high pressure transformation of eclogite to garnetite in subducted oceanic crust the mineral composition of oceanic crust is a function of pressure and temperature and thus changes as a slab of crust descends a subduction zone a knowledge of the mineralogy of subducted material would provide important constraints on its geophysical characteristics we have sought by means of high pressure laboratory experiments in the pressure range 4 6 18 gpa on a synthetic mix with the composition of mid ocean ridge basalt morb to determine the sequence of mineralogical changes we find that at 1 200 c solid solution of pyroxene in garnet begins around 10 gpa and increases substantially between 12 and 15 gpa complete transformation of eclogite to garnetite is achieved at 15 gpa the garnetite has a zero pressure density of 3 76 g cm 3 and accordingly would be denser than the surrounding mantle throughout its stability field which extends to depths of 600 km if subducted to greater depths garnetite may transform to perovskitite

cambrian ordovician acritarchs in the meguma terrane nova scotia canada resolution of early paleozoic stratigraphy and implications for paleogeography organic walled microfossils acritarchs provide age constraints for the previously poorly dated cambrian and lower ordovician turbiditic goldenville and halifax groups in the northern appalachian meguma terrane of nova scotia and address controversies about stratigraphy and provenance the oldest exposed formation of the 8 km thick goldenville group contains the trace fossil oldhamia which suggests an age of late early cambrian whereas the coticule bearing uppermost formation yielded an acritarch species consistent with middle cambrian epoch 3 age the conformably overlying 5 km thick halifax group includes basal pyritiferous units that yielded a late cambrian furongian assemblage of acritarch species providing further confirmation that the underlying manganese bearing formations are of cambrian epoch 3 age and not ordovician as recently claimed overlying nonpyritiferous formations contain the early ordovician graptolite rhabdinopora flabelliformis flabelliformis and acritarchs of similar age samples collected up section from the graptolite occurrence yielded acritarch species that are indicative of the later tremadocian and floian the new fossil data confirm a gap in age of 30 m y between the halifax group and the overlying silurian to lower devonian rockville notch group the new ages are consistent with stratigraphic units defined in regional mapping and support recent interpretation of fundamental differences in depositional and tectonic environments between the northwestern and southeastern parts of the meguma terrane they also provide new constraints on paleogeography of the terrane by confirming age similarities to stratigraphy in north wales with which correlation has been proposed previously based mainly on lithological similarities

coesite and pure pyrope in high grade blueschists of the western alps a first record and some consequences a pyrope quartzite originally described by vialon 1966 from the dora maira massif was resampled and reinvestigated garnet up to 25 cm in size phengite kyanite talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz the garnet is a pyrope almandine solid solution with 90 to 98 mol mg end member it contains inclusions of coesite which has partially inverted to quartz resulting in a typical radial cracking of the host garnet around the inclusions several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite

the tectonostratigraphy and structure of the eastern nepal himalaya six years of geological research in eastern nepal has resulted in a new geological map of the eastern nepal himalaya which includes the region stretching from the sikkhim border in the east to the kathmandu valley in the west and from the summits of the higher himalaya in the north to the ganges plain in the south this research has permitted the determination of the tectonostratigraphy and structure of one section of the central himalayan arc south of the tibetan plateau the eastern nepal himalaya can be divided into three distinct thrust bound tectonic packages 1 the higher himalayan thrust sheet composed of the higher himalayan crystallines 2 the lesser himalayan thrust sheet composed of the lesser himalayan series and 3 the sub himalayan imbricate zone composed of sedimentary rocks belonging to the siwalik group the higher himalayan thrust sheet of eastern nepal has been thrust over the lesser himalayan metasediments a minimum of 140 km and possibly as much as 175 210 km along the main central thrust mct the lesser himalayan thrust sheet is overlain by the mct and is underlain by the main detachment fault mdf and the main boundary thrust mbt out of sequence thrust faults in the hanging wall of the mbt have breached and offset the presently inactive mct the sub himalayan imbricate zone is an emergent imbricate fan bounded by the mbt to the north and the main frontal thrust mft to the south and is underlain by the mdf which lies at a depth of between 5 km and 7 km a balanced cross section constructed across the higher lesser and sub himalaya of eastern nepal shows that the eastern nepal himalayan orogenic wedge has undergone a minimum of between 210 and 280 km of horizontal north south tectonic shortening since the initiation of the mct the lesser and sub himalaya have absorbed 70 km of north south shortening by thrusting along the basal mdf of which the sub himalayan imbricate zone has accommodated 25 km the sun kosi thrust has accommodated about 10 km and the mbt has accommodated the remaining 35 km of shortening since the initiation of the mct between 15 ma and 25 ma shortening across the eastern nepal himalaya has occurred at an average rate of 8 4 18 6 mm per year the structural geometry of the eastern nepal himalaya suggests an overall piggyback sequence of thrusting with motion transferred from the mct to the underlying mdf and its emergent splay thrust the mbt and with the mbt rotated to its present steep orientation by imbricate thrusting within the sub himalaya

palaeogeographical controls on the cambrian trilobite immigration and evolutionary patterns reported in the western gondwana margin abstract southward drifting of the western gondwanan margin during the cambrian has been demonstrated by means of both palaeomagnetic methods and lithological indicators of climate such as carbonates and evaporites recent improvements in biostratigraphical correlations permit an enhanced understanding of the climatic and palaeobiogeographical constraints that controlled the distribution of cambrian benthic communities palaeogeographical and biogeographical reconstructions based on trilobites are reported in this paper in order to test interaction between migration speciation and extinction rates the variability of the documented biogeographical patterns is directly related to species diversity in which wider distribution coincides with transgressive trends and subsequent connection of neighbouring platforms early cambrian trilobite faunas show a high degree of both substrate control and endemicity although transgressions led to parallel shifts in faunal compositions by contrast mid cambrian trilobite faunas are relatively uniform across western gondwana and latest mid and late cambrian associations document influence of an increased similarity with asian trilobite faunas

sequence stratigraphy of the palaeozoic welsh basin the timing and extent of unconformities in the welsh basin are investigated using rock preservation curves derived from outcrop stratigraphic logs four basin wide unconformities occur focussed in late precambrian late tremadoc pusgillian early ashgill and mid devonian times these bound three megasequences equating with newly defined lithostratigraphic units the dyfed gwynedd and powys supergroups less extensive unconformities bound 18 component sequences the majority of the sequence boundaries reflect a component of tectonic or volcanotectonic activity rather than a pure eustatic sea level change the megasequence boundaries are attributed to late precambrian to early cambrian onset of rifting to form a passive margin tremadoc onset of subduction with intra arc then back arc extension late caradoc end to subduction and late early devonian collisional deformation the megasequences and controlling events can be tentatively matched with other basins on the avalonian margin more generally this study shows that sequence analysis is feasible in onshore basins lacking well and seismic data and that the global eustatic interpretation of sequence stratigraphy is only partially applicable to active margin basins

sinking slabs puncture layered mantle model seismologists are finding that oceanic plates sinking into the mantle plunge right through the supposedly impenetrable boundary between the upper and lower mantle

the crystalline units of the high himalayas in the lahul zanskar region northwest india metamorphic tectonic history and geochronology of the collided and imbricated indian plate in the high himalayan belt of northwest india crustal thickening linked to palaeogene collision between india and eurasia has led to the formation of two main crystalline tectonic units separated by the syn metamorphic miyar thrust the high himalayan crystallines sensu stricto hhc at the bottom and the kade unit at the top these units are structurally interposed between the underlying lesser himalaya and the very low grade sediments of the tibetan nappes they consist of paragneisses orthogneisses minor metabasics and chiefly in the hhc leucogranites the hhc registers a polyphase metamorphism with two main stages designated as m1 and m2 a metamorphic zonation with high temperature recrystallization and migmatization at middle structural levels and medium temperature assemblages at upper and lower levels in contrast the kade unit underwent a low temperature metamorphism rb sr and u th pb isotope data point to derivation of the orthogneisses from early palaeozoic granitoids while the leucogranites formed by anatexis of the hhc rocks and were probably emplaced during miocene time most of the complicated metamorphic setting is related to polyphase tectonic stacking of the hhc with the cooler kade unit and lesser himalaya during the himalayan history however a few inconsistencies exist for a purely himalayan age of some ml assemblages of the hhc as regards the crustal derived leucogranites the formation of a first generation mixed with quartzo feldspathic leucosomes was possibly linked to melt lubricated shear zones which favoured rapid crustal displacements at upper levels they intruded during stage m2 and the latest movements along the syn metamorphic miyar thrust but before juxtaposition of the tibetan nappes along the late metamorphic zanskar fault

