degradation of the mitchell river fluvial megafan by alluvial gully erosion increased by post european land use change queensland australia along low gradient rivers in northern australia there is widespread gully erosion into unconfined alluvial deposits of active and inactive floodplains on the mitchell river fluvial megafan in northern queensland river incision and fan head trenching into pleistocene and holocene megafan units with sodic soils created the potential energy for a secondary cycle of erosion in this study rates of alluvial gully erosion into incipiently unstable channel banks and or pre existing floodplain features were quantified to assess the influence of land use change following european settlement alluvial gully scarp retreat rates were quantified at 18 sites across the megafan using recent gps surveys and historic air photos demonstrating rapid increases in gully area of 1 2 to 10 times their 1949 values extrapolation of gully area growth trends backward in time suggested that the current widespread phase of gullying initiated between 1880 and 1950 which is post european settlement this is supported by young optically stimulated luminescence osl dates of gully inset floodplain deposits lidar terrain analysis historic explorer accounts of earlier gully types and archival records of cattle numbers and land management it is deduced that intense cattle grazing and associated disturbance concentrated in the riparian zones during the dry season promoted gully erosion in the wet season along steep banks adjacent floodplain hollows and precursor gullies this is a result of reduced native grass cover increased physical disturbance of soils and the concentration of water runoff along cattle tracks in addition to fire regime modifications episodic drought and the establishment of exotic weed and grass species geomorphic processes operating over geologic time across the fluvial megafan predisposed the landscape to being pushed by land used change across an intrinsically close geomorphic threshold towards instability the evolution of these alluvial gullies is discussed in terms of their initiation development future growth and stabilisation and the numerous natural and anthropogenic factors influencing their erosion

beach ridge plain evidence of a variable late holocene tropical cyclone climate north queensland australia abstract to date most studies of long term tropical cyclone records from beach ridge plains coral shell and sand have suggested that there has been little variation in the intensity of these events over the late holocene this study of a sand beach ridge plain in northeast queensland australia using sedimentary analysis and luminescence chronology suggests there has been considerable variation in both the intensity and frequency of tropical cyclones here since the mid holocene most of the previous beach ridge studies have been of relatively uniform elevation coral shingle shell and sand beach ridges within the plain here at rockingham bay the sediments are composed of coarse grained sand and there is considerable variation in ridge height and the number of ridges emplaced over different time intervals it may be that pure sand ridges provide a more sensitive record of variations in long term tropical cyclone climatology which in turn may contribute to a considerably improved understanding of the behaviour of this natural hazard

kinematic evolution of andean fold thrust structures along the boundary between the eastern cordillera and middle magdalena valley basin colombia 1 surface and subsurface data support a kinematic reconstruction of cenozoic fold thrust deformation along the eastern cordillera magdalena valley transition in colombia the la salina fault lsf marks the boundary between west vergent eastern cordillera structures and hinterland deposits of the middle magdalena valley basin apatite fission track and u th he thermochronological results for the west directed lsf reveal initial hanging wall exhumation during middle eocene early oligocene 45 30 ma shortening renewed exhumation in the early middle miocene 18 12 ma and accelerated late miocene pliocene 12 3 ma exhumation vitrinite reflectance data suggest maximum burial of 4 6 km helping constrain cenozoic basin architecture mapping of the lsf reveals hanging wall cretaceous eocene rocks in a broad anticline syncline pair with limited faulting and footwall eocene quaternary basin fill in a complex series of tight thrust related folds limited displacement along the westernmost frontal thrust suggests that shortening is largely accommodated by east directed thrusting within a broader triangle zone of a passive roof duplex and probable minor strike slip deformation in the preferred kinematic restoration the most recent phase of shortening to transpressional deformation represents out of sequence reactivation of the lsf consistent with irregular crosscutting relationships among footwall structures earliest exhumation by 45 30 ma in the eastern cordillera fold thrust belt is correlated with increased sedimentary lithic fragments and high compositional maturity in sandstones of the adjacent magdalena valley basin exhumation since 15 ma coincided with decreased compositional maturity and elevated accumulation rates for the real group the compositional provenance shifts are attributed to westward advance of fold thrust deformation into the proximal eastern segments of the magdalena valley basin

geomorphological variability among microtidal estuaries from the wave dominated south african coast abstract over 300 independent river outlets exist around the microtidal wave dominated south african coast most of these are located in drowned river valley settings and have acquired their present morphology during the holocene marine transgression a variety of geomorphological forms are identified in these estuaries that result from variation in antecedent topography fluvial sediment supply and marine sediment supply five distinctive estuary types are identified on the basis of contemporary morphodynamics these are categorised into three types of normally open estuary that maintain a semi permanent connection with the open sea and two types of normally closed estuary which are separated from the sea for long periods by a continuous supratidal barrier the contemporary morphodynamics and sedimentary environments of each estuary type are discussed open estuaries include barrier inlet systems maintained by fluvial discharge termed river dominated estuaries and tidal discharge termed tide dominated estuaries a third category of open estuary lacks a supratidal barrier due to inadequate marine sediment availability closed estuaries receive marine influence via barrier overwash and occasional breaching but are typically enclosed behind a continuous supratidal barrier two categories of closed estuary are identified perched and non perched perched estuaries develop behind high berms and maintain a water level above high tide level in the open sea they are often dominated by fresh to brackish water and breach and drain periodically non perched estuaries are developed behind low elevation barriers fronted by wide dissipative beach profiles high overwash frequency introduces marine water into such systems breaching of such estuaries does not produce dramatic draining as the water level may only drop according to the stage of the open sea tidal cycle the variety of estuary types suggests several potential pathways may exist in estuarine development and that the progressive infilling model is an over simplification

high frequency of super cyclones along the great barrier reef over the past 5 000 years understanding long term variability in the occurrence of tropical cyclones that are of extreme intensity is important for determining their role in ecological disturbances1 2 3 4 5 for predicting present and future community vulnerability and economic loss6 and for assessing whether changes in the variability of such cyclones are induced by climate change7 our ability to accurately make these assessments has been limited by the short less than 100 years instrumented record of cyclone intensity here we determine the intensity of prehistoric tropical cyclones over the past 5 000 years from ridges of detrital coral and shell deposited above highest tide and terraces that have been eroded into coarse grained alluvial fan deposits these features occur along 1 500 km of the great barrier reef and also the gulf of carpentaria australia we infer that the deposits were formed by storms with recurrence intervals of two to three centuries8 9 10 11 and we show that the cyclones responsible must have been of extreme intensity central pressures less than 920 hpa our estimate of the frequency of such super cyclones is an order of magnitude higher than that previously estimated which was once every several millennia12 13 14 and is sufficiently high to suggest that the character of rainforests and coral reef communities were probably shaped by these events

drivers of precipitation stable oxygen isotope variability in an alpine setting snowy mountains australia natural archives that preserve a stable isotopic signature are routinely used to reconstruct palaeoenvironmental conditions isotopic values of precipitation are known to be influenced by factors such as the amount and type of precipitation moisture pathway landscape and terrain factors and processes associated with precipitation formation and deposition this study investigates oxygen isotopic variability using real time rain and snow precipitation data from a moderate altitude 2250 m above sea level southern hemisphere alpine environment where the causes of isotopic variability are largely unknown previous research at global network of isotopes in precipitation sites skewed toward rain precipitation low altitude predominantly coastal locations identified amount effects as the dominant explanation of isotopic variability in southern australia this study based on within and between event real time sampling finds that the origin of moisture and terrain effects are the dominant cause of isotopic variability in this alpine region with little evidence of amount effects rainfall that originated from similar southern ocean latitudes showed a consistent moderate isotopic signature 18o 6 5 to 8 depleted isotopic signatures are associated with prefrontal activity and intense circulation such as east coast lows localized thunderstorms have a more neutral isotopic signature a windward to leeward depletion 0 5 18o and an elevation impact 0 5 18o 100 m 1 were found also these results have significant implications for understanding atmospheric drivers of isotopic variability from which oxygen isotope based palaeoclimate reconstruction is informed in regions with complex topography and geographically diverse moisture pathways such as the australian alps

continental margin response to multiple arc continent collisions the northern andes caribbean margin abstract an integration of diverse strain markers into a palinspastic reconstruction of the northern andes provides a first order quantitative approximation to the response of a complex margin to two consecutive arc continent collisions a palinspastic reconstruction highlights margin parallel displacements with crustal blocks traveling 400 to 500 km northward while the margin normal shortening component excluding subduction is limited to 100 km the first arc continent collision closed a 500 km wide ocean basin where subduction of atlantic lithosphere took place under an intra oceanic arc 90 to 65 ma old originally 1100 km long and currently stretched 2200 km following collision eastward directed oblique subduction started at 65 ma with 800 km of proto caribbean lithosphere consumed under northwestern south america igniting a short lived magmatic arc along the post collisional margin two molasse deposits track deformation cooling exhumation and erosion of the margin the first heralds the arrival of the first intra oceanic arc to the southernmost northern andes in late campanian times younging northward as the collision propagated north this latest cretaceous molasse deposit records also the first altitudinal gain in the northern andean orogen along the central and real cordilleras the second molasse follows middle to late eocene magmatic arc shut down and regional exhumation and cooling of the margin formation rise and docking of the intra oceanic panama arc closed a 1200 km wide middle eocene seaway and renewed miocene magmatism in the northern andes as the nazca plate started subducting behind the docked arc

facies evolution of holocene estuaries and deltas a large sample statistical study from australia abstract selected geomorphic features and sedimentary facies were mapped in 283 of australia s wave and tide dominated estuaries and deltas to quantitatively evaluate established evolutionary facies models that depict the evolution of estuaries into deltas during stable sea level conditions while diagnostic facies for wave and tide dominated estuaries and deltas approximate those specified by the models statistical analyses of the data also reveal two additional insights regarding the evolution of estuaries to deltas first there is an offshore shift in the locus of sand accumulation between tide dominated estuaries and deltas associated with the onset of delta development second the mean surface area of intertidal environments i e intertidal flats mangroves melaleuca saltmarsh salt flat facies is greater in wave dominated deltas than in wave dominated estuaries tidal penetration associated with the river establishing a more direct and permanent connection to the sea during late stage development presents a natural impediment to continued formation of an alluvial plain and full development of the classic wave dominated delta morphology a notional evolutionary pathway for wave dominated estuaries is developed from the distribution of facies that predicts the rate and susceptibility of geomorphic and habitat changes the classic deltaic geomorphology may be unattainable for wave dominated systems except those with significant terrigenous sediment inputs our study is the first published example of geomorphic and sedimentary data assembled from a large number of wave and tide dominated estuaries and deltas across an entire continent

morphological patterns of southeastern mediterranean river mouths the topographic setting of the beach as a forcing factor abstract israeli mediterranean river mouths are characterized by an extremely dynamic morphology as their channels tend to migrate hundreds of meters north and south along the shoreline this study aims to characterize the impact of the topographic setting of the beach on the dynamic morphology of seven of these river mouths this was achieved by morphologically mapping and monitoring the natural channel dynamics of each mouth over time recognizing their spatial and temporal migration and avulsion patterns describing generalizing and classifying the different types of river mouths present on the coast and investigating the influence of the adjacent topography on their morphology detailed geomorphologic mapping was achieved using remote sensing and gis techniques utilizing more than 300 aerial photographs taken between 1918 and 2005 this study revealed a number of typical differences in these patterns attributed to differences in the topographic setting of the beach in the vicinity of the mouths elongated strip topography coasts demonstrate a uniform slope beach with equally spaced elevation contours forming a narrow sandy strip between the shoreline and the back berm funnel topography coasts exhibit a non uniform slope with a funnel shaped topographic depression adjacent to the river mouth similarities were found between the spatial and the temporal morphological patterns of river mouths flowing in each of these two topographical settings elongated strip mouths are deflected alongshore a barrier and demonstrate high migration distances and little temporal change the morphology of funnel mouths was found to be highly temporally variable yet less spatially dynamic as these mouths channels are restricted by their funnel topography this study concludes that the topographic setting of the beach a constant element in the temporal scale of this study is a primary factor influencing the morphology of the studied mouths

