himalayan forelands palaeontological evidence for oligocene detrital deposits in the bugti hills balochistan pakistan in the southwestern sulaiman geological province balochistan pakistan terrestrial detri tal facies from the bugti hills region have yielded the richest tertiary vertebrate faunas to be found in asia thus far new fossils from five successive and distinct bone beds bridge the supposed oligocene sedimentary hiatus within the sulaiman geological province the lowermost continental levels of the previously described miocene chitarwata formation known as the bugti member are oligocene in age in the bugti area neither a mixture of heterochronic faunal elements nor endemism of any fauna is evident in this area additional microfaunal material from the bugti member constrains an oligocene age for the lower chitarwata formation in zinda pir northeast of the bugti hills this oligocene transition between the marine kirthar eocene and continental siwalik miocene deposits consists of a regressive fluvio deltaic system occupying a vast floodplain it represents an early stage molasse in the palaeo indus basin which drained western orogenic highlands resulting from the colli sion between the indian and eurasian plates

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

coordinated hydrological regimes in the indo pacific region during the past two millennia instrumental data suggest that major shifts in tropical pacific atmospheric dynamics and hydrology have occurred within the past century potentially in response to anthropogenic warming to better understand these trends we use the hydrogen isotopic ratios of terrestrial higher plant leaf waxes delta d wax in marine sediments from southwest sulawesi indonesia to compile a detailed reconstruction of central indo pacific warm pool ipwp hydrologic variability spanning most of the last two millennia our paleodata are highly correlated with a monsoon reconstruction from southeast asia indicating that intervals of strong east asian summer monsoon easm activity are associated with a weaker indonesian monsoon im furthermore the centennial scale oscillations in our data follow known changes in northern hemisphere climate e g the little ice age and medieval warm period implying a dynamic link between northern hemisphere temperatures and ipwp hydrology the inverse relationship between the easm and im suggests that migrations of the intertropical convergence zone and associated changes in monsoon strength caused synoptic hydrologic shifts in the ipwp throughout most of the past two millennia

compressional and shear wave velocities as a function of confining stress in dry sandstones a laboratory study was carried out to investigate the influence of confining stress on compressional and shear wave velocities for a set of rock samples from gas producing sandstone reservoirs in the cooper basin south australia the suite of samples consists of 22 consolidated sublitharenites with helium porosity ranging from 2 6 to 16 6 we used a pulse echo technique to measure compressional and shear wave velocities on dry samples cylindrical 4 6 2 cm at room temperature and at elevated confining stress 60 mpa compressional and shear wave velocities in samples increase non linearly with confining stress a regression equation of the form v a be dp gives a good fit to the measured velocities with improved prediction of velocities at high confining stresses compared with equations suggested by other studies the predicted microcrack closure stresses of the samples show values ranging from 70 mpa to 95 mpa and insignificant correlation with porosity permeability or clay content there is a positive correlation between change in velocity with core porosity and permeability but this association is weak and diminishes with increasing confining stress experimental results show that pore geometry grain contact type and distribution and location of clay particles may be more significant than total porosity and clay content in describing the stress sensitivity of sandstones at in situ reservoir effective stress the stress dependence of cooper basin sandstones is very large compared with data from other studies the implication of our study for hydrocarbon exploration is that where the in situ reservoir effective stress is much less than the microcrack closure stress of the reservoir rocks the variation of reservoir effective stress could cause significant changes in velocity of the reservoir rocks the velocity changes induced by effective stress in highly stress sensitive rocks can be detected at sonic log and probably surface seismic frequencies

ages and paleoenvironment of miocene mammalian faunas from thailand abstract the geological survey of continental basins in northern thailand has led to the discovery and the study of several mammalian assemblages in that area all localities from northern thailand occur in a time span ranging from about 16 to 14 ma in addition a diachronism is apparent among the different localities and is indicated by the different stages of evolution in the tooth morphology of rodents ruminants rhinos and mastodonts mae long li basin would be the oldest locality about 16 ma followed by had pu dai lampang basin and then huai siew and ban san klang both in pong basin ban na sai li basin and mae teep would be contemporaneous with ban san klang and mae moh is thought to be the youngest locality in order to study the paleoenvironment of the thai neogene faunas we have used the cenogram method in which structure reflects the general environment of a faunal community we also compared the faunal communities from thailand with those from the pakistan siwaliks and from china in the latter areas the microfauna is well represented and the large mammals are numerous thus suggesting a wet environment with a likely monsoonal climate the middle miocene paleoenvironment in south asia seems to have been quite open and small areas of forests were probably intermixed with grassland the cenogram structure completely excludes an environment dominated by primary forest or by steppe

a stalagmite record of holocene indonesian australian summer monsoon variability from the australian tropics oxygen isotopic data from a suite of calcite and aragonite stalagmites from cave kni 51 located in the eastern kimberley region of tropical western australia represent the first absolute dated high resolution speleothem record of the holocene indonesianeaustralian summer monsoon iasm from the australian tropics stalagmite oxygen isotopic values track monsoon intensity via amount effects in precipitation and reveal a dynamic holocene iasm which strengthened in the early holocene decreased in strength by 4 ka with a further decrease from w2 to 1 ka before strengthening again at 1 ka to years to levels similar to those between 4 and 2 ka the relationships between the kni 51 iasm reconstruction and those from published speleothem time series from flores and borneo in combination with other data sets appear largely inconsistent with changes in the position and or organization of the intertropical convergence zone itcz instead we argue that the el nino southern oscillation enso may have played a dominant role in driving iasm variability since at least the middle holocene given the muted modern monsoon rainfall responses to most el nino events in the kimberley an impact of enso on regional monsoon precipitation over northwestern australia would suggest non stationarity in the long term relationship between enso forcing and iasm rainfall possibly due to changes in the mean state of the tropical pacific over the holocene

a generalized biot gassmann model for the acoustic properties of shaley sandstones1 we obtain the wave velocities of clay bearing sandstones as a function of clay content porosity and frequency unlike previous theories based simply on slowness and or moduli averaging or two phase models we use a biot type three phase theory that considers the existence of two solids sand grains and clay particles and a fluid the theory which is consistent with the critical porosity concept uses three free parameters that determine the dependence of the dry rock moduli of the sand and clay matrices as a function of porosity and clay content testing of the model with laboratory data shows good agreement between predictions and measurements in addition to a rock physics model that can be useful for petrophysical interpretation of wave velocities obtained from well logs and surface seismic data the model provides the differential equation for computing synthetic seismograms in inhomogeneous media from the seismic to the ultrasonic frequency bands

misalignment of the orientation of fractures and the principal axes for p and s waves in rocks containing multiple non orthogonal fracture sets summary azimuthal anisotropy in rocks can result from the presence of one or more sets of partially aligned fractures with orientations determined by the stress history of the rock a shear wave propagating in an azimuthally anisotropic medium splits into two components with diverent polarizations if the source polarization is not aligned with the principal axes of the medium in the presence of two or more non orthogonal sets of vertical fractures the symmetry of the medium may be approximated as monoclinic with a horizontal plane of mirror symmetry if in the absence of fractures the rock is transversely isotropic ti with the symmetry axis perpendicular to the bedding plane for such a medium the fast and slow polarization directions for vertically propagating shear waves are not parallel or perpendicular to any of the fracture planes but lie in directions given by the principal axes of a second rank fracture compliance tensor this tensor is independent of the normal compliance of the fractures it follows that for vertical propagation of shear waves in a vertically fractured ti medium any number of arbitrarily oriented vertical fracture sets is equivalent to two mutually perpendicular fracture sets provided that the seismic wavelength is large compared to the size of the fractures for ovsets typical of surface seismic acquisition the p wave velocity at fixed ovset varies with azimuth as cos 2 w w 0 where w is the azimuth measured with respect to the fast polarization direction for a vertically polarized shear wave w 0 depends on both the normal and the shear compliance of the fractures and may diver from zero if the ratio of the normal to shear compliance of the fractures varies significantly between fracture sets if this ratio is similar for all fractures w 0 0 and the principal axes of the variation in p wave velocity with azimuth for fixed ovset are determined by the principal axes of the second rank fracture compliance tensor

glacial to holocene swings of the australian indonesian monsoon the australian indonesian monsoon is an important component of the climate system in the tropical indo pacific region 1 however its past variability relation with northern and southern high latitude climate and connection to the other asian monsoon systems are poorly understood here we present high resolution records of monsoon controlled austral winter upwelling during the past 22 000 years based on planktic foraminiferal oxygen isotopes and faunal composition in a sedimentary archive collected offshore southern java we show that glacial interglacial variations in the australian indonesian winter monsoon were in phase with the indian summer monsoon system consistent with their modern linkage through cross equatorial surface winds likewise millennial scale variability of upwelling shares similar sign and timing with upwelling variability in the arabian sea on the basis of element composition and grain size distribution as precipitation sensitive proxies in the same archive we infer that austral summer monsoon rainfall was highest during the bolling allerod period and the past 2 500 years our results indicate drier conditions during heinrich stadial 1 due to a southward shift of summer rainfall and a relatively weak hadley cell south of the equator we suggest that the australian indonesian summer and winter monsoon variability were closely linked to summer insolation and abrupt climate changes in the northern hemisphere the seasonality of the global monsoon is of central importance to the global hydrologic cycle and its environmental influence on human societies palaeoclimate reconstructions generally agree that the strengths of the east asian monsoon and the indian monsoon are tightly coupled to the northern hemisphere climate through zonal migrations of the monsoon convection centres also interpreted as intertropical convergence zone itcz migration 26 the mechanism of the australianindone

