late pliocene caribbean surface water dynamics and climatic changes based on calcareous nannofossil records abstract quantitative analyses of nannofossil assemblages from two odp sites were performed to determine changes in the surface water structure in the caribbean sea and implications for climatic changes during the late pliocene analysis was made by calculation of accumulation rates and division of nannofossils into ecological groups based on their depth distributions and trophic regime oligotrophic vs eutrophic between 3 5 and 2 7 ma separate surface water masses existed in the northern and southern caribbean the northern surface water was strongly oligotrophic with a deep thermocline nutricline prior to 3 1 ma the southern caribbean was characterized by a shallower thermocline nutricline with minor upwelling induced by the presence of the past itcz intertropical convergence zone after 3 1 ma the thermocline nutricline deepened in the southern caribbean and the upper water became oligotrophic as a result of the completion of the closure of the isthmus after an episodic invasion of cooler surface waters associated with high latitude cooling at approximately 2 7 ma coccolith productivity in the caribbean was at its lowest a deep thermocline existed between 2 7 and 2 4 ma and nutrient depleted waters spread on the suw subtropical under water in the caribbean after 2 4 ma the increase of terrigenous materials from the south american continent caused an abundance of eutrophic taxa this suggests that recent climate systems were established due to the intensification of the northern hemisphere glaciation

effect of early pliocene uplift on late pliocene cooling in the arctic atlantic gateway despite the undisputed role of the arctic ocean in the modern and pliocene climate system the arctic has only recently attracted public awareness that ongoing fundamental change in the arctic cryosphere could be a response to global warming clarification of the arctic s role in global climate during the pliocene is however largely hampered by equivocal stratigraphic constraints from a well dated pliocene sequence from the yermak plateau off nw spitsbergen we present sedimentological and geochemical data indicating that 4 million years ago terrigenous sediment supply and sources changed abruptly in response to a regional tectonic uplift event we argue that this event together with contemporary uplift and tilting along the northwestern european continental margin preconditioned the landmasses for glacial ice build up during intensification of the northern hemisphere glaciation inhg our data further suggest that the final deepening widening of the arctic atlantic gateway the fram strait between 6 5 and 5 ma gradually caused increased deep water mass exchange which in turn likely contributed to the intensification of the north atlantic thermohaline circulation coupled to the north atlantic warm pool as a regional moisture source declining atmospheric co2 levels and other feedback mechanisms during the pliocene the regional tectonic activities in the high northern latitudes caused decreased summer ablation and thus allowed the initial build up of glacial ice both in scandinavia and the sub aerially exposed svalbard barents sea culminating in the first large scale coastline shelf edge glaciations at 2 75 ma

tidal rhythmites of the marais vernier seine estuary france and their implications for relative sea level the marais vernier located in the upper reaches of the seine river estuary northern france preserves a thick holocene succession of laminated detrital deposits and peats the spectral analysis of one laminated deposit suggests that tidal processes were largely responsible for supplying sediments to this system two periods 16 and 32 laminae per cycle were identified these cycles can be related to either both the synodic neap spring cycle the so called fortnightly cycle and the anomalistic monthly cycle or both the semiannual and annual tidal cycles the recognition of tidal influence on these deposits provides insight into the likelihood of some relative sea level fluctuations previously inferred from these sediments the depositional rates calculated for the laminated deposits based on the recognition of these tidal cycles suggest that the time interval required to deposit the sediments was far shorter than is implied by considering rates based on regional sea level rise alone

glacial induced closure of the panamanian gateway during marine isotope stages mis 95 100 2 5 ma the final phase of the closure of the panamanian gateway and the intensification of northern hemisphere glaciation nhg both occurred during the late pliocene glacial interglacial g ig variations in sea level might therefore have had a significant impact on the remaining connections between the east pacific and the caribbean here we present combined foraminiferal mg ca and 18o measurements from ocean drilling program odp site 1241 from the east pacific and odp site 999 from the caribbean the studied time interval covers the first three major g ig marine isotope stages mis 95 100 2 5 ma 2 5 ma after the intensification of nhg analyses were performed on the planktonic foraminifera neogloboquadrina dutertrei and globigerinoides sacculifer representing water mass properties in the thermocline and the mixed layer respectively changes in sea water temperature relative salinity and water column stratification strongly suggest that the panamanian gateway temporarily closed during glacial mis 98 and 100 as a result of changes in ice volume equivalent to a drop in sea level of 60 90 m reconstructed sea surface temperatures sst from g sacculifer show a glacial decrease of 2 5 c at site 1241 but increases of up to 3 c at site 999 during glacial mis 98 and 100 suggesting that the panamanian gateway closed during these glacial periods the mg ca temperatures of n dutertrei remain relatively stable in the east pacific but do show a 3 c warming in the caribbean at the onset of these glacial periods suggesting that the closing of the gateway also changed the water column stratification we infer that the glacial closure of the gateway allowed the western atlantic warm pool to extend into the southern caribbean increasing sst g sacculifer and deepening the thermocline n dutertrei additionally ice volume appears to have become large enough during mis 100 to survive the relatively short lasting interglacial mis 99 so that the gateway remained closed towards the end of mis 98 during mis 97 and into mis 96 temperatures on both sides are mostly similar suggesting water masses exchanged again additionally caribbean variations in sst and 18owater follow a precession like cyclicity rather than the obliquity controlled variations characteristic of the east pacific and many other tropical areas suggesting that regional atmospheric processes related to the trade winds and the intertropical convergence zone itcz had a dominant impact in the caribbean

natural and anthropogenic factors affecting groundwater quality of an active volcano mt etna italy abstract new geochemical data on dissolved major and minor constituents in 276 groundwater samples from etna aquifers reveal the main processes responsible for their geochemical evolution and mineralisation this topic is of particular interest in the light of the progressive depletion of water resources and groundwater quality in the area multivariate statistical analysis reveal 3 sources of solutes a the leaching of the host basalt driven by the dissolution of magma derived co2 b mixing processes with saline brines rising from the sedimentary basement below etna c contamination from agricultural and urban wastewaters the last process highlighted by increased concentrations of so4 no3 ca f and po4 is more pronounced on the lower slopes of the volcanic edifice associated with areas of high population and intensive agriculture however this study demonstrates that natural processes a and b are also very effective in producing highly mineralised waters which in turn results in many constituents b v mg exceeding maximum admissible concentrations for drinking water

biogeography of neogene calcareous nannofossils in the caribbean and the eastern equatorial pacific floral response to the emergence of the isthmus of panama abstract principal components analysis of nannofossil assemblages in five odp sites in the caribbean and the eastern equatorial pacific was used to monitor neogene surface water circulation changes in 15 83 10 71 ma floral distributions clearly show the existence of the circum tropical current between the caribbean and the eastern equatorial pacific and no surface water communication between the northern and southern caribbean in 10 71 9 36 ma the circum tropical current weakened and the northward intra caribbean current had been initiated northern and southern caribbean surface waters again became separated in 8 35 3 65 ma and the circum tropical current was regenerated after 2 76 ma the northward intra caribbean current has completely been established and the circum tropical current disappeared this suggests that a barrier to the circum tropical current had formed indicating the final closure of the isthmus of panama

radiocarbon dated sediment sequences from the belgian coastal plain testing the hypothesis of fluctuating or smooth late holocene relative sea level rise the late holocene deposits of the coastal lowlands bordering the southern north sea were formed by a renewed expansion of the tidal environment replacing freshwater peats the sea level history during the last 2500 years inferred from the post peat deposits containing little to no datable organic material is characterized by two conflicting schools of thought the first one supports a smooth sea level curve the second approach underpins fluctuating sea level changes the fluctuating approach also uses facies variations recorded in the post peat deposits to provide a chronostratigraphical subdivision linked to transgressions and regressions this paper examines the controlling factors responsible for the facies variations in the post peat deposits in order to test the approach of the fluctuating sea level the results of sedimentological investigation coupled with radiocarbon dates of intertidal shells from four shallow outcrops located in nearby sand filled late holocene tidal channels in the belgian

closure of the isthmus of panama the near shore marine record of costa rica and western panama the final closure of the isthmus of panama at 3 5 ma divided the american tropical ocean into two separate and different oceanographic regions consequences for the marine biota were profound but hitherto correlation of the pacific and caribbean coastal sections has not been precise enough to track biologic patterns we present here a correlation of 31 sections from the pacific and caribbean coasts of costa rica and western panama using calcareous nannofossils and planktonic foraminifera at both the tops and bottoms of each formation we estimate that the caribbean section ranges from 8 2 ma to 1 7 ma and the pacific sequence from 3 6 ma to 1 7 ma these intervals bracket postulated dates for final closure of the isthmus and provide the first well dated record of middle and late pliocene faunas from the region the caribbean and pacific sections include very different environments of deposition yet there is sufficient overlap and diversity of habitats to permit meaningful biological comparisons on the caribbean side formations tied together by the overlap of the upper pliocene markers sphenolithus abies and pseudoemiliana lacunosa 3 5 ma to 3 6 ma range from very shallow to shallow inner shelf 200 m and upper slope 200 800 m the pacific coast sections were mostly deposited in a trench slope environment which is absent on the caribbean side these sections fortuitously include abundant thick intra formational slumps containing shallow water fauna more appropriate for biological comparison with the caribbean biota similarly the 1 9 ma to 1 5 ma interval well constrained by various taxa includes middle to outer shelf and inner shelf to upper slope deposits on the caribbean side and marginal marine to inner shelf deposits on the pacific coast using our new biostratigraphic framework to correlate previously poorly constrained mollusc collections we show that evolutionary divergence of the pacific and caribbean near shore marine faunas had occurred by 3 5 ma this strongly suggests that the isthmus was effectively closed by this time