assessing sedimentary records of paleohurricane activity using modeled hurricane climatology patterns of overwash deposition observed within back barrier sediment archives can indicate past changes in tropical cyclone activity however it is necessary to evaluate the significance of observed trends in the context of the full range of variability under modern climate conditions here we present a method for assessing the statistical significance of patterns observed within a sedimentary hurricane overwash reconstruction to alleviate restrictions associated with the limited number of historical hurricanes affecting a specific site we apply a recently published technique for generating a large number of synthetic storms using a coupled ocean atmosphere hurricane model set to simulate modern climatology thousands of overwash records are generated for a site using a random draw of these synthetic hurricanes a prescribed threshold for overwash and a specified temporal resolution based on sedimentation rates observed at a particular site as a test case we apply this monte carlo technique to a hurricane induced overwash reconstruction developed from laguna playa grande lpg a coastal lagoon located on the island of vieques puerto rico in the northeastern caribbean apparent overwash rates in the lpg overwash record are observed to be four times lower between 2500 and 1000 years b p when compared to apparent overwash rates during the last 300 years however probability distributions based on monte carlo simulations indicate that as much as 65 of this drop can be explained by a reduction in the temporal resolution for older sediments due to a decrease in sedimentation rates periods of no apparent overwash activity at lpg between 2500 and 3600 years b p and 500 1000 years b p are exceptionally long and are unlikely to occur above 99 confidence under the current climate conditions in addition breaks in activity are difficult to produce even when the hurricane model is forced to a constant el nino state results from this study continue to support the interpretation that the western north atlantic has exhibited significant changes in hurricane climatology over the last 5500 years

isotopic spikes from tropical cyclones in surface waters opportunities in hydrology and paleoclimatology abstract the stable isotopic ratio of precipitation from tropical cyclones is very low compared to that of normal summer precipitation lawrence and gedzelman 1996 tropical storms allison and chantal made landfall in southeast texas in the summer of 1989 and dumped large amounts of rain isotope ratios of surface waters measured at five different sites decreased markedly after the passage and remained low for a few weeks the return of isotope values to normalcy following these storms varied from site to site reflecting differences among the hydrological environments during other summers from 1985 to 1993 isotope ratios of rains were higher and in the normal range calculations using air temperatures and oxygen isotope measurements of the surface waters show that organically precipitated fresh water carbonate should have recorded the two oxygen isotopic spikes produced by allison and chantal at all five sites this suggests that isotopic analysis of ancient fresh water fossil carbonate shells fossil mammal teeth or tree rings might be used to document past tropical cyclone activity

tropical cyclone activity and western north atlantic stratification over the last millennium a comparative review with viable connections tropical cyclones tc are recognized to modify the thermal structure of the upper ocean through the process of vertical mixing assessing the role this mixing plays in the overall stratification of the upper ocean is difficult due to the relatively short and incomplete instrumental record proxy records for both tc landfalls and oceanographic stratification are preserved within the geological record and provide insight for how past changes in tc induced mixing have potentially affected water column structure prior to the instrumental record here we provide the first comparison between previously published paleo reconstructions of vertical ocean density and tropical cyclone activity from the western north atlantic a prominent lull in tc activity has been observed prior to approximately 1700 ce that extends back several centuries this interval of low tc activity is shown to be concurrent with the timing of increased ocean stratification near great bahama bank potentially due in part to reduced tc induced mixing to test whether this relationship is feasible we present numerical results from a coarse resolution ocean general circulation model experiment isolating the effect of tc surface wind forcing on the upper ocean an anomaly of roughly 0 12 kg m 3 in vertical stratification occurs above and below the mixed layer for model runs with and without tc mixing this anomaly is roughly 25 of the entire paleo density signal observed just prior to 1700 ce these results suggest that tc mixing alone cannot completely explain the density anomaly observed prior to 1700 ce but support tc variability as an important contributor to enhancing oceanic stratification during this interval copyright 2011 john wiley sons ltd

a new chalcolithic era tsunami event identified in the offshore sedimentary record of jisr al zarka israel abstract tsunami field evidence is a critical resource for determining coastal risk however in many cases there is low potential for long term preservation of such deposits on land a growing body of evidence suggests that tsunami deposits can be present in the shallow offshore realm and may present a largely untapped but important worldwide sedimentological reference set for investigating past tsunami events here different proxies for tsunami sediment identification and differentiation granulometry xrd xrf ft ir were used to determine the presence or absence of such deposits in a core collected offshore at jisr al zarka midway between tel aviv and haifa the study aimed to recognize anomalous deposits and test different analytical methods to define their origins five anomalous sedimentological horizons were identified four of which were interpreted as tsunamigenic by comparison to previously identified poorly sorted shell rich tsunamites found nearby in caesarea and contrast to the fine sand nile derived background sediments the remaining anomaly was distinctive but not determined to be tsunamigenic due to a lack of coarse shell in the matrix the oldest tsunamigenic layer coinciding with the chalcholithic cultural period 5 7 ka is the oldest such deposit identified offshore israel to date and the non tsunamigenic anomalous horizon may correspond with a transitional climatic phase 5 5 ka this research reinforces the importance of offshore investigations as a means of improving tsunami catalogues and identifying environment altering events

structure of the eastern cordillera of colombia implications for trap styles and regional tectonics the northwest margin of south america has undergone multiple phases of compressional deformation beginning in the late cretaceous and culminating in the pliocene pleistocene the latest phases miocene to pleistocene of this deformation created the eastern cordillera of colombia compressional structures in the eastern cordillera formed traps that have petroleum exploration potential these are generally in the form of fault bend and fault propagation folds containing top sealed reservoir and mature source rocks trap delineation although difficult to achieve because of the poor seismic quality obtained in the region can be accomplished by supplementing the seismic data with geometric analysis of surficial structures the eastern cordillera is asymmetrical with the dominant tectonic transport direction towards the east west directed thrust faults are localized along the western flank of the eastern cordillera and are interpreted to be back thrusts splaying off a deep mid crustal detachment a regional retrodeformable cross section across the eastern cordillera shows that basement detached deformation of late miocene to pliocene age was followed by pliocene to holocene uplift of the cordillera on high angle basement involved reverse faults these two structural styles were superimposed on preexisting jurassic and lower cretaceous grabens whose normal faults were partially inverted during the later stages of compressional deformation a palinspastic restoration of this regional cross section indicates that approximately 150 km of shortening 40 shortening has occurred 105 km eastward directed towards the llanos basin and 45 km westward directed towards the middle magdalena basin this calculated shortening is very close to that calculated by summing microplate motions for the northwest corner of south america shortening in the sedimentary cover rocks exceeds that in the basement rocks by about three times this shortening can be regionally balanced with a gently dipping mid crustal detachment that extends beneath the middle magdalena basin and central cordillera and which roots in the benioff zone beneath the western cordillera the presence of a mid crustal detachment as postulated here provides a mechanism to transmit the shortening from the convergent plate margin in the pacific to the andean foreland and is interpreted to have provided the structural link between the three ranges of the colombian andes the detachment also provides a mechanism to explain the imbalance of shortening seen between eastern cordillera basement and the overlying strata and implies that the western and central colombian andes have been tectonically transported eastwards a distance of at least 150 km

exploring typhoon variability over the mid to late holocene evidence of extreme coastal flooding from kamikoshiki japan sediment cores from two coastal lakes located on the island of kamikoshiki in southwestern japan lake namakoike and lake kaiike provide evidence for the response of a backbarrier beach system to episodic coastal inundation over the last 6400 years sub bottom seismic surveys exhibit acoustically laminated parallel to subparallel seismic reflectors intermittently truncated by erosional unconformities sediment cores collected from targeted depocenters in both lakes contain finely laminated organic mud interbedded with coarse grained units with depths of coarse deposits concurrent with prominent seismic reflectors the timing of the youngest deposit at kamikoshiki correlates to the most recently documented breach in the barrier during a typhoon in 1951 ad assuming that this modern deposit provides an analog for identifying past events paleo typhoons may be reconstructed from layers exhibiting an increase in grain size a break in fine scale stratigraphy and elevated sr concentrations

longshore sand transport estimates along the mediterranean coast of israel in the holocene abstract the nile littoral cell one of the world s longest runs 650 km along the southeastern mediterranean from abu quir bay near alexandria egypt to haifa bay on the northern israeli coast haifa bay constitutes the northernmost final depositional sink of nile derived quartz sand transported from the nile delta by longshore currents generated by approaching breaking waves the northward net sand transport along the mediterranean coast of israel results from larger waves approaching from west south west and south west compared to their counterparts from west north west and north west this study utilizes an extensive new database gathered from sediment drill cores marine geophysical maps and field observations to measure the volume of sand deposited in haifa bay and the adjacent zevulun plain during the holocene it then compares this volume to recent data including measurements of sand accumulation along haifa port s main breakwater constructed in the southern entrance of the bay as well as longshore sand transport estimates along the northern carmel coast research findings estimate the annual average quantity of sand transported to haifa bay throughout the period at 80 000 90 000 m3 the findings further conclude that this amount has not changed appreciably over the past 75 years evaluating calculated values over the long term it is suggested that the characteristics of longshore sand transport along the coast of israel have not changed significantly during the past 7900 8500 years it is obvious that this conjecture should be treated with reservations

10be constrains the sediment sources and sediment yields to the great barrier reef from the tropical barron river catchment queensland australia abstract estimates of long term background sediment generation rates place current and future sediment fluxes to the great barrier reef in context without reliable estimates of sediment generation rates and without identification of the sources of sediment delivered to the reef prior to european settlement c 1850 determining the necessity and effectiveness of contemporary landscape management efforts is difficult here using the 2100 km 2 barron river catchment in queensland australia as a test case we use in situ produced 10 be to derive sediment generation rate estimates and use in situ and meteoric 10 be to identify the source of that sediment which enters the coral sea near cairns previous model based calculations suggested that background sediment yields were up to an order of magnitude lower than contemporary sediment yields in contrast in situ 10 be data indicate that background 43 t km 2 y 1 and contemporary sediment yields 45 t km 2 y 1 for the barron river are similar these data suggest that the reef became established in a sediment flux similar to what it receives today since western agricultural practices increased erosion rates large amounts of sediment mobilized from hillslopes during the last century are probably stored in queensland catchments and will eventually be transported to the coast most likely in flows triggered by rare but powerful tropical cyclones that were more common before european settlement and may increase in strength as climate change warms the south pacific ocean in situ and meteoric 10 be concentrations of coral sea beach sand near cairns are similar to those in rivers on the atherton tablelands suggesting that most sediment is derived from the extensive low gradient uplands rather than the steep more rapidly eroding but beach proximal escarpment

low stable isotope ratios of tropical cyclone rains tropical cyclone rains have distinctly lower stable isotope ratios than rains in other tropical and summer precipitation systems with a mean value slightly above that of water vapor near the sea surface the isotope ratios also decrease radially inward to the eye wall but appear to be anomalously low even near the periphery of the rain shield these findings indicate that tropical cyclones are highly efficient precipitation systems and suggest the use of stable isotope ratios as dynamic tracers of a tropical cyclone s water and energy budgets

a 1900 year paleohurricane record from wassaw island georgia usa we present here the first paleotempestology record from wassaw island on the georgia bight located in the south atlantic coast of the united states in the historical period the georgia bight has experienced less frequent hits by hurricanes than other locations along the us gulf and atlantic coasts the 1900 year record inferred from the overwash sand layers from a back barrier marsh on wassaw island suggests that the island was directly struck by major storms on nine occasions during this interval the wassaw island record shows alternating regimes with periods of increased activity from 2000 a bp until 1100 a bp and 100 a bp until the present sandwiching a quiet period from 1100 to 250 a bp storm deposits from the most recent active period are perhaps amalgamated indicating that site specific conditions may result in event undercounting and suggests that the relative thickness of sand layers in the sedimentary record is not always indicative of hurricane strength copyright 2011 john wiley sons ltd

