relative age dating of transported regolith and application to study of landform evolution in the appalachians abstract surficial deposits in the appalachians generally are thin discontinuous and difficult to date in the absence of numerical dates particularly for older deposits relative age indices based on degree of weathering and soil development have been used to distinguish and correlate deposits of different ages a favorite locale of relative age studies has been stream terraces where chronosequences have been developed to shed light on the relationship between time and weathering soil development the lack of applicable numerical dating techniques has led some researchers to establish relative chronosequences in which height of stream or fan terraces above modern river level arl serves as a proxy for time approximate incision rates can then be used to estimate numerical ages of the deposits relative age correlations between the weathering indices on the terraces and comparable indices on dated deposits on the coastal plain and in nearby glaciated regions suggest that ages so estimated are the right order of magnitude relative age indices show correlations with height arl that are as high as those with time perhaps because more data sets are available for relative chronosequences than for true chronosequences analogous relative age sequences can be established for alluvial fans and even for hillslope colluvium many weathering indices have been employed but weathering rind thickness on mafic to intermediate clasts has proved to be a particularly consistent and useful parameter in addition to showing how weathering and soil development progress over time relative age dating has shed light on the manner in which landforms evolve along some rivers for example the areal extent of old highly weathered alluvium far exceeds that of younger alluvium suggesting that formerly floodplains and low terraces were much more extensive than at present in addition the manner in which weathering indices on some river terrace sequences vary with height arl suggests that incision rate has changed through time relative age mapping of alluvial fans produces a map pattern of older and younger fan surfaces that allows the sequence of fan development to be inferred in one case suggesting a scenario different from those previously described for fans mapping also shows that the relative abundance of young intermediate and old fan surfaces varies greatly from one area to another several studies have demonstrated clustering of relative age values into a small number of groups suggesting temporal grouping and thus episodic deposition on fans regression of weathering rind thickness against height above modern drainageways of remnant fan surfaces in two areas suggests that fans are being incised more rapidly in one area than in another relative age of hillslope colluvium also aids geomorphic interpretation young brown colluvium is much more common than old red colluvium near the glacier border where red colluvium rarely occurs at the surface but typically is covered by brown colluvium probably mobilized during the late pleistocene distant from the ice margin however red colluvium is extensively exposed on interfluves relatively stable hillslopes can also be distinguished from active ones in this manner for example colluvium on hillslope noses is somewhat more weathered than that on hollow floors and sideslopes

application of osl single aliquot and single grain dating to quartz from anthropogenic soil profiles in the se united states abstract reduced luminescence intensity in soils is a widespread phenomenon but is not understood we examine the distributions of equivalent dose d e values of quartz from surface and buried soils from earthen mounds in louisiana where pedoturbation is the likely cause of luminescence resetting we first investigated the effectiveness of optical bleaching in surface samples similar in composition and environment to those at depth resulting d e distributions from the top 10 cm of the topsoils approach 0 gy the concentration of zero age grains decreases rapidly with depth paleosol ages based on low values of the d e distribution demonstrate good agreement with previously published ages we propose a three zone model for the explanation of surface bleaching in which the soil surface is continuously stressed and loaded by subsurface turbation mechanisms creating surface relief surface relief is reduced by subaerial impact and transport forces causing disaggregation and single grain dispersion this results in a surface bleaching zone where soil particles and topography are in constant transition suggesting that many soils may offer frequent and thorough presentation of mineral grains to surface insolation and thus high concentrations of zero dose grains

paleoenvironmental characterization of a jurassic sequence on the bombarral sub basin lusitanian basin portugal insights from palynofacies and organic geochemistry abstract a middle upper jurassic sedimentary succession has been cut by the ramalhal 1 borehole in the bombarral sub basin lusitanian basin portugal the succession comprises the brenha montejunto abadia and lourinha formations which are composed of limestones marls sandstones and clays the main objective of this study was to characterize the organic matter using palynofacies and geochemical analyses to determine the depositional paleoenvironments and the hydrocarbon generation potential the total organic carbon content is generally less than 1 wt but reaches 4 1 wt in one sample due to the presence of perhydrous coal the rock eval pyrolysis results reveal lower values hi usually nether to 100 mghc gtoc showing that the studied samples have type iii kerogen and a low potential for oil generation the t max values varies between 319 and 443 c and biomarker data obtained for these samples indicate a maturation ranging between immature and eventually mature the palynofacies data indicate predominance of the phytoclast group 80 with different degradation degrees and a modest contribution of palynomorph group especially sporomorphs and the amorphous organic matter aom group solid bitumen was observed in some samples from the montejunto and brenha formations determining the relative percentages of the kerogen groups allowed for the identification of seven intervals that established variations in the depositional environment

late pleistocene braided rivers of the atlantic coastal plain usa abstract infrared landsat imagery band 4 clearly reveals braided river patterns on late pleistocene terraces of unglaciated rivers in the atlantic coastal plain of the southeastern united states a region that presently exhibits meandering patterns that have existed throughout the holocene these pleistocene braided patterns provide a unique global example of river responses to late quaternary climate changes in an unglaciated humid subtropical region at 30 35 north latitude detailed morphological and chronological results are given for the oconee altamaha river valley in georgia and for the pee dee river valley in south carolina including 15 optically stimulated luminescence osl dates and four radiocarbon dates correlative examples are drawn from additional small to large rivers in south and north carolina osl and radiocarbon 14 c dates indicate distinct braiding at 17 30 ka within oxygen isotope stage 2 ois 2 and braiding probably existed at least during parts of ois 3 and possibly ois 4 back to ca 70 ka the chronology suggests that braiding is the more common pattern for the late quaternary in the southeastern united states braided terraces appear to have been graded to lower sea levels and are onlapped by holocene floodplain deposits up to 10 60 km from the coast the braiding probably reflects the response of discharge and sediment yield to generally cooler and drier paleoclimates which may have had a pronounced runoff season sedimentation of eolian dunes on the braid plains is coeval with braiding and supports the conclusion of dry soils and thin vegetation cover during the late pleistocene our chronological data contribute to a body of literature indicating that reliable osl age estimates can be obtained from quartz rich bed load sand from braided rivers based on good correlations with both radiocarbon dates from braided fluvial sediment and osl dates from stratigraphically correlative eolian sand

geochemical characterization of oils and their correlation with jurassic source rocks from the lusitanian basin portugal abstract seeking to identify the oils groups accumulated in the jurassic of the lusitanian basin and the source rock of each group stable carbon isotope and gas chromatography coupled with mass spectrometry analyses were performed in oils and oil shows from the main discoveries and on representative organic extracts from the potential source rocks selected based on previous works and data obtained by total organic carbon and rock eval pyrolysis techniques the geochemical comparison between the oils and between the oils and the organic extracts allowed the identification of three oil groups whose differences depend on their source rocks oils generated at the coimbra formation lower upper sinemurian and accumulated in the same formation and in the agua de madeiros formation upper sinemurian lower pliensbachian in the northern sector of the basin oils originated from the top of the cabacos formation middle oxfordian and accumulated in the montejunto middle upper oxfordian and abadia lower upper kimmeridgian formations in the central and southern sectors of the basin and oil generated and accumulated at the base of the montejunto formation in the central sector of the basin the geochemical correlations between the oils and the organic extracts allowed the identification of the source rocks of the different accumulations of the jurassic succession allowing further guidance to the petroleum exploration in the lusitanian basin

divergent evolution and the spatial structure of soil landscape variability abstract the spatial structure of soil variability at the landscape scale was examined on adjacent geomorphic surfaces dating from 80 to 200 ka in eastern north carolina the purpose was to determine whether there is evidence at broader scales distances of 102 104 m for the divergent evolution observed in the field at very detailed scales distances of 100 102 m the state probability function spf which measures spatial dependence for categorical environmental data along a transect was applied to soil series mapped at a 1 24 000 scale the older talbot terrace and younger pamlico terrace surfaces showed distinctly different patterns of spatial variability the range of spatial dependence was shorter on the older surface about 200 vs 300 m and the spf was higher at any given distance indicating more variability the spf for the pamlico surface also indicates a periodicity related to fluvial dissection of the landscape which is not readily detectable on the talbot transect despite its greater degree of dissection the results confirm earlier field studies which suggest that pedogenesis is marked by divergence whereby differences in initial conditions or local perturbations persist and increase to produce a more variable soil cover

ring shear studies of till deformation coulomb plastic behavior and distributed strain in glacier beds a ring shear device was used to study the factors that control the ultimate steady strength of till at high shear strains tests at a steady strain rate and at different stresses normal to the shearing direction yielded ultimate friction angles of 26 3 and 18 6 for tills containing 4 and 30 clay sized particles respectively other tests at steady normal stresses and variable shear strain rates indicated a tendency for both tills to weaken slightly with increasing strain rate this weakening may be due to small increases in till porosity these results provide no evidence of viscous behavior and suggest that a coulomb plastic idealization is reasonable for till deformation however viscous behavior has often been suggested on the basis of distributed shear strain observed in subglacial till we hypothesize that deformation may become distributed in till that is deformed cyclically in response to fluctuations in basal water pressure during a deformation event transient dilation ofdiscrete shear zones should cause a reduction in internal pore water pressure that should strengthen these zones relative to the surrounding till a process called dilatant hardening consequent changes in shear zone position when integrated over time may yield the observed distributed strain

