a different perspective on glauconite as a chronometer for geologic time scale studies there are advocates of the use of glauconite as a chronometer for geologic time scale studies who insist that if the geohistory of the sample in question is known in detail one can ascertain before hand that the sample will yield a radiometric result that is accurate in the geological sense examples are presented indicating that while some glauconite samples may yield the correct age within their assigned analytical uncertainties when compared to high temperature minerals others clearly do not and are too young by varying degrees the outright acceptance of published results on glauconite can result in erroneous age estimates of various biostratigraphic levels and stage or epoch boundaries

mechanisms by which gulf of guinea and eastern north atlantic sea surface temperature anomalies can influence african rainfall abstract the sensitivity of precipitation over west africa to sea surface temperature anomalies sstas in the gulf of guinea and the eastern north atlantic is studied using a gcm results from nine perpetual july simulations with various imposed sstas are presented and analyzed to reveal associations between the precipitation and sst fields via large scale circulation and atmospheric moisture anomalies rainfall increases over the guinean coast and decreases over the congo basin when warm sstas are present in the gulf of guinea these precipitation perturbations are related to the forcing of a kelvin and a rossby wave the former is associated with a weakening of the walker circulation while the latter strengthens the west african monsoon rainfall over west africa is less sensitive to cold sstas than to warm anomalies three contributing factors are identified as follows 1 latitude of the sst forcing 2 background flow and 3 nonlinearity of the clausius clapeyron equation no more than a 20 effec

geometry and kinematics of recent deformation in the mondy tunka area south westernmost baikal rift zone mongolia siberia we used satellite imagery and field data to investigate the south westernmost baikal rift zone we focus our study in the mondy and ikhe ukhgun valleys site of an mw 6 9 seismic event in 1950 surface deformations are observed along the e w trending mondy strike slip fault and along the ikhe ukhgun thrust the mondy fault system is 80 km long and is composed of four segments 10 15 km long these segments are characterized by subvertical planes with left lateral movements the ikhe ukhgun thrust is 20 km long dips 40 to the south and shows reverse movement with a left lateral component these observations are consistent with the present day regional nne ssw compression and with the focal mechanism of the 1950 mondy earthquake that was recently re evaluated these features like those observed in the tunka basin demonstrate a recent change of regional strain regime from transtension to transpression that we place before the late pleistocene

the equatorial atlantic oscillation and its response to enso an internal equatorial atlantic oscillation has been identified by analyzing sea surface temperature sst observations the equatorial atlantic oscillation can be viewed as the atlantic analogue of the el nino southern oscillation enso phenomenon in the equatorial pacific but it is much less vigorous the equatorial atlantic oscillation is strongly influenced by the pacific enso with the equatorial atlantic sea surface temperature lagging by about six months this lag can be explained by the dynamical adjustment time of the equatorial atlantic to low frequency wind stress variations and the seasonally varying background state which favours strongest growth of perturbations in summer results of an extended range simulation with a coupled ocean atmosphere gcm support this picture

magnetotelluric multiscale 3 d inversion reveals crustal and upper mantle structure beneath the hangai and gobi altai region in mongolia

subtropical anticyclones and summer monsoons the summer subtropical circulation in the lower troposphere is characterized by continental monsoon rains and anticyclones over the oceans in winter the subtropical circulation is more strongly dominated by the zonally averaged flow and its interactions with orography here the mechanics of the summer and winter lowertropospheric subtropical circulation are explored through the use of a primitive equation model and comparison with observations by prescribing in the model the heatings associated with several of the world s monsoons it is confirmed that the equatorward portion of each subtropical anticyclone may be viewed as the kelvin wave response to the monsoon heating over the continent to the west a poleward flowing low level jet into a monsoon such as the great plains jet is required for sverdrup vorticity balance this jet effectively closes off the subtropical anticyclone to the east and also transports moisture into the monsoon region the low level jet into north america induced by its monsoon heating is augmented by a remote response to the asian monsoon heating the rossby wave response to the west of subtropical monsoon heating interacting with the midlatitude westerlies produces a region of adiabatic descent it is demonstrated here that a local diabatic enhancement can lead to a strengthening of the descent longitudinal mountain chains act to block the westerly flow and also tend to produce descent in this region below the descent sverdrup vorticity balance implies equatorward flow that closes off the subtropical anticyclone to the west and induces cool upwelling in the ocean through ekman transport feedbacks involving for example sea surface temperatures may further enhance the descent in these regions the conclusion is that the mediterranean type climates of regions such as california and chile may be induced remotely by the monsoon to the east hence it can be argued that the subtropical circulation in summer comprises a set of weakly interacting monsoon systems each involving monsoon rains a low level poleward jet a subtropical anticyclone to the east and descent and equatorward flow to the west in winter it is demonstrated how the nonlinear interaction between the strong zonal mean circulation associated with the winter hadley cell and the mountains can define many of the large scale features of the subtropical circulation the blocking effect of the longitudinal mountain chains is shown to be very important subsequent diabatic effects such as a local diabatic enhancement would appear to be essential for producing the observed amplitude of these features

asthenospheric imprints on the lithosphere in central mongolia and southern siberia from a joint inversion of gravity and seismology mobal experiment summary we present a joint inversion of gravity and teleseismic data to enlighten the lithospheric structures of the baikal mongolia region an area characterized by high topographic contrasts sporadic cenozoic volcanism extension and large transcurrent faulting in the vicinity of the baikal rift central asia the study uses a 1000 km long seismic transect that cross cuts the main tectonic structures from north to south namely the siberian platform tunka basin hangay dome and gobi altai belt the siberian platform depicts a high velocity lithosphere down to about 150 km we evidence strong velocity contrasts within the crust below the hangay dome and the tunka depression interpreted as a thickened crust a low velocity density region is located at various depths below the hangay dome thanks to the dense spatial coverage of gravity data we are able to define the 3 d geometry of this particular low velocity density anomaly the hangay dome anomalous body extends from 60 to 225 km depth at his largest point and slightly thins to no more than 40 km at its easternmost end a deep low velocity zone below 150 km with only a weak negative density contrast is observed on the eastern part of the transect we propose that the late cenozoic uplift of the whole mongolian plateau and associated rifting magmatism high heat flow and lithospheric thinning are not externally driven by the india asia collision but results from the interaction of two mantle plumes with the overlying lithosphere conversely recent faulting may be the major expression of the india asia collision in this region as well as n s striking rift basins that connect and interact with major strike slip faults such as the bolnai fault the comparison between time residuals of this experiment and the baikal rift seismic data shows an undeniable disproportion for the hangay anomaly the hangay time residuals are far more positive than through the baikal arguing for an asthenospheric signature that is not seen beneath the baikal rift furthermore the southern edge of the thick siberian cratonic lithosphere may favour the rise of a sublithospheric mantle flow at the contact with the baikal mongolia lithosphere

