seismic and geologic characteristics of drowning events on carbonate platforms carbonate platform drowning events are recorded in upper jurassic lower cretaceous carbonates of the baltimore canyon area offshore united states east coast and lower miocene carbonates of the pearl river mouth basin offshore people s republic of china cursory examination of seismic data from both areas would indicate that the platforms fit the classic definition of a drowning unconformity however detailed lithologic and paleontologic data indicate that the depositional erosional hiatuses vary widely in each area from 0 25 m y in the baltimore canyon area to a condensed section with no hiatus in the pearl river mouth basin the sedimentary sequence produced during drowning the drowning sequence in both areas is gradational with underlying shallow platform carbo ates and in some places overlying deeper marine limestones and shales the generalized facies models proposed for drowning events suggest that they may appear as instantaneous or gradual changes in geologic and seismic data however high resolution seismic data across the baltimore canyon and pearl river mouth basins show that some drowning sequences may be masked on conventionally processed seismic sections because of this resolution problem a distinction should be made between seismically and geologically defined unconformity surfaces the geologic characteristics of drowning events on carbonate platforms include a gradational lower and sometimes upper contact chemical sedimentation glauconite phosphate open marine shelf sediments and a variable hiatus at the upper boundary late growth shelf margin reefs also can be a diagnostic feature of drowned platforms seismic characteristics include horizontal to sub horizontal basinal marine onlap basin parallel reflector continuity above the carbonate sequence boundary and downlap of later highstand units evidence from platforms adjacent to continental margins baltimore canyon indicates that drowning occurs in a step wise fashion advancing more or less symmetrically across the platform from shelf to nearshore environments data from isolated open ocean atolls pearl river mouth basin indicate that they respond differently to drowning showing an asymmetric decrease in shallow platform environments as drowning occurs proper recognition by a geoscientist of the seismic and geologic characteristics of drowning events can lead to better reservoir and seal estimates and the correct reconstruction of the depositional tectonic and eustatic histories of an area

transgressive sand bodies on the maresme continental shelf western mediterranean sea abstract three large scale elongate asymmetrical sand bodies lie beyond the shoreface of the straight sandy coast of maresme barcelona in the northwestern mediterranean sea they are found on the continental shelf at water depths of 15 30 m 35 80 m and 95 113 m they are typically 12 20 m thick 1000 2000 m wide and trend parallel or subparallel to the coast for a distance of up to 24 km slopes on the steep offshore side vary between 3 and 20 while the shoreward slopes are gentler the shallowest sand body is modern in dynamic equilibrium with present conditions the other two however are relict bodies built up during the last postglacial rise in sea level development of these sand bodies occurs in the shoreface environment and in a space time evolution they show a punctuated but nearly continuous nature in the way that their preservation during the holocene transgression occurs only in specific locations on the continental shelf they begin growing on pleistocene scarps with offshore slopes and their growth pattern is mostly controlled by the sediment supply flow distribution and rate of sea level rise the formation of these sandy bodies is related to winter storms and southwesterly flows which cause large volumes of sediment to be transported downshelf and offshore by downwelling bottom currents generated by coastal set up the result is sand movement onto and across the sand body surface down to water depths of 15 20 m the thick sandy lenses of the maresme shelf are interpreted as topographically induced lee side sand bodies and not primarily as sand ridges in the classic sense the occurrence of these bodies on a low energy shelf may be significant for the interpretation of the geological record

seasonal cycle of mesoscale instability of the west spitsbergen current abstractthe west spitsbergen current wsc is a topographically steered boundary current that transports warm atlantic water northward in fram strait the 16 yr 1997 2012 current and temperature salinity measurements from moorings in the wsc at 78 50 n reveal the dynamics of mesoscale variability in the wsc and the central fram strait a strong seasonality of the fluctuations and the proposed driving mechanisms is described in winter water is advected in the wsc that has been subjected to strong atmospheric cooling in the nordic seas and as a result the stratification in the top 250 m is weak the current is also stronger than in summer and has a greater vertical shear this results in an e folding growth period for baroclinic instabilities of about half a day in winter indicating that the current has the ability to rapidly grow unstable and form eddies in summer the wsc is significantly less unstable with an e folding growth period of 2 days observations of the eddy kinetic energy eke show a p

the turbulent oscillator a mechanism of low frequency variability of the wind driven ocean gyres intrinsic low frequency variability is studied in the idealized quasigeostrophic midlatitude wind driven ocean gyres operating at large reynolds number a robust decadal variability mode driven by the transient mesoscale eddies is found and analyzed the variability is a turbulent phenomenon which is driven by the competition between the eddy rectification process and the potential vorticity anomalies induced by changes of the intergyre transport

the role of hydrothermal processes in the granite hosted zr y ree deposit at strange lake quebec labrador evidence from fluid inclusions abstract the strange lake zr y ree nb and be deposit is hosted by a small high level late proterozoic peralkaline granite stock that intruded into high grade metamorphic gneisses on the quebec labrador border the stock is extensively altered early alteration is manifested by the replacement of arfvedsonite with aegirine later alteration involved ca na exchange zr ti y rees nb and be are concentrated in ca bearing minerals that together with quartz commonly pseudomorph na bearing minerals fluid inclusions in pseudomorphs comprise several distinct types high salinity 13 to 24 wt nacl eq ca rich aqueous inclusions that homogenize to liquid between 135 and 195 c mixed aqueousmethane inclusions methane inclusions and solid bearing inclusions aqueous methane inclusions represent heterogeneous entrapment of immiscible high salinity aqueous liquid and methane bastnasite tentatively identified by sem analysis occurs as a daughter mineral other daughter or trapped minerals include a y hree bearing mineral possibly gagarinite and hematite galena sphalerite fluorite pyrochlore kutnahorite and griceite the first three inclusion types also occur in quartz in pegmatites and veins together with lower temperature lower salinity na dominated aqueous inclusions the entrapment temperature inferred for the aqueous inclusions from microthermometry and the na k ca geothermometer range from 155 to 195 c for the higher salinity inclusions and 100 to 165 c for the low salinity inclusions a model is proposed in which the intrusion of a peralkaline granite to high crustal levels initiated a ground formational water dominated hydrothermal system in adjacent gabbroic calc silicate and graphitic gneisses reaction of the high salinity ca rich liquid with the graphitic gneisses led to the production of an immiscible methane gas subsequent interaction of this liquid with the granite led to extensive replacement of sodic minerals by calcium analogues at temperatures of less than 200 c some time after the onset of ca metasomatism the high salinity liquid mixed with a ca poor low salinity low temperature liquid that had leached f and rare metals from the granite yttrium and ree mineral deposition occurred as a result of the decreased ligand concentration that accompanied fluorite deposition during mixing of the ca rich and ca poor aqueous liquids

seasonal variation and instability nature of the north pacific subtropical countercurrent and the hawaiian lee countercurrent 1 the relation between baroclinic instability of the north pacific subtropical countercurrent stcc and the hawaiian lee countercurrent hlcc and seasonal evolution of mesoscale sea surface height ssh variability was investigated by using historical hydrographic data and altimeter derived ssh anomaly data during 1992 2000 the annual and monthly mean dynamic height climatologies show two robust eastward flowing countercurrents the stcc extends typically along 24 n from 130 e to 160 w and slightly shifts to the north as it flows toward the east and the hlcc is located typically along 20 n and extends from about 150 e to just west of the hawaiian islands seasonal variations of the stcc in the western north pacific and the hlcc west of the hawaiian island where the eddy variability is relatively larger than the background were quite different the stcc hlcc is strong in winter summer to summer winter and weak in fall spring in contrast seasonal evolution of mesoscale ssh variability has almost the same cycle in the two countercurrent regions the eddy kinetic energy eke is a maximum in spring and a minimum in fall the dominant zonal scales are shortest in late winter and become longer with time a linear quasigeostrophic stability analysis using a three layer model indicates that instability properties are very similar between the two countercurrent regions the stcc and the hlcc become baroclinically more unstable during winter and late fall to winter respectively due to strong vertical velocity shear and weak stratification between the stcc hlcc and underlying westward flow and the most unstable wave during this season has an e folding timescale of about 2 3 months and a zonal wavelength of about 300 400 km the same behavior of the seasonal evolution of the mesoscale variability in the two countercurrent regions is a manifestation of these similarities in terms of increasing nonlinearity of the unstable waves and an inverse cascade of the eddy energy we discussed generation processes of the mesoscale ssh disturbances

exploration history of liuhua 11 1 field pearl river mouth basin china 1 stratigraphic analysis of sparse seismic data in 1981 indicated the presence of a lower miocene carbonate platform complex over the western part of the dongsha massif 220 km 137 mi southeast of hong kong two bank edge trends were recognized and a large structural closure within the carbonate platform was mapped along the axis of the uplift the study also predicted the presence of a widespread thick basal sandstone below the carbonate complex that could serve as a conduit for long distance migration of hydrocarbons into the closure although the prospect was a high risk play in deep water 38 km 24 mi south of the edge of a paleogene basin with possible oil source rocks it was intriguing because of its size and similarity to the giant bombay high oil field offshor india after drilling by other companies demonstrated that oil had migrated well out of the source basin huizhou sag amoco negotiated for contract area 29 04 and was awarded the area in november 1985 the first amoco well lh 11 1 1a tested 2240 bbl day of 21 degree api oil from a 75 m 246 ft pay section in a carbonate platform sequence topped at 1197 m 3927 ft a 401 m 1316 ft lower carbonate section and a 149 m 489 ft sandstone unit resting on basement were water bearing additional drilling has confirmed a giant in place oil accumulation but commerciality is yet to be determined the carbonate complex includes a leached limestone platform facies with a reefal southwestern margin and has excellent porosity and permeability the oil is less waxy and heavier than other huizhou ag sourced oils because of biodegradation after migration

ocean and atmosphere storm tracks the role of eddy vorticity forcing abstract signatures of eddy variability and vorticity forcing are diagnosed in the atmosphere and ocean from weather center reanalysis and altimetric data broadly covering the same period 1992 2002 in the atmosphere there are localized regions of eddy variability referred to as storm tracks at the entrance of the storm track the eddies grow providing a downgradient heat flux and accelerating the mean flow eastward at the exit and downstream of the storm track the eddies decay and instead provide a westward acceleration in the ocean there are similar regions of enhanced eddy variability along the extension of midlatitude boundary currents and the antarctic circumpolar current within these regions of high eddy kinetic energy there are more localized signals of high eady growth rate and downgradient eddy heat fluxes as in the atmosphere there are localized regions in the southern ocean where ocean eddies provide statistically significant vorticity forcing which acts to accelerate the mean flow