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

the carolina sandhills quaternary eolian sand sheets and dunes along the updip margin of the atlantic coastal plain province southeastern united states the carolina sandhills is a physiographic region of the atlantic coastal plain province in the southeastern united states in chesterfield county south carolina the surficial sand of this region is the pinehurst formation which is interpreted as eolian sand derived from the underlying cretaceous middendorf formation this sand has yielded three clusters of optically stimulated luminescence ages 1 75 to 37 thousand years ago ka coincident with growth of the laurentide ice sheet 2 28 to 18 ka coincident with the last glacial maximum lgm and 3 12 to 6 ka mostly coincident with the younger dryas through final collapse of the laurentide ice sheet relict dune morphologies are consistent with winds from the west or northwest coincident with modern and inferred lgm january wind directions sand sheets are more common than dunes because of effects of coarse grain size mean range 0 35 0 59 mm and vegetation the coarse grain size would have required lgm wind velocities of at least 4 6 m sec accounting for effects of colder air temperatures on eolian sand transport the eolian interpretation of the carolina sandhills is consistent with other evidence for eolian activity in the southeastern united states during the last glaciation

the structural and sedimentary evolution of the arruda and lower tagus sub basins portugal abstract the study discusses the jurassic structural and sedimentary evolution of the arruda and lower tagus sub basins located in the central and southern part of the lusitanian basin of portugal in the last five decades thousands of kilometres of 2d seismic reflection lines were acquired for oil exploration reprocessing and reinterpretation of over 700 km from the study area was carried out after the seismic to well ties based on well logs vsp analysis synthetic seismograms revised petrological analysis and stratigraphic reinterpretation of the wells nine key seismic geologic horizons were mapped and depth converted reinterpretation of the seismic profiles was carried out using outcrop data and reprocessed aeromagnetic and gravimetric data of the study area that was integrated in a gis environment several aspects of the tectonic and sedimentary evolution of the study area were enlightened from the triassic until the late jurassic two rift phases were recognised in agreement with data from other parts of the lusitanian basin the initial rifting phase in the triassic continued until the callovian with three prominent tectonic pulses a first in the late triassic a second in the hettangian and a third from the sinemurian onwards the latter episode lasted until the callovian in the arruda sub basin and at least until the bathonian in the lower tagus sub basin during the middle jurassic the arruda sub basin evolved to a nw deepening carbonate ramp the lower tagus sub basin constituted a platform since the early jurassic limited in the east by the setubal pinhal novo fault and in the west by the cadafais fault the third rifting episode occurred in the late oxfordian early kimmeridgian producing a major n s fault system already recognised by several authors and another important nw se and ne sw fault systems post dating the former

subterranean ant nests trace fossils past and future many species of ants excavate complex species typical nests in soil the basic structural units of many nests are descending tunnels connecting flattened generally horizontal chambers of oval to lobed outline the species typical structure of many nests results from variation in the size shape number and arrangement of these basic elements nest architecture can be rendered by filling subterranean nests with a thin slurry of orthodontal plaster then excavating and reconstructing the hardened cast photographs of such nest casts of nine species of ants from northern florida show the range and type of variation of architecture preservation conditions under which ant nests could form complex trace fossils are discussed and reports of such traces reviewed the images presented in this paper will help to alert trace fossil specialists to the potential range of appearance of such nest fossils 2002 elsevier science b v all rights reserved

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy

solid bitumen occurrences in the arruda sub basin lusitanian basin portugal petrographic features abstract the middle jurassic to cretaceous sedimentary record in the lusitanian basin portugal reveals the presence of disseminated solid bitumen the present work is focused on the petrographic characteristics of solid bitumen identified in the freixial 1 and benfeito 1 boreholes arruda sub basin lusitanian basin that display different thermal maturities microscopy techniques reflected and transmitted white light incident blue light and sem and organic geochemistry analyses total organic carbon total sulfur and insoluble residue were used to study these samples from the results obtained by optical microscopy fluorescence and reflectance it was possible to distinguish three types of solid bitumen they were labeled as solid bitumen a present in all the samples solid bitumen b and solid bitumen c these ones observed in some of them they correspond to allochthonous migrated bitumens in blue incident light some bitumen do not show fluorescence while others reveal fluorescence that range from yellow solid bitumen b to dark brown solid bitumen a all bitumens are optically isotropic bitumen reflectance varies between 0 70 and 2 60 r r and the vitrinite reflectance ranges from 1 11 to 1 48 r r based on the r r values the solid bitumen identified in these samples are classified as impsonite epi and cata or pyrobitumen no relation can be established with confidence for the reflectance of bitumens with the reflectance of vitrinite

quaternary eolian dunes in the savannah river valley jasper county south carolina usa sand hills in the savannah river valley in jasper county south carolina usa are interpreted as the remnants of parabolic eolian dunes composed of sand derived from the savannah river and stabilized by vegetation under prevailing climate conditions optically stimulated luminescence ages reveal that most of the dunes were active ca 40 to 19 ka ago coincident with the last glacial maximum lgm through early deglaciation modern surface winds are not sufficient for sustained eolian sand transport when the dunes were active winds blew at velocities of at least 4 m s from west to east and some vegetation was present the ratio of annual precipitation to potential evapotranspiration p pe was less than the modern ratio of 1 23 and may have been 0 30 caused by stronger winds which would have resulted in greater evaporation and or reduced precipitation the savannah river dunes are part of a larger assemblage of eolian dunes that were active in the eastern united states during and immediately after the lgm suggesting that eolian sediment behavior in this region has been controlled by regional forcing mechanisms during the quaternary

a re examination of the mechanism and human impact of catastrophic mass flows originating on nevado huascaran cordillera blanca peru in 1962 and 1970 abstract the 1962 and 1970 huascaran mass movements originated as rock ice falls from the mountain s north peak transformed into higher volume high velocity mud rich debris flows by incorporation of snow from the surface of a glacier below huascaran and the substantial entrainment of morainic and colluvial material from slopes below the glacier terminus water for fluidization of the entrained material originated in the melting of incorporated snow and the liberation of soil moisture contained within the entrained materials eyewitness reports indicate very high mean velocities for the events 17 35 m s 1962 and 50 85 m s 1970 the runout distances and velocity profiles of both events were simulated using dan w both mass movements continued downstream in the rio santa as debris floods aluviones that in 1970 reached the pacific at a distance of 180 km in strong contrast to publications in the geosciences literature 1961 peru census data indicates that the death toll of the 1970 event is ca 6000 and that total life loss in the two events did not exceed 7000 people

organic matter deposition and paleoenvironmental implications across the cenomanian turonian boundary of the subalpine basin se france local and global controls abstract the cenomanian turonian boundary is marked by global sea level highstands and one of the warmest periods of the mesozoic with high pco2 levels linked to a massive magmatic episode this is associated with the establishment of a worldwide marine anoxia the deposition of organic rich facies and disturbances of the global carbon cycle the so called oceanic anoxic event 2 oae2 the pont d issole section s subalpine basin se france sedimentary succession represents the reference record of oae2 in the tethyan domain although its organic fraction is extremely poorly studied therefore the main objectives of this study are the characterization of the pont d issole section s organic matter om for paleoenvironmental interpretation and the assessment of the om thermal maturity using organic petrology and organic geochemistry techniques the organic record characterizes a shallowing up marine system with varying redox and restriction conditions associated with periods of stratified oxygen regimen it displays the presence of two om enrichment episodes with different paleoenvironmental and geodynamic contexts the first om enrichment episode unit th1 is thought to be associated with the global mechanisms that trigger oae2 and is characterized by a palynofacies association co dominated by amorphous om and marine microplankton reflecting a context of high sea level this is followed by the plenus cold event unit th2 characterized by a decrease in amorphous om and increase in marine microplankton representing a reoxygenation associated with an increase in water level and an apparent decrease in temperature disappearance of classopollis sp the second om enrichment episode unit th3 and base of unit th4 is characterized by an association dominated by amorphous om the occurrence of freshwater microplankton and the development of a restricted environment with low sea level these depositional conditions are thought to be connected to the beginning phases of basin closure promoted by the regional tectonic framework compressive trend between africa and europe the molecular fraction showed the presence of unsaturated compounds monoaromatic steranes monoaromatic anthrasteroids and the biological hopanes indicating a low thermal evolution for the om this is corroborated by biomarkers ratios and organic petrographic data namely vitrinite reflectance 0 29 rr the presence of paleozoic reworked om in the samples was also identified presenting a more complex thermal history than the cretaceous om this om is possibly related to the subaerial erosion of hercynian massifs

glacier motion dominated by processes deep in underlying till black rapids glacier is a 40 km long surge type glacier in the central alaska range in spring 1997 a wireline drill rig was set up at a location where the measured surface velocities are high and seasonal and annual velocity variations are large the drilling revealed a layer of subglacial till up to 7 m thick that is believed to be water saturated at one location a string of instruments containing three dual axis tiltmeters and one piezometer was successfully introduced into the till the tiltmeters monitored the inclination of the borehole at the ice till interface and at 1 and 2 m into the till for 410 days they showed that no significant deformation occurred in the upper 2 m of the till layer and no significant amount of the basal motion was due to sliding of the ice over the till the measured surface velocity at the drill site is about 60 m a 1 of which 20 30 m a can be accounted for by ice deformation almost the entire amount of basal motion 30 40 m a 1 was taken up at a depth of 2 m in the till possibly in discrete shear layers or as sliding of till over the underlying bedrock we propose that the large scale mobilization of such till layers is a key factor in initiating glacier surges

