associations between burial diagenesis of smectite chemical remagnetization and magnetite authigenesis in the vocontian trough se france results of a paleomagnetic rock magnetic geochemical and petrographic study on jurassic and cretaceous carbonates in the vocontian trough support a hypothesized connection between burial diagenetic alteration of smectite and the widespread occurrence of a chemical remanent magnetization crm carried by magnetite where smectite has altered to other clay minerals limestones are characterized by a prefolding secondary normal polarity magnetization throughout the basin the magnetization is interpreted to be a crm based on low burial depths which cannot cause thermoviscous resetting where significant smectite is still present the crm is absent weakly developed and where the clays show no evidence for burial alteration the units are characterized by a primary magnetization crm intensity also varies with the amount of smectite and burial isothermal anhysteretic and natural remanent magnetization intensities increase where smectite has altered both stratigraphically and geographically this is interpreted to indicate magnetite authigenesis associated with clay diagenesis superparamagnetic magnetite is more dominant in highly altered units based on the results of low temperature experiments all sections away from the alps have 87sr 86sr values that are similar to coeval seawater and stable isotopes of carbon and oxygen show no sign of alteration orogenic type fluids therefore are not a likely agent of remagnetization near the alps the rocks are characterized by an additional reversed polarity component which is interpreted to reflect acquisition of the crm through a reversal a postfolding magnetization is also present there and strontium isotopic ratios are higher than elsewhere in the basin and might indicate some alteration by orogenic type fluids we conclude that burial diagenesis of smectite is the likely cause for the development of the widespread crm in the vocontian trough and that this mechanism might explain widespread chemical remagnetization elsewhere

neoformed magnetic minerals as an indicator of moderate burial the key example of middle paleozoic sedimentary rocks west virginia in order to help unravel the thermal history of middle paleozoic sedimentary rocks in west virginia a rock magnetic study was conducted with a focus on the marcellus shale vitrinite reflectance fluid inclusions microthermometry and conodont alteration index data yield contradictory burial temperature within the range 150 250 c 302 482 f the characterization of magnetite and pyrrhotite may be used as an index to track burial temperature around 200 c 392 f low temperature and room temperature magnetic measurements were performed in order to determine the magnetic assemblage three magnetic assemblages were identified that were stratigraphically distributed the goethite and nanosized magnetite a1 assemblage is mainly found in the clinton group oriskany sandstone stratigraphic interval silurian lower devonian nanosized fraction of magnetite and probably pyrrhotite a3 assemblage essentially constitutes the marcellus shale chemung formation sequence devonian microsized pyrrhotite is the typical mineral for a2 that is only identified near the alleghenian structural front overall the rare occurrence of micron pyrrhotite in our samples suggests that the study area has not experienced burial temperatures higher than 200 c 392 f

vitrinite reflectance property change during heating under inert conditions abstract the aim of the study was to determine optical properties of vitrinite subjected to temperatures within the range of 400 1200 c for durations of 1 7 h in an argon atmosphere the samples of vitrinite concentrate vt content 90 r r 1 17 were inserted in the furnace at room temperature and subjected to a heating rate of 60 c min to assess the effects of the experiment random reflectance as well as apparent maximum and minimum reflectances of vitrinite were measured on the raw and thermally treated concentrates employing the method and computer programme of w e kilby the true maximum intermediate and minimum reflectances of vitrinite as well as reflectance anisotropy and reflectance indicating surface ris shapes were evaluated transformation of vitrinite subjected to heating is influenced more by the increase of temperature than the time applied during the plastic stage 400 500 c vitrinite is subjected to substantial chemical and physical alteration it is manifested by chemical decomposition significant mass loss and mesophase appearance porosity relief reflectance and bireflectance of the vitrinite grains increase with heating at the temperature of 1200 c random vitrinite reflectance reaches 6 62 with bireflectance of 3 46 mesophase at 1200 c was characterised by mean reflectance equal to 9 25 and a bireflectance of 13 35 the reflectance character of vitrinite changes from biaxial negative into biaxial positive negative however the original ris shape resulting from the tectonic regime during the main phase of coalification is not fully transformed until heated to 1200 c reflectance character of mesophase is consistently biaxial negative the internal structure of mesophase is thought to be better organised than the internal structure of vitrinite

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

magnetic susceptibility of the rock matrix related to magnetic fabric studies non ferromagnetic minerals constitute what is called the rock matrix whose susceptibility k1 is directly accessible using only high magnetic fields measurements on minerals and a wide range of rock types show that k1 is mainly due to paramagnetism and hardly exceeds 10 3 si with an anisotropy degree p less than 1 35 different methods to estimate the role of the matrix component in low field susceptibility k and its anisotropy include petrological and chemical analysis evolution of p vs k low temperature studies and comparison of k with remanent magnetizations

exceptional preservation processes of 3d dinosaur footprint casts in costalomo lower cretaceous cameros basin spain theropod dinosaur footprints at the costalomo tracksite pinilla de los moros formation upper hauterivian lower barremian western cameros basin salas de los infantes burgos province spain show unusual preservation of a previously undescribed nature the footprints occur as casts positive epireliefs at the top of a sandstone bed and preserve exceptional details of the top of the digit and claw morphology and of digital interactions with the sediment during penetration and extraction from the sediment footprint formation and preservation occurred in the following stages

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

soft sediment deformation below mammoth tracks at white sands national monument new mexico with implications for biomechanical inferences from tracks abstract implicit in any biomechanical analysis of tracks footprints whatever the animal is the assumption that depth distribution within the track reflects the applied plantar pressure in some way here we describe sub track deformation structures produced by proboscidea probably mammuthus columbi at white sands national monument whsa in new mexico patterns of sub surface deformation are consistent with the plantar pressure data for modern proboscidea but do not reflect track morphology our work cautions against overinterpreting track topology of any large animal including extinct animals such as sauropods in terms of their biomechanics unless the subsurface stratigraphy and associated variation in shear strength is known

reply to discussion of defining the morphological quality of fossil footprints problems and principles of preservation in tetrapod ichnology with examples from the palaeozoic to the present by marchetti et al 2019

evolution of the raman spectrum of carbonaceous material in low grade metasediments of the glarus alps switzerland terra nova 22 354 360 2010 abstract the raman spectrum of carbonaceous material cm from advanced diagenesis 200 c to low grade metamorphism 320 c is documented in the helvetic flysch of the glarus alps switzerland the spectrum is complex with several defect bands at 1200 d4 1350 d1 1500 d3 and 1620 d2 cm 1 we document the evolution of these bands relative to the graphite g band with increasing metamorphic grade and we show that this qualitative evolution may be used as a proxy for temperature in the glarus alps we develop a robust peak fitting method and propose quantitative parameters that may be used as proxies for thermal metamorphism in this region further work in other geological contexts is needed to assess whether the spectral evolution observed in the glarus alps may be generalized and to critically assess the potential for calibrating a general empirical and quantitative thermometer based on the raman spectrum of cm in low grade rocks

palaeoichnology of an mis 3 cave bear settlement ursilor cave western carpathians romania abstract the palaeoichnology of the cave bear ursus spelaeus was studied at ursilor cave apuseni mountains romania to acquire new data about the ethology and the metrics of this extinct species eight stations containing footprints scratch marks and nests were surveyed using laser scanning to build tridimensional models for several cave bear nests wall scratch marks and footprints morphological observations were made using the models and precise measurements of the breadth or depth of the scratch marks were performed in addition 100 cave bear nests and 10 footprints were measured and analyzed the palaeoichnogical data were corroborated with previously obtained information on the taphonomy geomorphology sedimentology and geochronology from this site several bioglyphs e g scratch marks footprints were indirectly dated to marine isotope stage mis 3 by identifying and assigning them to co occurring cave bear skeletons as a consequence we stress the need for a multidisciplinary approach in order to assess the palaeoichnology of cave bear sites findings fill a gap in our knowledge because cave bear bioglyphs are one of the less studied branches of cave bear research due to the scarcity and fragility of ichnological features

