oceanographic and eustatic control of carbonate platform evolution and sequence stratigraphy on the cretaceous valanginian campanian passive margin northern gulf of mexico an integrated sequence stratigraphic study based on outcrop core and wireline log data documents the combined impact of cretaceous eustacy and oceanic anoxic events on carbonate shelf morphology and facies distributions in the northern gulf of mexico the diverse facies and abundant data of the comanche platform serve as a nearly complete global reference section and provide a sensitive record of external processes affecting cretaceous platform development regional cross sections across the shoreline to shelf margin profile provide a detailed record of mixed carbonate siliciclastic strata for the hauterivian to lower campanian stages ca 136 to 80 ma the study window on the slowly subsiding passive margin allows the stratigraphic response to external forcing mechanisms to be isolated from regional structural processes three second order supersequences comprised of eight composite sequences are recognized in the valanginian barremian the aptian albian and the cenomanian campanian the valanginian barremian supersequence transitioned from a siliciclastic ramp to carbonate rimmed shelf and is a product of glacial ice accumulation and melting as well as variable rates of mid ocean ridge volcanism the aptian albian supersequence chronicles the drowning and recovery of the platform surrounding oceanic anoxic events 1a and 1b the cenomanian campanian supersequence similarly documents shelf drowning following oceanic anoxic event 1d after which the platform evolved to a deep subtidal system consisting of anoxic dysoxic shale and chalk in the time surrounding oceanic anoxic event 2 each period of oceanic anoxia is associated with composite sequence maximum flooding termination of carbonate shelf sedimentation and deposition of condensed shale units in distally steepened ramp profiles composite sequences unaffected by oceanic anoxic events consist of aggradational to progradational shelves with an abundance of grain dominated facies and shallow subtidal to intertidal environments because they are products of eustacy and global oceanographic processes the three supersequences and most composite sequences defined in the south texas passive margin are recognizable in other carbonate platforms and published eustatic sea level curves

structure and evolution of the intracratonic basins of central australia summary the central australian geology is dominated by a series of parallel sedimentary intracratonic basins whose history spans time from the late proterozoic to the carboniferous the basins are separated by regions of exposed proterozoic crust that have a history of significant uplift the formation of the basins cannot be explained by conventional thermal or stretching mechanisms nor does the foreland basin model provide an adequate explanation for their occurrence the geophysical observations particularly gravity point to a structure whereby the crust is considerably thicker under the basins than it is under the regions where basement rock is exposed this suggests that the crust as a whole is involved in the process that led to the basin formation a mechanical model is developed which is based on the supposition that the lithosphere has been in a state of horizontal compression for long time intervals the lithosphere is considered as a viscoelastic plate that has been subjected to a small normal load distributed in an irregular manner under compression initial deflections due to this load are magnified according to the plate s physical properties the magnitude of the compressive force and the wavelength spectrum of the initial perturbations because of the viscosity the deflections grow with time at a rate that is determined by the balance of forces acting on the plate and by the lithosphere s rheology both the elastic and viscous deformations are much enhanced if erosion of the uplifted areas occurs with the sediments deposited into the downwarps these deformations take place at stresses that are much less than the buckling stresses as bending stresses increase with time failure by thrust faulting is predicted to occur within the basins with the exposed basement being thrust over the basins the model has been applied to the central australian region starting at about 900myr ago the first basins to develop are the officer and amadeus basins with uplift occurring in the intervening musgrave block initial rates of uplift and basin subsidence are small but they can increase rapidly with time if the compressive force is main

high heat flux on ancient mars evidence from rift flank uplift at coracis fossae 1 we have identified flexural uplift at the flanks of the coracis fossae rift valley modeling the topography the elastic thickness is constrained to 10 3 12 5 km the corresponding mechanical thickness and thermal gradient are 15 19 km and 27 33 k km 1 respectively the time of rifting is dated by evaluating the crater size frequency distribution of key surface units related to the rifting thus the heat flux between 3 5 and 3 9 ga is calculated to be 54 66 mw m 2 furthermore the stresses supported by the rift bounding faults are estimated to be below 5 mpa we speculate that this weakness may be connected to the presence of water below the surface

the timing of martian valley network activity constraints from buffered crater counting abstract valley networks concentrations of dendritic channels that often suggest widespread pluvial and fluvial activity have been cited as indicators that the climate of mars differed significantly in the past from the present hyperarid cold desert conditions some researchers suggest that the change in climate was abrupt while others favor a much more gradual transition thus the precise timing of valley network formation is critical to understanding the climate history on mars we examine thirty valley network incised regions on mars including both cratered upland valley networks and those outside the uplands and apply a buffered crater counting technique to directly constrain when valley network formation occurred the crater populations that we derive using this approach allow assessment of the timing of the last activity in a valley network independent of the mapping of specific geological units from these measurements we find that valley networks cluster into two subdivisions in terms characteristics and age 1 valley network activity in the cratered highlands has an average cessation age at the noachian hesperian boundary and all valleys that we crater counted are early hesperian or older no evidence is found for valley networks in the cratered uplands of late hesperian or amazonian age the timing of the cessation of cratered upland valley network activity at the noachian hesperian boundary also corresponds to a decline in the intensity of large crater formation and degradation and to the apparent end of phyllosilicate type weathering 2 a few valley network incised regions formed outside of the cratered uplands on volcanic edifices in association with younger impact craters and on the rim of valles marineris we applied our buffered crater counting technique to four such valleys on the volcanoes ceraunius tholus hecates tholus and alba patera and on the rim of echus chasma and find that each has distinctive and different late hesperian or early amazonian ages indicating that valley networks formed from time to time in the post noachian period unlike the cratered upland valley networks these isolated occurrences are very local and have been interpreted to represent local conditions e g snowpack melted during periods of intrusive volcanic activity in contrast to a gradual cessation in the formation of valley networks proposed by some workers our new buffered crater counting results indicate a relatively abrupt cessation in the formation of the widespread cratered upland valley networks at approximately the end of the noachian followed only by episodic and very localized valley network formation in later mars history very likely due to specific conditions e g local magmatic heating these valley network ages and correlations are thus consistent with a major change in the near surface aqueous environment on mars at approximately the noachian hesperian boundary the noachian environment supported surface running water and fluvial erosion across mars in the cratered uplands enhanced crater degradation and a weathering environment favoring the formation of phyllosilicates the hesperian amazonian environment was more similar to the hyperarid cold desert of today with valley networks forming only extremely rarely and confined to localized special conditions sources of water for these latter occurrences are likely to be related to periodic mobilization and equatorward migration of polar volatiles due to variations in spin axis orbital parameters and to periodic catastrophic emergence of groundwater

the heat flow of europa the heat flow from europa has profound implications for ice shell thickness and structure as well as for the existence of an internal ocean which is strongly suggested by magnetic data the brittle ductile transition depth and the effective elastic thickness of the lithosphere are here used to perform heat flow estimations for europa results give preferred heat flow values for a typical geological strain rate of 10 15 s 1 of 70 110 mwm 2 for a brittle ductile transition 2 km deep the usually accepted upper limit for the brittle ductile transition depth in the ice shell of europa 24 35mwm 2 for an effective elastic thickness of 2 9 km supporting a plateau near the cilix impact crater and 130 mwm 2 for effective elastic thicknesses of 0 4 km proposed for the lithosphere loaded by ridges and domes these values are clearly higher than those produced by radiogenic heating thus implying an important role for tidal heating the 19 25 km thick ice shell proposed from the analysis of size and depth of impact structures suggests a heat flow of 30 45 mwm 2 reaching the ice shell base which in turn would imply an important contribution to the heat flow from tidal heating within the ice shell tidally heated convection in the ice shell ould be capable to supply 100 mwm 2 for superplastic flow and at the cilix crater region 35 50 mwm 2 for dislocation creep which suggests local variations in the dominant flow mechanism for convection the very high heat flows maybe related to ridges and domes could be originated by preferential heating at special settings

effects of dispersed particulates on the rheology of water ice at planetary conditions we have investigated the effects of initial grain size and hard particulate impurities on the transient and steady state flow of water ice i at laboratory conditions selected to provide more quantitative constraints on the thermomechanical evolution of the giant icy moons of the outer solar system our samples were molded with particulate volume fractions of 0 001 to 0 56 and particle sizes of 1 to 150 m deformation experiments were conducted at constant shortening rates of 4 4 10 7 to 4 9 10 4 s 1 at pressures of 50 and 100 mpa and temperatures 77 to 223 k for the pure ice samples initial grain sizes were 0 2 0 6 mm 0 75 1 75 mm and 1 25 2 5 mm stress strain curves of pure ice i under these conditions display a strength maximum u at plastic strains e 0 01 after initial yield followed by strain softening and achievement of steady state levels of stress ss at e 0 1 to 0 2 finer starting grain size in pure ice generally raises the level of u petrography indicates that the initial transient flow behavior is associated with the nucleation and growth of recrystallized ice grains and the approach to ss evidently corresponds to the development of a steady state grain texture effects of particulate concentrations 0 1 are slight at these concentrations a small but significant reduction in u with respect to that for pure water ice occurs mixed phase ice with 0 1 is significantly stronger than pure ice the strength of samples with 0 56 approaches that of dry confined sand the magnitude of the strengthening effect is far greater than expected from homogeneous strain rate enhancement in the ice fraction or from pinning of dislocations orowan hardening this result suggests viscous drag occurs in the ice as it flows around the hard particulates mixed phase ice is also tougher than pure ice extending the range of bulk plastic deformation versus faulting to lower temperatures and higher strain rates the high pressure phase ice ii formed in 0 56 mixed phase ice during deformation at high stresses bulk planetary compositions of ice rock 0 4 0 5 are roughly 2 orders of magnitude more viscous than pure ice promoting the likelihood of thermal instability inside giant icy moons and possibly explaining the retention of crater topography on icy planetary surfaces

