large striated burrows from fluvial deposits of the neogene vinchina formation la rioja argentina a crab origin suggested by neoichnology and sedimentology abstract this study includes three aspects 1 the ichnotaxonomic treatment of large and dominantly vertical burrows ornamented with sharp bioglyphs from the fluvial neogene vinchina and toro negro formations northwest argentina 2 the description and interpretation of the sedimentary facies where these burrows occur and 3 neoichnologic observations on large ornamented burrows from seasonal wetlands of the rio pilcomayo national park argentina as possible modern analogues of the trace fossils and the sedimentary environment a new ichnogenus and ichnospecies capayanichnus vinchinensis is proposed to include the large striated burrows the new ichnotaxon is distinguished by a combination of a predominantly vertical orientation overall l shape when fully developed absence of lining and burrow bifurcation a distinct surface texture and lack of burrow enlargements the hosting sedimentary facies of the vinchina formation can be grouped into fluvial channel and splay floodplain facies associations the rivers of that unit were of two main types single channel rivers with frequent channel avulsion and overbank flow and multichannelised rivers with poorly defined margins at least some of these rivers were ephemeral or with intermittent discharge the climate was probably seasonal and semiarid as suggested by sedimentologic evidence c vinchinensis was dominantly recorded from the top of fluvial channels interpreted as abandoned channels and proximal intermediate and distal splay facies the large ornamented burrows found in an extant comparable example were constructed by freshwater crabs these burrows can be distinguished by the overall architecture the taxonomy and sex of its occupants and the environmental setting where they were found the neoichnologic signatures used in the interpretation of the fossil example include the common oval burrow cross section and the surface texture in particular the surface texture in the modern crab burrows includes abundant comma shaped marks sets of grooves oblique to burrow axis and long segmented grooves the predominantly oval cross section absence of lining and the strongly ornamented burrow surface suggest that c vinchinensis was produced by freshwater crabs the key features of the surface ornament are long sets of three four ridges whose width is in average one third of the burrow major axis other features that also point to a crab origin are a massive filling common burrow ends in a casing mudstone chevron pattern in sets of surface ridges and possible cheliped marks the new ichnotaxon is restricted in the vinchina and toro negro formations to fluvial facies and is absent in shallow lacustrine facies

burrows of a gopher like rodent possibly gregorymys geomyoidea geomyidae entoptychtinae from the early miocene harrison formation nebraska this study describes the architectural and surface morphology of small 5 6 6 7 cm diameter burrows that occur in close proximity to the daemonelix burrows of palaeocastorin beavers in the early miocene upper harrison formation nebraska the small diameter burrows are sinuous and rambling or weakly helical in morphology distinctive paired grooves from rodent incisors measuring 4 1 4 3 mm wide occur on the ceiling and sides of the burrows whereas ridge like claw marks of 4 1 mm width occur low on walls and floors scratched out chamber like areas on the sides of tunnel shafts are covered on all sides with claw marks whereas tooth marks are mostly confined to main tunnel shafts both types of marks are abundant indicating a mixed tooth and claw digging strategy that appears to have evolved in palaeocastorin beavers as well similar digging methods in two unrelated harrison rodents indicates the relative hardness of the volcanic ash rich soils which necessitated digging with teeth in addition to less resistant keratin claws the new ichnotaxon alezichnos trogodont is erected to describe these ichnofossils a possible excavator is gregorymys sp an extinct gopher like entoptychine rodent that occurs in these and correlative miocene units in the great plains the width of gregorymys incisors matches the width of incisor marks on a trogodont these burrows may represent the first recorded evidence of subterranean habitat and digging behavior in an otherwise common fossil rodent the excavator of a trogodont had a different burrow system and possibly different foraging behavior than the contemporaneous beavers providing new evidence for diversity in a subterranean miocene ecosystem

the late pleistocene palaeoclimatic record of north atlantic deep sea sediments revealed by mineral magnetic measurements eight cores of north atlantic deep sea sediment are correlated using simple rapid and non destructive measurements of magnetic susceptibility and isothermal remanence this stratigraphy is demonstrably related to late pleistocene palaeoclimatic variations by comparison with the oxygen isotope and microfossil records of these cores fluctuations in the concentration dependent magnetic properties of the cores largely reflect their lithological composition consisting of climatically modulated cycles of marl glacial horizons and nannofossil chalk interglacial horizons high magnetic concentration characterises glacial horizons which correspond to periods when carbonate productivity was severely restricted and ice rafted detrital inputs were prolific coincident with the migration south of the north atlantic polar front to within 3 of latitude north of the coring site in contrast interglacial horizons are characterised by low magnetic concentration and high carbonate content of the sediment consequent on the retreat of the polar front and the re establishment of coccolith floras in its wake during these periods ratios formed between individual magnetic parameters are independent of magnetic concentration and are thus free of any climatic influences wrought by carbonate oscillations in this study however such ratios exhibit a definite response to palaeoclimatic variations attributable to differences in the composition and grain size of the magnetic mineral assemblage of glacial vis a vis interglacial horizons of the cores these differences in mineral magnetic composition are substantially confirmed by mossbauer effect studies of selected samples representing peak glacial and interglacial horizons of one core such glacial interglacial contrasts in the concentration mineralogy and grain size of the magnetic assemblage most probably result from variations in the source and flux density of detritral inputs induced by changes in climate x ray diffraction studies of the same core indicate that variations in the mineralogy of the detrital fraction of the sediment are consistent with those of the magnetic assemblage together these data point to the conclusion that a subsidiary low latitude possibly aeolian detrital flux supplements high latitude ice rafted input in glacial horizons of the cores the low latitude flux however is also identifiable in interglacial horizons independent evidence suggests that this low latitude aeolian flux may be derived from the sahel region of north africa and transported to the coring site by harmattan winds associated with saharan dust outbreaks

