the use of multivariate statistics to elucidate patterns of floodplain sedimentation at different spatial scales floodplains are depositional features of riverine landscapes that display complex sedimentation patterns that are amenable to multi scale approaches we examined sedimentation in the lower balonne floodplain queensland australia at three different spatial scales the channel 103 km floodplain process zone 10 km and geomorphic unit 102 m scales and compared scale related patterns evident from stratigraphy with those evident from quantitative multivariate analysis three stratigraphic sequences were found in the lower balonne floodplain generally fining upward episodic fining upward and mud dominated stratigraphical analysis revealed the detailed character of sedimentary sequences embedded within the scale patterns derived from multivariate analysis multivariate statistical analyses of a range of textural and geochemical data revealed different patterns of floodplain sedimentation at each scale at the channel scale sediment texture and geochemistry were more heterogeneous in the culgoa river than in briarie creek at the floodplain process zone scale clear patterns of sediment texture and geochemistry were observed along the upper mid and lower floodplain process zones of briarie creek but not along the culgoa river at the geomorphic unit scale clear patterns of sediment texture and geochemistry were observed among the bank buried channel and flat floodplain units of the culgoa river but were not as clear in briarie creek recognition of rivers as hierarchically organized systems is an emerging paradigm in river science our study supports this paradigm by demonstrating that different sedimentation patterns occur at different scales to reveal a hierarchically organized floodplain environment copyright 2006 john wiley sons ltd

island forming processes in the okavango delta botswana article i nfo the okavango delta in botswana is a large 40 000 km 2 alluvial fan that is characterised by the presence of numerous tree covered islands thought to originate from the mound building activities of termites or through fluvial processes associated with development of scroll bars and inverted channels islands have been shown to play an important role in the structure and functioning of the delta through the creation of habitat diversity focusing of nutrients and disposal of toxic salts this study investigates the processes responsible for the maintenance and growth of two such islands in the seasonal swamps transpiration by vegetation is shown to result in substantial increases in groundwater salinity beneath the islands contributing to their growth through chemical precipitation detailed chemical analyses revealed that the precipitation of magnesian calcite and silica within the island soils contributes 30 40 of the total island volume isotopic analyses of carbonate samples show that vegetation plays an important role in providing carbon for carbonate precipitation variations in 13 c carbonate values appear to reflect the relative proportion of c3 to c4 plants on the island with c4 species becoming more dominant toward island centres in response to increases in ground water salinity the study suggests that continued island growth is also related to the deposition of aerosols and the accumulation of dust preferentially on islands and possibly to ongoing termite activity tall trees that cha racterise the island margins trap dust carried from the floodplains resulting particularly in the lateral growth of islands islands in the okavango are considered to be the product of long term aggradation processes with the two islands studied estimated to be in the order of tens of thousands of years old

coal creek serpentinite llano uplift texas a fragment of an incomplete precambrian ophiolite the precambrian coal creek serpentinite llano uplift texas occurs within the upper part of the packsaddle schist which appears to represent a thick sequence of shelf edge volcaniclastic arc flank metasediments the serpentinite has a foliation defined by lizardite pseudomorphs after original foliated harzburgite tectonite which deviates as much as 15 from the regional country rock foliation a few samples contain the relict assemblage olivine orthopyroxene anthophyllite reflecting re equilibration to regional metamorphic conditions near 710 c at 3 5 kb oxygen and deuterium isotopic data indicate the lizardite could have formed in equilibrium with magmatic water at about 300 to 400 c during regional uplift a likely petrogenetic model involves the olistostromal emplacement of a fragment of ophiolitic material the coal creek ultramafic body into the volcaniclastic arc flank sediments the island arc model suggested for the llano uplift and the existence of ophiolitic material imply that brittle plate collisions were locally important 1 200 m y ago and that the orogenic event that affected the llano terrane that is the grenvillian orogeny involved island arc continent interactions the llano uplift contains the only exposed ophiolitic material along the entire grenvillian orogenic belt

modeling the effect of wave current interaction on the three dimensional wind driven circulation of the eastern irish sea abstract a high resolution 0 5 north south by 1 0 west east three dimensional hydrodynamic model of the eastern irish sea is used to examine the influence of enhanced bed friction due to wind wave effects upon the three dimensional wind induced circulation of the eastern irish sea the model uses a mixed finite difference modal approach in which a standard finite difference grid is employed in the horizontal with the galerkin method with an expansion of functions modes in the vertical giving a continuous current profile from sea surface to seabed vertical eddy viscosity within the model is a function of the flow field the model is used to examine the wind induced response of the area to spatially uniform and constant in time northerly and westerly wind stresses of 1 n m 2 the effect upon bed stresses and hence the three dimensional circulation of the region of enhanced bed turbulence due to wind wave effects is also considered using idealized wave fields changes in bed stress particularl