overview of 20 years of field measurements in the coastal zone and at the petten sea dike in the netherlands abstract this paper intends to give an overview of almost 20 years 1994 2013 of field measurements at the petten site in the netherlands and to list the main research findings derived from these measurements the main objectives of the petten site were to obtain field data of i wave propagation from deep water through the surf zone to the dike ii wave run up against the dike and iii since 2006 wave overtopping the paper describes the evolution of the site lay out during its existence and discusses the data collection processing and dissemination the most important research findings based on petten site data have been obtained in research projects like opticrest 1998 2001 clash 2002 2004 and wti 2003 2013 the results of the wti project on wave overtopping wave run up redundant wave measurements and rapid bathymetric changes are described here in more detail because these results have not gained widespread attention yet

badrinath gangotri plutons garhwal india petrological and geochemical evidence for fractionation processes in a high himalayan leucogranite the gangotri leucogranite is the western end of the badrinath granite one of the largest bodies of the high himalayan leucogranite belt hhl it is a typical fine grained tourmaline muscovite biotite leucogranite the petrography shows a lack of restitic phases the inferred crystallization sequence is characterized by the early appearance of plagioclase quartz and biotite and by the late crystallization of the k feldspar this suggests that in spite of being of near minimum melt composition the granite probably had long crystallization or melting interval in agreement with previous experimental studies tourmaline and muscovite have a mainly magmatic origin even though the major element composition is homogeneous there are several geochemical trends when cao decreases there is an increase in na2o rb sn u b f and a decrease in k2o fe2o3 tio2 sr ba zr ree th which are best explained by a fractionation process with early crystallizing phases experimental solubility models for zircon and monazite in felsic melt support a magmatic origin for these two accessory phases as well rb sr isotope data show this granite to have like other hhl heterogeneous isotopic values for sr initial 87sr 86sr ratios calculated at 20 ma range between 0 765 and 0 785 therefore no mixing i e no convection occurred between the different batches of magma in contrast 18o data show little variation 13 04 0 25 implying a source with homogeneous 18o values differences in timing between fluid infiltration and the onset of melting related to differences in temperature of the source could explain why source homogenization occurred for the gangotri and not for the manaslu granite the use of experimental results for solubility and the position of the accessory minerals during melting predict a low viscosity for the melt during its extraction this in turn explains the lack of restitic phases major and accessory in the granite as well as some field features lensoid shape pronounced magmatic layering based on the petrographic and isotopic studies it is suggested that the mechanism of ascent was not diapiric but rather that the melt ascended along several fractures and the level of emplacement was partialy controlled by the density contrast between the melt and host rocks

automatic extraction of shorelines from landsat tm and etm multi temporal images with subpixel precision abstract a high precision geometric method for automated shoreline detection from landsat tm and etm imagery is presented the methodology is based on the application of an algorithm that ensures accurate image geometric registration and the use of a new algorithm for sub pixel shoreline extraction both at the sub pixel level the analysis of the initial errors shows the influence that differences in reflectance of land cover types have over shoreline detection allowing us to create a model to substantially reduce these errors three correction models were defined according to the type of gain used in the acquisition of the original landsat images error assessment tests were applied on three artificially stabilised coastal segments that have a constant and well defined land water boundary a testing set of 45 images 28 tm 10 etm high gain and 7 etm low gain was used the mean error obtained in shoreline location ranges from 1 22 to 1 63 m and the rmse from 4 69 to 5 47 m since the errors follow a normal distribution then the maximum error at a given probability can be estimated the results confirm that the use of landsat imagery for detection of instantaneous coastlines yields accuracy comparable to high resolution techniques showing the potential of landsat tm and etm images in those applications where the instantaneous lines are a good geomorphological descriptor

records of the evolution of the himalayan orogen from in situ th pb ion microprobe dating of monazite eastern nepal and western garhwal abstract in situ th pb monazite ages from rocks collected along two transects the dudh kosi everest eastern nepal and the bhagirathi river garhwal himalaya india perpendicular to the main central thrust mct suggest a striking continuity of tectonic events across the himalaya the youngest age reported in this study 5 9 0 2 ma mswd 0 4 from matrix monazite grains collected beneath the mct in the garhwal region is consistent with several age data from rocks at similar structural levels in central nepal providing support for widespread late miocene mct activity the lateral parallelism of orogenic events is further manifested by the 20 7 0 1 ma age of a high himalayan leucogranite from an injection complex that outcrops along the dudh kosi everest transect resembling ages of these bodies reported elsewhere the youngest monazite grain analyzed along the dudh kosi everest transect is 10 3 0 8 ma the absence of 7 3 ma monazite ages in eastern nepal may reflect a different nappe structure which obscures the reactivated ramp equivalent exposed in the garhwal and central nepal garnets from the mct hanging wall greater himalayan crystallines and footwall lesser himalaya display different major element zoning and the patterns are useful for constraining the location of the thrust system that separates the two lithologies pressure temperature paths for two upper lesser himalayan garnets that contain monazite inclusions indicate the utility of an in situ methodology to constrain the metamorphic evolution of the shear zone along the dudh kosi everest transect upper lesser himalayan monazite grains from three rocks record a clear signal at 14 5 0 1 ma mswd 8 4 and the 23 ma age that characterizes the hanging wall is notably absent monazites collected within a large scale greater himalayan crystallines fold yield the 14 ma age consistent with the structure forming due to mct related compression paleo mesoproterozoic 1407 35 ma matrix monazite grains are found within an augen gneiss unit located beneath the mct whereas cambro ordovician 436 8 548 17 ma inclusions are preserved within garnets of the greater himalayan crystallines the presence of 45 2 2 1 ma grains from lower structural levels of the greater himalayan crystallines indicates the unit realized conditions conducive for monazite growth during the eocene

guzhangian mid cambrian trilobites from siliceous concretions of the valtorres formation iberian chains ne spain in the carbonate siliciclastic strata of west gondwana e g in the montagne noire france the aftermath of the mid languedocian mid cambrian regression is characterized by a late languedocian major turnover of trilobite families and a furongian early tremadocian radiation related to the stepwise immigration of trilobite invaders from east gondwana under persistent transgressive conditions the scarcity of upper languedocian fossil accumulations in clayey substrates has inspired the sampling of the palaeogeographically most distal parts of the iberian chains spain where diagenetic dissolution of ubiquitous hexactinellid sponge spicules has favoured the formation of siliceous concretions these have yielded the trilobites peronopsis cf insignis oidalagnostus trispinifer proampyx difformis proampyx aculeatus bailiaspis glabrata holocephalina agrauloides by ontogeny holasaphus cf centropyge and a paradoxidid gen et sp indet despite preservation and sampling biases the identification of this taphonomic window in offshore clayey substrates of west gondwana allows the recognition of a strong biogeographical link with baltica and the correlation of the global guzhangian stage and the solenopleura brachymetopa zone of scandinavia with part of the mediterranean upper languedocian substage less

groin impacts on updrift morphology physical and numerical study abstract groins interfere with coastal dynamics and sediment transport leading to sediments accumulation at the updrift side while at downdrift the erosive process is anticipated due to the lack of sediments to improve numerical modeling capacity to simulate the groins impacts it is necessary to totally understand the shoreline evolution along time and its relationship with the cross shore profiles shape the main goal of this work was to analyze and compare the performance of physical and numerical studies on evaluating the evolution of updrift cross shore profiles geometry and shoreline position after the construction of a groin this study analyzed a coastal stretch updrift of the groin at a prototype and model scales considering the analytical formulation of pelnard considere the numerical model ltc long term configuration and the laboratory tests the laboratory tested scenario was designed with the aim to gather results which could be analyzed and compared with numerical simulations from ltc coelho 2005 allowing its improvement and with the pelnard considere 1956 analytical formulation both at model scale the developed study shows an important difference between ltc and pelnard considere 1956 approaches because the analytical solution for the shoreline in equilibrium does not include the wave refraction effects over the updated bathymetry ltc observed trend of the equilibrium shoreline is not parallel to the initial shoreline and this behavior was confirmed in the laboratory tests it was also observed that the sediment transport capacity has very small impact on the ltc shoreline configuration despite the refraction effects over the updated bathymetries along time the profile shape obtained in laboratory includes bed forms difficult to reproduce in long term numerical modeling evaluation of cross shore profiles because ltc transversal behavior is only based on geometrical considerations and does not represent cross shore sediment transport and its impact on profile geometry

