chronology of late wisconsinan glaciation in middle north america abstract we propose a chronology of late wisconsinan glacial fluctuations in middle north america from alberta to wisconsin based on radiocarbon dates derived solely from wood previous chronologies of the southwestern margin of the north american continental ice sheet have depended to a considerable degree on radiocarbon dates from fine grained organic sediment this material is commonly contaminated with older carbon resulting in chronologic confusion by using only dates from wood much of the confusion disappears however because of the scarcity of wood dates only four of the sixteen identified fluctuations are accurately dated an advance into iowa about 14 000 to 13 500 bp an advance into south dakota and iowa about 12 300 bp an advance into the lake michigan basin about 11 700 bp and an advance into the lake superior basin about 9900 bp in addition the beginning of late wisconsinan glaciation before 20 000 bp is fairly well documented none of the fluctuations in the western part of the region are accurately dated

quaternary stratigraphy of the buried valleys of the lower red deer river alberta canada the quaternary fills of the buried valleys of southern alberta and saskatchewan have provided a wealth of information for the reconstruction of the glacial interglacial record of the western plains of canada and this paper reports on the previously unstudied stratigraphy of the buried calgary valley and its former tributaries in the lower red deer river area we attempt to differentiate empress group sediments which potentially relate to pre glacial interglacial interstadial and post glacial lake and river deposition using sedimentology stratigraphy and palaeoecology twenty nine stratigraphical logs indicate that empress group sediments have infilled a considerably large area of badlands and tributary coulees that once drained into the calgary valley located 15 km to the north of dinosaur provincial park radiocarbon dates of 52 4 ka 27 4 ka and 42 4 ka and glacially modified quartz grains suggest that at least some of the valley fills date to interglacial or interstadial periods and may be mid wisconsinan in age however outcrops of an older till overlying other valley fills suggest that the buried valleys were only partially excavated during interglacials interstadials and that older even pre glacial sediments could have survived subglacial channels recognisable on air photographs largely coincide with buried valley positions due to the preferential excavation of the quaternary sediment by meltwater and are filled with post glacial lake sediment from which a radiocarbon date of 16 ka bp was obtained pre glacial and glacial post glacial empress group sediments are lithologically indistinct but cover a large time span in southern alberta

physical properties of the lithosphere asthenosphere system in europe abstract all the geophysical fields considered evidence a clear structural difference between the adriatic sea ionian sea basin on one side and the tyrrhenian sea western mediterranean basin on the other the former displays continental type characteristics while the latter shows features definitely related to young ocean basins lateral variations in the thickness of the high velocity sub crustal layer the lid are clearly evidenced in the whole european area the lateral changes in the shear wave velocities of the lithosphere asthenosphere system are quite pronounced gravity data imply a positive density contrast 0 03 0 07 g cm 3 in the upper mantle related to almost aseismic high velocity lithospheric roots which seem to characterize many orogenic belts the analysis of a transect along the longitudinal axis of the alps seems to indicate that relevant lateral variations in density are present in the lithospheric part of the mantle

rheological stratification of the lithosphere abstract the rheology of the lithosphere is estimated on the basis of pore pressure dependent frictional failure in the brittle regime and power law steady state creep in the ductile regime different petrological models of the continental and oceanic lithosphere combined with different geotherms and thicknesses are used to generate models covering a variety of geodynamic situations results show that the depth dependence of lithospheric rheology varies with the tectonic province and that in many instances the continental lithosphere has one at the bottom of the crust or two the previous one plus another at mid crustal levels soft ductile layers sandwiched between brittle layers the depth distribution of geophysical parameters seismicity seismic wave velocity and electrical conductivity matches the theological predictions well the lithospheric rheological profiles are used to analyze observed variations in the structural style of deformed continental margin and oceanic terranes in the southeastern canadian cordillera the large scale characteristics of the system show a satisfactory agreement with the inferred rheological structure sub horizontal decollements should be the rule rather than the exception where the lithospheric rheology is strongly stratified

stresses in the lithosphere and sedimentary basin formation abstract seven fundamental questions on the relationship of lithospheric stresses and sedimentary basin origin and evolution are posed and elaborated these are 1 1 how is the evolution of sedimentary basins tied to lithospheric dynamics 2 2 what are the sources of stress that lead to formation of sedimentary basins 3 3 how does the interaction between internally and externally applied stresses affect the formation and evolution of sedimentary basins 4 4 how do space and time variations of rheology and pore pressure affect stress transmission strain vertical motions and stratigraphy during basin evolution 5 5 what factors influence spatial and temporal variations of rheology in and around different kinds of sedimentary basins 6 6 what is the role of magmatism in basin formation and what deep seated processes does it reflect 7 7 what is the relationship between basin evolution thermal history and fluid flow these fundamental questions can be investigated by developing fully dynamic models of processes at the basin and sub basin scale models must incorporate or honour basin history and plate reconstructions the intregration of structural and sedimentological data direct observations of the physical state and the synthesis of geological and geophysical data including tectono dynamic stratigraphy petrological and geochemical data and geophysical data gravity magnetics heat flow deep and shallow seismics a number of type basins in passive margin foreland rift and strike slip tectonic settings suitable for modelling studies elucidating the fundamental questions are identified

tectonic variation in the dniepr donets basin from automated modelling of backstripped subsidence curves abstract the multiphase rift evolution of the dniepr donets dd basin is analysed by 1d backstripping and tectonic modelling of 66 stratigraphic sections mostly from well data distributed throughout the basin the backstripping results illustrate strong temporal and lateral variations in tectonic subsidence it is minor during an inceptive pre rift phase givetian early frasnian 380 8 370 ma and does not show clear spatial correlations within the dd basin framework the main rift phase frasnian famennian 370 362 5 ma corresponds to an acceleration in subsidence rates with tectonic subsidence up to 1500 m along the basin axis displaying a slight increase from the northwest to the southeast strong lateral variations perpendicular to the basin axis reflect the effects of major basin border faults a rift phase in the visean 345 340 ma is characterised by relatively minor subsidence up to about 500 m except for some wells in the southeast following a stage of extremely low rates of deposition in the earliest carboniferous the end of this rift phase can be taken to mark the onset of convex subsidence patterns in the later carboniferous and permian typical in shape of post rift thermal subsidence but significantly increasing in magnitude from northwest to southeast in the basin this trend shows no one to one relationship with late devonian syn rift subsidence the tectonic subsidence curves have been modelled using lithospheric stretching assumptions allowing different stretching factors for the crustal and sub crustal lithosphere and the incorporation of finite and multiple stretching phases a numerical technique was developed that automatically finds best fit stretching parameters for part or all of the tectonic subsidence data given the specification of onset and duration of the various rifting events maps of the 1d modelling results display intrabasinal variations in terms of timing and magnitude of rifting the results indicate that the observed spatial and temporal variations of tectonic subsidence in the dd basin specifically the increasing ratio of carboniferous to late devonian subsidence from northwest to southeast cannot be explained by either a uniform or depth dependent stretching model adopting only a single frasnian famennian rift phase a two phase model in which a significant part of carboniferous tectonic subsidence is related to visean rift activity strongly dominated by sub crustal lithospheric attenuation provides a satisfactory fit to the data although the tectonic implications of such a model are not easily reconcilable by independent constraints a semi quantitative investigation of the possible role of withdrawal of underlying devonian salt during the carboniferous to produce additional post devonian rift phase sediment accommodation space suggests that the effects of such a mechanism could be significant but that they are unlikely to preclude the necessity of the visean rifting event to explain the carboniferous basin evolution

contrasting styles of rifting models and examples from the eastern canadian margin we present the results of a dynamical model of lithospheric rifting and rupture which show that a wide range of crustal thinning patterns across rifted passive margins can be produced by varying the steady state geotherm lithospheric composition dry versus wet materials and strain rate the basic mechanism of continental rupture is assumed to be passive rifting and necking we use a numerical thermomechanical model of lithosphere extension based on a finite element approach when plasticity is significant i e at lower temperatures or for harder materials deformation is unstable and thinning takes place abruptly over a narrow area conversely a progressive thinning across the margin is observed when creep is dominant i e in warm or ductile conditions cooling and associated hardening of the thinned area can occur during extension and cause the locus of extension to migrate laterally in these circumstances rupture is likely to take place asymmetrically along one edge of the thinned area producing a narrow margin and a very wide conjugate the eastern margins of canada and their conjugates across the north atlantic provide examples which cover this range of theoretical profiles the crustal thinning patterns inferred from deep seismic data and the duration of rifting compare well with model results we discuss also the constraints that these geodynamical models provide on such current issues as the seismic reflectivity of the lower crust or the location of the ocean continent boundary in wide areas supposedly underlain by 5 km thin continental crust

geodynamic models of fault controlled extension results from geodynamic models for lithospheric extension that includes one or two large scale upper crustal faults are presented the study does not address the origin of these faults but the consequences if they exist model components include a solid mechanical lithosphere composed of thermoelastic plastic material with viscous creep that is subject to extension buoyant supporting forces and sedimentary loads and a coincident but thicker thermal lithosphere that includes the effect of sediment blanketing and radiogenic heating we have chosen for comparison purposes a standard reference model which minimizes creep in the crust consequently our results depend strongly on plastic deformation our models show that large faults can control the position and growth history of the mantle instabilities that can lead to rupture we observe that these instabilities have secondary normal mode like character models with two faults show that the normal mode behavior can interact and create an enhancement to the necking process provided the faults are an ideal distance apart we compare models with two rates of extension 1 2 cm yr 1 fast and 0 038 cm yr 1 slow which show remarkably little difference we compare our reference model with models using wet and dry rheologies and observe that flow in the crust can attenuate the propagation effect created by the faults

