discriminating between subglacial and proglacial lake sediments an example from the danischer wohld peninsula northern germany subglacial lakes are common features of contemporary ice masses however they are rarely identified in the geological record this is due to the difficulty in discriminating between subglacial and proglacial lake sediments a proglacial origin is typically preferred as the simplest explanation we hypothesise that numerous deposits currently interpreted to record proglacial lake sedimentation may actually have a subglacial origin here we try and find ways of distinguishing proglacial from subglacial lake sediments by investigating three sites along the danischer wohld peninsula northern germany which have been interpreted to record both proglacial and subglacial sedimentation we identify two major phases of ice activity and associated lake formation during the late weichselian glaciation 1 proglacial lake formation at 23 ka in front of the advancing baltic ice stream this lake was subsequently overridden and the sediments glaciotectonised as ice continued to advance to its maximum extent 2 retreat of ice back into the baltic basin at 19 ka and formation of a proglacial lake that persisted for 4 ka we suggest that subglacial lake activity may have occurred at two of the sites between 23 and 19 ka this is based on the presence of aggrading sediment deposits characterised by stratified laminated diamictons and interbedded tabular to channelized sorted sediments the juxtaposition of relatively undeformed waterlain sediment and subglacial till absence of glaciotectonic thrusting and folding or of fining coarsening successions and the geomorphic association with tunnel valleys to the south of the study area the style of sedimentation and deformation provided the greatest insight into the discrimination of proglacially vs subglacially deposited glaciolacustrine sediments the luminescence signal palaeodose distributions also offers a potentially powerful means of fingerprinting sediment transport pathways of young glacial systems

horizontal lamination and the sequence of bed phases and stratification under upper flow regime conditions two forms of horizontal laminae have been produced under upper flow regime conditions in a flume by deposition on a plane bed and on low in phase waves upper plane bed laminae consist of approximately equal numbers of fining upward fu and coarsening upward cu textural laminae heavy minerals when present are typically within or form cu laminae in horizontal laminae formed under low in phase waves fu laminae may predominate and are significantly thicker than cu laminae heavy minerals are associated with the tops of some fu laminae and are absent from cu laminae deposits aggraded on plane beds and low in phase waves both display low angle 13 14 upstream grain imbrication upper plane bed horizontal laminae are attributed to the effects of the burst sweep cycle on local bedload transport bursts form fu laminae and sweeps form cu laminae some fu laminae in in phase wave deposits are thought to form with downstream migration of bed waves on which sand size decreases from trough to crest heavy minerals are concentrated in the tops of these fu laminae due to their enrichment on the crests of the migrating bed waves other fu and cu laminae in in phase wave deposits probably formed by the action of bursts and sweeps as on upper plane beds a sequence of bed phases and stratification formed under upper flow regime conditions is described based on the observations here combined with descriptions from the literature with increasing flow strength the gradual sequence of bed phases is 1 plane bed 2 low relief downstream migrating inphase waves increasing in amplitude and wavelength with increasing flow strength 3 stationary in phase waves 4 upstream migrating including breaking wave antidunes the sequence of stratification formed under these bed phases is 1 upper plane bed horizontal lamination 2 in phase wave horizontal lamination to in phase wave foreset cross laminae 3 in phase wave drape laminae 4 antidune backset cross laminae

rapid deposition of sand and gravel mixtures downstream of a negative step the role of matrix infilling and particle overpassing in the process of bar front accretion an experimental flow channel was used to investigate the rapid deposition of sand and gravel mixtures downstream of a negative step hydraulic processes give rise to the quasi simultaneous accumulation of openwork gravels matrix filled contact framework and dilated framework gravels the resultant structure is analogous to a bar front in gravel bed streams flow conditions were non uniform but steady in time whereas open and closed gravel fabrics are usually interpreted as representing deposition from unsteady flows for example a varying discharge regime consideration of the percentage of sand in the deposits indicated that in terms of packing the sediments may be considered as a simple binary mixture with partial framework dilation occurring with sand percentages in excess of c 32 despite dilation for sand percentages less than 50 structural stability of the foreset gravels was maintained so that the bar front exhibited a distinct brinkpoint and a planar slip face at the angle of initial yield which made an angular contact with the base of the flume for sand percentages in excess of 80 individual gravel clasts were completely supported by sand the original structural stability was lost so that the bar front eroded by reverse currents assumed a tangential contact with the flume base below the angle of initial yield the brinkpoint was rounded and indistinct in addition to altering the bar front slope increasing the quantity of sand in the bed sediments had a major influence on the dip of gravel particles on the foresets in all experimental runs a surface sand seal with openwork gravels beneath developed upstream of the brinkpoint the mechanics of sand seal formation require further investigation however an overpassing mechanism was noted to be very important in sorting gravel particles rolling over the brinkpoint a published mathematical model describing the overpassing mechanism was found to be appropriate to the present experimental observations

three dimensional hydrostratigraphy of the orangeville moraine area southwestern ontario canada regional scale three dimensional modelling of quaternary sediments in the orangeville moraine area of southwestern ontario has been completed as part of the ontario geological survey groundwater in

facies architecture and sequence stratigraphy in glacially influenced basins basic problems and water level glacier input point controls with an example from the quaternary of ontario canada abstract sequence architecture is controlled by two fundamental factors the water level relative to the depositional surface which controls accommodation space and the points or areas of sediment injection which control how this space is filled in relative water level accommodation space and injection points normally vary together and various genetic terms are used to define systems tracts but in glacially influenced basins accommodation space is controlled not only by water level but also by the glacier injection points are similarly dually controlled by water level and by the terminus of the glacier during high lake levels the injection point of the glacier may be underwater at the base of the slope genetic terms like highstand and lowstand therefore are meaningless in successions controlled by sediment input points which are independent of water levels and accommodation space distinct water level and glacier input point systems can occur side by side the water level system controlled by lake level or sea level the glacier input point system controlled by the position of the subaqueous glacier front and both can form juxtaposed systems passing laterally into each other a bewildering and incompatible terminology is needed if the terms of genetic sequence stratigraphy are used for both water level and glacier input point systems because the sedimentary injection points and sequence boundaries of the two systems fluctuate out of phase with one another sequences developed by movement of the glacier are completely independent of those controlled by water levels if genetic sequence stratigraphy is applied to a basin with both lake level and glacier input point systems then each needs separate genetic terminologies to describe them which leads only to confusion however descriptive sequence stratigraphy allostratigraphy can be readily applied to successions like the quaternary of lake ontario we therefore suggest that genetic sequence terms be discarded and simpler allostratigraphic terminology used in glacially influenced basins

the nature of mineralizing fluids of the kipushi zn cu deposit katanga democratic repubic of congo quantitative fluid inclusion analysis using laser ablation icp ms and bulk crush leach methods fluid inclusions from the epigenetic zn cu deposit of kipushi central african copper belt katanga democratic republic of congo have been subjected to an integrated microthermometric bulk crush leach and laser ablation inductively coupled plasma mass spectrometric la icp ms study to elucidate the physicochemical conditions of ore formation and the origin of the mineralizing fluids the kipushi deposit is hosted in carbonates and partly in siliciclastic rocks that have undergone regional low grade greenschist facies metamorphism and which were strongly deformed during the lufilian orogeny main deformation phase 550 ma investigation of host rock gangue and ore samples enabled reconstruction of the paragenesis of ore deposition the main zn cu ge pb sulfide mineralization was accompanied by three generations of hydrothermal dolomite and a generation of coarse grained quartz primary and pseudosecondary fluid inclusions in these minerals contain predominantly halite saturated aqueous brines 30 43 wt nacl equiv with locally unidentified trapped solids these inclusions mostly decrepitate upon heating before total homogenization which could suggest that they also trapped excess carbonic vapor they show petrographic and microthermometric evidence for postentrapment reequilibration prohibiting their use as accurate geothermometers and geobarometers previous studies on chlorite and sphalerite geothermometry framed the formation temperature of the kipushi cu zn deposit between 290 to 380 c younger fluids are present as secondary inclusions in the gangue minerals and as primary fluid inclusions in sphalerite from a minor secondary mineralization phase these two phase aqueous inclusions have a slightly lower salinity 23 31 wt nacl equiv and have homogenization temperatures ranging from 170 to 80 c in successive fluid inclusion assemblages sporadically some mixed aqueous carbonic and gaseous co2 ch4 inclusions are present but their genetic position is un clear and they are insignificant with regard to the mineralization process as a whole crush leach bulk analysis of the fluid inclusions show that the mineralizing fluids had a molar cl br ratio close to or somewhat higher than the seawater value which rules out a major contribution from bittern brines and suggests that the fluids gained their salinity primarily by the dissolution of evaporites younger fluids that circulated through the deposit after the main phase of ore formation have cl br and na br signatures indicative of a greater involvement of halite dissolution brines values much higher than that of seawater la icp ms analyses of the mineralizing fluids reveal that they have molar li na ca na mg na mn na and sr na in the range of natural high salinity fluids in metamorphic environments worldwide however they have relatively high molar fe na zn na pb na and especially very high ba na ratios their molar k na is also somewhat higher than for other low grade metamorphic fluids but is nevertheless in agreement with the values predicted by the k na geothermometer at the conditions of ore formation this suggests that the major element composition of the fluids was buffered by fluid mineral equilibria their relatively high metal contents ba zn fe and pb suggest that they interacted with and leached these elements from felsic basement rocks at higher temperatures whatever the origin of the fluids their salinity and the metals their uniformly high ba and ore metal content together with the absence of barite and the occurrence of ba silicates at kipushi indicates that sulfide mineralization occurred when the metal bearing fluids encountered a reducing h2s rich reservoir the ubiquitous presence of preexisting metamorphosed carbonic material shungite in the sulfides and host rock and a sulfur isotope signature of the ores in agreement with thermogenic sulfate reduction suggests that this condition was likely created due to the high initial reduced carbon content of the host rocks at kipushi which seems to be exceptional in the copper belt therefore we postulate that a critical factor in the formation of major vein type zn cu mineralization was the presence of a hydrocarbon rich facies of the lower nguba carbonates at kipushi

