europa s south pole region a sequential reconstruction of surface modification processes abstract high resolution images of a region near the south pole of europa allow reconstruction of a series of events tectonic and thermal that displaced and modified the surface this approach is complementary to regional geological mapping which is based on less detailed images but covers a broader sample of the surface the events reconstructed in this locale resurfaced about half the area or more so they probably ranged over a substantial fraction of the age of europa s surface which in itself is quite young

a short term post lomagundi positive c isotope excursion at c 2 03 ga recorded by the wooly dolomite western australia it is generally accepted that carbon isotope variations in seawater were muted between c 2 06 ga after the end of the lomagundi carbon isotope excursion lcie and c 1 3 ga evidence is presented here that c 30 myr after the end of the lcie the biogeochemical cycle of carbon experienced a short term c 2 myr high amplitude up to 8 4 v pdb perturbation recorded in the horseshoe rift basin western australia the basin was initiated at c 2 03 ga with deposition of fluvial and shallow marine sandstones followed by the eruption of flood basalt and culminated with the deposition of platform carbonates and accompanying volcaniclastic and siliciclastic sediments wooly dolomite the horseshoe rift basin during deposition of the wooly dolomite was fault compartmentalized but connected to an ocean six depositional sequences make up the wooly dolomite sequence 1 records establishment of a carbonate platform conformably on basalt and coevally with volcaniclastic sedimentation all other sequences have dominant carbonate platform deposits and are unconformity bounded sequence 3 contains a c 57 m thick section with 13 c enriched carbonates bracketed between carbonates with close to 0 carbon isotope values further high resolution chemostratigraphic studies may reveal a more complex pattern of carbon isotope variations during the boring billion years but without precise geochronology similar short term carbon isotope excursions in carbonate successions could be incorrectly correlated to the lcie supplementary material table 2 including chemical and isotopic data sample locations and their position in figure 8 is available at https doi org 10 6084 m9 figshare c 2868055

europa s dynamic icy crust abstract europa s icy crust records active resurfacing by tectonic and thermal processes over tens of millions of years as rapidity demonstrated by a paucity of craters tidal working causes rotational torque surface stress internal heating and orbital evolution which can explain the formation of observed tectonic crack patterns ridges crustal displacement and chaotic terrain by processes involving connections between the surface and the underlying ocean through cracks melt sites and occasional impacts these processes were recent and thus most likely continue today the permeability of the crust allows exchange of materials including oxidants and exogenic organics from the surface and endogenic substances from the ocean such that a habitable biosphere might extend to within a few centimeters of the surface continual changes in environmental conditions in the ice crust such as deactivation of individual cracks after thousands of years due to non synchronous rotation and crustal thawing releasing any trapped organisms could provide drivers for biological adaptation as well as opportunity for evolution

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

provenance and time constraints on the formation of the first bend of the yangtze river 1 the upper yangtze river flows southward on the southeastern tibet characterizing by uniquely low and continuous relief the river makes a sharp turn at shigu heading northeast and forms the first bend of the yangtze river many previous studies assumed southward flow of the ancestral yangtze river from shigu to the south china sea however field evidence of southward flow of the paleo yangtze is lacking in this paper we report our identification based on detrital zircon u pb age distributions of a range of fluvial sands left by the paleo yangtze in tongdian madeng and nanjian basins cosmogenic10be and 26al burial dating provides burial ages for these fluvial sands from 1 7 to over 8 7 ma rerouting of the yangtze river therefore occurred within the last 1 7 ma postdating the major uplift of the central tibet we attribute the rerouting of the yangtze river to response to activation of the dali fault system and in a larger scale initiation of crustal deformation by clockwise rotation around eastern himalayan syntaxis 2 4 ma ago reorganization of the yangtze drainage pattern most likely reflects regional uplift and displacement due to lower crust flowing beneath major faults in the southeastern tibet and yunnan

observational constraints on the identification and distribution of chaotic terrain on icy satellites abstract we outline the observational constraints required to identify chaos regions on europa large incidence angle rather than high resolution appears to be the primary observational requirement for identifying chaos at incidence angles 70 chaos can be identified on europa at image resolutions as low as 1 5 km pixel similar images obtained at moderate or low incidence angles

