tectonosedimentary evolution related to extreme crustal thinning ahead of a propagating ocean example of the western pyrenees 1 in this paper we describe the tectonosedimentary evolution and its subsequent inversion of a basin that underwent extreme crustal thinning in a transtensional setting ahead of a propagating ocean in the western pyrenees the labourd mauleon area situated in the western pyrenees at the termination of the v shaped bay of biscay is an ideal natural laboratory to study how such complex basins evolve in time and space because of a mild inversion of the basin during pyrenean compression the rift structures and their relations to basement rocks and sediments are exposed and can be directly studied in the field the basin shows a complex polyphase evolution that starts with left lateral dominated transtension in latest jurassic early aptian time this event is overprinted by a late aptian early albian extension that is related to the counterclockwise rotation of iberia away from europe leading to the opening of the bay of biscay during this stage the late triassic to jurassic carbonate platform was stretched salt migrated and detachment faults exhumed upper and lower crustal and mantle rocks to the seafloor the final structure of the basin resembles a sag basin floored by exhumed rocks overlain by extensional allochthons and compartmentalized by n40 to n60 transfer faults the sedimentary architecture is characterized by late aptian synrift sediments e g urgonian limestones that were deposited in fault bounded basins and are overlain by thick latest aptian to albo cenomanian sediments e g flysch noir that define a sag sequence the complex tectonosedimentary evolution of the basin is associated with salt tectonics and overprinted by a major magmatic thermal event that postdates mantle exhumation

riverine dunes on the coastal plain of georgia usa abstract relict eolian dunes on the georgia coastal plain line the north and east sides of many se trending streams and contain important paleoenvironmental information a detailed analysis of four dune fields characterizes dune geomorphology stratigraphy sedimentology and soils georgia s inland dunes range from parabolic to infilled parabolic to irregular in form typically merge to form long chains that parallel source streams and can occur as distinct bands typically the dunes are composed of 95 quartz sand grains with more than half the sand falling in the medium sand fraction dunes overlie flood plain and pointbar sands backswamp and peat deposits fluvial terraces and other dunes in places organic deposits occur on top of dunes cross bedding is observable in dunes more than about 4 m thick and indicates eastward dune migration paleosols found within some dunes indicate holocene reworking conditions favoring dune formation likely included at least seasonal aridity postdepositional modification of the dunes includes a smoothing of the dune surface a clay increase in the c horizon spodic horizon development bioturbation removal of weatherable minerals and fluvial incision

three dimensional gravity and magnetic modeling of crustal indentation and wedging in the western pyrenees cantabrian mountains 1 the complex crustal structure of the boundary zone between the iberian and european plates from the western pyrenees to the cantabrian mountains is probed by three dimensional 3 d gravity and magnetic modeling constrained by deep seismic profiles the 3 d modeling results support the presence of a continuous iberian crustal root and suggest that the geometry of the orogenic belt that formed in latest cretaceous tertiary times along the northern margin of iberia was conditioned by oblique structures separating areas characterized by different tectonic styles in the western pyrenees and the basque cantabrian basin a thick mesozoic basin presently incorporated to the pyrenean cantabrian belt the relatively narrow thinning of the crust inherited from the mesozoic rifting stage conditioned a structural style in which portions of the southward indenting european lower crust are interpreted to be back thrusted toward the north and uplifted to shallow depths promoting the appearance of significant potential field anomalies in the basque cantabrian basin the strongest aeromagnetic anomaly of the whole iberian mainland is superimposed on the eastern part of a well defined positive gravity anomaly similar in amplitude and wavelength to those located along the north pyrenean zone these observations suggest that the eastern part of the dense lower crustal causative body is strongly magnetized and may correspond to a gabbroic cumulate originated in the axis of the ancient mesozoic rift to the west tertiary compression affected the north iberian cantabrian passive continental margin whose geometry and inherited structures conditioned the formation of a double crustal delamination and the uplift of the cantabrian mountains

deflation and redeposition of sand dunes in finnish lapland abstract deflation and redeposition of aeolian sands in finnish lapland have been studied by analysis of their sedimentology and stratigraphy by dating buried charcoal layers and by obtaining tl dates the thickness of redeposited sands on buried soils ranges from a few decimetres to more than two metres original dune formation after deglaciation finished around 7000 bp subsequent aeolian activity has been mainly destructive in nature deflation started in some regions about 4800 bp continuing with several breaks until the present some deflation basins have stayed active for at least 1300 years however it is too early to draw general conclusions for the whole area forest fires have been important reactivators of aeolian sand drift but tend to be rather local events change in the ground water table is a basic factor affecting deflation at present human impact and overgrazing by reindeer seem to increase deflation

