response of tide dominated mangrove shorelines in northern australia to anticipated sea level rise the exact response of mangrove shorelines to anticipated sea level rise will depend upon the balance between sedimentation and sea level change within the top end of the northern territory of australia there are extensive relatively unmodified tide dominated mangrove forests where tidal processes redistribute sediment harbours such as darwin harbour and tidal rivers such as the south alligator river with its associated coastal and estuarine plains represent opposite extremes in terms of holocene sedimentary infill and will respond differently to sea level rise in darwin harbour mangrove assemblages can be recognized in geomorphologically defined habitats similar topography within and between creeks implies morphodynamic equilibrium with tidal processes tidal reworking of sediment may maintain an equilibrial profile under gradually rising sea level with resuspension of lower intertidal and subtidal muds and their redeposition within upper intertidal mangrove habitats in contrast the plains along the coast and tidal rivers draining into van diemen gulf developed during the post glacial marine transgression and since sea level stabilized around 6000 years ago coastal plains have prograded these broad plains are presently not extensively influenced by salt water but are often at elevations close to or even below modern high tide levels they may therefore revert to saline conditions particularly rapidly if the sea rises the pattern of change may not be directly analogous to marine incursion experienced in the early holocene because broad plains have been able to prograde during the last 6000 years of relatively stable sea level

some forms of mountain peaks in the canadian rockies controlled by their rock structure abstract different mountain shapes in sedimentary sequences in the canadian rockies were enhanced by glacial erosion and have been modified post glacially by gravity driven slope processes slope modification by both glacial erosion and post glaciation landslides is related to slope geometry and rock structure particularly bedding dip five mountain peak shapes in monoclinal sequences each fall into different ranges of bedding dips 1 castellate and 2 matterhorn mountains occur in sub horizontal beds and their slopes are generally 35 65 and oblique to both bedding and joints 3 cuestas develop in gently to moderately dipping beds dip slopes and steeper normal escarpments form their cataclinal and anaclinal sides respectively with the dihedral angle between them about 90 4 hogbacks in moderately to steeply dipping beds have similar slope angles on both cataclinal and anaclinal slopes cataclinal slopes are either dip slopes or underdip slopes but anaclinal slopes are often steepened escarpments the dihedral angle between the slopes is usually slope gradients on a sample of 34 peaks are closely related to landslides particularly rock slides and rock topples these landslide modes are controlled by bedding dips

sedimentary facies and evolution in the qiantang river incised valley eastern china abstract this paper deals with the sedimentary facies and evolution of the qiantang river qr estuary and the characteristics and formation of the incised valley sequences and the related shallow biogenic gas reservoir on the basis of analysis of over 500 cores the result shows that since the last glaciation the late quaternary formation of the qr estuary area underwent three stages 1 deep cutting stage 2 rapid filling stage and 3 burial stage the fall of global sea level during the last glacial maximum enhanced the fluvial gradient and river cutting resulting in the formation of the large scale qr and taihu incised valleys with the interfluve being exposed to air on both flanks of the incised valley fluvial terraces at the elevations are present near the present qr estuarine mouth corresponding to 60 70 90 100 and 115 125 m burial depths the valleys were filled rapidly with fluvial sediments during the post glacial period with the rise of sea level the river mouth migrated to landward and backwater and retrogressive aggradation was enhanced the qr and taihu incised valleys are associated with an early filling and transgressive channel infilling sequence formation and a late filling and transgressive floodplain estuary formation subsequently the qr valley was buried under estuarine marine and estuarine sand bar sediments from bottom to top the incised valley successions can be grouped into four sedimentary facies river channel floodplain estuary estuary shallow marine and estuary sand bar the thickness of the river channel infilling deposits is controlled mainly by base level rising backwater retrogressive aggradation and neotectonism further localized thickening took place where deeper scour pools were present in the incised valley or fluvial terraces were formed during the fall of elative sea level during the deposition of the floodplain estuary facies the conditions of sea level rise tidal regime sediment supply and accommodation space were suitable for the development of a tidal ridge system the sand lenses associated with this facies may represent a tidal ridge system in the incised valley at the later stage when the estuarine sand bars were formed the sedimentary conditions were no longer favourable resulting in absence of sand ridge deposits biogenic gas is stored in the floodplain estuary sand lenses of the incised valleys the changjiang river provides the major sediment supply for the qr estuary sand bar and the qr carried sediments constitute only a small portion of the deposits

orbital control on carbon cycle and oceanography in the mid cretaceous greenhouse we established a new high resolution carbonate carbon isotope record of the albian interval of the marne a fucoidi formation central apennines italy which was deposited on the southern margin of the western tethys ocean bulk carbonate sampled with 10 15 cm spacing was used for the construction of a continuous carbon isotope curve through the albian stage spectral analyses reveal prominent 400 kyr cyclicity in the 13c curve which correlates with milankovitch long eccentricity changes cycles occurring in our record resemble those observed in several cenozoic 13c records suggesting that a link between orbital forcing and carbon cycling existed also under mid cretaceous greenhouse conditions based on comparisons with cenozoic eccentricity carbon cycle links we hypothesize that 400 kyr cycles in the mid cretaceous were related to a fluctuating monsoonal regime coupled with an unstable oceanic structure which made the oceanic carbon reservoir sensitive to orbital variations in the tethys these oceanographic conditions lasted until the late albian and then were replaced by a more stable circulation mode less sensitive to orbital forcing

the evolution of tidal creek networks mary river northern australia tidal creek networks have in 50 years extended over 30 km inland across the coastal plains of the mary river in northern australia invading freshwater wetlands and destroying the associated vegetation the networks have grown at an exponential rate through a combination of main channel extension and tributary development with concomitant widening of the creeks a large tidal range very small elevational differences over the plains and the availability of preexisting channel lines notably in the form of palaeochannels have been major factors contributing to the rapid rate of expansion close parallels exist between these networks and terrestrial networks as regards modes of growth and planimetric properties a channel is initiated when the diffuse flow of a seepage zone becomes concentrated through localized scour subsequent development is characterized by the rapid extension of long first order channels with most tributary addition occurring later model tests suggest that branching was more likely on exterior links in the early stages but that exterior and interior link branching became more equally likely through time although the headward limits of the main creeks seem to have been reached tributary infilling will continue to progress upstream only in the most downstream parts is a stable drainage density being approached the networks not only satisfy the laws of drainage network composition and the basic postulates of the random model but also depart from topologic randomness in similar ways to terrestrial networks both topologic and length properties have changed during evolution but largely at the link rather than network scale the close correspondence with terrestrial networks may be due to the low relief and the relatively unconstrained nature of growth in which availability of space was the main determining factor

fine sediment and its sources severn estuary and inner bristol channel southwest britain abstract a comparison of the clay mineral assemblages of 22 samples from the estuary with 22 samples from river floodplains strongly suggests that the fine sediment present in the contemporary severn estuary and inner bristol channel come almost exclusively from the river catchments that feed the system the catchments are geologically diverse and the clay minerals particularly expandable clays kaolinite and chlorite seem to come from preferred parts of the drainage area although the estuary is flood dominated and some fine sediment is supplied from seaward the amount appears negligible in comparison with the fluvial supply the sands however seem largely to have an immediate western origin

nd isotopic excursion across cretaceous ocean anoxic event 2 cenomanian turonian in the tropical north atlantic late cretaceous fish debris from demerara rise exhibits a dramatic positive excursion of 8 nd units during ocean anoxic event 2 oae2 that is superimposed on extremely low nd t values 14 to 16 5 observed throughout the rest of the studied interval the oae2 nd excursion is the largest yet documented in marine sediments and the majority of the shift is estimated to have occurred over nd values on demerara rise are explained as the nd isotopic signature of the south american craton whereas eruptions of the caribbean large igneous province or enhanced mixing of intermediate waters in the north atlantic could have caused the excursion

correlation of basinal carbonate cycles to nearshore parasequences in the late cretaceous greenhorn seaway western interior u s a upper cretaceous limestone shale couplets developed within the late transgressive stage of the greenhorn cyclothem may be correlated from carbonate dominated basinal sequences in central kansas and colorado westward to clastic cycles in southern utah six such basinal couplets have been traced to corresponding upward coarsening progradational cycles developed on the western margin of the western interior basin in the central basin in colorado and kansas these sedimentary cycles are represented by limestone shale and marlstone shale couplets 0 5 1 0 m in thickness more calcareous parts of these couplets may be correlated westward into condensed fossiliferous concretion and shell beds in proximal offshore lithofacies of arizona and utah these concretion and shell beds are physically traceable farther landward westward into bioturbated fossil rich transgressive lag deposits that bound 10 to 20 m thick coarsening upward progradational strand plain deposits parasequences in southwestern utah thus the progra dational phase of parasequence deposition correlates with accumulation of clay rich sediment in the central basin and the transgressive phase is characterized by reduced terrigenous input and deposition of carbonate rich sediment we consider milankovitch style orbital forcing of climate and tectonically induced fluctuations in rates of foredeep basin subsidence as possible forcing mechanisms for these basinwide events based on the widespread distribution of the limestone shale couplets as well as on estimated sedimentation rates and geochronology it has been widely speculated that these carbonate cycles reflect milankovitch cycles with periodicities on the order of 20 k y to 100 k y if so then stratigraphic data suggest that orbital forcing of climate affected eustasy and or sediment input and biogenic production in the western interior basin alternatively thrusting events in the sevier orogenic belt may have produced episodic changes in the rates of foredeep basin subsidence and consequent changes in base level which could have controlled the deposition of the greenhorn parasequences and carbonate cycles in either case correlation of these units demonstrates a consistent basinwide sedimentary response to high frequency base level or sediment input changes in the western interior epicontinental basin

reconnaissance of rockslide hazards in kananaskis country alberta kananaskis country is situated in the front ranges of the canadian rockies in southwestern alberta sedimentary rock thrust northeastwards forms mountain ridges that trend northwest southeast parallel to the major thrust faults older palaeozoic rocks mainly limestone and dolomite form the ridges and peaks younger mesozoic rocks sandstones quartzites siltstones shales conglomerates and coals are more easily eroded and form mountain passes and valleys a reconnaissance mapped 228 rockslides 8 km2 of rockslide debris and 96 km2 of talus the largest rockslide exceeds 50 106 m3 rockslides are most probable in the devonian palliser formation then in the permo pennsylvanian rocky mountain group mississippian rundle group devonian fairholme group mississippian banff formation and the younger detrital rocks rockslides are most probable on dip and overdip slopes followed by reverse dip slopes oblique and strike dip slopes and underdip slopes large rock masses have not slid on slopes below the

nutrient trap for late cretaceous organic rich black shales in the tropical north atlantic neodymium isotopes of fish debris from two sites on demerara rise spanning 4 5 m y of deposition from the early cenomanian to just before ocean anoxic event 2 oae2 cenomanian turonian transition suggest a circulation controlled nutrient trap in intermediate waters of the western tropical north atlantic that could explain continuous deposition of organic rich black shales for as many as 15 m y cenomanian early santonian unusually low nd isotopic data e nd t 11 to 16 on demerara rise during the cenomanian are confirmed but the shallower site generally exhibits higher and more variable values a scenario in which southwest flowing tethyan and or north atlantic waters overrode warm saline demerara bottom water explains the isotopic differences between sites and could create a dynamic nutrient trap controlled by circulation patterns in the absence of topographic barriers nutrient trapping in turn would explain the 15 m y deposition of black shales through positive feedbacks between low oxygen and nutrient rich bottom waters efficient phosphate recycling transport of nutrients to the surface high productivity and organic carbon export to the seafloor this nutrient trap and the correlation seen previously between high nd and organic carbon isotopic values during oae2 on demerara rise suggest that physical oceanographic changes could be components of oae2 one of the largest perturbations to the global carbon cycle in the past 150 m y

