automated detection of unstable glacier flow and a spectrum of speedup behavior in the alaska range surge type glaciers are loosely defined as glaciers that experience periodic alterations between slow and fast flow regimes glaciers from a variety of mountain ranges around the world have been classified as surge type yet consensus of what defines a glacier as surge type has not always been met a common source of dispute is the lack of a succinct and globally applicable delimiter between a surging and nonsurging glacier the attempt is often a boolean classification however glacier speedup events can vary significantly with respect to event magnitude duration and the fraction of the glacier that participates in the speedup for this study we first updated the inventory of glaciers that show flow instabilities in the alaska range and then quantified the spectrum of speedup behavior we developed a new method that automatically detects glaciers with flow instabilities our automated results show a 91 success rate when compared to direct observations of speedup events and glaciers that are suspected to display unstable flow based on surface features through a combination of observations from the landsat archive and previously published data our inventory now contains 36 glaciers that encompass at least one branch exhibiting unstable flow and we document 53 speedup events that occurred between 1936 and 2014 we then present a universal method for comparing glacier speedup events based on a normalized event magnitude metric this method provides a consistent way to include and quantify the full spectrum of speedup events and allows for comparisons with glaciers that exhibit clear surge characteristics yet have no observed surge event to date our results show a continuous spectrum of speedup magnitudes from steady flow to clearly surge type which suggests that qualitative classifications such as surge type or pulse type behavior might be too simplistic and should be accompanied by a standardized magnitude metric

seismic models of a prograding carbonate platform vercors south east france abstract the southern vercors area south east france displays superb exposures of a lower cretaceous prograding carbonate platform these exposures allow a geometrical sequence analysis to be combined with detailed outcrop observations two dimensional seismic modelling techniques were used to determine the seismic response of three of these exposures the montagnette the archiane valley and the rocher de combau the outcrops display prograding and retreating series of clinoforms interfingering with fine grained basinal sediments photographs from different angles of view combined with detailed field observations were used to construct lithological profiles with a resolution of f few metres p wave velocities and bulk densities were measured from cored hand specimens and selected values were assigned to lithostratigraphic units in each profile the vertical incidence modelling technique was then used to compute migrated time sections of reflectivity these were convolved with source wavelets of different frequencies to produce the final synthetic seismic profiles none of the modelled outcrop geometries is correctly portrayed seismically at 25 50 hz frequencies not only do the synthetic seismic profiles show less detail they also show misleading geometries in most seismic models for instance pseudo unconformities are present that correspond to rapid changes in dip and in facies in outcrop furthermore the seismic tool is not able to resolve between stratal patterns punctuated by unconformities and those with gradual shifts in facies belts accompanied by complex interfingering relationships this implies that an unconformity recognized on a real seismic line should not automatically be assumed to represent a true stratal unconformity large outcrops are often used to show the validity of sequence stratigraphy a concept mainly based on the analysis of seismic lines this study however shows that there is no one to one relationship between geometries observed in outcrop and in seismic lines seismic modelling of outcrops therefore provides a means for evaluating outcrop geometries in terms of seismic stratigraphy

barremian platform carbonates from the eastern vercors massif france organization of depositional geometries the vercors massif of southern france constitutes a world class and unique opportunity to visualize depositional geometries and diagenetic transformations of a barremian early aptian early cretaceous carbonate system the urgonian platform at a seismic scale and thus to constrain the three dimensional continuity and connectivity of reservoir prone facies deposited during periods of high and low sea level the integration of detailed outcrop analysis including diagenetic transformations with the sequence stratigraphic interpretation of cliff provides opportunities to study the precise relationship between sea level changes and facies distribution including reservoir prone examples such as slope and fan deposits to understand how local tectonics affect accommodation space and effects on sedimentation rates this integrated stratigraphic framework developed at surface conditions provides an analog for major petroleum systems of the middle east where platform carbonates are involved such as the aptian shu aiba or the cenomanian turonian mishrif formation

hydrological characteristics of the drainage system beneath a surging glacier a rare combination of natural circumstances permits assessment of current theories on water flow beneath glaciers outburst floods from the subglacial lake grimsvotn in iceland took place before during and after surging of skei ararjokull the glacier beneath which the outburst floods drain the observable drainage patterns associated with these floods show the different nature of the basal water conduit system of the glacier during surge and non surge phases during surge conditions basal water is dispersed slowly across the bed in a distributed drainage system but when the glacier is not surging water is transported rapidly through a system of tunnels

environmental control on granular clinoforms of ancient carbonate shelves the purpose of this paper is to document the influence of depositional environments on shallow water low relief clinoforms from the description of five ancient carbonate platforms the neoproterozoic namibia middle jurassic france lower cretaceous france upper cretaceous oman and miocene turkey these examples have been investigated on the basis of field observations the clinoforms are described with reference to geometric and compositional attributes declivity shape height sedimentary structures sediment fabric and components the results show great variability in stratal geometry declivity and facies distribution 1 depositional profiles vary from exponential to sigmoidal to oblique 2 maximal slope angles range from 3 to 25 most of them being grouped between 10 and 18 3 facies differentiation identified from lateral facies successions along beds and vertical facies successions through beds is pronounced to subtle this study documents linkages between depositional environments and clinoform attributes proximal shallow clinoforms display round edged exponential profiles sediment deposition has resulted from unidirectional currents in the upper convex section and storm generated oscillatory currents in the lower concave part the sediment fabric changes gradually along this type of clinoform there is little vertical facies differentiation through these clinobeds which have formed from a continuous amalgamation of deposits by contrast distal clinoforms shelf break distally steepened ramp settings yield a much broader spectrum of profiles and are generally shorter and steeper sedimentary structures in gravel sized deposits of the upper slope indicate pure traction by unidirectional currents conversely marks of oscillatory flows undular wavy top bounding surfaces of clinobeds are common in the lower slope intercalation of massive fine grained deposits suggests offshore transport of carbonate mud by suspension each distal clinobed represents a single flow event accordingly facies differentiation is weak laterally but may be pronounced through the clinobeds our study suggests that low relief forms of proximal shallow environments which contain coarse grained and photo independently produced debris record hydrodynamic equilibrium profiles whereas the higher relief forms of this setting rather reflect a high differential production rate of carbonate sediment with water depth the carbonate sediment of the distal clinobeds mainly derives from skeletal production by oligophotic and photo independent biota of the middle shelf ramp and upper portion of the clinoforms the contribution by in situ skeletal biota only becomes significant on the lower slope indicating that the distal submerged slopes of carbonate platforms are not organically but hydrodynamically generated our compilation shows that the slope angles of shallow marine low relief clinoforms do not simply correlate to the sediment grain size and fabric in contrast to what has been documented for the high linear slope profiles this difference stems from the depositional settings namely the involved transport mechanisms low relief clinoform accretion seems to be dominantly influenced by wave induced sediment transport in contrast to linear flanks of high relief clinoforms that build to the angle of repose and for which gravity is the primary transport process

the continental margin of the mesozoic tethys in the western alps abstract most of the structural units of the western alps were derived from the european continental margin of the ligurian ocean a segment of the mesozoic tethys ocean their mesozoic palaeotectonic and stratigraphic evolution bears witness of the following main stages 1 deposition of the triassic platform carbonates essentially prerift but nevertheless bearing the imprint of some extensional movements 2 the liassic middle jurassic rifting corresponds to the creation of a horst and graben system with especially tilted blocks and hence a shoal and basin palaeogeography but without a preliminary doming event 3 the late jurassic early cretaceous opening and spreading of the ligurian ocean began with a general collapse of the continental margin thermal subsidence latest middle jurassic and earliest late jurassic in this paper emphasis is given to the refting derived structures more especially to the major tilted crustal blocks a few tens of kilometres wide which can be either reconstructed or directly observed the rifting stage lasted roughly 40 m y with the alternation of extensional tectonic phases and of relatively quiet periods during the extensional phases movements along fault planes and related episodes of tilting were followed by sudden and rapid episodes of subsidence the latter may be interpreted as resulting from the isostatic and thermal readjustment that follows a phase of stretching of the crust and of the lithosphere the tectonic evolution of the margin continued but decreased during the late jurassic early cretaceous oceanspreading stage tectonic activity resumed in the late cretaceous this probably resulting from the beginning of contraction of both the ocean and the continental margin leading progressively to the continental collision in the tertiary

