slope instability from ground water seepage previous researchers have treated the magnitude and direction of the seepage vector as independent variables and found that seepage parallel to the surface does not result in the minimum stable seepage slope in the present paper the magnitude and direction of the seepage vector is shown to be uniquely related at the seepage face and seepage parallel to the slope results is the minimum stable seepage slope slope failures under seepage are found to be progressive and the stable slope angle depends on the direction of the seepage vector the effect of seepage direction on static liquefaction is investigated and the seepage directions that initiate static liquefaction depend on the slope angle and soil unit weight analytical predictions of the minimum stable seepage slope compare favorably with experimental results

mid ocean ridge and island arc affinities in ophiolites from iran palaeographic implications complementary reference abstract fifty six samples of ophiolitic rocks from various late cretaceous eocene suture zones in iran have been analyzed for major and trace elements in order to assess their petrogenetic affinity and to determine their original tectonic setting in both southern baluchestan i e between the makran range and the lut block the fanuj maskutan sequence and northeastern baluchestan i e in the east iranian ranges the tchehel kureh sequence the ophiolitic complexes are well developed the rocks display affinities with mid ocean ridge tholeiites the basaltic rocks are comparable to respectively transitional fanuj maskutan and normal tchehel kureh morb in contrast the sequence along the zagros the sahneh sequence appears to have formed in an island arc setting in iranshar i e in southeastern baluchestan ophiolites are dismembered into a melange which includes cumulate intrusives similar to those from fanuj maskutan and lavas with island arc tholeiitic affinity a similar island arc origin may be inferred for the sabzevar ophiolitic sequence north of the lut block studied by other authors the chemical data thus help to elucidate the development of the jigsaw puzzle of microplates of gondwanian origin that during the mesozoic were intermediate in position between afro arabia india and eurasia and that now constitute the middle east ophiolite obduction in iran occurred during arc basin continent or ocean continent collisions in the late cretaceous early paleogene largely predating the final suturing between arabia and india with eurasia to which the intermediate microplates were already attached which did not take place before the neogene

origin of minerals and elements in the late permian coals tonsteins and host rocks of the xinde mine xuanwei eastern yunnan china abstract this paper reports the mineralogical and geochemical compositions of the late permian c2 and c3 coals both medium volatile bituminous coal from the xinde mine near xuanwei in eastern yunnan which is located close to the area with the highest female lung cancer mortality in china the two coals are characterized by high ash yields and low sulfur contents three factors including sediment source region multi stage volcanic ash generation and multi stage hydrothermal fluid injections were responsible for variations in the geochemical and mineralogical compositions of the xinde coals trace elements including v sc co ni cu zn se zr nb hf and ta are enriched in the coals and were mainly derived from the sediment source kangdian upland region major minerals in the samples of coal roof floor and non coal sediment partings include quartz kaolinite and chamosite as well as interstratified illite smectite and anatase chamosite in the coal was derived from reactions between kaolinite and fe mg rich hydrothermal fluids however chamosite in the roof strata was directly precipitated from fe mg rich hydrothermal fluids or was derived from the alteration of precursor minerals e g biotite by hydrothermal fluids quartz in some samples is very high especially in the roof strata of the c2 and c3 coal such high quartz along with minor minerals including pyrite chalcopyrite sphalerite calcite celestite vanadinite barite clausthalite and silicorhabdophane were derived from multi stage hydrothermal fluids the floors of both the c2 and c3 coal seams are fully argillized fine grained tuffaceous claystone and the immediate roof of the c2 coal is argillized coarse grained tuff the original materials of the floors and roofs of these coal seams were high ti alkali basaltic volcanic ashes as indicated by high tio 2 nb and siderophile elements and the distribution patterns of rare earth elements two intra seam tonstein layers in the c3 coal were identified based on their lateral persistence mineralogical mode of occurrence and composition as well as their elemental composition the tonsteins are dominated by kaolinite with minor quartz and possibly mixed layer illite smectite both tonsteins were derived from dacitic magma the ratios of nb ta zr hf and u th are much lower in tonsteins than in the adjacent coal benches which is attributed to the hydrothermal leaching

subsurface structure of the eastern edge of the zagros basin as inferred from gravity and satellite data a data set of 10 505 points of land gravity measurements from southeast iran obtained from the bureau gravimetrique international combined with landsat imagery was used to investigate crustal and cenozoic lithospheric structure interpretation of the bouguer anomalies reveals three primary structural features the zagros mountain belt is characterized by a progressive decrease in gravity values from 70 mgal near the persian gulf to 160 mgal over the suture zone between the arabian margin and central iran crustal blocks the second feature is marked by a backward l shaped pair of anomalies that extends from the eastern peripheries of the zagros basin and wraps around southern iranian shores these 15 to 20 km deep source anomalies with amplitudes of as much as 10 mga are interpreted as intrabasement intrusions demarcating an ancient rift axis the shallow 6 8 km east west trending anomalies are perhaps interbasement uplifts bordered by reverse faults the third structure observed on both gravity and landsat displays a north striking eastward facing topographic escarpment has a gravity gradient of 0 85 mgal km and is right laterally offset approximately 100 km by the zagros main recent fault on landsat this escarpment is manifest by a system of north trending faults that seem to diverge into a horsetail pattern toward the east and by a set of north trending dike swarms that cut jurassic volcano sedimentary rocks it separates two distinct structural and sedimentary styles the zagros foreland basin anticlines of shallow marine precambrian to pliocene rocks on the west and the makran deep water eocene flysch belt on the east a comparison of gravity features with surface structures on thematic mapper and landsat multispectral scanner imagery indicates that a northeast trending fault system is the result of post miocene pervasive transpressive stress coupled with clockwise rotation of underlying basement blocks following the collision of arabia and iran accommodation structures such as forced folds and rabbit ear anticlines may develop over and on the flanks of the basement blocks providing remigration and trapping mechanisms for new oil and gas plays

