the characteristics of movable fluid in the triassic lacustrine tight oil reservoir a case study of the chang 7 member of xin anbian block ordos basin china abstract the micropore throat structure of a tight oil reservoir is complex and its movable fluid distribution differs from that of a conventional reservoir by using nuclear magnetic resonance nmr and centrifugation the movable fluid distribution in the chang 7 tight reservoir in the xin anbian block of the ordos basin was quantitatively evaluated combined with the results of the physical property and high pressure mercury intrusion experiments the effects of the porosity permeability pore size distribution and micropore throat structure on the movable fluid distribution in the chang 7 tight reservoir were analyzed the nmr results show that the t2 spectral morphology of the chang 7 tight oil reservoir in the xin anbian block can be characterized by three main patterns with different amplitudes of front and post peaks the front peak corresponds to the scale of small pores and the post peak corresponds to the scale of large pores based on the three t2 spectrum patterns the chang 7 tight reservoir can be divided into three types type 1 reservoir with more small pores and fewer large pores type 2 reservoir with similar amounts of small and large pores and type 3 reservoir with fewer small pores and more large pores thus the characteristics of these three types of reservoirs can be determined the movable fluid parameters were calculated by nmr and centrifugation the movable fluid saturation of the type 1 reservoir is low with an average of 20 38 and the average movable fluid porosity is 1 47 the type 2 and type 3 reservoirs have higher movable fluid contents of 40 79 and 47 04 respectively the average movable fluid porosities of the type 2 and type 3 reservoirs are 3 37 and 3 48 respectively the greater number of small pores and smaller number of large pores in the type 1 reservoir result in weak correlations of the movable fluid with the physical properties and pore throat structure parameters the movable fluid saturation is negatively correlated with the maximum pore radius mainstream throat radius and maximum mercury saturation and is strongly positively correlated only with the porosity of the large pores as the number of large pores increases the movable fluid saturation strongly correlates with the property parameters pore size distribution and pore throat structure parameters in the type 2 and type 3 reservoirs the movable fluid saturations are positively affected by the maximum pore radius median radius mainstream throat radius and effective porosity but are strongly negatively correlated only with the radius mean value these results indicate that the fluid mobility of these two types of reservoirs can be promoted by the pore throat system to obtain favorable seepage characteristics

occurrence stratigraphy and geochemistry of late quaternary tephra layers in the aegean sea and the marmara sea abstract several discrete tephra layers occur in 2 5 10 3 m long cores from the aegean sea whereas a single tephra is identified in 3 5 9 7 m long cores from the marmara sea major and trace element data on these tephras delineate eight distinct groups the geochemical data and multivariate statistics allow the correlation of the tephra layers with six previously described marine tephras from the eastern mediterranean sea potential terrestrial sources are suggested for the others the chronostratigraphy of the tephra layers was established using several radiocarbon dates and the oxygen isotope stratigraphy from two long piston cores four widespread tephra layers occur within the upper quaternary sediments of the aegean sea the two youngest widespread tephra layers were derived from the santorini volcano of south central aegean sea z2 the minoan eruption ca 3 6 ka and y2 the cape riva eruption ca 21 7 ka the y2 tephra is also identified in three piston cores from the marmara sea the two older widespread tephra layers originated from the eruptions which emplaced the campanian ignimbrite of the italian volcanic provinces i e the y5 tephra ca 39 3 ka and from the nisyros volcano of the southeastern aegean sea the consistent occurrence of the nisyros tephra below the y5 tephra confirms similar findings in a lake core on the island of lesbos linear extrapolations using the oxygen isotope stratigraphy suggest an age of 42 44 ka for the nisyros eruption three additional tephra layers with a limited regional distribution are identified in the aegean sea cores two of these tephras originated from the yali volcano of the southeastern aegean sea and from the aeolian islands i e x1 tephra a series of six mugearite tephra beds in the south skiros basin is interpreted as a set of redeposited turbidites

