sediment budgeting a case study in the katiorin drainage basin kenya the primary objective of this study was to compute a detailed budget for a small semiarid tropical drainage basin in kenya results indicated that transfer of sediments inputs from primary source areas was minor in comparison to changes in storage the major sediment source area within the katiorin drainage basin was the colluvial hillslope zone the net change in storage within this zone was approximately 2100 mg yr 1 surface wash and rilling were the dominant transport processes responsible for the remobilization of colluvial sediments sediment storage within the in channel reservoir increased by 60 mg yr 1 which was minor when compared to the total store of sediment in this reservoir during 1986 the channel network stored only a small fraction 3 per cent of the sediment delivered from the hillslope subsystem therefore the in channel reservoir had limited influence on sediment conveyance to the basin outlet these data indicate that a static equilibrium condition cannot be assumed within the katiorin drainage basin such an assumption would result in erosion estimates of approximately 5 5 mm yr 1 for the entire basin based on a sediment output of 7430 mg km 2 yr 1 and a measured bulk density of 1 35 mg m 3 however this masked the actual rates of 1 2 to 7 1 mm yr 1 in subbasin primary source areas and rates of 0 6 to 17 mm yr 1 for colluvial material in the various subbasins the extreme accelerated erosion rates resulted from minimal ground vegetation steep slopes soil crust formation an erodible substrate and a well integrated drainage network for rapid conveyance of sediments from the hillslope subsystem to the basin outlet

sources sinks and storage of river sediment in the atlantic drainage of the united states the history of sediment and its movement in the atlantic drainage demonstrate some of the difficulties of modeling sediment on a river basin scale soil erosion was accelerated by a factor of at least 10 when european settlers cleared forests and planted crops although increasing soil conservation practice and decreasing crop farming have since reduced the rates of erosion large quantities of eroded material are still stored on hillslopes and in stream valleys where they continue to augment the sediment loads of the rivers the sediment from this episode of erosion that is largely past can be expected to emerge from storage for many decades and perhaps even several centuries to come the reservoirs that have been built on many of the major rivers trap significant portions of the moving sediment which in some places may be remobilized by large floods essentially all the river sediment that reaches the atlantic coastal zone is trapped in estuaries and coastal marshlands probably less than 5 is deposi

the source of alluvium in large rivers of the lower coastal plain of north carolina summary despite high erosion rates in the north carolina piedmont and extensive sediment delivery to coastal plain reaches of piedmont draining streams sediment budget studies and estuarine sedimentology suggest that relatively little piedmont derived sediment reaches the lower coastal plain dominant sources of alluvium in the lower coastal plain reaches of piedmont draining rivers were inferred from alluvial floodplain soils piedmont derived alluvial soils are characterized by mixed mineralogy and presence of mica flakes alluvial soils derived from erosion of coastal plain uplands are characterized by siliceous mineralogy and an absence of mica flakes the coastal alluvial soils which occur in fluvial estuarine transition zones being drowned by rising sea level are organic or buried organic soils the distribution of these soils along the tar and neuse rivers in the lower coastal plain shows almost complete domination of fluvial estuarine transition zones by soils of the coastal group and by soils of the coastal plain and coastal groups for 40 km or more inland of the upper estuaries no soils of the piedmont group were found in fluvial estuarine transition zones or lowermost fluvial reaches this suggests that the piedmont is a relatively insignificant source of alluvium in the lower reaches of the rivers the absence of piedmont sediment in the lower coastal plain is attributed to extensive sediment storage upstream dilution by coastal plain sediments and coastal plain erosion rates which may be higher than was previously believed

the localized role of base level lowering on channel adjustment of tributary streams in the trinity river basin downstream of livingston dam texas usa the purpose of this study is to describe and explain river channel cross sectional change in tributary streams within the 60 km scour zone of the trinity river texas downstream of livingston dam this study investigates changes within the tributary systems to base level changes triggered by incision associated with scour and channel migration within the dammed trunk stream the dam represents a precise moment and place of a system perturbation and therefore represents an opportunistic geomorphic experiment geomorphological effects of the lower trinity river tributaries were investigated through three different types of data resurveys of bridge cross sections planform change as measured from aerial photographs and field mapping of changes in channel geometry using fallen trees undercut banks and other geomorphic indicators of change while field evidence of channel change was found at sites well upstream of tributary confluences with the trinity these were not consistent with responses to lower base level downcutting and lateral changes in response to lowered base level were confined to lower tributary reaches this suggests distance decay and lag times in transmission of responses upstream and or masking of dam induced effects by other processes and controls the most dynamic locations of geomorphic change are near the confluences of the tributaries with the trinity river where the response to dam induced incision is strongly influenced by local trunk stream morphology indicating a high degree of historical and geographical contingency

dam to delta sediment inputs and storage in the lower trinity river texas livingston dam on the trinity river in se texas usa disrupts the transport of sediment to the lower trinity river and the trinity bay galveston bay estuary however a sediment budget of the lower basin shows that the effects of this disruption are undetectable in the lower river sediment trapped in lake livingston is partly offset by channel erosion downstream of the dam and by inputs from the lower basin most importantly however the lower coastal plain reaches of the trinity are characterized by extensive alluvial storage and are a bottleneck that buffers the bay from effects of upstream changes in sediment flux storage is so extensive that the upper trinity basin and the lowermost river reaches were essentially decoupled in the sense that very little upper basin sediment reached the lower river long before the dam was constructed whereas sediment storage in lake livingston is extensive alluvial storage on the trinity flood plain is even more extensive dam related sediment starvation effects are noted for about 52 km downstream and the sediment budget suggests that a majority of the sediment in this reach is likely derived from channel scour and bank erosion the capacious alluvial storage in the lower trinity not only limits flux to the bay but the large amount of remobilizable alluvium also allows the system to adjust to localized sediment shortages as illustrated in the dam to romayor reach internal adjustments within the lower trinity river valley thus buffer the bay from changes in sediment supply upstream

slope channel linkage and sediment delivery on north carolina coastal plain cropland this paper presents the results of field measurements conducted in a small 19 4 ha agricultural basin on the north carolina coastal plain the overall objective of the study is to determine the magnitude of soil erosion and sediment delivery as a result of storm runoff the results suggest that erosion in the region is more rapid and extensive than previously thought fields at the site are experiencing accelerated soil loss with rates often comparable to those of the southeastern piedmont a region long recognized as having rapid and problematic soil loss this casts doubt on some assessments of the coastal plain as being a stable non eroding landscape however much of the soil mobilized is redistributed and stored within the watershed with only a small portion of the soil eroded from slopes leaving the basin on an event time frame copyright 2002 john wiley sons ltd

lake deposits of moderate salinity as sensitive indicators of lake level fluctuations example from the upper rotliegend saline lake middle late permian northeast germany abstract the rotliegend saline lake periodically covered wide areas of the southern permian basin in northwest europe during the permian the sedimentology mineralogy and geochemistry of lake deposits were studied to document very high frequency lake level fluctuations and to evaluate their triggers increased precipitation and marine ingressions into the basin resulted in lake extension increased run off is documented by intercalated fluvial deposits in low salinity deposits of the lake because lake deposits reflect mainly deposition in relatively wet climate phases they are not correlatable to halite deposits in other basin areas decreased precipitation is followed by shrinkage of the lake desiccation at its margins and higher lake salinity due to concentration of the brine carbonate and anhydrite contents of lake deposits increased considerably before the areas fell dry but halite is not preserved in the study area falling lake level is also reflected by the occurrence of wave ripples reflecting decreased water depth and finally by desiccation and formation of evaporite crusts not only the mineralogical content but also the colour of lake claystones changes with varying salinity anhydrite and carbonate free red claystones were replaced by violet to green and grey anhydritic and calcareous claystone or marls with increasing salinity the amount of boron adsorbed on illite also corresponds to changes in salinity and can therefore be used as a palaeosalinity indicator rare earth element concentrations within lake deposits do not reflect variations in salinity but different palaeogeographical settings marine ingressions into the lake are neither reflected by the amount of boron adsorbed onto illite nor by rare earth element contents of the lake deposits highly saline deposits are partly characterised by intensive deformation which can be interpreted as seismites or dissolution breccias

early permian rotliegendes palaeowinds of the north sea abstract the classical desert sediments of the early permian upper rotliegendes were deposited in a post variscan basin that extends from eastern england to the russo polish border which has been referred to as the southern permian basin these sediments comprise four main depositional facies fluvial wadi aeolian sabkha and lacustrine the lacustrine facies includes important bedded halites the southern permian basin is separated from the smaller northern permian basin by the fragmented mid north sea ringkobing fyn system of highs and beyond the grampian spur lies the even smaller moray firth basin these latter basins contain rock sequences similar to those of the southern basin with the exception that bedded halite has not been recognised in the lacustrine facies the rotliegendes of the southern basin apparently conforms to deposition in a northern hemisphere tradewind desert similar to the modern southern sahara apart from regional palaeomagnetic considerations and the occurrence of sediments of a non arid nature south of the variscan highlands the strongest evidence supporting this interpretation is the pattern of palaeowind directions deduced from the orientations of dune bedding this is seen in both outcrop and core and derived from the continuous dip meter logs of many north sea wells by plotting the poles to the bedding attitudes on polar nets palaeowind directions have also been deduced from the dip meter logs of wells drilled in the northern and moray firth basins in general they indicate winds that blew in a direction opposed to those of the southern basin thus an area of high barometric pressure seems to have been located over the mid north sea high when the bedding attitudes in a well are roughly unidirectional an origin on a transverse dune is normally indicated with some wells the indicated palaeowind direction is regionally anomalous in many cases this can be rectified if the well is presumed to have drilled down through one flank of a seif dune the indicated palaeowind is thus changed by up to 90 and then commonly fits the regional pattern these early permian desert basins were smaller and closer to the equator than the modern sahara their location in the centre of a continent between the caledonian and variscan mountain ranges suggests the analogy of a more tropical equivalent of the central asian takla makan desert

the stratigraphic and geochemical record of playa cycles monitoring a pangaean monsoon like system triassic middle keuper s germany abstract the combination of high resolution stratigraphy with high resolution geochemistry allowed monitoring the cyclicity of a playa system in two dimensions time and space the playa cycles of the middle upper triassic steinmergel keuper located in southern germany were studied both in terms of lateral facies shift variations and long term cyclic patterns the lateral variation was expressed by investigating a time equivalent transect that spanned the kieselsandstein horizon within a 130 km distance from marginal to mid playa position whereas the long term cyclic pattern was investigated in core malschenberg where a time record of ca 5 106 years was encountered mudstone dolomite cycles with dolomites representing the wet and mudstones the dry phases reflect cyclic playa lake level changes indicating varying intensities of monsoon like circulation moisture transport from the tethys ocean into the german basin is implied by 18o depletion trends of isochronous dolomite beds from the margin to mid playa position suggesting dominantly rayleigh like circulation patterns distinct covariance of 18o 13c is used as indicator of lake level stands the k al curve with inverse covariation compared to 18o reflects fluctuating weathering conditions on the fan and the vindelician high a hierarchic cycle stacking pattern composed of metre scale to tens of metre cycles is interpreted to be a result of changing pangaean monsoon like intensities in the milankovitch frequency band spectral analysis shows that the power spectra are dominated by precession and eccentricity