towards realistic aquifer models three dimensional georadar surveys of quaternary gravel deltas singen basin sw germany abstract understanding sedimentary heterogeneities has nowadays become crucial for sophisticated aquifer management the methods used so far for aquifer characterization e g pump test coring analysis cannot provide the needed resolution for a sufficient prediction of the subsurface properties e g sudicky 1986 this calls for the application of the outcrop analogue approach to aquifers e g macfarlan et al 1994 aigner 1995 in this project we used georadar ground penetrating radar or gpr to acquire the subsurface information for high resolution three dimensional images and radar facies mapping of glaciolacustrine delta sediments in the singen basin sw germany a three dimensional reconstruction of sedimentary heterogeneities for a detailed aquifer characterisation becomes possible by combining gpr profiling and outcrop information a case study is presented showing a complex three dimensional architecture of a quaternary gravel body consisting of the following three types of architectural elements 1 glaciolacustrine delta foresets 2 erosional surfaces with scour pool fills and 3 horizontal glaciofluvial gravel sheets although this seems a relatively simple architectural inventory the three dimensional georadar profiling shows considerable internal heterogeneities the radar data are interpreted following the seismic stratigraphic approach i e the delineation of radar facies types and of radar sequences the three dimensional heterogeneities are visualized by means of time slices 3 d block or chair diagrams or series of radar facies maps

new age constraints for the saalian glaciation in northern central europe implications for the extent of ice sheets and related proglacial lake systems abstract a comprehensive palaeogeographic reconstruction of ice sheets and related proglacial lake systems for the older saalian glaciation in northern central europe is presented which is based on the integration of palaeo ice flow data till provenance facies analysis geomorphology and new luminescence ages of ice marginal deposits three major ice advances with different ice advance directions and source areas are indicated by palaeo ice flow directions and till provenance the first ice advance was characterised by a southwards directed ice flow and a dominance of clasts derived from southern sweden the second ice advance was initially characterised by an ice flow towards the southwest clasts are mainly derived from southern and central sweden the latest stage in the study area third ice advance was characterised by ice streaming hondsrug ice stream in the west and a re advance in the east clasts of this stage are mainly derived from eastern fennoscandia numerical ages for the first ice advance are sparse but may indicate a correlation with mis 8 or early mis 6 new pirir290 luminescence ages of ice marginal deposits attributed to the second ice advance range from 175 10 to 156 24 ka and correlate with mis 6 the ice sheets repeatedly blocked the main river drainage pathways and led to the formation of extensive ice dammed lakes the formation of proglacial lakes was mainly controlled by ice damming of river valleys and major bedrock spillways therefore the lake levels and extends were very similar throughout the repeated ice advances during deglaciation the lakes commonly increased in size and eventually drained successively towards the west and northwest into the lower rhine embayment and the north sea catastrophic lake drainage events occurred when large overspill channels were suddenly opened ice streaming at the end of the older saalian glaciation was probably triggered by major lake drainage events

the pleistocene of schoningen germany a complex tunnel valley fill revealed from 3d subsurface modelling and shear wave seismics abstract the pleistocene deposits of schoningen represent an outstanding geological and archaeological archive where an up to 45 m thick middle to late pleistocene succession has been preserved and unique artefacts from the lower palaeolithic have been discovered the preservation of such a thick and complete glacial interglacial succession is very rare in the geological record and requires a specific depositional setting we will present a new depositional model for the pleistocene succession of schoningen integrating outcrop data borehole data and high resolution shear wave seismics a total of four outcrop sections and 744 borehole logs were examined to document the complex facies architecture all collected sedimentological and geophysical data sets were integrated into a high resolution 3d geological model gocad for reconstructing the spatial distribution of facies associations and the large scale depositional architecture the spatial distribution of the artefacts will be discussed with respect to the depositional environment the elsterian and holsteinian deposits are restricted to a nnw sse trending elongated trough which is deeply incised into unconsolidated lignite bearing palaeogene deposits the geometry of this erosional structure points to a tunnel valley origin that was incised below the elsterian ice sheet the basal tunnel valley fill consists of cross stratified pebbly sand and gravel overlain by till after deglaciation the tunnel valley remained underfilled and acted as a depocentre for interglacial deposition during the subsequent holsteinian interglacial mis 9 a lake formed within this depocentre and lacustrine sediments accumulated this interglacial succession consists of peat organic rich silt and fine grained sand interpreted as lake bottom and deltaic sediments fed by surface run off shed from the elm ridge the lacustrine deposition was controlled by repeated lake level fluctuations in the range of 1 6 m leading to the formation of laterally stacked delta systems these lake level changes were probably triggered by climate causing variations of precipitation and surface run off during the late saalian glaciation the remnant tunnel valley was completely filled with meltwater deposits the sedimentary facies and depositional architecture point to a shallow water delta subsequently the meltwater deposits were overlain by till the deposition of the middle pleistocene sediments within an elsterian tunnel valley explains the unique preservation of the sedimentary succession of schoningen the long lived interglacial lake provided an attractive site for animals and early humans ambushing them artefacts mainly became embedded on the delta plain which rapidly was transgressed during lake level rise and artefacts were thus preserved

depositional model in subglacial cavities killiney bay ireland interactions between sedimentation deformation and glacial dynamics subglacial meltwater drainage and sedimentary processes play a major role in ice sheet dynamic but there is a lack of study of subglacial environment because modern ice sheet beds remain inaccessible previous authors already intended to provide diagnostic criterion and recent investigations suggest that fluid pressure variations are a key factor in subglacial environment this paper investigated the late devensian sedimentary record in order to describe subglacial sedimentological facies associations and deformation features related to fluid overpressures we used an integrated approach based on stratigraphy sedimentology and deformations styles to demonstrate a subglacial depositional model the studied interval is composed of stratified gravel and sand interbedded with diamicton and boulder pavement deposited in depressions formed by irregularity of the upper surface of diamicton deformation structures include convolutes dykes and normal micro faulting dykes show different dip directions from vertical oblique to subhorizontal from which both directions of shortening and extension can be determined vertical dykes are formed under pure shear strain related to ice weight only oblique dykes imply both ice bed coupling and simple shear strain between ice and substrate induced by flowing ice related to progressively increasing meltwater drainage intensity horizontal dykes are formed when minimum strain is vertical and therefore the overpressure exceeds the weight of overburden they are associated with high meltwater drainage intensity and ice bed uncoupling and refer to hydrofracturing overall depositional and deformation sequence also illustrates the increasing intensity of meltwater drainage in small cavity as high energy channelised deposits and in large cavities where subaqueous fan are deposited under hydraulic jump conditions moreover large cavities represent lee side cavities formed by fast flowing ice over an obstacle hydrofracturing is likely to occur when a dense fluid potentially associated with catastrophic drainage of an upstream cavity enters the low pressure confined environment of a downstream cavity and is injected under pressure in the soft substrate the studied glacial sequence represents a regional pattern probably related to an allocyclic control on sedimentation linked to long term glacial dynamics rather than local depositional conditions based on these results we provided a synthetic model linking depositional and deformation processes during ice sheet growth and decay but also valid at different timescales from annual to seasonal scale

terrace styles and timing of terrace formation in the weser and leine valleys northern germany response of a fluvial system to climate change and glaciation abstract in glaciated continental basins accommodation space is not only controlled by tectonics and sea level but also by the position of ice sheets which may act as a regional base level for fluvial systems although the pleistocene terrace record of major river systems in northwestern europe has been investigated by many authors relatively little attention has been paid to base level changes related to glacier advance retreat cycles and how these regional changes in base level interacted with river catchment processes this study provides a synthesis of the stratigraphic architecture of middle pleistocene to holocene fluvial terraces in the upper weser and middle leine valley in northern germany and links it to glaciation climate and base level change the depositional architecture of the fluvial terrace deposits has been reconstructed from outcrops and high resolution shear wave seismic profiles the chronology is based on luminescence ages 230 th u ages 14 c ages and middle palaeolithic archaeological assemblages the drainage system of the study area developed during the early miocene during the pleistocene up to 170 m of fluvial incision took place a major change in terrace style from strath terraces to cut and fill terraces occurred during the early middle pleistocene before marine isotope stage mis 12 which may correlate with climate deterioration and the onset of glaciation in northern central europe during this time a stable buffer zone was established within which channels avulsed and cut and filled freely without leaving these vertical confines climate was the dominant driver for river incision and aggradation whereas the terrace style was controlled by base level changes during ice sheet growth and decay a major effect of glacio isostatic processes was the post elsterian re direction of the river weser and river leine the middle pleistocene fluvial terraces are vertically stacked indicating a high aggradation to degradation ratio corresponding with a regional base level rise during glacier advance at the beginning of the late pleistocene the terrace style changed from a vertical to a lateral stacking pattern which is attributed to a decrease in accommodation space during glacier retreat the formation of laterally attached terraces persisted into the holocene major incision phases took place during mis 5e 5d 5c and probably early mis 4 early mis 3 and mis 2 lateglacial during mis 5e and the lateglacial the braided river systems changed into meandering rivers indicated by preserved organic rich flood plain and point bar deposits the late pleistocene braided river systems mis 5c to mis 3 are characterized by a high sinuosity which may be a direct effect of an increased downstream gradient after deglaciation when the channel lengthened and the river adjusted to the increased gradient by increasing sinuosity these middle pleniglacial fluvial deposits are unconformably overlain by lateglacial to holocene meandering river deposits which form laterally attached terraces recording millennial scale channel shifts the lack of late pleniglacial deposits might be related to late weichselian forebulge formation

geology mineralogy and stable isotope geochemistry of the kabwe carbonate hosted pb zn deposit central zambia abstract the carbonate hosted kabwe pb zn deposit central zambia has produced at least 2 6 mt of zn and pb metal as well as minor amounts of v cd ag and cu the deposit consists of four main epigenetic pipe like orebodies structurally controlled along ne sw faults sphalerite galena pyrite minor chalcopyrite and accessory ge sulphides of briartite and renierite constitute the primary ore mineral assemblage cores of massive sulphide orebodies are surrounded by oxide zones of silicate ore willemite and mineralized jasperoid that consists largely of quartz willemite cerussite smithsonite goethite and hematite as well as numerous other secondary minerals including vanadates phosphates and carbonates of zn pb v and cu galena sphalerite and pyrite from the pb zn rich massive orebodies have homogeneous negative sulphur isotope ratios with mean 34 s cdt permil values of 17 75 0 28 1 16 54 0 0 27 and 15 82 0 25 respectively the zn rich and pb poor no 2 orebody shows slightly heavier ratios of 11 70 0 5 34 s for sphalerite and of 11 91 0 71 34 s for pyrite the negative sulphur isotope ratios are considered to be typical of sedimentary sulphides produced through bacterial reduction of seawater sulphate and suggest a sedimentary source for the sulphur carbon and oxygen isotope ratios of the host dolomite have mean 13 c pdb and 18 o smow values of 2 89 and 27 68 respectively which are typical of marine carbonates the oxygen isotope ratios of dolomite correlate negatively to the sio 2 content introduced during silicification of the host dolomite the depletion in 18 o in dolomite indicates high temperature fluid rock interaction involving a silica and 18 o rich hydrothermal solution two types of secondary fluid inclusions in dolomite both of which are thought to be related to ore deposition indicate temperatures of ore deposition in the range of 257 to 385 and 98 to 178 c respectively the high temperature fluid inclusions contain liquid vapour solid phases and have salinities of 15 to 31 eq wt nacl whereas the low temperature inclusions consist of liquid vapour with a salinity of 11 5 eq wt nacl fluid transport may have been caused by tectonic movements associated with the early stages of the pan african lufilian orogeny whereas ore deposition within favourable structures occurred due to changes in pressure temperature and ph in the ore solution during metasomatic replacement of the host dolomite the termination of the kabwe orebodies at the mine club fault zone and observed deformation textures of the ore sulphides as well as analysis of joint structures in the host dolomite indicate that ore emplacement occurred prior to the latest deformation phase of the neoproterozoic lufilian orogeny

