quantitative reconstruction of mid to late holocene climate in ne china from peat cellulose stable oxygen and carbon isotope records and mechanistic models there has been an increasing need to reconstruct past climate from proxy records quantitatively and mechanistically the inverse proxy modeling method stands out as a novel approach to quantitative palaeoclimate reconstructions through integrating process based models and proxy records representing a major progress in quantitative palaeoclimatology it has been proposed to incorporate multiple proxy records to produce a more robust constraint on the climate parameters sought for estimation and most of the work has been conducted using pollen records in conjunction with vegetation models here i show a worked example of using paired stable oxygen and carbon isotope records of peat cellulose from one single core to infer the climate history in ne china for the last 6000 years through solving a well posed inverse problem using bayesian statistics the quantitative palaeoclimate data obtained in this study may deepen our insight into the dynamics of the east asian summer monsoon mean growing season temper

major types and time space distribution of mesozoic ore deposits in south china and their geodynamic settings the ore deposits of the mesozoic age in south china can be divided into three groups each with different metal associations and spatial distributions and each related to major magmatic events the first event occurred in the late triassic 230 210 ma the second in the mid late jurassic 170 150 ma and the third in the early mid cretaceous 120 80 ma the late triassic magmatic event and associated mineralization is characterized by peraluminous granite related w sn nb ta mineral deposits the triassic ore deposits are considerably disturbed or overprinted by the later jurassic and cretaceous tectono thermal episodes the mid late jurassic magmatic and mineralization events consist of 170 160 ma porphyry skarn cu and pb zn ag vein deposits associated with i type granites and 160 150 ma metaluminous granite related polymetallic w sn deposits the late jurassic metaluminous granite related w sn deposits occur in a ne trending cluster in the interior of south china such as in the nanling area in the early mid cretaceous from about 120 to 80 ma but peaking at 100 90 ma subvolcanic related fe deposits developed and i type calc alkaline granitic intrusions formed porphyry cu mo and porphyry epithermal cu au ag mineral systems whereas s type peraluminous and or metaluminous granitic intrusions formed polymetallic sn deposits these cretaceous mineral deposits cluster in distinct areas and are controlled by pull apart basins along the south china continental margin based on mineral assemblage age and space time distribution of these mineral systems integrated with regional geological data and field observations we suggest that the three magmatic mineralization episodes are the result of distinct geodynamic regimes the triassic peraluminous granites and associated w sn nb ta mineralization formed during post collisional processes involving the south china block the north china craton and the indo china block mostly along the dabie sulu and songma sutures jurassic events were initially related to the shallow oblique subduction of the izanagi plate beneath the eurasian continent at about 175 ma but i type granitoids with porphyry cu and vein type pb zn ag deposits only began to form as a result of the breakup of the subducted plate at 170 160 ma along the nne trending qinzhou hangzhou belt also referred to as qin hang or shi hang belt which is the neoproterozoic suture that amalgamates the yangtze craton and cathaysia block a large subduction slab window is assumed to have formed in the nanling and adjacent areas in the interior of south china triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic w sn mineralization a relatively tectonically quiet period followed between 150 and 135 ma in south china from 135 ma onward the angle of convergence of the izanagi plate changed from oblique to parallel to the coastline resulting in continental extensional tectonics and reactivation of regional scale ne trending faults such as the tan lu fault this widespread extension also promoted the development of ne trending pull apart basins and metamorphic core complexes accompanied by volcanism and the formation of epithermal cu au deposits granite related polymetallic sn w deposits and hydrothermal u deposits between 120 and 80 ma with a peak activity at 100 90 ma

the role of caco3 compensation in the glacial to interglacial atmospheric co2 change the only viable explanations put forth to date for the glacial to interglacial change in atmospheric co2 content suggested from measurements of the co2 content of gas extracted from ice cores involve changes in the ocean s nutrient cycles any nutrient change capable of creating the 80 atm changes in atmosphere co2 pressure suggested by the ice core results also creates significant change in the deep ocean s co3 content evidence from deep sea sediments suggests that these co3 changes are compensated on the time scale of a few thousand years by reductions or increases in amount of caco3 accumulating in deep sea sediments this compensation process has two important consequences first it significantly increases the magnitude of the co2 change per unit of nutrient forcing second it causes a delay in the response of the atmospheric co2 change while the first of these consequences is a boon to those seeking to explain the co2 change the second may prove to be a curse the ice core co2 record shows no evidence of a significant lag between the co2 response and the polar warming in any case it is important that we improve our knowledge of the magnitude and timing of the caco3 preservation events which mark the close of episodes of glaciation and of the dissolution events which mark the onset of these episodes

oxygen and carbon isotope record of east pacific core v19 30 implications for the formation of deep water in the late pleistocene north atlantic abstract a detailed oxygen and carbon isotope record has been obtained from benthic foraminifera in core v19 30 from the carnegie ridge on the south side of the panama basin expressing these records and the oxygen and carbon isotope records previously published for atlantic core m 12392 on a common timescale it is apparent that the oxygen isotope records are very similar but that the carbon isotope records are quite different by obtaining the carbon isotope gradient between the two sites as a function of time we show that the production of north atlantic deep water has varied over a wide range during the late pleistocene and that the pattern of variation is not simply related to the well known oxygen isotope record although the two oxygen isotope records are very similar changes in the interoceanic gradient are detectable and support the hypothesis that in the glacial mode the north atlantic was colder and less oxygenated than it is today shackleton s 1 1977 interpretation whereby the carbon isotope record from the atlantic core reflects changes in the terrestrial biomass is an over simplification however the record from the pacific core v19 30 probably can be explained in these terms since it probably approximates the carbon isotope record of global mean oceanic dissolved co 2

inverse multiparameter modeling of paleoclimate carbon cycle indices abstract a simple linear response model describing the functional relationship between ocean carbon cycle parameters and paleoclimate tracers atmospheric p co2 13c caco3 saturation was derived from a set of sensitivity experiments performed previously using a three dimensional carbon cycle model the linear model is optimally fitted to ice and marine sediment core records for the last 120 000 yr to estimate the carbon cycle parameter changes that could have caused the observed reduction of atmospheric co2 partial pressure during the last glaciation the analysis indicates that the glacial pco2 reduction was primarily caused by a strengthening of the biological poc pump and a retardation of the oceanic circulation an increase in deep sea alkalinity and a change in the advective pattern of the ocean circulation have a smaller impact on atmospheric co2 but are necessary to explain the full set of paleoclimate tracers

into the deep a coarse grained carbonate turbidite valley and canyon in ultra deep carbonate setting abstract new high resolution multibeam mapping images detail the southern part of exuma sound southeastern bahamas and its unchartered transition area to the deep abyssal plain of the western north atlantic bounded by the bahama escarpment extending between san salvador island and samana cay the transition area is locally referred to as exuma plateau the newly established map reveals the detailed and complex morphology of a giant valley draining a long lived carbonate platform from its upper slope down to the abyssal plain this giant valley extends parallel to the slope of long island conception island and rum cay it starts with a perched system flowing on top of a lower cretaceous drowned main carbonate platform the valley shows low sinuosity and is characterized by several bends and flow constrictions related to the presence of the small relict isolated platforms that kept alive longer than the main platform before drowning and merging tributaries turbidite levees on either side of the valley witness the pathway of multiple gravity flows generated by upper slope over steepening around exuma sound through carbonate offbank transport some of them locally 15 and resulting slumping in addition additional periplatform sediments are transported to the main valley through numerous secondary slope gullies and several kilometre long tributaries draining the upper slopes of cays and islands surrounding exuma plateau some of them form knickpoints indicating surincision of the main exuma valley which is consistent with an important lateral supply of the main exuma valley prior to reaching the abyssal plain the main valley abruptly evolves into a deep canyon 5 km in width at its origin and as much as 10 km wide when it meets the abyssal plain through two major knickpoints named chutes with outsized height exceeding several hundred of meters in height both chutes are associated with plunge pools as deep as 200 m in the deepest pools the flows generate a hydraulic jump and resulting sediment accumulation when the canyon opens to the san salvador abyssal plain the narrow deep and strong flows release significant volume of coarse grained calcareous sediments in numerous turbidite layers interbedded with fine mixed siliciclastic and carbonate sediments transported by the western boundary undercurrent wbuc along the bahama escarpment carbonate gravity flows exiting the canyon decelerate at the abyssal plain level and construct a several kilometre wide coarse grained deep sea turbidite system with well developed lobe shape levees partially modified by the flow of strong contour currents along the bahama escarpment

absolute timing of sulfide and gold mineralization a comparison of re os molybdenite and ar ar mica methods from the tintina gold belt alaska new re os molybdenite dates from two lode gold deposits of the tintina gold belt alaska provide direct timing constraints for sulfide and gold mineralization at fort knox the re os molybdenite date is identical to the u pb zircon age for the host intrusion supporting an intrusive related origin for the deposit however 40ar 39ar dates from hydrothermal and igneous mica are considerably younger at the pogo deposit re os molybdenite dates are also much older than 40ar 39ar dates from hydrothermal mica but dissimilar to the age of local granites these age relationships indicate that the re os molybdenite method records the timing of sulfide and gold mineralization whereas much younger 40ar 39ar dates are affected by post ore thermal events slow cooling and or systemic analytical effects the results of this study complement a growing body of evidence to indicate that the re os chronometer in molybdenite can be an accurate and robust tool for establishing timing relations in ore systems

source rock distribution model of the periadriatic region the periadriatic area is a mosaic of geological provinces comprised of spatially and temporally similar tectonic sedimentary cycles tectonic evolution progressed from a triassic early jurassic liassic continental rifting stage on the northern edge of the african craton through an early jurassic middle liassic late cretaceous eocene oceanic rifting stage and passive margin formation to a final continental collision and active margin deformation stage in the late cretaceous eocene to holocene this evolution occurred in a transtensional and transpressional framework resulting from the oblique separation and convergence of the african and european plates extensive shallow water carbonate platform deposits covered large parts of the periadriatic region in the late triassic platform breakup and development of a platform to basin carbonate shelf morphology began in the late triassic and extended through the cretaceous on the basis of this paleogeographic evolution the regional geology of the periadriatic region can be expressed in terms of three main upper triassic paleogene sedimentary sequences the platform sequence sequence a the platform to basin sequence sequence b and the basin sequence sequence c these sequences developed during the initial rifting and subsequent passive margin formation tectonic stages three distinct episodes of source bed deposition can be identified middle upper triassic to lower jurassic liassic organic rich oil prone and mature source beds generally are structurally controlled and are closely associated with transtensional intraplatform basins formed in the early continental rifting stage the principal triassic source basins and most of the surface hydrocarbon indications and economically important oil fields of the periadriatic region are associated with sequence b areas the second episode of organic rich rocks deposition includes both shallow and deeper water facies of jurassic cretaceous age thin immature deep water epioceanic organic rich marls and shales are generally bathymetrically controlled these units are related to basin wide anoxic events in the tethys ocean and its submerged continental margin and are associated with sequence b areas middle upper cretaceous shallow water oil prone facies occur in isolated anoxic basins within carbonate platforms these source sequences are generally thicker and are associated with sequence a areas no major hydrocarbon accumulation can be directly attributed to the jurassic cretaceous epioceanic and intraplatform source rock sequences the third episode of source bed deposition characterizes the final active margin deformation stage and is represented by upper tertiary organic rich terrigenous units mostly gas prone these are essentially associated with turbiditic and flysch sequences of foredeep basins and have generated the greater part of the commercial biogenic gases of the periadriatic region

