magma chamber of the campi flegrei supervolcano at the time of eruption of the campanian ignimbrite a supereruption that occurred in the campi flegrei area italy ca 39 ka had regional and global scale environmental impacts and deposited the campanian ignimbrite ci we attempt to shed light on critical aspects of the eruption depth of magma chamber intensive pre eruptive magma conditions and the large volume magma plumbing system on the basis of information derived from analyzing melt inclusion mi data to achieve these aims we provide new measurements of homogenization temperatures and values of dissolved h2o within phenocryst hosted mis from pumices erupted during different phases of the ci eruption the mi data indicate that a relatively homogeneous overheated trachytic magma resided within a relatively deep magma chamber dissolved water contents in mis indicate that prior to the eruption the magma chamber underwent radical changes related to differential upward movement of magma decompression of the rising trachytic magma caused a decrease in water solubility and crystallization and trachytic bodies were emplaced at very shallow depths the proposed eruptive model links portions of the main magma chamber and apophyses with specific eruptive units

long term fluvial archives in the fen wei graben central china and their bearing on the tectonic history of the india asia collision system during the quaternary abstract staircases of large scale river terraces are striking features of the landscape in the fen wei graben adjacent to the qinling orogenic belts central china field investigations indicate that all five river terraces are composed of a basal channel gravel and an overlying thick loess palaeosol succession as chinese loess stratigraphy has been well studied it favours age determination of these terraces and their correlation with the marine oxygen isotope stages our research indicates that the ages of the five terraces are approximately 2 6 1 2 0 9 0 65 and 0 15 ma respectively the formation of these river terraces within the fen wei graben has been attributed to nw se crustal extension associated with left lateral displacement between the north and south china blocks in response to the northward movement of india towards asia since cenozoic time thus the stepped terraces in the fen wei graben reflects elements of the india asia collision systems in which terraces define episodes of accelerated northward movement of india towards asia during the quaternary

flexural subsidence by 29 ma on the ne edge of tibet from the magnetostratigraphy of linxia basin china abstract this study provides a detailed magnetostratigraphic record of subsidence in the linxia basin documenting a 27 myr long sedimentary record from the northeastern edge of the tibetan plateau deposition in the linxia basin began at 29 ma and continued nearly uninterruptedly until 1 7 ma increasing rates of subsidence between 29 and 6 ma in the linxia basin suggest deposition in the foredeep portion of a flexural basin and constrain the timing of shortening in the northeastern margin of the plateau to late oligocene late miocene time by late miocene early pliocene time a decrease in subsidence rates in the linxia basin associated with thrust faulting and a 10 clockwise rotation in the basin indicates that the deformation front of the tibetan plateau had propagated into the currently deforming region northeast of the plateau

pleistocene drainage reorganization driven by the isostatic response to deep incision into the northeastern tibetan plateau pleistocene drainage basin integration led to progressive excavation of tertiary quaternary sedimentary basins along the yellow river in the northeastern tibetan plateau cosmogenic burial dating of ancestral river deposits and basin fi ll from two key watershed divides confi rms a fl uvial connection between basins at 0 5 1 2 ma prior to excavation by the yellow river pres ervation of the relict depositional surface that represents the maximum height of basin fi ll allows reconstruction of the volume of eroded material across a broad region we quantify the iso static response to this erosional unloading using a two dimensional fl exural model calculated maximum vertical displacements for different effective elastic thicknesses vary from 160 m to 260 m near the pleistocene spillway from the qinghai paleo lake we suggest that the isostatic response to fl excavation along the yellow river defeated local tributaries isolated lake qinghai and led to the development of an internally drained basin in the past 0 5 1 2 m y

magma chamber evolution prior to the campanian ignimbrite and neapolitan yellow tuff eruptions campi flegrei italy the campi flegrei campanian region italy experienced two cataclysmic caldera forming eruptions which produced the campanian ignimbrite 39 ka ci and the neapolitan yellow tuff 15 ka nyt we studied the minor eruptions before both these large events to understand magma chamber evolution leading towards such catastrophic eruptions major trace element and sr and nd isotope compositions of pre campanian ignimbrite and pre neapolitan yellow tuff products define distinct geochemical groups which are here interpreted as distinct magma batches these batches do not show any transitional trend towards the ci and nyt eruptions the ci and nyt systems are decoupled geochemically and isotopically at least one of the pre ci and one of the pre nyt erupted magma batches qualifies as mixing endmembers for the large ci and nyt eruptions and thus must have been stored in reservoirs for some time to remain available for the ci and nyt eruptions the least evolved isotopically distinct magma compositions that are typical of the last phases of the nyt and ci eruptions did not occur before caldera forming events based on the new data we propose the following scenario multiple magma chambers with distinct compositions existed below the campi flegrei before the ci and nyt eruptions and remained generally separated for some time unless new magma was recharged in each case one of the residing magma reservoirs was recharged by a new large volume magma input of intermediate composition from a deeper differentiating magma reservoir this may have triggered the coalescence of the previously separated reservoirs into one large chamber which fed the cataclysmic caldera forming eruption large magma chambers in the campi flegrei may therefore be ephemeral features interrupted by periods of evolution in individual separated magma reservoirs

late pleistocene holocene landscape evolution in fossa bradanica basilicata southern italy abstract studies in the middle basento river basin supported by reliable chronological data tephra layers and a number of absolute datings have allowed the reconstruction of late pleistocene holocene geomorphological evolution of the middle to low fossa bradanica area basilicata southern italy the original upper pleistocene hillslope has been dissected by deep gullies leaving relict slope pediments holocene filling of the basento river valley and gullies occurred as a succession of downcut and fill episodes a first phase of accumulation occurred in the late neolithic which was followed by a downcutting between 4500 and 3700 cal yr bp a second deposition phase took place in the greek roman period between 2800 and 1620 cal yr bp which was interrupted at around 2500 cal yr bp another downcutting phase took place between 1620 and 1500 cal yr bp followed by a deposition phase between 1440 and 1000 cal yr bp after 1000 cal yr bp a deep downcutting took place evidence collected with this study coupled with climate data recorded in other italian and european locations suggests that filling and downcutting episodes in fossa bradanica were predominantly climate driven anthropogenic impact only intensified or weakened these processes

the campanian ignimbrite southern italy geochemical zoning insight on the generation of a super eruption from catastrophic differentiation and fast withdrawal more than ca 100 km3 of nearly homogeneous crystal poor phonolite and ca 100 km3 of slightly zoned trachyte were erupted 39 ka during the campanian ignimbrite super eruption the most powerful in the neapolitan area partition coefficient calculations equilibrium mineral assemblages glass compositions and texture were used to reconstruct compositional thermal and pressure gradients in the pre eruptive reservoir as well as timing and mechanisms of evolution towards magma chamber overpressure and eruption our petrologic data indicate that a wide sill like trachytic magma chamber was active under the campanian plain at 2 5 kbar before ci eruption thermal exchange between high liquidus 1199 c trachytic sill and cool country rocks caused intense undercooling driving a catastrophic and fast 102 years in situ fractional crystallization and crustal assimilation that produced a water oversaturated phonolitic cap and an overpressure in the chamber that triggered the super eruption this process culminated in an abrupt reservoir opening and in a fast single step high decompression sanidine phenocrysts crystal size distributions reveal high differentiation rate thus suggesting that such a sill like magmatic system is capable of evolving in a very short time and erupting suddenly with only short term warning

late pliocene establishment of exorheic drainage in the northeastern tibetan plateau as evidenced by the wuquan formation in the lanzhou basin abstract the fluvial archives in the upper reach yellow river basins provide important information about drainage history of the northeastern tibetan plateau tp associated with geomorphologic evolution and climate change however the pliocene fluvial strata within this region have not been studied in detail hence limiting the understanding of the late cenozoic development of regional fluvial systems in this paper we present the results of a study of the geochronology sedimentology and provenance of the fluvial sequence of the wuquan formation in the lanzhou basin in the northeastern tp magnetostratigraphic and cosmogenic nuclide burial ages indicate that the wuquan formation was deposited during 3 6 2 2 ma furthermore sedimentary facies gravel composition paleocurrent data and detrital zircon u pb age spectra reveal that the fluvial sequence resembles the terraces of the yellow river in terms of source area flow direction and depositional environment our results indicate that a paleo drainage system flowing out of the northeastern tp was established by ca 3 6 ma and that the upstream parts of the yellow river must have developed subsequently from this paleo drainage system the late pliocene drainage system fits well with the dramatic uplift of the northeastern tp an intensified asian summer monsoon and global increase in erosion rates which may reflect interactions between geomorphic evolution tectonic deformation and climate change

stacked 2 6 ma grain size record from the chinese loess based on five sections and correlation with the deep sea δ18o record 1 this study aims to establish a stacked climate record of the quaternary period from the chinese loess sequence and to address the forcing mechanisms for the regional climate history of the loess plateau by correlating the stacked record with a composite 18o record in deep sea sediments a total of 18 352 samples were obtained from five loess sections located at baoji lingtai jingchuan puxian and pingliang in the southern and middle loess plateau these yielded high resolution grain size records between section correlation of these shows that although small depositional hiatuses are present in places within a single section most parts of the sections display near continuous dust deposition throughout the quaternary the grain size records were tuned simultaneously to the theoretical variations in obliquity and precession of the earth s orbit the grain size records plotted on their orbital timescales were then averaged to form a stacked loess grain size time series termed the chiloparts record this resolves most of the orbital timescale paleoclimate events buried in the loess soil sequences of the southern and middle loess plateau and can be used as a regional archive of the pleistocene climate history in the loess plateau comparison of the chiloparts record with a composite marine 18o record shows that for the past 1 8 ma the loess paleosol record can be correlated almost cycle by cycle with the marine record several discrepancies in the climatic events between the two records have also been identified implying that regional forcing mechanisms may have played a part in the climatic evolution of the chinese loess plateau

the environmental effects of the uplift of the qinghai xizang plateau the intense upheaval of the qinghai xizang plateau took place 2 ma bp the terraces of the yellow river in the lanzhou region and its upper sections provide a record of the uplift of the plateau the interaction of glaciation cycles resulting from climatic changes and pulsating tectonic upheavals are both involved in the record of environmental change across the plateau three tectonic climatic events which are termed respectively the qinghai xizang movement the huanghe yellow river movement and the gonghe movement occurred 2 1 5 1 0 and 0 15 ma bp the upheaval of the qinghai xizang plateau was the trigger mechanism of the asian monsoon the loess plateau was formed in the monsoon triangle of east asia human origins and human evolution may have been stimulated by the uplift of the qinghai xizang plateau