the geochemistry of co and cu in the kafue river as it drains the copperbelt mining area zambia abstract samples of the dissolved 0 45 m phases have been collected in the kafue river during a 1 year cycle within the mining area the concentrations of co cu and s in the river occasionally increase more than 100 times compared to concentrations upstream from the mining area the highest concentrations of dissolved cu 3 4 m and fe 4 2 m are found during high water discharge probably indicating a washout of leached weathering products from spoil heaps high levels of co appear to originate from one point source the location where the co ore is treated in the kafue river secondary mn and fe rich particles are formed on which co and cu respectively are enriched the elements associated to secondary fe and mn particles are enriched at the sediment surface in the river due to redox processes hence secondary particles and sorbed trace elements may be resuspended and transported further downstream in the river system however very high concentrations of cu 1 and co 0 1 in the sediment are caused by primary sulphides

dating of u rich heterogenite new insights into u deposit genesis and u cycling in the katanga copperbelt abstract the katanga copperbelt region of the democratic republic of congo hosts world class cobalt deposits accounting for 50 of the world reserves heterogenite coooh is the most abundant co bearing secondary mineral in the region its occurrence is the result of oxidation of cu co sulfides and associated co reprecipitation in the uppermost part of the deposits during the pliocene in addition to sediment hosted copper and cobalt ore deposits the katanga copperbelt also hosts numerous uraniferous mineral occurrences and deposits which can be associated with heterogenite within these deposits heterogenite can have high concentrations of u up to 3 5 and pb up to 4 in situ sims u pb ages were obtained for heterogenite samples from the u deposits of shinkolobwe kalongwe and kambove these analyses yield distinct neoproterozoic ages at 876 ma 823 ma and in the 720 to 670 ma age range as the geological context prevailing at those times was not favorable for heterogenite formation these ages most probably record geological events that are not the formation of the mineral itself for instance the heterogenites could have inherited the u pb signature of a u rich mineral most likely uraninite formed and or yet reworked at 876 ma 823 ma and in the 720 to 670 ma time interval and spatially associated with primary co sulfides in this hypothesis the ages obtained in this paper are significant for understanding the cycling and re deposition of u at given moments in the regional geological history in such context the 876 ma and the 823 ma age are consistent with syn early diagenetic concentration of uranium in sediments of the katanga basin the 720 to 670 ma ages are interpreted as a phase of u remobilization related to hydrothermal fluid circulation induced by late nguba proto oceanic rifting or by early stages of congo kalahari craton convergence and associated hydrothermal circulation

jet efflux deposits of a subaqueous ice contact fan glacial lake rinteln northwestern germany abstract the coarse grained ice contact porta subaqueous fan delta complex was deposited in glacial lake rinteln at the margin of the saalian ice sheet that advanced south of the weser chains nw germany the ice proximal depositional system was up to 15 km long and 10 km wide the present study deals with ice proximal subaqueous fan deposits which are interpreted as products of a subcritical plane wall outflow jet that periodically passed into a supercritical jet with hydraulic jump the proximal facies assemblage consists of the coarse clast supported gravelly deposits of a hyperconcentrated high density effluent and of related cohesionless debris flows attributed to the conduit or immediate proximal jet outflow zone of flow establishment the intermediate facies assemblage attributed to the outflow jet proximal zone of flow transition is dominated by normally graded and cross stratified gravels with scour structures at their bases these gravels were deposited by a high density effluent capable of forming mouthbar like features these deposits pass downcurrent into an assemblage of planar parallel stratified and planar and trough cross stratified sands and pebbly sands partially interpreted as antidunes with abundant scour structures and intercalated layers of fine sand silt and silty mud attributed to the jet distal zone of flow transition the distal facies assemblage consists of trough cross stratified sands and pebbly sands and is attributed to the outflow jet proximal zone of established flow the sedimentary succession as a whole has wedge shape geometry with a gentle fan shaped inclination of the bedding from the southeast to the southwest repeated vertical alternations of supercritical and subcritical deposits and muddy interlayers can be attributed to temporary fluctuations in the meltwater outflow whereas the overall upward fining of the succession indicates a net decline of meltwater discharges

metal sources for the nkana and konkola stratiform cu co deposits zambian copperbelt insights from sr and nd isotope ratios abstract the central african copperbelt lies within the lufilian orogenic belt in the border region between the democratic republic of congo drc and zambia a sr and nd isotope study was performed on gangue carbonates associated with multiphase mineralisation at the zambian konkola and nkana deposits comparison with isotopic signatures of basement rocks provides new insights into the likely metal source s for the cu co mineralisation at least three mineralisation phases can be identified with respect to the lufilian orogeny gangue carbonates of the first pre to syn kinematic mineralisation phase in both deposits have sr and nd isotopic compositions that correspond to felsic rocks of the domes region a tectonic zone in the zambian part of the lufilian belt where basement rocks crop out however the isotopic signatures from both deposits differ this can be attributed to local variation in isotopic composition of the basement below the deposits radiogenic isotope ratios suggest that subsequent syn kinematic mineralisation at both sites occurred due to the remobilisation of precursor ore petrographic evidence indicates that the third late kinematic mineralisation phase at nkana resulted from a renewed input of metals with a mafic affinity e g co ni however sr and nd isotope ratios resemble those of the earlier mineralisation phases and do not reflect a change in source composition nonetheless comparison with the isotopic signatures of the co poor konkola deposit and co rich stratiform deposits in the drc might indicate a mafic component in the nkana metal source calculated mixed isotopic compositions support such a mafic component

glacial lake outburst erosion of the grand valley michigan and impacts on glacial lakes in the lake michigan basin abstract geomorphic and sedimentologic evidence in the grand valley which drained the retreating saginaw lobe of the laurentide ice sheet and later acted as a spillway between lakes in the huron and erie basins and in the michigan basin suggests that at least one drainage event from glacial lake saginaw to glacial lake chicago was a catastrophic outburst that deeply incised the valley analysis of shoreline and outlet geomorphology at the chicago outlet supports j h bretz s hypothesis of episodic incision and lake level change shoreline features of each lake level converge to separate outlet sills that decrease in elevation from the oldest to youngest lake phases this evidence coupled with the presence of boulder lags and other features consistent with outburst origin suggests that the outlets were deepened by catastrophic outbursts at least twice the first incision event is correlated with a linked series of floods that progressed from huron and erie basin lakes to glacial lake saginaw to glacial lake chicago and then to the mississippi the second downcutting event occurred after the two rivers advance of the lake michigan lobe outbursts from the eastern outlets of glacial lake agassiz to glacial lake algonquin are a possible cause for this period of downcutting at the chicago outlets

moraine formation in northwestern ontario product of subglacial fluvial and glaciolacustrine sedimentation long arcuate stratified end moraines in northwestern ontario may represent major and rapid sedimentation events in glacial lake agassiz rapid lowering of the lake or lift of a marginal ice dam m

quaternary glaciations of northern europe this paper presents the outcome of a workshop held in berlin in february 2009 concerned with current research on the glacial history of northern europe including the british isles the methodologies presently used to resolve this topic are outlined particular attention is given to new analytical methods deriving from high resolution remote imaging of glacial terrain both on land and on the sea bed key new stratigraphic sections higher resolution results from conventional geochronological methods like radiocarbon and more recently developed technologies such as luminescence and cosmogenic radionuclide dating the relationships between the results derived from these two methods are discussed in further detail along with possible explanations for these differences an outline of a most likely glacial history of the scandinavian and british and irish ice sheets is presented along with possible links to global climate change as represented by the marine isotope mis record tentative evidence for glaciation is identified in mis 22 16 12 10 8 6 4 and 2 and correlations of phases within the last glaciation are also explored for both the scandinavian and british and irish ice sheets the results show that the character and extent of glaciation in different parts of the region are not synchronous and much more geochronological work is required before regional correlations can be established with confidence

sedimentary imprints of former ice sheet margins insights from an end ordovician archive sw libya fromthe proterozoic to the quaternary the evolution of the earthwas characterised by recurrent periods of glaciation however the margins of many ancient ice sheets are poorly defined on palaeogeographic reconstructions the extent and outlines of ancient ice sheets can be better understood through careful documentation of sediments deposited at the ice sheet margin an outstanding example is provided herein based on an end ordovician archive in libya tihemboka area murzuq basin the four sets of structures include i subglacial glaciotectonic structures and soft sediment deformations from flowing glacier ice such as intraformational glacial striae intraformational deformation shear planes sheath folds normal microfaults and large scale glaciotectonic folds and thrusts ii structures resulting from overpressured subglacial meltwater flows such as clastic dykes and tunnel valleys iii proglacial depositional structures and facies related to highmagnitude meltwater floods such as sandstone intraclasts large scale bedforms resulting from supercritical flows climbing dune cross stratification and kettle holes and iv deformation structures resulting from free floating and nonglacier ice such as ice keel scours and ice crystal marks such a set of structures points to an ice marginal essentially continental depositional setting and provides an excellent suite of criteria to identify margins of ancient ice sheets in the stratigraphic record at a regional scale a reconstruction through time and space of the related depositional wedge is proposed this corresponded to a seismic scale n120 m in thickness 40 km in length ice marginal wedge in front of an essentially warm based ice sheet inducing concomitant large scale glaciotectonic deformation glacial basin and tunnel valley downcuttings the related ice front was associated with high energy meltwater flows feeding a network of deeply incised proglacial channels downstream and beyond them a fluvioglacial deltaic system shallow ice marginal permafrost most likely affected the depositional wedge at a larger scale the tihemboka ice marginal wedge is interpreted as related to a stillstand period over the gondwana platform developed over an estimated interval of a few thousands of years based on these data the conditions that arose in a particularly favourable context for the development the preservation and the identification of ice marginal wedges in the geological record are reviewed significant meltwater derived sediment deposition and aggradation in an accommodation space resulting either from preglacial inheritance glacial downcuttings and or glacio isostatic lithospheric flexure or active tectonic subsidence 1 myr are required for their formation and subsequent preservation

