clay mineralogy of the soils in the south ecuadorian paramo region abstract the paramo soils of the mountainous upper andean region 3300 m a s l of the rio paute basin in central ecuador are characterized by a thick dark highly organic epipedon and are classified as andosols and histosols their high water retention and buffering capacity play a key role in the hydrology of the region which is subject to land use changes and increased cultivation in the west western cordillera the soils are largely formed in the late miocene and pliocene volcanoclastic tarqui formation while in the east central cordillera they are formed in an older mostly intermediate low grade metamorphic rocks ten soil profiles were sampled and studied using extraction techniques oxalate and pyrophosphate and xrd techniques major differences in composition of the clay fractions were found that allow for distinction of three main groups of paramo soils a first group consists of soils influenced by recent volcanic ashes and dominated by organometallic complexes and with minor but distinct amounts of degraded mica most probably formed by weathering of primary mica present in these ashes the second group comprises soils formed in volcanoclastic material of various tertiary and earlier formations containing residual primary and secondary crystalline clay size minerals as well as organometallic complexes whose genesis can be linked to the abundant presence of easily weatherable materials in these formations a third group consists of soils in relicts of tertiary highly weathered regolith formed under humid tropical conditions before the andean uplift and occurring in the central cordillera these soils contain kaolinite and gibbsite and develop into histosols in the absence of significant organometallic complexation

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

long term fore arc basin evolution in response to changing subduction styles in southern alaska detrital zircon u pb and fission track double dating and hf isotopes from the mesozoic and cenozoic strata in the southern alaska forearc basin system reveal the effects of two different modes of flat slab subduction on the evolution of the overriding plate the southern margin of alaska has experienced subduction of a spreading ridge ca 62 50 ma and an oceanic plateau ca 40 0 ma when a subducting spreading ridge drives slab flattening our data suggest that after the ridge has moved along strike retro arc sediment sources to the forearc become more predominant over more proximal arc sources spreading ridge subduction also results in thermal resetting of rocks in the upper plate that is revealed by thermochronologic data that record the presence of young age peaks found in subsequent thin sedimentary strata in the forearc basin when a subducting oceanic plateau drives slab flattening our data suggest that basin catchments get smaller and local sediment sources become more predominant crustal thickening due to plateau subduction drives widespread surface uplift and significant vertical uplift in rheologically weak zones that combined create topography and increase rock exhumation rates consequently the thermochronologic signature of plateau subduction has generally young age peaks that generate short lag times indicating rapid exhumation the cessation of volcanism associated with plateau subduction limits the number of syndepositional volcanic grains that produce identical geochronologic and thermochronologic ages this study demonstrates the merit of double dating techniques integrated with stratigraphic studies to expose exhumational age signatures diagnostic of large scale tectonic processes in magmatic regions

description and classification of nonallophanic andosols in south ecuadorian alpine grasslands paramo abstract the paramo is a neotropical alpine ecosystem that covers more than 75 000 km 2 of the northern andes of colombia ecuador venezuela and peru it provides important environmental services more than 10 million people in the andean highlands benefit from the water supply and regulation function which is attributed to the volcanic soils that underlie the ecosystem the soils are also major carbon sinks of global significance severe land use changes and soil degradation threaten both the hydrology and carbon sink function nevertheless soil genesis and properties in the paramo is rather poorly understood nor are their ecological functions well documented the impact of the geomorphology of the paramo on soil genesis was studied in the rio paute basin south ecuador two toposequences were described and analysed in each toposequence four pedons were selected representing summit backslope undrained plain situation and valley bottom positions in the landscape the soils are classified as hydric andosols in the world reference base for soil resources and epiaquands or hydrudands in soil taxonomy they are very acidic and have a high organic matter content high p deficiency and al toxicity their water content ranges from 2 64 g g 1 at saturation down to 1 24 g g 1 at wilting point resulting in a large water storage capacity two major soil forming processes are identified 1 volcanic ash deposition and 2 accumulation of organic carbon volcanic ash deposits may vary in depth as a result of regional geomorphological factors such as parent material orientation slope and altitude organic carbon accumulation is an interaction of both waterlogging which depends on the position in the landscape and the formation of organometallic complexes with al and fe released during volcanic ash breakdown despite the high variability in parent material and topography the soil is characterised by a notable homogeneity in physico chemical properties statistical analysis reveals that only topographic location has a slight but significant influence on soil ph as well as the organic matter content saturated conductivity and water retention at high pressure finally the exceptional properties of these soils provide useful insights to improve classification of the andosols reference group of the fao world reference base for soil resources

