the proto earth as a significant source of lunar material geochemical evidence continues to challenge giant impact models which predict that the moon formed from both proto earth and impactor material analyses of lunar samples reveal isotopic homogeneity in titanium a highly refractory element suggesting lunar material was derived predominantly from the mantle of the proto earth

structural highs on the western continental slope of india implications for regional tectonics abstract integrated geological and geophysical explorations over the last two decades along the central western continental margin of india reveal from east to west a terrace like flat shelf an advancing shelf break a nw se oriented wide shelf margin basin the upper slope ridge the prathap ridge and the laccadive ridge the basin on the continental slope extends between the shelf break and the eastern slope of the laccadive ridge and is divided longitudinally into a relatively narrow eastern and a wide western basin by the prominent upper slope ridge detailed multibeam swath mapping now over an area of little more than 20 300 km 2 within the shelf margin basin located on the upper continental slope now reveals the occurrence of several isolated structural highs of variable height four of these highs are located over the upper slope ridge and a similar number on the prathap ridge of these four highs have summit height 1000 m two have heights between 500 and 999 m while the remaining two have heights less than 499 m the digital terrain model developed from the processed multibeam swath bathymetry data offers a three dimensional perspective of these structural highs the tectonic understanding from multibeam bathymetry findings and satellite gravity data supported by other geophysical information suggest that these structural highs are likely to be the peaks of the upper slope ridge and the prathap ridge we discuss the possible origin and mode of emplacement of these structural highs and ridges in the light of regional tectonics and suggest that both the upper slope and prathap ridges may have been formed during the separation of india from madagascar during the middle cretaceous

jurassic subsidence history in the hebrides n w scotland abstract geohistory analyses have been applied to the generally well dated triassic jurassic successions of three areas in the hebrides basin north west scotland and the importance of making corrections for decompaction palaeobathymetry and eustatic changes of sea level are assessed the thermo tectonic subsidence patterns in the skye areas north suggest a three phase history of crustal stretching though only the first phase is well developed in the mull area south episodes of relatively rapid subsidence are 1 1 late triassic c210 ma until earliest toarcian 186 ma 2 2 latest toarcian 180 ma until late bathonian c161 ma 3 3 early oxfordian 154 ma until at least early kimmeridgian incomplete these are separated by toarcian 186 180 ma and latest bathonian callovian c161 154 ma episodes of either little subsidence or of uplift but at slower rates than eustatic rise of sea level the intervals between phases at 30 ma and 26 ma are remarkably similar but the wider significance of this remains to be established

growth and demise of a paleogene isolated carbonate platform of the offshore indus basin pakistan effects of regional and local controlling factors based on high resolution seismic and well datasets this paper examines the evolution and drowning history of a paleocene eocene carbonate platform in the offshore indus basin of pakistan this study uses the internal seismic architecture well log data as well as the microfauna to reconstruct factors that governed the carbonate platform growth and demise carbonates dominated by larger benthic foraminifera assemblages permit constraining the ages of the major evolutionary steps and show that the depositional environment was tropical within oligotrophic conditions with the aid of seismic stratigraphy the carbonate platform edifice is resolved into seven seismic units which in turn are grouped into three packages that reflect its evolution from platform initiation aggradation with escarpment formation and platform drowning the carbonate factory initiated as mounds and patches on a cretaceous paleocene volcanic complex further the growth history of the platform includes distinct phases of intraplatform progradation aggradation backstepping and partial drownings the youngest succession as late stage buildup records a shift from benthic to pelagic deposition and marks the final drowning in the early eocene the depositional trend of the platform controlled by the continuing thermal subsidence associated with the cooling of volcanic margin lithosphere was the major contributor of the accommodation space which supported the vertical accumulation of shallow water carbonate succession other factors such as eustatic changes and changes in the carbonate producers as a response to the paleogene climatic perturbations played secondary roles in the development and drowning of these buildups

on the evolution of the southern oscillation abstract the evolution of the southern oscillation so is examined in the time domain by computing lagged cross correlations between sea level pressures at darwin and sea level or surface pressures at selected stations also in the northern hemisphere the historical and u s navy sea level pressure analyses are used all monthly time series are low pass filtered to retain periodicities greater than 20 months in order to highlight the interannual fluctuations which are primarily associated with the so a detailed analysis of the post 1941 period results in plotted maps of the phase lead or lag and magnitude of the maximum cross correlations with darwin in a manner analogous to a broadband coherence and phase spectrum the relationships within the so are further examined where possible back to 1882 using time series of running decadal cross covariances the dominant pattern reveals the two poles of the traditional standing oscillation or seesaw of the so with centers of opposite sign over indonesia

