late paleozoic glacial episodes in gondwanaland reflected in transgressive regressive depositional sequences in euramerica the late paleozoic glaciation of gondwanaland comprised two short episodes in the famennian i and visean ii confined to brazil and adjacent northwest africa and a long episode that started in the namurian iiia of eastern australia and bolivia argentina expanded to cover much of gondwanaland in the stephanian asselian iiib and collapsed in the early sakmarian iiic dropstones in eastern australia indicate that small ice centers lingered to the kazanian across the belt of low latitudes north of gondwanaland short ranging fossils in widespread shallow marine and paralic deposits indicate synchronous deposition of transgressive regressive sequences in different parts of euramerica these sequences correlate with glacial events in gondwanaland at three levels a four major regressions in euramerica in the famennian 1 visean 2 namurian 3 stephanian 4 and the tastubian transgression that preceded the sterlitamakian regression 5 also recorded in gondwanaland correlate with glacial episodes i ii and iiia iiib and iiic b the time interval of cyclothemic deposition in euramerica brigantian or latest visean to sterlitamakian correlates with that of glacial episode iii and c the dominant period of the euramerican cyclothems as estimated from the middle and late pennsylvanian deposits of the mid continent of north america and of the thickest known gondwanaland glacigenic sediment the earliest permian lyons group of western australia is 0 4 ma equivalent in turn to the long orbital eccentricity period of the quaternary ice age and the dominant period of fluctuation of the late miocene antarctic ice cap the three levels of correlations confirm wanless and shepard9s 1936 hypothesis that the late paleozoic cyclothems are controlled largely by sea level fluctuations related to the gondwanaland glaciation

proglacial deposition and deformation in the upper carboniferous to lower permian wynyard formation tasmania a process analysis abstract the wynyard formation of tasmania australia provides the youngest evidence of grounded ice during the late carboniferous early permian in the tasmania basin of southeastern gondwana during the late paleozoic ice age within the wynyard formation four facies associations are recognized 1 massive diamictite 2 stratified diamictite 3 conglomerate and sandstone and 4 deformed mudstone and fine sandstone a detailed facies analysis was performed in order to interpret the depositional processes and environments the massive diamictite facies association contains massive diamictite and sandstone and was deposited primarily by iceberg rain out in a subaqueous morainal bank setting the stratified diamictite facies association is composed of stratified diamictite sandstone and conglomerate and was deposited by debris flows and iceberg rain out and deformed by glacial pushing the conglomerate and sandstone facies association is made up of cross stratified channelized conglomerate and pebbly sandstone that were deposited by glacial outwash on grounding line fans the deformed mudstone and fine sandstone facies association is composed of pervasively deformed pebbly mudstone and fine grained sandstone that exhibit volcano flame and dyke structures this facies association was deposited by a combination of suspension settling iceberg rain out and soft sediment deformation in a quiet distal proglacial setting the facies analysis supports the interpretation that the wynyard formation was deposited by a wet based tidewater glacier or glaciers the depositing glacier s occupied a 40 km wide trough in northwest tasmania based on the distribution of the wynyard formation and the presence of glacial deposits in other eroded troughs in tasmania glaciation occurred in the region within broadly eroded valleys the wynyard formation and overlying mudstone of the inglis formation provide a glacial postglacial signature similar to those in south africa antarctica and eastern australia during the latest carboniferous early permian therefore the climate warmed in southern gondwana following this glacial interval the continued glaciation in eastern australia was a result of regional topography and oceanographic processes

ploughing boulders along shorelines with particular reference to the st lawrence estuary abstract ploughing boulders are defined as large stones moved by drift ice with a ploughing action into the substrate leaving a linear depression on the back and building a frontal push ridge they are commonly found on unconsolidated tidal flats and on rock shore platforms along cold region shorelines in the marine lacustrine and fluvial environments it is an erosional process of great significance particularly for consolidated substrates a total of 176 ploughing boulders were measured in eighteen localities along the st lawrence estuary the largest boulder weighed 176 tons and was moved 3 m while a 50 t boulder was moved 40 m on shore platforms cut in shales one boulder 49 t has scoured a depression 19 m long and up to 40 cm deep and built a frontal ridge 40 cm high along the st lawrence estuary about 95 of ploughing boulders were moved seaward by ice floes entrained by ebb currents