tracking ancient magmatism and cenozoic topographic growth within the northern andes forearc constraints from detrital u pb zircon ages a comparison of detrital zircon ages from the cenozoic forearc basins in sw ecuador nw peru and those derived from the amotapes massif offers a singular opportunity to shed some light on the evolution of the nw andean margin of south america an extensive set of pre andean u pb zircon ages older than late cretaceous was obtained from 18 detrital samples coming from the talara zorritos progreso and gulf of guayaquil tumbes forearc basins as well as from two metasedimentary rocks of the amotapes massif u pb age analysis on detrital zircon grains allows a general source to sink scenario to be determined for this section of the andes these analyses give consistent insights into the early topographic growth during the modern andean orogeny the occurrence of proto andean magmatic periods in the western margin of gondwana and the evolution of the amotapes massif within the geodynamical setting of northwestern south america zircon ages at ca 320 ma and neoproterozoic clusters for the amotapes metasediments show significant similarities along the strike of the metamorphic belt thus defining a common metasedimentary origin and can be compared with previously dated rocks from the eastern cordillera of peru these strong similarities demonstrate the presence of a wide polyphased metamorphic belt that includes the western parts of the eastern cordillera the northern section of the occidental cordillera of peru and the amotapes massif detrital sediments of the forearc are marked by a major gap in early cretaceous jurassic ages and the minor presence of ordovician famatinian orogeny and carboniferous permian 340 285 ma ages the age spectrum is not compatible with sediment input from the eastern andes and suggests that the external areas of the andean chain e g the western cordillera were already uplifted prior to or immediately after forearc initiation during the paleocene thus representing a pervasive drainage divide throughout all of the cenozoic the amotapes massif or other terrains sharing the same age affinities e g the olmos terrane occidental cordillera of peru are likely to represent the best potential sources for pre andean zircon grains in the forearc age clusters in both source and sink at ca 600 ma 570 560 ma and 520 ma most likely define magmatic periods and may represent first order constraints for the difficult correlation between proto andean magmatic and orogenic periods to the north and south of the huancabamba deflection it is unlikely that the neoproterozoic zircon grains came from the pan african braziliano belts thus suggesting the onset of significant magmatic activity in this section of the andes at around 570 560 ma and probably ca 600 ma the 520 ma cluster is compatible with the most prominent magmatic period in the southern andes related to the end of the pampean orogeny thus suggesting the existence of a regional proto andean magmatic arc during early cambrian times

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

petrogenetic evolution of arc magmatism associated with late oligocene to late miocene porphyry related ore deposits in ecuador we present a data set on the geochemical and isotopic composition of mineralized porphyry intrusions se riate intrusions and arc volcanic formations spatially associated with late oligocene to late miocene porphyry related ore deposits in ecuador our aim is to constrain the petrogenetic evolution of these arc magmas to evaluate geodynamic and tectonic impact factors on arc magmatism and to explore the metallogenic signifi cance of these parameters we distinguish four petrogenetic groups associated with the investigated magmatic centers indicating dif ferent paths of low and high pressure crustal magma evolution tertiary ecuadorian arc magmas which dif ferentiated at higher crustal pressures are commonly characterized by adakite like compositions related to fractionation and or restite equilibration effects of amphibole garnet titanite particularly in hydrous silicic melts without concomitant or subsequent major plagioclase fractionation trace element distribution patterns of arc magmas through time are broadly systematic and indicate that crustal magma differentiation progres sively extends to higher pressures from the late oligocene to the late miocene possibly related to crustal thick ening locally adakite like features possibly related to high melt h2o contents or accessory phase fractiona tion are already observed in the early miocene in a regional setting otherwise dominated by low pressure magma evolution compositional differences between mineralized porphyry intrusions and spatially associated seriate precur sor intrusions in ecuador mostly reflect regional scale changes in magma composition through time and are not observed if the relative emplacement age difference is small where porphyry intrusions are associated with shallow crustal batholith systems in northern central ecuador their emplacement is commonly late with re spect to batholith magmatism intrusive compositions indicate that porphyry parental melts mostly evolved at higher crustal pressures where metallogenically favorable melt preconditioning might possibly occur

palynology sedimentology and palaeoecology of the late holocene dead sea abstract palynological and sedimentological studies were performed at two holocene profiles in erosion gullies ze elim and ein feshkha which dissect the retreating western shore of the dead sea the aim of the project was to analyse possible links between climate lithology and vegetation development the section in ze elim shows both lacustrine and fluvial sediments whereas sedimentation at ein feshkha is predominantly lacustrine the ze elim profile previously used for paleo lake reconstruction provides an opportunity to compare climate triggered lake levels as paleo hydrological indicators and vegetation history by use of palynology the vegetation development in ze elim and ein feshkha is influenced by both climate and human impact the pollen record of ze elim begins in the pottery neolithic the section of ein feshkha in the late bronze age both records end in the middle ages the ze elim section is characterized by sedimentary hiati between the beginning of the chalcolithic period until the middle bronze age and within the late bronze age settlement periods during the middle bronze age iron age and hellenistic roman byzantine period are indicated by high values of anthropogenic indicators and or mediterranean trees collapses of agriculture which can be related to climate effects are evident during the late bronze age during the iron age and at the end of the byzantine period when the lake level curve indicates arid conditions a comparison of the two pollen records from different environments illustrates a more prominent influence of mediterranean vegetation and cultivated plants in the pollen diagram of ein feshkha the southern dead sea region at the desert fringe is more vulnerable to regional climate change