rejuvenated marsh and bay bottom accretion on the rapidly subsiding coastal plain of u s gulf coast a second order effect of the emerging atchafalaya delta abstract sedimentation processes in marshes and bays under the influence of the emerging atchafalaya delta are described the atchafalaya delta is a major geological event in the holocene history of the mississippi river delta system because it represents the initial stages of a new delta cycle the delta has resulted from the capture of the mississippi river flow by the hydraulically more efficient atchafalaya river using 137 cs and 210 pb dating techniques maximum sedimentation of delta flanking environments was found to occur in the bay bottoms and marshes closest to the emerging delta marshes directly under the influence of the emerging delta were accreting at rates as great as 1 4 cm y 1 with appreciable mineral sediment inputs in addition to increasing shoreline progradation the added sediment is providing nutrients for increased net plant productivity which provides the organic source needed for vertical marsh accretion results show that the major area of coastal progradation will be in the immediate vicinity of the delta and along down drift coasts updrift marshes east terrebonne marshes away from the delta are accreting at a slower rate with smaller mineral sediment input and a larger percentage of organic material these marshes are likely to continue experiencing rapid rates of deterioration

rare earth element behavior in soils and salt pan sediments of a semi arid granitic terrain in the western cape south africa the rare earth element ree contents of soils and pan sediments of the darling hills granitic terrain of southwestern south africa were determined to study the behavior of ree during weathering in a semi arid mediterranean climate the p rich stype bedrock granite has a middle ree mree enrichment relative to post archean australian sedimentary rocks paas that primarily reflects the ree content of feldspar and accessory apatite initial chemical weathering of the granite results in the loss of ree particularly ce eu and the heavy ree hree the enrichment of ree in soils relative to bedrock granite corresponds to clay mineral and amorphous fe oxide content in the case of the light ree lree and precipitation of pedogenic calcite in the case of the hree quartz sand dilutes the ree content and concentration of k feldspar produces positive eu anomalies cerium is rapidly precipitated during weathering and retained in clayey upper soil horizons as insoluble ceo2 most pan sediments have a bowl shaped ree pattern that is derived from the accumulation of eroded catchment soils modified by precipitation of evaporative carbonates ree enrichment particularly lree and the large negative ce anomaly of oxidized basal pan sediment relative to the bedrock granite suggest that ree entering the pan by groundwater flow are sorbed onto amorphous fe oxides in contrast goethite rich nodules from the pan have a low ree content and show hree enrichment relative to the granite precipitation of pedogenic calcite and evaporative pan carbonates greatly increases the retention of the hree in these semi arid soils diagenetic pan dolomite has a ree pattern similar to pedogenic and evaporative calcite but with a significantly lower ree content the ree patterns indicate that although most abundant in the bedrock granite the mree are least retained by soils during weathering the lree are generally retained by clayey and amorphous fe oxide rich soils and sediments whereas hree are retained by precipitation of soil and pan carbonates d 2003 elsevier b v all rights reserved

post glacial entrenchment and knickpoint migration of the yarlung tsangpo gorge southeastern tibetan plateau abstract the formation of the yarlung tsangpo river system is commonly thought to be controlled by tectonic processes initiated several million years ago however climate change may also play an important role in guiding drainage evolution here we reconstruct the drainage history of the yarlung tsangpo gorge using field observations age constraints from optically stimulated luminescence and radiocarbon dating paleosalinity reconstruction and grain size analysis of lacustrine deposits and river valley characteristics field observations clay boron derived paleosalinity reconstruction and grain size analysis of lacustrine deposits demonstrate that a closed inland saline lake existed upstream of the yarlung tsangpo gorge implying that cutting of the gorge postdated this paleolake optically stimulated luminescence and radiocarbon dating suggest that the paleolake formed at least 51 ka and terminated after 13 ka with a shift in global climate following the last glacial maximum the paleolake drained by river capture and the gorge entrenchment commenced at the village of jiala northwest of the namche barwa peak approximately 13 10 ka ago the evolution of the yarlung tsangpo occurred on a remarkably short timescale of just tens of thousands of years in response to drainage system reorganization the yarlung tsangpo incised at an average rate of at least 26 mm yr the rapid fluvial incision initiated at jiala 13 ka ago propagated rapidly upstream at 2 12 m yr the yarlung tsangpo knickpoint has not stabilized but will likely continue to migrate upstream

sedimentation in bottomland hardwoods downstream of an east texas dam dams and reservoirs are often efficient sediment traps and conventional wisdom holds that fluvial sediment supplies are reduced well downstream however there are reasons to question the extent to which fluvial and alluvial sediment supplies are reduced more than a few kilometers downstream of dams sedimentation in bottomlands of loco bayou east texas was investigated at a site less than 16 km downstream of loco dam and lake nacogdoches which controls 86 of the 265 km2 drainage area turbidity levels are generally as high or higher than those on loco bayou upstream of the lake sedimentation rates on the lower floodplain since the dam was completed are 11 mm year 1 or more this rate is high enough to suggest that the dam has no effect on sediment supplies 16 km downstream the spatial pattern of sedimentation and the vegetation distribution suggest that the elevation and frequency of flooding not fluvial sediment availability are the critical factors in determining sediment supplies to these floodplains

long term accretion rates on tidal salt marshes abstract long term variations in salt marsh accretion rates were estimated using data collected on the marshes of the north norfolk coast england fourteen discrete marsh areas were sampled all lying within a 20 km stretch of coast the age of each marsh had previously been determined using radiocarbon or archival evidence for the date of vegetation inception on each marsh surface marsh ages ranged from 10 years to 2000 years the elevation of each marsh surface was determined in the field using levelling techniques the relationship between age and surface elevation was assumed to be a function of the rate of marsh accretion within this area of coast statistical tests showed this to be a highly significant relationship while the accretion rates calculated from the age height curve agree closely with field measurements on these marshes accretion rates were found to vary from 1 7 cm yr on 10 year old marshes to less than 0 002 cm on marshes older than 500 years the age height relationship describes an asymptotic curve with the asymptote lying 0 8 m below the level of the highest spring tides and appears to be controlled by the frequency of tidal maxima which peaks at 0 8 m below the maximum value and declines sharply above that height

on the origin of the southern permian basin central europe abstract a detailed study of the structural and stratigraphic evolution of the southern permian basin during latest carboniferous to early jurassic times supported by quantitative subsidence analyses and forward basin modelling for 25 wells leads us to modify the conventional model for the rotliegend zechstein development of this basin the late permian early jurassic tectonic subsidence curves are typical for a permian to early triassic extensional stage that is followed by thermal subsidence however a purely extensional model is extremely problematic because active faulting during this time is minor and generally hard to document using inverse techniques to model the subsidence curves we quantitatively show that a significant component of late permian and triassic tectonic subsidence can be explained by thermal relaxation of early permian lithospheric thinning and by delayed infilling of paleo topographic depressions that developed during the early permian in this interpretation stephanian autunian wrenching resulted in thermal destabilisation of the lithosphere deep fracturing of the crust disruption and erosion of its sedimentary cover and regional uplift of the area of the future southern permian basin upon termination of wrench tectonics and associated volcanism towards the end of the autunian the southern permian basin began to subside in response to thermal contraction of the lithosphere the evolving basin was isolated from the world oceans and had subsided possibly up to some 700 m below their level at the beginning of upper rotliegend sedimentation after catastrophic flooding of this paleo topographic depression at the beginning of the zechstein changing sea level sedimentation and subsidence rates remained essentially in balance although the effects of triassic rifting overprinted parts of the southern permian basin its overall subsidence pattern persisted well into the jurassic in contrast to the remainder of the southern permian basin permian and triassic crustal extension contributed significantly to the subsidence of the polish trough

the sediment delivery problem abstract the linking of on site rates of erosion and soil loss within a drainage basin to the sediment yield at the basin outlet and improved knowledge and representation of the associated processes of sediment delivery represent a major research need within the field of erosion and sedimentation and also an important scale problem in drainage basin studies this paper reviews the limitations of the sediment delivery ratio concept by considering the problems of temporal and spatial lumping and its blackbox nature some recent advances in our understanding of the sediment delivery system and its modelling are described and the lack of detailed empirical investigations is highlighted the significance of recent concern for the role of sediments in the transport of nutrients and contaminants to sediment delivery studies is introduced and the need for further work in this field is emphasised

subsidence of the texas coast inferences from historical and late pleistocene sea levels abstract changes in sea level observed at tide gauges are caused by actual changes in water level and by changes in elevation at the observing station recent research has focused on the relationship between climatic change and sea level but vertical land movement can be just as important particularly in subsiding sedimentary basins the purpose of this study is to compare long term rates of subsidence estimated from upper pleistocene strata along the central texas coast with historical subsidence rates from the same area obtained from geodetic surveys and tide gauge data this comparison shows that historical subsidence rates are much greater than long term averages and are equal or greater than actual sea level change along the texas coast south of galveston bay long term 10 5 yr subsidence rates were estimated by establishing the extent of marine marine influenced and nonmarine strata within the upper pleistocene beaumont formation in the copano bay area of the central texas coast and comparing the maximum elevation of in place marine influenced deposits with published maximum sea level estimates of 5 8 m above mean sea level msl from correlative well dated coral terraces from stable and uplifted areas in place shell bearing horizons deposited at or below sea level occur no higher than 2 m msl in the copano bay area suggesting that there has been no more than 6 m of subsidence since the probable time of deposition during the sangamon interglacial at 120 ka the long term average subsidence rate for this part of the texas coast is thus 0 05 mm yr or less historical subsidence rates were obtained by 1 1 calculating relative elevation changes between national geodetic survey first order leveling surveys conducted in the early 1950s with those conducted in the late 1970s to early 1980s 2 2 normalizing the relative elevation differences between surveys to annual rates of change relative to an arbitrarily chosen benchmark 3 3 referencing these lines to sea level at three tide gauges and 4 4 comparing calculated rates of relative sea level rsl rise along the lines with estimates of eustatic sea level esl rise rates of rsl rise for the texas coast south of galveston bay were generally 4 8 mm yr locally rates were as high as 23 mm yr these rates are significantly higher than global averages of 1 mm yr much of the difference is probably caused by subsidence of the texas coastal zone at rates of 1 22 mm yr or 20 440 times the long term average of 0 05 mm yr the highest subsidence rates were found locally where there has been historical water level decline in shallow aquifers lower subsidence rates of 3 7 mm yr occur regionally where groundwater decline is minimal or nonexistent increased subsidence over the long term average in these areas may be caused by pressure decline in underlying oil and gas reseivoirs

soft sediment deformation structures interpreted as seismites in lacustrine sediments of the prebetic zone se spain and their potential use as indicators of earthquake magnitudes during the late miocene lacustrine formations of late miocene age in the prebetic area se spain show several types of deformational structures that are interpreted as seismites they are present in both marginal and deep lacustrine facies seismites formed in marginal lake environments comprise sand dikes pillows and intruded and fractured gravels in deep lacustrine facies the seismites are represented by pseudonodules mushroom like silts protruding into laminites mixed layers disturbed varved lamination and loop bedding the measured orientations of these structures are consistent with the orientations of the main faults limiting the basins showing that their origin is clearly related to the tectonic stress field that prevailed in the region during the late miocene the magnitudes of the earthquakes that deformed the sediments have been estimated after published data from both ancient and recent lake deposits accumulated in tectonic active regions elsewhere a rank of earthquake magnitudes with two end members i e the lowest magnitudes recorded by loop bedding in laminites and the highest magnitudes represented by intruded and fractured gravels is proposed

