sequence stratigraphic and genetic aspects of the tournaisian liegender alaunschiefer and adjacent beds this study reports the results of interdisciplinary investigations of tournaisian deposits from the german rheinisches schiefergebirge and provides a genetic and sequence stratigraphic interpretation microfacies and geochemical data confirm normal marine outer shelf to slope environments for the lower tournaisian hangenberg formation in contrast data from the condensed phosphatic liegender alaunschiefer black shale indicate low current energy and anoxic conditions in the sediment and the water column we suggest that anoxia was caused by eutrophication and high organic productivity due to factors such as upwelling a climate related improvement of oceanic ventilation and volcanic nutrient input the hangenberg formation represents the lowstand through the early transgressive systems tract of a third order depositional sequence while the liegender alaunschiefer is a late transgressive systems tract and maximum flooding deposit the richrath limestone was deposited during the highstand systems tract thus quickly rising sea level and eutrophication may account for the peculiar and uniform facies of the liegender alaunschiefer

patterns of fracture and tidal stresses due to nonsynchronous rotation implications for fracturing on europa this study considers the global patterns of fracture that would result from nonsynchronous rotation of a tidally distorted planetary body the incremental horizontal stresses in a thin elastic or viscous shell due to a small displacement of the axis of maximum tidal elongation are derived and the resulting stress distributions are applied to interpret the observed pattern of fracture lineaments on europa the observed pattern of lineaments can be explained by nonsynchronous rotation if these features formed by tension fracturing and dike emplacement tension fracturing can occur for a small displacement of the tidal axis so that the resulting lineaments may be consistent with other evidence suggesting a young age for the surface

model constraints on the opening rates of bands on europa a mid ocean ridge spreading analog is used to constrain the opening rates and brittle ductile transition depths for two axisymmetric ridged bands on europa estimates of brittle ductile transition depth based on the morphologies of yelland and ino lineae are combined with a conductive cooling model based on a mid ocean ridge analog to estimate the opening rates and active lifetimes of the bands this model limits local strain rates to 10 15 10 12 s 1 opening rates to 0 2 40 mm yr 1 and active lifetimes of the bands to 0 1 30 myr if the observed structures in the outer portions of ridged bands are indeed normal faults the estimated range for the tensile strength of ice on europa

evolution history of the hidaka oki offshore hidaka basin in the southern central hokkaido as revealed by seismic interpretation and related tectonic events in an adjacent collision zone abstract off the southern coast of hokkaido the hidaka oki offshore hidaka basin has developed on the western flank of a collision suture under the influence of long standing compressional plate motion and provoked tectonic stresses around the northwestern pacific rim throughout the late cenozoic the basin forming history of the japan arc and kuril arc collision zone is described on the basis of seismic reflection data interpretation we identify two stages of basin formation the older late oligocene miocene faulted en echelon graben pull apart basin and younger plio pleistocene regional downwarping paleoenvironmental changes recorded within the fore arc sediments indicate that the older basin filled up by the late miocene we inferred the volumes of the distinctive basins from the depth conversion of seismic data which suggest episodic uplifts and massive erosion of the hidaka mountains in the middle late miocene and the plio pleistocene estimated sediment supply rates into the basins have a similar level for the both stages cause of an episodic uplift in the older stage is attributed to the delayed opening of the japan sea the eastern eurasian margin underwent n s right lateral faulting at 25 ma as a result of rifting of the kuril back arc basin formation of the japan sea back arc basin since the early miocene ca 20 ma caused eastward motion of the western hokkaido block and transpressive regime along the pre existing n s shear deformation zone

analysis of very high resolution galileo images and implications for resurfacing mechanisms on europa abstract the young greeley et al 2000 during the e12 flyby of europa in dec 1997 this dataset is now two decades old but it has not been analyzed in detail until this work despite the largely different viewing and lighting conditions we mosaic these high resolution frames into the 220 m pixel regional context frame we then perform geomorphologic mapping of the high resolution image mosaic and the regional image frame for comparison and we also create a structural map of the high resolution image mosaic the units in the geomorphologic map are defined by surface texture landform shape morphology dimension and relative albedo the structural map units include interpretations from the geomorphologic map units and their interpretation implies potential kinematic processes for the formation of particular structures our primary mapping observations include the regular spacing and gentle slopes of the ridge and trough terrain the sharp boundaries and preserved structures of the chaos terrain and the symmetry but irregular size of double ridges we then evaluate proposed formation mechanisms for these and other mapped features the high resolution images also reveal an abundance of small

late paleozoic ice age glaciers shaped east antarctica landscape abstract the erosion history of antarctica is fundamental to our understanding of interlinks between climate and glacier dynamics however because of the vast polar ice sheet covering more than 99 of antarctica land mass the continental surface response to glacial erosion remains largely unknown over the last decade the subglacial topography of antarctica has been imaged by airborne radar surveys these studies revealed high and complex sub glacial relief in the core of the east antarctic shield interpreted as resulting from rifting episodes and low long term erosion rates or repeated large scale glacial retreats and advances in east antarctica thermochronology studies have revealed a spatially localized cenozoic erosion starting after 34 ma with a maximum denudation of 2 km in the lambert trough low pre glacial erosion rates before 34 ma have been inferred since the permian period following a phase of significant 2 km erosion during the late paleozoic between 350 and 250 ma however the exact extent magnitude and significance of this late paleozoic erosion phase remain elusive here we show that homogeneous exhumation occurred at the scale of the terre adelie margin of east antarctica in response to major glacial erosion during the late paleozoic ice age lpia our data require homogeneous exhumation and 4 km erosion between 340 and 300 ma along a 600 km profile along the terre adelie george v land coast the data are inconsistent with either exhumation during permian rifting or with significant 1 5 km cenozoic glacial erosion which requires lpia glaciers to have been temperate promoting glacial sliding erosion and sediment transfer even at high latitudes unlike in the present situation

stratigraphic and oxygen isotope evidence for my scale glaciation driving eustasy in the early middle devonian greenhouse world article i nfo million year scale 3rd order depositional sequences few 10s to 100 m thick are common in the devonian marine record and are correlated between sedimentary basins and across widely separated continents implying a eustatic origin tectonically driven changes in mid ocean ridge spreading rates lengths are too slow to account for the calculated 3rd order rise fall rates and typical orbital frequencies 20 400 ky are too fast we analyzed oxygen isotopes from conodont apatite to evaluate if early middle devonian 3rd order sea level changes were controlled by paleoclimatically driven ice volume glacio eustasy and seawater temperature change thermo eustasy two successive depositional sequences in the western u s nevada and czech republic prague basin were sampled the 18 o values range from 17 8

anoxia and fluctuating climate recorded from the devonian carboniferous black shales tethys himalaya india a multi proxy approach due to inaccessibility and tough conditions high altitude low oxygen region very less information is available about the indian tethys himalayan sequences particularly geochemical data are scarce an attempt is made in the present study to evaluate the sediment geochemistry and paleo redox conditions of devonian carboniferous black shales from the spiti region tethys himalaya using multi proxy approach besides black shales this paper also provides the first in depth study of the geochemistry of phosphatic nodules hosted by the black shales that will allow primary and secondary processes to be understood geochemical investigations particularly redox sensitive trace element ratios for e g v v ni 0 5 ni co 4 3 7 2 v cr 2 and positive ce anomalies suggest deposition of these black shales under sub oxic to anoxic marine conditions thus recording an ocean anoxic event in the region these ocean anoxic events of devonian carboniferous spiti black shales which possess distinctive geochemical signatures can very well be correlated with global events such as hangenberg events and the lower alum shale event the span of the chemical index of alteration cia values 54 78 variation of 4si parameter 82 3 and c values 0 1 0 6 recorded in the black shales strongly indicate varying degrees of weathering conditions in the source area which in turn reflect fluctuating climatic conditions prevailing during the deposition of these sediments in devonian carboniferous period in the spiti region the distinct geochemical characteristics such as y sr and rare earth element ree enrichments particularly middle ree enrichments with a hat shaped pattern with high p2o5 contents up to 14 wt distinguish the nodules from the host rocks black shales sem scanning electron microscope results supplemented by xrd x ray diffraction studies of the nodules show the dominance of calcium silica and phosphatic phases the diversity of clay minerals significant variations in mineralogical composition and lack of any continuous vertical trend in the nodules suggest a relatively low impact on the primary environmental signal by burial diagenesis

europa initial galileo geological observations abstract images of europa from the galileo spacecraft show a surface with a complex history involving tectonic deformation impact cratering and possible emplacement of ice rich materials and perhaps liquids on the surface differences in impact crater distributions suggest that some areas have been resurfaced more recently than others europa could experience current cryovolcanic and tectonic activity global scale patterns of tectonic features suggest deformation resulting from non synchronous rotation of europa around jupiter some regions of the lithosphere have been fractured with icy plates separated and rotated into new positions the dimensions of these plates suggest that the depth to liquid or mobile ice was only a few kilometers at the time of disruption some surfaces have also been upwarped possibly by diapirs cryomagmatic intrusions or convective upwelling in some places this deformation has led to the development of chaotic terrain in which surface material has collapsed and or been eroded

distribution of strike slip faults on europa study of four different regions on europa imaged by the galileo spacecraft during its first 15 orbits has revealed 117 strike slip faults europa appears to form preferentially right lateral faults in the southern hemisphere and left lateral faults in the northern hemisphere this observation is consistent with a model where diurnal tides due to orbital eccentricity drive strike slip motion through a process of walking in which faults open and close out of phase with alternating right and left lateral shear lineaments that record both left and right lateral motion e g agave linea may record the accommodation of compression in nearby chaotic zones nearly all identified strike slip faults were associated with double ridges or bands and few were detected along ridgeless cracks thus the depth of cracks without ridges does not appear to have penetrated to the low viscosity decoupling layer required for diurnal displacement but cracks that have developed ridges do extend down to such a level this result supports a model for ridge formation that requires cracks to penetrate to a decoupling layer such as a liquid water ocean

middle to late famennian successions at ain jemaa moroccan meseta implications for regional correlation event stratigraphy and synsedimentary tectonics of nw gondwana

the tice event perturbation of carbon nitrogen cycles during the mid tournaisian early carboniferous greenhouse icehouse transition abstract carbonate carbon 13ccarb and bulk nitrogen 15n isotopic variation during the mid tournaisian was analyzed in the malanbian and long an sections of south china their c isotope profiles document a large positive excursion herein termed the mid tournaisian carbon isotope excursion tice during the siphonodella isosticha conodont zone although its magnitude differed between the two sections 6 at malanbian versus 3 at long an the tice event coincided with sedimentologic and oxygen isotopic evidence of climatic cooling and glaciation during the mid tournaisian it was probably triggered by an increase in organic carbon burial rates linked to changes in global ocean circulation the study sections also document a large positive shift in 15n from 1 7 to 4 2 at malanbian and from 1 5 to 3 8 at long an the n isotope shift shows no termination within the study sections and is likely to mark the onset of an extended interval of 15n enriched marine nitrate that lasted for the duration of the late paleozoic ice age its initiation coincided with tice and thus may have been linked to ocean circulation changes that resulted in intensified upwelling and an increase in water column denitrification the continuation of the n isotope shift over millions of years may have been linked to glacio eustatic fall and a long term shift in the locus of denitrification from continental shelf sediments to continent margin oxygen minimum zones the tice event thus marks the onset of sustained continental glaciation during the late paleozoic ice age

europa stratigraphy and geological history of the anti jovian region from galileo e14 solid state imaging data a tidal bulge and associated deformation are predicted to occur in europa s anti jovian region voyager data showed polygonal low albedo bands in this region it was demonstrated that when the low albedo material comprising these bands was removed the margins could be reconstructed suggesting that fracturing and lateral separation has occurred higher resolution galileo images of a 300 000 km2 portion of the anti jovian region permit recognition and mapping of a variety of features and documentation of the geological history we identify background ridged plains several distinctive types of bands and ridges lenticulae and regions of chaotic terrain these images are at relatively low incidence angles thus albedo variations predominate over topography this presents a challenge to morphologically based mapping but does not preclude development of a regional stratigraphy stratigraphic relationships show that dark bands crosscut the bright ridged plains and are themselves disrupted by lenticulae and chaos suggesting a geological history beginning with background ridged plains followed by a period dominated by band formation with the most recent history predominantly characterized by formation of lenticulae and chaos the paucity of impact craters in this region indicates that the entire sequence of units is geologically recent

tectonic processes on europa tidal stresses mechanical response and visible features abstract europa s orbital eccentricity driven by the resonance with io and ganymede results in diurnal tides 3 5 day period and possibly in nonsynchronous rotation both diurnal variation and nonsynchronous rotation can create significant stress fields on europa s surface and both effects may produce cracking patterns and time sequences of apparent tectonic features on europa include lineaments that correlate with both sources of stress if we take into account nonsynchronous rotation after initial crack formation by amounts ranging up to several tens of degrees for example the crosscutting time sequence of features in the cadmus and minos linea region is consistent with a combined diurnal and nonsynchronous tensile stress field as it evolves during tens of degrees of nonsynchronous rotation constraints on the rotation rate from comparing voyager and galileo images show that significant rotation requires 104yr but could be fast enough to have allowed significant rotation since the last global resurfacing even if such resurfacing was as recent as a few million years ago once cracking is initiated diurnal tides work cracks so that they open and close daily although the daily effect is small over 105yr double ridges could plausibly be built along the cracks with sizes and morphologies consistent with observed structures according to a model in which underlying liquid water fills the open cracks partially freezes and is extruded during the daily closing of the cracks thus several lines of observational and theoretical evidence can be integrated if we assume nonsynchronous rotation and the existence of a liquid water layer

