identification of inherited radiogenic pb in monazite and its implications for u pb systematics the simplest interpretation of uranium lead mineral ages in igneous rocks embodies the assumption that melting of pre existing rocks leads to homogenization of the lead isotopes thus resetting the radiometric clock zircons often violate this assumption by only partially dissolving and preserving a component of lead inherited from before the melting episode but until now such behaviour has not been observed in monazite here we report u pb data for zircons and monazites from a tertiary granite from the himalayas in which zircons and monazites contain inherited radio genic lead an analysis of a single entirely igneous zircon crystal plots on concordia at 19 5 0 4 myr eight monazite fractions lie on a line from an upper intercept of 471 10 myr to the youngest fraction which plots slightly above concordia at 21 myr the presence of excess 206pb in the youngest monazite fractions indi cates that the monazite data represent a mixing line between young magmatic monazite and an older inherited component rather than a resetting of 471 myr monazites at 20 myr these data suggest a closure temperature for pb in monazite significantly higher than previously published estimates

accretion of a new england u s a salt marsh in response to inlet migration storms and sea level rise sediment accumulation rates were determined at several sites throughout nauset marsh massachusetts u s a a back barrier lagoonal system using feldspar marker horizons to evaluate short term rates 1 to 2 year scales and radiometric techniques to estimate rates over longer time scales 137cs 210pb 14c the barrier spit fronting thespartina dominated study site has a complex geomorphic history of inlet migration and overwash events this study evaluates sediment accumulation rates in relation to inlet migration storm events and sea level rise the marker horizon technique displayed strong temporal and spatial variability in response to storm events and proximity to the inlet sediment accumulation rates of up to 24 mm year 1were recorded in the immediate vicinity of the inlet during a period that included several major coastal storms while feldspar sites remote from the inlet had substantially lower rates trace accumulation to 2 2 mm year 1 during storm free periods accumulation rates did not exceed 6 7 mm year 1 but remained quite variable among sites based on137cs 3 8 to 4 5 mm year 1 and210pb 2 6 to 4 2 mm year 1 radiometric techniques integrating sediment accumulation over decadal time scales the marsh appeared to be keeping pace with the relative rate of sea level rise from 1921 to 1993 of 2 4 mm year 1 at one site the210pb based sedimentation rate and rate of relative sea level rise were nearly similar and peat rhizome analysis revealed thatdistichlis spicatarecently replaced this onces patenssite suggesting that this portion of nauset marsh may be getting wetter thus representing an initial response to wetland submergence horizon markers are useful in evaluating the role of short term events such as storms or inlet migration influencing marsh sedimentation processes however sampling methods that integrate marsh sedimentation over decadal time scales are preferable when evaluating a systems response to sea level rise

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

late pleistocene holocene paleoproductivity circulation in the japan sea sea level control on δ13c and δ15n records of sediment organic material organic carbon and total nitrogen contents and their isotope ratios were determined in a sediment core recovered from the japan sea to investigate the record of organic matter resources and paleoproductivity in a semi enclosed marginal sea 13c 15n relationships show that the composition of sediment organic material resulted from the mixing of terrestrial and marine organic matter we found synchronous down core variations in the carbon and nitrogen isotope records which are explained by surface productivity control on the composition of sediment organic material moreover these variations are related to sea level changes which caused variable surface water inflows last glacial sea level lowering increased continental run off leading to water column stratification in the japan sea anaerobic conditions due to basin water stagnation led to the deposition of laminated clay sediment organic c n and isotope ratios fluctuated markedly in the transitional stage from aerobic to anaerobic conditions the fluctuations are likely to have been caused by large scale oscillations in sea level just before the last glacial maximum

sedimentary record of recent climate impacts on an insular coastal lagoon in the gulf of california abstract sedimentary records are useful to evaluate environmental changes either from natural or anthropogenic causes such as global and climate change the recent changes in accumulation rates and geochemical characteristics grain size distribution elemental composition organic carbon and carbonate concentrations recorded in a sediment core from san jose island lagoon sjil gulf of california were evaluated to determine its relationship with anthropogenic impacts and climatic variability the 210 pb derived chronology was corroborated with 239 240 pu and 137 cs stratigraphic markers the mass accumulation rate increased up to 3 times during the past 100 years 0 16 0 03 to 0 51 0 06 g cm 2 yr 1 the contents of terrigenous and marine salinity indicator elements as well as fine grained sediments also increased considerably although no anthropization evidences were observed indeed the enrichment factor of trace elements indicated that the ecosystem is still a pristine environment by using multivariate statistical techniques we inferred that the larger input of fine grained terrigenous sediments could be related to the enhancement of soil erosion from the catchment under the influence of higher rainfall rates especially during the last 20 years in addition the higher concentrations of salinity indicator elements most likely resulted from higher evaporation rates in the lagoon caused by higher minimum atmospheric temperatures we concluded that recent climate variability has become the main driver for sedimentary geochemical changes in san jose island lagoon these observations confirmed the usefulness of 210 pb dated geochemical sediment records to study the impacts of recent climate variability where long term environmental data is scarce or non existent

evidence for multiple metamorphic events in the adirondack mountains n y field evidence consisting of 1 rotated foliated xenoliths 2 country rock foliation truncated by isoclinally folded igneous intrusions bearing granulite facies assemblages document one or more early dynamothermal event s of regional scale and high grade early metamorphism resulted in pronounced linear and planar fabric throughout the adirondacks and preceded the emplacement of the anorthosite mangerite charnockite granite alaskite amca suite which contains xenoliths of the metamorphosed rocks olivine metagabbros believed to be approximately contemporaneous with the amca suite also crosscut and contain xenoliths of strongly foliated metasediments these intrusive rocks caused contact metamorphism in the metasediments which locally exhibit both anatectite and restite assemblages subsequently this already complex framework underwent three phases of folding including an early recumbent isoclinical event and was metamorphosed to granulite facies p t conditions the age of the early metamor

groundwater geochemistry of the yucatan peninsula mexico constraints on stratigraphy and hydrogeology summary we report 87sr 86sr and ion concentrations of sulfate chloride and strontium in the groundwater of the northern and central yucatan peninsula mexico correlation between these data indicates that ejecta from the 65 95 m y old chicxulub impact crater have an important effect on hydrogeology geomorphology and soil development of the region ejecta are present at relatively shallow subsurface depths in north central yucatan and at the surface along the rio hondo escarpment in southeast quintana roo where they are referred to as the albion formation anhydrite gypsum and by inference celestite are common in impact ejecta clasts and in beds and cements of overlying paleocene and lower eocene rocks cored around the margin of the crater the sulfate rich minerals that are found in rocks immediately overlying the impact ejecta blanket may either be partially mobilized from the ejecta layer itself or may have been deposited after the k t impact event in an extensive pre oligocene shallow sea these deposits form a distinctive sedimentary package that can be easily traced by the eocene cretaceous 87sr 86sr signal a distinct sr isotopic signature and high so4 cl ratios are observed in groundwater of northwestern and north central yucatan that interacts with these rocks moreover the distribution of the gypsum rich stratigraphic unit provides a solution enhanced subsurface drainage pathway for a broad region characterized by dissolution features poljes extending from chetumal quintana roo to campeche campeche the presence of gypsum quarries in the area is also consistent with a sulfate rich stratigraphic package that includes ejecta the distinctive chemistry of groundwater that has been in contact with evaporite ejecta can be used to trace flow directions and confirms a groundwater divide in the northern peninsula information about groundwater flow directions and about deep subsurface zones of high permeability is useful for groundwater and liquid waste management in the area where it discharges at the coast the unique chemistry of the groundwater that has interacted with the evaporite ejecta strata may also have significant geomorphologic implications while groundwater seawater mixing at the coast has been shown to dissolve and erode limestone phreeqc modeling shows that mixing of water nearly saturated in caso4 with seawater has a less vigorous dissolution effect due to its high ca content

