comparative stratigraphy and subsidence history of mesozoic rift basins of north atlantic mesozoic rift basins around the north atlantic all possess many of the following upper jurassic to lower cretaceous oxfordian to albian stratigraphic elements 1 an early oxfordian hiatus 2 backfill deposits in upper jurassic paleovalleys 3 multiple tithonian transgressive regressive sequences 4 early berriasian regressive sequences 5 a sub valanginian unconformity overlain by coarse siliciclastic sandstones and conglomerates 6 valanginian to hauterivian fining upward sequences 7 condensed barremian sequences and 8 prominent aptian unconformities more local features include abrupt kimmeridgian deepening lusitanian basin portugal albian deepening cantabrian and aquitaine basins northern spain and southern france and late albian early cenom nian source rejuvenation cantabrian basin northern iberia decompaction and backstripping of sediments from well and outcrop sections in six basins also reveal broad similarities in trends of rates of apparent basement subsidence relatively high rates 50 100 m m y characterize onset of rift phases in the triassic and the kimmeridgian locally in the lusitanian basin of portugal kimmeridgian rates reach about 250 m m y in the cantabrian and aquitaine basins a third phase of rapid subsidence characterizes the aptian albian interval after the main phase of continental breakup around iberia this phase may be due to transtensional stresses as iberia continued to rotate relative to europe tensional intraplate stresses or gravity driven partial collapse of the new continental marg n the north atlantic mesozoic basins share many features because they had a common origin controlled by intracontinental rifting and subsequent separation of europe and north america pulses of extension generally are reflected in the stratigraphy of all of the basins superimposed on this record are the effects of eustatic sea level variations the main difference between the canadian jeanne d arc basin and iberian basins is the significantly greater early and middle jurassic basement subsidence rate in the former about 40 m m y vs 0 10 m m y this difference may result from prolonged extension on the canadian side perhaps due to northward transfer of shear stress from left lateral transform motion between the grand banks and northwestern africa

neogene vertical movements and constraints on extension in the catalan coastal ranges iberian peninsula and the valencia trough western mediterranean abstract the catalan coastal ranges mark the transition from the iberian massif to the active tectonic region of the western mediterranean sea in northeastern spain seismic gravity and thermal data indicate that the crust and lithosphere thin from the ebro basin of the iberian massif to the valencia trough of the western mediterranean consistent with the present elevations of these provinces mid tertiary sediment transport directions however indicate that the catalan coastal ranges were below the elevation of the valencia trough during the mid tertiary and that an inversion of their relative topographies has occurred associated with neogene extension in this region a formulation of lithospheric buoyancy has been used to back calculate possible pre extension lithospheric structures consistent with the mid tertiary elevation constraints and lithospheric strength constraints the back calculation method allows to obtain a range of stretching factors for the crust and for the lithospheric mantle independently from each other these calculations suggest a suite of modes of lithospheric deformation ranging from pure shear of an initially heterogeneous lithosphere to differential stretching of a homogeneous lithosphere both with significant components of thermal modification of the lithosphere not directly associated with convection through extension we conclude that although the basic features of basin formation may be explained by elegant simple models of lithospheric extension the details of elevation changes associated with extension suggest a significant degree of non uniqueness in these models

eolian dune interdune sand sheet and siliciclastic sabkha sediments of an offshore prograding sand sea dhahran area saudi arabia an offshore prograding sand sea exists along portions of the arabian gulf coastline near dhahran saudi arabia in this region sediments of eolian dune interdune sand sheet and siliciclastic sabkha intercalate with marine deposits this depositional setting is characterized by strong offshore winds which supply abundant sand to the coastline and cause at present time the outbuilding of the dune system this quartz detrital dominant setting contrasts markedly with the carbonate dominant setting resulting from onshore winds in the trucial coast area to the south the broad intercalation of eolian and marine deposits which results creates ideal potential for subregional stratigraphic petroleum traps due to pinch out of porous and permeable dune sands into impermeable m rine mudstones within the eolian system itself are potential reservoir rocks dunes sources organic rich sabkha and interdune deposits and seals zones of early cementation in all deposits early cementation is very common in all facies of the eolian sand sea the early cementation occurs owing to 1 soil formation 2 deposition of pore filling gypsiferous cements from saturated solutions near water table and 3 addition of sand size windblown evaporitic material to sands downwind of sabkhas

following the last neanderthals mammal tracks in late pleistocene coastal dunes of gibraltar s iberian peninsula abstract the aeolian pleistocene deposits recorded in the rock of gibraltar s iberian peninsula present a significant sedimentary thickness that fills the wide sea caves and covers its steep slopes in catalan bay these deposits register the development of cliff foot and rampant dunes that form a 35 sand ramp 1 km long and up to 300 m in height formed by moderately to well sorted sands slightly carbonated and weakly cemented this morphosedimentary evidence is associated with mis 5 2 sea level fluctuations its internal structure shows lamination sets of 2 3 m in thickness and planar and trough cross bedding in these beds five morphotypes of mammalian footprints have been recognized in vertical cross sections and convex hyporeliefs most of them present a moderate degree of conservation due to the poor cementation of the sands these icnites are related to the activity of terrestrial mammals possibly belonging to homininae proboscidea artiodactila and carnivora the affinity between the footprints and their tracemakers has been established in the basis of their physical parameters the shape of the footprints their comparison with similar footprints and the correlation with the fossil fauna of vertebrates described for the late pleistocene in gibraltar these findings represent the first palaeoichnological record in the aeolian sediments of gibraltar and indirectly corroborate the occupation of the coastal dune landscape by several terrestrial mammals during the late pleistocene in addition they help reconstructing the animal behaviour and interaction with the extensive dune systems that developed at the foot of the rock slopes the age of the tracks has been established within the mis 2 during the probable middle upper palaeolithic transition in the climate refuge of gibraltar

tectonic classification of cenozoic iberian foreland basins abstract the iberian microcontinent stands out because of its intense alpine intraplate deformation this is reflected in a large number of cenozoic basins of very different sizes most of the contacts between topographic highs and basins are thrust or strike slip faults all these basins seem to have undergone a common sedimentary evolution comprising four stages initiation of sedimentation intense syn tectonic infilling change from endorheic to exorheic drainage and accelerated erosion related to fluvial incision this simple evolutionary model shows a migration from east to west in which basins are still tectonically active at the atlantic margin of iberia this common evolution is also found in a series of geometrical characteristics such as the ratio r of length of strike slip fault and length of thrust fault that are very similar in both types of basin border settings thrust related basins are mainly associated with segmented pop downs whereas the main basins have the characteristics of open ramp basins strike slip related basins are mostly transpressive structures although small pull apart basins are usual along the vilarica and messejana faults for basin areas larger than 100 1000 km 2 a constant r value of 0 6 is found including the ebro duero madrid lower tagus and badajoz basins within the iberian microcontinent the total amount of cenozoic contractional deformation was distributed between strike slip and thrust faults with an r ratio close to 0 6 however for small basins this parameter seems to depend on the type of fault range or deformation belt pure strike slip transtension transpression and pop up independently of its local tectonic development

tracks and trackways of myotragus balearicus bate artiodactyla caprinae in pleistocene aeolianites from mallorca balearic islands western mediterranean tracks and trackways of the ruminant goat myotragus balearicus bate 1909 are abundant in the late pleistocene aeolianites of the south coast of mallorca spain the carbonate aeolianites form impressive dunes and related sand ramps that were initiated as echo dunes in front of a 20 40 m high paleocliff of miocene reefal limestone where the dunes built up to the cliff top they covered it as an aeolian ramp the dunes and sand ramps were active during the dry summer months but were passive during the wet winter period the small goat like animals were abundant on the island and for unknown reasons crossed the aeolian accumulations in large numbers this study deals with the tracks formed in the dune deposits all preserved trackways indicate impression into moist sand special features of the tracks include the structure produced by the withdrawal of the foot here called the axis and a disturbance zone of plastic deformation around this on dune crests the disturbance zone surrounds the axis more or less symmetrically however in addition a pressure pad of dislocated slightly rotated sediment bound by curved microfaults is commonly produced posterior to the axis by propulsive pressure of the foot on steep stoss and lee slopes the pressure pad becomes oriented in a down slope position as a result of gravitational slip of the walking animal combination of disturbance of the sediment in this way by manus followed by overprinting of similar disturbance by pes produces highly complicated track structure this structure may be characteristic of artiodactylous mammals in soft sand particularly aeolian deposits the structure is designated as bifidipes aeolis isp nov

stratigraphic context of old crow tephra holitna lowland interior southwest alaska abstract a thick deposit of old crow tephra was discovered in a bluff exposure along the middle holitna river near the kulukbuk hills 61 20 n latitude 157 10 w longitude in interior southwest alaska this locality is the southwesternmost known deposit of old crow tephra in alaska thickness and grain size data from this site support a source volcano in the eastern aleutian arc pleistocene stratigraphic sequences in the lowland are dominated by upward fining eolian sand sheet deposits and loess separated by organic silt these deposits record at least two episodes of regional glaciation and an intervening nonglacial period marine oxygen isotope stage 3 stage 5 or both old crow tephra crops out near the top of the lower upward fining eolian unit indicating that the ash erupted near the end of an interval of periglacial eolian sedimentation the sequence of eolian deposits that contain old crow tephra probably accumulated during the latter part of marine oxygen isotope stage 6 whereas the overlying eolian sequence formed during the last glaciation stage 2 this stratigraphic position is consistent with other stratigraphic contexts for the tephra and with fission track and thermoluminescence ages of ca 140 000 10 000 yr b p

tectonic variation in the dniepr donets basin from automated modelling of backstripped subsidence curves abstract the multiphase rift evolution of the dniepr donets dd basin is analysed by 1d backstripping and tectonic modelling of 66 stratigraphic sections mostly from well data distributed throughout the basin the backstripping results illustrate strong temporal and lateral variations in tectonic subsidence it is minor during an inceptive pre rift phase givetian early frasnian 380 8 370 ma and does not show clear spatial correlations within the dd basin framework the main rift phase frasnian famennian 370 362 5 ma corresponds to an acceleration in subsidence rates with tectonic subsidence up to 1500 m along the basin axis displaying a slight increase from the northwest to the southeast strong lateral variations perpendicular to the basin axis reflect the effects of major basin border faults a rift phase in the visean 345 340 ma is characterised by relatively minor subsidence up to about 500 m except for some wells in the southeast following a stage of extremely low rates of deposition in the earliest carboniferous the end of this rift phase can be taken to mark the onset of convex subsidence patterns in the later carboniferous and permian typical in shape of post rift thermal subsidence but significantly increasing in magnitude from northwest to southeast in the basin this trend shows no one to one relationship with late devonian syn rift subsidence the tectonic subsidence curves have been modelled using lithospheric stretching assumptions allowing different stretching factors for the crustal and sub crustal lithosphere and the incorporation of finite and multiple stretching phases a numerical technique was developed that automatically finds best fit stretching parameters for part or all of the tectonic subsidence data given the specification of onset and duration of the various rifting events maps of the 1d modelling results display intrabasinal variations in terms of timing and magnitude of rifting the results indicate that the observed spatial and temporal variations of tectonic subsidence in the dd basin specifically the increasing ratio of carboniferous to late devonian subsidence from northwest to southeast cannot be explained by either a uniform or depth dependent stretching model adopting only a single frasnian famennian rift phase a two phase model in which a significant part of carboniferous tectonic subsidence is related to visean rift activity strongly dominated by sub crustal lithospheric attenuation provides a satisfactory fit to the data although the tectonic implications of such a model are not easily reconcilable by independent constraints a semi quantitative investigation of the possible role of withdrawal of underlying devonian salt during the carboniferous to produce additional post devonian rift phase sediment accommodation space suggests that the effects of such a mechanism could be significant but that they are unlikely to preclude the necessity of the visean rifting event to explain the carboniferous basin evolution

