planetary surface dating from crater size frequency distribution measurements partial resurfacing events and statistical age uncertainty abstract we describe the procedure to fit a cumulative production function polynomial to a partial crater size frequency distribution the technique is of particular use in deriving ages for surfaces which have undergone partial resurfacing events namely erosional or depositional events which have affected a limited diameter range of the crater population we demonstrate its use in obtaining times for both the surface formation and the resurfacing event we give a practical outline of the method for making age measurements from crater counts and how to identify resurfacing effects in the results we discuss the conversion of production function polynomials between common presentations and the statistical uncertainty of the determined ages with respect to the non linear chronology function and a minor refinement of data binning

physical and compositional properties of impact melts for jackson and tycho craters implications for space weathering and degradation of lunar impact melts abstract impact melts are ubiquitous across the moon occurring in settings ranging from massive basin deposits to flows and ponds in and around small craters recent high spatial resolution imaging and spectroscopy datasets for the moon have enhabled the identification and study of impact melt units at increasingly small spatial scales including on the central peaks of complex craters lunar impact melts have unique physical properties at many scales e g smooth appearances in visual imagery low rock concentration implying smoothness and regolith cover at meter scale high s band radar returns implying roughness at decimeter scale and possible anomalously low omat values which may be due to their unique mode of emplacement or post emplacement modification processes we isolate impact melt regions in the crater interior of jackson and tycho as well as in the continuous ejecta blanket of tycho using the geologic maps of dhingra et al 2017 and analyze their spectral compositional and physical properties utilizing datasets from the selene multiband imager and terrain camera the lroc narrow angle camera and diviner lunar radiometer we leverage the unique high slope setting of impact melts on the central peaks of these two craters to assess the influence of slope on post emplacement modification processes compared with unique physical properties of impact melts on rock concentration and optical maturation we find that slope is the primary control on optical maturity while rock concentration plays a secondary role we also find that melt units are generally more optically mature than their non melt counterparts and that this difference attenuates with distance from the crater center until no difference is noted in the continuous ejecta blanket this suggests that melt units have different surface properties than the non melt units in similar settings potentially due to the increased degree of shock they experienced during crater formation

an integrated approach to define new plays in mature oil basins the example from the middle magdalena valley basin colombia an integrated approach to detect new areas of potential interest associated with stratigraphic traps in mature basins is presented the study was carried out in the middle magdalena valley basin colombia the workflow integrates outcrop and subsurface interpretations of facies activity of faults and distribution of depocenters and paleocurrents and makes use of them to construct a three dimensional exploration scale geocellular facies model of the basin the outcrop and well log sedimentological analysis distinguished facies associations of alluvial fan overbank floodplain and channel fill the last one constituting the reservoir rock the seismic analysis showed that tectonic activity was coeval with the deposition of the productive units in the basin and that the activity ended earlier before the middle miocene along the western margin than along the eastern margin paleogeographic reconstructions depict transverse and longitudinal fluvial systems alluvial fans adjacent to the active basin margins and floodplain facies dominating the structural highs and the southwestern depositional limit these reconstructions provided statistical data lateral variograms to construct the model the exploration scale facies model depicts the complete structure of the basin in three dimensions and the gross distribution of the reservoir and seal rocks the predictive capability of the model was evaluated positively and the model was employed to detect zones of high channel fill facies probability that form bodies that are isolated or that terminate upward in pinchouts or are truncated by a fault our approach can prove helpful in improving general exploration workflows in similar settings

how old are young lunar craters 1 the accurate definition of the lunar cratering chronology is important for deriving absolute model ages across the lunar surface and throughout the solar system images from the lunar reconnaissance orbiter narrow angle cameras and wide angle camera and the selene kaguya terrain camera provide new opportunities to investigate crater size frequency distributions csfds on individual geological units at lunar impact craters we report new csfd measurements for the copernican aged craters north ray tycho and copernicus which are crucial anchor points for the lunar cratering chronology we also discuss possible reasons for an age discrepancy observed between the impact melt and ejecta units our csfds for north ray and tycho crater ejecta deposits are consistent with earlier measurements however for copernicus crater and one of its rays we find significantly lower cumulative crater frequencies than previous studies our new results for copernicus crater fit the existing lunar absolute chronologies significantly better than the previous counts our derived model ages of the ejecta blankets of north ray tycho and copernicus agree well with radiometric and exposure ages of the apollo 16 17 and 12 landing sites respectively and are generally consistent with a constant impact rate over the last 3 ga however small variations of the impact rate cannot be resolved in our data and require further investigations

cooling fractures in impact melt deposits on the moon and mercury implications for cooling solely by thermal radiation we study the distribution morphology and geometrical properties of fractures in several young impact melt deposits on the moon and mercury and the ways that these fractures may form from cooling by thermal radiation in each impact melt complex the topography of the underlying terrain determines the orientation of cooling fractures such that interior fractures that formed in the relatively thick interior areas of the melt unit are wider and have a larger spacing than marginal fractures that formed in the relatively thin areas near the unit s margins solid debris entrained in molten deposits provides prefracture flaws that can seed cooling fractures but too much solid debris prevents cooling fractures from growing to macroscopic sizes the appearance of subparallel fractures is mainly caused by subsidence of the deposits during the process of cooling and solidification tensile stresses caused by thermal radiation are large enough to initiate cooling fractures on both the moon and mercury which may represent the initial stage of columnar joints formation but the cooling rate caused solely by thermal radiation is not large enough to form well organized columnar joints that feature polygonal colonnades we therefore propose that thermal conduction and convection are the major contributors in the formation of columnar joints on planetary bodies

occurrence and mechanisms of impact melt emplacement at small lunar craters abstract using observations from the lunar reconnaissance orbiter camera lroc we assess the frequency and occurrence of impact melt at simple craters less than 5 km in diameter nine hundred and fifty fresh randomly distributed impact craters were identified for study based on their maturity albedo and preservation state the occurrence frequency and distribution of impact melt deposits associated with these craters particularly ponded melt and lobate flows are diagnostic of melt emplacement mechanisms like larger craters those smaller than a few kilometers in diameter often exhibit ponded melt on the crater floor as well as lobate flows near the crater rim crest the morphologies of these deposits suggest gravity driven flow while the melt was molten impact melt deposits emplaced as veneers and sprays thin layers of ejecta that drape other crater materials indicate deposition late in the cratering process the deposits of fine sprays are particularly sensitive to degradation exterior melt deposits found near the rims of a few dozen craters are distributed asymmetrically around the crater and are rare at craters less than 2 km in diameter pre existing topography plays a role in the occurrence and distribution of these melt deposits particularly for craters smaller than 1 km in diameter but does not account for all observed asymmetries in impact melt distribution the observed relative abundance and frequency of ponded melt and flows in and around simple lunar craters increases with crater diameter as was previously predicted from models however impact melt deposits are found more commonly at simple lunar craters i e those less than a few kilometers in diameter than previously expected ponded melt deposits are observed in roughly 15 of fresh craters smaller than 300 m in diameter and 80 of fresh craters between 600 m and 5 km in diameter furthermore melt deposits are observed at roughly twice as many non mare craters than at mare craters we infer that the distributions and occurrences of impact melt are strongly influenced by impact velocity and angle target porosity pre existing topography and degradation additionally areally small and volumetrically thin melt deposits are sensitive to mixing with solid debris and or burial during the modification stage of impact cratering as well as post cratering degradation thus the production of melt at craters less than 800 m in diameter is likely greater than inferred from the present occurrence of melt deposits which is rapidly affected by ongoing degradation processes

