longwavelength gravity anomalies and the deep thermal structure of the baikal rift the analysis of the gravity field over the baikal rift area has been carried out in order 1 to detect the amount of the deep hot material and 2 to constrain the flexural rigidity of the lithosphere we removed a few first harmonics of the global field and the gravity effects due to the crust from the observed field and found a residual anomaly which is aligned with the rift this residual which we attribute to the mantle shows a minimum of about 15 mgal in amplitude and 900 km in width which is superimposed over a wider minimum with smaller amplitude a model involving a simple stretching of the lithosphere with diffusion of heat predicts right order of magnitude for both the amplitude and the wavelength of the 900 km anomaly our results confirm that the stretching factor is of the order of 1 2 to 1 5 interpretation of the coherence function computed between gravity and topography shows that the lithosphere in the area has a significant equivalent elastic thickness of about 30 km i e flexural rigidity about 2 3 1023n m

cryoturbation versus tectonic deformation along the southern edge of the tunka basin baikal rift system siberia new insights from an integrated morphotectonic and stratigraphic study the tunka basin is a broad emerging basin situated between the baikal lake to the east and the the hovsgol lake to the west the basin is bounded to the north and to the south by the tunka and the khamar daban mountain ranges respectively the tunka normal fault located at the southern foothills of the tunka mountain range is the main structure that controlled the development of the tunka basin during the neogene paleoearthquake surface ruptures attest of its present activity and show that its western and eastern terminations are undergoing a tectonic inversion characterized by left lateral reverse deformations the southern edge of the tunka basin is classically interpreted as being tectonically controlled in this paper we present the results of a geomorphological and stratigraphic analysis within its southwestern and southeastern parts suggesting that there is no active fault affecting the foothills of the khamar daban mountain range the different features observed in the quaternary deposits are interpreted to be the result of periglacial processes induced by alternating episodes of permafrost aggradation and degradation during the holocene our study concludes that the khamar daban range and the tunka basin are uplifting together and that the tunka and mondy faults are the two main triggers of regional earthquakes

geometry and rate of faulting in the north baikal rift siberia we present a detailed morphotectonic analysis of late quaternary faulting in the north baikal rift nbr a region characterized by ranges and basins distributed over more than 800 km along strike in eastern siberia remote sensing techniques spot meteor scenes and aerial photographs are used to map the active fault network which displays a general en echelon distribution from the northern lake baikal to the easternmost basin with 30 km spaced overstepping segments of 10 80 km in length most faults have a dominant dip slip component over their cenozoic history the inherited crustal fabric strongly influences the overall geometry of the rifted basins we use 54 14c ages of postglacial terraces near the foot scarps of the muya basin to date offsets measured inside alluvial fans the last main postglacial event in this area appears to be the early holocene optimum dated at 10 2 ka following the onset of deglaciation at 13 ka using these time constraints a detailed leveling across two terraces offset by the taksimo fault west muya basin shows consistent minimum vertical slip rates of 1 6 0 6 mm yr 1 using 30 other active scarps analyzed in the field we find a lower bound for horizontal velocity of 3 2 0 5 mm yr 1 across the nbr a rate close to the one found in the southern rift from global positioning system measurements we then compare directions of slip vectors from holocene field data and slip directions from earthquake fault plane solutions although local discrepancies appear the mean directions of lesser horizontal stress 3 inverted from theses values are n130 e and n155 e respectively which are comparable within uncertainties and favor a rifting obliquity of 30 40 extrapolating our holocene rates we estimate basin ages younger than those generally believed less than 7 ma and propose a spatial and temporal evolution of rifted basins consistent with experimental models of oblique rifting total amounts of extension and vertical throw 7 and 12 km respectively across major faults appear rather constant from the central to the northern rift these results favor a progressive development of asymmetric grabens in a rift zone that widens with times and they indicate a strong rheological control on deformation which seems enhanced by other contributions than the far field effects of the indo eurasian collision

the fluvial system research perspectives of its past and present dynamics and controls abstract during the conference the fluvial system past and present dynamics and controls held at the department of geography of bonn university from 16 to 22 of may 2005 the participants organised in 12 international organisations working in the fluvial environment were asked about their opinions about the main aspects to be considered for sustainable progress in future research projects the individual comments can be grouped by the following headlines integration and application of experiences considering system analytical approaches considering effects of climate and global change interdisciplinary work regarding extreme events and their frequencies and quantification of human impact detailed explanations and selected references of previous studies initially considering the mentioned aspects are given as a review

linking morphology across the glaciofluvial interface a 10be supported chronology of glacier advances and terrace formation in the garonne river northern pyrenees france abstract the garonne river drains an important part of the northern pyrenees and its northern foreland we investigated the middle reaches of the garonne river establishing a detailed morphogenetic profile of its foreland terrace staircase and the preserved palaeoglacier margins we particularly focussed on the glaciofluvial interface linking also genetically the fluvial sediment archives in the foreland with the terminal glacial basin upstream of the pyrenees mountain front using cosmogenic nuclide 10be analyses two terrace exposures have been dated including a prominent fluvioglacial outwash fan at the foreland transition we identified three terminal margins of late pleistocene glacier advances the prominent garonne staircase consists of three major terrace complexes comprising eight individual terrace levels results indicate a young age of the lower terrace complex of the garonne staircase mis 4 2 the morphogenetic relationships and the new 10be exposure age constraints suggest that during the last glaciation wurmian the garonne glacier reached its maximum extent at the north pyrenean mountain front apparently already during mis 4 two different ice margins were associated with mis 2 indicating close to maximum ice extent during early mis 2 lgm and relatively stationary ice recession in the late mis 2 the extensive garonne terrace complexes formed under cold climate conditions and were abandoned by incision during major glacial interglacial transitions during warm cold climate transitions lateral erosion caused the reworking of previously abandoned palaeofloodplains the long term quaternary incision of the garonne and other north pyrenean rivers indicates that the proximal aquitaine foreland basin experienced uplift however non uniform lateral course migrations and valley asymmetries of the north pyrenean piedmont rivers indicate that uplift magnitude is variable with maximum amounts in the centre of the molasse fan of lannemezan rivers on the western part of the fan were tilted toward the west whereas rivers in the eastern part like the garonne were tilted to the east

three dimensional seismic structure of the upper mantle beneath the central part of the eurasian continent summary this work is a study of the upper mantle seismic structure beneath the central part of the eurasian continent including the northern mongolia altai and sayan orogenic areas and the baikal rift zone seismic velocity models are reconstructed using the inverse teleseismic scheme this scheme uses information from earthquakes located within the study area recorded by the worldwide network the seismic anomaly structure is obtained for diverent volumes in the study area that partially overlap one another special attention has been paid to the reliability of the results several noise and resolution comparisons are made the main results are as follows 1 a cell structure of anomalies is observed beneath the altai sayan region positive cold anomalies correspond to regions of recent orogenesis negative anomalies are located beneath the depression of the great lakes in mongolia and hubsugul lake 2 a large negative anomaly is observed beneath the hangai dome in mongolia 3 strong velocity variations are obtained in a zone around baikal lake a large negative anomaly is traced beneath the southern margin of the siberian craton down to a depth of 700 km contrasting positive anomalies 4 5 per cent are observed at a depth of 100 300 km beneath the baikal rift our geodynamical interpretation of the velocity structure obtained beneath central asia involves the existence of two processes in the mantle thermal convection with regular cells and a narrow plume beneath the southern border of the siberian plate

crustal structure of the siberian craton and the west siberian basin an appraisal of existing seismic data abstract we present a digital model sibcrust of the crustal structure of the siberian craton sc and the west siberian basin wsb based on all seismic profiles published since 1960 and sampled with a nominal interval of 50 km data quality is assessed and quantitatively assigned to each profile based on acquisition and interpretation method and completeness of crustal model the database represents major improvement in coverage and resolution and includes depth to moho thickness and average p wave velocity of five crustal layers sediments and upper middle lower and lowermost crust and pn velocity maps and cross sections demonstrate strong crustal heterogeneity which correlates weakly with tectono thermal age and strongly with tectonic setting sedimentary thickness varies from 0 3 km in stable craton to 10 20 km in extended regions typical moho depths are 44 48 km in archean crust and up to 54 km around the anabar shield 40 42 km in proterozoic orogens 35 38 km in extended cratonic crust and 38 42 km in the west siberian basin average crustal vp velocity is similar for the sc and the wsb and shows a bimodal distribution with peaks at ca 5 4 km s in deep sedimentary basins and 6 2 6 6 km s in parts of the wsb and sc exceptionally high basement vp velocities 6 8 7 0 km s at the northern border between the sc and the wsb indicate the presence of magmatic intrusions and are proposed to mark the source zone of the siberian lip the cratonic crust generally consists of three layers and high velocity lowermost crust vp 7 4 km s is observed only locally pn velocities are generally 8 2 km s in the sc and wsb and abnormally high 8 6 8 9 km s around kimberlite fields we discuss the origin of crustal heterogeneity and link it to regional crustal evolution

a microseismic study in the western part of the gulf of corinth greece implications for large scale normal faulting mechanisms summary we present the results of a dense seismological experiment in the western part of the gulf of corinth psathopyrgos aigion area one of the most active rifts in the aegean region for which we have precise tectonic information the network included 51 digital stations that operated during july and august 1991 covering a surface of 40 x 40 km2 among the 5000 recorded events with ml ranging between 1 0 and 3 0 we precisely located 774 events we obtained 148 well constrained focal mechanisms using p wave first motions of these 60 also have mechanisms obtained by combining the p wave first motions with the s wave polarization directions the observed seismicity is mainly located between 6 and 11 km depth most of the fault plane solutions correspond to e w striking normal faulting in agreement with the geological evidence most of the well determined mechanisms indicate a nodal plane dipping 10 25 due north and a steep south dipping plane a similar asymmetry is also seen in the seismicity distribution and in the overall geological structure of the corinth rift we discuss this evidence and the inference of a deep detachment zone a structure where the major faults seen at the surface appear to root a large part of the microseismic activity appears to cluster in regions near the junctions of the main faults with the proposed detachment zone this feature of the microseismicity is interpreted in terms of stress transfer and stress concentration in regions of probable nucleation of future large earthquakes

climatic vs tectonic controls on peat accretion in non marine setting an example from the žacleř formation yeadonian bolsovian in the intra sudetic basin czech republic abstract the acle coalfield in the western part of the intra sudetic basin is an example of coal accumulation in an alluvial valley deposited under a long term 3 m y stable tectonic regime with climatic oscillations possibly operating on several time scales the resulting sedimentary record about 600 m thick encompasses about 60 coal bearing cycles formed in a relatively small and localized part of the valley whereas elsewhere a higher clastic input and or lower rate of subsidence resulted in deposition of strata with very little coal available data suggest that tectonics produced accommodation for sediments and via changes in topography and or size of the source area affected the volume and dispersal patterns of clastic material transported to the depocentre areas with long term tectonic stability were suitable places for recognition of climatic signals in the sedimentary record modified by the intensity of local clastic input climatic fluctuations generated coal bearing cycles probably through a variable intensity of precipitation which affected the density of vegetation cover across the landscape along with evaporation and groundwater table these factors influenced the intensity of chemical weathering and hence regulated the volume and composition of clastics delivered to the depocentre this in turn resulted in alternation of short periods of bedload dominated deposition during the seasonally dry part of the cycle with periods of dominantly suspended load and organic peat deposition during the more humid everwet part of the cycle estimated duration of the basic cycles 46 k y approximates the orbitally driven axial tilt cyclicity basic cycles are arranged into two larger scale cyclic patterns lasting for 270 k y and 1 5 m y respectively which broadly correspond with the timing of glacial maxima and minima inferred from high latitude glacial deposits of gondwanan basins all the coals of the acle coalfield display similar petrographic composition dominated by collotelinite and field observations as well as detailed petrographic study show that they formed in planar rheotrophic peat swamps where long lasting peat accretion was episodically interrupted only by major floods on a century to millennial scale