reconstruction of holocene high altitude vegetation cover in the french southern alps evidence from soil charcoal the study presented here from the southern french alps demonstrates the reliability of soil charcoal analysis for the study of holocene past treeline positions the occurrence of charcoal in mineral soils along transects from 1950 m up to 2920 m demonstrates the role of fire in the establishment of the present vegetation patterns the abrupt decrease of charcoal concentration at about 240 0 2 600 m which varies across the study sites corresponds to the modern transition between subalpine forest and alpine tundra charcoal particles formedinsitu providehighspatial resolutiondataforthereconstructionofpastforestandtreelinechanges soil charcoal analysis indicated that 1 treeline was 300 m higher around 6800 cal bp than today and 2 the uppermost forest belt up to 2810 m was colonized by larch larix decidua mill and arolla pine pinus cem bra l thispineispresenttodaybutpatchilydistributed itisabsentfromthethreeareasstudied radiocarbon dates ranging from c 6800 cal bp to the modern period along with historical and archaeological data sug gest that the present pattern of the uppermost forest belt and the patchy distribution of arolla pine in the stud ied area are the results of anthropogenic fire mainly agropastoral activities the question of global warming consequences on treelines in this part of the french alps is discussed

independence of geostatic stress from overconsolidation in some beaufort sea clays reply since 1982 extensive use has been made of the self bored pressuremeter in arctic offshore site investigations one finding of this work is that the in situ geostatic stress ratio k0 of beaufort sea clays is apparently unrelated to the overconsolidation ratio ocr the procedures and data to support this finding are documented and the finding is discussed in light of the present geological understanding for the area it is concluded that the independence of k0 from ocr may be quite widespread a finding that contradicts the widely held tenet regarding the existence of a single valued function relating k0 and ocr if k0 is regarded as important then it should be measured in situ key words self bored pressuremeter geostatic stress ratio k0 beaufort shelf geologic history overconsolidation ratio

deep structure of the ocean continent transition in the southern iberia abyssal plain from seismic refraction profiles ocean drilling program legs 149 and 173 transect we present a wide angle seismic refraction study of an 80 40 km region of the southern iberia abyssal plain south of galicia bank an intersecting grid of two e w and four n s wide angle reflection refraction profiles is used to define variations of the basement velocity structure within this unusually wide ocean continent transition oct these structures can be systematically linked to variations in acoustic basement morphology and to results from ocean drilling program odp boreholes lateral changes in the velocity structure of the basement occur abruptly over distances of 20 km where complex variations may be found thinned upper continental crust 2 5 km thick with velocities of 5 0 6 6 km s is limited to a series of n s fault blocks immediately south of galicia bank this crust is underlain by a high velocity layer 7 3 7 9 km s of weakly serpentinized i e 0 25 peridotite which exists throughout the eastern part of the survey area basement within the oct appears to consist dominantly of a broad region of exposed upper mantle that has been serpentinized heterogeneously both vertically and horizontally in the southeast sector of our survey where basement topography deepens and becomes subdued continental fault blocks are absent instead basement contains an upper layer of more pervasively serpentinized i e 25 45 peridotite that is 2 km thick this layer is characterized by low velocity at the top of basement 4 2 km s that increases rapidly with depth and it probably corresponds to a seismically unreflective layer previously identified in reflection profiles to the south of our survey in the western section of our survey beneath a series of elevated basement ridges velocities are reduced within both the upper basement layer 3 5 6 0 km s and lower layer 6 4 7 5 km s these changes suggest that both upper and lower layers have become more highly serpentinized with values of 60 100 in the upper layer and 25 45 in the lower layer probably during the last stages of rifting and immediately before formation of oceanic crust a normal or slow spreading oceanic crustal structure is not found within the survey region thus it appears that the onset of seafloor spreading occurs in the region west of the peridotite ridge sampled at odp site 897 and east of the j magnetic anomaly

the coefficient of earth pressure at rest laboratory experiments on undisturbed specimens of a large number of soft clay deposits as well as previous measurements on clays and granular soils were used to examine and explain the magnitude and behavior of the coefficient of earth pressure at rest k0 i after sedimentation primary consolidation ii during secondary compression aging iii after active or passive preshearing away from the laterally constrained condition iv during a decrease in effective vertical stress and v during an increase in effective vertical stress in the recompression or compression range in terms of the slope of the effective horizontal versus effective vertical stress path the behavior of k0 is explained using the concept of mobilized angle of friction in laterally constrained deformation condition the jaky equation provides in terms of the angle of internal friction a good estimate of k0 of sedimented normally consolidated young clays and granular soils as well as of of presheared clays and sands

plate reconstruction of the bay of biscay a plate reconstruction of the bay of biscay to a predrift stage is proposed on the basis of 1 an aptian albian tectonic pattern of the basque cantabrian region in northern spain which suggests major left lateral strike slip movements and 2 a continental margin that matches predrift stages plate reconstruction results from the juxtaposition of the two continental margins of the bay of biscay so that the eastern north spanish margin lies laterally adjacent to the southwest french margin landes plateau and the western north spanish margin borders the eastern part of the meriadzek terrace in the armorican margin the restoration obtained is supported by both the implied amount of clockwise rotation of iberia 37 very close to the 35 suggested by paleomagnetism and the positive matching of north south oriented transform structures from the south biscay margin with northeast southwest oriented transform structures from the north biscay margin