quantifying the role of oceanic feedbacks on enso asymmetry the role of oceanic feedbacks in determining the asymmetry of el nino southern oscillation enso magnitude spatial structure and duration is quantified on the basis of a novel temperature variance budget results confirm previous studies that in the eastern pacific el nino warm temperature anomalies are larger in magnitude than la nina cold temperature anomalies mainly due to stronger positive oceanic feedbacks for el nino we find that la nina cold anomalies are typically stronger than el nino warm anomalies in the central pacific with a faster growth rate for cold anomalies due to a stronger positive thermocline feedback and weaker nonlinear damping the thermocline feedback related to recharge oscillator dynamics plays a dominate role and leads to asymmetry in the duration of el nino and la nina events in particular the thermocline feedback becomes significantly negative during the late decaying phase of el nino and speeds up its demise

the modal evolution of the southern oscillation abstract the implementation of a progressive fourier transform applied to time series representative of the el nino southern oscillation enso provides a visual review of the frequency modes that have dominated throughout the available time series record the modal evolution maps constructed from the progressive fourier transform demonstrate that the enso is largely composed of a discrete number of low frequency modes and that these dominant modes demonstrate a localized influence in a temporal sense persisting for periods of years before showing deviations in characteristic frequency in support of other research significant energy is maintained in the quasi biennial and quasi quadrennial period modes throughout the length of available southern oscillation index soi record evident through the most recent record of both the soi and nino region sea surface temperature sst time series is the emergence of energy in the quasi decadal period modes the presence of a quasi decadal mode has also bee

remote forcing of sea surface temperature in the el nino region the relationship between oceanic kelvin waves forced over the western equatorial pacific and seasonal and nonseasonal sea surface temperature sst variability at the south american coast is investigated using harmonic dial analysis and lag correlation statistics the seasonal cycle of coastal sst is adequately described by the first two harmonics and is very regular in both el nino and non el nino years in contrast the seasonal cycle of zonal wind over the western equatorial pacific varies from year to year and is dominated by years of large negative swings of the southern oscillation index hence it seems unlikely that the winds over the western equatorial pacific contribute strongly to the seasonal cycle of coastal sst for nonseasonal variability the winds with periods shorter than 15 months precede fluctuations in coastal sst by 2 to 4 months consistent with the remote forcing hypothesis while for the lower frequencies the sst leads the winds by 2 to 3 months similar to el nino composite zonal winds of rasmusson and carpenter 1982

on the annual cycle in the tropical eastern central pacific abstract in the tropical eastern central pacific ocean the annual cycle in sea surface temperature sst surface winds and pressure and clouds are alternatively dominated by an antisymmetric with respect to the equator monsoonal mode in february and august and a quasi symmetric equatorial coastal mode in may and november both having a period of one year the monsoonal mode is forced by the differential insulation between the northern and southern hemispheres the surface wind variation of the monsoonal mode tends to lead sst variation in late spring fall the equatorial coastal mode originates from atmosphere ocean interaction its development is characterized by contemporaneous intensification and spatial expansion westward and poleward phase propagation the interaction between the forced monsoonal mode and the coupled equatorial coastal mode plays a critical role in the annual cycle from october to february the decline of the southern winter regime of the monsoonal mode initiates and sustains

the organic geochemistry of peru margin surface sediments i a comparison of the c37 alkenone and historical el nino records abstract the alkenone u k 37 paleothermometer has potential as a sedimentary marker for el nino southern oscillation enso events in the peru upwelling regime we assessed this potential by comparing the historical enso record with detailed u k 37 profiles for 210 pb dated cores from the peru margin oxygen minimum zone omz sediments with the greatest potential for holding a sedimentary u k 37 record of el nino events are sediments from the center of the omz sectioned at intervals the yearly sedimentation rate the u k 37 signals of individual el nino events were substantially attenuated in the sediments we examined and periods of frequent enso activity e g 1870 1891 were more readily identified than isolated enso events in periods of less frequent enso activity detailed depth profiles of the c 37 alkenones in a core from 253 m o 2 k 37 values for the five 2 mm sections from 0 1 cm suggests that the u k 37 may be unaffected by the alkenone loss correlation between the c 37 alkenone concentration profiles in two cores from 15 s collected nine years apart are consistent with the use of these compounds for molecular stratigraphy