ephemeral fluvial deposits integrated outcrop and simulation studies reveal complexity ephemeral fluvial sandstones form the main reservoirs in many oil and gas fields production histories and development difficulties suggest these deposits are more complex than is commonly supposed in the petroleum industry there is inadequate published information to account for this observation relevant sedimentological literature on such deposits is qualitative and unsuitable for detailed reservoir characterization studies therefore integrated sedimentological petrophysical and fluid flow simulation studies have been conducted on outcrop analogs in the southwestern united states our key objectives were to define flow units and to find areas of sensitivity inherent both in the sediments and in the analytical and statistical procedures used to describe and model s ch systems we report results of integrated studies on the lower jurassic kayenta formation in southeastern utah the kayenta formation is a relatively proximal sand rich succession dominated by channel fill sandstones sedimentological analysis identified eight main genetic units in contrast reservoir simulations based on probe permeameter data collected at outcrop show that six of the main genetic units have uniform flow behavior intraformational mudclast conglomerates are the dominant permeability barriers both because of the clasts themselves and because they act as sites of preferential cementation stochastic permeability models conditioned to the outcrop data produce results little different from models based on averaged values for each facies the most sensitive feature of the mode s concerns the assumptions made about the mudclast conglomerates the model results show that only by integrating analytical approaches can we understand the full character of an outcrop analog in such a way that we can use it predictively

rayleigh fractionation of heavy rare earths and yttrium during metamorphic garnet growth we present laser ablation microprobe inductively coupled mass spectrometry analyses of y yb er dy and gd in garnet crystals from high grade metamorphic and migmatitic rocks from the sierras pampeanas of argentina these rocks contain large garnet porphyroblasts 4 mm that are compositionally zoned rare earth element concentrations in the rims are typically one order of magnitude lower than those in the cores a notable feature of this zonation is the inversion of yb er and yb dy ratios from 1 in the cores to 1 in the rims we show quantitatively that the spatial distribution of these trace elements in garnet can be most simply and effectively explained as arising from rayleigh fractionation during garnet growth we also analyzed a small garnet crystal 2 mm representative of a garnet population that is associated with migmatitic leucosomes this crystal displays uniformly low concentrations of all trace elements that are virtually identical in both absolute and relative magnitudes to those in the rims of the larger garnet porphyroblasts the small crystals and perhaps part of the porphyroblast rims are likely to be peritectic products of incongruent melting reactions we argue that melts formed from garnet bearing sources may generally be unable to equilibrate with metamorphic garnet cores and may thus be more strongly depleted in heavy rare earth elements and y than modeling based on bulk source rock abundances of these elements would indicate

a new method in mineral magnetism for the separation of weak antiferromagnetic signal from a strong ferrimagnetic background 1 this paper describes a new magnetic method for determining the contribution of weakly magnetic hematite against a strongly magnetic e g magnetite background the method involves measurements of mfr a residual or final remanence after hysteretic demagnetization of saturated isothermal remanent magnetization in terms of sensitivity and precision our proposed method is superior to the currently popular approach known as the hirm method compared to the latter mfr has no error amplification caused by subtraction of terms the method utilizes the available software for hysteretic demagnetization function on an automated vibrating sample magnetometer vsm this in turn automatically decreases some of the disturbing effects of the strong magnetic background e g magnetic viscosity initially non zero offset of hirm for partially oxidized magnetite etc

trace fossil suites and composite ichnofabrics from meandering fluvial systems the oligocene lower freshwater molasse of switzerland abstract the oligocene lower freshwater molasse of switzerland is host to spectacular outcrops of fluvial deposits in distal areas of the swiss molasse basin deposits of a north eastward draining meandering system are exposed combined sedimentologic and ichnologic observations in the chli sunnhalde and roggwil quarries allow an improved understanding of animal substrate interactions in deposits of meandering fluvial systems strata include meander belt sandstone levee sandstone and mudstone crevasse channel and splay sandstone floodplain mudstone and sandstone and paleosols while the meander belt and the more proximal crevasse channel deposits are typically unbioturbated the more distal deposits show a clear biogenic overprint with distal crevasse channel crevasse splay and floodplain deposits being intensely bioturbated simple grazing and locomotion trails included in the cochlichnus anguineus helminthoidichnites tenuis suite were formed subaqueously in ponded areas of the floodplain meniscate burrows taenidium isp suite and root trace fossils occur along the margin of these floodplain water bodies and at the top of crevasse splay deposits some of the floodplain crevasse splay and crevasse channel deposits are pervasively bioturbated by crayfish burrows camborygma litonomos suite crevasse splay deposits locally host escape trace fossils where cross cutting relationships are apparent a colonization sequence can be established as follows the cochlichnus anguineus helminthoidichnites tenuis suite is cross cut by the taenidium isp suite which in turn is cross cut by the camborygma litonomos suite and root trace fossils composite ichnofabrics are common in these meandering river deposits recording progressive lowering of the water table in overbank subenvironments frequency of depositional events was a first order control on degree of bioturbation position of the water table and degree of substrate consolidation exerted considerable influence over the types of trace fossils produced distinct bioturbation phases may result in the formation of different trace fossil suites representative of disparate ichnofacies preserved on a single bedding plane this study further supports the notion that meandering fluvial systems are characterized by trace fossil suites belonging to the scoyenia camborygma and or mermia ichnofacies

occurrence of bioglyphs on ocypode crab burrows in a modern sandy beach and its palaeoenvironmental implications abstract the ichnological term bioglyph covers biogenic sculpture on burrow walls bioglyphs in the burrows of ocypodid crabs were studied in a modern unconsolidated sandy substrate looseground on irino coast southwestern japan they are seen exclusively on sides and roof of the burrow and are characteristically seen near the distal end of the burrow moist sandy substrate where sand particles are bound together by surface tension of interstitially suspended water might allow the production of such bioglyphs although bioglyphs are only partially developed in such burrows those interpreted to have formed in semi consolidated substrates firmground are known to be sculptured over the entire burrow surface such difference in the modes of bioglyph occurrence can be used as a criterion to reconstruct the substrate consistency in the rock record