differentiating pleistocene tectonically driven and climate related fluvial incision the sanggan river datong basin north china the sanggan river is an alluvial river flowing through a graben basin system of the northern shanxi rift zone north china during pleistocene times the river reach in the datong basin was affected successively by various external variables such as invasion by basaltic flow along valley faulting and climatic change therefore it provides excellent constraints for differentiating tectonically driven and climate related fluvial incision in the context of tectonic subsidence based on equilibrium profile analysis k ar dating of basalts 0 74 0 41 ma studies of the river terrace and of stream action history we present a conceptual model for differentiating fault driven and climate related fluvial incision by the river the results show that fluvial incision induced by tectonic lowering of the base level due to along valley movement on the sanggan river fault is equal to fault displacement the amount of post basalt fluvial incision of the reach upstream from the lava dam is 23 to 25 m of which the fault driven and climate related incisions are 15 m and 8 to 10 m respectively the former predominating over the latter the total amount of incision in the lava dam reach is 40 to 47 m of which the fault driven and climate related incisions are 10 m and 30 37 m respectively here the latter is predominant over the former since 0 41 0 10 ma the rate of fluvial incision of the lava dam reach of the river has reached 98 115 m ma which is 1 5 2 times as great as those of the reaches upstream and downstream from the lava dam the higher rate of fluvial incision can be attributed to high water levels supplied by the onset and maintenance of backwater conditions in the reach upstream from the lava dam due to the long period of warm and humid climate in this region plucking abrasion and knickpoint migration appear to be the primary erosional processes in the lava dam reach

controls on gravel termination in seven distributary channels of the selenga river delta baikal rift basin russia the selenga river delta lake baikal russia is 600 km2 in size and contains multiple distributary channels that receive varying amounts of water and sediment discharge the delta is positioned along the deep water 1600 m margin of lake baikal a half graben styled rift basin qualifying it as a modern analogue of a shelf edge delta system this study provides a detailed field survey of channel bed sediment composition channel geometry and water discharge the data and analyses presented here indicate that the selenga delta exhibits downstream sediment fining over tens of kilometers ranging from predominantly gravel coarse pebble and sand near its apex to silt and sand at the delta lake interface we developed an analytical framework to evaluate the downstream elimination of gravel within the multiple distributary channels the findings include the following 1 the selenga river delta consists of at least eight orders of distributary channels 2 with increasing channel order downstream channel cross sectional area width depth ratio water discharge boundary shear stress and sediment flux systematically decrease 3 the downstream elimination of gravel in distributary channels is caused by declining boundary shear stress as a result of water discharge partitioning among the bifurcating channels 4 over longer time scales gravel is contained on the delta topset due to frequent and discrete seismic events that produce subsidence and accommodation so that coarse sediment cannot be transported to the axis of the baikal rift basin the distribution of sediment grain size in deltaic channels as related to hydrodynamics and sediment transport plays a critical role in influencing stratigraphy because the sustained tectonism leads to high preservation potential of the delta topset sedimentary deposits therefore the selenga river delta provides an opportunity to explore the interactions between modern deltaic sedimentation processes and tectonics that affect the production of basin stratigraphy

interpreting drivers of change in fluvial archives of the western mediterranean a critical view abstract fluvial archives in particular late glacial to holocene floodplain records may provide valuable information regarding past environmental conditions and stages of landscape evolution in view of the high significance of floodplain dynamics for the development of entire landscapes the number of studies that have been performed on floodplain sediments remains comparatively low especially regarding the western mediterranean region however one of the reasons could be seen in the high complexity and diversity of processes and factors that control and influence fluvial activity that often hampers a straightforward interpretation of floodplain dynamics therefore a basic demand on fluvial archive research is to address the complexity of the factors that control the characteristics of fluvial sequences in order to provide a robust basis for their interpretation as a starting point for discussion this paper aims to give an overview of fluvial dynamic patterns in the western mediterranean for the last 15 ka in order to examine their relevance for palaeoenvironmental reconstructions the basis for this is provided by previous investigations on four different river systems in spain and northern africa the results of which are herein synthesized in order to propose a regional late pleistocene and holocene fluvial history for the western mediterranean realm basic results are related to alluvial floodplain deposits and visible features within them such as alluvial soils incision marks and aggradation phenomena since fluvial systems are open systems we discuss our findings against the background of different influencing factors that could modify fluvial architecture and may restrict palaeoenvironmental reconstructions a more comprehensive interpretation focuses on signals that are common to each of the studied river systems in this respect we critically discuss the customary nature of cumulative probability functions for the identification of regional flooding episodes and point out the benefits of a stratigraphy supported approach for characterizing regional floodplain dynamics finally three alluvial soil formation periods were found in all settings a first phase after 15 ka ending with the younger dryas event a second one from 7 to 5 ka with a break between 6 5 and 5 5 ka and a third phase between 3 and 2 ka these soil formation periods were interrupted and framed by fluvial dynamic phases accompanied by channel aggradation floodplain deposition floodplain erosion and or river incision in particular after 5 ka around 1 6 and at 1 ka and during the little ice age lia floodplain aggradation affected river systems in iberia and northern africa as well a cautious assessment of these results and extensive comparisons with secondary archive information prompts us to relate the aggradation periods with climate forcing by means of a supra regional aridification that effected large areas of the western mediterranean in contrast the three mentioned soil formation periods can be linked with landscape stability most probably triggered by favorable climate conditions in the western mediterranean apart from these large scale patterns we discuss the reliability of information emerging from floodplain records against the background of individualistic river behavior and self organization regarding future work we want to emphasize the great potential of yet rarely applied system oriented approaches that also attach importance to sub catchment dynamics as a link between catchment slopes and the main river floodplain

late glacial sedimentological and morphological changes in a lowland river in response to climatic change the maas southern netherlands the late pleniglacial and late glacial maas valley south of nijmegen contains four terraces three river systems are described based on the morphology of channel scars on these terrace surfaces and by sediment characteristics the river maas reacted to climatic warming at the start of the weichselian late glacial by changing its river system slowly from a braided system to a transitional phase between braiding and meandering and finally to a highly sinuous meandering system the maas reacted rapidly to the younger dryas climate deterioration by again establishing a braiding system at the onset of the holocene the river changed abruptly to a meandering river without a transitional phase the triggering factor for change in the maas river pattern is almost certainly the changing climate in the late glacial gradient lines on the terrace surfaces show that tectonic activity did not modify the morphology of the channels a division of the terraces is shown the morphological sedimentological and petrographical characteristics are presented and the linking of changing fluvial patterns with climatic changes or tectonic movements is discussed 1997 john wiley sons ltd

pliocene to quaternary deformation in south east sayan siberia initiation of the tertiary compressive phase in the southern termination of the baikal rift system the south east sayan area wof the lake baikal is subjected to a very complex tectonic setting where the extensional stress field of the baikal rift system meets the compressional stress field generated by the india asia collision further south using satellite images aerial photographs srtm dem field mapping of geomorphological structures and published neotectonics and geological data we show that most of the relief in the se sayan initiated during late pliocene pleistocene through compressive reactivation of inherited structures by late quaternary clockwise rotation of the compressive field generated strike slip faulting and local secondary extension still within a general compressional stress field we demonstrate that the formation of the small scale extensional basins within the east sayan range is not linked to general the extension in the baikal rift system nor to a possible asthenospheric plume acting at the base of the crust but rather to the rotation of small rigid tectonic blocks driven by the compression

quaternary depositional systems in northern lake baikal siberia abstract new high resolution seismic reflection data from northern lake baikal and detailed land based morphological and sedimentological data reveal a variety of coarse grained deposits in the northern baikal rift each depositional facies is assigned to a specific structural domain alluvial fans onshore and small fan deltas offshore dominate the western border fault flank glacial deposits onshore and large glacio lacustrine fans offshore characterize the eastern flexural margin in the north the axial rift termination comprises a large fluvial delta this distinct pattern of depositional environments reflects the pronounced asymmetry of the rift and emphasizes the role of rift structure in controlling drainage and the location and type of rift basin fill climate however exerts a profound influence on the generation and availability of coarse grained material this is best documented along the eastern rift margin where pleistocene valley glaciers advanced at 50 40 35 and 26 13 ka from th

the formation of proval bay as an episode in the development of the baikal rift basin a case study abstract this paper provides a cumulative review of important specific features in the formation and development of proval bay lake baikal as a large seismic dislocation element this bay appeared during one of the largest historical earthquakes in siberia m lh 7 5 on january 12 1862 as a result more than 230 km 2 of the shore was submerged the paper considers the formation of proval bay in the context of analysis conducted on general morphological characteristics of the baikal rift and in terms of the occurrence of the main elements in the mechanism of its neotectonic development it is precisely these seismotectonic phenomena associated with the subsidence of large tectonic blocks which primarily cause the growth of lake baikal basin in spite of the fact that the northwestern side of the rift has a more pronounced morphological structure whose general elements are high and steep monolithic tectonic escarpments major lithospheric extension and its associated extension of the rift thinning and rearrangement of blocks in the upper lithosphere slab occur on the more gently sloping eastern side

palaeostress reconstructions and geodynamics of the baikal region central asia part i palaeozoic and mesozoic pre rift evolution abstract this paper presents the first palaeostress results obtained for the basement of the baikal rift system in southern siberia russia large scale structural analysis and palaeostress reconstructions show that the palaeozoic mesozoic kinematic history precursor of the baikal cenozoic rifting is characterized by the succession of six regional palaeostress stages stress inversion of fault slip data and earthquake focal mechanisms is performed using an improved right dieder method followed by rotational optimization d delvaux tensor program the results are interpreted in the light of recent developments in the investigation of regional intraplate stress field and used as additional constraints for palaeogeodynamic reconstruction of central asia after the final palaeozoic closure of the palaeo asian ocean on the southern margin of the siberian platform the marginal suture with the sayan baikal caledonian belt was repeatedly and preferentially reactivated during the subsequent palaeozoic and mesozoic history this suture zone also controlled the opening of the baikal rift system in the cenozoic the progressive closure of the palaeo asian and mongol okhotsk oceans generated successive continental collisions which were recorded in the baikal area by brittle ductile and brittle deformations the first two palaeostress stages correspond to the successive collage of precambrian microcontinents and caledonian terranes along the southern margin of the siberian platform 1 late cambrian early ordovician n s compression and 2 late silurian early devonian nw se compression the next two stages are related to the remote effects of the complex evolution of the western palaeo asian ocean southwest of the siberian continent 3 late devonian early carboniferous n s compression recorded only in the altai region and 4 late carboniferous early permian e w compression recorded both in the altai and baikal regions the last stages are the consequences of the mongol okhotsk oceanic closure 5 late permian triassic nw se extension with development of cordilleran type metamorphic core complexes and volcanism along the active margin of the mongol okhotsk ocean 6 initial development of early middle jurassic 10 15 km wide molassic basins in trans baikal and large foredeeps along the southern margin of the siberian platform in probable extensional context but for which no palaeostress data are available and 7 final closure of the mongol okhotsk ocean in the cretaceous this last event results from the collision between the mongol china and the siberian plates and is evidenced by the inversion of the middle mesozoic basins and by late jurassic early cretaceous coal bearing sedimentation in trans baikal this long tectonic history yielded a highly heterogeneous basement in the baikal area precursor of the cenozoic rifting

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

extensional basins of the former soviet union structure basin formation mechanisms and subsidence history abstract we review the structure and evolution of a number of riphean phanerozoic rifts and extensional basins within the territory of the former soviet union fsu horst and graben formation in strong crustal and subcrustal lithosphere layers can explain the multi trough character of rift systems observed in the russian platform the vilyuy rift the west siberian rift system the pechora kolva rift system and the laptev sea rift many features in the evolution of these rifted basins are incompatible with predictions of classical stretching models basin subsidence often occurs in the absence of any noticeable stretching and over time scales much longer than predicted by models of thermal subsidence other observations include a time gap between rifting and the onset of post rift basin subsidence of tens to hundreds ma and a correlation in timing of subsidence phases of rifted basins and platforms with opening and closure events of adjacent ocean basins these observations point to an important role for mechanisms such as ecologite formation within or beneath the lithosphere as well as intraplate compression and stress induced lithospheric deflection