carbonate dissolution on the muir seamount western north atlantic interglacial glacial changes abstract although the history of carbonate dissolution has been studied for many years few records of dissolution through an entire glacial cycle are available for the western north atlantic north american basin using 14 cores from the muir and siboney seamounts located about 240 km northeast of bermuda changes in carbonate dissolution were examined over the last 125 000 years the core depth range spans more than 3000 m 1780 m 4980 m insuring that major changes in dissolution will be recorded weight percent carbonate was plotted as a function of water depth for five stratigraphically defined levels to determine temporal changes in the sedimentary lysocline and calcite compensation depth ccd during the holocene the lysocline is located between 4050 m and 4350 m the ccd is not pre ent even in the deepest sample 4980 m the late glacial 18 000 years b p lysocline may have shoaled to about 2500 m whereas during early glacial time 72 000 years b p it deepened to about 3400 m the mid glacial carbonate maximum 60 000 years b p interstadial is marked by a deepening of the lysocline to about 3800 m during the entire glacial episode the ccd aappears to have remained fixed at 4650 m the last interglacial 125 000 years b p was a time favorable to carbonate preservation the lysocline was deeper than 4650 m the deepest core containing sediments of this age increased glacial dissolution appears to result from changes in deep circulation the establishment of the ccd during glacial time is interpreted as indicating increased antarctic bottom water flow the lysocline on the other hand may reflect the degree of stagnation of north atlantic deep water

radiolarian age constraints on mesotethyan ocean evolution and their implications for development of the bangong nujiang suture tibet radiolarian discoveries indicate that deep marine conditions prevailed in central tibet from the early middle jurassic until well into the early cretaceous late hauterivian early aptian 131 121 ma and help to constrain the temporal extent of oceanic conditions along the bangong nujiang suture these new fossils occur in chert or siliceous mudstone blocks associated with the lagkor tso ophiolitic melange basin inversion associated with closure of mesotethys between the qiangtang and lhasa terranes was accompanied by melange formation and predated regionally widespread deposition of overlying shallow marine late aptian albian orbitolinid limestones

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

tectonics of western tibet between the tarim and the indus a tarim to indus traverse provides insight into the tectonics of western tibet the kunlun was the site of a mid paleozoic collision at least three phases of post paleozoic accretion have thickened the blanket of sediments that covers western tibet sizeable parts of western qiangtang have remained stable however since the mid mesozoic since the neogene deformation and volcanism have been localized near the edges of the plateau strike slip motion along the karakorum and altyn tagh faults has been coeval with overthrusting in the himalayas and kunlun such slip partitioning and the volcanism appear to result simply from northward subduction of india and southward subduction of the tarim as tibet is extruded eastwards by india s penetration into asia

a miocene tungsten mineralization and its implications in the western bangong nujiang metallogenic belt constraints from u pb ar ar and re os geochronology of the jiaoxi tungsten deposit tibet china abstract the jiaoxi quartz vein type wolframite deposit is the first tungsten mineralization discovered in the western part of the bangong nujiang metallogenic belt which is well known for the porphyry epithermal skarn cu au mineralization the jiaoxi deposit is associated with a porphyritic monzogranite that intrudes sandstone and shale in the shiquanhe ophiolite melange the ages of the magmatism and mineralization in the deposit are here constrained by the dates obtained from the porphyritic monzogranite hydrothermal muscovite and molybdenite laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating of two porphyritic monzogranite samples yields weighted mean 206pb 238u coincident age of 14 1 ma two samples of hydrothermal muscovite from wolframite bearing quartz veins yield plateau 40ar 39ar ages of 13 4 0 1 and 13 3 0 1 ma respectively re os model ages of five molybdenite samples range from 11 4 0 2 to 11 8 0 2 ma with a weighted mean model age of 11 6 0 2 ma these dates indicate that the tungsten mineralization at jiaoxi was formed during the middle miocene this miocene tungsten mineralization is significantly different from the early and late cretaceous cu au mineralization in the western part of the bangong nujiang metallogenic belt our dating results show that there is a middle miocene tungsten mineralization in the western part of the bangong nujiang metallogenic belt the tectonic setting for the tungsten mineralization is here interpreted to be the regional extension associated with the india asia continental collision the discovery of the jiaoxi deposit has important significance on regional tungsten prospecting

climatic change and caco3 preservation an 800 000 year bathymetric reconstruction from the central equatorial pacific ocean sixteen deep sea cores from the central equatorial pacific are used to reconstruct a continuous 800 000 year 800 kyr record of bathymetric variations in carbonate preservation as measured by calcium carbonate caco3 content the depth of the sedimentary lysocline has fluctuated markedly in conjunction with late pleistocene climate cycles while the carbonate critical depth ccrd which is the water depth where the sediments contain 10 caco3 has remained relatively constant as a result the depth of the lysocline controls the bathymetric position and thickness of the caco3 transition zone defined as the depth from the lysocline to the ccrd modern and interglacial aged sediments show poor caco3 preservation and thick caco3 transition zones glacial aged sediments show good preservation and deep thin zones due to the deepening of the lysocline detailed comparison of the caco3 preservation and oxygen isotope records from the central equatorial pacific confirms the observation that preservation maxima and minima tend to occur during the latter half of glacial and interglacial stages and on climate transitions rather than during the middle of climatic stages during the nine major glacial stages of the last 800 kyr the lysocline deepened by at least 400 to 800 m this deepening indicates an increase in the abyssal carbonate ion concentration co3 and a depression of the calcite saturation horizon best explained by the deeper presence of a more carbonate saturated water mass the bottom of the transition zone has remained at a relatively constant depth during the brunhes chron indicating a balance between caco3 sedimentation and dissolution in the deepest waters of the central equatorial pacific

seismic stratigraphy and depositional signatures of the maldive carbonate system indian ocean abstract as documented by industrial seismic reflection profiles and well data the cenozoic stratigraphic evolution of the maldive carbonate system shows three distinct intervals characterized by their own specific depositional signatures late palaeocene volcanics generated by the reunion hotspot filled deeper pull apart structures and created a flat topography that promoted the onset of the maldive carbonate system in the early eocene some of the initial structural depressions remained as deep internal seaways surrounded by reefal margins until the late oligocene the eocene early oligocene stratigraphic signature is essentially aggradational and corresponds to a transgressive cycle associated with a second order sea level rise in the mid oligocene a major sea level fall exposed the neritic carbonate system and restricted sedimentation to the former deep internal basins during the next transgression a neritic carbonate system re established itself on the newly flooded platform and was finally drowned near the oligocene miocene boundary the main effect of this second order transgressive cycle was the transformation of the central troughs into one single deep basin in the neogene the palaeo maldive inner sea when a reef framework was established in the early miocene near the present location of the platform edge systematic bank margin progradation toward the central inner sea basin became enhanced this neogene progradational phase is explained as the response to a long term sea level fall associated with a second order regressive cycle finally the late pliocene pleistocene depositional signature is mainly aggradational and corresponds to the regional modification from flat topped carbonate banks to atoll physiographies the antecedent karst theory suggests that increased karstification was triggered by high frequency eustatic and climatic changes in the last 3 0 ma

carbonate delta drift a new sediment drift type based on high resolution reflection seismic and core data from iodp expedition 359 we present a new channel related drift type attached to a carbonate platform slope which we termed delta drift like a river delta it is comprised of several stacked lobes and connected to a point source the delta drifts were deposited at the exit of two gateways that connect the inner sea of the maldives carbonate platform with the open ocean the channels served as conduits focusing and accelerating the water flow entrained material was deposited at their mouth where the flows relaxed the lobe shaped calcareous sediment drifts must have formed under persistent water through flow sediment supply was relatively high and continuous resulting in an average sedimentation rate of 17 cm ka 1 the two delta drifts occupy 342 and 384 km2 respectively with a depositional relief of approximately 500 m they have a sigmoidal clinoform reflection pattern with a particular convex upward bending of the foresets in the maldives the drift onset marks the transition from a sea level controlled to a progressively current dominated depositional regime this major event occurred in the serravallian about 13 ma ago leading to the partial drowning of the carbonate platform and the creation of shallow seaways the initial bank enclosed topography resembles an empty bucket geometry which is rapidly filled by the drift sediments that aggrade and prograde into the basin thereby the depositional environment of the delta drifts changes from deep water 500 to shallow water conditions at their topsets indicated by the overall coarsening upward trend in grain size and the presence of shallow water large benthic foraminifers at their top

seismic modelling of outcrop carbonate systems an application to the cretaceous platform to basin system of the maiella mountain central apennines italy

the oceanic salt pump does it contribute to the glacial interglacial difference in atmospheric co2 content sea ice formation drives salt from the surface to the deep sea in so doing it lowers the salinity of polar surface waters we show here that this reduction in turn lowers the co2 partial pressure of polar surface waters and hence also of the atmosphere we propose that during glacial time when more sea ice existed this pumping action may have been stronger if so part of the glacial to interglacial atmospheric co2 content change observed in ice cores may have been driven by the ocean s salt pump

monsoon induced partial carbonate platform drowning maldives indian ocean multibeam maps and high resolution seismic images from the maldives reveal that a late miocene to early pliocene partial drowning of the platform was linked to strong sea bottom currents in the upper miocene to holocene currents shaped the drowned banks the current moats along the bank edges and the submarine dune fields bottom currents in the maldives are driven by the monsoon it is proposed that the onset and the intensification of the monsoon during the neogene provoked platform drowning through injection of nutrients into surface waters since the late miocene topographically triggered nutrient upwelling and vigorous currents switched the maldives atolls into an aggradational to backstepping mode which is a growth pattern usually attributed to episodes of rising sea level

the uncertainties involved in extracting amplitude and frequency of orbitally driven sea level fluctuations from shallow water carbonate cycles in outcrops shallow water carbonates often form thick vertically stacked metre scale exposure bounded depositional packages here called carbonate cycles because the facies within carbonate cycles can be tied precisely to water depths they are considered ideal for reconstructing past sea level changes there is however increasing evidence that these depositional cycles are unreliable recorders of both the frequency and the amplitude of orbitally driven sea level fluctuations carbonate cycles record only a fraction of the amplitude of a sea level cycle a portion of the rise and nothing of the fall cores through the pleistocene cycles on great bahama bank illustrate this shortcoming although the amplitudes of the last nine sea level changes are each a hundred metres or more the thickness of the cycles varies from a few metres to ca 15 m the lack of correlation between sea level amplitude and cycle thickness is not eliminated for cycles deposited during times of lower sea level amplitudes for example the cretaceous upper cretaceous cycles on the maiella platform margin document the irregularly filled accommodation space and the resultant variability in cycle thickness and frequency uncertainties in assessing the frequencies of sea level changes from shallow water carbonate cycles are caused by missed beats and metre scale oscillations of sea level within highstands that potentially produce cycles of very short duration the random amplitude variability during the last 57 glacio eustatic sea level changes illustrates the difficulty of assessing missed beats where a sea level fluctuation is not recorded because the sea level rise does not reach the platform top missed beats are also produced by the depositional topography that is created by irregularly filled accommodation space as a result variable numbers of cycles are deposited across the platform further complicating orbital frequency analyses are decametre scale oscillations of the sea level during highstands the amplitude of these sub orbital sea level oscillations up to 17 m within the last interglacial marine isotope stage 5e are sufficient to expose shallow platforms like great bahama bank and subsequently produce an additional depositional cycle with similar facies successions the combined effects of missed beats and oscillations within highstands are likely to produce cycles and hiatuses of variable duration that are difficult to extract from the rock record consequently estimates of the orbital forcing mechanisms and frequencies from ancient shallow water carbonate cycles carry large uncertainties