tectonic subsidence modelling of the polish basin in the light of new data on crustal structure and magnitude of inversion abstract the polish basin pb is one of a set of basins developed on the paleozoic platform of western europe in the late paleozoic between the variscan orogen and the east european craton eec its main depocentral axis the mid polish trough mpt was active during most of the basin development as a maximum subsidence zone with almost uninterrupted sedimentation the present base of the permian in the mpt ranges in depth from ca 3000 to 3500 m near the baltic coast to up to 8000 m to the southeast the mpt lies parallel and adjacent to the edge of the eec and appears to be related to a distinct structural zone within the crust the tornquist teisseyre zone ttz subsidence of the mpt can be explained in terms of crustal extension transtension and related lithosphere cooling coupled with the structural predetermination of the underlying ttz tectonic subsidence analysis of the preserved and reconstructed stratigraphic record suggests the occurrence of a late permian early triassic rifting phase however there is a deficit of geologically observable extensional features faulting of this age implying an important relationship between this phase of apparent basin subsidence and earlier post variscan late carboniferous early permian tectonism the match between crustal structure implied by basin modelling studies and available deep seismic sounding dds data is not always clear this is probably related to the heterogeneous basement which comprises the outer zone of the variscan belt in the southwest eec crust in the northeast and a complex of caledonian reworked precambrian crustal blocks in the central part of the basin changes to crustal architecture as a result of alpine tectonics may also play a role increased tectonic subsidence rates during oxfordian kimmeridgian times late jurassic correlate with intensified rifting and wrench activity within the arctic north atlantic rift system and along the northern tethyan margin in contrast accelerating tectonic subsidence beginning in the cenomanian is a precursor of compressional deformations in the basin that culminated in alpine related basin inversion during the latest late cretaceous and earliest tertiary taking inversion into account the maximum depth of the base zechstein structural surface at the end of the cretaceous is estimated to have been as much as 5000 m near the baltic sea to more than 10 000 m in the southeasternmost part of the basin because of the erosion of these sediments however constraints on cretaceous subsidence and in turn the magnitude and exact timing of late cretaceous paleogene inversion are poor

some consequences of compressional tectonics for extensional models of basin subsidence changes in intraplate stress levels have important consequences for the stratigraphy of rifted basins and provide a tectonic explanation for the generation of sequence boundaries late stage compressional phases during the post rift evolution of basins produce unconformities with offlap phases that increase in magnitude with the age of the rifted basin late stage compression has not only a strong bearing on the generation of unconformities but also induces significant downbending of the centre of a basin ignorance of the vertical motions of the lithosphere induced by late stage compression during post rift evolution can therefore give rise to substantial errors in the estimates of crustal extension derived from analysis of basement subsidence using stretching models consequently late stage compression can be of great significance in estimates of depth and timing of the hydrocarbon window inferred from extensional models of basin subsidence quantification of the subsidence induced by post rift compression has important implications for integrated models of basin subsidence and hydrocarbon generation

dependence of the flexural rigidity of the continental lithosphere on rheology and temperature while the first order mechanical properties of oceanic and continental lithosphere are well defined and explain the observed increase in lithospheric flexural strength with thermal age the temporal variation of continental flexural rigidity following loading and its dependence on lithospheric composition and temperature structure is only just beginning to be appreciated we describe here the results of a quantitative theological model in which laboratory determined rock deformation data and transienttemperature distributions resulting from intra plate basin formation within continental interiors have been integrated continental flexural rigidity is shown to be controlled by crustal thickness lithospheric thickness through the temperature structure and the interaction of these factors during basin formation for thermally young lithosphere the flexural rigidity is dominated by the quartzo feldspathic theology of the crust while for the thermally older lithosphere it is dominated by the olivine rheology of the mantle flexural data through thermo mechanical models of lithospheric deformation provide a powerful constraint on both the transient and steady state temperature structure of the lithosphere

relation between salt diapirism and the tectonic history of the sverdrup basin arctic canada the sverdrup basin is a pericratonic sedimentary trough in northern canada containing up to 13 km of carboniferous to tertiary strata the basin formed by late paleozoic continental rifting and was subsequently affected by a series of alternating tectonic settings evaporite diapirs are well exposed at the present erosion level and occur mainly along the basin axis the diapiric source layer consists of about 400 m of anhydrite underlain by salt of unknown stratigraphic thickness deposited during the initial permo carboniferous synrift phase of basin subsidence large salt anhydrite diapirs rose into the sedimentary overburden when the overburden had reached a thickness of several kilometres they grew during a relatively long period of modest horizontal compression from the permo triassic to early cretaceous much smaller tabular anhydrite diapirs were rapidly emplaced during periods of high horizontal compression in the middle cretaceous when large flexural stresses were induced by sedimentary loadi

the glaciation of the cypress hills of alberta and saskatchewan and its regional implications abstract understanding the deglaciation sequence of the cypress hills and the surrounding area permits a deeper understanding of the style and chronology of deglaciation in southeast alberta and southwest saskatchewan this paper revises previously published chronologies five deglaciation events the underdahl advance middle creek advance altawan advance pakowki advance and the etzikom advance have been recognized in the study area of these the middle creek and altawan advances are newly recognized the late wisconsinan ice underdahl advance was the most extensive ice to affect the cypress hills area it terminated in montana erratics distributed on the flanks of the cypress hills beyond this ice limit are interpreted to reflect ice rafting across ice contact proglacial lakes the erratics are not remnants of older more extensive ice advances as previously thought the revised deglaciation sequence also indicates that the late wisconsinan ice west of the cypress hills was more active and was perhaps subject to repeated intervals of surging while the east ice lobe north and east of the cypress hills was much more stable it is possible that the west lobe was not coupled to the ice north and east of the cypress hills and that the west ice lobe flowed from an ice divide in the central part of the northwest territories the east lobe flowed from a laurentide ice divide from the vicinity of hudson bay the extensive coverage by late wisconsinan ice may indicate that this western ice divide had not formed during previous glaciations and that ice flow patterns of earlier glaciations differed significantly extensive late wisconsinan ice coverage of alberta means that the ice free corridor was restricted in extent

a dynamical model of lithosphere extension and sedimentary basin formation convection in the upper mantle can give rise to normal stresses on the base of the continental lithosphere that may cause localized elevation of its surface and extensional deviatoric stresses this possibility is investigated assuming homogeneous biaxial strain in a continental lithosphere whose strength is governed by a combination of brittle failure and power law creep in the crust and by brittle power law or dorn law behavior in the mantle for a given geotherm and for rheologies based on current laboratory data the lithosphere responds to convection induced uplift in one of three ways depending primarily on the magnitude of the driving stresses these regimes are as follows 1 when the driving stress exceeds a threshold value the resulting strain rates are high enough greater than about 3 10 16 s 1 that the lithosphere strains almost isothermally its effective rheology is strain thinning and it undergoes accelerating extension the magnitude of the dynamic uplift required to produce the threshold value of the driving stress depends on the geotherm characterized here by the moho temperature and varies from about 1 km for a moho temperature of 700 c to around 3 km for a moho temperature of 550 c an uncertainty of at least 100 c is attached to these temperatures owing to the inaccuracies in extrapolating laboratory data to geological strain rates 2 at stress levels due to less than about half of the critical uplift extensional strain is negligible 3 at intermediate stress levels moderate uplift produces extension that is bounded by strength increases due to cooling of the ductile portion of the lithosphere during extension

a critical assessment of subglacial mega floods a case study of glacial sediments and landforms in south central alberta canada the existing subglacial megaflood explanation of glacial sediment deposition and landform production in south central alberta relies upon four sets of observations and associated interpretations 1 a subglacial genesis for all glacilacustrine sediments lying stratigraphically below a local melt out till or ice stagnation facies 2 a melt out genesis for the ice stagnation facies 3 a syn depositional status for the glacitectonic disturbance visible in most exposures due to periodic ice bed re coupling and 4 a subglacial megaflood origin for a truncation surface and clast lag that occurs at the top of the sedimentary exposures and the carving of hummocky terrain and flutes in the area we provide alternative interpretations of the sediment landform assemblages of the area and demonstrate that alternative simpler interpretations of the evidence can be proposed specifically we propose 1 a proglacial rather than subglacial origin of glacilacustrine sediments 2 a glacilacustrine origin for the melt out till and its subsequent glacitectonic disturbance by minor glacier readvances 3 postdepositional rather than syn depositional glacitectonic disturbance due to a significant advance by glacier ice after the accumulation of a thick sequence of glacilacustrine sediments 4 that some linear chains of hummocks are the morphological expression of glacitectonic folding and thrusting 5 that the use of the truncation surfaces to propose a subglacial fluvial origin for hummocky moraine is flawed logic because they do not constitute the tops of hummocks but rather occur on the interfluves that separate the numerous small coulees incised into the valley sides during postglacial time truncation surfaces and clast lags occur locally on the beds of spillway tracts and can be explained as the products of erosion by subaerial spillway water the mega flood explanation of flutings and hummocky moraine in the region is also questioned because these landforms record a regional ice flow imprint of mis aligned and cross cutting flow sets terminating at series of inset and locally cross cutting and lobate transverse ridges moraines these landform associations preclude a subglacial flood origin for the flutings and demonstrate that the transverse ridges are more appropriately interpreted as recessional push moraines the similarity of the glacial landforms of this region to the active temperate glacial landsystem produced by historical glacier recession in modern glacierized catchments where sheetfloods have not been influential in subglacial landform production allows us to apply a modern analogue to landscape interpretation that does not include subglacial sheetflooding