rapid coastal geomorphic change in the river murray estuary of australia abstract the river murray estuary a ramsar wetland site has experienced considerable rapid coastal change during the quaternary the interplay of aeolian processes river flows tidal oscillations wave action and variations in relative sea level due to global sea level changes and land subsidence provides the energy for the ongoing dynamism often accelerated by human impacts the estuary is the terminus of the murray darling catchment which covers 1 073 million km 2 of the australian continent terminal lakes alexandrina albert and the coorong lagoon are holocene features occupying tectonically subsiding quaternary interdune areas they formed in response to eustatic sea level rise following the last glacial maximum ca 20 ka the last interglacial shoreline 125 000 yr bp parallels the modern shoreline several kilometres inland dislocation of the last interglacial shoreline demonstrates ongoing tectonic subsidence as does historical seismic activity the northern half of hindmarsh island formed during last interglacial times when it was the sink for dominant longshore transport from the southeast which pushed the river murray westward partly explaining the large bend in the river murray at goolwa the modern coastal barriers of sir richard peninsula and younghusband peninsula formed from 7000 yr ago following glacier melt and sea level rise subsequently the barriers have migrated landward sporadically exposing lagoonal sediments on the ocean beaches differential loading of the soft lagoonal sediments by advancing dunes possibly in conjunction with seismic events has deformed and elevated them to up to 10 m above present sea level apsl during the mid holocene an extensive sand flat with associated dunes formed immediately inland of the coastal barrier at least six generations of late pleistocene dune systems occur in the region for example during last glacial times the climate was drier colder and windier than at present and a system of parallel west east trending yellow red desert dunes developed around the lakes aeolian processes remain important with occasionally up to 5000 tonnes of sand being in motion along 10 km of the modern shoreline during mouth migration dunes up to 2 m high have been formed and vegetated in 12 months directly inland from the mouth and replicating the formation of older dunes on hindmarsh island elsewhere sand blown directly from the barrier system infills channels barrage construction on the beach facies of the last interglacial shoreline transformed the estuary into freshwater lakes with permanently raised water levels and reduced the tidal prism by 90 increased deposition upstream and downstream accompanied barrage construction as have accelerated lakeshore erosion and the growth and consolidation of the flood tidal delta bird island these human accelerated changes provide rapidly formed analogues of older quaternary features and aid their interpretation the shape and location of the murray mouth is constantly changing migrating over 1 6 km since the 1830s migrations of up to 6 km over the past 3000 yr have influenced sedimentation on the landward shore of the back barrier lagoonal system

vertical tectonics at a continental crust oceanic plateau plate boundary zone fission track thermochronology of the sierra nevada de santa marta colombia 1 the topographically prominent sierra nevada de santa marta forms part of a faulted block of continental crust located along the northern boundary of the south american plate hosts the highest elevation in the world 5 75 km whose local base is at sea level and juxtaposes oceanic plateau rocks of the caribbean plate quantification of the amount and timing of exhumation constrains interpretations of the history of the plate boundary and the driving forces of rock uplift along the active margin the sierra nevada province of the southernmost sierra nevada de santa marta exhumed at elevated rates 0 2 km my during 65 58 ma in response to the collision of the caribbean plateau with northwestern south america a second pulse of exhumation 0 32 km my during 50 40 ma was driven by underthrusting of the caribbean plate beneath northern south america subsequent exhumation at 40 25 ma 0 15 km my is recorded proximal to the santa marta bucaramanga fault more northerly regions of the sierra nevada province exhumed rapidly during 26 29 ma 0 7 km my further northward the santa marta province exhumed at elevated rates during 30 25 ma and 25 16 ma the highest exhumation rates within the sierra nevada de santa marta progressed toward the northwest via the propagation of nw verging thrusts exhumation is not recorded after 16 ma which is unexpected given the high elevation and high erosive power of the climate implying that rock and surface uplift that gave rise to the current topography was very recent i e 1 ma and there has been insufficient time to expose the fossil apatite partial annealing zone

magmatic consequences of the transition from orthogonal to oblique subduction in panama the closure of the central american seaway is linked with tectonic and magmatic processes that have controlled the evolution of the isthmus of panama we focus on the terminal stages of arc activity in the central panama region and present new geochemical data from 9 ma explosive silicic volcanism preserved in three syngenetic tuff beds from the gatun formation the magmatic evolution of the gatun formation is controlled by a series of magma mushes where pyroxene is the dominant early forming mafic mineral with amphibole appearing only relatively late in the fractionation sequence our data shows gatun lavas exhibit a strong subduction signature consistent with plate reconstruction models showing arc normal subduction from costa rica to panama pre 8 5 ma however large ion lithophile elements are depleted in the gatun formation in comparison to other regional suites indicative of a lower flux of subduction fluid to the gatun formation mantle source which is explained by a shift towards magma generation by decompression following the collision of the arc with south america oblique subduction commencing 8 5 ma resulted in the shutdown of normal arc activity throughout panama we interpret subsequent regional quaternary adakitic volcanism as a response to this oblique subduction the now more refractory mantle wedge required greater fluid flux in order to melt the resultant volatile rich melts were more prone to deep fractionation of amphibole and garnet cumulates forming adakites deep fractionation was potentially enhanced by changing stress regimes on the upper plate caused by oblique subduction this article is protected by copyright all rights reserved

dynamic characteristics of the yellow river mouth the yellow river delta is dynamic because the river carries a heavy sediment load and serious siltation occurs in the area massive sediment transport brings fertile soil to the river mouth leading to its expansion by 20 25 km2 per year the dramatic reduction in runoff and sediment in the delta due to increasing water demand has extended the period of flow cut off the river changes its delta channel about once every ten years the channel shifts affect the upstream flood stages since the river shifted to the present delta channel in 1976 the shape of the delta has changed remarkably sediment laden flow has been building channels by depositing sediment in low velocity areas and has extended the river mouth into the sea for more than 40 km the velocity of sea currents is enhanced by the growth of the river mouth spit at a rate of 1 m s 1 per 10 km extension which results in high capacity of sea currents carrying sediment away from the mouth the new river mouth area was silted up by 14 m and the old river mouth area was eroded by 5 m siltation takes place in the low flow season and scouring occurs in the flood season scouring occurs during the rising limb of a flood and siltation occurs during the receding limb of a flood the roughness of the river changes largely following the increase in discharge the minimum manning roughness occurs at non siltation and non erosion discharge tidal influence in the river is restricted to a section extending over only a few kilometres unlike in many other coastal areas the river water with its high sediment concentration develops into density current and flows underneath the seawater during flood this mechanism contributes to sediment transportation in the delta copyright 2000 john wiley sons ltd

morphostratigraphy of an ebb tidal delta system associated with a large spit in the piedras estuary mouth huelva coast southwestern spain abstract the piedras estuary is one of the most significative estuarine systems on the mesotidal huelva coast in the northwestern portion of the cadix gulf the river mouth is presently an estuarine lagoon partially closed by a large spit constructed from an old barrier island system this estuary is in an advanced state of infilling and its tidal prism has decreased during the holocene causing instability and clogging of old inlets and transforming the barrier island chain into a spit sedimentation is controlled by the interaction of ebb tide currents and the prevailing sw waves the main sediment supply is provided by an intensive west to east longshore current transporting sand material from portuguese cliffs and the guadiana river tidal range is mesotidal 2 0 m and the mean significant wave height is 0 6 m with an average period of 3 6 s a boxcore study allowed five depositional facies to be distinguished in the piedras estuary mouth 1 main ebb channels 2 marginal flood channels 3 ebb tidal delta lobes 4 marginal levees and 5 curved spits the recent evolution studied in this area suggests a cyclic evolutionary model for the ebb tidal delta system the architectural facies relations shown by the vibracore boxcore study confirm that the apical growth of the spit occurred over the innermost of these ebb tidal deltas consequently the preserved sequence shows the ebb tidal delta facies under the spit facies

plate motions in the north andean region repeated geodetic measurements with the global positioning system gps provide direct measurements of displacements due to plate motions and active crustal deformation in central america and northern south america an area of complex interaction of the nazca cocos caribbean and south american plates the displacement rates for the period 1988 1991 obtained from the results of the first three central and south america casa gps campaigns are in general agreement with the predictions of the nuvel 1 plate motion model but there are differences in detail between the observations and the model the nazca north andes convergence rate vector measured by gps is different from the nuvel 1 vector at 95 confidence the difference implies that the north andes are moving northward relative to south america the measured convergence between the caribbean plate and the north andes suggests that the southern margin of the caribbean plate is located in the south caribbean deformed belt the april 1991 costa rica earthquake and the cocos caribbean convergence rate determined by gps suggest the possibility of significant ongoing deformation between central america and the stable interior of the caribbean plate our gps results are consistent with deformation of the overriding plates at the convergent margins of central and south america and confirm that active convergence is occurring around much of the southern margin of the caribbean plate from colombia west to costa rica costa rica and panama are not part of the stable caribbean plate instead the south caribbean deformed belt and the north panama fold belt probably represent the southern margin of the caribbean plate

tectonic evolution and mantle structure of the caribbean we investigate whether predictions of mantle structure from tectonic reconstructions are in agreement with a detailed tomographic image of seismic p wave velocity structure under the caribbean region in the upper mantle positive seismic anomalies are imaged under the lesser antilles and puerto rico these anomalies are interpreted as remnants of atlantic lithosphere subduction and confirm tectonic reconstructions that suggest at least 1100 km of convergence at the lesser antilles island arc during the past 45 myr the imaged lesser antilles slab consists of a northern and southern anomaly separated by a low velocity anomaly across most of the upper mantle which we interpret as the subducted north america south america plate boundary the southern edge of the imaged lesser antilles slab agrees with vertical tearing of south america lithosphere the northern lesser antilles slab is continuous with the puerto rico slab along the northeastern plate boundary this results in an amphitheater shaped slab and it is interpreted as westward subducting north america lithosphere that remained attached to the surface along the northeastern boundary of the caribbean plate at the muertos trough however material is imaged until a depth of only 100 km suggesting a small amount of subduction the location and length of the imaged south caribbean slab agrees with proposed subduction of caribbean lithosphere under the northern south america plate an anomaly related to proposed oligocene subduction at the nicaragua rise is absent in the tomographic model beneath panama a subduction window exists across the upper mantle which is related to the cessation of subduction of the nazca plate under panama since 9 5 ma and possibly the preceding subduction of the extinct cocos nazca spreading center in the lower mantle two large anomaly patterns are imaged the westernmost anomaly agrees with the subduction of farallon lithosphere the second lower mantle anomaly is found east of the farallon anomaly and is interpreted as a remnant of the late mesozoic subduction of north and south america oceanic lithosphere at the greater antilles aves ridge and leeward antilles the imaged mantle structure does not allow us to discriminate between an intra americas origin and a pacific origin of the caribbean plate key points tectonic reconstructions for the caribbean validated by seismic tomography cenozoic lesser antilles and mesozoic greater antilles subduction confirmed tomography gives insight into geodynamics of lesser antilles

