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

history of late glacial runoff along the southwestern margin of the laurentide ice sheet abstract the routing of runoff from the retreating laurentide ice sheet was controlled by a combination of ice marginal position and topography isostatic depression also played an important role in the evolution of the ice marginal landscape a major redirection of drainage occurred after ice retreated north of the missouri escarpment about 12 ka bp runoff that had previously flowed south to the missouri river could then be routed eastward to lake agassiz which in turn drained to the upper mississippi river valley changes in drainage routing in the region west of glacial lake agassiz typically were abrupt as new and lower paths along the retreating ice margin became available each new basin was larger than its predecessor and its headwaters extended farther west four distinct sequential phases of ice marginal drainage occurred between 12 and 10 7 ka bp the james sheyenne souris pembina and qu appelle assiniboine starting with the qu appelle assiniboine phase about 11 2 ka bp lake agassiz collected runoff from as far west as the rocky mountains by about 10 7 ka bp ice had retreated north of the lower reaches of the saskatchewan river allowing meltwater to by pass the qu appelle assiniboine basin at about the same time the eastern outlets of lake agassiz opened initiating drainage to the north atlantic ocean from this vast region drainage routes evolved by a common sequence of events beginning with the impoundment of proglacial lakes along the ice margin most of these lakes drained catastrophically resulting in the formation of spillways with distincitve geomorphic features that include broad scoured and streamlined subupland channels along with subsequently incised narrow deep inner channels characteristic deposits of these outbursts include boulder mantles on subupland channel floors boulder gravel bars within the inner channels and large primarily subaqueous fans in lake basins that received the flood bursts these outbursts progressed from basin to basin causing the drainage of other proglacial lakes until they reached lake agassiz spillways associated with the next younger drainage phase were commonly incised across the abandoned lake floors

asian summer monsoonal variations during the holocene revealed by huguangyan maar lake sediment record abstract high resolution records of summer monsoonal evolution in the holocene are essential to paleoclimate reconstruction but are hard to obtain here we provide a continuous well dated high resolution record from huguangyan maar lake located in the west pacific climate regime multi proxies including chlorophyll a toc sr rb ratio and magnetic susceptibility have been used to reconstruct the monsoon variations in the holocene higher chlorophyll a values are related with stronger summer monsoon and vice versa high temporal resolution radiocarbon dating enables us to divide summer monsoon evolution stages summer monsoon in zhanjiang area was strongest in the early holocene but began to decline at 6080 yr bp and weakened substantially since about 3600 yr bp the transition around 6080 yr bp supported by our high resolution dating lags the previous estimates by 1700 years the decreasing summer solar radiation at 30 n through the holocene is probably responsible for gradually weakened summer monsoon the anti phased co variation of summer monsoon intensity and enso activity throughout the holocene suggests that they could be interlinked driven together by solar radiation at orbital scale

first whiffs of atmospheric oxygen triggered onset of crustal gold cycle lack of a suitable gold source has long been regarded as a major argument against a palaeoplacer model for the exceptionally well endowed witwatersrand gold province by comparing worldwide witwatersrand type deposits occurrences ranging in age from 3 1 to 1 8 ga we propose that the primary concentration of gold in the continental crust resulted from atmospheric and biological evolution in the mesoarchaean a high au flux off the archaean land surface orders of magnitude greater than today s was a consequence of the chemistry of the mesoarchaean atmosphere and hydrosphere when early life gradually changed from anaerobic anoxygenic to oxygenic photosynthesizers at around 3 0 ga the first whiffs of free oxygen produced by photosynthesis under an overall reducing atmosphere provided the ideal trap for au dissolved in the huge reservoir in meteoric and shallow sea water oxidative precipitation of gold on the surface of the o2 producing microbes probably cyanobacteria could fix huge amounts of gold over large areas some of this microbially mediated gold is still preserved in thin kerogen layers carbon seams that typically developed on erosional unconformities scour surfaces and bedding planes in near shore environments at around 2 9 ga this gold provided the principal source for the very rich placer deposits that formed by the subsequent sedimentary reworking of the delicate microbial mats on aeolian deflation surfaces into fluvial channels and delta deposits represented by meso to neoarchaean auriferous conglomerates tectonic reworking of these first gold rich sediments by orogenic processes explains the temporal peak of orogenic type gold formation at around 2 7 to 2 4 ga with time the strongly gold enriched archaean sediments became progressively eroded covered or tectonically reworked and their role as potential source of younger placer deposits diminished this explains why witwatersrand type deposits younger than 2 4 ga are rare and far less well endowed and effectively missing in the rock record after 1 8 ga

