architecture of an unconformity based tidal sandstone unit in the ametlla formation spanish pyrenees abstract this study is concerned with the sedimentary architecture of a shallow marine sandstone unit in the lower eocene ametlla formation ager basin spanish pyrenees the sandstone unit was formed in a tide dominated setting and is continuously exposed in a 10 5 km long mainly strike parallel cutcrop its base is a prominent unconformity sequence boundary and it consists of two sub units separated by a tidal ravinement surface sub unit 1 lower sub unit formed in an estuarine setting that was created by flooding of an incised valley system outside the incised valleys an oyster bed is present as a lateral equivalent to the estuarine deposits the sequence bounding unconformity was generated during relative sea level lowstand whereas the overlying estuarine and bioclastic deposits of sub unit 1 formed in the early stages of the transgressive systems tract in sub unit 2 above the tidal ravinement surface estuary mouth bar and tide dominated delta deposits are the main facies associations interfingering with offshore to inner shelf sediments westwards these deposits formed in later stages of the transgressive systems tract the large scale model of the sandstone unit served as a framework within which the internal arrangement of architectural elements ae was recorded twelve ae were recognized they mostly have a lensoid geometry and their lateral transitions are abrupt or occur by interfingering over distances of 50 250 m the ae distribution shows that the tide influenced setting was characterized by a high degree of spatial and temporal variability with regard to sedimentary processes this together with the prominent thickness variation of the unit studied makes correlation between vertical profiles difficult even over distances of only a few hundred metres stratal surfaces such as the sequence bounding unconformity the tidal ravinement surface and the flooding surfaces represent the only reliable correlation markers in this kind of environment

one kilometre thick ultramylonite sierra de quilmes sierras pampeanas nw argentina abstract we describe a 1 km thick ultramylonite forming the high strain base of the 3 5 km thick el pichao shear zone in the sierra de quilmes this shear zone thrusted granulite facies migmatites onto amphibolite facies rocks during the 470 ma famatinian orogeny strain grades upwards from ultramylonites to weakly sheared migmatites across the 3 5 km zone and the mylonitic rocks define a geochemical field narrower than the protolith suggesting they underwent mixing and homogenization through shearing ultramylonites this thick are uncommon the width of a shear zone in the absence of significant compositional rheological contrasts controlling strain localization is controlled by the balance between shear heat generation and diffusion under typical crustal conditions a strain rate of 10 12 s 1 is required to form a 1 km thick ultramylonite and this is achieved when large movement velocities are imposed across the shear zone we postulate that the el pichao shear zone and its thick ultramylonite accommodated a significant fraction of convergence velocities driving the orogeny and that the wide mylonitic shear zones characteristic of the cambrian ordovician deformation of the sierras pampeanas result from the convergent movement being taken up by only a few active major shear zones

bayhead deltas and shorelines insights from modern and ancient examples abstract bayhead deltas are important components of the rock record as well as modern estuaries hosting important hydrocarbon reservoirs and many coastal cities ports and large expanses of wetlands despite their significance few studies have summarized their occurrence and sedimentary characteristics in this paper we review the stratigraphic sedimentary and geomorphic characteristics of 68 modern and ancient bayhead deltas bayhead deltas are found in incised valleys structural basins fjords interdistributary bays of larger open ocean deltas and other backbarrier environments except for within fjords they generally prograde into shallower and more brackish waters than their open ocean equivalents as a result 80 of modern 68 of quaternary and 67 of ancient bayhead deltas have clinoform thicknesses of 10 m or less with 73 of modern bayhead deltas having clinoform thicknesses of 5 m or less additionally 89 of modern 81 of quaternary and 77 of ancient bayhead deltas examined are fluvial dominated we distinguish true bayhead deltas from their genetically similar bayhead shorelines which are not constructional features but sites of enhanced marsh or estuarine sedimentation near river mouths with inadequate rates of sediment delivery to form distributary channels and prograde into the estuary or lagoon we also distinguish confined bayhead deltas found in incised valleys structural basins and fjords from unconfined bayhead deltas found as incipient lobes of larger delta complexes and other back barrier lagoons the architecture of confined bayhead deltas is largely influenced by the limited accommodation brought about by the walls of the flooded valleys in which they are located as such confined bayhead delta ontogeny is controlled by many autogenic interactions within these valley walls both confined and unconfined bayhead deltas are sensitive to sea level rise climate controlled changes in sediment flux and tectonics their relatively small size connection with the terrestrial system and protected nature make them the ideal depositional system to record earth history including sea level and climate changes

spatiotemporal characterization of land subsidence and uplift in phoenix using insar time series and wavelet transforms the effects of land subsidence pose a significant hazard to the environment and infrastructure in the arid alluvial basins of phoenix arizona improving our understanding of the source and mechanisms of subsidence is important for planning and risk management here we employ multitemporal interferometric analysis of large synthetic aperture radar data sets acquired by ers and envisat satellites to investigate ground deformation the ers data sets from 1992 to 1996 and envisat 2003 2010 are used to generate line of sight los time series and velocities in both the ascending and descending tracks the general deformation pattern is consistent among data sets and is characterized by three zones of subsidence and a broad zone of uplift the multitrack envisat los time series of surface deformation are inverted to obtain spatiotemporal maps of the vertical and horizontal deformation fields we use observation wells to provide an in situ independent data set of hydraulic head levels then we analyze vertical interferometric synthetic aperture radar and hydraulic head level time series using continuous wavelet transform to separate periodic signal components and the long term trend the isolated signal components are used to estimate the elastic storage coefficient the inelastic skeletal storage coefficient and compaction time constants together these parameters describe the storage response of an aquifer system to changes in hydraulic head and surface elevation understanding aquifer parameters is useful for the ongoing management of groundwater resources

geologic evolution of the cuu long and nam con son basins offshore southern vietnam south china sea rifting and regional subsidence characterize the cuu long and nam con son basins offshore southern vietnam initial rifting began in the eocene early oligocene followed by the uplift and rotation of the crustal blocks in the late oligocene the erosion of the uplifted blocks marked the transition from rifting to regional subsidence in the cuu long basin a second phase of rifting began in the nam con son basin lasting until the late miocene parts of the nam con son basin experienced inversion in the middle to late miocene the synrift and postrift units in the cuu long basin consist of nonmarine deposits and paralic to shallow marine sediments respectively the synrift deposits in the nam con son basin can be divided into the early synrift unit corresponding to the initial rifting phase and the late synrift unit deposited during the second rifting phase the early synrift and late synrift units consist of nonmarine sediments and nonmarine to shallow marine sediments respectively the postrift unit is composed of shelf and deeper marine deposits the data compiled from the published reports suggest that the cuu long basin is oil prone with the oil reservoired mainly in fractured basement highs whereas the nam con son basin is generally gas prone with the gas trapped in miocene sands and late miocene carbonates these distinct trends may be attributed to differences in timing of trap formation and the disruption of trap integrity caused by prolonged rifting and inversion in the nam con son basin gwang h lee is associate professor at kunsan national university korea his research interests include application of seismic reflection to basin research and sequence stratigraphy he received his b s and m s degrees in oceanography from seoul national university korea in 1981 and 1983 respectively and a ph d in geological geophysical oceanography from texas a m university in 1990 from 1991 to 1994 he worked for shell offshore inc in new orleans keumsuk lee received a b s degree in mathematics 1994 and an m s degree in geological oceanography 1999 from kunsan national university kunsan korea he is currently attending florida atlantic university boca raton florida his main research interest is application of geophysical methods to various geological and environmental problems joel s watkins is the earl f cook professor department of geology and geophysics texas am co chief scientist on dsdp leg 66 middle america trench and project director manager and vice president with gulf oil 1977 1985 he is the author or co author of more than 130 scientific publications and senior editor of aapg memoirs 29 34 and 53 his interests are structure and stratigraphy of small ocean basins and seismic reservoir characterization

reply to comment by s h buttner on one kilometre thick ultramylonite sierra de quilmes sierras pampeanas nw argentina

sedimentary facies of the tide dominated paleo changjiang yangtze estuary during the last transgression abstract a large estuary was formed by marine inundation of the paleo changjiang yangtze incised valley during the transgression after the last glacial maximum this paper presents the sedimentary facies and architecture of the estuary fill based on the analysis of three sediment cores cm97 js98 and hq98 obtained from the present changjiang delta plain estuary fill deposits showing an upward fining succession were grouped into five depositional facies tidal river distributary channel muddy intertidal to subtidal flats transgressive lag and estuary front based on sedimentary textures lithology and physical sedimentary structures sand mud couplets are common in these deposits indicating that tides played a significant role in producing these sedimentary structures and that the estuary type was tide dominated some of the successive sand mud couplets probably recorded neap spring cycles as well as semidiurnal tidal cycles the nature of the estuary was very different from other representative tide dominated estuaries in sediment facies its distribution and sediment source for estuarine fill unlike the other estuaries that receive sediments mainly from the sea the paleo changjiang estuarine fill deposits were supplied largely from the river this difference would also have a great influence on the sedimentological and morphological component in the estuary the sediment distribution of the estuary showed fining seaward and estuary mouth sand bodies fed by marine source sand were absent the architecture model of tide dominated estuaries should be divided into two types by the degree of fluvial sediment supply the paleo changjiang estuary shows a good example for an estuary of large rivers

palaeo hydrogeological control on groundwater as levels in red river delta vietnam to study the geological control on groundwater as concentrations in red river delta depth specific groundwater sampling and geophysical logging in 11 monitoring wells was conducted along a 45 km transect across the southern and central part of the delta and the literature on the red river delta s quaternary geological development was reviewed the water samples n 30 were analyzed for as major ions fe 2 h 2 s nh 4 ch 4 18 and 8d and the geophysical log suite included natural gamma ray formation and fluid electrical conductivity the sw part of the transect intersects deposits of grey estuarine clays and deltaic sands in a 15 20 km wide and 50 60m deep holocene incised valley the ne part of the transect consists of 60 120 m of pleistocene yellowish alluvial deposits underneath 10 30m of estuarine clay overlain by a 10 20m veneer of holocene sediments the distribution of 18 o values range 12 2 to 6 3 o and hydraulic head in the sample wells indicate that the estuarine clay units divide the flow system into an upper holocene aquifer and a lower pleistocene aquifer the groundwater samples were all anoxic and contained fe 2 0 03 2 0mm mn 0 7 320 m so 4 2 1 m 0 75mm h 2 s 0 1 7 0 m nh 4 0 03 4 4 mm and ch 4 0 08 14 5 mm generally higher concentrations of nh 4 and ch 4 and low concentrations of so 4 were found in the sw part of the transect dominated by holocene deposits while the opposite was the case for the ne part of the transect the distribution of the groundwater as concentration 0 013 11 7 m median 0 12 m 9 g l is related to the distribution of nh 4 ch 4 and so 4 low concentrations of as 0 32 m were found in the pleistocene aquifer while the highest as concentrations were found in the holocene aquifer phre eqc 2 speciation calculations indicated that fe 2 and h 2 s concentrations are controlled by equilibrium for disordered mackinawite and precipitation of siderite an elevated groundwater salinity cl range 0 19 65 1 mm was observed in both aquifers and dominated in the deep aquifer a negative correlation between aqueous as and an estimate of reduced so 4 was observed indicating that fe sulphide precipitation poses a secondary control on the groundwater as concentration

an improved set of a x parameters for fe mg ca garnets and refinements of the orthopyroxene garnet thermometer and the orthopyroxene garnet plagioclase quartz barometer

seaward pinching out and internal stratigraphy of the gironde incised valley on the shelf bay of biscay abstract an incised paleovalley offshore the estuary mouth of the gironde river southwest france was evidenced recently comptes rendus de l academie des sciences de paris 326 1998 701 nevertheless its seaward extension to the shelf break was still unknown new high resolution geophysical data were acquired on the continental shelf in order to follow the incision until the shelf break after processing the seismic lines the shape of the valley was identified and the valley fill in terms of sequence stratigraphy was interpreted the valley fill contains a single sequence corresponding to a fifth order cycle 20 kyr the three systems tracks described onshore by allen and posamentier journal of sedimentary petrology 63 1993 378 sepm society for sedimentary geology special publication tulsa 1994 225 are present offshore the lowstand is poorly developed and is only present in the proximal part of the incised valley the transgressive systems tract tst constitutes the bulk of the valley fill it is composed of landward prograding estuarine clinoforms in the distal part of the valley early tst phase 1 and of landward migrating tidal inlet fill deposits in the proximal part of the valley late tst phase 2 the thin early highstand systems tracts hst strata downlap seaward onto the maximum flooding surface and caps the tst as expected in this wave and tide dominated environment the tidal and wave ravinement surfaces which bound the tst are particularly well developed the valley incision tapers 50 km offshore of the estuary mouth the depth of the basal sequence boundary gradually decreases seaward and is locally truncated by the wave ravinement surface around 70 m below the mean sea level these observations indicate that during the lowstand times rivers do not always generate continuous cross shelf incised valleys they may adjust to a rapid drop in base level by modifying their channel morphology i e deep large channels located upstream change downstream to shallow anastomosed channels with a weaker erosional ability therefore the lowstand fluvial channels will be poorly developed and will eventually died out in the proximal part of the shelf because they are unable to keep pace with a phase of rapid sea level drop similar observations have already been reported for the english channel paleoriver geological society special publication london 1996 203 these de geologie marine universite de bordeaux 1 1997 265

evolution of the coastal depositional systems of the changjiang yangtze river in response to late pleistocene holocene sea level changes abstract the paleo changjiang yangtze incised valley fills approximately 80 90 m thick provide an opportunity to document the evolution of coastal depositional systems with large sediment supply in response to late pleistocene holocene sea level fluctuations on time scales of 103 to 104 years the sedimentary facies of the incised valley fills record three main depositional systems fluvial tide dominated estuary and tide dominated delta radiocarbon ages for the incised valley fills suggest that these depositional systems developed before about 11 ka between 11 and 8 ka and after approximately 8 ka respectively by applying sequence stratigraphic concepts the evolution of the depositional systems can be divided into three systems tracts a lowstand systems tract lst a transgressive systems tract tst and a highstand systems tract hst sea level changes on a 104 year time scale controlled the basic architecture of the sequence of the incised valley fill on the other hand sea level changes on a millennial time scale affected the stacking pattern of the systems tracts in particular the continuous sea level rise with episodic rapid rises during the last deglaciation affected the stacking pattern of the tst which is characterized by a combination of aggradation and backstepping the aggradation of fluvial and estuarine systems was dominant and the shoreline migrated only gradually landward under the relatively slow rise in sea level and a very rapid sea level rise around 12 and 10 ka caused the system to migrate abruptly landward unlike the transgressive estuarine phase the stacking pattern of the regressive tide dominated delta hst which developed within the almost filled incised valley and on the surrounding interfluve zones was characterized by seaward progradation with clinoform architecture it was initiated with aggradational and progradational stacking about 8 ka during the last phase of decelerated sea level rise and was followed by a progradational phase after the highest sea level about 6 ka