post rift uplift and focused fluid flow in the passive margin of northern south china sea an important post rifting tectonic event with extensive uplift and fluid flow took place at the northern margin of the south china sea scs during the late miocene based on an analysis of two and three dimensional seismic data plus drilling well data the tectonic event mainly affected the dongsha rise and the adjacent depressions tectonic deformation likely occurred in the dongsha rise the eastern part of the panyu swell and several depressions of the zhu i sag the post rifting deformation in the study area was characterized by faulting erosion igneous activity and hydrothermal fluid flow the tectonic movement caused abundant secondary nw and wnw tensional and transtensional faults with lengths of 1 to 10 km it also created a clear angular unconformity which marks the time of the tectonic movement late neogene igneous rocks are found in the strata in the dongsha rise only close to the continent ocean transition zone geothermal activity occurred in the liuhua carbonate platform and adjacent depressions deformation is more intense in the eastern area than in the western area according to sequence stratigraphy we infer that the tectonic event mainly occurred in the late period of late miocene and ended at the mio pliocene boundary 5 5 ma the dynamic mechanism for tectonic movement could be associated with subduction of the south china sea slab beneath the philippine sea plate at the manila trench when subduction of lower density crust within the continental ocean transition zone was initiated large resistance stresses may have led to lithosphere bending and crustal uplift in the dongsha area c 2014 elsevier b v all rights reserved

kuroshio extension bimodality and the north pacific oscillation a case of intrinsic variability paced by external forcing abstracta previous north pacific ocean circulation model forced by climatological winds is extended here to include a time dependent north pacific oscillation npo forcing the kuroshio extension ke decadal bimodal cycle which is a self sustained intrinsic relaxation oscillation in the climatologically forced case is now excited by the npo forcing both the timing of the cycles and the rossby wave teleconnection mechanism that is found to govern the synchronization from 1993 to 2012 are in good agreement with altimeter observations sensitivity numerical experiments are carried out by varying the zonal location and amplitude of the npo forcing and the lateral eddy viscosity the emergence of the ke bimodality with a correct timing is found to be extremely sensitive to changes in the dissipative parameterization the implications of such sensitivity for deficiencies found in more realistic north pacific ocean general circulation models are discussed the dynamical mechanism that emerges from this stu

instabilities and multiscale interactions underlying the loop current eddy shedding in the gulf of mexico abstracta recently developed tool the multiscale window transform along with the theory of canonical energy transfer is used to investigate the roles of multiscale interactions and instabilities

acc meanders energy transfer and mixed barotropic baroclinic instability along stream variations in the dynamics of the antarctic circumpolar current acc impact heat and tracer transport regulate interbasin exchange and influence closure of the overturning circulation topography is primarily responsible for generating deviations from zonal mean properties mainly through standing meanders associated with regions of high eddy kinetic energy here an idealized channel model is used to explore the spatial distribution of energy exchange and its relationship to eddy geometry as characterized by both eddy momentum and eddy buoyancy fluxes variations in energy exchange properties occur not only between standing meander and quasi zonal jet regions but throughout the meander itself both barotropic and baroclinic stability properties as well as the magnitude of energy exchange terms undergo abrupt changes along the path of the acc these transitions are captured by diagnosing eddy fluxes of energy and by adopting the eddy geometry framework the latter typically applied to barotropic stability properties is applied here in the depth along stream plane to include information about both barotropic and baroclinic stability properties of the flow these simulations reveal that eddy momentum fluxes and thus barotropic instability play a leading role in the energy budget within a standing meander this result suggests that baroclinic instability alone cannot capture the dynamics of acc standing meanders a challenge for models where eddy fluxes are parameterized

kuroshio extension variability and forcing of the pacific decadal oscillations responses and potential feedback abstract a forcing mechanism is sought for the large scale circulation changes in the kuroshio extension region of the western north pacific ocean as inferred by topex poseidon sea surface height ssh data the low frequency signal of the kuroshio extension over the last decade was characterized by a modulation in its zonal mean flow intensity the mean kuroshio extension jet weakened progressively from 1993 to 1996 and this trend reversed after 1997 the ability to simulate the major trends in the observed ssh signals with linear vorticity dynamics leads the authors to conclude that the modulation in the zonal mean jet was remotely forced by wind stress curl anomalies in the eastern north pacific ocean related to the pacific decadal oscillations pdos to be specific the weakening strengthening trend in 1993 96 1997 2001 was caused by westward expansions of negative positive ssh anomalies south of the kuroshio extension and positive negative ssh anomalies north of the kuroshio extension emerg

radiocarbon dating and the reconstruction of late quaternary sea level changes in hong kong abstract radiocarbon dating is used widely for the reconstruction of late quaternary sea level changes in the present study eight case studies in hong kong have been chosen to highlight the difficulty in obtaining reliable radiocarbon dates pre holocene radiocarbon dates exceeding about 8100 yr bp have been found to show a young age bias a shell sample dated by two separate radiocarbon laboratories gave last interstadial ages differing by almost 9500 years while an oxygen isotope stage 5e age was obtained using uranium series dating other evidence including stratigraphy have shown that only the last interglacial age is acceptable the young age bias is attributed mainly to the post depositional introduction of young carbon into the sample for the reconstruction of sea level changes it is essential to select samples immediately above of the base of the holocene transgressive unit in offshore boreholes and excavations to satisfy the criteria of rapid burial these samples should preferably include mud plant matter and shells to facilitate interpretation furthermore as many samples as possible from a range of water depth down to about 130 m below the present sea level should be dated to reduce error introduced by counting statistics so the true signal of sea level changes can be reflected

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

spatiotemporal variability of the global ocean internal processes inferred from satellite observations abstractusing a new analysis tool namely multiscale window transform mwt and the mwt based theory of canonical transfer this study investigates the spatiotemporal variations of the nonlinear

metallogeny of south greenland a review of geological evolution mineral occurrences and geochemical exploration data abstract south greenland has been the site of historic mining of cryolite copper graphite and gold hosts mineral deposits with gold uranium zinc niobium tantalum zirconium hafnium ree iron titanium vanadium fluorite and graphite and has additional potential for lithium beryllium phosphorus gallium and thorium data from stream sediment geochemical surveys document that south greenland is enriched in a range of these elements relative to the rest of greenland and to estimates of the upper crust composition distribution patterns for individual elements within south greenland exhibit enriched regions that are spatially related to lithological units crustal structure and known mineralisation the northern domain of south greenland includes the southernmost part of the orthogneiss dominated north atlantic craton orogenic gold mineralisation is hosted by quartz veins and hydrothermally altered rocks associated with shear zones intersecting the mesoarchaean tartoq group of mafic metavolcanic rocks geochemical exploration indicates that additional potential for gold mineralisation exists within palaeoproterozoic supracrustal rocks overlying the archaean basement rocks formed during the palaeoproterozoic ketilidian orogeny occupy a major part of south greenland and has been divided into two domains the central domain is underlain by the julianehab igneous complex forming a 100 km wide ene wsw zone centrally across south greenland intrusive and extrusive mostly felsic magmatic rocks were emplaced in two main stages 1850 1830 and 1800 1780 ma in a continental arc setting positive anomalies in aeromagnetic data indicate that mafic plutons are common in the late igneous complex intra arc mafic metavolcanic rocks contain syngenetic stratabound copper sulphide and epigenetic shear zone hosted copper silver gold mineralisation at kobberminebugt and kangerluluk whereas metasedimentary and metapyroclastic rocks contain stratabound uraninite mineralisation orthomagmatic iron titanium vanadium mineralisation is hosted by a gabbro a potential for porphyry type mineralisation related to the late intrusive stages of the julianehab igneous complex is suggested by showings with copper molybdenum and gold together with stream sediment anomalies for these elements vein type uranium mineralisation occurs in fault zones in the julianehab igneous complex related to mesoproterozoic rifting the southern domain contains an assemblage of palaeoproterozoic metasedimentary and metavolcanic rocks that underwent moderate to strong deformation peak ht lp metamorphism and partial melting with subsequent retrograde exhumation at 1790 1765 ma the supracrustal rocks contain syngenetic au as sb u and zn mineralisation in volcanic or graphite and sulphide rich sedimentary environments graphite was mined historically at two sites many stream sediment gold anomalies are located in a ne trending belt along the boundary between the early julianehab complex and the supracrustal rocks to the south they reflect a number of auriferous quartz vein occurrences including the nalunaq gold deposit hosted in a system of shear zones and probably generated as orogenic gold during ketilidian accretion the 1755 1730 ma a type ilua plutonic suite is the latest magmatic event in the ketilidian orogen the 1300 1140 ma gardar period involved continental rifting sedimentation and alkaline magmatism numerous dykes and 10 ring shaped intrusion complexes were formed across south greenland an orthomagmatic iron titanium vanadium deposit is hosted by troctolitic gabbro residual magmas and fluids resulting from extreme magmatic differentiation possibly combined with assimilation of older crust created mineral deposits including cryolite that was mined at ivigtut large low grade deposits of uranium rare earth elements zinc at kvanefjeld and tantalum niobium rare earth element zirconium at kringlerne in the ilimaussaq complex as well as tantalum niobium rare earth elements at motzfeldt so in the igaliko complex the south greenland crustal evolution records effects of mantle processes such as lithospheric extension subduction and underplating which resulted in recurrent magma emplacement in tectonically active environments as such the geology of south greenland reflects events and circumstances that are favourable to the generation and preservation of hydrothermal ore forming fluid systems during the ketilidian orogeny as well as to the development of extreme rock compositions within the gardar alkaline igneous province

on the seasonal eddy variability in the kuroshio extension abstractusing a recently developed tool multiscale window transform mwt and the mwt based canonical energy transfer theory this study investigates the seasonal eddy variability in the kuroshio

