limitations on the role of pore pressure in gravity gliding a simple model has been developed to evaluate the gravity gliding of nappes in sedimentary terranes three factors play a critical role in the model 1 the ratio of horizontal to vertical stress 2 the rate of fluid flow to the detachment horizon and 3 the permeability of lithologies immediately above that horizon if the ratio of horizontal to vertical stress is less than one this ratio limits the maximum attainable pore pressure through hydrofracture existing in situ stress measurements suggest that vertical hydrofracturing rather than gravity gliding might be the result of elevated pore pressures unless a low strength cap rock exists if the stress ratio exceeds one a relatively simple equation relates the cap rock permeability and fluid flow necessary for gravity gliding effective cap rock permeabilities less than 10 sup 4 to 10 sup 5 md are required for gravity gliding in a sedimentary basin based on available in situ permeability measurements only shales and evaporites could have sufficiently low permeabilities on a regional scale 24 references

precise oxygen and hydrogen isotope determination in nanoliter quantities of speleothem inclusion water by cavity ring down spectroscopic techniques abstract speleothem inclusion water isotope compositions are a promising new climatic proxy but their applicability is limited by their low content in water and by analytical challenges we have developed a precise and accurate isotopic technique that is based on cavity ring down spectroscopy crds this method features a newly developed crushing apparatus a refined sample extraction line careful evaluation of the water carbonate adsorption effect after crushing chipped speleothem in a newly developed crushing device released inclusion water is purified and mixed with a limited amount of nitrogen gas in the extraction line for crds measurement we have measured 50 260 nl of inclusion water from 77 to 286 mg of stalagmite deposits sampled from gyokusen cave okinawa island japan the small sample size requirement demonstrates that our analytical technique can offer high resolution inclusion water based paleoclimate reconstructions the 1 reproducibility for different stalagmites ranges from 0 05 to 0 61 for 18 o and 0 0 to 2 9 for d the d vs 18 o plot for inclusion water from modern stalagmites is consistent with the local meteoric water line the 1000 ln values based on calcite and fluid inclusion measurements from decades old stalagmites are in agreement with the data from present day farmed calcite experiment combination of coeval carbonate and fluid inclusion data suggests that past temperatures at 9 10 thousand years ago ka and 26 ka were 3 4 0 7 c and 8 2 2 4 c colder than at present respectively

tectonic evolution of sw wales during the upper palaeozoic during the upper palaeozoic the development of several strike faults strongly influenced the deformation history of sw wales this aspect of the deformation is emphasized in this new description of the tectonic evolution of the region after the caledonian orogeny several strike faults caused crustal extension by normal dip slip and partially controlled the subsidence of depositional basins these faults ceased moving before the initiation of variscan deformation in sw wales two of the earlier faults were reactivated with reverse slip translations during variscan deformation when three strike faults were initiated as a result of gravitational spreading two of the new faults formed sole thrusts for northward translating nappes and the other developed as a subsidiary lag fault the sole thrusts transected some of the pre existing faults causing along strike variation in their motion the strike faults in sw wales were therefore initiated at different times and display contrasting displacement histories

an 800 kyr record of global surface ocean δ18o and implications for ice volume temperature coupling abstract the sequence of feedbacks that characterized 100 kyr glacial cycles of the past million years remains uncertain hampering an understanding of the interconnections between insolation ice sheets greenhouse gas forcing and climate critical to addressing this issue is an accurate interpretation of the marine 18 o record the main template for the ice ages this study uses a global compilation of 49 paired sea surface temperature planktonic 18 o records to extract the mean 18 o of surface ocean seawater over the past 800 kyr which we interpret to dominantly reflect global ice volume the results indicate that global surface temperature inferred deep ocean temperature and atmospheric co2 decrease early during each glacial cycle in close association with one another whereas major ice sheet growth occurs later in glacial cycles these relationships suggest that ice volume may have exhibited a threshold response to global cooling and that global deglaciations do not occur until after the growth of large ice sheets this phase sequence also suggests that the ice sheets had relatively little feedback on global cooling simple modeling shows that the rate of ice volume change through time is largely determined by the combined influence of insolation temperature and ice sheet size with possible implications for the evolution of glacial cycles over the past three million years