soil morphology of an alluvial chronosequence from the little river north carolina coastal plain usa abstract a soil chronosequence on terraces of the little river in the north carolina coastal plain was characterized to evaluate age related trends in pedogenesis five representative pedons per landform were studied from six late quaternary fluvial surfaces and temporal trends were assessed by regression of morphological parameters against previously reported terrace optical age estimates solum b horizon and bt horizon thickness subsoil clay content and buntley westin index rubification have strong positive correlations with age and together distinguish between soils of the floodplain 200 yr bp the first terrace 9 9 2 0 ka intermediate surfaces t2 t3b t4 17 4 4 2 74 6 10 4 ka and the oldest terrace t5b 94 0 15 9 ka over time soils develop from entisols with respective a c and a e bw c profiles on the floodplain and first terrace to ultisols with increasing argillic horizon thickness rubification and clay content on t2 t5b solum thickness bt horizon thickness and clay content display linear increases through time with soil thickening reflective of downward pedogenesis through permeable coarse grained alluvium increasing argillic horizon clay content is attributable to illuviation and possibly also to a combined bioturbation translocation process whereby clays scattered throughout sandy parent sediments are delivered to the surface by bioturbation then concentrated in b horizons by eluviation illuviation rubification increases with age and reflects transformation and subsoil concentration of inherited free iron rather than iron oxide formation from primary mineral weathering t5b pedons display morphologies comparable to those of 200 ka to 1 ma soils along coastal plain rivers that also drain the appalachian piedmont probably because sandy coastal plain derived little river alluvium has a higher hydraulic conductivity that promotes faster rates of downward weathering clay translocation and rubification than the more finely grained sediments of piedmont draining rivers thus textural differences related to sedimentary provenance should be recognized when interpreting chronosequences from the region although rates of pedogenesis differ among coastal plain alluvial soils linear trends in the 100 ka little river chronosequence may nonetheless correspond to the early more linear phases of development in studies from the region that span much longer intervals of time

modelled mass balance of xibu glacier tibetan plateau sensitivity to climate change due to a lack of in situ measurements model based studies of glacier mass balance in the tibetan plateau are very limited an energy balance model is applied to analyse the mass balance sensitivity of xibu glacier in the nyainqentanglha mountain range to climatic change a sensitivity calculation shows that a temperature change of 1 c or a precipitation change of 35 changes the equilibrium line altitude ela by 140 125 m we use a clustering method to link local weather parameters including wet season temperatures to weather types observed over the period 1955 2006 modelled variability of the xibu glacier mass balance seems to be controlled by air temperature variations during the wet season may september and by a long term warming trend that is unrelated to weather type the observed wet season temperature trend of 0 23 c 10a 1 leads to an estimated lengthening of the ablation season by 8 days at the glacier terminus 5000 m a s l and by 23 days at the ela 5590 m a s l over the period 1966 2005 the calculated rise in the ela was 49 m 10a 1

soil chronosequence of brasstown creek blue ridge mountains usa abstract a chronosequence of soils on alluvial terraces in the appalachian highlands of the southeastern united states is identified by simple methods of quantitative soil morphology and chemical analysis the chronosequence is from brasstown creek a 5th order stream draining 65 km 2 of the blue ridge mountains of north georgia the portion of the valley studied is about 1 km wide and contains five quaternary terrace remnants radiocarbon dates show that the floodplain t0 is late holocene and includes historical post ca 1830 a d sediment and the four older terraces t1 t5 are pre holocene the floodplain soils are either entisols in historical sediment or buried inceptisols with weak bw horizons in late holocene to protohistoric sediment the lowest terrace t1 is terminal pleistocene in age and its soils have bt horizons that are about 0 9 m thick 10yr 4 5 to 10yr 5 4 in colour and contain 25 to 35 clay soils on terraces older than t1 become progressively redder and contain more clay with increasing age culminating with 2 5yr hues and 40 to 52 clay in the bt horizon of t5 percent clay in bt horizons rubification indices iron oxide contents and element ratios progressively change with age of the terraces but other morphological properties ph and individual element concentrations are of less use as chronosequence variables

assessment of periglacial slope stability for the 1988 tschierva rock avalanche piz morteratsch switzerland the tschierva rock avalanche occurred on october 29 1988 in the area of the piz morteratsch switzerland releasing a total volume of 300 000 m3 the avalanche ran out over 1 km destroying a hiking trail before stopping on the tschierva glacier we analyze the setting of this periglacial slope failure combining geomechanical and cryosphere investigations to identify the primary factors contributing to the rock avalanche an approach to slope stability assessment is presented that copes with existing data limitations in an inaccessible alpine terrain results from the analyses of morphology geology glaciation history permafrost hydrology and meteorological data allowed preliminary inferences to be made regarding the influence of these factors on slope stability conceptual kinematic and numerical slope stability modeling critically analyzed the role of kinematic degrees of freedom glacier retreat and water infiltration from above the detachment zone results highlight the strong influence of discontinuity orientation with respect to the slope face the role of a fault zone with increased joint density and long term progressive development of persistent discontinuities induced by glacier retreat and groundwater loading cycles in leading to the rock avalanche the role of permafrost could not be clearly assessed however observations and analyses indicate that permafrost had no dominant influence on the slope failure extraordinary precipitation prior to the event is suggested to have played a role in triggering the rock avalanche especially in combination with observed superficial ice that could have sealed the rock face generating high water pressures our results emphasize the importance of analyzing multiple contributing factors when assessing alpine rock slope failures with careful consideration of data limitations prevailing in such areas

soil chronosequence studies in temperate to subtropical low latitude low relief terrain with data from the eastern united states the coastal plain of the eastern united states is a low latitude low altitude low relief terrain composed primarily of gently dipping marine and marginal marine sediments that range in age from cretaceous to quaternary population density of the area is moderate and most of the population is concentrated along the coast inland of the coast agriculture including growing trees for pulp is the dominant economy in this region soils have developed along two different pathways one pathway is dominated by the dissolution and movement of oxyhydroxides and the accumulation of organic matter the other by the accumulation of clays and oxyhydroxyides and the adsorption or oxidation of organic matter the first pathway has resulted in the formation of spodosols the second in the development of ultisols no clearly distinguishable age trends have been identified in the spodosols but the properties of ultisols can be measured to quantify surface material alteration through time ultisols are therefore suited to order of magnitude chronostratigraphic interpretations potentially data derived through the study of ultisols can be used to develop models that predict how surface processes will change due to continued weathering and pedogenesis or as the result of climate change

the mesozoic cenozoic organic facies in the lower tagus sub basin lusitanian basin portugal palynofacies and organic geochemistry approaches abstract studies of the mesozoic and cenozoic sequence crossed by the barreiro 4 borehole provide an improved understanding of the organic matter deposited in the lower tagus sub basin lusitanian basin portugal and the implications for the potential source rock and depositional environment this study focused on 43 samples middle jurassic to neogene that were subjected to palynofacies and organic geochemistry analyses total organic carbon rock eval pyrolysis and molecular biomarker analysis the palynofacies data indicate that the sequence contains mainly phytoclasts non opaque phytoclasts however the middle jurassic samples are dominated by amorphous organic matter aom continental and or marine palynomorphs are present in all the samples the cretaceous samples are characterized by small amounts of kerogen that have high contents of solid bitumen the total organic carbon toc content is generally less than 1 wt the rock eval s1 and s2 parameters vary from 0 01 to 3 50 mghc g rock and 0 15 to 34 03 mghc g rock respectively with the highest values corresponding to the cretaceous samples the hydrogen index hi and oxygen index oi values range from 35 to 552 mghc g toc and 4 to 180 mghc g toc respectively the tmax values range from 416 to 437 c the biomarker analysis showed that n alkanes with 15 30 carbon atoms are present and usually have a unimodal distribution with a predominance of low to medium molecular weight compounds the cpi values range between 0 63 and 3 65 and the pristane phytane ratios vary between 0 48 and 1 64 indicating alternation of oxic anoxic conditions along the sequence the distribution of terpanes shows small amounts of tricyclic and tetracyclic terpanes in most of the samples except for some cretaceous samples and a predominance of pentacyclic terpanes the amount of 17 h 22 29 30 trisnorhopane tm usually exceeds the amount of 18 h 22 29 30 trinorneohopane ts the 20s 20s 20r and ratios of the c29 steranes generally have values below the range of equilibrium indicating an immature stage of the om

flow thermal structure and subglacial conditions of a surge type glacier temperature measurements in a subpolar surge type glacier reveal a distinctive thermal structure associated with the boundary between the ice reservoir and receiving areas in the receiving area the glacier is cold based but bottom temperature has increased as much as 0 5 c between 1981 and 1982 and the basal heat flux is roughly 10 times the expected geothermal flux water percolation through permeable subglacial material is the probable energy source deformation of the substrate could destroy this drainage system and trigger a surge

geogenesis pedogenesis and multiple causality in the formation of texture contrast soils abstract coarse over fine vertical texture contrasts vtc are common in soils and weathering profiles in a variety of environmental settings including many where inheritance or surficial processes alone cannot account for them a multiple causality model is presented here which shows that texture contrasts can form in response to a combination of ubiquitous phenomena there are six key elements downward translocation by water erosional winnowing soil mixing by bioturbation the tendency for surface clay additions to be mobilized while subsurface clays are more likely to remain in place and biological facilitation of moisture flux no element alone is sufficient to create a vtc but not all are necessary in any given regolith the model is illustrated by application to case studies in the ouachita mountains arkansas ridgetops in eastern kentucky the lower coastal plain of north carolina and the upper coastal plain of east texas the implications for interpretation of soils paleosols and weathering profiles is that the presence of a textural contrast by itself does not connote any particular set of geogenic or pedogenic processs or controls texture contrasts may be geogenic pedogenic or both given the widespread occurrence of the mechanisms of the multiple causality model vertical texture contrasts are inevitable

