accelerator mass spectrometry radiocarbon dating of rock varnish accelerator mass spectrometry ams 14c dating off rock varnish provides minimum limiting ages for landforms and archaeological artifacts in arid and semiarid lands that are undatable by conventional radiocarbon methods experiments on sample collection the effect of different individuals preparing samples the influence of different chemical extraction procedures the incorporation of carbonate detritus possible contamination from rock underlying varnish the role of bio geochemical erosion of varnish and other influences reveal procedures that yield reproducible results conventional radiocarbon dates from charcoal beneath lava flows of hualalai volcano hawaii and from arid sites in western north america provide controls to test varnish radiocarbon dating ams radio carbon ages on the very bottom layer of varnishes are typically 10 younger than the 14c ages of these controls applications are illustrated here for fluvial aeolian peri glacial hillslope lacustrine and glacial geo morphology as well as rock art research in archaeology

cation leaching sites in rock varnish backscatter electron microscopy of subaerial rock varnish reveals porous textures that are sites of cation leaching with lowered k ca 2 ti 4 ratios and concentrations of manganese and iron laboratory studies show that rates of potassium and calcium leaching increase with temperature time and surface area and decrease when varnish interdigitates with coatings of amorphous silica only varnishes with continuous layering should be used in paleoenvironmental research and paleomagnetic studies not textures indicative of postdepositional modifications

models of rock varnish formation constrained by high resolution transmission electron microscopy nanometre scale transmission electron microscope imagery of manganiferous rock varnishes from death valley california peru antarctica and hawaii confirms prior infrared mineralogy studies the building blocks of rock varnish are clay minerals that are cemented to the rock by oxyhydroxides of manganese and iron rock varnish is layered on the scale of nanometres with the basic structure defined by the subparallel alignment of detrital clay minerals although only a few examples of bacteria were found possible cell wall encrustations are ubiquitous and aligned with the clay minerals mn fe oxides appear to be mobilized from bacterial casts and then reprecipitate on clay minerals that weather into monolayers these observations have implications for varnish dating and palaeoenvironmental techniques k ar and uranium series dating of rock varnish oxides can only yield minimum ages however this small spatial scale of mobilization would not alter the signal from micron scale microchemical laminations

structural control and tectonic setting of mesozoic volcanism in hong kong middle jurassic to lower cretaceous silicic volcanic rocks and granitoid plutons in hong kong form part of the broad ne trending yanshanian tectonomagmatic belt that extends through se china pyroclastic deposits in hong kong are typically proximal and infill linear flared vents and ellipsoidal calderas these pass down through elongate rift like conduits into extensive multiple fault and shear zone hosted 9sheeted9 dyke complexes and granitoid plutons dykes also emphasize the limits of calderas the spatial distribution and geometry of the vents calderas dykes and plutons are structurally controlled during each of four temporally well constrained periods of petrogenetically related volcanism and plutonism e and ene trending axes of extension and transtension were dominant nw trending faults increased in importance with time and their intersections with ene trending faults influenced the loci of volcanic centres nesting of the calderas confirms persistent reactivation of some faults the loci of magmatism migrated over 25 ma from nw to se zones of silicic crust created during these magmatic episodes have a broadly tripartite crustal 9stratigraphy9 pluton dyke volcanic reminiscent in very general terms of ophiolites the zones were created during periods of unusually rapid extension as the continental margin of se china changed from an active margin dominated by subduction to a back arc regime and dextral strike slip along ene trending faults gave way to sinistral strike slip

unravelling an allochthonous subaqueously deposited volcanic epiclastic to subaerial andesitic lava assemblage in hong kong age stratigraphy and provenance studies of the middle jurassic tuen mun formation the middle jurassic tuen mun formation hong kong is a fault bounded block of rare andesitic and related rocks that preserve a snapshot of the developing se china continental arc system during the late mesozoic the forearc depositional setting is considered to have been dominated by an emergent andesitic volcanic massif which shows a transition to a fluvial dominated volcanic plain and then to an offshore marine environment the youngest laser ablation inductively coupled plasma mass spectrometry u pb detrital zircon ages obtained from the three packages define a coherent group n 396 mswd 1 8 suggesting a maximum depositional age of 169 5 0 3 ma the dominance of large euhedral and concentrically zoned zircons reflects a common volcanic provenance hf isotope data e hf t 0 to 11 on the youngest representative zircon grains imply derivation of magmas from dominantly recycled crustal sources the detrital zircon age signatures and hf isotope data show no indication of magmatic interaction with adjacent late palaeozoic and early to middle jurassic sedimentary rocks or middle jurassic to early cretaceous magmatic rocks of hong kong on the basis of the structural zircon age and isotope data the tuen mun formation is interpreted to be an allochthonous block emplaced in the hong kong region during the late middle jurassic supplementary material a full dataset of u pb dating and hf isotope analysis of detrital zircons stratigraphic drillhole logs and a description of the terminology used in this paper are available at https doi org 10 6084 m9 figshare c 3736972

variations in sub tropical deep weathering profiles over the kowloon granite hong kong variations in the physical characteristics of the weathering profile over the kowloon granite in hong kong have been established using borehole records supported by field mapping there is a strong correlation between topography of the weathered profile base and the main structural trends linear zones of deep weathering have been preferentially eroded to create valleys which subsequently became sites of alluvial and colluvial accumulation variations in weathering patterns are primarily a function of the geometry and infilling of relict jointing which together determine local hydrogeology and hence intensity of weathering magnetic susceptibility is a reliable indicator of material weathering grade in the kowloon granite corestones are generally restricted to weathered profiles over topographically high areas the locations of which are controlled by regional joint spacing and orientation corestone bearing profiles are rare and more commonly deeply weathered granite without corestones passes abruptly into relatively fresh rock this has important implications for engineering ground models derived from borehole interpretation

baking black opal in the desert sun the importance of silica in desert varnish comment and reply reply we welcome the opportunity to reply to dorn 2007 who outlines the classical issues of desert varnish formation we agree that most previous research has suggested a biological mechanism bacterial enhancement of manganese in manganese rich coatings is intriguing however as we have published

manganese rich rock varnish does occur in antarctica abstract despite accounts to the contrary we have found that mn rich rock varnish is present in antarctica as others have before it is chemically and texturally similar to many varnishes found in lower latitudes antarctic varnishes show considerable potential as a dating and paleoenvironmental research tool

