organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

coherence between solar activity and the east asian winter monsoon variability in the past 8000 years from yangtze river derived mud in the east china sea ams 14 c dating and grain size analysis for core pc 6 located in the middle of a mud area on the inner shelf of the east china sea ecs were used to rebuild the holocene history of the east asian winter monsoon eawm the 7 5 m core recorded the history of environmental changes during the postglacial transgression the core s mud section the upper 450 cm has been formed mainly by suspended sediment delivered from the yangtze river mouth by the ecs winter coastal current ecswcc since 7 6 kyr bp using a mathematical method called grain size vs standard deviatiow we can divide the core pc 6 s grain size distribution into two populations at about 28 mu m the fine population 28 mu m is considered to be transported by the ecswcc as suspended loads content of the fine population changes little and represents a stable sedimentary environment in accord with the present situation thus variation of mean grain size from the fine population would reflect the strength of ecswcc which is mainly controlled by the east asian winter monsoon abrupt increasing mean grain size in the mud section is inferred to be transported by sudden strengthened ecswcc which was caused by the strengthened eawm thus the high resolution mean grain size variation might serve as a proxy for reconstruction of the eawm a good correlation between sunspot change and the mean grain size of suspended fine population suggests that one of the primary controls on centennial to decadal scale changes of the eawm in the past 8 ka is the variations of sun irradiance i e the eawm will increase in intensity when the number of sunspots decreases spectral analyses of the mean grain size time series of core pc 6 show statistically significant periodicities centering on 2463 1368 128 106 100 88 91 7678 and 70 72 years the eawm and the east asian summer monsoon easm agree with each other well on these cycles and the east asian monsoon eam and the indian monsoon also share in concurrent cycles in holocene which are in accord with the changes of the sun irradiance c 2005 elsevier b v all rights reserved

the mediaeval warm period drought recorded in lake huguangyan tropical south china the geochemistry of dated sediment cores from lake huguangyan 21o9 n 110o17 e tropical south china reveals distinct stratigraphical patterns in total organic and inorganic carbon toc tic biogenic silica bs and total nitrogen tn over the past 1400 years in this hydrologically closed lake tic variations may reeect changes in the precipitation evaporation ratio which controls the evaporative enrichment of carbonate toc bs and tn in the sediment are proxy indicators of lake productivity and nutrient input which we believe are linked to local precipitation high tic content correlates with low concentrations of toc bs and tn and indicates two drought episodes dated to ad 670 760 and ad 880 1260 in the sediments of lake huguan gyan local historical chronicles support these data suggesting that the climate of tropical south china was dry during the mediaeval warm period mwp and wet during the little ice age lia the detected mwp drought is temporally correlated with evidence for lower precipitation on the guliya china and quelccaya peru ice caps and with increased salinity in moon lake us great plains

could bacteria have formed the precambrian banded iron formations banded iron formations bifs are prominent sedimentary deposits of the precambrian but despite a century of endeavor the mechanisms of their deposition are still unresolved interactions between microorganisms and dissolved ferrous iron in the ancient oceans offer one plausible means of mineral precipitation in which bacteria directly generate ferric iron either by chemolithoautotrophic iron oxidation or by photoferrotrophy on the basis of chemical analyses from bif units of the 2 5 ga hamersley group western australia we show here that even during periods of maximum iron precipitation most if not all of the iron in bifs could be precipitated by iron oxidizing bacteria in cell densities considerably less than those found in modern fe rich aqueous environments those ancient microorganisms would also have been easily supported by the concentrations of nutrients p and trace metals v mn co zn and mo found within the same iron rich bands these calculations highlight the potential importance of early microbial activity on ancient metal cycling

holocene climate variability as reflected by mid european lake level fluctuations and its probable impact on prehistoric human settlements abstract a data set of 180 radiocarbon tree ring and archaeological dates obtained from sediment sequences of 26 lakes in the jura mountains the northern french pre alps and the swiss plateau was used to construct a holocene mid european lake level record the dates do not indicate a random distribution over the holocene but form clusters suggesting an alternation of lower and higher climatically driven lake level phases they provide evidence of a rather unstable holocene climate punctuated by 15 phases of higher lake level 11 250 11 050 10 300 10 000 9550 9150 8300 8050 7550 7250 6350 5900 5650 5200 4850 4800 4150 3950 3500 3100 2750 2350 1800 1700 1300 1100 750 650 cal bp and after 1394 ad a comparison of this mid european lake level record with the gisp2 polar circulation index pci record the north atlantic ice rafting debris ird events and the 14 c record suggests teleconnections in a complex cryosphere ocean atmosphere system correlations between the gisp2 pci the mid european lake level the north atlantic ird and the residual 14 c records suggest that changes in the solar activity played a major role in holocene climate oscillations over the north atlantic area

the little ice age recorded by sediment chemistry in lake erhai southwest china on the basis of concentrations of 21 major and minor elements in a well dated sediment core from the deepwater part of lake erhai principal component analysis pca reveals three main factors cont

variation of rb sr ratios in the loess paleosol sequences of central china during the last 130 000 years and their implications for monsoon paleoclimatology abstract rb sr and magnetic susceptibility have been measured in the last interglacial glacial loess profiles at luochuan and huanxian central china a high degree of similarity between the parameters in both profiles suggests that variations of rb sr ratios in the sequence can be regarded as an indicator of east asian summer monsoon strength matching the rb sr record with the specmap 18o curve suggests that the rb sr ratio responds sensitively to changes of the east asian monsoon induced by global ice volume variation

hydrological changes in shuangchi lake hainan island tropical china during the little ice age abstract hydrological changes in east asia during the last millennium have been addressed by numerous earlier studies but spatial characteristics and dynamics in precipitation variations during the little ice age lia remain unclear perhaps especially due to the sparse coverage of high resolution hydrological records from tropical and sub tropical regions in east asia in this study a sediment core was obtained from shuangchi lake in northern hainan island tropical china of which geochemical proxies including the ratios of rb sr rb k zr rb and si ti were analyzed using an x ray fluorescence xrf core scanner meanwhile the grain size distribution of sediments was also determined the results show that the rb sr and rb k ratios decreased significantly during the lia whilst the zr rb and si ti ratios increased along with higher median grain size the changes of these proxies likely suggest that precipitation was enhanced during the lia in this region and this was consistent with other hydrological records from tropical southern china the synthesis of hydrological records from east asia and the tropical pacific suggest that the co existence of a contracted intertropical convergence zone itcz and strengthened pacific walker circulation pwc could contribute synchronously to the increased precipitation in the tropical region of southern china during the lia

the huguang maar lake a high resolution record of palaeoenvironmental and palaeoclimatic changes over the last 78 000 years from south china abstract a series of seven piston cores from the huguang maar lake situated near the south china sea coastline provides insight into regional palaeoenvironmental and palaeoclimatic changes in southern china over the last 78 000 years the data set comprises a high resolution record of magnetic susceptibility dry density and water content total organic carbon and inorganic carbon total nitrogen biogenic silica bsio2 and palynological results the time scale was developed by ams 14c dating of 17 terrestrial plant macro fossils during the last glacial the huguang record is characterised by an alternation of more temperate and humid periods from 78 to 58 and 48 to 40 5 ka bp and periods with predominance of grassland vegetation and possibly lowered lake level from 58 to 48 and ca 40 5 to 15 ka bp the huguang data have been compared to regional marine and terrestrial records in order to discuss variability of the south east asian monsoon system for most of the last glacial period the huguang proxies do not exhibit marked millennial scale variability as known from some long se asian and many north atlantic records this picture changes at about 15 cal ka bp when the huguang and greenland records appear to correlate well a short climatic reversal which is assumed to reflect a younger dryas type event is well recorded in the huguang record during the holocene the huguang multi proxy data show a much higher variability than during the last glacial stage probably reflecting at least for the early mid holocene fluctuations in monsoon activity however the last 4000 years of the sediment record are clearly influenced by enhanced human activity and thus difficult to interpret in terms of palaeoclimate change