isotopic composition of displacive fibrous calcite veins reversals in pore water composition trends during burial diagenesis abstract stable isotope and petrographic analyses of diagenetic calcite cone in cone and beef veins from british jurassic and lower cretaceous shales have been used to determine the environment of precipitation of fibrous calcites successive growth took place by antitaxial displacive addition at the vein margins away from primary sedimentary laminations or early diagenetic concretions carbon and oxygen isotopic ratios 13c 0 and 18 4 to 11 indicate a relatively late dingenetic origin for the veins after tens or probably hundreds of meters of burial and after cessation of bacterial activity nd considerable modification of the oxygen isotopic composition of the pore water vein growth was discontinuous and took place in waters of changing isotopic and trace element composition changes are not unidirectional and are unlikely to result from the simple evolution of a single conhate pore water reversals in isotopic trends indicate that precipitation took place during periods of renewed lateral groundwater flow tapping different sources of bicarbonate bearing solution

smectite dehydration its relation to structural development and hydrocarbon accumulation in northern gulf of mexico basin a comparison of clay diagenesis data obtained from a study of tertiary shales from the brazos colorado river system of texas the mississippi river system of louisiana and the niger river system of nigeria illustrates significant differences in temperature intervals over which smectite diagenesis occurs the threshold temperature required to initiate diagenesis ranges from about 160 f 71 c in mississippi river sediments to more than 300 f 150 c in the niger delta water expelled from smectite into the pore system of the host shale during the process of diagenesis may migrate out of the shale early or may be totally or partially trapped and released slowly through time in either situation the water can act as a vehicle for hydrocarbon migration p ovided hydrocarbons are present in a form and in sufficient quantities to be transported observations from the northern gulf of mexico basin indicate a close relation between buildup of high fluid pressure and the smectite illite transformation process abnormal pressures exert partial control on the type and quantity of hydrocarbons accumulated because pressure potential determines the direction of fluid flow and overpressuring partly controls the geometry of growth faults and related folds in basins where shale structures are the dominant type formed the depths to which growth faults can penetrate and the angle of dip that these faults assume at depth are largely dependent on fluid pressure in the sedimentary section at the time of faulting dips of some faults in texas have been observed to change abruptly within the interval of smectite diagenesis and some faults formed in the overpressured miocene and younger sections become beddingplane types at depths where the temperature is near that required for thermal generation of petroleum although these faults may be important for fluid redistribution in shallow sandstone shale sections they are a minor factor in moving hydrocarbons out of shale below the faults in much of the texas offshore area fluid movement upward through microfracture systems in the deeply buried overpressured section overlying and extending upward from fault trends in the sub tertiary section is proposed as a mechanism for flushing hydrocarbons from the deeper portion of the northern gulf of mexico basin this flushing process would be enhanced by smectite diagenesis because water derived from smectite that was trapped during basin subsidence would cause the flushing process to continue for longer periods of time and to extend to greater depths than could be attained if only remnants of original pore water were present shale tectonism is also the primary mechanism for structural development in the tertiary section of the niger delta however seismic data indicate that the rate of dip change of seaward dipping listric growth faults is commonly less than that observed in texas where dips as low as 10 15 can occur at depths as shallow as 10 000 15 000 ft 3 048 4 572 m syndepositional faults in nigeria are formed in sandstone shale sections where the clay composition of shale is primarily kaolinite and where little water of smectite diagenesis has been added to the pore system of the host sedimentary section subtle differences in structural styles in the tertiary sections of texas and nigeria are probably the result of differences in clay composition of the shaly sections being deformed

tectonic framework of the celtic sea and adjacent areas with special reference to the location of the variscan front abstract structural trends in the celtic sea area indicate that variscan deformation patterns were inherited from caledonian basement structures and that the regional fold alignment is arcuate with a regional wsw ene direction rather than wnw ese armorican there is no lateral structural continuity between southern ireland and south wales southwest england three major structural provinces arranged en echelon across the variscan foldbelt are recognised a southwest england where there was complex deformation of a major basin b the south wales mendips foreland area with strong basement cover interaction and c the southern ireland graben and flanking platform province late palaeozoic depositional patterns indicate that southern ireland and southwest england were separated by a wsw ene trending platform bounded on the north by the inherited wexford boundary lineament and to the south by a previously unidentified major palaeozoic fault zone here termed the bristol channel lineament the south wales mendips variscan successions accumulated on this intervening wales celtic sea platform and were partly influenced by rejuvenated caledonian fault lines it is suggested that the northern margin of the rheno hercynian foldbelt the variscan front be taken along the bristol channel lineament which can be traced for some 400 km southwestwards towards the goban spur on the continental margin this permits a rationalisation of both tectonic and major facies boundaries in locating the front it is also suggested that the structurally localised nature of the southern ireland basin be recognised by designating it as the southern ireland zone of the variscan foldbelt the sites of mesozoic rifting in the celtic sea and adjacent areas although complex in detail appear to have been located along the wexford boundary and bristol channel lineaments