oxygen and carbon isotopes of early permian cold water carbonates tasmania australia abstract the permian carbonates of tasmania formed at a paleolatitude near 80 s during the gondwanan ice age contain abundant dropstones and are associated with glaciomarine sediments a shallow marine carbonate depositional model with floating icebergs calved from an adjacent ice shelf grading into an ice sheet has been proposed as the sea level rose during relatively warmer periods large volumes of melt waters mixed with marine waters retarding limestone deposition and causing deposition of shales siltstones these phases are preserved in the stratigraphic record as interbedded units australian permian brachiopods and molluscs are characterized by unusually light o18 pdb values and heavier c13 pdb values than those that occur in many modern cool temperate to subpolar cold water carbonates tasmanian permian whole rock o18 pdb values fall at the edge of the normal marine limestone field of keith and weber 1964 and range towards lighter values down to 16 9 pdb the o18 values of cements 7 6 to 25 6 pdb in the tasmanian early permian limestones partly overlap with those o18 values obtained for fresh water cements in the early permian continental tillites from antarctica and south africa gondwanaland indicating that the early permian sea was diluted by isotopically light melt waters during warming phases the o18 values of permian fauna if one assumes no diagenetic equilibration give unrealistic paleotemperatures because of this variable melt water dilution of the permian sea however calculated o18 values corresponding to marine c13 values of brachiopods and eurydesma and extrapolated from a model based on the linear trend of c13 o18 in modern and last glacial cold water carbonates give reasonable estimates of australian permian temperatures of up t 15 c with the coldest waters of less than 4 c around tasmania the sequential deviation lines of o18 c13 of both cements and the fauna associated with these cements indicate that the original o18 value of fauna was as high as 6 pdb this calculated original o18 value indicates an average seawater temperature for tasmania in the early permian of 1 8 c similar to the present average 1 9 c water temperature near ice shelves around antarctica the o18 values of ements suggest that the tasmanian limestones reacted with subfreezing melt waters during early diagenesis the o18 composition of the early permian sea is inferred to have been about 1 2 pdb similar to that observed during the pleistocene glaciations and was diluted by melt water as light as o18 smow 31 at 5 c 26 pdb in variable amounts it is unlikely that the o18 composition of the wellmixed open permian sea ever reached a value as light as o18 pdb 6 it is suggested that the permian sea c13 value was about 2 pdb heavier than that of modern and pleistocene seawater

evidence of a recent magma dike intrusion at the slow spreading lucky strike segment mid atlantic ridge 1 mid ocean ridge volcanic activity is the fundamental process for creation of ocean crust yet the dynamics of magma emplacement along the slow spreading mid atlantic ridge mar are largely unknown we present acoustical seismological and biological evidence of a magmatic dike intrusion at the lucky strike segment the first detected from the deeper sections 1500 m of the mar the dike caused the largest teleseismic earthquake swarm recorded at lucky strike in 20 years of seismic monitoring and one of the largest ever recorded on the northern mar hydrophone records indicate that the rate of earthquake activity decays in a nontectonic manner and that the onset of the swarm was accompanied by 30 min of broadband 3 hz intrusion tremor suggesting a volcanic origin two submersible investigations of high temperature vents located at the summit of lucky strike seamount 3 months and 1 year after the swarm showed a significant increase in microbial activity and diffuse venting this magmatic episode may represent one form of volcanism along the mar where highly focused pockets of magma are intruded sporadically into the shallow ocean crust beneath long lived discrete volcanic structures recharging preexisting seafloor hydrothermal vents and ecosystems index terms 3035 marine geology and geophysics midocean ridge processes 7280 seismology volcano seismology 8419 8149 tectonophysics planetary tectonics 5475 4259 oceanography general ocean acoustics 9325 information related to geographic region atlantic ocean keywords mid atlantic ridge earthquake hydroacoustic