true tracks undertracks and eroded tracks experimental work with tetrapod tracks in laboratory and field abstract to be able to distinguish between true tracks undertracks and tracks altered by erosion is of great importance in tetrapod track ichnotaxonomy this paper reports three experimental approaches to the study of undertracks using the footprints of an emu dromaius novaehollandiae experiment 1 describes successive horizontal sections down through a plaster cast of an emu footprint emplaced in soft mud revealing a steady downward decrease in the area of the track particularly the length this is the result of the movements of the trackmaking limb during impact forward swing of the body and final kick off experiments 2 and 3 describe vertical sections cut through footprints emplaced in packages of layered coloured cement admixed with water to produce different consistencies firm and semi fluid after hardening the cement block was serial sectioned vertically and removal of a lightly cemented layer gave access to two undertrack bedding plane views successive undertracks downward show an increase in horizontal dimensions and decrease in vertical topography of the structure representing gradual degradation of the track anatomy with depth in experiment 3 the true track at the tracking surface was deformed by collapse and flow of the substrate after withdrawal of the foot in this case the undertracks that were formed in layers subjacent to the foot reproduced the morphology of the foot more faithfully than did the true track

fluid inclusion technique for determining maximum temperature in calcite and its comparison to the vitrinite reflectance geothermometer theory laboratory experiments and empirical observation suggest that many aqueous fluid inclusions in calcite reequilibrate during overheating and therefore some homogenization temperatures t h record a temperature close to the maximum reached by the rock this characteristic suggests that aqueous fluid inclusions in calcite can be used to establish maximum temperature t peak to test this hypothesis we have compiled fluid inclusion t peak mean random vitrinite reflectance r m and present day t peak from 46 diverse geologic systems that have been at t peak from 10 4 to 10 6 yr present t peak ranged from 65 to 345 c t h modes and means ranged from 59 to 350 c and r m data ranged from 0 4 to 4 6 spanning the temperature and thermal maturity range associated with burial diagenesis hydrothermal alteration and low grade metamorphism plots of t h and t peak data for systems thought to be currently at maximum temperature demonstrate close agreement between t h and present t peak in sedimentary basins although caution should be applied the relation suggests that t h of aqueous fluid inclusions in calcite may be a useful measure of maximum temperature this study also compares t h to mean random vitrinite reflectance r m to offer further support for the use of t h as a measure of t peak and to provide a better understanding of r m t h correlates well with r m and results in a curve similar to r m vs t peak calibrations determined by other workers the strong correlation correlation coefficient r 0 93 between t peak and r m in these systems suggests that maximum temperature is the major control on thermal maturation

dinosaur tectonics a structural analysis of theropod undertracks with a reconstruction of theropod walking dynamics abstract a dinosaur trackway in the middle jurassic eolian entrada sandstone of southern utah u s a exposes three undertracks that we have modeled as isolated tectonic regimes showing the development of fold thrust ramp systems induced by the dinosaur s feet the faulted and folded sequence is comparable to crustal scale tectonics associated with plate tectonics and foreland fold thrust belts a structural analysis of the dinosaur tracks shows the timing and direction of the forces exercised on the substrate by the animal s foot during the stride based on the structural analysis we establish a scenario for foot movements and weight distribution in the feet during the end of the weight bearing phase of the stride the weight of the animal was transferred to the front of the digits creating a rotated disk below the foot that was bounded by an extensional fault at the front and a thrust ramp toward the back as the body accelerated the foot was forced backward the rotated disk was forced backward al

raman spectra of carbonaceous material in metasediments a new geothermometer metasedimentary rocks generally contain carbonaceous material cm deriving from the evolution of organic matter originally present in the host sedimentary rock during metamorphic processes this organic matter is progressively transformed into graphite s s and the degree of organisation of cm is known as a reliable indicator of metamorphic grade in this study the degree of organisation of cm was systematically characterised by raman microspectroscopy across several mesozoic and cenozoic reference metamorphic belts this degree of organisation including within sample heterogeneity was quantified by the relative area of the defect band r2 ratio the results from the schistes lustres western alps and sanbagawa japan cross sections show that 1 even through simple visual inspection changes in the cm raman spectrum appear sensitive to variations of metamorphic grade 2 there is an excellent agreement between the r2 values calculated for the two sections when considering samples with an equivalent metamorphic grade and 3 the evolution of the r2 ratio with metamorphic grade is controlled by temperature t along the tinos cross section greece which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks the r2 ratio is nearly constant consequently the degree of organisation of cm is not affected by the retrogression and records peak metamorphic conditions more generally analysis of 54 samples representative of high temperature low pressure to high pressure low temperature metamorphic gradients shows that there is a linear correlation between the r2 ratio and the peak temperature t c 445 r2 641 whatever the metamorphic gradient and probably the organic precursor the raman spectrum of cm can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism temperature can be estimated to 50 c in the range 330 650 c a few technical indications are given for optimal application

estimates of dinosaur speeds from a new trackway site in texas a method for estimating the speed of a dinosaurian trail maker from the size of its footprints and stride has been described by alexander1 however when applied to known trackways this method gave rather low speeds 1 0 3 6 m s 1 russell and beland2 estimated a speed of 1 77 m s 1 for a slowly moving ornithomimid and 7 54 m s 1 for an allegedly rapidly running ornithopod the latter estimate is questionable as there is some doubt concerning the number of prints and thus the stride length of the trail3 4 dinosaurs responsible for trackways in british columbia5 south wales6 and queensland7 all seem to have been moving slowly thus reliable estimates of dinosaur speeds are all rather low here i report dinosaur speeds based on trails at a new site from the lower cretaceous of texas some of which appear quite fast by alexander s method1

were non avian theropod dinosaurs able to swim supportive evidence from an early cretaceous trackway cameros basin la rioja spain a fundamental question remaining unanswered in dinosaur behavior is whether they had the ability to swim we report the discovery of an exceptional swimming dinosaur trackway with 12 consecutive footprints in lacustrine nearshore sediment from the early cretaceous cameros basin la rioja spain the singular morphology of these footprints strongly suggests a fl oating animal clawing the sediment as it swam diagnostic traits of theropod dinosaur footprints are identifi able in these peculiar elongated s shaped ichnites paleoenvironmental reconstruction indicates an upper shoreface setting with a maximum water depth of 3 m substantiating the swimming hypothesis ichnological analysis of the trackway shows that this theropod used a pelvic paddle motion similar to that of modern bipeds and swam with amplifi ed asymmetrical walking movements to maintain direction into a leftward water current after recent hints of swimming dinosaurs this new evidence persuasively demonstrates that some non avian theropod dinosaurs were swimmers

thermochemical remanence acquisition in single domain particle ensembles a case for possible overestimation of the geomagnetic paleointensity 1 single domain sd particle ensembles are the best studied systems in rock magnetism yet even for this simple system a complete theoretical treatment of the acquisition of thermochemical remanent magnetization tcrm is missing on the basis of the sd theory of chemical remanent magnetization it is generally taken for granted that tcrm acquisition must be less efficient than acquisition of a thermoremanent magnetization trm and that consequently the paleofield intensity is inevitably underestimated when a tcrm is interpreted as a trm here it is shown that this conclusion holds only when a continuous chemical change e g grain growth takes place during remanence blocking in cases where an initial trm at a later time and at lower temperature is modified by chemical processes the final tcrm can result in considerable paleofield overestimation when interpreted as a trm this is demonstrated for two different scenarios first partial grain dissolution after trm acquisition and second low temperature oxidation these mechanisms are not unlikely to occur in nature and numerical experiments indicate that both would lead to perfectly straight arai plots which makes such sd tcrms indistinguishable from true trms in the thellier experiment

