neoproterozoic iron formation an evaluation of its temporal environmental and tectonic significance article neoproterozoic iron formation nif provides evidence for the widespread return of anoxic and ferruginous ba sins during a time period associated with major changes in climate tectonics and biogeochemistry of the oceans here we summarize the stratigraphic contextof neoproterozoic iron formation and its geographic and temporal dis tribution it is evident that most nif is associated with the earlier cryogenian sturtian glacial epoch although it is possible that some nif may be ediacaran there is no incontrovertible evidence to support this age assignment the paleogeographic distribution of nif is consistent with anoxic and ferruginous conditions occurring in basins within rodinia or in rift basins developed on its margins consequently nif does not require whole ocean anoxia simple calculations using modern day iron fluxes suggest that only models that invoke hydrothermal and or detrital sourcesofiron are capable ofsupplying sufficient ironto account forthe mass of the largernif occurrences this con clusion is reinforced by the available geochemical data that imply nif record is a mixture of hydrothermal and de trital components a common thread that appears to link most if not all nif is an association with mafi cv olcanics

rare earth abundance patterns in ferromanganese concretions from the gulf of bothnia and the barents sea abstract ferromanganese concretions from the svalbard shelf in the barents sea show slightly convex shale normalized ree patterns with no eu anomalies concretions from the gulf of bothnia northern part of the baltic sea exhibit an enrichment of light ree and negative eu anomalies this difference is interpreted as a consequence of different conveyor mechanisms of the ree to the sediment it is suggested that dissolving biogenic debris contributes to the convex pattern obtained in the barents sea whereas an inorganic suspended fraction with scavenged ree is the main carrier in the gulf of bothnia during oxic diagenesis in the sediment the scavenged ree are set free into the porewater and contribute to the distribution pattern in concretions found in the gulf of bothnia small mn rich spheroidal concretions are enriched two to five times in ree compared to average shale whereas mn poor flat concretions are low in ree specific surface area of the concretion and the depth of burial in the oxidized surface sediment are two factors that strongly affect the enrichment of the ree weak ce anomalies are present in the analysed concretions and a redox level dependence is seen

the metal oxide fraction of pelagic sediment in the equatorial north pacific ocean a source of metals in ferromanganese nodules abstract pelagic sediment recovered at domes site a in the equatorial north pacific 151 w 9 15 n consists of a surface homogeneous layer approximately 10 cm thick overlying a strongly mottled layer that is lighter in color the radiolarian composition of both units is quaternary in areas where this sediment was only a few centimeters thick the underlying sediment was early tertiary clay mineralogy and major oxide composition of the two quaternary sediments are uniform their similarity to continental shale suggests that the sediment has a terrigenous source clay mineralogy and major oxide composition of the tertiary sediment also are uniform although they differ markedly from the quarternary sediment in contrast to the major oxides concentrations of mn co cu and ni soluble in hydroxylamine hydrochlorideacetic acid are strongly different in the surface and subsurface quaternary sediment mn and ni exhibit pronounced depletions in the subsurface sediment ni slightly more than mn cu is also depleted in the subsurface sediment but less than mn it is also depleted in the subsurface tertiary sediment whereas the mn concentration remains high concentration of co relative to mn increases into the subsurface quaternary sediment to a constant co mn ratio of 3 10 2 the trivalent ree the ree exclusive of ce and fe exhibit little down core variation distribution of elements in these sediments is closely related to their concentration in associated surface ferromanganese nodules the nodules are of two distinct types those from the area where the quaternary sediment is relatively thick have mno2 as the dominant manganese mineral the ratios of ni mn cu mn and fe mn in these nodules approximate the corresponding ratios of the soluble fraction of surface sediment todorokite is the dominant mineral of nodules recovered from areas where the quaternary sediment is thin relatively high cu mn ni mn and low fe mn ratios of these nodules mirror differences between the soluble fraction of surface and subsurface quaternary sediment these compositional trends of sediment and nodules at domes site a reflect a diagenetic origin for the todorokite nodules and a predominantly hydrogenous origin for the mno2 nodules

the distribution of rare earth and minor elements in manganese nodules and sediments from the equatorial and s w pacific abstract 62 manganese nodules and 17 associated sediments from the equatorial and s w pacific have been analyzed for a number of elements including the rare earth elements ree by instrumental neutron activation sc co as hf th and ree occur in higher concentrations in s w pacific than in equatorial pacific nodules reflecting the higher iron content of the s w pacific nodules these elements are probably incorporated nondiscriminantly into the iron oxyhydroxide structure by direct sorption from seawater because they are too large to be incorporated into the manganese oxide structure the highest ce la ratios are also found in the s w pacific nodules this may result from the fact that these nodules lie beneath the path of the fast flowing well oxygenated antarctic bottom water aabw which facilitates oxidation of ce to the tetravalent state if so this supports the idea that the ce la ratio of manganese nodules is an important redox indicator negative cerium anomalies were noted for nodules from areas f and g can be interpreted on the same model the ree contents in equatorial pacific siliceous oozes and s w pacific red clays are similar on a carbonate free basis the ce la ratio of the s w pacific red clays is however much higher than that of the equatorial pacific sediments possibly reflecting the preferential oxidation of ce to the tetravalent state beneath the aabw there appears to be no systematic relationship between the ree abundance in the nodules and their associated sediments although absolute ree abundances are higher in nodules than in their associated sediments nodules with the highest ce la ratios are however found on sediments with the highest ce la ratios the principal difference in the ree distribution pattern of the nodules and sediments lies in the well known cerium anomaly which is positive to slightly negative for nodules and always negative for sediments