dawn arrives at ceres exploration of a small volatile rich world on 6 march 2015 dawn arrived at ceres to find a dark desiccated surface punctuated by small bright areas parts of ceres surface are heavily cratered but the largest expected craters are absent ceres appears gravitationally relaxed at only the longest wavelengths implying a mechanically strong lithosphere with a weaker deep interior ceres dry exterior displays hydroxylated silicates including ammoniated clays of endogenous origin the possibility of abundant volatiles at depth is supported by geomorphologic features such as flat crater floors with pits lobate flows of materials and a singular mountain that appears to be an extrusive cryovolcanic dome on one occasion ceres temporarily interacted with the solar wind producing a bow shock accelerating electrons to energies of tens of kilovolts

the ac 5 fejokoo quadrangle of ceres geologic map and geomorphological evidence for ground ice mediated surface processes abstract nasa s dawn spacecraft arrived at ceres on march 6 2015 and has been studying the dwarf planet through a series of successively lower orbits throughout these mission phases dawn obtained photographic mineralogical elemental abundance and gravity data ceres is the largest object in the asteroid belt with a mean diameter of 940 km the dawn science team conducted a geologic mapping campaign for ceres similar to the one that was implemented on the asteroid vesta dawn s previous target including production of a survey and high altitude mapping orbit hamo based global map and a series of 15 low altitude mapping orbit lamo based quadrangle maps in this paper we present the lamo based geologic map of the ac 5 fejokoo quadrangle 21 66 n and 270 360 e and discuss its implications the ac 5 quadrangle is primarily composed of ancient cratered terrain punctuated with several moderately fresh impact craters of geologic interest six large tholi that are possibly cryovolcanic in origin and an abundance of flows that well represent the full spectrum of mass wasting features observed on ceres the fejokoo quadrangle hosts the majority of oxo crater the site of the first spectroscopic detection of h2o ice on the surface of ceres the h2o detection is closely related to two distinctive morphological units interpreted as possible high water ice content landslides these observations and interpretations are consistent with ground ice mediated surface processes on ceres

brittle failure mode plots for compressional and extensional tectonic regimes abstract equations governing different macroscopic modes of brittle rock failure extensional fracturing extensional shear fracturing compressional shear failure and reshear of existing faults can be represented on plots of differential stress vs effective vertical stress for a set of material properties such plots can be constructed for different tectonic regimes and correlated to depth for particular fluid pressure conditions allowing easy evaluation of the physical controls on brittle rock failure and ready comparison of the fields occupied by the three failure modes in different tectonic settings they emphasize the relative ease in terms of differential stress and fluid pressure levels of deforming a rock mass by brittle fracturing and faulting in extensional regimes compared with compressional aside from their relevance to general structural mechanics these generic failure plots have wide ranging application to understanding the initial development and progressive evolution of fault fracture systems both in sedimentary basins and as hosting structures for hydrothermal mineralization in different tectonic settings

detection and evaluation of hydrocarbons in source rocks by fluorescence microscopy abstract in pursuing the detection of hydrocarbons in sedimentary rocks by conventional petrological methods an attempt has been made to correlate standard fluorescence parameters with the quality and quantity of hydrocarbons present in crushed rocks embedded in epoxy resin the capacity of the embedding resin commonly used in the preparation of petrographic samples to extract and physically fix hydrocarbons is recognized this phenomenon permits one to measure monochromatic fluorescence parameters i 546 and q u v 650 500 on the trapped hydrocarbons and to correlate these parameters with selected geochemical data the potential application of using these petrological parameters to evaluate oil quantities and qualities is tested using real case studies it is also shown that it is possible to directly detect the mature zone in each case

fault controlled sequential vein dilation competition between slip and precipitation rates in the austin chalk texas abstract multi layered calcite veins in a dilatant jog of a left stepping left slipping shallowly buried fault segment are composed of alternating millimeter to submillimeter thick calcite veinlets and host lithons forming a coarse crack seal texture the grain fabrics in calcite veinlets are mostly equant or irregular suggesting face controlled grain growth in a fluid filled cavity the relatively thick veinlets can be developed by progressive fault slip and veinlet opening simultaneously with calcite precipitation under low effective stress continuous changes in the oxygen isotopic compositions of the calcite veinlets along the length of veins suggest that the individual calcite veinlets were sequentially developed from the footwall to the hanging wall there is no particular evidence that these veins represent excursions in fluid pressure or instantaneous fracture opening related to episodic fault slip the fracture formation and filling cycle could have taken place along a continuously slipping fault contained within a porous rock with normal fluid pressure

exposed h2o rich areas detected on ceres with the dawn visible and infrared mapping spectrometer abstract h2o rich materials are locally exposed at the surface of ceres as discovered from infrared reflectance spectra of the visible and infrared mapping spectrometer vir of the dawn mission nine locations on ceres exhibit diagnostic absorption bands of the h2o molecule at 2 00 1 65 and 1 28 m the detections are all consistent with h2o ice mixed with low albedo components all the reported h2o exposures occur at latitudes poleward of 30 in fresh craters near rim shadows have a surface area

viscous relaxation of ganymede s impact craters constraints on heat flux abstract measurement of crater depths in ganymede s dark terrain have revealed substantial numbers of unusually shallow craters indicative of viscous relaxation see companion paper singer k n schenk p m bland m t mckinnon w b 2017 relaxed impact craters on ganymede regional variations and high heat flow icarus submitted these viscously relaxed craters provide insight into the thermal history of the dark terrain the rate of relaxation depends on the size of the crater and the thermal structure of the lithosphere here we use finite element simulations of crater relaxation to constrain the heat flux within the dark terrain when relaxation occurred we show that the degree of viscous relaxation observed cannot be achieved through radiogenic heating alone even if all of the relaxed craters are ancient and experienced the high radiogenic fluxes present early in the satellite s history for craters with diameter 10 km heat fluxes of 40 50 mw m 2 can reproduce the observed crater depths but only if the fluxes are sustained for 1 gyr these craters can also be explained by shorter lived heat pulses with magnitudes of 100 mw m 2 and timescales of 10 100 myr at small crater diameters 4 km the observed shallow depths are difficult to achieve even when heat fluxes as high as 150 mw m 2 are sustained for 1 gyr the extreme thermal conditions required to viscously relax small craters may indicate that mechanisms other than viscous relaxation such as topographic degradation are also in play at small crater diameters the timing of the relaxation event s is poorly constrained due to the sparsity of adequate topographic information though it likely occurred in ganymede s middle history neither recently nor shortly after satellite formation the consistency between the timing and magnitude of the heat fluxes derived here and those inferred from other tectonic features suggests that a single event caused both ganymede s tectonic deformation and its crater relaxation future observations should permit more robust determination of the relative timing of the heating event that caused viscous relaxation

an analysis of cold season supercell storms using the synthetic dual doppler technique abstractcold season tornadic outbreaks occur with regularity in the southeastern united states however detailed analyses of parent supercell storms in the cold season environment often low cape high shear are scarce this is often because storms do not always move close enough to radars for a comprehensive single doppler analysis and significant topography or trees in the southeast make it difficult for mobile radars to operate thus limiting dual doppler coverage however during the super tuesday tornado outbreak of 5 6 february 2008 two tornadic supercell storms passed within 30 40 km of the weather surveillance radar 1988 doppler wsr 88d sites in memphis and nashville tennessee knqa and kohx respectively the relative steadiness of these storms during passage along with the large motion vector from the southwest at 20 25 m s 1 allowed the application of a synthetic dual doppler sdd analysis as such a detailed analysis of these storms was completed including examinations of low lev

furrow flexure and ancient heat flux on ganymede 0 5 km heat fluxes in the range 60 80 mw m 2 at the time of deformation and a brittle ductile transition depth of 2 3 km the elastic thicknesses are comparable to estimates for grooved terrain on ganymede and chaos regions on europa and may be characteristic of the point during cooling at which the available stresses can no longer cause significant ice shell deformation the furrowed dark terrain heat fluxes exceed likely chondritic values and are plausibly a result of early cooling of ganymede following accretion non synchronous rotation may have contributed to the 2 3 mpa stresses required to cause the observed deformation index terms 5418 planetology solid surface planets heat flow 5455 planetology solid surface planets origin and evolution 5475 planetology solid surface planets tectonics 8149 6218 planetology solar system objects jovian satellites 8149 tectonophysics planetary tectonics 5475 citation nimmo f and r t pappalardo 2004 furrow flexure and ancient heat flux on ganymede geophys res lett 31 l19701 doi 10 1029 2004gl020763