the micro topography of the wetlands of the okavango delta botswana the surface of the 40 000 km2 okavango alluvial fan is remarkably smooth and almost everywhere lies within two to three metres of a perfectly smooth theoretical surface deviations from this perfect surface give rise to islands in the okavango wetlands this micro topography was mapped by assigning empirical elevations to remotely sensed vegetation community classes based on the observation that vegetation is very sensitive to small local differences in elevation even though empirical the method produces fairly accurate results the technique allows estimation of depths of inundation and therefore will be applicable even when high resolution radar altimetry becomes available the micro topography has arisen as a result of clastic sedimentation in distributary channels which produces local relief of less than two metres and more importantly as a result of chemical precipitation in island soils which produces similar local relief the micro topography is therefore an expression of the non random sedimentation taking place on the fan volume calculations of islands extracted from the micro topography combined with estimates of current sediment in ux suggest that the land surface of the wetland may only be a few tens of thousands of years old constant switching of water distribution driven by local aggradation has distributed sediment widely mass balance calculations suggest that over a period of c 150 000 years all of the fan would at one time or other have been inundated and thus subject to sedimentation coalescing of islands over time results in net aggradation of the fan surface the amount of vertical aggradation on islands and in channels is restricted by the water depth restricted vertical relief in turn maximizes the distribution of water limiting its average depth aggradation in the permanent swamps occurs predominantly by clastic sedimentation rates of aggradation here are very similar to those in the seasonal swamps maintaining the overall gradient possibly because of the operation of a feedback loop between the two the limited amount of local aggradation arising from both clastic and chemical sedimentation combined with constant changes in water distribution has resulted in a near perfect conical surface over the fan in addition to providing information on sedimentary processes the micro topography has several useful hydrological applications copyright 2004 john wiley sons ltd

diagenesis in okavango fan and adjacent dune deposits with implications for the record of palaeo environmental change in makgadikgadi okavango zambezi basin northern botswana abstract this work considers the spatial distribution and ages of western moz basin siliclastic sediments prior to providing insights into the diagenesis of degraded dune and alluvial fan sands previously published and new tl osl ages imply that extensive over washing of dune sands took place at least 100 ka ago while ages on okavango floodplains imply that the fan was formed ca 40 ka and has since undergone periods of higher and lower flood regimes sediment analyses indicate that both dune and fan sands contain a diagenetic matrix of clay enhanced amorphous silica ceas which bonds weakly formed aggregates the time of formation of diagenetic matrix products is inconclusive but may have been accelerated during or shortly after events dated using osl tl techniques hence earlier dune over washing may have led to greater porewater of an acidic to near neutral nature which in turn promoted smectite formation and silicic acid precipitation 100 000 years ago the relatively abundant ceas matrix in floodplain sands implies more recent semi continuous flood events again of an acidic near neutral nature leading to the formation of smectite in this case the floodplain sediments are dated as having been deposited around 40 and 11 ka when porewater content may have accelerated clay formation and silica dissolution the dual nature of the ceas in the islands reflects a changing environment from smectite dominated flooding events to sepiolite dominated desiccation events flooding may also correspond to tl osl ages over the past 40 000 years which contributed to accelerated ceas formation the sepiolite is associated with a ca rich matrix implying desiccation which may relate to drying events over the 40 000 year period or to riparian tree root pumping and selective salt accumulation this work shows that sedimentation in incipient rifts is complex and rarely explained totally in terms of primary depositional events the implications of different stages of sand diagenesis may be significant in enhancing palaeo environmental interpretations in semi arid fluvial environments

large scale architecture in non marine basins the response to the interplay between accommodation space and sediment supply sedimentary successions of non marine basins can be considered in terms of accommodation space and sedimentary supply changes changes in accommodation space controlling the large scale architecture of non marine basins are different in areas with high and low sedimentary supplies uplift of intrabasinal monoclines and anticlines reduced the available accommodation space resulting in changes in both the geometry of the depositional sequences and the large scale architecture of fluvial mudflat and shallow carbonate lacustrine deposits main drainage fluvial systems record areas with a high sedimentary supply while mudflats and shallow fluctuating lakes represent areas that received less sediment two end members in the large scale architecture of main drainage fluvial system in the almazan basin spain are i ribbon shaped channel fills with low interconnectivity which pass laterally into mudflats dominated by mudstones and evaporites and into palustrine and shallow carbonate lacustrine deposits mainly in the a2 depositional sequence and ii sheet like channel fills with high interconnectivity laterally correlated with stacked calcretes in the marginal mudflats in the upper part of a3 ribbon shaped channel fills formed in areas of high accommodation space and sheet like channel fills formed in areas of reduced accommodation space

