review and test of reproducibility of subdecadal resolution palaeoenvironmental reconstructions from microfossil assemblages abstract very high even annual resolution quantitative palaeoenvironmental reconstructions have been generated from microfossil assemblage data using transfer functions evidence of the utility of some of these reconstructions is given by the high correlations between the reconstructions and instrumental records such performance is despite several ecological and taphonomic issues that can become more problematic at subdecadal resolution than at multidecadal resolution this paper explores these timescale dependent issues and tests the reproducibility of the several of published reconstructions it demonstrates that the previously reported exceptionally good performance of several published chironomid based reconstructions is not reproducible

sulfur isotope geochemistry of gypsiferous aridisols from central iran abstract gypsum accumulation is one of the prominent pedogenic processes occurring in many and regions of the world gypsiferous soils occur in large areas of the iranian central plateau the origin of gypsum in the aridisols of central iran and its distribution in different landscapes were studied using sulfur and oxygen isotopic composition of both solid and dissolved sulfates the results strongly support the hypothesis that the area was cut off from the tethys seaway at the end of the mesozoic era and as a result the lower cretaceous sulfate has controlled the s geochemistry of the younger sediments including the soils studied the mean values of 34 s and 18 o of the soil gypsum and of dissolved sulfate match with the average isotopic values of the marine sediments which are the most common soil parent materials the results also confirm that s and o in dissolved so 4 and so 4 in gypsum have not undergone any reduction and re oxidation reactions dissolution and reprecipitation appear to be the possible mechanisms responsible for the observed minimal isotope fractionation both 34 s and 18 o values of the soil gypsum decrease slightly with decreasing elevation in the study area these findings are important for understanding the landform evolution in this arid region

the occurrence and interpretation of carbonate and sulfate minerals in a sequence of vertisols in new caledonia abstract in the tamoa valley on the western coast of new caledonia a vertisol sequence shows a downslope transition from calcimagnesic vertisols containing gypsum aragonite and magnesium calcite derived from flysch colluvium to hypermagnesic vertisols rich in dolomite and magnesite and derived from peridotite and serpentinite alluvium deposited by the tamoa river gypsum magnesium calcite and magnesite were probably formed during the dry period of the last glaciation between 30 000 and 17 000 yr b p magnesite nodules seem to be allochtonous and were formed upstream by the weathering of serpentinite during the more humid period of last flandrian transgression 5000 yr b p floods of the magnesium rich waters of the tamoa river over the alluvial plain brought magnesium to the soils and lead to fluctuations of the water table these conditions favoured the formation of manganese deposits as mangans calcite pseudomorphs after lenticular gypsum crystallization of authigenic barite in calcimagnesic vertisols and dolomite formation in magnesic and hypermagnesic vertisols during the recent period apparently drier aragonite is forming in the lower part of calcimagnesic vertisols

sulfur isotope composition of soils and fertilizers differences between northern and southern hemispheres abstract the sulfur isotope composition 34s of available su lfate was measured for 44 soils developed on volcanic ashes and basaltic terrains in japan hawaii australia new zealand brazil and chile native soil sulfates are a mixture of seaspray 34 s 20 and anthropogenic around 5 on average sulfates the isotopic values are generally higher in areas of the southern hemisphere than in the northern hemisphere such a hemispheric difference is due to differences in the relative contribution of sulfur from marine aerosols and human activity native japanese soil samples collected at the sites more than 16 km inland from the coastal line tend to show lower 34s values 1 7 to 8 9 compared to those from the coastal regions 10 9 to 17 5 dominance of anthropogenic sulfur in the japanese islands apparently existed as early as the early 1950 s application of chemical fertilizers rich in sulfur has modified the sulfur isotope composition of native soils ammonium sulfate and single superphosphate from the current market in japan have relatively low 34s values 4 9 to 10 2 which reflect sulfur sources from crude oils and ore sulfides in contrast sulfur in fertilizers commonly used in new zealand and elemental sulfur in sulfur fortified single superphosphate from australia gave higher 34s values 15 7 to 20 7 extensive application of sulfur in the form of fertilizers as in japan and new zealand affects the sulfur isotope composition of arable soils

tholeiitic aleutian arc plutonism the finger bay pluton adak alaska the earliest representatives in the sequence of tertiary to recent magmatic rocks on adak island in the central aleutians are the finger bay volcanics and associated small shallow level gabbroic intrusives the tholeiitic finger bay pluton gabbro to quartz monzodiorite is among the least altered representatives of this earliest period the field relations mineralogy and geochemistry of the finger bay pluton contrast with the more recent calcalkaline plutons in the arc e g on adak hidden bay pluton 33 m y and on kagalaska kagalaska pluton 15 m y compared with the hidden bay pluton the finger bay pluton is smaller 8 km2 versus 100 km2 has a greater proportion of gabbro 84 versus 5 has a somewhat different mineralogy and has higher whole rock and mafic mineral feo mgo ratios higher k2o and higher concentrations of incompatable elements in rocks of equivalent sio2 particularly for the more siliceous units magmatic amphibole occurs only in the most siliceous units in the finger bay pluton whereas it is common in the calc alkaline plutons except for the size these differences parallel those between tholeiitic and calc alkaline volcanic rocks from the active aleutian volcanic centers textural miner alogical and trace element analyses indicate that mixing of magmas and gabbros generated some of the rocks of intermediate monzodiorite composition in the finger bay pluton most of the differences in magmatic trends between the calc alkaline and tholeiitic plutons are attributed to the physical conditions of magmatic evolution in the crust rather than to differences in initial magmatic types this conclusion rests on the similarity of fractionation independent isotope ratios and trace element ratios in aleutian magmas of all ages in particular compared to magmas of the north pacific ocean basin morb oceanic islands aleutian magmas show excess enrichment of ba k rb and u relative to ree and high 207pb 204pb ratios for a given 206pb 204pb ratio recognition of tholeiitic series plutons in the arc provides direct evidence for magmatic conditions accompanying fractionation and serves to emphasize the diversity of magmatic trends that are found over time and space at convergent plate margins

the volcano tectonic evolution of concepcion nicaragua we describe the evolution of concepcion volcano by integrating regional geology eruptive activity morphology stratigraphy petrology structure and active deformation data this nicaraguan volcano is set close to the back limb of the northwest trending tertiary rivas anticline a regional structure that bounds the southwest side of lake nicaragua concepcion rises 1 600 m above a 1 km thick sequence of quaternary lacustrine mud stones there is no record of volcanism in the lake prior to concepcion in addition the only nearby volcano maderas volcano has not deposited material on concepcion because of the trade winds thus concepcion and made ras too can be considered as pristine volcanic environments unaffected by other centres a topographic rise forms an annulus 20 km in diameter around the cone the rise is created by thrust related folds at the western base where the trade winds have accumulated a thick sequence of tephra and by mud diapirs at the eastern base where only lake mudstones are present four magmatic eruptive episodes exist in the stratigraphic record the first begins with primitive low alumina basalt and subsequently evolves to dacitic compositions the following three episodes begin with high alumina basalts and evolve only to silicic andesites the occurrence of the high alumina basalt after the first episode is indicative of crystal fractionation at lower crustal depths the first episode may be associated with a compressive phase of volcano evolution in this phase the edifice load compresses substrata allowing a longer magma residence time and differentiation in a shallow reservoir possibly located at the density contrast between the lake sediments and the tertiary flysch during the next three episodes the weak sediments below the volcano started to rupture and yield under its increasing load beginning a thrusting diapiring phase of volcano evolution because of outward thrusting vertical and horizontal stresses above the chamber were reduced allowing magma to erupt more easily and to reach a lesser degree of evolution if we consider the future evolution of concepcion the differentiation in the shallow reservoir has probably generated a cumulitic complex which eventually will start to deform and spread beginning another this time plutonic spreading phase this phase which may be beginning now could allow less evolved magmas to be erupted again four components influence the phases of volcano evolution 1 the regional geology that is the boundary condition of the environment 2 the substrata rheology that controls deformation 3 the load of the volcanic edifice and 4 the magma which provides the input of mass and energy our model of volcanic evolution suggests that concepcion is a complex geologic environment the volcanic activity tectonics and hazards can only be constrained through a complete knowledge of the many components of this environment

