recognition of 18β h oleanane in several crudes and tertiary upper cretaceous sediments definition of a new maturity parameter abstract ekweozor et al chem geol 27 11 28 and 29 37 first discovered an unknown compound with a gc retention time very close to that of the 18 h olenane peak in oils and tertiary sediments of the nigerian delta this compound was called j several authors wang et al advances in organic geochemistry 1981 pp 108 113 wiley chichester 1983 schoelle et al ibid pp 156 163 reported the occurrence of 18 h oleanane without underlying the presence of j because of their coelution in this study the presence of j has been confirmed in more than 150 rock extracts and 19 oils from different countries and is identified as the 18 h oleanane by comparison to retention time and mass spectrum and by its coelution with an authentic standard apart from tertiary sediments the 18 h and 18 h oleananes have also been found in upper cretaceous sediments which extends the occurrence of these compounds back in age a maturity correlation has been found between the relative concentration of 18 h oleanane and 18 h oleanane in fact an increase in the 18 h 18 h oleanane ratio has been observed with increasing depth in several wells the 18 h 18 h oleanane ratio has been correlated with other classical maturity parameters i e ts tm ro and tmax

antarctic lunar meteorites yamato 793169 asuka 881757 mil 05035 and met 01210 yamm launch pairing and possible cryptomare origin abstract the antarctic lunar meteorite meteorite hills met 01210 is a polymict regolith breccia dominantly composed of mare basalt components one relatively large 2 7 4 7 mm basalt clast in met 01210 met basalt shows remarkable mineralogical similarities to the lunar meteorite crystalline mare basalts yamato y 793169 asuka a 881757 and miller range mil 05035 all four basalts have similar rock texture mineral assemblage mineral composition pyroxene crystallization trend and pyroxene exsolution lamellae the estimated tio 2 contents 2 0 wt of the met basalt and mil 05035 are close to the bulk rock tio 2 contents of y 793169 and a 881757 these similarities suggest that y 793169 a 881757 mil 05035 and the met basalt came from the same basalt flow which we designate the yamm basalt the source basalt pairing of the yamm is also supported by their similar ree abundances crystallization ages approx 3 8 3 9 ga and isotopic compositions low u pb low rb sr and high sm nd the pyroxene exsolution lamellae which are unusually coarse up to a few microns by mare standards imply a relatively slow cooling in an unusually thick lava and or subsequent annealing within a cryptomare reported noble gas and cre data with close launch ages 1 ma and ejection depths deeper than several meters among the four meteorites further indicate their simultaneous ejection from the moon despite the marginally close terrestrial ages pairing in the conventional earth entry sense seems unlikely because of the remote recovery sites among the yamm meteorites the high abundance 68 of mare components in met 01210 estimated from a two component mixing model calculation could have resulted from either lateral mixing at a mare highland boundary or vertical mixing in a cryptomare the proportion of mare materials in met 01210 is greater than in apollo core samples at the mare highland boundary the burial depth several meters deep inferred from the lack of surface irradiation of met 01210 exceeds the typical mare regolith thickness a few meters thus the source of the yamm meteorites is likely a terrain of locally high mare highland mixing within a cryptomare we searched for a possible source crater of the yamm meteorites within the well defined cryptomare based on the multiple constraints obtained from this study and published data an unnamed 1 4 km diameter crater 53 w 44 5 s on the floor of the schickard crater is the most suitable source for the yamm meteorites the 238 u 204 pb value of the yamm basalts is extremely low relative to those of the apollo mare basalts but comparable to those of the luna 24 very low ti basalts the low source indicates a derivation from a less differentiated mantle with a lack of kreep components although the chemical sources of materials and heat source of melting might be independent the heat source that generated the source magma of the yamm and luna 24 basalts may not be related to kreep unlike the case of the apollo basalts the distinct chemical and isotopic compositions of mantle sources between the apollo basalts and the yamm lunar 24 basalts imply differences in mantle composition and thermal evolution between the procellarum kreep terrane pkt and non pkt regions of the nearside

crustal attributes of lunar basins from terrain correlated free air gravity anomalies 1 for the major lunar basins between 64 latitude uncompensated mass components as well as crustal ring and transient cavity attributes were evaluated from the free air anomaly components of the lunar prospector gravity model lp75g that are spectrally correlated at 100 km altitude with the gravity effects of the clementine terrain model gltm 2 inversion of the terrain correlated anomalies inferred incipient radial adjustments of the moho that equilibrate the basin topography assuming the lunar crust is mainly compensated by thickness variations nearly all nearside multiring basins are marked by mascon gravity anomalies that reflect mass concentrations from superisostatic mantle plugs plus mare fill farside basins by contrast are mostly characterized by maslite gravity anomalies from mass deficiencies due to subisostatic mantle plugs with marginal or no mare fill the preponderance of maslites on the farside is consistent with crust that responded more rigidly to impacts than the nearside crust which had a higher thermal gradient due to enhanced abundances of radioactive elements in the nearside mantle and crust however the extended thermal evolution of the lunar lithosphere also may have promoted the development of interfering mascon and maslite effects for tectonically complicated regions like the farside freundlich sharonov basin the moho adjustments also revealed well defined concentric zones of maxima and minima about the central basins that are strongly correlated with photogeologically inferred basin rings in addition the innermost zero contour of the radial adjustments provides an effective estimate for the diameter of the transient cavity the inferred transient cavity diameters correlated negatively with crustal thickness for basins with superisostatic mantle plugs and positively with the relative ages of the nearside basins on the farside superisostatic mantle plugs apparently developed in thinner crust up to thicknesses of about 30 km whereas in thicker crust mantle plugs developed only to subisostatic levels for the nearside mass balance calculations between the equilibrium mantle plug and excavated basin materials support the proportional scaling relation of roughly 0 1 for the excavation depth to diameter ratio of the transient cavity that photogeologic studies have obtained however for the serenitatis and imbrium basins with possibly atypical nearside crustal properties this proportionality may overestimate excavation depths by 28 and 37 respectively for nearside and farside basins apparently lacking mare flooding shallow excavation depths were also inferred

gravity data as a tool for landfill study this paper shows the potential of gravity data to map a buried landfill bottom topography to this end a gravity inversion method is presented for estimating the landfill s bottom depths at discrete points assuming a decrease of the density contrast with depth according to a hyperbolic law the method s efficiency was tested using synthetic data from simulated waste landfills producing estimated bottom topographies very close to the true ones the method s potentiality has been further evaluated in applying it to the gravity data from the abandoned thomas farm landfill site indiana usa whose bottom topography is known the estimated topography showed close agreement with the known thomas farm landfill s bottom topography

gravity inversion of 2d bedrock topography for heterogeneous sedimentary basins based on line integral and maximum difference reduction methods based on the line integral li and maximum difference reduction mdr methods an automated iterative forward modelling scheme li mdr algorithm is developed for the inversion of 2d bedrock topography from a gravity anomaly profile for heterogeneous sedimentary basins the unknown basin topography can be smooth as for intracratonic basins or discontinuous as for rift and strike slip basins in case studies using synthetic data the new algorithm can invert the sedimentary basins bedrock depth within a mean accuracy better than 5 when the gravity anomaly data have an accuracy of better than 0 5 mgal the main characteristics of the inversion algorithm include 1 the density contrast of sedimentary basins can be constant or vary horizontally and or vertically in a very broad but ap rioriknown manner 2 three inputs are required the measured gravity anomaly accuracy level and the density contrast function 3 the simplification that each gravity station has only one bedrock depth leads to an approach to perform rapid inversions using the forward modelling calculated by li the inversion process stops when the residual anomalies the observed minus the calculated falls within an error envelope whose amplitude is the input accuracy level the inversion algorithm offers in many cases the possibility of performing an agile 2d gravity inversion on basins with heterogeneous sediments both smooth and discontinuous bedrock topography with steep spatial gradients can be well recovered limitations include 1 for each station position there is only one corresponding point vertically down at the basement and 2 the largest error in inverting bedrock topography occurs at the deepest points

the nature of crater rays the copernicus example crater rays are formed during a cratering event as target material is ballistically ejected to distances of many crater radii forming narrow generally high albedo approximately linear features extending outward from the crater the nature of crater rays was examined for the lunar crater copernicus using new information on the composition of surface material from near ir reflectance measurements surface roughness from radar backscatter measurements and photogeologic data from available images part of the data analysis included use of mixing models to quantify the mixing systematics observed between primary ejecta and local substrate of the ray on the basis of compositional parameters from reflectance spectra primary material from copernicus can be detected in the surface material of rays in decreasing amounts with increasing radial distance e g 20 25 primary ejecta at six crater radii for distances greater than three crater radii the proportion of local material to primary ejecta observed from these compositional reflectance data is approximately equal to that predicted by previous laboratory and ballistic studies of craters within three crater radii the compositional data indicate a higher proportion of primary ejecta than predicted for extended areas along the ray that do not contain large secondary craters the primary ejecta is intimately mixed on the granular scale with local material throughout the regolith the relatively high albedo of the rays of copernicus is due to the feldspathic composition highland of the primary ejecta in rays emplaced on a mare substrate immature local substrate is only observed in copernicus s ray at large unmantied secondary craters or other areas with sufficient topographic slope to prevent the accumulation of mature soils crater rays are filamentous generally high albedo features that emanate nearly radially from young impact structures rays are narrow in relation to the crater radius extend distally for many crater radii and constitute a distinctive albedo feature around some of the largest and freshest lunar craters visible from earth synoptic views of ray systems figure la give the strong impression that the rays comprise bright material that has been excavated from the crater cavity and been emplaced beyond the continuous ejecta deposit if this visual impression is correct then the process that forms crater rays represents a significant mechanism for the lateral transport of primary material to great distances from its point of origin and particularly for craters larger than a let tens of kilometers in diameter constitutes a fundamental process for the regional mixing of crustal materials earth based telescopic images of the moon allowed the first studies and descriptions of rays and ray systems shoemaker 1962 described the arcuate and loop shaped streaks of the copernicus ray systems and showed that these patterns could be locally resolved into individual en echelon feather shaped elements 15 20 km in length with their long axes oriented approximately radially to the crater he noted the presence of elongate depressions or gouges in the ray system ranking in diameter from 8 km down to the limits of resolution and generally located at the proximal ends of the individual ray elements shoemaker observed that some of the gouges were