tidally driven stress accumulation and shear failure of enceladus s tiger stripes abstract straddling the south polar region of saturn s moon enceladus the four principal tiger stripe fractures are a likely source of tectonic activity and plume generation here we investigate tidally driven stress conditions at the tiger stripe fractures through a combined analysis of shear and normal diurnal tidal stresses and accounting for additional stress at depth due to the overburden pressure we compute coulomb failure conditions to assess failure location timing and direction right vs left lateral slip throughout the enceladus orbital cycle and explore a suite of model parameters that inhibit or promote shear failure at the tiger stripes we find that low coefficients of friction f 0 1 0 2 and shallow overburden depths z 2 4 km permit shear failure along the tiger stripe faults and that right and or left lateral slip responses are possible we integrate these conditions into a 3d time dependent fault dislocation model to evaluate tectonic displacements and stress variations at depth during a tiger stripe orbital cycle depending on the sequence of stress accumulation and subsequent fault slip which varies as a function of fault location and orientation frictional coefficient and fault depth we estimate resolved shear stress accumulation of 70 kpa prior to fault failure which produces modeled strike slip displacements on the order of 0 5 m in the horizontal direction and 5 mm in the vertical direction per slip event our models also indicate that net displacements on the order of 0 1 m per orbital cycle in both right and left lateral directions are possible for particular fault geometries and frictional parameters tectonic activity inferred from these analyses correlates with observed plume activity and temperature anomalies at enceladus s south polar region moreover these analyses provide important details of stress accumulation and the faulting cycle for icy satellites subjected to diurnal tidal stress

brine mobilization during lithospheric heating on europa implications for formation of chaos terrain lenticula texture and color variations the background lineated plains on europa are locally highly modified and destroyed in regions known as chaos and lenticulae produced there are 1 isolated fragments and polygons of background material which rotate and translate 2 matrix which fills in the areas between the fragments and polygons and 3 surface discolorations using observations and constraints from high resolution galileo images we find that a model for the formation of these terrains which involves mobilization and migration of brines and a possible percolation phase transition as the europan lithosphere is warmed can readily explain the vast majority of their characteristics in addition the presence of melt fractions of a few percent in the adjacent ice framework may enhance the creep rate and the accompanying deformation rates the characteristics and distribution of lenticulae suggest that among the strong candidates for heat sources for brine migration and ice mobilization processes is diapirism linked to solid state convection in a layer underlying a brittle lid and possibly overlying a liquid water layer

stable nitrogen isotope analysis of the upper devonian palynomorph tasmanites abstract bulk samples are commonly used in stable n isotope studies to infer climate changes however due to uncertainties in the composition of bulk samples the inconsistency of diagenetic alteration and the variation of dominant oceanic features such as n fixation and denitrification the isolation of specific sedimentary n fractions has become a crucial step to understanding the nitrogen cycle this paper describes the extraction techniques and the stable nitrogen isotope analysis on a nano ea irms of the palynomorph tasmanites spp 80 200 m found in upper devonian famennian black shales from kentucky usa tasmanites is a widely occurring and long ranging prasinophyte unicellular green algae genus palynomorphs such as tasmanites are highly resistant to most forms of decay it is therefore suggested that the 15n signature of this palynomorph may be a useful unaltered indicator of baseline isotopic change in future palaeoclimate studies the greatly reduced sample size accepted by the nano ea irms makes this technique a viable complement to bulk sediment analyses the results using the nano ea irms demonstrate that the 15n signature of the bulk organic samples differ significantly from that of the isolated tasmanites spp three distinct isotopic relationships were observed from the three different sample localities these include parallel changes in the 15n values of bulk samples and extracted tasmanites spp variation in the 15n of bulk samples with no corresponding change recorded in tasmanites spp and opposing 15n changes recorded between the bulk samples and the extracted tasmanites spp this inconsistent isotopic variation further emphasises the complexity of the nitrogen cycle possible explanations for the observed variation include changes in the rate of n fixation and denitrification due to climate change incomplete nitrification and variation in the bulk organic content

tectonics and water on europa the tectonics of europa one of jupiter s moons are complex this satellite probably hosts a subsurface water ocean but the thickness of the outer ice crust is poorly constrained and the episodic presence of liquid water at the surface is debated we argue that some surface features of europa are formed by soft ice that is heated by viscous dissipation of tidal motion along faults and do not depend on a shallow ocean our model suggests that transient pockets of liquid water or brine could form at shallow depths in the crust

geocarbsulf a combined model for phanerozoic atmospheric o2 and co2 abstract a model for the combined long term cycles of carbon and sulfur has been constructed which combines all the factors modifying weathering and degassing of the geocarb iii model berner r a kothavala z 2001 geocarb iii a revised model of atmospheric co2 over phanerozoic time am j sci 301 182 204 for co2 with rapid recycling and oxygen dependent carbon and sulfur isotope fractionation of an isotope mass balance model for o2 berner r a 2001 modeling atmospheric o2 over phanerozoic time geochim cosmochim acta 65 685 694 new isotopic data for both carbon and sulfur are used and new feedbacks are created by combining the models sensitivity analysis is done by determining 1 the effect on weathering rates of using rapid recycling rapid recycling treats carbon and sulfur weathering in terms of young rapidly weathering rocks and older more slowly weathering rocks 2 the effect on o2 of using different initial starting conditions 3 the effect on o2 of using different data for carbon isotope fractionation during photosynthesis and alternative values of oceanic 13c for the past 200 million years 4 the effect on sulfur isotope fractionation and on o2 of varying the size of o2 feedback during sedimentary pyrite formation 5 the effect on o2 of varying the dependence of organic matter and pyrite weathering on tectonic uplift plus erosion and the degree of exposure of coastal lands by sea level change 6 the effect on co2 of adding the variability of volcanic rock weathering over time berner r a 2006 inclusion of the weathering of volcanic rocks in the geocarbsulf model am j sci 306 in press results show a similar trend of atmospheric co2 over the phanerozoic to the results of geocarb iii but with some differences during the early paleozoic and for variable volcanic rock weathering lower co2 values during the mesozoic atmospheric oxygen shows a major broad late paleozoic peak with a maximum value of about 30 o2 in the permian a secondary less broad peak centered near the silurian devonian boundary variation between 15 and 20 o2 during the cambrian and ordovician a very sharp drop from 30 to 15 o2 at the permo triassic boundary and a more or less continuous rise in o2 from the late triassic to the present

constraints on europa s surface properties from primary and secondary crater morphology 1 we investigate the near surface properties of europa s ice shell by examining small crater morphology we use both primary and secondary craters for our analysis for primary craters the simple to complex transition provides an estimate of 0 19 0 36 mpa for the cratering effective strength through the aggregate statistics of over 100 profiles we find that secondary craters on europa tend toward smaller depth to diameter d d ratios than primary craters consistent with observations on other cratered surfaces the moon and mars in addition we find that adjacent secondaries tend to be more shallow than distant secondaries also consistent with trends seen on the moon and mars the presence of numerous and far flung secondaries requires a solid competent surface for spallation that is inconsistent with weak ice although the effective strength evaluated by crater scaling laws does not have a direct quantitative relationship to lab based measurements of shear or tensile strength comparison to other observationally derived effective strengths and geologic materials suggests that the mechanical properties of europa s surface ice should be consistent with terrestrial measurements of cold ice

fault induced perturbed stress fields and associated tensile and compressive deformation at fault tips in the ice shell of europa implications for fault mechanics secondary fractures at the tips of strike slip faults are common in the ice shell of europa large magnitude perturbed stress fields must therefore be considered to be a viable driving mechanism for the development of part of the fracture sequence fault motions produce extensional and compressional quadrants around the fault tips theoretically these quadrants can be associated with tensile and compressive deformational features i e cracks and anti cracks respectively accordingly we describe examples of both types of deformation at fault tips on europa in the form of extensional tailcracks and compressional anti cracks the characteristics of these features with respect to the plane of the fault create a fingerprint for the mechanics of fault slip accumulation when compared with linear elastic fracture mechanics lefm models of perturbed stress fields around fault tips tailcrack kink angles and curving geometry can be used to determine whether opening accompanies sliding motion kink angles in the 50e70 range are common along strike slip faults that resemble ridges and indicate that little to no opening accompanied sliding in contrast tailcrack kink angles are closer to 30 for strike slip faults that resemble bands with tailcrack curvatures opposite to ridge like fault examples indicating that these faults undergo significant dilation and infill during fault slip episodes anti cracks which may result from compression and volume reduction of porous near surface ice have geometries that further constrain fault motion history corroborating the results of tailcrack analysis the angular separation between anti cracks and tailcracks are similar to lefm predictions indicating the absence of cohesive end zones near the tips of europan faults hence suggesting homogeneous frictional properties along the fault length tailcrack analysis can be applied to the interpretation of cycloidal ridges chains of arcuate cracks on europa that are separated by sharp kinks called cusps cusp angles are reminiscent of tailcrack kink angles along ridge like strike slip faults cycloid growth in a temporally variable tidal stress field ultimately resolves shear stresses onto the near tip region of a growing cycloid segment thus resultant slip and associated tailcrack development may be the driving force behind the initiation of the succeeding arcuate segment hence facilitating the ongoing propagation of the cycloid chain 2005 elsevier ltd all rights reserved

resurfacing history of europa from pole to pole geological mapping abstract we produced geologic maps from two regional mosaics of galileo images across the leading and trailing hemispheres of europa in order to investigate the temporal distribution of units in the visible geologic record five principal terrain types were identified plains bands ridges chaos and crater materials which are interpreted to result from 1 tectonic fracturing and lineament building 2 cryovolcanic reworking of surface units with possible emplacement of sub surface materials and 3 impact cratering the geologic histories of both mapped areas are essentially similar and reflect some common trends tectonic resurfacing dominates the early geologic record with the formation of background plains by intricate superposition of lineaments the opening of wide bands with infilling of inter plate gaps and the buildup of ridges and ridge complexes along prominent fractures in the ice it also appears that lineaments are narrower and more widely spaced with time the lack of impact craters overprinted by lineaments indicate that the degree of tectonic resurfacing decreased rapidly after ridged plains formation in contrast the degree of cryovolcanic resurfacing appears to increase with time as chaos formation dominates the later parts of the geologic record these trends and the transition from tectonic to cryovolcanic dominated resurfacing could be attributed to the gradual thickening of europa s cryosphere during the visible geologic history that comprises the last 2 or 30 80 myr of europa s history an originally thin brittle ice shell could be pervasively fractured or melted through by tidal and endogenic processes the degree of fracturing and plate displacements decreased with time in a thickening shell and lineaments became narrower and more widely spaced formation of chaos regions could have occurred where the thickness threshold for solid state convection was exceeded and can be aided by preferential tidal heating of more ductile ice in a long term context it is not clear at this point whether this inferred thickening trend would reflect a drastic change in the thermal evolution of the satellite or cyclic or irregular episodes of tectonic and cryovolcanic activity

carbon and oxygen isotope stratigraphy of the lower mississippian kinderhookian lower osagean western united states implications for seawater chemistry and glaciation a positive carbon isotope 1 3 c excursion has been recognized in upper kinderhookian and early osagean carbonates in three sections in southeast idaho and nevada the oldest 1 3 c peak 7 is dated to the isostichaconodont zone and a younger peak occurs in the typicus zone the shifts are recorded in a range of carbonate lithofacies representing various water depths along the shelf lithofacies sampled for 1 3 c and 1 8 o at the samaria mountain section in southeast idaho record the shallowest water conditions indicated by cross bedded skeletal and peloidal grainstones the deepest water conditions are present in the pahranagat range section in eastern nevada which consists mainly of bioturbated lime mudstone and skeletal wackestone the 1 3 c values from these widely separated sedimentary basins show a consistent trend that correlates with early mississippian curves generated from brachiopod calcite in western europe and the midcontinent of north america as well as dolomites in utah and wyoming 1 8 o values become more positive up section generally paralleling the positive trend in 1 3 c during the late kinderhookian no subaerial exposure surfaces are recognized in the sections examined in southeast idaho and nevada and at least the 1 3 c trends are interpreted as primary seawater fluctuations sea level changes occurred near the beginning of the late kinderhookian 1 3 c shift early to middle parts of the isosticha zone and within the peak of the 1 3 c excursion kinderhookian osagean boundary although tectonic changes associated with the antler orogeny have likely modified the eustatic signature