evaluation of annual mean shoreline position deduced from landsat imagery as a mid term coastal evolution indicator abstract the shoreline is a useful indicator of mid term coastal evolution every shoreline is affected by instantaneous sea level the length of the run up and beach profile changes in this work annual mean shorelines are evaluated in a manner that avoids these effects by averaging the instantaneous shoreline positions registered during the same year a set of 270 shorelines obtained from landsat imagery between 2000 and 2014 using the method described in pardo pascual et al 2012 have been used it has been shown that the use of annual mean shorelines enables the same rate of change to be obtained as when using all the shorelines but that the data is simpler to manage and more useful when visualising local changes it has also been shown that annual mean shorelines largely remove the short term variability and are therefore useful for analysing mid term trend quantifications in addition we propose a methodology for annual mean shorelines obtained from landsat imagery that minimises the effects of sea level variation on the shoreline positions both shorelines instantaneous and mean annual appear to be about 4 or 5 m seaward from those obtained using more precise sources

stratigraphy structure and tectonic evolution of the himalayan fold thrust belt in western nepal regional mapping stratigraphic study and 40ar 39ar geochronology provide the basis for an incremental restoration of the himalayan fold thrust belt in western nepal tectonostratigraphic zonation developed in other regions of the himalaya is applicable with minor modifications in western nepal from south to north the major structural features are 1 the main frontal thrust system comprising the main frontal thrust and two to three thrust sheets of neogene foreland basin deposits 2 the main boundary thrust sheet which consists of proterozoic to early miocene lesser himalayan metasedimentary rocks 3 the ramgarh thrust sheet composed of paleoproterozoic low grade metasedimentary rocks 4 the dadeldhura thrust sheet which consists of medium grade metamorphic rocks cambrian ordovician granite and granitic mylonite and early paleozoic tethyan rocks 5 the lesser himalayan duplex which is a large composite antiformal stack and hinterland dipping duplex and 6 the main central thrust zone a broad ductile shear zone the major structures formed in a general southward progression beginning with the main central thrust in late early miocene time eocene oligocene thrusting in the tibetan himalaya north of the study area is inferred from the detrital unroofing record on the basis of 40ar 39ar cooling ages and provenance data from synorogenic sediments emplacement of the dadeldhura thrust sheet took place in early miocene time the ramgarh thrust sheet was emplaced between 15 and 10 ma the lesser himalayan duplex began to grow by 10 ma simultaneously folding the north limb of the dadeldhura synform the main boundary thrust became active in latest miocene pliocene time transport of its hanging wall rocks over an 8 km high footwall ramp folded the south limb of the dadeldhura synform thrusts in the subhimalayan zone became active in pliocene time the minimum total shortening in this portion of the himalayan fold thrust belt since early miocene time excluding the tibetan zone is 418 493 km the variation depending on the actual amounts of shortening accommodated by the main central and dadeldhura thrusts the rate of shortening ranges between 19 and 22 mm yr for this period of time when previous estimates of shortening in the tibetan himalaya are included the minimum total amount of shortening in the foldthrust belt amounts to 628 667 km this estimate neglects shortening accommodated by small scale structures and internal strain and is therefore likely to fall significantly below the actual amount of total shortening

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

distribution and transport of suspended sediments off the yellow river huanghe mouth and the nearby bohai sea abstract hydrological and sedimentological investigations were carried out off the yellow river huanghe mouth and the nearby bohai sea during august september 2007 to examine the distribution and transport of suspended sediments our data witnessed that suspended sediments from the yellow river mouth primarily extend southerly and southeasterly during the flood season high suspended sediment concentration ssc occurs as turbid plume on both sides of the river mouth where it can reach 20 mg l 1 in the surface water and 40 mg l 1 in the bottom water accordingly salinity varies from 25 to 29 psu mean grain size dmz is 200 m and volume concentration vc is 100 l l 1 high ssc was concentrated in the river mouth area as two muddy patches i e the north mud and south mud consisting mostly of fine grained silt and clayey silt sediments our results have verified the larger extent of the south mud than that of the north one implicating south and southeastward sediment dispersal paths that prevail near the river mouth area the existing anti clockwise and clockwise flows in the river mouth area were synthesized as the major hydrodynamics responsible for forming the two muddy patches tidal and residual currents are considered as the key hydrodynamic factors controlling the sediment distribution and transport in the region

partial melting zones in the crust in southern tibet from magnetotelluric results magnetotelluric studies in southern tibet along a north south traverse 200 km long crossing the yarlung zangbo suture zone near lhasa have enabled us to construct a two dimensional model in which layers of anomalously high conductivity exist at depths shallower than 33 km the electrical properties of these layers are different on the two sides of the suture zone we show here that the most plausible explanation of the high conductivity is the existence of partial melting zones in the upper part rather than the lower part of a crust 70 km thick this represents a powerful constraint for thermo mechanical models of continental collisions

role of subducted sediment in the genesis of ocean island basalts geochemical evidence from south atlantic ocean islands the south atlantic ocean islands of ascension bouvet st helena gough and tristan da cunha display considerable inter island and to a variable extent intra island heterogeneity in ratios of highly incompatible trace elements basaltic and hawaiitic lavas from ascension bouvet and st helena have consistent trace lenient ratios e g la nb ba nb ba la ba th rb th in contrast tristan da cunha and gough and walvis ridge lavas are depleted in nb and enriched in ba relative to other highly incompatible trace elements as compared to the other islands the trace element and pb isotopic geochemistry of these lavas is explicable by contamination of the ocean island basalt source that gave rise to ascension bouvet and st helena lavas by variable but small about 1 amounts of ancient 1 5 2 0 ga pelagic sediment

thermal and kinematic modeling of bedrock and detrital cooling ages in the central himalaya 1 we introduce a new method that convolves detrital mineral cooling ages with digital elevation models to test numerical models of erosion in collisional orogens along a trans himalayan transect in central nepal we develop a kinematic and thermal model to predict variations in bedrock cooling ages in modern himalayan topography the model assumes a thermal steady state and utilizes a simple ramp and flat style decollement representing the main himalayan thrust the model also assumes a topographic steady state such that overthrusting is balanced by erosion to maintain a constant topographic profile erosion rates display strong spatial variations as a function of the angle between the slope of the topographic surface and the trajectories of rock particles approaching the surface to predict the detrital cooling age signal we combine the distribution of bedrock cooling ages within a catchment with the rate of erosion and distribution of muscovite predicted cooling age distributions are compared with detrital 40ar 39ar muscovite data to assess varying tectonic and erosion scenarios such cooling age distributions are very sensitive to how much of the total plate convergence is expressed as erosion of the overthrusting plate the best fit model assigns 4 6 km myr 1 of overthrusting equivalent to as much as 1 5 2 km myr 1 of vertical erosion to the asian plate although a trade off exists between ramp geometry along the decollement and the best fit rate only a narrow range of ramp dips decollement depths and erosionally compensated overthrusting rates are compatible with the observed detrital ages

cambrian and ordovician metabentonites and their relevance to the origins of associated mudrocks in the northern sector of the lower palaeozoic welsh marginal basin

