ion microprobe analysis of oxygen isotopes in garnets of complex chemistry abstract accurate ion microprobe analysis of oxygen isotope ratios in garnet is possible if appropriate standards are employed to correct for instrumental bias a component of which depends on the cation chemistry of the analyzed mineral in this study 26 garnet standards including 14 new standards that span the compositional range of pyrope almandine grossular spessartine and andradite were analyzed repeatedly by ion microprobe to develop a new method of correcting for instrumental bias in garnets all analyses were normalized to a single master garnet standard uwg 2 before bias from cation composition was considered bias due to cation composition in garnet was found to correlate with grossular content in pyralspite garnets and with andradite in ugrandite garnets bias is correlated with molar volume in garnets of all compositions in this study although this correlation is suitable as a correction scheme for bias a more accurate correction scheme based on the grossular and andradite compositions of garnet is proposed this method reproduces the bias of all but one standard to within a range of 0 4 an accuracy that is on the same order as the reproducibility 0 3 2 s d of the master garnet standard uwg 2 but that remains an independent source of error the new correction scheme is used to successfully reproduce laser fluorination analyses along a traverse of a polymetamorphic zoned skarn garnet from the adirondack mountains while previous analyses were at the mm scale the new data resolve a gradient of 18 o of 2 1 over 16 m if experimentally derived diffusion coefficients are correct these new results show that granulite facies metamorphism was significantly faster than previously assumed and the thermal peak was less than 5 myr

neoproterozoic snowball earth simulations with a coupled climate ice sheet model ice sheets may have reached the equator in the late proterozoic era 600 800 myr ago according to geological and palaeomagnetic studies possibly resulting in a snowball earth but this period was a critical time in the evolution of multicellular animals posing the question of how early life survived under such environmental stress here we present computer simulations of this unusual climate stage with a coupled climate ice sheet model to simulate a snowball earth we use only a reduction in the solar constant compared to present day conditions and we keep atmospheric co2 concentrations near present levels we find rapid transitions into and out of full glaciation that are consistent with the geological evidence when we combine these results with a general circulation model some of the simulations result in an equatorial belt of open water that may have provided a refugium for multicellular animals

glacial and syntectonic sedimentation the upper proterozoic kingston peak formation southern panamint range eastern california a sedimentological stratigraphic study of the upper proterozoic kingston peak formation in the southern panamint range shows that it was deposited under glacial conditions with contemporaneous volcanism and tectonic activity evidence for glaciation rests primarily upon 1 the homogeneity thickness and lateral extent of two diamictite units 2 the facies association of the diamictite and 3 presence of striated stones and dropstones within the formation elsewhere in the death valley area in the panamint range pillowed basalt interbedded with diamictite demonstrates synchronous subaqueous volcanism lower kingston peak units rest on a variable substrate and locally overlap faults indicating tectonism prior to deposition tectonism during kingston peak deposition is inferred from abrupt thickness changes and buried faults sedimentation was chiefly on a submerged continental platform and locally terrestrial during a period of incipient rifting two ice advances are recorded with associated sea level fluctuations the formation thickens northward from 40 to about 1 200 m over 40 km initial sediments were fine grained and in basins a few kilometres across nearby islands provided coarse debris overlying sandstone and conglomerate indicate regression predominantly massive diamictite as much as 450 m thick and interpreted as lodgment till or glacioma rine sediment records the first ice advance a northward increase in diamictite thickness decrease in clast size and facies change from diamictite to argillite and graywacke suggest a southern source overlying laminated limestone marks a transgression succeeding interbedded sandy limestone thick bedded graywacke and parallel laminated siltstone and sandstone double in thickness over a few kilometres demonstrating local subsidence and renewed terrigenous input trough cross laminated arkosic sandstone and conglomerate overlain by predominantly massive diamictite as much as 190 m thick with a locally erosive base represent glaciofluvial deposits and lodgment till and record the second ice advance

neoproterozoic glacial rainout intervals observations and implications stratigraphically discrete glacigenic dropstone intervals have been identified within six separate neoproterozoic glaciomarine successions the ca 720 ma chuos formation southwestern congo craton and surprise diamictite southwestern laurentia the ca 600 ma ghaub formation congo craton blasskrans formation northwestern kalahari craton and wildrose diamictite southwestern laurentia and the post 595 ma lower southern highland group northeast laurentia these dropstone intervals are interstratified with hemipelagic dropstone free lithologies that record periods devoid of glacial rainout such episodic deposition requires at a most rudimentary level temporally compatible environmental fluctuations to generate melting of ice the ghaub diamictite is particularly revealing in this regard given that according to the snowball earth hypothesis it had to be deposited either during glacial maxima totally frozen seas or melt back geologically instantaneous owing to its low latitude setting and association with carbonates that record highly depleted 1 3 c values the consistency of facies features shared by all six glaciomarine successions leads us to speculate that the temporally discrete glacial rainout events including diamictites deposited in low latitudes record a dynamic glacial environment and that such conditions were characteristic of neoproterozoic glaciations in general these observations indicate that neoproterozoic seas were not totally frozen and that the hydrologic cycle was functioning

dropstones their origin and significance abstract dropstones are clasts which pose a hydrodynamic paradox or which have an exotic or extra basinal lithology with uncertain provenance recently dropstones have been consistently interpreted as the product of ice rafting and have been used to substantiate the presence of cool climatic phases in the geological record this review illustrates that not all dropstones are reliable as palaeoclimatic indicators dropstones are the product of two distinct entrainment and transport mechanisms by a rafting agent or as a projectile four main processes of transport and formation are identified biological rafting ice rafting floatation and projectiles biological rafting agents include vertebrate gastroliths and other stomach contents vegetational rafting and anthropomorphic activity ice rafting can be the product of ice bergs or seasonal sea river or lake ice floatation of clasts in calm waters has been recorded for stones up to 25 mm in length projectiles are most commonly of volcanic origin given the range of transport and depositional mechanisms reviewed we argue that great care is required in the interpretation of the origin of dropstones

nanometric inclusions of carbonates in kokchetav diamonds from kazakhstan a new constraint for the depth of metamorphic diamond crystallization abstract previous studies have revealed that microdiamonds from the kokchetav ultra high pressure metamorphic terrane of kazakhstan contain nanometric scale inclusions of si fe ti and cr oxides because the structure of sio 2 inclusions was not confirmed to be coesite or stishovite due to their very small size such diamonds formerly served only as an indicator of a minimum pressure ca 4 gpa geothermobarometry applied to kokchetav diamond bearing rocks yielded a wide range of conditions t 700 c 1250 c and p 4 9 gpa our paper presents transmission electron microscopy studies with focused ion beam assistance that indicate that diamonds from marbles contain inclusions of aragonite caco 3 and magnesite mgco 3 and that aragonite and nitrogen bearing nanometric particles are associated with dislocations reflecting diamond growth at relatively high temperature conditions we determined the boundary of dolomite stability using the reaction camg co 3 2 dolomite caco 3 aragonite mgco 3 this allowed us to utilize available experimental data to evaluate the pressure at which diamond was crystallized taking into consideration uncertainties existing between experimental data produced in different laboratories we propose the pressure for kokchetav diamond crystallization to be 6 to 9 gpa this evaluation is based on the assumption that temperature was determined correctly as 980 c minimum and 1250 c maximum for diamond grade dolomitic marbles our data provide strong evidence that the metasedimentary rocks of the kokchetav massif containing diamonds were subducted to the depth of 190 280 km

sedimentary challenge to snowball earth evidence from the magnetic field fossilized in sedimentary rocks suggests that more than 600 million years ago ice occupied tropical latitudes a popular explanation for these findings the snowball earth concept envisages a fully frozen earth for millions of years caused by a runaway ice albedo feedback a rapid catastrophic meltback at very high levels of atmospheric carbon dioxide is thought to have ended this extreme climatic state however sedimentary rocks deposited during these cold intervals indicate that dynamic glaciers and ice streams continued to deliver large amounts of sediment to open oceans throughout the glacial cycle the sedimentary evidence therefore indicates that despite the severity of glaciation some oceans must have remained ice free significant areas of open ocean have important implications for the survival and diversification of life and for the workings of the global carbon cycle the snowball earth concept envisages a fully frozen earth for millions of years several times during the neoproterzoic era between 1 000 and 542 million years ago however the sedimentary evidence suggests that despite the severity of glaciation some oceans must have remained ice free

the cryogenian record in the southern kingston range california the thickest death valley succession in the hunt for a gssp abstract the kingston peak formation of the death valley area california allows valuable insight into both regional cordilleran stratigraphy and the number of glacial cycles preserved in the cryogenian record in the kingston range the eponymous strata have been previously interpreted to record both sturtian and marinoan pan glacial events in the context of a search for a global boundary stratotype section and point gssp for the cryogenian we provide the first detailed description of the thickest diamictite bearing interval in the western usa two clast poor muddy diamictite intervals within the succession one at the base and one near the top have been used to support sturtian and marinoan events previously however new data from the southern part of the kingston range suggest that the upper diamictite interval is genetically related to underlying strata the deposits are interpreted as glaciogenic debris flow deposits which probably represent the proximal tract of a subaqueous fan medial to distal portions of this fan are dominated by turbidites which were transported down a consistent se oriented palaeoslope lowermost beds of the upper diamictite interval are intercalated with graded sandstones and sandy matrix supported conglomerates the graded beds turbidites and matrix supported conglomerates debrites testify to a subaqueous setting with the compositionally and texturally distinct diamictites indicating a glacial origin

dynamics of the 1984 rock avalanche and associated distal debris flow on mount cayley british columbia canada implications for landslide hazard assessment on dissected volcanoes abstract in 1984 a mass of quaternary pyroclastic rock est vol 0 74 106m3 slid from the western flank of mount cayley volcano in southwest british columbia the disintegrating rock mass entrained a further 0 20 106 m3 and formed a rock avalanche that travelled a horizontal distance of 3 46 km from its source over a vertical elevation difference of 1 18 km equivalent to a fahrboschung of 19 from the superelevation of the debris trimline in the mid path it is estimated that velocities reached at least 42 m s in the upper part of its path velocities may have approached 70 m s the rock avalanche was partially transformed into a distal debris flow that travelled a further 2 6 km down turbid creek in a narrow channelised path to the squamish river temporarily blocking it the motion of the rock avalanche including the production of a distal debris flow was successfully simulated using a dynamic analytical model both the results of this analysis and field evidence indicate that the rock avalanche did not come to a halt in the upper part of its path as suggested by cruden and lu 1992 but travelled to its distal limit in one uninterrupted movement this finding has important implications for landslide hazard assessment at mount cayley and similar sites the landslide is typical of those which occur on the steep slopes of dissected volcanoes and is one of seven high velocity rock avalanches that have occurred in the garibaldi volcanic belt of southwest british columbia since 1855

the frequency and distribution of recent landslides in three montane tropical regions of puerto rico landslides are common in steep mountainous areas of puerto rico where mean annual rainfall and the frequency of intense storms are high each year landslides cause extensive damage to property and occasionally result in loss of life average population density is high 422 people km2 and is increasing this increase in population density is accompanied by growing stress on the natural environment and physical infrastructure as a result human populations are more vulnerable to landslide hazards the blanco cibuco and coamo study areas range in surface area from 276 to 350 km2 and represent the climatologic geographic and geologic conditions that typify puerto rico maps of recent landslides developed from 1 20 000 scale aerial photographs in combination with a computerized geographic information system were used to evaluate the frequency and distribution of shallow landslides in these areas several types of landslides were documented rainfall triggered debris flows shallow soil slips and slumps were most abundant hillslopes in the study area that have been anthropogenically modified exceed 12 in gradient are greater than 300 m in elevation and face the east northeast are most prone to landsliding a set of simplified matrices representing geographic conditions in the three study areas was developed and provides a basis for the estimation of the spatial controls on the frequency of landslides in puerto rico this approach is an example of an analysis of the frequency of landslides that is computationally simple and therefore may be easily transferable to other settings