dynamical response of the tropical pacific ocean to solar forcing during the early holocene we present a high resolution magnesium calcium proxy record of holocene sea surface temperature sst from off the west coast of baja california sur mexico a region where interannual sst variability is dominated today by the influence of the el nino southern oscillation enso temperatures were lowest during the early to middle holocene consistent with documented eastern equatorial pacific cooling and numerical model simulations of orbital forcing into a la nina like state at that time the early holocene ssts were also characterized by millennial scale fluctuations that correlate with cosmogenic nuclide proxies of solar variability with inferred solar minima corresponding to el nino like warm conditions in apparent agreement with the theoretical ocean dynamical thermostat response of enso to exogenous radiative forcing

multi scale variability of the asian monsoon recorded in an annually banded stalagmite during the neoglacial from qixing cave southwestern china abstract solar forcing of the asian summer monsoon asm and the embedded feedback mechanism remain highly controversial in this study interannual scale asm variability from 3 58 to 2 28 ka bp is reconstructed based on the 18 o record of an annually laminated stalagmite from qixing cave in southwestern china the cave 18 o record agrees well with a record of solar activity on the centennial scale during the whole time series furthermore statistical analysis of singular spectrum and wavelet spectrum shows a significant cycle of 60 years one of the solar activity cycles the two lines of evidence have consolidated the solar impact on a centennial decadal time scale of asm variability timing and structure of the 2 8 ka event detected in various archives at a global scale have been well determined in our 18 o record with a high precision time scale established by absolute 230 th dating and annual layer counting we observed an asymmetrical pattern of the event i e a gradual transition at the onset with a rapid end which can be interpreted as a far field effect of changing thermohaline circulations in the north atlantic we further demonstrate a striking inverse correlation between the asm and the indonesian australian summer monsoon iasm on the centennial scale including three dominant asm depression events that are related to periods of weak solar activity the evidence we present here supports that ocean atmosphere interactions amplified the solar signal and caused abrupt cooling events in widespread areas during the holocene

chaungtha a new middle miocene mammal locality from the irrawaddy formation myanmar abstract we describe here a mammalian assemblage originating from the locality of chaungtha irrawaddy formation myanmar it represents one of the rare descriptions of a precisely located in space vertical section and time fossil mammal fauna from the irrawaddy formation classically the fossil record of irrawaddy formation is essentially known from isolated fossils of imprecise or unknown provenance especially concerning the stratigraphic position of the fossils along several hundred meter thick sections the chaungtha faunal association consists of the rhino brachypotherium fatehjangense the pig conohyus thailandicus the ruminants cf siamotragulus sanyathanai cf siamotragulus sp and a gomphotheriid proboscidean this assemblage indicates that the locality is miocene in age and not late eocene as previously claimed and roughly contemporaneous with the chinji formation of india pakistan ca 14 11 ma and with the mae moh group of northern thailand the chaungtha fauna even if it displays regional characteristics shows a strong resemblance to those of the middle miocene of india pakistan and of thailand and reinforces the idea that south east asia and pakistan were part of the same biogeographical province during the middle miocene

seismic and electrical properties of unconsolidated permafrost1 a model has been developed to relate the velocities of acoustic waves vp and vs in unconsolidated permafrost to the porosity and extent of freezing of the interstitial water the permafrost is idealized as an assemblage of spherical quartz grains embedded in a matrix composed of spherical inclusions of water in ice the wave scattering theory of kuster and toksoz is used to determine the effective elastic moduli and hence the acoustic velocities the model predicts vp and vs to be decreasing functions of both the porosity and the water to ice ratio the theory has been applied to laboratory measurements of vp and vs in 31 permafrost samples from the north american arctic although no direct measurements were made of the extent of freezing in these samples the data are consistent with the predictions of the model electrical resistivity measurements on the permafrost samples have demonstrated their essentially resistive behaviour the ratio of resistivity of permafrost in its frozen state to that in its unfrozen state has been related to the extent of freezing in the samples electromagnetic and seismic reflection surveys can be used together in areas of permafrost firstly an em survey to determine the extent of freezing and then the acoustic velocity model to predict the velocities in the permafrost the necessary transit time corrections can thus be made on seismic reflection records to compensate for the presence of permafrost

dynamics of the intertropical convergence zone over the western pacific during the little ice age precipitation patterns in the western pacific changed at the onset of the little ice age a synthesis of precipitation reconstructions suggests that this change resulted from a contraction of the intertropical convergence zone

lithofacies depositional environments regional biostratigraphy and age of the chitarwata formation in the bugti hills balochistan pakistan abstract the oligocene early miocene chitarwata formation records a critical interval of terrestrial sedimentation that predates the siwalik deposits on the potwar plateau of north central pakistan this oligocene early miocene time interval has long been considered as lacking in the entire indo pakistan region the chitarwata formation is widely exposed in the sulaiman range but has never been described in detail in the sulaiman lobe where the famous fossiliferous strata called bugti bone beds have been known for over a century and half the chitarwata formation represents coastal delta at the base and plain and fluvial environments at the top lithofacies and sedimentary structures of the chitarwata formation in the bugti area are described in detail and show a clearly distinct lithologic pattern different from that reported from the zinda pir area the chitarwata formation also records an important transition in the evolution of the drainage systems in the area during the late paleogene and early neogene this transition from the west flowing paleo indus fluvial system to the development of the ancestral indus drainage system may explain the numerous hiatuses that characterize the chitarwata formation the abundance of fossil mammals from the chitarwata and overlying vihowa formation in the bugti hills provides critical biochronologic information that sheds new light on biostratigraphic correlation with the zinda pir area and for the entire sulaiman range

holocene surface hydroclimate changes in the indo pacific warm pool abstract the indo pacific warm pool ipwp is an area hosting key tropical climate processes such as the el nino southern oscillation enso and indian ocean dipole iod the tropical climate processes via various feedback mechanisms control the surface ocean climate in the indian ocean and its surrounding continents on annual to inter annual timescales however little has been known about how the tropical processes are effective forcing climate mechanism over longer timescales here we presented a reconstruction of the spatiotemporal pattern of sea surface temperature sst with inferred hydroclimate changes since the early holocene 11ka using proxies of planktonic foraminifer shell mg ca organic biomarker tex86 foraminifer oxygen isotopes and a terrigenous bit index measured from a 220 cm long core bs24 2 724041 n 97 010943 e 1015 m water depth which was taken offshore of northwest sumatra in the eastern indian ocean with an age model of 13 ams 14c dating by the uses of planktonic foraminiferal shells from the core the tex86h temperatures of bs24 show as summer weighted and reflect integrated thermal effects from the surface to thermocline water while the mg ca temperature of bs24 better reflects mean annual sst our results along with a regional synthesis of published sst records from the ipwp suggest that the ipwp has migrated eastwardly since the mid holocene 5ka in phase with this eastward migration the ipwp ssts have decreased but the upwelling in the eastern indian ocean appears to have been a persistent feature since the mid holocene our empirical orthogonal function eof analysis on the compiled ipwp sst records indicates two dominant modes of spatio temporal variability of surface hydrographes in the ipwp that are attributed to a combined effect of orbital and solar forcing with expressions analogous to the indian ocean basin wide mode iobm and the indian ocean dipole model iod

forcing of wet phases in southeast africa over the past 17 000 years a continuous record of hydrologic variability for the past 17 000 years at the mouth of the zambezi river shows that hydrologic conditions in southeast africa were controlled by variations in local insolation and migrations of the intertropical convergence zone rather than by indian ocean temperature records of hydroclimatological variability in southern africa since the last glacial maximum have produced a conflicting picture of the relative influences of events in the remote northern hemisphere and the more local indian ocean this paper presents a continuous record of hydrological variability for the past 17 000 years from marine sediment core drilled off the mouth of the zambezi river the record shows that hydrological conditions in the region were influenced by variations in local insolation and migrations of the intertropical convergence zone which were probably driven by events in the northern hemisphere rather than the indian ocean intense debate persists about the climatic mechanisms governing hydrologic changes in tropical and subtropical southeast africa since the last glacial maximum about 20 000 years ago in particular the relative importance of atmospheric and oceanic processes is not firmly established1 2 3 4 5 southward shifts of the intertropical convergence zone itcz driven by high latitude climate changes have been suggested as a primary forcing2 3 whereas other studies infer a predominant influence of indian ocean sea surface temperatures on regional rainfall changes4 5 to address this question a continuous record representing an integrated signal of regional climate variability is required but has until now been missing here we show that remote atmospheric forcing by cold events in the northern high latitudes appears to have been the main driver of hydro climatology in southeast africa during rapid climate changes over the past 17 000 years our results are based on a reconstruction of precipitation and river discharge changes as recorded in a marine sediment core off the mouth of the zambezi river near the southern boundary of the modern seasonal itcz migration indian ocean sea surface temperatures did not exert a primary control over southeast african hydrologic variability instead phases of high precipitation and terrestrial discharge occurred when the itcz was forced southwards during northern hemisphere cold events such as heinrich stadial 1 around 16 000 years ago and the younger dryas around 12 000 years ago or when local summer insolation was high in the late holocene that is during the past 4 000 years