seismic gravity and magnetic surveys in the central part of the red sea their interpretation and implications for the structure and evolution of the red sea abstract while there is unanimous agreement that the axial part of the red sea has witnessed seafloor spreading since the early pliocene opinions diverge considerably with regard to the situation in the main trough and shelves new high precision data comprising palaeomagnetic seismic gravity magnetic and bathymetric measurements from the central and northern parts of the red sea have been examined to discriminate between the earlier proposed hypotheses and to formulate an evolutionary model for the red sea the results show that oceanic crust extends for about 80 km at 19 n on each side of the spreading axis symmetrical seafloor spreading magnetic anomalies are recognized out to anomaly 3a 6 m y b p between 18 30 and 19 45 n anomaly 2a between 19 45 and 20 n and near 21 n anomaly 2 near 22 n and only anomaly 1 near 23 30 n although anomaly 3a is the oldest recognizable magnetic anomaly the extent and configuration of the oceanic basement as determined from seismic measurements indicate that spreading has started and continued without a hiatus since 10 12 m y b p prior to the initiation of oceanic accretion an extension of 40 55 km i e 50 70 has taken place in the proterozoic continental lithosphere whereas a separation of 70 160 km has occurred during the seafloor spreading phase several lines of evidence indicate that the shelves and the marginal parts of the main trough are of continental nature

deep crustal structure and flexure of the arabian plate beneath the zagros collisional mountain belt as inferred from gravity observations the zagros mountain belt region a neogene continental collisional zone between arabia and iran that is characterized by a suture a folded belt and a foreland basin is unusual among active mountain belts in that its 6 12 km thick sedimentary cover is shortening predominantly by folding while the basement is apparently thickening along numerous high angle reverse faults we have used over 9000 gravity measurements in the region in conjunction with limited seismological observations and geological cross sections of the uppermost 10 km of crust to infer the deeper crustal structure beneath the region crustal models constrained by the bouguer anomalies and other seismological and geological data are characterized by a moho that dips about 1 to the northeast beneath the folded belt and increases in dip to about 5 near the main zagros thrust mzt the moho depth increases from 40 km beneath the leading edge of the foreland basin the mesopotamian foredeep and persian gulf to as much as 65 km beneath the mzt alternative models that incorporate a subducted oceanic crust that is attached to the underthrusting arabian crust deviate little in their moho configurations from the above simpler models negative isostatic residual anomalies are interpreted to indicate local overcompensation beneath the foreland basin and near the folded belt and beneath the mzt we show that underthrust sedimentary rocks of the converging margins along the suture zone may account for the negative isostatic residual anomalies near the mzt however to explain the rest of the isostatic anomalies requires other forces to be acting on this collisional plate boundary for example elastic flexure models required a combination of topography and subsurface loads or downward force the origin of which is not clear to approximate the bouguer or isostatic residual anomalies associated with the foreland basin and the folded belt the topography load of the zagros mountain belt is insufficient to cause the required deflection of the underthrusting arabian plate a combination of isostatic elastic flexure and horizontal compression forces acting on the edge of the arabian craton and the transitional lithosphere of central iran appears to best model the crust of the zagros region we propose a model in which the lower crust of the converging arabian plate located beneath the zagros is being shortened and thickened plastically between the seismogenic rigid upper crust and a rigid uppermost mantle lid the mantle lid probably decoupled from the lowermost crust un der thrusts the iranian crustal blocks thus confined from below the horizontally compressed plastic lower crust hydraulically depresses the moho and raises the faulted and folded brittle upper crust in isostatic equilibrium

40ar39ar ages and tectonic setting of ophiolite from the neyriz area southeast zagros range iran abstract an ophiolite considered to be an allochthonous fragment of tethyan oceanic crust and mantle crops out near neyriz in the zagros range iran 40 ar 39 ar ages ranging from 76 8 23 8 ma to 105 23 3 ma were measured on hornblende from five samples of plagiogranite and diabase from the ophiolite the most precise ages are 85 9 3 8 ma for a diabase and 83 6 8 4 ma for a plagiogranite the weighted mean age of hornblende from the five samples is 87 5 7 2 ma which indicates that the igneous part of the neyriz ophiolite formed during the early part of the late cretaceous pargasite from amphibolite below peridotite of the neyriz ophiolite has a 40 ar 39 ar age of 94 9 7 6 ma the pargasite age agrees within analytical uncertainty with the ages measured on diabase and plagiogranite comparable ages have been measured on igneous rocks from the samail ophiolite of oman and on amphibolite below peridotite of the samail ophiolite

petrographic and geochemical characteristics of organic rich shale and tuff of the upper triassic yanchang formation ordos basin china implications for lacustrine fertilization by volcanic ash the upper triassic chang 7 member lacustrine organic rich shale of the yanchang formation of the ordos basin is a significant hydrocarbon source rock containing abundant of tuff intervals ranging from millimeters to tens of centimeters thick the present study relies upon petrographic and geochemical data of chang 7 tuff intervals and organic rich shale to consider fertilization of the lake surface by volcanic debris as a triggering mechanism of black shale sedimentation paleoproductivity proxies including p al ni al and cu al display elevated values in association with tuff intervals suggesting increased productivity induced by volcanic nutrient seeding of the lake surface moreover vertical variations of toc mimic trends of paleoproductivity proxies indicating that primary productivity was critical to organic carbon enrichment of the chang 7 member previous studies have postulated that lake bottom redox conditions were predominantly oxic suboxic during deposition of the chang 7 and that these d

stability of streambanks formed in partially saturated soils and effects of negative pore water pressures the sieve river italy abstract streambanks of alluvial channels are usually composed of loose materials which are unsaturated in ambient conditions unsaturated soils are subject to negative pore water pressures which cause an apparent cohesion the latter is the main factor in allowing the stability of near vertical banks even during moderate in bank flow events the apparent cohesion can be strongly reduced as the material approaches full saturation therefore during the drawdown phase as the confining pressure of the water in the channel disappears a bank failure is likely to occur channel bed level lowering along the sieve river central italy has caused widespread bank instability a geomorphological reconnaissance of forms and processes was followed by in situ tests to determine the shear strength of the banks interpretation of the tests and a streambank stability analysis were based on concepts of soil mechanics for unsaturated soils in order to obtain relations between bank angle and height in limit equilibrium conditions a stability chart was obtained with curves for different apparent cohesion values and a stability analysis was performed taking into account the effects of flow events in order to investigate the pore pressure effects a series of piezo tensiometers were installed in a streambank of the sieve river data from a 1 year monitoring period show variations in pore water pressure and matric suction as a consequence of rainfall evapotranspiration and water stage variations a planar failure with a tension crack occurred in the upper cohesive part of the bank during december 1996 the safety factor has been expressed as a function of the geometry of the bank and of the shear strength of the material safety factor variations through time are therefore shown as a function of seasonal variations in matric suction