u pb zircon constraints on the tectonic evolution of southeastern tibet namche barwa area the eastern syntaxis of the himalayas is expressed in the crust as a pronounced southward bend in the orogen the change in strike of geologic features coincides with the high topography of the namche barwa region the exposure of granulite grade metamorphic rocks and a 180 degree bend in the yalu tsangpo we have conducted a geochronologic and geochemical investigation of several suites of granitoids collected from the namche barwa massif and subjacent terranes of southeastern tibet ranging from cm scale dikes and sills to larger outcrop scale intrusions u pb shrimp rg zircon ages establish at least five magmatic episodes 400 to 500 ma 120 ma 40 to 70 ma 18 to 25 ma and 3 to 10 ma these episodes broadly correlate to spatial patterns in sample localities as follows 400 to 500 ma ages occur in zircon cores collected from within the massif proper 120 ma granites related to early gangdese arc plutonism are primarily located northeast of namche barwa later 40 70 ma gangdese activity is expressed in granites west of namche barwa 18 to 25 ma granites occur both along the suture zone west of gyala peri and directly north of namche barwa along the area of the jiali fault zone and are attributed both to shearing within the jiali fault zone and to an early miocene gangdese thrust event exceptionally young 10 ma zircon ages are clustered near the core of the massif along the yalu tsangpo gorge trace element geochemical data indicates the presence of both fluid present and fluid absent melts with a fluid absent decompression melting regime dominating near the core of namche barwa

shoreline change caused by the increase in wave transmission over a submerged breakwater due to sea level rise and land subsidence abstract sandy beaches protected by submerged breakwaters which have crests below sea level are assumed to be vulnerable to relative sea level rise slr in this study the shoreline change due to sea level change and land subsidence along the niigata west coast in japan which is protected by submerged breakwaters was investigated using field data and a shoreline prediction model assuming that the shoreline change is caused by cross shore sediment transport the shoreline movement in the past 10 years was not directly caused by sea level change and land subsidence however our model predicts that over the next 100 years the shoreline will retreat 60 m owing to the increase in the energy flux of incoming waves over the breakwater caused by slr and land subsidence these results imply that other sandy beaches protected by low crested breakwaters as well as those behind coral reefs which are natural submerged breakwaters would experience non negligible erosions caused by future relative slr

high 3 he 4 he ratio in ocean sediments two decades ago merrihue1 reported 3he 4he ratios of 10 4 in ferromagnetic separates from a pacific deep ocean red clay and concluded that the high ratio is due to extraterrestrial debris amounting to 1 of the sediment a decade later krylov et al 2 compiled 3he 4he isotopic data on ocean sediments measured in the soviet union and observed that the 3he 4he ratio is generally higher in pelagic sediments where the sedimentation rate is lower they suggested that the high 3he 4he ratio was attributable to extraterrestrial materials which were concentrated in slowly accumulating ocean floor however these important discoveries were almost completely neglected until we re examined the problem we have measured 39 sediments from 12 different sites 10 sites from the western to central pacific and two sites from the atlantic ocean we find 3he 4he ratios 5 10 5 for six sites well above the values generally observed in common terrestrial materials the very high 3he 4he ratio in the sediments is probably due to input of extraterrestrial materials input of stratospheric dust of 1 p p m which corresponds to a fallout rate of 2 000 tons per year can explain the observation

drowning of the mississippi delta due to insufficient sediment supply and global sea level rise global sea level rise reduced sediment supply and subsidence threaten the stability of the mississippi delta calculations of riverine sediment load and storage indicate that 10 000 13 500 km2 of the delta could be submerged by ad 2100

discussion of the reply by r l romer and u kroner on geochemical signature of ordovician mn rich sedimentary rocks on the avalonian shelf in their article reply to the discussion by j w f waldron and c e white on geochemical signature of ordovician mn rich sedimentary rocks on the avalonian shelf r l romer and u kroner reinterpret geochronological data presented by j w f waldron d i schofield c e white and s m barr to imply an ordovician not a cambrian depositional age for the succession of the harlech dome north wales and meguma supergroup nova scotia however an extensive history of biostratigraphic and geological survey data refutes this interpretation and shows that the rocks are unequivocally cambrian waldron et al used the u pb zircon laser ablation multicollector inductively coupled plasma mass spectrometry technique primarily to provide information on sediment provenance and not depositional age investigation of anomalously young 206pb 238u ages showed evidence of pb loss these data provide little constraint on depositional age and cannot be used to infer that the harlech grits group is ordovician

acritarchs from the maclean brook formation southeastern cape breton island nova scotia canada new data on middle cambrian lower furongian acritarch zonation abstract we present here the results of a pilot study on cambrian acritarchs from cape breton island nova scotia based on a material from the maclean brook formation in the mira river valley an assemblage from the base of the formation contains 8 species including eliasum llaniscum cristallinium dubium and symplassosphaeridium cambriense and correlates with a position close to the paradoxides davidis p forchhammeri zone boundary an assemblage from the upper part of the formation contains 16 species of which 3 are new including cristallinium aciculatum petaloferidium lacrimiferum n sp pirea orbicularis stelliferidium pingiculum s magnum n sp s albanii n sp and timofeevia microretis correlated to the olenus zone the upper assemblage is particularly noteworthy as it provides the first direct evidence for the olenus zone in the maclean brook formation furthermore it contains stratigraphically significant taxa known from sections on baltica and northern gondwana but which have not been reported previously on avalonia the distinction between stelliferidium and timofeevia is discussed in part based on new data on timofeevia lancarae from its type area in northern spain it is suggested that many reports of furongian timofeevia phosphoritica and t lancarae are better referred to stelliferidium

cambrian acritarchs from the bourinot belt cape breton island nova scotia age and stratigraphic implications1this article is one of a series of papers published in cjes special issue in honour of ward neale on the theme of appalachian and grenvillian geology we present the first description of organic walled microfossils from cambrian strata of the bourinot belt central cape breton island age diagnostic acritarchs have been recovered from the dugald

granites and thermal structures in the lithosphere the production of melts of the granite clan on a significant scale requires participation of continental crust such crust will melt when heated from below by a mantle thermal anomaly or when thickend to 40 km or more sites of melting and the time sequences of melting associated with subduction and underplating processes and collision processes are complex in both these processes at least six melting sites may be involved the final chemical and isotopic composition of granitic melts depends on a very complex array of processes which include source composition composition of subducted materials magma mixing magma underplating assimilation fractionation cooling processes resolution of granite melt dynamics requires an integrated attack using modern seismic and electrical measurements in regions where the continental crust is abnormally thick or hot

subduction zone stresses constraints from mechanics and from topographic and geoid anomalies abstract there are in principle direct relations between several important phenomena associated with subduction zones the depth of oceanic trenches the magnitude of the net force from trenches acting on subducting plates the distribution and fault plane orientations of earthquakes the magnitude of stresses on subduction faults the bathymetry of back arc regions and the magnitudes of gravity and geoid anomalies these phenomena are related through the stresses transmitted through surface and subducted lithosphere and are associated with the mass anomaly of the subducted lithosphere quantitative estimates suggest that observed trench depths imply a trench pull force on subducting plates which is comparable to the ridge push force but much less than the excess weight of the subducted lithospheric slab it is further suggested that either the mass anomaly of subducted lithosphere is much less than would be expected on the basis of conventional thermal and compositional models or that a a large resistance acts on the upper part of slabs due to high stress corner flow and b the mass anomaly of the slab is 70 90 compensated either by a broad 1 km deep back arc depression or a low density mantle wedge above the slab or both

late cambrian deformation in the lesser himalaya abstract the tons valley situated in the central easternmost part of the himachal lesser himalaya adjoining the garhwal himalaya shows geological features suggestive of a strong pre tertiary deformational episode the paleoproterozoic dharagad group overlain by the mesoproterozoic deoban and neoproterozoic simla groups rest as a thrust sheet over the middle cambrian chilar formation which occurs as windows and also as tectonic slivers within the thrust sheet designated as the dharagad thrust sheet dts the mineral lineation inclination of tectonic slivers and overturned beds suggest that the dts was translated from the ne the westernmost and southwesternmost leading edges of the dts are exposed at subathu and morni wnw and wsw respectively of the tons valley the position of the leading edges of the dts vis a vis the windows in the tons valley suggest a minimum translation of about 50 km for the dts the simla group at subathu and the deoban at morni forming parts of the dts constitute basement for the thanetian lutetian subathu formation of the himalayan foreland basin hfb this stratigraphic relationship unambiguously demonstrates that the simla and the deoban groups forming leading edges of the allochthonous dts were already translated and emplaced at subathu and morni before the creation of the hfb in which the deposition commenced with the subathu formation in thanetian it implies that the dts was translated from the ne to the present position at subathu and morni in pre thanetian time there is no direct evidence to constrain the age of the thrusting in view of regional regression in late cambrian a distinct angular unconformity between the cambrian and the overlying ordovician early paleozoic metamorphism and extensive development of early paleozoic granites and their rapid exhumation a late cambrian age is suggested for the dts thrusting not only the direction of movement of the dts is same as that of the tertiary thrust sheets but also cambrian folds are co axial with the tertiary folds this strange coincidence shows that similar kinematic field existed during two tectonic events a ridge like the present central crystalline axis was elevated between the tethyan and lesser himalayan basins which contributed zircons of the early cambrian age to both basins