middle to late holocene landscape changes and geoarchaeological implications in the marshes of the dives estuary nw france abstract holocene palaeogeographic changes in the lower dives valley a small estuarine system in normandy france have been investigated using a combination of facies interpretation from borehole cores 14c dating and pollen analysis the palaeoenvironmental record is broadly similar to that of other coastal and estuarine systems along the english channel but exhibits specific features in comparison with large estuarine and coastal systems especially as regards the narrow lower valley and its margins the identified environments included uniform tidal 6800 5500 2200 2000 cal bp freshwater fen 5500 3300 cal bp and drained floodplain 300 0 cal bp in contrast landscape variability was high during the periods 3300 2300 and 1900 300 cal bp in relation to gradients in environmental conditions from downstream to the upper reaches of the valley a significant palaeogeographic change between ca 3000 and 2200 cal bp indicates that episodes of strong coastal hydrodynamic forcing notably storm events may have had dramatic consequences with significant implications for human activities the pollen diagrams show evidence of the opening up of woodland in order to develop pastures and agriculture on the edges of the freshwater marsh during the bronze age 4500 2800 cal bp although the settlement patterns remain unknown because of the sparse archaeological discoveries related to this period during the iron age increased land use in the valley bottom had a significant impact on the environment from the iron age to the late roman period 2800 1500 cal bp the dramatic change caused by marine flooding and the large size of the tidal environment favoured the development of salt extraction sites from the coast to the inner estuary from the early middle ages restricted tidal influences and the progressive silting of the valley bottom by overbank deposits enabled a lasting change with the development of pastureland and the miscellaneous exploitation of the various environments finally after the 17th century the systematic reclamation and drainage of the wetland produced marked changes inducing in particular a significant loss of landscape and ecological diversity in this regard the pattern of land use in the middle ages probably represents an example of sustainable landscape exploitation

fields of multi kilometer scale sub circular depressions in the carnegie ridge sedimentary blanket effect of underwater carbonate dissolution offshore ecuador the carnegie ridge is a volcanic ridge with a carbonate sediment drape during the salieri cruise multibeam bathymetry was collected across carnegie ridge with the simrad em120 of the r v sonne the most conspicuous features discovered on the carnegie ridge are fields of circular closed depressions widely distributed along the mid slope of the northern and southern flanks of the ridge between 1500 and 2600 m water depth these circular depressions are 1 4 km wide and typically 100 400 m deep most are flat floored and some are so densely packed that they form a honeycomb pattern the depressions were carved into the ridge sedimentary blanket which consists of carbonate sediment and has been dated from upper miocene to upper pleistocene several hypotheses including pockmark origin sediment creeping paleo topography of the volcanic basement effects of subbottom currents and both marine and subaerial karstic origins are discussed we believe that underwater dissolution process merits the most serious consideration regarding the origin of the closed depression

circulation through the central american seaway during the miocene carbonate crash changes in circulation associated with the shoaling of the isthmus of panama and the caribbean carbonate crash in the miocene were investigated using nd isotopes from fossil fish teeth and debris from two sites in the caribbean basin ocean drilling program sites 998 and 999 and two sites in the eastern equatorial pacific sites 846 and 1241 the total range for nd values measured from 18 to 4 5 ma in the caribbean is 7 3 to 0 these values are higher than atlantic water masses 11 and range up to values equivalent to contemporaneous pacific water masses confirming that flow into the caribbean basin was composed of a mixture of pacific and atlantic waters with an upper limit of almost pure pacific sourced waters throughout the caribbean record particularly during the carbonate crash 10 12 ma low carbonate mass accumulation rates mars correlate with more radiogenic nd values indicating increased flow of corrosive pacific intermediate water into the caribbean basin during intervals of dissolution this flow pattern agrees with results from general ocean circulation models designed to study the effect of the shoaling of the central american seaway low carbonate mars and high nd values also correlate with intervals of increased northern component water production and therefore enhanced conveyor circulation suggesting that the conveyor may respond to changes in circulation associated with shoaling of the central american seaway reduced pacific throughflow related to shoaling of the seaway led to a gradual increase in carbonate preservation and more atlantic like nd values following the carbonate crash

using 87sr 86sr δ18o and δ2h isotopes along with major chemical composition to assess groundwater salinization in lower shire valley malawi abstract groundwater resources in some parts of the lower section of shire river valley malawi are not useable for rural domestic water supply due to high salinity in this study a combined assessment of isotopic 87 sr 86 sr 18 o and 2 h and major ion composition was conducted in order to identify the hydro geochemical evolution of the groundwater and thereby the causes of salinity three major end members representing fresh and saline groundwater and evaporated recharge were identified based on major ion and isotopic composition the saline groundwater is inferred to result from dissolution of evaporitic salts halite and the fresh groundwater shows influence of silicate weathering conservative mixing models show that brackish groundwater samples result from a three component mixture comprising the identified end members hence their salinity is interpreted to result from mixing of fresh groundwater with evaporated recharge and saline groundwater on the other hand the groundwater with low tds found at some distance from areas of high salinity is influenced by mixing of evaporated recharge and fresh groundwater only close to the shire marshes where there is shallow groundwater composition of stable isotopes of water indicates that evaporation may also be an important factor

evidence for middle eocene and younger land emergence in central panama implications for isthmus closure the rise of the isthmus of panama linked to a number of climatic paleoceanographic and biological events has been studied mostly from indirect often distal geochemical and biotic evidence we have upgraded existing geologic mapping in central panama with more than 2000 field stations over 40 petrographic analyses and more than 30 new geochronological and thermochronological analyses this data set suggests that the isthmus was an uninterrupted chain above sea level from late eocene until at least late miocene times the basement complex of central panama is a folded faulted 3 km thick arc sequence intruded by granitoid bodies and onlapped by mildly deformed upper eocene and oligocene strata six u pb zircon ages in the granitoids along with published geochronological data reveal intense late paleocene to middle eocene magmatism 58 39 ma a temporary cessation of magmatic activity between 38 and 27 ma and renewed magmatism between 25 and 15 ma in a position 75 km south of the former magmatic axis thermochronological analyses in zircon eight u th he ages and in apatite crystals four u th he ages and nine fission track ages obtained from a subset of 58 54 ma granitoid bodies record a concordant lutetian age 47 42 ma cooling from 200 c to 70 c in 5 m y and cooling below 40 c between 12 and 9 ma cooling is linked to exhumation by an angular unconformity that separates the deformed basement complex below from mildly deformed upper eocene to oligocene terrestrial to shallow marine strata above exhumation and erosion of the basement complex are independently confirmed by lower miocene strata that have a detrital zircon signature that closely follows the central panama basement complex age distribution these results greatly restrict the width and depth of the strait separating southern central america from south america and challenge the widely accepted notion that the central american seaway closed in late pliocene time when the ice age began

final closure of panama and the onset of northern hemisphere glaciation abstract the greenland ice sheet is accepted as a key factor controlling the quaternary glacial scenario however the origin and mechanisms of major arctic glaciation starting at 3 15 ma and culminating at 2 74 ma are still controversial for this phase of intense cooling ravelo et al 1 a c ravelo d h andreasen m lyle a o lyle m w wara regional climate shifts caused by gradual global cooling in the pliocene epoch nature 429 2004 263 267 proposed a complex gradual forcing mechanism in contrast our new submillennial scale paleoceanographic records from the pliocene north atlantic suggest a far more precise timing and forcing for the initiation of northern hemisphere glaciation nhg since it was linked to a 2 3 c surface water warming during warm stages from 2 95 to 2 82 ma these records support previous models g h haug r tiedemann effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation nature 393 1998 673 676 2 claiming that the final closure of the panama isthmus 3 0 2 5 ma j groeneveld s steph r tiedemann d nurnberg d garbe schonberg the final closure of the central american seaway geology in prep 3 induced an increased poleward salt and heat transport associated strengthening of north atlantic thermohaline circulation and in turn an intensified moisture supply to northern high latitudes resulted in the build up of nhg finally culminating in the great irreversible climate crash at marine isotope stage g6 2 74 ma in summary there was a two step threshold mechanism that marked the onset of nhg with glacial to interglacial cycles quasi persistent until today

fault segmentation deep rift earthquakes and crustal rheology insights from the 2009 karonga sequence and seismicity in the rukwa malawi rift zone the rukwa malawi rift zone has a record of seismic events down to depths in excess of 30 km deep for a zone of active continental extension this deep seismicity as well as the presence of long 100 km border faults has previously been explained by the long term bulk rheology of intact old cold anhydrous strong crust in east africa or the presence of mafic material in the lower crust the karonga sequence of 2009 showed a style of faulting different from continuous slip along long border faults and is interpreted as segmented failure of hanging wall faults coulomb stress transfer in this sequence is calculated and found to be consistent with segmented slip on a fault system synthetic to a nearby border fault and restricted to depths 12 km the inferred thermal structure of the malawi rift indicates that slip at depths in excess of 30 km occurs at temperatures greater than the 350 450 c commonly inferred at the base of the seismogenic zone crustal strength calculations indicate that long border faults and deep seismicity require the presence of a weak zone of localized deformation with increased strain rate or fluid pressure within a strong lower crust a hypothesis is proposed where shallow segmented frictional failure occurs in regions of relatively strong intact crust e g the karonga sequence whereas long border faults and deep earthquakes are representative of zones of weakness within strong crust this hypothesis if correct implies that seismogenic thickness can vary within thick elastic lithosphere such that localized weak zones of the crust enable nucleation of larger seismic events whereas strong intact crust favors smaller segmented events and a shallower seismogenic zone

closing of the central american seaway and the ice age a critical review 1 what role did the closing of the central american seaway play in enabling continental ice sheets to wax and wane over north america and fennoscandia a summary of relevant evidence presented here permits a causal relationship between them but can be interpreted to show none the common denominator of such evidence is the approximate simultaneity of that closing with global cooling and the first major ice advance at the resolution of paleoclimate however geologic evidence from central america places only weak constraints on when interchange between pacific and caribbean water ceased the strongest evidence for when north and south america became connected by a continuous land bridge the great american exchange of vertebrates assigns climate change the causal role for an arid central american climate typical of glacial times seems necessary for animals that inhabited savannas to pass through panama paleoceanographic and geochemical studies of environments and water masses in the eastern pacific western caribbean and atlantic in general call for continual change since 6 ma or earlier if evidence concurrent with global change near 3 5 3 ma seems more widespread than for other times hypothesized connections between a closed seaway and glaciation commonly call for profoundly different north atlantic ocean circulation but simulations using general circulation models provide a spectrum of differences in circulation for open and closed seaways might much not all of the evidence implicating the closing of the seaway in global climate change in fact be a consequence of that change and blind to central america s tectonic development

driving mechanisms of coastal change peat compaction and the destruction of late holocene coastal wetlands abstract this paper examines the role of peat compaction as a driving mechanism behind the widespread inundation of a late holocene coastal wetland in southeast england uk detailed stratigraphic and dating evidence lithology grain size foraminifera pollen and radiocarbon dates from a sample site in romney marsh documents the gradual inundation of a coastal wetland after 1263 1085 cal yr bp c 700 850 ad and the establishment of a saltmarsh shortly thereafter there was a rapid increase in water depth that was associated with the deposition of nearly 4 m of laminated intertidal mudflat and tidal channel sediments prior to site reclamation from the sea by ad 1460 grain size data and statistical analysis of sand and mud laminae thicknesses suggest the laminated sediments accumulated rapidly c 0 2 m per year as heterolithic tidal rhythmites rapid compaction of the thick peat bed that underlies the study site provided the accommodation space for their deposition this process began with the gradual tidal inundation of the site but accelerated following the widening of a breach in a coastal barrier in the 13th century compaction lowered the peat surface by at least 3 m and was associated with widespread landscape change the study demonstrates the powerful influence that compaction had on the evolution of the late holocene landscape at this site and we believe at many other coastal lowlands in northwest europe this process is likely to have been a key driving mechanism behind rapid late holocene coastal change far exceeding the longer term effects of either eustatic change or crustal uplift subsidence

