formation of native iron in sediment contaminated magma i a case study of the hanekammen complex on disko island west greenland abstract for the first time a compositional range of native iron bodies is described in a cogenetic series of sediment contaminated volcanic rocks from the tertiary west greenland basalt province the iron bearing rocks occur in a high level composite intrusion the hanekammen complex reaction between a tholeiitic parent magma with 11 mgo and carbonaceous al2o3 rich shale took place in a reservoir 3 km below the paleosurface and created magmatic layering with basaltic magma overlain by less dense andesitic magma the contaminated rock series bears a strong imprint of assimilation but very little fractional crystallization which implies that the two processes were not intimately coupled in the present case most of the iron was formed at depth in a range of fo2 from 10 13 atm 1200 c to 10 16 atm 1100 c as determined by the p distribution between solid iron and magma this is far below the graphite gas cco buffer at the estimated pressure 800 bars and suggests a high hydrogen fugacity together iron in basalt and andesite form a general trend defined by co versus ni concentrations that reflects the degree of assimilation the amount of immiscible sulphide liquid and the degree of reduction in order of decreasing importance the zoning of single iron grains reflects the dynamics of their growth and to some extent subsequent homogenization and reaction with the magma weakly zoned iron spherules in viscous andesite were formed and remained in situ whereas iron grains in basalt settled through the layered magma and developed strong zoning all iron types contain co rich domains

gypsum caves as indicators of climate driven river incision and aggradation in a rapidly uplifting region detailed geomorphological analysis has revealed that subhorizontal gypsum caves in the northern apennines italy cut across bedding planes these cave levels formed during cold periods with stable river beds and are coeval with fluvial terraces of rivers that flow perpendicular to the strike of bedding in gypsum monoclines when rivers entrench renewed cave formation occurs very rapidly resulting in the formation of a lower level river aggradation causes cave alluviation and upward dissolution paragenesis in passages nearest to the river beds the u th dating of calcite speleothems provides a minimum age for the formation of the cave passage in which they grew which in turn provides age control on cave levels the ages of all speleothems coincide with warmer and wetter periods when co 2 availability in the soils covering these gypsum areas was greater this climate driven speleogenetic model of epigenic gypsum caves in moderately to rapidly uplifting areas in temperate regions might be generally applicable to karst systems in different geological and climatic conditions

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

thin section and s e m textural criteria for the recognition of cement dissolution porosity in sandstones cement porosity relationships are described from the lower triassic sherwood sandstone group and the middle jurassic ravenscar group in the united kingdom calcite cemented sandstones display a variety of replacement textures with preferential replacement of grains and of overgrowth faces with high free surface energy dolomite and siderite cemented sandstones display similar textures but replacement is less specific and euhedral overgrowth surfaces are commonly embayed by carbonates examination of the more porous sandstones with the scanning electron microscope reveals a range of pitting and embayment textures in authigenic overgrowths and in detrital grains these range from small v shaped notches and pits through regular and irregular shaped embayments into large depressions these textures appear to be morphologically similar to the quartz surfaces seen in thin sections of carbonate cemented sandstones and are interpreted to have been formed by the dissolution of pore filling and grain replacive authigenic carbonates this is confirmed by examination of experimentally exhumed overgrowth surfaces from carbonate cemented sandstones these textures indicate that part of the intergranular porosity in these sediments is secondary in origin and has been generated by the dissolution of carbonate cements the identification of such textures may lead to a more confident interpretation of the nature of intergranular porosity in the subsurface

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

formation of iron carbon alloys in basaltic magma at uivfaq disko island the role of carbon in mafic magmas two types of metallic iron were identified in a collection of samples from the tertiary iron bearing basalts of uivfaq disko island greenland high carbon iron has 2 9 4 0 wt carbon and eutectic textures of iron and cohenite fe 3 c similar to those of commercial white cast iron it occurs in approximately spherical bodies up to 15 mm in diameter that appear to have been immiscible metallic liquids within basaltic magma low carbon samples have 1 8 2 0 wt carbon and textures similar to those of commercial hypereutectoid steel they occur principally as large up to 22 tons cumulate masses both types of metal could have crystallized at low pressure from iron carbon liquids of their present bulk carbon contents fe ni co cu and p oxides in basaltic magma were reduced by carbon derived principally from assimilated cretaceous tertiary sediments niand ni cu ratios of the metal are similar to those of terrestrial basalts the magma contained excess carbon graphite so the metal formed as

evolving strain partitioning in the eastern himalaya the growth of the shillong plateau the shillong plateau is the only raised topography up to 2000 m elevation in the himalayan foreland it is proposed to have had a major influence on strain partitioning and thus tectonics in the eastern himalaya additionally its position on the trajectory of the summer monsoon means it has influenced the regional climate with reduced erosion rates proposed over geological timescales in its lee the timing of surface uplift of the plateau has been difficult to determine exhumation rates have been calculated over geological timescales but these seem at variance with estimates based upon extrapolating the present day velocity field measured with gps and it has thus been suggested that exhumation and surface uplift are decoupled we determine the timing of surface uplift using the sedimentary record in the adjacent surma basin to the south which records the transition from a passive margin with southward thickening sedimentary packages to a flexural basin with north thickening strata due to loading by the uplifting plateau our method involves using all available 2d seismic data for the basin coupled to well tie information to produce isochore maps and construct a simple model of the subsidence of the surma basin in order to assess the timing and magnitude of flexural loading by the shillong plateau we conclude that the major period of flexural loading occurred from the deposition of the tipam formation 3 5 2 ma onwards which is likely to represent the timing of significant topographic growth of the shillong plateau our isochore maps and seismic sections also allow us to constrain the timing of thinning over the north south trending anticlines of the adjacent basin bounding indo burman ranges as occurring over this same time interval the combined effect of the uplift of the shillong plateau and the westward encroachment of the indo burman ranges to this region served to sever the palaeo brahmaputra drainage connection between himalayan source and surma basin sink at the end of tipam formation times 2 ma

metal silicate thermochemistry at high temperature magma oceans and the excess siderophile element problem of the earth s upper mantle recent theoretical considerations indicate that earth should have been at least partly molten at the end of accretion and perhaps sufficiently to produce a magma ocean metal silicate partition coefficients applicable to a magma ocean 3000 k 4000 k and up to 130 gpa would be valuable to test such models against well known mantle siderophile element abundances but they have not been measured however an extrapolation of existing low temperature data to these extreme conditions has recently been attempted murthy 1991 murthy s results seem to account for many apparent excesses of siderophile elements in the mantle we examined his extrapolation method and found it to be inconsistent with published temperature dependencies for metal silicate partition coefficients we also attempted an extrapolation to magma ocean temperatures based on known chemical behavior for several elements and using published metal silicate partition coefficients if the chemistry quantified by the low temperature data is applicable at high temperature an important assumption then our results indicate that high temperature alone will not help ameliorate the excess siderophile element problem of the upper mantle in contrast to the conclusions of murthy 1991 for most elements a modest increase in siderophile behavior is predicted with rising temperature if an iron wustite redox buffer is paralleled but long range extrapolation of experimental data containing even modest experimental errors is hazardous extrapolated high temperature partition coefficients can differ by orders of magnitude for a given element even though the input from independent studies is consistent within quoted errors direct experimental measurements for at least some of the siderophile elements will be necessary to accurately assess siderophile element behavior in a magma ocean the excess siderophile element problem of the earth s upper mantle remains unsolved

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

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

terrestrial origin of the moon abundance patterns of siderophile elements in the earth s mantle have been determined by complex processes connected with internal segregation of a metallic core amounting to 32 of the earth s mass although the lunar core may be only 2 of the lunar mass and formed in very different conditions to the earth s core the lunar siderophile pattern is closely related to that of the earth s mantle implying that the material in the moon derived mainly from the earth s mantle after core formation new models for the accretion of the earth which require impacts by large planetesimals in the presence of a corotating primitive terrestrial atmosphere provide a mechanism for transferring material from the earth s mantle into geocentric orbit as a ring of proto lunarplanetesimals from which the moon later accreted

miocene rise of the shillong plateau and the beginning of the end for the eastern himalaya abstract a common feature of convergent plate boundaries is the self organization of strain exhumation and topography along discrete arcuate boundaries deviations from this geometry can represent first order changes in stress applied at a plate boundary that must affect how strain is partitioned within the interior of an orogen the simplicity of the himalayan fold and thrust belt seen along its central portion breaks down along the eastern extremity of the arc where the 400 km long shillong plateau has developed this change in strain partitioning affects nearly 25 of the arc and has not previously been considered to be important to the orogen s development new low temperature thermochronometry data suggest this structure initiated in mid to late miocene time significantly earlier than was previously estimated from the sedimentary record alone development of the shillong plateau may be linked to a number of kinematic changes within the himalayan and burman collision zones that occur at the same time these events include the onset of e w extension in central tibet eastward expansion of high topography of the tibetan plateau onset of rotation of crustal fragments in southeastern tibet and re establishment of eastward subduction beneath the indo burman ranges we suggest that the coincidence of these tectonic events is related to the dismemberment of the eastern himalayan arc signifying a change in regional stress applied along the india eurasia burma plate boundaries discrepancies between vertical long term faulting rates and geodetically derived far field convergence rates suggest that the collisional boundary in the eastern himalayan system may be poorly coupled due to introduction of oceanic and transitional crust into the eastern plate boundary the introduction of dense material into the plate boundary late in the orogen s history may explain regional changes in the strain field that affect not only the himalaya but also the deformation field more than 1000 km into the tibetan plateau