lake ohrid albania provides an exceptional multi proxy record of environmental changes during the last glacial interglacial cycle multi proxy analyses on core jo2004 1 recovered from lake ohrid 40 55 000 n 20 40 297e 705 m a s l provide the first environmental and climate reconstruction in a mountainous area in southern europe over the last 140 000 years the response of both lacustrine and terrestrial environments to climate change has been amplified by the peculiar geomorphological and hydrological setting with a steep altitudinal gradient in the catchment and a karstic system feeding the lake the karstic system was active during interglacials leading to high carbonate production in the lake and blocked during glacials as a result of extremely cold climate conditions with permafrost in the mountains at the riss eemian transition termination 2 the increase in lacustrine productivity predated forest expansion by about 10 000 years in contrast the late glacial holocene transition termination 1 was characterized by the dramatic impact of the younger dryas which initially prevented interglacial carbonate production and delayed its maximum until the mid holocene in contrast forest expansion was progressive starting as early as ca 38 000 ago the proximity of high mountains and the probable moderating lake effect on local climate conditions promoted forest expansion and contributed to make the surroundings of lake ohrid favourable to forest refugia during the last glacial usually steppic period our study of sedimentology mineralogy geochemistry magnetics palynology and isotopes illustrates the non linear response of terrestrial and lacustrine ecosystems to similar climate events and demonstrates the potential of lake ohrid as an excellent paleoclimatic archive during the quaternary

the last 40 ka tephrostratigraphic record of lake ohrid albania and macedonia a very distal archive for ash dispersal from italian volcanoes abstract a 1075 cm long core lz1120 was recovered in the south eastern part of the lake ohrid republics of macedonia and albania and sampled for identification of tephra layers magnetic susceptibility investigations show rather high magnetic values throughout the core with peaks unrelated to the occurrence of tephra layers but instead to the relative abundance of detrital magnetic minerals in the sediment naked eye inspection of the core allowed us to identify of two tephra layers at 896 897 cm and 1070 1075 cm laboratory inspection of the grain size fraction 125 m allowed for the identification of a third cryptotephra at 310 315 cm major element analyses on glass shards of the tephra layers at 896 897 cm and 1070 1075 cm show a trachytic composition and indicate a correlation with the regionally dispersed y 3 and y 5 tephra layers dated at ca 30 and 39 cal ka bp the cryptotephra at 310 315 cm has a mugearitic benmoreitic composition and was correlated with the fl eruption of mt etna dated at 3370 70 cal yr bp these ages are in agreement with five 14 c ams measurements carried out on plant remains and macrofossils from the lake sediments at different depths along the core the recognition of distal tephra from italian volcanoes allows us to link the lake ohrid succession to other archives located in the mediterranean area and in eastern europe the benmoreitic mugearitic tephra layer at 310 315 cm is the first recognition in the balkan area of a distal ash deposit from a mid intensity explosive eruption of mt etna as far as 600 km from the source

the climate in europe during the eemian a multi method approach using pollen data the last interglacial period the eemian offers a testbed for comparing climate evolution throughout an interglacial with the current warm period we present here results from climatic reconstructions from 17 sites distributed across the european continent allowing an assessment of trends and regional averages of climate changes during this period we use a multi method approach to allow for an improved assessment of the uncertainties involved in the reconstruction in addition the method takes into account the errors associated with the age model the resulting uncertainties are large but allow a more robust assessment of the reconstructed climatic variations than in previous studies the results show a traditional three part eemian with an early optimum followed by slight cooling and eventually a sharp drop in both temperatures and precipitation this sequence is however restricted to the north as this latter change is not observed in the south where temperatures remain stable for longer these variations led to marked variation in the latitudinal temperature gradient during the eemian the difference between the two regions is also noticeable in the magnitude of changes with greater variations in the north than the south some evidence is found for changes in lapse rates however a greater number of sites is needed to confirm this