reconciling physical properties with surface seismic data from a layered mafic intrusion abstract compositional layering of intrusive rocks is often cited as a source of seismic reflectivity in the crystalline crust direct evidence for this is based primarily on synthetic seismograms calculated from laboratory measurements of rock velocity and density or estimates of aggregate rock properties from measurements of mineral velocities and densities little is known about how in situ effects such as fracturing chemical alteration or anisotropy may change the reflectivity character of the surface seismic data an ideal dataset for examining the hazards of using physical properties data for estimating crustal reflectivity occurs at the nellie intrusion a middle proterozoic age layered mafic intrusion that lies beneath the permian basin of west texas due to a well that penetrated 4 5 km of the intrusion we have a dataset that spans the scale from compositional data on the intrusion derived from well cuttings to log data to surface reflection data sonic and density log data from the well measure velocities and densities 10 to 15 below the values calculated from modal mineralogy we attribute this difference primarily to pervasive post emplacement alteration and fracturing of the rock mass in situ thus this unique dataset provides a quantitative estimate of the magnitude of difference between observed and theoretical velocities that can be expected for crystalline rocks in the upper crust and its cause despite the difference analysis of synthetic seismograms shows that primary compositional variation of the intrusion is still responsible for sub horizontal layered reflectivity in both the log based and petrology based synthetic seismograms boundaries of intrusive cycles are characterized by large negative reflection coefficients due to the juxtaposition of mafic rich basal layers against plagioclase rich layer tops in detail only the log based synthetic provides a good match to the surface seismic reflection data this suggests that physical properties from modal mineralogy are useful in obtaining a generalized model for reflectivity but that differences in bulk physical properties of the rock mass preclude the possiblity of obtaining a one to one match with surface seismic data

effects of diagenesis and clays on compressional velocities in rocks experimental results at ultrasonic frequencies in brine or water saturated samples cut perpendicular to bedding demonstrate that compressional velocities vary linearly with porosity and volume fraction clay in detrital silicate rocks characterized by pores with low aspect ratios p wave velocity is more sensitive to porosity than clay content obeying the empirically derived expression vp 2 4c 8 6 5 8 at 800 bars confining pressure and 400 bars pore pressure where the units of vp are kilometers per second is the volume fraction pores and c is the volume fraction clay deviations from this equation are less than 2 with the exception of the high pore aspect ratio st peter sandstone which has a compressional velocity that is 17 higher than the predicted value the equation is insensitive to the chemical compostion of the dominant clay mineral and apparently insensitive to the location of the clay grains with respect to the mineral framework e g in free pore space or in contact zones between mineral grains of lower compressibilities

enso driven carbon see saw in the indo pacific 1 the sediment trap experiments have been carried out during the 2001 2002 el nino la nina transition in the monsoon driven and freshwater influenced upwelling system off south java the results indicate that enhanced precipitation rates and associated river discharges increase the co2 uptake of the biological pump by increasing the organic carbon export and reducing the carbonate precipitation the freshwater furthermore forms a buoyant low salinity surface layer that caps off the nutrient and co2 rich subsurface waters which shortens the upwelling season during wet la nina conditions a reduced capping effect during dryer el nino conditions strengthens the upwelling and as shown by our model results increase co2 emission into the atmosphere along the freshwater influenced continental margins in se asia by contrast el nino weakens upwelling and reduces the co2 emission in the equatorial pacific ocean

upwelling variability off southern indonesia over the past two millennia modern variability in upwelling off southern indonesia is strongly controlled by the australian indonesian monsoon and the el nino southern oscillation but multidecadal to centennial scale variations are less clear we present high resolution records of upper water column temperature thermal gradient and relative abundances of mixed layer and thermocline dwelling planktonic foraminiferal species off southern indonesia for the past two millennia that we use as proxies for upwelling variability we find that upwelling was generally strong during the little ice age lia and weak during the medieval warm period mwp and the roman warm period rwp upwelling is significantly anticorrelated to east asian summer monsoonal rainfall and the zonal equatorial pacific temperature gradient we suggest that changes in the background state of the tropical pacific may have substantially contributed to the centennial scale upwelling trends observed in our records our results implicate the prevalence of an el nino like mean state during the lia and a la nina like mean state during the mwp and the rwp

parameters controlling sonic velocities in a mixed carbonate siliciclastics permian shelf margin upper san andres formation last chance canyon new mexico we have measured the acoustic properties and mineralogic composition of 48 rock specimens from mixed carbonate siliciclastic outcrops of the permian upper san andres formation in last chance canyon new mexico the goals were 1 identify and model the parameters controlling the sonic velocities 2 assess the influence of postburial diagenesis on the acoustic velocities the variation in sonic velocity in the 0 to 25 porosity range is primarily controlled by porosity and secondly by the ratio of carbonate siliciclastic material linear multivariate fitting resulted in a velocity porosity carbonate content transform that accurately predicts sonic velocity at different effective stresses the slope of the velocity porosity transform steepens with increasing carbonate content which may be explained by the higher velocity of carbonate minerals another reason may be the property of carbonate minerals to form more perfect intercrystalline boundaries that improve the transmission properties of acoustic waves and are less sensitive to changes in effective stress the velocity ratio vp vs is an excellent tool to discriminate between predominantly calcitic lithologies ratio between 1 8 and 1 95 and predominantly dolomitic and quartz rich lithologies ratio between 1 65 and 1 8 gardner s experimental curve overestimates and the velocity porosity transforms by wyllie and raymer underestimate the observed sonic velocities probably because they do not account for variations in texture carbonate mineralogy and pore geometry petrographic observations show that postburial diagenesis is minor and does not seem to significantly affect porosity therefore the outcrop data set can be regarded as a proxy for the subsurface analog these findings underline the significantly more complex acoustic behavior in mixed carbonate siliciclastic sedimentary rocks than in pure siliciclastics where mineralogic composition explains most of the observed relationships between porosity and sonic velocity

velocities and quality factors of sedimentary rocks at low and high effective pressures summary techniques for measuring acoustic velocities and quality factors q of sedimentary rocks in the laboratory are sufficiently accurate to establish closely fitting regression curves which represent the variation of these acoustic properties with pressure ultrasonic p and s wave measurements of velocity v v and q q q were made on 16 different water saturated sandstone samples at various effective pressures using an ultrasonic reflection technique and the data were fitted using a simple regression equation containing a constant plus linear and exponential pressure dependent terms the redundancy of the linear term in the regression of q data suggests that microcracks alone govern the pressure variation of q whereas velocities are additionally dependent on another mechanism consistent with the changes in elastic moduli caused by intergranular compression causing small reductions in porosity the implied rates of microcrack closure with increasing effective pressure in all samples were found to be comparable the regression equations describe the data closely enough to enable the extrapolation of acoustic properties to both low and high effective pressures this is of practical use since laboratory techniques can produce uncertain results at low pressures due to coupling problems and low signal strengths whilst high pressures require large confining vessels low pressure and high pressure data are applicable to shallow seismic surveys and hydrocarbon exploration respectively

velocity porosity clay content systematics of poorly consolidated sandstones compressional velocities have been measured as a function of confining pressure for 14 west delta block louisiana sandstone cores the dry velocity data for these poorly consolidated sandstones at 10 mpa confining pressure plot on a linear velocity density trend with well consolidated sandstones but not loose sands the dry velocity data also show linear trends of decreasing velocity with increasing porosity along contours of constant clay content similar to those obtained at 40 mpa by tosaya and nur 1982 for saturated sandstones the spacing between clay contours indicates that a large portion of the velocity variation with clay content is due to microporosity which is not included in point counting within the clays the slope of the velocity porosity trends indicates that cementation increases with decreasing porosity

