the modern carbonate ramp slope of central west florida abstract a holistic investigation of the modern carbonate ramp slope of central west florida has been completed via analysis of approximately 1 500 km of air gun seismic reflection profiles tied to two drillcores and bottom samples recovered at 92 stations our primary goal has been to characterize modern depositional processes and products to compare and contrast results with modern rimmed platform slopes and to develop a model for application to the rock record the modern depositional environment of the west florida ramp slope was initiated 12 15 ma when depositional style changed from seaward prograding clinoforms to a pelagic slope front fill system bound along the shelf margin by contour parallel flow of the loop current a seaward thickening wedge 0 250 m of late miocene to recent pelagic carbonate ooze has been deposited across antecedent mid miocene topography in general the sea floor dips 1 2 seaward from water depths of about 200 2 000 m and slopes are relatively smooth however contemporary submarine geomorphology is controlled in part by earlier slope failures the primary control of modern sedimentation along the west florida slope is loop current flow which acts as a dynamic oceanographic boundary between outer shelf and upper slope winnows bottom sediments catalyzes early submarine cementation and stimulates pelagic production of calcium carbonate the axis of loop current circulation has also migrated laterally in response to climatically controlled sea level fluctuations which has resulted in a relatively wide 25 km band of winnowed sands and hardgrounds along the shelf margin climatic oscillations have also resulted in cyclic deposition of pelagically derived aragonite pteropods on the ramp slope that is out of phase with bank derived aragonite cycles of rimmed platform slope there are three major facies belts that parallel modern isobaths 1 a hardground facies of intraclastic grainstones and rhodolith rudstones as well as algal ridges along the outer shelf at water depths of approximately 200 400 m 2 a winnowed sand facies of planktonic forams intraclasts glauconite and reworked phosphorite grains as well as deep water coral mounds along the shelf margin at depths of approximately 400 600 m and 3 a bioturbated pelagic ooze facies along the ramp slope at depths of approximately 600 2 000 m these facies patterns geometries and grain types along with a general paucity of sediment gravity flow deposits readily distinguish this carbonate ramp slope from better known rimmed platform slopes of the bahamas

seismic and geologic characteristics of drowning events on carbonate platforms carbonate platform drowning events are recorded in upper jurassic lower cretaceous carbonates of the baltimore canyon area offshore united states east coast and lower miocene carbonates of the pearl river mouth basin offshore people s republic of china cursory examination of seismic data from both areas would indicate that the platforms fit the classic definition of a drowning unconformity however detailed lithologic and paleontologic data indicate that the depositional erosional hiatuses vary widely in each area from 0 25 m y in the baltimore canyon area to a condensed section with no hiatus in the pearl river mouth basin the sedimentary sequence produced during drowning the drowning sequence in both areas is gradational with underlying shallow platform carbo ates and in some places overlying deeper marine limestones and shales the generalized facies models proposed for drowning events suggest that they may appear as instantaneous or gradual changes in geologic and seismic data however high resolution seismic data across the baltimore canyon and pearl river mouth basins show that some drowning sequences may be masked on conventionally processed seismic sections because of this resolution problem a distinction should be made between seismically and geologically defined unconformity surfaces the geologic characteristics of drowning events on carbonate platforms include a gradational lower and sometimes upper contact chemical sedimentation glauconite phosphate open marine shelf sediments and a variable hiatus at the upper boundary late growth shelf margin reefs also can be a diagnostic feature of drowned platforms seismic characteristics include horizontal to sub horizontal basinal marine onlap basin parallel reflector continuity above the carbonate sequence boundary and downlap of later highstand units evidence from platforms adjacent to continental margins baltimore canyon indicates that drowning occurs in a step wise fashion advancing more or less symmetrically across the platform from shelf to nearshore environments data from isolated open ocean atolls pearl river mouth basin indicate that they respond differently to drowning showing an asymmetric decrease in shallow platform environments as drowning occurs proper recognition by a geoscientist of the seismic and geologic characteristics of drowning events can lead to better reservoir and seal estimates and the correct reconstruction of the depositional tectonic and eustatic histories of an area

trace fossils biology and taphonomy 1990 special topics in palaeontology 3 280 pp e17 95 pbk e40 00 hbk unwin hyman london isbn 004445 6867 pbk 3035 hbk

aptian lower albian serdj carbonate platform of the tunisian atlas development demise and petroleum implication abstract in this paper we present an updated biostratigraphic evaluation of the serdj formation of the tunisian atlas newly collected ammonites combined with available biostratigraphic data allowed the establishment of a new and robust stratigraphic framework for this well known formation for the first time the characterization of the mellegueiceras chihaouiae zone has permitted the specification of the aptian albian transition this study reveals an early albian age for the top of the serdj formation that includes the main reservoir flow unit which is producing oil in both onshore and offshore tunisia outcrop data analysis has revealed nine transgressive regressive cycles within the aptian early albian carbonates during early aptian the carbonate deposition occurred in deep marine settings that gave way to shallow open shelf carbonates deposition during the late aptian early albian these successions provide evidences enabling their correlation with the third order global depositional sequences detected in the sedimentary basins of the tethyan domains regional surface to subsurface stratigraphic correlation based on seismic and wire line logs enabled 1 a reliable correlation between the stratigraphic elements of the buried successions with those of the serdj formation 2 the characterization of the platform basin transition domain and 3 the verification of the hypothesis that the serdj formation carbonates constitute the surface analogue of the subsurface oil field reservoirs the detailed conceptual stratigraphic model suggests that the serdj platform developed diachronous its demise occurred in the early albian and not during the aptian albian transition as previously believed the hydrocarbon productive reservoirs developed during the regressive phases especially in the up dip settings of the platform where dolomitization greatly enhanced the reservoir quality

morphology faunas and genesis of ordovician hardgrounds from southern ontario canada abstract we have used associations of different microfacies to define facies or microfacies associations which form reasonably well defined sequences which we infer from analogies with recent and ancient carbonate environments to have been deposited in a shelf environment characterized by small scale topographic differentiation into shoal slope and basinal environments shoal environments are characterized by typically cross bedded well sorted bioclastic sands with intershoal areas consisting of interbedded bioclastic sands and heavily bioturbated finer grained carbonates slope and basinal environments are typically represented by proximal and distal cycles respectively these we compare with deposits of carbonate ramp bypass channels and with the more thoroughly studied deep water clastic submarine fans many of the strong variations in environmental energy in these proximal and distal cycles can be attributed to migration of channels on the fans and the effect of funnelling of storm surges down the channels although hardground morphology and faunas are mostly related to local effects such as intensity of scouring time of exposure topographic differentiation of the surface and other factors differing hardground types tend to be found in different environments smooth and rolling hardgrounds occur in the deeper distal environments where the beds were subject to only slight scour and often limited exposure before renewed sedimentation hummocky and undercut hardgrounds are characteristic of the middle parts of proximal cycles where they developed marginally to the main bypass channel and in intershoal areas both these areas are sites of intermittent sedimentation and moderate turbulence where cemented beds may be exposed for some time in environments optimal for attached benthos these hardgrounds usually contain the most diverse hardground biotas pebbly and reworked hardgrounds occur in coarse basal units of proximal cycles which are interpreted as the grain flow fillings of the central parts of bypass channels though isolated examples occur in intershoal areas and in the higher parts of proximal channels these hardgrounds contain low diversity faunas reflecting the stresses imposed by intermittent or constant abrasion though some contain more diverse faunal assemblages formed after redeposition

linking hydrological infinite slope stability and land use change models through gis for assessing the impact of deforestation on slope stability in high andean watersheds in the ecuadorian andes episodic slope movements comprising shallow rotational and translational slides and rapid flows of debris and soil material are common consequently not only considerable financial costs are experienced but also major ecological and environmental problems arise in a larger geographical area sediment production by slope movement on hillslopes directly affects sediment transport and deposition in downstream rivers and dams and morphological changes in the stream channels in developing countries world wide slope movement hazards are growing increasing population pressure and economic development force more people to move to potentially hazardous areas which are less suitable for agriculture and rangelands this paper describes the methods used to determine the controlling factors of slope failure and to build upon the results of the statistical analysis a process based slope stability model which includes a dynamic soil wetness index using a simple subsurface flow model the model provides a time varying estimate of slope movement susceptibility by linking land use data with spatially varying hydrologic soil conductivity evapotranspiration soil wetness and soil strength properties the slope stability model was applied to a high andean watershed gordeleg catchment 250 ha southern ecuadorian andes and was validated by calculating the association coefficients between the slope movement susceptibility map of 2000 and the spatial pattern of active slope movements as measured in the field with gps the proposed methodology allows assessment of the effects of past and future land use change on slope stability a realistic deforestation scenario was presented past land use change includes a gradual fragmentation and clear cut of the secondary forests as observed over the last four decades 1963 2000 future land use change is simulated based on a binary logistic deforestation model whereby it was assumed that future land use change would continue at the same rate and style as over the last 37 years 1963 2000 c 2002 elsevier science b v all rights reserved

global distribution of late paleogene hiatuses six global late paleogene hiatuses pha to phe have been identified from deep sea sequences these hiatuses occurred at the middle late eocene boundary late eocene eocene oligocene boundary late early oligocene late oligocene and oligocene miocene boundary horizons paleodepth distribution of hiatuses shows hiatus maxima characterized by major mechanical erosion below 4800 m at mid depth between 2000 and 3000 m and in shallower water above 1600 m paleodepth the geographic distribution and paleodepth of these hiatus maxima suggest that flow paths of major water masses and currents are the principal cause widespread short hiatuses due to carbonate dissolution or nondeposition occurred primarily during global cooling trends or climatic instability and appear to correlate to sea level transgressions or onlap sequences these hiatuses may have been caused by basin shelf fractionation of carbonates

diagenetically enhanced bedding in argillaceous platform limestones stratified cementation and selective compaction a field and petrographic study has been made of 34 massive beds in argillaceous limestones of open marine platform facies in the u k lithologies include grainstones packstones wackestones and lime mudstones the rocks are of silurian carboniferous and jurassic ages additional information was obtained from other limestones in the u k the u s a canada and continental europe the beds are parts of sequences composed of couplets of strata fissile limestones alternating with hard limestones in the fissile limestones the effects of mechanical compaction and pressure dissolution have been concentrated whereas in the hard limestones they are minimal or absent bedding planes visible in outcrop are diagenetic in origin and lie in the middle parts of the fissile limestones where compaction has been most severe the features produced by pressure dissolution are dissolution seams and fitted fabric there are no stylolites the original carbonate sediments were bioturbated and any structures produced by flowing water were destroyed the vertical distribution of the bedding planes bears no relation to primary depositional bedding planes which are rare or absent it is inferred that the strata which were to become the hard limestones were selectively cemented before mechanical compaction had been completed thenceforth mechanical compaction and then pressure dissolution were concentrated in the less cemented strata these became the fissile limestones pressure dissolution acted late in the diagenetic history and provided only an insignificant part if any of the carbonate for cementation it is concluded that the orientation of beds couplets is parallel to successive sea floors and that the sediments that eventually became single beds accumulated synchronously similar couplets in platform limestones of the mississippian and pennsylvanian of the u s a extend over thousands of square kilometres the signal that controlled the initial selective cementation must have been widespread and synchronous and also syndepositional in its timing but otherwise cannot be further defined on the basis of the data so far collected the presumed order of events was 1 accumulation of carbonate sediment terrigenous clay and organic matter 2 hydrodynamic reworking and bioturbation the latter finally overprinting the former 3 selective cementation of the more carbonate rich strata yielding couplets each consisting of a relatively well cemented stratum and a poorly cemented stratum 4 mechanical compaction concentrated in the less cemented strata 5 pressure dissolution concentrated in the same strata