radiative heat transfer in lithospheric geodynamics implications for asthenospheric partial melting and basin modelling concepts abstract in geodynamic models describing basin formation by stretching the base of the lithosphere is commonly defined by a fixed temperature an alternative definition is proposed where the base of the lithosphere is determined by the solidus of mantle rocks some consequences of this definition are illustrated in a one dimensional model the model applies the finite difference method and approximates the temperature regime in the upper 400 km of the earth the model uses temperature dependent thermal conductivity and includes effects from heat storage by partial melting in the mantle low velocity layer mlv radiative heat transfer contributes significantly at elevated temperatures giving rise to a steepening of the thermal gradient below the lithosphere this change in gradient allows the perturbed geotherm to exceed the mantle solidus in a limited depth interval which accounts for the mlv and thus defines the base of the lithosphere in the model variations in thickness of and degree of partial melting in the mlv results from thinning of the overlying lithospheric plate thus the thickness of the mlv is roughly inversely proportional to the thickness of the lithosphere whereas the base of the mlv is almost flat temperature dependent variations in the carrying capacity of the mlv where the main isostatic compensation occurs is proposed as an epeirogenetic agent this effect may be significant and is expressed as an enhancement of the initial subsidence if no preexisting mlv is available a secondary effect occurs as solidification of the mlv ceases a long time 300 ma after stretching and causes slow uplift

postglacial geomorphic development of the dinosaur provincial park badlands alberta experimental studies concerning current geomorphic processes and erosion rates in the badlands of dinosaur provincial park alberta have not explained the unusual extent of badland development or prominent nonstructural near horizontal surfaces that occur in the park two of these surfaces result from spillway development associated with wisconsin deglaciation and the extent of badland development is associated with major spillway concentration and exposure of highly erodible cretaceous strata a third surface is associated with erosion caused by locally generated runoff all surfaces are blanketed with aeolian sands and silts deposited around 5500 bp which profoundly affected the hydrology of the area and water and sediment discharge from the badlands to the red deer river subsequent stripping of the aeolian cover by streams along with piping and tunnel erosion has reexposed vulnerable cretaceous strata and restored the high erosion rates now observed in these badlands

relative importance of strain rate and rheology for the mode of continental extension summary both extension rate and rheology have been shown to influence the style of continental rifting so far their effect on the dynamics of extension has been discussed separately in the literature leading to diverging conclusions the rate of extension mostly affects the dynamics of rifting through the occurrence of syn rift cooling at low extension rates this cooling results in an increase of strength if the lithosphere has a temperature dependent rheology england 1983 first suggested that this effect will limit the amount of extension that an area may undergo kusznir park 1987 argued more generally that it will induce a widening of the rift and concluded that extension rate is the major control on wide versus narrow rifting later studies bassi 1991 bassi keen potter 1993 however have demonstrated the importance of rheological layering within the lithosphere for the mode of continental extension by showing that a plasticity dominated rheology will lead to rapid and narrow necking while a creep dominated rheology results in wider rifts and margins gravitational stresses arising from density anomalies due to lithosphere thinning also affect the style of rifting buck 1991 in this paper we examine the combined effect of these different parameters in order to reconcile earlier studies and assess the importance of syn rift cooling for the process of lithospheric necking the approach introduced in a previous study bassi 1991 uses a finite element technique to simulate extension of a vertical cross section of the lithosphere the effect of cooling on the necking pattern depends strongly on the rheology of the thinned lithosphere when it starts to cool if heat diffusion always induces strengthening and delays rupture in time it only modifies significantly the geometry of the rift when the upper mantle is weak and viscous in this case the locus of maximum strain rate migrates laterally once the central area starts to cool and harden as hypothesized by kusznir park 1987 eventually strain concentrates at the transition between deformed and undeformed lithosphere we predict that this pattern will induce asymmetric breakup and produce a very narrow margin and a wide uniformly thinned conjugate margin in all other cases i e when the upper mantle is initially in the low plasticity regime or if it reaches the yield stress during extension the rate of extension appears to have little effect on the rifting pattern

sedimentology and depositional setting of late pleistocene drumlins galway bay western ireland subaqueous sediments comprise the cores of a group of drumlins formed at about 17 ka ybp towards the margin of the late pleistocene ice sheet is galway bay western ireland four major lithofacies associations l f a s are identified regional ice flow patterns and isostatic depression together with sedimentary characteristics indicate that the three lowermost l f a s accumulated in shallow water settings fed by meltwater venting under high hydrostatic pressure these sediments are tabular lensate or channelled and have not been deformed by glacially influenced tectonics l f a 1 is an apron of interbedded mud and muddy diamict deposited from sediment plumes and ice rafting l f a 2 infills channels cut in the underlying muddy diamict and consists of interbedded poorly sorted pebbly gravels sands and diamicts formed by sediment gravity flows l f a 3 is tabular and comprises a massive diamict derived from powerful meltwater jets l f a 4 is a massive diamict carapace which overlies stratified facies and was deposited by basal ice processes the model presented envisages subaqueous deposition below floating ice followed by till deposition and drumlinization coarsening upwards facies transitions are interpreted in terms of progressive change from ice distal to ice contact sedimentation the sequence preserved in the drumlin cores forms part of a regional apron of sediments probably of glaciomarine origin which normally occurs in front of the drumlin belt in irish coastal areas deposition probably occurred in isostatically depressed zones around the drumlin ice sheet when high relative sea levels occurred local streamlining of ice marginal sequences was probably a result of accelerated ice flow triggered by rapid calving subglacial channel development sea level change or soft bed conditions it is concluded that high relative sea levels calving and high longitudinal stretching rates provide suitable mechanisms which help to explain drumlinization and the rapid disintegration of the last ice sheet in western ireland

summary of quaternary stratigraphy and history eastern canada deposits of three wisconsinan substages sangamonian stage and older quaternary stratigraphic units are recognized in eastern canada the age assignment of these units is based on radiocarbon dating and correlation of events quaternary deposits older than sangamonian are recognized locally in eastern canada in southern ontario glacial deposits directly underlie sangamonian sediments and are referred to as illinoian in age in other areas the ages of older sediments are largely unknown offshore core stratigraphy suggests that a major glaciation took place about 436 ka and that the illinoian oxygen isotope stage 6 was also a time of extensive glaciation in this report sangamonian is used as the name for the chronostratigraphic stage that includes all of deep sea oxygen isotope stage 5 and consequently on a regional basis it includes warm interglacial deposits glacial deposits and cool interglacial deposits in southern ontario the warm interglacial deposits are represented by the don formation the stadial deposits by the scarborough formation and the cool interglacial deposits by the pottery road formation warm interglacial deposits have not been recognized in quebec unless they are part of the pre johnville sediments the becancour till is included as glacial sangamonian sediments and the st pierre sediments are recognized as cool interglacial sediments the early wisconsinan appears to have been the time of maximum wisconsinan glaciation in eastern canada with ice moving south of the international boundary and well out onto the continental shelf the middle wisconsinan was primarily a nonglacial period in southern ontario and a glacial stade elsewhere in eastern canada in southern ontario the middle wisconsinan record has been subdivided into two interstades port talbot and plum point separated by a stade cherrytree the port talbot interstade began before the limit of radiocarbon dating before 48 ka and ended about 40 ka glacial or near glacial conditions of the cherrytree stage lasted from about 40 to 35 ka ago and the plum point interstade was from about 35 to 23 ka ago central st lawrence lowland was occupied by ice throughout the middle wisconsinan but southeastern quebec and the montreal area were briefly deglaciated scattered evidence in atlantic canada suggests local deglaciation of coastal areas during middle wisconsinan but extensive ice remained on the continental shelf and ice from centres located on the shelf flowed onto land in at least two areas glacial conditions predominated throughout eastern canada during the late wisconsinan at the late wisconsinan maximum through moving ice deposited the catfish creek drift in southern ontario but ice lobes which developed in the basins of the great lakes after 15 5 ka controlled ice flow during a period of ice margin oscillation and retreat a calving bay developed in lower st lawrence valley after the late wisconsinan maximum causing a reversal of flow on the south shore of the st lawrence and replacing ice in the valley with the champlain sea about 12 ka late wisconsinan glaciers were largely limited to land areas in atlantic canada local ice caps dominated with complicated patterns of flow and retreat developing as centres of accumulation shifted and competing ice centres achieved dominance the period of late wisconsinan retreat in atlantic canada appears to have lasted from about 14 to 10 ka

calibration review and geomorphic implications of postglacial radiocarbon ages in southeastern alberta canada abstract calibration of radiocarbon dates of postglacial geomorphic events in southeastern alberta canada reveals a strong association between type of geomorphic event and seasonality of insolation the late glacial and postglacial periods can be divided into four major episodes glaciation ca 20 000 cal yr b p deglaciation ca 20 000 12 000 cal yr b p landscape stability ca 12 000 10 000 cal yr b p and landscape instability ca 10 000 0 cal yr b p this indicates that there was significantly more time than previously thought 12 000 13 000 yr for postglacial processes glaciation deglaciation maximum landscape stability indicating maximum aridity and landscape instability did not lag behind minimum increasing maximum and decreasing seasonality of insolation respectively