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

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

modeling the response of the rhine meuse fluvial system to late pleistocene climate change abstract we use a landscape evolution model to infer the effect of late pleistocene climate change on the incision aggradation behaviour of the rhine meuse fluvial system we model the routing of runoff and sediment in the catchment in order to predict grainsize trends and the incision and aggradation behaviour in the downstream reach where we compare it to the sequence of events and grainsize characteristics inferred from borehole corings this sequence starts with an important incision taking place around the mis 3 to mis 2 climatic transition during the coldest part of mis 2 a coarse grained sedimentary unit is deposited that shows an upward increase in the sand gravel ratio the model experiments do not predict an incision at the mis 3 to mis 2 transition therefore the incision should be attributed to other causes most likely effects of glacio isostatic uplift however a relative upward increase in sand content of the sediments is predicted by the model this increase is the result of the difference in transport rates between sand and gravel starting from a homogeneous pre existing mis 3 deposit the gravel content in the active layer increases because the sand is removed quickly and transported further downstream whereas the gravel travels slowly and piles up with gravel originating from immediately upstream resulting in a net accumulation at a later stage sand originating from much further upstream progrades fan like over the gravelly deposits according to the record during the early late glacial warming part of mis 2 bolling allerod interstadial neither incision nor aggradation has taken place this is in accordance with modelling results which show that despite the reduction of sediment input due to re vegetation of hillslopes sufficient sediment remains available for fluvial transport in the channel network itself it takes several thousands of years before effects of sediment depletion in the catchment are noted downstream that is why we argue that the inferred incision at the late late glacial the start of the younger dryas in our downstream study area might reflect depletion effects related to the preceding early late glacial conditions in general our modelling results show that terraces along one large fluvial system are diachronic features in particular terrace surfaces are older upstream compared to downstream in addition complex responses to climate change are likely to occur in a large fluvial system like the rhine meuse and correlation of morphological features in the fluvial record to specific short term palaeo climatic events for example dansgaard oeschger events could be risky without consideration of catchment size characteristics and associated response times

normal faulting in central tibet since at least 13 5 myr ago tectonic models for the evolution of the tibetan plateau interpret observed east west thinning of the upper crust to be the result of either increased potential energy of elevated crust1 or geodynamic processes that may be unrelated to plateau formation2 3 4 5 6 a key piece of information needed to evaluate these models is the timing of deformation within the plateau the onset of normal faulting has been estimated to have commenced in southern tibet between about 14 myr ago7 and about 8 myr ago8 and in central tibet about 4 myr ago9 here however we report a minimum age of approximately 13 5 myr for the onset of graben formation in central tibet based on mineralization ages determined with rb sr and 40ar 39ar data that post date a major graben bounding normal fault these data along with evidence for prolonged activity of normal faulting in this and other tibetan grabens support models that relate normal faulting to processes occurring beneath the plateau thinning of the upper crust is most plausibly the result of potential energy increases resulting from spatially and temporally heterogeneous changes in thermal structure and density distribution within the crust and upper mantle beneath tibet this is supported by recent geophysical and geological data10 11 12 13 14 15 16 17 which indicate that spatial heterogeneity exists in both the tibetan crust and lithospheric mantle

accommodating large scale intracontinental extension and compression in a single stress field a key example from the baikal rift system the baikal rift system in southern siberia is one of the main intracontinental extensional features on earth the rift system represents the northwestern boundary of the amuria plate and in that respect can be considered as an evolving plate boundary the baikal rift system has been widely studied both in terms of geology and geophysics and many models have been proposed for its formation and evolution however the age of the initiation of deformation and the mechanism driving this deformation are still largely debated while major extension has occurred since the late miocene pliocene the onset of extension seems older than the india asia collision implying that several driving mechanisms may have acted together or in relay through time in this work we review the available data and models for deformation in an area encompassing the baikal rift system the sayan ranges to the west and the transbaikal to the east using a synthesis of this data and our own field and mapping observations we show that the baikal rift system along with transpressional deformation in the sayan ranges and transtension in the transbaikal area can be explained through major left lateral strike slip systems the deformation is strongly controlled by inherited crustal and lithospheric structures and is distributed over a wide area within the western amuria plate that consequently cannot be considered as a rigid block such distributed deformation is likely to have a strong effect on the structure of the future continental margin if extension evolves towards the formation of oceanic crust

climatic control on quaternary fluvial sedimentology of a fenland basin river england understanding and interpreting climate response from ancient fluvial deposits requires a combined approach of detailed sedimentological description and interpretation local climate proxies and the accurate comparison of these sequences with further independent climate records application of these multiple lines of evidence is particularly effective in the quaternary period where higher resolution and more detailed palaeoenvironmental reconstruction are possible this paper presents results from a devensian weichselian age sequence in northern fenland england that integrates these approaches detailed sedimentological description has identified three fluvial facies associations overlain by a period of ice wedge cast formation fossil plant and coleopteran material within these sediments have been studied to provide palaeoenvironmental reconstructions for the local landscape including quantitative temperature estimates using the mutual climatic range method on fossil coleoptera in addition joint application of radiocarbon and optically stimulated luminescence osl dating allows this sequence to be compared with the stacked marine isotope record although dates do not agree well at the limit of the radiocarbon technique sedimentological interpretations palaeoenvironments and global ice volume variations a proxy for climatic severity are all in agreement and show clearly how the river nene responded to subtle changes in climate and vegetation cover during the devensian weichselian stage the level of detail possible in this reconstruction shows the importance of this approach in understanding fluvial response to past climate changes

asymmetric upwarp of the asthenosphere beneath the baikal rift zone siberia in the summer of 1991 we installed 27 seismic stations about lake baikal siberia aimed at obtaining accurately timed digital seismic data to investigate the deep structure and geodynamics of the baikal rift zone and adjacent regions sixty six teleseismic events with high signal to noise ratio were recorded travel time and q analysis of teleseisms characterize an upwarp of the lithosphere asthenosphere boundary under baikal theoretical arrival times were calculated by using the international association of seismology and physics of the earth s interior 1991 earth model and travel time residuals were found by subtracting computed arrival times from observed ones a three dimensional downward projection inversion method is used to invert the p wave velocity structure with constraints from deep seismic sounding data our results suggest that 1 the lithosphere asthenosphere transition upwarps beneath the rift zone 2 the upwarp has an asymmetric shape 3 the velocity contrast is 4 9 in the asthenosphere 4 the density contrast is 0 6 and 5 the p wave attenuation contrast t is 0 1 s

holocene flooding history of the lower tagus valley portugal the present paper aims to reconstruct the lower tagus valley flooding history for the last ca 6500 a to explore the suitability of pollen based local vegetation development in supporting the reconstruction of flooding history and to explain fluvial activity changes in terms of allogenic climate human impact and autogenic system intrinsic processes the flooding history has been determined by cored sedimentary records located 18 km apart in distal low energy backswamps on both sides of the tagus channel in these low energy backswamps fine grained sediment layers deposited from suspended load of overbank flood water reflect periods with multiple overbank floods by means of a multi proxy approach sedimentology magnetic susceptibility grain size loss on ignition carbonate content and pollen sedimentary and environmental changes were identified at both sites synchronous lithological intervals accumulated suggesting a common origin for the changes in fluvial activity since ca 6500 cal a bp based on lithological changes three phases of high fluvial activity 6500 5500 4900 3500 and 1000 0 cal a bp and two phases of low fluvial activity 5500 4900 and 3500 1000 cal a bp were identified two periods with dominant allogenic controls on fluvial activity in the lower tagus valley were identified relative sea level 6500 5500 cal a bp and human impact 1000 0 cal a bp during the intermediate period changes in fluvial activity may have been caused by climate 5500 1000 cal bp but unambiguous correlations are difficult to make this is due to the way allogenic controls are translated through the fluvial system the geomorphological differences between upstream and downstream studies and autogenic processes the comparison of local vegetation development and flooding phases as reconstructed using sedimentology shows a limited added value of using local palynology as a proxy for fluvial activity 2010 john wiley sons ltd

deep structure of the baikal rift zone revealed by joint inversion of gravity and seismology 1 the question of plate boundary forces and deep versus shallow asthenospheric uplift has long been debated in intracontinental rift areas particularly in the baikal rift zone asia which is colder than other continental rifts as previous gravity and teleseismic studies support the dominance of opposing mechanisms in the baikal rift we reconsidered both data sets and jointly inverted them this more effective approach brings insight into location of the perturbing bodies related to the extension in this region our new joint inversion method allows for inverting the velocity density relationship with independent model parametrization we obtain velocity and density models that consistently show 1 crustal heterogeneities that coincide with the main tectonic features at the surface 2 a faster and denser cratonic mantle nw of lake baikal that we relate to the thermal contrast between old and depleted archean siberian platform and paleozoic orogenic belt sayan baikal belt 3 three dimensional topographic variations of the crust mantle boundary with well located upwarpings and 4 the lithosphere asthenosphere boundary uplift up to 70 km depth with a nw dip our resulting velocity and density models support the idea of a combined influence of lithospheric extension and inherited lithospheric heterogeneities for the origin of the baikal rift zone index terms 1234 geodesy and gravity regional and global gravity anomalies and earth structure 7218 seismology lithosphere and upper mantle 8122 citation tiberi c m diament j deverchere c petit mariani v mikhailov s tikhotsky and u achauer deep structure of the baikal rift zone revealed by joint inversion of gravity and seismology

evidence and causes of the two stage development of the baikal rift abstract the data on the geological and deep seated structures of the baikal rift zone are briefly summarized based on the analysis of the composition of the sedimentary infill in rift basins two stages of the zone development have been recognized 1 1 slow rifting 2 2 fast rifting as a consequence of the study of the deep seated structure and construction of the thermal model of the lithosphere it was assumed that the first stage is associated with a slow uprise of the surface of the asthenospheric upwelling and the second stage connected with sideways flows of the substance involved in this upwelling after the crustal base was reached

interaction of fluvial and eolian sedimentation processes and response to climate change since the last glacial in a semiarid environment along the yellow river interactions of fluvial and eolian processes are prominent in dryland environments and can significantly change earth surface morphology here we report on sediment records of eolian and fluvial interactions since the last glacial period in the semiarid area of northwest china at the limit of the southeast asian monsoon sediment sequences of last glacial and holocene terraces of the yellow river are composed of channel gravels overlain by flood sands eolian dunes and flood loams these sequences dated by optically stimulated luminescence record interlinks between fluvial and eolian processes and their response to climate change sedimentologic structures and grain size analysis show flood loams consisting of windblown sediment deposited from floodwater suspended sediment the gravel and sand were deposited during cold periods during transitions from cold to warm phases the river incised and dunes were formed by deflation of channel and floodplain deposits 70 and 21 16 ka dunes also formed at 0 8 ka probably after human intervention after dune formation flood loam covered dunes without erosion during peak discharges at the beginning of the subsequent warm period the fluctuations of the southeast asian monsoon as a moisture transporting agent have perhaps been the driving force for interactions between fluvial and eolian processes in this semiarid environment

long term fluvial archives in hungary response of the danube and tisza rivers to tectonic movements and climatic changes during the quaternary a review and new synthesis abstract the paper discusses the quaternary evolution of the danube and tisza rivers and their main tributaries in the context of evolution of the entire pannonian basin which is europe s largest intramontane basin within the alp carpathian orogen the palaeo drainage reconstruction of the pannonian basin for the pre quaternary period is outlined in connection with the gradual regression of lake pannon since the late miocene deltas of rivers that entered the basin from the northwest and northeast were gradually transformed into extended alluvial plains thus the earliest possible ancestor of the danube coming southeastwards from the alps could be as old as late miocene by the pliocene the whole lake pannon was infilled the former extensional basin formation was replaced by a compresional stress field which resulted in an uplift of the marginal flanks and late stage subsidence anomalies the increasing relief led to the formation of the quaternary drainage pattern the actively subsiding young basins were filled by fluvial sediments transported by the danube and tisza river systems from the uplifting mountains between the subsiding regions of the little and great plains the danube has formed an antecedent valley with terrace staircases between the uplifting sections of the transdanubian range and the north midmountains the formation of the terraces is attributed to periodic climate changes during the pleistocene combined with differences in the uplift rate the paper gives a complex overview of the classical chronology of the six terraces based on various data sources mostly dating of loess paleosol sequences travertines aeolian sand and tephra strata overlying the fluvial sediments complemented by scattered vertebrate faunal data and archaeological evidence directly from the terrace sediments the quaternary drainage pattern evolution of the great plain with a strong tectonic control is discussed in detail rivers originating from the uplifting marginal areas were drawn towards the subsiding depressions which served as local base level changes in subsidence rates in space and time throughout the quaternary resulted in the evolution of a complex drainage pattern a special emphasis is placed on the late pleistocene holocene development of the middle tisza region and the koros basin where the berettyo koros rivers form an eastern tributary system of the tisza river a comparative evaluation of these two areas is especially relevant as they provide insights into large scale late pleistocene avulsion of the tisza river osl dating complemented with inferred transport directions determined from heavy mineral analysis of fluvial sediments in the koros basin has revealed an ancient large meandering river system that can be identified with the palaeo tisza which was flowing along a tectonically controlled depression during the late pleniglacial successions in the middle tisza region have allowed differentiation between the older channels of the palaeo bodrog river and the sajo hernad alluvial fan and the younger meander belts of the new course of the tisza in the tisza system changes in river style braided to various scales of meandering show correspondence to millennial scale climate changes of the last 25 ka while in the koros basin the effects of tectonics are overprinted onto the regional climatic signals