3d s wave velocity pattern in the upper mantle beneath the continent of asia from rayleigh wave data abstract group velocities of rayleigh waves in the 10 150 s period range along about 1200 paths across central asia and siberia are used to obtain group velocity maps of the region to image the lateral variations of group velocities we used the tomography method developed earlier for spherical surface pepi 122 2000 19 the method is supplemented by the opportunity to estimate the resolving power of the data the locally averaged dispersion curves have been then inverted to vertical s wave velocity profiles up to depth of 500 km at different sites in the region which thus image a 3d velocity distribution in order to reduce the number of unknown parameters we assumed the relationships between s wave and p wave velocities and densities to be those of the prem model the 3d s wave velocity pattern is displayed in the form of maps at depths from 50 to 350 km with a step of 50 km and of 2d vertical velocity sections along some profiles crossing different tectonic units the most remarkable feature of the 3d velocity distribution is the presence of a high velocity rise at the depths of 250 350 km beneath southern siberia and western china which borders upon the low velocity asthenosphere along the longitude about 105 e collision of the high and low velocity substances results in pressing out the viscous asthenosphere material in the weakened zone of the baikal rift where the lithosphere is thinned the rise of the asthenosphere in this zone probably produces mantle upwelling and leads to uplift of the khangay plateau

on the origin of equatorial atlantic biases in coupled general circulation models many coupled ocean atmosphere general circulation models gcms suffer serious biases in the tropical atlantic including a southward shift of the intertropical convergence zone itcz in the annual mean a westerly bias in equatorial surface winds and a failure to reproduce the eastern equatorial cold tongue in boreal summer the present study examines an ensemble of coupled gcms and their uncoupled atmospheric component to identify common sources of error it is found that the westerly wind bias also exists in the atmospheric gcms forced with observed sea surface temperature but only in boreal spring during this time sea level pressure is anomalously high low in the western eastern equatorial atlantic which appears to be related to deficient excessive precipitation over tropical south america africa in coupled simulations this westerly bias leads to a deepening of the thermocline in the east which prevents the equatorial cold tongue from developing in boreal summer thus reducing atmospheric model errors during boreal spring may lead to improved coupled simulations of tropical atlantic climate

how ubiquitous is the dipole relationship in tropical atlantic sea surface temperatures several kinds of analysis are applied to sea surface temperature anomalies ssta 1856 1991 to determine the degree to which ssta of opposite sign in the tropical north and south atlantic occur antisymmetric dipole configurations of ssta on basin scales are not ubiquitous in the tropical atlantic unless the data are stratified by both season and frequency inherent dipole behavior cannot be demonstrated upon removing the global el nino southern oscillation signal in ssta which is symmetric between the north and south atlantic from the data the regions north or south of the intertropical convergence zone have qualitatively different temporal variabilities and are poorly correlated dipole configurations do occur infrequently 12 15 of the time but no more so than expected by chance for stochastically independent variables nondipole configurations that imply significant meridional ssta gradients occur much more frequently nearly half of the time cross spectral analysis of seasonally averaged ssta indices for the north and south atlantic show marginally significant coherence with antisymmetric phase in two period bands 8 12 years for the boreal winter spring and 2 3 years for the boreal summer fall antisymmetric coherence is optimal for a small subregion west of angola in the south atlantic with respect to ssta of basin scale in the tropical north atlantic dipole variability even where optimal explains only a small fraction of the total variance in tropical atlantic ssta 7

indian ocean capacitor effect on indo western pacific climate during the summer following el nino significant climate anomalies persist through the summer june august after el nino dissipates in spring over the equatorial pacific they include the tropical indian ocean tio sea surface temperature sst warming increased tropical tropospheric temperature an anomalous anticyclone over the subtropical northwest pacific and increased mei yu baiu rainfall over east asia the cause of these lingering el nino effects during summer is investigated using observations and an atmospheric general circulation model gcm the results herein indicate that the tio warming acts like a capacitor anchoring atmospheric anomalies over the indo western pacific oceans it causes tropospheric temperature to increase by a moist adiabatic adjustment in deep convection emanating a baroclinic kelvin wave into the pacific in the northwest pacific this equatorial kelvin wave induces northeasterly surface wind anomalies and the resultant divergence in the subtropics triggers suppressed convection and the anomalous anticyclone the gcm results support this kelvin wave induced ekman divergence mechanism in response to a prescribed sst increase over the tio the model simulates the kelvin wave with low pressure on the equator as well as suppressed convection and the anomalous anticyclone over the subtropical northwest pacific an additional experiment further indicates that the north indian ocean warming is most important for the kelvin wave and northwest pacific anticyclone a result corroborated by observations these results have important implications for the predictability of indo western pacific summer climate the spatial distribution and magnitude of the tio warming rather than simply whether there is an el nino in the preceding winter affect summer climate anomalies over the indo western pacific and east asia

geophysical model of the lithosphere across the variscan belt of sw iberia multidisciplinary assessment abstract a multidisciplinary geophysical study along a large seismic transect in the sw iberian peninsula has been carried out this study integrates the crustal structure geometry and composition obtained from normal incidence and wide angle seismic reflection data with other observables geoid gravity and topography the internal architecture of the lithosphere across the variscan orogen of sw iberia is constrained by the 300 km long high resolution deep normal seismic reflection iberseis transect the most prominent feature imaged by the seismic survey is the iberseis reflective body irb a 140 km long high amplitude reflective body located in the middle crust of the northern half of the transect the seismic velocity vp distribution within the crust and the upper mantle is constrained by two wide angle seismic transects acquired in the same area the velocity models show a complex crust with a specially complex middle crust which features higher velocities than the average continental crust also the wide angle data revealed that the irb is characterized by high velocities this feature was then interpreted as sill like structure built up by a series of mafic intrusions therefore a key issue is to study if this relatively mafic crust is consistent with other geophysical observables based on the velocity models two lithospheric density models have been derived along the iberseis wide angle transects the geoid gravity and topography response of these models have been calculated using a finite elements code that solves simultaneously the geopotential lithostatic and heat flow equations the resulting values are then compared with the measured observables and the crustal and lithospheric mantle geometry and density is modified until the best fit is obtained the initial density models calculated from the seismic data adjust quite well to the real potential field data however minor modifications have been required in order to properly fit the observables the final density models are consistent with the existence of relatively high density bodies in the mid crust providing further support to the seismic interpretation in addition they place new constraints on the location of the lithosphere asthenosphere boundary and on the tectonic evolution of sw iberia