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

tectono metamorphic evolution of a convergent back arc the famatinian orogen sierra de quilmes sierras pampeanas nw argentina

formation and evolution of strike slip faults rifts and basins during the india asia collision an experimental approach the processes which have governed the formation and evolution of large tertiary strike slip faults during the penetration of india into eastern asia are investigated by means of plane strain indentation experiments on layered plasticine models the steady state deformation of plasticine obeys a power creep flow law e c t n the stress exponent n is between 6 and 9 at 25 c uniaxial plane strain tests on cubic specimens show that the growth of faults in layered plasticine results from strain softening a process observed for strain rates ranging from 3 5 10 5 to 3 6 10 3 s 1 fault or shear zones form after only 7 10 bulk strain subsequent deformation is controlled by the geometry of the fault pattern rather than the physical properties of the plasticine a series of nine plane strain indentation experiments shows the influence of boundary conditions as well as that of the internal structure of the plasticine model on the faulting sequence the ubiquity of strain softening in experimental deformation of a variety of rocks as well as the widespread occurrence of shear zones in nature suggest that long term deformation of the continental lithosphere may also be primarily influenced by the geometry of large faults which rapidly develop with increasing strain the deformation and faulting sequence observed in the plasticine indentation experiments may thus be compared to collision induced strikeslip faulting in asia particularly to total offsets and rates of movements on the faults the experiments simulate the evolution of the western ends of the strike slip faults which have probably been analogous to trench fault fault triple junctions the experiments also illustrate mechanisms for the formation of extensional basins such as the south china sea north china basin and andaman sea near active continental margins the basins which appear to absorb terminal offsets along major strike slip faults near such margins may result from mismatch between the sharply angular shape of the deformed continental edge and the more regularly curved trench along which the smoothly flexed oceanic lithosphere subducts the existence of distinct phases of strike slip extrusion corroborates the idea that the discontinuities in time which typify intracontinental tectonics and orogenic cycles may often result from strain localization and the ensuing discontinuous non steady state deformation of the continental lithosphere

late pleistocene barrier island development reconstructed from genetic classification and timing of erosional surfaces paleo tokyo bay japan abstract formative processes of a retrogradational barrier island system and associated transgressive erosional surfaces are reconstructed from the upper pleistocene kioroshi formation developed in paleo tokyo bay japan the kioroshi formation provides high quality sedimentary records of a preserved barrier island system three volcanic ash beds intercalated in the formation provide a high resolution chronostratigraphic framework the barrier island system of the kioroshi formation developed in a glacio eustatically forced sea level cycle during oxygen isotope stages 6 to 5e in the early stage of the transgression paleo tokyo bay was non barred and was exposed to the pacific ocean affected by open ocean wave processes shoreface erosion in such a non barred environment developed a wave ravinement surface rs1 rs1 overlies incised valley fill deposits formed in the earliest stage of the transgression and is overlain by shoreface deposits that are further overlain by embayment deposits such as lagoonal and flood tidal delta deposits formed during succeeding barrier development during the later stage of the same transgression associated with the formation and landward migration of the barrier chain tidal currents in tidal inlet and flood tidal deltas became active and a tidal ravinement surface trs was formed trs is developed on the base of tidal inlet and flood tidal delta deposits furthermore shoreface erosion on the open ocean side of the barrier chain eroded underlying embayment deposits and formed a secondary wave ravinement surface rs2 a chronostratigraphic surface in embayment deposits defined by a volcanic ash bed intersects trs and is eroded by rs2 this relationship together with associated facies architecture indicates diachroneity of the formation of these marine erosional surfaces associated with the retrogradational barrier island system

uavsar observations of triggered slip on the imperial superstition hills and east elmore ranch faults associated with the 2010 m 7 2 el mayor cucapah earthquake the 4 april 2010 m 7 2 el mayor cucapah earthquake that occurred in baja california mexico and terminated near the u s mexican border caused slip on the imperial superstition hills and east elmore ranch faults the pattern of slip was observed using radar interferometry from nasa s uninhabited aerial vehicle synthetic aperture radar uavsar instrument collected on 20 21 october 2009 and 12 13 april 2010 right lateral slip of 36 9 and 14 2 mm occurred on the imperial and superstition hills faults respectively left lateral slip of 9 2 mm occurred on the east elmore ranch fault the widths of the zones of displacement increase northward suggesting successively more buried fault motion to the north the observations show a decreasing pattern of slip northward on a series of faults in the salton trough stepping between the el mayor cucapah rupture and san andreas fault most of the motion occurred at the time of the m 7 2 earthquake and the uavsar observations are consistent with field creepmeter gps and envisat observations an additional 28 1 mm of slip at the southern end of the imperial fault over a 1 km wide zone was observed over a 1 day span a week after the earthquake suggesting that the fault continued to slip at depth following the mainshock the total moment release on the three faults is 2 3 1023 1 2 1024 dyne cm equivalent to a moment magnitude release of 4 9 5 3 assuming shallow slip depths ranging from 1 to 5 km

dunlin group sequence stratigraphy in the northern north sea a model for cook sandstone deposition the dunlin group in the northern north sea consisting of the johansen amundsen burton cook and drake formations of late sinemurian toarcian age hosts important hydrocarbon reservoirs in the cook formation sandstones the johansen formation is associated with a relative fall of sea level and is interpreted to be a large sandstone delta confined within a broad incised valley at the base of the group during a later stage of relative sea level rise the finer grained amundsen and burton formations were deposited the overlying cook formation consists of four sandstone tongues each of which is characterized by a lower zone of sharp based upward coarsening thinly bedded shoreface sandstones and siltstones reflecting forced regression during falling relative sea level and an erosively based upper zone of thin tidal flat and thick deltaic estuarine sandstones reflecting lowstand incision as well as initial progradation and subsequent transgressive backfill of estuaries during relative sea level rise the drake formation shales were deposited during continued relative sea level rise several types of erosional surfaces are recognized within the studied succession 1 sequence boundaries occur at the base of the johansen formation and within the cook formation and represent the bottoms of incised valleys that truncate the underlying copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received may 4 1995 revised manuscript received march 27 1996 final acceptance september 12 1996 2department of geology paleontology university of zagreb 10000 zagreb croatia 3department of geology geophysics university of wyoming laramie wyoming 82071 this paper was part of the sequence stratigraphy research project at the university of bergen norway and is a product of studies on the architecture of lower jurassic shelf sandstones of the northern north sea the work was sponsored by statoil through a vista fellowship awarded to t marjanac and this support is gratefully acknowledged we are grateful to d mellere and l m falt for discussion and encouragement during the work we also thank else lien for drafting the sections and jane ellingsen for reprographs constructive criticism from d nummedal j webb and k t biddle on the final version of the manuscript is much appreciated

the displacement field of the landers earthquake mapped by radar interferometry geodetic data obtained by ground or space based techniques can be used to infer the distribution of slip on a fault that has ruptured in an earthquake although most geodetic techniques require a surveyed network to be in place before the earthquake1 3 satellite images when collected at regular intervals can capture co seismic displacements without advance knowledge of the earthquake s location synthetic aperture radar sar interferometry first introduced4 in 1974 for topographic mapping5 8 can also be used to detect changes in the ground surface by removing the signal from the topography9 10 here we use sar interferometry to capture the movements produced by the 1992 earthquake in landers california11 we construct an interferogram by combining topographic information with sar images obtained by the ers 1 satellite before and after the earthquake the observed changes in range from the ground surface to the satellite agree well with the slip measured in the field with the displacements measured by surveying and with the results of an elastic dislocation model as a geodetic tool the sar interferogram provides a denser spatial sampling 100 m per pixel than surveying methods1 3 and a better precision 3 cm than previous space imaging techniques12 13

comparative k ar and rb sr age determinations of retrograde processes on rocks from the ktb deep drilling project conventional k ar and rb sr age determinations were carried out on fine mineral fractions of the ktb rocks and of rocks from the surrounding area in order to get an idea of the timing of retrograde processes which the rocks had suffered in the late variscan and afterwards coarse grained mica minerals were used as reference minerals it can be demonstrated that conventional k ar dating on fine mineral fractions is a useful tool to date retrograde processes in crystalline rocks for methodical reasons the rb sr method is less suitable a complex age pattern was found which could be divided into different age groups representing different periods of either penetrative retrograde overprint or formation and reactivation of distinct cataclastic fault zones whereas the rocks of the ktb have undergone a penetrative retrograde overprint during the permo triassic without any visible deformation the jurassic brought a first reactivation of cataclastic fault zones in cretaceous time an overprint led to a pronounced second reactivation of cataclastic fault zones this latter process turned out to be the important one for the stacking and a repetition of the drilled profile in the ktb the data and interpretations obtained on the fine mineral fractions coincide excellently with fission track data on sphene from the drill site with sedimentological records concerning a larger regional scale and with hydrothermal alterations and ore forming events in mid europe

inverse modeling of interbed storage parameters using land subsidence observations antelope valley california 1 we use land subsidence observations from repeatedly surveyed benchmarks and interferometric synthetic aperture radar insar in antelope valley california to estimate spatially varying compaction time constants and inelastic specific skeletal storage coefficients s kv in a previously calibrated regional groundwater flow and subsidence model the observed subsidence patterns reflect both the spatial distribution of head declines and the spatially variable inelastic skeletal storage coefficient using the nonlinear parameter estimation program ucode we estimate compaction time constants between 3 8 and 285 years the s kv values are estimated by linear estimation and range from 0 to almost 0 09 we find that subsidence observations over long time periods are necessary to constrain estimates of the large compaction time constants in antelope valley the insar data used in this study cover only a three year period limiting their usefulness in constraining these time constants this problem will be alleviated as more sar data become available in the future or where time constants are small by incorporating the resulting parameter estimates in the previously calibrated regional model of groundwater flow and land subsidence we can significantly improve the agreement between simulated and observed land subsidence both in terms of magnitude and spatial extent the sum of weighted squared subsidence residuals a common measure of model fit was reduced by 73 with respect to the original model however the ability of the model to adequately reproduce the subsidence observed over only a few years is impaired by the fact that the simulated hydraulic heads over small time periods are often not representative of the actual aquifer hydraulic heads errors in the simulated hydraulic aquifer heads constitute the primary limitation of the approach presented here

stratigraphy and optically stimulated luminescence osl dating of a quaternary sequence along the dong nai river southern vietnam abstract the pre holocene cenozoic sequence outcrops in the terrestrial part of the eastern margin of the mekong basin however the stratigraphy of the sequence is still unclear its detailed stratigraphy and chronology were therefore studied along the dong nai river southern vietnam and the lithofacies and the relations among the formations were investigated from the outcrops the ages of the deposits were determined by using optically stimulated luminescence osl dating the ba mieu formation was deposited about 176 52 ka during marine isotope stage mis 7 6 the thu duc formation was deposited about 97 27 ka during mis 5 both the ba mieu and thu duc formations are composed of fluvial and tidally influenced coastal deposits the newly proposed nhon trach formation was originally an eolian blanket deposit but it has been partly reworked by fluvial processes the nhon trach formation was deposited about 10 9 4 7 ka in the last part of the pleistocene to the beginning of the holocene the osl ages for the ba mieu thu duc and nhon trach formations are younger than the ages previously assigned to these formations

tectonic controls on the stratigraphic development of the rifted taipei basin a late quaternary marine influenced inland half graben abstract we establish the three dimensional stratigraphic architecture of the taipei basin and its spatiotemporal palaeoenvironmental development during the past 50 kyr by analysing 36 borehole cores and 177 age dates we calculate the rates of basin subsidence from the borehole data at depths where radiocarbon age dates are available our results indicate that during the eustatic sea level falling period 35 20 ka low rates of sediment supply and or rapid basin subsidence controlled sedimentation leading to a change in the depositional environment from gravelly braided rivers through sandy braided rivers to meandering rivers with falling eustatic sea level during the early stage of eustatic sea level rise 20 10 2 ka balanced rates of sediment supply eustasy and basin subsidence maintained the meandering river environment rapid sea level rise led to the initial appearance of estuarine facies at 10 2 ka and widened the distribution of the estuarine environment after 8 5 ka however the coeval phases of rapid basin subsidence 10 6 10 2 ka and 9 8 5 ka promoted the first appearance and widening of the estuary respectively after 7 ka when the eustatic sea level and rate of basin subsidence remained relatively stable sufficient sediment supply gradually infilled the estuary the established stratigraphy improves our understanding of the factors controlling stratigraphic development in marine influenced inland half grabens specifically in the taipei basin with high rates of sediment supply accommodation space in the taipei basin was governed by eustatic fluctuations with modulations by basin subsidence and sediment supply since the last glacial period

