gulf stream variability during marine isotope stage 3 we have studied ocean drilling program site 1060 on the blake outer ridge which lies beneath the gulf stream we focus on marine isotope stage 3 60 25 thousand years before present ka sea surface temperatures ssts inferred both from foraminiferal fauna and alkenone ratios as well as counts of iceberg melt out debris and benthic stable isotope analyses enable our record to be interpreted in terms of regional hydrographic changes as well as changing thermohaline circulation thc the observed sst record is consistent with the air temperature record from the greenland ice cores however site 1060 exhibits important differences in detail compared with the ice core record and when compared to other sites within the north atlantic significant longitudinal differences emerge at site 1060 in the western atlantic all greenland stadials gs whether associated with heinrich events hes or not show a similar small amplitude of cooling mean faunal based sstaug during gs is only 1 5 c colder than during greenland interstadials gis in addition during gs the coldest ssts are limited to apparently brief events this is in contrast to several eastern atlantic sites where he stadials exhibit coolings that are enhanced by 2 c compared to other gs and where cold conditions are not restricted to cold pulses but cover 2 ka long intervals furthermore site 1060 ssts remained warm right through each interstadial in contrast to the sustained and uniform cooling trend through interstadials that is consistently observed in greenland indicated by measurements of 18o in ice

applying end member modeling to extricate the sedimentary environment of yardang strata in the dunhuang yardang national geopark northwestern china abstract formative mechanisms and sedimentary environments of yardang landform distribution in arid and semiarid regions of northwestern china remain poorly understood due to their unique formation and enigmatic causation considerable controversy remains as to whether yardang deposits evolve from aeolian or aqueous forces and no reliable quantitative method has yet been made available to resolve this issue this study conducted a comparative analysis between yardang strata and modern surface sediments to characterize the sedimentary environment using end member modeling analysis emma results show that yardang and surface sediment end members corresponded well and that the yardang depositional environment can be classified into three typical types aeolian 200 550 m mode value range alluvial 150 300 m and 8 20 m and lacustrine subclassified into shoreline 80 110 m lake center 3 15 m and transitional the transition between the littoral and limnetic zones 15 60 m based on this method we determined that lacustrine aeolian and alluvial concentrations were 63 92 20 80 and 15 28 ya profile respectively and 53 68 28 30 and 18 02 yb profile respectively additionally a significant difference was found between the sedimentary processes of the two profiles where ya had more lacustrine sediments and yb had more aeolian sediments likely resulting from paleotopography generally yardang derives from alternating lacustrine aeolian and alluvial sedimentary deposits although lacustrine sediments predominated aeolian sediments also accounted for a considerable overall proportion this study provides new insight into the formation and development of yardang landforms as well as evidence for the reconstruction of paleo geomorphologic patterns

the holocene history of lop nur and its palaeoclimate implications abstract the holocene hydrological history of lop nur in northwestern china s tarim basin and its response to climate conditions are inferred from a relatively well dated multi proxy record including grain size pollen and spores and soluble salt data a dated pit section ykd0301 with a depth of 570 cm in the center of the dry lop nur basin was investigated the sediments contain a total of twenty fining upward cycles as a result of strong discharge from the catchment to the lake during relatively wet conditions the fluvial sediments were probably widely dispersed by wind driven waves and currents in the large and shallow basin of lop nur higher runoff and dilution of lake waters are also indicated by lower contents of soluble salt in the sediments and recorded ostracod shells of brackish and oligohaline to freshwater species in contrast sediment sections with smaller mean grain size and fewer flood layers are dominated by aeolian sediments which were accumulated during drier periods ostracod shells are mostly lacking from these sections suggesting a higher salinity in the lake lop nur experienced six stages during the last 9 ka relatively wet conditions existed between 9 0 8 9 8 7 5 1 and 2 4 1 8 ka with periods of increased aridity in between and after 1 8 ka the lowest salinity was recorded between 8 7 and 5 1 ka which represents the wettest phase during the last 9 ka and probably the regional holocene optimum relatively wet climate conditions between 2 4 and 1 8 ka and dry conditions afterwards possibly first fostered and later on caused the devastation of the ancient loulan kingdom in the region the uppermost sediments of the section represent a massive salt crust formed during the final desiccation of the lake in the last century the effective moisture change pattern of the lop nur region is roughly consistent with synthesized holocene moisture records for western china dominated by the westerlies

holocene climate variations from zhuyeze terminal lake records in east asian monsoon margin in arid northern china zhuyeze palaeolake is a terminal lake situated in the arid northern china in the east asian monsoon margin in order to examine the holocene palaeoclimatic change in the east asian monsoon margin qingtu lake section qtl from zhuyeze palaeolake is sampled in high resolution palaeoclimatic proxies such as grain size carbonate toc c n and delta 13 c of organic matter were analyzed eleven 14 c samples and six optically stimulated luminescence osl samples were dated to provide chronological control we also investigated the geomorphic features of lake shorelines in this area the results show that the climate was warm and dry in early holocene 9 5 7 0 cal ka bp cool and humid in mid holocene 7 0 4 8 cal ka bp and increasingly drier in late holocene since 4 8 cal ka bp comparisons of our records with other records in adjacent areas as well as with the records in the asian monsoon areas suggested that changes in effective moisture was synchronous in east asian monsoon marginal zone i e the pattern of dry early holocene humid mid holocene and aridity increasing late holocene and that the moisture optimum during the holocene was out of phase between asian monsoon margin and asian monsoonal dominated region possibly due to the high temperature at that time c 2010 university of washington published by elsevier inc all rights reserved zhuyeze palaeolake is a terminal lake situated in the arid northern china in the east asian monsoon margin in order to examine the holocene palaeoclimatic change in the east asian monsoon margin qingtu lake section qtl from zhuyeze palaeolake is sampled in high resolution palaeoclimatic proxies such as grain size carbonate toc c n and delta 13 c of organic matter were analyzed eleven 14 c samples and six optically stimulated luminescence osl samples were dated to provide chronological control we also investigated the geomorphic features of lake shorelines in this area the results show that the climate was warm and dry in early holocene 9 5 7 0 cal ka bp cool and humid in mid holocene 7 0 4 8 cal ka bp and increasingly drier in late holocene since 4 8 cal ka bp comparisons of our records with other records in adjacent areas as well as with the records in the asian monsoon areas suggested that changes in effective moisture was synchronous in east asian monsoon marginal zone i e the pattern of dry early holocene humid mid holocene and aridity increasing late holocene and that the moisture optimum during the holocene was out of phase between asian monsoon margin and asian monsoonal dominated region possibly due to the high temperature at that time c 2010 university of washington published by elsevier inc all rights reserved

late holocene forcing of the asian winter and summer monsoon as evidenced by proxy records from the northern qinghai tibetan plateau abstract little is known about decadal to centennial scale climate variability and its associated forcing mechanisms on the qinghai tibetan plateau a decadal resolution record of total organic carbon toc and grainsize retrieved from a composite piston core from kusai lake nw china provides solid evidence for decadal to centennial scale asian monsoon variability for the northern qinghai tibetan plateau during the last 3770 yr intensified winter and summer monsoons are well correlated with respective reductions and increases in solar irradiance a number of intensified asian winter monsoon phases are potentially correlated with north atlantic climatic variations including bond events 0 to 2 and more recent subtle climate changes from the medieval warm period to the little ice age our findings indicate that asian monsoon changes during the late holocene are forced by changes in both solar output and oceanic atmospheric circulation patterns our results demonstrate that these forcing mechanisms operate not only in low latitudes but also in mid latitude regions the northern qinghai tibetan plateau

qualitative and quantitative approaches in palaeohydrography a case study from core top parameters in the gulf of cadiz palaeoceanography relies on the assumption that parameters measureable in sediment cores correlate reliably to hydrographic parameters areas of dynamic watermass mixing which generally have steep hydrographic gradients therefore provide both a tempting target large spatial and temporal differences in temperature and salinity and a significant challenge high flow velocities and high noise for palaeoceanographers here we investigate the ability of parameters measured on core tops to be used as the basis for simulating regional hydrography within one globally important area of watermass mixing the gulf of cadiz using grainsize sediment composition benthic foraminiferal assemblage and benthic foraminiferal stable isotope analysis it is possible to build an effective framework for qualitative constraint of the position of the modern mediterranean outflow water mw plume we propose that the gulf of cadiz slope can be sub divided into 8 hydrographic zones reflecting these parameters proximal mw core mw1 steep slopes core mw1 gentle slopes distal mw1 distal mw2 lower limit of mw plume north atlantic deep water and ambient atlantic water we anticipate that compilation of time slice data will reveal hydrographic sub divisions of the slope for the past in a similar manner improving our understanding of past changes in the size and position of the mw plume but more work needs to be done before a secure protocol for quantitative reconstruction can be created stable isotope analysis alone is insufficient for the task with 13c behaving in a non conservative manner and 18ocalcite acting in an ambiguous way due to the competing influences of 18owater and temperature it is likely that if a single parameter that unambiguously determines the difference between mediterranean water and atlantic water can be identified combination with 18ocalcite will allow extension of our qualitative analysis into a quantitative means of palaeohydrographic reconstruction for this region similar complexity to that found in this study would be expected in any mixing region and in particular on the majority of sediment drifts we recommend that core top surveys similar to this study are performed on these sediment drift systems before any form of quantitative palaeohydrology is attempted