reef development at the frasnian famennian mass extinction boundary a newly compiled global reef database indicates that the 5 6 myr long frasnian late devonian metazoan reef episode had relatively lowdiversity compared to middle devonian highs w ith over 200 genera of calcitic rugose and tabulate corals following an initial early rise after late givetian coral and stromatoporoid extinctions reefs expanded for the last time during mid frasnian sealevel highstands but declined markedly in the late frasnian rhenana linguiformis conodont zones belowthe frasnian famennian f f boundary globally metazoan reefs were wiped out by the end frasnian some famennian reefs while partly retaining the structure of the underlying carbonate platform were built by cyanobacterial consortia such as renalcis rothpletzella girvanella and epiphyton during the famennian foraminiferans with calcite walls became abundant for the first time in the phanerozoic adding a newdimension to carbonate platforms colonial rugose corals phaceloid cerioid and thamnasterioid modules were absent in the early post extinction phases up into the mid famennian and very rare and non reefbuilding later but solitary deep water lazarus corals survived locally coral sponge reefs are unknown from the 21 myr long famennian also a time of very lowplatform carbonate production rare small isolated stromatoporoid sponge and lithistid sponge patch reefs returned episodically during the famennian in north america western europe australia and china the aragonitic stromatoporoids became extinct at the end of the famennian during a late devonian tectonically very active collisional caledonian mountain building phase oceanic and atmospheric cooling accompanied by sealevel lowstand systems exposed most carbonate platforms accelerating coastal erosion and karsting this increased the amount of clastics in the shelf slope setting in the last 1 3 myr prior to the f f boundary often burying reefs immediately following there were protracted losses in nearly all major tropical shelf benthic marine invertebrates exceeded only by the end permian extinctions in severity there is no apparent link between black organic rich horizons and reef demise at or close to the f f boundary the f f boundary not also marks the largest change from widespread flooded early and mid paleozoic continental cratons to narrow distal shelves but also spikes the largest known global phanerozoic shift in atmospheric o2 enrichment and co2 drawdown this threshold matched the rise of the first tropical rainforests and expansion of terrestrial biomes on the tropical coastal lowlands formerly occupied by carbonate platforms 6 2002 elsevier science b v all rights reserved

upper devonian conodont zonation sea level changes and bio events in offshore carbonate facies lali section south china abstract the lali section guangxi province south china is composed of quiet water carbonates containing abundant conodonts which allowed recognition of 12 frasnian and 20 famennian biozones the kellwasser and annulata events are characterized by transgressive black carbonates while the hangenberg event is represented by black shale deposits other transgressive events recognized at lali include the middlesex nehden enkeberg and dasberg as well as the strunian transgression four regressive events were recognized on the basis of lithological and microfacies changes i e the linguiformis regression condroz event velifer regression and the derwer regression these sea level change events were of short duration and globally isochronous based on conodont correlations microfacies analyses and the abundance of palmatolepis indicate that the highest frasnian sea level lies in fz 12 13 upper rhenana zone whereas the highest famennian sea level was in the utahensis zone

evidence for shear failure in forming near equatorial lineae on europa 1 global stress models for europa are unable to readily explain the orientations of lineae in the equatorial region of europa s trailing hemisphere if lineae originate as tension cracks our analysis of two equatorial trailing regions reveals that lineae are predominantly oriented ne and nw and e w lineae are rare contrary to predictions of stress and formation models the measured orientations are consistent with an origin by shear failure the studied regions are located near the point of maximum differential stress and minimum surface tensile stresses where shear faulting may surmount tension fracturing several types of lineae are recognized their relative abundance is inferred to have changed with time consistent with formation models suggesting lineae evolve from simple troughs to complex ridges the opening of crevasse like tensile fractures is not required for generation of all lineae the observations are consistent with ridge formation models where troughs formed in tension or shear experience shear heating from tidal deformation allowing warm ice to buoyantly uplift creating ridges the stratigraphic relationships indicate the following ridged plains formed first followed by continued formation of a wide range of lineae and lastly emplacement of lenticulae and continued linea formation this sequence is consistent with an early thin brittle lithosphere that thickened with time and was subject to repetitive diurnal tides during 30 90 of nonsynchronous rotation ultimately the thickened shell underwent thermally induced solid state convection producing lenticulae the young surface age of europa implies that this entire stratigraphic sequence was emplaced in the geologically recent past

strike slip faults on europa global shear patterns driven by tidal stress abstract diurnal tides due to orbital eccentricity may drive strike slip motion on europa through a process of walking in which faults open and close out of phase with alternate right and left lateral shear mapping of five different regions on europa has revealed 121 strike slip faults including astypalaea linea a 800 km long fault with 42 km of right lateral offset at high southern latitudes near astypalaea linea all of the strike slip faults identified were right lateral europa appears to preferentially form right lateral faults in the southern hemisphere and left lateral faults in the northern hemisphere consistent with tidal walking at the five locations nonsynchronous rotation explains the azimuthal orientations and distribution of sense of shear which fit formation 60 to 90 west of their current positions alternatively stress due to differential rotation might also explain the observed shear patterns nearly all identified strike slip faults were associated with double ridges or bands but few were detected along ridgeless cracks even older ones thus cracks without ridges may not have penetrated to a decoupling layer consistent with the models for ridge formation that require cracks to penetrate to a liquid water ocean

rapid onset of late paleozoic glaciation on gondwana evidence from upper mississippian strata of the midcontinent united states direct evidence of the late paleozoic glaciation of gondwana from glacial deposits suggests that geographically extensive continental glaciation began some time in the namurian late mississippian however the timing and characteristics of the onset of glaciation are poorly understood because of a lack of reliable paleontological control and reworking of initial glacial deposits by subsequent glacial advances indirect evidence of glaciation preserved in unconformity bounded low latitude ramp sequences in the illinois basin united states suggests that geographically extensive continental glaciation of gondwana actually began in the late visean an abrupt change from carbonate dominated sequences bounded by disconformities with little evidence of erosion to mixed carbonate siliciclastic sequences bounded by unconformities with deep incised valleys was likely produced by a three fold increase in the magnitude of eustatic sea level fluctuations the increase in the magnitude of sea level fluctuations was likely driven by an equally abrupt increase in ice volume and marks the onset of the geographically extensive late paleozoic glaciation of gondwana a possible explanation for the rapid onset of glaciation is the closing of the equatorial seaway between laurussia and gondwana closing of this seaway would have led to an abrupt change in oceanic and atmospheric circulation patterns that could have initiated major continental glaciation in the southern hemisphere

geological history of the tyre region of europa a regional perspective on europan surface features and ice thickness galileo images of the tyre macula region of europa at regional 170 m pixel and local 40 m pixel scales allow mapping and understanding of surface processes and landforms ridged plains doublet and complex ridges shallow pits domes chaos areas impact structures tilted blocks and massifs and young fracture systems indicate a complex history of surface deformation on europa regional and local morphologies of the tyre region of europa suggest that an impactor penetrated through several kilometers of water ice to a mobile layer below the surface morphology was initially dominated by formation of ridged plains followed by development of ridge bands and doublet ridges with chaos and fracture formation dominating the latter part of the geologic history of the tyre region two distinct types of chaos have been identified which along with upwarped dome materials appear to represent a continuum of features domes platy chaos knobby chaos resulting from increasing degrees of surface disruption associated with local lithospheric heating and thinning local and regional stratigraphic relationships block heights and the morphology of the tyre impact structure suggest the presence of low viscosity ice or liquid water beneath a thin several kilometers surface ice shell at the time of the impact the very low impact crater density on the surface of europa suggests that this thin shell has either formed or been thoroughly resurfaced in the very recent past

stratigraphy and ages of four early silurian through late devonian early and middle mississippian glaciation events in the parnaiba basin and adjacent areas ne brazil abstract turbidity currents tectonism debris flows glaciation and other geologic processes are considered to be responsible for the generation of silurian mississippian diamictites in northern brazil processes that best account for the features observed in these strata are glaciation deglaciation and sedimentary deformation four main glacial ages are identified to have occurred in the parnaiba basin during the paleozoic glacially influenced deposits are found in the lower silurian upper devonian lower mississippian and middle mississippian strata the parnaiba basin is characterized by outcrops providing robust lithological evidence for three glacial ages identified by lithological features and dated by palynological studies a fourth glaciation as old as tournaisian was recently recognized only in the subsurface of the basin the glacial features were illustrated and the rocks accurately dated with palynomorphs based on very accurate palynological studies additional palynological information derives from outcrops and shallow boreholes drilled by a private company themag and the national state mineral production department departamento nacional de producao mineral dnpm and the brazilian geological survey company companhia de pesquisa de recursos minerais cprm the purpose of this reexamination including many new illustrations interpretations and conclusions is to evaluate primary sedimentological and paleontological data related to the above mentioned glaciations some authors remain skeptical about the record of early to early late paleozoic glaciations in western gondwana especially in brazil mainly because evidence provided in the literature is relatively scanty the parnaiba basin provides special conditions for the study of these glaciations although evidence for each of them varies considerably as discussed in the text

ecological ranking of phanerozoic biodiversity crises the serpukhovian early carboniferous crisis had a greater ecological impact than the end ordovician we propose a new ecological ranking of the major phanerozoic biodiversity crises in which the serpukhovian biodiversity crisis is ranked fifth in ecological impact lesser than the late devonian but greater than the end ordovician and the end ordovician mass extinction is ranked sixth it is interesting that both the end ordovician mass extinction and the serpukhovian biodiversity crisis were triggered by glaciations other than that common trigger the two events were very different glaciation in the ordovician triggered an enormous jump in the extinction rate of marine organisms and was taxonomically very severe yet the ecological impact of those extinctions was minimal glaciation in the serpukhovian triggered a precipitous drop in the speciation rate but only moderate diversity losses yet the ecological impact of those diversity losses and ecosystem restructuring was an ecological level of magnitude larger than that seen in the end ordovician mass extinction

stresses generated in cooling viscoelastic ice shells application to europa 1 a cooling viscoelastic ice shell overlying an ocean develops stresses due to two effects thermal contraction of the ice due to cooling and the expansion of the shell due to the ice water volume change the former effect generates near surface compression and deeper extension the second effect generates extension only in both cases stresses are smaller at depth due to viscous creep the resulting combined stresses are extensional except at shallow 1 km depths in thin ice shells for ice shells thicker than 45 km stresses are extensional throughout the extensional stresses exceed 10 mpa for shells thicker than 20 km and thus dominate all other likely sources of stress as long as shell cooling occurs the dominantly extensional nature of the stresses may help to explain the puzzling lack of compression observed on europa and other large icy satellites however after 100 myr of conductive cooling the maximum theoretical elastic strains for europa are 0 35 which are probably insufficient to explain the total amount of observed extension

cryomagmatic mechanisms for the formation of rhadamanthys linea triple band margins and other low albedo features on europa we investigate cryomagmatic mechanisms for the formation of the diffuse low albedo margins of triple bands and haloes associated with elliptical lenticulae on europa one mechanism involves explosive venting of a gas particle spray derived from a subsurface body of volatile bearing water assuming the dark features represent cryoclastic deposits erupted from a medial or central vent modeling the dynamics of the eruptive plumes indicates that eruption velocities of 30 to 250 m s 1 and volatile contents of 0 1 to 20 wt are required to produce deposits having the observed dimensions calculated heights for ballistic plumes range from 1 to 25 km as an alternative mechanism we consider conductive heating of lithospheric ice by a subsurface heat source e g a warm ice diapir or cryomagmatic intrusion which promotes enhanced sublimation of surface ice producing local enrichment of nonice material an analytical model describing a constant temperature infinite heat source places lower bounds on the time scales required to produce a detectable feature a numerical treatment of more realistic geometries and boundary conditions allows cooling of the heat source to be modeled we find that the thermal model satisfactorily explains features with the dimensions of minor lineaments and lenticulae haloes a few kilometers over time intervals of 104 to 105 years the formation of a sublimation lag deposit proceeds rapidly once the ice temperature exceeds a threshold of 130 k however for triple bands measuring up to 25 km in width additional heat sources such as repeated or multiple intrusions are necessary to reproduce the observed dimensions this is consistent with the observation that well developed triple bands typically have multiple medial ridge sets each of which may represent a discrete tabular heat source although neither the volcanic nor intrusive thermal model can be ruled out at this stage the latter is a more satisfactory explanation for some characteristics of the low albedo features analyzed in this study

a revised model for cycloid growth mechanics on europa evidence from surface morphologies and geometries although a single model currently exists to explain the development of curved europan cycloids there have been no systematic studies of the range of morphologies and quantifiable geometric parameters of cycloidal features we address variations in geometry along individual cycloid segments characterizing differences in cusp styles and angles and addressing the morphologic aspects of cycloid segments and cusps in so doing we illustrate how geometric and morphologic evidence imply a formation mechanism that differs from the existing model in several aspects the current model states that cycloids are initiated as tensile fractures that grow in a curved path in response to rotating diurnal tidal stresses on europa however the geometry of a cycloid cusp necessitates that shear stress was resolved onto the existing cycloid segment by the rotating diurnal stresses at the instant of cusp formation furthermore we observe that cycloid cusps have a strikingly similar geometry to tailcracks that developed at the tips of many ridge like strike slip faults on europa in response to shearing at the fault tip we suggest that this similarity in geometries can be attributed to an identical formation mechanism whereby cycloid cusps form by a tailcracking process we therefore present a revised mechanically based model for cycloid formation that retains the basic premise that crack growth is governed by diurnal stresses but describes the development of cycloid cusps in response to resolved shear stresses at the tips of existing cycloid segments the ratio of normal to shear stress at the time of tailcrack formation dictates the cusp angle and over longer time periods influences the morphologic evolution of the cycloid segment as it is repeatedly reworked by tidal stresses