sequential development of selected pyrenean thrust faults new mapping structural analysis and magnetostratigraphy reveal a polyphase deformational history at the leading edge of the spanish pyrenean foreland fold and thrust belt the present structural architecture is the consequence of three discrete periods of deformation map relationships between four syntectonic units and major structures provide tight geometric and age constraints for each deformational period d1 55 to 42 ma d2 30 1 to 28 0 ma d3 27 9 to 25 8 ma most of the shortening in the area accumulated during d2 thrusting at rates which varied from 0 7 mm y 1 to 2 8 mm y 1 along strike from northwest to southeast respectively removal of d2 and d3 displacement on thrust faults restores folds formed during d1 a sequential kinematic history during which an individual structure accommodates shortening by folding tightening of the fold and subsequent truncation by thrust faulting is inferred sequential restoration of three serial cross sections demonstrates that nearly every structure active during d1 was also active during d2 distributed deformation characterizes the temporal and spatial pattern on all time scales from structures active during each individual deformational period to the long term history encompassed by the total deformation

incorporating nutrients as a limiting factor in carbonate modelling abstract nowadays the use of process based numerical models to predict facies distribution and stratal architecture constitutes an essential tool in sedimentary basin analysis one of these models the simsafadim clastic program simulates clastic transport and sedimentation in three dimensions together with autochthonous marine carbonate production in this code carbonate modelling mainly follows predator prey relationships among species associations based on lotka volterra equations the carbonate model also considers other environmental factors such as the presence of siliciclastic sediments and carbonate mud in suspension and water depth although these parameters are important carbonate producers are largely conditioned by other variables which have to be taken into account in order to obtain a more realistic approach in this contribution nutrient availability is added as a new limiting environmental parameter which exerts control over carbonate producing organisms a synthetic sample experiment is used to show that inclusion of nutrient availability is critical to reproduce carbonate lithofacies heterogeneity in a more accurate temporal and spatial disposition as a function of trophic resources

constraints on the recent rate of lunar ejecta breakdown and implications for crater ages we present a new empirical constraint on the rate of breakdown of large ejecta blocks on the moon based on observations from the lunar reconnaissance orbiter lro diviner thermal radiometer we find that the rockiness of fresh crater ejecta can be quantified using the diviner derived rock abundance data set and we present a strong inverse correlation between the 95 th percentile value of the ejecta rock abundance ra 95 5 and crater age for nine craters with published model ages derived from crater counts on their continuous ejecta ra 95 5 decreases with crater age as age m y 0 46 this result implies shorter rock survival times than predicted based on downward extrapolation of 100 m crater size frequency distributions and represents a new empirical constraint on the rate of comminution of large rocks not previously analyzed experimentally or through direct observation in addition our result provides a new method for dating young lunar craters

gld100 the near global lunar 100 m raster dtm from lroc wac stereo image data 1 we derived near global lunar topography from stereo image data acquired by the wide angle camera wac of the lunar reconnaissance orbiter camera lroc system from polar orbit tracks the lroc wac provides image data with a mean ground resolution at nadir of 75 m pixel with substantial cross track stereo overlap wac stereo images from the one year nominal mission and the first months of the science mission phase are combined to produce a near global digital terrain model dtm with a pixel spacing of 100 m the global lunar dtm 100 m or gld100 it covers 79 s to 79 n latitudes 98 2 of the entire lunar surface we compare the gld100 with results from previous stereo and altimetry based products particularly with the lunar orbiter laser altimeter lola altimetry which is the current topographic reference for the moon we describe typical characteristics of the gld100 and based upon the comparison to the lola data set assess its vertical and lateral resolution and accuracy we conclude that the introduced first version of the stereo based gld100 is a valuable topographic representation of the lunar surface complementary to the lola altimetry data set further improvements can be expected from continuative investigations

geology and stratigraphy of king crater lunar farside abstract clementine and photographic data sets have been used to investigate the crustal stratigraphy and geology of king crater on the lunar farside 120 e 5 5 n pre existing topographic regimes or stress fields dominate many structures in the crater which has excavated materials from depths of up to 14 km the upper crust in the area is noritic anorthosite grading to a more anorthositic signature with depth a possible batholithic intrusion is also present in a 15 km wide band extending from the southern crater floor to at least 50 km north of king and from near surface levels down to at least the excavation depth of the crater it is generally feldspathic but is cut by mafic dykes now visible in the north wall king also shows evidence for the presence of a cryptomare exposed in regions of the peaks and in dark halo craters within the ejecta blanket localized olivine bearing mineralogies are observed on the central peaks suggesting isolated pockets of troctolitic mineralogies to have been present at 8 to 14 km depths copious volumes of crystalline melt produced from the impact event cover king s floor to a maximum thickness of 30 60 m and have pooled in a number of natural depressions outside of the main crater the main pool in the pre existing a1 tusi crater has a minimum depth of 150 m domes on the crater floor are verified as nonvolcanic in origin and did not act as a source for any of the lava like materials in king