cenozoic plate reconstruction of southeast asia abstract the india eurasia collision alone set up a series of chain reactions and caused the formation and destruction of sedimentary basins within the domain of the collision belt changes in the rate and angle of convergence between the india and eurasia plates reflect different stages of tectonic development in southeast asia for example extrusion of the indochina block induced the consumption of the pre existing proto south china sea along northeastern kalimantan and led to the eventual opening of the south china sea along the south china margin subsequent motions of the sino burma thailand malay peninsula sumatra and kalimantan blocks have produced a succession of basins stretching from north sumatra to central thailand and on to the natuna area we present reconstructions of the southeast asia region at 60 ma 50 ma 40 ma 30 ma 20 ma 15 ma 10 ma and 5 ma it is clear from the reconstructions that the impact between greater india and southeast asia took place in the northwestern part of southeast asia the duration for the impact was probably from the middle eocene to early miocene this timing is in good agreement with the dating of the main red river fault motion wu et al 1989 scharer et al 1990 since the impact between greater india and southeast asia was basically west of the burma block there is no reason to assume that the sumatra malay peninsula and kalimantan should extrude to the southeast first along the left laterally displaced mae ping and three pagodas fault zones as suggested by peltzer and tapponnier 1988 if the opening of the central thailand basins the gulf of thailand and the malay basin are taken into consideration a dextral megashear zone is required to compensate the relative motion between indochina and the malay peninsula this dextral megashear zone might even extend into western kalimantan and serve as a boundary between the indochina block and kalimantan

diagnosing the energy cascade in a model of the north atlantic spectral potential and kinetic energy densities and fluxes in horizontal wavenumber space are estimated in an eddy resolving model of the north atlantic in agreement to recent observational results near surface kinetic energy fluxes are negative over wide regions of the north atlantic indicative of an inverse energy cascade this inverse kinetic energy cascade is found over a wide depth range but both the spectral kinetic energy density and the corresponding flux show no clear dependency on rossby radius or rhines scale potential energy fluxes tend to be positive and show a direct potential energy cascade towards a scale which is related to the rossby radius in the subtropical north atlantic

sources of eddy kinetic energy in the labrador sea experiments with a suite of north atlantic general circulation models are used to examine the sources of eddy kinetic energy eke in the labrador sea a high resolution model version 112 quantitatively reproduces the observed signature a particular feature of the eke in the labrador sea is its pronounced seasonal cycle with a maximum intensity in early winter as already found in earlier studies based on altimeter data in contrast to a previously advanced hypothesis the seasonally varying eddy field is not related to a forcing by high frequency wind variations but can be explained by a seasonally modulated instability of the west greenland current wgc the main source of eke in the labrador sea is an energy transfer due to reynolds interaction work barotropic instability in a confined region near cape desolation where the wgc adjusts to a change in the topographic slope geostrophic contours tend to converge upstream of cape desolation such that the topographically guided wgc narrows as well and becomes barotropically unstable the eddies spawned from the wgc instability area dominating the eke in the interior labrador sea are predominantly anticyclonic with warm and saline cores in the upper kilometer of the water column while the few cyclones originating as well from the instability area show a more depth independent structure companion experiments with a model exhibit the strength of the wgc influenced by either changes in the wind stress or heat flux forcing as a leading factor determining seasonal to interannual changes of eke in the labrador sea

the depositional characteristics and oil potential of paleo pearl river delta systems in the pearl river mouth basin south china sea abstract delta systems in the zhuhai zhujiang and hanjiang formations are interpreted as having formed during periods of sea level rise from the late oligocene to mid miocene 30 10 5 my b p deltas in the zhuhai formation were developed in a shallow water environment on a sandy wave or fluvial dominated coasts thick and blanket like sandstones are common but mudstones are infrequent oil bearing zones have been found only in the upper part of the systems overlain by mudstone of the zhujiang formation deltas in the zhujiang formation are interpreted as having formed in a deeper water environment on sandy wave or fluvial dominated coasts carbonate platforms started growing on the dongsha massif as the sea level slowly rose the moderate sandstone mudstone ratio in the delta systems and a zone of secondary porosity in the carbonate rocks provide an excellent reservoir rock and seal rock for the basin deltas in the lower hanjiang formation are similar to those of the zhujiang formation but the upper part of the formation is interpreted as having formed in a shelf environment the thick shelf mudstone interbedded with offshore bar sandstones would be one of the better regional seal rocks in the study area no carbonate rock developed on the dongsha massif due to the rapid rise in sea level all delta systems from the zhuhai to the zhujiang formation are stacked in an onlap pattern indicating a more and more expanding marine transgression which was caused by eustatic sea level rise this marine transgression is almost unique and contrasts to the progradational offlap pattern of cenozoic delta systems in the gulf of mexico it resulted in thick sandstone deposits immature or poorly mature source rock and no ductile mudstones with no growth faults or rollover structures hydrocarbons generated from eocene oligocene lacustrine source rocks are trapped by drape structures related to local basement highs or by carbonate rock with secondary porosity most of the remaining undiscovered reserves in the basin will be found in non structural subtle traps especially stratigraphic traps

neotectonic regime on the passive continental margin of the northern south china sea abstract between 1989 and 1994 more than 6600 km of reflection seismic profiles were obtained in the south china sea off hong kong with the german research vessel sonne during cruises so 50b so 72a and so 95 a seismo stratigraphic interpretation of this data set leads to a new age assignment of the unconformity t0 which we place within the pleistocene both neogene unconformities t1 and t0 are generated by uplift of the dongsha rise and truncation of their overlying strata this uplift is caused by intrusion of magma into the upper crust our seismic profiles show plutons which have penetrated the sedimentary cover whereby their original stratification in the contact zone is eliminated these magmato tectonic events may be correlated to the two main collision phases between taiwan and the continental margin of east china 5 3 and 3 0 ma ago the collisional events subsequent to the nnw to wnw drift of taiwan transformed the compression into strike slip movements along the continental margin of southeastern china the accompanying stress regime is transtensional with subsidence of the cooling oceanic crust since the cessation of rifting and its consumption beneath the manila trench providing the extensional stress the strike slip movements remobilized many of the rift and drift faults providing pathways for magma ascent the tectonic framework of the northern south china sea is characterized by miocene faults trending ne sw these faults are scarce but are distributed throughout the study area pliocene faults striking ene wsw to ne sw are concentrated west of the dongsha islands and are mostly strike slip in character recent faults are generally oriented ne sw subparallel to the synrift faults they result in part from local uplifts where they are normal in character but strike slip motion also occurs most of the faults involve the basement and represent reactivated zones of weakness of the rift and drift phases

the origin of niobium and tantalum mineralization in the nechalacho ree deposit nwt canada the behavior of niobium and tantalum is poorly understood in rocks that have undergone significant hydrothermal alteration and niobium tantalum minerals of hydrothermal origin are rarely mentioned in the literature consequently the mobility of these critical metals although widely considered to be negligible has not been evaluated in this paper we present the results of a study of the genesis of niobium and tantalum mineralization in the nechalacho rare metal deposit northwest territories canada which contains one of the largest known resources of these metals in rocks that have undergone intense hydrothermal alteration analyses and examination of samples using the electron microprobe has led to the identification of a variety of niobium and tantalum bearing minerals in the nechalacho deposit niobium bearing zircon columbite fe fergusonite y and samarskite y were identified in the ore zones of the deposit uranopyrochlore and columbite fe were found outside the ore zones and magmatic fluornatropyrochlore was shown to be the sole niobium tantalum mineral in relatively unaltered syenites below the basal ore zone based on the paragenetic relationships among the above minerals variations in the composition of the columbite group minerals as a function of location in the nechalacho layered suite and the distribution of niobium tantalum zirconium and uranium in the bulk rocks we have developed a model to explain the occurrence of niobium and tantalum in the nechalacho deposit the first step in the concentration of these elements was the crystallization of niobium and tantalum bearing zircon and eudialyte in the subhorizontal upper and basal ore zones respectively this was accompanied by the crystallization of magmatic columbite fe in the upper ore zone fergusonite y crystallized in the basal ore zone and also formed due to the breakdown of eudialyte outside the ore zones there was crystallization of pyrochlore and to a lesser extent magmatic columbite fe this step led to the development of strong spatial associations among niobium zirconium and uranium that are evident as strong positive correlations in the bulk rock concentrations of these elements at the meter scale during the ensuing intense and widespread hydrothermal alteration niobium was locally remobilized hydrothermal columbite fe and fergusonite y formed at the cores of altered zircon grains wholesale replacement of magmatic columbite fe and fergusonite y by hydrothermal anhedral crystals occurred in the two ore zones the estimated relative proportions of the sources of these minerals in the ore zones although varying to some extent because of a dependence on the amount of niobium mobilized from zircon is 40 60 outside the ore zones columbite fe and uranopyrochlore are the present manifestations of the former pyrochlore with the exception of magmatic fluornatropyrochlore in the fresher syenites below the basal ore zone and a single example of magmatic columbite fe in an upper ore zone sample all niobium and tantalum minerals have a hydrothermal origin as a result of this pervasive alteration

forced regressions in a sequence stratigraphic framework concepts examples and exploration significance sequence stratigraphic concepts suggest that stratal geometries develop and are largely controlled by changes in relative sea level on the shelf lowstand deposits which form during falls and subsequent stillstands of relative sea level can be recognized by the presence of an unconformity at the base the isolated and basinward position relative to the previous shoreline and the abrupt seaward translation of shallow water and shoreline facies into the basin across an unconformity surface this seaward translation of facies and shoreline regression in response to relative sea level lowering is termed a forced regression a forced regression is independent of variations of sediment flux and is in contrast with normal regressions that occur in response to excess sediment flux relative to space available on the shelf i e accommodation forced regressions commonly are associated with a zone of sedimentary bypass subaerial exposure and possible fluvial erosion between the newly formed and preceding shorelines certain shelf sands previously interpreted as offshore or mid shelf sand bodies thus can be reinterpreted as stranded lowstand shorelines associated with forced regressions this alternative interpretation has economic significance insofar as it suggests different subsurface correlations and reservoir geometries with the potential for development of new play types and enhanced recovery in o der fields examples of forced regression can be observed at a variety of scales and ages several such examples include the modern east coulee fan delta and the lower cretaceous viking formation in alberta canada the quaternary rhone delta and the quaternary hudson valley system

