low concentration of heavy metals in the yangtze estuarine sediments china a diluting setting abstract an examination of the spatial and temporal distribution of 17 major heavy metals i e fe zn ni mg co mn etc was made in the yangtze estuarine sediments revealed by a number of vibrocores taken from the different sediment zones including delta front prodelta and delta shelf transition the results obtained from the numerous core samples which were also measured for pb 210 and cs 137 show that 1 the silty clay comprising the prodelta facies serves as a depositional sink attracting high concentrations of heavy metals delivered from the river mouth 2 after being normalized to aluminum as a proxy for grain size most heavy metals presented in the prodelta facies have lower concentrations than in the other adjacent sediment zones 3 also after normalization concentrations of most heavy metals in the vibrocore sediments tend to increase up core and 4 sedimentation rates in the study area range from 2 0 to 6 0 cm a hence the vibrocores contain a sedimentary record of metal deposition covering more than 50 years it has previously been assumed that sediments off the river mouth were heavily polluted due to industrialization of the shanghai metropolitan area which peaked about 50 years ago however the low concentrations of heavy metals in the study area before and after normalization do not support this assumption the yangtze estuary is characterized largely by the tremendous runoff and unpolluted sediments derived from the upper drainage basin to constitute a unique diluted setting in which the dispersal behavior of heavy metals from the adjacent industrialized coast is influenced substantially as a result the heavy metals in the study area are obviously lower than those previously determined along the coast

137cs and 210pb derived sediment accumulation rates and their role in the long term development of the mkuze river floodplain south africa abstract wetlands are well known to act as sinks for sediment and chemicals in the landscape within the mkuze river floodplain in northern kwazulu natal south africa deposition of clastic sediment occurs predominantly in close proximity to the river channel resulting in the formation of levees over time this leads to channel avulsion a process that may be accelerated by the activities of hippopotami whose trails create hydraulically favourable pathways sedimentation rates determined using the isotopes 210pb and 137cs indicate that the mkuze river floodplain is a relatively rapidly aggrading system that should experience frequent avulsion with average short term rates in the order of 0 25 to 0 50 cm y sediments on the floodplain are also an important sink for solutes which concentrate in the groundwater and precipitate out because of evapotranspiration over long timescales chemical sedimentation affects the landscape by influencing salinity vegetation distribution hydrological flows and local topography the mkuze river floodplain is an actively evolving system which continues to aggrade as a result of the combination of clastic and chemical sedimentation in a region characterised by a strong annual water deficit temporal patterns of clastic and chemical sedimentation are likely to exert influence on the long term development of wetland systems elsewhere in southern africa this study the first on sediment accretion rates using 210pb and 137cs dating for a southern african wetland demonstrates that radioisotopic methods are an important tool that can be applied toward fully understanding wetland formation evolution and functioning in the region

sediment characteristics of an extreme flood 1993 upper mississippi river valley the 1993 mississippi river flood was notable for its high magnitude long duration summer occurrence and low sediment discharge a field survey of a 70 km long reach in the vicinity of quincy illinois revealed that the event was characterized by 100 yr flood had remarkably little sedimentological or geomorphological impact on the flood plain within the study reach because the transport effectiveness of floods in large drainage basins is influenced by event sequencing in the same manner as floods in small watersheds and the cohesive flood plain soils were not susceptible to erosion

controls on overbank deposition in the upper mississippi river abstract floodplains contain valuable stratigraphic records of past floods but these records do not always represent flood magnitudes in a straightforward manner the depositional record generally reflects the magnitude frequency and duration of floods but is also subject to storm scale hysteresis effects flood sequencing effects and decade scale trends in sediment load many of these effects are evident in the recent stratigraphic record of overbank floods along the upper mississippi river umr where the floodplain has been aggrading for several thousand years on low lying floodplain surfaces in iowa and wisconsin 137cs profiles suggest average vertical accretion rates of about 10 mm year since 1954 these rates are slightly less than rates that prevailed earlier in the 20th century when agricultural land disturbance was at a maximum but they are still an order of magnitude greater than long term average rates for the holocene as a result of soil conservation practices accretion rates have decreased in recent decades despite an increase in the frequency of large floods the stratigraphic record of the upper mississippi river floodplain is dominated by spring snowmelt events because they are twice as frequent as rainfall floods last almost twice as long and are sometimes associated with very high sediment concentrations the availability of sediment during floods is also influenced by a strong hysteresis effect peak sediment concentrations generally precede the peak discharges by 1 4 weeks and concentrations are usually low the great flood of 1993 on the mississippi river focused attention on the geomorphic effectiveness and stratigraphic signature of large floods at mcgregor where the peak discharge had a recurrence interval of 14 years the flood was most notable for its long duration 168 days above 1600 m3s 1 high sediment concentrations three episodes 180 mg l and large suspended load 1 71 mt the flood of 2001 despite its greater magnitude recurrence interval 70 years was associated with relatively low sediment concentrations

heat flow in the ozark plateau arkansas and missouri relationship to groundwater flow abstract heat flow values were calculated from direct measurements of temperature and thermal conductivity at thirteen sites in the arkansas missouri ozark plateau region these thirteen values are augmented by 101 estimates of heat flow based on thermal conductivity measurements and temperature gradients extrapolated from bottom hole temperatures the regional heat flow profile ranges from 9 mw m 2 to over 80 mw m 2 but at least two distinct thermal regimes have been identified seven new heat flow determinations are combined with three previously published values for the st francois mountains sfm a precambrian exposure of granitic and rhyolitic basement rocks average 47 mw m 2 radioactive heat production of 76 samples of the exposed rocks in the sfm averages 2 4 w m 2 and a typical continental basement contribution of 14 mw m 2 is implied conversely the sedimentary rock sequence of the plateau is characterized by an anomalously low heat flow averaging approximately 27 mw m 2 groundwater transmissivity values that are based on data from 153 wells in deep regional aquifers demonstrate an inverse relationship to the observed heat flow patterns the areas of high transmissivity that correspond to areas of low total heat flux suggest that the non conservative vertical heat flow within the ozark sedimentary sequence can be attributed to the effects of groundwater flow

palaeoflood and floodplain records from spain evidence for long term climate variability and environmental changes abstract palaeoflood chronologies from seven spanish river basins and floodplain aggradation chronologies from thirteen rivers are analysed these fluvial records were divided in to two sub sets namely atlantic 10 ka record and mediterranean 3 ka record river basins which represent distinct modern hydroclimatic conditions in atlantic basins floods result from intense widespread rainfalls associated with atlantic frontal systems transported by westerly airflow mediterranean river flooding is related to heavy rainfall induced by mesoscale convective systems mcss during autumn months evidence from radiocarbon dates in slackwater flood deposits shows six periods of flood clusters at 10 750 10 240 9550 9130 4820 4440 2865 2350 960 790 and 520 290 cal bp despite the different flood producing weather conditions in atlantic and mediterranean rivers the radiocarbon sample clusters overlap and indicate changes in large scale atmospheric circulation and climatic conditions in the iberian peninsula comparison with proxy records of mean temperature for the northern hemisphere demonstrates a relationship between the period of slackwater flood deposition and cold climatic phases e g the 2650 yr bp climatic event or ad 1590 1650 period of the little ice age radiocarbon dates from aggraded floodplain sediments were clustered at 2710 2320 2000 1830 and 910 500 cal bp the first cluster period is in phase with the timing of slackwater deposition whereas the third 910 500 cal bp occurs in between two periods of increased flood frequency as indicated by the palaeoflood and documentary flood records it is argued that the 910 500 cal bp floodplain aggradation period reflects the first post roman evidence of environmental change related to generalised land use changes at the catchment scale which produced high sediment load transported to overbank areas during high flows

sedimentary records of large holocene floods from the middle reaches of the yellow river china slackwater deposits have been used as evidence for the magnitude and frequency of palaeofloods which occurred prior to gauged and historical data sets e g holocene extreme flood reconstruction in north america and australia the slackwater deposits from xiaolangdi reach of the yellow river have been identified and related to floods according to both eyewitness accounts and the analysis of sediments the technique successfully delineated the peak flood level and estimated a discharge of the 1994 ad flood in the yellow river the discrepancy of the estimated discharge was less than 5 compared with the instrumental records when we applied the technique to palaeoflood analysis the highest slackwater deposits and flood indicators from the tributary mouths the low river terraces and the loess platforms and loess alcoves together with radiocarbon dating provided evidence of at least six floods with peak discharges greater than 27 300 m3 s 1 at xiaolangdi section over the last 8500 yr the largest flood in ca 7362 yr b p had an estimated discharge of 42 900 m3 s 1 which is the maximum flood event known in the yellow river the results provide a basis for a determining the floods which were comparable to the most cataclysmic flood during the last 2360 yr in 1843 ad and b estimating the flood magnitude for a 10 000 yr time scale relevant for building xiaolangdi dam one of the largest dams under construction in the world the reconstruction of palaeofloods also provides evidence for a phase between ca 6000 8000 yr b p which was much wetter than today as a result of increased summer precipitation and enhanced pacific monsoon conditions in eastern china

a geochemical record of flooding on the upper river severn uk during the last 3750 years abstract projected future changes in climate call for more definite information on the magnitude frequency relationships of major floods than can be obtained from short instrumental or historical records alone floodplains represent a sedimentary archive of unrecorded flood events which can potentially be used to extend existing flood records by centuries or millennia in this study a c 3750 year flood record was produced using ln zr rb profiles from two 4 m deep cores through floodplain silts at the roundabout in the upper severn catchment uk sediment geochemical profiles were obtained using high resolution 500 m xrf core scanning ages were assigned to the flood record using 14c dating and contaminant pb profiles comparison of sediment ln zr rb with sediment grain size showed that ln zr rb increases with increasing grain size and indicates that it can be used as a grain size proxy at this site within the ln zr rb flood record two floods that occurred at c 235 and c 10 cal bc were probably the largest that have occurred at the site during the past 3750 years while the historical flood of a d 1795 appears to be the largest since c ad 200 the record shows that during the past c 3750 years multicentennial periods characterized by the occurrence of high magnitude floods return periods c 30 years have alternated with periods of similar length without such floods these periods correspond to large scale variations in hydroclimate recorded in the north atlantic region however the incidence of the highest magnitude floods appears to be unaffected by changes in catchment land use this study provides information about flood magnitude frequency relationships and their controls at a local level that could be used to help catchment managers in assessing future flood risk at a time of rapidly changing climate

taconian orogeny in the new england appalachians collision between laurentia and the shelburne falls arc tectonic models of the ordovician taconian orogeny in western new england usually invoke a collision between the laurentian margin and a magmatic arc identified as the bronson hill arc however in central massachusetts and southern new hampshire rocks in the bronson hill arc are 454 to 442 ma and therefore younger than much of the taconian deformation and metamorphism in western new england and eastern new york which began by 470 ma u pb and single grain evaporation zircon ages combined with geochemical analyses reveal the presence of an older magmatic arc the shelburne falls arc that formed west of the bronson hill arc at 485 to 470 ma the shelburne falls arc formed above an east dipping subduction zone by the early ordovician the taconian orogeny was the result of the collision between laurentia and the shelburne falls arc beginning ca 475 to 470 ma the younger bronson hill arc formed above a west dipping subduction zone that developed along the eastern edge of the newly accreted terrane during the final stages of and subsequent to the taconian orogeny the taconian orogeny ended when plate convergence between laurentia and iapetus was accommodated by the newly developed west dipping subduction zone instead of by crustal shortening in the taconian thrust belt the tectonic history of the new england appalachians is inconsistent with a middle ordovician collision between laurentia and the proto andean margin of gondwana

