geology and tectonics of the betic zone se spain abstract the southern margin of the iberian continent comprises a complex geological history which can be traced back into the proterozoic when a gneissic basement was formed a cover of nevado filabride rocks was deposited onto this proterozoic basement during the palaeozoic the permian intrusion of the bedar granite suggests that the palaeozoic sedimentary rocks now exposed in the betic cordilleras have been affected by the hercynian orogeny similar to that of palaeozoic rocks in the adjoining ossa morena zone the hercynian basement was probably covered by alpujarride carbonates in the mesozoic when rifting opened tethys and intruded 140 ma old basic dyke swarms the palaeozoic basement of the betic cordilleras comprises a suture of late cretaceous subduction 80 85 ma b p this can be inferred from hp lt metamorphic facies obducted in coeval thrust slices of nevado filabride rocks the nevado filabride nappes include mesozoic carbonates transformed into marbles macael the suture was probably annnealed after the closure of tethys the mesozoic boundary between africa and europe and the rifting in tethys ceased during the palaeogene when the atlas mountains were formed 36 ma b p subsequently relative movements between africa and europe in the neogene were accommodated by strike slip faults these define the iberian microplate moving eastward by atlantic spreading and possibly subducting under italy neogene deformation of iberia is most intensive in southeastern spain due to emplacement of a mantle diapir under the alboran area this occurred early in the neogene aquitanian and caused nappe spreading involving alpujarride and malaguide rocks the subsequent neogene history has now been studied in great detail and is reviewed here it involves clear examples of calc alkaline volcanism most probably not related to subduction seismic motion along strike slip faults within the iberian microplate and syntectonic deposition in intermontane neogene basins

rupture characteristics of the deep bolivian earthquake of 9 june 1994 and the mechanism of deep focus earthquakes the m w 8 3 deep 636 kilometers bolivian earthquake of 9 june 1994 was the largest deep focus earthquake ever recorded seismic data from permanent stations plus portable instruments in south america show that rupture occurred on a horizontal plane and extended at least 30 by 50 kilometers rupture proceeded at 1 to 3 kilometers per second along the down dip azimuth of the slab and penetrated through more than a third of the slab thickness this extent is more than three times that expected for a metastable wedge of olivine at the core of the slab and thus appears to be incompatible with an origin by transformational faulting these large events may instead represent slip on preserved zones of weakness established in oceanic lithosphere at the earth s surface

first report of oligocene vertebrate footprints from iran mammalian and avian footprints documented from the oligocene of the khaf area northeastern iran represent the first reported oligocene vertebrates in the country avian and mammalian footprints are located on the upper bedding plane of two successive medium bedded brownish litharenite sandstone layers layer one has more than 97 concave epirelief avian footprints that are arranged in 29 straight or curved trackways layer two contains dispersed mammalian footprints the avian footprints include four slender digits with sharp tips three oriented forward ii iv and one of them oriented backward i metapodium imprints are visible in some footprints as isolated circular concavities the avian footprints are attributed to gruipeda intermedia in order to establish this identification we re affirm the diagnostic features of gruipeda iranipeda and charadriipeda and also re evaluate the ichnospecies assigned to these ichnogenera the mammalian footprints from the khaf locality include khafipus khadari nov igen and nov isp which are large plantigrade footprints that have five dispersed digit imprints in the pes or manus and heel or digit imprints that are enclosed by circular ridges which are disconnected from each other palaeotheriipus isp is a tridactyl mammalian footprint that is large in the heel with forward oriented toe imprints platykopus isp includes one footprint as a broad plantigrade impression with imprints of five connected digits avian footprints are attributed to anisodactyl shore birds and mammalian footprints are those of perissodactyls and large mammals such as ursid carnivores the footprints from the oligocene of iran documented here add to a growing but much understudied global record of cenozoic tetrapod footprints and suggest a broad paleogeographic distribution of various particularly avian ichnogenera