hydrothermal alteration in the witwatersrand goldfields abstract alteration is recorded throughout much of the 3 km thick upper witwatersrand succession in south africa and extends for 300 km around the basin and 50 km into the basin the evidence for this alteration comes from petrography mineralogy geochemistry rock fabrics and stratigraphy the alteration conceived as a giant halo enveloping each major goldfield requires a major hydrothermal event focused on the auriferous upper wits central rand group the scale and nature of the alteration and its relationship to gold distribution on various scales strongly support a hydrothermal model for gold deposition such a model can account for the 50 000 t of gold mined from the witwatersrand goldfields the model works within the context of the major advances in understanding of the geological framework of the witwatersrand basin including the recognition of the importance of post burial processes it is highly significant that the age of witwatersrand sedimentation is much older than 2700 my and thus the host rocks for gold were deposited at least 100 my before the major global archean greenstone gold event the shale units from 40 major mines covering the seven goldfields are examined to establish the nature and distribution of the alteration and to make the connection between the fluid infiltration that caused the alteration and the introduction of gold into the witwatersrand basin in the hydrothermal model described here an auriferous low salinity fluid is produced at about 500 c during the metamorphism of mafic material that was below and adjacent to the witwatersrand basin large shear zones in the footwall of goldfields are the inferred fluid pathways into the upper wits succession and then unconformities smaller shear zones veins and the reef packages guide local fluid flow in this model gold precipitation occurs in response to the reaction of the fluid with carbon and iron bearing rocks that are abundant in the reef packages immediately overlying unconformity surfaces gold precipitation occurred at about 350 c and 10 km depth with the implication of a high geothermal gradient approaching 35 c per km the alteration of the shales but lack of abundant gold in them is predicted from the paucity of appropriate rocks or minerals in the shale units to precipitate gold but fluid infiltration still changed their composition fundamentally the source of the witwatersrand gold its present distribution and the alteration are explained within this hydrothermal model with similarities to the models invoked for other major gold provinces it is worth noting that quartz pebble conglomerate is a poor term for this gold type and has almost certainly limited exploration opportunities globally

climate change and social vicissitudes in china over the past two millennia abstract the relation between climate change and historical rhythms has long been discussed however this type of study still faces the lack of high resolution data concerning long term socio economic processes in this study we collected 1586 items of direct and proffered evidence from 29 chinese history books we used semantic analysis to reconstruct a quantitative series of the social vicissitudes of the past 2000 yr with a 10 yr resolution to express the phase transition of the social vicissitudes of the dynasties in china our reconstruction demonstrates that social vicissitudes have clear cyclical features on multiple time scales analysis of the association of social rise and fall with climate change indicates that temperature displayed more significant effects on social vicissitudes in the long term while precipitation displayed more significant effects on the social vicissitudes in the short term there are great overlaps between social and climatic variables around the predominant or periodic bands social rise mostly occurred in the centennial scale warm periods whereas social decline mostly occurred in the centennial scale cold periods under warm wet conditions social rise occurred over 57 of the time under cold dry conditions the social decline occurred over 66 of the time

yancheva et al reply replying to h zhou et al doi 10 1038 nature06408 2007 zhou 1 raise the possibility that the titanium ti record at lake huguang maar is controlled by local erosion and runoff to the lake or through hydrological changes in the lake such as level fluctuations rather than by changes in the inputs of airborne material2 the authors come to this conclusion by considering the ti record in isolation they ignore the redox sensitive parameters of the s ratio total organic matter content the mn fe ratio and magnetic susceptibility records we believe that their case against our interpretation of the ti record is weak and that their interpretation can be ruled out if the other measurements are taken into account2

preliminary observations on the geomorphic evolution of the guide basin qinghai province china implications for the uplift of the northeast margin of the tibetan plateau