hydrogeochemistry and rare earth element behavior in a volcanically acidified watershed in patagonia argentina abstract the rio agrio watershed in northern patagonia argentina is naturally acidic due to discharges of volcanic h 2 so 4 hcl and hf at its headwaters near the summit of copahue volcano a suite of water samples was collected from the summit of the volcano to a point roughly 40 km downstream where the ph of the rio agrio rose above 6 0 this suite included a sample of the hyperacidic ph the concentrations of ree in the rio agrio decreased by several orders of magnitude through the study area as a result of dilution and chemical attenuation a subtle shift in the slope of shale normalized profiles of dissolved ree concentration was observed from being weakly positive near the source of the rio agrio to showing a weak middle ree enrichment trend in lake caviahue to being weakly negative in the lower reaches of the river the trend to a negative slope across the lanthanide series in the lower river is explained by selective partitioning of the heavier ree to hydrous oxides of fe and al suspended in the water column and accumulating on the riverbed most of the decrease in ree load occurred immediately downstream of the confluence with a tributary that increased the ph of the rio agrio from 4 3 to 6 1 although the mixed water was supersaturated with ree phosphate compounds precipitation of lnpo 4 is not believed to have been a dominant process because the predicted pattern of inter element fractionation from phosphate deposition is inconsistent with the observed trends instead ree attenuation most likely occurred from adsorption onto freshly precipitated hydrous aluminum oxide the behavior of ree in the rio agrio watershed is broadly similar to what has been observed in watersheds that owe their acidity to oxidation of sulfide minerals

holocene evolution and anthropocene destruction of the krishna delta on the east coast of india delta lobe shifts human impacts and sea level history abstract the holocene evolution of the krishna delta was inferred using landform characteristics and 11 sediment cores with 59 accelerator mass spectrometry 14c dates the landform assemblages in a 5880 km2 area of the krishna delta indicate an upper landward river built fluvial plain and a lower seaward marine built beach ridge plain holocene sediment unconformably overlying a pleistocene basement consists of 11 sedimentary facies mainly shallowing upward and deltaic succession sea level indicators such as the basal mangrove peat layers above the pleistocene basement and the foreshore sediments indicate that the sea level rose from 9 m to 3 m during 8 3 6 3 cal ky bp and stabilised at the present level around 5 cal ky bp the 3539 km2 area of the krishna delta beach ridge plain developed in five major stages during the last 6 cal ky with distinct lateral and seaward migration of delta lobes depocentre shifts delta progradation accelerated in the last 500 years forming an out building lobate delta however predominant erosion along the sediment starved coast during the past five decades due to impoundment of riverine inputs at the burgeoning upstream dams has pushed the krishna delta into a persistent destruction phase

palaeomagnetism of the neoarchaean pongola and ventersdorp supergroups and an appraisal of the 3 0 1 9 ga apparent polar wander path of the kaapvaal craton southern africa the style of tectonic processes on the young earth is a topic of intense debate palaeomagnetism provides the only robust tests with which to settle theoretical disputes based on the rock record that infer large scale horizontal motions between palaeocontinents a possible apparent polar wander path apwp of the kaapvaal craton shows significant distances between adjacent palaeomagnetic poles that can be interpreted as evidence for such horizontal displacements during the archaean palaeoproterozoic there are however substantial uncertainties build into this apwp currently the published apwp for the kaapvaal craton comprises eight palaeopoles between 3 0 and 1 9 ga including several between 2 8 and 2 7 ma that indicate possible horizontal motions exceeding 6500 km the aim of this contribution is to increase the pole density within this interval and in doing so to test the robustness of the kaapvaal apwp within this time frame more than 250 samples of basalt diamictite and dolerite of the neoarchaean pongola ca 2 95 2 85 ga and ventersdorp ca 2 71 2 70 ga supergroups of the kaapvaal craton were sampled both at the surface and in an underground mine thermal demagnetisation revealed two magnetic components a high temperature component is present in three pongola formations and in two ventersdorp formations these may be recorders of the primary natural remanent magnetisation because of lack of precise geochronology and positive field tests this magnetisation can only be constrained to be older than ca 2 05 ga a medium temperature overprint in many samples probably records remagnetisation at ca 180 ma during the emplacement of basalts and dolerites of the mesozoic karoo large igneous province this remagnetisation appears to have affected a vast area of the kaapvaal craton our new palaeopoles together with those published previously demonstrate that the neoarchaean apwp of the kaapvaal craton remains poorly defined direct comparisons between the apwp of the kaapvaal craton with apwps of other archaean cratons to determine relative motions between archaean continents therefore need more reliable data

sedimentation accretion and subsidence in marshes of barataria basin louisiana1 vertical accretion and sediment accumulation rates were determined from the distribution of 137cs in cores collected from freshwater intermediate brackish and salt marshes in the barataria basin louisiana vertical accretion rates vary from about 1 3 cm yr l in levee areas to 0 7 in backmarshes mineral sediment content of the marsh soil profile decreased with distance from the coast however vertical accretion rates were about equivalent in areas of the same type autochthonous organic matter appears to be an important factor defining the process and rate of vertical accretion especially in the freshwater marshes except in natural levee areas marsh accretion rates are less than subsidence measured by water level data however this alone cannot account for observed land loss patterns in the basin area

riparian vegetation and fluvial geomorphic processes abstract riparian vegetation and fluvial geomorphic processes and landforms are intimately connected parts of the bottomland landscape relations among vegetation processes and landforms are described here for representative streams of four areas of the united states high gradient streams of the humid east coastal plain streams great plains streams and stream channels of the southwestern united states vegetation patterns suggest that species distributions in the humid east are largely controlled by frequency duration and intensity of floods along channelized streams vegetation distribution is largely controlled by variation in fluvial geomorphic processes cycles of degradation and aggradation in response to increases in channel gradient associated with channelization similarly riparian vegetation of great plains streams may be controlled by fluxes in sediment deposition and erosion along braided streams patterns of riparian vegetation in semi arid regions may be most closely related to patterns of water availability unlike most other streams in more humid environments channel equilibrium conditions control stability of the coincident fluvial landform and attendant vegetation pattern throughout the continent in most situations riparian vegetation patterns are indicative of specific landforms and thus of ambient hydrogeomorphic conditions

cyclicity of triassic to lower jurassic continental red beds of the argana valley morocco implications for palaeoclimate and basin evolution abstract cyclical playa deposits form a prominent part of the continental clastic succession of the argana valley western high atlas of morocco the red beds formed in triassic to lower jurassic times during rifting of the north american and african plates detailed stratigraphic work revealed asymmetrical metre scale cycles in mudstone dominated successions that constitute the intermediate and upper portion of the basin fill sedimentary cycles commonly comprise ephemeral lake shales at the base playa mudflat mudstones in the intermediate part and both fluvial and aeolian sandstones at the top cycles of the aglegal member t4 are mainly characterized by analcime rich playa mudflat deposits displaying features indicative of palaeo vertisols cycles of the sidi mansour t7 and hasseine t8 members are represented by ephemeral lake or dry playa mudflat deposits grading into saline mudflat mudstones that are overlain by sheet flow and minor aeolian sandstones sedimentary cycles of the imerhrane member t9 comprise sheet delta sandstones at the base overlain by ephemeral lake and dry playa mudflat mudstones upper cycle portions consist of aeolian dune and sand sheet sandstones cyclicity is attributed to palaeoclimatic and associated palaeohydrological fluctuations probably within the milankovitch frequency band sedimentary facies of each cycle provide evidence for a gradual climatic drying with time the asymmetrical drying upward cycles possibly record the precession cycle since they are modulated by symmetrical i e oscillating drying wetting cycles of a lower frequency indicative of eccentricity a long term change in palaeoclimate ranging from semi arid conditions with seasonal precipitation t4 towards an arid non seasonal climate t8 is preserved within the cyclical units spanning a time interval of several million years individual cycles can be traced laterally for tens of kilometres correlative sections are almost identical in thickness suggesting a phase of tectonic quiescence during their deposition sediment accumulation was not restricted to small scale grabens but took place continuously throughout the exposed area of the argana valley implying that accommodation space has not been controlled by syndepositional tectonism

variable response of coastal environments of the northwestern gulf of mexico to sea level rise and climate change implications for future change the results from nearly three decades of marine geological research in the northwestern gulf of mexico are compiled in an effort to understand those factors e g sea level rise sediment supply subsidence antecedent topography that influenced coastal evolution during the last eustatic cycle 120 ka to present armed with this information we evaluate coastal response to variable sea level rise of the holocene and accelerated rise during historical time to gain a better understanding of how the coast is likely to respond to future changes the early holocene evolution of northwestern gulf of mexico bays was punctuated by rapid and possibly synchronous flooding events that are interpreted as resulting from episodes of rapid sea level rise two of these events one between 8 4 and 8 0 ka and the other between 7 4 and 6 8 ka were associated with known episodes of ice sheet retreat in north america and antarctica respectively during the middle and late holocene the east texas and western louisiana coasts experienced episodes of stability and growth followed by rapid shoreline retreat while the central texas coast remained relatively stable this variability in coastal response to sea level rise resulted mainly from differences in sediment supply and the highly irregular antecedent topography on which coastal environments formed sand that nourished the evolving east and south texas as well as westernmost louisiana coasts was derived mainly from transgressive ravinement of deltas that were formed during the falling stage of sea level mis5e mis2 the loci of these deltas controlled the spatial variability of this offshore sand supply sand supply to the central texas coast has been dominated by converging longshore currents and throughout the middle to late holocene was large enough to keep pace with sea level rise moreover sand supply from rivers has varied considerably in response to climate change during the early holocene when the average rate of linear sea level rise was 4 2 mm yr the brazos colorado and rio grande rivers all formed deltas on the inner continental shelf today only the brazos contributes enough sediment to the gulf of mexico to form a delta but its sand delivery is minimal a reversal from late holocene growth of western louisiana east texas and south texas barrier islands and peninsulas to erosion occurred during the last 2 0 ka after the rate of sea level rise began to decelerate the actual timing of this reversal was diachronous across the coast and was caused by a decrease in sediment supply once offshore sand sources were bypassed by the landward advancing shoreface transgressive ravinement differences in the exact timing and rate of retreat also reflect variability in the offshore profiles of these barriers and their thickness which results from the underlying relief on the pleistocene surface the late holocene was also the time of chenier plain development in western louisiana and east texas that was marked by localized differences in growth and retreat the current rate of eustatic sea level rise in the northern gulf of mexico is in the range of 2 0 and 3 0 mm yr and is approaching rates of the early holocene this is on average about five times the long term rate of the past 4 0 ka this larger rate is associated with an increase in coastal erosion in historical time relative to long term rates current rates of gulf shoreline erosion are approaching rates of the early to mid holocene and the rate of retreat of some barriers is not sustainable core transects off central texas reflect a late holocene history of shoreface progradation but the modern shoreline is currently eroding albeit at slower rates than elsewhere along the coast overall the sand supply needed to sustain the gulf shoreline is lacking likewise baylines are experiencing erosion rates that are faster than the late holocene average and bayhead deltas are at the tipping point of catastrophic retreat spatial variability in erosion rates highlights the importance of factors such as sediment supply subsidence and anthropogenic influences on coastal evolution tropical storms and hurricanes while exerting the most noticeable coastal change merely exacerbate overall shoreline retreat and migration along the entire northwestern gulf coast the impact of human intervention to natural processes is particularly evident primarily due to alterations in river discharge and sediment supply to the coast interruptions in along shore and cross shore sand transport and increases in rates of subsidence through fluid withdrawal compared to natural changes that took place during the holocene the impacts of human activity have been virtually instantaneous the geological record indicates that the ongoing increase in the rate of sea level rise coupled with diminished sediment supply and human intervention will continue to severely impact the low gradient coastal environments of the northwestern gulf of mexico