40ar39ar thermochronological constraints on the structural evolution of the mesoproterozoic natal metamorphic province se africa abstract ten 40 ar 39 ar age spectra are presented for hornblende grains separated from mylonitized and weakly deformed amphibolites from the mesoproterozoic 1 2 1 0 ga natal metamorphic province nmp since the proposal of the sweat hypothesis the nmp has become a crucial area in which to study grenville aged locally termed namaquan accretion in this part of rodinia gondwana unlike many segments of the world s 1 1 ga belts the nmp is particularly suited to such studies since it is devoid of a high temperature pan african 500 ma overprint in this study we have dated hornblendes from within the earliest d1 ne directed thrust dominated structural domains of the belt the d1 domains are characterized by ne directed recumbent fold and thrust nappes and a pervasive generally s to sw dipping metamorphic foliation with down dip stretching lineations the new data constrain the minimum age of this early event which includes obduction of the northernmost tugela terrane onto the kaapvaal craton to 1135 9 ma in the d1 domains of the mzumbe terrane to the south cooling to below 550 c had only been attained by 1005 ma we also dated amphibolites from the later d2 structural domains which are characterized by sub vertical sinistral mylonite belts with sub horizontal to oblique stretching lineations our data show that d2 oblique shearing commenced at 1050 1035 ma in the mzumbe terrane and only terminated at 980 ma the youngest movements also included reactivation of major d1 structures such as the melville thrust mzumbe margate terrane boundary at 990 ma finally indications of minor pan african resetting was detected during the first 5 of the ar ar spectra from mylonites of the lilani matigulu shear zone tugela mzumbe terrane boundary indicating the polyphase nature of this major structure it has been suggested that the d1 event records the early ne sw directed arc continent collision history of the belt whilst the d2 event represents a continuation of essentially the same convergence vectors after extensive crustal thickening the new data place important time constraints on the major tectonic events in the nmp which appear comparable in many ways to other parts of the global grenvillian orogen

multiphase quaternary highstands at lake ngami kalahari northern botswana large lake basins now almost entirely devoid of water in the kalahari s semi arid environment can be clearly identified from landsat imagery of northern botswana these basins are delineated by a series of beach ridges marking the former shorelines of an inundated area that at its largest extent encompassed 60 000 km 2 in the last 30 yr over 150 radiocarbon ages have been produced from three component basins that make up the palaeo makgadikgadi system consisting of the ngami mababe and makgadikgadi basins thepaucityofwellpreservedorganicmaterialintheregionhasledtothese 14 cagesbeingderivedfrominorganiccarbonates whose open system behaviour and polygenetic origin frequently result in unreliable dates from uncertain contexts and then only within the temporal limits of the radiocarbon method the application of optically stimulated luminescence osl dating to beach ridge sediments from lake ngami shaw p a bateman m d thomas d s g davies f 2003 holocene fluctuations of lake ngami middle kalahari chronology and responses to climatic change quaternary international 111 1 23 35 improved chronological resolution but was limited by the use of hand dug pits the new application of osl to samples derived from deep coringofbeachridgeshasallowedaccesstoamuchlonger threedimensional geomorphicrecordthanpreviouslyavailable seventyfour ages new osl ages from shorelines are presented allowing for the first time the opportunity to unravel the complex history of lake stages in the ngami basin multiple lake highstands are identified in the period 0 3 ka to 140 ka with several causes of these events includingtropicalandlocalclimatesandupstream channelavulsion identified tounravelthefullpaleaoclimatic significance of these events it will be necessary to identify the timing of high stands in the other terminal basins within the okavango system 2007 elsevier b v all rights reserved

