rapid flooding of the southern vietnam shelf during the early to mid holocene a new sea level record derived from coastal deposits of the south vietnam shelf covers the deglacial sea level history between 13 0 and 9 0 ka bp this record reveals a relatively constant rate of sea level rise and matches well with model results based on the rses anu global ice sheet model however the sea level observations reveal a significant discrepancy with model results based on the ice 5g global ice sheet model which further questions the existence of meltwater pulse 1b the incised valley deposits of the south vietnam shelf also complete the deglacial coastal evolution of southern vietnam the regional sea level records of the south vietnam shelf the mekong delta and the cambodian lowlands reveal an offset of about 18 m between 9 0 and 8 2 ka bp the shoreline retreat of more than 200 km related to this offset was mainly caused by the differential hydro isostatic adjustment between the south vietnam shelf and the cambodian lowlands however the gia model results cannot fully explain this fast relative sea level rise due to the topographic changes and possibly alternative melt water sources not accounted for in the current models copyright c 2014 john wiley sons ltd

multi centennial scale sst and indian summer monsoon precipitation variability since the mid holocene and its nonlinear response to solar activity indian summer monsoon ism shows a weak correlation with solar variability in the 20th century however such climatological observations on solar activity monsoon relationship are very short and

structural evolution and tectonic setting of the porongos belt southern brazil the sw ne striking porongos belt located between juvenile neoproterozoic rocks in the west and the dom feliciano belt characterized by intense reworking of older crust in the east comprises a greenschist to amphibolite facies metavolcano metasedimentary succession porongos sequence of unknown age with some exposures of palaeoproterozoic gneisses encantadas gneisses high temperature ductile deformation of the basement gneisses comprises at least two magmatic events followed by three deformational phases including folding and shearing dt1 dt3 and can be attributed to the palaeoproterozoic trans amazonian orogeny the deformation of the porongos sequence occurred during the neoproterozoic brasiliano orogeny and comprises four ductile deformation phases db1 db4 including two phases of isoclinal folding associated with shearing recorded in mylonitic layers followed by closed nw vergent folding and thrusting leading to formation of a thrust stack uplift of the basement and formation of late tectonic sedimentary basins occurred as a result of semi ductile to brittle block faulting in a sinistral strike slip regime the porongos sequence can be subdivided into a southeastern and a northwestern part trace element analyses as well as sm nd and rb sr geochemical data indicate partial melting and significant contamination by old continental crust for the metavolcanic rocks the metavolcanic rocks show end t 780 ma values of 20 64 and 21 72 northwestern units and 6 87 southeastern sequence the metasedimentary rocks were derived from late palaeoproterozoic to archaean sources and the data indicate different sources for the northwestern and southeastern rock units of the porongos sequence end t 780 ma are 6 25 and 6 85 in the southeastern units with tdm model ages between 1734 and 1954 ma and vary between 14 72 and 17 96 in the northwestern parts which have tdm model ages between 2346 and 2710 ma high 87 sr 86 sr t values between 0 7064 and 0 7286 confirm reworking of older crust isotopic signatures of the porongos sequence do not show indications for a significant contribution from a neoproterozoic juvenile source a passive margin or continental rift environment is suggested for the tectonic setting of the porongos belt which is compatible with both deposition of shallow marine to deep marine sediments and stretching of continental crust leading to volcanism which is characterized by significant contamination by old continental crust

zircon and titanite recording 1 5 million years of magma accretion crystallization and initial cooling in a composite pluton southern adamello batholith northern italy abstract the southern part of the adamello batholith the so called re di castello unit is an example of a composite pluton ranging from gabbro to granodiorite in composition u pb dating of single zircon crystals from four tonalitic to granodioritic lithologies reveals that zircon crystallization is protracted in all studied lithologies showing apparent durations of growth between 90 and 700 ka the youngest zircons crystallized near the solidus and yield identical or slightly older ages than titanite the formation of these autocrystic zircons is considered to approximate the age of emplacement of the melt and its final crystallization in contrast to antecrystic zircons present in the same sample which had formed earlier in the magmatic column or were derived from re mobilized earlier magma the autocryst derived emplacement ages range from 42 43 0 09 ma to 40 90 0 05 ma recording 1 5 ma of intrusion and crystallization history we anticipate that extended periods of zircon crystallization may be common in silicic rocks whereas the zircons from residual melts from initially undersaturated mafic liquids should yield far more precise emplacement ages within our present analytical uncertainties of 0 1 0 2 in 206 pb 238 u age decreasing th u ratios of dated zircons within one melt batch document the depletion of the residual melt portion in th due to the contemporaneous crystallization of titanite preliminary hf isotopic compositions of the dated zircon grains suggest that the early stage melts of the southern re di castello unit represent hybrid melts with an important crustal component e hf between 2 8 and 3 0 subsequently emplaced melts are more juvenile at e hf values at 6 4 to 8 9 and may thus reflect the addition of large volumes of mafic melt to the magmatic system

the transpressional connection between dom feliciano and kaoko belts at 580 550 ma a new u pb shrimp age of 551 4 ma on a mylonitic porphyry that intruded into the sierra ballena shear zone southernmost dom feliciano belt uruguay and a review of relevant published data make possible a more refined correlation and reconstruction of brasiliano pan african transpressional events paleogeographic reconstruction kinematics and timing of events indicate a connection between the shear systems of the dom feliciano and kaoko belts at 580 550 ma sinistral transpression recorded in shear zones accommodates deformation subsequent to collision between the congo and rio de la plata cratons the correlation is strengthened by the similarity of magmatic and metamorphic ages in the coastal terrane of the kaoko belt and the punta del este terrane of the dom feliciano belt this post collisional sinistral transpression brought these units near to their final position in gondwana and explains the different evolution at 550 530 ma while in the kaoko belt an extensional episode resulted in exhumation as a consequence of collision in the damara belt in the dom feliciano belt sinistral transpression occurred associated with the closure of the southern adamastor ocean due to kalahari rio de la plata collision

should felsic magmas be considered as tectonic objects just like faults or folds abstract integrated studies that correlate gravity data with magmatic structures or geochemical analysis reveal that the organization of granitic plutons shape and feeder varies according to the tectonic regime brittle or ductile and type extension strike slip or compression under which magma was generated deformation clearly controls granite emplacement it also has influence during the ascent segregation of melt and indirectly during the phase of initial melting because of the contrast of viscosity between melt and its plastic matrix strain partitioning develops during magma ascent that facilitates melt flow which bears consequences for the chemical evolution of the magma fast rate of melt extraction out of the source may lead to chemical disequilibrium at a larger scale petrochemical zoning of plutons is described as a dynamic process that results from the competition between the rate of magma emplacement the rate of the room provided by deformation and the rate of magma delivery

hafnium isotopic heterogeneity in zircons from granitic rocks geochemical evaluation and modeling of zircon effect in crustal anatexis abstract we carried out a geochemical evaluation and modeled the mechanism responsible for varied hf isotopic ratios in magmatic zircons of a single granitic rock specimen five representative granitic samples were selected from southern china based on preliminary hf isotopic data our new dataset of zircon hf isotopes confirmed significant hf isotope variations 5 9 epsilon units for each sample and these zircons show roughly positive th u versus t crystallizing temperature correlations while the lu hf variation is independent from t in addition some zircons show significantly higher ti concentrations in the rims compared to the interiors implying reverse thermal zonation based on the ti in zircon thermometry these geochemical features in zircons suggest open system processes which may have resulted from frequent replenishment we modeled zircon dissolution during crustal anatexis to reveal the hf isotopic evolution in the extracted melts the model suggests that the extracted melts may have extremely variable hf isotope compositions 20 epsilon units if the bulk zr concentration in the source is initially above 100 ppm and the melting is rapid 10 4 yr 1 the decoupled release of zircon hf and non zircon hf from a single crust derived magma source can lead to significant hf isotope variations in a solidified granitic body this work provides an alternative explanation for the hf isotopic heterogeneity in magmatic zircons of granitic rocks which is in contrast to the common interpretation by mixing with mantle derived magmas

effects of rock fragments on soil erosion by water at different spatial scales a review this paper reviews the various effects of rock fragments on soil erosion by water since these effects are scale dependent they are investigated at three different nested spatial scales the microplot 4 10 6 100m2 the mesoplot 10 2 102 m2 and the macroplot 101 104 m2 for each scale the corresponding process mechanisms are discussed particular attention is paid to the effects of rock fragment cover on the intensity of soil erosion processes at the mesoplot scale i e on interrill areas rock fragments at the soil surface can have negative as well as positive effects on sediment yield these ambivalent effects are conditioned by the type of fine earth porosity soil surface slope vertical position and size of rock fragments and by the occurrence of horseshoe vortex erosion at the microplot scale i e the soil surface area which is covered by a single rock fragment and at the macroplot scale i e upland areas where both interrill and rill erosion takes place rock fragments at the soil surface have a negative effect on sediment yield in these two scales rock fragments can thus be considered as natural soil surface stabilizers at the macroplot scale the mean decrease of relative interrill and rill sediment yield with rock fragment cover can be expressed by an exponential decay function the scatter of the data indicates that a given rock fragment cover can have different efficiencies in reducing interrill and rill sediment yield depending on the varying intensities of the hydrological and erosion subprocesses these findings have implications for erosion modelling and soil conservation

punctuated eustatic sea level rise in the early mid holocene whether eustatic sea level rise through the holocene has been punctuated or continuous has remained controversial for almost two decades resolving this debate has implications for predicting future responses of remaining ice sheets to climate change and also for understanding the drivers of human settlement and dispersal patterns through prehistory here we present a sea level curve for the past 8900 yr from singapore a tectonically stable location remote from ice loading effects we also present critical and unique sedimentation rate organic 13c and foraminiferal 13c proxy records of sea level change derived from a shallow marine sediment core from the same area over the same time interval the sea level curve corroborated by the independent proxy records suggests rapid rise at a rate of 1 8 m 100 yr until 8100 cal calibrated yr b p a near cessation in the rate of sea level rise between 7800 and 7400 cal yr b p followed by a renewed rise of 4 5 m that was complete by 6500 cal yr b p we suggest that this period of relatively stable sea level during the early to mid holocene enabled modern deltas to advance providing a highly productive environment for the establishment of coastal sedentary agriculture periods of rapid sea level rise before and after may have catalyzed significant postglacial episodes of human dispersal in coastal regions

holocene climate change in the western part of taihu lake region east china abstract the taihu lake basin is one of the most sensitive areas to climate change in the east asian summer monsoon easm influenced region there are significant differences regarding the interpretation of climate history for this area during the holocene due to a lack of high resolution paleoclimate records to better understand this scientific issue here we provide a new record of holocene climate change from the western part of taihu lake region east china a 4 m depth profile from gaochun has provided a 13 200 year record of climate change holocene climate change was reconstructed for the western part of taihu lake area based on various proxy records including pollen charcoal degree of humification doh and loss on ignition loi from the gaochun site the results indicate that climate during the late pleistocene 13 200 10 700 cal yr b p and early holocene 10 700 8000 cal yr b p was warm and humid alternated with several cold and dry intervals the late pleistocene and early holocene was a transitional period from cold dry to warm wet climates the middle holocene 8000 4400 cal yr b p was still warm and humid with a relatively stable climate the period between 8000 and 5300 cal yr b p was the holocene climate optimum hco during the late holocene 4400 0 cal yr b p the climate was cool but still humid in addition climate change at the western part of taihu lake during the late pleistocene and holocene was unstable containing several short term climate events such as younger dryas yd 8 2 ka and 4 2 ka events these abruptly occurred climate events were indicated by various paleoclimatic proxy indicators and can be compared with related records from other regions our findings suggest that the easm strength was strongest during the middle holocene between 8000 and 5300 cal yr b p which can be depicted as the period of hco

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

a model of water and sediment balance as determinants of relative sea level rise in contemporary and future deltas abstract modern deltas are dependent on human mediated freshwater and sediment fluxes changes to these fluxes impact delta biogeophysical functioning and affect the long term sustainability of these landscapes for human and for natural systems here we present contemporary estimates of long term mean sediment balance and relative sea level rise across 46 global deltas we model scenarios of contemporary and future water resource management schemes and hydropower infrastructure in upstream river basins to explore how changing sediment fluxes impact relative sea level rise in delta systems model results show that contemporary sediment fluxes anthropogenic drivers of land subsidence and sea level rise result in delta relative sea level rise rates that average 6 8 mm y assessment of impacts of planned and under construction dams on relative sea level rise rates suggests increases on the order of 1 mm y in deltas with new upstream construction sediment fluxes are estimated to decrease by up to 60 in the danube and 21 in the ganges brahmaputra meghna if all currently planned dams are constructed reduced sediment retention on deltas caused by increased river channelization and management has a larger impact increasing relative sea level rise on average by nearly 2 mm y long term delta sustainability requires a more complete understanding of how geophysical and anthropogenic change impact delta geomorphology local and regional strategies for sustainable delta management that focus on local and regional drivers of change especially groundwater and hydrocarbon extraction and upstream dam construction can be highly impactful even in the context of global climate induced sea level rise

early holocene initiation of the mekong river delta vietnam and the response to holocene sea level changes detected from dt1 core analyses abstract the early holocene initiation of the mekong river delta vietnam was investigated based on sedimentary facies microfossil analyses and radiocarbon dating of dt1 core taken from the upper delta plain the dt1 core 105 38 51 e 10 17 02 n elevation 2 m is 51 5 m long and located in fill of a buried incised valley this incised valley of the paleo mekong river formed during the last glacial maximum which is 20 30 km wide has been traced spatially from the cambodian border to the south china sea coast by compilation of existing core data the dt1 core records the history of the estuarine channel and delta systems of the mekong river during the early to middle holocene the sedimentary facies determined particularly from sedimentary structures diatom and foraminifera assemblages grain size variation and the accumulation rate clearly show an upward deepening succession in the lower part of the core from marsh or intertidal flat to subtidal inner bay facies and an overlying upward shallowing succession from prodelta to intertidal flat floodplain the boundary between the two successions indicating the maximum flooding surface occurred at approximately 8 0 ka at the time that the mekong river delta was initiated the delta initiation and sediment facies succession are closely linked to holocene sea level changes particularly a standstill from 8 0 to 7 5 ka after a rapid rise of sea level from 8 8 to 8 2 ka during the further sea level rise from 7 5 to 7 0 ka sediments aggraded forming topset sedimentary deposits