oxygen isotope perspective on precambrian crustal growth and maturation in this study the authors contrast insights on precambrian crustal growth and maturation from radiogenic and oxygen isotope systematics in the superior 3 0 2 7 ga and grenville 1 3 1 0 ga provinces of the canadian shield oxygen isotope ratios in zircon provide the best evidence of supracrustal input into ancient orogens archean superior province zircons have relatively low delta sup 18 o values and a limited range 5 7 per thousand 0 6 per thousand while proterozoic grenville province zircons have elevated delta sup 18 o values and a wider range 8 2 per thousand 1 7 per thousand these data reflect fundamental differences in crustal evolution and maturation between the superior and the grenville provinces in the grenville province radiogenically juvenile supracrustal material with high delta sup 18 o values was buried or subducted to the base of the crust within 150 m y of initial crust production causing high magmatic delta sup 18 o values delta sup 18 o zircon ge 8 per thousand in anorthosite suite and subsequent plutons information about large volumes and rapid recycling of grenville crust is not accessible from radiogenic isotope data alone the grenville data contrast with the restricted delta sup 18 o values of superior province magmatism where subtle approximately 1 per thousand elevation in delta sup 18 o occurs only in volumetrically minor late to postorogenic sanukitoid plutons differences in sediment delta sup 18 omore values between the superior and grenville provinces are predominantly a function of the delta sup 18 o of source materials rather than differences in chemical maturity or erosion styles this study shows that zircon is a robust reference mineral to compare igneous processes in rocks that have undergone radically different histories less

age field and petrological relationships of the hyde school gneiss adirondack lowlands new york criteria for an intrusive igneous origin alaskitic and tonalitic rocks constituting hyde school gneiss hsg occur in 14 domical bodies in the adirondack lowlands recent models have interpreted these bodies as metamorphosed rhyolitic and dacitic ash flow deposits forming the basal member of a regional stratigraphic package in contrast this paper presents criteria and evidence for an intrusive origin for hsg field evidence includes intrusion breccias and complex crosscutting relationships involving mafic layers resembling synplutonic dikes petrological constraints supporting an intrusive origin include 1 the common occurrence of quartz mesoperthite hypersolvus assemblages 2 magmatic features in tonalitic trondhjemitic and alaskitic facies 3 local occurrences of orthopyroxene in all facies of hsg and 4 the development of marginal garnet sillimanite gneiss with corundum spinel garnet sillimanite assemblages yielding paleotempera tures of 780 810 c and interpreted as restite remaining after anatexis of country rock metapelite by

baddeleyite zircon relationships in coronitic metagabbro grenville province ontario implications for geochronology in the high grade gneiss terranes of the grenville province in ontario metagabbro with silicate coronas around primary olivine and fe ti oxide contains trace amounts of both baddeleyite and zircon single baddeleyite crystals with radiating columnar coronas of polycrystalline zircon in places with outer rims of garnet are analogous to the coronas around olivine and ilmenite single crystals of zircon and baddeleyite without zircon coronas also occur in the same rocks both zirconium minerals have been isotopically dated at three widely separated localities in each case baddeleyite records an igneous crystallization age of ca 1170 ma 125 ma older than the ca 1045 ma age of the zircons interpreted to be the age of metamorphism these data agree well with u pb ages obtained from other rocks in the same region and refute the alternative interpretation that silicate coronas in these metagabbros formed during cooling following magmatic crystallization the age does not support direct correlation with diabase dykes of either the sudbury or abitibi swarms northwest of the grenville front

variations in total organic carbon and acid volatile sulfide distribution in surface sediments from luan river estuary china the distribution of total organic carbon toc acid volatile sulfide avs and sediment grain sizes was studied in surface sediments collected from the coastal water near luan river estuary during spring and summer 2015 the aim was to examine the relationships between toc avs and sediment grain sizes the paired samples t test result revealed that seasonal variation had significant effects on the spatial distribution of toc and avs in the surface sediments p 0 05 the scatter plots indicated that avs concentration had significant positive correlations with toc content in both spring and summer spring r 0 475 p 0 05 summer r 0 689 p 0 01 the toc content had a good correlation with sediment grain size and for both seasons toc contents were relatively higher in fine grained sediments the relationship between avs concentration and sediment grain size was not significant in the spring but was significant in the summer cluster analysis further revealed that the spatial distribution of toc and avs in surface sediments was significantly affected by sediment grain size and these distributions varied slightly between the seasons according to avs concentrations in surface sediments the coastal water near luan river estuary during spring and summer 2015 was considered as the healthy area

distribution and sources of organic matter in surface sediments of bohai sea near the yellow river estuary china total organic carbon toc and total nitrogen tn concentrations and c and n stable isotope compositions in 64 surface sediment samples from the mouth of the yellow river yr and from the bohai sea bs outline the distribution and sources terrestrial and marine of sediment organic matter comparatively high toc 0 5 0 9 and tn 0 07 0 11 concentrations in the central bs correlate with fine grained sediments that contain high concentrations of algal derived organic carbon aoc and biogenic silica bsi together they indicate a dominant contribution of autochthonous organic matter from marine primary production low toc 0 2 and tn 0 03 contents characterize surface sediments in the bohai strait and are typically associated with coarse grained sediments of low aoc and bsi contents delta c 13 values 21 to 22 parts per thousand are characteristic of marine derived organic carbon in the central bs and the bohai strait whereas a significant terrigenous contribution of 40 50 is indicated by lower values 23 parts per thousand near the yr mouth the spatial pattern of rising delta c 13 from the yr mouth to offshore areas indicates rapid sedimentation of fluvial suspensions within the vicinity of the river mouth and in laizhou bay so that only approximately 10 20 of yr derived sediments are transported to and deposited in the central bs and or the bohai strait at most sites delta n 15 values are in the typical range of marine organic matter produced from assimilation of marine nitrate by phytoplankton 5 5 5 parts per thousand but some relatively high values 6 7 28 parts per thousand mark the southern area of the laizhou bay as a significant sink of anthropogenic nitrogen c 2015 elsevier ltd all rights reserved

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

late proterozoic ca 930 ma extension in eastern laurentia the northwest dipping carthage colton shear zone located near the eastern margin of the grenville province in northern new york separates the adirondack lowlands of the metasedimentary belt from the adirondack highlands of the granulite terrane published u pb sphene ages are 1156 1103 ma in the lowlands and 1050 982 ma in the highlands indicating an 100 m y offset in metamorphic ages across the boundary our reported hornblende 40 ar39 ar ages are 1060 ma in the lowlands and 950 ma in the highlands this confirms the offsets in sphene ages across the carthage colton shear zone and indicates an average cooling rate in both the lowlands and the highlands of 18 28 m y over 100 m y biotite 40

preservation of premetamorphic oxygen isotope ratios in granitic orthogneiss from the adirondack mountains new york usa the adirondack mountains new york expose a diverse group of proterozoic igneous rocks that were metamorphosed to granulite facies conditions during the ottawan phase of the grenville orogeny oxygen isotope data for seventy whole rock samples of gabbroic to granitic meta igneous rocks primarily from the charnockite suites from the tupper and saranac sheets in the central adirondacks demonstrate a correlation between 18 o wr and major element composition within continuous mappable meta plutonic units no such relationship is seen among nonconsanguineous granitoids variations in mineral 18 o values and large differences in 18 o between rocks with nonconsanguineous protoliths but similar bulk composition demonstrate that these rocks were not infiltrated by or isotopically equilibrated through a pervasive metamorphic fluid values of 18 o for mineral separates preserve generally high temperature fractionations indicative of dominantly closed system retrograde exchange values of 18 o wr in adirondack orthogneisses were not significantly shifted during granulite facies metamorphism and were dominantly controlled by processes active during premetamorphic magmatism values of 18 o wr may thus serve as a petrogenetic indicator allow discrimination of rock units and serve as a source constraint for meta igneous rocks fayalite meta granites with low 18 o values can be discriminated from surrounding granitoids having high 18 o values a record of assimilation in the evolution of differentiated granitic units is preserved the preservation of primary igneous 18 o values in granulite facies orthogneiss imposes constraints on the synmetamorphic and postmetamorphic fluid history of the adirondack highlands oxygen isotopic compositions at the hand sample scale have been preserved through granulite facies metamorphism fluid absence or low fluid rock ratios on a regional scale are indicated