collision induced rifting the grenville orogeny and the keweenawan rift of north america abstract we propose that the keweenawan rift formed as a result of convergence related to the synchronous grenville orogeny this proposal is based on 1 1 isotopic ages in the keweenawan rift and the grenville province are similar according to the best u pb and rb sr dates the grenville orogeny existed from 1150 to 1100 ma and keweenawan rifting occurred 1120 1100 ma 2 2 a similar modern orogenic belt and rift relationship in the middle east serves as an actualistic model the red sea gulf of aden rift system has formed as a continuous series of coalesced pull apart basins and is opening parallel to the orogenic front of the zagros and bitlis mountains rifting began in the early miocene while the collision began in the eocene suggesting that rifting is related to the collision 3 3 many other ancient rift collision pairs have a similar age relationship and geometrical configuration based on comparisons of these tectonic regimes we have derived a model whereby these rifts formed as a result of strike slip faults forming in either the foreland or the hinterland of orogenic zones

a three dimensional model of diurnal and semidiurnal tides on the european shelf a three dimensional hydrodynamic model of the continental shelf is used to examine the sensitivity of computed diurnal k1 and o1 and semidiurnal m2 s2 and n2 tidal elevations and currents to changes in eddy viscosity profile friction coefficient and water depth the influence of the tide generating potential is also considered the model uses a standard finite difference grid in the horizontal with a functional approach in the vertical thereby giving a continuous tidal current profile from sea surface to seabed the magnitude of the vertical eddy viscosity depends upon the flow field comparisons are made between model computed profiles and harmonic analyses of 278 current time series at a range of locations in varying water depths with particular emphasis on locations where there are current measurements at a number of points in the vertical a detailed examination of these comparisons shows that frictional effects in the near bed region are particularly important in determining near bed shear and that an accurate specification of water depth is critical for tidal current magnitude the spatial distribution of computed current ellipses shows that the semidiurnal currents are strongest in shallow water with the diurnal currents exhibiting an intensification in the shelf edge region the inclusion of the equilibrium tide is particularly important for the correct determination of the magnitude of the k1 tidal current as well as k1 elevations in the north sea the detailed comparisons show that the magnitude of the tidal currents is correctly determined to within 5 cm s 1 at 220 locations with the model accurately to within 2 cm s 1 reproducing the vertical variation the most sensitive test of a three dimensional model of the tidal current at most locations

groundwater dynamics and surface water groundwater interactions in a prograding delta island louisiana usa summary deltas in coastal environments are assumed to function as chemical buffers filtering nutrient rich terrestrial runoff through the island structures and aquatic ecosystems as it travels to the sea but the magnitude of this effect cannot be accurately quantified without understanding the physical relationships between the surface water and groundwater the groundwater hydrology of young prograding delta systems and its relationship to surrounding surface water dynamics are poorly understood this study developed a new conceptual model of the hydrology of a prograding delta island groundwater system the study was based on field data collected at pintail island a 2 km 2 island within the wax lake delta in louisiana hydraulic properties and processes were quantified at multiple depths and locations spanning the island elevation gradient groundwater and surface water levels were monitored a weather station recorded precipitation air and wind conditions the groundwater within pintail island was both spatially and temporally dynamic throughout the study period of 9 september 2013 to 4 february 2014 the aquifer within the distal limbs of the island responded to surface water dynamics as a connected saturated unconfined aquifer would and its groundwater was controlled by the surrounding surface water fluctuations of semi diurnal winds and tides the aquifer within the older higher elevation island apex was a lower permeability system with subaerial fine sediments overlying deeper sandier sediments in contrast to the more bayward zone of the island this more interior zone was controlled by storm recharge low permeability sediments and low head gradients but little affected by diurnal surface water fluctuations groundwater flow was directed outward from the interior of the island apex and the levees toward the delta channels and the central island lagoon but storms and high tides temporarily reversed flow directions at some locations and times likely with significant biogeochemical consequences this empirically based conceptual model of the heterogeneous and dynamic hydrogeology of a young prograding delta island provides an essential foundation for further study of prograding coastal delta island hydrology ecology and nutrient exchange