residual circulation in shallow estuaries 1 highly stratified narrow estuaries long wave theory and simple turbulence closures have been used to show that three distinct types of circulation highly stratified weakly stratified and partially mixed arise in narrow shallow estuaries from the finite amplitude of the tide and the interaction of stratification with vertical mixing each type has a different dominant process causing the vertical exchange of salt and fresh water on the flood and each gives rise to a characteristic residual circulation the tidal circulation in highly stratified shallow estuaries described herein is the result of a finite amplitude internal motion driven by the barotropic tide shear instabilities at the interface are the major vertical exchange mechanism the residual circulation is caused primarily by ebb flood asymmetry in interface position and thickness a model based on our theoretical analysis shows that the interface thickness on flood is much less than the depth of flow up to a critical tidal amplitude at which the two layer flow is destroyed and correctly predicts the tidal amplitude of the neap spring transition in the columbia river estuary tidal frequency internal wave motion is not found in weakly stratified and partially mixed estuaries because of the reduced tidal shear shear instabilities are weak or absent and the residual circulation assumes a very different character as described in part 2

effects of earthquake induced landslides on sediment budget and transport over a 50 yr period landsliding during a magnitude 7 7 earthquake in 1929 in northwestern south island new zealand delivered up to 400 000 m 3 km 2 of sediment to stream channels first to third order channels were buried to depths of as much as 10 m with sedimentary rock debris for distances ranging from 2 of the 92 km 2 study area because of the coarse grain size of the sedimentary rock debris and trapping of sediment in numerous landslide dammed lakes sand and pebble sized debris originating from landslides on a 6 6 km 2 area of granite has been transported downstream no more than 10 km at least 50 to 75 of this granitic debris is retained in the fourth order 92 km 2 catchment 50 yr after the earthquake the long retention times of sediment and the volume of debris supplied by landslides during a large earthquake suggest that earthquake induced landsliding is the principal sediment supply mechanism in the region

geomorphic imprint of landslides on alpine river systems southwest new zealand an inventory of 846 mass movements mainly landslides in two alpine regions of southwest new zealand was created to explore the geomorphic impacts of slope failure processes on river channels and valley floors in total 213 i e 27 per cent of the slope failures descended to valley floors affecting the geomorphology of trunk channels catchment area ac 10 km2 and valley floors in recurring patterns a nominal classification system is introduced for characterizing a the physical contact nature between landslides and river channels and b the resulting geomorphic consequences for drainage although landslide area a is useful for estimating the length of channel directly impacted by debris it does not necessarily predict the direction of fluvial response or type of impact dominant persistent geomorphic imprints of bedrock landslides include channel occlusions and landslide dams in south westland and fiordland respectively differences in size distribution and geomorphic effects on river systems between the two study regions are attributed to bedrock geology tectonics and sediment flux although south westland rivers are more frequently affected by landslides disrupting long term effects such as blockage are more persistent in fiordland copyright 2005 john wiley sons ltd

rare earth element geochemistry of ferromanganese crusts from the hawaiian archipelago central pacific abstract the rare earth element ree composition of ferromanganese deposits from the hawaiian archipelago was determined as part of a geochemical investigation into the origin and environment of deposition of crusts most samples exhibit shale normalized ree patterns which are typical of hydrogenous ferromanganese deposits patterns of two todorokite and manjiroite rich crusts are significantly different from those of the other samples the range of concentrations in typical hawaiian crusts sum of ree 0 15 0 25 wt is in the uppermost portion of that reported for deep sea fe mn nodules shallow water 2000 m as well as slightly greater ree fractionation large positive ce anomalies attributed to the oxidative scavenging at the mno 2 surface are observed on all samples except one the slight light ree lree depletion in shallow water crusts relative to deeper samples is discussed in terms of variations in the ree concentrations in the water column and the relative complexing behavior of the ree no significant trend in ce concentration with depth is observed partition coefficient calculations suggest that concentrations of trivalent ree in crusts are affected by their availability in seawater to a greater extent than by the composition of the scavenging ferromanganese oxide flocs

persistent alluvial fanhead trenching resulting from large infrequent sediment inputs we present laboratory and field evidence that in mountainous catchment fan systems persistent alluvial fanhead aggradation and trenching may result from infrequent large sediment inputs we suggest that the river fan systems along the fault bounded range front of the western southern alps new zealand are likely to be in a dynamic equilibrium on 103 yr timescales superimposed on which their fanheads undergo long term cumulative episodic aggradation these fanheads are active only in rare events do not take part in the usual behaviour of the catchment fan system and require much longer to exhibit dynamic equilibrium than the rest of the fan these findings 1 increase our knowledge of the effects of extreme events on alluvial fan morphodynamics in humid climates 2 question the general applicability of inferring past climatic or tectonic regimes from alluvial fan morphology and stratigraphy and 3 provide a conceptual basis for hazard zonation on alluvial fans copyright 2006 john wiley sons ltd

rare earth element distribution and behaviour in buried manganese nodules from the central indian basin eight buried manganese nodules taken in the upper metre of a siliceous ooze sediment core in the central indian basin at 14 s and 74 e were analysed for major trace and rare earth ree elements interelemental correlation yields a strong positive association r 0 75 between fe p ti and ree suggesting a single carrier phase for ree in these nodules namely a titaniumrich ferriphosphate this correlation significantly improved r 0 90 when the influence of detrital fe is eliminated and only authigenic fe is considered the buried nodules appear to retain the mineralogical and geochemical characteristics including positive ce anomaly acquired during the accretion at the sediment water interface prior to their burial at 225 kyr b p the effect of burial is observed only in the depletion of heavy ree hree in a nodule buried at 23 5 cm depth where the environment is suboxic to anoxic middle ree mree in the nodules exhibit enrichment over light ree lree and hree while lree exhibit enrichment over hree compared to the ratios in shale nasc this enrichment pattern suggests an uptake sequence of the ree as mree lree hree in the manganese nodules

