reverse engineering mother nature shale sedimentology from an experimental perspective abstract experimental study of the sedimentology of shales can take a variety of forms at its simplest one can experiment with suspensions in a glass jar and try to understand their settling behavior or one can manipulate mud in a tank or bucket to gain insights into its rheology this approach was championed over a century ago by sorby and the insights gained can be quite profound more recently tank and settling tube experiments of animal sediment interactions compaction behavior and sediment unmixing via re suspension have proven to be highly informative in spite of their simplicity flumes can be used to obtain quantitative information about depositional and erosional parameters and to generate fundamental bedforms in flume experiments however it is of critical importance that the flume be designed in a way that flocculated materials move under shear stress conditions that would be reasonable in natural environments although much flume work on muds has been conducted by hydraulic engineers the transfer of that knowledge to sedimentology is hampered by the fact that engineers and sedimentologists are interested in different though not mutually exclusive products from such experiments engineers and hydrologists are commonly concerned with quantifying fluid flow properties whereas sedimentogists are particularly interested in the sedimentary products that result from a variety of flow conditions recent sedimentologically oriented flume studies have shown that muds can form deposits at flow velocities and shear stresses that would suffice to transport and deposit medium grained sand mud suspensions are prone to flocculation and the resulting floccules travel in bedload and form ripples that accrete into beds the latter finding suggests that many laminated shales were deposited from currents rather than by settling from slow moving or still water there are many other sedimentary features in shales that can potentially be reproduced in flume studies and in the future serve to provide a quantitative basis for shale sedimentology

resolving mass flux at high spatial and temporal resolution using grace intersatellite measurements 1 the grace mission is designed to monitor mass flux on the earth s surface at one month and high spatial resolution through the estimation of monthly gravity fields although this approach has been largely successful information at submonthly time scales can be lost or even aliased through the estimation of static monthly parameters through an analysis of the grace data residuals we show that the fundamental temporal and spatial resolution of the grace data is 10 days and 400 km we present an approach similar in concept to altimetric methods that recovers submonthly mass flux at a high spatial resolution using 4 4 blocks at 10 day intervals we estimate the mass of surplus or deficit water over a 52 60 grid centered on the amazon basin for july 2003 we demonstrate that the recovered signals are coherent and correlate well with the expected hydrological signal

late cenozoic bending of the bolivian andes new paleomagnetic and kinematic constraints 1 new paleomagnetic measurements of essentially undeformed late cenozoic volcanic rocks in the bolivian andes south america constrain rigid body rotations about vertical axes during the last 13 myr on both limbs of the bolivian orocline in the eastern cordillera thermal and alternating field demagnetization was carried out on samples from 52 sites in three major volcanic complexes 1 13 2 ma los frailes ignimbritic volcanics outcropping at 19 5 s 2 9 5 ma morococala ignimbritic volcanics outcropping at 18 s and 3 13 5 ma shoshonitic to acidic lavas and intrusives outcropping at 17 5 s well defined magnetic components were isolated which are interpreted to represent the earth s magnetic field at the time of volcanic activity the mean magnetic vector for site groupings suggests regional tectonic rotations about vertical axes with respect to stable south america of 10 8 clockwise for the 13 2 ma los frailes volcanic complex 8 9 clockwise for only the miocene 13 5 ma los frailes volcanics and 1 18 anticlockwise for the combined 13 5 ma morococala and eucalyptus volcanic complexes these data are consistent with observed shortening gradients on the eastern margin of the bolivian andes in the sub andean zone suggesting rotation and shortening are synchronous a joint inversion for both tectonic rotation and the amount of shortening assuming a linear variation in the amount of rotation along the length of the southern limb of the bolivian orocline shows that rotation of the eastern cordillera in the last 10 15 myr relative to stable south america varies from zero at the oroclinal hinge at 18 s to a maximum of 13 5 clockwise at 22 s decreasing to zero south of 23 s with an average rotation in the range 5 to 10 clockwise concomitant with this shortening in the sub andean zone decreases from a maximum of 86 km at the oroclinal hinge to 47 km at 22 s and then 33 km at 23 s the lack of evidence for large scale internal faulting in the eastern cordillera since 9 ma suggests either bending of the eastern cordillera was accommodated by more distributed small scale faulting or that relative rotation here mainly occurred prior to 9 ma the small average rotation of the eastern cordillera on the southern limb of the orocline is consistent with only very small rotation 10 of the forearc region in northern chile during the last 20 myr rotation of the northern limb is less well constrained but it is also likely to be small 5 and anticlockwise

