neogene tectonic evolution and exhumation of the southern ecuadorian andes a combined stratigraphy and fission track approach abstract coastal marine and continental sedimentary facies of middle to late miocene age are exposed in the andes of southern ecuador cuenca giron santa isabel loja malacatos vilcabamba and catamayo gonzanama basins the chronostratigraphy of the basin series was established by zircon fission track dating on a total of 120 tephra layers subsequently the timing of tectonic events was estimated through the well dated stratigraphic sequences and intervening unconformities sedimentation from 15 to 9 ma termed pacific coastal stage was dominantly of coastal marine type extending over an area far greater than the present basin perimeters it ended when a period of east west oriented compression at 9 5 8 ma exhumed the region and sedimentation was then restricted to smaller basins termed intermontane stage these late miocene continental sediments were for the first time sourced from the west in the rising western cordillera apatite fission track analysis was applied to some of the tephras in the cuenca basin and also to the older eocene 42 35 ma quingeo basin series in order to quantify the basin histories with respect to timing and amount of burial and later exhumation in the quingeo basin burial of the oldest sediments reached temperatures of 100 c at 18 ma when they started to cool down during a period of exhumation this process preceded the pacific coastal stage development of the other basins in the cuenca basin the oldest sediments were buried to temperatures of ca 120 c by 9 ma when a period of inversion began and a phase of erosion was dominant this timing correlates well with that estimated from structural evidence at ca 6 ma the cooling rate slowed down and maybe even reverted to a small increase in temperature until 3 ma when the final stages of exhumation took place assuming a geothermal gradient of 35 c km total uplift for this part for ecuador is about 6100 m over the last 9 million years assuming a steady state continuous movement this means a mean rock uplift rate of 0 7 mm yr and a surface uplift of 0 3 mm yr to the present

late neogene sequence stratigraphic evolution of the foz do amazonas basin brazil the margin of the foz do amazonas basin saw a shift from predominantly carbonate to siliciclastic sedimentation in the early late miocene by this time the amazon shelf had also been incised by a canyon that allowed direct influx of sediment to the basin floor thus confirming that the palaeo amazon fan had already initiated by that time 9 5 8 3 ma above this interval during a prolonged lowstand messinian third order sequences are preserved only in the incised valley fills of the canyon with no equivalent strata on the shelf third and fourth order sequences younger than messinian are preserved on the shelf after sea level rise above the shelf by the early pliocene sequences younger than 3 8 ma often show fourth order cyclicity with an average duration of 400 ka larger scale eccentricity cycles often preserved in high sedimentation rate areas of river deltas mass wasting and transportation of slope sediments to the basin began to play an important role in sediment dispersal at least as far back as the mid pliocene after rapid progradation had produced steeper slopes more prone to failure

stratigraphic responses to a major tectonic event in a foreland basin the ecuadorian oriente basin from eocene to oligocene times the eocene to oligocene sediments of the ecuadorian oriente basin record two kinds of second order stratigraphic response to the tectonic evolution lower eocene shows evidences of local scale syntectonic deposits this tectonic activity can be related to right lateral convergent movements inverting pre cretaceous extensional structures upper eocene and oligocene sediments are integrated as the expression of an isostatic rebound characterizing a basin scale syntectonic deposition this response is evidenced by a reciprocal architecture of the depositional sequences identified in the sedimentary formations these data have allowed us to propose a new geodynamic model for the paleogene evolution of the oriente basin

low temperature thermochronology of the northern cordillera real ecuador tectonic insights from zircon and apatite fission track analysis the post early cretaceous tectonic development of the northern andean segment north of 5 s is loosely constrained by a series of partially and fully reset k ar ages new apatite and zircon fission track data from three traverses across the cordillera real of ecuador reveal distinct periods of accelerated crustal cooling during the cenozoic fission track ages range from 65 to 14 ma zircon and 44 to 8 ma apatite with apatite mean track lengths ranging from 14 6 to 12 1 m these results record rapid cooling rates during 43 30 ma 23 15 ma and 10 0 ma occurring at temperatures below 275 c the events reflect up to 9 km of crustal exhumation in various regions of the cordillera in response to relative changes in the kinematics of the farallon nazca and south american plates the exhumation history of the cordillera real was not continuous but rather evolved during separate phases these phases persisted for 10 myr and are partly coincident with tectonic phases of the central andes although extend for longer time periods possibly as a result of isostatically driven crustal exhumation large spatial variations in the zircon and apatite fission track data within the cordillera real indicate that local fault bounded massifs have experienced different thermal histories since 43 ma major variations are not restricted to the regional scale and exist within individual terranes faulted slivers within terranes demonstrate highly variable exhumation histories suggesting that deformation was not dominated by terrane bounding faults additionally n s variations in exhumation depths suggest that ne sw trending faults have been active since 10 9ma

gravity wave excitation during the coastal transition of an extreme katabatic flow in antarctica abstractthe offshore extent of antarctic katabatic winds exerts a strong control on the production of sea ice and the formation of polynyas in this study we make use of a combination of ground ba

tracking spatial variation in river load from andean highlands to inter andean valleys abstract mountains play an important role in the denudation of continents and transfer erosion and weathering products to lowlands and oceans the rates at which erosion and weathering processes take place in mountain regions have a substantial impact on the morphology and biogeochemistry of downstream reaches and lowlands the controlling factors of physical erosion and chemical weathering and the coupling between the two processes are not yet fully understood in this study we report physical erosion and chemical weathering rates for five andean catchments located in the southern ecuadorian andes and investigate their mutual interaction during a 4 year monitoring period we sampled river water at biweekly intervals and we analyzed water samples for major ions and suspended solids we derived the total annual dissolved suspended sediment and ionic loads from the flow frequency curves and adjusted rating curves and used the dissolved and suspended sediment yields as proxies for chemical weathering and erosion rates in the 4 year period of monitoring chemical weathering exceeds physical erosion in the high andean catchments whereas physical erosion rates do not exceed 30 t km 2 y 1 in the relict glaciated morphology chemical weathering rates range between 22 and 59 t km 2 y 1 the variation in chemical weathering is primarily controlled by intrinsic differences in bedrock lithology land use has no discernible impact on the weathering rate but leads to a small increase in base cation concentrations because of fertilizer leaching in surface water when extending our analysis with published data on dissolved and suspended sediment yields from the northern and central andes we observe that the river load composition strongly changes in the downstream direction indicating large heterogeneity of weathering processes and rates within large andean basins