low temperature magnetic behaviour near 35 k in unmetamorphosed claystones summary there is growing evidence that the magnetic assemblage of claystones illustrated by low temperature magnetic transitions at 120 k and 35 k may be representative of the peak burial temperature in the so called oil window 60 150 c in previous studies it was proposed that this magnetic assemblage is characterized by fine grained pyrrhotite fe7s8 and magnetite fe3o4 however evidence of pyrrhotite was not so obvious and the magnetic transition near 35 k of fine grained pyrrhotite has similarities with those of siderite feco3 or rhodochrosite mnco3 here we propose some diagnostic tests to distinct 50 k behaviours by studying claystones from netherlands borehole and borneo prism that experienced different peak burial temperatures we perform magnetic susceptibility temperature dependency of sirm zfc rt sirm and field cooled hysteresis loops on cooling of rt sirm 300 k to 10 k we applied a magnetic field of 5 t to enhance neel type magnetic transition it is found that our samples can be classified in two categories based on the shape of the rt sirm curve one displaying an abrupt break in slope in the remanence at 30 k called n behaviour and the other one characterized by a progressive increase of the remanent magnetization by 80 k named p behaviour the first category contains essentially magnetite and fe mn carbonates the second one magnetite and probably iron sulphides

authigenic or detrital origin of pyrrhotite in sediments resolving a paleomagnetic conundrum monoclinic pyrrhotite fe7s8 is widely claimed to carry magnetizations acquired during early diagenesis in anoxic sedimentary environments in contrast geochemical literature indicates that pyrrhotite formation is extremely slow below 180 c which makes it a highly unlikely carrier of early diagenetic remanences in sediments this view is confirmed by the occurrence of late diagenetic fe7s8 in ancient sediments and the general lack of fe7s8 in modern sediments horng et al c s horng m torii k s shea s j kao inconsistent magnetic polarities between greigite and pyrrhotite magnetite bearing marine sediments from the tsailiao chi section southwestern taiwan earth planet sci lett 164 1998 467 481 documented the presence of fe7s8 that carries a magnetic signal indistinguishable from that of detrital magnetite in pleistocene marine sediments from taiwan we tested the possibility that the fe7s8 could have a detrital origin by conducting a source to sink study and found fe7s8 in metamorphic rocks of the taiwan central range and in material eroded from these rocks in the transportation pathway and in the depositional sink this confirms that the fe7s8 has a detrital origin rapid transportation from source to sink e g by typhoon associated flood events probably assists preservation of the fe7s8 which might otherwise oxidize during transportation the widespread occurrence of exhumed metamorphic rocks in orogenic belts around the world makes them a likely source of fe7s8 in marginal sedimentary basins detrital fe7s8 should therefore be more routinely considered to be responsible for paleomagnetic records when it is present in sediments with partial metamorphic provenance

dominant covarying climate signals in the southern ocean and antarctic sea ice influence during the last three decades abstracta composite dataset comprising geopotential height sea surface temperature zonal and meridional surface winds precipitation cloud cover surface air temperature latent plus sensible heat fluxes and sea ice concentration has been investigated with the aim of revealing the dominant time scales of variability from 1982 to 2013 three covarying climate signals associated with variations in the sea ice distribution around antarctica have been detected through the application of the multiple taper method with singular value decomposition mtm svd features of the established patterns of variation over the southern hemisphere extratropics have been identified in each of these three climate signals in the form of coupled or individual oscillations the climate patterns considered here are the southern annular mode sam the pacific south american psa teleconnection the semiannual oscillation sao and the zonal wavenumber 3 zw3 mode it is shown that most of the sea ice temporal variance i

discussion defining the morphological quality of fossil footprints problems and principles of preservation in tetrapod ichnology with examples from the palaeozoic to the present by lorenzo marchetti et al

magnetic mineral diagenesis abstract reduction oxidation redox reactions occur during burial because sediments contain reactive mixtures of oxidised and reduced components diagenetic chemical reactions represent the approach of all sedimentary components toward equilibrium and control the long term stability of sedimentary iron bearing minerals magnetic minerals are sensitive indicators of sedimentary redox conditions and of changes in these conditions through time with diagenetic effects ranging from subtle to pervasive despite the importance of magnetic mineral diagenesis in paleomagnetism rock magnetism and environmental magnetism and the usefulness of these subjects in the earth and environmental sciences there is no systematic single published treatment of magnetic mineral diagenesis this paper is an attempt to provide such a treatment for the full range of diagenetic environments magnetic mineral diagenesis during early burial is driven largely by chemical changes associated with organic matter degradation in a succession of environments that range from oxic to nitrogenous to manganiferous to ferruginous to sulphidic to methanic where the free energy yielded by different oxidants decreases progressively in each environment in oxic environments the most important diagenetic processes involve surface oxidation of detrital minerals and precipitation of fe3 bearing minerals from solution in ferruginous environments the most reactive detrital and authigenic iron oxides undergo dissolution often mediated by dissimilatory iron reducing bacteria which releases fe2 that becomes available for other reactions the fe2 in solution can diffuse upward where it is oxidised to form new authigenic iron oxyhydr oxide minerals or it can become bioavailable to enable magnetotactic bacteria to biomineralise magnetite generally at the base of the overlying nitrogenous zone alternatively dissimilatory iron reducing bacteria can produce extracellular magnetite within ferruginous environments in sulphidic environments iron bearing detrital mineral assemblages undergo more radical alteration hydrogen sulphide which is a byproduct of bacterial sulphate reduction or of anaerobic oxidation of methane reacts with the fe2 released from iron mineral dissolution or directly with solid iron oxyhydr oxide minerals to form iron sulphide minerals mackinawite greigite and pyrite authigenic growth of ferrimagnetic greigite has important implications for paleomagnetic recording secondary iron sulphide formation can also occur as a result of anaerobic oxidation of methane methane migration through sediments in association with biogenic or thermogenic methane production or in association with gas hydrate dissociation can disrupt the diagenetic steady state and give rise to greigite and monoclinic pyrrhotite formation that remagnetises sediments most of the above described diagenetic processes occur below 50 c with continuing burial above 50 c but at sub metamorphic temperatures magnetic minerals can undergo further thermally induced chemical changes that give rise to a wide range of mineralogical transformations that affect the magnetic record of the host sediment these changes include remagnetisations magnetic analysis can provide much valuable information concerning diagenesis in environmental processes the range of processes discussed in this paper should assist researchers in analysing sediment magnetic properties for which the assessment of diagenetic effects has become a necessary component

ice atmosphere interactions during sea ice advance and retreat in the western antarctic peninsula region 1 the seasonal evolution of sea ice extent concentration and drift in the western antarctic peninsula wap region along with regional atmospheric synoptic variability are described for a winter period 1992 when sea ice advance and retreat were both anomalously early daily time series of winds opening and closing of the sea ice cover and volume fluxes in and out of the wap region indicate that synoptic variability in meridional winds determines whether the ice edge advances or retreats on daily to weekly timescales the importance of this finding is that the dynamics as opposed to the thermodynamics initiate and thereby dominate in the production of ice edge anomalies further the abrupt mid winter shift from persistently positive to negative ice edge anomalies indicates that there was a distinct change in the regional atmospheric circulation the ice atmosphere interactions in the winter of 1992 are then compared to those in the winter of 1990 when sea ice advance and retreat were both late instead of early but again the mid winter shift was abrupt the comparison highlights possible circumpolar and tropical polar atmospheric linkages in the south pacific that involve changes in the amplitude phase of the semi annual oscillation sao which in turn appear