drastic change in the late pliocene subarctic pacific diatom community associated with the onset of the northern hemisphere glaciation abstract to date there is scarcely clear understanding of the detailed responses of the subarctic pacific phytoplankton communities to the significant climate transition across the initiation of the northern hemisphere glaciation nhg approximately 2 7 million years ago we present more highly resolved evidence of the rapid and drastic change in the phytoplankton biosphere using diatom as a tracer of environmental changes and based on quantitative assemblage analysis of two marine cores from oceanic regions of the north pacific subarctic gyre in the late pliocene subarctic pacific coscinodiscus marginatus and neodenticula kamtschatica were widely dominant but the flora rapidly and drastically shifted to one rich in neodenticula complex n koizumii n seminae at the onset of nhg perhaps due to intense changes in paleoceanographic conditions such as cooling and or a collapse of the previously nutrient regime in the region we also suggest that vertical pumping of biogenic matter by diatoms may have been more efficient in this region earlier than the onset of nhg after the nhg intensification the major primary productivity role in the subarctic pacific shifted from the c marginatus rich flora to the neodenticula complex the drastic decrease of biogenic opaline accumulation reportedly associated with the initiation of nhg would have resulted from not only a decrease of primary production but also from the change in diatom assemblages and consequent effects on their principal role in export flux

strong influence of water vapor source dynamics on stable isotopes in precipitation observed in southern meghalaya ne india to calibrate 18o time series from speleothems in the eastern indian summer monsoon ism region of india and to understand the moisture regime over the northern bay of bengal bob we analyze the 18o and d of rainwater collected in 2007 and 2008 near cherrapunji india d values range from 18 5 to 144 4 while 18o varies between 0 8 and 18 8 the local meteoric water line lmwl is found to be indistinguishable from the global meteoric water line gmwl late ism september october rainfall exhibits lowest 18o and d values with little relationship to the local precipitation amount there is a trend to lighter isotope values over the course of the ism but it does not correlate with the patterns of temperature and rainfall amount 18o and d time series have to be interpreted with caution in terms of the amount effect in this subtropical region we find that the temporal trend in 18o reflects increasing transport distance during the ism isotopic changes in the northern bob surface waters during late ism and vapor re equilibration with rain droplets using an isotope box model for surface ocean waters we quantify the potential influence of river runoff on the isotopic composition of the seasonal freshwater plume in the northern bob temporal variations in this source can contribute up to 25 of the observed changes in stable isotopes of precipitation in ne india to delineate other moisture sources we use backward trajectory computations and find a strong correlation between source region and isotopic composition palaeoclimatic stable isotope time series from northeast indian speleothems likely reflect changes in moisture source and transport pathway as well as the isotopic composition of the bob surface water all of which in turn reflect ism strength stalagmite records from the region can therefore be interpreted as integrated measures of the ism strength

development of a pliocene mixed carbonate siliciclastic reef limon costa rica the miocene to pleistocene limon group of costa rica is a mixed carbonate siliciclastic succession that formed in association with the emergence of the central american isthmus our study focuses on a lower late pliocene reef unit the newly excavated contact cut which is located at the contact between the siliciclastic sediments of the rio banano formation and the mixed reefal and coral bearing deposits and siliciclastic sediments of the quebrada chocolate formation the siliciclastic sediments were deposited in a thick deltaic setting sourced by erosion of the cordillera de talamanca deposits of the limon group preserve a sequence of progressively shallowing near shore sediments that were exposed by uplift during the early to middle pleistocene the contact cut outcrop shows the first reef sequence in the stratigraphic sequence and thus illustrates the reestablishment of caribbean coral reef predominance in the neogene it shows extensive reef growth during a rise in sea level and a slight progradation during the succeeding sea level highstand three stages of reef evolution are recognized based on faunal diversity the contact cut reef complex is comparable to the time equivalent reef of the las islas roadcut situated west of limon which shows a rapid burial of the corals by siliciclastics both reefs document a distinct facies diversification during the final stages of the closing of the central american seaway the reefs developed in an environment stressed by siliciclastic input which ultimately caused a decrease in coral diversity and abundance followed by a temporary demise of the reefs the biotic composition of the patch reefs that occurred during the sea level rise las islas and contact cut did not differ from the reefs that developed during the final highstand in sea level the reefs of the overlying moin formation limon group differences in the position on the shelf relative to the source of the siliciclastics might have been the cause for the different response to the rise in sea level of the transgressive reefs with a very fast give up scenario for las islas reef and a catch up followed by a give up phase for contact cut reef

paleoceanography and the diachrony of radiolarian events in the eastern equatorial pacific the development of an orbitally tuned time scale for the odp leg 138 sites provides biostratigraphers a very high resolution chronostratigraphic framework with this framework we are better able to define which of the first and last appearances of species appear to be synchronous in addition the geographic distribution of sites provides the means with which the detailed spatial patterns of invasion of new species and the extinction of older species can be mapped these maps not only provide information on the process of evolution migration and extinction they can also be related to water mass distributions and near surface circulation of the ocean of 39 radiolarian events studied at 11 sites in the eastern equatorial pacific 28 were found to have a minimum range in their estimated age that exceeded 0 15 m y the temporal pattern of first and last appearances of these diachronous events have coherent spatial patterns that indicate shifts in the areas of high oceanographic gradients over the past 10 ma these changes in the locations of high gradient regions suggest that the south equatorial current sec was north of its present position prior to approximately 7 ma there was a southward shift in the northern boundary of this current between approximately 6 and 7 ma and the development of a relatively strong gradient between the northeastern and northwestern sites between approximately 3 7 and 3 4 ma there was a very slight northward shift in the northern boundary of the sec and the steep gradients between the northeastern and northwestern sites may have disappeared this change is thought to be associated with the closing of the isthmus of panama the temporal spatial patterns of diachronous events younger than 3 4 ma are consistent with patterns of circulation in the modern ocean

sequence mapping of holocene coastal lowlands the application of the streif classification system in the belgian coastal plain a geological map of the holocene deposits of a portion of the western belgian coastal plain is presented the map differs from a conventional geological map which is of little use for coastal lowlands because of the high lateral and vertical variability in lithology in the subsoil the method of sequence maps was chosen because these maps allow the representation of the entire vertical sequence of the holocene deposits a sequence map is constructed on the basis of profile types consisting of the vertical succession of the various mapping units in order to produce a user friendly map preference was given to lithogenetic units instead of formal lithostratigraphic units for the determination of mapping units the organisation of the mapping units was established according to the streif classification system the application of the system is demonstrated with two different sequence maps each constructed on a different level of the hierarchic system a general sequence map and a special sequence map showing further differentiation

isotopic and geochemical evolution of ground and surface waters in a karst dominated geological setting a case study from belize central america abstract analysis of stable isotopes and major ions in groundwater and surface waters in belize central america was carried out to identify processes that may affect drinking water quality belize has a subtropical rainforest savannah climate with a varied landscape composed predominantly of carbonate rocks and clastic sediments stable oxygen 18 o and hydrogen d isotope ratios for surface and groundwater have a similar range and show high d excess 10 40 8 the high d excess in water samples suggest secondary continental vapor flux mixing with incoming vapor from the caribbean sea model calculations indicate that moisture derived from continental evaporation contributes 13 to overhead vapor load in surface and groundwater concentrations of dissolved inorganic carbon dic ranged from 5 4 to 112 9 mg c l and 13 c dic ranged from 7 4 to 17 4 so 4 2 ca 2 and mg 2 in the water samples ranged from 2 163 2 6593 and 2 90 mg l respectively the dic and 13 c dic indicate both open and closed system carbonate evolution combined 13 c dic and ca 2 mg 2 and so 4 2 suggest additional groundwater evolution by gypsum dissolution and calcite precipitation the high so 4 2 content of some water samples indicates regional geologic control on water quality similarity in the range of 18 o d and 13 c dic for surface waters and groundwater used for drinking water supply is probably due to high hydraulic conductivities of the karstic aquifers the results of this study indicate rapid recharge of groundwater aquifers groundwater influence on surface water chemistry and the potential of surface water to impact groundwater quality and vise versa

changes in coastal zone processes at a high sea level stand a late holocene example from belgium this paper presents the results of an investigation of late holocene deposits on the belgian coastal plain the upper clastic deposits overlying the uppermost intercalated peat bed were studied on the basis of lithology radiocarbon dates and foraminiferal assemblages to determine why silting up phases or peat beds are lacking and to establish the evolution of the sedimentary environments as well as the age of the deposits two contrasting sites in quite different locations and showing a different stratigraphy were studied it appears that the coastal evolution was not gradual and continuous but characterised by short periods with high energy conditions alternating with long periods where low energy conditions and little sedimentation prevailed the evolution is determined mainly by tidal channel activity at about 3400 cal yr bp the peat was eroded in narrow zones by the main tidal channels and this until the landward limit of the plain the peat was only partly flooded and mudflats fringed the channels with time new tributaries formed and the channel network progressively enlarged the channels were rapidly filled followed by a period of little sedimentation which lasted at least until 1400 1200 cal yr bp the following channel activity is characterised by lateral sedimentation rather than vertical erosion together with increased sediment reworking the mechanisms of coastal change in the late holocene might be similar over the entire plain but the timing of the changes is certainly not copyright 2002 john wiley sons ltd

wetland landscape dynamics swifterbant land use systems and the mesolithic neolithic transition in the southern north sea basin abstract over the last decade excavations in the lower scheldt river basin nw belgium have identified the first presence of the transitional mesolithic neolithic swifterbant culture previously only known from the netherlands and one site in northwest germany these excavations have also yielded the first evidence for the presence of early neolithic linearbandkeramik limbourg blicquy and epi rossen cultural remains in these wetland landscapes high quality organic preservation at these sites offered the opportunity to reliably place the swifterbant within the absolute chronology of the mesolithic neolithic transition in this region as well as the reconstruction of swifterbant subsistence practices most notably the incorporation of cattle husbandry into a traditional hunting fishing gathering economy two different site types could be identified between the six excavated sites dune and natural levee sites which had contemporaneous periods of occupation but different occupation histories the integration of the dates from these different site types with the palaeoenvironmental dates provides an initial model of the swifterbant settlement system in the area and its role in the specific tempo and trajectories of cultural and economic change that occurred during the neolithisation of the scheldt basin this model consists of relatively specialized and temporarily inhabited cattle and hunting fishing camps on the dunes and larger more continuously occupied levee camps along the river valleys bayesian statistical modeling suggests that swifterbant occupation of the dune sites occurred during a brackish water flooding period and that occupation of the levee sites was more continuous

