spatial and temporal variations in growth rates along active normal fault systems an example from the lazio abruzzo apennines central italy abstract the geometry kinematics and rates of active extension in lazio abruzzo italian apennines have been measured in order to gain a better understanding of the spatial and temporal variations in fault growth rates and seismic hazards associated with active normal fault systems we present fault map traces throws throw rates and slip directions for 17 parallel en echelon or end on active normal faults whose 20 40 km lengths combine to form a soft linked fault array ca 155 km in length and ca 55 km across strike throw rates derived from observations of faulted late glacial features and holocene soils show that both maximum throw rates and throw rate gradients are greater on centrally located faults along the strike of the array total throws and throw gradients show similar spatial variations but with weaker relationships with distance along strike when summed across strike throw rates are increasingly high towards the centre of the array relative to summed throws we interpret the above to suggest that throw rates have changed in the recent past ca 0 7 ma from spatially random fault growth rates initiating at 2 5 3 3 ma to growth rates that are greater on centrally located faults we interpret this as evidence for fault interaction producing throw rate variations that drive throw profile readjustment on these crustal scale soft linked faults the results are used to discuss seismic hazards in the region which are quantified in a second paper in this issue

evidence of large scale deformation patterns from gps data in the italian subduction boundary abstract we present the velocity field in italy derived from over 300 continuous gps stations operated in the 1998 2009 time span the gps network maps the whole country with a mean inter site distance of about 50 km and provides a valuable source of data to study the ongoing deformation processes in the central mediterranean the estimated horizontal and vertical velocity fields show major significant features and also less known second order kinematic features a general uplift characterizes the whole apennines and alpine belts that follow the topographic ridge whereas the po plain shows a gradually increasing subsidence from west to east the apennines belt displays a distinctive extension 50 80 10 9 yr 1 while compressive tectonic regimes characterize northern sicily eastern alps and the northeast front of the northern apennines 25 50 10 9 yr 1 second order deformation patterns on large scale wavelength 100 km have been detected on the accretionary prism of central and southern apennines that are highly correlated with other geophysical data vp anomalies seismic anisotropy etc and related to deep rooted sections 70 100 km marked by different subduction regimes apparently at this scale length the observed deformations are governed by the lithosphere as a whole we interpret these deformations as a result of different subduction mechanisms such as variations of the subduction rollback velocity affecting different segments of the subduction zone and or to mantle flows in proximity of the slab edges further south in central southern sicily we detect a contraction of 1 1 0 2 mm yr that probably accommodates part of the africa eurasia convergence on the outer thrust front of the apennines maghrebides belt this hypothesis agrees with an independent analysis of the seismicity associated to the sicilian basal thrust thought to be still active the itrf2005 estimates of the new gps velocity field are available also in sinex format as supplementary file s1

influence of surface topography on the critical carbon dioxide level required for the formation of a modern snowball earth abstractthe influence of continental topography on the initiation of a global glaciation i e snowball earth is studied with both a fully coupled atmosphere ocean general circulation model aogc

patterns in the distribution of aptian rudists and corals within a sequence stratigraphic framework maestrat basin e spain abstract the ecological zonation of and environmental controls on rudist and coral assemblages on carbonate platforms of the old world have received more attention for late cretaceous examples than for their early cretaceous counterparts this study accordingly investigates the vertical and lateral distribution of aptian rudist bivalves and scleractinian corals on a carbonate platform succession from the western maestrat basin e iberian peninsula here colonial corals grew profusely on an isolated platform top environment during an earliest highstand stage of a long term trend of relative sea level as well as on marly slope settings during higher frequency transgressive pulses during the later highstand stage within a longer term relative sea level cycle a facies belt dominated by autochthonous rudist bivalves overlaid the coral meadow that had developed on the isolated platform top the internal part of this carbonate platform with rudists is dominated by slender elevator caprinids such as caprina parvula whereas requieniids and polyconitids predominate in the external zone the abundance of caprinids in the internal platform is remarkable given that caprinid lithosomes of late early aptian age are usually rare in the northern margin of the tethys the proliferation of caprinids in this case was probably favoured by the apparently more isolated nature of the carbonate platform on the slopes the coral communities that flourished during higher frequency transgressive pulses are overlain by carbonates with rudists mainly requieniids shed from the platform top during normal and forced regressive higher frequency changes of relative sea level accordingly the vertical change from coral dominated to rudist dominated facies in both platform top and slope settings records progradation to decipher the long term relative sea level changes that controlled the deposition of this carbonate succession a sequence stratigraphic analysis was performed two depositional sequences including a late early aptian intra dufrenoyia furcata zone forced regressive stage of relative sea level which subaerially exposed and incised the early aptian succession to a depth of 21 m were recognised the incisions were back filled with peritidal deposits during the subsequent marine onlap the rudist and coral bearing carbonates were deposited along platform top to slope profiles lacking a barrier margin and hence lagoon environments

co2 levels required for deglaciation of a near snowball earth geologic evidence suggests that in the late neoproterozoic 600 ma almost all land masses were glaciated with sea level glaciation existing even at the equator a recent modeling study has shown that it is possible to simulate an ice covered earth glaciation with a coupled climate ice sheet model however separate general circulation model experiments suggest that a second solution may exist with a substantial area of ice free ocean in the tropics although 0 1 to 0 3 of an atmosphere of co 2 300 to 1000 x is required for deglaciation of a snowball earth the exit co 2 levels for an open water solution could be significantly less in this paper we utilize a coupled climate ice sheet model to demonstrate four points 1 the open water solution can be simulated in the coupled model if the sea ice parameter is adjusted slightly 2 a major reduction in ice volume from the open water equatorial ice solution occurs at a co level of about 4x present values about two orders of magnitude less than required for exit from the hard snowball initial state 3 additional co 2 increases are required to get fuller meltback of the ice and 4 the open water solution exhibits hysteresis properties such that climates with the same level of co 2 may evolve into either the snowball open water or a warmer world solution with the trajectory depending on initial conditions these results set useful targets for geochemical calculations of co 2 changes associated with the open water solution

deep reaching versus vertically restricted quaternary normal faults implications on seismic potential assessment in tectonically active regions lessons from the middle aterno valley fault system central italy abstract we investigate the middle aterno valley fault system mavf a poorly investigated seismic gap in the central apennines adjacent to the 2009 l aquila earthquake epicentral area geological and paleoseismological analyses revealed that the mavf evolved through hanging wall splay nucleation its main segment moving at 0 23 0 34 mm year since the middle pleistocene the penultimate activation event occurred between 5388 5310 b c and 1934 1744 b c the last event after 2036 1768 b c and just before 1st 2nd century ad these data define hard linkage sensu walsh and watterson 1991 peacock et al 2000 walsh et al 2003 and references therein with the contiguous subequana valley fault segment able to rupture in large magnitude earthquakes up to 6 8 that did not rupture since about two millennia by the joint analysis of geological observations and seismological data acquired during to the 2009 seismic sequence we derive a picture of the complex structural framework of the area comprised between the mavf the paganica fault the 2009 earthquake causative fault and the gran sasso range this sector is affected by a dense array of few km long closely and regularly spaced quaternary normal fault strands that are considered as branches of the mavf northern segment our analysis reveals that these structures are downdip confined by a decollement represented by to the presently inactive thrust sheet above the gran sasso front limiting their seismogenic potential our study highlights the advantage of combining quaternary geological field analysis with high resolution seismological data to fully unravel the structural setting of regions where subsequent tectonic phases took place and where structural interference plays a key role in influencing the seismotectonic context this has also inevitably implications for accurately assessing seismic hazard of such structurally complex regions

volcanism co2 and palaeoclimate a late jurassic early cretaceous carbon and oxygen isotope record a composite tethyan late jurassic early cretaceous carbon and oxygen isotope curve is presented c isotope data provide information on the evolution and perturbation of the global carbon cycle o isotope data are used as a palaeotemperature proxy in combination with palaeontological information the resulting trends in climate and in palaeoceanography are compared with biocalcification trends and oceanographic conditions favouring or inhibiting biocalcification positive c isotope anomalies in the valanginian and aptian correlate with episodes of increased volcanic activity regarded as a source of excess atmospheric carbon dioxide a major warming pulse accompanies the aptian but not the valanginian c isotope event the observed change in early aptian temperatures could have triggered the destabilization of sedimentary gas hydrates and the sudden release of methane to the biosphere as recorded as a distinct negative carbon isotope pulse preceding the positive excursion both c isotope anomalies are accompanied by biocalcification crises that may have been triggered by p co 2 induced changes in climate and in surface water chemistry elevated nutrient levels in river influenced coastal waters and in upwelling regions further weakened marine calcification these conditions contrast with normal trophic conditions prevailing in the latest jurassic and favouring biocalcification the c and o isotope curves record a stable mode of carbon cycling and stable temperatures we conclude that biocalcification is mostly triggered and inhibited by co 2 conditions in the atmosphere ocean system