the role of the bay of biscay mesozoic extensional structure in the configuration of the pyrenean orogen constraints from the marconi deep seismic reflection survey 1 seismic interpretation of the marconi deep seismic survey enables recognition of the upper crustal structure of the eastern part of the bay of biscay and the main features of its alpine geodynamic evolution the new data denotes that two domains with different pyrenean and north foreland structures exist in the bay of biscay in the eastern or basque parentis domain the north pyrenean front is located close to the spanish coast and the northern foreland of the pyrenees is constituted by a continental crust thinned by a north dipping fault that induced the formation of the early cretaceous parentis basin in the western or cantabrian domain the north pyrenean front is shifted to the north and deforms a narrower and deeper foreland basin which lies on the top of a transitional crust formed from the exhumation of lithospheric mantle along a south dipping extensional low angle fault during the early cretaceous the transition between these two domains corresponds to a soft transfer zone linking the shifted north pyrenean fronts and a north to wnw directed thrust that places the continental crust of the landes plateau over the transitional crust of the bay of biscay abyssal plain comparison between this structure and regional data enables characterization of the extensional rift system developed between iberia and eurasia during the late jurassic and cretaceous and recognizes that this rift system controlled not only the location and features of the pyrenean thrust sheets but also the overall structure of this orogen

k o ocr relationships in soil the relationships between k o and ocr are investigated for primary loading unloading reloading conditions the study reviews laboratory data from over 170 different soils and presents an approach common to clays silts and sands simple empirical methods for predicting k o for normally consolidated and overconsolidated soils are evaluated the validity of the methods is supported by statistical analyses on the basis of the findings only the effective stress friction angle o and prior stress history ocr and ocrmax are needed to predict approximate values of k o

seismic image of the cantabrian mountains in the western extension of the pyrenees from integrated escin reflection and refraction data abstract integrated analysis of normal incidence and large aperture seismic reflection data collected in 1992 and 1993 within the spanish escin and complementary projects provide a first complete n s crustal transect across the northern iberian peninsula and continental margin images of the crustal structure of the cantabrian mountains and their transition to the duero basin and to the cantabrian margin are obtained from a a 65 km long vertical reflection profile escin 2 on land b a 200 km long reversed refraction profile and c wide angle recordings of the marine escin 4 profile consistent results between reflectivity pattern and velocity depth distribution reveal important lateral variations in the deep structure the reflective crust imaged in the escin 2 profile changes its attitude from sub horizontal beneath the duero basin to north dipping beyond the mountain front basement thrusts are observed in the upper crust merging into a detachment at 6 s twt and may have triggered the alpine uplift of the range the moho is identified at the bottom of the reflective lower crust and deepens from 12 to 15 s at the northern end of the profile about 35 km inland modelling of the refraction data laterally extends the seismic image and provides evidence for variscan crustal features beneath the duero basin northwards the velocity in the lower crust decreases and the moho constrained by the wide angle data from profile escin 2 deepens to about 60 km ending abruptly at the shoreline the velocity depth model is constrained along the asturian platform up to the continental slope where the crust mantle boundary is located at 24 km depth this margin moho shows a progressive deepening southwards and extends to the coast where it is found at 30 km depth the present seismic data support an important alpine reworking and thickening of the crust under the cantabrian mountains the onshore offshore transition is marked by an imbrication of two crusts of very different thicknesses this signature offers a strong parallelism with the one previously observed further east across the pyrenees in the ecors seismic profile

mid holocene environmental changes in the bay of skaill mainland orkney scotland an integrated geomorphological sedimentological and stratigraphical study a detailed multidisciplinary investigation of intertidal freshwater sediments exposed in the north of the bay of skaill mainland orkney scotland have revealed a complex sedimentary sequence this provided evidence for dynamic coastal environmental changes in the area since the mid holocene freshwater ponds developed on glacial sediments ca 6550 80 yr bp cal bc 5590 5305 from ca 6120 70 yr bp cal bc 5040 4855 these were infilled by blown sand from the distal edge of a dune ridge located to the west thereafter a series of sand blow events alternating with periods of quiescence occurred until ca 4410 60 yr bp cal bc 3325 2900 between ca 5240 160 and 4660 80 yr bp cal bc 4370 3115 pollen and charcoal records show evidence of anthropogenic activities associated with the nearby neolithic settlement of skara brae agriculture was probably affected by recurrent sand movement and widespread deposition of calcium carbonate in the hinterland of the bay machair development between ca 6100 and 5000 yr bp cal bc 5235 3540 corresponds to a mid holocene phase of dune formation recorded elsewhere in northwest europe the more recent and progressive formation of the bay has probably been related to increasing external forcing via storminess long term relative sea level change and sediment starvation within this exposed environment copyright 2000 john wiley sons ltd

charcoal and wood remains for radiocarbon dating upper pleistocene loess sequences in eastern europe and central siberia abstract the present paper concerns long upper pleistocene loess sequences from eastern europe with multiple upper palaeolithic occupations rich in charcoal as well as loess sequences from central siberia with abundant wood remains these complementary records have allowed establishing a high resolution climatic sequence integrating 24 interstadial episodes between ca 42 5 and 10 kyr bp here we discuss the methodology of dating used to fix the chronological framework of this climatic sequence based on a set of 240 available radiocarbon dates mainly produced on charcoal and wood remains special attention is paid to the strategy of sampling charcoal and wood material in strict accordance with stratigraphy as well as to the preparation process in the laboratory for extraction cleaning identification and selection of the best fragments to date careful stratigraphic drawing and detailed positioning of the samples for each geological layer are also considered in order to clarify the relationship of the obtained dates with respect to any sedimentary pedological or archaeological event to be dated the reliability and accuracy of the dates obtained from loess sequences are further controlled by the internal consistency with regard to stratigraphy palaeoenvironmental implications are also discussed