cold climate in the eastern australian mid to late permian may reflect cold upwelling waters a suite of ice rafted dropstones and glendonites throughout the permian succession of eastern australia indicates the cold climate associated with the late paleozoic ice age persisted longest in this part of gondwana paradoxically these cold climate indicators are preserved in transgressive and highstand facies and formed at mid to high latitudes at a time when paleofloral and sedimentological data suggest equable onshore environments during the intervening lowstands and temperate conditions at the pole these apparent inconsistencies suggest that eastern australia was anomalously cold in the context of post sakmarian gondwanan climates and the distribution of sedimentary indicators could indicate localized cooling by oceanographic processes modern upwelling of cold abyssal waters produces the specific physiochemical conditions necessary for ikaite for mation and is likely to have contributed to the development of glendonites in the eastern australian permian system such upwelling would have locally lowered surface water temperatures such that seasonal sea or river ice could form which rafted debris across the marine shelf and a cold water fauna could develop this hypothesis is supported by coupled atmosphere ocean models for the permian which suggest that wind systems may have driven upwelling along this section of the gondwanan coast colder conditions dissipated with the onset of the hunter bowen contractional event and the transformation of the basin system from an open marine shelf to a foreland basin this new hypothesis reconciles the prolonged deposition of cold climate indicators in the eastern australian permian with an apparent post sakmarian warming elsewhere in gondwana

co2 forced climate thresholds during the phanerozoic abstract the correspondence between atmospheric co2 concentrations and globally averaged surface temperatures in the recent past suggests that this coupling may be of great antiquity here i compare 490 published proxy records of co2 spanning the ordovician to neogene with records of global cool events to evaluate the strength of co2 temperature coupling over the phanerozoic last 542 my for periods with sufficient co2 coverage all cool events are associated with co2 levels below 1000 ppm a co2 threshold of below 500 ppm is suggested for the initiation of widespread continental glaciations although this threshold was likely higher during the paleozoic due to a lower solar luminosity at that time also based on data from the jurassic and cretaceous a co2 threshold of below 1000 ppm is proposed for the initiation of cool non glacial conditions a pervasive tight correlation between co2 and temperature is found both at coarse 10 my timescales and fine resolutions up to the temporal limits of the data set million year timescales indicating that co2 operating in combination with many other factors such as solar luminosity and paleogeography has imparted strong control over global temperatures for much of the phanerozoic

deterministic and stochastic analyses of acoustic plane wave reflection from inhomogeneous porous seafloor the propagator matrix technique for the acoustic plane wave reflection in layered porous anisotropic seafloor is combined with monte carlo simulation to investigate the layering effect of the sediment statistical data from a geologically known site are processed and used as a benchmark realizations of sediment property profiles are generated using a spectral technique a deterministic analysis demonstrates that the amplitude and phase of reflection coefficient is highly dependent on the variation of porosity in a stochastic analysis the effect of randomness is examined it is found that the fluctuation of the sediment physical properties around a mean profile has a significant influence on the seabed reflectivity particularly for the incident angles near and above the critical value frequency behavior of reflectivity is strongly dependent on the correlation length of medium inhomogeneities this behavior is attributed to the interaction among different waves that propagate in the porous sediment layers suggesting the possibility of obtaining the properties using the reflection loss data

sea ice transport of riverine particles from the laptev sea to fram strait based on clay mineral studies the aim of this study was to identify pathways and processes of modern sediment transport from the siberian hinterland to the laptev sea and further to the arctic ocean clay mineral analyses were performed on riverine suspended particulate material spm surface sediments of the laptev sea shelf and sea ice sediments sis material collected during seven expeditions was included in this study clay mineral assemblages are used to decipher the distribution of riverine sediments on the shallow laptev sea shelf the entrainment of fine particles into newly forming ice and the transport of sis from the laptev sea towards the ablation areas a cluster analysis of our data set shows that the clay mineral assemblages of laptev sea shelf sediments and sis are controlled mainly by the input of riverine spm supplied by the khatanga lena and yana rivers whereas the western shelf clay mineral province is characterized by enhanced smectite concentrations supplied by the khatanga river the eastern laptev sea is dominated by illite discharged through the lena and yana rivers the sis smectite concentration serves as an indicator for sediment source areas on the circum arctic shelves subsequently the transpolar drift can be distinguished into a siberian branch fed from the eastern kara sea and the western laptev sea and a polar branch originating from the eastern laptev sea