observational selection effects in europa image data identification of chaotic terrain abstract the identification of terrains on images of europa is highly dependent on the image resolution and illumination angle both of which are quite variable due to the observational selection constraints of the galileo mission higher resolution images allow for the identification of smaller patches of chaotic terrain which are indistinguishable from surrounding tectonic terrain in most other galileo imagery the incidence angle of light also introduces an observational bias in the identification of chaotic terrain images acquired closer to europa s terminator generally reveal more chaos features than images taken with higher sun proper accounting for selection effects has implications for the size distribution and chronology of chaotic terrain and the geologic history of the satellite at 200 m pixel 30 of europa s surface appears as chaotic terrain but with the effects of lighting and resolution taken into account the portion is 40 or more bias correction eliminates the 10 km size peak that had been the basis of an earlier thick ice model mottled terrain and lenticulae appear to be the same as chaotic terrain even though they have been mapped separately in the past and accounting for how observational bias affects the freshness of appearance of chaotic terrain and the identification of tectonic modification of chaotic terrain demonstrates that the formation of tectonic and chaotic terrain have been concurrent processes throughout europa s surface history

miocene cooling in the northern qilian shan northeastern margin of the tibetan plateau revealed by apatite fission track and vitrinite reflectance analysis apatite fission track and vitrinite reflectance data from phanerozoic rocks of the northern qilian shan and jiuxi basin at the northeastern margin of the tibetan plateau show a complex thermal history with multiple paleothermal events peak paleotemperatures reached in the middle cretaceous suggest that hydrocarbon generation occurred in the basin at that time paleozoic mesozoic samples show evidence of a middle tertiary cooling episode between 20 and 10 ma this thermal fingerprint is significant because stratigraphic evidence for miocene exhumation is overwhelmed by spectacular pliocene pleistocene deformation and erosion we interpret the miocene cooling as recording initial exhumation of the northern qilian shan earlier than other models have proposed i e after 6 5 ma miocene cooling is broadly coincident with cenozoic uplift and exhumation recorded elsewhere in the tibetan tarim region

heat flow lenticulae spacing and possibility of convection in the ice shell of europa abstract two opposing models to explain the geological features observed on europa s surface have been proposed the thin shell model states that the ice shell is only a few kilometers thick transfers heat by conduction only and can become locally thinner until it exposes an underlying ocean on the satellite s surface according to the thick shell model the ice shell may be several tens of kilometers thick and have a lower convective layer above which there is a cold stagnant lid that dissipates heat by conduction whichever the case from magnetic data there is strong support for the presence of a layer of salty liquid water under the ice the present study was performed to examine whether the possibility of convection is theoretically consistent with surface heat flows of 100 200 mw m 2 deduced from a thin brittle lithosphere and with the typical spacing of 15 23 km proposed for the features usually known as lenticulae it was obtained that under europa s ice shell conditions convection could occur and also account for high heat flows due to tidal heating of the convective nearly isothermal interior but only if the dominant water ice rheology is superplastic flow with activation energy of 49 kj mol 1 this is the rheology thought dominant in the warm interior of the ice shell in this case the ice shell would be 15 50 km thick furthermore in this scenario explaining the origin of the lenticulae related to convective processes requires ice grain size close to 1 mm and ice thickness around 15 20 km

time constraints for the yellow river traversing the sanmen gorge 1 the yellow river is the second longest river in china a total course of 5464 km the yellow river traverses 30 gorges within its main course and the last one is the sanmen gorge the timing of cut through the sanmen gorge indicates the final integration of the yellow river previous geological surveys identify a paleolake in the weihe basin located west of the sanmen gorge the lake was drained when the gorge was cut through using cosmogenic nuclide burial dating we obtain ages of transition from lake to fluvial environments in the weihe basin and formation of fluvial terraces within the sanmen gorge the timing of cut through the sanmen gorge is constrained to 1 3 1 5 ma zircon u pb age distributions further suggest that the weihe the largest tributary of the yellow river running from west to east along the northern section of the qinling mountains primarily flowed over the sanmen gorge followed by the upper and middle yellow river traversing 1 3 1 4 ma ago it appears that formation and integration of the yellow river occurred in a short duration in the early pleistocene probably related to global climate changes