morphological and sedimentological responses of small stream channels to extreme rainfall and land use in the darjeeling himalayas abstract three pairs of small fourth to sixth order catchments approximately 5 80 km2 draining the margin of the darjeeling himalayas into the piedmont were selected for a comparison of the land use impact on the morphology and sedimentology of their stream channels each pair experienced similar annual rainfall and comprised similar metamorphic bedrock steep topography and brown soils the members of each pair contrast with respect to their land use structure as they comprise large forest cover forest 90 and a significant contribution of agricultural land with tea plantations forest

late paleoproterozoic sedimentary rock hosted stratiform copper deposits in south china their possible link to the supercontinent cycle giant sedimentary rock hosted stratiform copper ssc deposits commonly occur in rift environments tem porally coincident with the breakup of the rodinia and pangea supercontinents however whether or not such deposits have also formed during the breakup of the paleo proterozoic columbia supercontinent is not well known a group of dolostone hosted cu deposits in late paleoproter ozoic rift related sedimentary sequences of the dongchuan group south china form one of the largest ssc districts in the world being one of the largest ssc deposits in the region the yinmin deposit has stratiform cu orebodies intruded by dolerite dykes one dyke has a sims zircon u pb age of 1 701 28 ma slightly younger than the ore hosting strata with a zircon u pb age of 1 742 13 ma for a tuff unit six chalcopyrite and bornite separates from strat iform orebodies contain highly radiogenic os and extremely low common os and yield a weighted mean re os model age of 1 666 82 ma and a 187 os 187 re errorchron age of 1 585 100 ma the present zircon u pb and sulfide re os ages thus constrain the timing of the mineralization at 1 700 ma the yinmin deposit and by inference other ssc deposits in the region arguably represent a large scale ssc mineralization event during the late paleoproterozoic the formation of these deposits was coeval with the initial breakup fragmentation of the columbia supercontinent this study highlights the temporal and likely genetic links between large sized ssc deposits and the supercontinent cycle

dynamics of tethyan carbonate platforms tethyan carbonate platforms are relatively short lived depositional systems which were born developed died and sometime resurrected in a tectonically active area in contrast with pericratonic platforms which are generally huge in size hundreds of kilometers across and show wide facies belts very gentle slopes ramps and transitional boundaries tethyan carbonate platforms are smaller tens of kilometers and have steep slopes generally faulted boundaries and abrupt facies changes it appears clear that the overall control on these two contrasting systems is the geodynamic milieu relatively stable in the first case where eustatic oscillations and long term subsidence are probably the main dictators quite dynamic and aggressive in the second one where carbonate platforms developed through the entire geodynamic spectrum rifting transtension transpression and collision of the wilson cycle primary controls on tethyan carbonate platforms appear to be tectonics most important and eustatic sea level oscillations which determine their emplacement growth and decay their overall shape and architecture are a function of these factors secondary factors affecting tethyan carbonate platform evolution are physiography oceanographic conditions and biology as a function of geologic time especially across the mesozoic tertiary boundary facies and facies distribution and to a lesser extent their shape are controlled by thesemore variables less

equatorial pacific seismic reflectors as indicators of global oceanographic events the origin of a series of regionally correlatable seismic horizons in the neogene sediments of the central equatorial pacific is examined through seismic modeling and the detailed analyses of stratigraphic and physical property relationships in deep sea drilling project cores these regionally traceable reflectors are synchronous the younger reflectors are the direct result of carbonate dissolution events the older ones of stratigraphically selective diagenetic processes the changes in ocean chemistry associated with these events appear to be linked to global reorganizations of surface and bottom water circulation patterns the most dramatic of which are associated with reorganizations of north atlantic bottom waters these deepwater seismic horizons appear to correlate with the major events on the relative sea level curve of vail et al for the neogene

a scenario of mesozoic cenozoic ocean circulation over the blake plateau and its environs after the continental breakup of north america africa and europe a sluggish wind driven circulation gyre probably formed in the juvenile north atlantic basin surface flow in the western atlantic ocean during the early cretaceous likely was northward along the seaward edge of an extensive reef that flourished offshore of north america sometime during the late cretaceous the surface circulation in the gulf of mexico had evolved into a clockwise rotary pattern as the exchange of water with the pacific ocean diminished by latest cretaceous time a vigorous easterly current flowed through the suwannee strait of southern georgia and northern florida injecting copious amounts of water and sediment into the western blake plateau basin this flow pattern apparently persisted into paleocene time during late paleocene and early eocene time strong northerly flow through the straits of florida and across the blake plateau was established this represented the onset of gulf stream circulation over the blake plateau the position of the gulf stream shifted repeatedly across the northern and central plateau during the tertiary and quaternary periods the westernmost track was located along the inner blake plateau parallel to the florida hatteras slope the easternmost track was 500 m lower bathymetrically and crossed the central plateau and continental slope just north of the blake spur the gulf stream apparently shifted in response to changes in water depth on the blake plateau that accompanied global fluctuations of sea level during rises of sea level the gulf stream drifted westward until it impinged on the florida hatteras slope and outer shelf during lowerings of sea level the gulf stream was deflected progressively eastward across the central plateau by the charleston bump a prominent bathymetric bulge of the northern blake plateau

planform channel dynamics along the ningxia inner mongolia reaches of the yellow river from 1958 to 2008 analysis using landsat images and topographic maps channel planform dynamics were analyzed for the ningxia inner mongolia reaches of the yellow river map data were analyzed by means of gis and used to determine the planform characteristics and changes in width sinuosity and shoreline migration rates between 1958 and 2008 the study was based on topographic maps of 1958 and 1967 which had been derived from aerial photos and a field survey and from satellite imagery of 1977 1990 2000 and 2008 the channel planform dynamics were determined by comparing sequential changes in the position of the shorelines in these years sinuosity adjustments were small during the study range 1 34 1 45 the initial sinuosity 1 45 in 1958 gradually decreased to 1 34 in 1990 and then increased to 1 40 in 2008 channel contraction had been the dominant planform process but periodic floods resulted in channel expansion 1958 1990 the river s channel area expanded substantially from 1958 to 1990 by 42 1 then sharply contracted from 1990 to 2000 by 45 8 with no subsequent changes the bank erosion and accretion rates were severe the mean erosion rates ranged from 30 7 to 68 3 m year on the left side and 27 1 to 58 3 m year on the right side the mean accretion rates ranged from 44 4 to 68 3 m year on the left side and 30 5 to 60 4 m year on the right side the mean channel midline shifted by 57 8 m toward the right from 1958 to 2008 the mean channel midline moved 4 8 m to right from 1958 to 1967 54 3 m to the left from 1967 to 1977 44 2 m to the right from 1977 to 1990 64 3 m to the right from 1990 to 2000 and 2 8 m to the right from 2000 to 2008

condensation processes in shallow platforms abstract sequence stratigraphy allows elucidation of the time space relationships of deposits in sedimentary basins however the relative distribution of unconformities and condensed sections can neither be used as diagnostic criteria for particular palaeogeographic settings nor as indicators of maximum regional transgressions condensation processes also occur in the shallowest portions of platforms and during maximum regression episodes three separate processes of condensation are here distinguished stratigraphic sedimentary and taphonomic these three categories of condensation can be used to analyze patterns of sediment distribution and also to estimate lateral and vertical variations in sedimentation rates contrary to the usual interpretation the maximum values of rate of sedimentation and degree of accommodation of sediments as well as the highest relative sea level occur in the lowest levels of the shallowing upward sequences the distinction between these condensation processes allows one to predict that the degree of sedimentary and stratigraphic condensation will be higher towards the distal portions of the platforms whereas the stratigraphic condensation processes without sedimentary condensation will show the maximum intensity and frequency in the shallowest portions of the platforms

style of atlassic tectonic deformation and geodynamic evolution of the southern tethyan margin tunisia the structure of the southern atlas fold and thrust belt of tunisia was investigated using new geologic mapping seismic reflection data together with the construction of a balanced cross section the structural architecture of the tunisian foreland consists in a mixed tectonic style with deep seated basement faults shallower decollements within sedimentary cover and salt diapirism the restoration of the cross section shows a surface shortening of 8 1 km similar to 7 3 sequential restoration of the balanced cross section has been permitted to decipher the structure and evolution of the southern tethyan margin of tunisia structural geometry and orientation of the pre existing permian to cretaceous extensional structures controlled subsequent contractional deformation within the sedimentary cover during the shortening this inherited tectonic framework controlled the development of ene trending thrust related anticlines such as the orbata and chemsi structures nw trending lateral ramp such as the gafsa and fejej faults and diapir structures as the beidha anticline the inversion of the margin can be correlated with the onset of the convergence between africa and eurasia the first phase of the orbata thrusting growth might occur in late cretaceous continuous inversion of the margin occurred during the eocene and mainly during the late miocene to present day this study underlines the predominant role of inherited basement structures acquired during the evolution of the southern tethyan margin and their influence on the geometry of the atlassic thrust belt this structural analysis provides new perspectives for future hydrocarbon exploration in this poorly explored region c 2015 elsevier ltd all rights reserved

recent geomorphological evolution of a natural river channel in a mediterranean chilean basin abstract in this paper we analyse the recent geomorphological evolution of the river nuble an unmodified wandering river in the mediterranean region of chile highlighting the relation between the observed hydroclimatic trends in the region and the morphology of the river the work documents the recent changes 2003 2016 in channel morphology i e narrowing simplification vegetation encroachment and in particular how the river has progressively reduced its geomorphic activity during the last decade changes have been detected using aerial imagery and quantified by means of a series of channel form indices that allow tracking the geomorphological evolution of an 8 km river segment the catchment has experienced a clear decrease in the frequency and magnitude of flood events although this fact is not fully supported by a generalized reduction in the analysed rainfall series we relate the observed river relaxation and the associated channel changes with the reported period of low hydroclimatic activity which follows a humid period that occurred in the pacific region during the 1970s and 1980s connected to the pdo pacific decadal oscillations that particularly affected the northern and the central parts of chile altogether this resulted in generalized river stability and a simplification of the drainage pattern of the channel in absence of river training practices and other major changes in the catchment the reduction of formative discharges appears thus to be the main control of the recent evolution of this gravel bed river

coarse sediment connectivity in river channel systems a conceptual framework and methodology identification of coarse sediment connectivity down river channel systems is important for understanding the linkages between river reaches the influence of sediment sources on channel morphology and the mechanisms and liability to propagation of morphological change a conceptual framework is developed in which several types and degrees of connectivity are proposed it is hypothesised that sediment connectivity varies with sediment sources and with stream competence to transport the coarse fractions a method of identifying the status of reaches is developed based on field mapping of morphology and sedimentology the analysis is exemplified by two channels one an ephemeral channel in se spain the other a perennial channel in nw england questions arise over whether reaches that lack channel stores transfer coarse sediment three scenarios are suggested 1 lack of flux due to lack of competence of the reach 2 flushing through of sediment due to high competence and 3 potential transport of coarse sediment but exhaustion or lack of availability changes in connectivity will take place over different time scales depending on the nature of exchange and time scales of storage short term variations in connectivity can be identified by repeated mapping