steric and mass induced sea level variations in the mediterranean sea revisited this work was elaborated during the stay of the first author at the national central university of taiwan thanks to a grant from the generalitat valenciana spain jean paul boy is currently visiting nasa goddard space flight center with a marie curie international outgoing fellowship piof ga 2008 221753 this work was partly funded by two spanish projects from micin esp2006 11357 and aya2009 07981 and one from generalitat valenciana acomp2009 031

climatically controlled marker layers in santa barbara basin sediments and fine scale core to core correlation varved sediments with annual layering can provide a detailed history of environmental conditions of marginal ocean basins and of lakes to reconstruct this history requires fine scale correlation and correct age assignment in the santa barbara basin a combination of x radiography water content profiles and microfossil stratigraphy yields correlations of the desired resolution x radiography permits identification of individual layers 1 2 mm thick that differ in porosity or pore water content and hence x ray absorption microfossils and sedimentological parameters provide the clues to the presence for el nino years e g in a d 1984 1959 and 1942 varves allowing the tie in to absolute years within this century el nino layers once identified are readily recognized on the radiographs and within the porosity profiles counting of laminae in x radiographs and core to core correlation via water content then allow establishing age scales for other cores a prominent shell layer in the first half of the 19th century is dated at a d 1838 this event macoma i is of supraregional significance

methods for inferring regional surface mass anomalies from gravity recovery and climate experiment grace measurements of time variable gravity 1 the gravity recovery and climate experiment grace will deliver monthly averages of the spherical harmonic coefficients describing the earth s gravity field from which we expect to infer time variable changes in mass averaged over arbitrary regions having length scales of a few hundred kilometers and larger to accuracies of better than 1 cm of equivalent water thickness these data will be useful for examining changes in the distribution of water in the ocean in snow and ice on polar ice sheets and in continental water and snow storage we describe methods of extracting regional mass anomalies from grace gravity coefficients spatial averaging kernels were created to isolate the gravity signal of individual regions while simultaneously minimizing the effects of grace observational errors and contamination from surrounding glacial hydrological and oceanic gravity signals we then estimated the probable accuracy of averaging kernels for regions of arbitrary shape and size

physical models of magmatic intrusion during thrusting to investigate how magma rises through the brittle upper crust in a context of compressional tectonics we have performed experiments on scaled physical models powdered silica having a cohesion of 300 pa and an angle of internal friction of 38 was used to represent brittle crust a vegetable oil with a newtonian viscosity of 10 2 paae sa t 50c was used to represent magma a moving piston shortened the models in a box while oil was injected steadily at the base on cooling to room temperature the oil solidified the resulting intrusions were thin sills dykes and laccoliths their shapes and emplacement modes depended on the ratio r between rates of shortening and injection from shapes and orientations of intrusions we infer that hydraulic fracturing was one mechanism of emplacement unconsolidated intrusions strongly influenced thrust formation on the basis of our experiments we suggest that magmas in orogenic belts can rise along thrust faults

k ar dating of miocene magmatism and related epithermal mineralization of the northeastern altiplano of bolivia this paper describes the age and geology of 13 centers of miocene magmatism with related epithermal precious and base metal mineralization on the eastern side of the northern altiplano of bolivia part of the central andean polymetallic belt twenty eight new k ar ages are reported together with a compilation of 12 from the literature the data show four magmatic episodes the two middle miocene episodes 17 15 ma 13 5 12 ma are characterized by clusters of small volcanic and hypabyssal porphyries which host the most important epithermal mineralization in contrast large volcanic centers formed during the two late miocene episodes 10 8 ma 6 5 ma no significance is attached to the secondary age groups the middle and late miocene magmatic mineralization episodes correlate with those of the southern part of the tin belt of the eastern cordillera and formed during the main arc broadening of the central andes

grace measurements of mass variability in the earth system monthly gravity field estimates made by the twin gravity recovery and climate experiment grace satellites have a geoid height accuracy of 2 to 3 millimeters at a spatial resolution as small as 400 kilometers the annual cycle in the geoid variations up to 10 millimeters in some regions peaked predominantly in the spring and fall seasons geoid variations observed over south america that can be largely attributed to surface water and groundwater changes show a clear separation between the large amazon watershed and the smaller watersheds to the north such observations will help hydrologists to connect processes at traditional length scales tens of kilometers or less to those at regional and global scales