late highstand patterns of shifting and stepping coastal barriers and washover fans late messinian sorbas basin se spain abstract the late messinian sorbas member up to 75 m thick consists in its type area of a parasequence set of three prograding coastal barriers sequences i iii associated with lagoon and washover sediments around the town of sorbas these strata can be studied exceptionally well due to absence of burrowing by raised messinian salinities and exposure along a network of up to 30 m deep canyons fifteen vertical sections were logged and carefully correlated this permits to reconstruct and discuss patterns of relative sea level movements between decimetres up to 15 m within a parasequence excellent examples of non tidal transgressive facies are characterized by lagoon and washover sediments instead of the usual combination of washover and tidal deposits channel and flood tidal delta implications for the sandstone connectivity are given the lower two sequences are deposited in a relatively large tectonically enhanced wedge shaped accommodation space they show both fining up deepening sequences followed by prograding coarsening up shoaling sequences and can be compared to the classical parasequences of the western interior basin usa progradation of sequence ii was interrupted by a major slide event most likely triggered by an earthquake which caused more than 400 m seaward slumping of a stretch of 1 km of coastal sands the architecture of sequence iii is more complex due to limited accommodation space characteristic for the late highstand so that this setting was very sensitive to sea level fluctuations this resulted in an intricate pattern of juxtaposed and superposed lagoonal muds washover fans and swash zones so called stranded coastal barriers occur which were left behind after seaward jump of the coastline over more than 1 5 km during forced regression the pattern of reconstructed sea level positions is well comparable to the sequential pattern shown by the correlated equivalents along the northern basin margin which belong to the so called terminal carbonate complex the problem of ranking the complex sequence iii as one or more parasequences and its consequences for cyclostratigraphy are shortly discussed two models of washover formation are given respectively during more rapid and more slow sea level rise the influence of synsedimentary folding on the location of barriers is discussed and also the source area of extra and intraclasts supplied to barriers and washovers after deposition of the sorbas member the sea withdrew from the sorbas basin probably as a result of the major downdrop in the mediterranean at the maximum isolation during the salinity crisis it is suggested that the semi enclosed setting of the basin resulted only in limited localized erosion in contrast to the deeper adjacent vera basin which was more open to the mediterranean

influence of fluids and magma on earthquakes seismological evidence abstract in this paper we present seismological evidence for the influence of fluids and magma on the generation of large earthquakes in the crust and the subducting oceanic slabs under the japan islands the relationship between seismic tomography and large crustal earthquakes m 5 7 8 0 in japan during a period of 116 years from 1885 to 2000 is investigated and it is found that most of the large crustal earthquakes occurred in or around the areas of low seismic velocity the low velocity zones represent weak sections of the seismogenic crust the crustal weakening is closely related to the subduction process in this region along the volcanic front and in back arc areas the crustal weakening is caused by active volcanoes and arc magma resulting from the convective circulation process in the mantle wedge and dehydration reactions in the subducting slab in the forearc region of southwest japan fluids are suggested in the 1995 kobe earthquake source zone which have contributed to the rupture nucleation the fluids originate from the dehydration of the subducting philippine sea slab the recent 2001 geiyo earthquake m 6 8 occurred at 50 km depth within the subducting philippine sea slab and it was also related to the slab dehydration process a detailed 3d velocity structure is determined for the northeast japan forearc region using data from 598 earthquakes that occurred under the pacific ocean with hypocenters well located with sp depth phases the results show that strong lateral heterogeneities exist along the slab boundary which represent asperities and results of slab dehydration and affect the degree and extent of the interplate seismic coupling these results indicate that large earthquakes do not strike anywhere but only anomalous areas which can be detected with geophysical methods the generation of a large earthquake is not a pure mechanical process but is closely related to physical and chemical properties of materials in the crust and upper mantle such as magma fluids etc

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

the shorebird ichnofacies an example from the miocene of southern spain the late miocene sorbas member of the sorbas basin almeria province southeast spain contains an extensive avian ichnofauna preserved in lagoonal marls three distinctive avian ichnotaxa can be identified antarctichnus fuenzalidae covacevich and lamperein 1970 iranipeda millumi n ichnosp and roepichnus grahami n ichnogen n ichnosp in common with many other cenozoic avian ichnofaunas these traces are associated with shorebirds including plovers storks ducks and or gulls respectively associated mammalian tracks include possible cat and artiodactyl footprints the avian tracks are abundant and show a range of behavioural aspects in common with other recorded examples of cretaceous recent shorebird tracks these include both solitary and group activities consistent with their postulated avian tracemakers

detection and analysis of microseismicity in multi anvil experiments abstract we present a new technique to measure microseismicity at gigapascal pressures this new technique uses existing acoustic emission ae and multi anvil press technologies with minor modifications to make them compatible as a proof of concept we present results from acoustic emission studies on serpentine dehydration to 8 gpa and the olivine wadsleyite transformation at 16 gpa these case studies demonstrate the power of gigapascal acoustic emission monitoring and point to future developments which will further strengthen the technique