structure and emplacement of the pliocene roque nublo debris avalanche deposit gran canaria spain abstract collapse of the flanks of the pliocene roque nublo stratocone on gran canaria lead to large debris avalanches that traveled far beyond the coastline with velocities that may have exceeded 100 m s the deposits comprised at least 14 km 3 of debris and covered an area of about 180 km 2 in the southern half of the island the debris filled deep canyons are largely exhumed at present incomplete disintegration poor fluidization and a good preservation of megablocks are thought to be mainly due to the confinement of the debris avalanche within deep canyons the rheological behavior of lithologic domains varies with their size internal strength and relative position within the deposit the deformation structures indicate that distinct components flowed whereas others slid throughout the transport in a relatively dense mode the following factors are believed to have been important in generating the roque nublo debris avalanche deposit 1 unusual abundance of pyroclastic flow and other volcaniclastic deposits making up the upper roque nublo cone 2 highly asymmetric basement beneath the cone with a very high southern ridge and a steep erosional southern slope leading to major instabilities 3 intrusion of dikes and cryptodomes as well as hydrothermal alteration in the crater area further weakening the volcano

crust derived potassic fluid in metamorphic microdiamond abstract a highly potassic coh fluid with dissolved phosphate chloride and sulfate sulfide was identified as nanometer size inclusions in metamorphic microdiamonds of kokchetav dolomite marble and garnet quartz pyroxene rock using an analytical electron microscope aem coupled with an energy dispersive x ray edx spectrometer this provides a direct piece of evidence for the formation of metamorphic microdiamonds from such a fluid although this crust derived potassic fluid and the associated solid precipitates are in some respects similar to the fluid inclusions in fibrous cloudy mantle diamonds distinct chemical differences exist this potassic coh fluid in addition has the potential to trigger high to ultrahigh k magmatic and k metasomatic processes in mantle

direct observation and analysis of a trapped coh fluid growth medium in metamorphic diamond the mechanism by which diamonds grow in earth s mantle has been a subject of discussion for many years arguments have been advanced for growth from a melt from a coh fluid and in the solid state the discovery of microdiamonds within ultra high pressure terranes of continental collision settings re energized this debate because of their very different but well defined continental crust environment we report here the discovery of filled nanometric fluid bubbles in diamonds from marble of the kokchetav massif kazakhstan and the serendipitous measurement of their contents due to bursting of a bubble very shortly after a measurement of chemical composition in the transmission electron microscope thereby allowing immediate re analysis with exactly the same settings of all parameters of the microscope the chemical composition of the fluid is c h o cl s ca fe and k the direct observation and composition of a low viscosity trapped fluid in microdiamond unambiguously establish their fluid growth medium

cyclic cold climate during the nantuo glaciation evidence from the cryogenian nantuo formation in the yangtze block south china abstract geological and paleomagnetic data indicate that the ice sheets might have extended to low latitude regions in the cryogenian 720 635 ma the snowball earth hypothesis proposed that the earth was completely ice covered during global glaciation however the glacial sedimentary record seems to contradict with the snowball earth hypothesis detailed sedimentological investigations of the glacial deposits would provide the first order constraint on the nature of global glaciation the nantuo formation 654 635 ma in the yangtze block of south china has been correlated with the marinoan snowball earth in this study we conducted systematic sedimentological analyses of six sections cores of the nantuo formation three facies associations were recognized the proximal glaciomarine distal glaciomarine and non glacial marine facies associations the vertical stacking pattern of facies associations can be correlated among the five slope and basin sections while their correlation with the shelf section remains obscure our data indicate two episodes of glaciation that are separated by an interglacial interval during the nantuo glaciation the first glacial episode is recorded by successions of coarse grained facies e g massive diamictite in the lower part of the nantuo formation the re appearance of massive diamictite in the middle to upper part of the nantuo formation indicates onset of the second glacial episode these two glacial episodes were separated by a siltstone shale sequence of several 10 s m thick suggesting an interglacial period with limited influence from glaciation the top of nantuo formation consists of alternative distal glaciomarine and non glacial marine facies associations representing the deglacial sequence of the nantuo glaciation the sedimentary facies analysis indicates that the cold climate during the nantuo glaciation may be cyclic finally our sedimentary analysis confirms a lag between the deglaciation and precipitation of cap carbonate

glaciers flows and fans origins of a neoproterozoic diamictite in the saratoga hills death valley california abstract the kingston peak formation of death valley california provides an exceptional archive of cryogenian glaciation and concomitant rifting of rodinia in the saratoga hills an 800 m thick succession of diamictite dominated strata is exposed allowing lithofacies and clast compositions to be studied in detail and for the relative influence of glacial versus slope processes on sedimentation to be critically assessed for the first time two detailed sections 400 m apart allow four facies associations to be established 1 thinly laminated argillaceous sandstone interpreted as low density turbidites 2 laminated deformed and brecciated limestone interpreted as carbonate sourced turbidites 3 bedded massive diamictite interpreted as glacially fed debrite and 4 interbedded mudstone sandstone and diamictite interpreted as stratified diamictite deposited via ice rafted debris and passing gradually into turbidites separated by intensely deformed intervals bedded massive diamictite is dominant in the succession and shows a gradual up section transition into interbedded mudstone sandstone and diamictite this succession is interpreted to record a waning glacial influence from glacially sourced debris flows to stratified diamictite strongly influenced by ice rafted debris clasts in the diamictite include carbonate siliciclastic intraclasts granite diabase gneiss and quartzite clast presence profiles suggest that in spite of the comparable along strike facies profiles between the two logs clast content is significantly different within the same stratigraphic unit this finding suggests that clast content is of little use in aiding correlation and lithostratigraphic subdivision of the kingston peak formation the differences in clast compositions is envisaged to be due to complex drainage network examinations of the sedimentary structures and stacking pattern of the lithofacies complex drainage network and localized deformation features of fa4 all support deposition as part of a trough mouth fan system

glacial origin of the cryogenian nantuo formation in eastern shennongjia area south china implications for macroalgal survival abstract the cryogenian period was characterized by global glaciations imposing extreme environmental stresses on early multicellular organisms globally distributed diamictite deposits are the major evidence for these glaciation events but the glacial origin of at least some of these diamictite deposits has been disputed complicating interpretations of the environmental conditions influencing the evolution of life in the cryogenian 720 635 ma in this study we conducted a systematic sedimentological investigation of the marinoan age 650 635 ma nantuo formation in six sections representing a 20 km long east west transect in the eastern shennongjia area of south china the nantuo formation which ranges in thickness from 2 m in the east to 300 m in the west comprises diamictite conglomerate lonestone bearing sandstone green siltstone and black shale facies the eastern sections e g longxi and wushanhu consist mainly of diamictite facies exhibiting micro scaled rotation structures microshear grain stacking grain to grain contacts and water escape structures supporting their deposition in a subglacial setting in contrast the western sections shijiahe liziping and songluo consist of massive and graded diamictite and conglomerate facies consistent with an origin as glacially induced submarine debris flows furthermore the lonestone bearing sandstone facies in these sections contain abundant dropstones and mud pellets within finely laminated turbidites indicating an ice rafted origin with locally reworking by turbidity currents the green siltstone and black shale facies lack glacigenic features and may represent late deglacial deposits based on thickness and facies variations among the study sections we infer that the nantuo formation records glacial sedimentation on a complex paleotopographic surface that was incised into the underlying bedrock with subglacial deposits to the east transitioning into glaciomarine deposits to the west of study area the distal songluo section likely records three cycles of glacial advance and retreat in the form of a facies alternation between diamictite and black shale consistent with a dynamically fluctuating ice margin in summary our sedimentological investigation supports a glacial origin for the nantuo formation in the eastern shennongjia area the occurrence of the benthic macroalgal dominated songluo biota in the black shale facies at songluo suggests that strong glacial retreats provided niches for macroalgal survival in the cryogenian glacial ocean

case history and hazard analysis of two lake damming landslides in the himalayas abstract in investigating the hazard and case history of natural dams in the himalayas two sites of landslides and their former dammed lakes in the hinterland were visited between may 1994 and october 1995 and analysed from the geomorphological geotechnical geohydrological tectonic sedimentary and climatic points of view one of the examples studied the landslide in the valley of birahi ganga northern india is one of the most impressive examples of recent hazards in alpinotype high mountain regions this study was complemented by a study of the ghatta khola landslide western nepal in both cases lithotectonic and climatic conditions led to the destabilisation and failure of carbonate bedrock the occurrence of lakes dammed over long periods behind the barriers is of great importance because after the sometimes fatal landslide event itself one is confronted and has to cope with a secondary natural hazard the possibility of a major flood due to the failure of the dam that is why the preparatory causal factors of the origin of the two lakes by damming up the river due to the landslide and their stepwise disappearance by secondary landslides within the barrier and sedimentation into the basin were additionally focused upon it is shown that due to very special circumstances availability of sediments heavy rainfall in the himalayas there is a progressive decrease in the potential hazard to the landscape and to human beings lower down the main valleys over a period of only a few decades

evolution of host inclusion systems a visco elastic model a visco elastic model is suggested to recover the p t t paths of spherically symmetrical host inclusion systems from residual pressure patterns for a coesite garnet aragonite garnet and diamond garnet system with partial transition of high pressure polymorphs to low pressure ones the model predicts that the exhumation history of ultra high pressure metamorphic rocks from depths below 90 km began with pressure decrease to 1 gpa 40 km depth while the temperature remained high 800 c then the system cooled and decompressed to ambient conditions non spherical inclusion shapes in the 3 d model lead to heterogeneities in residual pressure and shear stress distributions as well as to significant gradients of shear stress which may affect the kinetics and thermodynamics of phase transformation in the inclusions

the effects of rockfall volume on runout distance the main goal of this paper is to clarify the effects of rockfall volume on its fluidization for this purpose outdoor rockfall experiments were carried out to analyze runout distances and individual movements of rockfall blocks and numerical simulations were conducted for these experiments to learn more about the mechanism of rockfall fluidization the rockfall experiments were conducted using an artificial slope on which granite slabs were surfaced and overlaid with cubiformed granite blocks the size and number of blocks were varied in this series of experiments further numerical simulations were carried out in which the coordinates of individual rockfall blocks were traced in three dimensional space from rockfall initiation to final deposition it became clear from the experiments and simulations that the runout distance had a positive correlation with the rockfall volume number of rockfall blocks and the runout distance of the gravity center of deposited rockfall mass had a negative correlation with the rockfall volume to clarify the mechanism of these two phenomena the positions of individual blocks from initial arrangements to final depositions were traced in the experimental and numerical simulations this revealed that the relative positions of each block along the slope direction were not changed during rockfall movement the reason for the block sequence preservation was that front facing blocks in the initial cube arrangement accelerated and rear facing blocks decelerated along the slope by internal collision between blocks further as the rockfall volume increased the opportunities for impact among the rockfall blocks increased with the front facing blocks pushed farther whereas the gravity center of the deposited rockfall mass had an inclination to travel shorter distances as rockfall blocks increased according to the increase of kinetic energy dispersed by the collision of blocks

the kokchetav massif kazakhstan type locality of diamond bearing uhp metamorphic rocks abstract after the discovery of metamorphic coesite in crustal rocks from the western alps italy and the western gneiss region norway in the mid 1980s of the last century metamorphic diamond was observed only a few years later in situ in the kokchetav massif kazakhstan findings of such coesite and diamond bearing ultrahigh pressure metamorphic uhp rocks with protoliths formed or embedded in crustal levels and subsequently experienced pt conditions within or even higher than the coesite stability field have dramatically changed our geodynamic view of orogenetic processes these occurrences provide evidence that crustal rocks were subducted into mantle depths and exhumed to the surface recent studies even suggest continental subduction to depths exceeding 300 km these rocks have been extensively studied and many new and important observations have been made thus far more than 350 papers have been published on various aspects of kokchetav uhp rocks the kokchetav massif of northern kazakhstan is part of one of the largest suture zones in central asia and contains slices of hp and uhp metamorphic rocks classical uhp rocks mainly occur in the kumdy kol barchi kol and kulet areas and include a large variety of lithologies such as calcsilicate rocks eclogite gneisses schists marbles of various compositions garnet pyroxene quartz rocks and garnet peridotite most of them contain microdiamonds some of which reach a grain size of 200 m most diamond grains show cuboid shapes but in rare cases diamonds within clinozoisite gneiss from barchi kol occur as octahhedral form microdiamonds contain highly potassic fluid inclusions as well as solid inclusions like carbonates silicates and metal sulfides which favour the idea of diamond formation from a c o h bearing fluid nitrogen isotope data and negative 13c values of kokchetav diamonds indicate a metasedimentary origin pt estimates of kokchetav uhp rocks yield peak metamorphic conditions of at least 43 kbar at temperatures of about 950 1000 c some zircon separates show inherited proterozoic cores and 537 530 ma uhp metamorphic mantle zones several ar ar ages on micas scatter around 529 528 and 521 517 ma and reflect different stages of the exhumation history migmatization occurred during exhumation at about 526 520 ma isotopic studies on calcsilicate rocks confirm a metasedimentary origin 18o values of garnet and clinopyroxene of a layered calcsilicate rock rule out the possibility having a primitive mantle protolith similar studies on eclogites indicate their basaltic protolith having experienced water rock interaction prior to uhp metamorphism a number of unique mineralogical findings have been made on kokchetav uhp rocks k feldspar exsolutions in clinopyroxene demonstrate that potassium can be incorporated into the cpx structure under upper mantle pressures other significant observations are coesite exsolutions in titanite quartz rods in cpx the discovery of k tourmaline as well as new minerals like kokchetavite a hexagonal polymorph of k feldspar and kumdykolite an orthorhombic polymorph of albite the kokchetav uhp rocks represent a unique and challenging stomping ground for geoscientists of various disciplines from crystallography petrology and geochemistry to geophysics and geodynamics geotectonics it concerns all who are interested in the diverse metamorphic processes under upper mantle conditions