steric sea level variations inferred from combined topex poseidon altimetry and grace gravimetry in this study we propose to estimate the steric sea level variations over a 2 year period april 2002 through december 2003 by combining global mean sea level gmsl based on topex poseidon t p altimetry with time variable geoid averaged over the oceans as observed by the grace gravity recovery and climate experiment satellite in effect altimetry derived gmsl changes results from two contributions steric thermal plus salinity effects due to sea water density change and ocean mass change due to water exchange with atmosphere and continents on the other hand grace data over the oceans provide the ocean mass change component only the paper first discusses the corrections to apply to the grace data then the steric contribution to the gmsl is estimated using grace and t p data comparison with available thermal expansion based on in situ hydrographic data is performed

the hyper enrichment of v and zn in black shales of the late devonian early mississippian bakken formation usa abstract black shales of the late devonian to early mississippian bakken formation are characterized by high concentrations of organic carbon and the hyper enrichment 500 to 1000s of mg kg of v and zn deposition of black shales resulted from shallow seafloor depths that promoted rapid development of euxinic conditions vanadium hyper enrichments which are unknown in modern environments are likely the result of very high levels of dissolved h2s 10 mm in bottom waters or sediments because modern hyper enrichments of zn are documented only in framvaren fjord norway it is likely that the biogeochemical trigger responsible for zn hyper enrichment in framvaren fjord was also present in the bakken basin with framvaren fjord as an analogue we propose a causal link between the activity of phototrophic sulfide oxidizing bacteria related to the development of photic zone euxinia and the hyper enrichment of zn in black shales of the bakken formation

antarctic circumpolar current transport variability during 2003 05 from grace abstract gravity recovery and climate experiment grace gravity data spanning january 2003 november 2005 are used as proxies for ocean bottom pressure bp averaged over 1 month spherical gaussian caps 500 km in radius and along paths bracketing the antarctic circumpolar current s various fronts the grace bp signals are compared with those derived from the estimating the circulation and climate of the ocean ecco ocean modeling assimilation system and to a non boussinesq version of the regional ocean model system roms the discrepancy found between grace and the models is 1 7 cmh2o 1 cmh2o 1 hpa slightly lower than the 1 9 cmh2o estimated by the authors independently from propagation of grace errors the northern signals are weak and uncorrelated among basins the southern signals are strong with a common seasonality the seasonal cycle grace data observed in the pacific and indian ocean sectors of the acc are consistent with annual and semiannual amplitudes of 3 6 and 0 6 cmh2o 1 1 and 0

new insights on intraplate volcanism in french polynesia from wavelet analysis of grace champ and sea surface data in this paper we discuss the origin of superswell volcanism on the basis of representation and analysis of recent gravity and magnetic satellite data with wavelets in spherical geometry we computed a refined gravity field in the south central pacific based on the grace satellite ggm02s global gravity field and the kms02 altimetric grid and a magnetic anomaly field based on champ data the magnetic anomalies are marked by the magnetic lineation of the seafloor spreading and by a strong anomaly in the tuamotu region which we interpret as evidence for crustal thickening we interpret our gravity field through a continuous wavelet analysis that allows to get a first idea of the internal density distribution we also compute the continuous wavelet analysis of the bathymetric contribution to discriminate between deep and superficial sources according to the gravity signature of the different chains as revealed by our analysis various processes are at the origin of the volcanism in french polynesia as evidence we show a large scale anomaly over the society islands that we interpret as the gravity signature of a deeply anchored mantle plume the gravity signature of the cook austral chain indicates a complex origin which may involve deep processes finally we discuss the particular location of the marquesas chain as suggesting that the origin of the volcanism may interfere with secondary convection rolls or may be controlled by lithospheric weakness due to the regional stress field or else related to the presence of the nearby tuamotu plateau

steric sea level variations during 1957 1994 importance of salinity 1 spatially averaged 50 s 65 n temperature and salinity changes in the 0 3000 m layer during the 1957 1994 period resulted in a sea level rise at a mean rate of about 0 55 mm per year about 10 of this rate is due to a decrease of the volume mean salinity the magnitude of total steric sea level tssl changes and the ratio of thermosteric and halosteric anomalies to tssl anomaly are nonuniform geographically salinity effects are critically important to the tssl changes in some regions of the ocean for example the thermosteric anomaly is nearly compensated by the halosteric anomaly in the subpolar north atlantic this fact will cause erroneous heat content estimates based on altimetric observations from space if a climatological salinity is assumed based on the present historical archive of salinity data a decrease in global mean salinity has occurred this increase of fresh water would cause sea level rise at a rate of 1 3 0 5 mm yr if the added water comes from sources other than floating sea ice