teleseismic traveltimes topography and the lithospheric structure across central mongolia 1 teleseismic travel times recorded along a 1000 km long n s transect across central mongolia are used together with topography and gravity data to constrain the deep lithospheric structure of this region time residuals appear positively correlated with the topography suggesting that p wave velocity changes correspond to density variations which in turn cause an isostatic uplift of the topography using a simple local isostasy model and a monte carlo inversion for the crust and asthenosphere velocities and density velocity conversion factors we determine best fitting moho and lithosphere asthenosphere boundary lab geometries which satisfyingly reproduce the observed topography and gravity data the model is validated using previously published 1d s wave velocity models obtained from receiver function analyses our results indicate that most of the long wavelength topography is supported by the asthenosphere buoyancy the hangai dome in the southern half of the transect appears mainly supported by a rather shallow 60 70 km asthenospheric uplift whereas the siberian platform at the extreme north of the profile is underlain by a very thick 200 km lithosphere misfits to the observed bouguer gravity anomaly occur near major faults probably because of lithospheric flexure

seismic velocity variations beneath central mongolia evidence for upper mantle plumes abstract central mongolia is marked by wide spread recent volcanism as well as significant topographic relief even though it is far from any plate tectonic boundaries the cause of the recent magmatism and topography remains uncertain partially because little is known of the underlying mantle seismic structure due to the lack of seismic instrumentation in the region from august 2011 through august 2013 69 broadband seismic stations were deployed in central mongolia teleseismic traveltime residuals were measured using waveform correlation and were inverted to image upper mantle p and s velocity variations significant lateral variations in seismic velocity are imaged in the deep upper mantle 100 to 800 km depth most significant are two continuous slow anomalies from the deep upper mantle to near the surface one slow feature has been imaged previously and may be a zone of deep upwelling bringing warm mantle to beneath the hangay dome resulting in uplift and magmatism including the active khanuy gol and middle gobi volcanoes the second deep low velocity anomaly is seen in the east from 800 to 150 km depth the anomaly ends beneath the gobi desert that is found to have fast shallow mantle indicating a relatively thick lithosphere we interpret the second deep slow anomaly as a mantle upwelling that is deflected by the thick gobi desert lithosphere to surrounding regions such as the hentay mountains to the north the upwellings are a means of feeding warmer than normal asthenospheric mantle over a widely distributed region beneath mongolia resulting in distributed volcanic activity and uplift there is no indication that the upwellings are rooted in the deep lower mantle i e classic plumes we speculate the upwellings may be related to deep subduction of the pacific and indian plates and are thus plumes anchored in the upper mantle

mantle structure and rifting processes in the baikal mongolia region geophysical data and evidence from xenoliths in volcanic rocks abstract the origin of the baikal rift zone brz has been debated between the advocates of passive and active rifting since the 1970s a re assessment of the relevant geological and geophysical data from russian and international literature questions the concept of broad asthenospheric upwelling beneath the rift zone that has been the cornerstone of many active rifting models results of a large number of early and recent studies favour the role of far field forces in the opening and development of the brz this study emphasises the data obtained through studies of peridotite and pyroxenite xenoliths brought to the surface by alkali basaltic magmas in southern siberia and central mongolia these xenoliths are direct samples of the upper mantle in the vicinity of the brz of particular importance are suites of garnet bearing xenoliths that have been used to construct p t composition lithospheric cross sections in the region for the depth range of 35 80 km xenolith studies have shown fundamental differences in the composition and thermal regime between the lithospheric mantle beneath the ancient siberian platform sampled by kimberlites and beneath younger mobile belts south of the platform the uppermost mantle in southern siberia and central mongolia is much hotter at similar levels than the mantle in the siberian craton and also has significantly higher contents of basaltic major elements ca al na and iron higher fe si and fe mg the combination of the moderately high geothermal gradient and the fertile compositions in the off cratonic mantle appears to be a determining factor controlling differences in sub moho seismic velocities relative to the siberian craton chemical and isotopic compositions of the off cratonic xenoliths indicate small scale and regional mantle heterogeneities attributed to various partial melting and enrichment events consistent with long term evolution in the lithospheric mantle age estimates of mantle events based on os sr nd isotopic data can be correlated with major regional stages of crustal formation and may indicate long term crust mantle coupling the ratios of 143 144nd in many lree depleted xenoliths are higher than those in morb or oib source regions and are not consistent with a recent origin from asthenospheric mantle mantle xenoliths nearest to the rift basins 30 50 km south of southern lake baikal show no unequivocal evidence for strong heating unusual stress and deformation solid state flow magmatic activity or partial melting that could be indicative of an asthenospheric intrusion right below the moho comparisons between xenoliths from older and younger volcanic rocks east of lake baikal together with observations on phase transformations and mineral zoning in individual xenoliths have indicated recent heating in portions of the lithospheric mantle that may be related to localised magmatic activity or small scale ascent of deep mantle material overall the petrographic p t chemical and isotopic constraints from mantle xenoliths appear to be consistent with recent geophysical studies which found no evidence for a large scale asthenospheric upwarp beneath the rift and lend support to passive rifting mechanism for the brz

decadal interactions between the western tropical pacific and the north atlantic oscillation the relationship between interdecadal variations of tropical sea surface temperature sst in the last 120 years and circulation anomalies related to the north atlantic oscillation nao is investigated in this study using an atmospheric general circulation model agcm we confirm observational evidence that variations in the sst gradient in the western tropical pacific are related to the nao anomalies on decadal timescale and may be contributing to the shift towards the positive nao phase observed in the late 20th century the role played by the indian ocean nao teleconnection advocated in recent studies focused on the last 50 years is also assessed in the context of the 120 year long record it is suggested that a positive feedback between the pacific sst and the hemispheric circulation pattern embedding the decadal nao signal may act to enhance the internal variability of the coupled ocean atmosphere system and justify the stronger teleconnection found in observational data than in sst forced agcm experiments