reduction of long term bedrock incision efficiency by short term alluvial cover intermittency fluctuations of the sediment volume stored in mountain channels are driven by stochastic variations of discharge and sediment supply and can inhibit bedrock incision if sediment thickness is too large here i study how this short term stochasticity propagates into the long term reduction of bedrock incision efficiency the cover effect at geological time scales i introduce a new numerical model that resolves sediment transport and bedrock incision at daily time scales and is run for thousands of years it incorporates 1 a transport threshold and daily stochastic variations in water discharge and sediment supply 2 a freely evolving channel width and slope and 3 an explicit treatment of alluvial thickness variations and corresponding bed incision reduction for typical mountain river conditions the model predicts that alluvial cover oscillates between complete and negligible incision reduction in this intermittent regime the long term cover effect is mainly set by the fraction of time spent in full cover and the present day extent of alluvial cover is not representative of long term dynamics the long term integrated cover effect law differs strongly from proposed theoretical and experimental models and it is controlled by sediment supply stochasticity rather than the details of cover development at the hydraulic time scale model results also suggest that steady state channel configuration always depends on sediment supply rate while being never limited by transport capacity or strictly detachment limited these results point out that discharge and sediment supply stochasticity should not be considered less important than the intricate details of incision laws to model long term bedrock channel dynamics

slope distributions threshold hillslopes and steady state topography digital elevation models of two steady state mountain ranges the olympic mountains om and oregon coast range ocr are used to examine relationships between slope distributions the development of threshold hillslopes and steady state topography plots of drainage area versus slope for these mountain ranges exhibit substantial scatter that complicates comparison of range form to analytical theories and landscape evolution models contour plots of the density of such data reveal an attractor at the scale of the transition from hillslope processes to channel processes and log bin averaging reveals trends that parallel predictions of steady state erosion laws but with different rate laws for five distinct process domains hillslopes valley heads and colluvial bedrock and alluvial valley segments slope histograms computed for 100 km2 areas defined by a 10 10 km grid throughout the om exhibit approximately normal or exponential distributions in areas of active rock uplift and depositional topography respectively local slope distributions in the ocr also tend to be normally distributed but some are left skewed in areas with gentler slopes mean slopes determined both over the above referenced grid and a 10 km diam moving window are relatively invariant in the core of the om in spite of strong contrasts in bedrock erodibility and gradients in long term rock uplift rates in contrast the mean slopes in the ocr parallel latitudinal gradients in rock uplift rates and bedrock erodibility hence the slope distributions in the om and ocr reflect distinct relationships between development of threshold bedrock and soil mantled hillslopes and steady state topography

geochemistry of the rare earth elements in ferromanganese nodules from domes site a northern equatorial pacific abstract the distribution of rare earth elements ree in ferromanganese nodules from domes site a has been determined by instrumental neutron activation methods the concentrations of the ree vary markedly low concentrations characterize samples from a depression the valley in which quaternary sediments are thin or absent high concentrations are found in samples from the surrounding abyssal hills the highlands where the quaternary sediment section is relatively thick moreover the valley nodules are strongly depleted in the light trivalent ree lree and ce compared with nodules from the highlands some of the former showing negative ce anomalies the ree abundances in the nodules are strongly influenced by the ree abundances in coexisting bottom water some controls on the ree chemistry of bottom waters include a the more effective removal of the lree relative to the hree from seawater because of the greater degree of complexation of the latter elements with seawater ligands b the very efficient oxidative scavenging of ce on particle surfaces in seawater and c the strong depletion of both ce and the lree in or a larger benthic flux of the hree into the antarctic bottom water aabw which flows through the valley the distinctive ree chemistry of valley nodules is a function of their growth from geochemically evolved aabw in contrast the ree chemistry of highland nodules indicates growth from a local less evolved seawater source

rare earth elements in the nw indian ocean abstract dissolved rare earth element ree distributions have been determined at three stations in the high productivity nw indian ocean nwio upwelling zone dissolved ree distributions within the well oxygenated surface waters and deep portions of the water column are similar to those reported previously from other open ocean locations at depth dissolved ree concentrations are intermediate between those of the atlantic and pacific oceans consistent with the continuous regeneration and enrichment of the strictly trivalent rees in and the progressive oxidative removal of ce from the deep ocean within the mid depth oxygen minimum zone dissolved ree concentrations exhibit a notable enrichment superimposed upon these typical oceanic profiles further dissolved ce concentrations are preferentially enriched within the suboxic horizon compared to the rest of the series indicating the reduction of insoluble ce iv to dissolved ce iii at these depths by analogy with our previous studies of ree distributions in anoxic basins we propose that the more modest enrichments of the strictly trivalent rees observed in the nwio suboxic zone must derive from uptake through scavenging within the well oxygenated portions of the water column and regeneration from sediments and settling particles within the more reducing conditions of the oxygen minimum zone