traces in the dark sedimentary processes and facies gradients in the upper shale member of the upper devonian lower mississippian bakken formation williston basin north dakota u s a abstract black organic rich rocks of the upper shale member of the upper devonian lower mississippian bakken formation a world class petroleum source rock in the williston basin of the united states and canada contain a diverse suite of mudstone lithofacies that were deposited in distinct facies belts the succession consists of three discrete facies associations fas these comprise 1 siliceous mudstones 2 quartz and carbonate bearing laminated mudstones and 3 macrofossil debris bearing massive mudstones these fas were deposited in three facies belts that reflect proximal to distal relationships in this mudstone system the macrofossil debris bearing massive mudstones fa 3 occur in the proximal facies belt and contain erosion surfaces some with overlying conodont and phosphate lithoclast lag deposits mudstones with abundant millimeter scale siltstone laminae showing irregular lateral thickness changes and shell debris in the medial facies belt quartz and carbonate bearing laminated mudstones dominate exhibiting sub millimeter thick siltstone layers with variable lateral thicknesses and localized mudstone ripples in the distal siliceous mudstone facies belt radiolarites radiolarian bearing mudstones and quartz and carbonate bearing laminated mudstones dominate overall total organic carbon toc contents range between about 3 and 10 wt with a general proximal to distal decrease in toc content abundant evidence of bioturbation exists in all fas and the lithological and toc variations are paralleled by changes in burrowing style and trace fossil abundance while two horizontal traces and two types of fecal strings are recognized in the proximal facies belt only a single horizontal trace fossil and one type of fecal string characterize mudstones in the distal facies belt radiolarites intercalated into the most distal mudstones are devoid of traces and fecal strings bedload transport processes likely caused by storm induced turbidity currents were active across all facies belts suspended sediment settling from near the ocean surface however most likely played a role in the deposition of some of the mudstones and was probably responsible for deposition of the radiolarites the distribution pattern of high toc sediments in proximal and lower toc deposits in some distal facies is interpreted as a function of higher accumulation rates during radiolarian depositional events leading to a decrease in suspension derived organic carbon in radiolarite laminae the presence of burrows in all fas and nearly all facies in the upper bakken shale member indicates that dysoxic conditions prevailed during its deposition this study shows that in intracratonic high toc mudstone successions such as the upper bakken shale member bed load processes most likely dominated sedimentation and conditions promoted a thriving infaunal benthic community as such deposition of the upper bakken shale member through dynamic processes in an overall dysoxic environment represents an alternative to conventional anoxic depositional models for world class source rocks

time variability of the earth s gravity field hydrological and oceanic effects and their possible detection using grace the grace satellite mission scheduled for launch in 2001 is designed to map out the earth s gravity field to high accuracy every 2 4 weeks over a nominal lifetime of 5 years changes in the gravity field are caused by the redistribution of mass within the earth and on or above its surface grace will thus be able to constrain processes that involve mass redistribution in this paper we use output from hydrological oceanographic and atmospheric models to estimate the variability in the gravity field i e in the geoid due to those sources we develop a method for constructing surface mass estimates from the grace gravity coefficients we show the results of simulations where we use synthetic grace gravity data constructed by combining estimated geophysical signals and simulated grace measurement errors to attempt to recover hydrological and oceanographic signals we show that grace may be able to recover changes in continental water storage and in seafloor pressure at scales of a few hundred kilometers and larger and at timescales of a few weeks and longer with accuracies approaching 2 mm in water thickness over land and 0 1 mbar or better in seafloor pressure

time variable gravity from grace first results eleven monthly grace gravity field solutions are now available for analyses we show those fields can be used to recover monthly changes in water storage both on land and in the ocean to accuracies of 1 5 cm of water thickness when smoothed over 1000 km the amplitude of the annually varying signal can be determined to 1 0 cm results are 30 better for a 1500 km smoothing radius and 40 worse for a 750 km radius we estimate the annually varying component of water storage for three large drainage basins the mississippi the amazon and a region draining into the bay of bengal to accuracies of 1 0 1 5 cm

