holocene loess in illinois revealed by osl dating implications for stratigraphy and geoarchaeology of the midwest united states abstract most uplands in illinois are blanketed by late wisconsinan peoria loess and the conventional wisdom is that little or no dust accumulation occurred during the holocene 11 7 ka to present in a recent effort to investigate if illinois holocene loess was deposited and preserved we applied optically stimulated luminescence osl dating to seven locations where loess is thick these include four sites along the mississippi river in westernmost illinois and three loess bluffs south of the illinois river in central illinois our results suggest that holocene aged loess is preserved along the mississippi river in the state of illinois in contrast no holocene loess was found south of the illinois river in the central portion of the state in addition to its spatially limited distribution holocene loess thicknesses range only up to 1 m nevertheless loess stratigraphy and osl dating results provide the first holocene loess reported east of the missouri river our new finding also resolves the long time archeological puzzle that a number of artifacts of several thousand years old were buried by upland loess along the mississippi river

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

evidence of cyclic dust deposition in the us great plains during the last deglaciation from the high resolution analysis of the peoria loess in the eustis sequence nebraska usa the peoria loess unit is a well defined stratigraphical unit in the upper pleistocene of the north american quaternary deposited between 30 25 ka and about 12 ka ago it has been indicated that this unit shows the highest known worldwide depositional rate for eolian deposits as its thickness varies near the source area between 19 m and 46 m extreme values that are not even recorded in the chinese sequences the results of our present investigation indicate that this particular unit is not homogenous its shows different subunits where lithological variation can be observed through the occurrence of embryonic gley horizons alternating with laminated loess furthermore the grain size analysis shows cycles corresponding to variations in the eolian dynamics responsible for dust transportation and deposition a grain size index interpreted as characterizing the eolian dynamics higher values corresponding to stronger wind conditions shows higher values than those observed in europe a comparison of this index is proposed with the greenland dust and 18 o records it shows that the main climatic history as corresponding to events occurring mainly in north atlantic domain is recorded in the peoria loess deposits however the variation in the magnitude of the eolian events indicates differences from the european loess sequences the strong north atlantic coolings expressed by heinrich events as recorded in europe by coarser deposits are not differentiated in the studied sequence hence they follow more closely observations obtained off california for the north east pacific domain 2007 elsevier b v all rights reserved

a laboratory model for melting erosion of a magma chamber roof and the generation of a rhythmic layering 1 a hot magma chamber can ascend by melting the roof rock a process which in turn affects the magma composition the disaggregated mineral particles which consisted the roof rock will descend in the magma chamber to form a sedimentary cumulate however the fluid dynamics leading to the formation of the sediment and how we can decipher them is unknown here we conducted a series of experiments modeling melting erosion of the roof with particle size consisting the roof rock as the parameter we find that there is a critical particle size below which the melting erosion occurs rhythmically melting erosion stops because the disaggregated particles are suspended in the magma chamber and suppress the vertical heat transfer the suspension then separates into an upper clear layer and a lower suspension layer eventually the heated stratified layers become unstable an overturn occurs and melting erosion resumes when the particles consist of two sizes such that at least one of them is smaller than the critical size a rhythmic erosion occurs particles are sorted during each erosion period and a size graded rhythmic layering is spontaneously generated we estimate that rhythmic layering can be generated from melting erosion in a basaltic magma chamber when the grain size of the roof rock is 0 6 mm assuming a vertical temperature difference of 10 c we suggest that rhythmic roof melting coupled with particle settling is one possible mechanism for generating the rhythmic layering which is commonly observed in solidified magma chambers

a rapid mechanism to remobilize and homogenize highly crystalline magma bodies the largest products of magmatic activity on earth the great bodies of granite and their corresponding large eruptions have a dual nature homogeneity at the large scale and spatial and temporal heterogeneity at the small scale this duality calls for a mechanism that selectively removes the large scale heterogeneities associated with the incremental assembly of these magmatic systems and yet occurs rapidly despite crystal rich viscous conditions seemingly resistant to mixing here we show that a simple dynamic template can unify a wide range of apparently contradictory observations from both large plutonic bodies and volcanic systems by a mechanism of rapid remobilization unzipping of highly viscous crystal rich mushes we demonstrate that this remobilization can lead to rapid overturn and produce the observed juxtaposition of magmatic materials with very disparate ages and complex chemical zoning what distinguishes our model is the recognition that the process has two stages initially a stiff mushy magma is reheated from below producing a reduction in crystallinity that leads to the growth of a subjacent buoyant mobile layer when the thickening mobile layer becomes sufficiently buoyant it penetrates the overlying viscous mushy magma this second stage rapidly exports homogenized material from the lower mobile layer to the top of the system and leads to partial overturn within the viscous mush itself as an additional mechanism of mixing model outputs illustrate that unzipping can rapidly produce large amounts of mobile magma available for eruption the agreement between calculated and observed unzipping rates for historical eruptions at pinatubo and at montserrat demonstrates the general applicability of the model this mechanism furthers our understanding of both the formation of periodically homogenized plutons crust building and of ignimbrites by large eruptions

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

petrology of the 1991 1995 eruption at unzen effusion pulsation and groundmass crystallization abstract effusive eruption of dacite magma 2 1 108 m3 during 1991 1995 formed a lava dome at the summit of unzen volcano japan the effusion rate was highest at the beginning 4 0 105 m3 day 4 6 m3 s and decreased roughly with time to almost zero before this pattern was repeated with a second pulse of magma supply the whole rock chemistry of lavas shows significant variation attributable to variations in phenocryst abundance the more mafic the more abundant the phenocrysts the pattern of chemical variation with time shows some difference from that of the effusion rate all phenocrysts in dacite plagioclase hornblende biotite quartz and magnetite show evidence of disequilibrium with melt although a glomerophyric aggregation of phenocrysts suggests coexistence with each other phenocrysts are isotopically heterogeneous from species to species the calculated initial melt composition was rhyodacite and was nearly constant throughout the activity in contrast the bulk phenocryst population is andesite a model explaining the textures and the isotopic heterogeneity is the capture of diorite fragments or xenocrysts by parental rhyodacite magma it is suggested that when effusion rate was high less viscous crystal poor magma exited from the reservoir groundmass glass and plagioclase microlite rims show temporal chemical variations correlating with the effusion rate the higher the effusion rate the more evolved the compositions groundmass crystallinity increased with decreasing effusion rate from 33 to 50 textures in dome lavas suggest that groundmass crystallization had been mostly completed when magma reached the conduit top the fe ti oxide temperature 880 780 c was low when the crystallinity was high micropumice erupted before dome growth provided a sample recording magmatic foam in the conduit porosity of dome lavas was lower at lower effusion rates collapse of foam magma and simultaneous escape of volatiles through the conduit top were probably responsible for the accompanying low frequency earthquakes phenocrysts were broken and the breakdown rims on hornblende phenocrysts were torn off during collapse and successive compaction when effusion waned degassing and the resultant crystallization proceeded more completely so that the magma became too viscous to flow in the conduit top and behaved as a plug resulting in a temporary halt of effusion in turn groundmass crystallization in magma below the plug increased excess pressure in the upper parts of conduit due to slow cooling the plug was scavenged when rising excess pressure overcame its effective strength then the second pulse of magma supply began strong endogenous growth and extrusion of a lava spine in the later stage probably occurred for the same reason