a new proxy for bottom water ventilation in the eastern mediterranean based on diagenetically controlled magnetic properties of sapropel bearing sediments magnetic properties of eastern mediterranean sediments recovered during leg 160 of the ocean drilling program odp provide insight into non steady state diagenetic reactions associated with accumulation and degradation of organic matter in sapropels according to their magnetic properties sapropels can be classified as one of three types that correspond to increasingly anoxic conditions at the time of sapropel formation a combination of magnetic and geochemical data suggests a causal relationship that enables determination of the relative role of bottom water ventilation versus productivity in the resulting diagenetic stage reached for the three types of sapropels it appears that increased productivity is a prerequisite for sapropel formation but once organic matter is available in sufficient amounts variable efficiencies in bottom water ventilation are more important for modulating the diagenetic context in which different types of sapropels formed magnetic properties are more sensitive to variations in bottom water ventilation than to productivity and can be used to establish relative variations in bottom water ventilation both at and after periods of sapropel formation magnetic results and the distribution and type of sapropels at odp site 966 eratosthenes seamount between 2 3 and 4 0 ma suggest that bottom water ventilation was modulated by the orbital eccentricity component with ventilation being restricted during 400 kyr eccentricity maxima and enhanced during eccentricity minima enhanced ventilation during eccentricity minima as indicated by magnetic data is consistent with the occurrence of red intervals at site 966 and at other eastern mediterranean sites drilled during odp leg 160 and also with astronomically modulated variations in caco3 content found in mediterranean land sections this suggests that variations in bottom water ventilation modulated by 400 kyr eccentricity cycles operated at a basin wide scale

using fluvial cyclicity to decipher the interaction of basement and fold thrust belt tectonics in a broken foreland basin vinchina formation miocene northwestern argentina abstract the miocene vinchina formation is made up of more than 5100 meters of siliciclastic sediments deposited mostly in fluvial environments in a broken foreland basin without any connection with the sea during a period of arid to semiarid climatic conditions repetitive changes in fluvial facies allow the subdivision of the formation into seven cyclothems each floored by a subaerial unconformity within sequence changes in fluvial systems determined by the proportion of channel vs floodplain multi story vs single story channels and channel connectedness were controlled by changes in accommodation proximal i e northern and younger sequences show transitions from braided to low sinuosity wandering or high sinuosity meandering fluvial systems whereas more distal sequences southern and older show changes from sand bed dominated to anastomosed systems bounding unconformities and facies stacking patterns are used to define six third order depositional sequences depositional sequences in the vinchina formation are either asymmetrical showing a fining upward trend or nearly symmetrical sand clock type each cyclothem is bounded by an incision surface sequence boundary developed during a base level i e fluvial equilibrium profile fall and initial base level rise floored by basal coarse grained deposits representing the low accommodation systems tract last the overlying sediments fine upward and contain both isolated and multistory sandstone bodies within extensive flood plain deposits corresponding to the early high accommodation systems tract hast this interval is sometimes capped by sheets of amalgamated sandstones corresponding to the late hast and developed during a decline in the rate of base level rise the development and or preservation of the capping amalgamated sandstones and therefore the symmetrical shape of the sequences is favored in high accommodation settings vertical and lateral facies changes recorded in the vinchina formation indicate that both the fold and thrust belt located to the west and an uplifted basement block to the north played important roles controlling subsidence source areas and drainage patterns the stratigraphic record of this broken foreland basin differ from the existing models for simple foreland basins and can be compared to those of the laramide sedimentary basins in the united states

crevasse splays from the rapidly aggrading sand bed braided niobrara river nebraska effect of base level rise base level rise of 2 35 m on the niobrara river has resulted in aggradation of the channel belt and a recent avulsion overbank areas have become flooded by rising groundwaters and more than eight crevasse splays have formed between 1993 and 1997 two crevasse splays situated on the west and east sides of the niobrara have been studied using ground penetrating radar gpr shallow boreholes and topographic surveys the vibracores and gpr profiles provide a nearly three dimensional view of the architecture of crevasse splay deposits the east splay was initiated in the winter of 1993 94 and has expanded to cover an area 200 m by 1000 m with sediment up to 2 5 m thick the west splay which was initiated by the opening of a crevasse channel through a levee in the autumn of 1995 covers an area 150 m by 250 m with up to 1 2 m of sand deposited in a single year the niobrara splays are sand dominated and characterized by bedload deposition within channels 5 30 m wide and 0 5 2 m deep with the development of slipfaces where splays prograde into standing bodies of water sedimentary structures in cores include horizontal lamination ripple lamination and sets of cross stratification there is a slight tendency for splays to coarsen up but individual beds within the splays often fine up the abundance of crevasse splays on the niobrara river contrasts with other braided river floodplains in the niobrara crevasse splay formation followed aggradation within the channel belt which occurred in response to base level rise the link between crevasse splays channel aggradation and base level rise has important implications for the interpretation of ancient braided river and floodplain sequences it is suggested that crevasse splay deposits should be an important component of aggrading fluvial sediments and hence should be preserved within the rock record in this case the aggradation and crevassing have been tied to a rise in base level elevation and it is suggested that similar deposits should be preserved where braided rivers are affected by base level rise for instance during transgression and filling of palaeovalleys

improvements in long core measurement techniques applications in palaeomagnetism and palaeoceanography we report on new developments in the long core measurement techniques using u channels in connection with new small access cryogenic magnetometers with these new instruments u channel samples allow us to measure a wide range of magnetic parameters along entire core length with a spatial resolution and accuracy virtually equivalent to that obtained using discrete cubic samples an additional advantage is that the sediment disturbance when sampling is significantly less when using u channels we present comparisons of results from both continuous and discrete measurements and examine the effectiveness of minimal deconvolution using various techniques examples of continuous measurements of low field susceptibility nrm arm irm hrc from north atlantic deep sea cores show that it is possible to generate logs of combination of parameters related to rock magnetic characteristics of the sediments useful in palaeoceanography in particular the continuous method allows us to rapidly detect core regions with fast changing magnetic parameters useful for correlation between cores and also for understanding changes in palaeo environmental conditions the fast scan also allows us to detect regions of the core where the rock magnetic parameters are suitable or not suitable for palaeomagnetic studies related to changes in the geomagnetic field such as the relative changes in palaeointensity