changes in the magnitude and frequency of late holocene monsoon floods on the narmada river central india during the past three decades the narmada river of monsoon dominated central india has undergone extraordinarily large floods that rank among the highest recorded rainfall runoff discharges per drainage area in the world the floods on this river are a direct result of intense tropical cyclones embedded within the summer monsoon circulation the cluster of extreme floods in the past few decades represents an anomalous increase in both the magnitude and frequency of large floods when compared with the 1700 yr record of paleoflood deposits on this river sand deposits from recent floods consistently blanket older flood deposits at numerous slack water paleoflood sites along a 15 km reach of the narmada river at the site of the highest flood deposits 4 5 sandy flood deposits yielding post a d 1950 14c dates cap an underlying sequence of 7 10 silty flood deposits with a minimum 14c age of 650 70 b p and a maximum age older than 1720 185 b p the post a d 1950 floods are thus the largest in at least the past several hundred years an undisturbed surface archaeological site of microlithic artifacts 0 5 m above the post 1950 flood sands provides further evidence that no significantly larger floods have occurred in at least the past 3000 yr incipient soil development on the buried surfaces of some of the higher paleoflood deposits indicates long intervals in the past when no floods reached the highest slack water site the largest flood in the 1951 1991 gaged record of the narmada river at mortakka 55 323 m3s 1 in 1961 is equivalent to a 1000 yr flood in a probability distribution based on the 1700 yr paleoflood record but is less than a 50 yr flood based on the 1951 1991 gaged record alone demonstrating the enormous recent increase in the frequency of severe floods this cluster of severe floods could reflect changes in either climate or land use a number of paleoflood studies in tropical storm regions show a similar increase in high magnitude floods within the past four decades suggesting a widespread climatic cause for this pattern

model for the tectonic evolution of the mississippi embayment and its contemporary seismicity aeromagnetic and gravity surveys of the northern mississippi embayment have delineated a northeast trending basement depression about 70 km wide and more than 300 km long the feature the mississippi valley graben is remarkably linear over its known length has nearly parallel sides and has estimated depths relative to surrounding basement of more than 2 km both gravity and magnetic anomalies show an alignment of dense magnetic plutons along the boundaries of the graben estimated magnetization directions for the plutons indicate a mesozoic age the graben of probable earliest paleozoic age underlies the northwest side of the embayment and contains the area of major seismicity in particular much of the instrumentally located contemporary seismicity and the estimated locations of the large magnitude 1811 1812 earthquakes are in the central part of the graben we interpret the early paleozoic graben the mesozoic plutonism and the sedimentation cycles as evidence of stretching events seismicity is attributed to strain in and below the central graben area which would appear to be a focal point of deformation in the stretching model we suggest that the sequence of events can be explained by the action of a rotating horizontal stress field on a crustal flaw that persisted well back in pre cambrian time the postulated rotating stress field is presumably controlled by the system that drives the global plates

an ancient rift complex and its relation to contemporary seismicity in the new madrid seismic zone gravity magnetic geologic and seismicity data have been combined in a seismotectonic analysis of the new madrid seismic zone previous studies have presented evidence for several rift zones in this area upper mississippi embayment including the reelfoot rift a late precambrian early paleozoic failed arm which extends n ne from the ancient continental margin in this study we propose that the northern terminus of the reelfoot rift forms a rift complex which appears to correlate well with the seismicity in the area this correlation suggests that faults associated with this rift complex are being reactivated in the contemporary stress field ene compression if this interpretation is valid it represents a seismotectonic model which can be used to predict the extent of future seismicity in the new madrid seismic zone the proposed rift complex also provides a coherent model for the tectonic development of this region of the north american midcontinent

impact of monsoonal climatic change on holocene overbank flooding along sushui river middle reach of the yellow river china abstract in the semiarid loess regions slackwater deposition of overbank flooding over the piedmont alluvial plains was episodic and alternated with dust accumulation and soil formation throughout the holocene the records of past hydrological events are therefore preserved within the architecture of loess and soils and are protected from subsequent erosion and destruction several holocene loess soil sequences with the deposits of overbank flooding over the semiarid piedmont alluvial plains in the southeast part of the middle reaches of the yellow river drainage basin were investigated by field observation osl and c14 dating measurement of magnetic susceptibility particle size distribution and chemical elements this enables the reconstruction of a complete catalog of holocene overbank flooding events at a watershed scale and an investigation of hydrological response to monsoonal climatic change as well during the holocene there are six episodes of overbank flooding recorded over the alluvial plain the first occurred at 11 500 11 000 a bp i e the onset of the holocene the second took place at 9500 8500 a bp immediately before the mid holocene climatic optimum after an extended geomorphic stability and soil formation the third overbank flooding episode came at about 3620 3520 a bp i e the late stage of the mid holocene climatic optimum and the floodwater inundated and devastated a bronze age town of the xia culture built on the alluvial plain and therefore the town was abandoned for a period of ca 100 years during the late holocene the alluvial plain experienced three episodes of overbank flooding at 2420 2170 1860 1700 and 680 100 a bp respectively the occurrence of these overbank flooding episodes corresponds to the anomalous change in monsoonal climate in the middle reaches of the yellow river drainage basin when rapid climate change or climatic decline occurs during at least the last four episodes both extreme floods and droughts occurred and climate departed from its normal condition which was defined as a balanced change between the northwestern continental monsoon and southeastern maritime monsoon over time great floods occurred as a result of extreme rainstorms in summers caused by rare intensive meridianal airflows involving northwestward moving tropical cyclone systems from the pacific these results could be applied to improve our understanding of high resolution climatic change and of hydrological response to climatic change in the semiarid zones

bed sediment associated trace metals in an urban stream oahu hawaii of the 117 stream and lake systems sampled nationwide fish from manoa stream on oahu hawaii have consistently shown the highest pb concentrations therefore a detailed study was conducted to examine total metal contents in bed sediments from a 5 8 km stretch of manoa stream a total of 123 samples 63 m were examined for 18 elements and 14 samples for 21 elements selected samples were also examined using different leach solutions to examine metal phase associations all trace metal data computations of enrichment ratios and the modified index of geoaccumulation point to mineralogical control for cr and ni minor anthropogenic contamination for ba cd cu hg and zn and a very strong contamination signal for pb maximum pb contents up to 1080 mg kg 1 were associated with anthropogenic material dumping in minor tributaries storm sewer sediments and sediments in the lower section of the basin proportionally pb had the highest non residual component of elements examined dominantly in the reducible phase associated with mn and amorphous fe oxyhydroxides the contamination signal was typically lowest in the undisturbed headwater reach of the basin above 5 1 km with significant increases throughout the residential and commercial institutional zones of the mid basin the spatial pattern of bed sediment contamination and evidence from storm sewer outlet sediments strongly indicates that pb and to a lesser degree some other metals is still being transported to the stream and the primary agent is soil erosion and transport of metals sorbed to sediments the primary source of sediment associated metals is considered to be the automobile though other minor sources can not be ruled out

paleoflood hydrology origin progress prospects from an origin in diverse studies of flood geomorphology and quaternary geology paleoflood hydrology emerged as a geophysical and an applied hydrological science during the 1970s and 1980s since acquiring its formal name in 1982 the most productive approach in paleoflood hydrology has become energy based inverse hydraulic modeling of discrete paleoflood events recorded in appropriate settings as slackwater deposits and other paleostage indicators swd psi or as various threshold indicators of non exceedence technological advances particularly in hydraulic modeling and geochronology were instrumental in moving the discipline to its present status the most recent advances include 1 new techniques for the accurate geochronology of flood sediments notably tams radiocarbon analyses and osl dating and 2 the phenomenal increase in computer power that allows complex hydraulic calculations to become feasible for routine studies from its initial demonstration in the southwestern united states swd psi paleoflood hydrology proved its widespread applicability to various landscape environments particularly important studies have been accomplished in australia china india israel south africa spain and thailand paleoflood hydrology has also generated its share of controversy in part because of the differing viewpoints and attitudes of the two scientific traditions from which it emerged quaternary geology geomorphology versus applied hydrologic hydraulic engineering nevertheless the future growth of the discipline is assured given the rapid pace of discoveries that it engenders indeed so many international studies exist that it is appropriate to pursue global syntheses to address interesting and timely questions of extreme flood phenomena in relation to global climatic change

critical taper model of fold and thrust belts and accretionary wedges the fold and thrust belts and submarine accretionary wedges that lie along compressive plate boundaries are one of the best understood deformational features of the earth s upper crust although there is considerable natural variation among the many fold and thrust belts and accretionary wedges that have been recognized and explored several features appear to be universal in cross section fold and thrust belts and accretionary wedges occupy a wedge shaped deformed region overlying a basal detachment or decollement fault the rocks or sediments beneath this fault show very little deformation the decollement fault characteristically dips toward the interior of the mountain belt or in the case of a submarine wedge toward the island arc the topography in contrast slopes toward the toe or deformation front of the wedge deformation within the wedge is generally dominated by imbricate thrust faults verging toward the toe and related fault bend folding two north american fold and thrust belts that exhibit these features are shown in figure 1 neither of these two examples is tectonically active today the southern canadian fold and thrust belt was active during the late jurassic and cretaceous 150 100 ma whereas the southern appa lachians were deformed during the late carboniferous to permian alle ghenian orogeny 300 250 ma figure 2 shows two examples that are currently active the taiwan fold and thrust belt produced by the sub duction of the eurasian plate beneath the philippine sea plate suppe 1981 1987 and the barbados accretionary wedge produced by the sub

bouguer images of the north american craton and its structural evolution processing of existing gravity and aeromagnetic data with modern methods is providing new insights into crustal and mantle structures for large parts of the united states and canada1 3 more than three quarters of a million ground station readings of gravity are now available for this region these data offer a wealth of information on crustal and mantle structures when reduced and displayed as bouguer anomalies where lateral variations are controlled by the size shape and densities of underlying materials we have used digital image processing techniques to generate bouguer images that display more of the granularity inherent in the data as compared with existing contour maps a dominant nw se linear trend of highs and lows can be seen extending from south dakota through nebraska and into missouri fig 2 the structural trend cuts across the major precambrian boundary in missouri separating younger granites and rhyolites from older sheared granites and gneisses this trend is probably related to features created during an early and perhaps initial episode of crustal assembly by collisional processes the younger granitic materials are probably a thin cover over an older crust

palaeoflood record of the tagus river central spain during the late pleistocene and holocene abstract palaeoflood hydrology of the tagus river central spain was reconstructed from slackwater deposits and palaeostage indicators in two canyon reaches located at el puente del arzobispo in the central part of the catchment 35 000 km 2 in drainage area and in alcantara at the lower part of the catchment 52 000 km 2 in drainage area near the portuguese border the palaeoflood record with more than 80 flood events shows clusters of floods at specific periods from 9440 to 9210 14 c yr bp 8540 8110 bc 8500 to 8000 14 c yr bp 7500 7000 bc 6750 14 c yr bp 5000 bc 1200 to 950 14 c yr bp ad 785 1205 410 14 c yr bp ad 1450 1500 170 to 80 14 c yr bp ad 1670 1950 the largest flood s occurred during the periods 9440 to 9210 14 c yr bp 6750 14 c yr bp and 1200 to 950 14 c yr bp reaching minimum discharge estimates of between 4000 and 4100 m 3 s 1 in the el puente del arzobispo reach and 13 700 15 000 m 3 s 1 in the alcantara reach these periods with increased flood magnitude and or frequency in the tagus river are strongly related to increased moisture influx and winter precipitation in the iberian peninsula especially in the western zone proxy records sensitive to winter precipitation such as lake levels and vegetation changes indicated by pollen records are in good agreement with the clusters of floods found in the tagus river this flood variability seems to correspond to changes in the prevailing atmospheric circulation pattern affecting the iberian peninsula

