pleistocene chemical weathering history of asian arid and semi arid regions recorded in loess deposits of china and tajikistan quaternary loess soil sequences in china and tajikistan are valuable archives of the chemical weathering history for arid and semiarid regions of asia the development of new proxies independent of grain size are vital to reconstruct the long term chemical weathering history of eolian deposits in this study we analyze major elemental and rb sr and ba concentrations of decarbonated residue from representative loess and soil units along a north south transect on the chinese loess plateau and compare these concentrations among different grain size fractions results show that most of the elemental abundances and ratios vary considerably among different grain size fractions for both loess and paleosols indicating transport driven compositional differentiation of minerals during subaerial transport however cao na2o mgo tio2 ratios show little variation among different size fractions for the loess soil transect loess soil sequences at lingtai northern china and chashmanigar southern tajikistan for the past 1 50 1 77 ma show lower cao na2o mgo tio2 ratios in soil units than in adjacent loess horizons in good agreement with greater weathering intensity in soils than in loess units the cao na2o mgo tio2 ratio of the decarbonated residue is therefore a reliable proxy for chemical weathering of loess deposits that is independent of grain size the cao na2o mgo tio2 ratios of the lingtai and chashmanigar sections display a relatively regular oscillation within a narrow range in the early pleistocene and a rapid increase in average values and in variance from 0 85 0 6 ma to the present indicating lowered chemical weathering intensity in both the dust source regions and the depositional areas this event may be causally related to the expansion of northern hemisphere ice and or the regional tectonic uplift of high mountains in asia since the mid pleistocene

preliminary observations on the geomorphic evolution of the guide basin qinghai province china implications for the uplift of the northeast margin of the tibetan plateau

geochemical characteristics of the eolian deposits in the zoige basin and their implications for provenance and weathering intensity abstract eolian deposits in the zoige basin at the northeastern region of the tibetan plateau tp were analyzed for their major trace elements and sm nd isotopic compositions to explore the provenance and weathering intensity the results are compared with the data from the lingtai section lt in the chinese loess plateau clp eolian deposits from different sections in the zoige basin have resembling geochemical compositions reflecting similar provenance their major element compositions are close to those of the ucc and their ucc normalized major trace element abundances and chondrite normalized rare earth element ree abundances are similar to the lt samples however the sio2 al2o3 tio2 zr hf sc co v ni concentrations and sio2 tio2 tio2 al2o3 co th la sc th sc end 0 147sm 144nd ratios of the zoige sections are quite different from those of the lt section which suggests different provenances for the eolian deposits in these two regions the relatively high abundances of sio2 zr hf and low abundances of trace elements indicate that local sediments on the tp are the major contributors to the eolian deposits in the zoige basin eolian deposits from the zoige basin have experienced the early na and ca removal stage and chemical weathering parameters suggest a moderate weathering condition in the source and deposition regions

holocene aeolian activity in the zoige basin northeastern tibetan plateau china abstract the zoige basin is located in the northeastern tibetan plateau at an altitude of around 3500 m to fully understand and assess the current status and future trend of aeolian activity in the zoige basin it is necessary to reveal the history of aeolian activity of this region in this study 11 optically stimulated luminescence osl ages from three typical sections were used to reconstruct the history of aeolian activities in the region during the holocene the results of the chronologies show that the oldest osl age 10 27 0 81 ka occurred in the early holocene but aeolian sediment deposition primarily occurred in the late holocene after around 3 20 0 33 ka in the whole holocene the aeolian activities of the zoige basin occurred contemporaneously with nearby sites in the northeastern tibetan plateau episodic weak aeolian activities were recorded in nearby sites in the northeastern tibetan plateau however we postulate here that the combination of a flat low lying landscape along with higher precipitation during the mid holocene resulted in this area being relatively insensitive to short term arid climatic changes and aeolian activity

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

the acoustic turbid layer in muddy sediments of eckernfoerde bay western baltic methane concentration saturation and bubble characteristics in eckernfoerde bay in the western baltic an enclosed basin with organic rich mud acoustic turbidity has been observed since 1952 to investigate the relationships between acoustic properties and free gas we developed a method for rapid sub sampling of gravity cores to determine the total methane content from temperature measurements determinations of the salinity of the pore water and data from the literature saturation limits were calculated for each core it is demonstrated that there is a certain amount of free gas in the mud of eckernfoerde bay but subbottom depths of the oversaturation and of the acoustic turbidity do not correspond the existence of free gas implies the existence of bubbles in the sediment which are regarded to be responsible for the acoustic turbidity bubble sizes observed by x ray computed tomography while still under in situ pressure and temperature vary between 1 and 10 mm equivalent diameter the distribution of bubbles is discontinuous occurring in depth zones from 2 to 20 cm thickness

sedimentary organic matter preservation a test for selective degradation under oxic conditions the authors report here a test of the hypothesis that the extent of organic matter preservation in continental margin sediments is controlled by the average period accumulating particles reside in oxic porewater immediately beneath the water sediment interface oxygen penetration depths organic element compositions and mineral surface areas were determined for 16 sediment cores collected along an offshore transect across the washington continental shelf slope and adjacent cascadia basin individual amino acid sugar and pollen distributions were analyzed for a 11 to 12 cm horizon from each core and sup 14 c based sediment accumulation rates and stable carbon isotope compositions were determined from depth profiles within a subset of six cores from representative sites sediment accumulation rates decreased and dissolved o sub 2 penetration depths increased offshore along the sampling transect as a result oxygen exposure times oet increased seaward from decades mid shelf and upper slope to more than a thousand years outer cascadia basin organic contents and compositions were essentially constant within individual sediment cores but varied consistently with location in particular organic carbon surface area ratios decreased progressively offshore and with increasing oet three independent compositional parameters demonstrated that the remnant organic matter in farther offshore sediments is more degraded both concentrationmore and compositional patterns indicated that sedimentary organic matter exhibits a distinct and reproducible oxic effect oet helps integrate and explain organic matter preservation in accumulating continental margin sediments and hence provides a useful tool for assessing transfer of organic matter from the biosphere to the geosphere less