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

relative motion of the nazca farallon and south american plates since late cretaceous time by combining reconstructions of the south american and african plates the african and antarctic plates the antarctic and pacific plates and the pacific and nazca plates we calculated the relative positions and history of convergence of the nazca and south american plates despite variations in convergence rates along the andes periods of rapid convergence averaging more than 100 mm a between the times of anomalies 21 49 5 ma and 18 42 ma and since anomaly 7 26 ma coincide with two phases of relatively intense tectonic activity in the peruvian andes known as the late eocene incaic and mio pliocene quechua phases the periods of relatively slow convergence 50 to 55 30 mm a at the latitude of peru and less farther south between the times of anomalies 30 31 68 5 ma and 21 and between those of anomalies 13 36 ma and 7 correlate with periods during which tectonic activity was relatively quiescent thus these reconstructions provide quantitative evidence for a correlation of the intensity of tectonic activity in the overriding plate at subduction zones with variations in the convergence rate

cenozoic thermal evolution and tectonics of the coast mountains of british columbia 1 fission track dating apparent uplift rates and patterns of uplift the high relief of the coast mountains of british columbia has been produced in part by rapid late neogene uplift the relationship of this uplift to the presently diverse and complex plate tectonic regime off the west coast of british columbia however is not clear cut to study this problem the areal patterns rates and total amounts of cenozoic uplift from 50 to 55 n have been determined by using fission track dating of zircon and apatite separated from rocks collected at high and low altitudes along several traverses through the mountains accepting closure temperatures of 105 c 10 c and 175 c 20 c for apatite and zircon respectively and a likely closure temperature difference between zircon and apatite of 70 15 c paleogeothermal gradients have been measured at kemano c km 35 ma ago and near ocean falls king island c km 20 ma ago subcrustal heat flow is suggested to have significantly increased in the late neogene near king island uplift rates in the axial part of the northern 52 55 n coast mountains were 0 1 0 2 km ma from 25 to 15 ma ago this uplift was temporally and tectonically related to part of the subsidence in the adjacent queen charlotte basin uplift rates increased somewhat in the late miocene to about 0 4 km ma probably due to passage of the anahim hot spot beneath the area late miocene recent erosion in the north 52 55 n has reduced summit altitudes and been more extensive than farther south despite this relicts of miocene river valleys and topography are still locally preserved partly beneath 7 10 ma basalts the area of the present southern 50 to 52 n coast mountains was near sea level and experienced very low uplift rates 0 5 km ma of the southern coast mountains the profile of this uplift was broadly plateaulike and this uplift led to the inversion of the miocene coastal topography middle cenozoic uplift from 52 to 55 n was probably the result of denudation and diminishing uplift after the terminal paleocene eocene orogenic episode which grossly thickened the crust this middle cenozoic erosion resulted in the restoration of a normal crustal thickness late neogene uplift in the coast mountains was the result of thermal expansion in the mantle caused by a mantle hot spot near 53 n and changes in the geometry of the subducted slab farther south

observations and fine scale model simulations of gravity waves over davis east antarctica 69 s 78 e large vertical velocities were observed throughout the troposphere at davis east antarctica on 18 february 2014 by a vhf wind profiling radar simulations using the met office unified model at 2 2 0 5 and 0 1 km horizontal grid spacing were able to broadly capture the location timing and magnitude of the observed velocities as well as reveal that they are due to small scale orographic gravity waves resulting from the interaction between the coastal topography and strong easterly winds associated with a synoptic scale cyclone situated to the north the simulations indicated that the gravity waves are responsible for i temperature fluctuations which coincided with satellite observed cloud variations in the vicinity of davis suggesting that they have a crucial role in the formation of cirrus clouds and ii large vertical momentum fluxes in the troposphere the waves are prevented from propagating into the stratosphere by the background winds turning from near surface easterlies to lower stratospheric northerlies as well as illuminating and quantifying the role that weather systems have in producing orographic gravity waves along the east antarctic coastline studies such as this should be exploited to improve the representation of key localized atmospheric processes in global climate models

thermochronology of lower cretaceous source rocks in the idaho wyoming thrust belt lower cretaceous organic rich source rocks that are thermally mature to postmature crop out on the absaroka darby and prospect plates in linear belts that run parallel to the trace of the thrusts in the idaho wyoming portion of the idaho wyoming utah thrust belt although the common assumption is that burial by thrust plates and the synorogenic sediments derived from them have been responsible for thermal maturation of the organic rich strata commercial amounts of hydrocarbons have not been found in structural traps in this portion of the thrust belt in a companion paper burtner and nigrini demonstrated that gravity driven fluid flow in the idaho wyoming portion of the thrust belt was responsible for moving large amounts of heat from the depths of the early cretaceous foreland basin eastward toward the stable platform in this paper we demonstrate through the application of organic maturation indicators and a new refinement of the apatite fission track technique that this process heated lower cretaceous organic rich source rocks to temperatures sufficient to generate hydrocarbons hydrocarbon generation and migration occurred prior to the development of the thrusts that are often assumed to have played a major role in the generation and entrapment of hydrocarbons in this portion of the thrust belt

thermochronology of allochthonous terranes in ecuador unravelling the accretionary and post accretionary history of the northern andes the western cordilleras of the northern andes north of 5 s are constructed from allochthonous terranes floored by oceanic crust we present 40ar 39ar and fission track data from the cordillera occidental and amotape complex of ecuador that probably constrain the time of terrane collision and post accretionary tectonism in the western andes the data record cooling rates of 80 2 c my from temperatures of 540 c during 85 to 60 ma in a highly tectonised melange pujili unit at the continent ocean suture and in the northern amotape complex the rates were highest during 85 80 ma and decelerated towards 60 ma cooling was a consequence of exhumation of the continental margin which probably occurred in response to the accretion of the presently juxtaposing pallatanga terrane the northern amotape complex and the pujili unit may have formed part of a single regional scale tectonic melange that started to develop at 85 ma part of which currently comprises the basement of the interandean depression cooling and rotation in the allochthonous continental amotape complex and along parts of the continent ocean suture during 43 29 ma record the second accretionary phase during which the macuchi island arc system collided with the pallatanga terrane distinct periods of regional scale cooling in the cordillera occidental at 13 and 9 ma were synchronous with exhumation in the cordillera real and were probably driven by the collision of the carnegie ridge with the ecuador trench finally late miocene pliocene reactivation of the chimbo toachi shear zone was coincident with the formation of the oldest basins in the interandean depression and probably formed part of a transcurrent or thrust system that was responsible for the inception and subsequent growth of the valley since 6 ma

characteristics of mesospheric gravity waves over antarctica observed by antarctic gravity wave instrument network imagers using 3 d spectral analyses we have obtained horizontal phase velocity distributions of the gravity waves around 90 km from four antarctic airglow imagers which belong to an international airglow imager instrument network known as angwin antarctic gravity wave instrument network results from the airglow imagers at syowa 69 s 40 e halley 76 s 27 w davis 69 s 78 e and mcmurdo 78 s 167 e were compared using a new statistical analysis method based on 3 d fourier transform matsuda et al 2014 for the observation period between 7 april and 21 may 2013 significant day to day and site to site differences were found the averaged phase velocity spectrum during the observation period showed preferential westward direction at syowa mcmurdo and halley but no preferential direction at davis gravity wave energy estimated by i i was 5 times larger at davis and syowa than at mcmurdo and halley we also compared the phase velocity spectrum at syowa and davis with the background wind field and found that the directionality only over syowa could be explained by critical level filtering of the waves this suggests that the eastward propagating gravity waves over davis could have been generated above the polar night jet comparison of nighttime variations of the phase velocity spectra with background wind measurements suggested that the effect of critical level filtering could not explain the temporal variation of gravity wave directionality well and other reasons such as variation of wave sources should be taken into account directionality was determined to be dependent on the gravity wave periods