heavy metal trends in floodplain sediments and valley fill river lahn germany abstract sampling along the river lahn a major tributary to the river rhine that flows through an agrarian region of west central germany reveals that heavy metal pollution occurs outside major industrial regions and mined landscapes along a 60 km reach of the river between marburg and wetzlar mean concentrations of cu pb and zn at depths of 5 and 15 cm in four floodplain transects were greater than background levels concentrations declined sharply between 15 and 25 cm laterally concentrations peaked at the bank top and in the near channel zone of the floodplain beyond the near channel zone generally up to 100 m from the channel concentrations were much less and fairly uniform to the valley wall the clustering of metals close to the channel suggests that they are a fluvial rather than an eolian deposit during floods of a moderate magnitude sediments and attached metals are deposited soon after the river overtops its banks although the overall store of metals in the valley is less than that along the rhine near channel metal concentrations are similar to those along rivers draining major industrial and mined areas

stratigraphic relationships and detrital composition of the medial ordovician flysch of western new england implications for the tectonic evolution of the taconic orogeny a reply to rodgers we present new stratigraphic and petrographic data on the easterly derived medial ordovician flysch sequence of western new england and eastern new york state a conformable relationship exists between the flysch and underlying early paleozoic continental rise sediments within the western taconic allochthon farther east in the allochthon we observe a possibly disconformable relationship contrary to previous interpretations these facts suggest that at any place within this paleogeographic realm the sediments were undeformed and untransported at the initiation of flysch deposition at least three sources contributed detritus to the flysch 1 taconic sequence sediments 2 deformed and metamorphosed pelitic psammitic and volcanic lithologies and 3 igneous rocks of dominantly mafic ultramafic affinities these three sources are respectively interpretable as continental rise accretionary prism and ophiolitic volcanic arc assemblages which are recognized in the regional geology of western new eng

relationship between the ellisville pluton and chopawamsic fault establishment of significant late ordovician faulting in the appalachian piedmont of virginia

the decompensative gravity anomaly and deep structure of the region of the rio grande rift an isostatic correction is commonly made to bouguer anomaly gravity data to remove the gravity effect of isostatic compensation of topographic loads in the ussr a decompensative correction has then been made to the isostatic gravity anomaly to remove the gravity effect of isostatic compensation of geologic loads as well under an hypothesis of local as opposed to regional compensation the gravity effect of a shallow geological body can be separated from that of its inferred deep compensating root by deconvolution by contrast with the procedure originally defined by zorin we employ here calculations in the wave number domain leading to an efficient and exact solution the decompensative transfer function acts to increase amplitude of the isostatic anomaly at all wavelengths but especially at the low end of the isostatic anomaly spectrum in the 200 600 km wavelength region where anomaly amplitudes may increase by as much as a factor of 2 in a 1200 1200 km region centered on the rio grande rift the decompensative correction ranges from about 35 to 25 mgal the rift is not particularly apparent in the decompensative correction nor is the rift any more apparent in the decompensative anomaly than in the isostatic anomaly the decompensative anomaly however highlights an arcuate gravity low and a system of gravity highs inferred to reflect prerift welts of mass concentration which have indirectly influenced the position of the rift and its segmentation and zones of accommodation under the assumptions made if the decompensative anomaly is subtracted from the bouguer anomaly then the residual is the gravity anomaly field of deep structure without gravity effects of shallow sources in the upper crust we suppose this gravity field to be dominated by the gravity effects of the density contrast across the crust mantle boundary moho and the density contrast at the lithosphere asthenosphere boundary using available seismic data to weakly constrain the moho surface we invert the residual gravity field for topography of the base of the lithosphere lithosphere is found to be 200 km thick in the high plains 40 50 km in the eastern great basin 75 100 km in the colorado plateau and as thin as 40 km in the southern rio grande rift in the area studied the thickness of the lithosphere is everywhere greater than that of the crust an asthenosphere bulge closely tracks the axis of the rift and is symmetrical to it by contrast with asymmetry that might be inferred from broad features of the bouguer anomaly the separation of gravity effects made possible by the decompensative correction shows how the rift is fundamentally controlled by thinning of the lithosphere yet in detail is deflected by long lived tectonic welts in the shallow brittle crust

age and setting of the bronson hill magmatic arc a re evaluation based on u pb zircon ages in southern new england new u pb zircon ages of selected rocks from the bronson hill anticlinorium in southern new england are as follows microcline gneiss of the dry hill gneiss in the pelham dome believed to be metamorphosed alkali rhyolite is confirmed as late proterozoic yielding an age of 613 3 ma another sample shows strong evidence of zircon inheritance with a minimum mean age of 1402 ma plagioclase rich gneisses with associated amphibolites swanzey pauchaug monson and fourmile gneisses now believed to represent metamorphosed intrusive igneous rocks yield ages from 454 to 442 3 2 ma thus ranging from early late through latest ordovician consistent with other absolute ages of the oliverian plutonic series in the region quartz phyric rhyolite from the upper member of the ammonoosuc volcanics and rhyolite tuff from the partridge formation are dated at 453 2 ma and 449 3 2 ma respectively indicating that eruption of felsic lavas in the overlying volcanic section spanned an interval of approximately 4 m y additional zircon ages are reported from a crosscutting but deformed tonalite dike in the swanzey gneiss 381 3 ma and a coarse grained gabbro from the prescott intrusive complex 407 3 2 ma intrusive into the partridge formation metamorphic overprinting of the region during both the acadian and alleghanian orogenies is indicated by u pb titanite ages of 357 5 ma and 292 5 ma from a tonalite gneiss on prescott peninsula and the dry hill gneiss respectively the above ages and other zircon ages as well as petrography and geochemistry of the fourmile monson swanzey pauchaug and other plagioclase rich gneisses of the bronson hill anticlinorium suggest that they represent the plutonic root of a calc alkaline magmatic arc at least 250 km long that was produced partly or entirely on a continental margin in late ordovician time ca 454 442 ma the physically overlying cover sequence of chemically different tholeiitic arc volcanic and sedimentary rocks of the ammonoosuc volcanics and partridge formation previously thought to rest unconformably on the plagioclase rich plutonic gneisses is now shown to have had a magmatic history overlapping with them the zircon ages in the plutonic gneisses and the cover sequence indicate that both are the same age or slightly younger than the late ordovician caradocian emplacement of the giddings brook slice of the taconian allochthons and too young to have formed above an early and medial ordovician subduction zone

aeromagnetic images fresh insight to the buried basement rolla quadrangle southeast missouri aeromagnetic data from the rolla 1 2 quadrangle missouri displayed as a small scale grey tone image provide a lucid picture of basement features beneath sedimentary rock cover late stage tin granite plutons of the proterozoic st francois magmatic terrane are clearly delineated the plutons average about 11 km in diameter and occupy a significant fraction 12 percent of the area surveyed gravity data require that certain plutons are at least 3 km thick most of the plutons are fat ovals in plan view and show no flattening trend or structural alignment the ensemble indicates significant extension in an orthorhombic stress field with the minimum compressional stress being vertical exposed st francois terrane volcanic rocks show a characteristic intricate pattern in the magnetic signature this pattern is more widespread than the subsurface distribution of volcanic rocks indicated by drilling and likely also incorporates areas of st francois batholith granite the horseshoe shaped trend of

horizontal gravity gradient an aid to the definition of crustal structure in north america a map of the magnitude of the horizontal bouguer gravity gradient over the north american continent is used to delineate lateral discontinuities in upper crustal density and or thickness associated with such processes as suturing and rifting the usefulness of gradient trends in mapping major structural boundaries which are sometimes poorly exposed or completely buried is demonstrated by examples such as the buried southward extension of the grenville front and buried boundaries of the superior province gradient trends also draw attention to poorly known structures which may have major tectonic significance and to a continent wide structural fabric which may provide a record of the tectonic growth of the north american continent

crustal architecture beneath the southern midcontinent usa and controls on mesoproterozoic iron oxide mineralization from 3d geophysical models abstract several types of critical mineral bearing ore deposits in the southern midcontinent region of the u s are hosted in mesoproterozoic igneous rocks largely concealed beneath paleozoic cover discerning the architecture of igneous intrusions and volcanic centers in the crust is fundamental to understanding the geologic evolution of this vast region and its mineral resources to advance the understanding of the geologic framework beneath the southeast missouri iron metallogenic province we invert continental scale magnetic and gravity anomaly data to three dimensional 3d physical property models the regional models image altered and mineralized igneous rocks near the proterozoic basement surface and underlying intrusive complexes that extend down to the moho at shallow crustal levels our models confirm that iron oxide apatite rare earth element ioa ree deposits and iron oxide copper gold cobalt iocg deposits occur within or near the edges of large low density low susceptibility early mesoproterozoic ca 1 4 ga silicic calderas and ca 1 3 ga granitic plutons previous isotopic and geochemical studies conclude that the iron deposits and their volcanic host rocks originated from mantle derived and crustal melts that erupted during regional extension extension was associated with thermal event s that produced the large scale silicic magmatism related to the ca 1 45 ga eastern granite rhyolite province egrp and the 1 35 ga southern granite rhyolite province sgrp we postulate that early in the evolution of the egrp several trans crustal magmatic plumbing systems developed that are evident in the 3d models the southeast missouri metallogenic province is underlain by one such magmatic system that is expressed as a northwest trending 50 km wide by 200 km long elongate track of high susceptibility at deep crustal levels the high susceptibility corridor splays upward through the crust to the proterozoic surface where the iron deposits are the epigenetic manifestation of this magmatic event our findings confirm that the iron deposits with no distinct connection at the surface are connected to one large magmatic system at depth we propose that other similar susceptibility tracks which are present along the top of the mantle mark additional feeder zones that allowed magma to ascend to the main eruptive centers that produced the granite rhyolite provinces the early mesoproterozoic extensional tectonic framework established crustal scale pathways that controlled the distribution of subsequent magmatic activity including the ca 1 4 ga calderas and underlying intrusions ca 1 3 ga silicic plutons and phanerozoic alkaline intrusions if these interpretations are correct our study has identified large areas that are prospective for critical mineral bearing ore deposits and importantly suggests that the mesoproterozoic architecture may have influenced subsequent magmatism and hydrothermal activity in the southern midcontinent of the u s

holocene paleofloods related to climatic events in the upper reaches of the hanjiang river valley middle yangtze river basin china abstract holocene slackwater deposits along the river channels were used to study the magnitude and frequency of the paleofloods that occurred prior to gaged and historical data sets all over the world paleoflood hydrological investigations were carried out in the upper reaches of the hanjiang river china four bedsets of paleoflood slackwater deposits were found interbedded in the holocene loess soil sequence within the cliff riverbanks they were studied by field observations and laboratory analysis including magnetic susceptibility particle size distribution and optically stimulated luminescence osl dating these provide a complete catalog of holocene flood events at a watershed scale that is very important in understanding the regional hydrological response to monsoonal climatic change four episodes of holocene overbank flooding have been recorded over the basin these hydroclimatic events were dated to 8500 8400 4200 4000 3200 2800 and 1800 1700 ybp by using the osl method in combination with pedostratigraphic correlations with the previously studied holocene pedostratigraphy in the hanjiang river basin the peak discharges of these flood episodes vary in a range from 26 610 to 47 900 m 3 s 1 as estimated by using the slope area method of streamflow measurement these flood events are therefore considered a regional expression of known climatic events and demonstrate holocene climatic instability the study provides a solid reference that magnitudes and recurrence frequencies of floods are highly sensitive to climate change in the monsoonal zone in other parts of the world