permian to late triassic evolution of the longmen shan foreland basin western sichuan model results from both the lithospheric extension and flexure abstract the lithosphere was extended during the permian middle triassic in the yangtze craton where the sichuan basin located and then bent due to thrusting of the longmen shan orogen leading to formation of the longmen shan foreland basin western sichuan during the late triassic indosinian orogeny the lateral variation of the lithospheric strength resulted by former differential extension would inevitably influence the subsequent evolution of the foreland basin in order to investigate this both extensional and flexural models were applied in modeling permian late triassic basin evolution a 2d kinematic extensional model was initially developed along a profile crossing the yangtze craton to simulate the lithospheric thermal evolution during the permian middle triassic based on the thermal results the thermal rheological structure as well as the effective elastic thickness of the lithosphere te was then determined extension model show that the stretching factors decrease gradually from songpan ganzi to the sichuan basin leading to variable thermal rheological structure and increased te from west to east taking into account of the te variation a flexural model was finally constructed to investigate the evolution of the longmen shan foreland basin during the late triassic spanning the time period c 227 206 ma three episodes were divided according to the corresponding tectonostratigraphic units by matching the stratigraphic observations three phase advance distances eastward of the longmen shan along the qingchuan maowen fault turned out to be 18 22 and 18 km it implied a slow and similar thrust advance rate of 3 6 c 227 222 ma 2 2 c 222 212 ma and 3 mm yr c 212 206 ma respectively

sources of sr and s in aluminum phosphate sulfate minerals in early middle triassic sandstones iberian ranges spain and paleoenvironmental implications for the west tethys aluminum phosphate sulfate aps minerals formed during early diagenesis in relation to acid meteoric waters are the main host of sr and s in the early middle triassic continental sandstones of the iberian ranges east of the iberian peninsula the sources of these elements and the effects of paleoenvironmetal changes on these sources and on the formation of aps minerals during early middle triassic times were established on the basis of sr and s isotopic analyses the s and sr data d34s v cdt 11 to 14 and 87sr 86sr 0 7099 0 7247 respectively can be interpreted as resulting from mixing of different sources strontium was sourced from the dissolution of pre existing minerals like k feldspar and clay minerals inherited from the source areas causing high radiogenic values however the isotopic signal must also be influenced by other sources such as marine or volcanic aerosol that decreased the total 87sr 86sr ratios marine and volcanic aerosols were also sources of sulfur but the d34s was lowered by dissolution of pre existing sulfides mainly pyrite pyrite dissolution and volcanic aerosols would also trigger the acid conditions required for the precipitation of aps minerals aps minerals in the study area are found mainly in the canizar formation olenekian aegian which has the lowest 87sr 86sr ratios the lower abundance of aps minerals in the eslida formation aegian pelsonian may indicate change in the acidity of pore water towards more alkaline conditions while the increased 87sr 86sr ratios imply decreased sr input from volcanic activity and or marine aerosol inputs during anisian times therefore the decrease in abundance of aps minerals from the early to middle triassic and the variations in the sources of sr and s are indicative of changes in paleoenvironmental conditions during the beginning of the triassic period these changes from acid to more alkaline conditions are also coincident with the first appearance of carbonate paleosols trace fossils and plant fossils in the upper part of the canizar formation and more in the overlying eslida formation and mark the beginning of biotic recovery in this area the presence of aps minerals in other european basins of the western tethys such as the german basin the paris basin and the southeastern france and sardinia basins could thus also indicate that unfavorable environmental conditions caused delay in biotic recovery in those areas in general the presence of aps minerals may be used as an indicator of arid acidic conditions unfavorable to biotic colonization

stratigraphical and palaeogeographical significance of the continental sedimentary transition across the permian triassic boundary in spain abstract the permian triassic transition a time of phenomenal palaeoenvironmental and palaeogeographical change represents the largest episode of mass extinctions known to palaeontologists this episode is however very poorly understood and a lack of sediments and palaeontological data particularly in the continental record is a feature common to every basin despite compelling information on the continental permian triassic boundary ptb emerging from recent efforts evaluating vertebrate evolution fungal events and isotope curves results are still insufficient to make any valuable correlations among continental basins and are even less appropriate for relating sediments of continental to those of marine origin the present report discusses and attempts to locate the ptb in the basins of iberia and balearic islands through an analysis of the palaeontological and sedimentary record across the permian triassic transition the aim of the paper is to contribute to our present knowledge of the palaeogeographical and stratigraphical significance of the permian and triassic continental units of western europe the present day iberian ranges catalonian ranges and balearic islands hold the most complete late permian early triassic sedimentary record in iberia this record consists of alluvial sediments mainly of braided fluvial systems corresponding to the saxonian and buntsandstein facies all the units examined so far have been dated through palynological associations the two saxonian facies formations are of thuringian age although the lower one shows some palynological elements of autunian affinities the buntsandstein units range from thuringian to anisian in age there being no evidence up to now of the scythian in iberia the exact position of the ptb in iberia is up to now impossible to pinpoint with the precision of the marine series sedimentary characteristics and palynological data in the iberian ranges point that it lies at the sedimentary interval 10 to 30 m thick formed by the upper member of the la hoz del gallo formation and the lowermost beds of the canizar formation or its time equivalent the prades and eramprunya units in the catalonian ranges and the asa and b 1 in the balearic islands we compare a normalized standard late permian middle triassic column of the iberian ranges with standards from western and central europe and the southern urals using recent permian time scales a palaeogeographic essay map of the permian triassic transition is provided for the iberian plate the plate was located in a northern subtropical position 200 400 km from the westernmost tethys coast as part of the central pangean mountain range comprised of the appalachian mauretanide variscan orogenic belts of estimated altitudes 2000 4000 m based on this palaeogeographic location sedimentary characteristics and the main wind flows established for the tethys we can infer conditions of high precipitation dominated by monsoon and seasonal regimes with isolated semiarid areas for the iberian plate during the transition

crustal structure beneath spain from deep seismic sounding experiments major tectonic units of spain have been investigated by deep seismic sounding experiments since 1974 to determine crustal structures and to delineate their differences these areas are the central part of the hercynian meseta and the alpine chains the betic cordillera in the south including the balearic promontory and the alboran sea and the pyrenees in the north the main features of the crust and the upper mantle along a nne ssw cross section from the pyrenees to the alboran sea are described the crust under the meseta is typical of hercynian areas found elsewhere in europe with an average thickness of 31 km whereas the two alpine regions are characterized by very large lateral inhomogeneities such as rapid thickening of the crust to 50 and 40 km under the pyrenees and the betics respectively the deep reaching e w trending north pyrenean fault has a throw of 10 15 km at the base of the crust a pn velocity of 8 1 km s 1 is found under the entire iberian peninsula in the alboran sea strongly varying thicknesses of sediments shallow variable depths to the moho 13 km under the alboran ridge and strong variations of pn velocity between 7 5 and 8 2 km s 1 have been found

intraplate deformation and basin formation during the tertiary within the northern iberian plate origin and evolution of the almazan basin the tertiary almazan basin was a topographic high during the mesozoic rifting at the northern part of the iberian plate it was bordered by two mesozoic basins 1 the castilian basin with a maximum thickness of more than 2000 m to the south and 2 the cameros basin with a maximum thickness of 9000 m to the north to the east the almazan basin is bordered by paleozoic rocks of the nw se trending aragonian range which underwent little subsidence during the mesozoic the two mesozoic basins show an e w direction during the tertiary nne ssw compression mainly late eocene early miocene both mesozoic basins were inverted and uplifted and the almazan basin with an overall synclinal geometry was filled with syn tectonic terrestrial sediments reaching a maximum thickness of 3500 m deformation during the tertiary was strongly controlled by preexisting structures both mesozoic extensional faults and reactivated variscan folds the depocenter of the tertiary basin migrated southward during the paleogene this migration is consistent with a piggyback transport of the whole basin northward due to the movement on the underlying crustal scale north verging cameros thrust the geometry and sedimentary evolution of the almazan thick skinned piggyback basin was controlled by the uplift associated with the main crustal scale thrust which was the main source area and was separated from the foreland basin since the early stages of filling late eocene this makes the main difference with thin skinned piggyback basins controlled by the foreland thrust belt and separated from the foreland basin only at their late stages

geomorphic and tectonic implications of the endorheic to exorheic transition of the ebro river system in northeast iberia the ebro catchment includes a continental foreland basin that underwent an endorheic exorheic transition morphometric studies including hypsometric curves hypsometric integrals asymmetry factor mountain front sinuosity normalised stream length gradient and normalised concavity indices for the ebro river and 32 of its tributaries show the signals of transient response to this major drainage change the ebro river its upper catchment tributaries and the pyrenean tributaries have concave up longitudinal profiles concave hypsometric curves and low hypsometric integrals parameters typical of deeply dissected basins this suggests a mature stage of development controlled by the shift of the base level to the mediterranean sea iberian range tributaries display low concavity profiles with numerous knickpoints and high values of hypsometric integral indicating a transient state as a response to tectonic uplift ratified by the values of mountain front sinuosity surrounding the basin

stratigraphy and palaeoclimatic significance of late quaternary loess palaeosol sequences of the last interglacial glacial cycle in central alaska abstract loess is one of the most widespread subaerial deposits in alaska and adjacent yukon territory and may have a history that goes back 3 ma based on mineralogy and major and trace element chemistry central alaskan loess has a composition that is distinctive from other loess bodies of the world although it is quartz dominated central alaskan loess was probably derived from a variety of rock types including granites metabasalts and schists detailed stratigraphic data and pedologic criteria indicate that contrary to early studies many palaeosols are present in central alaskan loess sections the buried soils indicate that loess sedimentation was episodic or at least rates of deposition decreased to the point where pedogenesis could keep ahead of aeolian input as in china loess deposition and pedogenesis are likely competing processes and neither stops completely during either phase of the loess soil formation cycle loess deposition in central alaska took place before and probably during the last interglacial period during stadials of the mid wisconsin period during the last glacial period and during the holocene an unexpected result of our geochronological studies is that only moderate loess deposition took place during the last glacial period our studies lead us to conclude that vegetation plays a key role in loess accumulation in alaska factors favouring loess production are enhanced during glacial periods but factors that favour loess accumulation are diminished during glacial periods the most important of these is vegetation boreal forest serves as an effective loess trap but sparsely distributed herb tundra does not thus thick accumulations of loess should not be expected where tundra vegetation was dominant and this is borne out by modern studies near the treeline in central alaska much of the stratigraphic diversity of north american loess including that found in the central lowlands the great plains and alaska is explained by a new model that emphasizes the relative importance of loess production factors versus loess accumulation factors

late pleistocene mammoth trackway from fossil lake oregon abstract behavior of columbian mammoths mammuthus columbi is revealed by a newly discovered trackway at the pleistocene locality of fossil lake oregon our 8 by 20 m excavation of the mammoth trackway found 117 tracks including one 20 m long adult trail partial trackways of 3 additional adults a yearling and a baby all heading generally west the tracks are in the marble bluff biotite tuff 43 2 cal ka which forms a surface horizon to the pogani silty clay loam paleosol natrargid with a cracked surface and a columnar structured subsurface bn horizon like soils under desert soda pans with alkali shrubland directly below is the yada silty clay paleosol xeroll with crumb textured surface a horizon like grassland soils the pasiwa loam psamment is a thin brown siltstone with sparse roots and burrows of lake margin early successional vegetation the pui sandy loam aquent is well bedded tuff and sand a with subhorizontal calcareous rhizomes and adventitious roots like those of lake margin tule reeds schoenoplectus acutus columbian mammoths may have moved like modern elephants with infants in matriarchal groups through landscapes of sagebrush and grassland and this trackway includes a limping female attended by concerned juveniles grassland paleosols common in the fossil lake formation are now rare in the same region perhaps related to extinction of proboscidean and equine grazers