cenozoic plate kinematics subduction and magmatism south american andes revised plate reconstructions and enlarged isotopic age data sets strongly support three mechanisms for controlling the configuration and associated volcanism and tectonism of the andean subduction zone these include age of subducted plate convergence rate and interaction with hotspot traces from 50 to 25 ma in the andes the age of oceanic plate subducted progressively decreased apparently resulting in a9gradual decrease in subduction angle and consequent eastward shift in the loci of magmatic activity a major reorganization of plate motions at 25 ma resulted in an increased convergence rate normal to the chilean andes and was accompanied by subsequent broadening of the locus of magmatic activity into adjacent portions of bolivia and argentina convergence rates changed only slightly across the peruvian margin and no clear effect on subsequent magmatism is indicated interaction of the andean subduction zone with the juan fernandez and easter nazca hotspot traces apparently resulted in lower angle subduction and consequent gaps in magmatic activity as predicted continuations of the traces correspond with regions lacking dated volcanic rocks the current gaps in igneous activity correspond with contemporary subduction of the two traces and this association apparently occurred in the past as well

an integrated study of fill and deformation in the andean intermontane basin of nabon late miocene southern ecuador abstract the nabon basin is part of several miocene intermontane basins related to andean uplift continental arc formation and coeval deformation during subduction of the nazca plate under the south american continent the basin sequence consists of fluvial alluvial fan lacustrine and pyroclastic mass flow deposits corresponding with intereruptive and syneruptive stages of basin fill history combined zircon fission track and palaeomagnetic measurements suggest that the series lies within the 4r chron ca 8 5 7 9 ma it overlies unconformably the ignimbrite basement dated at ca 26 19 ma synsedimentary tectonic deformation in the basin is manifested by a master reverse fault along the western margin differential basement block uplift and related sedimentary bedding geometries such as cumulative sedimentary wedges the spatial orientation of the tectonic and sedimentary features indicates that the basin underwent wnw ese maximal shortening during the fill stage the short lived sediment fill history may be explained either by subduction related contractional pulses also recognized in the peruvian and colombian andes or by the particular position of the basin in the central axial part near the weak fault of a regional translational system

the gcm response to current parameterizations of nonorographic gravity wave drag abstract a comparison is undertaken of the response of a general circulation model gcm to the nonorographic gravity wave drag parameterizations of hines warner and mcintyre and alexander and dunkerton the analysis is restricted to a comparison of each parameterization s nonlinear dissipation mechanism since in principle this is the only component that differs between the schemes this is achieved by developing a new more general parameterization that can represent each of these dissipation mechanisms while keeping all other aspects of the problem identical the gcm simulations reveal differences in the climatological response to the three dissipation mechanisms these differences are documented for both tropopause and surface launch elevations of the parameterized waves the simulations also reveal systematic differences in the height at which momentum is deposited this behavior is investigated further in a set of experiments designed to reduce these systematic differences while leaving the det

geochemistry and tectonic setting of pre collision cretaceous and paleogene volcanic rocks of ecuador pre collision cretaceous lower tertiary volcanic rocks of western ecuador from the coastal area pinon and san lorenzo formations and western cordillera macuchi and celica formations consist of three rock suites the first suite includes tholeiites of ocean floor affinities that have distinct light ree depleted patterns and low la nb la hf and th hf ratios the island arc tholeiites of the second suite have lower contents of ti zr hf and nb the third suite comprises calc alkalic rocks mainly continental margin andesites and dacites the continental volcanic arc rocks crop out in an area east of the tholeiitic rocks the boundary between the two areas is the major suture separating continental south america from accreted terrenes to the west a model is suggested for the geodynamic evolution of what is now western ecuador during the late cretaceous it includes two east dipping subduction zones of turonian to santonian ages and the accretion of the oceanic island arc to the continent

transient river response captured by channel steepness and its concavity mountain rivers draining tropical regions are known to be great conveyor belts carrying efficientlymore than half of the global sediment flux to the oceans many tropical mountain areas are located in tectonically active belts where the hillslope and stream channel morphology are rapidly evolving in response to changes in base level here we report basin wide denudation rates for an east west transect through the tropical andes hillslope and channel morphology vary systematically fromeast towest reflecting the transition from high relief strongly dissected topography in the escarpment zones into relatively low relief topography in the inter andean valley the spatial pattern of differential denudation rates reflects the transient adjustment of the landscape to rapid river incision following tectonic uplift and river diversion in the inter andean valley upstream of the wave of incision slopes and river channels display a relatively smooth concave up morphology and denudation rates time scale of 104 105 a are consistently low 3 to 200 mm ka in contrast slopes and river channels of rejuvenated basins draining the eastern cordillera are steep to very steep and the studied drainage basins show a wide range of denudation rate values 60 to 400 mm ka that increase systematically with increasing basin mean slope gradient channel steepness and channel convexity drainage basins that are characterised by strong convexities in their river longitudinal profiles systematically have higher denudation rates as such this is one of the first studies that provides field based evidence of a correlation between channel concavity and basin mean denudation rates consistent with process based fluvial incision models

distribution timing and causes of andean deformation across south america the andean orogeny in south america has lasted over 100 ma it comprises the peruvian incaic and quechuan phases the nazca and south american plates have been converging at varying rates since the palaeocene the active tectonics of south america are relatively clear from seismological and global positioning system gps data horizontal shortening is responsible for a thick crust and high topography in the andes as well as in se brazil and patagonia we have integrated available data and have compiled four fault maps at the scale of south america for the mid cretaceous late cretaceous palaeogene and neogene periods andean compression has been widespread since the aptian the continental margins have registered more deformation than the interior for the peruvian phase not enough information is available to establish a tectonic context during the incaic phase strike slip faulting was common during the quechuan phase crustal thickening has been the dominant mode of deformation to investigate the mechanics of deformation we have carried out 10 properly scaled experiments on physical models of the lithosphere containing various plates the dominant response to plate motion was subduction of oceanic lithosphere beneath continental south america however the model continent also deformed internally especially at the margins and initial weaknesses