mass accumulation rates in asia during the cenozoic summary this work establishes estimates of mass accumulation rates in 18 mostly offshore sedimentary basins in asia since the beginning of the cenozoic 66 ma the estimates were derived from isopach maps cross sections and drill holes or stratigraphic columns assuming regional similarity of the strata average solid phase volumes and accumulation rates were calculated for nine epochs approximately corresponding to geological periods palaeocene 66 58 ma eocene 58 37 ma oligocene 37 30 and 30 24 ma miocene 24 17 17 11 and 11 5 ma pliocene 5 2 ma and quaternary 2 0 ma these rates shed new light on the geological history of asia since the onset of the collision of india with asia 50 ma the overall average accumulation rates curve for asian sedimentary basins since the beginning of the tertiary shows an exponential form with slow accumulation rates less than 0 5 106 km3 myr 1 until the beginning of the oligocene more than 15 myr after the onset of the collision from the oligocene onwards rates increase quickly in an exponential manner reaching their maximum values in the quaternary more than 1 5 106 km3 myr 1 from these observations we suggest that extrusion and crustal shortening are complementary processes that have been successively dominant throughout the india eurasia collision history at smaller scales one may distinguish between independent histories at the subcontinental and basin scales this permits a comparison of the relative importance of tectonic and climatic erosion processes affecting the different mountain belts of asia during the cenozoic

bathymetric highs in the mid slope region of the western continental margin of india structure and mode of origin analysis of the multi and single beam bathymetric seismic magnetic and free air gravity ship borne and satellite derived data from the western continental margin of india between 12 40 n and 15 n had revealed the presence of several flat topped nnw sse trending bathymetric highs of considerable areal extent 256 to 1165 km 2 area each at base they are interspersed by bathymetric lows thereby forming a chain of horst and graben structures covered by thick sediments 2 d modeling of the gravity and magnetic anomalies constrained by seismic results reflection and refraction had indicated 23 km thick crust consisting of 2 to 3 km thick sediments and a thin basaltic and granitic layer the model has brought into focus the presence of mantle based volcanic plugs their geomorphological and geophysical expressions and structural pattern and associated deep seated faults led to suggest continental crust these features are inferred as rifted fragments of the western continental margin of india formed during its northward movement they were subjected to sub aerial erosion during the paleogene due to lowered sea levels resulting in flat tops subsequently they were submerged to the present depths in the neogene the basic tectonic process appears to be regional

moon formation earth s titanium twin a giant impact on the young proto earth is thought to explain the formation of the moon high precision analysis of titanium isotopes in lunar rocks suggests that the moon and earth s mantle are more similar than existing models permit

surface temperature patterns associated with the southern oscillation abstract the typical global and large scale regional temperature patterns associated with the low warm and high cold phases of the southern oscillation so are investigated a total of 12 separate regions were found to have consistent temperature patterns associated with low phase of the so while 11 areas were found to have temperature patterns associated with the high phase of these areas 9 have expected temperature patterns during both phases of the so in the tropics temperature anomalies are of the same sign as the so related sea surface temperature sst anomaly in all land regions except for one area in the west pacific three extratropical responses to the low phase of the so are found over north america and one is found in japan high so temperature patterns were found in the extratropies for japan western europe and northwestern north america the identified temperature responses are more consistent in tropical regions than in the extratropies the so can influence the estimation of

influence of el nino southern oscillation enso events on the evolution of central california s shoreline significant sea cliff erosion and storm damage occurred along the central coast of california during the 1982 1983 and 1997 1998 el nino winters this generated interest among scientists and land use planners in how historic el nino southern oscillation enso winters have affected the coastal climate of central california a relative enso intensity index based on oceanographic and meteorologic data defines the timing and magnitude of enso events over the past century the index suggests that five higher intensity relative values 4 6 and 17 lower intensity relative values 1 3 enso events took place between 1910 and 1995 the enso intensity index correlates with fluctuations in the time series of cyclone activity precipitation detrended sea level wave height sea surface temperature and sea level barometric pressure wave height sea level and precipitation which are the primary external forcing parameters in sea cliff erosion increase nonlinearly with increasing relative enso event intensity the number of storms that caused coastal erosion or storm damage and the historic occurrence of largescale sea cliff erosion along the central coast also increase nonlinearly with increasing relative event intensity these correlations and the frequency distribution of relative enso event intensities indicate that moderate to high intensity enso events cause the most sea cliff erosion and shoreline recession over the course of a century