till stratigraphy and sedimentology at the margins of terrestrially terminating ice streams case study of the western canadian prairies and high plains complex glacigenic sediment sequences arranged in large arcuate assemblages and demarcating the lobate termini of fast ice flow corridors in western canada represent the terrestrial equivalents of the trough mouth fans of the marine palaeo ice stream record intensive sedimentological and stratigraphic investigations at a regional scale are employed in the interpretation of thick units or sequences of diamicton and two depositional scenarios are proposed first glacier marginal till thickening and the stacking of till wedges takes place in areas where an ice stream margin was stationary for short periods of time stacks of subglacial traction tills potentially record annual sub marginal incremental thickening at ice stream margins especially in areas where densely spaced recessional push moraines appear to record seasonal climatic forcing second proglacial lake and valley infilling with glacilacustrine rhythmites and mass flow diamictons is associated with the advection of sub marginal till into preglacial bedrock depressions and records ice stream marginal oscillations and debris influx into discontinuous proglacial lakes which act as subaqueous sediment sinks for materials that would otherwise have been used to construct sub marginal till wedges and moraines glacial overriding modifies the deposits produced in both scenarios through deformation and the dislocation and entrainment of bedrock and sediment rafts at the margins of bedrock valley walls resulting in the widespread development of glacitectonites and megablocks the occurrence of the thickest deposits as preglacial valley fills may be significant in groundwater siphoning away from subglacial deforming layers and the promotion of sticky spots

evolution of the west greenland margin offshore thermostratigraphic data and modelling the origin and age of topography along the west greenland margin is a matter of continued debate evidence for tectonically driven neogene uplift has been argued from interpretations of offshore seismic surveys onshore fission track data and inferred episodes of cooling here analysis of seismic reflection profiles and 1d modelling of exploration wells along the greenland margin of davis strait demonstrate that the data are consistent with a model of ancient continental topography affected by late cretaceous early palaeocene rifting followed by thermal subsidence where offshore neogene tectonic uplift is not required this interpretation for the offshore evolution of the west greenland margin has implications for the adjacent onshore evolution and for other continental margins developed throughout the atlantic arctic rift system

quaternary geology and geomorphology of the dinosaur provincial park area and surrounding plains alberta canada the identification of former glacial lobes drainage diversions and meltwater flood tracks abstract the quaternary geology and geomorphology of the lower red deer river drainage basin centred on the dinosaur provincial park badlands provides information on pre late wisconsinan drainage patterns and the dynamics of former lobes of the laurentide ice sheet in western canada patterns of deglaciation proglacial lake evolution and spillway incision are also reconstructed based upon the distribution of surface materials and glacial glaciofluvial landforms the empress group fluvial and glaciolacustrine sediments which could be as young as 27 ka bp infill the precursor red deer river and its tributaries and document the initial advance of glacier ice into southern alberta glaciotectonic disturbance of older sediments and bedrock the production of deformation tills and the construction of a megafluting complex and cupola hills record the advances of a glacier lobe centred over the study area stratified inter and intra till beds record pulses of subglacial meltwater between phases of subsole deformation the thickening of tills towards the margin of the lobe represents a till wedge an expected product of sediment advection by glaciers moving over deformable beds the eastern margin of the glacier lobe is demarcated by the interlobate suffield hummocky moraine belt which contains overprinted thrust ridges which record diachronous oscillations of neighbouring lobes within the ice sheet proglacial and glaciofluvial sediments were deposited in the area in association with proglacial lake bassano patricia which drained eastwards when the suffield moraine was dissected by spillways changes in the size of glacial lake bassano patricia are clearly documented by a sequence of spillway incisions which culminated in the erosion of scabland topography and the initiation of a new course for the red deer river a 15 km southward diversion of the main channel in distinct contrast to the documented incision histories of other small rivers in alberta one tree creek and little sandhill creek did not start major incisions of the quaternary sediments over buried valley positions until the late holocene when environmental conditions were characterized by higher precipitation

late pleistocene debris flow deposits in large glacial lakes in british columbia and alaska the movement of late wisconsin 30 000 b p ice sheet lobes counter to the direction of regional drainage ponded large lakes up to 5000 km2 in both the upper fraser river valley in british columbia and the cooper river valley in alaska along the fraser river near quesnel glaciolacustrine sediment gravity flow complexes contain thick up to 10 m and laterally extensive up to 3 km diamict units containing large rafts of poorly lithified tertiary rocks diamicts offlap and thin away from tertiary bedrock highs and were emplaced by subaqueous debris flows these flows probably evolved from slumps and slides associated with the downslope failure of unstable tertiary bedrock slopes triggered by rising lake levels a process akin to first filling slope failures around the margins of man made lakes in alaska along the copper river valley massive and stratified diamicts were also deposited by debris flows and are interbedded with thin bedded turbidites poorly sorted gravels and normally graded diamicts debris flow deposits show basal grooves internal compressional structures and rafted clasts that protrude from bed tops flows originated by slumping of rapidly deposited and underconsolidated glacial sediments around the basin margins an important factor in flow generation has been the combination of steep substrate slopes and frequent earthquake shock observations in both british columbia and alaska stress the significance of sediment gravity flow processes acting to deposit glacial sedimentary successions in large ice contact lake basins

factors controlling the style of continental rifting insights from numerical modelling passive continental margins similarly formed by lithospheric stretching and rifting can differ significantly in terms of width ranging from 50 to 400 km or subsidence history our interest lies in determining what properties of the lithosphere and what stress and strain boundary conditions control this regional variability and the siting of rupture continental breakup occurs probably as the result of a stretching instability which develops in a zone of material or geometrical heterogeneity to analyze the factors controlling these instabilities we use a numerical thermo mechanical model of lithosphere extension based on a finite element program the particular program was chosen because it combines constitutive models appropriate to our knowledge of lithosphere rheology elasticity plasticity and nonlinear temperature dependent creep with a kinematic formulation for large inelastic strain we choose to weaken the plate by locally increasing the crustal thickness by a very small amount and examine how this defect or perturbation acts to localize the deformation we compare the geometry and timing of necking for relatively wet versus dry rheology cold versus warm geotherm and fast versus slow strain rate we examine as well how the width and amplitude of the perturbation itself affects the deformation history since a velocity boundary condition is applied the required extensional forces are evaluated and compared to estimates of plate driving forces conditions that favor deformation by plasticity rather than creep cold geotherms dry rheologies lead to a more localized extension and rapid rupture but the forces involved 1013 n m are larger than typical plate driving forces increasing the amplitude of the defect i e crustal thickness contrasts accelerates necking as well cooling of the thinned area becomes significant at low extension rates depending on the initial rheology cooling simply delays the moment when deformation becomes unstable or conversely inhibits necking

melt out till in the edmonton area alberta canada till at two localities in the edmonton area alberta was formed mainly by passive melt out from glacier ice and not by lodgment by active ice or as a result of supraglacially derived flows this interpretation is based on the implications of in situ stratified glacial sediment below and within till and of large unlithified clasts of sediment derived from subtill deposits the interpretation is also supported by more general regional stratigraphic and structural observations such associated properties as subtill deformation a sharply planar till preglacial sediment contact sole marks and fabric support formation by melt out or illustrate local exceptions to this process regionally consistent preferred orientation of clasts is interpreted to represent preferred englacial orientation collective analysis of the principal eigenvectors of individual englacial fabrics and flow or resedimented till fabrics from a modem glacial environment and similar analysis for till at villeneuve near edmonton show the edmonton till to occupy the intermediate position in terms of orientation strength predicted by the melt out hypothesis in places preferred orientation is considered to have been disturbed by flow and diapirism induced by the process of thaw consolidation thus preferred clast orientation in till may show considerable deviation from a regional trend stratigraphy and sedimentology are used to classify the till and to relate individual exposures to regional environments of deposition

the origin of sedimentary basins a status report from the task force of the international lithosphere program abstract better insights into the mechanisms of basin formation have a direct bearing on the predictive power of forward models for basin fill models that link flexure normal faulting and thrusting on a subbasin scale provide important constraints on the tectonic control of the sedimentary record enabling a quantitative comparsion with eustatic contributions to the basin architecture thus of special importance is the need to link processes with different spatial and temporal scales involved in the evolution of extensional and compressional basins by numerical modelling a new generation of basin modelling concepts and techniques is one of the main objectives of the task force origin of sedimentary basins of the international lithosphere program the focus of this work is on the quantification of the effects of the thermomechanical structure of the lithosphere and its interplay with regional and local stress changes other important developments include the step towards three dimensional modelling and the full integration of rapidly expanding fission track and other data sets to constrain vertical motions in basins as natural laboratories for the interactive testing and development of new basin modelling techniques a number of basins with high quality data from industry government and academia have been selected on the basis of specific testable problems

glacial landsystems of the southwest laurentide ice sheet modern icelandic analogues landform assemblages and associated stratigraphy sedimentology and structure are used in the reconstruction of palaeo ice sheet dynamics in alberta western canada interpretations are based upon the modern analogues from four outlet glaciers at the margins of vatnajokull and myrdalsjokull iceland in the area between lloydminster and lac la biche central alberta an extensive landform assemblage of megaflutings crevasse squeeze ridges and thrust block moraine arcs document the former surging of part of the margin of the laurentide ice sheet during later stages of recession this landform assemblage including numerous exposures of glacitectonised bedrock and quaternary sediments is comparable to the landsystem of the surging glaciers eyjabakkajokull and bruarjokull in iceland near high river southern alberta the former existence of an ice lobe characterised by active recession is recorded by closely spaced low amplitude recessional push moraines that drape tunnel valleys these are comparable in form and pattern to annual push moraines and fluted till surfaces produced by breidamerkurjokull and sandfellsjokull iceland and also include rimmed depressions produced by the escape of artesian water during ice marginal pushing this study provides interpretations of the regional glacial geomorphology of alberta based upon comparisons of form and stratigraphy with modern glacial analogues and provides an alternative to recent models which invoke large floods of subglacial meltwater to explain many of these same features implications for ice dynamics and regional till stratigraphies are discussed copyright 1999 john wiley sons ltd