sedimentology of cold climate aeolian sandsheet deposits in the askja region of northeast iceland active aeolian sandsheets cover an area of 270 km2 in the askja region of ne iceland the sandsheet is divided into i a deflationary upwind part that is characterised by deflation lags ventifacted boulder fields and restricted aeolian sand patches in the lee of obstacles ii an accumulating central part that is characterised by continuous aeolian sand cover up to 10 m thick where three scales of aeolian ripples are evident along with larger scale forms including longitudinal zibars and iii a downwind part that is currently subject to aeolian bypass with only localised accumulation occurring in topographic hollows between basaltic lava fields trains of aeolian granule megaripples are a characteristic landform of the downwind part of the sandsheet these sinuous crested oblique bedforms attain heights of 0 35 m and downwind spacings of 6 m they are composed principally of low density pebble grade pumice clasts and other reworked volcaniclastic detritus derived from the nearby askja volcanic centre the distribution of landforms across the sandsheet reflects a regional aeolian sediment budget that is controlled by dynamic interactions between glacial ice margin fluvial aeolian and volcaniclastic processes under the influence of a distinctive climatic regime sediment supply at the upwind sandsheet margin adjacent to the dyngjujokull glacier increases during summer periods when rates of glacial ablation are at a maximum longer term controls on sediment supply rate are determined by episodes of glacier surging and retreat and by periodic eruptions of volcaniclastic debris from the askja volcanic centre the availability of sediment for aeolian transport is controlled by the level of the groundwater table the depth and continuity of the permafrost layer in the proglacial area the degree of development of armoured pebble lags and freezing of the sandsheet surface during winter months the transport capacity of the wind varies on a seasonal basis with mean wind velocities and wind gustiness reaching a maximum during winter periods both winter and summer mean wind velocities have been steadily increasing since formal records began in 1969 the suite of aeolian landforms developed within the askja region as defined by sediment texture and composition and bedform scale morphology and spatial distribution reflects a special set of controlling circumstances which mean that the askja sandsheet deposits differ significantly from those described from elsewhere

palaeogeographical significance of the triassic jurassic unconformity in the north iberian basin sierra del moncayo spain abstract field work carried out on the lower jurassic i e hettangian lower pliensbachian of the north iberian basin sierra del moncayo spain including the mapping of unconformities and sedimentary units as well as the facies analysis has allowed us to recognize two episodes in the sedimentary evolution of the basin a lower one hettangian in age includes sediments deposited during the period of extensional tectonic activity which involved the formation of half graben basins by normal listric faults sedimentary breccias and rudites located mainly at the edges of the half grabens are derived from the erosion of blocks uplifted during the triassic in the depocenter of the half grabens which show most subsidence these breccias pass into thick dolomitic and evaporitic successions deposited in sabkha environments under negligible marine influence the later episode sinemurian and lower pliensbachian in age consists of shallow marine carbonate units deposited in a low angle ramp setting evaporite accumulation took place during phases of relative lowstand of sea level i e lowstand systems tract when the basin was cut ooff from open marine conditions whereas the carbonate sediments mainly represent transgressive and highstand systems tracts in the iberian basin the lowstand episode during the hettangian was mainly induced by the breakup of the upper triassic ramp which favoured the isolation from open marine conditions of several subsident sub basins in addition it should be noted that the hettangian is considered as a lowstand sea level episode in some of the proposed global eustatic cycle charts so that a eustatic component may also be postulated for the isolation of the basin at this time the infilling of the hettangian half grabens left an even topography which was flooded during the sinemurian sea level rise leaving shallow carbonate deposits the results presented here give new information on the paleogeography of northeast iberia at the triassic jurassic boundary in the context of the opening of the western margin of the tethys

the moho in extensional tectonic settings insights from thermo mechanical models the lithospheric memory is key for the interplay of lithospheric stresses and rheological structure of the extending lithosphere and for its later tectonic reactivation other important factors are the temporal and spatial migration of extension and the interplay of rifting and surface processes the mode of extension and the duration of the rifting phase required to lead to continental break up are to a large extent controlled by the interaction of the extending plate with slab dynamics the finite strength of the lithosphere has an important effect on the formation of extensional basins this applies both to the geometry of the basin shape as well as to the record of vertical motions during and after rifting we demonstrate a strong connection between the bulk rheological properties of europe s lithosphere and the evolution of some of europe s main rifts and back arc systems the thermo mechanical structure of the lithosphere has a major impact on continental break up and associated basin migration processes with direct relationships between rift duration and extension velocities thermal evolution and the role of mantle plumes compressional reactivation has important consequences for post rift inversion borderland uplift and denudation as illustrated by poly phase deformation of extensional back arc basins in the black sea and the pannonian basin region

aeolian processes and features in cool climates this review concentrates on the characteristics of wind processes and products in cold lowland deserts its main aims are to show how difficult it can be to separate wind generated from water generated processes and features without detailed study of lamination types to suggest cold aeolian interpretations for some ancient pre quaternary rocks and to encourage students to revisit many ancient deposits with such interpretations in mind although upper quaternary and recent cold climate aeolian deposits have been studied for many years there are very few older examples described martian features are included since mars is now one of the most exciting areas of study

the neogene structure of the eastern iberian margin structural constraints on the crustal evolution of the valencia trough western mediterranean abstract the presence of a thinned crust beneath the valencia trough has been recognized for a long time however to date no attempt to link this thinning inferred from geophysical data with the superficial structures has been made a quantification of the neogene extensional processes in the crustal evolution of the valencia trough is presented as a consequence of the complexity of the betic balearic domain the analysis has been done for the catalan valencian domain northwestern areas of the trough crustal and superficial data in this area show that neogene extension was accommodated by a listric normal fault system detached in a deep upper crustal level 13 15 km in the marginal zone of the domain quantitative analysis of the neogene structure shows the incoherence between the upper crustal thinning inferred from the geometric analysis of the superficial structures factor 1 4 1 5 and from geophysical data 1 8 although the latter value agrees with that deduced from the analysis of neogene subsidence this incoherence suggests that the present thinned crust would be partially inherited from the mesozoic extension in this way mesozoic subsidence analysts and the recognized mesozoic structure show that the mesozoic extension was almost as important as the neogene one

on the tectonic origin of iberian topography the present day topography of the iberian peninsula can be considered as the result of the mesozoiccenozo ic tectonic evolution of the iberian plate including rifting and basin formation during the mesozoic and compression and mountain building processes at the borders and inner part of the plate during the tertiary followed by neogene rifting on the mediterranean side and surface processes acting during the quaternary the northern central part of iberia corresponding to the geological units of the duero basin the iberian chain and the central system shows a mean elevation close to one thousand meters above sea level in average some hundreds of meters higher than the southern half of the iberian plate this elevated area corresponds to i the top of sedimentation in tertiary terrestrial endorheic sedimentary basins paleogene and neogene and ii planation surfaces developed on paleozoic and mesozoic rocks of the mountain chains surrounding the tertiary sedimentary basins both types of surfaces can be found in continuity along the margins of some of the tertiary basins the bouguer anomaly map of the iberian peninsula indicates negative anomalies related to thickening of the continental crust correlations of elevation to crustal thickness and elevation to bouguer anomalies indicate that the dierent landscape units within the iberian plate can be ascribed to dierent patterns 1 the negative bouguer anomaly in the iberian plate shows a rough correlation with elevation the most important gravity anomalies being linked to the iberian chain 2 most part of the so called iberian meseta is linked to intermediate elevation areas with crustal thickening this pattern can be applied to the two main intraplate mountain chains iberian chain and central system 3 the main mountain chains pyrenees and betics show a direct correlation between crustal thickness and elevation with higher elevation crustal thickness ratio for the central systemvs the betics and the pyrenees other features of the iberian topography namely the longitudinal pro le of the main rivers in the iberian peninsula and the distribution of present day endorheic areas are consistent with the tertiary tectonic evolution and the change from an endorheic to an exorheic regime during the late neogene and the quaternary some of the problems involving the timing and development of the iberian meseta can be analysed considering the youngest reference level constituted by the shallow marine upper cretaceous limestones that indicates strong dierences induced by i the overall tertiary and recent compression in the iberian plate responsible for dierences in elevation of the reference level of more than 6 km between the mountain chains and the endorheic basins and ii the eect of neogene extension in the mediterranean margin responsible for lowering several thousands of meters toward the east and uplift of rift shoulders a part of the recent uplift within the iberian plate can be attributed o sostatic uplift in zones of crustal thickening

sequence stratigraphic analysis and paleogeographic interpretation of the buntsandstein and muschelkalk facies permo triassic in the se iberian range e spain abstract the iberian ranges is an alpine structure trending nw se in central spain they first appeared as small intracratonic basins in the early permian and experienced different periods of extensional tectonics during the mesozoic and cenozoic controlled by ancient hercynian or older fracture systems and at least two periods of compressive inversion tectonics the permian and triassic of the se iberian ranges are of germanic type within the prevailing buntsandstein and muschelkalk facies eight formations are recognized pollen and spore assemblages and some ammonoid horizons allow for age assessments ranging from thuringian late permian to carnian late triassic two phases of sedimentation can be distinguished during the early extensional period the first phase rift phase led to the development of the lower buntsandstein facies bounded by two angular unconformities and subdivided into two depositional sequences ds 1 and ds 2 the lower one is dominated by alluvial fans deposited in half grabens and the upper one by sandy braided rivers in more symmetrical grabens the second phase thermal or flexural subsidence phase led to the deposition of the uppermost buntsanstein rot and muschelkalk facies mostly shallow marine carbonates subdivided into two depositional sequences ds 3 and ds 4 with well developed lowstand transgressive and highstand systems tracts lst tst and hst intervals the criteria for separating systems tracts and the interplay of tectonics eustatism and rate of sedimentation are discussed ds 3 and ds 4 broadly correspond to 2 1 and 2 2 third order cycles but their limits are about 3 4 m y younger this may be explained by local tectonic factors

oblique strain partitioning and transpression on an inverted rift the castilian branch of the iberian chain the iberian chain is a wide intraplate deformation zone formed by the tectonic inversion during the pyrenean orogeny of a permian mesozoic basin developed in the eastern part of the iberian massif the n s convergence between iberia and eurasia from the late cretaceous to the lower miocene times produced significant intraplate deformation the nw se oriented castilian branch of the iberian chain can be considered as a key zone where the proposed models for the cenozoic tectonic evolution of the iberian chain can be tested structural style of basin inversion suggests mainly strike slip displacements along previous nw se normal faults developed mostly during the mesozoic to confirm this hypothesis structural and basin evolution analysis macrostructural bouguer gravity anomaly analysis detailed mapping and paleostress inversions have been used to prove the important role of strike slip deformation in addition we demonstrate that two main folding trends almost perpendicular ne sw to e w and nw se were simultaneously active in a wide transpressive zone the two fold trends were generated by different mechanical behaviour including buckling and bending under constrictive strain conditions we propose that strain partitioning occurred with oblique compression and transpression during the cenozoic 2008 elsevier b v all rights reserved

stretching factor estimation for the long duration and multi stage continental extensional tectonics application to the baiyun sag in the northern margin of the south china sea abstract conventional subsidence analysis methods are generally based on the assumption of instantaneous stretching which totally ignores the heat loss during continental rifting for long duration or multi episodic extensional tectonics such assumption is no longer valid and could cause significant deviation from real subsidence here i extend original finite stretching model to a multi stage scenario in terms of geothermal and structural successions between two adjacent rifting events a procedure is designed to estimate stretching factor by fitting the whole tectonic subsidence history in a self consistent manner on the basis of the extended model i apply this procedure to the baiyun sag in the continent slope of the south china sea subsidence analysis shows that the sag is characterized by two episodes of rifting the first stage 49 to 23 8 ma resulted in stretching factors in the range of 1 3 to 4 0 with the greatest stretching at the sag center while the second one 17 5 to 10 5 ma yielded minor stretching factors of 1 1 to 1 2 these estimates agree well with that determined from crustal thinning for the northern and central potions of the sag but significant discrepancy occurs between the southern edge of the sag and the present continent ocean boundary where the crustal thickness is less than 20 km and potentially extensive magmatic intrusion was well imaged in the seismic profiles i suggest that the magma assisted rheologically weakening and possible lower crust ductile flow contributed to the extension discrepancy the margin north of the baiyun sag having a relatively thick crust and vacant of magmatic activity was basically stretched in a depth uniform style it is inferred that preexisting weakness in the lithosphere and abundant sediment supply were responsible for the extremely thick cenozoic sediment developed in the baiyun sag