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

age determination of linear surface features using the buffered crater counting approach case studies of the sirenum and fortuna fossae graben systems on mars buffered crater counting bcc offers a possibility to determine ages of linear curvilinear surface features that provide no or only very limited surface areas for the conventional crater counting approach in this study we applied the bcc analysis to two tectonic fault systems fortuna fossae and a subsection of sirenum fossae we compared bcc results with age estimates derived from conventional crater counting on the surrounding geologic units and investigated to what extent crater ejecta blankets can be used for determining the stratigraphic placement of craters pre or post dating the formation of linear features furthermore we introduce a new functionality of the cratertools software for arcgis which allows for a user friendly semi automatic application of the otherwise time consuming procedure of bcc analysis the software provides the resulting crater size frequency data in a standard format which can be read and analyzed in the craterstats analysis software our case studies showed that the bcc approach provides equivalent or even more precise age results compared to the conventional stratigraphic approach here we found that the investigated section of sirenum fossae is younger than previously thought the derived formation age from the bcc analysis is 3 44 0 25 0 1ga which corresponds to late instead of early hesperian fortuna fossae formed shortly after the emplacement of its now fractured geologic host unit late hesperian ages derived from bcc analysis vary between 3 53 0 11 0 06ga and 3 50 0 11 0 07ga furthermore we recommend the use of crater ejecta blankets to position them in the stratigraphic sequence in order to improve crater statistics however the accuracy of the results depends on the extent and preservation state of the continuous ejecta blankets in the region of interest thus the applied buffer width has to be chosen carefully according to investigated crater sizes and local observations

flexural rigidity of the basin and range colorado plateau rocky mountain transition from coherence analysis of gravity and topography stochastic inversion for flexural loads and flexural rigidity of the continental elastic layer can be accomplished most effectively by using the coherence of gravity and topography however the spatial resolution of coherence analysis has been limited by use of two dimensional periodogram spectra from very large 105 km 2 windows that generally include multiple tectonic features using a two dimensional spectral estimator based on the maximum entropy method the spatial resolution of flexural properties can be enhanced by a factor of 4 or more enabling more detailed analysis at the scale of individual tectonic features this new approach is used to map the spatial variation of flexural rigidity along the basin and range transition to the colorado plateau and middle rocky mountains physiographic provinces large variations in flexural isostatic re sponse are found with rigidities ranging from as low as 8 7x102o n m elastic thickness t 4 6 km in the basin and range to as high as 4 1x1024 n m t 77 km in the middle rocky mountains these results compare favorably with independent determinations of flexural rigidity in the region areas of low flexural rigidity correlate strongly with areas of high surface heat flow as is expected from the contingence of flexural rigidity on a temperature dependent flow law also late cenozoic normal faults with large displacements are found primarily in areas of low flexural rigidity while deformation fronts of mesozoic tertiary overthrusts occur 0 to 100 km east of the low rigidity region the highest flexural rigidity is found within the archean wyoming craton where evidence suggests that deeply rooted cratonic lithosphere may play a role in deter mining the distribution of tectonism at the surface

airborne pseudo dual doppler analysis of a rear inflow jet and deep convergence zone within a supercell abstract on 22 may 1995 numerous thunderstorms several of which produced large hail and small tornadoes formed along a dryline in the central and northern texas panhandle the only long lasting daytime severe storms developed later south of the earlier storms by late afternoon new cells merged and evolved into two large supercells the northern supercell produced three weak tornadoes and hail the southern supercell did not produce a tornado but did produce very large hail for an extended period of time verification of the origins of rotation in tornadoes experiment crews collected data in the southern supercell from its early stage through much of its mature stage the national center for atmospheric research electra doppler radar collected pseudo dual doppler radar data on this storm continuously for well over an hour detailed analyses of this high resolution dataset revealed several unusual features most notably an intense elevated rear inflow jet at midlevels having maximum wind speeds app

friction of ice the frictional strength of ice seems to be well below that for all other rocks triaxial testing of cylinders of pure water ice containing a 45 inclined sawcut at temperatures of 77 t 115 k and confining pressures 0 1 p 250 mpa reveals the frictional laws 0 20 n 8 3 mpa for p 10 mpa and 0 55 n 1 0 mpa for p 5 mpa where and n are the shear and normal stresses on the sawcut surface friction is independent of t and over the one order of magnitude tested of average sliding velocity the sliding behavior is invariably stick slip examination of sliding surfaces shows only minor gouge development a curious arrangement of densely packed short vertical fractures occurs primarily in samples with anomalously low strength these results apply to models of near surface tectonic activity on jupiter s three large icy moons europa callisto and ganymede they indicate for example that a global expansion on ganymede of 3 linear percent will cause extensional movement on preexisting faults at depths to 7 3 km

effective elastic thickness and heat flux estimates on ganymede 1 we identify sites of apparent flexural uplift at rift zone boundaries on ganymede using galileo stereo derived topography the estimated effective elastic thickness te is 0 9 1 7 km for a nominal young s modulus of 1 gpa using a viscoelastic model of the ice crust we find that the temperature defining the base of the elastic layer is 185 k for likely strain rates the inferred local heat flux during deformation is less than 245 mw m 2 and probably close to 100 mw m 2 the stresses required to cause fault motion are around 1 mpa both the high heat flux and the high stresses are consistent with estimates of these quantities during an episode of transient tidal heating in ganymede s past

structural framework of the edwards aquifer recharge zone in south central texas the edwards aquifer the major source of water for many communities in central texas is threatened by population growth and development over its recharge zone the location of the recharge and confined zones and the flow paths of the aquifer are controlled by the structure of and deformation processes within the balcones fault system a major system of predominantly down to the southeast normal faults we investigate the geologic structure of the edwards aquifer to assess the large scale aquifer architecture analyze fault offset and stratigraphic juxtaposition relationships evaluate fault zone deformation and dissolution and fault system architecture and investigate fault block deformation and scaling of small scale intrablock normal faults characterization of fault displacement shows a pattern of aquifer thinning that is likely to influence fault block communication and flow paths flow path constriction may be exacerbated by increased fault segment connectivity associated with large fault displacements also increased fault zone deformation associated with larger displacement faults is likely to further influence hydrologic properties overall faulting is expected to produce strong permeability anisotropy such that maximum permeability is subhorizontal and parallel to fault bedding intersections at all scales aquifer permeability is either unchanged or enhanced parallel to faults and in many cases decreased perpendicular to faults

influence of p t conditions on the style of normal fault initiation and growth in limestones from the se basin france abstract a conventional and cathodoluminescence microscopy stable isotope and fluid inclusion study was undertaken on normal fault zones exposed on vertical cliffs in tithonian limestones of the french se basin the aim was to determine the chronology of deformation and factors controlling normal fault nucleation and evolution in carbonate rocks two models are proposed for fault zone development depending on the depths at which deformation takes place at depths of 3 3 5 km incipient shear zones consist of en echelon veins filled by fibrous calcite and confined to limestone layers bounded by thin clayey interlayers as deformation increases and the layers rotate slip occurs along the clay rich interlayers a system of pull aparts forms allowing displacement to increase pull aparts are commonly filled by fibrous calcite crystals at depths of 1 5 2 km faults initiate as small slip surfaces early nucleating in some limestone layers their propagation is impeded by thin clayey interlayers which enhances fracturing and bending of the limestone layers as slip surfaces propagate they overlap and can connect with one another by means of dilational jogs that are filled by large euhedral calcite crystals in the first case pull aparts are coupled with the solution seams that reuse preexisting rotated clay rich interlayers as they formed they progressively filled and the fluid circulation remained local in the second case longer slip planes connect by dilation jogs that are not immediately filled which enhance the circulation of fluids which show chemical variations it appears that p t conditions strongly control the relative role of brittle processes and solution crystallization mechanisms and the style of the early stages of normal faulting in the same limestone rocks

analysis of pinnate joints in the mount desert island granite implications for postintrusion kinematics in the coastal volcanic belt maine the mount desert island granite is cut by fractures displaying one of four types of surface morphology 1 smooth to undulatory 2 stepped in the form of en echelon cracks 3 striated with linear fibers and 4 irregular with cataclastic grains these surfaces belong to joints host fractures with pinnate joints reactivated joints or fractures and deformation bands shear fractures respectively pinnate joints like striations on slickensides are structures indicative of the orientation of a the slip vector and sense of shear on host fractures although fractures in the mount desert island granite cluster into two major sets n20 degree w and n45 degree e host fractures with pinnate joints and shear fractures favor the n45 degree e orientation a kinematic analysis of the pinnate joints indicates a predominantly dextral strike slip sense of movement on northeast trending fractures this result agrees with previous work suggesting that a prominent postintrusion tectonic event in southeast maine consisted of dextral strike slip motion on northeast trending faults