diversity and evolutionary trends of the family rhinocerotidae perissodactyla abstract diversity and evolutionary trends of the family rhinocerotidae are presented herein the sample has a temporal range from the middle eocene to recent including 41 genera and 142 species from europe asia north america and africa diversity and the first and last records have been established for each area along a temporal scale the relative body size and weight and the gracility index of the mciii have been also analysed the results show that the highest values in diversity and first and last records are reached in asia eurasia and africa share many taxa while north america is more independent at generic and specific levels very small and very slender taxa are present in eurasia and north america absent in africa they coexist with brachypodial and generally large forms in eurasia whereas in north america they are replaced by large more robust forms from the middle miocene onward middle large sized species with intermediate gracility predominate often together with the brachypodial ones the latter type disappears by the late miocene with just one genus remaining in asia during the pliocene at this time a general decline of the rhinocerotidae occurs related to a major climatic change becoming extinct in north america by the end of the pleistocene rhinocerotids disappear from europe and wide areas of asia but they remain in southeast asia and in africa south of the sahara

velocities of compressional and shear waves in limestones carbonate rocks are important hydrocarbon reservoir rocks with complex textures and petrophysical properties porosity and permeability mainly resulting from various diagenetic processes compaction dissolution precipitation cementation etc these complexities make prediction of reservoir characteristics e g porosity and permeability from their seismic properties very difficult to explore the relationship between the seismic petrophysical and geological properties ultrasonic compressional and shear wave velocity measurements were made under a simulated in situ condition of pressure 50 mpa hydrostatic effective pressure at frequencies of approximately 0 85 mhz and 0 7 mhz respectively using a pulse echo method the measurements were made both in vacuum dry and fully saturated conditions in oolitic limestones of the great oolite formation of southern england some of the rocks were fully saturated with oil the acoustic measurements were supplemented by porosity and permeability measurements petrological and pore geometry studies of resin impregnated polished thin sections x ray diffraction analyses and scanning electron microscope studies to investigate submicroscopic textures and micropores it is shown that the compressional and shear wave velocities vp and vs respectively decrease with increasing porosity and that vp decreases approximately twice as fast as vs the systematic differences in pore structures e g the aspect ratio of the limestones produce large residuals in the velocity versus porosity relationship it is demonstrated that the velocity versus porosity relationship can be improved by removing the pore structure dependent variations from the residuals the introduction of water into the pore space decreases the shear moduli of the rocks by about 2 gpa suggesting that there exists a fluid matrix interaction at grain contacts which reduces the rigidity the predicted biot gassmann velocity values are greater than the measured velocity values due to the rock fluid interaction this is not accounted for in the biot gassmann velocity models and velocity dispersion due to a local flow mechanism the velocities predicted by the raymer and time average relationships overestimated the measured velocities even more than the biot model

laboratory measurements of the acoustic and transport properties of carbonate rocks and their link with the amount of microcrystalline matrix laboratory data and computer tomography ct scan image analysis of carbonate rocks were combined demonstrating a quantitative link between acoustic and transport properties the fraction of microcrystalline calcite micrite in the matrix and the grain to micrite matrix ratio samples from the monte acuto formation gargano italy a transgressive system tract tst whose microstructure ranges from basal pelagic mudstones to coarse calciturbidites were analyzed results indicate that high micrite rocks with low grain to micrite matrix ratios typical of low energy depositional settings are relatively stiffer and more impermeable in contrast lower amounts of micrite due to high energy depositional settings or its removal from intergranular macropores by progressive leaching of the matrix leads to high grain to micrite matrix ratios this process will increase porosity and reduce rock stiffness both of which reduce velocity decreasing micrite content correlates well with increasing macroporosity

a review of fossil rhinoceroses from the neogene of myanmar with description of new specimens from the irrawaddy sediments abstract four genera and one indeterminate genus total eight species of fossil rhinoceroses mammalia perissodactyla rhinocerotidae are recognized from the neogene of central myanmar in the early miocene most area of central myanmar were under the shallow marine condition and no rhinocerotid remain has been documented yet during the middle to late miocene the rhinocerotid remains are commonly found and are represented by diceratherium naricum brachypotherium perimense brachypotherium fatehjangense and an indeterminate rhinocerotid in the latest miocene these archaic rhinoceroses became extinct in the late neogene the extant genera rhinoceros late miocene to pleistocene and dicerorhinus plio pleistocene first appeared in myanmar they appear to have dispersed to the island southeast asia from the continental asia during the early pleistocene to middle pleistocene when the eustatic sea level became low remarkably

fossil dripwater in stalagmites reveals holocene temperature and rainfall variation in amazonia abstract most proxy records used for reconstruction of holocene climate of amazonia are unable to quantitatively distinguish between the effect of temperature and rainfall amounts we present a new isotope technique applied to a 13 500 yr stalagmite archive from peruvian amazonia by analysing the coupled isotope composition of fossil dripwater trapped in stalagmite fluid inclusions and that of the calcite hosting the fluid inclusions we were able to calculate independent paleotemperatures and rainfall amounts this stalagmite record shows that holocene climate variation was controlled by orbitally forced southward migration of the inter tropical convergence zone while temperature remained constant isotope variation of rainwater reflected in fluid inclusion water 18o composition suggests a 15 30 increase in convective rainfall through the holocene a comparison of the low land peruvian fluid inclusion record with the high andean huascaran ice core record shows a constant 12 offset of 18o curves for the holocene suggesting that andean vertical temperature gradients lapse rates did not vary much over the last 9000 years during the younger dryas interval however the offset of 18o values was much higher than in the holocene this may be attributed to a relative drop in air temperatures in the highlands higher lapse rate caused by long distance teleconnections to climate perturbations in the north atlantic in a wider perspective fluid inclusion isotope analysis drastically improves paleotemperature reconstructions based on speleothem calcite 18o data because it provides the 18o value of drip water through time which is usually the most important unknown in paleotemperature equations

mid to late holocene australian indonesian summer monsoon variability abstract the australian indonesian monsoon has a governing influence on the agricultural practices and livelihood in the highly populated islands of indonesia however little is known about the factors that have influenced past monsoon activity in southern indonesia here we present a 6000 years high resolution record of australian indonesian summer monsoon aism rainfall variations based on bulk sediment element analysis in a sediment archive retrieved offshore northwest sumba island indonesia the record suggests lower riverine detrital supply and hence weaker aism rainfall between 6000 yr bp and 3000 yr bp compared to the late holocene we find a distinct shift in terrigenous sediment supply at around 2800 yr bp indicating a reorganization of the aism from a drier mid holocene to a wetter late holocene in southern indonesia the abrupt increase in rainfall at around 2800 yr bp coincides with a grand solar minimum an increase in southern indonesian rainfall in response to a solar minimum is consistent with climate model simulations that provide a possible explanation of the underlying mechanism responsible for the monsoonal shift we conclude that variations in solar activity play a significant role in monsoonal rainfall variability at multi decadal and longer timescales the combined effect of orbital and solar forcing explains important details in the temporal evolution of aism rainfall during the last 6000 years by contrast we find neither evidence for volcanic forcing of aism variability nor for a control by long term variations in the el nino southern oscillation enso

continuous 150 k y monsoon record from lake eyre australia insolation forcing implications and unexpected holocene failure our reconstructed history of lake eyre provides the first continuous continental proxy record of australian monsoon intensity over the past 150 k y this continental record s broad correspondence to the marine isotope record demonstrates that this very large catchment with its hydrology dependent on a planetary scale climate element responds to milankovitch scale climate forcing abrupt transitions from dry phases to wet phases ca 125 and 12 ka coincide with northern hemisphere winter insolation minima rather than southern hemisphere summer insolation maxima indicating that northern hemi sphere insolation exerts a dominant control over the intensity of the australian monsoon stratigraphic and dating uncertainties of other wet phases preclude conclusive correlation to specific insolation signals but within the uncertainties are consistent with northern hemisphere forcing regardless of the hemispheric forcing the low intensity of the early holocene australian monsoon by comparison with the last interglacial and particularly the last high level lacustrine event at 65 60 ka when all forcing elements were modest is an enigma that can be explained by a change in boundary conditions within australia

basic mechanism for abrupt monsoon transitions abstract monsoon systems influence the livelihood of hundreds of millions of people during the holocene and last glacial period rainfall in india and china has undergone strong and abrupt changes though details of monsoon circulations are complicated observations reveal a defining moisture advection feedback that dominates the seasonal heat balance and might act as an internal amplifier leading to abrupt changes in response to relatively weak external perturbations here we present a minimal conceptual model capturing this positive feedback the basic equations motivated by observed relations yield a threshold behavior robust with respect to addition of other physical processes below this threshold in net radiative influx r c no conventional monsoon can develop above r c two stable regimes exist we identify a nondimensional parameter l that defines the threshold and makes monsoon systems comparable with respect to the character of their abrupt transition this dynamic similitude may be helpful in understanding past and future variations in monsoon circulation within the restrictions of the model we compute r c for current monsoon systems in india china the bay of bengal west africa north america and australia where moisture advection is the main driver of the circulation