rapid environmental changes in southern europe during the last glacial period oxygen isotope records from greenland ice cores1 2 indicate numerous rapid climate fluctuations during the last glacial period north atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice rafted debris3 4 5 in contrast very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents here we present high resolution geochemical physical and pollen data from lake sediments in italy and from a mediterranean sediment core linked by a common tephrochronology our lacustrine sequence extends to the past 102 000 years many of its features correlate well with the greenland ice core records demonstrating that the closely coupled ocean atmosphere system of the northern hemisphere during the last glacial4 extended its influence at least as far as the central mediterranean region numerous vegetation changes were rapid frequently occurring in less than 200 years showing that the terrestrial biosphere participated fully in last glacial climate variability earlier than 65 000 years ago our record shows more climate fluctuations than are apparent in the greenland ice cores together the multi proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials and provide a step towards determining the underlying mechanisms of the centennial millennial scale variability

the influence of moisture on the development of soils of the cold deserts of antarctica abstract soils of the cold desert have many features in common with those of hot deserts they generally have dry surface horizons capped by a desert pavement of lag gravel a zone of accumulation of water soluble salts and a permanently frozen layer beneath which may be ice cemented in its lower part they are also distinguished by their very low temperatures and as a consequence of this they have very low moisture status and humidity soil moisture within cold desert soils is usually in the form of small ice crystals vapour or thin water films the influence of broad climatic differences in antarctica is reflected in the soils by differences in moisture supply in terms of precipitation and its availability which is dependent on the length of time any given soil is in whole or in part above freezing this in turn influences the development of morphological properties including soil depth and horizon development on the basis of these features it has been possible to group soils in terms of moisture availability those in which moisture is rarely if ever available and in which there is no leaching of soluble materials ultraxerous moisture class soils in which moisture is sufficient to allow some leaching of soluble material xerous moisture class and soils in which relatively large amounts of moisture are available subxerous moisture class characteristics of the soils formed under these regimes are described subsurface ice present during the early stages of soil formation as the soil parent material is formed by the ablation of ice cored moraine represents an important source of profile moisture during the early stages of soil formation its main influence on soil morphology however is in the mixing and sorting of coarse and fine materials during the formation of patterned and hummocky ground in local areas where there is an abundance of moisture often as a saline solution in hollows or depressions intrazonal soils may be developed apart from a wetter soil moisture regime these soils are characterised by the presence of higher concentrations of soluble salt by olive rather than brownish soil colours and by higher clay contents as well as by differences in weathering and clay mineral formation the profile features resulting from these moisture differences are described and illustrated

pollen analytical biostratigraphy of the last five climatic cycles from a long continental sequence from the velay region massif central france in the volcanic region of velay massif central france lake sediment sequences derived from maar craters situated close to one another ribains praclaux and lac du bouchet have been correlated on the basis of tephrostratigraphical analyses this has enabled the construction of a sequence 2980 pollen spectra that begins during the glaciation preceding the holsteinian and ends in the present this sequence covers the period from 450 ka i e from the end of marine oxygen isotope stage 12 to the present time and includes five climatic cycles the study of a second core from the praclaux site completed the long velay sequence the biostratigraphy of the whole sequence is described in detail and illustrated by a synthetic and simplified pollen diagram thirteen temperate forest episodes interglacials or interstadials and as many cold periods glacials or stadials are defined each temperate episode is characterised by particular forest development and vegetation dynamics and all of them with the exception of the holocene begin and end with a pinus forest the vegetation dynamics observed during the holocene resemble more closely those recorded during the interstadials than during the interglacials copyright 2000 john wiley sons ltd

holocene lakes from ramlat as sab atayn yemen illustrate the impact of monsoon activity in southern arabia abstract paleoecology and paleohydrology of the ramlat as sab atayn southern arabia are reconstructed from a comparative study including sedimentology mineralogy stable isotope ratios of carbonates and palynology of lacustrine sediments recovered from the al hawa depression the section dates from 8700 to 7200 yr b p and records an early phase of flooding followed by distinct lacustrine development from 7800 to 7200 yr b p coeval with maximum activity of the indian monsoon comparison of the pollen record with modern pollen deposition suggests that regional vegetation was then already of desert type and was related to strong seasonal trade winds