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

holocene palaeoecology of the golan heights near east investigation of lacustrine sediments from birkat ram crater lake abstract lacustrine deposits of the crater lake birkat ram located in the northern golan heights have been used as a paleoecological archive preliminary sedimentological and palynological investigations based on a composite profile allow the reconstruction of the environmental history of the last 6500 years fluctuations of the pollen composition trees and shrubs versus herbs values of oak and olive tree correspond to changes in different sediment parameters total organic carbon magnetic susceptibility which can be interpreted as the effects of human impact on the geo biosphere four phases with strong settlement activities can be identified for the northern golan heights 1 during the chalcolithic period early bronze age 2 during the hellenistic roman byzantine periods 3 during the crusader period and finally during modern time these periods were interrupted by wooded regeneration phases with low anthropogenic activities

geodynamic controls on tertiary arc magmatism in ecuador constraints from u pb zircon geochronology of oligocene miocene intrusions and regional age distribution trends abstract we obtained u pb zircon ages of late tertiary intrusions in the northern andes to provide robust time calibration points for the intrusive geochronologic framework of ecuador which is mostly based on k ar data magmatism associated with intrusion emplacement ranges from 31 to 7 ma with ages mainly pooling in the late oligocene early miocene where both k ar and u pb data exist for a given intrusive system ages obtained by the different methods are usually concordant within 1 4 m y suggesting that k ar ages are accurate indicators for the timing of tertiary arc magmatism on a regional multi m y scale except for a single sample the investigated intrusions completely lack externally inherited zircons in agreement with dominantly zircon poor oceanic crustal basement domains spatio temporal distribution trends of tertiary arc magmatism inferred from screened u pb k ar and zircon fission track geochronologic data allow tracking of the progressive along arc broadening of a flat slab segment below southernmost ecuador in the mid to late miocene and of moderate slab shallowing in northern central ecuador in the late miocene these regional arc migration patterns correlate in time with the subduction of the buoyant inca plateau and the carnegie ridge seamount chain the temporal distribution of tertiary ecuadorian arc magmatism indicates a late oligocene early miocene arc magmatic flare up event comprising widespread ignimbrite eruption and batholith construction initiation of the flare up event coincides in time with accelerating less oblique farallon nazca south america plate convergence suggesting a positive feedback between convergence rates asthenospheric melt production mantle crust melt flux and upper crustal arc magmatic productivity in ecuador

reconstruction of the mid holocene paleoclimate of the ecuadorian andean paramo at tres lagunas ecuador previous paleoclimate studies have suggested a warm dry event during the mid holocene in paramo vegetation of the tropical andes of south america however the timing of the mid holocene warm dry event in tres lagunas ecuador remains uncertain since a previously reported bog core record characterized the warm dry event during a hiatus in sediment deposition in order to understand the timing of the warm dry event in tres lagunas in relation to regional records a lake sediment core was collected subsamples from the core were analyzed for radiocarbon dates pollen magnetic susceptibility and charcoal to reconstruct the depositional vegetational and fire history of the area a near constant sedimentation rate in the lake core indicated that the lake did not dry in contrast to the adjacent previously reported bog core increases in lower elevation pollen types suggest

late holocene vegetation in the azraq wetland reserve jordan abstract shifts in aquatic and terrestrial vegetation associations and hydrology during the past 3100 yr are indicated by the pollen and sediment sequences in a core retrieved from the azraq wetland jordan the pollen sequence provides evidence for a relatively stable wetland during the period of study until ca ad 1400 when the wetland apparently declined as desert shrubland expanded springs continually supplied fresh water that maintained the shallow pools and marsh in periods of increased winter precipitation runoff from the surrounding wadis may have inundated the wetland and deposited silts and clays during dryer episodes the influx of winter storm water would have been much less but the springs would have still provided water to the wetland and deposited peat this is shown by the sequences of clay silty and sandy clay loam and peat in the core

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

interglacial and glacial desert refugia and the middle paleolithic of the azraq oasis jordan a geoarchaeological study of sediments in the azraq oasis in the eastern desert of jordan provides information on the fluctuations of the geomorphic and hydrologic systems in this region in relation to the local middle paleolithic and upper paleolithic occupations the study shows that local geomorphic and hydrological environments fluctuated between marsh lake and playa dry lake bed with eolian activity and or carbonate accumulation in some instances local wet conditions correlate with those registered in other regional paleoclimatic records as is the case of the period comprising mis 5a and probably early mis 4 in other cases however local wet conditions represented by marsh deposits with hominin occupations are asynchronous with regional wet conditions this suggests that the azraq oases may have acted as desert refugia at times of regional adverse climatic conditions the fact that azraq represents a potential desert refugia has important consequences for understanding major issues in the middle paleolithic of southwest asia namely 1 the arrival survival and extinction of populations of both neanderthals and early modern humans the location of azraq at a crossroads between the levant the arabian peninsula and other regions of the middle east is also an important geographic aspect of desert refugia during the critical period of hominin dynamics in the middle paleolithic

late oligocene miocene transgressions along the equatorial and eastern margins of brazil abstract the seaboard of brazil is a highly favorable setting for studying episodes of worldwide sea level rise because of its passive nature previous studies of the equatorial coast of brazil have led to the recognition of extensive oligo miocene and miocene marine influenced deposits but these deposits have been overlooked in other coastal areas of brazil the aim of the present study is to show the origin and evolution of late oligocene and miocene marine influenced strata exposed in more than 5000 km of coastal areas along the wnw trending equatorial and nne trending eastern brazilian continental margins we review the most relevant data concerning the strata of these ages exposed along the equatorial and eastern margins of brazil and combine them with new data based on these occurrences we analyze the history of sea level fluctuations and show that marine influenced strata are more widespread in these margins than originally thought our main results indicate that a marine influence is not only imprinted in the deposits exposed along the equatorial margin but it is also widespread in several areas of the eastern margin for a long geological time interval ranging from the end of the cretaceous or paleogene up to the late oligocene most of the brazilian coast remained a non depositional site exposed to subaerial erosion and lateritic soil development the combination of sea level rise and tectonic subsidence promoted sediment accumulation in the onshore portion of several basins two transgressive episodes occurred one in the oligo miocene and another in the early middle miocene the latter gave rise to deposition of the barreiras formation however during the supposedly middle miocene eustatic sea level highstand in coastal brazil there was a renewed and extensive phase of non deposition and subaerial erosion with lateritic soil formation a process that lasted up to the late quaternary this mismatching of the sedimentary record with other south american and continental areas is discussed herein as in many other areas of south america and of the world the regressive transgressive events recorded along the brazilian coast most likely responded to a combination of eustatic sea level fluctuations and local factors such as tectonic activity intraplate stresses and changes in dynamic topography during the post rift history of the eastern south american plate