geomorphic change of saltmarsh tidal creek networks in the dyfi estuary wales abstract planimetric changes of saltmarsh tidal creek networks in the dyfi estuary wales have been mapped from aerial photographs dating from 1966 to 1989 rates of these changes have been evaluated with reference to creek length and creek density creek densities have been increasing during their development ranging from 8 up to 11 km km 2 these changes are mainly attributable to the instability of the main dyfi tidal channel flood and storm surges saltmarsh vegetation development elevational differences of the estuarine intertidal zone and sea level fluctuations dissipation of tide and wave energies associated with storm surges is chiefly responsible for the morphological development of the dyfi tidal creeks the discontinuous stage prism asymmetry hydrodynamic model is applicable to explaining the dyfi estuarine tidal creek development a form process feedback between the vertical growth of the dyfi saltmarsh surface and the hydrodynamics of its network is also important in governing the dyfi tidal creek network development the rapid development of the dyfi tidal creek networks could result in the loss of the dyfi estuarine wetland

postglacial topographic evolution of glaciated valleys a stochastic landscape evolution model the retreat of valley glaciers has a dramatic effect on the stability of glaciated valleys and exerts a prolonged influence on the subsequent fluvial sediment transport regime we have studied the evolution of an idealized glaciated valley during the period following retreat of ice using a numerical model the model incorporates a stochastic process to represent deepseated landsliding non linear diffusion to represent shallow landsliding and an approximation of the bagnold relation to represent fluvial sediment transport it was calibrated using field data from several recent surveys within british columbia canada we present ensemble model results and compare them with results from a deterministic linear diffusion model to show that explicit representation of large landslides is necessary to reproduce the morphology and channel network structure of a typical postglacial valley our model predicts a rapid rate of fluvial sediment transport following deglaciation with a subsequent gradual decline similar to that inferred for holocene time we also describe how changes in the model parameters affect the estimated magnitude and duration of the paraglacial sediment pulse

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

the last eocene hyperthermal chron c19r event 41 5 ma chronological and paleoenvironmental insights from a continental margin cape oyambre n spain abstract the last hyperthermal event in the eocene the late lutetian thermal maximum or chron c19r event took place at 41 5 ma during a long term global cooling phase which occurred between the warm early eocene climatic optimum and the icehouse oligocene epoch this paleoclimatic event was first identified in the equatorial atlantic ocean drilling program odp site 1260 as an abrupt peak in bulk fe content and a short lived decline in stable isotopes 13c 18o and carbonate content additional studies have recently been carried from the southern atlantic odp sites 702 and 1263 however many issues were not addressed at these deep sea sites and no land based record of the event had been studied therefore the beach cliff at cape oyambre n spain was analyzed with the aim of identifying the c19r event and investigating its paleoenvironmental impact using magnetostratigraphic and biostratigraphic information the astronomically tuned cyclo stratigraphic record from oyambre was accurately correlated with odp site 1260 this combined with stable isotope data allowed identification of the event in a conspicuous dark marl bed given that the associated negative carbon isotope excursion extends for 2 3 of a precession driven hemicouplet a 7 11 kyr duration was estimated which agrees with recent estimates from the atlantic deep sea sites exceptional insolation conditions were found to have accelerated the hydrological cycle increasing rainfall and runoff on land and terrestrial sediment input to the sea which resulted in relatively low carbonate content in the deep sea sediments the terrestrial input also caused seawater eutrophication and freshening leading to low 13c and 18o values increased abundance of autochthonous and reworked calcareous nannofossil taxa peaks in the abundance of opportunistic reticulofenestra

isotopic variation in rhythmically bedded chalks paleotemperature variation in the upper cretaceous detailed sampling at 2 cm intervals of a rhythmically bedded chalk marl sequence in southeast england has revealed a cyclic variation in oxygen isotopic composition of the carbonate component these changes are most consistent with paleotemperature fluctuations of up to 4 5 c contrary to some recent models chalk horizons are interpreted to reflect periods of warmer temperature and higher primary productivity than those responsible for marl deposition the effects of different faunal content diagenesis and variations in the water chemistry can all be discounted

tertiary carbonate dissolution cycles on the sierra leone rise eastern equatorial atlantic ocean abstract most of the tertiary section on sierra leone rise off northwest africa consists of chalk marl and limestone that show cyclic alterations of clay rich and clay poor beds about 20 60 cm thick on the basis of biostratigraphic accumulation rates the cycles in oligocene and miocene chalk have periods which average about 44 000 years and those in eocene siliceous limestone have periods of 4000 27 000 years several sections were sampled in detail to further define the cycles in terms of content of caco 3 clay minerals and relative abundances of calcareous nannofossils extending information gained by analyses of pleistocene cores from the continental margin of northwest africa to the tertiary cycles on sierra leone rise both dilution by noncarbonate material and dissolution of caco 3 could have contributed to the observed relative variations in clay and caco 3 however dissolution of caco 3 as the main cause of the carbonate clay cycles on the sierra leone rise rather than dilution by clay is suggested by the large amount of change several thousand percent in terrigenous influx required to produce the observed variations in amount of clay and by the marked increase in abundance of dissolution resistant discoasters relative to more easily dissolved coccoliths in low carbonate parts of cycles the main cause of dissolution of caco 3 was shoaling of the carbonate compensation depth ccd during the early neogene and climatically induced fluctuations in the thickness of antarctic bottom water

recognition of diagenetic contribution to the formation of limestone marl alternations a case study from permian of south china abstract limestone marl alternations lmas have been extensively used in studies of sedimentology cyclostratigraphy and paleoclimatology however it has long been debated whether lmas are derived from primary sedimentation or from diagenetic alteration and the markers to distinguish one source from the other remain ambiguous in this study we investigate widespread permian lmas from various depositional settings in south china using traditional petrographic mineralogical and major element al2o3 vs tio2 methods as well as emerging trace and rare earth element ree analyses performed using solution based and in situ techniques the original depositional differences of the limestone and its coupled marl beds can be identified based on 1 the high volumes of siliciclastic minerals in the marls 2 unremarkable differential compaction 3 the recognizable signatures of the detrital admixture i e the al zr and th characteristics and 4 flattened shale normalized ree patterns diagenetic lmas are characterized by the compaction of fossils rare aragonite skeletons and abundant diagenetic clays sepiolite and talc preserved in the marl beds we also identified fully diagenetic lmas originating from primary carbonate sedimentation based on two almost completely consistent seawater like ree patterns with diagnostic positive la and negative ce anomalies la la sn 1 64 0 17 ce ce sn 0 73 0 05 superchondritic y ho 47 4 and depleted light rees relative to high rees pr yb sn 0 39 0 09 diagenesis also dominates the formation of lmas with limited terrigenous input in shallow water carbonate depositional environments it is likely that both the active metabolic processes in early diagenesis especially aerobic sulfide oxidation and the temporal palaeoceanographic conditions e g high levels of dissolved oxygen and sulfate play crucial roles in the genesis of the diagenetic lmas in the permian strata of south china

untangling the palaeocene climatic rhythm an astronomically calibrated early palaeocene magnetostratigraphy and biostratigraphy at zumaia basque basin northern spain abstract the magnetostratigraphy of a 54 m long section above the cretaceous tertiary boundary at the sea cliff section of zumaia in the basque basin northern spain has been established the section encompasses the entire danian and the lower part of the selandian stages as indicated by calcareous plankton biostratigraphy the studied interval consists of hemi pelagic limestone marl alternations in the form of couplets and bundles which range from centimetre decimetre to metre scale respectively and a few thin bedded calcareous turbidites the magnetostratigraphy based on samples from about 200 stratigraphic levels allows the identification of six reversal boundaries from chron c29r to c26r at a bed level the spatial or temporal evolution of periodicities from a lithologically coded series is studied with the continuous wavelet transform technique a preliminary age model based on the standard ck95 gpts indicates that the basic lithologic carbonate marl couplet corresponds to the 19 23 kyr precession cycle 21 31 cm cycle in the depth domain and that a bundle cycle usually groups of four to six basic couplets with global periodicity centred at 1 22 m corresponds to the 110 kyr eccentricity cycle we have tuned the bundle cycles to the va03 r7 eccentricity orbital solution astrophys j 592 2003 620 630 following an initial match of a node of the 2 4 ma eccentricity modulatory cycle in the target time series to particularly carbonate rich bundles from the upper part of the zumaia section that displays significant power of a 4 4 m period cycle corresponding to the 404 kyr eccentricity cycle consistency between lithologic patterns and characteristics in the eccentricity target is reasonably met although the 404 kyr eccentricity cycle is not persistent throughout the tuning however appears robust as it brings the age of the k t boundary at 65 8 ma it is argued that a sea level signal tectonically driven is superimposed on the climatic forcing at the milankovitch band masking the full expression of the low frequency astronomical periods we provide a cycle tuned duration for all intervening early palaeocene polarity chrons and estimate relative ages for bioevents the cycle tuned chronology indicates that the ck95 gpts overestimates the duration of chrons c28 and c27 by 20 and 26 respectively our data may prove useful to better constrain early palaeocene biostratigraphy of calcareous plankton and in the redefinition of the boundary between the danian and selandian stages

orbital cyclicities above and below the cretaceous paleogene boundary at zumaya n spain agost and relleu se spain abstract the rhythmicity of hemipelagic limestone marl successions covering the cretaceous paleogene k pg boundary is investigated and evidence of orbital control is presented three sections were surveyed and sampled in detail two are located near agost and relleu in the province of alicante and one near zumaya in the basque country the distance between agost and relleu is about 30 km between agost and zumaya about 600 km the carbonate content of 2779 samples was determined and used as a proxy to determine cyclicities lithologically all three successions are very similar although in the maastrichtian of the zumaya succession 63 7 m 339 light green siliciclastic turbidite layers varying in thickness between 0 1 and 12 cm intercalate with the calcisiltites conventional paleomagnetic and micropaleontologic datum planes are few and show the usual associated uncertainties power spectra based on the few reliable datum planes available are unstable more datum planes were created in an unconventional way i e by visual correlation of the local maxima and minima of the carbonate curves to those of the relevant part of the theoretical eccentricity curve the validity of the method is based on the assumption that the eccentricity periods are considered practically stable throughout geologic time the results support the hypothesis that the carbonate rhythmicity at agost relleu and zumaya are orbitally controlled most likely orbital forcing and random processes play a role in the frequency of occurrence and the thickness of turbidites in the maastrichtian of zumaya the age of the k pg boundary is estimated at 64 56 0 4 ma

rock topples in the highway cut west of clairvaux creek jasper alberta the topples exposed in the road cut along highway 16 17 km west of jasper alberta were caused by slope steepening by both glaciation and excavation the toppling of layers that underdip the cut slope was initiated by water pressure ice pressure and loose materials in the cracks of rock masses with large block ratios toppling formed well exposed sliding surfaces on steep slopes and rupture surfaces on shallower slopes key words rock slopes rock cuts rockies toppling sliding underdip slopes

exhaustion and steady state models for predicting landslide hazards in the canadian rocky mountains abstract the temporal distribution of landslides can be evaluated by steady state and exhaustion models the probability of landsliding remains constant through time in the steady state model but the probability decreases in the exhaustion model as more slopes fail rock sliding down bedding surfaces on overdip slopes exhausts hazardous sites to leave stable dipslope landforms in kananaskis country in the canadian rocky mountains the distribution of rock slides in this area can be better explained by the exhaustion model than by the steady state model