postglacial alluvial terraces and an incorporated bison skeleton ghostpine creek southern alberta department of geography the university of calgary calgary ab t2n in4 canada received july 12 1993 revision accepted june 21 1994 ghostpine creek near three hills southern alberta is a tributary of the red deer river it has three sets of paired alluvial terraces t 1 to t 3 in a downstream part of the valley the rare discovery of a largely intact skeleton of plains bison bison bison bison in a t 2 point bar prompted terrace mapping i4c dating and interpretation of the postglacial evolution of the valley downvalley portions of the creek began incision into the newly drained bed of glacial lake drurnheller probably about 13 000 bp localized valley deepening up to 20 m the production of erosional benches and residual spurs and the develop ment of partly convex up creek paleothalwegs occurred between about 13 000 and 7600 bp by which time basal t l alluvium was beginning to accumulate subsequent aggradation of t 1 sediment and then degradation of about 3 4 m were followed by aggradation of t 2 alluvium these trends had taken place by 2600 bp when the bison died and its skeletal remains were buried in uppermost sediment of a t 2 point bar between 2600 bp and now the creek incised about 5 m below the former t 2 channel position and aggraded partly synchronously up to 3 m of t 3 floodplain alluvium radiocarbon dated alluvial terrace sequences in alberta show generally comparable trends of rapid early creek incision followed by partially overlapping episodes of net aggradation and degradation from basin to basin however such episodes were not closely synchronized

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

relationship between detrital zircon age spectra and the tectonic evolution of the late archaean witwatersrand basin south africa abstract shrimp u pb detrital zircon age spectra for 14 samples from the west rand and central rand groups of the witwatersrand basin indicate that felsic source rocks mostly formed at 3090 3060 and 3000 2870 ma with a smaller proportion formed prior to 3100 ma provenance evaluation indicates that source rocks have largely vanished through erosion such that greenstone terrains extending from the amalia kraaipan belt in the southwest to the murchison belt in the northeast are models of but not the actual source areas analysis of detrital zircon age modes reveals that the west rand and central rand groups record different basins the west rand group is characterised by age subpopulations with a much smaller range and less complex distribution than those in the central rand group furthermore detrital zircon age spectra for the west rand group generally decrease in complexity up section whereas they become increasingly more complex in the central rand group it is concluded that the source area for the west rand group is consistent with a passive margin setting with the decrease in complexity up section of zircon age spectra being the consequence of increasing maturity of the hinterland conversely the source area of the central rand group was far more dynamic with an increasing age range of source rocks being exposed through time pulsed tectonic rejuvenation of the source area is implied contemporaneous emplacement uplift and erosion of granitoids supports a magmatic fold thrust belt as the source and a complementary retroarc basin setting detrital xenotime grains record the ages of high u granitoids emplaced in the fold thrust belt during deposition of the central rand group and are much closer to depositional ages than are detrital zircon grains change from a passive margin to a retroarc basin across the west rand central rand boundary is emphasised by change from simple to increasingly complex detrital zircon age spectra this study establishes that detrital zircon geochronology can overcome the problem of overly quartzose compositions in archaean sandstones due to severe chemical weathering and authigenic alteration thereby enabling distinction between passive margin and retroarc basin stages through systematic changes in the age complexity of the source area

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

constraints from strontium and neodymium isotopic ratios and trace elements on the sources of the sediments in lake huguang maar abstract the sediments in lake huguang maar in coastal south china were previously thought to originate mainly from wind blown dust transported from north china such that the lake sediments recorded the varying strength of the asian winter monsoon an alternative explanation was that the local pyroclastic rocks supplied the lake sediments but the actual contributions from the different sources remained unclear geochemical analyses including 87sr 86sr and 143nd 144nd and trace elements support the local pyroclastic rock as the dominant source

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

ti content in huguangyan maar lake sediment as a proxy for monsoon induced vegetation density in the holocene the provenance of element ti in huguangyan maar lake hgy sediment has been under debate since yancheva et al 2007a proposed its eolian source from the chinese loessplateau clp and applied it as a proxy for asian wintermonsoon we performed a comprehensive study on ti carryingminerals and ti uxes in lake sediments wall rocks andloess from the clp here we show that the chemicalcompositions and morphological features of magnetite the most important ti carrier in hgy surface sediments are identical to those in wall rocks around the lake butsubstantially different from those in clp loess samples ourcalculated modern eolian ti ux from the clp is negligiblecompared to the average total ti ux to hgy and ti uxfrom catchment erosion can provide enough ti indicating tiin hgy sediment are predominantly from wall rock erosion inverse correlation between total organic carbon toc vegetation density and ti ca ratio terrestrial input in theholocene suggests monsoon induced vegetation densitypredominates over runoff in controlling ti input to hgy s ratio represents toc directly mediated reductive diagenesisof iron oxides magnetite preservation rather than anoxic oxic condition at the bottom water induced by wintermonsoon our record shows a decreased vegetation density increased ti input and weakened reductive diagenesisthrough the holocene driven by a weakened summermonsoon