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

origin of crystal poor differentiated magmas insights from thermal gradient experiments crystal poor differentiated magmas are commonly erupted from shallow thermally zoned magma chambers in order to constrain the origin of these magmas we have experimentally investigated crystallization differentiation and crystal melt separation in presence of a thermal gradient experiments have been designed taking advantage of the innate temperature gradient of the piston cylinder apparatus and carried out on a phonolitic system at 0 3 gpa and temperature ranging from 1 050 to 800 c crystallization degree and melt composition in experimental products vary as a function of the temperature gradient in particular melt composition differentiates from tephri phonolite starting material to phonolite moving from the hotter glassy zone t 1 050 c towards the cooler heterogeneously crystallized zone t 900 c of the charge the heterogeneously crystallized zone is made up of 1 a crystal rich mushy region crystallinity 30 vol 2 a rigid crystal framework crystallinity 80 vol and 3 glassy belts of phonolitic glass at the top thermal gradient experiments picture crystallization differentiation and crystal melt separation processes occurring in a thermally zoned environment and reveal that relatively large volumes of crystal poor melt glassy belts can originate as a consequence of the instability and collapse of the rigid crystal framework analogously in thermally zoned magma chambers the development and collapse of a solidification front may represent the controlling mechanism originating large volumes of crystal poor differentiated magmas

absence of altonian glaciation in illinois abstract illinois was free of glacier ice from about 130 000 to 25 000 yr b p deposits of this time interval in northeastern illinois represented by core samples from test hole isgs s 30 are composed of leached nonglacigenic stratified or pedoturbated silty sediments that typically are organic rich and pedogenically modified these deposits overlie the sangamon soil which is identified by its stratigraphic position soil morphology and distinct alteration products in the clay mineral fraction including a variably swelling vermiculite like phase and a randomly interstratified kaolinite 10 a phase the regional extent of these deposits suggests that if altonian ice existed in the lake michigan basin it did not extend westward beyond the cuesta of silurian dolomite that rims the southwestern shore of lake michigan

remobilization of andesite magma by intrusion of mafic magma at the soufriere hills volcano montserrat west indies the 1995 1999 eruption of the soufriere hills volcano montintroduction serrat has produced a crystal rich andesite containing quenchthe soufriere hills volcano montserrat located in the textured mafic inclusions which show evidence of having been molten lesser antilles island arc in the west indies began to when incorporated into the host magma individual crystals in the erupt on 18 july 1995 after about 350 years of dormancy andesite record diverse histories amphibole phenocrysts vary from young et al 1998b the eruption was preceded by a pristine and unaltered to strongly oxidized and pseudomorphed by period of seismic swarms which began in january 1992 anhydrous reaction products plagioclase phenocrysts are commonly previous earthquake crises have occurred on montserrat reverse zoned often with dusty sieve textures reverse zoned rims are in 1896 1897 1932 1935 and 1966 1967 powell 1938 also common on orthopyroxene phenocrysts pyroxene geothermometry shepherd et al 1971 initial phreatic and phregives an average temperature of 858 20 c for orthopyroxene atomagmatic activity was followed by extrusion of an phenocryst cores whereas reverse zoned rims record temperatures andesitic lava dome in november 1995 pyroclastic flows from about 880 to 1050 c the heterogeneity in mineral rim generated by gravitational collapse of the unstable dome compositions zoning patterns and textures is interpreted as reflecting have been the dominant form of activity throughout the non uniform reheating and remobilization of the resident magma eruption but periods of explosive activity producing body by intrusion of hotter mafic magma convective remobilization pumice flows and falls have also occurred robertson et results in mixing together of phenocrysts that have experienced al 1998 young et al 1998b dome growth ceased different thermal histories depending on proximity to the intruding suddenly in march 1998 and further activity up to may mafic magma the low temperature and high crystallinity are 1999 has mainly involved gravitational collapses of the interpreted as reflecting the presence of a cool highly crystalline dome and periods of ash venting with some small scale magma body beneath the soufriere hills volcano the petrological vulcanian explosive events observations in combination with data on seismicity extrusion rate the soufriere hills volcano is the only active centre and so2 fluxes indicate that the current eruption was triggered by on montserrat the volcano is a composite of at least recent influx of hot mafic magma five andesitic lava domes flanked by pyroclastic deposits rea 1974 identified four other volcanic centres all

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

continuous mixing of crystal mush and replenished magma in the ongoing unzen eruption zoning profiles of magnetite phenocrysts in the successively effused dacite of the ongoing unzen eruption from 1991 wereanalyzed to estimate the time scale of magma mixing the dacite was formed by mixing of relatively high and low temperature t end member magmas the magnetite phenocrysts derived from the low t magma are reversely zoned by the mixing with high t magma a diffusion calculation for reequilibration of the reverse zonings gives the time interval from magma mixing to quenching for the mixed dacite erupted from may 1991 to may 1993 the typical diffusion time was estimated to be a few months regardless of the effused sequence for 2 yr this indicates that the mixing was continuous during the effusion the invariability of the other mixing signatures such as the thickness of reaction rims around biotite phenocrysts also supports the continuous mixing model low t end member magma is estimated by mass balance calculation to be a crystal rich mush of dacitic composition these observations lead to a model wherein the highly crystallized remnant magma of the preceding activity has been mixed with the newly injected hot magma of similar bulk composition just prior to the effusion the proposed mechanism implies that this type of magma mixing is an inevitable process in periodically erupting polygenetic volcanoes

rock cliffs hazard analysis based on remote geostructural surveys the campione del garda case study lake garda northern italy the town of campione del garda located on the west coast of lake garda and its access road have been historically subject to rockfall phenomena with risk for public security in several areas of the coast this paper presents a study devoted to the determination of risk for coastal cliffs and the design of mitigation measures our study was based on statistical rockfall analysis performed with a commercial code and on stability analysis of rock slopes based on the key block method hazard from block kinematics and rock slope failure are coupled by applying the rockfall hazard assessment procedure rhap because of the huge dimensions of the slope its morphology and the geostructural survey were particularly complicated and demanding for these reasons noncontact measurement methods based on aerial photogrammetry by helicopter were adopted a special software program developed by the authors was applied for discontinuity identification and for their orientation measurements the potentially of aerial photogrammetic survey in rock mechanic application and its improvement in the rock mass knowledge is analysed in the article

compaction in a mantle mush with high melt concentrations and the generation of magma chambers abstract most compaction models in the partially molten mantle have addressed the case of low intergranular melt concentrations up to a few percent here we develop a mathematical and numerical formalism adapted to the two dimensional modeling of compaction in mushes with higher melt concentrations up to a few tens of percents experimental data on mantle like mushes olivine crystals basaltic melts suggest that the mush viscosity depends in a complex way on the melt concentration three rheological thresholds occur at melt concentrations of about 5 20 and 40 respectively the first threshold corresponds to the establishment of full interconnectivity of the intergranular melt the second to the formation of a very dense suspension of crystals and the last to the development of crystal clusters in the suspension the present models take into account the stiff and drastic viscosity drops associated with these rheological thresholds intergranular melt migration associated with an initial melt pulse generates a horizon of high melt crystal ratio if the melt concentration in the initial pulse presents a local excess the horizon becomes slightly tilted as a consequence melt percolates upslope inside the tilted horizon pools at its summit and generates a pocket like zone due to the higher melt concentration the upward darcy velocity in the pocket markedly exceeds that in the horizon the result is that the pocket like impregnation is rapidly disconnected from the horizon and a new pocket develops at the summit of the partially fragmented horizon eventually the intergranular melt contained in the horizon is completely redistributed into pockets increasing the background melt concentration in the mush from 5 20 and 40 leads to an increase of the maximum melt concentration of 10 40 and 100 in the transient horizons and of 25 60 and 100 in the pockets these models suggest that magma chambers with a kilometer extent naturally result from the compaction of a mantle mush with an initial melt concentration exceeding 5