accretion rates in coastal wetlands of the southeastern gulf of california and their relationship with sea level rise sea level rise slr is one of the most conspicuous examples of the environmental impact of recent climate change since slr rates are not uniform around the planet local and regional data are needed for proper adaptation plans 210pb dated sediment cores were analyzed to determine the trends of sediment accretion rates sars at three tropical saltmarshes in the estero de urias lagoon gulf of california mexico in order to estimate the slr trends during the past 100 years under the assumption that these ecosystems accrete at a similar rate to slr a chemometric approach including multivariate statistical analysis factor analysis of geochemical data including 13c 15n c n ratios and br na and cl as proxies for marine transgression was used to identify the marine transgression in the sediment records based on core geochemistry only one of the three cores provided a long term record attributable to marine transgression slr trends estimated from sars showed increasing values from a min

the accumulation and cycling of biogenic silica in the southern ocean revisiting the marine silica budget abstract in many of the recent marine silica budgets e g science 268 1995 375 a majority of the world s biogenic silica accumulation is attributed to the siliceous ooze deposits in the antarctic deep sea based on 230 th normalized sediment accumulation rates as well as comparative studies of silica preservation seabed accumulation compared to surface biogenic production the rate of biogenic silica accumulation in antarctic siliceous ooze deposits has been over estimated by as much as 35 the current estimate for silica accumulation in these high latitude deposits is 3 1 10 12 mol yr 1 as compared to previous values of 4 1 4 8 10 12 mol yr 1 to maintain balance between silicate supply and biogenic silica removal in the oceans an additional repository is needed evidence from continental shelf and upper slope sediments suggests that biogenic silica accumulation in continental margin deposits may account for a much larger fraction of the marine silica burial than previously thought compensating for the diminished accumulation in the antarctic deep sea if biogenic silica accumulation in continental margin sediments replaces nearly a third of the silica accumulation in the antarctic deep sea the marine cycles of organic matter and biogenic silica are coupled to a greater extent than reported in previous budgets

granulite facies metamorphism palaeo isotherms and disturbance of the u pb systematics of zircon in anorogenic plutonic rocks from the adirondack highlands in the adirondack highlands of new york state the effect of granulite facies metamorphism on the physical and isotopic characteristics of zircon from anorogenic plutonic rocks has a distinct geographical pattern the location of zircon populations which appear to have been altered describes a roughly circular area where metamorphic palaeotemperatures have been determined to be in excess of 750 c zircons from anorogenic plutonic rocks outside this area were undisturbed during metamorphism and yield well constrained ages granitic charnockitic and mangeritic anorogenic plutonic rocks peripheral to the marcy anorthosite massif have large euhedral prismatic zircons that display fine internal magmatic growth zonations and abundant randomly orientated mineral inclusions co genetic zircon fractions yield linear discordant arrays and well constrained upper intercepts of 1125 1157 ma metamorphic zircon is limited to sporadically developed and volumetrically insignificant clear low u overgrowths or protuberances in marked contrast zircons from petrographically and geochemically identical rocks adjacent to or within the marcy anorthosite massif are typically large limpid anhedral to subhedral crystals or crystal fragments lacking internal features except for tubular cavities and co 2 rich inclusions co genetic zircon fractions yield nearly concordant non linear clusters with 207pb 206pb minimum ages of 1073 1095 ma metamorphic overgrowths cannot be readily identified by optical or cathodoluminscence techniques however many grains show complex and unusual external boundaries suggestive of post crystallization modification these data indicate that temperatures as low as 750 c in combination with other factors may have been sufficient to facilitate recrystallization and diffusion of radiogenic pb from the zircon crystal structure during the complex protracted metamorphism of the adirondack highlands

biophysical controls on accretion and elevation change in caribbean mangrove ecosystems abstract habitat stability of coastal ecosystems such as marshes and mangroves depends on maintenance of soil elevations relative to sea level many such systems are characterized by limited mineral sedimentation and or rapid subsidence and are consequently dependent upon accumulation of organic matter to maintain elevations however little field information exists regarding the contribution of specific biological processes to vertical accretion and elevation change this study used biogenic mangrove systems in carbonate settings in belize bz and southwest florida fl to examine biophysical controls on elevation change rates of elevation change vertical accretion benthic mat formation and belowground root accumulation were measured in fringe basin scrub and dwarf forest types plus a restored forest elevation change rates mm yr 1 measured with surface elevation tables varied widely bz dwarf 3 7 bz scrub 1 1 fl fringe 0 6 fl basin 2 1 bz fringe 4 1 and fl restored 9 9 root mass accumulation varied across sites 82 739 g m 2 yr 1 and was positively correlated with elevation change root volumetric contribution to vertical change mm yr 1 was lowest in bz dwarf 1 2 and fl fringe 2 4 intermediate in fl basin 4 1 and bz scrub 4 3 and highest in bz fringe 8 8 and fl restored 11 8 sites surface growth of turf forming algae microbial mats or accumulation of leaf litter and detritus also made significant contributions to vertical accretion turf algal mats in fringe and scrub forests accreted faster 2 7 mm yr 1 than leaf litter mats in basin forests 1 9 mm yr 1 but similarly to microbial mats in dwarf forests 2 1 mm yr 1 surface accretion of mineral material accounted for only 0 2 3 3 of total vertical change those sites with high root contributions and or rapid growth of living mats exhibited an elevation surplus 2 to 8 mm yr 1 whereas those with low root inputs and low or non living mat accumulation showed an elevation deficit 1 to 5 7 mm yr 1 this study indicates that biotic processes of root production and benthic mat formation are important controls on accretion and elevation change in mangrove ecosystems common to the caribbean region quantification of specific biological controls on elevation provides better insight into how sustainability of such systems might be influenced by global e g climate atmospheric co2 and local e g nutrients disturbance factors affecting organic matter accumulation in addition to relative sea level rise

early ordovician orogenic event in galicia nw spain evidence from u pb ages in the uppermost unit of the ordenes complex new u pb data zircon monazite and rutile obtained from rocks of the uppermost allochthon in the variscan belt of nw spain indicate that the hangingwall to the suture includes an allochthonous unit with a pre variscan tectonothermal evolution this evolution is characterised by an early ordovician 498 500 ma bimodal magmatism followed almost immediately 493 498 ma by a barrovian style metamorphism up to the granulite facies the metamorphism subsequent to the igneous intrusions requires convergence and crustal thickening in order to generate the barrovian facies pattern shown by the lithologies of the uppermost allochthon the almost coeval magmatism and metamorphism and the chemistry of the metabasites suggest an accretionary complex probably related to a volcanic arc as the most probable setting for the origin of the uppermost unit the implications of the existence of early ordovician convergent plate boundaries are discussed in the context of gondwana laurentia avalon interactions