syntectonic granite emplacement at different structural levels the closepet granite south india abstract the closepet granite in south india is a large 400 km long but only 30 km wide elongate late archaean granitic body structural levels from deep crust to upper levels crop out as evidenced by a shallowing of paleo depths from north to south all along the closepet granite this allows the study of the emplacement of the same granitic body at various crustal levels four zones have been identified a root zone where magmas are collected in active shear zones a transfer zone featuring large scale magma ascent and crystal liquid partitioning in the granitic mush a gap where the mush was filtered allowing only the liquids to rise shallow intrusions filled with this liquid the closepet granite was emplaced syntectonically field work and anisotropy of magnetic susceptibility allowed documentation of steep foliations with subhorizontal lineations both in the root and transfer zones and in the shallow intrusions remote sensing evidenced a network of shear zones bounding the closepet granite in the porphyritic root and transfer zones magmas cooled slowly thus developing strong fabrics during large scale dextral shearing ascent of residual liquids amidst the crystallizing solid framework was not recorded in the fabrics however these liquids were channelised through the gap and infilled the homogeneous shallow intrusions where rapid cooling only permitted the development of feint although wholly consistent fabrics

west gondwana amalgamation based on detrital zircon ages from neoproterozoic ribeira and dom feliciano belts of south america and comparison with coeval sequences from sw africa

an integrated approach to the late stages of neoproterozoic post collisional magmatism from southern brazil structural geology geochemistry and geochronology of the corre mar granite abstract the neoproterozoic post collisional stage in south brazil is marked by intense granitic magmatism controlled by transcurrent shear zones related to the southern brazilian shear belt sbsb the sbsb has controlled the ascent and emplacement of magmas from crust and mantle in such scenario the corre mar granite cmg represents a small intrusion emplaced in a low strain zone located between two important segments of the sbsb the major gercino and itajai perimbo shear zones the cmg has a diagnostic subvertical s c foliation pair present in all intrusions regardless of their size it was emplaced within a conjugate system where sinistral nne shearing and nw se extension were both active generating space along the ne direction solid state deformation associated to the nne shearing is attested to by microstructures as feldspar recrystallization and asymmetric recrystallization tails the opening is attributed to the regional dextral transcurrent dynamics of the major gercino and itajai perimbo shear zones and magma emplacement was essentially conditioned by the nw extension component zircon u pb la mc icp ms crystallization age of cmg at 615 4 ma very close to other regional granites as the 611 ma serra dos macacos smg and 620 ma rio pequeno granite rpg points these three granitic bodies as synchronous the strong deformation features present in the cmg as opposed to the other neoproterozoic granites demonstrate that space rather than time must be called upon to explain the difference in structural patterns identified in the cmg geochemical and sr nd isotopic signatures as the slightly peraluminous character high k contents high lree hree ratios moderate rb nb zr and ree contents to regular sio 2 together with low 87 sr 86 sr i and the strongly negative nd t values indicate that the cmg is derived from old crustal sources possibly related to the paleoproterozoic camboriu complex quartz feldspathic orthogneisses the coincidence of cmg archean to paleoproterozoic inheritance ages with the age of a migmatization event identified in the camboriu complex and moreover the coincidence of the crystallization age intervals of the granites 615 611 ma with the last migmatization event at 640 610 ma reinforces the genetic link between them the paleoproterozoic tdm ages the geochemical and isotopic signatures the zircon u pb crystallization and inheritance age and the resemblance of the cmg and the smg suggest that they represent comagmatic and contemporaneous granitic pulses with a possible genetic link with the neoproterozoic migmatization event in the camboriu complex

multiple accretion at the eastern margin of the rio de la plata craton the prolonged brasiliano orogeny in southernmost brazil the neoproterozoic eoplalaeozoic brasiliano orogeny at the eastern margin of the rio de la plata craton in southernmost brazil and uruguay comprises a complex tectonic history over 300 million years the southern brazilian shield consists of a number of tectono stratigraphic units and terranes the sao gabriel block in the west is characterized by c 760 690 ma supracrustal rocks and calc alkaline orthogneisses including relics of older c 880 ma old igneous rocks both igneous and metasedimentary rocks have positive end t values and neoproterozoic tdm model ages they formed in magmatic arc settings with only minor input of older crustal sources a trondhjemite from the sao gabriel block intruding dioritc and tonalitic gneisses during the late stages of deformation d3 yield an u pb zircon age la icp ms of 701 10 ma giving the approximate minimum age of the sao gabriel accretionary event the encantadas block further east containing the supracrustal porongos belt and the pelotas batholith is in contrast characterized by reworking of neoarchean to palaeoproterozoic crust the 789 7 ma zircon age of a metarhyolite intercalated with the metasedimentary succession of the porongos belt provides a time marker for the basin formation zircons of a sample from tonalitic gneisses constituting the palaeoproterozoic basement of the porongos belt form a cluster at 2 234 28 ma interpreted as the tonalite crystallization age zircon rims show ages of 2 100 2 000 ma interpreted as related to a palaeoproterozoic metamorphic event the porongos basin formed on thinned continental crust in an extensional or transtensional regime between c 800 700 ma the absence of input from neoproterozoic juvenile sources into the porongos basin strongly indicates that the encantadas and sao gabriel blocks were separated terranes that became juxtaposed next to each other during the brasiliano accretional events the tectonic evolution comprises two episodes of magmatic arc accretion to the eastern margin of the rio de la plata craton i accretion of an intra oceanic arc at c 880 ma passinho event and ii accretion of the 760 700 ma cambai vila nova magmatic arc sao gabriel event the latter event also includes the collision of the encantadas block with the rio de la plata craton to the west collision and crustal thickening was followed by sinistral shear along sw ne trending orogen parallel crustal scale shear zones that can be traced from southern brazil to uruguay and have been active between 660 and 590 ma voluminous granitic magmatism in the pelotas batholith spatially related to shear zones is interpreted as late to post orogenic magmatism possibly assisted by lithospheric delamination it marks the transition to the post orogenic molasse stage localized deformation by reactivation of preexisting shear zones continued until c 530 ma and can be assigned to final stages of the amalgamation of west gondwana

electron microprobe dating as a tool for determining the closure of th u pb systems in migmatitic monazites high spatial resolution dating of monazite by the electron probe microanalyzer epma enables systematic and detailed studies of small minerals like zircon monazite records the complex history undergone by the host rocks recent improvements in the statistical treatment of many in situ data now make it possible to decipher the related thermal events and so obtain reliable and precise ages our work shows that a significant number of individual spot analyses is required to reach such precise information i e more than 30 40 data using the examples of monazites from three migmatites and one granite we show how to select the most efficient method of age calculation according to the u and th geochemistry of the grains or grain domains that we are trying to date three situations may be met 1 monazites exhibiting significant th u ratio variation 2 monazites exhibiting a fairly constant th u ratio but significant u th heterogeneity and 3 monazites of constant u and th concentrations for the first case a precise mean age can be calculated using a method of data reduction in the th pb f u pb diagram whereby a precision of 5 10 ma 2 is commonly achieved for the second case an isochron age can be calculated according to the pb f th method with a common precision of around 20 ma 2 whereas for the third case a simple weighted average age can be calculated using these approaches coupled with a back scattered electron image study we demonstrate that inheritance is probably as common for monazite as for zircon in addition the combination of high spatial resolution and precise age determination show the limited extent of pb diffusion in monazite finally an example from a migmatite from southern french guiana demonstrates the especially robust behavior of the th u pb system in monazite this system remains closed during late migmatization and during the subsequent zircon crystallization and zircon overgrowth of protolith zircons the monazite yielded exactly the same age as the protolith zircons

wave influence in the construction shaping and destruction of river deltas a review abstract waves are an important agent in the construction shaping and destruction of river deltas notwithstanding the commonality of waves in oceans and seas wave influence on deltas varies considerably depending on the coastal morphology and nearshore bathymetry although there have been advances in understanding the way waves approaching a delta shape its shoreline much still remains to be known of the interactions between waves and river deltas deltas are built essentially from sediments supplied by rivers sand sized and coarser sediments may also be derived from nearby abandoned delta lobes or from older relict nearshore deposits transported by wave reworking and longshore currents alternatively delta erosion by waves can also release sediment that is redistributed alongshore or that accumulates offshore the extent to which bedload is supplied to and sequestered in or lost by deltas through waves and longshore transport strongly depends on interactions between waves and fluvial discharge at the river mouth these interactions and the mutual adjustments they engender are not only important in the overall balance between delta retreat progradation or aggradation but also in processes such as avulsion and channel switching as well as in the eventual survival of a delta in the face of sea level rise where waves are important fluvial liquid discharge is high and sediment supply is rich in bedload two important aspects are the blocking of waves and longshore currents by strong river discharge and the formation of bars at the river mouth field studies of the complex interactive processes prevailing where river flows encounter waves are however non existent and numerical modelling though promising hampered by scale constraints and the difficulty of replicating them and generating mouth bars in the presence of longshore currents this interaction influences the seaward extent of the delta mouth protuberance and its stability this protuberance then forming the regional shoreline template to which waves and longshore currents adjust longshore currents can redistribute wave reworked mouth bar deposits emplaced during strong river flow transport may be either divergent from the mouth or may be regionally unidirectional but wherein the symmetry of some deltas probably rare may be maintained by a strong river blocking effect on transport from the updrift flank the mouth protuberance may be such as to foster transport reversal counter drift at the delta margins that contributes to sediment sequestering within the delta these interactions largely contribute in shaping delta shorelines and together with the abundance of sediment supply and grain size determine the resultant wave formed shoreline barrier types which include spits more or less closely spaced beach ridges and barrier islands and cheniers in situations of punctuated progradation or retreat where several distributary mouths occur pronounced longshore variability in wave processes and wave induced sediment transport may ensue resulting in multiple drift cells that assure the retention of sand and coarse grained sediments within the delta waves can also be an important agent in the reworking and retreat of mud rich deltas that generally conform in morphology to the river dominated such as the mississippi or tide dominated such as the ganges brahmaputra or chao phraya types resulting in the episodic formation of sandy cheniers and beach ridges although sea level rise is likely to lead to enhanced wave reworking of deltas the possible prevalence of aggradation in lieu of progradation channel switching and avulsion and washover processes may contribute to the disorganization of waves and longshore transport fostering deltaic sequestering of sand and coarser sized sediment and delta survival the weakening of river discharges resulting from human activities will invariably lead however to enhanced wave reworking of deltas and to deltaic sediment redistribution by longshore currents the massive swing towards significant reductions in fluvial sediment supply today may signify the ultimate demise of many deltas in the coming decades through a process of delta shoreline straightening by waves in addition to accelerated sinking these various foregoing aspects of the relationship between waves and river deltas are reviewed here across a range of timescales and new interaction concepts proposed using numerous examples of deltas in the world and on the basis of case studies conceptual studies and numerical modelling studies in the literature spanning more than forty years

ages u pb shrimp and la icpms and stratigraphic evolution of the neoproterozoic volcano sedimentary successions from the extensional camaqua basin southern brazil abstract during the ediacaran southern brazil was the site of multiple episodes of volcanism and sedimentation which are best preserved in the 3000 km2 camaqua basin the interlayered sedimentary and volcanic rocks record tectonic events and paleoenvironmental changes in a more than 10 km thick succession in this contribution we report new u pb and sm nd geochronological constraints for the 605 to 580 ma bom jardim group the 570 ma acampamento velho formation and a newly recognized 544 ma volcanism depositional patterns of these units reveal the transition from a restricted fault bounded basin into a wide shallow basin the expansion of the basin and diminished subsidence rates are demonstrated by increasing areal distribution and compressed isopachs and increasing onlap of sediments onto the basement to the west the sm nd isotopic composition of the volcanic rocks indicates mixed sources including crustal rocks from the adjacent basement both neoproterozoic and paleoproterozoic sources are indicated for the western part of the basin whereas only the older paleoproterozoic signature can be discerned in the eastern part of the basin

morphosedimentary evolution of a delta sourced drift aligned sand barrier lagoon complex western bight of benin the coast of eastern ghana and togo is bounded by a major holocene sand barrier complex hinged on the volta delta to the west and subject to high rates of longshore sand drift 1 1 5 106 m3 yr in spite of its proximity to this major deltaic sediment source this barrier system shows marked longshore variations in progradation following the middle holocene eustatic stillstand it is a hybrid system in terms of internal facies composition and plan view morphology in that it has evolved from an essentially regressive to a stationary synonymous with cessation of progradation system both transgressive and barrier inlet facies have also developed through time and space these temporal and spatial changes in patterns of development reflect variations in longshore sand transport and deposition over the last 5000 years such variations have been controlled by sediment supply from the volta by antecedent topography by lagoonal and river drainage by sediment cell development and maturation and in the very recent past by anthropogenic perturbation barrier progradation in the western bight of benin diminished considerably or ceased probably as early as 3400 yr b p as a single major equilibrium drift aligned bight cell matured permitting transport of volta sand toward the rest of the eastern bight in benin and nigeria the eastward longshore supply from the volta has involved both direct inputs of upland derived sand by the volta river channel and reworking of nearshore deltaic deposits a recent reduction in direct fluvial supply exacerbated by the akosombo dam completed in 1961 has induced a wave of erosion of the downdrift delta mouth barrier and shoreface deposits to fulfil the strong drift requirements in togo construction of a deepwater port in 1967 has also affected the barrier system both of these changes have had considerable impacts on longshore sediment dynamics the most significant impact has been segmentation of the former unique sediment cell characterising the 400 km long bight of benin coast resulting in differential longshore erosion progradation or equilibrium these changes have also induced new patterns of barrier behaviour that include transgressive and regressive dynamics at various locations alongshore