geologic mapping of the northern leading hemisphere of europa from galileo solid state imaging data the northern leading hemisphere of europa was imaged at regional mapping resolution 230 m pixel by the galileo spacecraft ssi camera we produced geologic maps from a regional scale mosaic and a high resolution inset of this region twelve geologic units were sufficient to produce correlative geologic maps at both regional and local scales stratigraphic relationships indicate four major episodes in the geologic history of this area the first episode includes background plains formation and modification followed by a second period of extensive lineament formation the third episode included extensive chaotic disruption of the surface at low and middle latitudes the final episode includes the formation of new sets of ridges and bands especially at high latitudes the low crater density indicates that all these episodes in europa s geologic history are geologically recent the latitudinal distribution of chaos areas broadly matches that of areas of crustal thinning from models of tidal heating we show that stress directions rotated clockwise with time which is consistent with predictions from global stress models involving tidal deformation and nonsynchronous rotation of europa s crust on the basis of the change in lineament orientation with time the reconstructed longitudinal positions of the studied area indicate that europa s crust completed a full rotation relative to the tidally deformed interior

crustal scale strike slip deformation in hokkaido northern japan abstract field surveys in hokkaido reveal that the entire tectonic belt in northern japan was a right lateral shear zone from eocene to middle miocene time this zone of deformation can be followed northwards in sakhalin for more than 2000 km and formed at the same time as the opening of the japan sea a thrusting component during the strike slip deformation and later deformation stages led to the uplift of the deep parts of the shear zone exposing a complete section through the upper crust the stress field inferred from the analysis of fault sets is consistent with the non coaxial deformation observed in the deeper ductile parts of the shear zone there is a transition from west to east across the width of the belt 100 km from en echelon folds thrusts and nappes at upper structural levels through the brittle ductile transition with an incipient vertical schistosity into ductile deformation with a vertical foliation and metamorphic recrystallization in the amphibolite facies deep parts of the crust granulites were uplifted and retrogressed during the strike slip movement fault set analysis together with data concerning the direction and sense of nappe emplacement imply that thrusting west of the ductile deformation zone occurred during the strike slip deformation minor flat lying structures coexist with vertical pure strike slip structures this study and previous ones reveal a crustal scale half flower structure with superficial thrusting associated with a deep narrow ductile zone with a high gradient of deformation and temperature

europan double ridge morphometry as a test of formation models abstract double ridges on the jovian satellite europa consist of two parallel ridges with a central trough although these features are nearly ubiquitous on europa their formation mechanism s is are not yet well understood previous hypotheses for their formation can be divided into two groups based on 1 the expected interior slope angles and 2 the magnitude of interior exterior slope symmetry the published hypotheses in the first fracture group entail brittle deformation of the crust either by diapirism shear heating or buckling due to compression because these mechanisms imply uplift of near vertical fractures their predicted interior slopes are steeper than the angle of repose aor with shallower exterior slopes the second flow group includes cryosedimentary and cryovolcanic processes explosive or effusive cryovolcanism and tidal squeezing which are predicted to form ridge slopes at or below the aor explosive cryovolcanism would form self symmetric ridges whereas effusive cryolavas and cryo sediments deposited during tidal squeezing would likely not exhibit slope symmetry to distinguish between these two groups of hypothesized formation mechanisms we derived measurements of interior slope angle and interior exterior slope symmetry at multiple locations on europa through analysis of data from the galileo solid state imaging ssi camera two types of data were used i elevation data from five stereo pair digital elevation models dems covering four ridges 580 individual measurements and ii ridge shadow length measurements taken on individual images over 40 ridges 200 individual measurements our results shows that slopes measured on our dems located in the cilix and banded plains regions typically fall below the aor and slope symmetry is dominant two different shadow measurement techniques implemented to calculate interior slopes yielded slope angles that also fall below the aor the shallow interior slopes derived from both techniques weigh against brittle deformation mechanisms although shallow slopes could result from degradation interior exterior ridge symmetry weighs against ridge degradation as the sole reason for shallow interior slopes thus our results suggest that for the double ridges analyzed in this work cryovolcanic or cryosedimentary formation is more likely than brittle deformation and of those formation mechanisms explosive cryovolcanism is the double ridge formation mechanism best supported on the basis of interior exterior slope symmetry

formation of cycloidal features on europa cycloidal patterns are widely distributed on the surface of jupiter s moon europa tensile cracks may have developed such a pattern in response to diurnal variations in tidal stress in europa s outer ice shell when the tensile strength of the ice is reached a crack may occur propagating cracks would move across an ever changing stress field following a curving path to a place and time where the tensile stress was insufficient to continue the propagation a few hours later when the stress at the end of the crack again exceeded the strength propagation would continue in a new direction thus one arcuate segment of the cycloidal chain would be produced during each day on europa for this model to work the tensile strength of europa s ice crust must be less than 40 kilopascals and there must be a thick fluid layer below the ice to allow sufficient tidal amplitude

tracing paleoredox conditions across the devonian carboniferous boundary event a case study from carbonate dominated settings of belgium the czech republic and northern france the devonian carboniferous boundary was coeval with the hangenberg crisis which is regarded as a first order mass extinction event related with large sea level changes and widespread anoxia this study aims to trace the geochemical paleoproductivity and paleoredox proxies across the devonian carboniferous carbonate dominated successions of the namur dinant basin belgium northern france and the moravo silesian basin czech republic located in the variscan rhenohercynian zone the research was focused on the distribution of oxides sio2 al2o3 fe2o3 cao na2o k2o tio2 mno and trace elements th u v zr mo zn pb ni cu measured by icp oes and icp ms respectively the enrichment factors of mo and u and their ratios were used as the main paleoredox proxies whereas the enrichment factors of zn cu pb and ni were employed to trace the paleoproductivity changes high values of zr al2o3 0 001 tio2 al2o3 0 06 and fe ti 20 and low values of al al fe mn 035 coinciding with an increase of paleoredox proxies suggest a possible volcanic and hydrothermal source of nutrients related to late devonian and early carboniferous extensional magmatism in the rhenohercynian domain although a relationship between higher paleoproductivity and enhanced continental runoff of volcanic material cannot be excluded the studied devonian carboniferous boundary sections from the namur dinant basin gendron celles ardennes quarry reveal three levels with similar vectors of mo and u enrichments the pre crisis famennian pattern is typical for weakly restricted basins with fe mn redox cycling accompanying vertical fluctuations of the oxic anoxic chemocline close to the sediment water interface with the influence of particulate shuttle the mo ef and u ef patterns corresponding to the unrestricted or weakly restricted basin with alternating suboxic to anoxic conditions are considered to represent the transgressive hangenberg black shale event the lower tournaisian mo ef and u ef patterns fall along a vector in the direction of the strongly restricted marine conditions with prevailing suboxic conditions in the moravo silesian basin lesni lom section the pre crisis famennian mo ef and u ef vector indicates an unrestricted marine trend which converges with that of restricted systems redox conditions range from suboxic to euxinic in the tournaisian mo ef and u ef oscillate between oxic and anoxic conditions and fall along a vector of strongly restricted marine conditions increased isolation of both studied basins in the early tournaisian is regarded as a reflection of a significant eustatic fall during the hangenberg crisis linked to a severe episode of the gondwana glaciation these paleohydrographic patterns have correlative potential that should be considered for a revised devonian carboniferous boundary definition

late devonian glaciation in south america abstract an ice age in famennian late devonian time is documented by the presence of diamictites with striated faceted and polished pebbles rhythmites with dropstones erratic boulders and striated pavements and deformed sandstones the glacigenic beds occur in three huge intracratonic basins solimoes amazonas and parnaiba and in one pericratonic basin acre in northern brazil other possible late devonian diamictites may occur elsewhere in brazil and africa which if confirmed would extend considerably the area affected by this glacial age the onset of the late devonian glaciation caused a global narrowing of the warm climatic belts sharp regression increased clastic sedimentation massive biotic extinction reduced biochemical deposition and unconformities this resulted in important facies changes in the world geological record ice centers moved from northern africa to southwestern south america from late ordovician to early silurian time from mid silurian to early late devonian time no record of glaciation is known in late late devonian time intermittent glaciation began again in central south america and from late late devonian to early late permian time ice centers migrated towards antarctica across south america and south africa the devonian and ordovician silurian glaciations together with the better known permo carboniferous glaciations may all have primarily resulted from the shifting position of the gondwana continent with respect to the south pole

intensified oceanic circulation during early carboniferous cooling events evidence from carbon and nitrogen isotopes abstract the early carboniferous was a climatic transition interval from a mid paleozoic greenhouse world into the late paleozoic ice age it was marked by a long term cooling trend that was punctuated by short glaciations in the tournaisian and visean early to mid early carboniferous here we generated organic carbon and nitrogen isotope profiles for two widely separated lower carboniferous sections arrow canyon range nevada and namur dinant basin belgium in order to assess the global nature and timing of changes in the carbon nitrogen cycles linked to oceanic productivity and redox conditions during this climatic transition interval the carbon and nitrogen isotope profiles of both study sections record major perturbations during the mid tournaisian and visean a mid tournaisian event tice is marked by increases in 13ccarb 13corg and 15nbulk at arrow canyon from 0 6 to 7 0 25 2 to 23 7 and 0 6 to 8 9 respectively and namur dinant from 0 3 to 4 7 27 9 to 22 2 and 5 7 to 5 2 respectively an early visean event vice named herein is marked by increases in 13ccarb 13corg and 15nbulk at arrow canyon from 0 6 to 3 1 28 4 to 23 6 and 1 4 to 9 4 respectively and namur dinant from 2 1 to 4 3 26 7 to 25 0 and 1 4 to 3 3 respectively the positive excursions in all three isotopic records during these events are consistent with increased fractional burial of organic carbon and enhanced denitrification implying intensification of marine productivity and expansion of hypoxia in the global ocean given that each event coincided with lowering of sea surface temperatures and increased glaciation as documented from published conodont 18o and sea level records we hypothesize that global cooling led to intensified oceanic circulation and upwelling on continental margins triggering increased marine productivity and attendant redox changes within the affected upwelling zones our results provide new insights into changes in early carboniferous oceanic conditions in response to the initial stages of cooling leading into the late paleozoic ice age

patterns of fracture and tidal stresses on europa abstract the hypothesis that lineaments on europa are fractures produced by tidal distortion and planetary volume change is examined by comparing the orientations of dark bands triple bands and cuspate ridges to fracture patterns predicted for tidal distortion due to orbital recession and orbital eccentricity if short reticulate dark band nnear the anti jove point are tension cracks which formed in response to tidal distortion they could only have been produced by orbital eccentricity long arcuate dark band and triple bands peripheral to the anti jove point orientations which suggest that they are strike slip faults which formed in response to orbital recession if cuspate ridges are compressional features their orientations and distribution suggest that they formed in response to combined orbital recession and a decrease in planetary volume stresses due to orbital eccentricit could have produced tension cracks near the anti jove point only if tensile failure occurred either prior to the accumulation of orbital recession stresses or after they had relaxed surface fracturing if a consequence of tidal deformation places important constraints on the orbital evolution of europa

devonian climate sea level and evolutionary events an introduction the face of planet earth has changed significantly through geological time dynamic processes active today such as plate tectonics and climate change have shaped the earth s surface and impacted biodiversity patterns from the beginning organisms on the other hand have the capacity to significantly alter earth s hydrological and geochemical cycles its atmosphere and climate sediments and even hard rocks deep down under the surface abiotic biotic interactions characterize earth s system history and together with biotic competition and food webs were the main trigger of evolutionary change innovations and biodiversity fluctuations within the palaeozoic the devonian was an especially interesting time interval as it was characterized by the mid paleozoic predator revolution signor brett 1984 brett 2003 and the related nekton revolution klug et al 2010 characterized by the blooms of free swimming cephalopods including the oldest ammonoids and fish groups e g toothed sharks and giant placoderms the rise of more advanced vertebrates including the oldest tetrapods e g blieck et al 2007 2010 niedzwiedzki et al 2010 the most extensive reef complexes of the phanerozoic e g kiessling 2008 and the greening of land by the diversification and spread of land plants including the oldest forests e g stein et al 2012 giesen berry 2013 which resulted in new soil types and changing weathering these major evolutionary trends did not unfold in a long interval of environmental stability but in times of numerous and repeated geologically brief global events that punctuated prolonged periods up to several million years in duration of relative stability termed ecological evolutionary subunits ee subunits boucot 1990 brett baird 1995 brett et al 2009 the bounding events even those of lesser intensity produced major re structuring in local to global ecosystems and are seen as critical drivers of long term evolutionary patterns brett 2012 these linked abiotic and biotic events and extinctions of different magnitude have been summarized by house 1983 1985 2002 walliser 1984 1996 and more recently by becker et al 2012 the devonian event succession is summarized in figure 1 two first order mass extinctions at the frasnian famennian boundary kellwasser crisis and at the end of the devonian hangenberg crisis characterized by the loss of major fossil groups classes and orders and complete ecosystems e g metazoan reefs early forests have to be viewed in the context of a complex global event sequence there are important similarities between discrete pulses phases of the major biotic crises and individual smaller scale events in our understanding second order global events are characterized by sudden extinctions in many groups and ecosystems including the complete disappearance of several widespread and diverse organism groups orders and families examples are the basal emsian atopus event where the planktonic graptolites finally died out the taghanic crisis frasnes events and lower kellwasser event third order global events show globally elevated extinction rates often at lower taxonomic level genera and species but within many clades and in several ecosystems examples are the silurian devonian boundary klonk event and the daleje chot c kacak condroz and annulata events fourth order global extinctions refer to the sudden disappearance of relatively fewer but widespread groups which implies a global not regional trigger this category may include the lochkovian pragian boundary