u pb geochronology geochemistry and provenance of the grenvillian huiznopala gneiss of eastern mexico abstract the huiznopala gneiss is the smallest 25 km2 of four exposures of grenvillian granulites in eastern and southern mexico the gneiss comprises three major lithologic units 1 a main series of orthogneisses 2 an anorthosite gabbro complex and 3 a layered paragneiss sequence thirty one u pb zircon ages from seven samples all lie within a restricted range of 200 million years and the geochronological results are interpreted to reflect principally a two stage history the earliest stage was arc magmatism that extended from 1200 to 1150 ma the second stage included granulite facies metamorphism which peaked at about 725 50 c and 7 2 1 0 kbar and perhaps emplacement of the anorthosite gabbro complex at 1000 ma a pegmatite with an age of 988 3 ma post dates ductile deformation the timing of ductile deformation and granulite facies metamorphism of the huiznopala gneiss corresponds closely to that of final thrusting and deformation in the grenville province thus the huiznopala gneiss may be in the core of the orogen formed during the final thrusting event recognized in the grenville orogeny gondwanan faunal assemblages are found in lower paleozoic sedimentary rocks that overlie grenvillian granulites elsewhere in mexico however the pb isotope compositions of samples from the huiznopala gneiss overlap with those of the basement from laurentia adirondack highlands and lowlands texas and they are distinct from those of the gondwanan arequipa antofalla craton of southern bolivia and northern chile the magmas parental to the huiznopala arc and those parental to the laurentian crust may have shared a common isotope reservoir and the pb isotope compositions are consistent with the paleomagnetic results that place southern mexico adjacent to ontario quebec at about 950 ma

progressive increase in ice loss from greenland 1 laser altimeter measurements over greenland show increasing thickening rates above 2000 m reflecting increasing snowfall in a warming climate but near coastal thinning rates have increased substantially since the mid 1990s and net mass loss more than doubled from an average of 4 50 gt yr 1 between 1993 4 and 1998 9 to 57 105 gt yr 1 between 1998 9 and 2004 this increasing trend is very similar to findings from independent mass budget studies but differs widely from ers radar altimeter results this may result from limitations associated with the large ers footprint over sloping and undulating surfaces that typify fast narrow glaciers where thinning is most pronounced

temporal variability of carbon and nutrient burial sediment accretion and mass accumulation over the past century in a carbonate platform mangrove forest of the florida everglades the objective of this research was to measure temporal variability in accretion and mass sedimentation rates including organic carbon oc total nitrogen tn and total phosphorous tp from the past century in a mangrove forest on the shark river in everglades national park usa the 210pb constant rate of supply model was applied to six soil cores to calculate annual rates over the most recent 10 50 and 100 year time spans our results show that rates integrated over longer timeframes are lower than those for shorter recent periods of observation additionally the substantial spatial variability between cores over the 10 year period is diminished over the 100 year record raising two important implications first a multiple decade assessment of soil accretion and oc burial provides a more conservative estimate and is likely to be most relevant for forecasting these rates relative to long term processes of sea level rise and climate change mitigation second a small number of sampling locations are better able to account for spatial variability over the longer periods than for the shorter periods the site average 100 year oc burial rate 123 19 standard deviation g m 2 yr 1 is low compared with global mangrove values high tn and tp burial rates in recent decades may lead to increased soil carbon remineralization contributing to the low carbon burial rates finally the strong correlation between oc burial and accretion across this site signals the substantial contribution of oc to soil building in addition to the ecosystem service of co2 sequestration

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

diffusion in zircon despite its low abundance in most rocks zircon is extraordinarily useful in interpreting crustal histories the importance of u th pb isotopic dating of zircon is well and long established davis et al this volume parrish et al this volume zircon also tends to incorporate trace elements useful as geochemical tracers such as the ree y and hf a number of characteristics of zircon encourage the preservation of internal isotopic and chemical variations often on extremely fine scale which provide valuable insight into thermal histories and past geochemical environments the relative insolubility of zircon in crustal melts and fluids as well as its general resistance to chemical and physical breakdown often result in the existence of several generations of geochemical information in a single zircon grain the fact that this information is so frequently retained as evidenced through backscattered electron or cathodoluminescence imaging that often reveal fine scale zoning down to the sub micron scale has long suggested that diffusion of most elements is quite sluggish in zircon in this chapter we present an overview of the findings to date from laboratory measurements of diffusion of cations and oxygen in zircon because of its importance as a geochronometer attempts have been made to measure diffusion especially of pb for over 30 years but only in the last decade or so have profiling techniques with adequate depth resolution been employed in these studies resulting in a plethora of new diffusion data these findings have important implications for isotopic dating interpretation of stable isotope ratios closure temperatures and formation and preservation of primary chemical composition and zoning in zircon efforts have been made for some time to quantify and characterize diffusion in zircon most notably of pb in deference to its significance in interpreting pb isotopic signatures and refining understanding of thermal histories as is evident from

the timing of partial melting barrovian metamorphism and granite intrusion in the naxos metamorphic core complex cyclades aegean sea greece abstract the relationship between partial melting and granite intrusion in a classic barrovian metamorphic terrane has been assessed thirteen samples were dated by shrimp u pb zircon geochronology from the island of naxos greece one of the aegean metamorphic core complexes the effect of partial melting during peak barrovian metamorphism on naxos is recorded by fine

intergranular diffusion kinetics of fe and mg during retrograde metamorphism of a pelitic gneiss from the adirondack mountains abstract pelitic granulite gneiss from the irving pond formation in the southern adirondack highlands new york contains chemical zoning in fe and mg in both individual mineral grains and over a distance of millimeters in the polycrystalline matrix garnet porphyroblasts are zoned with increasing xalm and decreasing xprp towards crystal rims compositions of individual biotite grains in the matrix vary systematically with distance from the garnet porphyroblasts up to about 1 mm with the highest mg concentrations in grains adjacent to the garnet and progressive fe enrichment in grains further away we have constructed numerical models of the distribution of fe and mg components obtained during the retrograde reaction and diffusion history of this rock based on the mineral assemblage modes textural information and the preserved zoning trends these simulations indicate that the effective rate of intergranular transport of fe and mg components through the polycrystalline matrix was only one order of magnitude faster than the rate of volume diffusion in garnet the relatively slow intergranular kinetics indicate that grain boundaries did not provide rapid diffusion pathways absence of an interconnected fluid phase along grain edges and grain boundary annealing likely inhibited intergranular diffusivities during cooling our models also suggest that the mineral assemblage experienced metamorphic temperatures in excess of 700 c followed by rapid cooling this t t evolution is quite different than determined for the ca 1060 1000 ma regional granulite facies metamorphism in the adirondack highlands fe mg distribution in the gneiss likely reflects and earlier metamorphic episode

distribution and sources of particulate organic matter in the water column and sediments of the fly river delta gulf of papua papua new guinea suspended particles from surface and bottom waters and surficial sediments from the seabed were collected throughout the fly river subaqueous delta region during the monsoon season in january 2003 because of the unusually low river discharge associated with a strong el nino water column salinities were relatively high 10 to 32 throughout most of the delta with brackish salinities 4 wt relatively high organic carbon nitrogen molar ratios oc n 20 mol mol and quite depleted stable isotopic compositions of organic carbon 13coc 27 in contrast surface sediments in the seabed displayed spatially uniform compositions that were characterized by markedly lower oc contents 1 1 0 8 wt lower oc n ratios 17 9 mol mol and relatively enriched 13coc compositions 25 5 1 1 the radioisotopic compositions of oc from a selected set of seabed samples 14coc of 408 82 indicate om in surface sediments is old 14c ages of 2800 to over 6000 years before present the ratios of organic carbon to mineral surface area exhibited by these sediments are within the typical mono layer equivalent ranges characteristic of shelf sediments and do not reflect the preferential removal of terrigenous om overall these compositions indicate that while water column pom appears to be derived mainly from terrigenous vascular plant debris and riverine estuarine phytoplankton the source of most of the sedimentary pom is aged soil oc ultimately derived from c3 vegetation we speculate that the concentrations and sources of suspended pom in the water column of the fly river delta region reflect the conditions of low river discharge low wave energy and neap tides encountered at the time of sampling in contrast pom compositions in surface sediments are consistent with the transport and deposition of old mineral bound oc most likely eroded from the upland regions of the fly river watershed which is characterized by steep slopes high precipitation and c3 tropical forests and grasslands