the nsuze group pongola sequence south africa geochemical evidence for archaean volcanism in a continental setting abstract the archaean nsuze group in southeast south africa represents an important volcano sedimentary succession that is markedly different compositionally and lithologically from older and contemporaneous sequences elsewhere in southern africa the nsuze volcanic rocks cropping out in the vicinity of the pongola river in northern natal display a complete spectrum of chemical compositions from basalt to rhyolite with lavas of intermediate compositions predominant but ultramafic lavas absent flows of different compositions are complexly interdigitated the uppermost rocks of the nsuze group reflect a gradual decrease in volcanic activity accompanied by an increase in sedimentation the nsuze lavas are tholeiitic with total fe as fe 2 o 3 contents approaching 17 in the basaltic andesites all lithologies are characterized by moderate to strong light rare earth element ree enrichment heavy ree slopes range from moderate in the basalts and basaltic andesites to flat in the rhyolites with the exception of two basaltic andesites and a dacite which have flat heavy ree slopes basalts have small or no negative eu anomalies but increasingly larger negative anomalies are a feature of the intermediate and acid lavas variations in cr content appear to be related to stratigraphic position basalts and basaltic andesites in the lower part of the volcanic sequence have higher cr contents by a factor of six to eight times than lavas with similar mgo abundances in the upper part of the sequence provisional modelling of the available chemical data favours low pressure crystal fractionation from and evolved basaltic parent that could be derived by initial non modal melting of a garnet lherzolite source variable degrees of crustal contamination of the evolved magmas are considered probable

active near surface growth faulting and late holocene history of motion matagorda peninsula texas abstract the structural framework of the northern gulf of mexico coastal zone includes numerous growth fault systems neotectonic processes in coastal environments here have been shown to be important contributors to subsidence and relative sea level rise as well as having significant influences on sedimentary accretion processes one active growth fault at east matagorda peninsula texas was subjected to detailed study to address the hypotheses that 1 this fault was present and active before the peak of regional hydrocarbon recovery in the mid 20th century and that 2 slip along this fault has been episodic over the resolved period of record to characterize the late holocene behavior of this fault three core transects were established normal to the surface fault trace and stratigraphic analysis was conducted with the use of radiocarbon 14c for chronological control correlation of time equivalent stratigraphic boundaries reveals a maximum total late holocene offset of 0 7 m the matagorda fault was in place long before the peak of regional oil and gas extraction but experienced a late holocene rejuvenation initiated between 2500 and 1500 years bp the kinematic behavior of the fault expressed as temporally and spatially variable measures of expanded stratigraphic thicknesses on the downthrown extent suggest that sediment loading from the transgressive matagorda barrier complex may have contributed to this rejuvenation and that slip along the fault persists to the present radiocarbon chronology also revealed clear differences in the magnitude of fault throw during the late holocene with maximum displacement 0 7 m occurring at the southwestern most transect and minimum throw at the northeastern most transect 0 2 m

fluvial sediment delivery to a coastal plain estuary in the atlantic drainage of the united states abstract drastic changes in sediment production in drainage basins can have significant impacts on sediment yield to estuaries however significant but less spectacular changes in fluvial sediment regimes have not greatly influenced sediment output of some rivers in the united states atlantic drainage the limited influence of moderate or incremental changes in fluvial sediment systems on estuarine sediment delivery may be attributable to the large proportion of eroded sediment which is stored within the basins and the transport limited nature of long term sediment yields a sediment budget for the pee dee river basin and waccamaw river winyah bay estuary of the carolinas shows that only a small proportion of gross eroded sediment within the basin about 4 reaches the estuary on an average annual basis because the system appears to be transport limited it is estimated that an 88 reduction in the quantity of eroded sediment reaching streams would be necessary to produce significant change in sediment yield to the estuary any increase in sediment production would not be reflected at all in the estuary unless it was accompanied by a corresponding increase in fluvial sediment conveyance capacity estuarine sedimentary records thus may not reflect some significant changes in fluvial sediment systems

uranium thorium and lead nuclides in a delaware salt marsh sediment natural isotopes of uranium 234 238 thorium 232 230 and lead 210 have been assayed in sediments from a lower delaware salt marsh uranium is concentrated in the top sections of the core and decreases with depth 3 to 1 d min 1 g 1 a significant proportion of this uranium has been authigenically extracted from seawater as demonstrated by an excess ratio of 234u 238u 1 03 1 14 thorium 232 is rather constant 2 4 4 7 parts 10 6 for all but one sample while the concentration of 230th is deficient with respect to its uranium parent in contrast to the deep sea the fixation of authigenic reduced uranium dominates over the scavenging of 230th in these tidal sediments excess 210pb shows an exponential decay over the length of the core and when corrected for a correspondingly significant exponential decrease in organic carbon and salt yields a sedimentation rate of 0 47 cm year 1 although this rate approximates the local apparent rate of sea level rise a lower limit for the rate of salt marsh accumulation the actual rate is higher suggesting net filling and acccretion of salt marshes the total integrated flux of 210pb to this and other salt marsh surfaces in the eastern u s is calculated to more often exceed the reported local atmospheric flux it appears that salt marshes may scavenge 210pb as other trace metals from flooding waters

quantifying downstream impacts of impoundment on flow regime and channel planform lower trinity river texas abstract as human population worldwide has grown so has interest in harnessing and manipulating the flow of water for the benefit of humans the trinity river of eastern texas is one such watershed greatly impacted by engineering and urbanization draining the dallas fort worth metroplex just under 30 reservoirs are in operation in the basin regulating flow while containing public supplies supporting recreation and providing flood control lake livingston is the lowest as well as largest reservoir in the basin a mere 95 km above the trinity s outlet near galveston bay this study seeks to describe and quantify channel activity and flow regime identifying effects of the 1968 closure of livingston dam using historic daily and peak discharge data from usgs gauging stations flow duration curves are constructed identifying pre and post dam flow conditions a digital historic photo archive was also constructed using six sets of aerial photographs spanning from 1938 to 1995 and three measures of channel activity applied using a gis results show no changes in high flow conditions following impoundment while low flows are elevated however the entire post dam period is characterized by significantly higher rainfall which may be obscuring the full impact of flow regulation channel activity rates do not indicate a more stabilized planform following dam closure rather they suggest that the trinity river is adjusting itself to the stress of livingston dam in a slow gradual process that may not be apparent in a modern time scale

geochemical evolution of archean shales from south africa i the swaziland and pongola supergroups abstract the fig tree group and moodies group part of the swaziland supergroup are exposed in the barberton mountain land and are 3 3 3 5 ga old shales from the fig tree group are characterized by variable rare earth element ree patterns with lan ybn 5 5 1 8 95 confidence and eu eu 0 97 0 18 shales from the moodies group have more fractionated ree patterns lan ybn 8 7 2 0 and less variable eu anomalies eu eu 0 92 0 02 both groups are characterized by very high abundances of cr and ni modelling of those trace elements which are relatively unfractionated during sedimentary processes ree th sc is consistent with the derivation of these sedimentary rocks from a mixture of the archean bimodal igneous suite mafic volcanics tonalites trondhjemites felsic volcanics with the moodies group requiring a larger percentage of the felsic end member the data for shales from the swaziland supergroup support models suggesting that the archean exposed crust was of more mafic composition than the post archean upper crust and that intracrustal melting was relatively unimportant in differentiating the archean crust the pongola supergroup is younger than the swaziland supergroup but older than 2 9 ga shales and mudstones from the nsuze and mozaan groups show ree characteristics intermediate between the older shales of the swaziland supergroup and typical post archean shales one quartzite sample from the witwatersrand supergroup ca 2 6 ga has a ree pattern virtually parallel to average post archean shales but with much lower abundances the change from typical archean to post archean sedimentary trace element patterns has been documented in early proterozoic successions from canada and australia this change has been related to a short interval of intense growth and chemical differentiation of the continental crust during the late archean 2 7 2 5 ga in southern africa this change appears to have taken place much earlier 3 2 2 9 ga but can be related to similar processes thus the period of crustal evolution related to the archean proterozoic boundary while virtually episodic regionally occurred over a protracted period world wide during the period ca 3 2 2 5 ga

a smnd and pb isotope study of archaean greenstone belts in the southern kaapvaal craton south africa abstract a sm nd and pb study on a wide variety of lithologies in archaean greenstone belt fragments in the southern kaapvaal craton reveals a complex petrogenetic history the fragments are important because they represent a 350 km transect through the craton south of barberton to its southern margin the commondale greenstone belt yields a precise sm nd age of 3334 18ma on an exceptionally well preserved peridotite suite of komatiitic affinity the wide range of sm nd from 0 6 to 1 0 is attributed to the unusual occurrence of orthopyroxene in the spinifex bearing rocks a considerably younger age of about 3 2 ga is suggested for the nondweni greenstone belt close to the southern margin of the craton on the basis of separate sm nd isochrons on individual lithologies ranging from komatiite through komatiitic basalt and basalt to felsic volcanic rocks the most precise sm nd age for the greenstone belt of 3208 87ma is based on a combined mineral whole rock isochron for komatiitic basalts but the possibility cannot be excluded that this represents a later metamorphic age on the basis of the present study the greenstone belts appear to have been emplaced at progressively younger ages towards the southern margin of the craton of greater significance is that irrespective of age the individual lithologies of the nondweni sequence have isotopically distinct initial ratios combining isotopic data from these lithologies invariably yields apparent older ages the isotopic characteristics are consistent with a model of progressive contamination by older sialic crust thought to be the basement to the nondweni sequence

holocene environmental changes of the godavari delta east coast of india inferred from sediment core analyses and ams 14c dating abstract the godavari delta in india is a major wave dominated delta of a tropical monsoon fed river with one of the largest sediment deliveries in the world while several earlier studies revealed the nature of landforms and progradation style of the delta plain during the holocene the present study attempts to reconstruct the depositional environment of the godavari delta through the analysis of core sediment and accelerator mass spectrometry ams 14c dating from three locations the sediment core obtained from a 27 06 m deep borehole at vilasavilli vv supported by 13 14c dates revealed the complete succession of the holocene deposits unconformably overlying pleistocene sediments textural analysis indicates the lower upward fining and upper upward coarsening units in the holocene succession total organic carbon toc total nitrogen tn ratios of 20 high content of toc around 1 5 2 5 and black to very dark colored sediment throughout the muddy part of the holocene succession indicated a predominance of terrigenous material the vv core and two other cores drp and sdg with 14 14c dates indicated the thickness of the holocene sediments in the godavari delta plain is in the order of 20 50 m unconformably resting on a seaward sloping pleistocene basement sediment facies and sediment accumulation of the three cores show the evolution of the godavari delta a transgressive phase is recognized as an upward fining succession in the vv core 8 4 8 0 cal ky bp followed by a low accumulation period 8 0 6 3 cal ky bp including the holocene maximum transgression in the godavari delta after 6 3 cal ky bp areas of high accumulation rates have changed laterally between the central part vv site and southwestern part drp and sdg sites may be controlled by the location of river mouths further analysis coupled with 11 more 14c dates compiled from earlier works indicated that the strandplain of the godavari delta prograded seaward in three stages and that the rate of progradation accelerated during the past 3 ky particularly in the last millennium however pronounced shoreline erosion led to a net negative growth of the delta during the recent decades due to sediment retention by upstream dams although this study provided insights into the sedimentation patterns and rate of seaward progradation of the godavari delta further studies on three dimensional volume analysis of the deltaic sediments are necessary to estimate the overall rates of past sediment discharge and the holocene growth of the godavari delta