the impact of pro glacial lakes on downstream sediment delivery in norway glacier recessions caused by climate change may uncover pro glacial lakes that form important sedimentation basins regulating the downstream sediment delivery the impact of modern pro glacial lakes on fluvial sediment transport from three different norwegian glaciers nigardsbreen engabreen and tunsbergdalsbreen and their long term development has been studied all of these lakes developed in modern times in overdeepened bedrock basins the recession of nigardsbreen uncovered a 1 8 km long and on average 15 m deep pro glacial lake basin during 1937 to 1968 since then the glacier front has been situated entirely on land and the sediment input and output of the lake has been measured the suspended sediment transport into and out of the lake averaged 11 730 t yr 1 and 2340 t yr 1 respectively thus 20 remained in suspension at the outlet the measured mean annual bedload supplied to the lake was 11 800 t yr 1 giving a total transport of 23 530 t yr 1 which corresponds to a specific sediment yield of 561 t km 2 yr 1 a 1 9 km long and up to 90 m deep pro glacial lake basin downstream from engabreen glacier was uncovered during 1890 to 1944 the average suspended sediment load delivered from the glacier during the years 1970 1981 amounted to 12 375 t yr 1and the transport out of the lake was 2021 t yr 1 giving an average of 16 remaining in suspension the mean annual bedload was 8000 t yr 1 thus the total transport was 20 375 t yr 1 giving a specific sediment yield of 566 t km 2 yr 1 for tunsbergdalsbreen glacier measurements in the early 1970s indicated that the suspended sediment transport was on average 44 000 t yr 1 from 1987 to 1993 the recession of the glacier uncovered a small pro glacial lake 0 3 km long and around 9 m deep downstream from this the suspended sediment load measured in 2009 was 28 000 t yr 1 indicating that as much as 64 remained in suspension flow velocity grain size of sediment and morphology of the lake are important factors controlling the sedimentation rate in the pro glacial lakes a survey of the sub glacial morphology of tunsbergdalsbreen revealed that there are several overdeepened basins beneath the glacier the largest is 4 km long and 100 m deep when the glacier melts back they will become lakes and act as sedimentation basins despite an expected increase in sediment yield from the glacier little sediment will pass these lakes and downstream sediment delivery will be reduced markedly beneath nigardsbreen there was only a small depression that may form a lake and the sediment delivery will not be significantly affected 2014 the authors earth surface processes and landforms published by john wiley sons ltd

radiocarbon dating of aquatic gastropod shells and its significance in reconstructing quaternary environmental changes in the alashan plateau of northwestern china abstract using landform evolution and lake sediment records to reconstruct quaternary environmental changes requires reliable chronology however there is an ongoing debate regarding the fossil shells of aquatic gastropods in carbonate rock area to be used for radiocarbon dating the focus of this debate is whether living gastropods incorporate the dead carbon which would affect the accuracy of the dating results living aquatic gastropods were selected from habitats on carbonate terrain in arid region in this study 64 shell samples from living gastropods including cipangopaludina chinensis gyraulus convexiusculus and radix auricularia collected from the alashan plateau of northwestern china were dated by accelerator mass spectrometry ams 14c dating the results revealed that only five samples 8 from the same site contained no dead carbon the other 59 samples 92 contained dead carbon in various amounts 59 samples contained 0 10 dead carbon and 33 samples contained more than 10 dead carbon of the samples 56 were radix auricularia and their 14c ages varied from present to 3253 cal yr bp two of the samples were gyraulus convexiusculus samples dated at 379 and 290 cal yr bp which are highly consistent with 14c ages of radix auricularia samples from the same site the other six cipangopaludina chinensis samples were dated at 407 863 cal yr bp thus most of living aquatic gastropods from habitats on carbonate terrain contained dead carbon the amount of dead carbon in the gastropod shells was nonselective among the three species radiocarbon dating of aquatic gastropod shells may not be useful for studying processes that occurred over multi millennial timescales at different localities in areas of carbonate rock it is difficult to establish high resolution chronologies using 14c ages of gastropod shells in arid regions with carbonate rocks unless the limestone effect has been corrected

grain size of lake qinghai sediments implications for riverine input and holocene monsoon variability abstract grain size compositions of lake sediments can provide direct information on changes in transporting mechanism and sedimentary environment various grain size parameters have been employed to reconstruct hydrological conditions within the lake and dust influx from outside the lake here we present the grain size results of a 5 m core retrieved from lake qinghai northeastern tibetan plateau in order to address the links between holocene depositional process and climatic change our results indicate that two parameters skewness and grain size ratio of 8 50 2 8 m are sensitive to hydrodynamic changes in lake qinghai which are further linked to the strength of the asian summer monsoon variations of these two parameters reveal that summer monsoon intensity weakened gradually from early to late holocene superimposed by persistent centennial variability with dominant periods at 0 35 0 23 and 0 12 kyr comparison of grain size variations with solar activities and north atlantic cooling events reveals that solar forcing likely plays an important role in driving centennial monsoon variability

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

comparative molecular biomarker assessment of phytoplankton paleoproductivity for the last 160 kyr off cap blanc nw africa abstract we report high resolution molecular abundance data for alkenones dinosterol long chain diols and n alkanols from odp site 658 20 45 n 18 35 w 2263 m water depth these data are compared with previously reported data for toc chlorins opal and long chain n alkanes the contents and mass accumulation rates mars of chlorins are used as total phytoplankton productivity proxies while the contents and mars of opal dinosterol alkenones and diols are used as productivity proxies for diatoms dinoflagellates haptophytes and eustigmatophytes diatoms respectively five high productivity intervals hpis are identified two at the glacial interglacial transition boundaries of 132 122 and 15 8 ka two within the warmer periods of mis 3 50 30 ka and the late holocene 4 0 ka and one within the glacial period of mis 4 67 60 ka productivity was lowest during both the penultimate glacial maximum of mis 6 150 140 ka and the last glacial maximum 22 18 ka as revealed by both the total phytoplankton and individual phytoplankton productivity indicators phytoplankton community structure changed significantly over the last 160 kyr the termination i ii hpis were characterized by higher opal content possibly reflecting increased diatom contributions to total productivity eustigmatophyte diatom and haptophyte contributions were higher during mis 5 but decreased toward the holocene dinosterol revealed an opposite trend with the highest contribution in the holocene we ascribe such changes in phytoplankton communities to the effects brought about by the varying amounts and nature of nutrient inputs contributed regionally by eolian dusts river influxes ocean currents and upwelling water masses

a poisoned chalice deep sea sediments often carry information about past temperatures in the upper ocean directly above their location but as mccave cautions in this perspective interpretation of the sediments can be complicated by deep sea processes for example material transported laterally in the deep ocean may distort the upper ocean signal in the sediments a report by ohkouchi illustrates such processes at bermuda rise the study yields a detailed understanding of deep sea sediment transport processes aiding the interpretation of sediment records at this site and sounding a warning for others

holocene weak monsoon intervals indicated by low lake levels at hulun lake in the monsoonal margin region of northeastern inner mongolia china a 170 cm long sediment core spanning the last 10 000 years was recovered from hulun lake in the northeastern margin of the east asian summer monsoon the sediment core was analyzed at 1 cm intervals for grain size distribution and sedimentary component partition these data provide a proxy record of the monsoon variability on millennial to centennial scales during the holocene we used a lognormal distribution function fitting method to partition three to six components from fine to coarse modes within the individual polymodal distributions into overlapping lognormal distributions three coarse components representing nearshore suspension saltation and traction together with the sand fraction percentage and the median grain size of bulk samples indicate the lake levels that fluctuated in response to the intensity of the monsoonal precipitation higher percentages of the nearshore components accompanied by more sand fraction proportions and coarser median grain sizes reflect lower lake stands resulting