paraglacial history and structure of the moosfluh landslide 1850 2016 switzerland abstract rock slopes next to the tongue of the great aletsch glacier switzerland are characterized by rapid environmental adjustment to non glacial conditions this study investigates and describes in detail the historic development of the largest rock slope instability in this area called moosfluh landslide we study in detail the structure evolution and stability since the end of the little ice age lia until september 2016 and discuss their relationships with the evolution of the great aletsch glacier since the lateglacial period in 2016 around 50 m of glacial ice thickness were left at the moosfluh landslide toe where in 1850 glacial ice was 400 m thick the changing stability conditions at the interface with the melting valley glacier are studied based on novel balanced cross sections and kinematic model of the moosfluh landslide dominated by toppling phenomena in metamorphic rock the morphology and evolution of this landslide since the lia are investigated with multi temporal landslide maps based on aerial digital photogrammetry adp applied to historic images since 1961 internal deformation at moosfluh is accommodated by shear slip along uphill facing foliation and fault planes and by extensional faulting forming tension cracks and graben structures at the landslide head together with digital image correlation dic and total station monitoring tps the moosfluh landslide displacement history was reconstructed evidencing post egesen landslide displacements and an acceleration of movements since the lia and especially since 2007 the displacement rates increase from few mm per year until the nineties to several meter per day in september 2016 different kinematic models have been tested and changes in the moosfluh rock slope stability in response to retreating glacial ice and changing groundwater conditions was explored with limit equilibrium analysis of the stepped planar block toppling model of goodman and bray 1976 for the observed conditions and a toppling joint friction angle of 19 the simulated factor of safety drops non linearly from the lia maximum 1 12 to the year 2007 1 02 when the height of ice above the valley bottom melted down to 100 m this study illustrates with unprecedented detail the time scales displacement magnitudes and structural evolutions of a large toppling mode slope instability in a paraglacial setting the long term cumulative slope displacements between the egesen stadial and the lia are of the same magnitude as the cumulative displacements between the lia and the year 2016 as large portions of the studied slope underwent multiple retreats and advances of the great aletsch glacier during the lateglacial and postglacial period the observed onset of large slope displacements should be related to incremental damage slip weakening and weathering occurring along steeply dipping toppling fractures during the lia

retrograde isochemical phase transformations of majoritic garnets included in diamonds a case study of subcalcic cr rich majoritic pyrope from a snap lake diamond canada abstract homogeneity of a peridotitic garnet inclusion in diamond demonstrating excess in si concentration i e presence of majorite component was investigated by tem using fib prepared foils the host diamond is a low nitrogen brown stone which can be related to type iia with features of strong plastic deformation the studied sample is represented by ca poor cr pyrope of harzburgitic h paragenesis from snap lake dyke canada the garnet had been previously reported to contain si 3 16 apfu the revised examination of the sample resulted in detection of extremely fine grained symplectite consisting of low ca orthopyroxene clinopyroxene cr spinel and coesite completely located and isolated in the inner part of the garnet crystal which forms a sharp interface with the surrounding homogeneous garnet xrd study confirmed the presence of the minerals constituting the symplectite epma showed an identical bulk chemistry of the nanometer sized symplectite and garnet further polishing of the garnet inclusion on the same surface with diamond removed the symplectite which possibly was present as a thin lens within garnet the remaining garnet is completely homogeneous as checked by two profiles and contains unusually high ni 118 2 ppm and depleted ree patterns estimated pt formation conditions of this garnet are 10 8 gpa and 1450 c within asthenosphere symplectite testifies partial retrograde isochemical phase transformation of the examined garnet which is suggested to be caused by decompression along with plastic deformation of diamond within the coesite stability field at t 1000 c and depth no less than 100 km because previously published studies of rare majoritic garnets composition were performed by epma only it is possible that the traces of partial phase transformation symplectite formation could have been overlooked without additional xrd and or tem aem studies

the oxygen isotope composition of mantle eclogites as a proxy of their origin and evolution a review abstract in the past decade the oxygen isotope composition in rock forming minerals of mantle eclogites 18o 2 12 has been actively discussed as a most reliable proxy of their origin and evolution in the present study the possibility of using the oxygen isotope composition as a proxy for the origin of mantle eclogites is carefully tested and conclusions regarding its application limits are drawn contributions of all processes leading to variations in the isotope composition from protolith oceanic crust formation to ascent of eclogites in kimberlite to the surface are discussed including hydrothermal alteration by sea water fractionation of oxygen isotopes upon metamorphism dehydration and the removal of volatile components in subduction zone metasomatism in subduction zone partial melting mantle metasomatism and variation in the oxygen isotope composition upon the exhumation of mantle xenoliths by kimberlitic magma the total contribution of all processes excluding mantle metasomatism typically does not exceed a deviation of 3 5 from the initial 18o value established in a protolith variations of 18o in mantle eclogites 2 12 and 8 which subducts into the mantle up to 5 and the preferential erosion and partial melting of the uppermost layers of the oceanic crust the statistical data show that eclogite garnet mainly preserves more ancient oxygen isotope signatures including the initial 18o of protolith than clinopyroxene garnets with 18o of 1 5 a total of 451 samples oxygen isotope composition in a considerable portion of mantle eclogites that originated from the oceanic gabbro based on their chemical composition 18o 6

the contribution of landslides to landscape evolution in europe abstract after a review of some analytical and conceptual models of slope evolution with the intervention of mass movements a proposal is made of a series of indicators for the quantitative description of landscape evolution in relation to mass movements the ratio between landslide mobilisation rate and downwearing rate is proposed as a quantitative measure of the significance of mass movements in landscape evolution a subdivision of european regions with respect to their susceptibility to landsliding as a process of landscape evolution is proposed the role of landsliding for the evolution of landscape in some regions is described the data presented show that landsliding may in some cases be the main contributor to landscape change

a garnet zircon oxygen isotope record of subduction and exhumation fluids from the franciscan complex california tectonic blocks of high grade metamorphic rock hosted by the franciscan me lange commonly preserve textural and geochemical evidence for metasomatism and blueschist facies overprinting within a subduction zone these exhumation events can obscure information on the nature of subduction fluids at depth that might otherwise be preserved by these rocks in this tectonic setting cation and oxygen isotope zoning in garnets from eclogite and garnet hornblende rocks with minimal textural evidence of retrogression reveals separate prograde and retrograde fluid histories garnet cores preserve a homogeneous prograde oxygen isotope history with both high do 11o and low 4o values in different samples probably recording altered ocean crust protolith compositions multiple episodes of garnet resorption and regrowth record a dramatically changing bulk oxygen isotope ratio resulting in 6 7o neoformed garnet rims with sharp core rim boundaries in both samples matrix omphacite and hornblende are in profound oxygen isotope disequilibrium with garnet cores but are in equilibrium with garnet rims despite the appearance of overall textural equilibrium in thin section this cryptic metasomatism found in samples from different locations within the franciscan complex brings into question existing thermobarometry on non inclusion phases for this complex as well as interpretations based on whole rock geochemical data zircon ages and oxygen isotope equilibrium with late forming garnet are consistent with postmetasomatic formation of zircon the ability of garnet and zircon to record multiple fluid events and tie them to p t t fluid history is a powerful tool in gaining an improved understanding of the complex fluid environments within subduction zones

10be and 26al production rates deduced from an instantaneous event within the dendro calibration curve the landslide of kofels otz valley austria surface exposure dating requires the knowledge of cosmogenic nuclide production rates when determining time integrated production rates the exposure ages of the calibration samples need to be accurately known the landslide of kofels austria is very well suited for this purpose it is the largest landslide in the crystalline alps of austria dating back to 7800 100 years bc ams 14c dating of buried wood which is well within the 14c dendro calibration curve exposed quartz veins were sampled from the tops of large boulders from the toe of the landslide for analysis of 10be and 26al to calculate sea level high geomagnetic latitude 60 open sky radionuclide production rates corrections were applied for altitude and latitude for shielding by surrounding mountains for sample geometry vegetation and snow cover and for sample thickness the production rates for an exposure age of 10 000 years are 5 75 0 24 10be atoms yr g sio2 and 37 4 1 9 26al atoms yr g sio2 a 26al 10be ratio of 6 52 0 43 can be calculated the influence of the geomagnetic field on these production rates has been estimated using two different geomagnetic field records our production rates should be a good approximation for the use of surface exposure dating between about 5000 and 13 000 years bp

sedimentological signature of a deformable bed preserved beneath an ice stream in a late pleistocene glacial sequence ross sea antarctica abstract subglacial processes are described using a nested set of samples from and 1b drill core collected from beneath the ross ice shelf as part of the antarctic geologic drilling program andrill an interval from the late pleistocene was chosen for study because it is preserved in the sedimentary record yet the depositional processes are applicable to the widely studied glacial conditions at the last glacial maximum a complete glacial interglacial sequence between two glacial surfaces of erosion gses at 41 9 and 47 7 meters below sea floor was studied by centimeter scale core logging based on x radiographs of the archive core halves in addition to core description bulk samples and 45 mm 65 mm thin sections of diamictites for micromorphology analysis above the lower gse 4 6 m of subglacial till occurs including a sequence of thin muddy conglomerate with diverse pebble lithologies massive clast rich muddy diamictite and stratified diamictite with clast rich and clast free beds the sand size fraction of these deposits is dominated by aggregate grains termed till pellets following terminology used for ross sea deposits we present the first detailed description and two different conceptual models of tillpellet formation beneath an ice stream one is related to mechanical processes and the other is related to thermodynamics till pellets are rounded spherical to prolate in form and are associated with turbate structures and aligned grains in thin sections the core of the pellet is either a lithic grain or stiff till with additional clay plastered on the outside forming rounded grains from originally angular ones galaxy structures skelsepic fabric and pressure shadows around grains are indicative of rotational deformation within the till till pellets form in situ within a highly porous deformable bed under an ice stream either by mechanical shearing or by alternating thermal conditions in the till in the first model a slow glacial advance under dry subglacial conditions fractures the till increasing the porosity as shear induces dilation basal melting and high pore water pressure develop as the ice stream thickens decreasing the intergranular effective stress and inducing rotation of the angular till aggregates an alternative model calls for basal freezing with preferential ice growth in larger pore spaces causing rotation of fine grained till aggregates due to concentration of shear stresses in a thin zone beneath the glacier sole survival of till pellets is enhanced in subglacial diamictite as the thin zone of deformation moves upward toward the base of the ice stream a thin granular bed enriched in till pellets is melted out in the grounding zone and this deposit marks the transition from subglacial till to stratified silty claystone representing sub ice shelf deposits

formation of landslide dammed lakes during a wet period between 40 000 and 25 000 yr b p in northwestern argentina abstract new ams radiocarbon data from the deposits of landslide dammed lakes in the santa maria basin 26 s 66 w and the quebrada del toro 25 s 66 w in the eastern argentine cordillera show that important mass movements occurred during a wet period between 40 000 and 25 000 yr b p in addition to increased humidity during this time detailed analysis of annual layered lacustrine strata suggests enhanced inter and intra annual fluctuations in precipitation as compared to the present variations in sediment characteristics and diatom assemblages with mean periodicities of 2 to 5 and 10 to 14 years respectively suggest an influence of the el nino southern oscillation enso and the atlantic sea surface temperature dipole the atlantic dipole slightly increased rainfall every 10 14 years as at present in contrast the weak modern enso influence in this area differs from the past situation where rainfall increased significantly with enso type periodicities both increased humidity and seasonality are believed to have reduced thresholds for the generation of catastrophic mass movements in northwestern argentina