cenozoic sedimentation in the mumbai offshore basin implications for tectonic evolution of the western continental margin of india abstract interpretation of multichannel seismic reflection data along the mumbai offshore basin mob revealed the tectonic processes that led to the development of sedimentary basins during cenozoic evolution structural interpretation along three selected mcs profiles from mob revealed seven major sedimentary sequences 3 0 s twt thick and the associated complex fault patterns these stratigraphic sequences are interpreted to host detritus of syn to post rift events during rift drift process the acoustic basement appeared to be faulted with interspaced intrusive bodies the sections also depicted the presence of slumping of sediments subsidence marginal basins rollover anticlines mud diapirs etc accompanied by normal to thrust faults related to recent tectonics presence of upthrusts in the slope region marks the locations of local compression during collision forward gravity modeling constrained with results from seismic and drill results revealed that the crustal structure beneath the mob has undergone an extensional type tectonics intruded with intrusive bodies results from the seismo gravity modeling in association with litholog data from drilled wells from the western continental margin of india wcmi are presented here

magmatic evolution of lunar highland rocks estimated from trace elements in plagioclase a new bulk silicate moon model with sub chondritic ti ba sr ba and sr al ratios abstract the compositions of host magmas of ferroan anorthosites fan host magmas were estimated from secondary ion mass spectrometry analyses of plagioclase in lunar highland rocks the evolution of the magmas was investigated by considering phase relations based on the melts algorithm and by re examining partition coefficients for trace elements between plagioclase and melts data little affected by post magmatic processes were selected by using plagioclase with relatively primitive sc and co contents the fan host magma contained 90 174 ppm sr 40 119 ppm ba and 0 5 1 3 tio2 and had sub chondritic sr ba and ti ba ratios it is difficult to account for the formation of fan host magma on the basis of magma evolution processes of previously proposed bulk silicate moon models with chondritic ratios for refractory elements at global scale therefore the source of the fan host magma must have had primordial sub chondritic sr ba and ti ba ratios the fan host magmas were consistent in refractory elements with the estimated host mafic magma for feldspathic crust based on lunar meteorites and some very low ti mare rocks from lunar meteorites here we propose an alternative bulk silicate moon model the cbsm model which is enriched in crustal components of proto bodies relative to the present whole earth moon system

the very strong coastal el nino in 1925 in the far eastern pacific the 1925 el nino en event was the third strongest in the twentieth century according to its impacts in the far eastern pacific fep associated with severe rainfall and flooding in coastal northern peru and ecuador in february april 1925 in this study we gathered and synthesised a large diversity of in situ observations to provide a new assessment of this event from a modern perspective in contrast to the extreme 1982 1983 and 1997 1998 events this very strong coastal el nino in early 1925 was characterised by warm conditions in the fep but cool conditions elsewhere in the central pacific hydrographic and tide gauge data indicate that downwelling equatorial kelvin waves had little role in its initiation instead ship data indicate an abrupt onset of strong northerly winds across the equator and the strengthening weakening of the intertropical convergence zones itcz south north of the equator observations indicate lack of external atmospheric forcing by the panama gap jet and the south pacific anticyclone and suggest that the coupled ocean atmosphere feedback dynamics associated with the itczs northerly winds and the north south sst asymmetry in the fep lead to the enhancement of the seasonal cycle that produced this en event we propose that the cold conditions in the western central equatorial pacific through its teleconnection effects on the fep helped destabilize the itcz and enhanced the meridional ocean atmosphere feedback as well as helping produce the very strong coastal rainfall this is indicated by the nonlinear relation between the piura river record at 5 s and the sst difference between the fep and the western central equatorial pacific a stability proxy in summary there are two types of en events with very strong impacts in the fep both apparently associated with nonlinear convective feedbacks but with very different dynamics the very strong warm enso events like 1982 1983 and 1997 1998 and the very strong coastal en events like 1925

a description of low frequency atmospheric oscillations over the extratropical northern hemisphere using singular spectrum analysis the method of singular spectrum analysis ssa is used to describe low frequency atmospheric variability over the extratropical northern hemisphere nh from 500 hpa geopotential heights analysis reveals significant intraseasonal and interannual oscillations confined principally to eastern sections of the pacific ocean and northern sections of the atlantic ocean generally where earlier studies have identified persistent anomalies from the results it is suggested that persistent anomalies may undergo significant modulation on the quasi biennial time scale

correlation structure of the el nino southern oscillation phenomenon abstract relationships among the atmospheric phenomena associated with the southern oscillation and el nino are investigated using the comprehensive ocean atmosphere data set coads of marine surface observations from ships of opportunity and the world monthly surface land station climatology wmssc for the period 1950 79 annual mean april march sea level pressure at darwin australia is used as an index of the southern oscillation results are based on simple linear correlation techniques stratified by season as in the rasmusson and carpenter 1982 composite correlations on the order of 0 9 are observed between darwin pressure sea surface temperature sst and rainfall in the equatorial central pacific and zonal wind in the equatorial western pacific relations among these variables are strongest from july through november when the month to month autocorrelation is also at its strongest sea surface temperature along the peruvian coast and pressure in the eastern pacific are also most stron