low grade and very low grade regional metabasic ordovician rocks of llŷn and snowdonia gwynedd north wales metabasic assemblages belong to the prehnite pumpellyite and greenschist facies the isograds pumpellyite in pumpellyite out clinozoisite in and biotite in have been mapped and divide the area into four metamorphic zones field and petrographic evidence indicate that the metamorphic crystallization was largely syn and immediately post tectonic viz end silurian to devonian the use of published schreinemakers bundles indicates that most of the prehnite pumpellyite bearing assemblages formed at high grades within the facies and that the greenschist facies rocks crystallized in the higher pressure field as the amount of calcite increases so diagnostic ca al silicates are reduced and eventually eliminated from assemblages contrary to recent claims the evidence indicates that the gwna group and the gwyddel felsitic beds of ll n were metamorphosed prior to the arenig

the genesis of the llanrwst and llanfair veinfields north wales evidence from fluid inclusions and stable isotopes the llanrwst pb zn veinfield occupies fractures in an ordovician volcano sedimentary sequence with three separate mineralizing events m 1 m 2 and m 3 the llanfair pb zn cu veinfield consists of sporadic mineralization in silurian sediments fluid inclusion data from both veinfields indicate mineralization took place from cacl 2 bearing brines up to 26 wt nacl equivalent between 125 and 190 c with cooler 100 c more dilute fluids associated with later thrusting at llanrwst sulphur at both veinfields was derived during the main phases of sulphide precipitation from the host rocks with paragenetically late sulphides and sulphates deriving sulphur from 34 s enriched surface waters carbon and oxygen isotopic data on vein carbonates shows that both deposits formed from waters that had undergone extensive water rock interaction carbon was derived from at least two sources marine carbonate dominated at llanfair whereas organic matter in the host rocks was more significant at llanrwst these data indicate that the veins formed from evolved brines which migrated along fault systems to the loci of deposition during a phase of extensional tectonics in late devonian to tournasian times

high precision and high resolution carbonate 230th dating by mc icp ms with sem protocols abstract to facilitate the measurement of u th isotopic compositions suitable for high precision and high resolution 230th dating of coral and speleothem carbonates secondary electron multiplier sem protocol techniques for multicollector inductively coupled plasma mass spectrometry mc icp ms have been developed the instrumental sensitivities are 1 2 with a precision of 1 2 2 for abundance determination of 50 200 fg 234u 1 4 ng 238u or 230th this method features chemistry refinements improvements to procedural and instrumental blanks spectral inference reductions and careful consideration of non linear sem behavior measurement consistency of this mc icp ms combined with previous mass spectrometric results on u th standards and a variety of carbonates demonstrates the validity of the sem protocol method for fossil corals a routine u th isotopic determination at permil level precision requires only 10 50 mg of carbonate as little as 200 mg of young coral with an age of less than 20 yr can be dated with a precision of 0 3 0 8 yr about 20 200 mg speleothem samples with sub ppm to ppm u are required to earn a 5 precision on ages from 5 to 100 kyr requirement of small sample size 10 100s mg carbonate can permit high temporal resolution to date speleothems with slow growth rates i e 1 10 mm kyr this high precision 230th chronology is critical to accurately establish age models date events and splice geochemical proxy time series records from multiple samples in the fields of paleoclimatology and paleoceanography the u th isotopic determination techniques described here can also be applied to different environmental samples such as waters rocks and sediments