landscape evolution and development of eolian modified unconsolidated gravel surfaces and yardangs in the hami basin china abstract unconsolidated gravel surfaces alluvial terraces and yardangs are widespread in the turpan hami topographical depression of nw china these landscape features provide an opportunity to investigate the wind erosion history and landscape evolution of the hami basin along with anomalously high near surface wind speeds these features suggest that the hami basin was an important source of mineral dust during the pleistocene we present the results of an integrated geomorphologic stratigraphic and chronologic study on the genesis of unconsolidated gravel surfaces and yardang fields in the hami basin mobilization of silt to sand sized fractions from the surfaces of the quaternary alluvial sediments occurred under generally dry conditions leaving unconsolidated gravels to organize into inflationary type desert pavement surfaces type 1 and deflationary type desert pavements surfaces type 2 we propose that the pleistocene alluvial terraces of the hami basin formed principally during wetter intervals which are assumed to correspond with interglacial periods the coarse grained alluvium atop terraces protected underlying strata from wind erosion the bedrock then began to be sculpted into yardangs after the removal of the coarse grained armoring surfaces with mostly sub horizontal bedding the geometries of yardangs was controlled by lithology wind and water erosion based on uav 3d models optically stimulated luminescence osl and electron spin resonance esr ages we find an erosion rate of 0 23 mm yr since 200 ka this combined with widespread uneroded strata armored by unconsolidated gravel surfaces indicates that the hami basin had considerable dust emission potential in the past

a laboratory study of explosive volcanic eruptions this paper describes a series of laboratory experiments in which buoyant mixtures of methanol and ethylene glycol meg are injected as a downward propagating jet into a tank of fresh water as the meg mixes with water it becomes denser than the water if the meg mixes with sufficient water before its initial momentum is exhausted the jet fluid may become dense and continue downward into the tank as a convecting plume if the jet does not have sufficient initial momentum then a collapsing fountain develops and the material in the jet rises back toward the top of the tank and spreads laterally as a gravity current subsequent mixing can cause some of the material in the gravity current to become dense separate from the current and sink into the tank although the direction of gravity is reversed these experiments simulate many of the important dynamical features of eruption columns which can develop during explosive volcanic eruptions in the volcanic situation a hot dense and dusty mixture of gas ash and clasts is erupted from a vent at high speed if sufficient ambient air is entrained into the jet then the mixture may become buoyant through heating and expansion of the air it therefore continues rising high into the atmosphere otherwise the material collapses back to the ground these experiments allow one to investigate systematically the different styles of behavior of the erupted material as the eruption conditions change four different styles of behavior have been identified with transitions from one style to the next as the initial momentum flux of the jet is decreased 1 plinian style convecting columns 2 the periodic release of discrete convecting clouds originating close to the vent from a collapsed fountain 3 coignimbrite eruption columns centered some distance from the vent which are generated when a fraction of a pyroclastic flow becomes buoyant and 4 pyroclastic flows in which the majority of the material remains relatively dense and therefore spreads laterally from the vent using a simple theoretical model of the laboratory experiments an analytical expression describing the conditions necessary for collapse of the analogue laboratory columns has been derived this is successfully compared with the laboratory experiments the simple analysis predicts that column collapse may be induced by 1 increasing the density of the erupted material 2 decreasing the maximum buoyancy the mixture can attain on mixing with ambient 3 increasing the erupted mass flux for a given momentum flux or 4 decreasing the initial momentum flux for a given mass flux as may occur if the vent is eroded these results are consistent with earlier studies wilson et al 1980 wilson and walker 1987 bursik and woods 1991 although the analogue experimental system is somewhat simplified the observations of the periodic release of convecting thermals just after column collapse suggest a mechanism for the complex grading which is commonly found just below the collapse horizons in fall deposits for example the fogo a deposit walker and croasdale 1970 and the vesuvius a d 79 deposit carey and sigurdsson 1987 in conjunction with partial column collapse this periodicity also suggests a means by which flow deposits may become interspersed with fall deposits this feature has been observed in a number of cases including the taupo deposit wilson and walker 1985

step filling and development of a three layer magma chamber the neapolitan yellow tuff case history abstract the neapolitan yellow tuff the product of the largest known trachytic phreatoplinian eruption gives a good opportunity to investigate the filling mechanisms and internal dynamics of a trachytic magma chamber a detailed study of the geochemical mineralogical and isotopical features of the deposit was carried out to investigate the behaviour of the magma chamber before the eruption the collected data show three distinct compositional groups separated by gaps single depositional units contain glass shards formed contemporaneously although each of these shards is homogeneous they display the same compositional variations and gaps detected in pumice clasts this feature is taken as an evidence for interpreting the detected compositional gaps as real gaps in the chamber therefore the chamber was filled by three distinct magma bodies separated by compositional gaps the uppermost magma was alkali trachyte and highly homogeneous likely a consequence of vigorous convection the intermediate magma was trachyte with a slight and continuous compositional variation likely resulting from less intense convection the lowermost magma was compositionally zoned from alkali trachyte to latite downward this compositional zonation was most likely acquired during uprise from a deeper reservoir the three magmas entered the chamber sequentially from the uppermost to the lowermost the latter entered the chamber short before the beginning of the eruption its input was interpreted as a possible triggering factor for the eruption the results of this study strongly support a step filling mechanism for the neapolitan yellow tuff magma chamber and allow definition of the temporal succession of input of magma batches furthermore they also suggest that the magma bodies did not mix although at least the uppermost two coexisted inside the chamber for a time long enough to allow internal homogeneization by convection

crystallization kinetics of alkali feldspars in cooling and decompression induced crystallization experiments in trachytic melt cooling and decompression experiments have been carried out on trachytic melts in order to investigate crystallization kinetics of alkali feldspar the effect of the degree of undercooling t t liquidus t experimental and time on nucleation and crystal growth process this experimental work gives us new data about crystallization kinetics of trachytic melts and it that will be useful to better understand the natural system of campi flegrei volcanoes experiments have been conducted using cold seal pressure vessel apparatus at pressure between 30 and 200 mpa temperature between 750 and 855 c time between 7 200 and 57 600 s and redox condition close to the nno 0 8 buffer these conditions are ideal to reproducing pre and syn eruptive conditions of the campi flegrei volcanoes where the conditions pertain to the complete range of pressures temperatures and time at which the experiments were performed alkali feldspar is the main phase present in this trachyte and its abundance can strongly vary with small changes in pressure temperature and water content in the melt implying appreciable variations in the textures and in the crystallization kinetics the obtained results show that crystallization kinetics are strictly related to t time final pressure superheating t and water content in the melt t is the driving force of the crystallization and it has a strong influence on nucleation and growth processes in fact the growth process dominates crystallization at small t whereas the nucleation dominates crystallization at large t time also is an important variable during crystallization process because long experiment durations involve more nucleation events of alkali feldspar than short experiment durations this is an important aspect to understand magma evolution in the magma chamber and in the conduit which in turn has strong effects on magma rheology

the thermal regime of the campi flegrei magmatic system reconstructed through 3d numerical simulations abstract we illustrate a quantitative conductive convective thermal model incorporating a wide range of geophysical petrological geological geochemical and isotopical observations that constrain the thermal evolution and present state of the campi flegrei caldera cfc magmatic system the proposed model has been computed on the basis of the current knowledge of 1 the volcanic and magmatic history of the volcano over the last 44 ka 2 its underlying crustal structure and 3 the physical properties of the erupted magmas 3d numerical simulations of heat conduction and convection within heterogeneous rock magma materials with evolving heat sources and boundary conditions that simulate magma rise from a deep 8 km depth to shallow 2 6 km reservoirs magma chamber formation magma extrusion caldera collapse and intra caldera hydrothermal convection have been carried out the evolution of the cfc magmatic system through time has been simulated through different steps related to its changes in terms of depth location and size of magma reservoirs and their replenishment the thermal modeling results show that both heat conduction and convection have played an important role in the cfc thermal evolution although with different timing the simulated present heat distribution is in agreement with the measured geothermal profiles agip 1987 reproduces the thermal gradient peaks at the cfc margins in correspondence to the anomalies in surface gradients corrado et al 1998 and suggests temperatures of 700 c at depth of 4 km in the central portion of the caldera in agreement with the estimated temperature for the brittle ductile transition hill 1992

14c age of the museum breccia campi flegrei and its relevance for the origin of the campanian ignimbrite abstract field stratigraphic investigations and ams 14 c dating of carbon particles in paleosols has resulted in a framework of the sequence and age of the pyroclastic products in the campi flegrei area of southern italy the museum breccia cannot be the early phase of the campanian ignimbrite as was previously believed but is from a smaller and later eruption with an age of approximately 17 900 y b p this date also precludes its correlation with the neapolitan yellow tuff 12 000 y b p

a magnetostratigraphic reassessment of correlation between chinese loess and marine oxygen isotope records over the last 1 1 ma abstract we present a magnetic polarity based paleoclimatic correlation between chinese loess and marine oxygen isotope stage mis records over the last 1 1 ma this revised land ocean comparison indicates that inconsistent occurrence of the matuyama brunhes boundary which lies in mis 19 in marine sediments and occurs either at the base lower part of loess l8 or the uppermost part of soil s8 in chinese loess is due to regional and or local climate variability across the chinese loess plateau and does not need to be attributed to lock in effects of loess remanence acquisition associated with pedogenesis this result implies that the geomagnetic polarity boundaries in chinese loess in general are reliable chronostratigraphic time markers therefore astronomically tuned timescales for chinese loess that presume a downward shift of polarity boundaries due to a time lag in remanence acquisition may have overestimated ages of certain loess paleosol units