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

frictional sliding in serpentine at very high pressure abstract using a new four channel system for detecting acoustic emissions in a multianvil apparatus we have assessed the pressure temperature range for such emissions as well as the role of dehydration by deforming samples of extensively serpentinized peridotite we show that in the absence of dehydration and for samples initially faulted at low pressure acoustic emissions occurred well outside the expected pressure temperature field of unassisted brittle failure emissions were also detected during and after dehydration of serpentine microstructures of post run specimens revealed fault slip with offsets up to 500 m regardless of whether or not dehydration took place dehydration appears to effectively stop slip on pre existing faults and create new ones analysis of p wave travel times from the four sensors confirmed that the acoustic emissions originated within the specimen during fault slip these observations suggest that earthquakes can be triggered by slip along an existing fault containing serpentine under significantly higher pressure and temperature conditions than previously thought possible without dehydration

frictional melting during the rupture of the 1994 bolivian earthquake the source parameters of the 1994 bolivian earthquake magnitude m w 8 3 suggest that the maximum seismic efficiency was 0 036 and the minimum frictional stress was 550 bars thus the source process was dissipative which is consistent with the observed slow rupture speed only 20 of the locals wave velocity the amount of nonradiated energy produced during the bolivian rupture was comparable to or larger than the thermal energy of the 1980 mount st helens eruption and was sufficient to have melted a layer as thick as 31 centimeters once rupture was initiated melting could occur which reduces friction and promotes fault slip

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

faulting induced by precipitation of water at grain boundaries in hot subducting oceanic crust dehydration embrittlement has been proposed to explain both intermediate and deep focus earthquakes in subduction zones1 2 3 4 5 because such earthquakes primarily occur at shallow depths or within the core of the subducting plate dehydration at relatively low temperatures has been emphasized6 7 8 however recent careful relocation of subduction zone earthquakes9 10 shows that at depths of 100 250 km earthquakes continue in the uppermost part of the slab probably the former oceanic crust that has been converted to eclogite where temperatures are higher here we show that at such pressures and temperatures eclogite lacking hydrous phases but with significant hydroxyl incorporated as defects in pyroxene and garnet develops a faulting instability associated with precipitation of water at grain boundaries and the production of very small amounts of melt this new faulting mechanism satisfactorily explains high temperature earthquakes in subducting oceanic crust and could potentially be involved in much deeper earthquakes in connection with similar precipitation of water in the mantle transition zone 400 700 km depth of potential importance for all proposed high pressure earthquake mechanisms is the very small amount of fluid required to trigger this instability

antigorite high pressure stability in the system mgosio2h2o msh abstract the breakdown reactions of antigorite 1 forming talc forsterite water at low pressures and 2 forming forsterite clinoenstatite water at high pressures were determined in reversed equilibrium experiments results on reaction 1 were found to be in good agreement with former experimental determinations by both johannes johannes w 1975 zur synthese und thermischen stabilitat von antigorit fortschr mineral beih 53 36 and evans et al evans b w johannes w oterdoom h trommsdorff v 1976 stability of crysotile and antigorite in the serpentinite multisystem schweiz mineral petrogr mitt 56 79 93 from our experiments the invariant point i1 interconnecting the two reactions can be located at about 15 kbar 650 c this is consistent with the thermodynamic calculations using the dataset of berman berman r g 1988 internally consistent thermodynamic data for minerals in the system j petrol 29 445 522 however it is in contrast to recent experimental studies of ulmer and trommsdorff ulmer p trommsdorff v 1995a serpentine stability to mantle depths and subduction related magmatism science 268 858 861 who determined i1 at 21 kbar 730 c our pt conditions for i1 could be confirmed by equilibrium experiments on reaction 10 talc forsterite clinoenstatite water which is generated at i1 as well up to about 25 kbar the breakdown reaction 2 is nearly pressure independent towards still higher pressures the dp dt slope of reaction 2 bends and becomes negative schreinemakers analysis as well as thermodynamic calculations of the upper pressure stability of antigorite show that the possible antigorite breakdown reaction 3 antigorite clinoenstatite brucite water and reaction 4 brucite clinoenstatite forsterite water could originate at a new invariant point i2 provided that the reactions 2 and 11 brucite antigorite forsterite water intersect bracketing equilibrium 4 and combining these results with those on reaction 2 i2 was located at only about 51 kbar 490 c compared to 77 kbar 680 c according to berman s data however when taking into account the dense hydrous magnesium silicate dhms phase a mg7si2o8 oh 6 the phase relations of antigorite are changed resulting i in the metastability of i2 and reaction 3 and ii in a new invariant point i7 at about 44 kbar and 580 c generating the new antigorite breakdown reaction 16 antigorite phase a clinoenstatite water on the basis of these new data on the stability of antigorite earlier conclusions about dehydration depths in subducted serpentine bearing oceanic lithosphere have to be reconsidered the maximum pressure stability of antigorite according to reaction 16 extends between 44 and 55 kbar that is between about 130 and 160 km depths as opposed to about 75 kbar 220 km following ulmer and trommsdorff see above because many different thermal regimes are possible in subduction zones no specific dehydration depth can be expected but rather more continuous dehydration fronts in space and time

