sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

pyrite framboid evidence for oxygen poor deposition during the permian triassic crisis in kashmir abstract the khunamuh formation of the guryul ravine section in kashmir provides one of the most detailed deep water records of the end permian mass extinction in perigondwanan palaeolatitudes examination of pyrite framboid size distributions and sediment microfabric reveals a distinct change in the uppermost permian strata from nonlaminated pyrite free silty mudstones to finely laminated silty shales rich in framboidal pyrite around 1 m above the base of the formation the size frequency distribution of the framboids is identical to populations from severely oxygen restricted modern depositional environments this change to dysoxic benthic conditions coincides with the rapid demise of diverse permian brachiopod and bryozoan assemblages thus the link between extinction and anoxia is clearly seen at guryul ravine and it provides an interesting contrast to other perigondwanan sections developed in shallower water where both the onset of anoxia and the extinction occurred somewhat later in the earliest triassic

formation processes of framboidal pyrite abstract pyrite framboid formation may be the result of four consecutive processes 1 nucleation and growth of initial iron monosulfide microcrystals 2 reaction of the microcrystals to greigite fe 3 s 4 3 aggregation of uniformly sized greigite microcrystals i e framboid growth and 4 replacement of greigite framboids by pyrite the uniform morphology uniform size range and ordering of the microcrystals in individual framboids as well as the range of observed framboid structures from irregular aggregates to densely packed spherical aggregates and polyframboids are consequences of these processes using dlvo theory derjaguin landau verwey and overbeek we have evaluated the stability of colloidal iron monosulfide suspensions with ionic strengths typical of marine and lacustrine waters in addition to van der waals attractive and double layer repulsive forces a term is included to account for the ferrimagnetic properties of greigite numerical models predict that magnetically saturated greigite particles 0 1 m in diameter will rapidly aggregate in either marine or fresh water the aggregation model is in agreement with the sequence of greigite formation followed by pyrite framboid formation established in a previous experimental study sweeney and kaplan 1973 and is consistent with the occurrence of framboids composed of other magnetic minerals e g greigite magnetite and magnesioferrite based on the temperature dependent magnetic properties of greigite and aging experiments in hydrothermal solutions this mechanism for framboid formation via precursor greigite could operate to temperatures of 200 c consistent with the occasional occurrence of pyrite framboids in the paragenesis of metalliferous ore deposits

variations in pyrite texture sulfur isotope composition and iron systematics in the black sea evidence for late pleistocene to holocene excursions of the o2 h2s redox transition time dependent variations in the physicochemical properties of pyrite were investigated in four sediment cores from the black sea in the laminated deep basin sediments of unit i and unit ii 86 of pyrite particles are present as fine grained framboidal aggregates in these sediments the dominance of pyrite framboids with a narrow size distribution and maximum size 18 m is evidence of syngenetic water column pyrite formation subjacent to the o2 h2s boundary sediments from the basin margin collected below the impingement of the o2 h2s boundary contain an increased proportion of fine grained euhedral grains of pyrite relative to framboidal aggregates suggesting increased additions of diagenetic pyrite below the sediment water interface the more efficient reduction and sulfidation of iron in the water column of the central region of the basin implies a more reactive source of iron there compared to the basin margins and is tied to increasing pyrite as framboids and greater degrees of pyritization dop in the basin center relative to the basin margins an evaluation of fe s c relations indicates that pyrite formation was limited by sulfate availability during deposition of the oldest lacustrine sediments of unit iii c limited for upper unit iii due to the input of sulfate rich mediterranean seawater and fe limited in the laminated organic carbon rich sediments of units i and ii these changes in pyrite limiting factors occurred within 4 m of compacted burial representing 15 ka sediment fabric and framboid size distributions at a shallow basin margin site suggest that during two extended periods of unit ii deposition the o2 h2s transition retreated to depths below 200 m however during these same intervals the 34s of pyrite remains uniform compared to overlying and underlying laminated sediments implying that this chemical signature may not be uniquely tied to the position of the o2 h2s boundary relative to the sediment water interface but rather is likely related to biogeochemical processes

palaeoceanographic redox environments for the lower cambrian hetang formation in south china evidence from pyrite framboids redox sensitive trace elements and sponge biota occurrence abstract the lower cambrian hetang formation a black shale sequence contains a stone coal a flammable organic rich mudstone unit abundant pyrite framboids occur in this unit with the average mean sizes falling in a narrow range from 4 6 to 5 4 m and the maximum diameters being around 10 m the size distribution pattern of the pyrite framboids indicates a euxinic depositional environment the redox sensitive trace metals of the stone coal samples reveal a large enrichment of mo 10 180 times v 4 40 times u 10 60 times and ni 2 20 times compared to the average upper continental crust value consistent with an anoxic environment for their deposition the redox sensitive element ratios th u v v ni v cr indicate that the depositional environment for the lower part of the stone coal unit was the most anoxic and euxinic in contrast a sponge biota including eleven species of demosponges and hexactinellids and two undetermined forms indicate an oxic or dysoxic environment to reconcile these two facts we propose that although an anoxic euxinic environment predominated during the deposition of the lower cambrian hetang formation black shales occasional currents may also have brought free oxygen to the bottom water column to allow the growth of the sponges on the sea floor

oceanic water redox conditions of the region between tethys and panthalassa during the late early triassic abstract fossil evidence of a complex food chain in the marine ecosystem after the end permian mass extinction epme event has been reported from the osawa formation which consists of upper olenekian spathian shallow marine mudstone dominant strata in the south kitakami belt in northeast japan this sedimentary sequence offers an important material that records the paleoenvironment of the oceanic region between the eastern tethys and panthalassa this paper reports detailed records of the oceanic environment from two sections of the osawa formation focusing on the redox condition parallel undisturbed laminae suggesting limited benthic activity are prominent in the middle to upper parts of the osawa formation while disturbance of laminae by burrows occurs in the lower and uppermost parts suggesting active benthic activity in an oxygen rich depositional environment the amount of pyrites euhedral pyrite pyrite framboids and pyrite polyframboids increases in the well laminated mudstones a relatively broad size distribution of pyrite framboids indicates that these mudstones were deposited under dysoxic conditions and suggest that the water column was not sulfidic redox sensitive elements such as mn v and u show values close to the average values of the upper continental crust throughout the osawa formation mo is moderately enriched in the well laminated and pyrite abundant mudstone horizons although the degree of enrichment is lower than known examples of modern sulfidic basins these data suggest that the condition of the bottom water in this oceanic region during the spathian varied between oxic and dysoxic weakly oxygenated and was never sulfidic such an oceanic environment characterized by mildly reducing bottom water and oxic water column appears to have been the settings for the recovery and establishment of the early triassic marine ecosystem characterized by diverse nektonic motile animals and limited diversity of benthic in motile animals