finite amplitude bars in mixed bedrock alluvial channels we present a nonlinear asymptotic theory of fully developed flow and bed topography in a wide channel of constant curvature to describe finite amplitude perturbations of bottom topography subject to an inerodible bedrock layer the flow field is evaluated at the leading order of approximation as a slowly varying sequence of locally uniform flows slightly perturbed by a weak curvature induced secondary flow using the constraint of constant fluid discharge and sediment flux we calculate an analytical solution for the cross sectional profile of flow depth and bed topography and we determine the average slope in the bend necessary to transport the sediment supplied from a straight alluvial upstream reach both fully alluvial bends and bends with partial bedrock exposure are shown to require a larger average slope than a straight upstream reach the relative slope increase is much larger for mixed bedrock alluvial bends curvature and sediment supply are shown to have a strong effect on the characteristics of the point bars in mixed bedrock alluvial channels higher curvature bends produce bars of larger amplitude and more bedrock exposure through the cross section and increasing the sediment supply leads to taller and wider point bars differences in the relative roughness of sediment and bedrock have a smaller secondary effect on point bar characteristics our analytical approach can potentially be extended to the case of arbitrary yet slowly varying curvature and should ultimately lead to an improved understanding of the formation of meanders in bedrock channels

forces associated with mantle plumes this study addresses first order aspects of the physics of continental lithosphere extension above mantle plumes developing a testable model that predicts extension rates from flow parameters radial flow in the head of a plume causes a viscous force and uplift over this head causes a buoyancy force which both drive extension the viscous force is roughly proportional to the plume s volume flux and given my best estimates for flow parameters predominates for the most vigorous plumes extension is opposed by a viscous force beyond the plume head and its rate is thus affected by the dimensions of the plate on which this force acts extension rates are 2 mm yr 1 above yellowstone 1mm yr 1 above baikal and 0 7 mm yr 1 above the east african plume volume fluxes for all these plumes are 50 m3 s 1 the extension rates depend mainly on plate dimensions

comment on how plausible are high frequency sediment supply driven cycles in the stratigraphic record by s castelltort and j van den driessche 2003 sedimentary geology 157 3 13

three dimensional laboratory modelling of rifting application to the baikal rift russia abstract continental rifting is treated as a mechanical instability developing under horizontal tectonic tension the instability results in strain localization and the formation of a neck which is interpreted as a rift zone at the scale of the whole lithospheric plate this process occurs in plane stress conditions and can therefore be modelled to a first approximation by a one layer plate whose properties represent integral over thickness properties of the real lithosphere we have designed a scaled experimental single layer lithosphere model having elasto plastic rheology and lying upon a liquid substratum to study its behaviour under axial horizontal tension in a homogeneous plate the instability develops along a linear zone oriented at an angle of 60 to the tension axis this orientation is preserved even when the divergent displacement of the plate boundaries is not plain parallel but rotational in the latter case the strain localization zone is rapidly propagating when the plate length to width ratio is less than 2 5 the necking develops along two branches conjugated at an angle of about 120 which is frequently observed in actual rift systems if the model contains a local weak zone hot spot or fault zone the rift junction is located at this zone in the lithospheric models comprising strong cratonic and weak segments strain localization depends on the configuration of the boundary between different lithospheres the necking starts to form within the weak segment in the vicinity of the cratonic promontories and propagates in opposite directions again at an angle of ca 60 to the tension axis in the models containing both a strong lithosphere and local weak zones the rift configuration depends on their shape and relative positions with necking always going through the weak zones in a set of models we have reproduced the geometry of the boundary between the siberian craton and the thermally much younger 100 ma sayan baikal lithosphere in the baikal rift area in these models we were able to obtain the well known three branch configuration of the baikal rift system only by introducing a weak zone in the area of lake baikal such a zone simulates the paleozoic suture existing in this area as in nature two wide outer branches eastern and western are oblique to the regional tension axis whereas the central one is narrow and orthogonal to the tension direction in nature and in the model rifting starts in the central branch corresponding to lake baikal the modelling also predicts the formation of a fourth oblique ns trending branch to the south of baikal although poorly expressed in the field this branch has some seismotectonic and magmatic manifestations the orientations of all four branches with respect to each other and with respect to the regional tension direction are remarkably similar in nature and in the model

timing duration and role of magmatism in wide rift systems insights from the jiaodong peninsula china east asia in east asia widespread extensional sedimentary basins together with the close association of metamorphic core complexes and magmatism are prominent features of the large scale wide rift system developed during late mesozoic times this region thus appears as a proper place to study continental extension as well as questions about the link between continental extension and magmatism this paper primarily provides pioneer exhumation time constraints on the linglong mcc jiaodong peninsula including cooling and deformation ages mcc cooling at mid crustal levels occurred at ca 143 ma besides last ductile deformation occurred at ca 134 ma while final exhumation stages under brittle 2 conditions occurred as late as ca 128 ma continuous crustal stretching were then recorded by the emplacement of a synkinematic pluton in the upper crust at ca 128 ma that cooled fast below an intracrustal shear zone crossing the ductile brittle transition at ca 123 ma the ca 120 118 ma age cluster is ascribed to the fast cooling of undeformed plutons marking the end of extension that lasted in the area over a minimum period of ca 30 my combining other mcc exhumation constraints and the onset of subsidence in the sedimentary basins total duration of late mesozoic extension in east asia could be estimated at ca 60 my related with a rather long process for extension from 160 to at least 100 ma east asian continental extension is heterogeneously distributed in space and time as revealed by fundamental differences between two end member classes of migmatite cored mcc already described in other wide rift systems extension seems to have first favoured partial melting which subsequently in turn maintained continental extension

sedimentary basins tectonic recorders of sediment discharge from drainage catchments the sedimentary basin is to geology what the drainage system is to geomorphology with sediment flux being a unifying link between the two features and disciplines the global sediment discharge from contents to oceans contributes to major mass recycling associated with plate subduction major plate reorganization is accompanied by small fluctuations in continental volumes due to recycling of sediment stored along the sink like passive margins in continental sedimentary basins the sediment preservation ratio sepra depends upon the tectonic drawdown of sediment flux preserved in the subsurface until basin inversion major unsteadiness in sediment discharge arises from teconic or climatic causes the latter prominent in the quaternary to holocene record contrasting trends in sediment discharge reflect both the nature of climate and vegetation change and source rock lithology 1997 by john wiley sons ltd

characterizing the present day activity of the tunka and sayan faults within their relay zone western baikal rift system russia the sayan and tunka faults are located at the boundary between the northernmost mountain belt of central asia the sayan baikal ranges and the siberian platform these prominent crustal structures were involved in the opening of the southern baikal rift system since the beginning of the cenozoic and define large scale sharp morphotectonic features despite low instrumental seismic activity late pleistocene holocene morphotectonic features along the two faults indicate that the faults are active and have the capacity to produce strong earthquakes a careful mapping of the most recent trace of activity within the southeastern parts of the two faults where they merge within a relay zone demonstrates that they correspond now to left lateral reverse faults suggesting a recent inversion of their vertical component we also show that the two faults are now structurally connected via a young surface rupture and that no obvious post last glacial maximum ruptures are observed along the central part of the sayan fault beyond its junction zone with the tunka fault this suggests that the left lateral strike slip deformation is transferred from the eastern sayan fault to the tunka fault a detailed morphotectonic study along the southeastern sayan fault allows estimating a left lateral slip rate between 1 3 min and 3 9 mm year max finally a critical review of russian paleoseismic data combined with our paleoseismological investigations allows us to propose that the mean recurrence time along the two faults is on the order of 4 kyr and that they may have either ruptured together or during seismic clusters

a 40 ka record of temperature and permafrost conditions in northwestern europe from noble gases in the ledo paniselian aquifer belgium the ledo paniselian aquifer in belgium offers unique opportunities to study periglacial groundwater recharge during the last glacial maximum lgm as it was located close to the southern boundary of the ice sheets at that time groundwater residence times determined by 14c and 4he reveal a sequence of holocene and pleistocene groundwaters and a gap between about 14 and 21 ka indicating permafrost conditions which inhibited groundwater recharge in this paper a dataset of noble gas measurements is used to study the climatic evolution of the region the derived recharge temperatures indicate that soil temperatures in the periods just before and after the recharge gap were only slightly above freezing supporting the hypothesis that permafrost caused the recharge gap the inferred glacial cooling of 9 5 c is the largest found so far by the noble gas method yet compared to other palaeoclimate reconstructions for the region recharge temperatures deduced from noble gases for the cold periods tend to be rather high most likely this is due to soil temperatures being several degrees higher than air temperatures during periods with extended snow cover thus the noble gas derived glacial cooling of 9 5 c is only a lower limit of the maximum cooling during the lgm some samples younger than the recharge gap are affected by degassing possibly related to gas production during recharge in part of the recharge area especially during times of melting permafrost the findings of this study such as the occurrence of a recharge gap and degassing related to permafrost and its melting are significant for groundwater dynamics and geochemistry in periglacial areas copyright 2010 john wiley sons ltd

direct evidence of ancient shock metamorphism at the site of the 1908 tunguska event abstract shock metamorphism is rarely found at the surface of the earth the most used structures to identify shock metamorphism are true planar deformation features pdfs in quartz now accepted as diagnostic indicators of a meteorite impact here we present several lines of evidence for shock metamorphism and pdfs developed in quartz occurring on samples centered on a circular geological structure on mount stojkovic 60 54 06 n 101 55 40 e which lies within southern surface exposures of the siberian traps the shock event appears to have occurred during the eruption of the surface siberian traps basalts that cover this region curiously mount stojkovic lies within 3 km of the tree fall epicenter of the 1908 tunguska event based on current estimates of the phanerozoic impact distribution there is at most a 1 in 17 000 chance that the 1908 bolide would randomly fall on the site of a previous impact structure capable of creating shocked quartz just as improbable would be an airbust event incapable of creating a small crater that could have produced shock metamorphism our preferred least implausible hypothesis is that the shock metamorphism here was associated with a terrestrial event a hyperexplosive volcanic gas eruption called verneshot

late quaternary linkage of sedimentary records to three astronomical rhythms and the asian monsoon inferred from a coastal borehole in the south bohai sea china abstract the bohai sea was formed by subsidence during the cenozoic some 2000 3000 m of fluvial lacustrine and marine sediments has been deposited in this basin previous studies focused mainly on the transgression history with little examination of orbital variation in relation to other areas within the asian monsoon domain here we present the late quaternary results of a new borehole in the south bohai sea optically stimulated luminescence and radiocarbon dating which provide concordant age estimates were employed to generate an initial chronology for the borehole after refining the chronology through astronomical tuning the results showed that 1 the grain size variation represents asian monsoon intensity which was dominated by both solar insolation major and global ice volume minor forcing 2 the magnetic susceptibility indicates river incision processes which were sensitive to orbital tilt with influence from solar insolation 3 the vegetation coverage responded to global ice volume coupled obliquity changes and that 4 neither external nor internal factors could dominate the paleoenvironmental evolution on orbital timescales in an independent way and they are both integrated in a complex pattern we conclude that three different astronomical rhythms have affected coastal evolution and that the sedimentary records in the south bohai sea china result from the nonlinear interaction and the complex response to driving processes

finite element modelling of crustal deformation in the baikal rift zone new insights into the active passive rifting debate abstract the origin of the forces responsible for crustal extension in the baikal rift zone siberia is the object of a debate between passive rifting models where crustal extension is primarily caused by horizontal forces related to the kinematics of asia india eurasia collision and active rifting models where crustal extension is primarily caused by a diapiric mantle upwelling in this work we used a two dimensional visco elastic finite element model in order to determine whether horizontal forces alone can account for the present day deformation in the baikal rift zone we tested a number of kinematic boundary conditions and compared predictions of various models against the observed stress and strain field deduced from seismotectonic data earthquake focal mechanisms and microtectonic analyses by adjusting the kinematic boundary conditions and using a three plate model with a differential displacement between the mongolian and amurian plates we found a best fit model that correctly accounts for the observed strain and stress field over the entire baikal rift zone the fact that our model does not take into account vertical forces but still explains most of the observed deformation suggests that the present day opening of the baikal rift is essentially controlled by horizontal forces related to the regional kinematics these forces could have their origin in the india eurasia collision zone further south this result does not imply that the asthenosphere played no role in the rifting process in particular before the fast rifting stage of the baikal rift evolution 3 4 ma but might suggest a recent plio quaternary triggering effect of the india asia collision on the deformation in the baikal rift