geochemical and statistical evidence of deep carbonate groundwater within overlying volcanic rock aquifers aquitards of southern nevada usa abstract samples collected from springs and wells in southern nevada were analyzed for major solutes and trace elements as part of a larger study to characterize the geochemical signatures of these groundwaters in this study principal component analysis pca was used to reduce the large data sets including the four major cations ca mg na k and 27 trace elements analyzed in these groundwater samples principal components analysis of the major cation data indicates that groundwaters from cenozoic felsic volcanic rock aquifers aquitards of southern nevada exhibit strong chemical associations to each other but weak relationships to groundwaters from the regional carbonate aquifer which were instead chemically similar to each other however pca of the trace element data demonstrates that some groundwaters from the volcanic aquifers aquitards are chemically similar to those of the underlying regional carbonate aquifer the pca also reveals that these groundwaters from the volcanic aquifers aquitards have significantly different trace element compositions than perched groundwaters contained within similar felsic volcanic rocks moreover rare earth element ree data from groundwaters collected from wells finished in the volcanic aquifers aquitards of southern nevada have similar concentrations and similar shale normalized patterns to the carbonate aquifer groundwaters as well as local carbonate rocks these same southern nevada well waters do not exhibit ree concentrations or shale normalized signatures that resemble the perched volcanic groundwaters or the tuffs of southern nevada the ree data and trace element pca along with previous carbon isotope analyses water temperature data hydraulic head relations and results of a recent pump test of a well near yucca mountain suggest close contact of the regional carbonate groundwaters and groundwaters from the overlying volcanic rocks of southern nevada and possible upwelling of the carbonate groundwaters into the overlying volcanic rock units in the vicinity of yucca mountain

evolution of the northern nicaragua rise during the oligocene miocene drowning by environmental factors abstract possible causes to explain platform drowning have been hotly debated by carbonate sedimentologists for more than a decade now in this paper we present multiple evidence to explain the drowning of a carbonate megabank that covered most of the modern northern nicaragua rise nnr during an interval spanning from late oligocene to early miocene by the interaction of several environmental factors the recovery during odp leg 165 of late oligocene to middle miocene sedimentary sequences in the sub seafloor of the modern channels and basin pedro channel and walton basin respectively that dissect the nnr site 1000 and south of the rise in the colombian basin site 999 combined with information from dredged rock samples allows us to explore in more detail the timing and possible mechanisms responsible for the drowning of the megabank and its relationship to miocene climate change the modern system of isolated banks and shelves dissected by a series of intervening seaways and basins on the nnr has evolved from a continuous shallow water carbonate megabank that extended from the honduras nicaraguan mainland to the modern island of jamaica available information suggests that this megabank broke apart and partially drowned in the late part of the late oligocene at around 27 ma and finally foundered during the late early miocene around 20 ma resulting in limited neritic coral growth in the areas where the modern isolated carbonate banks and shelves are occurring today available information also suggests that the southern and central parts of pedro channel were already a deep water area before the major episode of platform drowning and its formation predates the initiation of the caribbean current however after the partial drowning of the megabank the channel has become a major pathway for the caribbean current stratigraphic units identified in deep water carbonates sampled at odp sites 999 and 1000 help to constrain the environmental setting leading to the drowning of the banks changes in lithology and mass accumulation rates of both the carbonate and non carbonate fraction parallel stable isotope shifts and likely indicate regional changes in climate and circulation during the late oligocene middle miocene interval carbonate mass accumulation rates mars at site 999 suggest increased regional productivity during the early miocene terrigenous mars at both sites 999 and 1000 show a general increase from the burdigalian through the serravallian the temporal association among episodes of neritic platform deposition followed by increased productivity as identified by higher carbonate mars and positive excursion in carbon isotopes suggests that oceanographic changes such as local upwelling and nutrification have led to the partial drowning of the nnr megabank

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

late neogene paleoceanography of the eastern caribbean the gulf of mexico and the eastern equatorial pacific abstract calcareous nannofossil census data from the late neogene of the caribbean the gulf of mexico and the eastern equatorial pacific were subjected to a multifold analysis in order to extract the paleoceanographic history of the region a detailed nannofossil biostratigraphy is the basic time framework the paleoenvironmental signals are deduced from fluctuations of diversity dominance and equitability through time by clustering of assemblages through time and examining the composition of cluster groups by comparison of fluctuations in carbonate content and coarse fraction with time and by factor analysis of the assemblage these measures variously reflect surface water characteristics such as productivity bottom water characteristics such as corrosiveness dissolution and conditions of sedimentation such as dilution of the pelagic biogenic carbonate diversity dominance and equitability which are determined by surface water characteristics show similar trends often in considerable detail in the caribbean and the gulf of mexico from the late miocene through pleistocene broad but definite similarities exist in these measures between the caribbean gulf of mexico and the eastern equatorial pacific in the late miocene to mid pliocene but not in the late pliocene clustering groups assemblages in a broad biostratigraphic pattern corresponding approximately to a major assemblage zone the structure and composition of cluster groups indicate strong similarity between the caribbean and the gulf of mexico during the late miocene through pleistocene but only weak similarity of the caribbean and gulf of mexico to the eastern equatorial pacific and only during the early pliocene surface water productivity is generally similar at the three locations into the late pliocene but seemingly diverges in the eastern equatorial pacific after about 2 4 m y variations in dissolution intensity have generally similar trends in the late miocene and early pliocene in the caribbean and the gulf of mexico but the trends diverge in the late pliocene and are dissimilar in the pleistocene in the eastern equatorial pacific dissolution intensity increases with the inferred thermal subsidence of the crust variations in the calcium carbonate content of the sediment essentially pelagic carbonate follow different trends at the three sites which is attributable to different sedimentary histories at the sites tectonic plus eustatic sea level changes for the caribbean eustatic sea level changes alone for the gulf of mexico and dilution by biogenic silica plus dissolution for the eastern equatorial pacific the various measured and derived parameters indicate that as late as the mid pliocene approximately 3 8 m y a deep water connection existed between the pacific and the caribbean gulf of mexico a shallower seaway permitting exchange of surface water between the pacific and gulf of mexico seems to have existed into the late pliocene to between 3 0 to 2 2 m y and final closure probably coincided with the sea level draw down associated with the initial buildup of a northern hemisphere ice sheet during the late pliocene and early pleistocene surface productivity oscillates markedly but seemingly with different intensities in the caribbean and the gulf of mexico the most important floral change occurs in both basins at about 0 9 m y when the smallgephyrocapsa dominated high productivity nannoflora of the preceeding 0 3 m y was replaced abruptly by a moderate productivity flora this turnover marks a major change in ocean circulation towards a relatively warm stably stratified tropical surface ocean which seems to have been affected remarkably little by some of the intense late pleistocene high latitude climatic changes

multivariate statistical analysis of geochemical data as indicative of the hydrogeochemical evolution of groundwater in a sedimentary rock aquifer system summary the study of groundwater hydrogeochemistry of the paleozoic basses laurentides sedimentary rock aquifer system in quebec produced a large geochemical dataset groundwater samples were collected at 153 sites over a 1500 km2 study area and analyzed for major and minor ions the large number of data can lead to difficulties in the integration interpretation and representation of the results two multivariate statistical methods hierarchical cluster analysis hca and principal components analysis pca were applied to a subgroup of the dataset to evaluate their usefulness to classify the groundwater samples and to identify geochemical processes controlling groundwater geochemistry this subgroup consisted of 144 samples and 14 parameters ca2 mg2 na k hco 3 cl so 4 2 fe2 mn2 br sr2 f ba2 hs seven geochemically distinct clusters c1 c7 resulted from the hca samples from clusters c3 c4 c6 and c7 are mostly located in preferential recharge areas the majority of these samples have ca mg hco3 recharge groundwater c3 c6 c7 and na hco3 evolved groundwater c4 samples from the other three clusters c1 c2 c5 are characteristic of an aquifer system under confined conditions the majority of these samples have na hco3 evolved groundwater c1 c5 and na cl ancient groundwater that exhibits elevated concentrations in br c2 in addition to recognizing the importance of hydrogeological conditions on groundwater geochemistry the distribution of clusters also showed the importance of the geological formations on minor and trace elements such as fe2 mn2 sr2 f and ba2 the first five components of the pca account for 78 3 of the total variance in the dataset component 1 is defined by highly positive loadings in na cl and br and is related to groundwater mixing with champlain sea water and solute diffusion from the marine clay aquitard the high positive loadings in ca2 and mg2 of component 2 suggest the importance of dissolution of carbonate rocks in this aquifer system from their characteristic loadings the first two components are defined as the salinity and hardness components respectively components 3 5 are related to more local and geological effects the integration of the hca and the pca with conventional classification of groundwater types as well as with the hydrogeological and geological contexts allowed the division of the region into four main geochemical areas providing an improved regional picture of the aquifer system dynamics and hydrogeochemical evolution of groundwater the following factors were recognized as influencing the evolution of groundwater identified in every geochemical area 1 geological characteristics including sedimentary rock type and till mineralogy 2 hydrogeological characteristics represented by the level of confinement and the hydraulic gradient and 3 the geological history including the latest glaciation and the champlain sea invasion with its integrated approach this hydrogeochemical study contributes to the characterization and understanding of complex groundwater flow systems and provides an example of the long term geochemical evolution of hydrogeological systems after a major perturbation in this case seawater invasion

transition from the farallon plate subduction to the collision between south and central america geological evolution of the panama isthmus this paper presents new geological constraints on the collision of southern central america with south america and the resulting deformational episodes that have affected the panama isthmus since the late cretaceous the panama isthmus is located in southwestern central america and it represents the zone of contact between the two land masses central america and south america this collision event is still active today it has resulted in regional uplift since the late miocene pliocene and is responsible for the great american biotic interchange between south and north america depending on the methods of investigation used and due to the lack of data available the time when this collision began is still widely debated and poorly constrained to better constrain this age we have studied the rock formations and the tectonic deformations in central and eastern panama that have occurred since the late cretaceous this study presents new rock ages field work documentation and analyses and seismic line interpretations and it is complemented by spatial images for the eastern panama area during the middle eocene a number of changes suddenly appeared in the geological records that were synchronous with the break up of southern central america into two smaller blocks chorotega and choco our main results identify the prevalence of an extensional tectonic regime from the middle eocene to the middle miocene that caused the formation of horst and graben structures with thick sedimentary basin fills and a synchronous clockwise block rotation here we propose that these geologic events are associated with the initiation of the oblique collision of southern central america with south america the first contact of the southeastern extremity of central america occurred around 40 ma to 38 ma and then propagated northwestwards we describe here this long term collision episode in relation to the history of the panama isthmus