dating the cooling of exhumed central uplifts of impact structures by the u th he method a case study at manicouagan abstract forty titanite grain fragments from 9 central uplift samples of metamorphosed anorthosite from the manicouagan impact structure were dated by the u th he technique a u th he central age of 207 1 6 4 ma 2 standard error se n 40 has been determined with 4 outlier ages removed the central age is refined to 208 9 5 1 ma 2 se both of these ages are within error of the previously determined u pb zircon age of 214 1 ma 2 derived from the impact melt manicouagan s central uplift formed due to rapid elevation from 7 10 km depth as part of the modification stage of the impact process which has facilitated the dating of its emplacement due to resulting rapid exhumation and cooling and closure of the u th he system in titanite correlation with the previous u pb zircon 214 1 ma impact melt crystallization age indicates that the u th he titanite dating technique offers a new approach to dating complex impact structures in the absence of viable melt sheets or other melt products the youngest ca 195 ma u th he dates preserved in some titanite fragments are synchronous with early jurassic rift induced lithospheric thinning and associated igneous activity that defines the central atlantic magmatic province camp the u th he titanite data from manicouagan indicate that the influence of this regional event may extend west of the previously proposed limit of camp activity

flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension we suggest that the uplift of rift flanks results from mechanical unloading of the lithosphere during extension and consequent isostatic rebound this mechanism is presented as an alternative to explanations for rift flank uplift involving thermal or dynamic processes and magmatic thickening of the crust our hypothesis is based on two critical concepts first the lithosphere retains finite mechanical strength or flexural rigidity during extension second isostatic rebound uplift of the lithosphere follows when the kinematics of extension produces a surface topographic depression that is deeper than the level to which the surface of the extended lithosphere would subside assuming local isostatic compensation we develop and analyze two kinematic models for instantaneous extension of the lithosphere to show that flexural rebound is a viable explanation for the uplift of rift flanks we first investigate the isostatic consequences of finite simple slip on an initially planar dipping normal fault cutting the entire lithosphere when the lithosphere retains flexural rigidity during extension the topography resulting from this model resembles a half graben and the footwall rift flank is flexurally uplifted this simple normal faulting model explains free air gravity anomalies and topography observed at rift flanks in oceanic lithosphere such as broken ridge in the eastern indian ocean the caroline ridges sorol trough in the western equatorial pacific and the coriolis trough behind the new hebrides island arc we then investigate a general kinematic model for lithospheric extension where simple slip on a surface of arbitrary shape is accompanied by pure shear extension in the upper and lower plates when the simple slip component is not zero or the distribution of pure shear in the upper and lower plates is not identical the surface of slip can be regarded as a detachment by simplification our general model accounts for pure shear extension of the lithosphere that is uniform with depth in this case detachments have no meaning in the geologic sense however the kinematics of depth independent pure shear may nevertheless be described in terms of a surface which we term a kinematic reference surface at some depth in the lithosphere we speculate that the depth of this surface may be rheologically controlled the magnitude of rift flank uplift by flexure depends critically on the depth of this reference surface in contrast if local isostasy is assumed when the lithosphere undergoes a given amount of depth independent pure shear the resulting topography will be the same regardless of how the kinematics of that extension are formulated the basin and rift flank topography and free air gravity anomaly over young continental rifts such as the rhine graben can be satisfied using our general extensional model with a small amount 5 km of extension along a listric shaped detachment soling into the crust mantle boundary because the flexural rebound mechanism explains the observed topography and gravity anomaly over both oceanic and continental extensional domains we suggest that rheological differences between the two lithospheric types may not be important in their overall response to extension

numerical simulation of tornadogenesis in a high precipitation supercell part i storm evolution and transition into a bow echo abstract a nested grid primitive equation model rams version 3b was used to simulate a high precipitation hp supercell which produced two weak tornadoes six telescoping nested grids allowed atmospheric flows ranging from the synoptic scale down to the tornadic scale to be represented in the simulation all convection in the simulation was initiated with resolved vertical motion and subsequent condensation latent heating from the model microphysics no warm bubbles or cumulus parameterizations were used part i of this study focuses on the simulated storm evolution and its transition into a bow echo the simulation initially produced a classic supercell that developed at the intersection between a stationary front and an outflow boundary as the simulation progressed additional storms developed and interacted with the main storm to produce a single supercell this storm had many characteristics of an hp supercell and eventually evolved into a bow echo with a rotating comma head structure an analysi

the geomorphology of ceres introduction observations of ceres the largest object in the asteroid belt have suggested that the dwarf planet is a geologically differentiated body with a silicate core and an ice rich mantle data acquired by the dawn spacecraft were used to perform a three dimensional characterization of the surface to determine if the geomorphology of ceres is consistent with the models of an icy interior rationale instruments on dawn have collected data at a variety of resolutions including both clear filter and color images digital terrain models have been derived from stereo images a preliminary 1 10 m scale geologic map of ceres was constructed using images obtained during the approach and survey orbital phases of the mission we used the map along with higher resolution imagery to assess the geology of ceres at the global scale to identify geomorphic and structural features and to determine the geologic processes that have affected ceres globally results impact craters are the most prevalent geomorphic feature on ceres and several of the craters have fractured floors geomorphic analysis of the fracture patterns shows that they are similar to lunar floor fractured craters ffcs and an analysis of the depth to diameter ratios shows that they are anomalously shallow compared with average ceres craters both of these factors are consistent with ffc floors being uplifted due to an intrusion of cryomagma kilometer scale linear structures cross much of ceres some of these structures are oriented radially to large craters and most likely formed due to impact processes however a set of linear structures present only on a topographically high region do not have any obvious relationship to impact craters geomorphic analysis suggests that they represent subsurface faults and might have formed due to crustal uplift by cryomagmatic intrusion domes identified across the ceres surface present a wide range of sizes 100 km basal shapes and profiles whether a single formation mechanism is responsible for their formation is still an open question cryovolcanic extrusion is one plausible process for the larger domes although most small mounds 10 km diameter are more likely to be impact debris differences in lobate flow morphology suggest that multiple emplacement processes have operated on ceres where three types of flows have been identified type 1 flows are morphologically similar to ice cored flows on earth and mars type 2 flows are comparable to long runout landslides type 3 flows morphologically resemble the fluidized ejecta blankets of rampart craters which are hypothesized to form by impact into ice rich ground conclusion the global trend of lobate flows suggests that differences in their geomorphology could be explained by variations in ice content and temperature at the near surface geomorphic and topographic analyses of the ffcs suggest that cryomagmatism is active on ceres whereas the large domes are possibly formed by extrusions of cryolava although spectroscopic analysis to date has identified water ice in only one location on ceres the identification of these potentially ice related features suggests that there may be more ice within localized regions of ceres crust figure 1 dawn high altitude mapping orbit imagery 140 meters per pixel of example morphologic features a occator crater arrows point to floor fractures b linear structures denoted by arrows c a large dome at 42 n 10 e visible in the elevation map d a small mound at 45 5 s 295 7 e e type 1 lobate flow arrows point to the flow front analysis of dawn spacecraft framing camera image data allows evaluation of the topography and geomorphology of features on the surface of ceres the dwarf planet is dominated by numerous craters but other features are also common linear structures include both those associated with impact craters and those that do not appear to have any correlation to an impact event abundant lobate flows are identified and numerous domical features are found at a range of scales features suggestive of near surface ice cryomagmatism and cryovolcanism have been identified although spectroscopic analysis has currently detected surface water ice at only one location on ceres the identification of these potentially ice related features suggests that there may be at least some ice in localized regions in the crust 1 pending yes

fault and joint measurements in austin chalk superconducting super collider site texas abstract structure maps of 9 4 mi of nearly continuous tunnel excavations and more than 10 mi of other exposures and excavations in austin chalk at the superconducting super collider ssc site in ellis county texas record normal fault and joint populations in the subsurface within the northern segment of the balcones fault zone with unmatched resolution for such a long traverse small faults 10 ft throw occur in clusters or swarms that have as many as 24 faults fault swarms are as much as 2 000 ft wide and spacing between swarms ranges from 800 to 2 000 ft averaging about 1 000 ft predominantly northeast trending joints are in swarms spaced 500 to more than 21 000 ft apart

the hybrid multicellular supercellular storm an efficient hail producer part i an archetypal example abstract this is the first of a two part series describing storms termed hybrid because their characteristics are intermediate between those classically defined as multicellular and supercellular they are important because they tend to produce more hail and in fact often produce the most severe hailfalls in the central oklahoma area part i discusses the structure and hail growth characteristics of an archetypal example as derived from doppler radar and surface hail collections the storm produced maximum diameter hail of 75 mm and a hailswath that was about 300 km long and at one point 40 km wide although the storm had the large bounded weak echo region and generally steady appearance associated with supercellular storms the data suggest that at any time there were three updrafts separated by a distance of 5 to 8 km another distinctive flow feature is an intense downdraft in an area of weak reflectivity to the west of the updraft hailstone embryos collected over a distance of 100 km and 1 5 h