tertiary provenance history of the northern and central altiplano central andes bolivia a detrital record of plateau margin tectonics abstract the internally drained altiplano plateau in the high elevation hinterland of the central andes contains an extremely thick up to 12 km succession of tertiary nonmarine strata that recorded the topographic evolution of eastern and western plateau margins in this study temporal and spatial variations in detrital composition based on 113 sandstone thin sections and 31 conglomerate clast counts combined with sediment dispersal patterns and regional stratigraphic correlations help delineate the tertiary history of altiplano basin development in relationship to thrust deformation and arc magmatism along plateau margins stratigraphic and provenance data suggest limited subsidence and west directed sediment dispersal during the early tertiary history of the altiplano region by late eocene time development of a rapidly subsiding basin probable foredeep was underway as recorded by extensive east directed fluvial systems of the 3 6 5 km thick potoco formation potoco compositional data are compatible with sediment sources in the incipient western cordillera and regions farther west including 1 a probable thrust belt source terrane composed of paleozoic mesozoic strata and precambrian granitic gneissic basement and 2 a subordinate magmatic arc source terrane composed of tertiary volcanic rocks increased abundances of plagioclase grains and volcanic lithic fragments upsection indicate a progressively greater arc influence due to either enhanced volcanism or eastward arc migration by late oligocene time west directed fluvial and alluvial fan systems of the upper potoco formation and the 3 km thick coniri formation reached the altiplano basin providing a minimum uplift age for the backthrust belt along the western flank of the eastern cordillera paleozoic clast conglomerate and relatively quartz rich sandstone containing sedimentary and metasedimentary lithic fragments show unroofing of predominantly paleozoic strata in the backthrust belt continued late oligocene to quaternary accumulation in the altiplano reveals that the basin persisted as a depositional region during a well documented period of neogene shortening and uplift in the andean thrust belt farther east this intra orogenic hinterland deposition between eastern and western highs during ongoing shortening suggests that the altiplano basin existed as a crustal scale piggyback basin possibly in an internally drained plateau like geomorphic setting since 25 ma provenance data and independent structural and thermochronological evidence for spatially and temporally varying tectonic histories along the eastern and western plateau margins imply that several modes of basin development were active during growth of the altiplano although flexural subsidence due to thrust loading along both plateau margins initially in the west and subsequently in the east may explain most tertiary subsidence possible closed basin conditions due to structural damming could have promoted additional sediment accumulation from late oligocene to quaternary time

denudation vertical crustal movements and sedimentary basin infill denudation and vertical crustal movements are linked through the isostatic equation for conservation of lithospheric mass recent empirical results from a wide range of sources are presented on the rates of these processes denudation alone can cause non tectonic isostatic surface uplift of the right magnitude predicted by theory a case is made following ahnert for a single linear relationship although with much scatter between denudation rate and mean drainage basin relief for large basins some recent determinations of denudational time constants have neglected to include tectonic and isostatic terms which oppose the reduction of relief by denudation application of diffusional transport models to determine the rate of sediment deposition are severely limited by inherent one dimensionality and neglect of suspended and washload contributions basin infill sequences may be used to determine past sediment transfer coefficients from a hinterland but problems arise in the apportionment of the various hinterland fluxes that occur in real world three dimensional basins sediment yields in smaller half graben and growth fold basins must reflect the magnitude of drainage basins and the complex local controls upon sediment yields examples are given from extensional basins in the western usa and greece the length of tectonic relief produced in tilt blocks and growth folds will control the area of drainage basin developed through the fractal form of hack s law and hence the magnitude of deposition in sedimentary basins adjoining tectonic uplands

modeling topographic and climatic control of east west asymmetry in sierra nevada glacier length during the last glacial maximum 1 glaciers draining westward from the sierra nevada divide california during the last glacial maximum lgm were 7 times longer than east draining glaciers we address the degree to which this difference may be attributed to the topographic asymmetry of the west tilted sierran block and the climate asymmetry resulting from orographic modification of pacific ocean storms we simulate kilometer scale glaciers within the 50 50 km kings canyon region of the southern sierra by employing a two dimensional numerical model that is driven by simple spatially variable climates and treats ice transport by deformation sliding and avalanching in numerical experiments we match simulated termini to lgm moraine positions to constrain the parameters of different climate scenarios the 38 km long lgm glacier in kings canyon was reproduced by a climate specified by an equilibrium line altitude ela of 3170 m a mass balance gradient of 0 01 m yr m and a maximum positive balance of 2 m yr this climate generates much shorter average 6 km long east draining glaciers that however overshoot the lgm moraines by 1 km roughly 97 of the e w difference in glacier lengths can therefore be attributed to topographic asymmetry alone a second experiment suggesting a 120 m higher ela of 3290 m east of the divide can explain the shorter east draining glaciers an experiment in which orographic precipitation is explicitly simulated and melt is prescribed using a positive degree day algorithm matches both kings canyon and the average east draining glacier length with an lgm climate that was 5 6 c cooler and 2 times wetter than the modern sierra nevada

morphological and microtectonic analysis of quaternary deformation from puna and santa clara islands gulf of guayaquil ecuador south america abstract this paper presents the neotectonic study of santa clara and puna islands sited in the gulf of guayaquil eastern part both islands are located on the south western segment of the fault zone bounding to the east the north andean block fault motion and morphostructural analysis were carried out from pleistocene age terrain a two step deformation characterises the south puna tectonics the first step involves the zambapala cordillera uplift that post dates pleistocene sediments and pre dates a marine terrace correlated with the m i s 11 or 13 440 550 ka the second step is the formation of a pull apart that shows evidence of 2 9 km dextral offset since the m i s 11 or 13 giving an offset mean rate of 5 3 to 6 6 mm yr this rate is higher than the one calculated on the pallatanga fault northeast of the study area in the western andean cordillera suggesting that deformation is split in different fault segments from the gulf of guayaquil to the continent the zambapala cordillera uplift and transpression deformation requires a compressive event that may have been induced by the subduction process during the early pleistocene

burial exhumation history of the central apennines italy from the foreland to the chain building thermochronological and geological data a clear correlation between regional unconformities and related exhumation events was documented by thermochronological and geological data in the central apennines this approach allowed i two major exhumation episodes to be identified corresponding to turning points in the long term burial history from rifting to convergent margin development and ii a quantification of the amount of section removed during the two exhumation events the first exhumation event was connected with the foreland buckling process associated with the coupling between the alpine apennines system the dinarides chain and their common foreland during the neogene a thrust system development the superposition of an allochthonous unit is envisaged to explain the second palaeoheating event the dismantling of this additional load in central apennines has been related to the formation of the middle pliocene unconformity during the development of the pliocene quaternary frontal thrust of the apennine chain

rayleigh raman lidar observations of gravity wave activity from 15 to 70 km altitude over syowa 69 s 40 e the antarctic the potential energy of gravity waves gws per unit mass ep at altitudes of 15 70 km has been examined from temperature profiles obtained by a rayleigh raman rr lidar at syowa station 69 s 40 e from may 2011 to october 2013 with the exception of the summer months the gws with ground based wave periods longer than 2 h and vertical wavelengths between 1 8 and 16 km were extracted from the temperature profiles ep was larger in winter than in spring and fall although in 2012 at altitudes below 30 km ep was larger in spring than in winter and fall ep increased with a mean scale height of 11 3 km ep profiles showed a local maximum at an altitude of 20 km and a minimum at 25 km in almost every month which has not been reported by previous studies observed by radiosondes the values of ep in october of 2012 were smaller at 35 60 km and larger at 20 35 km than those in october of 2011 and 2013 this difference in the ep profile is most probably caused by different seasonal variations of zonal winds the larger and smaller ep values seem to be observed both below and above the altitude at which the zonal wind speed reached 0 m s 1 this result suggests that wind filtering of gravity waves with small phase speeds is significantly important in early spring