early middle pleistocene deep circulation in the western subtropical atlantic southern hemisphere modulation of the north atlantic ocean early middle pleistocene climate and deep ocean hydrography have been reconstructed using oxygen and carbon isotope ratio measurements in planktonic and benthic foraminifera from a high deposition rate sedimentary succession recovered at the bermuda rise in the northern sargasso sea ocean drilling program leg 172 site 1063 the site s water depth makes it sensitive to changes in the balance between north atlantic deep water nadw and antarctic bottom water aabw in the deep north atlantic allowing the evaluation of perturbations in deep water production at different timescales millennial scale fluctuations superimposed on the longer period oscillations of orbital origin occurred during all the observed climate states the highest amplitude sub milankovitch fluctuations were mainly associated with interglacials particularly after the intensification of the glacial regime at c 900 ka using the benthic carbon isotope signal as a water mass tracer and by comparing the delta 13c record to a suite of drill sites in the north atlantic and pacific oceans it has been possible to infer that the relative strength of aabw production varied through time as did that of nadw a scenario in which the two different source components of deep water can undergo dramatic changes in their circulation regime through time should be taken into consideration when evaluating the role of thermohaline circulation in global climate change

seasonal controls on sediment transport and deposition in lake ohau south island new zealand implications for a high resolution holocene palaeoclimate reconstruction laminated sediments in lake ohau mackenzie basin new zealand offer a potential high resolution climate record for the past 17 kyr such records are particularly important due to the relative paucity of detailed palaeoclimate data from the southern hemisphere mid latitudes this paper presents outcomes of a study of the sedimentation processes of this temperate lake setting hydrometeorological limnological and sedimentological data were collected over a 14 month period between 2011 and 2013 these data indicate that seasonality in the hydrometeorological system in combination with internal lake dynamics drives a distinct seasonal pattern of sediment dispersal and deposition on a basin wide scale sedimentary layers that accumulate proximal to the lake inflow at the northern end of the lake form in response to discrete inflow events throughout the year and display an event stratigraphy in contrast seasonal change in the lake system controls accumulation of light winter and dark summer laminations at the distal end of the lake resulting in the preservation of varves this study documents the key processes influencing sediment deposition throughout lake ohau and provides fundamental data for generating a high resolution palaeoclimate record from this temperate lake

recharge to the inter dune lakes and holocene climatic changes in the badain jaran desert western china we present new estimates on evaporation and groundwater recharge in the badain jaran desert western inner mongolia of northwestern china based on a modified penman equation suitable for lakes in china geochemical data and water balance calculations suggest that local rainfall makes a significant contribution to groundwater recharge and that past lake level variations in this desert environment should reflect palaeoclimatic changes the chronology of lake level change established by radiocarbon and u series disequilibrium dating methods indicates high lake levels and a wetter climate beginning at ca 10 ka and lasting until the late mid holocene in the badain jaran desert the greatest extension of lakes in the inter dune depressions indicates that the water availability was greatest during the mid holocene relicts of neolithic tools and pottery of qijia culture 2400 1900 bc suggest relatively intensive human activity in the badain jaran desert during the early and middle holocene supporting our interpretation of a less harsh environment wetter climates during the holocene were likely triggered by an intensified east asian summer monsoon associated with strong insolation

abrupt wind regime changes in the north atlantic ocean during the past 30 000 60 000 years 1 the inputs of higher plants in blake outer ridge subtropical western north atlantic during marine isotope stage 3 mis3 have been recorded at high resolution by quantification of c23 c33 odd carbon numbered n alkanes and c20 c30 even carbon numbered n alkan 1 ols in sediment sections of ocean drilling program site 1060 the changes of these proxies at this open marine site are mainly related to eolian inputs their concentrations and fluxes exhibit major abrupt variations that are correlated with dansgaard oeschger d o patterns in greenland ice cores the ratios between interstadials and stadials range between 2 and 9 times the intense flux increases in the d o stadials are linked to strong enhancements of the westerly wind regime at these subtropical latitudes during stadials the observed variation was paralleled by changes in wind blown dust and the polar circulation index in greenland ice which is in agreement with previously hypothesized atmospheric teleconnections between northern and middle low latitudes of the northern hemisphere the close correspondence between sedimentary and ice core proxies is evidence that crossings of the glacial climate thresholds involved major reorganizations of the troposphere the observed large rise in higher plant biomarkers indicates that climate stabilization in the d o stadial conditions led to main increases in wind intensity

anomalously weak labrador sea convection and atlantic overturning during the past 150 years the atlantic meridional overturning circulation amoc is a system of ocean currents that has an essential role in earth s climate redistributing heat and influencing the carbon cycle1 2 the amoc has been shown to be weakening in recent years 1 this decline may reflect decadal scale variability in convection in the labrador sea but short observational datasets preclude a longer term perspective on the modern state and variability of labrador sea convection and the amoc1 3 5 here we provide several lines of palaeo oceanographic evidence that labrador sea deep convection and the amoc have been anomalously weak over the past 150 years or so since the end of the little ice age lia approximately ad 1850 compared with the preceding 1 500 years our palaeoclimate reconstructions indicate that the transition occurred either as a predominantly abrupt shift towards the end of the lia or as a more gradual continued decline over the past 150 years this ambiguity probably arises from non amoc influences on the various proxies or from the different sensitivities of these proxies to individual components of the amoc we suggest that enhanced freshwater fluxes from the arctic and nordic seas towards the end of the lia sourced from melting glaciers and thickened sea ice that developed earlier in the lia weakened labrador sea convection and the amoc the lack of a subsequent recovery may have resulted from hysteresis or from twentieth century melting of the greenland ice sheet 6 our results suggest that recent decadal variability in labrador sea convection and the amoc has occurred during an atypical weak background state future work should aim to constrain the roles of internal climate variability and early anthropogenic forcing in the amoc weakening described here

hydrological thresholds and basin control over paleoflood records in lakes the scarcity of long term hydrological data is a barrier to reliably determining the likelihood of floods becoming more frequent and or intense in a warmer world lake sediments preserve characteristic event layers offering the potential to develop widely distributed and unique chronologies of historical floods inferring flood magnitude remains a greater challenge previously overcome in part by analyzing sharply laminated polar or alpine sequences here we demonstrate an approach to obtain flood frequency and magnitude data from an unexploited resource the largely visually homogeneous organic sediments that typify most temperate lakes the geochemical composition and end member modeling of sediment trap and adjacent short core particle size data for brotherswater northwest england discriminates the signature of infrequent coarse grained flood deposits from seasonal and longer term allogenic enhanced discharge and sediment supply during winter and autogenic summer productivity thermal mixing depositional processes comparing the paleoflood reconstruction to local river discharges shows that hydrological thresholds censor event signature preservation with 4 yr recurrence intervals detectable in delta proximal sediments declining to 9 yr in the lake center event threshold discharge and process characterization are essential precursors to discerning flood magnitude from sediment archives implementation of our approach in globally prevalent temperate lakes offers a vast unique repository of long term hydrological data for hydrologists climate modelers engineers and policy makers addressing future flood risks

quantifying opening mode fracture spatial organization in horizontal wellbore image logs core and outcrop application to upper cretaceous frontier formation tight gas sandstones usa abstract the upper cretaceous frontier formation is a naturally fractured gas producing sandstone in wyoming regionally random and statistically more clustered than random patterns exist in the same upper to lower shoreface depositional facies east west and north south striking regional fractures sampled using image logs and cores from three horizontal wells exhibit clustered patterns whereas data collected from east west striking fractures in outcrop have patterns that are indistinguishable from random image log data analyzed with the correlation count method shows clusters 35 m wide and spaced 50 to 90 m apart as well as clusters up to 12 m wide with periodic inter cluster spacings a hierarchy of cluster sizes exists organization within clusters is likely fractal these rocks have markedly different structural and burial histories so regional differences in degree of clustering are unsurprising clustered patterns correspond to fractures having core quartz deposition contemporaneous with fracture opening circumstances that some models suggest might affect spacing patterns by interfering with fracture growth our results show that quantifying and identifying patterns as statistically more or less clustered than random delineates differences in fracture patterns that are not otherwise apparent but that may influence gas and water production and therefore may be economically important

fracture mapping with electrical core images naturally fractured reservoirs often contain a range of different fracture types and networks fractures that are relatively permeable and relatively impermeable unconnected and connected to the part of the fracture network that carries fluid flow and naturally occurring or drilling induced consequently in terms of their fluid connectivity fractures may be open or closed while individual fractures may be isolated or well connected we have adapted our approach to imaging sedimentary fabric in the laboratory where we related electrical core images to properties such as porosity permeability grain size and cementation to enable electrical imaging of fractures in core our approach uses similar principles to those employed in down hole electrical imaging the results demonstrate an ability to image conductive fractures in fully saturated low porosity water bearing core these fractures being electrically connected from the flat measurement surface through to the outer surface of the core published results for numerical modelling of down hole electrical imaging tools show the electrical response is related to fracture depth and fracture aperture our experimental results on fractured core in the laboratory support these numerical observations increased current flowing into the fracture as the aperture increases the finite size of the electrode however means that this technique cannot distinguish between a single fracture and smaller groups of fractures intersecting the electrode