dynamics of the intertropical convergence zone over the western pacific during the little ice age precipitation patterns in the western pacific changed at the onset of the little ice age a synthesis of precipitation reconstructions suggests that this change resulted from a contraction of the intertropical convergence zone

the wet little ice age recorded by sediments in huguangyan lake tropical south china abstract although temperature decreased in a similar trend in many regions around the word during the little ice age lia the reconstructed humidity is remarkably different from region to region the precipitation history during the lia is poorly understood as compared to the temperature history in tropical south china in this study a sediment core with a length of 117 5 cm was recovered in the central part of huguangyan lake in tropical south china total organic carbon toc total nitrogen tn inorganic carbon ic and non residual strontium sr were analyzed at approximately 1 cm intervals to study the regional precipitation changes during the lia generally sr containing minerals are sensitive to chemical weathering which is dominated by the precipitation in tropical south china thus the non residual sr in huguangyan sediments can be used as an indicator of precipitation changes which is also verified by the downcore variations of toc tn and ic in huguangyan lake the non residual sr correlated positively with toc and tn but negatively with ic in the sediment profile toc tn ic and the non residual sr jointly demonstrated a wet period from ad 1500 to 1750 which corresponds to the lia coincidently both the total solar irradiance tsi and northern hemisphere temperature have the lowest values between ad 1500 and 1750 over the past millennium therefore the wet lia in tropical south china was most likely caused by the low solar irradiation during the lia the low solar irradiation likely resulted in the decrease of the northern hemisphere temperature which weakened the intensity of the east asian summer monsoon easm and synchronously moved the north edge of the asian summer monsoon southward leading to an increase in the precipitation in tropical south china

glacial sedimentation in the late precambrian bebedouro formation bahia brazil abstract the possibility that diamictites of the late precambrian bebedouro formation of northern bahia brazil are glacial in origin has been based on the areal extent diversity of the lithology of the stones and the presence of outsize dropstones in rhythmites more detailed studies on the diamictites show that some of the stones are faceted and their shapes are typical of those developed by glacial transport additionally a small abraded pavement is described and garnets found in the matrix of the diamictite have chattermark trails taken in aggregrate these observations suggest a glacial origin for the bebedouro formation in the study area the texture of the diamictites range from stone rich to siltstones containing sporadic stones the stone rich diamictites are commonly found in layers up to a metre in thickness separated by poorly laminated siltstone the formation probably was deposited in a large lake or sea and the layered diamictites are debris flows which were derived from uneven piles of glacial debris deposited on the floor of the lake or sea

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

hydroclimatic changes in china and surroundings during the medieval climate anomaly and little ice age spatial patterns and possible mechanisms abstract investigating hydroclimatic changes during key periods such as the medieval climate anomaly mca 1000 1300 ad and the little ice age lia 1400 1900 ad is of fundamental importance for quantifying the responses of precipitation to greenhouse gas induced warming on regional and global scales this study synthesizes the most up to date and comprehensive proxy moisture precipitation records during the past 1000 years in china and surroundings the proxy data collected include 34 records from arid central asia aca and 37 records from monsoonal asia our results demonstrate a pattern of generally coherent regional moisture variations during the mca and lia in mid latitude asia north of 30 n monsoonal northern china north china and northeast china was generally wetter while aca northwest china and central asia was generally drier during the mca than in the lia a west east mode the boundary between wetter northern china and drier aca was roughly consistent with the modern summer monsoon boundary in monsoonal china to the east of 105 e the northern part was generally wetter while the southern part was generally drier during the mca than in the lia a north south mode with a boundary roughly along the huai river at about 34 n these spatial patterns of moisture precipitation variations are also identified by instrumental data during the past 50 years in order to understand the possible mechanisms related to the moisture variations during the mca and lia we investigate the major sst and atmospheric modes e g the el nino southern oscillation enso the atlantic multidecadal oscillation amo and the north atlantic oscillation nao which affect the moisture precipitation variations in the study region using both the instrumental data and the reconstructed time series it is found that the enso may play an important role in determining hydroclimatic variability over china and surroundings on a multi centennial time scale and that the foregoing spatial patterns could be attributed to the la nina like el nino like condition during the mca lia in addition amo and nao may also have their own contributions

late holocene isotope hydrology of lake qinghai ne tibetan plateau effective moisture variability and atmospheric circulation changes a sub centennial resolution record of lacustrine carbonate oxygen isotopes 18oc from the closed basin lake qinghai on the ne tibetan plateau shows pronounced variability over the past 1500 years changes in 18oc in hydrologically closed lakes are often interpreted in terms of changing effective moisture under this interpretation our record would imply increasing effective moisture during the little ice age lia compared to the medieval warm period mwp however independent evidence from other archives strongly suggests the asian summer monsoon was stronger during the mwp and weakened during the lia controls other than effective moisture the balance of water inputs over evaporative loss must therefore have contributed to the 18oc values we propose the lia signal in lake qinghai resulted from a reduction in evaporation caused by colder air temperatures coupled with a decrease in oxygen isotope composition of input waters as a result of an increase in the relative importance of westerly derived precipitation our results caution against simplistic interpretations of carbonate oxygen isotope records from hydrologically closed lakes and suggest all possible controlling factors must be taken into account in order to avoid misleading palaeoclimatic reconstructions

high resolution geochemical record for the last 1100 yr from lake toson northeastern tibetan plateau and its climatic implications abstract knowledge of the origin of past climatic variations on annual to decadal timescales is important for assessing the likelihood of the occurrence of similar variations in the future here we present a high resolution 82 m element record obtained using synchrotron radiation x ray fluorescence from the sediments of toson lake in the northeastern tibetan plateau the record which spans the last 1100 yr exhibits variability on an annual to decadal scale the results of principal component analysis of the element dataset indicates that the first three principal components reflect variations in detrital inputs via runoff and possibly eolian activity drought conditions and temperature variations respectively spectral analysis of samples scores on these components reveals strong el nino southern oscillation enso like variability at periods of 3 8 years which indicates that the regional climatic variability was effected by enso events over the last 1100 yr on the centennial time scale the element data and toc record suggest a warm and dry climate during the medieval warm period mwp and a cold and wet little ice age lia the early 20th century was a warm interval and drier than the lia but wetter than the mwp