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

sediment flux dynamics as fingerprints of catchment rehabilitation the case of western rift valley escarpment of northern ethiopia variability in supply and entrainment of stream bedload particles during storm events is an important hydrogeomorphologic response of steep mountain streams to land management in their catchments because of difficulties in its measurement and absence of accurate measuring equipment bedload transport in mountain streams is however poorly understood this study focuses on analyzing bedload supply and entrainment in 11 streams of sloping 27 65 catchments 0 4 25 km2 in northern ethiopia which have experienced severe deforestation and degradation processes until the first half of the 1980s and considerable rehabilitation thereafter field measurements of the median diameter of the 10 coarsest bedload particles max10 moved in each event n 332 and stream bed particle sampling were carried out in three rainy seasons 2012 2014 event peak discharges were calculated from daily measurements by 11 crest stage gauges using manning s equation percentages of land cover classes in the catchments were detected from high resolution 0 6 m google earth imagery 1 february 2014 morphometric characteristics of the catchments were computed from an aster digital elevation model and topographic maps hydraulic competence analysis for entrainment of the average max10 was carried out using peak discharge stream power and critical shear stress approaches the supply of max10 was positively related to scar density on the surrounding slopes r2 0 50 p 0 05 and catchment area r2 0 36 p 0 05 while negatively related with total forest cover r2 0 63 p 0 05 or vegetation cover r2 0 58 p 0 05 a multiple regression analysis showed that 98 of the variability in max10 is explained by scar density and catchment area entrainment of max10 was positively related to peak discharge qp r2 0 60 p 0 01 stream power r2 0 71 p 0 01 strickler s roughness sn r2 0 86 p 0 01 and critical shear stress c with reference to d50 r50 r2 0 96 p 0 01 and with reference to d84 r84 r2 0 93 p 0 01 the relationships between event max10 and event qp in each catchment were also used to extrapolate the peak discharges that would have prevailed in the first half of the 1980s and the results showed huge reductions in peak discharges p 0 01 as a result of the reforestation interventions overall this study demonstrates that i the supply of bedload in steep tropical mountains is determined negatively by forest or vegetation cover and positively by the presence of scar networks in the sloping parts of the catchments and catchment size ii entrainment of the coarsest bedload particles is determined positively by peak discharge stream power stream bed roughness and most strongly by critical shear stress and iii in steep mountain streams where direct measurement of bedload movement is difficult yet simple in situ measurement of the coarsest bedload particles max10 supplied and entrained in each event helps for understanding the dynamics of sediment flux in relation to catchment rehabilitation

spatial temporal evolution of the distribution pattern of river systems in the plain river network region of the taihu basin china abstract understanding the spatial temporal distribution characteristic and evolution tendency of river systems is important in integrated river basin management in this paper six indicators were adopted to describe the physical characteristic of river systems the spatial temporal evolution of the distribution pattern of river systems in the plain river network region of the taihu basin prnrtb during the 1960s 2000s was analyzed using exploratory spatial data analysis esda and the gravity centre model the impacts of urbanization were then investigated results indicated that the global distribution patterns of box dimension and river density were all statistically significant spatially clustered and river sinuosity was partially spatially clustered while water surface ratio main river area length ratio and river development coefficient were not spatially clustered moreover the water surface ratio was the most stable parameter box dimension was also relatively stable parameter but the others were unstable meanwhile the mutual transformations of hot and cold spots of river systems especially water surface ratio river development coefficient and river sinuosity were frequent the hot spot regions were mainly located in the northeast region in addition most gravity centres migrated gradually from southeast to northwest with low distance except those of river development coefficient and river density these aforementioned differences were caused by the rapid urbanization based on the integrated river basin management suggestions for prnrtb the river density box dimension and river sinuosity should be maintained and restored across the whole watershed and the river conservation and restoration should focus on countermeasures against the reduction of river development coefficient and main attention should be paid on the river systems conserving and restoring in haiyan and haining in southeast prnrtb

eoalpine and mesoalpine tectonics in the southern alps according to structural and stratigraphic data eoalpine and mesoalpine tectonics can be clearly recognized in the southern alps and distinguished from the better known neoalpine deformation

late cenozoic slip on the talas ferghana fault the tien shan central asia although cenozoic crustal shortening and thickening by thrust faulting have built the present tien shan active right lateral shear on the northwest trending talas ferghana fault appears to be the most rapid localized deformation in the belt ephemeral stream valleys have been offset right laterally tens of metres new and published radiocarbon dates of organic material deposited in depressions blocked by offset ridges place upper bounds on the average holocene slip rate at 18 localities uncertainties allow 14 upper bounds to overlap the range of 8 16 mm yr and 95 confidence limits on such bounds at 11 sites are entirely within this range we infer that the rate of 10 mm yr is not simply an upper bound but applies to the late holocene epoch although the bounds on rates permit more rapid slip in the northwest than the southeast they do not place a useful constraint on variations in slip rate along the fault offsets of paleozoic facies boundaries imply a total right lateral shear of 180 250 km but early cretaceous sedimentary rock appears to have been offset only 60 10 km published paleomagnetic declinations of cretaceous miocene rock demonstrate 20 30 of counterclockwise rotation of the ferghana valley which lies just west of the talas ferghana fault with respect to stable parts of eurasia and 20 11 with respect to the central tien shan east of the fault these declinations are consistent with a maximum northwestward translation of 70 210 km of the ferghana valley at the talas ferghana fault and therefore with a similar maximum horizontal shortening across the chatkal ranges which lie between the ferghana valley and the kazakh platform estimates of crustal thickness beneath the chatkal ranges however permit only 60 100 km of cenozoic shortening if 100 km of slip on the talas ferghana fault accumulated at a constant rate of 10 mm yr it would imply an initiation of slip more recently than ca 10 ma long after india collided with the rest of eurasia

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

sedimentary hiatuses as indicators of fluctuating oceanic water masses a new model the upper and sometimes lower boundaries of deep sea disconformities recognized as sedimentary hiatuses at ocean drilling sites are shown to be diachronous the age depth relationships of these hiatuses are used in conjunction with the geographical location of sites relative to individual water masses in order to explain the formation of hiatuses as the product of interaction between fluctuating oceanic water masses and the sea floor the fluctuations in the water masses are related to the glacial history of antarctica the method used is a departure from a traditional approach in which deep sea hiatuses were considered to have no diachronous component and were viewed as the products of instantaneous regional or global events sedimentary hiatuses have commonly been identified in deep sea cores recovered by the deep sea drilling project dsdp and the ocean drilling program odp the disconformity associated with a hiatus has three components firstly an upper boundary which represents a point in time when sedimentation recommenced secondly a lower boundary that is the product of either erosion i e of no temporal significance or non deposition i e of potential temporal significance and thirdly the time interval between these two boundaries termed intra hiatus in this paper earlier studies of hiatuses and hiatus forming events have been used to infer the influence of climatic e g keller barron 1987 and or tectonic e g watkins kennett 1972 changes on the development of erosive oceanic watermasses hiatus distributions have been interpreted as having ocean wide e g davies et al 1977 keller barron 1987 or even

the sediment delivery problem abstract the linking of on site rates of erosion and soil loss within a drainage basin to the sediment yield at the basin outlet and improved knowledge and representation of the associated processes of sediment delivery represent a major research need within the field of erosion and sedimentation and also an important scale problem in drainage basin studies this paper reviews the limitations of the sediment delivery ratio concept by considering the problems of temporal and spatial lumping and its blackbox nature some recent advances in our understanding of the sediment delivery system and its modelling are described and the lack of detailed empirical investigations is highlighted the significance of recent concern for the role of sediments in the transport of nutrients and contaminants to sediment delivery studies is introduced and the need for further work in this field is emphasised

morphological changes of gumara river channel over 50 years upper blue nile basin ethiopia summary in response to anthropogenic disturbances alluvial rivers adjust their geometry the alluvial river channels in the upper blue nile basin have been disturbed by human induced factors since a longtime this paper examines channel adjustment along a 38 km stretch of the gumara river which drains towards lake tana and then to the blue nile over a 50 years period agriculture developed rapidly in the catchment and flooding of the alluvial plain has become more frequent in recent times the objectives of this study were to document the changes in channel planform and cross section of the gumara river and to investigate whether the changes could have contributed to the frequent flooding or vice versa two sets of aerial photographs 1957 and 1980 were scanned and then orthorectified recent channel planform information was extracted from spot images of 2006 and google earth channel planform and bed morphology vertical changes were determined for these nearly 50 years period the vertical changes were determined based on aggradation along a permanent structure historic information on river cross sections at a hydrological gauging station and field observations the results indicate that the lower reach of gumara near its mouth has undergone major planform changes a delta with approx 1 12 km 2 of emerged land was created between 1957 and 1980 and an additional 1 km 2 of land has been added between 1980 and 2006 the sinuosity of the river changed only slightly negatively 1 1 i e meandering decreased for the period from 1957 to 1980 and positively 3 0 for the period 1980 2006 comparison of cross sections at the hydrological gauging station showed that the deepest point in the river bed aggraded by 2 91 m for the period 1963 2009 the importance of sediment deposition in the stream and on its banks is related to land degradation in the upper catchment and to artificial rising of lake tana level that creates a backwater effect and sediment deposition in gumara river direct anthropogenic impacts irrigation activities and building of dykes along the river banks have contributed to the huge deposition in the river bed where the abstraction of water for irrigation is intensive seepage water through the banks has contributed to river bank failure in general this study showed that changes to the planform at the mouth of the river and to the riverbed level are substantial moreover the study indicated that the flood carrying capacity of the gumara river channel has diminished in recent times

geology geochemistry and genesis of the cretaceous and paleocene sandstone and conglomerate hosted uragen zn pb deposit xinjiang china a review abstract the uragen zn pb deposit in wuqia county xinjiang china is hosted in sandstones and conglomerates of the lower cretaceous kezilesu group and argillaceous dolomite of the paleocene aertashi formation in the kashi sag northwestern tarim basin the deposit is characterized mainly by low grade zn pb 3 wt and large tonnage 3 mt metals in the southern ore zone potentially 10 mt metals for the whole deposit with an average zn pb ratio of about 5 8 the orebodies are tabular and stratiform mainly distributed in a syncline the ores are characterized by disseminated sulfides with minor massive veinlet patchy structures and fine grained locally colloform and framboidal textures the main primary metallic minerals are sphalerite galena pyrite and marcasite and minor supergene minerals include smithsonite hydrozincite anglesite calamine jarosite and limonite the ore minerals mainly occur as replacement of cements matrix and framework grains of the host rocks and as open space filling to a lesser extent based on the fact that orebodies straddle across a hiatus between the lower cretaceous and paleocene host rocks and on the replacement and open space filling textures and structures the mineralization is interpreted to be epigenetic the tightly clustered pb isotopic values of the main stage ore minerals 206 pb 204 pb ranging from 18 608 to 18 663 207 pb 204 pb from 15 619 to 15 669 208 pb 204 pb from 38 677 to 38 839 suggest that a single source supplied the metals whereas the wide range of s isotopes 34 s from 27 9 to 14 6 vcdt indicates multiple sources of reduced sulfur including those from thermal sulfate reduction tsr and bacterial sulfate reduction bsr the organic matter in the ores is characterized by relatively low concentrations of saturated hydrocarbons high concentrations of aromatic hydrocarbons asphaltenes and non hydrocarbons and low maturity compared to that in the host rocks and equivalent strata away from mineralization both hydrocarbons in the ores and host rocks show little biodegradation these characteristics of organic matter suggest that the site of mineralization was buried to significant depths and heated to above 80 c before the charging of hydrocarbons thus non development of biodegradation that some of the hydrocarbons were consumed in mineralization thus decreased maturity probably used as reducing agents for sulfate reduction in situ and that bacteria derived sulfur in the ores was not generated in situ mineralization probably resulted from mixing of a metal rich fluid with multiple fluids carrying reduced sulfur from different sources including some reduced sulfur from in situ tsr however it remains unclear whether the metal carrying fluid was derived from a near surface groundwater system and flowed downward to the site of mineralization at burial conditions or was derived from deeper parts of the basin and flowed up to the site of mineralization as part of a hydrothermal system the distinction of the two models requires a better understanding of the thermal profile across the deposit

