the active part of charlie gibbs fracture zone a study using sonar and other geophysical techniques a short survey with gloria side scan sonar and other geophysical instruments has revealed new information about charlie gibbs fracture zone between 29 and 36 w the traces of two transform faults have been clearly delineated they fit small circles about the pole of rotation with an rms error of only about 1 km but they do not always follow the deepest parts of the transform valleys the transforms are joined by a short spreading center at 31 45 w the median transverse ridge appears to have been produced by normal seafloor spreading at this center and bears identifiable vine matthews magnetic anomalies a transverse ridge along the eastern inactive part of the northern transform may be an intrusive feature considerable thicknesses of sediment appear to have been deposited in the northern transform valley from norwegian sea overflow water passing through the fracture zone but transverse ridges have prevented the sediment reaching the southern valley

craters boulders and regolith of 101955 bennu indicative of an old and dynamic surface small kilometre sized near earth asteroids are expected to have young and frequently refreshed surfaces for two reasons collisional disruptions are frequent in the main asteroid belt where they originate and thermal or tidal processes act on them once they become near earth asteroids here we present early measurements of numerous large candidate impact craters on near earth asteroid 101955 bennu by the osiris rex origins spectral interpretation resource identification and security regolith explorer mission which indicate a surface that is between 100 million and 1 billion years old predating bennu s expected duration as a near earth asteroid we also observe many fractured boulders the morphology of which suggests an influence of impact or thermal processes over a considerable amount of time since the boulders were exposed at the surface however the surface also shows signs of more recent mass movement clusters of boulders at topographic lows a deficiency of small craters and infill of large craters the oldest features likely record events from bennu s time in the main asteroid belt

implications for ice stability and particle ejection from high resolution temperature modeling of asteroid 101955 bennu the finding by the osiris rex origins spectral interpretation resource identification and security regolith explorer mission that its target 101955 bennu is an active asteroid has raised questions as to whether the observed particle ejection events are driven by temperature to investigate sublimation of water ice and rock thermal fracture as possible temperature driven causes we modeled the global temperatures of bennu and searched for correlations with the identified ejection points on the asteroid surface we computed temperatures with the advanced thermophysical model and the 75 cm resolution global shape model of bennu derived by the osiris rex mission we find that 1856 m 2 of bennu s polar regions have orbit averaged temperatures that are sufficiently cold to enable water ice if buried within the top few meters of the surface to remain stable over geological timescales millimeter thick layers of surface water ice are also stable over 10 3 year timescales within polar centimeter scale cold traps however we do not find evidence of conditions enabling ice stability in the warmer equatorial regions where ejection events have been observed implying that sublimation of water ice is not the cause of particle ejection conversely rock thermal fracture remains a possible mechanism of particle ejection we find high amplitudes of diurnal temperature variation a proxy for the efficacy of thermal fracturing at all latitudes on bennu due to its extreme ruggedness therefore if rock thermal fracture is the mechanism particles could be ejected from any latitude which is consistent with the continued observations of particle ejection by osiris rex

cracks in desert pavement rocks further insights into mechanical weathering by directional insolation the formation of cracks is a fundamental first step in the physical weathering of rocks in desert environments in this study we combine new field data from the mojave u s gobi mongolia and strzelecki australia deserts that collectively support the hypothesis that meridional cracks cracks with orientations not readily attributable to rock anisotropies or shape in boulders or cobbles form due to tensile stresses caused by directional heating and cooling during the sun s daily transit the new studies indicate that rock size surface age and latitude play important roles with respect to their influence on rock fracture rock size and pavement surface age exert an influence on the development of rock cracks as the average clast size of mature desert pavements may be at or below the threshold clast size for thermal cracking of rocks latitude controlled seasonal temperature variations play a key role as demonstrated by 1 tightly clustered mean resultant orientations that differ by latitude as predicted in mcfadden et al 2005 and 2 very cold wintertime temperatures and strong diurnal gradients that may favor crack development in wintertime given the likelihood for strong clast heating during early morning hours the consistent evidence for meridional cracks in surfaces of diverse age and desert environments climate vegetation and distance of clast transport indicate that directional insolation may play the key role in initially generating and propagating rock fractures rather than a secondary role as implied in recent field and modeling studies of physical weathering in deserts

density porosity and magnetic susceptibility of carbonaceous chondrites abstract we report physical properties bulk and grain density magnetic susceptibility and porosity measured using nondestructive and noncontaminating methods for 195 stones from 63 carbonaceous chondrites grain densities over the whole population average 3 44 g cm 3 ranging from 2 42 g cm 3 ci1 orgueil to 5 66 g cm 3 cb bencubbin magnetic susceptibilities in log units of 10 9 m3 kg 1 averaged log 4 22 ranging from 3 23 cv3 axtell to 5 79 cb bencubbin porosities averaged 17 ranging from 0 for a number of meteorites to 41 for one stone of the co ornans notably we found significant differences in porosity between the oxidized and reduced cv subgroups with the porosities of cvo averaging approximately 20 and cvr porosities approximately 4 overall porosities of carbonaceous chondrite falls trend with petrographic type from type 1 ci near 35 type 2 cm cr averaging 23 type 3 cv co 21 to type 4 ck and some co averaging 15 there is also a significant decrease in porosity between meteorites of shock stage s1 and those of s2 indicative of shock compression