new morphological mapping and interpretation of ejecta deposits from orientale basin on the moon abstract orientale basin is one of the youngest and best preserved multi ring impact basins in the solar system the structure is 950 km across and is located on the western edge of the nearside of the moon the interior of the basin which possesses three distinct rings and a post impact mare fill has been studied extensively using modern high resolution datasets exterior to these rings orientale has an extensive ejecta blanket that extends out radially for at least 800 km from the basin rim in all directions and covers portions of both the nearside and farside of the moon these deposits known as the hevelius formation were first mapped using photographic data from the lunar orbiter iv probe in this study we map in detail the morphology of each distinct facies observed within the orientale ejecta blanket using high resolution lunar reconnaissance orbiter lro wide angle camera wac and narrow angle camera nac images and lunar orbiter laser altimeter lola elevation data we identified 5 unique facies within the ejecta blanket facies a is identified as a region of hummocky plains located in a low lying topographic region between the outer rook and cordillera rings this facies is interpreted to be a mix of crater derived impact melt and km scale blocks of ballistic ejecta and host rock broken up during the modification stage and formation of the cordillera ring facies b is an inner facies marked by radial grooves extending outward from the direction of the basin center this facies is interpreted as the continuous ballistic ejecta blanket facies c consists of inner and outer groupings of flat smooth surfaced deposits isolated in local topographic lows facies d displays characteristic sinuous ridges and lobate extensions facies c and d are interpreted to be impact melt rich materials which manifest as flows and ponds our observations suggest that these facies were emplaced subsequent to the ballistic ejecta blanket most likely during the modification stage of crater formation and flowed and ponded in topographically low lying regions facies e consists of distinct crater chains emanating radially from the basin center and extending from 700 to 1000 km from the center of orientale this facies is considered to be chains of secondary craters formed from large blocks of ballistic ejecta our mapping effort shows that the individual ejecta facies were influenced and controlled to varying degrees by pre existing slopes and topography at the basin scale the overall downslope direction toward the lunar lowlands to the east and southeast of the basin center resulted in large impact melt flows 100 s of kilometers in length while the regional upslope trends in the west and northwest inhibited the development of extensive impact melt flows on a smaller scale it can be observed that ground hugging ejecta collected behind and flowed around high topographic obstacles while diverting into topographic low regions e g around uplifted pre existing crater rims but down into pre existing crater floors the dispersion of the various ejecta facies mapped here also indicates both a direction and an angle for the impact event that formed orientale basin the bilateral distribution of both ballistic and impact melt rich ejecta deposits across a line running northeast southwest suggests the impact occurred from the northeast toward the southwest careful mapping of the secondary impact crater chains facies e shows the development of a forbidden zone lacking these impacts to the northeast as well as a concentration of the longest secondary crater chains to the northwest and southeast perpendicular to the aforementioned line of bilateral ejecta distribution this distribution of secondary impact craters contrasts with the circularity of the basin and suggests that orientale basin was formed by 25 45 impact from the northeast

origin of discrepancies between crater size frequency distributions of coeval lunar geologic units via target property contrasts abstract recent work on dating copernican aged craters using lunar reconnaissance orbiter lro camera data re encountered a curious discrepancy in crater size frequency distribution csfd measurements that was observed but not understood during the apollo era for example at tycho copernicus and aristarchus craters csfds of impact melt deposits give significantly younger relative and absolute model ages amas than impact ejecta blankets although these two units formed during one impact event and would ideally yield coeval ages at the resolution of the csfd technique we investigated the effects of contrasting target properties on csfds and their resultant relative and absolute model ages for coeval lunar impact melt and ejecta units we counted craters with diameters through the transition from strength to gravity scaling on two large impact melt deposits at tycho and king craters and we used pi group scaling calculations to model the effects of differing target properties on final crater diameters for five different theoretical lunar targets the new csfd for the large king crater melt pond bridges the gap between the discrepant csfds within a single geologic unit thus the observed trends in the impact melt csfds support the occurrence of target property effects rather than self secondary and or field secondary contamination the csfds generated from the pi group scaling calculations show that targets with higher density and effective strength yield smaller crater diameters than weaker targets such that the relative ages of the former are lower relative to the latter consequently coeval impact melt and ejecta units will have discrepant apparent ages target property differences also affect the resulting slope of the csfd with stronger targets exhibiting shallower slopes so that the final crater diameters may differ more greatly at smaller diameters besides their application to age dating the csfds may provide additional information about the characteristics of the target for example the transition diameter from strength to gravity scaling could provide a tool for investigating the relative strengths of different geologic units the magnitude of the offset between the impact melt and ejecta isochrons may also provide information about the relative target properties and or exposure degradation ages of the two units robotic or human sampling of coeval units on the moon could provide a direct test of the importance and magnitude of target property effects on csfds

dating very young planetary surfaces from crater statistics a review of issues and challenges determining the ages of young planetary surfaces relies on using populations of small often sub km diameter impact craters due to the higher frequency at which they form smaller craters however can be less reliable for estimating ages as their size frequency distribution is more susceptible to alteration with debate as to whether they should be used at all with the current plethora of meter scale resolution images acquired of the lunar and martian surfaces small craters have been widely used to derive model ages to establish the temporal relation of recent geologic events in this review paper we discuss the many factors that make smaller craters particularly challenging to use and should be taken into consideration when crater counts are confined to small crater diameters establishing confidence in a model age ultimately requires an understanding of the geologic context of the surface being dated as reliability can vary considerably and limitations of the dating technique should be considered in applying ages to any geologic interpretation

cratering on mars with almost no atmosphere or volatiles pangboche crater pangboche crater 17 2 n 226 7 e 10 4 km dia lies close to the summit of olympus mons volcano mars at an elevation of 20 9 km above the datum given a scale height of 11 1 km for the atmosphere this relatively large fresh crater most likely formed at an atmospheric pressure 1 mbar in essentially volatile free young lava flows detailed analysis of pangboche crater from high resolution imaging science experiment hirise and context camera ctx images reveals that volatile related features e g fluidized ejecta layers and pitted floor material are absent in contrast abundant impact melt occurs on the floor inner walls and rim of the crater and there is an extensive field of secondary craters that extend up to approximately 45 km from the rim crest all of these attributes argue that it was the absence of volatiles in the target rocks at the time of crater formation rather than the thin atmosphere which had a controlling influence on crater morphology digital elevation data derived from the ctx images reveal that pangboche crater has a depth of about 954 m depth diameter approximately 0 092 and that uplifted target rocks comprise about 58 of the relief of the 180 m high north rim as the target material comprised a sequence of layered lava flows pangboche crater may well represent the best crater on mars for direct comparison with craters formed on the moon permitting variations in gravitational effects to be investigated or on mercury allowing the role of the atmosphere to be studied

differential melt scaling for oblique impacts on terrestrial planets abstract analytical estimates of melt volumes produced by a given projectile and contained in a given impact crater are derived as a function of impact velocity impact angle planetary gravity target and projectile densities and specific internal energy of melting applications to impact events and impact craters on the earth moon and mars are demonstrated and discussed the most probable oblique impact 45 produces 1 6 times less melt volume than a vertical impact and 1 6 and 3 7 times more melt volume than impacts with 30 and 15 trajectories respectively the melt volume for a particular crater diameter increases with planetary gravity so a crater on earth should have more melt than similar size craters on mars and the moon the melt volume for a particular projectile diameter does not depend on gravity but has a strong dependence on impact velocity so the melt generated by a given projectile on the moon is significantly larger than on mars higher surface temperatures and geothermal gradients increase melt production as do lower energies of melting collectively the results imply thinner central melt sheets and a smaller proportion of melt particles in impact breccias on the moon and mars than on earth these effects are illustrated in a comparison of the chicxulub crater on earth linked to the cretaceous tertiary mass extinction gusev crater on mars where the mars exploration rover spirit landed and tsiolkovsky crater on the moon the results are comparable to those obtained from field and spacecraft observations other analytical expressions and hydrocode simulations