stratigraphy and physical parameters of the plinian phase of the campanian ignimbrite eruption the campanian ignimbrite eruption 39 ka was the most powerful eruptive event of the campi flegrei caldera southern italy this event coincided with the onset of a cold climatic phase and the paleolithic transition from neanderthals to modern humans the eruption started with a sustained column that emplaced a widespread pyroclastic fall deposit covering an area 4000 km2 within the 15 cm isopach for the first time we present the complete longitudinal variation from the coarse and 10 m thick proximal down to 15 km sequence through the well stratified pumice lapilli deposit in medial areas 30 80 km to the distal tephra hundreds to thousands of kilometers distant the plinian pumice fall deposit shows a strong lateral heterogeneity due to variations in stratification grading and abundance of components all campanian ignimbrite fall layers display plinian dispersal variation of grain size with stratigraphic height suggests that the convective plume was far from steady state initially the plume dispersed 1 3 km3 of tephra toward the ene n75 e from a height of 29 km layer a a gradual increase in intensity resulted in inverse grading of layer b column height increased from 26 to 37 km at a vertical velocity of 3 6 m s it had a main dispersal axis to the east n97 e and a secondary lobe to the southeast n137 e during this phase a maximum volume of 1 73 km3 of tephra was emplaced accessory lithics concentrated in layer c are possibly due to vent clearing after partial blockage of the vent the 33 km high column dispersed ejecta to the east n95 e with only 0 2 km3 of tephra erupted during this phase during the successive gradual decline in eruption intensity column height decreased from 38 to 32 km at a velocity of 4 2 m s a normally graded layer d with a volume of 1 km3 accumulated to the east n95 e the sustained column phase ended with a pulsating and partially collapsing column that reached 23 km in height and dispersed 1 1 km3 of a stratified and lithic rich succession layer e to the southeast n112 e if we include the distal co plinian deposit a total volume of 7 8 km3 dense rock equivalent dre of magma was released containing 0 09 km3 of accessory lithics tephra mass for the single layers is on the order of 1011 kg and the total mass is 2 1012 kg 2 1013 kg including the co plinian ash mass discharge rates ranged from 0 9 to 6 7 108 kg s the calculated magnitude of the sustained column phase is 6 3 the duration of the plinian phase of this eruption based on the ratio of two parameters erupted mass divided by discharge rate is estimated to have been 20 h including co plinian ash this study shows that plinian deposits are not always homogeneous and as for pyroclastic current deposits can show an articulate architecture only the complete reconstruction of vertical and lateral variations in components stratification and grading might provide insights into the temporal and spatial evolution of the sustained plume

magnetostratigraphic dating of river terraces rapid and intermittent incision by the yellow river of the northeastern margin of the tibetan plateau during the quaternary up to 23 paleosols have been identified in loess sequences that overlie fluviatile sediments on seven terraces of huang he the yellow river and daxia he in the linxia basin at the northeastern margin of the tibetan plateau the magnetostratigraphic record in the oldest sequence appears to be fairly complete and spans the entire quaternary it includes evidence for the jaramillo and olduvai normal polarity subchrons within the matuyama chron as well as the cobb mountain and stage 54 formerly gilsa events age constraints within the brunhes are provided by 14c and thermoluminescence optical stimulated luminescence dating the magnetostratigraphic chronology of the quaternary sediments indicates that terraces were formed at about 1 66 1 4 1 1 0 6 0 12 0 055 and 0 01 ma the terraces may represent climatically induced pauses in long term tectonically induced incision by the rivers on the basis of terrace heights and ages incision rates were highest from 1 66 to 1 4 ma 1 m kyr decreased from 1 4 to 0 12 ma 0 1 m kyr and increased from 0 12 ma to present 0 75 m kyr if river incision is attributed solely to uplift of the tibetan plateau then this uplift appears to have been rapid as well as intermittent following the first evidence of the existence of huang he in this area at about 1 75 ma however the effects of uplift cannot be fully separated from incision caused by changes in climate copyright 1997 by the american geophysical union

early pleistocene river terraces of the gediz river turkey the role of faulting fracturing volcanism and travertines in their genesis abstract reconstructing and interpreting past hydrological system changes from the quaternary sediment landform record presents many challenges especially when trying to establish causality in such circumstances attempting to isolate individual drivers is perhaps unrealistic and thus inferences are made with respect to the combined influence of multiple controls and constraints in this paper we seek to interpret the landscape responses recorded in the sediment landform record of the early pleistocene gediz valley western turkey within the context of interacting geodynamic and hydrodynamic system changes our earlier work on the gediz sequence established the presence of a rich fluvial archive constrained by a comprehensive geochronology from overlying lava flows repeated damming of the gediz valley floor and consequent re routing of water flow testifies to a direct connection between fluvial activity and volcanism this volcanism has been linked to regional tectonic extension with regional uplift promoted as a major driver of the progressive river incision of the gediz river over the quaternary this incision has been punctuated by periods of deposition dictated by sediment and water budgets controlled principally by fluctuating climate and consequent vegetation change recently however the significance of more local fault movements and fracturing has been recognised and here we examine and attempt to quantify these geodynamics in greater detail in addition we examine and describe for the first time extensive associated travertine deposits isotopic analysis of these travertines confirms their thermogenic origin and directly links their creation to the faulting fracturing volcanism and the recycling of calcium rich groundwater the formation of mounds and sheets extend onto their contemporary valley floors thus directly connecting the fluvial and travertine archives and allowing linkage between surface and subsurface hydrological change by utilising both the fluvial and travertine archives a more complex picture of landscape evolution emerges the youngest terraces the gediz sequence demonstrates increasing complexity there is no reason to suggest this is unusual although climate and tectonics remain as key drivers the local landscape response is also conditioned by many additional factors while it is tempting to search for global patterns the big picture such reduced complexity may be over simplistic recognising complexity requires detailed observation and therefore more emphasis on the smaller picture which can only be obtained through extensive field observation

sea level change and volcano tectonic interplay the gulf of pozzuoli campi flegrei eastern tyrrhenian sea during the last 39 ka a geological study based on seismic profiles and sediment cores has been accomplished on the gulf of pozzuoli the marine sector of the campi flegrei an active volcanic area located west of the city of naples italy detailed seismo stratigraphic analysis led to the correlation between marine units and the on land volcanic deposits the absence of primary pyroclastic beds in cores highlights the role of the shallow marine environment in the reworking of the volcani clastic sediments the evolution of the area during the last 39 ka evidences the role of the eustatic change and volcano tectonic phenomena in the development of the local sedimentary record four main phases in the geological evolution have been distinguished in a first phase the emplacement of two volcanic units v1 between 60 and 39 ka and ci 39 ka took place a second phase developed between 39 and 15 ka and led to the formation of regressive depositional wedges fw and lw sedimentary bodies in the external sectors of the area outer shelf the eruption of the neapolitan yellow tuff 15 ka and the following eruptions that occurred up to 11 ka constitute the third phase during the fourth phase 11 ka to present generalized marine conditions were established in the area distribution and thickness of the sedimentary bodies formed during the latter time span are highly variable and constitute the result of a complex interplay between volcano tectonic movements and sea level change

plinian pumice fall deposit of the campanian ignimbrite eruption phlegraean fields italy abstract a plinian pumice fall deposit associated with the campanian ignimbrite eruption 36 ka phlegraean fields caldera italy occurs at the base of the distal grey ignimbrite in 15 localities spread over an area exceeding 1500 km2 between benevento and the sorrentina peninsula in the thickest stratigraphic section at voscone 130 cm 45 km east of the phlegraean caldera centre pozzuoli the deposit consists of two units the lower fall unit lfu is well sorted exhibits reverse size grading and is composed of equidimensional light grey pumice clasts with very subordinate accidental lithics the upper fall unit ufu is from well to poorly sorted crudely stratified richer in lithics and composed of both equidimensional and prolate pumice clasts the two fall units show slightly different dispersal axis n90 for the lfu and n95 for the ufu volumes calculated with the method of pyle 1989 are about 8 km3 for the lfu and 7 km3 for the ufu the maximum height of the eruptive columns are estimated using the model of the maximum lithic clasts dispersal at 44 km for the lfu and 40 km for the ufu classifying both fall units as ultraplinian in character reverse size grading within the lfu suggests an increase of the height of the column and magma discharge rate with time moderate sorting and crude stratification of the ufu are consistent with short period oscillation of the column possibly associated with repeated partial column collapses sharp increases in lithic content at the transition to ufu and within the ufu suggest that changes in the eruptive behaviour was produced by a dramatic increase in conduit vent erosion the phase of column instability preceded the emplacement of widely dispersed pyroclastic flow the ultraplinian nature of the fall fits well with the wide dispersal of the campanian ignimbrite with an estimated aspect ratio of 3 4 10 4 lari

evolution of volcanic eruption columns 1 the classical steady state model for plinian eruption columns is extended to allow the source conditions at the volcanic vent to change in time it is shown that when the source conditions change rapidly over time scales typically less than approximately 3 4 min this new time dependent volcano model becomes appropriate differences between changes in source velocity and source temperature are also considered qualitatively similar structures are formed when either the source velocity or source temperature is reduced a transient region is formed characterized by a narrowing of the top hat eruption column radius a first attempt to a model a plinian eruption column from its dynamic initiation in a volcanic eruption is made it is shown that the velocity at the front of the eruption column is significantly slower than the velocity at the same height in an established eruption column

ice age terminations 230th dated oxygen isotope records of stalagmites from sanbao cave china characterize asian monsoon am precipitation through the ends of the third and fourthmost recent ice ages as a result am records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments establishing the timing and sequence of major events in all four cases observations are consistent with a classic northern hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets meltwater and icebergs entering the north atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon causing increases in atmospheric co2 and antarctic temperatures that drive the termination in the southern hemisphere increasing co2 and summer insolation drive recession of northern ice sheets with probable positive feedbacks between sea level and co2

strontium neodymium and lead isotope characteristics of the granadilla pumice tenerife a study of the causes of strontium isotope disequilibrium in felsic pyroclastic deposits

the approximate age of the planation surface and the incision of the yellow river abstract the yellow river huang he downstream of the jinshaan canyon displays well preserved fluvial terrace sequences below an extensive planation surface at the northeastern ordos plateau despite a series of well developed geomorphic surfaces the landscape evolution of the plateau is largely unconstrained the jinshaan canyon formed by the deeply incising yellow river through the ordos plateau provides keys to understanding the landscape evolution of this plateau with respect to the nearby northeastern margin of the tibetan plateau this paper presents two sets of magnetostratigraphic results derived from the aeolian deposits red clay and loess on the planation surface and the uppermost yellow river terrace in the middle part of the jinshaan canyon magnetostratigraphic analysis reveals that the planation surface and the uppermost yellow river terrace formed respectively at circa 3 7 ma and circa 1 2 ma ago the ordos plateau is the product of a period of planation culminating just before circa 3 7 ma and then was interrupted by an episode of uplift which may be correlated with the accelerated growth of the tibetan plateau in the miocene pliocene the drainage system in the jinshaan canyon was re organized around 3 7 ma no correlation seems to exist between an older drainage existing prior to circa 3 7 ma and the present yellow river network in the jinshaan canyon even though sedimentary and tectonic evidence suggests that the drainage in the middle reach of the yellow river formed in the late miocene early pliocene the yellow river has developed its rectangular course around the ordos plateau only since circa 3 7 ma