physiographic and tectonic settings of high sulfidation epithermal gold silver deposits of the andes and their controls on mineralizing processes abstract gold and silver ores in the vast majority of andean high sulfidation epithermal au ag deposits occur at high present day elevations and typically 200 500 m below low relief landforms situated at 3500 to 5200 m a s l most deposits are middle miocene and younger and include el indio tambo pascua lama veladero el indio belt chile argentina cerro de pasco central peru pierina lagunas norte yanacocha northern peru quimsacocha ecuador and the california vetas mining district santander colombia jointly accounting for 130 moz au resources slightly older examples are only preserved in the atacama desert and include the middle eocene el guanaco and el hueso and the late oligocene early miocene la coipa deposits the absence of paleocene and older high sulfidation epithermal deposits can be explained by limited preservation potential imposed by transpressional tectonics within overall contractile episodes and surface uplift these conditions prevailed predominantly in segments of shallow angle subduction of the nazca or caribbean plate below the south american continent a tectonic setting also common for porphyry style cu au mo deposits stratovolcanoes are uncommon ore hosts and volcanic rocks coincident with mineralization are in most cases volumetrically restricted or absent recording the terminal stages of local arc magmatism however dacitic domes are important at e g yanacocha and la coipa at lagunas norte a small stratovolcano largely pre dating but temporally overlapping with mineralization occurs immediately east of the deposit and volcanic sector collapse may have occurred during hydrothermal activity mineralization is typically located near the backscarp of pediments or the heads of valleys incising now high elevation low relief surfaces in the california vetas mining district and el indio belt hydrothermal alunite ages become generally younger upstream along the incising valleys indicating that hydrothermal activity and by inference ore deposition were facilitated by erosion the lowering of the water table and reduction of hydrostatic and lithostatic pressure at these sites of high local relief are believed to have enhanced both boiling and mixing of magmatic with meteoric fluids ultimately enhancing ore deposition the host rock composition permeability and location of the water table control the distribution of alteration zones and ore intermediate volcanic rocks are the most common ore hosts but they typically pre date mineralization by several ma however high sulfidation epithermal mineralization can be hosted in any conceivable rock type including high grade metamorphic rocks california vetas mining district significantly older plutonic rocks pascua lama or quartzites lagunas norte large vuggy quartz alteration zones and commonly oxidized low grade large tonnage mineralization are best developed in relatively permeable volcaniclastic rocks or hydrothermal breccia bodies whereas coherent volcanic plutonic or metamorphic rocks may host fault and breccia controlled ores the near surface steam heated zone can attain a thickness of several hundred meters in dry climates e g veladero pascua lama tambo but is typically poorly developed and less than 20 m thick in humid climatic zones the physiographic and tectonic settings of high sulfidation epithermal deposits are distinct from low sulfidation epithermal districts such as those of patagonia el penon chile or fruta del norte ecuador the latter range to significantly older ages jurassic to early eocene occur at mainly lower elevations and were emplaced in extensional settings a temporal coincidence between uplift erosion and mineralizing processes as well as a spatial and temporal association with porphyry style mineralization is not evident for these low sulfidation districts

cenozoic continental arc magmatism and associated mineralization in ecuador most of the economic ore deposits of ecuador are porphyry cu and epithermal style gold deposits associated with tertiary continental arc magmatism this study presents major and trace element geochemistry as well as radiogenic isotope pb sr signatures of continental arc magmatic rocks of ecuador of eocene to late miocene 50 9 ma elm and late miocene to recent 8 0 ma lmr ages the most primitive elm and lmr rocks analyzed consistently display similar trace element and isotopic signatures suggesting a common origin most likely an enriched morb type mantle in contrast major and trace element geochemistry as well as radiogenic isotope systematics of the whole sets of elm and lmr samples indicate strikingly different evolutions between elm and lmr rocks the elm rocks have consistently low sr y increasing rb sr and decreasing eu gd with sio2 suggesting an evolution through plagioclase dominated fractional crystallization at shallow crustal levels 20 km and most likely at sub crustal levels 40 50 km the change in geochemical signatures of tertiary magmatic rocks of ecuador from the elm to the lmr type coincides chronologically with the transition from a transpressional to a compressional regime that occurred at 9 ma and has been attributed by other investigations to the onset of subduction of the aseismic carnegie ridge

the nature of miocene amazonian epicontinental embayment high frequency shifts of the low gradient coastline a sedimentological and ichnological data set that covers the lower upper miocene sedimentary series of western amazonian foreland basin indicates that widespread restricted marine ingressions shaped western amazonia throughout the miocene the late lower early upper miocene sedimentary series pebas formation consists of stacked 3 to 10 m thick tidally influenced brackish to freshwater bay margin sequences the overlying upper miocene post pebas strata bear tidally influenced low salinity channel deposits that are interbedded with continental deposits the data suggest that several tens of high frequency ingressions reached the basin during the miocene the ingressions were shallow and restricted and were interspersed with rapid progradation along with the prograding shorelines the continental environments swamps lagoons floodplains and forests constrained the extent of the marginal marine embayment consequently the miocene marginal marine and continental strata are closely interbedded throughout the basin these results refine the recent depositional models for miocene amazonia and challenge the theory that marine ingressions shaped the area only during one brief time interval late middle early late miocene during the epoch much of recent literature has documented fossils of mangrove pollen brackish euryhaline fish and brackish water ostracods brackish water trace fossil assemblages and tidal deposits from various miocene stratigraphic levels commonly these data sets are collected from the same outcrops as those for which data sets imply freshwater conditions we propose that these seemingly contrasting data sets can be unified if the repetitive nature of the ingressions is considered and all the paleoenvironmental data are presented in a detailed lithological and stratigraphical context

the importance of apatite composition and single grain ages when interpreting fission track data from plutonic rocks a case study from the coast ranges british columbia abstract fission track results determined from granitic rocks exposed within the coast ranges of british columbia indicate that significant variations in apatite chemistry may occur in small plutonic rock samples to test ages determined earlier by parrish using the population method of fission track dating new apparent apatite ages were completed using the external detector method so that single grain ages could be generated in most cases the new apatite ages were similar to the earlier ones within 2 however in many cases it was found that individual samples contained significant variations in single grain apatite ages microprobe analyses showed the spread in ages were directly related to variations in apatite chemistry such that chlorine rich apatites retained older ages than fluorine rich grains examination of the single grain age data suggested that the spread in single grain ages provided information which constrained the thermal history of the sample and that distributions of single grain ages reflected the temperatures at which they resided during cooling these results suggest that it is important to generate more than a few single grain fission track ages when dating apatite from granitic rocks since variations in the chlorine concentration in apatite grains may exist in kg sized granitic rock samples therefore it is no longer a valid assumption that each apatite grain separated from a small granite sample will have a similar chlorine concentration and in future apatite fission track studies of granitic terrains it is important to recognize that the apatite composition might be heterogeneous when interpreting results