structural textural geochemical and isotopic signatures of synglaciogenic neoproterozoic banded iron formations bifs at bafq mining district bmd central iran the possible ediacaran missing link of bifs in tethyan metallogeny abstract the neoproterozoic magnetite apatite hematite pyrolusite jaspilite deposits in the bafq mining district bmd contain more than 1 7 gt ores with an average grade of 50 wt fe and 0 01 to 7 78 wt p and were probably formed between 635 and 547 ma in a riftogenic felsic submarine exhalative sequence of the esfordi formation the ore zones occur in proximal zone of magnetite rich albitized rhyolite keratophyres interdistal zone of rhyolitic tuff tuffaceous sediments and distal zone of pyrolusite jaspilite these sequences are covered by the diamictites and cap carbonates the bifs are linked to the altered rhyolites rhyodacites jaspilites and diamictites and contain magnetite hematite and apatite the presence of spriggina dickinsonia medusites and persimedusites chahgazensis sennewald and kruger 1979 hahn and pflug mccall 2006 in the kushk shale member of the esfordi formation conforms to the australian fauna of the ediacaran period 635 540 this relative age is supported by some reliable pb isotopic data 635 547 ma on galena monazite and apatite huckriede et al 1962 torab 2008 stosch et al 2011 the most frequent structures textures in the ore zones include felsic autobrecciation massive colloidal banded detrital and glaciogenic the bifs are highlighted by high values of lree fractionation and no significant eu and ce anomalies the ores show high values of fe 2 o 3 14 60 and sio 2 4 34 and low contents of al 3 32 cr 21 48 ppm co 42 82 ppm ni 125 ppm v 868 ppm and ti 0 13 similar to those of the ediacaran rapitan bifs the cap carbonates show depletion in 13 c with a range from 0 43 to 6 6 per mil and then return to near excursion of about 2 97 in the lower cambrian carbonates these are followed by 18 o values which range from 6 64 to 11 86 the presence of jaspilites diamictites c and o isotopic signatures ree patterns and immobile element relationships highlights a glaciogenic bif importantly the glaciogenic structures textures and jaspilites do not support the misconception of the previously proposed magmatic carbonatitic and metasomatic hydrothermal iocg kiruna ore deposits

comparison of inductively coupled plasma and neutron activation analysis for precise and accurate determination of nine rare earth elements in geological materials abstract the performance of inductively coupled plasma spectrometry icp for the determination of nine rare earth elements ree was evaluated by comparison with neutron activation analysis naa data obtained for the same geochemical reference samples grs granite g 2 andesite agv 1 granite gs n diorite dr n potash feldspar fk n and two apatite samples were chosen as test materials and analysed by the same operator granite nim g granite ga green river shale sgr 1 and granite ac e were also included to access the accuracy and the precision of the combined cation exchange icp method for common silicate rocks and material rich in ree the accuracy and the precision of both those techniques are within the requirements needed these ree determinations show that icp applied under the proper working conditions lives up to the expectations

landscape response to tectonic forcing digital elevation model analysis of stream profiles in the mendocino triple junction region northern california the topographic evolution of orogens is fundamentally dictated by rates and patterns of bedrock channel incision quantitative field assessments of process based laws are needed to accurately describe landscape uplift and denudation in response to tectonics and climate we evaluate and calibrate the shear stress or similar unit stream power bedrock incision model by studying stream profiles in a tectonically active mountain range previous work on emergent marine terraces in the mendocino triple junction region of northern california provides spatial and temporal control on rock uplift rates digital elevation models and field data are used to quantify differences in landscape morphology associated with along strike northwest to southeast changes in tectonic and climatic conditions analysis of longitudinal profiles supports the hypothesis that the study area channels are in equilibrium with current uplift and climatic conditions consistent with theoretical calculations of system response time based on the shear stress model within uncertainty the profile concavity of the trunk streams is constant throughout the study area 0 43 as predicted by the model channel steepness correlates with uplift rate these data help constrain the two key unknown model parameters the coefficient of erosion k and the exponent associated with channel gradient n this analysis shows that k cannot be treated as a constant throughout the study area despite generally homogeneous substrate properties for a reasonable range of slope exponent values n best fit values of k are positively correlated with uplift rate this correlation has important implications for landscape evolution models and likely reflects dynamic adjustment of k to tectonic changes due to variations in orographic precipitation and perhaps channel width sediment load and frequency of debris flows the apparent variation in k makes a unique value of n impossible to constrain with present data

ferromanganese nodules from manop sites h s and r control of mineralogical and chemical composition by multiple accretionary processes abstract the chemical composition of ferromanganese nodules from the three nodule bearing manop sites in the pacific can be accounted for in a qualitative way by variable contributions of distinct accretionary processes these accretionary modes are 1 1 hydrogenous i e direct precipitation or accumulation of colloidal metal oxides in seawater 2 2 oxic diagenesis which refers to a variety of ferromanganese accretion processes occurring in oxic sediments and 3 3 suboxic diagenesis which results from reduction of mn 4 by oxidation of organic matter in the sediments geochemical evidence suggests processes 1 and 2 occur at all three manop nodule bearing sites and process 3 occurs only at the hemipelagic site h which underlies the relatively productive waters of the eastern tropical pacific a normative model quantitatively accounts for the variability observed in nearly all elements zn and na however are not well explained by the three end member model and we suggest that an additional accretionary process results in greater variability in the abundances of these elements variable contributions from the three accretionary processes result in distinct top bottom compositional differences at the three sites nodule tops from h are enriched in ni cu and zn instead of the more typical enrichments of these elements in nodule bottoms in addition elemental correlations typical of most pelagic nodules are reversed at site h the three accretionary processes result in distinct mineralogies hydrogenous precipitation produces mno2 oxic diagenesis however produces cu ni rich todorokite and suboxic diagenesis results in an unstable todorokite which transforms to a 7 a phase birnessite upon dehydration the presence of cu and ni as charge balancing cations influence the stability of the todorokite structure in the bottoms of h nodules which accrete dominantly by suboxic diagenesis na and possibly mn 2 provide much of the charge balance for the todorokite structure limited growth rate data for h nodules suggest suboxic accretion is the fastest of the three processes with rates at least 200 mm 106 yr oxic accretion is probably 10 times slower and hydrogenous 100 times slower since these rates predict more suboxic component in bulk nodules than is calculated by the normative analysis we propose that suboxic accretion is a non steady state process variations in surface water productivity cause pulses of particulate flux to the sea floor which result in transient mn reduction in the surface sediments and reprecipitation on nodule surfaces