eocene seasonality and seawater alkaline earth reconstruction using shallow dwelling large benthic foraminifera abstract intra test variability in mg ca and other trace elements within large benthic foraminifera lbf of the family nummulitidae have been investigated using laser ablation inductively coupled plasma mass spectrometry la icpms these foraminifera have a longevity and size facilitating seasonal proxy retrieval and a depth distribution similar to surface dwelling planktic foraminifera coupled with their abundance in climatically important periods such as the paleogene this means that this family of foraminifera are an important but under utilised source of palaeoclimatic information we have calibrated the relationship between mg ca and temperature in modern operculina ammonoides and observe a 2 increase in mg ca c 1 o ammonoides is the nearest living relative of the abundant eocene genus nummulites enabling us to reconstruct mid eocene tropical sea surface temperature seasonality by applying our calibration to fossil nummulites djokdjokartae from java our results indicate a 5 6 c annual temperature range implying greater than modern seasonality in the mid eocene bartonian this is consistent with seasonal surface ocean cooling facilitated by enhanced eocene tropical cyclone induced upper ocean mixing as suggested by recent modelling results analyses of fossil n djokdjokartae and operculina sp from the same stratigraphic interval demonstrate that environmental controls on proxy distribution coefficients are the same for these two genera within error using previously published test seawater alkaline earth metal distribution coefficients derived from an lbf of the same family raitzsch et al 2010 and inorganic calcite with appropriate correction systematics for secular mg casw variation evans and muller 2012 we use our fossil data to produce a more accurate foraminifera based mg casw reconstruction and an estimate of seawater sr ca we demonstrate that mid eocene mg casw was 2 mol mol 1 which is in contrast to the model most commonly used to correct deep time mg ca data from foraminifera but in agreement with most other paleogene proxy and model data this indicates that mg casw has undergone a substantial 3 4 rise over the last 40 ma

perturbation of the carbon cycle at the middle late jurassic transition geological and geochemical evidence a compilation of new and published stratigraphic paleontological and geochemical data is used to detect the reciprocal influences of carbon cycling and global environmental changes in the jurassic a major perturbation of the surface carbon cycling accompanied by pronounced climate and sea level fluctuations waxing and waning of continental ice affected earth history around the middle late jurassic transition mljt we establish the respective timing of changes of carbonate and organic matter sedimentation and global fluctuations of sea surface temperatures paleobiogeography and o isotope paleothermometry and sea level sequence stratigraphy so that causative mechanisms and feedback effects can be considered it is apparent that the global sea level rise and warming initiated in the late bathonian led to a constriction of carbonate platforms to low latitudes and enhanced marine organic deposition sea level and temperature optima were achieved several million years later during the middle callovian a detailed record of sea surface temperatures in the northern hemisphere based on migration of marine fauna and isotopic thermometry indicates that a drastic climatic decline set in during the early late callovian just post dating the increased capture of organic matter by marine sediments this decline in temperature is interpreted in terms of an inverse greenhouse effect triggered by drawdown of co 2 consequent upon excess carbon burial the magnitude of refrigeration and its coincidence in time with an abrupt global scale fall of sea level are both suggestive of continental ice formation at this time carbonate sedimentation was jeopardized at the mljt as a result of both global cooling and presumed p c o 2 lowering and resumed abruptly during the middle oxfordian by spreading again over mid latitude zones salient conclusions are that 1 the pattern of excess carbon burial coincident with elevated temperature but followed by climatic deterioration supports the general hypothesis that a major control on mesozoic climate was the abundance of atmospheric co 2 2 significant masses of continental ice may have formed during this part of the jurassic and correlatively high co 2 levels were certainly not sustained throughout this period 3 the global carbonate sedimentation budget correlated with the surface temperature and sea level but the latitudinal spreading of type tropical carbonates was not simply related to the thermal status of seawaters 4 on a global scale the c o r g and c i n o r g burial rates were coupled apparently through the correlation existing between the co 2 level and surface temperature

regional tectonic setting of hong kong implications of new gravity models hong kong lies on the se margin of the cathaysia block and straddles the ne trending lianhuashan fault zone one of the dominant structural features of se china isotope signatures of the mesozoic granites have indicated that the zone overlies a major crustal discontinuity the proposed gravity model of hong kong consists of a heterogeneous upper crust underlain by middle to lower crust composed of a felsic archaean segment approximately 25 km wide flanked by more mafic proterozoic crust the southern boundary of the felsic segment dips steeply to the north whereas the northern boundary is subvertical euler gravity anomalies define the fundamental faults in the upper crust and many of these can be correlated with faults that have been mapped at surface the middle to lower crustal discontinuities are considered to be associated with a major shear zone within the cathaysia block that has similar dimensions to transcratonic structures in other precambrian shield areas the geological development of hong kong and neighbouring se china has largely been controlled by periodic reactivation of this deep crustal shear zone since the late neoproterozoic

geochemistry of coeval mesozoic plutonic and volcanic suites in hong kong middle jurassic to lower cretaceous intermediate to silicic plutonic and volcanic rocks of hong kong record a transition from calc alkaline through high k calc alkaline to transitional shoshonitic compositions with time close spatial and temporal associations among comagmatic volcanic plutonic pairs indicate that magmatism occurred in discrete episodes mostly of less than one million years duration synchronous high k calc alkaline and transitional shoshonitic magmatic activity during at least one pulse suggests a relatively rapid transition from a subduction related to an extension related tectonic setting geochemical signatures indicate that the magmatic suites have a mantle origin with a decreasing crustal contribution from two distinct sources the earliest mantle derived magmas interacted strongly with a dominantly archaean crustal protolith younger magmas show evidence for interaction with a dominantly proterozoic crustal protolith the strongest mantle influence is shown by magmas which were intruded along the boundary between the two dominant crustal sources this interface marks a deep crustal discontinuity which promoted the passage of magmas to the surface