lithospheric mantle evolution evidences from ultramafic xenoliths in the lessinian volcanics northern italy abstract the lower middle eocene volcanic rocks from the monti lessini area veneto region carry a suite of inclusions of mostly lherzolitic composition the magmatic activity represents the most important example of alkaline within continental plate volcanism occurred within the south alpine domain during post collisional age the lavas including xenoliths range from alkali olivine basalts to basanites their anorogenic character is evidenced by the absence of any negative anomalies for nb and ti the high mg values the ni content and the forsteritic nature of the olivine indicate that these lavas may be considered undifferentiated or very slightly differentiated mantle derived magmas the great majority of xenoliths are spinel lherzolites plus minor harzburgites and rare websterites and olivine websterites protogranular textures are common to all xenoliths pyrometamorphic textures with sio 2 1bna 2 o 1bk 2 o 1brich glassy patches or blebs are widespread and have been related to local incipient melting possibly favoured by the uprising of the mantle materials incorporated in the mafic lavas the bulk rock and mineral chemistry of the nodules outlines a depletion sequence from the nearly primitive to the most depleted mantle material however variable and anomalously high contents of the most incompatible elements such as la ce rb sr nb zr k and to a lesser extent na indicate for most nodules a more complicated petrogenetic history a petrological model based on incompatible elements at mantle level suggests that peridotite inclusions have to be considered as variably depleted mantle material accidentally incorporated into the host magma during its ascent the proposed sequence of events is a partial melting episodes responsible for the depletion of mantle materials b partial equilibration of mantle materials caused by their upwelling to shallower levels and subsequent long residence time periods possibly in connection with the rifting stage which affected the southern alps during triassic time c contamination events by alkaline fluids with variable h 2 o co 2 ratio which occurred after the mantle depletion but before and or during the incorporation of xenoliths in the alkaline host magma and d local incipient melting episodes during the ascent and subsequent decompression of the nodules resulting in their pyrometamorphic textures

controls on channel sinuosity changes a case study of the tisza river the great hungarian plain abstract the planform geometry of the tisza the trunk river of the subsiding great hungarian plain is studied by reconstruction of the last pre regulation river course the thalweg sinuosity has been computed for the main alluvial section of the river remarkable sinuosity changes have been found to correlate with discharge and sediment load changes at the inflow of tributaries as well as with active deformation areas like differential subsidence and wrench fault zones analysing the change of the river pattern a new discrimination line has been derived which separates the meandering zone on the classic slope vs discharge diagram into two subzones the first subzone lower slope values corresponds to a range of true self organized meandering the second subzone higher slope values corresponds to a range of unorganized meandering this is a range where river sinuosity decreases although the channel slope increases in the case of the tisza river this subzone equals to the wandering river pattern

model of the transient temperature field of the baikal rift lithosphere abstract in order to coordinate available geophysical data on the deep seated structure with observed heat flow it has to be borne in mind that the thermal field of the baikal rift zone is not in a steady state a two dimensional model of the transient temperature field of the lithosphere was constructed by a numerical method for the solution of the energy conservation equation the authors suggest that asthenospheric upwelling 250 km wide was formed on account of roof block detachment such a mechanical replacement of the lithosphere by the asthenosphere was simulated by a positive compulsory upward movement of the 1200 c isotherm with constant velocity the duration of this movement was taken as long as 30 m y which corresponds to the duration of the first slow rifting stage as soon as the asthenosphere had reached the mohorovicic discontinuity its ascending movement on a wide scale ceased because the density of the crust was less than that of the asthenosphere temperature calculations were carried out in the lithosphere above the 1200 c isotherm this model permits us to reproduce theoretically the present value of the regional heat flow and the curie depth when the time passed from the cessation of the upwelling top movement became equal to 3 5 m y the last figure corresponds to the duration of the second fast stage of rifting on the regional scale the crust of the rift zone sayan baikal domal uplift continues to be heated cooling of the crust can only occur at the segments corresponding to the local heat flow anomalies which are suggested as being produced by dikes the intrusion time of the dike beneath the southern baikal is estimated to be 3 m y

controls of lithospheric structure and plate kinematics on rift architecture and evolution an experimental modeling of the baikal rift 1 analog models investigate the evolution and architecture of the baikal rift in relation to the rheology of the extending lithosphere and rift kinematics the models focus on the development of the narrow deep and asymmetric basins composing lake baikal and reproduce the extension between the strong siberian craton and the weaker sayan baikal belt model results suggest that the presence of a near vertical weak suture separating the cratonic keel from the mobile belt represents the more convenient rheological configuration leading to a narrow rift characterized by prominent vertical motions and deep depressions these depressions are typically asymmetric and model results suggest that this asymmetry is a consequence of lateral variations in lithospheric rheology which is in turn related to both the variation in thickness of the strong mantle and more importantly the variation in the brittle ductile transition depth between the craton and the belt a significant shallowing of the brittle ductile transition in the crust passing from the craton to the belt is required to fit the asymmetric architecture of the baikal basins with a master fault on the craton side and a monocline with no significant faulting on the belt side analysis of the model deformation pattern suggests that the overall architecture of the basins hosting lake baikal is best fitted for a n140 e directed extension similar to the current gps derived motion and compatible with the stress field inferred on the basis of fault and focal mechanism data this kinematics along with the shape of the siberian craton exerted the major control on the plan view fault architecture and its along axis variations

a reappraisal of the 1950 mw 6 9 mondy earthquake siberia and its relationship to the strain pattern at the south western end of the baikal rift zone the precise nature of the transition between the present day compressional tectonics in central mongolia and extensional deformation in the central baikal rift has still to be determined for that purpose we have built a comprehensive earthquake focal mechanism data base for the mongolia southern siberia area from which we map the variations of the stress field we focus our detailed investigations on the largest seismic event in the transition zone the 1950 mw 6 9 mondy earthquake for which several discordant focal mechanisms have been proposed using a new approach in source inversion we resolve the focal mechanism left lateral strike slip type on a steep south dipping fault and depth 14 3 km of the mondy earthquake with a satisfactory accuracy this seismological information combined with the geological observations allows us to decipher the connections between the 1950 mainshock the local stress tensor and the active faults which strongly suggest a partitioning of the deformation between two faults namely the mondy and ikhe ukghun faults

late quaternary geology of the tunka rift basin lake baikal region russia abstract the objective of this research is to obtain a better understanding of the evolution of the tunka rift basin part of the baikal rift zone and how it relates to the overall geologic history of the region particular for the quaternary period the tectonically active baikal rift zone began forming over 50 million years ago and continues today in the tunka basin during the oligocene and middle pliocene relatively weak tectonic disturbances took place and thick accumulations of organic rich sands silts and clays were deposited in lacustrine marshy subtropical environments tectonism increased between the miocene and pliocene and thick units of coarse alluvium and floodplain sediments were deposited during the late pliocene quaternary tectonism formed basins that are now filled with a variety of coarse clastic materials early and middle pleistocene sediments are poorly exposed covered by widespread late pleistocene deposits three late pleistocene sedimentary facies dominate boulder pebble gravels proluvial glacial fluvial and alluvial sediments alluvial sand and loess like sediments with associated slope deposits altered by post depositional wind erosion the relationship between these complexes including radiocarbon and other chronological data and fauna and flora remains indicates that they began forming c 70 000 yr ago paleosols glacial deposits and cryogenic material indicate that at times the climate was cool or cold during the early late pleistocene renewed tectonism took place causing increased deposition of coarse sediments the middle late pleistocene deposits consist mostly of sandy floodplain alluvium by the end of the late pleistocene holocene alluviation was reduced and replaced by a high degree of erosion and aeolian deposition

sensitivity of weichselian fluvial systems to climate change nochten mine eastern germany abstract this paper aims to contribute to the understanding of fluvial system response to climate change during the last glacial interglacial cycle fluvial and aeolian successions have been studied in the opencast brown coal mine nochten in eastern germany an absolute chronology was established by luminescence and 14 c dating enabling to demonstrate the relations between depositional units and changes in sedimentary environment over time with regional climatic and vegetational changes it is concluded that the major climatic periods coinciding with the oxygen isotope stages are generally reflected in the fluvial sequence by distinct fluvial environments major climatic changes oxygen isotope stage boundaries have been preserved in the fluvial record as erosional bounding surfaces and by changes in fluvial style rapid climate changes like the middle pleniglacial dansgaard oeschger cycles are in general not reflected in the fluvial succession these cycles were too short or with too low amplitude to cause a strong vegetational response and related changes in water and sediment supply it is emphasized that also the preservation potential of short lived climatic warming events in high energy fluvial systems is low warming events may however have been preserved in lacustrine successions in former thermokarst lakes a strong cooling event at ca 40 ka leading to continuous permafrost conditions and changes in the water and sediment budget was reflected in the fluvial archive by a change from sandy anabranching to braided river conditions

baikal rift zone structure and geodynamics abstract the cenozoic baikal rift zone is superimposed on the caledonian baikal fold belt representing the suture between the precambrian siberian craton and several microcontinents the baikal rift zone consists of a system of disconnected fault bounded basins and extensional and wrench faults that straddles a major arch having a topographic relief of 2 3 km rifting activity commenced during the oligocene and is still active as evident from high seismicity of the baikal rift zone across the baikal rift zone upper crustal extension is considerably smaller than would be expected from its crustal thickness which decreases by 8 11 km across the baikal basins as compared to the adjacent unextended areas the discrepancy between upper and lower crustal attenuation could be attributed to intrusion of a major diapir indeed geophysical data indicate that the sayan baikal dome coincides with such a diapir the top of which is located at the crust mantle boundary this intrusion is held responsible for oligocene and quaternary doming of the rift zone development of the intra continental baikal rift system is thought to be related to asthenospheric diapirism active rifting however intra plate stresses in conjunction with the himalayan collision may have played some role

lacustrine fluvial interactions in australia s riverine plains climatic forcing of fluvial systems has been a pre occupation of geomorphological studies in australia since the 1940s in the riverine plain southeastern australia the stable tectonic setting and absence of glaciation have combined to produce sediment loads that are amongst the lowest in the world surficial sediments and landforms exceed 140 000 yr in age and geomorphological change recorded in the fluvial fluvio lacustrine and aeolian features have provided a well studied record of quaternary environmental change over the last glacial cycle the region includes the willandra lakes whose distinctive lunette lakes preserve a history of water level variations and ecological change that is the cornerstone of australian quaternary chronostratigraphy the lunette sediments also contain an ancient record of human occupation that includes the earliest human fossils yet found on the australian continent to date the lake level and palaeochannel records in the lachlan willandra system have not been fully integrated making it difficult to establish the regional significance of hydrological change here we compare the willandra lakes environmental record with the morphology and location of fluvial systems in the lower lachlan an ancient channel belt of the lachlan willandra creek acted as the main feeder channel to willandra lakes before channel avulsion caused the lakes to dry out in the late pleistocene electromagnetic surveys geomorphological and sedimentary evidence are used to reconstruct the evolution of the first new channel belt following the avulsion single grain optical dating of floodplain sediments indicates that sedimentation in the new middle billabong palaeochannel had commenced before 18 4 1 1 ka a second avulsion shifted its upper reaches to the location of the present lachlan river by 16 2 0 9 ka the timing of these events is consistent with palaeohydrological records reconstructed from willandra lakes and with the record of palaeochannels on the lachlan river upstream willandra lakes shows high inflows during the last glacial maximum 22 ka but their subsequent drying between 20 5 ka and 19 ka was caused by river avulsion rather than regional aridity this case study highlights the benefits of combining fluvial with lacustrine archives to build complementary records of hydrological change in lowland riverine plains