petrogenesis of metaluminous a type rhyolites from the st francois mountains missouri and the mesoproterozoic evolution of the southern laurentian margin abstract predominantly acid volcanic and intrusive rocks of the approximately 1 48 ga eastern granite rhyolite province are exposed only in the st francois mountains inlier missouri combined nd isotopic major and trace element analyses are presented for the predominantly acid volcanic rocks of the st francois mountains they are metaluminous to mildly peraluminous a type compositions with positive initial e nd values of 3 1 5 0 they are interpreted to be the result of crystal fractionation of partially melted calc alkaline igneous rocks formed at a recently active subduction zone the likelihood of a juvenile calc alkaline subduction generated protolith for the st francois mountains rhyolites leads to a hypothesis in which dacitic parental magmas resulted from partial melting in a continental back arc setting basaltic magmatism due to decompression melting of the mantle resulted from lithospheric extension and thinning and provided the heat source for melting in the middle or lower crust penecontemporaneous magmatism elsewhere in laurentia included subduction related calc alkaline rocks in the pinware terrane of labrador some felsic igneous rocks of uncertain plate tectonic setting within the grenville province also have 1 5 1 6 ga t dm ages these are interpreted as magmatic products of approximately 1 5 ga northward dipping subduction beneath much of the length of the southern margin of laurentia the eastern granite rhyolite province is consequently seen as an integral inboard expression of this subduction related igneous activity petrogenetic models involving a mantle plume or the development of a continental rift are not required to explain this granite rhyolite terrane and evidence against their involvement is discussed

magnetic and gravity gradiometry framework for mesoproterozoic iron oxide apatite and iron oxide copper gold deposits southeast missouri high resolution airborne magnetic and gravity gradiometry data provide the geophysical framework for evaluating the exploration potential of hidden iron oxide deposits in mesoproterozoic basement rocks of southeast missouri the data are used to calculate mineral prospectivity for iron oxide apatite ioa rare earth element ree and iron oxide copper gold iocg deposits results delineate the geophysical footprints of all known iron oxide deposits and reveal several previously unrecognized prospective areas the airborne data are also inverted to three dimensional density and magnetic susceptibility models over four concealed deposits at pea ridge ioa ree boss iocg kratz spring ioa and bourbon iocg the pea ridge susceptibility model shows a magnetic source that is vertically extensive and traceable to a depth of greater than 2 km a smaller density source located within the shallow precambrian basement is partly coincident with the magnetic source at pea ridge in contrast the boss models show a large 625 m wide vertically extensive and coincident dense and magnetic stock with shallower adjacent lobes that extend more than 2 600 m across the shallow precambrian paleosurface the kratz spring deposit appears to be a smaller volume of iron oxides and is characterized by lower density and less magnetic rock compared to the other iron deposits a prospective area identified south of the kratz spring deposit shows the largest volume of coincident dense and nonmagnetic rock in the subsurface and is interpreted as prospective for a hematite dominant lithology that extends from the top of the precambrian to depths exceeding 2 km the bourbon deposit displays a large bowl shaped volume of coincident high density and high magnetic susceptibility rock and a geometry that suggests the iron mineralization is vertically restricted to the upper parts of the precambrian basement in order to underpin the evaluation of the prospectivity and three dimensional models an extensive statistical summary of density and apparent magnetic susceptibility measurements is presented that includes data on several hundred samples taken from the deposits altered wall rocks and unaltered country rocks

floodplain sediments of the 2002 catastrophic flood at the vltava moldau river and its tributaries mineralogy chemical composition and post sedimentary evolution fine grained floodplain sediments of the catastrophic 2002 flood deposited along the lower reaches of the berounka and vltava rivers czech republic were not highly contaminated with heavy metals and other toxic elements this is due to the dominantly mineral character of the sediments ctot in the range 3 97 5 01 relatively low content of clay minerals and due to the very high degree of contamination dilution by eroded pre industrial non contaminated floodplain sediments despite this high degree of dilution the influence of the small litavka river draining the historical pb zn ag p ibram ore region is well visible the litavka river is one of important sources of pb and zn contamination in the whole berounka vltava labe river system the 2002 flood sediments deposited in the floodplain of the berounka and vltava rivers show poor vertical chemical zoning except for some components enriched in the uppermost layer by precipitation from evaporated pore water contained in the mud i e secondary carbonate the content of ccarb of the sediments 0 05 0 15 is partly represented by this secondary carbonate which is later leached by rainwater and partly by fragments of river mollusk shells a majority of the heavy metals contained in sediments can be readily leached by diluted acids and to a much smaller degree by rainwater

rb sr and u pb geochronology and distribution of rock types in the precambrian basement of missouri and kansas most of what we know about basement rocks in kansas and missouri is derived from cores and cuttings from deep drilling these rocks may be divided into a northern terrane underlain by rocks consisting of abundant granite commonly showing cataclastic textures and by metavolcanic to metasedimentary rocks and a southern terrane underlain almost exclusively by rhyolitic flows and ash flow tuffs and epizonal granite plutons the northern terrane is interrupted in central kansas by mafic igneous rocks and flanking arkosic sedimentary rocks of the central north american rift system data from 63 rb sr whole rock analyses yield ages ranging from 1 153 to 1 748 m y but these are considered to represent only the minimum ages of the rocks ages derived from u pb analyses of suites of cogenetic zircons from 22 rock samples indicate that some rocks of the northern terrane were formed 1 610 to 1 650 m y ago these are apparently intruded by younger granite plutons formed 1 450 1 470 m y and 1 340 1 380 m y ago rocks of the southern terrane were formed 1 460 1 480 m y ago in the st francois mountains terrane of southeastern missouri and its buried equivalents but these are about 1 380 m y old in southwestern missouri and southern kansas rocks of the central north american rift system in kansas are assumed to be about 1 100 m y old by geophysical and drill hole extension to their outcrop in the lake superior region where they have been dated both the northern and southern terranes are notable for the great abundance of granitic rocks and the scarcity of intermediate to mafic igneous rocks quartzite is the most abundant metamorphic rock although the decrease in ages from north to south in the mid continent region suggests their sequential accretion at the edges of a pre existing continent the rock assemblages are not consistent with convergent plate margin suites of the andean type the great volumes of rhyolite and epizonal granite of the southern terrane may represent melting of thickened somewhat older crust following accretion at the continental margin major element chemical data are presented for basement rocks from kansas oklahoma and texas and these are compared with the compositions of similar rocks from the st francois mountains names and locations are given for wells from which samples were obtained

geotectonic imaging of the north western european continent and shelf abstract gridding and merging of onshore gravity and topography information from the british national gravity and topography data bank with offshore free air gravity anomalies derived from seasat altimeter data and bathymetry from the national geophysical data center usa has allowed for the first time the production of digital images for the north western european continent and shelf 48 62 lat 348 010 long further using image processing techniques the images have been selectively filtered using artificial illumination to enhance both caledonian and variscan trends as a large amount of terrestrially acquired offshore gravity data already exists within the north sea region it has been possible to test the accuracy of the seasat derived free air gravity anomaly data hence its use in geological and geophysical interpretations by comparing the two we conclude that while the derived seasat gravity trends are essentially correct significant error may exist in the amplitude determination especially where anomaly wavelengths are short and oceanographic components in the altimeter data are significant the potential value of geotectonic images is as an aid in recognising trends and relationships between geological and or tectonic domains that are not generally apparent in the more conventional representations of these data e g profile and contour maps we offer interpretations for both the local free air bouguer gravity anomalies in terms of the known geology of the british isles and offshore regions and the regional gravity anomalies in terms of the thermal and mechanical response of the north western european lithosphere during variscan compression continental collision and thrust sheet migration and palaeozoic mesozoic and cenozoic rifting events sedimentary basin formation

extraordinary floods related to the climatic event at 4200 a bp on the qishuihe river middle reaches of the yellow river china abstract palaeo hydrological study was carried out in the qishuihe river valley in the middle reaches of the yellow river several bedsets of flood slackwater deposit were identified in the holocene loess soil sequences on the riverbanks they were differentiated from aeolian loess and soils by the parallel and waving beddings and the distinctive stratigraphic breaks separating individual palaeoflood events chronology of the flood events was established by osl dating checked by archaeological identification of the anthropogenic remains retrieved from the sequences the results show that successive floods occurred between 4300 and 4000 a bp in association with the abrupt climatic event of 4200 a bp these overbank floods had the riverbank settlement inundated repeatedly another series of extraordinary floods occurred between 3200 and 3000 a bp when monsoonal climate shifted from the mid holocene climatic optimum toward late holocene dry conditions the climatic event of 4200 a bp and the climatic decline at 3100 a bp were believed to be characterized by droughts previously this work provides solid evidence that both severe droughts and extreme floods were parts of the climatic variability during abrupt climatic event and climatic decline in the semi arid to sub humid zones over the world

the sand ridge field of the south yellow sea origin by river sea interaction abstract the origin of a large field of sand ridges offshore from the north jiangsu coast in the south yellow sea has been investigated on the basis of bathymetry seabed samples high resolution seismic profiles and 31 to 71 m deep boreholes sediment composition including heavy minerals and clay minerals sampled from surface sediments shows that most of the sand was derived from the changjiang yangtze river but in the northern part of the field particularly the clay came from the huanghe yellow river seismic profiles show late pleistocene distributary channels of the ancient changjiang river underlying much of the southern part of the sand ridge field the holocene transgression cut a widespread ravinement surface reworking abundant late pleistocene sandy sediment the available sand was reworked by tidal currents into large ridges the location of the ridges is strongly influenced by relict channels in the southern part of the field and by tidal currents in the northern and especially the northeastern part of the field resulting in a radiating ridge pattern these ridges provide an example of the evolution of a large scale geomorphic feature resulting from river sea interaction in which climatic and sea level changes played an important role

rift structure of the northern mississippi embayment from the analysis of gravity and magnetic data gravity and magnetic data have been simultaneously inverted to derive a crustal model of the northern mississippi embayment which is compatible with geologic and seismic refraction data the results indicate that this region is a site of a late precambrian early paleozoic rift system an anomalously dense layer is present at the base of the crust and thickens beneath a broad northeast trending graben that formed during the initial phases of rifting the thickest part of anomalous crust occurs beneath the region of greatest seismic activity which lies within the geographic limits of the graben it is suggested from this correlation that strain accumulates within the anomalous crust layer which acts as an inhomogeneity in a relatively homogeneous lithosphere based on the results of this study and previous geophysical studies the complex tectonic evolution of the upper mississippi embayment since late precambrian time is rift formation possibly along a pre existing shear zone graben development in cambrian time reactivations in permian and cretaceous time and subsequent formation of the present mississippi embayment and fault zones with large influences from rift structures

sediment transport from the yangtze river china into the sea over the post three gorge dam period a discussion sediment loads from the yangtze river into the sea experienced a major increase in the late holocene when sand beaches along the deltaic coast changed into tidal flats sediment transport averaged about 472 million tons a year between the 1950s and the mid 1980s and decreased by 124 million tons a year after the mid 1980s followed by a dramatic drop since the closure of the three gorge dam tgd this paper discusses the major processes for the decline of sediment discharge since the 1950s and discusses the method for evaluating its future development over the post tgd period sediment loads in the post tgd period will be mainly determined by the major processes that may significantly contribute to the following three components i e 1 the sediment input from the upper basin into the three gorge reservoir tgr 2 the ratio of sediment export from the tgr relative to the input and 3 the amount of sediment recovery downstream the tgd restrained by available sediment sources an integrated evaluation shows that the annual sediment loads over the post tgd period will possibly vary from 1 12 to 1 32 million tons a year or less in ordinary years