weathering indices for rhyolitic tuff and granite in hong kong a series of chemical analyses and dry density tests of rhyolitic tuff and granitic samples have been carried out the test results have been interpreted using a newly developed theoretical weathering model for calculating a mobility index of major elements in rock and soil it is found that this index is useful for describing changes of rock and soil during weathering and classifying the degrees of weathering based on the theoretical model a new parameter called the volume index which combines chemical and physical data is suggested this index appears to be a good indicator for classifying the degree of weathering in hong kong a quantitative classification scheme is suggested

building southeast china in the late mesozoic insights from alternating episodes of shortening and extension along the lianhuashan fault zone abstract understanding the mesozoic intraplate structural response of south china inboard of the paleo pacific south china convergent margin is a key issue in unravelling the continental tectonics of se asia the lianhuashan fault zone of south china represents a high strain structure pivotal for constraining the multi phased intraplate deformation strain localization and partitioning in response to the subduction of the paleo pacific plate new data coupled with published work describes the geometry kinematics and age of this fault zone establishing a multi stage tectono thermal history the first stage late jurassic shortening involved top to the w thrust sense shear along ne striking shear zones the associated regional e w shortening is interpreted to have been related to the advancing nw ward subduction of the paleo pacific plate the second stage early cretaceous deformation is poorly documented in the lianhuashan fault zone but is associated regionally with magmatism and early cretaceous basins formed under nw se extension this extension has been correlated with the rollback of the paleo pacific plate the third stage late early cretaceous nw se shortening produced top to the se thrust sense shear zones the shortening inverted the extensional basins and caused a lull in the magmatic activity it possibly originated from the re initiation of low angle paleo pacific subduction the fourth stage deformation generated the top to the w wuhua detachment normal sense ductile fabrics and distributed shear zones in its footwall and widespread hanging wall basins in the late cretaceous this regional e w extension has been associated with the re initiation of slab rollback our work predicts episodes of slab steepening and shallowing in retreating and advancing settings changes in the slab geodynamics may have caused the alternating contractional and extensional episodes as well as the flare up lull and resumption of magmatism during the late mesozoic evolution of south china

desert varnish and environmental change near broken hill western new south wales abstract desert varnish is widespread in arid australia and occurs as a thin often discontinuous manganese enriched surface coating near broken hill western new south wales radiocarbon dating of calcium carbonate associated with this varnish indicated that major varnishing took place before about 10 000 years b p with varnish forming conditions continuing during the holocene small patches of varnish on secondary carbonate on non varnished rock and sometimes on existing varnish suggest that current environmental conditions allow for some varnish formation loss of varnish has resulted from within channel abrasion weathering by lichens minor breakdown of varnish substrates and localized weathering possibly related to a previously higher soil surface

nummulitic banks in the upper lutetian buil level ainsa basin south central pyrenean zone the impact of internal waves nummulites a particularly abundant and diverse genus of larger benthonic foraminifera formed huge accumulations banks during the eocene which are often good hydrocarbon reservoirs especially in north africa despite their economical interest these accumulations are not well understood and their origin is still under discussion reasons for this debate are the absence of living nummulites accumulations and the high variability of facies including the size shape and extension of the banks which reflect the array of processes controlling sediment production and accumulation the nummulitic banks near santa maria de buil in the ainsa basin south pyrenean foreland basin are composed of recurrent facies associations within mappable bed units bounded by physical surfaces the depositional processes that produced the nummulites deshayesi accumulations are interpreted considering the shape of the banks the type of bounding surfaces the distribution of sedimentary textures nummulites test shapes and the associated skeletal components within the banks this integrative analysis indicates that nummulitic banks accumulated from mass flows with very poor sediment sorting textural and compositional differences among banks suggest that globose nummulites thrived in the shallower part of the mesophotic zone with abundant nummulithoclasts whereas flat nummulitic forms thrived in deeper mesophotic clay dominated settings interbedded with nummulitic banks coral biostromes and coral mounds bearing operculina discocyclina and asterocyclina represent in situ accumulation near the base of the photic zone internal waves waves that propagate along the pycnocline are thought to be the triggering mechanism for the density flows internal waves and induced bottom currents are sporadic but strong enough to bring sediments into suspension in contrast to surface waves both fair weather and storm whose impact is strongest near the sea surface and decreases with bathymetry the impact of internal waves is usually strongest in the mid shelf region and weaker in shallow water this explains the compositional character of the nummulitic banks

late jurassic early cretaceous continental convergence and intracontinental orogenesis in east asia a synthesis of the yanshan revolution abstract the basic tectonic framework of continental east asia was produced by a series of nearly contemporaneous orogenic events in the late middle jurassic to early cretaceous commonly the late mesozoic orogenic processes were characterized by continent continent collision large scale thrusting strike slip faulting and intense crustal shortening crustal thickening regional anatexis and metamorphism followed by large scale lithospheric extension rifting and magmatism to better understand the geological processes this paper reviews and synthesizes existing multi disciplinary geologic data related to sedimentation tectonics magmatism metamorphism and geochemistry and proposes a two stage tectono thermal evolutionary history of east asia during the late middle jurassic to early cretaceous ca 170 120 ma in the first stage three orogenic belts along the continental margins were formed coevally at ca 170 135 ma i e the north mongol okhotsk orogen the east paleo pacific coastal orogen and the west bangong nujiang orogen tectonism related to the coastal orogen caused extensive intracontinental folding and thrusting that resulted in a depositional hiatus in the late jurassic as well as crustal anatexis that generated syn kinematic granites adakites and migmatites the lithosphere of the east asian continent was thickened reaching a maximum during the latest jurassic or the earliest cretaceous in the second stage ca 135 120 ma delamination of the thickened lithosphere resulted in a remarkable 120 km lithospheric thinning and the development of mantle derived magmatism mineralization metamorphic core complexes and rift basins the middle jurassic early cretaceous subduction of oceanic plates paleo pacific meso tethys and mongol okhotsk and continent continent collision e g lhasa and qiangtang along the east asian continental margins produced broad coastal and intracontinental orogens these significant tectonic activities marked by widespread intracontinental orogeny and continental reconstruction are commonly termed the yanshan revolution movement in the chinese literature