tetrapod tracks in a marginal lacustrine setting middle triassic argentina taphonomy and significance abstract fossil tetrapod footprints not only provide valuable information about trackmaker paleobiology but also to give insight into details of the depositional conditions of the substrate at the time of imprinting therefore in the present study the mode of formation and taphonomy of footprints in different substrates was used to investigate the gait and walking dynamics of the trackmakers as well as a source of additional information on the environmental conditions of the track bearing beds during imprinting the analyzed section corresponds to thick middle triassic lacustrine deltaic deposits of the ischichuca los rastros formation ischigualasto villa union basin that crops out at the quebrada de ischichuca in northwestern argentina part of the track bearing surfaces correspond to the top of sandy distributary channel mouth bars in a distal delta front setting that were exposed along the lake margin during a lake level fall cross cutting relationships observed among ripple marks the footprints and invertebrate traces of a softground suite of the scoyenia ichnofacies suggest an omission surface measured trackway orientations in the sandstones are perpendicular to the paleo shoreline with the animals coming and going along the exposed top of the bars probably for drinking laterally the distal delta front deposits interfinger with track bearing wackestone beds of palustrine origin deposited in a restricted local embayment lateral to the delta influenced environment trackway orientations in the wackestones are in contrast consistent with the animals moving nearly parallel to the lake border probably along a preferred route evidences of a relative high groundwater table at the time of imprinting in the track bearing surfaces are revealed by the well developed rims of extruded sediment and collapsed digits in the studied tracks and the nearly absence of associated desiccation cracks on the same surfaces nevertheless temporary emergence cannot be ruled out when paleosoil formation was probably promoted as can be observed in the microstructure of both sandstones and wackestones moreover footprint preservation in the wackestones might have been enhanced by partial hardening of the trampled surface during subaerial exposure combining ichnofossil content and taphonomy with facies analysis we identified in the lower part of the ischichuca los rastros succession a relatively rapid withdrawal of the water basinward that was probably due to a forced regression during early rifting of basin evolution footprints can also provide valuable information about locomotion dynamics and trackmaker behavior thus the sideways deformation observed in the studied footprints attributed to basal archosaurs and putative basal dinosaurs can be related to an outward rotation of the foot during the step cycle a condition that might allied to the development of the parasagittal posture in archosauria besides the densely trampled surface described herein constitutes the first documented evidence of putative social behavior among therapsid dicynodonts the most important group of herviborous animals in the early mesozoic terrestrial ecosystems throughout gondwana

tetrapod track assemblages from lower cretaceous desert facies in the ordos basin shaanxi province china and their implications for mesozoic paleoecology tetrapod ichnofaunas are reported from desert playa lake facies in the lower cretaceous luohe formation at baodaoshili shaanxi province china which represent the first asian example of an ichnnofauna typical of the chelichnus ichnofacies brasilichnium sub ichnofacies characteristic of desert habitats the mammaliomorph tracks assigned to brasilichnium represent the first report of this ichnogenus from asia the assemblages also contain three different theropod trackway morphotypes one very wide magnoavipes like morphotype one relatively wide broad toed small eubrontes like form with short steps and strides and wide straddle and an elongate morphotype sarmientichnus with longer steps and narrower straddle representing a didactyl trackmaker the latter being the first example of the enigmatic ichnogenus found outside its type area in argentina the sarmientichnus occurrence the first in asia has important implications demonstrating that the trackmaker was not monodactyl but didactyl with probable affinities to deinonychosaurians which are ichnologically well represented in the lower cretaceous of asia although morphologically distinctive sarmientichnus should be recognized as a form ichnotaxon compromised by suboptimal preservation the combination of brasilichnium isp sarmientichnus isp and tridactyl theropod tracks indicates mammaliomoprhs and small theropods and is comparable to ichnofaunas from similar desert facies on other continents thus cretaceous desert ichnofaunas from china are consistent with global ichnofacies predictions

extreme anomalous atmospheric circulation in the west antarctic peninsula region in austral spring and summer 2001 02 and its profound impact on sea ice and biota exceptional sea ice conditions occurred in the west antarctic peninsula wap region from september 2001 to february 2002 resulting from a strongly positive atmospheric pressure anomaly in the south atlantic coupled with strong negative anomalies in the bellingshausen amundsen and southwest weddell seas this created a strong and persistent north northwesterly flow of mild and moist air across the wap in situ satellite and ncep ncar reanalysis nnr data are used to examine the profound and complex impact on regional sea ice oceanography and biota extensive sea ice melt leading to an ocean mixed layer freshening and widespread ice surface flooding snow ice formation and phytoplankton growth coincided with extreme ice deformation and dynamic thickening sea ice dynamics were crucial to the development of an unusually early and rapid short retreat season negative ice extent anomaly strong winds with a dominant northerly component created an unusually compact marginal ice zone and a major increase in ice thickness by deformation and over rafting this led to the atypical persistence of highly compact coastal ice through summer ecological effects were both positive and negative the latter including an impact on the growth rate of larval antarctic krill and the largest recorded between season breeding population decrease and lowest reproductive success in a 30 yr adelie penguin demographic time series the unusual sea ice and snow cover conditions also contributed to the formation of a major phytoplankton bloom unexpectedly the initial bloom occurred within compact sea ice and could not be detected in sea viewing wide field of view sensor seawifs ocean color data this analysis demonstrates that sea ice extent alone is an inadequate descriptor of the regional sea ice state conditions from both a climatic and ecological perspective further information is required on thickness and dynamics deformation

towards pyrrhotite magnetite geothermometry in low grade metamorphic carbonates of the tethyan himalayas shiar khola central nepal abstract in mesozoic metacarbonates of the tethyan himalayas shiar khola area central nepal two characteristic remanent magnetisations chrm1 and chrm2 were identified by their unblocking temperature spectra the chrm1 is carried by pyrrhotite unblocking temperature 270 360 c and the chrm2 by magnetite unblocking temperature spectra 430 580 c the temperature related formation of pyrrhotite at the expense of primary magnetite during low grade metamorphism in marly carbonates allows the determination of thermal gradients by the pyrrhotite magnetite ratio this new method can be used as a geothermometer for t 300 c in low grade metamorphic carbonates where other methods are not available this method is applied for the first time in the tethyan himalayas of central nepal in the shiar khola valley systematic variations in the ferrimagnetic content of the metacarbonates along an e w profile were detected by the ratio of remanence intensity of pyrrhotite to magnetite derived from natural remanent magnetisation rpyr mag and saturation magnetisation spyr mag over a stretch of 10 km the rpyr mag and spyr mag increase from w to e from 0 42 to 0 91 and 0 48 to 1 0 respectively based on temperature estimates the eastern part experienced upper anchizone epizone 250 300 c conditions while the western part underwent only diagenesis 200 c the temperature gradient and the temperature ranges suggested are consistent with the findings of the calcite twin lamellae geothermometry which is a non magnetic method

effects of diagenesis on magnetic mineralogy in a jurassic claystone limestone succession from the paris basin we performed detailed rock magnetic and geochemical analyses on a previously published early jurassic magnetostratigraphic section the results improve our understanding of acquisition and preservation processes of magnetization in a series of alternating claystones and limestones the main carrier of magnetization is magnetite anhysteretic remanent magnetization arm varies by a factor of 40 and the arm variations are linked to magnetite grain size comparison of magnetic and geochemical data shows that when carbonate content is high 30 and 13 c0 magnetite is characterized by small grain sizes whereas when carbonate content is low 20 magnetite is coarse grained it appears that the oxidation of organic matter by sulfate reduction controls both 13 c and magnetite grain size h 2 s produced during sulfate reduction causes partial dissolution of magnetite grains with the finest magnetite grains those that best record the magnetic signal being dissolved first despite this partial dissolution both the direction and polarity of the original remanent magnetization are preserved

the late diagenetic conversion of pyrite to magnetite by organically complexed ferric iron abstract the geochemistry of late stage diagenetic replacement of pyrite by magnetite was investigated by laboratory experiments of pyrite dissolution and magnetite precipitation involving organically complexed ferric iron the design of the experiments is based on the hypothesized geochemical conditions for in situ diagenesis in the pennsylvanian age belden formation an organic rich carbonate in northwestern colorado with pyrite grains rimmed with magnetite that contains a cretaceous paleopole position the geochemistry is applicable to both deep and near surface reactions involving pyrite magnetite and organic matter and bears upon the geologic interpretation of secondary chemical remanent magnetizations crm aqueous solutions of ferric ligand complexes and pyrite were heated 60 c for 60 days in the absence of light and at low partial pressures of oxygen additional experiments with each ligand were performed both in the presence of bentonite and without ferric iron ligand only raising the ph to 8 5 produced a ferrous hydroxide precipitate and subsequent heating 90 c resulted in the formation of magnetite ferric complexes of oxalate salicylate and acetylacetonate resulted in pyrite dissolution and magnetite formation the activity of strongly reducing ligands e g catechol or unsaturated fe iii exchange capacity particularly in experiments with bentonite or with solutions of uncomplexed ligands can result in an effective reduction of ferric iron concentration and prevent pyrite dissolution and or interfere with the crystallization of magnetite the bentonite acted to adsorb dissolved species and also underwent direct dissolution especially by the oxalate ligands although these reactions could occur at any depth a continuing supply of molecular oxygen more available in near surface settings would result in the formation of hematite or the production of acidic sulfate conditions whereas at greater depths or restricted porosity the redox gradation is halted at magnetite the results of this study thus provide a likely geochemical mechanism for the replacement of pyrite by magnetite during the latter stages of diagenesis