rb sr geochronology of granites and gneisses from the mount everest region nepal himalaya nineteen samples of granites orthogneisses and paragneisses from the high himalaya basement nappe s of the mount everest region have been dated by the rb sr method the post metamorphic tourmaline leucogranites of the upper imja drangka nuptse lhotse glacier have high initial sr87 sr86 characteristic of an anatectic origin from crustal material a whole rock isochron age of 52 m y early eocene has been obtained for the samples from the granite body of lhotse glacier apparently sr isotopic homogenization was not reached throughout the much larger nuptse granite

mississippi delta subsidence primarily caused by compaction of holocene strata coastal subsidence causes sea level rise shoreline erosion and wetland loss which poses a threat to coastal populations this is especially evident in the mississippi delta in the southern united states which was devastated by hurricane katrina in 2005 the loss of protective wetlands is considered a critical factor in the extensive flood damage the causes of subsidence in coastal louisiana attributed to factors as diverse as shallow compaction and deep crustal processes remain controversial current estimates of subsidence rates vary by several orders of magnitude here we use a series of radiocarbon dated sediment cores from the mississippi delta to analyse late holocene deposits and assess compaction rates we find that millennial scale compaction rates primarily associated with peat can reach 5mm per year values that exceed recent model predictions locally and on timescales of decades to centuries rates are likely to be 10 mm or more per year we conclude that compaction of holocene strata contributes significantly to the exceptionally high rates of relative sea level rise and coastal wetland loss in the mississippi delta and is likely to cause subsidence in other organic rich and often densely populated coastal plains

south flank of the yangtze delta past present and future abstract chenier plain and mudflat development in the south flank of the yangtze delta are examined by multi disciplinary methods over different spatiotemporal scales and changing human earth interactions the study site contains a narrow belt of elongated ridge complexes that formed along the sediment deficient open coast from 6500 to 4000 yr bp since then and until the past two decades shoreline progradation has accelerated due to increasing sediment supply fueling rapid deltaic expansion superimposed on this trend are a series of discrete sand dominated ridges deposited during several stormy intervals tidal flat development is regulated by complex estuarine processes short term morphodynamic variations at the site are caused by the alternations of tides and waves while intermediate morphodynamic variations are controlled by the multi decadal shifting of river stem channel and stormy climates the ongoing rapid accretion on the tidal flats is predicted to continue into the near future because the estuarine buffer effect is expected to balance the adverse impacts of decreasing riverine sediment discharge and rising sea level technological developments during the last 2000 years are exemplified by seawall construction against sea flooding marking a transition from passive to active dike construction has been used more frequently and intensively to reclaim land since the 1970s in support of the booming socioeconomic development in the region lessons from complex morphodynamic change and human earth interactions in the southern yangtze delta admonish us to not reclaim coastal wetland by lower flat enclosures constructing new dikes near the low waterline while an optimal alternative would be to implement upper flat enclosures constructing new dikes around the high waterline on the continuously accretionary tidal flats with auxiliary biological restoration engineering to satisfy both socioeconomic development and sustainable wetland conservancy

phytoplankton dynamics from the cambrian explosion to the onset of the great ordovician biodiversification event a review of cambrian acritarch diversity most early palaeozoic acritarchs are thought to represent a part of the marine phytoplankton and so constituted a significant element at the base of the marine trophic chain during the cambrian explosion and the subsequent great ordovician biodiversification event cambrian acritarch occurrences have been recorded in a great number of studies in this paper published data on cambrian acritarchs are assembled in order to reconstruct taxonomic diversity trends that can be compared with the biodiversity of marine invertebrates we compile a database and calculate various diversity indices at global and regional i e gondwana or baltica scales the stratigraphic bins applied are at the level of the ten cambrian stages or of fourteen commonly used biozones in a somewhat higher resolved scheme our results show marked differences between palaeogeographical regions they also indicate limitations of the data and a potential sampling bias as the taxonomic diversity indices of species are significantly correlated with the number of studies per stratigraphic bin the total and normalized diversities of genera are not affected in the same way the normalized genus diversity curves show a slow but irregular rise over the course of the cambrian these also are the least biased a radiation of species and to a lesser extent of genera in the lower cambrian series 2 appears to mirror the cambrian explosion of metazoans this radiation not evident on gondwana is followed by a prominent low in species diversity in the upper series 3 and lower furongian highest diversities are reached globally and on both baltica and gondwana in the uppermost cambrian stage 10 more precisely in the peltura trilobite zone preceding a substantial phase of acritarch species extinction below and at the cambrian ordovician boundary nearly all the genera present in stage 10 survived into the ordovician the forms that emerged during the cambrian therefore became the foundation for the more rapid radiation of acritarchs during the great ordovician biodiversification event

beginning of melting in the granite system qz or ab an h2o the beginning of melting in the system qz or ab an h2 o was experimentally reversed in the pressure range p text h text 2 text o 2 15 kbar using starting materials made up of mixtures of quartz and synthetic feldspars with increasing pressure the melting temperature decreases from 690 c at 2 kbar to 630 c at 17 kbar in the an free alkalifeldspar granite system qz or ab h2o in the granite system qz or ab an h2o the increase of the solidus temperature with increasing an content is only very small in comparison to the alkalifeldspar granite system the solidus temperature increases by 3 c 7 c if albite is replaced by plagioclase an 20 an 40 the difference between the solidus temperatures of the alkalifeldspar granite system and of quartz anorthite sanidine assemblages system qz or an h2o is approximately 50 c

the progradation and retrogradation of two newborn huanghe yellow river delta lobes and its influencing factors abstract in this paper 342 landsat satellite images were used to study the evolution of the qingshuigou and qing8 lobes during 1976 2016 sea level correction and statistical analysis were used to eliminate the effect of sea level fluctuations on the shoreline positions the results revealed that the evolution of the two newborn huanghe delta lobes was mainly influenced by the river sediment discharges river channel changes course shifts floods droughts and marine hydrodynamic forces during 1976 2016 the total land gain of the two lobes was 377 km2 according to mean tide line and the average epeirogenetic efficiency of river sediment discharge was 0 020 m2 ton which was greatly less than that when the channels were natural the artificial stabilization of the deltaic channels had negative impact on the land gain assuming no artificial adjustment to the deltaic channels the total land gain would increase 435 km2 the land gain of the two lobes was a function of the cumulative sediment discharges shoreline lengths and course shift bonuses under the circumstance of historical river channel changes the critical sediment discharge maintaining the area balance of the two lobes was a function of historical shoreline lengths which increased linearly from 61 m ton in 1976 to an average of 163 m ton during 1996 2016 in the future there are two ways to increase the land gain under the less huanghe sediment discharge reducing artificial disturbance of deltaic channels and letting the river enter the sea through the southwest coast of qingshuigou lobe

lithoprobe southern vancouver island seismic reflection sees through wrangellia to the juan de fuca plate multichannel seismic reflection profiles obtained on vancouver island show that above a zone of decoupling between the north american and juan de fuca plates wrangellia is underplated by two accreted terranes of probable oceanic origin both the zone of decoupling and wrangellia are disrupted by easterly dipping faults some of which are thrusts the crustal structure of wrangellia comprises paleozoic and mesozoic volcanic and sedimentary rocks disposed as roof pendants upon and large irregular masses within a ubiquitous jurassic plutonic and metamorphic complex