convection along the coast of northern peru during 1983 spatial and temporal variation of clouds and rainfall abstract streamflow and historical records indicate that flooding in northern peru was more severe during 1983 than during any year since 1891 a case study of the meteorological conditions along the northwest coast of south america from 10 s to 10 n during 1982 83 is presented station rainfall and satellite derived outgoing infrared observations are used to deduce the structure and time evolution of convection in this region substantial rainfall amounts were first observed along the western slopes of the andes mountains and coastal plain of southern ecuador during november and december 1982 and it continued to rain in this region through june 1983 in northern peru the onset of the rains along the coastal plain was delayed until january 1983 and ended abruptly during mid june 1983 convective activity was much greater along the coastal strip than over the eastern equatorial pacific to the cast of 100 w until may june 1983 in addition cloudiness was strongly modulated on the diurnal time scale with

phase space representation and characteristics of el nino la nina the variability of el nino la nina events was analyzed in a low dimensional phase space a concept derived from dynamic system theory the space time extended eofs derived from the observed monthly mean sst field over tropical pacific were used as the basis of the phase space that describes the time evolution of enso signals it was shown that the essential features of the enso variability such as the irregular oscillation the phase locking to the annual cycle and the interdecadal changes in its propagation and onset can be effectively represented by a three dimensional phase space the typical el nino la nina life cycle is four years with its mature phases in boreal winter the intensity of the enso signal within one life cycle is closely linked to the frequency of its occurrence onset the interdecadal variability of the enso signals is characterized by both the intensity and the frequency of occurrence displaying an irregularity with the gross feature comparable to the regime behavior and intermittency of some low dimensional chaotic systems

spells of low frequency oscillations and weather regimes in the northern hemisphere abstract the low frequency variability in the midlatitudes is described through an analysis of the oscillatory phenomena in order to isolate nearly periodic components of the atmospheric flow the multichannel version of the singular spectrum analysis m ssa is developed and applied to an nmc 32 year long set of 700 hpa geopotential heights in the same way that principal component analysis identifies the spatial patterns dominating the variability m ssa identifies dynamically relevant space time patterns and provides an adaptive filtering technique three major low frequency oscillations lfos are found with periods of 70 days 40 45 days and 30 35 days the 70 day oscillation consists of fluctuations in both position and amplitude of the atlantic jet with a poleward propagating anomaly pattern the 40 45 day oscillation is specific to the pacific sector and has a pronounced pacific north american pna structure in its high amplitude phase the 30 35 day mode is confined over the atlantic region

geohistory analysis of bombay high region abstract geohistory diagrams have been constructed for three representative sites in the bombay high region offshore west coast india the model curve for 60 lithospheric injection matches the intitial part of a thermo tectonic curve for one of the sites where a complete tertiary sequence is developed the study suggests that the four paleogene unconformities recognised in this region were caused by eustatic falls a distinct phase of active subsidence occurred during the late middle late miocene probably due to more active spreading at the mid indian ocean ridge

characteristics of the response of sea surface temperature in the central pacific associated with warm episodes of the southern oscillation abstract the zonal distribution of sea surface temperature sst in the equatorial pacific 4 n 4 s 120 e 80 w associated with el nino southern oscillation enso has been studied by using the seasonal mean file of the comprehensive ocean atmosphere data set coads for the period 1940 to 1983 although the warmest ocean area in the western central pacific exhibits very little annual variation it is very sensitive to the enso displaying large variability during such episodes the eastward migration of this warmest area 28 5 c isotherm is used here as a criterion related to strong tropical convection and heavy rainfall is a common feature in the developing stage of almost all enso events since 1940 not only for the event of 1982 the extent of its eastward migration varies from event to event and represents a large contribution to the interannual variability of zonal sst distribution in the equatorial pacific comparable to the behavior of the equatorial cold tongue in the east the spread of the war

an insight into the fifty fathom flat off india s west coast abstract the architecture of the western continental margin of india wcmi is likely to have been influenced in the geological past by several episodes of volcanic eruptions rifting and continental break up the wcmi is characterized by a wide shelf in the north few hundreds of kilometers wide which tapers down to just few kilometers towards the south a detailed multibeam swath bathymetry study was made of a part of the wide flat shelf off mumbai encountered at an approximate depth of 50 fathom about 100 m that holds one of the world s richest offshore petroleum resources the multibeam bathymetry images suggest that the western boundary of the fifty fathom flat fff coincides with the shelf break with a fall much sharper than other places along the west coast this break also coincides with the western extremity of the carbonate platform the stratigraphic succession and petrology of the fff bear strong resemblance to that of the seychelles and mascarene plateau we discuss the tectonic implications of such resemblance and the possible reasons for the remarkably low bathymetric relief of the fff