pleistocene δ13c variability of north atlantic intermediate water variations in the stable isotopic composition of benthic foraminifera from deep sea drilling project dsdp site 502b in the caribbean sea are used to reconstruct atlantic intermediate water circulation variability over the last 1 2 m y comparison of this record with other north atlantic benthic isotope records indicates that atlantic intermediate water circulation was relatively enhanced during glacial maxima when north atlantic deep water nadw production was reduced however a simple compensatory relationship between intermediate and deepwater circulation is not apparent geochemical models have shown that such changes in ocean circulation can affect atmospheric co2 levels by changing vertical nutrient and alkalinity profiles the 13c difference between caribbean site 502b and deep equatorial pacific site 677 is highly coherent and in phase with ice volume like the 18o record there is an increase in amplitude 40 and a large increase in 100 kyr power after 0 7 ma the 1 2 13c amplitude scales to 70 ppm v in atmospheric co2 using boyle s 1986 box model result the implied increase in co2 amplitude after 0 7 ma may suggest a positive feedback role in effecting the higher amplitude climatic fluctuations which characterize the last 0 7 m y

evolution of the bangong nujiang tethyan ocean insights from the geochronology and geochemistry of mafic rocks within ophiolites abstract the bangong nujiang suture zone bnsz is located in the central tibetan plateau and represents the relict of the bangong nujiang tethyan ocean bnto this paper presents zircon u pb ages and whole rock geochemical and sr nd isotope data for the ophiolitic rocks from the rutog dongco dongqiao amdo and dengqen areas from west to east in the bnsz zircon u pb ages obtained from five gabbros and one leucogabbro from the five areas are 169 2 167 2 187 2 184 2 177 3 and 164 2 ma respectively mafic rocks gabbros and basalts in the bnsz can be divided into morb like and oib type based on geochemical data the morb like rocks are tholeiitic and can be further divided into n and e morb subtypes marked by depleted and flat ree patterns respectively all morb like rocks show supra subduction zone ssz geochemical affinities such as mild enrichment in the large ion lithophile elements and depletion in the high field strength elements coupled with high and positive whole rock e nd t values 8 1 to 5 4 the oib type rocks which formed in the early cretaceous 132 108 ma are exposed in the dongco dongqiao and tarenben areas and they consist mostly of alkali basalts with within plate geochemical characteristics and positive e nd t values 5 9 to 4 5 on the basis of these new data combined with information from the literature we further support that the bnto was an intra oceanic arc backarc basin that existed between the north lhasa subterrane nlt and the south qiangtang subterrane sqt during the early middle jurassic this basin may have been active until the early cretaceous when the oib type basalts erupted

controls on morphology and sedimentology of carbonate tidal deltas abacos bahamas abstract although the physical processes controlling siliciclastic shoal bodies are reasonably well understood the sedimentary processes that shape carbonate tidal shoal systems are poorly constrained the tidal deltas of the northwestern abaco islands bahamas provide a unique opportunity to explore the relationships between physical and sedimentary processes in a variety of sizes and shapes of tidal deltas the length of tidal deltas range in size from 350 m to 2 km from the inlet to the termination of the delta lobe and shoal crests consist primarily of well sorted ooid sands mean grain size between 400 and 500 m mcmanus sorting factor 0 70 coated grains are rare off the shoals and sorting decreases with distance from the shoal crests velocities in the rocky inlets can exceed 2 m s in the daily tidal cycles and the systematic distribution of grain types reflects tidal velocity variations areas with the highest velocities 0 80 m s correspond to hard rocky bottoms with some skeletal grains these regions of elevated velocities are focused within the inlets where jets of high velocity currents form during each tidal cycle these current jets extend outward from the inlet throat and velocities decrease outwards as the flow disperses velocities between 40 and 80 cm s occur in the regions with abundant ooids and peloids are most abundant in the lowest velocity regions the results of this study illustrate a clear relationship between quotidian physical processes and their geomorphic and sedimentologic products in a carbonate system in this context carbonates appear to share many geomorphic similarities with siliciclastic analogs the results represent an important step beyond qualitative facies interpretations and towards quantitative specified environmental and sedimentologic characterizations for carbonate systems

zircon u pb ages and sr nd hf isotopes of the highly fractionated granite with tetrad ree patterns in the shamai tungsten deposit in eastern inner mongolia china implications for the timing of mineralization and ore genesis abstract the shamai tungsten deposit is located in the eastern part of the central asian orogenic belt caob tungsten mineralization is closely related to the emplacement of fine to medium grained biotite monzogranite g1 and porphyritic biotite monzogranite g2 in the shamai granite nw trending joints and faults host orebodies in the shamai granite and devonian hornfels the mineralization is characterized by a basal veinlet zone progressing upwards to a thick vein zone followed by a mixed zone a veinlet zone and a thread vein zone at the top the ore related alteration typically consists of muscovite greisen and hornfels in order to constrain the timing of the shamai mineralization and discuss the ore genesis muscovite ar ar molybdenite re os and zircon u pb geochronological geochemical and sr nd hf isotopic studies were completed on the deposit the u pb zircon dating yielded weighted mean ages of 153 1 ma for g1 and 146 1 ma for g2 muscovite from a wolframite bearing quartz vein yielded an ar ar plateau age of 140 1 ma whereas two molybdenite samples yielded identical re os model ages of 137 2 ma these two ages are younger than the two monzogranites suggesting a prolonged magmatic hydrothermal interaction during tungsten mineralization major and trace element geochemistry shows that both g1 and g2 are characterized by high sio2 and k2o contents high a cnk values 1 08 1 40 a spectacular tetrad effect in their ree distribution patterns and non charac charge and radius controlled trace element behavior this suggests that both g1 and g2 are highly differentiated peraluminous rocks with strong hydrothermal interaction the nd hf isotope data for the shamai granite end t between 1 9 and 7 4 hf t from 5 2 to 12 8 are largely compatible with the general scenario for much of the phanerozoic granite emplaced in the caob it is here suggested that the shamai granite originated from partial melting of a juvenile lower crust with minor input of upper crustal material caused by the underplating of mafic magma in an extensional setting it can also be concluded that the prolonged fractional crystallization and magmatic hydrothermal interactions have contributed to the formation of the shamai tungsten deposit

deep marine tidal bottom currents and their reworked sands in modern and ancient submarine canyons abstract submarine canyons provide a unique setting for tidal processes to operate from shallow marine to deep marine environments in modern canyons current meter measurements at varying water depths 46 4200 m show a close correlation between the timing of up and down canyon currents and the timing of semi diurnal tides these tidal bottom currents in submarine canyons commonly attain maximum velocities of 25 50 cm s based on core and outcrop studies of modern and ancient deep marine deposits it is proposed here that sand mud rhythmites double mud layers climbing ripples mud draped ripples alternation of parallel and cross laminae sigmoidal cross bedding with mud drapes internal erosional surfaces lenticular bedding and flaser bedding can be used to interpret deposits of deep marine tidal currents this approach is an alternative to the conventional approach in which most deep water traction structures e g climbing ripples and cross bedding would be attributed to deposition from turbidity currents underwater photographs show active mass flows i e slides slumps grain flows and debris flows in modern canyons box cores taken from modern submarine canyons e g la jolla california and conventional cores and outcrops of ancient canyon fill facies oua iboe pliocene nigeria and the annot sandstone eocene oligocene se france contain deposits of both tidal processes and mass flows this facies association in the rock record can be used as a criterion for recognizing submarine canyon settings in a channel mouth environment deep marine tidal deposits are likely to develop elongate bars that are aligned parallel to the channel axis within the channel whereas turbidites are more likely to develop depositional lobes that are aligned perpendicular to channel axis turbidite depositional lobes are much larger than the channel width whereas tidal sand bars are much smaller than the channel width therefore the wrong use of a turbidite lobe model with sheet geometry in lieu of a tidal bar model with bar geometry will result in an unrealistic overestimation of sandstone reservoirs in deep water exploration

morphometric analysis of plunge pools and sediment wave fields along western great bahama bank abstract a systematic assessment of morphometric parameters of over 200 plunge pools along the steep escarpment base of western great bahama bank and 2000km2 of sediment wave fields of upslope migrating cyclic steps documents the importance of cascading density currents for sedimentation on the slope the abrupt downslope termination of the holocene mud wedge with the cyclic steps shows that strike parallel bottom currents interacting with the off bank currents are responsible for slope sediment distribution the plunge pools and sediment waves were generated by density cascading and both are related to a hydraulic jump caused by two gradient changes along the slope profile the bedforms highlight both the erosional and depositional nature of this current regime which is controlled by slope gradient and the directional confinement by either grooves on the steep escarpment or gullies on the middle to lower slope the 20 m deep plunge pools are ellipsoidal with an average width of 211 m and length of 283 m but variations between 80 360 m and 100 650 m for width and length occur they are caused by an average gradient break of 16 on the cemented upper slope gradient breaks of as low as 2 are reported to be sufficient to scour a plunge pool like the ones in the study area but higher gradient breaks between 10 and 20 are quite common for consistent plunge pool development a second gradient break further down slope changes flow conditions for the generation of cyclic steps with asymmetric waveforms of 4 m high average in large wave fields in the entire the study area orientation is mainly orthogonal to the main slope direction but wave lengths and sinuosity vary depending on the morphologic location of the wave field the comparison with sediment wave fields with similar geometries or in similar environments shows that flow reconstruction based on the wave height and wave length alone along with a characterization of sediment grain size however yields non unique results and is site specific