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

loess stratigraphy of the lower mississippi valley abstract loesses of the lower mississippi valley lmv are world famous sir charles lyell 1847 hilgard 1860 stafford 1869 call 1891 and mabry 1898 thought the lmv loess was a single water deposit although double submergence was noted by call 1891 and salisbury 1891 shimek 1902 and emerson 1918 recognized lmv loess as a wind deposit which came from the valley although wind deposited loess gained wide acceptance russell 1944a published his controversial theory of loessification which entailed weathering of backswamp deposits downslope movement and recharge by carbonates to form loess wascher et al 1947 identified three lmv loesses mapped distributions and strongly supported eolian deposition leighton and willman 1950 identified four loesses and supported eolian deposition as did krinitzsky and turnbull 1967 and snowden and priddy 1968 but krinitzky and turnbull questioned the deepest loess daniels and young 1968 and touchet and daniels 1970 studied the distribution of loesses in south central louisiana west et al 1980 and rutledge et al 1985 studied the source areas and wind directions which deposited the loesses on and adjoining crowley s ridge b j miller and co workers miller et al 1985 1986 miller and alford 1985 proposed that the loveland silt was early wisconsin rather than illinoian age and advanced the name sicily island loess they proposed the underlying loess was illinoian and advanced the name crowley s ridge we termed the loesses from the surface downward peoria loess roxana silt loveland sicily island loess crowley s ridge loess and marianna loess researchers agree that the surfical peoria loess is late wisconsin and the roxana silt is late to middle wisconsin but little agreement exists on the age of the older loesses pye and johnson 1988 proposed early wisconsin for the loveland sicily island mckay and follmer 1985 suggested this loess correlated with a loess under illinoian till clark et al 1989 agreed on crowley s ridge but suggested the loveland sicily island loess on sicily island was older mirecki and miller 1994 and millard and maat 1994 suggested an illinoian age for the loveland sicily island loess miller and co workers suggested as did pye and johnson 1988 an illinoian age for the crowley s ridge loess mckay and follmer 1985 suggested it correlated with a loess under kansan till stratigraphy indicates the marianna is the older of the five loesses researchers identified loess on both the east and west side of the lmv as well as on higher terraces within the valley many researchers assumed unaltered loesses were commonly yellowish brown and silts or silt loams west et al 1980 miller et al 1986 the nonclay fraction of unweathered lmv loesses was dominated by quartz followed corresponding author by carbonates mainly dolomites followed by feldspars and micas clays were dominated by montmorillonite followed by micaceous minerals kaolinite and vermiculite miller et al 1986 soils in the crowley s ridge loess are most developed followed by the soils in the loveland sicily island which are more developed than the modern soils in the peoria loess soils in the roxana and marianna loesses are least developed and the farmdale soil of the roxana is the weaker of the two miller et al 1986 there is certainly overlapping range in the degree of soil development in the various loesses

rayleigh taylor instability of a particle packed viscous fluid implications for a solidifying magma 1 we performed laboratory experiments of rayleigh taylor instability of superposed viscous fluids where the upper layer contains denser spherical solid particles a series of experiments are made by varying the viscosity and the particle diameter and we measure the growth rate and the wave length of the instability the instability consists of fine scaled plumes which coalesce as they descend plumes are observed to form intermittently and the particle layer thins with time which finally descend as blobs we find that the growth rate can be explained by using the linear stability analysis for rayleigh taylor instability of viscous fluids by taking the effective viscosity of particle bed to be 20 times that of the fluid and scale the thickness of the upper layer by twice the particle diameter using this scaling we find that a partially solidified layer beneath the surface of a lava lake may become unstable by this mechanism

paleoenvironmental interpretation of multiple soil loess sequence at milford reservoir northeastern kansas abstract a loess soil section near the republican river in northeastern kansas includes three superposed soils paleosols in at least three superposed loess units including peoria loess pl the gilman canyon formation gcf and loveland loess ll the gcf coincides with a composite soil with a 1 3 m thick buried organic rich a horizon that yields ams radiocarbon ages from 30 3 to 22 4 ka or 35 7 to 26 9 ka when calibrated that overlies a 1 6 m oxidized b horizon complex the b subhorizons stratigraphically and morphologically resemble the reddish pedocomplex described elsewhere in kansas and illinois that dates between about 69 and 35 ka the upper ll yields a tl age of about 136 and 130 30 ka thus pl the gcf and ll were probably deposited mainly during the late wisconsinan middle wisconsinan and illinoian oxygen isotope stages ois 2 3 and 6 or about 12 to 24 24 to 60 and 130 to 188 ka respectively soils 1 2 and 3 then formed mainly during ois stages 1 3 and 5 respectively or about 12 to 12 60 to 60 and 73 to 130 ka in comparison with other dated stratigraphic sections in the great plains soils paleosols have relatively simple cumulic horizon sequences as is typical at sites distal from principle loess source regions nonetheless they record a complex pedosedimentary history that reflects climatically driven variations in rates of sedimentation and pedogenesis soil 1 is an udic argiustoll with 21 cm a mollic 69 cm bt argillic 60 cm bk horizons that formed under modern type grassland and climate soil 3 the sangamon paleosol includes a 3 m thick highly rubified and clay rich argillic horizon that based on its morphological properties probably formed under a relatively warm moist equable climate and deciduous type forest soil 2 coincides with the gcf and as such is a pedolithostratigraphic unit that includes a 1 3 m mollic horizon and to 1 6 m oxidized 3btb and 3bcb horizons whereas the oxidized b horizons apparently represent relatively warm moist climatic conditions between about 65 to 35 ka the upper cumulic mollic a horizons of the gcf probably formed under progressively cooling climate and grassland between about 35 7 and 26 9 calibrated radiocarbon ka estimated mean accumulation rates mars of loess range from 0 12 m k yr for the gcf to about 0 5 m k yr for pl

