the soil leakage ratio in the mudu watershed china soil leakage in karst areas is an important geomorphic agent of environmental interest there are several viewpoints concerning soil leakage ratios one viewpoint states that the soil leakage ratio is high in karst regions whereas others consider that it is very low this paper s objective is to describe the soil leakage phenomena qualitatively and quantitatively in the chongqing karst china by conventional methods such as monitoring runoff plots and paint traces drawn on piles and walls found within runoff plots and by measuring the activity of the isotope 137cs at small medium and large spatial scales this paper s results show that soil filled karst cracks occurred at a small spatial scale with soil leakage ratios ranging from about 3 to about 34 at two abandoned quarries and six soil profiles with rock karst crack development the soil leakage ratio was almost zero at the medium spatial scale the soil leakage ratio was 4 50 and the surface soil erosion ratio was 95 50 of the total soil erosion at the large spatial scale it is concluded that soil leakage ratios in the study area were low at a large spatial scale and that cracks in karst were filled with soil at small spatial scales this paper s results indicate that soil leakage phenomena vary depending on the processes acting at the small medium and large spatial scales

a weathering related origin of widespread monazite in s type granites the s type granite suites comprising more than a quarter of the extensively developed granites in the lachlan fold belt australia contain monazite which may be related to the chemical weathering of the sedimentary source rocks we report a process whereby chemical weathering fixes mobile rare earth elements ree in hydrous phosphate phases such as florencite and rhabdophane this material contains up to 50 wt lree and occurs as very small particles 3 m dehydration of these hydrous ree phases during anatexis directly yields monazite the low solubility of phosphorus in s type granite melts inhibits dissolution of both monazite and apatite refractory monazite may be thus entrained and transported in s type granites in a manner similar to processes resulting in inherited zircon since both th and the light ree are major components in monazite materials containing this minute phase may be of widespread geochemical significance in both granites and metamorphic rocks

trace element modelling of pelite derived granites the presence or absence of a vapour phase during incongruent melt reactions of muscovite and biotite together with the composition of the protolith determines the trace element characteristics of the resulting melt provided that equilibrium melting occurs for those phases that host the tracc elements of interest for granitic melts rb sr and ba provide critical constraints on the conditions that prevailed during melting whereas ree are primarily controlled by accessory phase behaviour mass balance constraints for eutectic granites that are formed by the incongruent melting of muscovite in pelites indicate that melting in the presence of a vapour phase will result in a large melt fraction and deplete the restite in feldspar hence the melt will be characterized by low rb sr and high sr ba ratios in contrast vapour absent melting will result in a smaller melt fraction and an increase in the restitic feldspar consequently high rb sr and low sr ba ratios are predicted vapour absent melting will also enhance the negative eu anomaly in the melt granites that result from the incongruent melting of biotite in the source will be characterized by higher rb concentrations than those that result from the incongruent melting of muscovite the himalayan leucogranites provide an example of unfractionated crustally derived eutectic melts that are enriched in rb but depleted in sr and ba relative to their metasedimentary protoliths these compositions may be generated by the incongruent melting of muscovite as a low melt fraction f 0 1 from a pelitic source under vapour absent conditions

microprobe monazite geochronology understanding geologic processes by integrating composition and chronology abstractmonazite is a light rare earth element lree bearing phosphate mineral that is present in a wide variety of rock types has an extremely variable composition reflecting host rock conditions and is a robust geochronometer that can preserve crystallization ages through a long history of geological events monazite crystals typically contain distinct compositional domains that represent successive generations of monazite which in turn can provide a detailed record of the geologic history of its host rocks the electron microprobe can be used to characterize the geometry of compositional domains analyze the composition of each domain and when carefully configured determine the u th total pb age for domains as small as 5 m in width these data allow the monazite to be linked with and place timing constraints on silicate processes in the host rocks current applications span a broad range of geologic processes in igneous metamorphic hydrothermal and sedimentary rocks

incised channels and gully erosion in northern iberian peninsula controls and geomorphic setting abstract gully erosion has scarcely been reported in the cantabrian cordillera northern iberian peninsula even though this phenomenon is relatively frequent in this mountain range a total of 133 permanent channels with evidences of gully erosion have been mapped in a 71 8 km2 study area on the northern slope of this mountain range the underlying ordovician unit comprises quartzite sandstone and slate which are partially mantled by different surficial deposits the relief is fairly steep with average slopes of 27 and hillsides with level drops of the order of 700 m and generally vegetated by atlantic heaths a result of the degradation suffered by the natural vegetation following forest fires the mapped channels present different morphological features shallow and deep channels some of them with associated ravines and are usually related to headcut in first and second order pre existing channels although some of them are located on unchanneled hillsides with no evidence of pre existing channels moreover lower reaches of first and second order channels are often incised into bedrock a field description and morphometric study has been carried out on channels affected by gully erosion based on their cartography digital terrain models and several layers of thematic mapping this study describes some of the relations between relief factors the type of substratum and the development of gully erosion i there are robust correlations between morphometry relief and erosion intensity and ii gullying is strongly influenced by the presence of a deep regolith the erosion forms observed and the described relations suggest that gully development is associated to landsliding processes which are ultimately controlled by ground water movement through a porous regolith regional uplift and deforestation are argued to be the most likely causes of channel incision and gullying

contrasting low and high ca granites in the archean barberton mountain land southern africa abstract two distinct groups of granites can be recognized among the late plutons of the barberton mountain land discrimination between the two groups is provided by geochemical and mineralogical parameters which are considered to reflect the source material from which the magmas were derived a high ca suite has geochemical parameters consistent with derivation from an igneous source i type and an accessory mineral assemblage comprising zircon apatite allanite and sphene a low ca suite contains distinctly different accessory minerals comprising zircon apatite zirconosilicates ca th phosphates very rare xenotime and early monazite and has a chemical signature consistent with derivation from a metasedimentary precursor s type major and trace element trends on harker diagrams support the existence of two distinct granite suites the i type suite exhibits inverse relationships between sio2 and cao tio2 fe2o3 mgo and p2o5 while al2o3 k2o and na2o remain relatively constant these characteristics are consistent with magma formation from an intermediate parent composition and in equilibrium with a hornblendite restite the s type granites formed by vapour absent melting of siliceous metapelite and exhibit inverse correlations between sio2 and al2o3 na2o and k2o with the other major elements remaining relatively unchanged this interpretation of restite unmixing is not unambiguous since rb sr trends could be viewed as reflecting crystal fractionation and partial melting processes high field strength elements tend to reflect the character of accessory mineral phases and are not amenable to modelling in terms of crystal melt equilibria the recognition of possible s and i type suites among the late granite plutons of the barberton mountain land supports recent models which propose plate tectonic analogues in the region the two granite suites are distributed along two subparallel linear arrays which suggests scenarios invoking subduction or hot spot related magmatism with the i types forming in the time span 2740 2690 ma along a western array the putative s types occurring entirely along an easterly belt were emplaced at 3074 and 2820 ma the presence of s type plutons as old as 3074 ma implies that sediments such as the moodies and fig tree groups or their equivalents had been buried to depths of at least 15 km and that by this time at least in the barberton area granites had evolved beyond the ttg mode that typifies many early archaean shield areas