holocene diatom records of wetland development near weipa cape york australia abstract to better understand the response of tropical wetlands to holocene environmental changes two lacustrine diatom records from weipa cape york have been investigated the record from big willum bw01 commenced approx 7 9 calibrated thousand years before present k cal a bp and details stages of initial swamp development a phase of ephemeral conditions between approximately 5 7 and 2 2 k cal a bp and relative wetland stability after 2 2 k cal a bp lithological and to a lesser extent diatom assemblage changes in bw01 appear to be linked to broad scale changes in effective precipitation the record from little willum lw01 commenced around 0 9 k cal a bp and documents initial phases of swamp development until approximately 0 8 k cal a bp with subsequent relative wetland stability the uppermost 10 cm of this record approximately spanning the last 40 years coincide with mining activity in the region only minor changes in the diatom assemblage are recorded for this period implying that the overall character of the swamp probably remained unchanged both sites offer new insights into wetland dynamics in australia s dry tropics and demonstrate that changes in these lacustrine systems were probably driven by shifts in effective precipitation in particular during the late holocene

high and low latitude forcing of the east african climate since the lgm inferred from the elemental composition of marine sediments off tanzania abstract we present x ray fluorescence xrf scanner measurements from a 6 m long sediment core geob12624 1 on the upper slope of tanzania to reconstruct the climatic evolution in east africa since the last glacial maximum lgm log ratios of fe ca and ti ca are indicative for sediment discharge of the rufiji river which is controlled by climatic conditions in the rufiji catchment area the most significant changes in major elemental composition occurred at 15 1 and 7 4 ka highlighted by the regime shift index values the data set records distinct precipitation peaks during the early holocene this corresponds a maximum in the northern hemisphere nh summer insolation and results in a transition from the arid lgm to the humid early holocene our geochemical record also indicates that this climatic transition was interrupted by two severe droughts that occurred during nh cold intervals the heinrich stadial 1 hs1 and the younger dryas yd through a comparison with other nearby paleoclimatic records we suggest that arid climatic conditions only occurred in east africa north of 8 10 s whereas in southern east africa around 15 20 s increased humidity during the hs1 and yd prevailed we thus conclude that these two drought events were caused by a southward migration of the intertropical convergence zone itcz which was fostered by the nh cooling during the hs1 and yd hence our new geochemical record clearly documents that the east african climate not only responded to low latitude insolation forcing on sub orbital time scales but also was strongly influenced by high latitude cooling during the hs1 and yd periods

siwalik age faunas from the himalayan foreland basin of south asia abstract the himalayan foreland basin is characterised by three principal sedimentary successions these are the subathu group palaeocene eocene the murree or dharamsala group oligocene miocene and the siwalik group miocene pleistocene the basin was linked in the east to the bay of bengal through the bengal basin and its western part was connected to the arabian sea through rajasthan and kachchh gujarat the himalayan foothills have long been known for yielding rich mammalian fossil occurrences and significant localities in the indian siwaliks include kalagarh ramnagar haritalyangar chandigarh and jammu regions the bugti basin and zinda pir area of sulaiman range of pakistan were also part of the foreland basin as lower and middle siwalik fossils are known from the vihowa and litra formations respectively the marwat formation of bhittani and marwat ranges pakistan have also yielded pinjor age vertebrate fossils the middle and upper siwalik age fossils are also known from the irrawaddy formation of myanmar where older pegu beds have also yielded scanty lower siwalik age fossils this faunal succession in the irrawaddy valley may have geologically and biogeographically belonged to the himalayan foreland basin in the past additional mammalian fossils having an affinity with the lower and middle siwaliks are known from the khari nadi formation of kachchh the bokabil formation of tripura also yielded scanty lower to middle siwalik fossils a younger siwalik late miocene assemblage is known from piram island of gujarat these areas are also part of the foreland basin most recently a late miocene suid species was discovered and reported from near baripada odisha the paper discusses the respective faunal lists of the various successions mentioned above finally the paper discusses the implications of the foreland faunas the faunas of lower and middle siwaliks of foreland basin have links with europe turkey africa and central asia and throw light on the uplift of the himalaya the post siwalik faunas of central and peninsular india and indo gangetic plains have also yielded remnant siwalik taxa including stegodon insignis elephas hysudricus and potamochoerus theobaldi the kurnool cave fauna and recent fauna of india have also generic resemblance with the foreland faunas

variations in petrophysical properties along a mixed siliciclastic carbonate ramp upper jurassic ricla ne spain abstract a multi scale petrophysical study was performed on an upper jurassic siliciclastic carbonate ramp system near the village of ricla spain a combination of textural field observations thin section and grain size analysis chemical mineralogical thermo gravimetric analysis and physical porosity gamma ray and velocity measurements properties was used to capture the heterogeneity of this mixed sedimentary system subsequently synthetic seismic sections with varying resolution were created to show the characteristics of the internal ramp structures the translation from the measured petrophysical properties to a synthetic seismic section helps to better understand subsurface seismic although upscaling problems are a recurring issue the homogeneity of the samples and the continuity of the outcrop and facies reduce the number of uncertainties acoustic properties are generally controlled by the amount and type of pore spaces due to the low porosities the ramp geometry is characterized by an overall lateral homogeneity and vertical heterogeneity textural sedimentological and stratigraphic transitions in the outcrop are related to the defined facies each has its own unique mineralogical signature amplitude variations in the synthetic seismic profile are primarily caused by changes in mineral composition thus facies transitions

volcanic aerosol records and tephrochronology of the summit greenland ice cores the recently collected greenland ice sheet project 2 gisp2 and greenland ice core project ice cores from summit greenland provide lengthy and highly resolved records of the deposition of both the aerosol h2so4 and silicate tephra components of past volcanism both types of data are very beneficial in developing the hemispheric to global chronology of explosive volcanism and evaluating the entire volcanism climate system the continuous time series of volcanic so42 for the last 110 000 years show a strong relationship between periods of increased volcanism and periods of climatic change the greatest number of volcanic so42 signals many of very high magnitude occur during and after the final stages of deglaciation 6000 17 000 years ago possibly reflecting the increased crustal stresses that occur with changing volumes of continental ice sheets and with the subsequent changes in the volume of water in ocean basins sea level change the increase in the number of volcanic so42 signals at 27 000 36 000 and 79 000 85 000 years ago may be related to initial ice sheet growth prior to the glacial maximum and prior to the beginning of the last period of glaciation respectively a comparison of the electrical conductivity of the gisp2 core with that of the volcanic so42 record for the holocene indicates that only about half of the larger volcanic signals are coincident in the two records other volcanic acids besides h2so4 and other so42 sources can complicate the comparisons although the threshold level picked to make such comparisons is especially critical tephra has been found in both cores with a composition similar to that originating from the vatnaoldur eruption that produced the settlement layer in iceland mid a d 870s from the icelandic eruption that produced the saksunarvatn ash 10 300 years ago and from the icelandic eruption s that produced the z2 ash zone in north atlantic marine cores 52 700 years ago the presence of these layers provides absolute time lines for correlation between the two cores and for correlation with proxy records from marine sediment cores and terrestrial deposits containing these same tephras the presence of both rhyolitic and basaltic shards in the z2 ash in thegisp2 core and the composition of the basaltic grains lend support to multiple icelandic sources torfajokull area and katla for the z2 layer deposition of the z2 layer occurs at the beginning of a stadial event further reflecting the possibility of a volcanic triggering by the effects of changing climatic conditions

calcification depths and temperatures of planktonic foraminifera off southwest hainan island and their paleoceanographic implications abstract the east asian monsoon system influences the local oceanographic and climatic conditions of south china sea scs making the habitat depths of planktonic foraminifera pf specific for this region the previous paleo ocean reconstructions of scs have been based on calcification habitat depths derived from other oceans which may have affected the accuracy of interpretations in this study the calcification depths of globigerinoides ruber globigerinoides sacculifer and neogloboquadrina dutertrei from sediment traps deployed at 1000 m depth off southwest hainan island from july 2012 to april 2013 were analyzed with regard to the stable isotopes of oxygen 18o and carbon 13c to calculate their regional apparent calcification depths acds with the overall aim to improve the reconstruction of the upper ocean thermal structure acds and temperature estimated from foraminifera 18o ranged from 0 to 42 m and 25 c for g ruber 30 65 m and 23 3 c for g sacculifer and 75 100 m and 20 3 c for n dutertrei respectively the difference between the thermocline species n dutertrei and mixed layer species g ruber and g sacculifer 18o 18oth ml and the temperature t shows water column stratification the periods of lower and higher t and 18o were in phase with the changes in regional overlying wind speed additionally this study reveals that n dutertrei lives and calcifies its shells within the base of the mixed layer depth mld and upper thermocline depth in scs overall the results from this study provide a new insight to understand the mixed layer and thermocline depth in the northern scs

predicting lithology and transport properties from acoustic velocities based on petrophysical classification of siliciclastics based on the recently developed petrophysical classification of siliciclastics which takes into account the amount of the volumetric clay content c and textural position of clay it is shown that acoustic velocities can be fairly accurate tools in predicting lithology porosity and ultimately transport properties of these rocks four major petrophysical groups of carbonate and organic poor siliciclastics are distinguished 1 clean arenites c 35 percent the compressional velocity versus porosity relation for consolidated rocks in each of these groups is found to be linear with very high correlation coefficients this allows for remarkably accurate porosity estimates or lithology prediction in consolidated siliciclastics from acoustic velocities compared to the widely used time average wyllie equation or its improved modification raymer equations both of which neglect textural factors