submarine volcanic mounds in the pearl river mouth basin northern south china sea a number of enigmatic km scale mound structures have been discovered in the baiyun sag of the pearl river mouth basin using high resolution 2d and 3d seismic data combined with multi beam bathymetry based on detailed seismic characterization we interpret these as sill fed volcanic mounds associated structures include igneous sills trans tensional faults lava flows and compactional drape folds the igneous intrusions and associated mounds were emplaced in the late early miocene c 18 5 ma or shortly thereafter constrained by the onlap relationship between the mounds and their overburden the volcanic mounds are preferentially developed above or adjacent to basement highs indicating a structural control on the igneous plumbing system we propose that the fractures and tectonic faults above the raised basement follow pre existing zones of weakness and may have acted as feeding conduits for the magmatic material the discovery of the early miocene igneous province has important implications for the understanding of the evolution of the pearl river mouth basin and for regional hydrocarbon prospectivity c 2014 elsevier b v all rights reserved

decadal variability of the kuroshio extension observations and an eddy resolving model hindcast abstract low frequency variability of the kuroshio extension ke is studied using observations and a multidecadal 1950 2003 hindcast by a high resolution 0 1 eddy resolving global ocean general circulation model for the earth simulator ofes in both the ofes hindcast and satellite altimeter observations low frequency sea surface height ssh variability in the north pacific is high near the ke front an empirical orthogonal function eof analysis indicates that much of the ssh variability in the western north pacific east of japan is explained by two modes with meridional structures tightly trapped along the ke front the first mode represents a southward shift and to a lesser degree an acceleration of the ke jet associated with the 1976 77 shift in basin scale winds the second mode reflects quasi decadal variations in the intensity of the ke jet both the spatial structure and time series of these modes derived from the hindcast are in close agreement with observations a linear rossby wave

episodic rifting and subsidence in the south china sea the south china sea experienced at least three stages of rifting and two intervening stages of sea floor spreading since the early cretaceous its evolution can be described by an episodic model of tectonism one of thermal cooling and subsidence pulsed by temporally and spatially confined heating events analysis of regional geologic and geophysical data suggests episodes of rifting and associated thermal activities initiated during the late cretaceous the late eocene and the late early miocene the rift system corresponding to the first episode trends northeast southwest whereas those of the second and third trend east west these two trends coincide with the orientations of the major tectonic lineations within the basin age estimates from heat flow and bathymetric data suggest the oceanic crust in the southwest subbasin is considerably older 55 ma than that in the northwest 35 36 ma or east 32 ma subbasins the episodic tectonic model is supported by basin subsidence analysis subsidence especially subsidence rate curves derived from the regional well data demonstrates that unlike a classic atlantic passive margin thermal subsidence in the south china sea was punctuated by rapid subsidence events which are chronologically consistent with the rifting episodes in terms of hydrocarbon potential the episodes of rifting and drifting would be conducive to the development of overprinted structures and the deposition of several discrete transgressive packages of source rocks and reservoirs separated by widespread unconformities the thermal maturity of sedimentary organic matter affected by episodic rifting and subsidence may be greater than expected on a purely passive margin of equivalent age that had not experienced repeated heating

hemipelagic sediment accumulation rates in the south china sea related to late quaternary sea level changes sediments of 13 piston cores from opposite continental slopes of the south china sea off southern china and sabah northern borneo were analyzed by sedimentological methods and dated by oxygen isotope stratigraphy sediments mostly consist of hemipelagic clay with 20 carbonate off sabah and 40 off china we calculated terrigenous and carbonate accumulation rates for up to 11 time slices from the holocene to oxygen isotope stage 6 terrigenous accumulation rates generally increase with water depth and reach a maximum at the middle slope off sabah and at the lower continental slope off china during glacial and interglacial times this distribution pattern did not markedly change despite an increase of accumulation rates for glacial periods by a factor of 2 to 5 compared to interglacial periods rates are negatively correlated with positions of sea level which controls the partition of fluviatile terrigenous material for deposition on shelf slope and abyssal plain carbonate accumulation rates are higher off china by a factor of 2 compared to sabah probably indicating higher calcareous plankton productivity

from mantle to motzfeldt a genetic model for syenite hosted ta nb mineralisation abstract a genetic model for the motzfeldt tantalum niobium rich syenite in south west greenland considered to be one of the world s largest ta prospects is presented the motzfeldt primary magma formed early in regional gardar 1273 6 ma rifting isotope signatures indicate that the hf had multiple sources involving juvenile gardar hf mixed with older palaeoproterozoic or archaean hf we infer that other high field strength elements hfse similarly had multiple sources the magma differentiated in the crust and ascended before emplacement at the regional unconformity between ketilidian basement and eriksfjord supracrustals the hfse rich magmas crystallised ta rich pyrochlore which formed pyrochlore rich crystal mushes and it is these pyrochlore rich horizons rich in ta and nb that are the focus of exploration the roof zone chilled and repeated sheeting at the roof provided a complex suite of cross cutting syenite variants including pyrochlore microsyenite in a hot sheeted roof model the area was subject to hydrothermal alteration which recrystallized alkali feldspar to coarse perthite and modified the mafic minerals to hematite creating the friable and striking pink nature of the motzfeldt so centre carbon and oxygen isotope investigation of carbonate constrains fluid evolution and shows that carbonate is primarily mantle derived but late stage hydrothermal alteration moved the oxygen isotopes towards more positive values up to 21 the hydrothermal fluid was exceptionally fluorine rich and mobilised many elements including u and pb but did not transport hfse such as ta hf and nb although the u and pb content of the pyrochlore was enhanced by the fluid the hfse contents remained unchanged and therefore hf isotopes were unaffected by fluid interaction while the effect on hydrothermal alteration on the visual appearance of the rock is striking magmatic processes concentrated hfse including ta and the hydrothermal phase has not altered the grade exploration for hfse mineralisation commonly relies on airborne radiometric surveying which is particularly sensitive to the presence of u th a crucial lesson from motzfeldt is that the best target is unaltered pyrochlore which was identified less easily by radiometric survey careful petrological mineral studies are necessary before airborne survey data can be fully interpreted

spreading direction in the central south china sea recent work1 2 indicates that the south china sea is an atlantictype marginal basin of late tertiary age magnetic anomalies in the eastern part of the sea are consistent with seafloor spreading directed approximately north south1 2 we present here a new morphostructural study based on coupled seabeam mapping and single channel seismic reflection profiling which reveals dominant normal fault scarps striking n50 e between 113 and 119 e longitude near the axis of this basin such a structural fabric implies a nw se spreading direction at least in the 150 200 km wide axial region of the south china sea and places new constraints on geodynamic models for the formation of this basin in the tectonic and palaeogeographic framework of south east asia and the south west pacific

biotite equilibria and fluid circulation in the klokken intrusion chemical variation in biotite from the kjokken gabbro syenite intrusion in the proterozoic gardar province in south greenland has been investigated by electron probe and for f and li ion microprobe most mica occurs in small amounts as fringes on ilmenomagnetite or fayalite rarely as an intercumulus or poikilitic phase the micas range continuously from phlog70ann30 in a gabbro to phlog4ann96 in the most evolved slightly persilicic and peralkaline syenite in the syenites fe mg partitioning between biotite and olivine can be described by a single distribution coefficient k6 xfi x x xf 3 suggesting that these reactant phases mix ideally at the reaction t experimental data for fe mg exchange via aqueous chloride solutions schulien 1980 imply low t 320 q f was absent in the experiments and may significantly affect the exchange equilibrium k6 in the gabbros is 1 consistent with equilibrium via a fluid depleted in f because of crystallization of large amounts of amphibole al mn and ti vary regularly throughout the series and can be used as markers of cryptic variation in the layered syenites al si 22 o is always in the range 7 7 7 85 a1 a1 si decreases from o31 in gabbros to 0 25 in the most fe rich micas li is always 300 c subsolidus even when texturally intercumulus stable isotope data are consistent with the separation and retention of a deuteric fluid during the final stage of magmatic crystallization klokken was not generally subject to the pervasive long range in both distance and time dydrothermal interactions demonstrated in

a routine high precision method for lu hf isotope geochemistry and chronology a method for chemical separation of lu and hf from rock meteorite and mineral samples is described together with a much improved mass spectrometric running technique for hf this allows i geo and cosmochronology using the176lu 176hf decay scheme and ii geochemical studies of planetary processes in the earth and moon chemical yields for the three stage ion exchange column procedure average 90 for hf chemical blanks are 0 2 ng for lu and hf from 1 g of hf a total ion current of 0 5 10 11 ampere can be maintained for 3 5 h yielding 0 01 0 03 precision on the ratio176hf 177hf normalisation to179hf 177hf 0 7325 is used extensive results for the johnson matthey hf standard jmc 475 are presented and this sample is urged as an international mass spectrometric standard suitable aliquots prepared from a single batch of jmc 475 are available from denver lu hf analyses of the standard rocks bcr 1 and jb 1 are given the potential of the lu hf method in isotope geochemistry is assessed

geochemistry of pyrochlore minerals from the motzfeldt center south greenland the mineralogy of a syenite hosted ta nb deposit pyrochlore minerals are common accessory phases in the syenite and nepheline syenite rocks of the motzfeldt alkaline center gardar province south greenland and are of important economic interest due to their exceptional ability to host various high field strength elements in this study pyrochlore from two distinct intrusive units within the motzfeldt center have been studied the largely homogeneous syenite and nepheline syenite rocks of the flinks dal formation host oscillatory and sector zoned pyrochlore which have experienced minor alteration in the presence of high temperature dominantly juvenile magmatic fluids alteration is characterized by variable decrease in the na ca and f contents and addition of sr and k accompanied by introduction of a and y site vacancies pyrochlore from the more heterogeneous and intensely altered syenite rocks of the motzfeldt so formation are pervasively altered through interaction with lower temperature evolved hydrothermal fluids during this phase of alteration cations are preferentially leached from the a and y sites accompanied by progressively increasing hydration in both formations the proportion of b site cations remains unaltered regardless of the degree of alteration the alteration encoded in the pyrochlores of the motzfeldt center records the different hydrothermal conditions the two formations experienced during the subsolidus showing how evolution of fluids within one intrusive unit can vary both spatially and temporally

