strike slip faulting and nested block rotations structural evidence from the cordillera de domeyko northern chile abstract based on a structural analysis tectonic rotations around vertical axes have been found affecting the sedimentary sequence of the purilactis group from the cordillera de domeyko of northern chile the affected rocks form the northern part of a pre existing syncline that was offset by two sets of strike slip faults during the upper eocene incaic orogeny uplift and shortening in the hangingwall of two main bounding thrusts initiated the strike slip faults which divided the purilactis group into several fault blocks further contraction of the enclosed block faulted area led to domino style anticlockwise rotation of the central main blocks and the bounding block faults with rotations up to 40 additionally eastward displacement of these blocks was accompanied by local indentation of the adjacent smaller blocks to the east giving rise to opposite rotation directions the block rotations may have been accommodated by a decollement located in the mudstone and evaporite of the basal part of the sequence tonel formation based on a reconstruction of the initial rock distribution different fault models are discussed and a model resembling pure shear deformation is proposed to explain the initiation of strike slip faults the occurrence of block rotations and the distortion of the block faulted domain

variations in fluvial style on the eocene oligocene alluvial fan of the scala dei group se ebro basin spain the scala dei group represents one of several coarse clastic wedges along the eastern margin of the tertiary ebro basin this group of eocene oligocene age is partly concealed by faulted and locally overthrust older sediments but a segment of oligocene age is spectacularly exposed for about 15 km along the newly constructed a2 motorway near the edge of the basin multistorey conglomerate channel bodies are composed of large scale foresets up to 3 m high representing side bars or possibly point bars smaller up to 40 cm normally graded beds with imbricated clasts represent diagonal or transverse bars and horizontally stratified sheets may be longitudinal bars flow was highly variable the multistorey conglomerate bodies are restricted to several crudely radiating axes representing major feeder systems and give rise to a goose foot depositional palaeomorphology towards the basin centre and in quiet zones between the main feeder axes single storey channel bodies of conglomerate and sandstone are common some plug like conglomerate and sandstone channel bodies are ribbons which are essentially straight in plan and other generally asymmetrical sandstone channel bodies preserve the point bars of channel bends where limited lateral migration took place many channel bodies possess extremely well developed wings representing levees and locally amalgamated crevasse splay sequences conspicuous crevasse channels cut through the levees the wings and crevasse channel bodies contain carbonate rich palaeosols this sequence is interpreted as an essentially distributive but ephemeral fluvial system

cenozoic evolution of the northwestern salar de atacama basin northern chile 1 since 90 ma the nonmarine salar de atacama basin has been the largest deepest and most persistent sedimentary basin of northern chile integration of 200 km of two dimensional seismic reflection data with surface geological data clarifies oligocene and neogene evolution of the northern part of the basin a normal fault with 6 1 km of vertical separation controlled the western boundary of the basin during the accumulation of the oligocene lower miocene paciencia group the combination of this structure a similar one in the calama basin and regional structural data suggests that localized extension played an important role within a tectonic environment dominated by margin perpendicular compression and margin parallel strike slip deformation seismic data substantiate the surface interpretation that much of the cordillera de la sal ridge resulted from diapiric flow of the paciencia group diapiric flow initiated during the late early miocene or middle miocene associated with a deep reverse fault

climatic versus tectonic controls of fan sequences lessons from the dead sea israel tectonic activity is commonly held responsible for abrupt coarsening of alluvial fan sequences and the role of climate is often relegated the pleistocene fans of the dead sea rift indicate clearly the problems of differentiating the sedimentary signatures of climatic and tectonic adjustments in a closed lake basin exposures are excellent the rivers are currently incising in response to the low lake levels of the holocene producing cliffs 50m high these reveal an interdigitation of lake deposits dominantly fine grained carbonates and the coarse river gravels which characterize the fan deposits the bounds of each facies are sharp river sediments are superimposed on lake sediments with little evidence of either reworking or loading in turn aragonite crusts are draped over alluvial gravels indicating the sudden return of still water conditions neither can be explained by gradual adjustment of the hinterland river system after tectonic shock instead it is clear that the coarse alluvium was deposited by discrete high magnitude floods that occurred only sporadically because of the infrequent nature of rainfall in this arid environment in interpreting basin development in ancient settings it is always tempting to assume that coarse deposits are indicative of tectonism however the dead sea fans demonstrate that climate is just as likely to be responsible for the conglomerates in a sedimentary sequence

geochronology and stratigraphy of the ignimbrites from the 21 30 s to 23 30 s portion of the central andes of northern chile the central volcanic zone cvz of the andes which extends from 14 to 28 s is one of the largest provinces of late tertiary to recent ignimbrite volcanism in the world in the 21 30 s to 23 30 s portion of the cvz in northern chile ignimbrite volcanism was initiated at the beginning of the late miocene 10 4 ma ago and continued until the recent the stratigraphy is dominated by the products of five major dacitic ignimbrite eruptions 100 km3 the artola ignimbrite member 9 4 ma the sifon ignimbrite member 8 3 ma the pelon ignimbrite member 5 5 ma the puripicar ignimbrite member 4 2 ma and the atana ignimbrite member 4 1 ma at least three of these represent only portions of larger ignimbrite sheets erupted from centres of sw bolivia two of the ignimbrites the sifon and atana ignimbrites must represent erupted volumes in excess of 1000 km3 each the major units which represent 90 of the total volume of ignimbrite in this area are intercalated with smaller 50 km3 less extensive volcanic units some of which were erupted from source structures within the study area the upper tertiary to recent volcanic stratigraphy has been revised using the large ignimbrites as the major stratigraphic horizons the ignimbrite formations can be divided into two groups on a geographic basis those in the northern and central portions of the study area are known as the san bartolo group while those in the southern portion belong to the silapeti group these two groups appear to be contemporaneous although the silapeti group may represent a period of ignimbrite volcanism which was initiated later about 6 ma ago the ignimbrite formation of sw bolivia and the punense arancaniano formation of nw argentina are equivalent to the san bartolo and silapeti groups based on correlation of the stratigraphy into adjacent areas in sw bolivia and nw argentina the beginning of the late miocene 10 4 ma marks the onset of the most intense phase ignimbrite volcanism in the cvz this phase of volcanism is suggested to be the result of crustal melting in response to crustal thickening during the quechua phase of deformation and subduction approximately 10 000 km3 of ignimbrite erupted over a period of 9 ma in the 21 30 23 30 s portion and led to the development of a major ignimbrite province

pedostratigraphic models for alluvial fan deposits a tool for interpreting ancient sequences this paper reviews the scattered literature on quaternary arid type alluvial fan soil sequences and presents a series of model stratigraphies these are primarily influenced by the degree of entrenchment and by climatic controls these models are used to interpret well exposed miocene fan deposits from the madrid basin central spain

alluvial fan and playa sedimentation in an andean arid closed basin the pacencia group antofagasta province chile the mid tertiary pacencia group comprises over 2 km of continental sediments it was deposited in a half graben basin thought to have been active since early tertiary times conglomerates along the western basin margin were deposited as longitudinal bars rare transverse bars and channel fills with subsidiary debris flows all in a distal fan pebbly braided stream environment no proximal fan sediments are exposed petrographic and palaeocurrent analysis indicates these sediments were derived from cretaceous and possibly jurassic source areas to the northwest to the east within the basin a succession of sands silts muds thick evaporites and rare carbonates were deposited in playa sub environments saliferous muds central salt pan are overlain by interbedded red mudstones and thin high energy ribbon and sheet sands marginal dry mudflat and sandflat certain sand bodies carry stratiform cui agi au mineralization lakes existed at various stages and were fed by permanent fluvial systems the playa sediments were derived from crystalline source areas to the east proximal fan facies and sediment sources are now buried under the volcanic andes