amphibole bearing inclusions from boisa island papua new guinea evaluation of the role of fractional crystallization in an andesitic volcano boisa island is the tip of a quaternary island arc volcano it consists of an older cone made up of porphyritic amphibole free mafic rocks and two younger cumulodomes of hornblende bearing high silica andesite one of the cumulodomes contains coarse grained igneous inclusions consisting of amphibole plagioclase clinopyroxene orthopyroxene olivine and spinel some of these minerals in the andesites themselves have both cognate and xenocrystal components both the anhydrous phenocryst assemblage in the basalts and the amphibple bearing assemblage of the inclusions provide low residuals in least squares linear mixing calculations suggesting that fractionation of either assemblage in the basalts could have given rise to the andesites however this is not supported by the results of rayleigh fractionation calculations for several incompatible elements four possible interpretations are 1 the rayleigh fractionation results are inappropriate and misleading 2 the andesites were formed by crystal f

subduction of the cocos plate in the mid america trench the mid america trench off the pacific coast of southern mexico and central america is the site of northeastward subduction of the cocos oceanic plate under the north america and caribbean plates1 fig 1 in guatemala the north america and caribbean plates are separated by the polochic motagua left lateral strike slip faults fig 1 the trench itself appears to be divided into two distinct sections at its intersection with the tehuantepec ridge to the south the margin of the trench is wide and consists of a well developed shelf basin2 bounded on the east by a huge volcanic cordillera parallel with the trench axis at a distance of 200 km in contrast to the north the margin is narrow and devoid of shelf basin landwards the trans mexican volcanic belt trends oblique to the trench this volcanic chain would be anomalous if it were related to the subduction of the cocos plate off southern mexico in 1979 as part of the international phase of ocean drilling ipod of the deep sea drilling project legs 66 and 67 respectively explored the northern off acapulco mexico and southern off san jose guatemala section of the mid america trench3 6 fig 1 since then short topographical surveys of the trench have been carried out by rv jean charcot8 using the sea beam technique7 we report here that both sets of data together with utmsi multichannel seismic profiles10 11 can be used to reconstruct the processes of subduction along the mid america trench

boron geochemistry of the central american volcanic arc constraints on the genesis of subduction related magmas boron contents were measured in representative quaternary lavas from the central american volcanic arc to evaluate along strike variations in subduction processes despite the significant range in b concentrations 2 37 ppm in the mafic lavas b la ratios vary in a systematic fashion along the arc higher values 1 are typical between guatemala and northern costa rica whereas low values most 0 5 typify central costa rica and western panama b la is highly correlated with 10be 9be r2 0 94 excluding one sample and appears to be a useful indicator of subduction contributions to the magma sources if enrichments of both b and 10be are proportional to the flux of subducted sediment along strike variations in b la suggest at least a twofold variation in this flux with maximum values below western nicaragua and minimum values below costa rica and western panama where the cocos ridge is being subducted these data may also reflect significant differences in thermal state of the descending slab which in turn differentially affects release patterns of fluids and fluid mobile trace elements and possibly melting processes beneath different parts of the arc the following scenario is suggested to explain the geochemical results beneath the northwestern part of the arc steep subduction of older relatively cold slab favors more efficient subduction of fluid components to depths beneath the volcanic front the released fluids carry fluid mobile elements to the overlying mantle which upon melting produces calcalkalic magmas shallow subduction of warmer slab beneath the southeastern part of the arc favors shallow release of fluids and limits fluid related metasomatism of sub arc mantle beneath the volcanic front under such conditions b la and ba la ratios in the sub arc mantle vary little from values seen in oceanic island basalts magmas in this part of the arc nevertheless display the highest la yb and lowest ba la and b la ratios which are consistent with prior light rare earth element enrichment in the source significantly lower degrees of melting or a combination thereof because some of the largest volcanoes occur in costa rica and magma flux there is nearly an order of magnitude higher than elsewhere in the arc source enrichment is considered to be the more plausible explanation it is proposed that quaternary magma production below costa rica involved lithospheric sources containing trapped or stored melt components but this enrichment process is unlikely to have involved typical arc magmas or subduction fluids because we see no b enrichment

a 130 year micro and macrofossil record from regeneration peat in former peasant peat pits in the peel the netherlands a palaeoecological study with agricultural and climatological implications abstract two pollen diagrams a macrofossil diagram and a microfossil diagram from regeneration peat in old peat pits in the peel a former raised bog area in the southern part of the netherlands are presented the pollen diagrams reveal the local and regional flora and vegetation history these diagrams are correlated in a detailed way with historical data concerning the economic history of the region in the past two centuries especially with respect to developments in agriculture and afforestation as shown in acreage curves of a number of cultivated plants the changes in local bog vegetation as shown in the micro and macrofossil diagrams are attributed to climatic changes and to the impact of human activities in the direct surroundings of the core peat accumulation appeared to be 240 490 g m 2 yr 1 in the period studied

relation of lava compositions to volcano size and structure in el salvador abstract most of the lavas at the nine volcanic centers along the volcanic front of el salvador are basalts basaltic andesites and andesites the compositional variation within and among these centers can be explained by fractionation processes within the crust cognate gabbroic inclusions found in the lavas have appropriate mineralogy plagioclase olivine magnetite and augite to be cumulates formed by fractional crystallization two main variation trends occur depending on the proportion of plagioclase removal the more common or normal trend has a high 55 proportion of plagioclase being removed a less common al rich trend has a low 40 proportion of plagioclase being removed the al rich trend is found only at volcanoes that lack large negative bouguer gravity anomalies these volcanoes are unlikely to have large shallow magma chambers and fractionation probably occurs deeper in the crust where plagioclase removal is inhibited the incompatible element na 2 o k 2 o rb ba contents of lavas vary systematically with the volume of the volcanic centers at the same level of sio 2 large volcanic centers have higher incompatible element contents than small volcanic centers this suggests that open system fractionation in a periodically refilled chamber is the controlling factor the large difference in ba contents of lavas between eastern low and western high el salvador suggests a difference in the mantle source region