empirical calibration of oxygen isotope fractionation in zircon new empirical calibrations for the fractionation of oxygen isotopes among zircon almandine rich garnet titanite and quartz are combined with experimental values for quartz grossular the resulting a coefficients k2 are zrc alm grs ttn qtz 2 64 2 71 3 03 3 66 zrc 0 07 0 39 1 02 alm 0 32 0 95 grs 0 63 full size table table options view in workspace download as csv for the relation 1000 ln y x ay x 106 t2 the fractionation of oxygen isotopes between zircon and coexisting minerals can provide otherwise unavailable evidence of magmatic processes including crystallization remelting and assimilation fractional crystallization

dating the lower crust by ion microprobe ion microprobe uthpb ages of zircons from granulite facies lower crustal xenoliths from north queensland australia correlate well with the ages of major orogenic episodes manifest at the earth s surface about half of the xenoliths contain proterozoic zircons which are similar in age to the episodes of high grade metamorphism of the older surface rocks all the xenoliths contain late paleozoic zircons which show a real 100 ma range in206pb238 u ages from 320 to 220 ma which is attributed to granulite facies metamorphism followed by slow cooling in the deep crust the paleozoic zircon ages coincide in time with the prolonged episode of eruption of voluminous felsic ash flows and intrusion of high level granites in this region 320 270 ma mineral and melt inclusions in the zircons provide clues to the origin of some of the xenoliths and coupled with the age information can be used to infer the geological processes operating in the lower crust the zircons from two mafic xenoliths contain felsic and intermediate melt inclusions implying at least a two stage history for these rocks involving either partial melting of a more felsic protolith or crystal accumulation from an evolved melt some of the zircons from the felsic xenoliths contain co2 rich fluid inclusions indicating that those zircons grew during high grade metamorphism the isotopic and chemical data for the whole rock xenoliths show that they originate from a segment of the lower crust which is a heterogeneous mixture of supracrustal and mafic mantle derived lithologies the major orogenic event responsible for the formation of that crust occurred in the late paleozoic when proterozoic supracrustal rocks were emplaced into the lower crust possibly along thin skinned thrust slices this was accompanied by intrusion of high temperature mantle derived melts which caused partial melting of pre existing crust the most likely setting for such tectonism is a continental margin subduction zone

carbon and nutrient accumulation in tropical mangrove creeks amazon region abstract the marapanim river estuary mre is part of the amazon estuarine system located in northern brazil which is characterized as having extensive mangrove forests given that previous studies reported co2 and ch4 fluxes from mangrove creeks in this region here we investigate the potential organic carbon sequestration of the creek mudflats to get a better understanding of the carbon cycling through these systems sediment accumulation rates derived from 210pb dating indicated that sampled cores represent the previous 24 4 yr the approximately 24 year total organic carbon toc total nitrogen tn and total phosphorus tp burial rates were estimated to be 192 5 43 5 15 3 4 1 and 3 2 0 8 g m 2 yr 1 respectively a binary source mixing model based on carbon stable isotopes 13c revealed that the sedimentary organic matter om is mainly influenced by marine phytoplankton input 49 to 95 furthermore the toc accumulation rates found here were slightly higher than the global averages estimated for within mangrove forests suggesting that these unaccounted carbon sinks along creek mudflat environments are relevant for carbon budgets in mangrove colonized coastal zones the highest contents stocks and accumulation rates were found in the tidal creek sediments that are most influenced by nearby mangroves and are more protected than sediments from major river margins our results indicate that the creek mudflats play a major role in carbon and nutrients sequestration directly related to grain size and om sources

pb diffusion in zircon abstract chemical diffusion of ti under anhydrous conditions at 1 atm and under fluid present elevated pressure 1 1 1 2 gpa conditions has been measured in natural zircon the source of diffusant for 1 atm experiments was a zro2 tio2 zircon mixture with experiments run in crimped pt capsules diffusion experiments done in the presence of h2o co2 fluid were run in a piston cylinder apparatus using a source of ground tio2 zrsio4 and sio2 with oxalic acid added to produce h2o co2 vapor and partially melt the solid source material yielding an assemblage of rutile zircon melt vapor nuclear reaction analysis nra with the resonant nuclear reaction 48ti p 49v was used to measure diffusion profiles for both sets of experiments the following arrhenius parameters were obtained for ti diffusion normal to cover the temperature range 1350 1550 c at 1 atm d ti 3 33 10 2 exp 754 56 kj mol 1 r t m 2 s 1 ti diffusivities were found to be similar for experiments run under fluid present conditions a fit to all of the data yields the arrhenius relation d 1 34 102 exp 741 46 kj mol 1 rt m2 s 1 these data suggest that zircon should be extremely retentive of ti chemical signatures indicating that the recently developed ti in zircon crystallization geothermometer watson e b harrison t m 2005 zircon thermometer reveals minimum melting conditions on earliest earth science 308 841 844 will be quite robust in preserving temperatures of zircon crystallization titanium diffuses somewhat faster in zircon than larger tetravalent cations u th and hf but considerably more slowly than pb the ree and oxygen hence ti crystallization temperatures may be retained under circumstances when radiometric ages or other types of geochemical information are lost

carbon isotope thermometry in marbles of the adirondack mountains new york carbon isotope thermometry has been applied to coexisting calcite and graphite in marbles from throughout the adirondack mountains new york eighty nine calcite graphite pairs from the amphibolite grade nw adirondacks change systematically in temperature north westwards from 680 to 640 to 670 c over a 30 km distance reflecting transitions from amphibolite facies towards granulite facies to the north west and to the south east temperature contours based on calcite graphite thermometry in the nw adirondacks parallel mineral isograds with the orthopyroxene isograd falling above 675 c and indicate that regional metamorphic temperatures were up to 75 c higher than temperatures inferred from isotherms based on cation and solvus thermometry bohlen et al 1985 fifty five calcite graphite pairs from granulite grade marbles of the central adirondacks give regional metamorphic temperatures of 670 780 c in general agreement with cation and solvus thermometry data for amphibolite and granulite grade marbles show a 12 oo range in 13ccal and 13cgr a strong correlation between carbon isotopic composition and the abundance of graphite cgr crock indicates that the large spread in isotopic compositions results largely from exchange between calcite and graphite during closed system metamorphism the trends seen in 13c vs cgr crock and 13ccal vs 13cgr could not have been preserved if significant amounts of co2 rich fluid had pervasively infiltrated the adirondacks at any time the close fit between natural data and calculated trends of 13c vs cgr crock indicates a biogenic origin for adirondack graphites even though low 13c values are not preserved in marble delamination of 17 graphite flakes perpendicular to the c axis reveals isotopic zonation with higher 13c cores these isotopic gradients are consistent with new graphite growth or recrystallization during a period of decreasing temperature and could not have been produced by exchange with calcite on cooling due to the sluggish rate of diffusion in graphite samples located 2km from anorthosite show a decrease of 0 5 0 8 oo in the outer 100 of the grains while samples at distances over 8 km show smaller core to rim decreases of c 0 2 oo correlation between the degree of zonation and distance to anorthosite suggests that the isotopic profiles reflect partial overprinting of higher temperature contact metamorphism by later granulite facies metamorphism core graphite compositions indicate contact metamorphic temperatures were 860 890 c within 1 km of the marcy anorthosite massif if samples with a significant contact metamorphic effect cal gr 3 2 oo are not included then the remaining 38 granulite facies samples define the relation 13c cal gr 3 56 106t 2 k

age of xenolith bearing olivine metagabbro eastern adirondack mountains new york a u pb zircon age of 1143 6 pm 7 ma has been obtained on a xenolith bearing olivine metagabbro in the eastern adirondack highlands thus fixing a minimum age for metamorphism represented by truncated foliation in the xenolith and the igneous crystallization age of the rock the igneous age predates commonly accepted metamorphic ages of 1000 1100 ma for the adirondacks and documents that more than one high grade metamorphic event affected the region