campanian miocene tectonostratigraphy depocenter evolution and basin development of colombia and western venezuela abstract the position of the central axis of deposition over colombian and venezuelan continental crust has varied markedly through time the axis migrated from west to east from late cretaceous to oligocene but at times secondary drainage divides were established by local uplift events in oligocene times with initial inversion of the eastern cordillera the central axis of deposition was divided into two main axes the proto magdalena and the proto orinoco systems the west to east migration of the central axis of deposition had a tectonic origin and it occurred in combination with tectonically driven changes in accommodation space depocenter evolution can be divided as follows 1 the axis of the campanian and early maastrichtian depocenter was located few km east of the present position of the central cordillera of colombia it migrated east with gradual uplift of the central cordillera 2 the central axis of late maastrichtian deposition is positioned approximately over the present day western foothills of the eastern cordillera possibly crosses the eastern cordillera over the santander massif and continues into the maracaibo lake in western venezuela accommodation space decreased from campanian to maastrichtian times in cretaceous tertiary boundary times parts of the eastern margin of the eastern cordillera were uplifted by an initial phase of inversion of deeply rooted jurassic and early cretaceous normal faults 3 in paleocene times the central axis of deposition was located along the spine of the eastern cordillera and extended into the maracaibo basin and accommodation space continued to decrease 4 in latest paleocene times the central axis of deposition shifted to eastern regions of the eastern cordillera and accommodation space decreased 5 the early eocene central axis of deposition was located along the present day eastern foothills of the eastern cordillera accommodation space continued to decrease and the regional middle eocene unconformity began to develop in middle eocene times a regional unconformity developed marking the climax of the pre andean orogeny deposition during these times was dominant in the maracaibo basin area where large amounts of sediment derived from vast exposed areas accumulated 6 the late eocene central axis of deposition was confined to the present position of the llanos foothills late eocene deposition reflects a regional increase in accommodation space in oligocene times the initial uplift of the eastern cordillera divided the main depocenter into two central axes accommodation space diminished in uplifted regions but continued to increase in the depocenters allowing sporadic marine ingressions into the present position of the llanos foothills as uplift of the eastern cordillera continued the eastern depocenter axis proto orinoco migrated east and the western depocenter axis proto magdalena migrated west this process continued through the rest of the cenozoic

possible tsunami inundation identified amongst 4 5th century bce archaeological deposits at tel ashkelon israel abstract the eroding coastal sections of ashkelon israel contain exposed sequences of natural and anthropogenic sedimentological deposits some of unknown origin ashkelon an important and long occupied ancient coastal city is directly referred to within written records of past tsunami events yet field studies and archaeological descriptions have not yet corroborated these claims this is not unusual nor unexpected given the amount of anthropogenic and natural disturbance that can erase the sedimentary remains as well as the relatively recent advancements in identifying such deposits a sequence of sediments at the base of an eroding coastal archaeological section shows clear waterborne transport characteristics and was previously interpreted as alluvial however no alluvial sources could be associated to the deposit in this study the sedimentological characteristics of this section were described and analyzed in greater detail to determine their nearest similarity to possible transport mechanism such as storms rivers and tsunamis the deposits contain fining upward sequences rip up clasts imbricated inclusions fine mud layers microfauna foraminifera and broken diagnostic pottery from the 4 5th c bc reconstructions of the coastline at the time of the event place the sampled profile at least 100 m inland from the shoreline at an elevation 2 0 to 2 4 m above sea level river channel features were not identified in the section for this area modern observations of major storms show inundations of

river mouth bar formation riverbed aggradation and channel migration in the modern huanghe yellow river delta china this paper addresses the recent 1970s 1990s processes of river mouth bar formation riverbed aggradation and distributary migration in the huanghe river mouth area in the light of station based monitoring field measurements and remote sensing interpretation the results show that the morphological changes of the river mouth bar have been closely associated with the largely reduced fluvial discharge and sediment load landforrn development such as bar progradation occurred in two phases i e before and after 1989 which correspond to faster and lower bar growth rates respectively fast riverbed aggradation in the mouth channel was strongly related to river mouth bar progradation during 1976 1996 about 2 8 of the total sediment loads were deposited in the river channel on the upper to middle delta therefore the river water level rose by a few meters from 1984 to 1996 the frequent distributary channel migration which switched the radial channel pattern into the se directed pattern in the mid 1980s was linked with mouth bar formation marine conditions also constrain seaward bar progradation furthermore the history of river mouth bar formation reflects human impacts such as dredging and dyking in order to stabilize the coastal area c 2005 elsevier b v all rights reserved

chronostratigraphy and geomorphology of washover fans in the exmouth gulf nw australia a record of tropical cyclone activity during the late holocene abstract washover fans typically form due to barrier overwash or breaching and coastal inundation and generally represent geomorphological and depositional evidence of intense storms few studies have investigated the chronostratigraphy of washover fans in order to infer magnitude frequency patterns of extreme wave events over longer time scales here we present new data on the chronostratigraphy of late holocene washover fans in the exmouth gulf western australia by using ground penetrating radar and unmanned aerial vehicle uav survey techniques as well as geomorphological sedimentological and chronological investigations this study aims to i provide a detailed characterization of the washover fans geomorphology and stratigraphical architecture ii document depositional processes involved in their formation iii establish a chronostratigraphy based on optically stimulated luminescence osl and iv understand the significance of the washover fans for recording past tropical cyclone tc activity the fans consist of multiple sequences of sand shell debris and coral rubble comprising depositional units related to tc induced inundation the units are separated by palaeosurfaces with incipient soil formation formed during periods of reduced depositional activity in combination with the interpretation of a uav based high resolution digital surface model multiple phases of reactivation are inferred osl results allow the establishment of a local long term tc record and suggest storm induced deposition at 170 360 850 and 1300 years ago further units were dated to 1950 2300 and 2850 years ago the chronology of tc events is consistent with other work relating tc activity with el nino southern oscillation enso and sea surface temperature sst patterns corroborating the regional palaeotempestological relevance of this unique geomorphological record

masking of interannual climate proxy signals by residual tropical cyclone rainwater evidence and challenges for low latitude speleothem paleoclimatology 1 the anomalously low oxygen isotope ratio 18o values of tropical cyclone rainfall can transfer proxy information about past tropical cyclone activity to stalagmite oxygen isotope records isotopically distinct stormwater reaches the growing crystal surface as a coherent slug or after attenuation by mixing with isotopically normal vadose groundwaters a high resolution micromilled stalagmite stable isotope record from belize shows that residual tropical cyclone water from hurricane mitch masked the oxygen isotope record of a major el nino event on decadal time scales measured 18o values are affected by changes in local tropical cyclone frequency despite the tropical cyclone masking effect the structure of the missing el nino event is preserved in the atm 7 carbon isotope ratios 13c values in tropical cyclone prone regions the fidelity of stalagmite oxygen isotope proxy data to recording background climate signals is modulated by temporal variations in local tropical cyclone rainfall and the sensitivity of individual stalagmites to tropical cyclone masking varies with hydrology speleothem 13c values unaffected by tropical cyclones can preserve the underlying structure of climatic variability for low latitude speleothems with c o isotope covariance intervals in which the 18o values are significantly lower than 13c values predict may indicate periods when local tropical cyclone masking of isotope derived precipitation records is enhanced by greater infiltration of tropical cyclone rain the temporal structure in stalagmite c o isotope covariance has paleoenvironmental meaning that may be revealed by exploring factors associated with independent behavior in each isotope ratio respectively tropical cyclone masking presents new challenges to paleoclimatology and a source of hypotheses for paleotempestology

geologic records of holocene typhoon strikes on the gulf of thailand coast abstract washover sedimentation resulting from modern typhoon strikes on the gulf of thailand coast forms anomalous sand layers in low energy coastal environments including marshes ponds and swales the primary diagnostic for recognizing prehistoric typhoon deposited sand layers in the geologic record are sharp upper and lower contacts between coarser grained transported sand layers and finer grained in situ sediments in this first paleotempestology study in thailand cores from two low energy settings on the gulf of thailand coast a coastal marsh near cha am and beach ridge plain swales near kui buri reveal geologic evidence of up to 19 typhoon strikes within the last 8000 years the sand layers have sharp upper and lower contacts with enclosing finer sediments some sand layers also contain other evidence of a sudden powerful landward directed surge of ocean water including gravel sized clasts offshore foraminifera abundant shell fragments plant debris and mud rip up clasts sand layers record eleven typhoon strikes at cha am ranging in age from ad 1952 to 7575 cal yr bp and eight typhoon strikes at kui buri ranging in age from 4075 to 7740 cal yr bp bayesian age depth models derived from eight ams radiocarbon dates suggest that the frequency of typhoon strikes was 2 5 times greater from 3900 to 7800 cal yr bp compared to 0 3900 cal yr bp possible explanations for this variability in the typhoon record are that typhoons were more frequent and or more intense in southeast asia in the mid holocene because of climatic changes associated with the mid holocene warm period or that the record reflects site sensitivity changes resulting from a mid holocene sea level highstand the preliminary finding of a possible link between warmer conditions and a greater frequency of intense typhoon strikes could have important societal implications given possible consequences of ongoing global warming

palaeohurricane reconstructions from sedimentary archives along the gulf of mexico caribbean sea and western north atlantic ocean margins hurricanes annually threaten the atlantic ocean margins historical hurricane records are relatively short and palaeohurricane sedimentary archives provide a geological and climatic context that sheds light on future hurricane activity here we review palaeo trends in hurricane activity elucidated from sedimentary archives we discuss dating methods site selection and stat istics associated with previously published records these archives have been useful for under standing the long term evolution of coastal systems and the response of intense hurricane activity to climatic changes regional shifts in hurricane overwash on centennial to millennial timescales have been linked to various climatic modes of variability including el nino southern oscillation and the north atlantic oscillation but could also reflect regional scale controls on hurricane activity

controls on forearc basin formation and evolution insights from oligocene to recent tectono stratigraphy of the lower magdalena valley basin of northwest colombia abstract mechanisms of forearc basin evolution remain not very well understood mostly because of insufficient resolution of their temporal evolution and potential drivers the convergent margin of northwest colombia where the san jacinto and lower magdalena valley forearc basins are located offers a unique opportunity to study such mechanisms the formation of the lower magdalena amagmatic forearc basin occurred in a stable setting from the oligocene to the present characterized by the slow and nearly orthogonal low angle subduction of the caribbean plateau we use an exceptional regional database to reconstruct the subsidence extension sedimentation and paleo geographic history of the lower magdalena forearc basin we propose possible mechanisms controlling its evolution in the absence of major changes in plate kinematics and in a low angle subduction setting following the collapse of a pre oligocene magmatic arc late oligocene to early miocene fault controlled subsidence allowed initial basin fill at relatively low sedimentation rates after the connection of the lower and middle magdalena valleys the proto magdalena river in the north and the proto cauca river in the south both started delivering high amounts of sediments in middle miocene times fault controlled subsidence was gradually replaced by subsidence due to increased sedimentary load increase in sediment flux would have also caused the formation of an accretionary prism weakened the plate interface through lubrication with fluid rich sediment and initiated underplating with the development of forearc highs in the san jacinto area inherited basement structures allowed the tectonic segmentation of the basin with the formation its two depocenters plato and san jorge our results highlight the fundamental role of sediment flux of the basement structure and of flat subduction on the evolution of forearc basins such as the lower magdalena

high precision u th dating of storm transported coral blocks on frankland islands northern great barrier reef australia abstract high energy storm transported coral blocks are widespread on the reef flats of the great barrier reef gbr australia and have the potential to be used as proxies for reconstructing past storm cyclone events prior to historical or instrumental records in this study samples from 42 individual transported coral blocks were collected from the inshore frankland islands northern gbr for high precision mc icpms u th dating with their surface mortality ages recording the timing of individual storms or cyclones responsible for their uplift from their original growth position the dated mortality ages were found to match well with known historical storm cyclone events in the last century with 80 of them falling within episodes of increased storm activity 1910 1915 1945 1950 1955 1960 1975 1990 1995 2000 ad captured by instrumental historic records confirming that transported coral blocks on inshore reefs can be used as proxies for past storm cyclone occurrences using this approach this study also identified 17 additional storm cyclone events that occurred before european settlement in the 1850s including three oldest events at 758 4 3 7 777 9 4 9 and 985 2 4 8 ad respectively our results despite still preliminary suggest that the storm cyclone activity in this region tends to broadly correlate with the positive modes of the pacific decadal oscillation pdo during the last millennium in addition there appears to be a decreasing age trend from the shore to the reef edge from 758 4 3 7 ad to 1988 3 1 6 ad which can be attributed to sea level fall and or reef island progradation over the last 2000 years