cooling history of the upper cretaceous palgongsan granite gyeongsang basin se korea and its tectonic implication for uplift on the active continental margin abstract apatite and zircon fission track analyses were carried out to reconstruct the cooling and inferred uplift history of the cretaceous palgongsan granite gyeongsang basin korea the palgongsan granite is one of the bulguksa intrusive rocks that formed by arc related plutonism during late cretaceous to early tertiary time fission track dating of the palgongsan granite yielded nearly concordant ages of 53 and 65 ma for apatite and zircon respectively the palgongsan granite also shows a simple cooling pattern which suggests that it has not been affected by any thermal event after emplacement the cooling history derived from fission track data combined with other thermochronometric data indicates that the palgongsan granite experienced relatively rapid cooling in earlier stage 30 c ma the initial rapid cooling rate during the late cretaceous has been caused by the large thermal contrast between the granite body and the country rocks after reaching thermal equilibrium with the surrounding country rocks the cooling rate of the palgongsan granite was abruptly decreased in late stage in this late stage the decelerated cooling rate is interpreted to have been controlled by uplift and erosion processes and the average exhumation rate is calculated to be ca 50 m my over the temperature range from 100 c to the surface temperature the cooling history of the palgongsan granite is in good agreement with that of the ryoke granitic belt in southwest japan as well as those of the taebaeksan range and other bulguksa intrusive rocks in the gyeongsang basin this suggests that such cooling was probably caused by regional uplift and exhumation processes on the east asian active continental margin compared with the uplift rates of the andes the uplift rates on the eastern pacific margin appear to be higher than those on the western pacific margin

recent glacial recession in the rwenzori mountains of east africa due to rising air temperature based on field surveys and analyses of optical spaceborne images landsat5 landsat7 we report recent decline in the areal extent of glaciers in the rwenzori mountains of east africa from 2 01 0 56 km 2 in 1987 to 0 96 0 34 km 2 in 2003 the spatially uniform loss of glacial cover at lower elevations together with meteorological trends derived from both station and reanalysis data indicate that increased air temperature is the main driver clear trends toward increased air temperatures over the last four decades of similar to 0 5 degrees c per decade exist without significant changes in annual precipitation extrapolation of trends in glacial recession since 1906 suggests that glaciers in the rwenzori mountains will disappear within the next two decades

the characteristics of the lower stratospheric gravity wavefield above halley 75 s 26 w antarctica from radiosonde observations daily radiosonde observations between 2003 and 2013 from halley research station antarctica 75 s 26 w are used to determine climatologies of gravity wave properties in the lower stratosphere between 15 km and 22 km altitude individual waves are extracted from the radiosonde profile using wavelet analysis and separated into upward and downward propagating waves an increase in the percentage of downward propagating waves 30 of the waves is seen during the winter months for the upward and downward propagating waves their horizontal and vertical wavelength intrinsic frequency energy density pseudo momentum flux and direction of propagation are determined the upward propagating wave field is found to be dominated by waves with short vertical wavelength 1 km and low intrinsic frequency f the downward propagating wave field is composed of a wider distribution of vertical wavelength waves and has a larger proportion of higher frequency waves present the upward propagating waves show an increase in total energy density in autumn and spring the larger increase occurs during spring up to 1 7 j kg 1 in september the downward propagating waves increase in total energy density occurs during wintertime up to 0 7 j kg 1 in june during winter the contributions of the upward and downward propagating waves to the total energy density and pseudo momentum flux are almost equal this paper details the first study of individual gravity wave properties combined into upward and downward propagating wave climatologies in the lower stratosphere above halley

neogene stratigraphy and andean geodynamics of southern ecuador abstract the present paper reviews tertiary volcanic and sedimentary formations in the inter andean region of southern ecuador between 2 s and 4 20 s in order to develop a geodynamic model of the region the formations occur in the southern shallow prolongation of the inter andean valley between the cordillera real to the east and the cordillera occidental and amotape tahuin provinces to the west one hundred fifty zircon fission track analyses has established a detailed chronostratigraphy for the sedimentary and volcanic formations and several small intrusions the paleogene to early miocene formations are dominated by intermediate and acidic volcanic and pyroclastic rocks in addition relics of eocene continental sedimentary series have been identified the neogene sedimentary series lie unconformably on deformed and eroded metamorphic sedimentary and volcanic formations they were deposited in two stages which are separated by a major unconformity dated at 10 9 ma 1 during the middle and early late miocene 15 10 ma marginal marine deltaic lagoonal lacustrine and fluvial environments prevailed which we group under the heading pacific coastal sequences they presumably covered a greater surface area in southern ecuador than their present occurrence in small topographic depressions we suggest that they were deposited in the shallow marine cuenca and loja embayments deposition in a marginal marine environment is also supported by the occurrence of brackish water ostracods and other fauna 2 above the regional angular unconformity the coastal facies are overlain by late miocene 9 5 ma continental alluvial fan and fluvial facies which are in turn covered by mainly airborne volcanic material they represent the intermontane sequences of the basins of cuenca giron santa isabel nabon loja and malacatos vilcabamba sedimentologic and stratigraphic results are used to discuss the tectonic setting of neogene sedimentation in the forearc and arc domain of the ecuadorian subduction system during the pacific coastal stage northward displacement of the coastal forearc block along the calacali pallatanga fault zone has driven crustal collapse in the inter andean region as a result extensional subsidence drove the eastward ingression of shallow seas into the cuenca and loja embayments from the manabi and progreso basins to the west tectonic inversion in the forearc area during the early late miocene at 9 5 ma reflects the initiation of w e oriented compression and uplift in the inter andean region and the establishment of smaller intermontane stage basins which host the continental sequences coeval topographic rise of the cordillera occidental is indicated by the onset of clastic input from the west the small intermontane basin of nabon 8 5 7 9 ma formed during the period of maximum compression the present data prove that the neogene andean forearc and arc area in southern ecuador was a site of important but variable tectonic activity which was presumably driven by the collision and coupling of the carnegie ridge with the ecuadorian margin since 15 9 ma

shaping the rwenzoris balancing uplift erosion and glaciation the rwenzori mountains in africa represent an extremely uplifted basement fault block at the eastern edge of the western branch of the east african rift system a large scale rift system controlled by extensional stresses the rugged alpine topography reaches an altitude of up to 5109 m and the highest parts are ice covered glacial landforms and moraines proof repeated more extensive glaciations during the last glacial cycles in order to elucidate magnitudes and the varying role of erosional processes in shaping the relief of the rwenzori mountains over the past 2 mill years we performed numerical simulations with the landscape evolution programme ultima thule it is controlled by a climate driver with temperature as a master variable as well as changing precipitation and evapotranspiration over time the morphological processes considered are fluvial erosion hillslope diffusion and glacial abrasion and the latter controlled by the simulated glaciation of the landscape we provide three sets of model runs the first one starting from the present day topography and running for approx 800 ka the second one extending the modelling period to 2 ma and the third one starting from a peneplain and evolving for 2 ma our results provide constraints on the temperature history of the rwenzori mountains the interplay of morphological degradation and tectonic uplift and a time frame for the formation of the mountain chain from a peneplain to the present relief the modelled landscape evolves from a peneplain 2 ma ago to a rwenzori type mountain range when the fairly strong average rock uplift of 1 2 mm year 1 is compensated by a strong fluvial erosion component the rock uplift rate is needed to obtain elevations above the equilibrium line altitude around 500 ka bp and results in surface uplift over time around that time a periodic ice cap appears in the models and glacial abrasion then limits the height of the rwenzori mountains to its present elevation