dynamic depositional and early diagenetic processes in a deep water shelf setting upper cretaceous austin chalk north texas abstract the austin chalk of north texas was deposited on a deep water shelf north of the san marcos platform during a worldwide coniacian and santonian sea level highstand transgressive lowermost lower austin chalk highstand uppermost lower austin chalk and regressive middle and upper austin chalk phases of cyclic chalk and marl sedimentation are recognized in core and outcrop and on log cross sections sedimentary structures in excellent exposures in excavations and tunnels created in ellis county for the superconducting super collider provide new evidence of sediment transport during austin chalk deposition during transgression bottom currents syndepositionally reworked nannoplankton oozes incising channels as much as 120 ft across and 8 ft deep weakly burrowed channel fills having preservation of fine lamination document rapid infilling channel fills are composed of pyritized and carbonized wood and inoceramus lag deposits pellets echinoderm fragments and globigerinid grainstones and coccolith ooze during maximum highstand bottom reworking was suppressed detrital content of highstand marls is low 20 percent organic content is high 1 4 to 3 5 percent coccolith preservation is excellent because of minimal diagenetic alteration regression is marked by resumed channel cutting and storm bed winnowing in the middle and upper austin chalk suppressed resistivity log response and recessive weathering characteristics of the middle austin chalk are not primarily related to depositional environment but rather to increased input of volcanic ash during the accumulation of this interval early stabilization of ash produced clay coated microfabrics in sediments that are otherwise similar to the transgressive deposits

the schmidt hammer in rock material characterization the schmidt hammer provides a quick and inexpensive measure of surface hardness that is widely used for estimating the mechanical properties of rock material however a number of issues such as hammer type normalization of rebound values specimen dimensions surface smoothness weathering and moisture content and testing data reduction and analysis procedures continue to influence the consistency and reliability of the schmidt hammer test results this paper presents a a critical review of these basic issues and b the results of tests conducted on granitic rocks of various weathering grades in the light of the conclusions of this review it was found that a very good correlation exists between l and n hammer rebound values and that both hammers are fairly sensitive to the physical properties particularly to dry density though less so to effective and total porosities the n hammer producing a lesser scatter in the data proved to be more efficient than the l hammer in predicting uniaxial compressive strength and young s modulus the exponential form of the correlation curves was found to reflect microstructural changes during the course of weathering and the differences in the probing scales or mechanisms in the means of measuring these mechanical properties and could be generalized to other crystalline igneous rocks the possibility of predicting weathering grades from rebound values was also explored the changes in the rebound values during multiple impacts at a given point produced a better indication of the weathering grade than a single impact value it was concluded that increasing the impact energy and plunger tip diameter should significantly reduce the scatter in coarse grained weathered rocks and hence improve the reliability of the schmidt hammer as a rock material characterization tool

changes in structural style of normal faults due to failure mode transition first results from excavated scale models abstract the effects of failure mode transition from tensile to shear on structural style and fault zone architecture have long been recognized but are not well studied in 3d although the two modes are both common in the upper crust of earth and terrestrial planets and are associated with large differences in transport properties we present a simple method to study this in physical scale models of normal faults using a cohesive powder embedded in cohesionless sand by varying the overburden thickness the failure mode changes from tensile to hybrid and finally to shear hardening and excavating the cohesive layer allows post mortem investigation of 3d structures at high resolution we recognize two end member structural domains that differ strongly in their attributes in the tensile domain faults are strongly dilatant with steep open fissures and sharp changes in strike at segment boundaries and branch points in the shear domain fault dips are shallower and fault planes develop striations map view fault traces undulate with smaller changes in strike at branches these attributes may be recognized in subsurface fault maps and could provide a way to better predict fault zone structure in the subsurface

hybrid fracture and the transition from extension fracture to shear fracture fracture is a fundamental mechanism of material failure two basic types of brittle fractures are commonly observed in rock deformation experiments extension opening mode fractures and shear fractures for nearly half a century it has been hypothesized that extension and shear fractures represent end members of a continuous spectrum of brittle fracture types however observations of transitional fractures that display both opening and shear modes hybrids in naturally deformed rock have often remained ambiguous and a clear demonstration of hybrid fracture formation has not been provided by experiments here we present the results of triaxial extension experiments on carrara marble that show a continuous transition from extension fracture to shear fracture with an increase in compressive stress hybrid fractures form under mixed tensile and compressive stress states at acute angles to the maximum principal compressive stress fracture angles are greater than those observed for extension fractures and less than those observed for shear fractures fracture surfaces also display a progressive change from an extension to shear fracture morphology

tethys lithospheric thickness and heat flux from flexurally supported topography at ithaca chasma 16 20 km surface heat fluxes are 18 30 mw m 2 for adopted strain rates of 10 17 10 14 s 1 these heat fluxes are more than 4 times higher than those calculated from thermal history models of tethys and indicate a strongly enhanced local heat flux associated with the formation of ithaca chasma we use crater size frequency counts and a lunar like impact chronology to fix the time of formation of ithaca chasma at 4 ga from present day ithaca chasma predates the odysseus basin and thus could not have been formed by this impact feature citation giese b r wagner g neukum p helfenstein and p c thomas 2007 tethys lithospheric thickness and heat flux from flexurally supported topography at ithaca chasma geophys res lett 34 l21203

pitted terrains on 1 ceres and implications for shallow subsurface volatile distribution prior to the arrival of the dawn spacecraft at ceres the dwarf planet was anticipated to be ice rich searches for morphological features related to ice have been ongoing during dawn s mission at ceres here we report the identification of pitted terrains associated with fresh cerean impact craters the cerean pitted terrains exhibit strong morphological similarities to pitted materials previously identified on mars where ice is implicated in pit development and vesta where the presence of ice is debated we employ numerical models to investigate the formation of pitted materials on ceres and discuss the relative importance of water ice and other volatiles in pit development there we conclude that water ice likely plays an important role in pit development on ceres similar pitted terrains may be common in the asteroid belt and may be of interest to future missions motivated by both astrobiology and in situ resource utilization

the cenomanian turonian eagle ford group of south texas insights on timing and paleoceanographic conditions from geochemistry and micropaleontologic analyses abstract the interbedded organic rich marls and limestones of the eagle ford group of south texas were deposited on the shelf of the central texas platform during the upper cenomanian through the turonian micropaleontological analyses of thin sections and residue samples from subsurface cores taken in atascosa and karnes counties yielded 13 biostratigraphic datums which were integrated with calcareous nannofossil datums stable carbon isotopic and bulk inorganic geochemical analysis to gain an understanding of the paleoceanographic conditions of the study area and their relationship to regional and global events the paired thin section residue sampling was necessitated by poor recovery of planktonic foraminifera in washed samples which were however abundant in most thin sections lower eagle ford marls were deposited under euxinic conditions produced by a stratified water column periodic enhanced water column mixing increased oxygen levels and surface water primary productivity which promoted calcite diagenesis and generation of limestones containing calcispheres and radiolaria an oxygenated bottom water mass entered the basin in the uppermost cenomanian prior to the onset of oceanic anoxic event oae 2 causing a spike in benthic foraminiferal diversity and decreasing preservation of organic matter although the lower portion of the upper eagle ford is age equivalent to oae2 as indicated by positive shift in 13corg it contains less organic matter and evidence of more oxygen than the lower eagle ford so deposition of the eagle ford black shales is not contemporaneous to oae2

fluids in metamorphic rocks abstract basic principles for the study of fluid inclusions in metamorphic rocks are reviewed and illustrated a major problem relates to the number of inclusions possibly formed on a wide range of p t conditions having also suffered in most cases extensive changes after initial trapping the interpretation of fluid inclusion data can only be done by comparison with independent p t estimates derived from coexisting minerals but this requires a precise knowledge of the chronology of inclusion formation in respect to their mineral host the three essential steps in any fluid inclusion investigation are described observation measurements and interpretation observation with a conventional petrographic microscope leads to the identification and relative chronology of a limited number of fluid types same overall composition eventually changes in fluid density for the chronology the notion of gis group of synchronous inclusions is introduced it should serve as a systematic basis for the rest of the study microthermometry measurements completed by nondestructive analyses mostly micro raman specify the composition and density of the different fluid types the major problem of density variability can be significantly reduced by simple considerations of the shape of density histograms allowing elimination of a great number of inclusions having suffered late perturbations finally the interpretation is based on the comparison between few isochores representative of the whole inclusion population and p t mineral data essential is a clear perception of the relative chronology between the different isochores when this is possible as illustrated by the complicated case of the granulites from central kola peninsula a good interpretation of the fluid inclusion data can be done if not fluid inclusions will not tell much about the metamorphic evolution of the rocks in which they occur