quaternary sea level change on the continental shelf of hong kong high resolution seismic reflection profiles and continuously sampled boreholes have been used to investigate the quaternary offshore sequence that overlies weathered bedrock in hong kong four formations have been recognized the lowermost chek lap kok formation comprises dominantly fluvial sand and mud much of which probably accumulated prior to 130 000 years bp during sea level lowstands of middle pleistocene oxygen isotope stage 6 age and earlier the upper surface of the chek lap kok formation is defined by a fluvial tidal entrenchment surface that is overlain by transgressive fine grained marine sediments of the sham wat formation these were deposited during the eemian interglacial stage 5c at a time when sea level was similar to that of today in southeastern hong kong waters a late weichselian stage 5c ravinement surface is overlain by submerged shoreface sands succeeded by a back stepping wedge of marine sediments that comprise the waglan formation fluvial tidal entrenchment of the top of this formation occurred prior to the deposition of the uppermost dominantly marine hang hau formation deposited during the late weichselian to holocene transgression the main phase of which is represented by a ravinement surface

metasomatic overprinting by juvenile igneous fluids igdlerfigsalik south greenland the late igdlerfigsalik centre part of the igaliko nepheline syenite complex in the gardar province s greenland is bounded to the n and e by compositionally similar earlier syenites forming the early igdlerfigsalik and south qoroq centres in a circa 1 km wide zone parallel to its contact with late igdlerfigsalik the south qoroq centre shows recrystallisation and alteration of mafic phases south qoroq therefore comprises two zones termed the unaltered and the recrystallised zones a study of the biotites from the rocks of the area of the present study has demonstrated variations in biotite chemistry notably variations in elements inferred to reside on the octahedral and hydroxyl sites samples were chosen to provide a representative selection from each centre avoiding pegmatites and late stage veins electron probe microanalyses demonstrate little cl in these biotites fluorine contents of some biotites can be demonstrated to vary with fe fe mg and octahedral al and ti statistical analysis of the data sets as a whole however does not demonstrate simple relationships between fluorine content and these parameters and more complex crystallographic controls over fluorine uptake are inferred despite these variations the relative fluorine contents characteristic of each centre can be determined which it is believed reflect the characteristic f activity of fluids associated with each period of magmatism in south qoroq the unaltered zone has a distinctive f content in biotite reflecting the original f content of fluids associated with south qoroq magmatism however in the recrystallised zone the f contents are distinct more closely resembling f contents characteristic of late igdlerfigsalik rocks reaction between a fluorine rich younger fluid and older fluorine poor rocks is inferred despite evidence in the micas for fluid rock interaction whole rock chemical changes are irregular in nature and appear not to conform to simple trends mass balance equations are therefore unable to predict the levels of fluid rock interaction similar exchange between late stage fluids from younger centres and pre existing rocks may be commonplace in igneous plutonic environments and fluorine in micas may provide a relatively sensitive guide to fluid rock interactions

evaluation and models of cenozoic sedimentation in the south china sea abstract the south china sea is a marginal basin with the most complex geological structures in the west pacific region and is characterized by the extensive distribution large thickness diversity and complicated evolution of the cenozoic sediments the author believes that studies of the sedimentary features and evolution of the cenozoic are fundamental to understanding the cenozoic evolution of the south china sea and that the definition of sedimentation models will be helpful in inferring the basin development at early stages thus defining the basin patterns and guiding hydrocarbon exploration this article based on data obtained from hydrocarbon exploration in the south china sea together with related references analyses the characteristics of cenozoic sediments in the south china sea and infers their evolution and models of formation the cenozoic in the south china sea is divided into eight sedimentary provinces a brief introduction is given to changes in sedimentary environments of the south china sea during the eocene late oligocene early miocene middle late miocene and pliocene quaternary the line linking taiwan and natuna as this article points out was the sea land boundary of the south china sea in the early cenozoic the transgression cycle is dominant west of this line while regression prevails to the east during the cenozoic five different patterns of sedimentation existed in the south china sea offshore lake shallow sea deep sea transgression regression and platform the former two belong to the lower cycle whilst the latter three to the upper cycle the time and spatial variations in the sedimentary sequence of these patterns is also discussed

independent ages of magmatic and hydrothermal activity in alkaline igneous rocks the motzfeldt centre gardar province south greenland the motzfeldt centre is one of four major alkaline centres belonging to the igaliko complex part of the mid proterozoic gardar province of south greenland motzfeldt comprises syenites and nepheline syenites displaying complex magmatic and subsolidus histories ta nb and ree rich zones are associated with a pervasive hydrothermal alteration process in the north and east of the complex part of a subdivision of the centre called the motzfeldt so formation msf the zircons from the msf show textures that are both magmatic and altered whereas the textures of pyrochlore have a predominantly subsolidus chemistry we compare and contrast the radiogenic isotope geochemistry of the zircon and pyrochlore to obtain independent age estimates of the magmatic and hydrothermal episodes selected analyses of magmatic zircons are concordant with an age of 1 273 6 ma altered zircons are normally discordant with one intercept at 1 261 28 ma and the other at 349 49 ma this younger age would appear on face value to date the hydrothermal event at motzfeldt to 900 ma after the magmatism however the pb pb isotope systematics from altered pyrochlore define an isochron age of 1 267 6 ma for isotopic closure of the pyrochlore following alteration during the subsolidus there is no known magmatic event in southern greenland at 350 ma and discordant points have high common lead we therefore infer that the younger intercept age is spurious the overlap between the magmatic u pb zircon and the pb pb pyrochlore age suggests that alteration of the motzfeldt centre occurred shortly after magmatism

spectral energy fluxes in geostrophic turbulence implications for ocean energetics abstract the energy pathways in geostrophic turbulence are explored using a two layer flat bottom f plane quasigeostrophic model forced by an imposed horizontally homogenous baroclinically unstable mean flow and damped by bottom ekman friction a systematic presentation of the spectral energy fluxes the mean flow forcing and dissipation terms allows for a comprehensive understanding of the sources and sinks for baroclinic and barotropic energy as a function of length scale the key new result is a robust inverse cascade of kinetic energy for both the baroclinic mode and the upper layer this is consistent with recent observations of satellite altimeter data over the south pacific ocean the well known forward cascade of baroclinic potential and total energy was found to be very robust decomposing the spectral fluxes into contributions from different terms provided further insight the inverse baroclinic kinetic energy cascade is driven mostly by an efficient interaction between the baroclinic velo

deep penetration seismic soundings across the northern margin of the south china sea twenty reversed two ship expanding spread profiles esps with maximum source receiver offsets of 100 km were collected in three transects across the rifted northern margin of the south china sea source receiver offset versus two way travel time x t data were mapped into the intercept time versus ray parameter p domain and velocity depth solutions were obtained by a combination of sum inversion in the p domain and ray tracing in both the p and x t domains arrivals from the moho were detected on 17 of the esps the depths to moho determined for individual esp interpretations have reproducibilities of 0 1 km to 3 km in most cases the moho depth has been determined to within 1 5 km moho depths determined in this investigation represent a significant improvement over previous estimates of moho along the margin from gravity data variations in present day crustal thickness measured from top of prerift basement to moho are one measure of the amount and nature of the crustal thinning associated with the rifting of continental crust preceding the formation of the adjacent south china sea basin the esp interpretations reveal that across the eastern portion of the south china margin the crust appears to thin more or less continuously toward the continent ocean boundary in the west esp interpretations also show a general trend of seaward crustal thinning but in addition indicate at least two instances of focused localized crustal thinning crustal velocities and the relative proportion of upper crust vp 6 4 km s are used to identify areas of the south china margin with similar and contrasting crustal structures variations in these properties are believed to result primarily from contrasting prerift crustal structure across the margin however magmatic underplating during rifting depth dependent extension and pleistocene igneous intrusions may also have contributed to the variations in present crustal structure reliable information about variations in crustal thickness and velocity structure across and along the south china margin is an important prerequisite to understanding better the nature of the spatially variable rifting processes which dominated the formation of this margin

paleo oceanographic and tectonic settings of early miocene reefs and associated carbonates of offshore southeast asia the late oligocene to early middle miocene was a period of widespread reef and associated carbonate deposition over a wide latitudinal range in the offshore region of southeast asia a generally rising eustatic sea level during this period allowed the accumulation of thick reefal units an expansion of the coral algal regional facies belt north to japan and south to new zealand occurred during the early miocene as the result of a reduced oceanic latitudinal temperature gradient an episode of enhanced organic carbon burial is reflected in a positive dgr13c excursion from 17 5 to 13 5 ma increasing paleo oceanographic equability may have resulted in reduced ocean circulation with the resultant development of an expanded oxygen minimum zone marine oil prone or anic carbon was deposited in silled anoxic basins both bounded by and within island arc systems a combination of tectonic and paleo oceanographic factors therefore created conditions that favored contemporaneous deposition of organic carbon rich source beds and reef reservoirs during the latest early to early middle miocene paleogeographic and facies reconstructions for an 18 m y interval indicate that deposition occurred in three tectonic settings 1 passive continental margins 2 convergent plate boundaries and 3 obliquely convergent plate boundaries in all these settings the vertical motion histories of fault bounded blocks and of larger tectonic elements within which they are contained directly controlled the geographical distribution of carbonate buildups their scal and morphology duration diagenesis and relationship to siliciclastics

gas hydrates associated with gas chimneys in fine grained sediments of the northern south china sea drilling for gas hydrates at the northern continental margin of the south china sea scs provides a unique insight into the formation of the gas hydrate system in fine grained sediments even though most high concentrations of hydrates are found in coarse sediments detailed studies of 3d seismic data from a deep water basin baiyun depression of this region reveal the presence of overpressured fluid flow mostly manifested in gas chimneys gas chimneys are commonly characterized by disrupted reflections dr dim amplitude anomalies da and enhanced reflections er on conventional seismic profiles gas chimneys are also characterized by chaotic low continuity and low frequency on instantaneous frequency and instantaneous amplitude profiles gas hydrates and a prominent bsr were discovered in the region of gas chimney occurrence logging data and sample analyses from drill holes over the chimney structures indicate close relationships between active fluid flow and the formation and accumulation of gas hydrates our results document that gas chimneys consisting of a connected network of fractures provide a passageway along which fluids ascend beneath the gas hydrate stability zone ghsz for hydrate formation in fine grained sediments of the northern south china sea fluids accumulate in uppermost part of the slope where they are trapped beneath the prograding submarine delta sequence which is not permeable enough for fluids to migrate through gas charged fluids may originate from deep seated hydrocarbon reservoirs which are indicated by the molecular and isotopic signatures of gases in gas hydrates occurrence zone we suppose that the fractures extend into the ghsz creating a space for hydrate condensation in the fine grained sediments of the slope gas chimneys may account for the overpressured fluid activity and most likely the gas hydrate enrichment in the northern scs c 2012 elsevier b v all rights reserved