karakoram glacier surge dynamics quincey d j braun m glasser n f bishop m p hewitt k luckman a 2011 geophysical research letters 38 article number l18504

dynamics of surge type glaciers in west kunlun shan northwestern tibet here we examine 31 glaciers in the west kunlun shan of the northwestern tibetan plateau and identify 9 as surge type the method is based on satellite synthetic aperture radar and landsat optical images the former going back to 1992 the latter to 1972 to identify surge type glaciers we consider temporal changes in velocity changes in glacier terminus position propagation of a surge bulge presence of looped and or contoured medial moraines and extensive crevassing other than the nine surge type glaciers we identify two that have likely surged and six that may be surge type but no glacier surges more than once during the observation period meaning that the recurrence interval exceeds 42 years in addition we examine the evolution of the surface velocities at two surging glaciers with the unprecedented temporal resolution of down to 11 days over 7 years the results show clear seasonal modulations by as much as 200 in early winter against those in early summer this seasonal modulation in surface velocity suggests the presence of surface meltwater that reroutes through the englacial and subglacial drainage systems thus our findings suggest that the hydrological processes originating in the surface meltwater play an important role in maintaining the yearlong active surging phase

climatic and geometric controls on the global distribution of surge type glaciers implications for a unifying model of surging financial support was provided by the conocophillips lundin northern area program project crios

sea level highstand and lowstand shedding related to shelf margin aggradation and emersion upper eocene oligocene of maiella carbonate platform italy abstract sequence stratigraphic analysis of the upper eocene lower oligocene of the maiella carbonate platform allows the timing of shelf aggradation and erosion to be linked to shedding onto the slope and relative sea level stands the shelf was eroded during lowstands and the lowstand slope sediments are thin channelized lithic breccias with clasts eroded from an emerged reef tract highstand shedding of skeletal sands from the inner shelf resulted in thick coarsening and thickening upward successions of turbidites

the duration of the active phase on surge type glaciers contrasts between svalbard and other regions many glaciers in svalbard and in other glacierized areas of the world are known to surge however the time series of observations required to assess the duration of fast motion is very restricted data on active phase duration in svalbard come from aerial photographs satellite imagery field surveys and airborne reconnaissance evidence on surge duration is available for eight svalbard ice masses varying from 3 to 1250 km 2 worldwide active phase duration is recorded for less than 50 glaciers few observations are available on high polar ice masses the duration of the active phase is significantly longer for svalbard glaciers than for surge type glaciers in other areas from which data are available in svalbard the active phase may last from 3 to 10 years by contrast a surge duration of 1 2 years is more typical of ice masses in northwest north america iceland and the pamirs ice velocities during the protracted active phase on svalbard glaciers are considerably lower than those for many surge type glaciers in these other regions mass is transferred down glacier more slowly but over a considerably longer period svalbard surge type glaciers do not exhibit the very abrupt termination of the active phase over periods of a few days observed for several alaskan glaciers the duration of the active phase in svalbard is not dependent on parameters related to glacier size the quiescent phase is also relatively long 50 500 years for svalbard ice masses detailed field monitoring of changing basal conditions through the surge cycle is required from surge type glaciers in svalbard in order to explain the significantly longer length of the active phase for glaciers in the archipelago which may also typify other high polar ice masses the finding that surge behaviour in the form of active phase duration shows systematic differences between different regions and their environments has important implications for understanding the processes responsible for glacier surges

carbonate platform sequence stratigraphy in a rapidly subsiding area the late barremian early aptian of the organya basin spanish pyrenees abstract a detailed sedimentological and stratigraphical study of the late barremian early aptian urgonian carbonate platform of the organya basin spanish pyrenees has identified four depositional sequences the first two sequences consist of transgressive and highstand systems tracts and the last two sequences of lowstand transgressive and highstand systems tracts sequence boundaries at the top of sequences or 1 and or 4 are type 1 boundaries with evidence of exposure and erosion sequence boundaries at the top of sequences or 2 and or 3 are type 2 with no evidence of exposure or erosion sand shoal high energy facies characterise the first sequence or 1 sequences or 2 and or 3 are dominated by lagoonal facies with an important accumulation of lacustrine facies at the base of or 3 a succession of lacustrine deep platform and sand shoal facies characterises sequence or 4 the last sequence also contains the record of an anoxic event oae 1a all these characteristics have been largely influenced by the high subsidence rate of the organya basin 1100 m of compacted limestone deposited in about 5 ma however the main global eustatic changes registered in other contemporaneous basins were also identified

glacier shrinkage across high mountain asia an assessment of glacier shrinkage reductionof area for all of high mountain asia requires a complete compilation of measured rates of change and also a methodology for objective comparison of rates i present a compilation from 155 publications reporting glacier area changes and also a method ology that overcomes the main obstacles hindering comparison glacier areas are not always assigned uncertainties and this problem is addressed with an error model derived from published estimates the problem of discordant survey dates is addressed by interpolating measured areas to fixed dates at pentadal intervals interpolation error depends only incoherently on the time span between measure ments but strongly on glacier size smaller glaciers in addition to changing more rapidly on average exhibit more variable rates of change the overlapping boundaries of study regions are reconciled by mapping all of the information to a 0 5 geographical grid when coupled with glacier area information from the randolph glacier inventory the widely observed inverse dependence of shrinkage rates on glacier size shows promise as a tool for treating incomplete spatial coverage over high mountain asia as a whole from 1960 to 2010 the unweighted average shrinkage rate is 0 57 a 1 but corrections for variable glacier size raise the average to 0 34 a 1 and filling unmeasured gridcells with rates based on size dependence alters the latter estimate to 0 40 a 1 the uncertainties in these rates are large the karakoram anomaly is found to be a zonal feature extending well to the east of the karakoram proper

using surface velocities to calculate ice thickness and bed topography a case study at columbia glacier alaska usa information about glacier volume and ice thickness distribution is essential for many glaciological applications but direct measurements of ice thickness can be difficult and costly we present a new method that calculates ice thickness via an estimate of ice flux we solve the familiar continuity equation between adjacent flowlines which decreases the computational time required compared to a solution on the whole grid we test the method on columbia glacier a large tidewater glacier in alaska usa and compare calculated and measured ice thicknesses with favorable results this shows the potential of this method for estimating ice thickness distribution of glaciers for which only surface data are available we find that both the mean thickness and volume of columbia glacier were approximately halved over the period 1957 2007 from 281m to 143m and from 294km 3 to 134km 3 respectively using bedrock slope and considering how waves of thickness change propagate through the glacier we conduct a brief analysis of the instability of columbia glacier which leads us to conclude that the rapid portion of the retreat may be nearing an end

the distribution and flow characteristics of surge type glaciers in the canadian high arctic a systematic review of 1959 60 aerial photography and 1999 2000 landsat 7 imagery has identified 51 surge type polythermal glaciers in the canadian high arctic these were identified from the presence of features such as looped medial moraines intense folding visible at the surface rapid terminus advance heavy surface crevassing and high surface velocities these observations suggest that surging glaciers are much more common than previously believed in the canadian high arctic where only six surge type glaciers have previously been described of the 51 surge type glaciers identified in this study 15 were observed in the active phase in the 1959 60 and or 1999 2000 imagery the most dramatic advances have occurred on western axel heiberg island where iceberg good friday bay and airdrop glaciers have all advanced by 4 7 km between1959 and 1999 for glaciers with repeat landsat 7 coverage from 1999 and 2000 image correlation software was used to determine the magnitude and spatial distribution of surge velocities for example mittie glacier on manson icefield was moving at a rate of up to 1 kma over a distance of at least 25 km back from its terminus the terminus of this glacier has advanced by at least 4 km since 1959 and the glacier was observed to be heavily crevassed during overflights in april 2000 with clear signs of surface lowering of 10 25 m indicated by a strandline