development of the gulf of guayaquil ecuador during the quaternary as an effect of the north andean block tectonic escape 1 interpretation of industrial multichannel seismic profiles and well data are used to identify the main tectonic features of the gulf of guayaquil gg area these include two e w trending major detachments the posorja and the jambeli detachment systems which represent half grabens with oppositely dipping detachments to the south and to the north respectively the ne sw trending puna santa clara fault system developed as a transfer fault system between the posorja and the jambeli detachments the esperanza and the jambeli basins exhibit 3 4 km of sediment that accumulated during the past 1 6 1 8 myr the puna santa clara fault system bounds the esperanza and the jambeli basins evidencing that the evolution of these basins is tightly controlled by the two detachments at depth to the west the n s trending domito fault system bounding the posorja detachment system and the esperanza basin to the west acted as a transfer zone between the shelf area and the continental slope the pliocene series show no significant variations in thickness throughout the gulf of guayaquil area suggesting that no important tectonic deformation occurred from 5 2 to 1 8 1 6 ma the major period of tectonic deformation in the gulf of guayaquil area occurred during the pleistocene times three main tectonic steps are identified from early pleistocene to 180 ka major subsidence occurred along the esperanza and jambeli basins from 180 to 140 ka most of the gulf of guayaquil area was above sea level during the isotope substage 6 low stand from 140 ka to present tectonic activity is restricted along the normal faults bounding the esperanza basin the tenguel fault and the puna santa clara and domito fault systems a n s trending tensional stress regime characterizes the pleistocene times throughout the northward drifting of the north andean block is proposed to control the tectonic evolution and associated subsidence of the gulf of guayaquil area it is also accepted that the collision of the carnegie ridge with the trench axis has to play a major role in controlling the north andean block northward drift because the carnegie ridge subduction is possibly an ongoing process which began prior to the pliocene we postulate the along strike morphology of the ridge at the origin of interplate coupling variations the subduction of an along strike positive relief of the ridge is proposed at the origin of the major tectonic reorganization of the gg area occurring at 1 8 1 6 ma

the pan amazonian ucayali peneplain late neogene sedimentation in amazonia and the birth of the modern amazon river system abstract we review the neogene geologic history of lowland amazonia in an attempt to focus attention on areas of agreement as well as areas in dispute in this research arena we reinterpret pre existing hypotheses present new data and discuss new insights intended to support a unified synthesis of the amazon basin as a single sedimentary basin albeit on a vast scale during the late miocene to middle late pliocene we document the ucayali peneplain as an isochronous pan amazonian geologic feature that formed following the early to mid miocene quechua i orogenic phase of andean tectonism peneplanation began possibly as early as 15 ma and terminated abruptly near the beginning of the late miocene quechua ii orogenic event at 9 5 9 0 ma subsequently a thin cover of sediments comprising the madre de dios formation began blanketing most of lowland amazonia excepting only the eastern subandean fold and thrust belt and isolated highlands within the basin the buried peneplain is readily observed in river cutbanks throughout amazonia as the marked often angular ucayali unconformity that separates eroded older often folded faulted and weathered moderately to well consolidated tertiary formations from unconsolidated near horizontal upper neogene deposits the dates of formation of major unconformities and subsequent depositional events at widely separated areas within the andes of bolivia ecuador and peru are coincident with that of the ucayali unconformity and deposition of the madre de dios formation and suggest that the events are linked to a common cause which is interpreted to be the still on going collision between the south american and nazca tectonic plates the madre de dios formation has three members the oldest of which documents a short lived high energy depositional environment followed by a moderate energy depositional environment both occurring at a time when drainage from the basin was unobstructed the upper two members record fluctuations between moderate and low energy continental depositional environments during a period when drainage from the basin was obstructed disorganized and took place over long distances with extremely low gradients the sedimentology of the madre de dios formation particularly the thick massive beds of clay and the widespread presence of paleodeltas and associated geomorphic features on the amazonian planato are consistent with the hypothesis that much of the upper two members formed as lacustrine and deltaic deposits within a gigantic lake lago amazonas or more probably within a complex series of interconnected mega lakes that occasionally united to cover most or all of lowland amazonia to a shallow depth from the latest miocene until 2 5 ma the presence of the ucayali unconformity and the relatively uniform lithostratigraphy basin wide of the fluvial fluviolacustrine and lacustrine sediments of the upper neogene madre de dios formation are consistent with the hypothesis that the amazon basin acted as a single undivided sedimentary basin in the late neogene the biostratigraphic correlation across important modern drainage divides of both micro and macro sized late miocene fossil vertebrates recovered from basal conglomerates of the madre de dios formation and the absence therefrom of fossil vertebrates of any other age is also consistent with this hypothesis two 40ar 39ar dates on ash deposits within the madre de dios formation corroborate the upper miocene age of the basal horizons of that formation indicated by fossil vertebrates and support an upper pliocene age for the youngest sediments of the formation the modern amazon river drainage system was established in the late pliocene at 2 5 ma by the breaching of the eastern rim of the sedimentary basin as a result of the basin being overfilled or by headward erosion of the lower amazon river or both data on cenozoic mass accumulation rates and the chemistry of terrigenous sediments in the atlantic ocean obtained by ocean drilling project leg 154 ceara rise support the postulated timing of the establishment of the modern amazon river drainage system at 2 5 ma rather than the long held view that this event occurred in the late miocene we discuss the important role of ocean currents and sea level fluctuations on terrigenous mass accumulation rates on the ceara rise the postulated time of formation of the modern amazon river is nearly coincident with the onset of the plio pleistocene glacial climatic regime and the lowest sea level stands since the latest middle miocene this analysis indicates that modern amazonia is a product of terrain development within an erosional regime since 2 5 ma