reconstruction of redox conditions during deposition of organic rich shales of the upper triassic yanchang formation ordos basin china the concentration and distribution of organic matter phosphate nodules and framboidal pyrite preserved in shales are controlled by organic matter decomposition and the cycles of phosphorus sulfur and iron which in turn are controlled by bottom water redox conditions the organic rich shale in the 7th member of the upper triassic yanchang formation ch7 contains high organic carbon concentrations and abundant phosphate nodules and pyrite framboids providing an opportunity to better understand the redox conditions at the time of deposition framboidal pyrite in the ch7 organic rich shales are composed of octahedral pyritohedral and spherulitic microcrystals with uniform crystal size sem photographs and statistical data suggest that pyrite framboids have large mean diameters 10 0 to 18 1 m and standard deviations 2 8 to 5 9 m this may indicate that the organic rich shale was deposited under oxic suboxic bottom water conditions the corg p ratios of the organic rich shale exhibit considerable variation ranging from 7 2 to 216 but the majority of them 83 2 belong to the lower intermediate range 130 suggesting that the redox conditions were predominantly oxic suboxic and intermittently anoxic the corg p ratios also show periodic vertical variation which suggests that redox conditions fluctuated between oxic suboxic and anoxic additional support for the trends based on corg p ratios is provided by dopt values which show similar vertical variation and redox patterns all evidence shows that the redox conditions during deposition of the ch7 organic rich shale was predominantly oxic suboxic accompanied by intermittent anoxic environments the result of this study will be helpful in better understanding the formation mechanism of the ch7 organic rich shale

extended 3β methylhopanes up to c45 in source rocks from the upper cretaceous qingshankou formation songliao basin northeast china abstract 3 methylhopanes methylated at the c 3 position of the a ring have been detected ubiquitously in sedimentary rocks with carbon numbers of c28 and c30 c36 these compounds have been attributed to aerobic methanotrophs due to their strongly 13c depleted compositions here we report 3 methylhopanes with carbon numbers up to c45 in source rocks from the first member of the upper cretaceous qingshankou formation songliao basin northeast china the extended homologues up to c45 might be derived from long chain alkyl bacteriohopanetetrols by consecutive enzymatic additions of a c5 sugar extremely 13c depleted compositions combined with a high 3 methylhopane index suggest an intense ch4 cycle induced by blooms of aerobic methanotrophs in the songliao paleo lake

rock magnetic records of the qingshankou formation of sk 1 south borehole in songliao basin northeast china and their paleoclimate implications abstract the south borehole sk 1s of the china cretaceous continental scientific drilling project songke 1 penetrated the late cretaceous lacustrine sediments in the central depression of the songliao basin northeast china in order to reveal the terrestrial records of the cretaceous climate changes high resolution rock magnetic records were obtained on the qingshankou formation k 2 qn of sk 1s the results indicate that detrital magnetite is the main remanence carrier of the k 2 qn formation while both magnetite and paramagnetic minerals including clay minerals and pyrite dominantly contribute to magnetic susceptibility although reductive diagenesis may have more or less effect on the magnetic signals of the k 2 qn formation they recorded ancient lake level changes well resulting both from the tectonic development of the basin and from the milankovitch astronomical paleoclimatic changes the first order vertical trends of the rock magnetic records were controlled by the shallowing upwards of the lake level caused by the tectonic uplift of the basin the short term variations of the rock magnetic records were controlled by the lake level periodical drift caused by the fluctuations of the rainfall of the catchment area of the basin which were controlled by astronomical orbital forcing in addition the magnetic records also distinguished two most anoxic periods during the lacustrine anoxic event 1 lae1 the sections of 1758 1761 m and 1769 1771 5 m which may suggest the two most active periods of surface productivity of the lake

ice sheet erosion patterns in valley systems in northern sweden investigated using cosmogenic nuclides erosion patterns associated with glaciation of trunk and hanging valley systems in northern sweden were investigated using cosmogenic nuclide 10be apparent exposure ages and inferred nuclide inheritance sequences of samples taken across valleys known to have been covered repeatedly by the fennoscandian ice sheet revealed two primary patterns of erosion in vavlavagge the exposure age pattern is consistent with 2 m of glacial erosion during the last glacial cycle along the entire profile at ravtasvaggi dievssavaggi and alisvaggi exposure ages in the valley bottom contrast with apparent exposure ages two to four times older on the valley sides the older ages on the valley sides reflect cosmogenic nuclide inheritance due to limited 2 m bedrock erosion of the valley sides during the last glacial cycle the pattern and scale of erosion in these valleys indicates that glacial valley formation is a result of multiple glacial cycles rather than the result of topographic modification during a single glacial cycle initial data comparing hanging valley and trunk valley sites do not show distinct differences in apparent exposure ages slightly older ages for samples from hanging valley bottoms may suggest nuclide inheritance indicating lower erosion than in trunk valley bottoms as would be expected given the marked topographic step between hanging and trunk valleys although quantifying the amount of erosion depends on the assumed cosmogenic nuclide inheritance prior to the onset of erosion the pattern of erosion is independent of this hence the observed pattern of cosmogenic nuclide concentrations provides constraints on spatial patterns of erosion and helps to refine understanding of the timing and extent of landform modification by glaciation copyright 2005 john wiley sons ltd

enhanced framboidal pyrite formation related to anaerobic oxidation of methane in the sulfate methane transition zone of the northern south china sea abstract many studies have confirmed that size distributions of framboidal pyrite can be an effective indicator of bottom water redox conditions in modern as well as ancient sedimentary environments however one environment in which production of framboidal pyrite has not been sufficiently studied to date is the sulfate methane transition zone smtz in which anaerobic oxidation of methane aom is coupled with microbial sulfate reduction msr to enhance iron sulfide mineral precipitation e g fes2 fes and fe3s4 here we document for the first time size distributions for pyrite framboids from the smtz based on data from two sites in the methane hydrate bearing region of the northern south china sea on the basis of framboid size pyrite concentration and sulfur isotope data we propose new insights into the formation process of authigenic pyrite framboids within the smtz we conclude that 1 enhanced anaerobic oxidation of methane aom not only plays a dominant role in the accumulation of 34s enriched pyrite but also is responsible for formation of highly variable and sometimes exceptionally large pyrite framboids in the smtz 2 most framboids occur in framboid clusters which commonly exhibit rod like shapes secondary overgrowths heavier 34s values and unusual size distributions e g mean size 20 m and standard deviation 3 0 m in the smtz 3 pyrite framboids formed in the smtz which have characteristics different from those formed in the sulfate reduction zone srz do not comment on redox conditions of the overlying water column and 4 framboid occurrences with similar characteristics in ancient marine deposits may be considered indicators of enhanced aom and mark the former position of the smtz in the paleo marine system in addition significant quantities of elemental sulfur were observed in the smtz possibly related to anaerobic oxidation of hydrogen sulfide and fluctuations of the smtz