neogene stratigraphy paleoceanography and paleobiogeography in northwest south america and the evolution of the panama seaway abstract the atrato basin in the pacific coastal region of nw south america colombia exhibits stratigraphic and biostratigraphic characteristics similar to other neogene pacific coastal basins of southern central america and northern south america an evaluation of the neogene stratigraphy and foraminiferal biostratigraphy with emphasis on paleoceanographic and paleobiogeographic phenomena indicate the following 1 previous to the middle miocene well aerated deep and open oceanic conditions and free and active water circulation prevailed along the steep continental margins of nw south america 2 during the early middle miocene right after the neogene hiatus nh 2 15 2 ma tectonic disturbances triggered the initial uplift of the panama sill bottom water circulation foraminiferal and sedimentation changes are observed in both the pacific and caribbean coastal areas of nw south america 3 during the middle miocene coinciding with the neogene hiatus nh 3 12 9 11 8 ma an abrupt paleobathymetric change from lower to middle bathyal depths indicates a major uplift of the panama sill to about 1000 m reflecting the middle miocene tectonic disturbances in nw south america 4 during the late middle miocene immediately following this uplift a distinctive pacific benthic foraminiferal fauna abruptly appeared and extended from ecuador to california because these assemblages do not occur in the adjacent caribbean region a circulation barrier between the atlantic and pacific oceans as a result of intensification of the cool marginal california current is proposed anoxic middle to upper bathyal environments prevailed under well aerated cool surface waters in the pacific coastal areas of nw south america 5 during the latest miocene immediately following the neogene hiatus nh 6 7 0 6 3 ma surface water circulation between the caribbean and the pacific was re established and the previous influence of the california current disappeared a rapid filling and shallowing of the basin to mostly neritic depths is indicated along the pacific and caribbean coastal basins of colombia as well as a progressive increase in similarity between the coastal pacific and caribbean benthic biotas this shallowing in the early late miocene also appears to have been associated with the earliest terrestrial interchange of ground sloths to north america and raccoons and their allies to south america 6 immediately following early pliocene time the panamanian isthmus became completely emergent providing a terrestrial environment favourable for intermingling of terrestrial faunas and floras between north and south america i correlate this pliocene uplift with the neogene hiatus nh 8 3 7 3 1 ma four regional unconformities associated with tectonic disturbances in the nw corner of south america have also been recognized and correlated with neogene hiatuses recorded from the oceans early middle miocene middle miocene late miocene and early pliocene

palaeohydrological variation in a tropical river catchment a reconstruction using fluorescent bands in corals of the great barrier reef australia massive long lived corals in inshore waters of the great barrier reef contain yellow green fluorescent bands these bands are due to terrestrial humic and fulvic compounds incorporated into the coral skeleton during high river flow events fluorescence measurements are presented for two colonies of porites spp from locations in the path of the burdekin river floodwaters the major river in north queensland draining into the coral sea the records extend from ad 1737 to 1980 and 1644 to 1986 respectively the two independent coral records show a high degree of similarity the two series are combined and used to reconstruct burdekin river runoff for the period ad 1644 to 1980 the regression model accounts for 83 of the annual water year variability of burdekin river flow and is verified over independent data the 337 year reconstruction thus increases by threefold the length of record for considering interannual to decadal climate variations in northeast australia instrumental and reconstructed burde

geological history of the cretaceous ophiolitic complexes of northwestern south america colombian andes abstract the western cordillera of colombia was formed by intense alpine type nappe forming folding and thrusting the cretaceous 80 120 ma b p tholeiitic material of the western cordilleran nappes has been obducted onto the paleozoic and precambrian polymetamorphic micaschists and gneiss of the central cordillera near yarumal the antioquia batholith 60 80 ma b p intrudes both obducted cretaceous oceanic material and the polymetamorphic basement rock of the central cordillera therefore nappe emplacement and obduction onto the central cordillera occurred during late senonian to early paleocene the nappes travelled from northwest to southeast so that the highest unit the rio calima nappe therefore has the most northwestern source whereas the lowest units originated from a more southeastward direction sedimentological analysis of the volcanoclastic and sandy turbidite material from each unit suggests a marginal marine environment during cretaceous times the opening of this marginal sea from now on called the colombia marginal basin probably originated by detachment of a block from the south american continent related to the farallon south america plate convergence in the popayan area southern colombia the central cordilleran basement exhibits glaucophane schist facies metamorphism this high pressure low temperature metamorphism is of early cretaceous 125 ma b p age and is related to an undated metaophiolitic complex the ophiolitic material originating from the western cordilleran is thrust over both the blueschist belt and the metaophiolitic complex these data suggest that the occidente colombiano suffered at least two phases of ophiolitic obduction during mesozoic time

the importance of quaternary records in reducing risk from tropical cyclones numerous late holocene records of tropical cyclones have been collected from north east queensland australia they are in the form of multiple sedimentary ridges paralleling the shore the ridges are composed of coral fragments or shell and sand or pure sand a method to determine the intensity of the tropical cyclone responsible for deposition of the ridges at each site has been applied and the results suggest that in the majority of cases these features were deposited by very high magnitude events the results suggest that extrapolations of long term cyclone magnitude and frequencies from the 30 to 40 year long instrumental record which is the method commonly used to assess risk from this hazard substantially underestimate the risk from this hazard this is confirmed for the cairns region by an 800 year long high resolution isotope record of tropical cyclones preserved in a limestone stalagmite together the sedimentary and isotope records suggest that tropical cyclone activity in north east queensland has been in a phase of quiescence since before european settlement of the region in approximately ad 1870 it is suggested that the incorporation of the palaeo record into risk assessments will provide a more realistic guide to the magnitude frequency relationship of tropical cyclones and help reduce risk from this hazard as a consequence

600 year sedimentary archive of hurricane strikes in a prograding beach ridge plain southwestern louisiana abstract this study tests a novel approach to paleotempestology substituting the lateral time depth of a prograding beach ridge plain for the vertical time depth of an aggrading coastal lake pond lagoon swamp or marsh trenching and coring of a beach ridge plain in southwestern louisiana revealed six sand beds and one shell bed interpreted as hurricane washover deposits the sand beds are readily distinguished from enclosing marsh sediments by their higher sand content lower organic content and contrasting microfossil assemblages based on the modern analogs of hurricanes audrey 1957 rita 2005 and ike 2008 and consideration of nearby landfalling hurricanes in the historical record it was determined that the storm intensity threshold of the study site is equivalent to a category 3 hurricane there is a wide variation in hurricane strike frequency between this site and other sites bordering the gulf of mexico this variation results from differences in site sensitivity and the nature of geologic or geochemical proxies used to derive hurricane strike records the approach demonstrated by this study could have applicability at other sites around the world where beach ridge plains are subject to tropical cyclone strikes

too low δ18o of paleo meteoric low latitude water do paleo tropical cyclones explain it abstract isotopic analysis of rock samples showed anomalously 18 o depleted reconstructed isotopic composition of paleo meteoric water over southern israel between the late cretaceous and the early miocene with 18 o w as low as 14 smow this range is significantly lighter than the expected values for rain at the relevant paleo latitudes 8 n to 25 n it is similar or lighter than areas with meteoric water at the present climate in which rainfall contribution from tropical cyclone tc is significant rainfall from tcs is 18 o depleted because of the recirculation of the vapor into repeated precipitation or distillation cycles a paleo geographic reconstruction of the region shows that throughout the period there was a warm ocean to the east and southeast of the relevant area thus tcs formed over the ocean and made landfall on the coastline at a distance of 300 to 400 km to the east the reconstructed composition of the rainwater implies dominance of tcs at these times furthermore the combination of warmer seas and lighter rainwater than at present suggests that the tcs were more dominant than in the most tc prone coastal areas at the present climate the results of the present study suggest that climate during the relevant time periods was very different from the present with tc activity similar or exceeding the most tc prone locations in the world at the present climate this might also hint that warmer sea waters in the geological past were conducive to greater tc activity than in the present climate answering this question requires additional research

barrier formation on an actively prograding delta system the red river delta vietnam abstract an extensive barrier spit system 20 to 30 km long developed on the delta front platform of the ba lat delta within a relatively short period 10 20 years however it was not evident whether the formation was related to river floods typhoons or calm weather conditions or to cross shore or alongshore sediment transport mechanisms therefore a process based numerical model that simulates sediment transport and morphologic changes by waves tides wind and river flow is used to analyze the processes that govern this barrier formation the mechanism that initiates the barrier formation is concluded to be onshore transport by wave asymmetry of sediment previously transported seaward in the buoyant river plume the main mechanism that counteracts the barrier formation is probably destruction of the barrier by river flow during the subsequent transformation from a subaqueous barrier into a sub aerial barrier spit system overwashes and alongshore sediment transport become increasingly important this spit system therefore appears to be dominated by alongshore processes even though its initial formation is more strongly regulated by cross shore processes the importance of cross shore processes results in a minor contribution of typhoons to the initial formation of these barriers typhoons are not very important to destruction of barriers as well because wave energy is gradually dissipated over the gentle offshore profile which in turn results from river plume sedimentation

sedimentary evidence of intense hurricane strikes from new jersey nine vibracores from the backbarrier marsh at whale beach new jersey reveal three large scale overwash deposits associated with historic and prehistoric storms the uppermost and smallest overwash fan was deposited in the ash wednesday northeaster of march 5 8 1962 a second more substantial overwash fan between 100 and 35 cm depth dates to the late eighteenth or early nineteenth century this fan was most likely deposited during the 1821 hurricane the only intense hurricane to make landfall in new jersey in the past 350 yr a third larger overwash fan between 200 and 300 cm depth was deposited between a d 1278 and 1438 and is likely the result of a prehistoric intense hurricane strike the combination of historical and stratigraphic evidence indicates that two intense hurricanes winds 50 ms 21 have likely made landfall on the southern new jersey coast in the past 700 yr resulting in an annual landfall probability of 0 3

reconstruction of prehistoric landfall frequencies of catastrophic hurricanes in northwestern florida from lake sediment records abstract sediment cores from western lake provide a 7000 yr record of coastal environmental changes and catastrophic hurricane landfalls along the gulf coast of the florida panhandle using hurricane opal as a modern analog we infer that overwash sand layers occurring near the center of the lake were caused by catastrophic hurricanes of category 4 or 5 intensity few catastrophic hurricanes struck the western lake area during two quiescent periods 3400 5000 and 0 1000 14 c yr b p the landfall probabilities increased dramatically to ca 0 5 per yr during an hyperactive period from 1000 3400 14 c yr b p especially in the first millennium a d the millennial scale variability in catastrophic hurricane landfalls along the gulf coast is probably controlled by shifts in the position of the jet stream and the bermuda high

sediment dynamics and hydrographic conditions during storm passage waquoit bay massachusetts abstract the impact of storm events on the sediment dynamics of the shallow groundwater fed estuaries of cape cod massachusetts usa is little understood to address this the objectives of this study are to assess sediment dynamics during storm passage and determine whether shallow back barrier lagoons like waquoit bay have the preservation potential for a sedimentary archive of hurricanes when setting out in this study it was unclear whether paleotempestological methods could be applied successfully to cores collected from the landward reaches of shallow estuaries of southern new england water level and bottom current data using arm and float tide gauges and seahorse tilt current meters was collected during tropical storm irene 2011 and coupled with storm surge modeling projections to better elucidate storm induced sediment transport mechanisms three sediment cores were collected at the head of waquoit bay located 2 8 km from the barrier beach grain size analysis of sediment cores was conducted with a laser particle size analyzer at 1 cm increments in order to identify coarse grain anomalies which can act as a storm event proxy bayesian statistics were applied to develop age models of two of the cores based on three pb pollution chronomarkers and 21 continuous flow 14c ams ages the results yield variable sediment accumulation rates between 2 mm yr to 10 mm yr with significantly higher rates occurring in the upper 1 m of sediments grain size results are highly variable and contain numerous large amplitude short duration fluctuations suggesting that during storm passage coarse sand is deposited in the coring site the sensitivity of the site to both tropical and extratropical storm events uncertainties in the age model and the multiple sediment sources and transport pathways limits the utility of using the waquoit sediments to determine long term hurricane frequencies results nonetheless provide insights into how extreme storm events impact coastal lagoons