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

evaluation of amino acid racemization epimerization dating using radiocarbon dated fossil land snails the relation between age and amino acid epimer ratios alloisoleucine isoleucine a i of holocene land snails was quantitatively evaluated through 14 c and amino acid analysis of 33 samples from fluvial and colluvial sediments and rodent middens in the northern negev desert of israel a i is strongly correlated with 14 c ages in fluvial and rodent midden deposits r 0 95 and 0 94 respectively permitting age estimates from a i ratios with precisions of 700 and 660 yr the correlation is weaker in colluvial deposits r 0 74 and age estimates from a i ratios are correspondingly less precise 1580 yr this probably results from delayed burial which exposes the shells to intense radiation on the desert surface because of the generally strong relation between age and a i amino acid epimerization analysis of individual shells can be used to identify mixed age deposits and to reconstruct species chronologies from mixed age deposits

solution weathering rate and origin of karst landforms and caves in the quartzite of auyan tepui gran sabana venezuela abstract the paper reports the results of sio 2 analyses in the aonda cave system located on the auyan tepui one of the widest table mountains of the gran sabana south venezuela characterised by karst landforms developed in siliceous rock chemical analyses underline the very low concentration of sio 2 of the surface water percolation and cave drip waters have a sio 2 concentration of about 1 mg l the mean silica load of the cave stream is 184 mg s mainly derived from surface solution removal in the allogenic recharge area in the aonda cave system the mean sio 2 dissolved load is 40 mg s in part from surface solution 15 and mainly from underground processes 85 the low solubility of sio 2 in slightly acidic water implies the importance of the time factor in the formation of cave systems with the present dissolution rate about 10 ma would be necessary to form the known karst system this estimation can be significant only if we assume that climate has been stable in the last few tens of millions of years furthermore this age can be taken as a minimum estimate while according to the geomorphic evolution of the area the origin of the aonda cave system could be reasonably dated back to at least 20 30 ma that is to the oligocene

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

a hybrid model to evaluate subsurface chemical weathering and fracture karstification in quartz sandstone abstract a hybrid numerical finite differences and semi analytical empirical model has been developed to evaluate the spatial and time scale of chemical weathering along a fracture in quartz sandstones the model is based on the diffusion transport occurring from the bedrock mass toward the fracture walls driven by the sio2 concentration gradient between water in the bedrock pores high silica content and water flowing in the fracture low silica content because of molecular diffusion intergranular water becomes undersaturated with respect to silica this promotes dissolution of quartz at grain boundaries and results in a porosity profile decreasing from the fracture walls toward the rock interior bedrock individual grains are released and gradually removed by the water flowing into the fracture when a critical value of porosity is reached grain release threshold grt this process drastically increases the fracture enlargement rate the model outcomes establish a minimum time of 90 ka to reach the grt this time is independent of length aperture and dip of the fracture but is controlled by parameters such as the initial fracture aperture water temperature quartz grain size and initial bedrock porosity it is attested that the water flowing in the fracture remains undersaturated with respect to silica over very long timescales in the order of 105 years and over very long flow paths in turn this suggests that the extremely slow reaction between quartz and water is the key factor for the formation of subterranean karst like features in quartz sandstone otherwise silica saturation would be reached after short distances and deep weathering in this lithology would be prevented finally the model outcomes were compared to field data from the gran sabana caves venezuela and other quartz sandstone weathering landforms elsewhere showing that dissolution diffusion in the rock matrix is a reliable mechanism for the formation of these peculiar karst like features

the influence of feo on the solubilities of cobalt and nickel in silicate melts abstract the effect of iron on the solubilities of co and ni in silicate melts was determined at a wide range of oxygen fugacities from 10 8 1 to 10 12 6 atm and at temperatures ranging from 1305 1600 c four different systems were studied in system a an feo free silicate of anorthite diopside eutectic composition was equilibrated with pure co or pure ni metal in system b the same silicate starting material was equilibrated with feconi alloys in systems c and d feo containing silicates basaltic komatiite were equilibrated with pure co and pure ni metal system c and with feco and feni alloys system d experiments at temperatures below 1450 c were performed by equilibrating metal loops with silicates at higher temperature well mixed metal powder and silicates were equilibrated in alumina crucibles concentrations of ni and co in the silicate and in some of the alloys were determined by neutron activation analysis most of the alloy compositions were analyzed by electron microprobe at constant temperature 1400 c but variable oxygen fugacities co ni and fe metal silicate partition coefficients calculated from metal solubilities increase with decreasing oxygen fugacities the extent of the increase suggests that all three metals are dissolved as oxides coo nio feo in the silicate melt no evidence for the presence of metallic co ni or fe as major species in silicate melt was found within the oxygen fugacity range covered by the experiments even at oxygen fugacities three log units below the fe feo equilibrium iw 3 a minor fraction of metallic ni below 20 may be present in the most reducing experiments no difference in ni and co solubility was found for feo free and feo containing silicates depending on temperature all metal silicate partition coefficients of co and ni decrease slightly with increasing temperature along the oxygen fugacity appropriate for core formation 2 3 log units below the fe feo equilibrium iw 2 3 the experiments confirm that the relatively high present day upper mantle concentrations of co ni and fe and in particular the chondritic ni co ratio cannot be explained by equilibrium between coreforming metal and silicates of the earth s mantle in a low pressure environment even at temperatures as high as 4000 c thus supporting models of inhomogeneous accretion of the earth accumulation of differentiated planetesimals i e with metal cores as major building blocks of the earth can also be excluded in these bodies metal silicate equilibration would have occurred at low pressures and equilibration of metal cores of accreting planetesimals with the earth s mantle is unlikely homogeneous accretion models may only be possible if equilibration occurred between lower mantle minerals and liquid core forming metal during differentiation of the earth and if the relevant ni and co partition coefficients are sufficiently high the ni and co partition coefficients between liquid metal and mg wustite and mg perovskite are not well known

age and evolution of the grand canyon revealed by u pb dating of water table type speleothems the age and evolution of the grand canyon have been subjects of great interest and debate since its discovery we found that cave mammillaries water table indicator speleothems from nine sites in the grand canyon showed uranium lead dating evidence for an old western grand canyon on the assumption that groundwater table decline rates are equivalent to incision rates samples in the western grand canyon yielded apparent water table decline rates of 55 to 123 meters per million years over the past 17 million years in contrast to eastern grand canyon samples that yielded much faster rates 166 to 411 meters per million years chronology and inferred incision data indicate that the grand canyon evolved via headward erosion from west to east together with late stage 3 7 million years ago accelerated incision in the eastern block

a 45 000 yr record of a tropical lowland biota the land snail fauna from cave sediments at coco ree jamaica the land snail fauna from cave sediments in wet tropical lowland forest in central jamaica was analyzed with regard to their implications for the biogeographic history of the late quaternary eight radiocarbon dates on the shells range from 600 to 45 000 yr b p and show a close relationship to amino acid epimer ratios d alloisoleucine l isoleucine or a i values a i values of individual shells indicate that the faunas span a continuous time sequence but that a significant mixture of ages occurs within each level of the cave sediments the chronologies of individual species were therefore determined by a i values of individual shells calibrated against radiocarbon ages the land snail fauna consists of 40 species all endemic to the island and shows remarkable stability over the span of time covered by the deposit indicating the continuous persistence of forest the much lower epimerization rate for the late pleistocene compared to the holocene indicates much cooler late pleistocene temperatures but this appears to have had little effect on the fauna many species that are presently endemic to restricted regions which include the area of the cave are present throughout the sequence no changes are detected at the last glacial maximum but some changes are seen in the holocene at 3000 4000 yr b p two species disappear from the sequence one lives nearby at present whereas the other presently has a distribution farther to the west the first records of one species in the sequence occurs at this time and for another species at ca 10 000 yr b p no extirpations of species occur at the site following european settlement relatively stable climatic gradients rather than climatic change may be an important cause of the evolution of faunas endemic to different parts of the island