late quaternary sediment flux on sedimentary drifts in the northeast atlantic abstract comparison between the last glacial and holocene periods of the terrigenous and carbonate sediment flux distributions in the whole northeastern atlantic basin points out the role of deep circulation relative to other processes during the holocene the global terrigenous flux is similar to that during the glacial period 4 compared with 4 7 g cm 2 ky 1 despite a general decrease of terrigenous supplies the flux distribution however is different high values are located in areas of bottom current sedimentation contourite drifts instead of along continental margins where downslope processes are dominant and areas with major ice rafting the global carbonate flux is higher during the holocene 3 compared with 1 5 g cm 2 ky 1 but the carbonate flux distribution matches that of the terrigenous flux both flux patterns are strongly controlled by reworking and redeposition of sediments by bottom currents flux variation in three cores collected on the feni gardar and faro drifts compared to areas of little or no bottom current activity highlights the deep water circulation fluctuations since the last glacial maximum in areas dominated by downslope processes bay of biscay or by ice rafted sediment deposition mid atlantic ridge around 45 n the sediment fluxes are maximum during the deglacial warming and minimum during the holocene period areas dominated by bottom current sedimentation are all characterized by highest sedimentation during the holocene but the flux variations reveal that the norwegian sea water overflow nswo and the mediterranean outflow mo fluctuated differently according to the regional climatic context and the latitudinal transgression of climatic warming on the feni and gardar drifts higher holocene fluxes coincide with the re initiation of nswo at about 10 000 yrs bp the highest flux on the gardar drift results from a stronger outflow across the iceland faeroe ridge than across the faeroe scotland ridge this flow is responsible for high sediment fluxes all along the eastern side of the mid atlantic ridge as far south as 45 n on the faro drift the reactivation of the mediterranean outflow mo took place earlier as three episodes of greater bottom current activity occurred since about 15 000 yrs bp fluxes are maximum during the deglacial warming and remain high during the holocene

thermal expansion and pore pressure generation in oil sands the prediction of stress changes and deformations arising from ground heating requires the coupled solution of the heat transfer and consolidation equations heat consolidation as a class of problems is distinct from other thermally induced consolidation problems involving processes such as frost heave and thaw consolidation in that it involves heating to elevated temperatures well above normal ground temperatures two of the important parameters required in analyses of heat consolidation problems are thermal expansion coefficients and a coefficient of thermal pore pressure generation relationships describing thermal expansion behaviour and thermal pore pressure generation in oil sands are presented both drained and undrained thermal expansion coefficients for athabasca oil sand were determined by means of heating experiments in the temperature range 20 300 c the thermal pore pressure generation coefficient was evaluated in undrained heating experiments under constant total confining stresses and under

modal mineralogy of cm2 chondrites by x ray diffraction psd xrd part 1 total phyllosilicate abundance and the degree of aqueous alteration abstract cm carbonaceous chondrites are samples of incompletely serpentinized primitive asteroids using position sensitive detector x ray diffraction psd xrd and a pattern stripping technique we quantify the modal mineralogy of cm2 chondrites mighei murray murchison nogoya and cold bokkeveld there is a narrow range in the combined modal volume vol of the most abundant phases mg serpentine 25 33 and fe cronstedtite 43 50 cold bokkeveld is anomalous in containing more mg serpentine 49 59 than fe cronstedtite 19 27 even including cold bokkeveld the range in modal total phyllosilicate is 73 79 average 75 total phyllosilicate abundance provides a non ambiguous measure of the degree of aqueous alteration and indicates that these meteorites have all experienced essentially the same degree of aqueous alteration this reflects pervasive hydration of matrix across cm2 samples apparent differences in the alteration of chondrules observed in petrographic studies represent various stages in the progression towards complete hydration of all components but are not manifest in significant differences in modal mineralogy for all samples there is a limited range in olivine 6 9 and pyroxene 5 abundances modal abundances of the remaining identified phases also show a limited range calcite 0 1 3 gypsum 0 1 6 magnetite 1 1 2 4 pentlandite 0 2 1 and pyrrhotite 1 3 8 as expected we observe a strong negative correlation in the modal abundance of anhydrous fe mg silicates olivine pyroxene and total phyllosilicate mg serpentine fe cronstedtite consistent with the idea that phyllosilicate is forming by aqueous alteration of the anhydrous components the negative correlation in the modal abundance between mg serpentine and fe cronstedtite indicates a mineralogic transformation of fe cronstedtite to mg serpentine by fluid driven recrystallisation or b that these meteorites had different initial abundances of olivine and pyroxene the observed positive correlation in the relative proportion of mg serpentine with increasing total phyllosilicate abundance reflects the evolution of increasingly mg rich phyllosilicate during aqueous alteration fe cronstedtite is the dominant phyllosilicate while cm chondrule olivines are forsteritic and will form mg serpentine during aqueous alteration this implies that matrix olivine was more fe rich than chondrule olivine prior to aqueous alteration

a spheroidal weathering model coupling porewater chemistry to soil thicknesses during steady state denudation abstract spheroidal weathering a common mechanism that initiates the transformation of bedrock to saprolite creates concentric fractures demarcating relatively unaltered corestones and progressively more altered rindlets in the spheroidally weathering rio blanco quartz diorite puerto rico diffusion of oxygen into corestones initiates oxidation of ferrous minerals and precipitation of ferric oxides a positive v of reaction results in the build up of elastic strain energy in the rock formation of each fracture is postulated to occur when the strain energy in a layer equals the fracture surface energy the rate of spheroidal weathering is thus a function of the concentration of reactants the reaction rate the rate of transport and the mechanical properties of the rock substitution of reasonable values for the parameters involved in the model produces results consistent with the observed thickness of rindlets in the rio icacos bedrock 2 3 cm and a time interval between fractures 200 300 a based on an assumption of steady state denudation at the measured rate of 0 01 cm a averaged over times longer than this interval the rate of advance of the bedrock saprolite interface during spheroidal weathering the weathering advance rate is constant with time assuming that the oxygen concentration at the bedrock saprolite interface varies with the thickness of soil saprolite yields predictive equations for how weathering advance rate and steady state saprolite soil thickness depend upon atmospheric oxygen levels and upon denudation rate the denudation and weathering advance rates at steady state are therefore related through a condition on the concentration of porewater oxygen at the base of the saprolite in our model for spheroidal weathering of the rio blanco quartz diorite fractures occur every 250 yr ferric oxide is fully depleted over a four rindlet set in 1000 yr and saprolitization is completed in 5000 yr in the zone containing 20 rindlets spheroidal weathering thus allows weathering to keep up with the high rate of denudation by enhancing access of bedrock to reactants by fracturing coupling of denudation and weathering advance rates can also occur for the case that weathering occurs without spheroidal fractures but for the same kinetics and transport parameters the maximum rate of saprolitization achieved would be far smaller than the rate of denudation for the rio blanco system the spheroidal weathering model provides a quantitative picture of how physical and chemical processes can be coupled explicitly during bedrock alteration to soil to explain weathering advance rates that are constant in time