beyond goce for the ocean circulation estimate synergetic use of altimetry gravimetry and in situ data provides new insight into geostrophic and ekman currents accurate estimate of ocean surface currents is both a challenging issue and a growing end users requirement in this paper ocean currents are calculated at two levels surface and 15 m depth as the sum of the geostrophic and ekman components first a new global 14 mean dynamic topography called the cnes cls13 mdt has been calculated and is now available for use by the oceanographic community by exploiting information from surface drifters and argo floats the new mdt resolves spatial scales beyond the resolution permitted by the recent gravity and ocean circulation experiment goce geoid models 125 km associated mean geostrophic speeds in strong currents are increased by 200 on average compared to goce based mean currents in addition for the first time a two level monthly empirical ekman model that samples a spiral like behavior is estimated we show that combining both pieces of information leads to improved ocean currents compared to other existing observed products

seasonal and interannual modulation of the eddy kinetic energy in the caribbean sea abstractvariability of the mesoscale eddy field in the caribbean sea is analyzed over the period 1993 2009 using geostrophic anomalies derived from altimeter data and a high resolution regional model the colombia basin presents the largest values of eddy kinetic energy eke and its semiannual cycle with a main peak in august october and a secondary peak in february march is the dominant feature in the whole caribbean eke cycle the analysis of energy conversion terms between low frequency currents and eddies explains these peaks by enhanced baroclinic and barotropic instabilities in response to seasonally varying currents in the region of the guajira peninsula the semiannual acceleration of the atmospheric caribbean low level jet intensifies the southern caribbean current scc twice a year in this region together with its vertical and horizontal velocity shears the asymmetry of the eke seasonal cycle in the colombia basin is explained by a summer peak in the annual cycle of the whole scc numeric

biotites as indicators of fluorine fugacities in late stage magmatic fluids the gardar province of south greenland the major element chemistry and fluorine contents of biotites from the gardar alkaline province of south greenland provide an insight into the f contents of late stage fluids associated with the magmatism biotites were taken from composite intrusions ranging from alkali gabbro to syenites nepheline syenites and alkali granites in each complex they show a large range of fe fe mg from 02 to 1 and exhibit strong fe f avoidance there is considerable variation in ffor any value of fe fe mg but for each centre maximum f values plotted against fe fe mg define a nearly straight line of characteristic slope towards low or zero f at pure annite micas in the sio2 undersaturated centres have higher f contents than those from oversaturated centres cl is low 0 69 wt except in the kungnat intrusion where it reaches 1 4 wt phase equilibrium and textural considerations suggest that most or all biotites grew subsolidus in a pervasive deuteric fluid 5i8o values suggest that these fluids were largely magmatic in character and that extensive reactions with envelope fluids did not occur metasomatic resetting of f in biotites in early intrusive units in the aureole of later units can be demonstrated experimental data of munoz mineralogical society of america reviews in mineralogy 13 469 494 1984 were used to calculate families of curves showing variation in f with fe fe mg for biotites in equilibrium with fluids of fixed fugacity ratio i hf i h2o at fixed p andt the resulting curves cut sharply across the maximum fluorine lines observed in the natural examples as it seems highly unlikely that changes in fluid composition andt acting together could produce the observed linear relationship we conclude that the partitioning of f between fluid and mica in the plutonic environment is not well modelled by the experiments possible explanations are short range order sro of fe and mg on octahedral sites in biotite mason canadian mineralogist 30 343 354 1992 or effects resulting from different f speciation in alkaline fluids if perfect fe f avoidance is assumed fe mg sro can increase maximum f content the f levels seen in the silica saturated centres are broadly consistent with a cooling rate related control it is possible that the higher f in biotites in the undersaturated centres reflects different spedation in the fluid rather than higher f contents with strongly bound sif complexes more common

stratigraphic organization of late pleistocene deposits of the western part of the golfe du lion shelf languedoc shelf western mediterranean sea using high resolution seismic and core data detailed analysis of shallow penetration single channel seismic data integrated with piston core data reveals that the stratigraphic architecture on the rhone shelf of the western mediterranean sea is characterized by a complex stratigraphy comprising both the regressive and transgressive parts of late pleistocene depositional sequences several cycles of deposition are observed and are interpreted to be associated with fourth or possibly fifth order cycles of relative change of sea level the regressive parts of the sequence are inferred to have been deposited either during late highstand or during periods of relative fall of sea level these deposits are characterized in some instances by discrete downstepping wedges and internal downward shift surfaces however in other instances this evidence is not present the transgressive parts of the depositional sequences are characterized by backstepping wedges and isolated sand bars in general these types of deposits are more common on the western part of the rhone shelf and are largely absent on the extreme eastern part of the shelf the transgressive deposits seem to be preferentially preserved at both inner and outer shelf locations and less so in the middle shelf the exception to this is the area near the rhone delta depocenter where transgressive deposits are observed across the entire shelf key surfaces separating stratigraphic units include ravinement surfaces downlap surfaces and subaerially formed erosional surfaces these stratal discontinuity surfaces constitute the basis for analysis of the stratigraphic architecture this area is dominated by seismic reflection geometries suggesting a high energy depositional environment relatively steeply dipping seismic reflections bounded by horizontal to irregular erosional surfaces characterize most of the upper pleistocene section in this area the high energy seismic facies correspond to three types of deposits 1 thick regressive sands of lobate delta front origin 2 retrogradational beach barriers overlying the regressive wedge on the outer to middle shelf and 3 late transgressive beach sands and ridges observed at the inner shelf the stratigraphic complexity illustrated here is likely analogous to similar although commonly undetected complexity that characterizes petroleum fields in shallow shelf settings a variety of geomorphic elements have been interpreted here these include transgressive sand bars wave dominated distributary mouth bars recurved spits isolated shelf edge shoreface beaches and distributary channels these elements are consistent with an interpretation of a depositional environment characterized by wave dominated delta deposition the morphology of the delta in the eastern part of the shelf i e near the depocenter seems to be consistent from the outer to inner shelf location suggesting that the position of the shoreline relative to the shelf edge and the presence of submerged shelf outboard of the shoreline had only minor impact on deltaic deposition moreover climatic change and changes of fluvial discharge that likely characterized this area during the end page 119 late pleistocene similarly had only minor effect on delta morphology

timing of proterozoic magmatism in the gardar province southern greenland the gardar province in southern greenland is believed to have experienced three episodes of rifting all associated with the extrusion of large volumes of alkalic magma a nepheline syenite of the motzfeldt center yields a u pb apatite age of 1 35 0 01 ga an augite syenite from the ilimaussaq complex yields a sm nd pyroxene alkali feldspar magnetite age of 1 13 0 05 ga on the basis of field relationships the eriksfjord formation lavas have been interpreted as the oldest manifestation of gardar magmatism sm nd plagioclase pyroxene wholerock ages of 1 17 0 03 ga and 1 20 0 03 ga for the middle member of the eriksfjord formation however indicate that these lavas may be part of the youngest magmatic activity the available chronological data indicate that the gardar province was active for at least 200 m y from 1 35 to 1 12 ga it is difficult to reconcile this protracted history with plume models for the genesis of such alkaline flood basalt provinces

fluoride silicate melt immiscibility and its role in ree ore formation evidence from the strange lake rare metal deposit quebec labrador canada pegmatites and adjacent subsolvus granites two alkali feldspars of the mid proterozoic strange lake pluton quebec labrador canada host potentially economic concentrations of high field strength elements hfse including the rare earth elements ree zirconium and niobium previous studies have proposed that these concentrations were the result of a com bination of extreme fractionation of a peralkaline granitic magma and later hydrothermal remobilization however the recent discovery of melt inclusions which after heating to 900 or 950 c quench to immiscible fluoride and silicate glasses suggests an additional mechanism of hfse concentration crystallized melt inclusions are common in quartz phenocrysts of the early hypersolvus and transsolvus granite after heating four types of inclusions were discerned type 1 inclusions quench to a single silicate glass containing a high concen tration of zr nb and ti quenching of type 2 inclusions produces a zr nb ti rich silicate glass containing a globule of calcium rich fluoride glass with a high concentration of the ree the third inclusion type is similar to type 2 except that the calcium rich fluoride glass contains a globule of ree fluoride glass up to 50 wt total ree type 4 inclusions contain calcium fluoride glass with multiple silicate globules we propose that during or soon after emplacement the early granitic magma exsolved a calcium fluoride melt into which rare earth elements ree partitioned preferentially the conjugate silicate melt was consequently depleted in ca and the ree and enriched in zr nb and ti crystallization of the fluoride melt occurred late in the crystallization history of the silicate magma allowing it to accumulate in the volatile rich residual magma that formed the pegmatites this played a major role in the extreme enrichment of the pegmatites in ca f and ree crystallization of the pegmatites proceeded inwards from an outer zone in which feldspars quartz arfvedsonite and zirconosilicate minerals dominate to a core where the immiscible fluoride liquid collected and crystallized fluorite and ree minerals fluid exsolved from the silicate melt reacted with the products of both the silicate and fluoride melts remobilizing most of the hfse including the ree this study reports a rare example of silicate fluoride melt immiscibility and the first in which such immiscibility played a role in concentrating the ree to potentially economic levels 2014 elsevier ltd all rights reserved