greater frequency variability of landfalling tropical cyclones at centennial compared to seasonal and decadal scales assessing risk from tropical cyclones and predicting the impact of this hazard under a human altered climate is based exclusively upon the behaviour of these events over the past 50 100 yr and often less critical to these determinations is an understanding of the full extent of the natural variability of this hazard the coarse resolution of millennial scale sedimentary records brevity of the instrumental register imprecision of longer historical accounts and lack of any long term high resolution records has led to the assumption that the total variability of tropical cyclone behaviour is encompassed within the seasonal to multi decadal oscillations observed to date we present a near 800 yr long annual resolution isotope record of tropical cyclones in northeast australia which displays marked centennial scale regimes our record demonstrates that the frequency variability of intense landfalling cyclones is greatest at centennial scale compared to seasonal and decadal oscillations switching between centennial scale regimes in this record occurred rapidly 10 20 yr highlighting the importance of accounting for this phenomenon in coastal planning and risk assessment our study highlights the importance of obtaining high resolution multi century records of tropical cyclone activity in order to more accurately assess future impacts of this hazard to human society

paleostress evolution of the northern andes eastern cordillera of colombia implications on plate kinematics of the south caribbean region 1 new tectonic field data and paleostress determinations in the eastern cordillera of colombia enable us to identify stress regimes that prevailed in the northern andes since late cretaceous times until present day these regimes were characterized by an e w to wsw ene active contraction from late cretaceous to late paleocene this direction subsequently changed to nw se and finally became wnw ese during the andean tectonic phase the characteristics and relative chronology of these regimes were deduced from field structures and stratigraphic criteria using stress inversion of fault slip data sets to evaluate our model we used the rotation poles of the south america caribbean and nazca plates relative to north america and paleogeographic reconstructions of the caribbean region to derive a kinematic model of the northern andes assuming a general correspondence between the regional convergence directions and the regional compression we built a theoretical model of the regional stress regimes based on kinematics of the northwestern south america since late cretaceous times this model reveals a major variation at the end of the paleocene when relative divergence shifted to convergence between the americas this is in agreement with our tectonic model based on independent tectonic field data inversion in the eastern cordillera this regional kinematic and tectonic change which affected the caribbean at the end of the paleocene was responsible for and consistent with the major change in stress patterns and structural style in the eastern cordillera it is also coeval with the development of a major regional unconformity in colombia

coastal geoindicators of environmental change in the humid tropics the primary geoindicators appropriate for monitoring environmental changes in the humid tropics are transitory surface water levels shoreline position wetlands distribution coral reefs landforms and sediment sequence and composition lateral zonations and temporal successions of vegetation also can be used as geoindicators of riverine and shoreline changes all of these coastal geoindicators are sensitive to regional tectonic processes and anthropogenic alterations and they typically reflect significant changes in coastal conditions such as fluvial processes coastal energy water quality relative sea level and sediment supply where humid tropical coasts coincide with active tectonic margins indicators of seismic activity are critical to understanding coastal changes associated with co seismic subsidence or uplift tsunamis and liquefaction of coastal sediments coastal landforms and sedimentary deposits that record late quaternary environmental changes include perched fluvial and marine terraces delta plain morphologies crevasse splay deposits peats and other paleosols beach ridges mud capes and mud volcanoes although these features and deposits typically reflect environmental changes spanning more than 100 years they are relevant to modern processes management of coastal lands and resources and prediction of future conditions in some regions of the humid tropics large coastal areas are unaffected by hurricanes or typhoons nevertheless these tropical coasts are vulnerable to other non storm processes such as el nino events tsunamis and monsoons that increase water levels and cause widespread flooding and beach erosion the environmental and political significance of coastal geoindicators increases when they are integrated and applied to issues of human safety and health such as hazards mapping risk assessment and dispersion of contaminated sediments however to be relevant those socio environmental applications demand accurate predictions of future trends and rates of change

stable isotope proxy records in tropical terrestrial environments abstract the tropics refers to an area that is loosely equatorial characterized by relatively high temperatures at low altitude comparatively low seasonal contrast in temperatures and generally high or highly seasonal rainfall the stable isotopes of carbon oxygen and hydrogen are increasingly important tools of relevance to understanding trajectories and mechanisms of past environmental change in the tropics in the case of carbon this is because at the broadest level the carbon isotope composition of organic and carbon containing inorganic proxy materials formed in the tropics can be read as being derived from the balance between c3 tree and c4 grass photosynthesis hence providing a relative measure of vegetation type and indirectly climate likewise changes in the oxygen and hydrogen isotope composition of many proxy materials again at the broadest level can be read as indicative of changes in hydrological conditions and or altitude in the past this review provides an entry point into the literature relating to the use of stable isotopes as terrestrial environmental proxies for past environmental change with a focus on the measurement and interpretation of stable isotope data from the wide range of proxy materials preserved in tropical environments

basic building blocks and process variability of a cretaceous delta internal facies architecture reveals a more dynamic interaction of river wave and tidal processes than is indicated by external shape abstract although delta building processes and the resultant facies and facies associations have been studied for over a century there remains a lack of well documented facies architectural studies of ancient deltas in this study architectural element analysis is applied to determine the basic building blocks of a cretaceous delta at the top of the upper turonian wall creek member exposed along the western flanks of the powder river basin wyoming we document the bed scale basic building blocks of this ancient delta and show them in the context of their facies and stratal variability and their hierarchical spatial arrangement within a single deltaic parasequence we also test the idea that external sand body shape may not reflect the internal facies complexity as has recently been suggested in studies of several modern deltas including the burdekin in australia the brazos in the gulf of mexico and the baram trusan in borneo five orders of bounding surfaces separate six facies architectural elements in the prodelta and delta front deposits these elements are prodelta fines pf frontal splay fs channel ch storm sheet ss tidally modulated deposit tm and bar accretion ba seasonal to decadal river floods are thought to represent the main building phases of the delta producing channels bars and frontal splay elements during intervening periods the delta was reworked by waves storms and tides producing tidally modulated and storm sheet elements due to the complex interactions of river effluents with waves storms and tides the delta is interpreted as mixed influenced regional sandstone isolith facies and paleocurrent maps help to reconstruct the paleogeography and show how the various architectural elements varied across the delta front the channels bars frontal splays and tidally modulated elements are found only near the distributary mouth whereas the storm sheets occur extensively away from the distributary mouth the plan view morphology of the studied delta shows a smooth fronted arcuate to cuspate shape which should indicate wave dominance in contrast our analysis of the internal facies architecture shows that the delta was constructed rapidly during major river floods with significant tidal reworking additional outcrop mapping shows that storm wave reworked sands are attached to the flanks of the system previously published delta models predict incorrectly that the tidal reworking of a river flood dominated system should result in a more bird foot shape versus the lobate geometry that is actually mapped our analysis of internal facies versus external shape matches similar observations on several modern deltas and suggests that external shape is a poor indicator of internal facies complexity

rapid cycles of episodic adjustment understanding the holocene fluvial archive of the daintree river of northeastern australia the dramatic decline in the quality of coral reef cover of the great barrier reef gbr over recent decades has resulted in targeted research to better understand the dynamics of sedimentary sources within river systems of northeastern australia european land use practices are thought to have increased sediment yields to the gbr lagoon by 5 10 times yet there is a poor understanding of the pre 1850 sediment dynamics this study presents the first detailed alluvial chronology of the spatial and temporal responses of fluvial systems in the wet tropics of northeastern australia over the late holocene valley fill sequences of the daintree river one of the least disturbed catchments draining to the gbr lagoon are examined to investigate the significance of floodplain dynamics in sedimentary process an optically stimulated luminescence chronology combined with a detailed sedimentary analysis suggests that floodplain stripping is a major and hitherto unrecognised source of sediment furthermore rates of floodplain accretion are far greater than has been previously estimated from sediment modelling for wet tropical catchments spatial analysis of the topographical relationships between floodplain morphological units suggests that a total of 178 516 ton ha of sediment has been stripped from three small confined floodplain reaches between 1038 215 and 99 10 years evidence suggests that these erosion events are followed by phases of rapid accretion with an average depositional rate of 3 87 0 92 cm yr between 572 74 and 51 12 years across the study area the floodplain appears to be in a constant state of disequilibrium experiencing spatially discontinuous phases of erosion and aggradation resulting in much higher volumes of sediment being redistributed within the catchment than previously considered the unpredictable nature of these regimes and the shear volume of sediment mobilised poses significant challenges in managing sediment sources to the gbr lagoon

four phase tectonostratigraphic development of the southern caribbean abstract although the stratigraphy of northern south america and the southern caribbean has been studied in detail in many areas a clear understanding of the sequence of tectonic events and their relation to regional stratigraphy has not been forthcoming since northern south america collided with southern north america in the late palaeozoic we identify four discrete tectonic phases from the stratigraphy of the area that is now the southern caribbean these phases derived from a synthesis of regional stratigraphy were 1 panama arc collistion with colombia in the late miocene early pliocene which drove a complex triangular wedge bounded by strike slip faults northward into the caribbean 2 right lateral strike slip faulting associated with post eocene eastern motion of the caribbean ocean floor into the gap between the separating americas 3 island arc development and collision associated with the entry of the present caribbean ocean floor an area of buoyant ocean crust into the gap between the separating americas and 4 continental rifting and passive margin development in the late jurassic early cretaceous associated with the separation of north and south america approximately along the palaeozoic suture zone overprinting of younger structures on inherited structures from previous phases is responsible for the overall complexity of the region

a decadally resolved paleohurricane record archived in the late holocene sediments of a florida sinkhole article i nfo a 4500 year record of hurricane induced storm surges is developed from sediment cores collected from a coastal sinkhole near apalachee bay florida recent deposition of sand layers in the upper sediments of the pond was found to be contemporaneous with significant historic storm surges at the site modeled using slosh and the best track post 1851 a d dataset using the historic portion of the record for calibration paleohurricane deposits were identified by sand content and dated using radiocarbon based age models marine indicative foraminifera some originating at least 5 km offshore were present in several modern and ancient storm deposits the presence and long term preservation of offshore foraminifera suggest that this site and others like it may yield promising microfossil based paleohurricane reconstructions in the future due to the sub decadal 7 years resolution of the record and the site s high susceptibility to hurricane generated storm surges the average local frequency of recorded events approximately 3 9 storms per century is greater than that of previously published paleohurricane records from the region the high incidence of recorded events permitted a time series of local hurricane frequency during the last five millennia to be constructed variability in the frequency of the largest storm layers was found to be greater than what would likely occur by chance alone with intervals of both anomalously high and low storm frequency identified however the rate at which smaller layers were deposited was relatively constant over the last five millennia this may suggest that significant variability in hurricane frequency has occurred only in the highest magnitude events the frequency of high magnitude events peaked near 6 storms per century between 2800 and 2300 years ago high magnitude events were relatively rare with about 0 3 storms per century occurring between 1900 and 1600 years ago and between 400 and 150 years ago a marked decline in the number of large storm deposits which began around 600 years ago has persisted through present with below average frequency over the last 150 years when compared to the preceding five millennia