temperature and seawater isotopic controls on two stalagmite records since 83 ka from maritime japan abstract millennial scale interstadial dansgaard oeschger d o cycles and heinrich h stadial events are pronounced paleoclimatic features during the last glacial period which were first demonstrated in the north atlantic region these stadial and interstadial events are expressed in marine and terrestrial high resolution records elsewhere in the world but the magnitude and mode of the regional climate changes are still poorly quantified here we present new replicated stalagmite 18o profiles from two caves in central japan which extend back to 83 4 ka the records clearly display the h7 to h3 events but not d o cycles an important feature of the two japanese stalagmites is the small difference 2 9 in 18o values between the mid holocene and the last glacial maximum lgm long term trends of the stalagmite 18o values at the more maritime site generally follow that of the 18o record of seawater which is responsible for 1 1 of the 2 9 difference between mid holocene and lgm the remaining 1 8 in the difference can be accounted for by 9 c of warming between the lgm and mid holocene and 3 c cooling at h events which are comparable with the previous estimates of land paleo temperature in the japanese islands the attenuated isotopic signal associated with d o interstadials indicates that the warming in the atlantic did not significantly transfer to the maritime japan these unique features of the isotopic records of the japanese stalagmites are due to the geographic position at the vicinity of the moisture source kuroshio warm current

possible solar origin of the 1 470 year glacial climate cycle demonstrated in a coupled model dansgaard oeschger events are rapid climate fluctuations that occurred during and at the end of the last ice age with remarkable regularity there were 23 such events between 110 000 and 23 000 years bp with a periodicity of 1 470 years identify the source of this cycle and it should be possible to say what triggered these events the sun had been excluded as a possible cause because of the lack of a 1 470 year spectral contribution in records of solar variability despite this braun et al present a new hypothesis that convincingly explains the 1 470 year period as the net result of two well known solar cycles the devries and gleissberg cycles with periods of 210 years and 87 years many palaeoclimate records from the north atlantic region show a pattern of rapid climate oscillations the so called dansgaard oeschger events with a quasi periodicity of 1 470 years for the late glacial period1 2 3 4 5 6 various hypotheses have been suggested to explain these rapid temperature shifts including internal oscillations in the climate system and external forcing possibly from the sun7 but whereas pronounced solar cycles of 87 and 210 years are well known8 9 10 11 12 a 1 470 year solar cycle has not been detected8 here we show that an intermediate complexity climate model with glacial climate conditions simulates rapid climate shifts similar to the dansgaard oeschger events with a spacing of 1 470 years when forced by periodic freshwater input into the north atlantic ocean in cycles of 87 and 210 years we attribute the robust 1 470 year response time to the superposition of the two shorter cycles together with strongly nonlinear dynamics and the long characteristic timescale of the thermohaline circulation for holocene conditions similar events do not occur we conclude that the glacial 1 470 year climate cycles could have been triggered by solar forcing despite the absence of a 1 470 year solar cycle

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

ocean subsurface warming as a mechanism for coupling dansgaard oeschger climate cycles and ice rafting events 1 heinrich events have been attributed to surging of the laurentide ice sheet every 7 thousand years or so during glacial time these massive ice rafting events only occurred during cold phases of millennial scale dansgaard oeschger climate cycles other observed ice rafting events sourced from ice streams at various locations around the northern north atlantic occurred during all dansgaard oeschger cold phases and led heinrich events when the latter took place here it is suggested that ocean subsurface warming in the northern north atlantic during the cold phases may provide the key to explaining these climate ice rafting phasings such warming would lead to ice shelf melting and breakup without buttressing by ice shelves ice streams may surge leading to increased iceberg production this interpretation is supported by results of a simplified coupled climate model and by available sediment and ice sheet data

early veins as evidence of detachment in the lower palaeozoic rocks of the welsh basin abstract a suite of small scale structures mostly represented by veins is widely developed in the lower palaeozoic elastic sedimentary rocks of the welsh basin the structures were produced after considerable dewatering and diagenesis had taken place but before the host rocks were folded and cleaved by the regional deformation bedding parallel veins the most common of the structures are attributed to hydraulic jacking and mineralization by overpressured pore fluid probably at burial depths of several hundred metres or more the various burial processes including the production of the veins are regarded as being diachronous in effect propagating up through the sediment pile as sedimentation and burial progressed the bedding parallel veins are considered to represent inclined detachment surfaces sole planes down which rock masses slid due to gravity these surfaces were initiated in rocks originally inclined from the horizontal for sedimentological reasons or in horizontal host rocks which were later tilted by tectonic processes other structures in the suite were produced as a consequence of the downslope movement for example by compression in the toe regions of the glide sheet and by extension at the trailing edges slip directions recorded by striations on the bedding parallel veins were mainly wnw ese in w wales and n s in ne wales it is anticipated that these structures will be found to be widespread in other sedimentary basins that they have escaped attention elsewhere is probably because individual structures are small and seemingly insignificant whilst in deformed rocks they may have been attributed to folding or faulting