coupled ice till dynamics and the seeding of drumlins and bedrock forms the geomorphological effects of ice sliding over till internal deformation of till and till sliding over bedrock are considered two questions are examined 1 is the till sheet flow unstable i e is a layer of uniform thickness maintained or not and 2 does the slip of till over bedrock cause amplification of relief of the bedrock such instabilities seem to be necessary to explain such features as drumlins and whaleback forms it is found that the answer to 1 and 2 depends on the position of the system in a parameter space defined by the till rheology and applied shear stress the effective pressure at the ice till interface the thickness of ice and till and the wavelength of the instability two configurations are considered one where the wavelength of the perturbation is much less than the the ice thickness which is related to the classical nye kamb solution for flow over bumps and one where the wavelength is much greater than the ice thickness where the mechanics are described by the shallow ice approximation in both cases substantial areas of parameter space where till sheet and bedrock modes are unstable are found the conceptually related smalley unwin bifurcation is re examined the physical mechanisms by which ice and till flows couple are examined at very short wavelengths 10 m the ice is so rigid that it forces till waves to move at the ice velocity while at long wavelengths 1000 m the flows become essentially uncoupled and till waves move at the kinematic velocity at intermediate wavelengths 100 m high growth rates occur this is postulated to be the scale of drumlin seeding

sulfide mineral chemistry investigation of sediment hosted stratiform copper deposits nahand ivand area nw iran abstract copper mineralization in nahand ivand area nw iran appears as disseminated copper sulfides along a redox boundary between gray sandstone and microconglomerate and hematitic sandstones siltstones and shaly marl geochemical analyses of the nahand ivand deposits show as much 35 wt cu and 730 ppm ag in the gray sandstone electron probe micro analysis epma was used to determine the mineralogical composition and distribution patterns of copper and silver bearing phases mainly in pyrite and cu bearing sulfides the epma data were essential for evaluating the distribution and partitioning of potential economically valuable components between co existing minerals furthermore they contribute to a better understanding of the genesis of the nahand ivand copper deposits and will guide further exploration in the region the epma results from different types of pyrite reveal cu contents as high as 0 32 wt 1 10 wt and 2 88 wt for framboidal pyrite pyi overgrowths on framboidal pyrite pyii and diagenetic pyrite pyiii respectively this successive increase of copper from pyi to pyiii is attributed to a continuous supply of copper that replaces framboidal pyrite in turn by the more copper rich digenetic pyrite because of hydrothermal overprinting pyrite has been replaced by djurleite roxbyite and other nonstoichiometric cu s minerals that include covellite the epma study indicates that covellite contains significant concentrations of ag locally 1 wt in contrast only trace amounts of silver have been detected in pyrite and other copper sulfides indicating that covellite is the major ag carrier in the ore according to textural relationships such open space filling impregnation and replacement textures and the epma results later stage copper bearing fluids were responsible for the silver enrichment in the nahand ivand deposits

palaeo ice streams in the northern keewatin sector of the laurentide ice sheet evidence for ice streams in the laurentide ice sheet is widespread in the region of northern keewatin and the boothia peninsula nunavut canada palaeo ice streams have been recognized but their location size and potential role in ice sheet dynamics are poorly constrained based on the interpretation of satellite imagery we produce a palaeo ice stream map of this region glacial directional landforms eskers and moraines were mapped and integrated into landform assemblages using a glacial geological inversion model palaeo frozen bed areas were also identified relative age of the geomorphic swarms was assessed by cross cutting relationships and radiocarbon ages where available using this information we obtained a glaciologically plausible picture of ice stream evolution within the northernmost laurentide ice sheet on the m clintock channel corridor three generations of pure ice streams are found on baffin island and the gulf of boothia glaciation was dominated by frozen bed zones located on high plateaus and ice streams running along the troughs i e topographic ice streams a massive convergent pattern at the head of committee bay drained ice from both the keewatin and foxe sectors and was probably one of the main deglaciation channels of the laurentide ice sheet finally our results indicate that streaming flow was present in the deep interior of the laurentide ice sheet as recently shown for the greenland and antarctic ice sheets

pyrite framboid size distribution as a record for relative variations in sedimentation rate an example on the toarcian oceanic anoxic event in southiberian palaeomargin the early toarcian oceanic anoxic event t oae represents one of the major alterations of the carbon cycle of the mesozoic period despite being globally recognized and particularly represented within the tethys realm its expression in the sedimentary record is highly variable depending on the studied section which suggests local environmental factors exert a major control on the resulting lithological appearance of the event we investigated the fuente vidriera section in the eastern external subbetic of the betic cordillera spain where the lower jurassic is represented by alternate layers of marls and many limestones and the t oae is identified by a major delta c 13 excursion micropalaeontological ichnofacies and geochemical evidences 1 for this study we analyzed pyrite framboid size distribution of the sedimentary sequence in fuente vidriera the outcome according to previous studies on pyrite framboid distribution is contradictory when compared to all other evidences suggesting oxygen depletion during the t oae the results have been reinterpreted in the light of crystal size distribution theory and we conclude that not only growth time but also geochemical environment controls pyrite formation since growth time is directly related to burial rates this approach allows us to reconstruct relative variations of sedimentation rates during the early jurassic in this location based on the obtained results we provide new evidences for wide spread transgression during the early toarcian in the south iberian palaeomargin which induced low sedimentation rate and lower energetic conditions as well as favored oxygen impoverished bottom waters c 2015 elsevier b v all rights reserved less

felsenmeer persistence under non erosive ice in the torngat and kaumajet mountains quebec and labrador as determined by soil weathering and cosmogenic nuclide exposure dating soil analyses and terrestrial cosmogenic nuclide exposure dating are combined and a conceptual model proposed to explain altitudinal weathering contrasts in high latitude highlands we show that summits in the torngat and kaumajet mountains were covered by ice during the last glacial maximum and that their felsenmeer cover probably survived multiple glaciation events for similar lithologies soils on felsenmeer covered summits are signigicantly more weathered than those below the felsenmeer limit displaying higher concentrations of crystalline iron amorphous aluminium and silicium extracted with oxalate secondary minerals such as gibbsite and kaolinite occur in felsenmeer soils whereas those formed in till lacked these secondary minerals 10be and 26al exposure ages for nine of ten samples from high elevation tors and autochthonous felsenmeer blocks range from 73 6 to 157 15 ka by contrast ages of 11 4 1 0 and 11 7 1 0 ka are measured for bedrock in the much lower saglek zone indicating extensive 3 m glacial erosion of this zone during late wisconsinan glaciation 26al 10be ratios demonstrate that exposure of the high elevation surfaces was interrupted during at least one cosmic ray shielding event by either ice or till cover in either case late wisconsinan glaciers could not have extensively eroded these surfaces five erratics dated above the saglek zone including one in the felsenmeer zone have exposure ages ranging from 11 6 1 0 to 13 6 0 7 ka this indicates that valley and high elevation ice persisted through the younger dryas chron and provides further evidence that the highlands were not nunataks during the late wisconsinan period