partial melting of mantle wedge and evolution of island arc crust evolution of the crust in the northeast honshu arc is discussed on the basis of the melting experiments of a peridotite under hydrous conditions and the crustal compositions estimated from deep crustal xenoliths and seismic velocity data the chemical compositions of melts formed by partial melting of a hydrous peridotite within the pressure temperature conditions for shallow parts of the mantle wedge 1 2 2 0 gpa have been experimentally determined with the sandwich experiment technique the melts range from olivine tholeiitic to magnesian andesitic compositions sio2 48 56 wt mgo 9 14 wt beneath the volcanic front in the northeast honshu arc and are slightly less silicic beneath the coast of the sea of japan the crustal compositions of the volcanic zone in the northeast honshu arc estimated from deep seated crustal inclusions in volcanic rocks and the velocity structures of the crust are andesitic in the central zone and high alumina basaltic near the coast of the sea of japan the compositions of possible primary melts formed in the mantle wedge are significantly more mafic than these crustal compositions consequently if the major part of the crustal materials in the volcanic zone was formed by magmas generated in the mantle wedge thick up to 30 km ultramafic cumulates including olivine pyroxenite must have been formed beneath moho during fractional crystallization and would constitute the upper part of the mantle wedge the volume of the mantle wedge consisting entirely of even fertile peridotite was not sufficient to produce crustal materials and cumulates in the volcanic zone by such processes in the northeast honshu arc a static mantle wedge model is therefore not satisfactory for the growth of the crust in northeast honshu arc a dynamic model is suggested in which the mantle materials have been supplied into the mantle wedge from the back arc side by a convective flow

genesis of gypsum enriched soils in north west isfahan iran abstract most of gypsum enriched soils in isfahan and neighboring provinces occur on alluvial fans dissected flood plains old dissected alluvium and piedmont plains herein we investigate the processes of formation and alteration of gypsic horizons and their pedofeatures we described and sampled representative pedons on a transect from the mountain to the piedmont plain in the study area different gypsic pedofeatures have various kinds of internal lenticular cryslalitic fabrics micromorphologic observations confirmed that gypsic horizons have an evolutionary sequence across the different geomorphic surfaces from the upper fan to the piedmont plain in primary stages upper fan gypsum crystals occur individually in the soil groundmass or as clusters in voids with idiotopic or xenotopic fabrics eventually they form internal coatings or infillings and pendants in middle and lower fans in the more developed horizons dissected flood plains or plateaus the fibrous gypsum crystals are banded and perpendicularly distributed with reference to the gravels and soil surface these loosely compacted fibers constitute the bulk of the soil materials leaving non gypsic particles as islands between crystals in these pedofeatures perpendicularly oriented fibrous crystals with their lateral inter connections give rise to a continuous three dimensional firm structure the fabric of these lenticular gypsum crystals is xenotopic or hyp idiotopic in the piedmont plain the idiotopic crystals have no preferred orientation and have random distribution internal fabric of these pedofeatures is porphyrotopic this study indicates that physical environment plays a great role in formation of different gypsic pedofeatures

the mid holocene ulmus decline at diss mere norfolk uk a year by year pollen stratigraphy from annual laminations 3 m of annually laminated sediments were recovered from a small steep sided lake diss mere norfolk uk in an 8 cm section known to include the mid holocene elm decline the laminae were sampl

nejapa tephra the youngest c 1 ka bp highly explosive hydroclastic eruption in western managua nicaragua nejapa maar 2 5 1 4 km c 120 m deep the largest maar along the 15 km long holocene nejapa miraflores lineament nml is the source vent of the youngest relatively widespread basaltic tholeiitic tephra blanket nejapa tephra nt in western central nicaragua as shown by isopachs and isopleths rausch and schmincke 2008 the nt covers an area of 10 km2 in w nw managua the minimum total magma volume erupted is estimated as 0 09 km3 juvenile dominantly slightly vesicular 20 40 vol basically tachylitic cauliflower shaped lapilli with an average density of 2 1 g cm3 make up 90 vol of the deposit while lithoclasts comprise 10 vol except proximally this the paucity of fine grained tuffs and the dominant plane parallel bedding all suggest fragmentation by shallow interaction of a rising magma starting to vesiculate and fragment pyroclastically with external water the complex particles so generated erupted in moderately high eruption columns at least 7 10 km and were dominantly deposited as dry to damp warm to cool fallout minor surge transport is inferred from fine grained locally cross bedded tephra beds chiefly north of nejapa and just west of asososca maars synvolcanic faulting along the nml is inferred faults in the study area indicate that activation of the n s trending nejapa miraflores fault nmf representing the western flank of managua graben preceded deposition of nt and underlying masaya tuff c 1 8 ka bp chiltepe pumice c 1 9 ka bp and masaya triple layer 2 1 ka bp the nt deposit is underlain regionally by a paleosol and topped by a soil the basal paleosol contains pottery sherds made by the usulutan negative technique during the late formative period 700 bce 300 ce 2 7 1 7 ka bp the soil overlying nt contains pottery related to the ometepe technique dated as between 1350 and 1550 ce 650 450 a bp these and the radiocarbon dates of the pottery bearing paleosols 1245 125 and 535 110 a bp obtained by pardo et al 2008 indicate that nejapa maar erupted between c 1 2 and 0 6 ka bp future eruptions in this area of similar magnitude eruptive and transport mechanisms would represent a major hazard and risk to the densely populated western suburbs of managua a city expanding rapidly westward assuming a similar eruption scenario poor quality roofs common in nicaragua would be prone to collapse up to 12 km peripheral to nejapa maar or another close by eruptive site and buildings at a distance of up to 500 m are likely to be severely affected in view of the past frequency of eruptions along the nml further eruptions are likely to occur in the near future

dating raised bogs new aspects of ams 14c wiggle matching a reservoir effect and climatic change abstract high resolution ams dating of holocene raised bog deposits engbertsdijksvenen the netherlands shows natural 14c variations wiggles which can be matched with the dendrochronological calibration curve comparison of our results with other conventionally dated peat cores and the 14c record shows an unexpected and as yet unreported reservoir effect and a marked and sudden wetting of the bog surfaces coinciding with the advent of a sporer type solar minimum the homeric minimum the potential of ams dating to vastly improve the accuracy of holocene chronologies is demonstrated

tracing the source of gypsum in new caledonian soils by ree contents and ssr isotopic compositions gypsum minerals forming in pedogenic environments in new caledonia were examined for their s and sr isotope compositions and ree distributions three possible sources were identified volcanic soil derived and marine however differentiation based only on the ree contents and normalized patterns was not possible but the best preserved volcanic sample yields a negative eueu anomaly and the lowest gdnybn ratio due to the high content of organic matter mixing calculations of the 34s values and 87sr86sr ratios confirmed that the marine gypsum has a 34s value close to 21 and an 87sr86sr ratio close to 0 70912 and that the volcanic gypsum has a 34s value of 0 and an 87sr86sr ratio of about 0 70331 the soil derived gypsum samples yield intermediate values as a result of a mixing between the marine and volcanic end members negative 34s values for the volcanic gypsum are explained by low fo2 of the source rocks while high 87sr86sr ratios for the same gypsum are explained by probable atmospheric input the data confirm also that biological fractionation of 34s if any is limited