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

using stable isotopes and hydraulic head data to investigate groundwater recharge and discharge in a fractured rock aquifer summary groundwater recharge and discharge were studied in a gneissic terrain with minimal glacial overburden at a well instrumented field site adjacent to a 1 2 km section of the tay river near perth ontario canada seven 31 56 m deep monitoring wells were constructed characterized and sampled for 18 o and 2 h each well was first hydraulically tested using a 1 77 m straddle packer system and then instrumented with multi level piezometers detailed fracture mapping and electrical conductivity surveys were conducted in a 1 2 km section of the river to identify potential groundwater discharge points groundwater surface water and precipitation rain and snow samples were collected to measure 2 h and 18 o during and following several storm events and during baseflow conditions results showed that groundwater flow in the upper 30 40 m of bedrock is dominated by a few horizontal fractures which are weakly connected by sparsely arranged vertical fractures values of 2 h and 18 o indicate that precipitation does not directly influence the isotopic signature of river water and deep groundwater during a rain event recharge is localized and rapid where overburden is thin however it does not penetrate deeply into the flow system at this site there is no hydraulic or isotopic evidence that groundwater discharges into the river over the study section thus most of the groundwater underflows the river at this location flow in this reach and likely in the bulk of the river is controlled by an upstream dam and by surface water runoff the results of this study suggest that the use of traditional methods for water budgeting based on equivalent porous media are highly inappropriate for this crystalline bedrock setting

evolution of eastern pacific warm pool and upwelling processes since the middle miocene based on analysis of radiolarian assemblages response to indonesian and central american seaways a quantitative racholarian study at ocean drilling program site 1241 in the eastern tropical pacific enables us to reconstruct paleoceanographic changes that occurred since the latest middle miocene today this site is located just under the eastern pacific warm pool epwp based on the abundance variations of radiolarian characteristic species which are indicators of upwelling and thermocline changes it is suggested that three notable changes occurred at 10 6 9 8 and 4 2 ma in the region four distinct periods of oceanographic conditions bounded by these notable changes were characterized on the basis of the following 1 stratified seawater 12 0 to 10 6 ma 2 a shallowing of the thermocline and an increasing of upwelling 10 6 to 9 8 ma 3 significant inflow of warm water to the eastern tropical pacific caused by an intensified northern equatorial countercurrent necc resulting in the formation of epwp 9 8 to 4 2 ma and 4 the reduction of the epwp and the necc and an increase in upwelling 4 2 to 0 ma the timing of these paleoceanographic events indicated the strong relations with the opening and closing of the indonesian and central american panama seaways the reduction of the epwp this study and the deepening of the thermocline in western pacific at about 4 2 ma cannariato and ravelo 1997 chaisson and ravelo 2000 indicated a change from a state resembling el nino in the late miocene and the early pliocene time to a state resembling la nina by the late pliocene c 2009 elsevier b v all rights reserved

how subsoil morphology and erodibility influence the origin and pattern of late holocene tidal channels case studies from the belgian coastal lowlands abstract this paper aims at a better understanding of the late holocene re entrance of the tidal system in the belgian coastal plain after a 2 3 ka years long period of peat growth the re entrance was associated with the development of deeply incised tidal channels the initial cause of the re entrance still a missing link in the understanding of the late holocene coastal change is investigated by focusing on the specific location of the young tidal channels the research though based in the western belgian coastal plain is relevant to the lowlands of the southern north sea and english channel the investigation combines stratigraphic radiocarbon and sedimentological data together with maps showing the morphology of the pre holocene surface the distribution of the holocene deposits and the erosional surface produced by the late holocene channels it appears that the young channels re occupied the same position as their early and mid holocene predecessors the re entrance of the tidal system began by a removing of the upper part of the older channels which originated from the mainland once the channels were cleaned of sediment tidal waters could re enter and rework the easily erodable sand of the older channels and pleistocene deposits

surface temperatures of the mid pliocene north atlantic ocean implications for future climate the mid pliocene is the most recent interval in the earth s history to have experienced warming of the magnitude predicted for the second half of the twenty first century and is therefore a possible analogue for future climate conditions with continents basically in their current positions and atmospheric co2 similar to early twenty first century values the cause of mid pliocene warmth remains elusive understanding the behaviour of the north atlantic ocean during the mid pliocene is integral to evaluating future climate scenarios owing to its role in deep water formation and its sensitivity to climate change under the framework of the pliocene research interpretation and synoptic mapping prism sea surface reconstruction we synthesize mid pliocene north atlantic studies by prism members and others describing each region of the north atlantic in terms of palaeoceanography we then relate mid pliocene sea surface conditions to expectations of future warming the results of the data and climate model comparisons suggest that the north atlantic is more sensitive to climate change than is suggested by climate model simulations raising the concern that estimates of future climate change are conservative

a new gis approach for reconstructing and mapping dynamic late holocene coastal plain palaeogeography the geomorphological development of holocene coastal plains around the world has been studied since the beginning of the twentieth century from various disciplines resulting in large amounts of data however the overwhelming quantities and heterogeneous nature of this data have caused the divided knowledge to remain inconsistent and fragmented to keep improving the understanding of coastal plain geomorphology and geology cataloguing of data and integration of knowledge are essential in this paper we present a gis that incorporates the accumulated data of the netherlands coastal plain and functions as a storage and integration tool for coastal plain mapped data the gis stores redigitised architectural elements beach barriers tidal channels intertidal flats supratidal flats and coastal fresh water peat from earlier mappings in separate map layers a coupled catalogue style database stores the dating information of these elements besides references to source studies and annotations regarding changed insights using scripts the system automatically establishes palaeogeographical maps for any chosen moment combining the above mapping and dating information in our approach we strip the information to architectural element level and we separate mapping from dating information serving the automatic generation of time slice maps it enables a workflow in which the maker can iteratively regenerate maps which speeds up fine tuning and thus the quality of palaeogeographical reconstruction the gis currently covers the late holocene coastal plain development of the netherlands this period witnessed widespread renewed flooding along the southern north sea coast coinciding with large scale reclamation and human occupation our gis method is generic and can be expanded and adapted to allow faster integrated processing of growing amounts of data for many coastal areas and other large urbanising lowlands around the world it allows maintaining actual data overview and facilitates new ways of analysis at national regional and local scales 2016 elsevier b v

late middle miocene segmentation of an eocene early miocene carbonate megabank on the northern nicaragua rise tied to the tectonic activity at the north america caribbean plate boundary zone the northern nicaragua rise nnr is comprised today of the eastern honduras nicaragua and southern jamaica carbonate shelves and a series of relatively small detached carbonate banks i e pedro rosalind serranilla diriangen and bawika banks separated from each other by intervening basins and seaways the nnr basins and seaways because of their common north trending orientation have been previously interpreted as paleocene eocene and possibly oligocene rifts becoming progressively younger from the eastern to the western part of nnr results from three recent 1988 and 1992 high resolution seismic surveys within these major seaways and basins 1 walton basin 2 pedro channel and 3 seaways and serranilla basin on the western side of the nnr show that the present bank and basin configuration evolved from a once continuous megabank that covered the entire length of the nnr including the island of jamaica from eocene through early miocene times in the late middle miocene this megabank progressively broke up into a series of smaller banks basins and seaways mainly as the result of tectonic movements related to the overall strike slip displacement within the north american and caribbean plate boundary zone of the cayman trough at the same time late middlemore miocene the most eastern portion of the megabank was uplifted and today forms most of central and south jamaica the timing of the megabank segmentation has tentatively been constrained by dating several blocks of shallow water limestone dredged from parts of the megabank outcropping on the sea floor of different seaways less

late neogene benthic stable isotope record of ocean drilling program site 999 implications for caribbean paleoceanography organic carbon burial and the messinian salinity crisis we report on epibenthic foraminiferal 18o and 13c and percentage coarse fraction records from caribbean ocean drilling program odp site 999 12 44 n 78 44 w water depth 2828 m spanning the interval from 8 5 to 5 3 ma low epibenthic 13c values and low amounts of sand sized particles mostly foraminifer shells indicate a poorly ventilated deep caribbean throughout the late miocene at this time the deep caribbean was dominated by a nutrient rich and corrosive water mass a generally constant 13c gradient between the caribbean and deep atlantic records during the late miocene suggests that the fluctuations in 13c reflect global changes in 13c of the dissolved inorganic carbon due to varying erosion of organic carbon from terrigenous soils and shelf sediments the observed 100 kyr cyclicity of epibenthic 13c is in good accordance with the variability of terrigenous input to the equatorial atlantic as recorded by magnetic susceptibility records of the ceara rise however some short term gradient changes between 7 0 and 4 5 ma indicate a poorer ventilation of the deep atlantic related to a reduced production of deep water in the atlantic the messinian salinity crisis between 6 0 and 5 3 ma did not affect the intermediate to deep water gradient between the caribbean and the atlantic comparison to the bahama platform record of odp site 1006 however indicates a poorer ventilation of the shallower northern caribbean basins coincident with the isolation of the mediterranean sea

the streif classification system a tribute to an alternative system for organising and mapping holocene coastal deposits the classification system for organising and mapping holocene coastal deposits as introduced by streif is highlighted with respect to mapping requirements apart from the requirements such as a user friendly legend and map the linkage of the classification system with the history of deposition is demonstrated for the tide dominated lowlands of the southern north sea and english channel the linkage becomes obvious when considering the effect of the changes in the rate of relative sea level rise the difficulties that surrounded the lithostratigraphy of holocene coastal deposits and the principles of the classification system which eventually made an end to the well known and long standing debate about the lithostratigraphy are briefly recalled