carbonate sedimentation in a permian high latitude subpolar depositional realm queensland australia high latitude carbonate rocks that formed in subpolar paleozoic oceans contain critical information about past climate but they are neither well documented nor fully understood lower and middle permian limestones that were deposited in such paleoenvironments at 45 s to 55 s along the southeastern margin of gondwana are now exposed in eastern australia such carbonates constitute a small but important and well preserved part of the siliciclastic glacigene succession in the bowen basin from southern and central queensland cleanest limestones accumulated on topographic highs in the eastern seaward parts of the basin that were isolated from siliciclastic sediment input from the western craton shallow water deposits are composed of large eurydesmid bivalves spiriferid and productid brachiopods bryozoans infaunal and epifaunal benthic foraminifers calcareous sponge spicules and abundant crinoids in the form of locally cross bedded rudstones and grainstones deeper water muddy carbonates are dominated by bryozoans crinoids and productids shells and spines deepest water sediments are argillaceous floatstones or shales containing fenestrate bryozoans thin walled productids and siliceous sponge spicules when integrated with recent studies of coeval sedimentary rocks along the 2000 km long paleocontinental margin a clear pattern of sedimentation emerges wherein deposition took place in similar settings during three discrete periods of deglaciation late sakmarian late artinskian and wordian all of the carbonates are distinguished by a low diversity high abundance heterozoan biota with no phototrophs and express a recurring deepening upward stratigraphic motif that is interpreted to reflect rising sea level accompanying glacial meltdown they also record a strong poleward gradient of increasing ice rafted debris increasing skeleton size decreasing invertebrate diversity decreasing epifaunal calcareous benthic foraminifers and reduction in crinoids glendonites are confined to siliciclastic sediments deposited during glacial periods comparison with coeval northern hemisphere carbonates indicates a strong parallelism of facies and depositional systems this study helps to establish these deposits as a template for a global paleozoic high latitude carbonate facies model

stratigraphic signature of the late palaeozoic ice age in the parmeener supergroup of tasmania se australia and inter regional comparisons abstract recent research in eastern australia has established that rather than being a single long lived epoch the late palaeozoic ice age comprised a series of glacial intervals each 1 8 million years in duration separated by non glacial intervals of comparable duration in order to test whether the glacial events recognized in new south wales and queensland have broader extent we conducted a reappraisal of the parmeener supergroup of tasmania southeast australia a facies analysis of the pennsylvanian to permian section was carried out allowing rationalization of the succession into four recurrent facies associations a glacigenic facies association restricted to the basal pennsylvanian earliest permian wynyard formation and correlatives b glacially cold climate influenced to open marine shelf facies association which accounts for large parts of the permian succession c deltaic facies association which specifically describes the lower permian lower freshwater sequence interval and d fluvial to estuarine facies association which specifically addresses the upper permian cygnet coal measures and correlatives indicators of sediment accumulation under glacial influence and cold climate are restricted to four discrete stratigraphic intervals all of which indicate that glaciation was temperate in nature the lowermost of these incorporating the basal wynyard formation and its correlatives and overlying woody island formation shows evidence of proximal glacial influence subglacial grounding line fan and fjordal facies and is likely a composite of one or more pennsylvanian glacial event s and an earliest permian asselian glacial the second of late sakmarian to early artinskian age comprises an initial more proximal ice influenced section and an overlying more distal ice influenced interval the third kungurian to roadian and fourth capitanian intervals are both distal glacimarine records the four intervals are of comparable age to glacials p1 p4 respectively recognized in new south wales and queensland notwithstanding apparent discrepancies of

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

ice formed intertidal boulder pavements in the sub antarctic abstract boulder pavements are flat tightly packed mosaics of ice smoothed and striated boulders that occur in low gradient intertidal and lacustrine areas in polar regions in the sub antarctic intertidal boulder pavements are located in three morphogenetic environments spanning l0 of latitude some boulder pavements are composed of ice pushed or ice rafted boulders which have been forced into the substrate by the pressure of grounding ice blocks other pavements may result from wave winnowing of glacial till at sea level which has been subsequently modified by grounding ice shallow depressions in the pavement surface may correspond to the loci of large grounded ice blocks and this interpretation is supported by striation and boulder orientations on the ridges between the depressions the occurrence of the pavement appears to depend on the following factors a a boulder supply b frequent onshore movement of floating ice and c a low gradient intertidal zone given such conditions the degree of development of the pavement seems to be controlled by the frequency of onshore ice movement because the best formed pavements occur in areas subject to the highest frequencies of freely moving floating ice the occurrence of raised pavements in the south shetland islands suggests that little morphogenetic change has occurred in the area since 9 000 years ago radiocarbon dating indicates that where the frequency of ice grounding is relatively low periods in excess of 200 years are necessary for pavement development whereas at locations where the ice grounding frequency is high pavements are well formed within 300 years