groundwater in the wetlands of the okavango delta botswana and its contribution to the structure and function of the ecosystem abstract the okavango delta of northern botswana is a large 40 000 km2 alluvial fan located at the terminus of the okavango river the river discharges about 10 km3 of water onto the fan each year augmented by about 6 km3 of rainfall which sustains about 2500 km2 of permanent wetland and up to 8000 km2 of seasonal wetland interaction between this surface water and the groundwater strongly influences the structure and function of the wetland ecosystem the climate is semi arid and only 2 of the water leaves as surface flow and probably very little as groundwater flow the bulk of the water is lost to the atmosphere the okavango river also delivers about 170 000 tonnes of bedload sediment and about 360 000 tonnes of solutes to the delta each year most of which are deposited on the fan bedload is deposited in the proximal permanent wetland whilst much of the solute load is deposited in the seasonal wetland notwithstanding the high evapotranspirational loss saline surface water is rare between 80 and 90 of the seasonal flood water infiltrates the ground recharging the groundwater beneath the flood plains and the many islands on the flood plains the remainder is lost by evaporation this groundwater reservoir is transpired into the atmosphere by both aquatic vegetation on the flood plains and terrestrial vegetation on the islands and the water table is steadily lowered following passage of the seasonal flood trees which are almost exclusively confined to islands are particularly important as they lower the water table beneath islands relative to the surrounding wetlands there is therefore a net flow of groundwater towards islands accumulation of dissolved salts in this groundwater leads to precipitation of solutes mainly of silica and calcite in the soils beneath island fringes and the islands grow by vertical expansion islands are thus an expression of the chemical sedimentation taking place on the fan sodium bicarbonate accumulates in the groundwater beneath island centres and this impacts on the vegetation leading ultimately to barren island interiors dense saline brine thus produced subsides under density driven flow this cycling of seasonal flood water through the groundwater reservoir thus plays a key role in creating and maintaining the biological and habitat diversity of the wetland and inhibits the formation of saline surface water

mesoproterozoic chronostratigraphy of the southeastern llano uplift central texas the llano uplift of central texas exposes mesoproterozoic crystalline rocks affected by a grenvillian orogeny between 1 2 and 1 1 ga we report four new u pb zircon protolith ages of 1247 4 1257 3 1272 8 5 and 1366 3 ma for four quartzofeldspathic rocks from the regionally defined packsaddle schist and valley spring gneiss in the southeastern part of the uplift the 1366 3 ma gneiss also yields a metamorphic age of 1325 5 ma these new u pb ages in conjunction with previous u pb age data demonstrate that several regionally defined map units contain constituents with widely disparate ages we have identified four age suites for protoliths of metamorphic rocks in the southeastern part of the llano uplift that appear to represent rock packages of distinct tectonic origins 1 the northern 1366 1272 ma felsic gneisses of volcanic plutonic and continentally derived sedimentary origin valley spring gneiss and an older gneiss component 2 the geographically intermediate ca 1257 1247 ma and possibly older basinal sequence that formed along a continental shelf and slope near an arc packsaddle schist 3 the southern 1326 1275 ma remnant of an exotic ensimatic arc complex big branch gneiss and coal creek serpentinite and plutonic complex and 4 the 1239 1232 ma tectonized felsic rocks that intruded the first two suites the first three suites of rocks were structurally imbricated during grenville orogenesis and the fourth suite may either represent early synorogenic crustal melts or be related to the volcanic rocks in the packsaddle schist in addition these new data show that contrary to previous reports younger packsaddle schist lies in structural contact above older components of the valley spring gneiss moreover one of the dated meta igneous units is the oldest unit yet found in the uplift and records an early period of metamorphism prior to formation of most llano uplift rocks its 1366 3 ma protolith age is coeval with rocks of the western granite rhyolite terrane age and geochemical similarities link this unit of unknown regional extent with the western granite rhyolite terrane of known laurentian affinity thus this component of the llano uplift may be the basement on which the younger components of the valley spring gneiss and packsaddle schist formed in a tectonic setting proximal to laurentia and south of the western granite rhyolite terrane

a coupled atmosphere wave ocean modeling system simulation of the intensity of an idealized tropical cyclone abstract a coupled atmosphere wave ocean modeling system cawoms based on the integration of atmosphere wave atmosphere ocean and wave current interaction processes is developed the component models consist of the weather research and forecasting wrf model the simulating waves nearshore swan model and the princeton ocean model pom the coupling between the model components is implemented by using the model coupling toolkit the cawoms takes into account various wave related effects including wave state and sea spray affected sea surface roughness sea spray heat fluxes and dissipative heating in atmosphere wave coupling it also considers oceanic effects such as the feedback of sea surface temperature sst cooling and the impact of sea surface current on wind stress in atmosphere ocean coupling in addition wave current interactions including radiation stress and wave induced bottom stress are also taken into account the cawoms is applied to the simulation of an idealized tropical cyclo