high sea surface temperatures during the early aptian oceanic anoxic event 1a in the boreal realm the early aptian was characterized by the widespread occurrence of anoxia in the oceans known as oceanic anoxic event oae 1a intense degassing from submarine volcanic plateaus presumably resulted in high atmospheric co2 concentrations culminating in greenhouse conditions oae 1a can therefore be considered as a past natural experiment important to understand the future evolution of our climate paleotemperature estimates for oae 1a are however predominantly based on bulk oxygen isotopes which are susceptible to diagenetic overprinting while tex86 paleotemperature estimates are limited in number or derived from stratigraphically poorly constrained sections here we reconstructed for the first time sea surface water temperatures ssts based on the tex86 paleothermometer from an oae 1a section from the middle northern latitudes 39 n paleolatitude we find a sst rise starting prior to oae 1a and reaching a maximum during the event with ssts of 31 34 c 4 9 c higher than those of older hauterivian lower aptian sediments from the same sedimentary basin the end of oae 1a is marked by relatively lower ssts of 30 c these observations are supported by belemnite based oxygen isotope d18obel data and calcareous nannofossils our integrated data set clearly indicates that super greenhouse conditions prevailed during oae 1a at northern latitudes ssts are similar to those estimated for coeval low latitudinal sites suggesting that an equable warm climate with reduced latitudinal gradients characterized the early aptian

transient global cooling at the onset of early aptian oceanic anoxic event oae 1a the onset of the early aptian oceanic anoxic event oae 1a ca 120 ma coincided with a major perturbation of the carbon cycle which is reflected in the sedimentary carbon isotope record triggering mechanisms duration and climatic repercussions of this episode of accelerated organic matter burial remain poorly constrained here we present millennial scale bulk rock carbon and oxygen isotope data from a marly subtropical intrashelf basin la bedoule southeast france with unusually high sedimentation rates which track the onset of oae1a in unprecedented resolution our record reveals that the negative low amplitude delta 13 c excursion preceding oae1a lasted 100 k y implying that enhanced volcanic co 2 emission and or pulsed methane dissociation over a prolonged time span were instrumental in triggering oae1a the main positive carbon isotope shift at the onset of oae1a previously regarded as continuous occurred stepwise over an extended period of 300 k y transient climate cooling during the initial delta 13 c increase probably reflects ephemeral high latitude glaciation triggered by changes in radiative forcing and drawdown of atmospheric co 2

refugium for surface life on snowball earth in a nearly enclosed sea a numerical solution for sea glacier invasion through a narrow strait where photosynthetic eukaryotic organisms survived during the snowball earth events of the neoproterozoic remains unclear our previous research tested whether a narrow arm of the ocean similar to the modern red sea could have been a refugium for photosynthetic eukaryotes during the snowball earth using an analytical ice flow model we demonstrated that a limited range of climate conditions could restrict sea glacier flow sufficiently to allow an arm of the sea to remain partially free from sea glacier penetration a necessary condition for it to act as a refugium here we expand on the previous study using a numerical ice flow model with the ability to capture additional physics to calculate sea glacier penetration and to explore the effect of a channel with a narrow entrance the climatic conditions are made self consistent by linking sublimation rate to surface temperature as expected the narrow entrance allows parts of the nearly enclosed sea to remain safe from sea glacier penetration for a wider range of climate conditions

carbon isotope signatures of pedogenic carbonates from se china rapid atmospheric pco2 changes during middle late early cretaceous time lower cretaceous pedogenic carbonates exposed in se china have been dated by u pb isotope measurements on single zircons taken from intercalated volcanic rocks and the ages integrated with existing stratigraphy 13 c values of calcretes range from 7 0 to 3 0 and can be grouped into five episodes of increasing decreasing values the carbon isotope proxy derived from these palaeosol carbonates suggests p co 2 mostly in the range 1000 2000 parts per million by volume ppmv at s z co 2 contributed by soil respiration 2500 ppmv and 25 c during the hauterivian albian interval c 30 ma duration such atmospheric co 2 levels are 4 8 times pre industrial values almost double those estimated by geochemical modelling and much higher than those established from stomatal indices in fossil plants rapid rises in p co 2 are identified for early hauterivian middle barremian late aptian early albian and middle albian time and rapid falls for intervening periods these episodic cyclic changes in p co 2 are not attributed to local tectonism and volcanism but rather to global changes the relationship between reconstructed p co 2 and the development of large igneous provinces lips remains unclear although large scale extrusion of basalt may well be responsible for relatively high atmospheric levels of this greenhouse gas suggested levels of relatively low p co 2 correspond in timing to intervals of regional to global enrichment of marine carbon in sediments and negative carbon isotope 13 c excursions characteristic of the oceanic anoxic events oae1a selli event kilian and paquier events constituting part of the oae 1b cluster and oae1d short term episodes of high p co 2 coincide with negligible carbon isotope excursions associated with the faraoni event and the jacob event given that episodes of regional organic carbon burial would draw down co 2 and negative 13 c excursions indicate the addition of isotopically light carbon to the ocean atmosphere system controls on the carbon cycle in controlling p co 2 during early cretaceous time were clearly complex and made more so by atmospheric composition also being affected by changes in silicate weathering intensity

glacial flow of floating marine ice in snowball earth 1 simulations of frigid neoproterozoic climates have not considered the tendency of thick layers of floating marine ice to deform and spread laterally we have constructed a simple model of the production and flow of marine ice on a planetary scale and determined ice thickness and flow in two situations when the ocean is globally ice covered hard snowball and when the tropical waters remain open soft snowball in both cases ice flow strongly affects the distribution of marine ice flowing ice probably carries enough latent heat and freshwater to significantly affect the transition into a snowball earth climate we speculate that flowing marine ice rather than continental ice sheets may be the erosive agent that created some neoproterozoic glacial deposits

time intervals to assess active and capable faults for engineering practices in italy abstract the time span necessary to define a fault as active and capable can mainly be derived from the framework of the regulations and the literature produced since the 1970s on risk estimation in engineering planning of strategic buildings within this framework two different lines of thought can be determined which have mainly developed in the usa on the one side there is a tendency to produce narrow chronological definitions this is particularly evident in the regulatory acts for the planning of nuclear reactors the much more effective second line of thought anchors the chronological definitions of the terms active and therefore capable to the concept of seismotectonic domain as the domains are different in different regions of the world the chronological definition cannot be univocal i e different criteria are needed to define fault activity which will depend on the characteristics of the local tectonic domain and of the related recurrence times of fault activation current research on active tectonics indicates that methodological aspects can also condition the chronological choice to define fault activity indeed this practice implies the use of earth science methods the applications of which can be inherently limited for example limits and constraints might be related to the availability of datable sediments and landforms that can be used to define the recent fault kinematic history for the italian territory we consider two main tectonic domains a the compressive domain along the southern margin of the alpine chain and the northern and northeastern margins of the apennines which is characterised by the activity of blind thrusts and reverse faults and b the extensional domain of the apennines and the calabria region which is often manifest through the activity of seismogenic normal and normal oblique faults in case a the general geomorphic and subsurficial evidence of recent activity suggests that a reverse blind fault or a blind thrust should be considered active and potentially capable if showing evidence of activity during the quaternary i e over the last 2 6 myr unless information is available that documents its inactivity since at least the last glacial maximum lgm ca 20 ka the choice of the lgm period as the minimum age necessary to define fault inactivity is related to practical aspects the diffusion of the lgm deposits and landforms and to the evidence that ca 20 kyr to assess fault inactivity precautionarily includes a number of seismic cycles in the extensional domains of the apennines and calabria region the general geological setting suggests that the present tectonic regime has been active since the beginning of the middle pleistocene therefore we propose that a normal fault in the italian extensional domain should be considered active and capable if it displays evidence of activation in the last 0 8 myr unless it is sealed by deposits or landforms not younger than the lgm the choice of the lgm as the minimum age to ascertain fault inactivity follows the same criteria described for the compressive tectonic domain