late mesozoic to paleogene stratigraphy of the salar de atacama basin antofagasta northern chile implications for the tectonic evolution of the central andes abstract the salar de atacama basin the largest pre andean basin in northern chile was formed in the early late cretaceous as a consequence of the tectonic closure and inversion of the jurassic early cretaceous tarapaca back arc basin inversion led to uplift of the cordillera de domeyko cd a thick skinned basement range bounded by a system of reverse faults and blind thrusts with alternating vergence along strike the almost 6000 m thick upper cretaceous to lower paleocene sequences purilactis group infilling the salar de atacama basin reflects rapid local subsidence to the east of the cd its oldest outcropping unit tonel formation comprises more than 1000 m of continental red sandstones and evaporites which began to accumulate as syntectonic growth strata during the initial stages of cd uplift tonel strata are capped by almost 3000 m of sandstones and conglomerates of western provenance representing the sedimentary response to renewed pulses of tectonic shortening which were deposited in alluvial fan fluvial and eolian settings together with minor lacustrine mudstone purilactis formation these are covered by 500 m of coarse proximal alluvial fan conglomerates barros arana formation the top of the purilactis group consists of maastrichtian danian alkaline lava and minor welded tuffs and red beds cerro totola formation 70 64 ma k ar deposited during an interval of tectonic quiescence when the el molino yacoraite late cretaceous sea covered large tracts of the nearby altiplano puna domain limestones interbedded with the totola volcanics indicate that this marine incursion advanced westwards to reach the eastern cd slope cd shortening in the late cretaceous was accompanied by volcanism and continental sedimentation in fault bounded basins associated to strike slip along the north chilean magmatic arc to the west of the cd domain indicating that oblique plate convergence prevailed during the late cretaceous oblique convergence seems to have been resolved into a highly partitioned strain system where margin parallel displacements along the thermally weakened arc coexisted with margin orthogonal shortening associated with syntectonic sedimentation in the salar de atacama basin a regionally important early paleocene compressional event is echoed in the salar de atacama basin by a distinctive angular unconformity which separates paleocene continental sediments from purilactis group strata the basin also records the eocene early oligocene incaic transpressional episode which produced renewed uplift in the cordillera de domeyko and triggered the accumulation of a thick blanket of syntectonic gravels loma amarilla formation

antiquity of aridity in the chilean atacama desert the atacama desert of northern chile and southern peru has one of the longest histories of arid conditions known although most studies have focused on the hyper aridity prevalent since the miocene all terrestrial sediments in the region from the late triassic onwards also record evaporitic and thus arid climates supergene mineralization in the region did not develop under a more humid climate conducive to deep weathering but under arid conditions these processes may have been facilitated by hydrological changes during miocene uplift and drainage incision but were operational prior to the uplift similarly global cooling and changes to oceanic circulation in the post miocene period only accentuated existing conditions a whole regolith perspective is vital to understanding the history of aridity in the atacama desert and its relevance to arid zone morphogenesis regolith formation and supergene mineralization in particular the long history of aridity raises the possibility that supergene mineralisation under the appropriate conditions form in arid environments instead of requiring humid conditions

eocene exhumation and basin development in the puna of northwestern argentina 1 the puna is part of the larger puna altiplano plateau also known as the central andean plateau characterized by high elevation low relief and aridity located in the central andes of bolivia and argentina tertiary sedimentary rocks preserved within the puna contain a unique archive of information regarding the paleogeography depositional environments and timing of sediment source exhumation during the early stages of andean mountain building the eocene geste formation in the salar de pastos grandes area within the central puna of northwestern argentina consists of deposits that are the result of confined to unconfined flows in a sandy to gravelly braided fluvial system and alluvial fans proximal to the source terrane paleocurrent data document an overall eastward flow direction up section coarsening of the geste formation suggests that topographic relief in the source area increased through time possibly owing to enhanced tectonic activity and source terrane unroofing sandstone petrography and conglomerate clast count data document quartzose and phyllitic compositions typical of ordovician rocks preserved just west of the salar de pastos grandes area paleocene eocene detrital apatite fission track age populations p1 35 52 ma p2 52 65 ma of the geste formation and their consistent trends up section suggest moderate to rapid 0 4 mm a to 1 mm a exhumation of western sediment sources during the early to mid tertiary stages of andean mountain building sedimentation rates increase up section from 0 1 mm a to 1 mm a our data when combined with other structural stratigraphic and seismic evidence from surrounding regions suggest that the geste formation was deposited in response to crustal shortening and resulting erosion and sedimentation which started as early as cretaceous in the chilean cordillera de domeyko and in the salar de pastos grandes area by eocene time the geste formation could be interpreted either as a local wedge top accumulation on the eastward propagating central andean orogenic wedge or as a local intermontane basin the similarities between wedge top deposits preserved in bolivia and eocene deposits in northwestern argentina south of 25 s lead us to favor the wedge top scenario for the geste formation if correct this implies that the deformation front of the andean orogenic wedge incorporated both thin and thick skinned structures as it migrated possibly unsteadily from the cordillera de domeyko during the cretaceous paleocene to areas within the puna and eastern cordillera by mid late eocene time contemporaneously a regional scale foreland basin system developed over an along strike distance of at least 650 km

a permeability model for naturally fractured carbonate reservoirs abstract based on a detailed structural study performed on a reservoir surface analogue a fracture permeability model for carbonate reservoirs is proposed this involves four hierarchical systems each one assumed to convey fluids exclusively to that of immediately higher order new basic equations are then provided simulating hydrodynamic reservoir response the large scale first order structures consist of faults to which high permeability structures damage zones are associated at the meter scale stratabound joint systems together with bedding joints bounding the mechanical layers form a connected network transporting fluids to the fault system at a lower scale down to crystal size non stratabound joints constitute a pervasive and capillary fracture network which conveys fluids within the rock mass the non fractured host rock constitutes the lower permeability system at the crystal scale as no published works include an effective integration of detailed structural and numerical models the present study aims at covering a significant gap in the literature also providing appropriate theoretical basis for subsequent studies on fracture network modeling and reservoir simulation besides its application in the field of reservoir development and management the illustrated model may also be useful in environmental studies involving ground fluids such as e g in the field of special toxic nuclear waste management