mineralizations of the lavalleja group uruguay a probable neoproterozoic volcano sedimentary sequence abstract the lavalleja group is located in the southern extreme of the dom feliciano belt being tentatively correlated with the porongos and brusque groups of brazil the basement of the lavalleja group is probably represented by granitic gneissic rocks of the campanero unit with ages in the southern portion ranging from 1 75 to 2 1 ga u pb in zircon the lavalleja group is characterized by narrow bands of metasedimentary and metavolcanic rocks and it is separated in three formations namely from base to top zanja del tigre fuente del puma and minas outcrops assigned to the minas formation have been recently correlated with the arroyo del soldado group only the fuente del puma formation hosts base metals au and ag ocurrences the fuente del puma formation is divided into three informal units sedimentary volcanic and hornblenditic gabbros the sedimentary unit is characterized by an important amount of carbonates syn collisional to post tectonic granitic bodies carape complex intrudes the lavalleja group and the campanero unit several mineralizations are located in the fuente del puma formation those associated to arrospide ramallo reus chape valencia la oriental apolonia redondo hill la china and la paloma mines are the most important in addition many ocurrences of cu zn pb were recognized in the region the cu zn pb mineralization includes massive sulfides with pyrite chalcopyrite sphalerite galena pyrrothyte arsenopyrite hematite into small bodies with lenticular shape the host rock shows frequently hydrothermal alteration the geochemistry and the geological features of the mineralizations suggest besshi massive sulphide zn cu pb and sedex zn pb as most probably genetic models for the deposits related to the neoproterozoic orogeny early mineralizations are syngenetic and were formed on the sea floor although the main mineralizations are related to remobilization during syn to late metamorphic events and thrusting

u pb and lu hf isotopes applied to the evolution of the late to post orogenic transtensional basins of the dom feliciano belt brazil abstract the santa barbara and guaritas groups located in southern brazil represent the last episode of deposition in the camaqua basin which included deposition of sandstone siltstone and conglomerates during the late neoproterozoic and eopaleozoic as part of the collisional period of the brasiliano pan african orogeny combined u pb and lu hf analyses of detrital zircon grains from outcrops and drill holes in both groups together with an analysis of paleocurrent data provide information regarding the sedimentary provenance and tectonic evolution the u pb geochronological data from both groups include concordant ages that are predominantly paleoproterozoic and neoproterozoic with an increasing contribution by early neoproterozoic and paleoproterozoic zircon grains in the upper unit the guaritas group the maximum depositional age of the basal siltstone units of the santa barbara group is 567 9 5 9 ma and the maximum depositional age of the guaritas group is 540 535 ma the lu hf model ages tdm indicate that the zircon grains in both groups display a predominantly archean and paleoproterozoic inheritance with predominantly negative hf values which indicates that the source rocks originated from the subcontinental lithosphere

implications of incremental emplacement of magma bodies for magma differentiation thermal aureole dimensions and plutonism volcanism relationships abstract field observations and geophysical data indicate that many igneous bodies grow by amalgamation of successive magma pulses that commonly take the shape of horizontal sheets sills emplacement styles and emplacement rates of magma bodies have fundamental implications on magma differentiation country rock metamorphism and assimilation and for the formation of large magma chambers in the upper crust when a magma body begins to grow by slow accretion of sills each successive intrusion solidifies before the injection of the next one when the system is thermally mature sill temperatures equilibrate above the solidus melts accumulate and older sills can re melt the time needed for each magma injection to cool down and equilibrate with its surrounding is short relatively to the total emplacement time of the body the transition from a mafic crystal poor magma to a partially molten rock that retains a highly differentiated melt is fast whereas the resulting evolved residual melt can reside in the crust for protracted periods as long as temperatures in the system are relatively low highly differentiated melts are generated which may explain the bi modal character and the absence of intermediate compositions in some magmatic provinces the level of emplacement of successive magma pulses controls the shape of the thermal anomaly associated with the magma body growth metamorphism partial melting and assimilation of the country rock are favoured if successive magma sheets are emplaced at or close to the country rock magma body boundary if the magma emplacement rate is low the size of the thermal aureole is controlled by the size of one pulse and not by the size of the entire igneous body understanding emplacement of magma bodies is fundamental for our understanding of the plutonism volcanism relationship magma emplacement rates of several centimetres per year are needed for a magma body to evolve into a large magma chamber able to feed large silicic explosive eruptions the time averaged emplacement rates of plutons are lower than this critical emplacement rate eruptions of 100s to 1000s cubic kilometres of silicic products show that such high volumes of magmas can accumulate in the upper crust this suggests that the emplacement of magma bodies is a multi timescale process with the development of large magma chambers corresponding to the highest magma fluxes because they control magmatic processes and the impact of magma intrusion on the country rock future studies should focus on magma emplacement rates and on magma emplacement geometries these studies should integrate field observation on plutons and geophysical data on active magmatic systems coupled with laboratory experiments and numerical simulations

time scales of pluton construction at differing crustal levels examples from the mount stuart and tenpeak intrusions north cascades washington deciphering the magmatic history of continental magmatic arcs in general and the growth history of individual intrusions in particular is key to understanding the complex history of magma generation segregation and transport that define the dynamics of crustal growth we utilize high precision u pb geochronology to resolve a detailed magmatic history from two composite intrusions the 2 4 kbar mount stuart batholith and the 7 10 kbar tenpeak pluton emplaced in the cretaceous north cascades arc this temporal framework provides a way to evaluate models of pluton growth that explain common features of intrusions such as concentric compositional zoning and internal magmatic contacts u pb zircon crystallization ages were obtained from 12 samples of the mount stuart batholith and 8 samples of the tenpeak intrusion representing the range of compositional diversity and geographical extent these dates indicate that the mount stuart batholith was constructed over a 5 5 m y time period that was punctuated by four intervals of high magma flux the durations of the high flux periods are short a few hundred thousand years relative to the duration of the batholith the consistent pattern of magmatic fabrics and the lack of distinct contacts in the batholith may be explained by the juxtaposition of melt rich and mush zones with subtle contacts between mineralogically and texturally similar tonalite and time transgressive magma fabrics in contrast the tenpeak intrusion was constructed over a 2 6 m y time period with magma influx distributed throughout the intrusive history and texturally distinct magma bodies the tenpeak intrusion lacks distinct age domains which suggests that any magma reservoir was smaller in size and potentially more ephemeral although the distinct age domains and discrete compositional and textural phases indicate that pluton growth occurred incrementally neither pluton bears resemblance to a purely end member incremental growth model whereby a pluton is constructed from hundreds to thousands of discrete magma pulses that have little if any interaction in particular ages from the youngest domain of the mount stuart batholith indicate that a melt rich magma reservoir of 520 km 3 existed over a 170 90 k y time span

rethinking the emplacement and evolution of zoned plutons geochronologic evidence for incremental assembly of the tuolumne intrusive suite california new u pb geochronologic data indicate that the tuolumne intrusive suite california was assembled over a period of at least 10 m y between 95 and 85 ma and that the half dome granodiorite intruded over a period approaching 4 m y simple thermal considerations preclude the possibility that a magma chamber the size of the half dome pluton could have existed as a liquid at shallow crustal depths for that long rather field evidence for sheeting along the margins of the suite the range of ages and the regular decrease of ages toward the center of the suite and within individual plutons suggest incremental assembly geochronologic evidence for incremental assembly is consistent with the failure of geophysical methods to detect large magma chambers with more than 20 melt even in active volcanic areas because it is unlikely that the individual plutons composing the tuolumne ever coexisted as liquid rich magmas the chemical evolution of the suite cannot be the result of simple fractionation and or mixing between exposed units but instead must reflect processes occurring during magma generation

granites and the geodynamic history of the neoproterozoic brasilia belt central brazil a review abstract recent field and geochronological studies have demonstrated the importance of granitic magmatism in the evolution of the neoproterozoic brasilia belt in central brazil this is an orogenic belt developed in response to the convergence between the amazon sao francisco congo and parana continental blocks the presence of neoproterozoic juvenile arc rocks and syn collisional peraluminous granites challenged previous intracontinental evolution models for the belt the granitoid intrusions reviewed in this paper record the different stages of evolution of the orogen and their field and isotopic characteristics can be used to reconstruct the tectonic history of the belt the main field and isotopic characteristics of four granite suites associated with the brasilia belt are reviewed i 1 77 1 58 ga old rift related a type granite intrusions ii ca 0 8 0 7 syn collisional granitoids iii arc metatonalites and metagranodiorites ca 0 9 to 0 63 ga and iv bimodal post orogenic suite ranging in age from ca 0 59 to 0 48 ga these rocks suggest that during most of the neoproterozoic the western margin of the sao francisco continent faced a large oceanic basin where subduction and oceanic lithosphere consumption started at ca 0 9 ga roughly coeval with the initial stages of the break up of rodinia final ocean closure happened at ca 0 63 0 60 ga with crustal thickening uplift and erosion post orogenic extension related magmatism took place between ca 0 6 and 0 5 ga and was partially contemporaneous with the deposition of the paraguay and tucavaca sedimentary successions resulting from the rifting event related to the break up of laurentia from southwestern gondwana

holocene evolution of the song hong red river delta system northern vietnam abstract the song hong red river delta located on the western coast of the gulf of bac bo tonkin in the south china sea formed as a result of the song hong sediment discharge throughout the holocene the river s sedimentary basin upstream from the delta plain is not large the delta plain comprises emerged tidal mangrove flats formed during the sea level highstand at 2 3 m 6 4 cal kyr bp and a beach ridge strandplain with straight to lobate beach ridges on the landward and seaward sides of the delta plain respectively the delta affords us the opportunity to examine river mouth morphodynamics comprehensively in relation to sediment discharge and sea level changes in this paper we describe the holocene evolution of the song hong delta system and the river mouth morphodynamics on the basis of seven sediment cores each 30 70 m long taken from the delta plain during 1999 2001 and 101 radiocarbon dates obtained from the core sediments sediments from the seven cores consisting of incised valley fills since the last glacial maximum can be divided in ascending order into fluvial sediments composed of gravelly sand and mottled clay tide influenced estuarine sediments containing shell and wood fragments and deltaic sediments composed of tide influenced sand and mud deposits in which the contents of sand and wood fragments increase upward by applying sequence stratigraphic concepts a transgressive surface can be identified at the gravelly sand mottled clay boundary and the maximum flooding surface can be identified at the estuarine deltaic sediments boundary the lowstand systems tract transgressive systems tract and highstand systems tract record 15 15 9 and 9 0 cal kyr bp respectively during the past 9 kyr the majority of the sediment discharged by the song hong accumulated in the incised valley and enhanced progradation at the river mouth the river mouth prograded from the bay head toward the gulf and its morphology changed from funnel shaped 9 6 cal kyr bp to straight 6 2 cal kyr bp and finally to lobate 2 0 cal kyr bp the morphological change from a funnel shaped to straight coast is interpreted to have been closely related to a hydrologic regime shift from a tide dominated bay head setting to a wave influenced open coast setting the cessation of the sea level rise at 6 cal kyr bp may have played only a small role in the change of river mouth morphology because the progradation rate decelerated from 22 to 4 m yr instead of accelerating at that time the river mouth morphodynamic change from straight to lobate was largely caused by an increase in the song hong sediment discharge from 17 27 9 2 cal kyr bp to 49 million t yr 2 0 cal kyr bp as a result of anthropogenic deforestation along the upper reaches of the song hong

deformation and geochronology of syntectonic granitoids emplaced in the major gercino shear zone southeastern south america abstract the major gercino shear zone is one of the ne sw lineaments that separate the neoproterozoic dom feliciano belt of brazil and uruguay into two different domains a northwestern supracrustal domain from a southeastern granitoid domain the shear zone striking ne is composed of protomylonites to ultramylonites with mainly dextral kinematic indicators in santa catarina state southern brazil the shear zone is composed of two mylonite belts the mylonites have mineral orientations produced under greenschist facies conditions at a high strain rate strong flattening and coaxial deformation indicate the transpressive character while the role of pure shear is emphasized by the orientation of the mylonite belts in relation to the inferred stress field component the quartz microstructures point out that different dynamic recrystallization regimes and crystal plasticity were the dominant mechanisms of deformation during the mylonitization process additionally the fabrics suggest that the glide systems are activated for deformation conditions compatible with the metamorphism in the middle greenschist facies elongated granitoid intrusions belonging to two petrographically geochemically and isotopically distinct rock associations occur between the two mylonite belts the structures observed in the granites result from a deformation range from magmatic to solid state conditions points to a continuum of magma straining during and just after its crystallization conventional u pb analysis of multi crystal zircon fractions yielded essentially identical ages of 609 16 ma and 614 2 ma for the two granitic associations and constrain the transpressive phase of the shear zone k ar ages of biotites between 585 and 560 ma record the slow cooling and uplift of the intrusions some k ar ages of micas in regional mylonites are similar suggesting that thermo tectonic activity was intense up to this time probably related to the agglutination of the granite belt to the supracrustal belt nw of the mgsz