deep structure of the armorican basin bay of biscay a review of norgasis seismic reflection and refraction data the bay of biscay is bounded to the north by the north biscay margin which comprises the western approaches and armorican segments in the 1970s and 1980s most researchers considered this margin typical of a non volcanic passive margin it is characterized by a striking succession of tilted blocks beneath which occurs the s reflector and the continent ocean boundary is abrupt this paper examines the armorican segment and is based on a study of all early seismic profiles together with new multichannel reflection and refraction seismic data norgasis cruise an important result is the discovery of a 80 km wide ocean continent transition zone that coincides with the armorican basin a deep sedimentary basin it is characterized by a high velocity lower crustal layer 7 4 7 5 km s 1 overlain by sediments the other results are 1 the main crustal thinning occurs exclusively under the narrow continental slope 2 the tilted blocks and the s reflector are observed only at the base of the continental slope in the narrow domain called the neck area 3 the north biscay ridge is a large oceanic plateau present only off the nw armorican margin rather than a long ridge elongated off the whole north biscay margin

initiation of an active margin at the north iberian continent ocean transition 1 the north iberian or cantabrian margin located at the southern flank of the bay of biscay underwent successive tectonic regimes of rifting passive margin and compression from mesozoic to tertiary times a complete crustal cross section of the north iberian margin from the abyssal plain to the shoreline and a reconstruction of its undeformed upper cretaceous structure are presented here it is constrained after the compilation and interpretation of different geophysical data sets recently available in the area the reflective pattern is provided by deep seismic reflection profile escin 4 complemented by commercial profiles and well information from the north iberian platform and the velocity depth control comes from an onshore offshore wide angle seismic profile tested also with gravity modeling the detailed cross section of the meso tertiary basins that fill the platform and abyssal plain shows structures from the three main tectonic events 1 normal faults and asymmetric basins from the permian to lower cretaceous extensional stage 2 upper cretaceous sediments deposited under stable conditions during the passive margin period and 3 inverted faults thrusts and folds related to the tertiary compression the deep structure of the crust beneath the margin is poorly constrained from escin 4 profile that shows reflectivity in the lower crust only at a small area under the platform however the corresponding wide angle experiment provides a conspicuous image of the moho that shows a continued deepening toward the continent on the basis of the geophysical results we propose a new model for this margin where the lower crust is detached and underthrusted to the south as a result of the partial closure of the bay of biscay an interpreted mesozoic crustal scale extensional detachment could be the weakness zone that allowed the lower crust to slide southward under the upper crust resulting in the indentation of the cantabrian margin lower crust into the iberian crust plate convergence stopped at an early stage making this a unique area to study the initial stages of deformation of a passive margin

plant landscape reconstruction above the current timberline at the monte cimone and corno alle scale mountain areas northern apennines italy during the late holocene the evidence from soil charcoal this paper presents the first pedoanthracological study carried out on two mountains of the northern apennines monte cimone and corno alle scale where the results provided new palaeoenvironmenta

thermochronology of a convergent orogen constraints on the timing of thrust faulting and subsequent exhumation of the maladeta pluton in the central pyrenean axial zone abstract the pyrenees mountains of spain and france are a collisional orogen cored by a south vergent antiformal stack of paleozoic basement thrust sheets the axial zone thrusting accommodated shortening due to convergence between iberia and europe granitic plutons intruded during the hercynian orogeny form an important component of the basement units thermochronology of granodioritic samples collected from a vertical age elevation profile from the south central maladeta pluton provide new constraints on the timing of thrust faulting and rock exhumation of the pyrenean orogen the maladeta massif lies within the orri thrust sheet presently occupying the immediate footwall of the gavarnie thrust a major axial zone alpine age thrust fault new biotite and k feldspar 40ar 39ar and apatite u th he ahe data combined with previous apatite fission track aft thermochronology and structural studies of the maladeta pluton constrain the thermal evolution of this massif biotite weighted mean plateau and k feldspar maximum 40ar 39ar ages from the highest elevations of the maladeta pluton 2850 m are 280 ma close to the age of intrusion and are interpreted to date the timing of rapid cooling in the hercynian subsequently the maladeta massif remained close to the surface as indicated by the presence of unconformable triassic continental sediments k feldspar 40ar 39ar multiple diffusion domain thermal models from two samples at lower elevations 1780 m and 1400 m indicate heating initiated at 65 ma reaching maximum temperatures of 270 to 280 c these data are interpreted to record thrust burial of the maladeta pluton to depths of 6 10 km in the footwall of the gavarnie thrust burial and heating were followed by a period of relatively rapid cooling beginning at 50 ma recorded in three k feldspar thermal models from samples at different elevations 2850 m 1780 m and 1400 m aft thermal models in conjunction with the aft and apatite ahe age elevation profile interpretation reveal a lower temperature portion of the thermal history these data indicate the onset of rapid cooling that began at 30 35 ma slowed dramatically at 25 30 ma and continued at a reduced rate until 15 ma finally aft thermal models from the lowest elevation samples record rapid cooling in the late miocene pliocene most likely due to re excavation of the southern flank of the pyrenean orogen following burial by syn tectonic conglomerates the integrated thermochronologic data set from the age elevation profile within the maladeta pluton illustrates the potential for obtaining age constraints related to processes operating within the interior portions of convergent orogenic systems e g the onset and or duration of thrust fault activity that are otherwise unobtainable