use of chloride mass balance and environmental isotopes for evaluation of groundwater recharge in the alluvial aquifer wadi tharad western saudi arabia groundwater recharge estimation has become a priority issue for humid and arid regions especially in regions like saudi arabia where the precipitation varies over space and time as a result of topography and seasonality wadi tharad is a typical arid area in western saudi arabia within its drainage area of 400 km 2 the groundwater system shows a graded hydrochemical zonation from the hydrocarbonate in the upper reach to the chloride zone in the lower reach the saturation index si varies depending on the concentrations of carbonate minerals the mean for calcite and dolomite is about in equilibrium e g zero value as halite and gypsum indices are negative it is undersaturated isotopic compositions of h and o in the groundwater show that the groundwater recharge resources are mainly from meteoric water the chloride mass balance method was refined to estimate the amount of recharge which is probably 11 of the effective annual rainfall these results can be used to improve the accuracy of future groundwater management and development schemes

factors responsible for high arsenic concentrations in two groundwater catchments in taiwan abstract high as contents in groundwater were found in two neighboring catchments the chianan plain and the southern choushui river alluvial fan in taiwan the groundwater quality the redox potential and the as distribution of the chianan plain were characterized using factor analysis redox zoning and a geochemical program the results were compared with those of the southern choushui river alluvial fan possible as release mechanisms are also elucidated factors 1 and 2 of the groundwater in the chianan plain the salinization factor and the as enrichment factor are similar to those in the southern choushui river alluvial fan however the spatial distribution of reductive tendency in the chianan plain is different to that in the choushui river alluvial fan and yields spatially distinct hydrogeochemical environments in these two neighboring areas the reduction potential in the chianan plain is stronger than that in the choushui river alluvial fan the difference between the reduction potentials in these two vicinal areas influences the concentrations of as in groundwater the reductive dissolution of as rich fe oxyhydroxide is suggested to be the major mechanism for release of as to the groundwater in the chianan plain and the choushui river alluvial fan of taiwan

late miocene washhouse climate in europe abstract we present two eight million year long proxy records of precipitation for southwest and central europe covering the middle to late miocene 5 3 13 ma at a temporal resolution of about 60 kyr and 150 kyr respectively the estimates of precipitation are based on the ecophysiological structure of herpetological assemblages amphibians and reptiles from 13 0 ma until about 9 ma both records show a similar trend evolving from a long dry period 13 11 ma into a washhouse climate 10 2 9 8 ma characterized by global warm conditions and several times more precipitation than present the transition from washhouse to a dryer climate between 9 7 and 9 5 ma and the concomitant cooling episode appear to have triggered a severe biotic event known as the vallesian crisis which included the extinction of hominoids in western europe a second washhouse period 9 0 8 5 ma coeval with a global warm episode was unprecedentedly intense in southwest europe but less pronounced in central europe from 8 ma onward a divergence in the two precipitation records is observed with southwest europe staying wetter and central europe becoming dryer than present both precipitation records are combined into a common run off curve as a measure of the relative intensity of the hydrological cycle for moderate latitudes of continental europe the run off curve shows a remarkable positive correlation with atlantic deep water temperatures from ceara rise by lear et al 2003 which are significantly higher up to 3 c during the two washhouse periods and show no other positive excursion of comparable magnitude we discuss potential links and the role of the coeval temporary restriction of the central american seaway on ocean and atmosphere circulation

paleoceanographic implications of miocene deep sea hiatuses miocene paleoceanographic evolution exhibits major changes resulting from the opening and closing of passages the subsequent changes in oceanic circulation and development of major antarctic glaciation the consequences and timing of these events can be observed in variations in the distribution of deep sea hiatuses sedimentation patterns and biogeographic distribution of planktic organisms the opening of the drake passage in the latest oligocene to early miocene 25 20 ma resulted in the establishment of the deep circumpolar current which led to thermal isolation of antarctica and increased global cooling this development was associated with a major turnover in planktic organisms resulting in the evolution of neogene assemblages and the eventual extinction of paleogene assemblages the erosive patterns of two widespread hiatuses ph 23 0 22 5 ma and nh 1 20 18 ma indicate that a deep circumequatorial circulation existed at this time characterized by a broad band of carbonate ooze deposition siliceous sedimentation was restricted to the north atlantic and a narrow band around antarctica a major reorganization in deep sea sedimentation and hiatus distribution patterns occurred near the early middle miocene boundary apparently resulting from changes in oceanic circulation beginning at this time deep sea erosion occurred throughout the caribbean hiatus nh 2 16 15 ma suggesting disruption of the deep circumequatorial circulation and northward deflection of deep currents and or intensification of the gulf stream sediment distribution patterns changed dramatically with the sudden appearance of siliceous ooze deposition in the marginal and east equatorial north pacific by 16 0 to 15 5 ma coincident with the decline of siliceous sedimentation in the north atlantic this silica switch may have been caused by the introduction of norwegian overflow water into the north atlantic acting as a barrier to outcropping of silica rich antarctic bottom water the main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13 5 to 12 5 ma hiatus nh 3 coincident with the establishment of a major east antarctic ice cap antarctic glaciation resulted in a broadening belt of siliceous ooze deposition around antarctica increased siliceous sedimentation in the marginal and east equatorial north pacific and indian oceans and further northward restriction of siliceous sediments in the north atlantic periodic cool climatic events were accompanied by lower eustatic sea levels and widespread deep sea erosion at 12 to 11 ma nh 4 10 to 9 ma nh 5 7 5 to 6 2 ma nh 6 and 5 2 to 4 7 ma nh 7

isotopic paleoceanography of the caribbean and east pacific role of panama uplift in late neogene time comparisons of carbon isotopic data on benthic foraminifera from deep sea drilling project sites 502 western caribbean and 503 eastern pacific indicate that the difference between the atlantic and the pacific in the per mil enrichment in carbon 13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago when the difference reached the modern level 1 per mil comparisons of planktonic foraminiferal oxygen isotopic data for the caribbean and the pacific suggest that the salinity of caribbean surface waters began increasing 4 million years ago possibly in response to shoaling of the panama isthmus these results suggest that modern circulation patterns in the caribbean and eastern pacific developed by 3 million years ago in concert with changing tectonic climatic and biogeographic patterns

environmental isotope hydrology of salinized experimental catchments deuterium oxygen 18 tritium and chloride concentrations were used in three salinized experimental catchments to gain insight into the mechanism of solute concentration and flow processes in the saturated and unsaturated zones the three experimental catchments were studied because of their location in different rainfall regions their status with respect to clearing of native vegetation and with respect to secondary salinization two uncleared catchments have average annual rainfalls of approximately 820 and 1220 mm respectively the third cleared catchment has an annual rainfall of 650 750 mm this catchment was in an advanced state of secondary salinization and displayed large areas of saline groundwater discharge with halite encrustation at the ground surface the stable isotope compositions of the solution phase in solute bulge profiles in the unsaturated zone showed a close agreement with the amount weighted mean isotopic composition of rainfall and only surficial evidence of isotopic enrichment due to evaporation evaporation from the soil surface plays a minor role as a mechanism of solute concentration in the unsaturated zone the dominant process of solute concentration in the unsaturated zone was ion exclusion during uptake of water by tree roots which was evidently a solute but not isotope fractionating process tritium analyses of unsaturated zone water and grondwater indicated movement of recent recharge to 7 10 m depth at the low rainfall site but over the full depth of the 15 m unsaturated zone at the higher rainfall site the variability in 18o and 2h values of groundwaters was used in association with chloride concentrations to provide information on mixing characteristics of groundwaters within the catchments

drastic change in the geographical distribution of the cold water nannofossil coccolithus pelagicus wallich schiller at 2 74 ma in the late pliocene with special reference to glaciation in the arctic ocean abstract we reconstruct the late pliocene to quaternary paleoceanography of the pacific and atlantic oceans based on the geographical distribution of coccolithus pelagicus wallich schiller which has been regarded as a typical cold water species at 2 74 ma the distribution of c pelagicus defines a biogeographical boundary in the marginal seas of mid to high latitude regions of the pacific such as near the japanese islands kuril islands kamchatca peninsula aleutian islands alaska and the northeastern pacific off canada the relative abundance of c pelagicus is greater than 80 in these marginal sea areas in the north pacific and japan sea on the basis of characteristics of the nannofossil assemblages and recent nannoplankton biogeography in the norwegian greenland sea the change in the relative abundance of c pelagicus at 2 74 ma is thought to be the result of the southward migration of most species except c pelagicus with the onset of heavy glaciation the results also indicate that the geographical distribution of c pelagicus changed in three steps at 2 75 1 65 and 1 2 ma and it became rare to barren in low latitude regions

foraminiferal mg ca increase in the caribbean during the pliocene western atlantic warm pool formation salinity influence or diagenetic overprint we constructed a high resolution mg ca record on the planktonic foraminifer globigerinoides sacculifer in order to explore the change in sea surface temperature sst due to the shoaling of the isthmus of panama as well as the impact of secondary factors like diagenesis and large salinity fluctuations the study covers the latest miocene and the early pliocene 5 6 3 9 ma and was combined with 18o to isolate changes in sea surface salinity sss before 4 5 ma sstmg ca and sss show moderate fluctuations indicating a free exchange of surface ocean water masses between the pacific and the atlantic the increase in 18o after 4 5 ma represents increasing salinities in the caribbean due to the progressive closure of the panamanian gateway the increase in mg ca toward values of maximum 7 mmol mol suggests that secondary influences have played a significant role evidence of crystalline overgrowths on the foraminiferal tests in correlation with aragonite sr ca and productivity cyclicities indicates a diagenetic overprint on the foraminiferal tests laser ablation inductively coupled plasma mass spectrometry analyses however do not show significantly increased mg ca ratios in the crystalline overgrowths and neither do calculations based on pore water data conclusively result in significantly elevated mg ca ratios in the crystalline overgrowths alternatively the elevated mg ca ratios might have been caused by salinity as the 18o record of site 1000 has been interpreted to represent large fluctuations in sss and cultivating experiments have shown an increase in mg ca with increasing salinity we conclude that the mg ca record 4 5 ma can only reliably be considered for paleoceanographical purposes when the minimum values not showing any evidence of secondary influences are used resulting in a warming of central caribbean surface water masses after 4 5 ma of 2 c

late flandrian holocene tidal palaeochannels gwent levels severn estuary sw britain character evolution and relation to shore abstract the exceptionally well exposed flandrian sediments on the welsh shores of the severn estuary reveal tidal palaeochannel networks uniquely tied to vertically stacked peat silt couplets field relationships show that channels multiplied and were enlarged as each peat organogenic marsh was rapidly transgressed replaced by and buried beneath silt mineralogenic marsh the networks infilled and shrank as the silt marsh later gave way regressively to the next peat marsh simulation and hydraulic models show that this cycle depended on an increase followed by a decrease in the tidal prism imposed on the marsh during a sea level fluctuation coupled patterns of channel width downstream orientation and coarseness of fill suggest that the many networks tied to the final flandrian peat silt couplet cycle iii ranged inland from a marsh edge lying of the order of 2 km seaward from the modern coast