the sea level fingerprint of a snowball earth deglaciation cap dolostones are thought to represent deposition from seas transgressing over formerly glaciated continental margins during marinoan snowball deglaciation nevertheless facies associations within some cap dolostones indicate that an episode of regional regression punctuated these transgressive sequence tracts to date inferences of sea level change during and after the marinoan snowball deglaciation have been interpreted using simple qualitative arguments in the present study we explore the full spatio temporal variability of sea level change during snowball deglaciation and its aftermath using a gravitationally self consistent theory that accounts for the deformational gravitational and rotational perturbations to sea level on a viscoelastic earth model the theory is applied to model marinoan snowball deglaciation on a generalized ediacaran paleogeography with a synthetic continental ice sheet distribution we find that sea level change following a synchronous rapid 2 kyr collapse of snowball ice cover will exhibit significant geographic variability including site specific histories that are characterized by syn deglacial sea level fall or stillstand moreover some sites that experience syn deglacial transgression will continue to experience transgression in the post deglacial phase taken together these results suggest that sea level change recorded by strata capping snowball glaciogenic units may reflect a more complicated trajectory than previously thought including deposition that was not limited to the deglaciation phase these simulations as well as others that explore the response to asynchronous melting and deglaciation phases of longer duration demonstrate that an episode of regional regression interrupting a cap dolostone transgressive sequence tract may reflect one of several processes or their combination 1 near field adjustment associated with rapid local melting during an otherwise global hiatus in deglaciation 2 post glacial uplift of sites during a period of slowing deglaciation and 3 a transition at some sites from a sea level fall dominated by post glacial uplift to a phase of sea level rise due to eustasy and peripheral bulge subsidence throughout an extended order 50 kyr or greater snowball deglaciation

from deep seated slope deformation to rock avalanche destabilization and transportation models of the sierre landslide switzerland abstract sackung is a widespread post glacial morphological feature affecting alpine mountains and creating characteristic geomorphological expression that can be detected from topography over long time evolution internal deformation can lead to the formation of rapidly moving phenomena such as a rock slide or rock avalanche in this study a detailed description of the sierre rock avalanche sw switzerland is presented this convex shaped postglacial instability is one of the larger rock avalanche in the alps involving more than 1 5 billion m3 with a run out distance of about 14 km and extremely low fahrboschung angle this study presents comprehensive analyses of the structural and geological characteristics leading to the development of the sierre rock avalanche in particular by combining field observations digital elevation model analyses and numerical modelling the strong influence of both ductile and brittle tectonic structures on the failure mechanism and on the failure surface geometry is highlighted the detection of pre failure deformation indicates that the development of the rock avalanche corresponds to the last evolutionary stage of a pre existing deep seated gravitational slope instability these analyses accompanied by the dating and the characterization of rock avalanche deposits allow the proposal of a destabilization model that clarifies the different phases leading to the development of the sierre rock avalanche

anatomy of turbidites and linked debrites based on long distance 120 x 30 km bed correlation marnoso arenacea formation northern apennines italy much of our understanding of submarine sediment laden density flows that transport very large volumes ca 1 to 100 km3 of sediment into the deep ocean comes from careful analysis of their deposits direct monitoring of these destructive and relatively inaccessible and infrequent flows is problematic in order to understand how submarine sediment laden density flows evolve in space and time lateral changes within individual flow deposits need to be documented the geometry of beds and lithofacies intervals can be used to test existing depositional models and to assess the validity of experimental and numerical modelling of submarine flow events this study of the miocene marnoso arenacea formation italy provides the most extensive correlation of individual turbidity current and submarine debris flow deposits yet achieved in any ancient sequence one hundred and nine sections were logged through a ca 30 m thick interval of time equivalent strata between the contessa mega bed and an overlying columbine marker bed correlations extend for 120 km along the axis of the foreland basin in a direction parallel to flow and for 30 km across the foredeep outcrop as a result of post depositional thrust faulting and shortening this represents an across flow distance of over 60 km at the time of deposition the correlation of beds containing thick 40 cm sandstone intervals are documented almost all thick beds extend across the entire outcrop area most becoming thinly bedded 40 cm in distal sections palaeocurrent directions for flow deposits are sub parallel and indicate confinement by the lateral margins of the elongate foredeep flows were able to traverse the basin in opposing directions suggesting a basin plain with a very low gradient small fractional changes in stratal thickness define several depocentres on either side of the verghereto high area the extensive bed continuity and limited evidence for flow defection suggest that intrabasinal bathymetric relief was subtle substantially less than the thickness of flows thick beds contain two distinct types of sandstone ungraded mud rich sandstone intervals record evidence of en masse debrite deposition graded mud poor sandstone intervals are inferred to result from progressive grain by grain turbidite deposition clast rich muddy sandstone intervals pinch out abruptly in downflow and crossflow directions in a fashion consistent with en masse debrite deposition the tapered shape of mud poor sandstone intervals is consistent with an origin through progressive grain by grain turbidite deposition most correlated beds comprise both turbidite and debrite sandstone intervals intrabed transitions from exclusive turbidite sandstone to turbidite sandstone overlain by debrite sandstone are common in the downflow and crossflow directions this spatial arrangement suggests either i bypass of an initial debris flow past proximal sections ii localized input of debris flows away from available sections or iii generation of debris flows by transformation of turbidity currents on the basin plain because of seafloor erosion and or abrupt flow deceleration a single submarine flow event can comprise multiple flow phases and deposit a bed with complex lateral changes between mud rich and mud poor sandstone

geochemistry and age of ultrahigh pressure metamorphic rocks from the kokchetav massif northern kazakhstan isotopic and geochemical data of the zerenda series metamorphic rocks from the kokchetav massif are reported some of these rocks contain microdiamond inclusions in garnets and other indicators of ultrahigh pressure metamorphism p 40 kbar t 900 1000 c the diamond bearing rocks exhibit distinctive geochemical characteristics compared to typical crustal rocks the ree patterns range from lree depleted to slightly lree enriched chondrite normalized la yb n 0 1 5 4 with a negative eu anomaly they are depleted in incompatible elements e g sr ba u th with respect to the upper crust in contrast non diamondiferous rocks of the zerenda series exhibit normal crustal geochemistry all rocks of the zerenda series have very radiogenic lead isotopes the measured values 238u 204pb compared with those calculated for the interval between crust formation and ultrahigh pressure uhp metamorphism suggest a decrease by factors of up to 200 during the uhp metamorphism the sm nd mineral isochrons from the diamond bearing rocks and other rock types of the zerenda series give a middle cambrian 524 535 ma age of metamorphism the nd model ages show that crust formation occurred about 2 3 ga ago significant fractionation of sm and nd and loss of incompatible elements may be due to partial melting of the protoliths the ar ar age determinations of secondary biotite and muscovite from the diamond bearing rocks yield an age of 517 5 ma this cooling age requires a short time interval between uhp metamorphism and uplift to a crustal level ultrahigh pressure metamorphism might be a significant source of pb for the mantle we propose that the radiogenic pb of the oceanic array is the contamination traces of numerous uhp events beside the geological aspect we demonstrate a method of dating a high grade metamorphic terrain using nd isotopes we compare whole rock isochrons and mineral isochrons and in this way get some insight into the behaviour of the sm nd system during very high grade metamorphic events

the survival of benthic macroscopic phototrophs on a neoproterozoic snowball earth the greatest ice ages in earth s history occurred during the 654 635 ma marinoan glaciation when glaciers reached tropical oceans and our planet approached a snowball earth condition paleontological and genomic data suggest that several eukaryotic groups must have survived the marinoan glaciation but their fossil record is scarce and limited to microbes whose ecological and physiological ranges are poorly constrained thus hampering a full understanding of how and where eukaryotic life particularly macroscopic phototrophs survived this snowball earth here we report carbonaceous compression fossils from the marinoan age nantuo formation in south china these fossils are preserved in thin black shales sandwiched between glacial diamictites deposited in inner shelf environments of the mid latitudinal yangtze block some of these fossils are interpreted as benthic macroalgae thus the marinoan glaciation must have been punctuated by episodes of open waters where habitable benthic substrates were available in the photic zone and along the coast of mid latitudinal continents such open waters may have been the refugia where macroscopic phototrophs survived the marinoan glaciation and subsequently diversified in the early ediacaran period

cre dating on the head scarp of a major landslide sechilienne french alps age constraints on holocene kinematics cosmic ray exposure cre dating applied to the active sechilienne landslide romanche valley belledonne massif french alps provides information about its holocene dynamics from initiation to present day activity glacier retreat at 1100 m a s l is estimated at 16 6 0 6 10be ka from glacially polished bedrock samples with total deglaciation of the valley achieved at least by 13 3 ka application of the cre method along vertical profiles sampled with a high spatial resolution of 3 m on the head scarp yields 1 an initiation of the rock slope failure at 6 4 1 4 10be ka and 2 a continuous rock slope failure activity with a mean head scarp exposure rate of 0 6 cm yr the data suggest an increase of the head scarp exposure rate between 2 3 and 1 0 ka after this acceleration phase the exposure rate is similar to that obtained by the present day monitoring data over 20 years in the depletion zone 1 3 cm yr since the failure initiation occurred more than 5400 yr after the total deglaciation of the valley the slope failure does not appear as an immediate consequence of debutressing in the romanche valley this result is consistent with studies of other large alpine rockslides in the alps failure initiation of the sechilienne landslide occurred during the holocene climatic optimum a hot and wet period the temperature and precipitation changes of this climatic optimum seem to have a worsening effect at the regional scale to trigger large mass wasting in this glacial alpine valley

the cohesive naranjo debris flow deposit 10 km3 a dam breakout flow derived from the pleistocene debris avalanche deposit of nevado de colima volcano mexico abstract mass movement processes on volcanic terrains such as landslides and debris avalanches can cause the obstruction of main drainages producing the formation of temporary dams a good example of this occurred 18 5 ka ago when the eastern flank of the nevado de colima volcano collapsed producing a debris avalanche deposit that was previously described as one of the largest in the world the deposit extended from the volcanic summit as far as the pacific coast 120 km away new stratigraphic sedimentological and componentry data suggest that the volcanic collapse of nevado de colima resulted in a debris avalanche that traveled 20 km southeast to the naranjo river there it crashed against a topographic barrier consisting of cretaceous limestones cerro la carbonera and the flow direction was diverted to the south down the naranjo river channel for another 25 km before the avalanche came to a halt the obstruction of the drainage produced a temporary dam that stored ca 1 km3 of water and deposited fluvial and slack water sediments some time after the damming the accumulated water sediment load was able to overtop the obstructing material and to release a breakout flow with a calculated initial flow discharge of 3 5 million m3 s the resulting flood cohesive debris flow followed the channel of the naranjo river and due to the high erodibility of the channel and introduction of substrate material the debris flow progressively increased its volume up to 10 km3 six times its initial volume this study highlights the relevance of evaluating the potential remobilization of debris avalanche deposits to initiate large magnitude cohesive debris flows therefore the hazard and risk analysis of future potential events of this nature must consider the pre eruption conditions and the topography surrounding a volcano