nature of the red sea crust a controversy revisited whether the red sea floor is underlain mostly by oceanic or extended continental crustal material is a controversial topic to test between the two hypotheses we used a digital color mosaic of 23 landsat thematic mapper tm scenes with field geochemical and geochronological data to identify and correlate crosscutting geologic features on the african and arabian sides faults shear zones sutures granitic complexes volcano sedimentary units and dike swarms align if arabia is rotated relative to africa by 6 7 around a pole at lat 34 6 n long 18 1 e this solution implies that the amount of continental crust underlying the red sea is small because the restored red sea coasts are typically juxtaposed

fast evolving conduits in clay bonded sandstone characterization erosion processes and significance for the origin of sandstone landforms abstract in strelec quarry the czech republic an underground conduit network 300 m long with a volume of 10 4 m 3 and a catchment of 7 km 2 developed over 5 years by groundwater flow in cretaceous marine quartz sandstone similar landforms at natural exposures conduits slot canyons undercuts are stabilized by case hardening and have stopped evolving the quarry offers a unique opportunity to study conduit evolution in sandstone at local to regional scales from the initial stage to maturity and to characterize the erosion processes which may form natural landforms prior to stabilization a new technique was developed to distinguish erodible and non erodible sandstone surfaces based on measurements of relative erodibility drilling resistance ambient and water saturated tensile strength ts at natural and quarry exposures three distinct kinds of surfaces were found 1 erodible sandstone exposed at 60 of surfaces in quarry this sandstone loses as much as 99 of ts when saturated 2 sub vertical fracture surfaces that are non erodible already prior to exposure at ground surface and which keep considerable ts if saturated 3 case hardened surfaces that start to form after exposure in favorable conditions they became non erodible and reach the full ts in just 6 years an increase in the hydraulic gradient from 0 005 to 0 02 triggered conduit evolution based on long term monitoring of water table in 18 wells and inflows to the quarry rapidly evolving major conduits are characterized by a channel gradient of 0 01 a flow velocity 40 cm s and sediment concentration 10 g l flow in openings with a discharge 1 ml s and hydraulic gradient 0 05 exceeds the erosion threshold and initiates piping in the first phase of conduit evolution fast concentrated flow mobilizes erodible sandstone between sets of parallel fractures in the shallow phreatic zone in the second phase the conduit opening mainly expands vertically upward into the vadose zone by mass wasting of undercut sandstone slabs mass wasting is responsible for 90 of mobilized sandstone sides of the mature conduits are protected by non erodible fracture surfaces natural landforms were probably formed very rapidly by overland flow piping and possibly fluidization during or at the end of the glacial periods when sandstone was not yet protected by case hardening

tonsteins of hat creek british columbia a preliminary study abstract the four superimposed coal zones a b c d lie in the hat creek graben in folded and faulted eocene strata the tonsteins of hat creek although numerous distinctive and matchable have yet to be studied in detail a composite log of ddh 106 606 m long was therefore constructed using 76 consecutive samples and earlier drill records to show coal zones a b c d seam and interseam material up to 72 tonsteins each 0 5 to 18 cm thick and layers of petrified wood and siderite zone a contains 28 tonsteins one every 6 4 m zone b 5 one every 16 4 m zone c 9 one every 8 2 m zone d 17 one every 6 4 m local overturning is indicated sedimentologically and possibly by the order petrified wood tonstein siderite and the similar tonstein density of zones a and d tonsteins from 329 m 247 m 229 m 212 m numbered 1 2 3 4 examined microscopically and by xrd xrf aa and infra red spectrophotometry consist of crandallite caa1 phosphate phytoclasts kaolinite ankerite calcite quartz anatase apatite and siderite allophane elemental values are variable tio 2 for nos 1 and 4 indicate a silicic magma for no 2 a mafic magma while no 3 is neither tio 2 al 2 o 3 ratios show no 1 to be silicic whereas nos 2 3 4 are neither sio 2 al 2 o 3 ratios are inconclusive an upward increase in k rb from 1 to 3 indicates either incrasing mafic ness or an increase in contaminant k rb sr values are low while ba sr have more in common with mafic than silicic rock future work on the tonsteins should include optical and sem analysis of the shards quantitative trace element modelling to determine magma sources and elemental analysis of the associated coal to determine whether in addition to the volcanic explosions represented by the tonsteins the original coal swamps were subjected to a continuous drizzle of volcanc dust as it is the tio 2 and tio 2 al 2 o for 64 samples of coal would if these elements were of magmatic and not detrital origin indicate silicic dust

precise 40ar 39ar ages from the metamorphic sole of the mersin ophiolite southern turkey abstract the mersin ophiolite is located on the southern flank of the e w trending central tauride belt in turkey it is one of the late cretaceous neotethyan oceanic lithospheric remnants the mersin ophiolite formed in a suprasubduction zone tectonic setting in southern turkey at the beginning of the late cretaceous the mersin ophiolite is one of the best examples in turkey in order to study reconstruction of ophiolite emplacement along the alpine himalayan orogenic belt 40ar 39ar incremental heating measurements were performed on seven obduction related subophiolitic metamorphic rocks hornblende separates yielded isochron ages ranging from 96 0 0 7 ma to 91 6 0 3 ma all errors 1 five of the seven hornblende age determinations are indistinguishable at the 95 confidence level and have a weighted mean age of 92 6 0 2 2 ma we interpret these ages as the date of cooling below 500 c intraoceanic thrusting occurred 4 ma soon after formation of oceanic crust the sole was crosscut by microgabbro diabase dikes less than 3 m y later the final obduction onto the tauride platform occurred during the late cretaceous early paleocene our new high precision ages constrain intraoceanic thrusting for a single ophiolite mersin in the tauride belt

distribution of sulfur and pyrite in coal seams from kutai basin east kalimantan indonesia implications for paleoenvironmental conditions abstract thirteen miocene coal samples from three active open pit and underground coal mines in the kutai basin east kalimantan indonesia were collected according to our microscopical and geochemical investigations coal samples from sebulu and centra busang coal mines yield high sulfur and pyrite contents as compared to the embalut coal mine the latter being characterized by very low sulfur