tropical response to the atlantic equatorial mode agcm multimodel approach on the frame of the amma eu project sensitivity experiments for an atlantic equatorial mode aem which origin development and damping resembles the observed one during the last decades of the 20th century has been analysed in order to investigate the influence on the anomalous summer west african rainfall recent studies raise the matter of the aem influence on the next pacific enso episodes and also on the indian monsoon this paper evaluates the response of four different atmospheric global circulation models using the above mentioned aem sensitivity experiments to study the tropical forcing associated with the atlantic nino mode the results show a remote signal in both the pacific and indian basins for a warm phase of the aem the associated southward location of the itcz with rising motions over the equatorial atlantic leads to a global subsidence over the rest of the tropics weakening the asian monsoon and favouring the la nina conditions in the central pacific although ocean atmosphere coupled experiments are required to test the latter hypothesis the present studies shows how the aem is able to influence the rest of the tropics a result with important implications on enso seasonal predictability

influences of depositional environment and diagenesis on geophysical log response in the south carolina coastal plain effects of sedimentary fabric and mineralogy abstract interpretations of depositional environments and hydrologic units are made routinely from the study of geophysical well logs spontaneous potential sp and resistivity logs can be used as indicators of textural parameters gamma ray logs denote lithologic zones based on the presence of radioactive material particularly in fine grained sediments on the south carolina coastal plain surficial fluvially derived cobbles sands and clays are characterized by very low radioactivity weathered paleosurfaces enriched in hydroxy interlayered vermiculite hiv and associated mica produce higher gamma ray responses at discrete intervals the underlying sequence of siliciclastic shelf sands deposited under conditions of eustatic sea level rise has high concentrations of smectite and low gamma ray signatures small scale variability of gamma radiation reflects temporal changes of sub environments higher values are recorded in finer grained organic rich nearshore sediments calcareous ecocene sediments are characterized by highly variable signals on the gamma ray sp and resistivity logs phospharic material smectite and disseminated organic matter produced very high gamma ray values corresponding low sp readings are a function of low macro to microscale porosity resulting from the fine grain size and authigenic pore filling cement intervals that resemble massively bedded chalks at the macroscale are characterized by low gamma ray and resistivity values and high sp readings high sp values result from microposity preserved in biogenic tests rather than intergranular porosity that would be expected for a permeable sand these observations indicate the importance of incorporating sedimentologic techniques with well log data for a comprehensive evaluation of subsurface lithologic units

shear velocity structure of the crust and upper mantle of madagascar derived from surface wave tomography the crust and upper mantle of the madagascar continental fragment remained largely unexplored until a series of recent broadband seismic experiments an island wide deployment of broadband seismic instruments has allowed the first study of phase velocity variations derived from surface waves across the entire island late cenozoic alkaline intraplate volcanism has occurred in three separate regions of madagascar north central and southwest with the north and central volcanism active until 1 ma but the sources of which remains uncertain combined analysis of three complementary surface wave methods ambient noise rayleigh wave cross correlations and two plane wave illuminate the upper mantle down to depths of 150 km the phase velocity measurements from the three methods for periods of 8 182 s are combined at each node and interpolated to generate the first 3 d shear velocity model for sub madagascar velocity structure shallow upper 10 km low shear velocity regions correlate well with sedimentary basins along the west coast upper mantle low shear velocity zones that extend to at least 150 km deep underlie the north and central regions of recent alkali magmatism these anomalies appear distinct at depths 100 km suggesting that any connection between the zones lies at depths greater than the resolution of surface wave tomography an additional low shear velocity anomaly is also identified at depths 50 150 km beneath the southwest region of intraplate volcanism we interpret these three low velocity regions as upwelling asthenosphere beneath the island producing high elevation topography and relatively low volume magmatism

variations of sea surface temperature wind stress and rainfall over the tropical atlantic and south america abstract empirical orthogonal functions e0fs and composite analyses are used to investigate the development of sea surface temperature sst anomaly patterns over the tropical atlantic the evolution of large scale rainfall anomaly patterns over the equatorial atlantic and south america are also investigated the eof analyses revealed that a pattern of anomalous sst and wind stress asymmetric relative to the equator is the dominant mode of interannual and longer variability over the tropical atlantic the most important findings of this study are as follows atmospheric circulation anomalies precede the development of basinwide anomalous sst patterns over the tropical atlantic anomalous sst originate off the african coast simultaneously with atmospheric circulation anomalies and expand westward afterward the time lag between wind stress relaxation strengthening and maximum sst warming cooling is about two months anomalous atmospheric circulation patterns over northern tropical atlantic are phase

links between climate erosion uplift and topography during intracontinental mountain building of the hangay dome mongolia 1 the hangay mountain range a dome in central mongolia provides a window into understanding how climate influences the erosion and resulting geomorphic and sedimentary signatures of continental topography specifically asymmetric erosion of the hangay associated with a distinct orographic precipitation gradient offers a natural experiment for exploring uplift erosion and the isostatic response to erosional unloading the flat topped hangay peaks preserve low relief remnant surfaces that provide markers of rock uplift this makes it possible to map the deformation of a former planar surface during doming and hence to estimate the total extent of erosion by the difference from present day topography erosion into the hangay surface has been significant but incomplete the morphology of the range indicates a nonequilibrium landscape that may have persisted for millions to tens of millions of years implying a long response time in this semiarid climate the extent of erosion across the range correlates with mean annual precipitation variability in present day peak heights across the north south climatic and erosional gradient provides empirical support for the generally accepted theory that climate driven erosion will increase the height of mountain peaks by generating greater surface uplift through isostasy correction for this isostatic response makes it possible to reconstruct primary surface uplift of the hangay results highlight the importance of considering the interplay between climate erosion and uplift in shaping intracontinental topography and thus when interpreting the geomorphic sedimentary and geodynamic signatures associated with such topography