formation of sedimentary rock hosted stratiform copper deposits through earth history sedimentary rock hosted stratiform copper deposits form by movement of oxidized copper bearing fluids across a reduction front that results in the precipitation of copper sulfides large scale production of such oxidized fluids as well as the formation of mobile hydrocarbons oil has probably been common since the formation of the first red beds in the paleoproterozoic and deposits of this type occur in rocks from the paleoproterozoic to the tertiary however supergiant deposits are currently recognized in only three basins the paleoproterozoic kodaro udokan basin of siberia the neoproterozoic katangan basin of south central africa and the permian zechstein basin of northern europe the paucity of data regarding the udokan deposit makes understanding this system difficult in terms of earth history events both the neoproterozoic and the permian were times of supercontinent breakup with major landmasses at low latitudes this global tectonic framework favored the formation of failed rifts that subsequently became significant intracratonic basins with basal synrift red bed sequences overlain by marine and or lacustrine sediments and in some basins located at low latitudes by thick evaporitic strata the intracratonic setting of these basins allowed the development of a hydrologically closed basinal architecture in which highly oxidized and saline moderate temperature basinal brines were produced that were capable of supplying reduction controlled sulfide precipitation over very long time periods tens to hundreds of millions of years the length of time available for the mineralizing process may be the key factor necessary to form supergiant deposits however examination of the absolute ages for the kupferschiefer zechstein basin and katangan deposits allows speculation that other factors may also have been important both the neoproterozoic and permian were times of major glacial events glaciation may also be conducive for the formation of supergiant sediment hosted stratiform copper deposits glacial periods correspond to magnesium and sulfate rich oceans that could have been responsible for additional sulfur in basinal brines developed during evaporite formation and would then be available during the long mineralization process

atmospheric circulation upwelling and organic rich rocks in the mesozoic and cenozoic eras abstract by using the basic principles of atmospheric circulation and analogies from present circulation patterns it is possible to construct qualitative atmospheric circulation models on paleogeographic maps the wind patterns predicted by these models then serve as the basis for predicting the locations of ancient upwelling zones atmospheric circulation and upwelling models for seven geologic stages in the mesozoic and cenozoic were constructed and the distribution of the upwelling zones compared with the distribution of organic rich rocks for all time periods together the correlation was statistically significant when the individual time periods were analyzed separately the following pattern emerged significant correspondence between upwelling zones and organic rich rocks in the triassic middle early cretaceous to late cretaceous and middle paleogene to neogene no significant correspondence was found for the intervening times upwelling does not account for all organic rich rocks so called anoxic oceanic events and transgressions play an important role in their deposition it is suggested that upwelling contributes significantly to the pattern of organic rich rock distribution and is important in determining organic facies

middle miocene oceanographic event in the eastern gulf of mexico implications for seismic stratigraphic succession and loop current gulf stream circulation analysis of 1 500 km of high resolution single channel air gun seismic reflection profiles correlated with two drill cores demonstrates that the central west florida carbonate ramp slope experienced an oceanographic event in the middle miocene that resulted in a major stratigraphic break or succession of depositional sequences during the long term eustatic sea level rise in the early to middle miocene carbonate shelf margin deposition was characterized by seaward prograding sigmoidal clinoforms that built both laterally and vertically shelf margin sediments were relatively fine grained and rich in dolomite total organics and clay minerals approximately 12 15 m y ago tectonically controlled oceanographic closure of the isthmus of panama and or increased climatic gradients resulted in an intensification of oceanic circulation increased flow velocity of the loop current truncated antecedant clinoforms along the mid miocene shelf margin as the loop current for the first time became a dynamic oceanographic barrier to off shelf sediment transport carbonate deposition along the west florida slope changed dramatically from a series of prograding clinoforms to a pelagic slope front fill system bounded on its landward margin by contour current flow of an invigorated loop current shelf margin sediments presently represented as a condensed sequence became more carbonate rich coarser grained lower in organic content and depleted in dolomite our results suggest that oceanographic events can generate major seismic stratigraphic breaks that result in the succession of depositional sequences and systems along continental margins and that they may be as important as eustatic oscillations our data also suggest that modern loop current gulf stream circulation was initiated in the middle miocene controlled by tectono oceanographic and or climatic processes the challenge now is to identify seismic stratigraphic scale oceanographic events in the rock record differentiate them from eustatic responses and evaluate their paleoenvironmental significance

receiver functions for the tien shan analog broadband network contrasts in the evolution of structures across the talasso fergana fault we determined the structure of the crust beneath the central and western tien shan by analyzing broadband 1 20 s analog seismograms of converted p sv phases generated by earthquakes at teleseismic distances and recorded by 14 seismograph stations the one dimensional structures that best explain the waveforms reveal pronounced differences in crustal velocities east and west of the talasso fergana fault specifically the transition zone between the crust and the mantle east of the fault is about 2 times broader than that west of the fault also velocities at depths between 10 and 35 km are about 10 lower in the east although the depth range of these lower velocities is not well resolved the talasso fergana fault is an important boundary for other observables in addition to the structural discontinuities observed at the surface the areas east of the talasso fergana fault are associated with abnormally low mantle velocities outcrops of basalt low q and short wavelength variations in anisotropy integrating these observations we interpret the broad mantle gradient as being due to vertical intrusions of mantle material into the lower crust likewise the low velocities in the midcrust could be thermally induced or due to the introduction of magmatically derived fluids the gross contrast in structure east and west of the talasso fergana fault could reflect a contrast in the dynamics of mountain building in these two regions we postulate that while crustal shortening is the dominant mechanism controlling topography west of the talasso fergana fault vertical uplift caused by a mass deficiency in the upper mantle may contribute significantly to the generation and maintenance of the high elevations east of the fault

synsedimentary submarine slope failure and tectonic deformation in deep water carbonates cow head group western newfoundland the cow head group interpreted as a southeast dipping base of slope carbonate apron contains intraformational truncation surfaces and slide masses synsedimentary shear zones are formed 1 below intraformational truncation surfaces 2 in the basal parts of slide masses and 3 in the shallow subsurface because of downslope creep shear zones are characterized by a variety of synsedimentary deformation structures limestones are subject to folding brecciation rotation of fragmented beds and the development of fitted lenticular bedding in the interbedded shales there is both disruption of fine laminations and small scale isoclinal folding and faulting outcrops characterized by these features and the lack of truncation surfaces or slide masses may reflect minor downslope creep the presence of truncation surfaces slide masses and shear zones indicates deposition on an unstable sloping surface the recognition of intraformational truncation surfaces and slide masses usually requires extensive str

accommodation and supply a dual control on stratigraphic sequences abstract it is widely accepted that both eustatic and tectonically controlled regional changes of sea level have contributed to the record of stratigraphic sequences i suggest that environmental change be added as a third autonomous control sedimentologic principles clearly indicate that sequences and their systems tracts are controlled by the interplay of two rates the rate of change in accommodation space available for sedimentation and the rate of sediment supply sea level has direct control on accommodation but its influence on sediment supply is remote and easily overshadowed by environmental factors for instance the record of the most recent sea level rise is a transgressive systems tract where supply is low it is a prograding highstand systems tract in deltas where the supply is high examples of sequence boundaries generated by changes in sediment supply include tectonically driven shifts in sediment input into basins changes in ocean currents pulsating supply from failure of submarine slopes and drowning of carbonate platforms by environmental stress furthermore the stratigraphic sequences in fluviatile continental basins are physically removed from sea level induced changes in accommodation and must have formed by changes in the rate and pattern of supply subaerial exposure of marine sediments at the sequence boundary is a most important criterion for recognizing sea level cycles as opposed to supply cycles other criteria include downstepping of shelf breaks and characteristic patterns in the spacing of time lines within sequences some third order cycles ca 0 5 3 ma duration meet these criteria others do not cycle stacking patterns and the shifting facies belts on cratons indicate that many second and third order cycles lack pronounced exposure unconformities and represent gradual changes superimposed on more rapid shorter oscillations seismic data yield poor images of these gradational changes because they lack resolution seismic models of outcrops show that near the limits of resolution the seismic tool tends to portray rapid changes in facies and bed thickness i e lateral variations in supply as unconformities seismic unconformities do not necessarily correspond to unconformities in outcrop the succession of stratigraphic sequences is best considered a composite record of sea level and environmental change separating the various controls requires carefully planned experiments work on the oxygen isotope curve another proxy for sea level has set an example in this respect

high frequency moderate to high amplitude sea level oscillations during the late early aptian insights into the mid aptian event galve sub basin spain abstract this paper presents a field based stratigraphic architecture research from the aptian of spain in which high frequency 7 cycles ma moderate to high amplitude 8 127 m sea level oscillations are evidenced by the repeated incision of palaeovalleys in a carbonate platform developed during the late early aptian in a rift setting global eustacy tectonic uplift and mantle dynamic topography are considered as potential mechanisms to explain the observed relative sea level record glacioeustacy is interpreted as the most reliable mechanism to drive the observed sea level oscillations however other mechanisms as oscillations of the groundwater capacity of sedimentary basins and sudden flooding of major a basin as the south atlantic rift are also considered a major cooling event is proposed to occur during the late early aptian as a response to a large scale episode of ignimbritic volcanism increased burial of organic carbon during the aptian oae 1a and a significant demise of carbonate platforms this cooling event is interpreted as the origin for glacioeustatic sea level oscillations during the mid aptian

cretaceous paleogene basaltic rocks of the tuyon basin nw china and the kyrgyz tian shan the trace of a small plume abstract the tuyon basin nw china and the central portion of the kyrgyz tian shan preserve a volumetrically small series of basaltic extrusive and intrusive units emplaced primarily in mesozoic paleogene sedimentary rocks four units from the tuyon basin yield 40 ar 39 ar ages of 67 59 46 and between 110 and 120 ma major and trace element analysis combined with sr nd and pb isotopic data suggest that these units were derived from apparently ocean island basalts oib like mantle melts which have characteristics close to asthenospheric prema mixed with an enriched component in the continental mantle lithosphere or emplaced with some crustal contamination two basalts from kyrgyzstan were also dated by 40 ar 39 ar as 54 ma these results agree with previous k ar analysis which show that most kyrgyz basalts were emplaced during the eocene major element data from the kyrgyz basalts knauf et al 1980 fortuna et al 1994 show strong similarities with the tuyon data suggesting that the more extensive tuyon data can be taken as representative of the entire basaltic suite there is little geological data to support either late cretaceous paleogene rifting or the presence of a large plume beneath the region instead these magmas point to the presence of a small thermally anomalous region in the mantle beneath the central tian shan which might best be described as a small plume which probably rooted at a shallow level in the asthenosphere

paleomagnetism of paleogene basalts from the tien shan kyrgyzstan rigid eurasia and dipole geomagnetic field several conflicting explanations invoking persistent non dipole fields or tectonic motion on various scales were suggested to account for anomalously low paleomagnetic inclinations in cenozoic rocks of central asia in order to better understand this problem we undertook a paleomagnetic study of paleogene basalts from a part of the tien shan close to the china kyrgyzstan border stepwise thermal demagnetization showed that only a single component remanence of reversed polarity is present in these rocks above 200 260 c the overall mean direction of this remanence d 194 6 i 354 0 k95 3 8 n 18 sites agrees well with the eurasian reference directions for the paleogene which is in sharp contrast with most earlier published cenozoic inclinations from central asia which are 20 30 shallower than the expected values good agreement of the reference inclinations and those from basalts rules out models which invoke non dipole fields and or large scale tectonic motions for explanation of the cenozoic inclination anomaly instead a mechanism related to natural remanent magnetization acquisition in redbeds is strongly indicated the above conclusion also implies that the differences between the reference data and measured inclinations in cretaceous redbeds from central asia are also of non tectonic origin and a revision of our views on evolution of this region is required fl 2002 elsevier science b v all rights reserved

the response of soil erosion and sediment export to land use change in four areas of europe the importance of landscape pattern the response of erosion and sediment export to past land use change has been studied in four agricultural areas of europe three of these areas were subject to land abandonment or de intensification and one to intensification of land use practices erosion and sediment yield were modeled using the watem sedem model which combines the rusle equation with a sediment routing algorithm spatial relationships between the rusle c factor i e land use and other erosion and sediment export determining factors slope soil erodibility and distance to rivers were investigated as these account for non linearity in the response of erosion and sediment export to land use change erosion and sediment export have decreased enormously in the de intensified areas but slightly increased in the intensively cultivated area the spatial pattern of land use change in relation to other erosion and sediment export determining factors appears to have a large impact on the response of soil erosion and sediment export to land use change that the drivers of abandonment of arable land and erosion coincide indicates that de intensification leads to a more favourable landscape pattern with respect to reduction of erosion and sediment export this mechanism applies not only within the study areas but also among the european study areas where the process of intensification of some areas and de intensification of others might result in an overall decrease of erosion and sediment yield through time c 2007 elsevier b v all rights reserved