controls on coastal dune morphology shoreline erosion and barrier island response to extreme storms abstract the response of a barrier island to an extreme storm depends in part on the surge elevation relative to the height and extent of the foredunes which can exhibit considerable variability alongshore while it is recognized that alongshore variations in dune height and width direct barrier island response to storm surge the underlying causes of the alongshore variation remain poorly understood this study examines the alongshore variation in dune morphology along a 11 km stretch of santa rosa island in northwest florida and relates the variation in morphology to the response of the island during hurricane ivan and historic and storm related rates of shoreline erosion the morphology of the foredune and backbarrier dunes was characterized before and after hurricane ivan using empirical orthogonal function eof analysis and related through canonical correlation analysis cca the height and extent of the foredune and the presence and relative location of the backbarrier dunes varied alongshore at discrete length scales of 750 1450 and 4550 m that are statistically significant at the 95 confidence level cospectral analysis suggests that the variation in dune morphology is correlated with transverse ridges on the inner shelf the backbarrier cuspate headlands and the historical and storm related trends in shoreline change sections of the coast with little to no dune development before hurricane ivan were observed in the narrowest portions of the island between headlands west of the transverse ridges overwash penetration tended to be larger in these areas and island breaching was common leaving the surface close to the watertable and covered by a lag of shell and gravel in contrast large foredunes and the backbarrier dunes were observed at the widest sections of the island the cuspate headlands and at crest of the transverse ridges due to the large dunes and the presence of the backbarrier dunes these areas experienced less overwash penetration and most of the sediment from the beachface and dunes was deposited within the upper shoreface it is argued that this sediment is returned to the beachface through nearshore bar migration following the storm and that the areas with larger foredunes and backbarrier dunes have smaller rates of historical shoreline erosion compared to areas with smaller dunes and greater transfer of sediment to the washover terrace since the recovery of the dunes will vary depending on the availability of sediment from the washover and beachface it is further argued that the alongshore pattern of dune morphology and the response of the island to the next extreme storm is forced by the transverse ridges and island width through alongshore variations in storm surge and overwash gradients respectively these findings may be particularly important for coastal managers involved in the repair and rebuilding of coastal infrastructure that was damaged or destroyed during hurricane ivan

dynamics of deformation and sedimentation in the northern sierras pampeanas an integrated study of the neogene fiambala basin nw argentina reply the thick skinned sierras pampeanas morphotectonic domain of western and northwestern argentina 27 s 33 s is characterized by reverse fault bounded basement blocks that delimit internally deformed neogene sedimentary basins foreland basin evolution in this part of the andes is still not very well understood for example challenging questions exist as to how thick skinned deformation develops if there are distinct spatiotemporal trends in deformation and exhumation how such deformation styles influence sedimentation patterns and whether or not broken foreland basins are related to regional plate tectonic processes such as flat slab subduction the fiambala basin of the northwestern sierras pampeanas is the largest of several intermontane basins in the transition to the southern margin of the puna plateau this basin preserves a thick continental neogene sequence that provides information on the dynamics of thick skinned deformation and resulting sedimentation the fiambala basin contains 4 km of fluvial alluvial sedimentary rocks that comprise the tamberia guanchin and punaschotter formations u pb geochronology of ashes intercalated within the fiambala stratigraphic sequence demonstrates that these sedimentary rocks are late miocene to pliocene 8 2 0 3 ma to 3 05 0 4 ma in age sedimentology and provenance data indicate that the source of the tamberia formation was located to the west of the modern western basin bounding range the guanchin and punaschotter formations record input from local sources including the modern basin bounding range to the west and the southern puna plateau to the north suggesting reorganization of the catchment area at ca 5 5 ma the coarsening upward trends recorded by the fluvial tamberia and guanchin formations indicate enhanced tectonics and relief during sedimentation the punaschot ter conglomerates record alluvial fan sedimentation and local sources fault kinematic data document a contractional regime characterized by e w and ne sw shortening active throughout the middle late miocene and pliocene furthermore a comparison between the fiambala basin and similar sedimentary basins in the sierras pampeanas e g bermejo foreland basin and the eastern cordillera leads us to propose that the study area originally constituted an integral part of a continuous and more extensive foreland basin system thin skinned for much of its early history our data suggest coeval intrabasin deformation along strike from the bermejo region northward to the eastern cordillera the coeval change at ca 6 ma from a regional to more compartmentalized thick skinned tectono sedimentary environment in the regions adjacent to the eastern cordillera the southern puna margin and other sectors within the sierras pampeanas domain may thus reflect a regional tectonic process related to flat subduction our data combined with existing sedimentological and petrological evidence imply that the passage from steep to flat subduction occurred synchronously from 30 s to 26 s

the human role in changing fluvial systems retrospect inventory and prospect historical and modern scientific contexts are provided for the 2006 binghamton geomorphology symposium on thehuman role in changing fluvial systems the 2006 symposium provides a synthesis of research concerned with human impacts on fluvial systems including hydrologic and geomorphic changes to watersheds while also commemorating the 50th anniversary of the 1955man s role in changingthe face of the earth symposium thomas jr w l ed 1956a man srole in changing the face of the earth univ chicago press chicago 1193 pp this paper examines the 1955symposium from the perspective of humanimpacts on rivers reviews current inquiry on anthropogenic interactions in fluvial systems and anticipates future directions in this field although the 1955 symposium did not have an explicit geomorphic focus it set the stage for many subsequent anthropogeomorphic studies the 1955 conference provided guidance to geomorphologists by recommending and practicing interdisciplinary scholarship through the use of diverse methodologies applied at extensive temporal and geographical scales and through its insistence on an integrated understanding of human interactions with nature since 1956 research on human impacts to fluvial systems has been influenced by fundamental changes in why the research is done what is studied how river studies are conducted and who does the research rationales for river research are now driven to a greater degree by institutional needs environmental regulations and aquatic restoration new techniques include a host of dating spatial imaging and ground measurement methods that can be coupled with analytical functions and digital models these new methods have led to a greater understanding of channel change variations across multiple temporal and spatial scales and integrated watershed perspectives all changes that are reflected by the papers in this volume these new methods also bring a set of technical demands for the training of geomorphologists the 2006 binghamton geomorphology symposium complements the 1956 symposium by providing a more specific and updated view of river systems coupled with human interactions the symposium focuses on linkages between human land use structures and channel modification with geomorphology hydrology and ecology the emergence of sustainability as a central policy guideline in environmental management should generate greater interest in geomorphic perspectives especially as they pertain to human activities the lack of theories of anthropogeomorphic change however presents a challenge for the next generation of geomorphologists in this rapidly growing subfield

trends in research on beaches and dunes on sandy shores 1969 2019 abstract trends in research on morphologic changes on beaches and foredunes on sandy shores are identified from the 1960s to the present research during this period evolved from early descriptive explanation and classification of profile change to instrumented field investigations to modelling of landform change at larger scales research efforts have become increasingly more collaborative with increasing use of field instrumentation data acquisition systems and remote sensing rich datasets are resulting in more comprehensive computational models human altered systems are of increasing interest but knowledge of these systems lags far behind knowledge of natural systems research is becoming more relevant to societal needs as the vulnerability of coastal populations increases the need for investigation of understudied or unexplored environments including human altered ones is ongoing many basic research issues remain but future studies would profit from the development of new models rather than validating or reconfiguring old models collaboration between geomorphologists and engineers may open up research opportunities particularly in modifying beaches and dunes built for shore protection to provide natural values in restricted space application of models to enhance knowledge of effects of sea level rise and coastal storms would be useful to managers developing resiliency plans

sediments and processes on a small stream flow dominated devonian alluvial fan shetland islands abstract the main conglomerate type of a small devonian alluvial fan in shetland northern britain is an inverse to normally graded framework supported gravel the sedimentological details of these beds and fundamental considerations of the mechanics of movement of highly concentrated flows suggests that neither debris flow nor grain flow were responsible for the deposition of these conglomerates on the contrary these inverse to normally graded conglomerates were deposited by water as thick gravel sheets with little topographic relief but broadly analogous to longitudinal bars they were deposited under high aggradation conditions first on the rising and then on the falling flood the high concentration of material in transport on the rising and peak flood was responsible for the polymodal and unstratified nature of the conglomerates as the flood waned normal grading was developed and a preferred horizontal fabric was produced under low concentrations of sediment other conglomerate types comparatively of lesser importance were deposited from highly concentrated clast dispersions and are notably richer in matrix and locally possess inverse grading the hydrological environment was one of flashy discharges of short duration but of high velocity flow was dissipated rapidly perhaps due to extreme water loss this example from the devonian of shetland provides an interesting alternative to the mass transport dominated fan models currently in vogue