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

the lower permian wasp head formation sydney basin high latitude shallow marine sedimentation following the late asselian to early sakmarian glacial event in eastern australia the lower permian wasp head formation early to middle sakmarian is a 95 m thick unit that was depos ited during the transition to a non glacial period following the late asselian to early sakmarian glacial event in eastern australia this shallow marine sandstone dominated unit can be subdivided into six facies associa tions i the marine sediment gravity flow facies association consists of breccias and conglomerates deposited in upper shoreface water depths ii upper shoreface deposits consist of cross stratified conglomeratic sand stones with an impoverished expression of the skolithos ichnofacies iii middle shoreface deposits consist of hummocky cross stratified sandstones with a trace fossil assemblage that represents the skolithos ichnofacies iv lower shoreface deposits are similar to middle shoreface deposits but contain more pervasive bioturba tion and a distal expression of the skolithos ichnofacies to a proximal expression of the cruziana ichnofacies v delta influenced lower shoreface offshore transition deposits are distinguished by sparsely bioturbated carbo naceous mudstone drapes within a variety of shoreface and offshore deposits trace fossil assemblages repre sent distal expressions of the skolithos ichnofacies to stressed proximal expressions of the cruziana ichnofacies impoverished trace fossil assemblages record variable and episodic environmental stresses possibly caused by fluctuations in sedimentation rates substrate consistencies salinity oxygen levels turbidity and other physio chemical stresses characteristic of deltaic conditions vi the offshore transition offshore facies association con sists of mudstone and admixed sandstone and mudstone with pervasive bioturbation and an archetypal to dis tal expression of the cruziana ichnofacies the lowermost 50 m of the formation consists of a single deepening upward cycle formed as the basin transitioned from glacioisostatic rebound following the asselian to early sak marian glacial to a regime dominated by regional extensional subsidence without significant glacial influence the upper 45 m of the formation can be subdivided into three shallowing upward cycles parasequences that formed in the aftermath of rapid possibly glacioeustatic rises in relative sea level or due to autocyclic progra dation patterns the shift to a parasequence dominated architecture and progressive decrease in ice rafted de bris upwards through the succession records the release from glacioisostatic rebound and amelioration of cli mate that accompanied the transition to broadly non glacial conditions

co2 forced climate and vegetation instability during late paleozoic deglaciation the late paleozoic deglaciation is the vegetated earth9s only recorded icehouse to greenhouse transition yet the climate dynamics remain enigmatic by using the stable isotopic compositions of soil formed minerals fossil plant matter and shallow water brachiopods we estimated atmospheric partial pressure of carbon dioxide pco2 and tropical marine surface temperatures during this climate transition comparison to southern gondwanan glacial records documents covariance between inferred shifts in pco2 temperature and ice volume consistent with greenhouse gas forcing of climate major restructuring of paleotropical flora in western euramerica occurred in step with climate and pco2 shifts illustrating the biotic impact associated with past co2 forced turnover to a permanent ice free world

permian higher latitude bryozoan biogeography abstract bryozoans from gondwana and northern eurasia are within the higher latitude gondwana and boreal realms respectively and display a clear antitropical faunal distribution with lower diversity than tropical realms within these realms however faunas at highest latitudes are the least diverse and dominated by cosmopolitan genera further separate geological and oceanographic developmental histories of the boreal and gondwanan regions have resulted in the boreal realm showing much higher diversity than its southern counterpart gondwana was in a high latitude position during the permian experiencing the polar climatic conditions of the late palaeozoic ice age and the distribution of bryozoans show a distinct diversity decrease towards cold water high latitudes where the eurytopic fenestrates and trepostomes were the dominant groups the eastern australian margin with the least diverse faunas of the gondwanan realm is oriented north south as a narrow shelf hindering the migration of taxa into the southern coldest environments in contrast northern hemisphere mid to high latitude basins experienced cooling through the permian as pangaea moved northward and tectonics altered oceanographic circulation however glaciomarine deposits were not widespread even at highest latitudes the marine shelf of the northern eurasian margin was broad and oriented west east allowing establishment of widespread stable faunas in waters that became increasingly nutrient fed through the permian from cool water upwelling from the panthalassa ocean in the west this cool water mid latitude setting west east shelf and nutrient enrichment resulted in a boreal realm bryozoan fauna of over 100 genera more diverse than the gondwanan realm with only 61 genera antitropical taxa restricted to boreal and gondwanan realms only include diploporaria lyropora and metelipora however a number of other genera are more abundant outside the tropics even if they occur in all realms these genera include alternifenestella rectifenestella polypora polyporella shulgapora dyscritella stenopora streblascopora pinegopora maychella maychellina ramipora tabulipora and hexagonella the wide nutrient fed mid latitude shelf of the boreal realm also allowed development of a number of endemic taxa or taxa that are rare elsewhere including permoheloclema timanodictya permofenestella lyrocladia wjatkella parafenestralia triznella and gilmouropora in southern gondwana endemic taxa are limited to crockfordia and paramaychella however there is an abundance of evactinostella etherella and liguloclema that are distinctive of western australia