granitoid series in terms of magnetic susceptibility a case study from the barberton region south africa abstract magnetic susceptibilities were measured on a representative collection of archaean granitoids of the barberton region using a portable kt5 magnetic susceptibility meter the studied granitoids comprise 1 syn tectonic tonalite trondhjemite granodiorite ttg granitoids 132 samples 2 late tectonic calc alkaline granitoids 402 samples and 3 post tectonic low ca and high ca granitoids 12 samples most of the early stage syn tectonic granitoids 3450 ma have low magnetic susceptibilities less than 3 10 3 si units and correspond to ilmenite series granitoids the late stage kaap valley tonalite pluton 3230 ma contains sporadically distributed higher magnetic susceptibility values greater than 3 10 3 si units which are less than one third in magnetic susceptibility of typical magnetite series ttg of the japanese island arc and thus strictly belong to an intermediate series the barberton ttg suite is essentially derived from reduced amphibolitic lower crust that reflects the anoxic nature of the earth surface during the archaean eon the more oxidized nature of the kaap valley tonalite may be generated in an oxidized lower crust by fluids squeezed out of the subducting plate late tectonic granodiorite adamellite batholithic complexes 3105 ma belong mostly to the magnetite series and seem to suggest that relatively oxidized continental crust reflecting oxic atmosphere and subduction mechanism operating had evolved it by this time post tectonic granitic plutons formed largely between circa 2900 ma and 2700 ma can be subdivided into low ca ilmenite series and high ca magnetite series

empirical relations for the sediment transport capacity of interrill flow experiments were carried out in order to measure the sediment transport capacity of interrill flow with and without rainfall and to relate the transport capacity to selected hydraulic parameters such as effective stream power and shear velocity different sediments were used in order to study the effect of grain size the proposed relationships show considerable variations with grain size and there is only a minor effect of rainfall on the transport capacity which also seems to be grain size dependent the proposed relationships can be used to predict sediment transport capacity of interrill flow and can therefore contribute to the development of physically based erosion models

rock type control on erosion induced uplift eastern swiss alps abstract there is growing evidence that quaternary rock uplift in parts of the european alps is a consequence of climate and erosion driven isostatic rebound contemporary rates of rock uplift u in the swiss alps show two distinctive dome like peak regions that attain 1 6 mm yr 1 we focus on the alpenrhein catchment and its surroundings where one of these peak regions spatially coincides with widely exposed cretaceous bundner schist and lower tertiary flysch field assessments and analyses of hillslope gradient distributions quantitatively demonstrate the low rock mass strength and high erodibility of these rocks this is reflected in mean postglacial catchment erosion rates d 4 mm yr 1 as opposed to 0 7 mm yr 1 in more resistant crystalline rocks though largely inferred from landslide and debris flow prone tributary catchments 2 the localised erosion rates in bundner schist and flysch are among the highest documented for the alps and corroborated by historic suspended sediment yields and thus export from the region we further find that the steepness of bedrock rivers the density of large landslides and d correlate with the highest values of u our observations highlight the possibility that erosion of mechanically weak bundner schist and flysch enhanced by large landslides may have contributed to regional crustal unloading and concomitant rock uplift irrespective of whether this is betraying a coupling between long term uplift and erosion modulated by rock type our findings indicate that long term 10 3 to 10 4 yr geomorphic signals contained in bedrock river steepness spatial density of large landslides and postglacial erosion rates strikingly correlate with regional gradients of historic 10 1 yr rock uplift rates

effects of rock fragments incorporated in the soil matrix on concentrated flow hydraulics and erosion rock fragments can act as a controlling factor for erosional rates and patterns in the landscape thus the objective of this study is to better understand the role that rock fragments incorporated into the soil matrix play in concentrated flow hydraulics and erosion laboratory flume experiments were conducted with soil material that was mixed with rock fragments rock fragment content ranged from 0 to 40 per cent by volume other treatments were slope 7 and 14 and flow discharge 5 7 and 11 4 l min 1 an increase in rock fragment content resulted in lower sediment yield and broader width of flow rock fragment cover at the soil surface i e surface armour increased with time in experiments with rock fragments flow energy was largely dissipated by rock fragment cover for more turbulent flow conditions when roughness elements were submerged in the flow hydraulic roughness was similar for different rock fragment contents in experiments with few or no rock fragments a narrow rill incised flow energy was dissipated by headcuts total sediment yield was much larger than for experiments with rock fragments in the soil adding just a small number of rock fragments in the soil matrix resulted in a significant reduction of sediment yield copyright 2007 john wiley sons ltd

erosion creep collapse mechanism of underground soil loss for the karst rocky desertification in chenqi village puding county guizhou china carbonate rocks distribute widely in china the total area of the carbonate rocks is about 3 430 000 km 2 and the exposed area of the carbonate is approximately 13 of china s territory in 2003 soil loss in yunnan guizhou and guangxi provinces reached 179 600 km 2 which is almost 40 1 of the total area causing rocky desertification in this study the erosion creep collapse mechanism of underground soil loss for the karst rocky desertification in chenqi village puding county guizhou province is proposed the mechanism occurs under the following geological environment slope surface undulation underlying bedrock surface fluctuation and thin and inhomogeneous soil overlying overlying soil generation by bedrock weathering underground karst development and large groundwater depth and lying water table under the bottom of soils the erosion creep collapse mechanism of underground soil loss in the karst slopes is explained as follows power loss due to human cultivation activities that destroy the soil structure hydraulic force formed by rainfall infiltration wet dry cycle generated by rainfall erosion effect caused by rainfall penetration creeping and flowing of plastic stream soil and collapse the erosion creep collapse mechanism of underground soil loss has seven steps disturbance of soils filled in underground karst cave by human activities internal soil erosion and partial collapse caused by hydraulic power internal free surface formation within the soil in the filled karst cave internal soil creeping soil pipe formation soil pipe collapse and ground surface collapse and filling soil loss develops slowly and sudden transportation occurs by collapse soil loss can be explained by the proposed mechanism and soil loss can be prevented by controlling soil collapse

effects of rock fragment size and cover on overland flow hydraulics local turbulence and sediment yield on an erodible soil surface the interactions between overland flow hydraulics and sediment yield were studied in flume experiments on erodible soil surfaces covered by rock fragments the high erodibility of a non cohesive fine sediment d50 0 09mm permitted the effects of local turbulence and scour on sediment yield to be examined overland flow hydraulics and sediment yield were compared for experiments with pebble d50 1 5cm and cobble d50 8 6cm rock fragment covers cover percentages range from 0 to 99 per cent rock fragment size strongly affects the relations between flow hydraulics and rock fragment cover for pebbles spatially averaged hydraulic parameters flow velocity flow depth effective flow width unit discharge total shear stress darcy weisbach friction factor percentage grain friction and grain shear stress vary most rapidly within cover percentages at low covers power functions in contrast for cobbles these parameters vary most rapidly within cover percentages at high covers exponential functions as the type of the function that describes the relation between flow hydraulics and cover percentage can be deduced from the ratio of rock fragment height to flow depth the continuity equation can be employed to determine the actual coefficients of the functions provided the regression of one hydraulic parameter e g flow velocity with cover percentage is known and a good estimate exists for two values of another hydraulic variable for a low and a high cover percentage the variation of sediment yield with cover percentage is also strongly dependent on rock fragment size but neither the convex upward relation for pebbles nor the positive relation for cobbles can be solely attributed to the spatially averaged hydraulics of sheet flow rock fragments induce local turbulence that leads to scour hole development on the stoss side of the rock fragments while deposition commonly occurs in the wake this local scour and deposition substantially affects sediment yield however scour dimensions cannot be predicted by spatially averaged flow hydraulics an adjustment of existing scour formulas that predict scour around bridge piers is suggested sediment yield from non cohesive soils might then be estimated by a combination of sediment transport and scour formulas