late middle miocene volcanism in northwest borneo southeast asia implications for tectonics paleoclimate and stratigraphic marker abstract explosive volcanic events often produce pyroclastic materials that can be recognized from the geological record these discrete pyroclastics form regional marker beds here we report the occurrence of a tephra layer interbedded within very thick coal beds near mukah sarawak borneo traceable for tens of kilometers in the mukah area of sarawak this tephra layer can be considered as regional stratigraphic marker with precise chronostratigraphic control systematic sedimentological mineralogical geochemical and zircon u pb geochronological studies have revealed a major effusive volcanic event during the latest middle miocene presumably contemporaneous and or related to a magmatic event of an earlier phase of the mt kinabalu pluton or magmatism in west sarawak or east sabah the volcanic event had promoted catastrophic flooding of coastal swamps and fall out from the ash clouds that formed a regionally monotonous tephra layer across the serravallian tortonian boundary in conjunction with the regional occurrences of trap rocks structural trends and known tectonic events we constrained the regional depositional environments and climate the tephra layer was deposited in a coastal plain swamp seasonal shallow high moderate energy fluvial channel lacustrine environmental setting wherein atmospheric fallout and eroded material from regoliths formed over older basement and volcanic rocks of the hinterland which were mixed to produce the tephra layer this tephra layer is sandwiched between the very thick coal beds a pre existent volcanic chamber that was active for a long time also experienced periodic explosive activity from probably the same magma chamber and conduit and including a major explosive activity that recycled early formed crystals and felsic magma rhyolite dacite during the major effusive event are also recognized our findings provide robust evidence for the prevalence of intensive chemical weathering under a wet humid climate and relative tectonic quiescence before the major effusive event and the existence of vast monotonously gently sloping coastal plains and luxuriant vegetation akin to the present

collision and rifting in the tethys ocean geodynamic implication abstract the tethys ocean was formed 250 m y ago when gondwana collided with laurasia since then and up to its closure about 40 50 m y ago the development of the ocean was dominated by repeated jumps of the spreading axes to the passive margin of gondwana splitting of microcontinents their transportation across the ocean and accretion to the active margin of eurasia it appears that jumps of the spreading centre and rifting of the passive margin coincided with periods of major collisions on the active margin several epochs of collision and rifting are described the late permian mid late triassic late jurassic early cretaceous end of the early cretaceous late eocene the simultaneous occurrence of rifting and collision has important geodynamic implications and it cannot be explained if only the forces applied to plate margins i e slab pull and ridge push are considered as the plate drying forces slab pull did not act in times of collision when the subduction zone was blocked by continental fragments and the ridge push creates compression but not extension on the passive margin it is suggested instead that the conveyor belt process of transportation of continental masses from the passive to the active margin of tethys was governed by north directed convective flow in the asthenosphere in times of collision when lithospheric plates were unable to move with the flow the latter created great tensile stresses in the overlying lithosphere that led to formation of rifts and then to new spreading centres

origin and distribution of tonsteins in late permian coal seams of southwestern china abstract we have surveyed the areal and stratigraphic distribution of tonsteins in late permian coalfields of southwestern china over an area of several hundred thousand square kilometers we studied the relationship between tonstein distribution and sedimentary environment based on mineralogical and petrographic data we have concluded that these tonsteins originated as air fall volcanic ashes following accumulation in the peat swamps in situ alteration of the vitric and lithic components took place under acidic conditions leading to the formation of kaolinite based on petrologic mineralogic and chemical analytical data we have determined that the application of mineralogic and geochemical criteria for tonsteins may be useful in correlating coal beds predicting coal qualities and reconstructing related sedimentary paleoenvironmental conditions

measuring streambank erosion due to ground water seepage correlation to bank pore water pressure precipitation and stream stage limited information exists on one of the mechanisms governing sediment input to streams streambank erosion by ground water seepage the objective of this research was to demonstrate the importance of streambank composition and stratigraphy in controlling seepage flow and to quantify correlation of seepage flow erosion with precipitation stream stage and soil pore water pressure the streambank site was located in northern mississippi in the goodwin creek watershed soil samples from layers on the streambank face suggested less than an order of magnitude difference in vertical hydraulic conductivity ks with depth but differences between lateral ks of a concretion layer and the vertical ks of the underlying layers contributed to the propensity for lateral flow goodwin creek seeps were not similar to other seeps reported in the literature in that eroded sediment originated from layers underneath the primary seepage layer subsurface flow and sediment load quantified using 50 cm wide collection pans were dependent on the type of seep intermittent low flow lf seeps flow rates typically less than 0 05 l min 1 persistent high flow hf seeps average flow rate of 0 39 l min 1 and buried seeps which eroded unconsolidated bank material from previous bank failures the timing of lf seeps correlated to river stage and precipitation the hf seeps at goodwin creek began after rainfall events resulted in the adjacent streambank reaching near saturation i e soil pore water pressures greater than 5 kpa seep discharge from hf seeps reached a maximum of 1 0 l min 1 and sediment concentrations commonly approached 100 g l 1 buried seeps were intermittent but exhibited the most significant erosion rates 738 g min 1 and sediment concentrations 989 g l 1 in cases where perched water table conditions exist and persistent hf seeps occur seepage erosion and bank collapse of streambank sediment may be significant copyright 2007 john wiley sons ltd

empirical sediment transport function predicting seepage erosion undercutting for cohesive bank failure prediction summary seepage erosion is an important factor in hillslope instability and failure however predicting erosion by subsurface flow or seepage and incorporating its effects into stability models remains a challenge limitations exist with all existing seepage erosion sediment transport functions including neglecting the three dimensional geometry of the seepage undercut and the cohesive nature of soils the objective was to develop an empirical sediment transport function that can predict seepage erosion and undercutting with time based on three dimensional soil block experiments covering a wide range of hydraulic soil type slope and bulk density combinations the transport function was represented by an excess gradient equation r2 0 54 the critical gradient was predicted by the soil cohesion based on laboratory experiments using a three dimensional gaussian function the geometric relationships between the maximum distance and lateral and vertical dimensions of the undercut were then derived the proposed empirical relationships reasonably predicted the observed volume per unit area of undercut erosion rate and time at which a given amount of undercut developed the flow gradient can be used with the derived sediment transport function the first ever relationship proposed for predicting the dimensions and the geometry of the undercut to predict the impact of seepage erosion undercutting on hillslope stability users only need to input the seepage layer s cohesion bulk density and the hydraulic gradient over time in the near bank ground water system

space time patterns of magmatism along the tethysides a preliminary study five maps showing spatio temporal evolution of magmatism along the tethysides for the following time intervals late carboniferous and permian 320 248 ma triassic and early jurassic 247 188 ma

cenozoic palaeogeographic evolution of sulawesi and borneo abstract sulawesi and borneo are located in the middle of the indonesian archipelago an area which has been extremely tectonically active throughout the cenozoic this paper compiles current knowledge on the geology and palaeogeography of this complex region and includes the first attempt to synthesise palaeogeographic data onto plate tectonic reconstructions construction of palaeogeographic maps helped to identify some of the strengths and weaknesses of current plate tectonic models for the region thereby highlighting areas where further geological research is required palaeogeographic maps presented using plate tectonic reconstructions as a base illustrate the evolution of borneo and sulawesi and highlight important changes in the environment during the cenozoic the tertiary geological history of eastern borneo and sulawesi is inextricably linked to the progressive accretion of continental and oceanic material from the east onto the eastern margin of sundaland and to the resultant development of volcanic arcs large tracts of western sulawesi eastern borneo the east java sea and the makassar straits formed an extensive basinal area throughout much of the tertiary implications for plate tectonics exploration for natural resources and biogeography are discussed from the palaeogeographic reconstructions of sulawesi and borneo