crack azimuths on europa sequencing of the northern leading hemisphere 1 nonsynchronous rotation of europa should result in a periodic change in stress azimuths at any given location which may result in a corresponding change in crack azimuths an early study seemed to provide evidence for such variation within a crack sequence in the northern trailing hemisphere however more recent work with higher resolution imagery resulted in a more complete sequence of cracks in the region and showed that the azimuth variation with time was not systematic similar results were found in the southern leading region here we investigate whether the northern leading region contains a crack record on the basis of crosscutting relationships that is adequate to indicate nonsynchronous rotation as in the previous studies of other regions we find no clear evidence of nonsynchronous rotation within crack azimuth patterns however there are other lines of evidence in support of nonsynchronous rotation therefore the lack of a continuous pattern of azimuth change with time is likely due to only a few cracks forming per cycle thus hiding any discernable signal from nonsynchronous rotation in those regions in that case the cracks would have formed over numerous cycles of nonsynchronous rotation the study also reveals a distinctive distribution of crack azimuths with gaps at certain values this distribution may reflect a combination of observation selection due to illumination and less favorable cracking orientations

tidal stress modeling of ganymede strike slip tectonism and coulomb failure abstract high resolution galileo data of ganymede s complex surface provide strong and ubiquitous evidence of strike slip motion en echelon structures strike slip duplexes laterally offset pre existing features and strained craters in a previous study we performed a detailed mapping of these strike slip morphologies within nine regions of ganymede dardanus sulcus tiamat sulcus nun sulci byblus sulcus nippur and philus sulci the transitional terrain of northern marius regio anshar sulcus arbela sulcus and uruk sulcus strike slip indicators were inferred in various combinations at each site in addition to extensional processes however the prominence of strike slip indicators suggests shearing has been an important process to the structural development of ganymede s surface moreover tidal stresses on ganymede under particular circumstances may have been sufficient to induce coulomb failure and generate strike slip faulting here we investigate the role of both diurnal and non synchronous rotation nsr tidal stresses on ganymede using the numerical code satstress we resolve normal and shear tractions onto discrete fault segments of specified orientation and assess coulomb failure potential for the nine inferred fault zones testing a range of subsurface fault depths z 0 5 km and ice friction f 0 2 0 6 we find that tidal stress models of combined diurnal and nsr stress readily promote coulomb failure within each studied fault zone high friction f 0 6 limits failure depths to 1 km while low friction f 0 2 extends failure depths to 2 km consistent with elastic thickness estimates we also compare each fault zone s predicted shear sense to the inferred shear sense from our structural mapping efforts and find compatible senses of shear among six of the nine regions that exhibit notable fault offset and or prevalent inferences of en echelon duplexes and strained craters in addition principal stress orientations and failure feasibility computed on a global scale suggest that combined diurnal and nsr tidal stresses promote coulomb failure within the shallow

geologic mapping of europa galileo data enable the major geological units structures and surface features to be identified on europa these include five primary units plains chaos band ridge and crater materials and their subunits along with various tectonic structures such as faults plains units are the most widespread ridged plains material spans a wide range of geological ages including the oldest recognizable features on europa and appears to represent a style of tectonic resurfacing rather than cryovolcanism smooth plains material typically embays other terrains and units possibly as a type of fluid emplacement and is among the youngest material units observed at global scales plains are typically mapped as undifferentiated plains material although in some areas differences can be discerned in the near infrared which might be related to differences in ice grain size chaos material is composed of plains and other preexisting materials that have been severely disrupted by inferred internal activity chaos is characterized by blocks of icy material set in a hummocky matrix band material is arrayed in linear curvilinear wedge shaped or cuspate zones with contrasting albedo and surface textures with respect to the surrounding terrain bilateral symmetry observed in some bands and the relationships with the surrounding units suggest that band material forms by the lithosphere fracturing spreading apart and infilling with material derived from the subsurface ridge material is mapped as a unit on local and some regional maps but shown with symbols at global scales ridge material includes single ridges doublet ridges and ridge complexes ridge materials are considered to represent tectonic processes possibly accompanied by the extrusion or intrusion of subsurface materials such as diapirs the tectonic processes might be related to tidal flexing of the icy lithosphere on diurnal or longer timescales crater materials include various interior smooth central rough inner and annular massif and exterior continuous ejecta subunits structural features and landforms are shown with conventional symbols type localities for the units are identified along with suggestions for portraying the features on geological maps including colors and letter abbreviations for material units implementing these suggestions by the planetary mapping community would facilitate comparisons of maps for different parts of europa and contribute to an eventual global synthesis of its complex geology on the basis of initial mapping results a stratigraphic sequence is suggested in which ridged plains form the oldest unit on europa followed by development of band material and individual ridges band materials tend to be somewhat older than ridges but in many areas the two units formed simultaneously similarly the formation of most chaos follows the development of ridged plains although chaos is among the youngest materials on europa some chaos units might have formed contemporaneously with ridged plains smooth plains generally embay all other units and are late stage in the evolution of the surface c 1 craters are superposed on ridged plains but are crosscut by other materials including bands and ridges most c2 craters postdate all other units but a few c2 craters are cut by ridge material c3 craters constitute the youngest recognizable material on europa

glaciomarine sequence stratigraphy in the mississippian rio blanco basin argentina southwestern gondwana basin analysis and palaeoclimatic implications for the late paleozoic ice age during the tournaisian the late palaeozoic ice age lpia has been well recorded in the uppermost mississippian pennsylvanian of gondwana nevertheless little is known about the temporal and geographic dynamics particularly during the early mississippian we report on exceptional tournaisian glaciomarine strati graphic sections from central argentina rio blanco basin encompassing 1400 metres these succes sions contain conspicuous glacigenic strata with age constraints provided by palaeontological data and u pb detrital zircon age spectra a variety of marine glaciomarine and fan deltaic environments indicate relative sea level variations mainly associated with tectonism and repetitive cycles of glacial activity provenance analysis indicates a source from the sierras pampeanas basement located to the east fifteen sequences were grouped into three depositional models 1 transgressive systems tracts tst to high stand systems tracts hst sequences unaffected by glacial ice 2 lowstand systems tracts lst to tst and then to hst with glacial in uence and 3 non glacial falling stage systems tract fsst to tst and hst the glacial evidence indicates that the oldest mississippian glacial stage of the lpia in southwestern gondwana is constrained to the middle tournaisian in contrast with previous descriptions of gondwanan coeval glacial records our sequence analysis confirms complex hierarchical climate varia bility rather than a single episode of ice advance and retreat supplementary material https doi org 10 6084 m9 figshare c 5011424

stratigraphy and palaeoenvironmental evolution of the mid to upper palaeozoic succession in northwest peninsular malaysia abstract the stratigraphy of the devonian to permian succession in northwest peninsular malaysia is revised the timah tasoh formation consists of black mudstone containing graptolites and tentaculitids indicating a pragian or earliest emsian age the sanai limestone overlies the timah tasoh formation at sanai hill b and contains conodonts indicating a late devonian frasnian to possibly early famennian age in other places late tournaisian chert of the telaga jatoh formation overlies the timah tasoh formation the overlying kubang pasu formation is predominantly composed of mudstone and sandstone and can be divided into 3 subunits from oldest to youngest 1 chepor member 2 undifferentiated kubang pasu formation 3 uppermost kubang pasu formation the ammonoid praedaraelites tuntungensis sp nov is reported and described from the chepor member of bukit tuntung pauh the genus indicates a late visean age for part of the subunit dropstones and diamictites from the chepor member indicate a glacial marine depositional environment the carbo permian undifferentiated kubang pasu formation consists of similar interbedded mudstone and sandstone the uppermost kubang pasu formation of kungurian age consists of coarsening upward cycles of clastics representing a shallow marine wave and storm influenced shoreline the permian chuping limestone also represents shallow marine wave and storm influenced deposits a mid palaeozoic unconformity separating early late devonian rocks from overlying late devonian carboniferous deposits probably marks initiation of rifting on sibumasu which eventually led to the separation of sibumasu from australian gondwana during the late sakmarian early permian

distribution of chaotic terrain on europa the locations of chaotic terrain are mapped over all regions of europa for which we have adequate resolution 200 m or better and appropriate lighting geometry sun angle 35 from the local horizontal comprising 9 of the total surface of the satellite nearly 30 of the mapped area is occupied by chaotic terrain recognizable at 200 m resolution and sampling at higher resolution suggests that at least 10 more may be covered by small chaos features the largest contiguous area of chaotic terrain is 1300 km across chaotic terrain displays variations in freshness of appearance probably because of aging by fine scale tectonics resurfacing of previous chaotic terrain by larger scale tectonics or disruption by newer chaos are common chaos formation is not necessarily recent relative to tectonics both types of process appear to have gone on diachronously the size distribution shows no dominant or characteristic size and appears to have been controlled by competition from tectonics which has created terrain that occupies more than half of the surface of europa

evolution of lineaments on europa clues from galileo multispectral imaging observations abstract four distinct classes of lineaments can be described on the basis of galileo s improved spectral and spatial coverage of europa 1 incipient cracks are narrow the morphologies spectral properties and orientations of the lineaments vary systematically with age suggesting that these four classes represent different stages of development in an evolutionary sequence lineament formation appears to be the dominant resurfacing mechanism on europa and every landscape that has escaped erasure by heating from below is imprinted with generation after generation of intersecting ridges at various scales and orientations relatively recent fractures expose coarse grained clean ice in the shallow subsurface possibly accounting for the distinctive color of the satellite in comparison to the other icy moons of jupiter the process of lineament formation may be continuing today the bright band agenor linea is among the leading candidates for current activity

cyclostratigraphy across a mississippian carbonate ramp in the esfahan sirjan basin iran implications for the amplitudes and frequencies of sea level fluctuations along the southern margin of the paleotethys the tournaisian visean carbonate successions of the esfahan sirjan basin esb from sanandaj sirjan zone iran have been used to generate a sequence stratigraphic model that enhances facies characterization and improves paleoenvironmental interpretation of shallow marine successions deposited along the southern margin of the paleotethys detailed facies analysis allowed to differentiate seven facies which in order of decreasing abundance are 1 shaly and marly f1 2 peloidal mudstones wackestones f2 3 peloidal bioclastic packstones f3 4 intraclastic bioclastic packstones grainstones f4 5 oolitic bioclastic packstone grainstone f5 6 sandy intraclastic bioclastic grainstones f6 7 sandy oolitic bioclastic grainstones f7 the different facies can be grouped into three facies associations that correspond to different environments of a carbonate platform with ramp geometry homoclinal from outer ramp f1 and f2 mid ramp f3 f4 and f6 to inner ramp areas f5 and f7 meter scale cycles are the basic building blocks of shallow marine carbonate successions of the tournaisian visean ramp of the esb small scale cycles are stacked into medium scale cycles that in turn are building blocks of large scale cycles according to the recognized facies and the stacking pattern of high frequency cycles across the ramp five large scale cycles in the southeastern outcrops tournaisian visean and three large scale cycles in the northwest outcrops visean related to eustatic sea level changes can be recognized the overall retrogradational nature of the carbonate ramp illustrated by both vertical facies relationships and the stacking patterns of high frequency cycles within the third order cycles implies that the deposition of the tournaisian visean successions mainly took place under a long term transgressive sea level trend the stratigraphic architectural style of the sequences characterized by the lack of lowstand deposits and exposure surfaces associated with the evidence of progressive increase in the proportion of backstepping of facies belts across bounding surfaces and predominant subtidal characteristics is in accordance with the long term transgressive sea level trend and greenhouse conditions during the tournaisian visean the continued transgression on this broad shelfal platform could lead to the shutdown of the shallow water carbonate factory reduction in sediment supply or sediment transport towards the offshore setting and the development of give up sequences the association of transgressive events with the deposition of thick open marine marls shales is a common feature in tournaisian to visean times of the southern margin of the paleotethys