igneous rocks formed by hypervelocity impact abstract igneous rocks are the primary building blocks of planetary crusts most igneous rocks originate via decompression melting and or wet melting of protolith lithologies within planetary interiors and their classification and compositional petrographic and textural characteristics are well studied as our exploration of the solar system continues so too does the inventory of intrusive and extrusive igneous rocks settings and processes the results of planetary exploration have also clearly demonstrated that impact cratering is a ubiquitous geological process that has affected and will continue to affect all planetary objects with a solid surface whether that be rock or ice it is now recognized that the production of igneous rocks is a fundamental outcome of hypervelocity impact the goal of this review is to provide an up to date synthesis of our knowledge and understanding of igneous rocks formed by hypervelocity impact following a brief overview of the basics of the impact process we describe how and why melts are generated during impact events and how impact melting differs from endogenic igneous processes while the process may differ we show that the products of hypervelocity impact can share close similarities with volcanic and shallow intrusive igneous rocks of endogenic origin such impact melt rocks as they are termed can display lobate margins and cooling cracks columnar joints and at the hand specimen and microscopic scale such rocks can display mineral textures that are typical of volcanic rocks such as quench crystallites ophitic porphyritic as well as features such as vesicles flow textures and so on historically these similarities led to the misidentification of some igneous rocks now known to be impact melt rocks as being of endogenic origin this raises the question as to how to distinguish between an impact versus an endogenic origin for igneous like rocks on other planetary bodies where fieldwork and sample analysis may not be possible and all that may be available is remote sensing data while the interpretation of some impact melt rocks may be relatively straightforward e g for clast rich varieties and those with clear projectile contamination we conclude that distinguishing between impact and endogenic igneous rocks is a non trivial task that ultimately may require sample investigation and analysis to be conducted caution is therefore urged in the interpretation of igneous rocks on planetary surfaces

geology of the king crater region new insights into impact melt dynamics on the moon 1 new geologic sketch maps and digital elevation models for king crater and the surrounding lunar farside highlands were created from lunar reconnaissance orbiter camera lroc wide angle camera wac and narrow angle camera nac images nac images reveal that high volume impact melt accumulations exhibit evidence of dynamic processes during and following emplacement that resulted in downwarped zones and other morphologic anomalies visible at the 50 cm pixel scale among the most significant of these forms are negative relief features some of which may represent evidence for near surface caverns offering points of access to subsurface environments and possible shelter from surface hazards other negative relief features may represent regions of extension and separation in response to possible subsurface drainage together with isostatic readjustments contraction and or compaction in the cooling impact melt crater counts on the continuous ejecta blanket suggest a late eratosthenian to copernican age for king crater which is older than the estimate of young 1977 but consistent with those of others

paleo oceanographic utility of oxygen isotopic measurements on planktic foraminifera indian ocean core top evidence abstract isotopic analyses have been performed on narrow size ranges of seven species of planktic foraminifera picked from 43 core top locations in the indian ocean comparison of observed 18o for each species with calculated profiles of equilibrium 18o at each location yield three distinct depth habitat preferences for surface dwelling species globigerinoides ruber and globigerina bulloides observed oxygen isotopic compositions are in close agreement with the seasonal range of calculated 18o for calcite precipitated in surface waters observed 18o values for orbulina universa neogloboquadrina dutertrei and pulleniatina obliquiloculata are consistently enriched relative to calculated 18o for surface conditions in the northern indian ocean test precipitation for o universa n dutertrei and p obliquiloculata occurs over a narrow range of temperature 22 c 24 c with no systematic relationship with sea water t in contrast globorotalia inflata and g truncatulinoides observed 18o apparently reflect temperature and salinity variation along the 26 8 t isopycnal

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

numerical modelling of syntectonic subaqueous sedimentation the effect of normal faulting and a relay ramp on sediment dispersal abstract relay ramps are common in extensional settings and play a significant role in sediment dispersal as they control sedimentary pathways unlike for subaerial settings the impact of subaqueous relay ramps on sediment dispersal and clastic sedimentation is less studied in these subaqueous cases numerical approximations could be a good approach to understand syntectonic sedimentation considering this a numerical model is used to study the sedimentary infill in an extensional basin specifically related to a relay ramp system the study is carried out using a novel program that merges a discrete element code for tectonic deformation and a stratigraphic modelling code for sedimentation to perform a test study two configurations are designed with one normal fault and with two overlapping normal faults linked by a relay ramp to these initial configurations three different deformation velocities 10 5 and 2 cm y are applied in dip slip direction these scenarios are considered as initially submerged the same incoming amount of three different terrigenous sediments is considered in all the experiments these sediments are transported basinward in suspension by processes of advection dispersion and diffusion finally these examples also include four different boundary conditions for the sedimentary model which define the source area location for the incoming water and sediment results show that the source area location in relation to the available accommodation space plays the major role in the distribution of different sediment types into the basin nonetheless when the source area for water and sediment is defined as regional and parallel to the fault the grain size distribution obtained by the two overlapping faults configuration has clear asymmetries when compared with the ones obtained by one fault configurations therefore the different extensional experiments allow concluding that the relay ramp configuration can play an important role in the distribution of the sediments into the basin

oxygen isotope evidence for a stronger winter monsoon current during the last glaciation a variety of palaeoclimate data from the northern indian ocean has shown that the asian summer monsoon was weaker during the last glacial maximum 18 000 years ago than it is today1 5 it has also been inferred from these data that the winter monsoon was stronger at that time5 here we present evidence that the transport of low salinity water from the bay of bengal to the arabian sea caused by the winter monsoon6 was higher during the last glacial maximum this inference is based on a negative excursion up to about 1 in magnitude in the oxygen isotope ratios of three planktonic foraminiferal species detected in a sediment core from the arabian sea by high resolution 1 2 cm sampling our results place an upper limit of about 4 000 years on the length of time during which the winter monsoon was stronger than today