on the loss of 40ar from muscovite during polymetamorphism abstract recent laser studies have documented 40ar concentration gradients in micas that correspond to age variations of tens to hundreds of millions of years a fundamental problem to interpretation of such variations is to evaluate whether they represent loss via lattice diffusion or alternatively loss during chemical reactions and deformation new data of this study and comparisons with previous work suggest that muscovite is far less prone to lose accumulated 40ar via lattice diffusion during overprinting events than has been inferred previously kyanite muscovite assemblages in proterozoic schist along the eastern flank of the green mountain massif central vermont appalachians formed during proterozoic metamorphism at ca 1 1 ga and were remetamorphosed in the greenschist facies during both taconian ca 465 ma and acadian ca 390 ma events the overprinting events resulted in deformation of earlier kyanite and muscovite growth of chemically and isotopically distinct rims on earlier muscovite and growth of neoblastic muscovite and chloritoid with each event at inferred minimum temperatures of ca 425 c laser spot analyses of the grenville muscovite range from 988 11 ma in the centers of porphyroclasts to 397 7 ma along rims ages younger than 750 ma occur only on the deformed edges of porphyroclasts and in highly deformed areas within crystals parts of early formed muscovite that escaped late deformation and chemical reaction seem remarkably retentive of accumulated 40ar laser spot analyses along the outer 100 m of an undeformed growth face yield ages close to the timing of proterozoic metamorphism and cooling the present study suggests episodic heating events are ineffective for producing measurable diffusive argon loss along the edges of large muscovite crystals ca 1 mm in diameter particularly in comparison with deformation and reaction mechanisms and are unlikely to result in complete 40 ar 39 ar age resetting of such crystals the results of this study further emphasize that the argon diffusivity in muscovite is lower than commonly considered in previous work

influence of low amplitude high frequency relative sea level changes in a wave dominated estuary miocene sao luis basin northern brazil abstract miocene deposits exceptionally well exposed along several coastal cliffs between the towns of alc ntara and guimaraes maranhao state northern brazil record the history of low amplitude high frequency sea level changes in a wave dominated incised valley estuarine setting these deposits are interpreted as estuarine in origin based on i depauparated ichnological assemblage and occurrence of gyrolithes both typical of highly stressed brackish water conditions ii dominance of sedimentary structures diagnostic of tidal processes e g alternating thicker thinner sand bundles marked by reactivation surfaces and or mud drapes and iii presence of widespread channel deposits this estuarine fill consists of three stratigraphic units units 1 3 1 unit 1 shoaling shoreline sh and tidal channel ch 2 unit 2 shoaling shoreline sh tidal channel ch facies associations lagoon lg and flood tidal delta washover ftd w facies associations and 3 unit 3 tidal channel ch estuarine bay eb and fluvial influenced channel fch facies associations the individual units internally show a dominantly prograding character a pattern also reflected throughout the succession by the overall upward stacking of units showing successively more restricted conditions these characteristics combined with the position in the uppermost portion of the valley fill succession led to suggest that the deposits exposed in the study area likely formed during the transition from rising to highstand stages of relative sea level mapping of regionally significant discontinuity surfaces led to the recognition of a sequence boundary i e discontinuity surface ds1 marked by erosion and subaerial exposure at the valley floor this surface separates the miocene succession from underlying cretaceous rocks and it is attributed to a major period of incision that led to the genesis of the incised valley during relative sea level fall unit 1 onlaps against ds1 and is bounded above by discontinuity surface ds2 which probably formed by tidal ravinement during a period of transgressive erosion this ravinement surface is the boundary between two shoaling up successions i e units 1 and 2 interpreted as parasequences from a same depositional sequence discontinuity surface ds3 between units 2 and 3 is attributed to a sequence boundary marked by significant erosion and subaerial exposure and is interpreted as a reflex of a renewed period of incision within the estuary due to a strong drop in relative sea level the top of unit 3 is defined by another discontinuity surface i e ds4 with pronounced erosion and subaerial exposure which is attributed to a sequence boundary that ended the estuarine deposition in the study area thus unit 3 defined at the base and top by unconformities is a complete depositional sequence resulting from a low amplitude high frequency relative sea level cycle superposed upon the overall highstand stages of the estuary evolution

water contents of silicic to intermediate magmas silicic to intermediate magmas have water contents that range from 1 wt to around 7 wt depending on the character and depth of the magma source type of melting reaction and the degree of differentiation the condition of water saturation is rare implying that crustal magma genesis generally takes place under fluid absent conditions or that any fluid present must contain volatile species other than h2o the source and quantity of water present during partial melting profoundly affect the types of melting reactions residues and magmas as well as subsequent magma evolution for s type granitic magmas melting reactions involving muscovite breakdown in pelites yield low temperature wet melts that form veins pockets and small plutons in regional metamorphic terranes biotite breakdown in pelites near the amphibolite granulite facies transition yields hotter magmas with variable water contents these are emplaced at medium to high levels under granulite facies conditions biotite breakdown in quartzofeld spathic rocks yields high temperature dry magmas emplaced as subvolcanic batholiths and volcanics

the puncoviscana trough a large basin of late precambrian to early cambrian age on the pacific edge of the brazilian shield during the late precambrian to early cambrian a large basin with a homogeneous psammitic pelitic sediment fill existed in the area of the nw argentine andes it is now exposed in different tectonic levels this basin of meridional elongation was situated on a stable continental margin at the western edge of the brazilian shield it was underlain by segmented older continental crust according to the modal and chemical composition of the greywackes and subgreywackes a predominant metasedimentary source may be supposed four clastic facies types indicate a transport by gravity currents within a submarine fan system while massive red pelites represent cut off periods and rare carbonates deposition on rises the gravity currents derived from easterly directions the sedimentation age is proved by a rich ichnofauna and some medusoid impressions

pleistocene macrotidal tide dominated estuary delta succession along the dong nai river southern vietnam abstract this paper focuses on the facies and sequence stratigraphic interpretation of a tide dominated incised valley system that is rare among geological records of the world for its completeness the subject is the middle upper pleistocene ba mieu and thu duc formations exposed along the dong nai river southern vietnam both the ba mieu and the thu duc formations are interpreted as a transgressive tide dominated estuary succession overlain by a highstand tide dominated delta succession the tide dominated estuary succession is generalized as follows in ascending order fluvial facies in landward portions tidal flat upward coarsening and thickening succession of marine sands with a tidal ravinement surface trs created by tidal scouring during transgression at the base and subtidal lag in seaward portions this tide dominated estuary is distinguished from wave dominated and wave and tide dominated estuaries by 1 the lack of a central basin lagoon tidal delta or bayhead delta facies 2 the widespread presence of marine sands 3 the presence of a subtidal lag and 4 the presence of an upper flow regime sand flat facies the tide dominated delta succession is generalized as follows in ascending order upward convex unit of marine sand and onlapping tidal flat deposits a thick upward fining succession of tidal flat salt marsh deposits and coarse fluvial deposits this delta is distinguished from an estuary as follows 1 it shows thick regional upward fining successions indicating shallowing whereas upward coarsening successions indicating deepening are recognized in an estuary a maximum flooding surface mxfs is recognized in the coarsest part of the succession in marine sand and tidal flat deposits 2 fluvial processes dominate the sediment supply in contrast to an estuary in which a thick marine sand body fed from marine sources is dominant 3 ebb tidal currents are dominant whereas flood tidal currents are dominant in an estuary key features of the incised valley system are 1 amplification of the incised valley geometry by tidal ravinement erosion 2 development of tidal channels filled with mud clasts in the estuary 3 a thick marine sand body in the estuary and 4 upward convex unit of marine sand and a thick tidal flat fluvial succession in the delta the ba mieu formation is recognized as depositional sequence sq 1 between sequence boundary sb 1 below and sb2 above sq1 consists of transgressive systems tract tst 1 and highstand systems tract hst 1 sq1 was formed by a transgression regression cycle during marine isotope stage mis 7 sb2 was formed by fluvial incision during the mis 6 lowstand and is amalgamated with the trs of mis 5 the thu duc formation is recognized as sq2 between sb2 below and sb3 above and it consists of tst2 and hst2 sq2 was formed by a major transgression regression cycle on which a lower rank cyclicity was superposed during mis 5 tst2 thins seaward as a result of tidal ravinement erosion the landward extent of marine environment in mis 5 is inferred to have been of greater scale than that in mis 7 from the distribution of the facies and the trs

sedimentary facies and holocene progradation rates of the changjiang yangtze delta china abstract the changjiang yangtze river one of the largest rivers in the world has formed a broad tide dominated delta at its mouth during the holocene sea level highstand three boreholes cm97 js98 and hq98 were obtained from the changjiang delta plain in 1997 1998 to clarify the characteristics of tide dominated delta sediments and architecture based on sediment composition and texture and faunal content core sediments were divided into six depositional units in ascending order they were interpreted as tidal sand ridge prodelta delta front subtidal to lower intertidal flat upper intertidal flat and surface soil deposits the deltaic sequence from the prodelta deposits to the delta front deposits showed an upward coarsening succession overlain by an upward fining succession from the uppermost part of the delta front deposits to the surface soil thinly interlaminated to thinly interbedded sand and mud sand mud couplets and bidirectional cross laminations in these deposits show that tide is the key factor affecting the formation of changjiang deltaic facies sediment facies and their succession combined with ams 14c dating revealed that isochron lines cross unit boundaries clearly and delta progradation has occurred since about 6000 to 7000 years bp when the rising sea level neared or reached its present position the average progradation rate of the delta front was approximately 50 km kyear over the last 5000 years the progradation rate however increased abruptly ca 2000 years bp going from 38 to 80 km kyear the possible causes for this active progradation could have been an increase in sediment production in the drainage basin due to widespread human interference and or decrease in deposition in the middle reaches related to the channel stability caused by human activity and climatic cooling after the mid holocene

formation of deep incisions into tide dominated river deltas implications for the stratigraphy of the sego sandstone book cliffs utah u s a abstract the upper cretaceous sego member of the mancos shale in east central utah is composed of tidally deposited sandstones interbedded with intervals containing marine shales and thin wave deposited sandstones the tidal sandstones have been interpreted to comprise multiple amalgamated estuarine valley fills above a major sequence boundary that is incised into distal marine deposits of the underlying buck tongue shale according to this interpretation the deposits constitute the base of a thick transgressive succession within the sevier foreland clastic wedge alternatively lower sego sandstones have recently been interpreted by the authors to be tide dominated river delta deposits in an overall regressive interval of the foreland succession a cross section showing facies variations and stratigraphic surfaces within the lower sego member along 100 kilometers of the eastern book cliffs is used in this paper to refine depositional and sequence stratigraphic interpretations of these tidal deposits particularly the origin of deep incisions within the sego sandstones a strike oriented section of the lower sego member reveals tidal sandstone lenses 40 50 kilometers wide and tens of meters thick separated laterally by areas tens of kilometers wide that have no tidal sandstones facies variations within the tidal sandstones reflect depositional processes on tide dominated deltas that prograded obliquely into the shallow intracratonic western interior seaway of north america two major episodes of delta progradation and subsequent transgressions are interpreted to have formed tidal sandstone layers within the lower sego sandstone thinner tidal sandstone layers of more local extent are interpreted to reflect changes in tidal current strength but not necessarily shifts in shoreline position or major changes in water depth multiple origins are suggested for incised erosion surfaces within the lower sego sandstones firstly the tide dominated deltaic sandstones are floored by laterally discontinuous erosion surfaces these basal surfaces marking abrupt vertical changes in depositional process and coarsening of grain size are interpreted to record tidal scouring of the sea floor during shoreline progradation secondly sharp based upward coarsening deltaic sandstones are cut by numerous deep incisions with tens of meters of relief and locally they are entirely removed by erosion some of this deep erosion within the lower sego sandstone may reflect the upstream avulsion of incised distributaries during forced regression of deltas into the basin whereas others may have formed by tidal erosion of abandoned distributaries during more gradual progradation and subsequent retrogradation of deltas highly variable facies trends within incision fills are related to pronounced changes in sediment supply to different distributaries on the delta to differences between incisions cut during delta regression versus those cut during the start of transgression and to varying distances from delta axes when the entire coast was transgressed the influence of tides waned and wave generated currents ravined delta tops depositional interpretations of the sego member indicate that the buck tongue to neslen interval lies in a broadly regressive part of the foreland basin fill