the diatom stratigraphy and palaeoecology of lake ohrid yugoslavia abstract an 8 85 m core no 9 was taken from lake ohrid yugoslavia in august 1973 at a depth of 210 m approximately 6 km offshore of gorcia yugoslavia the core was sampled at 10 cm intervals and analyzed for moisture organic and caco3 content and diatoms there is a slight but steady decrease of moisture with depth probably due to sediment compaction the organic content showed little variation throughout the core x 2 73 0 39 of total weight the caco3 content from 885 110 cm depth also showed little change x 2 32 0 55 of total weight but increased in the top meter of the core 100 0 cm x 11 03 8 86 of total weight throughout the core there is an inverse relationship between organic and caco3 content particularly in the top meter extrapolation to the bottom of the core using linear regression based on 14c dating yields a date of ca 30 000 years b p results indicate that lake ohrid has remained an oligotrophic lake throughout the period represented by core 9 diatom analysis shows one persistent group of diatoms throughout the core this group consists of cyclotella fottii c hustedtii and c hustedtii var 1 and is referred to as the cyclotella complex between 885 650 cm ca 30 000 20 000 yr b p there is a sharp increase in numbers and a slight increase in diversity of species this may correspond with the beginning of the warmer more humid middle pleniglacial between 650 100 cm ca 20 000 10 000 yr b p the cyclotella complex appears usually alone in small number there are a few other scattered species in this section mainly opephora martyi and fragilaria pinnata this section of the core probably corresponds with the cold upper pleniglacial of the wurm weichselian between 100 0 cm ca 10 000 0 yr b p there is the largest increase in number and diversity of species particularly above 60 cm the cyclotella complex c ocellata cyclotella sp 1 stephanodiscus astraea var intermedia fo 11 and stephanodiscus sp 1 are dominant this is the only section of the core in which stephanodiscus species occur and probably corresponds with the holocene

duration of last interglacial conditions in northwestern greece a new astronomical calibration method for long pollen records from southern europe is applied to the last interglacial interval of the ioannina sequence northwest greece this shows that the last interglacial in this region as defined by the presence of forest communities lasted c 15 500 years from 127 300 to 111 800 yr b p interglacial conditions developed within marine isotope sub stage mis 5e and persisted into mis 5d lagging changes in global ice volume

pollen inferred late glacial and holocene climate in southern balkans lake maliq abstract high temporal resolution analysis of pollen records from lake maliq albania provides quantitative estimates of monthly temperature and precipitation changes since the last deglaciation the climate parameters were estimated using the best modern analogue technique with an updated modern pollen climate database composed of 2748 surface samples the record shows two main cooling phases in the maliq area the oldest and younger dryas and a cooling event around 8200 years which suggests that the forcing factors driving climate variations in the north atlantic area since the last glacial period also extended their influence into the mediterranean area the oldest and younger dryas are also characterized by an arid climate and a change in the seasonality of precipitation the summer precipitation tends to be greater during the cooling phases than during the temperate periods the holocene climate is relatively stable and the values of each parameter reach their modern levels except for an arid event between 8300 and 8100 cal bp

the campanian ignimbrite and codola tephra layers two temporal stratigraphic markers for the early upper palaeolithic in southern italy and eastern europe tephra layers from archaeological sites in southern italy and eastern europe stratigraphically associated with cultural levels containing early upper palaeolithic industry were analysed the results confirm the occurrence of the campanian ignimbrite tephra ci ca 40 cal ka bp at castelcivita cave southern italy temnata cave bulgaria and in the kostenki borshchevo area of the russian plain this tephra originated from the largest eruption of the phlegrean field caldera represents the widest volcanic deposit and one of the most important temporal stratigraphic markers of western eurasia at paglicci cave and lesser sites in the apulia region we recognise a chemically and texturally different tephra which lithologically chronologically and chemically matches the physical and chemical characteristics of the plinian eruption of codola a poorly known late pleistocene explosive event from the neapolitan volcanoes likely somma vesuvius for this latter we propose a preliminary age estimate of ca 33 cal ka bp and a correlation to the widespread c 10 marine tephra of the central mediterranean the stratigraphic position of both ci and codola tephra layers at castelcivita and paglicci help date the first and the last documented appearance of early upper palaeolithic industries of southern italy to ca 41 40 and 33 cal ka bp respectively or between two interstadial oscillations of the monticchio pollen record to which the ci and codola tephras are physically correlated corresponding to the greenland interstadials 10 9 and 5 in eastern europe the stratigraphic and chronometric data seem to indicate an earlier appearance of the early upper palaeolithic industries which would predate of two millennia at least the overlying ci tephra the tephrostratigraphic correlation indicates that in both regions the innovations connected with the so called early upper palaeolithic encompassing subsistence strategy and stone tool technology appeared and evolved during one of the most unstable climatic phases of the last glacial period on this basis the marked environmental unpredictability characterising this time span is seen as a potential ecological factor involved in the cultural changes observed