the microbial input in carbonate anhydrite facies of a sabkha palaeoenvironment from guatemala a molecular approach abstract nine representative rock samplesincluding four anhydrites an oil stained dolomite and a laminated mudstone source rock from a sabkha type palaeoenvironment la felicidad 1 well guatemala have been compared in order to tentatively characterize each facies by a geochemical signature each sample has been studied by using basic parameters toc rock eval pyrolysis yields and analyses of alkanes and aromatics by computerized gc ms the following families of compounds have been reviewed n alkanes branched and cyclic alkanes n alkylbenzenes benzohopanes monoaromatic steroids d ring aromatic 8 14 secohopanoids alkylnaphthalenes alkylphenanthrenes alkyldibenzothiophenes and triaromatic steroids despite close geochemical relationships of all the sample a more in depth investigation taking into account molecular patterns and semi quantitative data reveals significant differences among the samples anhydrites may be differentiated from carbonates which illustrates the efficiency of organic geochemistry in environmental palaeoreconstruction even in organiccarbon lean sediments toc 0 04 0 08 in anhydrites in these anoxic marginally mature sediments the strong predominance of triterpanes over steranes tt to st 20 associated with other molecular features leads to the conclusion that the main contribution to the organic matter of all facies is by bacteria several prominent components including novel families iso c23 and iso c27 alkanes tetracyclic terpanes d ring aromatic 8 14 secohopanoids 1 phenylpentadecane undecylnaphathalene and their mono and dimethylated counterparts have been interpreted as derived from halophilic bacteria these conclusions may be extended to all crude oils from the same area which may be considered as true bacterially derived petroleums the la felicidad 1 well data are discussed with reference to other palaeosabkha type sequences from the sw aquitaine basin france in which the bacterial input is less important however in these sabkha sequences 1 phenylpentadecane undecylnaphthalene and related structures have also been identified

remote sensing and geologic studies of the schiller schickard region of the moon near infrared reflectance spectra multispectral images and photogeologic data for the schiller schickard ss region were obtained and analyzed in order to determine the composition and origin of a variety of geologic units these include light plains deposits orientale related deposits mare units and dark haloed impact craters dhcs spectral data indicate that the pre orientale highland surface was dominated by noritic anorthosite near ir spectra show that dhcs in the region have excavated ancient 3 8 ga mare basalts from beneath highland bearing material emplaced by the orientale impact ancient mare basalts were widespread in the ss region prior to the orientale event and their distribution appears to have been controlled by the presence of several old impact basins including the schiller zucchius basin and a basin previously unrecognized both near ir spectra and multispectral images indicate that light plains and other orientale related units in the ss region contain major amounts of local pre orientale mare basalt the amounts of local material in these deposits approach but seldom exceed the maximum values predicted by the local mixing hypothesis of oberbeck and co workers

multispectral studies of western limb and farside maria from galileo earth moon encounter 1 new visible and near infrared multispectral images of the moon obtained by the galileo solid state imaging system along with lunar orbiter images for crater counts and spectral mixing analyses were used to characterize western limb and eastern farside maria and determine compositional and age relationships in selected regions results indicate that 1 western limb mare deposits have less variability in titanium content 6 wt tio2 mare basalts were observed on the western limb and farside which may reflect the inability of such denser magmas to penetrate the thicker farside crust

distribution and modes of occurrence of lunar anorthosite 1 we have utilized telescopic near infrared spectra and multispectral images of the moon provided by the galileo and clementine missions to determine the distribution and modes of occurrence of pure anorthosite anorthosites have now been identified in all portions of the nearside including the site of the putative procellarum basin anorthosite is associated with the rings of orientale grimaldi humorum nectaris nubium mutus vlaq and balmer basins major portions of the inner rings of grimaldi humorum crisium orientale and nectaris are composed of pure anorthosite the large spatial extent of these anorthosites appears to rule out an origin in the upper portions of discrete differentiated mg suite plutons in every instance the anorthosites were exposed from beneath a shallower near surface layer of more pyroxene rich material more mafic material also occurs beneath the pure anorthosite unit large expanses of the northern farside exhibit very low feo values this region contains abundant anorthosite and stands in stark contrast to the mafic composition exhibited by the interior of the south pole aitken basin spa the distribution of compositional units on large portions of the lunar farside as well as the southern portion of the lunar nearside appears to be largely attributable to the spa impact event the distribution and modes of occurrence of anorthosites clearly indicate that a thick global layer of anorthosite is present at various depths beneath most portions of the lunar surface this anorthosite layer dominated the upper portion of the primordial crust and was produced by plagioclase flotation in the global magma ocean

dark halo craters and the thickness of grooved terrain on ganymede dark halo craters in grooved terrain on ganymede represent potential probes of the subsurface geology these craters are surrounded by a broad diffuse low albedo annulus or halo halo radius is linearly proportional to crater radius indicating that the halo is related to the continuous ejecta deposit of the crater and is not removed by natural aging processes such as regolith development and exposure to the space environment the halos have orange violet albedo ratios that are intermediate between ratios associated with grooved terrain and cratered terrain we propose that halos result from the incorporation of cratered terrain material into crater ejecta in uruk sulcus only craters greater than 12 km in diameter have halos indicating that the cratered terrain material there forms a stratigraphic horizon buried at depth in the grooved terrain into which only larger craters can excavate this depth can be calculated from the transition diameter by reconstructing the transient crater we calculate a depth of excavation corresponding to the depth of burial of cratered terrain of 1 0 to 1 6 km this shallow burial is inconsistent with deep subsidence and burial stoping into the interior or lateral spreading apart of ancient cratered terrain units but is consistent with a filled graben model for grooved terrain where relatively clean ice has been emplaced over downdropped blocks of cratered terrain

lunar dark haloed impact craters origin and implications for early mare volcanism remote sensing and photogeologic data were used to determine the composition and origin of lunar dark haloed craters near infrared reflectance spectra were obtained for numerous dark haloed impact craters located on either the ejecta blankets of large impact craters or imbrian and nectarian age light plains deposits spectral thermal radar and photogeologic data conclusively demonstrate that copernicus h and other dark haloed craters on the ejecta blanket of copernicus excavated mare basalts from beneath lighter surface deposits rich in highlands material analyses of reflectance spectra of dark haloed craters on light plains indicate that in every instance these craters exposed mare basalt which had previously been covered by varying thicknesses of highlands debris in the schiller schickard region a relatively thick highlands unit was emplaced as a result of the orientale impact event on the interior of balmer basin marelike basalt has been excavated from beneath much thinner highlands deposits emplaced by nearby craters mafic orbital geochemical anomalies are commonly associated with regions with abundant light plains deposits which exhibit dark haloed impact craters apparently some mare material has been incorporated into the regolith either by local mixing during the emplacement of the highlands debris or by subsequent vertical mixing the results of recent remote sensing photogeologic and lunar sample studies strongly indicate that mare volcanism was a significant process during much of the pre imbrian and may have been initiated as early as 4 2 4 3 ga these very early volcanic episodes contributed materials to the lunar surface which were incorporated into the upper portion of the highlands crust by subsequent impact mixing models concerning the extent and duration of mare volcanism as well as those involving the composition and thermal evolution of the lunar interior will have to be revised

lunar crater detection based on terrain analysis and mathematical morphology methods using digital elevation models lunar impact craters are the most typical geomorphic feature on the moon and are of great importance in studies of lunar terrain features this paper presents a crater detection algorithm cda that is based on terrain analysis and mathematical morphology methods the proposed cda is applied to digital elevation models dems to identify the boundaries of impact craters the topographic and morphological characteristics of impact craters are discussed and detailed steps are presented to detect different types of craters such as dispersal craters connective craters and con craters the dem from the lunar reconnaissance orbiter which has a resolution of 100 m is used to verify the proposed cda the results show that the boundaries of impact craters can be detected the results enable increased understanding of surface processes through the characterization of crater morphometry and the use of crater size frequency distributions to estimate the ages of planetary surfaces

lunar surface imaging polarimetry iii langrenus abstract the program of lunar surface texture analysis conducted with polarimetry at observatoire de paris included crater langrenus the area was analyzed with the video polarimeter in terms of albedo surface roughness and grain size an image was produced mapping the terrain roughness at the surface of the moon parameter and another image mapped the median grain size parameter md it is when making these observations that transient bright features were discovered near the crater central peak they will be analyzed specifically in another paper the langrenus floor around the area on which the brightenings occurred is characterized as very rugged terrain at centimeter to meter scale mantled with a layer made of high albedo grains of large median size the ejecta blanket deposited around langrenus has disymetric textural properties suggesting that the crater was formed by an oblique impact a recent impact in the northern part of this aureole excavated the basaltic material beneath the layer and projected onto the surface a dark material which formed a smooth layer

inversion of gravity field inclination to map the basement relief of sedimentary basins this paper presents a method to map the basement relief of homogeneous sedimentary basins that does not require the knowledge of the basin density contrast to reach this task the proposed method relies on the invariance of the inclination of the anomalous gravity field with the density contrast caused by models constituted by two homogeneous media this invariance occurs because the density contrast appears as a constant factor in both vertical and horizontal gravity components therefore being canceled out when these components are divided during the evaluation of the field inclination for such media the field inclination is independent of the density contrast thus allowing the source geometry reconstruction even when the density contrast is unknown as the inclination is rarely measured the gravity anomaly i e the field vertical component is initially used to compute the horizontal component of the gravity field by applying a suitable linear transform the field inclination is estimated from both components and then used to invert the source geometry by fitting the inclination values under the geologic constraints attributed to the causative sources in this process the density contrast is not required nor introduced as an unknown parameter in the formulated inverse problem moreover it can be estimated later by solving a new inverse problem where the source geometry determined from the inverted inclination is fixed and the constant density contrast is determined by fitting the gravity anomaly this paper applies such ideas to map the basement relief of a sedimentary basin and to estimate its density contrast the inversion is implemented by a random search procedure that excludes extreme models and imposes constraints that the unknown interface is smooth everywhere and assumes known depth values at isolated points investigated by wells the proposed technique is tested with synthetic noisy data from homogeneous and heterogeneous basin models and is applied to invert a gravity profile from the reconcavo basin brazil the results from the real data application are compared with well data and previously published results