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

east asian winter monsoon variability over the last glacial cycle insights from a latitudinal sea surface temperature gradient across the south china sea article i nfo high resolution planktonic foraminifer mg ca sea surface temperature sst and 18 o records of images core md052896 from the southern south china sea scs provide a history of east asian winter monsoon variability over the past 23 kyr specifically we find that the latitudinal sst gradient of the north south scs shows promise as a useful proxy of east asian winter monsoon changes the sst record of core md052896 from the southern scs and odp site 1145 from the northern scs documents several positive anomalies indicating east asia winter monsoon maxima during cold periods of the past 23 kyr including the h1 and younger dryas events the sst record also indicates that after 8 5 ka the east asian winter monsoon strengthened relative to the deglaciation reaching levels of the last glacial period comparison of the scs sst record with stalagmite 18 o records suggests that both the east asian summer and winter monsoons strengthened from the last glacial to the holocene and that summer and winter monsoon strength probably are not anti correlated at least over the last glacial interglacial cycle

influence of the intertropical convergence zone on the east asian monsoon a palaeoclimate record spanning the past 16 000 years with nearly annual time resolution has been obtained from lake huguang maar in china the magnetic properties and titanium content of the lake sediments are thought to reflect changes in the east asian winter monsoon strength thus providing a complement to palaeoclimate archives that record the strength of the rain bearing summer monsoon the records point to an anti correlation between winter and summer monsoon strength best explained by migration of the intertropical convergence zone itcz a belt of low pressure air at the equator interestingly the decline of china s tang dynasty and the mayan civilization broadly coincide with drought periods recorded in lake huguang maar and cariaco basin sediments respectively did major shifts in the position of the itcz catalyse simultaneous events in civilizations on opposite sides of the pacific ocean the asian australian monsoon is an important component of the earth s climate system that influences the societal and economic activity of roughly half the world s population the past strength of the rain bearing east asian summer monsoon can be reconstructed with archives such as cave deposits1 2 3 but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct here we present high resolution records of the magnetic properties and the titanium content of the sediments of lake huguang maar in coastal southeast china over the past 16 000 years which we use as proxies for the strength of the winter monsoon winds we find evidence for stronger winter monsoon winds before the bolling allerod warming during the younger dryas episode and during the middle and late holocene when cave stalagmites suggest weaker summer monsoons1 2 3 we conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone similar migrations of the intertropical convergence zone have been observed in central america for the period ad 700 to 900 refs 4 6 suggesting global climatic changes at that time from the coincidence in timing we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the tang dynasty in china and the classic maya in central america

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

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

holocene geomorphology and stratigraphy of the lower falcon valley dinosaur provincial park alberta canada a tributary of the red deer river in dinosaur provincial park southern alberta contains evidence of a sequence of valley cutting and the deposition of three alluvial fills and one eolian deposit with the exception of the eolian deposit and minor amounts of shield and cordilleran rocks the sediments are derived from local bedrock incision of the bedrock valley occurred in the early postglacial period about 14 000 12 000 bp by rapid drainage of proglacial lakes and meltwaters the valley was subsequently partly infilled as locally fed stream discharges declined during the early to middle holocene by 6000 5000 bp alluvial fans had formed along the base of the valley walls fan development was followed by two phases of stream entrenchment and alluvial deposition including the most recent phase of cutting and filling that began approximately 800 bp the erosional and depositional events may reflect climatic changes as inferred in lacustrine deposits in southern alberta and in valleys elsewhere in the

record of winter monsoon strength arising from g yancheva et al 74 77 2007 10 1038 nature05431 yancheva et al reply the asian summer monsoon has been precisely reconstructed from the high resolution record from the speleothem1 but reconstruction of the asian winter monsoon is less satisfactory yancheva et al 2 provide such a reconstruction for the last 16 000 years from the titanium ti content of the sediments of lake huguang maar in coastal south china however we argue that the ti is likely to have come mainly from the catchment and so the ti content may instead be related to the hydrology of the lake