the representation of the south tropical atlantic teleconnection to the indian ocean in the ar4 coupled models a series of recent papers showed that sea surface temperature sst anomalies in the south equatorial tropical atlantic modulate the interannual variability of the african and indian monsoon rainfall physically this teleconnection can be explained by a simple gill matsuno mechanism in this work the output from five different models chosen within the cmip3 coupled model intercomparison project version 3 ensemble of coupled general circulation models cgcms are analyzed to investigate how state of the art cgcms represent the impact of the south tropical atlantic sta ssts on the indian and african region using a correlation regression technique it is found that four out of the five models display a teleconnection between sta and indian region which is generally weaker than in the observations but in agreement in the rainfall field pattern this teleconnection is also noticeable in the ensemble mean of the five models over africa however the significant changes in rainfall displayed in the observation are properly caught by only one of the cgcms additionally none of the models reproduces the symmetric upper level wind response around the equator seen over the indian ocean in the observations and all have significant biases also in the surface pressure field response to the tropical atlantic ssts nonetheless the sta response particularly over the southern hemisphere is indicative of the gill matsuno type mechanism identified in previous studies using idealized experiments with atmospheric gcms and observational data with a suite of atmospheric only gcm integrations it is shown that the differences in amplitude and pattern are not only due to the strong biases and reduced variabilities of the cgcms over the tropical atlantic but they are also caused by the different physical parameterizations used in models

eocene biostratigraphy of south carolina and its relationship to gulf coastal plain zonations and global changes of coastal onlap an assimilation of mega invertebrate assemblages in south carolina with gulf coast biozones allows for the subdivision of the middle and late eocene into four regional zonations that can be compared with proposed global sequences controlled by eustatic changes of sea level the middle eocene can be divided in ascending stratigraphic order into the cubitostrea perplicata zone c lisbonensis zone and c sellaeformis zone the late eocene is represented by the crassatella alta chlamys cawcawensis zone these zones are separated by type 1 or type 2 unconformities that bracket global sequence boundaries unconformity types after vail and todd 1981 the following sequences are proposed for the middle and upper eocene te2 1 cubitostrea perplicata zone followed by a type 2 unconformity te2 2 c lisbonensis zone followed by a type 2 unconformity te2 3 c sellaeformis zone followed by a type 1 unconformity and te3 crassatella alta chlamys cawcawensis zone followed by a type 2 unconformity although not recognized in the downdip areas of south carolina the te3 sequence can be further subdivided into a te3 1 sequence and te3 2 sequence separated by a type 2 unconformity this regional break lies at the gosport sand lower moodys branch formation upper moodys branch formation contact in the gulf coastal plain and at the base of the tivola tonque in georgia

active intracontinental transpressional mountain building in the mongolian altai defining a new class of orogen abstract mountain ranges that are actively forming around the western and northern perimeter of the indo eurasia collisional deformational field such as the mongolian altai comprise a unique class of intracontinental intraplate transpressional orogen with structural and basinal elements that are distinct from contractional and extensional orogens late cenozoic uplift and mountain building in the mongolian altai is dominated by regional scale dextral strike slip faults that link with thrust and oblique slip faults within a 300 km wide deforming belt sandwiched between the more rigid junggar basin block and hangay precambrian craton dominant orogenic elements in the mongolian altai include double restraining bends terminal restraining bends partial restraining bends single thrust ridges thrust ridges linked by strike slip faults and triangular block uplifts in areas of conjugate strike slip faults the overall pattern is similar to a regional strike slip duplex array however the significant amount of contractional and oblique slip displacement within the range and large number of historical oblique slip seismic events renders the term transpressional duplex more accurate intramontane and range flanking basins can be classified as ramp basins half ramp basins open sided thrust basins pull apart basins and strike slip basins neither a classic fold and thrust orogenic wedge geometry nor a bounding foredeep exists the manner in which upper crustal transpressional deformation is balanced in the lower crust is unknown however crustal thickening by lower crustal inflation and northward outflow of lower crustal material are consistent with existing geological and geodetic data and could account for late cenozoic regional epeirogenic uplift in the russian altai and sayan regions

contribution of the east west thermal heating contrast to the south asian monsoon and consequences for its variability the focus of this paper is to assess the relative role of the north south and east west contrasts in atmospheric heating for the maintenance of the south asian summer monsoon climatology the juxtaposition of the eurasian land mass and the indian ocean is responsible for the north south contrast while the greater diabatic heating above the western pacific compared to the one over the african and the tropical south atlantic ocean region introduces the east west gradient with a series of idealized atmospheric general circulation model experiments it is found that both contrasts contribute to the maintenance of the south asian monsoon climatology but their impact varies at regional scales the surface atmospheric cyclone and precipitation over northern india are mainly due to the north south contrast on the other hand when the indian ocean sea surface temperatures are close to their climatological mean values the low level cyclone and consequent rainfall activity in the bay of bengal and southern india result from the east west gradient the physical mechanism relays on the southern part of the upper level south asian monsoon high being forced by the east west diabatic heating contrast via sverdrup balance the east west heating difference controls also the strength of the tropical easterly jet finally the contribution of the el nino southern oscillation to the interannual variability of the indian monsoon is interpreted as the result of a longitudinal shift of one of the centers of diabatic heating contributing to the east west contrast

paleotopography and erosion rates in the central hangay dome mongolia landscape evolution since the mid miocene abstract standing over 2 km above the surrounding topography and flanked by orogen scale strike slip faults the hangay dome in central mongolia is characterized by long wavelength high topography basaltic eruptions spanning 30 million years and an abundance of flat topped summit plateaus however despite decades of research the origin and timing of the intraplate hangay dome uplift continues to be debated using landsat imagery gis and cosmogenic beryllium 10 we employ geomorphic investigations of 1 paleotopography preserved beneath basalt flows of known age 2 erosion rates at various temporal scales and 3 the relative contribution of glacial activity to total erosion to provide insight into the nature of landscape evolution in the egiin davaa region of the central hangay dome since the middle miocene reconstruction of paleo valleys cut into paleozoic basement rock that exhibit a degree of local relief 600 m similar to the modern landscape sluggish mean erosion rates