lunar surface dust dynamics and regolith mechanics 1 the lunar surface is characterized by a collisionally evolved regolith resulting from meteoroid bombardment this lunar soil consists of highly angular particles in a broad approximately power law size distribution with impact generated glasses the regolith becomes densified and difficult to excavate when subjected to lunar quakes or eventually manned and unmanned activity on the surface solar radiation and the solar wind produce a plasma sheath near the lunar surface lunar grains acquire charge in this environment and can exhibit unusual behavior including levitation and transport across the surface because of electric fields in the plasma sheath the fine component of the lunar regolith contributes to the operational and health hazards posed to planned lunar expeditions in this paper we discuss the mechanical response of the regolith to anticipated exploration activities and review the plasma environment near the lunar surface and the observations models and dynamics of charged lunar dust

thermally induced stresses in boulders on airless body surfaces and implications for rock breakdown abstract this work investigates the macroscopic thermomechanical behavior of lunar boulders by modeling their response to diurnal thermal forcing our results reveal a bimodal spatiotemporally complex stress response during sunrise stresses occur in the boulders interiors that are associated with large scale temperature gradients developed due to overnight cooling during sunset stresses occur at the boulders exteriors due to the cooling and contraction of the surface both kinds of stresses are on the order of 10 mpa in 1 m boulders and decrease for smaller diameters suggesting that larger boulders break down more quickly boulders 30 cm exhibit a weak response to thermal forcing suggesting a threshold below which crack propagation may not occur boulders of any size buried by regolith are shielded from thermal breakdown as boulders increase in size 1 m stresses increase to several 10 s of mpa as the behavior of their surfaces approaches that of an infinite halfspace as the thermal wave loses contact with the boulder interior stresses become limited to the near surface this suggests that the survival time of a boulder is not only controlled by the amplitude of induced stress but also by its diameter as compared to the diurnal skin depth while stresses on the order of 10 mpa are enough to drive crack propagation in terrestrial environments crack propagation rates in vacuum are not well constrained we explore the relationship between boulder size stress and the direction of crack propagation and discuss the implications for the relative breakdown rates and estimated lifetimes of boulders on airless body surfaces

origin of sheet structure 1 morphology and boundary conditions abstract sheet structure or large scale exfoliation is the division of a rock mass into lenses plates or sheets approximately parallel to the earth s surface sheet fractures which separate the plates are characterized by surface markings resembling those formed during the brittle fracture of metals glass and ceramics and those on joints in rock lineations or hackle marks parallel to the direction of fracture propagation are common branching occurs during propagation so that the fractures appear as many echelon segments in profile the opposing surfaces of sheet fractures observed in quarry walls and natural exposures are typically in contact damage if any to rock adjacent to sheet fractures is generally limited to a zone less than one centimeter wide sheets tend to parallel preferred orientations of microcracks in many rock masses most sheets that are exposed today are of prehistoric origin but in some rock masses such as chelmsford granite in massachusetts new sheets continue to form sheet structure forms in environments of high differential stress dominated by large scale compression parallel to an exposed rock surface in parts of the chelmsford granite the magnitude of this compression is greater than 30 mpa in the zone of sheeting high differential stresses near the ground surface can result from several natural agents including contemporary tectonic forces vertical unloading of a rock mass that formed at depth under high triaxial compression and suppression of expansion that would otherwise result from temperature increases or chemical alteration of the rock exfoliation of boulders during forest fires and spheroidal weathering of boulders appears to occur under similar states of stress although the agents responsible for the stresses differ

organic facies of the asbian early carboniferous queensferry beds lower oil shale group south queensferry scotland and a brief comparison with other carboniferous north atlantic oil shale deposits abstract the 71 m foreshore exposure of the queensferry beds at south queensferry is currently the best accessible section of the oil shale group of the midland valley of scotland a combination of bulk organic geochemistry and kerogen microscopy palynofacies organic petrology is used to define four organic facies and one variant organic facies 1 occurs in silty mudstones has a mean toc of only 2 and type iii iv gas prone or inert kerogen hi 800 variant 3a is additionally characterised by an abundance of small 4 m spherical cells of possible cyanobacterial origin occurring in one sample adjacent to a stromatolitic limestone organic facies 2 is transitional between 1 and 3 organic facies 4 has atypically low c s ratios and corresponds to the pumpherston marine band these organic facies can also be distinguished using biomarker parameters pr ph oep c25 c15 predominant carbon number etc the hi is very strongly correlated with the relative fluorescence of the organic matter and strongly correlated with the aom phytoclast ratio and the botryococcus and total alginite contents it is inversely correlated with the diameter of black equant phytoclasts the organic rich shales thus correspond to distal lower energy anoxic conditions during periods of meromixis high preservation low dilution similar carboniferous lacustrine source rocks occur in eastern canada and east greenland all are characterised by large lateral extents 500 2 000 km2 a geographic and temporal association with strong syndepositional subsidence generally low botryococcus contents and a dominance of amorphous type ii kerogen