experimental determination of the partitioning of gallium between solid iron metal and synthetic basaltic melt electron and ion microprobe study the distribution of ga between solid fe metal and synthetic basaltic melt has been investigated experimentally at two temperatures over a limited range of oxygen fugacities reversal experiments were conducted indicating a close approach to equilibrium analysis of run products was performed using an electron and an ion microprobe at 1 bar total pressure the solid metal silicate melt partition coefficient d ga is given by 1190 c logd ga 0 92 logfo2 11 91330 c logd ga 0 77 logfo2 8 8 for the common assumption of a valence state for ga of 3 in silicates and assuming ideal solution of ga in both phases a slope of 0 75 is predicted the slope obtained at 1300 c 0 77 is indistinguishable from this value while the slope at 1190 c 0 92 is somewhat higher henry s law is obeyed over the concentration range 0 007 wt to 0 15 wt ga in metal a factor of 20 in concentration these partition coefficients may be utilized to evaluate metal silicate fractionation processes in the earth moon and eucrite parent body the lunar mantle appears to be depleted in ga by a factor of 20 40 relative to ci abundances this depletion is consistent with extraction of ga into a geophysically plausible lunar core if ga was initially present at a subchondritic concentration a similar explanation probably accounts for the depletion of ga in the eucrite parent body the upper mantle of the earth appears to be depleted in ga by a factor of 4 7 relative to ci abundances this depletion is far smaller than would be expected as a result of core formation but is consistent with two quite different hypotheses i a small amount of solid metal and sulfur bearing metallic liquid was retained in the mantle after core formation or ii addition of a late stage chondritic component involving 5 to 10 of the upper mantle following core formation

aminostratigraphic correlation and geochronology of two quaternary loess localities central mississippi valley abstract amino acid epimeric aile ile values from terrestrial molluscs are used to define and correlate three aminozones in loess sequences exposed across the central mississippi valley in arkansas and tennessee three superposed aminozones are defined at wittsburg quarry arkansas primarily using aile ile values from total hydrolysates of the gastropod genus hendersonia peoria loess aile ile 0 07 0 01 roxana silt 0 14 0 02 and a third loess 0 28 0 06 loess units at wittsburg quarry can be correlated on lithologic characteristics eastward across the mississippi valley to the old river section near memphis tennessee however only one loess unit is fossil bearing peoria loess aile ile 0 05 at that section radiocarbon analyses of charcoal from the upper roxana silt ca 26 000 to 29 000 yr old and mollusc shell carbonate from the basal roxana silt ca 39 000 yr old are used to calibrate amino acid epimeric data for the central mississippi valley these data applied to the apparent parabolic kinetic model of r m mitterer and n kriausakul 1989 quaternary science reviews 8 353 357 suggest an illinoian 120 000 yr age for the third loess in the central mississippi valley that is correlative with part of the loveland loess in illinois and iowa

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

beyond 500ka progress and prospects in the upb chronology of speleothems and their application to studies in palaeoclimate human evolution biodiversity and tectonics abstract this review summarises current research aimed at extending the chronology and thus scientific utility of speleothems beyond the 500 ka limit previously imposed by conventional u th dating methods the u pb decay scheme is familiar to all geoscientists but its application to speleothems is a relatively recent development and one set to revolutionise their use in studies of climate change human evolution and migration biodiversity tectonics and landscape evolution technological advances such as the introduction of multi collector icpms instruments have played a key role in this breakthrough and multiple inter laboratory and inter method comparisons provide evidence that the methodology is now mature and that the ages obtained are robust some impediments remain in particular with respect to corrections for initial isotopic disequilibrium younger samples and the construction of internal chronologies older samples but these are areas of intense research activity and are likely to see significant advances in the near future the coupling of speleothem u pb dating with other nascent technologies offering the prospect of precise palaeotemperature estimation is an exciting development in palaeoclimate science while u pb chronologies of archaeological sites are producing important new insights into human evolution although less well developed at this point the methodology appears equally well suited and significant for future studies of past faunal change and landscape evolution

origin and evolution of the ureilite parent magmas multi stage igneous activity on a large parent body analyses of olivine and pigeonite cores interpreted as cumulate crystals in eight low shock ureilites show well defined correlations between fe x where x is one of the minor elements mn cr ca al ti p or ni and fe mg ratios for the lithophile minor elements these trends are linear with positive slope and pass through or near the origin indicating various degrees of feo reduction of the parent magmas the trends shown by p and ni are consistent with this interpretation and additionally require equilibrium crystallization of 20 27 mole metal graphite was most likely the reducing agent which implies that the ureilites equilibrated at different pressures because the graphite fo2 buffer is pressure dependent there is no evidence for fractionation of olivine or pryroxene in any of these trends the ca ti and al trends show significant scatter indicating that there must have been multiple parent magmas with very similar mg mn and mgcr ratios but different mgal mgca and mgti ratios cao al2o3 ratios vary by a factor of 3 among the eight magmas and are superchondritic 14 32 molar similar to lunar mare basalts we propose the following model for generation and crystallization of ureilite parent magmas upm chondritic material undergoes 10 25 partial melting leaving a plagioclase depleted residue the magma or magmas form a differentiated crust on the ureilite parent body upb with mafic cumulates and plagioclase cumulates spatially separated later remelting 10 of the mafic cumulates produced the upm siderophile elements indicate that the source region of the upm had not experienced segregation of metal such as would occur during core formation in the source region the pressure must have been at least 0 5 1 kb because only at pressures this high does the graphite buffer allow iron oxide to be the stable phase relative to metallic iron the graphite bearing upm were emplaced at various levels in the crust where they were reduced to various extents dependent on depth ureilites are early olivine pigeonite cumulates from these magmas compositions of interstitial low ca pyroxenes indicate that the trapped interstitial liquids from which they crystallized had lower mnmg crmg camg almg and namg ratios than the upm and indicate an abrupt change in liquid composition coincident with impact excavation of ureilites this interstitial material may be derived by mixing a shock melt of nearby olivine pigeonite cumulates with residual primary liquid our model predicts that the upb had a differentiated crust did not have a core and was at least 235 km in radius the lack of a ureilite like body among spectrally analyzed asteroids suggests that either the spectral signature of the upb is not that of ureilites themselves perhaps of carbon free feldspathic material instead that the upb is not intact or that ureilites did not originate in the asteroid belt

the constitution and structure of the lunar interior the current state of understanding of the lunar interior is the sum of nearly four decades of work and a range of exploration programs spanning that same time period missions of the 1960s including the rangers surveyors and lunar orbiters as well as earth based telescopic studies laid the groundwork for the apollo program and provided a basic understanding of the surface its stratigraphy and chronology through a combination of remote sensing surface exploration and sample return the apollo missions provided a general picture of the lunar interior and spawned the concept of the lunar magma ocean in particular the discovery of anorthite clasts in the returned samples led to the view that a large portion of the moon was initially molten and that crystallization of this magma ocean gave rise to mafic cumulates that make up the mantle and plagioclase flotation cumulates that make up the crust smith et al 1970 wood et al 1970 this model is now generally accepted and is the framework that unifies our knowledge of the structure and composition of the moon the intention of this chapter is to review the major advances that have been made over the past decade regarding the constitution of the moon s interior much of this new knowledge is a direct result of data acquired from the successful clementine and lunar prospector missions as well as the analysis of new lunar meteorites as will be seen results from these studies have led to many fundamental amendments to the magma ocean model much of what we know from sample analyses has been previously summarized elsewhere and only their most important aspects will be discussed in this chapter the reader is referred to the relevant chapters in the books basaltic volcanism on the terrestrial planets basaltic volcanism study project 1981 the

molybdenum in eucrites evidence for a metal core in the eucrite parent body molybdenum concentrations from 15 to 70 ppb in eucrites have been determined with a new method of neutron activation these values are very low compared to chondrites and are in agreement with the large depletions of other siderophile elements in eucrites the eucrites have a mean mo la ratio of 0 0066 which is a factor of 570 lower than the ci chondritic ratio 3 75 the depletions of siderophiles in eucrites were presumably caused by segregation of metal molybdenum however is fractionated as an incompatible element similar to la among the individual eucrites the variable concentrations but roughly constant ratio of mo to la indicate that metal was absent during the fractionation that produced the eucrites and imply that core formation occurred before the fractionation the need for a relatively large degree of partial melting to completely segregate metal argues for a fractional crystallization model for the production of the eucrite magmas the amount of metal in the eucrite parent body epb required to obtain the observed depletion of the mo la ratio depends on the degree of partial melting during metal silicate equilibrium the depletion of co has a dependence on the degree of partial melting different from mo and w and using co together with mo and w the metal content and degree of partial melting can be estimated a metal content of 30 to 50 and metal segregation at approximately 50 partial melting of the silicates is consistent with the data if the epb had a ratio of co to refractory lithophile elements less than ci chondrites a metal content as low as 20 with metal segregation at 20 partial melting is possible a large metal core in the epb vesta may therefore be detectable from a spacecraft

structural control on karst water circulation and speleogenesis in a lithological contact zone the bossea cave system western alps italy abstract geological surveys structural mapping and thin section analysis helped to unravel the speleogenesis and water circulation in the bossea cave northern italy an unconventional karst system at the contact between carbonates and underlying insoluble rocks the surveys within the cave and in the surrounding surface outcrops revealed a complex structural setting caused by the coupling of lithological mechanical heterogeneities with two major regional left lateral ese wnw strike slip faults transpression associated with the faults led to a disharmonic deformation accommodated by a detachment surface between the buckled basement meta volcanics and the disharmonically folded marble sequence laying on top low angle shear zones recumbent or drag folds and small stacks of duplexes are localized next to this detachment the preferential pathways for water circulation inside the vadose zone are the folded bedding interfaces in the meta carbonate sequence fracture clusters at slipping bed terminations on the other hand provide through sequence connectivity once underground stream water flow reached the cataclastic and highly deformed meta volcanics of the detachment core and damage zones erosion started removing large volumes of rocks the downward erosion of the permian basement rocks caused gravitational instability and subsequent roof collapses aided by structural control in the damage zone above the detachment surface slip surfaces in between duplexes or drag folds this gravitational instability ultimately led to the formation of the giant halls that are characteristic of the downstream part of the bossea cave