low latitude glaciation in the palaeoproterozoic era one of the most fundamental enigmas of the earth s palaeoclimate concerns the temporal and spatial distributions of precambrian glaciations through four billion years of precambrian history unequivocally glacial deposits have been found only in the palaeoproterozoic and neoproterozoic record nonetheless some of these deposits are closely associated with tropical rather than just polar palaeolatitudinal indicators such as carbonate rocks red beds and evaporites these observations are quantitatively supported by palaeomagnetic results indicating a 5 latitude for neoproterozoic glaciogenic rocks in australia similarly reliable palaeolatitudes for the older palaeoproterozoic glaciogenic rocks have not yet been obtained as such deposits commonly suffer from poor preservation and secondary magnetic overprinting the archaean palaeoproterozoic transvaal supergroup on the kaapvaal craton in south africa is however exceptionally well preserved and is thus amenable to the palaeomagnetic determination of depositional palaeolatitudes within this supergroup the 2 2 billion year old ongeluk lavas are a regionally extensive largely undeformed and unmetamorphosed extrusive volcanic succession which conformably overlies glaciogenic deposits the makganyene diamictite here we report a palaeomagnetic estimate of 11 5 depositional latitude for the lavas and hence for the underlying contemporaneous glacial rocks the palaeoclimate enigma is thus deepened a largely ice free precambrian world was apparently punctuated by two long ice ages both yielding glacial deposits well within tropical latitudes

laminated eocene maar lake sediments from eckfeld eifel region germany and their short term periodicities abstract the eocene age eckfeld eifel maar lake is interesting both because of the excellently preserved fossil remains and also for the laminated sediment sequence deposited under subtropical conditions the latitude however has a higher seasonal insolation difference than comparable recent environments due to the northward shift of climatic zones during the eocene the overall aim of this investigation was to compare sediment types and lake development of a tertiary subtropical maar lake with recent maar lakes to discuss the origin of laminations and search for their possible periodicities the main sediment types which were exposed during recent paleontological excavations are laminated oilshales partly laminated bituminous siltstones and graded beds mostly turbidites which sometimes include laminated clay tops some deeper parts of the profile drilled in 1980 are dominated by diatomaceous laminites the amount of organic carbon around 8 5 is comparable with recent lakes with low sedimentation rates the high c n ratios 25 30 of the eckfeld sediments as well as the fact that the highest corg values are found in the graded beds shows the importance of terrestrial plant debris for these lake sediments lamination of the oil shales was caused by the complex interrelationship of clastic supply mineral and plant detritus autochthonous organic deposition mainly green algae and early diagenetic siderite formation the darker sublaminae represent the coarser clastic organic and inorganic input together with the autochthonous supply from the lake green algae whereas the lighter sublaminae are composed of settled fine grained mostly siliciclastic detritus derived from the probable yearly turnover of the density stratification of the lake the thickness of the fine siliciclastic and organo clastic layers the morphology and palaeogeographical situation of the maar lake and the occurrence of algal layers strongly suggest that the laminated sediments are varves although there is no definitive proof of this thickness variations from ca 700 oil shale laminae were measured and computed time series analysis yielded at least one certain period of 5 5 yr accepting that the laminae are indeed varves the duration of the laminated lake sequence from eckfeld maar as deduced from sedimentation rates of the different sediment types is ca 82 000 yr and thus within the typical life time of other small maar lakes

summer monsoon precipitation variations in central china over the past 750 years derived from a high resolution absolute dated stalagmite abstract a 2 3 year resolution record of stalagmite oxygen isotope variations from the south flank of the qinling mountains central china has revealed the asian summer monsoon asm precipitation variations in the investigated area over the past 750 years the summer monsoon precipitation gradually increased since 1249 ad reaching its highest values in the period 1535 1685 ad and then decreased with substantial decadal to centennial scale fluctuations the monsoon precipitation increased again between 1920 and 1970 ad three intervals of high monsoon precipitation were identified 1535 1685 ad 1755 1835 ad and 1920 1970 ad three intervals of low precipitation were inferred in 1249 1325 ad 1390 1420 ad and 1890 1915 ad the 18 o composition and lithological features of the stalagmite coincidently indicate a wetter climate during the little ice age lia which is also confirmed by climate records from chinese historical documents within this area a comparison with other high resolution speleothem records indicates regional differences in monsoon precipitation variability from the south to the north of central china in the last 750 years on decadal to centennial scale power spectrum analysis of the 18 o record shows significant 117 8 34 6 14 10 3 and 6 year periodicities these periodicities are widely observed in the climate records from asm controlled areas of china and are consistent with the gleissburg periodicity br ckner periodicity sunspot periodicity of solar activity and el nino southern oscillation enso periodicity these correlations suggest that both solar activity and enso periodicity may have had important influences on asm precipitation in china over the past 750 years

delta o 18 sr ca and mg ca records of porites lutea corals from leizhou peninsula northern south china sea and their applicability as paleoclimatic indicators combined seasonal to monthly resolution coral skeletal delta 18 o sr ca and mg ca records are reported for one modem and two late holocene porites lutea corals from a fringing reef at leizhou peninsula the northern coast of the south china sea scs all the profiles for the period 1989 2000 reveal annual cycles well correlated with instrumental sea surface temperatures sst and display broad peaks in summer and narrow troughs in winter reflecting seasonal growth rate variations calibration against instrumental sst yields the following equations delta 18 o 0 174 0 010 xsst degrees c 1 02 0 27 mswd 5 8 sr ca mmol mol 0 0424 0 0031 xsst degrees c 9 836 0 082 mswd 8 6 and mg ca mmol mol 0 110 0 009 xsst degrees c 1 32 0 23 mswd 55 the scatter in the mg ca sst relationship is much larger than analytical uncertainties can account for suggesting the presence of sst unrelated components in the mg ca variation calculated sr ca sst values for two later holocene porites lutea samples u series ages similar to 541 bc and similar to 487 ad respectively from the same reef suggest that sst in the scs at similar to 541 bc was nearly as warm as in the 1990s the warmest decade of the last century but at similar to 487 ad it was significantly cooler this observation is consistent with climatic data reported in chinese historic documents confirming that the sr ca sst relationship is a reliable thermometer removing the sst component in the delta 18 o variation based on calculated sr ca sst values the residual delta 18 o reflects the deviation of the holocene seawater delta 18 o from the modem value which is also a measure of the holocene sea surface salinity sss or the summer monsoon moisture level in mainland china such residual delta 18 o was close to zero at similar to 541 bc and 0 3 parts per thousand at similar to 487 ad suggesting that it was as wet as in the 1990s at similar to 541 bc but significantly drier at similar to 487 ad in mainland china which are also consistent with independent historic records calculated mg ca sst values for the two late holocene corals are significantly lower than the sr ca sst values and are also in conflict with chinese historic records suggesting that coral mg ca is not reliable proxy for sst at comparable sr ca ranges fossil corals always display negative mg ca offsets if compared with the modem coral of the same site we interpret this observation as due to preferential loss of mg during meteoric dissolution of cryptic mg calcite bearing microbialites in the exposed fossil corals microbialites mgo up to 17 sr only 100 300 ppm are ubiquitous during reef building processes and their presence in only a trace amount will have a significant impact on coral mg ca ratios without detectable influence on coral sr ca ratios c 2004 elsevier b v all rights reserved