characterization of subaerial volcanic facies using acoustic image logs lithofacies and log facies of a lava flow deposit in the brazilian pre salt deepwater of santos basin abstract volcanic rock facies characterization in subsurface log data have always being challenging even though considerable types of well logs are acquired the results achieved on facies characterization with the conventional log suits are very limited conversely high resolution borehole image logs calibrated with side wall core samples can provide the necessary structural and textural information for facies definitions in this case study an integration of good quality acoustic image log data side wall core petrography and geochemical analyses provided a good understanding of volcanic facies and stratigraphic relationships additionally outcrop data from the analogous serra geral formation and other large igneous provinces were used for comparison in the studied well from santos basin brazil it was possible to identify several kinds of subaerial basaltic lava flow units such as compound pahoehoe sheet pahoehoe and rubbly pahoehoe lava flows vesicles amygdales vesicle cylinders sub horizontal vesicle sheets autobreccias and entablature are some of the structures described in this study as a result 2 image catalogues of subaerial volcanic rocks were produced characterizing facies and flow units along with a stratigraphic model of the history of this volcanism this is the first time that pahoehoe lava flow units could be characterized at an offshore brazilian basin the results achieved are important for the understanding of the cretaceous volcanism events in the pre salt layer and also provide support for the evaluation and geological modelling of the volcanic rocks in santos basin oil fields

heterogeneity of structure and stress in the rotokawa geothermal field new zealand geometric characterization of a geothermal reservoir s structures and their relation to stress field orientation is vital for resource development subsurface structure and stress field orientations of the rotokawa geothermal field new zealand have been studied for the first time using observations obtained from analysis of three acoustic borehole televiewer logs while an overall ne sw fracture strike exists heterogeneity in fracture dip orientation is evident dominant dip direction changes from well to well due to proximity to variously oriented graben bounding faults fracture orientation heterogeneity also occurs within individual wells where fractures clusters within certain depth intervals have antithetic dip directions to the well s dominant fracture dip direction these patterns are consistent with expected antithetic faulting in extensional environments a general shmax orientation of ne sw is determined from induced features on borehole walls however numerous localized azimuthal variations from this trend are evident constituting stress field orientation heterogeneity these variations are attributed to slip on fracture planes evidenced by changes in the azimuth of drilling induced tensile fractures either side of a natural fracture correlation of observed fracture properties and patterns to well permeability indicators reveal that fractures play a role in fluid flow in the rotokawa geothermal reservoir permeable zones commonly contain wide aperture fractures and high fracture densities which have a dominant ne sw strike orientation and nw dip direction studies of this kind which show strong interdependency of structure and stress field properties are essential to understand fluid flow in geothermal reservoirs where structural permeability dominates

transport of carbonate sediment in the western north atlantic evidence from oxygen and carbon isotopes abstract in most deep ocean environments the carbonate component is usually considered to be of pelagic origin deposited on the sea bed without extensive transport even when evidence exists that carbonate fractions have been transported the transport is usually viewed as being intrabasinal stable isotope analyses 18 o and 13 c of the carbonate contained in the fine fraction m of eight cores from the north american continental margin and the west flank of the mid atlantic ridge mar suggest that carbonate sedimentation patterns may be influenced by transport to a greater extent than previously recognized in holocene sections of all the cores the fine fraction and foraminiferal isotopic signals are comparable in cores from the flanks of the mar the fine fraction and foraminiferal isotopic signals remain comparable during the entire glacial interglacial cycle on the north american margin however the pattern is strikingly different starting about 10 ka and extending back into glacial times the fine fraction isotopic signal in margin cores becomes increasingly depleted reaching a value of 8 pdb the foraminiferal signal from these same cores follows the typical glacial interglacial pattern and gets heavier during glacial time the holocene correspondence of foraminiferal and fine fraction isotope curves throughout the north american basin suggests that both have the same intrabasinal pelagic source however in late glacial age sediments from the north american margin the divergence of foraminiferal and fine fraction isotope signals indicates different sources for each component based on the isotopic signals and the timing of changes in the signal a substantial proportion of the fine fraction carbonate on the north american margin appears to be derived from diagenetically altered carbonate rock this fine carbonate sediment probably resulted from physical erosion of carbonate rock by glacial processes and deposition in the north american basin by the retreating wisconsin glacier

atlantic sediments glacial interglacial comparisons to assess the regional effects of glaciation on sedimentation in the atlantic ocean we compare sediment types distributions and rates between recent core top and last glacial maximum lgm 18 000 years b p stratigraphic levels based upon smear slides and carbonate analyses in 178 cores we find that glacial age carbonate content is generally lower than recent during both the recent and lgm carbonate content shows an east west asymmetry with western basins exhibiting lower carbonate values input of ice rafted detritus into the north atlantic during lgm time interrupts this topographic control on carbonate distribution considerably farther south than at present in the south atlantic this effect is minor comparison of lgm and recent sediment distributions indicates that the lgm seafloor was dominated by biogenic oozes calcareous clays and clays while the recent is dominated by biogenic oozes and marls coarse grained detritus is much more prevalent in lgm sediments derived not only from glacial input but also from fluvial and aeolian sources sedimentation rates calculated from lgm to recent sediment thickness in cores are 4 cm 1000 yr for most of the ocean higher rates are typical of the continental margin off the amazon river the north american basin and a small region off west equatorial africa

geochemical and geomorphological evidence for the provenance of aeolian deposits in the badain jaran desert northwestern china abstract identifying provenance of aeolian deposits in the mid latitude deserts of asia is essential for understanding formation and changes of earth surface processes due to palaeoclimatic fluctuations while some earlier studies focused on the interpretation of palaeoenvironments on the basis of aeolian deposits mainly in the desert margins and inter dune lacustrine sediments research on provenance of desert sands in the vast asian mid latitude deserts is still rare in this paper we present new geochemical data which provide insight to the provenance of dune sands in the badain jaran desert northwestern china an important part of this desert belt we sampled aeolian and lacustrine sediments in various parts of the badain jaran desert and examined their major trace and rare earth elements ree in bulk samples coarse and fine fractions respectively in addition we took and analyzed samples from a rarely known dune field with red sands northeast of the badain jaran our results show that the sands from the badain jaran desert are generally different from those in the red sand dune field in terms of ree pattern and geochemical characteristics suggesting different sediment origins geochemical composition of the aeolian sand samples indicates these sediments should be mainly derived from mixed source rocks of granite granitoids and granodiorite comparing the immobile trace elements and ree ratios of the samples from the badain jaran desert red sand dune field with rocks of granite granitoids in their potential source areas we conclude that 1 the aeolian deposits in the badain jaran desert are predominantly derived from the qilian mountains northeastern tibetan plateau initially via fluvial processes 2 the altay mountains and mongolian gobi are the ultimate source areas for the red sand dune field 3 the altai mountains and mongolian gobi in the northwest that could produce massive amounts of materials via intensive deflation and alluvial process are additional sand sources of the badain jaran desert although their contribution is of secondary significance as the badain jaran desert acts as sediment sinks of sediments from the qilian mountains of northeastern tibetan plateau via fluvial processes it is likely that zircon grains of loess on the chinese loess plateau with age distributions similar to those of the northern tibetan plateau could be derived from the badain jaran desert as the wind data suggest

late pleistocene and holocene aeolian sedimentation in gonghe basin northeastern qinghai tibetan plateau variability processes and climatic implications abstract although stratigraphic sequences of aeolian deposits in dryland areas have long been recognized as providing information about past environments the exact nature of the environmental processes they reflect remains unclear here we report the results of a detailed investigation of eight outcrop sections in the gonghe basin northeastern qinghai tibetan plateau measurements of sediment grain size and chemical composition indicate that the deposits are primarily of aeolian origin consisting of interbedded well sorted sand silty sand loess and or palaeosol however their occurrence varies from site to site fossil dune sands mainly occur in or close to the currently stabilized or semi stabilized dune fields whereas loess is distributed along the downwind marginal areas this pattern of basin scale differentiation was controlled mainly by spatial variability of sediment supply due to the antecedent sedimentary patterns within the basin together with previously published optically stimulated luminescence osl ages 24 new osl dates are used to elucidate the history of aeolian activity and its relationship to climatic changes there is no apparent relationship between past dune activity and downwind loess deposits deposition of silty sand probably occurred during past phases of windy dry and cold climate in the late pleistocene however climatic factors alone cannot explain the occurrence of silty sand deposition this is because the deposition of silty sand was always preceded by episodes of fluvial deposition prior to river incision thereby indicating the importance of an activated sediment supply associated with fluvial processes deposition of well sorted sand occurred episodically not only during the late pleistocene but also during the early to mid holocene vegetation conditions controlled either by the occurrence of intervals of moisture deficit during the late pleistocene or by changes in the balance between precipitation and evapotranspiration at a local scale played an important role in sand mobility and deposition the effect of vegetation on sand mobility is also suggested by independent evidence of aeolian activity from genggahai lake in the gonghe basin here the deposition of aeolian sand in the basin during the early to mid holocene indicates a low level of effective moisture caused by high evaporation induced by higher summer insolation despite the coeval increased regional precipitation recorded by lacustrine sediments in contrast late holocene palaeosols represent a high level of effective moisture and their formation did not necessarily require increased regional precipitation overall our results suggest that the relationship between aeolian activity and regional climate change is complex and that sand accumulations do not represent the consistent action of surface processes that are related to climatic changes