models for granitoid evolution and source compositions this paper critically examines the bases of various models for the chemical evolution of granitoid suites the proposed mineralogical textural and chemical criteria for the recognition of restite components are found to be equivocal and can be plausibly explained by crystal fractionation and accumulation as well as by magma mixing and assimilation of non restitic solids these processes demonstrably account for the bulk of the chemical variation in a variety of granitic suites although restite controlled variation may have played a role in some types of metasediment derived suites granitoid magmas with non minimum melt chemistry are probably rather common the petrographic geochemical and isotopic features of individual plutons should be assessed carefully to elucidate the relative importance of various mechanisms for chemical evolution conclusions as to the character of magma source materials and magma evolution paths that are based on the restite model should be treated with caution

albitization in the antimony line murchison greenstone belt kaapvaal craton a geochemical and geochronological investigation abstract the 3 09 2 97 ga murchison greenstone belt is one of several archean volcano sedimentary belts within the kaapvaal craton in southern africa among the diverse ore deposits found within the belt a set of sb au deposits are located in a major quartz carbonate altered brittle ductile structure known as the antimony line the antimony line is thus clearly related to hydrothermal fluid circulation in this study we focus on albitites that run along the antimony line petrological and geochemical investigations indicate that albitization developed at the expense of a granodioritic protoliths under high fluid rock ratios and also that sb enrichment was concomitant with albitization oxygen isotopes on albitites point to a crustal origin for the hydrothermal fluid responsible for the albitization process geochronology on zircon and hydrothermal monazite identifies a 2 97 2 92 ga magmatic crystallization event disconnected from a ca 2 8 ga hydrothermal alteration and a potentially younger event around 2 0 ga these data highlight a likely magmatic related primary enrichment at 2 97 2 92 ga followed by a secondary metamorphic related mobilization event around 2 8 ga leading to a sb enrichment in the albitites and a last episode of alteration around 2 0 ga

deep marine tidal bottom currents and their reworked sands in modern and ancient submarine canyons abstract submarine canyons provide a unique setting for tidal processes to operate from shallow marine to deep marine environments in modern canyons current meter measurements at varying water depths 46 4200 m show a close correlation between the timing of up and down canyon currents and the timing of semi diurnal tides these tidal bottom currents in submarine canyons commonly attain maximum velocities of 25 50 cm s based on core and outcrop studies of modern and ancient deep marine deposits it is proposed here that sand mud rhythmites double mud layers climbing ripples mud draped ripples alternation of parallel and cross laminae sigmoidal cross bedding with mud drapes internal erosional surfaces lenticular bedding and flaser bedding can be used to interpret deposits of deep marine tidal currents this approach is an alternative to the conventional approach in which most deep water traction structures e g climbing ripples and cross bedding would be attributed to deposition from turbidity currents underwater photographs show active mass flows i e slides slumps grain flows and debris flows in modern canyons box cores taken from modern submarine canyons e g la jolla california and conventional cores and outcrops of ancient canyon fill facies oua iboe pliocene nigeria and the annot sandstone eocene oligocene se france contain deposits of both tidal processes and mass flows this facies association in the rock record can be used as a criterion for recognizing submarine canyon settings in a channel mouth environment deep marine tidal deposits are likely to develop elongate bars that are aligned parallel to the channel axis within the channel whereas turbidites are more likely to develop depositional lobes that are aligned perpendicular to channel axis turbidite depositional lobes are much larger than the channel width whereas tidal sand bars are much smaller than the channel width therefore the wrong use of a turbidite lobe model with sheet geometry in lieu of a tidal bar model with bar geometry will result in an unrealistic overestimation of sandstone reservoirs in deep water exploration

effects of rock fragment cover on hydrological response and soil loss from regosols in a semi humid environment in south west china abstract controlling soil hydrological processes and combating soil erosion on agricultural fields are high priorities for crop production and ecological environments in this research the effect of land application of rock fragments on surface runoff subsurface runoff infiltration and soil loss on regosols had been investigated under field conditions using a portable rainfall simulator experimental twin plot two subplot with 1 m wide by 2 m long 32 slope with different rock fragment covers ranging from 0 40 were exposed to three rainfall intensities low 57 2 mm h 1 medium 91 3 mm h 1 and high 122 5 mm h 1 fifteen treatments were conducted in the experiments in duplicates surface runoff subsurface runoff soil moisture and sediment were measured results show that surface rock fragment cover retarded surface runoff increased infiltration and subsurface runoff and diminished sediment concentration and soil loss the final infiltration rates which increased with increasing rock fragment covers were 16 5 42 7 mm h 1 at low intensity 19 7 50 8 mm h 1 at medium intensity and 23 8 56 4 mm h 1 at high intensity compared with bare soils surface runoff rates were reduced to 24 51 and 64 in soils with 40 rock fragment cover at low medium and high intensity rainfall respectively subsurface runoff volume was significantly higher and time to start subsurface runoff was shorter as surface rock fragment cover increased compared with bare soils subsurface runoff coefficients increased to 3 5 3 3 and 2 9 times in soils with 40 rock fragment cover at low medium and high intensity respectively sediment concentrations increased from 9 8 g l 1 for 40 rock fragment cover under high intensity rainfall to 51 5 g l 1 for bare soils with rain falling at high intensity the erosion rate was 15 g m 2 min 1 for bare soils under low intensity the relationship between rock fragment cover and soil loss ratio can be expressed by an exponential function with a high degree of reliability regardless of rainfall intensities overall results indicate the surface rock fragments can be influential in shaping hydrological processes and soil loss from sloping farmland

relationship between detrital zircon age spectra and the tectonic evolution of the late archaean witwatersrand basin south africa abstract shrimp u pb detrital zircon age spectra for 14 samples from the west rand and central rand groups of the witwatersrand basin indicate that felsic source rocks mostly formed at 3090 3060 and 3000 2870 ma with a smaller proportion formed prior to 3100 ma provenance evaluation indicates that source rocks have largely vanished through erosion such that greenstone terrains extending from the amalia kraaipan belt in the southwest to the murchison belt in the northeast are models of but not the actual source areas analysis of detrital zircon age modes reveals that the west rand and central rand groups record different basins the west rand group is characterised by age subpopulations with a much smaller range and less complex distribution than those in the central rand group furthermore detrital zircon age spectra for the west rand group generally decrease in complexity up section whereas they become increasingly more complex in the central rand group it is concluded that the source area for the west rand group is consistent with a passive margin setting with the decrease in complexity up section of zircon age spectra being the consequence of increasing maturity of the hinterland conversely the source area of the central rand group was far more dynamic with an increasing age range of source rocks being exposed through time pulsed tectonic rejuvenation of the source area is implied contemporaneous emplacement uplift and erosion of granitoids supports a magmatic fold thrust belt as the source and a complementary retroarc basin setting detrital xenotime grains record the ages of high u granitoids emplaced in the fold thrust belt during deposition of the central rand group and are much closer to depositional ages than are detrital zircon grains change from a passive margin to a retroarc basin across the west rand central rand boundary is emphasised by change from simple to increasingly complex detrital zircon age spectra this study establishes that detrital zircon geochronology can overcome the problem of overly quartzose compositions in archaean sandstones due to severe chemical weathering and authigenic alteration thereby enabling distinction between passive margin and retroarc basin stages through systematic changes in the age complexity of the source area