update of the carbon and oxygen isotopic records of the early late pliensbachian early jurassic 187ma insights from the organic rich hemipelagic series of the lusitanian basin portugal abstract a high resolution carbon and oxygen isotopic bulk carbonate record from organic rich hemipelagic series of early late pliensbachian age 187 ma is presented for the lusitanian basin portugal and compared to the record of other sedimentary basins this dataset provides an excellent basis for discussing newly raised questions concerning the hypothesis of major carbon cycle perturbations prior to the toarcian oceanic anoxic event in addition to the recognition in the studied series of two positive carbon isotope excursions previously defined elsewhere corresponding to the ibex and margaritatus uppermost stokesi gibbosus subzones zones a third positive excursion is identified here for the first time at the davoei zone in the lusitanian basin these excursions are associated with organic rich facies intervals the younger excursion may be related to worldwide enhanced preservation of organic matter in the margaritatus zone we suggest that until these organic rich facies are well age constrained at a wider scale and high resolution carbon data are provided from other locations and that worldwide anoxia is proven this interval should be referred to as an organic matter preservation interval late pliensbachian ompi this period is probably linked with the complex chain of events that eventually led to the toarcian oceanic anoxic event

organic facies of the oligocene lacustrine system in the cenozoic taubate basin southern brazil abstract a quantitative study of palynofacies and organic facies was carried out in the cenozoic sedimentary succession of the taubate basin the palaeoenvironmental distributions of particulate organic components were examined in relation to various potential controlling factors lithology depositional environment and stratigraphic sequence about 30 samples were analyzed from a single borehole drilled in sao paulo state this involved rigorous kerogen counts supported by 30 toc and sulphur 20 rock eval pyrolysis and 20 biochemistry analyses in the studied area the oligocene deposits are approximately 600 m thick data was obtained by counting 300 to 500 kerogen particles per sample and then recalculating the percentages of the different constituent groups phytoclast palynomorph and amorphous organic matter aom the kerogen assemblage is palynomorph dominated 70 consisting mainly of freshwater lacustrine algae pediastrum and botryococcus non opaque phytoclasts predominate in most of the kerogen samples however significant variations in the proportion of biostructured and non biostructured brown phytoclasts occur in some intervals the fluorescent aom content occurs in some levels and is composed of two main components an intensively fluorescing structureless organic matter which also has high lipid and protein content indicating a probable bacterial origin for the organic matter microbial mats and terrestrially derived amorphous organic matter which has been reworked to a different extent exhibiting a high content of carbohydrates comparison of the mean kerogen assemblages from different lithologies revealed that the finer grained lithologies generally have higher palynomorph percentages whereas coarser grained lithologies present higher percentages of phytoclasts emphasizing the important role of grain size in organic matter distribution the toc content is generally less than 10 but reaches as high as 44 in some intervals due mainly to the presence of coaly seams the t max spore coloration index and spectral fluorescence measurement values obtained from these samples indicate a low maturity stage the integration of these results together with the organic facies parameters indicate that the analyzed sedimentary section represents a variation from a freshwater lacustrine environment with an oxidant regime to a restricted saline lacustrine environment with a dysoxic anoxic regime there was an excellent correlation between the optical and geochemical parameters

a review of alpine tectonics in portugal foreland detachment in basement and cover rocks abstract the alpine foreland in portugal was deformed by compressional tectonism during the miocene in the nne ssw oriented lusitanian basin most folds and thrusts in the meso cenozoic cover are oriented ene wsw parallel to the alpine front in the betic cordillera and verge towards the north northwest and south southeast the thrusts are connected by lateral ramps most of these are oriented nne ssw to n s and show sinistral movement and some are transpressional the lateral ramps result from reactivation of older extensional faults related to crustal thinning of the continental margin in the e w oriented algarve basin a simpler basin inversion occurred with older e w normal faults reactivated as essentially pure thrusts in both basins alpine structures formed above decollements in the hettangian evaporite clastic complex variscan basement was also deformed by ene wsw reverse faults during miocene time the similarity in orientation and style of the basement structures to those in the cover suggests that they also occurred by detachment but their larger scale indicates that the detachment is deep and involves much of the crust thus we interpret the central cordillera in which basement rocks are thrust over miocene sediments on both sides as a pop up of crustal scale elevated above downward flattening faults that dip towards each other and merge into a single deep detachment alpine structures in the iberian foreland are therefore similar in structural style to those of the appalachian and laramide forelands of north america and the alpine foreland of northwest europe

correlation of the canol formation source rock with oil from norman wells abstract the source of the oil at norman wells has long been assumed to have been the canol formation and or the bluefish member of the hare indian formation these two units are stratigraphically above and below the kee scarp formation reservoir unit respectively and are both bituminous shales a wide range of analytical techniques including rock eval pyrolysis solvent extraction and fractionation capillary gas chromatography gas chromatography mass spectrometry and white light and fluorescence microscopy has been used to characterize core samples of these two units and two samples of crude oil from the norman wells field most of the analytical techniques were insufficiently refined to either differentiate the extracts from each other or to make a definitive oil source rock correlation collision activated decomposition coupled with multiple ion detection mass spectrometry gc ms ms did provide sufficient chemical compositional detail of the oils and the two potential sources to demonstrate that the canol formation has been the effective source of the norman wells oil whereas the bluefish member has not petrological analysis of the organic fractions also indicates that although the bulk organic composition of both units may be classified as type ii organic matter significant differences exist between them the bluefish member contains substantial amounts of megaspores whereas the organic matter in the canol formation is largely phytoplankton debris the level of thermal maturity of the core samples ranges from immature to moderately mature in the vicinity of the norman wells field to overmature for the samples obtained to the west and north of the field the level of thermal maturity of the oil was observed to be somewhat higher than that of the samples of the source formation directly above the field it was thus inferred that some lateral migration from more mature areas has occurred but the extent of this migration was not necessarily more than a few to tens of kilometers

soil forming processes and rates on uplifted marine terraces in southwestern oregon usa soil chronosequences were examined on flights of tectonically uplifted marine terraces near cape blanco and cape arago southwestern oregon all of the soils contain abundant organic c and are strongly acidic ph in h2o 30 of the exchange sites saturated with al the soils in the two areas show a progression in development from spodosols to spodosols with clay enriched horizons and eventually to ultisols although the spodic and argillic horizons appear to be forming concurrently in the soils evidence is presented to support the concept that the spodic horizon is eventually masked by clay accumulation because of weathering in situ neoformation of clays and clay translocation the primary age related trends include increases in 1 the relative abundance of silt and clay 2 the ratio of quartz to feldspars in the very fine sand 100 50 m fraction and 3 the amounts of dithionite extractable fe and al and crystalline forms of fe in the profile

chronology of inland eolian dunes on the coastal plain of georgia usa most inland eolian dunes associated with rivers on the georgia coastal plain probably date to glacial periods direct dating of the dune sand by optically stimulated luminescence dating combined with limiting ages from radiocarbon dating shows that dunes formed during isotope stage 2 stage 3 the transition between stages 4 and 5 and isotope stage 6 or earlier most of the dates indicate dune activity between 30 000 and 15 000 years ago holocene activity included limited and local reworking of the crests of some thick dunes along streams that flow from the piedmont

seismic and sedimentologic features of oxfordian kimmeridgian syn rift sediments on the eastern margin of the lusitanian basin following deposition of widespread middle oxfordian lacustrine carbonates and evaporites the lusitanian basin was differentiated into a number of sub basins the arruda sub basin is a half graben basin situated some 30 km north of lisbon it accumulated over 2 5 km of kimmeridgian siliciclastic sediments and is bounded to the east by the vila franca de xira fault zone carbonate deposition persisted over horsts along the fault zone from the oxfordian to the early kimmeridgian and in places to the late kimmeridgian and shows a pronounced west east facies zonation with higher energy framestones and grainstones accumulating along the exposed western margins seismic data indicate a major gap between the horst blocks that acted as a conduit through which basement derived siliciclastics were fed westwards into the sub basin to form a submarine fan system the presence of large blocks of framestone carbonates encased in siliciclastics indicates that carbonate sedimentation occurred in abandoned parts of the fan system the rapid changes of sediment thicknesses and facies types along the eastern margin of the arruda sub basin are indicative of contemporaneous strike slip movements

massive collapse of two glaciers in western tibet in 2016 after surge like instability surges and glacier avalanches are expressions of glacier instability and among the most dramatic phenomena in the mountain cryosphere until now the catastrophic collapse of a glacier combining the large volume of surges and mobility of ice avalanches has been reported only for the 2002 130 106 m3 detachment of kolka glacier caucasus mountains which has been considered a globally singular event here we report on the similar detachment of the entire lower parts of two adjacent glaciers in western tibet in july and september 2016 leading to an unprecedented pair of giant low angle ice avalanches with volumes of 68 2 106 m3 and 83 2 106 m3 on the basis of satellite remote sensing numerical modelling and field investigations we find that the twin collapses were caused by climate and weather driven external forcing acting on specific polythermal and soft bed glacier properties these factors converged to produce surge like enhancement of driving stresses and massively reduced basal friction connected to subglacial water and fine grained bed lithology to eventually exceed collapse thresholds in resisting forces of the tongues frozen to their bed our findings show that large catastrophic instabilities of low angle glaciers can happen under rare circumstances without historical precedent two catastrophic glacier collapse events in western tibet in 2016 were caused by a convergence of weather and glacier bed conditions according to an analysis of observations and modelling