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

influence of seepage undercutting on the stability of root reinforced streambanks several mechanisms contribute to streambank failure including fluvial toe undercutting reduced soil shear strength by increased soil pore water pressure and seepage erosion recent research has suggested that seepage erosion of noncohesive soil layers undercutting the banks may play an equivalent role in streambank failure to increased soil pore water pressure however this past research has primarily been limited to laboratory studies of non vegetated banks the objective of this research was to utilize the bank stability and toe erosion model bstem in order to determine the importance of seepage undercutting relative to bank shear strength bank angle soil pore water pressure and root reinforcement the bstem simulated two streambanks little topashaw creek and goodwin creek in northern mississippi simulations included three bank angles 70 to 90 four pore water pressure distributions unsaturated two partially saturated cases and fully saturated six distances of undercutting 0 to 40 cm and 13 different vegetation conditions root cohesions from 0 0 to 15 0 kpa a relative sensitivity analysis suggested that bstem was approximately three to four times more sensitive to water table position than root cohesion or depth of seepage undercutting seepage undercutting becomes a prominent bank failure mechanism on unsaturated to partially saturated streambanks with root reinforcement even with undercutting distances as small as 20 cm consideration of seepage undercutting is less important under conditions of partially to fully saturated soil pore water conditions the distance at which instability by undercutting became equivalent to instability by increased soil pore water pressure decreased as root reinforcement increased with values typically ranging between 20 and 40 cm at little topashaw creek and between 20 and 55 cm at goodwin creek this research depicts the baseline conditions at which seepage undercutting of vegetated streambanks needs to be considered for bank stability analyses copyright 2008 john wiley sons ltd

petrology and genesis of upper carboniferous seams from the ruhr region west germany abstract the petrology of 21 seam profiles of upper carboniferous age westphalian c and b has been studied in order to determine their depositional environments and diagenetic history the youngest profile was drilled at a depth of 790 m and is mainly overlain by cretaceous sediments the oldest seam was reached at a depth of 1470 m the seam thicknesses vary from 0 4 to 2 5 m the main petrographic compounds are vitrinite intertinite liptinite and minerals the last group occurs as clay bands with illite kaolinite minor chlorite and minor quartz contents or as crack or pore filling calcite fe dolomite siderite pyrite or marcasite or as syngenetic siderite concretions and pyrite crystals the percentages of the different macerals and minerals vary mainly because of different depositional environments diagenetic loss or genesis of compounds is a less important factor in their distribution three types of profiles are distinguished by their different petrologies type i is most abundant and contains much vitrinite many clay bands and syngenetic iron sulfides whereas type iii is rich in inertinite and certain characteristic spores type ii is intermediate but generally contains only low percentages of minerals generally this type is vitrinite rich in the lower and inertinite rich in the central and upper parts of the profiles spores and other liptinites are much better preserved in all the seams than in clay partings or in siltstones and sandstones above and below the seams the seams are interpreted to be former autochthonous peats type i profiles are probably derived from swamps which were sometimes inundated and covered by overbank deposits type ii and iii seams represent former peats which were not inundated by rivers and partly grew under the influence of more oxidizing conditions therefore they contain more inertinite and less sulfide and clay bands they can be interpreted as former raised bogs diagenetic changes are expressed as increases of vitrinite reflectances from 0 65 to 1 0 and of liptinite reflectances a red shift of fluorescence of liptinites was found increasing amounts of exudatinite and micrinite and decreasing amounts of fluorinite and resinite were found minerals seem to be less affected by diagenesis illite crystallinity for example remains poor

volcanogenic tonsteins from tertiary coal measures east kalimantan indonesia abstract laterally persistent tonsteins up to 30 cm thick occur in coal seams and associated sediments in the tertiary kutei basin of east kalimantan indonesia where neogene strata which form a generally eastward prograding marginal marine to fluvio deltaic sequence are disposed in a north northeast to south southwest striking fold belt centred on samarinda eight tonsteins have so far been recorded in the middle to upper miocene of the badak syncline some 40 km south southwest of samarinda and range from tonsteins in the strict sense kaolinite mudstones of wide stratigraphical extent including graupen and kristall varieties to smectite mudstones they may pass laterally into each other most contain pyroclasts in varying stages of alteration and are regarded as volcanogenic primary textures include microscopic vitroclastic aggregates completely argillised to smectite graded crystal tuffs with abundant sanidine glass shards and secondary vermiform kaolinite crystals and argillised lithic tuffs texturally and compositionally these tertiary tonsteins are closely similar to european carboniferous tonsteins and this strengthens the conclusion of a volcanogenic origin even where pyroclastic textures have been removed through alteration the east kalimantan tonsteins are of economic and stratigraphic significance in providing distinctive horizons which have proved useful in aiding correlation of boreholes drilled in a coal resource project in this area

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

seepage caused tension failures and erosion undercutting of hillslopes summary seepage has been suggested as an important factor in gully and river bank erosion this study investigated the underlying mechanisms of instability by seepage in laboratory studies a 25 cm tall 50 cm wide and 20 cm long soil block with a focused inflow reservoir was constructed to investigate seepage gradient forces and the three dimensional nature of seepage particle mobilization i e seepage erosion and undercutting experiments included sand and loamy sand soil blocks packed at prescribed bulk densities 1 30 1 70 mg m 3 and with an outflow face at various angles 90 75 and 60 constant heads of 15 25 and 35 cm were imposed on the soil to induce flow a laser scanner was utilized to obtain the three dimensional coordinates of the bank and undercut surfaces at approximately 15 30 s intervals the bulk density of the two different soil types controlled which seepage failure mechanism occurred 1 tension or pop out failures due to the seepage force exceeding the soil shear strength which was being concurrently reduced by increased soil pore water pressure or 2 particle entrainment in the seepage flow particle mobilization bank undercutting and bank collapse when the initial seepage force gradient was less than the resistance of the soil block for cases experiencing particle mobilization and undercutting seepage erosion initiated as unimodal i e concentrated at one point or as multimodal i e initiating at several locations across the bank face and this result was largely controlled by the bank angle a five parameter gaussian function was fitted to the measured three dimensional undercut shapes to derive parameters for the maximum depth of undercutting position of the center of the peak and the vertical and lateral spreads of the undercut the parameters of this distribution can be useful in the development of improved sediment transport functions and the incorporation of this failure mechanism into hillslope stability models