variegated glacier alaska usa a century of surges a 1995 surge of variegated glacier alaska usa is discussed in the context of its six 20th century predecessors especially the previous surge in 1982 83 which was studied in detail the average time between surge initiations is 15 years the 1995 surge was considerably weaker than its predecessors having a single phase or at most a very weak second phase the 1995 surge confirms that there is a seasonal cycle with surge initiation in winter and termination in the first part of the melt season and a correlation between weather and both surge termination date and surge extent two days of record high temperature correlated with the termination of the 1995 surge the most obvious issue is the absence of a strong second surge phase as there was in the 1982 83 surge culminating in a surge extent more in line with that of the predecessors this is considered in the light of a simple criterion for surge initiation and re initiation which depends upon the evolving basal shear stress

systems tracts and depositional sequences in a carbonate setting a study of continuous outcrops from platform to basin at the scale of seismic lines abstract the application of sequence stratigraphy concepts to carbonates is feasible and this paper presents an example of its successful application the continuity and lateral extent of outcropping sedimentary sections observed at the scale of a seismic line from platform to basin in the southern vercors plateau western alps france confirm the validity of sequence stratigraphy concepts when applied to carbonate depositional systems from the stratal patterns displayed in outcrop we determined that carbonate lowstand systems tracts are major components in the basin even in the deep pelagic realm transgressive and highstand systems tracts are very thin a response to starvation in contrast on the shelf transgressive and highstand systems tracts are the major components carbonate lowstand and shelf margin systems tracts pinch out in the vicinity of the offlap break it clearly appears that the stratal patterns and stratal termination patterns of carbonate systems tracts especially of carbonate lowstand systems tracts are basically similar to those of siliciclastic systems tracts this study documents that carbonate platforms may provide the basin with carbonate clastics during periods of relative sea level falls and lowstand this is one of the most controversial aspects of the application of sequence stratigraphy concepts in carbonate environments a second controversial aspect of the application of sequence stratigraphy concepts to carbonate rocks is the distinction between transgressive and regressive facies cycles and depositional sequences and systems tracts this paper demonstrates that the shoreline position for carbonates which indicates the facies transgression or regression is independent of prograding or retrograding shelf breaks the stratal pattern and facies within systems tracts vary depending on the overall evolution of the accommodation space i e on their position within the transgressive and regressive cycles

surges of glaciers in iceland surges are common in all the major ice caps in iceland and historical reports of surge occurrence go back several centuries data collection and regular obser vationover thelast several decadeshave permitteda detailed descriptionof several surges fromwhich it is possible to generalize onthe nature of surging in icelandic glaciers com bining the historical records of glacier front variations and recent field research we sum marize the geographic distribution of surging glaciers their subglacial topography and geology the frequency andduration of surges changes in glacier surface geometry during the surge cycle and measured velocity changes comparedto calculatedbalance velocities wenotetheindicatorsofsurgeonsetanddescribechangesinice waterandsedimentfluxes duringa surge surgesaccomplishasignificantfractionofthetotalmasstransportthrough the main outlet glaciers of ice caps in iceland and have important implications for their hydrology ouranalysisof the data suggeststhat surge type glaciersin icelandarecharac terizedbygentlysloping surfacesandthatthey movetoo slowlytoremain inbalance given their accumulation rate surge frequency is neither regular nor clearly related to glacier size or massbalance steeply sloping glaciers whetherhard or soft bedded seemto move sufficiently rapidly to keep inbalance with the annual accumulation

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

compositional variations during phases of progradation and retrogradation of a triassic carbonate platform picco di vallandro durrenstein dolomites italy in this paper data are presented on the composition of sediments deposited at the toe of slope during progradation or retreat of triassic carbonate platforms in the dolomites italy for this purpose a succession was studied from the toe of slope of a triassic carnian carbonate platform picco di vallendro durrenstein dolomites italy the microfacies analysis of selected calciturbidites sequences revealed a reduced input of oncolites and ooids during progradation and an increase in clasts the main input however was derived from the reefs on the platform retrogradation of the platform showed an increase of filaments and radiolarians open ocean biota as well as carbonate mud and a reduced input of grains that originated within the reefs on the platform both during progradation and retrogradation parts of the platform were flooded and could produce excess sediment that could be exported to the surrounding basins however the absence of platform interior biota documents that progradation occurred from sediments of the reefal belt probably during relative sea level lowstands carbonate composition varies systematically with toe of slope progradation retrogradation and thus argues for carbonate production as the main driver of the geometries observed at the toe of slope

facies architecture of an early jurassic carbonate platform slope jbel bou dahar high atlas morocco the plateau of jbel bou dahar high atlas morocco represents an outstanding example of a well preserved early mesozoic carbonate platform field observations of the large scale sedimentary structures and the arrangement of lithofacies associations within the mid and lower slope were combined with detailed microfacies analyses and gamma ray measurements the investigations were carried out in order to 1 resolve the sequence stratigraphic architecture of the slope and 2 reconstruct the sediment export patterns and depositional processes related to high frequency sea level variations the slope strata are arranged into two different types of lithofacies associations that are bounded by characteristic discontinuities and show a specific occurrence along the investigated slope section the steep 8 18 mid slope is dominated by thick to medium bedded limestone successions that were able to maintain a high angle of repose due to their detrital composition the sediment packages are bounded by basal low angle unconformities and wedge out within the lower slope or thin into the adjacent basin as single carbonate layers the sediments are characterized by coarse grained and poorly sorted floatstones to rudstones which show low gamma ray values and contain components derived mainly from the platform edge the facies associations were interpreted as debris flow deposits that were exported during sea level lowstands when the flattened platform top and extended parts of the margin were exposed and sediment production was restricted mainly to the outer margin and upper slope section in contrast the gently dipping lower slope 4 18 is characterized by rhythmic limestone marl alternations that show increasing thicknesses with increasing distance from the platform from the lower part of the mid slope down the successions onlap the debris flow deposits forming a characteristic interfingering pattern of different lithofacies associations the medium to thin bedded carbonates of the limestone marl alternations comprise two different microfacies types 1 mudstones to wackestones with high gamma ray values and a mixed shallow marine to deep marine microfacies overlain by 2 well sorted arenitic packstones to grainstones with low gamma ray values and a shallow marine component composition the latter points to the platform interior and margin as primary source areas the shallow marine material was exported during sea level highstands when the carbonate factory included the entire platform margin and the flooded lagoons of the platform top during these periods the exported fine grained sediments could maintain only low angles of repose thus they bypassed the steep upper and mid slope sections developed into turbidites during downslope transport and were finally redeposited on the gently dipping lower slope and in the adjacent basin the architecture of the investigated slope area shows a characteristic interfingering of different facies associations that can be interpreted as genetic highstand and lowstand stratigraphic sequences the arrangement of these sequences along the slope as well as their composition were controlled by high frequency sea level fluctuations affecting the primary sediment production source area export patterns and sedimentary processes resulting in a shift of the depositional centers during different sea level stands

stratal patterns sediment composition and sequence stratigraphy at the margin of the vercors carbonate platform lower cretaceous se france abstract conventional sequence stratigraphic concepts relate the large scale stratal architecture of sediment bodies to changes in relative sea level this paper evaluates the relationship between stratal geometry and sea level stand based on a study of large semicontinuous outcrops of cretaceous carbonate platform strata in the vercors southeastern france multiple lines of evidence for sea level change are combined including stratal geometry detailed quantitative microfacies analyses and diagenetic patterns at platform top hardground surfaces the studied outcrops of the cirque d archiane show two main prograding platform tongues both over 100 m thick the stratal geometries at the boundary between these platform tongues including an apparent pinchout of a wedge of slope sediments suggest the presence of a major lowstand unconformity however this stratal boundary does not coincide with the horizon containing the most extensive meteoric alteration furthermore detailed platform to basin correlation shows that the wedge of slope sediments is not basin restricted but makes a thin drape over the platform top the sedimentologic and diagenetic evidence suggest incipient drowning of the platform at the boundary between the two main platform tongues preceded by a minor exposure event only internally the main platform tongues consist of smaller 10 30 m thick units that prograde towards the basin and aggrade on the platform top and which are interpreted as stacked highstand wedges these wedges are usually topped by hardground surfaces with minor evidence for subaerial exposure the platform top horizon with the most extensive subaerial diagenesis and erosion correlates with a distinct but relatively thin unit of lithoclastic debris on the slope a pronounced scour in the clinoforms of the vercors does not correlate with a major exposure surface on the platform top this study shows that stratal geometries alone are a rather ambiguous guide to sea level history without the accompanying sedimentologic and diagenetic evidence for sea level change most of the stratal architecture of the vercors platform can be explained by either changes in accommodation or changes in carbonate production

