ion microprobe analysis of oxygen isotopes in garnets of complex chemistry abstract accurate ion microprobe analysis of oxygen isotope ratios in garnet is possible if appropriate standards are employed to correct for instrumental bias a component of which depends on the cation chemistry of the analyzed mineral in this study 26 garnet standards including 14 new standards that span the compositional range of pyrope almandine grossular spessartine and andradite were analyzed repeatedly by ion microprobe to develop a new method of correcting for instrumental bias in garnets all analyses were normalized to a single master garnet standard uwg 2 before bias from cation composition was considered bias due to cation composition in garnet was found to correlate with grossular content in pyralspite garnets and with andradite in ugrandite garnets bias is correlated with molar volume in garnets of all compositions in this study although this correlation is suitable as a correction scheme for bias a more accurate correction scheme based on the grossular and andradite compositions of garnet is proposed this method reproduces the bias of all but one standard to within a range of 0 4 an accuracy that is on the same order as the reproducibility 0 3 2 s d of the master garnet standard uwg 2 but that remains an independent source of error the new correction scheme is used to successfully reproduce laser fluorination analyses along a traverse of a polymetamorphic zoned skarn garnet from the adirondack mountains while previous analyses were at the mm scale the new data resolve a gradient of 18 o of 2 1 over 16 m if experimentally derived diffusion coefficients are correct these new results show that granulite facies metamorphism was significantly faster than previously assumed and the thermal peak was less than 5 myr

stratigraphic development of synkinematic deposits in a large growth fault system onshore brunei darussalam kilometre scale synsedimentary faults associated with well preserved sedimentary successions on both hanging wall and footwall sides are rarely seen in outcrop however one such example is found in a middle miocene deltaic sand shale sequence exposed along the jerudong anticline in onshore brunei darussalam integration of detailed outcrop information with regional geophysical subsurface data documents that 1 initiation of the jalan tutong growth fault was related to delta front instability and failure 2 sediment loading under shallow marine conditions maintained syndepositional faulting 3 growth fault abandonment coincided with a significant basinward shift of deposition and subaerial exposure high resolution analysis of facies characteristics stratal expansion and throw development within the studied growth sequence indicates that differential fault movement strongly influenced facies composition sedimentary geometry and bedding characteristics sandstone poor shelf to lower shoreface successions developed during periods of rapidly increasing fault movement whereas sandstone rich amalgamated upper shoreface deposits preferentially formed during intervals of constant or decreasing throw development the data and interpretations presented may help to focus attention on the complex interplay between tectonics and sedimentation associated with the growth and decay of deltaic faults by providing for the first time an outcrop based view on a feature documented in similar scale only by geophysical subsurface data

early to mid tertiary inverted metamorphic gradient under the colorado plateau evidence from eclogite xenoliths in ultramafic microbreccias navajo volcanic field mid tertiary ultramafic microbreccia diatremes from the navajo volcanic field in the four corners area of the colorado plateau contain an ultramafic xenoliths suite in which lower temperature prograde metamorphic eclogites are associated with higher temperature garnet clinopyroxenites that were retrograded and hydrated to chlorite eclogite assemblages and directions of metamorphic reactions are consistent with the model of a laramide age inverted metamorphic gradient established as prograde reactions in a dehydrating oceanic slab caused hydration and cooling in the overlying subcontinental upper mantle wedge comparison with an inverse metamorphic gradient in the pelona schists inferred to represent an exposed part of the same subduction system in southwestern arizona and southern california confirms the shallow dip of the laramide subduction zone predicted by the regional distribution of subduction related volcanic rocks

stratigraphy and age estimate of neogene shallow marine fossiliferous deposits in brunei darussalam ambug hill tutong district abstract the ambug hill in brunei is an exceptional geological site where a series of siliciclastic rocks crops out with some layers extremely rich in marine fossils such fossiliferous outcrops are extremely rare in the northern part of borneo and their description is of primary importance as their fossil content can be used to correlate the regional depositional sequences with global biostratigraphic zonations in this work we present for the first time a detailed sedimentary profile completed with sr isotopes and biostratigraphic dating the succession is divided into four sedimentary units the first unit comprises bioturbated sandstone followed by a second unit of clay silt rich levels whose first 9 5 m contain rich marine fossil assemblages calcareous nannoplankton data indicate a late tortonian early messinian nn11 age which is confirmed by sr isotope dating derived from bivalves giving a numerical age range from 8 3 to 6 2 my after a major emersion surface the third sedimentary unit of sand and siltstone lacks suitable fossils for bio and isotope stratigraphy the age of emersion and the related sedimentary gap can be either correlated with the me1 7 25 my or the me2 5 73 my sequence boundary a fourth thin sedimentary unit is recognized on the top of the profile with silt and claystone beds without age diagnostic remains and calcareous fossils