early to mid holocene rapid sea level rise and coastal response on the southern yangtze delta plain china we used accelerator mass spectrometry ams 14 c dated sediments of the holocene basal supratidal flat to upper tidal flat facies in 11 cores on the southern yangtze delta plain to reconstruct relative sea levels of 8 5 8 0 cal ka bp three cores were further ams 14 c dated and used to examine the evolution of sedimentary geomorphological environments in response to the rapid sea level rise during the early to mid holocene results demonstrate relative sea level rise of around 30mm a 1 from 8 5 to 8 3 cal ka bp and around 10mm a 1 from 8 3 to 8 0 cal ka bp retrogradation from supratidal to lower tidal flat environments occurred in response to the rapid sea level rise at 8 5 8 3 cal ka bp and aggradation from middle to upper tidal flat occurred at 8 3 7 9 cal ka bp further retreat of the tidal flat at 7 9 7 2 cal ka bp implies a mean sea level rise rate exceeding 5mm a 1 at this time we suggest that the rapid relative sea level rise during 8 3 8 5 cal ka bp and subsequent slower rise caused drastic changes in the coastal zone and that these changes are key phenomena for understanding the coastal response to future sea level rise copyright 2013 john wiley sons ltd

evolution of the major gercino shear zone in the dom feliciano belt south brazil and implications for the assembly of southwestern gondwana the dom feliciano belt developed during the brasiliano pan african orogenic cycle due to the tectonic interaction between the rio de la plata congo and kalahari cratons along with the amalgamation of smaller continental fragments together with its prolongations to the south the major gercino shear zone constitutes one of the main lineaments of the orogenic system establishing a more than 1000 km long ne trending tectonic boundary between a granitic batholith and a metavolcano sedimentary association based on combined field structural microstructural and textural data together with new and published geochronological data a refined model for the geological evolution of the major gercino shear zone is presented regional nw verging low dipping structures were generated between 650 and 615 ma preceding the formation of the shear zone this was followed by the main deformation phase corresponding to pure shear dominated dextral strike slip interpreted do be controlled by regional transpression during oblique convergence of the continental terranes this stage lasted until ca 585 ma and was coeval with the continuous emplacement of granitic magmatism along the structure strain partitioning and localization led to the development of mylonitic belts along the intrusion borders mostly under greenschist facies metamorphic conditions late stage ductile deformation along the structure was active during the cooling of the intrusions until ca 550 ma while the deformation front of the orogenic system migrated to counterpart orogenic belts in the african continent after tectonic stabilization the major gercino shear zone recorded episodic brittle reactivation possibly related to the phanerozoic evolution of the active margins and intracratonic basins in gondwana 2018 springer verlag gmbh germany part of springer nature

coast line evolution in portugal since the last glacial maximum until present a synthesis abstract an effort has been made to assemble a data set on the evolution of coastal morphology of the west iberian continental margin in portugal which has occurred since the last glacial maximum in this integrated review a particular attention was given to the analyses of coastline shaping phenomena on different time scales several overlapping processes such as shore erosion local sediment supply rate climatic changes anthropic impacts and mean sea level rise mslr were identified and their combined effects assessed the eustatic see level rise appears as a principal factor in shaping the shore line contour until mid holocene since then the non eustatic factors namely the terrigenous sediment supply rate and the dynamics of barriers and spits systems became dominant in the evolution of the near shore morphology since the 15th century ad the anthropogenic activities namely deforestation and land cultivation contributed decisively to the positive sedimentary balance in the portuguese coastal zone finally the multiple damming of the major rivers in 20th century and exploitation of sand and gravel from the river beds led to the sediment starving of the coastal zone and generalized shore line retreat

rates of magma differentiation and emplacement in a ballooning pluton recorded by u pb tims tea adamello batholith italy abstract geochemical structural field and geochronological data have been used to arrive at very different models for the construction of upper crustal batholiths models for pulsed intrusion of small magma batches over long timescales 1 ma versus transfer of larger magma bodies on shorter timescales predict a different thermal metamorphic and rheological state of the crust highlighting the importance of robust time constraints this study focuses on a well characterized upper crustal intrusion the 15 km2 lago della vacca complex lvc adamello batholith n italy previous studies used structural and petrologic data to argue that the lvc was emplaced through pulsed magma injection and in situ expansion or ballooning of a short lived 105 yr magma chamber we test this model using a dense sampling strategy and high precision id tims u pb geochronology of zircon and titanite combined with hafnium isotope and trace element analyses of the same volume of dated mineral u pb tims tea these data show that the marginal mafic pulses of magma crystallized zircon with primitive hf isotopes and negligible eu anomalies during fractional crystallization and ascent through the crust on 10 30 ka timescales subsequent more felsic pulses yield individual zircon dates spanning as much as 200 ka within single handsamples and restrict the total construction time of the lvc to

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

new evidence on the spatial temporal distribution of superlobes in the yellow river delta complex abstract unraveling the spatial temporal distribution of delta superlobes precisely is particularly important and challenging in the yellow river delta complex yrdc previous research on this issue can be dated back to the early 1990s when the paleoenvironmental reconstructions mainly hinged on the historical documents and geomorphologic analysis of well developed cheniers from the west coast of bohai bay and only few drilled cores with scant radiocarbon dates were available to build a refined model of the holocene stratigraphic architecture and reconstruct the sedimentary evolution of the yrdc detailed sedimentological investigation of 12 boreholes including 59 new ams 14c radiocarbon dates was combined with other published 25 cores and 174 ams 14c dates therein age depth curves were grouped by stratigraphic positions and facies characteristics of these 233 radiocarbon dated samples across different sectors of the yrdc exhibiting consistent patterns that can be used to identify distinct phases of delta superlobe activities eight new superlobes with relatively accurate dating spans were therefore proposed in the yrdc our results demonstrate that very high aggradation rates almost invariably correlate with the onset of deltaic deposition age depth patterns thus may be very useful to elucidate the complex sedimentary evolution of delta systems with multiple lobes

the sierra ballena shear zone in the southernmost dom feliciano belt uruguay evolution kinematics and deformation conditions the sierra ballena shear zone sbsz is part of a high strain transcurrent system that divides the neoproterozoic dom feliciano belt of south america into two different domains the basement on both sides of the sbsz shows a deformation stage preceding that of the transcurrent deformation recognized as a high temperature mylonitic foliation associated with migmatization grain boundary migration and fluid assisted grain boundary diffusion enhanced by partial melting were the main deformation mechanisms associated with this foliation age estimate of this episode is 658 ma the second stage corresponds to the start of transpressional deformation and the nucleation and development of the sbsz during this stage pure shear dominates the deformation and is characterized by the development of conjugate dextral and sinistral shear zones and the emplacement of syntectonic granites this event dates to 658 600 ma based on the age of these intrusions the third stage was a second transpressional event at about 586 to 560 ma that was associated with the emplacement of porphyry dikes and granites that show evidence of flattening deformation in the sbsz took place during the late stages under regional low grade conditions as indicated by the metamorphic paragenesis in the supracrustals of the country rocks granitic mylonites show plastic deformation of quartz and brittle behavior of feldspar a transition from magmatic to solid state microstructures is also frequently observed in syntectonic granites mylonitic porphyries and quartz mylonites resulted from the deformation of alkaline porphyries and quartz veins emplaced in the shear zone quartz veins reflect the release of silica associated with the breakdown of feldspar to white mica during the evolution of the granitic mylonites to phyllonites which resulted in shear zone weakening quartz microstructures characteristic of the transition between regime 2 and regime 3 grain boundary migration and incipient recrystallization in feldspar indicate deformation under lower amphibolite to upper greenschist conditions 550 400 c on the other hand the mylonitic porphyries display evidence of feldspar recrystallization suggesting magmatic or high t solid state deformation during cooling of the dikes

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

initiation of the changjiang yangtze delta and its response to the mid holocene sea level change abstract the changjiang yangtze delta in eastern china is one of the largest tide dominated deltas in the world to obtain a more detailed information on its initiation we drilled three sediment cores pk01 hg01 and xj03 from the uppermost region of the delta plain on the basis of sedimentary facies and ams 14c dating we identified three depositional systems 1 a fluvial system 2 an estuarine system and 3 a deltaic system including an initial delta estuary delta transition and a typical delta the maximum flooding surface separates the estuarine and deltaic systems and occurred at ca 8 0 cal kyr bp when brackish water intruded landward and reached the nanjing area the changjiang delta was initiated at the area between nanjing and yizheng when the sea level rise decelerated after the rapid rise in sea level during 9 0 8 2 cal kyr bp the subsequent evolution of the changjiang delta has been shown as a seaward development model of river mouth bars with shoreline migration the oldest river mouth bar called hongqiao sand body which is located most landward was dated at 6 0 5 5 cal kyr bp in this study nearly one thousand years younger than the previous estimates a tide dominated funnel shaped estuary was formed at 8 0 cal kyr bp and lasted until the hongqiao sand bar became exposed this stage is regarded as an aggradation dominated initial stage of the changjiang delta followed by a progradation dominated stage that is characterized by the formation of a series of seaward migrating river mouth bars a relative sea level highstand in the mid holocene may be associated with glacio hydro isostatic tilting

holocene and modern sediment budgets for the ganges brahmaputra river system evidence for highstand dispersal to flood plain shelf and deep sea depocenters the partitioning of fluvial sediment load across continental margins is an important control on strata formation and sequence development however few quantitative sediment budgets that encompass entire dispersal systems exist for the ganges brahmaputra river system sediment discharge is estimated to be 10 9 t yr at gauging stations 300 km inland of the coast but little has been known of the downstream fate of this material geochronological geophysical and stratigraphic investigations of the lowland flood plain delta plain and shelf help to delineate the extent of holocene fill and allow calculation of a first order sediment budget results reveal that 1500 10 9 m 3 of sediment fill has been sequestered within the flood plain and delta plain since ca 7000 yr b p or about one third of the annual discharge the remaining load appears to be apportioned between the prograding subaqueous delta 1970 10 9 m 3 and transport to the deep sea bengal fan via a nearshore canyon modern 100 yr budget estimates based on short term accretion rates indicate a similar dispersal pattern and show that contemporaneous deposition continues within these disparate depocenters the roughly equal partitioning of sediment among flood plain shelf and deep sea settings reflects the respective influence of an inland tectonic basin a wide shelf and a deeply incised canyon system the findings also support new sequence stratigraphic models for these settings and indicate the important insight that modern river deltas can provide for ancient margin systems furthermore results affirm that values of riverine sediment flux to the oceans may be considerably overestimated by not accounting for loss to the flood plains downstream of the gauging stations

post glacial sea level changes around the australian margin a review abstract it has been known since rhodes fairbridge s first attempt to establish a global pattern of holocene sea level change by combining evidence from western australia and from sites in the northern hemisphere that the details of sea level history since the last glacial maximum vary considerably across the globe the australian region is relatively stable tectonically and is situated in the far field of former ice sheets it therefore preserves important records of post glacial sea levels that are less complicated by neotectonics or glacio isostatic adjustments accordingly the relative sea level record of this region is dominantly one of glacio eustatic ice equivalent sea level changes the broader australasian region has provided critical information on the nature of post glacial sea level including the termination of the last glacial maximum when sea level was approximately 125 m lower than present around 21 000 19 000 years bp and insights into meltwater pulse 1a between 14 600 and 14 300 cal yr bp although most parts of the australian continent reveals a high degree of tectonic stability research conducted since the 1970s has shown that the timing and elevation of a holocene highstand varies systematically around its margin this is attributed primarily to variations in the timing of the response of the ocean basins and shallow continental shelves to the increased ocean volumes following ice melt including a process known as ocean siphoning i e glacio hydro isostatic adjustment processes several seminal studies in the early 1980s produced important data sets from the australasian region that have provided a solid foundation for more recent palaeo sea level research this review revisits these key studies emphasising their continuing influence on quaternary research and incorporates relatively recent investigations to interpret the nature of post glacial sea level change around australia these include a synthesis of research from the northern territory queensland new south wales south australia and western australia a focus of these more recent studies has been the re examination of 1 the accuracy and reliability of different proxy sea level indicators 2 the rate and nature of post glacial sea level rise 3 the evidence for timing elevation and duration of mid holocene highstands and 4 the notion of mid to late holocene sea level oscillations and their basis based on this synthesis of previous research it is clear that estimates of past sea surface elevation are a function of eustatic factors as well as morphodynamics of individual sites the wide variety of proxy sea level indicators used their wide geographical range and their indicative meaning some progress has been made in understanding the variability of the accuracy of proxy indicators in relation to their contemporary sea level the inter comparison of the variety of dating techniques used and the nuances of calibration of radiocarbon ages to sidereal years these issues need to be thoroughly understood before proxy sea level indicators can be incorporated into credible reconstructions of relative sea level change at individual locations many of the issues which challenged sea level researchers in the latter part of the twentieth century remain contentious today divergent opinions remain about 1 exactly when sea level attained present levels following the most recent post glacial marine transgression pmt 2 the elevation that sea level reached during the holocene sea level highstand 3 whether sea level fell smoothly from a metre or more above its present level following the pmt 4 whether sea level remained at these highstand levels for a considerable period before falling to its present position or 5 whether it underwent a series of moderate oscillations during the holocene highstand

timing of deformation in the sarandi del yi shear zone uruguay implications for the amalgamation of western gondwana during the neoproterozoic brasiliano pan african orogeny u pb and hf zircon sensitive high resolution ion microprobe shrimp and laser ablation inductively coupled plasma mass spectrometry la icp ms ar ar hornblende and muscovite and rb sr whole rock muscovite isochron data from the mylonites of the sarandi del yi shear zone uruguay were obtained in order to assess the tectonothermal evolution of this crustal scale structure integration of these results with available kinematic structural and microstructural data of the shear zone as well as with geochronological data from the adjacent blocks allowed to constrain the onset of deformation along the shear zone at 630 625 ma during the collision of the nico perez terrane and the rio de la plata craton the shear zone underwent dextral shearing up to 596 ma under upper to middle amphibolite facies conditions which was succeeded by sinistral shearing under lower amphibolite to upper greenschist facies conditions until at least 584 ma after emplacement of the cerro caperuza granite at 570 ma the shear zone underwent only cataclastic deformation between the late ediacaran and the cambrian the sarandi del yi shear zone is thus related to the syncollisional to postcollisional evolution of the amalgamation of the rio de la plata craton and the nico perez terrane furthermore the obtained data reveal that strain partitioning and localization with time magmatism emplacement and fluid circulation are key processes affecting the isotopic systems in mylonitic belts revealing the complexity in assessing the age of deformation of long lived shear zones