integrated ichnofacies models for deserts recurrent patterns and megatrends abstract although it is commonly assumed that the trace fossil record of eolian dunes and associated environments is invariably poor a systematic review of the available information indicates that this is not necessarily the case a model involving five main phases of colonization of desert environments through the phanerozoic is proposed in this paper the first phase cambrian silurian involved animal incursions into coastal dune fields directly from the sea although it is unlikely that these animals would have remained for long periods of time in coastal deserts the second phase devonian reflects the activities of dune pioneers that left their fluvial habitat to enter temporary or permanently into inland deserts the third phase carboniferous permian involved the colonization of deserts by tetrapods the fourth phase triassic cretaceous involved a major exploitation of the infaunal ecospace as reflected by the appearance of more varied behavioral patterns in sub superficial structures the fifth phase paleogene recent reflects the appearance of the ecological dynamic that characterizes modern desert communities the invertebrate ichnofacies for eolian dunes is re named herein as the octopodichnus entradichnus ichnofacies honoring the seminal work of previous workers who simultaneously tackled the issue of eolian dune ichnofacies the chelichnus ichnofacies is retained for vertebrate trace fossil assemblages in eolian settings both ichnofacies occur in mobile and temporary stabilized sandy substrates subject to frequent erosion and deposition and to strong seasonality desert settings consist of complex mosaics of habitats or physical units associated with organism activity trace fossil distribution can be understood as reflecting the partitioning of desert settings in a mosaic of landscape units characterized by water content and its temporal fluctuations nutrient availability nature of the substrate and the dominant organisms present in turn desert systems are dynamic entities that change as a response to regional climate landscape units such as eolian sand seas salt flat and playa lake systems ephemeral rivers and alluvial fans interact in response to regional scale climate variations in hyper arid arid and semiarid climatic settings ancient deserts completely developed under hyper arid climatic conditions rarely preserve trace fossils due to the absence of moisture near the surface however the alternation of wet periods may represent windows for life development and thus preservation of biogenic structures arid deserts display complex patterns of dunes combined with dry wet and flooded interdunes dry desert elements e g dunes interdunes sand sheets typically record the entradichnus octopodichnus and chelichnus ichnofacies slight rises in regional precipitation produce elevation of the water table and increase of fluvial discharges that provide water and sediment to the system these processes may result in the local concentration of trace fossils in wet interdunes and ephemeral fluvial systems illustrating the scoyenia and chelichnus ichnofacies in semiarid systems playa lakes expand by the addition of freshwater evolving into freshwater lakes and fluvial systems may become more common lake margins and fluvial overbanks typically contain trace fossil assemblages that may be ascribed to the scoyenia ichnofacies

post late paleozoic tectonism in the southern catalan coastal ranges ne spain assessed by apatite fission track analysis abstract we report the first apatite fission track thermochronologic data for 17 samples from the southern catalan coastal ranges of ne spain thermal histories of carboniferous metasediments late hercynian intrusions and lower triassic buntsandstein sediments from three tectonic blocks miramar prades and priorat are derived and interpreted within the geodynamic framework and tectonic evolution of the region the apatite fission track ages range from 198 24 to 38 5 ma and mean fission track lengths are all

two dimensional p t t modelling and the dynamics of extension and inversion in the betic zone se spain abstract the internal zone of the betic cordilleras offers a unique opportunity to study the dynamics of lithospheric processes at mid crustal levels which controlled the formation and evolution of the southeastern margin of iberia in this paper we present the result of two dimensional numerical modelling of p t t paths related to latest oligocene and early miocene extension and inversion in the betic zone the ages of p t t loops are constrained by an extensive data set of geothermo barometric and geochronological data including 40 ar 39 ar laser probe data we investigate the thermo mechanical evolution of the betic zone using numerical models for simple shear pure shear and combined shear the wernicke simple shear model fails to explain the observed temperatures in excess of 500 c and is not consistent with the occurrence of intrusions of ultramafic rocks in the western betics however the delaminated simple shear model with low angle faults located only at lower crustal levels is found to be consistent with the p t t data after a heating phase associated with a finite extension of 80 km rapid cooling occurred reflecting inversion of the extensional structure by nw se to n s directed compression palaeo rheological models for the latest oligocene early miocene times demonstrate the important role of the detachments produced during crustal extension for the dynamics of the subsequent inversion phase the modelling strongly suggest that inversion locked after 60 km of finite convergence after locking of the inversion overthrusting in a northward direction occurred which is compensated by pure shear deformation in the lower crust in the southeastern part of the betic zone

origin of the permian triassic iberian basin central eastern spain abstract the iberian basin was an intracratonic rift basin in central eastern spain developed since early permian times the basin boundary faults were normal listric faults controlling an asymmetric extension propagating northeast with time hercynian or older lineaments controlled the orientation of the iberian basin and extension was accommodated basically in the hanging wall block by the formation of secondary grabens and a central high the basin was related with the coeval ebro catalan and cuenca mancha basins and their connections are discussed subsidence curves show that the early permian early jurassic period of extension can be subdivided into three rifting episodes and a flexural one extension factor increases from 1 17 in the northwest to 1 29 near the mediterranean coast the increasing extension rate was accommodated by transfer faults trending nne ssw more important in the levante area the rift evolution is intermittent and seems to reflect distinct stress fields the collapse of the late hercynian orogen and related increased heat flux extension and rifting is the most probable origin of the iberian basin and related basins the origin of the catalan and the valencia prebetic basins is related to the southwards migration of the hesse burgundy rift along the eastern margin of the iberian microplate

late permian continental sediments in the se iberian ranges eastern spain petrological and mineralogical characteristics and palaeoenvironmental significance abstract a detailed mineralogical and petrological study and the analysis of paleosol profiles in continental alluvial sediments of the late permian in the se iberian ranges spain allow us to infer the significant environmental changes that occurred during this time period three parts have been distinguished in the late permian sediments alcotas formation the lower part includes abundant and well preserved carbonate paleosol profiles and fine grained sediments made up by quartz feldspar hematite and illite with scarce kaolinite the preservation of dolomicrite in some paleosols suggests that they originally developed as dolocretes in an arid to semi arid climate with marked seasonality a change towards more humid and acid conditions can be deduced from the presence of siderite and goethite in paleosols in the middle part of the alcotas formation moreover the presence of plant remains coal beds and or carbonaceous shales at the top of the middle part and the lack of carbonate paleosols in the upper part of the formation would indicate a further step towards acid conditions these conditions would increase until the early triassic as indicated by the lack of carbonates and the presence of sr rich aluminium phosphate sulphates aps minerals at the base of the triassic canizar formation which clearly indicates extreme acid conditions during the permian triassic transition of the study area

neogene avian and mammalian tracks from death valley national monument california their context classification and preservation abstract the copper canyon formation consists of over 3000 m of basalt and alluvial fan and lacustrine strata deposited in a small neogene basin lacustrine strata are of two typs fine grained dolomitic carbonates deposited in a playa lake environment and calcitic bioclastic carbonates deposited in a freshwater lake environment bedding surfaces of the playa lake carbonates deposited in shoreline environments commonly contain avian and mammalian footprints tracks of artiodactyls are most abundant those of birds horses carnivores and proboscideans are less common using the binomial avian and mammalian footprint classification scheme of vialov 1966 four different mammalian ichnogenera containing thirteeen ichnospecies as well as six ichnospecies of avian tracks are recognized environmental factors of the ancient copper canyon playa lake which contributed to good footprint preservation included 1 periods of flooding and intense evaporation which resulted in receding shorelines that presented wet fine grained sediment surfaces for impression and subsequent subaerial exposure and 2 periodically high sedimentation rates which insured quick burial of the tracks while vertebrate footprints also occur in sandstones and conglomerates deposited in alluvial fan environments the morphological distinctness of tracks is best preserved in fine grained dolomitic carbonate and siltstone strata deposited in the playa lake environment distinctness of preserved tracks also increases with apparent decrease within a certain range of sediment water content at the time of impression an examination of preserved morphologies has allowed several sediment water content states important to footprint preservation to be deduced changes in sediment water content at the time of impression acted to produce a wide range of track morphologies for each individual trackmaker an examination of track abundance and occurrence within the formation suggests increasing visitation by larger vertebrates to the playa lake as lake water freshened the rare ocurrence of tracks of small mammals and low amount of vertebrate bioturbation within the playa deposits also suggests that the ancient copper canyon playa lake lacked a resident vertebrate population of its own probably receiving only migrating visitors seeking food and water the footprints in the copper canyon formation reflect part of the wide diversity of vertebrates present in southern california during the hemphillian

the upper permian boniches conglomerates formation evolution from alluvial fan to fluvial system environments and accompanying tectonic and climatic controls in the southeast iberian ranges central spain the boniches conglomerates fm upper permian represents the first episode of sedimentation in the southeast border margin of the iberian basin central spain the iberian basin commenced development as a rift basin running mainly nw se during the early permian and underwent its first general extensional period during the late permian the boniches fm was deposited as a small segment less than 100 km long and 9 10 km wide of the iberian basin that extended in a northeast direction during this period detailed mapping and palaeocurrent analysis have shown that the boniches fm is of a curvilinear wedge shaped morphology sediments close to the southwest main faulted border are of a maximum thickness of 230 m clear lateral variation in thickness controlled by the activity of secondary transfer faults perpendicular to the main nw se axis may be observed this network of faults permitted the formation of blocks limited laterally by the transfer faults these blocks experienced subsidence and rotation against the elevated southwest footwall block which resulted in the isolation of reduced sub basins with different sedimentary characteristics based on facies and facies association the boniches fm is thought to have evolved vertically from two main alluvial fan systems in the lowest part of the formation into fluvial braided systems flowing southeast as expected no flow orientations towards the footwall block are observed during the first episodes of the refill this may be explained by erosion or simply a lack of sedimentation due to the gentle slope the change from alluvial fan to fluvial environments is interpreted as a relatively sudden tectonic reorganization of the whole segment favouring new longitudinal fluvial drainage from a transfer zone located to the northwest three different reorganization episodes clearly marked in the boniches fm as main boundary surfaces mbs separate four members subdivided into 4 5 levels 34 m thick each level consists of fining upward successions less than 1 m thick tectonics and climatic factors clearly controlled sedimentation tectonic activity was probably of greatest importance and was conditioned by the movement of the main nw se and ne sw transfer faults the role of climate in ancient conglomerate sediments has not been well established palaeogeographical mineralogical sedimentological and clast analyses suggest that the boniches fm was deposited under humid conditions by running water the differentiation between proper alluvial fans and fluvial environments during the transition period of the boniches fro is not clear since in many recent alluvial fans braided fluvial systems are associated with fans

inversion tectonics and magnetic fabrics in mesozoic basins of the western tethys a review abstract positive tectonic inversion of sedimentary basins has been recognized as one of the primary mechanisms of mountain building and intraplate deformation reconstructing the tectonic history of basins is relatively easy for the inversion stage but becomes more difficult for the basinal stage especially when strong deformation involving cleavage development is associated with the subsequent compressional tectonics since tectonic markers for the extensional episodes are not commonly well developed anisotropy of magnetic susceptibility ams has provided recently a tool for analyzing early stages in the evolution of sedimentary basins even in the absence of other outcrop scale mesostructures here we expose and discuss the applicability of magnetic fabrics by means of ams to different types of intra plate sedimentary basins in the western tethys region formed under extensional or transtensional regimes and which underwent different inversion styles total or partial inversion with or without cleavage development forming part of compressional thrust sheets etc owing to specific particular p t conditions and structural controls factors such as lithology magnetic mineralogy position within the sedimentary pile and deformation intensity are key to interpret the obtained magnetic fabrics in terms of tectonic evolution a basin classification is proposed according to inversion styles and magnetic fabrics where inversion did not involve cleavage development magnetic lineation is parallel to the stretching direction corresponding to the extensional stage the transition between non cleaved to inversion related cleaved units is marked by the switch of magnetic lineations from parallel to extension to parallel to the intersection lineation between cleavage and bedding these relationships are enhanced when extension and compression are roughly coaxial then favoring the clustering of axes of the magnetic ellipsoid even when extreme inversion occurs and the early extensional fabric is obliterated magnetic fabrics provide information about the interaction between preferred deformation directions associated with the main stages in basin evolution