sediment supply systems of the champion delta of nw borneo implications for deepwater reservoir sandstones abstract middle miocene to pliocene sedimentation on the nw borneo margin has been interpreted as the product of one relatively large deltaic system the champion delta however several lines of evidence indicate that the champion system was not a simple large delta its drainage basin was too small fluvial outcrops indicate multiple relatively small rivers and outcrop studies indicate the same facies associations as the diverse modern depositional systems the number and location of rivers reaching the shoreline changed as rapidly subsiding footwall synclines episodically active inversion anticlines and growth faults created an evolving structurally generated topography that not only controlled drainage pathways but also segregated champion strata into thick wave dominant and tide dominant successions although the principal rivers within the champion system the limbang padas and trusan rivers transport significant loads of coarse sediment the intermittent proximal ponding of sand in local basins as is currently occurring in brunei bay resulted in a variable delivery of sand to the shelf edge the number and distribution of shelf edge canyons also changed with time consequently the spatial and temporal distribution of deepwater sand accumulations sourced from the champion system are not solely related to relative sea level fluctuations such accumulations should be smaller and more scattered than those sourced from a large shelf edge delta because the catchments of the champion system s principal rivers represent different provenances the system s deepwater sands may carry the signal of specific rivers for example mineralogical contrasts between in the main reservoir sands of the deepwater gumusut and kikeh fields suggest that the relative contributions of the principal rivers shifted with time with the trusan and limbang rivers dominating sand supply for the youngest reservoirs at gumusut

stable carbon isotopes of c3 plant resins and ambers record changes in atmospheric oxygen since the triassic estimating the partial pressure of atmospheric oxygen po2 in the geological past has been challenging because of the lack of reliable proxies here we develop a technique to estimate paleo po2 using the stable carbon isotope composition d 13 c of plant resins including amber copal and resinite from a wide range of localities and ages triassic to modern plant resins are particularly suitable as proxies because their highly cross linked terpenoid structures allow the preservation of pristine d 13 cs ignatures over geological timescales the distribution of d 13 c values of modern resins n 126 indicates that a resin producing plant families generally have a similar fractionation behavior during resin biosynthesis and b the fractionation observed in resins is similar to that of bulk plant matter resins exhibit a natural variability in d 13 c of around 8 d 13 cr ange 31 to 23 m ean 27 which is caused by local environmental and ecological factors e g water availability water composition light exposure temperature nutrient availability to minimize the effects of local conditions and to determine long term changes in the d 13 co f resins we used mean d 13 c values d 13 c resin for each geological resin deposit fossil resins n 412 are generally enriched in 13 c compared to their modern counterparts with shifts in d 13 c resin of up to 6 these isotopic shifts follow distinctive trends through time which are unrelated to post depositional processes including polymerization and diagenesis the most enriched fossil resin samples with a d 13 c resin between 22 and 21 formed during the triassic the mid cretaceous and the early eocene experimental evidence and theoretical considerations suggest that neither change in pco2 nor in the d 13 c of atmospheric co2 can account for the observed shifts in d 13 c resin the fractionation of 13 c in resin producing plants d 13 c instead is primarily influenced by atmospheric po2 with more fractionation occurring at higher po2 the enriched d 13 c resin values suggest that atmospheric po2 during most of the mesozoic and cenozoic was considerably lower po2 10 20 than today po2 21 in addition a correlation between the d 13 c resin and the marine d 18 o record implies that po2 pco2 and global temperatures were inversely linked which suggests that intervals of low po2 were generally accompanied by high pco2 and elevated global temperatures intervals with the lowest inferred po2 including the mid cretaceous and the early eocene were preceded by large scale volcanism during the emplacement of large igneous provinces lips this suggests that the influx of mantle derived volcanic co2 triggered an initial phase of warming which led to an increase in oxidative weathering thereby further increasing greenhouse forcing this process resulted in the rapid decline of atmospheric po2 during the mid cretaceous and the early eocene greenhouse periods after the cessation in lip volcanism and the decrease in oxidative weathering rates atmospheric po2 levels continuously increased over tens of millions of years whereas co2 levels and temperatures continuously declined these findings suggest that atmospheric po2 had a considerable impact on the evolution of the climate on earth and that the d 13 c of fossil resins can be used as a novel tool to assess the changes of atmospheric compositions since the emergence of resin producing plants in the paleozoic

tectonic implications of the age composition and orientation of lamprophyre dikes navajo volcanic field arizona abstract fifty one lamprophyre dikes of the navajo volcanic field are randomly oriented in contrast to dikes of similar age from adjacent tectonic provinces k ar ages obtained on nine of these dikes indicate that they were emplaced between 28 and 19 m y ago initiation of dike emplacement was approximately coeval with the initial demarcation of the colorado plateau in the mid tertiary chemical analyses obtained on nine dike samples show a wide range in composition silica contents range from 33 6 in a phlogopite katungite to 55 9 in a felsic minette two of the samples have na 2 o k 2 o indicating that sodic volcanism was occurring concurrently with the dominant potassic volcanism published results of high pressure experimental studies of katungite suggest that this magma was derived from k metasomatised mantle because this potassium metasomatism produces a positive volume change we propose a model that relates uplift of the colorado plateau to metasomatism magma genesis and dike emplacement

chromium and manganese zoning in pelitic garnet and kyanite spiral overprint and oscillatory zoning patterns and the role of growth rate x ray composition maps and quantitative analyses for mn ca and cr have been made for six pelitic and calc pelitic garnet crystals and al fe and cr analyses maps have been made for two kyanite crystals from lower and mid upper amphibolite facies rocks from the grenville province of western labrador using an electron microprobe analyser and a laser ablation icp ms garnet with spiral snowball internal fabrics si has spiral zoning in major elements implying that growth was concentrated in discrete regions of the crystal at any one time spiral zoning cr zoning is parallel to si in low amphibolite facies garnet with both straight and spiral internal fabrics indicating that the garnet overprinted a fabric defined by cr rich mica chlorite epidote and cr poor quartz plagioclase layers during growth overprint zoning and that cr was effectively immobile in contrast in mid upper amphibolite facies garnet porphyroblasts lacking si cr zoning is concentric implying that cr diffusion occurred cr zoning in kyanite porphyroblasts appears superficially similar to oscillatory zoning with up to three or four annuli of cr enrichment and or depletion present in a single grain however the variable width continuity cr concentration and local bifurcation of individual annuli suggest that an origin by overprint zoning may be more likely the results of this study explain previously observed nonsystematic cr zoning in garnet and irregular partitioning of cr between coexisting metamorphic mineral pairs in addition this study points to the important role of crystal growth rate in determining the presence or absence of inclusions and the type of zoning exhibited by both major and trace elements during fast growth inclusions are preferentially incorporated into the growing porphyroblast and slow diffusing elements such as cr are effectively immobile whereas during slow growth inclusions are not generally included in the porphyroblast and cr zoning is concentric