non tetrapod trace fossils from the middle devonian tetrapod tracksite at zachelmie quarry holy cross mountains poland abstract the middle devonian eifelian dolomites exposed in the zachelmie quarry holy cross mountains southern poland contain the earliest fossil record of tetrapods low diversity but unique assemblages of trace fossils characterize the track bearing interval within the lower complex of the wojciechowice formation the reconstructed environment of the trace fossil rich beds includes ephemeral lakes and or shallow water lagoons separated from an open marine area by sparsely vegetated islands and spits the most abundant non tetrapod trace fossils from these beds are large horizontal to vertical burrows and dish circular to oval shaped shallow depressions the burrows are abundant on the upper surfaces of thick dolomicritic beds especially in some palaeosol levels but they are also associated with tetrapod trackways large semi aquatic or terrestrial animals e g arthropods or vertebrates most likely produced these burrows the circular to oval shaped depressions observed on a large surface and other smaller isolated blocks from the same stratigraphical level are interpreted as fish feeding nesting resting traces piscichnus sanctacrucensis isp nov is proposed as a new ichnospecies of the oval shaped fish trace fossil from the middle devonian of poland a single medium sized undichnia specimen a fish swimming trace is associated with the piscichnus traces the described trace fossils provide new insight into the palaeoecology and taphonomy of the middle devonian tetrapod tracksite from poland and clarify remaining controversies regarding the interpretation of some poorly preserved trace fossils from the zachelmie quarry

multiproxy studies of early miocene pedogenic calcretes in the santa cruz formation of southern patagonia argentina indicate the existence of a temperate warm vegetation adapted to a fluctuating water table abstract the lower miocene santa cruz formation in southern patagonia austral basin argentina contains several horizons of pedogenic calcretes which record 17 5 myr old vegetation adapted to a shallow and fluctuating water table at paleolatitude of 56 s to reconstruct the paleoenvironment paleoclimate and paleoecosystem we performed a multiproxy study of the calcretes examining abiotic and biotic components the calcretes exhibit a variety of morphologies horizontal and vertical rhizoliths laminar structure nodules massive crusts microfabrics beta predominant over alpha microfabrics and 18o and 13c values that fluctuate within each morphotype and throughout the analysed interval microfossils and phytoliths in the host material of the calcretes indicate fluctuating terrestrial freshwater and marine conditions and record an ecosystem dominated by herbaceous plants and arboreal elements in association with a typical coastal santacrucian vertebrate fauna we propose that the calcretes developed in soils in a coastal fluvial setting during pauses in floodplain aggradation that typically lasted between 8 25 ka and 400 ka years variable sedimentation rates in different parts of the coastal fluvial floodplain the fine texture of the host sediment and the influence of a fluctuating water table also influenced the formation of the calcrete a high water table in low relief areas of the floodplain created the conditions necessary to form a horizontally extended rhizolithic system that jointly with the biotic proxy can be correlated with a radicular pattern similar to the arboreal elements from coastal settings abiotic and biotic proxies of the studied interval attest to environmental fluctuations recorded at different scales that took place under temperate warm and subhumid climates with a marked rainfall seasonality with a slight increase in the aridity towards the top of the studied interval under these conditions a subtropical fauna and a c3 dominated ecosystem developed coincident with the onset of the mid miocene climatic optimum in patagonia

evidence against dust mediated control of glacial interglacial changes in atmospheric co2 the low concentration of atmospheric co2 inferred to have been present during glacial periods is thought to have been partly caused by an increased supply of iron bearing dust to the ocean surface1 this is supported by a recent model2 that attributes half of the co2 reduction during past glacial stages to iron stimulated uptake of co2 by phytoplankton in the southern ocean but atmospheric dust fluxes to the southern ocean even in glacial periods are thought to be relatively low and therefore it has been proposed that southern ocean productivity might be influenced by iron deposited elsewhere for example in the northern hemisphere3 4 which is then transported south via ocean circulation similar to the distal supply of iron to the equatorial pacific ocean5 6 7 here we examine the timing of dust fluxes to the north atlantic ocean in relation to climate records from the vostok ice core in antarctica around the time of the penultimate deglaciation about 130 kyr ago two main dust peaks occurred 155 kyr and 130 kyr ago but neither was associated with the co2 rise recorded in the vostok ice core this mismatch together with the low dust flux supplied to the southern ocean suggests that dust mediated iron fertilization of the southern ocean did not significantly influence atmospheric co2 at the termination of the penultimate glaciation

possible burrows of mylagaulids rodentia aplodontoidea mylagaulidae from the late miocene barstovian pawnee creek formation of northeastern colorado abstract the massive siltstone beds of the late miocene barstovian pawnee creek formation in logan county northeastern colorado contain abundant terrestrial vertebrate burrows among these are distinctive claw marked burrows attributable to the extinct mylagaulid rodent pterogaulus mylagaulus laevis korth 2000 these burrows differ in several respects from the spiraling daemonelix burrows of fossorial beavers the pawnee creek burrows are slightly ovate in cross section tubular and sinuous rather than helical they consist of primary tunnels of up to at least 7 m long and range from 11 to 18 cm in diameter they occasionally branch into secondary tunnels burrow walls and terminations show prominent parallel ridges in sets of two to three up to 9 3 mm deep and 3 7 mm wide the burrows are too large to have been made by anything but a vertebrate and their considerable length and complexity implies a mammalian excavator the meandering branching morphology resembles the burrow systems of extant fossorial rodents such as pocket gophers geomys and mole rats spalax myospalax skeletal remains of p laevis are abundant at sites where the burrows occur with at least eight individuals represented by humeri in a collected sample although mylagaulid remains are not unequivocally associated with fossil burrows the curved laterally compressed claws and phalangeal arrangement of mylagaulids produce marks very similar in size and morphology to the ridges on the burrows position and pattern of the ridges indicate downward and backward motions of the mani possibly supplemented by motions of the pedes to kick loosened soil backward a new ichnogenus alezichnos and new ichnospecies chelecharatos are erected to describe these burrows