late permian non marine marine transitional profiles in the central southern permian basin northern germany the transition from rotliegend to zechstein within the southern permian basin is one from continental desert to a marine environment during the upper rotliegend ii a huge playa lake existed there this lake was temporarily influenced by precursors of the zechstein transgression therefore the mega playa evolved into a sabkha system one of these early marine ingressions is known from an outcrop in schleswig holstein laminated silt and claystones deposited within a standing water body are intercalated in siltstones of a salt flat environment the lake sediments are characterised by high frequency cyclicity shown by the sedimentary record and also by palaeontological data the section contains fresh water as well as brackish marine and marine fauna climatically forced cycles interact with marine incursions after the zechstein transgression had flooded the basin completely sedimentation was controlled by sea level fluctuations two sections in the southern north sea and in schleswig holstein are presented in this paper cyclicities with different frequencies controlled the sedimentation of the kupferschiefer t1 and the werra carbonate ca1 sediments of the north sea sequence were deposited within a shallow bay at the margin of an elevation therefore the high frequency cyclicity became obvious within the sedimentary patterns and in the faunal content

prehistoric earthquake deformations near masada dead sea graben earthquake inducedfluidizations and suspensions of lake sediments associated with syndepositionalfaults formapaleoseismicrecordinthedeadseagraben theassociation offluidized beds with surface faulting supports the recognition of mixed layers as reliable earthquake indicators and provides a tool for the study of very long term 70 kar seismicity along the dead sea transform the faults compose a fault zone that offsets laminated sediments of the late pleistocene lake lisan they exhibit displacements of as much as 2 m layers of massive mixtures of laminated fragments are interpreted as disturbed beds each formed by an earthquake the undisturbed laminated layers between these mixed layers represent the interseismic interval a typical vertical slip of about 0 5 m per event is separated by several hundred years of quiescence the fault zone lies within the dead sea graben 2 km east of masada where archaeology and historical accounts indicate repeated strong earthquake damage the distribution of strikes in the fault zone resembles that of the faults exposed in and around the graben including the seismogenic ones the excellent exposures over hundreds of metres allow an unprecedented temporal and spatial resolution of slip events on faults

hydrologic inferences from tree ring studies on the hawkesbury river sydney australia abstract introduced salix trees in australian alluvial environments can be used to make a number of hydrologic inferences dendrochronological studies along the hawkesbury river near windsor suggest that the salix growth form and annual growth ring variability are closely associated with the local hydrologic regime detailed analyses of 33 trees showed that tree growth is suppressed close to water and increases with height above mean low stage levels because of the decreasing influence of flooding alluvial levels contain discrete vegetation patterns and growth characteristics that are not explained by variations in soil and climate growth of salix in thickets on low in channel benches is flood limited with fitted exponential growth curves having positive or zero slopes the high in channel bench contains vegetation influenced by flooding but growing according to classical exponential decay functions trees on floodplain levees show full canopy development and the most rapid growth because of fertile soils the high availability of water and limited influence of floods overtopping levee tops elevation and tree growth relations are used to develop a relation between growth and flood frequency this is applicable to catchments of similar size soil type and climate analyses of tree form and root distribution indicated that dendrochronological techniques may be used to determine the minimum land surface age and rates of accretion around the tree bole in alluvial areas of southeastern australia

permo carboniferous climate early pennsylvanian to late permian climate development of central europe in a regional and global context a well justified stratigraphical correlation of continental successions and new palaeogeographic reconstruction of pangaea reveal new insights into the northern pangaean climate development influenced by palaeogeography palaeotopography glacio eustatic sealevel changes and ocean currents the overall permo carboniferous aridization trend was interrupted by five wet phases these are linked to the gondwana icecap the aridization and weakening of wet phases over time were not only caused by the drift of northern pangaea to the arid climatic belt but also by the successive closure of the rheic ocean which caused the expansion of arid semi arid environments in the lower middle permian the end of the gondwana glaciation rearranged ocean circulation leading to a cold coast parallel ocean current west of northern pangaea blocking moisture coming with westerly winds the maximum of aridity was reached during the roadian wordian the trans pangaean mountain belt was non existent its single diachronous parts never exceeded an average elevation of 2000 m the maximum elevation shifted during time from east to west the hercynian orogen never acted as an orographic east west barrier and the inter tropical convergence zone was widely displaced causing four seasons dry summer winter wet spring autumn at the equator and a strong monsoon system the climate history of the european realm during the late carboniferous pennsylvanian and permian is stored in many solitary basins fig 1 within the hercynian orogen and the foreland basin the story of westphalian climate is well known because of the numerous investigations of the coal bearing variscan foredeep the younger westphalian is characterized by a slight aridization abbink van kronijnenburgvan cittert 2003 oplustil 2004 which was accompanied by an increase of seasonality nevertheless the environment was strongly influenced by the ocean and epi continental seas with multiple transgression events the last extensive marine ingression was the aegir mansfield band westphalian b c the post westphalian climate development is more differentiated and

identification of sequence stratigraphy in the dongying formation of the liaoxi low uplift bohai bay basin china a change in sea level or lake level causes a change in accommodation space and sediment compensation which then controls the formation and evolution of sequences a multidisciplinary approach ba

global sea level trend in the past century data derived from tide gauge stations throughout the world indicate that the mean sea level rose by about 12 centimeters in the past century the sea level change has a high correlation with the trend of global surface air temperature a large part of the sea level rise can be accounted for in terms of the thermal expansion of the upper layers of the ocean the results also represent weak indirect evidence for a net melting of the continental ice sheets

marine ingressions into the middle late permian saline lake of the southern permian basin rotliegend northern germany possibly linked to sea level highstands in the arctic rift system abstract a huge saline lake existed in the southern permian basin spb of northwest europe during late wordian to early wuchiapingian more than 2500 m thick continental siliciclastics and evaporites of the upper rotliegend ii were deposited before the marine zechstein transgression flooded the basin marine deposition took place in the arctic rift system between east greenland and the fennoscandian shield at that time interval sediments of the foldvik creek group reflect relative sea level fluctuations short termed pre zechstein ingressions from the boreal realm into the spb are known by the marine lamellibranch liebea reichei however sedimentological analysis of different saline lake horizons show that the marine influenced saline lake horizon does not differ lithologically from other saline lake claystone layers in the rotliegend succession the 87 sr 86 sr ratios of anhydrite 0 7089 0 7100 reflect deposition in a continental setting in contrast to this s isotopic values more than 11 7 cdt reflect marine pre zechstein ingressions into the spb in the middle niendorf and munster members s isotopic values of anhydrite can be used as an indicator for marine influence in the spb the pre zechstein ingressions superimpose the climatic triggered lake level fluctuations of the rotliegend saline lake two marine ingressions can be integrated into a set of regularly recurring abnormities in the depositional evolution these important evolutionary steps the saline lake formation the garlstorf ingression the p ameland and bahnsen lake level highstands the niendorf ingression and the zechstein transgression show a periodicity of more or less 1 ma one million year cyclicity is also known from deposits of the arctic rift system in east greenland wegener halvo and ravnefjeld formations a correlation of the upper rotliegend ii deposits with the succession of east greenland is proposed based on the assumption that the marine ingressions as well as the exceptionally intensive saline lake expansions could be linked to sea level highstands in the arctic rift system the result is the first correlation of upper rotliegend ii deposits with marine strata

a comparison of factors controlling sedimentation rates and wetland loss in fluvial deltaic systems texas gulf coast abstract submergence of coastal marshes in areas where rates of relative sea level rise exceed rates of marsh sedimentation or vertical accretion is a global problem that requires detailed examination of the principal processes that establish maintain and degrade these biologically productive environments using a simple 210 pb dating model we measured sedimentation rates in cores from the trinity lavaca navidad and nueces bayhead fluvial deltaic systems in texas where more than 2000 ha of wetlands have been lost since the 1950s long term average rates of fluvial deltaic aggradation decrease southwestward from 0 514 0 008 cm year 1 in the trinity 0 328 0 022 cm year 1 in the lavaca navidad to 0 262 0 034 cm year 1 in the nueces the relative magnitudes of sedimentation and wetland loss correlate with several parameters that define the differing fluvial deltaic settings including size of coastal drainage basin average annual rainfall suspended sediment load thickness of holocene mud in the valley fill and rates of relative sea level rise there is some evidence that upstream reservoirs have reduced wetland sedimentation rates which are now about one half the local rates of relative sea level rise the extant conditions indicate that fluvial deltaic marshes in these valleys will continue to be lost as a result of submergence and erosion

geochemical characteristics and origin of sodium carbonates in a closed alkaline basin the lower permian fengcheng formation in the mahu sag northwestern junggar basin china abstract the lower permian fengcheng formation in the mahu sag of northwestern china is well known for its alkaline lacustrine deposits however previous research is scarce due to this formation s notable burial depth up to 5000 m and limited oil and gas exploration using xrd xrf micro xrf and c o isotope analyses we determined 1 the stratigraphic trends in mineral compositions 2 the cyclic depositional processes and 3 paleoclimate variations the petrologic and geochemical data elucidate depositional and diagenetic processes in the mixed siliciclastic volcaniclastic and chemical strata of the fengcheng formation sodium carbonate minerals in the studied core are dominated by wegscheiderite na2co3 3nahco3 and trona na2co3 nahco3 2h2o nahcolite nahco3 and a mg na carbonate mineral northupite na2co3 mgco3 nacl also occur although their abundance is obviously lower than that of wegscheiderite and trona these substances grew as bottom growth crystals from lakes overlying tuffs the volumetrically important ca na carbonate mineral shortite na2co3 2caco3 and some northupite precipitated diagenetically from shallow groundwater brines in unlithified dark colored siliciclastic sediment and volcanic ash shortite mainly precipitated from the ca na co3 rich shallow groundwater whereas northupite precipitated from the mg na co3 cl rich shallow groundwater sodium carbonates and tuffs fine grained tuffaceous rocks and siliciclastic rocks formed repetitive centimeter and meter scale cycles that are shown as dark colored lithological layers during lake expansion and contraction stages or during volcanic eruptions the brine composition which controlled the precipitation of sodium carbonates was influenced strongly by volcanism and volcanism related hydrothermal activity changes in climate and volcanic eruptions controlled the deposition of alternating beds of sodium carbonates and dark colored lithologies changes in climate caused the expansion and contraction stages in the lakes during relatively humid climate stages diluted water entered the basin and resupplied the lake water with calcium and magnesium during flooding events sandy to silty beds were deposited by turbidity currents during this stage during arid climate stages bedded sodium carbonates grew in the lakes and their co occurrence suggests high atmospheric pco2 and high temperatures the ashes that are provided by volcanic eruptions during arid climate stages can also stop the precipitation of sodium carbonates