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

mudball surface dust and snowball earth deglaciation 1 recent modeling results have raised doubts about the ability to deglaciate from a global glaciation at atmospheric carbon dioxide levels that are realistic for a neoproterozoic snowball earth here we argue that over the lifetime of a snowball event ice dynamics should lead to the development of a layer of continental and volcanic dust at the ice surface in the tropics that would significantly lower the tropical surface albedo and encourage deglaciation this idea leads to the prediction that clay drapes found on top of neoproterozoic glaciations should be thicker in tropical than extratropical regions we test this idea by running the foam general circulation model gcm with an added tropical dust layer of different sizes and albedos and find that the tropical dust layer causes snowball deglaciation at pco2 0 01 0 1 bar in a reasonable regime of these parameters we find similar though more nuanced results from a limited number of test cases using national center for atmospheric research s cam gcm

calcite aragonite ratio fluctuations in aptian rudist bivalves correlation with changing temperatures understanding how bivalves responded to past temperature fluctuations may help us to predict specific responses of complex calcifiers to future climate change during the late early aptian aragonite rich rudist bivalves decreased in abundance in northern tethyan carbonate platforms while rudists with a thickened calcitic outer shell layer came to dominate those of iberia seawater cooling and variations in calcium carbonate saturation states may have controlled this faunal turnover however our understanding of how rudist lineages responded to changing environmental conditions is constrained by a lack of quantitative data on the evolution of thickness size and mineralogy of the shell this study is based on volumetric measurements of the shell and shows the transition in lineages of the family polyconitidae from aragonite rich mineralogy in the earliest aptian to low mg calcite dominated mineralogy in the middle aptian returning to aragonite dominated composition in the latest aptian the platform biocalcification crisis that occurred at the early late aptian boundary in the tethys was marked by a relative increase of calcite and a decrease in skeletal thickness and commissural diameters the highest calcite aragonite cc a ratios in polyconitid rudists accompanied the late aptian cold episode and the lowest values were reached during the warmer intervals of the earliest and latest aptian these results imply a correlation between cc a ratio values and temperature and suggest that some bivalves adapted to less favorable calcification conditions by changing calcite and aragonite proportions of their bimineralic shells and decreasing skeletal thickness thereby reducing the metabolic cost of shell growth

late aptian palaeoclimatic turnovers and volcanism insights from a shallow marine and continental succession of the apennine carbonate platform southern italy abstract this study reports an integrated facies analysis carried out on a new section from the upper aptian of the se matese mts civitella licinio northern campania s italy which includes several decimeter to meter scale lacustrine intervals straddling a meter scale plant rich plattenkalk these intervals are assigned to the late gargasian early clansayesian by their stratigraphic relationship with the upper salpingoporella dinarica acme as well as lithologic and biostratigraphic supra regional key markers found in the apennine carbonate platform apcp including the orbitolina level we infer that the monogeneric parautochthonous plant remains frenelopsis sp were deposited in a supratidal to paralic coastal mudflat close to a restricted shallow marine lagoon at the verge of an arid semiarid climatic phase the plattenkalk was rapidly replaced by persistent lacustrine lithofacies at the onset of a major climatic turnover glacial trigger the overlying shallow marine deposits are capped by a deeply incised palaeokarstic surface and in turn by unconformable middle clansayesian transgressive shallow marine deposits interlayering of reliable lithologic indicators of palaeoclimate and high resolution event stratigraphic hires correlation of the civitella licinio succession with the astrochronologically tuned mt faito reference section of the apcp bring evidence of rapidly fluctuating hydroclimatic conditions wet and arid phases in the short 100 ky and long 400 ky eccentricity time band hires and astrochronological age assignment to crucial key markers and humid arid phases at civitella licinio permit to further refine the detailed stratigraphy of the mt faito reference section and to assign the upper s dinarica acme of the apcp to a numerical age of 118 55 118 50 my sem and eds analyses document common to abundant windblown volcanic particles glass shards and sanidine crystals throughout the frenelopsis rich plattenkalk 118 3 to 118 2 my and the encasing units especially in the overlying brackish lacustrine deposits palaeogeographic and palaeoclimatic reconstructions suggest that the pyroclastic material was probably transported by northeasterly trade winds from orogenic volcanic centers located within the dinaridic carpatho balkan arc trench system and have been supplied to the apcp for a time span of 3 my during the late aptian a preliminary tephrostratigraphic correlation of the upper aptian volcaniclastic levels of the apcp with the bentonite levels of the vocontian basin is proposed

atlantic cooling associated with a marine biotic crisis during the mid cretaceous period most of the marine biotic crises that occurred during the hot mesozoic era have been linked to episodes of extreme warmth 1 2 others however may have occurred during cooler intervals that interrupted cretaceous greenhouse warmth 3 5 there are some indications of cooling in the late aptian 6 8 116 114 myr ago but it has not been definitively linked to biotic crisis here we assess the timing and magnitude of late aptian cooling and its association with biotic crises using a suite of geochemical and micropalaeontological assessments from a marine sediment core from the north atlantic ocean as well as global biogeochemical modelling sea surface temperatures derived from the tex86 proxy suggest that surface waters cooled by about 5 degrees c during the two million years coincident with a positive delta c 13 excursion of approximately 2 parts per thousand in carbonates and organic carbon surface productivity was enhanced during this period but the abundance of planktonic foraminifera and nannoconid phytoplankton declined our simulations with a biogeochemical model indicate that the delta c 13 excursion associated with the cooling could be explained by the burial of about 812 000 gigatons of carbon over 2 5 million years about 50 of the this carbon burial occurred in the atlantic southern and tethys ocean basins we conclude that global cooling during greenhouse conditions can cause perturbations to marine ecosystems and biogeochemical cycles at scales comparable to those associated with global warming

a major perturbation of the carbon cycle before the ghaub glaciation neoproterozoic in namibia prelude to snowball earth 1 a large 11 15 negative shift in 13c is observed in shallow water carbonates directly beneath neoproterozoic glacial deposits or correlative disconformity in northwest namibia ascribed to a snowball earth reproducibility and stratigraphic concordance of this anomaly in 16 sections across the ancient continental shelf support a primary origin and field relations show it predates the fall in sea level associated with the ghaub glaciation we crudely estimate the duration of the isotopic shift as 0 6 106 years from a simple thermal subsidence model similar or larger 13c anomalies are found directly beneath neoproterozoic glacial units in australia canada china scotland and svalbard after considering conventional interpretations for negative 13c anomalies we conclude that a prolonged methane release to the atmosphere is most consistent with the timescale magnitude and geological context of the anomaly in namibia counterintuitively an anomalous methane flux that is sustained for 100s kyr may be consistent with a snowball glaciation

migration of air bubbles in ice under a temperature gradient with application to snowball earth 1 to help characterize the albedo of sea glaciers on snowball earth a study of the migration rates of air bubbles in freshwater ice under a temperature gradient was carried out in the laboratory the migration rates of air bubbles in both natural glacier ice and laboratory grown ice were measured for temperatures between 36 c and 4 c and for bubble diameters of 23 2000 m the glacier ice was sampled from a depth near close off 74 m in the jems2 ice core from summit greenland migration rates were measured by positioning thick sections of ice on a temperature gradient stage mounted on a microscope inside a freezer laboratory the maximum and minimum migration rates were 5 45 m h 1 k cm 1 1 at 4 c and 0 03 m h 1 k cm 1 1 at 36 c besides a strong dependence on temperature migration rates were found to be proportional to bubble size we think that this is due to the internal air pressure within the bubbles which may correlate with time since close off and therefore with bubble size migration rates show no significant dependence on bubble shape estimates of migration rates computed as a function of bubble depth within sea glaciers indicate that the rates would be low relative to the predicted sublimation rates such that the ice surface would not lose its air bubbles to net downward migration it is therefore unlikely that air bubble migration could outrun the advancing sublimation front transforming glacial ice to a nearly bubble free ice type analogous to low albedo marine ice

mesozoic c cycle perturbations and climate evidence for increased resilience of the cretaceous biosphere to greenhouse pulses the mesozoic c isotope record traces the history of the global carbon cycle major perturbations of the carbon cycle triggered by extraordinary volcanic activity are recorded in negative spikes cou

