like and girvanella calcified microbes and microcrystalline microstromatolites in addition to minor brachiopods amsassia and rhabdotetradium the bivalves are thin walled and mostly articulated indicating in situ preservation the siliceous sponges are characterized by regularly spaced spicule networks embedded within micrite which partly grade into peloidal textures three main types of bivalve sponge associations are found 1 larger bivalves 2 13 mm encrusted by sponges 2 sponges occupying internal spaces of larger bivalves and 3 smaller 0 2 0 4 mm bivalves embedded within sponge spicule networks microbial carbonates either cover the upper surfaces of siliceous sponges and bivalves or occur independently as centimeter scale patches the reefal boundstones were constructed mainly by bivalves siliceous sponges and microbes which were subsequently encrusted and stabilized by additional sponges and microbes extensive early marine cementation forming fibrous cement helped stabilize the reef framework the co occurrence of bivalves and siliceous sponges is possibly analogous to modern day counterparts in which sponges encrust bivalves or bivalves are living within sponges suggesting a symbiotic relationship the bivalve siliceous sponge microbial reefs of this study together with other ordovician reefs represent the changeover from microbial to skeletal dominated reefs during the middle ordovician the current example may represent an ancestral association of bivalve siliceous sponge microbe reefs similar to those in the mesozoic and cenozoic thus shedding light on the roots of such associations

cavity dwelling biota in middle ordovician chazy bryozoan mounds from quebec bryozoan mounds dominated by batostoma chazyensis from the laval formation of the chazy group early middle ordovician near montreal quebec contain framework cavities that house a coelobiontic cavity dwelling biota reports of coelobionts of ordovician age are rare and this is the first report of chazy group mounds containing coelobionts algae sponges and bryozoa batostoma dominate the cavity biota and are found encrusting cavity walls and roofs the algae are represented by mammillary encrustations now micrite and solenpora sp on the roofs the sponges are not identified but occur both as isolated monaxial triaxial and six rayed spicules and as body fossils within the cavities coccoid cells of unknown affinities are also found these cavities provide the first evidence of coelobiontic biological erosion trypanites a compound morphogenus is the only macroborer and is found in cavity walls endolithic boring algae are present and indicate that as early as the middle ordovician b

cryptalgal metazoan bioherms of early ordovician age in the st george group western newfoundland bioherms are common in the st george group a sequence of shallow water carbonate rocks deposited on the western continental shelf of iapetus ocean they range from small heads and metre sized mounds to extensive banks and complexes many metres thick and hundreds of metres in lateral extent the cores of these bioherms are principally composed of thrombolites unlaminated branching columnar stromatolites structures quite distinct from laminated stromatolites which are common in intertidal beds associated with thrombolites is a diverse fauna of burrowing invertebrates trilobites nautiloids pelmatozoans brachiopods gastropods rostroconchs and archaeoscyphiid sponges on the basis of framework building components three main bioherm types are distinguished 1 thrombolite mounds 2 thrombolite lichenaria or sponge mounds and 3 thrombolite lichenaria renalcis reef complexes the framework of the last is the most complex with abundant cavities and a demonstrably uneven growth surface of thrombolites corals and free standing renalcis heads walls and roofs some cavities were active sediment conduits while others were protected their roofs draped with renalcis and their walls coated by cryptalgal laminites these bioherms possess the attributes of shallow water ecologic reefs they span a critical time gap in the development of reefs the transition period from algal dominated bioherms of the precambrian and cambrian to the metazoan dominated bioherms of the middle ordovician and remaining phanerozoic

sediment rating parameters and their implications yangtze river china abstract this study examines the characteristics of sediment rating parameters recorded at various gauging stations in the yangtze basin in relation to their controls our findings indicate that the parameters are associated with river channel morphology of the selected reaches high b values 1 600 and low log a values 1 000 occur in the middle and lower yangtze river associated with meandering reaches over low gradients and can be taken to imply aggradation in these reaches with low stream power higher b values 0 900 1 600 and lower log a values 4 000 to 1 000 characterize the reaches between yichang and xinchang immediately below the three gorges these values indicate channel erosion and bed instability that result from changes in channel gradient from the upstream steep valley to downstream low slope flood plain settings differences in channel morphology accompany these changes confined v shaped valleys occur upstream and are replaced downstream by broad u shaped channels the middle and lower yangtze shows an apparent increase in channel instability over the past 40 years this inference is based on sediment rating parameters from various gauging stations that record increasing b values against decreasing log a values over that time analysis of the sediment load data also reveals a strong correlation between changes in sediment rating curve parameters and reduction of annual sediment budget 4 70 108 t to 3 50 108 t year from the 1950s to 1990s largely due to the damming of the yangtze and sediment load depletion through siltation in the dongting lake short term deviations from the general trends in the sediment rating parameters are related to hydroclimatic events extreme low b values and high log a values signify the major flood years while the reverse indicates drought events when compared with rivers from other climate settings it is evident that the wide range of values of the yangtze rating parameters reflects the huge discharge driven by the monsoon precipitation regime of eastern china