the origin of gypsum in vertisols in new caledonia determined by isotopic characteristics of sulphur abstract gypsum crystals occur in vertisols on the west coast of new caledonia these soils are derived from the weathering of basic rocks that contain no gypsum the sulphur isotopic ratio 34 s 32 s was used as tracer to identify the origin of the gypsum a total of 26 measurements of 34 s were made on gypsum crystals from the vertisols and compared to those of continental sulphates and to marine gypsum in tidal flats the 34 s value of the crystals located in new caledonian vertisols decreases with increasing distance from the coast this suggests that the gypsum in the vertisols comes from two sources an oceanic source where the major part of the sulphur is introduced by atmospheric precipitation and a continental source where sulphides disseminated in various subsurface deposits are oxidized gypsum from atmospheric precipitation penetrates the vertisols through vertical cracks that probably formed in dry seasons during the last glacial period

rare earth element variations resulting from inversion of pigeonite and subsolidus reequilibration in lunar ferroan anorthosites we present results of a secondary ion mass spectrometry study of the rare earth elements rees in the minerals of two samples of lunar ferroan anorthosite and the results are applicable to studies of rees in all igneous rocks no matter what their planet of origin our pyroxene analyses are used to determine solid solid ree distribution coefficients d cree in low ca pyroxene cree in augite in orthopyroxene augite pairs derived by inversion of pigeonite our data and predictions from crystal chemical considerations indicate that as primary pigeonite inverts to orthopyroxene plus augite and subsolidus reequilibration proceeds the solid solid ds for orthopyroxene augite pairs progressively decrease for all rees the decrease is greatest for the lrees the ree pattern of solid solid ds for inversion derived pyroxene pairs is close to a straight line for sm lu and turns upward for rees lighter than sm the shape of this pattern is predicted by the shapes of the ree patterns for the individual minerals equilibrium liquids calculated for one sample from the compositions of primary phases using measured or experimentally determined solid liquid ds have chondrite normalized ree patterns that are very slightly enriched in lrees the plagioclase equilibrium liquid is overall less rich in rees than pyroxene equilibrium liquids and the discrepancy probably arises because the calculated plagioclase equilibrium liquid represents a liquid earlier in the fractionation sequence than the pyroxene equilibrium liquids equilibrium liquids calculated from the compositions of inversion derived pyroxenes or orthopyroxene derived by reaction of olivine are lree depleted in some cases substantially in comparison with equilibrium liquids calculated from the compositions of primary phases these discrepancies arise because the inversion derived and reaction derived pyroxenes did not crystallize directly from liquid and the use of solid liquid ds is inappropriate the lree depletion of the calculated liquids is a relic of formation of these phases from primary lree depleted minerals thus if one attempts to calculate the compositions of equilibrium liquids from pyroxene compositions it is important to establish that the pyroxenes are primary in addition our data suggest that experimental studies have underestimated solid liquid ds for rees in pigeonite and that ree contents of liquids calculated using these ds are overestimates our results have implications for sm nd age studies our work shows that if pigeonite inversion and or subsolidus reequilibration between augite and orthopyroxene occurred significantly after crystallization and if pyroxene separates isolated for sm nd studies do not have the bulk composition of the primary pyroxenes then the sm nd isochron age and end will be in error

walking through volcanic mud the 2 100 year old acahualinca footprints nicaragua we present the stratigraphy lithology volcanology and age of the acahualinca section in managua including a famous footprint layer exposed in two museum pits the ca 4 m high walls of the main northern pit pit i expose excellent cross sections of late holocene volcaniclastic deposits in northern managua we have subdivided the section into six lithostratigraphic units some of which we correlate to late holocene eruptions unit i 1 2 m thick chiefly of hydroclastic origin begins with the footprint layer the bulk is dominated by mostly massive basaltic andesitic tephra layers interpreted to represent separate pulses of a basically phreatomagmatic eruptive episode we correlate these deposits based on compositional and stratigraphic evidence to the masaya triple layer erupted at masaya volcano ca 2 120 120 a b p the eruption occurred during the dry season a major erosional channel unconformity up to 1 m deep in the western half of pit i separates units ii and i unit ii begins with basal dacitic pumice lapilli up to 10 cm thick overlain by a massive to bedded fine grained dacitic tuff including a layer of accretionary lapilli and pockets of well rounded pumice lapilli angular nonvesicular glass shards are interpreted to represent hydroclastic fragmentation the dacitic tephra is correlated unequivocally with the ca 1 9 ka plinian dacitic chiltepe eruption unit iii a lithified basaltic andesitic deposit up to 50 cm thick and extremely rich in branch molds and excellent leaf impressions is correlated with the masaya tuff erupted ca 1 8 ka ago unit iv a reworked massive basaltic andesitic deposit rich in brown tuff clasts and well bedded and cross bedded in the northwestern corner of pit i cuts erosionally down as far as unit i a poorly defined pale brown mass flow deposit up to 1 m thick unit v is overlain by 1 1 5 m of dominantly reworked chiefly basaltic tephra topped by soil unit vi a major erosional channel carved chiefly between deposition of units ii and i may have existed as a shallow drainage channel even prior to deposition of the footprint layer the swath of the footprints is oriented nnw roughly parallel to and just east of the axis of the channel the interpretation of the footprint layer as the initial product of a powerful eruption at masaya volcano followed without erosional breaks by additional layers of the same eruptive phase is strong evidence that the group of 15 or 16 people tried to escape from an eruption

correlating geochemistry tectonics and volcanic volume along the central american volcanic front the central american volcanic front consists of several distinct volcanic lineaments or segments separated by right steps and or changes in strike each volcanic line is rotated slightly counterclockwise from the strike of the inclined seismic zone right stepping volcanic lines oblique to the strike of the slab create a sawtooth pattern in the depth to the slab zr nb is the first geochemical signature with consistent large offsets at the right steps in the volcanic front moreover zr nb mirrors the sawtooth variation in depth to the slab within a segment it increases from se to nw and at the right steps separating segments it abruptly decreases unfortunately there is no simple negative correlation between zr nb and depth to the slab because zr nb also has a regional variation similar to previously documented regional variations in slab tracers in central america e g ba la u th and 87sr 86sr within a segment zr nb decreases with increasing depth to slab this can be explained in two ways a nb retaining mineral e g amphibole in the subducting slab is breaking down gradually with increasing depth causing more nb to be released and consequently a smaller nb depletion in deeper melts alternatively all melts have the same initial nb depletion which is then diluted by acquiring nb from the surrounding mantle wedge as melts rise and react deeper melts have longer paths and therefore more reaction with the mantle wedge diluting the initial nb depletion within each volcanic segment there is variation in eruptive volume the largest volcanoes generally occur in the middle of the segments and the smaller volcanoes tend to be located at the ends connecting the largest volcanoes in each segment suggests an axis of maximum productivity this is likely the surface projection of the center of the melt aggregation zone the largest volcanoes tap the entire melt zone those with shallow depths to the slab tap just the front part of the melt zone and have very large nb depletions those at greater depths tap the back part of the melt zone and have much smaller nb depletions