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 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

europa s rate of rotation derived from the tectonic sequence in the astypalaea region abstract the most recent visible tectonic features in the astypalaea region in the southern hemisphere of europa are a set of cycloidal ridges three of which have cross cutting relationships that define a time sequence for their formation the longitudes at which each of these features formed which may be different from the current location due to rotation of europa are constrained by models of their formation reconciling the time sequence with the inferred longitudes of formation appears to require that

impact penetration of europa s ice crust as a mechanism for formation of chaos terrain ice thickness estimates and impactor dynamics indicate that some impacts must breach europas ice crust and outcomes of impact experiments using ice over water targets range from simple craters to chaos like destroyed zones depending on impact energy and ice competence firstorder impacts into thick ice or at low impact energy produce craters second order impacts punch through the ice making holes that resemble raft free chaos areas third order impacts into thinnest ice or at highest energy produce large irregular raft filled zones similar to platy chaos other evidence for an impact origin for chaos areas comes from the size frequency distribution of chaos craters on europa which matches the impact production functions of ganymede and callisto and from small craters around the large chaos area thera macula which decrease in average size and density per unit area as a function of distance from theras center there are no tiny chaos areas and no craters 50 km diameter this suggests that small impactors never penetrate whereas large ones berpenetrators 2 5 km diameter at average impact velocity always do existence of both craters and chaos areas in the size range 2 40 km diameter points to spatial temporal variation in crust thickness but in this size range craters are progressively outnumbered by chaos areas at larger diameters suggesting that probability of penetration increases with increasing scale of impact if chaos areas do represent impact sites then europas surface is older than previously thought the recalculated resurfacing age is 480 302 960 ma greater than prior estimates but still very young by solar system standards

the search for current geologic activity on europa observational evidence and theoretical arguments suggest that jupiter s satellite europa could be geologically active and possess an ocean of liquid water beneath its surface at the present time we have searched for evidence of current geologic activity on europa in the form of active plumes venting material above the surface and by comparison of voyager and galileo images to look for any changes on the surface so far we have observed no plumes and have detected no definitive changes the lack of observed activity allows us to estimate a maximum steady state surface alteration rate of 1 km2 y 1 in the regions analyzed assuming alterations will cover contiguous areas of at least 4 km2 over a period of 20 years assuming this as a constant globally uniform resurfacing rate leads to a minimum average surface age of 30 million years we also suggest that the lack of obvious circular albedo patterns on the surface due to plumes coupled with the presence of bright rayed craters such as pwyll and the predicted sputtering erosion rate implies that no large scale plume activity has taken place over at least the last few thousand years we thus conclude that if europa s surface is currently active any changes must be relatively small in spatial scale or episodic in nature rather than continuous to detect potential small scale surface changes we need high resolution comparisons between the galileo data and future europa orbiter images

incision rate of the yellow river in northeastern tibet constrained by 10be and 26al cosmogenic isotope dating of fluvial terraces implications for catchment evolution and plateau building unlike other large rivers flowing out of tibet the yellow river escapes from the plateau towards the ne crossing no less than five nw se striking actively growing ranges and intervening basins thick plio quaternary deposits and fluvial terraces testify to a phase of aggra dation and sediment infill up to the average surface elevation 3200 3250 m a s l of the gonghe guide and qinghai lake basins a set of seven main terraces across the gonghe basin suggests progressive down cutting of the yellow river carving the 500 m deep longyang gorge at the basin exit 10be and 26al concentrations in quartz of surface and sub surface samples of four terraces constrain the timing of incision by determining the burial age of the deposit and the exposure age of its surface modelling the depth dependence of the 10be concentration and the 26al 10be ratio allows us to constrain the onset of the ongoing phase of incision to 120 250 ka these ages suggest long term incision rates between 2 6 mm a together with the present morphology of the yellow river terraces across the gonghe basin and the longyang gorge our results imply rapid river catchment evolution and interaction between river dynamics tectonic and climate in northeastern tibet

pits and uplifts on europa abstract a survey of depression and uplift features on europa based on galileo regional mapping images shows that these features come in a wide range of sizes with numbers increasing greatly with decreasing size down to the limits of resolution size distributions are similar in the northern leading and southern trailing hemispheres where they are distinctly different from the southern leading and northern trailing hemispheres suggesting an oblique antipodal symmetry pattern similar to that of chaotic and tectonic terrain this pattern is suggestive of polar wander uplifts are usually polygonal or irregular in shape and rarely are cracked patches of chaotic terrain which we had surveyed earlier are not included in the current study because their topography is generally unclear and because there is no a priori known genetic linkage with the pits and uplifts these results contradict generalizations based on the earlier pits spots and domes psd taxonomy most of the type examples for psds were simply patches of chaotic terrain selected from a limited portion of their full size range the use of the term lenticula to collectively describe psds is inconsistent with the iau definition of lenticula a small dark spot seen at low resolution pits and uplifts do not correlate with lenticulae although chaos often does properties of psds that have been widely cited as primary evidence for convective upwelling in thick ice e g that uplifts are generally dome shaped and often cracked that pits and domes are regularly spaced that there is a typical diameter of 10 km were premature and not supported by subsequent data most pits and uplifts are less than 10 km across so if they formed by diapirism or convective upwelling the sources must have been very shallow less than 5 km deep how they actually formed remains unknown