evaluation of the predictive capability of coupled thermo hydro mechanical models for a heated bentonite clay system he e in the mont terri rock laboratory process understanding and parameter identification using numerical methods based on experimental findings are key aspects of the international cooperative project decovalex development of coupled models and their validation against experiments http www decovalex org comparing the long term predictions from numerical models against experimental results increases confidence in the site selection and site evaluation process for a radioactive waste repository in deep geological formations in the present phase of the project decovalex2015 eight research teams have developed and applied models for simulating the he e in situ heater experiment in the opalinus clay in the mont terri rock laboratory in switzerland the modelling task was divided into two study stages related to prediction and interpretation of the experiment a blind prediction of the he e experiment was performed based on calibrated parameter values for both the opalinus clay which were derived from the modelling of another in situ experiment he d experiment in the mont terri rock laboratory and calibrated parameters for mx80 granular bentonite and a sand bentonite mixture which were derived from modelling of laboratory column tests after publication of the he e experimental data additional functions for coupled processes were analysed and considered in the different models moreover parameter values were varied to interpret the measured temperature relative humidity and pore pressure evolution generally the temperature field can be well reproduced and is mainly controlled by thermal conductivity in the heat conduction process the thermal conductivities of buffer materials and opalinus clay strongly depend on the degree of water saturation the distribution of relative humidity is acceptable as it is reproduced by using both the richards flow model and the multiphase flow model important here is to consider the vapour diffusion process the analysis of the predictive and interpretative modelling confirms that the main processes in the system have been understood at least for the short term experimental duration and captured using the models developed and associated parameters with respect to the thermal and hydraulic aspects in the high level nuclear waste disposal in clay formations the additional experimental results will help to increase confidence in the thm models and in process understanding

elements of the archean thermal history and apparent polar wander of the eastern kaapvaal craton swaziland from single grain dating and paleomagnetism abstract single grains of zircon hornblende biotite and feldspar have been dated to define the thermal history of the archean mbabane pluton swaziland coincident207pb 206pb zircon and40ar 39ar hornblende ages suggest that the pluton underwent rapid cooling to about 450 c at the time of emplacement at 2690 ma because the mbabane pluton is one of a suite of granites which represent the last major archean intrusive event in the eastern kaapvaal craton this time of emplacement marks the end of cratonization much younger biotite and feldspar ages indicate argon loss perhaps due to several low temperature events related to dike intrusion at 2000 2300 ma from such a thermal history the age of magnetization of a paleomagnetic pole polelatitude 19 7 n polelongitude 105 7 e a95 9 4 k 67 obtained from 5 sites can be determined based on the unblocking temperature of the magnetic carrier and the consistent direction seen in several sites it appears that the hornblende age and coincidently the207pb 206pb zircon age most accurately represents this age of magnetization thus the mbabane pluton yields a precisely dated archean 2687 6 ma 2 hornblende plateau age paleomagnetic pole which is different than other archean poles such as that from the nearby usushwana complex 2875 40ma although the two intrusions are separated by less than 12 km and there is no evidence of relative structural rotation between them the paleomagnetic poles from the two bodies are 65 apart this implies that there was significant apparent polar wander during the late archean

age and isotope geochemistry of the archaean pongola and usushwana suites in swaziland southern africa a case for crustal contamination of mantle derived magma the igneous rocks of the pongola supergroup ps and usushwana intrusive suite uis represent a case of late archaean continental magmatism in the southeastern part of the kaapvaal craton of south africa and swaziland u pb dating on zircons from felsic volcanic rocks of the ps yields a concordia intercept age of 2940 22ma that is consistent with a sm nd whole rock age of 2934 114ma determined on the ps basalt rhyolite suite the initial end of 2 6 0 9 is the lowest value so far reported for archaean mantle derived rocks rb sr whole rock dating of the ps yields a younger isochron age of 2883 69ma which is not significantly different form the accepted u pb zircon age an internal cpx opx plag whole rock isochron for a pyroxenite from the younger uis yields an age of 2871 30 ma and initial 143nd 144nd that lies off the chur growth curve by end 2 9 0 2 however sm nd whole rock data for the uis yield an excessively high age of 3 1 ga that conflicts with firm geological evidence showing the uis to be intrusive into the ps the negative deviations of initialend from the chondritic nd evolution curve suggest significant contamination of the ps and uis melts by older continental crust a mixing process with continental crust after magma segregation is supported by a high initial 87sr 86sr ratio of0 703024 24 for a clinopyroxene sample from a uis pyroxenite compared with an expected value of 0 701 for the 2 9 ga mantle we therefore interpret the linear array of data points for the uis gabbros as a mixing line between 2 87 ga old magma and older continental crust parallel lree enriched ree patterns negative nb ti anomalies a distinctive and uniform ratio of ti zr 46 and a narrow span of initial nd indicate a common source for both the ps and uis suites which is different from primitive mantle

comparative characteristics of the black sea and mediterranean ridge mud volcanoes morphological and structural characteristics of the black sea and mediterranean ridge mud volcanoes studied during several unesco esf cruises of the r v gelendzhik 1991 1994 are compared on the basis of single and multi channel seismic and sidescan sonar observations morphologically three types of mud volcanoes were distinguished in the black sea and six types in the mediterranean they differ in size shape and presence of the mud flows some types from both localities are very similar to each other but in any case their deep structure is very distinctive this difference in deep structure is explained by their development in different geological conditions under an extensional regime with high terrigenous input in the black sea and under strong lateral compression on the mediterranean ridge

archean foreland basin tectonics in the witwatersrand south africa the witwatersrand basin of south africa is the best known of archean sedimentary basins and contains some of the largest gold reserves in the world sediments in the basin include a lower flysch type sequence and an upper molassic facies both of which contain abundant silicic volcanic detritus the strata are thicker and more proximal on the northwestern side of the basin which is at least locally bound by thrust faults these features indicate that the witwatersrand strata may have been deposited in a foreland basin and a regional geologic synthesis suggests that this basin developed initially on the cratonward side of an andean type arc remarkably similar phanerozoic basins may be found in the southern andes we suggest that the continental collision between the kaapvaal and zimbabwe cratons at about 2 7 ga caused further subsidence and deposition in the witwatersrand basin regional uplift during this later phase of development placed the basin on the cratonward edge of a collision related plateau now represented by the limpopo province similarities are seen between this phase of witwatersrand basin evolution and that of active basins north of the tibetan plateau e g the tarim and tsaidam basins the geologic evidence does not appear so compatible with earlier suggestions that the witwatersrand strata were deposited in a rift or half graben