mesozoic and cenozoic tectonic evolution of the shiquanhe area of western tibet 1 in the shiquanhe area of far western tibet mid cretaceous strata lie unconformable on ophiolitic melange and jurassic flysch associated with the bangong nujiang suture zone on the basis of our mapping and geochronologic studies we suggest that these cretaceous strata were shortened by 57 over a north south distance of 50 km during late cretaceous early tertiary time the late cretaceous narangjiapo thrust placed permian strata 20 km over ophiolitic melange and cretaceous strata north of the narangjiapo thrust 40 km of shortening was accommodated by the late cretaceous early tertiary south directed jaggang thrust system that involves jurassic flysch and cretaceous strata and roots into a decollement within ophiolitic melange the most recent shortening was accommodated to the south of the narangjiapo thrust along the north dipping shiquanhe thrust the shiquanhe thrust cuts flat lying 22 6 0 3 ma volcanic rocks and underlying folded tertiary nonmarine strata in its footwall and was likely active during slip along the oligocene gangdese thrust system of southern tibet ophiolitic melange and structurally overlying jurassic flysch near shiquanhe are interpreted to represent remnants of a subduction accretion complex and forearc basin respectively that were obducted southward onto the margin of the lhasa terrane during late jurassic early cretaceous closure of the bangong nujiang ocean subsequent imbrication of the obducted sheet could have produced the two east west trending belts of ophiolitic melanges separated by 100 km in western tibet late cretaceous early tertiary thin skinned shortening may have been accommodated in the deeper crust by northward underthrusting and duplexing of lhasa terrane rocks beneath the obducted ophiolitic melange and the qiangtang terrane to the north

evolution of a carbonate delta generated by gateway funnelling of episodic currents cool water carbonate sedimentation has dominated mediterranean shelves since the early pliocene skeletal sand and gravel herein consist of remains of heterozoan organisms which are susceptible to reworking due to weak early cementation in non tropical waters this study documents the lower pleistocene carbonate wedge of favignana island italy which prograded from a 5 km wide passage between two palaeo islands into a perpendicular 10 to 15 km wide strait between the palaeo islands at one side and sicily at the other during the emilian highstand 1 6 ma to 1 1 ma the clinoformed carbonate wedge which is 50 m thick and 6 km long formed by east south east progradation of a platform on the submarine sill by currents that were funnelled between the two palaeo islands platform slope clinoforms evolved from initial aggradation thin and low angle into a progradation phase thick and high angle both clinoform types are characterized by a bimodal facies stacking pattern defined by sedimentary structures created by i subaqueous dunes associated with dilute subcritical currents and ii upper flow regime bedforms associated with sediment laden supercritical turbidity currents focusing of episodic currents on the platform by funnelling between the islands controlled the downstream formation of a sediment body here named carbonate delta the carbonate delta interfingers with subaqueous dune deposits formed in the perpendicular strait this study uses a reconstruction of bedform dynamics to unravel the evolution of this gateway related carbonate accumulation

tectonic evolution of the qinghai tibet plateau abstract the qinghai tibet plateau composed of several continental slivers within the eastern tethyan domain is one of the pivotal sites to examine to better understand the theory of plate tectonics and the orogenic evolution on earth this plateau is generally inferred to be a collage of several continental blocks that rifted from gondwanaland and subsequently accreted to the asian continent however recent recognition of over twenty ophiolite melange zones and their associated island arcs indicates that the traditional model of tectonic evolution requires revision based on 177 recently finished 1 250 000 scale geological maps and related studies we summarize the main tectonic context of the qinghai tibet plateau and propose a new integrated model to account for the new findings the complex orogen of the immense qinghai tibet plateau consisting of multiple island arc basin systems that developed at different stages while surrounded by the north china yangtze tarim and indian plates is emphasized the entire orogen surrounded by suture zones that mark the locations of oceanic closure is investigated by examining i the first order tectonic units and ophiolitic melanges including arc arc continent collision zones and ii their internally enclosed blocks as the second order tectonic units therefore the qinghai tibet plateau is divided into three major orogenic systems namely from northeast to southwest the early paleozoic qinling qilianshan kunlunshan qin qi kun the late paleozoic triassic qiangtang sanjiang and the late paleozoic to cenozoic gangdese himalaya orogenic systems which are separated by the kangxiwa muzitagh maqin mianxian and the bangong shuanghu changning menglian sutures respectively we propose that the formation and evolution of the qinghai tibet plateau to have been intrinsically related to those of the eastern tethys recorded by the longmu co shuanghu ophiolite melange zone the southern qiangtang paleozoic accretionary arc basin system the bangong nujiang suture zone and their associated composite island arc basin systems the present day bangong shuanghu changning menglian suture system marks the final closure of the tethyan ocean the yarlung zangbo ocean opened as a back arc basin in response to the southward subduction of the tethyan ocean lithosphere in the middle triassic and closed as a result of the india asia collision at the end of cretaceous followed by the northward indention of the indian plate that resulted in significant intra continental deformation and plateau uplift in the cenozoic

the bangong lake ophiolite nw tibet and its bearing on the tectonic evolution of the bangong nujiang suture zone abstract the jurassic bangong lake ophiolite nw tibet is a key element within the western part of the bangong nujiang suture zone which marks the boundary between the lhasa and qiangtang blocks it is a tectonic melange consisting of numerous blocks of peridotite mafic lavas and dikes the mantle peridotites include both clinopyroxene bearing and clinopyroxene free harzburgites the cpx bearing harzburgite contains al rich spinel with low cr s 20 25 resembling peridotites formed in mid ocean ridge settings on the other hand the cpx free harzburgite is highly depleted with cr rich spinel cr 69 73 typical of peridotites formed in subduction zone environments mafic rocks include lavas of n morb and e morb affinity and boninites the n morb rocks consist of pillow lavas and mafic dikes whereas the e morb rocks are brecciated basalts the boninites have high sio 2 53 2 57 9 wt mgo 6 5 12 5 wt cr 166 752 ppm and ni 63 213 ppm and low tio 2 0 22 0 37 wt and y 5 34 8 10 ppm and are characterized by having u shaped chondrite normalized ree patterns the n morb and e morb lavas probably formed by different degrees of partial melting of primitive mantle whereas the boninites reflect partial melting of depleted peridotite in a suprasubduction zone environment the geochemistry of the ophiolite suggests that it is a fragment of oceanic lithosphere formed originally at a mid ocean ridge mor and then trapped above an intraoceanic subduction zone ssz where the mantle peridotites were modified by boninitic melts the bangong nujiang suture zone is believed to mark the boundary between two blocks within gondwanaland rather than to separate gondwanaland from eurasia

carbon 13 in pacific deep and intermediate waters 0 370 ka implications for ocean circulation and pleistocene co2 stable isotopes in benthic foraminifera from pacific sediments are used to assess hypotheses of systematic shifts in the depth distribution of oceanic nutrients and carbon during the ice ages the carbon isotope differences between 1400 and 3200 m depth in the eastern pacific are consistently greater in glacial than interglacial maxima over the last 370 kyr this phenomenon of bottom heavy glacial nutrient distributions which boyle proposed as a cause of pleistocene co2 change occurs primarily in the 1 100 and 1 41 kyr 1 milankovitch orbital frequency bands but appears to lack a coherent 1 23 kyr 1 band related to orbital precession averaged over oxygen isotope stages glacial 13c gradients from 1400 to 3200 m depth are 0 1 greater than interglacial gradients the range of extreme shifts is somewhat larger 0 2 to 0 5 in both cases these changes in pacific 13c distributions are much smaller than observed in shorter records from the north atlantic this may be too small to be a dominant cause of atmospheric pco2 change unless current models underestimate the sensitivity of pco2 to nutrient redistributions this dampening of pacific relative to atlantic 13c depth gradient favors a north atlantic origin of the phenomenon although local variations of pacific intermediate water masses can not be excluded at present

geochronology and geochemistry of the c 80 ma rutog granitic pluton northwestern tibet implications for the tectonic evolution of the lhasa terrane the rutog granitic pluton lies in the gangdese magmatic arc in the westernmost part of the lhasa terrane nw tibet and has shrimp zircon u pb ages of c 80 ma the pluton consists of granodiorite and monzogranite with sio2 ranging from 62 to 72 wt and al2 o3 from 15 to 17 wt the rocks contain 2 33 4 93 wt k2o and 3 42 5 52 wt na2o and have na2o k2o ratios of 0 74 2 00 their chondrite normalized rare earth element ree patterns are enriched in lree la yb n 15 to 26 and do not show significant eu anomalies eu 0 68 1 15 on a primitive mantle normalized trace element diagram the rocks are rich in large ion lithophile elements lile and poor in high field strength elements hfse hree and y their sr y ratios range from 15 to 78 with an average of 30 the rocks have constant initial 87 sr 86 sr ratios 0 7045 to 0 7049 and slightly positive end t values 0 1 to 2 3 similar to i type granites generated in an arc setting the geochemistry of the rutog pluton is best explained by partial melting of a thickened continental crust triggered by underplating of basaltic magmas in a mantle wedge the formation of the rutog pluton suggests flat subduction of the neo tethyan oceanic lithosphere from the south crustal thickening may have occurred in the late cretaceous prior to the india asia collision

calcium carbonate preservation patterns in the central north atlantic during the last 150 000 years abstract the dissolution record of the canary and eastern north american basins was examined in 15 cores spanning the last 150 000 years stratigraphic control was based on fluctuations in percent carbonate and 18 0 16 0 dissolution changes were determined based on variations in percent planktonic foraminiferal fragments and benthonic foraminifera results indicate three main dissolution events coincident with 18 0 stages 2 4 and 6 the lysocline apparently shallowed about 300 m in the canary basin at these times there is no simple linear relationship between dissolution intensity and ice volume dissolution was more intense during stage 4 than during stage 2 even though 18 0 records indicate the reverse is true for ice volume also carbonate preservation during the lower part of stage 3 is comparable to stages 1 and 5e a comparison of atlantic pacific carbonate dissolution patterns indicates a tendency for out of phase preservation patterns in 18 0 stages 1 and 2 and an in phase dissolution event during stage 4 the out of phase pattern may partially reflect variations in the production rate of north atlantic deep water the in phase dissolution peak correlates with a major cooling regression transport of organic carbon from transient shallow reservoirs into the deep sea could have contributed to formation of such a pattern however additional evidence from longer atlantic pacific records is needed before the shelf basin model can be more fully evaluated

jurassic cretaceous granitoids and related tectono metallogenesis in the zapug duobuza arc western tibet abstract the zapug duobuza magmatic arc zdma located along the southern edge of the south qiangtang terrane in western tibet extends east west for 400 km small scattered granite and porphyry intrusions crop out in the zdma but a large amount of granite may be buried by late cretaceous to paleogene thrusting two stages of magmatism have been identified at 170 150 ma and 130 110 ma the widely distributed middle late jurassic granite intrusions in the zdma exhibit sr nd isotopic characteristics similar to those of ore bearing porphyries in the duolong giant cu au deposit and their ehf t values mostly overlap those of other porphyry cu mo deposits in the zdma and the gangdese zone the sr nd hf isotopic geochemistry suggests variable contributions of mantle and qiangtang crustal sources and indicates the presence of two new ore districts with potentials for cu au fe and pb zn ores located in the jiacuo liqunshan and larelaxin caima areas except for the duolong ore forming porphyries which show significant contributions of mantle components intruded into an accretionary melange setting the early cretaceous granites in other areas of the belt are of mostly crustal origin from sources in qiangtang felsic basement and permo carboniferous strata indicating the weak ore forming potential of skarn type fe and pb zn deposits the ephemeral but deep bangong co nujiang ocean in the early jurassic evolved into a shallow compressional marine basin in the middle late jurassic possibly transitioning to northward flat subduction of oceanic crust at this time the subducted slab broke off in the early cretaceous initiating a peak in arc magmatism and metallogenesis at 125 110 ma