microbioirrigation of marine sediments in dysoxic environments implications for early sediment fabric formation and diagenetic processes it is manifest in the study of dysoxic sediments from the geological record that infaunal burrowing is considered so severely limited by the lack of dissolved oxygen as to be nonexistent although the effects of megafauna and macrofauna on sedimentary and geochemical processes are well known the effects of meiofauna are largely ignored here we document abundant meiofauna in the recent severely dysoxic laminated sediments from the santa barbara basin california margin and also microcavities and microtunnels in laminated deglacial sediments from palmer deep west antarctic peninsula that we interpret to be open relict nematode burrows santa barbara basin box core subcores were sieved to quantify metazoan abundance and others were embedded with resin for examination of meiofaunal life positions using confocal microscopy metazoan densities in the surface centimeters of sediment range from 80 7 to 117 9 cm 3 and nematode populations together with their abundant burrows remain quite high to at least 3 cm scanning electron microscope analysis of fractured surfaces in palmer deep sediments revealed that the rigid diatom ooze framework aids the preservation of 50 m diameter open nematode burrows these structures were observed to at least 40 m below the seafloor surface this is the first description of a nematode produced open burrow network preserved in the geological record optical microscopy of resin embedded thin sections revealed widespread sediment redistribution without significant lamina disruption the implications of abundant nematode burrows in surface sediments and their preservation in the geological record are wide ranging for both modern and ancient dysoxic marine environments including for determining early sediment fabric production geochemical processes and diagenetic reactions in the oxic and suboxic zones

geophysical interpretation of observed geocenter variations geocenter variations are caused by mass redistribution within the earth system especially the atmosphere oceans and continental water using surface pressure fields and soil moisture and snow depth fields of the ncep ncar climate data assimilation system i cdas i 1 we estimate contributions from variations in atmospheric surface pressure and continental water storage to the earth s geocenter center of mass variation in addition sea surface anomalies determined by the topex poseidon altimeter are used to investigate geocenter variations resulting from ocean mass redistribution these sea surface height data were corrected using a simplified steric model a comparison with observed geocenter variations derived from lageos 1 and 2 satellite laser ranging data indicates that the atmosphere oceans and continental hydrological cycle all provide significant contributions at different frequencies geocenter variations estimated in this paper are in reasonably good agreement with results given by dong et al 1997 for atmospheric and ocean contributions but not for the estimates of continental hydrological contributions

time variations of land water storage from an inversion of 2 years of grace geoids by delivering monthly maps of the gravity field the grace project allows the determination of tiny time variations of the earth s gravity and particularly the effects of fluid mass redistributions at the surface of the earth however grace data represent vertically integrated gravity measurements thus are the sum of all mass redistributions inside the earth s system atmosphere oceans and continental water storage plus solid earth in this paper we apply a generalized least squares inverse approach previously developed by 1 g ramillien a cazenave o brunau global time variations of hydrological signals from grace satellite gravimetry geophys j int 158 2004 813 826 to estimate from the monthly grace geoids continental water storage variations and their associated uncertainties over a 2 year time span april 2002 to may 2004 tests demonstrating the robustness of the method are presented including the separation between liquid water reservoirs surface waters soil moisture groundwaters and snow pack contributions individual monthly solutions of total land water storage from grace with a spatial resolution of 660 km are presented for the 2 year time span we also derive the seasonal cycle map we further estimate water volume changes over eight large river basins in the tropics and compare with model predictions finally we attempt to estimate an average value of the evapotranspiration over each river basin using the water balance equation which links temporal change in water volume to precipitation evapotranspiration and runoff amplitudes of the grace derived evapotranspiration are regionally consistent to the predictions of global hydrological models

grace estimates of sea surface height anomalies in the gulf of carpentaria australia abstract the gulf of carpentaria in northern australia has a weather driven annual periodic amplitude in sea surface height of 0 4 m such a signal generates a mass variation that is readily detected by the grace mission we used this naturally occurring phenomenon over a region of 2 6 10 5 km 2 to evaluate the accuracy of the grace estimates of temporal mass variation comparison of the groupe de recherche de geodesie spatiale 10 day grace solutions and observations from a nearby tide gauge show a correlation of 0 93 indicating that the grgs grace solutions capture well the regional signal on the other hand the mog2d g barotropic model accounts for only 50 of the non gravitational annual signal suggesting either deficiencies in the model or that some other non barotropic process is occurring

experimental deposition of carbonate mud from moving suspensions importance of flocculation and implications for modern and ancient carbonate mud deposition abstract flume experiments with fine grained carbonate particles 62 5 m show that they form floccules that travel in bedload form current ripples and deposit laminated sediments in order to compare our flume experiments to work on sand transport we ran flume experiments with medium sand and observed that the velocities at which sand grains started to move and form ripples were in the same range as those where floccules move and form ripples these ripples are in essence identical to those formed by clay mineral floccules or sand grains under similar conditions in light of previous experiments with clay minerals these results indicate that of the key controls on mud deposition flocculation and suspended sediment concentration are more important than particle mineralogy or water chemistry and are about as important as bottom shear stress for deposition suspensions of carbonate mud show the same pattern of flocculation ripple formation and bed accretion as observed previously in experiments with clay mineral suspensions the resulting carbonate mud deposits show internal low angle 2 5 degrees laminae and in plan view a pattern of ripple foresets that is identical to rib and furrow structure in sandstones just as previously assumed for terrigenous muds there has been a long standing notion that accumulation of abundant carbonate mud reflects quiescent conditions of offshore and deeper water environments these experiments demonstrate unequivocally that carbonate muds can also accumulate in energetic settings in the sedimentary record of carbonate rocks interbedded grainstones and lime mudstones may thus not necessarily reflect shifts in depositional energy or water depth but alternatively may imply a shift in supplied sediment type the observations we report suggest that published interpretations of ancient lime muds and derived paleoceanographic conditions may need to be reevaluated