plio quaternary sedimentation processes and neotectonics of the northern continental margin of the south china sea abstract analyses of over 6600 km of reflection seismic profiles on the northern continental margin of the south china sea permit the recognition of four quaternary high frequency type 1 sequences of the 4th order deposited during the past ca 690 kyr at the present day shelf edge only lowstand systems tracts characterised by a prograding clinoformal internal reflection pattern are preserved the prograding complexes can be considered as regressive units accumulated during relative sea level falls they exhibit internal discontinuities which might point to minor sea level fluctuations of the 5th order a preliminary regional relative sea level curve for the past 630 kyr is established using the present positions of the delta fronts mapped the neotectonics curve derived by subtracting eustatic sea level changes from the relative sea level curve shows that the depths of the delta fronts today are controlled primarily by regional tectonic movements and the global sea level our seismo stratigraphic interpretation documents that the area off hong kong and around the dongsha islands experienced two uplift episodes during the past 5 ma namely at the miocene pliocene boundary and at the end of the lower middle pleistocene respectively these uplift events which are centred on the dongsha rise led to its subaerial exposure and to the erosion of the pliocene and most of the pleistocene strata the change from thermal subsidence of the continental margin initiated at the end of the drift phase to the phase of magmato tectonic uplift was caused by a reorientation of the tectonic regime the recent depositional environment on the northern continental margin of the south china sea is dominated by sediment accumulation within the inner shelf and the zhujiang pearl river estuary the outer shelf and upper slope especially around the dongsha islands are characterised by bypass of terrigenous material the sedimentary column in the deepsea basin has a thickness of more than 2 km and comprises 14 depositional units starting with terrestrial rift deposits it overlies oceanic as well as transitional crust

on the sedimentological origin of down core variations of bulk sedimentary nitrogen isotope ratios 1 the bulk sedimentary nitrogen isotopic composition of two cores from nearby sites on the northern slope of the south china sea site 17940 and ocean drilling program odp site 1144 differs by up to 2 during the last glacial period given their close proximity both core sites are located in the same biogeographic zone and nutrient regime and it is thus unlikely that this offset is due to a true gradient in surface ocean conditions in an attempt to resolve this offset we have investigated the possible effects of two sedimentological parameters that can affect bulk sedimentary 15n namely the variable contribution of inorganic n to bulk n in the sediment and the grain size dependence of bulk 15n we find that neither effect singly or in combination is sufficient to explain the significant 15n offset between the two down core records by elimination the most likely explanation for the observed discrepancy is a different origin of both the organic and inorganic nitrogen at each site this study adds to the growing body of evidence highlighting the complex nature and origin of the sedimentary components in sediment drifts such as odp site 1144

tectonic characteristics and evolution history of the pearl river mouth basin abstract on the basis of the new understandings from tens of thousand of kilometres of geophysical material and over 60 exploration and evaluation wells providing data on the pearl river mouth basin prmb this paper analyses the special tectonic position of the prmb where three major plates i e the eurasian the pacific and the indo australian plates meet and interact the characteristics of the basin geological structure and its tectonic evolution are also discussed situated on continental and transitional crust the prmb is a mesozoic cenozoic oil and gas bearing basin developed on caledonian folding basement which was reformed during the mesozoic in the process of its formation and evolution the prmb underwent extension slight compression and re extension with the eruption of intermediate acid and basic magma meanwhile it formed double structural layers with faulting below and depression above and sediments were laid down with marine facies following continental facies hydrocarbons accumulated from continental source rocks in the marine reservoir rocks by using a fracture structure model of the uplift and depression the mechanism of the prmb and its evolution history have been interpreted

instability of the north pacific subtropical countercurrent abstractthe north pacific subtropical countercurrent stcc has a weak eastward velocity near the surface but the region is populated with eddies studies have shown that the stcc is baroclinically unstable with a peak growth rate of 0 015 day 1 in march and the 60 day growth time has been used to explain the peak eddy kinetic energy eke in may observed from satellites it is argued here that this growth time from previously published normal mode instability analyses is too slow growth rates calculated from an initial value problem without the normal mode assumption are found to be 1 5 to 2 times faster and at shorter wavelengths due to the existence of i nonmodal solutions and ii sea surface temperature front in the mixed layer in winter at interannual time scales it is shown that because of rapid surface adjustments the stcc geostrophic shear hence also the instability growth is approximately in phase with surface forcing leading to eke modulation that peaks approximately 10 months later

structure stratigraphy and basin subsidence of tertiary basins along the chinese southeastern continental margin abstract in southeastern china offshore tertiary basins extend along the broad continental shelf from taiwan to hainan island these basins share similar characteristics of structure stratigraphy and tectonics based on their age and tectonic framework these tertiary basins can be divided into paleogene basins and neogene basins however observations of extensional structures indicate that the paleogene basins are rift basins with predominant structural features of ne sw trending half grabens and fault blocks on a regional scale these half grabens and adjacent uplifts represent a horst and graben structural style neogene basins are downwarp basins lying on the tilting continental shelf upper tertiary sequences are relatively undeformed but locally exhibit minor pliocene pleistocene folding and faulting seismic stratigraphy and well data indicate that the early tertiary strata are commonly tilted and were structurally disturbed as nonmarine to marginal marine facies that were deposited in the wedge shaped half grabens late tertiary strata are generally undisturbed marine facies which accumulated in the enlarged downwarp basins overlying the infilled half grabens the tectonic history of these basins shows two stages of basin subsidence first early basement rifting and basin subsidence accompanying displacement along the border faults formed the half grabens which received sediments in the late cretaceous to middle eocene second late thermal subsidence owing to cooling of the continental crust predominated and resulted in a tilting and subsiding continental shelf upon which relatively flat marine facies were deposited in the late tertiary

shallow anatomy of a continent ocean transition zone in the northern south china sea from multichannel seismic data the cenozoic tectonic evolution of the south china sea is reflected in diverse tectonic processes including continental rifting seafloor spreading subduction terrane collision and strike slip fault movement a continent ocean transition zone in the northern south china sea caused by the lithospheric extension when the continent underwent break up rifting and later seafloor spreading is clearly imaged in the multi channel seismic data presented in this study the morphological units of the continent ocean transition zone are the rift depression the volcanic zone and tilted fault blocks the volcanic zone represents a highest extension zone within the continent ocean transition zone and is mainly distributed in the southern slope uplift zone along the northern passive margin of the south china sea the large listric normal faults bounding the dongsha rise and baiyun sag are evidenced in the seismic image the passive margin in the northern south china sea underwent the wide rift to narrow rift process in the transition zone as inferred from the relation between the surface heat flow and initial rifted crustal thickness the continent ocean transition zone in the continental margin of the south china sea is consistent with high heat flow zone average 90 mw m 2 observed in the previous heat flow measurements and at odp site 1148 and is manifested in a sharp change of the p wave velocity the rifted margin of the south china sea is a non typical magma poor passive margin or an intermediary form between the iberian type non volcanic and the greenland type volcanic margin compared to the world s typical passive margins c 2012 elsevier b v all rights reserved

circumpolar response of southern ocean eddy activity to a change in the southern annular mode 1 analysis of satellite altimeter data reveals anomalously high eddy kinetic energy eke in the antarctic circumpolar current acc during the period 2000 2002 around 2 3 years earlier 1998 the circumpolar eastward wind stress as quantified by the southern annular mode sam showed a significant positive peak and we have shown previously that the acc peaked around 1998 in response an eddy resolving ocean model is used to investigate the delay between wind forcing and the eddy response and demonstrates that the lag is due to the time taken to influence the deep circulation of the acc winds over the southern ocean have shown a strong climatic increase over the past few decades if this increase in winds is also reflected as an increase in eddy activity as our analysis suggests it might then the increased poleward heat flux may have played a significant role in the observed warming of the southern ocean citation meredith m p and a m hogg 2006 circumpolar response of southern ocean eddy activity to a change in the southern annular mode geophys res lett 33 l16608 doi 10 1029 2006gl026499

the influences of suspended load on the sedimentation in the coastal zones and continental shelves of china abstract the coastline of china intersects belts of subsidence and uplift river sediments mainly discharge to the coastal zones of subsidence belts where they contribute more than 90 of the total suspended load of river sediment transported into the coastal zones rivers discharging into the coastal zones of the uplift belts contribute no more than 10 of the total in coastal zone subsidence belts tidal flat deposits develop and quaternary strata are quite thick in coastal zone uplift belts in contrast beach sand and gravel and aeolian sand develop only where great amounts of fine sediments are provided to coastal uplift zones by the adjacent major rivers can tidal flat deposits develop quaternary strata are thin in uplift belts and patchy relict sediments are present on the continental shelves on the continental shelves of the southern part of the east china sea and the south china sea where discharge of river sediments is fairly small relict sediments form a broad continuous deposit marine processes can transport the sediments of large rivers into the mouths of small adjacent rivers where various sand and mud bodies form so far in the coastal zones of china no coastal depositional body is known to have formed from sediments derived directly from the continental shelves

late quaternary paleoceanography of the south china sea surface circulation and carbonate cycles paleoceanographic information from 34 sediment cores is summarized to investigate the glacial interglacial variations in sea surface circulation and late quaternary carbonate cycles in the south china sea judging from the distribution pattern of deposition rates the enormous terrigenous supply by rivers is responsible for the high rate of hemipelagic sedimentation which was even higher during glacial periods paleotemperature maps based on transfer function temperature estimates have revealed a e w gradient of sst for glacial summer and a s n gradient for glacial winter and this agrees well with the clockwise surface circulation in summer and counterclockwise in winter during glacials as shown by a preliminary computer modelling the high resolution paleotemperature curves of core v36 3 from the northern slope show an abrupt cooling event which may belong to the younger dryas carbonate percentage in sediments and preservation of foraminifers and pteropods are used to study the carbonate cycles in the marginal sea it turns out that two mechanisms are functioning there being a basin with large drainage areas vast amount of river borne terrigenous input dilutes carbonate and its intensification during glacial decreases the glacial cac03 being a basin connected with the pacific the fluctuations of lysocline ccd and acd in the scs are related to those in the pacific ocean and dissolution is strengthened at interglacial thus above the present ccd the dilution factor predominates and the atlantic cycles are produced below the present ccd the dissolution factor prevails resulting in the pacific pattern of carbonate cycles