archaean ttgs as sources of younger granitic magmas melting of sodic metatonalites at 0 6 1 2 gpa two natural low k2o na2o ttg tonalitic gneisses one hornblende bearing and the other biotite bearing were partially melted at 0 8 1 2 gpa fluid absent the chief melting reactions involve the breakdown of the biotite and hornblende the hornblende tonalite is slightly less fertile than the biotite tonalite but melt volumes reach around 30 at 1 000 c this contrasts with results of most previous work on more potassic ttgs which generally showed much lower fertility though commonly producing more potassic melts garnet is formed in biotite bearing tonalitic protoliths at p 0 8 gpa and at 1 0 gpa in hornblende bearing tonalitic protoliths all fluid absent experiments produced peraluminous granitic to granodioritic melts typically with sio2 70 wt for the biotite tonalite increasing t formed progressively more melt with progressively lower k2o na2o however the compositions of melts from the hornblende tonalite do not vary significantly with t with increasing p melts from the biotite tonalite become less potassic due to the increasing thermal stability of biotite for the hornblende tonalite again there is no consistent trend fluid absent melting of sodic ttgs produces melts with insufficient k2o to model the magmas that formed the voluminous late potassic granites that are common in archaean terranes reconnaissance fluid present experiments at 0 6 gpa imply that h2o saturated partial melting of ttgs is also not a viable process for producing magmas that formed these granites the protoliths for these must have been more potassic and less silicic nevertheless at granulite facies conditions sodic ttgs will produce significant quantities of broadly leucogranodioritic melt that will be more potassic than the protoliths upward abstraction of this melt would result in some lile depletion of the terrane younger k rich magmatism is unlikely to represent recycling of ttg crust on its own and it seems most likely that evolved crustal rocks and or highly enriched mantle must be involved

soil erosion by surface water flow on a stony semiarid hillslope soil erosion on hillslopes occurs by processes of soil splash from raindrop impacts and sediment entrainment by surface water flows this study investigates the process of soil erosion by surface water flow on a stony soil in a semiarid environment a field experimental method was developed whereby erosion by concentrated flow could be measured in predefined flow areas without disturbing the soil surface the method allowed for measurements in this study of flow erosion at a much wider range of slopes 2 6 to 30 1 per cent and unit discharge rates 0 0007 to 0 007 m2 s 1 than have been previously feasible flow velocities were correlated to discharge and hydraulic radius but not to slope the lack of correlation between velocity and slope might have been due to the greater rock cover on the steeper slopes which caused the surface to be hydraulically rougher and thus counteract the expected effect of slope on flow velocity the detachment data illustrated limitations in applying a linear hydraulic shear stress model over the entire range of the data collected flow detachment rates were better correlated to a power function of either shear stress r2 0 51 or stream power r2 0 59 published in 1999 by john wiley sons ltd

correction factors in the determination of mean velocity of overland flow the velocity of overland flow has been conventionally measured using tracers but it is difficult to measure the mean flow velocity directly because the centroid of the tracer plume is not easily identified consequently previous investigators have measured the velocity of the leading edge of the plume and multiplied it by a correction factor to obtain an estimate of mean velocity an alternative method is to measure the velocity of the peak concentration in the tracer plume and multiply this velocity by another correction factor to estimate mean velocity to investigate the controls of and and develop predictive models for these correction factors 40 experiments were performed in a flume with a mobile sand bed multiple regression analyses reveal that both and vary inversely with slope and directly with reynolds number the derived regression equations may be used to calculate the mean velocity of other shallow overland flows at least within the range of slope and reynolds number for which the equations were developed in the experiments slope ranged from 2 7 to 10 and reynolds number from 1900 to 12 600

research on soil detachment rate and hydrodynamic parameters of dip anti dip slope in simulated karst trough valley bedding dip has an important influence on soil detachment and flow hydrodynamics in a karst trough valley the laboratory rainfall simulation was conducted with three bedding dips bare slope dip slope and anti dip slope under three rainfall intensities 30 60 90 mm h 1 the characteristics of soil detachment and hydrodynamic parameters were assessed including water flow shear stress stream power unit stream power and unit flow energy the significant effects of bedding dips and rainfall intensities and their interactions on soil detachment and hydrodynamic parameters were examined the results showed that 1 the soil detachment rate decreased with increasing rainfall duration and the soil detachment rate in 30 bedding dip of dip slope was much larger than those in bare slope and anti dip slope in most rainfall intensities 2 the 60 bedding dip of dip slope was the threshold that controlled the stream power unit stream power and unit flow energy increased or decreased under different rainfall intensities and 3 the soil detachment rate had extremely significant positive power relationships with water flow shear stress stream power unit stream power and unit flow energy meanwhile the stream power was the most suitable parameter for predicting soil detachment in a karst trough valley slope therefore these results could provide useful information for soil erosion prediction in a karst trough valley

growth styles of shelf margin clinoforms prediction of sand and sediment budget partitioning into and across the shelf abstract growth styles of shelf margin clinoforms are reliable but understudied predictors of sand and sediment budget partitioning into and across the shelf three discrete clinoform growth styles were recognized including 1 strongly progradational shelf margin clinoforms with low growth trajectory angles gct low aggradation to progradation ratios a p low clinoform heights hc and long clinoform length lc 2 mixed progradational and aggradational shelf margin clinoforms with moderate gct moderate a p intermediate hc and moderate lc and 3 strongly aggradational clinoforms with high gct high a p high hc and short lc in the south china sea dataset considered strongly progradational shelf margin clinoforms exhibit flat progradational and at times a mildly aggrading stacking patterns whereas mixed progradational and aggradational clinoforms display stacking patterns with significant progradation and aggradation strongly aggradational shelf margin clinoforms are dominated by aggradational stacking patterns each clinoform growth style therefore represents a specific stratal stacking pattern providing an important tool for approaching a model independent methodology in sequence stratigraphy in the study dataset strongly progradational and strongly aggradational shelf margin clinoforms are fronted by sand prone submarine fan systems with high sand shale ratios and mud dominated mass transport systems with low sand shale ratios respectively mixed progradational and aggradational clinoforms are associated with mixed sand mud submarine canyon systems with moderate sand shale ratios additionally strongly progradational clinoforms partitioned great volumes of sediment into deep water areas as reflected by high rates of shelf edge progradation and apparent toplap strongly aggradational clinoforms in contrast stored great volumes of sediment on the shelf itself as indicated by high rates of shelf edge aggradation and very thick clinoform topsets gct and hc therefore increase linearly with sediment volumes partitioned into the shelf but decrease linearly with sand and sediment budget partitioning into deep water areas given a constant sediment supply condition growth styles of shelf margin clinoforms are thus good predictors of source to sink sand and sediment volume partitioning into and across the shelf assisting greatly in developing a more dynamic stratigraphy

bedrock bedding landsliding and erosional budgets in the central european alps we explore the controls of the litho tectonic architecture on the erosional flux in the 370 km2 glogn basin european alps in this basin the bedding and schistosity of the bedrock dip parallel to the topographic slope on the nw valley flank leading to a non dip slope situation on the opposite se valley side while the dip slope condition has promoted the occurrence of landslides e g the c 30 km2 deep seated lumnezia landslide the opposite non dip slope side of the valley hosts 100 m deeply incised tributary streams 10be concentrations of stream sediments yield catchment averaged denudation rates that vary between 0 27 0 03 and 2 19 0 37 mm a 1 while the spatially averaged denudation rate of the entire basin is 1 99 0 34 mm a 1 our 10be based approach reveals that the lumnezia landslide front contributes c 30 65 of the entire sediment budget although it covers 5 of the glogn basin this suggests a primary control of the bedrock bedding on erosion rates and processes