strike slip fault evolution on europa evidence from tailcrack geometries secondary cracks are commonly produced at stress concentration points at the tips of slipping interfaces such as faults these so called tailcracks form an antisymmetric pattern at opposite tips of the fault with a fracture geometry that is a mechanical indicator of the sense of slip whether left lateral or right lateral i present descriptions of tailcracks along numerous strike slip faults on europa two distinct styles of strike slip faults are identified ridge like and band like the angles between faults and tailcracks are variable and are commonly less than the theoretical 70 5 angle that approximately characterizes many terrestrial examples involving fault surfaces that remain in contact during slip median tailcrack angles are lower for band like faults 30 than ridge like faults 52 in addition the sense of curvature of band like fault tailcracks is characteristically opposite to that of ridge like faults analytical models of stress orientations around strike slip faults on europa indicate that these effects result from dilation during strike slip motion band like faults characteristically underwent concurrent dilation and shearing but this dynamic coupling is not characteristic of ridge like faults the implication is that strike slip faulting was not a globally homogeneous process on europa and as a result the morphologies of strike slip faults are variable furthermore band like faults appear to corroborate the predictions of the tidal walking theory exhibiting predominantly right lateral motions in the southern hemisphere and left lateral motions in the northern hemisphere however ridge like faults do not obey this slip sense convention suggesting that the tidal walking theory may be appropriate for describing the evolution of dilational band like faults but that ridge like faults may have resulted from a different driving mechanism

europa morphological characteristics of ridges and triple bands from galileo data e4 and e6 and assessment of a linear diapirism model galileo solid state imaging ssi images of europa provide high resolution data on the morphological characteristics of ridges and permit the development of nomenclatural schemes for their description and classification key observations are that ridges 1 are remarkably consistent in their along strike linearity width and height 2 form long linear features in which preexisting structures can sometimes be traced up the outer slopes of the ridges and in other cases appear to be buried 3 contain narrow apical zones of small scale ridge parallel faulting 4 are sometimes flanked by narrow troughs and ridge parallel fractures and 5 often display associated color variations on the basis of the characteristics and associated features of ridges we find that a process in which initial fracturing most plausibly related to tidal deformation of a brittle layer overlying a buoyant ductile substrate leading to linear diapiric upwelling provides a consistent explanation for the observed features in this process the upwelling linear diapir causes flexure bending and faulting of the region marginal to the fracture the deformation and uplift of adjacent plains material and its preexisting structures to form the apical part of the ridge the exposure of the inner walls of the crack and the mass wasting of the inner and outer walls of the ridge to modify but often not completely destroy the preexisting structure of the adjacent plains specifically this mechanism can account for many characteristics of the ridges including their linearity their consistent and regular morphology over their great lateral extent their positive topography the presence of preexisting structure on the outer ridges caused by upbowing of background ridged plains the formation of marginal troughs as diapiric rim synclines the detailed nature of their outer and inner slopes caused largely by faulting and mass wasting processes and their sequential formation with multiple orientations related to tidal deformation processes linear diapirism also provides a possible explanation for color and albedo characteristics related to thermal effects of the upwelling warm ice e g inducing volatile migration and grain size variations as the vast majority of deformation is vertical in this scenario this mechanism minimizes the necessity for complementary compressional deformation required by some other models

polar wander of an ice shell on europa an ice shell on europa that is decoupled from the silicate core by a layer of liquid water has a thermal equilibrium thickness profile that varies with position over its surface because of spatial variations in the surface temperature and tidal dissipation within the ice g w ojakangas and d j stevenson 1989 icarus 81 220 241 the second spherical harmonic degree components of these thickness variations and of any fossil rotational and tidal bulges present on the shell contribute to the inertia tensor of the body the problem is that of a planetary elastic lithosphere that is topographically loaded from below following r j willemann and d l turcotte 1981 proc lunar planet sci b 12 837 851 we develop equations describing the variations in the inertia tensor of a body when second harmonic degree topography is added to the base of the crust for an ice shell on europa it is found that a state of thermal equilibrium may involve an unusual orientation of the principal axes of inertia when hydrostatic bulges are ignored in which the intermediate and maximum principal moments are interchanged to reach the preferred orientation for synchronous satellites a thermal equilibrium shell must execute a net reorientation of 90 about the satellite planet direction we present a simple model of rigid synchronously rotating satellite in a circular orbit for which the principal moment difference b c increases with time becoming positive for t 0 the model demonstrates that the expected reorientation is indeed dynamically favored we then consider a more realistic model in which europa s shell and ocean are assumed to reorient as a single entity independently of the core hindered only by viscous dissipation within the shell such coupling of the shell with the ocean and lack of coupling with the core is suggested by g w ojakangas 1988 coupled thermal and dynamical evolution of planetary bodies ph d thesis california institute of technology the model suggests that friction in the shell eliminates the possibility of polar wander unless a low conductivity regolith increases the near surface temperature by a few tens of degrees so the ice just below the regolith behaves viscously on the polar wander time scale however if the equator to pole near surface temperature difference is decreased by more than a critical model dependent amount the shell s inertia tensor no longer has an unstable form in thermal equilibrium alternatively polar wander may occur if preexisting surface fractures e g due to tidal stresses extend to a depth where the ice behaves viscously these fractures must be lubricated perhaps by liquid water from below if the temperature t f at the base of the regolith or the surface fractures is 125 k the model suggests that polar wander occurs on a time scale 2 x 10 6 years decreasing as t f increases after b c becomes postive in the absence of dissipation polar wander would occur in few x 10 3 years large scale polar wander may occur episodically separated by periods on the order of the thermal diffusion time for the shell 10 7 years although a state of slow continuous drifting of the pole is also possible the time scales of viscous flow of topography at the base of the ice is also near 10 7 years polar wander is a very effective means for fracturing the ice and may have contributed to the observed global fracture systems in europa s ice

late devonian glacial deposits from the eastern united states signal an end of the mid paleozoic warm period abstract a late devonian polymictic diamictite extends for more than 400 km from northeastern pennsylvania across western maryland and into east central west virginia the matrix supported unbedded locally sheared diamictite contains subangular to rounded clasts up to 2 m in diameter the mostly rounded clasts are both locally derived and exotic some exhibit striations faceting and polish the diamictite commonly is overlain by laminated siltstone mudstone facies associations laminites the laminites contain isolated clasts ranging in size from sand and pebbles to boulders some of which are striated the diamictite laminite sequence is capped by massive coarse grained pebbly sandstone that is trough cross bedded a stratigraphic change from red calcic paleo vertisols in strata below the diamictite to non calcic paleo spodosols and coal beds at and above the diamictite interval suggests that the climate became much wetter during deposition of the diamictite the diamictite deposit is contemporaneous with regressive facies that reflect fluvial incision during the late devonian of the appalachian basin these deposits record a late devonian episode of climatic cooling so extreme that it produced glaciation in the appalachian basin evidence for this episode of climatic cooling is preserved as the interpreted glacial deposits of diamictite overlain by glaciolacustrine varves containing dropstones and capped by sandstone interpreted as braided stream outwash the appalachian glacigenic deposits are contemporaneous with glacial deposits in south america and suggest that late devonian climatic cooling was global this period of dramatic global cooling may represent the end of the mid paleozoic warm interval that began in the middle silurian

a model of late cenozoic transcurrent motion and deformation in the fore arc of northeast japan constraints from geophysical studies abstract we use recently acquired seismic reflection data and reprocessed sections to interpret the structure of the northern part of the ne japan forearc we identify a nnw sse trending deformation zone bounded by large transcurrent faults trends t1 t4 from west to east on the upper continental slope the lower slope is characterized by a frontal prism and reverse faults bathymetric data reveal several en echelon topographic bulges with nw se elongation aligned parallel to the fault trends the bulges are interpreted as a dextral wrench zone that has developed since the neogene based on structural contours of two late cenozoic seismic horizons clockwise rotation associated the wrenching is indicated by the paleomagnetism of paleogene marine sediments obtained from a drill hole within the faulted zone close to trend t1 a previous seismic refraction study shows remarkable contrast in p wave velocity across trend t2 indicating a considerable rearrangement of crust associated with transcurrent motion along this fault we propose a paleogeographic reconstruction assuming 200 km southward trenchward lateral transportation along trend t2 and its northern extension in our model subduction erosion at the northern japan trench was enhanced by trenchward migration of the fore arc sliver but steadied following rearrangement of the sliver along the transect the calculated variation in subduction erosion is consistent with subduction histories based on existing well data

conamara chaos region europa reconstruction of mobile polygonal ice blocks new galileo images of europa reveal regions of chaotic terrain in otherwise highly lineated background plains examination of conamara chaos shows that 59 of the region is composed of fine textured matrix material lying at low elevations and formed by destruction of lineated plains while the remainder consists of 139 fragmented polygons of linear textured background plains using through trending linear features we reconstruct the original positions of chaos polygons and find that significant lateral translation and rotation have occurred 78 of the polygons have undergone horizontal translations with most moving between 1 and 5 km and 81 have rotated average rotation of 11 movement of polygons appears to be inward from the chaos margins and clockwise in the center while polygon rotation is evenly clockwise and counterclockwise chaos formation in this region thus involves destruction of over half of the pre existing terrain and mobilization translation and rotation of the remaining polygons implying elevated near surface temperatures and a highly mobile substrate over lateral scales of 100 km

a paleoclimatic review of southern south america during the late paleozoic a record from icehouse to extreme greenhouse conditions abstract this paper provides a review of the late mississippian to permian paleoclimatic history for southern south america based on lithologic indicators biostratigraphic information and chronostratigraphic data the region is divided into three major types of basins 1 eastern intraplate basins e g parana basin 2 western retroarc basins e g paganzo basin and 3 western arc related basins e g rio blanco basin four major types of paleoclimatic stages are recognized in these basins 1 glacial late visean early bashkirian 2 terminal glacial bashkirian earliest cisuralian 3 postglacial cisuralian early guadalupian and 4 semiarid arid late guadalupian lopingian the glacial stage began in the late visean and continued until the latest serpukhovian or early bashkirian in almost all of the basins in southern south america during the bashkirian earliest cisuralian terminal glacial stage glacial deposits disappeared almost completely in the western retroarc basins e g paganzo basin but glaciation persisted in the eastern basins e g parana and sauce grande basins a gradual climatic amelioration postglacial stage began to occur during the earliest permian when glacial deposits completely disappeared across all of south america during this interval glacial diamictites were replaced by thick coal beds in the parana basin while north south climatic belts began to be delineated in the western basins which were likely controlled by the distribution of mountain belts along the panthalassan margin of south america towards the late permian climatic belts became less evident and semiarid or arid conditions dominated in the southern south america basins eolian dunes playa lake deposits and mixed eolian fluvial sequences occur in the parana basin and in the western retroarc basins volcanism and volcaniclastic sedimentation dominated along the western margin of south america at that time the stratigraphic record obtained in southern south america supports a long duration transition from icehouse to extreme greenhouse conditions

high precision u pb calibration of carboniferous glaciation and climate history paganzo group nw argentina the duration and geographic extent of carboniferous glacial events in southern gondwana remain poorly constrained despite recent evidence for a more dynamic glacial history than previously considered we report 10 high precision 2 0 1 u pb ages for the permian carboniferous paganzo group nw argentina that redefi ne the chronostratigraphy of the late paleozoic paganzo and rio blanco basins and signifi cantly refi ne the timing of glacial events and climate shifts in the western region of southern gondwana radiometric calibration of the paganzo group indicates three pulses of carboniferous glaciation in the mid visean the late serpukhovian to earliest bashkirian and between the latest bashkirian to early moscovian an abrupt shift in depositional style from high sinuosity single storied fl uvial deposits and clay rich paleosols to low sinuosity multi storied feldspathic fluvial deposits inter calated with eolianites and calcic paleosols is constrained to the latest moscovian and earliest kasimovian these constraints indicate a relatively abrupt climate shift from humid subhumid to nonseasonal semiarid regional climate conditions that occurred signifi cantly earlier than previously inferred early permian this period of high latitude aridity was contemporaneous with a shift to dryland depositional environments and a major vegetation regime shift documented throughout the pangean paleotropics in the pennsylvanian

a high resolution multiproxy stratigraphic analysis of the devonian carboniferous boundary sections in the moravian karst czech republic and a correlation with the carnic alps austria a multidisciplinary correlation of the devonian carboniferous d c boundary sections from the moravian karst czech republic and the carnic alps austria based on conodont and foraminifer biostratigraphy microfacies analysis field gamma ray spectroscopy grs carbon isotopes and element geochemistry is presented in this paper the study is focused on the interval from the middle palmatolepis gracilis expansa zone late famennian to the siphonodella sandbergi zone early tournaisian in lesni lom moravian karst a positive 13 c excursion in the bisphatodus costatus protognathodus kockeli interregnum from a distinct laminated carbonate horizon is correlated with a carbon isotope excursion from the grune schneid section of the carnic alps and is interpreted as the equivalent of the hangenberg black shales and a local expression of the global hangenberg event sensu stricto higher up at both sections a significant increase in the terrigenous input which is inferred from the grs signal and elevated concentrations of terrigenous elements si ti zr rb al etc provides another correlation tieline and is interpreted as the equivalent of the hangenberg sandstone both horizons are discussed in terms of relative sea level fluctuations and palaeoceanographic changes recent studies show that conodont biostratigraphy is facing serious problems associated with the taxonomy of the first siphonodellids their dependence on facies and discontinuous occurrences of protognathodids at the d c boundary therefore the correlative potential of geochemical and petrophysical signatures is high and offers an alternative for the refining of the problematic biostratigraphic division of the d c boundary