the pontesford lineament welsh borderland the ne trending pontesford lineament centres on the pontesford linley and adjacent faults in the shelve longmynd inlier to the ne it is usually drawn along the se edge of the cheshire basin and to the sw along a variety of lines parallel to or converging with the church stretton fault new mapping and reassessment of published data suggest that sw of the pontesford linley fault the lineament is logically drawn along the clun forest disturbance a post pridoli late silurian fold fault belt then across the nw side of the llandrindod inlier to flank the tywi lineament the lineament was intermittently active at least from mid ordovician through to triassic time with both strike slip and dip slip displacements that involved the upper part of the precambrian basement late ordovician and early silurian strike slip was particularly important the lineament controlled the sites of several silurian sedimentary basins ordovician contrasts across the lineament can be explained either by contemporary fault control or by subsequent large displacements juxtaposing unlike terranes the long history of reactivation and basement control on the pontesford lineament is typical of lineaments throughout wales and the borderland it suggests that both caledonian and variscan structural trends n of the variscan front may be inherited from older pre silurian or even precambrian basement structures

fibrous calcite veins overpressures and primary oil migration the fibrous calcite veins found parallel to the bedding of certain shales may have been formed during burial as a consequence of overpressuring their presence could even be indicative of former overpressures this suggestion if it can be upheld carries implications for theories of primary oil migration

holocene east asian summer monsoon records in northern china and their inconsistency with chinese stalagmite δ18o records abstract monsoon precipitation over china exhibits large spatial differences it has been found that a significantly enhanced east asian summer monsoon easm is characterized by increased rainfall in northern china and by reduced rainfall in southern china and this relationship occurs on different time scales during the holocene this study presents results from a diverse range of proxy paleoclimatic records from northern china where precipitation variability is traditionally considered as an easm proxy our aim is to evaluate the evolution of the easm during the holocene and to compare it with all of the published stalagmite 18 o records from the asian monsoon region in order to explore the potential mechanism s controlling the chinese stalagmite 18 o we found that the intensity of the easm during the holocene recorded by the traditional easm proxy of moisture or precipitation records from northern china is significantly different from the chinese stalagmite 18 o records the easm maximum occurred during the mid holocene challenging the prevailing view of an early holocene easm maximum mainly inferred from stalagmite 18 o records in eastern china in addition all of the well dated holocene stalagmite 18 o records covering a broad geographical region exhibit a remarkably similar trend of variation and are statistically well correlated on different time scales thus indicating a common signal however in contrast with the clear consistency in the 18 o values in all of the cave records both instrumental and paleoclimatic records exhibit significant spatial variations in rainfall on decadal to centennial time scales over eastern china in addition both paleoclimatic records and modeling results suggest that holocene east asian summer monsoon precipitation reached a maximum at different periods in different regions of china thus the stalagmite 18 o records from the easm region should not be regarded as a reliable indicator of the strength of the east asian summer monsoon furthermore modern observations indicate that the moisture for precipitation in the east asian monsoon region is mainly derived from the indian ocean the moisture transport route from the indian ocean to the east asian monsoon region during the holocene is almost identical to that of modern precipitation therefore the strong correlation of 18 o records in the easm and indian summer monsoon ism regions and the similarity of the pattern of latitudinal changes in 18 o values in stalagmites and in modern meteoric precipitation along the water vapor transport route further suggests that the stalagmite 18 o records from the easm region are essentially a signal of the isotopic composition of precipitation which is determined mainly by changes in the 18 o of atmospheric vapor in the upstream source region over the indian ocean and indian monsoon region via the upstream depletion mechanism finally the main trends of the stalagmite 18 o records are strongly correlated with the known evolution of the ism and therefore these records reflect the history of the ism rather than that of the easm our findings support the conclusion that easm variability is mainly controlled by northern hemisphere summer insolation and was strongly modulated by ice volume during the last deglaciation and early holocene which delayed the response of the easm maximum to peak insolation forcing