quaternary evolution of the ria de vigo spain abstract the seismic analysis of the sedimentary infill of the ria de vigo reveals that the infill comprises of a fifth order sequence 18 ky bounded by a major discontinuity surface within the holocene sequence several seismic units have been identified the oldest one originated after the wurm glaciation and the origin of its top discontinuity was eroded during the regression sea level at 120 m of this last glacial episode isotopic stages 2 to 4 18 ky b p in some places below this ria infill another sequence can be identified this older sequence is associated with the pre existing faults and troughs in the deepest parts of the ria and it was deposited during the wurm glaciation miocene pleistocene eroded sediments were moved from the rias area to deeper zones where they accumulated in the lowstand system tract the next sea level rise occured in two steps producing two transgressive units separated by an hiatus surface this cycle was interrupted by the next sea level fall to 55 m marked on the seismic records by another recognizable boundary the next sea level rise took place in several steps back stepping with some stillstands generating another transgressive system tract in the ria from that time on the relative sea level continued rising depositing the most recent unit which represents the highstand system tract separating the highstand system tract and the transgresive unit below there is a consensed section the analysis of 29 cores provides groundtruthing for our hypothesis the identified main lithologic units show a transgressive sequence a granitic rock base an overlying second unit locally wedge shaped and most recently a marine muddy unit covering the present ria seafloor

diagenetic relationships of methanogenesis nutrients acoustic turbidity pockmarks and freshwater seepages in eckernforde bay abstract high organic loading 4 5 wt and sedimentation rates 1 4 mm yr 1 in eckernforde bay sediments lead to anaerobic conditions within the uppermost 15 cm intense bacterial sulphate reduction 0 011 0 15 mm so 4 red 2 yr 1 exhausts dissolved sulphate around 150 cm sediment depth resulting in methanogenesis at greater sediment depth by carbonate reduction 1 8 8 5 m ch 4 yr 1 extensive regions of eckernforde bay are characterized by acoustically turbid sediments 300 cm sediment depth resulting from deeper sediments supersaturated in methane forming free gas accumulation zones methane migrating upward into the sulphate reduction zone is effectively consumed by sulphate reducing bacteria at rates 3 10 times greater than methanogenesis i e 46 95 m ch 4 ox yr 1 the pathways of methane formation and anaerobic oxidation are confirmed by stable carbon and hydrogen isotope evidence pockmarks i e shallow surface depressions in some eckernforde bay sediments are not associated with gas ebullition rather these physical features result from the expulsion of freshwater these episodic springs or seepages of groundwater from the underlying holocene glacial lags and sands into the basin at pockmark sites have characteristic low chloride and methane concentrations the geochemical evidence indicates that the commercial accumulation of petroleum in the lower cretaceous dogger beta hauptsandstein schwedeneck field in eckernforde bay 1500 mbsf has no surface manifestation and does not influence either the occurrence of acoustic turbidity or pockmarks

characterisation and preliminary quantification of the methane reservoir in a coastal sedimentary source san simon bay ria de vigo nw spain abstract ria de vigo is a river valley flooded by the sea with a bay san simon bay at its innermost part the accumulation of holocene sediment in san simon bay has been studied by the integration of 1 large scale high resolution seismic data and 2 detailed geochemical analysis of a gravity core in san simon bay the majority of the seismic records are obscured by acoustic turbidity which represents gassy sediments but on records from rande strait it is possible to distinguish two quaternary seismic sequences an upper pleistocene sequence sq1 and a holocene sequence sq2 only sq2 is recognized in san simon bay where it is comprised of two seismic units the upper unit represents the hst sediment i e the period of highest sea level a gravity core taken within the gassy zone at 10 m water depth provided 3 55 m of fine grained sediments muds from the youngest seismic unit 4 m thick geochemical analysis show high values 4 to 10 of toc sediment and porewater analyses indicate a distinct sulphate methane transition zone smtz between 60 and 80 cm where sulphate is depleted to 0 4 mm the top of the acoustic turbidity the gas front at 80 cm corresponds to the lower limit of the smtz the methane cannot have been derived from the underlying metamorphic and granitic rocks but was probably derived by microbial degradation of the organic matter in the holocene sediments we estimate that the sediments of the bay contain approximately 1 8 10 6 m 3 of organic carbon and 275 ton of methane

linking mainland australia and tasmania using ambient seismic noise tomography implications for the tectonic evolution of the east gondwana margin for nearly half a century a number of conflicting tectonic models have been postulated to explain the enigmatic geological relationship between tasmania and victoria with a view to unifying our understanding of the evolution of the eastern margin of gondwana in australia in this study ambient noise data from an array of 24 broadband seismometers is used to produce a high resolution 3 d crustal shear wave velocity model of bass strait the key to understanding the missing link we apply a novel transdimensional and hierarchical bayesian inversion approach to construct group velocity maps in the period range of 2 30 s and subsequently invert group velocity dispersion for 3 d shear wave velocity structure this allows us to image for the first time the entire crust beneath bass strait in high detail and elucidate the geometry and position of key crustal features with corroboration from complementary datasets the three sedimentary basins related to the failed rifting event associated with the australia antarctica breakup in particular bass basin clearly emerge from the tomographic solution model a key feature of the 3 d shear wavespeed model is a distinct mid lower crustal nw se high velocity zone which extends from northwestern tasmania to south central victoria confirming a proterozoic geological connection we also image three north south high velocity belts that appear to span bass strait with some interruption from velocity variations possibly related to more recent tectonic events these belts are consistent with recent gravity and magnetic maps and may indicate the presence of an exotic precambrian terrane the selwyn block the model also images the crustal velocity structure of the southern stawell and bendigo zones and their internal large scale multi layer characters a legacy of their early paleozoic intra oceanic origins another high velocity anomaly imaged in the mid lower crust is an east west lineament beneath the northern part of bass strait which may be an intrusive feature associated with the failed rift

quaternary glaciations recorded by glacial and fluvial landforms in the shaluli mountains southeastern tibetan plateau abstract the shaluli mountains a tectonically controlled mountain range between the jinsha and yalong river rifts are located in southeastern tibetan plateau in the central shaluli mountains an ice cap of 3600 km 2 once developed on the haizi shan abundant glacial landforms are present on the haizi shan and in the surrounding river valleys together with the outwash terraces in the yazheku river the northeastern part of the haizi shan provides an ideal site to examine the quaternary glacial history of the region sedimentological and morphostratigraphical analysis field mapping and dating by electron spin resonance esr define at least seven major glacier advances in the haizi shan area six major glacier advances likely occurred during marine oxygen isotope stage mis 16 mis 14 12 mis 6 mis 3 early mis 2 and the global last glacial maximum these can be defined on the basis of esr dating and stratigraphical analysis of the glacial landforms in front of the kuzhaori glacial trough on the southern slope of the haizi shan the outwash terraces in the yazheku river also record four major glacier advances which occurred during mis 16 mis 12 mis 6 and mis 2 in addition the moraines preserved on the southwestern part of the haizi shan suggest that a glacial advance likely occurring during the lateglacial the extent of glaciation on the haizi shan decreased with time