oxygen isotope variations of garnets and clinopyroxenes in a layered diamondiferous calcsilicate rock from kokchetav massif kazakhstan a window into the geochemical nature of deeply subducted uhpm rocks calcsilicate and garnet pyroxene rocks with dolomite and mg calcite matrices occur with uhpm dia mondiferous biotite gneisses and schists of the kokchetav massif the calcsilicates are characterized by high dia mond grade k bearing diopside and very high mg garnets mg 77 with variable ca contents ca 42 5 80 a rare calcsilicate sample with alternating layers of different bulk compositions was selected for oxygen isotope and electron probe microanalysis of garnets and pyroxenes a grain of fresh garnet with a brownish yellow luminescent inner domain mg 94 and a non luminescent outer part mg 88 was selected for in situ analysis of d 18 o by ion microprobe 10 lm spot the profile demonstrates a d 18 o gradient of 1 5 200 lm from 11 3 rim to 12 8 core vsmow additional 2 mg samples of hand picked garnet and clinopyroxene fragments from different parts of the same sample selected by color and chemical differences were analyzed for d 18 o by laser fluorination yielding even larger differences in d 18 o 6 3 10 6 in garnets and 6 1 8 1 in clinopyroxenes the zonation in d 18 o among grains of the same mineral in different lithologies may in part reflect initial heterogeneities of the finely layered sedimentary precursors the d 18 o values for the garnets are among the highest observed for uhp origin both for crustal or mantle rocks confirming a sedimentary origin for these carbonate bearing rocks and ruling out a primi tive mantle derived protolith oxygen diffusion in garnet at peak metamorphism temperature 1 000c was arrested by rapid cooling

anatomy of a subaqueous ice contact fan and delta complex middle pleistocene north west germany this paper presents a detailed analysis of the high resolution facies architecture of the middle pleistocene porta subaqueous ice contact fan and delta complex deposited on the northern margin of glacial lake weser northwest germany a total of 10 sand and gravel pits and more than 100 wells were examined to document the complex facies architecture the field study was supplemented with a ground penetrating radar survey and a shear wave seismic survey all collected sedimentological and geophysical data were integrated into a high resolution three dimensional geological model for reconstructing the spatial distribution of facies associations the porta subaqueous fan and delta complex consist of three fan bodies deposited on a flat lake bottom surface at the margin of a retreating ice lobe the northernmost fan complex is up to 55 m thick 6ae2 km wide and 6ae5 km long the incipient fan deposition is characterized by high energy flows of a plane wall jet very coarse grained highly scoured jet efflux deposits with an elongate plan shape indicate a high froude number probably 5 these jet efflux sediments are deposited in front of a large 3ae2 km long up to 1ae2 km wide and up to 25 m deep flute like scour indicating the most proximal erosion and bypass area of the jet that widens and deepens with distance downstream to the region of maximum turbulence approximately five times the conduit diameter evidence for subsequent flow splitting is given by the presence of two marginal gravel fan lobes deposited in front of 1ae 3t o 2ae5 km long flute like scours that are 0ae8 to 1 km wide and 7 to 20 m deep in response to continued aggradation small jets developed at the periphery of these bar like deposits and filled in the low areas adjacent to the original superelevated regions locally raising the depositional surface and characterized by large scale trough cross stratified sand and pebbly sand the incision of an up to 1ae2 km wide and up to 35 m deep channel into the evolving fan is attributed to a catastrophic drainage event probably related to a lake outburst and lake level fall in the range of 40 to 60 m at the mouth of this channel highly scoured jet efflux deposits formed under hydraulic jump conditions during flow expansion subsequently gilbert type deltas formed on the truncated fan margin recording a second lake level drop in the range of 30 to 40 m these catastrophic lake level falls were probably caused by rapid ice lobe retreat controlled by the convex up bottom topography of the ice valley

sequencing the sturtian icehouse dynamic ice behaviour in south australia the cryogenian record of south australia includes the type region of the sturtian glaciation the oldest of three pan global icehouse intervals during the neoproterozoic data are presented from previously little described sections at holowilena creek oladdie creek and hillpara creek in the central and southern flinders ranges where five facies associations are recognized these are 1 diamictite and conglomerate 2 interbedded heterolithic deposits 3 hummocky cross stratified sandstone 4 lonestone bearing siltstone and 5 ferruginous siltstone and sandstone the succession reveals significant lateral and vertical facies variation which is linked to a complex inherited palaeotopography and distance from the sediment source repeated stratigraphic occurrences of striated clasts and abundant ice rafted debris strongly support recurrent glacial influence on sedimentation the intercalation of gravitationally reworked diamictites dropstone bearing siltstone and dropstone free siltstone testifies to dynamic sedimentation within a periodically glacially influenced subaqueous environment sequence stratigraphic analysis identifies four glacial advance systems tracts separated by three glacial retreat systems tracts wherein hummocky cross stratified sandstones attest to open water conditions these findings support dynamic ice sheet behaviour in south australia and provide clear evidence for repeated intra sturtian ice sheet recession

duration of deposition from decelerating high density turbidity currents using recent advances in the stability analysis of current ripples a new model for the calculation of duration of sediment deposition from decelerating high density turbidity currents is proposed the model named tdure refines a duration model proposed by allen 1991 j sediment petrol 61 291 295 by calculating the accumulation time of the rippled tc division separately from the massive and plane parallel laminated tab divisions in bouma type turbidites tdure consists of three modules in the first module the accumulation time for theta and tb divisions is approximated by assuming a linear decrease in sedimentation rate with height in the turbidite as in the original model a straight line is fitted through inferred sedimentation rates at the tab and tbc boundaries in the second module angle of climb of ripples thickness of the tc division and grain size distribution are used in empirical relationships between ripple migration rate and a grain related mobility parameter to estimate the accumulation time of the tc division in the third module the expected development of ripple size across the tc division is calculated using empirical relationships between rate of development of ripple height and grain related mobility parameter and subsequently compared with the observed development of ripple size in the turbidite in this way the accuracy of the accumulation time calculated in module 2 can be verified independently tdure was tested using bouma type turbidites from the doheny channel capistrano fm ca usa and the flysch di motta calabria italy accumulation times of 12 and 10 75 min for the tc division and 19 and 16 min for the tabc sequence were calculated for the doheny channel and the flysch di motta turbidites respectively although module 3 underestimates the rate of development of current ripples near the tbcboundary in both beds ripple size at the tcd boundary is calculated accurately the underestimation of development rate may be caused by differences between flow conditions in experimental flumes on which the model calculations are based and turbiditycurrent dynamics q 2000 elsevier science b v all rights reserved

the barranco de tirajana basin gran canaria spain a major erosive landform caused by large landslides the barranco de tirajana bdt located on the island of gran canaria spain has some specific features that differentiate it from the ravines of other volcanic islands in the atlantic ocean the origin of this unusually wide upper basin 35 km 2 has been under discussion over the last century although its erosional origin is nowadays widely accepted the purpose of this paper is to describe the landslide deposits that appear at the bottom of the basin and to assess their role in the geomorphological evolution of the basin we suggest that the bdt basin is a major erosional landform initiated by important ravine incision and widened by a large number of landslides there are 28 large landslides within the bdt basin the main movements were of rock slide and debris slide types affecting 70 and 25 of the total area respectively in addition modes of displacement were predominantly translational rock debris and earth slides consisting of 89 of the total compared to rotations and flows that constitute only 11 three main periods of landslide activity have been established in the development of the bdt basin using geomorphological criteria period i includes ancient movements that could have started at about 0 6 ma or even 2 7 ma ago and are considered as abandoned landslides period ii corresponds to old landslides considered as dormant which occurred within the middle upper pleistocene finally period iii includes recent upper pleistocene landslides and holocene landslides that are still active we suggest that interglacials in the canary islands and nw africa included humid and wet episodes that could account for the occurrence of periods of landslide activity in the bdt basin d 2002 elsevier science b v all rights reserved

zircon response to diamond pressure metamorphism in the kokchetav massif ussr ultrahigh pressure metamorphism of the diamond bearing gneisses in the kokchetav massif ussr has been dated at 530 7 ma 2 sgr by shrimp ion microprobe analysis of metamorphic zircons zircon xenocrysts as old as 2000 ma have retained original isotopic compositions through the extreme metamorphic conditions and indicate that the protolith that was buried to diamond forming pressures included early proterozoic components highly variable reset ting of u pb isotopic systems in zircon xenocrysts at the time of metamorphism suggests that diffusive lead loss had commenced but was incomplete a disequilibrium observation consistent with relatively transient exposure of the rocks to extreme crustal depths

quaternary moraines vs catastrophic rock avalanches in the karakoram himalaya northern pakistan a history and conception of glacial events for the central karakoram himalaya proposed some 80 years ago by giotto dainelli are largely accepted today however certain deposits identified as terminal moraine complexes marking glacial episodes were actually emplaced by rock avalanches in the skardu and shigar intermontane basins of baltistan at least 15 rock avalanche events were previously mapped as moraine or till criteria used for distinguishing these catastrophic landslide deposits emphasize homogeneous lithology of rubble and matrix clast shape facies characteristics the large scale unity of emplacement and morphological relations to valley topography the deposits of three events at katzarah satpura and the north end of shigar valley have been reconstructed in detail thick supraglacial debris does not result in similar deposits extensive valley fills river terraces large sediment fans and lacustrine sediments formerly attributed to late glacial conditions are reinterpreted as postglacial events involving rock avalanches that interrupted fluvial development existing reconstructions of glaciations are left in doubt especially late glacial events in the central karakoram as are the roles assigned to karakoram main indus valley and western himalayan ice

a comparison of the evolution of diamondiferous quartz rich rocks from the saxonian erzgebirge and the kokchetav massif are so called diamondiferous gneisses magmatic rocks abstract the petrography and chemical composition of minerals of quartz rich diamondiferous rocks from the kokchetav massif especially the zonation of garnet were studied and compared with diamondiferous quartzofeldspathic rocks from the saxonian erzgebirge many compositional and textural features were found to be similar for instance microdiamonds are enclosed systematically in a specific intermediate growth zone of garnet in these rocks on the basis of experimental data a magmatic scenario was constructed to check if the quartz rich diamondiferous rocks are of magmatic origin by this the p t paths derived here for the kokchetav rocks and the textural observations it is concluded that the minerals of the diamondiferous rocks have crystallized from silicate melts these melts originated by anatexis of deeply submerged metasediments erzgebirge at t as high as 1200 c kokchetav massif at 50 100 c lower t and ascended from at least 200 km depth relics of the pre anatectic evolution are still present for instance as garnet cores after ascent and emplacement of the magma in deep portions of thickened continental crust kokchetav massif 45 50 km close to 800 c erzgebirge 55 60 km at 30 50 c lower t considerable quantities of white and or dark micas formed by peritectic reactions from melt for instance garnets could be resorbed at this stage and biotite grew instead after the magmatic stage retrogression took place much stronger in the kokchetav massif this was accompanied by deformation transforming broadly the magmatic texture of quartz rich diamondiferous rocks from the kokchetav massif to a gneissic texture

high magnitude landslide events on a limestone scarp in central germany morphometric characteristics and climatic controls abstract there are both internal and external controlling factors leading to slope instability and susceptibility to mass movement processes this paper explores which external climatic variables of different temporal scales influence the occurrence of high magnitude landslide events the investigations were focused on the wellenkalk cuesta scarp in the thuringia basin thuringer becken in central germany the cuesta scarp is composed of a densely jointed limestone caprock wellenkalk and impermeable mudstones and marls of the upper bunter sandstone rot in the lower part of the slope mass movements are a typical feature of the wellenkalk scarp the entire scarp slope length 1000 km has been systematically mapped and investigated in a comprehensive research project in order to provide reliable information on the spatial distribution and control of the mass movements more than 20 of the scarp slope has been influenced by various types of holocene mass movements with strong differences in spatial frequencies sixteen high magnitude landslides sturzfliesungen were identified by field inspection and mapping of slope geomorphology information on locations morphometric characteristics stratigraphic positions and rainfall related attributes of the scarp slopes affected by the large landslides is presented mean annual rainfall amounts decrease from more than 800 mm in the western part of the basin to less than 550 mm in the east meteorological statistics on the spatial distribution of heavy rainfall intensities of different durations and return periods show that greatest precipitation intensities in short events 1 h are reached at the western margin differences in rainfall intensities between the western and eastern parts decrease with increasing duration of the events where available event related meteorological information was collected the spatial distribution of the landslides is most closely mirrored in the pattern of mean annual precipitation though this variable is generally not thought to be a satisfactory or reliable climatic controlling factor no landslides occur below a threshold value of 700 mm the empirical data show that some general level of average perennial water input into the slope system seems to be of decisive importance for the occurrence of high magnitude mass movements only when the precondition of a more general hydrological disposition is fulfilled a direct triggering of high magnitude mass movements by a short time intensive rainfall period or event can become effective