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

evidence for fluid and melt generation in response to an asthenospheric upwelling beneath the hangai dome mongolia abstract the hangai dome mongolia is an unusual high elevation intra continental plateau characterized by dispersed low volume intraplate volcanism its subsurface structure and its origin remains unexplained due in part to a lack of high resolution geophysical data magnetotelluric data along a 610 km profile crossing the hangai dome were used to generate electrical resistivity models of the crust and upper mantle the crust is found to be unexpectedly heterogeneous the upper crust is highly resistive but contains several features interpreted as ancient fluid pathways and fault zones including the south hangai fault system and ophiolite belt that is revealed to be a major crustal boundary south of the hangai dome a clear transition in crustal properties is observed which reflects the rheological differences across accreted terranes the lower crust contains discrete zones of low resistivity material that indicate the presence of fluids and a weakened lower crust the upper mantle contains a large low resistivity zone that is consistent with the presence of partial melt within an asthenospheric upwelling believed to be driving intraplate volcanism and supporting uplift

recognition and hydrologic significance of passive margin updip sequences an example from eocene coastal plain deposits u s a abstract sequence stratigraphic interpretations are extended to a passive margin updip setting using sedimentological observations from cores and well to well correlations in eocene coastal plain strata of south carolina in the succession studied formation contacts tend to follow sequence boundaries even as lithologies vary within individual sequences sequence boundaries at the base of the congaree formation and near the top of the tinker formation formed during relative sea level fall associated with second order global cycles these boundaries can be recognized clearly in both downdip and updip areas of the passive margin three other sequence boundaries which occur at the base and top of the warley hill formation and within the tinker formation are interpreted as formed during relative sea level fall associated with third order global cycles hydrostratigraphic units in the strata studied conform to depositional patterns that were controlled by changes in sea level and sediment influx sand of the gordon aquifer comprises a thick aggradational succession deposited predominantly in the nearshore shelf environment as accommodation increased during relative rise in sea level because of high rates of sedimentation in the proximal setting aggradational stacking of nearshore sands may be common to other updip marine strata in accommodation dominated regimes the overlying gordon confining unit consists of marine shelf clay and carbonate sediment deposited in response to maximum transgression during subsequent relative sea level fall accumulation of shoreface deposits produced a progradational succession that is represented by the lower part of the upper three runs aquifer unlike formation contacts boundaries between the clastic aquifers and confining units do not follow the third order sequence boundaries because of lithologic variations within the sequences an increasing degree of breaching through the gordon confining unit which results in downward contaminant migration into the gordon aquifer occurs in the updip direction because of nearly continuous sand deposition near the base of the interval studied contaminants migrate locally through the crouch branch confining unit because of erosional breaches formed by scour during sea level lowstand in this example and in other strata deposited in an updip passive margin setting the extent to which confining units are breached at sequence boundaries decreases in the downdip direction resulting in better protection of the adjacent aquifer

maintenance of summer monsoon circulations a planetary scale perspective abstract the monsoon circulation which is generally considered to be driven by the landmass ocean thermal contrast like a gigantic land sea breeze circulation exhibits a phase reversal in its vertical structure a monsoon high aloft over a continental thermal low is juxtaposed with a midoceanic trough underlaid by an oceanic anticyclone this classic monsoon circulation model is well matched by the monsoon circulation depicted with the observational data prior to the first global atmospheric research program garp global experiment fgge however synthesizing findings of the global circulation portrayed with the post fgge data it was found that some basic features of major monsoon circulations in asia north america south america and australia differ from those of the classic monsoon circulation model therefore a revision of the classic monsoon theory is suggested with four different wave regimes selected to fit the horizontal dimensions of these monsoon circulations basic features common to

physical processes associated with the tropical atlantic sst gradient during the anomalous evolution in the southeastern ocean abstract this work is focused on the evolution of the dominant air sea coupled mode in the equatorial and southeastern tropical atlantic and the associated physical processes it is shown that in june august jja the evolution of the dominant mode is mainly dynamically driven and displays a coherent warming or cooling pattern extending from the angola coast toward the equator in the gulf of guinea for anomalies peaking in jja the warming cooling is initiated near the angola coast in march may it is suggested that sst anomalies along the coast and near the equator are physically connected the air sea interaction along the coast may be a major factor in triggering the development of sst anomalies near the equator which is intensified by local positive feedbacks that may include bjerknes and ekman processes in return the warming or cooling near the equator weaken the sst anomalies along the coast by changing the direction of anomalous wind slow westward rossby wave propagation may also play a role

uplift age and rates of the gurvan bogd system gobi altay by apatite fission track analysis abstract the dating of the uplift onset of the mongolian mountain ranges the northernmost relief associated with the india eurasia convergence is a fundamental issue to better understand the mechanisms of propagation of the cenozoic transpressive deformation in central asia using apatite fission tracks we determined the timing and strain rates of the tectonics affecting the gurvan bogd system in the gobi altay since the middle mesozoic to the late cenozoic the region was firstly affected by a lower middle jurassic tectonic phase characterized by a vertical crustal movement larger than 2 km then followed a protracted period without major crustal vertical movements until the last uplift phase the peneplanation of the jurassic relief produced an erosional surface that has undergone negligible denudation or sedimentation for more than 100 ma this same surface corresponds to the present summit plateaux of the massifs standing about 2000 m above the surrounding region which corresponds to the vertical movement produced by the ongoing uplift modelling of fission track data from the massifs of ih bogd and baga bogd shows that this uplift phase probably started at 5 3 ma the gobi altay mountain range appears therefore as one of the youngest mountain ranges in central asia which is consistent with the idea of a northward propagation of the transpressional deformation from the himalayan front to the siberian craton the cenozoic uplift rate of the massifs is estimated to be between 0 25 and 1 mm yr which is slightly higher than the upper pleistocene vertical slip rates of the bordering faults this suggests that thrust faults observed within the massifs would increase the uplift rate inside the massifs compared to the uplift rate determined at their boundaries