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

episodic orogenic front migration in the northern andes constraints from low temperature thermochronology in the eastern cordillera colombia 1 new thermochronometric data from the eastern cordillera of the colombian andes reveal diachronous exhumation associated with cenozoic contractional deformation in this sector of the northern andes we present a comprehensive account of exhumation patterns along a 150 km long across strike transect between 4 and 6 n by integrating 29 new apatite fission track aft ages and 17 new zircon fission track zft ages with sparse published thermochronological data from this area our data reveal episodic eastward migration of the orogenic front at an average rate of 2 5 2 7 mm a during the late cretaceous cenozoic we identify three major stages of orogen propagation 1 slow propagation 0 5 3 1 mm a until early eocene 2 rapid orogenic advance 4 0 18 0 mm a during middle late eocene which accounts for 86 of the orogen s present width and 3 slow orogen propagation 1 2 2 1 mm a from oligocene to holocene times our data demonstrate that in the course of changes in plate kinematics the presence of inherited crustal anisotropies such as the former rift bounding faults of the eastern cordillera favor a nonsystematic progression of foreland basin deformation through time by preferentially concentrating accommodation of slip and thrust loading along these zones of weakness

marine connections of amazonia evidence from foraminifera and dinoflagellate cysts early to middle miocene colombia peru abstract species composition in the present day amazonian heartland has an imprint of past marine influence the exact nature timing and extent of this marine influence however are largely unresolved here we use calcareous tests of foraminifera and marine palynomorphs from miocene sediments in northwestern amazonia to extend on current estimates for salinity ranges paleoenvironments and paleogeography our samples mostly contain tests and or organic linings of euryhaline tolerant to a wide range of salinity foraminifera of the genera ammonia trochammina and elphidium with ammonia being by far the dominant genus at all locations organic walled dinoflagellate cysts dinocysts such as spiniferites brigantedinium and tuberculodinium vancampoae are also common at a number of sites this association of foraminifera and dinocyst taxa points at varying salinities with aberrant forms of ammonia indicating lower limits of 0 10 psu practical salinity units whereas dinocyst associations suggest more marine conditions such regional heterogeneity is common at the interface of shallow marine to freshwater environments like estuaries we conclude that during the early and middle miocene marginal marine conditions reached at least 2000 km inland from the caribbean portal global high sea level and fast subsidence in the sub andean zone are thought to be the controlling mechanisms of the marine incursions lowering of global sea level and a change in tectonic regime terminated the incursions in the course of the plio pleistocene

neogene ongoing tectonics in the southern ecuadorian andes analysis of the evolution of the stress field abstract microtectonic analysis of infilling deposits in south ecuadorian neogene basins brings to light a compressive stress field with 1 along a nne ssw to ne sw direction in the early miocene changing to an e w direction in the middle and late miocene the syn sedimentary deformations which affect the deposits of the basins suggest similar stress regimes due to a compressive ongoing tectonic system in the miocene for at least 15 ma there is a good correlation between rapid convergence in the neogene and the time period during which the continental south ecuadorian basins were deformed by compression quechua period

along strike variations in the thermal and tectonic response of the continental ecuadorian andes to the collision with heterogeneous oceanic crust oblique to strike geological segmentation in the andean chain has been previously recognised at various scales and is commonly attributed to changes in the convergence vectors of the oceanic and continental plates as well as the upperplate expressions of differing along strike subducted slab age strength and composition we present new white mica and biotite 40 ar 39 ar and zircon and apatite fission track data from several traverses across the cordillera real of ecuador in the northern andes that reveal distinct along strike differences in the timing of accelerated crustal cooling during the cenozoic the data record elevated cooling rates from temperatures of v380 c during v65 55 and v43 30 ma from all sampled regions of the cordillera real and at v15 ma and since v9 ma in the northern cordillera real each cooling period was probably driven by exhumation in response to the accretion and subduction of heterogeneous oceanic crust elevated cooling rates of up to v30 20 c myr were initiated during the palaeocene and eocene early oligocene along the entire contemporaneous margin of ecuador and were driven by the accretion of the oceanic pallatanga terrane and pin on macuchi block respectively onto northwestern south america both of these geological provinces originated at the southern parts of the leading and trailing boundaries of the caribbean plateau and accreted onto the margin during the approximately northeastward migration of the plateau into its current position within ecuador the development of higher topography and elevated cooling rates of up to 50 c myr at v15 ma and since v9 ma are restricted to the region north of 1 30ps and is situated above the postulated subducted flatslab section of the aseismic carnegie ridge plate convergence rate calculations suggest the carnegie ridge collided with the ecuador trench at v15 ma which caused the pre existing coastal provinces to displace to the northeast subsequently driving extension and marine ingressions in southern ecuador and compression and uplift in northern ecuador fl 2001 elsevier science b v all rights reserved

partitioning of oblique convergence in the northern andes subduction zone migration history and the present day boundary of the north andean sliver in ecuador along the ecuadorian margin oblique subduction induces deformation of the overriding continental plate for the last 15 ma both exhumation and tectonic history of ecuador suggest that the northeastward motion of the north andean sliver nas was accompanied by an eastward migration of its eastern boundary and successive progressively narrowing restraining bends here we present geologic data earthquake epicenters focal mechanisms gps results and a revised active fault map consistent with this new kinematic model all data sets concur to demonstrate that active continental deformation is presently localized along a single major fault system connecting fault segments from the gulf of guayaquil to the eastern andean cordillera although secondary faults are recognized within the cordillera they accommodate a negligible fraction of relative motion compared to the main fault system the eastern limit is then concentrated rather than distributed as first proposed marking a sharp boundary between the nas the inca sliver and the subandean domain overthrusting the south american craton the nas limit follows a northeast striking right lateral transpressional strike slip system from the gulf of guayaquil isla puna to the andean cordillera and with the north south striking transpressive faults along the eastern andes eastward migration of the restraining belt since the pliocene abandonment of the sutures and reactivation of north south striking ancient fault zones lead to the final development of a major tectonic boundary south and east of the nas favoring its extrusion as a continental sliver accommodating the oblique convergence of the nazca oceanic plate toward south america

oxygen and hydrogen isotopes in pedogenic minerals implications for paleoclimate evolution in amazonia during the cenozoic stable isotopes in gibbsite and kaolinite were analyzed to reconstruct the amazonia palaeoclimate during the cenozoic and to investigate the environmental conditions of the weathering process and the origin of the oxisol that cover the lateritic bauxite crust at least two types of kaolinite were identified in the oxisol near the surface the kaolinite is less fractionated and was developed at a higher temperature 35 c this is probably due to the effect of vegetation and or evapotranspiration or is a consequence of surface microenvironmental conditions or allochthonous inputs the other kaolinite samples ranged in formation temperatures from 21 c to 26 c and developed under conditions similar to the pleistocene and the modern climate of amazonia at least two types of gibbsite were found one type developed in the modern amazonia climate in a way similar to most kaolinite samples whereas the samples of the other type are more fractionated this is because they may have been formed in low recycling rainwater and or under a low amount of precipitation these two conditions indicate a seasonal climate for bauxite development that can be linked to the low exhumation of the andes cordillera and its geographical position relative to the trombetas region during the period ranging from the late oligocene to the early miocene at the end of the cenozoic the climate was less seasonal and wetter and the temperature was lower in addition there was the probable inland position of the trombetas region which allowed oxisol development the gibbsite developed earlier than the kaolinite of the oxisol but there is a partial inheritance or temporal equivalence among the bauxite horizon and the oxisol as well as multiple generations of gibbsite and kaolinite which is to be expected for materials developing over long periods in hard leaching conditions