genesis of copper lead mineralization in the regionally zoned agnigundala sulfide belt cuddapah basin andhra pradesh india shallow marine sandstone shale carbonate sedimentary rocks of the paleoproterozoic northern cuddapah basin host copper nallakonda deposit copper lead dhukonda deposit and lead mineralization bandalamottu deposit which together constitute the agnigundala sulfide belt the cu sulfide mineralization in sandstone is both stratabound and disseminated and pb sulfide mineralization occurs as stratabound fracture filling veins and or replacement veins within dolomite systematic mineralogical and sulfur carbon and oxygen isotope studies of the three deposits indicate a common ore fluid that deposited copper at nallakonda copper lead at dhukonda and lead at bandalamottu under progressive cooling during migration through sediments the ore fluid was of low temperature 200 c and oxidized thermochemical reduction of basinal water sulfate produced sulfide for ore deposition it is envisaged that basal red bed and evaporite bearing rift related continental to shallow marine sediments might have acted as the source for the metals rift related faults developed during sedimentation in the basin might have punctured the ore fluid pool in the lower sedimentary succession and also acted as conduits for their upward migration the ore bearing horizons have participated in deformations during basin inversion without any recognizable remobilization

sedimentological and deformational criteria for discriminating subglaciofluvial deposits from subaqueous ice contact fan deposits a pleistocene example ireland a pit located near ballyhorsey 28 km south of dublin eastern ireland displays subglacially deposited glaciofluvial sediments passing upwards into proglacial subaqueous ice contact fan deposits the coexistence of these two different depositional environments at the same location will help with differentiation between two very similar and easily confused glacial lithofacies the lowermost sediments show aggrading subglacial deposits indicating a constrained accommodation space mainly controlled by the position of an overlying ice roof during ice bed decoupling these sediments are characterized by vertically stacked tills with large lenses of tabular to channelized sorted sediments the sorted sediments consist of fine grained laminated facies cross laminated sand and channelized gravels and are interpreted as subglaciofluvial sediments deposited within a subglacial de coupled space the subglaciofluvial sequence is characterized by glaciotectonic deformation structures within discrete beds triggered by fluid overpressure and shear stress during episodes of ice bed recoupling clastic dykes and folds the upper deposits correspond to the deposition of successive hyperpycnal flows in a proximal proglacial lake forming a thick sedimentary wedge erosively overlying the subglacial deposits gravel facies and large scale trough bedding sand are observed within this proximal wedge while normally graded sand beds with developed bedforms are observed further downflow the building of the prograding ice contact subaqueous fan implies an unrestricted accommodation space and is associated with deformation structures related to gravity destabilization during fan spreading normal faults this study facilitates the recognition of subglacial submarginal depositional environments formed in part during localized ice bed coupling episodes in the sedimentary record the sedimentary sequence exposed in ballyhorsey permits characterization of the temporal framework of meltwater production during deglaciation the impact on the subglacial drainage system and the consequences on the irish sea ice stream flow mechanisms

autogenic response of fluvial deltas to steady sea level fall implications from flume tank experiments flume tank experiments on fluvial deltas conducted with constant fall of relative sea level rate a 0 constant sediment discharge q s and constant water discharge q w reveal a built in geomorphic process that inevitably causes valley incision autoincision after the beginning of the sea level fall and forms paired stream terraces on the abandoned alluvial slope despite steady sea level fall deltas aggrade without major incision until the autoincision threshold is attained at which time the aggradational regime is replaced by a degradational one results of the experiments imply that multiple valley incision and terrace formation can occur as an autogenic response of the depositional system to steady forcing by constant sea level fall changes of a q s and q w or changes in river energy are not required to account for these geomorphic events the understanding of the autogenic response when combined with the theory of shoreline autoretreat provides an alternative view of the geomorphic development of fluviodeltaic systems during base level fall

middle pleistocene saalian lake outburst floods in the munsterland embayment nw germany impacts and magnitudes abstract during the late saalian drenthe glaciation ice damming of the upper weser valley led to the formation of glacial lake weser the lake drained catastrophically into the munsterland embayment as the western ice dam failed releasing up to 110 km3 of water with a calculated peak discharge of 2 5 105 m3 s to 1 3 106 m3 s geographic information systems gis and high resolution digital elevation models dem were used to map streamlined landforms and channel systems in front of lake overspills geological maps 2450 boreholes and the dem were integrated into the 3d modeling program gocad to reconstruct the distribution of flood related deposits palaeotopographic surfaces and the internal facies architecture of streamlined hills the drainage pathways are characterized by the occurrence of deep plunge pools channels streamlined hills and 4 km long and 12 m deep v shaped megaflutes plunge pools are deeply incised into mesozoic basement rocks and occur in front of three major overspill channels the plunge pools are up to 780 m long 400 m wide and 35 m deep approximately 1 10 5 km downslope of the overspill channels fan shaped arrays of streamlined hills are developed each covering an area of 60 130 km2 indicating rapid flow expansion the hills commonly have quadrilateral to elongated shapes and formed under submerged to partly submerged flow conditions when the outburst flood entered a shallow lake in the munsterland embayment hills are up to 4300 m long 1200 m wide 11 m high and have characteristic average aspect ratios of 1 3 3 they are separated by shallow anabranching channels in the outer zones and up to 30 m deep channels in the central zones hills partly display v shaped chevron like bedforms that have apices facing upslope are 1 6 2 5 km long 3 10 m high 0 8 1 2 m from limb to limb with limb separation angels of 20 35 these bedforms are interpreted as mixed erosional depositional features it is hypothesized that the post saalian landscape evolution of the munsterland embayment has considerably been influenced by catastrophic floods of glacial lake weser creating large and deep valleys which subsequently became the new site of river systems the outburst floods probably followed the east west trending saalian rhine meuse river system eventually flowing into the north sea the strait of dover and the bay of biscay it is speculated that the hondsrug ice stream may have been enhanced or even triggered by the formation and outburst of glacial lakes in the study area

a methodology to reconstruct small and short lived ice dammed lakes in the appalachians of southern quebec abstract previous studies on the deglaciation of the appalachians of southern quebec reconstructed only the most extensive ice dammed lakes and the most stable glaciolacustrine water levels they only used the best developed shoreline features and thus were not able to reconstruct small or short lived ice dammed lakes both being characterized by a weak development of their features we propose a methodology to reconstruct glacial lakes which follows three main steps 1 the mapping of shoreline features generally the best developed ones as in previous studies 2 the delineation of the former shoreline for each water level by also considering the less well developed shoreline features which were found during field surveys designed as a function of the presumed shoreline position and 3 the mapping of the maximum extension of the water plane which includes the location of the former ice dam and of the former glacial lake spillway in southern quebec small ice dammed lakes were numerous and important because they shaped the geomorphology of the region during the deglaciation they are thus among the key components of a deglaciation model for this area

origin of the nchanga copper cobalt deposits of the zambian copperbelt the zambian copperbelt forms the southeastern part of the 900 km long neoproterozoic lufilian arc and contains one of the world s largest accumulations of sediment hosted stratiform copper mineralization the nchanga deposit is one of the most significant ore systems in the zambian copperbelt and contains two major economic concentrations of copper and cobalt hosted within the lower roan group of the katangan supergroup a lower orebody copper only and upper orebody copper and cobalt occur towards the top of arkosic units and within the base of overlying shales the sulfide mineralogy includes pyrite bornite chalcopyrite and chalcocite although in the lower orebody sulfide phases are partially or completely replaced by malachite and copper oxides carrollite is the major cobalt bearing phase and is restricted to fault propagation fold zones within a feldspathic arenite hydrothermal alteration minerals include dolomite phlogophite sericite rutile quartz tourmaline and chlorite quartz veins from the mine sequence show halite saturated fluid inclusions ranging from 31 to 38 wt equivalent nacl with homogenisation temperatures thtot ranging between 140 and 180 c diagenetic pyrites in the lower orebody show distinct relatively low 34s ranging from 1 to 17 whereas arenite and shale hosted copper and cobalt sulfides reveal distinctly different 34s from 1 to 12 for the lower orebody and 5 to 18 for the upper orebody there is also a clear distinction between the 34s mean of 12 1 3 3 n 65 for the upper orebody compared with 5 2 3 6 n 23 for the lower orebody the 13c of dolomites from units above the upper orebody give 13c values of 1 4 to 2 5 consistent with marine carbon however dolomite from the shear zones and the alteration assemblages within the upper orebody show more negative 13c values 2 9 to 4 0 and 5 6 to 8 3 respectively similarly shear zone and upper orebody dolomites give a 18o of 11 7 to 16 9 compared to lower roan dolomites which show 18o of 22 4 to 23 0 two distinct structural regimes are recognized in the nchanga area a weakly deformed zone consisting of basement and overlying footwall siliciclastics and a moderate to tightly folded zone of meta sediments of the katangan succession the fold geometry of the lower roan package is controlled by internal thrust fault propagation folds which detach at the top of the lowermost arkose or within the base of the overlying stratigraphy and show vergence towards the ne faulting and folding are considered to be synchronous as folding predominantly occurred at the tips of propagating thrust faults with local thrust breakthrough the data from nchanga suggests a strong link between ore formation and the development of structures during basin inversion as part of the lufilian orogeny sulfides tend to be concentrated within arenites or coarser grained layers within shale units suggesting that host rock porosity and possibly permeability played a role in ore formation however sulfides are also commonly orientated along but not deformed by a tectonic fabric or hosted within small fractures that suggest a significant role for deformation in the development of the mineralization the ore mineralogy hydrothermal alteration and stable isotope data lend support to models consistent with the thermochemical reduction of a sulfate and metal enriched hydrothermal fluid at the site of mineralization there is no evidence at nchanga for a contribution of bacteriogenic sulfide produced during sedimentation or early diagenesis to the ores