analysis of the seismic origin of landslides examples from the new madrid seismic zone by analyzing two landslides in the new madrid seismic zone we develop an approach for judging if a landslide or group of landslides of unknown origin was more likely to have formed as a result of earthquake shaking or in aseismic conditions the two landslides analyzed are representative of two groups of land slides that previous research on the geomorphology and regional distribution of landslides in this region indicates may have been triggered by the 1811 1812 new madrid earthquakes slope stability models of aseismic conditions show that neither landslide is likely to have formed aseismically even in unrealistically high ground water conditions dynamic stability analysis using newmark s method shows that both slides probably would have experienced large inertial displacements during earthquake shaking similar to that which occurred in 1811 1812 these displacements are large enough that catastrophic failure is highly probable thus the stability analyses are consistent with other lines of evidence that these landslides formed as a result of strong earthquake shaking during the 1811 1812 earthquakes our analysis yields a general relationship between newmark landslide displacement earthquake shaking intensity and the critical acceleration of a landslide using this relationship we estimate the minimum shaking intensities required to trigger the types of landslides studied an mb 5 8 or m 5 9 earthquake is the lower bound threshold at zero epicentral distance that could trigger catastrophic movement of typical block slides in the new madrid seismic zone for earth flows mb 5 4 or m 5 3 is the threshold earthquake

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

a model composition of the basaltic achondrite planetoid the basaltic achondrites eucrites diogenites and howardites have compositions on a common oxygen isotope mass fractionation line and probably formed from a chondritic precursor also lying on that same line no chondritic meteorite group has the same isotopic signature as the basaltic achondrites so the oxygen isotope ratios of several known chondritic groups were used to construct a two component mixing model for the composition of the precursor this model does not provide a unique solution as several mixtures of ordinary and carbonaceous precursors will satisfy the isotopic constraints the fe mn mg abundances of the precursors and of the eucrites were used to provide an additional constraint the precursor composition selected for study is a mixture of 70 wt h chondrite with 30 wt cm chondrtte this mixture generates a slightly feo rich silicate precursor that after reduction and separation of an iron sulfide core is compatible with the mantle of the basaltic achondrite planetoid bap having a similar composition to that modeled by dreibus and wanke 1980 partial melting experiments of this h cm precursor composition suggest that eucritic magmas could be formed in such a mantle these experiments also suggest that the mantle must have experienced metal loss to constrain the fe mn ratios and probably significant olivine fractionation as well diogenite precursors may also be generated in this mantle composition as feo reduction and olivine fractionation lead to the formation of sio2 enriched compositions from which diogenite source magmas may be extracted if mixing of material from two very distinct chondritic reservoirs h and cm chondrites is realistic then an asteroid scale mixing process is needed to generate the achondrite precursor large impact events would provide a plausible method for mixing material from reservoirs with quite different oxygen isotope characteristics to assemble the basaltic achondrite planetoid

aminostratigraphic relations and age of quaternary deposits northern espanola basin new mexico abstract amino acid ratios of gastropods provide a useful basis for correlation and approximate dating of middle to late quaternary fluvial deposits from the northern espanola basin new mexico sparsely fossiliferous slackwater deposits in the rio chama rio grande floodplain were buried episodically by piedmont alluvium during periods of climatic change as the axial river system cut down 120 m during the past 620 000 yr alloisoleucine isoleucine alle ile ratios in the total hydrolysate and free fraction of amino acids in succinea and vallonia are strongly correlated with elevation ratios in succinea range from 0 01 to 0 79 in the total hydrolysate and from 0 00 to 1 15 in the free fraction for deposits that range in age from modern to 620 000 yr old amino acid ratios are tightly clustered for deposits that contain the 620 000 yr old lava creek b tephra layer demonstrating their utility for correlation and providing a calibration point for a local dating curve two 14c ages from younger deposits and limiting ages for erosion surfaces that lie above gastropod bearing units tend to support the validity of much of the curve combining the dating curve with the geologic constraints suggests that aggradation events separated by episodes of net incision occurred at about 620 000 310 000 70 000 170 000 40 000 95 000 15 000 yr ago after 19 000 yr ago and during two minor periods between 80 000 and 25 000 yr ago

quaternary paleoecology of the lower mississippi valley copyright c 1996 elsevier science b v all rights reserved in 1938 clair a brown published his classic paleobotanical discoveries from the tunica hills of southeastern louisiana indicating ice age plant migrations of more than 1100km brown collected fossils of both boreal trees such as white spruce picea glaucar and southern coastal plain plants from deposits mapped as the port hickey prairier river terrace by harold n fisk subsequent revisions of terrace mapping radiocarbon dating and paleoecological analysis reconciled browns conceptual and stratigraphic mixingr of these two ecologically incompatible fossil plant groups an older terrace 2 of sangamonian to altonian ager contains the warm temperate assemblage a younger terrace 1 of farmdalian woodfordian and holocene ager includes full glacial and late glacial remains of both boreal and cool temperate plants and a warm temperate suite of plants dates from the holocene interglacial new plant fossil localities with radiocarbon chronologies are now available from within the lower mississippi valley of missouri and arkansas as well as from the adjacent ozark plateaus the interior low plateaus of kentucky and tennessee and the bordering blufflands of tennessee mississippi and louisiana these studies demonstrate that glacial and interglacial patterns of vegetation have been influenced by regional changes in climate glacial runoff and regime of the mississippi river

a multi proxy palaeoecological and palaeoclimatic record within full glacial lacustrine deposits western tennessee usa the fulton section along the mississippi river in western tennessee usa is a 1 km continuous exposure 20 m vertically of quaternary fluvial and lacustrine deposits inset within eocene sediments and buried by thick loess fossiliferous slackwater lake sediments record maximum aggradation during the last two major glaciations with deposition between ca 190 140 ka and q1 24 18 14 c ka bp based on amino acid and radiocarbon chronology respectively during the onset of full glacial conditions ca 24 22 14 c ka bp a relatively permanent shallow lake environment is indicated by ostracodes aquatic molluscs and both pollen and macrofossils of aquatic plants by 21 8 14 c ka bp increasing emergent plants amphibious gastropods pomatiopsis and heavier d 18 o compositions suggest marsh like conditions in a periodically drying lake the surrounding uplands consisted of picea pinus woodlands mixed with cool temperate hardwoods e g quercus populus carya grasses and herbs more open conditions ensued ca 20 14 c ka bp with loess and slopewash gradually infilling the former lake by 18 14 c ka bp modern analogue analyses of ostracodes and palaeontological evidence imply a full glacial climate similar to today s mixed boreal zone in central minnesota usa about 98c cooler in mean annual temperature than present day western tennessee copyright 2009 john wiley sons ltd

an updated global review of solutional weathering processes and forms in quartz sandstones and quartzites abstract quartz is considered one of the less soluble minerals of the earth s crust and thus hardly affected by chemical weathering despite this for more than forty years it is clear that the formation of caves and peculiar solutional weathering dominated landforms in quartz rich lithologies is common and shares several similarities to the well known karstic ones in carbonate rocks in the last thirty years great strides have been made in furthering our knowledge of the distribution of these forms around the world and the geochemical processes involved these studies have clearly shown that solutional weathering is a fundamental process acting through intergranular dissolution of quartz increasing the rock porosity and decreasing the rock strength to erosion this process has been described in the concepts of arenization and phantomization and the widespread evidences of the fundamental role of quartz solution in landform genesis has even developed to the extent of several geomorphologists reassessing the definition of the term karst and its application to these peculiar lithologies nonetheless the process is complicated by several factors related both to environmental conditions water chemistry and availability as well as to the compositional and textural characters of the lithology presence of clays iron hydroxides carbonate cement etc all these aspects have to be taken carefully in consideration in order to understand if solution is a dominant or accessory process in the landscape evolution in this review the state of knowledge on the relevant chemical processes weathering mechanisms and speleogenesisk involved in the surface and underground karstification and clear examples of quartz solution and solutional landforms from different world locations are outlined and discussed

sulfuric acid speleogenesis in the majella massif abruzzo central apennines italy abstract many active and inactive hypogene sulfuric acid cave systems are known along the apennines italy the cavallone bove cave system is located in the external part of the central apennine chain in the majella massif and opens at 1470 m asl along the taranta gorge south of chieti the presence in these caves of peculiar geomorphological features such as feeders rising channels megacusps cupolas and replacement pockets offers evidence of rising acidic fluids the secondary mineral deposits including meter size white gypsum deposits alunite jarosite black layers of iron manganese oxides and hydroxides along with a rare association of authigenic rutile ilmenite minerals indicate a sulfuric acid origin stable isotope analyses of sulfates further confirm a sulfuric acid speleogenetic sas origin of these minerals and in general of the whole cave system with h2s coming from the bacterial sulfate reduction of deep seated triassic evaporites interacting with hydrocarbons alunite dating demonstrates this water table sas cave to have been active at least until 1 52 0 28 ma all the evidence suggests that cavallone bove is an ancient sulfuric acid karst system that was uplifted