holocene environmental change in subarctic aeolian dune fields the chronology of sand dune re activation events in relation to forest fires palaeosol development and climatic variations in finnish lapland sand dune stratigraphy radiocarbon dated charcoal layers palaeosol development and luminescence dating are used to reconstruct the holocene environmental history of the dune fields in finnish lap

lake belau and its catchment northern germany a key archive of environmental history in northern central europe since the onset of agriculture the environmental history since the onset of agriculture was reconstructed from sediments and soils in the catchment area of lake belau schleswig holstein northern germany the established chron

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

large scale controls on the development of sand seas in northern china abstract although sand seas are located in arid regions given that the proportions of dune areas vary greatly from region to region they are clearly influenced by other factors as well as aridity this paper discusses the distribution pattern and major features of sand seas and large fields of stabilized dunes in northern china and demonstrates the main influences on their development it appears that the availability of onsite loose sediments not wind strength is critical to the occurrence of the sand seas on a regional scale tectonic endorheic basins or areas of alluvial fans or forelands of mountain ranges are advantageous to the accumulation of fluvial sediments and thus are ideal locations of large sand seas in an arid climate the large dune fields currently stabilized by vegetation were active sand seas during the drier periods of the late pleistocene and early holocene the distribution patterns of chinese sand seas suggest that the height or size of the dunes in the sand seas are determined more by the availability of sands than any other potential factors as the sand seas in china account for a large portion of deserts in the middle latitudes of the northern hemisphere taklamakan is the second largest sand sea on earth knowledge of these sand seas past changes is important for understanding climatic changes in the terrestrial regions of mid latitudes

wood charcoal analysis at riwi cave gooniyandi country western australia abstract wood charcoals excavated from archaeological sites provide a useful tool for palaeoenvironmental reconstruction particularly in arid and semi arid zones where suitable catchments for palynological archives are often limited preservation of organic material in northern australia is characteristically poor and wood charcoal analysis provides a viable alternative to understand shifts in woody vegetation in the past the analysis of charcoal from matrix contexts at riwi cave located in the southern kimberley region of northern western australia has allowed a reconstruction of the local woody vegetation during occupation over the last 45 000 years the wood charcoal assemblage from the holocene stratigraphic units reflects the composition of the modern vegetation and illustrates that people were occupying the site during periods of relative humidity the pleistocene stratigraphic units show a shift in vegetation composition from eucalyptus spp to corymbia sp dominated savanna with an understory of secondary shrub associated with a late mis 3 arid event observed in both terrestrial and marine archives suggesting that activities continued at riwi during this arid event further anthracological analysis of other sites in the kimberley will help to build a regional picture of woody vegetation change and will further disentangle local and regional climatic signals particularly in relation to phases of occupation

determination of erosion thickness by numerical back analysis the case study of badenian clays in the carpathian foredeep czech republic abstract the paper describes an application of the geotechnical numerical back analysis in estimating the thickness of eroded sedimentary overburden in shallow basinal sediments the approach is based on the back analysis of the coefficient of earth pressure at rest k 0 and on estimating the unloading from the obtained k 0 value this approach is compared with the conventional methods represented by baldwin butler s compaction curves and casagrande s concept of preconsolidation stress the results of these two commonly used methods are incorrect if the sedimentary profile is affected by ageing effects such as cementation secondary compression etc the method is demonstrated on the lower miocene marine clay often called tegl which was deposited in the carpathian foredeep in the vicinity of brno czech republic the numerical back analysis was applied to galleries and adits opened during site investigation of the kralovo pole tunnels in brno the application of baldwin butler s equation suggested the erosion thickness of 180 270 m and casagrande s method of 100 800 m while the numerical back analysis of 0 40 m

geophysical constraints on the deep structure of a limited ocean continent subduction zone at the north iberian margin 1 late cretaceous to cenozoic convergence between iberia and europe led to the partial closure of the bay of biscay with limited southward subduction of oceanic crust below the north iberian margin inclined sub moho reflections and diffractions observed in deep seismic reflection profiles shot across the margin are especially well represented in two reflection profiles escin 3 2 and escin 3 3 these two profiles have been chosen to test if the sub moho reflections correspond to true primary deep events and provided that they are reflecting off the subduction zone to investigate its deep structure spectral analysis together with travel time estimation and migration allow us to characterize a number of these sub moho events as deep source low frequency 19 hz reflections and diffractions synthetic seismograms were generated by three dimensional seismic modeling of a sub moho southward dipping surface interpreted to correspond to the top of subducted oceanic crust comparison between the real and synthetic data show that inclined low frequency sub moho reflections in both escin 3 2 and escin 3 3 profiles may correspond to reflections from southward subducted bay of biscay oceanic crust geoid free air gravity and absolute topography modeling provides additional constraints on the lithospheric scale structure of this limited ocean continent subduction zone beneath the north iberian margin