landform characterization using geophysics recent advances applications and emerging tools abstract this paper presents an overview of the strengths and limitations of existing and emerging geophysical tools for landform studies the objectives are to discuss recent technical developments and to provide a review of relevant recent literature with a focus on propagating field methods with terrestrial applications for various methods in this category including ground penetrating radar gpr electrical resistivity er seismics and electromagnetic em induction the technical backgrounds are introduced followed by section on novel developments relevant to landform characterization for several decades gpr has been popular for characterization of the shallow subsurface and in particular sedimentary systems novel developments in gpr include the use of multi offset systems to improve signal to noise ratios and data collection efficiency amongst others and the increased use of 3d data multi electrode er systems have become popular in recent years as they allow for relatively fast and detailed mapping novel developments include time lapse monitoring of dynamic processes as well as the use of capacitively coupled systems for fast non invasive surveys em induction methods are especially popular for fast mapping of spatial variation but can also be used to obtain information on the vertical variation in subsurface electrical conductivity in recent years several examples of the use of plane wave em for characterization of landforms have been published seismic methods for landform characterization include seismic reflection and refraction techniques and the use of surface waves a recent development is the use of passive sensing approaches the use of multiple geophysical methods which can benefit from the sensitivity to different subsurface parameters is becoming more common strategies for coupled and joint inversion of complementary datasets will once more widely available benefit the geophysical study of landforms three cases studies are presented on the use of electrical and gpr methods for characterization of landforms in the range of meters to 100 s of meters in dimension in a study of polygonal patterned ground in the saginaw lowlands michigan usa electrical resistivity tomography was used to characterize differences in subsurface texture and water content associated with polygon swale topography also a sand filled thermokarst feature was identified using electrical resistivity data the second example is on the use of constant spread traversing cst for characterization of large scale glaciotectonic deformation in the ludington ridge michigan multiple cst surveys parallel to an 60 m high cliff where broad 100 m synclines and narrow clay rich anticlines are visible illustrated that at least one of the narrow structures extended inland a third case study discusses internal structures of an eolian dune on a coastal spit in new zealand both 35 and 200 mhz gpr data which clearly identified a paleosol and internal sedimentary structures of the dune were used to improve understanding of the development of the dune which may shed light on paleo wind directions

erosion and deposition by supercritical density flows during channel avulsion and backfilling field examples from coarse grained deepwater channel levee complexes sandino forearc basin southern central america abstract erosion and deposition by supercritical density flows can strongly impact the facies distribution and architecture of submarine fans field examples from coarse grained channel levee complexes from the sandino forearc basin southern central america show that cyclic step and antidune deposits represent common sedimentary facies of these depositional systems and relate to the different stages of avulsion bypass levee construction and channel backfilling during channel avulsion large scale scour fill complexes 18 to 29 m deep 18 to 25 m wide 60 to 120 m long were incised by supercritical density flows the multi storey infill of the large scale scour fill complexes comprises amalgamated massive normally coarse tail graded or widely spaced subhorizontally stratified conglomerates and pebbly sandstones interpreted as deposits of the hydraulic jump zone of cyclic steps the large scale scour fill complexes can be distinguished from small scale channel fills based on the preservation of a steep upper margin and a coarse grained infill comprising mainly amalgamated hydraulic jump zone deposits channel fills include repeated successions deposited by cyclic steps with superimposed antidunes the deposits of the hydraulic jump zone of cyclic steps comprise regularly spaced scours 0 2 to 2 6 m deep 0 8 to 23 m long infilled by intraclast rich conglomerates or pebbly sandstones displaying normal coarse tail grading or backsets these deposits are laterally and vertically associated with subhorizontally stratified low angle cross stratified or sinusoidally stratified sandstones and pebbly sandstones which were deposited by antidunes on the stoss side of the cyclic steps during flow re acceleration the field examples indicate that so called spaced stratified deposits may commonly represent antidune deposits with varying stratification styles controlled by the aggradation rate grain size distribution and amalgamation the deposits of small scale cyclic steps with superimposed antidunes form fining upwards successions with decreasing antidune wavelengths indicating waning flows such cyclic step antidune successions form the characteristic basal infill of mid fan channels and are inferred to be related to successive supercritical high density turbidity flows triggered by retrogressive slope failures

impact of middle pleistocene saalian glacial lake outburst floods on the meltwater drainage pathways in northern central europe insights from 2d numerical flood simulation abstract the terrestrial margins of the middle pleistocene ice sheets in northern central europe were characterised by the formation of extensive ice dammed lakes which were controlled by the blockage of spillways by the ice margin the largest ice dammed lake had a volume of 224 km and formed in a late stage of the first saalian ice advance mis 6 in central germany the failure of the ice dam in the bedrock outlet channel triggered a major glacial lake outburst flood flood related erosional and depositional features include large scale scours trench like channels streamlined hills giant bars and run up deposits indicating a wide spreading of the outburst flood in an early stage and the incision of trench like valleys in a later stage the incision of large valleys in the proximal flood pathway strongly impacted the regional drainage system by providing an efficient drainage network the trench like channels initiated by the lake outburst flood became a crucial part of the ice marginal drainage and subsequent fluvial system the reconstructed outlet hydrographs imply peak discharges of 465 000 673 000 m s 1 the numerical simulation indicates flow depths of up to 87 m flow velocities of up to 7 ms 1 peaks of the bed shear stress of 2500 nm 2 and the inundation of large parts of northwestern germany and the northern netherlands the numerical simulation of the outburst flood was conducted on both the modern digital elevation model and on palaeotopographic models representing the palaeotopography prior to the outburst flood and during maximum flood related incision respectively distally the outburst flood probably followed an east west trending route through northwestern germany and the central netherlands into the ice dammed lake in the southern north sea basin the added water volume might have led to the overspill and drainage of the proglacial lakes in the central netherlands and the north sea lake in a chain reaction eventually opening an east west trending meltwater drainage pathway along the southwestern margin of the decaying ice sheet

iceberg drop dump and grounding structures from pleistocene glacio lacustrine sediments scotland abstract dropstone dump and grounding structures resulting from the melt out of debris contained in floating and grounded icebergs are described from a pleistocene ice marginal glacio lacustrine sequence in scotland dropstones display bending penetration rucking and complete rupture of stratum occurring beneath them and onlap above them with the degree of deformation varying as a function of the size shape and axial disposition of the clast and of the sediment type into which they fell dump structures are conical mounds of gravel or diamict formed by the break up and overturning of dirt laden icebergs and the consequent release of large quantities of debris to the lake floor grounding structures are caused by the grounding of icebergs the down warping of underlying lake floor se iment and the subsequent in situ melt out of contained debris to form isolated troughs of diamict

sediment rich meltwater plumes and ice proximal fans at the margins of modern and ancient tidewater glaciers observations and modelling turbid meltwater plumes and ice proximal fans occur where subglacial streams reach the grounded marine margins of modern and ancient tidewater glaciers however the spacing and temporal stability of these subglacial channels is poorly understood this has significant implications for understanding the geometry and distribution of quaternary and ancient ice proximal fans that can form important aquifers and hydrocarbon reservoirs remote sensing and numerical modelling techniques are applied to the 200 km long marine margin of a svalbard ice cap austfonna to quantify turbid meltwater plume distribution and predict its temporal stability results are combined with observations from geophysical data close to the modern ice front to refine existing depositional models for ice proximal fans plumes are spaced ca 3 km apart and their distribution along the ice front is stable over decades numerical modelling also predicts the drainage pattern and meltwater discharge beneath the ice cap modelled water routing patterns are in reasonable agreement with satellite mapped plume locations however glacial retreat of several kilometres over the past 40 years has limited build up of significant ice proximal fans a single fan and moraine ridge is noted from marine geophysical surveys closer to the ice front there are smaller recessional moraines and polygonal sediment lobes but no identifiable fans schematic models of ice proximal deposits represent varying glacier terminus stability i stable terminus where meltwater sedimentation produces an ice proximal fan ii quasi stable terminus where glacier readvance pushes or thrusts up ice proximal deposits into a morainal bank and iii retreating terminus with short still stands allowing only small sediment lobes to build up at melt stream portals these modern investigations are complemented with outcrop and subsurface observations and numerical modelling of an ancient ordovician glacial system thick turbidite successions and large fans in the late ordovician suggest either high magnitude events or sustained high discharge consistent with a relatively mild palaeo glacial setting for the former north african ice sheet

glacimarine processes at grounding line fans and their growth to ice contact deltas abstract grounding line fans originate from subglacial and basal stream tunnels at grounding lines of glaciers terminating in a marine environment during melt seasons discharge forms a turbulent jet beyond the efflux over the initial zone of flow establishment in the jet it may remain in contact with the sea floor for up to 13 4 d d tunnel diameter along a runout distance if velocity is constant plug flow in this zone deposits marine outwash sediment commonly having chaotic texture and graded and welded contacts texture may vary rapidly because of discharge pulses and the jet may move laterally to produce sheet or cut and fill geometries imbricate gravel is deposited near the efflux then farther out are sheet or weakly channelized finer grained gravels and sands in some instances a migrating barchanoid bar forms at the detachment zone and forms large scale trough cross beds beyond the detachment zone the turbulent jet becomes vertical and sediment cascades from it in a veil this sediment is added to by flows from continuous failures of bed load sediment in the detachment zone resulting deposits are interstratified sediment gravity flows and thick coarse end members of cyclopsams the jet changes to a plume when inertial forces become less than buoyancy forces turbulent vorticies within the jet can re entrain particles into a buoyant plume the plume remains vertical although continuously spreading until reaching neutral buoyancy fan depocentres have been observed to accumulate at over 10 6 m 3 a 1 in temperate glacial areas eventually at quasi stable grounding lines fans may aggrade to sea level to form ice contact deltas at incipient deltas when the delta plain is intertidal coarse sediment is redistributed to the prodelta with each tidal cycle intense prodelta rhythmites mark the transition of a fan into a delta

observed patterns of month to month storm track variability and their relationship to the background flow month to month storm track variability is investigated via eof analyses performed on era 40 monthlyaveraged high pass filtered daily 850 hpa meridional heat flux and the variances of 300 hpa meridional wind and 500 hpa height the analysis is performed both in hemispheric and sectoral domains of the northern and southern hemispheres patterns characterized as pulsing and latitudinal shifting of the climatologicalmean storm tracks emerge as the leading sectoral patterns of variability based on the analysis presented storm track variability on the spatial scale of the two northern hemisphere sectors appears to be largely but perhaps not completely independent pulsing and latitudinally shifting storm tracks are accompanied by zonal wind anomalies consistent with eddy forced accelerations and geopotential height anomalies that project strongly on the dominant patterns of geopotential height variability the north atlantic oscillation nao northern hemisphere annular mode nam is associated with a pulsing of the atlantic storm track and a meridional displacement of the upper tropospheric jet exit region whereas the eastern atlantic ea pattern is associated with a latitudinally shifting storm track and an extension or retraction of the upper tropospheric jet analogous patterns of stormtrack and upper tropospheric jet variability are associated with the western pacific wp and pacific north america pna patterns wave mean flow relationships shown here are more clearly defined than in previous studies and are shown to extend through the depth of the troposphere the southern hemisphere annular mode sam is associated with a latitudinally shifting storm track over the south atlantic and indian oceans and a pulsing south pacific storm track the patterns of storm track variability are shown to be related to simple distortions of the climatological mean upper tropospheric jet