the origin and disappearance of the late pleistocene early holocene short lived coastal wetlands along the carmel coast israel abstract the formation of short lived backswamps along the carmel coast of israel coincides with the rapid global sea level rise during the late pleistocene early holocene transition the current study shows that the wetland phenomena originated around 10 000 yr ago and dried up shortly before the local pre pottery neolithic humans settled on the wetland dark clay sediments 9430 cal yr bp palaeontological and stable isotope data were used in this study to elucidate previously published sedimentological reconstruction obtained from a core drilled into the western trough of the carmel coastal plain the water body contained typical brackish calcareous fauna with variable numerical abundance and low species richness of ostracods and foraminifera the 18o and 13c of the ostracod cyprideis torosa show close similarity to the present pleistocene coastal aquifer isotopic values this study therefore concludes that the wetlands were shallow water bodies fed by groundwater with no evidence of sea water mixing it seems that they developed as the result of high groundwater levels transportation of sediments landward and deposition of sand bars at the paleo river mouths it is still not fully understood why these wetlands deteriorated abruptly and disappeared within less than 1000 yr

sand beach ridges record 6000 year history of extreme tropical cyclone activity in northeastern australia sand beach ridges are considered to be derived either from aeolian processes and or waves but their deposition by individual or multiple storms has not been investigated in any detail we use numerical meteorological and oceanographic models to determine the origin of a sequence of 29 shore parallel sand beach ridges in northeastern australia the results suggest that the ridges were constructed by waves and that the final form or height of the ridges is a function of high energy tropical cyclone generated waves plus storm tides hence these landforms archive a nearly 6000 year long history of intense tropical cyclones the record implies that these extreme tempests occur considerably more frequently than that suggested by the short historical record for this region the genesis of this sand beach ridge plain has implications for the interpretation of similar sequences elsewhere along the northeast coast of australia and in comparable environments globally if other similar sand beach ridge plains have also been deposited by like processes it stands to reason that these long term records of high intensity tropical cyclones can be used to ascertain a regional scale risk assessment from this hazard

reconstructing tropical cyclone frequency using hydrogen isotope ratios of sedimentary n alkanes in northern queensland australia a peat record from quincan crater queensland australia spanning the past 200 years was used to test if hydrogen isotope ratios of leaf wax long chain n alkanes derived of higher plants can be used to reconstruct past tropical cyclone activity queensland is frequently impacted by tropical cyclones with on average 1 2 hits per year the most abundant n alkanes in the peat are c 29 and c 31 possible sources for long chain n alkanes in the peat core are ferns and grasses which grow directly on the peat layer and the tropical forest growing on the crater rim hydrogen isotope ratios of c 27 c 29 and c 31 n alkanes vary between 155 and 185 parts per thousand vsmow with the largest variability in the upper 30 cm of the record for the period 1950 2000 ad the variability in delta d of c 29 alkanes resembles a smoothed record of historical tropical cyclone frequency occurring within a 500 km radius from the site this suggests that the high number of tropical cyclones occurring in this period strongly impacted the delta d signal and on average resulted in more depleted values of precipitation in the period before 1900 ad the variability in the hydrogen isotope record is relatively small compared to the period 1950 2000 ad this might be the result of lower variability of tropical cyclones during this time period more likely however is that it results from the increasing age span per sampled interval resulting in a lower temporal resolution average delta d values between 1900 and 2000 ad are around 167 parts per thousand which is similar to average values found for the period between 1800 and 1900 ad this suggests that on average tropical cyclone frequency did not change during the past 200 years this study demonstrates the potential of stable hydrogen isotope ratios of long chain n alkanes for the reconstruction of past tropical cyclone frequency

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

regional provenance from southwestern colombia fore arc and intra arc basins implications for middle to late miocene orogeny in the northern andes andean orogenic processes controlled the spatial and temporal distribution of the magmatic and sedimentary record this contribution integrates new u pb zircon ages heavy mineral analyses and biostratigraphic constraints from the neogene sedimentary record of the fore arc and intra arc basins and volcano plutonic rocks of southwestern colombia to reconstruct these orogenic processes the results reveal continuous arc magmatism since the late oligocene with a major post middle miocene magmatic peak and exhumation when integrated with other geological constraints the tectonic evolution of the margin includes eocene oligocene oblique convergence with limited magmatic activity followed by the initiation of a late oligocene early miocene arc that migrated to the east in the middle miocene when it experienced a major increase in magmatic activity crustal deformation exhumation and thickening this orogenic evolution is related to the shallowing of the slab dip due to the subduction of the neogene nazca plate

late pleistocene evolution of the continental shelf of central israel a case study from hadera abstract sea level fluctuations are a dominant mechanism that control coastal environmental changes through time this is especially the case for the successive regressions and transgressions over the last interglacial cycle which have shaped the deposition preservation and erosion patterns of unconsolidated sediments currently submerged on continental shelves the current study focuses on creating an integrated marine and terrestrial geophysical and litho stratigraphic framework of the coastal zone of hadera north central israel this research presents a case study investigating the changing sedimentological units in the study area analysis suggest these represent various coastal environments and were deposited during times of lower than present sea level and during the later stages of the holocene transgression a multi disciplinary approach was applied by compiling existing elevation raster grids bathymetric charts one hundred lithological borehole data sets and a 110 km long sub bottom geophysical survey based on seismic stratigraphic analysis observed geometries and reflective appearances six bounding surfaces and seven seismic units were identified and characterized these seismic units have been correlated with the available borehole data to produce a chronologically constrained lithostratigraphy for the area this approach allowed us to propose a relationship between the lithological units and sea level change and thus enable the reconstruction of hadera coastal evolution over the last 100 ka this reconstruction suggests that the stratigraphy is dominated by lowstand aeolian and fluvial terrestrial environments subsequently transgressed during the holocene the results of this study provide a valuable framework for future national strategic shallow water infrastructure construction and also for the possible locations of past human settlements in relation to coastal evolution through time

two millennia of tropical cyclone induced mud layers in a northern yucatan stalagmite multiple overlapping climatic hazards during the maya terminal classic megadroughts an annually laminated stalagmite from the northern yucatan peninsula contains mud layers from 256 cave flooding events over 2240 years this new conservative proxy for paleotempestology recorded cave flooding events with a recurrence interval of 8 3 years during the twentieth century with the greatest frequency during the twentieth century and the least frequent during the seventeenth century tropical cyclone tc events are unlikely to flood the cave during drought when the water table is depressed applying tc masking to the chaac paleorainfall reconstruction suggests that the severity of the maya megadroughts was underestimated without a high resolution radiometric geochronology of individual local tc events speleothem isotope records cannot resolve whether the terminal classic period in the northern maya lowlands was punctuated by several brief drought breaks with normal tcs or whether the region was very dry and peppered by unusually severe and frequent hurricane seasons

early subduction related orogeny in the northern andes turonian to eocene magmatic and provenance record in the santa marta massif and rancheria basin northern colombia terra nova 23 26 34 2011 abstract the timing of orogeny in the northern andes and the mechanism driving it are still debated we have studied the age composition and provenance of granitoids and sandstones of the santa marta massif and rancheria basin northern colombia to relate deep seated and surface tectonic processes attending the late cretaceous palaeogene history of the northern andes our results indicate the development of five tectonic episodes 1 collision of northwestern south america with a 92 80 ma caribbean arc 70 ma 2 late collisional to early subduction metamorphism and magmatism 65 ma 3 distal accumulation of a thick siliciclastic sequence 60 58 ma 4 renewed arc magmatism 58 50 ma and 5 magmatic quiescence and block uplift post 50 ma the first episodes are related to the onset of subduction and the last episode is related to shallow subduction and oblique convergence similar events in colombia and ecuador reveal that the late cretaceous eocene orogeny of the northern andes was influenced by the collision and subduction of the caribbean oceanic plate

geodynamics of the northern andes subductions and intracontinental deformation colombia new regional seismological data acquired in colombia during 1993 to 1996 and tectonic field data from the eastern cordillera ec permit a reexamination of the complex geodynamics of northwestern south america the effect of the accretion of the baudo panama oceanic arc which began 12 myr ago is highlighted in connection with mountain building in the ec the istmina and ibague faults in the south and the santa marta bucaramanga fault to the northeast limit an e se moving continental wedge progressive indentation of the wedge is absorbed along reverse faults located in the foothills of the cordilleras northward of 5 n and transpressive deformation in the santander massif crustal seismicity in colombia is accurately correlated with active faults showing neotectonic morphological evidences intermediate seismicity allows to identify a n ne trending subduction segment beneath the ec which plunges toward the e se this subduction is interpreted as a remnant of the paleo caribbean plateau pcp as suggested by geological and tomographic profiles the pcp shows a low angle subduction northward of 5 2 n and is limited southward by a major e w transpressive shear zone normal oceanic subduction of the nazca plate np ends abruptly at the southern limit of the baudo range northward the np subducts beneath the choco block overlapping the southern part of the pcp cenozoic shortening in the ec estimated from a balanced section is 120 km stress analysis of fault slip data in the ec northward of 4 n indicates an e se orientation of 1 in agreement with the pcp subduction direction northward near bucaramanga two stress solutions were observed 1 a late andean n80 e compression and 2 an early andean nw se compression

the role of extreme floods in estuary coastal behaviour contrasts between river and tide dominated microtidal estuaries abstract contrasting modes of sedimentation and facies arrangement in tide and river dominated microtidal estuaries arise from the degree to which river or tidal discharge and sediment supply influences an estuary a distinct facies gradation exists in tide dominated systems from sandy barrier tidal delta associated environments at the coast through deep mud dominated middle reaches to fluvial sediment in the upper reaches in river dominated systems fluvial sediment extends to the barrier and flood tidal deltas are poorly developed or absent from the estuary a number of independent observations during extreme floods on the south african coast indicate that these types of estuary respond differently to extreme river floods and that the mode of response corresponds to estuary type tide dominated systems exhibit preferential erosion of noncohesive barrier and tidal delta sediments during river floods while the middle reaches remain little modified river dominated systems experience consistent erosion throughout their channel length during extreme floods the increased cohesion of riverine sediments and stabilisation of bars by vegetation in river dominated channels means that higher magnitude floods are necessary to effect significant morphological change barrier erosion including the tidal delta results in deposition of an ephemeral delta composed almost entirely of sands from these deposits in tide dominated estuaries in river dominated systems eroded channel sediments and material from the river catchment may augment barrier sediments in the ephemeral delta deposit post flood wave reworking of ephemeral delta sediments acts to restore barriers to pre flood morphology within a few years however in river dominated systems the additional sediment volume may produce significant coastal progradation that requires several years or decades to redistribute these different modes of flood response mediated by the nature of the estuary have implications for coastal behaviour at the time scale of months to several decades estuary coastal behaviour at river dominated estuaries may be influenced for several decades by post flood morphological adjustment tide dominated estuaries however respond more rapidly in reworking flood eroded sediment and are typically fully adjusted to modal wave and tidal conditions within a few months to a few years in addition the facies arrangement within the two estuary types renders tide dominated estuaries more responsive to minor floods while river dominated estuaries by virtue of more cohesive channel sediments require greater discharges to effect significant morphological change

mud diapirism fan sedimentation and strike slip faulting caribbean colombian margin abstract a closely spaced seismic survey carried out during the diapicar cruise off the caribbean coast of colombia permitted study of the interaction between thick deltaic sedimentation and tectonic stress the consequence of these combined tectonic and sedimentary processes is the formation of large mud diapirs the colombian accretionary wedge is divided into two parts by a more than 100 km long lateral ramp this observation replaced in a plate tectonic framework indicates that the northern south america is divided in several blocks which move to the northwest these blocks may overthrust the caribbean oceanic crust but we exclude the formation of a true subduction zone