stable isotopes in recent larger foraminifera abstract oxygen and carbon isotope analyses have been made on large benthic foraminifera from bermuda the persian gulf and the philippines the foraminifera belong to the two suborders rotallina and miliolina life spans range between one season to more than two years shells contain information about seasonal temperature ranges and life history stages recorded as fluctuations of oxygen and carbon isotopic values within the shell material almost all specimens studied showed the expected variations in 18o with respect to ambient conditions water isotopic composition and seasonal temperature fluctuations the specimens from bermuda seemed enriched in 18o whereas all specimens from the philippines independent of their taxonomic position seemed to the depleted in 18o with respect to calcita equilibrium specimens from the same species showed about the same level and range of 18o values the miliolid species marginopora vertebralis cyclorbiculina compressa archaias angulatus peneroplis proteus and praesorites orbitolitoides cf monensis commonly show carbon isotope values up to 2 5 lighter than expected equilibrium values independent of sample locality the rotaliid species heterostegina depressa operculina sp and calcarina spengleri show carbon isotope values more than 2 lighter than expected equilibrium values also independent of sample locality all analyzed miliolid species show a tendency with age towards lighter than equilibrium 13c values the analyzed rotaliid species showed the reverse that is shells tend toward increased 13 values with age

spatial temporal and geographic considerations of the problem of rock varnish diagenesis article i nfo the rock varnish literature hosts an abundance of prima facie contradictory empirical data past and perhaps future empirical contradictions however can be resolved by theoretical considerations of different spatial and temporal scales of varnish diagenesis as well as the geomorphic position of different types of varnishes for example twentieth century contamination by lead and other heavy metals has led to claims of accumulation rates in the last century far more rapid than prior published empirical studies a consideration of spatial scales resolves this contradiction nanoscale processes allow migration of lead into varnish deposited well before the twentieth century time of heavy metal pollution evidence of nanometer scale disequilibrium in three samples led to claims that varnish cannot be used in paleoclimatic research these data rest in contrast to replicable patterns in varnish deposition observed by dr tanzhuo liu and others in over ten thousand micro sedimentary basins this contraction can be resolved by understanding that the types of varnishes studied differ and that processes differ substantially between the nanoscale and the micron scale a lack of evidence of mn oxidizers in genetic analyses contrasts with culturing studies and in situ evidence of mn enhancement by bacteria this contradiction has a likely resolution in vastly different temporal scales dna material analyzed may be no older than 200 years but in situ fossilized remains of bacteria may be preserved for thousands of years recording palaeoecological conditions favoring growth of mn enhancing bacteria

rifting and reactivation of a cretaceous structural belt at the northern margin of the south china sea abstract the tiu tang lung fault hong kong special administrative region china is located on the northern stretched continental margin of the south china sea along this fault middle jurassic volcanic rocks of the tai mo shan formation are tectonically juxtaposed on lower cretaceous sedimentary rocks of the pat sin leng formation both extensional detachments and compressional features are observed and various genetic strain configurations are proposed for the tiu tang lung fault with implications for understanding the dynamics of the pre south china sea rifting during the cretaceous we have identified tilted bedding planes in the continental deposits of the pat sin leng formation which can be related to early cretaceous syn extensional deposition a mid cretaceous penetrative top to the south to top to the west shear fabric is also observed and serves as an indicator of the strain pattern this deformation is expressed by cleavages schistosity s c fabrics kink folds phacoids and stretched pebbles at both a macroscopic and microscopic scale cleavages and bedding are generally sub parallel to the local shear orientation the whole sedimentary pile is crosscut by cenozoic n70 and n150 normal faults these constraints together with previous fission track seismic and structural data allow us to reinterpret the kinematics of this domain during syn orogenic to syn extensional periods the observed top to the south thrusting event is coeval with ne sw strike slip sinistral fault movement subsequent n s extension can be correlated with south china sea rifting from eocene to oligocene these observations reveal a polyphase history associated with continental margin inversion which witnessed localized extension on previous compressional structures

winners and losers stable isotopes and microhabitats of living archaiadae and eocene nummulites larger foraminifera abstract this paper discusses isotopes in larger foraminiferal calcite from two contrasting settings modern florida bay dominated by archaiadae the winners and the upper eocene barton clay of england locally dominated by nummulites the losers the archaiads plus peneroplids and soritids were mainly collected from thalassia leaves they yield signatures that closely reflect strong isotopic gradients in sea water across florida bay and the outer patch reefs isotopic signatures of eurytopic androsina lucasi record extreme conditions to the north of the bay which includes 13 c evidence for much nutrient regeneration such tolerance of relatively eutrophic conditions may explain the capacity of archaiadae for survival in the caribbean region during the neogene isotopes of nummulites prestwichianus from the basal bartonian compare more closely with data from living nummulite heterostegina 18 o indicates a yearly growth cycle under tropical bottom water temperatures with an annual range of approximately 2 5 c carbon isotopes show a trend towards heavier values with growth here related to decelerating rates of calcification and perhaps the additional effects of test thickening on carbon isotope fractionation by endosymbionts the nummulitic data indicate a much more stable carbon and nutrient cycle in the basal barton clay than seen in the florida bay mudmound assemblage this is consistent with their presumed stenotopic and oligotrophic life habit it could well explain their vulnerability to extinction after the mid eocene and the post aquitanian decline of larger rotaliids and reefs in the caribbean region

stable isotope composition of benthic foraminifera from the equatorial pacific when ranked according to deviation from isotopic equilibrium deep sea benthic foraminifera exhibit no correlation between the rankings for oxygen and for carbon both rank sequences are stable from east to west in the equatorial pacific fertility independent and from glacial to post glacial time independent records for the past 15 000 yr suggest marked changes in deep sea circulation during this time interval

new u pb age and geochemical constraints on the stratigraphy and distribution of the lantau volcanic group hong kong abstract seven new high precision u pb single crystal zircon ages are reported from jurassic and early cretaceous volcanic rocks in the hong kong special administrative region sar these ages are used in combination with zr vs tio2 ratios to refine the stratigraphy of the lantau volcanic group on lantau island and in adjoining districts in hong kong as a result three major unconformities are proposed and the rift controlled paleogeography of the region which influenced the development of the lantau caldera and lacustrine basins during the latest jurassic to earliest cretaceous is clarified the data also suggest the possibility that the base of the cretaceous system may be preserved within the sequence