neap spring cycles in a subrecent tidal channel fill 3665 bp at schoorldam nw netherlands abstract neap spring tidal sequences are described from an intertidal channel fill the channel fill consists of a larger scale thinning up and fining up sequence of parallel laminations on a smaller scale more or less regular thickening up to thinning up sequences are formed separated from each other by more or thicker clay laminae peat detritus or echinocardium spicules deeper lying sequences contain about 28 laminae higher up the sequences become more irregular and contain gradually a lesser number of laminae these thickening up to thinning up sequences are interpreted as neap spring tidal sequences formed by semi diurnal flood tidal currents hence ca 28 laminae per 14 days three types have been found a cm thick sand clay alternations b ripple like sand mud alternations and c mm thick sand clay alternations these types show transitions to each other type a was deposited at higher current velocities and type c at lowest current velocities type b features are not linsen and flaser bedding but ripple like features which during flood only moved one cross lamina followed by one slackwater lamina clay peat or spicules they are called rippled tidal couplets the pattern of neap spring sequences is compared with recent hw water levels in the north sea and related to mean high water levels mhw and mean sea level msl

holocene evolution of relative sea level and local mean high water spring tides in belgium a first assessment abstract holocene age depth data from the belgian coastal plain basal peat data particularly are assessed in terms of local water and tide levels basal peat formation was generally induced by sea level rise effects of local seepage were limited and significant river gradient effects were absent no relation was found between the timing of basal peat inception and substrate permeability in general edaphic moisture conditions were unfavourable for organic accumulation prior to sea level related rise of the groundwater table error envelopes for the minimum level of local mean high water spring tides and for upper and extreme lower relative mean sea level limits during the last 9400 solar years 8400 yrs b p are presented these indicate that the rate of relative sea level rise showed marked retardations at ca 7500 7000 yrs cal b p 6650 6100 yrs b p and ca 5500 5000 yrs cal b p 4400 yrs b p a eustatic explanation appears to be plausible particularly for the former prior to ca 4000 yrs cal b p ca 3600 yrs b p the relative sea level rise in belgium differs noticeably from that established for the western netherlands with both diverging progressively back in time this implies that considerable differential crustal movement occurred between the two areas in the early holocene

abrupt intensification of north atlantic deep water formation at the nordic seas during the late pliocene climate transition knowledge of the evolution of north atlantic deep water nadw is key to understanding the past evolution of the climatic system here we developed a new rock magnetic method to determine the constituent magnetic minerals of sediments and report on the evolution of nadw during 2 2 2 9 ma we measured isothermal remanence acquisition curves of north atlantic deep sea sediments drilled at the gardar drift and decomposed the first derivatives of these curves into high coercivity and low coercivity components residuals of the decomposition were sufficiently small throughout the study interval confirming that the gardar drift sediments represent a mixing of the two end members fractional changes of the high coercivity component represent variation of the iceland scotland overflow water a branch of nadw formed at the nordic seas the high coercivity component increased significantly during an interglacial period just after 2 68 ma which suggests that nadw formation in the nordic seas abruptly intensified at this time

global cooling in marine climates and local tectonic events in southwest japan at the plio pleistocene boundary abstract this study reconstructs the temporal changes in water temperature and depth on the pacific coast of southwest japan from the latest pliocene to the earliest pleistocene ca 2 6 ma on the basis of the modern analog technique mat of fossil ostracodes and factor analysis of fossil planktonic foraminifera from the takanabe formation around the plio pleistocene boundary the mat results reveal that the mean annual warmest month and coldest month temperatures of bottom water were estimated at ca 6 17 6 17 and 6 16 c respectively the bottom water temperature before 2 6 ma was similar to modern temperatures of the study site since then the temperature dropped several degrees moreover the result of the analysis of fossil planktonic foraminifera suggests that the study site clearly changed from a marine climate under the influence of the axial part of the kuroshio current to that of transitional water at around 2 6 ma thus the results of the microfossil analysis reveal for the first time that a global cooling event at the plio pleistocene boundary influenced the pacific coast of sw japan the change in water depth at ca 2 6 ma in the study site was estimated to have been extremely large in comparison with the global sea level fluctuations during the late pliocene suggesting that the tectonic movement related to the rotation of the southern kyushu island southwest japan started at ca 2 6 ma and that subsidence occurred in the study area

the holocene lithostratigraphy of fenland eastern england a review and suggestions for redefinition the fenland basin is filled with unconsolidated holocene marine and freshwater deposits stratigraphic studies of the basin date back to 1877 this paper reviews the various lithostrati graphic schemes which have been proposed particular attention is paid to the presently accepted lithostratigraphy examples and a case study of a newly surveyed area are used to highlight its failings many of the difficulties experienced in fenland are common to problems of lithostratigraphic classification in coastal lowland environments as is demonstrated by reference to recent debate in the southeastern north sea in fenland as a result of the shortcomings of the various schemes it is proposed that a new lithostratigraphy with formal stratotypes is devised suggestions are made as to the form this new stratigraphy could take in the meantime an informal lithostratigraphy should be adopted which has no regional or chronostratigraphic connotations

middle to late miocene caribbean dinoflagellate assemblages and palynofacies dsdp leg 15 site 153 abstract changes in oceanic circulation and productivity patterns near central america have been explained using numerous different tools such as tectonics geochemistry and micropaleontology this paper aims to contribute to this discussion through the study of dinoflagellates and palynofacies in the drill core from dsdp site 153 based on foraminiferal data the studied section is divided into the middle and upper miocene and our dinoflagellate events also support an age model of 15 to 8 ma indval ecological indexes and the p g dinoflagellate ratios were used to develop paleoenvironmental inferences the indicator species are operculodinium centrocarpum and tectatodinium pellitum for the mm1 interval spiniferites spp and impagidinium strialatum for mm2 and selenopemphix armageddonensis lejeunecysta spp and l tenella for um3 intervals mm1 and mm2 are characterized by a dominance of gonyaulacoids and inner to outer neritic environments the um3 interval is interpreted as an outer neritic environment in the base middle portion and inner neritic in the uppermost part with a shift from gonyaulacoid to peridinioid dominance suggesting an increase in productivity during the middle miocene productivity is low due to intermittent marine circulation restrictions in the caribbean sea and there is a slight increase during the upper miocene following reestablishment of the global oceanic circulation this is directly connected to the occurrence of geotectonic and paleoceanographic events in the region during the miocene mainly by mass movements such as the panama gateway and the opening of the pedro channel to the north changing the surface conditions in the caribbean sea

ionic and isotopic ratios for identification of salinity sources and missing data in the gaza aquifer abstract groundwater is the only source of fresh water in the gaza strip however it is severely polluted and requires immediate effort to improve its quality and increase its usable quantity intensive exploitation of groundwater in the gaza strip over the past 40 years has disturbed the natural equilibrium between fresh and saline water and has resulted in increased salinity in most areas salinization in the coastal aquifer may be caused by a single process or a combination of different processes including seawater intrusion upconing of brines from the deeper parts of the aquifer flow of saline water from the adjacent eocene aquifer return flow from irrigation water and leakage of wastewater each of these sources is characterized by a distinguishable chemistry and well known isotopic ratios in this paper na cl so4 cl br cl ca hco3 so4 and mg ca ionic ratios were used to distinguish different salinization sources 11b and 87sr 86sr isotopic composition were also included in the model to study their importance in this monitoring task the task of monitoring and the associated decision making process are characterized by a high degree of uncertainty with respect to input data and accuracy of models for this reason probabilistic expert systems and more specifically bayesian belief networks bbns are used to identify salinization origins the bbn model incorporates the theoretical background of salinity sources area specific monitoring data that are characteristically incomplete in their coverage expert judgment and common sense reasoning to produce a geographic distribution for the most probable sources of salinization the model is also designed to show areas where additional data on chemical and isotopic parameters are needed

pliocene pleistocene planktonic foraminifera from the east pacific ocean off costa rica and their paleoceanographic implications abstract planktonic foraminifera from the ocean drilling program holes 1039b 1040c and 1043a off costa rica in the east pacific ocean indicate that the surface seawater temperature abruptly declined four times during the late pliocene early pleistocene these events occurred in the lower part of zone n19 5 4 2 ma the basal part of zone n22 ca 2 ma the middle part of zone n22 ca 1 5 ma and the basal part of zone n23 ca 0 65 ma the maximum divergence of surface and intermediate water dwellers begins at the basal part of zone n22 ca 2 ma which signals cooling episodes and faunal changes suggesting responses to the closing of the central american seaway

comments on shoreface sand supply and mid to late holocene aeolian dune formation on the storm dominated macrotidal coast of the southern north sea by e j anthony m mrani alaoui and a hequette marine geology 276 2010 100 104 abstract anthony et al 2010 published a recent paper in marine geology on the origin and chronology of an inland dune for which they presented an explanation for the regional pattern of mid to late holocene coastal development this explanation contradicts other data collected from this coastal area it is moreover in contrast to our current understanding of holocene coastal evolution of the southern north sea the data used by anthony et al 2010 includes a number of inconsistencies that led the authors to incorrect conclusions this discussion reports on our critical evaluation of data and reasoning in antony et al 2010 we propose an alternative model of coastal evolution which is in line with the current knowledge about mid to late holocene coastal evolution