facies and sediment dynamics in charlie gibbs fracture zone during the late quaternary abstract analysis of five cores from the charlie gibbs fracture zone enables us to define the sedimentary characteristics in four different types of environments a sill disrupting the southern valley open channels in the northern and southern valleys a flanking plateau of the northern side wall in the northern valley and an enclosed depression in the northern valley five lithofacies have been recognized clayey silty mud 40 clayey silty calcareous mud 25 calcareous sands 20 sedimentary breccia 10 and silty sandy calcareous mud 5 the predominance of terrigenous clayey material is evidence for a mainly continental origin of the fracture zone sediments yet another striking feature is the abundance of foraminiferal sands rich in pelagic calcareous and siliceous components associated with coarser ice rafted elements despite the pelagic origin of components a uniform draping of sediments which kind of sedimentation we call ubiquiste faugeres et al 1979 has not been noted in the survey area due to the reworking processes of already deposited materials by bottom geostrophic currents or gravity flows the influence of the bottom current processes on sedimentation is confirmed by the following characteristics 1 the presence of sharp or erosional contacts between two facies 2 low clay fraction in certain levels caused by winnowing of sedimentary materials 3 high clay fraction in other levels considered to be the result of dilution of pelagic material by clay particles transported in the nepheloid layer and trapped in a depression downstream of a sill and 4 icelandic smectites transported by iceland scotland overflow water i s o w the influence of gravity flow dynamic processes is indicated by sandy or silty sandy centimetric turbidites very thick mega sequences 8 m transported by a single mass flow and important sedimentary gaps whence gravity flows originated

ultrasonic imaging and acoustic emission monitoring of thermally induced microcracks in lac du bonnet granite concurrent ultrasonic tomography and acoustic emission monitoring were employed to study thermally induced microfracturing in an unconfined 15 cm cube of lac du bonnet granite from atomic energy of canada limited s underground research laboratory an electrical resistance cartridge heater placed in a central vertical borehole was used to cycle the sample to progressively higher peak temperatures between 75 c and 175 c tomography data were collected at room temperature before and after each thermal cycle acoustic emission monitoring proceeded during both heating and cooling phases of each thermal cycle microfractures opened above 80 c and eventually coalesced into a macroscopic fracture plane the macroscopic fracture originated at the outer edges of the sample and then extended inward parallel to the fast velocity direction and eventually intersected the borehole both acoustic emission locations and slowness difference tomography clearly delineated the fracture plane we attribute the development of the macroscopic fracture to a thermal gradient cracking mechanism acting upon a brittle anisotropic medium

physical weathering in arid landscapes due to diurnal variation in the direction of solar heating despite the prominent role of physical weathering in arid and semi arid landscapes there has been little study of the specifi c processes responsible for the rapid breakdown of subaerially exposed rocks for example many boulders and cobbles in deserts exhibit fi ne near vertical cracks although workers have hypothesized that these and other cracks are initiated by diurnal heating and cooling no convincing specifi c mechanism for their formation has been proposed we have characterized these cracks at eight sites on surfaces of different ages in the mojave sonoran and chihuahuan deserts and the high desert of central new mexico our data reveal four basic types of cracks longitudinal surfaceparallel fabric related and meridional the orientations of the fi rst three types are associated with clast shape and rock fabric the azimuths of meridional cracks however are preferentially aligned north south typically with a nonrandom multimodal distribution we propose that these cracks are caused by tensile stresses that arise in the interior of clasts due to strong radial gradients in temperature that evolve and rotate in alignment with the sun s rays we suggest that the multimodal nature of crack orientations may be in part attributable to the seasonally varying latitude dependent solar elevation angle over millennial time scales we suggest that this thermal cracking is an effi cient weathering process that together with cumulic soil epipedon development creates the key attributes of most desert pavements in addition to individual clasts exposed on desert surfaces this mechanism of cracking is potentially signifi cant in other climates and on other planets as well as for rock outcrops and for man made structures

thermal stress weathering and the spalling of antarctic rocks using in situ field measurements laboratory analyses and numerical modeling we test the potential efficacy of thermal stress weathering in the flaking of millimeter thick alteration rinds observed on cobbles and boulders of ferrar dolerite on mullins glacier mcmurdo dry valleys mdv in particular we examine whether low magnitude stresses arising from temperature variations over time result in thermal fatigue weathering yielding slow crack propagation along existing cracks and ultimate flake detachment our field results show that during summer months clasts of ferrar dolerite experience large temperature gradients across partially detached alteration rinds 4 7 c mm 1 and abrupt fluctuations in surface temperature up to 12 c min 1 the latter are likely due to the combined effects of changing solar irradiation and cooling from episodic winds the results of our thermal stress model coupled with subcritical crack growth theory suggest that thermal stresses induced at the base of thin alteration rinds 2 mm thick common on rocks exposed for 105 years may be sufficient to cause existing cracks to propagate under present day meteorological forcing eventually leading to rind detachment the increase in porosity observed within alteration rinds relative to unaltered rock interiors as well as predicted decreases in rind strength based on allied weathering studies likely facilitates thermal stress crack propagation through a reduction of fracture toughness we conclude that thermal stress weathering may be an active though undervalued weathering process in hyperarid terrestrial polar deserts such as the stable upland region of the mdv