a late triassic lake system in east greenland facies depositional cycles and palaeoclimate abstract the upper triassic fleming fjord formation of the jameson land basin in east greenland contains a well exposed succession 200 300 m thick of lake deposits the malmros klint member 100 130 m thick is composed of cyclically bedded intraformational conglomerates red siltstones and fine grained sandstones and disrupted dolomitic sediments paleosols the cyclicity is composite with cycles having mean thicknesses of 25 5 9 and 1 6 m the overlying carlsberg fjord beds of the orsted dal member 80 115 m thick are composed of structureless red mudstones rhythmically broken by thin greyish siltstones this unit also has a composite cyclicity with cycles having mean thicknesses of 5 0 and 1 0 m the uppermost tait bjerg beds of the orsted dal member 50 65 m thick can be divided into two units a lower unit is composed of cyclically bedded intraformational conglomerates or thin sandstones red mudstones greenish mudstones and yellowish marlstones an upper unit is composed of relatively simple cycles of grey mudstones and yellowish marlstones recognized cycles have mean thicknesses of 5 6 and 1 6 m the lake deposits contain evidence of seasonal orbital and long term climatic change seasonal change is documented by numerous desiccation surfaces especially in the malmros klint member and carlsberg fjord beds orbital change is suggested by the composite cyclicity and long term climatic change is indicated by the systematic upwards change in sedimentary characteristics of the lake deposits the sedimentary features of the malmros klint member suggest lacustrine deposition in a dry climate that fluctuated between desert and steppe conditions the carlsberg fjord beds probably record lacustrine lake deposition in a rather constant dry steppe climate while the tait bjerg beds record lake sedimentation in a climate that fluctuated between dry steppe and warm moist temperate in the tait bjerg beds the upward change in cycle characteristics indicates a shift towards more humid conditions climatic deductions from sedimentary facies are in good agreement with climate maps of laurasia as simulated by numerical climate models palaeomagnetic data indicate a northward drift of east greenland of about 10 from ca 25 n to ca 35 n in the middle to late triassic the fleming fjord formation which represents ca 5 m y of the late triassic interval was deposited during latitudinal drift of 1 2 it is possible that the observed long term upward shift in climatic indicators within the formation can be ascribed to plate drift but southward shift of climatic belts could also have been of importance

thermal control on the modes of crustal thinning leading to mantle exhumation insights from the cretaceous pyrenean hot paleomargins the pre rift mesozoic sequences of the cretaceous passive margins fossilized in the north pyrenean zone npz are characterized by high temperature deformation in relation with thinning of the continental basement our compilation of chronological and geological data confirms a clear correlation between the distribution of the highest paleotemperatures in the pre rift sedimentary cover and the loci of extreme crustal stretching geological evidences such as the occurrence of peridotite bodies directly underlying metamorphic pre rift sediments indicate an early attenuation of the rifted continental crust this leads us to propose a mechanism of rifting involving boudinage of the continental crust the lateral extraction of the paleozoic basement occurred under the pre rift cover that is decoupled on the triassic clays and evaporates the thermal conditions allowing coeval ductile deformation of the crust and of the pre rift sediments leaded to the widening of basins devoid of large faulted blocks we discuss the implications on the origin and significance of the granulites and the relations between flysch deposition and high temperature metamorphism of the pre rift sediments in the npz albian cenomanian flysch sequences were deposited synchronously with the syn metamorphic ductile deformation of the pre rift sequences since the base of the flysch deposits also recorded locally the high temperature tectonic event we propose an original mechanism for the evolution of the basins involving continuous deformation of the pre rift metamorphic sediments at the scale of the pyrenean domain our results suggest a strong lateral variability in the tectonic style of passive margins in direct link with their thermic pattern

preservation and erosion of theropod tracks in eolian deposits examples from the middle jurassic entrada sandstone utah u s a abstract the middle jurassic entrada sandstone exposed near the town of escalante southern utah consists of large scale cross bedded eolian deposits that are interbedded with horizontally laminated sand sheets and thin sets of eolian cross strata representing periods with a moister climate the flat bedded units contain numerous tracks and trackways from small to large sized theropod dinosaurs these tracks are today exposed in several distinct erosional states allowing detailed studies of track and undertrack formation in eolian deposits tracks that originally were emplaced on sloping surfaces show in their present day erosional state a morphology distinct from those originally emplaced on horizontal surfaces further the range of eroded track morphologies can help identify badly eroded tracks from nonbiogenic structures in similar deposits

archosaur footprints cf brachychirotherium with unusual morphology from the upper triassic fleming fjord formation norian rhaetian of east greenland the orsted dal member of the upper triassic fleming fjord formation in east green land is well known for its rich vertebrate fauna represented by numerous specimens of both body and ichnofossils in particular the footprints of theropod dinosaurs have been described recently an international expedition discovered several slabs with 100 small chirotheriid pes and manus imprints pes length 4 4 5 cm in siliciclastic deposits of this unit they show strong similarities with brachychirotherium a characteristic upper triassic ichnogenus with a global distribution a peculiar feature in the fleming fjord specimens is the lack of a fifth digit even in more deeply impressed imprints therefore the specimens are assigned here tentatively to cf brachychirothe rium possibly this characteristic is related to the extremely small size and early ontogenetic stage of the trackmaker the record from greenland is the first evidence of this morphotype from the fleming fjord formation candidate trackmakers are crocodylian stem group archosaurs how ever a distinct correlation with known osteological taxa from this unit is not currently possible while the occurrence of sauropodomorph plateosaurs in the bone record links the greenland assemblage more closer to that from the germanic basin of central europe here the described foot prints suggest a pangaea wide exchange supplementary material three dimensional model of cf brachychirotherium pes manus set from mguh 31233b from the upper triassic fleming fjord formation norian rhaetian of east greenland as pdf ply and jpg files 3d model created by oliver wings photographs taken by jesper milan is available at https doi org 10 6084 m9 figshare c 2133546

the record 2013 southern hemisphere sea ice extent maximum observations of southern hemisphere sea ice from passive microwave satellite measurements show that a new record maximum extent of 19 58 10 6 km 2 was reached on 30 september 2013 the extent is just over two standard deviations above the 1979 2012 mean and follows a similar record 19 48 10 6 km 2 in 2012 on the record day in 2013 sea ice extent was greater than the 30 year average 1981 2010 in nearly all southern ocean regions for the year as a whole southern hemisphere sea ice area and extent were well above average and numerous monthly and daily records were broken analysis of anomaly patterns and the atmospheric and oceanic events suggests that a sequence of regional wind and cold freshened surface waters is likely responsible for the record maximum and the generally high 2013 extent in particular the ross sea sector experienced a combination of cold southerly winds associated with the position and depth of the amundsen sea low and lower than normal sea surface temperatures up to 2 c below normal the resulting very high anomaly in ice extent in this region was a major component of the overall record maximum