geologic map of the northern hemisphere of vesta based on dawn framing camera fc images abstract the dawn framing camera fc has imaged the northern hemisphere of the asteroid 4 vesta at high spatial resolution and coverage this study represents the first investigation of the overall geology of the northern hemisphere 22 90 n quadrangles av 1 2 3 4 and 5 using these unique dawn mission observations we have compiled a morphologic map and performed crater size frequency distribution csfd measurements to date the geologic units the hemisphere is characterized by a heavily cratered surface with a few highly subdued basins up to 200 km in diameter the most widespread unit is a plateau cratered highland unit similar to although of lower elevation than the equatorial vestalia terra plateau large scale troughs and ridges have regionally affected the surface between 180 e and 270 e these tectonic features are well developed and related to the south pole veneneia impact saturnalia fossae trough unit elsewhere on the hemisphere they are rare and subdued saturnalia fossae cratered unit in these pre rheasilvia units we observed an unexpectedly high frequency of impact craters up to 10 km in diameter whose formation could in part be related to the rheasilvia basin forming event the rheasilvia impact has potentially affected the northern hemisphere also with s n small scale lineations but without covering it with an ejecta blanket post rheasilvia impact craters are small

automatic calibration of stratigraphic forward models for predicting reservoir presence in exploration understanding and predicting reservoir presence and characteristics at regional to basin scales is important for evaluating risk and uncertainty in hydrocarbon exploration simulating reservoir distribution within a basin by a stratigraphic forward model enables the integration of available prior information with fundamental geologic processes embedded in the numerical model stratigraphic forward model predictions can be significantly improved by calibrating the models to independent constraints such as thicknesses from seismic or well data a three dimensional basin scale stratigraphic forward modeling tool is coupled with an inversion algorithm the inversion algorithm is a modification of the neighborhood algorithm a type of genetic algorithm which is designed to sample complex multimodal objective functions and is parallelized on computer clusters to accelerate convergence the process generates a set of representative geological models that are consistent with prior ranges for uncertain parameters calibration constraints and associated tolerance thresholds the workflow is first demonstrated on two data sets a synthetic example based on a clastic passive margin and a real hydrocarbon exploration example for slope and basin floor stratigraphic traps in the neocomian lower cretaceous of the west siberian basin the analysis of calibrated models provides constraints on stratigraphic controls and allows prediction of locations with higher potential to develop stratigraphic traps these locations are related to complex interactions between paleobathymetry subsidence eustatic fluctuations characteristics of sediment input sources and sediment transport parameters results show the potential of stratigraphic forward modeling combined with inverse methods as an additional tool to support conventional play based exploration and reservoir presence prediction

ages of mare basalts on the lunar nearside the chronology of lunar volcanism is based on radiometric ages determined from apollo and luna landing site samples regional stratigraphic relationships and crater degradation and size frequency distribution data for units largely defined prior to the end of the apollo program here we report on new crater size frequency distribution data for 139 spectrally and morphologically defined basalt units which are exposed in six nearside impact basins australe tranquillitatis humboldtianum humorum serenitatis and imbrium crater size frequency distribution measurements are a statistically robust and accurate method to derive absolute model ages of unsampled regions of the moon compared to crater degradation ages crater size frequency ages performed on spectrally defined units offer significant improvements in accuracy our investigation showed that 1 in the investigated basins lunar volcanism was active for at least 1 5 2 0 b y starting at about 3 9 4 0 b y and ceasing at 2 0 b y 2 most basalts erupted during the late imbrian period at about 3 6 3 8 b y 3 significantly fewer basalts were emplaced during the eratosthenian period 4 basalts of copernican age were not found in any of the investigated basins 5 lunar basin filling volcanism probably started within 100 m y after the formation of the individual basins we also assessed the relationship between impact basin age and the history of mare basalt emplacement in these basins we found that 1 in all pre nectarian basins australe and tranquillitatis as well as in the humboldtianum basin which is of nectarian age the distribution of surface ages is clearly dominated by only a single peak in the number of erupted units at 3 6 3 8 b y 2 in the younger basins humorum serenitatis and imbrium a second peak at 3 3 3 5 b y is observed 3 basalt eruptions younger than 2 6 b y occur only intermittently and 4 in the youngest basins serenitatis and imbrium we see an extended period of active basin filling volcanism 1 5 1 6 b y which is 500 m y longer than in the australe and humorum and even 1 0 b y longer than in tranquillitatis and humboldtianum

limnogeology ancient and modern tales of an evolving earth between the late seventies and the present day sedimentology and basin research of lakes in the geologic record expanded from a marginal academic curiosity into a spectacular groundbreaking area of multidisciplinary research few earth science disciplines have experienced such greatprogressin methodsandprinciplesin thelast three decadesasthe field of limnogeology economic interest in ancient lacustrine basins initially drove research recognizing lake environments as suppliers of natural resourcesranging from evaporiticsalts andbrines e g lithium raw materials i e limestones tufas clays and diatomites and fossil energy oil gas and coals with this focus the collection of highresolution high quality depositional records of ancient and recent lacustrine systems opened an epoch of continuous expansion of research and improved understanding of these records consequently recognition of the importance of lacustrine deposits as archives of past global changes on continents which are complementary to marine records has been growing research on lacustrine systems in a wide arrayoftectonicandclimaticsettingshasbeenchallengedbythevariety

imaging of lunar surface maturity the physical evolution of the lunar surface with exposure to the space environment is termed maturation and maturity is the degree to which a particular lunar soil possesses quantitative characteristics consistent with that exposure several quantitative measures or indices of maturity have been proposed and employed including the abundance of solar wind gas abundance of various types of agglutinates various measures of grain size and is feo among the changes attendant with space exposure are striking changes in the optical characteristics of soils mature lunar soils are dark red and exhibit reduced spectral contrast relative to immature soils this paper presents an optical maturity index that quantifies the spectral effects of maturation we show that this optical maturity index correlates with other maturity indices about as well as the accepted maturity indices correlate among themselves and is only weakly coupled to composition the modest correlations among maturity indices suggest important controls on individual maturity indices other than age uncorrelated variations in the rates of accumulation of individual indicators or variations in depths over which indicators are emplaced in addition to mixing these effects conspire to reduce the equivalence of maturity and duration of surface exposure optical maturity illustrates some of these effects showing that ejecta of large and small craters mature at different rates and that the interiors and ejecta of large craters exhibit systematically different optical maturities the same or analogous effects are likely to influence other maturity indices