depletion of 13c in cretaceous marine organic matter source diagenetic or environmental sigal geochemical studies of cretaceous strata rich in organic carbon oc from deep sea drilling project dsdp sites and several land sections reveal several consistent relationships among amount of oc hydrocarbon generating potential of kerogen measured by pyrolysis as the hydrogen index hi and the isotopic composition of the oc first there is a positive correlation between hi and oc in strata that contain more than about 1 oc second percent oc and hi often are negatively correlated with carbon isotopic composition 13c of kerogen the relationship between hi and oc indicates that as the amount of organic matter increases this organic matter tends to be more lipid rich reflecting the marine source of the organic matter cretaceous samples that contain predominantly marine organic matter tend to be isotopically lighter than those that contain predominantly terrestrial organic matter average 13c values for organic matter from most cretaceous sites are between 26 and 28 and values heavier than about 25 occur at very few sites most of the 13c values of miocene to holocene oc rich strata and modern marine plankton are between 16 to 23 values of 13c of modern terrestrial organic matter are mostly between 23 and 33 the depletion of terrestial oc in 13c relative to marine planktonic oc is the basis for numerous statements in the literature that isotopically light cretaceous organic matter is of terrestrial origin even though other organic geochemical and or optical indicators show that the organic matter is mainly of marine origin a difference of about 5 in 13c between modern and cretaceous oc rich marine strata suggests either that cretaceous marine planktonic organic matter had the same isotopic signature as modern marine plankton and that signature has been changed by diagenesis or that oc derived from cretaceous marine plankton was isotopically lighter by about 5 relative to modern plankton oc diagenesis does not produce a significant shift in 13c in miocene to holocene sediments and therefore probably did not produce the isotopically light cretaceous oc this means that cretaceous marine plankton must have had 13c values that were about 5 lighter than modern marine plankton and at least several per mil lighter than cretaceous terrestrial vegetation the reason for these lighter values however is not obvious it has been proposed that concentrations of co2 were higher during the middle cretaceous and this more available co2 may be responsible for the lighter 13c values of cretaceous marine organic matter

biological markers in lacustrine chinese oil shales s u m m a r y a major objective in molecular organic geochemistry is the assessment and characterization of sedimentary depositional environments from the occurrence of specific biological marker compounds related to particular source organisms the aliphatic hydrocarbon distributions of petroleums and or sediments from chinese freshwater and hypersaline lacustrine environments are described and contrasted in the search for diagnostic features among their biological marker distributions the eocene maoming oil shale which crops out in guangdong province shows major differences in hydrocarbon composition through its stratigraphic succession these variations reflect changes in lithology and in the origins of the sedimentary organic matter as seen from petrographic examination the lower lignite and vitrinite layers contain significant contributions of biological markers from bacterial sources plus components derived from terrigenous higher plants such as c29 steroids in contrast the overlying shales show a dominance of dinoflagellate derived 4methylsteroids and culminate in an horizon with botryococcane homologues as their dominant alkanes thus the geochemical profile suggests that a swampy environment in which peats accumulated deepened to support populations of dinoflagellate and finally blooms of botryococcus green algae the aliphatic hydrocarbons of a series of sediments and petroleums from the eocene hypersaline sequence of the jianghan basin in southern hubei province shows various features that may be typical of such facies these include a dominance of even numbered n alkanes high amounts of phytane and gammacerane and an abundance of c35 hopanes similar characteristics are observed in shales from the eocene green river formation and in rozel point crude oil a petroleum thought to originate from sediments deposited under hypersaline conditions the same features also appear in a lower tertiary evaporitic mudstone from south of the renqui oil field in hebei province together with 4 methylsteranes fl carotane and 18c h oleanane a marker for terrigenous higher plants these data illustrate the potential of biological markers in the differentiation of different lacustrine environments and suggest that such characteristics may provide signatures for environmentally similar but geographically distant deposits

cooling dominated cracking in thermally stressed volcanic rocks most studies of thermally induced cracking in rocks have focused on the generation of cracks formed during heating and thermal expansion both the nature and the mechanism of crack formation during cooling are hypothesized to be different from those formed during heating we present in situ acoustic emission data recorded as a proxy for crack damage evolution in a series of heating and cooling experiments on samples of basalt and dacite results show that both the rate and the energy of acoustic emission are consistently much higher during cooling than during heating seismic velocity comparisons and crack morphology analysis of our heated and cooled samples support the contemporaneous acoustic emission data and also indicate that thermal cracking is largely isotropic these new data are important for assessing the contribution of cooling induced damage within volcanic structures and layers such as dikes sills and lava flows

in situ fragmentation of lunar blocks and implications for impacts and solar induced thermal stresses abstract this study deals with an aspect of blocks observed on many rocky planetary surfaces in situ fragmentation using lroc nac images we characterized the morphology morphometry and abundance of in situ fractured blocks observed on the rim of six large impact craters of known emplacement age on the moon the relative number of disrupted blocks increases with crater retention age of surfaces on which blocks are hosted consistent with fragmentation post emplacement due to impacts of small meteoroids the type of break up morphologies we observe appears to be independent of surface exposure age of the blocks the inferred flux and size frequency distribution of projectiles responsible for disrupting blocks is consistent with expected lunar impact fluxes block fragmentation due to insolation driven thermal stresses is subordinate to impacts the possible effects of thermal stresses are evident as meridional cracks which have preferred orientations in a young block population 4 ma and as loose material fillet developing on top of surviving blocks in old populations 800 ma

hydrocarbon compositions of bitumens from mineralized devonian lavas and carboniferous sedimentary rocks central scotland abstract solid bitumens occur in mineralized veins in the lower devonian ochil volcanic formation in the midland valley of scotland bitumens are also widespread in the carboniferous of the midland valley gas chromatography g c mass spectrometry m s studies undertaken on bitumens from the devonian rocks and on devonian and carboniferous mudrocks show that the bitumens contain biomarkers and that carboniferous rocks are the more likely source for the bitumens hydrocarbons may have migrated into the devonian rocks along the ochil fault zone from a downthrown carboniferous basin to the south of the fault the organic geochemistry of bitumen samples from the carboniferous rocks reflects varying degrees of biodegradation and heating by igneous intrusions

late quaternary calcareous clayey silty muds in the obock trough gulf of aden hemipelagites or fine grained turbidites