u pb geochronology of the granite magmatism in the embu terrane implications for the evolution of the central ribeira belt se brazil abstract the embu domain represents the central part of the ribeira fold belt in sao paulo brazil it hosts several granitic occurrences of varied composition ranging from small granitic bodies that outcrop in a domain bounded by the intersection of two major sutures taxaquara and guararema faults and batholitic masses outcropping to the east understanding the evolution of such granites is of vital importance to better constrain evolutionary models for the ribeira belt in the present study a set of samples from eleven main granite occurrences from the east of sao paulo state was selected for geochronological investigation using laser ablation multicollector inductively coupled plasma spectrometry la mc icp ms and thermal ionization mass spectrometry tims u pb dating of zircon and monazite crystals respectively the results indicate a remarkable cluster of ages around 590 ma with older events of granite magmatism between 660 and 600 ma registered for four plutons indicating a long history of crustal reworking and magma generation the ages of reworked sources were evaluated from inherited zircon cores although highly discordant these point to the predominance of paleoproterozoic 2 4 2 1 ga sources with minor contributions from mesoproterozoic 1 1 0 9 ga and archean sources 3 1 ga the new data bring important insights into the role played by the embu domain on the paleogeography and evolution of the ribeira belt

petrogenesis of syntectonic granites emplaced at the transition from thrusting to transcurrent tectonics in post collisional setting whole rock and sr nd pb isotope geochemistry in the neoproterozoic quatro ilhas and mariscal granites southern brazil abstract the neoproterozoic post collisional period in southern brazil 650 580 ma is characterized by substantial volumes of magma emplaced along the active shear zones that compose the southern brazilian shear belt the early phase syntectonic magmatism 630 610 ma is represented by the porphyritic high k metaluminous to peraluminous quatro ilhas granitoids and the younger heterogranular slightly peraluminous mariscal granite quatro ilhas granitoids include three main petrographic varieties muscovite biotite granodiorite mbg biotite monzogranite bmz and leucogranite lcg that although sharing some significant geochemical characteristics are not strictly comagmatic as shown by chemical and sr nd pb isotope data the most primitive muscovite biotite granodiorite was produced by contamination of more mafic melts possibly with some mantle component with peraluminous crustal melts the biotite monzogranite although more felsic has higher ca mgo tio 2 and ba and lower k 2 o feo t sr and rb contents possibly reflecting some mixing with coeval mafic magmas of tholeiitic affinity the leucogranite may be derived from pure crustal melts the mariscal granite is formed by two main granite types which occur intimately associated in the same pluton one with higher k 5 6 5 wt k 2 o high rb and lower cao na 2 o ba and zr as compared to the other 3 5 wt of k 2 o the two mariscal granite varieties have compositional correspondence with fine grained granites fgg that occur as tabular bodies which intruded the quatro ilhas granoitoids before they were fully crystallized and are inferred to correspond to the mariscal granite feeders an interpretation that is reinforced by similar u pb zircon crystallization ages the initial evolution of the post collisional magmatism marked by the emplacement of the quatro ilhas granitoids varieties activated sources that produced mantle and crustal magmas whose emplacement was controlled both by flat lying and transcurrent structures the transition from thrust to transcurrent related tectonics coincides with the increase in the proportion of crustal derived melts the transcurrent tectonics seems to have played an essential role in the generation of mantle derived magmas and may have facilitated their interaction with crustal melts which seem to be to a large extent the products of reworking of orthogneiss protoliths

impacts of sediment retention by dams on delta shoreline recession evidences from the krishna and godavari deltas india river deltas are the major repositories of terrestrial sediment flux into the world s oceans reduction in riverine inputs into the deltas due to upstream damming might lead to a relative dominance of waves tides and currents that are especially exacerbated by coastal subsidence and sea level rise ultimately affecting the delta environment analysis of multi date satellite imagery and maps covering the krishna and godavari deltas along the east coast of india revealed a net erosion of 76 km2 area along the entire 336 km long twin delta coast during the past 43 years 1965 2008 with a progressively increasing rate from 1 39 km2 yr 1 between 1965 and 1990 to 2 32 km2 yr 1 during 1990 2000 and more or less sustained at 2 25 km2 yr 1 during 2000 2008 at present the krishna has almost become a closed basin with decreased water discharges into the delta from 61 88 km3 during 1951 1959 to 11 82 km3 by 2000 2008 and the suspended sediment loads from 9 million tons during 1966 1969 to as low as 0 4 million tons by 2000 2005 in the case of the godavari delta although the water discharge data do not show any major change there was almost a three fold reduction in its suspended sediment loads from 150 2 million tons during 1970 1979 to 57 2 million tons by 2000 2006 a comparison of data on annual sediment loads recorded along the krishna and godavari rivers showed consistently lower sediment quantities at the locations downstream of dams than at their upstream counterparts reports based on bathymetric surveys revealed considerable reduction in the storage capacities of reservoirs behind such dams apparently sediment retention at the dams is the main reason for the pronounced coastal erosion along the krishna and godavari deltas during the past four decades which is coeval to the hectic dam construction activity in these river basins copyright 2010 john wiley and sons ltd

the huanghe yellow river and changjiang yangtze river deltas a review on their characteristics evolution and sediment discharge during the holocene abstract today asian rivers play an important role in delivering sediment from the land to the oceans however past sediment discharge before human activities modified the landscape is not well known and is estimated to have been roughly one third to one half of the present level chinese rivers have been strongly influenced by human activities and their sediment discharge has changed over the last 6000 years for the study of the long term human impact on rivers and catchment basins chinese rivers provide excellent examples because continuous historical records are available here the characteristics evolution and sediment discharge during the holocene of the deltas of two large chinese rivers huanghe yellow river and changjiang yangtze river are summarized the huanghe and changjiang deltas are different with respect to coastal environments water and sediment discharge the pattern of development of the delta lobe thickness of holocene sediments and basal topography of the incised valleys formed during the last glacial period the huanghe delta is characterized by a high concentration of sediment huge sediment discharge thin holocene deltaic sediments a lateral delta lobe shift and a steep longitudinal profile in its lower reaches the changjiang delta is characterized by a large water discharge a large interseasonal water level change a tide dominated coastal environment continuous seaward progradation with isolated river mouth sand bodies thick holocene sediments and a deep incised valley formed during the last glacial period based on the sediment volume of prograding deltaic sediments over the last 6000 years the sediment discharge of huanghe 1000 years ago is estimated to have been 1 10 8 tons year 1 10 of the present level an abrupt increase occurred at ca 1000 years ago as a consequence of human activities on the loess plateau especially involving cultivation and deforestation moreover the estimated sediment load of huanghe at sanmenxia station prior to 1000 years was 2 7 4 0 10 8 tons year or about 20 15 25 of the present level our recent study estimated that the sediment discharge of changjiang before 2000 years bp was ca 2 4 10 8 tons year total sediment discharge of both rivers before 2000 years bp is estimated to have been 3 4 10 8 tons year or only about 20 of the present level moreover the total sediment load to the lower reaches is estimated to have been 5 6 10 8 tons year or one fourth the present level

geochronological constraints on the evolution of the southern dom feliciano belt uruguay abstract new u pb sensitive high resolution ion microprobe k ar and ar ar data from the southernmost dom feliciano belt allow the identification of four major events orthogneisses from the punta del este terrane indicate a magmatic episode at c 770 ma and high grade metamorphism at 641 17 ma granitoid emplacement at 627 23 ma was roughly coeval with peak metamorphism volcaniclastic rocks of the las ventanas formation dated at 573 11 ma can be correlated with the peripheral foreland basin 571 8 ma transpression and coeval high k calc alkaline magmatism is recorded in the maldonado granite dated at 564 7 ma the following events are postulated 1 magmatism at 850 750 ma related to rifting 2 metamorphism and granite emplacement at 650 600 ma 3 molasse sequences and foreland basins at c 573 ma 4 late magmatism at 580 560 ma associated with transpression the data indicate that 1 the punta del este terrane could be a portion of the coastal terrane of the kaoko belt 2 granitoid emplacement at 650 600 ma in the punta del este and nico perez terranes favours westward subduction and 3 widespread post collisional synkinematic magmatism occurred in the dom feliciano and kaoko belts between 580 and 550 ma supplementary material analytical methods and data are available at http www geolsoc org uk sup18369

the identification and significance of pure sediment derived granites the characterization of the geochemical reservoirs of the earth s continental crust including the determination of representative upper and lower crustal compositions underpins our understanding of crustal evolution the classic i and s type granite classification has often been invoked to distinguish between melts derived from igneous protoliths and those derived from the melting of a sedimentary source recent geochemical studies suggest that most granites even those cited as typical examples of s type show evidence for a mixture of mantle and upper crustal sources thereby implying that granite formation is evidence for overall crustal growth we have examined the source of leucogranite bodies in one of the world s youngest collisional orogens using novel zircon techniques that can resolve the presence of even minor mantle contributions 232 zircons from 12 granites from the bhutan himalaya were analysed by in situ techniques for o hf and u pb isotopic signatures in combination with data from the granite host rocks our data show that the himalayan leucogranites were derived solely from metamorphosed crustal sediments and do not record any mantle contribution this finding is consistent with the time lag between crustal thickening and widespread crustal melting and the heat producing capacities of the pelitic source rocks we conclude that himalayan leucogranites provide a more suitable type locality for s type granites than the lachlan area in south east australia where the term was first defined the himalayan leucogranites therefore provide evidence that syn orogenic melting during collisional events does not necessarily result in crustal growth importantly crustal growth models should not always assume that crustal growth is achieved during collisional orogenesis

zircon u pb shrimp dating of a neoproterozoic overprint in paleoproterozoic granitic gneissic terranes southern brazil the neoproterozoic florianopolis batholith provides the major clue for unraveling the pre brasiliano cycle evolution of santa catarina state southern brazil because it contains septa of basement units such as the camboriu and aguas mornas complexes reactivated during the younger brasiliano orogeny at about 600 ma we establish precise u pb zircon shrimp ages and nd isotopic evolution of four key samples from the septa the zircon population displays complex internal structures in three of the four dated samples the complex crystals have well preserved magmatic cores and altered rim domains the core populations were dated at about 2180 ma aguas mornas complex about 2160 ma camboriu complex amphibolite xenolith and 2000 ma camboriu complex orthogneiss whereas the ages of the measured rims and altered domains are about 590 ma in all three samples on the other hand the presidente nereu tonalite has a simpler zircon population without core rim separation and yields magmatic ages about 2200 ma the nd isotopic analyses of the three samples emphasize the polycyclic evolution of the batholith which is much more complex than previously realized the evolution is marked by two successive paleoproterozoic accretionary orogenic events at about 2200 2175 ma and by a crustal melting event at about 2000 ma which had an archaean source sm nd depleted mantle model age tdm 2860 ma these orogenic events were followed 1 4 billion years later by a neoproterozoic hydrothermal metamorphic overprint at about 590 ma this time gap permits us to identify a long intracratonic period the atlantica supercontinent the unraveling of the proterozoic evolution and the precise characterization of the basement remnants show that the paleoproterozoic was a crust building orogenic interval and was the major source of the much later neoproterozoic granites the integrated use of back scattered electron and cathodoluminescence imaging with shrimp spot dating and nd isotopes provide a clear understanding of the timing of crustal generation and deformation in southern brazil including strong evidence for a long lasting supercontinent cycle

space time relation of post collisional granitic magmatism in santa catarina southern brazil u pb la mc icp ms zircon geochronology of coeval mafic felsic magmatism related to the major gercino shear zone abstract la mc icp ms u pb zircon dating was performed on syntectonic early post collisional granitic and associated mafic rocks that are intrusive in the brusque metamorphic complex and in the florianopolis batholith major tectonic domains separated by the neoproterozoic major gercino shear zone mgsz in south brazil the inferred ages of magmatic crystallization are consistent with field relationships and show that the syntectonic granites from both domains are similar with ages around 630 620 ma for high k calc alkaline metaluminous granites and ca 610 ma for slightly peraluminous granites although ca 650 ma inherited zircon components are identified in granites from both domains important contrasts on the crustal architecture in each domain are revealed by the patterns of zircon inheritance indicating different crustal sources for the granites in each domain the granites from the southern domain florianopolis batholith have essentially neoproterozoic 650 700 ma and 900 950 ma inheritance with a single 2 0 2 2 ga inherited age obtained in the peraluminous mariscal granite in the northern brusque metamorphic complex the metaluminous rio pequeno granite and associated mafic rocks have scarce inherited cores with ages around 1 65 ga whereas the slightly peraluminous serra dos macacos granite has abundant paleoproterozoic 1 8 2 2 ga and archean 2 9 3 4 ga inherited zircons our results are consistent with the hypothesis that the mgsz separates domains with distinct geologic evolution however the contemporaneity of 630 610 ma granitic magmatism with similar structural and geochemical patterns on both sides of this major shear zone indicates that these domains were already part of a single continental mass at 630 ma reinforcing the post collisional character of these granites

holocene aridification of india 1 spanning a latitudinal range typical for deserts the indian peninsula is fertile instead and sustains over a billion people through monsoonal rains despite the strong link between climate and society our knowledge of the long term monsoon variability is incomplete over the indian subcontinent here we reconstruct the holocene paleoclimate in the core monsoon zone cmz of the indian peninsula using a sediment core recovered offshore from the mouth of godavari river carbon isotopes of sedimentary leaf waxes provide an integrated and regionally extensive record of the flora in the cmz and document a gradual increase in aridity adapted vegetation from 4 000 until 1 700 years ago followed by the persistence of aridity adapted plants after that the oxygen isotopic composition of planktonic foraminiferglobigerinoides ruberdetects unprecedented high salinity events in the bay of bengal over the last 3 000 years and especially after 1 700 years ago which suggest that the cmz aridification intensified in the late holocene through a series of sub millennial dry episodes cultural changes occurred across the indian subcontinent as the climate became more arid after 4 000 years sedentary agriculture took hold in the drying central and south india while the urban harappan civilization collapsed in the already arid indus basin the establishment of a more variable hydroclimate over the last ca 1 700 years may have led to the rapid proliferation of water conservation technology in south india