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

landscape evolution of the five islands of south louisiana scientific policy and salt dome utilization and management abstract the five islands of south central louisiana are piercement type salt domes uplifted from several kilometers depth as the surrounding strata experiences regional subsidence in general the domes are nearly circular in plan with maximum land surface elevations 23 52 m asl geomorphic evidence of salt induced uplift includes surface lineations aligned gullies excessively steep land surface topography and shear fractures in surficial sediments evidence of subsidence includes sinkhole ponds a few hectares in area broad topographic saddles over tens of hectares in size and kilometer scale collapse structures on each of the five islands peoria loess and silty colluvium bury a paleosol developed in the late pleistocene prairie complex of the lower mississippi valley the loess represents a single genetic unit of eolian origin is typically thickest on lower side slopes and is thin or absent on ridge crests the silty colluvium around the perimeter of the islands is a reworked loess derived from higher elevations shear fractures with high angle average dips occur in both peoria loess and the prairie complex conjugate shear pairs probably develop from extensional stress associated with vertical uplift of the underlying salt prairie complex deposition and initial soil development in a low relief alluvial plain of the mississippi river predates the latest emergence of the five islands loess and colluvial stratigraphy indicate that the domes were emergent during loess deposition gully incision shearing of quaternary sediments and the distribution of colluvium indicate continued uplift after loess deposition sinkholes and collapse structures are influenced by salt dissolution and corrasion whereas broad subsidence areas and topographic saddles form over areas of structural weakness within the salt five islands landscape evolution is controlled by the interaction of driving and resisting forces that operate over various time scales diapiric uplift is a driving force of net upwards motion and the external and internal salt dome hydrology are driving forces of solution and corrasion the structure and lithology of the internal salt stocks and the surrounding sediments are heterogeneous and have variable strength collectively this interaction produces both uplift and subsidence features across the salt dome landscape resource use at the five islands correlate with instability of both underground facilities and the surface landscape uplift of the five islands has continued since at least the late pleistocene is probably still active at present and periods of tectonic and geomorphic instability are possible in the future sediments overlying salt domes record discrete periods of surface uplift and periods of episodic and incremental subsidence that is common where salt domes pierce surficial sediment the rate magnitude and pattern of landscape modification by salt domes have implications for the safe utilization of mineral extraction and geostorage facilities geomorphic evaluation of salt dome landscapes can help to develop policies that ensure safe salt dome utilization salt dome resource planning should include detailed characterization of internal and external stratigraphy and structure modeling of geomorphic soil and rock mechanic and hydrologic processes routine and emergency planning at operating facilities and closure and post closure plans

preeruptive magma viscosity an important measure of magma eruptibility 1 using a compilation of melt compositions meltwater contents temperatures and phenocryst contents the preeruptive viscosities under magma reservoir conditions are calculated for 83 erupted magmas the basaltic to rhyolitic magmas have preeruptive viscosities over the range 101 to 108 pa s although bulk sio2 content has often been used as a qualitative measure of preeruptive magma viscosity the bulk sio2 content shows a weak correlation with magma viscosity correlation coefficient r 0 5 because of a wide range of phenocryst contents from 0 to 50 vol andesitic magmas have viscosities ranging from 102 to 107 pa s which are lower or higher than those of phenocryst poor rhyolitic magmas with 105 to 106 pa s focusing on andesitic to rhyolitic magmas the r between bulk sio2 contents and magma viscosities changes to 0 1 in contrast the melt only sio2 content from a basaltic to rhyolitic melt shows a good linear correlation with melt only viscosity r 0 9 although most of the calculated viscosities of erupted magmas fall below 106 pa s as consistent with the previous compilation study this paper describes 20 examples of highly viscous magmas with 106 pa s in most cases composed of mixtures of high silica rhyolitic melt 75 79 wt sio2 and abundant phenocrysts 30 55 vol in these highly viscous magmas 9 examples have erupted following the precursory eruption of less viscous magma suggesting that precursory dike propagation and conduit formation by the less viscous magma with 106 pa s induced the following eruption of less eruptible highly viscous magmas

magnetic susceptibility and mineral zonations controlled by provenance in loess along the illinois and central mississippi river valleys abstract magnetic susceptibility ms patterns have proven useful for regional stratigraphic correlations of zones within thick oxidized peoria and roxana silts along the illinois and central mississippi river valleys for more than 350 km variations in ms of c horizon loess are controlled by silt sized magnetite content and are interpreted to reflect changes in sediment provenance due to fluctuations of the superior and lake michigan glacier lobes and the diversion of the mississippi river to its present course grain size distributions and scanning electron microscopic observations indicate that stratigraphic changes in ms are not significantly influenced by eolian sorting or diagenetic dissolution respectively three compositional zones lower middle and upper are delineated within peoria silt which usually can be traced in the field by ms the occurrence of clay beds interstadial soils and or subtle color changes these zones can be correlated with but are generally of more practical use than previously studied dolomite zones mckay 1977 or clay mineral zones frye et al 1968 however mineralogical analyses can help to substantiate zone boundaries when in question ms and compositional zones may indirectly record a climatic signal primarily through the effect that global cooling has had on ice lobe fluctuations in the upper mississippi drainage basin

coarse textured basal zones in thin loess deposits products of sediment mixing and or paleoenvironmental change abstract the purpose of this research was to characterize and interpret the coarse basal zones that are common in thin loess deposits that overlie coarser textured sediment to that end we sampled nine pedons in northeastern wisconsin and the upper peninsula of michigan each of which had formed in thin 55 cm loess over sandy glacial sediment at most of these sites the loess became noticeably coarser near the lithologic discontinuity the loess has a primary particle size mode in the coarse silt or fine very fine sand fraction 30 65 m and a secondary mode in the fine or medium sand fraction 200 400 m we attribute the secondary mode to mixing of underlying sands into the loess either during loess deposition or by post depositional pedoturbation in thin loess pedoturbation processes can penetrate into the underlying sediment facilitating mixing upward as far as 50 cm into the loess silt from the loess has also been mixed into the underlying sandy sediment alternatively in some pedons the loess itself coarsens with depth the particle size mode for the loess becomes increasingly coarser with depth this coarsening suggests that during loess deposition one or more of the following was occurring 1 wind velocities were decreasing over time 2 the textural character of the loess source area s were changing decreasing or 3 additional source areas with finer textured sediment became more dominant over time our research demonstrates the utility of detailed particle size data for detecting and interpreting the paleoenvironmental history of loess we also document the extent to which pedoturbation can impact the original textural characteristics of loess or any sediment that occurs as a thin surficial mantle

melt extraction in mush zones the case of crystal rich enclaves at the sabatini volcanic district central italy abstract a peculiar feature of the sabatini volcanic district svd central italy is the occurrence of crystal poor pumices and crystal rich enclaves within the same eruptive host deposit the stratigraphic sequence of pumices and enclaves indicates the tapping of a stratified magma chamber where a crystal poor phonolitic magma lay on top of a more primitive crystal rich magma the crystal rich enclaves are genetically related to the pumices and record the evolution of a solidification front in which a more differentiated melt was produced extracted and eventually erupted we collected and analyzed crystal rich enclaves from one of the largest phonolitic eruptions at the svd and used their petrological and geochemical features to reconstruct magma differentiation and crystal melt separation in the solidification front on this basis three groups of enclaves have been identified porphyritic enclaves holocrystalline enclaves and sanidinites the mineralogical variability faithfully reproduces the spatial and temporal evolution expected of a solidification front from early to intermediate crystallization conditions porphyritic and holocrystalline type to the late stage of solidification sanidinites in which the percolation of a more differentiated melt through the crystal mush triggered the instability of the solidification front results from numerical models indicate that gravitational instability is the most efficient mechanism to explain melt extraction in mush zones of medium sized 10 km 3 short lived 10 4 years magma chambers