rockfall triggering by cyclic thermal stressing of exfoliation fractures exfoliation of rock deteriorates cliffs through the formation and subsequent opening of fractures which in turn can lead to potentially hazardous rockfalls although a number of mechanisms are known to trigger rockfalls many rockfalls occur during periods when likely triggers such as precipitation seismic activity and freezing conditions are absent it has been suggested that these enigmatic rockfalls may occur due to solar heating of rock surfaces which can cause outward expansion here we use data from 3 5 years of field monitoring of an exfoliating granite cliff in yosemite national park in california usa to assess the magnitude and temporal pattern of thermally induced rock deformation from a thermodynamic analysis we find that daily seasonal and annual temperature variations are sufficient to drive cyclic and cumulative opening of fractures application of fracture theory suggests that these changes can lead to further fracture propagation and the consequent detachment of rock our data indicate that the warmest times of the day and year are particularly conducive to triggering rockfalls and that cyclic thermal forcing may enhance the efficacy of other more typical rockfall triggers some rockfalls occur without obvious triggers such as seismicity or freeze thaw conditions temperature and deformation patterns on a granite cliff suggest that cyclical thermal forcing can progressively open fractures and trigger rockfalls

meteoroid impacts as a source of bennu s particle ejection events asteroid 101955 bennu a near earth object with a primitive carbonaceous chondrite like composition was observed by the origins spectral interpretation resource identification and security regolith explorer osiris rex spacecraft to undergo multiple particle ejection events near perihelion between december 2018 and february 2019 the three largest events observed during this period which all occurred 3 5 to 6 hr after local noon placed numerous particles 10 cm on temporary orbits around bennu here we examine whether these events could have been produced by sporadic meteoroid impacts using the national aeronautics and space administration s nasa meteoroid engineering model 3 0 most projectiles that impact bennu come from nearly isotropic or jupiter family comets and have evolved toward the sun by poynting robertson drag we find that 7 000 j impacts on bennu occur with a biweekly cadence near perihelion with a preference to strike in the late afternoon 6 pm local time this timing matches observations crater scaling laws also indicate that these impact energies can reproduce the sizes and masses of the largest observed particles provided the surface has the cohesive properties of weak porous materials bennu s ejection events could be caused by the same kinds of meteoroid impacts that created the moon s asymmetric debris cloud observed by the lunar atmosphere and dust environment explorer ladee our findings also suggest that fewer ejection events should take place as bennu moves further away from the sun a result that can be tested with future observations

granitic boulder erosion caused by chaparral wildfire implications for cosmogenic radionuclide dating of bedrock surfaces rock surface erosion by wildfire is significant and widespread but has not been quantified in southern california or for chaparral ecosystems quantifying the surface erosion of bedrock outcrops and boulders is critical for determination of age using cosmogenic radionuclide techniques as even modest surface erosion removes the accumulation of the cosmogenic radionuclides and causes significant underestimate of age this study documents the effects on three large granitic boulders following the esperanza fire of 2006 in southern california spalled rock fragments were quantified by measuring the removed rock volume from each measured boulder between 7 and 55 of the total surface area of the boulders spalled in this single fire the volume of spalled material when normalized across the entire surface area represents a mean surface lowering of 0 7 12 3 mm spalled material was thicker on the flanks of the boulders and the height of the fire effects significantly exceeded the height of the vegetation prior to the wildfire surface erosion of boulders and bedrock outcrops as a result of wildfire spalling results in fresh surfaces that appear unaffected by chemical weathering such surfaces may be preferentially selected by researchers for cosmogenic surface dating because of their fresh appearance leading to an underestimate of age

thermal fatigue as a driving mechanism for activity on asteroid bennu many boulders on 101955 bennu a near earth rubble pile asteroid show signs of in situ disaggregation and exfoliation indicating that thermal fatigue plays an important role in its landscape evolution observations of particle ejections from its surface also show it to be an active asteroid though the driving mechanism of these events is yet to be determined exfoliation has been shown to mobilize disaggregated particles in terrestrial environments suggesting that it may be capable of ejecting material from bennu s surface we investigate the nature of thermal fatigue on the asteroid and the efficacy of fatigue driven exfoliation as a mechanism for generating asteroid activity by performing finite element modeling of stress fields induced in boulders from diurnal cycling we develop a model to predict the spacing of exfoliation fractures and the number and speed of particles that may be ejected during exfoliation events we find that crack spacing ranges from 1 mm to 10 cm and disaggregated particles have ejection speeds up to 2 m s exfoliation events are most likely to occur in the late afternoon these predictions are consistent with observed ejection events at bennu and indicate that thermal fatigue is a viable mechanism for driving asteroid activity crack propagation rates and ejection speeds are greatest at perihelion when the diurnal temperature variation is largest suggesting that events should be more energetic and more frequent when closer to the sun annual thermal stresses that arise in large boulders may influence the spacing of exfoliation cracks or frequency of ejection events

thermal fatigue as the origin of regolith on small asteroids space missions1 2 and thermal infrared observations3 have shown that small asteroids kilometre sized or smaller are covered by a layer of centimetre sized or smaller particles which constitute the regolith regolith generation has traditionally been attributed to the fall back of impact ejecta and by the break up of boulders by micrometeoroid impact4 5 laboratory experiments6 and impact models4 however show that crater ejecta velocities are typically greater than several tens of centimetres per second which corresponds to the gravitational escape velocity of kilometre sized asteroids therefore impact debris cannot be the main source of regolith on small asteroids4 here we report that thermal fatigue7 8 9 a mechanism of rock weathering and fragmentation with no subsequent ejection is the dominant process governing regolith generation on small asteroids we find that thermal fragmentation induced by the diurnal temperature variations breaks up rocks larger than a few centimetres more quickly than do micrometeoroid impacts because thermal fragmentation is independent of asteroid size this process can also contribute to regolith production on larger asteroids production of fresh regolith originating in thermal fatigue fragmentation may be an important process for the rejuvenation of the surfaces of near earth asteroids and may explain the observed lack of low perihelion carbonaceous near earth asteroids10