basin to platform chemostratigraphy and diagenesis of the early cretaceous vercors carbonate platform se france abstract cathodoluminescence petrography has been combined with bulk rock and micro sampled 87 sr 86 sr 18 o and 13 c analyses to reconstruct the diagenetic history of lower cretaceous barremian limestones exposed at the southern margin of the vercors carbonate platform in southeastern france stratigraphic and geographic trends in these analyses coupled with mass balance water rock interaction modeling have been used to constrain the chemical composition source and relative timing of the groundwaters responsible for diagenetic alteration this study was completed on the montagnette outcrop which is composed of two stacked 70 m thick units of prograding platform margin limestones that interfinger with marly basinal sediments the montagnette exposure is exceptional in that it is a single complete outcrop of basin to platform limestones that are preserved in their original lateral depositional continuity cathodoluminescence petrography indicates that the limestones have experienced a complex sequence of carbonate dissolution precipitation and fracturing events over one hundred bulk rock and micro sampled 87 sr 86 sr 18 o and 13 c analyses were completed to characterize each major event of deposition and diagenesis bulk rock analyses from the montagnette basin to platform transect exhibited no significant variations in 87 sr 86 sr 0 707523 to 0 707555 these values are consistent with estimated barremian seawater 87 sr 86 sr ratios in contrast micro sampled shell material in the platform margin and platform top deposits exhibit large variations in 87 sr 86 sr 0 706910 to 0 707450 the least radiogenic sr lowest 87 sr 86 sr occurs in shell material located toward the platform while the more seawater like ratios occur in sections without shells that are located toward the basin this pattern implies that selective diagenetic alteration of the shell material took place after basinal brines flowed up into the platform and spread out laterally the sr in the diagenetic waters was probably derived from water rock interaction with jurassic basinal sediments in the vocontian trough this conclusion is based on 1 the extremely low 87 sr 86 sr composition of shell material in the platform limestone 2 modeled co variation trends in 87 sr 86 sr 13 c and 18 o and 3 the absence of another nearby source of less radiogenic sr in the vercors region

geometric evolution and ice dynamics during a surge of bakaninbreen svalbard bakaninbreen svalbard started surging in 1985 and developed a steep surge front where fast moving ice impinged on stagnant non surging ice this front which was 20 25 m high in 1985 became a steep and heavily crevassed fcature about 60 m high the surge continued through 1986 95 annual surge front propagation rate was 1 0 1 8 km a 1 during 1985 89 this rate dropped considerably during 1989 95 and the front became less steep front propagation occurred largely by longitudinal compression and vertical extension of the ice and the effects of over riding appear minor ice velocities were slowe than the average propagation rate of the front the surge affected bakanin breen in four zones upper region where extensiv e flow fast propagation rates and negative vertical strain occurred resulting in widespread crevassing and stranded blocks tens of metres above the post surge ice surface 2 mid glacier region where initial strong compression was associated with ice thickening which started before the arrival of the surge front horizontal strain rates were very low but vertical strain rates were up to 300 mm d 1 as the front passed the horizontal velocity increased and about 500 m behind it became extensive negative vertical strain and ice down draw occurred as ice vclocities dropped 3 surge front where ice velocity w as high but vertical strain remained positive associated with compression 4 lower region below the front where only compression occurred resulting in the formation of a fore bulge a thickening of the ice of up to 50 m above pre surge levels the fore bulge affected the whole 1 7 km below the now halted surge front the glacier has not advanced ba kaninbreen s surge was characterized by a long active phase approximately 10 years low ice velocities and low basal shear stresses compared to glaciers in lower latitudes and an indistinet surge termination

clinoform composition and margin geometries of a lower cretaceous carbonate platform vercors se france the concept of sequence stratigraphy uses the stratal geometries at the margins of carbonate platforms to define depositional sequences and systems tracts the aim of this study was to research if prograding purely aggrading and retrograding phases of a cretaceous carbonate platform showed differences in the composition and facies type of the slope sediments the vercors plateau in se france provides excellent outcrops to study this relationship continuous exposure of the platform to basin transition allowed direct examination of the margin geometries five successions were measured and sampled in great detail samples were thin sectioned and point counted using point count groups characterizing palaeoenvironments along the platform to basin transect the composition logs as well as the numerical analysis of the point count data both show a clear relationship between grain composition and stratal geometry the prograding and purely aggrading intervals are similar in composition as they are both relatively coarse grained and enriched in platform biota and limeclasts retreating units are relatively fine grained and rich in basinal grains small benthic foraminifers sponge spicules non carbonate grains and embedding material these observations suggest that the retreating intervals represent incipient drownings of the platform however rather than distinctly separated groups the different phases of platform development form a continuous range of variation between high platform input and high basinal input compared to the prograding units the purely aggrading intervals are relatively rich in peloids which may be suggestive of relatively low energy conditions on the platform during aggradation the compositional analysis also revealed significant variation in the frequency of ooids but these variations showed no relationship with the progradation aggradation or retreat of the platform

carbonate platform flanks slope angle and sediment fabric more than 20 examples of fossil carbonate platform systems were compared for slope angle and sediment fabric plots of slope angle versus sediment fabric show that grainy non cohesive mud free sediments build steeper slopes than muddy cohesive sediments examples near the end members of grainy and muddy carbonate platform flanks are found in the triassic of the dolomites in northern italy and in the bahamas respectively they document the flank geometry and the processes readjusting the slope profile once the limiting slope angle is exceeded the grainy flank sediments in the dolomites modified by shearing and avalanching produce straight slope profiles with declivities up to 35 whereas the muddy bahamian flank sediments modified by large scale creep and rotational to translational sliding and slumping produce a concave upwards slope profile inclined at less than 4 the comparison between slope angle and sediment fabric indicates that the physical behaviour of sediments in the gravity field angle of shearing and mode of readjustment processes is linked to the composition of the slope sediment among the variables such as sea level subsidence climate plate motion and oceanographic setting windward leeward sediment fabric is suggested to be a major if not the major control on slope angle and slope curvature of carbonate platform flanks besides the recently documented tendency of carbonate sediments to build steeper slopes than siliciclastics this proposed relation sheds new light on the analysis and quantification of the variables influencing the geometry and depositional evolution of carbonate systems furthermore it provides an opportunity to deduce sediment composition from seismic lines and predict lithology prior to drilling

a spatially resolved estimate of high mountain asia glacier mass balances from 2000 to 2016 glacier mass balances in high mountain asia are uncertain satellite stereo imagery allows a spatially resolved estimate for about 92 of the glacierized area and yields a region wide average of about 16 gt yr 1 for 2000 to 2016

heterogeneity in karakoram glacier surges many karakoram glaciers periodically undergo surges during which large volumes of ice and debris are rapidly transported downglacier usually at a rate of 1 2 orders of magnitude greater than during quiescence here we identify eight recent surges in the region and map their surface velocities using cross correlation feature tracking on optical satellite imagery in total we present 44 surface velocity data sets which show that karakoram surges are generally short lived lasting between 3 and 5 years in most cases and have rapid buildup and relaxation phases often lasting less than a year peak velocities of up to 2 km a 1 are reached during summer months and the surges tend to diminish during winter months otherwise they do not follow a clearly identifiable pattern in two of the surges the peak velocity travels down ice through time as a wave which we interpret as a surge front three other surges are characterized by high velocities that occur simultaneously across the entire glacier surface and acceleration and deceleration are close to monotonic there is also no consistent seasonal control on surge initiation or termination we suggest that the differing styles of surge can be partly accounted for by individual glacier configurations and that while some characteristics of karakoram surges are akin to thermally controlled surges elsewhere e g svalbard the dominant surge mechanism remains unclear we thus propose that these surges represent a spectrum of flow instabilities and the processes controlling their evolution may vary on a glacier by glacier basis