growth rates of manganese rich nodules at manop site h eastern north pacific abstract estimates of the growth rates of ferromanganese nodules at manop site h 6 33 n 92 49 w lie between 7 and 1200 mm my the most probable range estimated from nodule size distributions nodule chemistry accumulation rates of authigenic elements and u series modeling is 30 300 mm my such rates are much faster than measured values for most pelagic nodules the distributions of u series and stable elements suggest that a typical nodule consists of two compositionally distinct non detrital components one rich in mn u and sb and the other in fe co ree ni cu and th when the uncorrected u series data which do not show simple decay patterns with depth are normalized to the relative proportion of the fe rich component the data yield well constrained growth rates of 55 mm my for a nodule top and 200 mm my for its bottom the component enriched in mn which is most abundant on nodule bottoms appears to accrete much faster than the component enriched in fe

bedrock incision rock uplift and threshold hillslopes in the northwestern himalayas the topography of tectonically active mountain ranges reflects a poorly understood competition between bedrock uplift and erosion dating of abandoned river cut surfaces in the northwestern himalayas reveals that the indus river incises through the bedrock at extremely high rates 2 12 mm yr 1 in the surrounding mountains the average angles of hillslopes are steep and essentially independent of erosion rate suggesting control by a common threshold process in this rapidly deforming region an equilibrium is maintained between bedrock uplift and river incision with landsliding allowing hillslopes to adjust efficiently to rapid river down cutting

geochemistry of polymetallic nodules from the central indian ocean basin abstract polymetallic nodules dredged at fourteen stations between 12 15 s and 76 80 e in the central indian ocean basin ciob display wide variations in shape size texture mineral phases and chemical composition among the thirteen different types of nodules present only spherical and ellipsoidal nodules ranging in size from in the ciob the nodules of a particular size range have common morphological mineralogical and chemical properties compared to the larger nodules the smaller nodules are enriched in mn cu and ni have higher growth rates and higher cu ni ce la and ce fe ratios and todorokite as the major mineral phase the smaller nodules also show enrichment in heavy rees and exhibit a negative ce anomaly comparison of the average cu ni co content in the different sized nodules indicates that only smaller nodules have grades 2 61 3 04 for nodules different sized nodules from the ciob suggest formation at different places and indicate movement due to bottom currents from the place of formation to the deeper water regions three models are suggested to explain the observed morphological mineralogical and geochemical variations with respect to nodule size 1 in the ccd model the smaller nodules 4 cm which have high fe and moisture and low todorokite contents are formed mainly by hydrogenesis 3 the mixing model indicated shifting of the smaller nodules formed close to the ccd to deep sea regions and mixing with larger nodules formed from hydrogenous precipitation

earthquake dammed lakes in new zealand eleven small lakes were formed by landslides caused by the 1929 buller earthquake four others were formed by other historic earthquakes in new zealand at least nine other new zealand lakes are also dammed by landslides and were probably formed by prehistoric earthquakes when recognized by morphology synchronous age and areal distribution earthquake dammed lakes could provide an estimate of paleoseismicity for the past few hundred or thousand years

paleoceanographic implications of rare earth element variability within a femn crust from the central pacific ocean abstract results of detailed geochemical analyses of thick fe mn oxide crust accumulations from the central pacific ocean lead to the suggestion that variations in their chemical composition and microstructure reflect the influence of prevailing environmental conditions at the time of formation of the deposit these findings imply that well preserved fe mn crusts represent a geologic record that may extend back to the onset of fe mn oxide precipitation on the subsrtate material current crust growth rate estimates of 1 3 mm m y imply that 6 10 cm thick fe mn oxide accumulations represent a growth record of 20 to a maximum of 100 m y detailed chemical and mineralogical analyses were performed on successive hand picked layers of a 95 mm thick fe mn crust recovered from schumann seamount in the hawaiian archipelago the analyses reveal significant variations in the elemental distribution and abundance of major constituents and rees as a function of depth within the crust the trivalent rees generally exhibit sympathetic concentration changes in pure fe mn oxides but the fractionation observed between the light and heavy rees differs in layers enriched in phosphatic matter the compositional variability and the extent of ree fractionation can be explained in large part by mineralogical control but can also be inferred to reflect differing depositional conditions in the seawater from which the deposits formed variations in the ce anomaly and ree fractionation patterns within the individual layers of the crust are related to their major element composition and mineralogy and to the anomalies observed by other workers these are used to attempt to reconstruct the growth history of the crust

rock slope failure and the river long profile this study examines the geomorphic effects of large 10 6 m 3 rock slope failures on long profiles of rivers in the swiss alps and the new zealand southern alps regression of channel slope versus drainage basin area objectively highlights knickpoints separating incised from aggraded reaches that often correspond to locations of large rock slope failures for a fixed concavity index the highest values of the steepness index and erosion index along a given profile spatially coincide with breach channels cut into formerly river damming rockslide debris as old as 10 k y assuming that the knickpoints do not predate slope failure data show that high profile steepness and inferred specific stream power are not always the cause but often a result of large river blocking rock slope failure in mountain basins omission of rockslide data from slope area plots lowers the steepness index and increases the concavity index on average yet only in few cases more than one standard deviation

glacier and landslide feedbacks to topographic relief in the himalayan syntaxes despite longstanding research on the age and formation of the tibetan plateau the controls on the erosional decay of its margins remain controversial pronounced aridity and highly localized rock uplift have traditionally been viewed as limits to the dissection of the plateau by bedrock rivers recently however glacier dynamics and landsliding have been argued to retard headward fluvial erosion into the plateau interior by forming dams and protective alluvial fill here we report a conspicuous clustering of hundreds of natural dams along the indus and the tsangpo rivers where these cross the himalayan syntaxes the indus is riddled by hundreds of dams composed of debris from catastrophic rock avalanches forming the largest concentration of giant landslide dams known worldwide whereas the tsangpo seems devoid of comparable landslide dams in contrast glacial dams such as river blocking moraines in the headwaters of both rivers are limited to where isolated mountain ranges intersect the regional snowline we find that to first order high local topographic relief along both rivers corresponds to conspicuously different knickzones and differences in the type and potential longevity of these dams in both syntaxes glacier and landslide dams act as a negative feedback in response to fluvial dissection of the plateau margins natural damming protects bedrock from river incision and delays headward knickpoint migration thereby helping stabilize the southwestern and southeastern margins of the tibetan plateau in concert with the effects of upstream aridity and localized rock uplift