deciphering the depositional environment of the laminated crato fossil beds early cretaceous araripe basin north eastern brazil the laminated limestones of the early cretaceous crato formation of the araripe basin north eastern brazil are world famous for their exceptionally well preserved and taxonomically diverse fossil fauna and flora whereas the fossil biota has received considerable attention only a few studies have focused on the sedimentary characteristics and palaeoenvironmental conditions which prevailed during formation of the crato fossil lagerstatte the nova olinda member represents the lowermost and thickest unit up to 10 m of the crato formation and is characterized by a pronounced rhythmically bedded pale to dark lamination to obtain information on palaeoenvironmental conditions sample slabs derived from three local stratigraphic sections within the araripe basin were studied using high resolution multiproxy techniques including detailed logging petrography xrf scanning and stable isotope geochemistry integration of lithological and petrographic evidence indicates that the bulk of the nova olinda limestone formed via authigenic precipitation of calcite from within the upper water column most probably induced and or mediated by phytoplankton and picoplankton activity a significant contribution from a benthonic carbonate secreting microbial mat community is not supported by these results deposition took place under anoxic and at least during certain episodes hypersaline bottom water conditions as evidenced by the virtually undisturbed lamination pattern the absence of a benthonic fauna and by the occurrence of halite pseudomorphs input of allochthonous catchment derived siliciclastics to the basin during times of laminite formation was strongly reduced the 18o values of authigenic carbonate precipitates between 7 1 and 5 1 point to a 18o poor meteoric water source and support a continental freshwater setting for the nova olinda member the 13c values which are comparatively rich in 13c between 0 1 and 1 9 are interpreted to reflect reduced throughflow of water in a restricted basin promoting equilibration with atmospheric co2 probably in concert with stagnant conditions and low input of soil derived carbon integration of lithological and isotopic evidence indicates a shift from closed to semi closed conditions towards a more open lake system during the onset of laminite deposition in the crato formation

oligocene range uplift and development of plateau morphology in the southern central andes 1 the puna altiplano plateau in south america is a high elevation low internal relief landform that is characterized by internal drainage and hyperaridity thermochronologic and sedimentologic observations from the sierra de calalaste region in the southwestern puna plateau argentina place new constraints on early plateau evolution by resolving the timing of uplift of mountain ranges that bound present day basins and the filling pattern of these basins during late eocene miocene time paleocurrent indicators sedimentary provenance analyses and apatite fission track thermochronology indicate that the original paleodrainage setting was disrupted by exhumation and uplift of the sierra de calalaste range between 24 and 29 ma this event was responsible for basin reorganization and the disruption of the regional fluvial system that has ultimately led to the formation of internal drainage conditions which in the salar de antofalla were established not later than late miocene upper eocene oligocene sedimentary rocks flanking the range contain features that suggest an arid environment existed prior to and during its uplift provenance data indicate a common similar source located to the west for both the southern puna and the altiplano of bolivia during the late eoceneoligocene with sporadic local sources this suggests the existence of an extensive longitudinally oriented foreland basin along the central andes during this time citation carrapa b d adelmann g e hilley e mortimer e r sobel and m r strecker 2005 oligocene range uplift and development of plateau morphology in the southern central andes tectonics 24 tc4011 doi 10 1029 2004tc001762

coalescence megafan multistorey sandstone complex of the late orogenic mio pliocene sub himalayan belt dehra dun india in the himalayan foreland basin a prominent multistorey sandstone complex in the middle siwalik subgroup is exposed along the southern flank of the dehra dun valley in the mohand anticline extending laterally for 40 km the middle siwalik subgroup consists of sandstone mudstone couplets 300 450 m thick in the lower part and the multistorey sandstone complex 900 1200 m thick in the upper which forms a gross coarsening upward sequence the major lithofacies are trough cross stratified sandstone planar cross stratified sandstone ripple drift laminated sandstone horizontal laminated sandstone and massive sandstone with subordinate amounts 20 of mudstone and conglomerate the multistorey sandstone complex is punctuated by several erosional surfaces over which abundant mud clasts are present the trough cross stratification exhibits a dominantly southward palaeoflow with much variation in the southeast and southwest quadrants however at outcrop level the palaeoflow data reveal internal consistency this spatial and temporal variability in palaeoflow direction indicates the existence of two major drainage systems of coalescing alluvial megafan type the estimated palaeochannel sinuosity is of the order of 1 04 to 1 23 with a return period of 4 to 8 103 years palaeoflow variability facies distribution frequent avulsion and the coarsening upward sequence collectively suggest the progradation of coalescing alluvial fans towards the south and southwest this was principally controlled by thrust movements and differential basin subsidence at the margin of the himalayan orogen

effects of sand fences on coastal dune vegetation distribution abstract sand fences are important human adjustments modifying the morphology of developed shores the effects of sand fences on sediment transport and deposition in their initial stages have been well studied but little is known about the effect of deteriorated sand fences that have become partially buried low scale barriers within the dune potentially benefiting vegetation growth by protecting it from onshore stress data on vegetation topography and fence characteristics were gathered at three dune sites in ocean city new jersey on september 2007 and march 2008 to evaluate the effect of fences within the dune on vegetation distribution variables include distance landward of dune toe degree of sheltering from onshore stressors net change in surface elevation deposition or erosion vegetation diversity and density presence of remnant fence and distance landward of fence results for the studied environment reveal that 1 vegetation diversity or density does not increase near remnant fences because most remnants are lower than average vegetation height and can not provide shelter but 2 vegetation distribution is related to topographic variables such as degree of sheltering that are most likely the result of sand accretion caused by fence deployment fence deployment that prioritizes the creation of topographically diverse dunes within a restricted space may increase the diversity and density of the vegetation and the resilience and value of developed dunes managers should consider the benefits of using sand fences on appropriately wide beaches to create a protective dune that is also diverse functional and better able to adapt to change

quantifying aperture spacing and fracture intensity in a carbonate reservoir analogue crato formation ne brazil abstract the characterization of fracture networks in carbonate reservoirs represents a primary approach to understand the processes of fluid flow the study of outcrop analogues has been used to enhance the understanding of the relative contribution of fracture networks to reservoir permeability the outcrop data can overcome scale limitations and or lack of consistency of subsurface datasets e g seismic well logs and cores this paper presents the fracture characterization of the aptian albian lacustrine laminites of crato formation araripe basin ne brazil which have been investigated as an analogue to some of the observed carbonate facies present in the pre salt reservoir sequence of the brazilian marginal basins in order to provide fracture attributes for discrete fracture network dfn modelling we investigate spacing and aperture distribution length and intensity of fractures based on the use of traditional scanline macro and microscale method the main fractures identified in the crato formation are shear and extensional fractures and with stylolites also present in this study we focused on vertical veins which strike in two principal directions nnw sse set 1 ne sw set 2 and are filled or partially filled by calcite or gypsum the relationship between length and aperture of vertical veins is linear apertures and spacings of fractures in both sets 1 and 2 follow power law and lognormal cumulative frequency distribution functions respectively fractures of set 2 are more likely to be clustered than are fractures of set 1 which have a wider kinematic aperture this structural database can be used to populate computational models that consider the widespread fracture system in the fluid flow simulation of carbonate reservoirs