mangrove expansion in the gulf of mexico with climate change implications for wetland health and resistance to rising sea levels abstract black mangroves avicennia spp are hypothesized to expand their latitudinal range with global climate change in the 21st century induced by a reduction in the frequency and severity of coastal freezes which are known to limit mangrove colony extent and individual tree size the gulf of mexico is a prime candidate for population expansion to occur because it is located at the northward limit of black mangrove habitat this may come at the expense of existing coastal saline wetlands that are dominantly spartina spp marsh grasses the present study was conducted to focus on the implications of a marsh to mangrove transition in gulf wetlands specifically 1 wetland resistance to accelerating eustatic sea level rise eslr rates 2 resistance to wave attack in large storms increased cyclonic storm frequency intensity is predicted with future climate warming and 3 organic carbon sequestration and wetland soil geochemistry field sites of adjacent and inter grown avicennia germinans mangrove and spartina marsh populations in similar geomorphological setting were selected in back barrier areas near port aransas and galveston tx elevation surveys in the more mature port aransas site indicate mangrove vegetated areas are 4 cm higher in elevation than surrounding marsh on an average regional scale and 1 2 cm higher at the individual mangrove scale 210pb and 137cs accumulation rates and loss on ignition data indicate that mineral trapping is 4 1 times higher and sediment organics are 1 7 times lower in mangroves at port aransas this additional mineral trapping does not differ in grain size character from marsh accumulation elevation change may also be effected by soil displacement of higher root volumes in mangrove cores port aransas porosities are lower in mangrove rooted horizons with a corresponding increase in sediment strength suggesting mangrove intervals are more resistant to wave induced erosion during storm events port aransas mangroves exhibit higher pore water redox potentials and salinities over entire core depths and depressed ph over rooted intervals suggesting a distinct diagenetic environment exists relative to marsh sites the rooting network which introduces oxygen into the sediment and focuses evapo transpiration and salt exclusion within this zone may prove advantageous when competing with grasses by elevating salinities to levels that are toxic for spartina trends observed in the more mature systems of port aransas are generally absent in galveston suggesting the youth and physically shorter stature of these systems means they have not yet established a unique sediment signature

the early archaean nondweni greenstone belt southern kaapvaal craton south africa part ii characteristics of the volcanic rocks and constraints on magma genesis the early archaean nondweni greenstone belt is dominated by mafic volcanic rocks which have a wide range in compositions primary volcanic structures and compositional characteristics point to this succession being unique in archaean geology and an important indicator of controls of magma formation and environment of deposition compositionally the nondweni lavas are broadly similar to those of the barberton sequence high values for cao al2o3 ti y and low al2o3 tio2 they are also distinctly different in that sio2 content is markedly higher and incompatible trace element ratios are also different the high silica content has promoted the subdivision of komatiitic and basaltic rocks into the following categories komatiite komatiitic andesite komatiitic basalt basalt and basaltic andesite the recognition of the distinct suite of komatiitic andesites is aided by the lower zr ti ratios than those lithologies of equivalent mgo content reported from other greenstone belts and sio2 contents as high as 58 these characteristics suggest similarity to recent high mg andesites none of the lava compositions exceed 23 mgo anhydrous and pyroxene rather than olivine dominates the crystallization assemblage olivine spinifex textures are entirely absent in the nondweni greenstone belt and instead pyroxene or amphibole after pyroxene spinifex is abundantly developed and is characterised by spectacular radial conical structures which have their apices towards the tops of the flow units some of the spinifex cone structures attain heights of up to 6 m branching pyroxene crystals and feathery textured plagioclase typify the spinifex textures of the komatiitic andesites the common occurrence of coned and branching spinifex textures in a wide range of magma compositions indicates that these were controlled by thermal characteristics and depositional environment for the flow units rather than solely by composition this may have been facilitated by emplacement in shallow water rather than in deep water as envisaged for the onverwacht group of the barberton sequence shallow water depositional environments in the nondweni group are supported by sedimentary lithofacies well preserved pillow structures also show a wide range in textural forms sizes of pillows degree of welding of pillow margins development of hyaloclastite and formation of shelf structures formed by repeated filling of lava tubes are related to both compositional type as well as physical controls such as extrusion rate and nature of the substrate komatiites seldom form pillows and very large pillow formation is restricted to the komatiitic andesite lava type komatiite flow successions are typified by spinifex textured units as well as by massive and highly brecciated aphyric flow units unaltered pyroxene and plagioclase characterise some of the massive flow units and pillowed basalts of the witkop formation the present paper is the second part of a series on the nondweni greenstone belt part i wilson and versfeld 1994 describes the stratigraphy sedimentology mineralization and depositional environment there are strong of kaapvaal craton may have been different to that of the barberton greenstone belt a present day analogue to the nondweni tectonic setting may be an ensialic back arc basin adjacent to a continental margin

rare earth element fractionation during the precipitation and crystallisation of hydrous ferric oxides from anoxic lake water abstract an enrichment of light rare earth elements lree is characteristic for most of the acidic fe and so 4 rich pit lakes and groundwaters in the lignite mining area of lower lusatia germany one of these acidic lakes the pit lake rl 1223 has a strong thermal and chemical stratification the upper water layer 0 9 m shows ph values of about 3 during all seasons the monimolimnion 10 17 m of the lake is anoxic and has ph values of about 7 the rare earth element ree patterns of the upper lake water show enriched lree la n yb n 1 6 whereas the opposite patterns depletion of lree la n yb n 0 4 are found in the anoxic water of the monimolimnion experiments were conducted to observe the behaviour of ree during fe oxidation in water from the monimolimnion depth 14 m the sampled monimolimnion water was placed in plastic bottles and the changing water chemistry was observed for 40 weeks after sampling due to the initial anoxic conditions almost all fe precipitated in the investigated water and the ph value decreased from about 7 to 3 during the oxidation the fe precipitates are identified as ferrihydrite which is transformed into goethite within the oxidation process stable ph conditions ph 3 0 were reached after about 10 weeks of oxidation the original ree patterns of the investigated water are generally reflected in the fe precipitates collected at the beginning of the experiment as well as after up to 40 weeks of oxidation however in the corresponding water lree were temporally enriched with a maximum la n yb n ratio of 1 0 and a maximum la n sm n ratio of 2 3 after 6 weeks of oxidation time ph 3 8 4 9 although complex geochemical changes took place between the start and the end of the experiment ree patterns observed at these points in time are nearly identical these differences of the ree pattern can be explained by the sampling procedure the experimental findings can be transmitted to the mining dump aquifers of the study area where geochemical conditions comparable to the experimental oxidation time from 3 to 6 weeks are found and hydrous ferric oxides are precipitating groundwater passing through the mining dumps can preferentially desorb lree from the fe precipitates and display the typical lree enrichment and carry it to the epilimnion of the acidic pit lakes in lower lusatia

chemistry and mineralogy of precambrian paleosols at the base of the dominion and pongola groups transvaal south africa abstract we have studied alteration zones found between sedimentary rocks of the lowest proterozoic dominion and archean pongola groups and underlying granitic rocks transvaal south africa the alteration zones have a transitional lower boundary primary igneous minerals are gradually destroyed upward toward the contact with overlying sedimentary rocks ca mg na p and mn are progressively lost upwards in the zone the chemical and mineralogical variations and available stratigraphic evidence are all consistent with the interpretation that these zones are paleosols formed by precambrian weathering 2 8 3 0 ga ago after formation the paleosols underwent metasomatism and metamorphism sericite now present in the paleosols was probably formed by low temperature potassium metasomatism of original clays andalusite in the pre pongola paleosol was probably formed by metamorphism of original clays in impermeable zones which prevented groundwater flow and potassium metasomatism the dominion paleosol was investigated at three localities the effects of weathering were similar at the three sites except for the behavior of iron one site lost about 20 of iron whereas the other sites lost 75 and 80 of initial iron content the differences in iron loss may be due to variation in soil ventilation and diffusion of atmospheric gases as a function of grain size and topography variations in iron loss may be used to place some constraints on the composition of the precambrian atmosphere given constraints imposed by dominion paleosols overlying uraniferous conglomerates requirements for chemical weathering and the greenhouse effect and possible presence of non diffusing photochemical oxidants the partial pressures of oxygen and carbon dioxide gases probably are in the ranges po1 0 02 to 0 5 pal present atmospheric level and pco2 5 to 30 pal

rare earth element geochemistry of lake baikal sediment its implication for geochemical response to climate change during the last glacial interglacial transition sediments deposited on the bottom of lake baikal have contributed to the understanding of a long term environmental history of continents rare earth elements rees along with major elements and loss on ignition loi of baikal sediments were determined with the aim of evaluating their suitability for a new paleoenvironmental proxy our interest is concentrated on paleoenvironmental change during the last glacial interglacial transition lgit chondrite normalized ree patterns for baikal sediments show a similar variation to those for typical upper continental crustal materials three parameters of la yb n n chondrite normalized value ratio sree tio2 and eu anomaly were used to express detailed characteristics of baikal sediments depth profile of la yb n ratio shows abrupt change whose timing corresponds to the beginning of climatic warming inferred from the profiles of sio2 tio2 and loi in addition la yb n ratio sree tio2 and the degree of eu anomaly correlate with each other this suggests that inflow process of particulate materials into the lake may have changed during the lgit the analytical results of this study lead to the conclusion that ree is a useful paleoenvironmental proxy in the baikal region r 2007 elsevier ltd all rights reserved

the late archean to mesoproterozoic major unconformity bounded units of the kaapvaal province of southern africa reply abstract the late archean to mesoproterozoic 3 1 1 4 ga sedimentary and volcanic successions in the kaapvaal province of southern africa previously have been subdivided into numerous lithostratigraphic units that generally were believed to have been deposited in local or regional basins however these lithostratigraphic units are remnants of thirteen unconformity bounded sequences or units 10 3 m thick with composite strike lengths of 250 1100 km and with durations of 10 7 to 10 8 yr all of these units rest somewhere on the crystalline basement the stratotypes but not the full geographic extents of these sequences from the base upward are the dominion group west rand group of the witwatersrand supergroup central rand group of the witwatersrand supergroup klipriviersberg group of the ventersdorp supergroup platberg group of the ventersdorp supergroup pniel group of the ventersdorp supergroup black reef quartzite formation and chuniespoort group of the transvaal supergroup pretoria group of the transvaal supergroup and the interval represented by the dullstroom formation rooiberg group and the loskop formation three or more major unconformity bounded units occur in younger proterozoic rocks in the kaapvaal province but are not definitive of it two occur in the soutpansberg group and one is most of the waterberg group some of these unconformity bounded units are remarkably similar to phanerozoic cratonic and miogeoclinal sequences they are the natural building blocks for reconstructing archean and proterozoic depositional basins plate tectonic events continents and a provincial time scale