the averno 2 fissure eruption a recent small size explosive event at the campi flegrei caldera italy the averno 2 eruption 3 700 50 a b p was an explosive low magnitude event characterized by magmatic and phreatomagmatic explosions generating mainly fall and surge beds respectively it occurred in the western sector of the campi flegrei caldera campanian region south italy at the intersection of two active fault systems oriented ne and nw the morphologically complex crater area largely filled by the averno lake resulted from vent activation and migration along the ne trending fault system the eruption generated a complex sequence of pyroclastic deposits including pumice fall deposits in the lower portion and prevailing surge beds in the intermediate upper portion the pyroclastic sequence has been studied through stratigraphical morphostructural and petrological investigations and subdivided into three members named a through c member a was emplaced during the first phase of the eruption mainly by magmatic explosions which generated columns reaching a maximum height of 10 km during this phase the eruption reached its climax with a mass discharge rate of 3 2 106 kg s intense fracturing and fault activation favored entry of a significant amount of water into the system which produced explosions driven by variably efficient water magma interaction these explosions generated wet to dry surge deposits that emplaced member b and c respectively isopachs and isopleths maps as well as areal distribution of ballistic fragments and facies variation of surge deposits allow definition of four vents that opened along a ne oriented 2 km long fissure the total volume of magma extruded during the eruption has been estimated at about 0 07 km3 dre the erupted products range in composition from initial weakly peralkaline alkali trachyte to last emplaced alkali trachyte isotopic data and modeling suggest that mixing occurred during the averno 2 eruption between a more evolved less radiogenic stored magma and a less evolved more radiogenic magma that entered the shallow reservoir to trigger the eruption the early phases of the eruption during which the vent migrated from sw to the center of the present lake were fed by the more evolved uppermost magma while the following phases extruded the less evolved lowermost magma integration of the geological and petrological results suggests that the averno 2 complex eruption was fed from a dyke shaped shallow reservoir intruded into the ne sw fault system bordering to the west the la starza resurgent block within the caldera floor

clinopyroxene liquid trace element partitioning in natural trachyte trachyphonolite systems insights from campi flegrei southern italy trace element partition coefficients between clinopyroxenes and associated glassy matrix cpx l d have been determined for 13 ree hfse4 5 u th sr pb sc and v from combined la icp ms emp analyses in selected trachytes and trachyphonolites from campi flegrei composition of clinopyroxene and glass is pretty homogeneous in the trachyphonolites pointing to an overall attainment of the equilibrium conditions in trachytes conversely phases show some compositional heterogeneity due to the presence of clinopyroxene xenocrysts that requested a more careful petrographic and geochemical inspection of the samples to assess the equilibrium clinopyroxene composition in the trachyte clinopyroxenes ree are compatible from nd to lu cpx l d up to 2 9 like y ti sc and v the cpx l d for eu is lower than those of the adjacent ree highlighting eu2 contribution high d values are also shown by u th pb zr hf nb and ta relatively to basaltic and andesitic systems whereas the d sr is roughly similar to that found for less evolved magmas trachyphonolites are characterized by an overall decrease of the cpx l d for highly charged cations with the exception of v and by a slight increase of d sr ree are still compatible from nd to lu cpx l d up to 2 1 like ti y sc and v this variation is also predicted for ree and y by models based on the elastic strain theory being consistent with the slightly lower polymerization degree estimated for the trachyphonolites however the observed cpx l d ree y are matched by the modelled ones only considering very low t 825 c which are believed unlikely this mismatch cannot be attributed to effects induced by the water rich composition of the trachyte trachyphonolite suite since they would lower the observed cpx l d ree y moreover the anomalous inflections of measured cpx l d for hree suggests some crystal chemical control such as the entrance of these elements in a site distinct from m2 it is concluded that the large cpx l d determined for trachytes and trachyphonolites are likely induced by hitherto unconstrained changes of the z3 activities related to the composition of melt and or solid all these considerations strongly highlight the importance of a direct characterization of trace element partitioning in natural samples from magmatic systems poorly characterized by experimental studies

multidisciplinary tephrochronological correlation of marker events in the eastern tyrrhenian sea between 48 and 105 ka abstract the basal portion 2 92 5 08 m from core top of the cet1 core located in a bathyal area of the eastern tyrrhenian sea is the subject of a multidisciplinary investigation encompassing tephrostratigraphy quantitative analyses of planktonic foraminifera and calcareous nannofossil assemblages and 18o measurements supported by a 40ar 39ar age determination calcareous nannofossil assemblages allowed the attribution of the analyzed sediments to the biozone mmn21a and the succession spans from more than 48 to ca 105 ka although there are at least two stratigraphic gaps and minor resedimentation episodes a paleoclimatic reconstruction obtained via 18o and planktonic foraminifera data identifies several of the major climatic events that occurred in the investigated time span a total of 13 visible tephra layers and cryptotephras are recognized and correlated with their volcanic sources campanian volcanic zone and pantelleria volcano and when possible with well known and dated events or with widespread marker tephras using a combination of biostratigraphic oxygen isotope and tephrostratigraphic correlations we develop a chronostratigraphy for the main climatic events and tephra layers in the core and pinpoint tephra markers for the climatic events comprised between gs 22 and gi 24 in the eastern tyrrhenian sea

correlation of deposits and vent locations of the proximal campanian ignimbrite deposits campi flegrei italy based on natural remanent magnetization and anisotropy of magnetic susceptibility characteristics abstract correlation of the distal deposits of the campanian ignimbrite with their proximal equivalents in the campi flegrei caldera is complicated by a lack of medial exposures complex and limited proximal stratigraphic sections and large lateral facies changes paleomagnetic data from 10 sites in and near the campi flegrei yield natural remanent magnetizations nrm that are statistically indistinguishable from the distal campanian ignimbrite in addition their virtual geomagnetic pole vgp yields a possible correlation with lac du bouchet france secular variation data that indicate an age of approximately 32 850 14 c years the secular variation curve at this age was only briefly at this vgp and did not return to it for 10 000 years so the paleomagnetic correlation of proximal and distal deposits is unique and robust the date is consistent with 14 c dates from the campanian ignimbrite but younger than 39 ar 40 ar dates for the same rocks this suggests that a better correction factor for cosmic flux for this time period is needed to calibrate older 14 c dates anisotropy of magnetic susceptibility ams data show that the proximal deposits have an oblate disk shaped poorly lineated magnetic fabric the distal deposits are much better lineated the difference may be due to chaotic depositional currents in the proximal areas in which particles were not well aligned with greater distance of travel and loss of energy particles within the flow became aligned and developed stronger ams lineations early eruptions of the piperno tuff were from a central vent north of pozzuoli whereas later tuffs that underlie the breccia museo may have been emplaced by flows associated with ring vents located on the northern and southern caldera margins

simulating internal and external controls on fluvial terrace stratigraphy a qualitative comparison with the maas record palaeohydrological studies indicate that the use of sedimentary palaeoclimatic indicators in fluvial sediments still requires rigorous calibration of the climatic controls on the formation of those indicators an explorative attempt is made using a simulation experiment with the fluver2 model the simulation illustrates that climate control on the erosion sedimentation behaviour of a large fluvial system differs along the fluvial system while in the uplifting hinterland only glacial extremes are recorded as sediments with a relatively limited preservation chance as terraces due to the uplift the more downstream reach towards the hinge zone displays a sensitive fluvial record registering even stadial interstadial dynamics well preserved in an extensive glacial interglacial terrace staircase downstream in a subsiding basin the most complete sedimentary record is preserved which still contains temporal gaps of approximately 20 related to the spatial delay effects of the external control of climate and related base level change a systematic comparison of simulated climate changes and resulting fluvial dynamics illustrates that due to the internal control of fluvial systems a one to one correlation between recorded fluvial dynamics and climate change becomes less the further one moves downstream along the longitudinal profile a qualitative comparison of the simulation results with the maas record reveals an interesting match suggesting that the simulated system dynamics may well apply the maas system

late miocene pliocene geomorphological evolution of the xiaoshuizi peneplain in the maxian mountains and its tectonic significance for the northeastern tibetan plateau as a remnant elevated peneplain the tangxian planation surface is widely distributed in north china and the ordos plateau further into the tibetan plateau tp the main planation surface can also be traced across this the highest plateau on the earth s surface what the relation is between these two planation surfaces and whether they represent the remnants of a unique planation surface remains open to question as the intermediate region between the low altitude north china and the high altitude tp the maxian mountains and such bilateral basins located in the northeastern tp margin retain a series of well preserved geomorphic features such as planation surfaces pediment surface and the fluvial terraces of the yellow river when and how the xiaoshuizi peneplain was formed are crucial questions to elucidate the geomorphic evolution of the northeastern tp and infer the tectonic history of the tp here we present two parallel red clay loess drill cores from the uplifted xiaoshuizi bedrock peneplain in the maxian mountains which document both the upper formation age of the planation surface and the evolution of asian aridification based on the integration of high resolution magnetostratigraphy analysis and pliocene mammal fossils we demonstrate that the red clay loess succession deposited on the xiaoshuizi peneplain probably began to accumulate at similar to 6 9 ma implying that the xiaoshuizi peneplain had begun to form before this these results support the hypothesis that the xiaoshuizi planation surface is equivalent to tangxian planation surface of north china and main planation surface of the tp furthermore the onset of red clay sequence may indicate that the xiaoshuizi peneplain was ultimately destroyed by the intensive tectonic uplift of the northeastern tp before 6 9 ma taking into account the synchronous late miocene red clay deposition between the xiaoshuizi peneplain and central chinese loess plateau clp we propose that the onset of interior asian aridification occurred in the late miocene and was principally triggered by the rapid uplift of tp