phosphorus distribution c n p ratios and δ13coc in arctic temperate and tropical coastal sediments tools for characterizing bulk sedimentary organic matter abstract onshore offshore trends in phosphorus p organic carbon oc and total nitrogen tn concentration p distribution elemental organic c n p ratios and stable carbon isotopic composition of oc 13 c oc of surficial sediments are presented from three river dominated coastal regimes the mackenzie river beaufort shelf in the canadian arctic the mississippi delta and louisiana shelf in the temperate gulf of mexico and the tropical amazon shelf these parameters measured in surficial sediments from the three sites are used to assess changes in the importance of terrestrial and marine organic matter sources to sediments as a function of distance from the locus of riverine discharge trends in elemental ratio data from the arctic transect and a portion of the gulf of mexico transects can be explained in terms of a two end member mixture of terrestrial and marine phytodetritus in the arctic transect covariation of organic c p ratios with 13 c oc is consistent with a two end member mixture of terrestrial and marine organic matter a similar relationship between c p ratios and 13 c oc is not evident in gulf of mexico or amazon shelf sediments at these sites the two end member model fails to explain the data adequately the most striking feature of the onshore offshore trends in elemental oc op and oc tn ratios is the occurrence of low ratios in sediments from deep water stations in the gulf of mexico and all stations on the amazon shelf resulting from p and n enrichments exceeding the redfield ratio for marine plankton three explanations are discussed to account for these low ratios 1 the dominance of refractory op and on compounds in the residuum of degraded organic matter 2 differential sorption of op and n compounds regardless of lability on the surfaces of the fine grained sediments characteristic of these sites and 3 a dominance of bacterial biomass or components derived from bacterial biomass elemental ratios and 13 c oc signatures indicate that differential sorption may be most important in the deep water gulf of mexico sites in contrast elemental ratios and 13 c oc on the amazon shelf are most consistent with a sedimentary organic matter pool dominated by bacterial biomass or derivative substances

rapid sediment accumulation and microbial mineralization in forests of the mangrove kandelia candel in the jiulongjiang estuary china abstract rates of sediment accumulation and microbial mineralization were examined at three kandelia candel forests spanning the intertidal zone along the south coastline of the heavily urbanized jiulongljiang estuary fujian province china mass sediment accumulation rates were rapid range 10 62 kg m 2 y 1 but decreased from the low to the high intertidal zone high levels of radionuclides suggest that these sediments originate from erosion of agricultural soils within the catchment mineralization of sediment carbon and nitrogen was correspondingly rapid with total rate of mineralization ranging from 135 to 191 mol c m 2 y 1 and 9 to 11 mol n m 2 y 1 rates were faster in summer than in autumn winter rates of mineralization efficiency 70 93 for c 69 92 for n increased as burial efficiency 7 30 for c 8 31 for n decreased from the low to the high intertidal mangroves sulphate reduction was the dominant metabolic pathway to a depth of 1 m with rates 19 281 mmol s m 2 d 1 exceeding those measured in other intertidal deposits there is some evidence that fe and mn reduction oxidation cycles are coupled to the activities of live roots within the 0 40 cm depth horizon oxic respiration accounted for 5 12 of total carbon mineralization methane flux was slow and highly variable when detectable range 5 66 mol ch 4 m 2 d 1 nitrous oxide flux was also highly variable but within the range 1 6 106 5 mol n 2 o m 2 d 1 measured in other intertidal sediments rates of denitrification were rapid ranging from 1106 to 3780 mol n 2 m 2 d 1 and equating to 11 20 of total sediment nitrogen inputs denitrification was supported by rapid nh 4 release within surface deposits range 3 6 6 1 mmol m 2 d 1 our results support the notion that mangrove forests are net accumulation sites for sediment and associated elements within estuaries especially kandelia candel forests receiving significant inputs as a direct result of intense human activity along the south china coast

sediment accretion and organic carbon burial relative to sea level rise and storm events in two mangrove forests in everglades national park abstract the goal of this investigation was to examine how sediment accretion and organic carbon oc burial rates in mangrove forests respond to climate change specifically will the accretion rates keep pace with sea level rise and what is the source and fate of oc in the system mass accumulation accretion and oc burial rates were determined via 210pb dating i e 100 year time scale on sediment cores collected from two mangrove forest sites within everglades national park florida usa enhanced mass accumulation accretion and oc burial rates were found in an upper layer that corresponded to a well documented storm surge deposit accretion rates were 5 9 and 6 5 mm yr 1 within the storm deposit compared to overall rates of 2 5 and 3 6 mm yr 1 these rates were found to be matching or exceeding average sea level rise reported for key west florida organic carbon burial rates were 260 and 393 g m 2 yr 1 within the storm deposit compared to 151 and 168 g m 2 yr 1 overall burial rates the overall rates are similar to global estimates for oc burial in marine wetlands with tropical storms being a frequent occurrence in this region the resulting storm surge deposits are an important mechanism for maintaining both overall accretion and oc burial rates enhanced oc burial rates within the storm deposit could be due to an increase in productivity created from higher concentrations of phosphorus within storm delivered sediments and or from the deposition of allochthonous oc climate change amplified storms and sea level rise could damage mangrove forests exposing previously buried oc to oxidation and contribute to increasing atmospheric co2 concentrations however the processes described here provide a mechanism whereby oxidation of oc would be limited and the overall oc reservoir maintained within the mangrove forest sediments

genesis of metapelitic migmatites in the adirondack mountains new york oxygen isotope ratios and rare earth element ree concentrations provide independent tests of competing models of injection v anatexis for the origin of migmatites from amphibolite and granulite facies metasedimentary rocks of the adirondack mountains new york values of 18o and ree profiles were measured by ion microprobe in garnet zircon pairs from 10 sample localities prior u pb sims dating of zircon grains indicates that inherited cores 1 7 1 2 ga are surrounded by overgrowths crystallized during the grenville orogenic cycle 1 2 1 0 ga cathodoluminescence imaging records three populations of zircon i featureless rounded whole grains interpreted as metamorphic or anatectic and rhythmically zoned igneous cores truncated by rims that are either ii discordant rhythmically zoned igneous or iii unzoned metamorphic or anatectic these textural interpretations are supported by geochronology and oxygen isotope analysis in both the amphibolite facies nw adirondacks and the granulite facies se adirondacks 18o zrc values in overgrowths and whole zircon are highly variable for metamorphic zircon 6 1 13 4 n 95 10 m spot in contrast garnet is typically unzoned and 18o grt values are constant at each locality differing only between leucosomes and corresponding melanosomes none of the analysed metamorphic zircon garnet pairs attained oxygen isotope equilibrium indicating that zircon rims and garnet are not coeval furthermore ree profiles from zircon rims indicate zircon growth in all regions was prior to significant garnet growth thus petrological estimates from garnet equilibria e g p t cannot be associated uncritically with ages determined from zircon the unusually high 18o values 10 in zircon overgrowths from leucocratic layers are distinctly different from associated metaigneous rocks 18o zrc 10 indicating that these leucosomes are not injected magmas derived from known igneous rocks surrounding melanosomes have similarly high 18o zrc values suggesting that leucosomes are related to surrounding melanosomes and that these migmatites formed by anatexis of high 18o metasedimentary rocks

zircon u pb chronometry of the pressure and temperature history of granulites in the musgrave ranges central australia ion microprobe u pb measurements of zircon in the musgrave ranges of central australia date the emplacement of a charnockite which is cut by a shear zone containing a garnet clinopyroxene assemblage m2 pt conditions 11 kb and 720 c at 1200 ma veinlets of a post m2 adamellite cut an m4 assemblage pt conditions 6 kb and 670 c contained in a metadolerite inclusion suggesting that the adamellite was emplaced during or after m4 igneous and metamorphic zircons in the adamellite however grew at about 1200 ma indicating that m2 and m4 were synchronous at the level of precision of our data the time interval between the growth of the two assemblages can not have been more than 20 ma we interpret the pressure temperature and time ptt path obtained by combining our thermobarometric data and zircon u pb ages in terms of magmatic heat input in a thickened crustal segment followed by rapid possibly technically driven uplift of the lower part of the thickened crust to a depth of 15 20 km