occurrence of polycadinene in fossil and recent resins abstract dammars produced by dipterocarpaceae growing in southeast asia are partly composed of a macromolecule with a polycadinene structure this polymer is the precursor of many specific compounds encountered in crude oils and sediment extracts from south asia until recently there was no evidence for a more widespread geographical occurrence of this resinous polymer using different pyrolysis methods it is shown that the polymers present in a resinite from utah usa and in resins contained in resin canals of eocene fossil fruits from germany and england are also polycadinenes the fossil fruits were undoubtedly produced by ancient representatives of mastixioid cornaceae a group of plants which was widespread in the tertiary of europe and north america and which is not related to dipterocarpaceae these findings extend the known occurrence and origin of the sesquiterpenoid type resin polymer it is to be expected that catagenetic products of these resin polymers should be present in oils coals and sediment extracts from areas outside southeast asia

timing of colorado plateau uplift initial constraints from vesicular basalt derived paleoelevations we have developed a technique for measuring paleoelevation on the basis of the vesicularity of basaltic lava flows we are currently applying this technique to determine the timing and extent of cenozoic uplift of the colorado plateau because the technique measures paleoatmospheric pressure it is not subject to uncertainties stemming from the use of proxies that depend on environmental factors other than elevation alone vesicular lavas preserve a record of paleopressure at the time and place of lava emplacement because the difference in internal pressure in bubbles at the base and top of a lava flow depends on atmospheric pressure and lava flow thickness the modal size of the vesicle bubble population is larger at the top than at the bottom this leads directly to paleoatmospheric pressure and thus elevation because the thickness of the flow can easily be measured in the field and the vesicle sizes can be measured in the laboratory on the colorado plateau volcanic fields are generally found around the margins of the plateau basaltic lavas range in age from 0 to 23 ma present elevations range from 1 7 km to 3 3 km samples were collected from lava flows in the areas of marysvale springerville grand mesa and the san juan mountains and analyzed to determine the timing and extent of uplift the analysis of the samples using x ray computed tomography imaging and our numerical techniques for determining vesicle population statistics indicate uplift of 350 2200 m depending on age there is a clear relationship between age and amount of uplift original elevation subtracted from present elevation the results indicate slow uplift of 40 m m y between 25 ma and 5 ma only 800 m of uplift during that time and rapid uplift of 220 m m y since 5 ma 1100 m during that time these results reconcile the long standing controversy between interpretations of ancient versus recent uplift by providing an uplift history curve for the colorado plateau

stable isotope geochemistry of alpine ophiolites a window to ocean floor hydrothermal alteration and constraints on fluid rock interaction during high pressure metamorphism the subduction of hydrated oceanic lithosphere potentially transports large volumes of water into the upper mantle however despite its potential importance fluid rock interaction during high pressure metamorphism is relatively poorly understood the stable isotope and major element geochemistry of pennine ophiolite rocks from italy and switzerland that were metamorphosed at high pressures are similar to that of unmetamorphosed ophiolites suggesting that they interacted with little pervasive fluid during high pressure metamorphism cover sediments also have oxygen isotope ratios within the expected range of their protoliths in the rocks that escaped late greenschist facies retrogression different styles of sub ocean floor alteration may be identified using oxygen isotopes petrology and major or trace element geochemistry within the basalts zones that have undergone high and low temperature sub ocean floor alteration as well as relatively unaltered rocks can be distinguished serpentinites have 18o and 2h values that suggest that they were formed by hydration on or below the ocean floor the development of high pressure metamorphic mineralogies in metagabbros occurred preferentially in zones that underwent sub ocean floor alteration and which contained hydrated fine grained reactive assemblages given that the transformation of blueschist facies metabasic rocks to eclogite facies assemblages involves the breakdown of hydrous minerals e g lawsonite zoisite and glaucophane and will thus liberate considerable volumes of fluids metamorphic fluid flow must have been strongly channelled high pressure quartz calcite omphacite glaucophane titanoclinohumite veins that cut the ophiolite rocks represent one possible channel however stable isotope and major element data suggest that they were not formed from large volumes of exotic fluids fluids were more likely channelled along faults and shear zones that were active during high pressure metamorphism such strong fluid channelling may cause fluids to migrate toward the accretionary wedge especially along the slab mantle interface which is probably a major shear zone this may preclude all but a small fraction of the fluids entering the mantle wedge to flux melting additionally because fluids probably interact with relatively small volumes of rock in the channels they cannot scavenge elements from the subducting slab efficiently