tidal tectonic processes and their implications for the character of europa s icy crust 1 jupiter s satellite europa is covered by an icy crust likely overlying a deep global liquid water ocean the mutually dependent relationship between the orbit and tidal processes controls europa s rotation heating and stress observations of the surface and investigation of tidal tectonic processes indicate that the dominant types of surface terrain have been created by frequent repeated exposure of an underlying ocean to the surface surface lineaments including ubiquitous cycloidal chains of arcs features are correlated with tidal stress patterns demonstrating that they form by crustal cracking but only if a substantial ocean is present to give adequate tidal amplitude stratigraphy of tectonic features combined with models of how and where they formed demonstrates a moderate rate of nonsynchronous rotation tidal driving of strike slip displacement in which surface areas shear passed one another by daily 85 hours on europa tidal stresses suggests that cracks penetrate to a liquid layer the characteristic ridge sets that cover tectonic terrain may be built by tidal pumping of fluid and slush to the surface on a daily basis widespread tectonic dilation creates new surface as material rises from below in addition to those tectonic terrains nearly half of the surface is chaotic terrain with morphology and other characteristics indicative of melt through from below consistent with the tectonic indications of thin ice and plausible tidal heating rates formation of both chaotic and tectonic terrains has continually resurfaced the satellite while connecting the ocean to the surface surface colorants correlate with locations where ocean water reached the surface such as along large scale ridge systems and around chaotic terrain as a result of tides liquid water may have bathed crustal cracks and surfaces with heat transporting and mixing substances vertically such daily transported materials would include substances from the oceanic reservoir oxidants and fuels created at the surface as well as any organisms and their chemical products thus a variety of habitable environments likely exist in the crust deactivation of individual cracks after thousands of years due to the tidally driven nonsynchronous rotation constrains processes like ridge building and strike slip displacement and would require any living organisms to adapt to such change

soil erosion rates on sloping cultivated land on the loess plateau near ansai shaanxi province china an investigation using 137cs and rill measurements sediment yields from the rolling hills area of the loess plateau in northern china 10 000 25 000 t km 2 yr 1 are amongst the highest in the world the sediment is believed to derive from both the deep gullies that dissect the rolling plateau and the steep cultivated fields on the slopes of the mounds between the gullies however there are few reliable data for erosion rates on the cultivated fields and it is suspected that current estimates 10 000 16 000 t km 2 yr 1 based on empirical relationships derived from erosion plot studies exceed the true values this study sought to address the need for more information concerning erosion of the cultivated fields through derivation of erosion rates from measurements of rill volume and caesium 137 cs 137 inventories for typical fields near the village of ansai shaanxi province the derived erosion rates are discussed and compared with estimates based on empirical relationships derived from erosion plot data where erosion rate estimates based on both rill volume data and cs 137 inventories are available they show good agreement in the pattern of downslope variation both show a sharp decline in erosion rates at a slope length of c 50 m this is tentatively attributed to a change from transport limited to detachment limited conditions where rill incision reaches the undisturbed loess at the base of the plough layer no such decline is visible in the predictions based on empirical relationships derived from erosion plot data further evidence is presented that supports the suggestion that these empirical relationships overestimate erosion rates at slope lengths in excess of c 50 m it is tentatively suggested that the rates of soil erosion from sloping cultivated fields in the rolling hills area are more likely to lie in the range 8000 10 000 t km 2 yr 1 than in the higher range suggested by the empirical relationships c 1998 john wiley sons ltd

neogene and quaternary faulting in and along the qinling shan the structure of the qinling shan mountain range shaanxi china involves major east south east strike slip faults field observations made during two expeditions in 1983 and 1984 show that the faults are active and may have undergone several tens of kilometres of post eocene left lateral displacement the faults cut the morphology sharply and offset left laterally small channels their trace is marked by cataclastic to mylonitic non coaxial deformation zones at least 50 100 m wide the qinling faults allow the eastward extrusion of south china and may be considered the easternmost continuation of the altyn tagh fault system they link extensional tectonics in northeastern china to the himalayan collision