sequence stratigraphy and condensed pelagic sediments an example from the rosso ammonitico veronese northeastern italy abstract correlation between eustatic and sedimentary cycles in the jurassic rosso ammonitico veronese suggests that the existence of a genetic link between them should be explored the red nodular limestones of this formation were deposited on a current swept submarine plateau pertaining to the south alpine passive continental margin in this setting of fault bounded blocks shelf derived sediments were trapped in the intervening troughs and only the very slow particle by particle rain of planktonic organisms took place the corresponding rock bodies typically show frequent omission surfaces of variable range current activity seems to be the prime controlling factor which affects the degree of winnowing early cementation and reworking and is decisive in bringing about all lithologic changes this hydrodynamic effect greatly depends on ocean circulation patterns which in turn are controlled by climatic and sea level changes highstands lead to equable climates and hence to a weak regime of currents impinging on sea bottoms the opposite happens during the following lowstands which reactivate ocean circulation through deteriorated climatic conditions it is envisaged that even though most of the geometric and sedimentologic criteria commonly used on shelf slope sediments are lacking depositional sequences i e physically the stratigraphic record of complete eustatic cycles may be recognized also in condensed pelagic successions they consist of thin rock units deposited during periods of sea level highstand when a slowed down current activity allows the preservation of the pelagic input and are bounded by lowstand induced hard grounds when accelerated winnowing prevent deposition these unconformities consequently don t correlate with condensed sections on shelves

human impact on the environment in the ethiopian and eritrean highlands a state of the art abstract this review analyses the environmental evolution of the ethiopian highlands in the late quaternary the late pleistocene 20 000 12 000 14c years bp was cold and dry with 1 low lake levels in the rift valley 2 large debris fans on the flanks of lake abhe basin and 3 the blue nile transporting coarse bedload then a period with abundant and less seasonal rains existed between 11 500 and 4800 14c years bp as suggested by increased arboreal pollen high river and lake levels low river turbidities and soil formation around 5000 4800 14c years bp there was a shift to more arid conditions and more soil erosion many phenomena that were previously interpreted as climate driven might however well be of anthropic origin thick sediment deposits on pediments as well as an increase of secondary forest scrub and ruderal species in pollen diagrams are witnesses of this human impact one important aspect of the late quaternary palaeoenvironment is unclear changes in nile flow discharges and rift valley lake levels have been linked to changes in precipitation depth most authors do not take into account changes in land use in the highlands nor changes in the seasonality of rain both of which can lead to a change in runoff coefficients tufa and speleothem deposition around 14 000 years ago tend to indicate that at the end of the last glacial maximum lgm conditions might have been wetter than generally accepted the most important present day geomorphic processes are sheet and rill erosion throughout the country gullying in the highlands and wind erosion in the rift valley and the peripheral lowlands based on existing sediment yield data for catchments draining the central and northern ethiopian highlands an equation was developed allowing to assess area specific sediment yields sy 2595a 0 29 n 20 r 2 0 59 where sy area specific sediment yield t km 2 year 1 and a drainage area km2 with respect to recent environmental changes temporal rain patterns apart from the catastrophic impact of dry years on the degraded environment cannot explain the current desertification in the driest parts of the country and the accompanying land degradation elsewhere causes are changing land use and land cover which are expressions of human impact on the environment deforestation over the last 2000 3000 years was probably not a linear process in ethiopia studies on land use and land cover change show however a tendency over the last decades of increasing removal of remnant vegetation which is slowed down or reversed in northern ethiopia by a set aside policy ongoing land degradation requires urgent action at different levels of society soil and water conservation swc structures are now widely implemented local knowledge and farmer s initiatives are integrated with introduced swc techniques at various degrees impact assessments show clear benefits of the soil conservation measures in controlling runoff and soil erosion in high rain areas runoff management requires greater emphasis during the design of soil conservation structures in such areas investment in swc might not be profitable at farm level although benefits for society are positive this pleads in favour of public support the present land degradation in the ethiopian highlands has a particular origin which includes poverty and lack of agricultural intensification causes of these are to be found in the nature of past and present regional social relations as well as in international unequal development this review strengthens our belief that under improved socio economic conditions land husbandry can be made sustainable leading to a reversal of the present desertification and land degradation of the ethiopian highlands

microfacies biostratigraphy and geochemistry of the hemipelagic barremian aptian in north central tunisia influence of the oae 1a on the southern tethys margin upper barremian lower upper aptian hemipelagic deposits of the hamada formation in the djebel serdj area north central tunisia were studied in detail with regard to microfacies biostratigraphy 13 c stratigraphy and geochemistry our data provide insights into the palaeoenvironmental evolution and sea level fluctuations of the tunisian shelf the unusually expanded deposits consist of mud wacke and packstones which reflect mid and outer ramp depositional environments planktonic foraminifer and 13 c stratigraphy allowed us to establish a detailed time frame and the recognition of the lower aptian oceanic anoxic event 1a oae 1a as well as time equivalent deposits of shallowmarine carbonate platform drowning based on our microfacies studies we subdivide the studied sections into four genetic intervals a pre oae 1a interval an oae 1a and platform drowning equivalent interval and a post platform drowning interval we present a 3rd order sea level curve for the tunisian shelf deriving from the results of our microfacies studies deposits of the oae 1a in the sections investigated are characterised by bioclastic wacke and packstones with high abundances of poorly preserved radiolarians and moderately to well preserved planktonic foraminifers suggesting a transgression and an eutrophication of the upper water column scarceness of benthic macrofossils low abundances of small benthic foraminifers and ostracods possibly suggest dysoxic conditions at the seafloor mudstones of the platform drowning time equivalent deposits directly overlying the oae 1a are partly showing a pronounced drop in carbonate content and are scarce of macrofossils 2008 elsevier b v all rights reserved

slope channel decoupling in wolumla catchment new south wales australia the changing nature of sediment sources following european settlement within a few decades of european settlement channel incision transformed discontinuous river courses throughout wolumla catchment on the south coast of new south wales australia the development of continuous channels greatly increased sediment delivery from the catchment this paper documents the character timing and proportion of sediment sourced from upland valley fills channel expansion sites and gully networks volumes of material transferred from these sources are compared with estimates of sediment eroded from hillslopes and the movement of sediment off the slopes to the valley floor is assessed although disturbance of slopes resulted in significant movement of materials most of this material has been stored on slope in trapped tributary fills and along lower order drainage lines the slopes are effectively decoupled from the channel sediment accumulation in farm dams over the past few decades has been negligible around 75 of the total volume of material released from creeks in wolumla catchment since 1865 i e 5500 103 m3 has been derived from channel incision into valley fills at the base of the escarpment sediment flushing occurred within a few decades of catchment disturbance bedrock confinement in the middle and lower catchment resulted in very efficient downstream transfer of materials although gully networks and channel expansion sites have released a relatively small volume of material these sources are the greatest contemporary source of sediment in wolumla catchment

effects of check dams reforestation and land use changes on river channel morphology case study of the rogativa catchment murcia spain this work has been financially supported by the project respuesta hidrologica y geomorfologica de los sistemas fluvio torrenciales afectados por proyectos de restauracion hidrologico forestal en cuencas semiaridas del sureste peninsular of the fundacion instituto euromediterraneo de hidrotecnia ce the first author was financially supported by an i3p postdoc contract csic ce and a ramon y cajal contract from the education and science ministry spain gonzalo g barbera also was supported by i3p postdoc contract

the role of nutrient availability in bioerosion consequences to carbonate buildups abstract zooxanthellate organisms which are among the major carbonate producers on coral reefs are highly adapted to nutrient deficient conditions and tend to be outcompeted by filamentous or fleshy algae if nutrients are abundant reef dwelling bioeroding organisms on the other hand seem to increase in abundance with increasing availability of nutrient and food resources maximum rates of calcium carbonate production in a reef system are comparable in magnitude to maximum rates of bioerosion the dynamic interplay between accretion destruction of coral reefs is therefore likely to be strongly influenced by nutrient availability nutrient availability may also influence development of carbonate facies in reef systems that develop in oligotrophic waters skeletal sands and framework should dominate carbonate buildups in systems that develop in mesotrophic waters enhanced bioerosion should reduce much of the skeletal material to carbonate muds increasing the prevalence of mud rich facies eutrophic conditions should result in bioeroded hardgrounds and carbonate depositional hiatuses when carbonate accumulation rates fail to equal or exceed rates of local relative sea level rise reefs drown bored and lithified pavements with crusts of ferromanganese oxides phosphates or glauconite often separate shallow reef from overlying deeper water deposits nondeposition bioerosion and evidence for low redox potentials at the sediment water interface all implicate excess nutrient availability as a factor in reef drowning some carbonate depositional hiatuses and bioerosional surfaces are local phenomena evidence of responses to local increases in nutrient availability resulting from submergence of soils runoff or topographic upwelling others appear to reflect regional or worldwide events because many carbonate producing organisms have life history strategies specialized to nutrient deficient conditions they are unable to compete when nutrients become plentiful events that triggered ocean turnover or sharp increases in the rate of deep ocean circulation would have increased sea surface nutrient availability worldwide such eutrophication could have caused widespread extinctions in reef communities because eutrophication promotes bioerosion details of the fossil records of those events are probably lost in bioerosional hiatuses

influence of vegetation distribution on sediment yield in forested marly gullies abstract the cover provided by forest vegetation makes it possible to fight erosion efficiently furthermore vegetation barriers can also play a major role by trapping eroded sediments and thus vegetation located downslope of a gully can be important the objective of this study is to highlight the role of vegetation distribution in a marly gully in reducing sediment loss at the outlet to do this sediment yield in gullies with similar geological and geomorphological components but with different vegetation cover and distribution was studied for 2 years sediment traps installed at gully outlets permitted the distinction of active gullies from inactive ones the results show that gully activity is not correlated with the percentage of total vegetation cover but with the percentage of cover of low vegetation in the gully floor this is due to sediment trapping processes and highlights the importance of the spatial distribution of forest vegetation in reducing sediment yield at the gully outlet thus gullies with similar total vegetation cover can have very different activities and inactive gullies exist that are only partially covered with vegetation inactive gullies with as low as 33 vegetation cover occur where vegetation is mainly present in the gully floor the results also show that above 50 cover of low vegetation in the gully floor as a percentage of the gully floor surface gullies are generally inactive

pressure solution features in a shallow buried limestone abstract three distinct types of pressure solution features are found in the alpena limestone devonian michigan stylolites solution seams and fitted fabric texture the style of pressure solution is different in grainstones packstones and wackestones the difference is interpreted to be the result of preferential cementation of the grainstones well cemented grainstones typically have stylolites whereas solution seams and fitted fabric texture are more common in poorly cemented grainstones packstones and wackestones pressure solution occurs at e80 percent of the lithologic transitions this is probably due to competency contrasts between adjacent units that material dissolved at pressure solution surfaces is not locally reprecipitated is indicated by porous allochems which abut against stylolites and units of abundant intergranular pressure solution fitted fabric texture which lack cement the style of pressure solution in the alpena limestone and its relationship to cementation is also observed in the tuscarora quartz arenite silurian appalachian basin

integrating channel form and processes in the gangetic plains rivers implications for geomorphic diversity abstract geomorphic diversity at a variety of spatial and temporal scales has been studied in the western ganga plains wgp india to isolate the dominating factors at each scale that have the potential to cause major geomorphic change the ganga river and its major tributaries draining the wgp have been investigated in terms of longitudinal cross sectional and planform morphology to assess the influence of potential controls such as climate geology topography land use hydrology and sediment transport these data were then compared with those from the rivers draining the eastern ganga plains egp to understand the geomorphic diversity across the ganga plains and the causal factors our investigations suggest that in channel geomorphic diversity over decadal scale in rivers with low width to depth w d ratio is caused by periodic incision aggradation but it is driven by channel avulsion in rivers characterized by high w d ratio similarly planform reach scale parameters such as sinuosity and braid channel ratio are influenced by intrinsic factors such as changes in hydrological conditions and morphodynamics cutoffs small scale avulsion that are in turn impacted by natural and human induced factors finally we have isolated the climatic and hydrologic effects on the longitudinal profile concavity of alluvial trunk channels in tectonically stable and unstable landscapes we demonstrate that the rivers flowing through a tectonically stable landscape are graded in nature where higher discharge tends to create more concave longitudinal profiles compared to those in tectonically unstable landscape at 103 year scale