organic facies as a tool for recording eustatic variations in marine fine grained carbonates example of the berriasian stratotype at berrias ardeche se france abstract sediments of the berriasian stratotype in southeastern france consist of marine fine grained carbonates deposited on an outer shelf at the western edge of the vocontian trough the limestones are monotonous but display some erosional surfaces and a condensed interval they are well dated by ammonites and calpionellids except at the base of the section where the boundary with the tithonian is not clearly established despite their very high carbonate content the limestones yielded enough organic residue to allow a study of palynofacies variations in time organic content consists of two fractions one is made of terrestrial components represented essentially by humic fragments of the inertinite and vitrinite maceral groups and accessorily by pollen and spores the other comprises marine components essentially dinocysts and accessorily foraminiferal linings absence of amorphous organic matter and the oxidized nature of dinocysts observable in uv light indicate that aerobic conditions prevailed throughout the berriasian probably associated with a low sedimentation rate the following qualitative and quantitative criteria indicating distal proximal trends were used to convert palynofacies observations into a tentative palaeoenvironmental curve ratio of continental to marine organic constituents diversity of dinocysts degree of biodegradation affecting humic fragments proportion of blade shaped inertinite and finally size sorting and rounding of equidimensional inertinite particles the palaeoenvironmental curve derived from organic matter shows oscillations between more proximal i e shallower water and more distal i e deeper water conditions these variations combined with biostratigraphic information and the few significant sedimentological data can be interpreted in terms of sequence stratigraphy and compared with the global sea level curve published earlier the fairly good correlation between this global curve and that established from palynofacies demonstrates the influence of relative sea level on the organic facies of the berriasian carbonates and the contribution of palynofacies studies to sequence stratigraphy

unusual biological marker geochemistry of oils and possible source rocks offshore beaufort mackenzie delta canada abstract tertiary oils and source rocks from the offshore beaufort mackenzie delta have been examined for their biological marker content the triterpane and sterane distributions suggest a predominant land plant contribution to the oils the oils range in maturity from extremely immature to moderately mature 18 h oleanne is a major triterpane of the oils together with probable bisnorlupanes and an excellent correlation is observed in the concentration of these components in individual oils an excellent correlation is also observed between the concentration of bisnorlupanes and oil maturity based on sterna and triterpane maturation parameters suggesting that the decrease in relative concentration of these components with increasing maturity is a result of progressive dilution by hydrocarbons generated by the cracking of kerogen only one formation in cores taken from the delta has been found to contain bisnorlupanes and were present they are the dominant hydrocarbons of the branched cyclic fraction

late quaternary climates and river channels of the atlantic coastal plain southeastern usa abstract late quaternary river patterns and sedimentation styles reflect past climate changes in atlantic drainages of eastern georgia and the carolinas past climate episodes for the region are summarized from pollen and eolian sedimentary records that exhibit correlation to major changes in river channel patterns records of past river responses are derived from luminescence and radiocarbon dated landforms and strata slow tectonic uplift does not explain temporal changes in channel patterns drainage networks have not received meltwater from continental or mountain glaciers eustatic influence would have been most pronounced on the now submerged continental shelf prior to 6 ka and currently manifests only within 60 80 km of the present highstand shoreline human impact overshadows climatic changes during historic time but was negligible during prehistoric time the late quaternary fluvial system primarily responded to climatic fluctuations that drove changes in vegetation precipitation and runoff patterns prehistoric meandering paleochannels of the holocene stand as important references to guide natural channel rehabilitation efforts during the coldest climate phases of the late wisconsin stage ca 30 16 ka when forest vegetation was sparse and interspersed with grasses and herbs many rivers and streams were braided with eolian dunes on the floodplains the terminal wisconsin stage ca 16 11 ka exhibited rapid warming and forest expansion characterized by pronounced change from braided to meandering patterns with intermediate forms of sandy scroll bar patterns the younger dryas cold excursion is not readily apparent in the regional fluvial record unusually large meandering channels of the terminal wisconsin stage continue into the first half of the holocene and indicate significantly larger bankfull flood discharges during those times than during the last half of the holocene bankfull channels during the last half of the holocene retained meandering patterns but decreased to modern like dimensions suggesting more modern like flood regimes no clear fluvial response occurs to the presumed middle holocene climatic optimum hypsithermal the medieval warm period and little ice age or to recent instrumentally observed fluctuations in climate but little research has been done in these realms

thermal structure of svalbard glaciers and implications for thermal switch models of glacier surging switches between cold and warm based conditions have long been invoked to explain surges of high arctic glaciers here we compile existing and new data on the thermal regime of six glaciers in svalbard to test the applicability of thermal switch models two of the large glaciers of our sample are water terminating while one is land terminating all three have a well known surge history they have a thick basal layer of temperate ice superimposed by cold ice a cold terminus forms during quiescence but is mechanically removed by calving on tidewater glaciers the other three glaciers are relatively small and are either entirely cold or have a diminishing warm core all three bear evidence of former warm based thermal regimes and in two cases surge like behavior during the little ice age in svalbard therefore three types of glaciers have switched from slow to fast flow 1 small glaciers that underwent thermal cycles during and following the lia switches between cold and warm based conditions 2 large terrestrial glaciers which remain warm based throughout the entire surge cycle but develop cold termini during quiescence and 3 large tidewater glaciers that remain warm based throughout the surge cycle our results demonstrate that thermal switching cannot explain the surges of large glaciers in svalbard we apply the concept of enthalpy cycling to the spectrum of surge and surge like behavior displayed by these glaciers and demonstrate that all svalbard surge type glaciers can be understood within a single conceptual framework

a 3 d thermal regime model suitable for cold accumulation zones of polythermal mountain glaciers analysis of the thermal and mechanical response of high altitude glaciers to climate change is crucial to assess future glacier hazards associated with thermal regime changes this paper presents a new fully thermo mechanically coupled transient thermal regime model including enthalpy transport firn densification full stokes porous flow free surface evolution strain heating surface meltwater percolation and refreezing the model is forced by daily air temperature data and can therefore be used to perform prognostic simulations for different future climate scenarios the set of equations is solved using the finite element ice sheet ice flow model elmer ice this model is applied to the col du dome glacier mont blanc area 4250 m a s l france where a comprehensive data set is available the results show that the model is capable of reproducing observed density and velocity fields as well as borehole temperature evolution the strong spatial variability of englacial temperature change observed at col du dome is well reproduced this spatial variability is mainly a result of the variability of the slope aspect of the glacier surface and snow accumulation results support the use of this model to study the influence of climate change on cold accumulation zones in particular to estimate where and under what conditions glaciers will become temperate in the future

10be accumulation in a soil chronosequence we have measured the concentration of the cosmogenic isotope10be in soil samples from various horizons at six sites including three independently dated rappahannock river terraces and a previously undated piedmont soil to which we have assigned an age all of the incident10be can be accounted for in one of these soils and a second is within a factor of two in three soils whose concentrations vary widely with depth a significant fraction of the incident10be cannot be accounted for incomplete sampling and enhanced be mobility caused by organic components are the probable reasons for the low inventory of be from these three soils overall the data from these six sites indicate that10be accumulation could be used to assign ages to soils if be is not mobilized and lost from the soil profile

biomarker distributions in oils from the akita and niigata basins japan abstract oils from the akita and niigata basins japan are characterized by the predominance of c 15 c 17 alkanes pristane phytane ratio 27 regular steranes and the presence of c 26 steranes these are consistent with the marine depositional environment of the source rocks however geochemical parameters for the niigata basin petroleums show higher terrestrial input and are characterized by enhanced concentrations of oleanane tetracyclic terpane and c 29 steranes abundances of diasteranes in oils are controlled both by maturation and lithology of source rocks comparatively low concentrations of diasteranes in the akita oils can be attributed to the low abundance of clay minerals in their siliceous source rocks oils from the akita and niigata basins can be well discriminated on the basis of geochemical indicators using factor analysis evaluation of maturity levels of oils from the akita basin shows that oil expulsion occurred at lower maturity levels in siliceous shales than in argillites in the niigata basin

how much do we really know about glacier surging some of the ideas about glacier surging are considered mainly but not entirely in the light of observations of temperate glaciers in alaska u s a made within the last 15 years climate has an influence on surge recurrence interval climate and weather also affect surge initiation termination and magnitude regional studies lead to the speculation that subglacial till plays a key role in surging and it has been found under all surge type glaciers studied so far including black rapids and variegated glaciers alaska in most of the glaciers studied till deformation processes dominate the motion in quiescence the linked cavity model of surge triggering and rapid motion is not consistent with these observations but the limited coverage of the observations does not rule it out under parts of the glaciers studied the till observations in alaska raise old questions about the interaction between till and the hydraulic systems of temperate glaciers the role of stored water which observations show to be active even in winter on black rapids glacier is noted