feedbacks in a coupled ice atmosphere dust model of the glacial neoproterozoic mudball earth 1 the climate state of an ice covered neoproterozoic snowball earth climate is highly sensitive to the presence of dust on the ice other authors have noted that the accumulation of dust can lower the albedo of an ice covered world enough to allow deglaciation even with fairly modest amounts of greenhouse gas warming here we model the accumulation transport and removal of dust in a coupled ice atmosphere dust climate model operating within the simplified framework of a one dimensional energy balance climate model we confirm that the buildup of low albedo dust makes our model easier to deglaciate requiring orders of magnitude less carbon dioxide than a no dust model and discover novel climate feedbacks and chaos in the dusty ice system as dust accumulates its low albedo warms the ice and can cause it to melt in our model the meltwater carries away dust leading to both a simple negative feedback the dust thermostat and chaotic oscillations the feedback is robust over a broad range of model parameters but the chaotic oscillations are sensitive to model resolution

insights from the mw 6 3 2009 l aquila earthquake central apennines unveiling new seismogenic sources through their surface signatures the adjacent san pio fault terra nova 23 108 115 2011 abstract we analysed a broad region around l aquila in search of seismogenic faults similar to that responsible for the 6 april 2009 earthquake mw 6 3 having in mind the lessons learned from this earthquake we focused on adjacent areas displaying similar morphotectonic geological and structural features the basin running from barisciano to civitaretenga navelli notably located near the southeastern edge of the 2009 aftershock pattern appears to be one such area we collected morphotectonic and structural data indicating that this basin is underlain by a major active normal fault the san pio fault all the observations are very much reminiscent of the morphotectonic geological and structural setting of the area struck by the l aquila earthquake suggesting that the newly identified fault has the potential for a mw 6 2 shock

robust elements of snowball earth atmospheric circulation and oases for life 1 atmospheric circulation in a snowball earth is critical for determining cloud behavior heat export from the tropics regions of bare ice and sea glacier flow these processes strongly affect snowball earth deglaciation and the ability of oases to support photosynthetic marine life throughout a snowball earth here we establish robust aspects of the snowball earth atmospheric circulation by running six general circulation models with consistent snowball earth boundary conditions the models produce qualitatively similar patterns of atmospheric circulation and precipitation minus evaporation the strength of the snowball hadley circulation is roughly double modern at low co2 and greatly increases as co2 is increased we force a 1 d axisymmetric sea glacier model with general circulation model gcm output and show that neglecting zonal asymmetry sea glaciers would limit ice thickness variations to o 10 global mean ice thickness in the 1 d sea glacier model is well approximated by a 0 d ice thickness model with global mean surface temperature as the upper boundary condition we then show that a thin ice snowball solution is possible in the axysymmetric sea glacier model when forced by output from all the gcms if we use ice optical properties that favor the thin ice solution finally we examine snowball oases for life using analytical models forced by the gcm output and find that conditions become more favorable for oases as the snowball warms so that the most critical time for the survival of life would be near the beginning of a snowball earth episode

snowball earth asynchronous coupling of sea glacier flow with a global climate model during snowball earth episodes of the neoproterozoic and paleoproterozoic limited amounts of tropical open ocean jormungand or tropical ocean with thin ice cover would help to explain 1 vigorous glacial activity in low latitudes 2 survival of photosynthetic life and 3 deglacial recovery without excessive buildup of atmospheric co2 some previous models have suggested that tropical open ocean or thin ice cover is possible however its viability in the presence of kilometer thick sea glaciers flowing from higher latitudes has not been demonstrated conclusively here we describe a new method of asynchronously coupling a zonal sea glacier model with a 3 d global climate model and apply it to snowball earth equilibrium curves of ice line vs co2 are mapped out as well as their dependence on ocean heat transport efficiency sea glacier flow and other model parameters no climate states with limited tropical open ocean or thin ice are found in any of our model runs including those with sea glaciers if this result is correct then other refugia such as cryoconite pans would have been required for life to survive however the reasons for the differences between our results and others should first be resolved it is suggested that small scale convective dynamics affecting fractional snow cover in low latitudes may be a critical factor accounting for these differences

the continuity of active fault systems in greece summary evidence from geomorphology the distribution of large earthquakes and geodetic measurements suggests that the active faulting in mainland greece and the north aegean sea is concentrated into a small number of discrete linear zones that bound relatively rigid blocks on land the zones are most clearly identified where the faulting is associated with large escarpments particularly in hard footwall rocks the zones can become indistinct and diffuse near their ends sometimes because they enter high unstable topography where landsliding obscures the fault morphology but mostly because the extension rates decrease along strike as a consequence of the relative rotation of the blocks they bound the main graben systems of chalkidiki southern thessaly and the north gulf of evia all seem to connect with the strike slip faulting in the offshore aegean and to die out in the west a configuration related to clockwise rotations in east central greece by contrast the gulf of corinth which is the fastest opening graben system in greece opens more rapidly in the west than the east both these features of the gulf of corinth are consequences of the motion of the south aegean and peloponnese as a single block late pliocene and quaternary geology and geomorphology indicate that the boundaries of the rigid blocks in central greece have changed over that time with faulting migrating into the hanging walls sometimes changing in orientation these changes are probably related to the way faulting in the seismogenic layer adapts to block rotation so as to maintain the general features of a velocity field that is controlled by larger scale effects such as buoyancy forces and the seaward migration of the subducting slab beneath crete the image of greece as a mosaic of rigid blocks whose boundaries change with time is a useful framework for seismic hazard evaluation but we emphasize that some moderate sized earthquakes do occur away from the main fault zones within the relatively rigid blocks and especially near their diffuse ends

carbon isotopic composition of neoproterozoic glacial carbonates as a test of paleoceanographic models for snowball earth phenomena consistently positive carbon isotopic values were obtained from in situ peloids ooids and stromatolitic carbonate within neoproterozoic glacial successions in northern namibia central australia and the north american cordillera because positive values continue upward into the immediately overlying postglacial cap carbonates the negative isotopic excursions widely observed in those carbonate rocks require an explanation that involves a short term perturbation of the global carbon cycle during deglaciation the data do not support the ecological consequences of complete coverage of the glacial ocean with sea ice as predicted in the 1998 snowball earth hypothesis of p f hoffman et al in the snowball earth hypothesis the postglacial cap carbonates and associated 5 negative carbon isotopic excursions represent the physical record of co2 transfer from the high p co2 snowball atmosphere 0 12 bar to the sedimentary reservoir via silicate weathering in the snowball aftermath stratigraphic timing constraints on cap carbonates imply weathering rates of 1000 times preglacial levels to be consistent with the hypothesis the absence of sr isotopic variation between glacial and postglacial deposits and calculations of maximum weathering rates do not support a post snowball weathering event as the origin for cap carbonates and associated isotopic excursions

ultra thick triassic dolomites control the rupture behavior of the central apennine seismicity evidence from magnetic modeling of the l aquila fault zone high resolution tomography from the 2009 l aquila extensional seismic sequence has shown that the mw 6 1 main shock and most of the aftershocks occurred within a high velocity body 6 6 vp 6 8 km s located between depths of 3 and 12 km the nature of the high vp body has remained speculative although exhumed mafic deep crustal and upper mantle rocks serpentinites have been favored we used 3d magnetic anomaly modeling to investigate the plausibility of these favored sources for the l aquila body the modeling does not support the presence of high velocity serpentinites with a 30 50 serpentinization degree and gabbros accordingly we conclude that the high vp body may represent non magnetic upper triassic and possibly lower liassic dolomites that have been drilled in neighboring wells for 2 4 km this conclusion is also consistent with the lack of a coherent gravity anomaly for the body we speculate that ultra thick triassic dolomites reaching a thickness of 8 km may have been deposited in syntectonic wedges formed at the northern margin of the ionian sea where oceanic spreading occurred in mid late triassic times

snowball earth a thin ice solution with flowing sea glaciers 1 the late neoproterozoic era 600 800 myr ago was marked by at least two intervals of widespread cold that left glacial deposits at low paleolatitudes both snowball solutions with global ice cover and slushball solutions with ice free tropical oceans have been proposed to explain the paleomagnetic data the snowball model is best able to explain the auxiliary geological evidence particularly the existence of cap carbonates but it implies drastic survival pressure on the photosynthetic biota if the ice cover was everywhere thick enough to prevent sunlight from reaching the underlying ocean a thin ice solution that avoids this problem has been proposed but is thought to be inconsistent with realistic optical properties of sea ice and with the equatorward flow of sea glaciers here we use a coupled energy balance climate sea glacier model to argue that these apparent difficulties can be overcome and that thin tropical ice may have prevailed during these remarkable glacial episodes we also suggest that 1 some processes beyond the scope of zonal mean energy balance models may significantly affect the solutions and 2 thin ice could have prevailed on low latitude seas or large lakes protected from large scale sea glacier flow by surrounding land even if most of the earth was in a hard snowball state