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

tephrochronology of the astronomically tuned kc01b deep sea core ionian sea insights into the explosive activity of the central mediterranean area during the last 200 ka abstract we present a major trace and rare earth element characterization of single glass shards from fifteen tephra layers found in the astronomically tuned kc01b deep sea core ionian sea central mediterranean 36 15 25 n 17 34 44 e 3642 m water depth kc01b is considered a reference core for the mediterranean area since it provides a new reliable astronomical tuned timescale for the last 1 112 my lourens 2004 the studied deposits punctuate the marine record in a time span ranging from ca 16 ka to ca 191 ka b p encompassing the climatic zones y x w and v they are related to volcanic activity of the campania plain aeolian islands mt etna and pantelleria island along with major main markers of the central mediterranean area such as y 1 y 5 and x 6 astronomically dated at 16 7 ka 39 1 ka and 110 5 ka respectively the succession contains a number of well preserved deposits which can represent useful inter archive instruments of correlation the campania plain in particular sourced at least nine compositionally homogeneous tephra layers prior to the campanian ignimbrite event the data obtained in this work provide a new detailed analytical reference database for ionian sea tephrochronology and for proximal distal correlation studies they may help to unravel from the marine record the history of poorly known or unknown explosive activity on land since the middle pleistocene along with chemical composition size and dispersal of the products

mobility of a large volume pyroclastic flow emplacement of the campanian ignimbrite italy abstract the trachytic campanian ignimbrite originally exposed over a 30 000 km 2 area around naples italy is the product of a highly energetic gas rich eruption the deposit lies in valleys and isolated watersheds and in its medial and distal extent to the south north and east of naples the campanian pyroclastic current encountered mountains exceeding 1000 meters anisotropy of magnetic susceptibility ams measurements indicate that the campanian pyroclastic current the transport system traveled radially outward from the phlegrean fields area but the ignimbrite forming flow the deposition system that developed from the base of the transport system moved downslope from mountainsides to valleys including slopes facing the eruption source and flowed down drainage systems from intermontane basins the campanian pyroclastic current flowed 35 km over the water of the bay of naples to deposit 43 m of ignimbrite on the south shore and also overtopped a 685 1000 m high ridge of the sorrento peninsula to deposit more on the other side the distribution of the ignimbrite and the measured flow directions suggest that the campanian pyroclastic current moved across the landscape as an expanded and therefore turbulent decompressing flow rather than as a high density nonturbulent sheet like current moving over mountains by momentum acquired by eruption column collapse strong expansion is corroborated by shard morphology that indicates derivation from highly inflated pumice and suggests vesicles must have been at least 80 by volume of the original magma

river terraces as a response to climatic forcing formation processes sedimentary characteristics and sites for human occupation abstract climate impact on the fluvial processes led to morphological and sedimentological differentiation of a terrace this diversity in the fluvial environment determined how people could adapt to the river although the climatic impact on development and initiation of river terraces seems to be well accepted a number of pertinent questions disturb this simplicity for instance the exact terrace development within a climate cycle is still under debate different kinds of terraces and their sedimentary successions may originate either from aggradation incision or lateral migration is there a typical sedimentary succession below terraces what is the genetic origin of each sedimentary layer what are the relative ages of those layers and erosion phases within a climate driven erosion aggradation cycle the variability in staircase preservation in relation to climatic cyclicity is analysed in three scenarios specific scenarios depend essentially on the preservation of the fluvial deposits dating from the warm periods finally a preliminary inventory is presented of the most favourable sites for human occupation in fluvial valleys as derived from a random selection of archaeological findings generally human occupation in that morphological position seems to be linked with at least temporarily dry conditions climatic conditions do not seem to play the major role the termination of a settlement may have been due to increased risks of flooding apart from other than natural fluvio environmental reasons

the last glacial termination a major puzzle of paleoclimatology is why after a long interval of cooling climate each late quaternary ice age ended with a relatively short warming leg called a termination we here offer a comprehensive hypothesis of how earth emerged from the last global ice age a prerequisite was the growth of very large northern hemisphere ice sheets whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation the southern hemisphere westerlies shifted poleward during each northern stadial producing pulses of ocean upwelling and warming that together accounted for much of the termination in the southern ocean and antarctica rising atmospheric co2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres

decoupling of erosion and precipitation in the himalayas the hypothesis that abrupt spatial gradients in erosion can cause high strain rates in active orogens has been supported by numerical models that couple erosional processes with lithospheric deformation via gravitational feedbacks1 2 3 most such models invoke a stream power rule in which either increased discharge or steeper channel slopes cause higher erosion rates spatial variations in precipitation and slopes are therefore predicted to correlate with gradients in both erosion rates and crustal strain here we combine observations from a meteorological network across the greater himalaya nepal along with estimates of erosion rates at geologic timescales greater than 100 000 yr from low temperature thermochronometry across a zone of about 20 km length spanning the himalayan crest and encompassing a more than fivefold difference in monsoon precipitation significant spatial variations in geologic erosion rates are not detectable decreased rainfall is not balanced by steeper channels instead additional factors that influence river incision rates such as channel width and sediment concentrations must compensate for decreasing precipitation overall spatially constant erosion is a response to uniform upward tectonic transport of greater himalayan rock above a crustal ramp

comment on the mid oxfordian late jurassic positive carbon isotope excursion recognised from fossil wood in the british isles by c r pearce s p hesselbo a l coe palaeogeography palaeoclimatology palaeoecology 221 343 357

climatic and tectonic controls on strath terraces along the upper weihe river in central china abstract the weihe river in central china is the largest tributary of the yellow river and contains a well developed strath terrace system a new chronology for the past 1 11 ma for a spectacular flight of strath terraces along the upper weihe river near longxi is defined based on field investigations of loess paleosol sequences and magnetostratigraphy all the strath terraces are strikingly similar having several meters of paleosols that have developed directly on top of fluvial deposits located on the terrace treads this suggests that the abandonment of each strath terrace by river incision occurred during the transition from glacial to interglacial climates the average fluvial incision rates during 1 11 0 71 ma and since 0 13 ma are 0 35 and 0 32 m ka respectively these incision rates are considerably higher than the average incision rate of 0 16 m km for the intervening period between 0 71 and 0 13 ma over all our results suggest that cyclic quaternary climate change has been the main driving factor for strath terrace formation with enhanced episodic uplift

climatic fluctuations and seasonality during the late jurassic oxfordian early kimmeridgian inferred from δ18o of paris basin oyster shells abstract oxygen isotope data from biostratigraphically well dated oyster shells from the late jurassic of the eastern paris basin are used to reconstruct the thermal evolution of western tethyan surface waters during the early oxfordian early kimmeridgian interval seventy eight oyster shells were carefully screened for potential diagenetic alteration using cathodoluminescence microscopy isotope analyses were performed on non luminescent parts of shells n 264 intra shell 18 o variability was estimated by microsampling along a transect perpendicular to the growth lines of the largest oyster shell the sinusoidal distribution of the 18 o values along this transect and the dependence of the amplitude of variations with bathymetry suggest that intra shell variability reflects seasonal variations of temperature and or salinity average amplitudes of about 5 c in shallow water environments and of about 2 3 c in deeper offshore environments are calculated these amplitudes reflect minimum seasonal temperature variation our new data allow to constrain existing paleotemperature trends established from fish tooth and belemnite 18 o data and are in better agreement with paleontological data more specifically a warming trend of about 3 c is reconstructed for oceanic surface waters during the early to middle oxfordian transition with maximum temperatures reaching 24 c in the transversarium zone late middle oxfordian from the transversarium zone to the bimmamatum zone a cooling of about 7 c is indicated whereas from the bimmamatum zone temperatures increased again by about 7 c to reach 24 c in average during the cymodoce zone early kimmeridgian

differential impact of small scaled tectonic movements on fluvial morphology and sedimentology the huang shui catchment ne tibet plateau abstract the aim of this paper is to investigate the morphological implications of the interplay between tectonic movements at different rates timescales and spatial extent in a catchment of intermediate size the huang shui river a main tributary of the yellow river in the ne tibet plateau river incision started from a peneplain like surface that developed in post miocene pliocene times at the end of the tertiary a general tectonic uplift of the tibetan plateau initiated river incision this general uplift also caused local fragmentation of the huang shui catchment into blocks kilometers or maximally a few tens of kilometers of local extent that have subsided and or uplifted relative to one another fluvial deposition of 30 m in the subsiding blocks contrasts with erosion and formation of gorges in the uplifted blocks incision into the former peneplain was not continuous but a staircase of terraces developed under climatic influences terrace deposits are sometimes capped by interglacial soils or soil derived material apparently terrace incision occurred at the transition to the next cold period the different rates of uplift and subsidence of the individual blocks resulted in the simultaneous development of erosion and accumulation terraces of different sizes within the same catchment even within the same tectonic block this makes it impossible to connect the terraces of the different blocks except for the three youngest terraces representing the last 300 000 years thus illustrating the uniform tectonic history of the catchment since that time

the fluvial cycle at cold warm cold transitions in lowland regions a refinement of theory abstract a previously established non linear theory of river cyclicity as a response to climate change states that short phases of fluvial instability occur both at the transition from relatively warm temperate to cold periglacial and from relatively cold to warm periods such instability typically starts with vertical erosion successively followed by sedimentary fill of the erosive scar in spite of frequent confirmation of this theory by geomorphological reconstructions a few problems arise first there are fewer incision phases than climatic transitions secondly remnants of erosion at cold warm transitions are scarce in contrast to obvious erosion relics at warm cold transitions furthermore it appears that the incision style is strikingly different at both kinds of climatic transitions similarly the long stable phases are also expressed in terms of different floodplain development in cold and warm periods these arguments require a modification of the general non linear theory at the transition from relatively temperate to colder conditions rivers transformed gradually from a regular low energy single channel course to a periodically high energy multi channel type the latter braided type is characterized by intense lateral movement rather than by deep vertical erosion this results in a well expressed morphology of wide extensive floodplains and terraces in contrast the linear and constrained meandering channels incise with small width depth ratio and build floodplains of limited lateral extent consequences are twofold 1 the spatial limitation of the deeply incised meandering valleys at the beginning of warm periods counts against their recognition 2 relatively strong lateral migration of the braided rivers removes most traces of previous meandering systems which contrasts with the limited lateral activity of confined meandering channels it means that in a warm cold warm alternation generally only one phase of vertical erosion is preserved the one that is caused by the high energy braided river at the start of the cold period

the restless resurgent campi flegrei nested caldera italy constraints on its evolution and configuration abstract we have collected new stratigraphic data in the campi flegrei caldera through surface geological mapping and study of cores drilled to various depths we integrate these data with geological geochronological and geophysical constraints available in the literature to reconstruct the volcanic and deformational history of the caldera the caldera is a resurgent nested structure resulting from two main collapses related to the campanian ignimbrite 37 ka and the neapolitan yellow tuff 12 ka eruptions while the structure is affected by a broad subsidence ongoing local resurgence and unrest occur inside the younger nested caldera structure although most of the caldera floor consists of multiple structural blocks due to long term deformations magmas were able to erupt only in one sector of the resurgent part the caldera has shown signs of unrest during the past 25 years with short term deformations that have generated a net uplift of 3 5 m the short term deformations are related to the neapolitan yellow tuff caldera resurgence and interpreted as the net result of brittle and ductile components the long term deformations likely represent the sum of the permanent brittle component of each short term deformational event