the geochemistry of loess asian and north american deposits compared abstract loess is widely distributed over asia and north america and constitutes one of the most important surficial deposits that serve as terrestrial records of the quaternary the oldest pleistocene loess in china is likely 2 6 ma thus spanning much or all of the pleistocene in north america most loess is no older than the penultimate glacial period with the exception of alaska where the record may go back to 3 0 ma on both continents loess deposits date primarily to glacial periods and interglacial or interstadial periods are represented by paleosols both glacial and non glacial sources of silts that comprise the bulk of loess deposits are found on both continents although loess has been considered to be representative of the average upper continental crust there are regionally distinctive compositions of loess in both asia and north america loess deposits in asia from yakutia tajikistan and china have compositionally distinct major element compositions due to varying abundances of silicate minerals carbonate minerals and clay minerals in north america loess in the mississippi river valley the great plains and alaska are also distinguishable with regard to major element composition that reflects highly diverse source sediments trace element geochemistry sc th zr and the rare earth elements also shows regional diversity of loess bodies in both asia and north america on both continents most loess bodies show significant contributions from later cycle altered sedimentary rocks as opposed to direct derivation from igneous rocks further some loess bodies have detectable contributions from mafic igneous rocks as well as major contributions from average upper crustal felsic rocks intercalated paleosols in loess sections show geochemical compositions that differ significantly from the underlying loess parent materials ratios of soluble to insoluble elements show depletions in paleosols due to chemical weathering losses of calcite dolomite plagioclase mica apatite and smectite in asia and north america the last interglacial paleosol is more weathered than equivalent modern soils which could be due either to a climate that was warmer and more humid a longer period of pedogenesis or both in asia early pleistocene loess and paleosols are both more weathered than those from the middle and late pleistocene forming prior to a mid pleistocene aridification of asia from uplift of the tibetan plateau understanding the geochemistry of loess and paleosols can tell us much about past atmospheric circulation past temperature and moisture regimes and even tectonic processes

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

correlations between tasmania and the tasman transantarctic orogen evidence for easterly derivation of tasmania relative to mainland australia reconstructions of southern gondwana place tasmania at the triple junction of paleozoic australia antarctica and new zealand tasmania however differs in pre jurassic stratigraphy and structural style from the southeastern australian mainland and northeast victoria land antarctica most notably 1 precambrian basement is exposed in tasmania but not in the lachlan fold belt of the australian mainland precambrian basement in northeast victoria land and the adelaide kanmantoo fold belt of southeast australia differ in stratigraphy and metamorphic history from that in tasmania and 2 western tasmania is dominated by west verging cambrian and devonian thrusts whereas the lachlan fold belt is dominated by east verging devonian thrusts the adelaide kanmantoo fold belt is dominated by westverging ordovician thrusts and northeast victoria land is dominated by east verging ordovician thrusts an explanation for the misfit between tasmania and the other regions is that ancestral tasmania 1 was positioned east of mainland australia with possible precambrian links to north america sweat hypothesis and 2 was progressively emplaced by a combination of west directed cambrian and devonian thrusting cretaceous crustal stretching to form the gippsland and bass basins and finally tertiary wrenching south of the gambier gabo line

assessing tectonic and climatic controls for late quaternary fluvial terraces in guide jianzha and xunhua basins along the yellow river on the northeastern tibetan plateau abstract this study focused on well preserved fluvial terrace sequences that span the past 100 ka in the guide jianzha and xunhua basins along the yellow river that drained the northeastern tibetan plateau new geomorphic stratigraphic sedimentologic and chronologic data from twelve depositional sequences within terraces yielded better constraints on rates of incision degradational and aggradational phases for the yellow river age control was established by sixteen osl ages on quartz grains from fluvial sediments three fluvial aggradational phases were identified between 100 and 80 ka 53 and 40 ka and 21 and 12 ka associated with terrace levels respectively at 120 to 95 61 to 45 and 25 to 15 m above river level these aggradational phases reflect multiple processes including enhanced fluvial discharge sediment availability with glaciation deglaciation and increased monsoonal precipitation the initiation of fluvial degradation was linked to mega floods released from landslide dammed lakes at ca 76 38 and 16 ka though these changes may also reflect variations in sediment load discharge relations with climate change the apparent net incision rate is 1 13 0 11 mm yr for the past 100 ka and is consistent with late cenozoic tectonic uplift rates 0 5 2 mm yr and recent gps based rates the fluvial dynamics of the upper reach of the yellow river was variably controlled by climate induced changes in discharge sediment load relations on stadial to interstadial timescales episodic mega floods from the breach of landslide dams and with net incision in the past 100 ka in response to tectonic uplift of the tibetan plateau

a reassessment of paleogeographic reconstructions of eastern gondwana bringing geology back into the equation abstract in recent years several tectonic reconstructions have been presented for australia antarctica break up with each putting the australian plate in a different location with respect to antarctica these differences reflect the different datasets and techniques employed to create a particular reconstruction here we show that some of the more recent reconstructions proposed for australia antarctica break up are inconsistent with both our current knowledge of margin evolution as well as the inferred match in basement terranes on the two opposing conjugate margins we also show how these incorrect reconstructions influence the fit of the indian plate against antarctica if its movement is tied to the australian plate such errors can have a major influence on the tectonic models of other parts of the world in this case we show how the position of the australia plate can predetermine the extent of greater india which is rightly or wrongly used by many as a constraint in determining the timing of india asia or india island arc collisions during the closure of tethys we also discuss the timing of australia antarctica break up and which linear magnetic features are a product of symmetric sea floor spreading versus those linear magnetic features that result from rifting of a margin the 46 ma to 84 ma rotational poles previously proposed for australia antarctica break up and confined to transitional crust and the continent ocean transition zone more likely formed during earlier stages of rifting rather than during symmetric sea floor spreading of oceanic crust so rotation poles that have been derived from magnetic anomalies in such regions cannot be used as input in a plate reconstruction a new reconstruction of the australia antarctica margin is therefore proposed that remains faithful to the best available geological and geophysical data