silicon in the earth s core the earth and moon have iron isotopic abundances that are slightly heavy compared with mars the asteroid vesta and primitive meteorites the reason for this has been unclear one suggestion is that there was a large scale isotopic equilibration during the giant impact the collision between the early earth and a mars sized body that created the moon but this has seemed unlikely given that most other elements do not show the effect an analysis of 44 meteorite and terrestrial samples now shows that the silicon isotopic compositions of basaltic rocks from the earth and moon are also distinctly heavy the finding is consistent with the isotopic equilibration model and it suggests that silicon was already partitioned into the earth s core as a light element before the moon formed the silicon isotopic compositions of basaltic rocks from the earth and moon are distinctly heavy the similar isotopic composition of the bulk silicate earth and the moon are consistent with large scale isotopic equilibration during the giant impact indicating that si was already a light element in the earth s core before the moon formed small isotopic differences between the silicate minerals in planets may have developed as a result of processes associated with core formation or from evaporative losses during accretion as the planets were built up basalts from the earth and the moon do indeed appear to have iron isotopic compositions that are slightly heavy relative to those from mars vesta and primitive undifferentiated meteorites1 2 3 4 chondrites explanations for these differences have included evaporation during the giant impact that created the moon when a mars sized body collided with the young earth however lithium5 and magnesium6 lighter elements with comparable volatility7 8 9 reveal no such differences rendering evaporation unlikely as an explanation here we show that the silicon isotopic compositions of basaltic rocks from the earth and the moon are also distinctly heavy a likely cause is that silicon is one of the light elements in the earth s core we show that both the direction and magnitude of the silicon isotopic effect are in accord with current theory10 based on the stiffness of bonding in metal and silicate the similar isotopic composition of the bulk silicate earth and the moon is consistent with the recent proposal11 that there was large scale isotopic equilibration during the giant impact we conclude that si was already incorporated as a light element in the earth s core before the moon formed

variations in near global sea level pressure abstract analysis of a near global sea level pressure slp data set for the period 1951 80 was carried out in terms of complex empirical orthogonal function a large scale propagating slp signal was discovered that seems to include variability previously associated with the southern oscillation monsoons and tropical midlatitude teleconnection patterns in this sense the new feature offers an empirical framework for many of the well known features of the global climate system extensive comparisons show the feature to be observable in the raw data field and thus not a figment of the analysis technique the large slp signal may have its origins in a slp snow feedback loop that acts over the region from siberia to india it is suggested that the maintenance of the slp signal involves slp precipation feedbacks and more importantly the excitation of a major natural mode of climate variation the slp signal is only excited at time scales larger than about 18 mouths i e time scales characteristic of ocea

recent developments in quantitative stratigraphy abstract during the past 10 years about 150 scientists in 25 countries have collaborated under the auspices of the international geological correlation programme project no 148 evaluation and development of quantitative stratigraphical correlation techniques this paper reviews mathematical methods of stratigraphical correlation mainly in biostratigraphy but also in chronostratigraphy and lithostratigraphy sequencing methods treat the relative order of stratigraphic events such as the highest occurrences of fossil taxa as observed in many sections intervals between successive events in an ordered sequence can be estimated and the results expressed in linear time if a subgroup of the stratigraphical events can be dated recently such methods have been used to develop a new deep water benthic foraminiferal zonation for the cenozoic strata of the central and viking grabens north sea several regional hiatuses of 2 to 5 m y in duration can be recognized and matched to changes in sea level the same methods have been used for automated isochron contouring with error bars in depth or time units in cenozoic and cretaceous basins off eastern canada such information may be used for automated basin history analysis time successive assemblages of fossils can be established by using multivariate methods applied to co occurrences of events or by the method of unitary associations in conjunction with graph theory on the overlap of stratigraphical ranges other methods for stratigraphical correlation reviewed in this paper include the composite standard method and estimation of the age of chronostratigraphical boundaries using maximum likelihood and cubic spline interpolations attractions of quantitative stratigraphy are the use of rigorous methodology which highlights many properties of the data the ability to handle large and complex data bases in an objective manner and statistical evaluation of the uncertainty in the results generally little conceptual orientation is required in order to use these methods and thereby gain more information from a particular dataset

tholeiitic dykes in the seychelles and the original spatial extent of the deccan we report geochemical data from c deccan age tholeiitic dykes from praslin island in the seychelles a continental fragment which lay adjacent to the coast of india before sea floor spreading started in the arabian sea at 64 ma the dykes have compositions very similar to the distinctive bushe magma type from the deccan and hence constitute the first traces of deccan activity recognized on the seychelles fitting the seychelles and india back together to reconstruct the original extent of the deccan we find that the present estimate of 1 million km 2 needs to be revised upwards by c 25 to account for the deccan magmatism in the seychelles if dipping reflectors found on seismic lines to the northwest of the seychelles are also deccan age flows this would increase still further the area and volume estimates