subsidence and sedimentation on jurassic passive continental margin southern alps italy the southern alps of italy preserve a tectonically intact array of jurassic facies that record the evolution of a part of the margin of the apulian plate from its ancestral beginnings in a complex of permian and triassic rifted continental basins through the initial stages of breakup and stepwise foundering of a carbonate platform breakup was accompanied first by the rapid accumulation of thick prisms of carbonate turbidites in newly formed fault troughs then as the new ligurian oceanic basin began to open farther west and as subsidence gradually slowed accumulation of a succession of slowly deposited biogenous pelagic sediments recorded not only the increasing depths of the seafloor but also fluctuations in oceanographic conditions of fertility carbonate dissolutio levels and the strength of bottom currents estimates of the history of seafloor depths based on a simple subsidence law of the form subsidence k age 12 provide a basis for the construction of a set of curves showing the changing depths of significant carbonate dissolution surfaces during the jurassic in this region the rapid 1 km deepening of the compensation depth for calcite during the late jurassic may be due to a change in regional oceanic vertical circulation patterns from upwelling fertile silica rich carbonate dissolving to downwelling less fertile silica poor carbonate preserving

stratigraphic completeness of carbonate dominated records from continental interiors versus continental margins stratigraphic thinning occurs via condensation and omission at multiple scales abstract over phanerozoic time scales stratigraphic records from continental interiors or cratons are dramatically thinner and are generally assumed to be relatively incomplete with more numerous and longer duration hiatuses compared to records from more rapidly subsiding continental margins however this assumption need not be true for the shorter time scales i e several 106 years and shorter over which accumulation of the preserved stratigraphic record on the continental interior actually takes place this study compares carbonate dominated sedimentary records from the devonian continental interior iowa and continental margin nevada to evaluate whether the continental interior record is 1 miniaturized i e thinner but equally complete 2 comparable in thickness and quality where the sedimentary record is preserved but certain portions of the record are notably absent i e omitted or truncated or 3 so invariably preserved that equivalent stratigraphic packages cannot be recognized compared to the continental margin record this study finds that fourth to fifth order cycles in iowa are on average approximately half as thick and half as numerous compared to the continental margin of nevada moreover the stratigraphic record on the continental margin of nevada is dominated by cycles that are composed of tidal flat and shallow subtidal lithofacies capped by simple flooding surfaces and exhibit catch up or keep up depositional styles the continental interior record in iowa is dominated by cycles that are composed of subtidal lithofacies capped by a range of bounding surfaces and exhibit catch down or give up depositional styles these findings suggest that the thin record in iowa is largely a result of low sedimentation rates associated with suppressed carbonate production in this epeiric sea setting rather than minimal subsidence rates and an increased potential for subaerial exposure and associated loss of record

dome and basin refolding and transpressive inversion along the karatau fault system southern kazakstan the karatau fault system of southern kazakstan forms a crustal scale zone of strike slip dominated transpressional tectonics which has undergone multiple phases and styles of deformation during a protracted history of reactivation from the neoproterozoic to the cenozoic ductile fabrics associated with dextral kinematic indicators are present in amphibolites along the main karatau fault the ages of the possibly ophiolitic protoliths and the ductile fabrics are not well constrained but they are plausibly pre late riphean late ordovician granites stitch thrusts and folds which deform late riphean to llanvirn clastics preserved beneath a regional late devonian angular unconformity this deformation may be related to a contemporary continental collision ne of the karatau two phases of late palaeozoic deformation affected the upper devonian and carboniferous carbonate succession the first phase is related to sinistral transpression along the karatau fault system the second to dextral transpressional reactivation the combination of these events produced a regional scale dome and basin fold interference pattern similar polyphase deformation appears to have affected large areas of central asia and was possibly caused by the late palaeozoic orogenies at asia s margins such as the accretion of tarim and the east european craton to asia and the closure of the kazakstan orocline normal faults in the karatau are related to the formation of the leontiev graben south turgay basin and the yarkand fergana basin in the early to mid jurassic during renewed dextral slip along the karatau talas fergana fault late cenozoic deformation is minor and resulted in the uplift and incision of a cretaceous palaeogene peneplain without a major tectonic overprint reversals in the sense of strike slip dominated transpressive deformation across major fault systems results in transpressive inversion this represents an ideal process with which to generate overprinting orthogonal fold systems resulting in classic dome and basin interference patterns on a regional scale

yangtze river of china historical analysis of discharge variability and sediment flux hydrological records covering a 100 year period from the upper middle and lower yangtze river were collected to examine the temporal and spatial distribution of discharge and sediment load in the drainage basin the yangtze discharge as expected increases from the upper drainage basin downstream only an estimated 50 of the discharge is derived from the upper yangtze with the rest being derived from the numerous tributaries of the middle and lower course however the distribution of sediment load along the yangtze is the reverse of that observed for discharge with most of the sediment being derived from the upper basin a dramatic reduction in sediment load by 0 8 108 tons year occurs in the middle yangtze because of a marked decrease in slope and the change to a meandering pattern from the upper yangtze rock sections considerable siltation also occurs in the middle yangtze drainage basin as the river cuts through a large interior dongting lake system sediment load in the lower yangtze while significantly less than that of the upper river is somewhat higher than the middle yangtze because of additional load contributed by adjacent tributaries a strong correlation exists between the discharge and sediment load along the yangtze drainage basin during the dry season as lower flows carry lower sediment concentration during the wet season a strong correlation is also present in the upper yangtze owing to the high flow velocity that suspends sand on the bed however a negative to poor correlation occurs in the middle and lower yangtze because the flow velocity in these reaches is unable to keep sand in suspension transporting only fine grained particles downstream hydrological data are treated for 30 years 1950 1980 when numerous dams were constructed in the upper yangtze drainage basin at yichang and hankou hydrological stations records revealed a decreasing trend in annual sediment load along with slightly reduced annual discharge at the same stations this can be interpreted as the result of water diversion primarily for agriculture sediment load at datong further downstream is quite stable and not influenced by slightly reduced discharge furthermore sediment concentration at the three hydrological stations increased which can be attributed to sediment loss in association with intensifying human activity especially in the upper drainage basin such as deforestation and construction of numerous dams mean monthly sediment load of these 30 years pulses about 2 months behind discharge implying dam released sediment transport along the entire river basin during the high water stage

the influence of landscape connectivity and landslide dynamics upon channel adjustments and sediment flux in the liwu basin taiwan catchment scale analyzes of spatial and temporal variability in landscape connectivity are critical considerations in appraisals of landscape evolution and disaster mitigation in tectonically active mountain belts such as taiwan this study uses historical aerial photographs flow discharge and seismic data to analyze landslide changes and channel adjustments over a 30 year period in the liwu basin recurrent earthquakes and typhoon events trigger frequent landslide activity channel adjustment and sediment reworking in this system spatial variability in magnitude frequency relations of hillslope valley floor lateral and upstream downstream longitudinal connectivity during the study period are shown to reflect annual reworking in source and accumulation zones while partly confined valleys in the mid catchment area trap sediment behind landslide induced dams that are formed and breached on an approximately decadal basis this promotes partial longitudinal connectivity in these areas landscape responses to disturbance events were especially pronounced following combinations of seismic and typhoon events prior to the 1998 and 2005 images although single high magnitude events and series of moderate events affect patterns of landscape connectivity in the liwu basin residence times for sediment storage are very short in this highly connected river system where confined valley settings extend virtually to the coast copyright 2014 john wiley sons ltd

latitudinally different responses of tethyan shoal water carbonate systems to the early aptian oceanic anoxic event oae 1a ocean wide anoxic events represent intensively investigated anomalies in the global carbon cycle most previous research has focussed on hemipelagic and pelagic settings and on the relationship between black shale deposition and carbon isotope excursions the study of ocean wide anoxic events and coeval shallow water settings is now increasingly seen as an interesting complementary approach but one that is not without problems whereas platform drowning characterizes the early aptian of the northern tethyan margin lithocodium bacinella rich facies and ongoing shoal water sedimentation at the southern tethyan margin oman bears important information on potential causes of carbon cycle perturbations the present paper seeks to test the supra regional relevance of the oman data by investigating coeval central tethyan limestones three lower aptian shoal water sections in istria croatia deposited on the isolated adriatic carbonate platform are investigated applying chemostratigraphy carbon and strontium and detailed sedimentological analysis the focus is on peritidal to lagoonal facies characterized by mass occurrences of lithocodium bacinella an enigmatic microencruster community lithocodium bacinella facies occurs predominantly in layers ranging from one to several centimetres in stratigraphic thickness with several layers merging to metre thick packages growth fabrics within the layers include oncoidal morphotypes lumps interconnected patches and columns layers and rare nodular to massive bindstone facies these growth patterns show a remarkable regional extent and consistency over study sites distributed several kilometres apart this widespread distribution suggests that specific lithocodium bacinella morphotypes might serve as regional stratigraphic markers the high resolution carbon isotope chemostratigraphy presented here is based on pristine rudist shells and matrix micrite samples and calibrated against strontium isotope data obtained from screened rudist low mg calcite the chemostratigraphic data are consistent with existing biostratigraphic data and place the studied strata at the onset of early aptian oceanic anoxic event 1a moreover results indicate the near coeval nature of lithocodium bacinella bloom facies in istria and oman the outcomes of this study point to latitudinally different responses of tethyan shoal water carbonate systems platform drowning versus lithocodium bacinella blooms to the ocean wide anoxic event 1a

coupling between hillslopes and channels in upland fluvial systems implications for landscape sensitivity illustrated from the howgill fells northwest england abstract the sensitivity of upland fluvial systems depends on the magnitude and frequency of sediment and flood producing events modified by the internal coupling characteristics of the system this paper assesses the role of hillslope channel coupling for the sensitivity of upland geomorphic systems using evidence from a 30 year monitoring programme of geomorphic change in the carlingill valley howgill fells northwest england in the hillslope zone there is little sediment supply to the stream system locally slope failures occur in response to extreme events six such events in 30 years within the ca 6 km 2 carlingill valley in the footslope coupling zone basally induced gullies are major sediment sources to the stream sediment production events occur ca 30 times per year feeding sediment to basal debris cones stream floods which can entrain these sediments occur once every ca 2 5 years stream channel morphology is adjusted to this regime downstream of gullies channels are wide and braided elsewhere they are narrow and single thread as the gullies develop however this coupling weakens and the eroding slopes eventually stabilise by revegetation over the 30 year monitoring period there has been a progressive trend towards gully stabilisation and an associated reduction in channel instability massive destabilisation may occur in response to rare extreme flood events such an event return period 100 years occurred in neighbouring langdale and bowderdale valleys in june 1982 that event destabilised the system causing slope failures fan deposition and in some places a switch in channel style to wide braided channels since 1982 there has been a progressive recovery by slope stabilisation and single thread sinuous channels have become reestablished a different style of extreme event occurred in carlingill in october 1998 in response to the wettest week in the 30 year period a slope failure fed debris flows 400 m downslope almost coupling with the channel system future climatic change could render the system prone to destabilisation through either extreme flood events or through major slope failures