permanent scatterer insar reveals seasonal and long term aquifer system response to groundwater pumping and artificial recharge received 4 may 2007 revised 30 july 2007 accepted 10 october 2007 published 5 february 2008 1 permanent scatterer insar psinsark p rovides an ew high resolution methodology for detecting and precisely measuring long term and seasonal aquifer system response to pumping and recharge in contrast to conventional insar the permanent scatterer methodology utilizes coherent radar phase data from thousands of individual radar reflectors on the ground to develop displacement time series and to produce velocity field maps that depict aquifer system response with a high degree of spatial detail in this study we present the first results of a prototype study in las vegas valley nevada that demonstrate how this methodology can be utilized in heavily pumped groundwater basins to analyze aquifer system response to long term and seasonal pumping we have developed a series of velocity field maps of the valley for the 1992 1996 1996 2000 and 2003 2005 time periods that show that despite rising water levels associated with an artificial recharge program long term residual inelastic aquifer system compaction subsidence is continuing in several parts of the valley in other areas however long term subsidence has been arrested and locally reversed the seasonal elastic responses to alternating pumping and recharge cycles were segregated from the long term trends and analyzed for spatial and temporal patterns the results show oscillations in which the maximum seasonal responses are associated with the late stages of the annual artificial recharge cycles and that similar seasonal subsidence signals are related to summer pumping cycles the differentiation of the seasonal response through the use of time series data further allows the estimation of elastic and inelastic skeletal storage coefficients providing a basis for future work that could characterize the storage properties of an aquifer system with a high degree of spatial resolution

depositional model of a macrotidal estuary and floodplain south alligator river northern australia the south alligator river northern territory of australia has a macrotidal estuary tidal influence spring tidal range 5 6 m at the mouth extends 105 km up the channel it is dominated by freshwater in the wet season december april with a salt wedge near the mouth but is well mixed and becomes saline throughout the dry season the tidal channel can be divided into four different channel types an estuarine funnel a sinuous meandering segment a cuspate meandering segment in which the inside of bends are pointed and an upstream tidal channel the distribution of morphologically defined land classes and morphological units within each land class on the floodplain flanking the estuary differs from one channel type to another several stratigraphic and morphostratigraphic units have been recognized from drill holes on the coastal and deltaic estuarine plains and a model of development is proposed on the basis of extensive radiocarbon chronology and palynology the coastal plain has prograded with most rapid sedimentation between 5000 and 3000 yr bp a similar pattern of progradation is identified in the estuarine funnel in the sinuous segment of the estuary the channel has migrated laterally across the floodplain previous channel positions are indicated by palaeochannels and the meander tract is occupied by laminated channel sediments within the cuspate segment there are numerous sinuous palaeochannels on the plains in the upstream segment the channel and palaeochannels have long straight reaches with irregular bends and discontinuous levees and channel avulsion is indicated mangrove mud is a widespread stratigraphic unit throughout the plains the initial phase of development is a transgressive phase 8000 6800 yr bp when mangrove forests extended landwards into a pre existing valley as sea level rose as sea level stabilized the transgressive phase was followed by a widespread mangrove phase termed the big swamp 6800 5300 yr bp the mangrove forests disappeared from most of the plains as vertical accretion continued and were replaced by grass and sedge covered floodplains during the sinuous phase about 5300 2500 yr bp the channel migrated laterally and eroded the deltaicestuarine plain and deposited lateral accretion deposits laminated channel sediments part of the channel of the south alligator river has then progressed from sinuous to cuspate in form and erosion of river banks has occurred transgressive and big swamp phases occurred under rising and stabilizing sea level respectively later morphodynamic channel adjustments occurred under conditions of stable sea level the depositional model has direct application to other estuaries in northern australia and may be applied to other areas where sea level change has been similar

specific storage as a poroelastic coefficient a definition for the specific storage coefficient ss is given which is unambiguous for general isotropic three dimensional aquifer elasticity in every representative elementary volume ss is the fluid volume released from storage per unit decline in hydraulic head per unit bulk volume under conditions such that there is no strain in two orthogonal directions and the total normal stress in the third orthogonal direction is constant the specific storage coefficient is a point property of the aquifer and is defined independently of problem domain stress and head boundary conditions the expression for ss in terms of aquifer and fluid compressibilities is identical to the familiar forms obtained assuming zero horizontal strain and constant overburden in an aquifer although it is not restricted to these conditions as a point property of the fluid saturated material the specific storage coefficient is one of four constants in the general constitutive poroelastic equations relating three dimensional aquifer stress and strain to fluid pressure and dilatation written in terms of ss these equations show that pore fluid mass diffusion is governed by a diffusivity equal to the ratio of hydraulic conductivity to specific storage under arbitrary boundary conditions it is shown that ss controls slow compressional body wave velocity in the low frequency limit and that the uniaxial aquifer compressibility is not necessarily related to the vertical direction

stratigraphic evolution of the inner continental shelf in response to late quaternary relative sea level change northwestern gulf of maine accumulations of deltaic and littoral sediments on the inner continental shelf of maine gulf of maine preserve a record of postglacial sea level changes and shoreline migrations the depositional response of coastal environments to a cycle of regression lowstand and transgression was examined with seismic reflection profiles vibracores and radiocarbon dates collected from sediments at the mouths of the kennebec and penobscot rivers sequence stratigraphic analysis of these data reveals two distinctly different successions of late quaternary deposits that represent end members in an evolutionary model for this glaciated coast seaward of the kennebec river coarse grained shorelines with foreset beds occur at depths of 20 60 m and outline the lobate margin of the kennebec river paleodelta a complex rock framed accumulation of glaciomarine and deltaic sediments capped by estuarine and marine deposits sand derived from this system today supports large barrier spits and extensive salt marshes in contrast the mouth of the penobscot river is characterized by thick deposits of glaciomarine mud overlain by marine mud of holocene age including gas charged zones that have locally evolved into fields of pockmarks the distinct lack of sand and gravel seaward of the penobscot river and its abundance seaward of the kennebec river probably reflect differences in sediment sources and the physiography of the two watersheds the contrasting stratigraphic framework of these systems demonstrates the importance of understanding local and regional differences in sediment supply sea level change bedrock structure and exposure to waves and tides in order to model river mouth deposition on glaciated coasts evolution of shelf deposits was largely controlled by relative sea level which locally fell from a highstand 60 to 70 m at 14 ka contemporary with deglaciation to a lowstand 55 m at 10 8 ka the sea level lowering was accompanied by fluvial incision of older deposits producing a regressive basal unconformity major rivers deposited abundant sediment over this surface sea level then rose at varying rates extensively reworking formerly emergent parts of the shelf and producing a shoreface ravinement surface in areas exposed to waves a tidal ravinement surface has developed in sheltered embayments where erosion is due mainly to tidal currents incised valleys in both settings preserve transgressive estuarine deposits that contain lagoonal bivalves and salt marsh foraminifera at depths of 15 30 m these deposits accumulated ca 9 2 7 3 ka locally a period of relatively slow sea level rise

transgressive systems tract development and incised valley fills within a quaternary estuary shelf system virginia inner shelf usa abstract high frequency quaternary glacioeustasy resulted in the incision of six moderate to high relief fluvial erosion surfaces beneath the virginia inner shelf and coastal zone along the updip edges of the atlantic continental margin fluvial valleys up to 5 km wide with up to 37 m of relief and thalweg depths of up to 72 m below modern mean sea level cut through underlying pleistocene and mio pliocene strata in response to drops in baselevel on the order of 100 m fluvially incised valleys were significantly modified during subsequent marine transgressions as fluvial drainage basins evolved into estuarine embayments ancestral generations of the chesapeake bay complex incised valley fill successions are bounded by or contain up to four stacked erosional surfaces basal fluvial erosion surface bay ravinement tidal ravinement and ebb flood channel base diastem in vertical succession these surfaces combined with the transgressive oceanic ravinement that generally caps incised valley fills control the lateral and vertical development of intervening seismic facies depositional systems transgressive stratigraphy characterizes the quaternary section beneath the virginia inner shelf where six depositional sequences sequences i vi are identified depositional sequences consist primarily of estuarine depositional systems subjacent to the transgressive oceanic ravinement and shoreface shelf depositional systems highstand systems tract coastal systems are thinly developed the quaternary section can be broadly subdivided into two parts the upper part contains sequences consisting predominantly of inner shelf facies whereas sequences in the lower part of the section consist predominantly of estuarine facies three styles of sequence preservation are identified style 1 represented by sequences vi and v is characterized by large estuarine systems ancestral generations of the chesapeake bay that are up to 40 m thick have hemicylindrical wedge geometries and occur within large coast oblique trending depressions paleo estuaries style 1 is dominated by fluvial through estuary mouth depositional systems seismic facies 1 4 style 2 sequence preservation represented by sequences iii and ii is dominantly an inner shelf and shoreface succession with a seaward thickening tabular wedge geometry that does not exceed 15 m in thickness these shoreface and inner shelf depositional systems of the upper transgressive systems tract seismic facies 9 and highstand systems tract seismic facies 7 and 11 are not associated with paleo estuaries style 3 sequence preservation is represented by sequence i the holocene sequence it consists of lower transgressive systems tract fluvial estuarine lagoonal and tidal inlet fill deposits seismic facies 1 6 and 8 overlain by upper transgressive systems tract shelf and shoreface sands seismic facies 9 style 3 has a crenulated wedge geometry and is thickest beneath and seaward of the modern chesapeake bay mouth it thins northward and landward onto late pleistocene interfluvial highs on the basinward side of the southern delmarva peninsula

time calibration of a pt path from the western tauern window eastern alps the problem of closure temperatures new hornblende k ar and 39ar 40ar and mica rb sr and k ar ages are used to place specific timemarks on a well constrained pressure temperature path for the late alpine metamorphism in the western tauern window after identification of excess 40ar the closure behavior of ar in hornblende is compared with that of sr and ar in phengite and biotite samples were collected in three locations whose maximum temperatures were 570 c zemmgrund 550 c pfitscher joch and 500 540 c landshuter hutte

tide influenced sedimentation in a rift basin cretaceous qishn formation masila block yemen a billion barrel oil field the lower cretaceous qishn clastics member in masila block 14 hadhramaut region republic of yemen has estimated reserves of 1 1 billion bbl recoverable oil and has produced 600 million bbl of oil sedimentation took place in an elongate paleogulf of the say un al masila basin with open marine carbonates to the east the qishn clastics member unconformably overlies mixed carbonates and clastics of the sa af member lower qishn onlap resulted in deposition of brackish and tidal likely macrotidal estuarine to open bay or gulf deposits the middle portion of the lower qishn clastics member shows evidence of arid nonmarine sedimentation including debris flow deposits red beds and shale clast conglomerates in turn overlain by interfingering coastal and nonmarine deposits the lower qishn clastics member is truncated by a sequence boundary overlain by an extensive sandstone deposited in a low accommodation braid plain close to the shoreline a flooding surface is present at the top of the sandstone over which progradational tide influenced deltaic strata were deposited delta progradation culminated in shallow water clastic dolomitic deposits on the coastal plain with subsequent transgression a rising water table caused a nonmarine flooding surface with lakes and lacustrine deltas overlain by tidal flat deposits ongoing transgression resulted in wave ravinement overlain by shallow shelf clastics and then deposition of slightly deeper shelf carbonates the uppermost unit comprises bioturbated clastic shelf deposits related to a drop in relative sea level throughout much of the qishn clastics interval accommodation was moderate except for low accommodation associated with regional sheet sandstone at the base of the upper qishn clastics member virtually all marine and brackish deposits show evidence of tidal sedimentation climate was arid and seasonally wet

evaluation of the global oxygen isotope curve as a proxy for quaternary sea level by modeling of delta progradation patterns of delta progradation in rapidly subsiding basins have been used previously as a proxy for quaternary sea level change major transgression surfaces and maximum lowstand positions are readily recognizable in seismic reflection profiles quaternary sea level change can be approximated by stacked and tuned oxygen isotope records but significant departures from this proxy result from variation in isotopic composition of ice sheets temperature variations in the deep sea and the effect of bioturbation in degrading the isotopic record we analyze the influence of rapid quaternary sea level change on delta progradation in the eastern mediterranean using delta a multi process sediment transport model subsidence rates and sediment inputs may vary through time but compared to quaternary sea level change such variations were minor and had little effect on model results for a variety of geologically reasonable sediment inputs and subsidence rates the delta architecture observed in seismic profiles could not be reproduced when the sea level estimates were taken directly from a scaled global oxygen isotopic curve however when this sea level curve was corrected to include independent estimates of sea level from geological data elsewhere in the world previously used sediment inputs and subsidence rates invariably predict the general form of the observed architecture the difference between isotopic and geological estimates of sea level for the last 200 ka follows a linear trend that was applied to previous glacial interglacial cycles producing a corrected sea level history for the last 540 ka using delta over this time span the sea level history based directly on the oxygen isotope curve was again less able to reproduce the observed delta architecture compared with a corrected sea level history this study shows the importance of modeling delta progradation as an avenue for testing and exploring quaternary sea level history

sedimentology and sequence stratigraphy of early syn rift tidal sediments the nukhul formation suez rift egypt abstract facies and tectono stratigraphic models for the tidally influenced miocene nukhul formation are presented based on outcrop data from hammam faraun fault block suez rift egypt deposits of the nukhul formation are attributed to two linked depositional settings offshore to shoreface and estuary settings and were deposited during initial stages of rifting in hanging wall depocenters of early formed propagating fault segments the offshore to shoreface deposits consist of variably bioturbated mudstones that pass gradationally upward to bioturbated bioclastic sandstones the more landward estuary deposits can be separated into a tripartite division of estuary mouth estuary funnel with bayhead delta and upper estuary channel deposits estuarine processes generated a complex intercalation of lithologies with both gradational and sharp facies transitions in the estuary deposits tidal ravinement surfaces are typically characterized by mudstones of the estuary funnel association below passing abruptly up to erosionally based estuary mouth sandstones maximum flooding surfaces are expressed by an abrupt erosional contact separating estuary mouth sandstones below and estuary funnel mudstones above stratigraphic development was strongly influenced by the evolving early rift structure depocenters were narrow 2 5 km wide and elongate 10 km long parallel to the strike of normal fault segments the shoreface shoal prevented wave energy in the estuary and increased the relative influence of tidal currents the elongate fault controlled geometry of the depocenters confined the bayhead delta and further enhanced tidal influence stratal geometry reflects deformation associated with low relief growth folds and surface breaking faults that together formed part of an evolving fault array this basin configuration and associated nukhul stratigraphy is markedly different to tectono stratigraphic models for crustal scale tilted fault blocks that are applicable from late stages of rifting