the hydrological setting occurrence and significance of gypsum in late quaternary salt lakes in south australia well exposed often laminated gypsum sequences occur in many quarternary salt lakes in southern south australia the gypsum in the salt lakes is classified by increasing grain size into gypsite gypsarenite and selenite the salt lakes are classified by age and hydrological setting into coastal salinas which are holocene sea water fed groundwater lakes and continental playas which are late pleistocene endorheic basins a study of the relationships between coastal salina hydrology and the associated gypsum deposition has shown the different types of gypsum form under distinct hydrological regimes as the hydrology above a coastal salina depositional surface changes through time so does the type of gypsum deposited application of a gypsum depositional model derived from a study of the coastal salina gypsum to those portions of a continental playa gypsum unit where deposition is no longer occurring confirms the applicability of the model to non salina gypsum deposits

pedogenesis and clay mineralogical investigation of soils formed on gypsiferous and calcareous materials on a transect southwestern iran abstract this study examined pedogenesis as well as the clay mineralogy of soil and rock samples obtained from a transect of gypsiferous and calcareous materials the main objectives of this research were to study the relationship between clay minerals and physiographic units as well as the relative importance of key pedogenic processes in controlling clay mineralogy palygorskite chlorite illite smectite quartz and interstratified minerals were observed in both soil and rock samples using xrd tem and edx analyses illite chlorite and interstratified minerals are inherited largely from parent rocks most of the smectite is inherited from highly smectite marl formations although some may be the product of palygorskite weathering and transformation of illite particularly at the surface horizons neoformation of palygorskite as a result of calcite and gypsum precipitation seems to be a major pathway for the occurrence of this mineral especially on plateau physiographic units although inheritance has less importance gypsiferous soils showed more pedogenic palygorskite as compared to calcareous soils three morphological forms of palygorskite related to degree of weathering were identified in the studied pedons new great groups and subgroups of ustepts aridic gypsiustepts and aridic calcic gypsiustepts are suggested to be included in soil taxonomy based on the properties of some of the studied pedons dissolution and transport of anhydrite from outcrops is considered the main source of pedogenic gypsum in these soils micromorphological studies including thin section observations and sem analyses indicated variable habits of gypsum crystals suggested a dynamic soil environment

the managua graben and las sierras masaya volcanic complex nicaragua pull apart localization by an intrusive complex results from analogue modeling abstract there is a well documented association between pull apart basins in strike slip zones and large volcanic caldera complexes las sierras masaya volcanic complex nicaragua is a large basaltic lava and ignimbrite shield with nested calderas the widest caldera is partly underlain by a large and dense intrusive complex evidenced by a positive gravity anomaly the las sierras caldera relating to this cumulate complex is less than 30 000 years old and is probably still hot and ductile the inner masaya caldera hosts an active magmatic system the volcanic complex is in a dextral transtensional tectonic context of the nicaraguan depression the highly active managua graben is on the northern part of the volcano we speculate that the graben and volcano are linked tectonically with the graben initiating in response of a regional stress field modified around the dense ductile intrusive complex previous field work and reappraisal of structures with digital elevation model morphological analysis show that the volcano is surrounded by a rhombic fault pattern that may form a nascent pull apart basin we have done scaled analogue models to test the effect of intrusion density and rheology anomalies on strike slip fault geometries the models show that intrusion density variations alone do not significantly change fault patterns in contrast ductile rocks silicone in the models as analogue for hot mafic intrusive rocks markedly alter strike slip fault patterns in transtension the presence of a ductile intrusion causes the formation of a pull apart while in pure strike slip or transpression uplift and thrusting is generated pull apart and uplift structures are rhomb shaped even when the ductile inclusion is circular we conclude that a pull apart is developing at las sierras masaya volcanic complex in response to the transtensive regional deformation regime and the dense ductile intrusive complex we suggest that the volcano and graben are one dynamic system and should be monitored as one entity

petrogenic implications of ree and ba data on mafic and ultramafic inclusions from itinome gata japan ultramafic and mafic inclusions from itinome gata in japan were studied systematically from a viewpoint of earth element ree and barium abundances mineral separates from lherzolites and their host basalt as well as andesite from an adjacent volcano were also analyzed for ree and ba garnet lherzolites which are believed to have formed at a depth of 50 to 70 km have a convex upwards chondrite normalized ree patterns similar to those of alpine type lherzolites spinel lherzolites which are believed to be derived from shallower depths than garnet lherzolites have various ree patterns and negative eu anomalies spinel lherzolites that are high in basaltic components have convex upwards ree patterns as do garnet lherzolites whereas mg rich strongly basalt depleted spinel lherzolites have v shaped ree patterns the ree variation among spinel lherzolites reflects the differing degrees of liquid phase extraction of basaltic components in times past the ree pattern of the liquid phase extracted from t

pollen percolation rates in euroamerican era cultural deposits in the northeastern united states abstract dimbleby s the palynology of archaeological sites new york academic press 1985 p 3 data from forested sites indicate that pollen percolates downward in soils at the rate of 1 cm in c 30 years data from archaeological sites and former agricultural fields in the northeastern united states suggest that pollen percolates downward at the faster rate of c 1 cm in 4 2 years in soils not sheltered by woodland this in turn suggests that the pollen sequences of former non forest soils preserved by rapid natural and cultural burial record much shorter periods of time than previously believed

positively correlated nd and sr isotope ratios of lavas from the central american volcanic front twenty four volcanic rocks from the central american arc have been analyzed for their sr and nd isotopic compositions on a nd sr isotope correlation diagram these lavas define an unusual positive trend that correlates strongly with crustal thickness nicaraguan lavas situated on the thinnest crust have morb like nd but elevated sr isotopes and provide strong evidence for incorporation of a subducted slab component lavas from costa rica and guatemala have lower values of both isotopes and are underlain by crust 30 thicker than that beneath nicaragua isotope correlations with trace elements support the idea that the central american volcanics are related by two component mixing of mantle above the subducted slab including a high sr sr fraction derived from altered oceanic crust and lower crust with isotopic values that lie along the mantle array the correlation of chemical parameters with crustal thickness can be explained if the lower crust acts as a density filter thus the least fractionated lavas nicaragua have the highest sr and nd isotopic ratios they have the highest mgo and lowest si02 and are the most isotopically similar to the melted mantle wedge if fractionation is coupled with assimilation and the extent of both is controlled by crustal thickness then lavas above thick crust will have isotopic values more similar to lower crust because they are the most fractionated

vegetation history and environmental development since ca 6000 cal yr bp in and around ispani 2 kolkheti lowlands georgia abstract the kolkheti lowlands of western georgia have a unique vegetation and a rich cultural history palynological and macrofossil analysis accompanied by ams 14c dates of the deposits of the ispani 2 mire near kobuleti allow the reconstruction of regional vegetation environmental history and local peatland development within the context of black sea level and cultural changes comparison of two adjacent peatland cores confirms spatial differences in wetland development prior to 5400 cal yr bp the ispani basin was a floodplain of an active river system where overbank deposits with fluvially transported castanea pollen were deposited subsequently a lake or lagoon developed in which reeds expanded these were succeeded by herb rich open alder carrs after 1900 cal yr bp carpinus and fagus expanded on the dry grounds where formerly quercus was more abundant also castanea declined local reedbeds that burned regularly succeeded the alder carr after 1000 cal yr bp a percolation bog developed resulting in the formation of 4 m of loose porous and largely undecomposed sphagnum austinii peat with molinia roots the upper 50 cm of the analysed section show extensive human impact on the landscape during the 20th century