geochemical characterization of source rocks and crude oils in the upper cretaceous qingshankou formation changling sag southern songliao basin abstract the upper cretaceous qingshankou formation is one of the main exploration target in the changling sag southern songliao basin however the origin of source rock deposition and crude oils remains undiscovered a comprehensive geochemical study including rock eval pyrolysis gas chromatography mass spectrometry and carbon isotope analysis on fifteen crude oils and twenty two source rock samples from the qingshankou formation were performed in order to provide new insights into source organic matter depositional environment and correlation between crude oils and source rocks bulk geochemical analysis on source rock samples indicates that the lower member of the qingshankou formation has more hydrocarbon generating potential than the middle member these two potential source rock members were interpreted to be deposited in slightly different environments and have different sources of organic matter determined by biomarker assemblages the lower member is organically rich average toc 1 27 wt oil prone mature and deposited under anoxic conditions with more contribution from sapropelic organic matter the middle member is organically poor average toc 0 78 wt gas prone less mature and deposited under less anoxic conditions with more terrigenous organic matter input biomarker fingerprints and carbon isotope compositions suggest that all the crude oils were genetically related and could be classified into one oil family which has significant contribution from the lower member source rocks and minor contribution from the middle member source rocks

late stage phases of glacial lake ojibway in the central abitibi region eastern canada abstract the decay of the laurentide ice sheet southern margin during the last deglaciation led to the development of lake ojibway that covered large expanses of northeastern ontario and northwestern quebec the history of ojibway lake phases is poorly detailed mainly because of the physical configuration of the lake basin and the dominance of fine grained glaciolacustrine sediments that prevent the formation of well developed and extensive sandy strandlines here we use a complex sequence of relict terraces carved in glaciolacustrine rhythmites to document the evolution of lake ojibway in northwestern quebec specifically lake levels were constrained by measuring the elevation of 154 raised wave cut scarps present in the eastern lake abitibi region results provide evidence for four distinct shorelines with elevations of 299 289 282 and 272 m 1 m at the latitude of la sarre the highest lake level documented appears to be linked to one of the two known kinojevis phases of lake ojibway while the three other lake levels project well below the main outlet system that controlled the elevation of the lake during the deglaciation the elevation uplift gradients and areal extent of these lower shorelines suggest that the two intermediate lake levels likely formed during late stages of the deglaciation following abrupt drawdowns of the lake s surface the fourth and lowest shoreline is associated with a postglacial lake that developed after the complete withdrawal of ojibway water from the region these low elevation shorelines bring new evidence for significant changes in the areal extent and depth of lake ojibway near the end of the deglaciation although the origin of these late stage phases remains unspecified the associated drawdowns likely implied routing events into newly deglaciated regions and or subglacial meltwater discharges into the north atlantic

upper mantle heterogeneities in africa deduced from rayleigh wave dispersion abstract rayleigh wave group velocities have been measured along 11 paths on the african continent north of the equator the results lead to a division of this part of the continent into three regions cratonic areas non cratonic areas mobile zones and a region located to the east of the meridian 31 e red sea neighbourhood ethiopia djibouti the highest velocities are found beneath the cratonic areas at 200 km depth 5 at greater depths the mobile zones exhibit higher velocities than the cratonic regions but the difference is not as marked 2 and the resolution is poor velocities in the eastern region are similar to those found under young oceanic regions

pyrite morphology in the first member of the late cretaceous qingshankou formation songliao basin northeast china abstract the study of sedimentary pyrite morphological characteristics provides useful information on depositional environments and early diagenic processes and can be used as an indicator of redox conditions in ancient lake bottom waters the results of this study in the songliao basin in northeastern china show that euhedral crystals and framboids are the dominant pyrite forms in the mudstones of the first member of the qingshankou formation k2qn1 the framboidal size distribution indicates that during the deposition of k2qn1 redox conditions in the bottom water fluctuated from oxic dysoxic to euxinic anoxic to oxic dysoxic the presence of euxinic anoxic bottom water suggests that an anoxic event developed in the songliao ancient lake and continued for 196 ka the development of an anoxic bottom environment was the most important factor in hydrocarbon source rock formation in the songliao basin

formation and evolution of nonmarine petroleum in songliao basin china in large lake basins source rocks containing sapropelic kerogen have a high transformation ratio and a high potential for petroleum and they offer the material basis for the formation of a large nonmarine oil field on the basis of geologic and geochemical data and the results of thermal simulation of kerogen it is confirmed that the maturation sequence of kerogen is type i type ii and type iii

geochemical compositional mapping of lower jurassic trace fossils palaeoenvironmental significance and methodological implications abstract analyses of x ray microfluorescence xrf elemental maps of the ichnofossil assemblages from the upper pliensbachian lower toarcian marl limestone rhythmite of the south iberian palaeomargin betic cordillera se spain show that the compositions of burrow infills are geochemically and mineralogically different with respect to the surrounding sediment xrf elemental maps and back scattered electron images show pyrite framboids within the burrows and enrichment in fe and s relative to the host sediment this is congruent with the position of burrows beneath the redox boundary at the time of their active or passive sedimentary infilling organic matter that accumulated at the seafloor was not preserved due to oxidation and consumption by benthic organisms however burrows located beneath the redox boundary served as traps for organic matter preservation the composition of burrow fills reflects the original signal of the redox conditions of pore waters below the sediment water interface which was not preserved in the surrounding sediment the xrf elemental maps also show that some trace fossils from limestone and marly limestone intervals contain high concentrations of si al k zn cr and ti with respect to the surrounding sediment this may reflect enrichment of clay minerals in the burrow fills derived from overlying marly layers this work proposes the use of elemental imaging of trace fossils prior bulk rock geochemical analyses in order to evaluate the potential for biogenic heterogeneity and elemental partitioning before sampling geochemical analysis of trace fossils represents an additional tool that may be of use in hydrocarbon exploration

sakami moraine quebec a 500 km long moraine without climatic control the laurentide ice sheet in eastern canada disintegrated step by step as evidenced by several morainic complexes although commonly interpreted as reflecting climatic events it seems probable that the disintegration simply related to changes in the dynamics of the ice margin without climatic control from the example of the late glacial sakami moraine in quebec formed during the drainage of lake ojibway into the tyrrell sea the concept of a re equilibration moraine already briefly proposed is developed the construction of such a moraine implies a stabilization of the ice front when the glacier margin previously floating or calving in a lacustrine or marine basin is suddenly grounded because of topographic blocking or abrupt drop of water level due to drainage the glacial retreat then pauses until the equilibrium profile of the ice is restored and a morainic accumulation can form during the halt