subtropical to temperate facies from a transition zone mixed carbonate siliciclastic system palaeogene north carolina usa palaeogene passive margin sediments on the us mid atlantic coastal plain provide valuable insight into facies interaction and distribution on mixed carbonate siliciclastic shelves this study utilizes well cuttings outcrop core and seismic data to document temporal and spatial variations in admixed bryozoan rich skeletal carbonates and sandy siliciclastic units that were deposited on a humid passive margin located in the vicinity of a major marine transition zone this zone was situated between north flowing warm waters of the ancestral gulf stream carbonate dominated settings and south flowing cold waters of the ancestral labrador current siliciclastic dominated settings some degree of mixing of carbonates and siliciclastics occurs in all facies however siliciclastic prone sediments predominate in nearshore settings while carbonate prone sediments are more common in more open marine settings of the inner shelf break and deep shelf a distinctive dual break shelf depositional profile originated following a major late cretaceous to palaeocene transgression that drowned the earlier shallow platform this profile was characterized by prominent mid shelf break dividing the shallow shelf from the deep shelf and a major continental shelf slope break incomplete filling of available accommodation space during successive buildup of the shallow shelf preserved the topographic break on this passive margin storm wave base also contributed to the preservation of the dual break shelf geometry by beveling shallow shelf sediments and transporting them onto and seaward of the mid shelf break sediment fines in deep shelf facies were produced in place transported downdip from the shallow shelf by storm ebb currents and boundary currents and reworked from adjacent areas of the deep shelf by strike parallel boundary currents regional climate and boundary currents controlled whether carbonate or siliciclastic material was deposited on the shelf with warmer waters and more humid climates favouring carbonate deposition and cooler more arid conditions favouring glaucony and siliciclastic dominated deposition continuous wave and current sweeping of the shallow shelf favoured deposition of mud lean facies across much of the shallow shelf skeletal components in much of the carbonate rich strata formed in warm nutrient rich subtropical waters as indicated by widespread occurrences of larger benthic foraminifera and molluscan assemblages these indicators of warm water deposition within the bryozoan mollusk rich carbonate assemblage on this shelf provide an example of a warm water bryomol assemblage such facies generally are associated with cooler water depositional settings

low frequency variability of the indian monsoon enso relationship and the tropical atlantic the weakening of the 1980s and 1990s abstract the indian monsoon el nino southern oscillation enso relationship according to which a drier than normal monsoon season precedes peak el nino conditions weakened significantly during the last two decades of the twentieth century in this work an ensemble of integrations of an atmospheric general circulation model agcm coupled to an ocean model in the indian basin and forced with observed sea surface temperatures ssts elsewhere is used to investigate the causes of such a weakening the observed interdecadal variability of the enso monsoon relationship during the period 1950 99 is realistically simulated by the model and a dominant portion of the variability is associated with changes in the tropical atlantic ssts in boreal summer in correspondence to enso the tropical atlantic ssts display negative anomalies south of the equator in the last quarter of the twentieth century and weakly positive anomalies in the previous period those anomalies in turn produce heating anomalies which excit

cenozoic normal faulting and regional doming in the southern hangay region central mongolia implications for the origin of the baikal rift province abstract the hangay dome in central mongolia is a mountainous region covering more than 200 000 km2 with numerous flat topped peaks over 3000 m that preserve a late cretaceous paleogene erosion surface doming began in the middle oligocene producing more than 2000 m of regional topographic uplift the range represents an important kinematic link between the baikal rift province to the north and altai transpressional ranges to the south and west structural field investigations of major faults visible on satellite imagery indicate that the southern hangay dome region is dominated by late cenozoic normal faults that bound small half graben most faults are ne striking and faults at the highest elevations are the most recently active most graben appear to be isolated systems that constitute small sediment sinks perched on the flanks and crests of the dome the first order feature is the dome itself and most sediment eroded off of the dome is deposited in the mongolian valley of lakes or is carried northwards by the selenga river and its extensive tributaries the basement of the dome is a precambrian craton although the shape and dimensions of the craton are poorly constrained to the north and east late cenozoic uplift of the southern dome region appears to be confined to the area underlain by cratonic basement whereas the altai region to the south and west is underlain by mechanically weaker palaeozoic arc and accretionary belts with respect to the regional northeast directed shmax the hangay craton appears to have acted as a rigid passive indentor focusing late cenozoic transpressional deformation around its west and southern margins models invoking a late cenozoic plume as the driving force for doming and widespread alkaline volcanism on the dome are not strongly supported by geochemical and isotopic data on neogene recent volcanics and the spatial correlation between areas that are domed and older cratonic crust appears too coincidental to be ignored convective removal of an overthickened lithospheric root leading to adiabatically decompressed asthenosphere could explain regional doming and volcanism however major crustal thickening last occurred in the permian in the southern hangay region and the time lag between thickening and postulated root removal and plateau uplift 200 myr appears too long an alternative model is explored based on speculated lithospheric mantle flow patterns driven by india s continued northeastward indentation it is suggested that lithospheric mantle flow diversion around the overthickened hangay craton crustal keel could cause lithospheric thinning beneath the craton and passive asthenospheric upwarp leading to regional topographic uplift and decompression melting alkali volcanism in general the angular relationship between precambrian craton boundaries and the prevailing northeasterly shmax appears to control the kinematics of late cenozoic deformation throughout the hangay altai sayan and baikal regions

crustal structure and gravity anomalies beneath the rif northern morocco implications for the current tectonics of the alboran region we analyse bouguer anomaly data and previously published moho depths estimated from receiver functions in order to determine the amount of isostatic compensation or uncompensation of the rif topography in northern morocco we use moho depth variations extracted from receiver function analyses to predict synthetic bouguer anomalies that are then compared to observed bouguer anomaly we find that moho depth variations due to isostatic compensation of topographic and or intracrustal loads do not match moho depth estimates obtained from receiver function analyses the isostatic misfit map evidences excess crustal root as large as 10 km in the western part of the study area whereas a missing crustal root of 5 km appears east of 4 3 e this excess root missing topography correlates with the presence of a dense mantle lid the noticeable southwestward drift of the western rif area and with a current surface uplift we propose that a delaminated mantle lid progressively detaching westward or southwestward from the overlying crust is responsible for viscous flow of the ductile lower crust beneath the rif area this gives rise to isostatic uplift and westward drift due to viscous coupling at the upper lower crust boundary at the same time the presence of this dense sinking mantle lid causes a negative dynamic topography which explains why the observed topography is too low compared to the crustal thickness

influence of the atlantic zonal mode on monsoon depressions in the bay of bengal during boreal summer the influence of the atlantic zonal mode azm or the atlantic nia o on monsoon depressions in the bay of bengal during the boreal summer june august is studied our analysis shows that there is a statistically significant difference in the number of monsoon depressions in the bay of bengal between the warm and cold phases of the azm more fewer monsoon depressions form during the cold warm phase of azm it also shows that there are differences in spatial pattern of trajectories of monsoon depressions during the cold phase of azm the tracks are relatively long and seem to cluster along the axis of core monsoon region compared to the warm phase of azm the analysis indicates an increase a reduction in low level cyclonic vorticity and midtropospheric humidity but a reduction an increase in vertical wind shear due to anomalous circulation pattern all of these changes are favorable for the enhancement suppression of monsoon depressions during the cold warm phase of the azm our analysis further shows a teleconnection pathway by which the azm can influence the remote indian ocean this could have implications for enhancing monsoon prediction skill especially during non el nia o southern oscillation years key points influence of the azm on monsoon depressions during boreal summer cold warm azm increases decreases number of monsoon depressions the difference in large scale atmospheric conditions in the bob during azm