effects of beach raking and sand fences on dune dimensions and morphology abstract raking beaches to remove wrack natural and human litter to enhance recreational use and using sand fences to build and stabilize dunes are common practices on developed shores but their effects on the landscape are not well understood managers in avalon nj ceased using sand fences and raking in a portion of beach in 1991 providing the opportunity to evaluate evolution of natural and managed dune systems over a 19 year period topographic and vegetation characteristics were evaluated on 15 transects within 5 sites in a managed area where raking and sand fences are still used and at 15 transects within 5 sites in a naturally evolving unmanaged area raking and deploying fences in the managed area restricted the size of the cross shore zone in which aeolian accretion occurred but resulted in greater dune crest heights than in the unmanaged area crest heights of the foredune in the managed area ranged from 4 45 m to 5 27 m crest heights in the unmanaged area ranged from 3 02 m to 4 27 m dune volume and beach volume were greater on average in the unmanaged area and the dune was wider mean of 72 m versus 40 m and had an additional ridge the unmanaged area had 35 more species and contained a greater percentage of all species encountered in the study area than the managed area 88 compared to 65 more species occurred in the swales than any other of the cross shore habitats and most of these species were observed in the deeper wider swales in the unmanaged area removing wrack from the beach prevents incipient dunes from forming thus reducing the number of dune crests and size of swales that create topographic variability and increase the number and types of habitats for flora and fauna suspension of raking can allow the dunes to build seaward while producing a greater variety and number of habitats but seaward growth does not mean that the height of the dune will increase substantially and fences may be needed to build an initial dune ridge for flood protection thereafter a policy of not raking in specially designated zones would be a good compromise between the need to accommodate nature and beach recreation

a general framework for modeling sediment supply to coastal dunes including wind angle beach geometry and fetch effects a series of spatially explicit equations are derived that form the foundation of a modeling framework that provides insight into how the interaction of the fetch effect and angle of wind approach leads to tradeoffs that govern the magnitude of aeolian sediment transport across beaches of different geometry the spatial distribution of sediment transport rate per unit width at any point on the beach is shown to vary predictably as a function of wind angle critical fetch and beach geometry and this has evident implications for the total volume and distribution of sediment transport into the dunes behind the beach as well as the proportion of sediment lost from the beach dune system at the downwind margin as the wind field shifts from onshore shore perpendicular to oblique shore parallel approach angle total sediment transport rate across a dune line segment will reflect a tradeoff between transport reduction because of the cosine effect and transport enhancement because of potentially longer fetch distances traversed by the wind prior to encountering the dune line this tradeoff is most evident on long narrow beaches when beach width is less than the critical fetch for such beaches and with onshore winds the total sediment transport rate across the dune line will be less than that predicted for a wide beach because of the constraint imposed by the fetch effect however as the angle of wind approach becomes oblique the available fetch becomes progressively longer transport limitations imposed by the fetch effect are negated and transport enhancement across the dune line is to be expected with very large angles of wind approach the cosine effect dominates the interaction and transport reductions across the dune line occur until the wind is shore parallel and sediment supply to the dunes ceases altogether this sequence of adjustments and tradeoffs were only partially understood prior to this study and yet they form the foundation of coastal dune modeling the framework proposed in this paper serves to place future studies of process form interaction in beach dune systems on a robust theoretical foundation it also facilitates the testing of various alternative hypotheses regarding the uneven spatial and temporal distribution of dune height and growth rate in coastal environments

aeolian transport rates across raked and unraked beaches on a developed coast wind characteristics and aeolian transport were measured on a naturally evolving beach and dune and a nearby site where the beach is raked and sand trapping fences are deployed the beaches were composed of moderately well sorted to very well sorted fine to medium sand the backshore at the raked site was wider and the foredune was more densely vegetated and about 1 m higher than at the unraked site wind speeds were monitored using anemometers placed at 1 m elevation and sand transport was monitored using vertical traps during oblique onshore alongshore and offshore winds occurring in march and april 2009 inundation of the low backshore through isolated swash channels prevented formation of a continuously decreasing cross shore moisture gradient the surface of the berm crest was dryer than the backshore making the berm crest the greatest source of offshore losses during offshore winds the lack of storm wrack on the raked beach reduced the potential for sediment accumulation seaward of the dune crest during onshore winds and the higher dune crest reduced wind speeds and sediment transport from the dune to the backshore during offshore winds accretion at wrack seaward of the dune toe on the unraked beach resulted in a wider dune field and higher narrower backshore although fresh wrack is an effective local trap for aeolian transport wrack that becomes buried appears to have little effect as a barrier and can supply dry sand for subsequent transport aeolian transport rates were greater on the narrower but dryer backshore of the unraked site vegetation growth may be necessary to trap sand within zones of buried wrack in order to allow new incipient foredunes to evolve copyright 2010 john wiley sons ltd

diagenesis of tertiary playa sandstones of northern chile implications for andean uplift and metallogeny the oligo miocene pacencia group of antofagasta province northern chile consists of over 2 km of molassic sediments deposited in a series of alluvial fan and playa sub environments sandstones of the artolla member exposed around san bartolo represent playa marginal sandflat deposits and locally host stratiform copper mineralization a detailed study of these sediments has revealed a complex sequence of diagenetic modifications to the arkosic detrital mineral assemblage early dissolution of unstable ferro magnesian minerals and calcic feldspar resulted in the release of ions into intra stratal solution and the subsequent formation of a suite of eogenetic authigenic minerals these include early hematite coatings on framework grains pore lining zeolite and pore filling calcite gypsum and celestite cements syntaxial overgrowths of albite quartz and less common k feldspar are well developed following early oxidative intrastratal conditions the influx of acidic fluids derived from mudrocks during mesogenesis resulted in an important secondary porosity generation and the establishment of an acidic reducing intrastratal environment this facilitated the subsequent introduction of low temperature mineralizing solutions and formation of the san bartolo copper deposit a return to oxidative diagenetic conditions is recorded by late stage overgrowths of k feldspar and quartz and the oxidation of native copper chalcopyrite cements to cuprite tenorite and chalcocite covellite assemblages this final telogenetic modification to the mineral assemblage is related to flushing by meteoric waters and provides independent evidence for an important phase of andean deformation and uplift in the middle to upper miocene

tectonic and magmatic evolution of the andes of northern argentina and chile abstract two orogenic cycles both with different evolution are developed in the western margin of the south american continent in northern argentina and chile the paleozoic hercynic cycle and the meso cenozoic andean cycle the hercynic cycle a wide marine basin extending westward of the cordillera oriental which developed in cambrian ordovician times marks the beginning of this cycle in contrast to peru and bolivia where this basin developed between two precambrian blocks the western margin of this basin in northern argentina and chile is still unknown the ordovician sedimentation and accompanied volcanism ends with the ocloyic deformation phase and its synkinematic granitic plutonism two basins were developed in the silurian devonian separated by the puna arc uplifted during this ocloyic phase the shallow water marine terrigeneous sediments which were deposited in them were deformed by a new tectono magmatic associated phase chanic phase carboniferous to lower permian marine carbonates were deposited west of the puna arc and red beds east of it later on during the permian to triassic a magmatic belt was developed along the cordillera occidental the rhyolites ignimbrites and the granitic to granodioritic related intrusives are well represented in chile although the overall geologic history of this period is known many problems concerning its origin and relations to plate tectonics are still unsolved the andean cycle during this cycle a series of magmatic arc systems related to the subduction of the pacific crust was built up along the western margin of south america huge volumes of calc alkaline lavas and related plutons were emplaced since the jurassic along belts parallel to the present coastline showing a general eastward migration trend up to the lower cretaceous an ensialic back arc basin was formed east of this magmatic arc thousands of meters of marine and continental sediments were deposited in it this basin disappeared during the middle cretaceous probably as a result of the final opening of the atlantic and the active westward movement of the south american plate since middle cretaceous times the magmatic arc has been the fundamental paleogeographic element the arc progressively migrated stepwise eastward each step marked by a tectonic phase subduction related crustal erosion could explain the lack of fore arc petrotectonic assemblages the eastward magmatic polarity which characterizes this section of the andes could also be explained by such a mechanism