the minimum confidence limit for diameters in crater counts abstract size frequency distribution i e sfd of impact craters are frequently used to study relative and absolute model ages for planetary surfaces it is well accepted that crater statistics are incomplete and crater recognition is inaccurate at diameter ranges approaching a few pixels of the images used but there is no benchmark about the minimum confidence limit for diameter dmin here we resolve this problem by comparing the sfd of each studied crater population using a same image dataset that has been down sampled by different folds a systematical study of several different aged lunar crater populations using various image datasets found that crater statistics can be regarded as completed and crater rim identification can be regarded as accurate at diameters larger than about 10 pixels of the base images integrating other potential difficulties in crater counts e g illumination conditions personal biases topography roughness size of counting areas would indicate that 10 pixels should be considered as a conservative suggestion using 10 pixels as dmin could substantially enhance the reliability of crater counts especially for prevalent high resolution regional geological studies that employ populations of small craters

new insight into lunar impact melt mobility from the lro camera 1 the lunar reconnaissance orbiter camera lroc is systematically imaging impact melt deposits in and around lunar craters at meter and sub meter scales these images reveal that lunar impact melts although morphologically similar to terrestrial lava flows of similar size exhibit distinctive features e g erosional channels although generated in a single rapid event the post impact mobility and morphology of lunar impact melts is surprisingly complex we present evidence for multi stage influx of impact melt into flow lobes and crater floor ponds our volume and cooling time estimates for the post emplacement melt movements noted in lroc images suggest that new flows can emerge from melt ponds an extended time period after the impact event

extracting accurate and precise topography from lroc narrow angle camera stereo observations abstract the lunar reconnaissance orbiter camera lroc includes two identical narrow angle cameras nac that each provide 0 5 to 2 0 m scale images of the lunar surface although not designed as a stereo system lroc can acquire nac stereo observations over two or more orbits using at least one off nadir slew digital terrain models dtms are generated from sets of stereo images and registered to profiles from the lunar orbiter laser altimeter lola to improve absolute accuracy with current processing methods dtms have absolute accuracies better than the uncertainties of the lola profiles and relative vertical and horizontal precisions less than the pixel scale of the dtms 2 5 m we computed slope statistics from 81 highland and 31 mare dtms across a range of baselines for a baseline of 15 m the highland mean slope parameters are median 9 1 mean 11 0 standard deviation 7 0 for the mare the mean slope parameters are median 3 5 mean 4 9 standard deviation 4 5 the slope values for the highland terrain are steeper than previously reported likely due to a bias in targeting of the nac dtms toward higher relief features in the highland terrain overlapping dtms of single stereo sets were also combined to form larger area dtm mosaics that enable detailed characterization of large geomorphic features from one dtm mosaic we mapped a large viscous flow related to the orientale basin ejecta and estimated its thickness and volume to exceed 300 m and 500 km 3 respectively despite its 3 8 billion year age the flow still exhibits unconfined margin slopes above 30 in some cases exceeding the angle of repose consistent with deposition of material rich in impact melt we show that the nac stereo pairs and derived dtms represent an invaluable tool for science and exploration purposes at this date about 2 of the lunar surface is imaged in high resolution stereo and continued acquisition of stereo observations will serve to strengthen our knowledge of the moon and geologic processes that occur across all of the terrestrial planets

geomorphologic mapping of the lunar crater tycho and its impact melt deposits abstract using selene kaguya terrain camera and lunar reconnaissance orbiter camera lroc data we produced a new high resolution 10 m pixel geomorphological and impact melt distribution map for the lunar crater tycho the distal ejecta blanket and crater rays were investigated using lroc wide angle camera wac data 100 m pixel while the fine scale morphologies of individual units were documented using high resolution 0 5 m pixel lroc narrow angle camera nac frames in particular tycho shows a large coherent melt sheet on the crater floor melt pools and flows along the terraced walls and melt pools on the continuous ejecta blanket the crater floor of tycho exhibits three distinct units distinguishable by their elevation and hummocky surface morphology the distribution of impact melt pools and ejecta as well as topographic asymmetries support the formation of tycho as an oblique impact from the w sw the asymmetric ejecta blanket significantly reduced melt emplacement uprange and the depressed uprange crater rim at tycho suggest an impact angle of 25 45

estimating accumulation rates and physical properties of sediment behind a dam englebright lake yuba river northern california 1 studies of reservoir sedimentation are vital to understanding scientific and management issues related to watershed sediment budgets depositional processes reservoir operations and dam decommissioning here we quantify the mass organic content and grain size distribution of a reservoir deposit in northern california by two methods of extrapolating measurements of sediment physical properties from cores to the entire volume of impounded material englebright dam completed in 1940 is located on the yuba river in the sierra nevada foothills a research program is underway to assess the feasibility of introducing wild anadromous fish species to the river upstream of the dam possible management scenarios include removing or lowering the dam which could cause downstream transport of stored sediment in 2001 the volume of sediments deposited behind englebright dam occupied 25 5 of the original reservoir capacity the physical properties of this deposit were calculated using data from a coring campaign that sampled the entire reservoir sediment thickness 6 32 m at six locations in the downstream 3 4 of the reservoir as a result the sediment in the downstream part of the reservoir is well characterized but in the coarse upstream part of the reservoir only surficial sediments were sampled so calculations there are more uncertain extrapolation from one dimensional vertical sections of sediment sampled in cores to entire three dimensional volumes of the reservoir deposit is accomplished via two methods using assumptions of variable and constant layer thickness overall the two extrapolation methods yield nearly identical estimates of the mass of the reservoir deposit of 26 106 metric tons t of material of which 64 7 68 5 is sand and gravel over the 61 year reservoir history this corresponds to a maximum basin wide sediment yield of 340 t km2 yr assuming no contribution from upstream parts of the watershed impounded by other dams the uncertainties and limitations of the estimates of overall sediment quantities are discussed implications for watershed management and future reservoir sedimentation studies are also presented

evolution of early cenozoic marine temperatures the equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals late paleocene early eocene early middle eocene late eocene and early oligocene paleotemperatures are calculated using standard oxygen isotope temperature equations with adjustments to account for 1 variations in sea water 18o related to changes in global ice volume over time and 2 latitudinal gradients in surface water 18o these reconstructions indicate that sea surface temperatures sst of the southern oceans in the early eocene were as high as 15 c whereas temperatures during the late paleocene and early middle eocene reached maximum levels of 10 12 c by the late eocene and early oligocene high latitude sst had declined to 6 and 4 c respectively for most of the early paleogene low latitude sub tropical temperatures remained constant and well within the range of holocene temperatures 24 ndash 25 c but by the late eocene and early oligocene declined to values in the range of 18 to 22 c the late paleogene apparent decline in tropical temperatures however might be artificial because of dissolution of near surface foraminifera tests which biased sediment assemblages toward deeper dwelling foraminifera moreover according to recent plate reconstructions it appears that the majority of sites upon which the late eocene and early oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling global deepwater temperature on average paralleled southern ocean sst for most of the paleogene we speculate based on the overall timing and character of marine sea surface temperature variation during the paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high latitude warmth of the early eocene