global time scale and regional stratigraphic reference scales of central and west europe east europe tethys south china and north america as used in the devonian carboniferous permian correlation chart 2003 dcp 2003 the boundaries of the devonian carboniferous and permian stages of the global stratigraphic reference scale abbreviated to global stratigraphic scale gss are described in relation to the biostratigraphic and or lithostratigraphic units of the regional stratigraphic reference scales abbreviated to regional stratigraphic scales rss of central and west europe east europe tethys south china eastern tethys and north america in their type regions the boundaries of gss units rarely coincide with those of homonymous rss units moreover the definitions of some rss units have changed several times over the last decades and subsequent misunderstanding of the stratigraphical significance of these changes has often introduced errors into proposed global correlation charts the stratigraphic framework proposed in our global devonian carboniferous permian correlation chart 2003 dcp 2003 devonian carboniferous permian correlation chart 2003 menning m schneider j w alekseev a s amon e o becker g von bitter p h boardman d r bogoslovskaya m braun a brocke r chernykh v chuvashov b i clayton g dusar m davydov v i dybova jachowicz s forke h c gibling m gilmour e h goretzki j grunt t a hance l heckel p h izokh n g jansen u jin y g jones p kading k ch kerp h kiersnowski h klets a klug ch korn d kossovaya o kotlyar g v kozur h w laveine j p martens th nemyrovska t l nigmadganov a l paech h j peryt t m rohn r roscher m rubidge b schiappa t a schindler e skompski s ueno k utting j vdovenko m v villa e voigt s wahlman g p wardlaw b r warrington g weddige k werneburg r weyer d wilde v winkler prins c f work d m 2004 abschlusskolloquium dfg schwerpunktprogramm 1054 evolution des systems erde wahrend des jungeren palaozoikums im spiegel der sedimentgeochemie abstracts univ erlangen germany 2004 p 43 herein abbreviated to dcp 2003 and cited as dcp 2003 in references is an attempt to reduce these errors the dcp 2003 is the stratigraphic base for project 1054 of the deutsche forschungsgemeinschaft dfg the evolution of the late palaeozoic in the light of sedimentary geochemistry this composite time scale has been carefully balanced as far as data allows to remove unnecessary artificial compression and expansion of time intervals biozonations and depositional events the ages selected in dcp 2003 are markedly different to those in the geologic time scale 1989 gts 1989 harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge pp 1 263 and in gradstein and ogg gradstein f m ogg j 1996 a phanerozoic time scale episodes 19 1 2 3 4 insert whereas they are closer to those of the geologic time scale 2004 gts 2004 gradstein f m ogg j g smith a g 2004 a geologic time scale 2004 cambridge univ press cambridge pp 1 589 mostly the ages are rounded to the nearest 0 5 ma in order to avoid estimates of questionable accuracy whereas ages of 0 1 ma in the gts 2004 and their error bars of 0 4 ma to 2 8 ma for the devonian to permian stage boundaries suggest an improved accuracy in contrast in the dcp 2003 questionable ages and positions of stratigraphic boundaries are marked by arrows c 2006 elsevier b v all rights reserved

late eocene clay boron derived paleosalinity in the qaidam basin and its implications for regional tectonics and climate abstract the qaidam basin located on the northeastern tibetan plateau and containing cenozoic sediments with a maximum thickness of 12 000 m is an ideal place to study the phased uplift of the ne tibetan plateau and regional climate change the estimation of the paleosalinity of sedimentary environments not only helps to evaluate the evolution of lakes in this region but offers insights into contemporaneous climate change we present detailed geochemical and mineralogical investigations from the lacustrine interval of the hongliugou section in the northern qaidam basin to reconstruct salinity fluctuations in the paleolake during the late eocene era 42 0 35 5 ma the clay mineral assemblages mainly contain smectite illite chlorite kaolinite and irregular illite smectite mixed layers clay boron derived paleosalinity estimates equivalent boron content couch s paleosalimeter and b ga ratios along with other proxies sensitive to salinity changes e g rb k ratios and ostracod assemblages collectively indicate an overall brackish sedimentary environment with a higher salinity period at approximately 40 0 39 2 ma this higher salinity period indicates a more arid environment and is probably related to global cooling however the global cooling in late eocene cannot explain the overall stable long term salinity pattern implying that other factors exist we propose that the migration of the yiliping depression depocenter in the northern qaidam and increased orographic rainfall induced by late eocene tectonic activity at the northern margin of the basin might have partly offset the increase in salinity driven by global cooling

palaeogeographic and palaeoclimate factors of salinity fluctuations in the eastern part of the late permian zechstein european basin case study from the salt basin in poland

sandstone composition and provenance of the rotliegend of the ne german basin abstract the ne german basin contains an approximately 2 5 km thick rotliegend sedimentary section subdivided into 4 formations these were deposited following the cessation of the late carboniferous early permian volcanic episode and a ca 20 ma period of erosion and non deposition initial deposition was confined to two areas but with increasing thermal subsidence the basin extended to the south petrographic 190 sandstones and geochemical 48 sandstones and mudstones analyses suggested that the sands are quartz rich and are derived largely from cratonic or recycled sources volcanic and sedimentary rock fragments form most of the labile grains the succession was deposited in a relatively stable tectonic environment with sediment input derived largely from the lower and upper palaeozoic strata of the variscan hinterland and the upper carboniferous and lower permian volcanics volcanic input increases with younger stratigraphic units this is interpreted as resulting from the unroofing of a more basic source

delivery of upper basin sediment to the lower neuse river north carolina u s a extensive storage of upper basin piedmont sediment and apparent low sediment supply to streams in lower basin coastal plain areas generates questions as to the source of alluvium in lower reaches of rivers of the u s atlantic drainage this was investigated on the neuse river north carolina using a mineralogical indicator of sediment source areas the utility of mica flakes for discriminating between piedmont and non piedmont sources of sediment in the lower coastal plain reaches of the neuse was established on the basis of an examination of the u s national soils database and of 26 soil surveys of the north carolina coastal plain from the neuse river estuary to 48 km upstream there are no mica flakes in floodplain soils or in river bank and channel shelf sediments mica flakes become more common upstream this suggests that a very small proportion of the sediment eroded in the piedmont portion of the watershed is delivered to the river mouth the small amounts which presumably do reach the lower coastal plain are so diluted by coastal plain derived alluvium that no piedmont origin can be discerned this demonstrates a dominantly coastal plain source and underscores the importance of storage and discontinuous transport in fluvial sediment systems more importantly results suggest that upper and lower basin sediment dynamics are not only non linearly related but may be virtually decoupled

interactions between upland catchment and lowland rivers an applied australian case study abstract persistent allegations have been made mainly by victorian farmers that channel and floodplain aggradation are occuring on the floodplain of the snowy river in victoris as a consequence of a accelaerated erosion of degraded agricultural land in parts of the new south wales upland catchment these claims prompted the victorian department of water resources to initiate geomorphological investigations involving reviews of historical evidence including the squential aerial photographs and a study of sediment sources based on environmental tracers a qualitative approach set within a sediment budget framework was adopted for data integration a detailed quantitative analysis being precluded by financial temporal and practical constrainsts no compelling evidence was found to support claims of recent channel aggradation in the downstream snowy river transfer of sediment eroded from catchment slopes in nsw to the lowland floodplain in victoria is indirect with some sediments stored temporarily in fans and floodplains within tributary catchments and in the snowy valley for long delay times storage and interbasin transfer of water as part of the snowy mountains scheme have affected sediment delivery the catchment upstream of lake jindabyne is effectively isolated by this large impoundment and sediment transport rates as far downstream as the delegate river junction appear to have significantly decreased as the result of the considerable reduction in discharge

permian climate development in the northern peri tethys area the lodeve basin french massif central compared in a european and global context abstract the lodeve basin which contains an exceptional long and nearly uninterrupted profile of early to late permian continental red beds is well correlated to the other european permocarboniferous basins together they cover the time span from the late pennsylvanian to the permian triassic boundary although these basins were placed within the equatorial belt for the whole permian several climatic changes are recorded in the sediments terrestrial sedimentation is governed by the interaction of climate and tectonics as well as by volcanism to a variable degree therefore small scale climatic variations of the milankovitch band are hardly discernable and if so they could not be correlated between different basins indeed larger scale climatic shifts could be identified it is shown that the shift from the carboniferous icehouse to the mesozoic warmhouse was a multi stage process this global warming resulted in a general aridisation of northern pangea indicated by outspreading playa and sabkha red beds aeolianites and evaporites several short phases of increased humidity interrupted this trend indicated by wet red beds lake sediments and coal deposits in central and southern europe these wet periods are traceable within the late stephanian lower rotliegend gzhelian asselian topmost lower rotliegend asselian sakmarian upper rotliegend i late artinskian early kungurian and upper rotliegend ii zechstein wuchiapingian the aridisation of the northern pangea which accelerated near the sakmarian artinskian transition is attributed to a reorganisation of the major ocean currents cold water currents along the western flank of the pangea indicated by the permian chert event blocks moisture transport from west onto the continent during roadian and wordian the onset of an additional cold water current along the cimmerian continents blocks moisture transport from the east both phenomena together are responsible for the maximum of aridity at the early to middle permian transition additionally the equatorial climate has been affected by an increasing seasonality within the late pennsylvanian and permian caused by the wide shifting of the zone of inter tropical convergence itc over the equator based on a new reconstruction of the pangean assembly in this paper climatic changes in the permian are interpreted and causes of the arid humid arid shifts are examined phases of higher humidity are often related to events of global impact like the waxing and waning of the gondwanan glaciation obtained in the south african karoo basin dwyka group but also regional events had strong climatic influence the zechstein transgression in the northern and southern permian basin as well as the bellerophon transgression of the southern alps caused the wet phase in the wuchiapingian

paleolake salinity evolution in the qaidam basin ne tibetan plateau between 42 and 29 ma links to global cooling and paratethys sea incursions abstract climate change in the asian interior during the early cenozoic remains poorly constrained due to difficulties in distinguishing the impacts of global cooling the early uplift of the tibetan plateau and the retreat of the paratethys a quantitative estimation of paleolake salinity enables a better understanding of the regional hydrological cycle and contemporaneous climate change here we present a quantitative record of paleolake salinity in the qaidam basin between 42 and 29 ma using detailed mineralogical investigations and clay boron content data this paleolake salinity record generally covers a tectonically less active period in the asian interior characterized by continuous global cooling the abrupt eocene oligocene climate transition and the paratethys transgression regression cycles thus offering an opportunity to explore the roles of global cooling and the paratethys retreat in regulating the regional hydrological cycle the results of two boron derived paleosalimeters equivalent boron and couch s salinity collectively indicate a two stage paleolake salinity evolution from an oligohaline mesohaline environment in the middle late eocene 42 34 ma to a mesosaline environment in the early oligocene 34 29 ma this transition is also supported by qualitative chloride based and ostracod based paleosalinity estimates in the qaidam basin our quantitative paleolake reconstruction between 42 and 29 ma in the qaidam basin yields a generally good match with the hydroclimate change in the neighboring xining basin thus indicating a comparable regional drying trend the synchronous changes in quantitative paleolake salinity and silicate weathering processes derived from the illite weathering index and chlorite content in the studied section suggest climate control of silicate weathering global cooling is speculated to have been the first order driving factor in regulating long term climatic evolution and weathering responses in the asian interior between 42 and 29 ma superimposed on this trend the paratethys transgression regression cycles served as an important factor regulating wet dry fluctuations in the asian interior between 42 and 34 ma