towards an understanding of the response of southern european vegetation to orbital and suborbital climate variability abstract in recent years the generation of high resolution terrestrial and marine long pollen sequences with improved chronological control has provided new insights into the vegetation response in southern europe to orbital and suborbital climate variability here a synthesis of our current understanding of the phase and amplitude relationships between climate forcing and vegetation changes is presented what emerges is that on orbital frequencies the timing of interglacial forest expansion is closely linked to the summer insolation maximum but does not have a fixed lag relative to the mid point of the deglaciation which may vary from one termination to another for the closing phases of interglacials the available evidence suggests that forest in southern europe usually extends into the interval of ice growth however suborbital variability may override the diachronous relationship between glacial inception and forest decline leading to a premature ending of forest periods during glacial intervals there is a close correspondence between tree population size and ice volume extent while during temperate intervals the extent of forest development is closely related to the amplitude of insolation and associated climate regimes but may diverge from the extent of residual ice volume on suborbital frequencies changes in tree population size are in phase with climate forcing while the amplitude of these changes is modulated by geographical position and local factors finally orbital mean state can lead to the modulation of the amplitude of suborbital scale variability examination of additional climatic cycles and increased resolution better than 200 years are needed to test further these preliminary conclusions

last interglacial palaeovegetation palaeoenvironments and chronology a new record from lago grande di monticchio southern italy abstract the sediments of lago grande di monticchio southern italy extend continuously from the present back to the penultimate glacial stage and have an independent lamination based chronology of high precision and accuracy results are presented here from a detailed palynological investigation of that part of the sediment sequence that extends from the last millennia of the penultimate glacial stage to the first stadial following the last interglacial li quantitative palaeovegetation and palaeoclimate reconstructions made from the palynological data are also presented the onset of the li is dated to 127 20 ka bp a date that is consistent with other recent estimates the duration of the li is estimated to have been 17 70 ka the palaeovegetation record indicates a transition period of 3 35 ka at the end of the penultimate glacial stage prior to the onset of the li no younger dryas like oscillation is recorded although the transition was interrupted by a brief event lasting ca 250 years during which pollen of woody taxa was reduced in abundance steppe vegetation dominated during the latter part of the penultimate full glacial stage but was replaced progressively by wooded steppe during the transition although the development of forest cover marked the onset of the li the forests were relatively open or discontinuous during the first 2 65 ka closing progressively thereafter and generally dominating between 123 00 and 109 50 ka bp the end of the li is dated to 109 50 ka bp after which date forest cover became discontinuous and wooded steppe or steppe dominated during the 1 90 ka of the subsequent stadial as might be expected given the location of the lake the composition of the li forests differs markedly from those recorded from northern europe as well as from those recorded at other localities in southern europe the palaeoclimate reconstructions reveal complex changes in seasonality the maximum coldest month mean temperatures being between 125 70 ka bp and 123 00 ka bp whereas maxima for both annual temperature sum and the ratio of actual to potential evapotranspiration were between 120 60 ka bp and 115 80 ka bp reconstructed zonal mean values for all three climatic variables in the zones in which they peak exceed values at the locality today comparison with other palaeovegetation records of the li from europe reveals that forest cover generally opened up north of the alpine region probably ca 115 ka bp coinciding with a marked decrease in sea surface temperatures in the nordic seas this probably corresponds to a marked shift in forest composition at lago grande di monticchio at 115 80 ka bp with an associated reconstructed decrease of ca 5 c in coldest month mean temperature nonetheless forest continued to dominate at lago grande di monticchio until 109 50 ka bp such comparisons also reveal considerable complexity in the geographical and altitudinal patterns of change in palaeovegetation during the li such complexity is to be expected given the parallel complexity of holocene changes systematic comparisons between reconstructions of palaeoclimate are hampered by a lack of consistency in approach and in the variables reconstructed further insight into this complexity of palaeoclimate development during the li requires a synthesis of the available data and application of a consistent reconstruction approach that also provides robust estimates of the uncertainty in the reconstructed values