climate and anthropogenic factors influencing an estuarine ecosystem from nw iberia new high resolution multiproxy analyses from san simon bay ria de vigo abstract two sedimentary sequences coastal and subtidal were studied in san simon bay ria de vigo situated on the atlantic coast of nw iberia the coastal record is a shallowing upward sequence which evidences a locally developed low marsh situated below the current beach and dated at the second half of the 4th century during the following decades this low marsh was progressively replaced by an alder swamp which formed on it this suggests an apparent stabilisation or slow down of the relative sea level rsl in this site at the beginning of the dark ages da the subtidal sequence studied reflects the main changes in the landscape the hydrological conditions climate and rsl affecting this part of nw iberia during the last 1250 years evidence of changing dinocysts content in the sediment reveals that two centennial or decadal scale episodes existed of shelf marine waters more intensely penetrating inside the bay between the 15th 18th centuries and at ca 1800 1930 ad besides we related different proxies with the occurrence of four main climatic stages namely the previously described dark ages da ca 350 750 ad the mediaeval climatic anomaly mca ca 750 1100 ad and the little ice age lia ca 1500 1930 ad in addition we propose a regional mca lia transition ca 1100 1500 ad that it has not been previously described our environmental characterization indicates a persistent north atlantic oscillation nao negative mode domain in ria de vigo during the mca but this became weaker during the lia and probably also during the earlier da nao mode become more irregular during the mca lia transition generally persisting in dominant negative mode except for a phase of minor upwelling intensification at ca 1150 1350 ad which mainly affected the external parts of the ria we postulate that an almost simultaneous phase ca 1100 1350 ad of stronger continental contribution in the sediments may be related to increasing storm intensities probably linked to a reinforcement of the easter atlantic ea pattern and also that the intertidal supratidal ecosystems inside san simon bay may have extended further in the past at least towards the end of the 5th century and between ca 1050 1350 ad and ca 1450 1750 ad a number of local historical references are consistent with our palaeoecological data and so support the chronology proposed as well as many of the environmental changes reconstructed this good agreement will help in the interpretation of other analogous sequences extending back in time

holocene aeolian activity in the headwater region of the yellow river northeast tibet plateau china a first approach by using osl dating abstract the headwater region of the yellow river hryr is the catchment upstream of duoshi gorge covering an area of 29 588 km2 the hryr is located in the northeastern tibet plateau with an altitude higher than 4000 m above sea level and is especially sensitive to climate change since the late 19th century the mean annual temperature in tibet plateau has increased sharply as a result of increasing air temperature a significant number of environmental problems have occurred during the past decades including aeolian desertification in recent decades aeolian desertification has become a severe environmental problem in the tibet plateau due to permafrost degradation because permafrost plays an important role in maintaining the grassland vegetation with the increase in ground temperature the aeolian activity in the hryr is likely to become more serious however the history of aeolian activity in the hryr remains unknown due to a lack of chronological studies in this study 15 optical stimulated luminescence osl ages from three typical sections were used to reveal the history of aeolian activities in the hryr during the holocene all of the osl ages were late holocene and the oldest age is 2 13 0 16 ka bp the relative young osl ages and deep aeolian sediment indicated very high sedimentation rates in the late holocene especially after around 1 ka bp the intensive aeolian activity and low toc content indicate a drier climate in the late holocene the well sorted sediments and similar grain size distributions of the three sections imply their similar wind regimes based on the evolution history of the yellow river s headward erosion it is inferred that little aeolian activity occurred in this region during the early and mid holocene

nature of organic matter in surface sediments from the pakistan continental margin and the deep arabian sea amino acids the role of organic carbon input sedimentation rate and bottom water oxygenation bwo for organic matter om degradation was investigated using surface sediments collected from above within and below the oxygen minimum zone omz within varying sedimentary regimes along the pakistan continental margin for this samples from 47 box cores and multi cores were analyzed for their bulk component organic carbon total nitrogen carbonate opal and amino acid concentrations the results are compared to plankton net samples from the arabian sea sinking particles collected at the pakistan continental margin cultured sedimentary deep sea bacteria and data from the deep arabian sea basins high organic carbon and amino acid concentrations were found in the laminated sediments of the omz in bioturbated sediments immediately below the omz and below regions of high productivity in the western arabian sea the contribution of amino acids to organic carbon and total nitrogen as well as the molar contribution of certain non protein amino acids do not mirror these differences in oc contents no clear trend in relation to sediment structure or water depth is observed in contrast to these established indicators of om degradation the molar contribution of the aromatic amino acid tyrosine tyr exhibits a distinct pattern its contribution is relatively high in sediments at depths above the omz and further increases towards the center of the omz below the omz it decreases continuously with increasing water depth in addition for samples from similar depths and bottom water oxygen contents tyr shows systematic differences between varying sedimentary regimes the lack of a distinct trend for the established indicators does not support the idea of a predominant control of bwo on quantitative om preservation nevertheless the variability of tyr in relation to water depth or the sedimentary regime suggests that i the productivity related oc input ii the bulk accumulation rate and iii bwo influence the alteration of the sedimentary om by controlling its oxygen exposure time

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

climatic and anthropogenic impacts on the ria de vigo nw iberia over the last two centuries a high resolution dinoflagellate cyst sedimentary record abstract a high resolution dinoflagellate cyst record spanning the period of 1830 2012 ce from ria de vigo atlantic margin of nw iberia is presented changes in concentrations and percentages of dinoflagellate cysts and freshwater algal spores reflect climatic and anthropogenic influences on the ria i e coastal inlet formed by the partial submergence of a river valley statistical analyses pca and clustering were used to identify the main patterns of change in the cyst assemblages the cyst record was compared with reconstructed and measured instrumental environmental data nao temperatures mean sea level etc to support palaeo reconstructions four main phases were identified the first phase 1830 1855 ce of lower relative sea level rsl temperatures and precipitations represents the last stages of the lia little ice age the second phase 1855 1910 ce is interpreted as a transition between the colder lia and the wetter and warmer conditions that prevailed through the 20th century the third phase 1910 1975 ce is characterized by strong river inputs and water stratification in the ria and the fourth phase 1975 2012 ce reflects impacts of anthropogenic warming and pollution the anthropogenic signal consists of increases in heterotrophic cyst proportions and cysts diversity as well as of a marked decline of potentially toxic lingulodinium machaerophorum increasing organic matter content nutrients and industrial wastes have likely caused detrimental impacts on the autotrophic dinoflagellates by increasing turbidity and toxicity the b5 cyst record and its comparison with previously published data suggest that increased concentrations of l machaerophorum in the 20th century were mainly related to river flow variations that in turn were primarily driven by nao changes rather than cultural eutrophication we also report high abundances of peridinium ponticum in our record determining that this species is not exclusive to the black and marmara seas and has much wider natural distribution