cosmic ray exposure dating on the large landslide of sechilienne western alps a synthesis to constrain slope evolution abstract the 60 10 6 m 3 sechilienne landslide belledonne massif western alps is located on the right bank of the east west trending romanche valley which is shaped by glacial and alluvial processes during the quaternary its head scarp 35 m high was dated by le roux et al 2009 using the cosmic ray exposure cre method even though these previous results revealed that the initiation of the instability occurred several thousand years after ice down wastage in the valley the internal landslide evolution is not constrained in this paper we provide 63 additional 10 be samples collected from the internal scarps and the main scarp as well as on glacially polished rock surfaces the aim is to constrain the global landslide kinematics internal and head scarps and its relationship with glacier retreat results from glacially polished surfaces point out that complex shielding processes relict moraines soil deposits and seasonal snow cover might have affected rock dating despite scattering of the resulting ages the dataset shows that the glacial retreat was achieved between 17 5 and 13 ka exposure ages obtained on gravitational scarps reveal that the landslide initiation occurred 8 to 6 ka ago from the initiation until 2 ka the gravitational kinematics was slow 2 mm year 1 and focused around the head scarp leading to a general slope subsidence after 2 ka the exposure rates increased significantly 8 mm year 1 with the development of pervasive internal deformation of the landslide mass this new scenario for the sechilienne slope reflects a progressive rock slope weakening since 8 ka associated with a continuous activity of a deep seated surface failure

columbia mountain landslide late glacial emplacement and indications of future failure northwestern montana usa abstract the well preserved and undissected columbia mountain landslide which is undergoing suburban development was studied to estimate the timing and processes of emplacement the landslide moved westward from a bedrock interfluve of the northern swan range in montana usa onto the deglaciated floor of the flathead valley the landslide covers an area of about 2 km2 has a toe to crown height of 1100 m a total length of 3430 m a thickness of between 3 and 75 m and an approximate volume of 40 million m3 deposits and landforms define three portions of the landslide from the toe to the head they are i clast rich diamictons made up of gravel sized angular rock fragments with arcuate transverse ridges at the surface ii silty and sandy deposits resting on diamictons in an internally drained depression behind the ridges and iii diamictons containing angular and subangular pebble to block sized clasts some of which are glacially striated in an area of lumpy topography between the depression and the head of the landslide drilling data suggest the diamictons cover block to slab sized bedrock clasts that resulted from an initial stage of the failure the landslide moved along a surface that developed at a high angle to the ne dipping thinly bedded metasediments of the proterozoic belt supergroup the exposed slope of the main scarp dips 30 37 w a hypothetical initial rotational failure of the lower part of a bedrock interfluve may have transported bedrock clasts into the valley the morphology and deposits at the surface of the landslide indicate deposition by a rock avalanche sturzstrom derived from a second stage of failure along the upper part of the scarp the toe of the columbia mountain landslide is convex west in planview except where it was deflected around areas now occupied by glacial kettles on the north and south margins landsliding therefore occurred during deglaciation of the valley while ice still filled the present day kettles available chronostratigraphy suggests that the 1 km thick glacier in the region melted before 12 000 14c years bp within 3000 years of the last glacial maximum deglaciation and hillslope failure are likely causally linked failure of the faceted interfluve was likely due tensile fracturing of bedrock along a bedding normal joint set shortly after glacial retreat from the hillslope open surficial tension fractures and grabens in the swan range are limited to an area above the crown of the landslide movement across these features suggests that extensional flow of bedrock sackung is occurring in what remains of the ridge that failed in the columbia mountain landslide the fractures and grabens likely were initiated during failure but their morphologies suggest active extension across some grabens continued movement of bedrock above the crown may result in future mass movements from above the previous landslide scarp landslides sourced from bedrock above the scarp of the late glacial columbia mountain landslide which could potentially be triggered by earthquakes are geologic hazards in the region

metamorphic evolution of diamond bearing and associated rocks from the kokchetav massif northern kazakhstan representative diamond bearing gneisses and dolomitic marble eclogite and ti clinohumite bearing garnet peridotite from unit i at kumdy kol and whiteschist from unit ii at kulet eastern kokchetav massif northern kazakhstan were studied diamond bearing gneisses contain variable assemblages including grt bt qtz pl kfs zo chl tur cal and minor ap rt and zrn abundant inclusions of diamond graphite chlorite or calcite phengite clinopyroxene k feldspar biotite rutile titanite calcite and zircon occur in garnet diamond bearing dolomitic marbles consist of dol di grt phl inclusions of diamond dolomite graphite biotite and clinopyroxene were identified in garnet whiteschists carry the assemblage ky tlc grt rt garnet shows compositional zoning and contains abundant inclusions of talc kyanite and rutile with minor phlogopite chlorite margarite and zoisite inclusions and zoning patterns of garnet delineate the prograde p t path inclusions of quartz pseudomorphs after coesite were identified in garnet from both eclogite and gneiss other ultrahigh pressure uhp indicators include na bearing garnet up to 0 14 wt na2o with omphacitic cpx in eclogite occurrence of high k diopside up to 1 56 wt k2o and phlogopite in diamond bearing dolomitic marble and cr bearing kyanite in whiteschist these uhp rocks exhibit at least three stages of metamorphic recrystallization the fe mg partitioning between clinopyroxene and garnet yields a peak temperature of 800 1000 c at p 40 kbar for diamond bearing rocks and about 740 780 c at 28 35 kbar for eclogite whiteschist and ti bearing garnet peridotite the formation of symplectitic plagioclase amphibole after clinopyroxene and replacement of garnet by biotite amphibole or plagioclase mark retrograde amphibolite facies recrystallization at 650 680 c and pressure less than about 10 kbar the exsolution of calcite from dolomite and development of matrix chlorite and actinolite imply an even lower grade greenschist facies overprint at c 420 c and 2 3 kbar a clockwise p t path suggests that supracrustal sediments together with basaltic and ultramafic lenses apparently were subjected to uhp subduction zone metamorphism within the diamond stability field tectonic mixing may have occurred prior to uhp metamorphism at mantle depths during subsequent exhumation and juxtaposition of many other tectonic units intense deformation chaotically mixed and mylonitized these lithotectonic assemblages

an ice grounding line wedge from the ghaub glaciation 635 ma on the distal foreslope of the otavi carbonate platform namibia and its bearing on the snowball earth hypothesis our detailed examination of the ghaub formation possibly 635 ma on the distal foreslope of the otavi carbonate platform is part of a regional study of the congo paleocontinental margin in northwestern namibia detrital carbonates of the ghaub formation disconformably overlie the franni aus member of the ombaatjie formation a coarsening upward stack of carbonate turbidites and oolite clast debris flow breccias interpreted to be a glacioeustatic falling stand wedge within the main ghaub formation carbonate diamictites are interleaved with mesoscale laminated to cross laminated climbing rippled grainstones and mudstones and conglomeratic carbonates amalgamation of diamictite units is observed where interleaved facies grainstones mudstones are laterally discontinuous due to reactivation of erosion followed by renewed deposition the diamictite package is progradational overall and 80 m thick on average it is overlain by the 5 15 m thick bethanis member which is unique in its lateral continuity composite fining upward trend and distinctive interbedding of turbidite grainstones argillaceous siltstones climbing rippled mudstones and meter scale stromatolite dropstones dropstones are ubiquitous within the finer grained ghaub lithofacies and their presence along with the facies context for subglacial and near grounding line deposition indicates a glacigenic origin for the ghaub formation despite its subtropical paleolatitude and distal foreslope setting we infer a glacial maximum represented by the sub ghaub disconformity followed by the main ghaub interval when an ice grounding line on the distal foreslope experienced abrupt step backs and readvances of limited magnitude terminated by the bethanis episode of unusually widespread iceberg calving and slope instability the bethanis member is overlain conformably by the keilberg member of the maieberg formation reconstruction of the foreslope places the ghaub grounding line wedge 1 3 km vertically below the rim of the platform implying an enormous base level change upon deglaciation when the platform was drowned below wave base for a period far exceeding the time scale for isostatic adjustment the magnitude of base level change supports the pan glacial hypothesis that dynamic thick ice sheets existed simultaneously on virtually all continents the snowball hypothesis that the oceans were also covered by glacial ice sea glacier provides a simple explanation for the main ghaub to bethanis transition terminal deglaciation was triggered by collapse of the sea glacier

evidence of fluid inclusions in metamorphic microdiamonds from the kokchetav massif northern kazakhstan abstract microdiamonds from garnet clinopyroxenites of the kokchetav massif northern kazakhstan and associated alluvial diamonds have been investigated using infrared spectroscopy all diamonds have high nitrogen contents from 747 up to 4488 20 at ppm and are of type ib iaa nitrogen data are consistent with a diamond formation over a narrow temperature range microdiamonds from garnet clinopyroxenites are characterized by water and carbonate inclusions similar to those ocurring in fibrous coated diamonds from kimberlite which suggest that diamonds grew from a c h o fluid in contrast alluvial microdiamonds do not contain any carbonate inclusions and h2o is absent or present in only minor amounts alluvial diamonds are considerably more n rich but have a similar range of nitrogen aggregation states it is suggested that alluvial diamonds belong to a separate diamond population compared with the microdiamonds from garnet clinopyroxenites the kokchetav microdiamonds are distinct from kimberlitic fibrous diamonds in that they contain abundant ib centres have high nitrogen contents and show different populations depending on host rock type these characteristics support a metamorphic origin for the microdiamonds from the uhpm rocks of the kokchetav massif

two diamictites two cap carbonates two δ13c excursions two rifts the neoproterozoic kingston peak formation death valley california stratigraphic mapping of the neoproterozoic glaciogenic kingston peak formation death valley california provides evidence for two temporally discrete extensional deformation episodes these episodes are bracketed by the sourdough limestone and noonday dolomite the facies characteristics and 13 c data ranging between 2 15 and 2 56 and 1 88 and 4 86 respectively of which make them equivalent to sturtian and varangian age cap carbonates respectively this constrains the two extensional episodes along the southwestern margin of laurentia to ca 700 ma and ca 600 ma these observations and data show that the field evidence for mid neoproterozoic breakup and the predictions from tectonic subsidence curves for a latest neoproterozoic breakup are both correct thus neoproterozoic plate reconstructions must account for two discrete rift episodes separated by 100 m y or more confining rifting to within the kingston peak formation thereby places the younger proterozoic rocks of the southwestern great basin in the rift to drift tectonic phase

slope instability in relation to glacial debuttressing in alpine areas upper durance catchment southeastern france evidence from field data and 10be cosmic ray exposure ages the upper durance catchment is an area prone to rock slope failures such failures reflect the combination of high relief litho structural controls and paraglacial stress release the aim of this study is to determine the role of deglacial unloading and resulting paraglacial stress release in conditioning or triggering slope failure former dimensions of the durance glacier are reconstructed then combined with digital elevation model data in a raster geographic information system to quantify the spatial pattern of stresses associated with glacial loading at the last glacial maximum preliminary calculations suggest that major rock falls and rock avalanches are associated with areas subject to the highest decompression stresses focus on two case studies allows the consequences of paraglacial stress release on slope instability to be evaluated description of slope failure runout deposits allows reconstruction of the nature of slope failure surface exposure dates based on concentration of cosmogenic 10be allows the timing of both deglaciation and that of post glacial rock slope failures to be established it is shown that rock slope failures are concentrated on lower valley side slopes within the area occupied by ice at the last glacial maximum and that their locations coincide with zones of inferred high glacial loading stress consistent with interpretation of both bedrock disruption and large scale rock slope failures as paraglacial phenomena induced by stress release following deglaciation timing of initial rock avalanche runout deposition at one site is consistent with this conclusion though later instability episodes at the same site may have occurred independent of the influence of paraglacial stress release

temporal behavior of deep seated gravitational slope deformations a review abstract deep seated gravitational slope deformations dsgsds are slow moving hillslope scale mass movements featuring characteristic landforms such as double crested ridges and upslope facing scarps that occur in diverse landscapes throughout the world although these deformations have been studied since the 1960s significant insights to the rates of dsgsds have only been gained within the last two decades owing to progress in geochronology remote sensing and instrumental monitoring absolute age and monitoring data indicate that dsgsd movements are observable over long term 102 years and short term future research directions include constraining the lifespan of dsgsds with absolute age dating and precise high resolution monitoring of spatio temporal displacement across dsgsd bodies it is of great importance to include absolute time scales in the numerical models of dsgsds furthermore combining remote sensing techniques such as synthetic aperture radar interferometry with high resolution lidar scanning and near surface geophysics offers a promising toolkit for collecting very detailed and accurate data on the short term deformation rates of dsgsds