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

faunal remains from recent excavations at shishan marsh 1 sm1 a late lower paleolithic open air site in the azraq basin jordan excavations from 2013 to 2015 at the site of shishan marsh 1 sm1 in the azraq basin of eastern jordan have yielded substantial late middle pleistocene lithic assemblages in association with faunal remains faunal preservation is poor but multiple taxa have been identified including cf panthera leo gazella sp bos cf primigenius camelus sp equus spp cf stephanorhinus hemitoechus palaeoloxodon cf recki and elephas cf hysudricus the overall azraq habitat may have been most similar to a savanna ecosystem with a mixture of open grassland shrub habitats and more closed vegetation along the wetlands margins these taxa were drawn to the relatively lush oasis environment where they were a dietary resource of the hominin groups exploiting the wetlands resources

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

abundance and morphometry changes across the high mountain lake size gradient in the tropical andes of southern ecuador the number size and shape of lakes are key determinants of the ecological functionality of a lake district the lake area scaling relationships with lake number and volume enable upscaling biogeochemical processes and spatially considering organisms metapopulation dynamics these relationships vary regionally depending on the geomorphological context particularly in the range of lake area 1 km2 and mountainous regions the cajas massif southern ecuador holds a tropical mountain lake district with 5955 water bodies the number of lakes deviates from a power law relationship with the lake area at both ends of the size range similarly to the distributions found in temperate mountain ranges the deviation of each distribution tail does not respond to the same cause the marked relief limits the size of the largest lakes at high altitudes whereas ponds are prompt to a complete infilling a bathymetry survey of 202 lakes selected across the full size range revealed a volume area scaling coefficient larger than those found for other lake areas of glacial origin but softer relief water renewal time is not consistently proportional to the lake area due to the volume area variation in midsize lakes the 85 of the water surface is in lakes 104 m2 and 50 of the water resources are held in a few ones 10 deeper than 18 m therefore midlakes and large lakes are by far more biogeochemically relevant than ponds and shallow lakes in this tropical mountain lake district

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

the border ranges ultramafic and mafic complex south central alaska cumulate fractionates of island arc volcanics a discontinuous elongate zone of mafic and ultramafic plutonic rock crops out in south central alaska for a distance of more than 1000 km intermediate and detailed scale geologic mapping petrographic study and compositional data suggest that the plutonic rocks are compositionally petrologically and mineralogically distinct from rocks in mid ocean ridge and back arc basin ophiolites the mafic and ultramafic rocks instead represent part of the plutonic core of an intraoceanic island arc the mafic ultramafic zone referred to as the border ranges ultramafic and mafic complex brumc is composed of ultramafic cumulates gabbronorite cumulates and massive gabbronorites a very minor amount of tectonized ultramafic rock of mantle origin is present in the southern part of the brumc a thick sequence of andesitic volcanic rocks the talkeetna formation of early jurassic age lies to the north of and structurally above the mafic ultramafic zone voluminous calcalkaline plutons composed of quartz diorite

cenozoic stages of forearc evolution following the accretion of a sliver from the late cretaceous caribbean large igneous province sw ecuador nw peru

accreted oceanic terranes in ecuador southern edge of the caribbean plate the western part of ecuador is made of several oceanic terranes which comprise two oceanic plateaus of early 120 ma and late cretaceous age 90 ma respectively the older oceanic plateau was accreted to the andean margin in the late campanian 75 ma fragments of the turonian coniacian plateau were accreted to the ecuadorian margin in the late maastrichtian 68 ma guaranda terrane and late paleocene 58 ma pinon naranjal terrane the guaranda terrane received either fine grained oceanic sediments of coniacian maastrichtian age or island arc back arc volcanic suites of middle campanian middle maastrichtian age the pinon naranjal terrane recorded a comparable history completed in the maastrichtian paleocene either by pelagic cherts or by island arc products macuchi arc the late cretaceous plateau of ecuador is interpreted as part of the caribbean oceanic plateau cop because their evolutions are comparable if so the cop was not formed by the galapagos hotspot but on the farallon oceanic plate south of ecuador and close to the south american margin the cop belonged to the farallon plate until a subduction zone separated both plates in the middle campanian giving way to a well developed mid campanian mid maastrichtian island arc accretion in the late maastrichtian triggered a change in the subduction system and the development of a new arc system of late maastrichtian late paleocene age which crosscut the south america cop plate boundary the last accretion occurred in the late paleocene