tephrostratigraphy of the last 170 ka in sedimentary successions from the adriatic sea abstract in this study are discussed new sem eds analyses performed on glass shards from five cores collected in the central adriatic sea and two cores recovered from the south adriatic sea a total of 26 tephra layers have been characterized and compared with the geochemical features of terrestrial deposits and other tephra archives in the area south adriatic sea and lago grande di monticchio vulture volcano the compositions are compatible with either a campanian or a roman provenance the cores located on the central adriatic inner and outer shelf recorded tephra referred to explosive events described in the literature ap3 sub plinian activity of the somma vesuvius 2710 60 14 c years bp avellino eruption somma vesuvius 3548 129 14 c years bp agnano monte spina phlegrean fields 4100 400 years bp mercato eruption somma vesuvius 8010 35 14 c years bp agnano pomici principali eruption phlegrean fields 10 320 50 14 c years bp neapolitan yellow tuff phlegrean fields 12 100 170 14 c years bp some of these layers were also observed in the south adriatic core in68 9 in addition to younger ap2 sub plinian eruption somma vesuvius 3225 140 14 c years bp and older layers pomici di base eruption somma vesuvius 18 300 150 14 c years bp significant is the tephra record of core rf95 7 that for the first time in the adriatic sea reports the occurrence of tephra layers older than 60 ka the well known mediterranean tephra layers x2 ca 70 ka w1 ca 140 ka and v2 roman origin ca 170 ka as well as other tephra layers attributed on the basis of geochemistry and biostratigraphy to explosive eruptions occurred at vico 138 2 and 151 3 ka bp and ischia 147 140 ka bp previous tephra correlations performed on other cores in the central adriatic sea were also critically revised according to new available data and integrated with the results of this study for a correlation at a regional scale the most important key beds for correlation are the agnano monte spina and neapolitan yellow tuff tephra layers which occur in both central and south adriatic sea other tephra layers younger than 15 ka are relatively less frequent the y1 etna 14 180 260 14 c years bp and agnano pomici principali in the more recent record in the shelf cores north of gargano promontory the ap3 tephra layer is also frequent

the eruptive history of pantelleria sicily channel in the last 50 ka six silicic eruptive cycles have been recognized in the last 50 ka at pantelleria the products of each cycle exhibit a compositional variation from pantellerite to less peralkaline rhyolite or to trachyte the relationships between the range of chemical variation the erupted volume and the time of eruptions allow us to estimate an average differentiation rate of 5 crystal fractionation per 1000 years and a constant long term rate of magma discharge of 0 1 km3 per 1000 years pressure increase in the magma chamber caused by the addition of new magma accumulation of highly differentiated volatile rich magma in the roof zone and a concomitant build up of a vapour phase is postulated as a possible triggering mechanism for eruptions