is there a single surge mechanism contrasts in dynamics between glacier surges in svalbard and other regions 1 during the 1990s monacobreen a 40 km long tidewater glacier in svalbard underwent a major surge we mapped the surge dynamics using ers synthetic aperture radar images differential dual azimuth interferometry and intensity correlation tracking a series of 11 three dimensional 3 d velocity maps covering the period 1991 1997 show a months long initiation and years long termination to the surge with no indication of a surge front travelling downglacier during the surge the front of the glacier advanced 2 km the velocity and derived strain rate increased by more than an order of magnitude and maximum ice flow rates measured during 1994 were 5 m d 1 the spatial pattern of both velocity and strain rate was remarkably consistent and must therefore be controlled by spatially fixed processes operating at the glacier bed we combine these results with those published in the literature to construct a typical svalbard glacier surge cycle and compare this to surge dynamics of glaciers from other cluster regions especially those of variegated glacier in alaska the strong contrast in dynamics suggests that there exist at least two distinct surge mechanisms

multi model photogrammetric analysis of the 1990s surge of sortebrae east greenland sortebrae is a surge type tidewater glacier complex draining southeastward from the geikie plateau east greenland sortebrae s main flow unit surged around 1950 and again between 1992 and 1995 the 1990s surge affected the lower 50 km of sorte brae over an area of approximately 335 km2 over a period of 5 km surge velocities in the order of kilometres per annum are about 100 fold the quiescent velocities multi model photogrammetric analysis shows a thinning of the reservoir zone of up to 219 m and thickening of the receiving zone of up to 74 m the surge transported approximately 18 6 km 3 of ice down glacier the total calving volume as a result of the surge amounted to 11 7 km 3 equivalent to a calving flux of 3 9 7 3 km a 1 the surge characteristics and environmental setting suggest that the surge mechanism involves a switch in the subglacial drainage this surge of sortebrae is more similar to the fast short alaskan type surges than to the sluggish long svalbard type surges

carbonate platform to basin correlation by means of grain composition logs an example from the vercors cretaceous se france quantitative logs of grain composition for several sections of platform top and flank of the vercors carbonate platform early cretaceous se france provide platform to basin correlation with a resolution of a few metres over an area of 70 km2 grain composition was determined by point counting thin sections point count groups that characterize palaeoenvironmental realms i e open sea platform margin were defined for the platform basin trajectory grain composition logs revealed marked peaks in the number of open sea biota and peaks in ooid abundance the peaks in open sea biota correspond to back stepping intervals and deepening upward facies successions at the platform margin these peaks probably relate to incipient drowning of the platform and may be used to delineate marine flooding surface bounded sequences peaks in ooid occurrence show no relationship with the progradation aggradation or retreat of the platform apparently the oolitic sands were not part of a facies tract that shifted up and down the platform instead they represent a depositional mode that was either on or off times of prolific ooid production and shedding probably occurred during wide but shallow submergence of the platform accompanied by suitable water chemistry peaks in both ooids and open sea biota are excellent markers for platform to basin correlation as they are recorded in successions on the platform top as well as on the flank altogether the grain composition logs show that each of the lithologically rather similar platform tongues of the vercors has a unique signature or compositional fingerprint these compositional fingerprints are most helpful in evaluating the lateral extent of different stratigraphic units in outcrops of the vercors platform the physical tracing of bedding surfaces delineate wedges of toe of slope sediments that show a conspicuous thinning towards the platform however our correlation shows that these sediment bodies are not truly basin restricted wedges but have a platform top equivalent this implies that these units were at least partly deposited during high stands of sea level that flooded the platform

petrography and environmental controls on the formation of phanerozoic marine carbonate hardgrounds early marine seafloor lithification of carbonate sediments leads to the formation of hardgrounds and is known from rocks as old as the proterozoic hardground surfaces however are more commonly recorded in the phanerozoic sedimentological archive while ecological studies of hardground biota abound the environmental and physico chemical parameters leading to the development of seafloor lithification remain in many cases poorly understood and documented this paper reviews published evidence on the petrography mineralogy and geochemistry of phanerozoic carbonate hardgrounds within a process oriented context of their environmental controls hardgrounds typically develop in warm and shallow agitated tropical waters that are saturated with respect to caco3 but are also reported from hemi pelagic to bathyal realms and from cool water temperate settings a range of early marine cement types are documented from present day hardgrounds whereas preserved cement fabrics and related mineralogies are less diverse in early phanerozoic hardgrounds carbonate hardgrounds are widespread during calcite sea periods e g ordovician and cretaceous as opposed to some preservation bias ancient aragonite seas e g permian and triassic obviously the relation between seawater chemistry and hardground abundance and attributes is not an easy one here the concept of aragonite versus calcite seas serves as a first order template for the sake of a structured discussion whereas modern aragonite mode oceans document a significant diversity in spatial and bathymetric seawater properties this spatio temporal complexity is perhaps reflected in the scarce record of calcite sea hardgrounds from the devonian or paleogene rock record contrasted by the abundance in aragonite holocene and recent seas holocene hardgrounds allow for the direct assessment of rates of and reasons for early subaquatic lithification and in most cases escaped subsequent non marine diagenetic overprint conversely studies of ancient hardgrounds are often biased by early biological and mechanical erosion the degree of diagenetic overprint and tectonic to orogenic processes the formation distribution and physical properties of hardgrounds depend on the global climatic context greenhouse icehouse modes on sea level changes on ocean stratification on the spatial extent of epicontinental seas and carbonate depositional environments and on the spatially different mineralogies and rates of carbonate production the fabrics and mineralogies of early hardgrounds cement seem to substantially hinge on variations in atmospheric co2 thus the application of lessons from modern to ancient hardground case examples is not straightforward a holistic model explaining the full variability of controls on submarine hardground formation and their cement petrography throughout the phanerozoic is as yet lacking a more critical view on secular changes in hardground formation patterns is clearly needed future work should rely on the combination of sedimentological stratigraphic palaeoecological petrographic and geochemical approaches specific emphasis should be given to time intervals triassic carboniferous cambrian etc where the bulk of reported case studies is at best scarce

monitoring surging glaciers of the pamirs central asia from space the evolution of surging glaciers of the pamirs central asia has been studied using repeat remote sensing surveys in the institute of geography russian academy of sciences since the early 1970s we use images obtained from national resurs f satellites 1972 91 as well as landsat 7 and terra 1999 2006 to provide a basis for monitoring of surging glaciers aimed at developing their inventory studying the causes and mechanisms of surges and examining the timing and extent of glacial catastrophes the inventory from the early 1990s allows identification of 215 glaciers with a dynamically unstable regime we discovered 51 surging glaciers up until 2006 10 more surges had occurred we use stereoscopic deciphering and photogrammetric processing of consecutive satellite images to study the morphology and ice velocity changes of several compound surging glaciers we analyze the results of monitoring of bivachny and oktyabr sky glaciers from 1972 to 1991 and sugran glacier from 1972 to 2006 two surges of sugran glacier occurred during this time an internal surge in 1976 80 and a surge with glacier tongue advance as far as 4 5 km in 2000 05 the role of damming in compound glacier systems is examined satellite based monitoring is now the only method for obtaining initial information about the state and fluctuations of such glaciers