boulders and ponds on the asteroid 433 eros abstract there are 300 features on the asteroid 433 eros that morphologically resemble ponds flat floored and sharply embaying the bounding depression in which they sit because boulders on eros are apparently eroding in place and because ponds with associated boulders tend to be larger than ponds without blocks we propose that ponds form from thermally disaggregated and seismically flattened boulder material under the assumption that repeated day night cycling causes material fatigue that leads to erosion of the boulders results from a simple boulder emplacement thermal erosion model with boulders emplaced in a few discrete events i e large impacts match well the observed size distribution under this scenario the subtle color differences of ponds somewhat bluer than the rest of the surface might be due to some combination of less space weathered material and density stratification of silicate rich chondrules and more metal rich matrix from a disaggregated boulder volume estimates of ponds derived from near laser rangefinder profiles are consistent with what can be supplied by boulders ponds are also observed to be concentrated in regions of low slope and high elevation which suggests the presence of a less mobile regolith and thus a contrast in the resistance to seismic shaking between the pond material and the material that makes up the bounding depression future tests include shake table experiments and temperature cycling fatigue of ordinary chondrites to test the thermal erosion mechanism

lunar equatorial surface temperatures and regolith properties from the diviner lunar radiometer experiment 1 the diviner lunar radiometer experiment onboard the lunar reconnaissance orbiter has measured solar reflectance and mid infrared radiance globally over four diurnal cycles at unprecedented spatial and temporal resolution these data are used to infer the radiative and bulk thermophysical properties of the near surface regolith layer at all longitudes around the equator normal albedos are estimated from solar reflectance measurements normal spectral emissivities relative to the 8 m christiansen feature are computed from brightness temperatures and used along with albedos as inputs to a numerical thermal model model fits to daytime temperatures require that the albedo increase with solar incidence angle measured nighttime cooling is remarkably similar across longitude and major geologic units consistent with the scarcity of rock exposures and with the widespread presence of a near surface layer whose physical structure and thermal response are determined by pulverization through micrometeoroid impacts nighttime temperatures are best fit using a graded regolith model with a 40 increase in bulk density and an eightfold increase in thermal conductivity adjusted for temperature occurring within several centimeters of the surface

sediment flux patterns in the northeastern atlantic variability since the last interglacial abstract the distribution of terrigenous and carbonate absolute accumulation rates in the northeastern atlantic during the last climatic cycle shows that climate and sediment accumulation are closely coupled either directly or through oceanic circulation and eustatic variation the strong contrast between the glacial and holocene flux distribution is related to oceanic circulation changes either surface circulation which governs both the ice rafting supply and the planktonic biogenic production or more particularly deep circulations via the reinitiation of the iceland scotland overflow glacial erosion and the low sea level stand enhance the terrigenous supply but the holocene deep circulation reinforcement leads to important material reworking as a consequence an almost constant average sediment flux is obtained 4g 2 ky 1 during the holocene compared to 4 7 g cm 2 ky 1 during the glacial period during the holocene period the notable increase in mean carbonate flux from 1 5 to 3 g cm 2 ky 1 is associated with carbonate biogenic production but the carbonate flux distribution shows the influence of redistributive agents on margins fluxes do not simply decrease from continental sources to the oceanic basin eustatic drops leads to a shift in the areas of preferential accumulation from the upper to the lower slope during the deglacial warming period the fluxes are respectively an average of two and three times higher than during the holocene and the glacial periods their importance highlights the major impact of rapid climatic changes finally local conditions the location of terrigenous sources and the presence of contour currents are among the many factors which will modify the trends observed on a global scale

classification of oil shales coals and other organic rich rocks abstract oil shales are a complex group of rocks which were deposited in a wide range of sedimentary environments and have a wide range of largely alginite dominated maceral assemblages a system of classifying oil shales and sapropelic coals is based on relative abundances of macerals classification of oil shales has applications to the commercial development of oil shale deposits and to the classification of petroleum source rocks

the efficiency of thermal fatigue in regolith generation on small airless bodies abstract regolith generation by thermal fatigue has been identified as a dominant mechanism for the breakdown of small cm sized rocks on certain airless bodies simple numerical models for thermal fatigue seemed to indicate that this breakdown occurs faster in the larger decimeter sized rocks which is in contrast to the predictions of disruption models through successive micrometeorite impacts the observation is justified by the existence of larger temperature gradient in bigger rocks but it is not clear that this conclusion can be extrapolated or scaled to meter sized boulders here we reveal a transition in the rock disaggregation rates by thermal fatigue when rock sizes rise above a critical length scale a simple analytic model is formulated to predict the time to fracture of rocks on small airless bodies we consider an uncoupled approach consisting of a one dimensional thermal model and a two dimensional fracture model the solution of the heat equation is used as input to the thermomechanical crack growth problem this new understanding could provide bounds on the survival rates of asteroidal rocks and may help in coupling thermal fatigue with a mechanical disruption model to obtain a multi mechanism view of regolith evolution in the solar system

introduction to the special issue exploration of the activity of asteroid 101955 bennu near earth asteroid 101955 bennu is an active asteroid experiencing mass loss the activity manifests itself in the form of ejection events emitting up to hundreds of millimeter to centimeter scale particles the origins spectral interpretation resource identification and security regolith explorer spacecraft monitored particle activity for a 10 month period that included bennu s perihelion and aphelion novel and classical methods were utilized to detect the particles and characterize their orbital and physical properties roughly 30 of the observed particle mass escaped to heliocentric orbit a majority of particles fell back onto the surface of bennu after ejection with the longest lived particle surviving for 6 days on a temporary orbit particle ejection events appear to preferentially take place in the afternoon and evening and from low latitudes although they can occur at any time or latitude the reaccumulation of material is biased toward low latitudes resulting in the possible in fill of craters and growth of bennu s equatorial bulge of the potential mechanisms behind this activity that were investigated in focused studies meteoroid impacts thermal fracturing and ricochet but not water ice sublimation were found to be consistent with observations while phyllosilicate dehydration was not investigated with a focused study it remains a possible mechanism these mechanisms are not unique to bennu suggesting that many near earth asteroids may exhibit activity that has gone undetected thus far spacecraft missions with wide field imagers are encouraged to further characterize this phenomenon