paleoflood hydrology and extraordinary flood events paleoflood hydrology is the study of past or ancient flood events the most accurate technique involves the analysis of slackwater deposits and paleostage indicators swd psi slackwater deposits are sand and silt emplaced from suspension in exceptionally deep high velocity floods that characterize narrow deep canyons in resistant geologic materials these and other paleostage indicators are used to establish hydraulic grade lines for the generating flow events favorable sites for slackwater deposition include channel margin areas where stresses and velocities are reduced below critical values necessary to maintain fine grained bedload material sand and silt in suspension computerized procedures for hydraulic flow modeling are used to tie the elevations of the highest slackwater deposits to surveyed river cross sections the flood discharges calculated by this method can be calibrated through the study of modern floods on gaged rivers correlation of multiple swd psi sites along a river reach is used to identify the maximum paleostage achieved by a given flood advances in the dating of flood deposits permit estimates of flood frequency to be made extending over a data base of thousands of years the major geochronologic tool is radiocarbon dating of various kinds of organic matter intercalated with the slackwater deposits an important development is the use of the tandem accelerator mass spectrometer for direct measurement of 14c tiny blebs of charcoal seeds and other organics can be analyzed in order to date ancient flood deposits of hydrologic significance since swd psi studies yield very accurate determinations of paleoflood ages and magnitudes there is a pressing need for new statistical procedures that make optimum use of the information content in paleoflood records for flood frequency analysis nevertheless swd psi paleoflood hydrology has moved beyond the research phase its use should be encouraged in evaluating past experience of extraordinary floods at appropriate hazardous sites

sedimentary lead pollution history lead isotope ratios and conservative elements at east taihu lake yangtze delta china abstract in 2009 two short sedimentary cores djz and dqg were collected from the east taihu lake at the lower yangtze river basin using a gravity corer lead isotopes and metals including pb al fe and ti were measured radio nuclides including 210pb and 137cs were also analyzed for dating of the sediments at both cores the averaged sedimentation rate at dqg site was 0 32 cm a since the early 1960s while at djz it was at least 1 cm a significant decline of 206pb 207pb ratios were observed in dqg from the deeper sediments to near surface sediments indicating increased anthropogenic lead load to the lake sediments due to human impact since the 1970s the uppermost sediments lead contents were 2 3 times of those before the 1950s trends of anthropogenic lead in both cores inferred from a lead isotope mixing model were found to be similar to those from al fe and ti normalization methods ti was found to be the best passive tracer element highly in accordance with pb isotope mixing model results in dqg anthropogenic lead increased sharply since the 1970s and reached a maximum in 2000s 28 mg kg from lead isotope mixing model while at djz the highest value was 20 mg kg these results revealed significant anthropogenic lead influx into the lake caused by human activities in good agreement with the economic development in the past three decades in china

a 4500 year record of large floods on the colorado river in the grand canyon arizona a sequence of flood deposits left by the colorado river in the grand canyon arizona provides evidence of at least 15 floods with peak discharges greater than 5500 m 3 sec 1 over the last 4500 yr ten floods during the last 2000 2300 yr had discharges greater than 6800 m 3 sec 1 one flood 1600 1200 yr ago had a discharge exceeding 14 000 m 3 sec 1 a flow rate more than twice the largest gaged flood this record of flooding is one of the longest for a major u s river and combined with the gaged record of twentieth century floods allows determination of the frequency and history of large floods that have affected key aspects of colorado river geomorphology

heavy metal contamination in overbank sediments of the geul river east belgium its relation to former pb zn mining activities overbank sediments of the geul river east belgium are highly contaminated by the heavy metals pb zn and cd due to former pb zn mining activities in the drainage basin geochemical variations in vertical overbank sediment profiles sampled 1 km north of the mine tailings of plombieres allow metal fluxes back to the 17th century to be reconstructed the vertical profiles are subdivided into three major units corresponding to different industrial periods based on sedimentological criteria as well as on the distribution of contaminants alluvial sediments with the highest heavy metal concentrations correspond to the major period of mining activity of the 19th century the fact that zn mining at the la calamine open mine started before large scale mining of the pbs zns subsurface exploitations is reflected in the vertical profiles by an increase in zn content before a marked increase in pb and cu the regional extent of contamination in the alluvial deposits was evaluated on the basis of the geochemical analysis of sediments at depths of the 0 20 cm and 80 100 cm most of the upper samples are extremely contaminated significant local variations in heavy metal concentration in the lower samples are interpreted in terms of which overbank sediment horizon has been sampled at a depth of 80 100 cm this indicates that blind sampling of overbank sediments to characterize the degree of contamination in shallow boreholes can give very erratic results

trace metal concentrations in lake and overbank sediments in southern norway as be cd co cr cu hg ni pb v se and zn concentrations were determined and compared in lake and overbank sediments from 33 catchments without local pollution sources in southern norway there were no significant differences in concentrations of be co cr cu ni and v in overbank and pre industrial lake sediments in areas with shallow overburden and significant influence from long range atmospheric pollution concentrations of as cd hg pb se and zn in overbank sediments were probably modified by vertical percolating water in such areas we suggest using lake sediments as a better sampling medium for mapping pre industrial concentrations pre industrial lake sediments yield natural concentrations of hg and se which consist of both geogenic and natural atmospheric deposition important covariables like organic carbon content fe oxides and fine mineral fraction were generally higher in pre industrial lake sediments as compared to overbank sediments by adjusting for such differences overbank sediments could be used as an alternative in mapping background concentrations of trace metals in regions with few lakes

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

age origin and tectonic significance of mesoproterozoic and silurian felsic sills in the berkshire massif massachusetts discontinuous sills of felsic gneiss in the interior and western margin of the berkshire massif and granite sills on the eastern margin of the massif were correlated by ratcliffe 1984a 1984b 1985 and ratcliffe and hatch 1979 and interpreted by them as syntectonic anatectic melts that intruded taconic thrusts we dated three felsic gneiss sills and two granite sills in an attempt to constrain the age of taconic thrusting but discovered that the sills are not coeval rather they were intruded during two widely separated episodes one during the mesoproterozoic at approximately 1000 ma and the other during the silurian at approximately 430 to 435 ma the 1000 ma sills of felsic gneiss in the interior of the massif are located in mesoproterozoic units and many of the mapped taconic thrusts within the massif closely follow the distribution of this unit here informally called the felsic gneiss of harmon brook these 1000 ma sills formed during the ottawan or rigolet orogeny and they have no connection to the taconic orogeny the 430 to 435 ma granite sills along the eastern margin of the massif informally called the granite of becket quarry are found in both mesoproterozoic basement and the neoproterozoic hoosac formation the sills are too young to have intruded during the ordovician taconic orogeny but they may have formed during later faulting near the contact between mesoproterozoic basement and neoproterozoic cover rocks the tyringham gneiss is one of the most common mesoproterozoic units in the berkshire massif zircons from the tyringham gneiss contain cores with oscillatory zoning and thin unzoned rims the weighted average of eight 206 pb 238 u analyses from the cores is 1179 9 ma whereas nine spot analyses from the rims yield an age of 1004 9 ma we interpret these two ages to represent the crystallization of the tyringham gneiss protolith and a subsequent high grade metamorphism coeval with the intrusion of the felsic gneiss of harmon brook the western contact between mesoproterozoic rocks of the berkshire massif and underlying early paleozoic rocks is clearly a thrust but there is no independent evidence that movement occurred during the taconic orogeny displacement may also have occurred during the silurian salinic or the devonian acadian orogeny many contacts mapped as taconic thrusts within the berkshire massif follow the distribution of the 1000 ma felsic gneiss of harmon brook the age of the sills is clearly incompatible with this interpretation and evidence for faulting along these mapped thrusts is lacking instead of being deformed into an imbricate stack the massif behaved as a rigid block during paleozoic uplift finally the age of granite sills along the eastern margin of the massif does not constrain the basement cover contact to be a taconic thrust as previously interpreted the contact may be a silurian fault possibly related to extension and the opening of the connecticut valley trough as a back arc basin according to this model the magma for the granite sills was generated above a west dipping subduction zone under the laurentian margin which developed after the taconic orogeny

identification of a precambrian rift through missouri by digital image processing of geophysical and geological data digital free air and bouguer gravity anomaly images have been constructed from approximately 287 000 station readings for the region bordered by 25 49 n latitude and 80 110 w longitude the technique used to interpolate between station locations was based on a two dimensional spatial filter where the average of the anomaly values located within the filter area was computed the images contain as many as 256 contours values in byte variable so that subtle anomaly patterns can be identified and traced with much greater certainty than on most contour maps a newly discovered feature in the midcontinent is a gravity low that begins at a break in the midcontinent gravity high in se nebraska extends across missouri in a nw se direction and intersects the mississippi valley graben to form the pascola arch the anomaly varies from 120 to 160 km in width extends about 700 km and is best expressed in southern missouri where it has a bouguer amplitude of approximately 34 mgal the magnitude of the anomaly cannot be explained on the basis of a thickened section of paleozoic sedimentary rock the gravity data and the sparse seismic refraction data for the region are consistent with an increased crustal thickness beneath the gravity low some of the discrete positive magnetic anomalies in missouri are located along the borders of the gravity low digitally enhanced thermal infrared images from the heat capacity mapping mission show a distinct alignment of linear structures with the gravity feature the linear features in some cases correspond to mapped high angle normal faults to drape folds over relief within the precambrian basement and in some cases to extensions of mapped structures the gravity anomaly also cuts across the major precambrian boundary in se missouri marking the change from older sheared granites and metasedimentary rocks to younger granites and rhyolites given the cumulative evidence the gravity anomaly is probably the present expression of a failed arm of a rifting event perhaps one associated with the spreading that led to or preceded formation of the granite and rhyolite terrain of southern missouri

floodplain sedimentation in the upper mississippi valley natural versus human accelerated abstract understanding the time scales and pathways for response and recovery of rivers and floodplains to episodic changes in erosion and sedimentation has been a long standing issue in fluvial geomorphology floodplains are an important component of watershed systems because they affect downstream storage and delivery of overbank flood waters and they also serve as sources and temporary sinks for sediments and toxic substances delivered by river systems here 14c and 137cs isotopic dating methods are used along with ages of culturally related phenomena associated with mining and agriculture to determine rates of sedimentation and morphologic change for a reach of the upper mississippi river and adjacent tributaries in southwestern wisconsin and northwestern illinois the most important environmental change that influenced fluvial activity in this region during last 10 000 years involved the conversion of a late holocene mosaic of prairie and forest to a landscape dominated by cropland and pastureland associated with euro american settlement results presented herein for the upper mississippi valley umv show that the shift from pre agriculture natural land cover to landscape dominance by agricultural land use of the last 175 200 years typically increased rates and magnitudes of floodplain sedimentation by at least an order of magnitude accelerated overbank flooding led to increased bank heights on tributary streams and in turn contributed to more frequent deep flows of high energy these high energy flows subsequently promoted bank erosion and lateral channel migration and the formation of a historical meander belt whose alluvial surface constitutes a new historical floodplain inset against the earlier historical floodplain the new historical floodplain serves as a flume like channel that provides efficient downstream transport of water and sediment associated with moderate and large magnitude floods floodplains on lower tributaries however continue to experience rates of overbank sedimentation that are of anomalously high magnitude given improved land cover and land conservation since about 1950 this lower valley anomaly is explained by minimal development of historical agriculture period meander belts because of relatively low stream power in these channel and floodplain reaches of relatively low gradient in general long term pre agriculture rates of vertical accretion between about 10 000 and 200 years ago averaged about 0 2 mm yr 1 in tributary watersheds smaller than about 700 km2 and about 0 9 mm yr 1 on the floodplain of the upper mississippi river where the contributing watershed area increases to about 170 000 km2 on the other hand rates of historical vertical accretion during the period of agricultural dominance of the last 200 years average between 2 and 20 mm yr 1 with short episodes of even higher rates during times of particularly poor land conservation practices significant hydrologic effects of mining and agricultural started by the 1820s and became widespread in the study region by the mid 19th century the hydrologic and geomorphic influences of mining were relatively minor compared to those related to agriculture high resolution dating of floodplain vertical accretion deposits shows that large floods have frequently provided major increments of sedimentation on floodplains of tributaries and the main valley upper mississippi river the relative importance of large floods as contributors to floodplain vertical accretion is noteworthy because global atmospheric circulation models indicate that the main channel upper mississippi river should experience increased frequencies of extreme hydrologic events including large floods with anticipated continued global warming instrumental and stratigraphic records show that coincident with global warming a shift to more frequent large floods occurred since 1950 on the upper mississippi river and these floods generally contributed high magnitudes of floodplain sedimentation