the madrid basin and the central system a tectonostratigraphic analysis from 2d seismic lines abstract data from deep boreholes seismic surveys and surface geology are used to reconstruct the sedimentary infilling of the cenozoic madrid basin eight main depositional sequences and seismic units are recognised from the paleogene the latter four of these sedimentary sequences were deposited in a continental environment under the influence of tectonic activity in the central system the toledo mountains the iberian chain and the sierra de altomira the sedimentary infill shows an overall coarsening upward trend from upper cretaceous formations to syn tectonic conglomerate deposits followed by a fining upward sequence and moderate reactivation of some faults during the late miocene pliocene the syn tectonic sediments are oligocene early miocene in age the foredeep is oriented northeast southwest and shows a sediment thickness of up to 3800 m in areas close to the central system several types of tectonic structures are recognised including imbricate thrust systems thrust triangle zones fault propagation folds back thrust systems and pop up structures the frontal thrusts were subjected to significant erosion and late miocene sediments onlap the anticlines of the onshore foreland nw se trending positive flower structures have been recognised in the eastern part of the basin the total northwest southeast shortening across the contact between the madrid basin and the central system is approximately 5 km of which 2 3 km occurred across the southern border thrust the simultaneous basement uplift of the central system and the tectonic escape of the sierra de altomira have been interpreted as a consequence of constrictive deformation within the pyrenean foreland of the iberian microplate

mesozoic extensional tectonics stratigraphy and crustal evolution during the alpine cycle of the eastern iberian basin abstract sequence stratigraphy subsidence analysis and the integration of the basin fill data allow to the identification of four successive evolutionary stages in the basins of the eastern iberian margin during mesozoic extension 1 triassic rift late permian hettangian 2 early and middle jurassic postrift sinemurian oxfordian 3 late jurassic and early cretaceous rift kimmeridgian middle albian and 4 late cretaceous postrift late albian maastrichtian the present day crustal structure of the eastern iberian range and evidence of its evolution are deduced from the analysis of a new gravity map and other geophysical data a regional gravity low along the iberian range is interpreted in terms of crustal thickening beneath the orogen as a result of the collision between the ebro block and the iberian plate during the paleogene the boundary between these blocks coincides with a magnetic lineament that is interpreted as an inherited signature of the thinning that occurred during mesozoic extension a geodynamic scenario for the crustal evolution of the eastern part of the iberian peninsula based on the evaluation of mesozoic extensional tectonics and an analysis of the available geophysical data includes three main successive evolutionary stages 1 1 mesozoic crustal thinning 2 2 paleogene crustal thickening 3 3 neogene crustal thinning based on new geological and geophysical arguments this study offers an alternative and a more complete geodynamic history of the eastern iberian basins related to the evolution of the iberian plate and the central north atlantic

evidence for the permo triassic transtensional rifting in the iberian range ne spain according to magnetic fabrics results abstract anisotropy of magnetic susceptibility ams techniques are applied to permo triassic red beds from the castilian branch iberian range ne spain that were deposited in an extensional basin inverted during cenozoic times the main goal of this work is to characterize the tectonic evolution of the basinal stage by differentiating synsedimentary to early diagenetic magnetic fabrics from the secondary tectonic fabrics related to compression which are scarcely developed because no penetrative structures related to compression have been recognized oblate magnetic fabrics with kmin axes perpendicular to bedding are observed in most cases magnetic lineations are variable showing a dominant ene wsw maximum which fits with a dextral transtensional regime acting on nw se master faults during the triassic we propose that variations in the orientation of the magnetic lineation are associated with transfer faults which fragment the basin and trigger strain partitioning in different areas magnetic fabrics are locally modified by cenozoic compression with intermediate and minimum axes distributed along girdles perpendicular to fold axes comparing all these results with macrostructures and mesostructural kinematic indicators we conclude that the fine grained hematite bearing rocks carry a consistent magnetic fabric which can be used to reconstruct the basin history

the rosa keystone dunes field the geoarchaeology and paleoecology of a late quaternary stabilized dune field in eastern beringia stabilized sand sheets and dunes hold a remarkable amount of information on paleoenvironmental conditions under which late quaternary landscapes evolved in northern subarctic regions we provide the results of a project focused on understanding the development of lowland environments and ecosystems including dunes and sand sheets which were critical habitat for early human occupations in subarctic regions our study area is the rosa keystone dunes field in the shaw creek flats of the middle tanana river basin interior alaska one of the oldest continuously occupied areas in north america 14 000 cal bp to present the disturbance regimes of reactivated dunes and associated forest fire cycles between 12 500 and 8800 cal bp fostered a unique early to mid successional mixed vegetation community including herbaceous tundra shrubs and deciduous trees this environment provided key habitats for large grazers and browsers significant resources for early hunter gatherer populations in central alaska aft

thermo mechanical modelling of black sea basin de formation abstract we present the results of a thermo mechanical modelling study carried out to investigate the effect of pre rift rheology on subsequent basin de formation in the black sea area important differences are inferred for the bulk lithosphere structure and mechanical properties expressed in terms of different estimates for levels of necking in the western and eastern black sea respectively gravity data provide constraints on the mode of flexure in the black sea pointing to significant lateral variations in pre rift lithospheric strength these features strongly affect predictions for mesozoic cenozoic basin stratigraphy and have implications for the presence and development of rift shoulder topography on the margins of the black sea basins differences in lithosphere strength affect the mode of stress propagation from the basin margins into the central parts of the black sea basins during the post rift phase these post rift compressional stresses could be of key importance for long wavelength late neogene differential motions within the basins superimposed on vertical motions induced by rifting and subsequent sediment loading thermo mechanical modelling of integrated lithospheric strength points to a rapid increase of strength during the later stages of post rift evolution and the presence of relatively strong lithosphere in the centre of the basin these features predict preferential shortening induced by compressional activity of surrounding orogens to be primarily accommodated at the basins margins

late pleistocene eolian sand sheets in alaska abstract nonglaciated lowlands in central and southwestern alaska contain extensive deposits of upper quaternary eolian sand derived largely from major outwash rivers although surface dunes are common deep exposures consistently reveal that subhorizontally stratified sand and silt deposits dominate over dune cross strata we hypothesize that 1 many of the subhorizontally stratified deposits represent full glacial eolian sand sheets formed when sand supply was limited by seasonally variable combinations of ice cementation snow cover high groundwater tables and vegetation and 2 many surface dunes reflect late glacial and postglacial reworking under conditions of increased short term availability of loose sand the morphology of some surface dunes may therefore reflect mainly the intensity of reworking since the last glacial maximum rather than full glacial paleowind vectors or the age of the bulk of the underlying deposits

a diverse pleistocene marsupial trackway assemblage from the victorian volcanic plains australia abstract a diverse assemblage of late pleistocene marsupial trackways on a lake bed in south western victoria provides the first information relating to the gaits and morphology of several megafaunal species and represents the most speciose and best preserved megafaunal footprint site in australia the 60 110 ka volcaniclastic lacustrine sedimentary rocks preserve trackways of the diprotodontid diprotodon optatum a macropodid probably protemnodon sp and a large vombatid perhaps ramsayia magna or phascolomys medius and possible prints of the marsupial lion thylacoleo carnifex the footprints were imprinted within a short time period demonstrating the association of the taxa present rather than the time averaged accumulations usually observed in skeletal fossil deposits individual manus and pes prints are distinguishable in some trackways and in many cases some digital pad morphology is also present several parameters traditionally used to differentiate ichnotaxa including trackway gauge and the degree of print in turning relative to the midline are shown to be subject to significant intraspecific variation in marsupials sexual dimorphism in the trackway proportions of diprotodon and its potential for occurrence in all large bodied quadrupedal marsupials is identified here for the first time

geochemical evidence for the origin of late quaternary loess in central alaska loess is extensive in central alaska but there are uncertainties about its source and the direction of paleo winds that deposited it both northerly and southerly winds have been inferred the most likely sources of loess are the tanana river south the nenana river southeast and the yukon river north late quaternary loess in central alaska has immobile trace element compositions cr sc th ta th sc th u eu eu gdn ybn that indicate derivation mostly from the tanana river however other ratios as sb zr hf lan ybn and quantitative modeling indicate that the yukon river was also a source during the last glacial period there may have been a longer residence time of the siberian and canadian high pressure cells along with a strengthened aleutian low pressure cell this would have generated regional scale northeasterly winds and explains derivation of loess from the yukon river however superim posed upon this synoptic scale circulation there may have been strong southerly katabatic winds from expanded glaciers on the northern flank of the alaska range these winds could have provided eolian silt from the tanana river yukon river and tanana river sediments are highly calcareous whereas fairbanks area loess is not this suggests that carbonate leaching in loess kept ahead of sedimentation and that late quaternary loess in central alaska was deposited relatively

application of vertebrate trace fossils to palaeoenvironmental analysis abstract this is a review of the main uses of vertebrate trace fossils ichnofabrics and ichnofacies in the palaeoenvironmental analysis of sedimentary sequences the article accounts for the significant developments produced in the last three decades including the application of the ichnofacies concept to vertebrate trace fossils recognition of footprints in cross sectional view and their distinction from inorganic structures and burrow fills is first discussed the response of different substrates showing contrasting water content and imprinted by different animals or devices is compared in terms of the morphology of the resultant footprint trackways with sand crescents are typical of aeolian cross strata and are absent in associated flat lying to low angle deposits thick packages of highly bioturbated sandy dune and interdune sediments have been interpreted as reflecting periods of increased rainfall neoichnological observations in modern lake basins suggest that distinct zones can be recognized in the margins of fossil ponds and lakes including onshore shoreline and shallow subaqueous zones abundant flamingo like footprints and flamingo nest mounds are good indicators of alkaline and or saline lake waters hippopotamus trails are found closely associated with modern and fossil freshwater wetlands dinosaur and pterosaur swim traces from lacustrine and fluvial deposits can be used to estimate water depth turtle crocodile amphibian hippopotamus and fish swim traces allow one to infer a subaqueous substrate certain modern intertidal fish feeding traces are oriented with the predominant tidal current and can be used as palaeocurrent indicators the preferential orientation of tetrapod trackways in lacustrine and fluvial deposits is analyzed vertebrate trace fossils can help to infer discharge variability in fluvial channels the descriptions of vertebrate ichnofabrics are commonly limited to heavily bioturbated beds due to trampling by vertebrates and to a few examples of ichnofabrics with discrete trace fossils the nature and implications of the recognized vertebrate ichnofacies are still being debated and have a limited utility in palaeoenvironmental analysis the distinction of a potential vertebrate burrow ichnofacies in carbonate bearing palaeosols is proposed to represent well drained soils developed under arid or semiarid climate

lithosphere dynamics and tectono stratigraphic evolution of the mesozoic betic rifted margin southeastern spain abstract quantitative subsidence analysis demonstrates that mesozoic sediments in the eastern betic cordilleras have been deposited on a thermally subsiding rifted margin the dynamics of rifting are related to regional trans tension in the atlantic realm modelling of this phase of rifting at the southern iberian margin shows that the associated stretching of the lithosphere significantly altered its geometrical and mechanical structure and exerted a major control on subsequent convergence tectonics the mesozoic stretching led to the formation of a ramp at the margin due to strong lateral variations in the effective elastic thickness eet of the lithosphere and the thickness of the crust in a direction perpendicular to the margin the existence of a ramp structure in the late mesozoic at the iberian margin which is also supported by stratigraphic and structural data is important for the style of subsequent deformation of the lithosphere in late cretaceous tertiary times the lateral variations in eet inferred from forward modelling of rifted margin stratigraphy could explain the observed multiple collapse of the betic margin and the partitioning of deformation between the converging units involved in the betic orogeny modelling of depth dependent palaeo rheological profiles of the margin shows that the mechanical properties of the lithosphere after stretching differed distinctly from those before stretching lithospheric deformation in the betic cordilleras during the tertiary orogeny seems therefore to be largely controlled by the previous rifting phase a comparison of the palaeo and present day rheologies in terms of estimates for eet during late cretaceous and present times indicates that the mechanical properties of the lithosphere underlying the betic orogen were also affected by rifting during late oligocene aquitanian times this phase of rifting is coeval with extension in the valencia trough the gulf of lions and the west european rift system which supports a causal relation with regional lithospheric processes the lateral and spatial variations in thermo mechanical properties of the lithosphere underlying the betics therefore reflect the dynamics of lithospheric extension on a larger scale