discriminating between onlap and lithologic interfingering in seismic models of outcrops seismic models of outcrops have shown that near the limits of resolution the seismic reflection tool records rapid facies changes as false lap outs we examined one such outcrop the triassic platform flank of picco di vallandro durrenstein in northern italy to develop criteria for recognizing false lap out patterns using measured sections photo mosaics of the continuous outcrop and petrophysical measurements on samples two contrasting impedance models were constructed one model supported by field observation shows interfingering between basin marls and slope carbonates the second model shows onlap of basin marls against slope carbonates but with similar overall geometries to the first model vertical incidence seismic models were produced at frequencies between 50 and 150 hz and with displays of seismic amplitude as well as two seismic attributes instantaneous phase and reflection strength at 50 hz the two lithologic models are seismically indistinguishable both showing onlap of basin units onto the slope at 90 hz displays of instantaneous phase begin to reveal the stratigraphic interfingering whereas seismic amplitude displays require frequencies of 150 hz to do so reflection strength accurately portrays the distribution of the two major facies in the entire range of examined frequencies but does not show sufficient detail to reveal interfingering vs onlap the same trends were visible with finite difference modeling of the full waveform here the differences between interfingering and onlap become visible at 150 hz in the phase model where seismic amplitude displays at this frequency are still ambiguous the phase model however fails to differentiate between slope dip and the basin sediment wedge whereas this wedge is clearly mapped by the reflection strength a combination of instantaneous phase and reflection strength provides a decisive advantage over conventional amplitude displays in recognizing rapid facies changes in seismic reflection data

controls on the distribution of surge type glaciers in svalbard we analyzed the possible controls on the distribution of surge type glaciers in svalbard using multivariate logit models including 504 glaciers and a large number of glacial and geological attributes specifically we examined the potential effect of geological boundaries mass balance conditions and thermal regime on surging it was found that long glaciers with relatively steep slopes overlying young fine grained sedimentary lithologies with orientations in a broad arc clockwise from northwest to southeast are most likely to be of surge type no relation between lithological boundaries and surge potential could be established possible explanations for length being conducive to surging are transport distance related substrate properties distance related attenuation of longitudinal stresses and the possible relation between thermal regime and glacier size analysis of glaciers with recorded radioecho sounding reveals that a polythermal regime accumulation area ratios close to balance and a large elevation span increase the surge potential the logit models also enabled us to detect 19 new surge type glaciers to reclassify six glaciers as normal and to identify unusual surge type glaciers our model results suggest that a polythermal regime and fine grained potentially deformable beds are conducive to the surge potential of svalbard glaciers

glacier changes in the west kunlun shan from 1970 to 2001 derived from landsat tm etm and chinese glacier inventory data

rapidity of freshwater calcite cementation implications for carbonate diagenesis and sequence stratigraphy abstract in less than 10 years subaerially exposed holocene oolitic sand on eleuthera island bahamas was completely case hardened by freshwater vadose calcite cementation this phenomenon demonstrates the rapidity of freshwater carbonate diagenesis and explains in part why carbonate platforms preferentially shed unconsolidated sediment during highstands and not during lowstands when they are subaerially exposed it further proves contrary to what the exxon conceptual sequence stratigraphic models imply that carbonate deposits do in fact respond differently to subaerial exposure than siliciclastic deposits case hardening of unconsolidated carbonate sediment in response to subaerial exposure and early near surface freshwater diagenesis helps explain why shallow water platform sediments are preferentially shed into adjacent basins during highstands of sea level and not during lowstands during lowstands rapid subaerial lithification of carbonate sediments retards their reworking by wind or water once lithified these deposits are further stabilized by vegetation and karstification inhibiting their transport as unconsolidated sediment into adjacent deeper water basins observations from eleuthera island also document the reciprocal processes associated with freshwater carbonate diagenesis calcium carbonate released by partial dissolution of aragonitic ooids was locally reprecipitated as pore filling low magnesian calcite cement this reciprocity is confirmed by the confinement of freshwater dissolution and cementation to the upper 10 20 cm of the subaerially exposed body of oolitic sand below this case hardened surface oolitic sands remained unconsolidated only very minor amounts of calcite cement were required for effective casae hardening

dynamics of tidewater surge type glaciers in northwest svalbard the evolution of ice dynamics through surges of four tidewater terminating glaciers in northwest svalbard is investigated by remote sensing a 20 year time series of glacier surface flow speeds and frontal positions is presented covering the recent surges of monacobreen comfortlessbreen blomstrandbreen and fjortende julibreen surface flow speeds were derived using feature tracking between pairs of ers sar and alos palsar images while frontal positions were taken from the same imagery as well as more frequent but lower spatial resolution envisat wide swath mode images during all four surges increased ice flow caused the tidewater margin to advance while the calving flux was initially reduced to near zero due to compressive stresses limiting crevasse propagation as ice speed decreased the terminus continued to advance until the glacier s speed had returned to its pre surge flow rate only at this time did the terminus start to retreat and peak iceberg calving flux was established we conclude that terminus advance closely tracks glacier speed up that there is little mass loss through calving during the most active phase of the surge and that seasonal cycles of terminus positions diminish during the active surge phase

benthic extinction and recovery patterns at the k t boundary in shallow water carbonates denmark abstract benthic extinction at the k t boundary in the danish basin is abrupt and indistinguishable from the termination of maastrichtian white chalk deposition the danian benthic fauna already fully established in the earliest danian nannoplankton zone np1 is essentially an impoverished maastrichtian fauna established through direct survival or limited evolution within well established clades already present in the maastrichtian of the danish basin however recovery of the early danian community is initially retarded the transition is illustrated in some detail for the locality nye klov here the lower 2 3 m of danian strata corresponding largely to the lower np1 subzone contains an extremely impoverished highly unusual dead zone community dominated by bourgueticrinid crinoids associated with other presumed soft ground specialists and devoid of such important faunal elements as cyclostome bryozoans brachiopods calcitic bivalves etc over the next metres the dead zone fauna is gradually replaced by more ordinary faunas and about 6 m above the boundary the characteristic early danian bryozoan limestone community is fully established

carbonate shedding and sedimentary cyclicities of a distally steepened carbonate ramp miocene great bahama bank depositional geometries as imaged in seis mic lines logging data and quantitative petrographic data were used to analyse the slope and toe of slope deposits of the miocene distally steepened carbonate ramp of great bahama bank the shedding pattern along the slope of this ramp is more complex than it is along the slope of the pliocene pleistocene flat topped carbonate platform compositional changes and compositional trends of periplatform sediments correlate with the positions of geophysically defined sequence boundaries two types of depositional sequences occur the first sequence is characterised by laterally traceable sequence internal reflections whereas the second type contains major intrasequen tial incisions erosional incisions and sedimentary infills of these canyons by turbidites formed during sea level lowstands as is indicated by the composition of the turbidites having a mixture of shallow water and pelagic particles highstand turbidites are charac terised by more extensive laterally traceable geome tries and by the occurrence of abundant shallow water particles in contrast to highstand turbidites shed from the pliocene pleistocene flat topped platform shal low water components in highstand turbidites of the miocene ramp are of skeletal origin the stacking pat tern of the periplatform deposits is controlled by sea level fluctuations four orders of sea level changes are distinguished third order cycles are delimited by sequence boundaries and fourth 100 000 a order cycles govern the bundling of turbidites into packages fifth 40 000 a and sixth 23 000 a order cycles are recorded in the background sediments and resolvable with spectral analysis

the 2008 09 surge of central yulinchuan glacier northern tibetan plateau as monitored by remote sensing the 2008 09 surge of central yulinchuan glacier cyg on the northwestern slope of muztag mountain tibetan plateau is studied based on satellite remote sensing the widely used cross correlation feature tracking method was used to collect satellite image control points and validate their geometric accuracies as well as to derive glacier surface velocity changes in glacier length and area were also retrieved results show that the surge of cyg initiated in may 2008 and terminated in july 2009 two diffluent glacier termini advanced 590 26 m 5 1 0 2 of the 2004 length and 182 26 m 1 8 0 3 respectively and glacier area increased by similar to 1 41 0 11 km 2 4 6 0 4 of the 2004 area during this period the most significant surge period was october 2008 to march 2009 when most of the terminus advances and area increases occurred the glacier surface drastically crevassed during this time as much as 1657 297 m of horizontal surface displacements were produced by surge ice and maximum surface speed reached 13 1 5 m d 1 results of transverse and longitudinal velocity profiles revealed two surge waves during this surge of cyg