in search of finiteness the limits of fine resolution palynology of sphagnum peat high resolution analysis of ombrogenous peats often reveals pollen frequencies that change markedly from one sample to the next indicating limited postdepositional mixing this raises the question whether with sufficiently thin samples seasonal differences in pollen deposition can be observed seasonal resolution in peat would provide a dating technique with an accuracy similar to that of other annually banded archives to study the limits of temporal resolution contiguous 0 5 mm thick slices of slightly humified sphagnum section cuspidata peat were palynologically analysed no seasonal patterns in the pollen stratigraphy could be observed this is ascribed to the mixing of pollen grains as a result of small scaled vertical water movements and to the horizontal mode of shoot layering in the sphagnum species the latter process may also be the cause of a smoothed annual signal because of the absence of seasonal differentiation the palynological distinction of annual peat layers is not feasible

sulfate in modern playa settings and in ash beds in hyperarid deserts implication for the origin of 17o anomalous sulfate in an oligocene ash bed abstract a large amount of calcite pseudomorphs after gypsum were discovered in a volcanic ash bed and its underlying sand siltstone in the gering formation late oligocene northwestern ne usa the highly positive 17o anomalies in the residual sulfate indicate that the sulfate could only have come from the oxidation of sulfur gases by ozone in the atmosphere we previously proposed that it was most likely the result of an extreme tropospheric sulfate haze dry fog event that was associated with volcanic eruptions in the west to test the dry fog hypothesis we examine here two alternative scenarios that also involve atmospheric sulfate deposition but do not imply a dramatic volcanic and dry fog source 1 is it possible that some playas in arid or semiarid regions accumulate the type of atmospheric sulfate deposits as we see in the mid gering bed by the inflow of surface water or groundwater 2 could a period of hyperaridity and stability during the late oligocene have caused a significant accumulation of atmospheric background sulfate onto the mid gering ash bed surface sulfates from a variety of playa settings were collected and measured for their 17o anomalies the sulfate isotope both o and s and concentration profiles of two volcanic ash beds that are currently exposed in the central atacama desert chile and in taylor valley of the antarctica dry valleys were studied along with their sedimentary features these two ash beds were chosen for comparison because of their significant levels of atmospheric sulfate accumulated during prolonged and hyperarid climatic conditions results showed no or minimal 17o anomalies in any of the playa sulfate samples from around the world and none of the parameters in the mid gering ash profile matches those in either of the two volcanic ash profiles in modern hyperarid settings conclusion the observed 17o anomalous gypsum deposit in the mid gering ash bed is most likely the result of a series of extreme dry fogs that resulted in an intense pulse of atmospheric sulfate deposition to a semiarid playa setting

endolithic cyanobacteria in soil gypsum occurrences in atacama chile mojave united states and al jafr basin jordan deserts 1 soil sulfates are present in arid and hyperarid environments on earth and have been found to be abundant in soils on mars examination of soil gypsum from the atacama desert chile the mojave desert united states and al jafr basin jordan revealed endolithic cyanobacteria communities just below the surface of soil gypsum samples optical and scanning electron microscope observations of the colonized layers indicated that the unicellular chroococcidiopsis is the dominant cyanobacterium in all studied communities 16s rrna gene analysis revealed that in addition to chroococcidiopsis a few other cyanobacteria are present heterotrophic bacteria are also abundant in the colonized zones of the fine grained gypsum from the atacama and mojave desert but insignificant in the fibrous gypsum from the jordan desert endolithic life forms similar to these described here may exist or have existed on mars and should be targeted by the mars science laboratory and future in situ missions

caribbean arc tholeiites the occurrences of arc tholeiites in the two active subduction zones involving the caribbean plate central america and the lesser antilles are quite restricted volcanic rock suites exhibiting strong iron enrichment are limited to five volcanoes all in central america three of the five occur along the nicaraguan portion of the volcanic front beneath which the arc crust is thinnest on the other hand volcanic rock suites with low absolute concentrations of large ion lithophile elements and light rare earth elements are largely confined to two northern islands in the lesser antilles st kitts and st eustatius and solely confined to the nejapa granada cinder cone alignments of nicaragua in central america these tholeiitic characteristics strong iron enrichment and low concentrations of certain incompatible elements are produced by dissimilar processes strong iron enrichment results from extensive fractional crystallization at low pressure or with low water contents perhaps in shallow magma bodies whereas low absolute concentrations of specific incompatible elements are governed by relatively high degrees of source melting the high degree of melting is made possible by a greater flux of material from the subducted plate crustal contamination exerts only a secondary and local control on incompatible element concentrations at least in central america

14c ams wiggle matching of raised bog deposits and models of peat accumulation abstract high resolution accelerator mass spectrometer ams 14 c dates of selected plant macrofossils from the raised bog engbertsdijksvenen eastern netherlands show century scale wiggles analogous to the radiocarbon calibration curve we used three relative time scales viz based on depth mass and pollen concentration respectively to match the peat ams dates to the calibration curve this procedure is repeated for one conventionally dated core for each relative time scale realistic confidence intervals are calculated depth appears to be the best time scale for certain stratigraphical units of a core this justifies using depth for wiggle matching conventionally dated mire cores published by others even when 14 c errors are larger our evidence shows four major sources of 14 c variation for mire deposits compared to treerings 1 dating error due to sample composition this includes a reservoir effect demonstrated for many bulk peat samples 2 hiatuses causing a sudden leap of peat 14 c age 3 changing accumulation rates apparent from a break in the slope of the peat 14 c ages 4 sampling error these results shed doubt on the assumed continuities in theoretical peat accumulation models both mire stratigraphy and changing accumulation rates can be explained in qualitative hydrological terms more evidence for a previously discovered reservoir effect in bog deposits is presented though the physical biological mechanisms remain uncertain

all age depth models are wrong but how badly the uncertainty and error associated with fitted age depth models were investigated by fitting a range of models to sets of simulated radiocarbon dates based on varved sediments and comparing the modelled relationship with the varve timescale with large numbers of dates cubic smooth splines out perform other models with few dates no model reliably provides a good fit to reality and calculated confidence intervals are over optimistic c 2003 elsevier ltd all rights reserved

can rapidly accumulating holocene peat profiles provide sub decadal resolution proxy climate data to test the potential for developing sub decadal resolution records of ombrotrophic bog surface wetness bsw selected abrupt climate events were identified in cores from four sites in north west europe and time slices over each event were investigated at 2 5 mm resolution using peat humification testate amoeba and plant macrofossil analyses age depth models based on radiocarbon spheroidal carbonaceous particle and tephra dates were applied and the error in these models was used to determine the effective temporal sampling resolution which in most cases was sub decadal fine resolution results revealed some inconsistencies in the co variability of individual proxies and there was a lack of correspondence between some results from adjacent cores however we found evidence of abrupt shifts in bsw occurring over ca 5 20 years indicating a more rapid proxy response than identified in previous research to maximize potential temporal resolution and produce reliable sub decadal bsw data in future research we recommended that peat based studies should obtain the best possible chronological control focus on sites with high species diversity and rapid accumulation rates and perform replicate coring or use open peat sections where the stratigraphy can be clearly seen to assess intra site differences in microtopography site specific factors should be a primary consideration in the selection of sites for future fine resolution research