river channel response to short term human induced change in landscape connectivity in andean ecosystems the drainage basin of the deleg river 88 km 2 located in the southern ecuadorian andes was studied to assess the geomorphic and hydrologic response of a fluvial system to human induced environmental change in its contributing area historical data on land use channel morphology and sedimentology were collected based on a spatial analysis of aerial photographs 1963 1995 and a field survey 2002 analysis of channel cross sectional profiles and sedimentological data revealed a major change in morphology and sedimentology of the deleg river during the past four decades i the active river channel narrowed by over 45 ii the riverbed incised on average by over 1 0 m and iii the median grain size of the bed surface decreased from 13 2 cm to 4 7 cm the spatial pattern of land cover within the deleg catchment also changed considerably highly degraded agricultural land in the low lying areas was abandoned and partially afforested for timber and wood production whereas secondary upland forest was increasingly cleared for expansion of cropland and pastures notwithstanding large changes in the spatial organization of land use within the catchment the overall land use did not change significantly during the past four decades this suggests that the response of the deleg river to land use change not only depends on the overall land use change but also on the spatial pattern of land use cover change within the catchment although forestation and regeneration of bare gully slopes and floors throughout the catchment only represented a minor part of the total land use change these land use cover changes had a major impact on the hydrological and sediment connectivity in the landscape c 2005 elsevier b v all rights reserved

geomorphic and tectonic evolution of the ecuadorian andes abstract in early miocene times the cordillera did not exist and the pacific ocean reached the oriente in the middle miocene the uplift of an elongated swell consisting of palaeozoic and older rocks created the eastern cordillera decollements were activated diverging away from the eastern cordillera in the eastern trench located approximately in correspondence with the present day interandean depression many thousands of meters of sediments were deposited a planation surface was created at the end of lower pliocene from the costa to the oriente graded to sea level later ignimbric flows covered much of the planation surface uplift brought the planation surface to 3500 4000 m the interandean depression bounded by normal faults was created during the upper pliocene and large strato volcanoes erupted at this time the volcanic activity contributed to the filling of an accumulation plateau preserved today in many parts of the interandean depression the creation of the interandean depression is the result of lateral spreading activated as a consequence of uplift of the cordillera in the middle and late pleistocene the cordillera and the accumulation plateau were mostly affected by downcutting with minor episodes of accumulation during the cold phases

discontinuities in carbonate successions identification interpretation and classification of some italian examples abstract the growing use of unconformities as bounding surfaces for new types of stratigraphic units seems not to be matched by a corresponding effort on process oriented researches on unconformities themselves this paper aims at giving a contribution to classification and understanding of discontinuities in carbonate successions from the outcrop perspective based on some italian examples a number of integrated criteria geometry sedimentology diagenesis biostratigraphy is proposed to recognise stratigraphic breaks old terms are discussed and sometimes redefined while some new terms are introduced the term discontinuity surface ds is proposed as a general one to indicate any stratigraphic interface where an interruption of sedimentation can be proved a ds can be characterized as a firm ground or a rock ground depending on its coherence at the moment of the renewal of sedimentation polygenic and simple omission surfaces are separated within firm grounds if a recognizable gap is either present or not a third kind of firm ground revealed only by biostratigraphy has been called hidden discontinuity surface two categories of rock grounds are also distinguished hard grounds and inherited rock grounds if respectively generation of the ds and or deposition of the overlying sediments took place in the same environment of the underlying sediments or not a genetic interpretation for each type of discontinuity is proposed the largest variety of ds s occurs in pelagic sediments some discontinuities hard grounds and simple omission surfaces are attributed to increased bottom current activity during sea level falls others polygenic omission surfaces and hidden ds s are interpreted as submarine slide scars either with or without the overprint due to exposure on the seafloor the ds s separating different facies e g platform and pelagic ones are interpreted to be due to tectonics the relevance of the recognized ds s to sequence stratigraphy is briefly discussed

sulfide bearing veinlets throughout the stratiform mineralization of the central african copperbelt temporal and genetic implications the central african copperbelt of zambia and democratic republic of congo along with its broad time equivalents in botswana and namibia the kalahari copperbelt is the world s largest sediment hosted stratiform copper province the economically dominant stratiform copper cobalt or silver mineralization accepted by many as at least partly early diagenetic in origin is ubiquitously accompanied by sulfide bearing quartz carbonate veins and veinlets traditionally this veining is considered to be the product of either metamorphic lateral secretion or discrete late diagenetic to synorogenic mineralization events this view is challenged because identical sulfide assemblages and textures characterize both the disseminated and accompanying veinlet mineralization throughout the zoned sulfide assemblages that constitute many of the stratiform orebodies a situation that is taken to imply contemporaneity of the two styles consequently during the mineralization the siltstone sandstone or dolomite host rocks must have been sufficiently competent to undergo widespread brittle fracturing implying that the disseminated mineralization cannot have been introduced by passive fluid infiltration during early diagenesis this conclusion is further supported by the local occurrence of minor disseminated and veinlet mineralization hosted by mafic sills and dikes both the disseminated and veinlet mineralization styles lack ductile deformation features in many congolese deposits but are variably metamorphosed and deformed in some deposits in zambia botswana and namibia in conjunction these observations suggest that the stratiform copper orebodies were the results of massive saline fluid expulsion by hydraulic fracturing after the mafic magmatism 765 715 ma most probably spanning peak damara lufilian metamorphism and ductile deformation 530 ma and continuing in places until at least 500 ma thus basin inversion contractional tectonism and associated uplift and exhumation and not the earlier extension and rifting seem more likely to have been the ultimate drivers for the fluid mobilization and expulsion

seismic model of a progradational carbonate platform picco di vallandro the dolomites northern italy we present a seismic model of a well exposed carbonate platform to basin transition from the triassic succession at picco di vallandro the dolomites northern italy the core of this model is a detailed lithologic cross section that represents 1500 m of stratigraphic section over a distance of 3 5 km the cross section is based on detailed measured sections photo interpretation and careful projection of surface mapping into the plane of section samples from the measured sections provide control on velocity and density distribution and these data were used to generate an impedance model from the cross section the impedance model was convolved with a zero phase 25 hz peak frequency wavelet to produce the seismic model the results illustrate how the platform to basin transition might be imaged by conventional seismic reflection data how the reflections relate to the distribution of lithology and through going geological surfaces and how constructive and destructive interference and seismic resolution combine to produce individual reflections the picco di vallandro section displays several scales of progradation and retrogradation ranging from stacked buildups that are several hundreds of meters thick to the interfingering of individual beds the seismic model displays this complexity with varying degrees of success the individual buildups are well imaged but as expected smaller features are not as clearly reproduced by the model intermediate scale sections that represent platform retrogradation are shown as surfaces of onlap in the seismic model but field work shows that the platform was still shedding sediment while retreating and that no simple onlap surface exists in the outcropping section a similar lack of stratigraphic resolution is shown by the model at the downlapping clinoforms which do not correspond to iscrete stratal surfaces but to the toe of slope position where major bedding units thin below seismic resolution smaller features such as the position of downslope terminations of carbonate breccia wedges are not resolved by the model toe of slope packages of limestone turbidites are represented only by reflection segments of higher amplitude the decreasing seismic resolution is caused by limited seismic bandwidths and by the effects of constructive and destructive interference interference has the largest effects at the complexly interfingering buildup to basin transition or at the most detailed part of our model an understanding of these types of seismic limitations and their controls is important as we try to extract more and more stratigraphic information from seismic data p

recognition and documentation of depositional sequences from outcrop an example from the aptian and albian on the eastern margin of the wessex basin stratigraphic data relating to the aptian and albian sediments around folkestone in southeast england on the eastern margin of the wessex basin are plotted graphically to illustrate biostratigraphic gaps and condensed intervals these are then used to suggest candidate sequence boundaries notated lg1 4 and gl 3 which are named after the lower greensand and gault the biostratigraphic subzones apparently unrepresented in the area are lg1 obsoletus and bodei lg2 gracite and debile lg3 schrammeni gl bulliensis candidate sequence boundaries g2 cristatum subzone and g3 auritus subzone are erosion surfaces correlating with probable biostratigraphic gaps elsewhere in the basin the age of lg4 is uncertain but must lie within the mammillatum superzone all candidate sequence boundaries correspond closely to those predicted by recent global sea level cycle charts and additionally there is a close match between predicted maximum flooding surfaces and the occurrence of condensed intervals most of the candidate sequence boundaries could have been formed as a result of rapid and at least regionally extensive relative sea level falls but the sedimentological contexts of lg3 and gl suggest that these may have been generated by transgression related sediment condensation the minor sequence boundary in the loricatus zone intermedius subzone illustrated in the cycle charts cannot be unambiguously recognized at outcrop in the folkestone area additional sequence boundaries not shown in the cycle charts may also be present in the wessex basin

depositional bias and environmental change important factors in sequence stratigraphy abstract differences among depositional systems here called depositional bias strongly influence sequence patterns siliciclastics and shallow water carbonates for instance shed most of their sediment during opposite phases of a sea level cycle lowstand shedding and highstand shedding respectively furthermore the two systems generate their own system specific relief on the sea floor disperse their sediment load along different avenues and differ in the way they are deactivated reefs and carbonate platforms can be drowned whereas siliciclastic deposition can be shut off and renewed at any depth as a consequence of these differences pronounced unconformities drowning unconformities develop where carbonate platforms are terminated and buried by siliciclastics the siliciclastic to carbonate transition tends to be more gradual drowned platforms and drowning unconformities appeared world wide in great abundance in the miocene cretaceous valanginian turonian jurassic toarcian and devonian frasnian famennian examples of drowning unconformities interpreted as sequence boundaries include those of the early cretaceous platforms off new jersey and off morocco the mid cretaceous unconformity in the gulf of mexico and miocene unconformities on top of reefs in the far east the eustatic cycles postulated from sequence stratigraphy are a very unlikely cause for the mass drownings of reefs and platforms either the rates of rise are an order of magnitude lower than the growth potential of platforms or cycle amplitudes are too small or the cycles are too short and subsidence too slow to remove platforms permanently from the photic zone the critical element in the mass drowning seems to be environmental stress that reduces the growth potential of carbonate systems thus drowning unconformities demonstrate the importance of environmental change as a control on sequence development other examples of dominantly environment controlled sequences include slope deposits shaped by shifting currents e g florida and blake plateau and basin fills that were controlled by changes in sediment input related to tectonic alteration of the drainage in the hinterland e g gulf of mexico environmental change must be considered as a third independent factor that competes with eustatic and tectonically driven regional changes of sea level for control of sequences the definition of sequences and sequence boundaries should be broad enough to include the possibility of non sea level controls

topography and significance of a basinwide sequence bounding erosion surface in the cretaceous cardium formation alberta canada abstract the cardium formation turonian coniacian upper cretaceous of the western interior seaway alberta contains six marine sandier upward successions bounded by seven basin wide erosion surfaces in the subsurface erosion surface e5 is associated with major oil and gas fields and is penetrated by thousands of wells a topographic map of e5 based on 6126 well logs and over 1100 measured cores shows a series of subparallel elongate highs steps and lows which trend northwest southeast parallel to tectonic trends and to the actively rising cordillera to the southwest the steps are about 10 km apart and the relative relief step to adjacent low is up to 25 m the steps are asymmetrical with a steeper face to the northeast the e5 erosion surface cuts into offshore marine hummock cross stratified sandstones and interbedded mudstones and it records a lowering of relative sea level our interpretation suggests that erosion was in neither a fully subaqueous nor a fully subaerial environment instead it involved relative sea level lowering and subaerial erosion followed by major modification of the landscape during transgressive shoreface erosion at times of relative stillstand during overall transgression gravel was supplied to the shoreface and was reworked a short distance alongshore by waves these conglomerates now form important oil and gas reservoirs the asymmetry of the steps and lows indicates that the originally flat sea floor was tilted northeastward immediately before erosion giving a gradient of about 1 1000 during transgression shorefaces were incised into the tilted surface to form a stepped morphology also during transgression the sea floor was gradually restored to its pre tilting position each of the six marine sandier upward sequences along with the erosion surface at the top occupies an average of 470 000 years and we estimate that transgression took at least 100 000 to 200 000 years