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

quaternary faulting in the southern mississippi embayment and implications for tectonics and seismicity in an intraplate setting the recently recognized saline river fault zone in the southwestern mississippi embayment strike 135 is characterized by moderate historic seismicity we document paleoseismicity possibly strong on the saline river fault zone that is outside the known region of neotectonism in the northern embayment six surface faults were excavated within the saline river fault zone and all faults displace marine eocene units and fluvial pliocene pleistocene units five show post wisconsin loess movement thermoluminescence tl age 23 6 3 ka and three deform middle to late holocene eolian silt tl age 5 1 0 6 ka and 3 6 0 5 ka as fault tip flexures along the principal excavated fault fault plane braiding and plunging drag folding suggest a strong component of left slip and subsidiary faults show both normal and reverse displacement 1m of pliocene pleistocene wisconsin and holocene units we interpret these faults as components of a left slip flower structure a shallow seismic reflection profile acquired across the principal fault and a subsidiary fault shows eocene stratigraphy separated in a reverse sense below 120 m depth and separated in a normal sense above 120 m supporting a strike slip interpretation in addition the only focal plane mechanism available in the area indicates left slip with a small reverse component we conclude that the saline river fault zone is a paleozoic mesozoic basement fault zone reactivated as a left slip system in a quaternary east west compressive stress field field evidence suggests that earthquakes with several meters of strike slip may be characteristic and the width of a liquefaction field on the saline river fault zone suggests an event of magnitude 5 5 6 considering a similarity of strike and sense of holocene movements of the meers fault of southern oklahoma and of the saline river fault zone there may be additional active fault zones that pose seismic hazards concealed by sediments in southern north america

rheology of crystal bearing silicate melts an experimental study at high viscosities the viscosity of partially crystallized mg3al2si3o12 melts has been measured under uniaxial compression in the interval 1010 1013 poise as a function of the volume fraction of crystals these inclusions are well rounded spherulites of aluminous enstatite having the same composition as the melt and whose growth rate is negligible at the temperature of the measurements the viscosity increases by less than 1 order of magnitude for crystal fractions of 40 vol and remains newtonian up to the maximum stress exerted namely 1 kbar the einstein roscoe equation 0 1 m n provides very good fits to the measurements only if either the m or n parameter is allowed to depend on temperature for modeling of magmatic processes however the widely recommended constant values m 0 6 and n 2 5 should be adequate the rheology changes abruptly when the clustered spherulites begin to oppose shear deformation at a crystal fraction of about 40 vol the viscosity becomes non newtonian with yield strengths of a few tens of bars at temperatures at which the viscosity of the melt is higher than 1010 poise as long as the crystal fraction remains lower than 70 vol the deformation proceeds in an irregular manner with a nonuniform distribution of crystals and melt the deformation becomes again regular at low stresses with lower melt fractions but samples undergo extensive fracturation along the direction of uniaxial stress similar rheology changes have been observed during the isothermal crystallization of li2si2o5 melts which produces small ellipsoidal inclusions these results suggest that the influence of solid suspensions on the rheology of magmas is primarily determined by the crystal fraction even though additional measurements would be useful to determine the possible influence of other factors such as the size distribution or the shape of the inclusions

analog experiments on melting and contamination at the roof and walls of magma chambers abstract a series of analogue laboratory experiments were carried out to model melting and mixing processes occurring at the roof and sides of a magma chamber when hot dense mantle derived magmas are emplaced in the deep crust the experiments investigated the influence of a viscosity contrast between crustal melts and input magma the presence of crystals in the input magma and roof geometry the crust was modelled by aqueous ice or a cold low melting point wax arranged as a flat roof or in an upside down u the input magma was modelled by a hot dense aqueous solution of nano3 or feso4 which was injected into the cavity between the walls the experiments revealed the potentially important role that side wall processes may have in crustal melting and mantle magma contamination in this environment the walls melted back much faster than the roof and the melts from the opposite walls ponded next to each other under the roof and mixed with each other only in the central region when the input solution was able to crystallise it did so preferentially in the active side wall boundary layers the tiny dense crystals which were dragged up in the melt boundary layer and then dropped into the interior fluid enhanced hybridisation of the melt and contamination of the input fluid and through their influence on the boundary layer structure reduced the melting rate

loess is not just the accumulation of dust most regrettably there is much misuse of terminology in connection with the concept of loess and the interpretation of its origin people often speak and write incorrectly about loess accumulation even loess specialists who are aware of the fact that loess as a concept has to satisfy at least 10 criteria loess is not simply dust carried and deposited by wind dust only becomes loess after the passage of a certain amount of time in a given geographical zone i e only through diagenesis in certain ecological environments to state that loess is of aeolian origin is an oversimplification and an incorrect definition because an aeolian origin applies only to the dust from which the loess has been formed we are aware of the fact that airborne dust cannot be transformed into loess in every geographical environment but only under those conditions typical of semi arid grassland or steppe or forested steppe the process primarily occurs where the rate of dust accumulation exceeds sheet wash or weathering soil formation rates if the rate of dust accumulation is less than that of surface erosion or of soil biogenetic processes the dust then develops into soil or through intensive weathering and increased precipitation into loam or clay only part of the aeolian dust transported and deposited in a zone suitable for loess formation remains there permanently and is transformed in situ into loess dust not affected by diagenesis is usually further transported by snowmelt or rainwash and is only transformed into loess after it has been redeposited the loess itself however is easily erodible and its minerals are readily reworked and reaccumulated and given the appropriate conditions it readily undergoes diagenesis again we do not always have sufficient evidence to determine whether a given loess body is of primary or secondary origin traditionally the minerals making up primary loess have been regarded as originating in dust accumulated by aeolian processes secondary loess by contrast is different from typical loess in many ways and it is not unusual to find various loess series in which superimposed dust fractions have been transformed into loess by different processes recently we have observed that the origin of various types of loess is governed by differences in litho ecological conditions rather than by the way in which the mineral material from which the loess is derived dust has been primarily accumulated loessification is therefore determined by environmental conditions

historical developments and recent advances in amino acid geochronology applied to loess research examples from north america europe and china abstract amino acid geochronology provides important chronostratigraphic insight in the regional correlation and paleoclimatic evaluation of loess paleosol sequences in the midwestern us throughout western central and eastern europe and in china in general loess of the last four glacial cycles corresponding to marine oxygen isotope stages ois 2 4 6 8 and 10 respectively can be distinguished on the basis of alloisoleucine isoleucine a i ratios measured in fossil gastropod shells preserved in the loess the racemization reaction is much slower in older samples resulting in decreased temporal resolution in the midwestern us and europe it is not possible to confidently subdivide the last glacial cycle on the basis of aminostratigraphic data however in china where effective temperatures were higher during the late pleistocene loess above and below l1ss1 the ois 3 interstadial paleosol can be distinguished using amino acid racemization data with improvements in analytical methods multiple amino acid d l enantiomers are now being measured using reverse phase liquid chromatography aspartic acid racemizes at a higher rate than the traditionally measured alloisoleucine isoleucine diastereomers and can be measured more rapidly this development offers hope for better temporal resolution and enhanced stratigraphic subdivision of loess units than has been achieved previously

mixing of stratified liquids by the motion of gas bubbles application to magma mixing mafic magma underlying more silicic magma in a reservoir can exsolve volatiles as it crystallizes forming bubbles that segregate upwards to the interface with the overlying silicic magma we describe laboratory experiments designed to investigate how gas bubbles migrate into the more viscous upper layer in one regime bubbles move individually across the interface entraining a small quantity of lower layer fluid and the two layers become progressively stirred into a homogeneous mixture in a second regime bubbles form a thin foam layer at the interface which becomes gravitationally unstable giving rise to two phase plumes which rise and produce a coarse mixture of the liquids for a given viscosity ratio the transition between these regimes occurs when the gas flux is greater than a critical value which we found to decrease with increasing viscosity ratio we estimate the critical gas flux for magmatic conditions and how vesiculation may vary with pressure degree of crystallization and the composition of volatile components mafic inclusions which are often found in silicic to intermediate lavas can form in the plume regime analysis of the instability of the foam predicts wavelengths of between 1 cm and 1 m which is consistent with the observed sizes of inclusions volatiles from the mafic magma may be efficiently transported by this mechanism into the viscous silicic magma as bubble plumes despite low stokes velocities for individual vesicles at small viscosity ratios or low gas fluxes the bubbling regime can produce hybrid magmas