the upper cretaceous carbonates of the gargano murge region southern italy a model of platform to basin transition the outcrops in gargano murge region are good examples of the upper cretaceous carbonate systems of the peri adriatic area they enable the architecture and the processes of the platform to basin transition to be studied in detail the platform carbonates are juxtaposed to the deeper marine carbonates by the intermediary of a faulted scarp the base of slope is characterized by bioclastic and conglomeratic aprons interbedded with pelagic mudstones the outer shelf domain which was the prolific source of rudistid bioclastic aprons is not preserved the platform is mainly built of mud dominated transgressive systems tracts whereas highstand systems tracts are developed as bioclastic base of slope aprons the volume of the resedimented bioclasts largely exceeds the volume of missing outer shelf indicating that carbonate production and sediment bypass are more critical for this stratigraphic response than carbonate erosion the lowstands which were controlled by tectonic deformations are characterized by base of slope breccia and blocks eroded from the shelf edge this erosion resulted in the progressive retreat of the shelf edge the best potentials for hydrocarbon reservoir are found in the bioclastic base of slope aprons formed during the cenomanian and maastrichtian highstands this model is considered as an analog for the hydrocarbon reservoirs formed by the deep marine deposits of cretaceous tamabra limestone in the gulf of mexico

glacier surges in the north west west kunlun shan inferred from 1972 to 2017 landsat imagery the west kunlun shan lie close to or are perhaps part of two significant glaciological phenomena the high mountain asia surge supercluster and the karakoram anomaly however glaciological studies and particularly surge studies in the range are limited here we extend the database of known surges in the region using landsat imagery and cross correlation feature tracking we examine 88 glaciers larger than 1 km2 in the hotan prefecture of xinjiang china and find evidence of nine surges occurring between 1972 and 2017 glaciers display low active phase velocities 0 2 1 5 km a 1 that show seasonal acceleration in the summer active phase periods as short as 2 years and build up and deceleration phases of months years although these observations display characteristics indicative of both the classic hydrological and thermal switch mechanisms the surging observed displays a close resemblance to that in the adjacent karakoram ranges furthermore the majority of the surges occur clustered at the end of a decadal scale warming period corroborating previously proposed causal links between climate and surging in the karakoram we suggest that the two regions should be considered part of one larger system when considering surge dynamics in high mountain asia

identification and characteristics of surge type glaciers on novaya zemlya russian arctic we present a comprehensive new inventory of surge type glaciers on the novaya zemlya archipelago using high resolution up to 4 m satellite imagery from 1976 77 hexagon 1989 landsat tm 2001 landsat etm and 2006 aster a total of 692 glaciers and their forelands were observed for glaciological and geomorphological criteria indicative of glacier surging e g looped moraines heavy surface crevassing surface potholes thrust block moraines concertina eskers this enabled the identification of 32 potential surge type glaciers compared with four previously identified representing 4 6 of the total but 18 by glacier area we assess the characteristics of surge type glaciers surge type glaciers are statistically different from non surge type glaciers in terms of their area length surface slope minimum elevation mid range elevation and terminus type they are typically long median length 18 5 km large median area 106 8 km 2 outlet glaciers with relatively low overall surface slopes median slope 1 7 and tend to terminate in water marine or lacustrine they are predominantly directed towards and located in the more maritime western region of the russian arctic and we suggest that surge occurrence might be related to large and complex catchment areas that receive increased delivery of precipitation from the barents sea

modeling carbonate microfacies in the context of high frequency dynamic relative sea level and environmental changes sequence stratigraphic models are used to interpret stratal architecture and key stratal bounding surfaces in ancient carbonate platforms within the context of changing accommodation space during third order relative sea level cycles however individual systems tracts are still described using standard microfacies that give a snapshot of limestone composition but they do not take into account gradual changes in the marine environment resulting from variations in water depth during the cycle of relative sea level change water depth is the single most significant collective control on a wide range of environ mental gradients affecting carbonate sediment composition during dy namic relative sea level fluctuations stratigraphic changes in carbonate sediment composition are characterized by systematic shifts in the rel ative importance of different limestone component grain types forming temporal continuums or relays relays are detected using computer optimized jaccard s similarity coefficient matrices to analyze presence absence compositional data individual relays between grain types may link together samples that are generically unrelated to one another but are nevertheless genetically related to deposition during the same uni directional dynamic environmental gradient a stratigraphic relay identified within the basal beds of the mid cretaceous urgonian carbonate platform succession of se france re cords unidirectional environmental gradients linked to changing water depth characteristic of a transgressive systems tract periods of static water depth such as the keep up phase of a late highstand systems tract at the top of the urgonian carbonate platform succession are characterized by fixed compositional assemblages stratigraphic breaks between individual compositional relays and assemblages occur at in flections in changing water depth marking the boundaries between individual systems tracts and sequences currently identified using stra tal geometries and key stratal surfaces the use of relays to model microfacies and identify individual system tracts and sequence boundaries has several advantages over existing methods this approach can be used where key stratal surfaces are difficult to distinguish such as in planar and concordantly bedded inner platform settings and in arid depositional environments where physical evidence of subaerial platform exposure such as karstification is poorly developed the technique can also be used to determine the genetic significance of unconformities preserved in outcrop or core within a sequence stratigraphic context by differentiating unconfor mities formed at the extremes of relative sea level cycles from those formed by other abrupt acyclical environmental changes

slow surge of trapridge glacier yukon territory canada 1 trapridge glacier a polythermal surge type glacier located in the st elias mountains yukon territory canada passed through a complete surge cycle between 1951 and 2005 air photos 1951 1981 and ground based optical surveys 1969 2005 are used to quantify the modifications in flow and geometry that occurred over this period yearly averaged flow records suggest that the active phase began 1980 and lasted until 2000 the average velocity in the central area of the glacier went from 16 m yr 1 in 1974 to 39 m yr 1 in 1980 it peaked at 42 m yr 1 in 1984 and remained above 25 m yr 1 until 2001 over that interval the flow decelerated by steps in 4 year pulses after a particularly vigorous acceleration in 1997 1999 the glacier gradually slowed to presurge velocities in 2005 the flow was less than 9 m yr 1 digital elevation models are generated by stereographic analysis of air photos for 1951 1970 1972 1977 and 1981 these models are updated annually using ground based survey data and a novel implementation of bayesian kriging over the course of the surge the front of active ice advanced 450 m and the glacier area increased by 10 with an associated thinning of the ice the previous surge of trapridge glacier starting before 1939 and ending before 1951 led to a terminus advance of 1 km comparison of the two surges suggests that the 1930s surge started with a slow progression similar to what we observed in the 1980s and 1990s and switched to a faster flow mode after 1941 this second phase was never attained in the recent surge probably owing to a lack of mass

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

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

changes in ice front position on greenland s outlet glaciers from 1992 to 2007 1 previous studies in greenland show that retreat of tidewater glaciers may be linked to recent increases in ice loss raising greenland s contribution to sea level rise we examined ice front changes of 203 tidewater glaciers land terminating glaciers and glaciers terminating with ice shelves to understand greenland glacier behavior over three periods 1992 2000 2000 2006 and 2006 2007 we observed synchronous ice sheet wide increases in tidewater retreat during 2000 2006 relative to 1992 2000 coinciding with a 1 1 c increase in mean summer temperature at coastal weather stations rates of retreat for the southeast and east slowed during 2006 2007 when temperatures were slightly cooler than the 2000 2006 average our work suggests that regional greenland tidewater retreat responds strongly to climate change with higher temperatures corresponding to increasing retreat and helps confirm a link between ice thickness velocity and ice front position

dolomitization associated with transgressive surfaces a mid cretaceous example abstract increased seawater circulation within a carbonate platform generated through transgression and flooding of the platform is proposed here as a cause of the common selective dolomitization of calcitic silts in the upper part of limestone sequences of the barremian aptian urgonian platform of se france which underwent selective porosity creation as a result of karstification during an aptian relative sea level fall parts of this porosity are infilled by microcrystalline dolomite and some of the host limestone is partially to completely dolomitized the microcrystalline dolomite is considered to have formed by dolomitization of calcitic silt internal sediment within the karstic cavities as a result of the pumping of seawater through the upper layers of the platform during subsequent transgression the calcitic silt provided abundant nucleation sites for the dolomitization seawater dolomitization following subaerial exposure of limestone is likely to be a common phenomenon if there is sufficient meteoric diagenesis and porosity production and a prolonged period of submarine erosion winnowing and condensed sequence formation enhancing the amount of circulation of seawater as seafloor sediment is lithified

slight mass gain of karakoram glaciers in the early twenty first century the mass balance of hindu kush karakoram himalaya glaciers has been debated partly because of a severe lack of observations from the region an analysis of the regional mass balance of karakoram glaciers by comparison of digital elevation models from 1999 to 2008 reveals a small glacier mass gain in the area