elastic properties of hydrate bearing sediments using effective medium theory accurate and detailed models of the seismic velocity structure of gas hydrate bearing sediments may be determined by careful analysis of controlled source seismic data however interpretation of these velocities in terms of hydrate saturation of the pore space has hitherto relied on semiempirical formulas and or simple effective medium theory we develop a rigorous theoretical scheme to relate the seismic properties of a clay rich hydrate bearing sediment to its porosity mineralogy microstructural features and hydrate saturation we consider separately the two possible end members for the distribution of hydrate in the pore space 1 hydrates are unconnected and located in the pore voids without appreciable grain contact and 2 connected hydrates are forming cement binding around the grains the scheme is transversely isotropic to allow for anisotropy due to alignment of clay platelets and is based on a combination of a self consistent approximation a differential effective medium theory and a method of smoothing for crystalline aggregates we have applied the scheme to lithological and seismic velocity data from ocean drilling program site 995 on the blake ridge southeastern u s continental margin to make estimates of the hydrate saturation it was found that the hydrates are probably unconnected and their volume concentration varies between approx 0 at 100 m below the seabed and approx 9 at 400 m depth just above the bottom simulating reflector if the clay platelet orientation distribution resembles the function we have used

tropical rainforest dynamics and palaeoclimate implications since the late pleistocene nilgiris india a multiproxy study involving sedimentology palynology radiocarbon dating stable isotopes and geochemistry was carried out on the parsons valley lake deposit nilgiris india to determine palaeoclimatic fluctuations and their possible impact on vegetation since the late pleistocene the 72 cm deep sediment core that was retrieved reveals five distinct palaeoclimatic phases 1 warm and humid conditions with a high lake stand before the last glacial maximum lgm 29 800 cal yr bp subsequently changing to a relatively cool and dry phase during the lgm 2 considerable dry conditions and lower precipitation occurred between 16 300 and 9500 cal yr bp during this period the vegetation shrank and perhaps was confined to moister pockets or was a riparian forest cover 3 an outbreak in the shift of monsoonal precipitation was witnessed in the beginning of the mid holocene around 8400 cal yr bp implying alteration in the shift toward warm and humid conditions resulting in relatively high pollen abundance for evergreen taxa 4 this phase exhibits a shift to heavier 13 c values around 1850 cal yr bp with an emergence of moist deciduous plants pointing to drier conditions 5 human activities contributed to the exceedingly high percentage of acacia and pinus pollen during the little ice age

evidence for holocene changes in australian indonesian monsoon rainfall from stalagmite trace element and stable isotope ratios abstract trace element and stable isotope ratios from an active stalagmite lr06 b1 recovered from liang luar cave on the island of flores eastern indonesia are used to reconstruct the position of the austral summer inter tropical convergence zone and australian indonesian summer monsoon variability during the holocene uranium series dating of the stalagmite shows that it commenced growth 12 640 years ago with hiatuses spanning 8 560 to 6 420 and 3 670 to 2 780 years ago stalagmite mg ca and sr ca ratios correlate significantly with one another and with 18 o and 13 c throughout the record this suggests that the mg ca and sr ca ratios are dominated by prior calcite precipitation a process whereby degassing in the vadose zone during periods of low recharge causes deposition of calcite and disproportionate loss of ca 2 ions relative to mg 2 and sr 2 upstream of the stalagmite the degree of initial 234 u 238 u disequilibrium also appears to have been controlled by recharge to the overlying aquifer together with the mg ca sr ca and 18 o values the initial uranium isotope activity ratios 234 u 238 u i imply a generally drier early holocene coincident with a lower sea level and lower southern hemisphere summer insolation comparison of speleothem 18 o time series from flores and borneo shows that they vary in unison for much of the holocene however there is a significant decrease in the borneo 18 o record 6 000 to 4 000 years ago that does not occur in the flores record this anomaly may be related to a change in the australian indonesian summer monsoon circulation in response to a protracted positive phase of the indian ocean dipole under this scenario stronger upwelling off of western indonesia would based on present day effects result in reduced summer convective activity over flores and a subsequent northward shift of the intertropical convergence zone

inconsistent sea surface temperature and salinity changing trend in the northern south china sea since 7 0 ka bp abstract the south china sea scs is an important moisture and heat source in the asian monsoon system and its environmental changes influence economic and social stability in southeast asia and east asian previous records on sea surface temperature sst and salinity sss were mostly from one sediment core and or only showed fragmentary information it is hard to provide insights into the mechanisms of the overall paleoceanographical environmental variability in the northern scs in this study paired 18o and mg ca records of planktonic foraminifer globigerinoides ruber from core s0204b nearby the luzon strait 21 13 818 n 118 3 077 water depth 1822 m and core ghe 27l 19 85 n 115 34 e water depth of 1533 m in the central northern scs were analyzed so as to better understand the physical process of the sst and sss changes in the northern scs and its relationship with the tropical pacific the results demonstrate that the sst is relatively stable and seawater 18o 18osw values a salinity proxy shows a decrease trend since 7 0 ka bp in core s0204b by contrast sst and 18osw in core ghe 27l exhibit an overall increasing trend at the same time indicating apparent regional discrepancy on the changing trend of the sst and sss in the northern scs we suggest that the thermal and hydrographic conditions in core s0204b were primarily influenced by the outer western pacific water however the thermal and hydrographic conditions in core ghe 27l may be predominantly controlled by the weakened asian monsoon during the mid late holocene which was induced by the southern migration of intertropical convergence zone itcz and stronger ei nino southern oscillation

mathematical modelling of anisotropy of illite rich shale summary the estimation of illite rich shale anisotropy to account for the alignment of clays and gas or brine filled cracks is presented via mathematical modelling such estimation requires analysis to interpret the dominance of one effect over another this knowledge can help to evaluate the permeability in the unconventional reservoir stress orientation and the seal capacity for the conventional reservoir effective media modelling is used to predict the elastic properties of the illite rich shale and to identify the dominant contributions to the shale anisotropy we consider two principal reasons of the shale anisotropy orientation of clay platelets and orientation of fluid filled cracks in reality both of these two factors affect the shale anisotropy the goal of this study is first to separately analyse the effect of these two factors to reveal the specific features in p and s wave velocity behaviour typical of each of the factors and then consider a combined effect of the factors when the cracks are horizontally or vertically aligned to do this we construct four models of shale the behaviour of p and s wave velocities is analysed when gas and water filled cracks embedded in a host matrix are randomly oriented or horizontally or vertically aligned the host matrix can be either isotropic or anisotropic of vti symmetry in such a modelling we use published data on mineralogy and clay platelet alignment along with other micromechanical measurements in the model where the host matrix is isotropic the presence of a singularity point when the difference changes its sign in shear wave velocities is an indicator of brine filled aligned cracks in the model with the vti host matrix and horizontally aligned cracks filled with gas an increase in their volume concentration leads to that the azimuth at which the singularity is observed moves toward the symmetry axis in this case if the clay content is small around 20 per cent the singularity point may even vanish the thomsen parameters are helpful in fluid type indication in shale an indicator of gas filled aligned cracks is if aligned cracks in illite rich shale are brine filled negative value of indicates brine filled cracks in illite rich shale a shale with brine filled cracks exhibits higher vp vs ratio in the vertical direction as compared to the gas filled shale a disorientation of clay platelets and brine filled cracks may lead to that the singularity point is absent for brine saturated shale as well in this case one can also observe and decreased values of vp vs in the vertical direction as in the case of gas filled cracks in the presence of vertically aligned cracks shales exhibit distinctly revealed features of orthorhombic symmetry the results have important applications where seismic measurements are applied to predict the maturity state of the shale

anisotropy correction for deviated well sonic logs application to seismic well tie borehole sonic logs acquired in deviated wells penetrating the hrz and colville shales in the niakuk field in alaska s north slope are seen to be significantly faster than vertical well logs these differences are attributed to shale anisotropy an iterative inversion scheme was created to invert for shale anisotropy parameters using multiple wells penetrating shale sections at different angles the inversion involves fitting the sonic log data at a range of borehole angles to the compressional wave group velocity surface the result is an estimate of the anisotropy parameters e and and the vertical p wave velocity the results show that the shales are strongly anisotropic with compressional wave anisotropy thomsen s parameter e on the order of 40 and the anisotropy parameter relates vertical velocity to short offset nmo velocity around 10 this large anisotropy can affect seismic imaging avo and time depth calculations a procedure was created to estimate the anisotropy corrected vertical s