historical levels of heavy metals and artificial radionuclides reconstructed from overbank sediment records in lower rhone river south east france trace metals cu cd cr ni pb zn hg and artificial radionuclides cs 137 am 241 pu 238 and pu239 240 were investigated in overbank sediments located in inter embankment areas of the lower rhone river enrichment factors ef and anthropogenic factors af were calculated to estimate the level of contamination in these sediment storages the results show that in the studied sites co ni and sc display low ef values and are mainly from lithogenic origin for the other studied trace metals a great variability of sedimentary record is observed significant anthropogenic enrichment was highlighted at a particular site that undergoes fluvial inputs occurring in the last 50 years lead is the element with the highest ef values ef 13 followed by cd ef 11 cu ef 5 hg ef 7 and zn ef 2 temporal variations of pb cd and hg show a maximum in the 1960 s and a decreasing trend afterward maximum enrichment of artificial radionuclides were observed in sediment deposit during the period 1960 1990 when maximum liquid releases from nuclear activities occurred these results indicate that despite the high energy conditions and the generally sandy nature of the riverbank sediments significant anthropogenic enrichments were observed in some areas of sediment accumulation in the lower rhone river these enrichments are however relatively low compared to some other rivers in france and europe due to the important suspended sediment discharge in this river in particular during strong floods which dilutes the anthropogenic inputs of contaminant c 2011 elsevier ltd all rights reserved

use of fallout 137cs in investigations of overbank sediment deposition on river floodplains abstract river floodplains have been recognised as important sinks for storing suspended sediment and associated contaminants mobilised from the upstream catchment however information on contemporary rates of overbank sedimentation is difficult to obtain using conventional methods measurements of the 137cs content of floodplain sediments provide an alternative approach to obtaining estimates of medium term rates ca 40 years of overbank sediment deposition the 137cs approach requires only a single site visit and minimum sample preparation furthermore it is capable of providing information on spatial patterns of sediment deposition on floodplains which is needed to improve our understanding of the processes involved in overbank flow and sediment deposition this paper reviews the basis for using 137cs measurements in floodplain sedimentation studies and presents improved procedures for interpreting 137cs profiles in floodplain sediments and for obtaining estimates of sedimentation rates from single measurements of the total 137cs inventories of bulk sediment cores the results obtained from a case study undertaken on the floodplain of the river stour dorset uk are presented

high resolution historical records from pettaquamscutt river basin sediments 2 pb isotopes reveal a potential new stratigraphic marker a high resolution record of pb deposition in rhode island over the past 250 yr was constructed using a sediment core from the anoxic pettaquamscutt river basin the sedimentary pb concentration record shows the well described maximum associated with leaded gasoline usage in the united states diminished pb variability during recorded periods of local industrial activity 1735 to 1847 supports the greater importance of regional atmospheric lead transport vs local inputs the pb isotopic composition at this site shows a clear maximum in anthropogenic 206 pb 207 pb in the mid 1800s similar peaks have also been observed in sediments from chesapeake bay and the great lakes suggesting a common source possible causes for this event include mining and smelting of pb ores in the upper mississippi valley district which accounted for almost all pb production in the united states in that period the timing of this event can provide an important stratigraphic marker for sediments deposited in the past 200 yr in the northeastern united states the downcore profile of anthropogenic 206 pb 207 pb provides a classic example of how changes in the mixture of ores for production of tetraethyl lead caused a regional scale shift in the sedimentary record and suggests that coal could have played a secondary role in pb emissions after 1920 copyright 2005 elsevier ltd

tectonic synthesis of the taconian orogeny in western new england a tectonic synthesis based on stratigraphic and structural analysis of western new england is proposed for the ordovician taconian orogeny it emphasizes arc continental collision in which ocean floor continental margin and ensialic rift rocks were imbricated westward in a repeatedly deformed accretionary wedge continued compression displaced segments of the north american sialic crust to the west and deformed the earlier emplaced slices of the taconic allochthons which were derived from the continental margin critical arguments for this synthesis are 1 the west to east stratigraphic relations among the basal rift clastic rocks of the dalton pinnacle and hoosac formations of late precambrian to early cambrian age 2 the stratigraphic and sedimentological similarities between the rocks of the lower taconic sequence and rocks in the pinney hollow and underhill slices to the east and north of the green mountain massif 3 the environmental similarities between the cambrian and lower ordovician section of the giddings brook slice and the age equivalent section in the st albans synclinorium 4 the presence of carbonate platform rocks as slivers between each of the successively higher and younger premetamorphic slices groups 1 and 2 of the taconic allochthons 5 the presence of synmetamorphic fault related structures in the youngest and highest slices group 3 of the taconic allochthons 6 the recognition of extensive thrust zones in the pre silurian eugeoclinal sequence east of the middle proterozoic basement of the housatonic berkshire green mountain and lincoln massifs 7 the location of the taconic root zone within the pre silurian eugeoclinal sequence 8 the recognition of numerous faults in the serpentinite belt 9 the similarity between the rocks of the moretown formation and modern fore arc basin sequences 10 the recognition that the volcanic arc continental complexes of the ascot weedon and bronson hill have been displaced westward over the moretown and or hawley formations along such faults as the bristol and coburn hill thrusts 11 the allochthonous and internally imbricated nature of the north american basement in the berkshire massif 12 the proposition that the housatonic green mountain and lincoln massifs as well as the middle proterozoic cored domes of southeastern vermont are also thick sialic slices of north american basement 13 the recognition of medium high to high pressure metamorphic mineral assemblages in the pre silurian eugeoclinal rocks of vermont and 14 the recent synthesis of isotopic age data by sutter and others 1985 on the basis of an analysis of the foregoing arguments and relationships a chronological sequence of seven structural sections between albany new york and the bronson hill anticlinorium in central massachusetts is used to depict the evolution of the taconian orogeny retrodeformed distances are based on structural overlap and restoration of the taconic slices to their depositional setting along the ancient north american continental margin these easterly younging diverticulated slices formed as a result of horizontal compression rather than gravity sliding this palinspastic analysis implies the following 1 approximately 1 000 km of shortening has occurred during the emplacement of the taconic allochthons and the subsequent imbrication of north american basement as thick sialic slices approximately 330 km of this shortening is attributed to multiple cleavage generations 2 repeated movement along such major surfaces as the cameron9s line whitcomb summit belvidere mountain thrust zone has buried the taconic root zone we suggest that the northern extension of this root zone is exposed to the east of the lincoln massif in vermont where the underhill pinney hollow and hazens notch formations are exposed these formations here considered thrust slices disappear along the belvidere mountain whitcomb summit thrust zone as it is traced southward into western massachusetts and western connecticut 3 taconian metamorphic rocks particularly the older medium high pressure rocks in northern vermont have been transported westward on such reactivated surfaces as the belvidere mountain thrust 4 the anticlinorial form of the middle proterozoic basement in the green mountain and lincoln massifs may have resulted from fault bend folding on deep mantle involved thrusts that developed late in the taconian orogeny

floodplain deposits a geochemical archive of flood history a case study on the river rhine germany abstract based on the correlation between discharge and carbonate content of the suspended load of the river rhine germany a systematic geochemical mineralogical and granulometric study was carried out to verify whether this geochemical signal is transferred to floodplain deposits and in what way these sediments and their chemostratigraphic characterization can be used as a tool for the reconstruction of the river flood history the analysis of the time resolved changes in the composition of particulate matter during a flood event revealed that the increase of carbonate content represented by cao sr with discharge was coupled to a simultaneous decrease in the relative amount of siliciclastics k 2 o rb the association of these two groups of diametrical parameters with specific grain size fractions carbonates with 40 200 m siliciclastics with 200 m were found to be slightly shifted relative to each other and showed different gradients during the surging and fading flood wave this together with the covariance of elements pertaining to minerals with different density e g carbonate and heavy minerals suggests a chemical response to the changes in discharge which is controlled primarily by hydraulic equivalence rather than grain size there is also a time lag between the amount of suspended load and discharge with a maximum in suspended load shortly after the peak discharge when the flood has already started to abate the flood plain sediments have similar composition to the suspended load suggesting the direct transfer of the geochemical flood signal to the floodplain sediments three lithological units could be distinguished in a 240 cm long sediment core collected from the floodplain grain size and geochemical composition indicate that only the top of the section 20 70 cm represents sediments deposited in an abandoned channel of the river and may have preserved the geochemical flood signals as identified during actual flood events the comparison of the chemostratigraphy of this part of the section estimated with optical stimulated luminescence to be deposited between ca 1650 and 1920 with a record of historically documented inundations however yielded only poor agreement the possible reasons for this inconsistency are discussed and suggestions are made for continuing investigations

geologic structures related to new madrid earthquakes near memphis tennessee based on gravity and magnetic interpretations new inversions of gravity and magnetic data in the region north of memphis tennessee and south of latitude 36 define boundaries of regional structures and igneous complexes in the upper crust microseismicity patterns near interpreted boundaries suggest that igneous complexes influence the locations of microseismicity a weak seismicity cluster occurs near one intrusion covington pluton at the intersection of the southwest margin of the missouri batholith and the southeast margin of the reelfoot rift a narrow seismicity trend along the reelfoot rift axis becomes diffuse near a second intrusion osceola intrusive complex and changes direction to an area along the northwest flank of the intrusion the axial seismicity trend also contains a tight cluster of earthquakes located just outside the osceola intrusive complex the mechanical explanation of the two seismicity patterns is uncertain but the first cluster may be caused by stress concentration due to the high elastic stiffness and strength of the covington intrusion the spatially changing seismicity pattern near the osceola complex may be caused by the preceding factors plus interaction with faulting along the rift axis the axial seismicity strand itself is one of several connected and interacting active strands that may produce stress concentrations at strand ends and junctions the microseismicity clusters at the peripheries of the two intrusions lead us to conclude that these stress concentrations or stressed volumes may be locations of future moderate to large earthquakes near memphis