spatial scale dependence of sediment dynamics in a semi arid badland drainage basin abstract problems of spatial scale transference are of key interest in drainage basin research the objective of this study was to investigate the spatial scale dependence of sediment dynamics in semi arid badland drainage basins simulated rainfall experiments indicated that on microscale plots runoff generation and sediment entrainment occurred when total rainfall exceeded 0 5 to 6 mm on pediment surfaces 1 5 to 4 mm on sandstone surfaces and 8 to 25 mm on shale surfaces the sediment concentration discharge relationship for two mesoscale basins displayed a change from clockwise to counterclockwise hysteresis when total rainfall exceeded the threshold rainfall for the initiation of flow in deep tunnel systems the initiation of tunnel flow causes counterclockwise hysteresis due to a delayed increase in sediment concentrations during a runoff event this contrasts with the clockwise hysteresis caused by flushing in the early stages of runoff for smaller rainstorms comparison of micro and mesoscale sediment dynamics indicates that microscale thresholds are not by necessity in evidence at the mesoscale in addition at the mesoscale elements exist which are non existent at the microscale e g a deep tunnel system the behaviour of the mesoscale basin is dominated by these elements rather than by the microscale components it contains

clay mineralogy as a crucial factor in badland hillslope processes abstract comprehensive and important work has been done in understanding badland processes on both the big scale and more recently on smaller scale in order to understand the subtle differences between sites however most studies lack important information regarding clay mineralogy and their importance for weathering processes type and rate of weathering depend on material physico chemical properties climatic regimes and slope characteristics as weathering progresses the surface conditions change influencing erosion processes usually badland lithologies are reported as sodium rich highly dispersive materials but that is not invariably true the primary objective of this study is to show that clay minerals have an important role in defining surface and subsurface processes on badland hillslopes field studies conducted in dinosaur park badlands alberta canada chinguacousy badlands ontario canada and sestino badlands tuscany italy have shown that there are two dominant clay rich lithologies smectite rich and smectite poor mudrocks different surface crust and weathering profiles were observed on smectite rich mudrocks during two field years with distinct precipitation inputs after a dry fall winter season the popcorn surface was very well developed 2 3 cm the subsurface layer 10 15 cm thick overlaid the layer of smaller shards followed by the unweathered material after a very wet fall winter season the surface layer was denser and thinner 0 5 cm with wider cracks and a thin subsurface layer attached to the crust weathering profiles on smectite poor lithologies did not show any differences with variable climatic conditions a thin surface layer was composed of soft thin and small 0 5 0 3 0 1 cm shards a layer of larger shards overlying unweathered material was beneath it in order to better understand the described occurrences badland materials were monitored in controlled laboratory conditions during an incremental weathering experiment six samples of each material were subjected to 10 cycles of simulated rainfall which duration ranged 10 60 min very short rainfalls 10 20 min can cause swelling of clay minerals in smectite rich materials and formation of popcorn surface during drying periods during subsequent wetting drying periods the crust becomes flatter and denser and desiccation cracks become wider and deeper samples subjected to 50 and 60 min of rainfall showed maximum swelling after only one cycle of rainfall after this swift swelling samples became unstable and dispersive during subsequent wetting dispersion became dominant resulting in flatter surfaces thinner crust and narrower desiccation cracks smectite poor mudrocks appeared to be resistant to variable wetting and drying large shards broke down into smaller due to differential swelling of illite and chlorite once they were reduced to tiny flaky shards the surface became compacted the surface cracks served as the initial pathways for sediment and water movement knowing if the material is smectite rich or smectite poor can help in prediction of processes and the erosion rates the amount intensity and duration of precipitation will determine not only the rate of weathering but also the type of the weathered surface on smectite rich surfaces smectite poor materials appear to be more resistant to change in precipitation

proglacial lakes and the retreat pattern of the southwest laurentide ice sheet across alberta canada abstract the extent of proglacial lakes following the initial separation of the southwest laurentide ice sheet from the cordilleran ice sheet and its eastward retreat from the canadian rocky mountains has been reconstructed across regions of alberta at a range of scales however to date no studies have integrated all available geological information to produce a province wide deglacial reconstruction that considers the evolution of proglacial lakes as components of the ice marginal system in this paper we utilize a geologically constrained shoreline projection method with a high resolution digital elevation model to reconstruct the evolution of the ice marginal system along the southwest lis during the last deglaciation this method provides new details on the configuration volume drainage history and routing of 240 proglacial lakes as they migrated across alberta and establishes a succession of paleogeographic reconstructions that can place geological evidence of regional and local ice flow reorganizations into a spatiotemporal context these reconstructions demonstrate that although the evolution of proglacial lakes was largely driven by the topography of the emerging landscape and the configuration of the ice margin positive feedbacks in the ice marginal system particularly where margins transitioned from terrestrial to subaqueous settings played a major role in deglacial ice dynamics narrow ribbon shaped lakes that paralleled the ice margin induced relatively minor changes in style and rate of deglaciation whereas the evolution of progressively larger longer lived lakes extending obliquely to the ice margin promoted surging and subsequent rapid retreat