the holocene environmental changes in southern indonesia reconstructed from highland caldera lake sediment in bali island diatom pollen geomagnetic and geochemical analyses were carried out on a 3 6 m long sediment core taken from lake buyan a highland caldera lake in central bali island to reconstruct the holocene climate changes in equatorial southern indonesia the core represents 8 thousand years sedimentation of organic diatomaceous lake mud constant inclusion of benthic diatom fossils as main components indicated that suspension and inflow of littoral materials were the main sedimentary process the core contained laminated sediments in two distinct intervals at 6 5 5 0 and 3 6 3 1 cal ky bp and multi proxy records showed generally drier climate in these sections especially at 3 6 3 1 cal ky bp lake bottom waters were more reducing condition in these laminated periods probably due to increased lake productivity by prolonged dry season and wind mixing laminae structures were made up of a layer composed of benthic diatoms and amorphous organic materials and a layer made by only planktonic diatom fossils each of which may represent rainy and dry period deposits although southern indonesia shows clear australian monsoon rainfall seasonality at present counting of layer numbers showed interannual cycles of laminae formation prolonged dry seasons could obscured the rainfall seasonality in these periods but precise depositional patterns were elusive unlaminated sections showed homogeneous sediment mixture of benthic planktonic diatoms and more volume of terrigenous materials indicating wetter climate and seasonality similar to the present time this was supported by the higher share of marsh environment pollens reflecting more stable lake level trends the dry climate from 6 5 cal ky bp was in line with the general perception of stronger enso dynamics from the mid holocene due to weaker than before boreal summer insolation but the sporadic appearances of dry periods imply the influence of regional climate forcings such as temporal migrations of inter tropical convergence zone itcz it was however possible that temporal shifts of large climate mode occurred in equatorial pacific and indian oceans wettest climate was inferred from 3 1 cal ky bp to the present and this might reflect increased importance of austral hemisphere atmospheric convection and subsequent southerly position of itcz in austral summer time

geophysical properties of cap rocks in qiongdongnan basin south china sea abstract based on measured petrophysical properties and statistical methods relationship between petrophysical properties and well log and seismic parameters are established empirically to evaluate the quality of cap rocks in qiongdongnan basin good cap rocks show high density and low sonic travel time four zones can be divided vertically according to displacement pressures in qiongdongnan basin best seal quality is found in the depth range of 2000 4000 m the ya 13 1 structure has excellent cap rock which contributes to its abundant gas accumulation

holocene changes in eastern tropical pacific climate inferred from a galapagos lake sediment record abstract paleoclimate records from the tropical pacific suggest the early to mid holocene was a period of reduced el nino southern oscillation enso variability with a transition to modern increased enso frequency occurring some time in the last few thousand years however the nature and timing of this shift remains uncertain due to the discontinuous nature and or coarse resolution of many enso proxies as well as a lack of agreement between previously published records a new continuous climate record from el junco crater lake in the galapagos islands reveals several abrupt changes in lake level and precipitation through the holocene hydroclimatic model simulations suggest that el junco lake level responds sensitively to increases in precipitation associated with el nino events rising during wet el nino events and falling during the intervening dry periods grain size data from el junco sediment cores indicate past lake level variability likely associated with changing seasonal precipitation and enso frequency the grain size data suggest increased precipitation intensity prior to 9000 120 cal years bp and after 4200 130 cal years bp as well as a two step increase in precipitation at 3200 160 and 2000 100 cal years bp maximum holocene precipitation and inferred enso variability occurred between 2000 100 and 1500 70 cal years bp during the same period that six other independent proxy records suggest higher enso frequency and longer stronger el nino events decreasing sediment carbon nitrogen c n ratios in el junco sediments indicate rising lake levels from the early holocene to present corroborating the grain size data the inferred increase in precipitation at 4200 130 cal years bp and at 2000 100 cal years bp coincides with decreasing southwest asian and east asian monsoon intensity suggesting tropical pacific climate and the asian monsoon were interconnected systems at centennial to millennial timescales during the holocene a weakening trend in the asian monsoon and the trend toward wetter conditions at el junco also coincide with a trend toward cooler and drier conditions inferred from cariaco basin sediment proxies from the mid holocene to present suggesting the migration of the intertropical convergence zone itcz likely influenced hydrological changes in both the eastern tropical pacific and the asian monsoon region during the holocene

sensitivity of the australian monsoon to insolation and vegetation implications for human impact on continental moisture balance general circulation model experiments test the geologically based correlation of high monsoon rainfall over interior australia with northern hemisphere insolation and evaluate the sensitivity of the australian monsoon to ecosystem change our results suggest that northern hemisphere insolation control on the intensity of the siberian high rather than summer insolation over the australian continent determines the strength of the australian monsoon on millennial time scales unlike a classic monsoon regime additional simulations show that the penetration of monsoon moisture into the interior is sensitive to biosphere atmosphere feedbacks linked to vegetation type and soil properties this sensitivity offers a resolution to the observed failure of the australian monsoon to penetrate the interior in the holocene postulated regular burning practiced by early humans may have converted a tree shrub grassland mosaic across the semiarid zone to the modern desert scrub thereby weakening biospheric feedbacks and resulting in long term desertification of the continent

estimation of marine sediment bulk physical properties at depth from seafloor geophysical measurements a combination of geophysical techniques can yield estimates of several physical properties versus depth an example is presented for a thick sequence of sediments in middle valley near the present spreading axis of the juan de fuca ridge we have computed the porosity temperature and thermal conductivity versus depth by combining the results of seafloor electrical and heat flow surveys the electrical resistivity of the sediments is empirically related to the porosity of the medium and to the pore fluid electrical conductivity which is in turn sensitive to the temperature the temperature profile is determined from the heat flow and the thermal conductivity the latter is determined from calculated porosity and estimates of the constituent mineral and pore fluid thermal conductivities the measured surface heat flow is assumed to be and the resistivity has been determined to be approximately constant with depth the computation of the variation of temperature porosity and thermal conductivity with depth yields physically realistic and reasonable results other physical properties void ratio bulk density water content compressional wave velocity are estimated from the porosity the shear wave velocity is calculated empirically from the compressional wave velocity and poisson s ratio is then computed from the compressional and shear wave velocities the results are in good agreement with values derived for similar rapidly deposited sediment sequences elsewhere but the model calculations indicate that deep sea drilling project measurements may be biased toward higher porosity samples

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

indonesian throughflow drove australian climate from humid pliocene to arid pleistocene late miocene to mid pleistocene sedimentary proxy records reveal that northwest australia underwent an abrupt transition from dry to humid climate conditions at 5 5 million years ma likely receiving year round rainfall but after 3 3 ma climate shifted toward an increasingly seasonal precipitation regime the progressive constriction of the indonesian throughflow likely decreased continental humidity and transferred control of northwest australian climate from the pacific to the indian ocean leading to drier conditions punctuated by monsoonal precipitation the northwest dust pathway and fully established seasonal and orbitally controlled precipitation were in place by 2 4 ma well after the intensification of northern hemisphere glaciation the transition from humid to arid conditions was driven by changes in pacific and indian ocean circulation and regional atmospheric moisture transport influenced by the emerging maritime continent we conclude that the maritime continent is the switchboard modulating teleconnections between tropical and high latitude climate systems

early rhinocerotids mammalia perissodactyla from south asia and a review of the holarctic paleogene rhinocerotid record the earliest rhinocerotids from south asia are identified on the basis of few dental remains originating from the late eocene of thailand wai lek mine krabi basin and the early oligocene of pakistan paali nala c2 bugti hills once synthesized the holarctic paleogene rhinocerotid record points out a westward diachronism of rhinocerotid first appearance data from north america to europe via asia throughout mid cenozoic times the faunal similarity among mammal localities from the late eocene and early oligocene of peninsular thailand southern china and pakistan suggests the existence of a single south asian paleoprovince during this interval and the persistence of a tropical subtropical climate substantial faunal changes recorded in eastern balochistan reveal a significant climatic deterioration from the middle part of the oligocene neither provinciality nor endemism is noticeable for rhinocerotoid taxa recognized in the oligocene of the indian subcontinent neither the himalayas nor the tibet plateau was a paleogeographic barrier for large mammals during this interval resume les plus anciens rhinocerotides d asie du sud sont identifies gr ce a quelques restes dentaires provenant de l eocene superieur de thailande mine de wai lek bassin de krabi et de l oligocene inferieur du pakistan paali nala c2 collines bugti la synthese du registre fossile paleogene holarctique des rhinocerotides revele un net diachronisme des premieres apparitions de rhinocerotides depuis l est amerique du nord vers l ouest asie puis europe au cours du cenozoique moyen la similarite des communautes de mammiferes entre les localites de l eocene superieur et de l oligocene inferieur de thailande peninsulaire de chine du sud et du pakistan suggere l existence d une seule paleoprovince sud asiatique pendant la periode consideree sous un climat tropical a subtropical les changements fauniques enregistres au balouchistan oriental revelent une deterioration climatique significative a partir du milieu de l oligocene aucun indice de provincialisme ou d endemisme n est releve pour les rhinocerotoides oligocenes du sous continent indien ni les himalayas ni le plateau du tibet ne constituaient a l epoque une barriere paleogeographique pour les grands mammiferes