rock varnish in the sonoran desert microbiologically mediated accumulation of manganiferous sediments rock varnish occurs in virtually all environments most commonly in arid and semi arid climates including antarctica rock varnish consists of thin layers of intimately mixed aeolian and chemical sediments often showing botryoidal and more rarely stromatolite like morphologies typical rock varnish samples collected at twin peak mountain park near phoenix arizona consist of abundant quartz with plagioclase illite and a mixed layer fe clay mineral probably corrensite eds sem bse and tem analyses revealed that the typical mn fe minerals occur as minute particles some of these particles and other mineral grains are attached to filaments xrd and electron diffraction showed that the mn fe bearing particles are poorly crystalline the filaments based on morphological criteria are virtually indistinguishable from fungal filaments most filaments are fragments probably broken by scraping during sample collection coccoid and rod shaped forms resembling cyanobacteria and other bacteria respectively are also present unlike definitive minerals these filaments disintegrated in the concentrated energy of the sem electron beam at the instrumental and experimental conditions used in addition no filamentous rod shaped or coccoid forms were observed in samples hydrolysed with 6 n hcl for 24 h at 100 c bacteria and fungi in powdered rock varnish were cultured on four media incubated aerobically in the dark at 25 c the culture media yielded dense growths of spore forming bacteria and filamentous fungi one fungus and two bacillus isolates oxidized and concentrated manganese control experiments revealed that fungi and bacteria are present on and below the surfaces of rock varnish free and hydrolysed peptide protein bound amino acids were identified in the rock varnish amino acids showed virtually no racemization with the exception of d l asp 0 1 relatively high molecular weight humic matter was also separated from the rock varnish high resolution mass spectrometry revealed non hydrocarbon moieties similar to a suwannee river fl humic acid standard micro organisms and their original biochemical compounds do not seem to be preserved for long in the accreting varnish layer the studies showed that the filaments helped to trap mineral particles of rock varnish and that bacteria and fungi abetted mn concentration some structures in the layers of rock varnish resemble stromatolites and present definitions would allow them to be termed as such

volcanic plutonic connections in a tilted nested caldera complex in hong kong 1 exceptional exposures of four precisely dated middle jurassic to early cretaceous silicic volcanic centers and their plutonic equivalents in hong kong have provided an excellent opportunity to examine close connections in time and space between magma chambers and their overlying calderas here we describe a 14 km crustal section through a collapsed caldera in southeastern hong kong where the intracaldera fill suggests that the magmatic discharge was of supereruption scale the main subvolcanic components that link a magma chamber with surface are revealed by well established field relationships supplemented by high precision geochronology whole rock geochemistry and geophysical data exposures and outcrop patterns reveal kilometer scale caldera subsidence and evidence of the simultaneous evacuation of hundreds of cubic kilometers of high silica rhyolite magma through dike like conduits from a shallow subcrustal reservoir the resultant volcanotectonic depression within which is preserved a single cooling unit of massively columnar jointed densely welded tuff high island tuff is interpreted to form part of a larger tilted early cretaceous nested caldera complex the high island eruption signaled the end of a 24 myr period of voluminous pulsed middle jurassic to early cretaceous silicic magmatism in the hong kong region characterized by four discrete ignimbrite flare ups

ecology of extant nummulitids and other larger benthic foraminifera applications in palaeoenvironmental analysis abstract larger benthic foraminifera lbf are important contributors to modern and ancient tropical shallow marine sediments over the past 30 years a substantial body of literature has built up on the ecology of modern lbf especially in terms of their environmentally sensitive depth distribution reproductive strategy and morphology and the symbiotic relationship between many larger foraminifera and photosynthetic algae over the same period the extinct genus nummulites which is abundant in eocene sediments of southern europe north africa and the arabian peninsula has increasingly been studied principally because significant volumes of hydrocarbons have been discovered reservoired within nummulitic limestones offshore tunisia and libya the modern ecological studies of lbf provide a powerful tool with which to develop palaeoecological models for fossil nummulites and other symbiont bearing larger foraminifera in the rock record

the significance of primary volcanic fabrics and clay distribution in landslides in hong kong most rain induced landslides on hong kong s volcanic rocks are shallow and small scale however two major landslides that occurred on hong kong island in 1995 highlight relationships between primary volcanic foliations and kaolin accumulations that may have general significance in determining loci of larger failures in the first case a bedding parallel shear zone was the locus for kaolin concentration in a shallowly dipping tuff this formed a weak planar low permeability layer which acted as the surface of rupture of a translational failure in the second case steeply inclined fabrics eutaxitic foliations and subparallel closely spaced joints occurred within a zone of syn volcanic folding and shearing deep weathering developed along the zone with kaolin concentrations present mainly above the soil rock interface the irregular and variably concave to planar rupture surface was closely associated with kaolin infilled relict joints towards the base of the soil profile kaolin distribution is largely associated with the weathering profile and may have been both physically and chemically redistributed within it halloysite is more abundant than kaolinite in most clay samples at and near both rupture zones and may have developed from kaolinite in response to strain detailed mapping of volcanic fabrics around the major landslides suggests that kaolinized bedding parallel shear zones are uncommon but that deep weathering zones associated with shearing and faulting are common mappable features

nanometer scale layering in rock varnish implications for genesis and paleoenvironmental interpretation manganiferous rock varnish collected from death valley and antarctica contains the smallest known terrestrial sedimentary deposits with some layers only a few nanometers thick irregularities in these nanometer scale layers are consistent with shrinking cracking and weathering of clay minerals in the death valley rock varnish very different high resolution transmission electron microscope hrtem textures coexist that may be related to climatic change hrtem observations contradict previous microbial models of mn fe enhancement requiring a new three step model of biomineralization and diagenesis for varnish formation

thermal evolution of tethyan surface waters during the middle late jurassic evidence from δ18o values of marine fish teeth 1 oxygen isotope compositions of phosphate from vertebrate tooth enamel were measured to determine the evolution of tropical sea surface 0 owing to limited growth of continental ice during the early middle oxfordian the resulting sea level fall is estimated to be at least 50 m and is compatible with a global regression stage the middle oxfordian thermal minimum is followed by a new warming stage of 3 4 c from the middle to the late oxfordian