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

toward a new 250 c pyrrhotite magnetite geothermometer for claystones abstract we investigate the effects of burial and moderate experimental heating on claystones from three regions with different degrees of maturation immature burial temperature 40 c of bure callovo oxfordian claystones in the basin of paris france early mature burial temperature 85 c of opalinus lower dogger claystones from the mont terri anticline in front of the jura fold belt switzerland and mature to overmature burial temperature 7 s 8 the p transition is also detected in early mature to mature opalinus and chartreuse claystones we conduct additional experimental heating of natural opalinus claystones one set of experiments is referred to as short term heating 1 h from 100 c to 200 c it is dedicated to an investigation of the effect of short lived heating processes in geology a second set of heating experiments is designed to approach burial conditions using a gold capsule in burial like experiments we heated opalinus claystones from 150 c to 250 c for several weeks under a pressure of 100 mpa in both experiments we observe a correlative diminution of the pyrrhotite signature at 35 k with increasing temperature we interpret this trend as the appearance of magnetite we derive a parameter pm from the warming curve of a saturated isothermal remanent magnetization acquired at 10 k zfc we report on a consistent evolution of pm with temperature in the range of 40 c to 250 c including natural samples heated samples at 95 c and burial like heated samples pm first increases between 40 c up to 85 c implying that pyrrhotite gradually dominates the magnetic assemblage at low temperature for temperatures above 85 c pm decreases up to 250 c implying that the formation of magnetite gradually overshadows the magnetic input of pyrrhotite pm values obtained from mature to overmature claystones from the chartreuse are lower than the pm values obtained from the burial like heated opalinus claystones suggesting that the formation of magnetite is driven by kinetics the continuous trend of the pm parameter suggests that the magnetic properties of pyrrhotite magnetite claystones can be used to infer paleo temperatures and we propose to name this geothermometer mageval

remagnetization and chemical alteration of sedimentary rocks remagnetization is a common phenomenon in rocks and developing a greater understanding of its mechanisms has several benefits acquisition of a secondary magnetization is usually tangible evidence of a diagenetic or thermal event which can be dated using palaeomagnetic techniques this is important because the timing of diagenetic and thermal events is commonly difficult to determine remagnetization can also obscure primary magnetizations and a better understanding of remagnetization could improve our ability to uncover primary magnetizations many chemical remagnetization mechanisms have been proposed including those associated with chemical alteration by a number of different fluids e g orogenic weathering mineralizing hydrocarbons and burial diagenetic processes e g clay diagenesis maturation of organic matter this book contains case studies and review articles that focus on remagnetization chemical remagnetization mechanisms and magnetic changes associated with chemical alteration by hydrocarbons

recurrent deformations of aeolian desert dunes in the cretaceous of the south china block trigger mechanisms variability and implications for aeolian reservoirs abstract deposits of aeolian dunes accumulated in cretaceous intramontane deserts in the south china block underwent recurrent deformation processes affecting their toesets and foreset sediments the mid cretaceous matoushan formation preserves examples of soft sediment deformation deformations associated with theropod tracks in aeolian dune apron sandstones the late cretaceous tangbian formation in the xinjiang basin shows i seismites associated with dry interdune laminated deposits and sand injection into the interdune laminated facies generating intraclast breccias ii mass flow deposits associated with heavy rains generating interbedding of non deformed and deformed intervals in aeolian dune foresets deformed intervals display a variety of deformation styles including thrust duplexes upturned and deformed stratification recumbent folds and microfolds and liquefied intervals covered by overlying draa mega cross bedded sets animal tracks seismites monsoon rains and earthquakes are proposed as the main trigger mechanisms of the failures that led to deformation hydroseismicity associated with monsoon rains is a probable but difficult to prove trigger mechanism this process could be an important deformation agent in the case of large scale deformation recorded in ancient erg sequences mass wasting deposits in ancient erg extensive sandy deserts characterized by aeolian dunes sequences constitute significant heterogeneities for hydrocarbon migration and its architectural variability could determine the development of effective sedimentary traps in aeolian reservoirs

magnetic transition at 30 34 kelvin in pyrrhotite insight into a widespread occurrence of this mineral in rocks abstract a characteristic magnetic transition at 30 34 k is shown to provide a powerful tool for the identification of pyrrhotite with concentration down to 10 ppm through the same low temperature techniques as applied to magnetite and hematite extended down to liquid helium temperature a review of rock magnetic and petrological data on pyrrhotite suggests that this mineral should be considered as a major carrier of paleomatnetic signals unblocking temperature up to 350 c and extreme resistance against af may be encountered in fine grained pyrrhotite

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

long lived pluvial episodes during deposition of the navajo sandstone abstract the navajo sandstone of the american southwest was deposited at approximately 190 ma in a giant subtropical dune field near the western margin of pangea from this unit we report thick intervals of dune cross strata that were churned by insects and trampled by reptiles although dunes continued to migrate freely the distribution of trace fossils shows that plant life in wet interdune areas sustained high levels of animal activity on the dunes for many thousands of years we interpret this suite of structures as the record of a pluvial episode climatologically similar to the period of greening in the sahara 4000 10 000 yr ago a high percentage of the rainfall on the navajo erg recharged the water table and led to the development of highly dilute local groundwater flow systems that discharged into interdune areas

the clay fabric of shales is a strain gauge abstract shales with their large clay fraction are prone to deform in an almost ductile way under tectonic loading here we propose to monitor and quantify the evolution of strained shales clay fabric in the field of illite diagenesis by using magnetic fabric in the footwall of a south pyrenean thrust 281 shales samples have been collected along a 2 km long exceptional exposure the cleavage evolves from pencil structures at 1 km of the thrust to pencil cleavage at 850 m and slaty cleavage at 170 m the average magnetic foliation of illite remains nearly parallel to bedding over a distance of 600 m despite development of pencil cleavage it is at 600 m of the thrust that illite foliation shifts gradually from bedding to cleavage by contrast the magnetic fabric scalar data reflect a more continuous evolution of the deformation the application of a rigid rotation model of the clays allows to quantify the strain magnitude using eigen values of tensor this strain magnitude is consistent with distance to the thrust and conforms favorably with a trishear modelling of this thrust damage we demonstrate therefore that the magnetic fabric of illite rich shales is a strain gauge

burrow architecture and burrowing dynamics of ctenomys in foredunes and paleoenvironmental implications abstract ctenomys sp also known as tuco tuco is a solitary subterranean small rodent that inhabits sandy soils in south america we studied burrow system architecture of ctenomys flamarioni communities from the foredunes of the southern brazil coastal plain by inserting plaster of paris and excavating the tunnels the structure of the burrow system is complex with interlinked tunnels one occasionally open entrance multiple chambers and turnarounds blind laterals varying slopes t junctions bifurcations and two different levels a specific isolated chamber is used as a latrine while another is used as a nest the burrow entrance is open only when the rodent is taking out sand or feeding the tunnels have an average depth of 35 cm deepest at 55 cm and the most superficial at 15 cm near the entrance the average burrow length ranges from 190 to 500 cm the tunnels have different heights and widths varying from 5 5 9 3 cm wide to 6 11 cm high the entrance is inclined 28 the central part of the burrow system has a steeper slope with an inclination of 38 the plaster molds preserve claw marks of four digits of up to 4 mm in depth collapsed burrows are rapidly sealed to avoid the entrance of predators ctenomys sp burrows provide a suitable microhabitat which is used by the animals as protection from adverse environmental conditions particularly during the winter when wind impacts the coastal area the extensive interlinking tunnels provide underground routes to escape from predators ctenomys burrows in coastal dune environments are appreciably more complex than those excavated in arid environments which are shallower with no chambers and a slope of up to 20 such difference in the architecture of the burrows can be used as a criterion to reconstruct the paleoenvironment of burrow systems in the rock record

speeds and gaits of dinosaurs abstract the known relationships of speed gait and body size derived mainly from mammals are used to determine the gaits and theoretical maximum speeds of dinosaurs speed estimates are made for 62 dinosaurs representing 51 genera and are supplemented with information from comparative anatomy and from dinosaur trackways it is concluded that smaller bipedal dinosaurs were capable of running at speeds up to 35 or 40 km h the so called ostrich dinosaurs are credited with maximum speeds less than 60 km h and possibly as low as 35 or 40 km h larger bipedal dinosaurs were probably restricted to walking or slow trotting gaits with maximum speeds in the range 15 20 km h most quadrupedal dinosaurs seem to have been restricted to a walking gait stegosaurs and ankylosaurs may have had maximum speeds as low as 6 8 km h sauropods may have attained 12 17 km h and some ceratopsians may have been capable of trotting at speeds up to 25 km h on a weight for weight basis the speeds of dinosaurs are generally lower than those of mammals