the middle late jurassic forced regression and disconformity in central portugal eustatic tectonic and climatic effects on a carbonate ramp system successions across the middle upper jurassic disconformity in the lusitanian basin west central portugal are highly varied and were probably developed on a large westward inclined hangingwall of a half graben the disconformity is preceded by a complex forced regression showing marked variations down the ramp and provides an example of the effects of rapid relative sea level falls on carbonate ramp systems in the east middle jurassic inner ramp carbonates candeeiros facies are capped by a palaeokarstic surface veneered by ferruginous clays or thick calcretes in the west mid outer ramp marls and limestones brenha facies are terminated by two contrasting successions 1 a sharp based carbonate sandbody capped by a minor erosion surface overlain by interbedded marine lagoonal deltaic deposits with further minor erosion exposure surfaces 2 a brachiopod rich limestone with a minor irregular surface overlain by marls lignitic marls with marine and reworked non marine fossils and charophytic limestones with further minor irregular surfaces and capped by a higher relief ferruginous erosional surface the age ranges from late bathonian in the east to late callovian in the west this disconformity assemblage is succeeded by widespread lacustrine lagoonal limestones with microbial laminites and evaporites cabacos facies attributed to the middle oxfordian over the whole basin increasingly marine facies were deposited afterwards in middle jurassic inner ramp zones in the east the overall regression is marked by a major exposure surface overlain by continental sediments in middle jurassic outer ramp zones to the west the regression is represented initially by open marine successions followed by either a sharp marine erosion surface overlain by a complex sandbody or minor discontinuities and marginal marine deposits in both cases capped by the major lowstand surface reflooding led to a complex pattern of depositional conditions throughout the basin from freshwater and brackish lagoonal to marginal and shallow marine settings additional complications were produced by possible tilting of the hangingwall of the half graben the input of siliciclastics from westerly sources and climate change from humid to more seasonally semi arid conditions the middle late jurassic sea level fall in the lusitanian basin is also recorded elsewhere within the iberian and other peri atlantic regions and matches a transgressive to regressive change in eustatic sea level curves indicating that it is related in part to a global event

alluvial soil chronosequence in the inner coastal plain central virginia abstract a chronological sequence of soils formed on a series of alluvial depositional surfaces ranging in age from late middle miocene to late pleistocene was characterized to clarify soil geomorphic relations and provide a basis for allostratigraphic subdivision of the inner coastal plain on quaternary river terraces ultic hapludalfs containing abundant weatherable mineral species and clast types are estimated to have formed in 60 000 120 000 yr whereas typic hapludults greatly depleted in weatherable minerals and showing strong weathering of clast types are estimated to be 700 000 1 600 000 yr old typic paleudults with incipient plinthite duripan and ferricrete development characterize interfluves that have been little eroded since early pliocene time 3 4 5 3 myr ago typic plinthic paleudults with intense weathering of siliceous clasts and moderate to strong duripan and ferricrete development are found on surfaces that formed near the beginning of late miocene time 10 8 13 0 myr ago chemical weathering in the chronosequence may be classified into three progressive stages 1 decomposition of unstable sand and silt sized minerals into a mixed stable unstable clay mineral suite stable fe al si bulk chemical composition 107 yr not all soil properties show unidirectional development nor is a steady state of pedon development observed even after approximately 107 yr of chemical weathering soil development in the chronosequence is episodic the transition from one phase to the next is marked by a change in rate and sometimes a reversal in the direction of development of one or more soil properties

aspects of the structural evolution of the lusitanian basin in portugal and the shelf and slope area offshore portugal abstract the study provides a regional seismic interpretation and mapping of the mesozoic and cenozoic succession of the lusitanian basin and the shelf and slope area off portugal the seismic study is compared with previous studies of the lusitanian basin from the late triassic to the cretaceous the study area experienced four rift phases and intermittent periods of tectonic quiescence the triassic rifting was concentrated in the central part of the lusitanian basin and in the southernmost part of the study area both as symmetrical grabens and half grabens the evolution of half grabens was particularly prominent in the south the triassic fault controlled subsidence ceased during the latest late triassic and was succeeded by regional subsidence during the early early jurassic hettangian when deposition of evaporites took place a second rift phase was initiated in the early jurassic most likely during the sinemurian pliensbachian this resulted in minor salt movements along the most prominent faults the second phase was concentrated to the area south of the nazare fault zone and resulted here in the accumulation of a thick sinemurian callovian succession following a major hiatus probably as a result of the opening of the central atlantic resumed deposition occurred during the late jurassic evidence for late jurassic fault controlled subsidence is widespread over the whole basin the pattern of late jurassic subsidence appears to change across the nazare fault zone north of the nazare fault fault controlled subsidence occurred mainly along nnw sse trending faults and to the south of this fault zone a nne ssw fault pattern seems to dominate the oxfordian rift phase is testified in onlapping of the oxfordian succession on salt pillows which formed in association with fault activity the fourth and final rift phase was in the latest late jurassic or earliest early cretaceous the jurassic extensional tectonism resulted in triggering of salt movement and the development of salt structures along fault zones however only salt pillow development can be demonstrated the extensional tectonics ceased during the early cretaceous during most of the cretaceous regional subsidence occurred resulting in the deposition of a uniform lower and upper cretaceous succession marked inversion of former normal faults particularly along ne sw trending faults and development of salt diapirs occurred during the middle miocene probably followed by tectonic pulses during the late miocene to present the inversion was most prominent in the central and southern parts of the study area in between these two areas affected by structural inversion fault controlled subsidence resulted in the formation of the cenozoic lower tagus basin northwest of the nazare fault zone the effect of the compressional tectonic regime quickly dies out and extensional tectonic environment seems to have prevailed the miocene compressional stress was mainly oriented nw se shifting to more n s in the southern part

palynofacies and organic geochemistry of the sinemurian carbonate deposits in the western lusitanian basin portugal coimbra and agua de madeiros formations abstract the lower jurassic in the lusitanian basin portugal is mainly represented by hemipelagic carbonated deposits rich in organic matter om in this study supported by a high resolution stratigraphic and sedimentological framework the analysis of the om content of the coimbra and agua de madeiros formations in the reference outcrop sections of s pedro de moel and peniche is presented this is a multidisciplinary approach to the study of 31 samples in these series supported by organic petrography palynofacies spore coloration index sci and random vitrinite reflectance rr and organic geochemistry total organic carbon toc and biomarkers the palynofacies analysis provides evidence that the om is mainly composed of particles belonging to the amorphous organic matter aom group the phytoclasts correspond mostly to the non opaque translucent subgroup generally degraded and oxidized with significant representation in some stratigraphic levels of the coimbra formation and the polvoeira member at peniche the palynomorphs are mainly composed of classopollis pollen grains zygospores acritarchs and prasinophyte phycomata the toc data confirm that most samples are om rich with some stratigraphic horizons of the coimbra formation reaching 8 8 wt the predominance of marine om was confirmed by the pr nc17 and ph nc18 ratios the pr fi and homohopane ratios c35 c34 indicate that some stratigraphic horizons were deposited under dysoxic anoxic conditions despite the organic rich nature of these two units the random vitrinite reflectance rr 0 45 the spore coloration index 3 0 4 0 and the presence of hopanes suggest that these rocks in terms of om maturity are thermally immature

pedogenesis of a chronosequence in the sacramento valley california u s a i application of a soil development index abstract a quantitative soil development index based on field morphologic data has been applied to a chronosequence of six soils at honcut creek in central california the soils range from 600 yr to 1 6 m y in age and exist in a xeric thermic soil climatic regime plots of the development of individual properties versus the log of soil age are generally linear of the eight soil properties used in the index clay films texture plus wet consistence structure and rubification color hue and chroma are most highly correlated with soil age correlation coefficients for linenar regression of 0 96 0 87 dry consistence moist consistence melanization color value and ph lowering are not as highly correlated with soil age correlation coefficients of 0 68 0 55 although correlation coefficients for all eight soil properties are significant at 0 01 or 0 05 level depth functions of a horizon index that incorporates all eight soil properties chart the development of the a horizons in holocene soils and the development of the cambic and then argillic horizons in older soils total depth of soil development increases from about 60 cm in holocene soils to more than 5 m in the oldest soils lithologic discontinuities and stratification are brought out in the horizon index because of their effects on soil development soils on the alluvial terraces of honcut creek have developed systematically over the 1 6 m y age span of the chronosequence correlation coefficients for regressions of the profile index versus the log of soil age are 0 97 significant at 0 01 level the coefficient of variation of replicate profiles decreases with increasing soil age the soil development index substantiates the geologic and pedologic correlations made during geologic mapping and soil survey of the area although differences among soils in parent material and topographic factors complicate the age trends

100 000 year long terrestrial record of millennial scale linkage between eastern north american mid latitude paleovegetation shifts and greenland ice core oxygen isotope trends abstract we document frequent rapid strong millennial scale paleovegetation shifts throughout the late pleistocene within a 100 000 yr interval 115 15 ka of terrestrial sediments from the mid atlantic region mar of north america high resolution analyses of fossil pollen from one core locality revealed a continuously shifting sequence of thermally dependent forest assemblages ranging between two endmembers subtropical oak tupelo bald cypress gum forest and high boreal spruce pine forest sedimentary textural evidence indicates fluvial paludal and loess deposition and paleosol formation representing sequential freshwater to subaerial environments in which this record was deposited its total age depth model based on radiocarbon and optically stimulated luminescence ages ranges from terrestrial oxygen isotope stages ois 6 to 1 the particular core sub interval presented here is correlative in trend and timing to that portion of the oxygen isotope sequence common among several greenland ice cores interstades gi2 to gi24 ois2 5 d this site thus provides the first evidence for an essentially complete series of dansgaard oeschger climate events in the mar these data reveal that the 100 000 yr preceding the late glacial and holocene in the mar of north america were characterized by frequently and dynamically changing climate states and by vegetation shifts that closely tracked the greenland paleoclimate sequence