sedimentology of fraser river delta peat deposits a modern analogue for some deltaic coals abstract on the recent lobe of the fraser river delta peat accumulation has actively occurred on the distal lower dilta plain the transition between upper and lower delta plains and the alluvial plain distal lower delta plain peats developed from widespread salt and brackish marshes and were not influenced appreciably by fluvial activity lateral development of the marsh facies were controlled by compaction and eustatic sea level rise the resulting thin discontinuous peat network contains numerous silty clay partings and high concentrations of sulphur freshwater marsh facies formed but were later in part eroded and altered by transgressing marine waters the peats overlie a thin fluvial fining upward sequence which in turn overlies a thick coarsening upward prodelta delta front succession lower delta plain upper delta plain peats initially developed from interdistributary brackish marshes and were later fluvially influenced as the delta prograded the thickest peats occur in areas where distributary channels were abandoned earliest sphagnum biofacies replace sedge grass dominated communities except along active channel margins where the sedge grass facies is intercalated with overbank and splay deposits the peats are underlain by a relatively thin sequence of fluvial deposits which in turn is underlain by a major coarsening upward delta front and pro delta sequence alluvial plain peats accumulated in back swamp environments of the flood plain earliest sedge clay and gyttjae peats developed over thin fining upward fluvial cycles or are interlaminated with fine grained flood deposits thickest accumulations occur where peat fills small avulsed flood channels overlying sedge grass and sphagnum biofacies are horizontally stratified and commonly have sharp boundaries with fine grained flood sediments at active channel margins however sedge grass peats are intercalated with natural levee deposits consisting of silty clay these levees reduce both the number and size of crevasse splay deposits coal originating from peats of the different environments of the fraser delta would vary markedly in character peats of the lower delta plain will form thin lenticular coal seams with numerous splits and have a high ash and sulphur content peats from the lower to upper delta plain will be laterally extensive and of variable thickness and quality basal portions of the seams will contain numerous splits and have a high sulphur content whereas upper portions will be of higher quality peats from the upper delta plain alluvial plain will form thick isolated and laterally restricted coal seams characterized by low ash and sulphur contents

geometrical control of subduction related magmatism the mesozoic and cenozoic plutonic history of western colombia radiometric age data from western colombia combined with geological evidence allow five main plutonic episodes ranging in age from triassic to tertiary to be recognized it is suggested that variation in the convergence angle of the oceanic plate relative to the continental edge was an important factor affecting the timing and spatial distribution of plutonic activity on a regional scale major breaks in activity are probably best attributed to either low angle parallel convergence or periods of accretion along the convergent margin

tectonic segmentation of the north andean margin impact of the carnegie ridge collision the north andean convergent margin is a region of intense crustal deformation with six great subduction earthquakes mw 7 8 this century the regional pattern of seismicity and volcanism shows a high degree of segmentation along strike of the andes segments of steep slab subduction alternate with aseismic regions and segments of flat slab subduction this segmentation is related to heterogeneity on the subducting nazca plate in particular the influence of the carnegie ridge collision is investigated four distinct seismotectonic regions can be distinguished region 1 from 6on to 2 5on with steep ese dipping subduction and a narrow volcanic arc region 2 from 2 5on to 1os showing an intermediate depth seismic gap and a broad volcanic arc region 3 from 1os to 2os with steep ne dipping subduction and a narrow volcanic arc region 4 south of 2os with flat subduction and no modern volcanic arc the carnegie ridge has been colliding with the margin since at least 2 ma based on examination of the basement uplift signal along trench parallel transects the subducted prolongation of carnegie ridge may extend up to 500 km from the trench as suggested by the seismic gap and the perturbed broad volcanic arc these findings conflict with previous tectonic models suggesting that the carnegie ridge entered the trench at 1 ma furthermore the anomalous geochemical adakitic signature of the volcanoes in the broad ecuador volcanic arc and the seismicity pattern are proposed to be caused by lithospheric tears separating the buoyant shallowly subducting carnegie ridge from segments of steep subduction in regions 1 and 3 it is further suggested that carnegie ridge supports a local flat slab segment similar to that observed in peru the impact of the carnegie ridge collision on the upper plate causes transpressional deformation extending inboard to beyond the volcanic arc with a modern level of seismicity comparable to the san andreas fault system the pattern of instrumental and historical seismicity indicates 1 great earthquakes on the northern and southern flanks of the colliding ridge 2 a slight reduction in observed seismicity at the trench ridge intersection 3 increased stress far into the continent and 4 a nne displacement of the n andes block to be further effects of the collision 1999 elsevier science b v all rights reserved

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

plio quaternary volcanism in ecuador extensive sampling major element chemistry on over 300 samples and k ar radiometric dating have been carried out on the ecuadorian upper tertiary quaternary volcanoes the results show important space time variations of the volcanic activity between late miocene time and the present in late miocene time a continuous volcanic belt located approximately along the present volcanic front vf affected the whole country from the cuenca basin to the south up to colombia to the north major changes occurred at about 5 ma volcanic activity stopped south of the guayaquil fault belt and never resumed to the north the active volcanic axis shifted eastward to the cordillera real cr area with a simultaneous relative decrease in intensity since early quaternary time the volcanic belt widened westward to the western cordillera where the volcanism resumed at about 1 5 1 0 ma giving rise to the very wide active volcanic zone of ecuador the plio quaternary products show significant longitudinal and latitudinal chemical and mineralogical changes volcanics of the vf and interandean depression contain amphibole and define a calc alkaline trend with a k 2 o content lower than that of the cr products which are characterized by a mostly anhydrous phenocryst assemblage in both areas andesites dominate but extreme compositions basaltic andesites and rhyolites are more diffuse in the cr than the vf no significant transverse zoning has been detected in the northern region north of the chota mira transverse tectonic line the observed temporal and spatial variations are interpreted as a result of the subduction of the carnegie ridge anomalous oceanic crust underthrusting of which began approximately 6 ma ago