geology of mare deposits in south pole aitken basin as seen by clementine uv vis data a multispectral analysis of 21 discrete lunar mare deposits within the south pole aitken basin was undertaken in order to model the general mineralogical composition of farside mare deposits so that the near and farside may be compared in terms of magma generation and emplacement determination of each deposit s mineralogy was based upon albedo the 0 75 0 95 m ratio indicating the presence of a 1 0 m absorption band and the strength and shape of that band a combination of improved spatial resolution and the availability of the general multispectral signature for each pond allowed deposits to be examined for homogeneity in order to assess the nature and number of flows represented feo and tio 2 abundances were also estimated based upon the resultant data 19 out of 21 ponds were determined to be mare deposits of these 19 15 had spectra well defined enough to classify general mineralogy nine having high ca pyroxene signatures indicative of basalt and six showing low ca signatures suggesting a substantial noritic component we believe these noritic signatures can plausibly be attributed to vertical lateral soil mixing processes for the smallest ponds although a unique lithology cannot be ruled out for the largest pond a majority of ponds in this study region have homogeneous spectral signatures interpreted to represent individual eruptive phases this indicates that very large volumes for these regions may be typical also because such volumes are comparable to the largest terrestrial eruptions they may have formed by a similar mechanism of emplacement the vast majority of mature soils are spectrally redder and thus have a lower estimated feo abundance than the mare serenitatis soil standard ms 2 in particular and nearside basalts in general these soils also average low to medium estimated tio 2 abundance similar to apollo 12 and 15 and luna 24 the observations made here are consistent with a scenario in which basalts with low feo and low to medium tio 2 contents were deposited during the lunar peak volcanic period that occurred in the late imbrian 3 80 3 20 ga and because of their small areal extent were more susceptible to mixing processes than nearside basalts

mariner 10 multispectral images of the eastern limb and farside of the moon we present the first analysis of mariner 10 multispectral image data for the eastern limb and farside of the moon a new rigorous calibration of these data is used that provides results that are consistent with independently derived data sets from these newly calibrated data a color ratio image 0 48 0 58 m is produced to show relative tio2 abundances in mare units on the eastern limb and farside of the moon our results indicate that the farside lunar mare deposits examined have tio2 contents that are intermediate to low 2 5 tio2 relative to mare deposits on the nearside we find no evidence for areally extensive deposits of either very low titanium vlt or high to very high titanium vht basalts in these portions of the moon our findings support previous interpretations that the source regions for lunar mare basalts are laterally heterogeneous additionally examination of highland units reveals a relatively blue region that corresponds with a previously proposed cryptomare suggesting enhanced tio2 for this unit finally based on these mariner 10 data telescopic spectral data galileo multispectral image data and lunar meteorite analyses we speculate that volcanism in farside mare deposits did not include high titanium basalts 8 wt

volcanism in mare fecunditatis and mare crisium ar ar age studies the laser 40ar 39ar dating technique has been applied to five luna 16 basalt fragments and one impact glass and nine luna 24 basalt fragments and one breccia the textures of these basalts are fine grained ophitic and coarse grained basalts the samples contain high levels of solar and lunar atmospheric argon acquired during their residence on the lunar surface these trapped argon components are predominantly released at low temperature steps and can be distinguished from radiogenic and cosmogenic released at intermediate and high temperature steps the apparent ages obtained for luna 16 samples span a narrow range of 3 29 to 3 38 ga a young age of 0 988 ga was obtained for a basaltic impact glass indicating the age of an impact event in the vicinity of luna 16 landing site the ages obtained for luna 24 samples suggest the existence of at least three periods of volcanism occurring over a protracted interval of between 3 45 and 2 52 ga the long period of volcanism suggested for the mare crisium was likely due to a combination of geophysical and geochemical features in the surrounding and underlying areas of the crisium basin attempts at dating three luna 20 samples were inconclusive due to their high trapped argon contents

australia s moho a test of the usefulness of gravity modelling for the determination of moho depth abstract in general seismic methods provide a reliable way to image the crust mantle interface which is marked by a rapid increase in seismic velocity the moho however the coverage provided by seismic networks is necessarily limited due to access difficulties and the cost and labour involved in collecting data gravity data provide an alternative way to model the depth to the moho and provide more consistent and broader coverage we discuss the usefulness of gravity data to model moho depth and the advantages and disadvantages of several gravity modelling methods as an example a model of australia s moho is generated through seismically constrained gravity inversion including an estimate of modelling uncertainty the inversion results demonstrate that gravity inversion is generally useful but that its usefulness is subject to the following limitations 1 gravity inversion cannot spontaneously generate thick high density crust nor thin low density crust and unless constrained will not generate a correct moho where such crust exists 2 major errors in the definition of the a priori density structure in particular features that are fixed during inversion will influence the moho results 3 applying a broad range of inversion parameters is necessary to characterise uncertainty model variability maps for australia show that the average error is less than 5 km there is a general relationship with seismic coverage but the areas of highest uncertainty are not necessarily those with the lowest seismic estimate density comparison with previous seismic and seismic gravity models of australia s moho indicates that low seismic data density limits usefulness due to higher uncertainty in the gravity inversion high seismic data density also limits usefulness because moho depth is largely known and there is little scope for change the usefulness of gravity inversion is maximum under conditions where seismic coverage is moderately dense but estimates are well distributed

unusual biomarker maturation ratio changes through the oil window a consequence of varied thermal history abstract saturated and aromatic biomarker ratios continue to change systematically through the oil window and into the gas condensate window to high vitrinite reflectances r o 1 16 in mature marine and lacustrine mesozoic clastic samples from a south african basin two of the ratios reverse above r o 0 9 these unusual maturation effects result from isolated periods of high rates of maturation increase the basin cooled regionally after the break up of gondwana but high heating rates prevailed during the late cretaceous early tertiary as africa moved across a hotspot and again in the late tertiary as a result of a possible hotspot and hydrothermal event

molecular measurements of maturity for lias δ shales in n w germany abstract the extractable aliphatic and aromatic hydrocarbons of twenty four lias shales from n w germany have been analysed by gas chromatography mass spectrometry particular attention has been paid to seven molecular measurements of thermal maturation which are based on appropriate ratios of the concentrations and products of certain reactions a sequence of increasing maturity towards the area of the bramscher massiv was determined because the reactions involved occur at different rates they reach completion at different levels of maturity and at variable distance from the centre of the bramscher massiv as defined by iso vitrinite reflectance contours reported previously for rhaetic lias and malm shales this has allowed the designation of zones of increasing maturity the molecular measurements appear more reliable assessors of maturity than vitrinite reflectance for samples less mature than the zone of oil generation but are not applicable to samples from within this zone because the reactions concerned have normally reached completion a mathematical model suggests that the maturity of samples less mature than a vitrinite reflectance of 1 can adequately be explained by substantial subsidence during early and middle cretaceous followed by major uplift and inversion in late cretaceous time without recourse to further heating from a deep seated igneous intrusion

magmatic evolution of the moon although incomplete because of the imperfect and somewhat random sampling of rock types by the apollo and luna missions 1969 1976 the history of lunar magmatism has been reconstructed by numerous researchers over the past three decades these reconstructions have illustrated the continuous nature of lunar magmatism from 4 6 to approximately 2 0 ga and the large influence of early differentiation and catastrophic bombardment on lunar mantle dynamics magmatism and eruptive style in this review we group magmatism into multiple stages of activity based on sampled rock types and evaluate the models for each stage stage 1 is early lunar differentiation and associated magmatism partial melting of the moon soon after accretion was responsible for producing an anorthositic crust and a differentiated lunar interior the extent of lunar melting and mantle processing depends strongly on the mechanisms that induced melting estimates for the time over which melting and crystallization occurred range from tens to hundreds of millions of years stage 2 is the disruption of lunar magma ocean cumulates soon after the crystallization of most of the lunar magma ocean the cumulate pile experienced gravitational overturn this resulted in transport of late forming cumulates into the deep lunar mantle and mixing of magma ocean cumulates on a variety of scales stage 3 is the post magma ocean highland magmatism whereas the ferroan anorthositic crust was probably produced during the crystallization of a magma ocean the slightly younger mg suite and alkali suite plutonic rocks may have been generated by decompressional melting of early magma ocean cumulates during cumulate pile overturn a kreep and crustal signature was incorporated into these primitive basaltic magmas through assimilation near the base of the lunar crust or through melting of a hybridized mantle the alkali suite could represent either the differentiation products of mg suite parental magmas or a separate but contemporaneous episode of basaltic magmatism stage 4 is pre basin volcanism sample analysis and remote sensing data indicate that early lunar volcanism kreep basalts and high alumina basalts was contemporaneous with periods of highlands plutonism and catastrophic bombardment of the lunar surface the relationship between early stages of lunar volcanism and the contemporaneous plutonism is not clear the kreep basalts may be volcanic equivalents to both the mg suite and alkali suite stage 5 is the late remelting of magma ocean cumulates and eruption of mare basalts basin associated eruption of mare basalts occurred during and following the late stages of catastrophic bombardment this volcanic activity was possibly an extension of the thermal event that initiated pre basin volcanism mare basalts exhibit a wide range of composition resulting from near surface fractionation of chemically distinct primary basaltic magmas most likely mare basalts were produced by small to moderate degrees of partial melting of hybrid cumulate sources in the deep lunar mantle alternatively the mixed chemical signatures observed in many mare basalts may be interpreted as indicating assimilation of late stage evolved cumulates by melts produced deep in the cumulate pile the wide range of compositions exhibited by the mare basalts compared with earlier episodes of basaltic magmatism may reflect the thermal regime in the lunar mantle that limited the extent of partial melting and melt source homogenization