the δ13c of equatorial atlantic surface waters implications for ice age pco2 levels carbon isotopic records of nutrient depleted surface water place constraints on the past fertility of the oceans and on past atmospheric pco2 levels the best records of nutrient depleted 13c are obtained from planktonic foraminifera living in the thick mixed layers of the western equatorial and tropical atlantic ocean we have produced a composite stacked globigerinoides sacculifer 13c record from the equatorial atlantic which exhibits significant spectral power at the 100 000 and 41 000 year milankovitch periods but no power at the 23 000 year period similar to the record presented by shackleton and pisias 1985 surface deep ocean 13c produced with the g sacculifer record leads the 18o ice volume record however the glacial interglacial amplitudes of 13c differ between our record and shackleton and pisias 1985 record although large changes in 13c occur in the equatorial atlantic during early stages of the last three glacial cycles surface deep 13c at glacial maxima 18o stage 2 late stage 6 and late stage 8 was only about 0 2 greater than during the subsequent interglacial our results imply that nutrient driven pco2 changes account for about one third of the pco2 decrease observed in ice cores and consequently 13c should not be used as a proxy pco2 index enough variance in the ice core pco2 records remains to be explained that conclusions about pco2 and ice volume phase relationships should also be reexamined as much as 40 ppm pco2 change still has not been accounted for by models of past physics and chemistry of the ocean

the cause of the glacial to interglacial atmospheric co2 change a polar alkalinity hypothesis in an attempt to create a scenario for the cause of the glacial to interglacial co2 change recorded in air trapped in polar ice we call on an increase in the alkalinity of polar surface waters in this way we circumvent a major deficiency of the polar nutrient scenarios of sarmiento and toggweiler 1984 siegenthaler and wenk 1984 and knox and mcelroy 1984 namely our scenario does not require a drop in the nutrient content of polar surface waters in conformity with the demonstration by boyle 1988a b that the cadmium content of planktonic foraminifera from polar regions did not decrease from late glacial to holocene time the rise in alkalinity required by our model is a natural consequence of the demise during glacial time of north atlantic deep water as a major force in ocean circulation and of the nutrient maximum deepening of boyle 1988b rather than being original our hypothesis builds on the concept basic to the polar nutrient hypotheses namely that the co2 partial pressure in polar waters controls that for both the atmosphere and warm surface ocean it also requires the alkalinity increase in surface waters produced by boyle s nutrient deepening

the timing of w sn rare metals mineral deposit formation in the western variscan chain in their orogenic setting the case of the limousin area massif central france new 40ar 39ar dating performed on rare metal granites and w sn deposits in the northern limousin has provided evidence of two metallogenic episodes an early namurian episode c 325 ma was contemporaneous with the emplacement of the large peraluminous leucogranite bodies which are associated with small w sn deposits but also with some larger deposits at puy les vignes 323 4 0 9 ma and moulin barret 323 7 0 8 ma formed at a shallower level above cryptic granite plutons these new data indicate that the metallogenic potential of the namurian leucogranites might have been underestimated most other w sn deposits in the northern limousin area are attributed to a mid westphalian episode c 310 ma and are contemporaneous with the emplacement of all the rare metal granites both episodes were related to leucogranite emplacement and associated fluid circulations but in two different geodynamic contexts the early namurian episode may be related to syncollisional extension of the variscan belt whereas the mid westphalian one occurs during generalized extension and rapid exhumation of the belt associated with the granulite facies metamorphism of the lower lithosphere probably related to the delamination of the lower lithosphere thus w sn and rare metals ta nb be li deposits are clearly temporally and probably genetically related to leucogranitic magmatism

sedimentary patterns and geometries of the bahamian outer carbonate ramp miocene lower pliocene great bahama bank core logging and high resolution seismic data from odp leg 166 were used to analyse deposits of the neogene miocene lower pliocene bahamian outer carbonate ramp ramp sediments are cyclic alternations of light and dark grey wackestones packstones with interbedded calciturbidite packages and minor slumps cyclicity was driven by high frequency sea level changes light grey layers containing shallow water bioclasts were formed when the ramp exported material whereas the dark grey layers are dominantly pelagic calciturbidites are arranged into mounded lobes with feeder channels internal bedding of the lobes shows a north directed shingling as a result of the asymmetrical growth of these bodies calciturbidite packages occur below and above sequence boundaries indicating that turbidite shedding occurred during third order sea level highstands and lowstands highstand turbidites contain shallow water components such as green algal debris and epiphytic foraminifera whereas lowstand turbidites are dominated by abraded bioclastic detritus gravity flow depocentres shifted from an outer ramp position during the early miocene to a basin floor setting during the late miocene to early pliocene this change was triggered by an intensification of the strength of bottom currents during the tortonian which was also responsible for shaping the convex morphology of the outer ramp the miocene and lower pliocene of the leeward flank of great bahama bank provides an example of the poorly known depositional setting of the outer part of distally steepened carbonate ramps the contrast between its sedimentary patterns and the well known upper pliocene quaternary slope facies associations of the flat topped great bahama bank shows the strong control that the morphology of a carbonate platform exerts on the depositional architecture of the adjacent slope and base of slope successions

magnetic and sequence stratigraphy of redeposited upper cretaceous limestones in the montagna della maiella abruzzi italy abstract the carbonate platform margin of the montagna della maiella in the abruzzi region of central italy has a complex history of sedimentation consisting of aggradational and progradational episodes along the shelf margin and pelagic deposition in the basin a paleomagnetic study at 12 regionally distributed limestone sites of late cretaceous to miocene age in the maiella anticline was unable to define stable magnetic directions at most sites largely due to the weakness of the magnetizations at the few usable sites inclinations agreed with reference values based on an african polar wander path declinations were inconsistent indicating local tectonic rotations both normal and reversed polarities were preserved at some sites a magnetostratigraphic section consisting of 280 samples spaced at 1 1 5 m intervals was sampled along a profile in the valle delle tre grotte near the village of pennapiedimonte sequence stratigraphy based on two dimensional analysis of outcrops formed the stratigraphic framework for the magnetostratigraphic study rock magnetic analyses showed that magnetite is the dominant ferromagnetic mineral in the limestones both alternating field and thermal demagnetization were satisfactory in defining two main components in the weak magnetizations a component with low coercivity low unblocking temperature and normal polarity was close in direction to the present axial dipole field direction at the site a higher coercivity higher unblocking temperature component with both polarities was interpreted as the characteristic remanent magnetization chrm although the mean directions of samples with normal and reversed polarity are not exactly antipodal a stratigraphic sequence of magnetozones is very clearly defined the pennapiedimonte magnetostratigraphy correlates well with late cretaceous chrons c30r to c34n in the established polarity timescale numerical ages can thus be allocated to the reversals correlation to the gubbio section allows paleontological dates for the reversal sequence to be inferred the correlations allow more precise dating of formational and sequence boundaries and a better evaluation of stratigraphic hiatuses in particular the boundary between the tre grotte formation supersequence 1 turonian to middle campanian and the orfento formation supersequence 2 upper campanian to upper maastrichtian is shown to be associated with a significant hiatus spanning most of the middle campanian g ventricosa zone likewise the absence of chron c29r at the top of the orfento formation ss2 documents non deposition during the latest maastrichtian or

tectono stratigraphic and kinematic evolution of the southern apennines calabria peloritani terrane system italy abstract temporal controls such as sedimentation ages in foredeep and wedge top basins combined with information about stratigraphic and metamorphic evolution ages and characterization of magmatic rocks deep structures burial and exhumation histories allowed us to obtain kinematic estimations of the southern apennines calabria peloritani terrane system evolution from the late oligocene to recent calculated thrust front velocities suggest to subdivide the orogenic evolution in main five kinematic stages characterized by different velocity trends nine kinematic complexes from a to i i e sets of tectonic units deformed in the same time range are determined according to foredeep ages these complexes bounded by main regional thrust faults encompass one or more tectonic sub units and successions of different paleoenvironment domains paleogeographic evolution model indicates according to available paleomagnetic data a counterclockwise rotation with a mean angle of 60 for the apennine platform carbonates whereas a mean angle of 20 for the eastern sector of the apennine platform and western side of apulian platform shortening estimations for the apennine successions show values ranging between 55 and 88 and a linear best fit indicating an increase from 60 nw sector to ca 90 se sector such high values are consistent with a deformation dominated by a thin skinned tectonics on the contrary the low value of 28 calculated for mt alpi suggests an exhumation ruled by high angle deep seated structures characterized by limited displacements tectonic vergences referred to middle late miocene late miocene and pliocene middle pleistocene when restored indicate an average eastward tectonic transport finally tectonic evolution is summarized in eleven schematic cross sections and corresponding paleogeographic maps

the role of vertical chemical fractionation in controlling late quaternary atmospheric carbon dioxide the 30 decrease in atmospheric carbon dioxide during glacial maxima must be driven by some change in the chemical circulation of the ocean here a new model for late quaternary co2 variability is presented which resolves some problems occurring in previous models including the timing of carbon dioxide response and changes in the oxygen content of the deep ocean the primary driving factor in this model is a rearrangement of chemical distributions in the ocean whereby labile nutrients and metabolic co2 are concentrated in deep waters rather than in intermediate waters as observed in the modern ocean this new bottom heavy chemical structure does not affect atmospheric carbon dioxide directly instead co2 induced acidity lowers the deep ocean carbonate ion concentration and temporarily increases carbonate dissolution rates oceanic alkalinity then rises until the deep ocean carbonate ion is restored to its steady state value the resulting increase in oceanic alkalinity draws co2 out of the atmosphere into the ocean alkalinity and atmospheric co2 lag several thousand years behind the change in oceanic chemical structure this delayed response is determined by the limited rate of continental weathering and deep ocean carbonate dissolution relative to the oceanic alkalinity inventory it is proposed that characteristic deglacial and preglacial states of the ocean are leading factors driving glacial interglacial climate changes this concept reinterprets the carbon isotope contrast between surface water and deep waters 13c p b as due to a shift of light metabolic carbon from intermediate waters into deep waters the process is illustrated here by a simple equilibrium five box ocean model the observed intermediate depth nutrient depletion is not sufficient in itself to determine which of several possible mechanisms are operating and some mechanisms are not as effective in changing atmospheric co2 as others the largest response is seen from deepening the regeneration cycle of organic carbon the least response is seen from converting north atlantic deep water into intermediate water

interactions between tidal flows and ooid shoals northern bahamas abstract oolitic strata are common through the geologic record ooids generally form in high energy environments but it remains unclear how ooids remain in such systems and form geomorphic features such as bars and shoals integrating remote sensing hydrodynamic bathymetric granulometric and field observations of modern tidal systems in the bahamas provides insight into this fundamental question oolitic tidal sands in the northern abacos display a geomorphic pattern in which bedrock islands restrict and focus tidal flow down a main channel within the channel a shallow shoal separates an ebb dominated subchannel from a flood dominated subchannel tidal velocities in these subchannels can exceed 1 m s enough to transport the oolitic sediments hydrodynamics and bathymetry in these subchannels produce a net circular hydrodynamic pattern around the shoal the spin cycle allowing the sands to remain in motion without being transported out of the ooid factory this general pattern is apparent in several other ooid shoal complexes this concept provides integrated insights into the physical influences impacting the formation suspension transport and deposition of ooids and the resulting geomorphic forms these results represent first steps toward developing more comprehensive and predictive analogs of spatial heterogeneity in ancient tidally dominated oolitic shoals