sequences cycles and hiatuses in the upper albian cenomanian of the iberian ranges spain a cyclostratigraphic approach abstract the upper albian cenomanian deposits in the iberian ranges are composed of a complex alternation of continental sandstones coastal lime sandstones and marls and marine carbonates facies facies are arranged mainly in transgressive and deepening upward sequences and parasequences but deepening shallowing upwards sequences and parasequences also exist depositional sequences and parasequences are bounded by subaerial erosive surfaces or ferruginous crusts and by their correlative conformities it is evident from the facies alternation that deposition reflects a cyclic process in which is superimposed several orders of cycles of relative sea level rise and fall the cycles are preserved as 3rd order depositional sequences and 4th and 5th order discontinuity bounded parasequences the latter being the basic blocks of the field record a cyclostratigraphic model for sedimentation shows that each of the 3rd order cycles is composed of five 4th order cycles a 4th order cycle is also composed of five 5th order cycles this 1 5 5 ratio reflects the maximum number of parasequences observed in the most complete and marine sections the ratio remains unchanged throughout the basin except by onlap caused by relative sea level rises or truncations caused by relative sea level falls a detailed correlation of sections separated by more than 200 km shows that thickness differences are caused mainly by parasequence disappearance not parasequence thinning cycles are mainly eustatic in origin controlled by accommodation space increased accommodation generates thick parasequences of wider regional extension they contain the more marine facies in any section only some sequences with a restricted regional distrubution are recorded if the accommodation is low the average duration of 3rd order cycles was 1 95 ma ranging from 1 33 to ma an average 4th order cycle was 390 ka 266 533 ka and a 5th order cycle was 78 ka 53 106 ka

diagenesis and distribution of acyclic isoprenoid hydrocarbons in late miocene to pliocene marine siliceous rocks from horonobe hokkaido japan abstract a sequence of late miocene to pliocene siliceous mudstones from boreholes hdb 3 and hdb 4 from horonobe hokkaido japan is homogeneous and useful for the study of diagenetic degradation and transformation of sedimentary organic matter using these siliceous mudstones the diagenetic change in acyclic isoprenoid hydrocarbons was investigated the palaeotemperatures of the samples were estimated to be in the range 30 60 c on the basis of the silica mineral transformation and the present day geothermal gradient in the region the relative abundances of pristane to pristenes and phytane to phytenes increase drastically with depth the remarkable changes in pristane pristene and phytane phytene occur in a temperature range of about 35 50 c the relative abundances could be potential parameters for palaeotemperature analysis of immature sedimentary rocks remarkable increases in pristane and phytane concentration with maturity show that in addition to extractable free pristenes and phytenes bound acyclic isoprenoids are the major source of pristane and phytane pristane phytane and pristenes phytenes are nearly constant through the entire boreholes showing that the relative abundance of the precursor c 19 c 20 acyclic isoprenoids was determined at the time of deposition and or in the early stage of diagenesis pristene phytene as well as pristane phytane could be useful parameters for assessing palaeodepositional environment

on a tectonic mechanism for regional sealevel variations abstract no satisfactory tectonic explanations have yet been offered for the apparent sealevel fluctuations of about 1 cm 1000 years and a magnitude of up to a few hundred meters that have been proposed by vail et al 1 we propose a mechanism that does appear to be able to explain these changes if horizontal stresses of the order of a few kilobars occur in the lithosphere and if changes in these stress fields occur on geological time scales the proposed model is one of an interaction between these stresses and the deflections of the lithosphere caused by sedimentary loading apparent sealevel changes of up to 100 m can be produced at the flanks of the sedimentary basins by this interaction the mechanism is most effective for young margins that are subject to rapid sediment loading by its nature the tectonic model can explain contemporaneous fluctuations in apparent sealevel in neighbouring depositional environments in principle it implies the possibility of regional correlations in different basinal settings

fungus plant interaction in a thuringian late permian dadoxylon sp in the se iberian ranges eastern spain abstract this report describes an anatomical and taphonomical study of a large exceptionally well preserved late permian dadoxylon sp trunk the specimen found in siliciclastic red bed sediments of fluvial origin of the landete formation iberian ranges eastern spain includes the first described fungus plant interaction for this time interval in europe this finding is all the more significant since a fungi enriched layer recently reported in sediments of different continents corresponding to the end of the permian has been related to a world wide crisis whereby fungi were responsible for the breakdown of massive amounts of vegetation already suffered by a possible catastrophic event or events leading to a global drop in photosynthesis the well known humid temperate climatic conditions of the late permian sediments and the sedimentary environment represented by the landete formation would have favoured the proliferation of fungi which was probably unaffected by any other significant biotic activity fungal activity is likely to have started soon after the fall of the plants indicated by the good preservation state of areas of the trunk unaffected by the fungal infection later diagenesis suggests different fluid migration stages clearly conditioned by the original anatomical characteristics of the trunk and the results of fungal activity physical signs left by the enzyme action of wood decay fungi can be recognised in the fossilised wood using this information and sedimentological data we reconstructed the taphonomic processes incurred by the specimen including both biostratinomic and diagenetic stages ullmania sp and pollen grains such as lueckisporites and nuscoisporites dulhuntyi produced by species of late permian walchiaceae or ullmanniaceae that did not cross the permian triassic boundary were also found in levels stratigraphically below the fossil specimen none occurred above the trunk site this flora and fungal activity could relate this level of iberian permian sediments to the level or one of the levels associated with the worldwide late permian crisis and fungal proliferation

the atlas east variscan elbe shear system and its role in the formation of the pull apart late palaeozoic basins the variscan orogeny occurred as a result of the late devonian to late carboniferous collision and accretion of gondwana derived microcontinents and continental masses with those of laurussia the irregular boundaries of the colliding continents caused isochronous transpressional and transtensional tectonics accompanied by a complex pattern of intracontinental shear zones at the scale of the southern european variscides these shear zones and their configuration controlled the subsequent evolution of permian to middle triassic paleogeography the geographic distribution from morocco to the eastern alps of the late carboniferous permian up to triassic basins most of which are considered as pull apart basins was related with the development of the late palaeozoic intracontinental shear network our analysis of the stratigraphic tectonic and volcanic features of the late carboniferous permian continental basins across the laurussia gondwana boundary reveals the role of the east variscan shear zone during this time as a precursory lineament for the development of the permian to triassic rifting of pangaea and the following opening of oceanic basins e g the neothetyan ocean

a finite difference technique to incorporate spatial variations in rigidity and planar faults into 3 d models for lithospheric flexure summary we present a finite difference formulation for 3 d elastic flexure of the lithosphere which is solved by a direct matrix method to incorporate the effect of spatial variations in rigidity additional terms for the bi harmonic 3 d flexure equation have been derived from a variational displacement formulation as used in finite element methods additionally planar faults are treated as discontinuities these are implemented by an additional degree of freedom for fault heave and a coupled continuum equation for zero differential tilting across the fault the 3 d finite difference results have been tested for line loads point loads and disc loads by analytical solutions and for spatial variation in effective elastic thickness eet by 2 d finite difference solutions fault related flexure patterns are compared to the 2 d analytical broken plate model developed by vening meinesz 1950 we subsequently apply the 3 d fault model to investigate fault controlled 3 d basement geometries in lake tanganyika east africa we show that our model is capable of predicting 3 d basement geometries characteristically observed in rifted basins the modelling results indicate that fault controlled upper crustal flexure patterns are associated with low values for eet a comparison with regional scale model studies showing a superposition of high eet flexure effects supports a multilayered rheological control on continental rifting

short paper fossil vertebrate tracks and indenter mechanics a reconnaissance study is outlined showing how an improved understanding of the formation and character of fossil vertebrate tracks in soft sediments is provided by the application of the mechanical engineer s indenter theory supported by complementary scaled laboratory experiments only the footprint at the bottom of the shaft cut by the animal9s limbs in general offers the best preservation of the shape of the underside of the foot the character of the foot is less well preserved in the deformed bedding beneath the footprint and among laminae deposited in the shaft after the passage of the animal this understanding will help to reduce errors in the use of tracks in taxonomic biostratigraphic palaeoecological behavioural and environmental studies when a limbed vertebrate traverses yielding sediment the limbs deform the substrate into tracks which vary with the nature size and gait of the animal the forcefulness of its limb movements and the sediment properties most previous geological work on tracks and trackways has emphasized their taxonomic biostratigraphical palaeocological and behavioural significance lockley 1986 leonardi 1987 but without an adequate understanding of their environmental implications lockley 1986 and in particular their genesis and preservation as trace fossils the response of an elastic plastic material to an indenter or punch both in terms of theory calladine 1969 hill 1971 johnson et al 1982 and in the light of qualitative laboratory experiments provides a general mechanical model for track formation and a basis for the assessment of track preservation in sediments the indenter represents the animal9s

quantitative subsidence analysis of the mesozoic evolution of the lusitanian basin western iberian margin abstract quantitative subsidence analysis of 26 wells in the lusitanian basin provides new constraints on the western iberian mesozoic passive margin development backstripped tectonic subsidence curves show a three fold subdivision of vertical motions from late triassic onward continental rifting was initiated during the late triassic and early jurassic from middle jurassic onward a distinct different behaviour is expressed in the subsidence curves for the north and the south lusitanian basin during the middle jurassic the south lusitanian basin records a stretching episode with stretching factors of about 1 08 while the north lusitanian basin typically has a middle jurassic hiatus this different development is also expressed in the late jurassic and early cretaceous sedimentary sequence when both the north and south lusitanian basin are subjected to another stretching episode with a more pronounced development of the southern than of the northern part of the basin the stretching factors for this last phase are about 1 03 for the northern part and 1 08 for the southern part of the area this north south difference during the middle jurassic to early cretaceous for which the transition roughly coincides with the location of the nazare fault zone is probably a result of differences in pre rift crustal composition or thickness late cretaceous sediments are mostly absent in the analysed wells in the southern part of the basin the absence of the cretaceous record is a consequence of erosion due to cenozoic inversion of the basin the generally low estimates for stretching factors suggest that the analysed eastern part of the lusitanian basin forms the distal part of the mid cretaceous continental breakup a comparison with subsidence curves of neighbouring basins of iberia reflects general patterns in mesozoic basin development and confirms the generally held view that the extension leading to continental breakup migrated from south to north during the middle jurassic to early cretaceous in west iberia

temporal and spatial variations in tectonic subsidence in the iberian basin eastern spain inferences from automated forward modelling of high resolution stratigraphy permian mesozoic by subsidence analysis on eighteen surface sections and 6 wells which cover large part of the iberian basin e spain and which are marked by high resolution stratigraphy of the permian triassic jurassic and cretaceous we quantify the complex permian and mesozoic tectonic subsidence history of the basin backstripping analysis of the available high resolution and high surface density of the database allows to quantify spatial and temporal patterns of tectonically driven subsidence to a much higher degree than previous studies the sections and wells have also been forward modelled with a new automated modelling technique with unlimited number of stretching phases in order to quantify variations in timing and magnitude of rifting it is demonstrated that the tectonic subsidence history in the iberian basin is characterized by pulsating periods of stretching intermitted by periods of relative tectonic quiescence and thermal subsidence the number of stretching phases appears to be much larger than found by earlier studies showing a close match with stretching phases found in other parts of the iberian peninsula and allowing a clear correlation with discrete phases in the opening of the tethys and atlantic

identification of systems tracts in low angle carbonate ramps examples from the upper jurassic of the iberian chain spain abstract the upper jurassic of the iberian chain in northeast spain was selected for the study and identification of sequence boundaries and systems tracts in low relief carbonate ramp systems the study area provides a special opportunity for sequence stratigraphic analysis because the outcropping upper jurassic carbonate ramps are relatively undeformed well exposed from proximal to distal areas and have an established ammonite zonation two sequences are recognized sequence a uppermost callovian to uppermost oxfordian in age up to 60 m thick in the proximal areas and between 15 and 5 m thick in the middle and distal areas and sequence b kimmeridgian to lowermost tithonian from 80 to 160 m in thickness across the basin the evolution of the first sequence is related to regional relative sea level changes i e tectono eustatic changes superimposed on the sedimentary basin on the other hand the larger accommodation created during the second sequence is regarded as controlled mainly by steady subsidence sequence boundaries indicative of subaerial exposure show as unconformities with stratigraphic hiatuses in the proximal areas of the basin the lowstand systems tract in sequence a is represented by a decimetre thick reworked level consisting of several ammonite biozones in sequence b this systems tract consists of a thick wedge shaped marly unit in both sequences the transgressive surface overlaying these lowstand deposits is generally planar and marks a sharp boundary between the restricted and open marine fossils however in sequence b in the middle part of the basin the transgressive surface can be absent instead a transitional change to open marine facies exists the transgressive systems tracts show sedimentary condensation at least in the distal areas of the basin with mostly ammonites and benthic fossil wackestones the transgressive unit is generally overlain by a hard ground surface that corresponds to a maximum flooding surface finally in the upper part of both sequences highstand systems tracts are represented by progradational siliciclastic and shallow carbonate complexes in the proximal areas of the basin in sequence a sedimentation is condensed in the distal areas with glauconite marl levels present the descriptions of sedimentary features of the systems tracts of these two sequences developed in a low angle carbonate ramp are suggested to be used as tools for the recognition of systems tracts patterns within sequences in comparable depositional settings