delta progradation and chenier formation in the huanghe yellow river delta china abstract to clarify holocene development of the huanghe yellow river delta and the relationship between delta progradation and chenier formation detailed sediment analyses and high resolution radiocarbon dating were done on borehole samples taken from two sites on the present huanghe h9601 latitude 37 40 5 n and longitude 118 28 7 e with an altitude of 5 5 m and h9602 lat 37 47 8 n and long 118 54 3 e 4 8 m downcore changes of sediment facies and accumulation rate show that delta progradation occurred at least twice during ca 2 6 1 2 c 14 yrbp and 1855 present at the two borehole sites these phases of progradation correlate with superlobes 6 and 7 and superlobe 10 respectively of ten superlobes composing the holocene huanghe delta shown by c xue historical changes in the yellow river delta china marine geology 113 321 329 1993 the boundary of these sediments at h9602 is sharp and erosional and correlates with cheniers located between borehole sites on the delta plain the diastem period between these phases of progradation almost coincides with the periods when the river mouth of the huanghe was located in the northwestern part of the bohai sea during 1048 1128 ad superlobe 8 and the jiangsu region facing the yellow sea during 1128 1855 superlobe 9 this suggests that chenier formation and delta progradation are linked and controlled by sediment supply and river course shifts of the lower reaches of the huanghe

initiation of the mekong river delta at 8 ka evidence from the sedimentary succession in the cambodian lowland abstract modern deltas are understood to have initiated around 7 5 9 ka in response to the deceleration of sea level rise this episode of delta initiation is closely related to the last deglacial meltwater events and eustatic sea level rises the initial stage of the mekong river delta one of the world s largest deltas is well recorded in cambodian lowland sediments this paper integrates analyses of sedimentary facies diatom assemblages and radiocarbon dates for three drill cores from the lowland to demonstrate holocene sedimentary evolution in relation to sea level changes the cores are characterized by a tripartite succession 1 aggrading flood plain to natural levee and tidal fluvial channel during the postglacial sea level rise 10 8 4 ka 2 aggrading to prograding tidal flats and mangrove forests around and after the maximum flooding of the sea 8 4 6 3 ka and 3 a prograding fluvial system on the delta plain 6 3 ka to the present the maximum flooding of the sea occurred at 8 0 0 1 ka 2000 years before the mid holocene sea level highstand and tidal flats penetrated up to 20 50 km southeast of phnom penh after a period of abrupt 5 m sea level rise at 8 5 8 4 ka the delta progradation then initiated as a result of the sea level stillstand at around 8 7 5 ka another rapid sea level rise at 7 5 7 ka allowed thick mangrove peat to be widely deposited in the cambodian lowland and the peat accumulation endured until 6 3 ka since 6 3 ka a fluvial system has characterized the delta plain and the fluvial sediment discharge has contributed to rapid delta progradation the uppermost part of the sedimentary succession composed of flood plain to natural levee sediments reveals a sudden increase in sediment accumulation over the past 600 1000 years this increase might reflect an increase in the sediment yield due to human activities in the upper to middle reaches of the mekong as with other asian rivers

evolution of the coastal depositional systems of the changjiang yangtze river in response to late pleistocene holocene sea level changes abstract the paleo changjiang yangtze incised valley fills approximately 80 90 m thick provide an opportunity to document the evolution of coastal depositional systems with large sediment supply in response to late pleistocene holocene sea level fluctuations on time scales of 103 to 104 years the sedimentary facies of the incised valley fills record three main depositional systems fluvial tide dominated estuary and tide dominated delta radiocarbon ages for the incised valley fills suggest that these depositional systems developed before about 11 ka between 11 and 8 ka and after approximately 8 ka respectively by applying sequence stratigraphic concepts the evolution of the depositional systems can be divided into three systems tracts a lowstand systems tract lst a transgressive systems tract tst and a highstand systems tract hst sea level changes on a 104 year time scale controlled the basic architecture of the sequence of the incised valley fill on the other hand sea level changes on a millennial time scale affected the stacking pattern of the systems tracts in particular the continuous sea level rise with episodic rapid rises during the last deglaciation affected the stacking pattern of the tst which is characterized by a combination of aggradation and backstepping the aggradation of fluvial and estuarine systems was dominant and the shoreline migrated only gradually landward under the relatively slow rise in sea level and a very rapid sea level rise around 12 and 10 ka caused the system to migrate abruptly landward unlike the transgressive estuarine phase the stacking pattern of the regressive tide dominated delta hst which developed within the almost filled incised valley and on the surrounding interfluve zones was characterized by seaward progradation with clinoform architecture it was initiated with aggradational and progradational stacking about 8 ka during the last phase of decelerated sea level rise and was followed by a progradational phase after the highest sea level about 6 ka

abrupt weakening of the summer monsoon in northwest india 4100 yr ago climate change has been suggested as a possible cause for the decline of urban centers of the indus civilization 4000 yr ago but extant paleoclimatic evidence has been derived from locations well outside the distribution of indus settlements here we report an oxygen iso tope record of gastropod aragonite 18 o a from holocene sediments of paleolake kotla dahar haryana india which is adjacent to indus settlements and documents indian summer mon soon ism variability for the past 6 5 k y a 4 increase in 18 o a occurred at ca 4 1 ka mark ing a peak in the evaporation precipitation ratio in the lake catchment related to weakening of the ism although dating uncertainty exists in both climate and archaeological records the drought event 4 1 ka on the northwestern indian plains is within the radiocarbon age range for the beginning of indus de urbanization suggesting that climate may have played a role in the indus cultural transformation

correlation of neoproterozoic terranes between the ribeira belt se brazil and its african counterpart comparative tectonic evolution and open questions

tracking the sources and the evolution of the late neoproterozoic granitic intrusions in the brusque group dom feliciano belt south brazil la icp ms and shrimp geochronology coupled to hf isotopic analysis abstract the central domain of the neoproterozoic dom feliciano belt in the brazilian state of santa catarina is mainly composed of a metavolcano sedimentary sequence the brusque group and its crystalline basement such as the camboriu complex this association was intruded in its late deformational stage by voluminous granitic magmatism related to the metamorphic climax of the area the intrusions share a distinct crustal affinity and are divided into three suites from oldest to youngest as indicated by field criteria sao joao batista valsungana and nova trento we present seven new la icp ms and two shrimp u pb zircon ages coupled with in situ analysis of hf isotopes and use them to discuss the magmatic sources and evolution of the intrusions and propose an evolutionary model for this plutonic association intrusion mostly took place at 615 585 ma but the field stratigraphy is not necessarily reflected by u pb ages which establish considerable overlaps between intrusions from different suites inherited zircon crystals are common and reflect a long geological history that matches the geochronological record of the brusque group and the camboriu complex hf ratios are remarkably widespread but strengthen the characteristic crustal signature of the magmatism and partially overlap with whole rock isotopic data for the same rocks we propose that the intrusions were caused by a regional heating event within the central domain of the dom feliciano belt in santa catarina with limited direct mantellic contribution and more significant indirect thermal contribution through the voluminous magmatism of the recently juxtaposed florianopolis batholith this triggered large scale partial melting of the local continental crustal and formed the studied granites the long lasting magmatic event promoted the protracted generation and emplacement of numerous distinct intrusions synchronically leading to contrasts between the field and u pb stratigraphy the suites varied geochemical and isotopic characteristics probably reflect a combination of the heterogeneities of their source rocks with the impact of different magmatic processes during granitogenesis and emplacement while the valsungana and nova trento suites were probably generated within a deeper crustal level and underwent some degree of magmatic interaction the peraluminous sao joao batista suite has an upper crust signature that indicates the assimilation of metasedimentary rocks

zircon growth and recycling during the assembly of large composite arc plutons abstract concordant u pb zircon dates have been interpreted traditionally to date the crystallization ages of plutons because until recently analytical uncertainties have generally been large enough to encompass the anticipated duration of pluton growth advances in zircon tims analysis and geochronological studies by sims on zircon from young volcanic rocks along with evolving views of the evolution of magmatic systems makes it necessary to revaluate this interpretation assignment of unique pluton crystallization ages based on zircon dating is complicated by the propensity of zircon to survive multiple intrusive events that culminate in a large pluton distinctions must be made between true inherited zircon xenocrystic zircon derived from host rocks during magma ascent and or emplacement and multi stage growth of zircon during waxing and waning of magma reservoirs that solidify to form large plutons these complications are exemplified by recent high precision u pb zircon age dating from the cretaceous tuolumne and mt stuart batholiths which clearly show that the timeframe of pluton assembly was long 5 ma for mt stuart and 8 ma for tuolumne zircon crystals from samples from both batholiths exhibit appreciable concordant age dispersion for zircon several 10 5 yr up to 2 10 6 yr and assignment of statistically valid rock solidification ages is not possible from these data low zr in the rocks of each batholith indicates that magmas were initially strongly undersaturated in zircon when emplaced and inherited zircon is rare or absent recycling of zircon antecrysts during successive magmatic injections is the primary cause of the modest age dispersion of concordant zircon ages and is compatible with progressive growth of a large long lived crystal mush body because eruption of magma requires low to moderate crystal fraction and high temperatures relative to stored crystal mushes zircon crystals are more likely to be eradicated during thermal rejuvenation preceding major eruptions

holocene evolution of the danube delta an integral reconstruction and a revised chronology abstract the danube delta is one of the few large deltas in the world the evolution of which has involved numerous and varied episodes within a complex framework of interactivity between river sediment supply allochthonous sediments supplied by longshore currents marine dispersing forces vertical movements neotectonics sediment compaction and sea level the resulting complex morphology comprises diversified landscapes varying from labyrinthic net of channels and lakes fluvial delta to massive tracts of monotonous reed marshes large lagoons divided by barriers or beach ridge plains accommodating large transgressive dunefields maritime delta whilst previous studies have focused on various sectors of the danube delta the current paper proposes for the first time an integral reconstruction of delta evolution based on existing and new sedimentological and morphological analyses and absolute ages ams 14 c and osl enabling a comprehensive synthesis in terms of both evolutionary phases and growth patterns a chronological framework was established for all the deltaic lobes and beach ridge plains highlighting the relationship between formation timespan growth rates and the resultant morphology this work unveils the early stage of delta formation including the reconstruction of delta front advancement into danube bay old danube lobe prior to 7 5 5 5 ka and initial spit barrier development 6 7 6 5 5 8 ka inception of the bayhead delta started 1000 yr before the relative stabilization of sea level and of the initial spit formation the original fluvial delta plain topography is now buried at a depth of 4 6 m depth below the present topography representing the current stage of fluvial aggradation as a result of subsidence and sea level rise regarding the maritime delta six large open coast lobes developed in the last six millennia of which four were formed by the sf gheorghe branch attesting the long uninterrupted activity of this branch whereas the other two were created respectively by the sulina and the chilia branches the evolution of each lobe is derived from successive chronological shoreline positions and discussed in relation with changes in danube discharge special attention has been paid to their growth stages and progradation rates for the southern delta we bring in new arguments for an active southern distributary the dunav derived from the sf gheorghe branch that formed successive open coast lobes between 2 6 and 1 3 ka additionally we discuss the effects of modern anthropogenically driven fluvial sediment reduction on the morphology and morphodynamics of the active lobes of the danube

magma assisted strain localization in an orogen parallel transcurrent shear zone of southern brazil in a lithospheric scale orogen parallel transcurrent shear zone of the pan african dom feliciano belt of southern brazil two successive generations of magmas an early calc alkaline and a late peraluminous have been emplaced during deformation microstructures show that these granitoids experienced a progressive deformation from magmatic to solid state under decreasing temperature conditions magmatic deformation is indicated by the coexistence of aligned k feldspar plagioclase micas and or tourmaline with undeformed quartz submagmatic deformation is characterized by strain features such as fractures lattice bending or replacement reactions affecting only the early crystallized phases high temperature solid state deformation is characterized by extensive grain boundary migration in quartz myrmekitic k feldspar replacement and dynamic recrystallization of both k feldspar and plagioclase decreasing temperature during solid state deformation is inferred from changes in quartz crystallographic fabrics decrease in grain size of recrystallized feldspars and lower ti amount in recrystallized biotites final low temperature deformation is characterized by feldspar replacement by micas the geochemical evolution of the synkinematic magmatism from calc alkaline metaluminous granodiorites with intermediate 87sr 86sr initial ratio to peraluminous granites with very high 87sr 86sr initial ratio suggests an early lower crustal source or a mixed mantle crustal source followed by a middle to upper crustal source for the melts shearing in lithospheric faults may induce partial melting in the lower crust by shear heating in the upper mantle but whatever the process initiating partial melting lithospheric transcurrent shear zones may collect melt at different depths because they enhance the vertical permeability of the crust these zones may then act as heat conductors by advection promoting an upward propagation of partial melting in the crust synkinematic granitoids localize most if not all deformation in the studied shear zone the regional continuity and the pervasive character of the magmatic fabric in the various synkinematic granitic bodies consistently displaying similar plane and direction of flow argue for accommodation of large amounts of orogen parallel movement by viscous deformation of these magmas moreover activation of high temperature deformation mechanisms probably allowed a much easier deformation of the hot synkinematic granites than of the colder country rock and consequently contributed significantly to the localization of deformation finally the small extent of the low temperature deformation suggests that the strike slip deformation ended approximately synchronously with the final cooling of the peraluminous granites the evolution of the deformation reflects the strong influence of synkinematic magma emplacement and subsequent cooling on the thermomechanical evolution of the shear zone magma intrusion in an orogen scale transcurrent shear zone deeply modifies the rheological behavior of the continental crust it triggers an efficient thermomechanical softening localized within the fault that may subsist long enough for large displacements to be accommodated therefore the close association of deformation and synkinematic magmatism probably represents an important factor controlling the mechanical response of continental plates in collisional environments