improving the time control of the subboreal subatlantic transition in a czech peat sequence by 14c wiggle matching to achieve an optimal time control for a late subboreal to early subatlantic peat sequence from pancavska louka in the czech republic different strategies are applied to convert a series of radiocarbon dates into a calendar time scale the methods of selection and preparation of the samples for ams 14c dating are presented the results of calibrating single radiocarbon dates are compared with a 14c wiggle match strategy as the accumulation rate of the peat was not constant the concentrations of arboreal pollen are used to estimate the accumulation rate changes and to correct for these changes the resulting time control represents the best solution for this peat sequence with the methods currently available

picritic primary magma and its source mantle for oshima ōshima and back arc side volcanoes northeast japan arc oshima shima volcano is an endmember of a geochemical variation which is characterized by a low feo content toward the back arc side across the ne japan arc analyses of the basalts show primitive characteristics variation trends of the chemical compositions indicate initial olivine control then olivine clinopyroxene control from a picritic to a differentiated basalt the more magnesian basalts have the more magnesian olivine phenocrysts the most magnesian mgo 15 of all rock samples contains olivine phenocrysts with a composition of fo 93 7 as a liquidus phase and is considered a product of a mantle derived magma the possible range in feo and mgo content of source mantle for the oshima shima magma can be demonstrated ichinomegata lherzolite inclusions also from the back arc side of ne japan is unlikely to be a candidate for the source mantle for high feo the upper mantle beneath the back arc side is considered to be compositionally zoned a fe rich mantle ichinomegata lherzolite at shallower place and a fe poor mantle the source mantle for back arc side volcanoes

basalt produced by mechanical mixing of andesite magma and gabbroic fragments hakone volcano and adjacent areas central japan abstract rocks from hakone volcano and the adjacent hata and aziro areas were studied to clarify the anomalous partition coefficient of ce between olivine and groundmass in the basalts of hakone in addition the most primitive basalt is more enriched in ree than the other basalts from this volcano the ree features are well explained by a mechanical mixing model the basaltic rocks from the volcano are mixtures of basic andesite magma and fragments of gabbroic rock most of minerals of phenocrystic size and glomeroporphyritic crystal aggregates in the basaltic rocks are xenocrysts and were derived from a gabbroic body lying beneath the volcano this conclusion is consistent with major element mineralogical and petrographical data

melting experiments on a high magnesian andesite abstract melting experiments were conducted on a high magnesian bronzite olivine andesite teraga ike andesite which is considered to be a primary andesite the high magnesian andesite magma is in equilibrium with both olivine and orthopyroxene at about 15 5 kbar and 1080 c under h2o saturated conditions and at lower pressure and higher temperature under h2o undersaturated conditions this suggests that high magnesian andesites could be generated by the partial melting of upper mantle peridotite containing a small amount of h2o

petrogenesis of lavas from cinder cone fields behind the volcanic front of central america small monogenetic cinder cones and shield volcanoes occur in platform cone fields behind the volcanic front of central america their lavas bvf suite are distinctly different from typical volcanic front lavas vf suite most vf lavas are nearly aphyric basalts containing only olivine and plagioclase phenocrysts they have high al 2 o 3 na 2 o k 2 o ba and sr contents and moderate ni cr and rb contents in contrast to petrographic observations major and trace element modeling and the decrease in the cao al 2 o 3 ratio with fractionation require substantial clinopyroxene fractionation and moderate degrees of fractionation for the bvf lavas the contradiction between petrography and compositional trends can be resolved by the following model 1 crystallization and separation of plagioclase clinopyroxene and olivine at approximately 5 10 kb and 2 rapid magma ascent and surface eruption of nearly aphyric lavas near surface crystallization involves only plagioclase and olivine du

the 1245 yr bp asososca maar new advances on recent volcanic stratigraphy of managua nicaragua and hazard implications abstract asososca maar is located at the western outskirts of managua nicaragua in the central part of the active n s trending and right lateral nejapa miraflores fault that marks an offset of the middle america volcanic arc it constitutes one of the 21 vents aligned along the fault between the chiltepe volcanic complex to the north and ticomo vents to the south asososca consists of an east west elongated crater filled by a lake which is currently used for supplying part of managua with drinking water 10 of the capital city demand the crater excavated the previous topography allowing the observation of a detailed holocene stratigraphic record that should be taken into account for future hazard analyses we present a geological map together with the detailed stratigraphy exposed inside and around asososca crater aided by radiocarbon dating of paleosols the pre existing volcanic sequence excavated by asososca is younger than 12 730 255 250 yr bp and is capped by the phreato plinian masaya tuff 2 are dominated by accidental clasts including basaltic to basaltic andesitic olivine bearing scoriae lapilli porphyritic and hypocrystalline andesite blocks and lapilli altered pumice lapilli and ash and ignimbrite fragments juvenile fragments were only identified in size fractions smaller than 1 in proportions lower than 25 and consist of black moss like fused shape and poorly vesiculated fresh glass fragments of basaltic composition sio2 48 the asososca tephra is interpreted as due to the emplacement of several pyroclastic surges originated by phreatomagmatic eruptions from asososca crater as suggested by impact sags geometry and dune crest migration structures according to radiocarbon dating these deposits were emplaced at 1245 125 120 yr bp the stratigraphic position of the asososca tephra and the well preserved morphology of the crater indicate that asososca is the youngest vent along the nejapa miraflores fault explosive eruptions might therefore occur again along this fault at the western outskirts of managua such kind of activity together with the strong seismicity associated to the active fault represents a serious hazard to urban infrastructure and a population of ca 1 3 million inhabitants

melting of the shallow upper mantle a new perspective detailed examination of liquidus phase relationships in binary and ternary joins of the cfmas cr system has permitted a rigorous determination of the dry melting path of an initially fertile spinel peridotite composition resembling bulk silicate earth or morb pyrolite it is demonstrated that it is impossible to model mantle melting accurately using only one set of ratios of phases entering the melt this implies that the melting process is primarily controlled by solid solution rather than eutectic behaviour the proportions of phases entering a melt depend on whether a phase reacts and or disappears from a system and on the choice of the initial and final peridotite compositions four discrete domains in the melting regime of upper mantle peridotites are distinguished each characterized by different phase melting coefficients relating to the melting of 1 lherzolites 2 clinopyroxene bearing harzburgites i e free clinopyroxene 3 clinopyroxene saturated harzburgites i e clinopyroxene in solid solution in orthopyroxene and 4 clinopyroxene free harzburgites i e no clinopyroxene the proposed non linear fashion in which mantle lithologies melt explains the inadequacy of all previous models to reproduce the observed compositions of upper mantle peridotite melting residues it is suggested that 1 olivine and orthopyroxene will melt cotectically 2 clinopyroxene and spinel will lose most of their aluminous component after 8 melting within the first 4 kb 12 km of ascent from the dry solidus and that 3 clinopyroxene will disappear completely from a morb pyrolite mantle after 42 melting although such a number is significantly higher than that dictated by the position of the clinopyroxene out curves from peridotite isobaric equilibrium melting experiments 22 it is emphasized that the latter are a gross oversimplification of the natural melting process and are not equivalent to melting during adiabatic upwelling it is concluded that the commonly postulated disappearance of clinopyroxene from fertile peridotite compositions at 22 melting is greatly in error if melting in an adiabatically rising mantle is considered thus providing an explanation for many unsuccessful attempts by various authors to model the behaviour of transition elements in sub oceanic and supra subduction zone mantle and derivative magmas