morphodynamics of ebb tidal deltas a model approach abstract the results of 2dh numerical models of the frisian inlet located in the dutch wadden sea are discussed to gain further knowledge about the physical mechanisms causing the presence of both ebb tidal deltas and of channels and shoals in tide dominated inlet systems a hydrodynamic model extended with sediment transport formulations was used to verify earlier conceptual models that deal with ebb tidal delta characteristics the model does not confirm their hypothesis concerning the observed spatial asymmetry of ebb tidal deltas and suggests that long term morphological simulations are needed to understand this aspect furthermore the model indicates that the initial formation of the ebb tidal delta is mainly due to convergence of the tidally averaged sediment flux related to residual currents whilst the net sediment transport in the basin is mainly caused by tidal asymmetry a second model accounting for feedbacks between tidal motion and the erodible bottom was used to simulate the long term bathymetric evolution of the frisian inlet under fair weather conditions this model reproduces the gross characteristics of the observed morphology the presence of a double inlet system with two distinct ebb tidal deltas having different sizes and the presence of channels and shoals the role of the engelsmanplaat a consolidated shoal in the middle of the frisian inlet was not found to be crucial for the morphodynamic stability of this inlet system

small graben in the southeastern ejecta blanket of the lunar copernicus crater implications for recent shallow igneous intrusion on the moon abstract dozens of linear graben that are about 10 400 m wide and less than 1 km long are recognized in the southeastern continuous ejecta deposits of copernicus supporting that copernican aged tectonism has occurred on the moon fault geometry analysis suggests that the bounding faults of the graben have formed within the ejecta deposits the graben are exclusively located on a local high relief area but they are not formed by mass wasting because the topographic slope is substantially less than the repose angle of typical lunar materials and no other extensional structures are visible on similar high relief areas at the continuous ejecta deposits of copernicus the orientations of the graben all point to the center of copernicus but the topography of copernicus is little compensated after formation suggesting that the graben were not caused by possible crustal isostatic readjustment this graben system is one of the three examples on the moon that were interpreted to be caused by shallow igneous intrusions in the format of laccoliths the currently available grail gravity data have a lower spatial resolution than the size of the graben so the gravity data cannot resolve the hypothesized sub kilometer scale laccoliths beneath the graben while laccolith intrusion to a depth of about 80 m is required to explain the formation of this graben system the laccolith intrusion scenario is not consistent with the geological context of the graben a compressional structure is visible close to the graben system and their spatial configuration and similar preservation states are consistent with being generically related a close examination of the other two sets of graben that were also interpreted to have no associated compressional structures actually reveals spatially related lobate scarps and wrinkle ridges in the vicinity therefore shallow igneous intrusion is not plausible or necessary to explain to formation of copernican aged graben on the moon and they are most likely formed by the late stage global contraction of the moon

origin of large volume pseudotachylite in terrestrial impact structures large volume pseudotachylite bodies in impact structures are dike like and consist of angular and rounded wall rock fragments enveloped by a microcrystalline and sporadically glassy matrix that crystallized from a melt knowledge of the formation of pseudotachylite bodies is important for understanding mechanics of complex crater formation most current hypotheses of pseudotachylite formation inherently assume that fragmentation and melt generation occur during a single process based on the structure of pseudotachylite bodies at sudbury canada and vredefort south africa we show that these processes differ in time and space we demonstrate that the centimeter to kilometer scale bodies are effectively fragment and melt fi lled tension fractures that formed by differential rotation of target rock during cratering highly variable pseudotachylite characteristics can be accounted for by a single process i e drainage of initially superheated impact melt into tension fractures of the crater fl oor

simulating transport and deposition of clastic sediments in an elongate basin using the simsafadim clastic program the camarasa artificial lake case study ne spain abstract predicting facies distribution and the stratigraphic architecture of sedimentary basins by process oriented numerical models is nowadays an essential tool in geologic studies they constitute a new approach to predict the geologic heterogeneity and the spatial distribution of the diverse facies generated in a depositional system jointly with the distribution of the physical chemical and petrophysical characteristics of the sedimentary deposits in a quantitative way simsafadim clastic is a 3d process based forward numerical model for the simulation of clastic sediment transport and sedimentation in aquatic systems it simulates the physical process of clastic transport using the advective diffusive and dispersive terms of the transport equation and clastic sediment deposition as a result of a variety of processes the capabilities of simsafadim clastic have been confirmed through the application of the program to a large deep elongated artificial lake the camarasa reservoir in the noguera pallaresa river ne of spain simulation results yield sedimentation rates ranging from 0 04 to 0 09 cm yr 1 close to the dam and from 1 73 to 1 63 cm yr 1 in the upper reservoir section the sample experiment results match well with the observed transport pattern linked to the flow system in camarasa s reservoir near bottom water layer which transports more than 50 of the sediment that is supplied to the reservoir opening and closure of turbine gates and the basin geometry are the main controlling factors on the fluid flow and depositional pattern in the reservoir with a more diversified pattern obtained when an open boundary is defined however the resulting model also shows some limitations of the program as it does consider a stratified water column that is consistently observed in the reservoir refined modeling exercises of the type described in this paper are of potential application to predict and quantify sedimentation patterns allowing the implementation of efficient preservation measures against reservoir siltation

distribution formation mechanisms and significance of lunar pits abstract lunar reconnaissance orbiter camera images reveal the presence of steep walled pits in mare basalt n 8 impact melt deposits n 221 and highland terrain n 2 pits represent evidence of subsurface voids of unknown extents by analogy with terrestrial counterparts the voids associated with mare pits may extend for hundreds of meters to kilometers in length thereby providing extensive potential habitats and access to subsurface geology because of their small sizes relative to the local equilibrium crater diameters the mare pits are likely to be post flow features rather than volcanic skylights the impact melt pits are indirect evidence both of extensive subsurface movement of impact melt and of exploitable sublunarean voids due to the small sizes of pits mare highland and impact melt and the absolute ages of their host materials it is likely that most pits formed as secondary features

the lunar reconnaissance orbiter mission six years of science and exploration at the moon abstract since entering lunar orbit on june 23 2009 the lunar reconnaissance orbiter lro has made comprehensive measurements of the moon and its environment the seven lro instruments use a variety of primarily remote sensing techniques to obtain a unique set of observations these measurements provide new information regarding the physical properties of the lunar surface the lunar environment and the location of volatiles and other resources scientific interpretation of these observations improves our understanding of the geologic history of the moon its current state and what its history can tell us about the evolution of the solar system scientific results from lro observations overturned existing paradigms and deepened our appreciation of the complex nature of our nearest neighbor this paper summarizes the capabilities measurements and some of the science and exploration results of the first six years of the lro mission