dynamic evolution of badlands in the roglio basin tuscany italy abstract the roglio basin in the relatively arid central tuscany italy is characterised by the presence of 191 badlands that have developed on pliocene fine grained blue clays a morphometric analysis on the badlands has highlighted that these landforms formation and distribution are primarily related to the steepness of the hill flanks which favour runoff and gravitational processes along with favourable aspects typically the southern ones that experience a stronger solar induced daily thermal variation a detailed physico chemical analysis of the clayey material involved has also been carried out with the specific aim of testing whether this plays a role in the various stages of activity shown by the roglio basin badlands the results indicate that there are no significant differences in the physico chemical properties of an active vs an inactive dormant badland observation and field data however indicate that the dynamic of the roglio basin badlands is strongly controlled by the occurrence of earth flows and the velocity of sediment removal at the bottom of the badlands these two processes variously combined at different intensity in relationship to many local factors are likely to be the main responsible for the different stages of activity shown by the roglio basin badlands

control of climate and local topography on dynamic evolution of badland from southern italy calabria abstract this work deals with an integrated geomorphological and chemical physical study of calanchi landforms in site caulonia of se calabria southern italy developed on of late pliocene quaternary clay deposits the aim of this paper is to investigate how topography and rainfall quantity may affect runoff and slope processes in calanchi landforms by influencing the physical chemical and mineralogical properties of clayey sediments to this purpose a comparison has been made among the physical chemical and mineralogical features of calanchi materials sampled after a rainy period precipitation mean annual rainfall of 709 6 mm wet year with those sampled after relatively dry period mean annual rainfall of 431 4 mm dry year and in different topographic settings opposite flanks of a catchment exhibiting different steepness and lengths i e w to nw facing and e to ne facing slopes using a multivariate statistic approach which adopts the principal component analysis pca method to extract factors it has been possible to make a hypothesis of the main processes responsible for dynamic evolution of the study area the rainfall quantity coupled with topography has to be considered as the main control factor inducing changes in the physical chemical mineralogical parameters

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

ages of altered granites adjoining the witwatersrand basin with implications for the origin of gold and uranium one of the main problems in understanding the origin of the witwatersrand basin mineralization concerns the source of the prodigious concentrations of gold and uranium in the basin another problem is the age and nature of the rocks in the source area recent data1 2 indicate that the source area was largely 3 200 2 900 myr old becoming progressively younger as the basin evolved granites adjoining the basin are commonly overprinted by pervasive and vein related hydrothermal alteration which resulted in an enrichment of both gold and uranium3 4 here we report uranium lead data demonstrating that these hydrothermally altered granites were intruded sporadically both before and during the 360 myr period5 constraining witwatersrand sediment deposition and that hydrothermal alteration was associated with granitoid intrusion and subsequent cooling thus fertilization of the crust occurred during basin evolution a feature that supports the idea19 that gold and uranium mineralization occurred simultaneously with sediment deposition

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

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

gold mobility during palaeoarchaean submarine alteration abstract seafloor alteration provides large amounts of solutes to the hydrosphere in order to investigate gold mobility during water rock interaction prior to 3 billion years ago low detection limit analysis of au concentrations was carried out on rocks from marine alteration zones stratiform zones recording low temperature 150 c seafloor alteration are a characteristic feature of greenstone belts older than 3 0 ga hydrothermal processes were operating on and immediately below the seafloor giving rise to extensive silicification of sub seafloor volcanic rocks and silicification of seafloor sediments in order to investigate gold mobility during silicification unaltered and variably silicified volcanic rocks and associated cherts from palaeoarchaean greenstone successions c 3 4 ga of south africa were analyzed results show mobility of gold during silicification of mafic ultramafic rocks and transfer to the archaean ocean some gold was incorporated into carbonaceous marine sediments overlying the alteration zones a combination of pervasive silicification rarity of black shales and low gold content in komatiites can explain the low mineralization potential of palaeoarchaean greenstone belts for orogenic gold deposits