infilling of the younger kathmandu banepa intermontane lake basin during the late quaternary lesser himalaya nepal a sedimentological study the kathmandu and banepa basins central nepal are located in a large syncline of the lesser himalayas the older kathmandu lake evolved during the pliocene and early pleistocene the younger kathmandu lake which is the focus of this study is infilled with late quaternary sediments three formations arranged in stratigraphical order the kalimati gokarna and thoka formations formed during the infilling stage of this lacustrine basin structural and textural sedimentological analyses a chemical survey across the basin and mineralogical investigations of fine grained sediments form the basis of this palaeogeographical study the basin under investigation was covered by a perennial freshwater lake before 30 000 yr bp the lake was infilled with alluvial and fluvial sediments delivered mainly from the mountains north of the basin a fairly low gradient was favourable for the formation of diatomaceous earths carbonaceous mudstones and siltstones which were laid down in the centre of the lake and in small ponds towards the basin edge lacustrine sediments gave way to deltaic deposits spread across the delta plain crevasse splays and anastomosing rivers mainly delivered suspended load for the widespread siltstones and mudstones the proximal parts of the alluvial fluvial sedimentary wedge contain debris flows that interfinger with fine grained floodplain deposits three highstands of the water level 30 000 yr bp 28 000 19 000 yr bp 11 000 4000 yr bp have been recognised in the sedimentary record of the younger kathmandu lake in the late quaternary second order water level fluctuations are assumed to be triggered by local processes damming by tectonically induced landslides first order water level fluctuations are the result of climatic changes copyright 2003 john wiley sons ltd

geophysical investigation of a suture zone the border ranges fault of southern alaska the border ranges fault separates structurally complex accreted cretaceous rocks from less deformed middle or late paleozoic and younger rocks in the cook shelikof basin of the five types of geophysical data used to investigate this fault gravity data give the clearest indication of its presence and crustal structure for at least 400 km along the fault gravity anomalies include a 20 to 30 mgal peak along the fault s upper plate and a 40 mgal trough along the lower plate the paired anomaly can be modeled satisfactorily by a simple step in a deep dense layer that lies within 3 km of the projected offshore location of the fault relatively low density rocks lie along the fault s lower plate to a depth of about 10 km and the upper part of the fault dips within 20 of vertical satellite altimetry data show that two circular geoid lows lie along the border ranges fault and coincide with lows in free air gravity data seismic refraction and seismic reflection data suggest that the large scale density anomalies that cause both types of lows must lie at depths greater than about 1 km within the margin three regional magnetic anomalies knik arm seldovia and shelikof terminate at the border ranges fault suggesting that the fault truncates obliquely rocks that lie along its northwest side six seismic reflection lines cross the border ranges fault but none of them shows reflections from it the absence of such reflections probably results from the fault s steep dip and from the presence of strong water bottom multiples in the data from the late jurassic until the early late cretaceous the magmatic arc near the cook shelikof basin was inactive and we infer that the predominant motion along the border ranges fault was strike slip resurgent late cretaceous magmatism was contemporaneous with uplift of rocks along the northwest side of the border ranges fault and with deformation of turbidite sequences in the fault s lower plate we propose that during the late cretaceous motion along the border ranges changed from strike slip to reverse cenozoic rocks near the fault show no evidence for post cretaceous fault movement

possible seismic reflections from the downgoing pacific plate 275 kilometers arcward from the eastern aleutian trench multichannel seismic reflection data collected near the southern kenai peninsula alaska show deep events that could stem either from a linear diffractor or from a curved reflector whichever is the cause it must be at a minimum depth of 12 km if a linear diffractor causes the most obvious events it strikes at a 60 angle across the surface trend of mesozoic rocks thus the diffractor could be associated with a transverse tectonic boundary that on the basis of other evidence is thought to strike through the area of this study alternatively these deep events could be reflections from rocks associated either with a detached piece of oceanic crust or with the downgoing pacific plate these associated rocks could be porous and overpressured sedimentary rocks that are squeezed between indurated or metamorphosed sedimentary rocks in the overthrust plate and igneous rocks in the downgoing oceanic crust