simulation of the parma river blockage by the corniglio landslide northern italy abstract near the village of corniglio in the northern apennines about 40 km sw of parma a big landslide was recently 1994 1996 subjected to reactivation damaging many buildings and partially obstructing the parma river in this work we have carried out a quantitative analysis of the recent evolution of the landslide with the help of a geographic information system gis in order to predict the most plausible future developments then various simulations of landslide descent were carried out and above all to evaluate the possibility of blockage formation to this purpose two computer programs that simulate the material descent through a cellular automata model and define blockage characteristics were written many different simulations were carried out 16 of which are presented here for each of them the computer output consists of a table defining the quantity of displaced material area and volume of the dam and lake and of a map showing the areas involved in the landslide movement and upstream flooding in order to assess the probability of blockage formation and dam stability we applied the simulation results to some empirical rules defined by preceding authors through statistical analysis carried out on a high number of analogous phenomena these rules suggest that it is very unlikely that blockage takes place as the result of very slow landslide velocity riverbed width and high erodibility of the material if it were to occur the size and shape of the dam seem sufficient to guarantee a considerable degree of stability making a sudden failure improbable

morphology and acoustic character of the antarctic wilkes land turbidite systems ice sheet sourced versus river sourced fans the wilkes land continental slope contains an intricate network of submarine canyons that on the continental rise develop into a series of channel and overbank deposits of turbidite systems we can define upper fan middle fan and lower fan provinces the wilkes land upper fans are characterized by large channels with relief up to 900 m distances between levee crests up to 18 km and channel floor widths up to 6 km middle fan channels also have high relief 300 m and locally interchannel areas exhibit mounded contourite style deposits with high relief up to 490 m within middle fan sediment mounds there are acoustic facies of channel overbank deposits from turbidity currents and of sediment waves from contour current sedimentation the lower rise is characterized by small shallow channels 50 75 m relief and by interchannel areas of low relief both characteristic of a lower fan environment the wilkes land turbidite systems show the following significant morphological differences compared to most river sourced fans 1 multiple large tributary channels across the upper and middle fan 2 channel relief several times greater 900 m than typical relief 100 200 m for channels on fans less than 300 km in diameter and 3 steep middle fan and lower fan gradients we interpret the differences in channel network patterns channel size and middle fan and lower fan gradients between the wilkes land fans and other fans to result from the continental ice sheet feeding glacial ice streams that reached the outer continental shelf at times of glacial maxima the wilkes land canyon channel network patterns are comparable with the high latitude laurentian fan and labrador sea channels the laurentian fan also has large upper fan channels with larger relief 800 m than typical relief 200 300 m expected for fans that are 600 km in diameter both the labrador sea and laurentian fan are fed by continental ice sheets at the shelf edge

karst geomorphology of carbonatic conglomerates in the folded molasse zone of the northern alps austria germany abstract the folded molasse zone of the northern alps consists of clastic sedimentary rocks that are usually not considered to be karstifiable however large areas within this zone are composed of carbonatic conglomerates numerous karst landforms have recently been discovered but are not recorded on official maps and in the literature therefore a research programme was initiated at the hochgrat site austria germany that included geomorphological mapping and characterisation of the karst phenomena both fracture controlled and hydrodynamically controlled karren were observed on conglomerate outcrops the predominant karst landforms dolines are typically circular funnel shaped most often 2 to 9 m in diameter 1 to 6 m deep and frequently act as swallow holes poljes that are atypically small 1 ha occur in either glacial cirques or syncline depressions are flat floored and lined with sediment and soil and drain underground via swallow holes short caves springs with marked discharge variations and estavelles are further evidence for karst development karstic landforms are widespread in carbonatic conglomerate terrains but their dimensions are smaller than in typical limestone karst the practical implications of these findings are also briefly mentioned in this paper

the full range of turbidite bed thickness patterns in submarine lobes controls and implications a widely misused criterion to interpret lobe deposits in submarine fan systems at outcrop and in core and well logs is a thickening and or coarsening upward profile lobe deposits from the laingsburg depocentre sw karoo basin demonstrate that a full range of bed thickness patterns exists within lobes when lobes are defined by their laterally extensive bounding surfaces that are marked by abrupt facies changes five types of bed stacking patterns are identified thickening upward thinning upward thickening then thinning upward thinning then thickening upward and constant the abrupt bounding surfaces are interpreted to record avulsion of feeder distributive channels the stratigraphic bed thickness pattern preserved in a lobe reflects the internal organization of smaller scale lobe elements rather than lobe wide initiation and progradation as implied by a thickening upward only pattern the full range of bed thickness patterns in lobes can be used to understand the stacking of lobe elements the evolution of sediment deposition through time and space and the relative movement of depocentres

oxygen isotope variations in cr poor megacrysts from kimberlite abstract as radiogenic isotope compositions of cr poor megacrysts from kimberlite demonstrate that the megacrysts and kimberlite hosts are genetically related megacrysts are likely deep seated liquidus phases the oxygen isotope compositions of cr poor megacrysts are indicative of the 18o of the host kimberlites and their mantle source regions oxygen isotope ratios of garnet megacrysts from group i kimberlites from slightly depleted mantle sources worldwide north america southern africa australia are restricted 18ovsmow 5 24 sd 0 15 se 0 01 n 121 and typical of phenocrysts in magmas derived from upper mantle with normal oxygen isotope compositions no significant involvement of subducted oceanic crust is indicated in the genesis of group i kimberlites garnet megacrysts from group ii kimberlites from enriched mantle and restricted to southern africa have anomalously high 18o 16o ratios 18ovsmow 5 59 sd 0 18 se 0 02 n 55 similarities in equilibration temperature and major element composition between garnet megacrysts from group i and ii kimberlites rule out roles for these parameters in producing the marked difference in 18o 16o between these two suites instead the high 18o 16o values of the group ii garnets suggests incorporation of anomalously heavy oxygen from subducted ocean floor material in the source region of group ii kimberlites as much as 30 if eclogite with 18o approximately 6 5 with an ocean floor protolith is the contaminant less if the source of anomalous oxygen is pelagic or terrestrial sediment with higher 18o actual samples of potential group ii kimberlite source rocks e g mica amphibole veined peridotites or plutonic crystallization products of such kimberlites e g mica amphibole rutile ilmenite diopside rocks should have elevated 18o values but no such material has been previously described in southern african xenolith suites

buckling of high natural slopes the case of lavini di marco trento italy abstract layered limestones with marly clayey interbeds are widespread in mountain regions where tectonics has not changed the original structure they frequently form homocline slopes that since the last deglaciation have evolved through planar block slides along bedding joints a typical dip slope showing this evolution is represented by the left flank of the adige river valley south of rovereto north eastern italy even though layers never daylight at the slope toe the exceptional persistence and weakness of bedding joints allows buckling of layers which occasionally collapse causing rock avalanches before monitoring started deformations were believed to be no longer active this conviction being strengthened by the high safety factors provided by limit equilibrium analyses sar satellite interferometry performed between 1990 and 2002 and probe inclinometer measures indicate that the slabs located uphill from the buckle folds are slowly sliding since some doubts have been raised about rock mass behaviour slope geometry and hydraulic conditions assumed in the analyses buckling was back analysed using the distinct element method dem and the discontinuous deformation analysis dda these treat the rock mass as a discontinuum and account for deformation and failure of the rock material to perform numerical analyses rock mass structure strength and stiffness were determined through extensive in situ and laboratory investigations for this purpose field surveys borehole core logging and geophysical surveys were performed and laboratory geotechnical tests on the rock material clayey interbeds and bedding joints were conducted discontinuous analyses confirmed that buckling deformations are definitely possible if some conditions are present high water pressure minor flexures modelling also indicate that buckling deformations may evolve into failures and should therefore be taken into account in evaluating long term stability of the slope

a multi annual landslide inventory for the assessment of shallow landslide susceptibility two test cases in vorarlberg austria abstract geomorphological landslide inventories provide crucial input data for any study on the assessment of landslide susceptibility hazard or risk several approaches for assessing landslide susceptibility have been proposed to identify areas particularly vulnerable to this natural hazard what they have in common is the need for data of observed landslides therefore the first step of any study on landslide susceptibility is usually the compilation of a geomorphological landslide inventory using a geographical information system recent research has proved the feasibility of orthophoto interpretation for the preparation of an inventory aimed at the delineation of landslides with the use of distinctive signs in the imagery data in this study a multi annual landslide inventory focusing on shallow landslides i e translational soil slides of 0 2 m in depth was compiled for two study areas in vorarlberg austria from the interpretation of nine orthophoto series in addition derivatives of two generations of airborne laser scanning data aided the mapping procedure landslide scar areas were delineated on the basis of a high resolution differential digital terrain model the derivation of landslide volumes depths and depth to length ratios are discussed results show that most mapped landslides meet the definition of a shallow landslide the inventory therefore provides the data basis for the assessment of shallow landslide susceptibility and allows for the application of various modelling techniques

discriminating glacier thermal and dynamic regimes in the sedimentary record abstract this paper provides a description and evaluation of the sedimentary facies and environments associated with a range of glacier thermal and dynamic regimes with additional consideration given to the tectonic context new and previously published data are evaluated together and are presented from modern terrestrial and marine glacial sedimentary environments in order to identify a set of criteria that can be used to discriminate between different glacier thermal regimes and dynamic styles in the sedimentary record sedimentological data are presented from a total of 28 glaciers in 11 geographical areas that represent a wide range of contemporary thermal dynamic and topographic regimes in the context of landsystems representatives from terrestrial environments include temperate glaciers in the european alps patagonia new zealand the cordillera blanca peru cold glaciers in the dry valleys of antarctica and the antarctic peninsula region and polythermal valley glaciers in svalbard northern sweden the yukon and the khumbu himal nepal the glaciomarine environment is illustrated by data from cold and polythermal glacier margins on the east antarctic continental shelf and from a polythermal tidewater glacier in svalbard along with general observations from temperate glaciers in alaska these data show that temperate glacial systems particularly in high relief areas are dominated by rockfall and avalanche processes although sediments are largely reworked by glaciofluvial processes debris in polythermal glaciers is both thermally and topographically influenced in areas of moderate relief debris is mainly of basal glacial origin and the resulting facies association is dominated by diamicton in high relief areas such as the himalaya the debris load in polythermal glaciers is dominated by rockfall and avalanche inputs resulting in extensive accumulations of sandy boulder gravel cold glaciers are dominated by basal debris entrainment but sediments are little modified from the source materials which are typically sandy boulder gravel from older till and sand from glaciofluvial glaciolacustrine and aeolian sources similar facies associations but with different facies geometry and thickness occur in equivalent glaciomarine settings application of these concepts can aid the interpretation of glacier thermal regime and hence palaeoclimate in quaternary and ancient glacial systems

neoproterozoic ice sheets and olistoliths multiple glacial cycles in the kingston peak formation california the kingston peak formation is a diamictite bearing succession that crops out in the death valley region california usa an exceptionally thick 1 5 km outcrop belt in its type area the kingston range provides clear insights into the dynamics of mid cryogenian sturtian ice sheets in laurentia seven detailed logs allow the lateral and vertical distribution of facies associations to be assessed we recognize 1 diamictite facies association ice proximal glacigenic debris flows 2 lonestone bearing facies association ice marginal hemipelagic deposits and low density gravity flows with iceberg rafting 3 pebble to boulder conglomerate facies association ice proximal cogenetic glacigenic debris flows and high density turbidites 4 megaclast facies association olistostrome and hemipelagic sediments subject to ice rafting and 5 interbedded heterolithics facies association low density turbidites and hemipelagic deposits the stratigraphic motif allows three glacial cycles to be inferred across the range ice minimum conditions interrupting the kingston peak succession are associated with the development of an olistostrome complex succeeded by a thick accumulation of boulder conglomerates deposited during ice readvance the data testify to a strong glacial influence on sedimentation within this ancient subaqueous succession and to highly dynamic ice sheet behaviour with clear glacial cycles during the sturtian glaciation