synrift stratigraphic geometry in a transfer zone coarse grained delta complex miocene pohang basin se korea the gojusan fan delta is a coarse grained delta complex on the western margin of the miocene pohang basin se korea the deposits consist of five facies associations fa alluvial fan conglomerates fa i shallow marine mouthbar sandstones fa ii fluvial and mouth bar conglomerates fa iii gilberttype foreset conglomerates fa iv and hemipelagic mudstones fa v different facies associations characterize the northern central and southern parts of the delta complex to the north fa iv is laterally juxtaposed with fa i or the basement with scarp derived breccias along the contact centrally and to the south fa i is laterally juxtaposed with fa ii with an abrupt facies change and local inliers of basement rocks along the contact early alluvial fan and mouth bar deposits are overlain by the topset fa iii and truncated by the foreset fa iv of a gilbert type delta in the central part of the fan delta complex whereas fa ii passes transitionally upward into fa iii in the south with the latter extending basinward into a gently inclined shoal water delta front gilbert type and shoal water geometries are therefore developed in the same delta complex the composite delta geometry is interpreted as reflecting 1 its development near an extensional transfer zone where the hangingwall relief was variable over short distances along strike and 2 the operation of intrabasinal faults this interpretation contrasts with previous studies that viewed the delta complex as having formed along a pull apart basin margin

polymetallic mineralization at the browns deposit rum jungle mineral field northern territory australia the rum jungle mineral field northern territory australia forms part of the paleoproterozoic pine creek orogen the geology of the area comprises two archean granitic basement domes overlain by a paleoproterozoic sequence of metasedimentary and subordinate metavolcanic rocks the rocks have been deformed and metamorphosed to greenschist facies during the 1880 ma barramundi orogeny but the original stratigraphic succession has been preserved the browns deposit browns and its extension browns east hosted within black carbonaceous pelites of the paleoproterozoic whites formation is the largest base metal deposit found to date in the pine creek orogen present resource estimates are 39 million metric tons mt at 0 44 percent cu 3 61 percent pb 0 11 percent co and 0 09 percent ni browns and 31 mt at 1 29 percent cu 1 28 percent pb 0 13 percent co and 0 13 percent ni browns east major sulfide minerals in the ore zone are galena sphalerite chalcopyrite pyrite and the main carrier of ni and co siegenite ni co 3 s 4 digenite group minerals and bornite ca bearing plumbogummite pbal 3 po 4 2 oh 5 h 2 o arsenopyrite and gersdorffite are present in minor quantities ore minerals occur as fine grained wisps parallel to the main bedding parallel foliation and as coarse grained mono and polyminerallic aggregates that crosscut the foliation total noncarbonate carbon contents of unaltered rocks range from 1 07 to 7 51 wt percent total sulfur contents range from 2 13 to 6 14 wt percent petrographic studies and raman spectroscopy identify three varieties of carbonaceous matter primary syngenetic premetamorphic epigenetic grain coating and postmetamorphic epigenetic uraniferous migrated altered rocks are rarely encountered values of 34 s for sulfides range from 5 to 15 per mil and are interpreted to reflect a combination of inorganic thermochemical reduction of seawater and bacterial activity no specific sulfur isotope patterns for individual minerals can be established indicating nonequilibrium conditions homogeneous lead isotope signatures of galena 206 pb 204 pb 16 20 16 22 207 pb 206 pb 15 48 15 51 208 pb 207 pb 35 86 35 92 suggest that all pb was derived from a single crustal source and paragenetically late crosscutting galena appears to have been remobilized from bedding parallel galena despite the occurrence of uranium in similar rocks nearby uranium is quantitatively insignificant in the browns deposit and is not genetically related to base metal mineralization instead it is linked to brittle deformation in the waning stages of orogenesis the browns deposit differs from other well known sediment hosted stratiform ore deposits both the zambian copperbelt and the polish kupferschiefer deposits are copper dominant and hosted in sedimentary sequences with significant psammitic components the pb zn ag deposits of the proterozoic australian zinc province also have significant carbonate in their host rocks e g carbonaceous dolomitic and siltstone at mcarthur river and lack economically interesting cu co and ni the nearby woodcutters pb zn ag deposit in rocks of similar age also differs in structural setting veins dominant metals and pb isotopes from the browns deposit

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

mineralization controls and source of metals in the lufilian fold belt shaba zaire zambia and angola the pan african lufilian fold belt hosts extensive and rich polymetallic mineralization dominated by cu co and zn pb sulfides u oxides and noble metals stratiform vein and skarn deposits are present in the late proterozoic rocks of the katangan supergroup mineralization is regionally widespread the sedimentary basin evolution included three phases the first two characterized by rift fault controlled rapid subsidence followed by slower thermal subsidence were associated with bimodal magmatism and probably related to two thermal events the third phase reflects the onset of tectonic deformation and uplift in the southern part of the basin the stratiform mineralization emplaced before the folding of the basin is concentrated in lithologically varied permeable rocks of the roan group that underlie the impermeable rocks of the lower kundelungu group the stratiform mineralization was emplaced by convective circulation of basinal brines forced by a thermal gradient created by a wedge shaped lithosome of lower kundelungu pelitic rocks with low thermal conductivity hypabyssal igneous intrusions and volcanic and volcaniclastic rocks were the source of metals the metals were introduced to the aquifer horizons saturated with basinal brines by hydrothermal circulation associated with the hypabyssal intrusions and by compactional dewatering of a 5 000 m thick body of pelitic rocks rich in volcaniclastic material vein mineralization located on major late faults resulted from regional metamorphism driven dewatering of the folded basin the skarn metasomatic mineralization is associated with small post katangan acid intrusions and blocks of thermally rejuvenated basement details of the distribution of mineralization are stratigraphically and structurally controlled

deglaciation lake levels and meltwater discharge in the lake michigan basin abstract the deglacial history of the lake michigan basin including discharge and routing of meltwater is complex because of the interaction among 1 glacial retreats and re advances in the basin 2 the timing of occupation and the isostatic adjustment of lake outlets and 3 the depositional and erosional processes that left evidence of past lake levels in the southern part of the basin a restricted area little affected by differential isostasy new studies of onshore and offshore areas allow refinement of a lake level history that has evolved over 100 years important new data include the recognition of two periods of influx of meltwater from lake agassiz into the basin and details of the highstands gleaned from sedimentological evidence major disagreements still persist concerning the exact timing and lake level changes associated with the algonquin phase approximately 11 000 bp a wide variety of independent data suggests that the lake michigan lobe was thin unstable and subject to rapid advances and retreats consequently lake level changes were commonly abrupt and stable shorelines were short lived the long held beliefs that the southern part of the basin was stable and separated from deformed northern areas by a hinge line discontinuity are becoming difficult to maintain numerical modeling of the ice earth system and empirical modeling of shoreline deformation are both consistent with observed shoreline tilting in the north and with the amount and pattern of modern deformation shown by lake level gauges new studies of subaerial lacustrine features suggest the presence of deformed shorelines higher than those originally ascribed to the supposed horizontal glenwood level finally the lake michigan region as a whole appears to behave in a similar manner to other areas both local other great lakes and regional u s east coast that have experienced major isostatic changes detailed sedimentological and dating studies of field sites and additional development of geophysical models offer hope for reconciling the field data with our understanding of earth rheology

effects of mass wasting on the stratigraphic architecture of a fjord valley fill correlation of onshore shear wave seismic and marine seismic data at trondheim norway abstract a combined record of onshore high resolution shear wave seismic and marine p wave seismic data shows the near shore stratigraphic organisation of a fjord valley fill at trondheim central norway the overall stratigraphy shows a typical fjord valley fill of up to 160 m in thickness that is composed of glaciomarine and fjord marine sediments overlain by deltaic deposits which in the onshore section are draped by an anthropogenic fill an interval characterised by low shear wave velocities below the onshore anthropogenic fills is shown by sampled drillings to comprise part clay and part organic deposits the seismic record reveals evidence of recurrent mass wasting events that include landslide debris turbidite deposits and channel features a chronological framework for the stratigraphy is provided by existing radiocarbon dates for local deglaciation and mass wasting events the combined onshore offshore datasets document the lateglacial to holocene development of an emerging fjord and delta system affected by major mass wasting events the architectural development of the younger part of the stratigraphy is interpreted as particularly affected by two known mass wasting events each involving several million m 3 of debris a thick layer of debris from a 3500 cal yr event probably resulted in a blockage of the subaqueous channels diversion of turbidity currents and deposition of lateral accretion packages whereby local fjord sedimentation temporarily increased a 2200 cal yr event resulted in a sudden reorganisation of the distributary system whereby distal delta sedimentation abruptly shifted north to northeastwards to an area temporarily subjected to marine erosion during fall of relative sea level the study adds to the understanding of landslides and low stiffness zones in the area of importance for near shore geohazard assessment the study also provides insight into the stratigraphic variability of fjord valley fills and highlights the interplay between fjord marine sedimentation marine abrasion delta progradation and mass wasting during late stages of fjord filling

macroforms large bedforms and rhythmic sedimentary sequences in subglacial eskers south central ontario implications for esker genesis and meltwater regime abstract eskers of south central ontario were deposited in closed subglacial conduits which were continuous main conduits this interpretation is supported by the intimate association of eskers with an anastomosing network of tunnel channels relatively continuous esker ridges minimal post formational disturbance of esker sediments intercalation of till and stratified sand and gravel diapiric folding at an esker core low variability in palaeocurrent direction and upslope flow paths down esker trends in clast lithology roundness and sphericity indicate continuous conduits with sediment supply by subglacial deformation of adjacent material into the conduits melt out of sediment from the conduit walls and fluvial resedimentation esker ridge morphology is attributed to synchronous erosion transportation and deposition along the main conduits such that ridge discontinuities are primarily explained as zones of non deposition during esker formation composite pseudoanticlinal and oblique accretion avalanche bed macroforms are identified gravel facies within these macroforms were deposited from fluidal flows or hyperconcentrated dispersions progradation of macroforms or migration of constituent large bedforms through the main conduits may have temporarily blocked constricted portions of those conduits and acted as possible internal autogenic controls on sediment availability and flow resistance the location of macroforms within conduits was primarily controlled by conduit geometry and sediment availability and later by feedback between macroform and conduit geometries sand and gravel units alternate rhythmically in vertical section rhythmicity is interpreted as a response to episodic flood flows controlled by seasonal changes in water supply but not necessarily representing annual events fans beads anabranched reaches and extended hummocky deposits are intimately associated with the main esker ridges they are interpreted in terms of subglacial cavities and localized flotation zones connected to the main conduits during flood events in phase wave structures are the products of hydraulic jumps in hyperconcentrated flood flows at flow expansions into swells within the main conduits into cavities connected to the main conduits or at a grounding line esker ridges record only the most powerful flood events whereas fans and beads record flow events in finer detail being primarily depositional reservoirs laterally fining deposits record the waning stages of conduit operation