volatile element zonation in campanian ignimbrite magmas phlegrean fields italy evidence from the study of glass inclusions and matrix glasses the distribution of h2o f cl and s in the campanian ignimbrite ci magma chamber was investigated through study of primary glass inclusions and matrix glasses from pumices of the plinian fall deposit the eruption fed by trachytic to phono trachytic magmas mainly produced a trachytic non welded to partially welded tuff underlain by a minor cogenetic fallout deposit the entire chemical variability of the eruptive products is well represented in the pumices of the plinian fall deposit which we divide into a basal lower fall unit lfu and an overlying upper fall unit ufu primary glass inclusions were only found in clinopyroxenes associated with the lfu pumice and contain a mean of 1 60 0 32 wt h2o analysed by ftir 0 11 0 08 wt f 0 37 0 03 wt cl and 0 08 0 04 wt so3 emp analysis co2 concentrations were below the ftir detection limit 10 20 ppm the coexisting matrix glasses contain similar amounts of halogens and sulfur but less water 0 60 wt partially degassed matrix glasses from ufu pumices contain a mean of 0 30 0 02 h2o 0 28 0 10 f 0 04 0 02 so3 and 0 80 0 04 wt cl to reconstruct the total amount of volatiles dissolved in the most evolved trachytes we have used experimental solubility data and mass balance calculations concerning the amount of crystal fractionation required to produce the most evolved trachyte from the least evolved trachyte these yield an estimated pre eruptive magma volatile content h2o cl f of 5 5 wt for the most evolved magmas on the basis of new determinations of cl solubility limits in hydrous trachytic melts coexisting with an aqueous fluid phase hydrosaline melt brine we suggest that the upper part of the magma chamber which fed the ci eruption was fluid s saturated and at a minimum depth of 2 km variations in eruptive style plinian fallout pyroclastic flows do not appear to be related to significant variations in pre eruptive volatile contents

chinese loess and the paleomonsoon abstract this paper presents a general review of the recent research advances of the east asian paleomonsoon based mainly on studies of the loess soil sequences in the chinese loess plateau in the last 2 6 million years the paleomonsoonal history may be divided into about 166 events on a time scale of the earth s orbital variations during the last glacial period millenial scale oscillations of the monsoon system were prominent which can be fairly well correlated with the dansgaard oeschger cycles recognized in the greenland ice cores the monsoonal rainfall belt has experienced a wide repeated advance retreat change during the glacial interglacial cycles of the pleistocene both temporal and spatial changes of the monsoon system in the quaternary could have been linked closely to global ice volume variations

timing of magma extraction during the campanian ignimbrite eruption campi flegrei caldera a core drilled within the northern part of the city of napoli has offered the unique opportunity to observe in one single sequence the superposition of the four pyroclastic flow units emplaced during the campanian ignimbrite ci eruption such a stratigraphic succession has never been encountered before in natural or in man made exposures therefore the ci sequence was reconstructed only on the basis of stratigraphic correlations and compositional data in literature the occurrence of four superposed ci flows together with all the data available in literature allowed us to better constrain the chemical stratigraphy of the deposit and the compositional structure of the ci magma chamber the ci magma chamber includes two cogenetic magma layers separated by a compositional gap the upper magma layer was contaminated by interaction with radiogenic fluids the two magma layers were extruded either individually or simultaneously during the course of the eruption in the latter case they produced a hybrid magma but no evidence of input of new geochemically and isotopically distinct magma batches just prior or during the eruption has been found comparison with the exposed ci deposits has permitted reconstruction of variable eruption phases and related magma withdrawal and caldera collapse episodes the eruption was likely to have began with phreatomagmatic explosions followed by the formation of a sustained plinian eruption column fed by the simultaneous extraction from both magma layers towards the end of this phase the upward migration of the fragmentation surface and the decrease in magma eruption rate and or activation of fractures formed an unstable pulsating column that was fed only by the most evolved magma layer this plinian phase was followed by the collapse of the eruption column and the beginning of caldera formation at this stage expanded pyroclastic flows fed by the upper magma layer in the chamber generated during the following major caldera collapse episode the maximum mass discharge rate was reached and both magma layers were tapped generating expanded pyroclastic flows towards the end of the eruption only the deeper and less differentiated magma layer was tapped producing more concentrated pyroclastic flows that traveled short distances

isotopic evidence for open system processes within the campanian ignimbrite campi flegrei italy magma chamber new sr and nd isotope data for whole rocks glasses and minerals are combined to reconstruct the nature and origin of mixing end members of the 200 km3 trachytic to phonolitic campanian ignimbrite campi flegrei italy magmatic system the least evolved magmatic end member shows equilibrium between host glass and the majority of the phenocrysts and is less radiogenic in sr and nd than the most evolved magma on the contrary only the fe rich pyroxene from the most evolved erupted magma is in equilibrium with the matrix glass while all other minerals are in isotopic disequilibrium these magmas mixed prior to and during the campanian ignimbrite eruption and minerals were freely exchanged between the magma batches combining the results of the geochemical investigations on magma end members with geophysical and geological data we develop the following scenario in stage 1 a parental less differentiated magma rose into the middle crust and evolved through combined crustal assimilation and crystal fractionation in stage 2 the differentiated magma rose to shallower depth fed the pre campanian ignimbrite activity and evolved by further open system processes into the most evolved and most radiogenic campanian ignimbrite end member magma in stage 3 new trachytic magma isotopically distinct from the pre campanian ignimbrite magmas rose from ca 6 km to shallower depth recharged the most evolved pre campanian ignimbrite magma chamber and formed the large and stratified campanian ignimbrite magmatic system during the course of the campanian ignimbrite eruption the two layers were tapped separately and or simultaneously and gave rise to the range of chemical and isotopic values displayed by the campanian ignimbrite pumices glasses and minerals

phase equilibria constraints on the chemical and physical evolution of the campanian ignimbrite the campanian ignimbrite is a 4200 km trachyte phonolite pyroclastic deposit that erupted at 39 3 0 1ka within the campi flegrei west of naples italy here we test the hypothesis that campanian ignimbrite magma was derived by isobaric crystal fractionation of a parental basaltic trachyandesitic melt that reacted and came into local equilibrium with small amounts 5 10 wt of crustal rock skarns and foid syenites during crystallization comparison of observed crystal and magma compositions with results of phase equilibria assimilation fractionation simulations melts is generally very good oxygen fugacity was approximately buffered along qfm 1 where qfm is the quartz fayalite magnetite buffer during isobaric fractionation at 0 15 gpa 6 km depth the parental melt reconstructed from melt inclusion and host clinopyroxene compositions is found to be basaltic trachyandesite liquid 51 1 wt sio2 9 3 wt mgo 3 wt h2o a significant feature of phase equilibria simulations is the existence of a pseudo invariant temperature 883 8c at which the fraction of melt remaining in the system decreases abruptly from 0 5 to50 1 crystallization at the pseudo invariant point leads to abrupt changes in the composition properties density dissolved water content and physical state viscosity volume fraction fluid of melt and magma a dramatic decrease in melt viscosity from 1700 pa s to 200 pa s coupled with a change in the volume fraction of water in magma from 0 1 to 0 8 and a dramatic decrease in melt and magma density acted as a destabilizing eruption trigger thermal models suggest a timescale of 200 kyr from the beginning of fractionation until eruption leading to an apparent rate of evolved magma generation of about 10 3 km year in situ crystallization and crystal settling in density stratified regions as well as in convectively mixed less evolved subjacent magma operate rapidly enough to match this apparent volumetric rate of evolved magma production

pressure evolution during explosive caldera forming eruptions abstract caldera forming eruptions of silicic magmas result from a complex coupling of the mechanics and fluid dynamics of the associated magma chamber field studies of caldera forming eruption products suggest that great pressure variations occur inside the magma chamber and associated conduits during these eruptions pressure evolution during explosive caldera forming eruptions is investigated through a simple model that describes the first order quantitative behaviour of the chamber we consider a piston like model that assumes a coherent block subsiding along circular sub vertical ring faults into the magma chamber this subsidence occurs after significant decompression of the chamber by an initial central vent eruption we assume that the initial pressure distribution in the chamber is magmastatic once collapse has begun the chamber roof is supported by the magma so that magma pressure at the chamber roof increases to lithostatic we suggest that pressure variations during caldera forming eruptions are mainly controlled by variations in magma volatile content regardless of what induces the formation of ring faults the model suggests that the occurrence of explosive caldera forming events depends on the strength of the chamber walls and the depth water content and aspect ratio of the magma chamber no significant differences exist between model results for a cylindrical or a more realistic elliptical magma chamber geometry of comparable aspect ratio assuming a constant strength of the host rock the mass fraction of magma that must be erupted during the central vent phase in order to trigger caldera collapse ranges for deep gas poor chambers from a few percent up to 40 for shallow gas rich chambers the model suggests that zoned chambers tend to collapse earlier than homogeneous chambers dike shaped chambers will erupt less magma than sill like chambers before caldera collapse initiates although dike like geometries are not associated with stress fields appropriate to create ring faults the model suggests that once initiated caldera collapse will tend to force out most or all of the volatile rich magma from the chamber for volatile rich magma chambers the total volume of erupted magma during caldera forming event is of the same order as the chamber volume the model also explains the variation in the erupted mass during the different phases of explosive caldera forming eruptions and is in good agreement with natural examples

terrace formation and river valley development along the lower taohe river in central china abstract a flight of nine river terraces has been well developed and preserved along the course of the lower taohe river based on optically stimulated luminescence osl electron spin resonance esr paleomagnetic and loess paleosol stratigraphic analyses we found that the accumulation ages of the gravel layers of terraces t9 t1 correspond to the loess layers l13 l9 l8 l6 l5 l4 l3 l2 l1 4 and l1 1 respectively the chronologic results indicate that the formation and development of the modern river valley in this area occurred between 1 4 and 1 14 ma the topographic fluctuation caused by the kunhuang movement appears to have been the main reason for the reorganization of the river system and valley development in the area in the context of this tectonic uplift fluvial processes were coupled with the regional climate on a geomorphic equilibrium scale i e over a glacial interglacial cycle that is river aggradation appears principally to have occurred during glacial periods while a graded state existed during interglacial periods in addition rapid river downcutting in response to climate change occurred during the transition periods from glacial to interglacial climates

a typology of pleistocene cold based rivers abstract a classification of periglacial rivers is proposed it is based on the generally valid laws relating the ratio of stream power to bed load with fluvial processes and morphology however river patterns may be modified by the special characteristics of the periglacial environment snowmelt especially in areas of continuous permafrost and river ice especially in zones of discontinuous permafrost determine the respective hydrological regimes the frozen state of the subsoil as well as the density of the vegetation cover contributes significantly to the bank cohesion and the sediment load of the rivers these specific periglacial characteristics have a complex influence on the thresholds in river activity resulting in a high diversity of periglacial river types