uranium thorium isotopes and transition metal fluxes in two oriented manganese nodules from the central indian basin implications for nodule turnover transition metal fluxes to the top and bottom of two oriented manganese nodules ss 657 and sk 176 were determined by combining radiochemical and geochemical analyses distinct differences in transition metal fluxes 230th contents 230th232th and mnfe ratios and silicate mineralogy in the top and bottom of nodule ss 657 suggest that since the time of inception of oxyhydroxide accretion 1 m y b p it has been growing with a fixed orientation on the seafloor in nodule sk 176 in contrast nearly uniform accumulation rates 230thexc and 230thexc232th extrapolated to surface activities transition metal fluxes and increasing diagenetic influence outwards in the top and bottom are thought to be suggestive of rotation of the nodule several times over time intervals which are smaller than the time resolution involved in u th isotope dating techniques

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

an automated method for producing synoptic regional maps of river gradient variation procedure accuracy tests and comparison with other knickpoint mapping methods abstract the study of abrupt changes in longitudinal river profiles or knickpoints is currently approached through an empirical power law the slope area relationship results based on digital elevation model dem analyses and stream extractions are generally intended to determine crustal uplift rates and identify transient landscape conditions in this article we present an alternative geomorphometric method for locating knickpoints and knickzones based on local slope gradient and curvature attributes intended as a rapid regional scale automated knickpoint detection technique the accuracy of this slope curvature method is tested on two digital elevation grids nasa s srtm ground resolution of 90 m resampled here to 75 m and the aster dem 15 m in the sierra nacimiento new mexico usa a basement cored mountain range recently exhumed by waves of headward drainage integration in response to remote tectonic deformation in the adjacent rio grande rift out of every 10 gradient anomalies detected by the srtm derived numeric routine up to 8 are certifiable knickpoints recognized among a population of georeferenced occurrences surveyed in the field an independent comparison with the slope area method provided a further accuracy test which was particularly useful at sites that could not be validated in the field for practical reasons given the low tectonic activity of the study area the majority of knickpoints was also found to coincide with lithologic boundaries making it difficult without further geomorphological data to single out dynamic knickpoints directly caused by the upstream propagation of channel instabilities relating to base level change

distribution des terres rares dans les fractions de sediments et nodules de fe et mn associes en l ocean indien abstract the ree distribution in size fractions of sediments and associated ferromanganese nodules from the indian ocean was studied bulk sample patterns of sediments result from the combination of coarsest fractions depleted in ce and fine fractions enriched in ce ce depletion of the coarsest fractions is related to biogenic silica on the contrary ree distribution patterns of fine fractions are closely similar to those of associated ferromanganese nodules the ce excess in fine fractions is probably of continental origin but it could also be derived from submarine weathering of volcanic glass or related to ce oxydation in the marine environment in fine fractions ce is probably in its tetravalent state hence it can easily be scavenged by fine clays and oxyhydroxydes trivalent ree can be incorporated in nodules partly by occlusion of fine clays or oxyhydroxydes and partly by surface to surface transfer as was proposed by ehrlich 1968 comparison between ree patterns of fine sized fractions nodules and seawater also supported adsorption as a possible mechanism governing the incorporation of ree of sediments and nodules from seawater light ree are probably incorporated as oxyhydroxyde complexes whereas heavy ree are markedly fractionated with increasing atomic number this fractionation reflects the complexed form of the heavy ree in seawater

trace and rare earth elemental variation in arabian sea sediments through a transect across the oxygen minimum zone we have determined the calcium carbonate caco3 organic carbon coorg trace element and rare earth element ree composition of surface sediments collected from a transect on the central western continental shelf and slope of india in the eastern arabian sea the transect samples across the oxygen minimum zone omz allows us to compare the relative abundances of trace elements and rees in the sediments beneath and beyond the omz shale normalized ree patterns lan ybn ratios and eu eu anamolies indicate that the sediments in the study area are either derived from the adjoining archaean land masses or from distal indus source sediment deposited in the omz have high u values from 3 6 to 8 1 ppm with their uexcess of that can be supplied by continental particles values ranging between 82 91 of the total u indicating that the u may be precipitated as u 4 in the reducing conditions of omz sediments deposited beneath the intense omz 0 2 ml l and away from the omz 1 2 ml l show slight negative ce anomalies with no significant differences between these two sets of sediments the ce ceshale values are poorly related to u and corg which are indicators of suboxic bottom waters normative calculations suggest that two sources namely terrestrial and seawater terrestrial seawater contribute to the total cc anomaly of the sediments the cc anomaly values of the calculated seawater derived component are similar to the anomalies reported for other coastal waters and the oxygenated surface waters of the arabian sea and do not show any correspondence to the lowered redox state of the overlying water probably due to the redirection of dissolved ce into the oxic deeper water this data on recently deposited sediments from a known oxygen poor environment suggest that the ce cesh in high sedimentation areas of continental margin environments may not be a good paleoredox proxy u th ratios above 1 25 noticed in omz are in accordance with the earlier usage of this ratio for identifying reducing environment of ancient sediments