early diagenesis of organic matter rich sediments in a ria environment organic matter sources pyrites morphology and limitation of pyritization at depth abstract the subtidal sediments of the inner ria de vigo nw spain are fine grained rich in organic matter and accumulate at rates of around 3 mm yr redoxomorphic pyrites formation was studied in four sediment cores four operationally defined iron fractions were determined hcl extracted silicate bound organic and pyritic and the dimensions and morphology of pyrites which mainly occurred as isolated framboids 3 5 m in diameter were studied by sem sediment appearance and degree of pyritization dop identified an oxic zone limited to the top few millimetres a suboxic zone that in most cores was just a few decimetres thick the exception was a core obtained in an area of strong turbulent currents and an underlying anoxic zone with dop values of around 60 pyritic iron increased at the expense of the hcl extracted fraction in approximately the top metre but no further pyrite formation occurred at greater depths pyrite formation in these lower levels was not limited by lack of either hcl extracted iron or metabolizable organic matter but apparently by lack of sulphate ion the diffusion of which to these depths was probably prevented by the fine texture of the sediments our findings highlight the interest of studying transitional sedimentary environments in order to explore in detail the geochemical parameters controlling pyrite formation

shallow gas charged sediments off the indian west coast genesis and distribution abstract geophysical and geochemical surveys were carried out off goa central west coast of india to understand the genesis and distribution of shallow gases in marine sediments shallow gas charged sediments within the water depths of 15 to 40 m are reported all along the west coast and are characterized by gas masking high amplitude and reverse polarity reflections in high resolution seismic sparker data attributed to the presence of free gas these high amplitude reflections gas front are observed within a holocene fine grained wedge shaped sediment package overlying the maximum flooding surface the gas front lies between 1 2 and 5 m below the seabed and demarcates the transition from gas in the dissolved phase to bubble phase when the gas concentration exceeds the saturation level the observed and extrapolated sulfate methane transition zone smtz lies between 0 7 and 2 25 m below the seabed and it is related to the depth of the gas front methane concentration reaches saturation below the smtz and produces a bubble phase which lowers the p wave velocity and produces high amplitude reflection observed in the seismic data depleted carbon isotope ratios as low as 88 9 suggest a microbial origin for the methane in the study area high sulfate reduction rate high concentrations of pore water methane phosphate and ammonium in the shallowest site sasu123 1 at 14 7 m water depth suggest an enhanced availability of reactive organic matter required for microbially mediated biodegradation processes high gas flux in the shallow waters is also indicated by the shallowing of the gas front and the widening of the gas masked zone towards shore the present investigations do not testify the origin of holocene shallow gases either from buried channel deposits or the pleistocene sediments

modeling the residual circulation of a coastal embayment affected by wind driven upwelling circulation of the ria de vigo nw spain 1 the barotropic and baroclinic nontidal circulations of the ria de vigo nw spain are studied using the three dimensional finite difference model hamsom hamburg shelf ocean model the external forcing acting on the system includes winds freshwater inflow in the inner part of the ria and all over its surface and heat exchange with the atmosphere modeled velocity is compared with data from an aanderaa dcm12 acoustic doppler current meter at one site of the ria and predicted salinity and temperature fields contrasted with seabird conductivity temperature depth data along the main channel of the ria all predicted current salinity and temperature fields are in good agreement with experimental data a new residual circulation pattern of the ria de vigo and its dependence on coastal winds is described according to this pattern the typical estuarine two layer circulation overlays in the outer part of the ria with a lateral circulation resulting in a three dimensional dynamics the lateral circulation is induced by interaction between the southward northward alongshore coastal jet associated with upwelling downwelling winds and the topographic configuration of the ria

reinterpretation of the quaternary sedimentary infill of the ria de vigo nw iberian peninsula as a compound incised valley abstract seismic data have been used to investigate the stratigraphy of the galician rias for more than two decades here we present a new interpretation of the sedimentary infill of an incised valley ria de vigo nw iberian peninsula based on high resolution seismic profiles core sediment analysis and radiocarbon 14 c data the new data indicate that the stratigraphic architecture of the galician rias result from multiple incision infill phases and therefore they are reclassified as compound rather than simple incised valleys seven seismic units were identified one of tertiary age u 1 four of pleistocene age u 2 u 5 which are interpreted as 4 th order sequences deposited between mis 11 and mis 2 and late pleistocene u 6 and holocene u 7 units corresponding with post glacial sedimentation the sedimentary infill overlies a highly faulted irregular granitic and metamorphic basement the inherited morphology is shown to be important for controlling the pathway and evolution of the fluvial network as well as preservation of the sedimentary deposits during several glacial interglacial cycles the presence of a rocky barrier at the mouth of the ria is a distinctive feature that conditions sedimentation and exchange of sediment between the ria and the adjacent shelf for the first time faults and tilted blocks affecting late pleistocene mis 3 deposits have been identified the new data presented here provide the opportunity to reconstruct the evolution of the sedimentary infill of a ria with especially high resolution during the last post glacial transgression