buried stratigraphic relationships along the southwestern shores of oceanus procellarum implications for early lunar volcanism the composition of mare highland boundaries is investigated in the region of southwestern oceanus procellarum using multispectral images from the galileo solid state imaging system the data are analyzed using a linear image based spectral mixture model to map the distribution and abundance of spectral end members representing mare basalt mature highland soils and fresh crater materials the fraction images that result from the mixture modeling are then integrated into a geographic information system database to analyze the relationship between the compositional gradients and regional geologic and geomorphic units within this framework three basic types of mixing gradients are recognized narrow mixing zones broad mixing zones and complex mixing zones the narrow zones appear to be the result of simple postformation lateral mass transport of surface materials due to the time averaged effects of impact cratering and regolith gardening the broad or moderate mixing zones exhibit evidence for significant incorporation of basalt into the distal basin ejecta of orientale and thus are interpreted to indicate that pre orientale volcanism and volcanic deposits were widespread in the procellarum region this is further corroborated by the mare rich ejecta blanket observed for the 100 km diameter impact crater letronne the complex mixing zones show evidence for extensive pre orientale and perhaps pre imbrium cryptomare as well as some volcanism extending into the late imbrian period these results indicate that mare highland boundaries frequently contain a convolved geologic record that allows insight into the geologic events prior to the final one apparently recorded by surface deposits for this region of the moon we now recognize that volcanism was well established and widespread in early imbrian time but had become more focused to a few major volcanic regions humorum procellarum by the late imbrian

the formation of mercury s smooth plains there has been extensive debate about whether mercury s smooth plains are volcanic features or impact ejecta deposits we present new indirect evidence which supports a volcanic origin for two different smooth plains units in borealis planitia stratigraphic relations indicate at least two distinct stages of smooth plains formation at least one of these stages must have had a volcanic origin in the hilly and lineated terrain petrarch and several other anomalously shallow craters apparently have been volcanically filled areally extensive smooth plains volcanism evidently occurred at these two widely separated areas on mercury these results combined with work by other researchers on the circum caloris plains and the tolstoi basin show that smooth plains volcanism was a global process on mercury present data suggest to us that the smooth and intercrater plains may represent two distinct episodes of volcanic activity on mercury and that smooth plains volcanism may have been triggered by the caloris impact high resolution and multispectral imaging from a future mercury spacecraft could resolve many of the present uncertainties in our understanding of plains formation on mercury

a latest cretaceous hotspot and the southeasterly tilt of britain the southeasterly regional dip of england and wales is usually ascribed to miocene movements loss of up to 2 km of cover from northern england shown by apatite fission track analysis has been related to uplift and erosion induced by a mantle hotspot but its effects were far more widespread than considered hitherto outcrop patterns throughout much of england wales and eastern ireland can be related to a hotspot beneath the irish sea uplift occurred within the late maastrichtian and erosion continued into the late palaeogene after post oligocene down faulting of the irish sea the modern drainage was initiated on the eroded surface unconformities provide the best means of dating orogenic movements in some localities the time interval between the youngest rocks preserved beneath the unconformity and the oldest preserved above may be small enough to enable the dating of fold movements to be determined with some precision thus in southeastern britain the major e w structures of the hampshire basin the weald and the london basin can be dated as miocene as rocks of oligocene age are involved in the folding in the hampshire basin and pliocene sands rest in erosional pockets of the chalk of se england because fold movements tend to affect large areas of the crust at discrete intervals of time the southeasterly tilt of britain evident from the fact that a nw se transect from anglesey to london crosses outcrops of rocks getting progressively younger from the precambrian of anglesey to the tertiary of the london basin has

remote sensing studies of the lomonosov fleming region of the moon 1 lomonosov fleming is a 620 km pre nectarian impact basin centered at 19 n 105 e clementine multispectral images and a variety of spacecraft photographs were used to investigate the composition and origin of geologic units in the region mare basalt deposits in the lomonosov fleming region are small and exhibit varying degrees of highlands contamination four previously unrecognized dark mantle deposits of probable pyroclastic origin were identified and mapped a major expanse of cryptomare was mapped in and around the lomonosov fleming basin spectral and chemical data obtained for dark haloed craters dhc established that these impact craters excavated mare basalt from beneath higher albedo highlands rich surface units the buried basalts exposed by dhcs in the region exhibit a variety of compositions which range from very low titanium basalt to intermediate tio2 mare basalt nectarian aged units with subjacent cryptomare are much more extensive than imbrian aged deposits with underlying basalt at least some of the buried mare basalts in the region may have been emplaced during pre nectarian time while both impact basins and craters played a role in cryptomare formation by transporting highlands material to mare surfaces the evidence indicates that most of the cryptomare inside the basin are of the distal basin ejecta type the enhanced feo and tio2 abundances exhibited by these cryptomare surfaces usually light plains units demonstrate that ballistic erosion and sedimentation played an important role in their formation

ages and stratigraphy of mare basalts in oceanus procellarum mare nubium mare cognitum and mare insularum accurate estimates of mare basalt ages are necessary to place constraints on the duration and the flux of lunar volcanism as well as on the petrogenesis of lunar mare basalts and their relationship to the thermal evolution of the moon we performed new crater size frequency distribution measurements in order to investigate the stratigraphy of mare basalts in oceanus procellarum and related regions such as mare nubium mare cognitum and mare insularum we used high resolution clementine color data to define 86 spectrally homogeneous units within these basins which were then dated with crater counts on lunar orbiter iv images our crater size frequency distribution measurements define mineralogical and spectral surface units and offer significant improvements in accuracy over previous analyses our data show that volcanism in the investigated region was active over a long period of time from 3 93 to 1 2 b y a total of 2 7 b y volumetrically most of the basalts erupted in the late imbrian period between 3 3 and 3 7 b y and we see evidence that numerous units have been resurfaced during the eratosthenian period significantly less basalt was erupted depending on the absolute model ages that one can assign to the lunar chronostratigraphic systems five units might be of copernican age younger basalts are generally exposed in the center of the investigated area that is closer to the volcanic centers of the aristarchus plateau and marius hills older basalts occur preferentially along the northwestern margin of oceanus procellarum and in the southeastern regions of the studied area i e in mare cognitum and mare nubium combining the new data with our previously measured ages for basalts in mare imbrium serenitatis tranquillitatis humorum australe and humboldtianum we find that the period of active volcanism on the moon lasted 2 8 b y from 4 b y to 1 2 b y on the basis of the basalts dated so far which do not yet include the potentially young basalts of mare smythii e g schultz and spudis 1983 we conclude that oceanus procellarum not only exhibits the widest range of ages of all investigated basins but probably also is the location of some of the youngest basalts on the lunar surface

simultaneous 3d depth to basement and density contrast estimates using gravity data and depth control at few points we have developed a gravity inversion method for simultaneouslyestimatingthe3dbasementreliefofasedimentary basin and the parameters defining a presumed parabolic decay of the density contrast with depth in a sedimentary pack assumingpriorknowledgeaboutthebasementdepthatafew points thesedimentarypackisapproximatedbyagridof3d vertical prisms juxtaposed in both horizontal directions of a right handed coordinate system the prisms thicknesses representthedepthstothebasementandaretheparametersto be estimated from the gravity data to estimate the parameters defining the parabolic decay of the density contrast with depthandtoproducestabledepth to basementestimates we imposed smoothness on the basement depths and proximity between estimated and known depths at boreholes we applied our method to synthetic data from a simulated complex 3d basement relief with two sedimentary sections having distinct parabolic laws describing the density contrast variationwithdepth theresultsprovidegoodestimatesofthetrue parameters of the parabolic law of density contrast decay with depth and of the basement relief inverting the gravity data from the onshore and part of the shallow offshore almadabasinonbrazil snortheasterncoastshowsgoodcorrelationwithknownstructuralfeatures

the isotopic record of lunar volcanism abstract the timing and extent of lunar volcanism was determined primarily by the internal thermal evolution of the moon a late heavy bombardment produced most of the observable lunar basins easily recognized stratigraphic markers and also may have influenced lunar volcanism most of the nearside basins seem to have been produced 3 8 4 0 ga ago during a period often referred to as the lunar cataclysm the pre cataclysm period was characterized by formation of the lunar crust plutonic rocks within the crust and pre mare volcanism isotopic analysis of breccia clasts pre dating the cataclysm has yielded an outline of this period the isotopic record of post cataclysm mare volcanism is clear but incomplete because samples from the youngest mare areas are lacking specifically the isotopic data show that some lunar anorthosites formed 4 45 ga ago consistent with early formation of an anorthositic lunar crust some mg suite norites troctolites and dunites also formed approximately contemporaneously with the oldest anorthosites but others are up to 200 300 ma younger more evolved rocks granites and quartz monzodiorites also formed between 4 4 and 4 0 ga ago the earliest known pre mare volcanism at 4 25 ga ago included aluminous mare like basalts and an olivine gabbronorite similar to apollo 12 basalts kreep basalt volcanism began at least 4 1 ga ago approximately contemporaneously with that of the ancient mare like basalts and continued during the cataclysm recorded instances of high ti mare basalt volcanism began during or immediately after the cataclysm low ti mare basalt volcanism is the most recent for which samples are available the isotopic data record an early primary lunar differentiation during which mare basalt sources formed probably by crystallization of cumulus minerals from a lunar magma ocean the isotopic record of post cataclysm basalts indicates a heterogeneous lunar mantle and can be explained by partial melting of cumulate sources but more complex petrogenesis also has been suggested more complex petrogenetic processes including assimilation and assimilation fractional crystallization afc seem to be required for pre mare volcanics the isotopic data contain a hint that petrogenesis of the oldest pre mare volcanics may be linked to formation of the so called procellarum basin possibly the oldest and largest lunar basin such a basin would provide a geologic context for the pre mare volcanics and its formation may have been a defining moment in lunar history