local impact of palaeolithic man on the environment during the end of the last glacial in the netherlands abstract comparison of palynological data from lake deposits and soils from locations along a transect approaching the remains of a palaeolithic settlement in the younger dryas stadial shows four cycles in the vegetation from open pine forest to open ground vegetation and back to open pine forest this outcome is discussed in terms of the impact of man on the vegetation in the later part of the weichselian lateglacial

pollen and macrofossils attributable to fagopyrum in western eurasia prior to the late medieval an intercontinental mystery abstract the widespread perception that buckwheat fagopyrum esculentum and f tataricum did not occur in western eurasia prior to the late medieval is challenged by numerous pollen finds we traced some 240 localities from the area with pollen or macrofossils attributed to fagopyrum in often much earlier time slices this paper evaluates various explanations for these finds within the context of palaecological methods vegetation history and cultural development the clear morphological characteristics make large scale misidentification of the pollen unlikely although some records are suspect contamination is improbable for the vast majority of the pollen diagrams also long distance transport of pollen of fagopyrum snowdenii or oxygonum from africa seems unlikely as the pollen rain of that continent hardly contains that pollen the option that fagopyrum was present in western eurasia already much earlier than the late medieval must therefore be seriously considered cultivated species may have reached the area by trade between the mediterranean and eastern chinese realms which was regular since 2000 bce as the low pollen values argue against large scale cultivation the taxon may merely have occurred as a weed or its pollen was transported with other products and subsequently re emitted the pervasive notion that buckwheat was cultivated on large scale by the scythians in the ukrainian realm since 800 bce is highly ambiguous and probably wrong there are some indications that wild fagopyrum or a related taxon may have occurred widespread in eurasia during the pleistocene glaciations and the early middle holocene i e predating 2000 bce

surficial deposits on salt diapirs zagros mountains and persian gulf platform iran characterization evolution erosion and the influence on landscape morphology the surfaces of salt diapirs in the zagros mountains are mostly covered by surficial deposits which significantly affect erosion rates salt karst evolution land use and the density of the vegetation cover eleven salt diapirs were selected for the study of surficial deposits in order to cover variability in the geology morphology and climate in a majority of the diapirs in the zagros mountains and persian gulf platform the chemical and mineralogical compositions of 80 selected samples were studied mainly by x ray powder diffraction and x ray fluorescence changes in salinity along selected vertical profiles were studied together with the halite and gypsum distribution the subaerial residuum formed from minerals and rock detritus released from the dissolved rock salt is by far the most abundant material on the diapirs fluvial sediments derived from this type of residuum are the second most common deposits found while submarine residuum and marine sediments have only local importance the mineralogical chemical composition of surficial deposits varies amongst the three end members evaporite minerals gypsum anhydrite and minor halite carbonates dolomite and calcite and silicates oxides mainly quartz phyllosilicates and hematite based on infiltration tests on different types of surficial deposits most of the rainwater will infiltrate while overland flow predominates on rock salt exposures recharge concentration and thick accumulations of fine sediment support relatively rich vegetation cover in some places and even enable local agricultural activity the source material diapir relief climatic conditions and vegetation cover were found to be the main factors affecting the development and erosion of surficial deposits a difference was found in residuum type and landscape morphology between the relatively humid nw part of the studied area and the arid persian gulf coast in the nw the medium and thick residuum seems to be stable under current climatic conditions large sinkholes and blind valleys with sinking streams are common on other diapirs the original thick residuum is undergoing erosion and the new morphology is currently represented by salt exposures and badland like landscapes or by fields of small sinkholes developed in the thin residuum models for evolution of the subaerial residuum and the diapir landscape morphology are described in this paper while the thick residuum with vegetation has very low erosion rates the salt exposures and thin residuum are eroded rapidly during wet periods e g early holocene the diapirs rose and salt glaciers expanded as the influx of salt mass was much faster compared to erosion after the onset of an arid climate c 6 ka bp the rising of the some diapir surfaces decreased or even reversed due to acceleration of erosion thanks to vegetation degradation and changes in the residuum type and thickness

symmetrical and segmented variation of physical and geochemical characteristics of the central american volcanic front abstract the regional variation of physical and geochemical characteristics of central american volcanoes occurs in two fundamentally different patterns the first pattern is symmetrical about nicaragua crustal thickness silica contents of mafic lavas and volcanic edifice heights are lowest in nicaragua and increase smoothly toward costa rica to the south and guatemala to the north magma density is maximum in nicaragua and decreases smoothly outward the regional variation in crustal thickness is just enough so that magma densities calculated at appropriate moho pressures are the same at the base of the crust throughout the region this is consistent with magma ponding at the base of the crust the bulk compositions of central american basalts show the same symmetrical variation suites of nicaraguan basalts plotted in pseudo ternary cmas projections indicate large olivine and plagioclase primary phase volumes toward costa rica and guatemala the olivine and plagioclase fields inferred from suites of basaltic lavas are smaller which is consistent with fractionation at increasing depth the second pattern is the segmentation of the volcanic front and the plate margin in general the segmentation strongly affects the spacing and size of volcanic centers at segment boundaries volcanic centers are generally small and unusually widely spaced toward segment interiors volcano spacing and size increase systematically the lil element contents of lavas strongly reflect this pattern for lavas with similar silica contents the larger the volcano the higher the lil element contents the relationships between segmentation volcano spacing and volcano size are compatible with diapiric rise of magma accumulated in narrow ribbons near the upper surface of the underthrust slab the relationship between volcano volume and lil element content is qualitatively in agreement with an open system fractionation model

large scale hydration of the lithosphere above subducting slabs during subduction oceanic lithosphere capped by variably hydrated uppermost mantle oceanic crust and sediments undergoes progressive metamorphism and devolatilization the petrologic evolution of subducting oceanic lithosphere and the overriding continental oceanic lithosphere can be predicted by integrating thermal models with petrologic phase equilibria in mature subduction zones that have achieved thermal steady state the subducting slab lies at subsolidus conditions for depths 100 150 km most subducting oceanic crust passes through the blueschist to eclogite facies transition where large amounts of h2o are released by the breakdown of na amphibole lawsonite or clinozoisite and chlorite the large amounts of h2o released by continuous blueschist eclogite reactions can cause large scale hydration of the overriding lithosphere and can trigger partial melting of the mantle wedge lowermost lithosphere and asthenosphere upward migration of slab derived fluids add h2o co2 sio2 and incompatible elements to the overlying lithospheric plate that result in the formation of new phases e g serpentine amphibole and mica and chemical modification of existing phases e g trace element enrichment of clinopyroxene evidence for large scale lithospheric hydration above subducting slabs includes serpentinite diapirs observed in the marianas forearc low p wave velocities observed in the hanging wall of the alaskan and japanese subduction zones and studies of high pressure metamorphic terrains