cenozoic behind arc volcanism in the bolivian andes south america implications for mantle melt generation and lithospheric structure we develop a model of arc and behind arc volcanism as well as constraining the evolution of the lithospheric mantle structure beneath the bolivian andes during the last 25 ma using new geochronological and geochemical data on behind arc mafic volcanic rocks together with a regional isotopic study of geothermal helium emissions and a comparison with seismic tomographic images of the same region helium isotopes measured in natural gas emissions in geothermal and mineral water springs suggest recent mantle melting in a wide zone extending at c 20 s from a few tens of kilometres west of the volcanic arc to over 300 km behind the arc where the subducted slab is at depths increasing from c 100 to c 250 km during the neogene there has been behind arc mafic felsic magmatism right across the high andes between 17 and 22 s in the altiplano and western margin of the eastern cordillera modelling of plio pleistocene basalts and basaltic andesites c 15 depleted mid ocean ridge basalt morb source at depths between c 75 km and c 110 km for mafic volcanic rocks that crop out c 65 km and c 90 km for those that crop out 100 km behind the arc ree inversions for oligo miocene shoshonites and basalts c 25 21 ma suggest that they originated at significantly shallower depths c 45 km to c 100 km from a slightly enriched morb source eruption of shoshonitic lavas also occurred in the altiplano between 13 and 11 ma and widespread behind arc intermediate felsic volcanism has been more or less continuous since the early miocene all this suggests that since c 25 ma there has been a thin c 25 ma by the opening up of a mantle wedge and inflow of hot asthenosphere as a consequence of the steepening of the subducted slab and detachment of hydrated and weakened mantle lithosphere and possibly mafic lower crust

cenozoic uplift of the central andes in northern chile and bolivia reconciling paleoaltimetry with the geological evolution the cenozoic geological evolution of the central andes along two transects between 17 5 s and 21 s is compared with paleo topography determined from published paleo altimetry studies surface and rock uplift are quantified using simple 2 d models of crustal shortening and thickening together with estimates of sedimentation erosion and magmatic addition prior to 25 ma during a phase of amagmatic flat slab subduction thick skinned crustal shortening and thickening nominal age of initiation 40 ma was focused in the eastern and western cordilleras separated by a broad basin up to 300 km wide and close to sea level which today comprises the high altiplano surface topography at this time in the altiplano and the western margin of the eastern cordillera appears to be 1 km lower than anticipated from crustal thickening which may be due to the pull down effect of the subducted slab coupled to the overlying lithosphere by a cold mantle wedge oligocene steepening of the subducted slab is indicat

detection of a large scale mass redistribution in the terrestrial system since 1998 earth9s dynamic oblateness j2 had been undergoing a decrease according to space geodetic observations over the past 25 years until around 1998 when it switched quite suddenly to an increasing trend that has continued to the present the secular decrease in j2 resulted primarily from the postglacial rebound in the mantle the present increase whose geophysical cause s are uncertain thus signifies a large change in global mass distribution with a j2 effect that considerably overshadows that of mantle rebound

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

large scale ocean circulation from the grace ggm01 geoid 1 the grace gravity model 01 ggm01 computed from 111 days of grace k band ranging kbr data is differenced from a global mean sea surface mss computed from a decade of satellite altimetry to determine a mean dynamic ocean topography dot as a test of the ggm01 gravity model large scale zonal and meridional surface geostrophic currents are computed from the topography and are compared with those derived from a mean hydrographic surface reduction in residual rms between the two by 30 60 and increased correlation indicates that the ggm01 geoid represents a dramatic improvement over older geoid models which were developed from multiple satellite tracking data altimetry and surface gravity measurements for the first time all major current systems are clearly observed in the dot from space based measurements