estimating free parameters in 2d inversion example of gravity inversion in a rifted basement abstract we advance a principle directed to assigning numerical values to free parameters usually present in inversion methods it may be formulated as optimum estimates of free parameters in an inversion procedure must lead in tests using synthetic data to solutions whose geometrical expression reflects the main qualitative or semiquantitative geological characteristic of the study area to this end the interpreter should i specify a typical anomalous source geometry which incorporates the most relevant geological information for the study area ii compute the corresponding gravity anomaly and iii invert the anomaly for the source geometry finding the numerical values of the free parameters that lead to a solution closest to the typical source application of the above methodology to synthetic and real data from the basement relief of a rift basin has asserted its efficacy

remote sensing and geologic studies of the balmer kapteyn region of the moon 1 the balmer kapteyn b k region is located just east of mare fecunditatis on the east limb of the moon it is centered on the balmer kapteyn basin a pre nectarian impact structure that exhibits two rings approximately 225 km and 450 km in diameter clementine multispectral images and lunar prospector lp gamma ray spectrometer grs data were used to investigate the composition age and origin of geologic units in the region a major expanse of cryptomare was mapped within the b k basin spectral and chemical data obtained for dark haloed craters dhcs established that these impact craters excavated mare basalt from beneath higher albedo highland rich surface units the buried basalts exposed by dhcs in the region are dominated by low titanium mare basalts the fresh dhc feo values 15 0 15 7 wt that best represent those of buried mare basalts are well within the range of values exhibited by high alumina mare basalts while most cryptomare deposits occur beneath surfaces that range in age from imbrian to nectarian it is possible that some mare flows were emplaced during pre nectarian time most cryptomare deposits in the b k region were formed by the contamination of mare surfaces by highland rich distal ejecta from surrounding impact craters these balmer type cryptomare deposits are usually associated with light plains units major lp grs feo enhancements are associated with cryptomaria in the balmer kapteyn lomonosov fleming schiller schickard and mendel rydberg regions

the distribution of olivine in the crater copernicus we employed multispectral imaging in the visible and near ir at four wavelengths 0 73 0 96 1 45 and 1 99 m of copernicus crater in order to map the distribution of olivine rich pyroxene poor material known previously to occur in the central peak complex we identified three additional portions of the crater to exhibit spectral characteristics similar to those of the central peaks strongly suggesting the presence of material similar to that exposed in the central peaks these areas are a scarp forming a portion of the northern rim of copernicus and two slump blocks in the north wall which may have been derived from the same portion of the ejecta now exposed in the rim scarp these occurrences decrease the minimum allowable depth for this unusual material in the copernicus target site though still represent some of the deepest material exposed by copernicus

ages and stratigraphy of lunar mare basalts in mare frigoris and other nearside maria based on crater size frequency distribution measurements 1 we report on ages derived from impact crater counts for exposed mare basalt units in the northern part of the lunar nearside hemisphere mare frigoris the eastern and northeastern part of the nearside hemisphere lacus temporis joliot hubble goddard mare marginis and mare smythii the central part of the nearside hemisphere palus putredinis mare vaporum and sinus medii and the southwestern part of the nearside hemisphere grimaldi cruger rocca a lacus aestatis and schickard in mare frigoris we dated 37 basalt units showing ages from 2 61 to 3 77 gyr with most units being formed in the late imbrian period between 3 4 and 3 8 gyr ago in mare vaporum we dated six spectrally homogeneous units that show model ages of 3 10 to 3 61 gyr our model ages of basalts in mare marginis range from 3 38 to 3 88 gyr and are mostly older than basalts in mare smythii 3 14 3 48 gyr the model ages of four units in sinus medii indicate that the basalts in this region formed 3 63 to 3 79 gyr ago we find an excellent agreement of our crater size frequency model ages of the palus putredinis area which contains the apollo 15 landing site with the radiometric ages of apollo 15 samples according to our crater counts basalts in palus putredinis are 3 34 gyr old and this compares favorably with the radiometric ages of 3 30 3 35 gyr of the olivine normative and quartz normative basalts of the apollo 15 landing site lacus aestatis is a small irregular shaped mare patch in the southwestern nearside and shows an imbrian age of 3 50 gyr basalts in lacus temporis in the northeastern nearside formed between 3 62 and 3 74 gyr ago and are therefore older than the basalts in lacus aestatis we found that basalts in craters of the southwestern nearside schickard grimaldi cruger and rocca a are also mostly younger than basalts in craters of the northeastern nearside hubble joliot and goddard while basalt ages vary between 3 16 and 3 75 gyr in the southwest basalts in the northeast are 3 60 3 79 gyr old these results confirm and extend the general distribution of ages of mare basalt volcanism and further underline the predominance of older mare basalt ages in the eastern and southern nearside and in patches of mare peripheral to the larger maria in contrast to the younger basalt ages on the western nearside oceanus procellarum

a spectral survey of the crisium basin region of the moon the crisium basin region harbors a number of interesting features including geochemical and radar anomalies light plains units and possible hidden mare deposits cryptomaria this report presents preliminary results of a telescopic near infrared spectral study concerning a variety of surface units in the crisium region observations were made of mare crisium light plains deposits north of taruntius crater and the terra associated with the crisium basin

regional maturity as determined by organic petrography and geochemistry of the schei point group triassic in the western sverdrup basin canadian arctic archipelago abstract maturity and source rock potential of organic rich beds in the triassic schei point group in the sverdrup basin arctic canada have been investigated using reflected light microscopy and the results are compared with other maturity parameters determined geochemically i e rock eval and biomarker maturation parameters the samples evaluated belong to the eden bay member of the hoyle bay formation and contain a predominance of marine algal material in the form of tasmanales and dinoflagellates along with mixed terrestrial organics the rock matrix is dominantly carbonate with some shaly input indicating that the rocks were deposited in an iron poor highly euxinic environment with few exceptions there is good agreement between parameters determined using microscopy namely r o max and r gq and geochemical parameters t max hi dia c 27 dia c 27 reg c 27 steranes s s r c 29 steranes the ternary diagram showing the abundance of normalized c 27 c 28 and c 29 regular steranes indicates a mostly marine depositional environment for the schei point source rock this is confirmed by the abundance of marine fauna and flora in these samples analytical results from several different techniques indicate that the source rocks become more mature from the margin towards the axis of the sverdrup basin this is due in part to the increase in overburden of sediments in the axis of the basin also the high thermal conductivity of salt has strongly influenced the maturity of schei point source rocks over the crest of the salt cored structures i e well hazen f 54 and the proximity of salt has enhanced maturation levels at well rock point j 43 the sections investigated were also considered to have an excellent gas potential due to their higher than average toc content

hansteen alpha a volcanic construct in the lunar highlands 1 we have used data from the clementine and lunar prospector spacecraft in conjunction with near ir reflectance spectra collected with earth based telescopes to study the composition and origin of hansteen alpha an arrowhead shaped highlands feature located on the southern margin of oceanus procellarum hansteen alpha is a member of a class of lunar spectral anomalies red spots that are characterized by a relatively high albedo and a strong absorption in the uv it has been suggested that at least some of these spectral anomalies were produced by nonmare volcanism the stratigraphic relationships among the geologic and compositional units in the region show that hansteen alpha was emplaced by extrusive igneous processes the imbrian aged craters hansteen and billy emplaced relatively feo and tio2 rich ejecta hansteen alpha exhibits much lower feo and tio2 values if hansteen alpha was present prior to the billy and hansteen impact events it should have been covered with feo and tio2 rich ejecta because it is located within one crater diameter of the rim crest of each crater since it is not hansteen alpha was superposed on these ejecta units nonmare volcanism is the only viable process for the formation of hansteen alpha the morphology and surface texture of hansteen alpha is similar to many terrestrial features of dacitic and rhyolitic composition formed by extrusions of relatively viscous lavas such highly evolved compositions should be very enriched in th but hansteen alpha exhibits th abundances of 6 ppm hence hansteen alpha is not composed of a highly evolved highlands lithology

moon near infrared spectral reflectance a first good look a positive identification of the minerals olivine plagioclase and several types of pyroxenes were made at several locations on the lunar surface by using remote measurements for example the crater aristarchus is found to have an average pyroxene composition of augite and plagioclase is obviously present a dark mantle deposit in the crater j herschel is at least partly composed of a mixture of 70o7o olivine and 30o7o pyroxene these determinations were possible because the reflectance spectra for 10 20 km diameter lunar areas have been measured for the first time in the ir spectral region 0 65 2 5 m with sufficient spectral resolution and photometric precision to define mineral electronic absorption bands the reflectance for all lunar regions observed over 100 to present continues to increase toward longer wavelengths to at least 2 5 m and several mineral absorption bands appear the telescopic spectra are of similar quality and contain features similar to laboratory spectra of lunar samples the absorption features in several spectra have been quantitatively analyzed using newly developed computer processing techniques including thermal flux removal and absorption band fitting to produce these mineral identifications detection and quantitative analysis of these absorptions provide a much improved basis for remotely determining and mapping surface mineralogy quantitatively from the ground or using airborne or spacecraft platforms

crustal diversity of the moon compositional analyses of galileo solid state imaging data the multispectral images of the lunar limb and farside obtained by the solid state imaging ssi system on board the galileo spacecraft provide the first new pulse of compositional data of the moon by a spacecraft in well over a decade the wavelength range covered by ssi filters 0 4 1 0 m is particularly sensitive to the composition of mare basalts the abundance of mafic ferrous minerals and the maturity of the regolith to a first order the limb and farside material is consistent with previous characterization of nearside lunar spectral types for mare and highland soils and craters most basalts are of an intermediate tio 2 composition and most of the highland crust is feldspathic with local variations in mafic content identified principally at impact craters dark manfling material on the farside can be interpreted in terms of known properties of lunar pyroclastic glass regions of cryptornate are shown to have spectral properties intermediate between those of highland and mare soils as would be expected from a mixture of the two there are several important exceptions and surprises however unlike the basalt types identified on the nearside limb and farside basalts exhibit an exceptionally weak 1 xm ferrous absorption band this may indicate a compositionally distinct lunar basalt group that for example is more mg rich than most basalts of the nearside some of the most notable compositional anomalies are associated with south pole aitken basin this large region has a much lower albedo than surrounding highlands the inner darkest portion of the basin exhibits optical properties indistinguishable low ti basalts deposits to the south exhibit unique properties with a strong and broad ferrous 1 xrn absorption most consistent with abundant olivine the unusual compositions associated with south pole aitken and their spatial e3tent suggests the impact creating this huge lunar basin excavated mafic rich lower crust or perhaps mantle material 1 intro oucri ion