tertiary diachronic extrusion and deformation of western indochina structural and 40ar 39ar evidence from nw thailand the wang chao and three pagodas fault zones cut the western part of the indochina block and run parallel to the red river fault evidence of intense ductile left lateral shear is found in the lansang gneisses which form a 5 km wide elongated core along the wang chao fault zone dating by 40 ar 39 ar shows that such deformation probably terminated around 30 5 ma the wang chao and three pagodas faults offset the north striking lower mesozoic metamorphic and magmatic belt of northern thailand 40 ar 39 ar results suggest that this belt suffered rapid cooling in the tertiary probably around 23 ma these results imply that the extrusion of the southwestern part of indochina occurred in the upper eocene lower oligocene it probably induced rifting in some basins of the gulf of thailand and in the malay and mekong basins in the oligo miocene the continuing penetration of india into asia culminated with the extrusion of all of indochina along the ailao shan red river fault this occurred concurrently with the onset of e w extension more to the south plotting in a geographical reference frame the diachronic time spans of movement on left lateral faults east and southeast of tibet implies that the northward movement of the indian indenter successively initiated new strike slip faults located farther and farther north along its path

fluids p t paths and the fates of anatectic melts in the earth s crust this paper presents a model for the longevity and physical behaviour of anatectic melts in the earth s crust it is assumed that a thermal anomaly has caused partial fusion of biotite plagioclase quartz rocks to produce a granitic melt and restitic solids the focus is on the potential chemical and physical outcomes as a function of the various p t fluid conditions rocks undergoing fluid present melting will sustain an increase in bulk density and will become more gravitationally stable diapiric up welling of such material should not occur in fluid absent melting the bulk density will decrease and foster gravitational instability stresses in the surrounding rocks could however lead to fracture and rapid evacuation of the melt with excess fluid and without melt segregation isobaric cooling will cause immediate freezing if t rises above the biotite quartz melting reaction freezing will still occur at the original reaction t diapiric up welling should not occur biotite bearing diatexites might be formed by large degrees of fusion but magma ascent is unlikely in isothermal decompression immediate freezing will ensue and the migmatite should contain orthopyroxene rather than biotite with excess fluid and melt segregation cooling will induce freezing at the fluid saturated granite solidus magma ascent could however occur even for xflh2o 1 in isothermal decompression melt will persist to the granite solidus for the imposed xflh2o limited magma ascent could occur all granites should contain primary igneous biotite for fluid deficient rocks without melt segregation freezing will occur at the t of the original melting if the reaction is overstepped solidification will occur at the original xflh2o magma formation is unlikely migmatites should contain either pyroxene retrogressed to biotite or biotite alone on decompression immediate freezing is likely if t remains at the biotite quartz reaction for higher t melt will survive decompression and freeze at the fluid saturated solidus for some increased xflh2o magma ascent is possible and the melt will freeze very close to the wet granite solidus in fluid deficient rocks with melt segregation cooling and crystallization will cause fluid saturation in situ segregated melt will freeze at the original xflh2o melt ascent will however cause exsolution of a co2 rich fluid with fluid escape melt will freeze close to the wet granite solidus an increase in melt proportion may accompany magma ascent or source up welling any low p granite intrusion should be charnockitic for fluid absent rocks without melt segregation freezing will occur on cooling to the t of the original reaction only transitory migmatites could be formed but melt will survive decompression almost to the h2o saturated granite solidus the rocks will reveal former melt presence only in the existence of veins of coarse retrograde biotite with isothermal decompression further melting may occur forming an orthopyroxene bearing granulite facies migmatite in fluid absent situations with melt segregation magma could be efficiently transported to higher crustal levels if the melt proportion were insufficient for magma formation granulite facies migmatites would result ascending melt would progressively dissolve any entrained restite the granites produced should be charnockitic to aid in interpretation of the modelling results we suggest that it may be slightly more common for the highest grade metamorphic terranes to exhibit isobaric cooling paths that fluid present anatexis is normally limited to the shallower parts of the crust and that fluid absent reactions are more likely at greater depths we conclude that the best models for natural fluid present anatexis are those dealing with essentially pure h2o fluid and that fluid deficient conditions will dominate over fluid excess we also believe that it is common for melts to be physically segregated on scales larger than the diffusion paths of many elements

rapid drought induced land subsidence and its impact on the california aqueduct abstract the central valley in california is characterized by a semi arid climate prone to droughts a variable surface water supply and immense agricultural areas dependent on groundwater irrigation the groundwater is stored in a complex aquifer system composed of alternating layers of coarse sediments and fine grained sediments acting as confining materials groundwater fluctuations are coupled with both the elastic and inelastic land surface deformation historically observed in the central valley surface deformation poses a hazard to the california aqueduct which supports central valley agriculture and large urban populations in southern california the risk of reduced aqueduct efficacy and expensive repairs compels water resource managers to carefully monitor land deformation in the valley a persistent drought in the region began in 2012 intensified in 2014 and was abruptly alleviated by a wet period from dec 2016 to feb 2018 nasa s uavsar l band synthetic aperture radar acquired 31 high resolution radar images between may 2013 and nov 2018 the interferometric phase difference between acquisitions is used to develop a time series of vertical displacement and identify and track a rapidly forming subsidence feature adjacent to the california aqueduct the surface area of the feature that subsided 10 cm or more by the end of the time series reaches 4452 ha and a 10 5 km segment of the aqueduct this study also incorporates extensometer measurements precise leveling surveys sentinel 1a displacement concurrent water elevation data well construction reports nearby extensometer measurements aquifer material characterization and environmental conditions spatiotemporal data availability limits the appropriateness of calculations and models able to be performed for different sites along the aqueduct we aim to offer insight into heterogeneous subsurface properties and mechanics estimate the permanent loss of aquifer storage volume and identify additional data that would aid water management

detailed architecture of a compound incised valley system and correlation with forced regressive wedges example of late quaternary tet and agly rivers western gulf of lions mediterranean sea france abstract quaternary incised valley systems are usually characterized by the preservation of a single valley fill attributed to the last post glacial period moreover there are very few cases of correlation between incised valley system developed on inner shelf and sedimentary units observed on the mid to outer shelf mainly forced regressive wedges the roussillon shelf in the western part of the gulf of lion is a particular example of preserved quaternary compound incised valley system also characterized by a direct correlation with the forced regressive lowstand wedges on the mid outer shelf high resolution seismic data and a borehole 60 m deep located on the beach barrier permit an accurate study of the geometry and lithology of the system six imbricated and more or less preserved incised valleys and valley fills are observed up to the inner to mid shelf the key surfaces associated to the incised valleys are correlated to the boundaries of the forced regressive wedges they are assumed to be reworked surfaces at the borehole location only few thin layers less than 1 m thick of coarse grain and or floating pebbles are observed and should correspond to preserved fluvial lowstand deposits reworked under marine influence the valley fills are mainly composed of estuarine muddy silts from ams 14c age dating it is inferred that the uppermost incised valley system is younger than 45 ky cal bp based on those observations the six preserved incised valley systems are assumed to be controlled by the last six 4th order sea level cycles 100 ky of the middle to late quaternary the paleo topography of the underlying plio quaternary deposits controls the compound incised valley system location the deep topography of the messinian erosionnal surface is a controlling factor at a lower degree the partial preservation of the successive valley fill is attributed not only to the differential subsidence but also to the lateral migration of each incision and to the hydrodynamic regime

fault zone controls on the spatial distribution of slow moving landslides slow moving landslides earthflows can dominate hillslope sediment flux and landscape erosion in hilly terrain with mechanically weak fine grained rock controls on the occurrence of slow moving landslides are poorly constrained and need to be understood for landscape evolution models sediment budgets and infrastructure and hazards planning here we use airborne interferometric synthetic aperture radar insar and aerial photographs to document 150 previously unidentified active earthflows along the central creeping portion of the san andreas fault california the earthflows move seasonally in response to winter rainfall occur on hillslopes at 20 40 gradients less than typically associated with rapid catastrophic landslides and have similar morphological characteristics to earthflows in different climatic and tectonic settings although our data extend up to 10 km from the fault trace 75 of detected landslides occur within 2 km of the active fault topographic precipitation and rock type metrics alone are not enough to explain the observed spatial distribution of earthflows instead we hypothesize that earthflows cluster near the creeping san andreas fault because of a fault induced zone of reduced bulk rock strength that increases hillslope susceptibility to failure in addition similar lithology topography and climate exist north of the creeping section of the fault yet earthflows there are rare this may be due to large magnitude earthquakes episodically triggering coseismic rapid landslides which preferentially remove weak rock from the fault damage zone our analysis suggests that the necessary conditions for earthflow formation in central california include some combination of reduced rock strength fine grained sedimentary rock threshold precipitation and relief and possibly the absence of large magnitude earthquakes these conditions likely hold for earthflow development in other areas and our work suggests that local variations in rock strength and seismicity such as those associated with fault zones need to be taken into account in order to accurately predict earthflow occurrence

bayou corne louisiana sinkhole precursory deformation measured by radar interferometry catastrophic sinkholes are formed through the collapse of natural or human made subterranean caverns and are common in areas with evaporite and carbonate rock despite their danger advance warning of these events is rare we report a measurement of precursory surface deformation of as much as 260 mm derived with interferometric synthetic aperture radar insar and evident over a month before surface collapse at the site of the bayou corne louisiana usa sinkhole that formed in august 2012 data collected by the airborne uninhabited aerial vehicle sar uavsar instrument were used for the study analysis of data acquired from two flight tracks with near opposing imaging geometries reveal a deformation pattern consistent with compressive loading at the surface due to loss of support from a subterranean cavity collapse related to texas brine oxy geismar well 3 the precursor deformation was nearly entirely horizontal i e oriented along the surface and manifested as movement of surface material toward the location where the sinkhole later formed the sinkhole formed in the area with the largest gradient in surface strain but did not cover the full extent of the precursory deformation detected with radar this work suggests that insar data collected operationally for hazard monitoring could in some cases identify sinkhole development before surface collapse and decrease subsequent danger to people and property

estimating the permanent loss of groundwater storage in the southern san joaquin valley california in the san joaquin valley california recent droughts starting in 2007 have increased the pumping of groundwater leading to widespread subsidence in the southern portion of the san joaquin valley vertical subsidence as high as 85 cm has been observed between june 2007 and december 2010 using interferometric synthetic aperture radar insar this study seeks to map regions where inelastic not recoverable deformation occurred during the study period resulting in permanent compaction and loss of groundwater storage we estimated the amount of permanent compaction by incorporating multiple datasets the total deformation derived from insar estimated skeletal specific storage and hydraulic parameters geologic information and measured water levels during our study period we used two approaches one that we consider to provide an estimate of the lowest possible amount of inelastic deformation and one that provides a more reasonable estimate these two approaches resulted in a spatial distribution of values for the percentage of the total deformation that was inelastic with the former estimating a spatially averaged value of 54 and the latter a spatially averaged value of 98 the former corresponds to the permanent loss of 4 14 108 m3 of groundwater storage or roughly 5 of the volume of groundwater used over the study time period the latter corresponds to the loss of 7 48 108 m3 of groundwater storage or roughly 9 of the volume of groundwater used this study demonstrates that a data driven approach can be used effectively to estimate the permanent loss of groundwater storage this article is protected by copyright all rights reserved

sharp based tide dominated deltas of the sego sandstone book cliffs utah usa the lower part of the cretaceous sego sandstone member of the mancos shale in east central utah contains three 10 to 20 m thick layers of tide deposited sandstone arranged in a forward and then backward stepping stacking pattern each layer of tidal sandstone formed during an episode of shoreline regression and transgression and offshore wave influenced marine deposits separating these layers formed after subsequent shoreline transgression and marine ravinement detailed facies architecture studies of these deposits suggest sandstone layers formed on broad tide influenced river deltas during a time of fluctuating relative sea level shale dominated offshore marine deposits gradually shoal and become more sandstone rich upward to the base of a tidal sandstone layer the tidal sandstones have sharp erosional bases that formed as falling relative sea level allowed tides to scour offshore marine deposits the tidal sandstones were deposited as ebb migrating tidal bars aggraded on delta fronts most delta top deposits were stripped during transgression where the distal edge of a deltaic sandstone is exposed a sharp based stack of tidal bar deposits successively fines upward recording a landward shift in deposition after maximum lowstand where more proximal parts of a deltaic sandstone are exposed a sharp based upward coarsening succession of late highstand tidal bar deposits is locally cut by fluvial valleys or tide eroded estuaries formed during relative sea level lowstand or early stages of a subsequent transgression estuary fills are highly variable reflecting local depositional processes and variable rates of sediment supply along the coastline lateral juxtaposition of regressive deltaic deposits and incised transgressive estuarine fills produced marked facies changes in sandstone layers along strike estuarine fills cut into the forward stepped deltaic sandstone tend to be more deeply incised and richer in sandstone than those cut into the backward stepped deltaic sandstone tidal currents strongly influenced deposition during both forced regression and subsequent transgression of shorelines this contrasts with sandstones in similar basinal settings elsewhere which have been interpreted as tidally influenced only in transgressive parts of depositional successions