holocene evolution of the coast of holland abstract the holocene evolution of the coast of holland was controlled by the complex interaction of such diverse parameters as wave and tidal climate the rate of sea level rise and the morphology of the pre transgressional surface the latter in combination with the rate of sea level rise mainly determines the location of sediments sources and sinks while the hydrodynamic parameters mainly determine the rate and direction of sediment transport in the early holocene the low sea level in the shallow southern north sea strongly affected wave climate and tidal regime however the barrier and back barrier sedimentary record since 5000 14c yrs b p gives us no reason to assume major changes in these parameters since then so we conclude that breaks in barrier development are due to variations in rate of sea level rise inl combination with the morphology of the pre transgressional surface the transformation from an open tide dominated to a closed wave dominated coast which occurred in the subboreal period and the concomitant change in barrier movement from transgressive to regressive around 5000 yrs b p are the main events in the development of the coast of holland up to the middle ages the morphology of the pre transgressional surface gives a shoreline in the late atlantic which consists of two protruding headlands separated by a large tidal basin the southern headland is the alluvial plain of the rhine and the meuse the northern headland constitutes the moraines of the texel high the tidal basin in between is connected to the north sea by a large number of inlets the rate of sea level rise at that time 1 m century outran the supply of sediment to the tidal basin after 6000 yrs b p the rate of sea level rise decreased gradually whereas the rate of sediment supply remained constant this led to a gradual decrease in the tidal prisms of the inlets as the tidal basin was filled in with sediment shortly before 5000 yrs b p the first channels silted up and closed the last tidal channel disappeared around 3300 yrs b p leaving two inlets along the coast which were both connected to the river rhine the closure of the first inlets occurred at the same time as the barrier began prograding because 1 the rate of sea level rise diminished considerably 2 not all the sand supplied by longshore and cross shore transport disappeared into the tidal basin but instead could be used for barrier progradation and 3 ebb tidal deltas of the closed inlets provided major sand sources the prograding barrier sequence enclosed between the two headlands roughly forms a closed system using the relationships between tidal prism cross sectional area of inlets and volume of the ebb tidal delta and the results of modelling of longshore transport along the subboreal coast under present day wave conditions a simple sand budget for the coast of holland is given which shows that a large part of the sand now stored in the barrier sequence was obtained by cross shore transport from the north sea

effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation the late cenozoic closure of the seaway between the north andsouth american continents is thought to have caused extensive changes in ocean circulation and northern hemisphere climate1 2 but the timing and consequences of the emergence of the isthmus of panama which closed the seaway remain controversial1 2 3 4 5 here we present stable isotope and carbonate sand fraction records from caribbean sediments which when compared to atlantic and pacific palaeoceanographic records indicate that the closure caused a marked reorganization of ocean circulation starting 4 6 million years ago shallowing of the seaway intensified the gulf stream and introduced warm and saline water masses to high northern latitudes these changes strengthened deep water formation in the labrador sea over the next million years as indicated by an increased deep water ventilation and carbonate preservation in the caribbean sea and favoured early pliocene warming of the northern hemisphere the evaporative cooling of surface waters during north atlantic deep water formation would have introduced moisture to the northern hemisphere although the pronounced intensification of northern hemisphere glaciation between 3 1 and 2 5 million years ago substantially lagged the full development of north atlantic deep water formation we propose that the increased atmospheric moisture content was a necessary precondition for ice sheet growth which was then triggered by the incremental changes in the earth s orbital obliquity

trace element geochemical evolution and groundwater origin in north rukuru songwe alluvial aquifer of northern malawi this study used multivariate analysis and geochemical modeling to appreciate the trace element evolution in north rukuru songwe alluvial aquifer of northern malawi from the isotopic studies the 2h 18o ratios revealed that groundwater is of meteoric origin through vertical recharge and mixing processes the isotopic depletion along the west east transect is due to mixing and fractionation processes generally the d excess value approximated the y intercept of global meteoric water line of 10 which ruled out the influence of secondary evaporative processes on isotopic variation hierarchical cluster analysis identified four distinct clusters c1 c2 c3 and c4 in the study area among these four clusters it was observed that c1 had relatively high median concentrations of fe 716 7 g l cr 0 85 g l pb 7 90 g l and sb 3 80 g l while c2 was characterized by high levels of cu 3 20 g l cluster 3 was comparably defined by high median levels of f 1 00 mg l and mn 338 g l while c4 revealed high median concentrations of as 8 70 g l ba 635 g l li 22 2 g l ni 2 80 g l se 6 20 g l and sr 677 g l clusters c1 and c4 described a flow path along the north rukuru river which is characterized by higher levels of evaporites as shown by higher concentrations of na k cl and so4 it was also observed that this path was defined by high levels of hco3 and total hardness the principal component analysis suggests that carbonate dissolution and silicate weathering are the main mineralization control mechanisms furthermore it is revealed that samples in the west had higher factor scores for as ba li ni se and sr with higher tds while the eastern is characteristic of higher heavy metals fe and pb geochemical modeling using phreeqc showed that surface complexation reactions significantly impact trace elements of higher redox state in addition inverse modeling confirms the significance of carbonate dissolution silicate weathering and cation exchange processes along the north rukuru river flow path

benthic foraminiferal response to the emergence of the isthmus of panama and coincident paleoceanographic changes abstract late cenozoic benthic foraminiferal faunas from the caribbean deep sea drilling project dsdp site 502 3052 m and east pacific dsdp site 503 3572 m were analyzed to interpret bottom water masses and paleoceanographic changes occurring as the isthmus of panama emerged major changes during the past 7 myr occur at 6 7 6 2 3 4 2 0 and 1 1 ma in the caribbean and 6 7 6 4 4 0 3 2 2 1 1 4 and 0 7 ma in the pacific prior to 6 7 ma benthic foraminiferal faunas at both sites indicate the presence of antarctic bottom water aabw after 6 7 ma benthic foraminiferal faunas indicate a shift to warmer water masses north atlantic deep water nadw in the caribbean and pacific deep water pdw in the pacific flow of nadw may have continued across the rising sill between the caribbean and pacific until 5 6 ma when the pacific benthic foraminiferal faunas suggest a decrease in bottom water temperatures after 5 6 ma deep water to intermediate water flow across the sill appears to have stopped as the bottom water masses on either side of the sill diverge the second change recorded by benthic foraminiferal faunas occurs at 3 4 ma in the caribbean and 4 0 3 2 ma in the pacific at this time the caribbean is flooded with cold aabw which is either gradually warmed or is replaced by glacial bottom water gbw at 2 0 ma and by nadw at 1 1 ma these changes are related to global climatic events and to the depth of the sill between the caribbean and atlantic rather than the rising isthmus of panama benthic foraminiferal faunas at east pacific site 503 indicate a gradual change from cold pdw to warmer pdw between 4 0 and 3 2 ma the pdw is replaced by the warmer poorly oxygenated piw at 2 1 ma although the pdw affects the faunas during colder intervals between 1 4 and 0 7 ma the piw remains the principal bottom water mass in the guatemala basin of the east pacific

influence of the amazon river development and constriction of the central american seaway on middle late miocene oceanic conditions at the ceara rise abstract sediment samples from odp 154 site 926a ceara rise western equatorial atlantic ocean spanning the neogene from 12 8 to 9 2 ma were investigated on their calcareous dinoflagellate contents to better understand the oceanographic changes in relation to the closure of the central american seaway and the development of the amazon river intervals with increased cyst accumulation rates and dissolution sensitive species occur from 12 4 ma onward they correspond to periods of enhanced north atlantic deep water production indicating the presence of this water mass at the research site during these intervals this suggests that pulses of north atlantic deep waters sporadically flew into the south atlantic related to uplift phases of the panama sill at about 11 2 ma the first appearance of leonella granifera indicates river influence at the sample site this first indication of river influence in the western equatorial atlantic can be linked to the developing amazon river the cyst association changes at about 11 2 ma from almost monospecific to highly diverse and the permanent presence and increased abundance of l granifera suggest that river waters were able to reach the study site by now probably as a result of the southward flowing north brazil current after 10 5 ma the cyst association indicates a decrease in amazon influence at site 926a this change can be correlated to a reducing inflow of pacific waters through the central american seaway leading to a reverse of the north brazil current to its modern northwards flow pattern

interpretation of radiocarbon dates from the upper surface of late holocene peat layers in coastal lowlands marine brackish clastic sediments replace freshwater peats in the stratigraphic column of many coastal lowland areas bordering the north sea during the late holocene radiocarbon dates are routinely used to provide a chronology for this shift we examine the assumptions underpinning this approach the results of investigations from 13 sites in the rye area of romney marsh southeast england are reported dates from apparently gradational contacts of a highly humified laterally persistent peat layer range from 3170 2840 cal yr bp to 1290 1050 cal yr bp multiple inundations or prolonged gradual inundation are nevertheless rejected as discrete post peat bodies of sediment are absent and because peat growth appears to have slowed down or ceased at many sites in advance of inundation additionally in the rye area sharp contacts are widespread and the pollen assemblages rarely indicate the occurrence of transitional plant communities a review of the dating evidence from other coastal lowland regions reveals that multiple dating of the upper surface of peat beds invariably produces diachronous results as a consequence time transgressive processes feature prominently as causal mechanisms underlying this shift however many of the dating difficulties recognized in the rye area appear to apply to other regions we conclude that radiocarbon dates from the upper surface of peat layers should in most instances only be regarded as limiting ages for the deposition of the overlying clastic sediments new chronologies need to be built without a priori assumptions as to the underlying processes ideally through the direct dating of the clastic sediments

a plate kinematic framework for models of caribbean evolution abstract we define the former relative positions and motions of the plates whose motions have controlled the geological evolution of the caribbean region newly determined poles of rotation defining the approximate spreading histories of the central north and the south atlantic oceans are given for the late jurassic early cretaceous anomaly sequence of the central north atlantic we have used previously published definitions of fracture zone traces and magnetic anomaly picks redetermining the pole positions and angular rotations for various isochrons on an evans and sutherland interactive graphics system for magnetic anomalies younger than the cretaceous quiet period in both oceans we 1 used seasat altimeter data to help define fracture zone traces and 2 identified and used marine magnetic anomalies to determine the positions of spreading isochrons along the flowlines indicated by the fracture zones by the finite difference method the relative paleopositions and the relative motion history between north and south america were computed this analysis defines the size and shape and the rate at which the size and shape changed of the interplate region between north and south america since the middle jurassic thus a plate kinematic framework is provided for the larger plates pertaining to the caribbean region in which can be derived more detailed scenarios for gulf of mexico and caribbean evolution north and south america diverged to approximately their present relative positions from late triassic to early campanian about 84 m y ago time this is the period during which the gulf of mexico and a proto caribbean seaway were formed since the campanian only minor relative motion has occurred from early campanian through to middle eocene times south america diverged only another 200 km and since the middle eocene minor n s convergence has occurred these very minor post early campanian motions have probably been accommodated by imperfect shear and compression along the atlantic fracture zones to the east of the lesser antilles and along the northern and southern borders of the caribbean plate accordingly it is suggested that from campanian time to the present the relative motions between the north and south american plates have had only minor effects on the structural development of the caribbean region primarily using the data of engebretson et al the convergence history of pacific plates with north america was calculated for two points near the western caribbean by completing finite difference solutions the convergence history of the pacific plates with the caribbean and south american plates can be approximated the direction and rate of convergence of the pacific plates with the americas may have controlled the style of subduction and possible microplate migration along the north american south american and western caribbean boundaries that define the eastern pacific plate margin