the palliser rockslide canadian rocky mountains characterization and modeling of a stepped failure surface abstract this paper presents the results of an investigation of the prehistoric palliser rockslide rocky mountains canada conventional aerial photograph interpretation and field mapping are complemented by terrestrial digital photogrammetry these techniques allow quantification of the rockslide debris volume and reconstruction of the pre slide topography it has been estimated that the volume of rock involved in the most recent large rockslide is 8 mm 3 terrestrial digital photogrammetry is used in the characterization of the failure surface morphology which is subdivided into four types of step path geometry comprising both pre existing discontinuities and intact rock fractures incorporation of these data into various rock slope stability numerical modeling methods highlights a complex failure mechanism which includes sliding along a large scale curved failure surface intact rock bridge fracturing and lateral confinement a preliminary quantification of the contribution of intact rock bridges to the shear strength of the failure surface is presented in terms of the apparent cohesion apparent tensile strength and cumulative length of the intact rock segments

controls on geochemical expression of subaerial exposure in ordovician limestones from the nashville dome tennessee u s a abstract stable isotope and trace element data from 301 samples in six stratigraphic sections largely support previous inferences of subaerial exposure at third order sequence boundaries in mohawkian and cincinnatian limestones of the nashville dome they also reveal the presence of previously unrecognized surfaces of subaerial exposure for example evidence of subaerial exposure at the tops of parasequences suggests that at least some of the latter are better interpreted as high frequency sequences clusters of surfaces of subaerial exposure near some previously interpreted sequence boundaries suggest that the latter may represent sequence boundary zones some surfaces of subaerial exposure are at neither recognized sequence boundaries nor parasequence boundaries and may represent missed beats in which sea level fluctuations are preserved geochemically but not recognized on stratigraphic criteria recognition of these unexpected surfaces of subaerial exposure may in part depend on the close spacing of samples used in this study different sequence boundaries exhibit different degrees of geochemical alteration and more extensive alteration appears to characterize sequence boundaries of greater temporal significance overprinting of exposure surfaces is controlled by accommodation rate in that meteoric alteration as suggested by low c isotope composition and sr concentration is seemingly pervasive in an interval of slow accommodation but not in an interval of rapid accommodation 18o values show little relationship to exposure surfaces in these strata so that sr 13c plots are more useful than 18o 13c plots in recognizing meteoric diagenesis in aggregated data in this data set 13c excursions interpreted to result from pedogenic processes are at most 2 4 and extend at most only 1 5 meters below exposure surfaces less than the extent of such signatures in younger carbonates such minima are best developed in paleo lowland and paleo coastal settings and they are essentially unrecognizable in paleo inland settings where more section was removed by lowstand and transgressive erosion

the shapes of cold high mountains in sedimentary rocks abstract terzaghi geotechnique 12 1962 251 and young young a 1972 slopes oliver and boyd edinburgh 288 pp described the stable forms of slopes in sedimentary rock masses assuming penetrative discontinuities which are parallel to bedding and joints which are perpendicular to bedding the only movements considered were slides along bedding experience in the canadian rockies indicates that the cohesionless rock masses that exist at or above tree line may also move by toppling buckling and sliding along joints these processes also act to limit the inclinations of stable slopes rock strength is a factor in the critical height of a slope that buckles the processes can be represented as fields on a process diagram a plot of slope inclination against bedding dip using the basic friction angles of the rocks present the process diagram also separates five common mountain peak shapes which form on homoclinal sequences of beds castellate and matterhorn mountains occur in sub horizontal beds cuestas develop in gently to moderately dipping beds hogbacks formed in moderately to steeply dipping beds have similar slope angles on both cataclinal and anaclinal slopes dogtooth mountains occur in steeply dipping sub vertical beds

diagenesis by burial fluids middle ordovician platform to platform margin limestones east tennessee relationship to mississippi valley type deposits abstract we compare relative timing and geochemistry of different paragenetic phases in platform margin and platform interior limestones within a nearly 400 m thick succession of middle ordovician strata emphasis is on late stage cements that include ferroan coarse sparry calcite and ferroan baroque dolomite platform interior rocks contain two late cements clear sparry calcite and nonferroan dolomite not observed in platform margin rocks depleted 18o and high iron content of these four calcite and dolomite phases indicate a fluid that had interacted with siliciclastic material late stage diagenetic cements in the platform margin limestones generally have more lower values of 18o higher iron and manganese contents and more radiogenic 87sr than their counterparts from the platform multiple interpretations for the different diagenetic phases and geochemistry are possible we favor a water rock interaction hypothesis because it requires a single source and is therefore the simplest explanation ferroan coarse sparry calcite and ferroan baroque dolomite could have been generated from brines expelled from the sevier basin before the end of the middle ordovician ca 450 ma these fluids could have moved up dip into platform carbonates under pressures induced by burial alone this is based on an analysis of burial curves possible temperatures and an assumed range of likely brine compositions bitumen associated with some ferroan baroque dolomite may be synchronous with mississippi valley type main ore stage sphalerite the timing for fluid migration that we suggest here contrasts with conventional thinking which places the major fluid migration during the alleghenian orogeny 332 250 ma at the end of the late paleozoic

the coniacian santonian sedimentary record in southern tanzania ruvuma basin east africa planktonic foraminiferal evolutionary geochemical and palaeoceanographic patterns a 101 m thick stratigraphically complete late coniacian early santonian ca 89 to 83 ma sedimentary sequence drilled in tanzania tanzania drilling project site 39 allows for the first time examination of the planktonic foraminiferal biostratigraphy and evolution the depositional history and geochemical patterns of the subtropical tropical indian ocean region the sedimentary succession corresponds to an outer shelf to upper slope setting and is dominated by calcareous clayey siltstones and mudstones the occurrences of tethyan marker species enable application of the tropical biozonation including identification of the dicarinella concavata and d asymetrica zones in addition tanzania drilling project site 39 is proposed as reference section for the coniacian santonian boundary in the indian ocean with the boundary placed at the lowest occurrence of globotruncana linneiana in agreement with the gssp stratotype spain the record at tanzania drilling project 39 provides a unique opportunity to document the planktonic foraminiferal evolution in a subtropical marginal sea environment during a key period in their evolutionary history characterized by a major radiation among the deep dwelling taxa combined documentation of lithological and geochemical changes caco3 corg 13ccarb and 18ocarb reveal a setting influenced by continental derived nutrients in the d concavata zone lindi formation with a change to higher carbonate production and reduced surface water primary productivity in the overlying d asymetrica zone nangurukuru formation planktonic foraminiferal assemblage changes mirror the depositional and geochemical trends and indicate a progressive shift from a more eutrophic to a more oligotrophic regime through time at the local scale this palaeoceanographic scenario is consistent with the deepening of coastal tanzania in response to the late cretaceous marine transgression registered in south east tanzania because the tectonic evolution and sea level rise along the east africa continental margin is superimposed on the coniacian campanian global long term sea level high this study hypothesizes that the epicontinental invasion of blue waters may have favoured radiation among deep dwelling taxa this article is protected by copyright all rights reserved

signature of rhine valley sturzstrom dam failures in holocene sediments of lake constance germany abstract landslide dammed lakes that form upstream of large scale rockslide avalanches sturzstroms present an enormous potential hazard to downstream areas such failures are recorded in the early holocene sediments of upper lake constance germany by the presence of two clastic layers that were emplaced around 9400 cal ybp the sedimentology of these layers contrasts sharply with the typical late glacial and holocene lacustrine sediments present beneath the floor of the lake sedimentary structures and the magnetic fabric of these clastic deposits strongly suggest that they were emplaced by hyperpycnal underflows related to catastrophic floods that entered the lake from the rhine river from stratigraphic and geologic data it is inferred that the hyperpycnite deposits are directly related to the failure of two sturzstrom dams and the draining of the dammed lakes that developed upstream from them these lakes were dammed by the flims and the tamins sturzstrom deposits respectively sedimentologic data from lake constance indicate that the two successive events occurred within a very short time interval probably not exceeding several years consequently these lacustrine deposits provide essential information about the morphogenic evolution of the rhine river valley during the early holocene and about the sturzstrom events that occurred during the same time interval

effects of climate tectonics and sea level changes on rhythmic bedding patterns in the niobrara formation upper cretaceous u s western interior regional correlation of interbedded pelagic hemipelagic limestones and calcareous shales of the fort hays limestone member of the niobrara formation confirms development of at least two levels of cyclicity occurrence of time parallel rhythmically deposited beds that can be correlated over distances exceeding 800 km lends strong support to the hypothesis that these cycles were induced by milankovitch type climatic forcing however visual observation and fourier analysis of variations in shale and limestone thickness demonstrate that the pattern of fort hays cyclicity lacks regional uniformity complications in the cyclic pattern may have resulted from the influence of orbital parameters having differing periodicities additionally departures from simple cyclical patterns resulted from sedimentary effects of the sevier orogeny and from erosional events associated with sea level changes documentation of thickness variations within the regionally persistent fort hays bedding sequence furnishes a basis for fine scale analysis of cretaceous crustal movements within the western interior seaway

water mass circulation on demerara rise during the late cretaceous based on nd isotopes abstract circulation in the north atlantic during the late cretaceous has implications for poleward heat transport and nutrient distribution during an extreme greenhouse interval with episodes of ocean anoxia nd isotopes of fossil fish teeth and debris represent one of the few water mass tracers that can be used to reconstruct deep ocean circulation we present nd isotopic data interpreted as bottom water values for 290 samples from three ocean drilling program sites on demerara rise sites 1258 1260 and 1261 along with 102 analyses from four other north atlantic sites cape verde goban spur bermuda rise and blake nose that provide additional geographic and bathymetric control our results confirm the presence of a water mass with low end values 14 to 17 that are believed to be influenced by continental material during local water mass formation at low latitudes this demerara bottom water dbw is the primary water mass in the region from the cenomanian to coniacian and from the late campanian through early maastrichtian following a hiatus of 10 my a positive 8 end unit excursion occurs during ocean anoxic event 2 oae2 that cannot be explained by changes in weathering inputs diagenesis or magmatic sources of nd instead it appears to represent an influx of bottom waters sourced from the tethys or north atlantic this replacement of dbw during oae2 argues for decreased production of dbw or enhanced production of tethys north atlantic waters during peak greenhouse conditions from the late campanian through early maastrichtian dbw becomes the only water mass recorded at demerara rise and it appears to expand to abyssal depths at cape verde in the campanian this water mass is ultimately replaced by waters that appear to be sourced from the north atlantic starting in the late maastrichtian observed variations in circulation in the tropical north atlantic during the late cretaceous can account for extensive deposition of black shales in the region prior to the hiatus as well as local warming during a global cooling event in the maastrichtian

quaternary stratigraphy geochronology and evolution of the magela creek catchment in the monsoon tropics of northern australia abstract magela creek a major tributary of the east alligator river in northern australia has left a detailed sedimentary record of a fluvial landscape dominated by climatic and eustatic changes associated with quaternary glacial interglacial cycles uranium series dates from young pisoliths in floodplain deposits indicate that ferruginisation is probably ongoing under present conditions while ferricretes in degraded terraces that flank the lower valley reveal a fluvial history extending back to early pleistocene or tertiary time inset within this older alluvium is a valley fill which from thermoluminescence dates was initiated about 300 kyr ago with each glacial climate change and associated fall in sea level distinct palaeochannels have been eroded into these floodplains infilling later with alluvium when climate and base level conditions were conducive to fluvial deposition radiocarbon dates show that the most recent palaeochannel beneath the modern magela creek last started to fill by downstream progradation and vertical accretion of bedload sand about 8 kyr the palaeochannel filled at an accelerating rate probably as a result of declining stream competence associated with drier conditions in the late holocene augmented by the backwater effects of sea level rise continued aggradation blocked the mouths of tributary valleys along magela creek forming alluvial dammed tributary lakes and deferred junction tributary streams from about 300 kyr cyclic episodes of channel incision and sediment evacuation in this tropical monsoon river valley have become less effective possibly because increasing aridity in the late quaternary has reduced the erosional effectiveness of australia s northern rivers reduced flow regime and rising sea level in the late holocene has resulted in the latest phase of alluvial accretion