quantitative palaeoclimate reconstruction as an inverse problem a bayesian inference of late holocene climate on the eastern tibetan plateau from a peat cellulose δ18o record there has been a sustained need to quantify past climate changes from proxy records to better understand the driving mechanisms and thus to improve the prediction of the future transfer function is an intuitive and frequently used method in this regard however this method is unable to provide interpretive and predictive results from proxy records because physical processes are not included the inverse proxy modelling method opened up a new avenue for quantitative palaeoclimate reconstructions through the integration of proxy records with deterministic models it is fundamentally different from the statistical approach representing a conceptual advance in quantitative palaeoclimatology here we demonstrate the potential of this method by placing a mechanistic model and a 6000 year long peat cellulose 18o record obtained from the high cold and monsoonal eastern tibetan plateau c 3500 m a s l in a bayesian paradigm in this worked example the marginal posterior probability distributions of palaeo

upper triassic platform margin biofacies and the paleogeography of southern apennines abstract the upper triassic dolomitic successions of the monti della maddalena area southern apennines consist of white heavily recrystallized and cataclastic dolomites generally unsuitable for detailed facies analysis nevertheless evidences of bioconstructions can be found in several localities these evidences are represented by rudstones and possibly boundstones whose main components are fragments of sponges sphinctozoans inozoans chaetetids and corals generally encrusted by foraminifera red algae and problematica this association is much more diversified with respect to that of the microbial serpulid buildups which characterize the platform margin facies of most upper triassic successions of the southern apennines the monti della maddalena biofacies can be more readily compared with the bioconstructed facies of sicily and in general with the dachstein type reef of the tethyan realm the studied successions are interpreted according to the model of cirilli et al 1999 as formed at the margin of a carbonate platform facing a deep basin having good connection with the open sea while the microbial serpulid buildups formed on the margin of intraplatform restricted troughs with poorly oxygenated bottom waters our study discusses the relative paleogeographic position of the apennine platforms and the lagonegro basin the overall picture of the bioconstructed triassic facies distribution in southern apennines together with biofacies data from resedimented facies of lucania are compatible with paleogeographic reconstructions interpreting the monti della maddalena successions as representing the more external sector of the apennine platforms system flanking the lagonegro basin the latter bordered on its external side by apulia was part of a deep mesozoic domain comprising the imerese sicani basin of sicily and connected westward with the east mediterranean branch of western tethys our data exclude the possibility that the lagonegro basin was located in an internal position with respect to all the apenninic and apulian platforms system

a cretaceous carbonate delta drift in the montagna della maiella italy the upper cretaceous campanian maastrichtian bioclastic wedge of the orfento formation in the montagna della maiella italy is compared to newly discovered contourite drifts in the maldives like the drift deposits in the maldives the orfento formation fills a channel and builds a miocene delta shaped and mounded sedimentary body in the basin that is similar in size to the approximately 350 km2 large coarse grained bioclastic miocene delta drifts in the maldives the composition of the bioclastic wedge of the orfento formation is also exclusively bioclastic debris sourced from the shallow water areas and reworked clasts of the orfento formation itself in the near mud free succession age diagnostic fossils are sparse the deposi tional textures vary from wackestone to float rudstone and breccia conglom erates but rocks with grainstone and rudstone textures are the most common facies in the channel lensoid convex upward breccias cross cut ting channelized beds and thick grainstone lobes with abundant scours indi cate alternating erosion and deposition from a high energy current in the basin the mounded sedimentary body contains lobes with a divergent progradational geometry the lobes are built by decametre thick composite megabeds consisting of sigmoidal clinoforms that typically have a channel ized topset a grainy foreset and a fine grained bottomset with abundant irregular angular clasts up to 30 m thick channels filled with intraforma tional breccias and coarse grainstones pinch out downslope between the megabeds in the distal portion of the wedge stacked grainstone beds with foresets and reworked intraclasts document continuous sediment reworking and migration the bioclastic wedge of the orfento formation has been vari ously interpreted as a succession of sea level controlled slope deposits a shoaling shoreface complex or a carbonate tidal delta current controlled delta drifts in the maldives however offer a new interpretation because of their similarity in architecture and composition these similarities include i a feeder channel opening into the basin ii an excavation moat at the exit of the channel iii an overall mounded geometry with an apex that is in shallower water depth than the source channel iv progradation of stacked lobes v channels that pinch out in a basinward direction and vi smaller channelized intervals that are arranged in a radial pattern as a result the upper cretaceous campanian maastrichtian bioclastic wedge of the orfento formation in the montagna della maiella italy is here interpreted as a carbonate delta drift

preliminary estimates for the radiocarbon age of deep water in the glacial ocean radiocarbon ages for benthic and planktonic foraminifera from the late glacial sections of two atlantic and two pacific cores are reported the differences for benthic planktonic pairs suggest that the radiocarbon age for deep atlantic water was somewhat larger than today s i e 600 250 as opposed to 400 years and that the radiocarbon age for deep pacific water was also slightly larger than today s 2100 400 as opposed to 1600 years our results suggest that during glacial time the deep pacific was as it is today significantly depleted in radiocarbon relative to the deep atlantic as many questions remain unanswered regarding the reliability of this approach these conclusions must be considered to be preliminary

the maldives a giant isolated carbonate platform dominated by bottom currents abstract the maldives a 900 km north south trending paired chain of atolls that surround a ca 100 km wide central basin the inner sea represent a giant isolated carbonate platform in the indian ocean new reflection seismic multibeam and acoustic doppler current profiler data show that its development exhibits a distinct change from sea level to mainly bottom current controlled sedimentation at the end of the middle miocene the post middle miocene intra basinal fill consists of 9 mega units that have been formed and shaped by strong bottom currents entering the inner sea between the inter atoll passages at the end of the middle miocene the maldives represent a rimmed platform with the inner sea forming an empty bucket a connection to the indian ocean existed only in the northeastern part of the platform namely the kardiva channel probably concomitant with the onset of the indian monsoon the current pattern around the maldives changed significantly resulting in the formation of channels in the rimmed platform margin the latter process was encouraged by local drowning of large platform parts and additionally by bottom current forced submarine erosion that widened the channels to passages disintegrating the platform into separated atolls of different sizes the reworked material was dumped into the inner sea where it formed large contourite fans along slope bottom currents entering the inner sea from the north further redistributed the material leading to a southward shift of these sedimentary bodies in this way the inner sea was filled from west to east mega units 1 5 starting with mega unit 6 the opening of a southern gateway introduced a prominent northward flow of bottom waters in the inner sea it leads to the deposition of giant elongated drifts at the eastern flank of the basin filling it from east to west because the current swept away most of the material around the atolls the system was not able to prograde and the steady subsidence was compensated by aggradation accordingly a fundamental characteristic of a current controlled carbonate system is that aggradation occurs irrespective of platform sediment export or differently worded the rate of change in accommodation is always positive and greater than the rate of sediment supply adcp measurements in the winter monsoon season show two water masses in the inner sea one at the surface 0 150 m and a second below it that reaches its sea floor by the use of the grain size distribution of odp leg 716 located in the inner sea as proxy for the flow intensity of the bottom water we recognized an inverse proportional relationship to the monsoon strength from late upper miocene to present some of the current controlled deposits form sigmoidal prograding clinoforms preferably at the edges of the atolls adjacent to the passages where the velocity of the current entering the inner sea is high the anatomy of these prograding wedges is similar to sea level controlled clinoforms described for large isolated carbonate platforms in the sequence stratigraphic concept however our results document that they are not influenced by sea level fluctuations because of the high current velocities involved in their deposition they predominately consist of coarse sand sized carbonate fragments exhibiting large pore space and high permeability therefore these drift deposits comprise a possible exploration target

assembly of the lhasa and qiangtang terranes in central tibet by divergent double subduction abstract integration of lithostratigraphic magmatic and metamorphic data from the lhasa qiangtang collision zone in central tibet including the bangong suture zone and adjacent regions of the lhasa and qiangtang terranes indicates assembly through divergent double sided subduction this collision zone is characterized by the absence of early cretaceous high grade metamorphic rocks and the presence of extensive magmatism with enhanced mantle contributions at ca 120 110 ma two jurassic cretaceous magmatic arcs are identified from the caima duobuza rongma kangqiong amdo magmatic belt in the western qiangtang terrane and from the along tso yanhu daguo baingoin daru tso magmatic belt in the northern lhasa terrane these two magmatic arcs reflect northward and southward subduction of the bangong ocean lithosphere respectively available multidisciplinary data reconcile that the bangong ocean may have closed during the late jurassic early cretaceous most likely ca 140 130 ma through arc arc soft collision rather than continent continent hard collision subduction zone retreat associated with convergence beneath the lhasa terrane may have driven its rifting and separation from the northern margin of gondwana leading to its accretion within asia

the lhasa terrane record of a microcontinent and its histories of drift and growth article i nfo the lhasa terrane in southern tibet has long been accepted as the last geological block accreted to eurasia before its collision with the northward drifting indian continent in the cenozoic but its lithospheric architecture drift and growth histories and the nature of its northern suture with eurasia via the qiangtang terrane remain enigmatic using zircon in situ u pb and lu hf isotopic and bulk rock geochemical data of mesozoic early tertiary magmatic rocks sampled along four north south traverses across the lhasa terrane we show that the lhasa terrane has ancient basement rocks of proterozoic and archean ages up to 2870 ma in its centre with younger and juvenile crust phanerozoic accreted towards its both northern and southern edges this finding proves that the central lhasa subterrane was once a microcontinent this continent has survived from its long journey across the paleo tethyan ocean basins and has grown at the edges through magmatism resulting from oceanic lithosphere subduction towards beneath it during its journey and subsequent collisions with the qiangtang terrane to the north and with the indian continent to the south zircon hf isotope data indicate significant mantle source contributions to the generation of these granitoid rocks e g 50 90 0 70 and 30 100 to the mesozoic magmatism in the southern central and northern lhasa subterranes respectively we suggest that much of the mesozoic magmatism in the lhasa terrane may be associated with the southward bangong nujiang tethyan seafloor subduction beneath the lhasa terrane which likely began in the middle permian or earlier and ceased in the late early cretaceous and that the significant changes of zircon ehf t at 113 and 52 ma record tectonomagmatic activities as a result of slab break off and related mantle melting events following the qiangtang lhasa amalgamation and india lhasa amalgamation respectively these results manifest the efficacy of zircons as a chronometer u pb dating and a geochemical tracer hf isotopes in understanding the origin and histories of lithospheric plates and in revealing the tectonic evolution of old orogenies in the context of plate tectonics