moderate pressure metamorphism and anatexis due to anorthosite intrusion western adirondack highlands new york garnet sillimanite biotite gneiss near port leyden in the western adirondack highlands new york contains mineral assemblages and textures that formed during high temperature metamorphism and anatexis at mid crustal pressures evidence for melting includes thin plagioclase rich veins sieve textures in biotite and the presence of small euhedral garnet neoblasts hercynite silicate equilibria in combination with the solidus for biotite dehydration melting indicate metamorphic pressure was between 4 and 6 4 kbar at the temperature of melting ca 735 c the gneiss is intruded by a small discordant fe ti oxide apatite nelsonite dike reported field occurrences of nelsonite demonstrate its common association with anorthosite plutons although no anorthosite bodies are exposed in the port leyden region the presence of nelsonite is evidence of anorthositic magmatism in the western adirondacks post intrusion metamorphism has caused partial apatite recrystallization and produced a weak foliated texture in the dike u pb ages from zircon and monazite from both the gneiss and the nelsonite dike indicate that these rocks experienced a complex polymetamorphic history that we interpret to reflect two thermal episodes an older event is recorded by discordant zircons in the gneiss which indicate a minimum age of 1129 6 ma a linear best fit to the data yields an upper intercept at 1166 53 ma this range of ages coincides with anorthosite suite magmatism in the adirondacks a minimum zircon age of 1104 3 ma was obtained from the nelsonite dike lead loss or late zircon crystallization at about 1020 ma affected the u pb systematics of zircon in the dike monazite ages from both rocks also indicate high temperature metamorphism 700 c between 1040 and 960 ma the older zircon ages and textural relations in the metapelite are viewed as evidence for anatexis at ca 1150 ma and the presence of nelsonite suggests that the intrusion of anorthosite was coincident with partial melting in the gneiss p t estimates of metamorphism therefore imply that anorthosite was emplaced to about 15 km depth in the western adirondack highlands

preliminary study of the dynamic origin of the distribution pattern of bottom sediments on the continental shelves of the bohai sea yellow sea and east china sea the bottom sediment types in the bohai sea yellow sea and east china sea byecs are diversified and their distribution pattern is very complicated however the bottom sediment types can be simplified to be sandy sediment clayey sediment and mixed sediment which comprise the complicated distribution pattern of bottom sediment in the byecs the continental shelves of the byecs are broad with shallow water depths and tidal currents which are permanent and dominate the marine dynamics in the byecs based on numerical simulation of tidal elevations and currents in the byecs the rates of suspended load transport and bed load transport during a single tidal cycle for sediments of eight different grain size ranges are calculated the results show that any sediment whose threshold velocity is less than that of tidal current has the same transport trend suspended load transport rare bed load transport rate and the ratio of the former to the latter decrease with grain size becoming coarser and coarser the erosion accretion patterns of sediments with different grain sizes are determined by the sediment transport rate divergences and the results show that the patterns are the same for sediments with different grain sizes three main bottom sediment types i e sandy sediment mainly composed of fine sand clayey sediment mainly composed of silty clay and mixed sediment mainly composed of fine sand silt and clay are obtained by computation the three bottom sediment types and their distribution pattern are consistent not only with sediment transport field and the sea bed erosion accretion pattern obtained by simulation but also with field data of bottom sediment types and divisions in the byecs sand ridges form mainly in the areas with strong rectilinear tidal currents sand sheets form mainly in the areas dominated by strong rotatory tidal currents and clayey sediments i e mud patches form mainly in the areas with weak tidal currents hence not only the sandy sediments but also the clayey sediments in the byecs are formed under the control of the whole tidal current field of the byecs the three main bottom sediment types are not isolated respectively in fact they constitute a whole tidal depositional system under the condition with no cyclonic cold eddy the clayey sediments in the byecs can form in weak tidal current environments therefore a cold eddy is not necessary for the deposition of clayey sediments in the byecs c 2000 academic press

organic matter origin and distribution in suspended particulate materials and surficial sediments from the western adriatic sea italy abstract in this study organic carbon oc total nitrogen tn stable carbon isotopic 13 c oc and cuo reaction product compositions were used to identify the sources of organic matter om and to quantify the relative importance of allochthonous and autochthonous contributions to the western adriatic sea italy suspended particulate material 195 samples and surficial sediments 0 1 cm 70 samples from shallow cross shelf transects were collected in february and may 2003 respectively vertical water column profiles were acquired along the same transects data include depth potential temperature salinity density and chlorophyll fluorimetry along the western adriatic shelf in the near shore region the phytoplankton growth was influenced by dynamics of the buoyant plumes from the po and appennine rivers a small amount of very fine terrigenous material remained suspended within the coastal current and was exported southward along the shelf to the slope high variability in the bulk composition was detected in the po prodelta surficial sediments whereas the western adriatic shelf although a larger area exhibited a narrower range of values a significant decoupling was observed between suspended particles in the water column and surficial deposits the organic material collected in the water column was compositionally heterogeneous with contributions from marine phytoplankton riverine estuarine phytoplankton and soil derived om frequent physical reworking of surficial sediments likely leads to the efficient oxidation of marine oc resulting in the observed accumulation and preservation of refractory soil derived oc delivered by the po and appennine rivers

effect of human controlled hydrological regime on the source transport and flux of particulate organic carbon from the lower huanghe yellow river evaluating the role of fluvial transfer of terrestrial organic carbon oc and subsequent burial in the global carbon cycle requires the sources and fluxes of fluvial oc to be assessed which remains poorly constrained in the huanghe yellow river here we report the elemental stable isotopic and radiocarbon activity of particulate organic carbon poc sampled at the outlet of huanghe in 2012 2013 we show that the huanghe riverine poc can be explained by binary mixing of fossil pocfossil and non fossil pocnon fossil components the former may reach 40 of the total poc the huanghe pocnon fossil is mostly sourced from c3 plants with a mean residence time of c 2200 years the current human controlled hydrological regime strongly influenced the poc sources transport modes and fluxes in 2012 2013 the huanghe delivered 0 73 tg 1 tg 1012 g of poc to the sea and about 28 of the annual poc flux occurred within a short human induced flood event globally the huanghe should be one of the largest rivers in the transfer and re burial of fossil oc however the fate of huanghe fossil oc is still unconstrained and needs to be further investigated copyright 2015 john wiley sons ltd

sea level rise sedimentary record and organic carbon fluxes in a low lying tropical coastal ecosystem abstract sea level rise one of the most evident effects of recent climate change is already impacting coastal ecosystems because of its low relief population increase and economic development during the last century the celestun lagoon is highly vulnerable to global change including sea level rise here we study a sediment core from a tropical saltmarsh to evaluate the impact of sea level rise on sediment accretion and carbon fluxes some geochemical indicators in a 210pb dated sediment core showed clear signals of marine influence this was reflected on increased accretion rates from 0 3 0 1 mm yr 1 in 1941 to 2 9 1 2 mm yr 1 in 2012 these accretion rates were similar to eustatic sea level rise and mean acceleration ranged from 0 037 0 22 mm yr 2 implying a slr by 2100 ranging from 14 to 86 cm the one century 1917 2013 organic carbon stock in sediments was calculated to be 10 1 0 2 mg c ha 1 during the same period the organic carbon flux corrected for organic carbon degradation increased from 7 3 g c m 2 yr 1 to 73 26 g c m 2 yr 1 attributed to the impact of sea level rise in this ecosystem this work shows that tropical saltmarshes may provide useful information on sea level rise and the presented methodology may be used where instrumental records do not exist or they are too short