late miocene mediterranean desiccation topography and significance of the salinity crisis erosion surface on land in southeast spain reply abstract the result of sea level fall at the margins of the mediterranean during the late miocene salinity crisis was the creation of an extensive erosion surface however the shape of this salinity crisis unconformity reflects local factors and in turn significantly determined local conditions during subsequent reflooding at sorbas in southeast spain erosional overdeepening of a pre existing basin during drawdown created a depression over 200 m deep with an incised floor patterned by 30 m deep gullies during reflooding this semi enclosed palaeovalley temporarily became a barred basin in which gypsum was deposited these sorbas evaporites thus resulted from local basin sculpture diverse local effects elsewhere during drawdown and reflooding account for marked stratigraphic variations that continue to complicate recognition and correlation of the salinity crisis in marginal successions the drawdown erosion surface is itself the key indicator of this important event in marginal mediterranean basins

instability of deformation this chapter addresses the mechanisms by which instabilities can develop in rocks in the nominally ductile regime under conditions that the authors believe are relevant to earth we will not address brittle failure or frictional sliding processes in detail but much of our discussion will be couched in terms of knowledge gained in studies of these processes as a consequence we will begin by discussing why brittle failure and frictional sliding cannot be the mechanism by which rocks become unstable at depth despite the strong evidence that they are the underlying mechanism of earthquakes at shallow depths e g scholz 1990 2002 brittle shear failure in the normal sense is fundamentally a tensile process tensile microcracks must first nucleate and self organize via interaction of the stress concentrations at their tips as a consequence brittle failure and frictional sliding are strongly inhibited by pressure because work must be done against the pressure to open the mode i cracks the inhibition is so strong that the stress required to create a fault or initiate sliding on an existing fault becomes greater than the room temperature flow stress of many rocks at pressures equivalent to only a few tens of kilometers in earth increasing temperature has little effect on brittle processes but in contrast the ductile flow stress of rocks falls exponentially with temperature because both pressure and temperature increase with depth in earth earthquakes by unassisted brittle fracture mechanisms or frictional sliding can only occur at depths less than 30 50 km nevertheless earthquakes occur to depths of almost 700 km in earth and seismological evidence demonstrates unequivocally that they occur by displacement across a surface or narrow zone i e they occur by faulting this conundrum can be explained qualitatively by certain specific types of mineral reactions occurring under certain restricted conditions the

intermediate depth earthquake faulting by dehydration embrittlement with negative volume change earthquakes are observed to occur in subduction zones to depths of approximately 680 km even though unassisted brittle failure is inhibited at depths greater than about 50 km owing to the high pressures and temperatures it is thought that such earthquakes particularly those at intermediate depths of 50 300 km may instead be triggered by embrittlement accompanying dehydration of hydrous minerals principally serpentine a problem with failure by serpentine dehydration is that the volume change accompanying dehydration becomes negative at pressures of 2 4 gpa 60 120 km depth above which brittle fracture mechanics predicts that the instability should be quenched here we show that dehydration of antigorite serpentinite under stress results in faults delineated by ultrafine grained solid reaction products formed during dehydration this phenomenon was observed under all conditions tested pressures of 1 6 gpa temperatures of 650 820 degrees c independent of the sign of the volume change of reaction although this result contradicts expectations from fracture mechanics it can be explained by separation of fluid from solid residue before and during faulting a hypothesis supported by our observations these observations confirm that dehydration embrittlement is a viable mechanism for nucleating earthquakes independent of depth as long as there are hydrous minerals breaking down under a differential stress