a parametric model for dry beach equilibrium profiles abstract predictions of dry beach morphologies are extensively required in coastal research for multiple purposes e g dune erosion forecasting inundation heights determination and beach fill design optimization in this paper we introduce and test a parametric model that describes the equilibrium shape of the dry beach in the cross shore direction i e an equation for the dry beach equilibrium profile the model consists of a three parameter equation formed by two terms an exponential that defines the foreshore and berm morphology plus a linear term that defines the slope from the berm to the landward limit as a planar far field behaviour the three morphological parameters that shape the equation are related to the nearshore wave climate hs and tp and the sediment characteristics d50 in a form which is consistent with previous knowledge of dry beach morphodynamics thus proposing the runup driver h l 1 2 and the dimensionless fall velocity as the fundamental variables defining the equation parameters we tested the predictive capacity of the model against an independent data set from narrabeen beach which depending on longshore location and the time of year offers beach modal states ranging from dissipative to reflective the exponential term of the equation correctly explains the foreshore and berm morphology under mean wave climate and the linear term predicts the slope of the asymptotic planar segment all with good correlation coefficients 0 95 between modelled cross shore transects and observations the proposed model helps in defining the main shapes of subaerial beach profiles over the long term and it may also be useful as a coastal management tool for predicting dry beach morphologies

andean uplift and climate change sedimentological data indicate that a semi arid arid climate prevailed across the central andes from 15 ma to 4 ma between 4 and 3 ma a switch to hyperaridity occurred along the western margin of south america palaeoaltitude data suggest that a substantial proto central andean mountain range was in place between 15 and 9 ma these data support the idea that the andean rain shadow existed by 15 ma and that it reinforced the pre existing climatic regime rather than changing it the change to hyperaridity in western south america is attributed to a combination of global climate cooling and enhanced upwelling of the humboldt current generated by closure of the central american seaway between 3 5 and 3 ma and not to the andean rain shadow

on developing thermal cave detection techniques for earth the moon and mars abstract the purpose of this study is to 1 demonstrate the viability of detecting terrestrial caves at thermal infrared wavelengths 2 improve our understanding of terrestrial cave thermal behavior 3 identify times of day when cave openings have the maximum thermal contrast with the surrounding surface regolith and 4 further our understanding of how to detect caves on earth the moon and mars we monitored the thermal behavior of two caves in the atacama desert of northern chile through this work we identified times when temperature contrasts between entrance and surface were greatest thus enabling us to suggest optimal overflight times the largest thermal contrast for both caves occurred during mid day one cave demonstrated thermal behavior at the entrance suggestive of cold trapping while the second cave demonstrated temperature shifts suggestive of airflow we also collected thermograms without knowing optimal detection times these images suggest both caves may also be detectable during off peak times we suggest cave detection using thermal remote sensing on earth and other planetary objects will be limited by 1 capturing imagery in the appropriate thermal wavelength 2 the size of cave entrance vs the sensor s spatial resolution 3 the viewing angle of the platform in relation to the slope trajectory of the cave entrance 4 the strength of the thermal signal associated with the cave entrance and 5 the time of day and season of thermal image capture through this and other studies we will begin to identify the range of conditions under which caves are detectable in the thermal infrared and thus improve our detection capabilities of these features on earth the moon and mars

fold and thrust belt structures and strike slip faulting at the se margin of the salar de atacama basin chilean andes 1 a tectonic reinterpretation is reported for the southeastern margin of the salar de atacama basin of northern chile detailed structural mapping revealed the presence of an east vergent thin skinned fold and thrust belt affecting oligocene miocene paciencia group rocks and the overlying plio pleistocene volcanic rocks along strike segmentation of the main fold implies local foreland influence on footwall ramp geometry leading to local thrust sheet rotation to the east the adjacent western slope of the western cordillera displays two different structural domains probably controlled by preexisting basement structures the southern domain comprises two n s oriented sigmoidal belts of linear arranged pressure ridges indicating left lateral transpression in contrast the northern domain is characterized by east vergent fold and thrust belt structures and reactivated nw se striking sinistral strike slip faults governing clockwise block rotations an indenter driven deformation model is proposed to explain sinistral transpression and clockwise block rotations around vertical axes this variant of a small block rotation mechanism is discussed in the context of oroclinal bending of the central andes emphasizing the significance of ancient structures in controlling rotations

the effect of sand fencing on the morphology of natural dune systems abstract sand fences are a frequently used management tool on developed coastlines because they are inexpensive and easy to install while the geomorphic effect of sand fences has been investigated before previous studies have been limited in both temporal and spatial domains here we present the evolution of bogue banks a developed barrier island along the outer banks of north carolina over a 20 year period from 1997 to 2016 where sand fences were emplaced along parts of the island in 2010 we use lidar derived cross shore transects n 38 454 to measure beach and foredune features along the extent 40 km of bogue banks for every available year of lidar data as well as the locations of sand fences which we identify in 39 of the transects following fence construction first we found that vertical growth of the natural foredunes along bogue banks was slightly positive between 2010 and 2016 despite an increased amount of shoreline erosion this pattern was coincident with a combination of sand fence installation and beach nourishment efforts which were most heavily focused on the eastern end of the island second we found that natural foredunes located behind fenced dunes are typically shorter wider and smaller in volume than natural foredunes in non fenced and undeveloped areas although this may partly be due to a tendency for fences to be installed in front of more vulnerable dunes our results suggest that once emplaced sand fences prevent growth of the landward foredune behind fenced dunes these findings suggest that sand fences block sediment supply to landward dunes leading to a shorter and wider complex foredune than would otherwise naturally occur

seagrass berm deposition on a mediterranean embayed beach abstract seagrass leaf litter is commonly found along shores all around the world the mediterranean sea is not an exception and along the sandy shore wide and thick deposits of leaf litter can be found the deposition of these structures has not yet been studied our aim is to clarify the depositional erosive process of seagrass leaf litter on a mediterranean beach a video image system consisting of a camera and a video camera was used to investigate the dynamics of the deposition of seagrass litter on beaches time exposure images proved useful in investigating the seagrass berm deposition over the monitored period by using the eof analysis while videos are used to describe every deposition and erosion cycle the deposition of seagrass berms occurred from late october to early april while during the rest of the year the beach was free of litter the first deposition occurred in october when seagrass litter was available on the submerged bay domain the seagrass berm erosion occurred after several peaks of wind speed while the deposition started when the wind speed increases and the waves start to break near to the shoreline the deposition of the leaf litter on the beach starts as a strandline at the landward edge of the wave action and proceeds seaward up to the shoreline litter residue eroded away by the waves and floating in the inner surf zone can be redeposited in little patches at the end of an erosion cycle in conclusion leaf litter may be relevant to berm formation and litter floating in the inner surf zone and in the lower swash zone is part of the materials exchanged between submerged and emerged beach