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

geomorphic evidence of active deformation and uplift in a modern continental wedge top foredeep transition example of the eastern ecuadorian andes abstract the eastern ecuadorian andes appear as a fold and thrust belt adjacent to a continental foredeep represented by one of the world s largest tropical alluvial megafans the pastaza megafan debouching into the amazonian lowland the apex of the pliocene pleistocene megafan situated in the present day wedge top subandean zone has been cut by an erosion surface the western part of which has been uplifted of 500 m along the frontal thrust forming a poorly dissected plateau the mera plateau this erosion surface erased most of the previous fluvial landscape but preserved a large thrust related anticlinal hinge deforming less erodible underlying strata the mirador fold and smaller sized anticlines this surface has been then incised by two antecedent major rivers the pastaza and the napo and few tributaries the plateau edge is marked by a series of large scale gently sloping landslides clustered along a 70 km long concave eastward line associated with the frontal thrust fault the newly formed immature rivers issued from the landslides or sourced within east dipping remnants of the erosion surface downstream of the landslide line constitute the greatest part of the streams feeding the ecuadorian amazonian basin at 70 to 100 km from the landslide line the drainage abruptly changes from highly immature to mature with a well defined hinge line representing the outer limit of landslide and tectonic control the diversions of the pastaza river indicate ongoing fold growth since at least the late pleistocene in the eastern cordillera and the early holocene in the mera plateau the preserved terraces of the pastaza valley are all degradational and are ascribed to periods of tectonic seismic activity alternating with periods of tectonic quiescence or decreased seismic activity rather than to climatic events 14c dating of the plateau erosion surface and of the upper pastaza terraces indicates that the minimum average incision rate since 18 000 years bp varies locally in the upper pastaza valley from 0 5 to 0 67 cm year 1 increasing from 18 000 years bp to now a comparison of these incision rates with fold and thrust fault uplift rates indicates that incision in the upper pastaza valley was a result of rapid uplift up to 1 cm year 1 along the mirador fold and thrust which caused a restoration of the local equilibrium profile of the upper reach combined with smaller local fault uplift along the westernmost thrust faults the uplift of the whole mera plateau with respect to the upper amazonian basin gives a minimum average uplift rate of 2 8 cm year 1 since 18 000 years bp the overall uplift of the mera plateau and the eastern cordillera is likely to have been caused by a regional scale low angle thrust ramp emerging as the frontal thrust fault

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

provenance of the upper cretaceous to upper eocene clastic sediments of the western cordillera of ecuador geodynamic implications abstract the late cretaceous eocene clastic deposits of the western cordillera of ecuador record significant changes in the source areas grain size and location of the depocenters related to the accretion of oceanic terranes that constitute the present day western cordillera and coast major changes in the source areas occurred in the late maastrichtian and late middle eocene they are interpreted as corresponding to the accretion of the guaranda and macuchi oceanic terranes respectively major increases in the grain sizes occurred in the late maastrichtian late paleocene and late middle eocene and seem to coincide with the accretion of the guaranda pinon and macuchi terranes respectively the increasing occurrence of plutonic or metamorphic fragments and the westward shift of the depositional areas through the paleocene upper eocene interval indicate an increasing uplift and erosion of the cordillera real continuous although jerky uplift of the latter during the maastrichtian eocene period supports the idea that the accreted oceanic material contributed to the crustal thickening and relief creation of the ecuadorian andes

late holocene climates of the near east deduced from dead sea level variations and modern regional winter rainfall the dead sea is a terminal lake of one of the largest hydrological systems in the levant and may thus be viewed as a large rain gauge for the region variations of its level are indicative of the climate variations in the region here we present the decadal to centennialresolution holocene lake level curve of the dead sea then we determine the regional hydroclimatology that affected level variations to achieve this goal we compare modern natural lake level variations and instrumental rainfall records and quantify the hydrology relative to lake level rise fall or stability to quantify that relationship under natural conditions rainfall data pre dating the artificial dead sea level drop since the 1960s are used in this respect jerusalem station offers the longest uninterrupted pre 1960s rainfall record and jerusalem rains serve as an adequate proxy for the dead sea headwaters rainfall principal component analysis indicates that temporal variations of annual precipitation in all stations in israel north of the current 200 mm yr 1 average isohyet during 1940 1990 are largely synchronous and in phase 70 of the total variance explained by pc1 this station also represents well northern jordan and the area all the way to beirut lebanon especially during extreme drought and wet spells we a determine the modern and propose the past regional hydrology and eastern mediterranean em climatology that affected the severity and length of droughts wet spells associated with multiyear episodes of dead sea level falls rises and b determine that em cyclone tracks were different in average number and latitude in wet and dry years in jerusalem the mean composite sea level pressure and 500 mb height anomalies indicate that the potential causes for wet and dry episodes span the entire em and are rooted in the larger scale northern hemisphere atmospheric circulation we also identified remarkably close association within radiocarbon resolution between climatic changes in the levant reflected by level changes and culture shifts in this region

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

restoring dense vegetation can slow mountain erosion to near natural benchmark levels tropical mountain areas may undergo rapid land degradation as demographic growth and intensified agriculture cause more people to migrate to fragile ecosystems to assess the extent of the resulting damage an erosion rate benchmark against which changes in erosion can be evaluated is required benchmarks reflecting natural erosion rates are usually not provided by conventional sediment fluxes which are often biased due to modern land use change and also miss large episodic events within the measuring period to overcome this we combined three independent assessment tools in the southern ecuadorian andes an area that is severely affected by soil erosion first denudation rates from cosmogenic nuclides in river sediment average over time periods of 1 100 k y and establish a natural benchmark of only 150 100 t km 2 yr 1 second we find that land use practices have increased modern sediment yields as derived from reservoir sedimentation rates which average over periods of 10 100 yr to as much as 15 10 3 t km 2 yr 1 third our land cover analysis has shown us that vegetation cover exerts first order control over present day erosion rates at the catchment scale areas with high vegetation density erode at rates that are characteristically similar to those of the natural benchmark regardless of whether the type of vegetation is native or anthropogenic therefore our data suggest that even in steep mountain environments sediment fluxes can slow to near their natural benchmark levels with suitable revegetation programs a set of techniques is now in place to evaluate the effectiveness of erosion mitigation strategies