asynchronous glacier dynamics during the antarctic cold reversal in central patagonia abstract we present 14 new 10be cosmogenic nuclide exposure ages quantifying asynchronous readvances during the antarctic cold reversal from glaciers in the baker valley region of central patagonia we constrain glacier and ice dammed palaeolake dynamics using a landsystems approach concentrating on outlet glaciers from the eastern northern patagonian icefield npi and monte san lorenzo msl soler glacier npi produced lateral moraines above lago bertrand from 15 1 0 7 to 14 0 0 6 ka when it dammed the drainage of lago general carrera buenos aires through rio baker at a bedrock pinning point at this time soler glacier terminated into the 400 m deseado level of the ice dammed palaeolake later calluqueo glacier msl deposited subaerial and subaqueous moraines in the salto valley near cochrane at 13 0 0 6 ka these moraines were deposited in an ice dammed palaeolake unified through the baker valley lago chalenko 350 m asl the salto valley glaciolacustrine landsystem includes subaqueous morainal banks ice scoured bedrock glacial diamicton plastered onto valley sides perched delta terraces kame terraces ice contact fans palaeoshorelines and subaerial push and lateral moraines boulders from the subaqueous salto moraine became exposed at 12 1 0 6 years indicating palaeolake drainage these data show an asynchronous advance of outlet glaciers from the northern patagonian icefield and monte san lorenzo during the antarctic cold reversal these advances occurred during a period of regional climatic cooling but differential moraine extent and timing of advance was controlled by topography and calving processes

occurrence of hyperpycnal flows and hybrid event beds related to glacial outburst events in a late ordovician proglacial delta murzuq basin sw libya abstract a late ordovician glacially related delta is documented based on architecture and facies from outcrops in the western murzuq basin libya sandstone megabeds highlight clinoform geometries of a proglacial low angle shallow water delta the progradational wedge extends over 25 km from the sse to the nnw and is about 100 m thick two types of clinothems have been distinguished and eleven facies sequences are characterized in relation with their along slope positions sand prone facies sequences in type 1 clinothems relate to high magnitude low frequency glacial outburst floods generating a freshwater highly concentrated plunging hyperpycnal flow at the river mouth during the waxing stage the slope adjustment of an out of grade profile causes significant erosion the resulting additional sediment charge involves along foresets a downslope flow transformation into a co genetic sandy debris flow and high density turbidity flow hybrid event beds including linked debrites and turbidites are the resulting deposits in the lower slope decreasing sediment concentration of the high density turbidity flow leads to sediment lofting and to a second flow transformation resulting in a lower density turbidity flow and a concomitant rising sediment plume deposition results in crude ripple cross stratification debrite deposition is temporally restricted to an early segment of the rising limb of the flood hydrograph during the ensuing waxing stage uninterrupted sustained flow conditions maintain up to the peak flow permitting the aggradation of thick sandstone successions with crude ripple cross stratification during the waning stage backstepping of the whole depositional system leads to prevailing sedimentation in the delta plain setting mouth bar development and channel plugs are characterized by climbing dune cross stratification cdcs shale prone sedimentation in type 2 clinothems essentially corresponds to background ablation related sedimentation but also includes minor debrite bearing outburst related event beds this study documents the links between glacial outbursts hyperpycnal flows and hybrid beds in low angle delta settings and illustrates a type of proximal sand dominated hyperpycnite dam failure of subglacial lakes is inferred for the outburst generation comparison with modern and pleistocene examples may suggest that outburst events were days to several years in duration type 1 clinothem with a 1 40 ky recurrence period type 2 clinothem

deposition in an esker bead and fan complex lanark ontario canada abstract a glaciofluvial landform complex comprising a single esker ridge proximally multiple ridges and beads in the middle section and a complex of ridges and fans distally is mapped and described we present detailed successions in the associated sediment showing sedimentary structure grain size and palaeocurrent estimates sediment in the esker is mainly coarse grained and varies from boulders with a fine sand matrix deposited at maximum discharges to diamicton interpreted as a product of ice pressing under low discharges early stage deposition in the esker at high flow was from suspension and bed load intermediate stage deposition was mainly from bed load and late stage deposition was from hyperconcentrated suspension the esker rests in a bedrock channel which functioned as a nye channel prior to esker formation the channel surface carries a variety of fluvial erosional marks short distributary ridges of the ridges and beads complex contain mainly cobbles and boulders but beads are mainly in sand with rapid down flow fining and change in sedimentary structure faulting and overfolding of bead sediment suggest a subglacial origin deposition of the esker fan complex was highly variable in space and time down fan sedimentary changes with transitions from gravel to cross laminated fine sand in a few tens of metres indicate rapid loss in competence fan location lateral to the esker indicates a broadening of the zone of subglacial meltwater with time deposition from suspension and steep sided scours are interpreted to result from deposition and erosion by hyperconcentrated flows a model of underflows with submerged hydraulic jumps spilling laterally from the esker tunnel into subglacial cavities explains the morphological and sedimentary characteristics of the fans detailed analysis of small scale fining upwards sequences in the fans and beads indicates deposition by a large number of flow events these events are explained by glacier hydraulics whereby periodic separation of the glacier from its bed caused water with a high suspended sediment concentration to spill out from the esker tunnel into adjacent subglacial cavities evolution of the subglacial drainage system indicates a complexity of subglacial sedimentation near to a grounding line which is not readily apparent from observations at modern glaciers terminating in relatively deep water

sedimentary facies and depositional architecture of ice contact glaciomarine systems abstract the characteristics of ice contact glaciomarine systems are reviewed based on a range of weichselian and holocene examples from the fjordal basins in norway and svalbard these depositional systems occur as large morphological ridges end moraines including push moraines which are coarse grained and show large scale foreset bedding the paper addresses some of the major problems with regard to the recognition classification and stratigraphic analysis of these systems the ice proximal glaciomarine systems are classified here into three categories 1 ice contact submarine fans 2 ice contact deltas and 3 glaciofluvial deltas this classification integrates morphological and sedimentological criteria and renders these glaciomarine systems not only easier to recognize in the stratigraphic record but also possible to compare with common non glacial deltaic systems the emphasis is on the criteria for the recognition of the ice contact glaciomarine systems i e ice contact fans and ice contact deltas and their discrimination from common gilbert type deltas and fan deltas the review further focuses on ice contact glaciomarine systems as highly sensitive recorders of glacier dynamics and climatic fluctuations it is shown that both the periods of ice front stability and changes in the ice front position as well as the magnitude and rate of those changes are all recorded in the ice contact depositional system the sedimentary record further reflects glacio isostatic sea level changes and local palaeogeography a new conceptual model is suggested which places these ice contact glaciomarine systems in a dynamic stratigraphic context the model integrates sedimentary facies and their depositional architecture in an allostratigraphic framework and is meant to be a guide for the analysis of the sedimentary record of ice contact systems

lateral and vertical facies relationships of bedforms deposited by aggrading supercritical flows from cyclic steps to humpback dunes abstract the preservation of bedforms related to supercritical flows and hydraulic jumps is commonly considered to be rare in the geologic record although these bedforms are known from a variety of depositional environments this field based study presents a detailed analysis of the sedimentary facies and stacking pattern of deposits of cyclic steps chutes and pools antidunes and humpback dunes from three dimensional outcrops the well exposed middle pleistocene successions from northern germany comprise glacilacustrine ice contact subaqueous fan and glacial lake outburst flood deposits the studied successions give new insights into the depositional architecture of bedforms related to supercritical flows and may serve as an analogue for other high energy depositional environments such as fluvial settings coarse grained deltas or turbidite systems deposits of cyclic steps occur within the glacial lake outburst flood succession and are characterised by lenticular scours infilled by gently to steeply dipping backsets cyclic steps formed due to acceleration and flow thinning when the glacial lake outburst flood spilled over a push moraine ridge these bedforms are commonly laterally and vertically truncated and alternate with deposits of chutes and pools and antidunes the subaqueous fan successions are dominated by laterally extensive sinusoidal waveforms which are interpreted as deposits of aggrading stationary antidunes which require quasi steady flows at the lower limit of the supercritical flow stage and high rates of sedimentation humpback dunes are characterised by downflow divergent cross stratification displaying differentiation into topsets foresets and bottomsets and are interpreted as deposited at the transition from subcritical to supercritical flow conditions or vice versa gradual lateral and vertical transitions between humpback dunes and antidune deposits are very common the absence of planar parallel stratification in all studied successions suggests that the formation of these bedforms is suppressed in flows characterised by hydraulic jumps under highly aggradational conditions the large scale lateral and vertical successions of bedforms are interpreted as representing the temporal and spatial evolution of the initial supercritical flows which was strongly affected by the occurrence of hydraulic jumps small scale facies changes and the formation of individual bedforms are interpreted as controlled by fluctuating discharge bed topography and pulsating unstable flows

channelized sandstone bodies cordons in the tassili n ajjer algeria libya snapshots of a late ordovician proglacial outwash plain

sequence analysis of early saalian glacial lake deposits nw germany evidence of local ice margin retreat and associated calving processes abstract this paper presents a detailed analysis of high resolution facies architecture of glaciolacustrine ice margin deposits which formed at the southern margin of the scandinavian ice shield the ice margin depositional systems are characterised by coarse grained deltas and subaqueous fans which are formed by stacked transgressive regressive sequences recording an overall lake transgression interrupted by minor short term lake level falls the delta complexes at the northern margin of glacial lake rinteln are thought to reflect a relatively stable position of the ice margin in front of the weser chains mountain ridges the onset of delta progradation probably represents a halt in ice advance and a related high sediment supply period the sedimentary facies and depositional architecture resemble those of nonglacial gilbert type deltas except for the deposition of glacial debris the main delta progradation is recorded from the highstand systems tract when high meltwater and sediment discharge occurred during the melt season a forced regression during opening of outlets led to the formation of subaerially exposed sequence boundaries and the erosion of the highstand systems tract deeply incised channels incised valleys were filled during the subsequent transgression at the eastern lake margin subaqueous fan deposits reflect an unstable ice front that was rapidly retreating and subject to periodic calving which resulted in the generation of floating icebergs dumping ice rafted debris and ploughing into subaqueous fan deposits the rapid retreat of this eastern ice margin is interpreted to result from the overall lake level rise the fan stacking pattern and bulk geometry were determined by the ice front fluctuations the shifting of meltwater outlets and the short term lake level fluctuations depositional processes reflect the character of sediment supply and distance from the ice margin ice proximal upper fan deposits are characterised by coarse grained gravel deposited by debris flows that document continuous discharge slump and slide deposits are related to steep depositional slopes the mid fan contains basinward fining and thinning deposits of quasi steady and surge type high and low density turbidity currents indicating more ice distal and periodic deposition the outer fan deposits mainly consist of surge type low density turbidites and glacial debris dumped by icebergs the forcing parameters governing the development of depositional sequences in both delta and fan settings were lake level fluctuations sediment yield rates and physiography the depositional sequences were deposited on a time scale of seventh and eighth order high frequency cycles 101 102 years in this short time span lake level fluctuations were on the order of 120 m therefore accommodation space was largely controlled by lake level and subsidence can be ignored