transamazonian orogeny in the southern sao francisco craton region minas gerais brazil evidence for paleoproterozoic collision and collapse in the quadrilatero ferrifero abstract the paleoproterozoic transamazonian orogeny yielded a series of discrete orogens in brazil the present field study in the quadrilatero ferrifero qf indicates that the southern sao francisco craton region of the brazilian highlands preserves a portion of one of these orogens two sets of transamazonian structures occur in this region the first consists of northwest verging folds and thrusts affecting supracrustal sequences it is suggested that this set formed in a fold thrust belt setting shortly after 2 125 ga during the closure of a passive margin basin that had initiated along the margins of a preexisting continental mass at ca 2 5 ga the second set consists of structures defining the prominent dome and keel architecture of the qf this set a consequence of the emplacement of basement domes against supracrustal rocks at 2 095 ga may reflect the consequences of orogenic collapse narrow conglomerate filled intermontane basins may have formed coevally with dome emplacement formation of an ocean basin east of the present day sao francisco craton eventually occurred in late mesoproterozoic in effect the transamazonian orogen of the qf represents the collision and collapse stages of a paleoproterozoic wilson cycle the contractional phase of the transamazonian orogeny probably represents accretion of an offshore arc to the eastern and southeastern margin of the present day sao francisco craton region the arc and an associated suture may be traced in the brasiliano pan african orogen east of the sao francisco craton northwards into the northeastern lobe of the sao francisco craton clearly initial assembly of crustal blocks to form a larger continent involving south america occurred during the paleoproterozoic 2 1 ga post transamazonian rifting of this continent created the basins which were later inverted during the brasiliano assembly of gondwana

the little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap the analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent annual variations in visible dust layers oxygen isotopes microparticle concentrations conductivity and identification of the historical a d 1600 huaynaputina ash permit accurate dating and time scale verification the fact that the little ice age about a d 1500 to 1900 stands out as a significant climatic event in the oxygen isotope and electrical conductivity records confirms the worldwide character of this event

abnormal rb sr ratio in lacustrine sediments of qaidam basin ne qinghai tibetan plateau a significant role of aeolian dust input abstract the rb sr ratio is an important indicator of weathering intensity in both lacustrine and loess sediments because of the inertness of the rb element and the activity of the sr element during the weathering process generally the environmental interpretation of rb sr ratio proxy in lacustrine sediments is contrary to that in the loess paleosol sequence it shows a negative correlation between the rb sr ratio and chemical weathering intensity in lacustrine sediments but shows a positive pattern in the loess paleosol sequence however in this study we investigated the rb sr ratio of a lacustrine core isl1a from qarhan salt lake qsl in eastern qaidam basin qb and found the rb sr ratio indicated a positive correlation with regional precipitation this pattern is similar to that of the loess paleosol sequence rather than the lacustrine sediments according to grain size statistics and the comparison of rb sr ratio with other proxies halite and calcite contents grain size and f values of grain size discriminant function we preliminarily proposed that the abundant input of aeolian materials transported by the strong northwest wind cause these unexpected rb sr ratio fluctuations in the isl1a core the comparison between background rb and sr elemental data of relevant regions and these of the core indicated the aeolian origin of rb sr ratio in the lacustrine sediments and the rb and sr elemental composition probably represents the geochemical characteristics of the dust source area the sr nd isotopic composition indicates that the erosive paleo lake strata in western qb could be the origin of aeolian materials in lacustrine sediments in the qsl as well as the loess deposits in dulan county qinghai lake basin and xining basin the regional correlation between proxies of the isl1a core and other aeolian records also supports the aeolian origin of detrital input in the core finally we propose that the origin of the detrital input must be distinguished before the rb sr ratio is applied as a weathering intensity proxy in lacustrine sediments especially in arid basins

solar activity during the last 1000 yr inferred from radionuclide records identification of the causes of past climate change requires detailed knowledge of one of the most important natural factors solar forcing prior to the period of direct solar observations radionuclide abundances in natural archives provide the best known proxies for changes in solar activity here we present two independent reconstructions of changes in solar activity during the last 1000 yr which are inferred from be 10 and c 14 records we analyse the tree ring c 14 data shcal intca104 from 1000 to 1510 ad and annual data from 1511 to 1950 ad and four be 10 records from greenland ice cores camp century grip milcent and dye3 together with two be 10 records from antarctic ice cores dome concordia and south pole in general the be 10 and c 14 records exhibit good agreement that allows us to obtain reliable estimates of past solar magnetic modulation of the radionuclide production rates differences between be 10 records from antarctica and greenland indicate that climatic changes have influenced the deposition of be 10 during some periods of the last 1000 yr the radionuclide based reconstructions of past changes in solar activity do not always agree with the sunspot record which indicates that the coupling between those proxies is not as close as has been sometimes assumed the tree ring c 14 record and be 10 from antarctica indicate that recent solar activity is high but not exceptional with respect to the last 1000 yr c 2006 elsevier ltd all rights reserved less

holocene climate development on the central tibetan plateau a sedimentary record from cuoe lake abstract we present a climate record for central tibet spanning the time between 10500 and 1600 cal years bp from a 5 3 m long sediment core from cuoe lake the analyses show that high sr concentration high toc content high c n ratio and enriched 13c of lake sediments corresponded to stronger chemical weathering high productivity high lake level and warmer wetter climate and vice versa as revealed by the variations of these proxies the climatic evolution during this period can be divided into five stages and several substages these are a cold dry stage before 10140 cal years bp a transition stage from 10140 to 8560 cal years bp an optimum stage warm wet from 8560 to 5750 cal years bp a cool dry stage from 5750 to 4000 cal years bp a transition stage from 4000 to 3000 cal years bp and a drying up stage after 3000 cal years bp these changes are presumably reflections of variations in indian monsoon intensity which according to that interpretation should have been enhanced from 8560 cal years bp slightly weakened after 5750 cal years bp and gradually diminished since 3000 cal years bp in this region

palaeoclimatic interpretation of high resolution oxygen isotope profiles derived from annually laminated speleothems from southern oman high resolution stable isotope profiles of three contemporaneously deposited stalagmites from a shallow cave in southern oman provide an annually resolved record of indian ocean monsoon rainfall variability for the past 780 years uranium series age dating and counts of annual growth bands enable an excellent age calibration although modern speleothems do not grow in perfect isotopic equilibrium oxygen isotope ratios 18o are a proxy for the amount of monsoon rainfall this is supported by the statistically significant correlation between 18o and the thickness of annual bands whereas 18o is inversely correlated with annual band thickness additionally overlapping 18o profiles are very similar in pattern and range indicating that sample specific noise did not blur the climatic signal the longest oxygen isotope profile derived from stalagmite s3 clearly shows the transition at 1320 ad from a generally wetter medieval warm period to a drier little ice age that lasted from approximately ad 1320 1660 in southern oman the decrease in monsoon rainfall since the 1960s is also obvious in meteorological records from northern africa and india indicating that our speleothem based rainfall records do not only reflect local monsoon rainfall variability