experimental sytectonic dehydration of serpentinite under conditions of controlled pore water pressure we have studied the mechanical behavior of serpentinite under conditions favouring dehydration to olivine talc water at temperatures ranging between 300 and 600 and at total pressures from 100 to 300 mpa constant stress stress relaxation and constant displacement rate testing techniques permitted a wide range of deformation rates and paths to be accessed effective confining pressure was held constant during the dehydration process by means of a controlled pore water pressure system stress supported by the samples was almost independent of deformation rate at temperatures below those required for the onset of the breakdown reaction at 500 and 600 c however the strength was linearly dependent on the inverse of the deformation rate and independent of effective confining pressure over the range investigated microstructural studies revealed that the weakening was associated with sliding in narrow shear zones containing ultrafine grained 0 1 m olivine produced in the breakdown reaction the enhanced deformability is interpreted in terms of flow of the olivine in these shear zones by diffusion accommodated grain boundary sliding these experimental results suggest that metamorphic transformations affect the deformability of rocks and demonstrate enhancement of deformability through the transient existence of fine grained reaction products the results may also be applicable to the mechanics of deformation processes in oceanic transform faults and give some indication of the degree of weakening that might be expected from grain size reduction by dynamic recrystallization in plastically deforming rocks

deep focus earthquakes and recycling of water into the earth s mantle for more than 50 years observations of earthquakes to depths of 100 to 650 kilometers inside earth have been enigmatic at these depths rocks are expected to deform by ductile flow rather than brittle fracturing or frictional sliding on fault surfaces laboratory experiments and detailed calculations of the pressures and temperatures in seismically active subduction zones indicate that this deep focus seismicity could originate from dehydration and high pressure structural instabilities occurring in the hydrated part of the lithosphere that sinks into the upper mantle thus seismologists may be mapping the recirculation of water from the oceans back into the deep interior of our planet

neoichnology at lake margins implications for paleo lake systems abstract neoichnological studies provide significant information that can aid in the interpretation of ancient ichnological assemblages here we examine for the first time the pattern in both vertebrate and invertebrate trace distribution and abundance that can be seen in two geographically separate but broadly analogous contemporary semi arid climate lake margin settings in an effort to describe taphonomic processes relevant to paleo lake systems lake margin to supralittoral zone transects were made at ruby reservoir montana usa and la sotonera spain and vegetation cover trace cover trace diversity and substrate characteristics were recorded similar patterns in trace distribution were seen through the eulittoral to supralittoral zones with the majority of traces identified within a single transect present at both sites however a few traces attributed to larger organisms were found to be unique to each and in some instances could to be assigned to a specific trace maker the eulittoral zone was considered to have characteristics attributable to the scoyenia ichnofacies however analysis of the supralittoral zone shows some characteristics of both the coprinisphaera and the mermia ichnofacies in addition a transitional zone between a scoyenia like ichnofacies and a fully terrestrial assemblage was found which may enable continental ichnofacies to be further refined for application to paleo lake systems study of the distribution of traces with distance along the transects also suggests taphonomic biases against the preservation of certain types of traces e g avian due to seasonal fluctuations of the lake level and the subsequent reduced preservation potential for lake proximal traces

rapid subglacial streamlined bedform formation at a calving bay margin using the lidar derived swedish national height model we have identified previously undescribed shallow streamlined glacial bedforms small scale drumlins on the narke plain in south central sweden these drumlins could only be detected with high resolution lidar due to both their subtle size and forest cover in this area the ice margin receded in a subaqueous environment with a proglacial water depth in the order of 100 m during the last deglaciation as indicated by the configuration of marginally formed de geer moraine ridges draping the drumlinoids the receding ice margin formed deeply indented calving bays these were located around subaqueous outlets of the subglacial melt water drainage with their apex position marked geomorphologically by beaded esker ridges the mapped small scale drumlins are aligned perpendicular to the reconstructed ice sheet margin and suggest formation along flow lines adjusted to the configuration of these calving embayments as they propagated up flow with ice margin retreat based on these geometric relationships we argue that the emplacement of the drumlins was near marginal 7 7 1 km from the margin on a short timescale 5 35 years less