3d stratigraphic forward modeling of an ancient transgressive barrier system a case study of accuracy and sensitivity abstract accuracy of geological modeling and understanding of the controlling parameters in sedimentary systems evolution are challenges in both academy and industry uncertainty in the prediction of spatial and temporal facies distributions and difficulties in quantitative analysis of controlling parameters are current challenges to increase geological model certainty and sedimentary process understanding computational modeling has evolved exponentially during the last 50 years in this study 3d stratigraphic forward modeling technique is used to simulate an ancient transgressive barrier system of southern brazil deposited during the lower permian in the parana basin upper part of the rio bonito formation in the study area the depositional systems are part of a large transgressive cycle that includes fluvial estuarine facies at the base and barrier lagoon deposits associated with the development of salt marshes at the top throughout the region offshore strata cover the barrier lagoon facies the simulation successfully represented the retrograde evolution of the coastal barrier system with longshore currents as the main transport mechanism of sediments the evolution of the barrier system started with upper shoreface deposits overlying the lagoon system facies in the south later lower shoreface sediments covered upper shoreface deposits then shoreline migration continued landward finally offshore transition deposits covered all previous deposits simulations and tests of controlling parameters allowed an adjustment to actual thickness and lithologies up to 83 these simulations allowed for the analysis of model sensitivity in particular to the influence of parameters that control sedimentary evolution the main controlling parameter was sediment supply volume and composition followed by time step initial bathymetry and sediment velocity had less of an impact

flexural and stratigraphic development of the west indian continental margin subsidence curves for 27 wells from the western continental margin of india show a characteristic late oligocene to early miocene 24 5 ma rapid increase in subsidence rate superposed on the long lived slow subsidence typical of the thermal subsidence phase of passive continental margins by subtracting a best fit negative exponential subsidence from the observed subsidence curves we obtain an estimate of the distribution and magnitude of the excess subsidence affecting the neogene development of the west indian margin the magnitude of this excess subsidence increases seaward from the coast ranging from a few meters to 2000 m near the shelf edge we examine the following hypotheses to explain the distribution and timing of this excess subsidence 1 modification of basin stratigraphy due to the effects of lithospheric in plane compression 2 creation of accommodation space on the margin by flexural effects associated with indus fan loading and 3 rapid growth of the continental margin and associated flexural effects of the three hypotheses tested the least important mechanism to account for the observed excess subsidence is that of variations of lithospheric in plane force principally because maximum in plane compression within the indo australian plate was only achieved in the late miocene because indus fan sediment deposition began in the late oligocene to early miocene we investigated three dimensional flexural effects associated with fan loading as a cause of the excess subsidence beginning at 24 ma the distribution and magnitude of modeled flexural deflection however are not consistent with the observed excess subsidence interpretation of seismic reflection data indicates that the margin has aggraded and prograded by 100 km basin ward since the oligocene therefore we evaluate the flexural effects of this margin growth by estimating the amount of space infilled by margin progradation and aggradation since 24 ma and computing the resulting deflection this deflection matches the distribution and magnitude of observed excess subsidence along the margin in addition the distribution of the flexural bulge predicted from the combined deflections due to indus fan and margin loading is spatially coincident with the distribution of exposed marine terraces and drainage divides in the saurastra peninsula and the regions surrounding the gulfs of cambay and kutch respectively available gravity seismic reflection refraction and well data are consistent with our prediction of a 4000 to 5000 m thick sediment load developed during the neogene along the outer margin we propose that flexural deformation due to sedimentary loading provides a potential tectonic feedback mechanism that affects coastal and fluvial depositional processes as regions in close proximity to the load are depressed regions farther from the load experience uplift i e the peripheral bulge which is sufficient to cause subaerial exposure of large portions of the shelf and to modify existing drainage networks this feedback represents a mechanism for inducing relative sea level changes without invoking glacial eustasy