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

a surge of north gasherbrum glacier karakoram china between 2003 and 2007 north gasherbrum glacier on the northeastern slope of the karakoram mountains in asia underwent a dramatic acceleration during which a velocity wave propagated down the glacier there was a significant transfer of ice from up glacier downstream which resulted in a strong surface elevation increase over the lower tongue but only a moderate advance of the glacier snout we interpret this behaviour as that of a glacier surge and we explain the observations by means of a simple version of the kamb drainage switching theory

pseudo unconformities in seismic models of large outcrops traditionally seismic modeling has concentrated on one dimensional borehole modeling and two dimensional forward modeling of basic structural stratigraphic schemes which are directly compared with real seismic data two dimensional seismic models based on outcrop observations may aid in bridging the gap between the detail of the outcrop and the low resolution of seismic lines examples include the dolomites north italy the vercors se france and the high atlas morocco the seismic models are generally constructed using the following procedure a construction of a detailed lithologic model based on direct outcrop observations b division of the lithologic model into lithostratigraphic units c assignment of petrophysical properties to these lithostratigraphic units d ray tracing to compute time or depth sections of reflectivity e convolution of the reflectivity sections with source wavelets of different frequencies the lithologic detail modeled in the case studies led to some striking results particularly the discovery of pseudo unconformities pseudo unconformities are unconformities in seismics but correspond to rapid changes of dip and facies in outcrop none of the outcrop geometries studied were correctly portrayed seismically at 25 hz peak frequency however in some instances the true relationship would gradually emerge at peak frequencies of 50 100 hz the examples given in this study demonstrate that detailed outcrop derived seismic models can reveal what stratigraphic relationships and features are likely to be resolved under ideal or less ideal conditions and what pitfalls may befall the interpreter of real seismic data

evidence for stratigraphically controlled paleogeotherms in the illinois basin based on vitrinite reflectance analysis implications for interpreting coal rank anomalies coal rank reflects the temperature of coalification with higher rank coal forming at higher temperatures if the temperature of coalification depended only on the earth s geothermal gradient then the maximum rank of coal in a sedimentary basin should be directly proportional to the thickness of strata above the coal this association does not occur in the illinois basin a continental interior basin in the midwestern united states where the overall coal rank observed is higher than can be explained by past burial depth alone recognition of this anomaly has led many authors to suggest that hot groundwater flowing from south to north during a paleozoic basin scale groundwater migration event increased coal rank we analyzed vitrinite reflectance formula 1 a measure of rank as a function of depth in wells across the basin to determine how paleogeotherms representing variation in temperature with depth change with location our results show that the basin can be divided into three zones 1 in the southern zone the paleogeotherm varies irregularly with depth in strata above the sub absaroka unconformity the contact separating pennsylvanian and mississippian strata 2 in the central zone the paleogeotherm displays a distinct inflection at the unconformity for the rate of increase in formula 2 with depth is greater above the unconformity than below the unconformity and 3 the observed inflection in the paleogeotherm dies out northward until in the northern zone the paleogeotherm has the same slope both above and below the unconformity we propose that the inflection in the paleogeotherm of the central zone indicates that the hot groundwater responsible for causing an increase in coal rank flowed through a high permeability zone just below the sub absaroka unconformity this flow which advected heat into pennsylvanian strata above cooled as it moved northward so it did not influence the paleogeotherm in the northern zone preliminary studies of vein paragenesis stable isotope composition and fluid inclusions as well as computer modeling of flow related heat advection support this proposal 1 embed mml math 1 gif 2 embed mml math 2 gif

a facies distribution model controlled by a tectonically inherited sea bottom topography in the carbonate rimmed shelf of the upper tithonian valanginian southern tethyan continental margin nw sicily italy the upper tithonian valanginian shallow water carbonates outcropping in the palermo mts nw sicily consist of several facies associations reflecting different depositional environments of a carbonate rimmed shelf pertaining to the southern tethyan continental margin the reconstructed depositional model based on the sedimentological features cyclic facies arrangement and biota distribution shows that a wide protected lagoon dominated by algae molluscs and scattered patch reefs was bordered landward by a tidal flat where stromatolitic algal mats were cyclically subaerial exposed and seaward by a marine sand belt and reef complex oolitic packstone grainstone lithofacies cyclically subjected to subaerial exposure suggests the occurrence of a barrier island located nearly to the lagoonal carbonate shoreline allowing the development of narrow embayments with restricted circulation in the outer platform the oolitic lithofacies of the marine sand belt pass landward into the protected lagoon where washover oolite sands occur and seaward into a high energy zone back reef apron gradually merging in the reef complex in the latter coral framestone occupied the inner sector reef flat while the facies association dominated by boundstone with ellipsactinia sp developed in the outer sectors reef wall adjacent to the fore reef and upper slope environments stratigraphic evidence associated with the recognized facies associations helped to reconstruct the geo tectonic setting of the carbonate platform where the distribution of the depositional facies along the shelf and their extension were influenced by the tectonically inherited sea bottom topography in a regime of extensional tectonics localized and thin succession of high energy prograding oolite sand belt depositional facies occupied structural highs footwall uplift while the largely diffused and thick low energy aggrading peritidal to lagoonal depositional facies developed in subsiding hanging wall the reef complex and the fore reef depositional facies exhibiting lateral migration and prograding geometries with clinoforms and downlap stratal terminations developed on a subsident stepped margin adjacent to a faulted shelf break this morphostructural setting can be comprised in a model where the tilted and faulted blocks inner platform and stepped margin outer platform paleo topography inherited from the rifting tectonics was the most important factor controlling the geometry and depositional architecture of a carbonate platform growing on the southern tethyan passive margin

short term glacier velocity changes at west kunlun shan northwest tibet detected by synthetic aperture radar data abstract seasonal glacier velocity changes across the high arctic including the greenland ice sheet have been observed and have attracted significant attention over the past decade however it remains uncertain how much short term variability exists in other polythermal glaciers particularly those in high asia here we report satellite radar image analyses that reveal diverse glacier surface velocities and their evolution in west kunlun shan wks nw tibet where little is known about glacier dynamics on the basis of radar images obtained from 2003 to 2011 we examined 36 glaciers and classified them into two classes according to their multi temporal velocity profiles 25 as normal flow type surface velocity reaches maxima around the middle part and gradually approaches zero toward downstream and upstream and four as surging type surface velocities are greater than 150 m yr and or the terminus advance is recognized from the radar images seven other glaciers do not fit the former two classes and reveal stagnant velocity profiles that are nearly zero in the lower part but are similar to those of the normal type in the upper part although these glaciers could be just stagnant tongues indicative of receding normal type glaciers given the temporal evolution at the zhongfeng glacier the stagnant type possibly represents a quiescent phase of the surging type glaciers while glacier surfaces are mostly clean with limited debris cover except near the termini surge type glaciers might be common in wks the observed short term velocity changes provide us with evidence for efficient basal slip even at the high elevation polythermal glaciers this study demonstrates that frequent radar image acquisitions are helpful to understand short term velocity changes at remote glaciers in detail

tributary glacier surges an exceptional concentration at panmah glacier karakoram himalaya four tributaries of panmah glacier have surged in less than a decade three in quick succession between 2001 and 2005 since 1985 13 surges have been recorded in the karakoram himalaya more than in any comparable period since the 1850s ten were tributary surges in these ten a full run out of surge ice is prevented but extended post surge episodes affect the tributary and main glacier the sudden concentration of events at panmah glacier is without precedent and at odds with known surge intervals for the glaciers interpretations must consider the response of thermally complex glaciers at exceptionally high altitudes and of high relief to changes in a distinctive regional climate it is suggested that high altitude warming affecting snow and glacier thermal regimes or bringing intense short term melting episodes may be more significant than mass balance change