origin of limestone marlstone cycles astronomic forcing of organic rich sedimentary rocks from the cenomanian to early coniacian of the cretaceous western interior seaway usa abstract we present an integrated multidisciplinary study of limestone marlstone couplets from a continuously cored section including parts of the upper buda limestone the entire eagle ford group boquillas formation and lower austin chalk from the shell iona 1 research borehole texas usa which provides a 8 million year myr distal clastic sediment starved intrashelf basin record of the early cenomanian to the earliest coniacian stages results show that despite variable yet minimal diagenetic overprints several unambiguous primary environmental signals are preserved and support greater water mass ventilation and current activity promoting increased silica carbonate productivity during the deposition of limestone beds compared to deposition of marlstone beds which reflect greater organic matter productivity and preservation furthermore our astronomical analyses demonstrate that the limestone marlstone couplets in the iona 1 core reflect climatic forcing driven by solar insolation resulting from integrated milankovitch periodicities in particular we propose that obliquity and precession forcing on the latitudinal distribution of solar insolation may have been responsible for the observed lithological and environmental variations through the cenomanian turonian and coniacian in this mid latitude epicontinental sea setting our data also suggests that rhythmic lithological alternations deposited in greenhouse periods in general may simply reflect climate driven cycles related to earth sun dynamics without the need to invoke significant sea level variations

thermal stability of ice on ceres with rough topography the dwarf planet ceres may have an ice rich crust and subsurface ice exposed by impacts or endogenic activity would be subject to sublimation we model surface and subsurface temperatures on ceres to assess lifetimes of water ice and other volatiles topographic shadowing allows a small but non negligible fraction 0 4 of ceres surface to be perennially below the 110 k criterion for 1 gyr of stability these areas are found above 60 latitude other molecules ch3oh nh3 so2 co2 may be cold trapped in smaller abundances a model for the transport gravitational escape and photoionization of h2o molecules suggests net accumulation in the cold traps buried ice is stable within a meter for 1 gyr at latitudes higher than 50 an illuminated polar cap of water ice would be stable within a few degrees of the poles only if it maintained a high albedo 0 5 at present obliquity if the obliquity exceeded 5 in the geologically recent past then a putative polar cap would have been erased at latitudes 0 30 ice is stable under solar illumination only briefly 10 100 yr unless it has high albedo and thermal inertia in which case lifetimes of 104 yr are possible finally a small hemispheric asymmetry exists due to the timing of ceres perihelion passage which would lead to a detectable enhancement of ice in the northern hemisphere if the orbital elements vary slowly relative to the ice accumulation rate our model results are potentially testable during the dawn science mission

cratering on ceres implications for its crust and evolution introduction thermochemical models have predicted that the dwarf planet ceres has to some extent formed a mantle moreover due to viscous relaxation these models indicate that ceres should have an icy crust with few or no impact craters however the dawn spacecraft has shown that ceres has elevation excursions of 15 km cliffs graben steep sided mountains and a heavily cratered surface rationale we used dawn s framing camera to study the morphology size frequency and spatial distribution of the craters on ceres these data allow us to infer the structure and evolution of ceres outer shell results a large variety of crater morphologies are present on ceres including bowl shaped craters polygonal craters floor fractured craters terraces central peaks smooth floors flowlike features bright spots secondary craters and crater chains the morphology of some impact craters is consistent with water ice in the subsurface although this might have favored relaxation there are also large unrelaxed craters the transition from bowl shaped simple craters to modified complex craters occurs at diameters of about 7 5 to 12 km craters larger than 300 km are absent but low pass filtering of the digital elevation model suggests the existence of two quasi circular depressions with diameters of 570 km 125 56 e and 19 60 n and 830 km 24 76 w and 0 5 n craters are heterogeneously distributed across ceres surface with more craters in the northern versus the southern hemisphere the lowest crater densities are associated with large well preserved southern hemisphere impact craters such as urvara and yalode because the low crater density lcd terrain extends across a large latitude range in some cases e g urvara and yalode 18 n and 75 s kerwan 30 n and 46 s its spatial distribution is inconsistent with simple relaxation driven by warmer equatorial temperatures we instead propose that impact driven resurfacing is the more likely lcd formation process although we cannot completely rule out an internal endogenic origin we applied two different methodologies to derive absolute model ages from observed crater size frequency distributions the lunar derived model adapts the lunar production and chronology functions to impact conditions on ceres taking into account impact velocities projectile densities current collision probabilities and surface gravity the asteroid derived model derives a production function by scaling the directly observed object size frequency distribution from the main asteroid belt extended to sizes 5 km by a collisional model to the resulting size frequency distribution of cerean craters using similar cerean target parameters as the lunar derived model by dating a smooth region associated with the kerwan crater we determined absolute model ages of 550 million and 720 million years depending on which chronology model is applied conclusion crater morphology and the simple to complex crater transition indicate that ceres outer shell is likely neither pure ice nor pure rock but an ice rock mixture that allows for limited relaxation the heterogeneous crater distribution across the surface indicates crustal heterogeneities and a complex geologic evolution of ceres there is evidence for at least some geologic activity occurring in ceres recent history figure 1 spatial density of craters larger than 20 km on ceres crater rims are shown as black solid circles blue indicates areas with lcds yellow and red represent more highly cratered areas the smallest dashed ellipse denotes the idealized former rim of an extremely degraded impact crater at 48 9 e and 44 9 s which is barely recognizable in imagery but apparent from the global digital elevation model also shown as dashed circles are the outlines of two large putative basins unambiguously recognized basins 300 km in diameter are missing and there are several areas with lcds associated with large impact craters e g yalode urvara kerwan ezinu vinotonus dantu and two unnamed craters northeast and southeast of oxo areas a and b are topographic rises with central depressions that also show lcds thermochemical models have predicted that ceres is to some extent differentiated and should have an icy crust with few or no impact craters we present observations by the dawn spacecraft that reveal a heavily cratered surface a heterogeneous crater distribution and an apparent absence of large craters the morphology of some impact craters is consistent with ice in the subsurface which might have favored relaxation yet large unrelaxed craters are also present numerous craters exhibit polygonal shapes terraces flowlike features slumping smooth deposits and bright spots crater morphology and simple to complex crater transition diameters indicate that the crust of ceres is neither purely icy nor rocky by dating a smooth region associated with the kerwan crater we determined absolute model ages amas of 550 million and 720 million years depending on the applied chronology model 1 pending yes

hybrid failure field evidence and influence on fault refraction abstract the occurrence of hybrid failure the transition from tensile to shear failure has been controversial production of hybrid failure in laboratory experiments in recent years has strengthened the case for hybrid failure but field recognition has remained elusive in this paper we present data from a small displacement fault in the hidden valley fault zone at canyon lake gorge texas which is refracted through mechanically layered carbonates and exhibits surface characteristics expected for hybrid failure on steep fault segments we discuss field criteria for identifying hybrid fractures and the deformation conditions under which hybrid failure is to be expected documented field examples of hybrid fractures are rare yet presence of hybrid fractures can be useful indicators of stress conditions at the time of failure specifically hybrid fractures are likely indicators of tensile minimum effective stress and low differential stress at failure

role of shale thickness on vertical connectivity of fractures application of crack bridging theory to the austin chalk texas abstract contrasting material properties of alternating chalk and shale layers control vertical connectivity of fractures our field observations within the austin chalk texas indicate that 1 the majority of vertical fractures occur in chalk layers and abut against contacts with shale layers 2 thicker shale layers have greater resistance to fracture propagation than thinner shale layers from these observations we hypothesize both the resistance of shale to fracturing and the thickness of shale layers may inhibit fracture propagation across the shale and into the next chalk layer we model crack propagation within a three layered system brittle chalk fracture resistant shale brittle chalk the modeled crack extends across the shale but closing tractions applied to the crack segment within the shale layer simulate resistance of shale to fracturing the crack tip lies a short distance within the unfractured chalk layer simulating a coplanar flaw with potential to propagate if the stress intensity factor at the flaw exceeds the chalk fracture toughness the crack propagates thereby bridging and eventually rupturing the shale layer for any chalk thickness there is a critical shale thickness above which fractures cross the shale layer and below which fractures arrest at shale finite element method fem analysis evaluates the influence of shale ductility within the chalk shale chalk system although remote and fluid pressure driven fractures produce identical stress intensity factors in elastic chalk shale systems lower driving stresses are required to propagate fluid pressure driven fractures through a system ductile shale layers than fractures under remote tension

geomorphological evidence for ground ice on dwarf planet ceres despite evidence for an ice rich outer shell little water ice has been observed on the surface of ceres lobate morphologies observed on ceres that are increasingly prevalent towards the dwarf planet s poles are consistent with ice rich flows

