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

correlation of reservoired gases using the carbon isotopic compositions of wet gas components the carbon isotopic compositions of the wet gas components particularly propane isobutane and normal butane have been found to be particularly valuable for correlating one reservoired gas with another the usefulness of these components for correlation results from their carbon isotopic compositions reflecting both the nature of their source and their maturity this source control is strongest for gases derived from the more highly structured types of kerogen i e woody coaly type iii although the wet gas components carbon isotopic compositions of most gases are at least partly controlled by their source for levels of maturity below the point at which thermal destruction of the wet components occurs as a result the wet gas components are found to provide more ositive correlations than is methane alone three exploration examples illustrate the use of the carbon isotopic compositions of the wet gas components for correlation the leduc reef trend of alberta canada the sleipner area in the north sea and the lena field offshore louisiana united states the three examples also illustrate the need to integrate geochemical interpretations with regional geology to obtain a good understanding of the hydrocarbon source

relation between soil age and silicate weathering rates determined from the chemical evolution of a glacial chronosequence long term weathering rates rlt were determined from base cation depletion in soil profiles developed on six granitic glacial moraines varying in age from 0 4 to 297 ka in the wind river mountains wyoming weathering rates were found to decrease with soil age t according to the power law equation rlt 15 t 0 71 where rlt is in meq m 2 yr 1 and t is in ka comparable data from the literature are consistent with this function and it is similar to power law equations describing changes in laboratory weathering rates with time on the basis of our study we predict that for a catchment unaffected by anthropogenic inputs and in a steady state with respect to the organic and cation exchange pools rlt should be higher than present day weathering rates derived from stream fluxes rpd by a factor of about 3 4

are time and temperature the only constraints to the simulation of organic matter maturation abstract confined pyrolysis hydrous pyrolysis and high pressure hydrous pyrolysis were performed with various samples toarcian shale and kerogen woodford shale and kerogen manakam coal and under different experimental conditions in order to test the effects of pyrolysis variables on the simulation of maturation of organic matter results show that i experimental time and temperature are not exchangeable parameters as suggested by first order kinetic law models ii increasing confining pressure 300 1300 bars in gold cell experiments performed on woodford samples has a limited influence on the reduction rate of the oil potential the tsom total soluble organic matter yield and the structure of the polars iii the presence of excess liquid water 0 100 weight in confined pyrolysis experiments does not significantly influence organic matter maturation however comparisons with classic hydrous pyrolysis 200 weight water could indicate major differences in timing and composition of the tsom bitumen expelled fraction as well as of the solid residue it appears that excess water is not necessary to simulate organic matter maturation when the system is sufficiently confined hydrous pyrolysis conditions low partial pressure of products delay woodford kerogen conversion in addition results concerning the mahakam coal suggest that the structure of the organic matter plays an important role concerning the water effect iv increasing water pressure in hydrous conditions 220 1300 bars drastically lowers and delays woodford kerogen maturation quantitative analysis of the water produced during confined pyrolysis and comparison of the extent of aromatization in hydrous and confined pyrolysis suggests that two competing hydrogen transfer mechanisms occur during organic matter pyrolysis this study shows that additional parameters must be defined when comparing the results of the experimental simulation of organic matter maturation

southern laurentide ice sheet retreat synchronous with rising boreal summer insolation establishing the precise timing for the onset of ice sheet retreat at the end of the last glacial maximum lgm is critical for delineating mechanisms that drive deglaciations uncertainties in the timing of ice margin retreat and global ice volume change allow a variety of plausible deglaciation triggers using boulder 10 be surface exposure ages we date initial southern laurentide ice sheet lis retreat from lgm moraines in wisconsin usa to 23 0 0 6 ka coincident with retreat elsewhere along the southern lis and synchronous with the initial rise in boreal summer insolation 24 23 ka we show with climate surface mass balance simulations that this small increase in boreal summer insolation alone is potentially sufficient to drive enhanced southern lis surface ablation we also date increased southern lis retreat after ca 20 5 ka likely driven by an acceleration in rising isolation this near instantaneous southern lis response to boreal summer insolation before any rise in atmospheric co 2 supports the milankovic hypothesis of orbital forcing of deglaciations

composition and stable isotope geochemistry of natural gases from kansas midcontinent u s a abstract more than 28 1012 ft 3 79 1010 m3 of natural gas and 5 3 109 bbl 8 4 108 m3 of oil have been produced in kansas u s a from paleozoic carbonate and sandstone reservoirs on structural uplifts and shallow embayments along the northern margin of the anadarko basin a heavily explored geologically well characterized state kansas is an excellent place to study hydrocarbon migration and to test geochemical models for the origin of natural gases immature to marginally mature rocks of eastern kansas cherokee and forest city basins produce mixed microbial and thermogenic gases gases in this region have wetness 0 03 51 methane 13c 65 to 43 and methane d 260 to 150 gases from central and western kansas nemaha uplift to hugoton embayment are entirely thermogenic and have wetness 4 51 methane 13c 48 to 39 and methane d 195 to 140 ethane and propane 13c values throughout kansas vary from 38 to 28 and from 35 to 24 respectively mature thermogenic gas generated from source rocks in southwestern kansas and the anadarko basin with 1 0 ro 1 4 is recognized throughout the state lateral migration into shallow reservoirs on the central kansas and northern nemaha uplifts and in the cherokee basin probably occurred along basal pennsylvanian conglomerates and weathered lower paleozoic carbonates at the regional sub pennsylvanian unconformity early thermogenic gas generated by local source rocks with ro 0 7 is recognized in isolated fields in the salina and forest city basins in ordovician reservoirs beneath the sub pennsylvanian unconformity in the cherokee basin and in reservoirs generally above the unconformity in the cherokee and sedgwick basins the eastern central kansas uplift and the hugoton embayment

middle wisconsinan marine shells near repulse bay nunavut canada implications for marine isotope stage 3 ice free conditions and laurentide ice sheet dynamics in north west hudson bay

constraining the late pleistocene history of the laurentide ice sheet by dating the missinaibi formation hudson bay lowlands canada abstract well dated paleorecords from periods prior to the last glacial maximum lgm are important for validating models of ice sheet build up and growth however owing to glacial erosion most late pleistocene records lie outside of the previously glaciated region which limits their ability to inform about the dynamics of paleo ice sheets here we evaluate new and previously published chronology data from the missinaibi formation a pleistocene aged deposit in the hudson bay lowlands hbl canada located near the geographic center of the laurentide ice sheet lis available radiocarbon ams 44 conventional 36 amino acid n 13 uranium thorium u th n 14 thermoluminescence tl n 15 and optically stimulated luminescence osl n 5 data suggest that an ice free hbl may have been possible during parts of marine isotope stage 7 mis 7 ca 243 000 to ca 190 000 yr bp mis 5 ca 130 000 to ca 71 000 yr bp and mis 3 ca 29 000 to ca 57 000 while mis 7 and mis 5 are well documented interglacial periods the development of peat forest bed and fluvial deposits dating to mis 3 n 20 radiocarbon dates 4 tl dates 3 osl dates suggests that the lis retreated and remained beyond or somewhere within the boundaries of the hbl during this interstadial ice sheet models approximate the margin of the lis to southern ontario during this time which is 700 km south of the hbl therefore if correct our data help constrain a significantly different configuration and dynamicity for the lis than previously modelled we can find no chronological basis to discount the mis 3 age assignments however since most data originate from radiocarbon dates lying close to the reliable limit of this geochronometer future work on dating the missinaibi formation using other geochronological methods e g u th osl is necessary in order to confirm the age estimates and strengthen the boundaries of the lis during this period

paleo constraints on sea level rise palsea ice sheet and sea level responses to past climate warming abstract here we summarize the motivation and issues surrounding the responses of ice sheets and sea level to past climate warming as part of the paleo constraints on sea level rise palsea working group papers in this special issue of quaternary science reviews focus on the timescale of glaciations during the late pliocene the magnitude of ice sheet fluctuations and volume leading up to and during the last glacial maximum the timing and persistence of ice sheet impacts on deglacial and future relative sea level change and relative sea level change during peak interglacial climate a more dynamic cryosphere is noted under both late pliocene and last glacial cycle climate conditions while relative sea level changes during the last deglaciation appear to correspond closely with individual ice sheet deglaciation lastly relative sea level change during peak interglacial conditions may have fluctuated by as much as a meter although the sources of such variability greenland antarctica or elsewhere remain elusive

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

sources and mechanisms of formation of gaseous hydrocarbons in sedimentary rocks abstract accepted concepts of principal stages of hydrocarbon formation fail to satisfactorily explain the accumulation of supergiant gasfields in west siberia u s s r such as for example urengoy which comprise 30 of the proven gas reserves of the world a new mathematical model has been developed which applies the concept of activation energy distribution to the formation of gases characteristic differences in the molecular structure of humic and sapropelic source organic matter are expressed in different activation energy distributions the model allows the calculation of isotope values for different types of organic matter and their dependence on maturity application of the model to west siberia suggests that the supergiant gas accumulations in urengoy are more likely formed from terrestrial organic matter through thermochemical reactions at moderate depths and are not the result of either deep overmature or bacteriogenic processes the new mathematical model suggests that humic organic matter in general has a high methane generating capacity at comparably low maturities of organic matter equivalent to 0 5 0 7 on the vitrinite reflectance scale

refining the laurentide ice sheet at marine isotope stage 3 a data based approach combining glacial isostatic simulations with a dynamic ice model abstract while glacial geologic records track the retreat history of the laurentide ice sheet constraints on the ice sheet build up history are more elusive as the laurentide ice sheet expanded to its maximum extent at the last glacial maximum 26 ka it erased most evidence of previous glaciations however an increasing number of dated non glacial deposits point to a relatively confined laurentide ice sheet during marine isotope stage 3 mis 3 60 26 ka suggesting rapid ice growth rates leading to the last glacial maximum in this study we demonstrate that predictions of relative sea level change due to glacial isostatic adjustment involving a late and rapid growth of the laurentide ice sheet are consistent with sea level bounds associated non glacial deposits of mis 3 age in canada we also run a simple dynamic ice model that adopts the paleotopography generated from the glacial isostatic adjustment simulation and show that using accumulation rates similar to that of the present day arctic rapid glaciation rates starting at mid mis 3 44 ka are predicted

a comparison of pyrolysis products with models for natural gas generation abstract hydrous pyrolysis using progressive heating from 150 to 365 c is used to study the generation and isotopic composition of hydrocarbon gases and carbon dioxide different source rocks from the draupne heather dunlin and brent formations in the north sea a miocene brown coal from germany a coal from the middle jurassic ness formation in the northern north sea and a rich marine type source from the late jurassic kimmeridge clay formation onshore uk are studied the experimental results are related to vitrinite reflectance as a maturity reference parameter and to existing models for natural gas generation hydrous pyrolysis simulates the observed isotopic composition of natural systems fairly closely the largest deviations are found for methane which is most sensitive to fractionation effects the obtained results mainly reflect variations in source rock type and initial isotopic composition different maturity dependent trends are found between coal derived and marine type ii derived gases trends in the experimental data fit well with basic assumptions of existing models for natural gas generation

carbon isotope fractionation during natural gas generation from kerogen abstract in petroleum exploration it is important to be able to determine the origin of any gas which is found this paper describes a new method of estimating the source type and maturity of a gas based on a rayleigh fractionation model kerogen is divided conceptually into a labile dominantly oil generating fraction and a refractory gas prone component 13 c of methane from either kerogen type and ethane propane and butane for gases from labile kerogen can be defined as a function of 13 c of the gas precursor groups in kerogen a kinetic isotope fractionation factor k and the extent of gas generation the isotopic ratio of the methane precursors relative to bulk kerogen determined from laboratory pyrolysis are 17 5 for labile kerogen and 1 4 for refractory kerogen values for ethane propane and butane from labile kerogen based on field correlations are 4 9 2 2 and 1 6 respectively the corresponding fractionation factors are 0 9892 0 9919 0 9947 and 0 9975 for methane ethane propane and butane respectively from labile kerogen and 0 9984 for methane from refractory kerogen using these parameters summary diagrams are constructed which allow differentiation of these sources from each other and from biogenic gases and cracked oil and recognition of gases of mixed origin if an independent estimate of 13 c for the source kerogen is possible then 13 c of the gas components can be used to estimate maturity in terms of the gas generation index the fraction of gas potential which has been realized

joint inversion of surface and three component borehole magnetic data the inversion of magnetic data is inherently nonunique with respect to the distance between the source and observation locations this manifests itself as an ambiguity in the source depth when surface data are inverted and as an ambiguity in the distance between the source and boreholes if borehole data are inverted joint inversion of surface and borehole data can help to reduce this nonuniqueness to achieve this we develop an algorithm for inverting data sets that have arbitrary observation locations in boreholes and above the surface the algorithm depends upon weighting functions that counteract the geometric decay of magnetic kernels with distance from the observer we apply these weighting functions to the inversion of three component magnetic data collected in boreholes and then to the joint inversion of surface and borehole data both synthetic and field data sets are used to illustrate the new inversion algorithm when borehole data are inverted directly three component data are far more usefu

recent advances in petroleum isotope geochemistry abstract organic matter is isotopically heterogeneous lipids tend to be depleted in the heavy carbon and hydrogen isotopes as compared to carbohydrates and lignite the c and h isotopic composition of kerogens is determined by many factors such as environmental conditions during formation and deposition and variability of sources of organic matter stable isotope concentrations in mature kerogens are not significantly altered during maturation and hence reflect the variability of the organic matter during deposition isotope variations in kerogens therefore reflect to some extent the paleogeographic situation and can be used for paleoreconstruction a basin facies with anoxia and a marginal facies with detrital input can be differentiated isotopically in the toarcian of central europe coals are isotopically heterogeneous due to different isotopic composition of macerals inertinite and vitrinite tends to be enriched in deuterium as compared to exinite also boghead coals tend to be depleted in dueterium which possibly reflects various lipid contents of respective precursor materials petroleums can be genetically classified through the patterns of covariance of their compound classes carbonate and shale sourced petroleums may be additionally differentiated through their deuterium content the general world wide applicability of such genetic differentiations needs still to be proved carbon and hydrogen isotope variations in methane are genetically controlled bacterial methane in freshwater environments is characteristically depleted in deuterium even complex origins of natural gases can be unraveled using compositional and isotopic variations new analytical developments led to the application of carbon isotope analyses of gaseous hydrocarbons desorbed from sediments for geochemical surface exploration a discussion reveals that processes such as isotope effects during degassing and bacterial oxidation as well as indigenous formation of hydrocarbons may completely obscure the results

understanding of reservoir gas compositions in a natural case using stepwise semi open artificial maturation abstract in a study of the gas distribution and composition in different reservoirs of multilayered gas fields in south east asia two types of variations with depth of the 13c values of gases in particularly methane were observed in the normally pressured zones the 13c values of methane increase steadily with depth whilst in some overpressured zones they first decrease with depth and then follow a regular trend in order to explain these patterns these data were compared to those obtained by artificial maturation of a coal using confined pyrolysis experiments were conducted in perfectly closed and in semi open conditions the free gases recovered were quantified by gas chromatography and the carbon isotopic composition of individual compounds c1 c5 hydrocarbons determined the evolution of the 13c versus pyrolysis temperature obtained for the artificially generated methane is very similar to that of the natural gas the use of the 13c2 13c3 versus c2 c3 mol diagram eage 58th conference and technology exhibition 1996 chem geol 147 1998 249 allows recognition of two trends in the artificial maturation data related to the degree of opening of the experimental systems comparison of the data provide evidence that the closed pyrolysis results are very similar to those observed in high pressured reservoirs while those obtained in the normal pressured reservoirs follow the values of semi open pyrolysis the gas distributions and carbon isotope composition in the reservoirs can therefore be explained in terms of degree of opening of the system high pressure reservoirs can be considered as fairly closed systems with in situ gas generation while normally pressured zones are more open and subject to important lateral migration the composition of the gas richness in methane is controlled by the degree of opening of the system thus our findings do not support the hypothesis that the generation of methane rich gases in nature is controlled by transition metal catalysis

multiple origins of methane in the earth methane occurrences in the earth s crust are predominantly of biogenic origin i e their ultimate source is biologically formed organic matter methane can also form through inorganic reactions and is consequently termed abiogenic biogenic methanes can either form through bacterial or thermogenic processes bacterial processes follow a co2 reduction and or fermentation pathway the fermentation processes are quantitatively more important in recent fresh sediments and swamps methane formed by co2 reduction however is most common in older sediments and commercial gasfields temperature organic substrate and age may be the major factors controlling the relative importance of the two pathways stable isotope concentrations in thermogenic methanes seem to be controlled by the extent of conversion of organic matter the timing of gas expulsion and trapping the different character of methane in individual sedimentary basins may be a result of the geologic history geothermal methanes are most likely derived from pyrolysis of organic matter abiogenic methane occurs in hydrothermal vents and ophiolite complexes inorganic reactions either surficial or deep seated are the likely source of such methanes a uniform mantle origin of methane is not supported by the observed isotope variations in naturally occurring methanes

absence of glaciation in illinois during marine isotope stages 3 through 5 a10be inventory and14c ages of material from a core from northernmost illinois support previous interpretations that this area was ice free from ca 155 000 to 25 000 yr ago during much of this period from about 155 000 to 55 000 yr ago 10be accumulated in the argillic horizon of the sangamon geosol wisconsinan loess containing inherited10be was deposited above the sangamon geosol from ca 55 000 to 25 000 yr ago and was subsequently buried by late wisconsinan till deposited by the lake michigan lobe of the laurentide ice sheet the sangamonian interglacial stage has been correlated narrowly to marine oxygen isotope substage 5e our data indicate instead that the sangamon geosol developed during late stage 6 all of stages 5 and 4 and early stage 3

too young or too old evaluating cosmogenic exposure dating based on an analysis of compiled boulder exposure ages cosmogenic exposure dating has greatly enhanced our ability to define glacial chronologies spanning several global cold periods and glacial boulder exposure ages are now routinely used to constrai

geochemistry and mineralogy of late quaternary loess in the upper mississippi river valley usa provenance and correlation with laurentide ice sheet history abstract the midcontinent of north america contains some of the thickest and most extensive last glacial loess deposits in the world known as peoria loess peoria loess of the upper mississippi river valley region is thought to have had temporally varying glaciogenic sources resulting from inputs of sediment to the mississippi river from different lobes of the laurentide ice sheet here we explore a new method of determining loess provenance using k rb and k ba values in k feldspars and micas in loess from a number of different regions in north america results indicate that k rb and k ba values can distinguish loess originating from diverse geologic terrains in north america further different loess bodies that are known to have had the same source sediments using other criteria have similar k rb and k ba values we also studied three thick loess sections in the upper mississippi river valley region at each site the primary composition of the loess changed over the course of the last glacial period and k rb and k ba values parallel changes in carbonate mineral content and clay mineralogy we thus confirm conclusions of earlier investigators that loess composition changed as a result of the shifting dominance of different lobes of the laurentide ice sheet and the changing course of the mississippi river we conclude that k rb and k ba values are effective robust and rapid indicators of loess provenance that can be applied to many regions of the world

landscape evolution degrades the geologic signature of past glaciations glaciers on land leave behind characteristic landforms and bedrock topography the spatial extent of this signature and dating of the erosional and depositional features has led to a good understanding of temporal and spatial shifts of past glaciers and climate at best the landscape contains considerable information on past glacial processes in the form of moraines and other depositional landforms however evidence suggests that all unconsolidated landforms degrade manifested in the general degradation and smoothing of the topography over time to determine the relative amount and pattern of degradation on glacial moraines we use a well documented moraine degradation model that uses both local slope and a proportionality constant to determine the diamicton transport rate this formulation results in diffusion type topographic smearing and smoothing of the initially angular topographic features more specifically diamicton is eroded at the crest of a moraine transported downhill and deposited on the gentler lower flank collectively this produces moraine cross profiles that closely resemble observations in the field by assuming an initial constant boulder frequency per unit volume of the diamicton the model tracks the surface lowering and the related exhumation of boulders to the moraine surface this produces a tightly constrained set of testable predictions 1 modelled moraine cross profile 2 modelled spatial pattern of surface boulders no boulders on the lower flank and 3 relative frequency of surface boulders smallest frequency of surface boulders at the inflection point highest frequency at the crest these characteristics were measured in the field of alpine tropical and antarctic moraines the correspondence between model predictions and field data is remarkably good and strongly supports our understanding of the time dependent evolution of glacial landscapes these results highlight the evolving nature of glacial landforms and indicate the complete removal of original moraine surfaces and postglacial emergence of spatial pattern in boulder frequency

origin source mixing and thermal maturity of natural gases in the panyu lower uplift and the baiyun depression pearl river mouth basin northern south china sea multiple natural gas fields have been discovered in the baiyun depression and the adjoining panyu lower uplift in the pearl river mouth basin northern south china sea the natural gases are associated with condensate and are characterized by relatively heavy carbon isotopes with methane and ethane 13c values ranging from 44 2 to 33 6 and 30 0 to 25 4 respectively nearly all methane and ethane are derived from oil prone type ii kerogen in the wenchang formation source rock whereas the heavy hydrocarbon gases propane butanes and pentanes are derived from both the wenchang and enping type iii kerogen formations based on an integrated comparison of carbon isotopic compositions of the natural gases typical type i ii and type iii kerogen derived gases and the enping and wenchang kerogens the gases from the eastern parts of the baiyun depression and the panyu lower uplift mainly originate from secondary oil cracking and primary kerogen cracking respectively the gases from the northern slope of the baiyun depression are a mixture of oil cracking and kerogen cracking gases both oil cracking and kerogen cracking gases were mainly generated from the wenchang formation source rock in the maturity range of 1 5 2 5 vitrinite reflectance with a corresponding present day depth range of 5400 6500 m 17 700 21 300 ft the apparent contribution of the wenchang formation to the discovered gas accumulations demonstrates that it is the most important source rock in the area instead of the enping formation the search for more gas derived from oil cracking will be the next natural gas exploration direction in the baiyun depression

hudson bay was not deglaciated during mis 3 abstract the debate over the dimensions of the laurentide ice sheet during the middle wisconsinan has been reinvigorated recently by a claim that hudson bay was deglaciated sometime between 57 and 29 ka based on 735 published dates purported to support a dramatic reduction of the ice sheet we review the evidence and conclude that an ice free hudson bay in the proposed time window is inconsistent with major plumes of sediment laden icebergs and meltwater i e heinrich events derived from a hudson strait ice stream that deposited clastic layers on the sea floor from ne north america to the coast of europe we also show that almost all of the 735 published dates are either irrelevant to the claim of an ice free hudson bay or are mis interpreted a careful evaluation of the 40 14c ages on hudson bay lowland wood the most reliable medium for 14c dating sites 35 ka suggests that only two of these dates can be plausibly considered to be finite ages while the rest of those 14c ages can only be taken at best as minimum limiting ages collectively the sum of the stratigraphic and geochronologic data from the hudson bay lowlands indicate that hudson bay was likely deglaciated during marine isotope stage 5a consistent with late quaternary sea level records high northern hemisphere summer insolation and relatively high atmospheric co2 but coupled with the nature of heinrich events we conclude that hudson bay remained under a thick laurentide ice sheet throughout mis 3

laurentide ice sheet meltwater and abrupt climate change during the last glaciation 1 a leading hypothesis to explain abrupt climate change during the last glacial cycle calls on fluctuations in the margin of the north american laurentide ice sheet lis which may have routed fresh water between the gulf of mexico gom and the north atlantic affecting north atlantic deep water variability and regional climate paired measurements of 18o and mg ca of foraminiferal calcite from gom sediments reveal five episodes of lis meltwater input from 28 to 45 thousand years ago ka that do not match the millennial scale dansgaard oeschger warmings recorded in greenland ice we suggest that summer melting of the lis may occur during antarctic warming and likely contributed to sea level variability during marine isotope stage 3

initiation and development of the laurentide and cordilleran ice sheets following the last interglaciation abstract fossil records from sites overridden by or adjacent to the laurentide ice sheet indicate that the climate of the last interglaciation oxygen isotope substage 5e ca 130 116 ka was warmer than today following the last interglaciation the laurentide ice sheet first developed during stage 5 over keewatin quebec and baffin island along its northern margin the ice sheet reached its maximum extent of the last glaciation during stage 5 the ice sheet advanced across baffin island onto the continental shelf early during stage 5 5d whereas the advance into the western canadian arctic occurred late during stage 5 5b the ice sheet also may have advanced into the st lawrence lowland during substage 5b although this event may be younger stage 4 the hudson bay lowland became ice free during substage 5a retreat of the ice sheet on baffin island occurred during late stage 5 probably substage 5a the exact timing of retreat from the western canadian arctic is unknown but it occurred before 48 ka the southern sector including the st lawrence lowland was ice free during late stage 5 the hudson bay lowland may have remained ice free through stage 4 and much of stage 3 because of conflicting chronologies however it is more likely that this area was glaciated throughout stage 3 and perhaps stage 4 nevertheless the data demonstrate that the lowland was ice free during part of the last glaciation an independent ice cap developed over the appalachian uplands and advanced across nova scotia during stage 4 perhaps as far as the edge of the continental shelf the ice cap remained active over nova scotia as a setellite to the laurentide ice sheet throughout the remainder of the last glaciation the ice sheet advanced into the st lawrence lowland during stage 4 and subsequently overwhelmed the local ice cap in the appalachian uplands advancing perhaps into northern new england but not farther south the lowland remained covered by the ice sheet until late stage 2 the ice sheet may also have advanced into the lake ontario basin during stage 4 the position of the northern margin of the laurentide ice sheet during stage 4 is not known but it remained an unknown distance behind its maximum position reached during stage 5 cores from baffin bay indicate a substantial decrease in high latitude glaciation during stage 4 following retreat the keewatin sector of the ice sheet may have remained over much of northwestern canada as a quasi stable ice mass until it readvanced during stage 2 similarly the baffin island sector of the ice sheet may have remained largely intact the southern margin of the ice sheet may have advanced into the lake ontario basin and upper mississippi valley during the middle of stage 3 ca 50 ka reaching its maximum extent of the last glaciation during stage 2 ca 18 21 ka advance of the northern margin was younger ca 8 13 ka than that of the southern margin this advance was less extensive than the penultimate advance stage 5 paleoenvironmental records indicate that the last interglaciation in areas covered by and near the cordilleran ice sheet was as warm as or warmer than present the cordilleran ice sheet appears to have developed during stage 5 or 4 at that time it advanced over southern british columbia and into the northern puget lowland there is no record of this event in northern areas that were later covered by the ice sheet the ice sheet disappeared before 59 ka at the beginning of a lengthy nonglacial interval paleoenvironmental records indicate that climate was similar to the present during part of this interval the ice sheet was absent and glaciers probably were confined to mountain areas throughout stage 3 climatic deterioration marking the end of this nonglacial interval may have begun as early as 29 ka by 14 15 ka the ice sheet had achieved its maximum extent of the last glaciation because there are few suitable dating methods capable of resolving events beyond the radiocarbon limit and because sites that preserve a record of events from the last glaciation are spatially restricted we consider this synthesis as tentative and subject to significant revision as dating methods improve nevertheless this perspective of the north american ice sheets through the last glaciation demonstrates their complex and dynamic behavior and attendant rapid fluctuations in ice volume

geochemistry of natural gases in deep strata of the songliao basin ne china chemical composition and stable carbon isotopic studies were undertaken for 27 gas samples from deep strata of the xujiaweizi depression in the songliao basin to investigate their origin gas molecular and carbon isotopic compositions show great variety methane is the main component for all studied samples and its content ranges from 57 4 to 98 2 with an average of 90 1 gas wetness ranges from 0 8 to 16 7 with an average of 2 7 the main non hydrocarbon gases are carbon dioxide and nitrogen with an average of 4 0 and 3 2 respectively carbon isotope data suggest that these deep strata gases are mainly coal type gases mixed with minor amounts of associated oil type gases coal type gases are characterized by heavier carbon isotopic values and drier chemical compositions these gases were generated from the lower cretaceous shahezi formation coals interbedded shales with type iii kerogen during the postmature stage of hydrocarbon generation oil type gases are characterized by lighter carbon isotope and higher wetness which were generated from the lower cretaceous shales with type ii kerogen in the shallow strata during the early mature stage of hydrocarbon generation mixing of two different gases causes unusual carbon isotopic distribution patterns with lighter isotopic values in higher numbered carbons in most gases the discovery of coal type gases in the songliao basin provides new prospects for the exploration in this region

revision of the epica dome c co2 record from 800 to 600 kyr before present the european project for ice coring in antarctica dome ice core from dome c edc has allowed for the reconstruction of atmospheric co2 concentrations for the last 800 000 years here we revisit the oldest part of the edc co2 record using different air extraction methods and sections of the core for our established cracker system we found an analytical artifact which increases over the deepest 200 m and reaches 10 1 2 4 ppm in the oldest deepest part the governing mechanism is not yet fully understood but it is related to insufficient gas extraction in combination with ice relaxation during storage and ice structure the corrected record presented here resolves partly but not completely the issue with a different correlation between co2 and antarctic temperatures found in this oldest part of the records in addition we provide here an update of 800 000 years atmospheric co2 history including recent studies covering the last glacial cycle

kerogen conversion and thermal maturity modelling of petroleum generation integrated analysis applying relevant kerogen kinetics abstract kerogen transformation to petroleum and thermal maturity modelling calibrated to vitrinite reflectance utilizing arrhenius equation reaction kinetics are important oil and gas exploration tools for conventional and non conventional resources the range and correlation between activation energies e and frequency factors a on a geological scale is presented to support the theory and application of the time temperature index tti arr method of thermal maturity proposed in 1988 with a single set of e a values e 218 kj mol 52 1 kcal mol a 5 45e 26 my the tti arr method provides a highly sensitive and transparent thermal maturity index it is well correlated with vitrinite reflectance and produces comparable results with models applying theoretically tenuous distributions of e with single a values the sensitively scaled tti arr methodology has the added benefit of providing detailed insight to petroleum generation via the calculation of related transformation factors tf for oil and gas by applying a range of e a values referencing the tti arr thermal maturity scale as a benchmark this study provides analysis of detailed modelling of the transformation process with representative and realistic kinetics for kerogens and mixtures of kerogens for a wide range of heating rates at geological and laboratory scales the results reveal that novel metrics such as maximum transformation gradient and temperature at which it occurs average transformation gradient between 10 and 90 conversion and temperature spread from 10 to 90 conversion can discriminate between the transformation processes of kerogens and mixtures of kerogens at geological and laboratory scales these metrics offer the potential to more precisely define sweet spots of petroleum generation in organic rich shales they also have potential at the laboratory scale to assist in the extraction of kinetic information from existing and future pyrolysis test furthermore the analysis suggests that mixtures of kerogens can in most cases be more effectively identified and characterized and their petroleum transformation modelled with just two or three e a sets as kinetic inputs this approach is preferred to the common practice of using a complex distributions of multiple e values linked with a single a value unrelated to the geological scale e a trend established for kerogens

rapid laurentide ice sheet advance towards southern last glacial maximum limit during marine isotope stage 3 abstract marine isotope stage mis 3 58 28 ka is a period of intermediate global ice volume between mis 4 and the last glacial maximum of mis 2 here we report geologic evidence for southern laurentide ice sheet rapid growth to near its last glacial maximum extent after a period with limited ice in the southernmost hudson bay lowland a14c age on wood in lacustrine sediments interbedded with glacial tills in central eastern wisconsin dates a laurentide ice sheet advance southwards to an extent at least equivalent to at least its 17 ka deglacial limit by 39 1 0 4 ka this advance ended before 30 4 0 9 ka based on another 14c date on wood in lacustrine sediment overlying the till layers this advance is consistent with 14c ages from michigan and iowa and gulf of mexico runoff records that support a concurrent southern laurentide ice sheet advance we infer changes in north american ice volume using ice sheet model simulations from a large ensemble that are consistent with 14c data and gulf of mexico discharge constraints the simulations show the laurentide ice sheet growing from a volume equivalent to 25 30 m of global mean sea level gmsl before 40 ka to 40 45 m of gmsl at 40 ka and reaching 65 70 m gmsl by 30 ka consistent with glacial isostatic adjustment assessments of near to intermediate field sea level data we thus show from our terrestrial field data and ice sheet model simulations that an individual ice sheet can grow rapidly which has only been inferred previously for global ice volume from gsml records

global ice volume during mis 3 inferred from a sea level analysis of sedimentary core records in the yellow river delta abstract estimates of global ice volume during the glacial phase of the most recent ice age cycle are characterized by significant uncertainty reflecting the relative paucity of geological constraints on sea level relevant to this time interval for example during the middle stages of marine isotope stage 3 published estimates of peak global mean sea level gmsl relative to the present range from 25 m to 87 m the large uncertainty in gmsl at mis 3 has significant implications for estimates of the rate of ice growth in the period leading to the last glacial maximum 26 ka we refine estimates of global ice volume during mis 3 by employing sediment cores in the bohai and yellow sea that record a migration of the paleoshoreline at 50 37 ka through a transition from marine to brackish conditions in particular we correct relative sea level at these sites for contamination due to glacial isostatic adjustment using a sea level calculation that includes a gravitationally self consistent treatment of sediment redistribution and compaction and estimate a peak global mean sea level of 38 7 m during the interval 50 37 ka with suitable sedimentary core records the approach described herein can be extended to refine existing constraints on global ice volume across the entire glacial period

variations in the carbon isotope composition and production yield of various pyrolysis products under open and closed system conditions production rates and carbon isotopic compositions of various pyrolysis products were investigated for three sediments from the williston basin under open and closed pyrolysis conditions in the temperature range of 300 600 c both parameters do not show any significant differences for kerogens and carbon dioxides with the analytical procedure contrary to open system pyrolysis however decreasing yields of pyrolysates and higher amounts of gaseous hydrocarbons c2 4 compounds at temperatures of 500 and 600 c point to their decomposition to give ultimately methane moreover these pyrolysis products display distinct carbon isotopic variations under open and closed pyrolysis conditions they are due to a kinetic isotope effect i e the preferential cleavage of 12c 12c over 13c 12c bonds but the extent of the shift in isotopic composition seems to depend primarily on the reservoir size and the type of source material

origin of nitrogen rich natural gases in the california great valley evidence from helium carbon and nitrogen isotope ratios abstract dry natural gases produced from the sacramento and northern san joaquin basins contain up to 87 nitrogen 15n measurements for gases with n2 8 vary from 0 9 to 3 5 methane 13c values vary from 61 to 15 3 he 4 he ratios indicate the presence of mantle derived helium in addition to radiogenic crustal helium and suggest that the gases may originate from mixing between three principal components a hydrocarbon rich gas with 3 he 4 he 0 1r a derived from the microbial and thermogenic alteration of sedimentary organic matter a hydrocarbonrich gas with 3 he 4 he 2 75r a derived from the localized pyrolysis of sediments by magmatic volatiles and a nitrogenrich gas with 3 he 4 he 1r a the nitrogen rich component is characterized by methane 13c less negative than 25 and n 2 ar ratios as high as 22 000 nitrogen concentrations tend to increase towards the basement along the shallow eastern margin of the valley suggesting that the nitrogen rich component is derived from metasedimentary rocks deep within the crust the coast ranges fraciscan complex which was thrust well beneath the great valley during late mesozoic and early cenozoic subduction appears to be the most likely source

late wisconsin landform distribution and glacier bed conditions in wisconsin abstract the late wisconsin laurentide ice sheet advanced across permafrost and reached its maximum extent in wisconsin between about 18 000 and 15 000 years ago deep permafrost persisted in southern wisconsin until about 14 000 years ago and in northern wisconsin until about 13 000 years ago we suggest that during maximum glaciation a zone about 5 km wide in the south and 20 km wide in the north along the margin of the late wisconsin glacier was frozen to its bed meltwater from farther behind the margin where the bed was at least locally thawed cut a series of closely spaced tunnel channels through the frozen bed zone these channels most likely formed episodically and they were the source for much of the meltwater stream sediment deposited in broad outwash plains beyond the ice margin frozen bed conditions near the margin also likely contributed to increased upward shearing of sediment and the accumulation of thicl supraglacial sediment in northern areas up ice from the frozen bed zone the glacier bed was at least locally thawed in a zone about 75 km wide extensive drumlin fields formed in the area of the bed that was thawed by about 13 000 years ago permafrost melted in northern wisconsin and thawed bed conditions probably extended to the ice margin throughout wisconsin and adjacent areas after about 13 000 years ago in northern wisconsin the glacier was sliding on its bed and forming drumlins out to the ice margin and thick supraglacial sediment no longer accumulated

the effects of tunnel channel formation on the green bay lobe wisconsin usa abstract subglacial water drainage plays a significant role in glacier flow dynamics various forms of subglacial drainage have been observed beneath modern ice sheets and the same forms of drainage likely occurred beneath paleo ice sheets such as the laurentide ice sheet records of paleo drainage are occasionally preserved in the geomorphic record and can serve as a widespread and easily accessible means to investigate aspects of subglacial drainage that are difficult to directly study on modern day glaciers linear surface depressions that extend tens of kilometers inward from the margin of laurentide lobes are found throughout the midwest of north america and are hypothesized to form from incision by channelized subglacial water flow here we estimate the subglacial hydropotential and its gradient along the western margin of the marine isotope stage 2 laurentide ice sheet s green bay lobe to identify potential locations for subglacial water pooling we find that linear surface depressions correlate well with areas where subglacial water likely pooled we use a combination of active and passive seismic analyses to estimate the actual size of an incised subglacial channel in waushara county wisconsin that was subsequently infilled with sediment after the formation we find that the channel incised ca 65 m into the surrounding unlithified material which is 6 times greater than the modern surface expression and has a width of 450 m which is nearly equal to the width of the surface expression we estimate the channel would have taken ca 60 days of water flow to form and that the flow of pore water from the surrounding till into the low pressure channel could have increased the strength of the till by as much as 140 kpa following a single drainage by as much as 175 kpa in a smaller region following a series of 15 day long drainage events till strengthening could have been a factor of 7 to 25 greater than predrainage strength values

was the laurentide ice sheet significantly reduced during marine isotope stage 3 accurately reconstructing the paleogeography of the laurentide ice sheet lis during marine isotope stage 3 mis 3 ca 57 000 to ca 29 000 yr b p is critical for understanding glacial growth toward the last glacial maximum lgm refining sea level histories and studying the earth system response to rapid climate change events here we present a geochronological data set useful for testing hypotheses of global sea level and refining ice sheet configuration through this interval data n 735 span the entire mis 3 interval and consist of 14c determinations n 651 cosmogenic exposure ages n 52 and optically stimulated luminescence dates n 32 on that basis we hypothesize that the central region of the lis underwent a dramatic reduction in ice from ca 52 to 40 ka key to this hypothesis are geological records at sites in the hudson bay lowlands east central canada that suggest a marine incursion and development of terrestrial landscapes we show that these landscapes are consistent with recently published glacial isostatic adjustment predictions that include widespread deglaciation of the eastern labrador sector of the lis with ice buildup over the western keewatin sector at 42 ka ice growth from this minimum toward the lgm is likely to have been rapid the agreement between this data set and modeling predictions prompts the reassessment of key late pleistocene records including heinrich events loess deposition in the continental united states and sedimentological records from the gulf of mexico