nd and sr isotope geochemistry of plutonic rocks from hong kong implications for granite petrogenesis regional structure and crustal evolution abstract combined nd and sr isotope data allow the plutonic rocks of hong kong to be grouped into three ne trending domains those of zone 1 in the northwestern part of the territory have nd t 87 sr 86 sr 0 0 71 the plutonic rocks in the central zone 2 exhibit a broad spectrum of isotope characteristics with nd t values of 4 2 to 7 0 tdm between 1 30 and 1 51 ga and 87 sr 86 sr 0 ratios in the range 0 7061 0 7102 granites of zone 3 in the southeastern part of the territory display relatively homogeneous isotope signatures with nd t between 5 5 and 6 5 and 87 sr 86 sr 0 ratios in the range 0 7067 0 7109 tdm model ages are between 1 39 and 1 47 ga the contrasting isotope signatures between zone 1 granites and those in zones 2 and 3 suggest there are inherent differences in the source regions and point to the existence of a basement terrane boundary in this part of southeast china the presence of a deep crustal discontinuity transecting hong kong would also account for the distribution and compositional variation of the granites and the dominant northeast structural control on dyke emplacement the variation in isotope signatures and tdm model ages observed in the hong kong rocks are consistent with a model involving the progressive interaction of mantle derived melts with two distinct crustal sources during a transition from compressional to extensional tectonics the boundary between these two crustal sources is marked by zone 2 in which isotope characteristics are more variable and a stronger mantle influence is preserved

high precision u pb zircon ages for mesozoic igneous rocks from hong kong abstract sixteen new high precision u pb zircon ages are reported from jurassic and early cretaceous silicic volcanic and plutonic rocks of hong kong when combined with the existing age dataset the new ages constrain more tightly the timing of major periods of volcanism and plutonism at 162 6 4 5 ma 146 7 1 1 ma 143 0 1 0 ma and 140 8 0 6 ma however two ages of 151 9 0 2 ma and 148 1 0 2 ma from eastern new territories and southern hong kong indicate additional and therefore more continuous albeit pulsed magmatic activity than previously thought

u pb dating of mesozoic igneous rocks from hong kong twenty two new zircon and monazite u pb ages have been obtained for mesozoic plutonic and volcanic rocks of hong kong these have revealed the existence of four distinct periods of mid jurassic to lower cretaceous volcano plutonism 164 6 0 2 to 159 3 0 3 ma 146 6 0 2 to 146 2 0 2 ma 143 7 0 3 to 142 5 0 3 ma and 140 9 0 2 to 140 4 0 2 ma a concordant monazite age of 236 3 0 8 ma has also been obtained from one intrusive body representing the first known occurrence of a mid triassic granitoid in the territory among these rocks discordant u pb data projected to the concordia curve have given a broad range of inheritance ages from early phanerozoic to late archaean a xenocrystic zircon from one sample has yielded a concordant age of 1872 3 ma the new u pb ages have refined the results of recent rb sr whole rock age dating of the granitoid rocks and have considerably improved correlation between intrusive and extrusive units the occurrence of inherited components in many of the analysed rocks indicates that they were derived from or erupted through older crust containing a wide variety of age components either as primary igneous or detrital material

stable carbon isotope ratios of rock varnish organic matter a new paleoenvironmental indicator stable carbon isotope ratios of organic matter in rock varnishes of holocene age from western north america and the middle east show a strong association with the environment this isotopic variability reflects the abundance of plants with different photosynthetic pathways in adjacent vegetation analyses of different layers of varnish on late pleistocene desert landforms indicate that the carbon isotopic composition of varnish organic matter is a paleoenvironmental indicator

petrogenesis of jurassic fractionated i type granites in southeast china constraints from whole rock geochemical and zircon u pb and hf o isotopes abstract whole rock geochemical and sr nd hf isotopic data and zircon in situ u pb ages and hf o isotopes are reported for twelve granitic intrusions from inland to coastal areas of the cathaysia block southeast se china in order to constrain their magma sources and petrogenesis they are mainly composed of biotite granites with minor granodiorites zircon u pb dating by la icpms and sims methods gave emplacement ages of 165 154 ma for these rocks which are metaluminous to weakly peraluminous a cnk 0 95 1 10 with variable sio 2 contents and high k 2 o contents they are all depleted in high field strength elements hfses and enriched in light rare earth elements lrees and large ion lithophile elements liles and show negative sr ba and eu anomalies in the spidergrams petrographic and geochemical features suggest the granodiorites that contain hornblende to be typical of i type while the biotite granites without hornblende are fractionated i type granites their variable major and trace element concentrations are due to fractional crystallization of feldspar biotite hornblende and accessory minerals including apatite allanite and monazite moreover our data indicate significant variations in isotopic compositions of these granitoids from inland to coastal areas the inland granites from the lapu fogang xinfengjiang and baishigang plutons have relatively high initial 87 sr 86 sr ratios 0 7105 0 7155 and low e nd t 11 2 to 7 3 and e hf t 10 9 to 6 3 values for whole rocks and variable 18 o values of 7 69 9 25 and e hf t values of 13 5 to 6 7 for zircons in contrast the coastal granites from the longwo wushikeng lianhuashan shigushan chiliao hulutian mantoushan and fenghuang plutons show relatively low initial 87 sr 86 sr ratios 0 7056 0 7110 and high e nd t 7 6 to 6 2 and e hf t 6 5 to 2 8 values for whole rocks together with e hf t values of 7 2 to 3 9 and 18 o values of 6 69 8 38 for zircons the spatial isotopic variations suggest that these jurassic granitoids were generated by different percentage mixing of mantle and ancient paleoproterozoic crust derived magmas with subsequently minor crustal assimilation our results highlight that jurassic fractionated i type granites occur widely from inland to coastal areas of se china arguing against the previous view that jurassic granites occur only in inland while coastal granites are mainly cretaceous the widespread occurrence of jurassic granitoids in se china is attributed to ascending of mantle derived magmas which provide heat for partial melting of lower crustal materials in an extensional setting