an andesitic sill complex in the southern permian basin volcanogenetic model and stratigraphic implications subvolcanic intrusions are highly variable in shape and structure and occur in nearly all parts of the upper crust as a result of extensive volcanic activity processes of subvolcanics interacting with the host rock are insufficiently understood as they are rarely exposed in the southernmost part of the flechtingen altmark subprovince sub volcanic rocks of the flechtingen volcanic complex fvc are exposed in several quarries it is built up of silicic tuffs ignimbrites and lava flows but also of intermediate lavas and extended sill sheets additionally major granitic intrusions exposed by drillings are associated with the fvc in the mammendorf quarry a sill intruded in between lithified turbiditic series of early carboniferous visean serphukovian age at the base and widely consolidated volcanoclastic deposits of late carboniferous late pennsylvanian age at the top various magma host rock interactions were found indicating brittle and ductile deformation patterns occurring at the basal contact and secondary fluidal mixing predominantly occurring at the top contact most probably caused by fluids accompanying the intruding magma we present an extended volcanogenetic model for the fvc volcanic activity initiated at 302 3 ma with fallout deposits represented by mostly re deposited silicic ashfall deposits of the flechtingen formation and cumulated in depositing major ignimbrite series most likely forming a caldera later the sills intruded at the rheological boundary of the lithified mississippian turbiditic series and the partly consolidated volcanoclastic series finally major granitic intrusions emplaced in the basement rocks at around 298 4 ma the study contributes to clarify stratigraphic constraints of late carboniferous to early permian continental deposits and sheds light on stratigraphy of significant late paleozoic volcanic deposits of the flechtingen altmark subprovince in the southern permian basin

geochemistry and provenance of sediments from the pongola supergroup south africa evidence for a 3 0 ga old continental craton abstract the 3 0 ga pongola supergroup of south africa is one of the oldest well preserved supracrustal successions the sequence is divided into the nsuze chiefly volcanics quartzites and pelites and the overlying mozaan groups chiefly quartzites and pelites relative to north american shale composite nasc most pongola pelites have similar la yb and eu eu ratios and large ion lithophile elements lile high field strength elements hfse ree v and sc contents ni 30 300 ppm and cr 100 800 ppm contents are greater than those of nasc while cr ni ratios are generally higher than shales and pelites of all ages these trends may reflect residual cr enrichment during intense chemical weathering of komatiitic source rocks local populations of nsuze pelites based on major and trace element data may result from source heterogeneities and or contemporaneous volcanic input into the sedimentary basin pongola quartzite compositions and detrital modes are similar to those of sandstones from phanerozoic passive margin and basement uplift tectonic settings ree lile and hfse contents in pelites suggest that pongola source rocks were remarkably similar in composition to average phanerozoic upper continental crust trace element geographic and isotopic constraints favor 3 2 to 3 0 ga hood granites as a major source for pongola detritus moderate contributions from mafic sources are also required whereas relatively minor contributions from tonalite and komatiite are allowed these results indicate the existence of a chemically evolved felsic craton in southern africa by 3 0 ga this craton appears to have been more evolved than sources for either older moodies 3 3 ga or most of the younger witwatersrand sediments 2 8 2 7 ga pelites from the kaapvaal craton record at least two mafic to felsic source area compositional cycles in pelites deposited from the mid to late archean additional cycles may be masked by a depositional or erosional hiatus between the moodies and pongola sequences these sedimentary patterns suggest that crustal development in southern africa was episodic in nature during the early precambrian

cumulative effects of channel correction and regulation on floodplain terrestrialisation patterns and connectivity abstract one of the main drivers of overbank fine deposition and floodplain formation is the hydrological connectivity between the channel and the floodplain channel correction i e groyne field construction within the main flow channel and secondary channel disconnections and flow regulation can typically lead to a disconnection of riverine floodplains and disturbances that directly affect terrestrialisation channel correction and flow regulation can sometimes occur successively and it is challenging to distinguish the roles of each this work attempts to assess the respective effects of two phases of channel regulation correction versus flow regulation on floodplain terrestrialisation by comparing three bypassed reaches of the rhone france pierre benite peage de roussillon and donzere mondragon we applied a transversal methodology coupled with gis analysis old maps orthophotos dem s etc to understand processes of channel planform evolution conducted a sediment survey metal rod to assess floodplain terrestrialisation and performed sediment sampling manual auger to obtain surface sediment metal content levels x ray fluorescence and inductively coupled plasma mass spectrometry we found a general trend of channel narrowing within the three reaches among which approximately 40 was found to be associated with correction works while 20 was attributed to flow lowering caused by channel bypassing the number of flowing channels in all sections declined significantly and local anabranching reaches evolved into very stable single thread channels overbank sedimentation declined significantly over the period with very high sedimentation levels observed immediately after correction works and with very low sedimentation levels observed after diversion we also found overbank flooding in the number of days per year decreased while fine sediment thickness increased similarly the highest concentrations of metals zc pb and cu were found to be associated with a low connection frequency and vice versa when similar 2 staged terrestrialisation patterns are observed in all three reaches they differ in chronology and driving factors because of their longitudinal positioning and specific local conditions

relationships among vertical accretion coastal submergence and erosion in a louisiana gulf coast marsh abstract vertical accretion in a southwest louisiana spartina patens brackish marsh has not kept pace with coastal submergence during the past three decades the rate of accretion determined from 137cs dating and the use of artificial marker horizons averaged 0 8 cm yr 1 whereas coastal submergence obtained from tide gauge data averaged 1 2 cm yr 1 conversion from marsh to open water bodies closely paralleled the increase in coastal submergence if the resulting aggradation deficit continues the marsh will likely complete its transformation to an open bay in less than 40 years in view of recent projections of increasing sea level rise the results presented may foreshadow a more widespread phenomenon

stratigraphy and petrology of the archaean nsuze group northern natal and southeastern transvaal south africa abstract the nsuze group is the lower dominantly volcanic division of the pongola supergroup that accumulated on a sialic basement between 3 1 and 2 9 ga the nsuze group is subdivided into a lower sedimentary unit 800 m thick a middle volcanic unit 7500 m thick and an upper volcaniclastic sedimentary unit 5 600 m thick the predominant sediments in the lower unit are immature medium to very coarse grained quartz wackes with thin intercalated lenses of quartz and arkosic arenites and minor conglomeratic wackes these sediments were deposited in a distal braided stream environment there followed a major period of volcanism during which lavas showing a continuous spectrum of compositions from basalt to rhyolite were extruded subaerially flows of both different and similar compositions are complexly interfingered on both regional and local scales as volcanism waned pyroclastic and sedimentary rocks became dominant in the upper unit the nsuze group is gently dipping and is metamorphosed to low greenschist grade the nsuze group is significant in that it provides evidence for the existence of high standing continental sialic crust in the southeastern part of the kaapvaal province at ca 3 0 ga volcanism and sedimentation in the pongola supergroup are more typical of proterozoic basins than of archaean environments despite their age komatiitic and high mg basalts were however being extruded in zimbabwe contemporaneously with the nsuze lavas

u pb and hf isotopes of detrital zircons from the pongola supergroup constraints on deposition ages provenance and archean evolution of the kaapvaal craton abstract the c 3 0 2 9 ga pongola supergroup located on the south eastern margin of the kaapvaal craton preserves some of the most pristine archean successions but the timing of volcanic and sedimentary processes and sediment sources remain relatively poorly known combined zircon u pb ages and hf isotope data of sandstones from the nsuze and mozaan groups are presented from key locations of the northern central and southern domains of the 270 km long belt these data indicate important lateral and temporal variations and therefore changes in source areas the basal pongola sedimentary rocks mantonga formation in the northern domain were derived from the c 3 4 ga basement and also most likely from reworked moodies group sedimentary rocks of the barberton greenstone belt zircon detritus in nsuze and lower mozaan groups sandstones shows similar age hf isotope spectra and a remarkable overlap with data from magmatic and meta sedimentary rocks of the southeastern kaapvaal craton the data point to a proximal source for nsuze sandstones in the northern domain and a different provenance for the southern domain sandstones a possible signature of the extensive 3 10 3 07 ga mpuluzi granite is seen only in the nsuze sandstones and basal mozaan of the central domain the data indicate for the first time that cr rich sandstones of the ndikwe thrust segment of the southern domain were deposited at

surface and subsurface sedimentary structures produced by salt crusts the growth and subsequent dissolution of salts on or within sediment may alter sedimentary structures and textures to such an extent that it is difficult to identify the depositional origin of that sediment and as a result the sediment may be misinterpreted to help to overcome such problems with investigating ancient successions results are presented from a comprehensive study of the morphology and fabrics of three large areas of modern salt flats in se arabia the sabkhat matti inland region and the at taf coastal region both in the emirate of abu dhabi and the umm as samim region in oman these salt flats are affected by tidal marine alluvial and aeolian depositional processes and include both clastic and carbonate dominated surficial sediments the efflorescent and precipitated salt crusts in these areas can be grouped into two main types thick crusts with high relief 10 cm and a polygonal or blocky morphology or thin crusts with low relief 10 cm and a polygonal or blister like appearance the thin crusts may assume the surface morphology of underlying features such as ripples or biogenic mats a variety of small scale textures were observed pustular growths hair like spikes and irregular wrinkles evolution of these crusts over time results in a variety of distinctive sedimentary fabrics produced by salt growth sediment deformation salt solution sediment collapse sediment aggradation and compound mixtures of these processes salt crust processes produce features that may be confused with aeolian adhesion structures an example from the lower triassic ormskirk sandstone formation of the irish sea basin demonstrates how this knowledge of modern environments improves the interpretation of the rock record a distinctive wavy laminated facies in this formation had previously been interpreted as the product of fluvial sheetfloods modified by soft sediment deformation and bioturbation close inspection of laminations seen in core reveals many of the same sedimentary fabrics seen in se arabia associated with salt crusts this facies is the product of salt growth on aeolian sediment and is not of fluvial origin

where do coastlines stabilize following rapid retreat we present a numerical model that shows that the transgressing upper shoreline of wave dominated estuaries bayhead deltas which commonly contain populous urban and industrial centers stabilizes and their rate of retreat decreases at tributary junctions the decreased rate of retreat across a tributary junction is caused by a decrease in the total accommodation while sediment supply remains conserved our model predicts that bayhead deltas from smaller systems will be located closer to tributary confluences than their larger counterparts an examination of the modern bayhead deltas in albemarle sound u s atlantic coast reveals that bayhead deltas from smaller tributaries are located closer to tributary confluences than bayhead deltas associated with larger tributaries supporting our model prediction our results highlight the importance of antecedent topography created during falling sea levels on shaping the nature of transgression during the ensuing sea level rise in particular tributary junctions act as pinning points during transgression

coastal land loss in texas an overview abstract nearly 1 500 acres of prime coastal real estate and productive wetlands are destroyed each year in texas along the gulf shoreline near bay margins and within alluvial valleys primarily as a result of erosion and submergence wetland losses constitute about 75 of the total land losses historical analyses of maps and aerial photographs indicate that land losses are accelerating and that human activities are either directly or indirectly responsible for the increased losses natural decreases in sediment supply have been exacerbated by 1 river basin projects that reduce the volume of sediment transported to the coast and 2 coastal structures and navigation projects that prevent redistribution of littoral sediments along the coast erosion caused by high wave and current energy and an inadequate supply of sediment is responsible for higher local rates of land loss than submergence erosion losses are also more perceptible especially after major storms when the greatest losses occur boat traffic causes substantial erosion along some navigation channels the principal components of submergence are subsidence and the eustatic rise in sea level submergence converts uplands to wetlands and wetlands to open water these surficial changes occur mostly on the coastal plain but are also observed on barrier islands on bayhead deltas and within entrenched valleys recent accelerated submergence is induced by extraction of shallow ground water or production of hydrocarbons at moderate depths faults activated by the withdrawal of these fluids concentrate the subsidence near fault planes coastal land losses directly caused by dredging marinas subdivisions canals rig locations are less than those caused by erosion and submergence but they constitute a growing percentage of total land losses in texas