lithology of the basement underlying the campi flegrei caldera volcanological and petrological constraints abstract a geologically reasonable working hypothesis is proposed for the lithology of the basement underlying the campi flegrei caldera in the ca 4 8 km depth range in most current geophysical modeling this portion of crust is interpreted as composed of meso cenozoic carbonate rocks underlain by a ca 1 km thick sill of partially molten rock thought to be a main magma reservoir shallower magma reservoirs likely occur in the 3 4 km depth range however the lack of carbonate lithics in any campi flegrei caldera volcanic rocks does not support the hypothesis of a limestone basement considering the major caldera forming eruptions which generated widespread and voluminous ignimbrites during late quaternary times including the campanian ignimbrite and neapolitan yellow tuff eruptions the total volume of trachytic to phonolitic ejected magma is conservatively estimated at not less than 350 km 3 results of least squared mass balance calculations suggest that this evolved magma formed through fractional crystallization from at least 2500 km 3 of parent shoshonitic magma in turn derived from even more voluminous more mafic k basaltic magma calculations suggest that shoshonitic magma likely emplaced at ca 8 km depth must have crystallized about 2100 km 3 of solid material dominated by alkali feldspar and plagioclase with a slightly lower amount of mafic minerals during its route toward shallower magma reservoirs before feeding the campi flegrei large volume eruptions the calculated volume of cumulate material likely syenitic in composition at least in its upper portions is more than enough to completely fill the basement volume in the 4 8 km depth range beneath the campi flegrei caldera estimated at ca 1250 km 3 thus it is proposed that the basement underlying the campi flegrei caldera below 4 km is composed mostly of crystalline igneous rocks as for many large calderas worldwide syenite sensu lato would meet physical properties requirements for geophysical data interpretations explain some geochemical and isotopic features of the past 15 ka volcanics and justify the carbon isotopic composition of fumaroles at the campi flegrei caldera this implies that meso cenozoic limestones if still present today beneath the campi flegrei caldera no longer constitute significant portions of its basement

uplift driven valley incision and river terrace formation in southern england outside the limits of middle pleistocene glaciation the river basins of southern england contain long cenozoic terrestrial sedimentary records of greatest importance are the river terrace sequences which contain biostratigraphical and sedimentary evidence that testifies to the high amplitude climatic changes of the quaternary however trends in valley development cannot easily be accommodated within the framework of quaternary climatic change it is argued in this paper that episodic incision and terrace development result from uplift a consequence of the interplay between continuing alpine orogenic movements and erosion driven isostasy using a simple linear model height age an uplift rate of ca 7 cm ka 1 is estimated for the terrace sequence in the upper thames valley this preliminary model is evaluated using the records of adjacent basins 1997 john wiley sons ltd

termination of fluvial alluvial sedimentation in the xining basin ne tibetan plateau and its subsequent geomorphic evolution the xining basin in northern china lies topographically in the transitional zone between the tibetan plateau and the loess plateau and climatically in the transitional zone between humid east asia and the arid asian interior during the cenozoic the basin accumulated a thick continuous sequence of fluviolacustrine dominated red beds and subsequent eolian loess the termination of sediment deposition in the xining basin is the key to understanding its subsequent evolution the development of the modern yellow river and the history of dust deposition here we present the results of a detailed paleomagnetic study of the upper sedimentary sequence of the xining basin below the river terraces and in addition we review previous studies of river evolution development our results indicate that the age of the uppermost part of the continuous sequence of fluviolacustrine dominated red beds in the xining basin ranges from ca 20 ma to 4 8 ma suggesting that basin sedimentation ended at the earliest at 4 8 ma and they also provide an earliest age constraint for the subsequent river terrace development and eolian dust deposition in addition these results demonstrate that the termination of sedimentation in the xining basin and the nearby linxia basin was approximately coeval suggesting the rapid regional tectonic uplift of the ne tibetan plateau and resulting reorganization of the landforms and development of the paleo yellow river in the late pliocene c 2017 elsevier b v all rights reserved

the growth of northeastern tibet and its relevance to large scale continental geodynamics a review of recent studies recent studies of the northeastern part of the tibetan plateau have called attention to two emerging views of how the tibetan plateau has grown first deformation in northern tibet began essentially at the time of collision with india not 10 20 myr later as might be expected if the locus of activity migrated northward as india penetrated the rest of eurasia thus the north south dimensions of the tibetan plateau were set mainly by differences in lithospheric strength with strong lithosphere beneath india and the tarim and qaidam basins steadily encroaching on one another as the region between them the present day tibetan plateau deformed and its north south dimension became narrower second abundant evidence calls for acceleration of deformation including the formation of new faults in northeastern tibet since 15 ma and a less precisely dated change in orientation of crustal shortening since 20 ma this reorientation of crustal shortening and roughly concurrent outward growth of high terrain which swings from nne ssw in northern tibet to more ne sw and even ene wsw in the easternmost part of northeastern tibet are likely to be in part a consequence of crustal thickening within the high tibetan plateau reaching a limit and the locus of continued shortening then migrating to the northeastern and eastern flanks these changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation

late miocene quaternary rapid stepwise uplift of the ne tibetan plateau and its effects on climatic and environmental changes abstract the way in which the ne tibetan plateau uplifted and its impact on climatic change are crucial to understanding the evolution of the tibetan plateau and the development of the present geomorphology and climate of central and east asia this paper is not a comprehensive review of current thinking but instead synthesises our past decades of work together with a number of new findings the dating of late cenozoic basin sediments and the tectonic geomorphology of the ne tibetan plateau demonstrates that the rapid persistent rise of this plateau began 8 1 ma followed by stepwise accelerated rise at 3 6 ma 2 6 ma 1 8 1 7 ma 1 2 0 6 ma and 0 15 ma the yellow river basin developed at 1 7 ma and evolved to its present pattern through stepwise backward expansion toward its source area in response to the stepwise uplift of the plateau high resolution multi climatic proxy records from the basins and terrace sediments indicate a persistent stepwise accelerated enhancement of the east asian winter monsoon and drying of the asian interior coupled with the episodic tectonic uplift since 8 ma and later also with the global cooling since 3 2 ma suggesting a major role for tectonic forcing of the cooling

late quaternary tephra layers along the cilento coastline southern italy abstract the results of stratigraphic and tephrostratigraphic analyses of several pyroclastic levels collected along the coastal sector of the cilento region southern italy are presented some of these levels are here described for the fist time others already known in literature were reconsidered in order to better understand their stratigraphic position and to point out the possible volcanic sources the main outcrops are located along the southern coast of the campania region cilento coast all pyroclastic layers are interbedded within coastal or continental successions younger than the substage 5e of the last interglacial the results of sem eds analyses on well preserved glass fragments indicate a composition falling between the trachyte and phonolite fields of the tas plot as typical of phlaegrean fields products by comparing their composition with those of the main tephra marker layers recorded in southern italy the correlation of the cilento pyroclastic layers with well known eruptive episodes was hypothesised in summary four different eruptions were recognised the first one is testified by a pyroclastic layer not correlated with a terrestrial counterpart covered by a middle pleistocene alluvial fan the second one is the eruptive event emplacing the x 6 marker tephra layer and dates around 107 ka the third is the campanian ignimbrite eruption 39 ka and the last one is testified by the layers correlated with the y 3 tephra about 30 ka these pyroclastic layers can be useful tools for stratigraphic correlations of late quaternary successions in southern italy

a chemostratigraphic study of the campanian ignimbrite eruption campi flegrei italy insights on magma chamber withdrawal and deposit accumulation as revealed by compositionally zoned stratigraphic and facies framework abstract petrochemical analyses of juvenile samples from twenty stratigraphic sections of the campanian ignimbrite medial deposits located from 30 to 79 km from the vent are presented here sampling has accurately followed a well defined stratigraphic framework and the new component facies scheme the campanian ignimbrite succession is formed by a basal plinian pumice fall deposit overlain by a complex architecture of pyroclastic density current deposits emplaced from a single sustained pyroclastic density current through a mechanism of vertical and lateral accretion the deposit is broadly zoned from more evolved trachyte at its base to less evolved trachyte at its top and is similarly less evolved with increasing distance from the area of emission irregular chemical trends are locally observed and interpreted to represent only a limited patchy record of the entire vertical geochemical trend the petrochemical variation observed horizontally was ascribed to changes in the flow dynamics and interaction between the advancing flow and the underlying topography the results of this study were used to propose a unified volcanological petrological model for the campanian ignimbrite eruption taking into account the emplacement of both the proximal i e the breccia museo formation and medial deposits

crystal mush reactivation by magma recharge evidence from the campanian ignimbrite activity campi flegrei volcanic field italy abstract processes of crystal mush remobilization by mafic magma recharges are often related to the outpouring of large volumes of silicic melt during caldera forming eruptions this occurred for the campanian ignimbrite ci eruption campi flegrei italy which produced a voluminous trachy phonolitic ignimbrite in southern central italy about 40 ka ago we focussed on the proximal ci deposits at san martino that are composed of a main sequence of early erupted crystal poor units and a late erupted post caldera collapse crystal rich upper pumice flow unit upfu detailed micro analytical geochemical data were performed on glasses and crystals of pyroclasts from these deposits and coupled with sr nd isotopic measurements on glasses results show that the ci eruption was fed by two distinct melts for the early erupted units and the late upfu respectively the glasses of the early erupted units have negative eu anomalies and show more evolved compositions and higher nd isotope ratios than those of the upfu which have positive eu eu the magmas of the early units formed the main volume of eruptible melt of the ci reservoir and are interpreted as having been extracted from cumulate crystal mush without a vertical geochemical gradient within the magma reservoir the data indicate that the generation of the distinctive upfu melts involved the injection of a new batch of mafic magma into the base of the ci reservoir the mafic magma allowed heating and reactivation of the ci crystal mush by melting of low or sanidines low an plagioclases leaving high an plagioclases and high mg clinopyroxenes as residual phases and a crystal mush melt made of 20 of the initial mush interstitial melt with a composition similar to the early erupted units and 80 of sanidine melt when the mush crystallinity was sufficiently reduced the mafic magma was able to penetrate into the reactivated crystal mush mixing with variable proportions of crystal mush melt and generating cooler hybrid melts which underwent further crystallization of high or sanidine at variable degrees 10 25 finally possibly a short time before the eruption the upfu magmas were able to mix and mingle with the crystal poor eruptible melts still persisting in the ci reservoir at the time of upfu emission we suggest that the complex mechanisms described for the magma evolution feeding the ci eruption may occur whenever a crystal mush is reactivated by new mafic magma inputs