increased terrigenous influx but no drowning palaeoenvironmental evolution of the tunisian carbonate platform margin during the late aptian during the aptian some carbonate platforms of the sub tropical realm for example on the northern tethys margin or in the gulf of mexico were affected repeatedly by severe perturbations in the carbonate production factory and drowning preferentially during global warming events such as the early aptian oceanic anoxic event 1a and a prominent mid late aptian warming interval these platform growth crises have been explained mainly by strongly increased coastal runoff for example siliciclastics and nutrients in combination with pronounced eustatic sea level rises in the last few years increasing evidence suggests that carbonate platforms of lower latitudes were generally less or even not affected by environmental perturbations during these events this raises the question as to the responsible factors that promoted platform growth or decline in different latitudinal areas in this study upper aptian middle gargasian to uppermost clansayesian inner tropical carbonate ramp deposits of the serdj formation at djebel serdj north central tunisia are studied in detail with regard to microfacies lithology biostratigraphy and chemostratigraphy these data allow reconstruction of the palaeoenvironmental evolution of the tunisian carbonate platform margin and investigation of its response to the prominent mid late aptian warming interval the unusually expanded 600 m thick serdj formation consists of limestones marlstones and siltstones suggesting deposition within mid ramp to inner ramp palaeoenvironments deposits of the mid late aptian are represented by quartz rich platform carbonates and siltstones probably resulting from increased coastal runoff on the tunisian shelf as a response to global warming and accelerated water cycling the siliciclastic input was accompanied by elevated nutrient levels as indicated by a partial decline in the abundance of oligotrophic biota and mass occurrences of orbitolines and green algae carbonate platform drowning during the mid late aptian as reported from the sub tropical realm has not been identified a comparison with other tropical river influenced platforms suggests that none of them drowned during the mid late aptian one important reason might be widespread arid to semi arid climatic conditions within lower latitudes during that time promoting platform growth due to comparably low nutrient runoff

synsedimentary slides and bedding formation in apennine pelagic limestones abstract jurassic to lower tertiary pelagic carbonates in the umbria marches apennines of northern peninsular italy are well bedded and synsedimentary submarine slide deposits are common bedding planes were formed by pressure solution during compaction where original rhythmic alternations in clay content were present bedding formed along the clay rich horizons where the original sediments were uniform stylolitic pseudobedding approximately marks paleohorizontal even where true bedding departs from paleohorizontal because of the presence of soft sediment folds deformational facies observed in synsedimentary slides are compared to a conceptual model of a bedding plane glide with a longitudinal sequence of four deformational facies 1 the slide scar where section is missing may be identified if biostratigraphic or magnetostratigraphic zones are missing 2 the stretched rear of the slide is thinned and shows extensional shear joints and sedimentary boudinage 3 the transported but undeformed main body of the slide may be identified paleomagnetically if it has been rotated and the basal shear surface may show deformational structures 4 the shortened front of the slide commonly shows on a small scale the ramp thrusts and folds typical of foreland fold and thrust belts the state of induration of the sediments at the time of movemen is shown by their theological behavior in areas of major subsea relief slides may have moved far enough for the distal parts to lose their coherence and all the transitional stages from a slide to a pebbly mudstone can be identified

catchment scale cumulative impact of human activities on river channels in the late anthropocene implications limitations prospect abstract evidence for the proposed anthropocene epoch in fluvial geomorphology hinges on the influence of human activities relative to natural forcing however research on cause effect understanding in river channel evolution has rarely focused on the cumulative impact of multiple drivers for change limiting insights systematic review of 25 recent studies professing to explain reach scale channel responses to cumulative impacts of human activities and natural forcing over the recent past ca 1880 2005 reveals some consistencies in spatio temporal response across various catchment sizes median 3000 km2 in mostly industrialized nations common drivers for change include changing flood and flow regimes dam construction changing land uses and forest cover bank protection and instream aggregate mining recent channel evolution has predominantly involved narrowing incision and terrace development reduced bed sediment storage lower activity rates and simplified channel geometries rates of channel change frequently peaked 1955 1990 providing some support for the anthropocene great acceleration evidence here suggests that many river systems are now in morphologically novel configurations coinciding temporally with dramatic recent declines in global freshwater aquatic biodiversity sustainable approaches to freshwater management must acknowledge these configurations placing emphasis on process based approaches to river ecosystem health in which sediment cascades are reconceived to reflect altered longitudinal and lateral connectivity however the reviewed studies are driven largely by expert judgment depicting cause effect associations through summary conceptual models based on spatial proximity and temporal synchronicity providing insufficient scientific proof for the anthropocene based on the overwhelming impact of human factors more conclusive cause effect statements will require hypothetic deductive approaches explicit functional criteria and best practice environmental model building geomorphologists should now move beyond the phase of discovery and develop rigorous proofs for cause effect relationships of cumulative impact this may be enhanced by developing an avowedly anthropocene perspective in which rivers are viewed critically as socio biophysical systems co evolving with human activity

the prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models the accuracy of the predictions of distributed hydrological models must depend in part on the proper specification of flow pathways this paper examines some of the problems of deriving flow pathways from raster digital terrain data in the context of hydrological predictions using topmodel distributed moisture status is predicted in topmodel on the basis of spatial indices that depend on flow path definition the sensitivity of this index to flow path algorithm and grid size is examined for the case where the surface topography is a good indicator of local hydraulic gradients a strategy for the case where downslope subsurface flow pathways may deviate from those indicated by the surface topography is described with an example application

contemporary channel changes in the eygues basin southern french prealps the relationship of subbasin variability to watershed characteristics the southern french prealps are sub mediterranean mountains in which forest cover has increased since the end of the 19th century forest development linked with agricultural decline and planned reafforestation has induced a decrease of bedload supply from hillslopes in response to this evolution several channel changes are observed in mountain streams channel narrowing channel degradation and pavement development the intensity of these adjustments differs from one stream to another twenty catchments 10 100 km2 located in the eygues river basin 1150 km2 a tributary of the rhone river are studied to highlight the subbasin variability of channel changes and to give causal interpretations we conducted field surveys and analyzed aerial photographs to characterize present channel morphology and contemporary channel changes and gis was used to quantify morphometry relief land use and geology of the watersheds multivariate statistical analysis determined relations between channel changes and watershed characteristics the potential bedload supply of these mountain streams is controlled largely by watershed morphometry and land use the most active tributaries of the eygues river are characterized mainly by high drainage density and poor vegetation cover linked to agricultural land use

pyrite re os geochronology of the sareke sediment hosted cu deposit xinjiang nw china abstract the sareke cu deposit in the western tarim region xinjiang nw china is hosted in continental sedimentary rocks of the upper jurassic kuzigongsu formation and lower cretaceous kezilesu group stratabound orebodies occur mainly in conglomerate and minor in siltstone both stratabound major and vein type minor ores are composed of chalcocite chalcopyrite bornite and pyrite with minor sphalerite and galena which show a zonation pattern of chalcocite chalcopyrite sphalerite galena pyrite from north to south of sareke carbonation is the most important hydrothermal alteration at sareke and dolomite together with calcite are the dominant gangue minerals six pyrite samples which coexist closely with copper sulfides are re os dated and yielded a re os isochron age of 115 8 4 7 ma and a weighted mean age of 114 3 1 8 ma which constrain the sareke cu mineralization to the late early cretaceous this age is synchronous with the tectonic inversion event and the basaltic magma activities of the tuyon basin which could been sources of dynamics and thermodynamics during the ore forming process this is the first unambiguous evidence for an appreciable copper concentration of mesozoic age and based on this evidence additional mesozoic sediment hosted stratabound copper mineralization event may have occurred elsewhere within basins along the talas fergana fault

channel response to increased and decreased bedload supply from land use change contrasts between two catchments abstract the catchments of pine creek idaho usa 200 km 2 and the drome river in the drome department france 1640 km 2 illustrate contrasting changes in land use bedload sediment production and channel response hard rock mining began in the catchment of pine creek near the end of the 19th century and together with road construction timber harvest and historically heavy grazing of uplands resulted in increased tributary bedload yield increased bedload migrating to the channel combined with removal of large cedar trees on the floodplain resulted in channel instability which propagated downstream over a period of decades on many reaches of pine creek active channel width has increased by over 50 since 1933 over roughly the same time period the drome river catchment was extensively reforested after at least one century of denudation and heavy grazing and numerous check dams were constructed on torrents to reduce erosion as a result the drome river has experienced a reduction in bedload sediment supply since the late 19th century in addition gravel has been extracted from some reaches consequently the channel has degraded and gravel bars have been colonized with woody riparian vegetation channel widths in wide braided reaches decreased from 1947 to 1970 by 60 on pine creek channel instability has resulted in bank erosion exposing contaminated mine tailings and increased flood hazard on the drome river degradation has undermined bridges and embankments and lowered the water table in areas dependent on groundwater for irrigation resulting in loss of 6 million m 3 of groundwater storage since 1960 though they differ in drainage area by nearly an order of magnitude pine creek and the drome river provide an excellent contrast in that they represent two sides of an epicycle of alluvial sedimentation set off in each case by land disturbance in both cases the most recent channel changes though in opposite directions were viewed as negative by river managers on pine creek managers have removed or protected from erosion mine tailings and have attempted to train the stream into a more stable channel and most rock waste piles the principal sediment sources have recently been controlled on the drome river managers have prohibited gravel mining and adopted new policies to permit coarse sediment to migrate through the river system

diagenetic origin of the stratiform cu co deposit at kamoto in the central african copperbelt sediment hosted stratiform ore deposits that underwent metamorphism and orogenesis are interpreted either to have a multiphase origin that might in part predate these events or to be exclusively related to fluid migration during the orogeny this controversy concerns the formation of many world class sediment hosted ore deposits such as in the central african copperbelt here we present re os dating results for disseminated and stratiform cu co sulfide pseudomorphs after anhydrite in nodules and layers from the copperbelt results demonstrate that at least some of the ores formed at around 800 ma during rifting and basin development and thus predate the pan african lufilian orogeny younger re os ages i e between 682 28 and 230 36 ma may be due to the replacement of the early cu co sulfides by younger sulfide phases alternatively these younger ages may result from the disturbance or resetting of the re os system during recrystallization metamorphism or the transition of chalcocite from its high to its low temperature polymorph

vegetation and topographic controls on sediment deposition and storage on gully beds in a degraded mountain area active gully systems developed on highly weathered or loose parent material are an important source of runoff and sediment production in degraded areas however a decrease of land pressure may lead to a return of a partial vegetation cover whereby gully beds are preferred recolonization spots although the current knowledge on the role of vegetation on reducing sediment production on slopes is well developed few studies exist on the significance of restoring sediment transport pathways on the total sediment budget of degraded mountainous catchments this study in the ecuadorian andes evaluates the potential of vegetation to stabilize active gully systems by trapping and retaining eroded sediment in the gully bed and analyses the significance of vegetation restoration in the gully bed in reducing sediment export from degraded catchments field measurements on 138 gully segments located in 13 ephemeral steep gullies with different ground vegetation cover indicate that gully bed vegetation is the most important factor in promoting short term 1 15 years sediment deposition and gully stabilization in well vegetated gully systems 30 of ground vegetation cover 0 035 m 3 m 1 of sediment is deposited yearly in the gully bed almost 50 per cent of the observed variance in sediment deposition volumes can be explained by the mean ground vegetation cover of the gully bed the presence of vegetation in gully beds gives rise to the formation of vegetated buffer zones which enhance short term sediment trapping even in active gully systems in mountainous environments vegetation buffer zones are shown to modify the connectivity of sediment fluxes as they reduce the transport efficiency of gully systems first calculations on data on sediment deposition patterns in our study area show that gully bed deposition in response to gully bed revegetation can represent more than 25 per cent of the volume of sediment generated within the catchment our findings indicate that relatively small changes in landscape connectivity have the potential to create strong positive feedback loops between erosion and vegetation dynamics copyright c 2009 john wiley sons ltd