tectonic controls on taupo volcanic zone geothermal expression insights from te mihi wairakei geothermal field information on structure stress and their interrelationship is essential for understanding structurally controlled geothermal permeability active fault mapping borehole image analysis and well testing in the te mihi geothermal area new zealand allows us to refine structural and fluid flow architecture of this resource the te mihi area is structurally complex comprising a set of nw dipping master faults containing pervasive se dipping antithetic and splay structures in their hanging walls these faults are also intersected by e w striking faults a localized n s striking structural trend is also observed at te mihi in consideration with global navigation satellite system velocity vectors both active ne sw and e w striking faults create biaxial extension at te mihi though the observed ne sw shmax direction suggests that contemporary extension is nw se dominated stress field perturbations coincide with structural complexities like fault splays and intersections and or proximity to recently active e w and ne sw striking structures borehole fluid flow at te mihi is concentrated at nw dipping master fault intersections travel time fractures on acoustic image logs halo fractures on resistivity image logs ne sw and e w striking fractures intervals of high fracture density and spatial concentrations of wide aperture fractures and recently active ne sw and e w striking fractures this study suggests te mihi geothermal expression results from biaxial extension evident from active structural trend intersections and the predominance of ne sw and e w striking structures within permeable well zones biaxial extension is therefore an important control on crustal fluid flow within the taupo volcanic zone and thus geothermal resource delineation

the paleoenvironmental significance of spatial distributions of grain size in groundwater recharged lakes a case study in the hinterland of the badain jaran desert northwest china for lakes in desert hinterlands that are not recharged by river runoff sediment input solely comes from wind transport while the processes of sediment transport and deposition in these lakes differ significantly from those with river discharge the spatial distribution of sediment grain size in these groundwater recharged lakes remains largely unknown moreover whether the grain size distribution in these lake sediments can be used as a proxy in the study of past climatic change and environmental evolution studies is unclear in this study five lakes with a range of surface areas that had no runoff recharge were selected from the hinterland of the badain jaran desert of northwestern china and a total of 108 samples of lake surface sediments were collected to examine the spatial distribution of grain size moreover an end member modeling algorithm was used to calculate end members from all grain size measurements our results showed that both the median and mean grain sizes in the lake sediments decreased from the nearshore to the offshore deep water zone however the lowest median and mean grain sizes were not found in the center of the lakes in contrast to lakes recharged by surface runoff the median grain size of sediment in the lake center was negatively correlated with lake level and thus could help reveal lake evolution at low resolutions moreover em1 and em2 were interpreted as wind transported sediment and sediment perturbed by lake waves after wind transport respectively the modal grain size of em1 varied slightly between lakes while changes in the modal grain size of em2 were related to lake area given the positive relationship found between em2 content and lake level changes in the em2 content can serve as a rough indicator of lake level fluctuations at low temporal resolutions

the dry holocene megathermal in inner mongolia the paleoclimate since 14 kyr bp 14c age was reconstructed based on a 16 22 m long sediment core collected from lake yanhaizi a saline lake located near the northern limit of the east asian summer monsoon in inner mongolia coarse sediments were deposited there during a shrinkage phase of the lake when sand dunes reactivated these sediments have low organic carbon contents but high maturity indices indicating that they were deposited in an arid environment by contrast based on high organic contents and low maturity indices fine sediments were deposited during periods of high lake stand in a humid environment it was in general dry between 8 0 and 4 3 kyr bp the above dry and wet phases are consistent with those recovered from the arid semiarid transition zone elsewhere but are unlike the widely perceived humid holocene megathermal reported in east china and the newly reconstructed record in the alpine retreat lake in taiwan the discrepancy may be due to a relative insensitivity to humidity changes in these two areas since they have both been under the total influence of the summer monsoon on the other hand much enhanced evaporation over higher monsoon precipitation at lake yanhaizi reduces the effective humidity in the warm climate near the northern boundary of the summer monsoon this also accounts for the fact the high temperature holocene megathermal as revealed in the okinawa trough and the northern south china sea is correlated to the dry phases at lake yanhaizi conversely the 4 2 kyr bp coldest period in the holocene corresponds to a wet phase at lake yanhaizi

quaternary environmental changes in the drylands of china a critical review abstract this paper reviews our current understanding of quaternary climate and landscape changes in the desert areas of northern china a key portion of the middle latitude drylands on earth combining earlier studies with our recent research and experience we offer a comprehensive picture of the state of chinese deserts during the quaternary and in the interest of enhancing future research identify knowledge gaps and areas of uncertainty lacustrine deposits found over an area ranging from china s western taklamakan desert to the eastern hunshandake sandy lands suggest that extensive lakes occurred in china s deserts during the pleistocene analysis of digital elevation models from srtm shuttle radar topography mission data supports this interpretation and shows the significant extent of these former lakes new estimates of mean annual evaporation of ca 1000 mm from lake surfaces and ca 100 mm from land surfaces confirms that local and regional rainfall is critical for maintenance of desert lakes in this temperate zone especially during intervals when the mean annual rainfall is more than 100 mm rapid shifts between sand seas and lakes in geologically and environmentally diverse settings suggest that the drylands of china are very sensitive ephemeral systems and not long lasting as previously thought available chronologies suggest that there were large lakes in the western taklamakan desert and the chadamu basin during mis marine isotope stage 3 at 30 ka probably related to a period of strong influence of northern hemispheric westerly winds channels and elevation models revealed by srtm data and remains of lacustrine sediments also indicate that there was a large lake in the hunshandake sandy lands in the eastern portion of the desert belt during the quaternary there is significant evidence that during the middle holocene strong summer monsoons led to a relatively large increase in moisture availability in the entire desert belt of northern china lacustrine records from the badain jaran desert in western inner mongolia suggest that it was generally dry before 10 cal ka becoming wetter from 10 to 4 cal ka and dry again afterwards study of palaeosols widely occurring in dune stratigraphy in the eastern portion of the desert belt suggests that there was a period of wet and warm climate in this region during the mid holocene optimum at a minimum between 6 ka and 4 ka but possibly lasting longer recent observations dealing with the generation and transport of dust from central asia indicate that the causal relationship between sand seas and loess sequences is not as close as previously assumed these results suggest that there is an urgent need to examine whether the frequency and amplitude of climatic variation in chinese deserts are somehow similar to that having occurred in the sahara desert of north africa deserts in northern china were also important focal regions for neolithic cultures during intervals when environmental conditions supported a denser vegetative cover there is evidence that some areas of woody vegetation to the west of badain jaran desert were deforested by humans by ca 4000 yr b p although it is still debatable whether humans have had a significant impact in other areas at that time opinions on the severity of desertification vary and are sometimes contradictory due to the lack of long term field based investigations

holocene environmental and climatic changes inferred from wulungu lake in northern xinjiang china abstract sedimentological geochemical and palynological data from wulungu lake in northern xinjiang china are used to reconstruct environmental and climate changes since 9550 cal yr bp high abundance of sparganium and poaceae low md median diameter and 13 c organic values indicate aridity between 9550 and 6730 cal yr bp high md and 13 c organic values and the prevalence of desert steppe and steppe vegetation between 4200 and 560 cal yr bp indicate that effective moisture increased after 6730 cal yr bp peaking at 4200 and 560 cal yr bp low md values a negative excursion of 13 c org and the transition from steppe to desert vegetation since 560 cal yr bp reflect a decrease in effective moisture during the latest holocene late holocene human activities were indicated by sharp increase in the abundance of pediastrum then variations in carbonate contents indicate that temperature was generally high between 9550 and 7740 cal yr bp low between 7740 and 6730 cal yr bp intermediate between 6730 and 560 cal yr bp and low during the last 560 yr regional comparison indicates that the asian monsoon did not extend to wulungu lake and westerlies were the main factor in determining the moisture availability during the holocene