tetradiid siliceous sponge patch reefs from the xiazhen formation late katian southeast china a new late ordovician reef association decimetre scale domal to tabular patch reefs consisting of dendroid tetradiids are found in the late ordovician late katian xiazhen formation southeast china it is intriguing to observe that siliceous sponges occur together with the tetradiids in many patch reefs as this has not been previously reported the tetradiid rhabdotetradium jiangshanense are preserved in situ and the siliceous sponges where present as spicule networks calcimicrobe ortonella encrusting tetradiid tubes and burrows filled with faecal pellets also constitute as subordinate components of the patch reef the tetradiid tubes are regarded as frame builders that are commonly surrounded and encrusted by the siliceous sponges the sponges wherever observed form the bulk of the patch reef and are regarded as a primary constructor as well as binder of the patch reef burrows filled with faecal pellets often penetrate the area between tetradiids and sponge spicule networks in the boundstone and these are considered to be the loci of dweller where the sponges and tetradiids co occur the tetradiid tubes are sparsely distributed and commonly display non quadripartite fission i e bipartite or tripartite in contrast where the sponges are rare in the patch reef the tetradiid tubes are densely spaced and predominantly display quadripartite fission this indicates that the tetradiid growth was influenced by the presence of siliceous sponges this finding of the new late ordovician reef association and their mutual interplay extend our understanding of the early palaeozoic carbonate reefs it reaffirms the need for multidisciplinary studies of carbonate buildups where similar interactions with siliceous sponges might have been overlooked

contrasting mountain and piedmont dynamics of sediment discharge associated with groundwater storage variation in the biobio river supply and transport of sediment in catchments involve processes with fundamental consequences for river management land use and the prediction of climate driven sediment fluxes in the present study we addressed spatial variability in the water routes through the surface and subsurface of a catchment and the suspended sediment discharge qs over a mountain piedmont system we analyzed daily suspended sediment concentration cs and water discharge q measurements at stations located in different topographic settings mountain and piedmont in the biobio river basin southern central andes 37 39 s in steep catchments the q versus qs relationship has a marked seasonal hysteresis in the piedmont qs is proportional to q with no seasonal hysteresis the contrast in the hysteresis pattern between catchments with different topographies is explained by differences in the routing of rainfall derived water in the piedmont most of the rainfall is converted into surface runoff because the water table is near the surface in the mountains groundwater storage results in large seasonal variations in the proportion of q that flows at the surface and transports sediment from the hillslopes producing hysteresis by separating the total q into two components direct discharge qd and base flow qb we observed the response of qs to the fraction of water that quickly leaves the catchment after a rainfall event qd similar results between the mountain and piedmont and the absence of hysteresis simplify the behavior of qs into a linear relationship with qd over the entire catchment and lead us to propose that sediment mobilization to the river along the biobio catchment is primarily controlled by overland flow our findings highlight the importance of an adequate hydrological model for understanding the erosion and transport processes of a catchment and which can be applied to other natural and modeled mountain piedmont systems

slabs in the lower mantle and their modulation of plume formation numerical mantle convection models indicate that subducting slabs can reach the core mantle boundary cmb for a wide range of assumed material properties and plate tectonic histories an increase in lower mantle viscosity a phase transition at 660 km depth depth dependent thermal expansivity and depth dependent thermal diffusivity do not preclude model slabs from reaching the cmb we find that ancient slabs could be associated with lateral temperature anomalies 500 c cooler than ambient mantle plausible increases of thermal conductivity with depth will not cause slabs to diffuse away regional spherical models with actual plate evolutionary models show that slabs are unlikely to be continuous from the upper mantle to the cmb even for radially simple mantle structures the observation from tomography showing only a few continuous slab like features from the surface to the cmb may be a result of complex plate kinematics not mantle layering there are important consequences of deeply penetrating slabs our models show that plumes preferentially develop on the edge of slabs in areas on the cmb free of slabs plume formation and eruption are expected to be frequent while the basal thermal boundary layer would be thin however in areas beneath slabs the basal thermal boundary layer would be thicker and plume formation infrequent beneath slabs a substantial amount of hot mantle can be trapped over long periods of time leading to mega plume formation we predict that patches of low seismic velocity may be found beneath large scale high seismic velocity structures at the core mantle boundary we find that the location buoyancy and geochemistry of mega plumes will differ from those plumes forming at the edge of slabs various geophysical and geochemical implications of this finding are discussed