estimation of steric sea level variations from combined grace and jason 1 data abstract we estimate the mean steric sea level variations over the 60 s 60 n oceanic domain for the recent period from august 2002 to april 2006 by combining sea level data from jason 1 altimetry with time variable gravity data from grace the observed global mean sea level change from satellite altimetry results in total from steric plus ocean mass change as grace measurements averaged over the ocean represents the ocean mass change component only the difference between grace and altimetry observations provides an estimate of the mean steric sea level two different sets of grace geoid solutions the grgs eigen gl04 and the gfz eigen grace04s products have been used each grace data set ranges over approximately 3 yr or more august 2002 april 2006 for the grgs geoids and february 2003 february 2006 for the gfz geoids we first focus on the seasonal variations the two grace data sets agree very well in terms of mean annual mass variation both in amplitude approximately 7 3 mm equivalent sea level and phase maximum on october 14 for both time spans jason 1 sea level minus grace ocean mass has an annual amplitude of approximately 5 8 mm with a maximum on march 11 the latter signal compares well with the steric annual sea level estimated from the world ocean 2004 climatology and the ishii et al m ishii m kimoto k sakamoto and s i iwasaki steric sea level changes estimated from historical ocean subsurface temperature and salinity analyses journal of oceanography 62 2 2006 155 170 ocean temperature data we also examine the interannual fluctuations of the jason 1 minus grace sea level the two resulting steric sea level time series based on the two grace data sets agree well the inferred steric sea level curve exhibits an increasing trend during the last 3 5 yr august 2002 april 2006 of the same order of magnitude as the 1993 2003 steric sea level trend computed with in situ hydrographic data however over the last 3 5 yr we note a strong discrepancy between altimetry minus grace and in situ based steric sea level trend the latter exhibiting a negative slope the cause for such a discrepancy is yet unknown but may be related to inadequate sampling of in situ ocean temperature measurements

antarctic regional ice loss rates from grace abstract using recent improved time variable gravity solutions from the gravity recovery and climate experiment grace we estimate rates of antarctic ice mass change for the period january 2003 through september 2006 combined improvements in data and filtering techniques allow observation of ice loss in the northern antarctic peninsula ap and along the coast of the west and central amundsen sea embayment ase in west antarctica there is also evidence of ice loss along the coast near the stancomb wills sta and jutulstraumen jut glaciers in queen maud land apparent rates are adjusted for influences of limited spatial resolution filtering and estimated postglacial rebound pgr to obtain ice loss rates for the northern ap coastal ase and sta jut of 28 8 7 9 81 17 and 16 7 9 7 km3 yr respectively this is the first estimate for the northern ap from satellite gravity data the ase estimate 81 17 km3 yr is consistent with a previous value 77 14 km3 yr using an earlier grace data release these results indicate significant improvement in grace data quality increased spatial resolution and applicability of grace data to a wider class of problems than previously possible

traces in the dark sedimentary processes and facies gradients in the upper devonian lower mississippian upper shale member of the bakken formation williston basin north dakota u s a discussion i would like to comment on a recent paper by egenhoff and fishman 2013 that discusses observations made on cores of the bakken shale and presents a methodology to examine and describe these cores in this contribution i would like to discuss some of their observations and conclusions related to perceived bioturbation features the authors very eloquently came up with an attractive title for their paper traces in the dark and it is this darkness that i would like to shine some light on some of the burrows that are shown like the burrow tubes with contrasting fill in their figure 4 are rather clear and there is no disagreement others like those in their figure 5 may just as well be cross sections of pellets and probably a thin section parallel to bedding would be required to sort out their actual origin e g macquaker et al 2010 the aspects that i found the most troubling are shown in their figure 6 a and b where a laminated black shale is shown on which the authors drew white lines to highlight what they interpret to be burrows that penetrate this laminated shale and there is the rub without these white lines i would never have been able to see these burrows and i have seen plenty of subtle bioturbation in shales before e g schieber 2003 having worked on devonian black shales for two decades i actually have hundreds of thin sections like this one in my collection the silt laminae in sections from my collection especially if only a few grains thick show gaps and discontinuities in the ten to hundred micron range quite commonly but i personally would not interpret these gaps in terms

estimates of the regional distribution of sea level rise over the 1950 2000 period abstract topex poseidon satellite altimeter data are used to estimate global empirical orthogonal functions that are then combined with historical tide gauge data to estimate monthly distributions of large scale sea level variability and change over the period 1950 2000 the reconstruction is an attempt to narrow the current broad range of sea level rise estimates to identify any pattern of regional sea level rise and to determine any variation in the rate of sea level rise over the 51 yr period the computed rate of global averaged sea level rise from the reconstructed monthly time series is 1 8 0 3 mm yr 1 with the decadal variability in the computed global mean sea level it is not possible to detect a significant increase in the rate of sea level rise over the period 1950 2000 a regional pattern of sea level rise is identified the maximum sea level rise is in the eastern off equatorial pacific and there is a minimum along the equator in the western pacific and in the eastern indian ocean a g