reduced solar activity as a trigger for the start of the younger dryas it is generally assumed that changes in ocean circulation forced the abrupt climate changes during the late pleistocene including the younger dryas event recently however it was proposed that variations in solar irradiance could have played a much more prominent role in forcing pleistocene climate changes furthermore two physical mechanisms were recently published that explain how relatively small changes in solar irradiance could have had a strong impact on the climate system we discuss the possibility that an abrupt reduction in solar irradiance triggered the start of the younger dryas and we argue that this is indeed supported by three observations 1 the abrupt and strong increase in residual c 14 at the start of the younger dryas that seems to be too sharp to be caused by ocean circulation changes alone 2 the younger dryas being part of an similar to 2500 year quasi cycle also found in the c 14 record that is supposedly of solar origin 3 the registration of the younger dryas in geological records in the tropics and the mid latitudes of the southern hemisphere moreover the proposed two physical mechanisms could possibly explain how the north atlantic thermohaline circulation was perturbed through an increase in precipitation together with iceberg influxes in addition the full magnitude of the younger dryas cooling as evidenced by terrestrial records in europe could be explained we conclude that a solar triggering of the younger dryas is a valid option that should be studied in detail with climate models c 2000 elsevier science ltd and inqua all rights reserved

pan african rifting and orogenesis in southern to equatorial africa and eastern brazil abstract the upper proterozoic pan african belts of africa and brasiliano belts of south america are assumed to have evolved from an elaborate system of continental rifts which formed on the west gondwana continent 1100 1000 ma ago reviews of the damara belt kaoko belt gariep belt saldania belt west congolian belt lufilian arc and zambezi belt of southern and equatorial africa and the ribeira mantiqueira belt of brazil show the applicability of the continental rifting model to all these belts strict application of the rifting model describing the formation and further evolution of rift structures in the continental crust leads to the conclusion that the west congolian belt as traditionally described is incomplete and has to be supplemented by the mayumbian belt and a rift structure situated farther to the west the lufilian arc is assumed to have evolved from two rift structures separated from each other by the later domes region the golfe du katanga which branches off northeastwards from the lufilian arc is interpreted as an aulacogen shaba aulacogen the pan african brasiliano rift system is comparable to the mesozoic arctic north atlantic rift system with regard to size and distribution of rifts ocean floor spreading and opening of a proto south atlantic ocean most probably occurred along a main line of rifting situated between the west coast of africa and eastern brazil the wedge like ocean may have terminated at the sao francisco congo cratonic bridge between northeastern brazil and gabon cameroon there is no evidence of ocean floor spreading in the zambezi belt the lufilian arc and the traditional west congolian belt which are arranged along another major line of rifting closure of the pan african brasiliano rift system took place during two successive orogenic episodes the zambezi belt lufilian arc and west congolian belt underwent their main orogenic deformation with prevailing ene and wsw oriented tectonic transportation directions during the katangan episode at 900 750 ma the transcontinental sinistral mwembeshi shear zone adjusted opposite movement directions in the zambezi belt and lufilian arc and at its western prolongation concurrently supported opening of the khomas trough in the southern damara belt the proto south atlantic ocean still opening during the katangan episode was gradually closed during the damaran episode at 750 500 ma closure proceeded from north to south and was accompanied by northwest directed subduction underneath the brazilian plate and southeast directed tectonic transportation in the kaoko damara and gariep belts in the previously formed west congolian belt lufilian arc and zambezi belt a second deformation phase characterized by strike slip faulting and local emplacement of nappes occurred during this episode

a 400 000 year record of vegetational and climatic changes from a volcanic basin leizhou peninsula southern china abstract the tianyang lake in leizhou peninsula is an enclosed crater formed during the early to middle pleistocene over 200 m of diatomaceous mud and clay were deposited in the last 400 000 years providing a continuous middle and late quaternary lacustrine sequence for paleoenvironmental studies the pollen record spans the last four glacial interglacial cycles equivalent to oxygen isotope stages ois 10 to 1 during most of the glacial phases fagaceous monsoon forest was replaced by altitudinal vegetation indicating a regional landscape transformation on the peninsula the montane forest reached down to the lowland by at least 600 m during the ois 6 and 8 in a cool and relatively wet condition with temperature estimated to be more than 4 c lower than present a further lowering of the montane forest belts by about 800 1000 m occurred in the ois 4 2 as implied by the appearance of many temperate elements during the last glacial maximum this mixed forest subsequently gave way to the poaceae grassland a savanna vegetation type favored by drier and cooler climatic conditions this drastic change implies a more significant drop in temperature and precipitation than the previous three glacial periods ois 10 8 and 6 it is thus inferred that the weakening of summer monsoon was more significant towards the end of the late pleistocene particularly during the last glacial maximum lgm

evidence for solar forcing on the indian monsoon during the last millennium abstract solar influence on the intensity of the indian monsoon is demonstrated using a sediment core from the eastern arabian sea dating back to 1200 yr through pattern matching as well as spectral analysis of proxy records of monsoon and solar activity the intensity of the indian monsoon is found to have decreased during periods of solar minima during the last millennium periodicities of 200 20 105 15 and 60 10 yr are observed in the proxy records coinciding with those known for solar cycles the 60 yr periodicity observed in the instrumental rainfall data appears to be of solar origin and supports the hypothesis of solar control on the indian monsoon on a multi decadal time scale evidence for the presence of a coupled atmospheric forcing for the indian and east african monsoons on a centennial time scale is also seen

review secular tectonic evolution of archean continental crust interplay between horizontal and vertical processes in the formation of the pilbara craton australia the archean pilbara craton contains five geologically distinct terranes the east pilbara karratha sholl regal and kurrana terranes all of which are unconformably overlain by the 3 02 to 2 93 ga de grey superbasin the 3 53 3 17 ga east pilbara terrane ep represents the ancient nucleus of the craton that formed through three distinct mantle plume events at 3 53 3 43 3 35 3 29 and 3 27 3 24 ga each plume event resulted in eruption of thick dominantly basaltic volcanic successions on older crust to 3 72 ga and melting of crust to generate first tonalite trondhjemite granodiorite ttg and then progressively more evolved granitic magmas in each case plume magmatism was accompanied by uplift and crustal extension the combination of conductive heating from below thermal blanketing from above and internal heating of buried granitoids during these events led to episodes of partial convective overturn of upper and middle crust these mantle melting events caused severe depletion of the subcontinental lithospheric mantle making the ep a stable buoyant unsubductable continent by c 3 2 ga extension accompanying the latest event led to rifting of the protocontinent margins at between 3 2 and 3 17 ga after 3 2 ga horizontal tectonic forces dominated over vertical forces as revealed by the geology of the three terranes karratha sholl and regal of the west pilbara superterrane the c 3 12 ga whundo group of the sholl terrane is a fault bounded 10 km thick volcanic succession with geochemical characteristics of modern oceanic arcs including boninites and evidence for flux melting that indicate steep archean subduction at 3 07 ga the 3 12 ga sholl terrane 3 27 ga karratha terrane and c 3 2 ga regal terrane accreted together and onto the ep during the prinsep orogeny this was followed by development of the de grey superbasin an intracontinental sag basin and widespread plutonism 2 99 2 93 ga as a result of orogenic relaxation and slab break off craton wide compressional deformation at 2 95 2 93 ga culminated with 2 91 ga accretion of the 3 18 ga kurrana terrane with the ep this compression caused amplification of the dome and keel structure in the ep final cratonization was effected by emplacement of 2 89 2 83 ga post tectonic granites