faulting within the eastern baikal rift as characterized by earthquake studies earthquake relocations focal mechanism determinations waveform modeling and stress analyses using focal mechanism information are used to examine the faulting processes within the western baikal rift 95 to 108 5 results of the study show that high angle dip 70 faulting is most likely to occur in the more youthful parts of the rift and is most likely to be associated with m 4 5 events like the eastern rift nearly all earthquakes occurred on faults dipping 30 suggesting that in no part of the rift is significant deformation occurring on low angle structures focal mechanism information does not indicate there is a sharp boundary to the western rift as observed in the eastern rift less normal faulting rakes 60 to 120 occurs in the western rift than the eastern rift waveform modeling of the two largest earthquakes 1950 mondy and 1959 srednebaikal in the western rift gives focal depths of 10 to 15 km the 1959 event appears to have occurred along the eastern boundary fault on lake baikal just to the north of proval bay a feature created a m 7 1 earthquake in 1862 the 1950 event may have occurred along the southern boundary fault of the tunka depression stress orientation information indicates a near horizontal nw se to wnw ese striking 3 in the eastern part of the western rift

aeolian deposits of rift zones the evolution of contemporary aeolian processes in continental rift zones is one of the poorly explored issues in quaternary geology associated with rift zones is the formation of aeolian zircon rutile ilmenite sands which are rich in various mineral resources and primarily in titanium zirconium uranium and in other rare earth elements using the baikal rift system as an example the characteristics of the occurrence at the rift zones hollows of contemporaneous unfixed aeolian sands are examined analysis of the morphological elements of aeolian deposits their substance composition and development patterns is based on long term field work on the study of aeolian sands in the depressions of the baikal rift system as well as on graphical representations of riftogenic structures on remotely sensed material and primarily on space acquired images

reconstruction of a pleistocene meandering river in east hungary by vhr seismic images and its climatic implications abstract the upper 20 30 m of the pleistocene alluvial sequence on the tisza river hungary is investigated by 200 km of vhr single channel seismic sections frequent internal configurations such as 1 bundles of inclined reflections 2 trough shaped converging and 3 horizontal parallel reflections are interpreted respectively as lateral accretion of point bars abandoned channel fills and floodplain deposits the series of 5 8 m thick inclined strata sets occurring at the same depth throughout the area suggest the presence of a meandering river dated to about 43 47 ka in the late pleistocene according to osl data newly recorded quasi 3d seismic profiles reveal that each 1 3 km long inclined series correlates with an individual point bar continuously migrating in the same direction small deviations in the direction of migration are caused by natural wandering of the meander bend morphometric parameters of point bars are used to calculate ancient channel parameters width and depth of 200 500 m and 5 8 m respectively values imply a channel forming discharge of q 400 900 m 3 s these results imply a greater amount of runoff and supply in the basin during mis3 compared to the present day long lasting meandering indicates the role of local factors and a different fluvial environment compared to the commonly anastomosing systems in nw europe our data support the thesis of the three axis drainage system for the basin new evidence is provided for the antecedent existence of a temporally active third trunk river in addition to the ancestors of danube and tisza rivers contrary to the present day two axis drainage pattern

asthenospheric imprints on the lithosphere in central mongolia and southern siberia from a joint inversion of gravity and seismology mobal experiment summary we present a joint inversion of gravity and teleseismic data to enlighten the lithospheric structures of the baikal mongolia region an area characterized by high topographic contrasts sporadic cenozoic volcanism extension and large transcurrent faulting in the vicinity of the baikal rift central asia the study uses a 1000 km long seismic transect that cross cuts the main tectonic structures from north to south namely the siberian platform tunka basin hangay dome and gobi altai belt the siberian platform depicts a high velocity lithosphere down to about 150 km we evidence strong velocity contrasts within the crust below the hangay dome and the tunka depression interpreted as a thickened crust a low velocity density region is located at various depths below the hangay dome thanks to the dense spatial coverage of gravity data we are able to define the 3 d geometry of this particular low velocity density anomaly the hangay dome anomalous body extends from 60 to 225 km depth at his largest point and slightly thins to no more than 40 km at its easternmost end a deep low velocity zone below 150 km with only a weak negative density contrast is observed on the eastern part of the transect we propose that the late cenozoic uplift of the whole mongolian plateau and associated rifting magmatism high heat flow and lithospheric thinning are not externally driven by the india asia collision but results from the interaction of two mantle plumes with the overlying lithosphere conversely recent faulting may be the major expression of the india asia collision in this region as well as n s striking rift basins that connect and interact with major strike slip faults such as the bolnai fault the comparison between time residuals of this experiment and the baikal rift seismic data shows an undeniable disproportion for the hangay anomaly the hangay time residuals are far more positive than through the baikal arguing for an asthenospheric signature that is not seen beneath the baikal rift furthermore the southern edge of the thick siberian cratonic lithosphere may favour the rise of a sublithospheric mantle flow at the contact with the baikal mongolia lithosphere

paleostress reconstructions and geodynamics of the baikal region central asia part 2 cenozoic rifting abstract investigations on the kinematics of rift opening and the associated stress field present a renewed interest since it has recently been shown that the control of the origin and evolution of sedimentary basins depends to a large extent on the interplay between lithospheric strength and applied stresses it appears that changes of stress field with time are an important factor that either controls or results from the rifting process the object of this paper is to study the changes of fault kinematics and paleostress field with time in the baikal rift system during the cenozoic reduced paleostress tensors were determined by inversion from fault slip data measured in the central part of the rift and its southwestern termination between 1991 and 1995 results show that the stress field varies as well in time as in space two major paleostress stages are determined corresponding broadly to the classical stages of rift evolution late oligocene early pliocene and late pliocene quaternary the first paleostress stage is related to the rift initiation and the second to the major stage of rift development similarities between the recent paleostress field and the present day stress field inverted from focal mechanisms indicate that the second paleostress stage is still active therefore we propose to use proto rift for the late oligocene early pliocene stage and active rift for the late pliocene quaternary stage of rift development during the proto rift stage the stress field was characterized by a compressional to strike slip regime a progressive change from transpression to transtension is suspected for the central part of the rift baikal and barguzin basins during this period in the western termination of the rift sayan massif tunka depression a strongly compressional stress field with oblique thrusting kinematics is well constrained in the late miocene early pliocene interval the active rift stage was initiated by a marked change in fault kinematics and stress regime in the late pliocene in the central part of the rift the stress regime changed into pure extension while in the southwestern extremity it changed into pure strike slip fault kinematics suggests that rifting was initiated by an extrusion mechanism due to the interaction of far field compressional stress on a mechanically heterogeneous crust with the southwards pointing wedge of the siberian craton acting as a passive indentor the cenozoic time space evolution of the stress field is believed to reflect the increasing influence of locally generated buoyancy extensional stresses associated with density anomalies of the lithosphere on intraplate stresses generated by the india eurasia convergence and the west pacific subduction

climate related river activity at the weichselian holocene transition a comparative study of the warta and maas rivers huvial systems from the dutch and polish lowlands are compared for their evolution during the weichselian deglaciation period in both regions the pleniglacial braided river pattern changed to a meandering pattern in the beginning of the lateglacial several transitional stages between braided and high sinuosity meandering systems have been recognized a difference in fluvial activity is found during the younger dryas when the maas transformed to a braided pattern while the warta maintained its meandering pattern phases of erosion and aggradation are more or less synchronous in the different river basins but their intensity may differ greatly the major characteristics of the fluvial systems are obviously a response to the general climatic evolution and related to changes in vegetation the regional differences are of minor importance and can be explained by site specific factors threshold values within the latter factors define the changes in river dynamics

control on off rift magmatism a case study of the baikal rift zone abstract the baikal rift zone brz is an active intracontinental rift zone with almost no rift related magmatism along the rift axis most magmatism is observed outside the rift center and e g the major vitim volcanic field is displaced more than 200 km from the rift center the reasons for this regional distribution of the magmatism are enigmatic in particular regarding the off rift magmatism we present results of numerical modeling of rift structures similar to brz that develop in the transition between craton and orogenic belt geophysical evidence suggests that pre existing weak zones control the location of the brz the models therefore include a pre set fault weak zone within the transition zone between the craton and the orogenic belt as an initial condition in the model if the pre existing fault is close to the craton partial melting in the mantle due to sub crustal extension is offset from the surface rift graben by over 200 km a horizontal shear zone in the lower crust transfers the extension from the shallow crust to the lithospheric mantle far from the rift graben a pre set fault close to the orogenic belt zone is required to explain magmatism close to the rift center in the southernmost brz we conclude that the location of the pre existing fault zone relative to a change in lithosphere thickness may shift the magmatism away from the surface expression of the rift graben and may explain the location of the off rift magmatism e g the basaltic vitim plateau the predicted geometry of the sedimentary graben along the rift strike is consistent with seismic observations in the northern and central brz

lower crustal intrusions beneath the southern baikal rift zone evidence from full waveform modelling of wide angle seismic data abstract the cenozoic baikal rift zone brz is situated in south central siberia in the suture between the precambrian siberian platform and the amurian plate this more than 2000 km long rift zone is composed of several individual basement depressions and half grabens with the deep lake baikal at its centre the best baikal explosion seismic transect project acquired a 360 km long deep seismic refraction wide angle reflection profile in 2002 across southern lake baikal the data from this project is used for identification of large scale crustal structures and modelling of the seismic velocities of the crust and uppermost mantle previous interpretation and velocity modelling of p wave arrivals in the best data has revealed a multi layered crust with smooth variation in moho depth between the siberian platform 41 km and the sayan baikal fold belt 46 km the lower crust exhibits normal seismic velocities around the rift structure except for beneath the rift axis where a distinct 50 80 km wide high velocity anomaly 7 4 7 6 0 2 km s is observed reverberant or ringing reflections with strong amplitude and low frequency originate from this zone whereas the lower crust is non reflective outside the rift zone synthetic full waveform reflectivity modelling of the high velocity anomaly suggests the presence of a layered sequence with a typical layer thickness of 300 500 m coinciding with the velocity anomaly the p wave velocity of the individual layers is modelled to range between 7 4 km s and 7 9 km s we interpret this feature as resulting from mafic to ultra mafic intrusions in the form of sills petrological interpretation of the velocity values suggests that the intrusions are sorted by fractional crystallization into plagioclase rich low velocity layers and pyroxene and olivine rich high velocity layers the mafic intrusions were probably intruded into the ductile lower crust during the main rift phase in the late pliocene as such the intrusive material has thickened the lower crust during rifting which may explain the lack of moho uplift across southern brz

cenozoic tectonic evolution of asia a preliminary synthesis abstract asia has been a major testing ground for various competing models of continental deformation due to its relatively well understood plate boundary conditions in the cenozoic exceptional exposure of active structures and strain distribution and widespread syn collisional igneous activity as a proxy for the thermal state of the mantle and crust two cenozoic orogens dominate the continent the himalayan tibetan orogen in the east induced by the india asia collision and the turkish iranian caucasus orogen in the west induced by the arabia asia collision the development of the two orogens was accomplished by shortening in the early stage followed by strike slip faulting and extension in the late stage in the himalayan tibetan orogen shortening across two discrete thrust belts at 55 30 ma in southern and northern tibet created a large intracontinental basin the paleo qaidam basin in between subsequent crustal thickening and a possible thermal event in the mantle e g convective removal of central tibetan mantle lithosphere may have raised the elevation of this early intra plateau basin up to 2 3 km to its current height collision between india and asia also caused lateral extrusion of southeast asia between 32 ma and 17 ma the latest stage of the india asia collision was expressed by north trending rifting and the development of trench facing v shaped conjugate strike slip faults in central mongolia central tibet eastern afghanistan and southeast asia in the turkish iranian caucasus orogen early crustal thickening in the orogenic interior began at or prior to 30 20 ma this style of deformation was replaced by strike slip faulting at 15 5 ma associated with further northward penetration of arabia into asia westward extrusion of the anatolia turkey block and rapid extension across the sea of crete and sea of aegean the late stage extension in both orogens was locally related to extensional core complex development the continental margin extension of east asia was developed in two stages initially in a widely distributed zone that has an east west width of 500 800 km during 65 35 ma which was followed by localized extension and opening of back arc basins associated with the development of spreading centers at 32 17 ma e g japan sea or east korea sea bohai bay and south china sea opening of the back arc basins could be induced by 1 rapid eastward migration of the western pacific trench system or 2 oblique subduction of pacific plate beneath asia that had produced a series of en echelon right slip primary shear zones linking with back arc spreading centers oriented obliquely to the strike of the nearby trench since 15 ma the eastern margin of asia became contractional in the east west direction as indicated by the collapse of back arc basins in the western pacific and the development of fold thrust belts along the eastern continental margin coeval with the contraction is widespread east west extension in siberia north china and the tibetan plateau the above observations can be explained by a change in boundary condition along the eastern margin of asia that allowed the thickened asian continent to spread eastward causing east west extension in its trailing edge and east west compression in its leading edge in west asia continental margin extension started at about 25 20 ma in the aegean and cretan regions which was associated with a rapid southward retreat of the hellenic arc the complex evolution of cenozoic deformation in asia may be explained by a combined effect of temporal changes in plate boundary conditions thermal evolution of the upper mantle perturbed by collisional tectonics and the built up of gravitational energy through crustal thickening and thermal heating although the past research in asia has treated the india asia and arabia asia convergence as separate collisional processes their interaction may have controlled the far field cenozoic deformation in asia the most pronounced result of this interaction is the creation of a northeast trending 300 400 km wide and 1500 km long zone of northwest striking right slip faults which extends from the zagros thrust belt in the south to western mongolia in the north and links with the active tian shan and altai shan intracontinental orogens cenozoic deformation and coeval igneous activity spatially overlap with one another in the himalayan tibetan and turkish iranian caucasus orogens a large cenozoic magmatic gap exists between tibet in the south and mongolia in the north where cenozoic deformation has not been associated with any coeval igneous activity finally cenozoic igneous activity is always associated with jurassic cretaceous magmatic arcs suggesting a causal relationship between the early arc magmatism and later syn collisional magmatism