pleistocene macrotidal tide dominated estuary delta succession along the dong nai river southern vietnam abstract this paper focuses on the facies and sequence stratigraphic interpretation of a tide dominated incised valley system that is rare among geological records of the world for its completeness the subject is the middle upper pleistocene ba mieu and thu duc formations exposed along the dong nai river southern vietnam both the ba mieu and the thu duc formations are interpreted as a transgressive tide dominated estuary succession overlain by a highstand tide dominated delta succession the tide dominated estuary succession is generalized as follows in ascending order fluvial facies in landward portions tidal flat upward coarsening and thickening succession of marine sands with a tidal ravinement surface trs created by tidal scouring during transgression at the base and subtidal lag in seaward portions this tide dominated estuary is distinguished from wave dominated and wave and tide dominated estuaries by 1 the lack of a central basin lagoon tidal delta or bayhead delta facies 2 the widespread presence of marine sands 3 the presence of a subtidal lag and 4 the presence of an upper flow regime sand flat facies the tide dominated delta succession is generalized as follows in ascending order upward convex unit of marine sand and onlapping tidal flat deposits a thick upward fining succession of tidal flat salt marsh deposits and coarse fluvial deposits this delta is distinguished from an estuary as follows 1 it shows thick regional upward fining successions indicating shallowing whereas upward coarsening successions indicating deepening are recognized in an estuary a maximum flooding surface mxfs is recognized in the coarsest part of the succession in marine sand and tidal flat deposits 2 fluvial processes dominate the sediment supply in contrast to an estuary in which a thick marine sand body fed from marine sources is dominant 3 ebb tidal currents are dominant whereas flood tidal currents are dominant in an estuary key features of the incised valley system are 1 amplification of the incised valley geometry by tidal ravinement erosion 2 development of tidal channels filled with mud clasts in the estuary 3 a thick marine sand body in the estuary and 4 upward convex unit of marine sand and a thick tidal flat fluvial succession in the delta the ba mieu formation is recognized as depositional sequence sq 1 between sequence boundary sb 1 below and sb2 above sq1 consists of transgressive systems tract tst 1 and highstand systems tract hst 1 sq1 was formed by a transgression regression cycle during marine isotope stage mis 7 sb2 was formed by fluvial incision during the mis 6 lowstand and is amalgamated with the trs of mis 5 the thu duc formation is recognized as sq2 between sb2 below and sb3 above and it consists of tst2 and hst2 sq2 was formed by a major transgression regression cycle on which a lower rank cyclicity was superposed during mis 5 tst2 thins seaward as a result of tidal ravinement erosion the landward extent of marine environment in mis 5 is inferred to have been of greater scale than that in mis 7 from the distribution of the facies and the trs

rock slope movements in the canadian cordillera some recent work on natural rock slope movements in the cordillera is reviewed climate geology and seismicity combine to produce rockslides in the mackenzies and rockies slower more complex be

bottom water anoxia inoceramid colonization and benthopelagic coupling during black shale deposition on demerara rise late cretaceous western tropical north atlantic 1 the bulk rock geochemistry and inoceramid isotopic composition from cenomanian to santonian finely laminated organic rich black shales recovered during ocean drilling program leg 207 on demerara rise western tropical north atlantic suggest persistent anoxic free h2s conditions within the sediments and short term variations within a narrow range of anoxic to episodically dysoxic bottom waters over a 15 ma time interval in addition to being organic rich the 50 90 m thick sections examined exhibit substantial bulk rock enrichments of si p ba cu mo ni and zn relative to world average shale these observations point to high organic burial fluxes likely driven by high primary production rates which led to the establishment of intensely sulfidic pore waters and possibly bottom waters as well as to the enrichments of cr mo u and v in the sediments at the same time the irregular presence of benthic inoceramids and foraminifera in this facies demonstrates that the benthic environment could not have been continuously anoxic the 13c and 15n values of the inoceramid shell organics provide no evidence of chemosymbiosis and are consistent with pelagic rain as being a significant food source demerara rise inoceramids also exhibit well defined regularly spaced growth lines that are tracked by 13c and 18o variations in shell carbonate that cannot be simply explained by diagenesis instead productivity variations in surface waters may have paced the growth of the shells during brief oxygenation events suitable for benthic inoceramid settlement these inferences imply tight benthopelagic coupling and more dynamic benthic conditions than generally portrayed during black shale deposition by invoking different temporal scales for geochemical and paleontological data this study resolves recent contradictory conclusions e g sulfidic sedimentary conditions versus dysoxic to suboxic benthic waters drawn from studies of either sediment geochemistry or fossil distributions alone on demerara rise this variability may be relevant for discussions of black shales in general

late pleistocene debris flow deposits in large glacial lakes in british columbia and alaska the movement of late wisconsin 30 000 b p ice sheet lobes counter to the direction of regional drainage ponded large lakes up to 5000 km2 in both the upper fraser river valley in british columbia and the cooper river valley in alaska along the fraser river near quesnel glaciolacustrine sediment gravity flow complexes contain thick up to 10 m and laterally extensive up to 3 km diamict units containing large rafts of poorly lithified tertiary rocks diamicts offlap and thin away from tertiary bedrock highs and were emplaced by subaqueous debris flows these flows probably evolved from slumps and slides associated with the downslope failure of unstable tertiary bedrock slopes triggered by rising lake levels a process akin to first filling slope failures around the margins of man made lakes in alaska along the copper river valley massive and stratified diamicts were also deposited by debris flows and are interbedded with thin bedded turbidites poorly sorted gravels and normally graded diamicts debris flow deposits show basal grooves internal compressional structures and rafted clasts that protrude from bed tops flows originated by slumping of rapidly deposited and underconsolidated glacial sediments around the basin margins an important factor in flow generation has been the combination of steep substrate slopes and frequent earthquake shock observations in both british columbia and alaska stress the significance of sediment gravity flow processes acting to deposit glacial sedimentary successions in large ice contact lake basins

depositional model for a chenier plain gulf of carpentaria australia the southern coast of the gulf of carpentaria northern australia consists of a broad chenier plain which is comparable in size and morphology to those reported on the coasts of surinam and south western louisiana the carpentaria chenier plain has at some locations prograded over 30 km since the middle holocene by deposition of low tide muds over subtidal muds during periods of increased sediment input by the rivers chenier ridges are formed during periods of reduced sediment flux by wave induced sorting and redistribution processes an alternation of increased and decreased sediment flux from fluvial sources has occurred several times during the upper holocene such variation in sediment supply is believed to be related to temporal fluctuations in rainfall over the drainage basin which surrounds the southern and eastern gulf

relative sea level and climatic changes in the amazon littoral during the last 500 years abstract an integrated approach focused on sedimentology geochemistry palynology c and n isotopes and radiocarbon dating of a sediment core from an herbaceous plain not flooded by tides of the amapa littoral near the amazon river mouth allowed identification of two phases with marine and terrestrial influences mangroves occurred over tidal mud flats with marine influence between 5610 5470 and 470 310 cal yr bp the absence of mangrove vegetation since 470 310 cal yr was followed by the transition of brackish water organic matter to terrestrial c3 plants also the geochemical data indicate a decrease in sea water influence during this last time interval likely the displacement of mangrove forest to lower surfaces was caused by a relative sea level fall that may be associated with drier conditions with less rainfall during the second part of the last millennium as suggested by this work slight relative sea level fluctuations caused by regional or global climatic change may affect significantly the current mangrove area

depositional model of a macrotidal estuary and floodplain south alligator river northern australia the south alligator river northern territory of australia has a macrotidal estuary tidal influence spring tidal range 5 6 m at the mouth extends 105 km up the channel it is dominated by freshwater in the wet season december april with a salt wedge near the mouth but is well mixed and becomes saline throughout the dry season the tidal channel can be divided into four different channel types an estuarine funnel a sinuous meandering segment a cuspate meandering segment in which the inside of bends are pointed and an upstream tidal channel the distribution of morphologically defined land classes and morphological units within each land class on the floodplain flanking the estuary differs from one channel type to another several stratigraphic and morphostratigraphic units have been recognized from drill holes on the coastal and deltaic estuarine plains and a model of development is proposed on the basis of extensive radiocarbon chronology and palynology the coastal plain has prograded with most rapid sedimentation between 5000 and 3000 yr bp a similar pattern of progradation is identified in the estuarine funnel in the sinuous segment of the estuary the channel has migrated laterally across the floodplain previous channel positions are indicated by palaeochannels and the meander tract is occupied by laminated channel sediments within the cuspate segment there are numerous sinuous palaeochannels on the plains in the upstream segment the channel and palaeochannels have long straight reaches with irregular bends and discontinuous levees and channel avulsion is indicated mangrove mud is a widespread stratigraphic unit throughout the plains the initial phase of development is a transgressive phase 8000 6800 yr bp when mangrove forests extended landwards into a pre existing valley as sea level rose as sea level stabilized the transgressive phase was followed by a widespread mangrove phase termed the big swamp 6800 5300 yr bp the mangrove forests disappeared from most of the plains as vertical accretion continued and were replaced by grass and sedge covered floodplains during the sinuous phase about 5300 2500 yr bp the channel migrated laterally and eroded the deltaicestuarine plain and deposited lateral accretion deposits laminated channel sediments part of the channel of the south alligator river has then progressed from sinuous to cuspate in form and erosion of river banks has occurred transgressive and big swamp phases occurred under rising and stabilizing sea level respectively later morphodynamic channel adjustments occurred under conditions of stable sea level the depositional model has direct application to other estuaries in northern australia and may be applied to other areas where sea level change has been similar

origin of limestone marl alterations in the upper maastrichtian of zumaya spain abstract near the town of zumaya in northern spain upper maastrichtian strata consist of limestone marl rhythms with thin interbedded sandstones the marls and limestones are primarily pelagic and hemipelagic deposits while the sandstones are the product of turbidity currents stratigraphic variations in the volume of marl and limestone form three hierarchical or composite cycles the first order cycles consist of 20 30 m alternations between stratal sequences consisting of interbedded limestone and marl and sequences composed almost exclusively of marl within the interbedded limestone marl sequences second order cycles occur that consist of 5 10 m alternations between limestone or marl domination the third order cycles consist of the bed by bed alternation of limestone and marl these hree composite cycles are the product of shifts in the clay carbonate ratio on various rock and time stratigraphic scales in order to determine if the cyclicity was the result of changes in the supply of siliciclastic material or carbonate material detailed stratigraphic measurements were made of volume percent average bed thickness and stratigraphic frequency for each lithology product moment coefficients indicate that a negative correlation exists between percentage marl and sandstone frequency and a positive correlation exists between limestone percent and sandstone frequency assuming that turbidite deposition is not genetically related to limestone or marl deposition the correlation coefficients suggest that there were increased sedimentation rates during marl accumulation correlation coefficients also showed that increases in amount of marl in a section occur through bed thickening rather tha the increased number of marl beds in contrast limestone dominated intervals are achieved by reduction of marl bed thickness and increases in marl and limestone bed frequency this confirms the suggestion that marl dominated episodes were associated with increases in the sedimentation rate from this analysis we propose that changes in the influx of siliciclastic material and not changes in productivity or dissolution led to the production of limestone marl rhythms as well as the first and second order cycles seen in the zumaya section