numerical calibration of the devonian carboniferous boundary two new u pb isotope dilution thermal ionization mass spectrometry single zircon ages from hasselbachtal sauerland germany the hasselbachtal section sauerland germany is an auxiliary global stratotype of the devonian carboniferous boundary and one of the most important reference sections for the evolution of the latest famennian to earliest tournaisian pelagic fauna biostratigraphically well controlled altered volcanic ash layers metabentonites intercalated in the section afford a perfect opportunity for a numerical fixing of this important paleozoic period boundary we have performed u pb isotope dilution thermal ionization mass spectrometry id tims analyses on sub microgram sized single zircons and zircon fragments extracted from two metabentonites beds 79 and 70 in the lowermost tournaisian part of the section bed 79 metabentonite is positioned directly above the devonian carboniferous boundary within the siphonodella sulcata conodont zone five concordant analyses form a cluster with a 2 0 6 pb 3 3 8 u concordia age of 360 5 0 8 ma zircons of the next younger metabentonite bed 70 in the lower siphonodella duplicata conodont zone yielded a tightly grouped cluster of 10 concordant analyses with a 2 0 6 pb 2 3 8 u concordia age of 360 2 0 7 ma on the basis of these two new single zircon ages and previously published late famennian u pb id tims ages the devonian carboniferous boundary is reinterpolated herein to 360 7 0 7 ma

chaos on europa the characteristics of chaos regions on europa suggest they may be sites of melt through from below they are wide ranging in size location and age the largest are hundreds of kilometers across most are similar to conamara with a matrix reminiscent of frozen slush and often rafts of preexisting crust edges are of two types ramps perhaps the tapering of crustal thickness to zero or cliffs where rafts appear to have broken clear from the shore the small features called lenticulae generally appear to be small chaoses with textured matrix and occasional rafts and many domes may be small chaoses raised by isostatic compensation following refreezing of the crust the extent of chaoses often appears to be limited by ridge systems with the coastline parallel and set back by a distance comparable to the width of the ridge system preexisting ridges often survive as causeways or chains of rafts boundaries of chaoses are apparently not controlled by preexisting cracks consistent with formation by a thermal rather than mechanical process ridges may thicken the crust such that melt through is more likely but not always between ridge systems subsequent cracks and ridges form across preexisting chaoses ranging from fresh cases with few cracks or ridges across them with paths somewhat jagged as they meander among rafts to heavily dissected examples isolated tilted raft like blocks surrounded by densely ridged terrain may be relics of former chaotic terrain thus two fundamental resurfacing processes have alternated over europa s geological history melt through at various places and times forming chaos terrain and tectonic cracking and dilation building densely ridged and banded terrain mapping of chaos features based on morphology at 200 m shows that they correlate albeit imperfectly with dark regions in global 2 km resolution mosaics except dark regions due to ridge margins or craters extrapolating from our mapping of the 5 of europa covered by appropriate images at least 18 of the surface of europa is fresh appearing chaos an additional 4 is slightly modified chaos and much more older chaotic terrain has been overprinted by tectonic structures considerable area has been available globally to accommodate the expansion of crust that occurs along extensional ridges and bands chaos ubiquity suggests that europan geology has been dominated by the effects of having liquid water under a very thin ice shell with chaos regions being widespread indicators of occasional zero shell thickness

local overprints on the global carbonate δ13c signal in devonian carboniferous boundary successions of south china abstract an integrated study of the litho bio and chemostratigraphy of the devonian carboniferous boundary at four sections qilinzhai malanbian gedongguan and long an in south china was undertaken in order to better understand paleoenvironmental changes and controls on 13 c carb variation during the hangenberg crisis sedimentological data record a major regression in the middle siphonodella praesulcata zone which coincided with the hangenberg extinction he in south china our new 13 c carb data document a negative 13 c carb shift near the base of the middle s praesulcata zone which may have been related to the he prior to and during the he respiration of organic matter contributed abundant 12 c enriched dissolved inorganic carbon dic to the restricted nanning carbonate platform resulting in a negative vertical 13 c dic gradient in the study area in the upper s praesulcata zone all four sections exhibit a positive 13 c carb shift suggesting that a vigorous biological pump existed in the aftermath of the latest devonian glaciation however peak 13 c carb values differ markedly among the study sections suggesting that local carbon cycling processes played an important role during the initial post glacial transgression

devonian sea level change in bolivia a high palaeolatitude biostratigraphical calibration of the global sea level curve article i nfo available online xxxx during the devonian period the cool water malvinokaffric realm was located at high palaeolatitudes in the southern hemisphere the realm is defined by its highly endemic marine benthic fauna which makes extra malvinokaffric correlations problematic investigation of the devonian palynomorphs from an extensive regional sub surface dataset 24 wells in the chaco basin bolivia reveals the presence of a number of stratigraphically restricted and regionally correlative epiboles peak abundances of the distinctive palynomorphs bimerga bensonii crucidia camirense evittia sommeri petrovina connata and ramochitina magnifica these palynomorph epiboles were then located at outcrop by a high resolution palynological investigation 225 samples of two bolivian outcrop localities in the chaco basin bermejo santa cruz department and campo redondo chiquisaca department the important evittia sommeri epibole in the basal los monos formation is related to a marine transgression that is present in both these outcrop sections additional chronostratigraphic control on this marine transgression comes from the occurrence of rare goniatites in the base of the huamampampa formation at campo redondo which are at least early eifelian in age post chot c event based on the goniatite together with spore data the marine transgression with evittia sommeri in the basal los monos formation can be tentatively assigned to the mid devonian mid late eifelian kacak event the presence of a datable malvinokaffric goniatite has shown that key spore taxa which are used zonally in both laurussia and gondwana do not all have coincident first occurrences in both areas furthermore despite the appearance of some cosmopolitan elements in the microflora mid and late devonian spore assemblages in bolivia are distinct from other regions in being relatively impoverished in both progymnosperm and lycopod spores this floral difference is attributable to the malvinokaffric realm continuing to retain a distinctive cool climatic signature throughout this interval however the sporadic occurrences of extra malvinokaffric macrofauna in restricted stratigraphic intervals of the middle devonian in south america and south africa are significant the oldest known occurrence of the extra malvinokaffric brachiopod tropidoleptus in bolivia is coincident with the late eifelian basal los monos formation transgression hence there was a relationship between influxes of this fauna and marine transgressions i e temporary periods of reduced climatic gradient the migration of devonian spores and particularly heterosporous spores between gondwana and laurussia clearly occurs during the mid and late devonian this is at variance with models claiming a wide rheic ocean during much of the devonian

is there evidence for polar wander on europa abstract the orientations of the albedo lineaments bands and lineations on europa s surface have been compared in previous studies with the global stress fields set up by orbital eccentricity orbital recession and nonsynchronous rotation of these orbital and rotational effects nonsynchronous rotation combined with an offsetting of the tidal bulge comes closest to providing agreement between the stress field generated and the lineation orientations if the lineations trace tension or extension fractures mcewen 1986 nature321 49 51 however inferred minimum principal stress directions for a broad region of wedge shaped bands near the anti jove point cannot satisfactorily be accounted for by any of the stress fields above but are consistent with the stresses resulting from a rotation of europa s ice shell about an axis through the sub and anti jove points clockwise as seen from the anti jove hemisphere p m schenk and w b mckinnon 1989 icarus79 75 100 calculations by ojakangas and stevenson 1989 icarus81 220 241 of the thermal state of europa s ice shell indicate that spatial variations in the thickness of the shell may cause it to undergo such a reorientation we have investigated whether any reorientation of the shell about an axis through the sub and anti jove points produces a stress field consistent with the full global set of prominent lineations on europa s surface we find that no such reorientation provides a good fit between the lineations and plausible fracture orientations derived from the principal stress trajectories topographic ridges identified in a limited zone south of the anti jove point are roughly consistent with compression due to clockwise polar wander but the orientations of these ridges may be strongly biased by illumination direction within the limitations of the presently available imagery nonsynchronous rotation is still the most likely cause of the prominant fractures on europa s surface and the best specific albeit regionally limited tectonic evidence consistent with recent polar wander remains the wedge shaped bands

greenhouse to icehouse a biostratigraphic review of latest devonian mississippian glaciations and their global effects the latest devonian mississippian interval records the long term transition from devonian greenhouse conditions into the late palaeozoic ice age lpia this transition was punctuated by three short glaciation events in the latest famennian mid tournaisian and visean stages respectively primary evidence for glaciation is based on diamictite deposits and striated pavements in south america appalachia and africa the aim of this review is to assess the primary biostratigraphic and sedimentological data constraining diamictite deposits through this transition these data are then compared to the wider record of eustasy mass extinction and isotope stratigraphy in the lower palaeolatitudes precise age determinations are vital to integrate high and low palaeolatitude datasets and to understand the glacial control on wider global changes palynological techniques currently provide the best biostratigraphic tool to date these glacial deposits and to correlate the effects of glaciation globally this review highlights a high degree of uncertainty in the known history of early lpia glaciation as much of the primary stratigraphic data are limited and or unpublished future high resolution stratigraphic studies are needed to constrain the history of glaciation both spatially and temporally through the latest devonian and mississippian

climatic and hydrologic controls on upper paleozoic bauxite deposits in south china abstract the late paleozoic era was an interval of major tectonic and climatic changes including formation of the supercontinent pangea and the 60 myr long late paleozoic ice age lpia although bauxite formation declined globally from the carboniferous to the permian in conjunction with global cooling it was an interval of widespread bauxite formation in china in south china 1 the jiujialu formation bauxite deposits in central and northern guizhou zunyi area are of early middle visean age 2 the dazhuyaun formation bauxite deposits in northern guizhou wuchuan zheng an daozheng area to southern chongqing nanchuan area and southeastern guizhou fuquan kaili area are of late pennsylvanian early permian age and 3 the heshan formation bauxite deposits in western guangxi to yunnan are of middle late permian age in north china the benxi formation bauxite deposits are of late mississippian middle pennsylvanian age the contrasting trends in bauxite metallogenesis between china and the rest of the world imply different climatic patterns in the eastern tethys high annual humidity with seasonal dryness and pangea aridification this hypothesis is further supported by differences in the chemical index of alteration or cia 80 in the eastern tethys vs 50 in western pangea and in paleotemperatures mean annual temperature or mat 20 c in the eastern tethys vs 4 c in western pangea determined from permo carboniferous siliciclastic deposits permo carboniferous bauxite deposits in south china formed in coastal plain and coastal karstic depression environments in which the position of the groundwater table was related to sea level changes during the late paleozoic high frequency eustatic fluctuations caused by waxing and waning of gondwana icesheets controlled sedimentation in these coastal depositional systems leading to cyclic accumulation of coal and bauxite deposits and cycles of vadose and phreatic type bauxite formation the results of the present study show that during interglacial stages lateritization resulted from high pco2 high sea level and groundwater table elevations low precipitation and limited vegetation cover whereas during glacial stages bauxitization of these ferralitic weathering products was promoted by low pco2 low sea level and groundwater table elevations high precipitation and more extensive vegetation cover thus a unique combination of geographic climatic and eustatic factors accounted for widespread formation of bauxite in south china during the lpia

global events of the late paleozoic early devonian to middle permian a review abstract the late paleozoic early devonian to middle permian was an interval of profound changes in earth surface systems reflected in dynamic interplay among the biosphere hydrosphere atmosphere and geosphere major events transpired including the colonization of landmasses by vascular plants the assembly of the supercontinent pangea two first order mass extinctions the frasnian famennian and devonian carboniferous boundary events and the most severe icehouse climate mode of the phanerozoic the late paleozoic ice age lpia the goals of the present review are 1 to summarize major global developments in climate oceanography and paleobiology during the late paleozoic 2 to examine the roles of land plant evolution global tectonics and large igneous province magmatism in driving these developments and 3 to serve as an introduction to the 23 contributions to this special issue of palaeogeography palaeoclimatology palaeoecology indicating how they advance our knowledge of various scientific issues related to these developments