morphotectonic evolution of two depressions at the southern border of the baikal rift system abstract detailed study of two dry depressions in the baikal rift system the e w khoito ghol tunka bistraya depression and the sw ne gusinoje ivolga depression aims to provide a better understanding of tectonic control on the intershoulder relief evolution after the rift opened both depressions are grabens and both feature a suite of 10 20 km wide basins alternating with more or less massive highs field and laboratory analysis shows that this pattern is of recent tectonic origin and that local breaking up and subsidence followed the general sinking which originally formed the grabens the subsidence belts seem to have gradually shifted north and northeastwards geomorphological analysis reveals that in both depressions the highs are remnants of a former pediment which was broken up the young basins display numerous relevant hydrographic anomalies of the secondary channels and a general water logging they also suggest that the subsidence belts have gradually shifted north and northeastwards in the gusinoje ivolga depression evidence was found of a plio pleistocene river course parallel to the selenga river which was later dismantled by the breaking up this depression parallel to the baikal rift and belonging to the mesozoic system of grabens in the caledonian fold belt seems to have been included into the general system of rifts during the pliocene tectonic phase as for the main hydrographic axes the selenga river was set on a palaeogene age planation surface before the first tectonic phase and kept its original course the irkut river flowed in the khoito gol tunka bistraya depression after the first tectonic phase and was not affected by the later breaking up in contrast the secondary drainage network is largely discordant despite their different geotectonic contexts the two depressions show a similar development of relief pattern which poses the question of the style of rift dynamics after the main pliocene tectonic phase

sedimentary history of the western bohai coastal plain since the late pliocene implications on tectonic climatic and sea level changes abstract thick cenozoic deposits from the western bohai coastal plain a tectonic subsiding region provide the potential to study the relations between sedimentary environments and tectonic climatic and sea level changes however sedimentary history of this region extending to the whole quaternary as well as their links to tectonic climatic and sea level changes are still poorly understood mainly because of the lack of long term records with well constrained chronology in this study we present an integrated record based on sedimentology and proxies grain size and color reflectance of a 203 6 m core recovered from the western bohai coastal plain near tianjin the core was chronologically well constrained using paleomagnetic and optically stimulated luminescence dating methods the results show that from the late pliocene 3 3 ma to the late pleistocene 0 10 ma the study region was mainly dominated by fluvial setting and the extensive incursion of sea water into this region began during the last interglacial period 0 10 ma the sedimentology and the color index suggest that tectonic subsidence of the bohai basin during the plio quaternary must have played a significant role in controlling the sedimentary environments in this region the changes in base level because of sea level fluctuations during the quaternary influenced the fluvial development greatly and led to the alternations of coarse crevasse splay channel and finer floodplain deposits in the core sequence in addition climatic changes since the late pliocene also have had significant effects on the sedimentary settings in the bohai coastal plain by influencing the fluvial process with a series of mechanisms

morphotectonic analysis and 10 be dating of the kyngarga river terraces southwestern flank of the baikal rift system south siberia the formation of the baikal rift system basins is controlled by active faults separating each basin from the adjacent horsts the kinematics of these faults is mainly explored through investigation of complex sequences of the fault intersecting river terraces that record both tectonic and climatic events this study focuses on the northern margin of the major tunka basin that develops south west of lake baikal the development of the basin is controlled by the segmented tunka fault we performed a detailed mapping of the kyngarga river terraces the best preserved terraces staircase in baikal rift system at their intersection with the tunka fault in order to decipher the chronology of seismic events and the slip rates along that segment of the fault key terraces were dated using in situ produced cosmogenic 10be we demonstrate that the formation of the terrace staircase occurred entirely during mis1 mis2 the obtained data allowed us to estimate the rate of incision at different stages of the terrace staircase formation and the relationship between the vertical and horizontal slip rates along this sub latitudinal segment of the tunka fault making respectively 0 8 and 1 12 mm yr 1 over the past 12 5 ka analysis of the paleoseismology and paleoclimate data together with terrace dating provided the possibility to estimate the influence of tectonic and climatic factors on the terrace formation our proposed model of the kyngarga river terrace development shows that the incisions into terraces t3 and t6 were induced by the abrupt climatic warming episodes gi 1 and gi 2 respectively whereas terraces t5 t4 and t2 were abandoned due to the vertical tectonic displacement along the tunka fault caused by coseismic ruptures

long term bedload mobility in gravel bed rivers using iron slag as a tracer abstract bedload dispersion is evaluated in gravel bed rivers using slag elements from ironworks established along rivers in the ardenne region between the fourteenth and the nineteenth centuries large quantities of slag were dumped close to these rivers or even directly into the channels for centuries slag elements were dispersed in the bedload and transported by floods of varying importance consequently slag may be considered as a reliable tracer to analyze bedload dispersion over several centuries the size of slag elements was studied along 16 ardenne rivers the longitudinal size trend of the largest slag particles allows the effective competence of these rivers to be determined between 19 and 129 mm for rivers where specific stream power for the bankfull discharge ranges between 20 and 134 w m a direct relationship doesn t exist between these two parameters as the size of slag elements must be considered with regard to the d 50 of the bed selective transport was analyzed directly downstream of the input sites the sorting distance varies from river to river and depends on the velocity of the coarse elements introduced into the river since the inception of the iron industry downstream of two metallurgic sites the slag propagation fronts were located as the periods of activity at these sites are known from historical studies the virtual velocity of bedload movement in these rivers was estimated to be 2 4 km century

multiple climatic cycles imprinted on regional uplift controlled fluvial terraces in the lower yalong river and anning river se tibetan plateau abstract the development of fluvial systems on the southeastern margin of the tibetan plateau is linked to significant and rapid late cenozoic uplift the relatively complete fluvial terrace sequence preserved along the yalong river valley and that of its tributary the anning river provides an excellent archive for studying the development of terraces in rapidly uplifting mountainous areas this study reveals that terrace development is predominantly controlled by multiscale climate cycles and long term uplift as shown by terrace dating sedimentary characteristics and incision rates at least six alluvial terrace units were identified in 20 transverse sections through the terraces along about a 600 km length of river and were dated using electron spin resonance esr and optically stimulated luminescence osl the climatostratigraphic positions of the terrace deposits and their respective age constraints suggest that fluvial aggradation was concentrated during marine isotope stages mis 32 22 18 4 2 and the younger dryas yd and that incision occurred during the succeeding cold to warm transitions the changes in fluvial style marked by terraces 6 5 and 4 predominantly occurred in synchrony with the 100 ka milankovitch climate cycles while terraces 3 and 2 were controlled by the obliquity driven 41 ka climate cycles finally the aggradation of terrace t1 occurred in response to the yd stadial during the intervening time between 0 72 and 0 063 ma terraces either did not form or were not preserved which may suggest that uplift rates varied through time and influenced terrace formation preservation the progressive valley incision recorded by these fluvial terraces cannot be entirely explained by climate cycling alone temporal and spatial variations in incision rates indicate that the continuing long term incision has been driven by uplift the temporal distribution of the incision rates reveals two rapidly uplifting stages in the southeastern tibetan plateau including an accelerated uplift that has been taking place since 0 06 ma the spatial distributions of differing incision rates reflect the geomorphological response to crustal shortening and differential uplift in this region

rift flank segmentation basin initiation and propagation a neotectonic example from lake baikal new surficial data field landsat tm and topography define morpho tectonic domains and rift flank segmentation in the ol9khon region of the central baikal rift deformation drainage and depositional patterns indicate a change in the locus of active extension that may relate to a recent

no moho uplift below the baikal rift zone evidence from a seismic refraction profile across southern lake baikal 1 the late cenozoic baikal rift zone brz in southern siberia is composed of several individual topographic depressions and half grabens with the deep lake baikal at its center we have modeled the seismic velocity structure of the crust and uppermost mantle along a 360 km long profile of the baikal explosion seismic transects best project across the rift zone in the southern part of lake baikal the seismic velocity structure along the profile is determined by tomographic inversion of first arrival times and 2 d ray tracing of first arrivals and reflections the velocity model shows a gently deepening moho from the siberian platform 41 km depth into the sayan baikal fold belt 46 km depth we can exclude the presence of any moho uplift around the 10 km deep sedimentary graben structure of southern lake baikal the lower crust includes a distinct 50 80 km wide high velocity anomaly 7 4 7 6 0 2 km s slightly offset to the northeast from the rift axis we interpret this feature as resulting from mafic intrusions their presence may explain the flat moho by compensation of lower crustal thinning by intrusion of mafic melts the pn wave velocities 8 15 8 2 km s are normal for the area and do not show any sign of decompression melting in the sub moho mantle such that possible lithosphere thinning has not reached the base of the crust on the basis of the results of the best project we suggest that the brz is formed by passive rifting in the rheologically weak suture between the siberian platform and the amurian plate

mantle structure and rifting processes in the baikal mongolia region geophysical data and evidence from xenoliths in volcanic rocks abstract the origin of the baikal rift zone brz has been debated between the advocates of passive and active rifting since the 1970s a re assessment of the relevant geological and geophysical data from russian and international literature questions the concept of broad asthenospheric upwelling beneath the rift zone that has been the cornerstone of many active rifting models results of a large number of early and recent studies favour the role of far field forces in the opening and development of the brz this study emphasises the data obtained through studies of peridotite and pyroxenite xenoliths brought to the surface by alkali basaltic magmas in southern siberia and central mongolia these xenoliths are direct samples of the upper mantle in the vicinity of the brz of particular importance are suites of garnet bearing xenoliths that have been used to construct p t composition lithospheric cross sections in the region for the depth range of 35 80 km xenolith studies have shown fundamental differences in the composition and thermal regime between the lithospheric mantle beneath the ancient siberian platform sampled by kimberlites and beneath younger mobile belts south of the platform the uppermost mantle in southern siberia and central mongolia is much hotter at similar levels than the mantle in the siberian craton and also has significantly higher contents of basaltic major elements ca al na and iron higher fe si and fe mg the combination of the moderately high geothermal gradient and the fertile compositions in the off cratonic mantle appears to be a determining factor controlling differences in sub moho seismic velocities relative to the siberian craton chemical and isotopic compositions of the off cratonic xenoliths indicate small scale and regional mantle heterogeneities attributed to various partial melting and enrichment events consistent with long term evolution in the lithospheric mantle age estimates of mantle events based on os sr nd isotopic data can be correlated with major regional stages of crustal formation and may indicate long term crust mantle coupling the ratios of 143 144nd in many lree depleted xenoliths are higher than those in morb or oib source regions and are not consistent with a recent origin from asthenospheric mantle mantle xenoliths nearest to the rift basins 30 50 km south of southern lake baikal show no unequivocal evidence for strong heating unusual stress and deformation solid state flow magmatic activity or partial melting that could be indicative of an asthenospheric intrusion right below the moho comparisons between xenoliths from older and younger volcanic rocks east of lake baikal together with observations on phase transformations and mineral zoning in individual xenoliths have indicated recent heating in portions of the lithospheric mantle that may be related to localised magmatic activity or small scale ascent of deep mantle material overall the petrographic p t chemical and isotopic constraints from mantle xenoliths appear to be consistent with recent geophysical studies which found no evidence for a large scale asthenospheric upwarp beneath the rift and lend support to passive rifting mechanism for the brz