the holocene gas system of the ria de vigo nw spain factors controlling the location of gas accumulations seeps and pockmarks abstract high resolution seismic profiles cored sediment gravity cores and vibro cores and radiocarbon data from suitable shell material were used to establish the stratigraphic context of gassy sediments in the ria de vigo mapping of seeps and pockmarks were compared with the stratigraphy of gassy sediment to ascertain the relationships in the ria de vigo three holocene seismic units were identified the first two uh 1 and uh 2 correspond to the transgressive systems tract tst and the third uh 3 corresponds to the highstand systems tract hst the presence of acoustic turbidity within the three seismic units indicates that generation of gas took place during the relative sea level rise that occurred after the younger dryas event i e during the tst and mainly during the hst the relative sea level variations are shown to be a major factor controlling the type fine vs coarse grained and distribution of facies lateral and vertical that generate and or allow gas accumulation or escape acoustic turbidity due to presence of free gas was recognized in the three holocene units with a total of 12 acoustic turbidity fields mapped in the ria de vigo no significant variations in the spatial distribution or extent of the gas fields or in their vertical location below the present sea bed have been observed during the seismic surveys carried out in the ria during the last decade furthermore gas escape from the sediment and active pockmark has been observed therefore we conclude that gas escape seeps pockmark generation and maintenance and methane formation are in equilibrium the combined analysis of high resolution seismic profiles sediment temperature pore water salinity and hydrostatic pressure revealed 1 a direct relationship between depth of free gas and hydrostatic pressure and 2 a direct link between sediment temperature and number of acoustic plumes from seabed to water column more acoustic plumes were detected in summer when the temperature of the sediment was higher than in winter indicating a seasonal variation of seeps within the ria salinity showed no significant differences between sea bottom water and sediment pore water and was therefore not a major factor controlling gas front variations

formation and evolution of the badain jaran desert north china as revealed by a drill core from the desert centre and by geological survey abstract the deserts in north china are regarded as direct records of the process of inland asian aridification amongst these deserts those proximal to the chinese loess plateau clp are especially important because of their role as sediment source areas in order to investigate the formation history of the badain jaran desert the largest desert proximal to the clp a 310 m long drill core was obtained from the desert centre which reached the underlying basement rock the lithology of the core consists of an upper layer of aeolian sand with three intercalated layers of lacustrine sediments overlying alluvial fluvial deposits which are developed unconformably over red coloured basement rock a geological survey indicates that the lower red coloured basement rock is of late cretaceous age and is cut by a mesozoic erosion surface widely developed over the badain jaran area on the basis of optically stimulated luminescence and electron spin resonance dating and stratigraphic correlation a preliminary chronological framework was established which was improved by tuning the aeolian sand proportion of the drill core to earth orbital obliquity and precession this final chronology suggests that 1 the basal age of the desert strata is at least 1100 ka corresponding to the formation of the badain jaran desert and 2 that the formation of the erosion surface terminated and the surface had begun to subside by at least 1200 ka the formation of the desert can be summarized as follows the alluvial fluvial fan formed by the heihe river draining the qilian mountains provided sufficient sedimentary material to form the desert under an arid climate while the asian winter monsoon and the westerlies entrained the clastic sediments from the fan area which finally accumulated downwind more distant sediment transport was prevented by the intervening mountainous terrain these coupled processes were driven by tibetan plateau uplift and ongoing global climatic cooling after initial formation of the desert three humid phases occurred in mis 13 15 mis 5 and the holocene during which extensive lakes developed the sequential drying out of the lakes may reflect inter relationships between global climate and the intensity of the asian summer monsoon and the westerlies

assessing sulfate reduction and methane cycling in a high salinity pore water system in the northern gulf of mexico pore waters extracted from 18 piston cores obtained on and near a salt cored bathymetric high in keathley canyon lease block 151 in the northern gulf of mexico contain elevated concentrations of chloride up to 838 mm and have pore water chemical concentration profiles that exhibit extensive departures concavity from steady state linear diffusive equilibrium with depth minimumd 13 c dissolved inorganic carbon dic values of 55 9 to 64 8 at the sulfate methane transition smt strongly suggest active anaerobic oxidation of methane aom throughout the study region however the nonlinear pore water chemistrydepth profiles make it impossible to determine the vertical extent of active aom or the potential role of alternate sulfate reduction pathways here we utilize the conservative non reactive nature of dissolved chloride to differentiate the effects of biogeochemical activity e g aom and or organoclastic sulfate reduction relative to physical mixing in high salinity keathley canyon sediments in most cases the dic and sulfate concentrations in pore waters are consistent with a conservative mixing model that uses chloride concentrations at the seafloor and the smt as endmembers conservative mixing of pore water constituents implies that an undetermined physical process is primarily responsible for the nonlinearity of the pore water depth profiles in limited cases where the sulfate and dic concentrations deviated from conservative mixing between the seafloor and smt the d 13 c dic mixing diagrams suggest that the excess dic is produced from a 13 c depleted source that could only be accounted for by microbial methane the dominant form of methane identified during this study we conclude that aom is the most prevalent sink for sulfate

environmental changes at the inner sector of ria de muros nw spain during middle to late holocene abstract a multiproxy approach has been performed on sediments collected by gravity and box coring at the inner part of the ria de muros to reconstruct its environmental evolution since the middle holocene this reconstruction is based on the chronological framework provided by radiocarbon dating of foraminifera samples three distinct facies were identified in the sedimentary record the oldest characterised by coarse grained sediments and a strong terrestrial signature is likely linked to the progradation of the delta fan of the maior river during a period of standstill subsequent to the holocene sea level maximum ca 6900 cal yr bp the second facies started to deposit approximately 2865 335 cal yr bp and is characterized by the deposition of finer grained marine influenced sediments linked to a period of reduced local hydrodynamic energy most likely due to a progression of sea level rise the third facies started to deposit approximately 1720 180 cal yr bp and shows a progressively stronger marine influence the characteristics of the last facies are explained as the result of the added effects of progressive sea level rise and an intensified upwelling reaching the inner ria this facies shows clear anthropogenic features since 555 65 cal yr bp associated with the important mediaeval development of the area the obtained results suggest that high resolution studies are key to resolve possible sea level oscillations during the late holocene and allow distinguishing local regional changes superimposed to the global signals

geochemical and microbial context of the gassy sediments in the ria de vigo nw of spain abstract multidisciplinary data coming from high resolution seismic profiles gravity core analysis sedimentology and geochemistry radiocarbon dating and metagenomics has been used to establish the stratigraphic framework as well as the geochemical and microbial context of the gassy sediments in the ria de vigo gas appears within the muddy sediments that compound the youngest holocene seismic unit of the infilling of the ria and is mainly methane generated by microbial decomposition in a rich organic matter depositional environment within the ria the biogeochemical zonation is affected by the quality quantity and age of the buried organic matter the 16s ribosomal rna gene amplicon clone libraries sequencing suggests that prokaryotic composition may be linked to the sediment type uncultured archaea common to the marine sub sea floor of the miscellaneous crenarchaeotal group mcg and marine benthic group d mbgd are dominant in these organic rich estuarine and shallow marine sediments the presence of methanomicrobia and anme in the sulphate methane transition zone smtz from the estuarine gassy area indicates anaerobic oxidation of methane aom in these sediments desulfobacteraceae are also homogeneously distributed along the sediment columns even in the methanogenic zone suggesting the existence of a cryptic sulphur cycle driven by iron under the smtz the older sediments retrieved from the non gassy outer area of the ria contain less organic matter and appear to represent mainly a sulphate reducing environment where smtz is not yet reached at the bottom of the sediment core methanogens of various affiliations and traces of methane are detected in this sulphate reducing environment with an unusual increase in concentration towards the sediment surface microbial methanogenesis in the sulphate reducing zone of surface sediments a process recently described in organic rich sediments able to supply methanogenic substrates could reconcile these observations