paleolimnology of lake tubutulik an iron meromictic eocene lake eastern seward peninsula alaska abstract sideritic lacustrine mudstone was found in drill core from a uranium deposit in the death valley area in the eastern part of the seward peninsula alaska the precursor sediments for this rock were deposited in an unusual iron meromictic eocene lake herein named lake tubutulik which occupied part of the boulder creek basin a structural graben that is probably a southern extension of the larger death valley basin the boulder creek basin is bounded on the west by granite of the late cretaceous darby pluton on the east by precambrian to paleozoic metasedimentary rocks the lake basin was formed by basaltic flows that dammed the river valley of the ancestral tubutulik river in early eocene time lake tubutulik contained a nearshore facies of fine grained organic mud and an offshore facies of laminated sideritic mud the offshore profundal laminated mudstone consists of alternating layers of authigenic siderite and detrital layers containing mostly quartz and clay minerals both lacustrine facies contain turbidities the lacustrine sediments graded laterally into an onshore facies of colluvial and fluvial sandstone paludal mudstone and coal the ancient lake apparently occupied a small deep basin in a tectonically active area of high relief meromixus was probably stabilized by reduced iron and bicarbonate dissolved in the monimolimnion the intensity of meromixus decreased as the lake became shallower from sediment filling the source of the iron abundant in the monimolimnion of lake tubutulik was probably the eocene basalt based on carbon isotope analysis of the siderite the dissolved bicarbonate in the profundal facies was largely inorganic sideritic carbon in one sample from the onshore paludal facies has an isotopic signature 13 c 16 9 consistent with residual carbon formed during methanogenic fermentation

proterozoic first order sedimentary sequences of the sao francisco craton eastern brazil abstract the sao francisco craton in eastern brazil hosts sedimentary sequences deposited between the paleoarchean 3300 ma and late neoproterozoic 580 ma proterozoic successions occurring in this region comprise five 1st order sedimentary sequences which besides episodes of global significance record major basin forming events the ca 8000 m thick minas itacolomi 1st order sequence exposed in the brazilian mining district of the quadrilatero ferrifero and containing as marker bed the lake superior type caue banded iron formation tracks the operation of a wilson cycle in the paleoproterozoic era the quartz arenite dominated espinhaco i and ii sequences record at least two major rift sag basin forming events which affected the host continent of the sao francisco craton at around 1 75 ga and 1 57 ga the macaubas sequence and its correlatives in the extracratonic domains witness the individualization of a sao francisco congo plate in synchronicity with the break up of rodinia in the cryogenian period the sao francisco congo plate together with various fragments derived from rodinia reassembled to form gondwana in the ediacaran period in the course of the gondwana amalgamation orogenic belts developed along the margins of the craton its interior converted into foreland basins received the shallow water carbonates and pelites of the bambui 1st order sequence and its correlatives

a rb sr record of catchment weathering response to holocene climate change in inner mongolia variation in the rubidium to strontium rb sr ratio of the loess palaeosol sequences has been proposed to reflect the degree of pedogenesis and weathering in the northwestern region of china to characterize the rb sr ratio of the dissolved loads of a single catchment we analysed a 12 08 m sediment core from daihai lake in inner mongolia north china dating control was provided by 210pb 137cs and ams 14c sequential extraction experiments were conducted to investigate the concentrations of rb and sr on various chemical fractions in the lake sediments down core variation in the rb sr ratios provides a record of holocene weathering history from 9 to 3 5 ka bp accelerated chemical weathering was experienced throughout the daihai catchment under mainly warm and humid conditions and this reached a maximum at c 5 ka bp however weathering was reduced between c 8 25 and 7 90 ka bp which may reflect the global 8 2 ka cooling event after c 2 5 ka bp increased rb sr ratios with higher frequency of fluctuations indicate reduced weathering within the daihai catchment the highest rb sr ratios in the little ice age lake sediments indicate the weakest phase of holocene chemical weathering resulting from a marked reduction in sr flux into the basin the rb sr record also shows an enhancement of chemical weathering under today s climate but its intensity is less than that of the medieval warm period increased rb sr in lake sediment corresponding to reduced catchment weathering is in striking contrast to rb sr decrease in the glacial loess layers in the loess palaeosol sequence copyright 2005 john wiley sons ltd

centennial to decadal scale monsoon precipitation variations in the upper hanjiang river region china over the past 6650 years abstract the upper hanjiang river region is the recharge area of the middle route of south to north water transfer project the region is under construction of the hanjiang weihe river water transfer project in china monsoon precipitation variations in this region are critical to water resource and security of china in this study high resolution monsoon precipitation variations were reconstructed in the upper hanjiang river region over the past 6650 years from 18 o and 13 c records of four stalagmites in xianglong cave the long term increasing trend of stalagmite 18 o record since the middle holocene is consistent with other speleothem records from monsoonal china this trend follows the gradually decreasing northern hemisphere summer insolation which indicates that solar insolation may control the orbital scale east asian summer monsoon easm variations despite the declined easm intensity since the middle holocene local precipitation may not have decreased remarkably as revealed by the 13 c records a series of centennial to decadal scale cyclicity was observed with quasi millennium quasi century 57 36 and 22 year cycles by removing the long term trend of stalagmite 18 o record increased monsoon precipitation during periods of 4390 3800 a bp 3590 2960 a bp 2050 1670 a bp and 1110 790 a bp had caused four super floods in the upper reach of hanjiang river dramatically dry climate existed in this region during the 5 0 ka and 2 8 ka events coinciding with notable droughts in other regions of monsoonal china remarkably intensified and southward westerly jet together with weakened summer monsoon may delay the onset of rainy seasons resulting in synchronous decreasing of monsoon precipitation in china during the two events during the 4 2 ka event and the little ice age the upper hanjiang river region was wet which was similar to the climate conditions in central and southern china but was the opposite of drought observed in northern china we propose that weakened summer monsoon and less strengthened or normal westerly jet may cause rain belt stay longer in the southward region which reduced rainfall in northern china but enhanced it in central and southern china

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

non residual sr of the sediments in daihai lake as a good indicator of chemical weathering abstract the rb sr ratio of lake sediments has been demonstrated to be a potential indicator of chemical weathering by increasing work however rb and sr in lake sediments are derived from both chemical weathering and physical erosion rb and sr of different forms in lake sediments may record different environmental processes and information in this study the variation patterns of rb and sr of different forms in sediments of daihai lake were investigated the results show that rb and sr of different forms display noticeably different variation patterns due to their different sources and associated environmental processes using the rb sr ratios of bulk lake sediments to reflect chemical weathering is not accurate the non residual sr of the sediments without detrital carbonates representing the sr leached from the catchment can be used as an index of chemical weathering because the weathering of sr minerals is very sensitive to climate change and the non residual sr content of the sediment is determined more by sr2 influx than by the physicochemical conditions of lake water the correspondence between the non residual sr and tic toc in daihai lake also indicates that the non residual sr of the sediments is a good indicator of chemical weathering in the catchment