metabasalts and metagabbros from the llano uplift texas petrologic and geochemical characterization with emphasis on tectonic setting the 1 0 1 2 b y old rocks of the southeastern llano uplift texas include a 7 km thick sequence of amphibolite grade stratified mafic metasedimentary rock packsaddle schist which is intruded by a varied suite of syntectonic and late kinematic intrusions the metasediments contain large blocks of serpentinized peridotite coal creek serpentinite and coarse hornblendite and metagabbro prior to the end of maximum deformation the sequence was intruded by low to medium k2o tholeiitic basalts 0 40 0 72 k2o late kinematic low k2o tholeiitic basalts 0 38 0 40 k2o were intruded as dikes into the folded rocks the coal creek serpentinite contains both syntectonic and late kinematic low k2o tholeiitic metabasalts 0 13 0 36 k2o the llano metabasalts and metagabbros are characterized by low cr 67 378 ppm and ni 36 170 ppm variable rb 1 5 14 7 ppm sr 140 1229 ppm tio2 0 40 2 20 p 568 2707 ppm and zr 18 230 ppm and y 16 45 ppm co 40 57 ppm and sc 36 49 ppm similar to modern morb the metabasalts have la abundances from 7 to 39 times chondritic and exhibit light ree enrichment with la sm n from 1 13 to 1 45 and la yb n from 1 12 to 2 99 the metabasalts show a strong correlation of increasing zr ti and y and decreasing eu eu 1 56 1 00 cao tio2 al2o3 tio2 and mgo mgo feo with increasing ree enrichment lan the llano metabasalts and metagabbros have initial 87sr 86sr 0 7029 0 0001 a likely petrogenetic model for these metabasalts is an island arc in which events from early arc development to final late kinematic intrusion were dominated by tholeiitic volcanism and intrusion the chemical systematics of the llano mafic metaigneous rocks suggest they are products of fractionation of olivine clinopyroxene and plagioclase from more primitive basaltic magmas generated beneath the island arc complex

characterization and tectonic evolution of a mesoproterozoic island arc in the southern grenville orogen llano uplift central texas abstract integrated field and u pb geochronologic data document the presence and tectonic evolution of a distinct lithotectonic terrane in the southeastern llano uplift here termed the coal creek domain ccd the ccd consists of tonalitic and amphibolitic gneisses foliated gabbroic tonalitic and granodioritic intrusions and the structurally emplaced coal creek serpentinite the oldest rocks in the ccd consist of tonalitic gneisses with protolith crystallization ages of 1326 ma and 1301 ma and pre 1292 ma amphibolitic gneisses all ages are u pb zircon they were intruded by dominantly mafic and intermediate with subordinate amounts of felsic low k plutonic rocks between 1286 ma and 1275 ma high temperature metamorphism and local anatexis that resulted in the formation of gneisses and migmatites occurred between 1301 ma and 1286 ma and is suggested to have occurred at 1292 ma metamorphism at 1256 ma resulted in the growth of zircons in mafic rocks the regional significance of this metamorphic event is unclear but it may be related to dynamothermal metamorphism of the ccd the contemporaneous emplacement of low k gabbro tonalite and granodiorite and their spatial association with serpentinite combined with published geochemical data strongly suggest that the ccd represents an ensimatic arc the coal creek serpentinite is interpreted as a fragment of oceanic crust that formed either basement to the arc or in a related back arc or intra arc setting combined field u pb geochronologic isotopic and geochemical data indicate that the magmatic metamorphic and structural history of the ccd differs from that of coeval rocks elsewhere in the llano uplift the boundary between the ccd and deformed and metamorphosed granitic and supracrustal rocks to the north is a zone of intense mylonitization and polyphase deformation this zone is interpreted as the structural boundary between the arc terrane and units to the north

geomorphic controls and transition zones in the lower sabine river instream flow science and management requires identification of characteristic hydrological ecological and geomorphological attributes of stream reaches this study approaches this problem by identifying geomorphic transition zones along the lower sabine river texas and louisiana boundaries were delineated along the lower sabine river valley based on surficial geology valley width valley confinement network characteristics divergent versus convergent sinuousity slope paleomeanders and point bars the coincidence of multiple boundaries reveals five key transition zones separating six reaches of distinct hydrological and geomorphological characteristics geologic controls and gross valley morphology play a major role as geomorphic controls as does an upstream to downstream gradient in the importance of pulsed dam releases and a down to upstream gradient in coastal backwater effects geomorphic history both in the sense of the legacy of quaternary sea level changes and the effects of specific events such as avulsions and captures are also critical the transition zones delineate reaches with distinct hydrological characteristics in terms of the relative importance of dam releases and coastal backwater effects single versus multi channel flow patterns frequency of overbank flow and channel floodplain connectivity the transitional areas also represent sensitive zones which can be expected to be bellwethers in terms of responses to future environmental changes copyright 2007 john wiley sons ltd