whole grain evaporation for 207 pb 206 pb age investigations on single zircons using a double filament thermal ion source a technique has been developed and tested to analyse 207pb 206pb apparent ages by thermal evaporation of radiogenic lead directly from untreated whole zircon grains 0 3 mm the evaporation analyses are performed in the double filament arrangement of a thermal ion mass spectrometer thims the method is a powerful tool to distinguish between different lead components occurring in the same grain because differing activation energies of the competing lead components cause their sequential evaporation from the zircons the evaporation of test samples results in 207pb 206pb apparent ages in good agreement with u pb ages known from literature single zircons from a granite of the marble mountains california yield an age of crystallization of 1 410 30 ma ceylon zircons from heavy mineral bearing gravels yield 560 40 ma as age of crystallization of the pegmatitic gravel sources individuals from a heterogeneous zircon population of a diatexite from the southern schwarzwald sw germany indicate metamorphic zircon formation around 500 ma and the existence of middle proterozoic relics 1 95 0 05 ga

isotopic constraints on emplacement age of anorthositic rocks of the marcy masiff adirondack mts new york the igneous emplacement age of anorthositic rocks comprising the marcy massif have been constrained by fixing minimum and maximum ages for their intrusion minimum ages have been fixed by a u pb dating of cores of air abraded zircons from the anorthosite 1113 ma b u pb dating of baddeleyite within the anorthosite 1087 ma c u pb dating of baddeleyite from an olivine metagabbro crosscutting marcy massif anorthosite 1109 ma d u pb zircon dating of jotunitic rocks crosscutting the marcy anorthosite massif 1143 pm 31 ma maximum emplacement ages are based upon a sheets of anorthositic rock crosscutting mangeritic charnockitic gneiss dated by u pb zircon at 1125 pm 10 ma 1134 pm 4 ma and 1135 pm 43 ma and b anorthosite related pyroxenite dikes crosscutting mangerite that contains xenoliths of identical pyroxenite these results constrain emplacement of the marcy anorthosite to 1113 1138 ma with the most probable age in the interval 1125 1135 ma this time of in

age and regional relationships of granitoid rocks of the adirondack highlands approximately 55 of the adirondack highlands is underlain by granitic to tonalitic rocks that can be subdivided into five groups based on age composition and field occurrence 1 early calcalkaline tonalites ca 1300 ma and associated granitic rocks ca 1250 ma of the southern and eastern highlands 2 older anorogenic plutonic rocks 1145 1160 ma that occur throughout the highlands 3 younger anorogenic plutonic rocks ca 1130 ma that envelop anorthosite massifs in the central highlands 4 younger granitic rocks 1095 1105 ma of the northwest highlands and 5 late leucogranitic rocks 1060 1080 ma that occur throughout the northern highlands the data presented here are in good agreement with zircon ages from the green mountains of vermont as well as from southern ontario and quebec and suggest similar geologic histories for these regions these results document a protracted and complicated evolution for this portion of the grenville province

210pb sediment radiochronology an integrated formulation and classification of dating models abstract environmental archives such as sediments banded corals and tree rings are widely used to reconstruct past environmental conditions of ecosystems in particular 210 pb has been used during more than 4 decades through dating of undisturbed sediment cores to study ecosystem changes during the last 100 yr since its inception diverse dating models have been proposed developed used and validated in numerous environments but their nomenclature and formulation is not homogenous in this work we emphasize that conceptual models used to date undisturbed sediment cores can be deduced from a single fundamental equation which relates excess 210 pb concentration in sediment its flux to the sediment surface and mass accumulation rate from this equation models were consistently named based on the main hypothesis used and using a unified and logical nomenclature dating equations were derived in detail we applied in detail most of the described models to a sediment core from mexico and uncertainty expressions were also included finally some recommendations to use the models are proposed we believe that this work can facilitate the use of 210 pb as a tool to date sediment cores in a more homogeneous way

zircon u pb geochronology of two basement cores kentucky usa implications for late mesoproterozoic sedimentation and tectonics in the eastern midcontinent abstractbasement cores from two wells drilled west and east of the grenville front consist of feldspathic litharenite and granitic orthogneiss respectively detrital zircon u pb ages for the litharenite define a broad dominant u pb age mode at ca 1115 ma the dominant mode matches that for the type locality of the middle run formation in the ohio subsurface and is interpreted to consist of detrital zircons sourced from east continent rift volcanic sources ca 1100 ma and grenville shawinigan granites gneisses 1120 1180 ma the youngest detrital zircon ages ca 1020 ma require a maximum depositional age that is at least 70 my younger than the time of midcontinent and east continent rifting and magmatism we propose that the litharenite is correlative with the middle run formation in ohio and was deposited in an evolving late grenville rift foreland basin adjacent to the exhuming grenville orogen zircon u pb secondary ion mass spectrometry ages from orthogneiss define a discordant array with interc

simultaneous estimation of global present day water transport and glacial isostatic adjustment global water transport between oceans and continents during the transition from glacial to interglacial times has been enormous the viscoelastic solid earth has been responding to this unloading of large ice masses with a rise of the land masses in a process termed glacial isostatic adjustment in addition significant changes in the land ocean water distribution occur at present as both present day changes in the ice water thickness and glacial isostatic adjustment affect space geodetic measurements it is difficult to untangle the relative contributions of these two processes here we combine gravity measurements and geodetic data of surface movement with a data assimilating model of ocean bottom pressure to simultaneously estimate present day water transport and glacial isostatic adjustment we determine their separate contributions to movements in the geocentre which occur in response to changes in the earth s mass distribution with uncertainties below 0 1 mm yr 1 according to our estimates mass losses between 2002 and 2008 in greenland alaska yukon and west antarctica are 104 23 101 23 and 64 32 gt yr 1 respectively our estimates of glacial isostatic adjustment indicate a large geocentre velocity of 0 72 0 06 mm yr 1 in the polar direction we conclude that a significant revision of the present estimates of glacial isostatic adjustments and land ocean water exchange is required present day changes in the thickness of ice sheets and glacial isostatic adjustment both affect space geodetic measurements a combination of gravity measurements and geodetic data of surface movement with a data assimilating model of ocean bottom pressure allows the simultaneous estimation of present day water transport and glacial isostatic adjustment

a global marine fixed nitrogen isotopic budget implications for holocene nitrogen cycling 1 a nitrogen stable isotopic model was constructed in order to constrain the holocene marine fixed nitrogen budget the primary sources and sinks considered were riverine and atmospheric sources nitrogen fixation sedimentary and water column denitrification and sediment burial the source budget was found to be insensitive to changes in nitrogen fixation rates and thus could not be used to constrain this term however the isotopic value of fixed nitrogen losses was very sensitive to the amount of sedimentary denitrification if the isotopic value of marine fixed nitrogen has not changed during the holocene as supported by sedimentary records then in order to balance the isotopic value of sinks and sources approximately 280 tg n yr 1 of sedimentary denitrification is required if such a high rate of denitrification has been sustained throughout the holocene it implies that present day estimates of marine nitrogen fixation are grossly underestimated it also implies that the marine nitrogen budget has a residence time of less than 2000 years

u pb zircon geochronology of the adirondack mountains and implications for their geologic evolution u pb zircon studies of metamorphosed igneous rocks in the adirondack mountains have yielded preliminary ages within the range 1420 990 ma several geochronologically and geochemically distinct episodes of igneous intrusion and at least one pre granulite facies dynamothermal metamorphic event are documented this information is consistent with recent field and geochronological studies throughout the grenville province and suggests that a complex sequence of events occurred in the adirondack mountains prior to the widespread deformation and metamorphism commonly attributed to the approximately 1100 1000 ma ottawan phase of the grenvillian orogenic cycle