numerical modelling of salt diapirism influence of the tectonic regime abstract in the context of sedimentary basin mechanics salt diapirism has usually been described as a phenomenon initiated and driven by gravity instabilities associated with buoyant forces or differential loading this result holds essentially for an approximation of linear rheologies of both salt and overburden this has been contested by recent analog models and analytical studies buoyancy alone cannot drive salt diapirism through a brittle overburden regional extension or compression could be a necessary mechanism likely to promote salt diapirism numerical models are presented here to describe the relative effects of gravity and lateral forces on the dynamics of salt diapirism the numerical scheme is based on a viscoplastic approximation of deformations and an updated lagrangian description of kinematics which allows a study of large non linear deformations of salt bodies and the evolution of material interfaces this scheme takes into account brittle and ductile deformations of sediments moreover it describes the initiation and evolution of shear bands which play a crucial role in basin mechanics and especially in the dynamics of salt diapirism we show why extension is the most propitious driving mechanism of diapirism necking and faulting induced by extension promote and drive salt diapirism in the case of a brittle overburden this result holds with or without buoyancy forces this demonstrates that buoyancy which alone is not sufficient to break a brittle overburden is not a necessary mechanism either buoyancy however enhances diapirism induced by lateral forces in contrast with extension salt diapirism during compression is strongly constrained by the rheology of the overburden a brittle mode of deformation favours faulting rather than buckling induced thrusting and thickening of the overburden inhibit massive diapirism and favour the confinement of small salt plugs finally the post extension stability of a mature diapir produced by extension is presented

tectonic evolution of the north sea basin crustal stretching and subsidence summary the lithospheric stretching model for the formation of sedimentary basins was tested in the central north sea by a combined study of crustal thinning and basement subsidence patterns a profile of crustal structure was obtained by shooting a long range seismic experiment across the central graben the main axis of subsidence a seabed array of 12 seismometers in the graben was used to record shots fired in a line 530 km long across the basin the data collected during the experiment were interpreted by modelling synthetic seismograms from a laterally varying structure and the final model showed substantial crustal thinning beneath the graben subsidence data from 19 exploration wells were analysed to obtain subsidence patterns in the central north sea since jurassic times changes in water depth were quantified using foraminiferal assemblages where possible and observed basement subsidence paths were corrected for sediment loading compaction and changes in water depth through time the seismic model is shown to be compatible with the observed gravity field and the small size of observed gravity anomalies is used to argue that the basin is in local isostatic equilibrium both crustal thinning and basement subsidence studies indicate about 70 km of stretching across the central graben during the mid jurassic to early cretaceous extensional event this extension appears to have occurred over crust already slightly thinned beneath the graben and the seismic data suggest that total extension since the early permian may have been more than 100km the data presented here may all be explained using a simple model of uniform extension of the lithosphere

fe isotope fractionation between chalcopyrite and dissolved fe during hydrothermal recrystallization an experimental study at 350 c and 500 bars abstract equilibrium fe isotope fractionation between chalcopyrite and dissolved fe was determined in acidic chloride bearing fluid at 350 c and 500 bars the study utilized deformable gold cell technology which allowed time series sampling of solution during chalcopyrite recrystallization and isotope exchange a key element of the experimental design involved the addition of anomalous dissolved 57 fe to an on going experiment as a means of determining the degree and rate of isotope exchange taking explicit account of imposed chemical and isotopic mass balance constraints of fe in fluid and mineral chalcopyrite reservoirs these data indicate that no more than 1000 h is required for the isotopically anomalous dissolved fe reservoir to exchange completely with the coexisting chalcopyrite the experimental calibration of the rate of fe isotope exchange for the 57 fe spiked experiment provides critical insight for the time necessary to achieve fe isotope exchange in two non spiked but otherwise identical experiments the fe isotope data indicate that the equilibrium fractionation between chalcopyrite and dissolved fe 56 fe cpy fe aq at 350 c is small 0 09 0 17 2 and is in good agreement with recent theoretical equilibrium predictions owing to the apparent rate of fe isotope exchange at 350 c it is likely that chalcopyrite formed at high temperature deep sea vents black smoker systems achieves isotopic equilibrium and effectively records the fe isotopic composition of the coexisting end member hydrothermal fluid comparison of the experimental mineral fluid equilibrium fractionation factors with conjugate chalcopyrite and dissolved fe pairs sampled from high temperature hydrothermal vent systems at axial caldera and main endeavour field juan de fuca ridge are in agreement with this inference the experimental data were further used to determine the mineral mineral equilibrium fe isotope fractionation between pyrite chalcopyrite 56 fe pyr cpy at 350 c by combining previously determined pyrite fe 2 aq equilibrium fractionation data with chalcopyrite fe 2 aq from this study the empirically determined 56 fe pyr cpy value 0 90 0 34 2 is consistent with theoretical predictions and when coupled with mineral fluid fe isotope fractionation systematics and experimentally determined exchange rates helps to delineate processes of sulfide mineralization in hydrothermal systems

subduction platform subsidence and foreland thrust loading the late tertiary development of taranaki basin new zealand borehole seismic and gravity data are used to investigate deformation of continental lithosphere at a miocene collisional zone deformation is manifested in the three following principal forms a long wavelength 500 km platform subsidence ascribed to mantle convection flexural deformation on a scale of 100 200 km due to crustal thrusting at the eastern boundary of the taranaki basin and a ductile thickening evident on the deep seismic section of taranaki basin that occurs on a scale of 10 km evidence for flexural deformation principally comes from the deep seismic section that shows a 150 km wavelength bending of the moho down toward the major zone of thrusting within the taranaki fault zone paleowater depths however provide evidence for an initial early miocene regional subsidence that is too long in wavelength to be explained by flexure induced from thrust sheet loading instead we propose that this broad platform subsidence was driven by loading from a deep source probably subduction induced flow in the mantle by 22 19 ma 1 2 km of water existed over most of the area now occupied by south taranaki basin by 19 17 ma the water depth in the zone east of the taranaki basin the taranaki fault zone had been replaced by rock due to submarine thrusting and crustal thickening this build up of submarine topography in the taranaki fault zone constitutes part of the load 25 8 mpa that created and maintains south taranaki basin gravity data place further constraints on loading at the thrust front and point to an additional intracrustal loading equivalent to 15 7 mpa over a 50 km wide zone this intracrustal load is explained as being due to thick skinned thrusting bringing denser lower crustal rocks nearer to the surface in the thrust zone the complete load on the taranaki foreland is therefore in three parts the submarine topographic load the intracrustal load and the loading of infilling sediments

glaciotectonism and landsliding in little sandhill creek alberta abstract slope failure and gully erosion along little sandhill creek a tributary of the red deer river alberta canada has exposed large stratigraphic sections in which the effects of glaciotectonism and landsliding are clearly revealed six main units are identified ranging from a deposit of coarse fluvial sands through various glacial diamictons and gravels and sands to postglacial fluvial and lacustrine pond and aeolian sediments incision by little sandhill creek since late wisconsinan deglaciation ca 12 500 b p resulted in periodic landslides culminating in the main slope failure which occurred post ca 5400 b p the slide was reactivated by irrigation water return flow from the adjacent prairie surface

a new multilayered model for intraplate stress induced differential subsidence of faulted lithosphere applied to rifted basins in plane horizontal stresses acting on predeformed lithosphere induce differential flexural vertical motions a high precision record of these motions can be found in the sedimentary record of rifted basins originally it was proposed that rifted basins experience flank uplift and basin center subsidence in response to a compressive change of in plane stress which agrees well with observed differential motions subsequently published models predicted that the vertical motions may be opposite because of the flexural state of the lithosphere induced by necking during extension however the total flexural and permanent geometry of the lithosphere underlying the rifted basin is the controlling parameter for the in plane stress caused vertical motions the largest part of this preexisting geometry is caused by faulting in the uppermost brittle part of the crust and ductile deformation in the underlying parts of the lithosphere we present a new multilayered model for stress induced differential subsidence taking into account the technically induced preexisting geometry of the lithosphere including faults in the upper crust as continental lithosphere may exhibit flexural decoupling due to a weak lower crustal layer the new multilayer in plane stress model discriminates the geometries of the separate competent layers at a basin wide scale the new model predicts that a compressive change of in plane force results in basin center subsidence and flank uplift confirming the original hypothesis compared to all previous models the new model requires a lower horizontal stress level change to explain observed differential vertical motions