late mesozoic tectonic evolution and growth of the tibetan plateau prior to the indo asian collision abstract the elevation of the tibetan plateau is a revolutionary event in the earth history which resulted in change not only of cenozoic regional and global climate but also of monsoon intensity a critical aspect for the development of the tibetan plateau that remains open to intense debate is whether the collision among the tibetan continental blocks or the subduction of the tethys prior to the indo asian collision in the cenozoic contributed to the plateau growth we propose here that an andean type orogen could have been present in southern tibet from the jurassic to early cretaceous but collapsed during the middle cretaceous based on a synthesis of existing structural sedimentary geochronological and geochemical data the orogeny is marked by north verging jurassic early cretaceous thrusting in the lhasa block a result of flat subduction of the yarlung zangpo neo tethys that is recorded by a narrow belt of 205 174 ma adakitic rocks along the southernmost margin of the lhasa block denudation of the orogen produced a thick up to 15 km sequence of jurassic turbidites and molasse type sediments on the northern lhasa block widespread middle cretaceous 135 100 ma postorogenic strongly peraluminous to calc alkaline magmatism and extensional deformation in the lhasa block and an extensive marine transgression in tibet indicate that the orogen broke down due to extension resulting from lithosphere delamination and asthenosphere upwelling meanwhile the north dipping subduction of the bangong meso tethys produced a wide jurassic middle cretaceous magmatic arc along the southern margin of the qiangtang block findings of 132 108 ma aged ophiolites rich with middle cretaceous radiolarians in central tibet indicate that the bangong meso tethys did not close until the late cretaceous repeated flat slab subduction of the yarlung zangpo neo tethys occurred during the late cretaceous 90 78 ma as indicated by the adakites in the southernmost lhasa block which together with the ongoing qiangtang lhasa collision could have contributed to the growth of the tibetan plateau

age and petrogenesis of a type granites in the middle segment of the bangonghu nujiang suture tibetan plateau abstract during geological investigations conducted over the past several years the authors found a group of a type granites in the middle segment of the bangonghu nujiang suture on the tibetan plateau these granitic plutons occur as stocks with exposed areas of less than 1 km 2 and lithologically include biotite granite and granodiorite porphyry which had intruded into cretaceous sedimentary rocks petrogeochemically the a type granites contain high sio 2 levels varying from 68 62 75 36 wt moreover they contain relatively high fe 2 o 3 t 0 86 5 39 wt and low al 2 o 3 12 76 15 54 wt levels and are weak peraluminous to metaluminous a trace element n morb normalized spider diagram showed apparent enrichment of the large ion lithophile elements lile rb th u k and pb with marked depletions of ba and sr the high field strength elements hfse nb ta and ti were sharply depleted with relative enrichment of zr and hf these signatures are characteristic of a type granite the granite samples had high rare earth element ree contents with ree 122 37 291 19 ppm light ree were rich relative to heavy ree with lree hree 4 89 9 58 and negative eu anomalies were sharp with eu varying from 0 14 0 5 and a mean value of 0 34 their chondrite normalized rare earth element distribution patterns appear as gently right dipping v types zircon u pb laicpms dating for three granitic plutons yielded weighted mean ages of 109 6 1 4 ma mswd 3 7 112 3 0 51 ma mswd 0 21 and 113 73 0 5 ma mswd 0 21 indicating that they formed in the late stage of the early cretaceous epoch the nd sr and pb isotopic results showed that the granites were rich in radiogenic isotopes the 87 sr 86 sr and i sr ratios varied from 0 719842 0 786395 and 0 706900 0 710378 respectively the 143 nd 144 nd ratios were from 0 512123 0 512392 with relatively large negative e nd values 3 37 to 10 34 the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios ranged from 18 703 19 070 15 680 15 732 and 39 121 39 576 respectively exhibiting isotopic signatures typical of crustal sources all of the data demonstrated unanimously that these granites were derived from partial melting of arc basaltic rocks underplated in the lower crust during oceanic crust subduction the high temperature heat source for melting of anhydrous basaltic rocks of the lower crust was from upwelling asthenosphere through slab windows formed as a result of slab break off during post collisional extension of the orogenic zone

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

cyclic steps review and aggradation based classification abstract cyclic steps are a type of upper flow regime bedform consisting of trains of upstream and upslope migrating bed undulations the overriding flow is characterised by a series of hydraulic jumps occurring in the troughs of the undulations cyclic steps form in open channel flows such as rivers and comprise a common bedform in subaqueous density flows in oceans lakes and reservoirs cyclic steps are associated with alternating froude subcritical and froude supercritical flow on respectively the stoss side and lee side of individual bedforms the transition between these flow states is embodied by the hydraulic jump in the trough of the bedform leading to the permanent or quasi permanent morphology of cyclic steps over the past decade numerous studies affirmed the dominant role of cyclic steps in generating bed undulations in modern and ancient glacial outwash fluvial delta and turbidite environments as reviewed here cyclic steps were previously discriminated as net depositional climbing transportational and net erosional falling in different parts of sedimentary systems the following cyclic step descriptors with distinct depositional signatures are proposed fully depositional partially depositional transportational partially erosional and fully erosional partially depositional cyclic steps are most common they are associated with backset bedded sets high aggradation rate and nested scours filled with massive to backset bedded deposits low aggradation rate the new classification can be used as a predictive tool in the reconstruction of modern and ancient sedimentary successions using repeat bathymetry seismic reflection or outcrop data it is applied in three turbidite case studies classical deep sea system small scale delta slope and line sourced carbonate slope

early cretaceous subduction related adakite like rocks of the gangdese belt southern tibet products of slab melting and subsequent melt peridotite interaction abstract the limited geochronology and geochemistry data available for the early cretaceous igneous rocks of the southern gangdese belt southern tibet has resulted in the proposal of conflicting geodynamic models for the generation of the widespread cretaceous igneous rocks in the middle and northern parts of the belt to explore this issue we present shrimp u pb zircon data and geochemical and sr nd pb hf isotopic data for the mamen andesites from the southern margin of the gangdese belt the mamen andesites emplaced at 136 5 ma are sodic na2o k2o 1 2 2 3 and have geochemical characteristics typical of adakites i e high al2o3 high la yb ratios and sr contents low y and hree contents and positive eu anomalies except for high cr ni and mgo contents the andesites have initial 87sr 86sr t ratios of 0 70413 0 70513 positive end t values of 3 7 5 8 and 206pb 204pb t ratios of 18 37 18 51 207pb 204pb t ratios of 15 59 15 65 and 208pb 204pb t ratios of 38 43 38 72 in situ hf isotopic analyses of zircons that had previously been dated by shrimp yielded positive initial ehf t values ranging from 11 0 to 15 5 a model calculation using trace element and sr nd pb isotopic data indicates that several percent of subducted sediment is required to generate the mamen andesites which were derived via the partial melting of subducted neo tethyan slab morb sediment fluid and subsequently hybridized by peridotite in the mantle wedge our data indicate that the neo tethyan oceanic crust was subducted northward beneath the gangdese belt during the early cretaceous at a high angle our results are inconsistent with a tectonic model that advocates the low angle or flat slab subduction of neo tethyan oceanic crust in generating the widespread cretaceous magmatism recorded in the gangdese belt

structural architecture of the central apennines interpretation of the crop 11 seismic profile from the adriatic coast to the orographic divide 1 we present an interpretation of the eastern half portion of the crop 11 line a deep reflection seismic profile 265 km long that cuts across the central apennines from the tyrrhenian coast to the adriatic coast in the study area the line cuts across a pile of thrust sheets that underwent tectonic transport between the messinian and the pleistocene in its easternmost part the line runs through the plio pleistocene deposits of the adriatic foredeep in the foreland region the crop 11 line integrates previous information on the crustal structure derived from petroleum exploration and from deep seismic sounding refraction experiments in particular the crop 11 line confirms the existence of a very thick sedimentary sequence underlying the mesozoic tertiary carbonates of the apulia platform interpreted as the paleozoic triassic sedimentary cover of a pre cambrian crystalline basement in the mountain chain where the base thrust of the orogenic wedge reaches a depth of about 25 km this sedimentary sequence appears to be the deepest geological unit incorporated in the thrust system this interpretation of the crop 11 profile suggests an unusual thin skin tectonic style implying the detachment from the original basement and the incorporation in the post tortonian tectonic wedge of a very thick paleozoic triassic sedimentary sequence possibly affected by low grade metamorphism in the lower part other new suggestions from the crop 11 seismic data concern the origin of the fucino basin one of the most remarkable plio pleistocene intramontane basins the normal faults bordering this structural depression as other important normal faults present in the central apennines e g the caramanico fault system in the majella region seem to have been controlled by gravitational collapse processes driven by uplift during crustal shortening rather than by a generalized extension subsequent to the apennine compression as usually reported in the geological literature if this interpretation is correct the strong seismic activity in correspondence to the apennine watershed may be related to the very recent increase in the structural relief caused by an out of sequence propagation of the active thrusts

differential compaction as a control on depositional architectures across the maiella carbonate platform margin central apennines italy abstract the role of differential compaction as a control in the creation of accommodation and on compaction modified depositional features and stratal geometries across the maiella platform margin has been investigated through a combined analysis of seismic scale outcrops porosity evaluation and modeling geologic evolution and large exposures make the platform margin of the maiella an ideal place to investigate the effects of differential compaction a high relief cemented carbonate platform a deep basin filled with highly compactable deposits and a prograding grain rich succession sealing morphologic differences across the platform margin represent suitable features for promoting differential compaction stratal relationships across the platform margin exhibit evidence of differential compaction induced effects such as basinward divergence and thickening of strata updip pinch out of wedge shaped stratal packages and an anticline hinge porosity analysis and modeling indicate that through progressive loading mechanical and chemical processes act in concert to destroy most of the depositional porosity mechanical compaction appears to have played the greatest part in the total budget of compaction however chemical compaction seems to have played a prominent role in the formation of geometrically consistent depositional profiles during progradation due to differential compaction across the platform margin a compaction hinge formed concomitantly with the beginning of progradation producing a basin facing monocline characterized by the progressive steepening of basinward stratal dips the resulting compaction induced stratal deformation together with sea level changes controls the distribution and depositional timing of wedge shaped stratal packages during late cretaceous and paleocene and the distribution of coral algal reef buildups during the late eocene early oligocene the development of the compaction hinge usually follows the progressive increase of loading but a decrease in compaction dissipation may be caused by overburdening of compactable deposits this will cause a delayed compaction induced subsidence whose effects will be produced after deposition i e during loading interruption this mechanism is thought to have an important role in the timing of compaction induced subsidence throughout the end of cretaceous and the early tertiary and it is considered together with sea level as the main controlling process of the occurrence and distribution of downslope sediments during a long lasting period of platform emersion

tibetan basement rocks near amdo reveal missing mesozoic tectonism along the bangong suture central tibet the u pb and 4 0 ar 3 9 ar studies of a unique exposure of crystalline basement along the jurassic early cretaceous bangong suture of central tibet reveal previously unrecognized records of mesozoic metamorphism magmatism and exhumation the basement includes cambrian and older orthogneisses that underwent amphibolite facies metamorphism coeval with extensive granitoid emplacement at 185 170 ma the basement cooled to 300 c by 165 ma and was exhumed to upper crustal levels in the hanging wall of a south directed thrust system during early cretaceous time we attribute jurassic metamorphism and magmatism to the development of a continental arc during bangong ocean subduction and early cretaceous exhumation to northward continental underthrusting of the lhasa terrane beneath the qiangtang terrane we speculate that a jurassic arc extended regionally along the length of the bangong suture but in all other places in tibet has been buried either depositionally or structurally beneath supracrustal assemblages