hydraulics and erosion in eroding rills rills often act as sediment sources and the dominant sediment and water transport mechanism for hillslopes six experiments were conducted on two soils and a uniform sand using three experimental methodologies the results of this study challenge the assumption often used in hydrologic and erosion models that relationships derived for sheet flow or larger channel flow are applicable to actively eroding rills velocity did not vary with slope and reynolds number was not a consistent predictor of hydraulic friction this result was due to interactions of slope gradient flow rate erosion and the formation of rill roughness bed structures and head cuts a relationship for rill flow velocities was proposed stream power was found to be a consistent and appropriate predictor for unit sediment load for the entire data set while other hydraulic variables were not the data for stream power and sediment load fit the form of a logistic curve r2 0 93 which is promising relative to recently proposed erosion models which are based on probabilistic particle threshold theory

a sediment transport equation for interrill overland flow on rough surfaces a model for predicting the sediment transport capacity of turbulent interrill flow on rough surfaces is developed from 1295 flume experiments with flow depths ranging from 3 4 to 43 4 mm flow velocities from 0 09 to 0 65 m s 1 reynolds numbers from 5000 to 26 949 froude numbers from 0 23 to 2 93 bed slopes from 2 7 to 10 sediment diameters from 0 098 to 1 16 mm volumetric sediment concentrations from 0 002 to 0 304 roughness concentrations from 0 to 0 57 roughness diameters from 1 0 to 91 3 mm rainfall intensities from 0 to 159 mm h 1 flow densities from 1002 to 1501 kg m 3 and flow kinematic viscosities from 0 913 to 2 556 10 6 m2 s 1 stones cylinders and miniature ornamental trees are used as roughness elements given the diverse shapes sizes and concentrations of these elements the transport model is likely to apply to a wide range of ground surface morphologies using dimensional analysis a total load transport equation is developed for open channel flows and this equation is shown to apply to interrill flows both with and without rainfall the equation indicates that the dimensionless sediment transport rate is a function of and therefore can be predicted by the dimensionless shear stress its critical value c the resistance coefficient u u the inertial settling velocity of the sediment wi the roughness concentration cr and the roughness diameter dr the model has the form 1 where and testing reveals that the model gives good unbiased predictions of in flows with sediment concentrations less than 0 20 flows with higher concentrations appear to be hyperconcentrated and to have sediment transport rates higher than those predicted by the model copyright 2001 john wiley sons ltd

late orogenic post orogenic and anorogenic granites distinction by major element and trace element chemistry and possible origins granites classified into four categories based solely on tectonics of occurrence and associated rock types also have compositional characteristics that are consistent within groups and different am

morphology and sedimentary processes on the continental slope off pine island bay amundsen sea west antarctica morphology and sedimentation on the pine island bay continental margin eastern amundsen sea is investigated using swath bathymetry parametric subbottom profiler topas records and sediment cores a major cross shelf trough extends to the continental shelf edge at 114 w through which fast flowing ice drained the west antarctic ice sheet under full glacial conditions the slope adjacent to the trough mouth is 4 whereas to the east and west it is steeper a bulge in bathymetric contours beyond and east of the trough mouth indicates some slope progradation elsewhere seismic reflection profiles indicate major shelf aggradation and minor slope progradation networks of gullies and channels dominate the slope adjacent to pine island bay in front of the trough mouth gullies at the shelf edge and uppermost slope connect directly with channels that continue to the continental rise other gullies connect indirectly with channels further downslope topas records indicate that gully channel systems acted as conduits for coarse grained sediment transfer cores comprise turbidites representing channel deposits and diamicton facies deposited by debris flows sandy turbidites interbedded with hemipelagic muds occur on the rise and abyssal plain the west antarctic ice sheet extended to the shelf edge during full glacials delivering water saturated till and turbid water directly to the continental slope along a line source gully channel systems are probably a product of sediment gravity flows derived from the release of water saturated till and turbid water along the ice sheet margin perhaps augmented subsequently by downslope flow of dense cold and saline water associated with sea ice production during the holocene the gully channel systems enable sediment to bypass the continental slope spatial variations in gully channel system morphology along the amundsen sea continental slope are probably linked to differences in sediment gravity flow processes and the rate and composition of sediment delivered to the shelf edge from the ice sheet cored sediments on the slope and abyssal plain record the widespread presence of turbidite sands indicating that downslope transfer of glacier derived sediments has taken place this supports our interpretation that submarine channels are derived from and are conduits for mass wasting submarine channels on the upper slope continue into the abyssal plain as far north as 67 s they are separated by sediment drifts and sediment waves resulting from the interaction between downslope turbidity current processes and along slope bottom currents similar deep sea sedimentary processes operate along much of west antarctica and the western side of the antarctic peninsula

influence of rock fragment coverage on soil erosion and hydrological response laboratory flume experiments and modeling two laboratory flume experiments on the effect of surface rock fragments on precipitation driven soil erosion yields were carried out the total sediment concentration the concentration of seven individual size classes and the flow discharge were measured digital terrain models dtms were generated before and after one of the experiments the results revealed that the rock fragments protected the soils from raindrop detachment and retarded the overland flow therefore decreasing its sediment transport capacity rock fragments were found to affect selectively the different size classes in a manner that changed according to the time scale for short times the rock fragment coverage reduced erosion of the finer particles 100 m was unaffected at long times the rock fragment cover decreased the concentration of the individual size classes in proportion to effective rainfall intensity and the area exposed to raindrops an area based modification of the hairsine and rose h r soil erosion model was employed to analyze the experimental data the h r model predictions agreed well with the measured sediment concentrations when high rainfall intensity and low rock fragment cover were used predictions were instead less accurate with low rainfall intensity and high rock fragment cover the dtm results showed that the presence of rock fragments on the soil surface led to increased soil compaction perhaps due to higher soil moisture content from greater infiltration within the rock fragment covered flumes

mudflow gully characteristics formation and impact on reservoir heterogeneity a gas field in the yinggehai basin south china sea abstract mudflow gullies are well developed in offshore areas and on the upper deepwater slope in this paper we discuss the formation and characteristics of mudflow gullies in a gas field in the yinggehai basin along the northwestern south china sea margin and address their impacts on sand body distribution reservoir heterogeneity and hydrocarbon accumulation the geological setting and sedimentary characteristics indicate that the sedimentary environment of the study intervals is located in an area between lower shore face and offshore the gullies are several meters to a few tens of meters wide and are filled mainly with thick mudstones interbedded with thin siltstones gully fills show an overall fining upward depositional trend and exhibit a high value low amplitude linear gr wireline log shape mudflow gullies always incise the underlying sand bars or sand sheets are overlain by offshore shales and are therefore considered to have developed in a transgressive setting they are of three basic types i e deep moderate and shallow classes according to the incision depth the mudflows developed in offshore environment with rapidly varying topography and deeply cut the underlying sand bars in lower shore face environment influenced by diapiric events plastic mud rich sediments were apt to slump yielding the studied gullies gullies can converge to generate a lobe at front of them in particular during marine transgression due to the high depositional rate of muddy sediments and tectonic activity marine transgression offered the most favorable scenario for the development of these gullies the mudflows also slumped down the slope into the deep water areas of the basin because of the incision of mudflow gullies and transgressive wave ravinement from the southeast the pre existing sand bars on the lower shore face were reworked by waves and oriented in a ne sw direction perpendicular to the east shoreline to hainan island the sand bars were affected by the mudflow gullies and diapir faults often isolated from each other resulting in a weak sand connectivity vertically and laterally the degree of erosion of the sand bodies by mudflows decreases with depth in addition diapiric activity not only induces the formation of mudflow but also causes co2 in the deep buried intervals to migrate into gas reservoir attached by faults the mudflow gullies are important causes of gas reservoir compartmentalization co2 filling process and gully development in the area resulted in more heterogeneity than the areas without them therefore mudflow gullies control not only the reservoir compartments but also the gas content in the reservoir