timing and mechanism of the rise of the shillong plateau in the himalayan foreland island arcs provide insights into the origin and recycling of continental crust but questions remain concerning source metasomatism the depth of differentiation the potential role of amphibole fractionation and the time scales involved basaltic andesites on batan island philippines contain 150 ma peridotite fragments encased in hornblendite and gabbroic rinds produced via melt rock reaction the peridotites have some of the lightest 7li and 57fe values yet measured in mantle rocks these values are too fractionated to have been created solely by equilibrium partial melting and thus require a combination of melt depletion and slab fluid addition and may be derived from diffusion modified melt channel wall rocks stable isotope signals are easily modified by diffusive equilibration between peridotite and host magma so the preservation of light 7li and 57fe here suggests magma ascent rates of 10 km yr 1 we show that melt wall rock reactions at 25 30 km depth led to the crystallization of amphibole plagioclase followed by gabbroic fractionation at 7 km depth the former provides a location and mechanism for the cryptic amphibole fractionation observed in these and perhaps many other arc lavas and may obviate the requirement for delamination of cumulates

early palaeogene in the south shillong plateau ne india local biostratigraphic signals of global tectonic and oceanic changes abstract the early palaeogene in the history of the earth is noted for large scale plate reorganisation believed to be associated with a changeover from the laramide tectonic regime old crustal configuration to the himalayan tectonic regime new crustal configuration this tectonic change possibly proved to be a turning point in the evolution of lithosphere and ushered in drastic changes in the physical environment and evolutionary course of biosphere in the cenozoic the consequent changes in the sedimentary environment and biotic development during early palaeogene have been pointed out for the indian ocean region this paper examines the biostratigraphic data of the early palaeogene late palaeocene middle eocene succession of the south shillong plateau in the light of climatic and oceanic changes and explores the possible role the regional tectonic changes may have played in shaping the course of environmental and biotic development preserved in the rock record of the sylhet limestone group an attempt has also been made to propose a model to explain the underlying tectonic changes in the shillong plateau the biostratigraphic data from the area of investigation indicate that the major stratigraphic sequences recognised in the sylhet limestone group can be broadly correlated with the stratigraphic succession of the early palaeogene identified in the indian ocean region the succession of the sedimentary facies in this region seems to be the result of sea level and climatic changes controlled by major tectonic reshuffling from this correlation it appears that the litho and biostratigraphic markers of the sylhet limestone were created by sea level and climatic events related to tectonic changes occurring in the adjoining indo burmese orogen as part of the large scale global plate reorganisation mentioned as above

structural control on epigenic gypsum caves evidences from messinian evaporites northern apennines italy abstract we documented the relations among fractures bedding geological structures and the development of epigenic gypsum caves in the bologna sector of the northern apennines italy different methods such as surface and subsurface surveys aerial photo interpretation structural analyses and hydrogeological observations were integrated to unravel different types of structurally controlled epigenic gypsum karst speleogenesis data collected highlight a close relationship between the main directions of caves development and structural trends in the northern apennines nw se and ne sw the results show that large offset faults 10 m bedding interfaces and anticline axes control the development of underground drainage basins and compartmentalize flow among adjacent areas furthermore collapse hall morphology is mostly controlled by high angle joints bedding and splay joints associated with bedding plane parallel faults while the main structural weaknesses focus the surface flow leading to a concentrated pattern of underground drainage and the formation of dominant conduits

plateau pop up in the great 1897 assam earthquake the great assam earthquake of 12 june 1897 reduced to rubble all masonry buildings within a region of northeastern india roughly the size of england and was felt over an area exceeding that of the great 1755 lisbon earthquake1 hitherto it was believed that rupture occurred on a north dipping himalayan thrust fault propagating south of bhutan2 3 4 5 but here we show that the northern edge of the shillong plateau rose violently by at least 11 m during the assam earthquake and that this was due to the rupture of a buried reverse fault approximately 110 km in length and dipping steeply away from the himalaya the stress drop implied by the rupture geometry and the prodigious fault slip of 18 7 m explains epicentral accelerations observed to exceed 1g vertically and surface velocities exceeding 3 m s 1 ref 1 this quantitative observation of active deformation of a pop up structure confirms that faults bounding such structures can penetrate the whole crust plateau uplift in the past 2 5 million years has caused the indian plate to contract locally by 4 2 mm yr 1 reducing seismic risk in bhutan but increasing the risk in northern bangladesh

constraints on the moon s origin from the partitioning behaviour of tungsten the moon earth and eucritic meteorites display w la ratios which correspond to depletions of w relative to chondrites by factors of 19 ref 1 this depletion can be attributed to metal silicate fractionation ordinary chondrites and cl chondrites with widely varying metal contents and oxidation states have similar w la ratios suggesting that nebular fractionations were unimportant therefore assuming that both w and la are refractory and incompatible the depletions of w relative to la in the earth moon and eucrites are presumably due to separation of metal from silicate during planetary scale igneous events for the moon rammensee and wanke2 concluded that any geophysically reasonable metallic lunar core would be too small to explain the large lunar depletion of w it was therefore suggested2 that the moon acquired its depletion of w in a non lunar igneous event supporting the hypothesis that the moon formed by fission from the proto earth the upper portion of which was depleted in w due to terrestrial core formation3 5 we show here that this conclusion is implicity based on a special case namely equilibrium between metal and silicate phases with total melting of silicates in the geologically more general case where metal fractionates from silicate at relatively low degrees of partial melting the incompatible nature of w may negate this conclusion a geophysically plausible metallic core can account for the depletion of w in lunar surface and presumably lunar mantle rocks the low w la ratio in the moon cannot be used as unconditional evidence for a terrestrial origin of the moon

the polymict eucrites the polymict eucrites are a suite of about 14 polymict achondritic meteorites that contain at least 90 vol of eucritic material and are found both in antarctica and elsewhere they are part of a continuum of polymict breccias that includes howardites and polymict diogenites rare gas data suggest that some are gas rich regolith breccias the clasts contained in polymict eucrites sample a variety of lithologies from their parent body and include eucritic clasts alkali enriched eucrites pyroxene cumulate eucrites two pyroxene mafic rocks possibly feldspar cumulate eucrites diogenites fayalitic lithologies and a variety of other mineral clasts the eucritic clasts are probably samples of near surface lithologies on the parent body but the presence of two pyroxene mafic rocks is considered to be evidence of magmatic activity at pressures in excess of 1 kbar in the parent body partial melt models may explain some of the diversity among the clasts but cumulus processes are believed to have been important if pressures greater than 1 kbar are confirmed then the basaltic achondrite parent body bap must have a diameter in excess of 200 km the variety of lithologies suggests that not all basaltic achondrites are samples of igneous rocks formed by single stage melting of a chondritic asteroid but are instead samples of an evolved and diverse crust produced by serial magmatism

mare glasses from apollo 17 constraints on the moon s bulk composition two previously unreported varieties of mare volcanic glass have been discovered in apollo 17 samples twenty three chemical types of volcanic glass have now been analyzed from the six apollo landing sites these volcanic glasses which may be samples of primary magmas derived from the differentiated lunar mantle define two linear arrays that seem to reflect regional if not global regularities among the source regions of these melts additional systematics among these glasses have been used to estimate the bulk composition of the moon the results suggest that the refractory lithophile elements e g ca al ti ree u are present at abundances of 1 7 chondrites the silicate portion of the moon appears to have a major element composition similar to a volatile si na k depleted earth s upper mantle the theory involving an earth fission origin of the moon can be tested further through trace element analyses e g ni on the volcanic glasses and through determination of the n 36ar ratio and noble gas isotopes from primordial lunar gas trapped within vesicles associated with mare volcanic glass

differences between the last two glacial maxima and implications for ice sheet δ18o and sea level reconstructions studies of past glacial cycles yield critical information about climate and sea level ice volume variability including the sensitivity of climate to radiative change and impacts of crustal rebound on sea level reconstructions for past interglacials here we identify significant differences between the last and penultimate glacial maxima lgm and pgm in terms of global volume and distribution of land ice despite similar temperatures and radiative forcing our analysis challenges conventional views of relationships between global ice volume sea level seawater oxygen isotope values and deep sea temperature and supports the potential presence of large floating arctic ice shelves during the pgm the existence of different glacial modes calls for focussed research on the complex processes behind ice age development we present a glacioisostatic assessment to demonstrate how a different pgm ice sheet configuration might affect sea level estimates for the last interglacial results suggest that this may alter existing last interglacial sea level estimates which often use an lgm like ice configuration by several metres likely upward