extensional collapse of the northern taiwan mountain belt as an active collision zone between the luzon arc and the china continental margin the taiwan mountain belt particularly its south central part is undergoing crustal shortening and rapid uplift the northern part of the orogen is however subjected to crustal stretching and rifting as a result of flipping of subduction from the northwest facing luzon arc system to the south facing ryukyu arc system taiwan and its neighboring southern ryukyu used to be part of the rifted china continental margin before the collision started in late miocene time engineered by the northwest movement of the philippine sea plate in the past 5 m y the north south trending luzon arc obliquely overrode the northeast southwest trending continental margin and tectonized it into a collision orogen that progressively enlarged and migrated from northeast to southwest following the southwest propagating collision the north dipping philippine sea plate which was subducting beneath the ryukyu arc also extended westward and caused flipping of subduction in the northern part of the collision orogen in consequence the orogen lost the compressive support by the colliding plates and became subjected to lithospheric stretching induced by the trench suction the collision orogen collapsed as a result of crustal thinning and its central part foundered into a deep submerged basin a whole spectrum of active tectonic scenarios ranging from orogenic buildup by collision to orogenic collapse by rifting and subsidence can be readily observed in the taiwan ryukyu area and provides a vivid example for the process of orogenic collapse

a new isostatic residual gravity map of the conterminous united states with a discussion on the significance of isostatic residual anomalies to display more clearly the gravity anomalies caused by geologic bodies in the upper parts of the crust a new colored isostatic residual gravity map of the conterminous united states has been prepared using the gravity data set compiled for the gravity anomaly map of the united states society of exploration geophysicists 1982 the new isostatic residual gravity map is based on an airy heiskanen model of local compensation in which the surface load requiring compensation is defined by 5 min topographic and bathymetric data sets a colored first vertical derivative map of isostatic residual gravity further enhances the short wavelength anomalies produced by bodies at or near the surface and emphasizes the regional fabrics and trends in the gravity field for the purpose of displaying gravity anomalies caused by shallow bodies of geologic significance the nature of the isostatic model and the values of its parameters are of lesser importance than the application of an isostatic correction of some sort most isostatic models result in residual gravity maps that appear nearly identical in their main patterns and features anomalies on isostatic residual gravity maps should not be casually interpreted in terms of undercompensation or overcompensation because large amplitude anomalies can be produced by crustal bodies in complete local isostatic equilibrium many isostatic residual gravity anomalies less than several hundred kilometers wide can be related to known geologic bodies we present here a classification scheme that attempts to categorize such anomalies on the basis of tectonic environment in general highs correlate with intruded or accreted mafic material or with upthrusted crustal sections whereas lows occur over low density sedimentary or volcanic sections felsic intrusive bodies or down warped crustal sections although some longer wavelength anomalies such as the broad gravity high centered over montana could be manifestations of density contrasts deep in the mantle many such anomalies can also be modeled by geologically reasonable density contrasts that are isostatically compensated and confined to depths of less than several hundred kilometers so that their source bodies need not be deep the fact that certain of these broader anomalies have well defined boundaries which correlate with near surface geologic features increases the likelihood that their sources lie entirely within the lithosphere if so then the density contrasts required to explain the gravity data imply fundamental anomalies in chemical composition or thermal state for the crustal and upper mantle columns under these regions we have investigated spectral analysis as a method to quantitatively characterize regional anomaly patterns contoured plots of normalized amplitude spectra were prepared for various areas of the isostatic residual gravity field of the united states these fourier domain representations show characteristic patterns that can be interpreted in terms of the trends and wavelengths of anomalies and may help to more objectively distinguish geologic basements with different origins or tectonic histories

diagnostic heavy minerals in plio pleistocene sediments of the yangtze coast china with special reference to the yangtze river connection into the sea abstract this present study revealed five heavy mineral zones in the yangtze coastal borehole sediments ilmenite garnet and zircon suite of zone i of the pliocene characterizes the derivation of basaltic bedrock and local andesitic granitic rocks indicative limonite in the zone i sediments formed as alluvial fan facies shows strong chemical weathering the assemblage of amphibole straurolite kyanite and idocrase of metamorphic derivation together with a few zircon and tourmaline of andesitic granitic origin in zone ii represents the extension of sediment sources to the lower and middle yangtze basin in early pleistocene as the study area subsided also the braided to meandering riverine facies demonstrates a longer distance sediment transport few heavy minerals remained in zone iii of mid pleistocene when mottled thicker stiff mud occurred as the lacustrine facies suggesting a quasi coastal floodplain with lower capability of sediment transport heavy minerals appeared significant and continuous in zone iv of late pleistocene when changing to the shallow marine facies inferring much extended sediment sources to the upper yangtze hypersthene identified primarily in zone iv was closely associated with the er mei mountain tholeiite basalt of the upper yangtze heavy minerals of zone v remained almost the same as iv during holocene when the modern delta evolved the heavy minerals suggested the timing of the yangtze connection to the sea at ca 0 12 ma bp

a newly identified gondwanan terrane in the northern appalachian mountains implications for the taconic orogeny and closure of the iapetus ocean the taconic and salinic orogenies in the northern appalachian mountains record the closure of the iapetus ocean which separated peri laurentian and peri gondwanan terranes in the early paleozoic the taconic orogeny in new england is commonly depicted as an ordovician collision between the peri laurentian shelburne falls arc and the laurentian margin followed by silurian accretion of peri gondwanan terranes during the salinic orogeny new u pb zircon geochronology demonstrates that the shelburne falls arc was instead constructed on a gondwanan derived terrane preserved in the moretown formation which we refer to here as the moretown terrane metasedimentary rocks of the moretown formation were deposited after 514 ma and contain abundant ca 535 650 ma detrital zircon that suggest a gondwanan source the moretown formation is bound to the west by the peri laurentian rowe belt which contains detrital zircon in early paleozoic metasedimentary rocks that is indistinguishable in age from zircon in laurentian margin rift drift successions these data reveal that the principal iapetan suture in new england is between the rowe belt and moretown terrane more than 50 km farther west than previously suspected the moretown terrane is structurally below and west of volcanic and metasedimentary rocks of the hawley formation which contains laurentian derived detrital zircon providing a link between peri laurentian and peri gondwanan terranes the moretown terrane and hawley formation were intruded by 475 ma plutons during peak activity in the shelburne falls arc we propose that the peri laurentian rowe belt was subducted under the moretown terrane just prior to 475 ma when the trench gap was narrow enough to deliver laurentian detritus to the hawley formation interaction between peri laurentian and peri gondwanan terranes by 475 ma is 20 m y earlier than documented elsewhere and accounts for structural relationships early ordovician metamorphism and deformation and the subsequent closure of the peri laurentian taconic seaway in this scenario a rifted arc system on the gondwanan margin resulted in the formation of multiple terranes including the moretown that independently crossed and closed the iapetus ocean in piecemeal fashion

late taconian and pre acadian history of the new england appalachians of southwestern connecticut new u pb age determinations and field observations combined with published field relations refine the late taconian and pre acadian history of the new england appalachians of southwestern connecticut foliation within the camerons line shear zone was developed after 514 11 ma but prior to 445 1 5 ma this structure probably experienced renewed movement in the early silurian 437 2 ma as suggested by new xenotime growth in protomylonite metasedimentary and metavolcanic rocks east of camerons line were deposited were isoclinally folded and reached temperatures in excess of about 550 c before emplacement of small dioritic plutons of the 453 3 ma brookfield plutonic series igneous titanites in brookfield plutons cooled below u and pb diffusion e g 525 25 c in the latest ordovician to earliest silurian and were not reset in the acadian the newtown gneiss is a composite magmatic complex composed of quartz diorite 446 2 ma granodiorite 436 2 ma and granite 438 2 ma low 207 pb 204 pb feldspar isotopic compositions and 1150 ma zircon inheritance in the newtown gneiss and brookfield plutonic series are consistent with interaction with grenvillian crust or crustally derived material we propose that the newtown and harrison gneisses and possibly the brookfield plutonic series make up the plutonic roots of a late ordovician to early silurian 454 438 ma magmatic arc complex generated during subduction along the eastern north american continental margin magmatic activity was coeval with that in the bronson hill anticlinorium to the east ca 454 442 ma

reconstruction of multi century flood histories from oxbow lake sediments peace athabasca delta canada floods caused by ice jams on the peace river are considered to be important for maintaining hydro ecological conditions of perched basins in the peace athabasca delta pad canada a highly productive and internationally recognized northern boreal ecosystem concerns over the potential linkages between regulation of the peace river in 1968 for hydroelectric production and low peace river discharge between 1968 and 1971 during the filling of the hydroelectric reservoir absence of a major ice jam flood event between 1975 and 1995 and low water levels in perched basins during the 1980s and early 1990s have sparked numerous environmental studies largely aimed at restoring water levels in the pad lack of sufficient long term hydrological records however has limited the ability to objectively assess the importance of anthropogenic factors versus natural climatic forcing in regulating hydro ecological conditions of the pad here we report results of a paleolimnological study on laminated sediments from two oxbow lakes in the pad which are located adjacent to major flood distributaries of the peace river sediment core magnetic susceptibility measurements supported by results from several other physical and geochemical analyses as well as stratigraphic correspondence with recorded high water events on the peace river provide proxy records of flood history spanning the past 180 and 300 years in these two basins results indicate that inferred flood frequency has been highly variable over the past 300 years but in decline for many decades beginning as early as the late nineteenth century well before peace river regulation additionally several multi decadal intervals without a major flood have occurred during the past 300 years while climate related mechanisms responsible for this variability in flood frequency remain to be determined as does quantifying the relative roles of river regulation and climate variability on hydro ecological conditions in the pad since 1968 these results suggest that ecosystem management strategies for the pad need to explicitly account for natural variations in flood recurrence intervals copyright 2006 john wiley sons ltd

quantitative investigations of the missouri gravity low a possible expression of a large late precambrian batholith intersecting the new madrid seismic zone analysis of gravity and magnetic anomaly data helps characterize the geometry and physical properties of the source of the missouri gravity low an important cratonic feature of substantial width about 125 km and length 600 km filtered anomaly maps show that this prominent feature extends nw from the reelfoot rift to the midcontinent rift system geologic reasoning and the simultaneous inversion of the gravity and magnetic data lead to an interpretation that the gravity anomaly reflects an upper crustal 11 km thick batholith with either near vertical or outward dipping boundaries considering the modeled characteristics of the batholith structural fabric of missouri and relations of the batholith with plutons and regions of alteration a tectonic model for the formation of the batholith is proposed the model includes a mantle plume that heated the crust during late precambrian and melted portions of lower and middle crust from which the low density granitic rocks forming the batholith were partly derived the batholith called the missouri batholith may be currently related to the release of seismic energy in the new madrid seismic zone earthquake concentrations occur at the intersection of the missouri batholith and the new madrid seismic zone three qualitative mechanical models are suggested to explain this relationship with seismicity

vertical accretion sand proxies of gaged floods along the upper little tennessee river blue ridge mountains usa abstract understanding environmental hazards presented by river flooding has been enhanced by paleoflood analysis which uses sedimentary records to document floods beyond historical records bottomland overbank deposits e g natural levees floodbasins meander scars low terraces have the potential as continuous paleoflood archives of flood frequency and magnitude but they have been under utilized because of uncertainty about their ability to derive flood magnitude estimates the purpose of this paper is to provide a case study that illuminates tremendous potential of bottomland overbank sediments as reliable proxies of both flood frequency and magnitude methods involve correlation of particle size measurements of the coarse tail of overbank deposits 0 25 mm sand from three separate sites with historical flood discharge records for the upper little tennessee river in the blue ridge mountains of the southeastern united states results show that essentially all floods larger than a 20 probability event can be detected by the coarse tail of particle size distributions especially if the temporal resolution of sampling is annual or sub annual coarser temporal resolution 1 0 to 2 5 year sample intervals provides an adequate record of large floods but is unable to discriminate individual floods separated by only one to three years measurements of 0 25 mm sand that are normalized against a smoothed trend line through the down column data produce highly significant correlations r 2 values of 0 50 to 0 60 with p values of 0 004 to