formation of an archaean continent about 30 of the earth is covered by continents but only about 10 small kernels of these continentsae known as archaean cratonsae are continental fragments formed before 2 5 gyr ago the kaapvaal craton of south africa which formed and stabilized between 3 7 and 2 7 gyr ago is one of the oldest reasonably sized examples of these continental fragments it consists of a mosaic of subdomains that have been welded together by processes similar to those of modern day plate tectonics the earliest subdomains may have owed their origin to the onset of efficient recycling from the earth s hydrosphere into the mantle

sediment transport capacity of sheet and rill flow application of unit stream power theory theoretical equations for calculating the unit stream power of both sheet and rill flow were developed and used to predict the sediment transport capacity of such flows independent data sets from three sources representing both finely aggregated clay soils and coarse textured nonaggregated soils sheet rill and composite sheet rill flow systems and a range of slopes were used to test the utility of the method the results were very good and demonstrated the simplicity and robustness of the method for shallow overland flow the best results were obtained when the critical unit stream power at incipient sediment motion was treated as a constant value that was independent of slope the results also suggest that a unique value of critical unit stream power for rill initiation exists that is independent of soil type for noncohesive loams or fine sands and finely aggregated clay soils the sediment transport capacity can be accurately predicted from a knowledge of the physical characteristics of the soil or bed material alone for aggregated clay soils this requires information on the aggregate size distribution and the effects of soil particle size differentiation as flow rates and unit stream powers increase with the transition from sheet to rill flow

a review of the geochronological constraints on the evolution of the kaapvaal craton south africa abstract all the published u pb geochronological data from zircon titanite sphene and monazite and pb pb evaporation data applicable to the palaeoarchaean to neoarchaean geology of the kaapvaal craton are employed to reconstruct the history and crustal architecture of the ca 3600 2500 ma cratonic basement in south africa only data interpreted as representative of the age of crystallisation or the 207 pb 206 pb ages from zircon xenocrysts have been considered in constructing graphs of cumulative probability versus age of rock formation in this manner it has been possible to identify the main magmatic events that have contributed to the assembly of the craton for convenience of data handling the kaapvaal craton has been subdivided into eastern central northern and western geographic domains these domains are not intended as discrete geological terranes although each one has its own geological and chronological character although consanguinity of events is also evident the oldest rocks so far recognised are located in the swaziland barberton areas where ages 3600 ma have been recorded the early stages of shield development are best exposed in the barberton mountain land where it is now apparent that continent formation took place by magmatic accretion and tectonic amalgamation of small protocontinental blocks at barberton several diachronous blocks formed between 3600 and 3200 ma have been identified each of which represents a cycle of arc related magmatism and sedimentation this phase of crustal development was followed by a period of mesoarchaean cratonic magmatism particularly prevalent between approximately 3100 3000 ma and marked by the development of a major crescent shaped juvenile arc that was accreted onto the northern and western margins of the evolving kaapvaal shield cratonisation was accomplished by the emplacement of major granitoid batholiths which thickened and stabilised the continental crust during the early stages of this cycle subsequent evolution of the craton between 3000 and 2700 ma was associated with continent arc collision during which time the witwatersrand basin and its correlatives were deposited as foreland sequences followed by episodic extension and rifting when the gaborone kanye and ventersdorp sequences were developed

syn and post eruptive erosion gully formation and morphological evolution of a tephra ring in tropical climate erupted in 1913 in west ambrym vanuatu abstract syn and post eruptive erosion of volcanic cones plays an important role in mass redistribution of tephra over short periods descriptions of the early stages of erosion of tephra from monogenetic volcanic cones are rare particularly those with a well constrained timing of events in spite of this lack of data cone morphologies and erosion features are commonly used for long term erosion rate calculations and relative age determinations in volcanic fields this paper offers new observations which suggest differing constraints on the timing of erosion of a tephra ring may be operating than those conventionally cited in 1913 a tephra ring was formed as part of an eruption in west ambrym island vanuatu and is now exposed along a continuous 2 5 km long coastal section the ring surrounds an oval shaped depression filled by water it is composed of a succession of a phreatomagmatic fall and base surge beds interbedded with thin scoriaceous lapilli units toward the outer edges of the ring base surge beds are gradually replaced in the succession by fine ash dominated debris flows and hyperconcentrated flow deposits the inter fingering of phreatomagmatic deposits with syn volcanic reworked volcaniclastic sediments indicates that an ongoing remobilisation of freshly deposited tephra was already occurring during the eruption gullies cut into the un weathered tephra are up to 4 m deep and commonly have c 1 m of debris flow deposit fill in their bases there is no indication of weathering vegetation fragments or soil development between the gully bases and the basal debris flow fills gully walls are steep and superficial fans of collapsed sediment are common most gullies are heavily vegetated although some active ephemeral channels occur these observations suggest that the majority of the erosion of such tephra rings in tropical climates takes place directly during eruption and possibly for only a period of days to weeks afterward after establishment of the gully network tephra remobilisation is concentrated only within them therefore the shape of the erosion modified volcanic landform is predominantly developed shortly after the eruption ceases this observation indicates that gully erosion morphology may not necessarily relate to age of such a landform different intensities of erosion during eruption related to water supply or rainfall are probably the major influence on gully spacing modal depth and form longer term post eruption processes that could be indicators of relative age may include internal gully deepening below basal debris flow fill sediments and possibly widening and side slope lowering due to undercutting and side collapse

ages of altered granites adjoining the witwatersrand basin with implications for the origin of gold and uranium one of the main problems in understanding the origin of the witwatersrand basin mineralization concerns the source of the prodigious concentrations of gold and uranium in the basin another problem is the age and nature of the rocks in the source area recent data1 2 indicate that the source area was largely 3 200 2 900 myr old becoming progressively younger as the basin evolved granites adjoining the basin are commonly overprinted by pervasive and vein related hydrothermal alteration which resulted in an enrichment of both gold and uranium3 4 here we report uranium lead data demonstrating that these hydrothermally altered granites were intruded sporadically both before and during the 360 myr period5 constraining witwatersrand sediment deposition and that hydrothermal alteration was associated with granitoid intrusion and subsequent cooling thus fertilization of the crust occurred during basin evolution a feature that supports the idea19 that gold and uranium mineralization occurred simultaneously with sediment deposition