current and future mudflat losses in the southern huanghe delta due to coastal hard structures and shoreline retreat abstract coastal wetlands especially broad mudflats are facing an unprecedented crisis due to combined influence of intensified coastal development activities drastic river sediment reduction and rapid relative sea level rise however it is still a huge challenge to accurately assess the evolution of mudflats for the lack of reliable shoreline indicators on satellite images especially the indicators for shoreline at low tide this study based on instantaneous shoreline positions derived from 430 landsat satellite images during 1983 2019 uses sea level correction and statistical analysis methods to study the evolution of laizhou mudflat and the intertidal mudflat loss in laizhou mudflat was accurately assessed and the effects of multiple factors especially the effects of various coastal hard structures on the evolution of laizhou mudflat were quantitatively estimated for the first time the results show that the intertidal mudflat loss caused by the construction of cofferdams was 98 km2 93 of the total intertidal mudflat loss although the previous intertidal mudflat loss caused by shore parallel structures was less the shore parallel structures will cause great mudflat loss in the future and the broad laizhou mudflat will disappear in 110 years owing to the barrier effect of the widespread shore parallel structures if the current rapid shoreline retreat is not improved the construction of shore normal structures can slow the shoreline retreat of adjacent mudflat but accelerate downstream shoreline retreat as far as coastal protection is concerned the construction of shore normal structures in laizhou mudflat is inadvisable diverting 13 m ton year of huanghe sediment can totally offset the mudflat loss on the upstream of dongying pier however the mudflat located on the downstream of dongying pier is hard to restore owing to the block effect of the shore normal structures to the alongshore transported sediment another option is demolishing the shore parallel structures to recover the landward movement of shoreline avoiding the mudflat loss at the expense of land loss

acritarchs from the hanford brook formation new brunswick canada new biochronological constraints on the protolenus elegans zone and the cambrian series 2 3 transition diverse and well preserved acritarchs are reported from the type section of the cambrian hanford brook formation at hanford brook southern new brunswick this section fills an important gap in acritarch studies by providing the first detailed picture of changing acritarch associations close to the traditional lower middle cambrian boundary in avalonia acritarchs from the st martins member at the base of the succession include skiagia ciliosa heliosphaeridium notatum h longum and liepaina plana and suggest attribution to cambrian stage 4 acritarchs from the somerset street member in the middle of the formation include eliasum llaniscum and comasphaeridium silesiense this information adds new biochronological context to an ash bed in the somerset street member previously dated as c 510 ma or 508 ma and to the endemic trilobites from the same member including protolenus elegans it also places absolute ages on the basal range of stratigraphically important acritarchs both the acritarch assemblage and the radiometric age are consistent with a position very close to the traditional lower middle cambrian transition and likely within cambrian stage 5 acritarchs from the long island member at the top of the succession include additional taxa demonstrating assignment to cambrian stage 5 both the somerset street and long island members probably correlate with the morocconus notabilis zone the new acritarch species retisphaeridium striatum palacios is described new data are presented on acritarchs from the upper part of the hell9s mouth formation wales and correlation proposed with the long island member

structural events and metamorphic consequences in almora nappe during himalayan collision tectonics abstract almora nappe in uttarakhand india is a lesser himalayan representative of the himalayan metamorphic belt that was tectonically transported over the main central thrust mct from higher himalaya the basal shear zone of almora nappe shows complicated structural pattern of polyphase deformation and metamorphism the rocks exposed along the northern and southern margins of this nappe are highly mylonitized while the degree of mylonitization decreases towards the central part where the rocks eventually grade into unmylonitized metamorphics mylonitized rocks near the roof of the basal shear zone show dynamic metamorphism m2 reaching upto greenschist facies 450 c 4 kbar in the central part of nappe the unmylonitized schists and gneisses are affected by regional metamorphism m1 reaching upper amphibolite facies 4 0 7 9 kbar and 500 709 c four zones of regional metamorphism progressing from chlorite biotite to sillimanite k feldspar zone demarcated by specific reaction isograds have been identified these metamorphic zones show a repetition suggesting that the zones are involved in tight f2 folding which has affected the metamorphics south of the almora town the regionally metamorphosed rocks have been intruded by almora granite 560 20 ma resulting in contact metamorphism the contact metamorphic signatures overprint the regional s2 foliation it is inferred that the dominant regional metamorphism in almora nappe is highly likely to be of pre himalayan precambrian age

time relationships between magmatism tectonics and metamorphism in three plutonic belts in southern tibet new k ar data from north to south the three plutonic belts in southern tibet are the transhimalaya or kangdese the north himalaya or lhagoi kangri and the high himalaya 25 new mineral and whole rock k ar dates added to previous data enable a precise analysis to be made of the time relationships between different magmatic tectonic and metamorphic events that occurred on both sides of the indus tsangpo suture zone these include 1 the emplacement of a large part of the eastern transhimalaya magmatism occurred during eocene time suggesting a close relationship between this emplacement and the late stages of conver gence between india and eurasia 2 south of the suture the ages obtained fall mainly between 11 and 15 ma the greatest age allows us to fix a lower limit on the timing of metamorphic recrystallization of the paleozoic north himalaya granites an intermediate age may correspond to a minimum age of emplacement of the high himalaya and part of the north himalaya cenozoic granitoids finally the youngest age may characterize the northernmost cenozoic granitoids of the north himalaya belt the consistency of these tenuous age variations with field and structural data suggests that they may be significant 3 our determinations give ages often significantly younger than those usually proposed for the same events as suggested by some authors such a discrepancy might reflect relatively late india eurasia collision in this eastern part of the suture

mean flow and turbulence around a laboratory spur dike the three dimensional turbulent flow field around a spur dike in a plane fixed bed laboratory open channel was studied experimentally using a microacoustic doppler velocimeter mean and turbulence characteristics in all three spatial directions were evaluated at upstream and downstream cross sections near the dike results showed that the primary flow separated in both lateral and vertical directions two counter rotating flow circulations consisting of the lateral and vertical velocity components originated at the dike section downstream of the dike the circulation in the flow separation zone is stronger than the one in the contracted primary flow zone the maximum bed shear stresses estimated using reynolds stresses is about three times as large as the mean bed shear stress of incoming flow

death valley bright spot a midcrustal magma body in the southern great basin california a previously unrecognized midcrustal magma body may have been detected by cocorp deep seismic reflection profiles in the death valley region of the southern great basin high amplitude relatively broad band reflections at 6 s 15 km are attributed to partially molten material within a subhorizontal intrusion this bright spot extends laterally at least 15 km beneath central death valley a moderately dipping normal fault can be traced from the inferred magma chamber upward to a 690 000 yr old basaltic cinder cone the fault zone is inferred to have been a magma conduit during the formation of the cinder cone vertical variations in crustal reflection character suggest that the death valley magma body may have been emplaced along a zone of decoupling that separates a faulted brittle upper crust from a more ductile and or intruded lower crust the death valley bright spot is similar to reflections recorded by cocorp in 1977 in the rio grande rift where both geophysical and geodetic evidence support the inference of a tabular magma chamber at 20 km depth

continental underthrusting beneath the southern alps of new zealand both the inferred thermal regime and the variation in crustal thickness beneath the southern alps suggest that the mode of crustal shortening changes substantially along the length of the alpine fault north of mt cook crustal shortening is being accommodated predominantly by uplift and erosion of pacific plate continental crust as postulated in the wellman adams tectonic model however south of mt cook the absence of high heat flow and a large crustal root that is not in isostatic equilibrium may have resulted from underthrusting of as much as 100 km of indian plate continental crust