crustal thinning on the aquitaine shelf bay of biscay from deep seismic data in recent years an increasing amount of new scientific data on the structure and nature of the whole continental crust has been acquired from deep seismic profiling the bay of biscay profile was recorded in 1984 at sea along the aquitaine platform for the french ecors group in association with hispanoil it collected a unique set of two ship multi channel seismic data with constant offset and expanded spread profiles in a complex geological area the data are of very good quality and contain clear moho and lower crust reflections as seen under most parts of western europe where similar experiments have been conducted1 4 this profile provided for the first time the most convincing evidence for an anomalously thin crust below a rifted basin the parentis basin which is directly connected to the oceanic area of the bay of biscay it gives new constraints for understanding the formation of extensional sedimentary basins

stiff sedimentary clays geological origins and engineering properties this keynote paper summarises and extends earlier work on the characterisation of clays with particular reference to stiff sedimentary clays examples of clay characterisation are given that include the various main geological events from sedimentation to erosion and weathering and other phenomena such as diagenesis and brecciation the examples demonstrate the value of plotting basic data such as the current stress state and undrained strength in terms of the void index these three parameters permit an immediate simple categorisation in terms of geological history of sedimentary clays further examples illustrate the engineering consequences of weathering of stiff clays and the associated phenomenon of brecciation produced by the processes of cambering and valley bulging it is emphasised that at all stages in a clay s geological history it is the bond strength between the soil particles not the geological preconsolidation stress that controls the mechanical behaviour of sedimentary clays

paleomagnetic structural and stratigraphic constraints on transverse fault kinematics during basin inversion the pamplona fault pyrenees north spain 1 the pamplona fault in the pyrenees is a major transverse structure that has been classically interpreted as a strike slip fault however lack of consensus concerning the sense of movement casts doubt on its actual kinematics and as a consequence its role in the cenozoic evolution of the pyrenees remains controversial in order to assess its kinematics we have conducted a paleomagnetic structural and stratigraphic study focused on the mesozoic and tertiary sedimentary rocks that outcrop around the southern segment of the fault restoration of balanced cross sections allows us to examine the present day spatial relationship of the sedimentary sequences on both sides of the fault and to reconstruct the geometry of the extensional basins formed during mesozoic rifting episodes in the bay of biscay and pyrenean domains paleomagnetic results indicate that no significant tectonic rotations occurred around the fault during tertiary inversion of the pyrenees the lack of tectonic rotations and revaluation of previous hypotheses argues against a strike slip movement of the fault we propose a new model in which the pamplona fault is treated as a large scale hanging wall drop fault whose kinematics was determined by variations in the geometry and thickness of mesozoic sequences on both sides of the fault these variations influenced the geometry of the thrust sheet developed during tertiary compression we are unaware of any other transverse fault that has been interpreted in this fashion thus the pamplona fault serves as a case study for the evolution of transverse faults involved in basin inversion processes

hydrological and climatic changes in deserts of china since the late pleistocene article i nfo article history large areas in western china were wetlands or less arid between 40 and 30 ka corresponding to the greatest lake period on the adjacent tibetan plateau during the last glacial maximum some of these western chinese deserts again experienced wetter conditions however at the same time the sandy lands in the eastern chinese desert belt experienced an activation of aeolian dunes while interpretations of the mid holocene environment in the deserts of china are controversial it is quite likely that it was more humid not only in the eastern areas influenced by monsoon climate systems but also in the western deserts where moisture is currently associated with westerlies evaluation of lacustrine records in the lakes recharged by dryland rivers and the complex interactions of these systems as well as other paleoenvironmental proxies such as the artemisia chenopodiaceae ratio should be interpreted with greater caution facing the highlighted uncertainties in our understanding of climate changes in chinese deserts it is hoped that this special issue will improve our knowledge considerably

assessing holocene vegetation and fire history by a multiproxy approach the case of stodthagen forest northern germany the woodland history of the forest of stodthagen northern germany was investigated by using complementary palaeobotanical indicators six soil profiles from the study plot were sampled the wood charcoal pieces extracted from the soil samples were quantified taxonomically identified and some were radiocarbon dated peat sequences from a small adjacent mire were also sampled and the pollen microcharcoal and macrocharcoal were analysed the pollen record shows a continuous forestation during the holocene with small indication of a disturbance phase during the late holocene this continuity of the woodland presence is confirmed by the weak quantity of macrocharcoal indicating that fire did not have a serious impact during the holocene in terms of canopy opening despite the identification of three local fire events however large amounts of wood charcoal pieces were found in the soil samples allowing the identification of at least one more fire event dated in the iron age unrecorded in the charcoa