changes in north atlantic circulation at the end of the cretaceous greenhouse interval ocean circulation patterns during the late cretaceous greenhouse interval remain disputed marine sediment geochemistry suggests that the end of the greenhouse interval coincided with the onset or intensification of deep water formation in the north atlantic ocean

the formation and impact of landslide dams state of the art abstract the blocking of river courses by mass movements is very common in mountainous areas with deep and narrow valleys landslide dams may pose serious threats to people and their livelihoods downstream in the case of abrupt dam failure since the publication of benchmark reviews of costa and schuster 1988 and korup 2002 there is a growing number of studies focusing on the formation stability and short term impacts of landslide dams this review combines the insights of all these studies builds on current concepts of landslide dams and suggests ways to unify terminologies and classifications we furthermore present a new worldwide database compiled from literature data it contains 410 landslide dams 1 million m3 in volume that were formed since 1900 since these have the most complete data entries these data show that dam longevity is among other factors correlated with the type of landslide forming the dam those formed by rock debris avalanches and rockslides have longest lifespans however the influence of landslide type or material on dam longevity decreases with time after dam formation to ensure consistency in the next database generation we suggest guidelines for data collection to provide a solid basis for evaluating dam stability and governing factors a preliminary classification matrix for landslide dam stability that combines topographic setting and the internal structure of the dam body is another outcome of our review furthermore an evaluation of the various geomorphic stability indices proposed in the literature regarding their suitability and limitations in assessing dam formation and stability shows that they predict the probability of dam formation reasonably well but that their application to longevity estimates requires further assessment the geomorphic impacts of landslide dams in the short medium and long term are summarized and illustrated with key examples finally for a better understanding of the factors controlling dam stability we recommend to 1 include dam composition and sedimentary structures in future case studies 2 maintain and update the worldwide database for sound statistical analyses 3 refine landslide dam stability indices and test them for different landslide types and 4 study hazard cascades related to multiple dams in one watershed for long term landscape evolution studies we suggest to 5 quantify terrestrial sediment flux related to landslide dams 6 detect ancient landslide dams in river profiles and 7 further exploit the sediment archives in former impoundment areas

human influence in geomorphology abstract the human influence in geomorphology has a long history and major contributions have for example been made by shaler mcgee gilbert and marsh however in the last two decades concern with global environmental change has brought the role of anthropogeomorphology into sharper focus global warming if it occurs will have important implications for many geomorphological processes and phenomena as a result of the direct effects of warming as a consequence of other related climatic changes e g precipitation change and as a result of climatically moderated changes in major geomorphologically significant variables e g vegetation cover large uncertainties exist with respect to such matters as hydrological response the frequency of tropical cyclones the speed and degree of permafrost degradation the response of glaciers and ice caps the extent of sea level rise the reaction of beaches to rising sea levels and the state of wetlands deltas and coral reefs other human activities may serve to compound the effects of global geomorphological proccesses given the uncertainties of so many of the environmental changes there is a great need to obtain a greater understanding of the rates and mechanisms of landform response geomorphologists need inter alia to establish long term study sites that will generate base line data to monitor the location and rate of change using sequential cartographic and remote sensing materials to determine information on natural background levels and long term trends by means of data gained from cores to gain a more profound understanding of the operation of geomorphological systems particularly with regard to sensitivities and thresholds and to appreciate the consequences of deliberate manipulation of environmental systems by humans

oxygen isotope composition of diagenetic calcite in organic rich rocks evidence for 18o depletion in marine anaerobic pore water upper cretaceous organic rich carbonates in israel contain benthonic foraminifera and varying amounts of early diagenetic infilling of sparry calcite the sparry calcite has oxygen isotope values down to 9 5 pdb that are significantly lower than those of the coexisting skeletal calcite averaging 2 pdb low 18o values are very common in carbonates that are associated with organic matter these occurrences are conventionally explained as being due to carbonate formation under conditions of low salinity and or elevated temperature on the basis of petrographic data and local geologic evidence however none of the conventional explanations can be applied in this case we advance an alternative model that relates the light oxygen compositions of the diagenetic calcite to depletion of 18o in pore water of normal salinity the proposed operating mechanism is a direct consequence of organic matter decomposition in the sulfate reducing zone being inherent to reducing marine environments this model can be applied to many organic rich rock associations

dynamic sedimentary conditions during periods of enhanced sequestration of organic carbon in the central southern tethys at the onset of the cenozoic global cooling abstract stagnant bottom water conditions e g low and stable redox potential long water residence time is an assumption commonly used to explain the preservation and burial of high amounts of organic carbon c org in marine sediments rather than stagnant conditions the evidence presented here from north central tunisia supports dynamic conditions during formation of variably c org rich outermost shelf carbonates of the early middle eocene the dynamic conditions are inferred by the deposition of four distinct lithofacies in this outermost shelf setting shedding of carbonate i e mud and fragmented bioclasts from the shallower source areas controlled the distribution of all lithofacies with higher amounts of transported benthic debris occurring in the most proximal lithofacies and vice versa this carbonate shedding also controlled the deposition of three orders of lithological cycles from limestone marly limestone couplets grading to cycles made up of groups of couplets bottom water redox potential varied in intensity throughout this depositional setting with moderate oxygen depletion suboxic conditions in the southern sector of north central tunisia and much higher oxygenation in the northern area evidence for suboxic bottom waters in the southern sector higher c org contents is provided by higher trace metal cu ni zn cr mo u and v enrichments than in the northern area regionally heterogeneous primary productivity of surface waters is suggested to have caused a higher c org burial flux in the southern sector compared to the north a situation interpreted to have been related to varying upwelling patterns due to the effects of regional palaeogeography and the dominant wind patterns the deposition of the studied c org rich carbonates spanned part of the calcareous nannofossil zones np13 to np14 50 48 m y ago and coincided with the initiation of the cenozoic global cooling subsequent to the early eocene climatic optimum eeco 52 50 m y ago an implication is that an increased c org burial in north central tunisia could have been part of a major event sequestering atmospheric co 2 in marine sediments that caused climatic cooling immediately after the eeco this implication however is difficult to reconcile with the data available elsewhere other than our tunisian carbonates major c org sequestration in marine sediments of the early middle eocene transition are poorly documented globally if this scenario is confirmed other negative feedbacks such as enhanced continental weathering increased terrestrial carbon stock decreased co 2 outgassing and or changes in ocean circulation would have been more influential to the onset of the cenozoic global cooling

use of airborne lidar to investigate mangrove accommodation space in macrotidal estuaries of northern australia abstract extensive mangroves in the northern territory of australia reflect the large tidal range along that coast airborne lidar enables interpretation of ground elevation along transects through mangroves and across coastal and estuarine plains supplementing past levelling surveys of elevation range of the principal mangrove taxa mangrove distribution in the upper intertidal varies geographically in response to tidal variations in the well mapped darwin and bynoe harbours sonneratia alba grows at elevations below mean sea level whereas rhizophora occupies a prominent zone that is inundated by neap tides ceriops is generally found at higher elevations often showing a canopy height gradation a number of mangroves including avicennia occur at the upper bound of the mangrove forest adjacent to the hinterland which occurs at 2 8 m above australian height datum ahd on the open coast and at 3 6 m ahd reflecting tidal amplification in the embayments along the less known macrotidal estuaries of the alligator rivers accommodation space and species distribution varies with distance from the open coast on the coastal plain that has formed along the southern margin of van diemen gulf lidar reveals that landwardmost mangroves also occur up to an elevation of 2 8 m ahd amplification of tides in the cuspate meandering middle sections of the south and east alligator rivers enables mangroves to occur up to 3 5 3 6 m ahd in contrast to the less infilled west alligator river the lidar reveals substrate topography and vegetation structure the rhizophora zone is particularly distinct and its steeper gradient implies rapid sediment accretion rhizophora has played a disproportionately large role in the sequestration of blue carbon low lying parts of these estuarine plains particularly former channels are already experiencing tidal creek extension and saline intrusion and topography of the landscape behind the mangroves will mean many areas will be vulnerable to future salinization in response to rising sea level

contrasting environmental effects of astronomically driven climate change on three eocene hemipelagic successions from the basque cantabrian basin several processes can contribute to the formation of hemipelagic limestone marl alternations as a consequence of astronomically driven climate change the aim of this work is to decipher which environmental factors governed the formation of three eocene hemipelagic successions of the basque cantabrian basin using a comprehensive set of physical and bulk carbonate geochemical data bed thickness mineralogy caco3 13c and 18o the results show that the significance of several environmental processes varied depending on the palaeogeographic setting and eccentricity modulated precessional seasonality in the sopelana starved deep sea basin limestones were formed as a consequence of high pelagic carbonate productivity during periods of warm seawater and sluggish circulation which corresponded to periods of low seasonality summers at aphelion conversely marls accumulated when pelagic carbonate productivity decreased during periods with cooler waters and more vigorous circulation which occurred when seasonality was higher summers at perihelion in the gorrondatxe submarine fan fringe marls accumulated when high seasonality produced significant continental rainfall and runoff causing the dilution of pelagic carbonate sedimentation with terrigenous supplies in the oyambre upper slope marls also accumulated when seasonality was high as pelagic carbonate productivity decreased due to both the expansion of low salinity waters on the ocean surface and the increase in continentally derived nutrients which caused detrimental seawater conditions for calcareous plankton both in gorrondatxe and oyambre limestones accumulated when boreal summer at aphelion caused low seasonality which allowed relatively stable conditions to prevail at minimum eccentricity when precession driven seasonality contrast diminished changes in pelagic carbonate productivity were significant in the three sections on the contrary at maximum eccentricity when seasonality peaked due to summers occurring at perihelion the effects of other environmental processes such as continental and oceanic currents became influential however the influence of these processes minimized when summertime coincided with aphelion at maximum eccentricity and seasonality was weakest this article is protected by copyright all rights reserved

contrasting holocene sedimentary geologies of lower daly river northern australia and lower sepik ramu papua new guinea abstract the estuarine plain of the macrotidal daly river in monsoonal northern australia is underlain by extensive mid holocene mangrove swamp sediments which accumulated during the last stages of post glacial sea level rise sediment yield from the catchment is too low to account for the volume which accumulated during sea level rise and onshore transport is invoked this is supported by radiocarbon ages and facies analysis of the transgressive sediment tract beneath the maximum flooding surface mfs and of the tract of vertical sedimentation which extends from the mfs to the surface of estuarine fluvial transition the eft the eft occurred about 5000 to 6000 bp throughout the estuarine plain a contrasting situation exists in the lowland holocene basin of the microtidal sepik and ramu rivers in papua new guinea which derive sediment from highly tectonic catchments a tectonic basin which was a shallow brackish inland sea after post glacial transgression is separated by a low divide from a deltaic plain progradation of the deltaic plain commenced about 3500 bp after regressive sedimentation eclipsed the inland sea in the tectonic basin contrasting organic facies mangrove in the daly and freshwater swamp deposits in the sepik ramu highlight differences between facies models of the two systems differences between fluvio tidal regimes are reflected by the eft which is synchronous in the daly and diachronous in the sepik ramu and possibly by the mfs which is diachronous in the daly and may be synchronous in the sepik ramu