deep structure and mechanical behavior of the lithosphere in the hangai hovsgol region mongolia new constraints from gravity modeling we investigate the deep structure and mechanical behavior of the lithosphere beneath the hangai ho vsgo l region central mongolia asia in order to explain the origin and support of large scale doming in this deforming area we propose a gravity and topography based model which accounts for constraints provided by other independent results from xenolith and tomography studies deviations of the measured gravity from the theoretical airy compensation model are examined a long wavelength low gravity anomaly is spatially correlated with low pressure and shear velocity anomalies in the mantle and with the extent of cenozoic volcanic outcrops we interpret it as a deep seated low density asthenosphere and model its effect on the bouguer gravity signal using a 600 km wide light asthenospheric body density reduction 310 kg m 33 located between 100 and 200 km north and south of the hangai ho vsgo l dome short wavelength highs and lows in the bouguer gravity field are clearly correlated with fault activity they seem to reflect opposite senses of flexure of a rigid lithosphere across two major active faults the sayan and bogd transpressional systems and are modeled by moho deflections of 10 and 5 km respectively finally a shortwavelength 200 km high amplitude 350 mgal gravity residual remains beneath the highest part of the mountain bulge namely the hangai dome based on previously published xenolith analyses we interpret it as an anomalous low density body which may represent underplated cumulates or mafic granulites at the uppermost mantle we conclude that upper mantle dynamics necessarily play an important role in the origin and evolution of the hangai ho vsgo l dome but without requiring significant thinning of the lithosphere fl 2002 elsevier science b v all rights reserved

west african monsoon dynamics and eastern equatorial atlantic and pacific sst anomalies 1970 88 abstract the laboratoire de meteorologie dynamique atmospheric gcm is used to investigate relationships between west african monsoon dynamics and sst anomalies in the eastern equatorial atlantic and pacific for the period 1970 88 positive sst anomalies in the eastern equatorial pacific mainly associated with a larger east west divergent circulation over the tropical atlantic are found to coincide with negative rainfall anomalies over west africa this is the case for the composite enso warm episodes of 1972 1976 1982 and 1983 by contrast positive sst anomalies in the eastern equatorial atlantic are accompanied by a southward shift of the intertropical convergence zone along with negative rainfall anomalies in the sahel and positive rainfall anomalies in the guinean region this was the case in 1987 the enso warm event during this year had apparently no significant impact on west african monsoon dynamics a zonal atmospheric coupling associated with differences of sst anomalies between the eastern

sedimentology and depositional environments of middle eocene terrigenous carbonate strata southeastern atlantic coastal plain usa abstract basin margin sediments of middle eocene age in the savannah river site area consist of five terrigenous carbonate lithofacies quartz sand calcareous quartz sand sandy carbonate muddy carbonate and a transitional lithofacies that ranges from sandy muddy carbonate to calcareous mud the middle eocene sediment package which includes calcareous parts of the upper congaree warley hill and santee formations dips southeast at 4 7 m km and thickens from 2 m at its updip edge to 95 m downdip the presence of glauconite and a diverse faunal assemblage in all lithofacies suggests deposition in clear well oxygenated open marine waters of normal salinity on the inner to middle shelf with periods of marginal marine nearshore and deltaic influence coarse grained terrigenous sand and calcareous sand deposited in higher energy nearshore environments occur near the updip limit fine grained terrigenous mud calcareous mud and sandy and muddy carbonate are located downdip and accumulated in quieter water conditions on the inner and middle shelf the transition from terrigenous to carbonate sediment occurs near the updip limit in a narrow zone less than 5 km wide three depositional sequences which contain transgressive and highstand system tracts are recognized within the middle eocene calcareous interval one is assigned to the upper congaree formation ta 3 5 3 6 cycles the main control on areal distribution hill formation ta3 4 cycle and one to the santee formation ta 3 5 3 6 cycles the main control on areal distribution of facies was depositional environment which was controlled primarily by sea level eustasy and the amount rate and locus of terrigenous influx in updip areas however sediment distribution and thickness were also influenced by middle eocene growth faulting diagenetic pathways vary with facies type but generally include 1 marine phreatic boring of skeletal fragments by algae and fungi grain micritization and radially fibrous cementation and 2 freshwater phreatic inversion of high mg calcite to low mg calcite dissolution of aragonitic allochems formation of moldic porosity precipitation of syntaxial calcite overgrowths on echinoderms formation of calcite spar and isopachous calcite cement neomorphism of micrite to microspar and pseudospar precipitation of opal ct lepispheres replacement of mollusk shells by chalcedony and precipitation of zeolites within secondary moldic pores quartz rich facies have high interparticle porosity and excellent permeability mud rich facies have low to moderate porosity and permeability owing to the isolation of moldic and vug pores

deep structure of the baikal rift zone revealed by joint inversion of gravity and seismology 1 the question of plate boundary forces and deep versus shallow asthenospheric uplift has long been debated in intracontinental rift areas particularly in the baikal rift zone asia which is colder than other continental rifts as previous gravity and teleseismic studies support the dominance of opposing mechanisms in the baikal rift we reconsidered both data sets and jointly inverted them this more effective approach brings insight into location of the perturbing bodies related to the extension in this region our new joint inversion method allows for inverting the velocity density relationship with independent model parametrization we obtain velocity and density models that consistently show 1 crustal heterogeneities that coincide with the main tectonic features at the surface 2 a faster and denser cratonic mantle nw of lake baikal that we relate to the thermal contrast between old and depleted archean siberian platform and paleozoic orogenic belt sayan baikal belt 3 three dimensional topographic variations of the crust mantle boundary with well located upwarpings and 4 the lithosphere asthenosphere boundary uplift up to 70 km depth with a nw dip our resulting velocity and density models support the idea of a combined influence of lithospheric extension and inherited lithospheric heterogeneities for the origin of the baikal rift zone index terms 1234 geodesy and gravity regional and global gravity anomalies and earth structure 7218 seismology lithosphere and upper mantle 8122 citation tiberi c m diament j deverchere c petit mariani v mikhailov s tikhotsky and u achauer deep structure of the baikal rift zone revealed by joint inversion of gravity and seismology