sea level and environmental changes around the devonian carboniferous boundary in the namur dinant basin s belgium ne france a multi proxy stratigraphic analysis of carbonate ramp archives and its use in regional and interregional correlations abstract the paper focuses on high resolution multidisciplinary research on three devonian carboniferous boundary sections in shallow water carbonate rocks in the namur dinant basin belgium france the aim of the study is to provide palaeo environmental reconstructions and correlations supported by several independent quantitative proxies we describe several correlative horizons and provide their sequence stratigraphic interpretation based on facies analysis spectral gamma ray data element concentrations xrf and 13ccarb with foraminifer biostratigraphy age control the most prominent surface is a basal surface of forced regression which is indicated by a sharp basinwards facies shift and a drop in clay gamma ray values and al concentrations at the base of the hastiere and avesnelles formations in more distal settings in proximal settings this surface merges with a hiatus at the devonian carboniferous boundary inferred from foraminifer biostratigraphy this hiatus can be correlated with the global hangenberg sandstone event which indicates a glacioeustatic sea level fall increasing values of zr al k al sr al and mn al coincide with the proximal facies of the falling stage system tract and lowstand system tract in the hastiere and avesnelles formations as a consequence of the enhanced input of siliciclastics and nutrients during low sea levels the top of the middle hastiere member is interpreted as the maximum regression surface which is overlain by transgressive system tract of the upper hastiere member the patterns of gamma ray 13ccarb th k al and zr al curves are well correlated between the studied sections the 13ccarb excursions are correlated with the unnamed excursion in the upper expansa conodont zone carnic alps and with the global hangenberg event s l excursion in the kockeli conodont zone this sequence stratigraphic framework is used for correlations with deltaic successions from the tafilalt basin morocco the basal surface of the forced regression equivalent to the hangenberg sandstone event which is typical for deeper water settings is easily recognisable and correlatable with gaps in more shallow water settings we suggest that it should be taken into account as a possible candidate for the natural solution of the devonian carboniferous boundary in discussions concerning its redefinition

palynological calibration of devonian events at near polar palaeolatitudes in the falkland islands south atlantic in the devonian the falkland islands were part of the high latitude cape basin west falkland palynological assemblages are at a low thermal maturity level but also very low in diversity and dominated by simple spores with rare chitinozoans and acritarchs the south harbour member contains rare verrucate and sculptured trilete spores and is early lochkovian the fish creek member palynofloras are late lochkovian the best correlative datum is the transgressive fox bay formation where the palynological assemblage includes ramochitina magnifica and is equivalent to the sequence b transgression in brazil dated as late pragian earliest emsian the early eifelian upper fox bay formation spore assemblage is comparable to the sequence c transgression in brazil and the chote event the facies and position of the base port philomel formation prasinophyte rich black shale suggests the late eifelian transgression ka ak event above this level is the inception of geminospora lemurata base givetian the upper port stanley formation contains a late but not latest famennian assemblage comparisons with both south africa and south america indicate a number of correlative transgressive and regressive events that match to euramerica these correlations are at a continental scale and confirm eustatic control of these devonian events

tidal reorientation and the fracturing of jupiter s moon europa the most striking characteristic of europa is the network of long linear albedo markings over the surface suggestive of global scale tectonic processes various explanations for the fractures have been proposed freezing and expansion of an early liquid water ocean1 planetary expansion due to dehydration of hydrated silicates2 localization by weak points in the crust generated by impacts3 and a combination of stresses due to planetary volume change and tidal distortions from orbital recession and orbital eccentricity4 5 calculations by yoder6 and greenberg and weidenschilling7 have shown that europa may rotate slightly more rapidly than the synchronous rate with a rotation period reorientation through 360 ranging from 20 to 103 yr if a liquid mantle is present or up to 1010 yr if the satellite is essentially solid7 helfen stein and parmentier8 modelled the stresses due to nonsynchronous rotation and concluded that this could explain the long fractures in part of the anti jovian hemisphere in this note i present a global map of lineaments with long arc lengths 20 or 550 km and compare the lineament orientations to the tensile stress trajectories due to tidal distortions changes in the lengths of three principal semiaxes and to nonsynchronous rotation longitudinal reorientation of two of the principal semiaxes an excellent orthogonal fit to the lineaments is achieved by the stresses due to nonsynchronous rotation with the axis radial to jupiter located 25 east of its present position this fit suggests that nonsynchronous rotation occurred at some time in europa s history

a new ecological severity ranking of major phanerozoic biodiversity crises a new ecological severity ranking of the major phanerozoic biodiversity crises is proposed in which the capitanian crisis is ranked lesser than the frasnian late devonian but greater than the serpukhovian end mississippian and the famennian end devonian crisis is ranked as equal in ecological impact to the hirnantian end ordovician two new decouplings between taxonomic severity and ecological severity are revealed in these analyses the capitanian and famennian crises in which the ecological impact of the biodiversity loss was markedly different from the magnitude of the biodiversity loss these analyses also reveal that the great devonian interchange gdi invasive species event in the givetian biodiversity crisis may provide an important palaeoecological analog for the study of present day extinction and homogenization in ecosystems produced by modern invasive species

mass extinctions and sea level changes abstract review of sea level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions the degree of certainty with which these eustatic oscillations are known varies considerably thus the late ordovician and end cretaceous extinctions are associated with unequivocal major regressions demonstrated from numerous widespread regions in contrast the multiple high frequency sea level changes reported for the frasnian famennian crisis based on the supposed depth preferences of conodont taxa have little support from sequence stratigraphic analyses which reveals the interval to be one of highstand the end permian mass extinction has long been related to a severe first order lowstand of sea level newell n d 1967 revolutions in the history of life geol soc am spec pap 89 63 91 based primarily on the widespread absence of latest permian ammonoid markers but field evidence reveals that the interval coincides with a major transgression newell s hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end guadalupian and end triassic extinction events but not for other crises rapid high amplitude regressive transgressive couplets are the most frequently observed eustatic changes at times of mass extinction with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive the ultimate cause of the sea level changes is generally unclear a glacioeustatic driving mechanism can only be convincingly demonstrated for the end ordovician and end devonian events at other times it is speculated that they may relate to the widespread regional doming and subsequent collapse caused by the impingement of superplumes and ultimate eruption on the base of the lithosphere

pulses of enhanced continental weathering associated with multiple late devonian climate perturbations evidence from osmium isotope compositions anomalously high rates of continental weathering have frequently been proposed as a key stimulus for the development of widespread marine anoxia during a number of late devonian environmental and biospheric crises which included a major mass extinction during the frasnian famennian transition marked by the upper and lower kellwasser horizons here this model is investigated by presenting the first stratigraphic record of osmium isotope trends 187os 188os in upper devonian strata from the kowala quarry holy cross mountains poland changes in reconstructed 187os 188os seawater values to more radiogenic compositions are documented at the base of both the lower 0 42 to 0 83 and upper 0 31 to 0 81 kellwasser horizons characteristic of the frasnian famennian transition and additionally within upper famennian shales that record a more minor environmental perturbation known as the annulata event 0 20 to 0 53 these shifts indicate the occurrence of extremely enhanced continental weathering rates at the onsets of the kellwasser crises and during the later annulata event the similarity of 187os 188os values in this study from frasnian famennian boundary and lower famennian strata between 0 4 and 0 5 to those from north american stratigraphic equivalents suggests that the 187os 188os values record global trends these findings support a causal relationship between increased continental weathering and thus nutrient supply to the marine shelf and the environmental perturbations that occurred during numerous late devonian events including both of the biospherically catastrophic kellwasser crises as well as other less severe oceanic anoxic events

climate controlled mass extinctions facies and sea level changes around the devonian carboniferous boundary in the eastern anti atlas se morocco abstract detailed sedimentological and biostratigraphical studies of successions in the eastern anti atlas se morocco focused on changing depositional environments and reconstructions of sea level changes during the late famennian to middle tournaisian the investigations cover a transect from the central maider to the easternmost and southern tafilalt regions near the moroccan algerian border the moroccan data are compared with the standard succession of the german rhenish massif and with the regional and global stratigraphic record the results testify to high frequency sea level changes including two global transgressive and anoxic events the main hangenberg event hangenberg black shale level at the top of the wocklumeria zone upper devonian vi e and the lower alum shale event at the lower middle tournaisian lower carboniferous i ii boundary regionally both anoxic intervals coincided with mass extinctions followed by rapid radiation especially of pelagic biota a significant shallowing and regression occurred just below the devonian carboniferous boundary at the northern margin of gondwana and caused the sudden n nw progradation of a large deltaic complex over 300 500 km thick siliciclastic successions filled fast subsiding synsedimentary troughs of the maider and amessoui syncline southern tafilalt correlation with the glacial phases of southern gondwana south america south africa indicates a glacial eustatic origin of sea level changes and a major sea level fall in the scale of 100 m or more coinciding with the main regressive phase of the extended hangenberg crisis interval the new results are in accord with the hypothesis of an episode of cool humid climate at the end of the devonian that allowed contemporaneous glacial buildup in high latitudes and extensive clastic discharge in the middle latitudes of nw africa

formation of bands and ridges on europa by cyclic deformation insights from analogue wax experiments 1 we perform a set of analogue wax experiments aimed at understanding the processes and conditions that lead to lineament formation on europa we heat a layer of wax from below and cool it from above so that a solid layer of wax forms above a molten layer simulating either the liquid ocean or the actively convecting part of the ice shell the solid layer of wax is then deformed periodically simulating the cyclic strain caused by tides or by the satellite s nonsynchronous rotation we find that the formation and morphology of lineaments that develop in the solid wax layer are governed by two main dimensionless parameters the ratio of the cooling timescale for the solid layer to the deformation timescale and the dilation quotient which is defined as the magnitude of net extension during one cycle of deformation divided by the amplitude of the periodic deformation for 1 features form that qualitatively resemble bands and ridge complexes on europa we conclude that diurnal tides may be responsible for the formation of bands on europa if the conducting layer of ice is a few hundred meters thick and is underlain by a convecting layer of ice features resembling double ridges can form if the ice shell has a thickness of a few kilometers and periodic strains are caused by europa s nonsynchronous rotation

revised perspectives on devonian biozonation and environmental volatility in the wake of recent time scale revisions abstract revised time scales for the devonian period have highlighted major discrepancies in the frequency of evolutionary eustatic carbon cycle and biotic events the number of conodont biozones per million years shows strong variation among stages using two alternative time scales the lowest values are in the emsian and highest in the givetian frasnian and famennian stages a similar result is obtained by dividing the devonian time scale into 12 equal 5 million year bins and determining the number of conodont zonal subdivisions in each bin the record of ammonoid biozones also shows interesting parallels the acuity of biostratigraphic zonation and zonal subdivisions appears to be correlative with the frequency of environmental perturbations including eustatic positive carbon isotopic excursions and hypoxic anoxic related bioevents and these are similarly unevenly distributed all calculations of environmental volatility metrics show the late eifelian through early frasnian to be the most volatile interval of the devonian followed by the mid late famennian while the lochkovian through emsian and mid frasnian through early famennian are the least volatile furthermore the majority of major bioevents occur in the eifelian through early frasnian and late famennian the strong evidence for higher biotic and environmental volatility in the late eifelian through early frasnian and late famennian rock record corresponds to the coolest paleoclimate conditions in the devonian according to recent conodont apatite 18o compilations and the transition from an overall cooling to warming paleotemperature trend during the mid givetian regardless of mechanism strong variations in volatility occurred during the devonian period intervals with greater biostratigraphic resolution also show much stronger environmental volatility including a series of relatively quasi stable conditions punctuated by major turnovers with abrupt sea level rise widespread hypoxia and changes in the carbon cycle it was during these intervals that much net evolutionary and ecological change appears to have taken place

does europa have a subsurface ocean evaluation of the geological evidence it has been proposed that jupiter s satellite europa currently possesses a global subsurface ocean of liquid water galileo gravity data verify that the satellite is differentiated into an outer h2o layer about 100 km thick but cannot determine the current physical state of this layer liquid or solid here we summarize the geological evidence regarding an extant subsurface ocean concentrating on galileo imaging data we describe and assess nine pertinent lines of geological evidence impact morphologies lenticulae cryovolcanic features pull apart bands chaos ridges surface frosts topography and global tectonics an internal ocean would be a simple and comprehensive explanation for a broad range of observations however we cannot rule out the possibility that all of the surface morphologies could be due to processes in warm soft ice with only localized or partial melting two different models of impact flux imply very different surface ages for europa the model favored here indicates an average age of 50 myr searches for evidence of current geological activity on europa such as plumes or surface changes have yielded negative results to date the current existence of a global subsurface ocean while attractive in explaining the observations remains inconclusive future geophysical measurements are essential to determine conclusively whether or not there is a liquid water ocean within europa today

linking orography climate and exhumation across the central andes quantifying interactions between uplift climate deformation and exhumation remains difficult in many cases due to a paucity of data relevant to all processes we synthesize new and existing data to understand the orogen scale orographic changes across the central andes bolivia we use a regional climate model and geo thermochronologic data to identify the correlations between changes in precipitation due to surface uplift and spatiotemporal patterns of deformation and erosional exhumation mean orographic rainfall patterns do not reach near present day gradients and values until the topography grows to 75 modern elevations new fission track data near the orocline apex indicate that rapid exhumation moved eastward beginning in the eastern cordillera ca 50 15 ma the interandean zone ca 18 6 ma and in the subandes ca 7 3 ma throughout bolivia exhumation is consistent with deformation until ca 15 11 ma after which the pattern corresponds better with the increased rainfall toward modern values these linked observations suggest that ca 15 11 ma regional elevations reached threshold values 75 modern necessary to generate near present day enhanced rainfall gradients these gradients have resulted in variable exhumation implied by the structural level of rocks exposed across the thrust belt and confirmed by fission tracks in apatite the main insight is that the climate induced middle miocene recent exhumation varies over scales of a few hundred kilometers across bolivia and implies that high mean rainfall 3 m yr and long time scales 10 m y may be necessary for climate to induce orographically driven exhumation patterns recorded by fission tracks