upper cretaceous marl limestone sequences of alabama possible products of sea level change not climate forcing marl limestone sequences in the arcola limestone member campanian of alabama have been cited as key examples of climate forced sedimentation resulting from cycles of production and dilution however sedimentologic and stratigraphic data from the arcola presented herein suggest a more probable link between short term sea level changes and marl limestone sequence genesis either relative sea level change caused by intraplate deformation or short term eustatic sea level change is suggested as the causative mechanism for deposition of the marl limestone sequences

long term morphodynamic evolution and the equilibrium mechanism of a flood channel in the yangtze estuary china the stability of flood channels has attracted considerable attention because of their complicated interactions with the prevailing hydrodynamics and importance in ship navigation this research examines long term morphodynamic evolution in the yangtze estuary from 1861 to 2002 and the equilibrium mechanism of the xinqiao channel in the yangtze estuary by digitizing 15 selected maritime charts and calculating the volume of the channel although the total period of channel development is much longer than the historical data used in this paper three stages are identified during the study period the first embryonic stage 66 years the second formation stage 33 years and the third equilibrium stage 45 years variations in coastline location channel volume and hydrodynamics in the channel during the three stages indicate that the channel equilibrium was reached and maintained when the channel direction was aligned with the direction of offshore tidal wave propagation variations in river and sediment discharges affect erosion and deposition in the channel and thus channel geometry however future reduction in sediment supply by 10 33 due to the ongoing river engineering projects would increase the volume of the xinqiao channel only by 1 3 it seems unlikely that the above change in sediment discharge will disrupt the equilibrium of the xinqiao channel

the shapes of some mountain peaks in the canadian rockies different mountain shapes in sedimentary sequences in the canadian rockies were enhanced by glacial erosion and have been modified postglacially by gravity driven slope processes slope modification by both glacial erosion and postglaciation landslides is related to rock structure particularly bedding dip rock mass strength and slope geometry five mountain peak shapes in monoclinal sequences each fall into different ranges of bedding dips castellate 1 and matterhorn 2 mountains occur in sub horizontal beds and their slopes on all sides follow combinations of bedding planes and joints the overall slopes are generally 37 to 65 and oblique to both bedding and joints slopes in sub horizontal beds may be controlled by their rock mass strength cuestas 3 develop in gently to moderately dipping beds dip slopes and steeper normal escarpments form their cataclinal and anaclinal sides respectively with the dihedral angle between them about 90 hogbacks 4 in moderately to steeply dipping beds have similar slope angles on both cataclinal and anaclinal slopes cataclinal slopes are either dip slopes or underdip slopes but anaclinal slopes are often steepened escarpments the dihedral angle between the slopes is usually less than 90 dogtooth 5 mountains occur in steeply dipping to sub vertical beds and the dihedral angle can be as low as 60 slope gradients in inclined beds are closely related to landslides whose modes are controlled by bedding dips copyright 1999 john wiley sons ltd

cretaceous rhythmic bedding sequences a plausible link between orbital variations and climate abstract simple oscillation cycles have been recognized in cretaceous pelagic sequences as a marked periodicity in carbonate and or organic carbon content the estimated periodicities of these cycles resemble milankovitch type variations in orbital elements however during warm geologic periods the nature of the link between orbital variations and the sedimentary record has been problematic climate model studies show that the intensity of continental margin precipitation in specific low latitude regions is a function of land sea thermal contrast which is sensitive to orbital variations cretaceous climate model simulations are characterized by regions of intense precipitation the locations of which are controlled by geographic configuration in particular in the model simulation the northern margin of the tethys ocean has all the climatic characteristics necessary to exhibit a sensitivity to orbital variations detailed studies of the biota sedimentology and geochemistry of the bedding rhythms in greenhorn cyclothem in the western interior seaway of north america are best interpreted in terms of variations in precipitation runoff and stable stratification of the seaway combined the geologic and model studies support a link between orbital periodicities variations of intense precipitation associated with specific paleogeographic situations and cretaceous bedding patterns this hypothesis has important implications for the sensitivity of the atmosphere hydrosphere lithosphere system to external forcing

late cretaceous to late eocene palaeogeographic evolution of southwest europe abstract a synthesis of personal research concerning the peri pyrenean region and previously published data is presented as a series of palaeogeographic reconstructions subsequent to the progressive regression at the end of the cretaceous the sea invaded three times parts of the earlier senonian marine domain on both sides of the eastern palaeo pyrenees pre cuisian climatic rewarming combined with cuisian continental epeirogenic deformations resulted in major biogeographic modifications during the cuisian local tectonics forced the sea from the northern pyrenean basin whereas in the southern pyrenean basin the sea retreated much later as a consequence of the pyrenean tectonic phase however the pyrenean tectogenesis seems to have affected a much larger region including the alps shoreline migrations are compared and related to the geodynamic behaviour of the meridional and septentrional european provinces in order to distinguish between tectonic and eustatic causes

high resolution intra and interbasinal correlation of the danian selandian transition early paleocene the bjala section bulgaria and the selandian gssp at zumaia spain abstract the danian selandian d s boundary has been identified for the first time in the black sea coast at bjala bulgaria based on a new integrated bio magneto and cyclostratigraphic study several correlation criteria as established for the basal selandian gssp from zumaia basque basin are evaluated noteworthy is the almost complete lack of calcareous nannoplankton species braarudosphaera bigelowi in the bulgarian sections a sharp decrease of which was indicated as suitable criteria for defining the d s boundary as it occurred both at zumaia and in the classical locations of the north sea basin conversely the second evolutionary radiation of the calcareous nannofossil genus fasciculithus together with the occurrence of fasciculithus tympaniformis that define the np4 np5 zonal boundary seem to be reliable criteria to approximate the d s boundary in detail however the best approach is to integrate biostratigraphic data within a magnetostratigraphic and or cyclostratigraphic framework refinements on the placement of chron c27n at zumaia and robust bed by bed correlation between several basque sections and bjala indicates that the d s boundary is located 30 precession cycles 630 ky above c27n in addition to the precession related marl limestone couplets and 100 ky eccentricity bundles recognized in the studied sections expression of the stable 405 ky long eccentricity allows direct tuning to the astronomical solutions a correlation of the land based sections with previously tuned data from odp site1262 from the southern atlantic is challenged our choice is consistent with original tuning at zumaia but shifts one 100 ky cycle older previous tuning from site 1262 along the interval above c27n under the preferred tuning scheme the d s boundary can be given an age of 61 641 0 040 ma on the la04 orbital solution

climatic and oceanographic isotopic signals from the carbonate rock record and their preservation stable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases terrestrial carbonates meteoric cements calcretes and speleothems similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover primary environmental isotopic signals may be obscured by the effects of post depositional diagenetic alteration cementation and replacement reactions can take place in a wide range of diagenetic environments the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting together with subsequent changes in relative sea level and burial history carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration water rock interaction and fluid mixing may produce non linear distributions attempts to determine long term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow water limestones must include an assessment of the diagenetic history of the materials analysed petrographic examination using conventional microscopy backed up where appropriate by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary environmental isotopic signals recent research has shown that these techniques can be successfully employed in both phanerozoic and precambrian sediments

implications of sea level rise in a modern carbonate ramp setting abstract this study addresses a gap in our understanding of the effects of sea level rise on the sedimentary systems and morphological development of recent and ancient carbonate ramp settings many ancient carbonate sequences are interpreted as having been deposited in carbonate ramp settings these settings are poorly represented in the recent the study documents the present day transgressive flooding of the abu dhabi coastline at the southern shoreline of the arabian persian gulf a carbonate ramp depositional system that is widely employed as a recent analogue for numerous ancient carbonate systems fourteen years of field based observations are integrated with historical and recent high resolution satellite imagery in order to document and assess the onset of flooding predicted rates of transgression i e landward movement of the shoreline of 2 5 m yr 1 0 2 m yr 1 based on global sea level rise alone were far exceeded by the flooding rate calculated from the back stepping of coastal features 10 29 m yr 1 this discrepancy results from the dynamic nature of the flooding with increased water depth exposing the coastline to increased erosion and thereby enhancing back stepping a non accretionary transgressive shoreline trajectory results from relatively rapid sea level rise coupled with a low angle ramp geometry and a paucity of sediments the flooding is represented by the landward migration of facies belts a range of erosive features and the onset of bioturbation employing intergovernmental panel on climate change church et al 2013 predictions for 21st century sea level rise and allowing for the post flooding lag time that is typical for the start up of carbonate factories it is calculated that the coastline will continue to retrograde for the foreseeable future total passive flooding without considering feedback in the modification of the shoreline by the year 2100 is calculated to likely be between 340 and 571 m with a flooding rate of 3 40 8 64 m yr 1 however adopting the observation that global sea level rise only accounts for 15 of the recorded shoreline retreat this figure rises dramatically to a total likely dynamic flooding considering modifications to the shoreline of between 2 3 and 3 8 km loss of microbial and mangal habitats will subject the exposed shoreline to increasing erosion shoreline retreat will threaten existing coastal infrastructure

holocene development of the lower mary river plains northern territory australia extensive coastal and estuarine plains associated with several large seasonal rivers characterize the southern shore of van diemen gulf northern territory australia the mary river is unique among these rivers in that despite a catchment of 7700 km 2 it fails to reach the sea as a discrete channel but breaks up into a series of terminating multiple channels leaving much of the freshwater discharge to evaporate from the plains the extent and morphology of these plains have changed markedly during the holocene drilling radiocarbon dating and pollen analysis indicate a transgressive phase that began about 7000 years ago as the rising seas flooded the prior valley this was followed by a big swamp phase as sea level stabilized around 6000 years ago during which widespread mangrove forest development occurred rapid progradation of the coast occurred between 6000 and 4000 years bp the shoreline has prograded little since that time but has been modified by episodic chenier ridge deposition and palaeochannel abandonment infill and reoccupation the lower mary river differs from adjacent systems in that several former estuarine channels across the plains appear to have become completely blocked with sediment leaving low lying billabongs and palaeochannels which have been preferentially reinvaded by later channels several alternative explanations are examined but it remains unclear what has driven major variations in palaeochannel activity and sedimentation during the mid holocene and why these have decreased so markedly in the last 2000 years

limestone marl alternations as environmental archives and the role of early diagenesis a critical review limestone marl alternations and other micritic calcareous rhythmites have long appealed to sedimentologists as they appeared to directly reflect high frequency environmental change in particular when orbital forcing gained popularity amongst sedimentologists and paleoclimatologists in 1980s such rhythmites seemed to offer an ideal tool for high resolution chronostratigraphy and environmental reconstruction however in spite of the fact that orbital forcing has become a routine interpretation of calcareous rhythmites and that the processes of formation of calcareous rhythmites are considered well understood research in the past 10 years again has questioned their primary origin and their direct interpretability detailed petrographic paleontological and geochemical data from numerous successions through geological time provided the basis for testing whether or not the regular alternation of limestone beds and marl or shale interlayers represents bimodally fluctuating environmental conditions in a direct way in particular these data supplemented by box model simulations imply that post depositional alteration diagenesis has the potential to not only seriously distort primary environmental signals but also to mimic primary signals this questions the use of micritic calcareous rhythmites for high resolution chronostratigraphy and for environmental interpretations where independent data of diagenetically inert parameters are not available diagenetic changes appear to have a yet widely underestimated influence on the appearance of limestone marl alternations and other calcareous rhythmites the aim of the present review is to summarize new approaches and give an overview of our research results in this field of the past decade this review also aims at pointing to still enigmatic aspects that need to be addressed before the interpretation of micritic calcareous rhythmites can be considered a reliable tool for high resolution chronostratigraphy and paleoenvironmental interpretation