crustal structure of central lake baikal insights into intracontinental rifting this is the published version copyright 1976 american geophysical union all rights reserved

holocene floodplain sediment storage and hillslope erosion within the rhine catchment the response of fluvial systems to land use and climate change varies depending on catchment size while forcing response mechanisms of small catchments are reasonably well understood the response of larger drainage basins is less clear in particular the impact of land use and climate change on the rhine system is poorly understood because of the catchment size 185 000 km 2 and the long history of human cultivation which started approximately 7500 years ago a sediment budget is calculated to specify the amount of alluvial sediment that was deposited during the holocene and to estimate long term soil erosion rates the results suggest that 599 14 10 9 t of holocene alluvial sediment is stored in the non alpine part of the rhine catchment south and central germany eastern france the netherlands about 50 of holocene alluvial sediment is deposited along the trunk valley and the delta upper rhine lower rhine coastal plain while the rest is stored along the tributary valleys the floodplain sediment storage corresponds to a mean erosion rate of 0 559 0 16 t ha per yr 38 59 10 7 mm kyr across the rhine catchment outside the alps this holocene averaged estimate amounts for sediments that were delivered to the channel network and is at the lower limit of erosion rates from other studies of different methodology

geomorphic mesozoic and cenozoic evolution in the oka jombolok region east sayan ranges siberia the east sayan ranges are a key area to understand the interactions between the transpressive deformation linked to the far field effects of the india asia collision and the extension linked to the opening of the baikal rift system the active deformation that affects this range is very recent around 5 ma but occurs in a very complex morphotectonic setting and the understanding of the tertiary deformation relies entirely on a detailed knowledge of the pre deformation situation using apatite fission track thermochronology cosmogenic 10be and morphological study on tertiary lava flows we demonstrate that prior to the oligocene the morphology of the east sayan area was characterized by a wide constantly rejuvenated erosion surface apatite fission track thermal modelling indicates that this surface started to form at least in late jurassic early cretaceous 140 120 ma the long term exhumation rates several tens of million years derived from apatite fission track data 17 5 m ma and the short term erosion rates over a few hundred thousand years derived from cosmogenic 10be data 12 20 m ma are coherent implying a near constant mean erosion rate since late jurassic this constant slow erosion prevented the formation of a lateritic kaolinic weathering crust on the planation surface by oligocene early miocene times a long wavelength uplift that remains to be explained induced incision that created shallow valleys later filled by basaltic lava flows finally the present short wavelength topography initiated during the pliocene

dynamics of intracontinental extension in the north baikal rift from two dimensional numerical deformation modeling we model the recent deformation along a lithospheric scale cross section perpendicular to the northern part of the baikal rift zone brz with two dimensional finite element models using realistic lithospheric structure and rheological properties and imposing extension as a far field boundary condition we find a model that matches reasonably well the topography observed deformation pattern gravity anomalies and age of formation of the northern brz our results suggest that 1 extensional strain can occur away from the main rift basin in the sayan baikal range and create depending on the rheological properties of the lithosphere a large off rift basin analogous to the barguzin basin or a series of basins and ranges as observed in the southern part of the sayan baikal range 2 anelasticity plays a major role by participating in the uplift of rift shoulders and hanging wall deformation and allowing the subsidence and tilting of the hanging wall along high angle planar normal faults 3 the lower crust accommodates differential strain between the brittle upper crust and upper mantle by horizontal shear and lateral flow towards the regions of crustal and mantle thinning 4 far field extensional stress and a lithospheric discontinuity inherited from paleozoic tectonic events are sufficient to initiate rifting and basin subsidence and 5 there is no or very little dynamic contribution of a hypothetic asthenospheric plume under the brz at least in the recent phase of its evolution fast rifting stage 3 5 myr

morphotectonic and paleoseismological studies of late holocene deformation along the primorsky fault baikal rift abstract the baikal rift is the largest cenozoic continental rift in asia and has developed at the boundary between the siberian craton and a collage of microplates composing the amurian lithospheric plate gps data show that the amurian plate moves southeastward at a rate of 3 4 mm yr with respect to stable eurasia but the slip rates along the main faults that control the opening of basins within the baikal rift system are still poorly quantified the recent graben system of the olkhon region of the central baikal rift is a key example for studying of synrift faulting we discovered a previously unknown paleoseismic structure in the course of our morphometric study of the primorsky fault scarp one of the youngest grabens within the baikal rift detailed topographic mapping of the deformation area and trenching across the fault scarp revealed two paleoseismic events responsible for scarp formation dating of organic remnants found in the trench walls allowed us to estimate a late holocene age for the paleoearthquakes and bracket the vertical slip rates along the primorsky fault to between 0 5 0 1 mm yr min and 0 9 0 2 mm yr max over the last 2 5 kyr the geomorphological and paleoseismological data in combination with the analysis of recent seismicity and horizontal geodetic rates suggest that the primorsky fault has accumulated elastic stress with the potential for a m 6 6 earthquake large earthquakes of this magnitude have occurred at least twice on the investigated fault segment during the last 1 4 kyr

modelling the loading stresses associated with active continental rift systems abstract the loading stress associated with an ideal active continental rift system underlain by a hot low density upper mantle such as that of baikal or east africa is modelled at various possible stages of evolution using elastic viscoelastic finite element analysis the first set of models excludes faulting an incipient hot upper mantle with anomalously low density of only 6 kg m 3 between 400 and 200 km depths produces a small uplift of 300 m and deviatoric tension of up to 70 mpa possibly sufficient to initiate a rift system the stress is transferred upwards into the upper elastic lithosphere by a combination of excess pressure and shearing stress produced by the deep load much larger deviatoric tension of up to 230 mpa occurs when the hot low density region extends upwards to the base of the lithosphere so as to produce 1 5 km isostatic uplift the tension is further increased by an asthenospheric upwelling but a small opposing compression is caused by crustal thinning in contrast local loading stresses associated with simple passive rifting are small symmetrical faulting is incorporated in the next set of models and a graben forms in response to the deviatoric tension the rate of faulting is critically influenced by the underlying viscosity distribution faulting slightly reduces the deviatoric tension except within the graben where it is generally slightly increased it is shown that the local loading tension can produce subsidence of a sediment loaded rift graben of 8 km or more by constraining the distant edge of a model with a faulted or otherwise weak central rift it is shown that a substantial rift push force can develop which may be of importance in the continental splitting mechanism the modelling explains the occurrence of tension in the present day uplifted rift systems which were initiated in the tertiary in presence of predominant continental compression it suggests that a hot upper mantle produced by a plume can initiate continental rifting in association with directional plate interior stresses and basement weaknesses

cenozoic normal faulting and regional doming in the southern hangay region central mongolia implications for the origin of the baikal rift province abstract the hangay dome in central mongolia is a mountainous region covering more than 200 000 km2 with numerous flat topped peaks over 3000 m that preserve a late cretaceous paleogene erosion surface doming began in the middle oligocene producing more than 2000 m of regional topographic uplift the range represents an important kinematic link between the baikal rift province to the north and altai transpressional ranges to the south and west structural field investigations of major faults visible on satellite imagery indicate that the southern hangay dome region is dominated by late cenozoic normal faults that bound small half graben most faults are ne striking and faults at the highest elevations are the most recently active most graben appear to be isolated systems that constitute small sediment sinks perched on the flanks and crests of the dome the first order feature is the dome itself and most sediment eroded off of the dome is deposited in the mongolian valley of lakes or is carried northwards by the selenga river and its extensive tributaries the basement of the dome is a precambrian craton although the shape and dimensions of the craton are poorly constrained to the north and east late cenozoic uplift of the southern dome region appears to be confined to the area underlain by cratonic basement whereas the altai region to the south and west is underlain by mechanically weaker palaeozoic arc and accretionary belts with respect to the regional northeast directed shmax the hangay craton appears to have acted as a rigid passive indentor focusing late cenozoic transpressional deformation around its west and southern margins models invoking a late cenozoic plume as the driving force for doming and widespread alkaline volcanism on the dome are not strongly supported by geochemical and isotopic data on neogene recent volcanics and the spatial correlation between areas that are domed and older cratonic crust appears too coincidental to be ignored convective removal of an overthickened lithospheric root leading to adiabatically decompressed asthenosphere could explain regional doming and volcanism however major crustal thickening last occurred in the permian in the southern hangay region and the time lag between thickening and postulated root removal and plateau uplift 200 myr appears too long an alternative model is explored based on speculated lithospheric mantle flow patterns driven by india s continued northeastward indentation it is suggested that lithospheric mantle flow diversion around the overthickened hangay craton crustal keel could cause lithospheric thinning beneath the craton and passive asthenospheric upwarp leading to regional topographic uplift and decompression melting alkali volcanism in general the angular relationship between precambrian craton boundaries and the prevailing northeasterly shmax appears to control the kinematics of late cenozoic deformation throughout the hangay altai sayan and baikal regions

late quaternary sedimentation history of the lena delta abstract core and outcrop analysis from lena mouth deposits have been used to reconstruct the late quaternary sedimentation history of the lena delta sediment properties heavy mineral composition grain size characteristics organic carbon content and age determinations 14c ams and ir osl are applied to discriminate the main sedimentary units of the three major geomorphic terraces which form the delta the development of the terraces is controlled by complex interactions among the following four factors 1 channel migration according to the distribution of 14c and ir osl age determinations of lena mouth sediments the major river runoff direction shifted from the west during marine isotope stages 5 3 third terrace deposits towards the northwest during marine isotope stage 2 and transition to stage 1 second terrace to the northeast and east during the holocene first terrace deposits 2 eustasy sea level rise from last glacial lowstand to the modern sea level position reached at 6 5 ka bp resulted in back filling and flooding of the palaeovalleys 3 neotectonics the extension of the arctic mid ocean ridge into the laptev sea shelf acted as a halfgraben showing dilatation movements with different subsidence rates from the continent side differential neotectonics with uplift and transpression in the siberian coast ridges are active both likely have influenced river behavior by providing sites for preservation with uplift in particular allowing accumulation of deposits in the second terrace in the western sector the actual delta setting comprises only the eastern sector of the lena delta 4 peat formation polygenetic formation of ice rich peaty sand ice complex was most extensive 7 11 m in thickness in the southern part of the delta area between 43 and 14 ka bp third terrace deposits in recent times alluvial peat 5 6 m in thickness is accumulated on top of the deltaic sequences in the eastern sector first terrace

baikal rift active or passive comparison of the baikal and kenya rift zones abstract the comparison of geological and geophysical data from the kenya and baikal rift zones permits us to consider the formation of these zones to be associated with the development of wide asthenospheric upwellings beneath them in this sense both rifts are active differences between them in amounts of volcanics and geological features may be explained by a higher degree of partial melting of asthenospheric material beneath the kenya rift

the influence of a stratified rheology on the flexural response of the lithosphere to un loading by extensional faulting summary we present a two layered finite diverence model for the flexural response of the lithosphere to extensional faulting the model allows for three modes of flexure 1 fully coupled with the upper crust and mantle welded together by the lower crust 2 fully decoupled with the upper crust and mantle behaving as independent layers and 3 partly decoupled signifying that the response of the upper crust to small wavelength loads is superimposed on the response of the entire lithosphere to long wavelength loads which of these modes of flexure is to be expected depends on the rheology and especially the thermal state of the lithosphere coupled behaviour is related to a cold and strong lithosphere the baikal rift zone provides a typical example for this mode of flexure a fully decoupled lithosphere is an exceptional case related to anomalous high temperatures in the lower crust and is observed in the basin and range province the most common case is a partly decoupled lithosphere with the degree of decoupling depending on the thickness and viscosity of the lower crust this is inferred for example for the bay of biscay margin

timescales climate and river development abstract in the long term glacial interglacial sequences river development follows general climatic evolution however at the scale of one cold warm cycle it appears that the geomorphological effect of river activity is best expressed at times of climatic change such periods of pronounced fluvial action last only a short time in more detail the internal evolution in a drainage basin after a climatic event results in a delayed response of the morphology and sedimentation pattern finally on the shortest timescale local thresholds may play a decisive role in the reactions of river systems it is concluded that the relation between fluvial development and climate is not a simple one but is fundamentally dependant on the timescale