the geotectonic history of the makran and adjacent areas of southern iran abstract the makran mountain range in southern iran has been entirely covered by regional mapping on a scale of 1 250 000 but in contrast to the mapping of oman on the other side of the gulf the recent mapping is little known the cenozoic accretionary prism in the south fronts onto a mesozoic melange zone representing earlier subduction and to the north of this is an eastwards tapering microcontinental sliver which is followed by a zone of largely intact mesozoic ophiolite complexes to the north of this lies the jaz murian depression a desert expanse with no bedrock outcrop the sanandaj sirjan bajgan dur kan microcontinental sliver which extends from turkey through the zagros to the makran is one of a number of microcontinents which detached from gondwana no later than the early triassic nw iran yazd tabas lut birk helmand farah during the mesozoic these were enclosed by tracts of ocean now represented by ophiolites and the sectors closed at different times ranging from early cretaceous to end palaeogene an analogy is drawn with the present day mediterranean the sistan ocean in the east was infilled with an immense thickness of abyssal turbidites during the eocene before it closed the field evidence indicates that there was a second cenozoic accretionary prism here but sedimentation ceased after the eocene on its collision with the back of the main makran prism this eastern sistan trough now completely occluded is compared with the still open tract separating the makran from oman at the present time and its northern extension which has been similarly occluded by collision beneath the zagros some residual very shallow inland seas persisted inland from the makran through the neogene the occurrence of blueschists in the inner ophiolite belt of the makran is discussed abyssal turbidite sedimentation continued in the main southern zone of the makran into the early miocene to be succeeded by thick shallow water sequences including reefal limestones intense tectonic dislocation at the end of the miocene was accompanied by a shift of the subduction front to its present position out in the indian ocean and uplift leading to the deposition of spectacular pliocene pleistocene fanglomerates

mechanisms of ephemeral gully erosion caused by constant flow through a continuous soil pipe ephemeral gully erosion is considered to be driven by convergent surface flow while the role of subsurface flow is often overlooked this study sought to characterize and quantify the soil erosion mechanisms associated with ephemeral gully erosion by pipe flow a soil pipe 1 cm o d was formed in a 10 cm soil bed immediately above a 5 cm water restricting layer flow into the soil pipe was established at steady state rates of 190 and 284 l h 1 experiments were performed for pipe flow alone and with rainfall despite a constant flow rate into soil pipes pipe flow was highly unstable due to internal mass wasting clogging soil pipes until pressure increases forced the debris plug out of the pipe short 10 20 seconds periods of negligible flow were followed by surges in flow with high sediment concentrations that included a high proportion of aggregates increases in soil water pressures associated with these debris flows were observed but were likely not representative of the pressures inside the soil pipes due to hydraulic non equilibrium between the soil pipe and soil matrix hydraulic non equilibrium resulted in hydraulic gradients in the opposite direction of flow through the soil pipe during early stages of pipe flow pipe flow rates and sediment concentrations during debris flow periods were likely more extreme than observed due to integration over the three minute sample collection interval the slot erosion test set was extended to conditions of constant flow rate through an internal soil pipe that was observed at the front face of a soil bed the modified set provided estimates of shear stress between 2 2 to 5 3 kg m 1 s 2 however the technique did not prove effective for estimation of the soil erodibility coefficient published in 2009 by john wiley sons ltd

differentiation of volcanic ash fall and water borne detrital layers in the eocene senakin coal bed tanjung formation indonesia abstract the sangsang deposit of the eocene senakin coal bed tanjung formation southeastern kalimantan indonesia contains 11 layers which are thin 70 these layers are characterized by their pelitic macroscopic texture examination of eight of the layers by scanning electron microscopy energy dispersive x ray and x ray diffraction analyses show that they are composed primarily of fairly well crystallized kaolinite much of which is vermicular accessory minerals include abundant ti oxide rare earth element rich ca and a1 phosphates quartz that luminescences in the blue color range and euhedral to subhedral pyroxene hornblende zircon and sanidine although this mineral suite is suggestive of volcanic ash fall material only the four pelitic layers in the middle of the bed are thought to be solely derived from volcanic ash falls on the basis of diagnostic minerals replaced glass shards and lithostratigraphic relationships observed in core and outcrop the three uppermost pelitic layers contain octahedral chromites some quartz grains that luminesce in teh orange color range and some quartz grains that contain two phase fluid inclusions these layers are interpreted to be derived from a combination of volcanic ash fall material and hydrologic transport of volcaniclastic sediment in contrast the lowermost pelitic layer which contains large rounded femg rich chromites is thought to have been dominantly deposited by water the source of the volcanic ash fall material may have been middle tertiary volcanism related to plate tectonic activity between kalimantan and sulawesi the volcanic ash was deposited in sufficient amounts to be preserved as layers within the coal only in the northern portions of the senakin region the southern coal beds in the region do not contain pelitic layers

constraints on arabian plate motion and extensional history of the red sea analysis of the geologic and geophysical data from the western and northern margin of the arabian plate combined with data from the red sea gulf of aden leads to an interpretation of arabian plate motion that supports an episodic extensional history in the red sea and gulf of aden phase 1 extension began in medial to late eocene and was caused by the nw propagation of the reoriented central indian ridge spreading center it stretched and thinned continental crust along numerous wrench and normal faults that reactivated preexisting structures first phase extension stopped when the arabian plate terminally sutured to eurasia in the medial miocene and halted northward movement of arabia relative to africa the combined african arabian plates moved north more slowly constricting and thickening continental crust in the bitlis zagros sutures while the red sea remained technically quiescent and accumulated salt by the early pliocene continued northward movement was accommodated by lateral extrusion of large continental wedges north of the bitlis zagros sutures this allowed arabia to move northward faster than africa and reopen the red sea where phase 2 extension was expressed by seafloor spreading extension within the red sea gulf of aden rift system has been controlled by the interactions and effects of two factors 1 convergent processes between the north margin of the arabian plate and the eurasian plate to the north and 2 northwest propagation of extension associated with the medial eocene reorganization of the central indian spreading center