space geodesy constrains ice age terminal deglaciation the global ice 6g_c vm5a model a new model of the last deglaciation event of the late quaternary ice age is here described and denoted as ice 6g c vm5a it differs from previously published models in this sequence in that it has been explicitly refined by applying all of the available global positioning system gps measurements of vertical motion of the crust that may be brought to bear to constrain the thickness of local ice cover as well as the timing of its removal additional space geodetic constraints have also been applied to specify the reference frame within which the gps data are described the focus of the paper is upon the three main regions of last glacial maximum ice cover namely north america northwestern europe eurasia and antarctica although greenland and the british isles will also be included if peripherally in the discussion in each of the three major regions the model predictions of the time rate of change of the gravitational field are also compared to that being measured by the gravity recovery and climate experiment satellites as an independent means of verifying the improvement of the model achieved by applying the gps constraints several aspects of the global characteristics of this new model are also discussed including the nature of relative sea level history predictions at far field locations in particular the caribbean island of barbados from which especially high quality records of postglacial sea level change are available but which records were not employed in the development of the model although ice 6g c vm5a is a significant improvement insofar as the most recently available gps observations are concerned comparison of model predictions with such far field relative sea level histories enables us to identify a series of additional improvements that should follow from a further stage of model iteration

ice flow evolution of the labrador sector of the laurentide ice sheet a review with new evidence from northern quebec abstract outcrops bearing stained striated facets indicative of north northeastward moving ice truncated by unstained striated facets indicative of various younger flows occur in the caniapiscau area of north central quebec this is the first report of differential staining of striated facets in the region we propose that the staining occurred in an ice free interval of probable interglacial age this early ice flow probably occurred during ice retreat toward the quebec highlands ice flow and glacial transport data from the southern hudson bay and james bay basins indicate that the next major regional ice flow was toward the northwest and resulted from the expansion of an early wisconsinan glacier in the quebec highlands the northern part of this flow was diverted northwestward through hudson bay and the southern part southwestward across james bay following a progressive counterclockwise rotation of flow a zone of intersection zi of two major glacier bedform systems often referred to as the horseshoe shaped labrador ice divide represents the head of a large northward convergent ice flow system that extended to ungava bay and beyond the ungava flow propagated southward and captured the head of the opposing flow from an outflow centre located east of caniaspiscau reservoir we propose that this capture event correlates with the gold cove advance in ungava bay and on baffin island at about 9900 14c yr bp it is the largest advance of quebec labrador ice yet proposed for the region this correlation is based on the relative ice flow chronology accommodation of glacial lakes naskaupi and mclean in the deglaciation sequence the constraints placed on last glacial maximum lgm ice configuration by the postglacial uplift pattern and events in the deep sea record therefore the ungava ice flow pattern is not a relict pre wisconsinan glacial landscape as recently proposed

ice stream sticky spots a review of their identification and influence beneath contemporary and palaeo ice streams rapidly flowing ice streams are the arterial drainage routes in continental ice sheets and exert a major influence on ice sheet mass balance recent observations have revealed that ice stream flow exhibits considerable variability with relatively rapid changes taking place in speed and direction this spatial and temporal variability is intimately linked to the conditions at the base of the ice streams and the distribution of localised patches of basal friction known as sticky spots in this paper we provide a detailed review of sticky spot observations from both contemporary and palaeo ice stream beds in order to better understand their nature and influence observations and theoretical considerations reveal four primary causes of stickiness i bedrock bumps ii till free areas iii areas of strong well drained till and iv freeze on of subglacial meltwater these may act together in one location or in isolation and a progressive increase in their distribution could lead to ice stream shut down bedrock bumps are influential under active ice streams where they provide form drag and can create thinner ice which increases the likelihood of basal freeze on increased bed roughness may prevent the lateral migration of some ice streams but bedrock bumps are unlikely to cause ice stream shut down because over long time scales ice stream erosion might be expected to reduce their amplitude the influence of till free areas beneath an ice stream will depend critically on the amount of water that might be drawn out of the surrounding till to lubricate such areas they are likely to be most important in ice stream onset zones but their identification has proved difficult beneath active ice streams if an ice stream operates solely by till deformation it is conceivable that a progressive increase in the exposure of till free areas could lead to shut down through a process of sediment exhaustion areas of strong well drained till have been identified beneath both active and ancient ice streams and are most likely to result from the reorganisation of subglacial meltwater the collapse of an inefficient cannalised system to a more efficient channelised system can occur rapidly and this mechanism has been hypothesised as a candidate for ice stream shut down in both contemporary and palaeo settings basal freeze on has also been observed and inferred from beneath modern and palaeo ice streams and a reduction in basal meltwater supply coupled with ice stream drawdown and the advection of cold ice increases the likelihood of switching off an ice stream a paucity of data from ice stream sticky spots limits a better understanding of their nature distribution and evolution beneath ice streams future technological advances are likely to improve the resolution of the data collected from the beds of modern ice streams but well preserved palaeo ice stream beds also hold potential for investigating their influence on ice stream flow and we present simple landsystems models to aid their identification such data will considerably enhance the basal boundary condition in ice stream models which will ultimately refine our predictions of the response of contemporary ice sheets to future changes in climate

automated drumlin shape and volume estimation using high resolution lidar imagery curvature based relief separation a test from the wadena drumlin field minnesota abstract resolving the origin s of drumlins and related megaridges in areas of megascale glacial lineations msgl left by paleo ice sheets is critical to understanding how ancient ice sheets interacted with their sediment beds msgl is now linked with fast flowing ice streams but there is a broad range of erosional and depositional models further progress is reliant on constraining fluxes of subglacial sediment at the ice sheet base which in turn is dependent on morphological data such as landform shape and elongation and most importantly landform volume past practice in determining shape has employed a broad range of geomorphological methods from strictly visualisation techniques to more complex semi automated and automated drumlin extraction methods this paper reviews and builds on currently available visualisation semi automated and automated extraction methods and presents a new curvature based relief separation cbrs technique for drumlin mapping this uses curvature analysis to generate a base level from which topography can be normalized and drumlin volume can be derived this methodology is tested using a high resolution 3 m lidar elevation dataset from the wadena drumlin field minnesota usa which was constructed by the wadena lobe of the laurentide ice sheet ca 20 000 years ago and which as a whole contains 2000 drumlins across an area of 7500 km 2 this analysis demonstrates that cbrs provides an objective and robust procedure for automated drumlin extraction there is strong agreement with manually selected landforms but the method is also capable of resolving features that were not detectable manually thereby considerably expanding the known population of streamlined landforms cbrs provides an effective automatic method for visualisation of large areas of the streamlined beds of former ice sheets and for modelling sediment fluxes below ice sheets