high resolution palynological record off the iberian margin direct land sea correlation for the last interglacial complex abstract we present high resolution pollen dinocyst and isotopic data for the last interglacial complex from marine core md952042 southwestern margin of the iberian peninsula 37 48 n 10 10 w 3148 m direct land sea correlation from this core indicates that during this period north atlantic sea surface temperatures were in phase with iberian climate our palynological analysis suggests a younger dryas like event at the marine isotope stage mis 6 5 transition the analysis also indicates that the eemian spans from the lightest isotopic values of mis 5e ca 126 ky bp to the heavier isotopic values towards the mis 5e 5d transition therefore the eemian is not entirely equivalent to mis 5e pollen analysis identifies four climatic phases of low amplitude during the eemian a mediterranean climate in southwestern europe is gradually replaced by oceanic conditions the middle of the eemian is characterized by an increase in precipitation on the land and ocean associated with a slight cooling this seems to be the result of a displacement of the polar front as far south as southern europe during this period after the eemian three relatively short climatic phases on land melisey i st germain ia and montaigu cold event occurred contemporaneously with three shifts of sea surface temperatures the montaigu event first identified in terrestrial pollen sequences is therefore also recorded in core md952042 on the basis of pollen dinocyst and planktonic isotopic data our results also show that the warm periods of mis 5 are not characterized by similar climatic conditions on land

geochemical and geophysical implications of the radiocarbon calibration abstract a precise and accurate chronological framework is crucial to study the dynamics of a variety of phenomena which occurred during the last 45 000 years although the 14 c dating method has been widely applied since the 1950s it is recognized that the atmospheric 14 c 12 c ratio has not been stable during the past in order to calculate accurate ages these fluctuations have to be corrected by means of a calibration curve obtained by comparing raw 14 c measurements with true calendar ages provided by independent dating methods the calibration curve obtained so far is characterized by a long term trend with raw 14 c ages being significantly younger than calendar ages during most of the last 45 000 years abrupt 14 c shifts which occurred over centuries to millennia are superimposed on this long term trend of decreasing atmospheric 14 c 12 c ratio to a certain extent it is possible to outline the different causes of atmospheric 14 c variations by considering complementary information obtained from other cosmogenic nuclides studied at different latitudes 1 most high frequency changes in the atmospheric 14 c 12 c ratio are linked to magnetic fluctuations of solar origin as revealed by studying the last three centuries for which direct observations of the sun are available a similar conclusion is derived by comparing 14 c 12 c events with 10 be and 36 cl concentration maxima in polar ice cores 2 the long term trend shift of 14 c ages is due to a long period of decreased shielding effect of the geomagnetic dipole field which occurred over the interval between 10 000 and 40 000 years bp this interpretation is supported by paleomagnetic measurements performed on volcanic and sedimentary rocks and by 10 be and 36 cl analysed in low and high latitude records 3 a prominent and rapid atmospheric 14 c 12 c excursion occurred between 13 000 and 11 500 cal yr bp thus corresponding to the younger dryas cold period by contrast with the 14 c variability mentioned above which is linked to 14 c production changes this so called 14 c age plateau is probably due to an abrupt variation in the rates of exchange within the global carbon cycle this interpretation is supported by independent geochemical proxies and by numerical modelling of the carbon cycle

a 12 000 year pollen record from lake maliq albania abstract pollen data from lake maliq the first from albania contribute new information to the discussion of the vegetational hydrological and climatological history of the balkans since 12 000 yr b p during late glacial time a perennial lake expanded at maliq it was surrounded by a complex vegetation association composed of steppe and mixed forest elements the highly diverse forest flora suggest that late glacial forest refugia were more developed here at middle altitude rather than at higher altitude as previously suggested the forest developed after 9800 yr b p while the water level remained high in the korce basin until 5000 yr b p different environmental conditions characterized by lower available moisture and warmer winters progressively took place after this date human activity in the korce basin ca 4500 yr b p was coeval with conditions characterized by an increase in winter temperatures and a decrease in summer moisture