provenance of eolian sands in the ulan buh desert northwestern china revealed by heavy mineral assemblages abstract accurate identification of the provenance of eolian sand in deserts is essential to study sedimentation processes in the earth system exposed bedrock surrounding the desert has been regarded as the main source of eolian sand in some deserts of the world however few studies have focused on whether paleolacustrine deposits and bedrock outcrops in desert hinterlands are the main sources of eolian sand in this study we selected the ulan buh desert in northwestern china as the study area and a total of 99 samples were collected throughout the desert and nearby regions to study the provenance of the current eolian sand based on their heavy mineral assemblages and contents the results showed similar heavy mineral assemblages among the eolian sand the bedrock to the northwest of the desert and the paleolacustrine deposits and exposed bedrock in the desert hinterlands suggesting multiple provenance for the eolian sand in the ulan buh desert the sources of the eolian sand in the ulan buh desert include bedrock to the northwest gobi to the west and paleolacustrine deposits and exposed bedrock in the desert hinterlands helan mountains bedrock and yellow river fluvial deposits near the desert contribute little to the eolian sand moreover the paleolacustrine deposits and exposed bedrock in the desert hinterlands should not be neglected as the potential provenance of eolian sand in other studies this study enhances understanding the provenance of eolian sand in the deserts of northern china

stress magnitudes in the basel enhanced geothermal system abstract this paper presents the results of an evaluation of stress magnitudes in the granitic egs reservoir in basel switzerland the profile of minimum principal horizontal stress shmin is constrained by hydraulic tests but the magnitude of the maximum horizontal principal stress shmax is uncertain here we derive estimates for shmax by analysing breakout width data from an acoustic televiewer logs run in the granitic basement section of the bs 1 borehole some 81 of the borehole in the granite is affected by breakouts the approach employed to derive shmax magnitude from the estimated breakout widths is taking into account all stress components at the borehole wall including the remnant thermal stress arising from the cooling of the borehole wall by the drilling in bs 1 breakouts width tends to decrease with depth assuming there is no significant systematic change in the strength characteristics of the rock along the length of the hole for which there is no evidence the large scale trend has the consequence of implying a small gradient of the shmax profile a low shmin gradient was also implied by a stress analysis that additionally considered the occasionally coincident presence of drilling induced tension fractures the absolute values of shmax depend upon the failure criterion used criteria that consider the strengthening effect of the intermediate stress mogi coulomb and hoek brown 3d yield profiles that violate frictional limits on the strength of the crust above 4 km whereas the profiles of the mohr coulomb and rankine criteria do not the mohr coulomb criteria profiles indicate a trend in shmax from favoring strike slip faulting above 4200 m to strike slip normal faulting below this is consistent with focal mechanisms recorded during the reservoir stimulation which show a mix of strike slip and normal faulting throughout the depth range considered

holocene moisture evolution in arid central asia and its out of phase relationship with asian monsoon history we synthesize palaeoclimate records from the mid latitude arid asian region dominated today by the westerlies arid central asia aca to evaluate spatial and temporal patterns of moisture changes during the holocene sediment records from i i takes with reliable chronologies and robust proxies were selected to reconstruct moisture histories based on a five class ordinal wetness index with assigned scores from the driest to wettest periods at individual sites for 200 year time slices the proxies used in these records include pollen and diatom assemblages sediment lithology lake levels and geochemistry mainly isotope data the results of our synthesis show that aca as a whole experienced synchronous and coherent moisture changes during the holocene namely a dry early holocene a wetter less dry early to mid holocene and a moderately wet late holocene during the early holocene most of the lakes experienced very low water levels and even dried out before ca 8 ka 1 ka 1000cal a bp hence the effective moisture history in aca is out of phase with that in monsoonal asia as documented by numerous palaeoclimate records in monsoonal asia a strong summer monsoon and humid climate characterized the early holocene and a weakened summer monsoon and drier climate prevailed during the late holocene which were mainly controlled by changes in low latitude summer insolation in contrast we propose that the pattern of holocene effective moisture evolution in the westerly dominated aca was mainly determined by north atlantic sea surface temperatures ssts and high latitude air temperatures that affect the availability amount and transport of water vapor also topography of the tibetan plateau and adjacent asian highlands could have contributed to the intensification of dry climate in aca during the early holocene as a result of strengthening the subsidence of dry air masses associated with stronger uplift motion on the plateau by intense heating under a stronger summer insolation summer insolation might have played a key role in directly controlling moisture conditions in aca but only after the northern hemisphere ice sheets had disappeared in the mid and late holocene c 2007 elsevier ltd all rights reserved

determination of turbidity current erosional characteristics from reworked coccolith assemblages canary basin north east atlantic turbidites contain mixtures of sediments of various ages these sediments can include both material that was eroded to form the initial turbidity current plus additions derived from erosion of the sea floor during transport it has been possible to interpret the age range of sediments incorporated into individual turbidites from the madeira abyssal plain by examining the proportions of microfossil coccolith species that they contain the pelagic record of coccoliths is well known for the quaternary period and shows a succession of dominant species or acmes each lasting a few tens of thousand years hence erosion of sediment representing more than a few tens of thousand years will produce coccolith mixtures not seen in the pelagic record but dependent upon the age range of the sediments that were eroded this age range can be estimated by comparison with synthetic ratios of coccolith species created by combining ratios of species from successively older layers in the pelagic record these can then be compared with the ratios found in individual turbidites until a match is found the results show age ranges of 54 500 kyr for the sediment mixture in seven turbidites from the madeira abyssal plain since the volumes of these turbidites are also known and accumulation rates in their source areas can be estimated it is possible to determine both the thickness and the area of the eroded sediment mass that generated the turbidity current minimum depths of erosion on the north west african continental margin vary from 8 to 50 m and minimum areas eroded from 1600 to 5800 km2 none of the turbidites examined contains a significant excess of surface sediment suggesting that once formed the turbidity currents that transported them were virtually non erosional and that they travelled several hundred kilometres in this state

bottom current pathways in the argentine basin revealed by mean silt particle size regional circulation patterns in the deep sea are very difficult to determine because of time constraints on the acquisition of large physical oceanographic data sets from abyssal depths in addition the large number of long term 1 yr current meter arrays needed to delineate bottom current pathways are extremely costly an alternative method for inferring benthic flow patterns described here is to map the mean size of the silt fraction of sediment on the sea floor because of the availability of a large number of core samples in the argentine basin the particle size approach provides a useful method for determining bottom current pathways in that deep basin

determination of sediment provenance at drift sites using hydrogen isotopes and unsaturation ratios in alkenones the large 20 hydrogen isotopic gradient in surface waters of the northwest atlantic ocean is exploited to track changes in the source of alkenones to the bermuda rise sediment drift cultures of the predominant alkenone producing coccolithophorid e huxleyi were grown in deuterium enriched seawater and shown to possess alkenones with a d h ratio that closely tracked the water d h ratio r 2 0 999 n 5 isotopic enrichments with a fractionation factor between 0 732 and 0 775 a hydrogen isotopic depletion of 193 3 n 9 was measured in alkenones from suspended particles relative to seawater in the subpolar and subtropical northwest atlantic ocean this value was used to calculate the water d values in which alkenones from bermuda rise sediment were synthesized and by extension the water mass in which they were produced applying this technique we find that 60 to 100 of the alkenones in late holocene bermuda rise sediment were produced in deuterium depleted subpolar water to the northwest of the drift to reconcile values of the alkenone unsaturation ratio u k 37 a widely used proxy for sea surface temperature with the d values of alkenones in late holocene sediments from the bermuda rise at least three sources of sediment must be invoked a cold very isotopically depleted source almost certain to be the scotian margin a warm moderately isotopically depleted source likely to be the northwestern edge of the subtropical gyre and a cold isotopically enriched source which we hypothesize to be the subpolar waters overlying the main branch of north atlantic deep water flowing southwest from the nordic seas copyright 2005 elsevier ltd paleoclimate records with sufficient length and temporal resolution to study the occurrence and causal mechanisms of abrupt climate change are exceedingly rare rapidly deposited ocean sediments provide the best archive for studying these events through geologic time but such sites in the open ocean are limited to sediment drift deposits such as the bermuda rise in the northwest atlantic using multiple climate proxies in a single core is becoming more common in high resolution pa leoclimate investigations but a major potential concern for this approach arises from the possibility that the fine fraction of sediment e g 63 m and the climate proxies within it may represent conditions far from the deposition site here we propose and test the hypothesis that hydrogen isotope ratios of alkenones a class of lipids from phytoplankton may provide insight into the source of fine grained sediment because of their restricted sources broad geographic distri bution and excellent preservation properties alkenones are of particular interest in the emerging field of compound specific hydrogen isotopic analysis the sedimentary abundances ex tents of unsaturations and isotopic compositions of alkenones provide quantitative and near continuous records we isolated alkenones from cultured unicellular algae haptophyte emil iania huxleyi surface ocean particulate material and open ocean sediments to determine the extent and variability of hydrogen isotopic fractionation in the di tri and tetraunsat urated c37 compounds we then compared the d values of the alkenones in surface sediments between the bermuda rise and the scotian margin above which a large 20 d gradient exists we determined the fractionation between alkenones from suspended particulate samples and the water in which the phytoplanton lived and examined the variability of alkenone d values during the medieval warm period little ice age climate transition cf keigwin 1996 at the bermuda rise