the late palaeozoic early mesozoic from the catalan pyrenees spain 60 myr of environmental evolution in the frame of the western peri tethyan palaeogeography the eastern catalan pyrenees form the southernmost segment of the pyrenean axial zone they experienced complex multistage process as the result of both the variscan and the pyrenean orogenic cycles after the late palaeozoic several small extensional sub basins were filled by continental successions as a response to the changing tectonic setting within the frame of the southwestern europe this stratigraphic record perfectly exposed in the studied eastern pyrenean areas preserves the signatures of the late palaeozoic pangea break up during the progressive dismantling of the variscan chain up to the triassic diffused extension despite structural network being severely affected by cenozoic reworking the stratigraphic framework can be unravelled by the detailed sedimentological and stratigraphical analysis of the well exposed sequences in short this paper addresses facies patterns and architectural elements of late carboniferous permian triassic continental sections studied in the catalan pyrenees and aims to use these signatures for correlation not only at a regional scale but also within the broader picture of the southwestern europe our stratigraphical reconstruction clearly demonstrates that the thick studied succession consists of fluvial lacustrine basal units affected by intense volcanic activity and overlaying predominantly fluvial fining upwards units for each unit several lithofacies architectural elements and bounding surfaces of different order have been identified and their lateral and vertical staking characterized deposition and erosion processes are controlled by alternating periods of tectonic activity producing different stages of high and low subsidence the uplift of the sub basin margins and subsequent extended erosive events marked by angular unconformities on the strength of the major rank bounding surfaces analysis the studied sedimentary packages have been grouped into different tectono stratigraphic units and then correlated they have been contextualized within the latest palaeogeographic reconstructions of the studied sector contributing to detail the role of the study area within the frame of the s european palaeogeography

lithospheric folding in iberia integration of stress indicator data gravity data crustal kinematics data and analysis of topography and recent vertical motions demonstrates the occurrence of consistently oriented spatial patterns of large scale alpine to recent intraplate deformation in iberia the inferred upper crustal and lithospheric deformation patterns and the timing of the associated expressions at or near the surface support the existence of a close coupling with plate boundary processes operating at the margins of iberia patterns of lithosphere and upper crustal folds are oriented perpendicular to the main axis of present day intraplate compression in iberia inferred from structural analysis of stress indicator data and focal mechanism solutions these findings suggest the presence of lithospheric folds with wavelengths compatible with theoretical predictions of folding wavelengths of variscan lithosphere stress induced intraplate deformation set up by plate interactions is compatible with indications for the absence of present day deep mantle lithosphere interactions inferred from seismic tomography

triassic stretching directions in iberia and north africa inferred from magnetic fabrics during the triassic iberia and western north africa displayed a unique situation in relation with the central and north atlantic opening and westward expansion of the tethys unravelling the stretching direction in triassic deposits of the studied area can help in our understanding of this scenario the tectonic setting is characterized by localized basins with strong thickness variations greatly influenced by previous post variscan mechanical discontinuities in this work we revise and compile magnetic fabric data from eight triassic depocentres in terms of defining the stretching direction i e magnetic lineation resulting from extensional deformation of this period data show the importance of the opening of the atlantic rift as the leading process during the triassic dextral transtension can explain the deflection of the extensional direction observed in most studied depocentres that is caused by the activity of previous major oblique faults

fracture distribution along an upper jurassic carbonate ramp ne spain abstract understanding the distribution of natural fractures in sedimentary systems is of high relevance for the exploration and production of fluids in the subsurface this study focuses on a kimmeridgian mixed siliciclastic carbonate ramp system which is part of the jurassic limestones outcropping in the northeastern iberian chain the study area is located north of the ricla village fifty kilometers southwest of zaragoza the outcrop stretches over six kilometers in length it allows for recording detailed fracture patterns and facies variations a gis based software package digifract is used to measure and digitize fractures in vertical outcrops fracture orientation measurements obtained from vertical and horizontal outcrops are used to create a conceptual three dimensional image of the fracture distribution of the mixed ramp system the fracture data are processed by integrating outcrop logs and sample data obtained from thin sections and rock property analysis the continuous facies belts of the shallow low angle ramp system show limited lateral variations the studied sediments are subdivided in four main facies tracts ft s ft 1 bioclastic siltstones ft 2 alternating sandy limestones and marls ft 3 cross bedded and channelled oolitic bioclastic sand and grainstones and ft 4 coralgal float to mudstones with eventites measured fracture orientations of the vertical and horizontal outcrops are identical throughout the entire exposure two main fracture sets are identified the first set set 1 has a n s direction and the second set set 2 has a ne sw direction the lateral homogeneity of the sedimentary system thus facies layer thickness and slope angle can be translated to the observed fracture patterns within one single facies belt fractures tend to behave the same in the proximal middle and distal part of the ramp system however vertical facies variations are an important factor for the measured vertical fracture heterogeneity fine grained mud supported facies correspond to periods of a sea level highstand coarse grained cemented facies on the other hand are related to a sea level lowstand the physical contrast of the sediments caused by sea level fluctuations forces fractures to solely concentrate in the brittle layers fracture density and termination patterns observed on this ramp stand in contrast to fracture geometries observed in flat topped carbonate platforms lateral facies heterogeneity and platform anatomy of flat topped carbonate platforms are key parameters for the eventual fracture distribution for the studied mixed ramp type system the vertical facies variations are key parameter

the tectonic evolution of the southern dutch north sea during the palaeogene basin inversion in distinct pulses abstract in this paper we discuss the response of a sedimentary basin to compressional reactivation of extensional faults in distinct pulses the inversion of the broad fourteens basin in the southern dutch north sea is used as a case study the first pulse of inversion occurred during the late mesozoic as a result of the sub hercynean phase a second pulse occurred during the mid palaeocene laramide phase a final inversion pulse occurred around the eocene oligocene boundary coinciding with the pyrenean tectonic event we reconstructed the stratigraphic and structural development of the area during the palaeogene in detail basic data are two 2d seismic surveys supported by 74 geophysical wireline logs on which newly constructed depth and thickness maps are based the reconstruction is aided by a quantitative subsidence analysis cessation of compression resulted in relaxation and tensional reactivation of faults caused differential subsidence inheritance of geological structures is a key element in the tectonic activity in the broad fourteens basin during the palaeogene tectonic movement during the palaeogene was always accommodated by reactivation of palaeozoic mesozoic faults the intensity of inversion in the southern north sea basin during the pyrenean phase appears much larger than previously noticed moreover the area affected by the inversion is much wider than during previous phases minor differences in the direction of the local stress field between the tectonic phases and by the deposition of a thick sedimentary succession during the periods of tectonic quiescence between the inversion phases can account for this

paleogeographical significance of the rot anisian triassic facies marines clays muds and marls fm in the iberian ranges eastern spain abstract the marines clays muds and marls formation consists of fine grained sediments recording the transition from distal fluvial facies to shallow marine sediments representing the onset of the first marine transgression of the tethys sea in the iberian basin muds show irregular parallel lamination of possible cryptalgal origin wave ripples linsen bedding mud cracks vertical burrows and halite pseudomorphs and contain anisian palynomorphs the carbonate content increases towards the se the deposition of the marines formation took place in a rift the iberian basin during a period of distensive tectonics and probably during a marine transgression of eustatic origin but the relative importance of the tectonic and eustatic factor is a matter of speculation in the area up to now

magmatism in the intracratonic central iberian basins during the permian palaeoenvironmental consequences abstract recent studies have confirmed the important role played by magmatism during the late carboniferous permian transition in this report we describe the characteristics of this magmatism in the central iberian realm iberian ranges and eastern spanish central system and discuss its palaeoenvironmental impact in the studied area the late variscan transtensional to extensional tectonic regime favoured the emplacement of a calc alkaline magmatism during the late stephanian permian this magmatism is expressed both as pyroclastic rocks filling small half graben basins and hypabyssal intrusions sills and dykes pyroxenic and amphibolic andesites are the main rock compositions while basalt dacite and rhyolite are less represented the available k ar isotopic data suggests a lower permian age for this magmatism also supported by its complete macro and microflora content and by features related to its emplacement hypabyssal intrusions crosscut stephanian rocks and are in turn overlain by late permian triassic sediments frequent xenoliths of middle and lower crustal levels indicate considerable magma crust interaction this interaction may have led to substantial crustal assimilation during the first emplacement stages in conditions of a low extension rate crustal contamination barely affected the final magmatic products emplaced under conditions of greater extension the palaeoecological effects of explosive manifestations of this volcanism are expressed in the varied macroflora record in volcaniclastic basins the number and volume of hypabyssal intrusions suggest that the original geological record of explosive activity in these basins was much greater and was reduced by subsequent erosion processes

a comparison of the iberian and ebro basins during the permian and triassic eastern spain a quantitative subsidence modelling approach the permian triassic sediments of the iberian plate are a well studied case of classical buntsandstein muschelkalk keuper facies with good sedimentological interpretations and precise datings based on pollen and spore assemblages ammonoids and foraminifera synrift postrift cycles are recorded in these facies but there are only a few studies of quantitative subsidence analysis backstripping method and only a previous one using forward modelling for the quantification of synrift postrift phases of this period here we present the results obtained by the quantitative analysis of fourteen field sections and oil well electric log records in the iberian and ebro basins spain backstripping analysis showed five synrift phases of 1 to 3 million years duration followed by postrift periods for the permian triassic interval the duration however shows lateral variations and some of them are absent in the ebro basin the forward modelling analysis assuming local isostatic compensation has been applied to each observation point using one layer and two layer lithospheric configurations the second one shows a better fit between observation and model prediction in a systematic way so a two layer configuration is assumed for the sedimentary basin filling analysis lithospheric stretching factors and obtained in the forward modelling analysis are never higher than 1 2 but sometimes 1 in the same section if surficial extension is compensated by deep compression either at the roots of the rift basins or in far away zones is not yet clear but this anomaly can be explained using a simple shear extensional model for the iberian and ebro basins 2008 elsevier b v all rights reserved

a change from warm humid to cold dry climate conditions recorded in lower barremian clay dominated continental successions from the se iberian chain ne spain abstract a combined facies and clay mineralogy analysis of the continental succession recorded in the lower part of the blesa formation early barremian oliete subbasin ne spain allowed us to specify the palaeoclimatic and palaeoenvironmental conditions under which this sedimentary record originated six outcrops including clays clays marls and dm thick interbedded palustrine lacustrine limestone levels were logged and sampled for x ray diffraction and optical and electron microscopy analysis the lower levels consist of red clays with abundant ferruginous pisoids 1 5 mm in size and macropisoids 5 mm whereas the intermediate and upper levels are ochre and violet clays marls with few or no pisoids the pisoids normally consist of a nucleus and a cortex made up of several layers some pisoids have a fragment of a previous pisoid acting as a nucleus indicating local re working processes both the nucleus and the cortex are formed by hematite goethite variable contents of kaolinite and minor proportions of ilmenite their texture and mineralogy show an in situ growth interbedded limestone beds within the clay and clay marl dominated levels are formed by micrite microsparite and sparite these limestones are cemented by kaolinite and they also have pisoids indicating the occurrence of edaphic processes the red clays have the lowest calcite content and the highest hematite anatase diaspore goethite and kaolinite content by contrast the ochre and violet clays marls have higher illite content smectite is only detected in the ochre clays marls this mineral association is characteristic of lateritic palaeosols formed under warm and humid conditions kaolinite and smectite textures indicate that they are authigenic whereas illite may be of detrital origin the upward decrease in kaolinite hematite anatase diaspore and goethite content along with the increase in quartz content and the presence of smectite and illite reflect a change from warm and humid conditions to drier and colder conditions during the early barremian in the studied area