the effects of early diagenesis on the chemical and stable carbon isotopic composition of wood abstract studies of modern and ancient buried wood show that there is a linear correlation between carbohydrate content and the stable carbon isotope composition as carbohydrates are preferentially degraded during early diagenesis as the carbohydrate content decreases the 13 c value of the degraded wood decreases 1 to 2 per mil approaching the value of the residual lignin these results indicate that carbohydrate degradation products are lost and not incorporated into the aromatic structure as lignin is selectively preserved during early diagenesis of wood these results also indicate that attempts to quantify terrestrial inputs to modern sedimentary organic matter based on 13 c values should consider the possibility of a 1 to 2 per mil decrease in the 13 c value of degraded wood

an oxygen isotopic profile through the upper kilometer of the oceanic crust dsdp hole 504b dsdp hole 504b is the deepest basement hole in the oceanic crust penetrating through a 571 5 m pillow section a 209 m lithologic transition zone and 295 m into a sheeted dike complex an oxygen isotopic profile through the upper crust at site 504 is similar to that in many ophiolite complexes where the extrusive section is enriched in18o relative to unaltered basalts and the dike section is variably depleted and enriched basalts in the pillow section at site 504 have 18o values generally ranging from 6 1 to 8 5 smow mean 7 0 although minor zeolite rich samples range up to 12 7 rocks depleted in18o appear abruptly at 624 m sub basement in the lithologic transition from 100 pillows to 100 dikes coinciding with the appearance of greenschist facies minerals in the rocks whole rock values range to as low as 3 6 but the mean values for the lithologic transition zone and dike section are 5 8 and 5 4 respectively oxygen and carbon isotopic data for secondary vein minerals combined with the whole rock data provide evidence for the former presence of two distinct circulation systems separated by a relatively sharp boundary at the top of the lithologic transition zone the pillow section reacted with seawater at low temperatures near 0 c up to a maximum of around 150 c and relatively high water rock mass ratios 10 100 water rock ratios were greater and conditions were more oxidizing during submarine weathering of the uppermost 320 m than deeper in the pillow section the transition zone and dikes were altered at much higher temperatures up to about 350 c and generally low water rock mass ratios 1 and hydrothermal fluids probably contained mantle derived co2 mixing of axial hydrothermal fluids upwelling through the dike section with cooler seawater circulating in the overlying pillow section resulted in a steep temperature gradient 2 5 c m across a 70 m interval at the top of the lithologic transition zone progressive reaction during axial hydrothermal metamorphism and later off axis alteration led to the formation of albite and ca zeolite rich alteration halos around fractures this enhanced the effects of cooling and18o enrichment of fluids resulting in local increases in 18o of rocks which had been previously depleted in18o during prior axial metamorphism

evolution of navajo eclogites and hydration of the mantle wedge below the colorado plateau southwestern united states 1 eclogite and pyroxenite xenoliths from ultramafic diatremes of the navajo province on the colorado plateau have been analyzed to investigate hydration of continental mantle and effects of low angle subduction on the mantle wedge xenoliths have been characterized by petrographic and electron probe analysis and by sm nd rb sr k ar and o isotopic analysis of mineral separates from one eclogite and by u pb isotopic analysis of zircons from three samples k ar analysis of phengite establishes eruption of a garnet ridge arizona diatreme at 30 ma sm nd and rb sr analyses of clinopyroxene and garnet from that eclogite document recrystallization shortly preceding eruption three zircon fractions have been analyzed from that eclogite and from two others representing the nearby moses rock and mule ear diatremes seven of nine small multigrain fractions scatter about a poorly fit discordia between ca 35 ma and 1515 ma fractions range from overlapping concordia at the lower intercept to a 207pb 206pb age of ca 1220 ma the discordant fractions establish a mid proterozoic zircon component in each eclogite inconsistent with an origin from basalt of the farallon plate the pressure recorded by one of these eclogites 3 3 gpa exceeds that of an eclogite previously attributed to the farallon plate nonetheless each of the eclogites contains a fraction of nearly concordant zircons with ages in the range 35 to 41 ma and one rock also contains a fraction that is nearly concordant at 70 ma these concordant ages are interpreted to record episodic zircon growth during recrystallization of proterozoic mantle the concordant zircon ages are consistent with published data that establish recrystallization of navajo eclogites from 81 to 33 ma a time interval similar to that of the laramide orogeny the eclogite facies recrystallization and growth of new zircon are attributed to the catalytic effects of water introduced into the mantle from the farallon slab water penetrated fracture zones extending for at least tens of kilometers into the mantle wedge above the farallon slab during low angle subduction magmatism in the san juan volcanic field to the northeast of the diatremes may be related to similar hydration

rates of fe mg mn and ca diffusion in garnet extraction of the thermal and chemical histories preserved by modified compositional zoning in garnet is compromised by large uncertainties in experimentally determined diffusion coefficients for principal divalent cations some of this uncertainty derives from long down temperature extrapolations but much of it arises from an inability to account accurately for large variations in diffusivity as a function of garnet composition numerical simulation of stranded diffusion profiles in partially resorbed natural garnets constrains diffusivities at low temperature and reveals a systematic dependence of diffusion rates on host garnet composition a comprehensive model incorporating a simple compositional dependence allows accurate prediction of diffusion rates for fe mg mn and ca for nearly all garnet compositions across the full range of geologically relevant temperatures pressures and oxygen fugacities