lead evolution of the pre mesozoic crust in the central andes 18 27 progressive homogenisation of pb abstract pb isotope composition of feldspar determined for a suite of granitoid magmatic and metamorphic rocks of cambrian to permian age provides a guide to the crustal composition in the central andes as it evolved during the paleozoic the large range of pb isotope composition of magmatic rocks older than 500 ma contrasts with the homogeneous pb isotope composition of magmatic and metamorphic rocks that formed between 500 ma and the late paleozoic there are four isotopically distinct crustal domains discernible three of them associated with pre 500 ma old rocks are characterised by similar 206pb 204pb of ca 16 6 17 0 and are distinguished from each other by contrasting 207pb 204pb and 208pb 204pb signatures we distinguish i an unradiogenic source with 207pb 204pb of ca 15 4 and 208pb 204pb of ca 36 5 which may have been the principal source of crustal lead for cenozoic magmatic rocks north of 21 s ii an old high source with 207pb 204pb of ca 15 8 and 208pb 204pb of ca 36 5 37 5 and iii an arequipa type source with 207pb 204pb of ca 15 6 and 208pb 204pb of ca 38 5 the fourth crustal lead source a radiogenic source is characterised by a relatively small range of pb isotope compositions of paleozoic gneisses of the basement 206pb 204pb ca 18 0 18 8 207pb 204pb ca 15 55 15 75 208pb 204pb ca 37 5 38 5 and most intrusions which formed after high grade metamorphism at ca 500 ma the compositional range given by present day pb isotope ratios of the radiogenic source average values of whole rock pb isotope ratios 206pb 204pb 19 10 207pb 204pb 15 70 208pb 204pb 39 02 and the feldspar data average values 206pb 204pb 18 38 207pb 204pb 15 64 208pb 204pb 38 11 which also represent the present day composition of those parts of the radiogenic source depleted in u at ca 500 ma is clearly reflected in the pb isotope ratios of the widespread cenozoic ignimbrites and andesites from the central andes south of 21 s rocks of all lead sources have proterozoic crustal residence ages tdm ca 1 6 2 0 ga however the three sources of little radiogenic 206pb 204pb experienced a dominantly metamorphic redistribution of u th and pb early in their history the early paleozoic major metamorphic magmatic cycle incorporated these inherited pb isotope domains of minor volume into the radiogenic source south of 21 s

pre requisites processes and prediction of chlorite grain coatings in petroleum reservoirs a review of subsurface examples abstract deeply buried reservoirs containing chlorite coated quartz sand grains commonly have higher than expected porosity and permeability although prediction of such positive anomalies still remains elusive a total of 54 published examples based on information and data from 62 scientific papers was collated quantification of some of the most common parameters including depositional environment age and latitude of sand deposition effect on reservoir quality and chemical composition of chlorite is presented the dataset indicates that chlorite coats are found in sandstones deposited in a range of depositional environments but most commonly occur in delta related environments 44 with fluvial environments the second most common 19 age relationships indicate that there is an overall exploration bias in published examples with chlorite coats becoming increasingly common through time the latitude at the time of deposition of sands with chlorite coats is wide 60 n 60 s and indicates that temperate and tropical climates are important for the generation of this clay mineral chlorite can have a variable effect on reservoir quality but is typically positive iron rich chlorites occur overwhelmingly in coastal environments while mixed iron and magnesium rich chlorites are principally found in marine and terrestrial sandstones analysis of these factors suggests that hinterland geology basinal soil development and geochemical weathering and proximity to river systems are essential to the formation of chlorite precursor phases these characteristics have been combined to define situations where chlorite coats were more likely or more unlikely to form these parameters will provide insights into the formation of chlorite and to further refine predictive models for the presence or absence of chlorite coated sandstones

the ordovician sierras pampeanas puna basin connection basement thinning and basin formation in the proto andean back arc article i nfo the ordovician sierras pampeanas located in a continental back arc position at the proto andean margin of southwest gondwana experienced substantial mantle heat transfer during the ordovician famatina orogeny converting neoproterozoic and early cambrian metasediments to migmatites and granites the high grade metamorphic basement underwent intense extensional shearing during the early and middle ordovician contemporaneously up to 7000 m marine sediments were deposited in extensional back arc basins covering the pre ordovician basement extensional ordovician tectonics were more effective in mid and lower crustal migmatites than in higher levels of the crust at a depth of about 13 km the separating boundary between low strain solid upper and high strain lower migmatitic crust evolved to an intra crustal detachment the detachment zone varies in thickness but does not exceed about 500 m the formation of anatectic melt at the metamorphic peak and the resulting drop in shear strength initiated extensional tectonics which continued along localized ductile shear zones until the migmatitic crust cooled to amphibolite facies p t conditions p t d t data in combination with field evidence suggest significant ca 52 crustal thinning below the detachment corresponding to a thinning factor of 2 1 ductile thinning of the upper crust is estimated to be less than that of the lower crust and might range between 25 and 44 constituting total crustal thinning factors of 1 7 2 0 while the migmatites experienced retrograde decompression during the ordovician rocks along and above the detachment show isobaric cooling this suggests that the magnitude of upper crustal extension controls the amount of space created for sediments deposited at the surface upper crustal extension and thinning is compensated by newly deposited sediments maintaining constant pressure at detachment level thinning of the migmatitic lower crust is compensated by elevation of the crust mantle boundary the degree of mechanical coupling between migmatitic lower and solid upper crust across the detachment zone is the main factor controlling upper crustal extension basin formation and sediment thickness in the back arc basin the initiation of crustal extension in the back arc however crucially depends on the presence of anatectic melt in the middle and lower crust consumption of melt and cooling of the lower crust correlate with decreasing deposition rates in the sedimentary basins and decreasing rates of crustal extension

a petrogenetic grid for pelitic schists in the system sio 2 al 2 o 3 feo mgo k 2 o h 2 o a quantitative petrogenetic grid for pelitic schists in the system kfmash that includes the phases garnet chlorite biotite chloritoid cordierite staurolite talc kyanite andalusite sillimanite and pyrophyllite with quartz h2o and muscovite or k feldspar in excess is presented the grid is based on thermodynamic data of berman et al 1985 and berman 1988 for endmember kfash and kmash equilibria and natural fe mg partitioning for the kfmash system calculation of p t slopes and the change in fe fe mg along reactions in the kfmash system were made using the gibbs method in addition the effect on the grid of mno and cao is evaluated quantitatively the resulting grid is consistent with typical buchan and barrovian parageneses at medium to high grades at low grades the grid predicts an extensive stability field for the paragenesis chloritoid biotite which arises because of the unusual facing of the reaction chloritoid biotite quartz h2o garnet chlorite muscovite which proceeds to the right with increasing t in the kfmash system however the reaction proceeds to the left with increasing t in the mnkfash system so the assemblage chloritoid biotite is restricted to bulk compositions with high fe fe mg mn typical metapelites will therefore contain garnet chlorite at low grades rather than chloritoid biotite

a tectonic model for the tertiary evolution of strike slip faults and rift basins in se asia abstract models for the tertiary evolution of se asia fall into two main types a pure escape tectonics model with no proto south china sea and subduction of proto south china sea oceanic crust beneath borneo a related problem is which if any of the main strike slip faults mae ping three pagodas and aliao shan red river asrr cross sundaland to the nw borneo margin to facilitate continental extrusion recent results investigating strike slip faults rift basins and metamorphic core complexes are reviewed and a revised tectonic model for se asia proposed key points of the new model include 1 the asrr shear zone was mainly active in the eocene oligocene in order to link with extension in the south china sea the asrr was less active during the miocene tens of kilometres of sinistral displacement with minor amounts of south china sea spreading centre extension transferred to the asrr shear zone 2 at least three important regions of metamorphic core complex development affected indochina from the oligocene miocene mogok gneiss belt doi inthanon and doi suthep around the asrr shear zone hence paleogene crustal thickening buoyancy driven crustal collapse and lower crustal flow are important elements of the tertiary evolution of indochina 3 subduction of a proto south china sea oceanic crust during the eocene early miocene is necessary to explain the geological evolution of nw borneo and must be built into any model for the region 4 the eocene oligocene collision of ne india with burma activated extrusion tectonics along the three pagodas mae ping ranong and klong marui faults and right lateral motion along the sumatran subduction zone 5 the only strike slip fault link to the nw borneo margin occurred along the trend of the asrr fault system which passes along strike into a right lateral transform system including the baram line

high resolution sequence stratigraphy of a mid cretaceous estuarine complex the woburn sands of the leighton buzzard area southern england

puncoviscana folded belt in northwestern argentina testimony of late proterozoic rodinia fragmentation and pre gondwana collisional episodes stratigraphic correlations and tectonic analysis suggest that the puncoviscana fold belt of northwestern argentina was an intracontinental basin with bimodal igneous suites that formed in connection with the breakup of the rodinia supercontinent at 800 ma several lines of evidences point to an initial lithosphere rupture possibly induced by a rising mantle plume the earliest synrift igneous products are represented by ultra potassic dykes and alkaline lava flows of high lree hree and low zr nb y nb ratios the dyke emplacements and the initiation of rifting were probably synchronous they pass laterally and upwards middle part of the puncoviscana succession into basalts of alkaline transitional character oib like source the distinctive chemical feature of these lavas are very similar to the source of oceanic island basalts thus they are thought to represent a magmatism associated with the rift and rift drift transition stage during this stage of rifting probably true oceanic crust was formed the upper part of the puncoviscana sequence late precambrian lower cambrian in age comprises a thick and monotonous sequence of pillow lavas massive basaltic flows and minor volcanic breccias and hyaloclastites these lavas exhibit morb trace element characteristics with high feot and tio2 low k2o and p2o5 flat light ree spectra little or no depletion in nb and ta this volcanism consists of the major and latest effusive episode from the puncoviscana basin which was slightly modified by subduction processes the geodynamical model proposed for the generation of these volcanic rocks could have been developed in two stages in the first stage the volcanic event is compatible with a progressive opening of a continental rift leading to formation of a mature oceanic basin in contrast the second stage shows the effects of a completed wilson cycle including a primitive volcanic arc which continued until the accreted cuyania arequipa belen antofalla caba terrane against the proto gondwana western borderland of the amazonian shield 535 ma

amphibolite to granulite transition in aluminous greywackes from the sierra de comechingones cordoba argentina we discuss upper amphibolite to granulite facies early palaeozoic metamorphism and partial melting of aluminous greywackes from the sierra de comechingones se sierras pampeanas of central argentina consistent p t estimates obtained from equilibria involving al and ti exchange components in biotite and from more traditional thermobarometric equilibria suggest that peak metamorphism of the exposed section took place at an essentially constant pressure of 7 8 kbar and at temperatures ranging from 650 to 950 c mineral compositions record an initial decompression after peak metamorphism of c 1 5 kbar which was accompanied by a cooling of c 100 c upper amphibolite facies gneisses consist of the assemblage qtz pl bt grt rt ilm the transition to the granulite facies is marked by the simultaneous appearance of the assemblage kfs sil and of migmatitic structures suggesting that the amphibolite to granulite transition in the sierra de comechingones corresponds to the beginning of melting rocks with structural and or chemical manifestations of partial melting range from metatexites to diatexites to melt depleted granulites consisting of the assemblage grt crd pl qtz ilm ath the melting stage overlapped at least partially with decompression as suggested by the occurrence of cordierite in both the migmatites and the residual granulites of two distinct textural types idiomorphic porphyroblasts probably representing peritectic cordierite and garnet rimming coronas metapelitic rocks are unknown in the sierra de comechingones therefore it appears most likely that the al rich residual assemblages found in the migmatites and residual granulites were formed by partial melting of muscovite and sillimanite undersaturated metagreywackes we propose a mechanism for this that relies on the sub solidus stabilization of garnet and the ensuing changes in the octahedral al content of biotite with pressure and temperature

monitoring of subsidence with uavsar on sherman island in california s sacramento san joaquin delta abstract sherman island the westernmost island in the sacramento san joaquin delta in california plays a crucial role in maintaining the water flux between saline ocean water from the san francisco bay to its west and the rest of the delta to its east land elevation below mean sea level and continuous subsidence over the past century has made this island a high priority area for investigations of subsidence and restoration in the delta this study reports the results of successful application of interferometric synthetic aperture radar insar data and technique to measure subsidence in the delta which is a coherence challenged non urban area we carried out a time series interferometric analysis of uninhabited aerial vehicle synthetic aperture radar uavsar l band 23 8 cm data collected from july 2009 august 2014 to assess both the spatial and temporal variation of subsidence on sherman island we report both large scale island wide subsidence trends and small scale levee farm scale subsidence features in sherman island assuming the subsidence is linear during the five years of uavsar data acquisition subsidence rates across the island range from 0 5 cm yr with an average of 1 3 0 2 cm yr we estimate our systematic uncertainty to be 0 3 cm yr overall the central region in the island has subsided at a faster rate than the rest of the island we find our results to be consistent with previous measurements of subsidence rates at electric transmission line towers scattered throughout the island the results of this study provide insights into several factors influencing subsidence including soil type water table depth land use land elevation and the location and time of levee repairs subsidence monitoring on sherman island is essential for maintaining a reliable water supply for the state of california and for protecting the delta ecosystem