regions of rapid sea ice change an inter hemispheric seasonal comparison this bi polar analysis resolves ice edge changes on space time scales relevant for investigating seasonal iceocean feedbacks and focuses on spatio temporal changes in the timing of annual sea ice retreat and advance over 1979 80 to 2010 11 where arctic sea ice decrease is fastest the sea ice retreat is now nearly 2 months earlier and subsequent advance more than 1 month later compared to 1979 80 resulting in a 3 month longer summer ice free season in the antarctic peninsula and bellingshausen sea region sea ice retreat is more than 1 month earlier and advance 2 months later resulting in a more than 3 month longer summer icefree season in contrast in the western ross sea antarctica region sea ice retreat and advance are more than 1 month later and earlier respectively resulting in a more than 2 month shorter summer ice free season regardless of trend magnitude or direction and at latitudes mostly poleward of 70 n s there is strong correspondence between anomalies in the timings of sea ice retreat and subsequent advance but little correspondence between advance and subsequent retreat these results support a strong ocean thermal feedback in autumn in response to changes in spring sea ice retreat further model calculations suggest different net ocean heat changes in the arctic versus antarctic where autumn sea ice advance is 1 versus 2 months later ocean atmosphere changes particularly in boreal spring and austral autumn i e during march may are discussed and compared as well as possible inter hemispheric climate connections

paleomagnetism of the notch peak contact metamorphic aureole revisited pyrrhotite from magnetite pyrite under submetamorphic conditions 1 on the basis of new demagnetization and rock magnetic experiments a scattered two polarity remagnetization extending throughout the contact metamorphic aureole surrounding the jurassic notch peak granitic stock in western utah is now thought to reside in metamorphic pyrrhotite rather than in fine grained hematite in part the pyrrhotite formed by in situ reduction of magnetite by pyrite and organic compounds it could not have been formed by the large scale introduction of reducing fluids as isotopic evidence indicates that these metalimestones remained impermeable at higher grades some pyrrhotite probably also formed by the reaction of pyrite and fe bearing silicates as magnetite destruction and pyrrhotite formation extends into rocks that are not obviously metamorphosed the reactions responsible could proceed at very low less than 200 c temperatures and the feasibility of such low temperature reactions in a closed system is shown by detailed thermodynamic calculations this study demonstrates that under reducing conditions in the presence of sufficient pyrite pyrrhotite can form at the expense of magnetite under very mild conditions indeed magnetite may be destroyed merely by deep burial such a mechanism may help explain the paucity of primary magnetite in ancient sedimentary rocks particularly since the single domain and pseudo single domain grains capable of retaining a stable paleomagnetic signature over geologic time are extremely fine grained and hence particularly vulnerable to destruction

fault related folding in sandbox analogue models of thrust wedges abstract the nucleation and growth of thrust fault related folds has been simulated using high resolution sandbox coulomb wedge type analogue models thrust related anticlines grew progressively from initial layerparallel shortening to decollement folding thrust tip folding and eventually thrust ramp folding thrust ramps nucleated in the central sector of the overturned forelimb of decollement folds as a consequence of limb thinning thrust tip folding occurred during outward migration of the ramp tips the fault propagation rate was greater at the lower ramp tip which quickly joined the basal thrust flat while folding continued beyond the upper tip the development of the analogue model thrust fault related folds by progressive changes in kinematics from decollement folding to thrust tip folding and finally thrust ramp folding compares well with analyses of naturally occurring thrust fault related folds

the vertebrate bearing late triassic fleming fjord formation of central east greenland revisited stratigraphy palaeoclimate and new palaeontological data

simulated weathering of dinosaur tracks and the implications for their characterization digital models of the tracks of bipedal theropod and ornithopod dinosaurs and the quadrupedal tracks of a sauropod were computationally eroded to investigate the effects of erosion on the shapes sizes and diagnostic details of fossil tracks narrow and or angular details such as claw marks interdigital ridges and internal ridges are removed early in erosion creating the potential for misidentification of eroded theropod tracks as those of ornithopods however with the erosion models presented here all tracks retain their basic shapes as indicated by the relative constancy of their interdigital angles and by the relative constancy of their footlength footwidth ratios surface lengths of tracks did not increase significantly with erosion so that dinosaurian hip height and speed estimates derived from trackways would not be greatly in error if based on eroded surface tracks synthetic undertracks from the surface tracks were also produced using information from published physical models of trac

application of neoichnological studies to behavioural and taphonomic interpretation of fossil bird like tracks from lacustrine settings the late triassic early jurassic santo domingo formation argentina abstract the purpose of this study is to apply neoichnological observations to the behavioural and taphonomic interpretation of a late triassic early jurassic track surface from the santo domingo formation argentina containing hundreds of bird like tracks and trackways in addition the factors affecting the formation and preservation of bird tracks in lacustrine settings are particularly addressed the 5 5 m2 fossil track surface contains different types of trace fossils the avian ichnotaxa gruipeda dominguensis the most abundant bird like tracks with elongated hallux impressions small epichnial rounded pits and invertebrate traces skolithos taenidium the modern environmental analogue chosen for the neoichnological studies was a coastal freshwater pond the bajo de los huesos chubut argentina seasonally occupied by sandpipers calidris bairdii and calidris fuscicollis charadriiformes the comparison between the fossil succession and the modern example suggests that they share lithology and sedimentary structures and that sedimentary processes and local palaeoenvironment were fairly similar and do not bias ichnological comparisons field observations allowed to distinguish twenty one behaviours that produced distinct traces and four modern footprint types 1 to 4 related to specific substrate conditions in particular the preferential formation of bird tracks parallel to the waterline also confirmed by studies on droppings and invertebrate fauna of the pond and other associated sedimentary features ripple marks wrinkle marks mud drape thickness and trace fossils were important for recognition of the shoreline in the fossil example these observations also allowed us to distinguish the adjacent deeper and shallower parts of the fossil pond and can be applicable to other similar case studies contrasting sediment properties and footprint types some relationships and constraints on the formation and preservation of modern footprints are proposed although these are very complex processes that will require further studies five of the behaviours recognised in the modern pond were inferred from the sixteen trackways distinguished on the fossil track surface including walking walking with a zig zag path short runs probing and landing with legs directed forward possible trace of flight the recognition of traces of flight volichnia probing marks and tracks showing morphology similar to modern shorebirds g dominguensis strongly suggest an avian affinity for the producers of the fossil tracks and in consequence the santo domingo track site would be younger than supposed

preorogenic folds and syn orogenic basement tilts in an inverted hyperextended margin the northern pyrenees case study the chainons bearnais cb north pyrenean zone resulted from the cenozoic contractional reactivation of the salt tectonics bearing hyperextended margin that initiated at the europe iberia transition during the early cretaceous in this tectonic scenario assessing the relative contribution of extension and contraction to the present day structure is crucial to reconstruct the hyperextended margin geometry and to quantify the subsequent shortening this study undertakes this issue by defining the relationship between folding and two bedding independent references peak temperature isotherms and paleomagnetic data isotherms were reconstructed from 76 new measurements of raman spectroscopy on carbonaceous materials rscm and indicate temperatures at the time of peak metamorphism in the cb 110 85 ma end of extension they are shallowly to moderately northwards dipping and cut across most of the folds deforming the mesozoic units paleomagnetic data from 29 sites evidence a widespread remagnetization carried by pyrrhotite that was probably blocked during the early paleogene before the onset of continental collision and postdated folding in the cb abnormal inclinations in this remagnetization suggest syn collision tilts up to 60 to the north in the back limb of the axial zone based on the presented data set we propose that the folding of the cover above the evaporitic decollement was almost fully completed by the end of the cretaceous extension with 85 100 of the dip of fold limbs being acquired before the remagnetization time cenozoic contraction reactivated the extensional faults in the shallow basement as top to the s thrusts leading to the passive transport and northwards tilting of the folded cover

downward remagnetization of a 74 m thick zone in lake sediments from palaeo lake idaho nw united states locating the gauss matuyama geomagnetic boundary within a dual polarity zone