sedimentology and palaeoecology of lonestone bearing mixed clastic rocks and cold water carbonates of the lower permian basal beds at fossil cliffs maria island tasmania australia insight into the initial decline of the late palaeozoic ice age

deglaciation sequences in the permo carboniferous karoo and kalahari basins of southern africa a tool in the analysis of cyclic glaciomarine basin fills the late westphalian to artinskian glaciomarine deposits of the karoo and kalahari basins of southern africa consist of massive and stratified diamictite mudrock with ice rafted material sandstone silty rhythmite shale and subordinate conglomerate forming a cyclic succession recognizable across both basins a complete cycle comprises a resistant basal unit of apparently massive diamictite overlain by softer bedded stratified diamictite sandstone and mudrock with a total thickness of as much as 350 m four major cycles are observed each separated by bounding surfaces lateral facies changes are present in some cycles the massive diamictites formed as aprons and fans in front of the ice grounding line whereas the stratified diamictites represent more distal debris flow fans the sandstones originated in different environments as turbidite sands small subaqueous outwash channel sands and delta front sands the rhythmites and mudrock represent blanket deposits derived from turbid meltwater plumes cycles represent deglaciation sequences which formed during ice retreat phases caused by eustatic changes in the karoo and kalahari basins evidence for shorter term fluctuation of the ice margin is present within the major advance retreat cycles hardly any sediment was deposited during lowstand ice sheet expansion whereas a deglaciation sequence was laid down during a sea level rise and ice margin retreat with the volume of meltwater and sediment input depending on temporary stillstands of the ice margin during the retreat phase the duration of the cycles is between 9 and 11 ma suggesting major global tectono eustatic events smaller cycles probably linked to orbital forcing were superimposed on the longer term events a sequence stratigraphic approach using the stacking of deglaciation sequences with the ice margin advance phases forming bounding surfaces can be a tool in the framework analysis of ancient glaciomarine basin fills

depositional framework of permian coal bearing strata southern victoria land antarctica abstract the permian weller coal measures of antarctica are exposed in a narrow belt that extends along the edge of the polar plateau from the mawson glacier to the mulock glacier in southern victoria land these rocks record a rapid change from glacial to postglacial conditions with the establishment of polar peat forming conditions during the late paleozoic in antarctica the 222 m thick weller consists of interstratified fine to coarse grained quartzo feldspathic sandstone laminated siltstone mudstone and coal regional lithofacies patterns and paleocurrent orientations define a narrow elongate basin in the lower weller coarse grained sandstone sheets occur along both eastern and western basin margins these deposits are similar to those of modern sandy braided streams toward the axis of the basin this lithofacies grades into coarse grained tabular sandstone lateral accretion beds suggest that deposition of this lithofacies occurred within meandering streams coarse grained basin margin deposits interfinger with fine grained basin axis lithofacies of interstratified laminated siltstone and graded sandstone beds deposited from suspension and underflow currents within a lacustrine environment in the upper weller braided stream deposits dominate much of the basin grading downstream into meandering streams establishment of vegetation in southern victoria land occurred immediately following late paleozoic deglaciation upward in the weller the distribution of plant fossils and coal seams is lithofacies dependent thick coals and abundant plant fossils occur in meandering stream lithofacies while they are scarce within the lacustrine and braided stream deposits abrasion during transport probably contributed to the destruction of vegetable material in the braided stream environments and to material introduced into the axial lake depositional patterns within the weller coal measures are similar to those in the takrouna formation in northern victoria land similarities suggest deposition in either the same or a similar basin comparison of the weller coal measures with permian strata in the central transantarctic mountains suggest deposition in two separate basins which are now juxtaposed across the byrd glacier the sight of a possible cenozoic strike slip fault causes for the formation of the depositional basin containing the weller coal measures are unknown however the geometry of the basin and the regional distribution of lithofacies are similar to those of rift basins and to basins excavated by glacial erosion the ultimate cause of basin subsidence however may be related to long distance stress produced during late paleozoic orogenic activity along the paleo pacific margin of antarctica