holocene stratigraphy in the paranagua bay estuary southern brazil abstract the paranagua bay estuary is a 50 km long microtidal barrier estuary that is still far from infilled even after 3 5 m of continuous sea level fall during the last 5000 years data derived from several independent studies including surface sediment samples jet probe cores vibracores and seismic records were compiled in order to provide an assessment of the quaternary stratigraphy of the estuary the estuary displays the longitudinal tripartite zonation of surface sedimentary facies marine sand estuarine mud fluvial sand that is characteristic of many coastal plain estuaries five sedimentary facies were identified overlying the bedrock pre holocene fluvial and continental deposits within the paleo valley form the substrate for the more recent sedimentation a transgressive mud facies marks the initial stages of estuary inundation this deposit is observed only in the lower half of the estuary where greater accommodation space existed and less intensive tidal scouring associated with the subsequent deposition of the transgressive sand facies occurred the onset of the regressive stage is marked by the deposition of the regressive mud facies which is presently the most extensive sedimentary deposit within the estuary the regressive sand facies which is composed of fluvially derived sediments and is restricted to the head of the estuary is the least developed sedimentary facies the vertical succession of the sedimentary facies shows an almost complete stratigraphic sequence and the presence of several bounding surfaces a transgressive surface a maximum flooding surface a tidal ravinement surface and a tidal diastem a comparison of the paranagua bay gironde and james estuaries all of similar size illustrates various stages of sequence development in modern incised valley systems

high resolution seismic stratigraphy of a narrow bedrock controlled estuary the guadiana estuarine system sw iberia abstract the late quaternary sedimentary architecture of the guadiana estuary southwestern iberian peninsula a narrow bedrock controlled estuary with moderate sediment supply was studied by applying concepts of high resolution seismic stratigraphy the estuarine sedimentary infill consists of a discontinuous basal interval overlain by five seismic units bounded by laterally continuous seismic horizons the correlation between seismic facies and a stratigraphic section of the guadiana valley enables the proposal of a detailed sequence stratigraphic interpretation of the estuarine infill during the last glacial lowstand the guadiana was a subaerial valley with no significant accumulation of fluvial deposits because of increased sediment bypass towards the present day middle and outer shelf towards the end of the postglacial transgression the subaerial valley was transformed into an estuary and sediments began preferentially accumulating in structural depressions furthermore flood tidal currents constrained by basement highs enhanced sand deposition in the upper part of the estuary wave influence was reduced and confined to the lower estuarine system here the narrow morphology of the valley led to an increased sediment export to the shelf during the holocene highstand period the lower part of the estuarine infill consists of four fifth order depositional sequences composed of regressive deposits hst the last glacial maximum is recorded by a distinct stratigraphic surface representing simultaneously the sequence boundary and the transgressive surface a tidal ravinement surface is characterized by strong erosion and channel formation in the outer estuarine zones the maximum flooding surface is identified by change of stratal patterns between landward prograding transgressive deposits and downlapping highstand deposits both transgressive tst and regressive tracts hst were deposited during the final part of the postglacial transgression and subsequent highstand

a crustal scale orogen parallel strike slip fault in the middle urals age magnitude of displacement and geodynamic significance the kinematic evolution of an orogen parallel strike slip fault in the middle urals demonstrates that orogen parallel mass transfer was an important previously underestimated process during the syncollisional evolution of the middle urals the kyshtym strike slip fault extends nne parallel and adjacent to the main uralian fault which is the main suture of the uralide orogen the kyshtym fault is interpreted as one of two conjugate strike slip fault zones that have accomodated the longitudinal transfer of material along the margins of a rigid indenter belonging to the east european craton the dextral kyshtym shear zone was active under retrograde lower amphibolite to middle lower greenschist facies conditions four metagranitic muscovite bearing mylonites yielded rb sr internal mineral isochron ages of 247 5 2 9 244 5 6 5 240 0 1 4 and 240 4 2 3 ma whereas a biotite rich sample without muscovite gave a mineral isochron age of 229 1 3 2 ma the results indicate almost complete sr isotopic reequilibration on the hand specimen scale during mylonitization the muscovite ages are interpreted as deformation ages and demonstrate a late permian early triassic age for the kyshtym shear zone the shear zone transects a pre orogenic syenite intrusion of ordovician age a maximum shear strain of 7 3 is estimated from the shape of the ductily deformed syenite body in map view and from the length width ratios of deformed amphibolite bodies in the country rock this shear strain suggests a maximum displacement of 28 12 km for the 4 km thick kyshtym shear zone a younger brittle fault oriented subparallel to the shear zone accomplished an additional horizontal displacement of 15 3 km thus the total displacement along the fault system is 43 15 km

timing of high grade metamorphism early palaeozoic u pb formation ages of titanite indicate long standing high t conditions at the western margin of gondwana argentina 26 29 s concordant u pb ages of c 530 510 ma and c 470 420 ma on titanite from calcsilicate orthogneiss and amphibolite rocks constrain the age of high t metamorphism in the early palaeozoic mobile belt at the western margin of proterozoic gondwana argentina 26 29 s the u pb ages document the time of titanite formation at high t conditions according to the stable mineral paragenesis and occurrence of titanite in the metamorphic fabric the presence of migmatite at all sample sites indicates temperatures were c 650 c titanite formed at similar metamorphic conditions at different times on the regional and on the outcrop scale the titanite crystals preserved their u pb isotopic signatures and chemical composition under ongoing upper amphibolite to granulite facies temperatures different thermal peaks or deformations are only detected by the different u pb ages and not by changes in the mineral paragenesis or metamorphic fabric of the samples the range of u pb ages e g in the ordovician and silurian c 470 460 440 430 420 ma is interpreted as the effect polyphase deformation with deformation enhanced recrystallization of titanite and or different thermal peaks during a long standing geographically fixed high t regime in the mid crust of a continental magmatic arc a clear correlation of the different ages with distinct tectonic events e g collision of terranes is not possible based on the present knowledge of the region

phase relations singularities and thermobarometry of metamorphic assemblages containing phengite chlorite biotite k feldspar quartz and h 2 o the phase relations of divariant and trivariant assemblages involving combinations of phengite chlorite biotite k feldspar quartz and h2o in the kfash kmash and kfmash systems were calculated using a single thermodynamic data set holland and powell 1998 the stability fields of the various equilibria are represented in p t projections by contouring sets of compositional isopleths for the tschermak al2 fe mg 1si 1 and femg 1 exchanges controlled by the coexisting phases five multivariant continuous equilibria which occur in different regions of p t x space are calibrated as thermobarometers in metamorphic rocks of pelitic to quartzofeldspathic composition more subtle p t information relating to the trajectories dt dz along which reacting rocks have been buried or exhumed can be extracted from the continuous reactions by investigating the recorded compositional trends in the al2 fe mg 1si 1 and femg 1 solutions singularities in p t space are associated with some of these reactions and may result in unusual mineral textures and compositional trends a fluid absent singularity has particular petrological significance because it marks the transition between hydration and dehydration along a single reaction with increasing pressure and temperature this behaviour causes the sequence of reactions among these minerals observed during metamorphism to be critically dependent on the p t trajectory thermobarometric calculations show good agreement with respect to experimental and field based data for phengite compositions less than about 50 mol celadonite 3 5 si p f u phengite

formation and fate of sedimentary depocentres on southeast asia s sunda shelf over the past sea level cycle and biogeographic implications abstract sea level variations are the major factor controlling sedimentation as well as the biogeographic patterns at continental margins over late quaternary times fluctuations on millennial time scales produce locally complex deposits in coasts and on shelves associated with short term influence on species development this article reviews the sedimentary and biogeographic history of the tropical siliciclastic sunda shelf as an end member of continental shelves regarding extreme width an enormous sediment supply and highest biodiversity in response to rapid sea level fluctuations we describe particular depositional segments as part of a genetic succession of zones from land to the deep sea based on literature data field observations and calculation of hydro isostatic adjustment effects on changing relative sea level these segments are characterized by individual sedimentary processes and deposits and by a specific potential for material storage and re mobilization long term regressive intervals led to overall sigmoidal promoting extremely thick and wide succeeding units in contrast rapid lateral shifts of defined depocentres over long distances took place in response to short term sea level fluctuations fully isolated small scale sediment bodies formed when sea level changed at exceptionally high rates as a result of the high availability of organic rich sediments mangrove and freshwater peats formed frequently over late quaternary times the appearance of thick massive and widespread peats is mainly linked to time intervals of a sea level rise at slow rates whilst organic matter appears much more dispersely in the sediments during episodes of rapidly changing sea level the preservation potential of the regressive units is generally high due to highest initial sediment supply stabilizing soil formation during exposure and rapid subsidence preservation of depositional elements from other periods is more exceptional and either restricted to local morphological depressions or to episodes of rapid sea level change besides complex channel incision an overall lowering of the sediment surface related to erosion as deep as 20 m or more over wide areas took place mainly during sea level lowering the final export of shelf material is documented by enormous mass wasting packages on the associated continental slope from a palaeogeographic perspective the rapid formation or disappearance of special habitat zones such as mangrove fringes and extended mud flats led to species establishment or truncation in distribution in addition the opening or closure of ocean passages as narrow bridges allowing limited species crossing or as fully colonized corridors had severe impact on eco fragmentation and the expansion or contraction of species independent of such particular conditions sea level changes have been too rapid over the past climatic cycle to allow full regeneration and mature development of coast related ecosystems

seasonal subsidence and rebound in las vegas valley nevada observed by synthetic aperture radar interferometry analyses of areal variations in the subsidence and rebound occurring over stressed aquifer systems in conjunction with measurements of the hydraulic head fluctuations causing these displacements can yield valuable information about the compressibility and storage properties of the aquifer system historically stress strain relationships have been derived from paired extensometer piezometer installations which provide only point source data because of the general unavailability of spatially detailed deformation data areal stress strain relations and their variability are not commonly considered in constraining conceptual and numerical models of aquifer systems interferometric synthetic aperture radar insar techniques can map ground displacements at a spatial scale of tens of meters over 100 km wide swaths insar has been used previously to characterize larger magnitude generally permanent aquifer system compaction and land subsidence at yearly and longer timescales caused by sustained drawdown of groundwater levels that produces intergranular stresses consistently greater than the maximum historical stress we present insar measurements of the typically small magnitude generally recoverable deformations of the las vegas valley aquifer system occurring at seasonal timescales from these we derive estimates of the elastic storage coefficient for the aquifer system at several locations in las vegas valley these high resolution measurements offer great potential for future investigations into the mechanics of aquifer systems and the spatial heterogeneity of aquifer system structure and material properties as well as for monitoring ongoing aquifer system compaction and land subsidence

prism and basal plane parallel subgrain boundaries in quartz a microstructural geothermobarometer empirical data on quartz subgrain patterns from various metamorphic rocks show that at least up to 10 kbar in the stability field of low quartz prismatic subgrain boundaries are dominant whereas basal subgrain boundaries are not developed in the high quartz stability field both prismatic and basal subgrain boundaries occur and form typical rectangular chessboard patterns the likely reason behind the different occurrence of these subgrain patterns is that in high quartz prismatic glide becomes as easy as or probably even easier than basal glide the two types of subgrain patterns can be clearly distinguished by optical microscopy consequently the occurrence of chessboard subgrain patterns in quartz represents a practicable geothermobarometer the possibilities of its application are far reaching and include the specification of deformation conditions at high grade metamorphism the recognition of syntectonic intrusions and the distinction between pluton emplacement at lower and at higher crustal levels

marine transgression and regression in miocene sequences of northern pegu bago yoma central myanmar abstract neogene strata of the northern part of the pegu bago yoma range central myanmar contain a series of shallow marine clastic sediments with stratigraphic ages ranging from the early to late miocene the studied succession around 750 m thick is composed of three major stratigraphic units deposited during a major regression and four major transgressive cycles in the early to late miocene the transgressive deposits consist of elongate sand bars and broad sand sheets that pass headward into mixed flats of tidal environments marine flooding in transgressive deposits is associated with coquina beds and allochthonous coral bearing sandy limestone bands major marine regressions are associated with lowstand progradation of thick estuary point bars passing up into upper sand flat sand bodies encased within the tidal flat sequences and lower shoreface deposits with local unconformities the succession initially formed in a large scale incised valley system and was later interrupted by two major marine transgressions in the generally regressive or basinward stepping stratigraphic sequences successive sandbodies were formed during a sea level lowstand and early stage of the subsequent relative rise of sea level in a tide dominated estuary system in the eastern part of the central myanmar tertiary basin during early to late miocene times

residual transport model in correlation with sedimentary dynamics over an elongate tidal sandbar in the gironde estuary southwestern france abstract this study qualitatively describes by a multidisciplinary approach hydrodynamic and residual sediment transport over a sandbar in a macrotidal environment the sandbar is elongated and attached to a headland that is located in the gironde estuary southwestern france bathymetric surveys side scan sonar sonograms grain size trends of surficial sediment and 2dh numerical simulations of current patterns were used to define a conceptual model for the dynamics of this sandbar the sandbar is oriented anticlockwise with respect to the main flow the channel oriented bar face is ebb dominated whereas the opposite face is flood dominated resulting in a clockwise residual transport the line of sediment flux convergence corresponds to the crest of the bar the residual flow over the bar appears to originate from the regional estuarine flow the dominant process responsible for the maintenance of the sandbar seems to be the depth averaged main tidal flow rather than secondary circulation due to headlands or the interaction between the tidal flow and the seabed to generalize this regional conceptual model a qualitative comparison is made with the theories of sandbar dynamics due to tidal currents pingree and maddock 1979 zimmerman 1981 huthnance 1982 and others the seabed stability approach developed by huthnance 1982 seems to be the most reliable theory to explain the saint georges bank dynamics even though many natural factors are not taken into account