where is the fossil evidence for gondwanan crayfish abstract crayfish body and ichnofossils recently reported from lower permian and lower triassic strata of antarctica have been reinterpreted to be the body fossils of euthycarcinoid arthropods and the burrows of small to large sized therapsids mammal like reptiles the earliest fossil evidence of crayfish presence and activity in continental deposits is still from the laurasian continents of pangea this evidence is in the form of body fossils and burrows from the upper triassic and burrows from the lower permian of the american southwest for that matter nearly all ichno and body fossils have been described from laurasian rocks with the exception of the occurrence of an isolated claw of a parastacid crayfish from paleogene deposits in queensland australia where is all the fossil evidence for gondwanan crayfish there is a rich extant diversity of parastacid crayfish in australia and they are dispersed between other gondwanan continents with the exception of africa and antarctica paleontological and ichnological evidence when taken into consideration with paleogeographic reconstructions indicates that they originated early during or slightly after the formation of pangea thus at the very least there should be trace and body fossil evidence in australia indicating the long evolutionary history of the parastacids evidence for ancient gondwanan crayfish in terrestrial and freshwater ecosystems should occur in rocks of similar ages to those in north america where ichno and body fossils have been identified

the earliest known spongeliomorpha from the lower devonian of the northwestern yangtze platform south china abstract crustacean trace fossils provide invaluable information to paleobilogical environmental and ecological interpretations in the earth history here we report an unusually large segments up to 58 mm across three dimensional burrow system from the lower devonian pingyipu formation which was deposited in a nearshore setting on the northwestern yangtze platform south china the burrow system is dominated by horizontally developed networks probably with vertical shafts connecting to the sediment water interface the burrow surfaces show no signs of lining but are characterized by scratches including ridges and bundles of ear shaped striae implying an assignation to spongeliomorpha aff s chevronensis muniz and mayoral 2001 the overall morphological and taphonomic features suggest permanent open burrows produced in a substrate with considerable firmness further investigation indicates that the burrow system may have been constructed by a colony of large unknown crustacean with thoracic appendages decorated with acute seta or denticulations they generally served a combined purpose of dwelling and perhaps feeding on microbial growth accumulating on the tunnel margins these burrows represent the earliest known three dimensional burrow systems constructed by a crustacean that may be comparable to their modern analogues in both morphological and functional aspects the unusually large size of the burrows may have been favored by a higher atmospheric oxygen level during the early devonian

paleobiology and paleoecology of an arid semiarid miocene south american ichnofauna in anastomosed fluvial deposits abstract miocene deposits of the toro negro formation in la rioja province argentina host a rich vertebrate and invertebrate ichnofauna trace fossils are recorded from the lower part of the lower member of the toro negro formation at quebrada de la troya this succession consists of sandstone intraformational breccia mudstone and few conglomerate deposited in sandy anastomosing fluvial systems developed under a semi arid climate the invertebrate ichnofauna is composed of meniscate trace fossils taenidium barretti scoyenia gracilis dwelling structures palaeophycus tubularis and grazing trails helminthopsis hieroglyphica the vertebrate ichnofauna includes avian fuscinapeda sirin incumbent footprint slender anisodactyl footprint and mammalian footprints macrauchenichnus rector cf venatoripes riojanus small heteropod footprint kidney like footprints and oval impressions tetrapod footprints and rare palaeophycus and helminthopsis are preserved on the top of exposed sandbars crevasse splay deposits preserve abundant meniscate trace fossils and dwelling tubes e g taenidium scoyenia and palaeophycus ascribed to the scoyenia ichnofacies two suites of invertebrate trace fossils can be differentiated meniscate backfill structures t barretti and other burrows p tubularis without ornamentation developed in a soft substrate and striated traces s gracilis that crosscut the former developed in a firmer substrate the toro negro depositional system displays a high preservation potential for tracks due to seasonal flooding events which rapidly buried the footprints the favorable preservational conditions and good exposure of the track bearing surface enable us to interpret the track assemblage of the toro negro formation as a sample of the original tetrapod fauna that inhabited that region at central western argentina during the miocene the identification of possible trackmakers is utilized in this work as a useful tool that contributes to our understanding of the ancient environment the paleoichnocommunity is characterized by the number of trackmakers and the relative abundance of each type of footprints a new method to measure footprint abundance is proposed the relative bioturbed area rba this measurement provides numerical characterization of the degree of bioturbation of the whole tracking surface caused by each ichnotaxa the tetrapod fauna indicated by the footprint record was compared with the body fossil record of the toro negro formation these records overlap in some ways and in other ways they are complementary the presence of large and medium to small ground sloth proterotheriid litopterns caviid rodents and birds is pointed out by both body fossils and ichnofossils body fossils include remains attributed to dasypodids glyptodontids and abrocomid rodents ichnofossils indicate the presence of macraucheniid litopterns and three types of birds shorebirds perching birds and large cursorial birds

crayfish burrows from late jurassic late cretaceous continental deposits of patagonia argentina their palaeoecological palaeoclimatic and palaeobiogeographical significance abstract the trace fossil loloichnus baqueroensis igen and isp nov from late jurassic late cretaceous continental deposits of patagonia argentina includes thickly lined mostly passively filled and y branched burrows other important features of this ichnofossil are the inner surface texture of lining showing transversal elongated and adjacent grooves and less commonly the pelletal filling of burrows l baqueroensis is recorded from the bajo grande bajo tigre punta del barco and laguna palacios formations which were deposited in different volcaniclastic environments of the deseado massif and san jorge basin geological provinces respectively the described burrows are found in many levels of palaeosols developed in reworked piroclastic deposits where they are the main component of the ichnofabrics in association with meniscate and thinly lined burrows and a diffuse and complex boxwork of small diameter burrows root traces are also present and in many cases occur inside l baqueroensis considering general morphology surface texture filling types palaeoenvironments in which they occur and comparisons with extant and fossil decapod burrows the likely trace makers of l baqueroensis were crayfishes decapoda astacidea probably parastacidae the producers of l baqueroensis inhabited soils where their burrows probably reached the water table and contained roots that were used for feeding considering climatic preferences of extant parastacids it is proposed a temperate climate for central patagonia during the deposition of the studied units the widespread presence of crayfishes during late jurassic late cretaceous times in central patagonia supports the monophyletic origin of this group during the triassic and suggests that the present restricted geographic distribution in southern south america is a relict of a broader one