a comparison of radiolarian and foraminiferal paleoecology in the southern indian ocean new evidence for the interhemispheric timing of climatic change the deglacial transition between oxygen isotope stages 6 and 5e about 127 000 yr b p is marked by both oxygen isotopic depletion and estimated sea surface temperature sst increase in two subantarctic indian ocean cores the data show synchroneity between warming of foraminifera based sst estimates and depletion of 18o but an earlier warming trend on the basis of radiolarian sst estimates these data have been previously interpreted to indicate that the high latitude southern ocean warms prior to significant melting of glacial age ice sheets comparison of core top assemblages with surface and subsurface conditions in the southern indian ocean reveals that 1 a three part foraminiferal zonation reflects the surface hydrographic regime with abrupt faunal transitions at two major fronts the subtropical convergence stc and the antarctic polar front apf and 2 a two part radiolarian zonation coincides with a two part subsurface hydrographic regime with an abrupt faunal transition corresponding to the southern terminus of subtropical lower water stlw between the stc and the apf it is suggested that shifts of these surface and subsurface regimes are recorded by these foraminiferal and radiolarian assemblages in this interpretation the observed lead of radiolarian sst with respect to 18o indicates an early response to a southward shift of stlw while the later foraminiferal sst warming indicates a southward shift of the stc thus the origin of the southern hemisphere sst lead may be related to stlw which emanates from the subtropical gyres rather than the polar regions

stratigraphic simulation of sedimentary basins concepts and calibration a two dimensional stratigraphic simulation program based on semiempirical algorithms has been successfully applied to clastic carbonate and mixed clastic carbonate depositional regimes the program may be used to predict reservoir distribution to constrain interpretations of well and seismic data to test exploration scenarios in frontier basins and to evaluate the fundamental controls on basin stratigraphy applications to seismic and well log data sets from main pass u s gulf coast offshore sarawak malaysia and the baltimore canyon u s east coast demonstrate that the program simulates stratigraphy on a basin wide scale as well as on the scale of individual prospects the main pass section is an offlapping sequence of neogene clastics the model simulates 17 m y of geologic history at a 200 000 yr resolution and reproduces gross basin geometry major sequence boundaries depth and location of nearshore marine sands intervals of sediment bypass into deep water shelf margin positions and paleobathymetry three neogene carbonate buildups of central luconia offshore sarawak malaysia were simulated using a sea level history optimized to reproduce the carbonate growth anatomy the model reproduced observed seismic reflection geometries and transgressive aggradational progradational retrogradational and subaerial exposure phases the program has also simulated jurassic pleistocene basin and stratigraphic sequence geometries and mixed clastic carbonate facies distribution along a 300 km regional dip line of the baltimore canyon trough modeled features of interest include a progradational middle jurassic carbonate margin punctuated by clastic deposition during sea level lowstands and a late jurassic early cretaceous aggradational carbonate margin culminating in the development and subsequent drowning of isolated carbonate buildups simulated bathymetries facies relations and subaerial exposure surfaces for the early cretaceous aggradation margin are consistent with detailed petrographic paleontologic and seismic stratigraphic interpretations

sediment type distribution in reservoirs sediment source versus morphometry bottom sediments were collected from seven texas reservoirs to assess the spatial distribution of sediment types in reservoirs the sediment samples were analyzed for water content organic content and grain size distributions the reservoirs are characterized by distinct water content patterns referred to in this paper as types i ii and iii that reflect the lithologic units comprising their drainage area the water content organic content and percent mud decreases from type i shale marl through type ii limestone marl sandstone to type iii granite gneiss schist sandstone reservoirs reported elemental concentrations in the reservoir sediments are consistent with concentrations in the dominant rocks within their drainage area while water depth accounts for part of the spatial distribution sediment source explains the overall distribution of sediment types coarse grained source rocks multiple source rocks and multiple tributaries which input sediment at different points contribute to an inconsistent sediment type distribution depending on the sediment source sand and gravel size sediments are present in the deeper regions of some reservoirs this disrupts the classical morphometry water depth slope controlled sediment distribution pattern coarser sediments in shallower regions and finer sediments in deeper regions of natural lakes thus the location of tributaries and the type of sediments they carry are the dominant factors that control the sediment type distribution in reservoirs

the structural stability of lunar lava tubes abstract mounting evidence from the selene lro and grail spacecraft suggests the presence of vacant lava tubes under the surface of the moon grail evidence in particular suggests that some may be more than a kilometer in width such large sublunarean structures would be of great benefit to future human exploration of the moon providing shelter from the harsh environment at the surface but could empty lava tubes of this size be stable under lunar conditions and what is the largest size at which they could remain structurally sound we address these questions by creating elasto plastic finite element models of lava tubes using the abaqus modeling software and examining where there is local material failure in the tube s roof we assess the strength of the rock body using the geological strength index method with values appropriate to the moon assign it a basaltic density derived from a modern re analysis of lunar samples and assume a 3 1 width to height ratio for the lava tube our results show that the stability of a lava tube depends on its width its roof thickness and whether the rock comprising the structure begins in a lithostatic or poisson stress state with a roof 2 m thick lava tubes a kilometer or more in width can remain stable supporting inferences from grail observations the theoretical maximum size of a lunar lava tube depends on a variety of factors but given sufficient burial depth 500 m and an initial lithostatic stress state our results show that lava tubes up to 5 km wide may be able to remain structurally stable

sr ca u ca and δ18o records in recent massive corals from bermuda relationships with sea surface temperature abstract high resolution records of sr ca u ca ratios and 18o have been obtained in two recent colonies of massive corals diploria labyrinthiformis from bermuda the three geochemical proxies display regular seasonal variations and are well correlated with each other however some important discrepancies are observed between the two colonies the average seasonal variations of the three geochemical proxies are lower by almost 50 in one of the profiles where the seasonal oscillation also displays a strong asymmetry with narrower summer maxima different calculations are discussed for calibrating sr ca and 18o with sea surface temperatures sst we show that the method using only temperature minima and maxima is slightly more accurate and is also more reliable our results from bermuda corals confirm that the temperature dependency of sr ca u ca and 18o is species dependent as previously shown by others and that vital effects are clearly involved in the geochemical incorporation of trace elements in the coral skeleton finally a simple model involving seasonal variation of the growth rate and a kinetic fractionation related to growth rate is presented to explain the differences between the two bermuda colonies it is shown that these factors may prevent corals from recording the complete temperature seasonality and could be the cause for the discrepancies observed between profiles resulting in significant biases of the sst reconstructions