jurassic tectono sedimentary evolution of the northern lusitanian basin offshore portugal abstract the lusitanian basin is one of a series of rift related basins developed during the rifting that led to the break up of iberia and canada the strong influence of halokinesis on the depositional evolution of its northern sector provides an analogue for the development of other evaporite prone rift basins on atlantic type passive margins in this paper the pre valanginian evolution of the northern lusitanian basin is documented based on regional seismic stratigraphy isochron and time structure maps tied with sonic and stratigraphic data from 10 exploration wells the pre salt structure of the study area is marked by two sets of faults i a n s to ne sw striking set active throughout the jurassic period and ii a nw se striking set active during the late jurassic the latter defines five late jurassic sub basins northeast of a basin margin structure the marinha grande fault the development of half graben basins in the northern lusitanian basin during the jurassic was overprinted by halokinesis over the marinha grande fault and other major marginal basement faults halokinesis climaxed during the oxfordian kimmeridgian rifting with the formation of a 10 km long salt ridge over the marinha grande fault the ridge limited the southward progradation of fluvial deltaic units derived from hanging wall drainage systems and restricted the syn rift sediments to a 15 km long 5 km wide bowl shaped depocentre located 10 km west of the present coastline in order to better characterise the jurassic tectono sedimentary evolution of the northern lusitanian basin the interpreted seismic data is compared with physical models for extensional forced folds above active normal faults and with stratigraphic information from well and outcrop

reprint of solid bitumen occurrences in the arruda sub basin lusitanian basin portugal petrographic features abstract the middle jurassic to cretaceous sedimentary record in the lusitanian basin portugal reveals the presence of disseminated solid bitumen the present work is focused on the petrographic characteristics of solid bitumen identified in the freixial 1 and benfeito 1 boreholes arruda sub basin lusitanian basin that display different thermal maturities microscopy techniques reflected and transmitted white light incident blue light and sem and organic geochemistry analyses total organic carbon total sulfur and insoluble residue were used to study these samples from the results obtained by optical microscopy fluorescence and reflectance it was possible to distinguish three types of solid bitumen they were labeled as solid bitumen a present in all the samples solid bitumen b and solid bitumen c these ones observed in some of them they correspond to allochthonous migrated bitumens in blue incident light some bitumen do not show fluorescence while others reveal fluorescence that range from yellow solid bitumen b to dark brown solid bitumen a all bitumens are optically isotropic bitumen reflectance varies between 0 70 and 2 60 rr and the vitrinite reflectance ranges from 1 11 to 1 48 rr based on the rr values the solid bitumen identified in these samples are classified as impsonite epi and cata or pyrobitumen no relation can be established with confidence for the reflectance of bitumens with the reflectance of vitrinite

the kolka karmadon rock ice slide of 20 september 2002 an extraordinary event of historical dimensions in north ossetia russian caucasus on 20 september 2002 an enormous rock ice slide and subsequent mud flow occurred on the northern slope of the kazbek massif northern ossetia russian caucasus it started on the north northeast wall of dzhimarai khokh 4780 ma s l and seriously affected the valley of genaldon karmadon immediate governmental actions available scientific information first reconstructions hazard assessments and monitoring activities as well as initial expert judgments recommendations are documented in order to enable more detailed analyses and modelling of the event by the wider scientific community among the most remarkable aspects related to this event are 1 the relation between the recent event and somewhat smaller but quite similar events that occurred earlier in historical times 1835 1902 2 the interactions between unstable local geological structures and complex geothermal and hydraulic conditions in the starting zone with permafrost cold to polythermal hanging glaciers and volcanic effects hot springs in close contact with each other 3 the erosion and incorporation of a debris covered valley glacier largely enhancing the sliding volume of rocks ice firn snow water and probably air to a total of about 100 106m3 and 4 the astonishingly high flow velocities up to 300 km h 1 and enormous length of travel path 18 km plus 15 km of debris mud flow this extraordinary case illustrates that large catastrophic events in high mountain regions typically involve a multitude of factors and require integrated consideration of complex chains of processes a task which must be undertaken by qualified groups of experts

solid bitumen bituminite and thermal maturity of the upper jurassic lower cretaceous chia gara formation kirkuk oil field zagros fold belt kurdistan iraq abstract the upper jurassic lower cretaceous chia gara formation a proven marine source rock characterised by predominance of amorphous organic matter aom is known from few outcrops in ne iraq and a number of exploration wells in the zagros fold belt this study presents comprehensive organic petrographic and mineralogical investigations of the dispersed organic matter and rock forming minerals of the tithonian berriasian chia gara formation intersected by the kirkuk well k 109 drilled in the giant kirkuk oil field ne iraq the organic petrographic analyses including incident light microscopy and confocal laser scanning microscopy clsm were applied to carbonate source rocks with low to moderate organic carbon contents our data demonstrate the predominance of bituminite and solid bitumen among the examined dispersed organic matter followed by oil exudates and oil globule inclusions as well as the presence of minor contributions of alginite i e tasmanites and leiospheridia liptodetrinite and vitrinite based on optical characteristics and clsm spectral fluorescence measurements examinations of bituminite point towards the presence of bituminite type iii the bituminite type iii encloses dark orange fluorescent amorphous components suggesting a genetic relationship either with liptodetrinite and or with solid bitumen the qualitative assessment of solid bitumen reveals several dissimilar forms identified in the analysed samples the photometric and spectral fluorescence measurements point to distinct reflectance values ranging between 0 19 and 0 43 sbrr and lambda max values extending from 515 nm to 590 nm respectively the corresponding results of the solid bitumen exhibit 1 a lack of a relationship with depth and 2 suggest its poor property as a reliable maturity indicator for the examined samples the presence of oil exudates oil globule inclusions and their association with solid bitumen suggests a genetic relation with the examined residues of liquid hydrocarbon phase the performed thermal maturities assessments of dispersed organic matter point towards early mature to peak mature oil window with vitrinite reflectance values ranging between 0 52 vrr at 2801 m to 0 83 vrr at 3089 m depth mineralogical analyses revealed the predominance of calcite over dolomite in the examined limestone to marl lithofacies e g clear rimmed dolomite with localised intensive dolomitisation in the phyllosilicate rich matrix predominance of calcite and siderite is observed followed by zinc blende and pyrite the composition of organic matter in the examined chia gara formation with predominance of bituminite and solid bitumen makes the major marine source rock of iraq s cretaceous petroleum systems distinctive in terms of hydrocarbon generation and migration at an oil window stage as it provides suitable explanations for its generally low hydrogen index hi with only minor terrestrial input in addition the results presented herein can be helpful for future evaluation of thermal maturities and characterisation of optical appearances of dispersed organic matter in carbonates by incident light microscopy and especially by clsm during hydrocarbon prospecting

slow surge of trapridge glacier yukon territory canada 1 trapridge glacier a polythermal surge type glacier located in the st elias mountains yukon territory canada passed through a complete surge cycle between 1951 and 2005 air photos 1951 1981 and ground based optical surveys 1969 2005 are used to quantify the modifications in flow and geometry that occurred over this period yearly averaged flow records suggest that the active phase began 1980 and lasted until 2000 the average velocity in the central area of the glacier went from 16 m yr 1 in 1974 to 39 m yr 1 in 1980 it peaked at 42 m yr 1 in 1984 and remained above 25 m yr 1 until 2001 over that interval the flow decelerated by steps in 4 year pulses after a particularly vigorous acceleration in 1997 1999 the glacier gradually slowed to presurge velocities in 2005 the flow was less than 9 m yr 1 digital elevation models are generated by stereographic analysis of air photos for 1951 1970 1972 1977 and 1981 these models are updated annually using ground based survey data and a novel implementation of bayesian kriging over the course of the surge the front of active ice advanced 450 m and the glacier area increased by 10 with an associated thinning of the ice the previous surge of trapridge glacier starting before 1939 and ending before 1951 led to a terminus advance of 1 km comparison of the two surges suggests that the 1930s surge started with a slow progression similar to what we observed in the 1980s and 1990s and switched to a faster flow mode after 1941 this second phase was never attained in the recent surge probably owing to a lack of mass

biomarkers as environmental indicators in a carbonate complex example from the middle to upper devonian holy cross mountains poland abstract autochthonous biomarker distributions were studied in an array of different subfacies of a devonian carbonate complex represented in platform reef and off platform shelf basinal systems it revealed that biomarkers are sensitive indicators of depositional environments and may serve to refine palaeoenvironmental interpretations of carbonate complexes based on classical sedimentological facies analyses the contrasting biomarker composition of the carbonate platform and reef complex versus shelf basin deposits is here interpreted as the effect of both more diverse biotic sources of a primary organic matter in the former environments highly scattered results of sterane distribution and contrasting styles of decay and bacterial reworking of the primary biomass peritidal dolostones deposited under anoxic to suboxic conditions and with scarce sedimentological evidence of elevated salinity reveal the highest potential of organic matter preservation among other platform reefal facies their biomarker composition includes several compounds indicating hypersaline conditions and anoxia whereas others in particular gammacerane indicate that the water column was stratified during sedimentation this observation constrains environmental interpretation of these deposits pointing to shallow subtidal lagoons with elevated salinity and low oxygen near bottom waters most probably originating from a salinity controlled stratification of the water column biomarkers diagnostic of green sulphur bacteria were found in both peritidal lagoonal dolostones and shelf basinal facies this indicates the existence of photic zone anoxia in the latter environment thus suggesting a shallow position of the redoxcline the frasnian famennian mass extinction event s apparently had no impact on the biomarker distribution in the shelf basinal system continuous across the stage boundary