nature and classification of waterlain glaciogenic sediments exemplified by pleistocene late paleozoic and late precambrian deposits this study of waterlain glaciogenic sediments is designed to present both a review and new information on glaciogenic subaquatic deposits of differing age in a number of localities in north and south america and south africa the late paleozoic glaciogenic deposits of the parana basin in brazil and the karoo basin of south africa are singled out for special attention as they show a reasonably complete lateral sequence of terrestrial to off shore glaciogenic sedimentation although the environment of subaquatic glaciogenic sedimentation varies from one area to the next certain common elements are found which can be used to develop a generalized model for both glaciomarine and glaciolacustrine sedimentation for descriptive purposes the model is divided into two broad categories a shelf facies and a basinal facies the shelf facies is marked by massive diamicton ite which may be 200 m or more in thickness and which is frequently overlain by a complex of clastic sediments consisting primarily of gravity and fluid flows the basinal facies is marked by products of subaquatic slumps and more distal turbidites and glaciomarine sediments new terminology is introduced the massive diamicton ite which is diagnostic of the shelf facies probably represents deposition from the base of active ice in a subaquatic environment and is termed undermelt diamicton ite the gravity and fluid flows which are usually found overlying undermelt diamicton ite and in the basinal facies are subdivided into six categories glaciogenic subaquatic outwash glaciogenic suspension flow glaciogenic chaotic debris flow glaciogenic subaquatic debris flow glaciogenic slurry flow and glaciogenic turbidity flow the relative abundance of undermelt diamicton ite and the various types of gravity and fluid flows can be used to define inner shelf outer shelf inner basin and outer basin facies of glaciomarine sedimentation

geomorphology and till architecture of terrestrial palaeo ice streams of the southwest laurentide ice sheet a borehole stratigraphic approach abstract a multidimensional study utilising geomorphological mapping and the analysis of regional borehole stratigraphy is employed to elucidate the regional till architecture of terrestrial palaeo ice streams relating to the late wisconsinan southwest laurentide ice sheet detailed mapping over a 57 400 km2 area of southwestern saskatchewan confirms previous reconstructions of a former southerly flowing ice stream demarcated by a 800 km long corridor of megaflutes and mega scale glacial lineations ice stream 1 and cross cut by three formerly southeast flowing ice streams ice streams 2a b and c analysis of the lithologic and geophysical characteristics of 197 borehole samples within these corridors reveals 17 stratigraphic units comprising multiple tills and associated stratified sediments overlying preglacial deposits the till thicknesses varying with both topography and distance down corridor reconciling this regional till architecture with the surficial geomorphology reveals that surficial units are spatially consistent with a dynamic switch in flow direction recorded by the cross cutting corridors of ice streams 1 2a b and c the general thickening of tills towards lobate ice stream margins is consistent with subglacial deformation theory and variations in this pattern on a more localised scale are attributed to influences of subglacial topography including thickening at buried valley margins thinning over uplands and thickening in overridden ice marginal landforms

submarine flow tills at victoria british columbia sea cliffs at victoria expose submarine flow tills within an ice contact complex of flow till outwash proglacial cones interbedded with dinoflagellate bearing glaciomarine fine sediments glacial debris flow lobes mainly flow tills were formed by supraglacially englacially and basally transported sediment slumping off an ice margin grounded in the strait of juan de fuca the structures and textures reveal that lobes formed by a conveyor mechanism in some lobes a double sorting phenomenon apparently developed involving an outer winnowed layer of pseudo plastic flow around an inner core of till that was sorted by dewatering and expulsion of fines outward from the centre during flow structures and fabric data indicate lobe travel was gravitationally controlled down cone flanks and independent of ice movement a depositional model for the complex proposes the ice margin produced a proglacial apron of interdigitating cones which accumulated on the sea floor sediment facies variations were probably c

lithospheric dynamics and the rapid pliocene quaternary subsidence phase in the southern north sea basin abstract we present stratigraphic modeling and quantitative analysis of the pliocene and quaternary subsidence of the southern north sea basin during the late pliocene well before the onset of quaternary glaciation the subsidence rate in the southern part of the north sea basin showed a ten fold increase relative to previous tertiary rates the high pliocene quaternary subsidence rate is consistent with the direction and state of the present intraplate stress field in northwest europe one possible consequence of the modern compressional stress field in northwest europe is reactivation of faulting in the central graben resulting in localized stretching and the development of pull apart basins alternatively the acceleration in late pliocene subsidence rates could be due to localized flexural downwarping of the lithosphere in the central graben caused by an increase in the level of intraplate compression both mechanisms succesfully predict the major characteristics of the overall quaternary subsidence history and stratigraphy gravity modeling suggests that the mechanism of localized stretching dominates the recent tectonostratigraphic evolution of the southern north sea

an eulerian technique for thermomechanical modeling of lithospheric extension a two dimensional eulerian spline function finite element method for modeling the coupled thermomechanical processes which control lithospheric extension is presented the model domain comprises a cross section through the lithosphere and part of the asthenosphere material may enter or leave through the bottom and side boundaries on the side boundary a fixed velocity or a fixed force condition can be applied highly nonlinear and thermally activated creep laws are used for the brittle and ductile rheologies of the lithosphere compositional differences between crust and mantle are described by a continuous function which is advected and which affects density rheology and heat production an approximate topography is calculated from the normal stress at a free slip surface boundary a set of sample case studies is presented which highlights the capabilities and possible applications of the method it also serves to study the influence of numerical parameters and of conceptual assumptions in various nontrivial applications the examples comprise narrow rifting continuing into the stage of seafloor spreading formation of a wide basin formation of a metamorphic core complex and impact of a mantle plume onto the bottom of the lithosphere in the last case the entire upper mantle is modeled and the instability of a thermal bottom boundary layer gives rise to a diapiric mantle plume the main weakness of the eulerian approach as compared to the lagrangian technique was found to be the effective blurring of material discontinuities like the moho this is of little consequence in pure shear deformation but when strong simple shear occurs it impairs the resolution the main advantage of the eulerian technique is that very large deformation poses no problem as it does for the lagrangian method the new approach is especially suited to study processes where strong differential flow occurs in part of the modeled system a further possible advantage of the method is its efficiency in terms of computer time

response of the lithosphere to in plane force variations the earth s lithosphere deforms when subjected to vertical and horizontal tectonic forces because it is not perfectly rigid the deformation has both elastic flexural and inelastic brittle and ductile creep components we use the yield strength envelope formulation of a depth dependent rheology to predict how the lithosphere will deform in response to applied in plane force brittle deformation of the upper lithosphere is influenced by the distribution of existing faults and fractures in the crust and their orientation with respect to the applied tectonic force the sense of fault reactivation indicates the sign of the applied in plane force the induced flexural deformation is governed by the pre existing lithospheric deflection the effective elastic thickness of the lithosphere when the force was applied and the magnitude of the applied force using this framework we compare the predicted response of the lithosphere to in plane force variations with that observed in the central indian ocean and the jeanne d arc basin offshore newfoundland the brittle deformation in both regions is readily observed in seismic reflection data the upper oceanic crust in the central indian ocean is broken into blocks bounded by high angle reverse faults the dip of these basement faults and their orientation parallel to the marine magnetic lineations suggest that they represent a reactivated crustal fabric imparted during the formation of oceanic crust the reverse sense of fault reactivation is consistent with the north south compression determined from earthquake focal mechanisms in the jeanne d arc basin episodes of northwest southeast extension reactivated the basin bounding faults in a normal sense during late barremian early aptian and late aptian time in the late albian the same crustal blocks were reactivated and uplifted in response to north northeast in plane compression flexural deformation due to applied in plane force is observed only in the central indian ocean case where the oceanic crust and most of the overlying bengal fan sediments were deformed into broad east west trending undulations with wavelengths of 100 300 km and amplitudes up to 2 km in the jeanne d arc basin the flexural deformation which should accompany the fault reactivation is difficult to recognize from the preserved stratigraphy consequently brittle deformation within extensional basins which appears to be the most recognizable response of the lithosphere to in plane force variations obscures the effects of the flexural deformation however it is this flexural deformation that has been postulated as a tectonic alternative to glacial eustasy in explaining the 3rd order sea level cycles because it is difficult to recognize the effects of the flexural deformation in the preserved stratigraphy we surmise that it is not a viable alternative to glacial eustasy in generating either regional or global unconformities instead we propose that the flexural and brittle deformation due to applied in plane force may locally enhance or diminish the effects of other processes responsible for unconformity generation

the origin of soft sediment deformation structures in permo carboniferous glacial and proglacial beds south africa abstract soft sediment deformational structures in subsurface glacial and proglacial beds of the permo carboniferous dwyka formation include faults folds boudins sigmoidally shaped laminae and sandstone siltstone injections within specific zones ranging in thickness from 1 to 12 m the zones consist of rhythmite shale with ice rafted debris siltstone and minor sandstone and diamictite but often the original character of the sediments is completely destroyed by the deformation the deformation structures predominantly formed during extensional strain of the sediments and form part of complex shear zones diapiric structures load coasts and convolute lamination the deformation zones are lithologically controlled and intimately associated with debris flow deposits indicating that gravitational forces giving rise to slumping were the predominant cause of the deformation excess pore water pressures and subsequent liquefaction of the fine grained sediments on oversteepened depositional slopes apparently generated the sheetlike slumps but the possibility of grounded ice initiating slumps in the lowermost deformation zone cannot be excluded a new type of coarse grained matrix supported deposit designed melange diamictite which formed during slumping under a soft sediment slab is described for the first time