rates of floodplain accretion in a tropical island river system impacted by cyclones and large floods abstract fluvial processes especially rates of floodplain accretion are less well understood in the wet tropics than in other environments in this study the caesium 137 137cs method was used to examine the recent historical sedimentation rate on the floodplain of the wainimala river in the basin of the rewa river the largest fluvial system in fiji and the tropical south pacific islands 137cs activity in the floodplain stratigraphy showed a well defined profile with a clear peak at 115 cm depth our measured accretion rate of 3 2 cm year 1 over the last ca 45 years exceeds rates recorded in humid regions elsewhere this is explained by the high frequency of tropical cyclones near fiji 40 since 1970 which can produce extreme rainfalls and large magnitude floods since the beginning of hydrological records large overbank floods have occurred every 2 years on average at the study site the biggest floods attained peak flows over 7000 m3 s 1 or six times the bankfull discharge concentrations of suspended sediments are very high max 200 500 g l 1 delivered mainly by channel bank erosion in the future climatic change in the tropical south pacific region may be associated with greater tropical cyclone intensities which will probably increase the size of floods in the rewa basin and rates of floodplain sedimentation

precise timing of the late ordovician sandbian super eruptions and associated environmental biological and climatological events two of the largest known eruptions in the phanerozoic produced the ordovician millbrig k bentonite of north america and the kinnekulle k bentonite of scandinavia which have been previously suggested to be coeval the millbrig k bentonite from kentucky usa and the kinnekulle k bentonite from bornholm denmark yielded chemical abrasion thermal ionization mass spectrometry u pb zircon dates of 452 86 0 29 and 454 41 0 17 ma 2 analytical uncertainty respectively thus showing significant age differences contrary to what is generally held these data and four additional newly dated k bentonites directly establish the first radioisotopic age constraints for the ordovician katian sandbian global stage boundary refine global stratigraphic correlations date associated chemostratigraphic events and suggest an alternative volcanic climate hypothesis for the late ordovician supplementary material u pb radioisotopic data table and analytical methods are available at www geolsoc org uk sup18636

the petrogenesis of the highlandcroft and oliverian plutonic suites new hampshire implications for the structure of the bronson hill terrane both laurentian and peri gondwanan origins for the oliverian and highlandcroft plutonic suites of new hampshire have been proposed a peri gondwanan origin places the red indian line the principle iapetus suture to the west of the bronson hill anticlinorium and requires the plutons to be allochthonous in contrast a laurentian margin emplacement setting places the red indian line farther to the east in new hampshire the combination of e nd and 207 pb 204 pb values are most compatible with the suites representing mixtures of arc derived magmas and laurentian crust indicating that both suites were derived to the west of the red indian line the tectonic setting for the arc probably was a westerly dipping subduction zone under the laurentian margin resulting from a polarity flip after the collision of the shelburne falls arc during the taconic orogeny bulk rock major and trace elements as well as nd sr and pb isotopic results indicate that the highlandcroft and oliverian plutonic suites of new hampshire are both members of the same arc complex

sediment characteristics floods and heavy metal pollution recorded in an overbank core from the lower reaches of the yangtze river overbank sediments contain abundant information about floods paleoenvironmental changes and recent pollution history of a river basin for the purpose of understanding modern overbank sediments and their environmental significance this multidisciplinary study sampled a core from the overbank and a short core from the overbank outcrop at nanjing in the lower reaches of the yangtze river the overbank deposit comprises fine grained discontinuous strata including silt sandy silt silty sand and sand layers field and laboratory observations indicated that the overbank sediment contained a series of layers of sandy silt coupled with thin silty sand layers each a few millimeters thick which formed muddy layers that were dozens of centimeters thick between the muddy layers were coarser sand layers grain size analyses 137cs dating and heavy metal measurements contained information on flood events and pollution history over the past 60 years the coarser sand layers corresponded with severe floods in 1954 and 1983 between the two severe floods the study area experienced an overbank building stage from the 1990s to the early 2000s the overbank sedimentation rate declined reflecting human activities especially the dams in the yangtze river basin that trapped more sediment the average heavy metal concentrations in the overbank sediments are higher than the background levels for suspended sediment in the yangtze river heavy metals in overbank sediments were assessed by enrichment factors and sediment quality assessment values for freshwater sediment cr and ni values were high especially from the early 1980s to the early 2000s the impacts of floods economic development and environmental management on these heavy metal variations were discussed

tectonic setting of outer trench slope volcanism pillow basalt and limestone in the taconian orogen of eastern new york the only pillow basalt in synorogenic sedimentary rocks at the exterior margin of the taconic orogen in eastern north america is at stark s knob in eastern new york earlier reported as extrusive into allochthonous ordovician slope and rise facies this small lens ca 125 m long 39 m thick is a fault bounded block in upper ordovician melange under the taconian frontal thrust its n morb normal mid ocean ridge basalt basalt geochemistry and spinel composition are characteristic of oceanic ridge settings at a water depth of 2 km or more abundant limestone lenses on pillows and lava shelves within pillows yielded a middle late ordovician gastropod the limestones are reconciled with this extrusion depth and with limited early paleozoic pelagic carbonate production by lime mud transport from the laurentian platform or abiotic carbonate precipitation with sea water heating during basalt extrusion a genetic relationship between the parautochthonous stark s knob basalts and the allochthonous jonestown volcanics in slope and rise facies of the hamburg klippe eastern pennsylvania is likely both are ordovician morb basalts that reflect volcanism on the subducting outer trench slope prior to the taconic arc laurentia collision taconic orogenesis may have led to basalt production on the subducting plate by 1 the setting up of orogen parallel predominantly strike slip motion on the subducting slab with morb basalt generated at offsets in a setting analogous to the gulf of california or 2 development of faults in a flexure induced extensional regime by either process mafic volcanism appears to be a rare but tectonically significant process on outer trench slopes as continental margins or oceanic plates enter subduction zones resume l unique basalte a coussinet dans les roches sedimentaires syntectoniques a la bordure exterieure de

high resolution evaluation of recent bank accretion rate of the managed rhone a case study by multi proxy approach abstract we determined the sedimentation rates near a managed embankment on the lower rhone for the second half of the twentieth century this was carried out using a combination of chronological indicators 137 cs 241 am dendrochronology and archived data and sedimentological measurements a high resolution chronological sequence has emerged from these data sets the average annual sedimentation rate of 14 cm has increased progressively over the last 50 years and at a much faster rate than observed elsewhere on this river this is probably due to a combination of factors such as the size of the river abundance and coarse texture of the solid load and local impact of river engineering works we also studied hydrological and sedimentological characteristics for a number of flood events

sediment deposition and erosion during the extreme flood events in the middle and lower reaches of the yangtze river abstract floods often are accompanied by intensified soil erosion and thus high sediment supply from the catchment into the main channel of the river this paper examined the sediment processes especially deposition and erosion during the two extreme flood years in 1954 and 1998 in the middle and low reaches of the yangtze river the total amount of sediment supplied to the middle and lower reaches from yichang hankou and hankou datong was 1095 mt in 1954 and 855 9 mt in 1998 or 176 and 137 of the averaged 622 mt a from 1950 to 2006 a high deposition occurred in the floodplains lakes and channels along the section yichang hankou both in 1954 and 1998 the total deposition reached 635 mt and 499 mt in 1954 and 1998 or 138 and 124 of the sediment load measured at the datong station respectively however different processes in the downstream section hankou datong during the two flood events were found severe erosion 140 mt happened in 1954 but only a slight erosion occurred 22 mt in 1998 thus the floodplains and channels in the middle and lower reaches of the yangtze river play an important role in regulating sediment discharge during extreme flood events the heavy deposition in the middle reaches effectively reduced the amount of sediment discharged into the river mouth and thus acted as a major depocenter in the extreme flood year the results also suggested that the yichang hankou tended to shift from a depositional section to an erosional section whereas the hankou datong changed from an erosion dominated section to a deposition dominated section even before the three gorges reservoir infilling in 2003 it is anticipated that this tendency would be accelerated and the historical role of sediment regulation by the two reaches could eventually be changed due to the reduced sediment supply from the upper yangtze

where is the iapetus suture in northern new england a study of the ammonoosuc volcanics bronson hill terrane new hampshire 1 the 470 ma ammonoosuc volcanics of the bronson hill terrane of new hampshire have back arc basin basalt compositions major and trace element compositions compare favorably to coeval volcanic rocks in the miramichi highlands of new brunswick and the munsangan and casco bay volcanics of maine back arc basin basalts of known peri gond wanan origins additionally the ammonoosuc volcanics have nd and pb isotopic compositions indicative of peri gond wanan provenance thus the ammonoosuc volcanics correlate with middle ordovician peri gondwanan tetagouche exploits back arc rocks of eastern new england and maritime canada this correlation indicates that the red indian line the principle iapetus suture lies along the western margin of the bronson hill terrane however the younger 450 ma oliverian plutonic suite rocks that intruded the ammonoosuc volcanics forming domes along the core of the bronson hill anticlinorium have laurentian isotopic signatures this suggests that the ammonoosuc volcanics were thrust westwardly over the laurentian margin and that laurentian basement rocks are present under the bronson hill terrane a plausible ex planation for these relationships is that an easterly dipping subduction zone formed the ammonoosuc volcanics in the tetagoughe exploits oceanic tract just east of the coeval popelogan arc with the closure of the iapetus ocean this terrane was thrust over the laurentian margin subsequent to obduction of the ammonoosuc volcanics subduction polarity flipped to the west with the oliverian arc resulting from a westerly dipping subduction zone that formed under the taconic orog eny modified laurentian margin resume les roches volcaniques ammonoosuc 470 ma du terrane de bronson hill au new hampshire ont des compo sitions de bassins basaltiques d arriere arc les compositions en elements majeurs et traces se comparent favorablement aux roches volcaniques contemporaines des terres hautes de miramichi au nouveau brunswick et les roches volcaniques de munsangan et de casco bay au maine des bassins basaltiques d arriere arc d origine peri gondwanienne connue de plus les roches volcaniques ammonoosuc ont des compositions d isotopes de nd et de pb qui indiquent leur provenance peri gondwanienne ainsi les roches volcaniques ammonoosuc sont correlees avec les roches d arriere arc tetagouche exploits ordovicien moyen peri gondwana de l est de la nouvelle angleterre et des provinces maritimes canadiennes cette correla tion signifie que la ligne red indian la principale suture iapetus se situe le long de la bordure ouest du terrane de bronson hill toutefois les roches de la suite plutonique olivierian plus jeune 450 ma formant des domes le long du c ur de l anticlinorium bronson hill ont des signatures isotopiques laurentiennes cela suggere que les roches volcaniques ammo noosuc aient ete chevauchees vers l ouest par dessus la bordure laurentienne et que les roches du socle laurentien se retrou vent sous le terrane de bronson hill une explication plausible pour ces relations est qu une zone de subduction a pendage vers l est a forme les roches volcaniques ammonoosuc dans l etendue oceanique tetagouche exploits tout juste a l est de l arc popelogan contemporain avec la fermeture de l ocean iapetus ce terrane a ete chevauche par dessus la bordure lau rentienne apres l obduction des roches volcaniques ammonoosuc la polarite de la subduction a bascule vers l ouest l arc oliverian proviendrait d une zone de subduction a faible pendage vers l ouest qui s est formee sous la bordure laurentienne modifiee par l orogenese taconienne traduit par la redaction