biomarker and n alkane isotope profiles for tertiary oils relationship to source rock depositional setting abstract biomarker and n alkane isotope profiles have been measured for 29 late cretaceous tertiary oils from se asia china papua new guinea new zealand and the u s a the results are interpreted with respect to six kinds of source rock depositional setting fluvio deltaic fd freshwater transitional tr lacustrine lac saline lacustrine sal marine deltaic md and marine carbonate mc a comparison of biomarker and n alkane isotope results suggests that parameters such as the oleanane hopane ratio may overestimate the higher plant contribution to marine oils the abundance of bicadinanes is much more variable than that of oleanane probably because of a specific association with the highly resinous dipterocarp hardwoods of se asia however traces do occur in an oil from outside the paleogeographic range of the dipterocarp family confirming that there is also a more general angiosperm source the bicadinane isomeric distribution is shown to depend on maturity leading to new maturity parameters which are resistant to even very heavy biodegradation retention indices based on the regular hopane series are provided for the main bicadinane and methyl bicadinane isomers and for a group of oleanane related triterpanes of unknown structure the presence of the latter compounds may indicate locally deposited as opposed to transported higher plant matter in the source source rock depositional setting is the primary control on the shape of the n alkane isotope profile with negatively sloping curves being characteristic of fd and tr oils and flat or positively sloping curves typical of marine oils the difference is probably related to the bacterial reworking of higher plant matter in the fd environment a slight isotopic anomaly at n c 17 correlates with the abundance of algal derived steranes and may indicate a minor marine contribution to the source of an fd oil

massive fluid influx beneath the colorado plateau usa related to slab removal and diatreme emplacement evidence from oxygen isotope zoning in eclogite xenoliths

large rotaliid foraminifera as biostratigraphic and palaeoenvironmental indicators in northwest borneo an example from a late miocene section in brunei darussalam abstract palaeonvironmental interpretations and biostratigraphic zonations in northwest borneo are still a matter of debate but are important for petroleum related applications the outcrop of ambug hill a late miocene marine siliciclastic sequence in brunei darussalam has been investigated for its foraminifera assemblage from a 9 5 m clay rich interval 50 taxa have been recognized and classified whenever possible to species level the studied fauna is characterized by mostly hyaline foraminifera dominated by two rotaliid species cavarotalia annectens and heterolepa dutemplei additionally a number of miliolids lageniids bolivinids and also planktonic foraminifera are present but in much lower abundance the dominance of the rotaliids points to a sea floor rich in organic carbon characterized by muddy substrates with very low light penetration and the possible growth of patchy sea grass or macroalgae in the system as indicated by epiphytic foraminifera in the samples the results obtained give additional insights on how the environmental conditions might have been during the deposition of the deltaic sequences very widespread in the region and how the fauna coped with such settings throughout the investigated samples the dominance of the assemblages clearly shows alternating stress conditions typical of pro deltaic environments the large abundance of rotaliid foraminifera points toward possible biostratigraphic applications as several taxa within this group have short biozones in the region even though have strong facies dependency if their role as biostratigraphic indicators could be finally proven they might be used to date the large depositional sequences occurring in the region since planktonic index fossils are scarce due to the very proximal settings of the sediments

eclogite facies fluid infiltration constraints from δ 18 o zoning in garnet in situ analysis reveals that eclogite facies garnets are zoned in 18o with lower values in the core and rims that are 1 5 to 2 5 higher this pattern is present in 9 out of 12 garnets analyzed by sims from four orogenic eclogite terranes and correlates with an increase in the mole fraction of pyrope and mg fe ratio from core to rim indicating prograde garnet growth at the maximum temperatures and the time scales experienced by these garnets calculated intragranular diffusion distances for oxygen are small 5 from two kimberlites are homogeneous in 18o possibly due to diffusive exchange which is possible for prolonged periods at higher mantle temperatures homogeneity of 18o in garnets outside the normal mantle range 5 6 may be common in kimberlitic samples

stable carbon isotope record of terrestrial organic materials for the last 450 ma yr abstract the timing and magnitude of carbon isotope excursions is essential for understanding the global transfer of carbon among the oceansland and atmosphere numerous studies have focused on data collection of stable carbon isotopes 13c from marine sediments and by extension to the atmosphere but many fewer systematic studies have been conducted on land plants over long time intervals we pursued three approaches to determining stable carbon isotope trends for the past 450 ma yr from c3 plants 13cp in 5 ma yr time steps first a compilation of 6888 13cp values from ten carbon sources from the literature average 24 6 1 7 isoorg data base the second approach assumes the 13cp is controlled primarily by the 13c of atmospheric co2 13ca and subsequent isotopic fractionation from diffusion and carboxylation during photosynthesis mod1 the third approach assumes changes in atmospheric co2 concentration pco2 causes physiological driven isotopic fractionation during photosynthesis when pco2 is greater than average holocene conditions mod2 compared to isoorg and mod1 mod2 reveals lower 13cp by up to 6 during periods when pco2 is elevated as secular governors of 13cp the 13ca and pco2 are most influential when they are directional and amplify the isotopic signal despite potential influences from local and regional environmental conditions and averaging the 13cp of multiple plant sources in many of the 5 ma yr age bins ten positive carbon isotopic excursions pcies are identified in isoorg of this study most of the excursions occurred during cool to glacial conditions or ocean anoxic events one prominent negative isotopic excursion ensued from 260 to 240 ma yr which may have been a response to oxidation of light c methane outbursts volcanic eruptions or bolide impact