subtropical north atlantic temperatures 60 000 to 30 000 years ago a reconstruction of sea surface temperature based on alkenone unsaturation ratios in sediments of the bermuda rise provides a detailed record of subtropical climate from 60 000 to 30 000 years ago northern sargasso sea temperatures changed repeatedly by 2 to 5 c covarying with high latitude temperatures that were previously inferred from greenland ice cores the largest temperature increases were comparable in magnitude to the full glacial holocene warming at the site abrupt cold reversals of 3 to 5 c lasting less than 250 years occurred during the onset of two such events greenland interstadials 8 and 12 suggesting that the largest most rapid warmings were especially unstable

millennial scale environmental changes in the asian monsoon margin during the holocene implicated by the lake evolution of huahai lake in the hexi corridor of northwest china the pattern of holocene environmental changes in the asian monsoon margin on a millennial timescale remains controversial based on lithological characteristics and sedimentological proxies we reconstructed holocene effective humidity changes and the lake evolution of huahai lake in the marginal area of the asian monsoon in the hexi corridor of nw china our results show that alluvial and aeolian deposition before 10 4 cal ka bp indicate an arid environment that lacustrine deposition from 10 4 to 8 8 cal ka bp indicates a transition from an arid to a humid environment and that lacustrine deposition from 8 8 to 5 5 cal ka bp occurred during the most humid conditions indicated by proxy records grain size carbonate toc and c n after 5 5 cal ka bp a depositional hiatus implicates an arid environment in the late holocene holocene environmental changes on millennial timescales in huahai lake imply that climate was arid to humid in the early holocene most humid in the mid holocene and arid in the late holocene these moisture changes were influenced by the asian monsoon particularly the transportation of water vapor by the indian monsoon in addition these moisture changes could have been affected by westerly winds that could have contributed to the water vapor supply to this region during the mid holocene the most humid conditions that occurred in the study area during the mid holocene may have been caused by strong westerlies and low levels of evaporation

a holocene climatic record from arid northwestern china abstract the history of climatic changes during the interval 8500 3000 cal yr b p has been reconstructed from stratigraphical and chronological studies and the results of total organic carbon toc total inorganic carbon tic element composition pollen and stable isotope analyses of a section along the hongshui river in the southern tengger desert nw china the record suggests that from 8450 bottom of the studied section to 7500 yr b p the climate was characterized by instability from 7500 to 5070 yr b p the climatic conditions improved and can be divided into two parts a warm humid spell between 7290 and 6380 yr b p during which the average temperature was 3 4 c higher than that of today and a warm dry spell lasting from 5950 to 5720 yr b p the climate deteriorated between 6380 and 5950 yr b p from 5720 to 5070 yr b p the temperature decreased but humidity increased an abrupt temperature drop occurred between 5340 and 5290 yr b p that indicated the decline of the warmer and humid mid holocene climate from 5070 yr b p onward the climate oscillated significantly and there were three large temperature decreases coinciding with high mountain glacier advances between 5070 4670 yr b p 4300 3740 yr b p and 3410 3230 yr b p top of the section respectively the climatic fluctuations recorded in the southern tengger desert appear in phase with climatic changes recognized in the tibetan plateau suggesting that the period between 7290 and 6380 yr b p was the most warm humid spell one extremely dry event occurred at ca 3000 yr b p and subsequently the fluvial lacustrine depositional process terminated and wind action prevailed in the area both of these features can be attributed to the rapid strengthening and weakening of the summer monsoon circulation which are closely connected with global changes

indication of millennial scale moisture changes by the temporal distribution of holocene calcareous root tubes in the deserts of the alashan plateau northwest china abstract calcareous root tubes or rhizoliths have a strong potential for paleoenvironmental studies especially in reconstructing paleoenvironmental conditions and paleovegetation previous studies suggested that the effectivity of the moisture level affects the formation of calcareous root tubes in the deserts of the alashan plateau northwest china however it remains unclear whether the temporal distribution of calcareous root tubes can be used to reconstruct paleo effective moisture in this area in this study based on conventional 14c dating results of 34 holocene calcareous root tube samples collected from the badain jaran desert the tengger desert and the ulan buh desert in the alashan plateau of northwestern china millennial scale changes in paleo effective moisture during the holocene in this area were reconstructed the frequency of the 14c dating results demonstrates that 62 of the holocene samples were dated to 7 5 cal kyr bp and 38 of the holocene samples were dated to 4 2 cal kyr bp indicating an arid period during the early holocene before 8 0 cal kyr bp a humid period during the mid holocene 8 0 5 0 cal kyr bp and a humid to arid period during the late holocene after 5 0 cal kyr bp the reconstruction results were consistent with other previous reconstruction results from lake sediments and aeolian sand lacustrine sequences which indicated that temporal distribution of calcareous root tubes can reflect millennial scale changes in paleo effective moisture in this area however a single sample could indicate local environmental changes that may differ from the overall desert environmental changes hence the relatively humid environmental record obtained from the presence of calcareous root tubes is a local signal or a regional signal that should be noted

geological effects of the gulf stream system on the northern bermuda rise abstract the gulf stream system contains a clockwise rotating set of bottom currents which influence the sea bed in the northern north american basin it is possible to interpret the present day and historical record of current activity in this basin in terms of the deep flow of the gulf stream this interpretation provides a much more satisfactory and consistent explanation of the geologic record than previous interpretations based strictly on the influence of the classic abyssal circulation the present day circulation of the gulf stream actively resuspends large quantities of sediment on and near the northern bermuda rise and it is suggested that this resuspension may be due to the eddy field which is embedded in the westward flowing return flow during the late cenozoic the gulf stream system was responsible for depositing and shaping the major acoustic sedimentological units on the relatively smooth surface of the horizon a complex fine grained mont morillionite rich sediments derived from the chemically weathered saprolites of the hudson and st lawrence drainage basins were injected into the deep ocean basins by turbidity currents during the late paleogene and the neogene fine grained turbidites from the st lawrence spread southward down the southeastern sohm abyssal plain across the eastward flowing gulf stream and its westward flowing return flows portions of these fine grained sediments were entrained by the main and return flows and deposited downstream as acoustically non laminated accumulations on the corner and bermuda rises respectively the hudson river input was injected into the deep basin through the hudson canyon system the interaction of these fine grained turbidites with the northward flowing deep flow of the gulf stream system led to the formation of the gulf stream outer ridge here defined for the first time during the late neogene or early pleistocene the gulf stream outer ridge was partially eroded by the gulf stream system and portions subsequently covered by coarse grained pleistocene turbidites the coarse grained illite rich turbidites that flowed across the southeastern sohm abyssal plain also crossed the main and return flows of the gulf stream system the finer portions of these sediments were entrained and deposited as pleistocene acoustically laminated sediments on the plateaus of the bermuda and corner rises

muddled or mixed inferring palaeoclimate from size distributions of deep sea clastics abstract one of the outstanding problems of palaeoclimate reconstruction from physico chemical properties of terrigenous deep sea sediments stems from the fact that most basin fills are mixtures of sediment populations derived from different sources and transported to the site of deposition by different mechanisms conventional approaches to palaeoclimate reconstruction from deep sea sediments do not distinguish between provenance and dispersal related variations and therefore often fail to recognise the true significance of variations in sediment properties we formulate a set of requirements that each proposed palaeo environmental indicator should fulfil and focus on the intrinsic coupling between grain size and chemical composition a critical review of past achievements in grain size analysis serves to introduce a conceptual model of spatio temporal grain size variation based on dynamic populations each dynamic population results from a characteristic combination of production and transport mechanisms that corresponds to a distinct subpopulation in the data analysed the mathematical statistical representation of the conceptual model can be obtained by means of the end member modelling algorithm emma applications of the model to several ocean basins are discussed as well as methods to examine the validity of grain size based palaeoclimate reconstructions palaeoclimate reconstructions of a high and low latitude basin illustrate the common degree of complexity of deep sea grain size records