variations in organic matter composition in sediments from lake huguang maar huguangyan south china during the last 68 ka implications for environmental and climatic change abstract this study presents a continuous and long term palaeoenvironmental and palaeoclimatic record from a lacustrine sediment core lake huguang maar at the northern coast of the south china sea extending back to about 68 cal ka bp we provide a comprehensive ecosystem analysis from the opportunity to combine organic geochemical and palynological data several climatically induced changes to the flora and fauna have been recognised from 68 to 58 and 48 to 40 5 cal ka bp relatively depleted 13 c toc 31 3 to 25 0 and 13 c values of mid and long chain n alkanes 34 3 to 30 2 as well as high percentages of tropical pollen indicate a vegetation dominated by subtropical tropical forest c 3 plants an expansion of a mixed c 3 c 4 open grassland between 58 and 48 and particularly after 40 5 cal ka bp mirrors drier climatic conditions in conjunction with a lowering of atmospheric co 2 concentrations 13 c toc 24 1 to 16 8 and 13 c values of n alkyl lipids 28 9 to 24 1 are heavier higher percentages of non arboreal pollen were observed and the wood grass lignin index wgli from open pyrolysis py gc indicates a higher input of grass lignin abundant oxidised terrigenous particles that resulted from increased fire activity and or greater erosion rates are a further hint of enhanced dryness the clear drop in moisture availability suggests that this site is sensitive in fluctuations of the summer and winter monsoon activity in accordance with other proxy records in south east asia the response of the aquatic ecosystem is documented by an extremely large 13 c shift of algal derived botryococcenes from 35 4 to 6 2 which records a change towards a bicarbonate carbon source at low dissolved co 2 concentrations

chemical weathering since the little ice age recorded in lake sediments a high resolution proxy of past climate because of the different geochemical behaviour of rubidium and strontium in earth surface processes variations of the rb sr ratios in lake sediments were used as a geochemical proxy of chemical weathering and past climate in a single watershed low magnetic susceptibility low caco3 low sr concentration and hence high rb sr ratio in the lake sediments indicate weak chemical weathering under a cold but wet climate during the little ice age lia in the closed daihai lake watershed the concordant change in both sr and caco3 concentrations with 18o values in the dunde ice core suggests that weak chemical weathering during the wet lia was controlled by air temperature after the lia however precipitation played a dominant role in chemical weathering copyright 2001 john wiley sons ltd

plateau uplift forcing climate change around 8 6 ma on the northeastern tibetan plateau evidence from an integrated sedimentary sr record abstract the uplift of the northern tibetan plateau tp has long been regarded as one of major factors accounting for both the enhanced process of aridification recorded in central asia and the shifts in the asian monsoonal circulations that are known to have occurred at approximately 8 ma until now there have been few sedimentary records reported on which can directly and in an integrated fashion shed light on the region s tectonic and climate regimes this can be largely attributed to the fact that the influence exerted by the presence of source materials and subsequent sedimentary sorting in this tectonically active region would be likely to bias significantly any paleoclimatic interpretation of silicate derived proxies based on detailed investigations of strontium sr distributions revealed by multi step leaching in a fluvial sequence from the linxia basin which includes paleosols we reconstructed the long term late miocene regional climatic and environmental changes likely to have occurred on the northeastern tp from 12 1 to 5 2 ma we investigated sr related proxies in two typical paleosol profiles to constrain sr mobility in paleosol weathering and thus to further prompt the interpretation of sr related proxies along the whole section we would suggest that carbonate derived sr concentrations and sr ca ratios are suitable proxies for tracing regional climate change associated with weathering and pedogenesis together they exhibit weakened chemical weathering intensity and pedogenesis at 8 6 ma the concomitant appearance of immature sediments through poor sedimentary sorting revealed by silicate derived rb sr 87 sr 86 sr and eu anomaly eu eu alongside a sharp increase in sedimentation rates noted at this time suggests that it was indeed tectonic uplift that principally controlled the dramatic climatic and environmental changes this multi proxy record of concomitant tectonic uplift and climate change in the linxia basin provides direct geological evidence for uplift driven climate change in the northeastern tp region

archean and paleoproterozoic crust of the sao francisco craton bahia brazil geodynamic features abstract recent geological geochronological and isotopic studies allow the identification of four important crustal segments in the basement of the sao francisco craton in bahia the oldest is the gaviao block in the wsw part of the studied area and comprises granitic granodioritic and migmatitic continental crust including remnants of 3 4 ga ttgs which are amongst the oldest rocks in south america and are associated with archean greenstone belts the youngest segment is exposed in the itabuna salvador curaca belt which extends from se bahia along the atlantic coast to salvador then northwards into ne bahia it is mainly composed of a low k calc alkaline plutonic suite and also contains strips of intercalated metasediments and ocean floor back arc basin gabbro and basalt in the ssw part of the area the jequie block comprises granulitic migmatites with inclusions of supracrustal rocks intruded by many charnockite plutons in the ne the serrinha block is composed of orthogneisses and migmatites which form the basement for paleoproterozoic greenstone belts during the paleoproterozoic transamazonian cycle these four crustal segments collided resulting in the formation of an important mountain belt the regional metamorphism resulting from the crustal thickening associated with the collision occurred at around 2 0 ga major mineralizations were formed during the evolution of the four archean blocks and also during and after the paleoproterozoic collision

stable isotope composition of siderite as an indicator of the paleoenvironmental history of oil shale lakes the sediments of two eocene oil shale lakes messel graben and eckfeld maar west germany were analyzed with respect to the distribution chemical and stable isotope composition of siderite the data allow a reconstruction of different stages in the sedimentary and early diagenetic history of the lakes in the messel lake siderite formation started when the sedimentation of laminated sapropelic corg rich sediments was already established the early stage of oil shale sedimentation was characterized by pyrite precipitation in the siderite stage the stable isotope composition of the carbonate suggests methanogenesis to have been an important process at the sediment water boundary layer in the eckfeld lake siderite formation started even before sedimentation of the first sapropelic laminae the stable isotopic composition of the carbonate again indicates an anoxic sediment water boundary layer and strong methanogenesis with the expansion of this environment into the deep water mass sapropel sedimentation became established for both sequences the chemistry and stable isotope composition of the siderites correlates with petrographic and paleontological information about climate dependent fluctuations in the ecological chemical and early diagenetic environment the strong relationship of siderite formation to methanogenesis may be explained by the rate of microbial organic matter degradation which governed both methanogenesis and pco2

the significance of siderite in the sediments from lake nyos cameroon abstract small amounts 1 3 wt of endogenic siderite feco3 and traces of pyrite fes2 are present in a 1 m long sediment core from lake nyos thermodynamic modeling shows that the deep waters are supersaturated with respect to siderite and pyrite no other carbonates were found to be stable this rare occurrence of siderite is symptomatic of the build up of large concentrations of co2 and fe2 in the lake nyos waters a search for siderite in the deeper sediments could reveal the existence of previous gas burst events that have occurred at lake nyos or in other cameroon lakes

sun coupled climate connection between eastern asia and northern atlantic 1 few of annually resolved proxy temperature records are reported to coincide with centennial to millennial scale solar oscillations here we show that the warm season temperature inferred from the layer thickness of a stalagmite from beijing in eastern asia is consistent with oscillations in total solar irradiance inferred from cosmogenic 10be and 14c on the other hand this climate record is remarkably consistent with northern atlantic drift ice cycles that were identified to be controlled by the sun through the entire holocene the synchronism between the two independent sun linked climate records therefore suggests that the sun may directly couple hemispherical climate changes on centennial to millennial scales