the origin of pyrite mineralization implications for late cambrian geology of the holy cross mountains south central poland abstract this paper presents results of a petrographic mineralogical and geochemical study of ore gangue and rock forming minerals that occur within the upper cambrian furongian age siliciclastic rocks of the wi niowka massif western part of the main range holy cross mountains south central poland this area is characterized by the presence of ubiquitous pyrite that makes up two stratiform mineralization zones assigned to the early and middle late cambrian giving rise to acid mine drainage the oldest zone comprises additionally sedimentary breccias with intraclast supported pyrite cement the predominant microscopic colloform and partly framboidal pyrite typically shows high concentrations of as up to 8 23 wt and a distinct enrichment in the light sulfur isotope 34s from 41 4 to 23 6 the occurrences of large amounts of as rich pyrite showing strongly negative 34s values are rather uncommon in paleozoic sedimentary formations worldwide that exhibit distinctly smaller amounts of as and mostly enrichments in heavier sulfur isotope 34s up to 63 another specific feature of the wi niowka rock series is the presence of ree bearing aluminophosphate and phosphate minerals that occur primarily in clayey silty shales and bentonites based on the results obtained a sequence of hydrothermal index minerals was discriminated including pyrite whose grains are usually made of alternating arsenic rich and arsenic poor bands as well as paragenetic assemblages of dickite nacrite xenotime and the crandallite series of aluminum phosphate sulfate minerals both mineral composition and specific microtextures are indicative of multistage hydrothermal activity that took place in the wi niowka depositional basin during the late cambrian time this is in distinct contrast to the remaining part of the main range which is devoid of the hydrothermal pyrite imprint moreover the results of this study give insight into the complex sedimentary and early diagenetic history of the southwestern passive margin of the baltica craton this currently makes up a part of the ysogory block terrane that borders on the trans european suture zone separating the precambrian east european craton from the paleozoic platform of central europe this study is important because we still lack the full knowledge about the hydrothermal processes that took place in early paleozoic depositional basins

depositional environment thermal maturity and shale oil potential of the cretaceous qingshankou formation in the eastern changling sag songliao basin china an integrated organic and inorganic geochemistry approach abstract the changling sag in the petroliferous songliao basin has produced large amounts of conventional petroleum but studies on unconventional resources are rare a suite of core samples from the cy 1 well drilled in the eastern changling sag was analysed employing a series of micropetrographic geochemical and pyrolysis techniques to reveal the shale oil potential of the lower k2qn1 and middle k2qn2 qingshankou formation in this area for the first time from the lower k2qn1 upwards the sampled section the ratio of k al delineates an increasing palaeo temperature trend but still within a warm climate based on element ratios al2o3 toc and tio2 toc the highest terrestrial matter and nutrient supply on average occurred in the lower k2qn1 triggering bioproductivity toc ts and fe mn show that bottom water anoxia prevailed in the upper k2qn1 and lower k2qn2 providing excellent conditions for organic matter om preservation as compared to the lower k2qn1 high maturity of the studied layers is implied by e g vitrinite reflectance vrr of 1 03 1 09 tmax values over 445 c and molecular organic geochemical indices which correlate very well with vrr kinetic data on petroleum generation from open system pyrolysis were implemented in a numerical 1d basin and petroleum system model the k2qn1 has generated and expelled large amounts of petroleum 78 and 36 transformation of kerogen to petroleum based on kinetics of the low mature qingshankou shale om consisted originally of type i ii kerogen but has lost more than half of its original hydrocarbon generation potential upon maturation oil saturation index osi and s1 suggest that the studied layers show fair shale oil potential but are regarded as good conventional petroleum source rocks a newly proposed shale oil potential index sopi takes also thickness into account application to the qingshankou formation implies that the lower k2qn2 holds the highest shale oil potential

paleo ocean redox environments of the upper ordovician wufeng and the first member in lower silurian longmaxi formations in the jiaoshiba area sichuan basin a study of paleo ocean redox environments is important for understanding the deposition of black shale and has practical implications for shale gas exploration here we selected a total of 52 shal

an ice sheet scale comparison of eskers with modelled subglacial drainage routes eskers record the signature of channelised meltwater drainage during deglaciation providing vital information on the nature and evolution of subglacial drainage in this paper we compare the spatial pattern of eskers beneath the former laurentide ice sheet with subglacial drainage routes diagnosed at discrete time intervals from the results of a numerical ice sheet model perhaps surprisingly we show that eskers predominantly occur in regions where modelled subglacial water flow is low eskers and modelled subglacial drainage routes were found to typically match over distances of 10 km and most eskers show a better agreement with the routes close to the ice margin just prior to deglaciation this supports a time transgressive esker pattern with formation in short 10 km segments of conduit close behind a retreating ice margin and probably associated with thin stagnant or sluggish ice esker forming conduits were probably dominated by supraglacially fed meltwater inputs we also show that modelled subglacial drainage routes containing the largest concentrations of meltwater show a close correlation with palaeo ice stream locations the paucity of eskers along the terrestrial portion of these palaeo ice streams and meltwater routes is probably because of the prevalence of distributed drainage and the high erosion potential of fast flowing ice

landscape preservation under fennoscandian ice sheets determined from in situ produced 10be and 26al some areas within ice sheet boundaries retain pre existing landforms and thus either remained as ice free islands nunataks during glaciation or were preserved under ice differentiating between these alternatives has significant implications for paleoenvironment ice sheet surface elevation and ice volume reconstructions in the northern swedish mountains in situ cosmogenic 10be and 26al concentrations from glacial erratics on relict surfaces as well as glacially eroded bedrock adjacent to these surfaces provide consistent last deglaciation exposure ages 8 13 kyr confirming ice sheet overriding as opposed to ice free conditions however these ages contrast with exposure ages of 34 61 kyr on bedrock surfaces in these same relict areas demonstrating that relict areas were preserved with little erosion through multiple glacial cycles based on the difference in radioactive decay between 26al and 10be the measured nuclide concentration in one of these bedrock surfaces suggests that it remained largely unmodified for a minimum period of 845 418 461 kyr these results indicate that relict areas need to be accounted for as frozen bed patches in basal boundary conditions for ice sheet models and in landscape development models subglacial preservation also implies that source areas for glacial sediments in ocean cores are considerably smaller than the total area covered by ice sheets these relict areas also have significance as potential long term subglacial biologic refugia