lattice preferred orientation and seismic anisotropy in sedimentary rocks summary although it is well known that sedimentary rocks can be seismically anisotropic there have been few detailed investigations of the underlying cause of such anisotropy here we investigate anisotropy due to the preferred orientation of minerals or lattice preferred orientation lpo in a suite of sedimentary rocks seismic properties are predicted by averaging single crystal elastic constants of minerals according to their crystal orientation and modal volume fraction in the rock aggregate both electron backscattered diffraction ebsd and x ray texture goniometry xtg are tested as quantitative techniques for measuring the lpo of sedimentary rocks although ebsd has promise for future lpo measurements in polymineralic sedimentary rocks problems currently remain in measuring low symmetry phases e g feldspars and very small clay or mica particles however the lpo of very fine grained phyllosilicates can be measured using xtg and the lpo of low symmetry minerals can be measured using manual ebsd pattern analysis here we use such a hybrid approach to estimate lpo in a suite of sedimentary samples the seismic properties calculated from lpo data show anisotropy values for p waves ranging from 1 5 per cent in sandstones to over 3 5 per cent in a siltstone to 12 per cent in a shale the effect of thin multilayering on long wavelength propagation in a siltstone is predicted by applying backus type averaging the layering does not enhance the anisotropy because of the small differences in density and in elasticity between the two layer types the lpo of phyllosilicates and to a lesser extent dolomite and siderite seem to contribute significantly to the seismic anisotropy of phyllosilicate rich rocks siltstones and shales the weak lpo of quartz in sandstones causes a few per cent anisotropy cumulatively our results suggest that field observations of seismic anisotropy have the potential to be used as an indicator of rock lithology

stable isotope analysis of the tooth enamel of chaingzauk mammalian fauna late neogene myanmar and its implication to paleoenvironment and paleogeography abstract the tooth enamel of a mammalian fauna from the uppermost miocene lower pliocene irrawaddy sediments at chaingzauk west central myanmar were analyzed using stable carbon and oxygen isotopes the 13 c values of porcupines tragulids rhinocerotids suids and proboscideans show that these mammals preferentially consumed c 3 plants in a wooded environment whereas the 13 c values of bovids and hippopotamids indicate that they were grassland adapted grazers to mixed feeders in contrast to the thorn scrub grassland and shrubland vegetation of present day central myanmar stable carbon isotope results of the chaingzauk fauna suggest a presence of wooded environment in the chaingzauk area at that time present day arid conditions are likely to have been caused by the uplift of the indo burman ranges due to the himalayan orogeny during the late miocene to pliocene resulting in a rainshadow effect in central myanmar furthermore southward marine regression due to the rapid influx of sediments from the indo burman ranges eastern himalayan ranges and sino burman ranges into the central myanmar basin in the miocene to pliocene might have played an important role in the aridification of this region since the lower pliocene

increasing australian indonesian monsoon rainfall linked to early holocene sea level rise the australian indonesian summer monsoon affects rainfall variability across the indo pacific region reconstructions of monsoon strength from stalagmites show that precipitation increased from 11 000 to 7 000 years ago as rising global sea level caused the flooding of the indonesian continental shelf the australian indonesian summer monsoon affects rainfall variability and hence terrestrial productivity in the densely populated tropical indo pacific region it has been proposed that the main control of summer monsoon precipitation on millennial timescales is local insolation1 2 3 but unravelling the mechanisms that have influenced monsoon variability and teleconnections has proven difficult owing to the lack of high resolution records of past monsoon behaviour here we present a precisely dated reconstruction of monsoon rainfall over the past 12 000 years based on oxygen isotope measurements from two stalagmites collected in southeast indonesia we show that the summer monsoon precipitation increased during the younger dryas cooling event when atlantic meridional overturning circulation was relatively weak4 monsoon precipitation intensified even more rapidly from 11 000 to 7 000 years ago when the indonesian continental shelf was flooded by global sea level rise5 6 7 we suggest that the intensification during the younger dryas cooling was caused by enhanced winter monsoon outflow from asia and a related southward migration of the intertropical convergence zone8 however the early holocene intensification of monsoon precipitation was driven by sea level rise which increased the supply of moisture to the indonesian archipelago

seismic velocities for hydrate bearing sediments using weighted equation a weighted equation based on the three phase time average and wood equations is applied to derive a relationship between the compressional wave p wave velocity and the amount of hydrates filling the pore space the proposed theory predicts accurate p wave velocities of marine sediments in the porosity range of 40 80 and provides a practical means of estimating the amount of in situ hydrate using seismic velocity the shear s wave velocity is derived under the assumption that the p to s wave velocity ratio of the hydrated sediments is proportional to the weighted average of the p to s wave velocity ratios of the constituent components of the sediment in the case that all constituent components are known a weighted equation using multiphase time average and wood equations is possible however this study showed that a three phase equation with modified matrix velocity compensated for the clay content is sufficient to accurately predict the compressional wave velocities for the marine sediments this theory was applied to the laboratory measurements of the p and s wave velocities in permafrost samples to infer the amount of ice in the unconsolidated sediment the results are comparable to the results obtained by repeatedly applying the two phase wave scattering theory the theory predicts that the poisson s ratio of the hydrated sediments decreases as the hydrate concentration increases and the porosity decreases in consequence the amplitude versus offset avo data for the bottom simulating reflections may reveal positive negative or no avo anomalies depending on the concentration of hydrates in the sediments

controls on acoustic properties of upper jurassic siliciclastic rocks boulonnais northern france more than 200 plugs from outcrop and a nearby borehole in a carbonaceous siliciclastic interval of late jurassic kimmeridgian to tithonian age were quantitatively analyzed for texture mineralogy and acoustic properties our primary goal was to study the effect of clay fraction smaller than 8 m silt sand fraction larger than 8 m and carbonate on the acoustic properties the quantitative nature and volume of the data made it possible to observe four dimensional relationships in contoured ternary diagrams primary control on the acoustic properties is exerted by porosity but the trend of this relationship significantly deviates from popular velocity transforms the contribution of clay silt sand and carbonate particular material and cement explains the remaining variation in acoustic properties although no clear linear thresholds are defined a general trend is that clay and carbonate content have opposite and overlapping effects on acoustic properties the influence of clay content progressively increases with decreasing carbonate content and visa versa with increasing carbonate content the variation of acoustic velocity at a given porosity value increases to nearly twice of that in the clay dominated sediment traditional classification boundaries are present but strongly overprinted by this interplay between clay and carbonate this study may have important implications for porosity and lithofacies prediction from wireline logs in similar mixtures of sediment in addition the quantitative character of the textural and mineralogical data may provide a direct link from acoustic properties to the primary depositional system and sequence stratigraphy

diagnostics of seismic time lapse effects of sandstones based on laboratory data we evaluated a viscoelastic modeling of p and s wave velocity dispersion attenuation pressure and fluid effects for a set of siliciclastic rock samples our analysis used a published laboratory data set of 63 sandstones with a wide range of compositional heterogeneities we observed a notable correlation between the velocity and attenuation pressure sensitivity and the abundance lack of quartz in the samples we included compliant pores low aspect ratio proportionally to the content of secondary minerals to account for the differential sensitivity to pressure the observed velocity and attenuation were well reproduced by the applied viscoelastic modeling we found that pores of significantly different scale required pore fluid relaxation time constants of proportionally different magnitudes to reproduce the velocity and attenuation measurements the relaxation time constant of crack sized pores can be one order of magnitude smaller than the constant of mesopores moreover the velocity dispersion and attenuation signatures revealed that a pore textural model dependent on lithological composition is critical in the prediction of time lapse fluid and pressure responses

fundamentals of seismic rock physics during the past 50 years or so tremendous progress has been made in studying physical properties of rocks and minerals in relation to seismic exploration and earthquake seismology during this period many theories have been developed and many experiments have been carried out some of these theories and experimental results have played important roles in advancing earth sciences and exploration technologies this tutorial paper attempts to summarize some of these results

the effect of systematic diagenetic changes on the mechanical behavior of a quartz cemented sandstone abstracta key goal of petrophysical studies of sandstones is to relate common field measurements particularly seismic or sonic velocities to parameters defining the rock s mechanical and hydrologic characteristics these include elastic and inelastic mechanical properties porosity and permeability we explored relationships among these properties in variably quartz cemented mature arenites of the st peter sandstone with porosities ranging from 9 to 25 in a previous paper we described microstructural changes accompanying progressive quartz cementation and related porosity and permeability reduction in this sample suite here we report ultrasonic velocities ultrasonic velocities dynamic and static elastic properties confined compressive strength and tensile strength analyses of these data demonstrated that factors controlling permeability also fundamentally determined the elastic and inelastic mechanical properties we found that the number of grain contacts or bonds per number of grains vi