geochemistry of early permian cold water carbonates tasmania australia abstract the permian carbonates of tasmania formed at a paleolatitude near 80 s during the gondwanan ice age contain abundant erratic fragments and dropstones and are associated with glacio marine sediments a shallow marine carbonate depositional model with floating icebergs calved from an adjacent ice shelf grading into an ice sheet which was recently proposed by the author has been used as sea level rose during warmer periods large volumes of melt waters mixed with marine waters retarding limestone deposition and causing deposition of shales siltstones in ignited samples cao sio2 and al2o3 account for 90 of major elements with minor amounts of k2o na2o mgo and fe2o3 the silt size terrigenous fraction in most samples have a high sio2 content far in excess of that attributable to clay minerals the ga and rb concentrations indicate a change from normal marine conditions during limestone deposition to brackish and freshwater conditions during shale deposition decreasing values of sr with increasing concentrations of mn indicate an open flow of waters in a mixed marine environment higher mn and lower sr values in the shoreward sequences than in the offshore sequence might be due to regional flow of meltwater from shore to offshore regions the calculated 18osmow values 8 to 21 of waters in equilibrium with the berriedale limestone carbonates correspond to high latitude waters indicating substantial subsurface low temperature diagenesis involving melt waters the sr mn values decrease with increasingly lighter 12c values due to extensive dissolution of caco3

the movement of isolated boulders on tidal flats by ice floes the ability of ice floes to move isolated boulders on tidal flats by flotation and by pushing and or rolling them along the bed is considered in the standard format of sediment movement entrainment transport and deposition analysis shows that flotation competence depends on ice thickness and floe size and is sufficient to transport most of the boulders reported from eastern canadian tidal flats however a limiting factor in the transportation of large boulders by this mode is likely to be the entrainment mechanism analysis of movement of grounded boulders by lateral ice thrust shows that on both deformable and non deformable beds rolling rather than sliding will occur rolling competence depends on floe size ice roughness the ice rock coefficient of friction and current and or wind strength resistance to movement is a function of the embedment ratio and bed properties rolling could account for most of the observed short distance transport of large boulders

a guide to phanerozoic cold polar climates from high latitude ice rafting in the cretaceous the high latitude extent of warm climate indicators at certain times in earth history has been considered as evidence that the globe was ice free for long intervals despite theoretical considerations and results from numerical modelling experiments1 2 indicating that this was unlikely one of the warmest periods the cretaceous displays faunal and floral evidence for cool temperate to sub tropical conditions very near to the poles however our studies of lower cretaceous mudstones of central australia that contain outsized exotic blocks have led to the conclusion that the blocks were emplaced by ice rafting implying that high latitude ice was present at sea level strata of a similar origin of mid jurassic to mid cretaceous age occur on other continents that were positioned between 65 and 78 palaeolatitude indeed there is a record of high latitude ice rafting throughout the phanerozoic suggesting that ice was present on earth for much of its history and that ice free conditions could have been at most only episodic over the past 600 myr

iceberg rafting and scouring in the early permian shoalhaven group of new south wales australia evidence of heinrich like events abstract this paper describes multiple layers of ice rafted debris and an ice scour structure in early permian marine strata within the shoalhaven group of the sydney basin new south wales australia strata were deposited on a high latitude glacially influenced continental margin during the final stages of late palaeozoic glaciation between 277 and 260 ma poorly sorted ice rafted debris forming layers up to 1 25 m thick is common within inner to outer shelf and continental slope facies of the shoalhaven group more than 120 layers can be identified these are argued to record the enhanced delivery of debris by icebergs drifting north from marine based antarctic ice margins deformation structures in associated sediments are interpreted as iceberg scours and ice keel turbates associated glendonites record early diagenesis of organic rich sediment and bottom water temperatures close to freezing a speculative hypothesis relates layers of ice rafted debris within the shoalhaven group to multiple episodes of accelerated calving at the margins of a marine based early permian ice sheet in east antarctica these events may be analogous to late pleistocene heinrich events when huge armadas of icebergs were released from the marine based laurentide ice sheet and triggered abrupt changes in ocean circulation and climate similar forcing may have characterized the early permian ice ocean system regardless of the climatic significance of ice rafted layers this is the first time such facies have been documented in the pre pleistocene literature to date few ice scour structures and no ice keel turbates have been reported