oxygen isotope heterogeneities and diffusion profile in composite metamorphic magmatic garnets from the pyrenees unusually large 1 8 o heterogeneities 4 within single crystals are reported in garnets from dioritic migmatites in the pyrenees these heterogeneities together with contrasting ca and p zoning allow the identification of different growth zones garnet cores with high 1 8 o values 12 14 are relatively poor in ca 7 9 mol grs and rich in p 400 900 ppm p 2 o 5 in contrast garnet rims with lower 1 8 o values 7 12 o are richer in ca 12 14 grs and poorer in p 100 200 ppm these growth zones can be ascribed to a metamorphic event followed by crustal partial melting and contamination by magmas from the mantle high 1 8 o intra crystalline contrasts result from mineral growth in an open magmatic system involving the interaction of partial melts with distinct 1 8 o signatures at the garnet core rim interface compositional profiles in major divalent cations are consistent with the relaxation of an initial sharp step in ca fe and mg by ca fe mg interdiffusion at the same interface an o isotope profile is documented the analogy of ca and o isotope profiles suggests that the 1 8 o distribution may also result from a diffusion process in this particular case temperature garnet composition oxygen fugacity o diffusion appears to be of the same order of magnitude as ca fe mg interdiffusion considering a duration of 10 ma for the plutono metamorphic event in the pyrenees ca and o diffusivities in the range 10 2 2 m 2 s at 850 c are retrieved from the measured profiles like ca o diffusion in garnet at magmatic temperatures 850 900 c is both slow enough to preserve large 1 8 o heterogeneities and fast enough to generate relaxation profiles

rock mass collapse mechanism of concealed karst cave beneath deep tunnel abstract local collapse of the surrounding rock often occurs during tunnel construction in a karst area particularly when the rock pillar between the tunnel and the karst cave is very thin the collapse of the surrounding rock in tunnel construction is sudden and may lead to great economic loss or even loss of life to predict the collapse of rock mass where a tunnel is excavated above a karst cave an analytical expression of the collapse surface is derived from variational calculation in the framework of the upper bound theorem based on the analytical solution the shape of the collapse surface is plotted to investigate the effects of rock parameters on the collapse surface of the rock mass where a karst cave exists beneath a tunnel according to the changing law of the collapse surface varying with the distance between tunnel and cave the computational formula of the minimum safety thickness for preventing the collapse of rock pillar is derived to evaluate the validity of the proposed method in this paper we compared the analytical solution with numerical solution the comparison result indicates the analytical solution matches up with the numerical solution very well which suggests that the analytical approach proposed in this paper is valid

origin and structure of the fossil resin from an indonesian miocene coal abstract the structure of a fossil resin from miocene coal outcrops of the bukit asam region sumatra has been studied the fossil material has been formed from sesqui and tri terpenes from trees of the dipterocarp family the original terpenes have lost virtually all oxygen containing functions and the resulting mono and di olefins have polymerized to a mainly non crosslinked resin whose components have molecular weights of up to 300 000

taphonomy and chemotaxonomy of eocene amber from southeastern australia abstract amber is a complex organic polymer that offers unparalleled utility as a preservation medium providing insights into past organisms and environments however under specific circumstances this information can be compromised through alteration of the amber structure understanding the degradation of amber in the geosphere could improve prospecting techniques and maximise the quality and validity of chemical information from altered samples this study analysed 114 amber samples retrieved from two new eocene australian deposits at strahan tasmania and anglesea victoria using a combination of attenuated total reflectance fourier transform infrared and solid state 13c cross polarised magic angle spinning nuclear magnetic resonance spectroscopy results identified both class ib polylabdanoid and class ii cadinene based amber the presence of class ii amber in australia suggests one of two possibilities 1 a local dipterocarpaceae source the primary producer of class ii resins despite the absence of this family from the australian eocene fossil record or 2 a local unidentified botanical source of cadinene based amber a third alternative that class ii amber was transported to australia from southeast asia via ocean currents is rejected taphonomic analysis revealed four mechanisms of alteration prevalent in amber across the two study regions with evidence of oxidation and metal carboxylate formation both the nature and extent of these alterations were found to vary significantly between classes i and ii suggesting that amber class may play a defining role in determining the chemical pathways by which amber degrades of note was the high proportion of amber that exhibited no significant chemical changes despite extensive visible alteration features suggesting the integrity of palaeobiological and palaeoenvironmental information in these samples may be preserved

organic geochemistry of resins from modern agathis australis and eocene resins from new zealand diagenetic and taxonomic implications abstract a maturation series of resins and fossil resins from new zealand ranging in age from modern to eocene and ranging from uncoalified to high volatile c bituminous coal were analyzed by elemental pyrolysis gas chromatography py gc fourier transform infrared ftir and solid state 13 c nuclear magnetic resonance 13 c nmr techniques for comparison four resin samples from the latrobe valley australia were analyzed all of the resins and fossil resins of this study show very high h c atomic ratios and are characterized by dominant peaks in the 10 60 ppm range of solid state 13 c nmr spectra and prominent bands in the aliphatic stretching region 2800 3000 cm 1 of ftir spectra all indicating a highly aliphatic molecular structure the 13 c nmr and ftir data indicate a diterpenoid structure for these resins there is an abrupt loss of oxygen that occurs at the lignite a subbituminous c stage which is attributed to a dramatic loss of carboxyl cooh from the diterpenoid molecule this is a new finding in the diagenesis of resins this important loss in oxygenated functional groups is attributed to a maturation change also there is a progressive loss of exomethylene ch 2 groups with increasing degree of maturation as shown by both 13 c nmr and ftir data this change has been noted by previous investigators exomethylene is absent in the fossil resins from the eocene high volatile c bituminous coals this progressive loss is characteristic of class i resinites ftir data indicate that the oxygenated functional groups are strong in all the resin samples except the fossil resin from high volatile c bituminous coal this important change in oxygenated functional groups is attributed to maturation changes the 13 c nmr and ftir data indicate there are minor changes in the agathis australis resin from the living tree and soil which suggests that alteration of a australis resins begins shortly after deposition in the soil for as little as 1000 years the morwell and yallourn fossil resins from brown coal lignite b australia do not have some of the ftir characteristics of the new zealand resins which most likely indicates they have a different plant source because different degrees of oxidation and weathering and changes due to fires i e charring can be ruled out our results have implications for studies of the maturation provenance and botanical sources of fossil resins and resinites in eocene and miocene coals and sediments of new zealand and australia