quantified rates of geomorphic change on a modern carbonate tidal flat bahamas comparison of aerial photographs and ultrahigh resolution remote sensing data reveals changes in the geomorphology of a modern carbonate tidal flat in the 58 yr between acquisition of the two data sets several tidal channels have extended headward more than 100 m channel bars have stabilized the shoreline has eroded as much as 50 m the inland algal marsh locally has prograded as much as 90 m and many mangrove ponds have increased in size these changes over the known time interval allow quantification of the rates of these geomorphic processes and suggest rates of migration of landforms to several meters per year some observed rates appear to be different than rates averaged over the past several thousand years however possibly because of changes in storm activity or circulation patterns these data illustrate the dynamic nature of the entire coastal tidal flat system not just the shoreline and reflect the system9s response to factors including relative rises in sea level

an overview of the post messinian paleoenvironmental history of the western mediterranean a review of the pliocene pleistocene paleoenvironmental history of the western mediterranean is presented based on micropaleontological and geochemical studies of ocean drilling program odp leg 107 material and marine outcrops in southern italy the calcareous plankton biochronology proposed for the mediterranean by rio et al 1990 and 1991a provides the necessary age control for determining the timing of major climatic and oceanographic changes in the region the early pliocene period in the mediterranean was not a time of warm stable climate rather it was marked by relatively high amplitude climatic oscillations in marginal areas these climatic oscillations resulted in the rhythmic deposition of limestone marl couplets which have an average duration of approximately 19 000 years it is proposed that these sedimentary couplets are the result of precessionally induced changes in monsoon intensity which in turn cause variability in coastal divergence and upwelling the 18o and the calcareous plankton foraminifera and coccoliths records for tyrrhenian sea odp site 653 reveal a cooling of surface waters at 3 1 ma coincident with this cooling is an increase in the frequency of diatomite formation in southern italy bianco section the global cooling at 2 4 ma and the associated expansion of northern hemisphere glaciation resulted in a shift to more arid conditions in the mediterranean region this climate change may have altered the mediterranean water balance resulting in the establishment of antiestuarine water exchange with the atlantic at this time the 18o record for site 653 is also marked by a sharp cooling across the pliocene pleistocene boundary in the boundary stratotype section at vrica this cooling is manifested as an increase in the abundance of the planktonic foraminifer neogloboquadrina pachyderma

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

estuarine infill and coastal progradation southern van diemen gulf northern australia abstract there are several estuaries associated with the pronouncedly seasonal rivers which drain northwards from the middle proterozoic sandstone arnhem land plateau and the tertiary koolpinyah land surface into the macrotidal van diemen gulf in the northern territory of australia the holocene development of these investigated in greatest detail for the south alligator river with an upland catchment of 10 000 km2 through drilling palynology and radiocarbon dating comprises both estuarine infill and coastal progradation three phases of estuarine infill can be recognised i a transgressive phase 8000 6800 years b p of marine incursion ii a big swamp phase 6800 5300 years b p of widespread mangrove forest development and iii a sinuous cuspate phase of floodplain development since 5300 years b p during which the tidal river has meandered and reworked earlier estuarine sediments since 6000 years b p the south alligator coastal plain has prograded at a decelerating rate with two phases of chenier ridge formation a similar pattern of estuarine infill and decelerating coastal plain progradation is demonstrated for the adelaide and mary rivers both with catchments of 6000 km2 the southern shore of van diemem gulf appears to have changed its overall position little during the last 2000 years the major source for the clay silt and fine sands which have infilled the estuary and coastal plain has been from seaward dispite the similarity of development coastal sediment build up has had different effects on the morphology of each tidal river the adelaide has undergone a major diversion and no longer flows directly into van diemen gulf but occupies a former fluvial course and the mary has been blocked entirely and its former estuarine palaeochannels have been infilled with tide transported sediment

holocene evolution of coastal wetlands in wet tropical northeastern australia pollen in sediments drilled from the innisfail coastal plain northeast queensland australia was examined to reconstruct the evolution of holocene wetlands in a wet tropical environment in contrast to monsoonal australia stable environmental conditions created by year round rainfall and low tidal range caused abrupt unidirectional transitions in wetland zonation as marine influence changed this has enabled a detailed reconstruction of the marine transgression and subsequent progradation mangroves colonized in response to marine transgression at c 7400 bp as riverine mangroves of low salt tolerance migrated up the mulgrave river these were replaced around 7000 bp by extensive rhizophora dominated mangroves coinciding with the development of a rhizophora dominated community in wyvuri embayment mangroves reached their greatest extent as sea level rise slowed towards 6000 bp with a stillstand indicated by a brief return to terrestrial conditions at one site high freshwater input depressed salt i

latest cretaceous cone in cone structures and soft sediment deformation basque cantabrian basin north spain a record of deep marine paleoseismicity unusual cone in cone structures are preserved in fibrous celestite veins hosted by carbonatic rocks the veins are early diagenetic features formed near the water sediment interface in a deep marine environment of latest cretaceous early maastrichtian age new field and microscopic evidence on the veins and their host rocks indicates that they predate sediment compaction and were related to synsedimentary soft sediment deformation structures the mechanism of cone in cone formation has been related to fluid pressure drops following sediment overpressurization but instantaneous loading during emplacement of submarine slides or other mechanisms might be viable alternatives we argue that this cone in cone structure is an overprinting feature penetrative conical fractures that resulted from seismic wave propagation through a mechanically anisotropic medium submarine amplification of seismic surface waves rayleigh waves induced shock wave formation in the contacts between veins and the bounding lithified calcarenite and unlithified marl sediment layers fracture front wave propagation normal to the seafloor and the rayleigh source across the veins and along the celestite crystal fibers induced crack nucleation in heterogeneities and penetrative conical fracturation the cone in cone structure might thus be regarded as a new paleoseismological indicator in deep sea sediments

proximate environmental forcing in fine scale geochemical records of calcareous couplets upper cretaceous and palaeocene of the basque cantabrian basin eastern north atlantic abstract calcareous couplets are key elements in reconstructing the evolution of a sedimentary basin due to the influence of forcing mechanisms such as climate sea level and tectonism on their depositional patterns proposed forcing mechanisms however are often not mutually exclusive and even constraining the relative importance of different processes is problematic added to the question of discriminating forcing mechanisms a major challenge is to produce high sampling density so that observations lie within temporal resolutions equal to or finer than the timescales on which different forcing operates here we show fine scale 1 sample 2 cm caco3 18o and 13c records and sedimentological observations from three different sites isla de castro sopelana ma and sopelana da with calcareous couplets in the basque cantabrian basin eastern north atlantic to illustrate the potential of fine sampling strategies to help distinguish proximate environmental forcing partial redistribution of carbonate during burial diagenesis has been proposed for these sediments our caco3 18o and 13c data could thus be dismissed as diagenetic signals if only one sample was collected from each bed detailed observations of the fine scale geochemical records however challenge purely diagenetic explanations combined with sedimentology the caco3 18o and 13c values partially altered by diagenesis are interpreted to have resulted from alternating climates the proximate forcing through which alternating climates caused the geochemical patterns though was different in each section due to their specific palaeogeographic positions in the basin and the properties of the seawater masses the proximity of continental areas of high relief to the isla de castro section supported a high continental influence during its deposition the sopelana ma sediments are assigned to a transgressive system tract a condition that is interpreted to have promoted a high influence of oceanic processes in its depositional setting finally a relatively cool oxygen rich water mass with high oxidation potential influenced the geochemical and depositional patterns of sopelana da beyond the climatic and oceanographic dynamics inferred for a basin that linked the western tethys with boreal domains during major marine transgressions of the late cretaceous to palaeocene an implication of our work is that if similar fine scale geochemical records were applied to calcareous couplets spanning major events in earth s history e g ocean anoxic events alternative forcing scenarios leading to and out of these events could be discriminated

catastrophic landslides and their effects on the upper indus streams karakoram himalaya northern pakistan abstract the paper examines the nature and geomorphic influences of deposits from rock avalanches that obstruct rivers most of the 115 rockslide rock avalanche events identified in the karakoram himalaya straddled one or more stream valleys at least 73 of these landslides formerly dammed the indus or its tributaries upstream of the barriers remnants exist of once very extensive lacustrine deposits the stability and long term survival of dams from large rock avalanches is addressed and the reasons for the gradual or phased rather than catastrophic and sudden breaching case histories emphasise the erosional and depositional forms associated with the barriers they are reconstructed in terms of the emplacement and properties of the deposits from rock avalanches and the response of the river to interruption by them these barriers have exerted a substantial control over stream response and development for most of the holocene at least today they are associated with distinctive features of channel form and thalweg river terrace systems intermontane sediment sinks and sources and local erosional forms in bedrock more broadly the landslide barriers have created a naturally fragmented river system deposition and erosion in the lower few tens or hundreds of meters of the upper indus stream valleys have been dominated by epicycles of aggradation trenching and downcutting that mainly reflect the scale timing and history of each barrier the landforms involved are only indirectly related to the late glacial and paraglacial conditions that have hitherto been regarded as the main explanation

influence of differential diagenesis on primary depositional signals in limestone marl alternations an example from middle permian marine successions south china abstract the diagenetic alteration of rhythmic successions remains one of the main challenges in paleoclimatology and cyclostratigraphy to address this very important problem thin sections and geochemical data of the limestone marl alternations from middle permian carbonate successions in south china are examined to identify differential diagenetic effects in the petrography organic and inorganic compositions strontium concentrations and stable isotopic compositions of limestone beds and marl interlayers in the lengshuixi outcrop and the jy66 1 drill core the most conspicuous features are that the limestone beds exhibit dense cementation high strontium concentrations negative oxygen isotopic values and positive carbon isotopic values in contrast the marl interlayers contain talc and exhibit strongly deformed and oriented bioclasts low strontium concentrations positive oxygen isotopic values and negative carbon isotopic values although differential diagenesis has occurred some paleoclimate proxies e g computed gamma ray values still preserve their primary signals and thus are suitable for cyclostratigraphic research eccentricity rhythm and millennial scale rhythm are obviously recorded in middle permian limestone marl alternations in south china the variations in the oxygen and carbon isotopic values of limestone marl alternations from different basins represent responses to different processes of differential diagenesis this knowledge assumes that differential diagenesis occurs in diagenetically closed systems under the deep sea floor however this assumption may not be valid in diagenetically open systems where exotic fluids may add unexpected disturbances hence it is crucial to understand diagenetic systems by determining the variations in strontium concentrations which are as important as variations in carbon and oxygen isotopic values

sedimentary controls on modern sand grain coat formation abstract coated sand grains can influence reservoir quality evolution during sandstone diagenesis porosity can be reduced and fluid flow restricted where grain coats encroach into pore space conversely pore lining grain coats can restrict the growth of pore filling quartz cement in deeply buried sandstones and thus can result in unusually high porosity in deeply buried sandstones being able to predict the distribution of coated sand grains within petroleum reservoirs is thus important to help find good reservoir quality here we report a modern analogue study of 12 sediment cores from the anllons estuary galicia nw spain collected from a range of sub environments to help develop an understanding of the occurrence and distribution of coated grains the cores were described for grain size bioturbation and sedimentary structures and then sub sampled for electron and light microscopy laser granulometry and x ray diffraction analysis the anllons estuary is sand dominated with intertidal sand flats and saltmarsh environments at the margins there is a shallowing fining upwards trend in the estuary fill succession grain coats are present in nearly every sample analysed they are between 1 m and 100 m thick and typically lack internal organisation the extent of grain coat coverage can exceed 25 in some samples with coverage highest in the top 20 cm of cores samples from muddy intertidal flat and the muddy saltmarsh environments close to the margins of the estuary have the highest coat coverage mean coat coverage of 20 2 and 21 3 respectively the lowest mean coat coverage occurs in the sandy saltmarsh 10 4 beyond the upper tidal limit and sandy intertidal flat environments 8 4 close to the main estuary channel mean coat coverage correlates with the concentration of clay fraction the primary controls on the distribution of fine grained sediment and therefore grain coat distribution are primary sediment transport and deposition processes that concentrate the clay fraction in the sediment towards the margins of the estuary bioturbation and clay illuviation mechanical infiltration are secondary processes that may redistribute fine grained sediment and produce grain coats here we have shown that detrital grain coats are more likely in marginal environments of ancient estuary fills which are typically found in the fining upward part of progradational successions