geologic mapping of the urvara and yalode quadrangles of ceres abstract we conducted geologic mapping of the urvara ac 13 and yalode ac 14 quadrangles 21 66 s 180 360 e of the dwarf planet ceres utilizing morphologic topographic and compositional information acquired by nasa s dawn mission the geologic characteristics of the two large impact basins urvara 170 km diameter and yalode 260 km diameter and their surroundings were investigated using dawn framing camera datasets including survey 415 m pixel hamo 140 m pixel and lamo 35 m pixel images and mosaics color and color ratio images and dtms derived from stereo photogrammetry geologic mapping demonstrates that impact cratering has dominated the geologic history of the urvara and yalode quadrangles with early cratered terrain formation followed by formation of the large basins and widespread emplacement of basin related smooth material impact craters display a wide range of preservation states from nearly completely buried degraded forms to more recent pristine craters with terraced inner walls and lobate ejecta deposits cross cutting relationships and morphologic signatures show that the urvara impact followed the yalode impact consistent with ages derived from crater size frequency distributions 580 40 ma for yalode and 550 50 ma for urvara observed differences in basin materials and rim morphology suggest heterogeneities in the substrate excavated by impact smooth deposits that cover large areas of the quadrangles including the basin floors rims and exterior zones are interpreted to be dominated by urvara ejecta but yalode ejecta and localized ice rich flow material may be minor components geologic mapping results and simulations of ejecta emplacement suggest that urvara and yalode ejecta deposits extend for large distances more than two crater diameters from the basin centers and may serve as important stratigraphic markers for the geologic record of ceres

fibrous calcite veins overpressures and primary oil migration the fibrous calcite veins found parallel to the bedding of certain shales may have been formed during burial as a consequence of overpressuring their presence could even be indicative of former overpressures this suggestion if it can be upheld carries implications for theories of primary oil migration

the formation and evolution of bright spots on ceres the otherwise homogeneous surface of ceres is dotted with hundreds of anomalously bright predominantly carbonate bearing areas termed faculae with bond albedos ranging from 0 02 to 0 5 here we classify and map faculae globally to characterize their geological setting assess potential mechanisms for their formation and destruction and gain insight into the processes affecting the ceres surface and near surface faculae were found to occur in four distinct geological settings associated predominantly with impact craters 1 crater pits peaks or floor fractures floor faculae 2 crater rims or walls rim wall faculae 3 bright ejecta blankets and 4 the mountain ahuna mons floor faculae were identified in eight large deep and geologically young asteroid derived model adm ages of 420 60 ma craters occator haulani dantu ikapati urvara gaue ernutet and azacca the geometry and geomorphic features of the eight craters with floor faculae are consistent with facula formation via impact induced heating and upwelling of volatile rich materials upwelling excavation of heterogeneously distributed subsurface brines or their precipitation products or a combination of both processes rim wall faculae and bright ejecta occur in and around hundreds of relatively young craters of all sizes and the geometry of exposures is consistent with facula formation via the excavation of subsurface bright material possibly from floor faculae that were previously emplaced and buried a negative correlation between rim wall facula albedo and crater age indicates that faculae darken over time models using the ceres crater production function suggest initial production or exposure of faculae by large impacts subsequent dissemination of facula materials to form additional small faculae and then burial by impact induced lateral mixing which destroys faculae over timescales of less than 1 25 gyr cumulatively these models and the observation of faculae limited to geologically young craters indicate relatively modern formation or exposure of faculae indicating that ceres surface remains active and that the near surface may support brines in the present day

fault zone processes and fluid history in austin chalk southwest texas faults are commonly the largest fractures in a fracture network forming the backbone of the permeability system in low permeability rocks faults in outcrops of the austin chalk an important oil and gas reservoir in south texas louisiana and westernmost mississippi exemplify deformation and fluid histories of subseismic scale faults in mechanically layered chalk dominated strata exposures of near horizontal austin chalk in southwest texas contain northwest and southeast dipping normal faults with exposed heights of meters to tens of meters and displacements of centimeters to decimeters local fault dips are steep to vertical through chalk and limestone beds and moderate through marl mud rock and clay rich ash beds producing refracted fault profiles failure surface characteristics indicate various failure modes including tensile hybrid shear and locally compactive shear behavior depending on the host lithology dilational zones associated with steep fault segments host calcite veins crack seal textures in fault zone veins record repeated reactivation of refracted fault profiles fluid inclusion and stable isotope geochemistry analyses of fault veins indicate formation at depths of 1 4 to 2 9 km 4593 to 9514 ft and possibly of 4 2 km 13 780 ft fluids include locally sourced saline waters and externally sourced waters and oil in rocks that did not reach oil maturation conditions inclusions of 30 api to greater than 50 api oil are found in veins 30 km 19 mi updip from the eagle ford formation oil zone these results illustrate the migration of oil and other fluids within subseismic scale austin chalk faults and fundamental control of lithology on fault zone architecture

constraints on ceres internal structure and evolution from its shape and gravity measured by the dawn spacecraft ceres is the largest body in the asteroid belt with a radius of approximately 470 km in part due to its large mass ceres more closely approaches hydrostatic equilibrium than major asteroids pre dawn mission shape observations of ceres revealed a shape consistent with a hydrostatic ellipsoid of revolution the dawn spacecraft framing camera has been imaging ceres since march 2015 which has led to high resolution shape models of the dwarf planet while the gravity field has been globally determined to a spherical harmonic degree 14 equivalent to a spatial wavelength of 211 km and locally to 18 a wavelength of 164 km we use these shape and gravity models to constrain ceres internal structure we find a negative correlation and admittance between topography and gravity at degree 2 and order 2 low admittances between spherical harmonic degrees 3 and 16 are well explained by airy isostatic compensation mechanism different models of isostasy give crustal densities between 1 200 and 1 400 kg m3 with our preferred model giving a crustal density of 1 287 70 87 kg m3 the mantle density is constrained to be 2 434 5 8 kg m3 we compute isostatic gravity anomaly and find evidence for mascon like structures in the two biggest basins the topographic power spectrum of ceres and its latitude dependence suggest that viscous relaxation occurred at the long wavelengths 246 km our density constraints combined with finite element modeling of viscous relaxation suggests that the rheology and density of the shallow surface are most consistent with a rock ice salt and clathrate mixture

the early thermal and magnetic state of the cratered highlands of mars surface heat flows are calculated from elastic lithosphere thicknesses for the heavy cratered highlands of mars in terms of the fraction of the surface heat flow derived from crustal heat sources previous heat flow estimations for mars used linear thermal gradients which is equivalent to ignoring the existence of heat sources within the crust we compute surface heat flows following a methodology that relates effective thickness and curvature of an elastic plate with the strength envelope of the lithosphere and assuming crustal heat sources homogeneously distributed in a radioactive element rich layer 20 or 60 km thick the obtained results show that the surface heat flow increases with the proportion of heat sources within the crust and with the decrease of both radioactive element rich layer thickness and surface temperature also the results permit us to calculate representative temperatures for the crust base rock strength for the upper mantle and lower and upper limits to the crustal magnetization depth and intensity respectively for terra cimmeria an effective elastic thickness of 12 km implies between 30 and 80 of heat sources located within the crust in this case the uppermost mantle would be weak at the time of loading and temperatures in the lower crust cold enough to favor unrelaxed crustal thickness variations and to permit deep curie depths in the highlands as suggested by the observational evidence d 2005 elsevier b v all rights reserved

enceladus an estimate of heat flux and lithospheric thickness from flexurally supported topography fluxes of 200 270 mw m 2 at the time of formation the heat fluxes are comparable to average heat flux values measured in enceladus active south polar region and they are consistent with estimates derived via models of unstable extension of the lithosphere at this location surface porosity can reduce the obtained heat fluxes to an estimated minimum of 45 60 mw m 2 c rater size frequency counts fix the time of formation from presentday of the rift zone at either 3 5 0 4 0 1 ga assuming an

ceres evolution and current state 1 we modeled several thermal evolution scenarios for ceres to explore the nature of large wet protoplanets and to predict current day evidence that might be found by close inspection such as by the dawn mission the density for ceres is near 2 1 suggesting a water content between 17 and 27 by mass short and long lived radioactive nuclide heating is considered even if only long lived radionuclide heating is assumed the water ice in ceres melts quickly and a water mantle forms but an approximately 10 km crust does not melt the circulating warm water would alter the silicates as heat is lost by conduction through the frozen crust water begins to freeze out at the base of the crust solid state convection begins and transports more heat as well as perhaps material dissolved or entrained in the water to or near the surface ceres water layer eventually but perhaps not entirely freezes forming a layered density structure with perhaps some liquid water remaining today our differentiated models are in agreement with the recently measured difference between the equatorial and polar radii we find that ceres existence and evolution depend critically on it containing water at formation and this depends strongly on the combination of when it accreted and the amount of 26al present in the pre ceres 1 km sized objects slightly more 26al or earlier accretion produces a dry vesta like object melting and freezing plus mineralization would lead to several dimensional changes over time creating topographic features zones of weakness and perhaps disruptions in the crust