new insights on illinoian deglaciation from deposits of glacial lake quincy central indiana abstract the deposits of glacial lake quincy overlie a diamicton associated with the classically defined illinoian limit in central indiana this lake covered at least 180 km 2 with a depth of 20 m and developed when the illinoian ice sheet retreated 15 km from the maximum limit causing lake impoundment against devore ridge overflow from glacial lake quincy eroded across the ridge forming a number of steeped walled outlets a section along mill creek exposes a sedimentologic sequence associated with glacial lake quincy from a subglacial diamicton to ice proximal to ice distal glacial lacustrine sediments we report new optical ages by multiple aliquot regenerative dose procedure for the fine grained rhythmically bedded sediments presumed to represent the lowest energy depositional facies dominated by suspension settling which maximized sunlight exposure in turn optical ages were determined on the fine grained 4 11 m polymineral and quartz fractions under infrared and blue excitation which yielded statistically similar ages optical ages span from ca 170 to 108 ka with the average of 16 optical ages indicating deglaciation at ca 135 ka generally coincident with marine oxygen isotope stage 6 to 5 transition and rise in global sea level

simultaneous crystallization and melting at both the roof and floor of crustal magma chambers experimental study using nh4cl h2o binary eutectic system abstract thermal and compositional evolution of magmas after emplacement of basalt into continental crust has been investigated by means of fluid dynamic experiments using a cold solid mixture with eutectic composition and a hot liquid with higher salinity in the nh 4 cl h 2 o binary eutectic system the experiments were designed to simulate cases where crystallization of a basalt magma is accompanied by melting at both the roof and floor of a crustal magma chamber the results show that thermal and compositional convection occur simultaneously in the solution the thermal convection is driven by cooling at the roof and the compositional convection is driven by melting and crystallization at the floor the roof was rapidly melted by the convective heat flux which resulted in formation of a separate eutectic melt layer the upper liquid layer with negligible mixing of the underlying liquid the lower liquid layer on the other hand a mushy layer formed at the floor the compositional convection at the floor carried a low heat flux so that the heat transfer at the floor was basically explained by simple heat conduction the thermal boundary layer in the lower liquid layer at the interface with the upper liquid layer became thicker with time and subsequently temperature decreased upward throughout the lower liquid layer compositional gradient with nh 4 cl content decreasing upward formed by compositional convection in the lower liquid layer the formation of these gradients resulted in formation of double diffusive convecting layers in the lower liquid layer the upward heat transfer was suppressed when compared with the case where the liquid region is homogenized by vigorous convection these experimental results imply that when a basalt magma is emplaced in continental crust floor melting does not always enhance the cooling of the magma but it may even reduce the total heat loss from the magma to the crusts due to suppression of convection by formation of a stabilizing compositional gradient

the contribution of experimental volcanology to the study of the physics of eruptive processes and related scaling issues a review abstract the experimental approach has become a major tool increasingly used by volcanologists in recent decades to investigate the physics of eruptive processes in complement to field and theoretical works researchers have developed various methodologies to study volcanic phenomena at reduced length scale the works involve natural or analogue materials and their types range from first order tests to identify fundamental processes and make qualitative comparison with field observations to more sophisticated experiments in which precise data obtained in a controlled environment can be used to validate outputs of theoretical models scaling is a central issue to ensure dynamic similarity between the small scale experiments and the large scale volcanic phenomena when natural conditions cannot be simulated due to inherent length scale difference and or technical limitations in this respect dimensionless numbers are used to map physical regimes and to define scaling laws which allow experimental results to be extrapolated to natural scale this review presents the variety of experimental studies conducted to investigate subterraneous and aerial volcanic phenomena involving in particular fluid particle mixtures we focus on the major scaling issues and the physical regimes investigated and we also highlight in a historical perspective some of the major advances achieved through experimental studies finally we conclude on some perspectives for future works

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

experiments on upward migration of a liquid rich layer in a granular medium implications for a crystalline magma chamber 1 we perform a series of experiments to investigate the situation in which a melt rich layer formed by a magma intrusion ascends through a crystalline magma chamber the initial condition is such that a heavier granular layer overlies a liquid layer the particles consisting the upper granular layer are in a jammed state and only the particles near the interface can move to form a dilated boundary layer the dilated layer detaches from the upper granular layer and forms downwelling plumes which drive a cellular convection within the liquid rich layer the convection erodes the upper granular layer and the liquid rich layer migrates upwards with time this upward migration of the liquid rich layer differs from the previously known mechanisms of liquid transport permeable flow in which the liquid migrates at the darcy velocity the stokes settling in which the individual particle settles and diapirs formed by the rayleigh taylor instability we find that the velocity of the upward migration of the liquid rich layer can be scaled by the volumetric flux of the liquid ascending through the narrow channel between the particles the upward migration of the liquid rich layer is faster than the darcy velocity in a mushy magma chamber whose crystals are in a jammed state neither the stokes settling nor the rayleigh taylor instability can occur we propose that the upward migration of the melt rich layer observed in our experiments can become an efficient mechanism of melt transport in a crystalline magma chamber

loess studies in central united states evolution of concepts abstract few words in the realm of earth science have caused more debate than loess it is a common term that was first used as a name of a silt deposit before it was defined in a scientific sense because this loose deposit is easily distinguished from other more coherent deposits it was recognized as a matter of practical concern and later became the object of much scientific scrutiny loess was first recognized along the rhine valley in germany in the 1830s and was first noted in the united states in 1846 along the lower mississippi river where it later became the center of attention the use of the name eventually spread around the world but its use has not been consistently applied over the years some interpretations and stratigraphy correlations have been validated but others have been hotly contested on conceptual grounds and semantic issues the concept of loess evolved into a complex issue as loess and loess like deposits were discovered in different parts of the us the evolution of concepts in the central us developed in four indefinite stages the eras of 1 discovery and development of hypotheses 2 conditional acceptance of the eolian origin of loess 3 bandwagon popularity of loess research and 4 analytical inquiry on the nature of loess toward the end of the first era around 1900 the popular opinion on the meaning of the term loess shifted from a lithological sense of loose silt to a lithogenetic sense of eolian silt however the dual use of the term fostered a lingering skepticism during the second era that ended in 1944 with an explosion of interest that lasted for more than a decade in 1944 r j russell proposed and h n fisk defended a new non eolian property based concept of loess the eolian advocates reacted with surprise and enthusiasm each side used constrained arguments to show their view of the problem but did not examine the fundamental problem which was not in the proofs of their hypothesis but in the definition of the term between 1944 and about 1950 the debates about loess reached a maximum level of complexity the main semantic problem was submersed in peripheral arguments about physical properties and genetic interpretations the scholarly treatment of the subject by fisk and russell stimulated quality responses from a diversity of earth scientists interested in academic and applied studies particularly geo history pedology soil mechanics and stratigraphy the long lasting popularity of loess studies during the bandwagon era lasted to about 1970 by that time the analytical and technical interests had attracted the mainstream into the fourth era with a focus beyond the old arguments although fisk and russell found themselves defending an unpopular theory they stimulated a scientific interest in the late quaternary history of the mississippi valley that may never be exceeded