sediment transport off the huanghe yellow river delta and in the adjacent bohai sea in winter and seasonal comparison abstract based on the data on the current velocity water temperature salinity turbidity and concentration of suspended sediment collected in november 2006 along three survey transects at three time series ship based stations off the huanghe yellow river delta and at twenty four grid survey stations in the adjacent bohai sea sediment transport off the huanghe delta and in the adjacent bohai sea under winter regime were studied and compared with those from the summer season the homogeneous distribution of salinity temperature and sediment in the water column indicated a well mixed body of water a zone of high suspended sediment concentrations ssc 100 mg l 1 with a width of 35 km was identified along the delta coast two highest ssc centers were found in the surface and middle water layers around the abandoned diaokou huanghe river mouth and the present huanghe river mouth and the third one in the bottom layer around the abandoned qingshuigou huanghe river mouth these three highest ssc centers become major sediment source areas in winter based on the location of the high bottom shear stress zone the prevailing wave directions and the protuberant topography of the river mouths we identified the resuspension origin of the three highest ssc centers caused mostly by the winter storm waves partially by tidal currents suspended sediment flux ssf along the three coastal transects indicated that the sediment in the northwest part of the delta was transported northeastward and southeastward along the coast of the recent delta lobe the ssc and ssf were higher in winter than summer by 1 7 27 1 and 2 122 5 times respectively except around the present river mouth this indicates that the intensity of sediment transport in winter is much stronger than in summer due to the powerful effect of winter storms although the river water and sediment discharges to the sea were much greater in summer the massive huanghe sediment to the sea was accumulated in a narrow coastal area due to weak hydrodynamics in summer and then strongly resuspended mostly by storm waves in winter and transported to the offshore area the coastal area off the huanghe delta acts as a sediment sink in summer and converted to be a sediment source in winter in response to the seasonal variation of the east asian monsoon in this region the erosion accumulation pattern of the huanghe subaqueous delta from 1976 to 2003 illustrates that river laden sediment is deposited mainly in the southern part off the coastal area and it is also the result of intensive southward sediment transport in winter

rate of serpentinization in seafloor environments the permeability of partially serpentinized peridotites has been measured near room temperature and found to be in the range of 10 11 to 10 12 darcys or 10 7 to 10 8 cm2 sec 1 comparable to shaley materials serpentinites act as semipermeable membranes to salt ions in ocean crust and deep groundwater environments serpentinization must be a continuous process controlled only by water access to ultramafic rocks through their cover given this it will generate high local strains and stresses with episodic cracking the serpentinization process may also contribute to heat flow and ocean floor topography

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

mitigating land loss in coastal louisiana by controlled diversion of mississippi river sand the bonnet carre spillway diverts floodwaters from the mississippi river to lake pontchartrain and was opened for 42 days during the 2011 flood according to measurements of the newly deposited sediments at least 31 46 of the river s sand load was diverted into the spillway at this time suggesting that such diversions can help mitigate coastal wetland loss

late cambrian middle furongian shallow marine dysoxic mudstone with calcrete and brachiopod olenid lotagnostus faunas in avalonian cape breton island nova scotia the common belief that organic rich mudstones formed in quiescent distal settings is further weakened by study of an upper cambrian leptoplastus lower peltura superzones succession in the chesley drive group in avalonian cape breton island that is comparable to alum shale successions in baltica dramatic sea level likely eustatic changes are now recognized by punctuation of deposition of shallow wave influenced black mudstone with brachiopod orusia lenticularis and olenid trilobite bearing limestones by offlap and formation of a subaerially cemented calcrete clast conglomerate subaerial exposure was followed by transgression and accumulation of clastic pyrite sand and phosphatic granules with leptoplastus superzone l ovatus zone trilobite sclerites dynamic processes are shown by wave ripples in the mudstone and limestone sorting and winnowing of fossil rudstones and pre compactional fracture of the conglomerate and rudstones orusia rudstones in the succession below the conglomerate are regarded as analogues of eoorthis and billingsella rudstones in the biomere extinction intervals of the laurentian basal sunwaptan the lowest orusia rich beds are no older than the p spinulosa zone but as elsewhere in avalonia they range into the higher leptoplastus cape breton and even the peltura britain new brunswick superzones rare agnostoid sclerites in lower peltura superzone ctenopyge tumida zone olenid rudstone resemble those traditionally assigned to lotagnostus trisectus in avalonian britain and sweden and are distinct from laurentian l americanus an l americanus zone cannot be identified in avalonia or baltica and the first appearance datum fad of purported l americanus is not suitable as a standard for the base of the highest cambrian stage

thrust tectonics crustal shortening and the structure of the far eastern nepal himalaya balanced and restored structural sections across the far eastern nepal himalaya have been constructed in order to determine the structure and evolution of the himalayan orogenic wedge and the amount of tectonic shortening the region has undergone since the initiation of thrusting along the main central thrust mct the far eastern nepal himalaya is comprised of three distinct thrust bound tectonic packages the higher himalayan crystalline thrust sheet the lesser himalayan metasediment thrust package and the sub himalayan imbricate fan the higher himalayan crystallines consisting of kyanite and sillimanite bearing gneisses intruded by the miocene jannu leucogranites have been thrust over the lesser himalayan metasediments along the mct for a distance of 140 km to 175 km the lesser himalayan metasediments are a 12 km thick unit consisting primarily of phyllites metaquartzites and mylonitic augen gneisses in which garnet biotite and chlorite metamorphic zones are exposed in progressively deeper structural levels the lesser himalayan metasediment thrust package is underlain by a decollement the main detachment fault mdf which lies at a calculated depth of between 6 and 10 km underneath the mahabharat lekh and at a calculated depth of 20 to 25 km north of the tamar khola dome the tamar khola dome overlies a footwall ramp along the mdf where the mdf cuts upsection through the lesser himalayan metasediments the lesser himalayan thrust package probably has an internal structure aproximating a hinterland dipping duplex with the mct and the mdf corresponding to the roof and floor thrusts respectively both the tamar khola thrust an out of sequence breach thrust and the main boundary thrust mbt are splay thrusts off of the mdf the sub himalaya consisting of nonmetamorphosed sedimentary rocks displays an emergent imbricate fan geometry and is underlain by the southern continuation of the mdf which lies at a depth of 5 5 km to 6 km beneath the siwalik hills folding and thrusting within the lesser himalayan thrust package and the sub himalayan imbricate fan have accomodated 45 to 70 km of tectonic shortening total north south shortening across the higher lesser and sub himalaya of far eastern nepal south of the tibetan plateau has been of the order of 185 km to 245 km and has occurred at an average rate of 7 4 mm to 15 3 mm per year since the initiation of the mct between 16 and 25 ma

morphological response of a sandy barrier island with a buried seawall during hurricane sandy abstract coastal populations continue to increase globally causing potential damage costs of coastal hazards to rise and community resiliency to become a worldwide priority recently hurricane sandy 2012 devastated areas of new york and new jersey and caused overwash and breaching of several urbanized barrier islands along the u s eastern seaboard this study focuses on the morphological response of bay head nj a township on a barrier island fronted with a buried seawall the hydrodynamics and morphology of bay head during hurricane sandy are simulated with xbeach a numerical model designed to study these processes during storm events from the simulations the seawall protected bay head by effectively dissipating wave energy during the peak of the storm and from rapidly increasing bay water levels that flood the backbarrier region of the island when the seawall is removed from the simulation dune heights are lowered allowing bay side flooding to cause a devastating erosive event that completely destroys the remaining dune system xbeach indicates severe erosion seaward of oceanfront buildings in the absence of a seawall vertical erosion under the dune peak about 15 m more than in the presence of the seawall and wave energy propagates further inland even after the storm has passed however with the seawall present wave attack is reduced on the island by a factor of 1 7 and prevents bay side flooding from causing significant morphological change on the island therefore the seawall increased resiliency of the bay head community during and after peak hurricane sandy forcing by preserving the dune system

metamorphic evolution of the high himalayan crystallines in se zanskar india the high himalayan crystallines hhc of se zanskar consist of biotite paragneisses of orthogneisses that derive from early palaeozoic granitoids of minor metabasics and of post metamorphic leucogranites of miocene age two main metamorphic events have been documented in the hhc the first event occurred at p 12 0 0 5 kbar and t 750 50 c in rare metabasics intruded by early palaeozoic granitoids in the biotite paragneisses thermobarometric estimates of the first event point to comparable t at p 4 5 kbar lower the first event is followed by a pervasive syn tectonic crystallization characterized by lower p and t on the basis of the cooling ages of the metamorphic minerals and on the geological evidence the second event is referred to the tertiary himalayan crystallization further petrological and geochronological studies are necessary to prove whether a few mineral relics ascribed to the first event define a polyphase himalayan evolution or if they record the incomplete obliteration of an older history during the himalayan event the hhc of se zanskar show a decrease in metamorphic grade from the middle structural levels upward close to the kade unit and downward close to the lesser himalaya from sillimanite k feldspar biotite bearing assemblages to kyanite staurolite muscovite bearing assemblages this metamorphic zonation is probably a consequence of the polyphase history of intracontinental thrusts and of the tectonic emplacement of hot crustal slabs within shallower and colder thrust sheets at relatively late stages of the continental collision between india and eurasia