oxygen carbon and strontium isotope geochemistry of diamond bearing carbonate rocks from kumdy kol kokchetav massif kazakhstan abstract diamond bearing carbonate rocks from kumdy kol kokchetav massif kazakhstan were strongly altered by fluids flowing through fractures and infiltrating along grain boundaries during exhumation alteration includes retrogradation of high grade silicate assemblages by hydrous minerals replacement of diamond by graphite and of dolomite by calcite diamond bearing carbonate rocks are among the most intensely altered isotopically with 18 o vsmow values as low as 9 13 c vpdb 9 and 87 sr 86 sr as high as 0 8050 evidence of isotopic equilibration between coexisting dolomite and high mg calcite during ultrahigh pressure metamorphism uhpm is preserved only rarely in samples isolated from infiltrating fluids by distance from fractures isotopic heterogeneity and isotopic disequilibrium are widespread on a hand specimen scale because of this lack of homogeneity bulk analyses cannot provide definitive measurements of 13 c 12 c fractionation between coexisting diamond and carbonate our study adequately documents alteration on a scale commensurate with observed vein structures but testing the hypothesis of metamorphic origin of microdiamonds has not fully succeeded because our analytical spatial resolution limited to 0 5 mm is not small enough to measure individual dolomite inclusions or individual diamond crystals

climate simulations of neoproterozoic snowball earth events similar critical carbon dioxide levels for the sturtian and marinoan glaciations abstract the sturtian and marinoan snowball earth episodes initiated 720 and 650 million years ago respectively are among the most dramatic events in earth s history the ultimate causes of these events remain obscure however and there is still uncertainty about the critical levels of greenhouse gas concentrations at which the snowball transition occurs furthermore earlier modelling results with incomplete representations of important boundary conditions provided conflicting indications for differences between the critical carbon dioxide concentrations for the marinoan and the sturtian reporting either the earlier or the later epoch to be more susceptible to global glaciation both the absolute values of and possible differences between these glaciation thresholds have profound implications for scenarios of snowball initiations during the neoproterozoic here we present coupled climate simulations using an ocean general circulation model with dynamic thermodynamic sea ice coupled to a fast atmosphere focusing on the differences between the neoproterozoic glaciations for the first time our simulations use realistic boundary conditions in terms of changes in solar luminosity between the two epochs and the most recent continental reconstructions in agreement with previous studies with models including ocean and sea ice dynamics we report low values for the critical carbon dioxide concentration during the neoproterozoic but in contrast to hints from earlier studies we find very similar values of 100 130 ppm for the snowball bifurcation point during the sturtian and marinoan this highlights the importance of realistic boundary conditions for climate simulations of the neoproterozoic glaciations

cryptic climatic signatures and tectonic controls on cryogenian diamictites in the nw tarim craton china unravelling the origins of cryogenian diamictites is vital in determining their significance in a snowball earth context and their relationship to environmental processes here we present new sedimentological and geochemical data for the cryogenian sedimentary rocks from the tarim craton nw china the diamictite member of the east qiaoenbrak formation contains 1 granitic pebbles with high sphericity 2 well developed stratification and 3 bed scale grain size changes suggesting cyclicity also 4 ice rafted debris is conspicuously absent rather than deposits of direct glacial origin the succession is instead interpreted as a subaqueous fan complex the major and trace element ratios and ree patterns are consistent throughout 22 sampled intervals in the qiaoenbrak group suggesting a uniformly felsic source area probably from an island arc chemical index of alteration cia analysis indicates low cia values 49 5 54 3 average 51 6 throughout the qiaoenbrak group we suggest that both the qiaoenbrak group and yuermeinak formation were deposited during the marinoan glaciation in a long lasting cold and dry interval it is likely that the qiaoenbrak group was deposited in a fault controlled basin adjacent to an active continental margin although the material may ultimately have derived from a glacial source e g outwash

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

diamond inclusions in garnets from metamorphic rocks a new environment for diamond formation diamonds commonly occur in kimberlites lamproites and alluvial sediments derived from these rocks more recently diamonds or their graphite pseudomorphs have been discovered in ultramafic massifs1 and picrites2 here we report the occurrence of diamonds in situ in crustal rocks highly retrograded high pressure metamorphic garnet pyroxene and pyroxene carbonate garnet rocks biotite gneisses and schists from the kokchetav massif northern kazakhstan ussr the diamonds are cubo octahedral averaging 12 m in size and occur in zircons and with euhedral graphite as inclusions in unzoned garnets we believe that the zircon and garnet matrices protected these diamonds from retrogressive transformation to graphite mica rutile titanite clinopyroxene kyanite and zircon also occur as inclusions in garnet often intergrown with the diamonds equilibration relations of inclusions and host garnets indicate that both diamonds and graphite crystallized from a fluid phase under static conditions at pressures of 40 kbar and temperatures 900 1 000 c

the failure mechanism of a late glacial sturzstrom in the subalpine molasse leckner valley vorarlberg austria a number of prehistoric landslides and rock avalanches occurred in the folded and faulted section of the molasse zone in vorarlberg austria some developed into a sturzstrom defined as a rapidly moving fluidised mass movement of large volumes of rock derived from the disintegration of a falling rock mass that spread under the influence of gravity their impact on the landscape usually is related to obstruction of rivers and valleys in this paper we analyse the geomorphology and the failure mechanism of a relative small sturzstrom the failure mechanism can be described as a buckling failure the morphological situation indicates that failure took place after local deglaciation by the end of the upper wurm the period of failure coincides with glacial and ice marginal remnants which developed between 15 000 and 14 600 bp the lithological sequence and rock structure as well as the impact of the processes related to the former glacial environment were major causal conditions the rock sequence consists of conglomerates sandstone layers and marls next to glacial scouring which increased the inclination of the valley slopes the effect of late glacial unloading and postglacial processes such as weathering and fluvial erosion subsequently weakened the mass rock fabric until failure occurred discontinuity orientation measurements geostructural and geomechanical conditions and the former hydrological and geomorphological conditions support bucklings failure in fact three hinge buckling may have occurred the frontal section of the sturzstrom consists mainly of large conglomerate blocks averaging 1 5 m3 in volume although megablocks reaching of up to 4000 m3 are present as well the volume of the entire sturzstrom equals approximately 10 107 m3 present activity is only restricted to minor rock falls derived from the conglomerates and mudflows originating from the marl layers

new constraints on equatorial temperatures during a late neoproterozoic snowball earth glaciation intense glaciation during the end of cryogenian time 635 million years ago marks the coldest climate state in earth history a time when glacial deposits accumulated at low tropical paleolatitudes the leading idea to explain these deposits the snowball earth hypothesis predicts globally frozen surface conditions and subfreezing temperatures with global climate models placing surface temperatures in the tropics between 20 c and 60 c however precise paleosurface temperatures based upon geologic constraints have remained elusive and the global severity of the glaciation undetermined here we make new geologic observations of tropical periglacial aeolian and fluvial sedimentary structures formed during the end cryogenian marinoan glaciation in south australia these observations allow us to constrain ancient surface temperatures we find periglacial sand wedges and associated deformation suggest that ground temperatures were sufficiently warm to allow for ductile deformation of a sandy regolith the wide range of deformation structures likely indicate the presence of a paleoactive layer that penetrated 2 4 m below the ground surface these observations paired with a model of ground temperature forced by solar insolation constrain the local mean annual surface temperature to within a few degrees of freezing this temperature constraint matches well with our observations of fluvial deposits which require temperatures sufficiently warm for surface runoff although this estimate coincides with one of the coldest near sea level tropical temperatures in earth history if these structures represent peak marinaon glacial conditions they do not support the persistent deep freeze of the snowball earth hypothesis rather surface temperatures near 0 c allow for regions of seasonal surface melting atmosphere ocean coupling and possible tropical refugia for early metazoans if instead these structures formed during glacial onset or deglaciation then they have implications for the timescale and character for the transition into or out of a snowball state

exhumation of high pressure rocks of the kokchetav massif facts and models abstract the exhumation of ultrahigh pressure uhp metamorphic units from depths more than 100 120 km is one of the most intriguing questions in modern petrology and geodynamics we use the diamondiferous kumdy kol domain in the kokchetav massif to show that exhumation models should take into consideration initially high uplift velocities from 20 down to 6 cm year and the absence of the deformation of uhp assemblages the high rate of exhumation are indicated by ion microprobe shrimp dating of zircons from diamondiferous rocks and supported by the low degree of nitrogen aggregation in metamorphic diamonds diamondiferous rocks in the kumdy kol domain occur as steeply dipping 60 80 thin slices few hundred metres within granite gneiss using geological petrological and isotopic geochemical data we show that partial melting of diamondiferous metamorphic rocks occurred a very important factor which has not been taken into account in previous models deformation of diamondiferous rocks at kumdy kol is insignificant diamond inclusions in garnet are often intergrown with mica crystals carrying no traces of deformation all these facts could be explained by partial melting of metapelites and granitic rocks in the kumdy kol domain the presence of melt is responsible for an essential reduction of viscosity and a density difference between crustal rocks and mantle material and reduced friction between the upwelling crustal block the subducting and overriding plates besides the exhumation rate seems to depend on internal pressure in the subducting continental crustal block which can be regarded as a viscous layer between subducting continental lithosphere and surrounding mantle we construct different models for the three stages of exhumation a model similar to corner flow for the first superfast exhumation stage an intermediate stage of extension most important from structural point of view and a very low rate of exhumation in final diapir erosional uplift

pulsed iceberg delivery driven by sturtian ice sheet dynamics an example from death valley california the kingston peak formation is a cryogenian sedimentary succession that crops out in the death valley area california usa it is widely accepted to record pre glacial conditions kp1 followed by two glaciations of pan global extent the older sturtian kp2 to kp3 and younger marinoan glaciation kp4 in the type area the kingston range detailed facies analysis of the sturtian succession reveals that a basal diamictite unit and an upper boulder conglomerate were deposited by proglacial subaqueous sediment gravity flows an olistostrome unit punctuating the succession is interpreted to result from tectonically induced downslope mobilization during isostatic rebound triggered by significant ice meltback focussing on strata onlapping the olistostrome this article provides insight into the processes of glacial re advance following an intra sturtian glacial minimum the first 50 m of strata above the olistostrome are thinly bedded turbidites that are devoid of lonestones a trend towards thicker graded beds upsection in concert with the gradual appearance and then abundance of lonestones testifies to the influence of ice rafting and to the resumption of a direct ice sheet influence upon sedimentation stratigraphic organization into thickening and coarsening upward bedsets over a multi metre scale reveals a subaqueous gravity flow dominated succession composed of a spectrum of high to low density turbidites with thick graded boulder conglomerates at intervals the finer grained facies assemblage is heterolithic current ripple cross laminated sandstones intercalated with shales that bear delicate granule to pebble sized dropstones in abundance intervals of dropstone bearing and dropstone free strata are attributable to dynamic oscillation of the ice margin in the hinterland integrating palaeocurrent data with observations from neighbouring outcrop belts allows a detailed palaeogeographic map of the eastern death valley area to be compiled for the first time

late holocene catastrophic slope collapse affected by deep seated gravitational deformation in flysch ropice mountain czech republic the region of the flysch western carpathians is characterized by abundant deep seated gravitational slope deformations dsgsds this study deals with a detailed analysis of late holocene catastrophic collapse of a fault created slope of mountain ropice in the moravskoslezske beskydy mountains eastern czech republic the catastrophic collapse was initialized by huge compound rotational slide toppling deformation which occurs on the upper part of the studied slope and affects tectonically weakened subhorizontally inclined sandstone beds detailed geomorphological mapping accompanied by morphotectonic analysis and geophysical sounding revealed at least two historic flowslides the older event f1 affected 0 5 0 8 mm3 of bedrock and created a 1000 m long and up to 150 m wide accumulation with abundant transverse steps and a carapace like surface the landslide toe blocked an adjacent valley which led to the development of a small impoundment with 4 m thick deposits containing lacustrine peat bog floodplain and alluvial fan facies radiocarbon dating and pollen analysis indicate the valley blockage at 1 5 ka bp the other flowslide f2 of much smaller dimensions 10 000 12 000 m3 overlaid the main landslide body and according to the dating of minerogenic horizon in the impoundment may have taken place 0 3 ka bp the organisation of landforms character of slope failures and dynamic back modelling point to a likely rock avalanche or combined rock slide debris avalanche mechanism of movement this case study shows that rapid rock avalanches can operate also in mountainous terrain with moderate relief if toppling together with deep seated gravitational deformation of slopes modifies the original stable position of bedding planes