a 90 000 200 000 yrs marine tephra record of italian volcanic activity in the central mediterranean sea abstract a detailed tephrochronological study was undertaken in three deep sea cores collected in the tyrrhenian and ionian seas the age and the origin of the marine tephra were inferred from oxygen isotope records of foraminifera and from major element compositions of glass shards seventy one eruptions were detected in the time interval 90 000 200 000 yrs during which the volcanoes of the roman and campanian regions and of the southern italy were in activity this is attested by the consistency of the geochemical compositions of both marine and terrestrial deposits most of the marine tephra consisted in trachytes and phonolites characterizing a roman and campanian origin several tephra were proposed as key horizons for proximal and distal sediments among them one tephra originating from mount etna 149 300 yrs and five tephra from pantelleria island 130 000 yrs 163 600 yrs 192 500 yrs 197 400 yrs and 198 400 yrs were northerly dispersed several other key horizons originated from the campanian or roman provinces were detected as far as 1000 km from the vents

groundwater flow near vertical recirculatory wells effect of skin on flowgeometry and travel times with implications for aquifer remediation abstract flow structure around a recirculation well in a uniform anisotropic aquifer is investigated using potential theory and stokes stream function techniques a vertical recirculation well consists of two screened sections chambers separated by an impermeable casing one section extracts water from the aquifer and the other section injects the water back into the aquifer analytical formulae are derived for the drawdown and the stream function for a model in which the extraction and injection chambers of the well are modeled as uniformly distributed cylindrical sinks and sources respectively travel times are analyzed for water particles traveling from the injection chamber to the extraction chamber along streamlines containing various percentages of the flow we consider a disturbed zone skin having properties which are different from those in the uniform anisotropic aquifer owing to disturbance of the area near the well during installation the effects of this skin on the streamlines and travel times are analyzed for various lengths separating the chambers and for various skin conductivities the method completely eliminates the use of numerical finite difference or finite element methods and can be used for optimization of technological parameters in a remediation system

geology of the peralkaline volcano at pantelleria strait of sicily situated in a submerged continental rift pantelleria is a volcanic island with a subaerial eruptive history longer than 300 ka its eruptive behavior edifice morphologies and complex multiunit geologic history are representative of strongly peralkaline centers it is dominated by the 6 km wide cinque denti caldera which formed ca 45 ka ago during eruption of the green tuff a strongly rheomorphic unit zoned from pantellerite to trachyte and consisting of falls surges and pyroclastic flows soon after collapse trachyte lava flows from an intracaldera central vent built a broad cone that compensated isostatically for the volume of the caldera and nearly filled it progressive chemical evolution of the chamber between 45 and 18 ka ago is recorded in the increasing peralkalinity of the youngest lava of the intracaldera trachyte cone and the few lavas erupted northwest of the caldera beginning about 18 ka ago inflation of the chamber opened old ring fractures and new radial fractures along which recently differentiated pantellerite constructed more than 25 pumice cones and shields continued uplift raised the northwest half of the intracaldera trachyte cone 275 m creating the island s present summit montagna grande by trapdoor uplift pantellerite erupted along the trapdoor faults and their hingeline forming numerous pumice cones and agglutinate sheets as well as five lava domes degassing and drawdown of the upper pantelleritic part of a compositionally and thermally stratified magma chamber during this 18 3 ka episode led to entrainment of subjacent crystal rich pantelleritic trachyte magma as crenulate inclusions progressive mixing between host and inclusions resulted in a secular decrease in the degree of evolution of the 0 82 km3 of magma erupted during the episode

precise dating of dansgaard oeschger climate oscillations in western europe from stalagmite data the signature of dansgaard oeschger events millennial scale abrupt climate oscillations during the last glacial period is well established in ice cores and marine records but the effects of such events in continental settings are not as clear and their absolute chronology is uncertain beyond the limit of 14 c dating and annual layer counting for marine records and ice cores respectively here we present carbon and oxygen isotope records from a stalagmite collected in southwest france which have been precisely dated using 234u 230th ratios we find rapid climate oscillations coincident with the established dansgaard oeschger events between 83 000 and 32 000 years ago in both isotope records the oxygen isotope signature is similar to a record from soreq cave israel and deep sea records indicating the large spatial scale of the climate oscillations the signal in the carbon isotopes gives evidence of drastic and rapid vegetation changes in western europe an important site in human cultural evolution we also find evidence for a long phase of extremely cold climate in southwest france between 61 2 0 6 and 67 4 0 9 kyr ago