cambrian successions of the meguma terrane nova scotia and harlech dome north wales dispersed fragments of a peri gondwanan basin abstract the meguma terrane of nova scotia and the harlech dome of north wales preserve similar sedimentary successions of cambrian age both successions comprise a thick succession of early cambrian sandstone turbidites overlain by early to middle cambrian alternating mud rich and sand rich units in which manganese is concentrated in two stratigraphic intervals above these both successions comprise anoxic organic rich turbidites shallowing upward into paler more bioturbated tremadocian mudstone with rhabdinopora within the limited constraints of the available biostratigraphic and geochronological data major changes in environment occurred synchronously in the two successions both successions show much greater similarity to each other than to adjacent successions on avalonia9 a detrital zircon analysis from the rhinog formation low in the harlech dome succession reveals distinct clusters of ages around 537 ma and 2 0 2 1 ga a close similarity to analyses from the meguma terrane suggests proximity between the two terranes on the margin of gondwana during the cambrian period we suggest the term megumia for the palaeogeographical domain that included the two successions which was dispersed during subsequent appalachian and caledonian movements these observations suggest that megumia may have separated terranes previously regarded as parts of avalonia supplementary material u pb detrital zircon analytical data are available at http www geolsoc org uk sup18431

spatial temporal evolution of the eastern nanhui mudflat in the changjiang yangtze river estuary under intensified human activities abstract the eastern nanhui mudflat enm located in the southern flank of the changjiang yangtze river estuary plays a key role in storm protection defense against sea level rise and land resource provision for shanghai china s largest city recently there has been a great deal of concern for its evolutionary fate since a drastic reduction in the changjiang sediment discharge rate and an increased number of estuarine enclosures might negatively impact the environmental protection functions that this mudflat provides in this paper a novel method which employed the envelope lines of instantaneous shoreline positions identified in 436 landsat satellite images from 1975 to 2016 was used to demonstrate the evolution of the mudflat high and low tide lines in a detailed quantitative way our study reveals the southeast progradation rate of the mudflat doubled from 24 m yr in 713 1974 ce to 49 m yr in 1975 1995 ce probably due to the influence of the estuarine turbidity maximum zone shifting to the enm under the ample sediment input directly from the turbidity maximum zone the spatial evolution of the enm was governed predominantly by the changing morphology of the south passage due to the quick progradation of the enm which narrowed the south passage by pushing the south passage trumpet southeastward therefore the enm experienced rapid accretion during 1975 2016 the accretion rate of the high tide line increased 2 13 times due to vegetation and intertidal enclosures resulting in the rapid reduction of the intertidal area the area decreased from 97 km2 in 1976 to 66 km2 in 1995 mainly due to vegetation and continued decreasing to 12 km2 in 2006 due to the intertidal enclosures in contrast the accretion rate of the low tide line increased by 25 times due to subtidal enclosures and caused the intertidal area increased to 78 km2 in 2015 the almost disappeared intertidal zones in 2006 reappeared however this reappearance might be a temporary transitional state and once the subtidal enclosures are completed most of the intertidal zones will be replaced by enclosure land our study reveals that the drastic reduction in the changjiang sediment flow to the sea has not caused a decline in the enm in contrast the enm has experienced rapid accretion in the past 40 years resulting in the strengthening of its functional abilities to protect shanghai an unexpected outcome

spatial and temporal shoreline changes of the southern yellow river huanghe delta in 1976 2016 abstract in this study 364 landsat satellite images were utilized to study the spatial and temporal shoreline changes of the southern yellow river delta in 1976 2016 and a new method revised and improved after zhang et al 2016 was proposed by employing that method the calculated sea levels calculated from simulated tidal heights and instantaneous shoreline positions rather than simulated tidal heights were used to correct fluctuations in instantaneous shoreline positions caused by tidal height and seasonal sea level changes and other random sea level fluctuations when calculating the shoreline erosion rates and beach slopes a statistical analysis of a large number of corrected shoreline positions was used to reduce the influence of random errors that were mainly caused by waves and other casual factors the shoreline erosion rates and beach slopes presented in this paper are therefore more precise and reliable than those derived in previous studies which only used two satellite images the results of this study show that the shoreline of the southern yellow river delta primarily experienced gradual erosion during 1976 2016 with an average erosion rate of 26 9 m year the average shoreline erosion rate increased from 24 9 m year in 1976 1996 to 34 9 m year in 1996 2016 an increase of 40 probably due to the reduction in sediment discharge and shifting northward course of the yellow river after 1996 the shoreline erosion rate of the central coast decreased from 50 2 m year in 1976 1996 to 27 1 m year in 1996 2016 a decrease of 46 probably due to the protection offered by coastal hard structures the average shoreline erosion rate caused by relative sea level rise was 8 5 m year or 32 of the total average shoreline erosion rate relative sea level rise plays an important role in the erosion of the southern yellow river delta due to its flat beach the beach slope of the southern yellow river delta was flat and stable in 1976 2016 and the average slope over most of the beach was 0 043

geochemical comparison between himalayan and hercynian leucogranites abstract isotopic sr pb nd o ree and trace element data from three himalayan nepal and six hercynian brittany france leucogranites are compared for the himalayan granites makulu mustang and especially manaslu the 87sr 86sr versus 87rb 86sr scatter diagrams and hence variability of the initial 87sr 86sr ratios reflect heterogeneity of the source materials these ratios are very high 0 730 0 770 for manaslu the very high 207pb 204pb ratios 15 8 at the corresponding 206pb 204pb ratio of 18 8 the very low 143nd 144nd ratios i nd 13 to 17 and the very high 18o 16o ratios 12 confirm the crustal origin with the paragneisses of the tibetan slab formation i as the probable parent source for the six hercynian granites with an individual rb sr isochron established for many of them the initial 87sr 86sr ratios range from 0 706 to 0 717 the lead neodymium and oxygen isotope compositions confirm their crustal source of presumably palaeozoic age but not specifically identified the rare earth patterns and thorium contents are comparable to those for himalayan granites the similarities of the geochemical signatures isotopes and trace elements of the himalayan and hercynian leucogranites suggest that the petrogenetic processes were comparable and that the himalayan continental collision model can be applied to the hercynian the depletion in ree and th implies either interaction of the granitic liquids with fluid or more probably early precipitation of monazite the increase in sm nd in the granites compared to their parent materials implies that the neodymium model ages of primary mantle extraction are maximum rather than minimum ages in contrast to the hercynian leucogranites the extremely radiogenic sr of the himalayan leucogranites reflects the very long crustal residence time before the melting event the apparent uniformity of the initial 87sr 86sr ratios of the individual hercynian granites may be related to an aging effect where the straight line fitting improves with increase in age of the pluton

quartz spessartine metasediments coticules and their protoliths in north wales thin beds and small pods of quartz spessartine metasediments coticules occur in pelites of the gamlan formation cambrian of the harlech dome the original microfabric of these sediments has been largely destroyed by recrystallization under low greenschist facies conditions the quartz spessartine pods occur throughout the pelites and appear to have formed by the metamorphism of diagenetic mn carbonate concretions the thin beds of quartz spessartine rock appear to have formed by the metamorphism of a protolith which was deposited rapidly and repeatedly over a wide area although there is no direct evidence of the nature of this protolith the presence of altered mn carbonate rich tuff beds in anchizonal mudstones of similar age in the st tudwal s peninsula suggests that the bedded quartz spessartine rocks are in fact metamorphosed mn carbonate rich tuff units both the bedded and podiform quartz spessartine metasediments appear to have formed by reaction between clay minerals and mn carbonates of earlier diagenetic origin