location of the border ranges fault southwest of kodiak island alaska a positive magnetic anomaly extends discontinuously from the south side of the copper river basin along the southeast side of cook inlet and shelikof strait and southwestward from kodiak island to near sutwik island regionally this anomaly parallels the border ranges fault and is within 10 km of it along the kodiak islands the most probable source for the anomaly near kodiak island is mainly early jurassic plutonic rocks and locally ultramafic rocks that are associated with a melange the border ranges fault lies between these two rock types and given the regional parallelism of the fault and the magnetic anomaly the fault can be traced offshore southwest of kodiak island to near sutwik island using marine magnetic data lithologic evidence suggests that the fault continues southwest of sutwik island toward the southwest end of the alaska peninsula

correlations between nazca farallon plate kinematics and forearc basin evolution in ecuador the tertiary evolution of the forearc basins of ecuador shows a close correlation between the changing convergence rate of the farallon and later nazca oceanic plates and continental south america the correlation occurs during the subduction of a relatively young slab and in the late miocene onset of the subduction of the carnegie aseismic ridge the ecuador forearc basins lie on a basement of oceanic crust known as the pinon terrane the accretion of this terrance occurred in the paleocene as the leading edge of the farallon plate the macuchi island arc collided with south america in the middle eocene this forearc terrane was the site of major pull apart basin formation and turbiditic sedimentation coincident with a phase of very rapid convergence between chron 21 and chron 13 48 37 ma this deformation was bounded by the trench and a major dextral strike slip fault zone and resulted in the northward translation of the forearc with respect to continental south america during the oligocene a phase of extension normal to the trend of the active margin occurred coincident with a phase of relatively slow convergence chron 13 to chron 6 37 20 ma this extension was followed in the middle miocene by inversion of most of the forearc basins coincident with a return to relatively fast convergence from chron 6 20 ma to the present day subduction of the carnegie aseismic ridge occurred during this period circa 8 ma to present and may have enhanced the compressive event further northward translation of the forearc silver accompanied this later deformation the relationships outlined for the forearc may be modeled in terms of a dynamic orogenic wedge which responds directly to changes in convergence rate at the subduction zone the convergence rate appears to be an important control on the coupling between the downgoing slab and overriding continental plate

gradual diversions of the rio pastaza in the ecuadorian piedmont of the andes from 1906 to 2008 role of tectonics alluvial fan aggradation and enso events the successive courses of the rio pastaza in the upper amazonian puyo plateau ecuador during the past century have been followed using historical maps aerial photographs satellite imagery topographic and river long profiles and field studies the abrupt change in direction of the rio pastaza from transverse to longitudinal was a result of two avulsions occurred between 1906 and 1976 at the braided meandering transition of the former alluvial plain these avulsions are related to aggradation at the toe of a braided piedmont fan prograding on to a hinterland dipping topographic slope formed by ongoing tectonic backtilting the main avulsion proceeded by annexation of a south dipping depression created in front of the cordillera by backtilting of the plateau a partial and gradual avulsion having occurred upstream of the former site between 1976 and 2008 is marked by the progressive predominance of a newly formed inner branch tectonic backtilting enhanced aggradation upstream of the initial site while it offered the newly avulsed channel a still more favorable way along the cordillera by creating a westward lateral slope the correlation between enso events and the occurrence of the 1976 2008 avulsions strongly suggests that the triggers of the avulsions were the floods caused by the high water and sediment discharges associated with enso la nina events contrasting with the regular monthly discharge and the lack of actual normal floods during the inter enso periods

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

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

vegetation and topographic controls on sediment deposition and storage on gully beds in a degraded mountain area active gully systems developed on highly weathered or loose parent material are an important source of runoff and sediment production in degraded areas however a decrease of land pressure may lead to a return of a partial vegetation cover whereby gully beds are preferred recolonization spots although the current knowledge on the role of vegetation on reducing sediment production on slopes is well developed few studies exist on the significance of restoring sediment transport pathways on the total sediment budget of degraded mountainous catchments this study in the ecuadorian andes evaluates the potential of vegetation to stabilize active gully systems by trapping and retaining eroded sediment in the gully bed and analyses the significance of vegetation restoration in the gully bed in reducing sediment export from degraded catchments field measurements on 138 gully segments located in 13 ephemeral steep gullies with different ground vegetation cover indicate that gully bed vegetation is the most important factor in promoting short term 1 15 years sediment deposition and gully stabilization in well vegetated gully systems 30 of ground vegetation cover 0 035 m 3 m 1 of sediment is deposited yearly in the gully bed almost 50 per cent of the observed variance in sediment deposition volumes can be explained by the mean ground vegetation cover of the gully bed the presence of vegetation in gully beds gives rise to the formation of vegetated buffer zones which enhance short term sediment trapping even in active gully systems in mountainous environments vegetation buffer zones are shown to modify the connectivity of sediment fluxes as they reduce the transport efficiency of gully systems first calculations on data on sediment deposition patterns in our study area show that gully bed deposition in response to gully bed revegetation can represent more than 25 per cent of the volume of sediment generated within the catchment our findings indicate that relatively small changes in landscape connectivity have the potential to create strong positive feedback loops between erosion and vegetation dynamics copyright c 2009 john wiley sons ltd