pre late wisconsinan pleistocene biota from southeastern michigan u s a abstract fossiliferous sediments underlie the late wisconsinan mill creek and fisher road tills at the mill creek site northwest of port huron michigan fragmentary remains of 5 fish and 11 mammal taxa occur with 39 taxa of molluscs 6 of ostracodes and a pine spruce pollen assemblage while the fish are wide ranging the mammals include distinctly northern elements such as dicrostonyx sp lemmus sp mictomys borealis and microtus xanthognathus the molluscs include a mixture of cold vertigo alpestris oughtoni and v modesta and warm lioplax sulculosa taxa none of the vertebrates have been found at michigan sub till sites before and lioplax is new to michigan fossil or living vertigo hannai is known only as a pleistocene fossil at present the age of the biota is indeterminate the stratigraphy indicates a middle wisconsinan or greater age a finite 14c age of 48 3 0 8 ka ql 1215 was later supplemented by a tl date of 57 9 ka but perhaps as old as 300 ka two clusters of amino acid allo isoleucine isoleucine values obtained from six genera of molluscs are interpreted to represent the co occurrence of early sangamonian aile ile values ranging from approximately 0 15 to 0 25 and illinoian aile ile values ranging from approximately 0 25 to 0 35 mollusc fossils at the mill creek site these results highlight the need for more reliable quaternary dating methods

amino acid geochronology resolution and precision in carbonate fossils changes in indigenous proteins preserved in carbonate skeletons can be used to estimate the time elapsed since death of the organism racemization the most widely used reaction in amino acid geochronology refers to the inversion of l amino acids to their d configuration for the protein amino acid l isoleucine racemization occurs about only one of the two chiral carbon atoms this reaction epimerization proceeds from an initial dl ratio near zero to an equilibrium ratio of about 1 30 the reaction rate is controlled primarily by temperature and to a lesser degree by the nature of the proteins themselves a variable related to taxonomy and the extent of protein degradation analyzing monospecific samples minimizes the taxonomic variable the resolving power of dl ratios as relative age indices is a function of the reaction rate degree of natural variability and analytical uncertainty natural variability is defined as the spread in ratios in five well preserved shells of the same age from a single stratum and is primarily related to taxonomy it can range from 20 or more in taxa of low reliability to 1 in taxa of greatest integrity 5 to 10 is to be expected analytical uncertainty within a single laboratory is relatively insignificant amounting to no more than 2 but interlaboratory comparisons suggest caution in comparing ratios determined at different laboratories or by different techniques sampling appropriate portions of a shell is essential to minimize variability in dl ratios site temperature exerts the greatest control on reaction rate hence resolving power for tropical sites 25 c age differences 1 ka can be resolved within the holocene and ca 5 to 10 ka for older samples as the rate decreases equilibrium is attained after 150 to 300 ka the reaction rate is substantially lower at mid latitude sites ca 10 c where equilibrium requires about 2 ma and resolution within the last glacial cycle is no better than 10 to 20 ka arctic sites 10 c show almost no measurable racemization within the holocene and in extreme cases even within the last 100 ka equilibrium is not attained in 10 ma the extent of amino acid racemization epimerization in carbonate fossils provides chronological information for the critical time period beyond radiocarbon dating dl ratios can be used directly as relative age indices and with suitable calibration can provide reasonable estimates of absolute age and or effective diagenetic temperature improving the accuracy of racemization based age estimates requires a better understanding of racemization kinetics in carbonate systems

development of a deep karst system within a transpressional structure of the dolomites in north east italy abstract the piani eterni karst system is one of the longest and deepest caves of italy situated in the southern sector of the dolomiti mountain range the area where the cave was formed displays peculiar structural settings confined in a tectonic transpressive corridor between two regional thrusts belluno and valsugana during miocene uplift of the range the inheritance of mesozoic structures led to the formation of a deep and wide upward branching flower or palm tree structure cutting the carbonate sequence and exposing the surrounding surface to karst processes after erosion the relative lowering of the hydrologic base level due both to the uplift of the area and then to the carving of deep glacial valleys in the quaternary allowed the formation of paleo phreatic conduits at subsequently deeper levels interconnected by vadose shafts and canyons this work gives a detailed tectonic interpretation of the transpressive structure and picks out the tectonic features most favorable to the karst development a detailed statistical analysis of the distribution and orientation of the karst conduits was performed using 31 km of 3d surveys showing that the development of the cave was strictly guided by a few favorable surfaces of stratigraphic and tectonic origin these features are known in the literature as inception horizons and tectonic inception features respectively cave levels are usually related to lithologic favorable conditions associated with standings of the paleo water table here we suggest that some tectonic surface geometries could have led to the opening of voids in the active tectonic phase leading to the formation of the original proto conduit network different types of tectonic inception features identified in the cave were described in terms of geometry and kinematics tensional fractures as well as fault plane undulations and flexural slip surfaces between beds are described as the most favorable tectonic surfaces for the development of the conduits finally we discuss why transpressional settings and related flower structures in soluble rocks can enhance the karst process allowing the formation of huge and deep karst systems

lithological control on the geomorphic evolution of the shillong plateau in northeast india abstract the shillong plateau in northeast india is a block of raised topography in the himalayan foreland which consists of crystalline basement rocks partially covered by a cretaceous to miocene sedimentary succession it is dominated by a mature low relief landscape surrounded by high relief fluvially dissected margins particularly along its southern flank which is bounded by the dauki thrust fault we use river profiles and geological relationships to show that the low relief plateau is a topographic expression of a re exposed basement palaeosurface following the stripping of sedimentary cover by scarp retreat we show that initiation of the wave of incision does not require surface rupture on the dauki fault or an increase in fault slip rate at the end of the miocene as suggested by previous studies we propose that incision has been spatially controlled by the slope of the basement palaeosurface likely moderated by an incision threshold river profiles in the shillong plateau cannot be interpreted as simple records of surface uplift the observed heterogeneous spatial pattern of steepness is a function of a dynamic landscape response to the erosion of layered lithology with contrasting erodibility such dynamics have implications for fluvial geomorphology highlighting that near horizontal lithological contacts can strongly influence river profiles and topography even when no longer physically preserved the topography of the northern shillong plateau is controlled by the structure of basement rocks and is reminiscent of stable cratonic interior landscapes consistent with its surface exposure during late cretaceous times

tungsten isotopic evolution during late stage accretion constraints on earth moon equilibration abstract we couple the results of n body simulations of late stage accretion o brien et al 2006 to a hafnium tungsten hf w isotopic evolution code to investigate the evolution of planetary bodies in the inner solar system simulations can simultaneously produce planets having earth and mars like masses and hf w systematics by assuming that the tungsten partition coefficient decreases with increasing semi major axis e g due to increasing oxidation simulations assuming that jupiter and saturn occupy circular orbits are more successful at reproducing the hf w systematics than those assuming present day jupiter and saturn orbits to generate earth like tungsten anomalies 30 80 of each impactor core is required to re equilibrate with the target mantle some model outcomes yield a target and final impactor having similar earth and moon like tungsten anomalies however in no case can the inferred lunar hf w ratio be simultaneously matched this result suggests that the moon isotopically equilibrated with the earth s mantle in the aftermath of the giant impact cf pahlevan and stevenson 2007 alternatively either the dynamical models which show the moon being derived primarily from the impactor mantle or the accretion timescales obtained by the n body simulations are incorrect

suggested terminology for quaternary dating methods abstract classification of quaternary dating methods should be based on the level of quantitative information and the degree of confidence contained in the age estimates produced by the dating methods we recommend the use of the terms numerical age calibrated age relative age and correlated age to describe these levels we also classify dating methods by type into sideral isotopic radiogenic chemical and biological geomorphic and correlation methods the use of absolute is inappropriate for most dating methods and should be replaced by numerical the use of date should be minimized in favor of age or age estimate we recommend use of the abbreviations ka and ma for most ages calender dates can be used where appropriate and yr b p can be used for radiocarbon ages

phosphoran pyroxene and olivine in silicate inclusions in natural iron carbon alloy disko island greenland a survey of literature data on the p contents of olivine pyroxene and garnet in mantle xenoliths and the bulk p contents of mantle xenoliths shows that available data is ambiguous as to whether mantle p is primarily contained in silicates or in phosphates even though phosphates are rarely observed in mantle xenoliths garnet probably contains more of the mantle s p than olivine or pyroxene bulk p contents of mantle xenoliths vary significantly estimation of the primitive mantle p content from xenoliths requires interpretation of the partial melting and contamination histories of the xenoliths

geochemical constraints on the origin of the moon abstract hypotheses for the origin of the moon involve variants on capture double planet and fission processes double planet and fission hypotheses are examined in the light of siderophile trace elements the siderophile trace elements chosen w re mo p ga ge have well understood geochemical behavior such that appropriate metal silicate partition coefficients are available and their abundances in the lunar and terrestrial mantles 4 4 4 5 109 years ago may be reasonably inferred the fission hypothesis of ringwood 1979 is not consistent with the behavior of re mo and p the hybrid fission hypothesis of wanke et al 1983 overcomes many of the deficiencies of ringwood s hypothesis but is not readily reconcilable with the behavior of re and ir the double planet hypothesis as most recently advanced by newsom and drake 1982 1983 appears to be consistent with siderophile element behavior in the moon