miogeoclines and suspect terranes of the caledonian appalachian orogen tectonic patterns in the north atlantic region the caledonian appalachian orogen was formed by the closing of a paleozoic iapetus ocean the continental margins of iapetus are identified in the deformed early paleozoic miogeoclines of the caledonian appalachian orogen ophiolitic vestiges of iapetus its oceanic plateaus microcontinents and volcanic arcs are caledonian appalachian suspect terranes these were assembled in interior parts of the orogen and locally they were emplaced structurally upon the adjacent miogeoclines the modern north atlantic ocean opened along an axis that traversed the paleozoic orogen longitudinally its opening dispersed the elements of the paleozoic orogen and led to the present arrangement of disjunct paleozoic miogeoclines and suspect terranes throughout the north atlantic borderlands the western or north american margin of iapetus is represented by the miogeoclines along the west flank of the north american appalachians and caledonides of east greenland a small north american miogeoclinal segment occurs in the britis

growth of granite greenstone terranes at convergent margins and stabilization of archean cratons abstract archean granite greenstone terranes represent juvenile continental crust formed in a variety of plate tectonic settings and metamorphosed through a complex series of structural and magmatic events most archean granite greenstone terranes appear to have acquired their first order structural and metamorphic characteristics at convergent plate margins where large accretionary wedges similar in aspect to the chugach makran and altaids grew through offscraping and accretion of oceanic plateaux oceanic crustal fragments juvenile island arcs rifted continental margins and pelagic and terrigenous sediments buoyant slabs of parts of archean oceanic lithosphere may have been underplated beneath these orogens forming thick crustal roots characterized by interleaving between the depleted slabs and undepleted asthenosphere back stepping of the subduction zones after accretion of plateaux and arcs caused the arcs magmatic fronts to migrate trenchward through the accretionary wedges dehydration of the subducting slabs hydrated the mantle wedges below the new arcs and generated magmas sanukitoid suite in the mantle wedge whereas other magmas tonalite trondhjemite granodiorite or ttg suite appear to have been generated by melting of hot young subducted slabs eventual collision of these juvenile orogens with other continental blocks formed anatectic granites then thickened the crust beyond its ability to support its own mass which initiated gravitational collapse and decompressional release of syn to late tectonic granitoids from wedges of fertile mantle trapped between underplated oceanic lithospheric slabs and aided in the cratonization of the granite greenstone terranes deeply penetrating structural discontinuities such as shear zones and sutures provided pathways for fluids and granitoids to migrate into the mid and upper crust forming ore deposits and plutons most preserved granite greenstone terranes have been tectonically stable since the archean and form the cratonic interiors of many continents

modelling and numerical simulation of turbulence waves and suspended sediments for pre operational use in coastal seas abstract the role of small scale processes in models of coastal seas is reviewed and the respective uses of vertically integrated and vertically resolving models are described although applied with heavily tuned empirical parameters to the holderness coast a vertically integrated model shows the importance of surface waves for predicting suspended particulate matter spm and their distributions in formulating a generic vertically resolving module as kernel the k e turbulence closure has been selected on a uniform vertical grid this model gave reasonably accurate results for a neutrally stratified channel flow forced by an m2 tidal wave elbe estuary as well as on a nonuniform grid highly refined in the high dissipation near bed region for short period 8 s surface waves in a laboratory flume the model was completed with modules accounting for the effect of waves on the turbulent kinetic energy tke influx at the surface and on the apparent roughness at the bottom it was finally coupled with different versions of vertically high resolving spm models in test applications to the english channel and to the sylt romo bight germany denmark the generic model versions performed with sufficient accuracy however in both cases i fine tuning of erosion and deposition terms was necessary thus underlining the need for further experimental research towards an improved data base on erodible sediments and spm ii the parameters of the submodel for the tke injection by surface waves could not be determined consistently and indicate the existence of a further still hidden parameter iii the technical basis for in situ observations of small scale processes in the coastal zone needs further improvements and consolidation

modelling the response of the north channel of the irish sea to idealized time varying winds and boundary forcing abstract a three dimensional high resolution horizontal grid of order 1 km model of the north channel of the irish sea is used to examine the response of the region to wind and open boundary forcing at a number of periods calculations show that with wind forcing at the inertial period currents are produced through the water column although with longer and shorter period forcing the depth of penetration of the wind s momentum is confined to a near surface layer in the case of short period forcing the wind stress and elevation gradient terms are balanced by the acceleration term whereas at longer periods the acceleration term is small and the balance is between rotational and elevation gradient terms and the wind stress the direction of the wind stress which produces a maximum out flowing current in the centre of the north channel depends upon the period of the forcing and the depth below the surface of the out flowing current although calculations show that to first order the motion in the centre of the channel can be described by linear dynamics coupling between the time varying eddy viscosity and wind shear in the surface layer modifies the m 2 tidal current in the surface region in the case of flow produced by open boundary forcing the current is in essence aligned with the orientation of the channel and above the near bed region is dominated by currents at the period of the boundary forcing close to the bed higher frequency harmonics are generated although there is no evidence at any depth of the m 2 harmonic found in the wind driven flow case