influence of the tibetan plateau and its northern margins on the mid latitude westerly jet over central asia in summer abstract the upper troposphere westerly jet is currently maintained in the mid latitudes of central asia during summer the strength and movement of which are closely related to the variations in precipitation in arid central asia however little is known about how this westerly jet has changed during the cenozoic although it is known that the tibetan plateau has a crucial role in the modern asian climate we conducted a set of numerical experiments to examine the effects of the tibetan plateau and the topography of its northern margins the pamir plateau the tian shan mountains and the mongolian plateau on the westerly jet in summer the mid latitude westerly jet is significantly intensified with the uplift of the tibetan plateau the center of the jet stream moves about 1 to the north this strengthening and shift in the westerly jet are primarily due to the strong atmospheric heat source induced by the uplift of the tibetan plateau with the inclusion of the pamir plateau and tian shan mountains the westerly winds in the northern axis of the jet are strengthened while the southern part is weakened resulting in a continuous northward shift in the westerly jet stream similar to the effects of the tibetan plateau anomalous diabatic heating appears with the inclusion of the pamir plateau and tian shan mountains and the intensity of the westerly jet is slightly weakened the westerly jet is also weakened but stops moving northward when the mongolian plateau is uplifted this is a result of continuous northward warming the mid latitude westerly jet therefore experienced distinct changes during the cenozoic in association with the development of the atmospheric heat source in summer as a result of the stepwise uplift of the tibetan plateau tian shan mountains and mongolian plateau this may have influenced the aridity of the asian interior and the transport of eolian dust

paleocurrent and fabric analyses of the imbricated fluvial gravel deposits in huangshui valley the northeastern tibetan plateau china abstract gravel deposits on fluvial terraces contain a wealth of information about the paleofluvial system in this study flow direction and provenance were determined by systematic counts of more than 2000 clasts of imbricated gravel deposits in the xining region northeastern tibetan plateau china these gravel deposits range in age from the modern huangshui riverbed to miocene aged deposits overlain by eolian sediments our major objectives were not only to collect first hand field data on the fluvial gravel sediments of the xining region but also to the reconstruct the evolution of the fluvial system these data may offer valuable information about uplift of the northeastern tibetan plateau during the late cenozoic era reconstructed flow directions of the higher and lower gravel deposits imply that the river underwent a flow reversal of approximately 130 180 in addition the lithological compositions in the higher gravel deposits differ significantly from the lower terraces suggesting that the source areas changed at the same time eolian stratigraphy overlying the gravel deposits and paleomagnetic age determination indicate that this change occurred sometime between 1 55 ma and 1 2 ma we suggest that tectonic activity could explain the dramatic changes in flow direction and lithological composition during this time period therefore this study provides a new scenario of fluvial response to tectonic uplift a reversal of flow direction in addition field observation and statistical analyses reveal a strong relationship between rock type size and roundness of clasts

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

towards understanding the early gondwanan margin in southeastern australia abstract this review synthesizes the proterozoic and early paleozoic geology of tasmania bass strait and western and central victoria we examine the many different conflicting hypotheses that have been proposed to solve the paradoxical relationships between tasmanian geology and that of mainland australia most notably the prevalence of proterozoic basement of western and central tasmania while immediately across bass strait evidence of proterozoic rocks is much more cryptic we conclude that the selwyn block model is the most satisfactory hypothesis to date since it fits best with the obvious patterns in the magnetic and gravity data this model proposes that the central victorian melbourne zone is underlain by the northern extension of thin tasmanian proterozoic and cambrian crust under bass strait and that the silurian to middle devonian melbourne zone was shortened along a decollement during the tabberabberan orogeny the ordovician rocks of eastern tasmania correlate more closely with the tabberabbera zone than the melbourne zone in victoria however the silurian and devonian correlations are less certain major unresolved issues are the origins of the proterozoic and early cambrian lithostratigraphic packages tectonic models for their assembly during the tyennan orogeny and how these models fit with those for mainland australia

timing of orogenic gold mineralisation in northeastern tasmania implications for the tectonic and metallogenetic evolution of palaeozoic se australia new 40ar 39ar data from sedimentary rock hosted orogenic gold deposits in northeastern tasmania constrain most ore formation to between 395 ma and 385 ma these 385 395 ma ages for the formation of orogenic gold agree well with an inferred early to middle devonian timing for peak deformation and folding across much of northeastern tasmania data from micas within alteration halos in some deposits give dates of 420 430 ma these dates confirm the occurrence of an earlier silurian phase of deformation and suggest that at least some of the mineralisation was possibly generated during this event gold mineralisation hosted by middle devonian post tectonic granites may be genetically related to magmatism following orogeny but these deposits formed virtually synchronously with peak deformation related systems early to middle devonian deformation in northeastern tasmania also reactivated older structures in western tasmania and the formation of quartz vein hosted gold mineralisation there based on geological structural tectonic and metallogenetic similarities northeastern tasmania is interpreted as a lateral equivalent of the turbidite dominated fold thrust belt of the western lachlan orogen however unlike victoria where the sedimentary rock sequence developed on oceanic crust northeastern tasmania was probably underlain by thinned proterozoic crust either as part of a promontory along the gondwana margin or as a microcontinental fragment this may have protected the palaeozoic succession from large scale pre devonian orogeny with collision not beginning until the middle devonian these variations in the structural and tectonic evolution and the timing of deformation and ore formation can explain the difference in contained gold and the distribution and number of major orogenic gold deposits within the palaeozoic of northeastern tasmania