space time distribution of afterslip following the 2009 l aquila earthquake 1 the inversion of multitemporal dinsar and gps measurements unravels the coseismic and postseismic afterslip slip distributions associated with the 2009 mw 6 3 l aquila earthquake and provides insights into the rheological properties and long term behavior of the responsible structure the paganica fault well resolved patches of high postseismic slip 10 20 cm appear to surround the main coseismic patch maximum slip 1 m through the entire seismogenic layer above the hypocenter without any obvious depth dependent control time series of postseismic displacement are well reproduced by an exponential function with best fit decay constants in the range of 20 40 days a sudden discontinuity in the evolution of released postseismic moment at 130 days after the main shock does not correlate with independent seismological and geodetic data and is attributed to residual noise in the insar time series the data are unable to resolve migration of afterslip along the fault probably because of the time interval six days between the main shock and the first radar acquisition surface fractures observed along the paganica fault follow the steepest gradients of postseismic line of sight satellite displacements and are consistent with a sudden and delayed failure of the shallow layer in response to upward tapering of slip the occurrence of afterslip at various levels through the entire seismogenic layer argues against exclusive depth dependent variations of frictional properties on the fault supporting the hypothesis of significant horizontal frictional heterogeneities and or geometrical complexities we support the hypothesis that such heterogeneities and complexities may be at the origin of the long term variable behavior suggested by the paleoseismological studies rupture of fault patches with dimensions similar to that activated in 2009 appears to have a 500 year recurrence time interval documented by paleoseismic and historical studies in addition to that paleoseismological evidence of large 0 5 m coseismic offsets seems to require seismic events recurring every 1000 2000 years characterized by 1 multisegment linkage 2 surface ruptures larger than in 2009 and 3 complete failure of the 2009 coseismic and postseismic patches

evolution of the mg ca ratio of cretaceous seawater implications from the composition of biological low mg calcite abstract for the evaluation of variations in the cretaceous seawater mg ca ratio 12 shells of rudist bivalves ranging in age from the late barremian 112 2 ma to the early campanian 81 4 ma have been analysed for intra shell variations in chemical mg sr fe mn and isotopic 18 o 13 c compositions of low mg calcite preservation of fibrous prismatic ultrastructure low fe and mn concentrations as well as sr concentrations within the range of marine biological calcite indicate only very minor diagenetic alteration in all studied shells mg concentrations and 18 o values show a more or less well defined inverse covariance this pattern is similar to the conditions observed in modern skeletal calcite and interpreted to result from a combination of a temperature effect and an unidentified metabolic control on the incorporation of mg into calcite average mg concentrations in rudist calcite are significantly lower than those of modern bivalves and increase from the barremian albian to the campanian while slopes of 18 o mg regressions are similar to those of modern bivalves assuming that the mg incorporation is linearly dependent on the mg ca ratio of seawater and that mg incorporation into calcite of modern bivalve mollusks follows the same metabolic pathway than in their extinct cretaceous relatives the mg ca molar ratio of cretaceous seawater increased from 1 in the late barremian to 3 in the early campanian this trend matches previous model predictions of seawater composition and experimental results from fluid inclusions in halite a very low mg ca ratio of seawater is confirmed here to have occurred before the onset of the significant mid cretaceous increase of seafloor production rates in the late barremian uncertainties in the secular variations of seafloor spreading are discussed as hydrothermal alteration of young oceanic crust is an important driver of changes in the seawater mg ca ratio

calcareous nannoplankton response to surface water acidification around oceanic anoxic event 1a ocean acidification induced by atmospheric co2 may be a major threat to marine ecosystems particularly to calcareous nannoplankton we show that during the aptian 120 million years ago oceanic anoxic event 1a which resulted from a massive addition of volcanic co2 the morphological features of calcareous nannofossils traced the biological response to acidified surface waters we observe the demise of heavily calcified nannoconids and reduced calcite paleofluxes at the beginning of a pre anoxia calcification crisis ephemeral coccolith dwarfism and malformation represent species specific adjustments to survive lower ph whereas later abundance peaks indicate intermittent alkalinity recovery deepwater acidification occurred with a delay of 25 000 to 30 000 years after the dissolution climax nannoplankton and carbonate recovery developed over 160 000 years under persisting global dysoxia anoxia

plate tectonic control on the evolution of cretaceous platform carbonate production carbonate producing biota on cretaceous carbonate platforms changed from early cretaceous aragonitic coral algal and coral rudist associations to turonian maastrichtian calcite dominated rudist associations abundance patterns of rudist bivalves examined from a large database show a shift from barremian cenomanian aragonite dominated to post cenomanian calcite dominated shells these skeletal mineral changes agree with a decrease in the mg ca ratio of seawater owing to high rates of production of oceanic crust during the barremian early turonian and its effect on seawater saturation with respect to aragonite and calcite increasing sr concentrations in biotic calcite from the barremian to the maastrichtian reflect the shift from aragonite dominated to calcite dominated platform sedimentation because aragonite precipitation is a major sink for seawater sr it is speculated that a particularly low mg ca ratio and the corresponding low supersaturation of seawater with respect to aragonite during the middle cretaceous was a major cue for the radiation of calcite dominated rudist bivalves which became important carbonate producers on turonian maastrichtian carbonate platforms changing mg ca ratios of seawater are not considered to have caused middle cretaceous crises in the evolution of carbonate platforms but seawater composition could have selected for calcite dominated biota when carbonate production resumed

fault and basin depocentre migration over the last 2 ma in the l aquila 2009 earthquake region central italian apennines abstract morphological stratigraphical and structural investigations integrated with palaeomagnetic and tephrostratigraphic studies and 40 ar 39 ar measurements allowed us to define the quaternary tectonic sedimentary evolution of the epicentral area of the l aquila 2009 earthquake m w 6 3 this area roughly matches the paganica san demetrio castelnuovo psc intermountain basin filled by a fluvio lacustrine succession that is variously deformed by normal faults at its early stage early pleistocene ca 2 ma the basin hosted a lake that was characterised by whitish carbonate silt and mud deposition towards the end of the early pleistocene this was partly filled by a south eastward prograding deltaic system the south easternmost portion of the deltaic system was successively abandoned and eroded while sedimentation of a braided river system developed in a smaller area westwards before 780 ka this fluvio lacustrine system the lower psc syntheme ended and the area underwent erosional and pedogenic processes these processes continued up to 460 ka with the onset of fluvial gravel and volcanic rich silty sand deposition over a narrow area of the south western psc basin an earlier unit of the upper psc syntheme early middle pleistocene around 460 ka when most of this area was again subjected to denudational processes the sedimentation migrated into the previously exposed north western area of the psc basin where fluvial alluvial sediments were deposited between ca 460 ka and ca 350 ka a later unit of the upper psc syntheme between ca 350 ka and the present the sedimentation continued uninterrupted in a slight westwards restricted area of the psc basin upper late psc syntheme the significant contraction of the basin the shifting of its depocentre the variation in its geometry and in the spatial distributions and thicknesses of the units constituting the lower upper and late psc synthemes provide evidence for strong tectonic control this resulted in progressive reduction of the activity of the south easternmost tectonic structures and parallel migration of the fault activity on the westernmost structures in this perspective the fault system responsible for the l aquila 2009 earthquake can be seen as the most recent expression of a long lasting westwards polarised process of tectonic activity transfer

the importance of ice vertical resolution for snowball climate and deglaciation sea ice schemes with a few vertical levels are typically used to simulate the thermodynamic evolution of sea ice in global climate models here it is shown that these schemes overestimate the magnitude of the diurnal surface temperature cycle by a factor of 2 3 when they are used to simulate tropical ice in a snowball earth event this could strongly influence our understanding of snowball termination which occurs in global climate models when the midday surface temperature in the tropics reaches the melting point a hierarchy of models is used to show that accurate simulation of surface temperature variation on a given time scale requires that a sea ice model resolve the e folding depth to which a periodic signal on that time scale penetrates this is used to suggest modifications to the sea ice schemes used in global climate models that would allow more accurate simulation of snowball deglaciation