paleohydrological significance of trace fossil distribution in oligocene fluvial fan to lacustrine systems of the ebro basin spain the ichnological study of fluvial fan and lacustrine oligocene deposits in the ne ebro basin has allowed the recognition of three ichnoassemblages having a strong correlation with depositional facies associations lacustrine deposits lack bioturbation due to the hydrologically closed character of the lake that caused hypersalinity and made it inhospitable for benthic life terminal lobe deposits of the fluvial fan which were sedimented in low wetland areas around the lake bear a moderately diverse ichnoassemblage dominated by horizontal taenidium barretti cochlichnus anguineus and bird footprints gruipeda isp this assemblage can be assigned to the shorebird ichnofacies a subset of the scoyenia ichnofacies that characterizes the subaerial part of low energy shore areas crevasse splay deposits in medial fluvial fan areas present a different assemblage also belonging to the scoyenia ichnofacies it includes most of the trace fossils found in the terminal lobes except for the bird tracks plus very abundant vertical burrows taenidium barretti and unnamed ornamented burrows the presence of deep tier traces of terrestrial invertebrates is consistent with the more proximal fan setting having greater relief and consequently a lower mean groundwater position than lowland areas fluvial channels only bear irregularly clustered tunnel structures of unknown affinity formed after abandonment of the channel thus trace fossil assemblages are mostly controlled by the position and fluctuations of water tables which are the cause for their composite nature

existence of a seismic belt in the upper plane of the double seismic zone extending in the along arc direction at depths of 70 100 km beneath ne japan 1 we relocated microearthquakes using data obtained via a dense seismic network and systematically detected the characteristic distribution of the upper seismic plane seismicity within the pacific slab beneath ne japan we found a seismic belt parallel to the iso depth contour of the plate interface that is beneath the forearc area at depths of 70 100 km indicating that the distribution of the upper plane earthquakes is non uniform the location of the deeper limits of this belt and seismicity of the upper seismic plane appear to correspond respectively to two facies boundaries where h2o contents change in the slab crust events in the upper seismic plane have mainly down dip compression type focal mechanisms but several events have normal fault type nf type versions whose spatial distribution appears to correspond to these boundaries these nf events might be induced by the tensional stress field that is caused by volume reduction due to dehydration reactions

eocene bird tracks from the chuckanut formation northwest washington early tertiary nonmarine sediments occur as a discontinuous series of outcrops that extends throughout large areas of northwest washington and southwestern british columbia these fluvial and deltaic deposits contain abundant plant fossils but faunal remains are rare the recent discovery of an outcrop of chuckanut formation arkose containing nine fossil bird tracks provides the first clear evidence of terrestrial vertebrate life in the extensive coastal wetland zone that existed prior to the uplift of the cascade range

nondilatant brittle deformation of serpentinites implications for mohr coulomb theory and the strength of faults we conducted deformation experiments to investigate the strength deformation processes and nature of the brittle ductile transition of lizardite and antigorite serpentinites a transition from localized to distributed deformation occurs as confining pressure increases from 200 to 400 mpa at room temperature deformation in both brittle localized and ductile distributed regimes is accommodated by shear microcracks which form preferentially parallel to the 001 cleavage axial microcracks mode i are infrequently observed volumetric strain measurements demonstrate that brittle deformation is mostly nondilatant consistent with the shear dominated microcracking three observations indicate that deformation in the ductile regime is accommodated by cataclastic flow 1 a lack of evidence for crystal plastic deformation 2 a positive pressure dependence of the maximum differential stress and 3 abundant evidence for brittle microcracking the weakness of serpentinites relative to other brittle rocks is explained by a low fracture strength along the 001 cleavage combined with the low pressure dependence of strength the transition from brittle to ductile deformation occurs at the crossover between the strength of intact serpentinite and the friction law unique to each type of serpentinite rather than the more general byerlee s law if brittle deformation regimes are defined based on the mode of microcracking and on the occurrence of crystal plasticity serpentinites define an end member style of nondilatant brittle deformation this deformation style may result in extremely weak faults in nature and it may also strongly influence the tectonic evolution of the oceanic lithosphere where serpentinite is present