landform and sediment imprints of fast glacier flow in the southwest laurentide ice sheet evidence for former fast glacier flow ice streaming in the southwest laurentide ice sheet is identified on the basis of regional glacial geomorphology and sedimentology highlighting the depositional processes associated with the margin of a terrestrial terminating ice stream preliminary mapping from a digital elevation model of alberta identifies corridors of smoothed topography and corridor parallel streamlined landforms megaflutes to mega lineations that display high levels of spatial coherency ridges that lie transverse to the dominant streamlining patterns are interpreted as a series of minor recessional push moraines b thrust block moraines or composite ridges hill hole pairs constructed during readvances surges and c overridden moraines cupola hills apparently of thrust origin together these landforms demarcate the beds and margins of former fast ice flow trunks or ice streams that terminated as lobate forms localised cross cutting and or misalignment of flow sets indicates temporal separation and the overprinting of ice streams lobes the fast flow tracks are separated by areas of interlobate or inter stream terrain in which moraines have been constructed at the margins of neighbouring competing ice streams outlet glaciers this inter stream terrain was covered by more sluggish non streaming ice during full glacial conditions thin tills at the centres of the fast flow corridors in many places unconformably overlying stratified sediments suggest that widespread till deformation may have been subordinate to basal sliding in driving fast ice flow but the general thickening of tills towards the lobate terminal margins of ice streams outlet glaciers is consistent with subglacial deformation theory in this area of relatively low relief we speculate that fast glacier flow or streaming was highly dynamic and transitory sometimes with fast flowing trunks topographically fixed in their onset zones and with the terminus migrating laterally the occurrence of minor push moraines and flutings and associated landforms because of their similarity to modern active temperate glacial landsystems are interpreted as indicative of ice lobe marginal oscillations possibly in response to seasonal climatic forcing in locations where meltwater was more effectively drained from the glacier bed further north the occurrence of surging glacier landsystems suggests that persistent fast glacier flow gave way to more transitory surging possibly in response to the decreasing size of ice reservoir areas in dispersal centres and also locally facilitated by ice bed decoupling and drawdown initiated by the development of ice dammed lakes copyright 2008 john wiley sons ltd

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

glacial geomorphology of terrestrial terminating fast flow lobes ice stream margins in the southwest laurentide ice sheet glacial geomorphological mapping of southern alberta canada reveals landform assemblages that are diagnostic of terrestrial terminating ice streams fast flowing outlet glaciers with lobate snouts spatial variability in features that comprise the landform assemblages reflects changes in a palaeo ice stream activity switch on off and b snout basal thermal regimes associated with climate sensitive steady state flow palaeo ice stream tracks reveal distinct inset sequences of fan shaped flowsets indicative of receding lobate ice stream margins former ice lobe margins are demarcated by a major often glacially overridden transverse moraine ridges commonly comprising glacitectonically thrust bedrock and b minor closely spaced recessional push moraines and hummocky moraine arcs details of these landform types are well exhibited around the former southern margins of the central alberta ice stream where larger scale more intensive mapping identifies a complex glacial geomorphology comprising minor transverse ridges mtr types 1 3 hummocky terrain ht types 1 3 flutings and meltwater channels spillways the mtr type 1 constitute the summit corrugation patterns of glacitectonic thrust moraines or major transverse ridges and have been glacially overrun and moderately streamlined the mtr type 2 sequences are recessional push moraines similar to those developing at modern active temperate glacier snouts the mtr type 3 document moraine construction by incremental stagnation because they occur in association with hummocky terrain the close association of hummocky terrain with push moraine assemblages indicates that they are the products of supraglacial controlled deposition on a polythermal ice sheet margin where the ht type 3 hummocks represent former ice walled lake plains the ice sheet marginal thermal regime switches indicated by the spatially variable landform assemblages in southern alberta are consistent with palaeoglaciological reconstructions proposed for other ice stream fast flow lobes of the southern laurentide ice sheet where alternate cold polythermal and temperate marginal conditions associated with climate sensitive steady state flow sequentially gave way to more dynamic streaming and surging activity

morphological analysis and evolution of buried tunnel valleys in northeast alberta canada abstract tunnel valleys are large elongated depressions eroded into unconsolidated sediments and bedrock tunnel valleys are believed to have been efficient drainage pathways for large volumes of subglacial meltwater and reflect the interplay between groundwater flow and variations in the hydraulic conductivity of the substrate and basal meltwater production and associated water pressure variations at the ice bed interface tunnel valleys are therefore an important component of the subglacial hydrological system three dimensional modelling of geophysical and lithological data has revealed numerous buried valleys eroded into the bedrock unconformity in northeast alberta many of which are interpreted to be tunnel valleys due to the very high data density used in this modelling the morphology orientation and internal architecture of several of these tunnel valleys have been determined the northeast alberta buried tunnel valleys are similar to the open tunnel valleys described along the former margins of the southern laurentide ice sheet they have high depth to width ratios with undulating low gradient longitudinal profiles many valleys start and end abruptly and occur as solitary straight to slightly sinuous incisions or form widespread anastomosing networks typically these valleys are between 0 5 and 3 km wide and 10 and 30 m deep although the depth of incision along some thalwegs exceeds 100 m several valleys extend for up to 60 km but most are between 10 and 30 km long valley fills comprise a range of lithofacies including stacked sequences of diamict glaciofluvial sands and gravels and glaciolacustrine silts and clays displaced bedrock presumably of glaciotectonic origin also occurs within several anastomosing valleys several channel bodies are exposed along a number of valley sections suggesting progressive valley development through repeated cycles of sediment discharge cut and fill structures that are capped by fine grained sequences of rippled sand and mud rich drapes within these channel bodies suggest unstable flow regimes within the valley and the discharge of sediment laden basal meltwater under flood like conditions followed by wane flow events or periods of lower meltwater discharge likely concomitant with localized modification by glacial ice basal meltwater is inferred to have been released as episodic jokulhlaups beneath the western laurentide ice sheet which at times re used existing valley systems which were spatially and temporally stable features and at other times incised new valleys

tectonic evolution of the mid polish trough modelling implications and significance for central european geology abstract the polish basin forms the easternmost part of the permian mesozoic northwest european basin the depocentral axis of the polish basin the mid polish trough mpt is superimposed on the boundary between the west european phanerozoic and east european proterozoic crustal domains within the trans european suture zone the presence of this fundamental crustal boundary may be paramount in structurally controlling the position of the mpt concentrating stresses during post variscan wrench and extensional tectonics in central europe tectonic subsidence analysis of the preserved and reconstructed stratigraphic record of the polish basin indicates the occurrence of an initial late permian early triassic 255 241 ma rifting phase that was followed by subsequent episodes of increased tectonic subsidence during the oxfordian kimmeridgian 157 152 ma and beginning in the cenomanian 97 ma the oxfordian kimmeridgian episode is interpreted as corresponding to a second extensional event which correlated with intersified rifting and wrench activity within the arctic north atlantic rift system and along the northern tethyan margin while the cenomanian may be considered a precursor of compressional deformations in the basin which culminated in basin inversion in the latest cretaceous and paleocene forward modelling results in view of existing geophysical interpretations which show the presence of a deep moho and a very velocity lower crustal layer beneath thempt suggest that permo mesozoic basic development may be related at least in part to the intrusion of mantle material into and densification of the lower crust rather than exclusively to crustal extension and thinning

glacial and postglacial stratigraphy of dinosaur provincial park and surrounding plains southern alberta canada abstract thirty one stratigraphic logs from the dinosaur provincial park area reveal seven major lithofacies associations lfa s lfa 1 is a preglacial fluvial deposit recording deposition on a sandy braided floodplain this lfa fines upwards to lfa 2 a glacilacustrine deposit which records the first advance of laurentide glacier ice into the region erosional contacts between lfa s 1 and 2 and bedrock suggest that large expanses of badlands may have existed prior to glaciation lfa 3 is a grey till which together with glacitectonized bedrock records ice movement from the northeast lfa 4 represents supraglacially derived diamictons and outwash its oxidized colour indicates either a considerable period of subaerial weathering or groundwater activity and the deposit is tentatively assigned an interstadial or interglacial age a second glaciation is recorded by lfa 5 heterogeneous diamicton and lfa 6 homogeneous diamicton lfa 5 records a period of subglacial molding and then cavity filling by fluvial and debris flow deposits lfa 6 records lodgement and melt out of the same glacier ice after it had glacitectonically thrust large rafts of older lfa s the sequence of molding cavity fill tectonism melt out represents large scale decoupling of the glacier from its bed and later surges creating extensive deformation of the substrate melt out was interrupted in some places by remobilization caused by surges which continued throughout ice retreat lfa s 7a 7e record deposition in glacilacustrine fluvial pond and aeolian environments after deglaciation some previously reported and new radiocarbon dates on regional and local surface drainage are discussed with reference to fluvial incision and holocene climate all lfa s are tentatively correlated with stratigraphic sequences reported from adjacent areas of southern alberta and former regional glaciodynamics are assessed

a model for sedimentation by tidewater glaciers sampling of sediment from the fjord floor in front of tidewater glaciers in glacier bay alaska has provided information about processes in this restricted glacimarine dreimanis 1979 setting sediment sampling in conjunction with oceanographic and glacial dynamics data has also enabled the discrimination of sediment types and their facies associations deposits are strongly controlled by sea water characteristics position and sediment discharge of melt water streams iceberg calving and rate of glacierfront retreat five distinct facies associations have been found to reflect glacier fjord regimes the facies associations and ice fjord conditions responsible for them form the basis for constructing a preliminary model for glacimarine sedimentation by tidewater glaciers the model can be used to predict i rapid retreat of an actively calving ice front ii slow retreat or stabilization of a calving ice front at a channel constriction iii stabilization of a melting very rarely calving ice front when the glacier base is near tidewater elevation and iv large outwash delta progradation into a fjord when the ice front retreats onto land this model can be used to interpret facies associations found in a stratigraphic record