sea glacier flow and dust transport on snowball earth 1 accumulation of dust on the surface of ice in the tropics has been proposed as a possible mechanism for the termination of neoproterozoic snowball earth episodes this mudball hypothesis relies on the assumption that sea glacier flow transports dust to the tropical ablation zone leading to the accumulation of a dust moraine there and consequent lowering of tropical albedo here we use a 1 d sea glacier flow model to simulate the ice thickness and flow on a globally glaciated earth and study the dust transport associated with the ice flow dust is entirely confined to a meteoric ice layer which does not exchange water with the ocean dust falling onto the surface of this layer is carried downward with the ice flow in extratropical regions carried equatorward by the global ice flow and re emerges on the top of the ice in the tropical ablation zone the ice flow acts as a dust conveyor belt which converges dust to tropics resulting in an amplification of effective tropical dust flux by a factor of 2 to 20 over the global average this lends support to the mudball hypothesis

toward the snowball earth deglaciation the current state of knowledge suggests that the neoproterozoic snowball earth is far from deglaciation even at 0 2 bars of co2 since understanding the termination of the fully ice covered state is essential to sustain or not the snowball earth theory we used an atmospheric general climate model agcm to explore some key factors which could induce deglaciation after testing the models sensitivity to their parameterizations of clouds co2 and snow we investigated the warming effect caused by a dusty surface associated with ash release during a mega volcanic eruption we found that the snow aging process its dirtiness and the ash deposition on the snow free ice are key factors for deglaciation our modelling study suggests that under a co2 enriched atmosphere a dusty snowball earth could reach the deglaciation threshold

the jormungand global climate state and implications for neoproterozoic glaciations 1 geological and geochemical evidence can be interpreted as indicating strong hysteresis in global climate during the neoproterozoic glacial events 630 ma and 715 ma standard climate theory only allows such strong hysteresis if global climate enters a fully glaciated snowball state however the survival of photosynthetic eukaryotic marine species through these glaciations may indicate that there were large areas of open ocean a previously proposed slushball model for neoproterozoic glaciations could easily explain the survival of these organisms because it has open ocean throughout the tropics but there is only a small amount of hysteresis associated with the slushball state in this paper a new state of global climate the jormungand state is proposed in this state the ocean is very nearly globally ice covered but a very small strip of the tropical ocean remains ice free the low ice latitude of the jormungand state is a consequence of the low albedo of snow free bare sea ice if the ice latitude propagates into the subtropical desert zone it can stabilize without collapsing to the equator because subtropical ice covered regions have a relatively low top of atmosphere albedo as a result of the exposure of bare sea ice and relatively lower cloud cover moreover there is strong hysteresis associated with the jormungand state as greenhouse gas levels are varied because of the high albedo contrast between regions of bare and snow covered sea ice the jormungand state is illustrated here in two different atmospheric global climate models and in the budyko sellers model by offering a scenario that could explain both strong hysteresis in global climate and the survival of life the jormungand state represents a potential model for neoproterozoic glaciations although further study of this issue is needed

snowball earth ice thickness on the tropical ocean 1 on the tropical oceans of a neo proterozoic snowball earth snow free ice would have existed in regions of net sublimation photosynthesis could have continued beneath this bare ice if it was sufficiently thin and sufficiently clear the steady state ice thickness is determined by the necessity to balance the upward conduction of heat with three subsurface heating rates the heat flux from the ocean to the ice base the latent heat of freezing to the ice base and the solar energy absorbed within the ice a preliminary study using a broadband model for solar radiation and assuming a large freezing rate had indicated that tropical ice might be only a few meters thick here we show that the vertical throughput of ice by surface sublimation and basal freezing would be too slow to keep the ice thin and that the broadband model had exaggerated the absorption depth of sunlight we use a spectral model for solar absorption computing radiative transfer at 60 wavelengths considering absorption by the ice and scattering by bubbles with the spectral model the computed ice thickness is much greater for a solar flux of 320 w m 2 at the equatorial surface and expected albedo of 0 5 for bare sea ice we find that surface temperatures below 12 c generate ice layers too thick for photosynthesis 100 m if the albedo were as low as 0 4 thick ice would occur only for surface temperatures below 25 c but such low temperatures would be difficult to maintain with such low albedo for surface temperatures warmer than these limits the ice becomes thin 1 m and is unlikely to represent a coherent ice layer however glacial deformation of thick floating ice from nearby oceanic regions may preclude the existence of thin or ice free patches

effects of bubbles cracks and volcanic tephra on the spectral albedo of bare ice near the transantarctic mountains implications for sea glaciers on snowball earth 1 spectral albedo was measured along a 6 km transect near the allan hills in east antarctica the transect traversed the sequence from new snow through old snow firn and white ice to blue ice showing a systematic progression of decreasing albedo at all wavelengths as well as decreasing specific surface area ssa and increasing density broadband albedos under clear sky range from 0 80 for snow to 0 57 for blue ice and from 0 87 to 0 65 under cloud both air bubbles and cracks scatter sunlight their contributions to ssa were determined by microcomputed tomography on core samples of the ice although albedo is governed primarily by the ssa and secondarily by the shape of bubbles or snow grains albedo also correlates highly with porosity which as a proxy variable would be easier for ice sheet models to predict than bubble sizes albedo parameterizations are therefore developed as a function of density for three broad wavelength bands commonly used in general circulation models visible near infrared and total solar relevance to snowball earth events derives from the likelihood that sublimation of equatorward flowing sea glaciers during those events progressively exposed the same sequence of surface materials that we measured at allan hills with our short 6 km transect representing a transect across many degrees of latitude on the snowball ocean at the equator of snowball earth climate models predict thick ice or thin ice or open water depending largely on their albedo parameterizations our measured albedos appear to be within the range that favors ice hundreds of meters thick

salt precipitation in sea ice and its effect on albedo with application to snowball earth during the initial freezing of the tropical ocean on snowball earth the first ice to form would be sea ice which contains salt within inclusions of liquid brine at temperatures below 23 c significant amounts of the salt begin to crystallize with the most abundant salt being hydrohalite nacl 2h2o these crystals scatter light increasing the ice albedo in this paper we present field measurements of the albedo of cold sea ice and laboratory measurements of hydrohalite precipitation precipitation of salt within brine inclusions was observed on windswept bare ice of mcmurdo sound at the coast of antarctica 78 s in early austral spring salinity and temperature were measured in ice cores spectral albedo was measured on several occasions during september and october the albedo showed a gradual increase with decreasing temperature consistent with salt precipitation laboratory examination of thin sections from the ice cores showed that the precipitation process exhibits hysteresis with hydrohalite precipitating over a range of temperatures between 28 c and 35 c but dissolving at about 23 c the causes of the hysteresis were investigated in experiments on laboratory grown sea ice with different solute mixtures all mixtures showed hysteresis suggesting that it may be an inherent property of hydrohalite precipitation within brine inclusions rather than being due to biological macromolecules or interactions between various salts in seawater this article is protected by copyright all rights reserved

life geology and snowball earth according to the snowball earth hypothesis a series of global glaciations occurred 750 580 million years ago each lasting for millions of years and ending in a scorching heat caused by an extreme enrichment of atmospheric greenhouse gases hyde et al 1 have used climate models to simulate this global glaciation finding in one case an alternative climate scenario in which a partially frozen earth has ice free oceans equatorward of 25 latitude we do not believe that this slushball earth is consistent with the most striking geological and palaeomagnetic observations explained by the snowball earth hypothesis

rudist bivalves and the pacific in the late jurassic and early cretaceous although rudists of late jurassic to earliest cretaceous age are known from nova scotia to japan the oldest specimens recovered from pacific seamounts are barremian or possibly hauterivian the lack of evidence for disjunct endemism limited to either side of the ocean then precludes the inference that earlier rudists might have been present within it yet trans pacific range expansion of caribbean derived taxa by means of larval island hopping was accomplished by the early aptian following a mid aptian mass extinction the pacific then became an important nursery of rudist re diversification late aptian rudists in japan and derivative late aptian albian polyconitids in the japanese seamounts and cebu show affinities with those from the eastern himalayan sector of the northern tethyan margin by contrast the caprinid caprina mulleri in the mid pacific mountains is most closely allied with the c choffati c adversa lineage known from the atlantic mediterranean tethyan region however the pacific species could have been derived from an early aptian caribbean caprina that survived in some pacific refuge later reintroducing the genus to the tethyan region in the late albian colonization of pacific volcanic prominences ceased in the latest albian with the demise of carbonate platforms there and was not resumed until the campanian maastrichtian