characteristics and origin of rock varnish from the hyperarid coastal deserts of northern peru abstract the characteristics of a new type of rock varnish from the hyperarid coastal deserts of northern peru combined with laboratory experiments on associated soil materials provide new insights into the formation of rock varnish the peruvian varnish consists of an fe rich mn poor component covering up to 95 of a varnished surface and a fe rich mn rich component found only in pits and along cracks and ridges the alkaline soils plus the catalytic fe oxyhydroxides that coat much of the varnish surfaces make the peruvian situation ideal for physicochemical precipitation of mn however the low mn content of the dominant fe rich mn poor component suggests that such precipitation is minor this plus the presence of abundant bacteria in the mn rich varnish and the recorded presence of mn precipitating bacteria in varnish elsewhere suggests that bacteria are almost solely responsible for mn precipitation in rock varnish a set of experiments involving peruvian soil samples in contact with water co2 solutions indicates that natural fogs or dews release mn but not fe when they come in contact with eolian materials on rock surfaces this mechanism may efficiently provide mn to bacteria on varnishing surfaces the lack of fe in solution suggests that a large but unknown proportion of fe in varnish may be in the form of insoluble fe oxyhydroxides sorbed onto the clay minerals that form the bulk of rock varnish the results of this study do not substantively change r i dorn s paleoenvironmental interpretations of varnish mn fe ratios but they do suggest areas for further inquiry

cretaceous tectonic evolution of south china a preliminary synthesis abstract the cretaceous tectonic evolution of south china is characterized by widespread extensional basin and dome generation voluminous magma intrusion eruption and associated polymetallic mineralization all of which are of world wide interests that have stimulated the attention of geologists for more than half a century due to the lack of a comprehensive understanding of regional tectonic evolution and geodynamics of south china many controversies regarding the nature and origin of these features remain this paper attempts to make a review by synthesizing existing structural petrological geochronological and geochemical data of the cretaceous structures and magmas which guides us to propose a three stage tectono thermal evolutionary history of south china during the cretaceous period the earliest cretaceous 145 137 ma tectonic stage was characterized by syn orogenic shortening deformation and metamorphism under a nw se compressional setting which generated voluminous porphyry cu au ore bearing adakitic rocks in the lower yangtze river belt and gneissic granites in the coastal area its geodynamic origin was interpreted as combined effects of the pacific izanagi ridge subduction beneath the lower yangtze river belt and the pacific subduction beneath the cathaysia block this syn orogenic shortening stage was followed by a post orogenic stage 136 86 ma comprising two episodes of alternate extensional and shortening events the extension 136 118 ma in the earlier episode was dominated by a nw se extensional regime it led to significant taphrogenesis manifested by large scale extensional basins and voluminous magma intrusion eruption this extensional event was associated with a combination of the slab window opening during the ridge subduction and the rollback of the subducted pacific slab the subsequent nw se transpressional event led to cessation of active marginal magmatism and resulted in tectonic inversion of previous rift basins this transpression lasted from 117 ma to 108 ma and its driving mechanism was attributed to the collision between the eastern asian margin and the west philippine block the extension 107 86 ma in the later episode was dominated by a wnw ese extensional regime which led to a second phase of basin subsidence and produced numerous a and i type granites and bimodal volcanoes the tectonic regime then changed at ca 85 ma to wnw ese oriented transpression causing inversion of the late cretaceous rift basins and cessation of extension related magmatism the change of stress field from wnw ese extension to wnw ese transpression was related to the variations of the subducted slab dynamics i e the transition from either the ese ward retreat to wnw ward subduction of the pacific slab or the alternate stress during slab break off during the latest cretaceous a drastic change of regional tectonic stress orientation from wnw ese to n s occurred in south china the third stage predominated by n s extension was developed which caused a new phase of regional crustal subsidence along the youngest e w trending extensional structures

geochemistry of the sedimentary rocks from the nanxiong basin south china and implications for provenance paleoenvironment and paleoclimate at the k t boundary cretaceous and tertiary clastic sedimentary rocks from the nanxiong basin south china have been analyzed to constrain their provenance depositional climate and environment evidence from discrimination diagrams for sedimentary provenance and tectonic setting show that the nanxiong basin sediments were derived from typical continental sources geochemical signatures e g eu eu th ti la ti ta ti y b ti and y ti ratios of the claystone are nearly constant suggesting the provenance of the nanxiong basin remained similar throughout the late cretaceous to early paleocene 83 56 ma in contrast rb ti cs ti ratios and toc and caco3 concentrations require an obvious change in climate across the late cretaceous and early paleocene boundary singularly higher caco3 contents and lower toc values and rb ti cs ti ratios in the late cretaceous indicate that a long period extreme dry climate occurred at that time in south china rb ti cs ti ratios and toc values escalated and caco3 contents decreased in the early paleocene suggesting that the climate became relatively wet which resulted in greater vegetation cover the lasting extreme dry climate in the late cretaceous may provide a clue to the extinction of the dinosaurs in the nanxiong basin c 2006 elsevier b v all rights reserved

middle jurassic collision of an exotic microcontinental fragment implications for magmatism across the southeast china continental margin abstract thrusting folding and metamorphism of late paleozoic to middle mesozoic sedimentary rocks together with high precision u pb zircon ages from middle to late jurassic volcanic and granitic rocks reveal evidence for a major deformation event in northwestern hong kong between 164 and 161 ma this episode can be linked with collision of an exotic microcontinental fragment along the southeast china continental margin determined from contrasting detrital zircon provenance histories of late paleozoic to middle mesozoic sedimentary rocks either side of an ne trending suture zone through central hong kong the suture zone is also reflected by isotopic heterogeneities and geophysical anomalies in the crustal basement detrital zircon provenance of early to middle jurassic rocks from the accreted terrane have little in common with the pre middle jurassic rocks from southeast china instead the zircon age spectra of the accreted terrane show close affinities to sources along the northern margin of east gondwana these data provide indisputable evidence for mesozoic terrane accretion along the southeast china continental margin in addition collision of the exotic terrane accompanied by subduction rollback is considered to have hastened foundering of the postulated flat slab beneath southeast china leading to a widespread igneous flare up event at 160 ma