algal blooms and marine snow mechanisms that enhance preservation of organic carbon in ancient fine grained sediments abstract combined petrographic and geochemical methods are used to investigate the microfabrics present in thin sections prepared from representative organic carbon rich mudstones collected from three successions the kimmeridge clay formation the jet rock member of the whitby mudstone formation and the pebble shale and hue shale this study was initiated to determine how organic carbon rich materials were being delivered to the sediment water interface and what happened to them after deposition prior to deep burial analyses of the fabrics present shows that they exhibit many common attributes in particular they are all 1 highly heterogeneous on the scale of a thin section 2 organized into thin beds the organomineralic aggregates present in these mudstones are interpreted to be ancient examples of marine snow this marine snow likely formed in the water column particularly during phytoplankton blooms and was then transported rapidly to the seafloor the existence of the thin beds with homogenized tops and an in situ infauna indicates that between blooms there was sufficient oxygen and time for a mixed layer to develop as a result of sediment colonization by diminutive organisms using either aerobic or dysaerobic metabolic pathways these textures suggest that the constituents of these mudstones were delivered neither as a continuous rain of sediment nor were the bottom waters persistently anoxic in addition the presence of thin lags and sharp based beds suggests that the seafloor was being episodically reworked during deposition these fabrics indicate that conditions in the water columns and at the seafloors while these rocks were being deposited were very dynamic and episodic fluxes of high concentrations of organic carbon to the seafloor during phytoplankton blooms likely enhanced preservation of organic carbon

magmatism in the huarina belt bolivia and its geotectonic implications abstract the huarina belt is a tectono stratigraphic unit extending along the western side of the eastern cordillera and southern altiplano it includes the well known bolivian tin belt both geophysical and isotopic evidence suggest that the huarina belt is located between three cratonic blocks in a major lithospheric weakness zone that has probably been inherited from the proterozoic most of the phanerozoic backarc magmatism in the bolivian andes occurred along this belt local ordovician basalts and andesites and clasts of devonian granitoids occurring in late devonian early carboniferous sedimentary units are testimonies of a scarce palaeozoic igneous activity during the mesozoic rift related magmatism resulted in peraluminous to metaluminous high k calcalkaline triassic granitoids as well as discrete cretaceous centers of alkaline and carbonatitic rocks in the cenozoic huge high k generally peraluminous ignimbrite sheets along with numerous volcanic and intrusive centers were generated along the belt shoshonitic alkaline and ultrapotassic rocks have been locally described on the basis of both geochemical and geophysical evidence a general evolution model is proposed for the huarina belt during paleozoic and mesozoic times the predominant extensional regime of the continental crust led to lithospheric thinning basin generation and production of within plate magmas during the cenozoic prevailing compressional conditions led to a gradual thickening of the lithosphere inducing delamination of its denser and less viscous root the mantle generated magmas interplayed widely with crustal melts giving rise to the dominantly peraluminous magmas

late cenozoic uplift of the eastern cordillera bolivian andes abstract this paper analyses late cenozoic uplift in the bolivian andes using the morphology of well preserved regional paleosurfaces in the eastern cordillera that define three axially draining braided river catchments that formed between 12 and 9 ma rock uplift since the formation of the paleodrainage systems which has been quantified using four different methods is 1705 695 m with a mean erosion of 230 90 m as a consequence of entrenchment of the drainage systems the lack of faulting or tilting in the regions immediately farther west strongly suggest that rock uplift of the paleodrainage systems also extends to the western margin of the eastern cordillera balanced structural cross sections require crustal deformation at depth beneath the eastern cordillera in order to accommodate underthrusting of the brazilian shield beneath the thin skinned fold and thrust belt on the eastern margin of the bolivian andes in this case the observed uplift of the eastern cordillera is easily explained by sliding up a ramp in the major decollement dipping in the range 4 16 w as a consequence of the observed 60 110 km of shortening farther east in the subandean zone contemporaneous uplift of the western margin of the eastern cordillera is easily explained in terms of crustal thickening as a result of ductile squeezing in the lower crust accommodating at depth the subandean shortening it remains unclear how this uplift relates to that of the regions farther west in the altiplano and volcanic arc except that uplift in the eastern cordillera coincides with a phase of intense shortening in the northern altiplano commencing at 9 5 ma and continuing to 2 7 ma and possibly younger