time perspectives on glacial landscape formation glacial flow chronology at lac aux goelands northeastern quebec canada we used mapping from aerial photographs and field investigations around lac aux goelands whitegull lake northeastern quebec to establish a glacial flow chronology that involves three different glacial landform systems we interpret the youngest of these systems as related to the late wisconsinan deglaciation this system has an up glacier discontinuity that marks a temporal shift from warm based subglacial conditions to non erosive cold based subglacial conditions whereby older glacial landscapes are preserved in the interior of quebec labrador furthermore our results support theories suggesting a northward migrating ice divide to a final position south of ungava bay during the final deglaciation the recognition that a glacial landscape is fragmented and consists of smaller temporally unrelated units is of considerable significance in understanding ice sheet dynamics and patterns of subglacial preservation and destruction this is because a fragmented landscape implies a fragmented formation history where formation of subglacial landforms occurred in restricted subglacial zones during restricted time periods periods of formation must have been separated by periods of preservation and inhibited subglacial reshaping based on estimates of the ice margin retreat velocity and the velocity of the warm based inward migrating zone we suggest that periods of preservation were orders of magnitude longer than periods of subglacial landform formation copyright 2003 john wiley sons ltd

marine transgressional events in the gigantic freshwater lake songliao paleontological and geochemical evidence abstract the fossil remains of euryhaline organisms in the mesozoic cenozoic non marine sedimentary records of eastern china may have resulted from either marine transgressions or inland hypersaline lacustrine environments paleontological and organic geochemical results of this study have provided new evidence for marine transgressional events in the gigantic freshwater lake songliao during the late cretaceous

pyrite framboids in the permian triassic boundary section at meishan china evidence for dysoxic deposition pyrite framboid evidence from the permian triassic global stratotype at meishan china indicates the late permian mass extinction is closely associated with a dramatic decline of benthic oxygen levels sizes and abundances of the framboids were determined from acid residues and in situ on polished sections of the samples the framboids are abundant in the thin pyrite lamina on the top of bed 24e the upper layer of bed 24 and beds 25 26 and 29 rare in bed 24e and bed 28 but absent in bed 27 they have narrow size distributions with average diameters from 4 6 mu m to 8 7 mu m which are similar to those formed under anoxic dysoxic conditions the abundances and mean diameters of the pyrite framboids indicate redox conditions of deposition changing from upper dysoxia bed 24e and lower dysoxia pyrite lamina beds 25 and 26 to oxygenation bed 27 and again to upper dysoxia bed 28 and lower dysoxia bed 29 our discovery confirms a worldwide dysoxic marine event during the permian triassic transition suggestive of a direct relationship with the permian triassic marine mass extinction c 2007 elsevier b v all rights reserved

late deglaciation of the central labrador coast and its implications for the age of glacial lakes naskaupi and mclean and for prehistory the age of the marine limit and associated deglaciation has been estimated from relative sea level curves for the hopedale and nain areas of the central labrador coast as approximately 7600 200 and 8500 200 yr ago respectively these ages indicate that the ice margin remained on the coast for up to 3000 yr longer than previously estimated because the central coast is due east of glacial lakes naskaupi and mclean the earliest the lakes could have formed was 8500 200 yr ago with their largest phases being fully established only after 7600 200 yr ago this suggests that the age of the lakes and associated deglaciation of the central labrador ungava region is younger by at least 1500 yr than previously estimated a late glacial marine based ice mass in ungava bay that dammed the lakes collapsed ca 7000 yr ago within this time frame therefore the glacial lakes only existed for 500 yr the persistence of the laurentide ice sheet margin on the central labrador coast until 7600 yr ago probably restricted the northward movement of early prehistoric people into northern labrador

framboidal chalcopyrite and bornite constrain redox conditions during formation of their host rocks in the copper stratabound mineralization of picachos north central chile abstract the picachos project is a copper deposit that occurs in manto type orebodies in north central chile and it exhibits common features of chilean stratabound or manto type copper deposits 1 an increase of copper contents from the margins to the centre of the orebodies 2 sodic and potassic hydrothermal alteration of host rocks with subsequent chloritization and sericite alteration and 3 its occurrence in sequences of limestones that are intercalated with volcanic rocks the most salient characteristic of the picachos project is the presence of pervasive framboidal pyrite in both the non mineralized limestones and the host rocks of the copper mineralization these framboidal pyrites are well preserved probably due to their close relationship with organic matter and have no evident textures of overgrowth recrystallization or dissolution moreover framboidal chalcopyrite and bornite are formed in the external and internal areas respectively of the orebodies sharing common morphological characteristics with framboidal pyrite and are formed by the replacement of the original pyrite framboids without changing their shape and size distribution representative size distributions of framboidal pyrite chalcopyrite and bornite are determined using high resolution x ray tomography micro ct this study highlights the effectiveness of these analytical techniques to obtain the representative size distribution of framboids in mineralized rocks the preservation of the original framboidal texture of pyrite makes it possible to infer anoxic to near dysoxic conditions the size distributions of framboidal chalcopyrite and bornite are hypothesized to be additional potential paleo redox indicators referring to the same formation dynamic as typical framboidal pyrites

formation of mega scale glacial lineations on the dubawnt lake ice stream bed 1 size shape and spacing from a large remote sensing dataset abstract mega scale glacial lineations msgls are the largest flow parallel bedforms produced by ice sheets and are formed beneath rapidly flowing ice streams knowledge of their characteristics and genesis is likely to result in an improved understanding of the rate at which ice and sediment are discharged by ice sheets but there is little consensus as to how they are formed and there are few quantitative datasets of their characteristics with which to formulate or test hypotheses this paper presents the results of a remote sensing survey of 46 000 bedforms on the dubawnt lake palaeo ice stream bed focussing on a central transect of 17 038 that includes highly elongate bedforms previously described as msgls within this transect lineations exceed 10 km in length max 20 km and 23 have elongation ratios 10 1 max 149 1 highly elongate features are interspersed with much shorter drumlin like features but longer bedforms are typically narrower suggesting that their length develops more quickly than or at the expense of their width bedforms are broadly symmetrical in plan form and have a preferred lateral spacing of 50 250 m which implies a regular rather than random pattern of corrugations comparison with drumlins reveals that the more attenuated msgls simply extend the tail of the distribution of data rather than plotting as a separate population taken together this supports the idea of a subglacial bedform continuum primarily controlled by ice velocity but existing hypotheses of msgl formation are either not supported or are insufficiently developed to explain our observations rather we conclude that under conditions of rapid ice flow msgls attain their great length relatively quickly decades through a probable combination of subglacial deformation which attenuates ridges and erosional processes that removes material from between them

organic matter enrichment of the late triassic yanchang formation ordos basin china under dysoxic to oxic conditions insights from pyrite framboid size distributions abstract pyrite framboids are spherical or ellipsoidal compact aggregates of submicron pyrite microcrystals the various lithologies in the chang 7 member of the upper triassic yanchang formation contain abundant pyrite framboids which provide an opportunity to understand the fluctuation in paleoredox conditions and relative sedimentation rates during deposition the measured diameters of the pyrite framboids in the chang 7 member are characterized by large mean diameters 9 7 16 6 m with a wide distribution range that plots in the area indicative of dysoxic to oxic paleoredox conditions during deposition of the chang 7 sediments based on correlation analysis the strong correlation between paleoredox sensitive trace elements ratios v cr u th and cu zn and the mean size of framboids indicate that the latter can serve as a reliable indicator of paleoredox conditions the results of the framboid size distribution can also be interpreted through crystal size distribution theory csdt according to csdt the relative sedimentation rate of the chang 7 member fluctuated during deposition in parallel with fluctuation in lacustrine levels furthermore the strongly positive correlation between total organic carbon toc and paleoredox conditions indicates that although relatively high sedimentation rate may have contributed to the dysoxic oxic conditions that were harmful to the preservation of organic matter but it may also have brought nutrients to increase productivity similarly the correlation between toc and relative sedimentation rates suggests that the relative sedimentation rates can affect organic matter enrichment in several ways a high sedimentation rate is favourable for the preservation of organic matter which can be prevented from oxidation but large amounts of sediments can dilute the organic matter which reduces the organic matter abundance in a potential source rock

subglacial drainage by groundwater channel coupling and the origin of esker systems part 1 glaciological observations this work is presented in two parts part i presents observations on the coupling between subglacial channel flow and groundwater flow in determining subglacial hydraulic regime and creating eskers from an icelandic glacier that is suggested as an analogue for many parts of pleistocene ice sheets part ii develops a theory of perennial subglacial stream flow and the origin of esker systems and models the evolution of the subglacial stream system and associated groundwater flow in a glacier of the type described in part i it is suggested that groundwater flow may be the predominant mechanism whereby meltwater at the glacier bed finds its way to the major subglacial streams that discharge water to glacier margins

early holocene glacial lakes and ice marginal retreat pattern in labrador ungava canada abstract the existence of glacial lakes naskaupi mclean minto melezes and wapussakatoo during the deglaciation of labrador ungava canada was recognized at the end of 1950s however glacial lakes have seldom been included in regional reconstructions to constrain the outline of successive ice margins during the glacial retreat in labrador ungava reconstruction of the ice flow succession in labrador ungava has often primarily focused on till lineation systems these reconstructions often depict a late glacial ice dispersal center situated over central labrador ungava more recent studies on glacial geomorphology including meltwater features however suggest that north central labrador ungava exhibited cold based conditions at least during the latest deglaciation cold based conditions inhibit basal sliding and formation of landforms except for meltwater traces such as meltwater channels glacial lake shorelines and deltas this situation implies that meltwater traces are the main source of information when reconstructing the spatial retreat pattern during a cold based deglaciation evidence presented in this study such as glacial lake shorelines fossil deltas and spillway and drainage channels in north central labrador ungava indicates the existence of numerous previously unmapped glacial lakes the mapped glacial lake features are synthesized to a reconstruction of several glacial lake stages which in turn are used to constrain the late glacial ice margin retreat pattern over the inferred cold based areas of north central labrador ungava a total of 26 glacial lakes 65 sub stages existed during the deglaciation of labrador ungava these lakes were impounded along the southern margin of the shrinking ice sheet the required damming ice margins indicate that the last ice remnant of the laurentide ice sheet in labrador ungava was situated over the southern ungava bay and the adjacent southern shore

marine incursion events in the late cretaceous songliao basin constraints from sulfur geochemistry records abstract songliao basin in ne china developed the most productive oilfield in the world sourced from terrestrial rocks the main source rock of the basin includes member 1 of the qingshankou k2qn1 and members 1 and 2 of the nenjiang formation k2nj1 2 however the exact reasons for the formation of the source rock especially the k2qn1 are still controversial former paleontological and organic geochemical research suggested that organic matter was deposited during marine incursion events of k2qn1 but further geochemical evidence is needed this paper explores the distinct sulfate levels that distinguish marine from fresh waters of the songliao paleo lake we undertook a systematic investigation the sulfur geochemistry of the sediments from top of member 4 of the quantou formation k1q4 to top of member 1 of the qingshankou k2qn1 the ratio of organic carbon to the pyrite sulfur toc pys proved the previously suggested saline conditions during the deposition of k2qn1 and the pyrite sulfur isotope indicated that marine incursion may not only have occurred for k2qn1 but also for top of k1q4 the exact time for the beginning of marine incursion is to be determined the marine incursion within k2qn1 is not strong and partially controlled by the fluctuation of paleo lake level the present study will be helpful for understanding the contribution of marine incursion events to the burial of organic carbon in the songliao paleo lake although further studies are still needed

reorganization of ice sheet flow patterns in arctic canada and the mid pleistocene transition 1 evidence for the evolution of laurentide ice sheet lis basal thermal regime patterns during successive glaciations is poorly preserved in the geologic record here we explore a new approach to constrain the distribution of cold based ice across central baffin island in the eastern canadian arctic over many glacial interglacial cycles by combining till geochemistry and cosmogenic radionuclide crn data parts of the landscaped with geomorphic evidence for limited glacial erosion are covered by till characterized by high chemical index of alteration cia values and crn concentrations requiring complicated burial exposure histories till from regions scoured by glacial erosion have cia values indistinguishable from local bedrock and crn concentrations that can be explained by simple exposure following deglaciation crn modeling results based on these constraints suggest that the weathered tills were deposited by 1 9 to 1 2 ma and by that time the fiorded baffin island coastline must have developed close to its modern configuration as piracy of ice flow by the most efficient fiord systems resulted in a major shift in the basal thermal regime across the northeastern lis the resultant concentration of ice flow in fewer outlet systems may help explain the cause of the mid pleistocene transition from 41 to 100 kyr glacial cycles

geomorphological reconstruction of the labrador sector of the laurentide ice sheet abstract the labrador sector formed one of three major domes of the laurentide ice sheet during the last wisconsinan glaciation reconstruction of its evolution is important because it modulated atmospheric and oceanic circulation over 1 100 ka time scales this paper reports new geomorphological evidence of ice flow which is used to reconstruct glimpses of the behaviour of the labrador sector during its evolution flow evidence indicates a southern position 51 n of the labrador ice divide presumed to be the usual location when the ice sheet was close to its maximum extent a previously inferred dramatic surge of labrador ice across hudson strait and onto baffin island at 9 9 9 4 ka is verified seemingly contradictory evidence regarding deglaciation in northern quebec has been analysed and a reconstruction developed that solves this problem deglacial retreat of the labrador ice sheet was highly asymmetric with rapid retreat of the southern margin northwards migration of the centre of mass by 500 km and slow retreat along the northern margin as it shrank its thermal regime changed from cold centred to entirely cold based and it finally fragmented into many residual ice caps and glaciers this dynamic and asymmetric behaviour may be due to destabilisation of the labrador ice sheet triggered by heinrich event ice streaming through hudson strait