gravity inversion of basement relief and estimation of density contrast variation with depth we present a method to estimate the basement relief as well as the density contrast at the surface and the hyperbolic decaying factor of the density contrast with depth assuming that the gravity anomaly and the depth to the basement at a few points are known in both cases the interpretation model is a set of vertical rectangular 2d prisms whose thicknesses are parameters to be estimated and that represent the depth to the interface separating sediments and basement the solutions to both problems are stable because of the incorporation of additional prior information about the smoothness of the estimated relief and the depth to the basement at a few locations presumably provided by boreholes the method was tested with synthetic gravity anomalies produced by simulated sedimentary basins with smooth relief providing not only well resolved estimated relief but also good estimates for the density contrasts at the surface and for the decaying factors of the density contrast with depth the method was ap

gravity anomalies of 2 d bodies with variable density contrast a new method is presented to compute gravity anomalies that result from 2 d bodies with variable density contrast the cross section of a body is approximated by a polygon density is assumed to vary as any order of polynomial function with depth and lateral position results calculated by the proposed method for models with variable density contrast compare well with other methods liaohe basin northeast china is modeled from field gravity anomalies using the formulas given showing the method is valid and effective

hotspots in the southern oceans an absolute frame of reference for motion of the gondwana continents abstract the geometry and geochronology of aseismic ridges and oceanic islands in the southern oceans provide a good test of the proposition that hotspots remain fixed over long periods of time that is motion of an order of magnitude less than the relative motion between plate pairs in most cases it is concluded that inter hotspot movement cannot be discerned for the period 100 m y to present and that widely distributed hotspots in the atlantic and indian oceans provide a frame of reference for plate motions following the disintegration of gondwanaland which is independent of paleomagnetism this frame of reference is absolute in that it gives the motion of the lithosphere with respect to the mantle hotspots the absolute motion model indicates that africa and antarctica are now moving only very slowly that there has been significant relative movement between east and west antarctica since the cretaceous and prescribes the relative motion between the somali and african plates

remote sensing studies of the dionysius region of the moon 1 the dionysius region is located near the western edge of mare tranquillitatis and is centered on dionysius crater which exhibits a well developed dark ray system proposed origins for these dark rays included impact melt deposits and dark primary ejecta the region also contains extensive deposits of cayley type light plains clementine multispectral images and a variety of spacecraft photography were utilized to investigate the composition and origin of geologic units in the dionysius region the portions of the dark rays for which spectral and chemical data were obtained are composed of mare debris contaminated with minor amounts of highland material both five point spectra and values of the optical maturity omat parameter indicate that the dark rays are dominated by mare basalts not glassy impact melts the high albedo rays associated with dionysius exhibit feo and tio2 values that are lower than those of the adjacent dark ray surfaces and omat values that indicate that bright ray surfaces are not fully mature the high albedo rays are bright largely because of the contrast in albedo between ray material containing highlands rich ejecta and the adjacent mare rich surfaces the mafic debris ejected by dionysius was derived from a dark iron rich unit exposed high on the inner wall of the crater this layer probably represents a mare deposit that was present at the surface of the preimpact target site with one possible exception there is no evidence for buried mare basalts associated with cayley plains in the region

lunar mare volcanism stratigraphy eruption conditions and the evolution of secondary crusts abstract lunar mare basalt deposits cover 17 of the lunar surface occur preferentially in topographic lows on the nearside and have a total volume estimated at 1 107 km3 analysis of returned samples and photogeologic and remote sensing studies shows that mare volcanism began prior to the end of heavy bombardment the period of cryptomare formation in pre nectarian times and continued until the copernican period a total duration approaching 3 5 4 ga stratigraphic analyses show that the flux was not constant but peaked in early lunar history during the imbrian period which spans the period 3 85 3 2 ga average volcanic output rate during this peak period was about 10 2 km 3 a very low relative to the present global terrestrial volcanic output rate and comparable to the present local output rates for individual volcanoes such as vesuvius and kilauea hawaii volcanic landforms indicate that many eruptions were of high volume and long duration some eruptions associated with sinuous rules may have lasted of the order of a year and emplaced 103 km3 of lava representing the equivalent in one year of about 70 000 years at the average flux shallow magma chambers were uncommon the nearsidefarside mare deposit asymmetry can be readily explained by differences in crustal thickness magma ascending from the mantle or from a buoyancy trap at the base of the crust should preferentially extrude to the surface on the nearside but should generally stall and cool in dikes in the farside crust extruding only in the deepest basins the occurrence of farside maria within craters whose diameter is generally near to or less than the thickness of the crust may be accounted for by the difference between local and regional compensation dikes that establish pathways to the surface on the nearside should have very high volumes comparable to the volumes associated with many observed flows and sinuous rilles an abundance of dikes should exist in the lower crust of the moon many more than those feeding surface eruptions the upper limit is 37 50 of the crust by volume the presence and abundance of such dike swarms have important implications for the interpretation of the average composition of the lunar crust and the composition of basin and crater ejecta the interplay between thermal contraction and differentiation leads to net cooling and ultimate contraction of the outer portions of the moon resulting in a regional horizontal compressive stress acting on the lunar crust in addition overall cooling and deepening of sources require the production of ever larger volumes of magma in order to reach the surface with time stresses became high enough so that few dikes could open to the surface causing eruptive activity to be severely diminished in the eratosthenian and perhaps to cease in the copernican period lower stress levels are required to terminate eruptive activity on the lunar farside consistent with the imbrian age of the farside maria and the nearside location of the youngest maria lunar mare deposits provide an example of the transition from primary crusts to secondary crusts and illustrate the significance of several factors in the evolution of secondary crusts such as crustal density variations in crustal thickness presence of impact basins state and magnitude of stress in the lithosphere and general thermal evolution these factors are also responsible for the extremely low volcanic flux even during periods of peak extrusion

beginning and end of lunar mare volcanism mare volcanism on the moon is commonly attributed to an important but relatively short lived epoch of internal heating after 3 900 myr bp but before about 2 500 myr bp refs 1 2 although some studies suggested that mare volcanism had started earlier3 5 than times indicated by dated lunar samples only recently have photogeological spectral and geochemical data6 8 documented the importance of a pre 4 000 myr bp epoch similarly early earth based geological mapping revealed a bright rayed crater lichtenberg superposed by mare units9 thereby indicating that mare volcanism must have extended to times significantly more recent than 3 100 myr bp lunar orbital photography confirmed this inferred strati graphical relationship10 but crater statistics indicated that the youngest units were at least twice the age of copernicus or between 1 700 and 2 000 myr bp refs 11 13 we present here the inferred distribution and style of the early phases of mare volcanism based on current evidence and conclude that certain regions of the moon underwent two distinct pulses of igneous activity we then examine crater statistics for the post lichtenberg mare unit and other selected units and conclude that mare volcanism extended to a time comparable with that of the copernicus impact or 1 myr bp these reassessments of the oldest and youngest maria provide new constraints on geophysical models of the internal thermal history of the moon

gravitational search for cryptovolcanism on the moon evidence for large volumes of early igneous activity abstract we define lunar cryptovolcanism as volcanic deposits on the moon hidden by overlying material notably cryptovolcanism includes both cryptomaria subsurface extrusive basaltic deposits that are obscured by overlying higher albedo basin and crater ejecta and earlier candidate extrusives such as the mg suite knowledge of the volume and extent of cryptovolcanism is necessary for a comprehensive understanding of lunar volcanic history particularly in early pre 3 8 ga epochs when abundant impact craters and basins obscured surface volcanic deposits by lateral emplacement of ejecta we use gravity recovery and interior laboratory grail gravity and lunar orbiter laser altimeter lola topography data to construct maps of the moon s positive bouguer and isostatic gravity anomalies and explore the possibility that these features are due to mass excesses associated with cryptovolcanism by cross referencing the regions with geologic data such as dark halo craters we model the potential cryptovolcanic deposits as buried high density rectangular prisms at depth in the upper crust and find a volume of candidate buried cryptovolcanism between 0 4 10 6 km 3 and 4 8 10 6 km 3 depending on assumptions about density and crustal compensation state these candidate deposits correspond to a surface area of between 0 50 10 6 km 2 and 1 14 10 6 km 2 which would increase the amount of the lunar surface containing volcanic deposits from 16 6 to between 17 9 and 19 5 the inferred volume of cryptovolcanism is comparable to the smallest estimates of the volume of visible mare basalts and up to 50 of the largest estimates the high resolution grail and lola observations thus would collectively indicate that early pre 3 8 ga lunar volcanism is an important element of lunar thermal evolution alternatively the buried material could represent the presence of intrusive mg suite sills or plutons

southern ocean hotspot tracks and the cenozoic absolute motion of the african antarctic and south american plates abstract a detailed analysis based on an antarctica africa finite reconstruction at chron c29 64 ma an assumption of no relative wander between the marion prince edward and tristan hotspots and on recently revised bathymetric maps of the southern ocean region shows that the fixed hotspot reference frame is tenable for absolute plate motions bouvet hotspot and probably trinidade as well also shows little or no cenozoic relative motion contrary to previous models bouvet hotspot is unrelated to the meteor rise cape rise seamount chain instead the bathymetric data when compared with the predicted hotspot tracks indicate another hotspot exists near the southernmost south atlantic spreading ridge segment new geochemical evidence from the latter region supports this hypothesis in showing the effects of plume enrichment from a source that is compositionally distinct from bouvet the peculiar zig zag shape of the cape rise meteor rise lineament is the result of this hotspot crossing the active transform segment of the falkland agulhas fracture zone in late mesozoic times followed by an early cenozoic ridge jump to the pre weakened trace on the then south american plate from the averaged cenozoic absolute motions of the african antarctic and south american plates it is evident that antarctica has been most nearly stationary in an absolute motion sense