petrography and geochemistry of tonsteins from the 4th member of the upper triassic xujiahe formation in southern sichuan province china petrographic and geochemical studies on five layers of tonsteins from the 4th member of the upper triassic xujiahe formation t3xj4 in the southern sichuan province of china are presented in this paper the results suggest that these tonsteins were derived from synsedimentary acid volcanic ash fallout which was subsequently altered into relatively pure kaolinitic rocks through hydrolysis and diagenesis in a peat bog environment for definition of tonsteins refer to geol soc am spec pap 285 1993 the petrographic texture is mainly of dense and granular types with a subordinate crystalline type each tonstein layer is characterized by its unique petrographic texture mineral content and assemblage of lithophile elements which is related to the composition of its parent magma the trace element geochemistry of these tonsteins is elaborated in this paper which also suggests an origin as silicic volcanic ash fallout typically these features are relatively consistent within the same tonstein layer over a broad lateral extent and are characteristic of each specific tonstein layer therefore some tonsteins in this region serve as distinct marker beds for correlation of coal seams within the framework of regional chronostratigraphy

numerically predicting seepage gradient forces and erosion sensitivity to soil hydraulic properties summary research has suggested that streambank seepage can be an important mechanism of bank instability however limited information is available on the level of soil characterization necessary to accurately predict seepage gradient forces and erosion the objective of this research was to quantify the expected range of predicted seepage gradients for various degrees of site characterization uncertainty analysis on seepage gradient predictions was performed relative to variability in soil hydraulic properties a two dimensional unsaturated saturated groundwater flow model was used to simulate a homogeneous soil layer for sand and loamy sand soils packed at various bulk densities qb a pedotransfer function rosetta designed to estimate unsaturated hydraulic properties from surrogate soil data i e texture and bulk density was used to derive the saturated hydraulic conductivity ks and water retention parameters for various levels of site information i e only textural class percent sand silt and clay ssc ssc and qb and ssc qb and ks statistical distributions were derived for each soil hydraulic parameter and monte carlo simulations were performed to generate distributions of maximum seepage gradient the deviation in predicted seepage gradient was calculated using assumed baseline conditions ranges in predicted soil hydraulic parameters and maximum seepage gradients were considerably reduced when using ssc as compared to soil texture therefore at a minimum soil samples should be taken for particle size analysis for qb between 1450 and 1500 kg m 3

a new tectonic scenario for the sanandaj sirjan zone iran abstract recent geochemical studies of volcanic rocks forming part of the ophiolites within the zagros and naien baft orogen indicate that most of them were developed as supra subduction ophiolites in intra oceanic island arc environments intra oceanic island arcs and ophiolites now forming the naien baft zone were emplaced southwestward onto the northeastern margin of the south sanandaj sirjan zone while those now in the high zagros were emplaced southwestward onto the northern margin of arabia thereafter subduction continued on opposite sides of the remnant oceans the floor of neo tethys ocean was subducted at a low angle beneath the entire sanandaj sirjan zone and the floor of the naien baft ocean was subducted beneath the central iranian micro continent the naien baft ocean extended into north west iran only temporarily this failed ocean arm between the urumieh dokhtar magmatic assemblage and the main zagros thrust was filled by thick upper triassic upper jurassic sediments the naien baft ocean finally closed in the paleocene and neo tethys closed in the early to middle eocene after arabia was sutured to iran the urumieh dokhtar magmatic assemblage recorded slab break off in the middle eocene

the influence of groundwater on surface flow erosion processes during a rainstorm surface erosion rates on a disturbed natural soil in a 10 m indoor flume increased by an order of magnitude when a water table developed at a 10 cm depth during simulated rainstorms erosion rate increases did not correlate well with surface hydraulic flow conditions and all significant erosion increases began before the full soil depth was saturated before the water table reached the soil surface and before seepage was possible groundwater influenced erosion processes primarily by increasing unsaturated pore water pressures and decreasing soil shear strength in surface rainflow rather than through the direct entrainment of soil particles by seepage flow there was no unique morphologic expression of the influence of groundwater during a rainstorm subsurface processes influencing surface erosion were detected only by appropriate subsurface instrumentation which included micropiezometers tensiometers and time domain reflectometry erosion rate increases occurred all along the slope and were not concentrated at the base of slope due to a seepage zone soil depth was crucial to determining surface erosion increase it is likely that confusing trends in surface flow erosion rates in past studies have occurred due to unrecorded groundwater development or an emphasis on seepage effects groundwater must be monitored along hillslopes under all moisture and soil conditions in order to avoid misleading and inconsistent conclusions derived solely from surface flow or seepage data copyright 2002 john wiley sons ltd

the petrogenesis and tectonic setting of lavas from the baft ophiolitic melange southwest of kerman iran a late cretaceous ophiolite complex in the baft area southwest of kerman iran is characteristic of the central iranian ophiolitic melange belt which wraps around the lut block despite the extensive tectonic disruption of the baft complex most ophiolitic lithologies are present and many original igneous contacts are preserved a lack of cumulate gabbros within the sequence suggests that a large and continuous magma chamber did not exist beneath the baft spreading axis geochemical data confirm the presence of two distinct compositional groups in the mafic lavas 1 tholeiitic basalt and 2 transitional tholeiitic basalt the tholeiitic lavas are similar to typical mid ocean ridge basalt compositions whereas the transitional tholeiites are similar to intraplate basalts the available data suggest that the baft ophiolite complex formed in a small ocean basin possibly at or near a ridge transform intersection emplacement may have occurred as a result of conversion of the transform fault to a subduc

mineral and chemical composition of some claystones from the troyanovo 3 mine maritsa east lignite basin bulgaria abstract this paper presents the results of a detailed mineralogical and geochemical study on five types of claystones from the maritsa east lignite basin in bulgaria the studied samples of each claystone type are composite taken from outcrops at the operated pre stripping and stripping horizon of the mine most of the minerals in claystones such as quartz illite montmorillonite kaolinite plagioclase feldspar zircon and mica have terrigenous origin pyrite arsenopyrite barite calcite apatite gypsum and goethite are authigenic a total of 66 elements were analyzed in samples based on coefficient of enrichment of elements compared to clarke values for clays the samples can be arranged as follows yellow claystone 43 elements black claystone 1 42 elements blue claystone 25 elements black claystone 2 20 elements and white claystone 17 elements the black and yellow claystone have highest content of rare earth elements and yttrium rey gold ag pt and pd are highly and unusually enriched in some samples the dominant mode of occurrence of elements is mineral matter as sorbed on clay minerals illite montmorillonite and kaolinite structurally bound in other silicates plagioclase feldspar apatite and goethite a portion of the studied elements also show affinity to organic matter ca sr mg p s mo sc cr cu cd hg tl as ag and hree y mercury also has clear relation to kaolinite as does u to calcite the la lu sm lu and gd lu refer the claystones to mix l m type yellow blue and black claystones and h type white claystone the rey in claystones is as follows black claystone 1 400 ppm yellow claystone 366 ppm blue claystones 188 ppm black claystone 2 162 ppm and white claystone 146 ppm these concentrations do not imply that the claystones would be a possible source for extraction of rey