age and origin of the moon the age and origin of the moon have been studied with the use of the recently developed short lived hafnium tungsten chronometer 182hf 182w half life of nine million years the tungsten isotopic compositions of 21 lunar samples range from chondritic to slightly radiogenic w 0 50 0 60 to 6 75 0 42 this heterogeneity may have been inherited from material excavated from earth and the putative impactor but it is more likely the result of late radioactive decay within the moon itself in this case the moon formed 4 52 to 4 50 billion years ago and its mantle has since remained poorly mixed

geochemistry of surface and subsurface waters in quartz sandstones significance for the geomorphic evolution of tepui table mountains gran sabana venezuela summary in situ measurements of discharge ph electric conductivity ec temperature and sio2 content have been carried out during five expeditions in the last 20 years on the summit plateaus inside caves and along the rivers of the surrounding lowlands of three tepui massifs in venezuela auyan roraima and chimanta additionally detailed chemical analyses were performed on waters sampled in a newly discovered extensive quartz sandstone cave system on the auyan tepui rock samples of the quartz sandstone bedrock from different locations have been analysed to obtain their chemical composition with a wavelength dispersive x ray fluorescence spectrometer these data show that the majority of silica present in surface and subsurface water comes from dissolution of quartz and only in minor amount from hydrolysis of other silicate minerals probably the presence of a hardened crust of iron hydroxides limits the dissolution of silica on the top surface of tepuis dissolution in the subsurface instead is more significant and causes in the long term the arenisation of the quartz sandstone and its subsequent removal by mechanical erosion on the other hand waters flowing on the arkosic rock outcropping on the lowland below the tepuis obtain their high dissolved silica content mainly from hydrolysis of silicates the morphological evolution of these table mountains appears thus to be controlled mainly by the underground weathering of the quartz sandstone with the opening of deep fractures grietas and the collapse of large underground horizontal cave systems scarp retreat instead seems to be related to the higher weathering rate of the more arkosic formations underlying the quartz sandstones

structural and lithological guidance on speleogenesis in quartz sandstone evidence of the arenisation process a detailed petrographic structural and morphometric investigation of different types of caves carved in the quartz sandstones of the tepui table mountains in venezuela has allowed identification of the main speleogenetic factors guiding cave pattern development and the formation of particular features commonly found in these caves such as funnel shaped pillars pendants and floor bumps samples of fresh and weathered quartz sandstone of the mataui formation roraima supergroup were characterised through wds dispersive x ray chemical analyses picnometer measurements edax analyses sem and thin section microscopy in all the caves two compositionally different strata were identified almost pure quartz sandstones with content of silica over 95 and high primary porosity around 4 and phyllosilicate rich quartz sandstone with contents of aluminium over 10 and low primary porosity lower than 0 5 phyllosilicates are mainly pyrophyllite and kaolinite sem images on weathered samples showed clear evidence of dissolution on quartz grains to different degrees of development depending on the alteration state of the samples grain boundary dissolution increases the rock porosity and gradually releases the quartz grains suggesting that arenisation is a widespread and effective weathering process in these caves the primary porosity and the degree of fracturing of the quartz sandstone beds are the main factors controlling the intensity and distribution of the arenisation process weathering along iron hydroxide or silt layers which represent inception horizons or a strata bounded fracture network predisposes the formation of horizontal caves in specific stratigraphic positions the loose sands produced by arenisation are removed by piping processes gradually creating anastomosing open fracture systems and forming braided mazes geometric networks or main conduit patterns depending on the local lithological and structural guidance on the weathering process this study demonstrates that all the typical morphologies documented in these quartz sandstone caves can be explained as a result of arenisation which is guided by layers with particular petrographic characteristics primary porosity content of phyllosilicates and iron hydroxides and different degrees of fracturing strata bounded fractures or continuous dilational joints

volatile and siderophile element geochemistry of the moon a reappraisal abstract lunar volcanic glasses lvg contain high abundances of many volatile elements as compared to mare basalts whereas the latter were derived from devolatilized source regions in the outer few hundred kilometers of the moon lvg are believed to come from a globally extensive source region at greater depths which is relatively rich in volatile components abundances of volatile elements in lvg and their source regions are reviewed and in many cases found to resemble those in the earth s mantle likewise siderophile element abundances including the highly siderophile elements ir os au and re are similar in the earth s mantle and in the source regions of lvg the close geochemical similarity between the lvg source region i e the lunar lower mantle and the terrestrial mantle constitutes strong evidence that protolunar material was derived primarily from the earth s mantle since highly siderophile elements are believed to have been added to the earth as an oxidised veneer at the end of its accretion and then convectively mixed into the mantle the removal of protolunar material from the earth must have occurred after this late addition which may represent carbonaceous chondritic or cometary material from the outer solar system it is widely believed that the moon was formed by the impact of a giant planetesimal on the protoearth the planetesimal is presumed to have formed in the inner solar system and to have differentiated internally into a mantle and core numerical modelling of the giant impact shows that most of the material now in the moon would have been derived from the mantle of the impactor however this is contradicted by the geochemical evidence provided by lvg which implies that the moon is composed mainly of material derived from the terrestrial mantle a possible answer to this dilemma is provided by the observation that the lvg source region reflects the geochemistry of the late oxidised veneer which accreted on the earth this suggests that protolunar material may have been removed from the earth s mantle by impacts from one or more high velocity 30 km s planetesimals composed mainly of ices and derived from the outer solar system the volatiles from the impacting planetesimals were lost after these collisions the impacts probably ejected material from the earth s mantle as jets of molten matter which was rapidly quenched thereby retaining a large proportion of its terrestrial volatile inventory

genesis of giant sinkholes and caves in the quartz sandstone of sarisarinama tepui venezuela abstract quartz sandstone of the sarisarinama massif in venezuela hosts the world biggest collapse dolines in quartz rich lithologies with volumes up to some millions of cubic meters due to extremely complex logistics required to reach the massif the genesis of these depressions and of the underlying caves has never been studied in detail the lack of field campaigns and extended data has fostered a decade long scientific debate on whether their origin was due to epigenic or hypogenic processes this study integrates petrological structural and hydrochemical observations including analyses of silica concentration ph conductivity of surface and cave waters ec to investigate the speleogenetic processes acting underground petrographic and compositional analyses of the host rock mataui formation show that in the sarisarinama region quartz sandstones are regularly characterized by clay interlayers with significant content of pyrophyllite and kaolinite and minor amount of iron hydroxides compared to surface waters subsurface infiltration along vertical fractures and fault planes show enrichment in silica higher ph and lower ec confirming that chemical weathering is effective underground provoking intergranular silica dissolution along structural discontinuities the weathering of the clay and iron hydroxide interlayers guides the speleogenesis weakening specific stratigraphic levels and causing the collapse and fragmentation of the more resistant quartz sandstone strata the initial void created by piping of the loose sand released by quartz sandstone weathering can migrate upwards by means of roof and wall breakdown this chain of events eventually triggers a collapse at the surface which generates a circular or squared sinkhole the weathering acts mainly along the dominant fracture networks showing a clear guidance by regional tectonics these speleogenetic controls rule out the hypothesis of a hypogenic origin of the simas suggesting a primary role of long term epigenic chemical weathering and mechanical erosion guided by joints weak clay and iron hydroxide interlayers followed by subsequent massive collapses

hypogenic contribution to speleogenesis in a predominant epigenic karst system a case study from the venetian alps italy abstract buso della rana and buso della pisatela are two karstic caves located in north east italy they are part of the same karst system and are developed in the castelgomberto calcarenitic marine sediments which were deposited in a shallow caribbean type sea during the eocene the buso della rana pisatela system developed mostly at the contact between the castelgomberto calcarenite and underlying volcanic rocks the system of caves is 37 km long and has only three entrances two of which are semi artificial the overlying karst plateau is not directly connected to the buso della rana pisatela system and with the exception of one deep abyss exhibits a rather poorly developed karst this is unexpected considering the presence at depth of such a large and long cave gypsum caso 4 2h 2 o has locally been observed on the walls of the buso della pisatela cave energy dispersive x ray spectroscopy eds performed with a scanning electron microscope sem reveals the presence of sulfur bearing minerals within the host rock gypsum was formed by oxidation of these minerals as indicated by negative 34 s values the oxidation of sulfide minerals forms a sulfuric acid solution that dissolves the castelgomberto calcarenite and once it is oversaturated in calcium precipitates as gypsum the lack of well developed karst on top of the plateau and the analyses suggest that the formation mechanisms for the buso della rana pisatela system differ from classical epigenic speleogenesis the pyrite effect has been recognized in other caves and described in literature in our case pyrite is responsible of two hypo speleogenetic processes i the dissolution of a portion of the host rock and ii the enlargement of the karst voids as a consequence of the haloclastic effect

experimental investigation of the partitioning of phosphorus between metal and silicate phases implications for the earth moon and eucrite parent body abstract the solid metal silicate melt partition coefficient for p d p has been determined experimentally at 1190 c and 1300 c the dependence of the partition coefficient on oxygen fugacity has been investigated and is consistent with a valence state of 5 for p in the silicate melt the experimental partition coefficients are given by log d p 1 21 log o 2 15 95 at 1190 c log d p 1 53 log o 2 17 73 at 1300 c the experimentally determined partition coefficients may be used to interpret the low p la ratios of the earth moon and eucrites relative to c1 chondrites the low p la ratios in the eucrites may be explained by partitioning of p into 5 to 25 of a sulfur bearing metallic liquid assuming equilibration and separation of the liquid metal from the silicates at low degrees of partial melting of the silicates the low w la ratios in the eucrites compared to c1 chondrites require the separation of an additional 2 to 10 solid metal the lowering of both p la and w la ratios in the moon may be explained by partitioning of p and w into metal during formation of a small core by separation of liquid metal from silicate at low degrees of partial melting of the silicates the w la ratios in the earth and moon are virtually indistinguishable while p la ratios differ by a factor of two the concentrations of feo also appear to be different these observations are difficult to reconcile with the hypothesis of a terrestrial origin of the moon following formation of the earth s core but are consistent with independent formation of the earth and moon