coarse clast ridge sequences as suitable archives for past storm events case study on the houtman abrolhos western australia prehistoric storm records are relatively scarce in most parts of the world this article presents storm records derived from coral rubble based geological archives of the houtman abrolhos archipelago located off the west coast of australia where the southernmost coral reefs of the indian ocean are found winter storm swell from the circum antarctic brave westerlies as well as tropical cyclone waves have left numerous ridge systems on dozens of islands of the archipelago all composed of coral rubble from adjacent reefs at three islands seven ridge systems were dated by three different methods u series 68 dates radiocarbon 64 dates electron spin resonance 7 dates 139 radiometric dates span the last 5500 years of the holocene in contrast to the geomorphological interpretation the age sequences show inversions hiatuses and different ages for the same ridge all pointing to complicated ridge formation processes time gaps some exceeding 1000 years are interpreted as phases of erosion and not as phases without storm activity

chenier type ridges in giralia bay exmouth gulf western australia processes chronostratigraphy and significance for recording past tropical cyclones abstract past coastal flooding events may be inferred from geomorphic and sedimentary archives including particular landforms e g beach ridges washover fans deposits e g washover sediments in lagoons or erosional features e g erosional scarps within strandplains in giralia bay southern exmouth gulf western australia sandy ridge sequences in supratidal elevations form the landward margin of extensive mudflats the formation of these ridges is assumed to be mainly driven by tropical cyclones tcs although their depositional processes need to be clarified we investigated the supratidal sandy ridge sequence in giralia bay by carrying out process monitoring geomorphological mapping by means of an unmanned aerial vehicle survey as well as sedimentological and geochronological investigations and multivariate statistics based on the resulting data this study aims at i identifying the most important driving processes to form the sandy ridges ii establishing their chronostratigraphy and iii understanding their significance for recording past tc activity trench excavations revealed sandy units that are interbedded with mud layers at the base similar to the present distal mudflat sediments on top mud intercalations recede and sand layers of varying grain size distribution dominate in the upper part of the trenches younger sediment layers onlap older ones documenting the stepwise seaward accretion of the ridges onto the mudflat while our data suggests that tidal processes have only limited effects on ridge activity sediment transport erosion and deposition seems to be driven by both tc induced storm surges and high magnitude precipitation events causing surface discharge most accretionary sand units are thus assumed to represent events of morphodynamic activity during tc induced flooding since the mid holocene ridge activity is recorded in a roughly decadal resolution and over historical as well as prehistorical holocene time scales while the ridges do not represent beach or chenier ridges sensu stricto they may be described as chenier type ridges due to their stratigraphical architecture ridge evolution however over a millennial time scale seems to be indicated by the landward rise of the sequence possibly corresponding to the mid holocene sea level highstand of western australia of at least 1 2 m above present mean sea level

holocene changes in biome size and tropical cyclone activity around the northern south china sea abstract the south china sea scs characterized by a large continental shelf is located at the edge of the asian monsoon domain in this study two marine sediment cores from the northern scs nscs continental slope were investigated to construct composite vegetation and precipitation isotopic composition records based on the 13c and d values of plant wax n alkanes throughout the holocene last 11 200 years i e 11 2 ka the composite 13cwax record indicates an overall predominance of c3 vegetation over the last 11 2 ka before 8 ka bp higher 13cwax values are attributed to preferential wax input from grassland and wetland biomes on the exposed continental shelf after the inundation of the shelf by eustatic sea level rise until ca 8 ka bp grassland and wetland biomes suffered a major size reduction and arboreal vegetation became better represented in the 13cwax record the composite temperature corrected dwax t record suggests that moisture source variability drove precipitation isotopic composition changes during the holocene lower dwax t values before 8 3 ka bp are interpreted as a larger moisture contribution by pacific ocean tropical cyclones whereas higher dwax t values after 8 5 ka bp are interpreted as a larger moisture contribution from the indian ocean summer monsoon higher incidence of tropical cyclones in the nscs during the early holocene was related to a temporary westward shift of the western pacific warm pool and enhanced insolation over the northern hemisphere both external and internal forcing mechanisms regulated moisture source changes in east asia during the holocene

the hydrogeomorphic influences on alluvial gully erosion along the mitchell river fluvial megafan hydrogeomorphic processes influencing alluvial gully erosion were evaluated at multiple spatial and temporal scales across the mitchell river fluvial megafan in tropical queensland australia longitudinal changes in floodplain inundation were quantified using river gauge data local stage recorders and hec ras modelling based on lidar topographic data intra and interannual gully scarp retreat rates were measured using daily time lapse photographs and annual gps surveys erosion was analysed in response to different water sources and associated erosion processes across the floodplain perirheic zone including direct rainfall infiltration excess runoff soil water seepage river backwater and overbank flood inundation the frequency of river flood inundation of alluvial gullies changed longitudinally according to river incision and confinement near the top of the megafan flood water was contained within the macrochannel up to the 100 year recurrence interval but river backwater still partially inundated adjacent gullies eroding into pleistocene alluvium in downstream holocene floodplains inundation of alluvial gullies occurred beyond the 2 to 5 year recurrence interval and contributed significantly to total annual erosion however most gully scarp retreat at all sites was driven by direct rainfall and infiltration excess runoff with the 24 h rainfall total being the most predictive variable the remaining variability can be explained by seasonal vegetative conditions complex cycles of soil wetting and drying tension crack development near surface pore water pressure soil block undermining from spalling and overland flow and soil property heterogeneity implications for grazing management impacts on soil surface and perennial grass conditions include effects on direct rainfall erosion water infiltration runoff volume water concentration along tracks and the resistance of highly dispersible soils to gully initiation or propagation under intense tropical rainfall copyright 2012 john wiley sons ltd

a holocene fluvial archive of the mulgrave river notheastern australia influence of tropical cyclones and sediment delivery to the great barrier reef abstract the sedimentology geomorphology and chronology of late quaternary fluvial landforms and sedimentary sequences within the mulgrave river catchment in northeast queensland suggest that episodic stripping or wholesale erosion of holocene floodplains is a major mode of sediment delivery to the great barrier reef lagoon the last major phase of holocene valley sediment removal likely occurred sometime between approximately 1200 and 250 years ago and was possibly associated with a phase of heightened tropical cyclone activity and consequent riverine flooding that occurred between ad1400 and 1800 since then relative tropical cyclone quiescence may be the cause of a phase of valley aggradation that has been occurring over the past two centuries the results of this investigation suggest that in this catchment there have been alternating phases of holocene valley floodplain stripping and subsequent aggradation with the latter being the current dominant mode this suggests that at least here in this relatively confined valley sediment delivery to the great barrier reef may be relatively low compared to other periods over the past millennium and this may be due to low levels of tropical cyclone activity over the past 200 years

dynamic morphology of small south eastern mediterranean river mouths a conceptual model river mouths along the israeli mediterranean coast are characterized by a dynamic morphology as their channels migrate hundreds of meters along the coast this study examines the dynamic morphology of seven such river mouths it offers a conceptual model aimed at generalizing and describing their spatial and temporal morphological patterns and the environmental factors influencing them the study methodology comprised a detailed monitoring and mapping by gis techniques with quantitative data derived from historic aerial photographs river discharge records wave measurements and a digital elevation model these data were incorporated into a homogenous database and subsequently applied in the investigation of the morphological patterns of these mouths and the analysis of their influencing factors river mouths in this study occur in two distinctive topographic settings in one setting here termed barrier topography the river mouth is deflected alongshore by a sandy barrier in the second setting termed funnel topography the river mouth is confined to a funnel shaped topographic depression perpendicular to the coast the behavior of river mouths in these two settings is quite distinctive barrier mouths usually migrate over larger distances as they tend to deflect along a sand barrier and establish semi permanent channels along the dune toe this enables the wide range migration of semi permanent channels over decades funnel topography mouths deflect over shorter distances and they rapidly migrate within the funnel boundaries this study concludes that the topographic setting of the beach a constant element in the temporal scale of this study is the primary influencing factor on the morphology of the mouths studied the influence of other factors on the morphology of these mouths differs in space and time and depends on the topographic settings

paleomagnetism and magnetic fabric of the eastern cordillera of colombia evidence for oblique convergence and nonrotational reactivation of a mesozoic intracontinental rift we report the paleomagnetic and magnetic fabric results of 58 sites from cretaceous miocene marine and continental strata from the eastern cordillera ec and the cucuta zone at the junction between the santander massif and the merida andes of colombia the ec is an intracontinental doubly vergent range inverting a triassic to early cretaceous rift zone twenty three sites reveal nonsystematic tectonic rotations including unrotated areas of the ec range with respect to stable south america our data show that the ec inverted a nne oriented rift zone and that the orientation of the mesozoic rift and the mountain chain roughly correspond interestingly magnetic lineations from anisotropy of magnetic susceptibility analysis do not trend parallel to the chain but rather are oblique to the main orogenic trend by also considering gps evidence of a 1 cm yr ene displacement of central western colombia accommodated by the ec we suggest that the miocene recent deformation event of this belt arises from ene oblique convergence reactivating a nne oriented rift zone oblique shortening was likely partitioned into pure dip slip shear characterizing thick skinned frontal thrust sheets well known along both chain fronts and by range parallel right lateral strike slip faults which have not been identified yet but likely exist in the axial part of the ec finally the 35 9 clockwise rotation observed in four post miocene magnetically overprinted sites from the cucuta zone reflects late cenozoic and ongoing right lateral strike slip displacement occurring along faults parallel to the bocono fault system possibly connected with the right lateral faults inferred to exist along the axial part of the ec

caribbean tectonics and relative plate motions during the last century three different ways of interpreting the tectonic evolution of the gulf of mexico and the caribbean have been proposed taking into account the bailey willis school of a permanent pre jurassic deep sea basin the edward suess school of a subsided continental terrain and the alfred wegener school of continental separation the present investigation is concerned with an outline of an interpretation which follows that of pindell and dewey 1982 an attempt is made to point out ways in which the advanced hypotheses can be tested the fit of africa north america and south america is considered along with aspects of relative motion between north and south america since the early jurasic attention is given to a framework for reconstructing caribbean plate evolution the evolution of the caribbean the plate boundary zones of the northern and southern caribbean and the active deformation of the caribbean plate

in situ measurement of seasonal δ18o variations and analysis of isotopic trends in a modern speleothem from southwest australia we present a record of seasonal and inter annual oxygen o and carbon c isotope ratios from an 81 year old stalagmite from moondyne cave southwest australia the growth history of stalagmite mnd s1 is known since it grew on a cave boardwalk that was installed in 1911 and removed in 1992 this stalagmite provides an excellent test of speleothem climate proxies because the regional climate is strongly seasonal wet winter dry summer and has experienced a 200 mm 20 reduction of mean rainfall since the mid 1960s and a 0 8 c temperature rise since 1953 seasonal variations in calcite o were measured in situ by high spatial resolution ion microprobe whilst inter annual variations of o and c were measured by conventional gas source mass spectrometry comparison of the speleothem stable isotopes and instrumental temperature records reveals that o variations are too large to be driven by temperature alone and are in the opposite sense however daily rainfall o measurements show that the mean seasonal range in o of rainfall in southwest australia is large 2 and inversely correlated with rainfall amount a rainfall driver for the speleothem o is confirmed by the detection of seasonal shifts of 0 7 1 5 in speleothem that track rainfall o smoothed by storage in the overlying limestone the seasonal range in speleothem o is larger than any inter annual and decadal variation observed in the record the prominent annual cycles in speleothem o revealed by ion microprobe analysis indicate that subtle changes in the frequency of intense winter rainfall events or possibly also moisture sources could produce significant changes in mean speleothem o the ion microprobe results also raise the possibility that the masses of speleothem calcite deposited in winter and summer could vary as a function of the seasonal drip rate and carbonate saturation state of these waters if this is the case then small changes in the relative masses of calcite deposited in winter and summer could produce significant shifts in mean o and c that have a complex relation to climate this finding should be generally applicable to the interpretation of long term trends in speleothem geochemical records for shallow cave sites where seasonal variations in geochemical tracers are relatively large including most of the sub tropical monsoon belts and mid to high latitudes with distinct rainfall seasons