the permeability controlled accumulation of primary magma the initial accumulation of primary magma occurs just after the mantle has become permeable the accumulation is caused by the compaction of the residuum which either may be controlled by the rate of creep or by the rate of flow of the interstitial melt experimental results suggest that the rate of compaction is controlled by the permeability and a model for the accumulation process is worked out on this basis the compaction causes the formation of a lower compaction boundary and an upper layer of melt the ascending mantle of plumes and convection currents will form layers of melt situated 20 100 m apart the type of partial melting for this accumulation is critical melting

non newtonian behavior of plagioclase bearing basaltic magma subliquidus viscosity measurement of the 1707 basalt of fuji volcano japan abstract laboratory measurements of viscosity were done for basalt erupted in 1707 ad from fuji volcano japan using a concentric cylinder rotational viscometer at temperatures of 1297 1157 c 1 atm pressure and fo 2 near the ni nio buffer on cooling elongated plagioclase crystals with a mean length width ratio of ca 8 5 appeared at 1237 c followed by olivine at 1157 c at progressively lower temperatures the total crystal volume fraction increased monotonously to ca 0 25 viscosity increased from 38 9 to 765 pa s at a shear strain rate of 1 s 1 this basalt magma behaves as a newtonian fluid at temperatures greater than 1217 c but shear thinning behavior occurs at temperatures less than 1197 c because of the suspended plagioclase crystals this behavior is well approximated as a power law fluid at the onset of shear thinning the crystal volume fraction was between 0 06 and 0 13 which is attributed to the pronounced lath shape of plagioclase crystals the relative viscosity increases monotonously with increase of crystal volume fraction at a constant shear strain rate and with decrease of shear strain rate at a constant crystal volume fraction a modified form of the krieger dougherty equation is introduced herein it enables us to describe the dependencies of relative viscosity on both the crystal volume fraction and shear strain rate and consequently the onset of shear thinning behavior

episodic deposition of illinois valley peoria silt in association with lake michigan lobe fluctuations during the last glacial maximum the chronology and cause of millennial depositional oscillations within last glacial loess of the central lowlands of the united states are uncertain here we present a new age model that indicates the peoria silt along the illinois river valley accumulated episodically from 28 500 to 16 000 cal yr bp as the lake michigan lobe margin fluctuated within northeastern illinois the age model indicates accelerated loess deposition coincident with regional glacial advances during the local last glacial maximum a weakly developed paleosol the jules geosol represents a period of significantly slower deposition from 23 700 to 22 000 cal yr bp a gastropod assemblage based reconstruction of mean july temperature shows temperatures 6 10 c cooler than modern during peoria silt deposition stable oxygen and carbon isotope values 18 o and 13 c of gastropod carbonate do not vary significantly across the pedostratigraphic boundary of the jules geosol suggesting slower loess accumulation was a result of reduced glacial sediment supply rather than direct climatic factors however a decrease in 18 o values occurred between 26 000 and 24 000 cal yr bp synchronous with the lake michigan lobe s southernmost advance this 18 o decrease suggests a coupling of regional summer hydroclimate and ice lobe position during the late glacial period

viscosity of high crystal content melts dependence on solid fraction 1 the rheological properties of suspensions containing high solid fractions are investigated attention is focused on viscosity of silicate and magmatic melt systems a general empirical equation which describes the relative viscosity of suspensions as a function of suspended solid fraction is proposed in the limit of very dilute solid concentrations it reduces to the einstein equation the proposed relationship is satisfactorily applied to reproduce available experimental data relative to silicate melts moreover the extrapolation of the model to very high concentrations is compared with experimental observations on partially melted granite

modelling of melt segregation processes by high temperature centrifuging of partially molten granites ii rayleigh taylor instability and sedimentation summary the present experimental study deals with the laboratory modelling of two different mechanisms of gravitational percolation in partially melted rocks 1 diapiric percolation of heavy material and 2 the sedimentation of heavy particles these two mechanisms of mass transport in partially melted rocks result in different scales of the segregation process in the melt crystal matrix a centrifuge furnace was used to simulate the percolation of the heavy particle layer through the partially molten granite at temperatures of up to 1000 c samples of beauvoir granite massif central france grain size 0 16 0 5 mm with an initial degree of partial melting 45 per cent were used as a matrix a layer of pt powder suspended in a melt of the same composition as the partially melted matrix was placed on the top of the granite sample after centrifuging for various times up to 2 x lo4 s x ray images of samples were obtained and the evolution of the percolation process of heavy suspension in the partially molten granite was monitored from the pt particle distribution the diapiric or finger regime of percolation starts when the growth rate of a raleigh taylor instability of the heavy layer is faster than the stokes sedimentation velocity of individual particles in the upper layer this relationship is a complex function of the size and initial concentration of heavy particles as well as the ratio of particle to crystal size the permeability of the matrix and the heterogeneity scale in the partially melted matrix at small concentrations several per cent and at large concentrations where close packing of heavy particles results in an anomalous viscosity increase in the upper heavy layer stokes sedimentation is dominant in the vertical percolation of the heavy material the sinking velocity of the diapir decreases when the size of heavy particles in it becomes comparable with the size of crystals in the partially melted granite in this situation the vertical sinking of the diapir is not stable and the horizontal instability of the vertical mass transport starts to become important mass transport via diapiric percolation results in more efficient crystal melt segregation of partially melted rocks the percolation of individual particles provides only local melt crystal flow on a scale comparable with the heavy particle size the diapiric percolation provides a much larger scale of partial melt segregation with a length scale comparable with the diapir size

location and expression of fragic soil properties in a loess covered landscape southern illinois usa abstract fragic soil properties often develop in thin loess units overlying residual parent materials in the midwest usa morphologic indicators of these fragic properties are often weakly expressed making consistent mapping of soils difficult this study was initiated in a small watershed in union county illinois to determine location and degree of development of fragic materials and fragipans on the landscape we also sought to assess factors influencing the degree of expression of these features and document accessory soil properties that reflect the presence of these fragic soil materials nine pedons from two catenas were sampled and selected chemical physical and mineralogical analyses were conducted results indicate that loess thickness across the watershed ranged from about 2 to 4 m fragic soil properties were observed in argillic horizons on side slope and head slope geomorphic components at depths ranging from 51 to 111 cm depths to horizons meeting fragipan criteria ranged from 140 to 175 cm discontinuity between two loess units peoria and roxana silts was verified by both particle size analysis fine coarse silt ratios clay free fine and coarse silt and magnetic susceptibility these data suggest that the development of fragic soil properties is not controlled solely by the discontinuity between loess deposits fragipans are weakly developed based on rupture resistance morphological features such as structure bulk density