the palaeogeography of part of southwestern gondwana during the permo carboniferous glaciation abstract the elevation of the base of the glacial deposits areas where glaciated bedrock is overlapped by post glacial sediments palaeoice flow directions thickness of the glacial sequence and the lithology lithofacies and clast composition were used as integrated parameters to reconstruct the permo carboniferous glaciated land surface over southern africa the palaeography is depicted by pre glaciation westphalian maximum glaciation end of carboniferous and post glaciation sakmarian maps the pre glaciation palaeogeography was dominated by a fluvially dissected highland surrounded in the south and southwest by flat lying lower palaeozoic marine sediments this surrounding platform in part covered by shallow seas and in the south and southwest bounded by a possible island arc system was the main depocentre for the glacial debris the palaeogeography during maximum glaciation consisted of a platform region karoo basin overdeepened troughs e g kalahari basin highlands windhoek cargonian and southern with extensive glacial valleys incised into these highlands and a shallow palaeo pacific sea arm reaching into the interior the alpine type southern highlands formed by late subduction from the south the post glaciation palaeogeography was controlled by isostatic crustal movements ratio of crustal depression by the weight of the ice and sediments to post glacial rebound and sea level rises large areas including major valleys were inundated by shallow seas irati and whitehill seas and fjords so that the land surfaces represent remnants including islands of the former highlands local high rebound rates caused erosion of the glacial sediments and the deposition of fluvial and deltaic beds in fjord heads and embayments favourable conditions for the formation of fossil fuels and base mineral and metal deposits occured in parts of the inundatedbasins

high precision u pb calibration of carboniferous glaciation and climate history paganzo group nw argentina the duration and geographic extent of carboniferous glacial events in southern gondwana remain poorly constrained despite recent evidence for a more dynamic glacial history than previously considered we report 10 high precision 2 0 1 u pb ages for the permian carboniferous paganzo group nw argentina that redefi ne the chronostratigraphy of the late paleozoic paganzo and rio blanco basins and signifi cantly refi ne the timing of glacial events and climate shifts in the western region of southern gondwana radiometric calibration of the paganzo group indicates three pulses of carboniferous glaciation in the mid visean the late serpukhovian to earliest bashkirian and between the latest bashkirian to early moscovian an abrupt shift in depositional style from high sinuosity single storied fl uvial deposits and clay rich paleosols to low sinuosity multi storied feldspathic fluvial deposits inter calated with eolianites and calcic paleosols is constrained to the latest moscovian and earliest kasimovian these constraints indicate a relatively abrupt climate shift from humid subhumid to nonseasonal semiarid regional climate conditions that occurred signifi cantly earlier than previously inferred early permian this period of high latitude aridity was contemporaneous with a shift to dryland depositional environments and a major vegetation regime shift documented throughout the pangean paleotropics in the pennsylvanian

stratigraphic imprint of the late palaeozoic ice age in eastern australia a record of alternating glacial and nonglacial climate regime stratigraphic and sedimentological data from new south wales and queensland eastern australia indicate that the late palaeozoic ice age comprised at least eight discrete glacial intervals each 1 8 ma in duration here termed glaciations separated by nonglacial intervals of comparable duration these events spanned an interval from mid carboniferous c 327 ma to the early late permian c 260 ma and illustrate a pattern of increasing climatic austerity and increasingly widespread glacial ice from initial onset until an acme in the late early permian followed by an opposite trend towards the final demise of glaciation in the late permian the alternating glacial nonglacial motif suggests that the late palaeozoic ice age was considerably more dynamic than previously thought these patterns are remarkably consistent with recent interpretations of palaeofloral change eustatic sea level fluctuations and co 2 climate glaciation relationships for this interval of time the detailed record of alternating glacial and nonglacial climate mode disclosed herein may facilitate more closely resolved evaluations of stratigraphic records elsewhere notably in far field ice distal northern hemisphere successions

an algorithm for u pb isotope dilution data reduction and uncertainty propagation this is the publisher s version also available electronically from http onlinelibrary wiley com