young danube delta documents stable black sea level since the middle holocene morphodynamic paleogeographic and archaeological implications new radiocarbon and optical dates show that the holocene danube delta started to build out of a black sea embayment 5200 yr ago delta lobe development phases differ by as much as 5 k y from previously proposed ages the new chronology allows for a better understanding of the danube delta paleogeography includ ing the demise of istria the main ancient greek roman city in the region prior reconstructions of sea level in the black sea inferred fluctuations to 15 m in range however stratigraphy of beach ridg es in the delta shows that the relative black sea level for the past 5 k y was stable in the danube delta region within 2 m and 1 5 of the current level hydroisostatic effects related to a proposed catastrophic reconnection of the black sea to the world ocean in the early holocene may have been responsible for the sea level reaching the highstand earlier than estimated by models the new sea level data suggest that submergence at several ancient settle ments around the black sea may be better explained by local fac tors such as subsidence rather than by basin wide sea level fluctuations

shear zone evolution and timing of deformation in the neoproterozoic transpressional dom feliciano belt uruguay abstract new structural microstructural and geochronological u pb la icp ms ar ar k ar rb sr data were obtained for the dom feliciano belt in uruguay the main phase of crustal shortening metamorphism and associated exhumation is recorded between 630 and 600 ma this stage is related to the collision of the rio de la plata and congo cratons at ca 630 ma which also involved crustal reworking of minor crustal blocks such as the nico perez terrane and voluminous post collisional magmatism subsequent orogen parallel sinistral shearing gave rise to further deformation up to ca 584 ma and resulted from the onset of the convergence of the kalahari craton and the rio de la plata congo cratons sinistral shear zones underwent progressive strain localization and retrograde conditions of deformation during crustal exhumation dextral ene striking shear zones were subsequently active at ca 550 ma coeval with further sinistral shearing along n to nne striking shear zones the tectonothermal evolution of the dom feliciano belt thus recorded the collision of the rio de la plata and congo cratons which comprised one of the first amalgamated nuclei of gondwana and the subsequent incorporation of the kalahari craton into western gondwana

regional stratigraphic framework and gas hydrate occurrence offshore eastern india core log seismic integration of national gas hydrate program expedition 02 nghp 02 area b drill sites abstract the indian national gas hydrate program expedition 02 nghp 02 was designed to study the occurrence of gas hydrate along the passive continental margin of the indian peninsula in the bay of bengal twelve holes were logged and measured with logging while drilling lwd and five holes were cored in area b of nghp 02 the lwd and coring results in area b helped to understand the geological significance of sequence stratigraphy in krishna godavari basin and identified the occurrence of gas hydrate this study summarized the log and litho units in area b and establish three integrated units based on the core log seismic integration most of the downhole log and core inferred gas hydrate occurrences are in the late miocene integrated unit b with several sets of reservoir sections exhibiting favorable conditions for hosting gas hydrate the gas hydrates reservoirs associated with reflectors r1 and r2 were identified and the r1 reservoirs are characterized by fracture and pore filling gas hydrate and the r2 is in sand rich sediments with pore filling gas hydrate at high saturations the thickness variations associated with the r1 and r2 are possibly associated with the development anticlinal structure and are likely related to syn sedimentary growth of the folding structures major gas hydrate zones exist in and around the r1 and r2 near the bsr depth and mostly have coincident with the fractures and mass transport deposits the spatial distribution of gas hydrate in the r1 and r2 reservoirs is highly influenced by the anticlinal structure this study can be considered a good case for the future gas hydrate studies and explorations in the nearby areas

geochronology of polygenetic monazites constrained by in situ electron microprobe th u total lead determination implications for lead behaviour in monazite abstract monazite grains are generally concordant and with an electron microprobe give th u total pb isochron ages in agreement with conventional u pb data monazites from four samples of post archean migmatite from the ivory coast record two main ages an archean age at 2 80 ga partly overprinted by a late migmatization event at 2 03 ga the in situ electron microprobe determination has also shown a third event that systematically appears at 2 72 ga for all the monazites from two of the four studied rocks the three events at 2 80 2 72 and 2 03 ga recorded by the th u total pb system in monazite were each obtained on independent homogeneous parts of a single grain with no sign of pb diffusion thus the oldest monazite remained closed during a high grade resetting migmatization at a temperature estimated at around 700 c and also remained closed during the growth of secondary monazite conventional u pb data isotope dilution on monazite from the same rocks did not allow precise age determinations because the representative points were highly up to 83 discordant and did not fit well along a chord in the concordia diagram the u pb isotope dilution method gave a lower intercept age of 2029 25 ma in agreement with the electron microprobe age although with an unusually high uncertainty due to a poor fit of the data the pb evaporation method gave an old archean age at 2830 7 ma and proterozoic ages ranging from 2417 10 to 2074 7 ma thus although the oldest archean age obtained with the pb evaporation and electron microprobe methods is similar within the analytical error the proterozoic ages obtained by the pb evaporation method are significantly older than the th u total pb proterozoic age obtained with the electron microprobe this discrepancy is presumed to be due to the influence in the pb evaporation method of radiogenic lead contained within archean zones of the monazite grains in other words it means that migmatization took place later than 2074 7 ma and probably around 2030 ma the second archean event at 2 72 ga revealed by high spatial resolution of the electron microprobe could not be determined by other methods the th u total pb method appears to be an inexpensive alternative method for dating simple monazites with a precision close to 20 ma even if the u pb isotopic dilution technique remains the reference method moreover owing to the very high spatial resolution 1 m of the electron microprobe it appears to have no competitor for dating complex polygenetic monazites especially when more than two events are recorded homogeneous zones of different ages coexist in a single grain with no major indication of lead diffusion a procedure for age and error calculations is defined

deformation in rocks from itajai basin southern brazil revealed by magnetic fabrics magnetic measurements were performed on sedimentary and volcanic rocks from the itajai basin rock magnetism analyses reveal that magnetite and hematite and paramagnetic minerals show different contributions to magnetic susceptibility magnetic fabrics were determined in 19 sites by applying both anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanence magnetization aarm the analysis at the individual site scale defines three ams fabric types the first type shows kmin perpendicular to the bedding plane while kmax and kint are scattered within the bedding plane itself this fabric is usually interpreted as primary the second type 77 of the sites shows the three well clustered ams axes with kmin still perpendicular to the bedding plane the third type is characterized by well clustered kmax in the bedding plane while kmin and kint are distributed along a girdle perpendicular to kmax the second and third fabric types are interpreted as combinations of sedimentary compactional and tectonic contributions at the earliest and at a slightly later stage of deformation respectively ams represents the contribution of all the rock forming minerals while aarm isolates the contribution of remanence bearing minerals with coercivity 100 mt for some sites the ams and aarm fabrics are non coaxial mainly with respect to the lineation orientations the comparison of magnetic lineations and the regional structural data indicates that the rocks with no mesoscopic or macroscopic deformation were affected by the two deformation phases that occurred in the region one of them results from compressional tectonics related to the collisional orogen d1 and the other is extensional related to post collisional orogen d2 after the former tectonic event the volcanic rocks were emplaced at the top of the stratigraphic sequence and after that the itajai basin as a whole was deformed by the extensional tectonic d2 that occurred after 560 ma which is the age of the intrusion

depositional age and provenance of the itajai basin santa catarina state brazil implications for sw gondwana correlation abstract the itajai basin is a fault bounded late to post orogenic basin deposited adjacent to the dom feliciano belt in the state of santa catarina brazil the basin is composed of alluvial deltaic and platformal successions followed by a turbiditic complex and fan delta deposits u pb zircon dating of a tuff and five sandstone samples indicates a maximum depositional age of 563 3 ma for the intermediate and upper sections of the itajai basin and zircon dating of a rhyolite stock indicates a minimum depositional age of 549 4 ma these dates are compatible with the previous assignment of an ediacaran age to the sediments based on the discovery of ediacara type fossils such as parvancorina charniodiscus cyclomedusa and aspidella the u pb detrital zircon ages show a change in the sedimentary input from the base to the top at the base zircon grains from the transamazonian and brasiliano pan african orogenic cycles occur as major sources with some archean contribution the upper section is dominated by brasiliano pan african zircon grains most of which range in age from 824 to 770 ma and 656 to 563 ma pb and sm nd whole rock isotope data suggest that the main source area for the basin infill was a reworked crust such as the dom feliciano belt we also present the regional correlation of the itajai basin with the basins formed during the late stages of the sw gondwana

post collisional transition from calc alkaline to alkaline magmatism during transcurrent deformation in the southernmost dom feliciano belt braziliano pan african uruguay abstract in the southernmost dom feliciano belt of uruguay highly fractionated calc alkaline granites mildly alkaline granites shoshonitic volcanics and peralkaline intrusions and volcanics are spatially and temporal associated with the evolution of shear zones four representative magmatic unites of this diverse association were petrographic and geochemically investigated the solis de mataojo complex a medium to high k2o calc alkaline granite with signature typical of mature continental arcs and post collisional settings the maldonado granite highly fractionated calc alkaline to alkaline with characteristics that are transitional between both types of series the pan de azucar pluton with characteristics typical of post collisional alkaline granites and the las flores shoshonitic basalts geochemistry and geotectonic setting point out that slab breakoff was most likely the mechanism associated with the generation of high k calc alkaline magmas solis de mataojo and maldonado shortly after collision extension associated to the formation of molassic basins and emplacement of dolerites and basalt flows with shoshonitic affinity las flores 15and finally a shift to magmas with alkaline signatures pan de azucar simultaneous with a second transpressional phase were probably linked with lithospheric thinning through delamination this evolution took place between 615 and 575 ma according to available data contrary to previous proposals which considered this magmatism to represent the root of a continental magmatic arc a post collisional environment transitional from orogenic to anorogenic during transcurrent deformation is proposed

a mid to late holocene record of vegetation decline and erosion triggered by monsoon weakening and human adaptations in the south east indian peninsula the mid to late holocene monsoon decline led to aridification of the indian peninsula impacting the early agricultural practices in the region our analysis of organic carbon mineral magnetic properties and ams 14c dating of a 54 2 m long sediment core cy from the godavari delta india showed changes in the organic carbon source and sediment provenance which are linked to the changes in vegetation and soil rock erosion caused by widespread aridification and associated human adaptation in central india our results show a decline in the concentration of ferrimagnetic minerals indicating reduced input from the basalts of the deccan plateau after 6 0 cal ka bp in response to the weaker indian monsoon 13c values show a distinct increase from 4 9 cal ka bp indicating an increase in c4 plant sources under the continued weak monsoon phase whereas a higher ferrimagnetic mineral concentration in the sediment suggested an increased deccan basalt source abrupt increase in 13c values and decrease in

human impact on land ocean sediment transfer by the world s rivers abstract land ocean transfer of sediment by rivers is a key pathway for material transfer on earth contemporary data on the sediment loads of rivers provide clear evidence of significant recent changes in the sediment fluxes of several rivers in response to human impact the key drivers of increased sediment loads include land clearance for agriculture and other facets of land surface disturbance including logging activity and mining although programmes for soil conservation and sediment control can result in reduced sediment loads the trapping of sediment by dams represents the dominant cause of reduced loads this influence is currently assuming increasing importance at the global scale any attempt to link these drivers to changes in the global land ocean sediment flux must take account of the aggregation and buffering effects that operate in larger basins which can cause damping and even removal of signals of increasing flux within the upstream basin and complicate the link between upstream and downstream response to human impact further work is required to provide a precise quantitative assessment of the human impact on global land ocean sediment fluxes and the net effect of increasing and decreasing fluxes particular attention must be paid to the temporal perspective and the variation of impact trajectories in different areas of the globe and for river basins of different sizes

palaeogeography and evolution of the godavari delta east coast of india during the holocene an example of wave dominated and fan delta settings abstract we investigated the holocene evolution of the godavari delta along the east coast of india by analyses of landforms and 11 borehole cores collected from the delta plain during 2010 2013 with 113 14c dates the godavari delta covering an area of 5820 km2 is one of the world s largest wave dominated deltas fringed by a 30 km wide beach ridge plain our analysis of sediment facies and their ages indicated that the holocene marine sequence thickens seaward from 10 m to more than 50 m and that the local relative sea level rapidly rose from 43 5 m to 7 5 m below the present sea level during 10 9 8 0 cal ky bp followed by a slow rise up to its current level around 5 cal ky bp spatio temporal variations in sediment accumulation rates and palaeo shorelines for the last 6 ky revealed successive changes of the main depocentre delta lobe we recognised six stages of delta evolution with distinct cyclic shifts of delta lobes controlled by avulsions a linear beach ridge located 12 14 km inland from the present shoreline which separates the first three lobes from the last three represents the effect of coastal erosion of past cuspate delta lobes as does the current linear shoreline of the central part of the delta our study documents continuous net progradation during the holocene on millennial to centennial time scales however a considerable decrease of sediment discharge due to dam construction and water diversion since the 1970s has exacerbated coastal erosion resulting in shrinking of the godavari delta plain and tipping it into a persistent destruction phase