sedimentary structures made by shore ice in muddy tidal flat deposits st lawrence estuary quebec abstract well preserved sedimentary structures formed by shore ice are exposed in emergent muddy tidal flat deposits along the shoreline of the st lawrence estuary the sedimentary features are exposed in high marsh micro cliffs 1 to 2 m high features from two localities where they are the most abundant sainte anne de beaupre north shore and montmagny south shore are reported here two categories are distinguished first bowl shaped circular and elongated structures 30 to 100 cm across which are former scoured depressions subsequently filled by stratified mud fine sand and organic debris and second deformations folds a few decimeters to a few meters in size produced by ice block pressure pebble to boulder size dropstones are associated with these structures most features were observed in mud flat and low marsh units facies vertically exposed at these localities the age of these tidalite deposits ranges from about 200 to 600 years these ice made structures and deformations well preserved in a sequence of recent emerged tidal sediments suggest that similar features may be preserved in older rock formations consequently they can be considered as a promising tool for interpreting the former climatic conditions in which tidalites and other shallow marine and lacustrine formations may have been deposited

pleistocene periglacial eolian deposits in southwestern alaska sedimentary facies and depositional processes abstract pleistocene periglacial eolian sediments are widespread in the nushagak holitna and upper kuskokwim lowlands of southwestern alaska these sediments comprise mainly sand sheet deposits and sand loess intergrades with subordinate sand dune deposits and loess sand sheet deposits range from 1 sharply defined parallel low angle laminae formed by migrating wind ripples to 2 irregular subhorizontal strata which reflect migration of poorly segregated wind ripples accumulation on a sparsely vegetated surface adhesion on a quasi planar bed and or niveo eolian deposition sand loess intergrades represent alternating bed load and suspension deposition related mainly to the stochastic and seasonal variability of former wind systems the dominance of sand sheet deposits over deposits of well formed dunes in the pleistocene eolian record of southwestern alaska reflects the limited availability of loose dry sand in this former periglacial environment immobilization of sand after deposition as low relief sheets resulted from a seasonally variable combination of ice cementation sparse vegetation high water tables and snow cover

late pleistocene vertebrates and other fossils from epiguruk northwestern alaska abstract sediments exposed at epiguruk a large cutbank on the kobuk river about 170 km inland from kotzebue sound record multiple episodes of glacial age alluviation followed by interstadial downcutting and formation of paleosols vertebrate remains from epiguruk include mammoth bison caribou an equid a canid arctic ground squirrel lemmings and voles radiocarbon ages of bone validated by concordant ages of peat and wood span the interval between about 37 000 and 14 000 yr b p the late pleistocene pollen record is dominated by cyperaceae with artemisia salix betula and gramineae also generally abundant the fossil record from epiguruk indicates that the kobuk river valley supported tundra vegetation with abundant riparian willows during middle and late wisconsin time large herbivores were present during the height of late wisconsin glaciation as well as during its waning stage and the preceding interstadial interval the kobuk river valley would have been a favorable refugium for plants animals and possibly humans throughout the last glaciation

analogue modelling of a reactivated basement controlled strike slip zone sierra de albarracin spain application of sandbox modelling to polyphase deformation this paper presents the results of an analogue modelling study on the reactivation of riedel shears generated by basement induced sinistral strike slip faulting it is based on a natural example in the sierra de albarracin iberian range spain the area has a polyphase deformation history defined by the variscan and alpine orogenies late variscan deformation was concentrated in a wide nw se shear zone with accompanying kilometre scale e w riedel shears which divided the palaeozoic basement into large fault blocks alpine reactivation resulted in differential movements on the riedel shears as evidenced by a nw se chain of palaeozoic inliers surrounded by a mesozoic cover that generally shows minor deformations except near the e w riedel shears where strata locally appear in near vertical to overturned position sandbox analogue modelling was applied to improve insight into the structural history it focused on the kinematics of spontaneously developed en echelon riedel shears reactivated in a rotated stress field sand with a controlled added strength was used to form riedel shears in a first deformation phase to act as weak zones for a second phase the modelling showed that in the first deformation phase large pop up structures developed between the riedel shears in a basement induced sinistral strike slip zone later reactivation in the n060 e and n135 e shortening directions was taken up respectively by sinistral reverse and dextral reverse shear along the pre existing riedel shears but only if the sand on one side of the fault zone was allowed to move freely along the other scissor faulting along the riedel shears with their complex 3d geometry increased the height of the up squeezed blocks for experiments with fixed boundaries and no oil water emulsion layer between the base plate and sand pack thrusting at the backstop occurred rather than reactivation of the riedel shears this approach provided robust insights on the 4d development of the sierra de albarracin area the geological society of london 2006

early marine isotope stage 5 sea levels coastal dune palaeoenvironments and human occupation on the southeast coast of south africa abstract quaternary age human and animal footprints have been reported from coastal deposits along the south african coast these footprints and their sedimentary contexts can inform on quaternary palaeoenvironments and processes stratigraphically associated with the palaeoanthropological record of past human occupation in the coastal zone and exploitation of its resources this study examines the palaeoenvironmental context and sedimentology of marine isotope stage 5 aeolianite at nahoon point southeastern coast of south africa where preserved human footprints have been previously recorded this study identifies seven sedimentary facies from 20 logged profiles through the coastal aeolianite in order to develop a landscape scale stratigraphic framework for coastal palaeoenvironmental reconstruction during the period of the mis 5 highstand two phases of aeolianite deposition are identified which bracket a single stepped sea level transgression phase up to 7 82 0 82 m asl evidenced by intraformational beachrock facies and marine benches this correlates with the second known global mis 5e highstand no evidence for the first highstand reported from the literature was found in the study area aeolianite bed geometries and sedimentary structures indicate that wind regimes and rainfall seasonality were similar to present newly discovered faunal tracks in aeolianites of the first depositional phase suggest the presence of unidentified bovids of varying sizes evidence for human activity is preserved in all three recorded depositional phases suggesting people were present throughout the early mis 5 sequence despite changing environmental conditions this evidence suggests that human occupation of coastal areas and the exploitation of marine food resources was more widespread than generally thought in southern africa during early mis 5

vertebrate tracks in pleistocene eolian sand sheet deposits of alaska abstract deformation structures interpreted as vertebrate hoof and foot tracks occur within upper pleistocene eolian sand sheet deposits in the stabilized kantishna sand sea of central alaska and in the nushagak lowland of southwestern alaska exposures of tracks are generally limited to cross sections which reveal concave up deformation structures in which displacement of preexisting strata diminishes downward deposits in both areas contain tracks that are 6 to 16 cm in diameter and are divided by a central ridge reflecting formation by artiodactyl even toed ungulates larger 21 34 cm tracks without a central ridge observed in the nushagak lowland were formed by proboscideans probably woolly mammoth large vertebrate tracks occur within irregularly stratified sand and silty sand that accumulated upon partially vegetated sand sheets and within thin even wind ripple laminae of unvegetated sand sheets the presence of tracks at multiple stratigraphic levels and preservation of roots and rhizocretions within the eolian deposits suggest that vegetated sand sheets may have formed a locally important grazing habitat for large herbivores during at least part of the last glaciation recognition that vertebrate tracks are preserved in eolian sand sheet deposits and in deposits of other environments as well opens a new source of stratigraphic and paleoecological data to aid reconstruction of the vanished ecosystems of beringia

the role of pre existing faults in basin evolution constraints from 2d finite element and 3d flexure models the lithospheric driving forces which cause intraplate basin deformation are relatively constant over large areas consequently lateral variations in deformation and stress and strain concentrations seem to be primarily caused by pre existing heterogenities in the rheological signature of the continental lithosphere underlying the sedimentary basins in this paper we explore the weak character of upper crustal faults and their control on basin shape for a number of case studies on intraplate phanerozoic basin settings using a 2d finite element and a 3d flexure model of key importance is the integration of seismic data and field observations with the tectonic modelling allowing the investigation of deformation processes and their expressions on different scales operating on different levels of the lithosphere finite element models for sub basin scales incorporating weak upper crustal faults predict strong control of these weak zones on local stress distributions and subsequent deformation in agreement with observed deformation patterns slip along upper crustal faults control stress distribution and subsequent faulting in overlying sedimentary rocks the effect of weak upper crustal fault movements on basin wide regional upper crustal flexure is looked at in two case studies on 1 extensional tectonics in the lake tanganyika rift zone east africa and 2 compressional tectonics in the central system and tajo basin central spain both settings indicate that basement warpings are controlled by large amounts of slip along so called weak crustal scale border faults which are mostly planar adopting border fault displacements in the 3d flexure model the results indicate low effective elastic thickness eet values in a range of 3 7 km for induced basement deflection patterns in accordance with observations the low eet values most likely reflect a partly decoupling of upper crustal and subcrustal deformation facilitated by the weak lower crust and in agreement with standard rheological assumptions for phanerozoic lithosphere in contrast the inferred weakness of upper crustal faults relative to surrounding rock is not evident from uniform rheological assumptions however observations of reactivations of faults which are not preferably aligned with the stress field and reactivations of basin deformation on long time scales are in support of this feature

could acidity be the reason behind the early triassic biotic crisis on land abstract in recent years there is growing evidence of the importance of the smithian spathian early triassic ecological crisis to explain the delayed recovery of life after the permian triassic boundary mass extinction this study focuses on sedimentary continental rocks of middle permian to middle triassic age from four different peritethys basins in subequatorial latitudes similar distribution patterns of aluminum phosphate sulfate aps minerals contents in these rocks in the four studied basins provide evidence of increased acidity during the smithian spathian transition coinciding with a lack of indicators of organic activity in the same interval thus this period of high acidity on land may have been one of the causes of this biological crisis based on the quantification of aps minerals in the studied sedimentary sequences we propose that it was not until acidity in the environment diminished that biotic recovery was possible aps data may also be useful to interpret other past biotic crises

3d flexure and intraplate compression in the north sea basin we apply a recently developed 3d flexure model incorporating lateral variations in flexural rigidity eet and necking depth zn to study the 3d effects of intraplate stresses on quaternary accelerated subsidence and uplift in the north sea basin and adjacent areas in the model approach lateral variations and magnitude of predicted quaternary vertical motions are largely dependent on the pre existing late tertiary flexural state of the area and the relative change in magnitude and orientation of intraplate stresses in the quaternary the late tertiary deflections are reconstructed by incorporating lithospheric stretching values calculated from the mesozoic subsidence record and by adopting admissible variations in necking depth z and flexural rigidity eet from earlier work the 3d model results for the north sea and adjacent areas indicate that an increase of compressive intraplate forces with a magnitude of about 2 25 10 2 n m can predict accelerated subsidence values up to 700 m largely in agreement with observed patterns of quaternary isopach values corrected for effects of shallowing waterdepth the magnitude of the intraplate forces is 2 to 3 times lower than predicted by earlier 2d studies it is believed that the 2d model results actually overestimate required stress levels since they do not take into account the effect of out of plane stresses the relative increase in compressive forces is in agreement with observed compressive stresses and the magnitude corresponds to characteristic values for plate boundary forces the adopted values for zn and eet do not show a clear relation with the preceding basin history

post rift compressional reactivation potential of passive margins and extensional basins poly phase deformation of a compressional nature is a common feature in the post rift evolution of passive margins and rifts the compressional mode of deformation in these sedimentary basins originally formed by extension in an intraplate setting is characterized by a spectrum of spatial wavelengths spanning several tens of kilometres up to several hundreds of kilometres the actual mode of compressional deformation appears to be strongly affected by the rheological structure of the underlying lithosphere the level of the regional intraplate stress field and the geometry of the rifted basin configuration prior to late stage compressional reactivation the interplay of plumes and intraplate compressional deformation can lead to temporal transitions from basin inversion to lithospheric folding these modes of deformation lead to substantial differential vertical motions late stage anomalies in subsidence and uplift patterns the development of innovative combinations of numerical and analogue modelling techniques is the key to differentiating different modes of compressional deformation of passive margins and extensional basins the geological society of london 2008