natural fractures in carbonate rich tight oil reservoirs from the permian lucaogou formation southern junggar basin nw china insights from fluid inclusion microthermometry and isotopic geochemistry abstract natural fractures within tight reservoirs form preferred pathways for hydrocarbon charge and provide space for hydrocarbon preservation however the mechanism that controls the formation of natural fractures in tight reservoirs remains controversial this study investigates natural fractures within carbonate rich tight oil reservoirs from the permian lucaogou formation in the jimsar sag southern junggar basin drill core and image log observations show that fractures in the lucaogou formation can be categorized into two types bedding parallel fractures and inclined fractures the carbon and oxygen isotopic compositions of calcite cements in the bedding parallel fractures range from 0 6 to 6 0 13cpdb and from 15 5 to 8 9 18opdb respectively which are similar to those of the organic rich host rock this suggests that the bedding parallel fractures likely formed in a closed fluid system fluid inclusion analyses of the aqueous inclusions in calcite cements from the bedding parallel fractures record homogenization temperatures of 91 5 c 130 4 c indicating that they formed at the cretaceous to cenozoic during when the lucaogou formation reached peak oil generation stage therefore the bedding parallel fractures were most likely generated by hydrocarbon generation overpressure the presence of hydrocarbon inclusions in bedding parallel fracture cements supports natural fracturing by high pore fluid pressure the 13cpdb and 18opdb of calcite cements within the inclined fractures vary from 3 6 to 9 6 and from 11 0 to 2 9 respectively which are close to those of the carbonate rich parent rock this also supports a closed fluid system scenario the relatively lower fluid inclusion trapping temperatures 70 5 c 109 7 c suggest that they were likely generated by decrease of confining stress during uplift processes therefore both an increase in pore fluid pressure and a decrease in confining stress contribute to the formation of natural fractures in the lucaogou formation tight oil reservoirs

spatial and temporal offsets between proxy records in a sediment drift chronologies for late quaternary marine sediment records are usually based on radiocarbon ages of planktonic foraminifera signals carried by other sedimentary components measured in parallel can provide complementary paleoclimate information a key premise is that microfossils and other indicators within a given sediment horizon are of equal age we show here that haptophyte derived alkenones isolated from bermuda rise drift sediments are up to 7000 years older than coexisting planktonic foraminifera this temporal offset which is apparently due to lateral transport of alkenones on fine grained particles from the nova scotian margin markedly influences molecular estimates of sea surface temperatures more broadly the observation raises questions about both the temporal and the geographic fidelity of paleoenvironmental records encoded by readily transported components of sediments

an end member algorithm for deciphering modern detrital processes from lake sediments of lake donggi cona ne tibetan plateau china abstract deciphering significant sedimentological processes from a set of sediment samples is an important step in reconstructing environmental changes one approach going beyond classical methods is the unmixing of grain size distributions this paper presents a flexible end member modelling algorithm that is based on eigenspace analysis and considers inherent uncertainties it has been applied to the detrital grain size components of lacustrine surface sediment samples of lake donggi cona qinghai province china it allows up to five grain size end members to be characterised and quantified in an optimal model an end member with a major mode in the clay domain accounts for 34 of variance within the grain size data set it may represent sedimentation of suspension load from linear and laminar runoff during heavy precipitation events in summer three end members in the fine sand to medium silt domains make up 60 of lacustrine sedimentation they may represent local to remote aeolian processes that peak in wintertime a multimodal end member explaining the remaining 6 of variance may represent further fluvial and littoral dynamics or random fluctuations and measurement errors several model runs of different scaling and numbers of end members provided a suitable way to determine uncertainties inherent to the model a comparison of 12 different model runs and their respective uncertainties yielded a distinct model of robust end members the clay and medium silt end members are robust features of detrital sedimentation within lake donggi cona they alone explain 54 4 of total variance in the data however no spatial pattern or relation to water depth is found for any of the grain size end members thus when past detrital sedimentation at lake donggi cona is reconstructed a special focus should be on the robust features attributed to aeolian and suspension related sedimentation processes as well as on effective sediment mixing processes impeding a distinct correlation between grain size and spatial attributes further applications of the end member modelling algorithm to other depositional environments are encouraged to demonstrate its universal applicability

stress field interactions between overlapping shield volcanoes borehole breakout evidence from the island of hawai i usa acknowledgments this pta2 borehole investigation was funded by the international continental scientific drilling program icdp and by vmapp volcanic margin petroleum prospectivity project vbpr dougalearth tgs in collaboration with the humu ula groundwater research project d a j and s p are partly funded through a norwegian research council centres of excellence project project number 223272 ceed we thank marco groh for the logging operations we thank two anonymous reviewers for the comments and suggestions we are particularly grateful to the associate editor mike poland for his valuable comments and his critical review that greatly improved the manuscript

a 2000 year dust storm record from lake sugan in the dust source area of arid china 1 arid northwestern china is considered to be a major source of atmospheric dust supply to the northern hemisphere however dust storm evolution and dust emission processes in the past remain unclear due to the scarcity of geologic archives in this region hydrologically closed lakes in dust source areas act as a trap providing the opportunity to trace the history of dust emission or eolian activity here we present the results of dust storm proxies and a dust storm history from lake sugan in the qaidam basin a dust source area on the northern qinghai tibetan plateau grain size analyses of the materials deposited during modern dust storms and of the lake surface sediments demonstrate that the coarse component of the lake sediments was transported primarily by ambient winds when dust storms occurred in combination with a sediment chronology generated by counting annual laminations a 2000 year dust storm history was reconstructed on the basis of changes in the coarse component and magnetic susceptibility of the lake sediments frequent and or intensive dust storms occurred during the intervals ad 300 500 ad 1180 1240 and ad 1500 1700 the occurrence of dust storms largely coincided with the strengthening of the siberian high with colder air masses from high latitudes such as during the little ice age frequently encroaching into the dust source areas in northwestern china our results suggest that wind strength plays an important role in dust emissions in arid source areas however dust storms in the late 20th century are most likely associated with disturbance of the ground surface caused by petroleum exploitation in the qaidam basin

grain size distribution function of polymodal sediments in hydraulic and aeolian environments and numerical partitioning of the sedimentary components most continental sediments are polymodal composed of overlapping components of which the grain size generally obeys some type of natural distribution the grain size components and their function types can be determined from frequency and cumulative curve plots in order to define the function formula of the grain size distribution the function parameters can be estimated by fitting a defined function formula to the measured grain size data of the sample which simultaneously achieves numerical partitioning of the sedimentary components genetic analysis of grain size components of hydraulic and aeolian sediments demonstrates the following environmental implications fluvial sediment is composed of isolated saltation and suspension components the sediments in closed lake basins are dominated by a suspension silt clay component with a small proportion of saltation sand the fine sand component makes up the majority of desert sand overlapping with a small proportion of fine dust aeolian loess is composed of two overlapping components a short suspension time silt component and a long suspension time fine component aeolian material in the north pacific deep sea sediments is dominated by long suspension time fine dust the fine component in aeolian sediments shows a consistent grain size distribution and genetic connection from the desert sand loess of northern china to the north pacific ocean which is mainly transported by westerly winds and is dispersed in the atmosphere forming a background dust c 2002 elsevier science b v all rights reserved

radiocarbon and 230th data reveal rapid redistribution and temporal changes in sediment focussing at a north atlantic drift abstract in locations of rapid sediment accumulation receiving substantial amounts of laterally transported material the timescales of transport and accurate quantification of the transported material are at the focus of intense research here we present radiocarbon data obtained on co occurring planktic foraminifera marine haptophyte biomarkers alkenones and total organic carbon toc coupled with excess thorium 230 230thxs measurements on four sediment cores retrieved in 1649 2879 m water depth from two such high accumulation drift deposits in the northeast atlantic bjorn and gardar drifts while 230thxs inventories imply strong sediment focussing no age offsets are observed between planktic foraminifera and alkenones suggesting that redistribution of sediments is rapid and occurs soon after formation of marine organic matter or that transported material contains negligible amounts of alkenones an isotopic mass balance calculation based on radiocarbon concentrations of co occurring sediment components leads us to estimate that transported sediment components contain up to 12 of fossil organic matter that is free of or very poor in alkenones but nevertheless appears to consist of a mixture of fresh and eroded fossil material considering all available constraints to characterize transported material our results show that although focussing factors calculated from bulk sediment 230thxs inventories may allow useful approximations of bulk redeposition they do not provide a unique estimate of the amount of each laterally transported sediment component furthermore our findings provide evidence that the occurrence of lateral sediment redistribution alone does not always hinder the use of multiple proxies but that individual sediment fractions are affected to variable extents by sediment focussing