estuarine infill and coastal progradation southern van diemen gulf northern australia abstract there are several estuaries associated with the pronouncedly seasonal rivers which drain northwards from the middle proterozoic sandstone arnhem land plateau and the tertiary koolpinyah land surface into the macrotidal van diemen gulf in the northern territory of australia the holocene development of these investigated in greatest detail for the south alligator river with an upland catchment of 10 000 km2 through drilling palynology and radiocarbon dating comprises both estuarine infill and coastal progradation three phases of estuarine infill can be recognised i a transgressive phase 8000 6800 years b p of marine incursion ii a big swamp phase 6800 5300 years b p of widespread mangrove forest development and iii a sinuous cuspate phase of floodplain development since 5300 years b p during which the tidal river has meandered and reworked earlier estuarine sediments since 6000 years b p the south alligator coastal plain has prograded at a decelerating rate with two phases of chenier ridge formation a similar pattern of estuarine infill and decelerating coastal plain progradation is demonstrated for the adelaide and mary rivers both with catchments of 6000 km2 the southern shore of van diemem gulf appears to have changed its overall position little during the last 2000 years the major source for the clay silt and fine sands which have infilled the estuary and coastal plain has been from seaward dispite the similarity of development coastal sediment build up has had different effects on the morphology of each tidal river the adelaide has undergone a major diversion and no longer flows directly into van diemen gulf but occupies a former fluvial course and the mary has been blocked entirely and its former estuarine palaeochannels have been infilled with tide transported sediment

transgressive changes from tidal estuarine to marine embayment depositional systems the lower cretaceous woburn sands of southern england and comparison with holocene analogs the lower cretaceous woburn sands lower greensand group in southern england constitutes one of the most intensively studied tidal sandstone outcrops for sedimentological and reservoir analog studies most recent workers have interpreted the whole 30 60 m 100 200 ft thick succession around leighton buzzard as representing an ancient tide dominated estuary however unequivocal estuary characteristics are limited to the lowermost part about 15 20 m 50 66 ft we suggest that a significant portion of the woburn sands and most of the middle part was formed in a tide dominated marine embayment hence the vertical facies change from the lower to middle part of the woburn sands is interpreted as a change from 1 a narrow estuary to 2 a broad marine embayment the wash embayment in eastern england is a striking modern analog it receives most of its sediments and waters from marine sources and is largely filled with nondiluted seawater moreover the holocene transgressive history of the wash is remarkably similar to the transgressive evolution of the woburn sands early estuarine sequence models predict landward translation of facies zones along the valley thalweg during transgression but eventual facies translation in the strike direction has not been fully documented or discussed an embayment facies that is not commonly confined in the early incised valley can occur vertically between the estuarine valley fill and marine shelf deposits and is probably underrepresented in current models however this segment of the transgression comprising along strike bay expansion and the development of a broad marine embayment may be more important than previously thought

sedimentary controls on modern sand grain coat formation abstract coated sand grains can influence reservoir quality evolution during sandstone diagenesis porosity can be reduced and fluid flow restricted where grain coats encroach into pore space conversely pore lining grain coats can restrict the growth of pore filling quartz cement in deeply buried sandstones and thus can result in unusually high porosity in deeply buried sandstones being able to predict the distribution of coated sand grains within petroleum reservoirs is thus important to help find good reservoir quality here we report a modern analogue study of 12 sediment cores from the anllons estuary galicia nw spain collected from a range of sub environments to help develop an understanding of the occurrence and distribution of coated grains the cores were described for grain size bioturbation and sedimentary structures and then sub sampled for electron and light microscopy laser granulometry and x ray diffraction analysis the anllons estuary is sand dominated with intertidal sand flats and saltmarsh environments at the margins there is a shallowing fining upwards trend in the estuary fill succession grain coats are present in nearly every sample analysed they are between 1 m and 100 m thick and typically lack internal organisation the extent of grain coat coverage can exceed 25 in some samples with coverage highest in the top 20 cm of cores samples from muddy intertidal flat and the muddy saltmarsh environments close to the margins of the estuary have the highest coat coverage mean coat coverage of 20 2 and 21 3 respectively the lowest mean coat coverage occurs in the sandy saltmarsh 10 4 beyond the upper tidal limit and sandy intertidal flat environments 8 4 close to the main estuary channel mean coat coverage correlates with the concentration of clay fraction the primary controls on the distribution of fine grained sediment and therefore grain coat distribution are primary sediment transport and deposition processes that concentrate the clay fraction in the sediment towards the margins of the estuary bioturbation and clay illuviation mechanical infiltration are secondary processes that may redistribute fine grained sediment and produce grain coats here we have shown that detrital grain coats are more likely in marginal environments of ancient estuary fills which are typically found in the fining upward part of progradational successions

aquifer mechanical properties and decelerated compaction in tucson arizona in recent decades high groundwater extraction rates often coincident with periods of severe drought result in the widespread decline of water levels overexploitation of aquifers also causes land subsidence which poses a severe threat to infrastructure tucson arizona experiences land subsidence coupled with the depletion of groundwater a critical water resource for the desert city to understand the spatiotemporal evolution of land subsidence and its implications for aquifer properties we examine long time series of surface deformation and head levels measurements at extensometer stations indicate rapid compaction of fine grained material up to 8 5 mm yr from 1990 to 2005 which results in permanent storage volume losses up to 4 1 the analysis of densely populated sets of interferograms generated from envisat and radarsat c band acquisitions yields multitemporal maps of surface deformation at unprecedented resolution these maps reveal that subsidence significantly slows by the late 2000s corresponding with the implementation of artificial recharge efforts subsequent to groundwater level recovery we observe a brief 6 6 year interval of residual compaction suggesting a high vertical hydraulic conductivity which is then shown to be up to 9 8x10 4 m day we also estimate the average elastic and inelastic skeletal storage coefficients for the aquifer system to be 3 78x10 3 and 6 01x10 3 respectively insar shows deformation nearly ceases by 2015 likely reducing hazards associated with earth fissuring and infrastructure damage this study highlights successful outcomes of water management and conservation plans that preserve existing groundwater reserves and increase artificial recharge

ordovician metamorphism and plutonism in the sierra de quilmes metamorphic complex implications for the tectonic setting of the northern sierras pampeanas nw argentina towards unravelling the geodynamic setting of the northern sierras pampeanas nw argentina we describe the tectono metamorphic and geochronologic evolution of sub greenschist to granulite facies metamorphic sediments granitoid plutons and pegmatites in the ordovician sierra de quilmes metamorphic complex the protoliths of the metasediments are represented by a sequence of turbidites and minor calcsilicate rocks of the neoproterozoic to cambrian puncoviscana formation the metamorphic complex consists of four zones including the 1 chlorite 2 biotite muscovite 3 garnet cordierite sillimanite and 4 orthopyroxene zones zones 3 and 4 show an increasing degree of anatexis reaching large scale diatexis in the orthopyroxene zone at p t conditions exceeding 800 c and 600 mpa at or shortly after the metamorphic peak the granitic to tonalitic cafayate pluton intruded approximately along the boundary between anatectic and non anatectic rocks retrograde near isobaric cooling of the middle crust was accompanied by non penetrative ductile shearing at granulite to amphibolite facies p t conditions evidence for significant prograde deformation is absent in the sierra de quilmes metamorphic complex monazite and titanite u pb isotopic data constrain the metamorphic peak in migmatites and calcsilicate rocks to be at or slightly prior to 470 ma retrograde amphibolite facies mineral reactions led to continuous formation of monazite and titanite during slow cooling between 470 ma and 455 ma u pb data the composite cafayate pluton intruded over a time interval of several million years between 477 ma sm nd isochron and 460 ma monazite and titanite u pb isochron followed by pegmatites a younger group of pegmatites was emplaced in the country rocks at the end of the ordovician 440 ma rb sr mineral isochrons postdating most of the retrograde shear zones resetting of the muscovite k ar and 40ar 39ar system in weakly deformed pegmatites and crystallisation of new muscovite in low grade metamorphic sediments at 400 416 ma is attributed to minor late greenschist and sub greenschist facies metamorphism and deformation the massive early ordovician heat transfer the absence of major prograde deformation and subsequent prolonged phases of non penetrative deformation in the high grade metamorphic zones during slow near isobaric cooling contradict crustal thickening and continent collision models as have been proposed for the southern sierras pampeanas we suggest continuous or stepwise extensional tectonics in a back arc or a mobile belt tectonic environment for the ordovician sierra de quilmes and the northern sierras pampeanas in general an extensional setting of the northern sierras pampeanas in the ordovician is in agreement with the coeval formation of marine extensional sediment basins in vicinity of the sierras pampeanas in northwestern argentina and southern bolivia

rb sr geochronology of granitoid rocks from the pampean ranges argentina a reconnaissance rb sr geochronological investigation of granitoid rocks from the pampean range provides a framework whereby four culminations of igneous activity are delineated granitoids emplaced prior to 500 ma pre and synkinematic bodies ca 475 ma late kinematic bodies and ca 440 and 340 ma post kinematic bodies a number of the post kinematic granitoids have disturbed sr isotope systematics which is related to the formation of microcline megacrysts the carboniferous granitoids are distinguished by their high initial sr ratios i e 0 710 a feature compatible with an origin involving reworking of upper crust or crustal contamination there appears to be no systematic e w migration of granitoid emplacement during the ca 300 ma evolution of the basement rocks in the pampean ranges

textural chemical and isotopic insights into the nature and behaviour of metamorphic monazite monazite is a mineral of choice for dating metamorphism in amphibolite and granulite grade metapelites however there exist a number of difficulties that complicate the interpretation of monazite geochronological data and prevent its application to many geological problems the two main obstacles addressed in this contribution are firstly the minor but significant e g 1 30 ma dispersal in duplicate isotope dilution thermal ionisation mass spectrometry id tims u pb age data commonly recorded from a single rock and secondly the difficulty of attaching monazite age data to pressure and temperature information through a multidisciplinary approach utilising tims and laser ablation multicollector inductively coupled plasma mass spectrometry la mc icpms isotope data quantitative and qualitative emp chemical analyses of monazite and textural studies we assess the significance of pb loss older components and continuous and episodic monazite growth in the generation of dispersed age data three samples from the canadian cordillera and one sample from the himalaya of pakistan are examined each sample exhibits an age dispersion of between 1 and 12 ma for single crystal and multi grain tims u pb monazite age determinations consideration of the closure temperature for pb diffusion in monazite and the metamorphic temperatures experienced by these samples suggests diffusive pb loss did not play a significant part in generating this age dispersal the la mc icpms study indicates that an older component 100 ma older than the tims ages contributed to the age dispersal in three of the four samples in all the samples however chemical analyses identified that the majority of monazites examined exhibited significant intra crystalline zoning in y content the la mc icpms analysis of one sample that was constrained to zones of distinct y content indicates that these zones are of distinct age we suggest that monazite grown before the appearance of garnet and during garnet breakdown is relatively rich in y whereas monazite grown after garnet is relatively poor in y a combination of these chemical data with textural observations suggests that once monazite had entered the mineral assemblage it grew or recrystallised episodically throughout the prograde and retrograde paths of the metamorphic event this behaviour contributes to and in one of the samples controls the observed age dispersal this recognition allows the generation of pressure temperature time points by combining textural and chemical information of monazite with in situ age determinations and pressure temperature information from garnet thus the episodic growth of compositionally distinct monazite throughout a metamorphic event provides the geochronologist with a very valuable chronological tool

early paleozoic accretionary orogenies in nw argentina growth of west gondwana abstract two early paleozoic orogenic cycles in the gondwana margin of nw argentina were driven by subduction and interrupted by collision of continental ribbons of laurentian affinity subduction started at the passive margin of gondwana possibly in response to the end of amalgamation of the supercontinent the passive margin was underlain by a hyper extended continent ocean transition and low angle subduction gave rise to a wide and hot fore arc region during the pampean orogenic cycle the arrival of the first continent ribbon ended the pampean cycle steepened the subduction further heating the fore arc and restarting arc magmatism after a magmatic lull 250 300 km trenchwards initiating the famatinian orogenic cycle this cycle started with a 30 ma long period of extension and marine sedimentation followed by the arrival of the second continent ribbon and inversion the back arc initiating a 20 ma long shortening event culminating with the shutting down of the arc this event gave rise to a 300 km wide low topography hot orogeny thus the many peculiarities of the two paleozoic orogens of nw argentina result from a subduction history that efficiently transferred heat to a 300 400 km wide belt of turbidite dominated sediments that was first part of the pampean fore arc and then part of the famatinian retroarc developed at the extended continental margin of gondwana the two orogenies with continued high heat flux lasted 110 ma giving rise to two calc alkaline arcs separated by a 300 km belt of high t low p migmatites and peraluminous granites formed by anatexis of sediments deposited on the passive margin as well as those deposited in the wide pampean fore arc these turbidite dominated sequences were metamorphosed and melted to form a continental crystalline basement and accreted to the cratonic margin adding 500 km of crystalline rocks to the margin of gondwana at the same time that a similar process was happening in eastern australia along the same continental margin interestingly this wide accretionary orogen has now become the region where the andean system developed a wide orogeny above flat slab subduction