nd and sr isotope chronostratigraphy of colorado plateau lithosphere implications for magmatic and tectonic underplating of the continental crust nd sr isotopes and major and trace element abundances were measured in lower and upper crustal xenoliths carried in tertiary minettes and kimberlitic diatremes of the colorado plateau the objective was to establish the vertical distribution of mantle extraction ages for an undisturbed precambrian crustal province characterized by normal thickness and low cratonic heat flow and to thereby evaluate the importance of magmatic or tectonic underplating in crustal growth mid proterozoic age 1 7 2 0 ga material is found at all levels of the crust although mafic granulites and amphibolites have major and trace element compositions compatible with an origin as magmatically underplated material nd model ages do not indicate that there has been significant mantle contribution to the lower crust by igneous processes such as magmatic underplating since the main crust forming event ca 1 85 ga ago the meta igneous lower crustal xenoliths have relatively radiogenic nd isotopic compositions and unradiogenic sr compositions there is little variability in nd model ages in spite of large variability in sm nd high and variable sm nd ratios were therefore established early in the history of the protolith during igneous or metamorphic processes coincident with or shortly after extraction from the mantle metapelitic xenoliths tectonically emplaced into the lower crust have the same proterozoic model ages as meta igneous parts of the lower crust these paragneisses are probably arc associated sediments that were underthrust during terrane accretion in the proterozoic the isotopic data indicate that eclogite xenoliths are likely to represent proterozoic lithosphere rather than subducted mesozoic morb as previously proposed a number of the eclogite xenoliths have experienced a metasomatic event which introduced lree sio2 and na2o and shifted the nd and sr isotopic compositions the least altered eclogite xenoliths have major and trace element and radiogenic nd isotopic compositions similar to those of other proterozoic mafic lower crustal xenoliths a more plausible protolith for the eclogites is proterozoic lithosphere that was metamorphosed to eclogite facies conditions either during precambrian continental assembly or in more recent times

an o isotope profile through the hp lt corsican ophiolite france and its implications for fluid flow during subduction abstract subduction zones are important sites for fluid generation as the downgoing slab undergoes progressive high pressure metamorphism these fluids are thought to play an important role in the generation of arc magmas but their affect on the subducted slab itself is less clear in this study the stable isotope geochemistry of the corsican ophiolite which is variably affected by subduction related metamorphism was investigated to assess the impact of subduction zone fluid flow on the downgoing slab a total of 170 stable isotope analyses oxygen and carbon showed the following features 1 overall the ophiolite preserves the same oxygen isotope profile with depth as unmetamorphosed ophiolites 2 the variation in oxygen isotope values for different areas does not correlate with metamorphic grade 3 oxygen and carbon isotope values for calcite in the ophiolite are not in equilibrium with the ophiolite but are similar to those of the overlying calc schists schistes lustres and 4 hydrogen isotopes indicate that serpentinitisation of ultramafics occurred during sub seafloor hydrothermal alteration and probably also during tectonic emplacement of the ophiolite these features indicate that large scale fluid flow did not affect the corsican ophiolite during subduction zone metamorphism calcite in the ophiolite was probably precipitated from co2 bearing fluids derived from decompression dehydration reactions affecting the overlying schistes lustres during exhumation of the ophiolite bearing schistes lustres nappes given that ocean crust must undergo at least some dehydration during prograde subduction zone metamorphism the evolved fluids must be either highly channelled or exit the slab relatively quickly so as to not interact with it the results of this study indicate that the important fluid pathways on corsica have yet to be identified but are probably the shear zones and fault systems that bound different slices of the high pressure nappe stack

the bruneian record of borneo amber a regional review of fossil tree resins in the indo australian archipelago abstract in this study we intend to provide an overview on fossilized tree resins amber commonly found in southeast asia more particularly in the indo australian archipelago iaa these remains are often referred in literature as indonesian amber borneo amber or simply as dammar they are very common in the region and the brunei sultanate is no exception as most of its neogene sedimentary successions contain amber rich layers although amber is a common fossil in the country and in northern borneo to our knowledge it has not been studied in great detail so far here we present an account on the borneo ambers from brunei regarding their stratigraphic origin basic physical properties their interaction with the biosphere and their botanical origin using fourier transform infrared spectroscopy ftir additionally a number of ambers and modern tree resins were analysed for their carbon isotope composition and a few were tested with gas chromatography we discuss the results in a regional and global context in comparison with available data from the iaa the ambers come from four different lithostratigraphic units with an age range of 12 to 3 million years middle miocene to pliocene recently reworked ambers from the coast ambers from younger alluvial deposits and several modern tree resins from dipterocarpaceae and araucariaceae agathis borneensis were also included in the study the 60 ftir analyses of modern and fossil specimens suggest that all the brunei ambers were produced by trees of dipterocarpaceae there is no indication of agathis in the fossil record in agreement with their lower abundance in the forests of borneo modern and fossil dipterocarp resins were found to be different based on the following criteria 1 different reactions to solubility hot needle and uv tests with faster reaction time and less fluorescence for the modern ones 2 clear distinction based on certain ftir absorbance band ratios mostly by those that represent carboxylic acids and esters e g 1700 and 1243 cm 1 3 modern resin yielded on an average 3 lower 13c values 4 gas chromatography data reflect maturation differences among the samples although there is some overlap in the chemical results between the two groups generally all these differences reflect different maturation stages of the resinous material and point towards loss of low 13c components from the organic structure of the resin the minor timewise decreasing trend in average 13c from the late middle miocene to late miocene can be explained by 1 gradual changes in local environmental conditions and or 2 increased amount of less mature specimens among the younger samples in contrast the highest obtained 13c values were found in the youngest pliocene ambers instead of maturation bias this can be linked to environmental factors such as cooler drier climate with increased seasonality probably reflecting the onset of the northern hemisphere glaciation