sheet flow dominated gravel fans of the non marine middle cenozoic simmler formation central california abstract alluvial fan conglomerates of the middle cenozoic simmler formation in the cuyama gorge and southern la panza range of west central california were deposited in two half graben basins on the basis of paleocurrents and down fan fining of sediment both to the northeast the basins are thought to have been adjacent to the then active nacimiento and la panza faults three contiguous conglomerate lithofacies from most proximal to most distal are 1 clast supported crudely stratified coarse conglomerate with imbrication proximal talus and powerful sheet flow 2 clast supported well bedded internally unstratified conglomerate with common imbrication less common grading and thin interbedded coarse sands mid to upper fan deposits of highly sediment charged density modified grain flow sheet flows 3 stratified sandy conglomerate with imbrication distal alluvial sheet flows two additional lithofacies cut across the first three 4 parallel bedded graded coarse sands turbidity currents in floodbasin lakes and 5 matrix supported very poorly sorted conglomerates cohesive debris flows the alluvial fan deposits of the more northeasterly basin are overlain directly by the marine vaqueros formation the fans were dominated by sheet flow events the lack of cross bedding and minor occurrence of channels indicate that permanent streams were not established cohesive debris flows were unimportant the relationship of fan gravels both to the lake turbidites and to the conformably overlying marine sands indicates the existence of fan deltas as a result of late cenozoic transcurrent movement on the la panza fault a strand of the early san andreas system the two half graben basins have been moved so as to create a sedimentary mismatch

distal alluvial fan sediments from the upper jurassic of portugal controls on their cyclicity and channel formation the lusitanian basin of west central portugai is an iberian atlantic margin basin during a late jurassic rifting event a series of alluvial fans distributed coarse basement derived clastics southeastward from the western margin of the basin the distal part of this sequence which is about 140 m thick consists of heterolithic massive sandstone and massive mudrock facies arranged in crude fining upwards cycles 1 15 m thick these form discrete packets of sediment in a strongly aggrada tional sequence and are interpreted as the products of sheetflooding as the active area of sedimenta tion on the fan surface switched channelized flow was not necessarily an early feature of cycle development considerable fluctuations in discharge occurred and were probably related to climatic factors large quantities of tractional and suspended sediment were transported at high stages and were rapidly deposited as flows waned caliche soil profiles indicate a seasonal semi and climate however other features such as widespread soft sediment deformation the lack of desiccation structures and the absence of evaporites suggests that areas of active sedimentation often remained wet three fining upward megacycles are distinguished these indicate rapid advance of fan toes triggered by tectonic activity followed by gradual retreat

a review of tertiary climate changes in southern south america and the antarctic peninsula part 2 continental conditions abstract climate changes in southern south america and the antarctic peninsula during the tertiary show a strong correlation with ocean warming and cooling events which are in turn related to tectonic processes during periods of accelerated sea floor spreading and mid ocean ridge activity sea levels rose so that parts of the continents were flooded and forests were destroyed however this was balanced by the large scale release of co2 during volcanic outgassing and carbonate precipitation on the continental shelves which caused rising air temperatures and the poleward expansion of sub tropical and temperate forests cooling episodes generally caused an increase in the north south thermal gradient because of an equatorward shift in climate belts so that the westerly winds intensified and brought higher rainfall to the lower latitudes an increase in wind blown dust caused temperatures to drop further by reflecting sunlight back into space the rising andes range had a marked influence on climate patterns up to the middle miocene it was still low enough to allow summer rainfall to reach central and north central chile but after about 14 ma it rose rapidly and effectively blocked the spill over of moisture from the atlantic ocean and amazon basin at this time the cold humboldt current was also established which together with the andes helped to create the arid diagonal of southern south america stretching from the atacama desert to the dry steppes of patagonia this caused the withdrawal of subtropical forests to south central chile and the expansion of sclerophytic vegetation to central chile however at the same time it intercepted more rain from the northeast causing the effect of the south american monsoon to intensify in northwestern argentina and southern bolivia where forest communities presently occur in patagonia glaciation started as early as 10 5 ma but by 7 ma had become a prominent feature of the landscape and continued apparently uninterruptedly into the pleistocene the antarctic peninsula saw its first mountain glaciation between 45 and 41 ma with major ice sheet expansion commencing at about 34 ma isolated stands of nothofagus forests were still present in low lying areas suggesting that the glaciers were initially wet based but dry based glaciers were established at around 8 ma although temperatures rose briefly during the messinian pliocene transition causing sub antarctic flora to retreat to higher elevations of the transantarctic mountains the present cold polar conditions were finally established by about 3 ma

cenozoic stratigraphic development in the north chilean forearc implications for basin development and uplift history of the central andean margin abstract analysis of the cenozoic stratigraphic development of the forearc of northern chile between 18 s and 23 30 s allows constraints to be placed on the timing and nature of basin formation and the uplift history of the central andes chronostratigraphic charts have been constructed from 20 lithostratigraphic sections distributed throughout the forearc sections were taken from the longitudinal valley central depression calama basin salar de atacama precordillera and the western flank of the western cordillera correlation and timing of events is largely based on the presence of dated volcanic horizons in all the studied sections three chronostratigraphic units are defined based upon the presence of regional unconformities deposition of the late eocene to early miocene chronostratigraphic unit 38 19 ma commenced across an irregular unconformity surface between 38 and 30 ma with alluvial fan and fluvial sediments derived from the east interbedded with rhyolitic ignimbrites aggradation after 25 ma resulted in development of a large broad basin over much of northern chile that expanded eastwards through onlap onto basement deposition terminated around 19 ma with the development of an angular unconformity over much but not all of the study area during deposition of the early to late miocene chronostratigraphic unit 18 10 ma emergent volcanic source areas to the east provided catchments for large fluvial systems that drained westwards into endorheic ephemeral lacustrine basins fold growth affected sedimentation restricting accommodation space to small intra thrust basins in the precordillera and localised disruption and unconformity development in the longitudinal valley the late miocene to present day chronostratigraphic unit 10 0 ma followed the development of a regional angular unconformity at 10 ma sedimentation was restricted to a series of thrust bounded endorheic basins in both the central depression and the precordillera sourced from the east with volcanic activity limited to the periodic eruption of extensive ignimbrite sheets alluvial fan fluvial and lacustrine sedimentation dominated within the endorheic basins from 8 to 3 ma after development of a regional unconformity at 3 ma a change to isolated evaporite sub basins took place in the central depression with small lacustrine basins developed along the flank of the western cordillera the scale and grain size recorded in the sedimentary systems indicates that a substantial source area was located in the present day area of the western cordillera by 30 ma and that this has persisted to the present day this area also shed material eastwards into the altiplano the presence of such a topographic feature by 30 ma suggests that a significant proportion of andean uplift had occurred prior to the late miocene this important uplift phase should be incorporated into any model of andean uplift the evidence from the basin fill succession suggests that sediments accumulated in a basin developed in front of a broad monocline between 38 and 19 ma and that a transition to a thrust bounded foreland style basin took place after the development of the unconformity at 19 ma