taphonomic controls on animal tracks at saline alkaline lake bogoria kenya rift valley impact of salt efflorescence and clay mineralogy abstract the morphologies of subaerial vertebrate tracks and invertebrate traces in surficial sediments can be used in paleoenvironmental reconstructions by providing details about the initial substrate conditions e g water content and any changes experienced during trace preservation a qualitative field study was undertaken to identify the factors affecting track taphonomy in saline lake margin environments supported by experiments to isolate selected factors that modify track morphology and substrate characteristics flamingo tracks ubiquitous around saline alkaline lake bogoria in the kenya rift were the focus of field study although other vertebrate tracks and surficial invertebrate trails and tunnels were also considered a complex and interacting set of environmental factors were identified such as the effect of lake level fluctuations on substrate grain size and capillary evaporation several factors affect the early taphonomic modification destruction stabilization and or cementation of tracks and their associated substrates the laboratory experiments tested the effects of pore water salinity clay mineralogy e g swelling or non swelling clays drying method e g solar radiation or wind and wetting and drying cycles on tracks these data were supported by statistical analyses of impression depth and planimetric area the results show that track morphology in smectitic substrates is altered rapidly by wetting and drying particularly if the substrates contain saline pore waters but morphology is less affected in non swelling clays the degree of morphologic alteration and or resistance to wetting and drying varies with the rate of substrate drying and the type of the resulting salt efflorescence e g interstitial vs surficial crust these short term process related taphonomic effects help to explain the morphologic variants of tracks in lake marginal settings and provide insights into the preserved distribution patterns of subaerial ichnofossil assemblages

use of low cost multistripe laser triangulation mlt scanning technology for three dimensional quantitative paleoichnological and neoichnological studies abstract the purpose of this paper is to test the application of a new low cost 2995 00 us multistripe laser triangulation mlt scanner and three dimensional 3d software for semiquantitative and quantitative analyses of ichnofossils and modern traces the goal of this research is to improve on existing analytical techniques and apply new methods to 3d digital models of ichnofossils and modern traces objectives are to 1 provide researchers with new ways to develop and test hypotheses quantitatively in the fields of paleoichnology neoichnology sedimentology and soil science and 2 discuss uses advantages and limitations of mlt technology related to ichnology we scanned and created digital models of a variety of mostly continental ichnofossils and modern terrestrial traces produced by invertebrates and vertebrates visual methods applied include making uniformly colored specimen surfaces stereo pairs anaglyph stereo images animations and cross sections quantitative methods applied include measuring distances tortuosity indices and angles and producing contour maps of tracks two of the most useful properties measurable from digital models are surface area sa and volume v these are used rarely in ichnology because they are difficult to measure with traditional methods we use sa to calculate area exploited and introduce a method of quantifying surface roughness adapted from research on soil surfaces we measure v of burrows tracks and coprolites as well as introduce a new measure termed volume exploited we hypothesize that different tracemakers make burrows with characteristic v to sa ratios this is partially supported by statistical tests of previously published data we also use v to sa ratios to determine relative compactness a metric adapted from building physics digital models ensure perpetuity of specimens because they preserve 3d data that can be used to make physical copies placed in museums and disseminated easily to researchers and educational institutions of all levels data from digital models can be used to interpret ichnocoenoses bioturbation rates and pedogenic properties and processes in soils and paleosols note that mlt scanning digitizes only surfaces of objects so it is best suited for exogenic traces and casts of endogenic traces

defining the morphological quality of fossil footprints problems and principles of preservation in tetrapod ichnology with examples from the palaeozoic to the present abstract the morphology of fossil footprints is the basis of vertebrate footprint ichnology however the processes acting during and after trace fossil registration which are responsible for the final morphology have never been precisely defined resulting in a dearth of nomenclature therefore we discuss the concepts of ichnotaphonomy ichnostratinomy taphonomy biostratinomy registration and diagenesis and describe the processes acting on footprint morphology in order to evaluate the morphological quality of tetrapod footprints we introduce the concept of morphological preservation which is related to the morphological quality of footprints m preservation acronym mp and distinguish it from physical preservation p preservation acronym pp which characterizes whether or not a track is eliminated by taphonomic and diagenetic processes m preservation includes all the morphological features produced during and after track registration prior to its study and may be divided into substages ichnostratinomic registrational taphonomic stratinomic diagenetic moreover we propose an updated numerical preservation scale for m preservation it ranges from 0 0 worst preservation to 3 0 best preservation intermediate values may be used and specific features may be indicated by letters in vertebrate footprint ichnotaxonomy we regard the anatomy consistent morphology and to a lesser extent the trackway pattern as the only acceptable ichnotaxobases only footprints showing a good morphological preservation grade 2 0 3 0 are useful in ichnotaxonomy whereas ichnotaxa based on poor morphological preservation grade 0 0 1 5 are considered ichnotaphotaxa nomina dubia characterized by extramorphologies we applied the preservation scale on examples from the palaeozoic to the present time including three ichnotaphotaxa and 18 anatomy consistent ichnotaxa morphotypes attributed to several vertebrate footprint producers results indicate the utility feasibility and suitability of this method for the entire vertebrate footprint record in any lithofacies strongly recommending its use in future ichnotaxonomic studies

three dimensional preservation of foot movements in triassic theropod dinosaurs dinosaur footprints have been used extensively as biostratigraphic markers environmental indicators measures of faunal diversity and evidence of group behaviour1 2 3 4 trackways have also been used to estimate locomotor posture gait and speed6 7 8 9 10 11 but most prints being shallow impressions of a foot s plantar surface provide little evidence of the details of limb excursion here we describe late triassic trackways from east greenland made by theropods walking on substrates of different consistency and sinking to variable depths that preserve three dimensional records of foot movement triassic theropod prints share many features with those of ground dwelling birds but also demonstrate significant functional differences in position of the hallux digit i foot posture and hindlimb excursion

a late spring surge in the open water of the antarctic sea ice pack mean annual cycles of open water area within the antarctic sea ice pack are presented for 1978 87 and 1987 97 compiled using mean daily data a minimum of the open water area occurs in mid february followed by a steady increase until a plateau is established in october before a sudden surge in early november to a peak of 4 5 106 km as this antarctic open water surge aos occurs on timescales of around one month its temporal structure only becomes truly clear when using daily means the aos is shown to be the result of the relative timings of the sea ice area and extent annual cycles it is suggested these reflect the late spring crossing of the antarctic circumpolar trough over the sea ice edge thus shifting the dominant winds ekman forcing from westerly northerly to easterly southerly

significance of thin sets of eolian cross strata abstract thin cosets composed of thick sets of trough cross strata record episodes when ergs were sand saturated and erg buildup exceeded the rate of subsidence and water table rise interdunes were enclosed and dry thin sets with irregular set boundaries accumulated when ergs were unsaturated as at white sands dune field in southern new mexico interdunes were flat extensive and moist thin lenses of cross strata with irregular upper surfaces are the erosional remnants of lowermost portions of dunes that were within the zone of capillary rise thin flat bedded to massive interdune deposits were also preserved in this setting due to low sand supply upbuilding of the erg surface was limited to the rate of subsidence water table rise like sediments deposited in shallow subaqueous settings bu unlike most colian sands bed by bed accumulation of the thin sets was limited by short term accommodation space the allogenic interpretation presented above contrasts strongly with the widely accepted climbing interdune autogenie interpretation of the entrada we question this gradualistic interpretation not only on the basis of stratal relationships between dune and interdune deposits but on theoretical grounds as well to maintain moist wet interdunes when large bedforms are climbing to preserve thick tabular sand bodies deposition must not exceed the rate of groundwater rise we have seen very few irregular erosion surfaces between thick sets of eolian cross strata they are extremely common between thin sets widespread moist interdunes in modern ergs and evidence of high water tables in ancient eolian sequences are signals of low sand supply thin eolian sets with irregular upper b unding surfaces record the birth and demise of ergs as well as the fluctuations of erg margins the absence of animal tracks in the thick jurassic cross strata and their great abundance in and adjacent to the thin sets may be a result of an erg margin origin of the thin sets or of ameliorated climatic conditions during their deposition because they accumulate in zones and episodes of low sand supply cosets composed of thin sets are akin to deflation surfaces in for example the permian cedar mesa sandstone the movement of the groundwater table after the initial deflationary phase slow rise in the jurassic rapid drop in the permian may reflect the higher amplitude of late paleozoie sea level fluctuations