evaluating the use of amber in palaeoatmospheric reconstructions the carbon isotope variability of modern and cretaceous conifer resins abstract stable carbon isotope geochemistry of fossilized tree resin amber potentially could be a very useful tool to infer the composition of past atmospheres to test the reliability of amber as a proxy for the atmosphere we studied the variability of modern resin 13 c at both local and global scales an amber 13 c curve was then built for the cretaceous a period of abundant resin production and interpreted in light of data from modern resins our data show that hardening changes the pristine 13 c value by causing a 13 c depletion in solid resin when compared to fresh liquid viscous resin probably due to the loss of 13 c enriched volatiles modern resin 13 c values vary as a function of physiological and environmental parameters in ways that are similar to those described for leaves and wood resin 13 c varies between plant species and localities within the same tree and between different plant tissues by up to 6 and in general increases with increasing altitudes of the plant growing site we show that as is the case with modern resin cretaceous amber 13 c has a high variability generally higher than that of other fossil material despite the high natural variability amber shows a negative 2 5 3 13 c trend from the middle early cretaceous to the maastrichtian that parallels published terrestrial 13 c records this trend mirrors changes in the atmospheric 13 c calculated from the 13 c and 18 o of benthic foraminiferal tests although the magnitude of the shift is larger in plant material than in the atmosphere increasing mean annual precipitation and p o 2 could have enhanced plant carbon isotope fractionation during the late cretaceous whereas changing p co 2 levels seem to have had no effect on plant carbon isotope fractionation the results of this study suggest that amber is a powerful fossil plant material for palaeoenvironmental and palaeoclimatic reconstructions improvement of the resolution of the existing data coupled with more detailed information about botanical source and environmental growing conditions of the fossil plant material will probably allow a more faithful interpretation of amber 13 c records and a wider understanding of the composition of the past atmosphere

oxygen isotope zoning in garnets from franciscan eclogite blocks evidence for rock buffered fluid interaction in the mantle wedge the oxygen isotope compositions of eclogite and amphibolite garnets from franciscan complex high grade blocks and actinolite rinds encasing the blocks were determined to place constraints on their fluid histories sims oxygen isotope analysis of single garnets from five eclogite blocks from three localities ring mountain mount hamilton and jenner beach shows an abrupt decrease in the 18o value by 1 3 from core to rim at a distance of 120 50 m from the rim in nine out of the 12 garnets analyzed in contrast amphibolite garnets from one block ring mountain analyzed show a gradual increase in 18o value from core to rim implying a different history from that of the eclogite blocks values of 18o in eclogite garnet cores range from 5 7 to 11 6 preserving the composition of the eclogite protolith the abrupt decrease in the 18o values of the garnet rims to values ranging from 3 2 to 11 2 suggests interaction with a lower 18o fluid during the final stages of growth during eclogite facies metamorphism 450 600 c we hypothesize that this fluid is sourced from the serpentinized mantle wedge high mg ni and cr contents of actinolite rinds encasing the blocks also support interaction with ultramafic rock oxygen isotope thermometry using chlorite and phengite versus actinolite of rinds suggests temperatures of 185 240 c at ring mountain and mount hamilton rind formation temperatures together with the lower 18o garnet rims suggest that the blocks were in contact with ultramafic rock from the end of garnet growth through low temperature retrogression we suggest a tectonic model in which oceanic crust is subducted at the initiation of subduction and becomes embedded in the overlying mantle wedge as subduction continues metasomatic exchange between high grade blocks and surrounding ultramafic rock is recorded in low 18o garnet rims and later as temperatures decrease with rind formation

oceanic transport of fossil dammar resin the chemistry of coastal resinites from south australia abstract fragments of resin and fossilised resin resinites occasionally wash ashore along the southern australian coast chemical and isotopic analyses were carried out on a suite of coastal and reference resinites to determine the likelihood of a local as opposed to a distant origin all of the coastal resinites were found to contain a polymer based on the sesquiterpenoid cadinene skeleton and were markedly different to the diterpenoid resinites found in local victorian coals the coastal resinites closely resemble both fossil and recent dammar resin a material associated primarily with the tropical angiosperm hardwoods of southeast asia and one which has no known australian source minor variations in the composition of our resinite samples are attributed to differences in their thermal history these findings confirm the viability of long distance oceanic transport not only for the resinites but also for the waxy bitumens that strand along the same coastline analytical data on the coastal resinites also help to clarify the role of dammar resin in generating bicadinanes a class of source and age specific triterpanes found commonly in the cainozoic oils and sediments of southeast asia