assessing soil erosion in mediterranean karst landscapes of lebanon using remote sensing and gis abstract maps showing the potential for soil erosion at 1 100 000 scale are produced in a study area within lebanon that can be used for evaluating erosion of mediterranean karstic terrain with two different sets of impact factors built into an erosion model the first set of factors is soil erodibility morphology land cover use and rainfall erosivity the second is obtained by the first adding a fifth factor rock infiltration high infiltration can reflect high recharge therefore decreasing the potential of surface runoff and hence the quantity of transported materials infiltration is derived as a function of lithology lineament density karstification and drainage density all of which can be easily extracted from satellite imagery the influence of these factors is assessed by a weight rate approach sharing similarities between quantitative and qualitative methods and depending on pair wise comparison matrix the main outcome was the production of factorial maps and erosion susceptibility maps scale 1 100 000 spatial and attribute comparison of erosion maps indicates that the model that includes a measure of rock infiltration better represents erosion potential field investigation of rills and gullies shows 87 5 precision of the model with rock infiltration this is 17 5 greater than the precision of the model without rock infiltration these results indicate the necessity and importance of integrating information on infiltration of rock outcrops to assess soil erosion in mediterranean karst landscapes

role of erosion processes on the morphogenesis of a semiarid badland area bardenas reales ne spain abstract bardenas reales badlands are located in the middle western sector of the ebro depression northern spain this consists of a big erosional depression with deeply dissected valley bounded by steep slopes labile argillaceous bedrock scarce high intensity rainfall and high temperatures make erosion the dominant morphogenetic process several erosion processes operate in the bardenas reales rilling gullying piping and mass movements the relative role played by these processes on the morphogenesis is largely controlled by physico chemical properties of the materials and climatic conditions precipitation distribution over the year controls the development of mass movements whereas regolith physical chemical properties favor piping gullying and rilling during the rainfall maxima soil erodibility in this area is clearly controlled by the sodium content and the presence of swelling clays these factors determine the distribution and appearance of piping processes cracking in holocene clay deposits devoid of swelling clays is related to high sodium content that confers a dispersive character clay dispersion causes loss of cohesion favoring piping in the rainfall maxima soil loss is significant and controlled by precipitation amount and maximum intensity conversely during periods of cyclonic rain erosion is scarce and mass movements are the dominant process in the slopes underlain by tertiary mudstones mud flows are frequent during the winter months in winter time when rains are of low intensity and evapotranspiration is limited infiltration through cracks is high consequently water content in the regolith may increase until the plastic limit is reached under these conditions and due to the high gradient of the slopes 34 shear strength is surpassed and the clay material is able to slide and flow

sediment properties flow characteristics and depositional environment of submarine mudflows bear island fan abstract recent gravity flows on the bear island fan consist of fine grained sediments that presently exhibit high densities 1 8 2 0 g cm 3 low water contents 30 40 dry weight and high estimated yield strengths 1100 1350 pa rheological analyses however reveal exceptionally low yield strengths 3 5 pa and lower for laboratory slurries 3 made with the mudflow sediments the low yield strengths are inconsistent with previous interpretations that the mudflows were spawned from glacial sediments that were rapidly deposited as till deltas on the upper slope of the fan or that they were emplaced as low density low cohesion fluidized mud abundant glacial flour in the mudflow samples is indicative of subglacial meltwater discharge this in turn suggests that the sediment originated from turbid plumes that settled into a low density high water content mud deposit in an open marine tidewater glacier environment such an environment may have existed during the mid late weichselian when an embayment in the barents shelf ice sheet left much of the inner shelf ice free subsequent advance of the ice front closed the embayment compressing the mud loss of water during compression increased the bulk density and yield strength of the mud the modified embayment mud was gradually pushed off the shelf generating mudflows on the fan morphologic evidence suggests that some mudflows may have hydroplaned indicating that flow speeds varied above and below a critical speed ca 5 m s marking the onset of hydroplaning

proterozoic ferroan feldspathic magmatism abstract the proterozoic eon is characterized by an unusual abundance of ferroan feldspathic rocks that range in composition from granite to quartz syenites to feldspathoid bearing syenites three associations of ferroan rocks may be recognized on the basis of major element compositions 1 metaluminous alkalic to alkali calcic syenites and granites associated with anorthosites and iron rich basaltic rocks 2 alkaline intrusions in continental rifts and 3 calc alkalic metaluminous to peraluminous granitoid plutons that are less strongly ferroan than the other two groups the first two groups form by differentiation of tholeiitic to alkali basaltic parental magmas the third by partial melting of quartzo feldspathic crust although all three associations may form in intraplate settings only the alkaline intrusions which typically contain high incompatible trace element abundances plot entirely within the within plate granite fields on trace element discrimination diagrams processes of crustal melting and magma mixing have had a greater effect on the trace element compositions of ferroan granitoids from the other two associations causing some rocks to plot outside this field of these three associations the granitoids associated with anorthosites are the most voluminous and are essentially restricted to the proterozoic special conditions perhaps related to the presence of a long lived supercontinent under which widespread mantle upwelling took place appear required to explain the abundance of these rocks ferroan alkaline rocks although rarely preserved in archean crust are present in proterozoic and phanerozoic rifts the earliest alkaline intrusions thus may mark the establishment of rigid continents capable of rifting the formation of ferroan calc alkalic granites does not appear to be time dependent these granites have been generated throughout earth history in response to crustal melting

spatial distribution of mud flows chemoautotrophic communities and biogeochemical habitats at hakon mosby mud volcano marine mud volcanoes are significant source locations contributing to the marine methane cycle enhanced heat flow unique chemoautotrophic communities occurrence of massive gas hydrates and large gas plumes are direct evidences of elevated methane concentrations and the dynamic environment of mud volcanoes related to the high concentrations and large inventories of ch4 in surface sediments only a fraction of the methane is exported to the bottom water this is mainly due to chemoautotrophic communities oxidizing methane and proving a microbial filter reducing ch4 fluxes although these processes were studied for several mud volcanoes still little is known about the spatial pattern and the areas covered by chemoautotrophic communities or by present mud flows for this purposes the hakon mosby mud volcano hmmv which is located at the continental slope of the barents sea was studied by several dives with the remotely operated vehicle victor6000 during these dives a high resolution microbathymetric map with a footprint of 25 25 cm and a vertical resolution of better than 10 cm was derived furthermore video streams of the bottom camera were converted into georeferenced mosaics providing a detailed image about the spatial distribution of seafloor features as bacterial mats pogonophorans both indicating methane oxidation or mud flows based on visual inspection of 2310 georeferenced mosaics covering an area of 46 160 m 2 different biogeochemical habitats were identified and quantified on a m 2 basis by application of geostatistic techniques as indicator kriging the distribution of different biogeochemical habitats was quantified and mapped for the entire hmmv considering the flat and hummocky area of hmmv approximately 16 115 165 m 2 of the flat centre is nearly void of any benthic communities this area is considered as a region of high methane discharge into bottom water an area of 5 38 244 m 2 located in the south eastern part is densely inhabited by beggiatoa the hummocky outer part is colonised dominantly by pogonophoran tube worms 37 3 276 121 m 2 and only occasional by beggiatoa source locations and drainage directions for current mud flows were identified by computation of trend surfaces and consideration of temperature data this suggests that present mud flow ascend close to the northern edge of the flat unit of hmmv and that the drainage pattern of mud flows shifted from a westward to a south south eastern direction 2007 elsevier b v all rights reserved