refugium for surface life on snowball earth in a nearly enclosed sea a first simple model for sea glacier invasion 1 the existence of photosynthetic eukaryotic algae during the so called snowball earth events presents a conundrum if thick ice covered the oceans where could such life persist here we explore the possibility that photosynthetic life persisted at the end of long narrow seas analogous to the modern day red sea in this first analytical model we test the ability of the global sea glacier to penetrate a red sea analogue under climatic conditions appropriate during a snowball earth event we find the red sea is long enough to provide a refugium only if certain ranges of climatic conditions are met these ranges would likely expand if the restrictive effect of a narrow entrance strait is also considered

cold based mountain glaciers on mars western arsia mons surface environmental conditions on mars are currently extremely cold and hyperarid most equivalent to polar deserts on earth coupling newly acquired mars data with fieldbased observations regarding the flow surface morphology and depositional history of polar glaciers in antarctica we show that the multiple facies of an extensive fan shaped deposit on the western flanks of arsia mons volcano are consistent with deposition from cold based mountain glaciers an outer ridged facies that consists of multiple laterally extensive arcuate and parallel ridges resting without disturbance on both well preserved lava flows and an impact crater is interpreted as drop moraines formed at the margin of an ablating and predominantly receding cold based glacier a knobby facies that consists of equidimensional knobs each to several kilometers in diameter is inward of the ridges this facies is interpreted as a sublimation till derived from in situ downwasting of ashrich glacier ice a third facies comprising distinctive convex outward lobes with concentric parallel ridges and aspect ratios elongated downslope likely represents rock glacier deposits some of which may still be underlain by a core of glacier ice taken together these surficial deposits show that the western flank of arsia mons was occupied by an extensive mountain glacial system accumulating on and emerging from the upper slopes of the volcano and spreading downslope to form a piedmont like fan

changes in sedimentary patterns of coastal and deep sea successions from the north atlantic portugal linked to early cretaceous environmental change coastal mixed carbonate siliciclastic and carbonate deposits of late barremian to early aptian age from the lusitanian basin portugal are compared with a deep sea succession odp 641 off the coast of portugal the coastal deposits show an abrupt cessation of rudist dominated carbonate deposition marked by an emersion horizon and followed by the deposition of orbitolinid rich marls during the early aptian the subsequent development of the carbonate platform during the late aptian is masked by a hiatus for this time interval shallow water debris deposits of the deep sea succession odp 641 indicate that carbonate production in shallow water areas resume in the early late aptian carbon isotope stratigraphy in combination with available biostratigraphic data is used for intrabasinal correlation and for the correlation of the portuguese with shallow water successions from switzerland france oman and the pacific the correlation reveals that during the early aptian similar changes in their sedimentary patterns occur at the beginning of a marked negative shift of carbon isotope values associated with the global deposition of organic rich black shales in the deep sea oae 1a in all compared sections rudist dominated carbonate deposition is stopped and followed either by orbitolinid rich deposits the deposition of microbial carbonates or by the drowning of the carbonate platform the comparison shows that the deterioration for carbonate platform growth conditions during the early aptian occurred essentially simultaneously at the various localities during this episode the ocean waters were in a preconditioned state of acidification stressing biocalcifying organisms sea level change combined with local effects like elevated nutrient levels and higher temperatures were probably determining the nature of sedimentary change in shallow water environments during the carbonate crisis in the sections studied in portugal the high abundance of orbitolinids overlying rudist limestones indicates that increased nutrient input may have played an important local role among the factors that caused an overall deterioration for carbonate producers during the late early aptian

through thick and thin marine and meteoric ice in a snowball earth climate 1 marine ice cover in the frigid neoproterozoic climate system tends to isolate the ocean the thickness of this ice and thus the degree of isolation is an important unknown in geochemical and biological arguments regarding the fully glaciated snowball earth hypothesis the pollard and kasting 2005 coupled atmosphere ice model has been modified to track ice of marine and atmospheric origin separately and model their different optical properties in contrast to pollard and kasting s results a tropical region of thin ice is not stable in this model ice is hundreds of meters thick everywhere the overall pattern of the hydrological cycle in a snowball climate is also discussed

rudists and carbonate platforms in the aptian a case study on biotic interactions with ocean chemistry and climate variations in aptian carbonate platform growth and associated turnover among rudists are reviewed and the results synthesized with evidence for climate change to yield an explanatory model extensive platform growth throughout the atlantic tethys low palaeolatitude pacific seamount belt in the earliest aptian was accompanied by prolific rudist diversification especially among the predominantly aragonitic caprinids occupying platform margins it was ubiquitously interrupted in the mid early aptian in tandem with major perturbations of the global carbon cycle that culminated in oceanic anoxic event 1a although the causal linkages remain contentious platform growth terminated along most of the northern tethyan margin and maybe also in the new world meanwhile lithocodium bacinella or similar microbial encrustations became widespread in lower palaeolatitudes recovery of tethyan platforms in the late early aptian was limited to lower palaeolatitudes caprinid rich platform margin facies again prevailed in central and southern tethyan areas but gave way to those dominated by rudists with a thickened calcitic outer shell layer polyconitids and requieniids in marly successions around iberia the end of the early aptian saw the lazarus style disappearance of caprinids and renewed tethyan platform growth in the late aptian was dominated by calcite rich rudists although rudists remained scarce in the new world until the terminal aptian this study postulates that sea water acidification influenced both the mid early aptian platform debacle and the subsequent late early aptian geographical restriction of platform recovery although in contrasting atmospheric regimes at first it was forced by the increasing atmospheric levels of volcanically derived co2 with mitigation in low latitudes from thermal expulsion of aqueous co2 here termed the kettle effect due to greenhouse warming however subsequent cooling due to drawdown of atmospheric co2 by organic carbon burial could have sustained acidification of platform waters in higher latitudes by reducing the protective kettle effect there caprinid susceptibility to such assaults may have been as much due to exposure on their preferred outer platform habitats as to their mineralogy the increased calcite aragonite ratio among rudists through the aptian resulted largely from this taxonomic turnover

time contrasting palaeobiogeographies among hauterivian lower aptian rudist bivalves from the mediterranean tethys their climatic control and palaeoecological implications abstract from the mediterranean tethys the hauterivian barremian rudist genera lovetchenia agriopleura pachytraga and offneria simplex show contrasting palaeobiogeographies through time lovetchenia is a western european form in the hauterivian whereas it is an eastern european and apulian form in the late barremian and early aptian agriopleura is also a western european form in the late hauterivian and barremian p p whereas in the early aptian this genus is only found on the southern tethyan margin pachytraga documented from the hauterivian of both the european and southern tethyan margins disappeared during the barremian and re occupied western europe and some parts of africa during the early aptian offneria simplex a barremian form from the caribbean province is recorded in the uppermost lower barremian of se france the regional disappearance of these taxa is not linked to platform or rudist community demise whereas community changes reflect the resulting modifications in biodiversity there is a good correspondence between the regional disappearance of western european taxa cooling events documented by oxygen isotope studies and biological interchanges between the boreal and tethys realms the regional disappearance of lovetchenia and possibly pachytraga are coeval with the pseudothurmannia ohmi cooling episode whereas that of agriopleura is coeval with the ancyloceras vandenheckii cool episode by contrast the intrusion of offneria simplex in western europe coincides with the coronites darsi warm peak thermal shifts between cool and warm episodes fluctuate from 3 to 5 c and the thermal threshold assumed to control the demise of western european taxa is in the range of 18 to 20 c a value similar to those controlling the geographic distribution of modern coral reefs or the boundary between tropical and subtropical seas the southward displacement of the rudist biomes also accounts for the migration of climatic belts and a decreasing of 3 to 5 c in palaeotemperatures spatial contractions of lovetchenia and agriopleura biomes and the o simplex intrusion suggest that these rudists were more sensitive than others to the thermal regime this observation shows that rather than considering rudists in general as tropical some of them may have been both tropical and subtropical and others tropical for pachytraga other factors than temperature possibly oceanographic changes may have been responsible for the overall mediterranean disappearance of this genus in the barremian

comment on are proterozoic cap carbonates and isotopic excursions a record of gas hydrate destabilization following earth s coldest intervals kennedy et al geology 29 5 442 446