the role of airborne dust in the growth of tree islands in the okavango delta botswana the okavango delta situated in the kalahari desert botswana is host to extensive areas of seasonal swamp that are characterised by the presence of numerous tree covered islands islands have been shown to play an important role in the landscape through the creation of habitat diversity focusing of nutrients and sequestration of salts islands are thought to grow through the subsurface precipitation of carbonate and silica although recent work has suggested that other factors may be involved notably airborne dust accumulation in this study we investigate the role of airborne dust in the maintenance and growth of tree islands in the seasonal swamps of the okavango delta chemical and grain size analyses indicate that whilst the channels and floodplains in the okavango are dominated by well sorted kalahari sand that covers the entire region material on the surface of islands is distinctly different island soils are enriched in al2o3 and are characterised by higher proportions of poorly sorted fine grained material that we attribute to the addition of airborne dust large quantities of material that circulate in anticyclonic systems over southern africa represent a potentially significant source of particulate sediment to the okavango whilst peat fires and the desiccation of the surrounding floodplains during the dry season are also considered to be important sources of local dust the data suggest that varying proportions of kalahari sand dust and chemical precipitate give rise to the range of compositions found on and within the islands of the delta dust typically accounts for between 20 and 60 of material found on the surface of islands whilst dust and chemical precipitate dominate the subsurface material islands thus appear to grow through a combination of ongoing surface and subsurface processes that result in considerable heterogeneity in soil composition in both instances vegetation especially trees is the main driving force behind island development not only causing the subsurface accumulation of caco3 and sio2 in island soils but also trapping airborne dust on the surface of islands our study suggests that dust fallout is an equally or possibly even more important contributor to the local topographic irregularities and thus habitat diversity in the okavango delta despite the potential importance of airborne material to the biogeochemistry and development of tree islands in wetland systems our knowledge regarding these processes remains poor

holocene environmental change in the okavango panhandle northwest botswana abstract this paper documents the first holocene palaeoecological record for the okavango delta northwest botswana sedimentological stable carbon isotope and palynological data supported by conventional and ams radiocarbon assays are presented from coring sites at gauxa lagoon and the ncamasere and tamacha valleys along the western margin of the okavango panhandle earliest holocene vegetation patterns are not readily distinguished at the three sites owing to poor pollen preservation conditions a wet phase or period of enhanced okavango flooding is tentatively identified around 9000 bp on the basis of increased accumulation of organic matter within floodplain sediments palynological and sedimentological data combined with stable carbon isotope analyses suggest that relatively dry conditions extended from 7000 to 4000 bp punctuated by a wet phase at around 6000 bp this is interpreted as indicating reduced rainfall over the okavango headwaters in angola conditions from around 4000 bp became progressively wetter initially in response to increased water throughputs via the okavango system wettest conditions occurred from 2300 to 1000 bp due to a combination of increased regional rainfall and raised okavango flood levels conditions approach those of the present day after this time a major shift from grass to sedge dominated vegetation communities apparent at all three sites in the past thousand years is attributed to anthropogenic disturbance these changes are subsequently discussed in light of regional continental and marine palaeoenvironmental records and the implications for the future management of the okavango river considered

channels wetlands and islands in the okavango delta botswana and their relation to hydrological and sedimentological processes the okavango wetland in northern botswana is one of the world s largest inland deltas the delta is a dynamic environment with shifting channel routes causing growth and decay of flanking wetlands

sticky waters in the great barrier reef the great barrier reef is a mosaic of regions of high and low reef density current meter observations upstream from a region of high reef density revealed that the tidal and low frequency currents were steered away from the region during spring tides but not during neap tides a mathematical model suggests that this effect was due to both tidal friction and to the dissipation of energy by eddies behind reefs at spring tides for a high reef density region this results in a longer residence time at spring tides than at neap tides conversely this effect also diminishes connectivity between regions of high and low reef density at spring tides this process may affect the recruitment and dispersion of fish and other larvae in the great barrier reef it may also invalidate the use of satellite altimetry and tidal harmonic analysis for currents in the great barrier reef