geology market and supply chain of niobium and tantalum a review tantalum ta and niobium nb are essential metals in modern society their use in corrosion prevention micro electronics specialty alloys and high strength low alloy hsla steel earns them a strategic designation in most industrialised countries the ta market is unstable due in part to historic influx of conflict columbite tantalite concentrate or coltan that caused ta mines in australia and canada to be placed on care and maintenance more recently the growing appetite of modern society for consumer goods made of conflict free minerals or metals has put pressure on suppliers pegmatites rare element enriched granites related placer deposits and weathered crusts overlying carbonatite and peralkaline complexes account for the majority of ta production several carbonatite related deposits e g upper fir and crevier canada are being considered for potential co production of ta and nb pyrochlore nb ta columbite tantalite nb ta wodginite ta nb and sn and microlite ta and nb are the main ore minerals approximately 40 of ta used in 2012 came from ta mines 30 from recycling 20 from tin slag refining and 10 from secondary mine concentrates due to rapid industrialisation and increased use of nb in steel making in countries such as china and india demand for nb is rising weathered crusts overlying carbonatite complexes in brazil and one hard rock carbonatite deposit in canada account for about 92 and 7 of nb world mine production respectively since the bulk of the production is geographically and politically restricted to a single country security of supply is considered at risk other prospective resources of nb beside carbonatites and associated weathered crusts are peralkaline complexes e g nechalacho where nb is considered as a potential co product of ree and zirconium economically significant deposits of ta and nb contain pyrochlore columbite tantalite fersmite loparite and struverite assuming continued elasticity of ta and nb prices and that the law of the supply and demand applies new sources of these metals can be developed in the long term there is no need to worry about ta and nb availability temporary disruptions in ta and nb supply are possible and could be difficult to cope with so new sources of supply may be developed to diversify geographic sources of supply for strategic reasons

concurrent decadal mesoscale eddy modulations in the western north pacific subtropical gyre abstractsatellite altimeter data of the past two decades are used to investigate the low frequency mesoscale eddy variability inside the western north pacific subtropical gyre eddy activity modulations with a decadal time scale are detected concurrently within the 18 28 n band including the three branches of the subtropical countercurrent stcc and the hawaiian lee countercurrent hlcc lagging behind the pacific decadal oscillation pdo index by six months enhanced eddy activities were detected in 1995 98 and 2003 06 whereas the eddy activities were below the average in 1999 2002 and 2009 11 analysis of the temperature and salinity data that became available after 2001 via the international argo program reveals that the modulating eddy activities are due to the decadal change in the upper ocean eastward shear in the broad scale stcc hlcc band by conducting an upper ocean temperature budget analysis the authors found that this observed eastward shear change can be effectively accounted for by t

on the structure and origin of major glaciation cycles 2 the 100 000 year cycle climate over the past million years has been dominated by glaciation cycles with periods near 23 000 41 000 and 100 000 years in a linear version of the milankovitch theory the two shorter cycles can be explained as responses to insolation cycles driven by precession and obliquity but the 100 000 year radiation cycle arising from eccentricity variation is much too small in amplitude and too late in phase to produce the corresponding climate cycle by direct forcing we present phase observations showing that the geographic progression of local responses over the 100 000 year cycle is similar to the progression in the other two cycles implying that a similar set of internal climatic mechanisms operates in all three but the phase sequence in the 100 000 year cycle requires a source of climatic inertia having a time constant similar to 15 000 years much larger than the other cycles similar to 5 000 years our conceptual model identifies massive northern hemisphere ice sheets as this larger inertial source when these ice sheets forced by precession and obliquity exceed a critical size they cease responding as linear milankovitch slaves and drive atmospheric and oceanic responses that mimic the externally forced responses in our model the coupled system acts as a nonlinear amplifier that is particularly sensitive to eccentricity driven modulations in the 23 000 year sea level cycle during an interval when sea level is forced upward from a major low stand by a milankovitch response acting either alone or in combination with an internally driven higher frequency process ice sheets grounded on continental shelves become unstable mass wasting accelerates and the resulting deglaciation sets the phase of one wave in the train of 100 000 year oscillations whether a glacier or ice sheet influences the climate depends very much on the scale the interesting aspect is that an effect on the local climate can still make an ice mass grow larger and larger thereby gradually increasing its radius of influence

transgressive depositional systems of the mississippi delta plain a model for barrier shoreline and shelf sand development abstract depositional sequences generated in the mississippi river delta plain consist of a regressive and a transgressive component the transgressive component has been considerably less studied but accounts for the majority of the surface area on the lower mississippi river delta plain and up to 50 percent of the total sequence thickness in shallow water deltas the development and preservation of transgressive depositional systems in abandoned delta complexes follows the process of transgressive submergence in which the horizontal component of reworking occurs during shoreface retreat combined with a vertical component of submergence acting to preserve the sequence the evolution of transgressive depositional systems in each of the abandoned holocene mississippi river delta complex s can be summarized in a three stage model beginning with stage 1 an erosional headland and flanking barriers in this stage regressive sand deposits contained within abandoned deltaic headlands are reworked by the eroding shoreface and dispersed longshore into contiguous flanking barriers enclosing restricted interdistributary bays submergence of the delta plain during relative sea level rise generates an intradeltaic lagoon separating the former stage 1 sand body from the shoreline forming stage 2 a transgressive barrier island arc the landward migrating barrier island arc is unable to keep pace with relative sea level rise and the retreating mainland shoreline resulting in submergence and the formation of stage 3 an inner shelf shoal following submergence the former barrier island arc sand body continues to be reworked into a marine sand body on the inner continental shelf during stage 3 this sequence of coastal evolution provides direct evidence of barrier island formation with each stage producing a distinctive stratigraphic signature the current sea level rise models of shoreface retreat and in place drowning developed for the u s atlantic continental shelf do not adequately explain either the morphology or the stratigraphy of transgressive mississippi river delta sand bodies current models of mississippi deltaic stratigraphy emphasize the deep water artificially maintained balize delta which differs considerably from the shallow water shelf phase delta complexes that are the primary depositional constituents of he holocene mississippi river delta plain

the magmatic and fluid evolution of the motzfeldt intrusion in south greenland insights into the formation of agpaitic and miaskitic rocks the 1 275 ga motzfeldt intrusive complex in the gardar failed rift province in south greenland formed from six successively intruding melt batches sm1 sm6 interpreted to be derived from a common magma source at depth five units sm1 sm5 crystallized an alkaline to peralkaline miaskitic mineral assemblage of amphibole clinopyroxene feldspar nepheline fe ti oxides zircon apatite fluorite and rarely olivine the last magmatic batch sm6 is characterized by an agpaitic mineral assemblage of aegirine nepheline alkali feldspar eudialyte and rare fluorite or sodalite coexisting mafic minerals constrain the crystallization conditions of the miaskitic rocks to about 850 6008c whereas solidus temperatures below 5008c are indicated by coexisting alkali feldspars in the agpaitic rocks oxygen fugacities during the orthomagmatic stage are below the fmq fayalite magnetite quartz buffer fmq 0 5t o 2 0 whereas late hematite provides evidence of a higher relative oxygen fugacity during late stage alteration the nd and oxygen isotope compositions of amphiboles and pyroxenes are homogeneous throughout the complex and suggest a common mantle derived magma source for all six units which is comparable with other gardar intrusions the hydrogen isotopic composition of amphiboles dd 99 to 132 indicates lowtemperature fluid rock interaction with low fluid rock ratios fluid inclusion studies indicate that h2o nacl fluids present during the magmatic stages in the miaskitic units had salinities of510 wt nacl eq calcite crystals in fluid inclusions within these rocks suggest that co2 or hco3 was an important component of the original fluid phase in contrast the agpaitic unit is characterized by a ch4 h2o naclfluid the c o h isotope compositionsofthefluid inclusions in all units are consistent with mixing between a small volume of magmatic fluid and a large volume of meteoric water the chemical evolution of the motzfeldt complex is a type example of the connection of the transition from miaskitic to agpaitic mineral assemblages with redox dependent fluid solid equilibria thetransitionfromarelatively oxidized to a relatively reduced fluid is correlated with a change from a more reduced fe 2 bearing miaskitic taramite arfvedsonite zircon sm1 sm5 to a more oxidized fe 3 bearing agpaitic assemblage aegirine eudialyte sm6 we suggest that coupled fluid solid redox equilibria involving fe 2 f e 3 c o2 and ch4 in this case were simply driven by temperature decrease and an overall increase in na k in the melt this observation sheds light on the heavily debated miaskite agpaite transition the combined temperature and compositional effect stabilized fe 3 c h 4 and enhanced the solubility of zr possibly as na zr si o complexes in the latest stage melt sm6 resulting in the crystallization ofan agpaitic mineral assemblage in terms of redox conditions during crystallization the motzfeldt rocks represent an intermediate case in the gardar province between more oxidized co2dominated intrusions such as the syenite carbonatite complex of

the instabilities and multiscale energetics underlying the mean interannual eddy interactions in the kuroshio extension region abstractusing a recently developed energetics diagnostic methodology namely the localized multiscale energy and vorticity analysis ms eva this study investigates the intricate nonlinear mutual interactions among the decadally modulating mean flow the interannual fluctuations and the transient eddies in the kuroshio extension region it is found that the mean kinetic energy maximizes immediately east of the izu ogasawara ridge while the transient eddy kinetic energy does not peak until 400 km away downstream the interannual variabilities which are dominated by a jet trapped rossby wave mode provide an energy reservoir comparable to the other counterparts in the upstream strong localized barotropic and baroclinic transfers from the mean flow to the eddies are observed whereas those from the interannual variabilities are not significant besides fueling the eddies the unstable mean jet also releases energy to the interannual scale processes between 144 and 154 e both transfers from the mean

annual and interannual variability of the tropical instability vortices in the equatorial eastern pacific observed from lagrangian surface drifters abstractthis study documents the spatial distributions and temporal variations of anticyclonic eddies with identified radii 100 km in the equatorial eastern tropical pacific ocean viz tropical instability vortices tivs using lagrangian surface drifters the tivs identified from lagrangian surface drifters are distributed in a band along 5 n and are closely associated with latitudinal barotropically unstable shear between the westward south equatorial current sec and the eastward north equatorial countercurrent necc fewer tivs are identified from february to june when the shear between the sec and necc is weak whereas more tivs are found from july to january when the shear is enhanced the number of identified tivs also exhibits substantial interannual variability with fewer tivs identified during el nino events and more tivs found during la nina events this relationship is likely associated with the interannual variations of the zonal circulation in the equatorial pacific modulated by el ni