the effects of out of plane seismic energy on reflections in crustal scale 2d seismic sections abstract crustal scale seismic surveys mostly collect data along single profiles and the data processing has an underlying assumption that the data have imaged two dimension 2d structure striking at right angles to the seismic profile however even small amounts of out of plane topography on a reflector can result in reflections that do not map the reflector shape accurately out of plane energy will migrate within the plane of the section to an apparent depth represented as two way time twt that is greater than the depth of the reflection point out of the plane of the section it will fall within the plane of the section at depths less than equal to or greater than the intersection of the reflector with the plane of the section depending on both the amount of out of plane topographic relief on the reflector and the offset of the topographic relief from the plane of the section reflectors that are a single surface can therefore be manifested in the seismic section as a band of several reflections rather than a single reflection more complex reflectors such as shear zones that have a finite thickness because they are made up of several to many anastomosing layers of altered and anisotropic rock embedded in protolith will appear as laterally short reflections within a laterally continuous reflection band other examples of such reflectors would be the moho in some places and rock with compositional layering with increasing out of plane topographic relief on the reflector the top of the reflection band for both single and multi layer reflectors will be a poor indicator of the top of the reflector in the earth the bottom of the reflection band will always be a poor indicator of the bottom of the reflector because out of plane energy can arrive at twts that are different from those of the reflector in the plane of the section out of plane energy has the potential to interfere constructively or destructively with the in plane energy in synthetic data calculated for a simple model assuming one layer and topographic relief of 250 m over wavelengths of 4 5 km similar to that imaged in a real sub horizontal detachment amplitudes ranged up to 2 6 times the expected amplitude for the layer a model with anastomosing layers built to resemble a thick shear zone rather than a discrete fault surface allowed tuning between layers the effects of out of plane energy when combined with the effects of tuning caused amplitudes up to 3 1 times those expected larger amplitudes could be achieved if a suitable model was contrived the results indicate that care must be taken when calculating impedance contrasts using real data the highest amplitude reflections are likely to yield overestimates of the true impedance contrast

precambrian sequence stratigraphy abstract sequence stratigraphy studies the change in depositional trends in response to the interplay of accommodation and sediment supply from the scale of individual depositional systems to entire sedimentary basin fills as accommodation is controlled by allogenic mechanisms that operate at basinal to global scales the change in depositional trends is commonly synchronized among all environments established within a basin thus providing the basis for the definition of systems tracts and the development of models of facies predictability all classical sequence stratigraphic models assume the presence of an interior seaway within the basin under analysis and are centered around the direction and types of shoreline shifts which control the timing of all systems tracts and sequence stratigraphic surfaces in overfilled basins dominated by nonmarine sedimentation the definition of systems tracts is based on changes in fluvial accommodation as inferred from the shifting balance between the various fluvial architectural elements the method of sequence stratigraphy requires the application of the same set of core principles irrespective of the age of strata under analysis from precambrian to phanerozoic the study of precambrian basins is often hampered by poorer stratal preservation and by a general lack of time control however where sedimentary facies are well preserved the lack of time control may be partially compensated by a good knowledge of facies architecture and relationships as well as by paleocurrent data the latter are particularly important to understand the stratigraphic record of tectonically active basins where abrupt shifts in paleoflow directions allow one to infer tectonic events and map the corresponding sequence bounding unconformities arguably the most important contribution of precambrian research to sequence stratigraphy is the better understanding of the mechanisms controlling stratigraphic cyclicity in the rock record and hence of the criteria that should be employed in a system of sequence stratigraphic hierarchy there is increasing evidence that the tectonic regimes which controlled the formation and evolution of sedimentary basins in the more distant geological past were much more erratic in terms of origin and rates than formerly inferred solely from the study of the phanerozoic record in this context time is largely irrelevant as a parameter in the classification of stratigraphic sequences and it is rather the stratigraphic record of changes in the tectonic setting that provides the key criteria for the basic subdivision of the rock record into basin fill successions separated by first order sequence boundaries these first order basin fill successions are in turn subdivided into second and lower order sequences that result from shifts in the balance between accommodation and sedimentation at various scales of observation irrespective of the time span between two same order consecutive events sequences identified in any particular basin are not expected to correlate to other first and lower order sequences of other basins that may be similar in age but may have different timing and duration

lacustrine organic fluxes and palaeoclimatic variations during the last 15 ka lac du bouchet massif central france to assess the influence of climatic changes on organic lacustrine sedimentation two cores recovered from the centre of the lac du bouchet were studied by petrographical palynofacies and geochemical methods only core ldb h was used for estimation of the organic fluxes the variation of these fluxes with climo stratigraphic periods showed low organic fluxes during the lateglacial an increase at the beginning of the holocene a minimum at the end of the atlantic period resulting from the climatic cooling and a maximum at the end of the sub boreal related to the installation of the present climatic conditions

huguangyan maar lake se china a solid record of atmospheric mercury pollution history in a non remote region abstract mercury is a highly toxic metal that can cause harm to environment and human health as atmospheric deposition is the main source of total hg input to aquatic system in remote and pristine regions almost all the studies on atmospheric hg pollution history concentrated in these areas while the studies in non remote areas are much limited especially for the long history records in this study huguangyan maar lake an undisturbed lake system at low altitude in china was selected to reconstruct the atmospheric mercury pollution history variation patterns of toc hg and non residual sr in the sediment core indicated that compared to the direct atmospheric hg deposition the effect of either hg scavenging from water column by algae or the catchment inputs of previously deposited hg on the hg accumulation in the lake sediment was limited the sediment hg content in huguangyan lake was mainly controlled by the atmospheric hg deposition and thus accurately reflected the atmospheric hg pollution history the hg a hg content from atmospheric deposition in huguangyan lake presented a comparable variation pattern to that in remote sites it had the same variation trend as the global atmospheric hg before 1950 ce which could be attributed to the industrial revolution after that it was mainly controlled by hg emissions from asian countries the variation of hg a also indicated that atmospheric hg deposition accelerated significantly since 2000 ce this study along with other investigations in remote sites in china showed that the sediment hg in huguangyan lake responded to the atmospheric hg pollution more sensitively than in the alpine regions it should be noted that the more intensive acceleration of hg deposition in huguangyan lake may imply that the south of china suffered from much more serious atmospheric hg pollution than previous studies revealed

wet and cold climate conditions recorded by coral geochemical proxies during the beginning of the first millennium ce in the northern south china sea abstract the past two millennia include some distinct climate intervals such as the medieval warm period mwp and the little ice age lia which were caused by natural forcing factors as well as the current warm period cwp that has been linked to anthropogenic factors therefore this period has been of great interest to climate change researchers however most studies are based on terrestrial proxy records historical documentary data and simulation results and the ocean and the tropical record are very limited the eastern han three kingdoms and western jin periods 25 316 ce cover the beginning first millennium ce in china and were characterized by a cold climate and frequent wars and regime changes this study used paired sr ca and 18o series recovered from a fossil coral to reconstruct the sea surface water conditions during the late eastern han to western jin periods 167 309 ce at wenchang eastern hainan island in the northern south china sea scs to investigate climate change at this time the long term sea surface temperature sst during the study interval was 25 1 c which is about 1 5 c lower than that of the cwp 26 6 c compared with the average value of 0 40 during the cwp the long term average seawater 18o 0 06 was more negative these results indicate that the climate conditions during the study period were cold and wet and comparable with those of the lia this colder climate may have been associated with the weaker summer solar irradiance the wet conditions were caused by the reduced northward shift of the intertropical convergence zone monsoon rainbelt associated with the retreat of the east asian summer monsoon interannual and interdecadal climate variability may also have contributed to the variations in sst and seawater 18o recorded over the study period