chaotic oscillations of tropical climate a dynamic system theory for enso abstract based on first principles a theoretical model for el nino southern oscillation enso is derived that consists of prognostic equations for sea surface temperature sst and for thermocline variation considering only the large scale equatorially symmetric standing basin mode yields a minimum dynamic system that highlights the cyclic chaotic and season dependent evolution of enso for a steady annual mean basic state the dynamic system exhibits a unique limit cycle solution for a fairly restricted range of air sea coupling the limit cycle is a stable attractor and represents an intrinsic interannual oscillation of the coupled system the deepening rising of the thermocline in the eastern western pacific leads eastern pacific warming by a small fraction of the cycle which agrees well with observation and plays a critical role in sustaining the oscillation when the nonlinear growth of sst anomalies reaches a critical amplitude the delayed response of thermocline adjustment provides a n

modulation of western north pacific tropical cyclone activity by the atlantic meridional mode this study examines the year to year modulation of the western north pacific wnp tropical cyclones tc activity by the atlantic meridional mode amm using both observations and the geophysical fluid dynamics laboratory forecast oriented low ocean resolution version of cm2 5 flor global coupled model 1 the positive negative amm phase suppresses enhances wnp tc activity in observations the anomalous occurrence of wnp tcs results mainly from changes in tc genesis in the southeastern part of the wnp 2 the observed responses of wnp tc activity to the amm are connected to the anomalous zonal vertical wind shear zvws caused by amm induced changes to the walker circulation during the positive amm phase the warming in the north atlantic induces strong descending flow in the tropical eastern and central pacific which intensifies the walker cell in the wnp the intensified walker cell is responsible for the suppressed enhanced tc genesis in the eastern western part of the wnp by strengthening weakening zvws 3 the observed wnptc amm linkage is examined by the long term control and idealized perturbations experiment with flor fa a suite of sensitivity experiments strongly corroborate the observed wnptc amm linkage and underlying physical mechanisms

new evidence for enhanced preservation of organic carbon in contact with oxygen minimum zone on the western continental slope of india paropkari a l prakash babu c and mascarenhas a 1993 new evidence for enhanced preservation of organic carbon in contact with oxygen minimum zone on the western continental slope of india mar geol i 11 7 13 in order to evaluate the reason for organic enrichment on the western continental slope of india we provide rock eval pyrolysis data of 25 surficial sediment samples from this area results show that the organic matter on the slope is hydrogenrich type ii kerogen which suggests that the organic carbon there is mostly marine the low productivity of overlying waters rules out surface productivity as a possible cause of organic enrichment the association of higher hydrogen index hi values average 306 and higher organic carbon contents av 3 28 wt with the sediments of the upper slope in contact with the oxygen minimum zone omz clearly indicates enhanced preservation under reducing conditions in the anoxic waters of the omz it is suggested that the sediments of the upper slope in contact with the omz have excellent hydrocarbon generation potential and that these slope beds deserve preferential attention for hydrocarbon exploration

tidal evolution of the moon from a high obliquity high angular momentum earth in the giant impact hypothesis for lunar origin the moon accreted from an equatorial circum terrestrial disk however the current lunar orbital inclination of five degrees requires a subsequent dynamical process that is still unclear in addition the giant impact theory has been challenged by the moon s unexpectedly earth like isotopic composition here we show that tidal dissipation due to lunar obliquity was an important effect during the moon s tidal evolution and the lunar inclination in the past must have been very large defying theoretical explanations we present a tidal evolution model starting with the moon in an equatorial orbit around an initially fast spinning high obliquity earth which is a probable outcome of giant impacts using numerical modelling we show that the solar perturbations on the moon s orbit naturally induce a large lunar inclination and remove angular momentum from the earth moon system our tidal evolution model supports recent high angular momentum giant impact scenarios to explain the moon s isotopic composition and provides a new pathway to reach earth s climatically favourable low obliquity

el nino events and their relation to the southern oscillation 1925 1986 relationships among sea surface temperatures ssts at the coast of peru and offshore river discharge in northern peru and sea level pressure at darwin australia during the period 1925 1986 are investigated using time series plots frequency distributions and a simple statistical analysis it is shown that ssts undergo a larger seasonal cycle offshore than at the coast exhibit more interannual variability during the warm than the cool season are positively skewed during much of the year and exhibit greatest month to month persistence during the cool season many but not all episodes of above normal coastal ssts are accompanied by enhanced river discharge in northern peru comparison of the darwin pressure and coastal sst records during the past 60 years shows that el nino events episodes of above normal ssts along the coast of peru have occurred both in advance of and subsequent to major negative swings of the southern oscillation and associated climatic changes in the central equatorial pacific in addition el nino events and negative swings of the southern oscillation have occurred separately hence el nino and the southern oscillation are more loosely coupled than other studies would imply