dominance of an 150 year cycle of sand supply change in late holocene dune building along the eastern shore of lake michigan outcrops of buried soils on lake plains and glacial headlands along lake michigan s eastern shore suggest that periodic dunebuilding has occurred there after relatively long 100 yr periods of low sand supply we located described and radiocarbon dated 75 such buried soils that crop out in 32 coastal dune fields beside the lake we assume that peaks in probability distributions of calibrated 14 c ages obtained from wood charcoal and other organic matter from buried a horizons approximate the time of soil burial by dunes plotted against a late holocene lake level curve for lake michigan these peaks are closely associated with many 150 yr lake highstands previously inferred from beach ridge studies intervening periods of lower lake levels and relative sand starvation apparently permitted forestation and soil development at the sites we studied while late holocene lake level change led to development and preservation of prominent foredunes along the southern and southwestern shores of lake michigan the modern dune landscape of the eastern shore is dominated by perched dunes formed during 150 yr lake highstands over the past 1500 yr 2000 university of washington

anthropogenic influence on rates of aeolian dune activity within the northern european sand belt and socio economic feedbacks over the last 2500 years in north western europe pleistocene sand sheets have been reactivated during phases of holocene deforestation and agricultural land use although there are temporal overlaps between anthropogenic activity and sand sheet reactivation the root cause and subsequent feedbacks between aeolian activity and societal response remain largely unknown here we seek to establish cause and effect by examining the detailed co variation in both timing and magnitude of aeolian and anthropogenic activity through the quantification of holocene dune sediments in combination with archaeological and pollen records these records indicate a series of complex phases of aeolian activity followed by landscape stabilization which we attribute primarily to changing patterns of human impact we find that a steady increase in dune deposition rates in the medieval period corresponds to an increase in settlement activity and deforestation ad 1000 1500 at their peak medieval deposition rates were 3 4 times larger than during th

kinematic evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we present an updated series of kinematic reconstructions of the major plates around the tethys from the atlantic ocean to the pamirs between the early jurassic and the present this set is used elsewhere as a basis for paleogeographic maps of the entire region the problems related to the positions of the continents in the lower triassic are also discussed no direct analyses of magnetic anomalies and fracture zones in the atlantic have been made rather all available poles and rotations have been tested in order to eliminate or minimize possible kinematic errors the reconstructions are shown for nine key geological periods which correspond to well recognized magnetic anomalies except for the jurassic cretaceous boundary and the cretaceous tertiary boundary which correspond to interpolated positions paleolatitudes have been drawn using the study of westphal et al 1986 an attempt has been made to take into account the displacements caused by formation of the continental margins and basins by stretching the resulting relative vector of motions along the northern boundary of the tethys shows a significant change 80 m y ago left lateral motion with compression dominates before whereas right lateral motion with compression dominates after to the east rates of motion vary by a factor of three with time and four maxima can be clearly related to tectonic events in the late jurassic late cretaceous eocene and post middle miocene to the west north of apulia on the contrary the motion rate has not changed significantly since the early cretaceous and is close to 1 cm yr as an average these rather complex adjustments in rates and directions of relative motion are produced in great part through a complex migration of the africa eurasia pole of rotation and seem to be mostly governed by the tectonics of the tethys plate boundary

transpressional inversion in an extensional transfer zone the saltacaballos fault northern spain abstract this paper deals with an extensional transfer zone and its main structure the saltacaballos fault developed during early cretaceous times and obliquely inverted during the alpine shortening geological mapping and structural analysis were carried out to determine the kinematic history of the deformation the saltacaballos ridge is the relay zone between two major and conjugate normal fault systems the bilbao and the la granja samano fault systems three distinct phases in the structural evolution of this transfer zone can be identified 1 during the initial stages of extensional deformation shallow water marine limestones were deposited on the relay ridge and deep water marls on the flanking depocenters at the same time submarine landslides developed on paleoslope generated either by normal drag or by a fault propagation fold related to the saltacaballos normal fault 2 with increasing displacement normal faults antithetic to the saltacaballos fault were developed probably in response to the collapse of its hanging wall 3 during the subsequent alpine compressional stage these normal faults were reactivated as dextral strike slip faults as a result of transpressional inversion whereas previous extensional fault related folds were tightened at the same time some normal faults were overturned as a consequence of passive rotation in fold limbs

wood charcoal from an inland dune complex at joldelund northern germany information on holocene vegetation and landscape changes abstract the charcoal content of an inland dune complex close to joldelund in northern germany was analysed as part of a project which aims to reconstruct holocene aeolian activity in high spatial and temporal resolution the eleven investigated profiles contained numerous charcoal enriched layers providing evidence for the potential of inland dunes as palaeoarchives for anthracology earlier studies have found late roman iron age settlement activity and iron ore productions in the research area and in its vicinity charcoal assemblages date to roman iron age as well as early high and late medieval times according to radiocarbon dating of single species identified charcoal fragments and the stratigraphic correlation of sedimentary units the dominance of quercus oak and significant proportions of ericaceae charcoal probably calluna vulgaris heather especially in the early and high medieval samples indicate the presence of a heathland with quercus trees which was managed by fire in the younger layers of sand a greater diversity of taxa were found including the dominant quercus fagus beech alnus alder betula birch corylus hazel fraxinus ash salix willow populus salix poplar willow type acer maple pinus pine maloideae apple subfamily tilia lime as well as some ericaceae the diversity of species indicates that some charcoals were transported by wind together with the sand from the surrounding areas and do not represent the local vegetation on the dunes but rather a nonspecific regional input the differences in the charcoal assemblages and thus the possible correlation of aeolian units support the stratigraphic correlation of the sedimentary aeolian units the comparison with the available pollen data from nearby mires showed a good agreement of the proportions of woody taxa with only few exceptions