three dimensional numerical modeling of deltaic depositional sequences 1 influence of the rate and magnitude of sea level change abstract a three dimensional numerical model of deltaic deposition is used to investigate the influence of sea level changes on delta development and sequence variability results illustrate the three dimensional morphology of key stratal surfaces and architecture of stratal units systems tracts and highlight the importance of the rate and magnitude of sea level change in controlling the evolution of deltaic depositional sequences high rates of sea level fall lead to the development of a limited number of major incised channels that focus sediment supply to a few elongate finger like forced regressive lobes separated by large areas of nondeposition in contrast low rates of sea level fall cause only minor channel incision which occurs late during sea level fall as a result sediment is supplied more uniformly to the delta front leading to an attached laterally continuous forced regressive apron during lowstand and subsequent sea level rise the delta morphology and internal geometry are strongly controlled by the rate of rise high rates lead to i poorly developed lowstand wedges that are drowned early ii high magnitude transgressions and iii the late development of maximum flooding surfaces the stratigraphy developed during sea level rise is also strongly influenced by the incised valley system created during the preceding sea level fall if deep major valleys developed that captured most of the sediment supply the resultant stratigraphy has well developed lowstand wedges that are flooded relatively late during sea level rise even within a single delta systems tracts and key stratal surfaces show three dimensional variability and two dimensional sections often lack significant elements of the stratigraphy as a result analysis of two dimensional sections can often lead to miscorrelation and erroneous interpretations of the controlling processes

lithostratigraphy basin development base metal deposits and regional correlations of the neoproterozoic nguba and kundelungu rock successions central african copperbelt abstract the neoproterozoic katangan supergroup comprises a thick sedimentary rock succession subdivided into the roan nguba and kundelungu groups from bottom to top deposition of both nguba and kundelungu groups began with diamictites the mwale grand conglomerat and kyandamu petit conglomerat formations respectively correlated with the 750 ma sturtian and supposedly 620 ma marinoan varanger glacial events the kaponda kakontwe kipushi and lusele formations are interpreted as cap carbonates overlying the diamictites petrographical features of the nguba and kundelungu siliciclastic rocks indicate a proximal facies in the northern areas and a basin open to the south the carbonate deposits increase southward in the nguba basin in the southern region the kyandamu formation contains clasts from the underlying rocks indicating an exhumation and erosion of these rocks to the south of the basin it is inferred that this formation deposited in a foreland basin dating the inversion from extensional to compressional tectonics and the northward thrusting sampwe and biano sedimentary rocks were deposited in the northernmost foreland basin at the end of the thrusting the zn pb cu and cu ag au epigenetic hypogene deposits occurring in nguba carbonates and kundelungu clastic rocks probably originate from hydrothermal resetting and remobilization of pre existing stratiform base metal mineralisations in the roan group

ages and stratigraphical architecture of late miocene deposits in the lorca basin betics se spain new insights for the salinity crisis in marginal basins unlike most neogene basins of the betic cordillera where the salinity crisis is dated to the messinian a contradictory tortonian dating was proposed for evaporites of the lorca basin as a consequence complex structural models have been proposed in the literature to explain this discrepancy in the timing of evaporites in order to integrate the lorca basin into the geological context of the western mediterranean domain during the late miocene new sedimentological and stratigraphical studies coupled with new dating were performed which allow us to propose a messinian age for both diatomite bearing deposits and evaporites of the lorca basin these new ages challenge the idea of a tortonian salinity crisis in the lorca basin three main events of base level drop were evidenced during the messinian each event is correlated with successive steps of basin restriction shallow salina evaporites were deposited after a base level fall during the messinian before a final base level drop which led to the entire exposure of the basin this last exposure is interpreted as coeval with the deposition of first evaporites and halite in the deep mediterranean basins the reflooding which allowed the deposition of brackish deposits and a short lived marine incursion occurred at the end of the messinian base level drops occurred during eustatic falls amplified by the gradual uplift of the betic cordillera the exhumation of the tercia ridge along the strike slip alhama de murcia fault system during the messinian probably favoured the gradual restriction of the basin a discussion on correlations of main unconformities between several neogene basins of the betics is proposed suggesting a similar structural evolution at the regional scale

structural control on the dikulushi cu ag deposit katanga democratic republic of congo the dikulushi cu ag deposit is located in the kundelungu plateau region in the southeast katanga province of the democratic republic of congo the kundelungu plateau is a triangular shaped area to the north of the lufilian arc which contains part of the central african copperbelt the largest known sediment hosted copper province in the world the lufilian arc and the kundelungu plateau comprise neoproterozoic sedimentary rocks of the katanga supergroup that attain an overall thickness of more than 7 000 m the lufilian orogeny imposed a northeast directed shortening on the kundelungu plateau region forming several gentle northwest oriented anticlines above subparallel detachment surfaces at depth a north northwest oriented thrust is exposed in the western part of the dikulushi mine marked by ductile deformed shale that was transported upward and is in faulted contact with an overlying dolomite sandstone sequence this upward emplacement of the shale caused brecciation and the local development of kink folds in the dolomite sandstone sequence the brecciated layers in the west and nonbrecciated sandstone layers in the central part of the mine are crosscut by several east west and northeast oriented faults this complex set of faults produced a damage zone that was a favorable site for the migration of mineralizing fluids the faults and brecciated layers contain cu pb zn fe mineralization consisting of chalcopyrite bornite and chalcocite with minor pyrite arsenopyrite sphalerite and galena with dolomite calcite and quartz as gangue minerals the northeast oriented fault direction was reactivated several times with dextral strike and oblique slip fault movement these fault zones were sites of remobilization and enrichment of the previously deposited cu pb zn fe mineralization the remobilized sulfides consist of ag rich chalcocite with barite calcite and quartz as gangue minerals the study has shown that the deposit of dikulushi is structurally controlled by a crosscutting set of east west and northeast oriented faults similar structural settings in the mine and in the dikulushi region represent important future exploration targets

sediment hosted zn pb cu deposits in the central african copperbelt abstract stratabound epigenetic sulphide zn pb cu ore deposits of the central african copperbelt in the democratic republic of congo and zambia are mostly hosted in deformed shallow marine platform carbonates and associated sedimentary rocks of the neoproterozoic katanga supergroup economic orebodies that also contain variable amounts of minor cd co ge ag re as mo ga and v occur mainly as irregular pipe like bodies associated with collapse breccias and faults as well as lenticular bodies subparallel to bedding kipushi and kabwe in the democratic republic of the congo and zambia respectively are the major examples of carbonate hosted zn pb cu mined deposits with important by products of ge cd ag and v in the lufilian arc a major metallogenic province famous for its world class sediment hosted stratiform cu co deposits the carbonate hosted deposits range in age from neoproterozoic to early palaeozoic 680 to 450 ma the formation of the relatively older neoproterozoic deposits is probably related to early collision events during the lufilian orogeny whereas the younger palaeozoic deposits may be related to post collisional processes of ore formation fluid inclusion and stable isotope data indicate that hydrothermal metal bearing fluids evolved from formation brines during basin evolution and later tectonogenesis ore fluid migration occurred mainly along major thrust zones and other structural discontinuities such as karsts breccias and faults within the katangan cover rocks resulting in ore deposition within favourable structures and reactive carbonates of the katangan supergroup

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

particle over passing on depth limited gravel bars an experimental channel is used to examine the transport of mixed sand and gravel bedload over the crestal platform of hump back bars and along the top of planar gravel sheets hydraulic processes result in the simultaneous transport of cobbles and pebbles over a static closely packed bed consisting of like sized and finer particles for prescribed conditions flat upper stage plane sand beds develop over the crestal location with pebbles rolling easily over the sandy bed at the brinkpoint flow separation ensures effective segregation of the gravel from the sand over the slip face the deposition rate of the sand is insufficient to fill fully the interstices within the gravel foresets before rapid deposition of gravel further advances the bed form consequently distinctive vertical assemblages of open work and closed contact framework gravels could be generated as another bar migrates over and preserves the initial structure in respect to the observed mechanisms of sorting over the bars a mathematical expression is developed to explain the critical conditions allowing coarse particle mobility over planar sand or gravel beds under upper stage plane bed conditions on the crestal platform the model then is used to ascertain whether the depositional environment ascribed to certain facies in the bunter pebble beds described in a recent publication is appropriate given the distinctive facies assemblages generated in this experiment and the known hydrodynamic control of the particle segregation process

ordovician proglacial sediments in algeria insights into the controls on hydrocarbon reservoirs in the in amenas field illizi basin abstract ordovician proglacial deposits form gas reservoirs in the in amenas field illizi basin algeria depositional models were developed to understand the context and disposition of the main reservoirs through an evaluation of core and analogous outcrops from the tassili n9ajjer tunnel valleys initially accumulated sandstones with tractional structures subsequent failures of subaqueous grounding line sediment deposited proglacial debrites comprising poorly sorted argillaceous sandstone with granules these were interbedded with high density turbidity sandstones their fine grain size indicates they were dynamically disconnected from the lithologically varied debrites a lobate geometry has been defined for one subsurface composite turbidite periodic catastrophic outflows possibly evacuating subglacial lakes incised the network of subglacial tunnels and in the process delivered sand to the turbidite outwashes bedforms indicate high energy transcritical to supercritical outflows that were stable for extended periods during ice retreat a period of ice margin stability may have occurred due to grounding over the in amenas granitic palaeohighs outwash fan apices were located along this grounding line with feeder channels developing where the substrate was more easily eroded such as between the palaeohighs following further ice retreat deposition evolved to variably sinuous channels and thence to pelagic fines with dropstones