concept of effective density key to gravity depth determinations for sedimentary basins the gravity anomaly observed over a layered sedimentary basin is close to that calculated over a basin with the same configuration and depth but filled by homogeneous sediments with density equal to the effective weighted average density of the real layered basin therefore it is possible to calculate the effective density contrast of a basin from the residual gravity anomaly over it if the depth of the basin is known at least at one point assuming a mathematical function for density depth dependence an expression for the gravity depth dependence using the infinite slab bouguer formula can be developed this expression makes it possible to calculate the depth of a basin or an isopach map from gravity data an exponential function and a new hyperbolic density depth function and their gravity depth functions are analyzed and implemented for determining the depths of basins from gravity data for the san jacinto graben california and the tucson basin southern arizona the hyperbolic functions are m

exposure of spectrally distinct material by impact craters on mercury implications for global stratigraphy abstract messenger s mercury dual imaging system mdis obtained multispectral images for more than 80 of the surface of mercury during its first two flybys those images have confirmed that the surface of mercury exhibits subtle color variations some of which can be attributed to compositional differences in many areas impact craters are associated with material that is spectrally distinct from the surrounding surface these deposits can be located on the crater floor rim wall or central peak or in the ejecta deposit and represent material that originally resided at depth and was subsequently excavated during the cratering process the resulting craters make it possible to investigate the stratigraphy of mercury s upper crust studies of laboratory terrestrial and lunar craters provide a means to bound the depth of origin of spectrally distinct ejecta and central peak structures excavated red material rm with comparatively steep red spectral slope and low reflectance material lrm stand out prominently from the surrounding terrain in enhanced color images because they are spectral end members in mercury s compositional continuum newly imaged examples of rm were found to be spectrally similar to the relatively red high reflectance plains hrp suggesting that they may represent deposits of hrp like material that were subsequently covered by a thin layer 1 km thick of intermediate plains in one area craters with diameters ranging from 30 km to 130 km have excavated and incorporated rm into their rims suggesting that the underlying rm layer may be several kilometers thick lrm deposits are useful as stratigraphic markers due to their unique spectral properties some rm and lrm were excavated by pre tolstojan basins indicating a relatively old age 4 0 ga for the original emplacement of these deposits detailed examination of several small areas on mercury reveals the complex nature of the local stratigraphy including the possible presence of buried volcanic plains and supports sequential buildup of most of the upper 5 km of crust by volcanic flows with compositions spanning the range of material now visible on the surface distributed heterogeneously across the planet this emerging picture strongly suggests that the crust of mercury is characterized by a much more substantial component of early volcanism than represented by the phase of mare emplacement on earth s moon

total variation regularization for depth to basement estimate part 1 mathematical details and applications we have developed an inversion approach that estimates the basement relief of a fault bounded sedimentary basin the sedimentary pack is approximated by a grid of 3d or 2d vertical prisms juxtaposed in the horizontal directions of a right handed coordinate system the prisms thicknesses represent the depths to the basement and are the parameters to be estimated from the gravity data to obtain depth to basement estimates we introduce the total variation tv regularization as a stabilizing function this approach lets us estimate a nonsmooth basement relief because it does not penalize sharp features of the solution we have deduced a compact matrix form of the gradient vector and the hessian matrix of the approximation to the tv function that allows a regularized gauss newton minimization approach because the hessian matrix of the approximation to the tv function is ill conditioned we have modified this hessian matrix to improve its condition and to accelerate the convergence of the gauss newton algorithm tests conducted with synthetic data show that the inversion method can delineate discontinuous basements presenting large slips or sequences of small slip step faults tests on field data from the almada basin brazil and from the san jacinto graben california u s a confirm the potential of the method in detecting and locating in depth normal faults in the basement relief of a sedimentary basin

lunar cryptomaria physical characteristics distribution and implications for ancient volcanism cryptomaria lunar volcanic deposits obscured by crater and basin impact ejecta can provide important information about the thermal and volcanic history of the moon the timing of cryptomare deposition has implications for the duration and flux of mare basalt volcanism in addition knowing the distribution of cryptomaria can provide information about mantle convection and lunar magma ocean solidification here we use multiple datasets e g m3 lola lroc diviner to undertake a global analysis to identify the general characteristics e g topography surface roughness rock abundance albedo etc of lunar light plains in order to better distinguish between ancient volcanic deposits cryptomaria and impact basin and crater ejecta deposits we find 20 discrete regions of cryptomaria covering approximately 2 of the moon which increase the total area covered by mare volcanism to 18 of the lunar surface comparisons of light plains deposits indicate that the two deposit types volcanic and impact produced are best distinguished by mineralogic data on the basis of cryptomaria locations the distribution of mare volcanism does not appear to have changed in the time prior to its exposed mare basalt distribution there are several hypotheses explaining the distribution of mare basalts which include the influence of crustal thickness mantle convection patterns asymmetric distribution of source regions kreep distribution and the influence of a proposed procellarum impact basin the paucity of farside mare basalts means that multiple factors such as crustal thickness variations and mantle convection are likely to play a role in mare basalt emplacement

correlation of different maturity parameters in the ahmedabad mehsana block of the cambay basin abstract the potential use of organic matter maturation parameters in assessing the diagenetic catagenetic transition zone with the help of various known molecular parameters has been investigated in the ahmedabad mehsana block of the cambay basin a set of 24 conventional cores from the eocene shales covering a depth regime of 922 2500 m has been studied the oil generation threshold i e the boundary between the diagenetic and catagenetic maturation regimes is assessed to be at 1800 m based on a combination of parameters including percent hydrocarbons in eom saturate aromatic hydrocarbon ratio in eom and the rock eval production index the pr n c17 ratio rock eval hi and oi were not suitable for reliable maturation profiling nor for independently indexing the stages of maturation the extent of the catagenetic regime is distinguished by ph n c18 ratios

thermal and magmatic evolution of the moon as with all science our continually developing concepts of lunar evolution are firmly tied to both new types of observations and the integration of these observations to the known pool of data this process invigorates the intellectual foundation on which old models are tested and new concepts are built just as the application of new observational tools to lunar science in 1610 galileo s telescope and 1840 photography yielded breakthroughs concerning the true nature of the lunar surface the computational and technological advances highlighted by the apollo and post apollo missions and associated scientific investigations provided a new view of the thermal and magmatic evolution of the moon 1 1 pre apollo view of the thermal and magmatic evolution of the moon many of the early views of the moon manifested in mythology and art throughout the world were primarily tied to lunar and terrestrial cycles and the relationships between the sun and the moon prophetically myths involving the lunar deities mwuetsi from zimbabwe and coyolxauhqui from mexico told of rather violent or catastrophic events in which the moon was expunged from the earth numerous ancient scientific observations were made about the nature of the moon ranging from those uncovered in early neolithic sites that correctly identified mare crisium and mare humorum to the insights made by greek philosophers such as anaxagoras ca 500 428 b c and democritus ca 460 370 b c who attached terrestrial analogues to its character stone mountains with the advent of the telescope 1610 and photography 1840 as scientific tools for lunar exploration semiquantitative data could be collected that would provide an intellectual foundation for scientific interpretation initially modern terrestrial geological analogs were extended to the moon lunar highlands volcanic craters seas combined with the rigors of computational modeling these observational data were extended to predict the original thermal state of the moon and its thermal and magmatic history its proximity to the earth

fast nonlinear gravity inversion in spherical coordinates with application to the south american moho estimating the relief of the moho from gravity data is a computationally intensive non linear inverse problem what is more the modeling must take the earths curvature into account when the study area is of regional scale or greater we present a regularized non linear gravity inversion method that has a low computational footprint and employs a spherical earth approximation to achieve this we combine the highly efficient botts method with smoothness regularization and a discretization of the anomalous moho into tesseroids spherical prisms the computational efficiency of our method is attained by harnessing the fact that all matrices involved are sparse the inversion results are controlled by three hyper parameters the regularization parameter the anomalous moho density contrast and the reference moho depth we estimate the regularization parameter using the method of hold out cross validation additionally we estimate the density contrast and the reference depth using knowledge of the moho depth at certain points we apply the proposed method to estimate the moho depth for the south american continent using satellite gravity data and seismological data the final moho model is in accordance with previous gravity derived models and seismological data the misfit to the gravity and seismological data is worse in the andes and best in oceanic areas central brazil and patagonia and along the atlantic coast similarly to previous results the model suggests a thinner crust of 30 35 km under the andean foreland basins discrepancies with the seismological data are greatest in the guyana shield the central solimoes and amazonas basins the parana basin and the borborema province these differences suggest the existence of crustal or mantle density anomalies that were unaccounted for during gravity data processing

remote sensing studies of the orientale region of the moon a pre galileo view we have acquired both an extensive data base of visible and near infrared spectra and multispectral images ultraviolet and visible of the orientale region of the moon our results show that the eastern inner rook mountains are composed of anorthosite portions of the main ring of the humorum basin and the inner ring of grimaldi are also composed of anorthosite other deposits within the orientale basin and the major ejecta unit outside the basin are dominated by noritic anorthosites mature surfaces have spectra nearly identical to those taken of areas in the vicinity of the apollo 16 site thus it appears that orientale ejecta are more mafic than materials that are thought to have originated at depth i e the anorthosites in the inner rook mountains there are large areas that have mare basalt signatures mixed with highland rock types indicating the existence of ancient pre orientale mare volcanism present mare surfaces in the orientale region contain basalts of intermediate to very low tio2 content

galileo multispectral imaging of the north polar and eastern limb regions of the moon multispectral images obtained during the galileo probe s second encounter with the moon reveal the compositional nature of the north polar regions and the northeastern limb mare deposits in these regions are found to be primarily low to medium titanium lavas and as on the western limb show only slight spectral heterogeneity the northern light plains are found to have the spectral characteristics of highlands materials show little evidence for the presence of cryptomaria and were most likely emplaced by impact processes regardless of their age