palaeonvironmental and palaeoecological significance of flamingo like footprints in shallow lacustrine rocks an example from the oligocene miocene vinchina formation argentina abstract this article describes the lacustrine trace fossil assemblage of the late oligocene early miocene vinchina formation of northwest argentina the thick 5000 m continental succession of the formation is essentially fluvial with thin aeolian and lacustrine intervals the trace fossil assemblage from the lacustrine facies is dominated by bird footprints notably flamingo like palmate bird footprints and also contains invertebrate traces the assemblage is of contrasting composition with those of the ubiquitous fluvial facies of the vinchina formation we identify the possible trace maker of the web footed bird footprints and infer the palaeoenvironmental and palaeoecological meaning of the lacustrine trace fossil assemblage of the vinchina formation the lacustrine succession is mainly composed of wave rippled fine grained sandstones and siltstones and wave rippled heterolithic facies with subordinate laminated mudstone and medium grained sandstone with parallel lamination or cross bedding metre scale shallowing upward cycles are typical and desiccation cracks were observed in a single bedding plane the analysed interval was deposited in a wave dominated littoral zone of a shallow permanent lake basin ichnofossils were found mostly in three trampled horizons of the upper part of the analysed succession the trace fossil assemblage is dominated by phoenicopterichnum isp flamingo like footprints slender bird tracks without web traces and triangular and fusiform hypichnial ridges interpreted as bird undertracks the remaining trace fossils are lockeia siliquaria bivalve resting trace rusophycus isp shallow arthropod burrow taenidium barretti endostratal meniscate burrow and small hypichnial double knobs possible beak probing marks neoichnological observations on modern chilean flamingo footprints phoenicopterus chilensis suggest that phoenicopterichnum isp is morphologically akin to modern flamingo footprints although its average size is slightly smaller the likely producers of the fossil footprints are members of the palaelodidae and phoenicopteridae which are recorded in south america since the late oligocene phoenicopterichnum isp appears in cuasi parallel trackways with short pace length and forming a low angle with ripple crests by comparison with observations of modern flamingo behaviour during this study and of shorebird studies from the literature these tracks and trackways likely reflect flock feeding behaviour probably filter feeding in a subaqueous belt parallel to the waterline invertebrate ichnofossils that appear on the same slabs from trampled horizons are mainly triangular and fusiform hypichnial ridges while phoenicopterichnum isp and sparse small hypichnial double knobs also occur in consequence it is possible that these birds were foraging on small invertebrates represented by lockeia siliquaria rusophycus isp and probably taenidium barretti in the coast of the vinchina lake the only fossil evidence for these invertebrates is the impression of articulated valves probably belonging to a small mollusc potential producer of lockeia trace fossil assemblages dominated by flamingo like footprints including ichnogenera phoenicopterichnum culcitapeda and similar unnamed tracks are indicative of alkaline and or saline waters as suggested by the specialised filter feeding mechanism of late oligocene to modern phoenicopteriformes these particular assemblages are distinguished as a subset within the shorebird ichnofacies with a definite palaeoenvironmental and palaeoecological meaning the phoenicopterichnum ichnosubfacies

amphibian burrows and ephemeral ponds of the lower permian speiser shale kansas evidence for seasonality in the midcontinent abstract burrows attributed to the lysorophid brachydectes elongatus occur within a green mudstone lens in the lower permian wolfcampian speiser shale council grove group of eastern kansas the burrow bearing unit consists of a 100 m long lens of massive calcareous silty mudstone with a maximum thickness of 35 cm the lens also contains the fossils of fish amphibians reptiles charophytes stomachara and ostracodes carbonita the mudstone lens pinches out laterally into red pedogenically modified mudstone the burrows occur in three layers at the top of each layer is a subaerial exposure surface indicated by rhizoliths mudcracks and coarse grained lags the mudstone lens is interpreted as the deposit of a shallow ephemeral pond the burrows occur in three vertically and temporally separated clusters with concentrations up to 20 m2 the burrows show two types of architecture type i burrows are elongate elliptical tubes 4 32 cm long and 2 7 cm in width type ii burrows are short elliptical tubes 1 5 3 5 cm in length and 2 5 5 cm in width the burrow fill consists of a mudstone capped by sandy siltstone each burrow layer contains a varying number of articulated and disarticulated lysorophid skeletons within the burrows and surrounding matrix while similar to permian lungfish burrows the architecture and surficial morphology of the lysorophid burrows permits their distinction even in the absence of body fossils the occurrence of burrow layers capped by subaerial exposure surfaces and separated by layers of non burrowed massive mudstone indicates that burrowing occurred in response to episodic perhaps seasonal droughts on the permian coastal plain the lysorophid burrowing behavior is analogous to that of the extant amphibians amphiuma sp and siren intermedia which inhabit rivers and ponds in the southeastern usa

environmental magnetism past present and future environmental magnetism involves the application of rock and mineral magnetic techniques to situations in which the transport deposition or transformation of magnetic grains is influenced by environmental processes in the atmosphere hydrosphere and lithosphere the first explicit description of environmental magnetism as a distinct field was in 1980 since that time environmental magnetism has become a broad field that is finding application in an ever increasing array of scientific disciplines in this review of the present state of environmental magnetic studies we divide the field into three broad but arbitrary categories the first involves the use of mineral magnetic assemblages in the geological record to study physical processes in depositional environments this category includes the correlation of sediment cores using magnetic susceptibility measurements studies of geomagnetic field behavior the analysis of depositional and postdepositional mechanical processes that affect sediments and the examination of magnetic parameters that might represent proxies for paleoclimatic variation the second category encompasses studies of the processes responsible for variations in the magnetic minerals brought into a sedimentary environment these provenance investigations include studies of changes in catchment derived sediment in lakes fluctuations in contributions from terrigenous aeolian and glaciogenic components in deep sea sediments and the origin of atmospheric particulates the final category addresses in situ changes and transformations of magnetic minerals in sedimentary environments including pedogenesis authigenetic diagenetic formation of ferrimagnetic phases dissolution of magnetic minerals due to reductive diagenesis and contributions of biomagnetism to sedimentary magnetism because environmental magnetism can address problems in so many disciplines and because many of these problems may be inaccessible to other techniques it is likely that the scope of environmental magnetism will continue to expand rapidly environmental magnetism is capable of providing important data for studies of global environmental change climatic processes and the impact of humans on the environment all of which are major research initiatives in the international scientific community these factors suggest that environmental magnetism has a bright and diverse future