formation of gold deposits a metamorphic devolatilization model a metamorphic devolatilization model can explain the enrichment segregation timing distribution and character of many goldfields such as those found in archean greenstone belts slate belts and other gold only provinces in this genetic model hydrated and carbonated greenschist facies rocks particularly metabasic rocks are devolatilized primarily across the greenschist amphibolite facies boundary in an orogenic setting devolatilization operates on the scale of individual mineral grains extracting not just h2o and co2 but also s and in turn au elevated gold in solution is achieved by complexing with reduced s and by h2co3 weak acid buffering near the optimal fluid ph for gold solubility the buffering is more important than being at the point of maximum gold solubility low salinity ensures low base metal concentrations in the auriferous metamorphic fluid migration of this fluid upwards is via shear zones and or into hydraulic fracture zones in rocks of low tensile strength the geometry of the shear zones dictates the kilometre scale fluid migration paths and the degree of fluid focusing into small enough volumes to form economic accumulations of gold deposition of gold from solution necessitates breakdown of the gold thiosulphide complex and is especially facilitated by fluid reduction in contact with reduced carbon bearing host rocks and or by sulphidation of wallrocks to generate iron bearing sulphide and precipitated gold as such black slate carbon seams banded iron formation tholeiitic basalt magnetite bearing diorite and differentiated tholeiitic dolerite sills are some of the important hosts to major goldfields gold deposition is accompanied by carbonation sulphidation and muscovite biotite alteration where the host rock is of suitable bulk composition the correlation of major gold deposits with rock type even when the gold is primarily in veins argues for rock dominated depositional systems not fluid dominated ones as a consequence a general role in gold deposition for fluid mixing temperature decrease and or fluid pressure decrease and boiling is unlikely although such effects may be involved locally several geological features that are recorded at gold only deposits today reflect subsequent modifications superimposed upon the products of this generic metamorphic devolatilization process overprinting by higher grade metamorphism and deformation and or palaeo weathering may provide many of the most obvious features of goldfields including their mineralogy geochemistry geometry small scale timing features geophysical response and even mesoscopic gold distribution

post glacial fluvial response and landform development in the upper muskegon river valley in north central lower michigan u s a article i nfo this study focuses on the upper part of the muskegon river system in north central lower michigan and is the first to reconstruct the post glacial history of fluvial landform development in the core of north america s great lakes region results indicate that the upper muskegon river valley contains four alluvial terraces and numerous paleomeanders radiocarbon dating of peats within these old channels provides a good chronology for stream behavior and landform development the t 4 terrace is a paired pleistocene outwash lacustrine surface that probably formed about 12 500 years ago the t 3 terrace is a fill strath surface that was cut between about 12 000 and perhaps 9500 years ago the geometry of macromeanders on this surface suggests that stream discharge was 8 times greater than during the holocene the pleistocene holocene transition is marked by a major period of downcutting that likely began as the climate warmed dried and sediment yield diminished this period of downcutting potentially lasted through the drier middle holocene creating a 6 m high escarpment in the valley the muskegon river then began to aggrade when the climate became wetter subsequently the river again incised creating the paired t 2 terrace about 3400 years ago when the climate became still wetter t 2 paleomeanders indicate that stream discharge at this time was consistent with the modern river in the past 2500 years the stream has constructed a poorly defined complex of t 1 terraces these surfaces likely formed due to complex response associated with more variable climate this study demonstrates that the upper muskegon river has a similar post glacial history as streams on deglacial and periglacial landscapes elsewhere in the world

error in polygon overlay processing of geomorphic data predictive models for calculating sediment yield and discharge require accurate areal data such models may be unrealistic when using digitized data given the potential error involved in compiling and digitizing thematic polygon maps the estimation of boundary variability for digitized polygon maps of a 0 34 km2 area of badlands in dinosaur provincial park alberta shows the effects of positional errors introduced during mapping and digitizing processes polygon overlay of maps of surface features and slopes produced high frequencies of very small polygons and some unlikely combinations of slopes and surface features and decreased reliability in areal measurements in the composite map at an epsilon band width of 0 7 m a reasonable estimate of boundary variability 31 7 per cent of the resultant overlaid map can be considered unreliable