alluvial pedogenesis in pleistocene and holocene mississippi river deposits effects of relative sea level change comparison of pleistocene and holocene soils developed in mississippi river meander belt deposits in louisiana illustrates the influence of relative sea level change on pedogenesis holocene and pleistocene meander belts have similar landscape morphologies lithofacies and soil characteristics and probably formed under similar hydrologic regimes the pleistocene avoyelles prairie meander belt is now terraced but it was originally graded to a lower relative sea level position than the holocene flood plain holocene alluvial soils are generally weakly expressed cumulative profiles with abundant redoximorphic features and formed on an aggrading flood plain with a shallow fluctuating water table the soil morphology varies with respect to landscape position and overbank lithofacies pleistocene alluvial paleosols show evidence for two stages of pedogenesis during the first stage of pedogenesis water table fluctuations and flood plain aggradation produced profiles with color mottles iron and carbonate nodules and weak b and c horizons similar to holocene flood plain soils the second stage of pedogenesis occurred after the avoyelles prairie was terraced and the regional water table fell a minimum of 30 m improved soil drainage created oxidizing and acidic conditions removed free carbonates dehydrated iron oxides and transformed clay minerals this stage produced pleistocene profiles with brighter matrix and mottle hues lower ph values larger and harder iron nodules and greater kaolinite contents than comparable holocene flood plain soils the primary influence on regional water table lowering in the southern lower mississippi valley was relative sea level fall mississippi river flood plain lowering adjacent to the avoyelles prairie most likely occurred between the end of oxygen isotope stage 3 and the maximum period of valley entrenchment during oxygen isotope stage 2 water table fall affected pedogenic processes a minimum of 400 km upvalley of the continental shelf margin pleistocene mississippi river paleosols represent excellent analogs for interpreting ancient alluvial paleosols formed during episodes of base level fall and valley incision as fluvial entrenchment terraced the meandering avoyelles prairie a pedogenic threshold was crossed that altered the pathway of chemical weathering the complexity of a multiple step pedogenic history also highlights the fact that interpretation of relative profile development as a function of time can be problematic

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

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

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

a biota associated with matuyama age sediments in west central illinois a fossil assemblage containing molluscs mammals insects ostracodes and plants has been recovered from a silt filled depression near lima in west central illinois the reversed remanent magnetic signature of the sediments and the temporal ranges of two mammals microtus paroperarius and lasiopodomys deceitensis constrain the age of the assemblage to between 730 000 and 830 000 yr b p the extent of isoleucine epimerization in the molluscan shell is consistent with this age interpretation the fauna includes at least 43 taxa of beetles from 11 families 35 nominal species of molluscs and two genera of ostracodes the mammals include two shrews three rodents and a rabbit the plant macrofossils no pollen recovered include 25 species of seed plants and four kinds of terrestrial or wetland mosses most of the plant species identified still occur in the upper midwest although a few of the taxa are found mainly to the north of the site the fauna is characterized by an almost total absence of true aquatic taxa the association of both boreal and thermophilous faunal and floral elements suggest that summer temperatures were not greatly different from present ones but cooler moist areas must have been available to support the boreal elements local conditions were probably similar to those now found in northeastern iowa where rains blocks fissures and joints in carbonate bedrock serve as traps for debris accumulations provide shade and are kept cool and moist during the hot summer months by cold air drainage and groundwater seepage summer mean temperature in these microhabitats was probably between 18 and 20 c similar to temperatures that now occur near the northern hardwood spruce fir transition in the eastern united states

late quaternary loess in northeastern colorado part i age and paleoclimatic significance loess in eastern colorado covers an estimated 14 000 km 2 and is the westernmost part of the north american midcontinent loess province stratigraphic studies indicate there were two periods of loess deposition in eastern colorado during late quaternary time the first period spanned ca 20 000 to 12 000 14 c yr b p ca 20 14 ka and correlates reasonably well with the culmination and retreat of pinedale glaciers in the colorado front range during the last glacial maximum the second period of loess deposition occurred between ca 11000 and 9000 14 c yr b p this interval may be holocene or may correlate with a hypothesized younger dryas glacial advance in the colorado front range sedimentologic mineralogic and geochemical data indicate that as many as three sources could have supplied loess in eastern colorado these sources include glaciogenic silt derived from the colorado front range and two bedrock sources volcaniclastic silt from the white river group and clays from the pierre shale the sediment sources imply a generally westerly paleowind during the last glacial maximum new carbon isotope data combined with published faunal data indicate that the loess was probably deposited on a cool steppe implying a last glacial maximum july temperature depression relative to the present of at least 5 6 c overall loess deposition in eastern colorado occurred mostly toward the end of the last glacial maximum under cooler and drier conditions with generally westerly winds from more than one source

mineral disequilibrium in lavas explained by convective self mixing in open magma chambers characteristic features of many porphyritic andesite and dacite lavas are that they are rich in crystals and display a range of disequilibrium features including reversely zoned crystals resorption surfaces wide ranges of mineral compositions and minerals which are not in equilibrium with the surrounding rock matrix these features are often interpreted as evidence of the mixing of magmas of contrasting composition temperature and origin1 2 here however we propose that such features can also be caused by convection within a magma body with a single composition that is heated from below and cooled from above we describe petrological observations of andesite lava erupted at the soufriere hills volcano montserrat which indicate a heating event and the intermingling of crystals that have very different thermal histories we present experimental data on a representative groundmass composition of this lava which indicate that it is difficult to explain the calcic compositions of plagioclase overgrowth rims and microphenocrysts unless parts of the magma were at temperatures much higher than the inferred average temperature the concept of convective self mixing allows us to explain the occurrence of compositions of minerals that apparently cannot coexist under equilibrium conditions

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

experiments on metal silicate plumes and core formation short lived isotope systematics mantle siderophile abundances and the power requirements of the geodynamo favour an early and high temperature core formation process in which metals concentrate and partially equilibrate with silicates in a deep magma ocean before descending to the core we report results of laboratory experiments on liquid metal dynamics in a two layer stratified viscous fluid using sucrose solutions to represent the magma ocean and the crystalline more primitive mantle and liquid gallium to represent the core forming metals single gallium drop experiments and experiments on rayleigh taylor instabilities with gallium layers and gallium mixtures produce metal diapirs that entrain the less viscous upper layer fluid and produce trailing plume conduits in the high viscosity lower layer calculations indicate that viscous dissipation in metal silicate plumes in the early earth would result in a large initial core superheat our experiments suggest that metal silicate mantle plumes facilitate high pressure metal silicate interaction and may later evolve into buoyant thermal plumes connecting core formation to ancient hotspot activity on the earth and possibly on other terrestrial planets

convection and particle entrainment driven by differential sedimentation when a suspension of small particles is overlain by a clear fluid whose density is greater than that of the interstitial fluid but less than that of the bulk suspension the settling of the dense suspended particles can lead to vigorous convection in the overlying fluid this novel situation is investigated experimentally and theoretically a sharp interface is observed between the convecting upper region and a stagnant lower region in which there is unimpeded sedimentation at low reynolds number there is no transport of fluid from the upper region into the lower though there is mixing of both buoyant fluid and entrained particles from the lower region into the upper the interface between the two regions is found to descend at a constant velocity systematic laboratory measurements have determined how this velocity depends on the densities of the layers and the distributions of settling velocities of the particles a theoretical description is developed which calculates the evolution of the density of the lower region due to differential sedimentation of polydisperse particles buoyancy arguments based on the calculated density profile are used to placc upper and lower bounds on the amount of particle entrainment into the upper layer and on the rate of fall of the interface between the convecting and sedimenting regions the theoretical predictions are in good agreement with the experimental observations the analysis of the interaction between convection and sedimentation in the system considered here may be particularly relevant to the description of evolving crystal rich layers in magma chambers and of silt laden outflow from rivers and has a wide range of other industrial environmental and geological applications