how and when did the yellow river develop its square bend the current course of the yellow river china involves an unusual 1500 km long angular bend around the ordos tectonic block although sedimentary evidence suggests that the river once followed a more direct path eastward into the bohai sea geologic evidence reveals that the yellow river formed in the eocene as an eastward draining river and developed its square bend around the ordos block in late miocene early pliocene time as a result of folding and uplift that are most probably related to the collision and penetration of india into eurasia as well as rifting around the ordos block the change in course of the yellow river predates flat lying pliocene pleistocene sediment deposits that unconformably overlie folded eocene miocene strata the yellow river provides a typical example of tectonic controls on the size morphology and longevity of rivers

tephra dispersal during the campanian ignimbrite italy eruption implications for ultra distal ash transport during the large caldera forming eruption the campanian ignimbrite eruption dispersed ash over much of the central eastern mediterranean sea and eastern europe the eruption started with a plinian phase that was followed by a series of pyroclastic density currents pdcs associated with the collapse of the plinian column and the caldera the glass compositions of the deposits span a wide geochemical range but the plinian fallout and pdcs associated with column collapse the lower pumice flow only erupted the most evolved compositions the later pdcs the breccia museo and upper pumice flow erupted during and after caldera collapse tap a less evolved component and intermediate compositions that represent mixing between the end members the range of glass compositions in the campanian ignimbrite deposits from sites across the central and eastern mediterranean sea allow us to trace the dispersal of the different phases of this caldera forming eruption we map the fallout from the plinian column and the plumes of fine material associated with the pdcs co pdcs across the entire dispersal area this cannot be done using the usual grain size methods as deposits in these distal regions do not retain characteristics that allow attribution to either the plinian or co pdc phases the glass compositions of the tephra at ultra distal sites 1500 km from the vent match those of the uppermost pdc units suggesting that most of the ultra distal dispersal was associated with the late co pdc plume that was generated during caldera collapse

uplift driven valley incision and climate controlled river terrace development in the thames valley uk abstract the sequence of terraces of the river thames in southeast england has previously been shown to span the period from the earliest pleistocene to the present this terrace sequence contains biostratigraphical and sedimentary evidence that testifies to the high amplitude climatic changes of the quaternary large scale fluvial incision resulting in basin wide terrace formation appears to have been concentrated at the warming limbs of the major climatic glacial interglacial cycles when sediment supply was greatly reduced this incision and subsequent valley floor widening created the accommodation space for the later aggradation of the terrace sediments during the following warm cold transitions and during the cold stages when high sediment supply conditions prevailed although the timing of terrace aggradation may be controlled by climate change the progressive valley incision recorded by terrace staircases cannot easily be explained in terms of quaternary climatic change alone and recently developed models suggest that long term incision by the thames has been driven by uplift this paper presents an overview of the available terrace data and tabulates incision amounts and rates between key stratigraphic horizons superimposed upon these broad changes revealed by the complex internal sedimentary architecture of many terrace sediments are the geomorphological system responses to both higher frequency climate driven changes and more localized intrinsic fluvial system adjustments

the breccia museo formation campi flegrei southern italy geochronology chemostratigraphy and relationship with the campanian ignimbrite eruption the breccia museo is one of the most debated volcanic formations of the campi flegrei volcanic district the deposit made up of six distinctive stratigraphic units has been interpreted by some as the proximal facies of the major caldera forming campanian ignimbrite eruption and by others as the product of several more recent independent and localized events new geochemical and chemostratigraphical data and ar ar age determinations for several units of the breccia museo deposits 39 ka correlate well with the campanian ignimbrite forming eruption the chemical zoning of the breccia museo deposits is interpreted here to be a consequence of a three stage event that tapped a vertically zoned trachytic magma chamber

paleomagnetic age of the tangxian planation surface northwestern zhongtiao shan of the shanxi graben system north china abstract a numerical formation age for the tangxian planation surface txps in north china is still controversial the txps beveled across paleoarchean basement rocks is overlain by late cenozoic conglomerate aeolian red clay and loess the magnetostratigraphy of two late cenozoic deposition sections is established and two other sections are recorded and measured in this work the magnetostratigraphy indicates six normal magnetozones n1 to n6 and six reverse magnetozones r1 to r6 these magnetozones are correlated to chron c1n through c2an 1r indicating that the txps was formed at 3 12 3 03 ma the characteristics of the zhongtiao shan tectonic uplift and its relationship with the tibetan plateau and ordos block are discussed in terms of tectonic uplift the txps formation and accumulation of the late cenozoic sediments are mainly controlled by tectonic activities the formation and uplift of the txps with a lag in the shanxi graben system is consistent with the activities of the tibetan plateau and ordos block implying that the ne extension of the tibetan plateau epeirogenic uplift advances successively

climatically controlled river terrace staircases a worldwide quaternary phenomenon a comparison of fluvial terrace sequences from around the world based on data collected as part of international geoscience programme igcp project no 449 has revealed significant patterns river terraces provide important records of uplift which is essential for their formation and of landscape evolution their cyclic formation however almost invariably seems to have been a response to climatic fluctuation sequences in the european core area of igcp 449 which has the longest and most extensive research history have been used as templates for worldwide comparison there is evidence for a global acceleration of uplift at the time of and perhaps in response to the mid pleistocene revolution when climatic fluctuation switched to 100 kyr milankovitch cycles terraces formed prior to this generally consist of wide aggradational sheets that probably each represent formation over several 41 kyr cycles subsequently river valleys became more steeply entrenched and terraces formed in response to the stronger 100 kyr climatic forcing in many cases at approximately one per cycle this paper uses the new data resource to explore differences between records in different climate zones between sequences with variable numbers of middle late pleistocene terraces and between systems in which the all important incision event has occurred in different parts of climatic cycles key records discussed include european examples from the rhine thames somme dniester dnieper don volga and aguas from asia the gediz turkey and orontes syria from north america the south platte and colorado from south africa the vaal and sundays from australia the shoalhaven and from south america the amazon paraguay and tributaries of the colorado and negro

thermal evolution of cretaceous tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels 1 the evolution of subtropical 30 35 n upper ocean temperatures through the cretaceous is inferred from the oxygen isotope compositions of 64 fish teeth enamel coming from the western tethyan platform mean 18o values of 22 at the berriasian valanginian boundary decrease with oscillations to 18 5 around the cenomanian turonian boundary and progressively increase to 21 5 by the end of the cretaceous the similarity of this oxygen isotope curve for bioapatites from platform environments with those for foraminifera and bulk carbonates that were deposited in deeper waters and at other paleolatitudes indicates that they record global climatic signals major cooling events at the million year scale can be distinguished 1 at the berriasian valanginian boundary and 2 during the earliest late valanginian a third cooling event is detected during the earliest aptian these events already proposed as icehouse interludes during the lower cretaceous are also recorded at subtropical latitudes a progressive warming is identified from the aptian to the cenomanian turonian interval that corresponds to a thermal optimum and then upper ocean temperatures decreased to the maastrichtian minimum isotopic temperatures range from 15 c to 28 c assuming a 18oseawater of 1 for an ice free world taking more realistic 18oseawater values of 0 for tropical waters during glacial periods within the berriasian valanginian interval and earliest aptian or with above average salinities possibly the maastrichtian temperatures are increased by 4 5 c temperature differences between climatic extremes of the valanginian and cenomanian turonian are estimated to have been 10 c latitudinal thermal gradients for the albian cenomanian turonian and maastrichtian were 0 2 0 3 c latitude and thus weaker than modern oceanic values at about 0 4 c latitude

the taupo eruption new zealand i general aspects the ca a d 186 taupo eruption was the latest eruption at the taupo volcanic centre occurring from a vent at horomatangi reefs now submerged beneath lake taupo in the central north island of new zealand minor initial phreatomagmatic activity was followed by the dry vent 6 km 3 hatepe plinian outburst large amounts of water then entered the vent during the 2 5 km 3 hatepe phreatoplinian ash phase eventually stopping the eruption though large amounts of water continued to be ejected from the vent area causing gullying of the ash deposits after a break of several hours to weeks phreatoplinian activity resumed generating the 1 3 km 3 rotongaio ash notable for its fine grainsize and for containing significant quantities of non or poorly vesicular juvenile material the vent area then became dry again and eruption rates and power markedly increased into the 23 km 3 taupo ultraplinian phase which is the most powerful plinian outburst yet documented synchronous with this ultraplinian activity lesser volumes of non to partially welded ignimbrite were generated by diversion of ejecta from or partial collapse of the eruption column the rapid rate of magma withdraw al during this phase removed support from the vent area to trigger local vent collapse and initiate the catastrophic eruption of the ca 30 km 3 taupo ignimbrite finally after some years lava was extruded on to the floor of the reformed lake taupo and floating fragments derived from the lava carapace were driven ashore the known eruption volume is more than 65 km 3 while additional volumes are represented by primary material now beneath lake taupo and layer 3 to the ignim brite phases a total volume of more than 105 km 3 is likely equivalent to more than 35 km 3 of magma plus more than 3 km 3 of lithic debris airfall deposits more than 10 cm thick blanketed 30000 km 2 of land east of the vent while ignimbrite covers a near circular area of 20000 km 2 widespread and locally severe ground shaking occurred during but mostly after the eruption associated with subsidence in the lake taupo basin secondary deposits are abundant above and extending beyond the taupo ignimbrite consisting of the products of surface water interacting with the still hot ignimbrite and subsequent water reworking of the light pumiceous materials the complexity and size of this eruption preclude accurate forecasting of the size nature and return period of the inevitable next eruption from the taupo volcanic centre

evaluating the role of climate and tectonics during non steady incision of the yellow river evidence from a 1 24 ma terrace record near lanzhou china abstract the competing roles of bedrock uplift and climatic change in the formation of fluvial terraces remain uncertain most of recent studies have attributed terrace formation to climatic changes and held that even in tectonically active settings climate variations control cycles of terrace planation and abandonment based on field investigations of loess paleosol sequences magnetostratigraphy and optically stimulated luminescence osl dating we develop a new chronology for a spectacular flight of terraces along the yellow river near lanzhou china over past 1 24 ma all the terraces are strikingly similar in that they have several meters of paleosol developed directly above fluvial deposits on the terrace treads suggesting that the abandonment of each terrace due to river incision occurs during the transition from glacial to interglacial climates however the ages of terraces cluster in two relatively short time periods 1 24 0 86 ma and 0 13 ma present during the intervening time between 0 86 ma and 0 13 ma terraces either did not form or were not preserved we suggest that this record indicates that rock uplift rates varied through time and influenced terrace formation preservation thus our results demonstrate the utility of deep chronologic records from fluvial terraces for deconvolving the effects of tectonics and climate on fluvial incision