sedimentary vs diagenetic control on rhythmic calcareous successions pliensbachian of asturias spain the diagenetic overprint in rhythmic hemipelagic successions can either enhance or change the original distribution of caco3 but it is difficult to evaluate its effect because in most field examples it is not possible to distinguish between sedimentary and diagenetic features the rhythmic succession of the pliensbachian of asturias spain shows alternation of bioclastic and laminated burrowed intervals the original content of carbonate brought by storms from shallow areas was larger in the bioclastic horizons however there is a widespread mismatch between facies alternations and the observed lithological rhythms the diagenetic redistribution of caco3 resulted in successive limestone marl clay couplets that do not match either in number or in the location of the boundaries the sedimentary cycles defined by facies alternations we conclude that interpreting the limestone marl rhythms as a direct response to primary changes is highly questionable unless there is unequivocal proof of a sedimentary origin of the alternation of the two lithologies

storm impact and evolution of a mangrove fringed chenier plain shoal bay darwin australia abstract storms are considered to have significant impacts on the development of chenier plains particularly through the devastation of mangrove vegetation but also in terms of winnowing sand and shell from mudflats and forming chenier ridges shoal bay in the beagle gulf northern australia contains a small chenier plain which was struck by a severe tropical cyclone cyclone tracy on christmas day 1974 as it devastated the city of darwin the morphology vegetation and stratigraphy of the plain are described the plain is underlain by lower intertidal sand with shell hash a radiocarbon age of 6130 years bp indicates mangrove colonisation of this flat at the time that sea level stabilised around its present level after the postglacial transgression subsequently progradation of mudflats has occurred especially around 2300 years ago and shells of this age are found both in growth position from within the mudflats and incorporated into the shelly chenier ridges a further phase of build out and subsequent erosion is reflected by stumps and in situ bivalves being excavated presently on the foreshore radiocarbon dating about 900 1100 years bp within this context of evolution cyclone tracy can be seen to have had severe consequences upon the patterning of mangroves with extensive windthrow of ceriops and defoliation of rhizophora at the western end of the plain recovery of the mangrove vegetation has been gradual and is still incomplete however the storm had little influence on the pattern of landform development indeed the aerial photographic sequence indicates a trend by which sand shoals are gradually reworked landwards in places moving through mangrove vegetation the study suggests that rather than pronounced regional episodes of alternative mudflat buildout and erosion both processes occur simultaneously at different points along this foreshore

maastrichtian foraminiferal and paleoceanographic changes on milankovitch timescales milankovitch scale alternations in maastrichtian hemipelagic strata from ocean drilling program hole 1050c blake nose provide a natural experiment of paleoceanography and foraminiferal paleoecology in a tropical subtropical greenhouse ocean cycles are 30 50 cm thick and thought to reflect the 21 kyr precessional cycle high planktic 18o values are correlated with high planktic but low benthic 13c values indicating that cooler and or more saline surface waters were associated with higher productivity high productivity intervals are also characterized by high ca concentrations enrichment in feldspar and kaolinite and high relative abundance of heterohelix spp globigerinelloides spp and laeviheterohelix glabrans conversely low productivity intervals have low planktic 18o values high fe and ti concentrations enrichment in quartz illite and chlorite and relative increases in globotruncana spp and pseudoguembelina spp potential forcing mechanisms for observed covariation include cyclic variation in water column stratification variation in continental nutrient fluxes and changes in the intensity of upwelling

bedding rhythms and cyclic sequences as documented in organic carbon carbonate patterns upper cretaceous western interior u s abstract a three component sedimentation model is introduced for estimating the relative effects of major changes in sediment flux coupled organic carbon carbonate changes reflecting different dilution concentration styles are utilized to detect the changing flux between the carbonate siliciclastic and organic matter components the three component model is then applied to upper cretaceous rhythmically bedded units of the greenhorn and niobrara cycles of the western interior seaway the cycles are related to third order sea level changes the western interior seaway was sensitive to small scale climatic cycles only during periods of maximum flooding due to combined variations in carbonate productivity redox conditions and siliciclastic supply from continental sources rhythmic deposition is different for different parts within the periods of maximum flooding for each of the two investigated third order sea level cycles section intervals reflecting peak flooding show variations in carbonate productivity and variations in redox conditions slightly more regressive intervals show variations in calcareous productivity and siliciclastic dilution with stagnant dysaerobic bottom waters for most of the investigated bedding rhythms persistent dysaerobic bottom waters are largely uninfluenced by variations in pelagic carbonate productivity except for section intervals representing peak flooding this suggests the existence of a circulation pattern in which a mixed surface water zone was underlain by more stratified oxygen depleted water masses with slow circulation

secular variation in late cretaceous carbon isotopes a new δ13c carbonate reference curve for the cenomanian campanian 99 6 70 6 ma carbon stable isotope variation through the cenomanian santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven chalk successions in england the sections show consistent stratigraphic trends and 13c values that provide a basis for highresolution correlation positive and negative 13cexcursions and inflection points on the isotope profiles are used to define 72 isotope events key markers are provided by positive 13c excursions of up to 2 the albian cenomanianboundary event mid cenomanian event i thecenomanian turonian boundary event the bridgewick hitch wood and navigation events of late turonian age and the santonian campanian boundary event isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons an age calibrated composite 13c reference curve and an isotope event stratigraphy are constructed using data from the english chalk the isotope stratigraphy is applied to successions in germany france spain and italy correlation with pelagic sections at gubbio central italy demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the cenomanian turonian stages confirming established relationships between tethyan planktonic foraminiferal and boreal macrofossil biozonations correlation of the coniacian santonian stages is less clear cut magnetostratigraphic evidence for placing the base of chron 33r near the base of the upper santonian is in good agreement with the carbon isotope correlation but generates significant anomalies regarding the placement of the santonian and campanian stage boundaries with respect to tethyan planktonic foraminiferal and nannofossil zones isotope stratigraphy offers a more reliable criterion for detailed correlation of cenomanian santonian strata than biostratigraphy with the addition of campanian 13c data from one of the english sections a composite cenomanian campanian age calibrated reference curve is presented that can be utilized in future chemostratigraphic studies the cenomanian campanian carbon isotope curve is remarkably similar in shape to supposedly eustatic sea level curves increasing 13c values accompanying sea level rise associated with transgression and falling 13c values characterizing sea level fall and regression the correlation between carbon isotopes and sea level is explained by variations in epicontinental sea area affecting organic matter burial fluxes increasing shallow sea floor area and increased accommodation space accompanying sea level rise allowedmore efficient burial ofmarine organic matter with the preferential removal of 12c from the marine carbon reservoir during sea level fall reduced seafloor area marine erosion of previously deposited sediments and exposure of basin margins led to reduced organiccarbon burial fluxes and oxidation of previously deposited organic matter causing falling 13c values additionally drowning of carbonate platforms during periods of rapid sea level rise may have reduced the global inorganic relative to the organic carbon flux further enhancing 13c values while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition variations in nutrient supply changing rates of oceanic turnover and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon isotope ratios

the evolution time scale of macro tidal estuaries examples from the pacific rim the evolution of shallow macro tidal estuaries is a process that has been taking place since the last glaciation it is site specific and dependent on tides wave climate and relative fluvial dominance it is suggested that because of the increased efficiency of the tidal pumping effect with decreasing water depth these estuaries are geomorphologically unstable and may evolve much faster in the future than in the past as a result of human disturbances in the catchment principally the damming of rivers and increasing erosion from poor land use practices these estuaries may become further destabilised by a sea level rise

tidal creek extension and saltwater intrusion in northern australia low lying holocene coastal plains supporting freshwater wetlands are often close to or even below the level reached by the highest tides the vulnerability of such freshwater systems to saltwater intrusion will increase should the sea level rise as a consequence of global warming in areas with a large tidal range one of the main processes inducing a reversion to saltwater influence is likely to be the rapid extension of tidal creek systems this is demonstrated with an example from the coastal plains of the mary river in northern australia where tidal creek systems have extended more than 30 km inland in 50 years invading freshwater wetlands and destroying associated vegetation over an area of at least 17000 ha networks have grown at an exponential rate through a combination of headward extension along main channels and tributary development large tidal range very small elevational differences over the plains the presence of incompletely infilled paleochannels and uncontrolled feral buffalo have been major factors contributing to the rapid rate of expansion

sedimentation elevation and marsh evolution in a southeastern australian estuary during changing climatic conditions mangrove and salt marsh vertical accretion and surface elevation change was measured at kooragang island within the ramsar listed lower hunter estuarine wetlands in new south wales australia using surface elevation tables and marker horizons over a ten year period we surveyed mangrove salt marsh and a zone of mangrove encroachment into salt marsh the period of analysis was dominated by el nino drought climatic conditions though included a series of east coast low pressure systems and associated storms over the central coast of nsw in june 2007 the storms may have initially caused scouring of sediments in the mangrove zone followed by significant accretion within both the mangrove and salt marsh during the six months following the storms with most of this accretion corresponding to spring tides several months after the storms these accretion events were not accompanied by an equivalent elevation change and robust elevation trends over the study period in mangrove and salt marsh indicate that the storms may have had little impact on the longer term elevation dynamics within both the mangrove and salt marsh at kooragang island elevation dynamics in these zones appear to be regulated by vertical accretion over longer time periods and modulated by hydrology at shorter temporal scales elevation declined in the mangrove encroachment zone despite continued vertical accretion and we propose that this discrepancy may be associated with expansion of tidal creeks near the zone of mangrove encroachment or loss of salt marsh vegetation this pattern of encroachment is consistent with observations from sites throughout the region and may be related to climatic perturbations el nino southern oscillation rather than directly attributed to the storms

an astronomical time scale for the maastrichtian based on the zumaia and sopelana sections basque country northern spain the rhythmically bedded limestone marl alternations in the coastal cliffs of sopelana and zumaia in the basque country northern spain permit testing and refining of existing maastrichtian chronologies latest cretaceous the recently established astronomical time scale for the late maastrichtian at zumaia is extended into c31n with the integrated stratigraphy of the sopelana section the cyclic alternations of hemipelagic limestones and marls at sopelana show a strong influence of eccentricity modulated precession together the zumaia and sopelana sections span almost the entire maastrichtian and encompass thirteen 405 kyr cycles spanning a total duration of 5 3 myr from the cretaceous paleogene k pg boundary downwards 405 kyr minima in the lithological magnetic susceptibility and reflectance data records are tuned to successive 405 kyr minima in the new la2011 eccentricity solution assuming a k pg boundary age of 65 97 ma we present orbitally tuned ages of biostratigraphic and magnetostratigraphic events whereas the bases of chrons c29r and c30n were reliably established at zumaia and are in good agreement with previous studies new data from sopelana provide a refinement of the basal age of chron c31r additional planktonic foraminifera and calcareous nannoplankton data from zumaia and new calcareous nannoplankton data from sopelana allow for worldwide correlation of the cyclostratigraphy of the basque country supplementary materials a geological map and additional data are available at www geolsoc org uk sup18696