soil properties controlling seepage erosion contributions to streambank failure the majority of sediment leaving catchments may be from streambank failure seepage erosion of unconsolidated sand above a restrictive layer is an important erosion process in incised streams that leads to streambank failure by undercutting banks the objective of this study was to determine the impact of soil properties on seepage erosion and the resulting streambank failure seepage flow and sediment concentrations were measured in situ at eight locations along the banks of a deeply incised stream in northern mississippi using field observations as a guide the soil profile conditions of a shallow 45 cm streambank consisting of 30 cm of topsoil a 10 cm conductive layer and a 5 cm restrictive layer were mimicked in laboratory lysimeter experiments to quantify the hydrologic properties controlling seepage erosion and bank failure under a 40 cm head the time to flow initiation and the flow rate were linearly related to the slope of the restrictive layer seepage erosion began within minutes of flow initiation and resulted in substantial 3 to 34 cm undercutting of the bank sediment concentrations of seeps were as high as 660 g l 1in situ and 4500 g l 1 in the lysimeters sediment concentrations were related to the layer slope thereby indicating the importance of detailed site characterization the usda ars streambank stability model demonstrated the increase in instability of banks due to undercutting by seepage erosion but failed to account for the sediment loss due to sapping for stable banks and overestimated the sediment loads for failed banks published in 2006 by john wiley sons ltd

numerical simulation of widening and bed deformation of straight sand bed rivers ii model evaluation in this paper the numerical model presented in the companion paper is tested and applied assessment of model accuracy was based on two approaches first predictions of evolution of a 13 5 km reach of the south fork of the forked deer river in west tennessee were compared to observations over a 24 yr period results suggest that although the model was able to qualitatively predict trends of widening and deepening quantitative predictions were not reliable simulated widths and depths were within 15 of the corresponding observed values but observed change in these parameters at the study sites were also close to these values simulated rates of depth adjustment were within 15 of observed rates but observed rates of channel widening at the study sites were approximately three times those simulated by the model in the second approach the model was used to generate relationships between stable channel width and bank full discharge the model was able to successfully replicate the form of empirically

mineralogy of the volcanic influenced great northern coal seam in the sydney basin australia abstract the mineralogy of the individual coal plies and intra seam claystone bands in the great northern seam of the sydney basin has been evaluated using optical and scanning electron microscopy and quantitative x ray diffraction techniques the uppermost two claystone bands are tonsteins consisting mainly of well ordered kaolinite with graupen to vermicular textures idiomorphic crystals of k feldspar within these tonsteins may represent members of the anorthoclase sanidine series or a sodic sanidine and indicate an acid to intermediate volcanic ash input in contrast the lowermost parting was largely derived from epiclastic sediment admixed with minor volcanic material such as high temperature quartz and a different type of k feldspar component the mineral fraction of the coals especially in the middle and upper parts of the seam is dominated by authigenic kaolinite with a very low abundance of quartz apart from the tonsteins authigenic processes therefore appear to be the dominant mechanism of mineral matter formation authigenic k feldspar also occurs in the lower few metres of the seam with a variety of modes of occurrence including cell and cleat infillings cross cutting veins and thin laminae parallel to the organic matter and detrital clay bands a late syngenetic low temperature hydrothermal fluid injection process is suggested for formation of the feldspar veins the origin of the fluid is uncertain but is most likely associated with contemporaneous volcanic activity

laboratory soil piping and internal erosion experiments evaluation of a soil piping model for low compacted soils mechanistic models have been proposed for soil piping and internal erosion on well compacted levees and dams but limited research has evaluated these models in less compacted more erodible soils typical of hillslopes and streambanks this study utilized a soil box 50 cm long 50 cm wide and 20 cm tall to conduct constant head soil pipe and internal erosion experiments for two soils clay loam from dry creek and sandy loam from cow creek streambanks packed at uniform bulk densities initial gravimetric moisture contents prior to packing were 10 12 and 14 for dry creek soil and 8 12 and 14 for cow creek soil a 1 cm diameter rod was placed horizontally along the length of the soil bed during packing and carefully removed after packing to create a continuous soil pipe a constant head was maintained at the inflow end flow rates and sediment concentrations were measured from the pipe outlet replicate submerged jet erosion tests jets were conducted to derive erodibility parameters for repacked samples at the same moisture contents flow rates from the box experiments were used to calibrate the mechanistic model the influence of the initial moisture content was apparent with some pipes 8 moisture content expanding so fast that limited data was collected the mechanistic model was able to estimate equivalent flow rates to those observed in the experiments but had difficulty matching observed sediment concentrations when the pipes rapidly expanded the jets predicted similar erodibility coefficients compared to the mechanistic model for the more erodible cases but not for the less erodible cases 14 moisture content improved models are needed that better define the changing soil pipe cross section during supply and transport limited internal erosion especially for piping through lower compacted more erodible soils as opposed to more well compacted soils resulting from constructing levees and dams copyright 2013 john wiley sons ltd

is the vourinos complex an island arc ophiolite abstract a geochemical study has been undertaken on the vourinos ophiolites northern greece a complex long known for its unusual characteristics such as an environment of acidic rocks and a calc alkaline chemical affinity the nd sr isotopic ratios and the hf th and ta th ratios are indicative of an island arc origin for vourinos as opposed to the mid oceanic ridge origin inferred for other ophiolites such as inzecca corsica other data on trace elements confirm that the cumulative suite and the lavas originated from the same magma through a simple fractional crystallization process and show that this magma would have formed through partial melting of an already highly depleted material it is thus possible to distinguish ophiolites with morb characteristics from island arc ophiolites such as the vourinos complex the existence of the latter type imposing new constraints on the possible tectonic processes for emplacement

on slope instability induced by seepage erosion this paper is focused on seepage erosion causing liquefaction processes and rapid slope failures one case history which occurred along an old fluvial terrace in the po plain northern italy is