background seismicity in the central apennines of italy the abruzzo region case study abstract we investigate background seismic activity of the abruzzo region a 5000 km2 area located within the central apennines of italy where in the past 600 years at least 5 large earthquakes i xi x have occurred between april 2003 and september 2004 a dense temporary seismic network composed of 30 digital three component seismic stations recorded 850 earthquakes with 0 9 the seismicity occurs at a low and constant rate of 2 6 e 04 events day km2 and is sparsely distributed within the first 15 km of the crust minor increases in the seismicity rate are related to the occurrence of small and localised seismic sequences that occur at the tip of major active normal faults along secondary structures we observe that during the 16 months of study period the fucino fault system responsible for the 1915 fucino earthquake ms 7 0 and the major normal faults of the area did not produce significant seismic activity fault plane solutions evaluated using p wave polarity data show the predominance of normal faulting mechanisms 55 with ne trending direction of extension coherent with the regional stress field active in this sector of the apennines around 27 of the focal solutions have pure strike slip mechanisms and the rest shows transtensional faulting mechanisms that mainly characterise the kinematics of the secondary structures activated by the small sequences we hypothesize that the largest known nw trending normal faults are presently locked and we propose that in the case of activation the secondary structures located at their tips may act as transfer faults accommodating a minor part of the extensional deformation with strike slip motion

drowning events development and demise of carbonate platforms and controlling factors the late barremian early aptian record of southeast france abstract in provence and languedoc se france four drowning events were identified in platform carbonates of late barremian bedoulian age their timing referred to ammonite zones or subzones is as follows 1 late barremian d1 at the gerhardtia sartousiana imerites giraudi boundary 2 middle bedoulian d2 at the deshayesites weissi deshayesites deshayesi boundary 3 mid late bedoulian d3 in correspondence with the roloboceras hambrovi subzone and 4 late bedoulian d4 at the deshayesites grandis dufrenoya furcata transition notwithstanding their relatively wide regional lateral continuity the depositional hiatus linkage with exposure paleobathymetric range and offset and geographical extent of drowning discontinuities are not uniform the late barremian drowning d1 is marked either by the development of a permanent intra shelf basin with ammonites associated with the re organization of platform basin relationships or by the wide extent of palorbitolina heteraster facies which develops to the detriment of the antecedent rudist facies the drowning event is followed by platform recovery during the early bedoulian but the corresponding development of shallow water carbonates is subsequently interrupted by the emergence of an uplifted bulge trending sub parallel to the provence languedoc margin the middle bedoulian drowning d2 is concurrent with the sealing of the antecedent paleotopography and the wide development of palorbitolina facies then bioclastic and coral facies tend to recover the mid late bedoulian drowning d3 is characterized by an overall deepening phase with ammonite bearing marly facies or cherty limestones shallow bioclastics being locally present the late bedoulian drowning d4 records the deposition of deep water marls evidence is lacking that global sea level changes or transgressive regressive cycles had a significant impact on drowning events and some evidence that changes in temperature and productivity of the ocean may have contributed to these phenomena in conjunction with other factors though distension fault activity is regarded as a major controlling factor for the origin of the late barremian deepening event its associated paleogeographic re organization ensuing emergence of the provence languedoc marginal bulge and its subsequent detumescence coeval with the middle bedoulian drowning associated changes in facies types from rudist to palorbitolina reflect sea water deepening coupled with trophic modifications as agents of differential subsidence tectonic phenomena are also testified by the contrasting regional patterns of paleobathymetric offsets combined with drowning events they are a clue for understanding thickness changes and coeval modifications in the overall orientation of the progradational polarity of the platform system towards the adjacent basinal areas environmental changes essentially the two main oae1a subevents are regarded as significant agents of the mid late and late bedoulian drownings whereas tectonic processes are also involved in the corresponding deepening however the effects of the oae events on the functioning of the shallow carbonate factory are poorly understood and still need to be investigated the rise in atmospheric carbon dioxide pressure and as a consequence the reduction of the calcification potential of benthic organisms both reported in the literature are not clearly reflected in the composition of the biota aragonite dominated organisms such as caprinid rudists thrive throughout the bedoulian the role of acidification in platform demise is therefore questionable

deep structural heterogeneities and the tectonic evolution of the abruzzi region central apennines italy revealed by microseismicity seismic tomography and teleseismic receiver functions abstract the crustal structure of central apennines italy is still poorly defined leaving uncertainties on the tectonic style thin or thick skinned responsible for the development of the thrust and fold belt the today active extension which replaced compression since early quaternary is presumably influenced by the pre existing structure that yields location and segmentation of the fault system to focus on such issues we computed p and s wave velocity models of the crust by using the independent methodologies of local earthquakes tomography and teleseismic receiver function we document strong lateral and vertical heterogeneities that define shallow imbricate sheets of the mesozoic cover that overlay exceptionally high vp and high vs bodies these bodies can be interpreted as either dolomitic or partially hydrated mafic rocks the two alternative interpretations respectively imply an ultra thick deposition of dolomitic rocks in the hanging wall of triassic normal fault or a deep exhumation of the pre mesozoic basement during the early mesozoic sin rift tectonic in both cases these bodies influenced the evolution of the thrust and fold belt very remarkably active normal faults like those ruptured during the still ongoing 2009 l aquila sequence concentrate at the border of these bodies suggesting that they have an active role in the segmentation of the normal fault system the rheological behavior of such high vp high vs bodies weak or strong is still uncertain but of utmost importance to understand the risk of future normal faulting earthquakes

formation of segmented normal faults a 3 d perspective the interpretation of fault kinematics from geometric data is an essential step in developing an understanding of the growth of fault systems constraints on fault geometry are however often restricted to 2 d maps or cross sections in this article we consider the extent to which kinematic interpretations of faulting benefit from a 3 d rather than 2 d geometrical perspective concentrating on relay zones and segmented normal fault arrays we suggest that very different interpretations of their evolution arise from the recognition that the propagation directions of faults and fault segments will rarely be contained within the inspection plane of 2 d data a 3 d perspective favours an interpretation in which the segments of a fault array are kinematically interrelated from their initiation individual segments in such systems may link into a single fault surface out of the plane of inspection or may be unconnected in 3 d we argue that this interpretation which conflicts with the often suggested model of incidental overlap of originally isolated faults should be the preferred model for the generation and growth of segmented normal fault arrays

entrainment at cold glacier beds here we present measurements of the gas content and isotopic composition of debris rich basal layers of a polar glacier meserve glacier antarctica which has a basal temperature of 17 c these measurements show that debris entrainment has occurred without alteration of the glacial ice and provide the most direct evidence to date that active entrainment occurs at the beds of cold glaciers without bulk freezing of water entrainment at subfreezing temperatures may have formed the u shaped trough containing meserve glacier in addition to possibly allowing some cold based glaciers to be important geomorphic agents entrainment at subfreezing temperatures provides a general mechanism for formation of the dirty basal layers of polar glaciers and ice sheets which are rheologically distinct and can limit the time span of ice core analyses furthermore accumulating evidence suggests that geomorphologists should abandon the assumption that cold based glaciers do not slide and abrade their beds

radiography of a normal fault system by 64 000 high precision earthquake locations the 2009 l aquila central italy case study 1 we studied the anatomy of the fault system where the 2009 l aquila earthquake mw 6 1 nucleated by means of 64 k high precision earthquake locations spanning 1 year data were analyzed by combining an automatic picking procedure for p and s waves together with cross correlation and double difference location methods reaching a completeness magnitude for the catalogue equal to 0 7 including 425 clusters of similar earthquakes the fault system is composed by two major faults the high angle l aquila fault and the listric campotosto fault both located in the first 10 km of the upper crust we detect an extraordinary degree of detail in the anatomy of the single fault segments resembling the degree of complexity observed by field geologists on fault outcrops we observe multiple antithetic and synthetic fault segments tens of meters long in both the hanging wall and footwall along with bends and cross fault intersections along the main fault and fault splays the width of the l aquila fault zone varies along strike from 0 3 km where the fault exhibits the simplest geometry and experienced peaks in the slip distribution up to 1 5 km at the fault tips with an increase in the geometrical complexity these characteristics similar to damage zone properties of natural faults underline the key role of aftershocks in fault growth and co seismic rupture propagation processes additionally we interpret the persistent nucleation of similar events at the seismicity cutoff depth as the presence of a rheological i e creeping discontinuity explaining how normal faults detach at depth