new and revised set of cretaceous paleomagnetic poles from hong kong implications for the development of southeast china a paleomagnetic study of upper cretaceous 80 ma dikes from hong kong was conducted with the aim of better understanding the late cretaceous cenozoic kinematic history of southeast china twelve out of seventeen sites collected from four dikes revealed primary trms and yield a late cretaceous paleopole at 69 38n 211 28e where a95 8 98 and k 107 a synthesis of south china block cretaceous poles indicates that coastal southeast china which is bounded by the lianhuashan fault zone to the northwest and the changlenanao fault zone to the southeast has moved relative to inland central south china the discordant cretaceous paleopoles from the south china block suggest a moderate net clockwise rotation of the coastal southeast china relative to central south china since the late cretaceous this clockwise rotation is probably the result of micro blocks along the south china margin experiencing vertical axis rotations in response to the penetrative dextral shear along the se china margin during oblique subduction of the pacific plate beneath south china an alternative interpretation involves regional extension that displaced a raft block southeastwards of the margin generating apparent paleomagnetic records with no real block rotations q 2004 elsevier ltd all rights reserved

u pb zircon geochemical and sr nd hf isotopic constraints on age and origin of jurassic i and a type granites from central guangdong se china a major igneous event in response to foundering of a subducted flat slab abstract the mesozoic geology of se china is characterized by widespread jurassic to cretaceous igneous rocks consisting predominantly of granites and rhyolites and subordinate mafic lithologies however the tectonic regime responsible for the inland jurassic granites remains controversial we report here u pb zircon ages geochemical and sr nd hf isotopic data for the nankunshan alkaline granite and the fogang granitic batholith in central guangdong mineralogical and geochemical features suggest that the fogang and nankunshan rocks are i and aluminous a type granites respectively shrimp u pb zircon analyses yield consistent ages ranging from 159 3 ma to 165 2 ma for four samples from the fogang batholith and an age of 158 5 ma for the nankunshan granite the fogang granites having i sr 0 7098 0 7136 e nd t 4 3 to 12 2 and e hf t 11 5 to 3 1 for the magmatic zircons were derived from paleoproterozoic mafic intermediate igneous protolith with minor addition of mantle derived magmas the nankunshan rocks have relatively lower i sr 0 706 0 708 higher e nd t 0 3 to 2 4 and e hf t 5 7 to 1 1 for the magmatic zircons and some oib like trace element ratios they were likely generated through extensive fractional crystallization of mantle derived alkaline parental magma associated with crustal assimilation these 160 ma i and a type granites in central guangdong were emplaced coeval with the widespread 165 155 ma i and a type granites and syenites following the initiation of intraplate basaltic and or bimodal igneous magmatism at 180 170 ma in the adjacent regions we interpret these jurassic igneous rocks as anorogenic magmatism formed during a major igneous event in response to foundering of an early mesozoic subducted flat slab beneath se china continent

genetic types mineralization styles and geodynamic settings of mesozoic tungsten deposits in south china abstract south china hosts the most abundant and largest tungsten w deposits in the world being a famous w metallogenic region located at the eastern part of the south china block which was formed by amalgamation of the yangtze and cathaysia blocks during the neoproterozoic these w deposits were mainly formed during the mesozoic the w mineralization is dominanted by greisen quartz vein skarn and porphyry types all of which are genetically related to the evolution of highly fractionated granitoids four episodes of w mineralization are recognized 1 late triassic 230 210 ma in the central and western parts of south china 2 middle jurassic ca 170 ma to early cretaceous ca 140 ma in the interior of south china with the mineralization being concentrated in southern jiangxi province between 165 and 150 ma 3 early cretaceous 136 120 ma with deposits across south china and 4 late cretaceous 100 80 ma mainly in the southwestern parts of south china these four periods of mineralization are closely related to the closure of paleo tethys and subduction of the paleo pacific plate in the late triassic these two events caused local extensional environments facilitating emplacement of the peraluminous granitoids and formation of the w deposits in the middle jurassic break off of the subducting oceanic plate resulted in emplacement of highly fractionated granites in the nanling region later anticlockwise rotation of the paleo pacific plate created widespread s type granitoids and associated middle jurassic to early cretaceous w mineralization in the interior of south china since 136 ma rollback of the subducting pacific plate resulted in weak w mineralization across south china finally a change of direction in the retreating plate from se to ese resulted in intensive mineralization of the southwestern part of south china

continentward dipping detachment fault system and asymmetric rift structure of the baiyun sag northern south china sea abstract the rift architecture and deep crustal structure of the distal margin at the mid northern margin of the south china sea have been previously investigated by using deep seismic reflection profiles however one fundamental recurring problem in the debate is the extensional fault system and rift structure of the hyperextended rift basins baiyun sag and liwan sag within the distal margin because of the limited amount of seismic data based on new 3d seismic survey data and 2d seismic reflection profiles we observe an array of fault blocks in the baiyun sag which were tilted towards the ocean by extensional faulting the extensional faults consistently dip towards the continent beneath the tilted fault blocks and extensional faults a low angle high amplitude and continuous reflection has been interpreted as the master detachment surface that controls the extension process during rifting the continentward dipping normal faults evolved in a sequence from south to north generating the asymmetric rift structure of the baiyun sag the baiyun sag is separated from the oceanic domain by a series of structural highs that were uplifted by magmatic activity in response to the continental breakup at 33 ma and a ridge jump to the south at 26 24 ma therefore we propose that magmatism played a significant role in the continental extension and final breakup in the south china sea

microtextures in mudrocks as revealed by backscattered electron imaging abstract this report is one of the first attempts to examine polished mudrock sections with backscattered scanning electron microscopy bse in order to image characterize and understand their microtextures as well as to help reconstruct sedimentary and diagenetic environments over 180 polished thin sections of mudrocks from precambrian to early middle tertiary age were examined in this study using bse seven common microtextures have been identified in the samples examined with bse microlaminations fossil forms pyrite clay minerals and micas chemical and physical alteration glauconization and porosity microlaminations have been examined at the single grain level foraminifera in the gulf coast tertiary reflect a sequence of preservation relations from shallow depths to a few thousand meters fecal pellets in a black mudrock from spitsbergen of upper jurassic age contain what appear to be well preserved fossil vertebrates replaced by pyrite the chemical and physical variations within micas and clay minerals seem to be the result of selective alteration along cracks and defects in the minerals and these have been imaged mineral growth and dissolution at the submicron level can be imaged particularly in the clay minerals quartz and feldspar glauconite growth conditions geochemical complexities of carbonate formation and the size shape and orientation of micron sized pore spaces in shales have been obtained thus the microtextural analysis of mudrocks not only is possible but can be accomplished in great detail with existing techniques