post impact thermal structure and cooling timescales of occator crater on asteroid 1 ceres abstract occator crater is perhaps the most distinct surface feature observed by nasa s dawn spacecraft on the cerean surface contained within the crater are the highest albedo features on the planet cerealia facula and vinalia faculae and relatively smooth lobate flow deposits we present hydrocode simulations of the formation of occator crater varying the water to rock ratio of our pre impact cerean surface we find that at water to rock mass ratios up to 0 3 sufficient volumes of occator s post impact subsurface would be above the melting point of water to allow for the deposition of faculae like deposits via impact heat driven hydrothermal effusion of brines this reservoir of hydrothermally viable material beneath the crater is composed of a mixture of impactor material and material uplifted from 10 s of kilometers beneath the pre impact surface which could sample a deep subsurface volatile reservoir if present using a conductive cooling model we estimate that the lifetime of hydrothermal activity within such a system depending on choice of material constants is between 0 4 and 4 myr our results suggest that impact heating from the occator forming impact provides a viable mechanism for the creation of the observed faculae with the proviso that the faculae formed within a relatively short time window after the crater itself formed

the application of fluid inclusions to migration of oil and diagenesis in petroleum reservoirs abstract fluid inclusions can be used to interpret thermal history and petroleum maturation and migration relative to burial history temperature pressure and composition data collected from fluid inclusions are used to determine the environment of diagenesis and the timing of cementation and migration cements in petroleum reservoirs contain both oil and aqueous fluid inclusions fluorescence spectroscopy is used to identify oil inclusions and to determine the maturity of entrapped oil the lifetime of fluorescence induced by a pulsed laser is related to the api gravity of entrapped oil interpretation of fluid inclusion data depends on knowing the origin of fluid inclusions and the probability that they survive in the burial environment those aspects of fluid inclusion study are investigated by synthesizing oil and aqueous inclusions in calcite crystals in laboratory experiments examples of how fluid inclusions are used to determine the physico chemical environments of diagenesis in petroleum reservoirs and the timing of cementation and migration are given for the wealden basin england the mishrif formation dubai the smackover formation gulf coast u s a and jurassic sandstones offshore norway in the wealden basin temperature data from fluid inclusions are used to determine that oil migration occurred in the cretaceous and that the reservoir rocks have been uplifted to varying degrees at a time after migration distribution of oil inclusions indicates that generation and migration of oil was principally in the western part of the basin the geochemistry of oil inclusions in calcite cements from the mishrif formation dubai are used to determine the type and maturity of entrapped oil temperature data from oil and water inclusions are used to relate reservoir diagenesis to burial history and the migration of oil in deep smackover reservoirs oil contains h 2 s the origin of the h 2 s is examined by study of fluid inclusions containing h 2 s in jurassic sandstones offshore norway fluid inclusion studies show that silica cementation is related to burial depth whereas a later calcite cementation originated from invasion of a hot fluid

lithospheric flexure and thermal anomalies plots of effective elastic thickness te of the oceanic lithosphere as a function of age when elastically deformed show a general increase in te with the square root of age although there is much scatter some of the scatter can be eliminated by correcting for the effect of finite yield strength in rocks which makes te for more sharply bent plates underestimate the true depth tm to the rheological boundary at the base of the high strength mechanical lithosphere after converting effective values te to true thicknesses tm it appears that the mechanical lithosphere is always thinner beneath islands and seamounts compared to lithosphere of similar age flexed at subduction zones from several other lines of evidence such as depth anomalies seamount subsidence and heat flow data it has been suggested that the thermal structure in plates subjected to hot spot type volcanism is reset to values appropriate for much younger lithosphere the reduction in mechanical plate thickness beneath hot spot volcanoes is also consistent with this concept of thermal rejuvenation since the strength of rocks decreases exponentially with rising temperature this dependence implies that variations in mechanical plate thickness can be used to map temperature anomalies in the lithosphere since the mechanical plate thickness depends principally upon the temperature at one depth specifically the depth at which the temperature reaches 550 600 c depending on strain rate flexural data are particularly sensitive indicators of the vertical structure of lithospheric reheating compared to quantities dependent on depth integrals of temperature such as swell height and subsidence the thermal rejuvenation hypothesis predicts that the flexural profile should mimic viscoelastic relaxation in the first 10 ma after loading if initially reheating is confined to depths close to and below the 550 c isotherm the flexural data combined with depth anomaly information for hawaii point to extremely rapid reheating localized in the lower lithosphere rejuvenation in the society islands on the other hand is compatible with slower methods of heat injection involving the entire lithospheric column

eagle ford shale prospecting with 3d seismic data within a tectonic and depositional system framework the south texas eagle ford shale formation in is an important emerging shale play in the united states more than 1510 wells have either been drilled or permitted in the play what has emerged is a well defined downdip gas play that transitions rapidly updip into less well defined wet gas and oil fairways with initial gas well rates exceeding 17 million cubic feet per day and initial oil well rates in excess of 1000 barrels of oil per day common in the expanding play exploration companies are pursuing methods to optimize drilling plans limited well and core data describing the eagle ford require the use of 3d seismic to help characterize reservoir quality variations avoid drilling hazards and help predict sweet spots modern long offset full azimuth 3d is an essential tool for building a geophysical description of the shale between wells anisotropic time imaging feeding both acoustic and elastic inversions is helping operators gain better insight into the reser voir s variability the following discussion highlights components of an ongoing effort to extract value from seismic data in shale prospecting unfortunately limited well data for calibration as in many immature shale plays remains the primary constraint on confident linkage between the actual reservoir quality and seismic measurements

sequential vein growth with fault displacement an example from the austin chalk formation texas to determine the opening and precipitation history and characteristics of vein forming fluids analyses of oxygen and carbon isotopes and trace elements were carried out on multilayered crack seal calcite veins in the austin chalk formation near san antonio texas the veins developed within the normal fault zones possessing unique chemical and textural characteristics which indicate sequential vein development they are composed of alternating millimeter to submillimeter thick calcite veinlets and host lithons occasionally crosscut by coarse equant grained secondary calcite veins regular changes in 18o e g 2 6 to 5 6 pee dee belemnite pdb of the calcite veinlets along the length of veins suggest that the individual calcite veinlets were sequentially developed a systematic 18o decrease in the vein opening direction primarily resulted from a continuous increase in temperature of the ascending fluids delivered to the austin chalk relatively constant 13c approximately 1 4 0 4 pdb for the multilayered veins and most secondary veins indicates that the composition of fluids from which the calcite veins precipitated was initially buffered by the bulk chalk there is no spatial variation in trace element composition of the calcite veinlets along the length of veins low sr concentrations in both calcite veinlets and secondary veins relative to those of the host chalk reflect a low partition coefficient of sr in calcite during vein formation normal faults in the cretaceous austin chalk were conduits to upwardly mobile vein forming fluids

fault zone deformation controlled by carbonate mechanical stratigraphy balcones fault system texas normal faults in cretaceous carbonates in the balcones fault system provide important analogs for fault zone architecture and deformation in carbonate reservoirs worldwide mechanical layering is a fundamental control on carbonate fault zones relatively planar faults with low displacement gradients develop in massive strong clay poor limestones and dolomites in less competent clay rich strata shale beds impede fault propagation resulting in fault related folding and locally steep bedding dips faults in clay poor massive limestones and dolomites tend to be steep 70 or more whereas weaker clay rich limestones develop faults with shallower dips 60 or less fault zone rocks show evidence of cataclasis cementation deformation of cement by mechanical twinning and pressure solution and multiple generations of cement with differing degrees of deformation indicating contemporaneous cementation and fault slip in stratigraphic sequences consisting of both competent and incompetent strata the ratio of incompetent to competent strata by thickness is a useful guide for inferring the relative rates of fault displacement and propagation low displacement to propagation ratios associated with competent strata generate low displacement gradients inhibiting fault related folding conversely high displacement to propagation ratios associated with incompetent strata promote high displacement gradients and fault related folding

changing fluid conditions during folding an example from the central appalachians abstract fluids inclusion microthermometry and stable isotope analyses of vein minerals in the central appalachian patterson creek anticline record dynamic changes in fluid temperature pressure and chemistry during folding these changes resulted from variations in fracture connectivity and fluid communication between stratigraphically restricted fluid reservoirs minerals in early formed bed parallel and ene nnw striking cross fold veins show that prior to folding fluids in silurian through lower upper devonian rocks were well stratified based temperature salinity and isotopic composition stable isotopes data indicates that the fluid systems were essentially closed with no communication between layers as folding commenced early minerals in ne nw striking veins in the siluro devonian carbonate rocks record 2 km of burial by syn tectonic sedimentation with corresponding increases in fluid temperature and pore fluid pressure an additional 2 km of burial along with the influx of low salinity methane saturated brines into the middle and upper devonian clastic rock sequence is recorded by later quartz in the ne nw striking veins at some point during folding stable isotope data indicate that fluid communication increased along fracture and faults between major stratigraphic fluids reservoirs the culmination of this process was the breaching of the stratigraphic seal at the base of the devonian shales allowing fluid infiltration from the devonian shale sequence into the upper portion of the helderberg group this resulted in the local precipitation of quartz and possibly the enhancement of solution structures