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

geophysical constraints on lunar bulk composition and structure a reassessment theoretical lunar mantle seismic velocity and density profiles are calculated for a series of proposed bulk compositions present day selenotherms and models for early differentiation and evolution the seismic velocity profiles are compared to the most recent observational model derived from the complete apollo data set to evaluate compositional implications the mantle density profiles are compared to mean density moment of inertia and crustal density thickness constraints to evaluate the need for a metallic core the calculated seismic velocity profiles are in qualitative agreement with the observational model in two general respects 1 a quasicontinuous velocity decrease occurs in the upper mantle due to the large thermal gradients that characterize all three of the considered thermal models 2 a discontinuous velocity increase occurs at the spinel to garnet transition approximately 500 km depth due mainly to the higher garnet velocities as compared to olivine and orthopyroxene in the upper mantle all four of the considered bulk compositions spanning a range of plausible feo and al2o3 contents are allowed when uncertainties in the temperature profile and depth of differentiation are taken into account however in the middle mantle depths 500 km the most aluminous models those with larger garnet abundances consistently produce larger velocity increases that are most nearly in accord with the observational model in general models that assume differentiation of the upper mantle only that are more aluminous in bulk composition and that have strong thermal gradients in the upper mantle but smaller gradients in the middle mantle result in calculated velocity profiles that most nearly agree with the observational velocity model an alternate differentiation model in which the middle mantle is dominated by mgo rich mafic silicates is also in accord with the observational seismic velocity model but results in density decreases that appear to violate stability arguments in every case calculated mantle density increases are insufficient to match the one standard deviation upper limit on the moment of inertia even when the most favorable combinations of allowed crustal thickness and density are assumed agreement with the moment of inertia upper limit is obtained if metallic cores representing 1 4 of the lunar mass are added to the bulk composition such cores are larger than needed to explain the observed depletions of lunar siderophile elements if the moon formed entirely from terrestrial mantle material

evidence of inception horizons in karst conduit networks this paper outlines the conclusion from an analysis of 18 large cave systems around the world comprising more than 1500 km of conduits the 3d geometry of complex cave systems have been analysed in relation to their geological context as well as their hydrogeological boundary conditions the methodology allowed for the first time statistical evidence of the inception horizon concept thereby it confirms that the development of karst conduits under phreatic conditions is strongly related to a restricted number of so called inception horizons an inception horizon is a part of a rock succession that is particularly susceptible to the development of karst conduits because of physical lithological or chemical deviation from the predominant carbonate facies within the limestone sequence it passively or actively favours the localisation of dissolutional voids

coupling erosion and topographic development in the rainiest place on earth reconstructing the shillong plateau uplift history with in situ cosmogenic 10 be abstract the uplift of the shillong plateau in northeast india between the bengal floodplain and the himalaya mountains has had a significant impact on regional precipitation patterns strain partitioning and the path of the brahmaputra river today the plateau receives the highest measured yearly rainfall in the world and is tectonically active having hosted one of the strongest intra plate earthquakes ever recorded despite the unique tectonic and climatic setting of this prominent landscape feature its exhumation and surface uplift history are poorly constrained we collected 14 detrital river sand and 3 bedrock samples from the southern margin of the shillong plateau to measure erosion rates using the terrestrial cosmogenic nuclide 10be the calculated bedrock erosion rates range from 2 0 to 5 6 m my 1 whereas catchment average erosion rates from detrital river sands range from 48 to 214 m my 1 these rates are surprisingly low in the context of steep tectonically active slopes and extreme rainfall moreover the highest among these rates which occur on the low relief plateau surface appear to have been affected by anthropogenic land use change to determine the onset of surface uplift we coupled the catchment averaged erosion rates with topographic analyses of the plateau s southern margin we interpolated an inclined pre incision surface from minimally eroded remnants along the valley interfluves and calculated the eroded volume of the valleys carved beneath the surface the missing volume was then divided by the volume flux derived from the erosion rates to obtain the onset of uplift the results of this calculation ranging from 3 0 to 5 0 ma for individual valleys are in agreement with several lines of stratigraphic evidence from the brahmaputra and bengal basin that constrain the onset of topographic uplift specifically the onset of flexural loading and the transgression from deltaic to marine deposition ultimately our data corroborate the hypothesis that surface uplift was decoupled from the onset of rapid exhumation which occurred several millions of years earlier

speleogenesis of the world s longest cave in hybrid arenites krem puri meghalaya india abstract meghalaya nw india is one of the regions in the world with highest recorded rainfalls because of these peculiar climatic conditions and intense solutional weathering karstic caves are widely reported in the numerous limestone areas of this part of india likewise the extremely high rainfall and the tropical monsoon climate have fostered the formation of several caves in silicate rich lithologies the most important of these caves is krem puri over 25 5 km long characterized by a fracture controlled labyrinth forming a bi dimensional maze with mostly phreatic morphologies and some recent still active vadose entrenchments a detailed petrographic study of the host rocks has shown this cave to be formed along a set of quartzarenite hybrid arenite and calcarenite layers in a mostly siliciclastic sedimentary succession xrf elemental analysis of the different rock strata guiding the speleogenesis confirms that the early stage of cave development is confined mainly in the calcium carbonate rich layers geochemical analyses carried out on water flowing in the cave drips streams have shown that carbonate dissolution is the dominant chemical weathering process contributing to krem puri water solutes whereas the dissolution of quartz feldspars and clays play only a secondary role in rock weathering the morphology of the cave points to a lithology guided dissolution of the carbonate rich layers and piping of the residual quartz sand in phreatic conditions when the surface river network was not yet evolved and the water table was at the level of or higher than the cave this phreatic speleogenetic phase predates the start of river network entrenchment that started not earlier 5 ma ago and probably accelerated around 3 5 ma which deactivated the karst maze with a low denudation rate of 0 15 mm yr this active phreatic cave level which currently lies beneath a more or less 120 m overburden was originally covered by a sedimentary sequence at least 1 2 km thick after its decoupling from the underground drainage system denudation slowly brought the surface close to the maze system gradually introducing infiltration of vadose waters into the conduits this caused the formation of the vadose entrenchments probably

a new chronology for the age of appalachian erosional surfaces determined by cosmogenic nuclides in cave sediments the relative chronology of landscape evolution across the unglaciated appalachian plateaus of kentucky and tennessee is well documented for more than a century geomorphologists have carefully mapped and correlated upland erosional surfaces inset by wide valley straths and smaller terraces constraining the timing of river incision into the appalachian uplands was difficult in the past due to unsuitable dating methods and poorly preserved surface materials today burial dating using the differential decay of cosmogenic 26al and 10be in clastic cave sediments reveals more than five million years of landscape evolution preserved underground multilevel caves linked hydrologically to the incision history of the cumberland river contain in situ sediments equivalent to fluvial deposits found scattered across the eastern highland rim erosional surface cave sediments correlate with 1 thick lafayette type gravels on the eastern highland rim deposited between c 5 7 and c 3 5 ma 2 initial incision of the cumberland river into the eastern highland rim after c 3 5 ma 3 formation of the parker strath between c 3 5 ma and c 2 0 ma 4 incision into the parker strath at c 2 ma 5 formation of a major terrace between c 2 0 ma and c 1 5 ma 6 shorter cycles of accelerated incision and base level stability beginning at c 1 5 ma and 7 regional aggradation at c 0 85 ma initial incision into the appalachian uplands is interpreted as a response to eustasy at 3 2 3 1 ma incision of the parker strath is interpreted as a response to eustasy at 2 5 2 4 ma a third incision event at c 1 5 ma corresponds with glacial reorganization of the ohio river basin widespread aggradation of cave passages at c 0 85 ma is interpreted as the beginning of intense glacial interglacial cycling associated with global climate change copyright 2006 john wiley sons ltd