ancient pine forest on inland dunes in the spanish northern meseta abstract we present a new stratigraphic pollen and nonpollen microfossils and charcoal particle sequence with five ams dates covering about the last 9000 yr of a core collected from the spanish northern meseta one of the territories of the iberian peninsula for which little paleobotanical information is available the results support the hypothesis of the permanence of the pine forests in more or less pure masses or large timber stands during the holocene in some iberian continental zones the typical substitution in postglacial dynamics of heliophyllous species such as pines or cupressaceae by broadleaf trees did not occur in this inland region presumably factors linked to the substrate in this case very deep sand dunes covering vast areas may have contributed to the scarce local competitiveness of the broadleaf trees which would account for the hegemony of pines in this region based on the dynamics of aquatic plants and nonpollen microfossils an initial phase previous to 7500 14c yr b p of high levels in the lake can be identified by high percentages of hydrophytes a progressive increase in helophytes and the gradual infilling of the lake over the last 5000 yr appear to indicate a phase of aridification similar to those established for the western mediterranean study of charcoal particles more abundant in the last 2500 yr has given rise to certain hypotheses regarding the incidence of recurring fires of a local or regional nature

tectonosedimentary evolution of the deep iberia newfoundland margins evidence for a complex breakup history most of the conceptual ideas concerning sedimentary architecture and tectonic evolution of deep rifted margins are based on either intracontinental rift basins or proximal margins both of which underwent only small amounts of crustal thinning in this paper we investigate the tectonosedimentary and morphotectonic evolution related to continental breakup of the highly extended deep iberia newfoundland margins our results show that continental breakup is a complex process distributed in time and space on the basis of mapping of dated seismic units and borehole data we are able to identify two major phases of extension during a first phase dated as tithonian to barremian 145 128 ma deformation is related to exhumation of mantle rocks basins become younger oceanward and fault geometry changes from upward to downward concave resulting in complex sedimentary structures and basin geometries a second phase dated as latest aptian 112 ma overprints previously exhumed mantle and accreted juvenile oceanic crust over more than 200 km leading to the formation of basement highs the observed complex breakup history challenges classical concepts of rifting and leads to new interpretations for the tectonosedimentary evolution of deep rifted margins

seismic evidence of alpine crustal thickening and wedging from the western pyrenees to the cantabrian mountains north iberia 1 the alpine collision between the iberian and european plates resulted in a complex crustal structure beneath the northern iberian peninsula as revealed from a new set of seismic refraction wide angle reflection profiles the study area is characterized by two major e w ranges the cantabrian mountains and the pyrenees which are relayed to the south by the iberian chain important variations in crustal thickness and velocity distribution are found in a 560 km long e w transect in contrast to the typical 30 to 32 km thick european variscan crust of the western end of the profile a continuous alpine crustal root is evidenced from the cantabrian mountains to the central pyrenees with a moho depth of 46 48 km locally rising to 40 km depth in between beneath the basque cantabrian basin another outstanding feature is the inferred presence of high velocities of 6 40 6 75 km s at midcrustal depths which can be associated with portions of a lower crustal wedge from the northern european domain indenting the southern iberian crust during the alpine stage of compression this indentation produces the delamination of the iberian crust with northward underthrusting of its lower half and the consequent crustal thickening the indenting wedge has a discontinuous presence along the longitudinal section as it was controlled and or affected by n s to ne sw structures further evidence of the northward subduction of the iberian plate is provided by another profile toward the aquitaine basin while a n s profile across the iberian chain reveals an alpine midcrustal thickening beneath this belt with moho depths of 42 km

aptian albian carbonate episode of basque cantabrian basin northern spain the aptian albian episode of the basque cantabrian basin in northern spain contains up to 4000 m of rudistid limestones changing laterally into marls and other terrigenous materials ten deposystems with environments ranging from alluvial fan to carbonate intraplatform basin and three deposequences corresponding to late aptian upper aptian early late albian and late late albian middle albian respectively have been distinguished within it wide patch reefs with ramp like margins appeared in the late aptian thick platform or bank limestones bearing big reef mounds in the margins and megabreccias in the slopes built up in the upper aptian and particularly in the albian a general terrigenous arrival in the upper albian finally put an end to most of the carbonate deposition several controls determined the appearance and characteristics of the carbonate episode block faulting in the basement created differential subsidence inducing limestones to deposit in highs and terrigenous materials in troughs and bringing about halokinesis and tectonic pulses four relatively short lived lowstands of sea level in pre aptian middle aptian late albian and middle albian and their intervening highstands have been established which can be correlated interregionally and so attributed to eustatism besides tectonism sedimentary dynamics specially terrigenous arrivals also controlled carbonate sedimentation as didmore warm wet climate which induced reef and coal formation finally the general extensional tectonic pattern deduced from the northwest southeast and southwest northeast oriented troughs and highs can be better explained through the synsedimentary action of several major and sinistral strike slip faults these took advantage of former basement lineaments as a result of the counterclockwise drift of iberia with respect to eurasia less