gravity inversion of basement relief using approximate equality constraints on depths we present a gravity interpretation method for estimating the relief of an arbitrary interface separating two homogeneous media the upper medium is discretized into rectangular juxtaposed prisms whose thicknesses represent the depths to the interface and are the parameters to be estimated from the gravity anomaly the density contrast of each prism is assumed to be constant and known to stabilize the inversion we introduce two kinds of constraints on the depths the first one requires proximity between the observed and computed depths at isolated points such as those obtained from boreholes absolute equality constraint the second one requires that groups of depths approximately follow an established linear relationship among the depths relative equality constraint both kinds of constraints are imposed in the least squares sense we illustrate the method performance by applying it to a synthetic anomaly produced by a simulated basement relief consisting of four narrow and adjacent structural lows

characteristics of lunar mare deposits in smythii and marginis basins implications for magma transport mechanisms an analysis of 34 lunar lava flows and ponds in the eastern limb smythii and marginis basins was undertaken to examine and model the first stages of secondary crustal formation and assess processes involved in magma transport and eruption in order to isolate the characteristics of single eruptive episodes we focused on discrete mare ponds adjacent to the major mafia mean values for areas and volumes of deposits estimated to be good candidates for single eruptive phases are large approximately 950 1000 km 2 and 200 km 3 respectively these eruptive volumes are commensurate with the largest known terrestrial eruptions flood basalts the lack of geomorphological structures indicative of shallow magma reservoirs indicates that deep probably subcrustal source regions are prevalent with respect to crustal thickness relationships the magnitude and frequency of eruptive events are observed to be greatest in areas of thinnest crust specifically regions of major maria mare smythii mare marginis occur in areas of thinnest crust while isolated ponds occur where the crust is relatively thicker this is consistent with the correlation observed globally between crustal thickness and the magnitude and frequency of eruptive events ages of volcanic flows and pyroclastic events range from early imbrian to imbfian eratosthenian but are concentrated most heavily between 3 80 3 60 ga suggesting a period of peak volcanism beginning around 3 85 ga and lasting approximately 200 ma however the existence of dark halo crater clusters in non mare units within the region suggests the presence of cryptomaha which would indicate an earlier onset of volcanism and a volume of mare matehal potentially greater than that currently exposed on the surface typical nearest neighbor distances suggest deposits derive from reservoirs 100 km in diameter the observations made here are consistent with a magma transport model in which plumes rising diapirically stall at a density boundary under the lunar crust and propagate dikes to the surface through overpressufization

composition of the lunar highland crust from near infrared spectroscopy near infrared reflectance spectra of the lunar highlands are synthesized to obtain global information about the composition of the lunar near side crust immature exposed surfaces from small fresh craters mountains and massifs and large craters with central peaks are included in a survey of rock types across the lunar near side compositions recognized in these data include anorthosite noritic gabbric and troctolitic mineral assemblages three quarters of the areas studied that represent samples from the upper 1 2 km of lunar crust exhibit noritic compositions with different amounts of pyroxene and or brecciation alteration norites are ubiquitous across the near side and show no spatial clustering associated with any of the major basins in contrast to this noritic megaregolith of the upper crust material representing stratigraphically deeper zones 5 15 km of the lunar crust is dominated by gabbros anorthosites and troctolites with less than a quarter of the areas studied exhibiting a noritic composition the origin of the noritic megaregolith and its relation to deeper crustal material is thus somewhat of an enigma the current limited statistics for areas identified as anorthosites and troctolites are insufficient to derive global spatial distributions gabbroic areas however are notably concentrated in the western hemisphere although incomplete for a global assessment of crustal materials these data demonstrate that the lunar near side crust is clearly mineralogically heterogeneous both laterally and vertically and not well mixed below 1 2 km

lunar impact basins new data for the western limb and far side orientale and south pole aitken basins from the first galileo flyby compositional aspects of impact basin materials can be analyzed using multispectral image data acquired by the galileo solid state imaging ssi experiment during the december 1990 lunar encounter these data provide important information on the spectral properties of the western lunar limb and parts of the far side the ssi images cover the wavelength range 0 4 1 0 m allowing measurement of spectral slope and estimation of the strength of the 1 m absorption due to iron in the mafic minerals olivine and pyroxene among deposits of the 930 km diameter orientale basin exterior ejecta comprising the hevelius formation is relatively homogeneous and spectrally similar to mature apollo 16 soils suggesting an upper crustal source the centrally located maunder formation is distinct from the younger mare basalts but comparable to the hevelius formation in its spectral reflectance properties supporting an interpretation as basin impact melt the montes rook formation located in an annulus between the maunder and the hevelius shows a slightly stronger mafic absorption and may be the deepest crustal material excavated the distal orientale deposits show local mafic enhancements in the schiller schickard and mendel rydberg regions interpreted to represent pre orientale mare deposits or cryptomaria intermixed with overlying basin ejecta in this case maria of sizes comparable to those presently observed were widespread in this region before the orientale impact mixing model analyses are consistent with the ballistic erosion and sedimentation model for ejecta emplacement in the distal regions beyond the continuous ejecta deposit on the southern lunar farside a huge area with an enhanced mafic absorption corresponds to the interior and rim of the pre nectarian south pole aitken impact basin 2000 2500 km in diameter the anomaly is interpreted to be due to several factors including excavation into the more mafic lower crust and the presence of extensive early volcanic fill cryptomare similar to that seen in ancient basins such as smythii and australe these results show that although basin forming events are an important factor in producing lateral heterogeneities in crustal composition and in modifying preexisting deposits such as cryptomaria the majority of material in even the largest basins was excavated from crustal levels our results suggest a gradational vertical crustal stratigraphy consisting of an uppermost mixed crustal layer of anorthosite basin ejecta and cryptomaria deposits generally corresponding to the megaregolith an upper crustal layer of anorthosite and a lower more noritic layer many of the basic questions remaining from this study could be addressed by global high resolution geochemical and mineralogical data obtained by polar orbiting spacecraft

modelling of sedimentary basins from gravity anomalies with variable density contrast summary the decrease of density contrast with depth in sedimentary basins could be approximated by a quadratic function the sedimentary basin is viewed as a number of outcropping vertical prisms put in juxtaposition at each observation point equations are derived for the gravity anomaly of a vertical prism for a quadratic density function the initial model is obtained by calculating the thicknesses of the prisms at each station by an infinite slab formula the differences between the observed anomalies and the anomalies of the initial model at each station are used to modify the initial model a computer program is developed for initial estimates and refinement of the model the method is applied to interpret the gravity anomaly of san jacinto graben california where sediments filling the graben have a density contrast that can be approximated to a quadratic function finally the convergence of the method is discussed

gravity inversion of basement relief constrained by the knowledge of depth at isolated points we present an interpretation method for the gravity anomaly of an arbitrary interface separating two homogeneous media it consists essentially of a downward continuation of the observed anomaly and the division of the continued anomaly by a scale factor involving the density contrast between the media the knowledge of the interface depth at isolated points is used to estimate the depth d1 of the shallowest point of the interface the density contrast between the two media and the coefficients c1 and c2 of a first order polynomial representing a linear trend to be removed from data the solutions are stabilized by introducing a damping parameter in the computation of the downward continued anomaly by the equivalent layer method different from other interface mapping methods using gravity data the proposed method 1 takes into account the presence of an undesirable linear trend in data 2 requires just intervals for both rather than the knowledge of its true value and coefficients c1 and c2

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy

galileo imaging observations of lunar maria and related deposits the galileo spacecraft imaged parts of the western limb and far side of the moon in december 1990 ratios of 0 41 0 56 gin filter images from the solid state hnaging ssi experiment provided information on the titanium content of mare deposits ratios of the 0 76 0 99 gm images indicated 1 gin absorptions associated with fe 2 in mafic minerals mare ages were derived froin crater statistics obtained from lunar orbiter images results on mare coinpositions in western oceanus procellarum and the humorurn basin are consistent with previous earth based observations thus providing confidence in the use of galileo data to extract compositional information mare units in the grimaldi and riccioli basins range in age froin 3 25 to 3 48 ga and consist of medium to medium high titanium 4 to 7 tio2 content lavas the schiller zucchius basin shows a higher 0 76 0 99 gm ratio than the surrounding highlands indicating a potentially higher mafic mineral content consistent with previous interpretations that the area includes mare deposits blanketed by highland ejecta and light plains materials the oldest mare materials in the orientale basin occur in south central mare orientale and are 3 7 ga old youngest mare materials are in lacus autumni and are 2 85 ga old these units are medium to medium high titanium 4 to 7 tio2 basalts thus volcanism was active in orientale for 0 85 ca but lavas were relatively constant in composition galileo data suggest that mendel rydberg mare is similar to mare orientale cryptomare are present as well thus the mare lavas on the western limb and far side to 178oe are remarkably uniform in coinposition being generally of medium to medium high titanium content and having relatively low 0 76 0 99 gin ratios this region of the moon is between two postulated large impact structures the procellarum and the south pole aitken basins and may have a relatively thick crust in areas underlain by an inferred thinner crust i e zones within large basins as at apollo titanium content is often higher however no mare deposits with titanium abundances approaching those of the high titanium 9 to 14 tio2 apollo 11 and 17 basalts nor of the high titanium regions of central oceanus procellarum are seen on the western limb or eastern far side light plains deposits are generally indistinct froin the surrounding highlands in the ssi data and are inferred to be derived primarily from the same material that forins the highlands some of the light plains are too young to be related to basin forming impacts suggesting possible volcanic origin dark mantle deposit compositions derived from ssi data are consistent with earth based observations of similar near side deposits and are interpreted to be pyroclastic materials however the modernitc albedo and 1 gin absorption of the dark mantle deposit on the southwest margin of the orientale basin suggest it is a local pyroclastic deposit contaminated with underlying highland materials from the orientale impact