helical burrow casts of therapsid origin from the beaufort group permian of south africa abstract large helical burrow casts of vertebrate origin have been discovered at several localities in the lowermost strata of the teekloof formation of the beaufort group permian in the southwestern karoo basin south africa they are not only the oldest but also the first vertebrate burrows of helical geometry to be found in rocks of pre mammalian age the burrow casts are vertically disposed spiralling tubes filled with fine grained sandstone or siltstone often with a calcareous cement tube diameters gradually increase from 60 mm in the upper entrance decline through two non contacting dextral coils to about 160 mm at the base of the spiral whereupon the tube straightens and widens into a horizontal terminal chamber burrow depths range from 0 5 0 75 m and the ramp angle ranges from 10 to 32 although within any single spiral it is constant articulated skeletons of the small dicynodont diictodon have been found within the terminal chambers and spirals of three sand filled burrows linear ridges preserved on the outer walls and floor of some of the terminal chambers resemble scratch marks possibly made by the claws and beak of diictodon during burrow excavation the sedimentary sequences at two separate localities are interpreted as having been deposited by episodic sheet floods and distributary splay fans in the proximal floodbasin areas flanking an aggrading meanderbelt rise comparison is drawn between helical burrow casts in the lower beaufort and other recorded occurrences in particular daimonelix a beaver burrow from the miocene of nebraska fundamental similarities far outweigh differences to the extent that the beaufort helical burrows may be grouped with the daimonelices it is concluded that the excavation of large helical burrows an activity usually attributed to rodents was pre empted by mammal like reptiles some 50 million years before the first anatomical mammals evolved

recognition of the sedimentary architecture of dryland anabranching anastomosing rivers abstract the application of rigorous criteria for identifying fluvial style from sedimentary deposits is crucial if environmental reconstructions from stratigraphy are to be reliable from modern observations it appears that anabranching anastomosing rivers can be divided into separate humid and dryland classes each class has dissimilar characteristics to the other necessitating different criteria for their recognition in the rock record the criteria being used by sedimentologists to recognize deposits of anabranching rivers are derived solely from modern examples in humid regions heavily biased to a few specific cases in canada these criteria are dominated by the concept of ribbon sandstone bodies encased in fine grained floodplain sediment with an overall low sand to mud ratio in the succession there has been a general failure to appreciate that dryland anabranching rivers have characteristics significantly different from these and almost certainly leave a sedimentary record quite dissimilar to that previously expected avulsion or obtrusion the gradual formation of an alternative channel are the characteristic dynamic of anabranching rivers forming and maintaining coexisting multiple anabranch channels avulsion or obtrusion require stream banks to have a high resistance to erosion usually achieved by cohesive bank sediments or the reinforcement of banks by vegetative root mats in some drylands riparian vegetation can be sparse and bank resistance may depend in large part on a high clay content here channel fills are mud dominated and floodplains have a uniform fine grained character which is usually structureless because of intense pedoturbation and some bioturbation the evidence from such present day dryland anabranching rivers suggests that their sedimentary record is likely to be one of laterally extensive mud rich beds with weak or enigmatic fluvial indicators elsewhere dryland anabranching systems are sand dominated their banks reinforced with riparian gallery forests sustained by infrequent flow and a shallow water table though the stratigraphy of these has barely been investigated they are clearly different from humid region anabranching systems for their channels and islands are predominantly sandy anabranching rivers with prominent channel sandbodies separated by muddy islands have never been described from contemporary drylands the interpretation of a dryland origin for ancient stratigraphic successions with this form is made therefore without evidence that they can actually exist in the light of this such interpretations should be reevaluated

neogene deformation of the flat subduction segment of the argentine chilean andes magnetostratigraphic constraints from las juntas la rioja province argentina substantial neogene deformation occurred in the part of the andes mountains and the sierras pampeanas that overlie a subhorizontal segment of the subducting nazca plate in northern argentina the history of the volcanic arc suggests that the nazca plate attained the present low angle inclination between about 17 and 10 ma with the region underlain by the flat nazca plate widening eastward thereafter we compare the history of deformation provided by magnetostratigraphy of miocene strata in foreland and intermontane basins to the history of the subducting plate at las juntas in the precordillera thin skinned thrust belt 4 780 m of neogene nonmarine strata record the initiation and termination of sedimentation in a segment of a foreland basin magnetostratigraphic data complemented by fission track dating of an interbedded tuff indicate that the strata span from 18 to 9 ma the earliest strata correlate to the end of a time of volcanic activity in the magmatic arc and the beginning of reverse faulting in the frontal cordillera subsequently the deformation front migrated eastward generating the precordillera thrust belt and finally the sierras pampeanas basement uplifts the rate of strata accumulation varied systematically as new uplifts arose with a maximum rate exceeding 1 0 mm a between 15 and 12 ma a correlation between the deformational history and the geometric history of the subducted slab suggests that thrusting migrated eastward as the angle of subduction shallowed although large scale factors affecting the plate margin beyond the flat slab segment may have partly induced the compressional deformation this correlation suggests that processes related to flat subduction are of importance in deforming the continental plate