gas charged sediments in the ria de arousa short to long term fluctuations repeated surveys at control sites in the gas accumulation fields from the ria de arousa galicia nw spain have shown that the top of the acoustic turbidity fluctuates vertically the vertical movement of gas fronts is more apparent in the gas fields located in the outer ria where fluctuations of up to 1 5 ms 1 1 m have been detected at the inner ria the depth to the top of the gas horizons varied between 0 5 and 1 ms 40 to 80 cm short term diurnal fluctuations associated with the hydrostatic pressure variations of the water column during a tidal cycle have been identified as the most likely factors to explain fluctuations of gas fields in the outer ria at the inner ria gas fields are affected by these short term pressure changes superimposed on long term temperature and salinity variations of bottom water masses this combination produces a different pattern of variation in gas fields from the inner and the outer ria prominent pockmarks and acoustic plumes have also been monitored throughout the three seismic surveys many of these pockmarks exhibit active characteristics including the observance of plumes of escaping fluids and sediment

stratigraphic evidence for the uplift of the tibetan plateau between 1 1 and 0 9 myr ago uplift of the tibetan plateau is manifest not only in widespread denudation but also by an increased deposition rate of sediment near or far from the exhumed regions our results indicate that the mass accumulation rate mar of eolian dust increased between 1 1 and 0 9 myr ago we associate this increase in mar and median grain size with uplift of the tibetan plateau and its adjacent regions during this period this middle pleistocene uplift can also be evidenced by the age of volcanism in the marginal region the existence of thick conglomerate deposits surrounding the uplifted plateau and the increased sedimentation rate of lacustrine deposits in the qaidam basin northeastern tibetan plateau between 1 1 and 0 9 myr ago the correlation between the loess and marine records indicates that after 0 9 myr ago these two records correlate well this good correlation probably suggest that the middle pleistocene upheaval event not only brought the plateau into the cryosphere but also enhanced the coupling of regional scale chinese loess transportation and deposition to the global ice volume variations through its effects on glacial grinding rock denudation and east asian monsoonal circulation

a seeping sea floor in a ria environment ria de vigo nw spain the occurrence of gas accumulations in the ria de vigo nw spain have been characterized by the authors in previous research pockmarks frequently appear on seismic and sonar records covering ca 45 of the sea floor of the study area which indicates that gas expulsion is not an uncommon phenomena in the coastal ria environment here we report the occurrence of gas seepage for the first time along the coast of nw spain side scan sonar echo sounder and high resolution seismic techniques were used for mapping gas expulsion features some expulsion pockmarks sit over elongated features that represent bottom marks created by anthropogenic activity thus these anthropogenic sites may act as preferential venting zones for gas as well as being potential hazards on a muddy sea bed such as that of the ria where gas accumulates just below the surface of the sea floor

quaternary paleoenvironmental change on the tibetan plateau and adjacent areas western china and western mongolia abstract this paper summarises the nature of climatic change during the last glacial interglacial cycle on the tibetan plateau and adjacent areas the results are derived from inland glacier fluctuations lake level changes and dust loess records of central asia including tibet these are based on our field investigations from 1988 to 1998 and literature surveys the changing extents of different climatic controlled geomorphic landscapes and vegetation zones help to provide estimates of the magnitude of climatic change features such as ice wedge casts loess and palaeosols ela reconstruction s and palaeobotanical data are used to help reconstruct palaeoprecipitation and palaeotemperatures weathering characteristics the overlying strata and some luminescence dates indicate that there are two main glacial ice advances during the last glacial cycle these correspond to marine oxygen isotope stages ois 2 and 4 in some areas as the eastern or northern margin of the tibetan plateau remnants of older glaciations are preserved higher lake levels in the deserts of central asia and on the tibetan plateau are dated to 40 to 25 ka ois 3 and to late glacial early to mid holocene periods our work supports the view that in many areas of central asia cold phases during the last glacial correspond with the maximum extent of glaciers and the periglacial activity the last glaciation produced large alluvial fans alternating with periods of high lake stands on the tibetan plateau however at the northern margin of the plateau in the qaidam basin and in some particular desert areas in western china high lake levels occurred also during the pleistocene and are related with alluvial fans

geochemical characteristics of lake clay drilled in well qz 4 its implication for geochemical response to climate change in the central tibetan plateau in the middle late pleistocene a colour sequence which is composed of a yellow subsequence in the lower unit and a grey subsequence in the upper unit is an important climate archive for the central tibetan plateau in the middle late pleistocene however little study has been done on it in well qz 4 this colour sequence is thicker than 116 m which is an important climate archive for the central tibetan plateau in the middle late pleistocene in this work the esr dating and geochemistry analysis have been carried out to provide a preliminary insight into the paleo climate change in the central tibetan plateau it can be concluded that the 23 56 ka 125 96 149 52 ka bp time interval which is marked by the angular unconformity surface at 272 48 m in depth proves that the deposition of this colour sequence is dominated by gonghe movement after this movement chemical weathering is reduced however the sedimentation rate is increased from 0 18 to 3 5 m ka in the central tibetan plateau the climate became colder and drier in the middle late pleistocene which is roughly consistent with global paleo climate change at that time all these changes are correlated with the change of elevation and atmospheric circulation in the tibetan plateau and its surrounding area which are driven by the tectonic uplift of gonghe movement the gonghe movement is likely a driving force for the short lived spike at about 120 ka

uplift of the tibetan plateau and its environmental impacts qin dahe chinese acad sci cold arid reg environm engn res inst state key lab cryospher sci lanzhou 730000 peoples r china

gaia s breath global methane exhalations abstract methane ch 4 is the most abundant organic compound in the earth s atmosphere where it acts as a greenhouse gas and thus has implications for global climate change the current atmospheric ch 4 budget however does not take into account geologically sourced ch 4 seepage geological sources of ch 4 include natural macro and micro seeps mud volcanoes and other miscellaneous sources such as gas hydrates magmatic volcanoes geothermal regions and mid ocean ridges macro seeps contribute 25 tg teragrams ch 4 yr to the atmosphere whereas micro seepage contributes perhaps 7 tg ch 4 yr mud volcanoes emit 5 tg ch 4 yr and miscellaneous sources emit 8 tg ch 4 yr to the atmosphere thus the total contribution to the atmosphere from geological sources is estimated to be 45 tg ch 4 yr which is significant to the atmospheric organic carbon cycle and should be included in any global inventory of atmospheric ch 4 we argue that the atmospheric ch 4 global inventory of the interplanetary panel on climate change must be adjusted in order to incorporate geologically sourced ch 4 from naturally occurring seepage

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