glacial sedimentary processes and environmental reconstruction based on lithofacies glacigenic sediments exposed in pits around villeneuve near edmonton alberta are subdivided into facies based on grain size sedimentary structure glacially induced deformation and faulting and groove marks two diamicton facies are recognised one of which is interpreted as a primary till deposited directly from glacier ice and the other as a product of mass movement the diamicton facies are closely associated with current bedded facies interpreted as fluvioglacial deposits the stratigraphic sedimentological and tectonic aspects of these fluvial deposits suggest subglacial deposition in channels and cavities at any one place the glacier appears to have alternated between being attached to the bed causing thrusting and sole marking and being separated from the bed by a cavity in which fluvial and mass movement sediments accumulated the net result is a highly complex and laterally variable stratigraphy produced by a single glacial advance the correct interpretation of such sequences is essential if lithostratigraphy is to be used to establish glacial history in addition the interpretations presented here have implications regarding the formation of soft zones in till they indicate that the soft zones are beds of sorted sediment redeposited by mass movement

isostatic response of the lithosphere with in plane stress application to central australia the relation between gravity and topography in central australia cannot be described by a conventional isostatic response function whether it assumes local or regional compensation or whether the crust behaves as an elastic or viscoelastic medium in particular the response function exhibits considerable anisotropy hence a theory for isostatic response has been developed for a crust in mechanical equilibrium of surface loads buoyancy and in plane forces and subject to erosion sedimentation and stress relaxation the observed north south response function exhibits extreme isostatic overcompensation at some wavelengths and this can be fully explained by the viscoelastic plate model with in plane compression the observed east west response function is consistent with models of regional or local isostatic compensation the response function implies an effective flexural rigidity of 5 10 1022 n m an effective maxwell relaxation time of 25 50 m y an in plane compression of 125 150 mpa and an erosion time constant of about 200 m y these parameters assume that the model evolved over a period of about 700 m y and are wholly consistent with the evolutionary model developed from geological observations

stratigraphy and correlation of the glacial deposits on the montana plains till units representing at least three pre illinoian continental glaciations at least one illinoian glaciation and a late wisconsin glaciation have been identified on the montana plains early wisconsin or middle wisconsin till units have not been identified the southernmost limit of late wisconsin glaciation is in montana more than 170 km south of the lethbridge moraine in alberta canada figs 1 and 2 an interpretation that the lethbridge moraine is the limit of late wisconsin glaciation stalker 1977 1980 1983b stalker and harrison 1977 rutter 1980 1981 jackson 1983 is incompatible with stratigraphic and morphologic evidence from montana

dynamical models of the role of crustal shear zones in asymmetric continental extension abstract this paper presents a simple quantitative model for the transfer of lithospheric extension along deep crustal shear zones during rifting of continents these shear zones are interpreted to connect laterally offset pre existing weaknesses in the crust to the centre of mantle lithospheric thinning the rift axis for quartz and quartz over feldspar dominated crustal models we predict the formation of major crustal shear zones which transfer extension to offset crustal weak zones as much as several hundreds of kilometres from the rift axis the length scale of this transfer depends on the initial thermal regime of the lithosphere the composition and thickness of the crust and the relative strengths of the crust at the rift axis and in the offset weak zones when rifting results from a combination of in plane tensile stress and active heating of the mantle lithosphere from below the lateral transfer of strain occurs for a period of time early in the rifting process later crustal thinning switches to the rift axis because heat diffusing from below weakens the crust at this location and it is no longer energetically preferable to transfer strain to offset weak zones for the parameter values used in our models the sedimentary basins formed by extension at the offset weak zones remain tectonically active for no more than 10 my transfer of strain to the offset or rift flank basins is most efficient when the rate of active heating of the lithosphere is similar to the rate of deformation along the crustal shear zone results from a more complete plane strain finite element model agree with the basic predictions of the simple quantitative model they do however indicate that effects ignored in the simple model will reduce our estimates of the maximum distance of shear transfer this is particularly true when the deformation is large we interpret sedimentary basins located on the flanks of rifts or atlantic type margins to be the products of this process of strain partitioning in an inhomogeneous lithosphere the models provide an explanation for flank or offset basins that were active for a short interval early in a rift phase that have no thermal subsidence phase and that cannot be attributed to the gravitationally driven extension and collapse of orogenically overthickened crust

postglacial evolution of a fine grained alluvial fan in the northern great plains canada abstract this paper reports on the first subsurface core taken from an alluvial fan in the interior plains of western canada sedimentary structures grain size grain roundness loss on ignition charcoal abundance bulk authigenic geochemistry colour mineralogy and microscopic charcoal identifications show that a fine grained fan developed through a succession of depositional environments within each environment sediment erosion transportation and deposition processes were conditioned by changing dominant partial area contributions and complex geomorphic responses neither the rate nor the processes of aggradation have been constant through time succession from one depositional environment to another involved the crossing of geomorphic thresholds while climate may have affected sediment yield and therefore the timing of threshold crossings the basic sequence was controlled by aggradation alone the sensitivity of this site to climate change is thus overwhelmed by internal processes

sedimentation and stratigraphy at eyjabakkajokull an icelandic surging glacier a model for sedimentation by surging glaciers is developed from analysis of the debris load sedimentary processes and proglacial stratigraphy observed at the icelandic surging glacier eyjabakkajokull three aspects of the behavior of surging glaciers explain the distinctive landformsediment associations which they may produce a sudden loading of proglacial sediments during rapid glacier advances results in the buildup of excess pore pressures failure and glacitectonic deformation of the overridden sediments b reactivation of stagnant marginal ice by the downglacier propagation of surges is associated with large longitudinal compressive stresses these induce intense folding and thrusting during which basal debris rich ice is elevated into an englacial position in a narrow marginal zone as the terminal area of the glacier stagnates between surges debris from this ice is released supraglacially and deposited by meltout and sediment flows c local variations in overburden pressure beneath stagnant crevassed ice cause subglacial lodgement tills which are sheared during surges to flow into open crevasses and form crevasse fill ridges

subglacial till formation sedimentary characteristics and classification we review the major subglacial till forming processes as presently understood by glacial researchers and define the parameters within which tills are produced and reconcile them with sedimentary end members processes of deformation flow sliding lodgement and ploughing coexist at the base of temperate glacier ice and act to mobilize and transport sediment and deposit it as various end members ranging from glacitectonically folded and faulted stratified material to texturally homogeneous diamicton the dominance of any one subglacial process varies both spatially and temporally giving rise to the possibility that a till or complex till sequence contains a superimposed signature of former transportation deposition at the ice bed interface we recommend that while glacial geologists and geomorphologists should be able to recognize the sedimentary imprints of various subglacial processes genetic fingerprinting of subglacial tills should be less process specific and till classification must reflect the range of products encompassed by the subglacial till production continuum glacial geologists can presently unequivocally identify a glacitectonite rock or sediment that has been deformed by subglacial shearing deformation but retains some of the structural characteristics of the parent material b subglacial traction till sediment deposited by a glacier sole either sliding over and or deforming its bed the sediment having been released directly from the ice by pressure melting and or liberated from the substrate and then disaggregated and completely or largely homogenised by shearing and support the theoretical case for c melt out till sediment released by the melting of stagnant or slowly moving debris rich glacier ice and directly deposited without subsequent transport or deformation because observations on contemporary glaciers reveal that their beds are most likely to be mosaics of deformation and sliding and warm based and cold based conditions the patterns of which change temporally and spatially it is extremely unlikely that subglacial till end members in the geological record will be anything but hybrids produced by the range of processes operative in the subglacial traction zone

solute release and sediment entrainment on microcatchments in the dinosaur park badlands alberta canada abstract this paper first considers the uptake of solutes and entrainment of sediments in runoff generated by simulated rainstorms on different badland surfaces then properties of the regolith materials related to solute uptake are described and studied in a number of simple laboratory experiments field and laboratory results are in close agreement runoff solute and sediment uptake are profoundly influenced by the large amounts of sodium montmorillonite present in the regolith shale surfaces although responding late to rainfall release increasing amounts of sediment and solutes sodium and sulphate as they swell and increase in erodibility on other surfaces low rates of rainfall acceptance are caused by the secretion of montmorillonite gels and there is a gradual decrease in solute and sediment concentration as accumulated salts are flushed from the surface the effect of the chemistry of the simulated rainfall on the experimental results is examined it is considered possible to characterize the pattern of solute and sediment uptake on the different badland surfaces and to apply this information to the identification of runoff sources in mesoscale drainage basins and to the routing of storm runoff

assumptions and observations in tectonic modelling of rift basins some implications of thermo isostasy stress and rheology for intrabasinal structure abstract there has been a multitude of studies showing to what extent alterations in fundamental tectonic assumptions and or modelling parameters can affect predictions on how extensional sedimentary basins evolve however that little is known about how mantle processes initiate lithospheric rifting extension and affect basin evolution limits the extent to which improvements in tectonic modelling assumptions and parameter resolution can lead to a better understanding of intrabasinal or reservoir development processes the tectonic heat budget appears to be constrained by empirical means with the aid of kinematic models without the necessity of a thorough understanding of the dynamic processes involved in basin formation nevertheless the thermal coupling of tectonic model with intrabasinal development is sensitive to the choice of sediment thermal conductivities an important but often neglected tectonic modelling parameter to resolve is when the state of stress changes through time as a result of the interaction of all the known and unknown tectonic processes actively affecting the basin lithosphere system the occurrence of geologically short lived episodes of rapid basin subsidence may be a response to a change in the tectonic setting regardless of the relative sense of change of the ambient stress field recent theoretical studies suggest the same may be true for the evolution of salt diapirs