volcanogenic mineralization related to the snowdon volcanic group ordovician gwynedd north wales the ordovician caradoc volcanic rocks of ne snowdonia constitute two major groups the llewelyn volcanic group and the snowdon volcanic group which accumulated predominantly in shallow water marine conditions the younger snowdon volcanic group comprised a bimodal basalt rhyolite suite and included a major caldera forming eruption of acidic ash flow tuffs superseded by both surtseyan and strombolian basaltic volcanism rhyolite domes were intruded into the volcanic sequence in the vicinity of the caldera the snowdon cu pb zn vein mineralization comprises five paragenetic mineral assemblages the veins cut rocks deposited within and over the caldera and it is proposed that the dominant controls of mineralization were volcanogenic circulation in hydrothermal cells involving both juvenile fluids and seawater deposited the minerals at a late stage in the evolution of the caldera

the distinction between caledonian burial and regional metamorphism in metapelites from north wales an analysis of isocryst patterns in snowdonia and ll n three prograde stages in metapelites gwna group to wenlock are recognized stage i with white mica crystallinity values 0 43 2 stage ii 0 43 0 26 2 stage iii isocrysts at 0 03 2 intervals are drawn separately for pelites above and below the sub arenig unconformity approximately concordant isocryst patterns characterize the unconformity in the northwestern and southeastern limbs of the snowdonia syncline whereas discordant patterns are developed northwest of the aber dinlle fault and at the closure of the ynyscynhaiarn anticline the contrasting patterns are the result of a pre arenig burial metamorphism in post tremadoc pelites belts of steep metamorphic gradient coincide with belts of high strain and a broad area of higher grade caradoc pelites coincides with the core of the snowdonia syncline the later metamorphism is related to caledonian deformation rather than to burial pelite alteration adjacent to small intermediate to acid plutons suggests emplacement before the caledonian regional metamorphism a close correlation exists between metabasite zones and metapelite stages

very low oxygen concentration in basal ice from summit central greenland oxygen concentration as low as 3 has been detected in the basal silty ice of the grip core such values were never observed in ice from ice sheets they are most probably the consequence of organic matter oxidation in ice developed in a peaty deposit when the greenland ice sheet was not present at the site flow induced mixing has further incorporated this ice into glacier ice during the ice sheet build up the part of the local ice component in the mixing process diminishes with the distance from the bed this is the process which explains the oxygen profile

evidence for an additional heinrich event between h5 and h6 in the labrador sea 1 an additional heinrich ice rafting event is identified between heinrich events 5 and 6 in eight cores from the labrador sea and the northwest atlantic ocean it is characterized by sediment rich in detrital carbonate 40 caco3 with high concentration of floating dropstones high coarse fraction 150 m content and has a sharp contact with the underlying but grades into the overlying hemipelagic sediment it also shows lighter 18onpl values indicating freshening due to iceberg rafting and or meltwater discharge this event is correlated with dansgaard oeschger event 14 and interpreted as an additional heinrich event h5a the thickness of h5a in the labrador sea reaches up to 220 cm this additional heinrich event has also been reported in cores ps2644 and so82 5 from the northern north atlantic with the recognition of h5a the temporal spacing between heinrich events 1 to 6 becomes more uniform 7 ka

land ocean linkages over orbital and millennial timescales recorded in late quaternary sediments of the japan sea late quaternary sediments of the japan sea are characterized by centimeter to meter scale alternations of dark and light layers which are synchronous basinwide high resolution analyses of the sediments from ocean drilling program site 797 reveal that deposition of the meter scale alternations reflect variations in paleoceanographic conditions which were closely associated with glacio eustatic sea level changes through the modulation of the volume and character of the influx to the sea through the tsushima strait the centimeter to decimeter scale alternations reflect millennial scale variations which are possibly associated with dansgaard oeschger d o cycles with each dark layer appearing to correspond to an interstadial this variability is attributed to the development of a humid climate in central to eastern asia and the consequent increase in discharge from the huanghe and changjiang rivers during interstadials this caused expansion of the east china sea coastal water ecscw which penetrated more strongly into the japan sea the increased influence of the lower salinity nutrient enriched ecscw reduced deep water ventilation and enhanced the surface productivity leading to the development of anoxic bottom waters and deposition of the dark layers thus the centimeter to decimeter scale alternations of the dark and light layers record wet and dry cycles in central to eastern asia possibly associated with d o cycles