lungfish burrows in the upper triassic chinle and dolores formations colorado plateau abstract vertical to inclined cylindrical trace fossils that occur in the upper triassic chinle and dolores formations on the colorado plateau are interpreted to be the casts of lungfish burrows the casts which are as much as 11 cm in diameter and as much as 1 6 m long were formed by passive silicilastic and carbonate sedimentation into apparently abandoned lungfish burrows locally the burrow fillings are overwhelmingly abundant and many intersect and have destroyed former burrow fillings superposition of bioturbation episodes has obliterated most primary sedimentary structures this bioturbation has contributed to the mottled coloration and the knobby weathering texture of the rocks the burrow fillings occur ubiquitously in three lithofacies comprising 1 purple and white mottled ilicified sandstone and siltstone 2 red and brown siltstone and mudstone and 3 pink and green limestone these strata were deposited in a continental environment that included fluvial channels and floodplains sand sheets and playa mudflats and lacustrine basins marshes and deltas the identification of the trace fossils as the positive casts of lungfish burrows is based on their morphologic similarity to previously identified lungfish burrows and to available hand specimens the widespread occurrence of the lungfish burrows in the chinle and dolores formations attests to the extensive habitat that supported lungfish in the late triassic and to conditions favorable for burrow preservation analogy with the environments that support modern lungfish populations suggests that the late triassic climate in the study area provided sufficient moisture to support large populations of lungfish and that this climate was probably punctuated by seasonally dry periods

what do the hirm and s ratio really measure in environmental magnetism the hard isothermal remanent magnetization hirm and the s ratio are widely used in environmental magnetism to quantify the absolute and relative concentrations respectively of antiferromagnetic minerals hematite and goethite in mineral mixtures we demonstrate that synthetic al substituted hematite and goethite exhibit a wide range of coercivities which significantly influences the hirm and s ratio these parameters are therefore not necessarily straightforward indicators of the absolute and relative concentrations of hematite goethite to circumvent this problem we propose a new parameter the l ratio which is the ratio of two remanences after alternating field af demagnetization of an irm imparted in a 1 t field with a peak af of 100 mt and 300 mt irmaf 300mt irmaf 100mt these parameters are easily measured using modern vibrating sample or alternating gradient magnetometers changes in hirm only reflect changes in the absolute concentration of hematite and or goethite if the l ratio is relatively constant conversely l ratio fluctuations indicate variable coercivities that possibly reflect changes in the source of hematite goethite corresponding hirm and s ratio variations should be interpreted with caution in such cases the l ratio can be determined using equivalent terms depending on available instrumentation and measurement protocols for example the hirm is equivalent to irmaf 300mt likewise 0 5 sirm irm 100mt where irm 100mt represents the remanent magnetization obtained by first saturating the sample in a high field and then applying a back field of 100 mt is equivalent to irmaf 100mt the hirm 0 5 sirm irm 100mt ratio is therefore a suitable substitute for the l ratio when measurements are made with a long core magnetometer the newly proposed l ratio is straightforward to measure on a wide range of instruments and can provide significant new insights and reduce ambiguities associated with interpretation of two widely used parameters in environmental magnetism the hirm and s ratio

lungfish burrows in the upper triassic chinle and dolores formations colorado plateau comments on the recognition criteria of fossil lungfish burrows discussion and reply

paleoenvironmental analysis of the neotropical fossil mammal site of cerdas bolivia middle miocene based on ichnofossils and paleopedology abstract the early middle miocene langhian age site of cerdas in the southern bolivian altiplano has produced a diverse fauna of extinct mammals 15 species in seven orders and 11 families in this study we use paleosols and ichnofossils to reconstruct its paleoenvironment and the conditions in which its fossils were preserved the described paleosols represent three pedotypes and three distinct landscape surfaces in an alluvial system type 1 paleosols are interpreted as haplusteps inceptisols that formed on a proximal floodplain in a subhumid to humid patchy shrubland with seasonal variation in precipitation and associated changes in soil moisture conditions landscape 1 type 2 paleosols are interpreted as dystrudepts that formed on a well vegetated distal floodplain in a seasonal humid climate with ground covering shrubland vegetation landscape 2 type 3 paleosols are interpreted as calciustolls mollisols that formed in a shifting alluvial environment in a seasonal sub humid to semi arid open environment landscape 3 ichnofossil assemblages of cerdas include skolithos planolites macanopsis parowanichnus rhizohaloes and rhizotubules these were produced by detritivorous herbivorous and faunivorous soil arthropods as well as plant roots and represent soil communities not normally preserved as body fossils that were living within a heterogeneous alluvial environment the physical and geochemical properties of the paleosols and associated ichnofossil assemblages indicate that the paleolandscapes were composed of shrublands and open environments that experienced changes in moisture regimes due to seasonal precipitation and flooding events and had varying degrees of temporal stability our analysis is the first detailed study of pre pleistocene cenozoic paleosols and trace fossils from the southern tropics mid latitudes of south america and one of the few focused on important fossil mammal bearing sediments

sedimentology and architecture of the douglas creek terminal splay lake eyre central australia douglas creek terminal splay sited on the western shoreline of lake eyre north central australia covers a surface area of approximately 4 km2 with a down system length of 2 5 km from the distributary channels terminus to the splay fringe two distributary channels feed two sediment lobes which have amalgamated to form the terminal splay three primary facies associations have been identified sub dividing the creek terminus into distributary channel proximal and distal splay sections proximal splay sediments are characterized by erosionally based relatively thick 100 mm stacked sheets of coarse to medium sand which commonly display trough and planar cross bedding whereas the distal splay is characterized by thin generally 50 mm massive beds of very fine sand silt and clay the change in splay sedimentology is interpreted as reflecting the transition from bedload dominated deposition to suspended load dominated deposition from decelerating sheetfloods as they spread out from the channel onto the dry lake bed a proximal to distal splay transition zone is also noted where deposits of both facies associations interfinger laterally and vertically in scale geometry and facies associations the douglas creek terminal splay is very different to the often cited neales terminal splay complex located 70 km to the north it is suggested that these architectural differences reflect variations in discharge volume input sediment distribution and the degree of vegetation cover understanding the variation in terminal splay architecture has very significant implications for the modelling of analogous subsurface petroleum systems which at present relies on few modern day analogues