mediterranean messinian salinity crisis constraints from a coeval marginal basin sorbas southeastern spain abstract the extent timing and effects of late miocene desiccation and evaporite deposition in the mediterranean sea remain controversial marginal basins containing messinian 5 3 7 1 ma sequences now exposed onland supplement information from the deep mediterranean but have evaporites of a variety of ages some of these messinian evaporites pre date and others post date deep desiccation none appears to be exactly coeval with those of the deep mediterranean in the betic cordillera of southern spain basins e g granada basin far from the present day mediterranean lost connection with the mediterranean due to uplift 1 ma before the salinity crisis and have marine evaporites of early not late messinian age in contrast basins such as the sorbas basin in southeastern spain adjacent to the present day mediterranean record events directly reflecting the course of the salinity crisis the sorbas basin retained marine connection with the western mediterranean up until evaporative drawdown in the mid messinian and was rapidly reflooded immediately afterwards the sorbas messinian sequence is up to 320 m thick it is complete and normal marine except for an incised basinwide erosion surface overlain by a 130 m thick gypsum deposit we propose that this surface marks the interval of deep desiccation of the adjacent mediterranean basin erosion occurred shortly after 5 9 ma and the irregular unconformity has relief of at least 240 m confirming mediterranean drawdown significantly below the atlantic level sorbas gypsum deposits overlie the unconformity and are intercalated with marls estimated at 5 5 ma containing normal marine messinian biotas these gypsum deposits therefore post date deep desiccation and formed in a silled basin immediately following marine reflooding they mark the end of the salinity crisis and are overlain by 70 m of normal marine sediments containing unreworked foraminifers of latest messinian age this succession demonstrates that the salinity crisis occurred faster and was completed sooner than previously believed it took place within 0 4 ma time scale of berggren et al 1995b is 0 2 ma on the time scale of baksi 1993 and was completed before the end of the messinian this corrects previous views that the salinity crisis continued until the early pliocene there is no evidence in the sorbas basin for brackish lago mare conditions and the normal marine biotas that directly precede and follow drawdown rebut earlier suggestions of prolonged salinity effects

impacts of flamingos on saline lake margin and shallow lacustrine sediments in the kenya rift valley abstract studies of modern holocene and pleistocene sediments around saline to hypersaline alkaline lake bogoria and lake magadi show that evidence of flamingo activity in marginal areas of these lakes is nearly ubiquitous flamingos produce discrete structures such as webbed footprints 9 cm long 11 cm wide and nest mounds 30 cm wide 20 cm high and they also extensively rework sediments in delta front delta plain and shoreline areas large 0 5 2 cm in diameter pinched bubble pores and ped like mud clumps are formed by the trampling and churning of wet clay rich sediments in these settings flamingo nest mounds although superficially similar to some thrombolite mounds are typically internally structureless unless formed on pre existing sediments that preserve internal structures the flamingo mounds consist of a dense packed oval shaped core a surrounding body of packed sediment and an external layer with a ped like texture of clumped mud the nests may contain open holes from roots or feather shafts incorporated into the nest and or burrows produced once the nests are abandoned in areas with high densities of flamingos lake margin sediments may be preferentially compacted particularly at breeding sites and become resistant to subaerial erosion and the effects of transgressive ravinement on time scales ranging from seasons to tens of thousands of years the relatively well compacted nest mounds and associated sediments also contribute to the stability of delta distributary channels during regressive transgressive cycles and can lead to the minor channelization of unconfined flows where currents are diverted around nest mounds pleistocene exhumed surfaces of relatively well indurated lake margin sediments at lake bogoria and lake magadi that are interpreted as combined regressive and transgressive surfaces flooding surface sequence boundary preserve evidence of flamingo activities and are overlain by younger porous lacustrine silts that preserve large bubble pores produced by flamingos

the maastrichtian danian maimara tracksite yacoraite formation salta group quebrada de humahuaca argentina environments and ichnofacies implications fil console gonella carlos alfredo consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet tucuman instituto superior de correlacion geologica universidad nacional de tucuman facultad de ciencias naturales e instituto miguel lillo departamento de geologia catedra geologia estructural instituto superior de correlacion geologica argentina