closing off the southern ocean surface equilibrium integrations with the three dimensional hamburg ocean carbon cycle circulation model show the effect of a southern ocean surface outcrop that is closed off for gas exchange with the atmosphere and export production of particulate organic carbon and caco3 south of 32 5 s for such a close off the northern atlantic outcrop assumes a greater degree of control of atmospheric co2 partial pressure contrary to expectations the atmospheric pco2 increases compared to a control run without close off maximizing the nutrient utilization in the north atlantic can compensate for this increase however it does not draw down the pco2 to glacial levels

evidence for elevated alkalinity in the glacial southern ocean an increase in whole ocean alkalinity during glacial periods could account in part for the drawdown of atmospheric co2 into the ocean such an increase was inevitable due to the near elimination of shelf area for the burial of coral reef alkalinity we present evidence based on downcore measurements of benthic foraminiferal b ca and mg ca from a core in the weddell sea that the deep ocean carbonate ion concentration co32 was elevated by similar to 25 mu mol kg during each glacial period of the last 800 kyr the heterogeneity of the preservation histories in the different ocean basins reflects control of the carbonate chemistry of the deep glacial ocean in the atlantic and pacific by the changing ventilation and chemistry of weddell sea waters these waters are more corrosive than interglacial northern sourced waters but not as undersaturated as interglacial southern sourced waters our inferred increase in whole ocean alkalinity can be reconciled with reconstructions of glacial saturation horizon depth and the carbonate budget if carbonate burial rates also increased above the saturation horizon as a result of enhanced pelagic calcification the weddell records display low co32 during deglaciations and peak interglacial warmth coincident with maxima in percent caco3 in the atlantic and pacific oceans should the burial rate of alkalinity in the more alkaline glacial deep waters outstrip the rate of alkalinity supply then pelagic carbonate production by the coccolithophores at the end of the glacial maximum could drive a decrease in ocean co32 and act to trigger the deglacial rise in pco 2

supercritical and subcritical turbidity currents and their deposits a synthesis common facies models of turbidite deposits are based on idealized sequences of turbidite units which are assumed to reflect the depositional processes of a decelerating turbidity current we show how suites of turbidite units i e distinct turbidite facies associations that are easily described from core and outcrop may characterize the entire range of large scale dynamics of turbidity currents enabling estimates of their densimetric froude number fr subcritical versus supercritical and suspension fall out rate stratified versus nonstratified flows the linking of facies associations with large scale flow dynamics resolves process facies links that were hitherto unresolved by the common turbidite facies models

backset lamination produced by supercritical backwash flows at the beachface shoreface transition of a storm dominated gravelly beach middle pleistocene central italy abstract bedforms and resulting sedimentary structures of interpreted upper flow regime origin are fairly common in various ancient and modern depositional settings yet outcrop examples of shallow water strata dominated by sedimentary structures arising from such flow conditions are rarely documented this outcrop based study presents the first detailed analysis of mid pleistocene beachface shoreface strata containing sedimentary structures interpreted to have been formed by storm generated backwash flows during the transition in flow regime from supercritical to subcritical here we propose that moving down the steep beachface backwash flows rapidly accelerated and became thinner experienced abrupt deceleration and flow thickening passing through an erosional hydraulic jump in the trough at the toe of the beachface and then waned to thicker and subcritical conditions just downflow of the hydraulic jump in this frame landward dipping backset laminae deposited on the downflow side of the trough evolved into thinner upper stage plane parallel laminae further downstream the transition from the proximal to the distal upper shoreface records a significant increase of preserved wave ripples and burrowed intervals in concert with a progressive decrease in thickness and grain size of individual sets of plane parallel laminae and increase of gravel filled gutter casts

2d modelling of large scale platform margin collapses along an ancient carbonate platform edge maiella mt central apennines italy geological model and conceptual framework abstract results of numerical simulations of large scale platform margin collapses along the edge of the cretaceous platform of the maiella central apennines are presented adding a new contribution to the understanding of the role and quantification of the various factors that control triggering of these phenomena and the production of breccias and megabreccias for this purpose a sophisticated numerical code widely used in recent contexts to simulate overall mass movements and deep gravity driven deformation is applied for the first time to an ancient system on a scale of several kilometres the modelling carried out is a simplified attempt to understand a very complex phenomenon produced over a very long time span it tests whether the perturbing causes in the model acting together or separately are able to activate such large scale collapse and helps to understand the effects of perturbing causes and their variations in particular modelling was carried out considering both static variations in sea level and dynamic seismic events without and with fault formation conditions and combinations of them variations in sea level alone do not produce all the effects observed but may certainly be a predisposing element seismic shock simulations show that fracturing and shear stresses are concentrated on the platform margin representing the most sensitive and vulnerable area earthquake swarms associated with an active fault are the most likely means of triggering large scale platform margin collapses such as those occurring during the early cretaceous in the maiella

bioclastic sediment lobes on a supply dominated upper cretaceous carbonate platform margin montagna della maiella italy a thick bioclastic sediment wedge was deposited on the slope of the maiella carbonate platform margin in the late campanian to late maastrichtian the wedge consists of lobate depositional units laterally and vertically convex structures the complex internal geometries of the lobes combine characteristics of unidirectional sandwaves and the alternating point sources of deltas excellent outcrop permits a detailed documentation and discussion of the depositional processes the sediment wedge constitutes a supersequence which prograded along the platform margin as a result of high sediment supply and forced regression within the supersequence a hierarchy of higher order stratigraphic units sequence sets and sequences are developed the individual bioclastic sediment lobes are interpreted as systems tracts and parasequences of the sequences within the sequence sets

ice core sample measurements give atmospheric co 2 content during the past 40 000 yr recent measurements1 2 on ice samples from camp century greenland 77 10 n 61 08 w byrd station antarctica 80 01 s 110 31 w and dome c 74 40 s 125 10 e suggest that during the late part of the last glaciation the atmospheric co2 concentration was significantly lower than during the holocene further investigation of this natural increase of the atmospheric co2 concentration in the past should aid our understanding of the climatic implications of the man made co2 increase since the beginning of industrialization3 here we report new and precise measurements of the co2 concentration of the air occluded in bubbles of ice samples from camp century and byrd station using a new dry extraction technique the extracted gases were analysed with an ir laser spectrometer irls samples from 22 different depths were analysed from each core the samples are distributed over a depth interval corresponding approximately to the past 40 000 yr in addition results for ice samples from selected depth horizons from a colder region north central greenland 74 37 n 39 36 w and from a warmer region dye 3 greenland 65 11 n 43 50 w are given based on these results we estimate the trend of the atmospheric co2 concentration during the past 40 000 yr

the origin and pre cenozoic evolution of the tibetan plateau different hypotheses have been proposed for the origin and pre cenozoic evolution of the tibetan plateau as a result of several collision events between a series of gondwana derived terranes e g qiangtang lhasa and india and asian continent since the early paleozoic this paper reviews and reevaluates these hypotheses in light of new data from tibet including 1 the distribution of major tectonic boundaries and suture zones 2 basement rocks and their sedimentary covers 3 magmatic suites and 4 detrital zircon constraints from paleozoic metasedimentary rocks the western qiangtang amdo and tethyan himalaya terranes have the indian gondwana origin whereas the lhasa terrane shows an australian gondwana affinity the cambrian magmatic record in the lhasa terrane resulted from the subduction of the proto tethyan ocean lithosphere beneath the australian gondwana the newly identified late devonian granitoids in the southern margin of the lhasa terrane may represent an extensional magmatic event associated with its rifting which ultimately resulted in the opening of the songdo tethyan ocean the lhasa northern australia collision at similar to 263 ma was likely responsible for the initiation of a southward dipping subduction of the bangong nujiang tethyan oceanic lithosphere the yarlung zangbo tethyan ocean opened as a back arc basin in the late triassic leading to the separation of the lhasa terrane from northern australia the subsequent northward subduction of the yarlung zangbo tethyan ocean lithosphere beneath the lhasa terrane may have been triggered by the qiangtang lhasa collision in the earliest cretaceous the mafic dike swarms ca 284 ma in the western qiangtang originated from the panjal plume activity that resulted in continental rifting and its separation from the northern indian continent the subsequent collision of the western qiangtang with the eastern qiangtang in the middle triassic was followed by slab breakoff that led to the exhumation of the qiangtang metamorphic rocks this collision may have caused the northward subduction initiation of the bangong nujiang ocean lithosphere beneath the western qiangtang collision related coeval igneous rocks occurring on both sides of the suture zone and the within plate basalt affinity of associated mafic lithologies suggest slab breakoff induced magmatism in a continent continent collision zone this zone may be the site of net continental crust growth as exemplified by the tibetan plateau c 2012 international association for gondwana research published by elsevier b v all rights reserved

geochronology geochemistry and zircon hf isotopic compositions of mesozoic intermediate felsic intrusions in central tibet petrogenetic and tectonic implications abstract mesozoic intermediate felsic intrusions are widely distributed in the southern qiangtang terrane central tibet zircon u pb dating shows that these intrusions formed in two periods in the jurassic 169 150 ma and cretaceous 127 113 ma they mostly belong to the high k calc alkaline series and show strong enrichments in large ion lithophile elements e g cs rb and k depletions in nb ta and ti and negative ba anomalies on primitive mantle normalized diagrams p 2 o 5 contents decrease with increasing sio 2 content and th contents increase with increasing rb content consistent with the evolution trend of i type magmas these intrusions show a wide range of zircon ehf t values from 19 4 to 11 2 including in rocks with similar sio 2 contents suggesting variable contributions from mantle and qiangtang crustal sources fine grained mafic to intermediate igneous enclaves in jurassic intrusions have similar zircon u pb ages and similar or slightly higher zircon ehf t values to the host rocks suggesting that the enclave magmas were derived from mixed magmas at depth and injected into more evolved magmas in upper crustal magma chambers magma mixing is also supported by the wide range of zircon hf isotopic compositions ehf t 19 4 to 2 5 from within individual jurassic and cretaceous intrusions and jurassic enclaves the jurassic cretaceous magmas likely formed in a continental arc setting during subduction of the bangong nujiang ocean between 170 and 110 ma and evolved in the upper plate crust by mash processes

benthic foraminiferal δ13c and accumulation rates of organic carbon uvigerina peregrina group and cibicidoides wuellerstorfi the glacial to interglacial 13c records of the benthic foraminifera cibicidoides wuellerstorfi and the uvigerina peregrina group from deep sea cores cannot be adjusted by a generally valid constant the 13c values of the u peregrina group largely correlate with the accumulation rates of organic carbon suggesting a local habitat effect those of c wuellerstorfi vary independently with respect to the carbon flux and record fluctuations in the 13c of the ambient bottom water isotopic composition

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr