source and origin of roxana silt and middle wisconsinan midcontinent glacial activity abstract thick roxana silt middle wisconsinan in central and southwestern illinois traditionally has been interpreted as loess derived from valley train deposits in the ancient mississippi river valley winters et al h a winters j j alford and r l rieck quaternary research 29 25 35 1988 recently suggested that the roxana was not directly related to glacial activity but was derived from sediment produced by increased shoreline and spillway erosion associated with a fluctuating ancestral lake michigan because 1 paleoenvironmental and paleohydrologic conditions inferred in the hypothesis are unlikely for a loess depositional system and 2 loess did not accumulate during late wisconsinan deglaciation under conditions similar to those hypothesized we suggest the hypothesis should be rejected roxana distribution suggests the major source was drainage from the upper mississippi river valley and variations in loess thickness in illinois can be explained by consideration of valley width depth orientation and postdepositional erosion tills in the headwaters region of the ancient mississippi drainage system in minnesota and wisconsin occur in the appropriate stratigraphic position and have colors and mineralogic compositions that suggest they could be the parent till of the roxana we believe a valley train source for thick roxana is most probable and urge continued consideration of middle wisconsinan glaciation in the upper great lakes area

micromorphology of a welded sangamonian to wisconsinan age paleosol in southwestern wisconsin abstract micromorphological characteristics indicate that in southwestern wisconsin pedogenesis transgressed the sangamonian wisconsinan chronostratigraphic boundary in conjunction with colluvial and eolian sedimentation the use of micromorphology helps to distinguish between pedological colluvial and eolian components in the paleosol horizon sequence which can be difficult to resolve and interpret solely from field investigations and from other laboratory analyses results show that a basal loess mixed zone within the welded paleosol profile contains features that are the products of colluvial reworking processes we present micromorphology data which support stratigraphic relationships suggesting that colluvial processes were important in the formation of basal loess mixed zones in addition to other possible mixing processes such as pedoturbation and bioturbation

floodplain aggradation and pedogenesis in a semiarid environment alluvial valley fills in the upper republican river basin southwestern nebraska provide evidence for processes of aggradation and pedogenesis on semiarid cut and fill floodplains sheetflow deposition on unchanneled valley floors represents an important mechanism of valley aggradation sheetflow deposits contain parallel to sub parallel laminae and discontinuous lobate sedimentary structures rates of sediment deposition on cut and fill floodplains strongly determine the degree to which pedogenic features develop within aggrading alluvium three pedofacies common to semiarid alluvial deposits correspond with increasing aggradation rates 1 cumulic soils 2 multiple buried soils and 3 no pedogenic features radiocarbon age determinations from alluvial fills indicate that floodplain aggradation greater than approximately 0 5 cm year 1 limits soil formation this represents a threshold rate of pedogenic assimilation floodplain soils formed under aggradation rates lower than this exhibit a strong positive relationship between aggradation rate and total caco3 percent and a negative relationship between aggradation rate and organic carbon percent recognizing the associations between pedogenic sedimentologic features and floodplain aggradation rates can help interpret past rates of sediment transport storage and deposition

quaternary aminostratigraphy of mississippi valley loess five pleistocene loess units in the mississippi valley that contain terrestrial gastropod fossils are differentiated by amino acid ratios aile ile values in the total acid hydrolysate of the fossil terrestrial gastropods hendersonia occulta catinella and succinea late wisconsin peoria loess which has been independently dated by radiocarbon and thermoluminescence methods is identified by alle ile values in fossil gastropods which progressively increase from northern illinois to southern louisiana early to middle wisconsin roxana silt is characterized by alle ile values in hendersonia only slightly greater and values in catinella and succinea distinctly greater than those of the peoria loess aiie ile values in hendersonia suggest that the chinatown silt informal term in illinois and the loveland silt in arkansas are the same age independent geologic evidence suggests that they predate the sangamon last interglacial aile ile values in hendersonia from the sicily island loess informal term in louisiana indicate that it is significantly older than the loveland silt and the chinatown silt the oldest loess unit recognized by alle ile values in hendersonia from the mississippi valley is the county line silt informal term in illinois the study shows that amino acid ratios in fossil gastropods from loess are an extremely valuable relative age indicator and provide a means of long distance correlation of midcontinent loess deposits

the end permian mass extinction a rapid volcanic co2 and ch4 climatic catastrophe abstract the end of the permian was a time of crisis that culminated in the earth s greatest mass extinction there is much speculation as to the cause for this catastrophe here we provide a full suite of high resolution and coeval geochemical results trace and rare earth elements carbon oxygen strontium and clumped isotopes reflecting ambient seawater chemistry and water quality parameters leading up to the end permian crisis preserved brachiopod low mg calcite based seawater chemistry supplemented by data from various localities documents a sequence of interrelated primary events such as coeval flows of siberian trap continental flood basalts and emission of carbon dioxide leading to warm and extreme greenhouse conditions with sea surface temperatures sst of 36 c for the late permian although anoxia has been advanced as a cause for the mass extinction most biotic and geochemical evidence suggest that it was briefly relevant during the early phase of the event and only in areas of upwelling but not a general cause instead we suggest that renewed and increased end permian siberian trap volcanic activity about 2000 years prior to the extinction event released massive amounts of carbon dioxide and coupled with thermogenic methane emissions triggered extreme global warming and increased continental weathering eventually these rapidly discharged greenhouse gas emissions less than 1000 years before the event ushered in a global hothouse period leading to extreme tropical ssts of 39 c and higher based on these sea surface temperatures atmospheric co 2 concentrations were about 1400 ppmv and 3000 ppmv for the late and end permian respectively leading up to the mass extinction there was a brief interruption of the global warming trend when sst dropped concurrent with a slight but significant recovery in biodiversity in the western tethys it is possible that emission of volcanic sulfate aerosols resulted in brief cooling just after the onset of intensified warming during the end of the permian after aerosol deposition global warming resumed and the biotic decline proceeded and was accompanied by suboxia in places of the surface ocean which culminated in the greatest mass extinction in earth history

late guadalupian to lopingian permian carbon and strontium isotopic chemostratigraphy in the abadeh section central iran abstract the abadeh section well exposed in the hambast valley in central iran has long been one of the most extensively studied sections because of its continuous carbonate dominated strata from lower permian to lower triassic however biostratigraphy and correlation with the equivalent sequences in other regions remain controversial in this paper both carbon isotope excursion 13 c carb and strontium isotope ratio 87 sr 86 sr based on bulk carbonate samples have been measured to serve as chemostratigraphical proxies to estimate the three different chronostratigraphical boundaries in the lopingian at the abadeh section including the permian triassic event pteb the guadalupian lopingian glb and the wuchiapingian changhsingian boundaries wcb these three boundaries are important for understanding the marine biological evolution around this critical interval based on the 13 c excursions the rising trend of 87 sr 86 sr and the value around 0 7073 and the occurrence of microbialite beds the permian triassic event boundary bed 25 at the meishan section is suggested at 0 5 m below the base of the main microbialite bed the glb is suggested at 46 5 m based on the position of the minor 13 c carb negative depletion coupled with the values between 0 7069 and 0 7070 of 87 sr 86 sr and its beginning point of the rising trend which is above the lowest value 0 7068 of 87 sr 86 sr ratio in the paleozoic the relationship between section thickness and their high resolution depositional age projecting age is interpolated for the whole lopingian using locally weighted regression scatter plot smoother lowess of strontium isotopic ratio based on the negative 13 c excursion and the value 0 7072 of 87 sr 86 sr ratio the wcb is estimated at 1 m above the lithologic boundary between unit 6 and unit 7 much lower than the boundary defined by previous conodont biostratigraphy but similar to other index fossils this boundary is projected as ca 254 6 ma in 87 sr 86 sr age projecting model and is close to zircon u pb dating age from south china

plastic deformation of wadsleyite and olivine at high pressure and high temperature using a rotational drickamer apparatus rda abstract large strain plastic deformation experiments of wadsleyite and olivine were conducted using a rotational drickamer apparatus rda up to pressure and temperature conditions corresponding to the earth s mantle transition zone sintered ring shaped mg fe 2sio4 wadsleyite and olivine samples were deformed at p 16 gpa and t 1600 and 1800 k and p 11 gpa and t 1800 k respectively with equivalent strain rate of e e 6 10 5 s 1 in situ observations of deforming samples were carried out using the synchrotron radiation facility at brookhaven national laboratory nsls x17b2 stress was measured by x ray diffraction at six different angles with respect to the compression axis the stress estimated by x ray diffraction was in good agreement with the stress estimated from dislocation density for olivine strain was determined using x ray radiographs of a strain marker re or mo foil deformation of samples with a rda involves both uniaxial compression and simple shear a new formulation is developed to analyze both components to determine the rheological properties of a sample stress strain curves show strain hardening up to the equivalent strain of e 0 2 followed by the quasi steady state deformation wadsleyite is found to be stronger than olivine compared at similar conditions and the creep strength of olivine at p 11 gpa is much higher than those at lower pressures

glacial and nonglacial sediment contributions to wisconsin episode loess in the central united states the relative contributions of various glacial and nonglacial sediments to wisconsin episode loess units along the lower illinois and central mississippi valleys are estimated on the basis of a comparison of magnetic susceptibility and silt and clay mineralogy a mathematical method of source area calculation using four compositional parameters was guided by current knowledge of the regional glacial history on the basis of this technique the roxana silt along the illinois and mississippi river valleys is composed of significant superior lobe sediment 35 40 as well as wadena or des moines lobe sediment about 35 this can account for its high magnetic susceptibility feldspar content kaolinite content and pink hue lower peoria silt contains about 25 35 lake michigan lobe sediment with reduced contributions of the other sources after the mississippi river s diversion 20 4 ka the supply of superior des moines and wadena lobe sediment was cut off from the illinois valley in favor of lake michigan lobe sediment 75 80 contribution this major source area shift accounts for higher dolomite and illite contents and a more yellow hue in approximately the upper two thirds of peoria silt in the study area in loess south of st louis less pronounced compositional shifts occur because superior lobe sediment was not cut off and because des moines lobe wadena lobe and missouri river sediments having more intermediate composition compose 40 50 of the loess thereby diluting other source area changes nonglacial sediment from fluvial and periglacial sources is estimated to compose 10 40 of loess in both regions

the permian triassic boundary event a geochemical study of three chinese sections abstract trace elements were determined in two well documented chinese permian triassic p tr boundary sections meishan and shangsi and in a new section liangfenya iridium concentrations range from 3 to 87 pg g at or below levels in common sedimentary rocks the results contrast with previous reports of high ir concentration in the meishan and shangsi sections and offer no support to suggestions of a major meteoroid impact at the end of the permian a notable feature in each of these widely separated p tr sections 500 1500 km is the existence of 2 5 light colored clay layers at and near the boundary these clay layers are strongly enriched in cs zr hf ta and th and depleted in cr co and ir indicating that they are altered ash apparently from the same massive silicic volcanic eruptions we estimate the magnitude of these eruptions to be a few thousand km3 of magma a volume comparable to the great toba eruption

the anomalous roxana silt and mid wisconsinan events in and near southern michigan abstract thick deposits of roxana silt are recognized only along the illinois river downstream from the woodfordian terminal moraine and are generally interpreted as being mainly loess with the bulk accumulating from about 40 000 to 30 000 yr ago in association with an altonian age glacier in northeastern illinois yet 11 14c dates indicate that southern michigan was not ice covered during that interval thus any proximate ice must have at best been restricted to great lakes basins an interpretation supported by the absence of late altonian till at critically located michigan and nearby sites late mid wisconsinan ice did however obstruct eastern drainage of the ancestral great lakes such glacial blockage the distribution of many michigan organic deposits within pre woodfordian lacustrine sediments and radiocarbon dates suggest that more than once late altonian lakes associated with the lake michigan basin drained into the illinois river erosion of lake and spillway bluffs along with repeated river fluctuations provided a source for the thick geographically restricted roxana silt meanwhile along other nearby rivers the supply was meager and the loess thin

age genesis and paleoclimatic interpretation of the sangamon loveland complex in the lower mississippi valley u s a for more than a century the sangamon paleosol the sangamon has been an integral part of geologic and pedologic investigations in the central united states including the upper mississippi and lower missouri river valleys compositional pedologic micromorphologic stratigraphic and age data indicate that the prominent reddish paleosol developed in silt rich deposits of the lower mississippi valley from southernmost illinois to northwestern mississippi represents multiple periods of soil formation and is wholly or in part time equivalent to the sangamon of the central united states thermoluminescence data for localities where the sangamon developed in loess indicate that the primary period of loess deposition was from 190 to 130 ka oxygen isotope stage ois6 that loess deposition continued intermittently from 130 to 74 ka ois5 and that deposition was wholly or in part coeval with loveland loess deposition in the central united states beryllium 10 chemical and pedologic data indicate that in the lower mississippi valley 1 the sangamon represents a minimum time period of 60 80 k y 2 there were at least two periods of soil formation ca 130 90 ka and 74 58 ka ois4 and 3 rates of weathering and pedogenesis equaled or exceeded the net loess accumulation rate until at least 46 ka ois3 and resulted in development of a paleosol in the overlying basal roxana silt along a n s transect from southern illinois to western mississippi sangamon macroscopic characteristics as well as the micromorphology chemistry and mineralogy suggest a regional paleoclimate during periods of soil formation that 1 was warm to hot with a wider range in temperature precipitation and evapotranspiration than present 2 had seasonal to decadal or longer periods of drought and 3 had down valley southward trends of increasing temperature and precipitation and decreasing seasonality and variation in annual to decadal precipitation

middle to late pleistocene loess record in eastern nebraska usa and implications for the unique nature of oxygen isotope stage 2 abstract new subsurface data reveal a nearly continuous stratigraphic record of middle to late pleistocene loess sedimentation preserved beneath upland summits in eastern nebraska usa thickness and grain size trends as well as pedologic evidence indicate significant changes in loess sources accumulation rates and depositional environments the newly defined kennard formation accumulated in the middle pleistocene and may represent multiple thin increments of distal loess from nonglacial sources on the great plains the overlying loveland loess up to 18 m thick and deposited during oxygen isotope stage 6 ois 6 illinoian glaciation probably records the emergence of the missouri river valley as a major glaciogenic loess source the prominent sangamon geosol formed through long term pedogenic alteration of the upper loveland loess during ois 5 and 4 thin loess of the gilman canyon formation records slow loess accumulation and pedogenic alteration in ois 3 the peoria loess ois 2 is similar in thickness to loveland loess but may have accumulated more rapidly in an environment less favorable to bioturbation more importantly comparison of peoria and loveland loess thickness trends indicates much greater influx of nonglaciogenic loess from the great plains during ois 2 than in ois 6 suggesting colder and or drier conditions in the midcontinent during ois 2 than in earlier glacial stages

heterogeneity cyclicity and diagenesis in a mississippian brachiopod shell of palaeoequatorial britain a shell of gigantoproductus okensis shows twenty growth lines with marked changes of fabric indicating periodical reduction of growth rates caused by environmental perturbations the number of growth lines suggests a lifespan of 20 years in agreement with the survival rates of extant brachiopods and with spiral deviation analysis geochemical analyses across the growth profile show a heterogeneous distribution of stable isotopes and trace elements it is possible to distinguish primary from altered carbonate and to interpret the isotopic data the oxygen isotope signal in the unaltered parts is periodical and annual with oscillation of 1 1 the higher values are at the growth lines winter and therefore most likely related to monsoon circulation during the visean the annual periodicity seems also present in the altered part of the shell suggesting that diagenesis could have reset the primary values but preserved their cyclicity

interpreting benthic oxygen levels in mudrocks a new approach quantified paleoecology and gamma ray spectrometry have been applied in the analysis of the kimmeridge clay a highly organic rich british jurassic mudrock decreasing benthic oxygen trends are reflected in decreasing species richness and dominance diversity values similarly the degree of fragmentation of the benthos reflects the benthic energy levels and covaries with benthic oxygen the calculation of authigenic uranium values from data gathered by gamma ray spectrometry shows enrichment in more oxygen deficient environments the good correlation between the independently derived paleoecological and authigenic u data indicates the importance of these techniques in environmental analysis of marine petroleum source rocks

modern sangamon and yarmouth soil development in loess of unglaciated southwestern illinois abstract the thebes section in unglaciated southwestern illinois contains a well preserved 500 kyr loess paleosol sequence with four loesses and three interglacial soils various magnetic mineralogical and elemental properties were analyzed and compared over the thickness of soil sola these proxies for soil development intensity have the following trend yarmouth geosol sangamon geosol modern soil quartz plagioclase zr sr and tio 2 na 2 o ratios were most sensitive to weathering frequency dependent magnetic susceptibility and anhysteretic remanent magnetization greatest in a horizons also correspond well with soil development intensity neoformed mixed layered kaolinite expandables suggestive of a warm humid climate were detected in the sangamon and yarmouth soil sola clay illuviation in soils was among the least sensitive indicators of soil development differences in properties among interglacial soils are interpreted to primarily reflect soil development duration with climatic effects being secondary assuming logarithmic decreases in weathering rates the observed weathering in the sangamon geosol is consistent with 50 kyr of interglacial weathering oxygen isotope stage 5 compared to 10 kyr for the modern soil oxygen isotope stage 1 we propose that the yarmouth geosol in the central midwest formed over 180 kyr of interglacial weathering including oxygen isotope stages 7 9 and 11

loess mantle spatial variability and soil horizonation southern wisconsin usa abstract loess is an important quaternary sediment that records evidence of landscape instability in sediment source areas and landscape stability in accumulation areas in wisconsin usa loess mantles glaciogenic deposits dating to the last glaciation but the landscape distribution and effects of the loess mantle on soil formation have received very little attention this study investigates the influence of glacial landforms on the spatial pattern of loess thickness and how the presence or absence of a loess mantle overlying glaciogenic sediments has influenced soil profile morphology namely thickness and nature of horizonation loess thickness follows systematic trends along hillslopes with slope percentage explaining most loess thickness variation between summit and backslope positions in the presence of a loess mantle solum and bt horizon thickness is proportional to the thickness of the loess mantle in well drained profiles in the absence of a loess mantle landscape and sediment characteristics that control permeability and water throughflow appear to be the most important determinants of profile characteristics the loess mantle modulates soil formation above the lithologic discontinuity with sandy calcareous glacial sediments by controlling soil water behavior and having physical and chemical characteristics conducive to transformation to soil genetic horizons

isotope excursions and palaeotemperature estimates from the permian triassic boundary in the southern alps italy abstract the end permian mass extinction event coincides with a dramatic negative shift in both the 13c and the 18o isotope record at or near the extinction horizon from multiple marine and terrestrial sections round the globe this study has identified the isotope excursions in a shallow water carbonate dominated section at val brutta in the southern alps high resolution bulk rock sampling revealed that there is an average 13ccarb negative shift of 4 and a 18ocarb shift of 6 this is similar to the isotope record at other nearby localities this section like many others shows a degree of recrystallisation which hampers absolute palaeotemperature calculations however some brachiopod fossils including specimens of comelicania and janiceps found within the beds that contain the bulk rock anomaly appear to be remarkably well preserved and still retain their internal structure and the primary isotopic variation across the shell as such they have been successfully analysed and the data used to produce a palaeotemperature estimate at the time of the isotope anomaly of between 26 and 29 c for latest permian

preservation and recognition of middle and early pleistocene loess in the driftless area wisconsin abstract an exceptional stratigraphic and pedologic record of pleistocene environmental conditions occurs at the kieler site in the driftless area of southwestern wisconsin peoria roxana loveland and pre loveland loesses overlie weathered bedrock residuum the pre loveland unit previously has been included as part of the residuum at other driftless area sites early and middle pleistocene loesses in the mississippi valley are normally absent at most localities rather than nondeposition we suggest the apparent absence of pre illinoian loess units is due in part to erosion but also to weathering that renders loesses unrecognizable so they are classified as residuum

ams radiocarbon age of the upper mississippi valley roxana silt abstract accelerator mass spectrometer radiocarbon ages of the roxana silt loess along the upper mississippi valley of wisconsin and minnesota indicate that loess sedimentation of the roxana silt occurred between about 55 000 and 27 000 14 c yr b p however due to local environmental controls the basal age at any given site may range from 55 000 to 35 000 14c yr b p the radiocarbon ages presented here are in agreement with previous radiocarbon ages for the roxana silt in its type area of west central illinois but indicate that long term sedimentation rates along the bluffline of the upper mississippi valley were very slow 4 8 cm 1000 yr compared to long term sedimentation rates along the bluffline of the type area 40 70 cm 1000 yr comparison of radiocarbon ages for midcontinent middle wisconsinan loess deposits indicates that sedimentation along the mississippi river valley may have preceded loess sedimentation along the missouri river valley by as much as 20 000 yr or that basal ages for middle wisconsinan loess along the missouri valley are erroneously young the bracketing ages for the upper mississippi valley roxana silt indicate that the mississippi river valley was receiving outwash sedimentation between 55 000 and 27 000 14c yr b p

geochemistry of modern brachiopods applications and implications for oceanography and paleoceanography abstract modern rhynchonellida terebratulida thecideida and a few inarticulated brachiopods were collected live or soon after death at 30 locations from depths of 2 3940 m from the equator to high latitudes covering the atlantic pacific indian caribbean and mediterranean oceans seas well preserved fibers of the secondary layer combined with sr 450 1928 mg kg mn 1 199 mg kg and fe 1 610 mg kg contents confirm with few exceptions the excellent preservation of the modern brachiopod material evaluation of the stable isotope compositions was conducted on 276 specimens and on 374 published samples for a total database of 650 samples from 80 locations it revealed that oxygen isotope incorporation into shell calcite secondary layer of modern articulated brachiopods in most cases occurs in equilibrium with the ambient water and as such reflects surrounding environmental conditions thecideida as a group shallow water and low latitude incorporate oxygen isotopes 3 04 to 0 35 into shell calcite in equilibrium with their ambient water a large majority of genera and species of the terebratulida shallow water and low mid latitude also incorporate oxygen 2 30 to 3 48 into shell calcite in isotopic equilibrium with their surrounding water in contrast equilibrium incorporation of oxygen isotopes into shell calcite by the rhynchonellida is uncertain but a vital effect probably applies to the craniida the question of equilibrium disequilibrium incorporation of carbon isotopes into shell calcite of modern brachiopods remains unresolved at this time isotope compositions range up to 4 5 5 6 and 1 5 for 13 c and up to 5 5 5 9 and 0 3 for 18 o for shallow water low mid and high latitude brachiopods respectively strontium isotopes of modern brachiopods as expected show no significant variation with location latitude water depth temperature salinity and general water conditions once local habitat and ecological influences of fossil brachiopods from similar latitudes are considered their isotopic elemental values should be valuable diagenetic indicators and important oceanographic chemostratigraphic proxies

mineralogical and geochemical evidence of weathering in a middle to late pleistocene paleosol sequence in the driftless area of wisconsin paleosols occur in the driftless area of southwestern wisconsin because this area escaped direct pleistocene glaciation allowing long term loess and colluvium accumulation in selected settings the most complete known depositional sequence at oil city wisconsin contains eight lithologic units with five paleosols all with normal remanent magnetism i e 2 cao zr sr and rb sr generally align with the pedological evidence of weathering mineral ratios plagioclase quartz and k feldspar quartz display greater scatter and less certainty in interpretation the paleosols with bt horizons have ratios indicating greater weathering than the modern soil the most weathered paleosol is formed in the unnamed fourth loess unit stratigraphically below the loveland member the stratigraphic position and higher degree of weathering support correlation of the fourth loess with the yarmouth geosol and crowley s ridge silt of the middle mississippi valley geochemical indices by pxrf are more consistent with established lithologic breaks than mineralogy by xrd our results support the use of pxrf for stratigraphic and weathering studies of quaternary sediments

a mid late quaternary loess paleosol record in simmons farm in southern illinois usa abstract in unglaciated areas of the mississippi valley region the typical full loess paleosol succession contains the modern soil developed in peoria silt weakly developed farmdale geosol developed in roxana silt sangamon geosol developed in loveland silt and yarmouth geosol developed in crowley s ridge silt although a fifth loess called the marianna silt is reported at one area the paleosol that separates the crowley ridge and marianna silts is not well defined previous thermoluminescence tl and optical stimulated luminescence osl age chronology has suggested multiple phases of sangamon geosol developed in loveland silt but clear morphological evidence of polygenetic sangamon geosol profiles have not been found recently a thick loess paleosol sequence has been studied in the middle mississippi valley in unglaciated southern illinois usa soil morphology and analytical results revealed five loesses and associated paleosol units two sangamon bt horizons were found separated by a thick actk horizon interpreted to indicate two phases of sangamon geosol development this well preserved loess paleosol succession provides one of the most complete mid late quaternary loess records in the middle mississippi valley to date and is important for studying the stratigraphic framework and paleoclimate and environment changes

pedogenesis of a catena of the farmdale sangamon geosol complex in the north central united states abstract the farmdale sangamon geosol pedocomplex consists of the sangamon geosol and the overlying farmdale geosol which form the most extensive terrestrial record of the last interglacial to glacial transition in the midwest united states the geosol complex formed for upwards of 100 ka extending from the end of mis 6 through 4 for the sangamon geosol then the farmdale geosol for during a brief episode at the end of mis 3 following slow accumulation and pedogenic modification of eolian silt deposited on top of the sangamon geosol our study site consists of a buried paleo hillslope transect that forms a catena enabling evaluation of slope effects on interglacial scale soil formation the sangamon geosol is formed in calcareous and illitic glaciogenic sediment along the catena the sangamon geosol profiles display some morphological changes namely in terms of colors that we interpret as indicators of differences in drainage most thickness and horizonation characteristics are similar all along the transect with intact upper sola horizons ae and e horizons that overlie clay enriched bt horizons the bt horizons contain abundant clay that exists as illuvial clay coatings matrix infills and as mosaic speckled domains the clay originated both by in situ weathering and through illuviation from the clay depleted upper sola slope does not appear to affect bt characteristics beyond redder hues of the matrix and clay coatings in the upper slope position with depth effects of carbonate leaching and infilling of clay in the matrix decrease and clay coatings are restricted to walls of voids adjacent to aggregates clay mineralogy shows illite depletion but no interstratified kaolinite expandable minerals indicating the degree of weathering is not as great as is typical of sangamon geosol profiles formed in loess or in glaciogenic sediment of the central illinois type area clay mineralogy is also stratified with depth coincident with particle size which probably indicates sorting of layers of illitic dolomite and shale variation of horizon and profile characteristics appears to largely be a function of particle size variability and stratification than topographic position in the catena the influence of hillslope position on soil redistribution during formation of the sangamon geosol appears negligible given the uniformity of upper solum horizon thickness and sandy particle size characteristics so we conclude that a bioturbation and rainwash origin of the upper solum and the texture contrast in these profiles is not the best process model explanation we suggest that the base rich nature of these soils led to ecosystem characteristics that discouraged erosion and encouraged infiltration and a lessivage type origin of the texture contrast no convincing evidence of mis 6 through mis 4 loess occurs at this site the farmdale geosol formed in the robein silt which is roxana silt mis 3 loess that was redistributed downslope the robein silt is thicker and finer in the topographic low and indicates the cooler and forested environmental conditions during mis 3 were conducive to downslope movement of soil and also produced greater differences in drainage induced soil morphological changes in the farmdale geosol

late pleistocene evolution of the lower mississippi river valley southern missouri to arkansas the mississippi river served as the principal conduit for meltwaters discharging from the southern margins of north american ice sheets the northern half of the mississippi river alluvial valley in missouri and arkansas can be subdivided into two distinct channel courses the western and eastern lowlands which are separated by crowleys ridge the eastern lowlands contain two entry points the bell city oran and thebes gaps the latter is a narrow bedrock gorge that contains the modern river this paper summarizes a model for evolution of channel courses in the western and eastern lowlands during the illinoian and wisconsin glacial stages for the western lowlands stratigraphic relations between loess units and subjacent fluvial deposits show that major continuous terrace surfaces or valley trains are illinoian or late wisconsin in age investigations of tributary valley fills further show the western lowlands were deeply incised during the early to middle wisconsin stage then aggraded during the late wisconsin stage to such an extent that tributary valleys were backfilled with slackwater deposits moreover analysis of loess thinning and fining trends shows that early to middle wisconsin roxana silt and the late wisconsin peoria loess covers on western lowlands valley trains were derived from deflation of valley trains in the eastern lowlands we conclude that the western lowlands were the primary mississippi river course during illinoian deglaciation but were abandoned shortly thereafter then episodically reoccupied during the late wisconsin stage for the eastern lowlands course valley trains of early to middle wisconsin age are not preserved with the exception of a small remnant where the mississippi river broke through a gap in the southern margins of crowleys ridge and reentered the western lowlands all valley trains in the eastern lowlands are late wisconsin age a series of discontinuous terrace surfaces in the bell city oran gap represent dissected remnants of the primary late wisconsin full glacial and early late glacial course of the mississippi river or combined mississippi and ohio rivers whereas younger continuous braided stream surfaces in the bell city oran and thebes gap courses represent valley trains of latest wisconsin and earliest holocene age hence the bell city oran gap was the primary course during the entire wisconsin stage and the thebes gap was permanently occupied in earliest holocene time as much as 5 m difference in elevation between successive late wisconsin terrace surfaces of the eastern lowlands indicates that valley trains were rapidly constructed incised and abandoned in response to fluctuations in the delivery of meltwater and outwash from the former ice margin moreover a variety of data indicates that deglacial meltwater floods were commonly of sufficient magnitude to overflow from the primary course in the bell city oran gap throughout the late wisconsin substage floodwaters overflowed into the western lowlands constructed a series of secondary valley trains and filled tributary valleys with slackwater deposits during the latest wisconsin stage perhaps in association with the drainage of glacial lake agassiz floodwaters overflowed into the western lowlands and broke through the thebes gap the charleston fan represents the initial deposits of the thebes gap course following deposition of a large crevasse splay at the western lowlands entrance that course was no longer active but flow was routed through the thebes gap during periods of high magnitude flooding until the bell city oran gap was abandoned and the thebes gap course was permanently occupied during earliest holocene time

transport direction of peoria loess in nebraska and implications for loess sources on the central great plains abstract in the midwestern united states large rivers draining the laurentide ice sheet lis were the most important sources of peoria loess deposited during the last glaciation loess deposition near those rivers may have responded primarily to ice sheet dynamics rather than direct effects of climatic change in contrast it has been proposed that thick peoria loess on the central great plains was derived mainly from unglaciated landscapes northwest of the main loess deposits in this study transport directions inferred from more than 600 measurements of peoria loess thickness in nebraska are used to test the hypothesis that much of the peoria loess on the great plains is nonglaciogenic a strong northwest to southeast thickness trend indicates that most peoria loess in nebraska was transported from one or more unglaciated northwestern source areas rather than from glacially influenced river floodplains the missouri river draining the lis the platte river draining alpine glaciers and the elkhorn river unglaciated basin were secondary sources their contribution is not detectable beyond a distance of 40 60 km peoria loess deposition on the central great plains was largely a direct response to climatic change in the unglaciated source region

sequencing events across the permian triassic boundary guryul ravine kashmir india abstract the permian triassic boundary ptb section at guryul ravine kashmir india comprises a 100 m thick apparently conformable succession of mixed siliciclastic carbonate sediments deposited in a deep shelf or ramp setting this section although long important in debates concerning placement of the ptb has not previously been the focus of an integrated chemostratigraphic study in the present study samples from a 20 m thick interval straddling the ptb were analyzed for major and trace element concentrations toc tic rees and organic 13c 15n to investigate contemporaneous environmental changes the guryul ravine section exhibits a sequence of discrete events that provide potentially important information about the character and cause s of the ptb two transient negative c isotopic excursions within the upper changxingensis zone predate the late permian event horizon lpeh i e the global mass extinction event by 200 400 kyr and are associated with the onset of a major eustatic rise and with secondary extinction peaks these excursions may record minor environmental disturbances prior to the main end permian crisis supporting an intrinsic mechanism such as volcanism and climate change rather than an extrinsic mechanism such as a bolide impact the onset of a large 4 0 to 4 5 sustained negative c isotope shift marks the lpeh which is located at the zewan khunamuh formation contact 260 cm below the biostratigraphically defined ptb the guryul ravine section exhibits a stepwise extinction pattern with the largest peak between the lpeh and ptb and a secondary peak just above the ptb a pattern similar to that observed in the meishan d gssp

numeric control on the late glacial chronology of the southern laurentide ice sheet derived from ice proximal lacustrine deposits abstract we used a combination of radiocarbon and osl dating in ice proximal lacustrine silt and clay and outwash sand to estimate when ice of the green bay lobe of the laurentide ice sheet began retreating from its maximum position in south central wisconsin the radiocarbon ages indicate that lakes had formed in the two tributary valleys by 17 2 and 20 1 ka respectively the osl ages indicate that the green bay lobe was at its maximum position from about 26 4 5 1 ka to 21 4 3 3 ka these data provide entirely new chronologic control on late wisconsin marine isotope stage 2 glacial event in the upper midwest as well as the opportunity to directly compare radiocarbon and osl ages in this setting

isotopic and rock magnetic expression of environmental change at the pleistocene holocene transition in the central great plains abstract in a region too dry for the effective use of the traditional palynological approach loess deposits of the central great plains offer a source of proxy information for the reconstruction of past climates the brady soil a ubiquitous feature developed within the uppermost late pleistocene peoria loess recorded the character of vegetation change associated with climate shifts during the pleistocene holocene transition stable carbon isotope ratio analysis and two room temperature magnetic parameters were used to examine the nature of the change during this period 13 c values derived from soil organic matter indicate that in the late pleistocene minor populations of drought tolerant c4 plants were interspersed among the dominant cool season grasses c3 in the west while c3 grasses were accompanied by trees in the east by the early holocene c4 grasses were the dominant vegetation in the west and contributed substantially to the 13 c signal in the east magnitude of the 13 c shift suggests an increase in july mean daily temperature of 8 10 c according to existing models magnetic susceptibility and frequency dependence signal the cessation of loess deposition and development of the brady soil and indicate a spatial pattern in the intensity of weathering across the region

geochemical variations in peoria loess of western iowa indicate paleowinds of midcontinental north america during last glaciation peoria loess deposited in western iowa during the last glacial maximum lgm shows distinct geochemical and particle size variations as a function of both depth and distance east of the missouri river geochemical and particle size data indicate that peoria loess in western iowa probably had two sources the missouri river valley and a source that lay to the west of the missouri river both sources indicate that lgm paleowinds in western iowa had a strong westerly component similar to interpretations of previous workers a compilation of loess studies in iowa and elsewhere indicates that westerly winds were dominant during loess transport over much of the midcontinent south of the laurentide ice sheet which is not in agreement with paleowinds simulated by atmospheric general circulation models agcms agcms consistently generate a glacial anticyclone with easterly or northeasterly winds over the laurentide ice sheet and the area to the south of it loess deposition in the midcontinent during the lgm may be a function of infrequent northwesterly winds that were unrelated to the presence of the glacial anticyclone

surface winds across eastern and midcontinental north america during the last glacial maximum a new data model assessment abstract last glacial maximum lgm proxy evidence of surface wind direction across eastern and midcontinental north america comes primarily from loess and dune deposits and overwhelmingly suggests surface winds had a strong westerly component however the season of sediment deposition and the temporal scale of wind information preserved in these deposits remains uncertain furthermore paleoclimate model simulations over the last several decades have indicated a predominance of easterly winds across this region due to the presence of an anticyclone over the laurentide ice sheet as well as katabatic winds flowing off the ice sheet and over the adjacent land surface here we reassess model data near surface wind direction agreement using nine general circulation models participating in the lgm experiment of the third paleoclimate model intercomparison project pmip3 and a compilation of previously published paleowind directions from loess and dune deposits dating to the lgm we find the highest overall model proxy data agreement in winter december february indicating predominantly westerly winds across the region in the lgm model simulations we also find high zonal and meridional wind direction agreement in spring march may and fall september november in many models winter spring and fall also have faster mean daily near surface wind speeds in the lgm simulations relative to pre industrial control simulations thus this model data assessment suggests lgm aeolian deposition in the study region likely occurred dominantly in these three seasons at times when local conditions favorable for aeolian deflation coincided with high wind speed events models that agree best with the proxy data have strengthened aleutian and icelandic low pressure systems and a weakened laurentide high pressure system which constrains the spatial footprint of the laurentide high to the ice sheet reducing northeasterly winds near the ice sheet margin a weaker laurentide high in turn coincides with warmer surface temperatures over the ice sheet and the north atlantic the strength and location of semi permanent pressure systems were thus key controls on surface wind direction across midcontinental and eastern north america during the lgm

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

a new model of topographic effects on the distribution of loess a model of topographic influence on the regional transport and accumulation of loess in sparsely vegetated landscapes is proposed based on the critical role played by saltating eolian sand in the entrainment and long distance transport of finer grained suspended dust in this model long term accumulation of loess occurs mainly downwind of topographic obstacles that limit eolian transport of sand and associated re entrainment of dust regional and local patterns of distribution of late wisconsinan loess in parts of the upper mississippi river basin are closely related to the distribution of topographic obstacles to sand transport these cases of topographic influence occur in a region where evidence exists for sparse tundra like vegetation during the deposition of loess in the late wisconsinan similar topographic effects may not be evident further south in the missouri and mississippi river basins because vegetation density was generally sufficient to prevent the movement of eolian sand out of source valleys thus topographic obstacles and dense vegetation may have similar effects on loess distribution under different environmental conditions

chemical diagenesis of a multicomponent carbonate system 2 stable isotopes abstract this study examines the oxygen and carbon isotopic distribution in the brachiopods crinoids rugose corals and matrix cement from the mississippian burlington limestone iowa and missouri and the silurian read bay formation arctic canada the isotopic data can be reconciled with textural and trace element observations only if the 18o content of ancient oceans differed from that of the present oceans this postulated secular variation in the 18o content of seawater requires a separate evaluation of the mississippian and silurian carbonate components examination of the 18o content of the least altered low mg calcite fossil components of the two formations suggests that the 18o of mississippian seawater was on average about 1 5 lighter and that of silurian seawater was about 5 5 lighter than the 18o of present day ocean water the average diagenetic shift in 18o for the read bay formation which stabilized in a partly closed diagenetic phreatic meteoric system is about 1 for the original low mg calcite and about 2 for the original high mg calcite and aragonite components conversely for the burlington limestone which stabilized in an open diagenetic phreatic meteoric system the average diagenetic shift in 18o is about 3 for the original low mg calcite and about 4 f r the original high mg calcite components the 13c values of the originally low mg calcite or high mg calcite with less than 7 mole mgco3 brachiopods and rugose corals the originally high mg calcite crinoids and the originally aragonite lime mud of the burlington limestone and read bay formation are bimodally distributed this bimodal 13c distribution is independent of geologic age inferred original mineralogy of the component degree of diagenetic alteration and the type of diagenetic meteoric system with components from both the read bay formation and burlington limestone contributing to both 13c groups the mode of the light 13c group is 0 25 and for the heavy 13c group it is 3 25 pdb both 13c groups also show a decrease in 13c of about 1 with increasing diagenetic alteration stabilization

δ18o and δ13c of permian brachiopods a record of seawater evolution and continental glaciation abstract two hundred sixty four 18 o and 13 c values of permian articulate brachiopod shells were analyzed and 81 of these values were characterized as well preserved and biostratigraphically well defined these were then utilized for construction of baseline oxygen and carbon isotope curves for the permian interval in addition 21 13 c whole rock values are reported for the wordian and capitanian the early permian asselian to artinskian times are characterized by 2 5 decrease in oxygen isotope values from 0 7 to 3 3 v pdb this is attributed to a 4 7 c increase in temperature in the southern urals concomitant with the retreat of the permo carboniferous ice sheets and return of the 18 o depleted melt water into the oceans the late permian samples from iran jolfa at kuh e ali bashi and china meishan yield 18 o values and presumably temperatures similar to those that followed the termination of the large scale glaciation in the lower permian in between the upper kungurian to capitanian samples from the delaware basin guadalupe mountains are enriched in 18 o at 1 5 to 3 we have no definitive explanation for these data but tentatively suggest that the anomaly can potentially be a result of evaporative enrichment of seawater in 18 o due to intracratonic arid setting of the basin the 18 o enriched nature of the zechstein samples 1 2 to 2 5 on the other hand is in all probability a reflection of the high evaporation rates in the zechstein sea the permian interval is characterized by a relatively constant 13 c at about 4 the exceptions are again the brachiopods from the delaware basin guadalupe mountains which show 1 6 increase in the guadalupian to values of up to 5 9 in the wordian a tentative explanation as in the case of oxygen is based on the proposition that the semi enclosed delaware basin was likely stratified with sequestration of the 13 c depleted carbon to the deeper water layers and a complementary 13 c enrichment in the upper oxygenated layer the coeval open ocean water dic may have been similar to that of the remainder of the permian interval at 4 as indicated by whole rock carbonate samples from oman sicily and iran in the latest permian the trend mimics the well known 13 c drop at the permian triassic boundary

pedostratigraphy of chinese loess deposits and climatic cycles in the last 2 5 myr summary the pedostratigraphy and magnetostratigraphy of several sections in the loess plateau of north central china have been investigated and correlated the most complete and distinct loess paleosol sequence occurs in the baoji section of the southern part of the plateau thirty seven pedostratigraphic units are identifiable in the baoji section and correlated with those in other parts of the plateau the sequence represents thirty seven major cold to warm climatic cycles in the last 2 5 myr at about the time of the matuyama gauss magnetic reversal an abrupt climatic event occurred in north china represented by the shift of the well weathered red clay formation below the m g boundary to the alternating loess and paleosol units above marking the beginning of a new epoch in the course of climatic evolution in addition there are two other major shifts of dominant periods of climatic cycles recorded in the loess paleosol sequences one occurring at about 1 5 myr and another at about 0 8 myr the pedostratigraphy of loess deposits in north central china provides an independent measure of the world wide climatic fluctuations and is now the most complete and reliable record of the major climatic cycles in the last 2 5 myr

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

autogenic incision and terrace formation resulting from abrupt late glacial base level fall lower chippewa river wisconsin usa abstract a paucity of research exists regarding the millennial scale response of inland alluvial streams to abrupt base level fall studies of modern systems indicate that over short time scales the response is a diffusion like process of upstream propagating incision in contrast evidence from the lower chippewa river lcr located in the upper midwest of the usa suggests that autogenic controls operating over time scales of several millennia can overwhelm diffusion resulting in incision that is prolonged and episodic during the last glacial maximum the lcr drained the chippewa lobe of the laurentide ice sheet to the glacial upper mississippi river umr as a meltwater stream it aggraded and filled its valley with glacial outwash as did its largest tributaries which were also meltwater streams its nonglacial tributaries aggraded too filling their valleys with locally derived sediment during deglaciation the umr incised at least twice abruptly lowering the lcr s base level 15 m at 16 ka or earlier and an additional 40 m at ca 13 4 ka each of these base level falls initiated incision of the lcr led by upstream migrating knickpoints the propagation of incision has however been a lengthy process the optically stimulated luminescence osl ages of terrace alluvium indicate that by 13 5 ka incision had advanced up the lcr only 15 km and by 9 ka only 55 km the process has also been episodic resulting in the formation of fill cut terraces inferred from gpr surveys and exposures of terrace alluvium that are younger and more numerous in the upstream direction autogenic increases in sediment load and autogenic bed armoring the result of periodic tributary stream rejuvenation and preferential winnowing of fines by the incising river may have periodically caused knickpoint migration and incision to slow and possibly stop allowing lateral erosion and floodplain formation to dominate a decline in sediment flux from stabilizing incised tributary stream systems would have led to renewed knickpoint migration and incision when floods of sufficient magnitude to breach the channel armor occurred minimal floodplain development along the upper section of the present day lcr along with the channel morphology of an unstable wandering gravel bed river immediately downstream from it suggest that the river is still responding to the base level falls that happened many millennia ago the autogenic controls on the lcr s response to umr incision are a direct consequence of the thick fills of noncohesive sediment that accumulated in its valley and the valleys of its tributary streams during the late wisconsinan making the lcr a prime example of a former proglacial river that remains a paraglacial fluvial system

neotethys seawater chemistry and temperature at the dawn of the end permian mass extinction abstract the end of the permian was a time of great death and massive upheaval in the biosphere atmosphere and hydrosphere over the last decades many causes have been suggested to be responsible for that catastrophe such as global warming anoxia and acidification the gyanyima limestone block was an open ocean seamount in the southern neotethys at subtropical latitude and it affords us insight into open ocean oceanographic changes during the end of the permian after careful screening using multiple tests we reconstructed carbonate seawater curves from the geochemical data stored in pristine brachiopod shell archives from the shallow water limestone of the changhsingian gyanyima formation of tibet the reconstructed strontium isotope curve and data for the late changhsingian are relatively invariant about 0 707013 but in the upper part of the succession the values become more radiogenic climaxing at about 0 707244 the 87 sr 86 sr curve and trend are similar to those observed for the upper permian succession in northern italy but dissimilar less radiogenic to whole rock results from austria iran china and spitsbergen the ce ce anomaly results ranging from 0 310 to 0 577 for the brachiopods and from 0 237 to 0 655 for the coeval whole rock before the event and of 0 276 for whole rock during the extinction event suggest normal redox conditions these ce values are typical of normal open ocean oxic water quality conditions observed in modern and other ancient counterparts the biota and ce information clearly discounts global anoxia as a primary cause for the end permian biotic crisis carbon isotopes from brachiopod shells and whole rock are relatively invariant for most of the latest permian interval which is in stark contrast to the distinct negative carbon isotope excursion observed near and about the event estimates of seawater temperature at shallow depth fluctuated from 22 2 to 29 0 c up to unit 8 2 and then gradually rise from 29 7 c in unit 8 13 to values exceeding 35 c at a stratigraphic level about 120 ky before the permian triassic boundary and just before the onset of the extinction interval this dramatic increase in seawater temperature has been observed in global successions from tropical to mid latitude and from restricted to open ocean localities e g northern italy iran the brachiopod archive and its geochemical proxies from tibet support the paradigm that global warming must have been an important factor of the biotic crisis for the terrestrial and marine faunas and floras of the late paleozoic world

provenance and pedology of a long term pleistocene depositional sequence in wisconsin s driftless area abstract soil coring in the driftless area of wisconsin has revealed an approximately 9 m stratigraphic sequence containing five buried soils formed in seven lithologic units below the youngest late wisconsin loess the sequence is preserved on a toeslope remnant 30 m above the present valley floor and provides the most complete stratigraphic section known for the upper mississippi valley region the stratigraphic sequence is

brachiopods recording seawater temperature a matter of class or maturation calcite fibres of the innermost secondary layer of low magnesium calcite brachiopod shells are in oxygen isotope equilibrium with ambient seawater previous work on terebratalia transversa indicates that the first formed calcite fibres of the secondary layer are not in isotopic equilibrium while the later fibres of mature valves are in oxygen isotope equilibrium with seawater here secondary ion mass spectrometry sims analyses reveal that this trend of oxygen isotope equilibrium being attained towards the innermost shell rather than being a feature throughout the secondary layer occurs in brachiopods from two orders and two sub orders this suggests a general pattern among brachiopods with low magnesium calcite shells and leads to the recommendation that only the innermost fibres of mature valves be included in proxy calculations of seawater temperature although the trend is common in the three species studied here the extent of the isotopic range is much less marked in the species that lacks punctae

new insights on the loess paleosol quaternary stratigraphy from key sections in the u s midwest abstract three key quaternary loess paleosol sections were examined in the missouri valley iowa eustis ash pit nebraska and in the wittsburg quarry arkansas to gain insights into the sedimentation environment and climate change of the u s midwest four loess units are present separated by three well developed paleosols crowley s ridge loess oxygen isotope stage ois 8 is pre illinoian in age and is the oldest loess unit investigated a well developed paleosol interpreted as yarmouth soil ois 7 is found in this loess in all three sections overlying the yarmouth soil is loveland loess ois 6 which has been pedogenically altered by the sangamon soil ois 5 it has luvisolic properties but a more clayey pedogenic texture than modern luvisols and has no clear eluvial horizon the overlying roxana silt ois 4 is pedogenically altered at wittsburg and missouri valley the farmdale soil ois 3 is developed in the roxana silt based on pedogenic features we correlate this paleosol to that developed in the gilman canyon formation at eustis in missouri valley and eustis sections the paleosol has chernozemic properties and therefore the gleyic features observed at missouri valley are interpreted as later alterations overlying the farmdale soil is the widespread peoria loess ois 2

sea surface temperature and salinity variability at bermuda during the end of the little ice age 1 we use geochemical and isotope measurements on a 225 year old brain coral diploria labyrinthiformis from the south shore of bermuda 64 w 32 n to construct a record of decadal to centennial scale climate variability the coral was collected alive and annual density bands visible in x radiographs delineate cold and warm seasons allowing for precise dating coral skeletons incorporate strontium sr and calcium ca in relative proportions inversely to the sea surface temperature sst in which the skeleton is secreted previous studies on this and other coral colonies from this region document the ability to reconstruct mean annual and wintertime sst using sr ca measurements goodkin et al 2007 2005 the coral based records of sst for the past 2 centuries show abrupt shifts at both decadal and centennial timescales and suggest that sst at the end of the little ice age between 1840 and 1860 was 1 5 0 4 c colder than today 1990s coral reconstructed sst has a greater magnitude change than does a gridded instrumental sst record from this region this may result from several physical processes including high rates of mesoscale eddy propagation in this region oxygen isotope values 18o of the coral skeleton reflect changes in both temperature and the 18o of seawater ow where ow is proportional to sea surface salinity sss we show in this study that mean annual and wintertime 18o of the carbonate oc are correlated to both sst and sss but a robust quantitative measure of sss is not found with present calibration data in combination however the sr ca and oc qualitatively reconstruct lower salinities at the end of the little ice age relative to modern day temperature changes agree with other records from the bermuda region radiative and atmospheric forcing may explain some of the sst variability but the scales of implied changes in sst and sss indicate large scale ocean circulation impacts as well

catastrophic dispersion of coal fly ash into oceans during the latest permian extinction the eruption of the siberian trap flood basalts resulted in the heating and combustion of coals and organic rich sediments at the time of the permian mass extinction the presence of char in distant lake sediments linked to the eruption suggests that fly ash could have been generated by the coal combustion and then dispersed globally creating toxic marine conditions

loess of the upper mississippi valley driftless area abstract loess of the driftless area includes four distinct late quaternary lithostratigraphic units the wyalusing new loveland roxana and peoria formations erosion has removed parts or all of the pre late wisconsian loess at many sites these formations consist largely of loess and retransported loess that typically occurs on uplands terraces and valley margins in the region the oldest widespread formation probably 125 000 yr b p is here formally named the wyalusing formation the three younger formations correlate with the loveland probably 125 000 yr b p roxana 55 000 25 000 yr b p and peoria 25 000 12 000 yr b p loesses recognized elsewhere in the midcontinental united states the soil stratigraphic morphology of the wyalusing loveland and roxana peoria couplets appears to represent two distinct loess sedimentation sequences related to major expansion and contraction of the laurentide ice sheet during oxygen isotope stages 6 and 3 2 respectively the occurrence frequency of loess units is inversely related to age illustrating the erosional nature of the driftless area landscape the occurrence of four loess units at some sites in driftless area stratigraphic sections corroborates loess stratigraphy along the length of the mississippi valley where typically not more than four or five loess units are found and they represent only the late and middle pleistocene

floodplain sedimentation in the upper mississippi valley natural versus human accelerated abstract understanding the time scales and pathways for response and recovery of rivers and floodplains to episodic changes in erosion and sedimentation has been a long standing issue in fluvial geomorphology floodplains are an important component of watershed systems because they affect downstream storage and delivery of overbank flood waters and they also serve as sources and temporary sinks for sediments and toxic substances delivered by river systems here 14c and 137cs isotopic dating methods are used along with ages of culturally related phenomena associated with mining and agriculture to determine rates of sedimentation and morphologic change for a reach of the upper mississippi river and adjacent tributaries in southwestern wisconsin and northwestern illinois the most important environmental change that influenced fluvial activity in this region during last 10 000 years involved the conversion of a late holocene mosaic of prairie and forest to a landscape dominated by cropland and pastureland associated with euro american settlement results presented herein for the upper mississippi valley umv show that the shift from pre agriculture natural land cover to landscape dominance by agricultural land use of the last 175 200 years typically increased rates and magnitudes of floodplain sedimentation by at least an order of magnitude accelerated overbank flooding led to increased bank heights on tributary streams and in turn contributed to more frequent deep flows of high energy these high energy flows subsequently promoted bank erosion and lateral channel migration and the formation of a historical meander belt whose alluvial surface constitutes a new historical floodplain inset against the earlier historical floodplain the new historical floodplain serves as a flume like channel that provides efficient downstream transport of water and sediment associated with moderate and large magnitude floods floodplains on lower tributaries however continue to experience rates of overbank sedimentation that are of anomalously high magnitude given improved land cover and land conservation since about 1950 this lower valley anomaly is explained by minimal development of historical agriculture period meander belts because of relatively low stream power in these channel and floodplain reaches of relatively low gradient in general long term pre agriculture rates of vertical accretion between about 10 000 and 200 years ago averaged about 0 2 mm yr 1 in tributary watersheds smaller than about 700 km2 and about 0 9 mm yr 1 on the floodplain of the upper mississippi river where the contributing watershed area increases to about 170 000 km2 on the other hand rates of historical vertical accretion during the period of agricultural dominance of the last 200 years average between 2 and 20 mm yr 1 with short episodes of even higher rates during times of particularly poor land conservation practices significant hydrologic effects of mining and agricultural started by the 1820s and became widespread in the study region by the mid 19th century the hydrologic and geomorphic influences of mining were relatively minor compared to those related to agriculture high resolution dating of floodplain vertical accretion deposits shows that large floods have frequently provided major increments of sedimentation on floodplains of tributaries and the main valley upper mississippi river the relative importance of large floods as contributors to floodplain vertical accretion is noteworthy because global atmospheric circulation models indicate that the main channel upper mississippi river should experience increased frequencies of extreme hydrologic events including large floods with anticipated continued global warming instrumental and stratigraphic records show that coincident with global warming a shift to more frequent large floods occurred since 1950 on the upper mississippi river and these floods generally contributed high magnitudes of floodplain sedimentation

age erosion constraints on an early pleistocene paleosol in yukon canada with profiles of 10be and 26al evidence for a significant loess cover effect on cosmogenic nuclide production rates abstract wounded moose type paleosols developed on remnant deposits of late pliocene to early pleistocene pre reid cordilleran ice sheet cis glaciations in central yukon canada it is an important regional soil geomorphic marker at the boundary between early cis advances and the non glaciated regions of yukon and alaska yet at present its age is poorly constrained between the reid 0 2 ma and earliest 2 84 ma cis advances here we apply depth profiles of in situ produced cosmogenic 26al and 10be to obtain both a minimum exposure age 1 12 0 44 0 36 ma 2 and maximum erosion rate 1 1 0 9 0 5 m myr 1 for the wounded moose paleosol our results show that this soil formed under exceptionally stable conditions max erosion rate similar to polar bedrock erosion rates and that it pre dates the emergence of the 100 ka eccentricity climate cycle contrasting our results from single and joint nuclide depth profile models reveals a significant discrepancy between calculated and effective 10be and 26al production rates 40 65 of expected values we interpret this discrepancy as the result of intermittent loess cover with a time averaged depth between 60 and 110 cm which significantly reduced apparent exposure ages obtained from the single nuclide model the observation of such a significant loess cover effect on cosmogenic nuclide production has implications for exposure dating in glacial and periglacial environments a multi nuclide sampling strategy is required to quantify this effect

last glacial loess in the conterminous usa the conterminous united states contains an extensive and generally well studied record of last glacial loess the loess occurs in diverse physiographic provinces and under a wide range of climatic and ecological conditions both glacial and non glacial loess sources are present and many properties of the loess vary systematically with distance from loess sources united states midcontinent last glacial loess is probably the thickest in the world and our calculated mass accumulation rates mars are as high as 17 500 g m 2 yr at the bignell hill locality in nebraska and many near source localities have mars greater than 1500 g m 2 yr these mars are high relative to rates calculated in other loess provinces around the world recent models of last glacial dust sources fail to predict the extent and magnitude of dust flux from the mid continent of the united states a better understanding of linkages between climate ice sheet behaviour routing of glacial meltwater land surface processes beyond the ice margin and vegetation is needed to improve the predictive capabilities of models simulating dust flux from this region r 2003 elsevier ltd all rights reserved

stratigraphy geochemistry and thermoluminescence ages of lower mississippi valley loess four periods of loess deposition in the lower mississippi valley can be identified on the basis of geochemical and mineralogical criteria radiocarbon dating and thermoluminescence dating these are designated loess units 1 2 3 and 4 in order of increasing age carbonate rich unit 1 loess comprises more than 70 per cent of the thickness of the loess profiles 14c and tl dates indicate this loess was deposited between 9 000 and 20 000 years ago a maximum sedimentation rate of 2 17 mm yr 1 has been recorded near vicksburg just after the last laurentide glacial maximum between 17 190 and 15 580 years ago the unit 2 loess which is thin and partly decalcified was deposited slowly between about 25 000 and 20 000 years ago the unit 3 and unit 4 loess formations which are both highly weathered have yielded tl ages of 76 000 85 000 years and 119 000 132 000 years suggesting they were deposited during the altonian substage of the early wisconsinan and the illinoian glacial stage respectively the four loess units are stratigraphically equivalent to the peoria farmdale roxana and loveland loess formations previously recognized in illinois the source of dust in both areas was glacial outwash in the mississippi valley during interglacials and interstadials when the supply of glacial debris was reduced and the mississippi river changed from a braided to a meandering regime dust sedimentation in southern mississippi virtually ceased allowing weathering and pedogenesis to proceed

climate forced change in hudson bay seawater composition and temperature arctic canada abstract global climate change impacts marine ecosystems directly and indirectly especially in the arctic and antarctic we show the first long term 1920 2011 time series of oceanographic change in hudson bay an arctic marine ecosystem based on coupled brachiopod calcite stable and clumped isotope results long term decrease in brachiopod 13c parallels that of seawater dic in hudson bay and after considering its seasonal sea ice coverage it is similar to that of the 13c suess effect observed in the north atlantic and other regions acidification of hudson bay seawater leads warming by about 10 20 years and with intensified warming from the 1970s to 2010s closely coupled to earlier sea ice breakup post industrial warming of hudson bay is initially slow but in later years faster and of greater magnitude than of the coeval global oceans our observations for the past 90 years suggest that climate forced change contributed to an average increase of about 0 1 c and 3 6 c in sea surface water temperature of hudson bay over the first 50 and subsequent 40 years respectively this 3 7 c post industrial warming of hudson bay seawater is about six times the 0 67 c increase observed during the past 100 years in global ocean sea surface temperature which is about double the postulated increase of about 2 c for polar regions our results are consistent with the general notion that polar marine environments such as hudson bay can serve as sensitive indicators of change in climate and of change still to come for lower latitude ecosystems

the loess cover of northeastern wisconsin abstract we present the first study of the distribution genesis and paleoenvironmental significance of late pleistocene loess in northeastern wisconsin and adjacent parts of michigan s upper peninsula loess here is commonly 25 70 cm thick upland areas that were deglaciated early and remained geomorphically stable preferentially accumulated loess by providing sites that were efficient at trapping and retaining eolian sediment data from 419 such sites indicate that the loess was mainly derived from proglacial outwash plains and to a lesser extent hummocky end moraines within and near the region particularly those toward the east of the loess deposits most of the loess was transported on katabatic winds coming off the ice sheet which entrained and transported both silt and fine sands the loess fines markedly and is better sorted distal to these source regions only minimal amounts of loess were deposited in this area via westerly winds this research 1 reinforces the observation that outwash plains and end moraines can be significant loess sources 2 provides evidence for katabatic winds as significant eolian transport vectors and 3 demonstrates that the loess record may be variously preserved across landscapes depending on where and when geomorphically stable sites became available for loess accumulation

sampling species abundance and the stratigraphic signature of mass extinction a test using holocene tidal flat molluscs assume that a catastrophe caused the sudden extinction of the molluscan biota of a holocene tidal flat would this event be recorded accurately in the stratigraphic record how accurately would the extinction of rare species be recorded how would sudden gradual and stepwise patterns of extinction compare bivalve and gastropod species occurrences were recorded from eight tidal channel sediment cores up to 70 cm long from bahia la choya northern gulf of california the distribution of last occurrences of 45 species suggests that a sudden extinction would appear to be gradual in the stratigraphic record due to error in biostratigraphic range end points signor lipps effect extinction is typically not accurately recorded for species with less than 15 stratigraphic abundance i e occurring in less than 15 of the sample intervals 71 of the species the data were subjected to simulations of stepwise and gradual extinction differences between the sudden stepwise and gradual scenarios are apparent in 1 frequency distributions of biostratigraphic last occurrences 2 graphic relations between stratigraphic abundance and last occurrence and 3 patterns of apparent diversity decline below the extinction boundary extinction studies in outcrops and cores could utilize last occurrence and stratigraphic abundance data readily available in the fossil record to distinguish among sudden stepwise and gradual patterns of extinction

using pca to characterize and differentiate loess deposits in wisconsin and upper michigan usa abstract data on loess thickness as well as a variety of particle size fractions were determined for 875 samples taken from several loess sheets across wisconsin and upper michigan because the particle size characteristics of these samples varied widely within and between the loess sheets we used principal components analysis pca as a way of isolating the major textural components or signals that exist across the various loess sheets the purpose of this research was to examine and interpret these principal components or particle size signatures common to the different loesses in order to better understand the loess sheets character formation mechanisms and likely sources our initial assumption that many of these loesses varied markedly from the classical silty loess was supported by the particle size data and the pca although component 1 was interpreted as thick silty loess dominated by medium silts component 2 was mainly composed of very fine sand and coarse silt and is better viewed as coarse loess components 3 and 4 were less texturally homogeneous and may reflect mixing between the loess and the underlying sediment especially where the loess is

chronologic evidence for multiple periods of loess deposition during the late pleistocene in the missouri and mississippi river valley united states implications for the activity of the laurentide ice sheet abstract the loess stratigraphy of the mid continental u s is an important proxy record for the activity of the laurentide ice sheet in north america one of the most outstanding problems is deciphering the age of loess deposits in this area during the late pleistocene radiocarbon dating of snails and thermoluminescence dating of the fine silt fraction 4 11 m from loess at the loveland loess type section loveland iowa and a recent excavation at the pleasant grove school section madison county illinois provide new chronologic control on loess deposition in the mississippi missouri river valley chronology indicates that the loveland loess is illinoian in age 135 20 ka but is not correlative with the teneriffe silt which is dated to 77 8 ka concordant radiocarbon and thermoluminescence age estimates demonstrate that the roxana silt and a correlative loess in iowa the pisgah formation is probably 40 30 ka old these age estimates in conjunction with previous results indicate that there were four periods of loess deposition during the last 150 ka at 25 12 ka 45 30 ka 85 70 ka and at ca 135 20 ka this chronology of loess deposition supports the presence of both a late illinoian and early wisconsinan loess and associated soils thus there may be more than one soil in the loess stratigraphy of the mid continental u s with morphologies similar to the sangamon soil the last three periods of loess deposition may be correlative with periods of elevated dust concentrations recorded in the dye 3 ice core from southern greenland this is particularly significant because both areas possibly had the same source for eolian particles reconstructions of atmospheric circulation for glacial periods show a southerly deflected jet stream that could have transported dust from the mid continental usa to southern greenland lastly the inferred record of loess deposition is parallel to a chronology for deglaciation of the laurentide ice sheet deciphered from chronologic and stratigraphic studies of raised glacial and marine sediments in the hudson bay lowlands canada these chronologies indicate that the laurentide ice sheet was quite dynamic during the late pleistocene advancing and retreating across north america at least four times during the last 150 ka

geology of the pre illinoian sediment in the bridgeport terrace lower wisconsin river valley wisconsin the bridgeport terrace in the lower wisconsin valley is characterized by pre iuinoian till like sediment at the west end of the terrace that grades eastward into fluvial sediment with eastward dipping foreset beds that underlie an eastward sloping depositional surface the bridgeport sediment overlies a rock bench that protected it from erosion stratigraphic relationships indicate the valley was already incised below the rock bench by the time the bridgeport sediment was deposited a pre iuinoian age for the bridgeport terrace is indicated by deeply weathered sediment and by the reversed remanent magnetism of fine grained units in the terrace gravel furthermore a well developed probable sangamon age paleosol is developed underneath two loess units that overlie the fluvial sediment the clay mineralogy of till like sediment at the west end of the terrace is similar to pre illinoian till units in iowa and west central wisconsin

mississippi valley regional source of loess on the southern green bay lobe land surface wisconsin loess has been recognized on the glacial land surface of the green bay lobe for over 100 yr but no systematic explanation of the source of the loess has been advanced intriguingly the loess on the green bay lobe land surface is thicker than predicted by regional thinning trends from the mississippi valley and is geographically separated from much loess of southwest wisconsin by a sandy region devoid of loess mapping based on soil survey interpretation indicates that the loess occurs above an escarpment marking the eastern end of the sandy loess free region particle size fining trends demonstrate that the loess was transported by northwesterly winds clay mineralogy of the green bay lobe loess is distinctly different than glaciogenic sediments and matches loess of the mississippi valley indicating a regional source and long distance transport of the loess we propose the loess was transported from the regional source along a surface of transport produced by migration of eolian sand through low relief landscapes including the glacial lake wisconsin basin eolian sand migration caused repeated entrainment of dust leading to east southeastward transport the loess accumulated above an escarpment that limited sand mobility and re entrainment of loess beyond this topographic barrier

up in the refrigerator geomorphic response to periglacial environments in the upper mississippi river basin usa abstract james c knox was best known for his work on holocene and historical changes in fluvial systems but he also had a long standing interest in the effects of late pleistocene periglacial environments on landscape evolution in parts of the upper mississippi river basin that were just outside the laurentide ice sheet margin or as knox put it up in the refrigerator knox and others in the quaternary community of the midwestern u s often suggested that hillslope erosion was accelerated under periglacial conditions so that glacial periods have had a dominant effect on the landscape we see today this paper reviews the evidence and reasoning supporting that view in a study area of the upper mississippi basin bordered on three sides by ice margins of the last glaciation including the wisconsin driftless area and adjacent landscapes sparse but compelling paleoecological data and relict ice or sand wedge polygons provide clear evidence for a cold climate and widespread permafrost around the peak of the last glaciation in highly dissected relatively high relief parts of the study area the loess and soil stratigraphy on ridgetops and the colluvial mantles on steeper slopes are best explained by highly effective hillslope erosion including solifluction during and just after the last glacial maximum knox used the post depositional truncation of a loess unit to quantify contrasting late pleistocene and holocene sediment yields from a small driftless area watershed while the late pleistocene yield indicates accelerated erosion it is still lower than modern sediment yields in many tectonically active or semiarid landscapes and it may reflect deposition of highly erodible loess as well as effects of periglacial conditions the views of knox and other midwestern geomorphologists on landscape evolution through glacial interglacial cycles were highly influenced by the work of robert v ruhe ruhe proposed that an episode of widespread erosion during and just after the last glacial maximum can explain enigmatic aspects of quaternary stratigraphy and the soil landscape on the iowan erosion surface a very low relief landscape of the study area ruhe s key evidence is still valid though it needs to be separated from an implausible model of landscape evolution interpretation of the iowan erosion surface and other low relief landscapes just outside the ice margin also requires recognition of the profound effect of eolian processes on those landscapes under periglacial conditions many new insights on landscape evolution in the study area could result from wider application of cosmogenic nuclide based methods to assess glacial interglacial changes in basinwide rates of erosion and residence time of soils just as important a need exists for much more field based characterization of hillslope fluvial and eolian sediments for comparison with those of modern permafrost regions and past periglacial environments in europe

roxana silt of the upper mississippi valley lithology source and paleoenvironment significant lithological differences exist between the middle wisconsinan roxana silt loess of the upper mississippi valley the valley north of 41 5 and that of the type area near st louis missouri primary differences are that the upper mississippi valley roxana silt is much thinner finer textured and more weathered than that of the type area extrapolation of radiocarbon dates brackets sedimentation of upper mississippi valley roxana silt between 55 and 27 ka which is in close agreement with dates from the type area radiocarbon dates and paleobotanical data indicate that the upper mississippi valley roxana silt accumulated at a maximum long term average sedimentation rate of about 7 cm 1 000 yr within a boreal forest environment whereas the type area roxana silt accumulated at a maximum long term average sedimentation rate of about 60 cm 1 000 yr within a prairie like environment multiple regression analysis shows that more than 75 of the variance in thickness and texture between the upper mississippi valley roxana silt and that of the type area is explained by parameters of source valley width source valley azimuth and distance of the depositional site from the source valley this indicates that although the lithologic characteristics and sedimentation rates between the two regions are quite different they are consistent with a unified loess sedimentation sys tem linked to the ancient mississippi river valley a proglacial source for the roxana silt and a middle wisconsinan advance of the lauren tide ice sheet is a topic of scientific debate because recent findings show a lack of roxana correlative till deposits in the midwest alternative hypotheses include a glaciolacustrine source a regional slope erosion source and a cold climate desert dust source tests of these hypotheses support a proglacial origin for the roxana silt multiple regression analysis of loess thickness and texture along with paleobotanical evidence indicates that the roxana silt was blown from the ancient mississippi valley rather than from a cold climate desert source or from flood plains linked to a glaciolacustrine source geochemical and mineralogical composition of the upper mississippi valley roxana silt compared to out wash derived peoria loess indicates that detritus from regional hillslope erosion is not a unique component of the roxana silt combined data indicate that the midcontinental roxana silt was derived as loess blown from flood plains of middle wisconsinan proglacial rivers between 55 and 27 ka

shell structure patterns and trends of oxygen and carbon stable isotopes in modern brachiopod shells this study investigates 13c and 18o variations in the shells of modern brachiopods representing all extant groups of calcite precipitating brachiopods collected live from 8 locations sem examinations determined the ultrastructural characteristics of each species prior to isotope analyses 13c and 18o analyses of shell carbonate were carried out with samples representing disparate morphological features and ultrastructural shell layers of both ventral and dorsal valves generally 18o values from the fibrous secondary or prismatic tertiary shell layers of the articulated terebratulida and rhynchonellida species were in oxygen isotopic equilibrium with ambient seawater isotopic temperatures extrapolated from these values are close to measured annual mean seawater temperatures 18o values were relatively unaffected by shell specialisation the only exception was antarctic species liothyrella uva which did not have a complete tertiary shell layer typical of this genus and had 18o values of the innermost layer strongly correlated with 13c and mostly not in oxygen isotopic equilibrium with ambient seawater with the exception of the rhynchonellid notosaria nigricans the outer primary layer material was depleted in 13c and 18o and highly variable inclusion of this material even as part of a whole shell sample could lead to misinterpretation of seawater temperature therefore only fossil secondary layer material should be used the anomalous articulated thecideidine brachiopod thecidellina barretti is composed of mainly primary shell material and was not in oxygen isotope equilibrium 18o values from the laminar secondary layer material of the inarticulated craniida are highly variable therefore these species are not recommended for use as palaeoenvironmental proxies this study suggests caution when employing fossil brachiopod shells with similar ultrastructures to modern craniid and thecideidine brachiopods the carbon isotope composition is highly variable in all of the brachiopods studied analysis of samples from specialised regions of the secondary shell layer show a pattern of depletion in 13c relative to non specialised secondary material the carbon isotope variability is independent of 18o and is repeated in most of the articulated species regardless of geographical location this is possibly a vital effect produced by metabolic prioritisation

the nature and origin of gleyed polygenetic paleosols in the loess covered glacial drift plain of northern missouri usa abstract at four study sites in northern missouri the farmdale and sangamon paleosols which are developed in loess are welded to the underlying yarmouth paleosol developed in till upon initial examination however they appear to be a single thick continuous gleyed horizon gleysol along flat tabular drainage divides this welded solum is gleyed and is identical in all respects with the historical definition of gumbotil the solum may exceed 4 m in thickness but has little discernable horizonization the profiles are nearly homogeneous containing approximately 50 clay throughout most of the solum of which 70 80 are expandable clay minerals variations in texture clay mineralogy and weathering indices are typical of a welded solum which forms a complex polygenetic profile the base of the solum retains abundant slickensided joints and upon exposure it rapidly develops shrink swell features typical of vertisols this behavior coupled with the remarkable homogeneity within the solum indicates that these soils underwent significant mixing primarily by pedoturbation a characteristic of modern vertisols

the permian triassic boundary in western slovenia idrijca valley section magnetostratigraphy stable isotopes and elemental variations stable isotope analyses of carbonate 13ccarb and total organic carbon toc 13corg together with geochemical analyses of 54 major minor and trace elements and magnetic susceptibility measurements were carried out on whole rock samples of the undisturbed permian triassic p tr limestone boundary sequence in the idrijca valley w slovenia at the p tr boundary there is a 0 8 cm thick clayey marl layer ptb showing a characteristic magnetic susceptibility pulse and considerable enrichment in most major minor and trace elements the p tr transition is characterized by 1 an abrupt decrease in sedimentation rate from 32 to 5 cm 100 ka 2 a well known prominent negative excursion of 13ccarb and 13corg reflecting global perturbations in the carbon cycle and 3 the drastic disappearance of typically upper permian marine fauna although the shape of the 13ccarb curve indicates gradual long term change across the p tr boundary the sharp negative 13corg anomaly within an interval from 30 cm below to 6 cm above the boundary suggests an interruption of those gradual processes our observations for selected redox sensitive elements mo u v and zn abundances for organic carbon and sulphur and the rare earth elements ree distribution in the boundary sequence as well as the shape of the ce ce curve suggest that oceanic anoxia was typical of the upper permian and that the transition to oxygenated conditions occurred at the p tr boundary oxygenation at the p tr transition is coincidental with the terminal phase of the upper permian marine regression the shape of the ce ce curve indicates that the redox environmental conditions changed again in the earliest triassic resulting once more in oxygen deficient conditions

biochemostratigraphy of the upper frasnian in the namur dinant basin belgium implications for a global frasnian famennian pre event the upper frasnian sequence of the namur dinant basin in southern belgium consists of mixed siliclastic carbonate succession of a ramp setting where the sequence spans the rhenana linguiformis conodont zones earlier studies investigated the chemostratigraphic variations during the frasnian famennian event but little has been yet known about the nature of the counterpart variations that immediately preceded that time interval despite the scarcity of well preserved brachiopods sixty one calcitic shells were collected mainly from beds of the neuville and les valisettes formations lower and upper rhenana zones to investigate biochemostratigraphic profiles of oxygen carbon isotope and rare earth element ree variations of the time interval immediately before the frasnian famennian boundary the 18o and 13c values of the well preserved shells range from 9 5 to 5 6 vpdb 7 7 1 1 n 33 and from 1 8 to 3 8 vpdb 1 1 1 7 n 33 respectively which are within the documented global values the c and o isotope profiles exhibit parallel shifts particularly at the top of the neuville formation top of the lower rhenana zone which are associated with a sea level rise and shrinkage in the brachiopod community also the th u 0 9 0 6 n 16 and ce ce 2 2 0 5 n 16 ratios suggest deposition under reducing conditions consistent with sea transgression

provenance of loess in the central great plains u s a based on nd sr isotopic composition and paleoenvironmental implications abstract loess of the central great plains u s a records intervals of quaternary aeolian dust accumulation at rates among the highest known worldwide this study used nd sr isotopic analysis to investigate the provenance of middle pleistocene to holocene loess in western and central nebraska u s a essential information for understanding the paleoenvironmental conditions that allowed such rapid accumulation to occur at some times and not others nd sr isotopic data suggest that dust from unglaciated great plains landscapes has been the primary component of loess accumulated at both very high and low rates since the middle pleistocene however loess isotopic compositions all require an additional minor source with higher 87sr 86sr and lower end most likely debris from precambrian rocks in the rocky mountains carried to the great plains by the platte river system the contribution from this secondary source probably including glacially eroded sediment was greater in marine isotope stage mis 3 and early mis 2 but decreased somewhat just after the last glacial maximum lgm at the bignell hill section earlier research showed that the highest accumulation rates in that section also occurred after the lgm thus our results likely indicate increased dust emission from unglaciated landscapes at that time greater plant moisture stress in a warming climate with still low co2 could have played a role in that increased dust production along with lagged vegetation response however a strengthened westerly component of surface winds is the most straightforward explanation

δ18o and δ13c values of modern brachiopod shells abstract researchers have not rigorously tested the hypothesis that calcite from modern brachiopod shells is precipitated in oxygen isotope equilibrium with ambient seawater isotopic variability at the intraspecimen and intertaxon levels has not been examined without such data for modern brachiopods similar data from ancient brachiopods cannot be accurately interpreted in this study a survey is made of 18 o and 13 c values of terebratulid rhynchonellid thecideidine and craniacean brachiopods from antarctica the bay of fundy curacao japan new zealand norway puget sound palau sicily and south africa this suite of samples provides a wide range of taxonomic levels temperatures salinities and depositional environments for evaluating the degree of isotopic equilibrium attained during precipitation of brachiopod calcite new data indicate that modem brachiopod calcite is not always precipitated in oxygen and carbon isotope equilibrium with ambient seawater calcite from the primary layer and specialized shell structures hinge brachidium foramen interarea muscle scars are depleted in both 18 o and 13 c a characteristic of biological fractionation or vital effects often found in other calcerous marine organisms our findings suggest that these portions of the brachiopod shell should be avoided during sampling of ancient brachiopods secondary layer calcite the material most often analyzed in ancient brachiopods has higher 18 o and 13 c values which approach and sometimes correspond with predicted equilibrium values therefore secondary layer calcite is the most suitable portion of the brachiopod shell for use as an ancient seawater proxy although near equilibrium precipitation in secondary layer calcite is encouraging to those studying the isotopic composition of ancient oceans these data come with caveats large intraspecimen variability in the 18 o values of secondary layer calcite 1 in some samples limits the use of brachiopods as precise indicators of the 18 o value or temperature of ancient seawater the 18 o and 13 c values of secondary layer calcite deviate from predicted equilibrium values toward the lower values of the primary layer and specialized shell structures indicating a measurable vital effect in most cases measured 18 o values are lower than the calculated equilibrium values dictated by seasonal variations in the 18 o value and temperature of seawater ontogenetic variations in the 13 c values of secondary layer calcite have also been measured and must be assessed when interpreting ancient data modern brachiopods occur in a wide range of seawater salinities and temperatures therefore the relation between salinity and the 18 o value of seawater must be known to correctly calculate the temperature of calcite precipitation from secondary layer 18 o values errors of up to 15 c are found if ambient seawater is assumed to have a constant 18 o value e g 0 smow and the 18 o values of secondary layer calcite are used to calculate temperature coupled with vital effects and intraspecimen variability these errors can obscure the resolution of secular variations in the rock record