controls on supergene enrichment of porphyry copper deposits in the central andes a review and discussion the central andes host some of the world s largest porphyry copper deposits the economic viability of these deposits is dependent on the size and quality of their supergene enrichment blanket published models that have strongly influenced exploration policy suggest that supergene enrichment ceased at 14 ma due to an increase in aridity here we discuss these models using published geochronological geomorphological and geological data geochronological data indicate that supergene oxidation and enrichment has been active between 17 and 27 s across the forearc of northern chile and southern peru from 44 to 6 ma and on the bolivian altiplano and eastern cordillera of argentina from 11 ma to present there is evidence for cessation at 20 14 and 6 ma however a major problem is that as more geochronological data become available the age ranges and periods of enrichment increase this suggests that the full spectrum of enrichment ages may not have been sampled the relationship between supergene enrichment and the age of regional pediplain surface development is not well constrained only in two areas have surfaces related to enrichment been directly dated southern peru and south of 26 s in chile and suggest formation post 14 ma sedimentological data indicate that a fluctuating arid semi arid climate prevailed across the atacama desert until between 4 and 3 ma climatic conditions that are thought to be favourable for supergene enrichment the balance between uplift erosion burial and sufficient water supply to promote enrichment is complex this suggests that a simple model for controlling supergene enrichment is unlikely to be widely applicable in northern chile general models that involve climatic desiccation at 14 ma related to rainshadow development and or the presence of an ancestral cold upwelling humboldt current are not supported by the available geological evidence the integration of disparate sedimentological geomorphological and supergene age data will be required to fully understand the controls on and distribution of supergene oxidation and enrichment in the central andes

the biomass of macro and interstitial fauna on clean and wrack covered beaches in western australia the benthic faunal spectrum including bacteria protozoans meiofauna wrack epifauna and macrofauna was quantitatively surveyed on two modally reflective moderate energy western australian beaches the more exposed beach had coarser sand no intertidal macrofauna and a poor interstitial fauna the less exposed beach had a large deposit of wrack totalling 161 kg m 1 dry mass concentrated on the lower shore the amphipod allorchestes compressa was abundant in the fresh wrack comprising most of the macrofauna there were also fairly abundant small epifauna on the wrack dry biomass of macrofauna epifauna meiofauna protozoans and bacteria was 0 0 15 4 and 180 g m 1 on the more exposed beach and 160 3 112 9 and 901 g m 1 on the less exposed beach with wrack on the latter beach there was an inverse correlation between meiofaunal densities and the densities of protozoans and bacteria suggesting grazing by the former on the latter on both beaches meiofauna was concentrated in the mid to upper beach protozoans near the surface and bacteria in the mid to lower beach it is estimated that bacteria are responsible for most of the secondary production on both beaches

dynamics of coupled human landscape systems a preliminary dynamical analysis of landscapes and humans as hierarchical complex systems suggests that strong coupling between the two that spreads to become regionally or globally pervasive should be focused at multi year to decadal time scales at these scales landscape dynamics is dominated by water sediment and biological routing mediated by fluvial oceanic atmospheric processes and human dynamics is dominated by simplifying profit maximizing market forces and political action based on projection of economic effect also at these scales landscapes impact humans through patterns of natural disasters and trends such as sea level rise humans impact landscapes by the effect of economic activity and changes meant to mitigate natural disasters and longer term trends based on this analysis human landscape coupled systems can be modeled using heterogeneous agents employing prediction models to determine actions to represent the nonlinear behavior of economic and political systems and rule based routing algorithms to represent landscape processes a cellular model for the development of new orleans illustrates this approach with routing algorithms for river and hurricane storm surge determining flood extent five markets home labor hotel tourism and port services connecting seven types of economic agents home buyers laborers home developers hotel owners employers hotel developers tourists port services developer and port services owners employers building of levees or a river spillway by political agents and damage to homes hotels or port services within cells determined by the passage or depth of flood waters the model reproduces historical aspects of new orleans economic development and levee construction and the filtering of frequent small scale floods at the expense of large disasters

paleomagnetic evidence for rotation in the precordillera of northern chile structural constraints and implications for the evolution of the andean forearc abstract palaeomagnetic results are reported for two late mesozoic to early cenozoic continental sedimentary sequences from the precordillera cordillera de domeyko of northern chile comparison of isolated components of magnetisation from the late cretaceous palaeocene purilactis formation and the unconformably overlying oligo miocene paciencia group with reference poles for south america indicate that significant post palaeocene and post lower miocene clockwise rotation has taken place a structural study of the area has revealed the presence of a number of thrust sheets that were periodically active throughout the cenozoic stratigraphie structural and palaeomagnetic data indicate that thrust sheet movement took place following deposition of both the purilactis formation lower eocene incaic orogeny and the paciencia group lowest miocene peheunche orogeny and resulted in the folding uplift and clockwise rotation of the two sequences differences in the amount of rotation between the two units reflect incremental movement of the thrust sheets 12 of rotation took place prior to deposition of the paciencia group followed by 17 of post lower miocene clockwise rotation this study demonstrates that palaeomagnetically detected rotation in the precordillera of northern chile 250 km inland of the peru chile trench is related to the periodic movement of an easterly propagating thin skinned thrust front between 22 30 and 23 30 s the north chilean forearc contains areas of non rotation thin skinned compressional related rotations and large block fault rotations indicating that the simplistic models previously presented to account for forearc rotation in the central andes should be modified in particular evidence implies that rotation could be related to a number of tectonic events and may not simply be due to one deformation event

patterns of sand transport on vegetated foredunes the aeolian development of coastal foredunes is studied at two sites along the dutch coast amounts of sand transport are measured in cross sections over the foredunes and changes in surface height are monitored sand transport decreases rapidly landward of the vegetation boundary near the dunefoot changes in surface roughness and topography generate turbulence and upward flow causing a small part of the sand to be transported in suspension patterns of transport are found to be closely related to air flow which in turn is related to topography and vegetation density with steeper topography the amounts of sand transported landward from the dunefoot increase if vegetation density is low during oblique onshore winds most of the sand accumulates at the dune front during perpendicular onshore winds a large proportion of the sand is deposited landward of the slope when deflection of flow occurs landward transport of sand is interrupted

sedimentological response of an alluvial system to neogene thrust tectonics atacama desert northern chile the llano de la paciencia is a thrust sheet top basin in which the sedimentological and topographic evolution can be linked to thrust tip propagation it is an elongate gravel plain which borders the salar de atacama a major intermontane basin in the andean forearc of northern chile the llano is bounded to the west by the cerros de purilactis a cretaceous paleocene sequence uplifted by the frontal domeyko thrust the eastern margin of the llano is formed by the cordillera de la sal which was uplifted by a linked back thrust frontal thrust system the salar de atacama is thus divided into a number of discrete sub basins the llano de la paciencia the pampa visachita and the western sub llano which from east west are bounded by the cordillera de la sal the northern imbricates and the ignimbrite back thrust two phases of sedimentological evolution can be distinguished within the llano on the basis of quaternary to recent sediment dispersal patterns initially phase 1 alluvial fan lobes prograded eastwards into the main salar de atacama basin subsequently uplift of the cordillera de la sal deflected drainage systems southwards parallel to the structural strike these phase 2 alluvial deposits drain into the salar de atacama at the lateral termination of the cordillera de la sal frontal thrust in places where thrust tip ramps are emergent within the llano gullies have been incised into the drainage pathways this has resulted in the reworking of the early phase 1 gravels and progradation of the phase 2 fan lobes the evolution of the llano de la paciencia illustrates the close link between topography and syntectonic alluvial drainage patterns in an arid intermontane basin