development of texture contrast soils by a combination of bioturbation and translocation abstract soils and weathering profiles in a wide variety of parent materials and environmental settings exhibit coarse over fine vertical textural contrasts where these cannot be attributed to inherited texture contrasts or erosion deposition the most common explanations are based on translocation eluviation illuviation which removes clays from surface layers and deposits them in the subsoil or bioturbation where preferentially fine material is delivered to the surface by organisms from whence erosional winnowing creates a coarse surface layer in some soils of the lower coastal plain of north carolina u s a neither explanation is sufficient to explain the observed texture contrasts a heuristic model based on a combination of translocation of fine material from surface to subsoil and bioturbation driven delivery and recycling of material to the surface can explain the observed vertical textural contrasts the key elements in the model are coastal plain sediments which include some fine material eluviation illuviation by percolating water delivery of additional fine and mixed grain size material to surface by bioturbation making it available for translocation concentration of fine material originally scattered throughout the parent material in a b horizon and maintenance of vertical moisture fluxes by bioturbation the model is supported by morphological evidence of the key mechanisms argillic horizons that are finer than both the surface layers and underlying parent material evidence that argillic horizon formation is not limited by the rate of clay synthesis and the absence of texture contrasts in nearby soils formed from dune sands which lack fines

unraveling driving factors for large rock ice avalanche mobility large rock ice avalanches have attracted attention from scientists for decades and some of these events have caused high numbers of fatalities a relation between rock slope instabilities in cold high mountain areas and climate change is currently becoming more evident and questions about possible consequences and hazard scenarios in densely populated high mountain regions leading beyond historical precedence are rising to improve hazard assessment of potential rock ice avalanches their mobility is a critical factor this contribution is an attempt to unravel driving factors for the mobility of large rock ice avalanches by synthesizing results from physical laboratory experiments and empirical data from 64 rock ice avalanches with volumes 1x106 m3 from glacierized high mountain regions around the world the influence of avalanche volume water and ice content low friction surfaces and topography on the apparent coefficient of friction as a measure of mobility is assessed in laboratory experiments granular ice in the moving mass was found to reduce bulk friction up to 20 while water led to a reduction around 50 for completely saturated material compared with dry flows evidence for the effects of water as a key driving factor to enhance mobility was also found in the empirical data while the influence of the ice content could not be confirmed to be of much relevance in nature besides liquefaction it was confirmed that mobility increases with volumes and that frictional surface characteristics such as flow paths over glaciers are also dominant variables determining mass movement mobility effects of the topography along the flow path as well as channeling are assumed to be other critical factors the results provide an empirical basis to roughly account for different path and flow characteristics of large rock ice avalanches and to find appropriate ranges for friction parameters for scenario modeling and hazard assessments copyright 2011 john wiley sons ltd

progressive and regressive pedogenesis and complex soil evolution abstract the simultaneous operation of regressive and progressive pedogenetic pathways raises the possibility that soil evolution may exhibit patterns far richer and more complex than increasing development over time this possibility is explored via a numerical model incorporating the relative rates of progressive and regressive pedogenesis and feedbacks between these rates and the degree of soil development this model may exhibit deterministic chaos and sensitive dependence on initial conditions with realistic parameter values variations in profile development in a region of the north carolina coastal plain where soil forming factors are relatively constant is consistent with deterministic chaos chaotic soil evolution suggests that soil development may reflect the interplay between progressive and regressive soil forming processes in addition to or instead of the age of a surface or deposit the former may produce a state of development which is unique to a particular time sensitively dependent on the unknown initial conditions and not simply related to age soils and their genetic signatures as indicators of relative ages and quaternary environments may need to be reinterpreted in this light

geochemical evidence for african dust inputs to soils of western atlantic islands barbados the bahamas and florida 1 we studied soils on high purity limestones of quaternary age on the western atlantic ocean islands of barbados the florida keys and the bahamas potential soil parent materials in this region external to the carbonate substrate include volcanic ash from the island of st vincent near barbados volcanic ash from the islands of dominica and st lucia somewhat farther from barbados the fine grained component of distal loess from the lower mississippi river valley and wind transported dust from africa these four parent materials can be differentiated using trace elements sc cr th and zr and rare earth elements that have minimal mobility in the soil forming environment barbados soils have compositions that indicate a complex derivation volcanic ash from the island of st vincent appears to have been the most important influence but african dust is a significant contributor and even mississippi river valley loess may be a very minor contributor to barbados soils soils on the florida keys and islands in the bahamas appear to have developed mostly from african dust but mississippi river valley loess may be a significant contributor our results indicate that inputs of african dust are more important to the genesis of soils on islands in the western atlantic ocean than previously supposed we hypothesize that african dust may also be a major contributor to soils on other islands of the caribbean and to soils in northern south america central america mexico and the southeastern united states dust inputs to subtropical and tropical soils in this region increase both nutrient holding capacity and nutrient status and thus may be critical in sustaining vegetation

deciphering the history of hydrologic and climatic changes on carbonate lowstand surfaces calcrete and organic matter evaporite facies association on a palimpsest middle jurassic landscape from portugal abstract the unusual occurrence of calcretes and prominent organic matter in the middle jurassic lower bathonian serra de aire formation of the lusitanian basin of western portugal western iberian margin revealed a complex palimpsest exposure record here interpreted as reflecting hydrological changes caused by phases of emergence and immersion it serves as a potential model for understanding stratigraphic development at lowstand surfaces in carbonate successions the exposure dominated facies association grades upwards into peritidal and lagoonal limestones and the interval is assigned to the regressive peak of a transgressive regressive facies cycle 2nd order of the thick middle jurassic carbonate ramp succession the galinha quarry fatima region ne of lisbon a type section for this lowstand assemblage exhibits varied calcretes with black clasts interbedded with and grading into organic rich marly clayey seams and lenses locally with carbonate nodules carbonates with evaporite traces microbial laminites black clast and fenestral limestones some lithofacies are dolomitized the palynofacies contains phytoclasts associated with less refractory more prone to degradation components which suggests natural combustion pyrolysis wild fires the lowstand surface represents a low relief landscape with small depressions ponds bordering a more distal marginal littoral setting the partly subaerial and partly subaqueous settings were subjected to lengthy exposure and to fluctuating very shallow water bodies and water table coeval climatic regime was a seasonally dry wet one with dry semi arid phases dominating over the sub humid as shown by the combined record of intense calcrete development rhizogenic structures microbial mats brecciation desiccation evaporites and wild fire evidence however sea level rise caused changes to shallow sea water influenced restricted lagoonal peritidal settings comparisons and differences with modern and ancient coast marginal carbonates are made to provide a guide to the variability in such lowstand deposystems in the stratigraphic record

avalanching glacier instabilities review on processes and early warning perspectives avalanching glacier instabilities are gravity driven rupture phenomena that might cause major disasters especially when they are at the origin of a chain of processes reliably forecasting such events combined with a timely evacuation of endangered inhabited areas often constitute the most efficient action recently considerable efforts in monitoring analyzing and modeling such phenomena have led to significant advances in destabilization process understanding improving early warning perspectives the purpose of this paper is to review the recent progress in this domain three different types of instabilities can be identified depending on the thermal properties of the ice bed interface if cold 1 the maturation of the rupture is associated with a typical time evolution of surface velocities and passive seismic activity a prediction of the final break off is possible using these precursory signs for the two other types water plays a key role in the development of the instability if the ice bed interface is partly temperate 2 the presence of meltwater may reduce the basal resistance which promotes the instability no clear and easily detectable precursory signs are known in this case and the only way to infer any potential instability is to monitor the temporal evolution of the thermal regime the last type of instability 3 concerns steep temperate glacier tongues switching for several days weeks during the melting season into a so called active phase followed in rare cases by a major break off event although the prediction of such events is still far from being achievable critical conditions promoting the final instability can be identified

palynofacies and source rock potential of jurassic sequences on the arruda sub basin lusitanian basin portugal abstract the study of the organic matter present in sedimentary rocks is fundamental for the characterization of the potential source rocks as well as to define the depositional paleoenvironments parameters of organic petrology and organic geochemistry and their variations along sedimentary successions are essential tools to achieve these goals two borehole successions freixial 1 and benfeito 1 from arruda sub basin lusitanian basin that comprise siliciclastic carbonate deposits of jurassic age have been studied in order to characterize the organic matter and its vertical variability as well as its hydrocarbon potential palynofacies and geochemical data indicate both marine including zooclasts and terrestrial organic matter where the phytoclasts predominated despite an important contribution of the amorphous organic matter aom different types of solid bitumen were observed most of the analyzed samples have total organic carbon content toc lower than 1 wt and hydrogen index hi values lower than 100 mghc g toc revealing types iii and iv kerogen however one set of samples exhibit toc values higher than 1 wt and higher hi values depicting a type ii kerogen the biomarker data showed a dominance of n alkanes with 15 30 carbon atoms having a unimodal distribution pristane phytane ratio varies between 0 04 and 1 84 indicating an alternation of oxic anoxic conditions along the sequences typical terpane distributions are characterized by the presence of tricyclic and tetracyclic terpanes as well as pentacyclic terpanes rare in carbonated samples from freixial 1 borehole the amount of 17 h 22 29 30 trisnorhopane tm usually exceeds the amount of 18 h 22 29 30 trinorneohopane ts the values of the ratio 22s 22s 22r epimers of c32 homohopanes revealed that most samples reached equilibrium values the 20s 20s 20r and isomerization ratios in c29 sterane calculated for the studied samples range between 0 19 0 61 and 0 20 0 70 respectively with several samples reaching the equilibrium values the vitrinite reflectance values are higher than 0 5 indicating that the organic matter reached the oil generation window according to the data obtained in this study the abadia montejunto cabacos and brenha formations can be considered potential source rocks of hydrocarbons gas and or oil in this section of the lusitanian basin