episodes of particle ejection from the surface of the active asteroid 101955 bennu introduction active asteroids are small bodies in the solar system that show ongoing mass loss such as the ejection of dust which may be caused by large impacts volatile release or rotational acceleration studying them informs our understanding of the evolution and destruction of asteroids and the origin of volatile materials such as water on earth the osiris rex origins spectral interpretation resource identification and security regolith explorer spacecraft has rendezvoused with the near earth asteroid 101955 bennu the selection of bennu as the osiris rex target was partially based on its spectral similarity to some active asteroids observations designed to detect mass loss at bennu were conducted from earth and during the spacecraft s approach but no signs of asteroid activity were found however when the spacecraft entered orbit in january 2019 we serendipitously observed particles in the vicinity of bennu that had apparently been ejected from its surface rationale we analyzed the properties and behavior of particles ejected from bennu to determine the possible mechanisms of ejection and provide understanding of the broader population of active asteroids images obtained by the spacecraft indicate multiple discrete ejection events with a range of energies and resultant particle trajectories we characterized three large ejection events that respectively occurred on 6 january 19 january and 11 february 2019 tracking of individual particles across multiple images by means of optical navigation techniques provided the initial conditions for orbit determination modeling by combining these approaches we estimated the locations and times of ejection events and determined initial velocity vectors of particles we estimated the particle sizes and the minimum energies of the ejection events using a particle albedo and density consistent with observations of bennu results particles with diameters from 3 m s 1 estimated energies ranged from 270 mj for the 6 january event to 8 mj for the 11 february event the three events arose from widely separated sites which do not show any obvious geological distinction from the rest of bennu s surface however these events all occurred in the late afternoon between about 15 00 and 18 00 local solar time in addition to discrete ejection events we detected a persistent background of particles in the bennu environment some of these background particles have been observed to persist on temporary orbits that last several days in one case with a semimajor axis 1 km the orbital characteristics of these gravitationally bound objects make it possible to determine the ratio of their cross sectional area to their mass combined with their photometric phase functions this information constrains the parameter space of the particles diameters densities and albedos conclusion plausible mechanisms for the large ejection events include thermal fracturing volatile release through dehydration of phyllosilicates and meteoroid impacts the late afternoon timing of the events is consistent with any of these mechanisms bennu s boulder geology indicates that thermal fracturing perhaps enhanced by volatile release could occur on the asteroid surface smaller events especially those that occur on the night side of bennu could be attributable to reimpacting particles our observations classify bennu as an active asteroid active asteroids are commonly identified by major mass loss events observable with telescopes on scales much greater than we observed at bennu our findings indicate that there is a continuum of mass loss event magnitudes among active asteroids

deciphering the role of solar induced thermal stresses in rock weathering a dearth of direct field observations limits our understanding of individual mechanical weathering processes and how they interact in particular the specific contributions of solar induced thermal stresses to mechanical weathering are poorly characterized here we present an 11 mo data set of cracking using acoustic emissions aes combined with measurements of rock temperature strain and other environmental conditions all recorded continuously for a granite boulder resting on the ground in open sun we also present stresses derived from a numerical model of the temperature and stress fields in the boulder idealized as a uniform elastic sphere experiencing simple solar temperature forcing the thermal model is validated using this study s data most observed cracking coincides with the timing of calculated maximum insolation driven tensile thermal stresses we also observe that most cracking occurs when storms or other weather events strongly perturb the rock surface temperature field at these times we hypothesize that these weather actuated thermal perturbations result in a complex thermal stress distribution that is superimposed on the background stresses arising from simple diurnal forcing these additive stresses ultimately trigger measurable cracking measured locations of observed cracking and surface strain support this hypothesis in that they generally match model predicted locations of maximum solar induced tensile stresses also recorded rock surface strain scales with diurnal temperature cycling and records progressive cumulative extension dilation consistent with ongoing thermal stress driven subcritical crack growth in the boulder our results therefore suggest that 1 insolation related thermal stresses by themselves are of sufficient magnitude to facilitate incremental subcritical crack growth that can subsequently be exploited by other chemical and physical processes and 2 simple insolation can impart an elevated tensile stress field that makes rock more susceptible to cracking triggered by added stress from other weathering mechanisms our observed cracking activity does not correlate simply with environmental conditions including temperature extremes or the often cited 2 c min thermal shock threshold we propose that this lack of correlation is due to both the ever varying ambient stress levels in any rock at earth s surface as well as to the fact that ongoing subcritical crack growth itself will influence a rock s stress field and strength because similar thermal cycling is universally experienced by subaerially exposed rock this study elucidates specific mechanisms by which solar induced thermal stresses may influence virtually all weathering processes

shape of 101955 bennu indicative of a rubble pile with internal stiffness the shapes of asteroids reflect interplay between their interior properties and the processes responsible for their formation and evolution as they journey through the solar system prior to the osiris rex origins spectral interpretation resource identification and security regolith explorer mission earth based radar imaging gave an overview of 101955 bennu s shape here we construct a high resolution shape model from osiris rex images we find that bennu s top like shape considerable macroporosity and prominent surface boulders suggest that it is a rubble pile high standing north south ridges that extend from pole to pole many long grooves and surface mass wasting indicate some low levels of internal friction and or cohesion our shape model indicates that similar to other top shaped asteroids bennu formed by reaccumulation and underwent past periods of fast spin which led to its current shape today bennu might follow a different evolutionary pathway with an interior stiffness that permits surface cracking and mass wasting near earth asteroid bennu has a top like shape with longitudinal ridges macroporosity prominent boulders and surface mass wasting suggesting that it is a stiff rubble pile according to early observations by the osiris rex mission