quantitative relationships between uplift and relief parameters for the southern alps new zealand as determined by fission track analysis the southern alps mountain chain new zealand has formed as a consequence of late cenozoic collision of the continental parts of the pacific and australia plates fission track analysis has yielded estimates of the amount age of initiation and rate of late cenozoic rock uplift for 82 surface samples taken from transects across the southern alps the mean surface summit and valley elevations in the vicinity of each of the rock sample sites have also been measured regression of the geomorphic variables on the uplift variables has been used to establish quantitative relationships between uplift and geomorphology there are strong and consistent linear associations between uplift and the elevations of the mean surface summits and valleys the preferred regression models have uniform slope but varying elevation response between transects substitution of space for time has allowed the evolution of landforms to be studied to the east of the main divide elevation and relief are proportional to and closely related to the age of initiation of rock uplift uplift age and the amount of rock uplift r2 0 8 mean surface uplift was delayed for 2 ma after the start of rock uplift a result of the stripping of a soft cover rock succession that prior to rock uplift overlaid the harder greywacke basement inter transect variations in regression response and x intercept are inferred therefore to reflect the variable preuplift thickness of cover rocks however the regular regression slope for the transects reflects the consistent nature of the interaction between uplift and the erodibility of greywacke basement uplift of the mean surface proceeded at 0 4 km km and 0 4 km ma of rock uplift while the rock uplift rate was 0 8 km ma summit elevations have increased at a rate of 0 6 km ma and valley elevations have increased at 0 2 km ma regression lines relating mean surface summit and valley elevations to rock uplift and uplift age diverge from common intercepts it is concluded therefore that the mountains east of the main divide have continued to increase in elevation and relief and change in form over time since the start of mean surface uplift mountain elevation has little relationship with late cenozoic mean rock uplift rates of 0 8 1 0 km ma or inferred contemporary rock uplift rates r2 0 3 in contrast to the west of the main divide elevation is shown to be closely related to rock uplift rate r2 0 3 in contrast to the west of the main divide elevation is shown to be closely related to rock uplift rate r2 0 8 transects with higher rock uplift rates support higher topography landforms are therefore in a stable equilibrium with rock uplift rate and the landscape contains no residual evidence of the total amount of rock uplift or the age of uplift lithological variation appears to have no relationship with elevation

rare earth element indicators of mn fe oxyhydroxide crust formation on krylov seamount eastern atlantic abstract ree distributions are presented for mn fe oxyhydroxide encrustations from krylov seamount cape verde abyssal plain eastern atlantic the distributions of rees light and heavy rees ce and eu indicate that during the early stages of crust formation a hydrothermal input is evident whereas during later stages when the area had moved to the east by plate motion hydrogenetic precipitation was dominant

origin of negative ce anomalies in mixed hydrothermal hydrogenetic fe mn crusts from the central indian ridge abstract layered fe mn crusts from the off axis region of the first segment of the central indian ridge north of the rodrigues triple junction were studied geochemically and mineralogically vernadite mno2 is the main mineral oxide phase 230thxs and co concentrations suggest high growth rates of up to 29 mm myr and a maximum age of the basal crust layer of 1 ma whereas most of the major and minor elements show concentrations which are typical of hydrogenetic formation co pb ni and ti concentrations are strikingly lower concentrations and distribution of the strictly trivalent rare earths and yttrium rey are typical of hydrogenetic ferromanganese oxide precipitates but in marked contrast the crusts are characterized by negative cesn shale normalized anomalies and ce pr sn ratios less than unity profiles through the crusts reveal only minor variations of the rey distribution and ce pr sn ratios range from 0 45 to 0 68 compared to ratios of up to 2 for typical hydrogenetic crusts from the central indian basin the apparent bulk partition coefficients between the crusts and seawater suggest that for the strictly trivalent rey the adsorption desorption equilibrium has been reached positive ce anomalies in the partition coefficient patterns reveal preferential uptake of ce but to a lesser extent than in normal hydrogenetic crusts a new parameter excess ce cexs to quantify the degree of decoupling of ce from rey iii is established on the basis of partition coefficients cexs cebulk ratios suggest that the cir crusts formed by precipitation of fe mn oxides from a hydrothermal plume and that in hydrothermal plumes and normal seawater the enrichment of ce results from the same oxidative sorption process the growth rates calculated with 230thxs data as well as with the co formula are inversely related to cexs

rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments abstract analyses have been made of ree contents of a well characterized suite of deep sea 4000 m principally todorokite bearing ferromanganese nodules and associated sediments from the pacific ocean ree in nodules and their sediments are closely related nodules with the largest positive ce anomalies are found on sediments with the smallest negative ce anomalies in contrast nodules with the highest contents of other rare earths 3 ree are found on sediments with the lowest 3 ree contents and vice versa 143 nd 144 nd ratios in the nodules 0 51244 point to an original seawater source but an identical ratio for sediments in combination with the ree patterns suggests that diagenetic reactions may transfer elements into the nodules analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to ree contents of nodules and sediments is negligible inter element relationships and leaching tests suggest that ree contents are controlled by a p rich phase with a ree pattern similar to that for biogenous apatite and an fe rich phase with a pattern the mirror image of that for sea water it is proposed that 3 ree concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate processes which favour the enrichment of transition metals in equatorial pacific nodules favour the depletion of 3 ree in nodules and enrichment of 3 ree in associated sediments in contrast ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions

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

fine scale study of major and trace elements in the fe mn nodules from the south china sea and their metallogenic constraints abstract many marine fe mn polymetallic nodules may contain high concentrations of mn cu ni zn co and rare earth elements plus yttrium rey to determine the occurrence and enrichment processes of these metals in the fe mn nodules we conducted high resolution mineralogical and geochemical studies on the fe mn nodules collected from the south china sea in situ epma and la icp ms analyses and elemental imaging were performed on individual microlayers of the nodules to reveal the major and trace element distributions the whole rock mineralogical and chemical compositions of the fe mn nodules indicate a hydrogenetic origin the mn mineral phases are mainly composed of nanocrystalline vernadite with interlayered 10 a and 7 a phyllomanganates such as todorokite birnessite and buserite fe ti oxides hydroxides are intergrown and essentially x ray amorphous feroxyhyte and goethite we recognize two main types of microlayers type a layer suboxic diagenetic precipitates containing a high mn fe ratio and high concentrations of cu ni zn ba li and mg and type b layer oxic hydrogenetic accretions with low fractionation of mn and fe and high contents of co rey ti sr and pb furthermore elemental mapping indicates that the enrichments of co and rey are mainly associated with fe mineral phases rather than mn ones which are enriched in mg cu ni zn li and ba two mineralization processes and metal distributions in the individual microlayers are identified in the fe or mn mineral phases the occurrence of 10 a and 7 a phyllomanganates in type a layers are commonly enriched in trace metals such as ni cu zn li ba and mg whereas the metals for the type b layers include co ti pb sr rey which may be carried by the intergrowing fe ti oxyhydroxides and vernadite thus hydrogenesis and diagenesis facilitate the enrichment of fe co ti sr pb rey and mn ni zn cu li ba mg respectively during the mineralization of the south china sea nodules

reconstructing the transport history of glacigenic sediments a new approach based on the co variance of clast form indices abstract two indices are used to describe the aggregate shape and roundness characteristics of glacially transported clasts the c40 index the percentage of clasts with c a ratios 0 4 and the ra index the percentage of very angular and angular clasts in a sample analysis of the between and within sample co variance of these indices provides a powerful tool for discriminating actively and passively transported clasts in glacigenic deposits use of these indices is illustrated in an analysis of the form characteristics of clasts from lateral and frontal moraines at storbreen jotunheimen these fall between those of actively transported clasts in basal till low c40 and ra values and those of unmodified frost weathered clasts high c40 and ra values both indices decline down moraine within sample analyses of clast shape demonstrates that these aggregate clast form gradients reflect changes in the relative proportions of actively and passively transported debris on the moraines rather than progressive modification of actively transported clasts these analyses also indicate that actively transported clasts form the dominant component of the moraines particularly near the former glacier terminus further applications of the approach developed here are suggested

the role of landslides in mountain range evolution abstract we review the role of landslides in current concepts of the topographic development of mountain ranges we find that many studies in this field address basin or orogen scale competition between rock uplift and fluvial bedrock erosion hillslopes in general and bedrock landslides in particular are often assumed to respond rapidly to incision and development of the fluvial drainage network this leads to a one sided view of the geomorphic coupling between hillslopes and rivers that emphasizes the fluvial control of hillslopes but ignores the alternative view that landslides can affect the fluvial network there is growing evidence that landslides are a dominant source of sediment in mountain belts and that they exert a direct geomorphic control on fluvial processes landslides can influence the river network in a variety of ways from determining basin area and drainage divide positions to setting streamwise variations in sediment load and calibre the geomorphic legacy of large landslides on hillslope and channel morphologies may persist for up to 104 yr adding considerable variability to fluvial erosion and sedimentation patterns over these timescales we identify a number of questions for future research and conclude that a better understanding and quantification of the geomorphic feedbacks between landslides and river channels builds an important link between short term 105 yr landscape evolution models

post rock avalanche dam outburst flood sedimentation in ram creek southern alps new zealand rock avalanches are common in mountainous regions that are tectonically active they are capable of forming natural dams of uncertain persistence that have significant impacts on the river system over wide spatial scales and possibly over geological time scales here we combine field data and digital elevation model dem analysis to show the response of ram creek new zealand to 28 years of sediment dispersion following the 1968 emplacement of a co seismic rock avalanche dam that breached catastrophically in 1981 the results show a system that has not attained equilibrium being unable to move the quantity of dam derived sediments and will likely not attain equilibrium before the next major sediment input it is in a state of persistent disturbance where localised reworking dominates erosion in ram creek is focussed on lateral bevelling and bedrock gorge widening rather than vertical incision to keep pace with tectonic uplift importantly for studies of tectonic geomorphology this widening which if sustained will form a strath terrace does not represent a period of reduced uplift stream metrics concavity and steepness are unable to differentiate the identified rock avalanche induced knickpoint from tectonic and lithological knickpoints

cerium anomaly variations in ferromanganese nodules and crusts from the indian ocean fifty analyses of rare earth elements as well as mineralogical studies have been carried out on a suite of manganese nodules and crusts from the central indian basin and the western indian ocean the aim was to identify the processes controlling the ree patterns of the phases hosting the ree in the manganese nodules with an emphasis on an understanding of the ce anomaly this has involved separating the encrusting layers and nuclei physically as well as fe mn oxides from the aluminosilicate phase chemically using a 2 m hcl leach prior to analysis the presence of nodule nuclei seems to have little influence mostly 5 to a maximum of 30 on the overall magnitude of the ce anomalies in these nodules the ratios of concentrations of elements in the acid leachates and the corresponding bulk values yield flat ree patterns indicating that the aluminosilicate phase contributes very little to the ce anomalies interelement relations indicate that the ce anomalies are largely controlled by the amorphous mineral phase feooh xh2o the relationship of fe ce anomaly and mno2 further suggests that ce is chemisorbed onto iron oxyhydroxides which are epitaxially intergrown with mno2 the regional distribution of the ce anomaly values appears to depend on many of the factors responsible for the uptake of other minor metals in nodules and crusts

a fragmentation spreading model for long runout rock avalanches based on the observation that deposits of large rock avalanches consist predominantly of intensely fragmented rock debris it is proposed that the processes of rock fragmentation are significant ca