pan african rifting and orogenesis in southern to equatorial africa and eastern brazil abstract the upper proterozoic pan african belts of africa and brasiliano belts of south america are assumed to have evolved from an elaborate system of continental rifts which formed on the west gondwana continent 1100 1000 ma ago reviews of the damara belt kaoko belt gariep belt saldania belt west congolian belt lufilian arc and zambezi belt of southern and equatorial africa and the ribeira mantiqueira belt of brazil show the applicability of the continental rifting model to all these belts strict application of the rifting model describing the formation and further evolution of rift structures in the continental crust leads to the conclusion that the west congolian belt as traditionally described is incomplete and has to be supplemented by the mayumbian belt and a rift structure situated farther to the west the lufilian arc is assumed to have evolved from two rift structures separated from each other by the later domes region the golfe du katanga which branches off northeastwards from the lufilian arc is interpreted as an aulacogen shaba aulacogen the pan african brasiliano rift system is comparable to the mesozoic arctic north atlantic rift system with regard to size and distribution of rifts ocean floor spreading and opening of a proto south atlantic ocean most probably occurred along a main line of rifting situated between the west coast of africa and eastern brazil the wedge like ocean may have terminated at the sao francisco congo cratonic bridge between northeastern brazil and gabon cameroon there is no evidence of ocean floor spreading in the zambezi belt the lufilian arc and the traditional west congolian belt which are arranged along another major line of rifting closure of the pan african brasiliano rift system took place during two successive orogenic episodes the zambezi belt lufilian arc and west congolian belt underwent their main orogenic deformation with prevailing ene and wsw oriented tectonic transportation directions during the katangan episode at 900 750 ma the transcontinental sinistral mwembeshi shear zone adjusted opposite movement directions in the zambezi belt and lufilian arc and at its western prolongation concurrently supported opening of the khomas trough in the southern damara belt the proto south atlantic ocean still opening during the katangan episode was gradually closed during the damaran episode at 750 500 ma closure proceeded from north to south and was accompanied by northwest directed subduction underneath the brazilian plate and southeast directed tectonic transportation in the kaoko damara and gariep belts in the previously formed west congolian belt lufilian arc and zambezi belt a second deformation phase characterized by strike slip faulting and local emplacement of nappes occurred during this episode

parameterizing parasequences importance of shelf gradient shoreline trajectory sediment supply and autoretreat the basic reservoir flow unit in shallow marine depositional systems is the parasequence since it is bounded top and base by regionally extensive shales that can form barriers to fluid flow as a result it is the key stratigraphic unit requiring parameterization for both exploration and development purposes a database comprising 3385 measurement points from 385 parasequences from 28 locations and 16 different passive margin and foreland basins was compiled from outcrop and subsurface data analysis of the data suggests that a mean value for parasequence thickness is 17 m 56 ft mean parasequence sandstone fraction is 0 60 and mean shoreface sand body thickness is 8 m 26 ft the mean maximum parasequence progradation distance is 23 km 14 mi the results indicate that there are two critical controls that can significantly vary the parameter values stated above 1 stacked shoreline trajectory or systems tract and 2 shelf gradient the analyses indicate that shelf gradient is the most important parameter that has a first order control on parasequence properties shelf gradient in the ancient can be approximated to high gradient or low to moderate gradient categories via analysis of parasequence thickness change versus progradation distance from wells mean parasequence thickness or mean progradation distance from seismic attribute data parasequence progradation distance is to some degree predictable if stacked shoreline trajectory shelf gradient category and mean parasequence thickness are known the data suggest that there are two types of parasequences accommodation dominated and supply dominated parasequences the progradation distance of these parasequences are controlled by delta autoretreat mechanisms modulated by the combination of fifth and fourth order milankovitch scale orbitally forced climate change driven sediment supply cycles interacting with eustatically and tectonically driven accommodation cycles

time constraints on magmatism along the major gercino shear zone southern brazil implications for west gondwana reconstruction the dom feliciano belt situated in southernmost brazil and uruguay contains a large mass of granite gneissic rocks also known as florianopolis pelotas batholith formed during the pre syn and post orogenic phases of the brasiliano pan african cycle in the ne extreme of this granitic mass pre syn and post tectonic granites associated with the major gercino shear zone mgsz are exposed the granitic manifestation along the mgsz can be divided into pre kinematic tonalitic gneisses peraluminous high k calc alkaline early kinematic shoshonitic and metaluminous post kinematic granites u pb zircon data suggest an age of 649 10 ma for the pre tectonic gneisses and a time span from 623 6 ma to 588 3 ma for the early to post tectonic magmatism negative ehf t values ranging from 4 6 to 14 6 and hf model ages ranging from 1 64 to 2 39 ga for magmatic zircons coupled with whole rock nd model ages ranging from 1 24 to 2 05 ga and end t values ranging from 3 84 to 7 50 point to a crustal derivation for the granitic magmatism the geochemical and isotope data support a continental magmatic arc generated from melting of dominant paleoproterozoic crust and a similar evolution for the granitic batholiths of the eastern dom feliciano belt and western kaoko belt

river avulsions and sedimentary evolution of the luanhe fan delta system north china since the late pleistocene abstract the luanhe fan delta lfd is one of the most important coastal deltas in north china numerous investigations on the late quaternary evolution of this fan delta system have been implemented during the 1980s however few detailed sedimentologic studies have been undertaken based on comprehensive analysis of sedimentary facies grain size microfossils radiocarbon dates ams14c and optically stimulated luminescence osl ages from three 30 m long cores along with recent reports from a series of cores and seismic profiles from the coastal areas we reconstructed the detailed late quaternary sedimentary evolution of the northern bohai coast which evolved from a coastal barrier lagoon system during mis5 to an alluvial plain with river channels and floodplains between mis4 and the early holocene a variety of transgressive coastal depositional environments freshwater marshes beach ridges sandy barriers shallow seas developed during the early holocene these environments were followed by delta progradation the delta system then gradually turned into a coastal barrier lagoon system under the combined impact of prevailing wave driven currents and local subsidence two dramatic 90 degree diversions of the lower luanhe river course likely influenced the sedimentary evolution of the lfd in its inner portion the first avulsion took place in qianxi probably at the end of the late pleistocene 15 000 cal a bp it led to the abandonment of the luanhe alluvial fan in the western part of the northern bohai coastal plain nbcp and to the formation of a new alluvial fan in the eastern nbcp this alluvial fan evolved into a fan delta system 7000 3500 cal a bp during the holocene transgression the second avulsion occurred at zhuacun during the late holocene probably at 3600 100 cal a bp following this latter avulsion the luanhe river shifted toward the east and formed a new fan delta system 3700 cal a bp present with its apex in luanzhou abrupt tectonic uplift in this highly seismic region likely controlled the two avulsions and the dramatic shift of the alluvial fan complexes climate and sea level changes may also have partly influenced the development of the lfd

multiscale magmatic cyclicity duration of pluton construction and the paradoxical relationship between tectonism and plutonism in continental arcs abstract the close relationship between crustal magmatism an expression of heat dissipation and tectonics an expression of stress dissipation leads to the question of their mutual relationships indeed the low viscosity of magmas and the large viscosity contrast between magmas and surrounding rocks favor strain localization in magmas and then possible magmatic initiation of structures at a wide range of scales however new data about 3 d pluton shape and duration of pluton construction perturb this simple geological image and indicate some independence between magmatism and tectonics in some cases we observe a direct genetic link and strong arguments for physical interactions between magmas and tectonics in other cases we observe an absence of these interactions and it is unclear how magma transfer and emplacement are related to lithospheric plate dynamics a simple explanation of this complexity follows directly from the pulsed incremental assembly of plutons and its spatial and temporal characteristics the size of each pluton is related to a magmatic pulsation at a particular time scale and each of these coupled time space scales is related to a specific process in small plutons we can observe the incremental process the building block of plutons in larger plutons the incremental process is lost and the pulsation which consists of a cycle of injections at different timescales must be related to the composition and thermal regime of the source region itself driving magmatic processes melting segregation and transfer that interact with tectonic boundary conditions the dynamics of pulsed magmatism observed in plutonic systems is then a proxy for deep lithospheric and magmatic processes from our data and a review of published work we find a positive corelation between volume and duration of pluton construction the larger a pluton the longer its construction time large fast or small slow plutons have not been identified to date one consequence of this observation is that plutonic magmatic fluxes seem to be comparable from one geodynamic setting to another and also over various geologic time spans a second consequence of this correlation is that small plutons which are constructed in a geologically short length of time commonly record little about tectonic conditions and result only from the interference between magma dynamics and the local geologic setting the fast rate of magma transfer in the crust on the order of cm s relative to tectonic rates on the order of cm yr explain why the incremental process of pluton construction is independent of but not insensitive to the tectonic setting however in large plutonic bodies which correspond to longer duration magmatic events regional deformation has time to interact with the growing pluton and can be recorded within the pluton wall rock structure magma transfer operates at a very short timescale comparable to volcanic timescales which can be sustained over variable periods depending on the fertility of the magma source region and its ability to feed the system the fast operation of magmatic processes relative to crustal tectonic processes ensures that the former control the system from below

refining the eustatic sea level curve since the last glacial maximum using far and intermediate field sites the eustatic component of relative sea level change provides a measure of the amount of ice transferred between the continents and oceans during glacial cycles this has been quantified for the period since the last glacial maximum by correcting observed sea level change for the glacio hydro isostatic contributions using realistic ice distribution and earth models during the last glacial maximum lgm the eustatic sea level was 125 5 m lower than the present day equivalent to a land based ice volume of 4 6 4 9 107 km3 evidence for a non uniform rise in eustatic sea level from the lgm to the end of the deglaciation is examined the initial rate of rise from ca 21 to 17 ka was relatively slow with an average rate of ca 6 m ka 1 followed by an average rate of ca 10 m ka 1 for the next 10 ka significant departures from these average rates may have occurred at the time of the younger dryas and possibly also around 14 ka most of the decay of the large ice sheets was completed by 7 ka but 3 5 m of water has been added to the oceans since that time

early post collisional granitic and coeval mafic magmatism of medium to high k tholeiitic affinity within the neoproterozoic southern brazilian shear belt abstract the post collisional stage of the brasiliano pan african orogenic cycle in the garopaba region southern brazil began at 630 620 ma by the emplacement of large granitic massifs with associated mafic rocks the paulo lopes suite pls is composed of metaluminous to slightly peraluminous biotite hornblende paulo lopes and garopaba granitoids and by the silveira gabbro containing augite pigeonite and orthopyroxene mafic microgranular enclaves and mutual intrusive relations attest to the coeval character of mafic and felsic magmas the pls intruded during regional transcurrent shearing and microstructures indicative of high temperature solid state deformation are described in the mafic and granitic rocks mafic rocks are medium to high k tholeiitic and show mineralogical and geochemical features including isotopic ones that are compatible with magmas from sources modified by previous lithospheric subduction such as oib em1 the pls granitic magmas are interpreted as evolved from a mafic magma that was compositionally equivalent to the silveira gabbro contaminated by crustal melts or by more complex mechanisms hence they may be considered as granitic magmas of tholeiitic affinity transcurrent shearing seems to be essential for promoting the generation of mantle derived magmas and their interaction with crustal melts with consequent generation of abundant granitoids basic magmas have resulted from melting of heterogeneous mantle reservoirs and their highly evolved character is indicated by their low contents of mgo ni and cr the compositional similarity of pls granitoids particularly the garopaba granitoids with a type granitoids discriminates them from the medium to high k granitoids of mature magmatic arcs and this difference probably reflects the tholeiitic character of their primary magmas typical of the early magmatic stages of post collisional settings in southern brazil trace element and isotopic geochemical data indicate subduction modified oib mantle sources for the mafic magmas which is coherent with the post collisional character of this magmatism

the itajai foreland basin a tectono sedimentary record of the ediacaran period southern brazil the itajai basin located in the southern border of the luis alves microplate is considered as a peripheral foreland basin related to the dom feliciano belt it presents an excellent record of the ediacaran period and its upper parts display the best brazilian example of precambrian turbiditic deposits the basal succession of itajai group is represented by sandstones and conglomerates bau formation deposited in alluvial and deltaic fan systems the marine upper sequences correspond to the ribeirao carvalho channelized and non channelized proximal silty argillaceous rhythmic turbidites ribeirao neisse arkosic sandstones and siltites and ribeirao do bode distal silty turbidites formations the apiuna formation felsic volcanic rocks crosscut the sedimentary succession the cambrian subida leucosyenogranite represents the last felsic magmatic activity to affect the itajai basin the brusque group and the florianopolis batholith are proposed as source areas for the sediments of the upper sequence for the lower continental units the source areas are the santa catarina sao miguel and camboriu complexes the lack of any oceanic crust in the itajai basin suggests that the marine units were deposited in a restricted internal sea the sedimentation started around 600 ma and ended before 560 ma as indicated by the emplacement of rhyolitic domes the itajai basin is temporally and tectonically correlated with the camaqua basin in rio grande do sul and the arroyo del soldado piriapolis basin in uruguay it also has several tectono sedimentary characteristics in common with the african equivalent nama basin

mid holocene mangrove succession and its response to sea level change in the upper mekong river delta cambodia abstract middle holocene vegetation and mangrove successions are clearly evident in the palynological records of two cores from the upper mekong river delta in cambodia spanning from 9 4 to 6 3 cal ka bp the cores mainly record a transgressive sequence from floodplain freshwater marsh to tidal flat which was overlain by mangrove corresponding to the decelerated sea level rise at 8 3 cal ka bp pioneer mangrove species sonneratia alba and sonneratia caseolaris appeared in the sediments and then was replaced by regressive mangrove succession containing upward increasing abundances of rhizophora apiculata and bruguiera spp high salinity and flooding tolerant community s alba was developed at the western core site psg at 8 2 cal ka bp and the eastern core site pk at 7 5 cal ka bp the time difference of s alba appearance between the two sites might be resulted from the complexity of sedimentary environment where a higher sediment supply was provided to the western floodplain than to the eastern floodplain after 7 5 cal ka bp aggradational stacking of intertidal sediments of which the thickness is larger than the present maximum tidal range may have resulted from continuous sea level rise during 7 5 7 0 cal ka bp